[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J] | [K]| [L] | [M] |[N]
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
171|100|118| | 40| 79 | 39 | 2.03| .2| .8 |177°| .229| |
173| |140| | 80|110 | 30 | 3.67| .4| 1.6 |176 | .423| |
175| |168| |120|144 | 24 | 6 | .6| 2.4 |174 | .590| |
177| |202| |160|181 | 21 | 8.62| .8| 3.2 |172 | .661| |
179| |232| |200|216 | 16 | 13.5 | 1 | 4 |170 | .897| |
181| |268| |240|254 | 14 | 18.1 | 1.2| 4.8 |167 | .993| |
183| |302| |280|291 | 11 | 26.5 | 1.4| 5.6 |163 | 1.15 | |
184| |318|110|300|309 | 9 | 34.3 | 1.6| 6.4 |160 | 1.27 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
185|100|150|115|140|145 | 5 | 29 | 1.6| 6.4 |180 | 1.02 | |[A]
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+
186|200|258| |240|249 | 9 | 27.4 | 1.2| 4.8 |180 | 1.05 | |
188| |290| |280|285 | 5 | 57 | 2.2| 8.8 |180 | 1.29 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
189|300|412| |400|406 | 6 | 67.7 | 1.7| 6.8 |180 | 1.34 | |
190| |428| |420|424 | 4 |106 | 1.8| 7.2 |180 | 1.48 | |
191| |446|275|440|443 | 3 |148 | 3.3|13.2 |180 | 1.59 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+
192|400|570|360|560|565 | 5 |113 | 2 | 8 |180 | 1.47 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
329|100|110| | 40| 75 | 35 | 2.14| .3| .6 |177 | .246| |[B]
330| |135| | 80|107.5| 27.5| 3.90| .6| 1.2 |175 | .446| |
331| |198| |160|179 | 19 | 9.42| 1 | 2 |171 | .751| |
332| |275| |240|257.5| 17.5| 14.7 | 1.5| 3 |169 | .911| |
334| |345| |320|232.5| 12.5| 18.6 | 2 | 4 |165 | 1.01 | |
336| |420|110|400|410 | 10 | 41 | 3.2| 6.4 |162 | 1.31 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
339|200|230| |160|195 | 35 | 5.86| .8| 1.6 |176 | .576| |
340| |360| |320|340 | 20 | 17 | 1.6| 3.2 |171 | .949| |
341| |435| |400|417.5| 17.5| 23.8 | 2 | 4 |169 | 1.07 | |
342| |505| |480|492.5| 12.5| 39.4 | 2.7| 5.4 |165 | 1.28 | |
343| |590|200|560|575 | 15 | 38.3 | 5 |10 |168 | 1.24 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
344|300|400| |320|360 | 40 | 9 | 1.4| 2.8 |175 | .719| |
345| |450| |400|425 | 25 | 17 | 1.7| 3.4 |173 | .938| |
346| |520| |480|500 | 20 | 25 | 2.1| 4.2 |171 | 1.08 | |
347| |600| |560|570 | 10 | 57 | 3 | 6 |162 | 1.43 | 1 min.|
348| |600|280|560|570 | 10 | 57 | 3.4| 6.8 |162 | 1.43 | 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
350|400|500| |400|450 | 50 | 9 | 1.6| 3.2 |176 | .715| |
352| |605| |560|577.5| 17.5| 21.3 | 2.3| 4.6 |169 | 1.04 | |
353| |680| |640|660 | 20 | 33 | 3.2| 6.4 |171 | 1.17 | 1 min.|
354| |680| |640|660 | 20 | 33 | 3.7| 7.4 |171 | 1.17 | 5 min.|
355| |680| |640|660 | 20 | 33 | 4.1| 8.2 |171 | 1.17 |10 min.|
356| |680| |640|660 | 20 | 33 | 6.1|12.2 |171 | 1.17 |15 min.|[C]
357| |600| |560|580 | 20 | 29 |10 |20 |171 | 1.13 |20 min.|[D]
358| |600| |560|580 | 20 | 29 |17.2|34.4 |171 | 1.13 |25 min.|
359| |530| |480|505 | 25 | 20.2 | 5.2|10.4 |173 | .955|30 min.|
360| |530|350|480|505 | 25 | 20.2 | 2.8| 5.6 |173 | .955|35 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
361|500|570| |400|485 | 85 | 5.71| 1.3| 2.6 |178 | .561| |
364| |700| |640|670 | 30 | 22.3 | 2.3| 4.6 |174 | 1.02 | |
365| |755| |720|637.5| 17.5| 36.4 | 3.2| 6.4 |169 | 1.22 | |
366| |820| |800|810 | 10 | 81 | 6.6|13.2 |162 | 1.55 +-------+[E]
367| |750| |720|735 | 15 | 49 | 5.1|10.2 |168 | 1.32 | 1 min.|
368| |750| |720|735 | 15 | 49 |11 |22 |168 | 1.32 | 5 min.|
369| |690| |640|665 | 25 | 26.6 |12 |24 |173 | 1.09 +-------+[F]
370| |610| |560|585 | 25 | 23.4 |14.4|28.8 |173 | 1.05 | 1 min.|
371| |610| |560|585 | 25 | 23.4 |20 |40 |173 | 1.05 | 4 min.|
372| |550| |480|515 | 35 | 14.7 | 7.4| 14.8|175 | .880| 1 min.|
373| |550|410|480|515 | 35 | 14.7 | 2.3| 4.6|175 | .880| 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
374|600|680| |480|580 |100 | 5.8 | 1.5| 3 |178 | .566| |
376| |755| |640|697.5| 57.5| 12.1 | 2.1| 4.2 |177 | .807| |
378| |850| |800|825 | 25 | 33 | 2.8| 5.6 |173 | 1.16 | 1 min.|
379| |850| |800|825 | 25 | 33 | 3.5| 7 |173 | 1.16 | 5 min.|[G]
380| |780| |720|750 | 30 | 25 | 8.8|17.6 |174 | 1.06 | 1 min.|
381| |680| |560|620 | 60 | 10.3 |11.2|22.4 |177 | .755| 5 min.|
382| |680| |560|620 | 60 | 10.3 | 2 | 4 |177 | .755+-------+[H]
383| |730| |640|685 | 45 | 15.2 | 2.5| 5 |176 | .886| 1 min.|
384| |730| |640|685 | 45 | 15.2 | 2.4| 4.8 |176 | .886| 5 min.|
385| |780| |720|750 | 30 | 25 | 4.6| 9.2 |174 | 1.06 | 1 min.|
388| |780|550|720|750 | 30 | 25 | 8.8|17.6 |174 | 1.06 | 5 min.|
389| |780| |720|750 | 30 | 25 | 4 | 8 |174 | 1.06 | 1 min.|[I]
390| |780| |720|750 | 30 | 25 | 6.4|12.8 |174 | 1.06 | 5 min.|[E]
391| |730| |640|685 | 45 | 15.2 | 3.7| 7.4 |176 | .886| 1 min.|
392| |730|550|640|685 | 45 | 15.2 | 3.9| 7.8 |176 | .886| 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
396|600|680| |400|540 |140 | 3.86| 2 | .45|170 | .432| |[J]
397| |820| |720|770 | 50 | 15.4 |17.2| 3.87|176 | .890| |
398| |750| |640|695 | 55 | 12.6 |15 | 3.37|177 | .874| |
399| |700| |560|630 | 70 | 9 | 9.4| 2.17|177 | .711| |
400| |670| |480|575 | 95 | 6.05| 4.5| 1.12|178 | .579| |
401| |630|550|400|515 |115 | 4.48| 3.5| .75|178 | .483| |
402| |830| |720|775 | 55 | 14.1 |26 | 5.85|177 | .856| |
403| |630| |320|475 |155 | 3.06| 1.5| .30|179 | .358| |
404| |610| | 60|335 |275 | 1.22| .7| .16|180 | .063| |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
408|600|610| |120|365 |245 | 1.49| .2| .09|180 | .127| |[K]
413| |660| |400|530 |130 | 4.08| 1 | .45|179 | .450| |
415| |710| |560|635 | 75 | 8.46| 1.9| .86|177 | .691| |
416| |750| |640|695 | 55 | 12.6 | 3.2| 1.44|177 | .820| |
417| |800| |720|760 | 40 | 19 | 3.8| 1.71|175 | .964| |
418| |340| |200|274 | 70 | 3.91| .6| .27|177 | .441| |
419|300|380| |280|330 | 50 | 6.6 | 1.2| .54|176 | .614| |
421| |450| |400|425 | 25 | 17 | 3.2| 1.44|173 | .938| |
423| |515| |480|497.5| 17.5| 28.4 | 4 | 1.8 |169 | 1.13 | |
425| |580| |560|570 | 10 | 57 | 5 | 2.25|162 | 1.43 | |
427| |695| |680|687.5| 7.5| 91.7 | 7 | 3.15|155 | 1.67 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
Legend Remarks: [A] = Slack side of belt running on a board to prevent
sagging.
[B] = 10" cast-iron pulleys.
[C] = Belt slipped off 4 m. later.
[D] = Continuing.
[E] = Belt slipped off 2 m. later.
[F] = Belt slipped off 3 m. later.
[G] = Belt slipped off 5 m. later.
[H] = After running 5 minutes at _T_ - _t_ = 560.
[I] = Belt scraped.
[J] = 18 r. p. m. 10" cast-iron pulleys.
[K] = 20" cast-iron pulleys. 18 r. p. m.
These experiments, however, are subject to an error arising from the
friction of the belt upon the board, the amount of which was not
determined. All of the experiments, in fact, are subject to slight
errors which were extremely difficult to eliminate or properly allow
for, but an effort has been made throughout to obtain results which
should approximate as closely as possible to the truth. The sum of the
tensions, as determined by measuring scales, was subject only to errors
in observation. This part of the apparatus was carefully tested by a
horizontal pull of known amount and made to register correctly.
The difference of the tensions _T_ - _t_, as computed from the reading
of the scales, was measured by the force of an equivalent moment at 20"
radius. This moment, divided by the radius of the pulley was taken to be
the difference _T_ - _t_.
In this calculation, it will be noticed that two slight corrections have
been omitted which are opposite in effect and about equal in degree. One
is the friction of the brake shaft in its bearings, which of course was
not recorded on the scales, and the other is the thickness of the belt
which naturally increases the effective radius of the pulley. Both of
these errors are somewhat indefinite, but the correctness of the results
obtained was tested in a number of cases by the sag of the belt, and the
tension _t_, as calculated from the sag, was found to agree closely with
the tension calculated by the adopted method.
As the limiting capacity of the belt was reached, the difficulty of
obtaining simultaneous and accurate observations was increased by the
vibrations of the scale beams. This was apparently due to irregularity
in the slip, and it was only by the use of heavily loaded beams and a
dash-pot that readings could then be taken at all. The dash-pot
consisted of a large flat plate suspended freely in a bucket of water by
a fine wire from the scale beam. This provision, however, was applied
only to the scales on which the vibrations were more pronounced.
TABLE IV.
DOUBLE OAK-TANNED LEATHER BELT 4" WIDE BY 5/16" THICK AND 30 FT. LONG,
WEIGHING 17 LBS., ON 10" CAST-IRON PULLEYS. 160 R. P. M.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Duration of run at time of experiment.
[N] = Remarks.
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J] | [K]| [L] | [M] |[N]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
209|120|120| | 48| 84 | 36 | 2.33| .4| .8 |176°| .275| |
210| |140| | 80|110 | 30 | 3.67| .6| 1.2 |175 | .426| |
211| |168| |120|144 | 24 | 6 | .9| 1.8 |174 | .590| |
212| |198| |160|179 | 19 | 9.42| 1.6| 3.2 |170 | .756| |
213| |235| |200|217.5| 17.5|12.4 | 2.3| 4.6 |174 | .829| |
214| |270| |240|255 | 15 |17 | 3.2| 6.4 |168 | .966| |
215| |310| |280|295 | 15 |19.7 | 5.1|10.2 |168 |1.02 | |[A]
216| |345|122|320|332.5| 12.5|25.8 | 9.4|18.8 |164 |1.13 | |[B]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
217|200|200| | 48|124 | 76 | 1.63| .4| .8 |179 | .156| |
219| |240| |160|200 | 40 | 5 | 1 | 2 |176 | .524| |
220| |360| |320|340 | 20 |17 | 2.7| 5.4 |170 | .954| |
221| |430| |400|415 | 5 |27.7 |15 |30 |167 |1.13 | |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
222|300|318| |160|239 | 79 | 3.03| .8| 1.6 |179 | .354| |
223| |350| |240|295 | 55 | 5.36| 1.2| 2.4 |177 | .543| |
224| |400| |320|360 | 40 | 9 | 2 | 4 |175 | .719| |
225| |470| |440|455 | 15 |30.3 | 8 | 1.6 |167 |1.17 | |[C]
226| |450| |400|425 | 25 |17 | 4 | 8 |172 | .943| 1 m.|
227| |450| |400|425 | 25 |17 | 8 |16 |172 | .943| 5 m.|
228| |450| |400|425 | 25 |17 |17.3|34.6 |172 | .943| 10 m.|[D]
229| |418| |360|389 | 29 |13.4 | 3 | 6 |173 | .859| 15 m.|[E]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
230|400|405| |160|282.5|122.5| 2.30| .8| 1.6 |179 | .267| |
232| |455| |320|387.5| 67.5| 5.74| 1.4| 2.8 |177 | .566| |
233| |495| |400|447.5| 47.5| 9.42| 1.9| 3.8 |176 | .730| 1 m.|
234| |495|370|400|447.5| 47.5| 9.42| 2.1| 4.2 |176 | .730| 5 m.|
235| |560| |480|520 | 40 |13 | 2.7| 5.4 |175 | .859|Start.|
236| |560| |480|520 | 40 |13 | 4.5| 9 |175 | .859| 5 m.|
237| |560| |480|520 | 40 |13 | 7.5|15 |175 | .859| 10 m.|
238| |550|380|480|465 | 85 | 5.47|20 |40 |178 | .547| 15 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
239|400|560| |480|520 | 40 |13 | 3.4| 6.8 |175 | .859| 1 m.|[F]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
240|500|610| |480|545 | 65 | 8.38| 2.1| 4.2 |177 | .688| 1 m.|
241| |610| |480|545 | 65 | 8.38| 2.5| 5 |177 | .688| 5 m.|
242| |660| |560|610 | 50 |12.2 | 3.2| 6.4 |176 | .814| 1 m.|
243| |655| |560|607.5| 47.5|12.8 | 8.4|16.8 |176 | .830| 5 m.|[G]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
244|600|700| |560|630 | 70 | 9 | 1.9| 3.8 |177 | .711| 1 m.|
245| |700| |560|630 | 70 | 9 | 2.1| 4.2 |177 | .711| 5 m.|
246| |690|550|560|625 | 65 | 9.69| 2.3| 4.6 |177 | .735| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
247|600|750| |600|675 | 75 | 9 | 2.2| 4.4 |177 | .771| 1 m.|
248| |740|585|600|670 | 70 | 9.57| 2.4| 4.8 |177 | .731| 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
249|600|770| |640|705 | 65 |10.8 | 2.5| 5 |177 | .770| 1 m.|
250| |765| |640|702.5| 62.5|11.2 | 3.5| 7 |177 | .782| 5 m.|
251| |770|600|640|685 | 85 | 8.06| 4.2| 8.4 |178 | .672| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
252|600|790| |680|735 | 55 |13.4 | 4.3| 8.6 |176 | .845| 1 m.|
253| |790| |680|735 | 55 |13.4 | 6.3|12.6 |176 | .845| 5 m.|[H]
---+---+---+---+---+-----+-----+-----+-----+-----+----+-----+------+---
254|100|100| | 44| 72 | 28 | 2.57| .6| 1.2 |176 | .307| |[I]
256| |160| |120|140 | 20 | 7 | 2.1| 4.2 |172 | .648| |
257| |200| |160|180 | 20 | 9 | 4 | 8 |171 | .736| |
258| |230| |200|215 | 15 |14.3 | 6.6|13.2 |168 | .907| 1 m.|
259| |230|100|200|215 | 15 |14.3 | 7.2|14.4 |168 | .907| 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
261|100|100| | 44| 72 | 28 | 2.57| .6| 1.2 |176 | .307| |[J]
263| |160| |120|140 | 20 | 7 | 2.8| 5.6 |172 | .648| |
264| |200| |160|180 | 20 | 9 | 5.1|10.2 |171 | .736| |
265| |230| |200|215 | 15 |14.3 | 7.3|14.6 |168 | .907| 1 m.|
266| |230| |200|215 | 15 |14.3 | 7.9|15.8 |168 | .907| 5 m.|
267| |270| |240|255 | 15 |17 |10.7|21.4 |168 | .966| 1 m.|[K]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
268|300|350| |240|295 | 55 | 5.36| 1.4| 2.8 |177 | .544| |
269| |400| |320|360 | 40 | 9 | 3 | 6 |175 | .719| |
270| |450| |400|425 | 25 | 17 | 6.8|13.6 |172 | .943| 1 m.|[K]
271| |418| |360|389 | 29 |13.4 | 8.8|17.6 |173 | .859| 1 m.|
272| |418| |360|389 | 29 |13.4 |15.6|31.2 |173 | .859| 5 m.|[G]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
273|600|700| |560|630 | 70 | 9 | 6.3|12.6 |177 | .711| |
274| |650| |480|565 | 85 | 6.65| 3.1| 6.2 |178 | .610| 1 m.|
275| |650| |480|565 | 85 | 6.65| 3.9| 7.8 |178 | .610| 5 m.|
276| |650| |480|565 | 85 | 6.65| 4.4| 8.8 |178 | .610| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
277|600|652| |400|526 |126 | 4.17| 1.4| 2.8 |178 | .460| |[L]
279| |715| |560|637.5| 77.5| 8.23| 2.4| 4.8 |177 | .682| |
280| |705| |560|632.5| 72.5| 8.72| 2.8| 5.6 |177 | .701| |
281| |700|560|560|630 | 70 | 9 | 3 | 6 |177 | .711| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
282|560|750| |640|695 | 55 |12.6 | 4.1| 8.2 |176 | .824| 1 m.|
283| |735|535|640|682.5| 47.5|14.3 |22 |44 |176 | .866| 5 m.|[M]
284| |770| |640|705 | 65 |10.7 | 5.4|10.8 |177 | .767| 1 m.|[N]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
285|300|350| |240|295 | 55 | 5.36| 1.2| 2.4 |177 | .543| |[O]
286| |400| |320|360 | 40 | 9 | 1.8| 3.6 |175 | .719| |
287| |430| |360|395 | 35 |11.3 | 2.7| 5.4 |174 | .798| |
289| |465| |400|432.5| 32.5|13.3 | 5.3|10.6 |174 | .852| |
290| |455| |400|427.5| 27.5|15.5 | 7.3|14.6 |173 | .907| |
291| |460| |400|430 | 30 |14.3 |11.6|23.2 |173 | .881| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
292|100|100| | 44| 72 | 28 | 2.57| .5| 1 |176 | .307| |
293| |125| | 80|102.5| 22.5| 4.55| .8| 1.6 |173 | .502| |
294| |165| |120|142.5| 22.5| 6.33| 1.2| 2.4 |173 | .611| |
295| |200| |160|180 | 20 | 9 | 2.1| 4.2 |171 | .736| |
296| |230| |200|215 | 15 |14.3 | 3.4| 6.8 |168 | .907| |
297| |230| |200|215 | 15 |14.3 | 3.9| 7.8 |168 | .907| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
298|100|270| |240|225 | 15 |17 | 5.7|11.4 |168 | .966| 1 m.|
299| |270| |240|255 | 15 |17 | 7.6|15.2 |168 | .966| 5 m.|
300| |270| |240|255 | 15 |17 | 9.3|18.6 |168 | .966| 10 m.|[P]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
303|100|110| | 40| 75 | 35 | 2.14| .1| .4 |177 | .246| |[Q]
304| |132| | 80|106 | 26 | 4.08| .4| 1.6 |174 | .463| |
305| |160| |120|140 | 20 | 7 | 1 | 4 |172 | .648| |
306| |195| |160|177.5| 17.5|10.1 | 1.9| 7.6 |169 | .814| |
307| |230| |200|215 | 15 |14.3 | 3 |12 |168 | .907| 1 m.|
308| |230| 90|200|215 | 15 |14.3 | 3.5|14 |168 | .907| 5 m.|
309| |270| |240|255 | 15 |17 | 4.5|18 |168 | .966| 1 m.|
310| |270| |240|255 | 15 |17 | 5.8|23.2 |168 | .966| 5 m.|
311| |270| |240|255 | 15 |17 | 6.2|24.8 |168 | .966| 10 m.|
312| |270| |240|255 | 15 |17 | 6.2|24.8 |168 | .966| 15 m.|[R]
313| |270| |240|255 | 15 |17 | 2 | 8 |168 | .966| 1 m.|
314| |270| |240|255 | 15 |17 | 2.1| 8.4 |168 | .966| 5 m.|[S]
315| |305| |280|292.5| 12.5|23.4 | 3.4|13.6 |165 |1.09 | 1 m.|
316| |305|100|280|292.5| 12.5|23.4 | 3.5|14 |165 |1.09 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
317|100|335| |320|327.5| 7.5|43.7 | 5.2|20.8 |152 |1.42 | 1 m.|
318| |335| |320|327.5| 7.5|43.7 | 6.5|26 |152 |1.42 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
319|300|380| |320|350 | 30 |11.7 | 1.3| 5.2 |173 | .814| 1 m.|
320| |380| |320|350 | 30 |11.7 | 1.4| 5.6 |173 | .814| 5 m.|
321| |440| |400|420 | 20 |21 | 2.1| 8.4 |170 |1.03 | 1 m.|
322| |440|260|400|420 | 20 |21 | 2.4| 9.6 |170 |1.03 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
323|300|480| |440|460 | 20 |23 | 2.8|11.2 |170 |1.06 | 1 m.|[T]
324| |480|285|440|460 | 20 |23 | 3 |12 |170 |1.06 | 5 m.|
325| |510| |480|495 | 15 |33 | 3.2|12.8 |167 |1.20 | 1 m.|
326| |510| |480|495 | 15 |33 | 5 |20 |167 |1.20 | 5 m.|[U]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
Legend Remarks: [A] = Sag 10" at middle of belt.
[B] = Finally slipped off.
[C] = Belt finally slipped off.
[D] = Belt slip'd off.
[E] = Continuing.
[F] = After running 5 m. without load.
[G] = Belt slipped off 2 m. later.
[H] = Belt sl. off 2 m. lat. Pul. warm.
[I] = Belt scraped.
[J] = Belt dres'd with preparation recommend'd by
maker.
[K] = Belt slipped off 3 m. later.
[L] = One day later.
[M] = Belt slipp'd off.
[N] = After 3 min. intermission.
[O] = Temp. 52°.
[P] = Belt slipped off 4 m. later.
[Q] = 20 in. pulleys.
[R] = Temp. 56°.
[S] = Temp. 42°.
[T] = Temp. 46°.
[U] = Belt sl. off 5 m. lat. Pul. warm.
A peculiar and important feature of Tables III. and IV. is the effect of
time upon the percentage of slip. In previous experiments the percentage
of slip was measured at once after the load was applied, but it was
accidentally discovered that repeated measurements seldom agreed, and
investigation showed that these discrepancies were principally due to
the duration of the experiment. The continual slipping of the belt was
found to cause a deposit of a thick black substance upon the surface of
the pulley, which, acting as a lubricant, continued to increase the slip
still further.
Upon removing the load on brake-wheel, this deposit would be again
absorbed by the belt, and the original adhesion would be restored. The
temperature was also found to affect the slipping, and, in general, the
colder the weather the slower would this deposit take place.
Experiments 353 to 360 inclusive were made to determine the limit at
which the belt would run continuously without increasing its percentage
of slip. After the pulleys had become well coated and the slip had
reached a high per cent., the load on the brake-wheel was gradually
removed until a marked improvement was reached, as shown by experiments
359 and 360. The highest allowable coefficient of friction for this belt
is therefore estimated to be somewhere between 1.13 and .995, or we may
safely say 1. The highest coefficient obtained was 1.67, but, of course,
this was temporary. The diameter of the pulley also appears to affect
the coefficient of friction to some extent. This is especially to be
noticed at the very slow speed of 18 revolutions per minute on 10 in.
and 20 in. pulleys, where the adhesion on the 20 in. pulleys is
decidedly greater; but, on the other hand, at 160 revolutions per minute
the adhesion on the 10 in. pulleys is often as good, and sometimes
better, than appears for the 20 in. at the same velocity of sliding.
It might be possible to determine the effect of pulley diameter upon
adhesion for a perfectly dry belt, where the condition of its surface
remains uniform, but for belts as ordinarily used it would be very
difficult, on account of the ever-changing condition of surface produced
by slip and temperature. It is generally admitted that the larger the
diameter the greater the adhesion for any given tension, but no definite
relation has ever been established, nor, indeed, does it seem possible
to do so except by the most elaborate and extensive experiments.
It should be observed, however, that such a variation, if true, implies
a corresponding variation in the coefficients of friction for different
intensities of pressure upon the same pulleys, and that, consequently,
our experiments should show higher coefficients under the lighter loads
for the same velocity of sliding. Referring to Table II., where the
condition of the belt is dry and uniform for a large range of tensions,
we find that this inference is generally sustained, although there are
some few exceptions.
Experiment 106 may be compared with 116, and 112 with 133, also 108,
113, and 135, all showing great reductions in the coefficients of
friction for increments in tension. The exceptions are all to be found
under the smallest velocities of sliding, and appear only in the third
decimal place, so that the weight of their record against the
probability of such a law is light. By a similar inference it should
also follow that a wide belt would drive a little more at a given
tension than a narrow one, on account of the reduction in pressure per
square inch against the pulley. The mean intensity of pressure of a belt
against its pulley may be considered as proportional to the sum of the
tensions divided by the product of pulley diameter and width of belt,
and an analysis of the experiments referred to will show the relation
there existing between intensity of pressure and coefficient of
friction.
If we let [Iota] = intensity of pressure, and [phi] = coefficient of
friction, we shall find that [phi] is approximately proportional to
[Iota]^{-.15}, or, in other words that doubling the width of belt or
diameter of pulley would apparently increase the coefficient of friction
about 10 per cent. of its original value. This relation is not proved,
of course, and it is given only as a suggestion toward the solution of
the question. If the coefficient of friction does vary with the
intensity of pressure, the problem of determining the driving power of a
belt on strictly mathematical principles will indeed be complicated.
The coefficient of friction in the tables has been calculated by a
well-known formula, developed upon the assumption of a uniform
coefficient around the arc of contact, but this could no longer be
considered as correct if the coefficient is known to vary with the
pressure. Referring from Table II. to Table III., we shall find at once
the proof and contradiction of the inferences drawn from Table II., and
we are left as much in the dark as ever respecting the value of pressure
intensity.
Practical millwrights all know, or think they know, that an increase of
pulley diameter increases the drive, and it is a matter of common
observation that when large and small pulleys are connected by a crossed
belt, the smaller pulley will invariably slip first.
On one side a great deal of testimony can be adduced to show that
pressure intensity should be an important factor in the theory of belt
transmission, and, on the other hand, we have strong evidence to the
contrary. I may refer, in this connection, to the experiments of Mr.
Holman in _Journal of Franklin Institute_ for September, 1885, in which
there is no indication that the coefficient of friction varies at all
with the pressure. The coefficients obtained by Mr. Holman follow the
variations in slip like our own, and it gives us pleasure to observe
that our general results and conclusions are so strongly corroborative
of each other. There is at the same time a great difference in the
methods pursued in arriving at the same results. In his experiments, the
velocity of sliding was the fixed condition upon which the coefficient
of friction was determined, while, in ours, the conditions were those of
actual practice in which the percentage of slip was measured. Our least
amount of slip, with a dry belt running at the extremely slow speed of
90 feet per minute, was 1.08 inches, and ten times this would be
perfectly proper and allowable. A great many of Mr. Holman's experiments
are taken at rates below 1" per minute, and the coefficients obtained
are very much below the average practice, as himself seems to believe.
The velocity of sliding which may be assumed in selecting a proper
coefficient is directly proportional to the belt speed, and may safely
be estimated at .01 of that speed. For a pair of pulleys we should have
.01 on each pulley, and therefore .02 for slip. Few belts run slower
than 200 or 300 ft. per minute, and consequently a slip of less than 2
or 3 ft. per minute need seldom be considered. Another point of
difference which may possibly affect the coefficients obtained, is that,
in Mr. Holman's case the same portion of belt surface was subject to
continuous friction, while in ours, the friction was spread over the
belt at successive portions as in actual work. This we consider a new
and important feature of our experiments. As a matter of practical
importance, care was taken to observe, as nearly as possible, the
maximum slip which might safely take place before a belt would be thrown
from its pulley. A number of observations taken throughout the
experiments led to the final conclusion that 20 per cent. of slip was as
much as could safely be admitted. This information has been found of
value in cases where work is done intermittently by a fly-wheel and the
belt has to restore the speed of the wheel. It cannot be said in regard
to a maximum value of [phi] that any was determined or even indicated,
although it is certain that the increase at high rates of slip becomes
less rapid.
We have now seen that the driving power of a leather belt depends upon
such a variety of conditions, that it would be manifestly impracticable
if not impossible to correlate them all, and it is thought better to
admit the difficulties at once than to involve the subject in a
labyrinth of formulæ which life is too short to solve.
The relative value of pulley diameters may vary with different belts,
and all that can be expected or desired is some general expression
covering roughly the greatest number of cases. Our apparatus did not
admit of extensive variations in this respect, and our attention was
given principally to the question of slip.
The coefficients given in Table III. are remarkably high, and show a
great superiority for the rawhide over tanned leather in point of
adhesion. The belt in question was very soft and pliable, but a little
twisted from use on a cone pulley where it had rubbed against one side.
It is not desirable, on account of its soft and adhesive nature, to use
this kind of belt where frequent shifting is required, and when used on
cone pulleys it is liable to climb and stretch against the side of the
cone; but for a plain straight connection, there seems to be little room
for improvement. Table IV. contains the results of similar experiments
upon an oak-tanned leather belt made by Chas. A. Shieren & Co. Here the
coefficients are much smaller than those given in Table III., and there
is quite a marked difference between the coefficients for 10 in. and 20
in. pulleys.
As before noticed, the outside temperature has its effect, and it is
probable that much lower results would have been obtained had the
experiments been made in the heat of midsummer. The high coefficients
obtained, together with the rapid increase of tension, show that the
pulling power of a long horizontal belt must, in many cases, be limited
by its strength rather than by its adhesion.
Table V. gives the results of experiments upon a light planer belt at
very slow and very high speeds. As would naturally be expected, much
higher coefficients were found at the high speed on account of the
greater velocity of sliding.
TABLE V.
OAK-TANNED LEATHER BELT 2" WIDE BY 3-16" THICK AND 30' 4" LONG, WEIGHING
4 LBS., ON 20" CAST-IRON PULLEYS. DRY AND SMOOTH, TAKEN FROM SERVICE ON
PLANER.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Duration of run at time of experiment.
[N] = Remarks.
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
[A]|[B]|[C]|[D]|[E]| [F] | [G]|[H] | [I]| [J] | [K]| [L]| [M] |[N]
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
429|100|110| | 40| 75 |35 |2.14| 1.2| .54|179°|.243| |18
430| |115| | 60| 87.5|27.5|3.18| 6.1| 2.75|178 |.372| |r.
431| |118| | 70| 94 |24 |3.92|16.5| 7.42|178 |.440| |p.
432| |105| | 20| 62.5|42.5|1.47| .3| .14|179 |.123| |m.
433| |112| | 50| 81 |31 |2.61| 3.5| 1.57|178 |.309| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
435|200|204| | 40|132 |82 |1.61| .2| .09|180 |.152| |
436| |206| | 60|133 |73 |1.82| .7| .32|180 |.191| |
437| |208| | 80|144 |64 |2.25| 1.8| .81|179 |.260| |
438| |210| |100|155 |55 |2.82| 3.7| 1.66|179 |.332| |
439| |212| |120|166 |40 |3.61| 7.7| 3.47|179 |.411| |
440| |215| |140|177.5|37.5|4.73|18.4| 8.28|179 |.497| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
442|100|110| | 60| 85 |25 |3.40| .3| 7.12|178 |.394| |950
443| |120| | 80|100 |20 |5 | .7| 16.62|178 |.518| |r.
445| |125| | 90|107.5|17.5|6.14| 3 | 71.25|177 |.587|Start.|p.
446| |125| | 90|107.5|17.5|6.14|25 |593.7 |177 |.587|min. |m.
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
448|200|200| | 80|140 |60 |2.33| .4| 9.5 |179 |.271| |
449| |200| |100|150 |50 |3 | .5| 11.87|179 |.352| |
450| |195|175|120|157.5|37.5|4.20| .8| 19 |179 |.459| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
451|150|175| |120|147.5|27.5|5.36| .9| 21.38|178 |.540| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
452|135|160| |120|140 |20 |7 |20 |475 |178 |.626| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
It may here be mentioned that the sum of the tensions was the horizontal
pressure of the belt against the pulleys, and that no allowance was
necessary for the effect of the centrifugal force. At the speed here
used, the tension indicated in the belt at rest was about 50 lbs.
greater than when in motion.
TABLE VI.
SHOWING THE AVERAGE COEFFICIENT OF FRICTION AND VELOCITY OF SLIP FOR A
NUMBER OF EXPERIMENTS IN WHICH THE SLIP APPROXIMATED 2 PER CENT.
-------------------------------------+--------------+-----------------
No. exper'ts in av'ge. | |
|Percentage of Slip. | |
| |Veloc. of Sl. in ft. per m. | |
| | |Coefficient of Fric- | |
| | |tion. | |
| | | | Belt. | Pulleys. | Remarks.
--+----+-----+-----+-----------------+--------------+-----------------
3|1.4 | 5.6 | .661|5-1/2" old belt. |20" diam. |Belt in nor.
| | | |Table I |pap. cov'd |w'k'g con.
--+----+-----+-----+-----------------+--------------+
2|1.7 | 6.8 | .44 |5-1/2" old belt. |20" di. | " "
| | | |Table I |cast-iron sur.|
--+----+-----+-----+-----------------+--------------+-----------------
2|1.55| 6.2 | .575|5-1/2" old belt. |20" di. |Belt dressed
| | | |Table I |cast-iron sur.|with "Beltiline."
--+----+-----+-----+-----------------+--------------+-----------------
5|1.7 | 6.8 | .452|2-1/4" dbl. belt.|20" di. |B't dry as us.
| | | |Table II |cast-iron sur.|on plan'r.
--+----+-----+-----+-----------------+--------------+-----------------
2|1.5 | 6 | .818|2-1/4" dbl. belt.|20" di. |Belt dressed
| | | |Table II |cast-iron sur.|with "Sankey's
| | | | | |Life of Leather."
--+----+-----+-----+-----------------+--------------+-----------------
2|1.7 | 6.8 |1.38 |4" r´hide b. |20" di. |Belt in nor.
| | | |Table III |cast-iron sur.|w'k'g con.
--+----+-----+-----+-----------------+--------------+
11|1.8 | 3.6 | .861|4" r´hide b. |10" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
1|2 | .45| .432|4" r´hide b. |10" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
1|1.9 | .86| .691|4" r´hide b. |20" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
7|1.94| 3.88| .617|4" o.tan'd b. |10" diameter. | " "
| | | |Table IV | |
--+----+-----+-----+-----------------+--------------+
4|1.85| 7.40| .906|4" o.tan'd b. |20" diameter. | " "
| | | |Table IV | |
--+----+-----+-----+-----------------+--------------+-----------------
2|1.5 | .67| .251|2" o.tan'd b. |20" diameter. |B't dry as us. on
| | | |Table V | |plan'r.
--+----+-----+-----+-----------------+--------------+
2| .8 |38 | .529|2" o.tan'd b. |20" diameter. | " "
| | | |Table V | |
--+----+-----+-----+-----------------+--------------+-----------------
The conclusion to be drawn from this series of experiments is the great
importance of high speed in the economy of belt transmission. The
friction of belts on pulleys is evidently dependent on the velocity of
sliding, and, as a general rule, the greater the velocity the greater
the friction. There are but few apparent exceptions to this rule, and
investigation of them has led to the inference that in all such cases,
the condition of the belt or pulley surface had undergone a change
either by heating or by deposit from the belt on the pulley. The
percentage of slip is the measure of the power lost in transmission by
the belt itself, and the higher the speed the less this becomes. There
is a limit, however, to the power which may be transmitted as the speed
is increased, and this limit is caused by the reduction in pressure
against the pulley arising from the action of centrifugal force.
This point has been clearly demonstrated in a paper read before this
Society by Mr. A. F. Nagle on the "Horse Power of Leather belts,"[43]
and the formula there developed is written thus:
_HP_ = _CVtw_(_S_ - .012_V_^{2}) ÷ 550, (1.)
in which _C_ is a constant to be determined from the arc of contact and
coefficient of friction as expressed in the equation:
_C_ = 1 - 10^{-.00758_f[alpha]_}, (2.)
_V_ = velocity of belt in feet per second.
_t_ = thickness of the belt in inches.
_w_ = width " "
_S_ = working strength of leather in lbs. per square inch.
_f_ = coefficient of friction.
_[alpha]_ = arc of contact in degrees.
[43] Transactions A. S. M. E., Vol. II., page 91. See also Mr. Nagle's
Tables I., II., and III., in Appendix VI. to this paper for values of
_C_ and _H.P._
The velocity at which the maximum amount of power can be transmitted by
any given belt is independent of its arc of contact and coefficient of
friction, and depends only upon the working strength of the material and
its specific gravity.
From equation (1.) we obtain for the maximum power of leather belts the
condition:
_____
_V_ = \/28_S_, (3.)
and for any other material whose specific gravity is _y_, we find
____
/_S_
_V_ = \ / ---
\/ _y_
The coefficient of friction .40, adopted by Mr. Nagle, appears from
these experiments to be on the safe side for all working requirements,
except in cases where dry belts are run at slow speeds.
If we assume 2 per cent. as the greatest allowable slip, and select
within this limit the coefficient corresponding to the nearest
approximations to it, we can form some idea of the coefficients which
can be relied upon at different speeds.
Table VI. gives the average results obtained for this maximum allowance
of slip, and shows an extreme variation in the coefficient of friction
from .251 for a dry oak-tanned belt at the slow speed of 90 feet per
minute to 1.38 for a rawhide belt at the moderate speed of 800 feet per
minute.
For continuous working, it is probable that the coefficient 1.38 is too
high, but still it is certain that a coefficient of 1.00 can be steadily
maintained for an indefinite length of time, and we may say that in
actual practice the coefficient of friction may vary from .25 to 1.00
under good working conditions. This extreme variation in the coefficient
of friction does not give rise, as might at first be supposed, to such a
great difference in the transmission of power. It will be seen by
reference to formula (1.) that the power transmitted for any given
working strength and speed is limited only by the value of _C_, which
depends upon the arc of contact and the coefficient of friction.
For the usual arc of contact, 180°, the power transmitted when _f_ = .25
is about 24 per cent. less than when _f_ = .40, and when _f_ = 1.00, the
power transmitted is about 33 per cent. more, from which it appears that
in extreme cases the power transmitted may be 1/4 less or 1/3 more than
will be found from the use of Mr. Nagle's coefficient of .40.
TABLE VII.
SHOWING THE TORSIONAL MOMENT IN LBS. REQUIRED TO OVERCOME JOURNAL
FRICTION AND OTHER INTERNAL RESISTANCES, FOR BELTS AT VARIOUS SPEEDS AND
TENSIONS ON DIFFERENT ARRANGEMENTS OF PULLEYS.
------+-----+-------+-----+-----+-----+------+-------------+--------------
No. of|Ten- |Moment |Dia- |Revo-|Width|Thick-| |
exper-|sion.|in inch|meter|lut's| of | ness | Manner of |
im'nt.|_T_ +| lbs. | of |per |Belt.| of | Driving. | Remarks.
| _t_ | |pul- |min. | |Belt. | |
| | |leys.| | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
1 | 100| 20 | 20" | 160 | 6" |7/32" |Straight open|
3 | 300| 25 | | | | |belt. |
5 | 500| 30 | | | | | |
7 | 700| 35 | | | | | |
10 | 1000| 45 | | | | | |
45 | 100| 15 | | | | | |
47 | 300| 22.5 | | | | | |
49 | 500| 27.5 | | | | | |
51 | 700| 35 | | | | | |
54 | 1000| 50 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
163 | 100| 17.5 | 20" | 160 | 4" |9/32" |Straight open|
165 | 300| 25 | | | | |belt. |
167 | 500| 30 | | | | | |
169 | 700| 35 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
194 | 100| 17.5 | 10" | 160 | 4" |5/16" |Straight open|
196 | 300| 27.5 | | | | |belt. |
198 | 500| 40 | | | | | |
200 | 700| 55 | | | | | |
202 | 900| 70 | | | | | |
203 | 1000| 80 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
327 | 100| 20 | 10" | 18 | 4" |5/16" |Straight open|
328 | 1000| 80 | | | | |belt. |
393 | 100| 20 | | | | | |
394 | 1000| 100 | | | | | |
395 | 600| 60 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
405 | 100| 20 | 20" | 18 | 4" |9/32" |Straight open|
406 | 1000| 160 | | | | |belt. |
407 | 600| 100 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
428 | 100| 20 | 20" | 18 | 2" |9/32" |Straight open|
434 | 200| 25 | | | | |belt. |
------+-----+-------+-----+-----+-----+------+-------------+--------------
441 | 100| 25 | 20" | 950 | 2" |3/16" |Straight open|
447 | 200| 30 | | | | |belt. |
------+-----+-------+-----+-----+-----+------+-------------+--------------
453 | 100| 25 | 20" | 160 | 6" |7/32" |Crossed belt.|14' 6" between
454 | 500| 60 | | | | | |pulleys.
455 | 1000| 110 | | | | | |14' 6" bet.
| | | | | | | |pul'ys.
------+-----+-------+-----+-----+-----+------+-------------+--------------
459 | 100| 15 | 20" | 160 | 6" |7/32" |Straight open|14' 6" between
460 | 500| 25 | | | | |belt. |pulleys.
461 | 1000| 65 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
462 | 100| 25 | 20" | 160 | 6" |7/32" |Straight open|With 8"
463 | 500| 60 | | | | |belt. |tightener.
464 | 1000| 110 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
465 | 100| 45 | 20" | 160 | 6" |7/32" |Crossed belt.|8 feet between
466 | 500| 105 | | | | | |pulleys.
467 | 1000| 180 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
470 | 100| 25 | 20" | 160 | 6" |7/32" |Quarter turn |
471 | 500| 80 | | | | |belt on 16" |
472 | 750| 145 | | | | |diameter mule|
473 | 1000| 250 | | | | |pulleys. |
474 | 750| 170 | | | | | |
475 | 500| 110 | | | | | |
476 | 1000| 220 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
477 | 1000| 140 | 20" | 160 | 6" |7/32" |Quarter turn |Freshly oiled.
478 | 750| 100 | | | | |belt on 16" |
479 | 500| 70 | | | | |diameter mule|
480 | 100| 20 | | | | |pulleys. |
481 | 50| 60 | 20" | 160 | 6" |7/32" |Quarter turn |Belt rub.
482 | 25| 120 | | | | |on 16" mule |against low.
| | | | | | |pulleys. |guide m. pul.
------+-----+-------+-----+-----+-----+------+-------------+--------------
483 | 100| 20 | 20" | 160 | 6" |7/32" |Quarter turn |Well oiled,
484 | 500| 50 | | | | |on 16" mule |after a run of
485 | 750| 70 | | | | |pulleys. |2 hrs. at _T_
486 | 1000| 105 | | | | | |+ _t_ = 100.
------+-----+-------+-----+-----+-----+------+-------------+--------------
495 | 250| 30 | 20" | 160 | 6" |7/32" |Half turn |
496 | 500| 50 | | | | |belt on 16" |
497 | 750| 90 | | | | |mule pulleys.|
498 | 1000| 170 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
503 | 1000| 260 | 20" | 160 | 6" |7/32" |Quarter |10 feet
504 | 750| 190 | | | | |twist. |between
505 | 500| 130 | | | | | |pulleys.
506 | 250| 80 | | | | | |
507 | 100| 30 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
513 | 100| 50 | 20" | 160 | 6" |7/32" |Quarter |7' 6" between
514 | 250| 105 | | | | |twist. |pulleys.
515 | 500| 200 | | | | | |
516 | 750| 290 | | | | | |
517 | 1000| 380 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
523 | 100| 25 | 20" | 160 | 4" | 1/4" |Quarter |10 feet
524 | 250| 50 | | | | |twist. |between
525 | 500| 95 | | | | | |pulleys.
526 | 750| 145 | | | | | |
527 | 1000| 210 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
528 | 100| 65 | 20" | 160 | 4" | 1/4" |Quarter |6 feet between
529 | 250| 135 | | | | |twist. |pulleys.
530 | 500| 245 | | | | | |
531 | 750| 380 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
533 | 100| 25 | 20" | 160 | 6" |7/32" |Quarter |16' 6" between
534 | 250| 40 | | | | |twist. |pulleys.
535 | 500| 75 | | | | | |
536 | 750| 105 | | | | | |
537 | 1000| 165 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
539 | 1000| 130 | 20" | 160 | 6" |7/32" |Quarter twist|7' 6" between
540 | 750| 110 | | | | |with 16" |pulleys.
541 | 500| 90 | | | | |diameter |
542 | 250| 60 | | | | |carrying |
543 | 100| 40 | | | | |pulley. |
544 | 100| 30 | | | | | |
545 | 250| 55 | | | | | |
546 | 500| 90 | | | | | |
547 | 750| 120 | | | | | |
548 | 1000| 170 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
569 | 100| 25 | 20" | 160 | 6" |7/32" |Straight open|
571 | 500| 55 | | | | |belt. |
572 | 750| 70 | | | | | |
573 | 1000| 90 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
The percentage of slip is the most important factor affecting the
efficiency of belt transmission, but in addition to this we have journal
friction, the resistance of the air, and with crossed belts the friction
of the belt upon itself. These have been termed internal resistances,
and their values for some of the most common arrangements of pulleys are
given in Table VII. From this table it appears that the moment required
to run a straight belt varies from 15 to 25 inch lbs. at 100 lbs.
tension for all speeds. At 160 revolutions per minute and 1,000 lbs.
tension, the required moment varied from 45 to 90 inch lbs., and at 18
revolutions per minute and at the same tension it varied from 80 to 150
inch lbs.
From the average of these quantities we find the moment of resistance to
be expressed by the following formulæ for straight open belts between 2"
journals:
At 160 r. p. m.:
_M_ = .053_S_ + 14.7, (5.)
At 18 r. p. m.:
_M_ = .11_S_ + 9, (6.)
in which
_M_ = moment of resistance in inch lbs.
_S_ = sum of tensions.
When a crossed belt does not rub upon itself, the resistance is the same
as for an open belt.
The resistance offered by the introduction of carrying pulleys and
tighteners is appreciable, and depends upon the pressure brought to bear
against their journals. If the belt rubs against the flanges of the
carrying pulleys, the resistance is very much increased, and this is
often liable to occur in horizontal belts from a change of load. The
friction on journals of carrying pulleys may be estimated by the formulæ
already given if we substitute for _S_ the pressure against their
journals. In the experiments which were made upon internal resistances,
the greatest resistance was offered by a quarter-twist belt 6 feet
between journals on 20-inch pulleys.
The equation for this belt may be written:
_M_ = .35_S_ + 58, (7.)
but the introduction of a carrying pulley reduced the resistance to no
more than what might be expected from the same number of journals with a
straight belt.
With quarter-twist belts the resistance lies chiefly in slip, which
occurs as the belt leaves the pulleys, and this naturally depends upon
the distance between journals in terms of the diameters of the pulleys.
The effect of time upon the tension of the belt used in Table VIII. is
plainly shown by experiments 588 to 613 inclusive, between which the
pulleys remained at a fixed distance apart, and the belt slowly
stretched from a tension of 380 to 280 lbs.
To estimate the efficiency of belt transmission for an average case, we
may assume 40 in. lbs. as the moment of internal resistance for a belt
whose tension is 500 lbs. and 40 in. lbs. statical moment = about 20 ft.
lbs. per revolution. If the belt is transmitting 400 lbs. with two per
cent. of slip on 20 in. pulleys, then .02 × 400 × 5 = 40 ft lbs. are
lost per revolution in slip, making a total loss of 60 ft. lbs. per
revolution.
TABLE VIII.
SHOWING THE INCREASE IN THE SUM OF THE TENSIONS ON A VERTICAL BELT 4"
WIDE BY 1/4" THICK, AND 24 FT. LONG, ON 20" CAST-IRON PULLEYS, AT 120 R.
P. M.
------+---------+-----------+-----+-----+--------+---------+----------
No. of| Scales | Tension | | | Incre- |Percen'e |
exper-+----+----+-----+-----+ | | m´nt |of Incre-| Date.
im'nt.| A. | B. |_T_ +|_T_ -| _T_ | _t_ |of _T_ +| ment. |
|[44]|[44]| _t_ | _t_ | | | _t_ | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
578 | 93 | 101| 194 | 16 |105 | 89 | 0 | |5-15-1885.
579 | 70 | 142| 212 | 144 |178 | 34 | 18 | |
580 | 67 | 170| 237 | 206 |221.5| 15.5| 43 | |
581 | 66 | 180| 246 | 228 |237 | 9 | 52 | |
582 | 66 | 188| 254 | 244 |249 | 5 | 60 | .323 |
583 | 91 | 101| 192 | 20 |106 | 86 | -2 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
584 |202 | 210| 412 | 16 |214 |214 | 0 | |5-15-1885.
585 |167 | 250| 417 | 166 |292.5|292.5| 5 | |
586 |145 | 300| 445 | 310 |376.5|376.5| 33 | .171 |
587 |185 | 195| 380 | 20 |200 |200 | -32 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
588 |190 | 199| 380 | 0 |190 |190 | 0 | |5-18-1885.
589 |133 | 250| 393 | 214 |303.5| 89.5| 13 | .033 |
------+----+----+-----+-----+-----+-----+--------+---------+----------
590 |177 | 177| 354 | 0 |177 |177 | 0 | |5-19-1885.
591 |156 | 203| 359 | 94 |226.5|132.5| 5 | |
592 |138 | 235| 373 | 194 |283.5| 89.5| 19 | |
593 |135 | 250| 385 | 230 |307.5| 77.5| 31 | |
594 |128 | 275| 403 | 294 |348.5| 34.5| 49 | |
595 |125 | 300| 425 | 350 |387.5| 37.5| 71 | |
596 |123 | 325| 448 | 404 |426 | 22 | 94 | .333 |
597 |168 | 168| 336 | 0 |168 |168 | -18 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
598 |143 | 143| 286 | 0 |143 |143 | 0 | |5-25-1885.
599 |140 | 148| 288 | 16 |152 |136 | 2 | |
600 |130 | 160| 290 | 60 |175 |115 | 4 | |
601 |122 | 170| 292 | 196 |194 | 98 | 6 | |
602 |116 | 180| 296 | 28 |212 | 84 | 10 | |
603 |112 | 190| 302 | 156 |229 | 73 | 16 | |
604 |108 | 200| 308 | 184 |246 | 62 | 22 | |
605 |105 | 210| 315 | 210 |262.5| 52.5| 29 | |
606 |102 | 220| 322 | 236 |279 | 43 | 36 | |
607 |100 | 230| 330 | 260 |295 | 35 | 44 | |
608 | 99 | 240| 339 | 282 |310.5| 28.5| 53 | |
609 | 98 | 250| 348 | 304 |326 | 22 | 62 | |
610 | 98 | 260| 358 | 316 |337 | 21 | 72 | |
611 | 99 | 270| 369 | 342 |355.5| 13.5| 83 | |
612 |100 | 280| 380 | 360 |370 | 10 | 94 | .357 |
613 |140 | 140| 280 | 0 |140 |140 | -6 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
[44] Scales A recorded the reduction of the load on the testing device
for _vertical_ belts by the tension of the loose part of the belt
(_t_). Scales B, by that of the tight side of the belt (_T_).
The total power expended per revolution is about 2,000 ft. lbs.,
therefore .03 is lost.
Under light loads, the internal resistance, which is nearly constant in
amount, may be a large percentage of the power transmitted, while under
heavy loads the percentage of slip may become the principal loss.
It would be difficult to work out, or even to use, a general expression
for the efficiency of belt transmission, but, from the foregoing, it
would seem safe to assume that 97 per cent. can be obtained under good
working conditions.
When a belt is too tight, there is a constant waste in journal friction,
and when too loose, there may be a much greater loss in efficiency from
slip. The allowance recommended of 2 per cent. for slip is rather more
than experiment would indicate for any possible crawl or creep due to
the elasticity of the belt, but in connection with this, there is
probably always more or less actual slip, and we are inclined to think
that in most cases this allowance may be divided into equal parts
representing creep and slip proper. Under good working conditions, a
belt is probably stretched about 1 per cent. on the tight side, which
naturally gives 1 per cent. of creep, and to this we have added another
per cent. for actual slip in fixing the limit proposed.
The indications and conclusions to be drawn from these experiments are:
1. That the coefficient of friction may vary under practical working
conditions from 25 per cent. to 100 per cent.
2. That its value depends upon the nature and condition of the leather,
the velocity of sliding, temperature, and pressure.
3. That an excessive amount of slip has a tendency to become greater and
greater, until the belt finally leaves the pulley.
4. That a belt will seldom remain upon a pulley when the slip exceeds 20
per cent.
5. That excessive slipping dries out the leather and leads toward the
condition of minimum adhesion.
6. That rawhide has much greater adhesion than tanned leather, giving a
coefficient of 100 per cent. at the moderate slip of 5 ft. per minute.
7. That a velocity of sliding equal to .01 of the belt speed is not
excessive.
8. That the coefficients in general use are rather below the average
results obtained.
9. That when suddenly forced to slip, the coefficient of friction
becomes momentarily very high, but that it gradually decreases as the
slip continues.
10. That the sum of the tensions is not constant, but increases with the
load to the maximum extent of about 33 per cent. with vertical belts.
11. That, with horizontal belts, the sum of the tensions may increase
indefinitely as far as the breaking strength of the belt.
12. That the economy of belt transmission depends principally upon
journal friction and slip.
13. That it is important on this account to make the belt speed as high
as possible within the limits of 5,000 or 6,000 ft. per minute.
14. That quarter-twist belts should be avoided.
15. That it is preferable in all cases, from considerations of economy
in wear on belt and power consumed, to use an intermediate guide pulley,
so placed that the belt may be run in either direction.
16. That the introduction of guide and carrying pulleys adds to the
internal resistances an amount proportional to the friction of their
journals.
17. That there is still need of more light on the subject.
CHAPTER XXXIII.--FORGING.
FORGING.--The operation of forging consists in beating or compressing
metal into shape, and may be divided into five classes, viz.,
hand-forging, drop-forging, machine-forging, forging under trip or steam
hammers, and hydraulic forging. In purely hand forging much work is
shaped entirely by hand tools, but in large shops much work is roughed
out under trip or steam hammers, and finished by hand, while some work
is finished under these hammers. In drop forging the work is pressed
into shape by dead blows, which compress it into shape in dies or
moulds. In machine forging the work is either formed by successive quick
blows rather than by a few heavy ones, or in some machines it is
compressed by rolling. In hydraulic forging the metal is treated as a
plastic material, and is forced into shape by means of great and
continuous pressure.
In all forging the nature or quality of the iron is of primary
importance; hence the following (which is taken from _The English
Mechanic_), upon testing iron, may not be out of place.
"The English Admiralty and Lloyds' surveyor's tests for iron and steel
are as follows:--
"Two strips are to be taken from each thickness of plate used for the
internal parts of a boiler. One-half of these strips are to be bent cold
over a bar, the diameter of which is equal to twice the thickness of the
plate. The other half of the strips are to be heated to a cherry-red and
cooled in water, and, when cold, bent over a bar with a diameter equal
to three times the thickness of the plate--the angle to which they bend
without fracture to be noted by the surveyor. Lloyds' Circular on steel
tests states that strips cut from the plate or beam are to be heated to
a low cherry-red, and cooled in water at 82° Fahr. The pieces thus
treated must stand bending double to a curve equal to not more than
three times the thickness of the plate tested. This is severe treatment,
and a plate containing a high enough percentage of carbon to cause any
tempering is very unlikely to successfully stand the ordeal. Lloyds'
test is a copy of the Admiralty test, and in the Admiralty Circular it
is stated that the strips are to be one and a half inches wide, cut in a
planing machine with the sharp edges taken off. One and a half inches
will generally be found a convenient width for the samples, and the
length may be from six to ten inches, according to the thickness of the
plate. If possible, the strips, and indeed all specimens for any kind of
experimenting, should be planed from the plates, instead of being
sheared or punched off. When, however, it is necessary to shear or
punch, the piece should be cut large and dressed down to the desired
size, so as to remove the injured edges. Strips with rounded edges will
bend further without breaking than similar strips with sharp edges, the
round edges preventing the appearance of the small initial cracks which
generally exhibit themselves when bars with sharp edges are bent cold
through any considerable angle. In a homogeneous material like steel
these initial cracks are apt to extend and cause sudden fracture, hence
the advantage of slightly rounding the corners of bending specimens.
[Illustration: Fig. 2824.]
"In heating the sample for tempering it is better to use a plate or bar
furnace than a smith's fire, and care should be taken to prevent unequal
heating or burning. Any number of pieces may be placed together in a
suitable furnace, and when at a proper heat plunged into a vessel
containing water at the required temperature. When quite cold the
specimens may be bent at the steam-hammer, or otherwise, and the results
noted. The operation of bending may be performed in many different ways;
perhaps the best plan, in the absence of any special apparatus for the
purpose, is to employ the ordinary smithy steam-hammer. About half the
length of the specimen is placed upon the anvil and the hammer-head
pressed firmly down upon it, as in Fig. 2824. The exposed half may then
be bent down by repeated blows from a fore-hammer, and if this is done
with an ordinary amount of care it is quite possible to avoid producing
a sharp corner.
[Illustration: Fig. 2825.]
"An improvement upon this is to place a cress on the anvil, as shown at
Fig. 2825. The sample is laid upon the cress, and a round bar of a
diameter to produce the required curve is pressed down upon it by the
hammer-head.
[Illustration: Fig. 2826.]
"The further bending of the pieces thus treated is accomplished by
placing them endwise upon the anvil-block, as shown in Fig. 2826. If the
hammer is heavy enough to do it, the samples should be closed down by
simple pressure, without any striking.
[Illustration: Fig. 2827.]
"Fig. 2827 is a sketch of a simple contrivance, by means of which a
common punching machine may be converted temporarily into an efficient
test-bending apparatus. The punch and bolster are removed, and the
stepped cast-iron block A fixed in place of the bolster. When a sample
is placed endwise upon one of the lower steps of the block A the
descending stroke of the machine will bend the specimen sufficiently to
allow of its being advanced to the next higher step, while the machine
is at the top of its stroke. The next descent will effect still further
bending, and so on till the desired curvature is attained. It would seem
an easy matter, and well worth attention, to design some form of machine
specially for making bending experiments; but with the exception of a
small hydraulic machine, the use of which has, I believe, been abandoned
on account of its slowness, nothing of the kind has come under the
writer's notice.
"The shape of a sample after it has been bent to pass Lloyds' or the
Admiralty test is that of a simple bend, the sides being brought
parallel. While being bent the external surface becomes greatly
elongated, especially at and about the point of the convex side, where
the extension is as much even as fifty per cent. This extreme elongation
corresponds to the breaking elongation of a tensile sample, and can only
take place with a very ductile material. While the stretching is going
on at the external surface, the interior surface of the bend is being
compressed, and the two strains extend into pieces till they meet in a
neutral line, which will be nearer to the concave than to the convex
curve with a soft specimen. When a sample breaks, the difference between
the portions of the fracture which have been subject to tensile and
compressive strains can easily be seen.
[Illustration: Fig. 2828.]
"Fig. 2828 shows a piece of plate folded close together; and this can
generally be done with mild steel plates, when the thickness does not
exceed half an inch.
"Common iron plates will not, of course, stand anything like the
foregoing treatment. Lloyds' test for iron mast-plates 1/2 inch thick,
requires the plates to bend cold through an angle of 30° with the grain,
and 8° across the grain; the plates to be bent over a slab, the corner
of which should be rounded with a radius of 1/2 inch.
[Illustration: Fig. 2829.]
"When the sample of metal to be tested is of considerable thickness, as
in the case of bars, it is often turned down in a lathe to the shape
shown in Fig. 2829, so as to reduce its strength within the capacity of
the machine. The part to be tested has usually a length between the
shoulders of 8, 10, or 12 inches, and must be made exactly parallel with
a cross-sectional area apportioned to the power of the machine and the
strength of the material to be tested. When it is desired to investigate
the elastic properties of materials, it is desirable to have the
specimens of as great a length as the testing apparatus will
accommodate.
[Illustration: Fig. 2830.]
[Illustration: Fig. 2831.]
"Many of the early experiments on the tensile strength of wrought iron
were made with very short specimens, such as in Fig. 2830, which is a
sketch of that used formerly in the royal arsenal at Woolwich. This had
no parallel length for extension at all, its smallest diameter occurring
at one only point. Mr. Kirkaldy, to whom is due in a great measure the
honour of having raised 'testing' to an exact science, discovered that
this form of specimen gave incorrect results. He found that experiments
with such specimens, more especially when the metals were ductile, gave
higher breaking strains than were obtained with specimens of equal
cross-sectional area having the smallest diameter parallel for some
inches of length. This was due to the form of the specimen resisting to
some extent the 'flow' or alteration of shape which occurs in soft
ductile materials previous to fracture. He accordingly commenced to use
a specimen of the form shown in Fig. 2831, with a parallel portion for
extension of several inches in length, and specimens like that in Fig.
2830 became a thing of the past.
"The specimens shown in the figures admit of being secured in the
testing machine in many different ways. But whatever description of
holder be employed, two absolute requirements must be kept in view. The
holders must be stronger than the sample, and they must transmit the
stress in a direction parallel to the axis of the sample without any
bending or twisting tendency.
[Illustration: Fig. 2832.]
"Fig. 2832 gives two views of a very effective method of holding round
specimens, used by Mr. Kirkaldy in his earlier experiments carried out
for Messrs. Napier & Sons, of Glasgow. The enlarged ends of the samples
are clasped in split sockets provided with eye-holes for attaching them
to the shackles of the testing machine, the halves of the sockets being
held together during the experiment by small bolts passing through the
projecting lugs.
[Illustration: Fig. 2833.]
"Fig. 2833 explains the plan adopted for testing the strength of bolts
and nuts in the same series of experiments.
[Illustration: Fig. 2834.]
"A good holder for lathe-turned samples is shown in Fig. 2834. Close
fitting socket-pieces _b_ _b_ embrace each end of the specimen, and also
the turned collar at the extremity of the shackle _a_. The halves of the
socket are held together by a collar _c_, the interior of which and
exterior of the socket rings are turned to an equal taper, so that the
socket-pieces are held quite firmly when the collar _c_ is simply
slipped over them by hand. When the experiment is over, a few taps with
the hammer will remove the collar _c_.
[Illustration: Fig. 2835.]
"Samples of plates for tensile testing are usually shaped like Fig.
2835. The parallel portion B is generally 8, 10, or 12 inches long, as
in the case of the turned specimens. Two minor points in the preparation
of specimens may be here alluded to. In the first place the holes _a_
_a_ must be made large enough to obviate any danger of the pins which
are placed in these holes to secure the specimen being sheared in two
before the specimen breaks. In the second place, enough material must be
left around these pin or bolt holes to prevent the probability of the
metal tearing away between the hole and the edge of the plate. The pin
holes must be placed exactly in a line with the axis of the specimen,
and the part B must be quite parallel in width, so that the strength
(and the elongation during the testing) may be, as nearly as possible,
equal throughout the length of B. The shoulders, as _c_, should be easy
curves, so that sharp corners may be avoided. When a number of such
specimens are required at the same time, the strips of plate may be
clamped together and planed or slotted to the desired width as one
piece, but the tool marks should be afterwards removed by careful
draw-filing.
"When the plates are thin, small side pieces are riveted on the sides of
the ends to be clamped, as shown in Fig. 2836. These stiffen those ends
and afford a larger bearing for the securing pins. The connection with
the shackles is made by means of steel pins passing through the end
holes, and when specimens like 2835 are properly prepared, the direction
of the stress on them must be in a line with their axis. Fig. 2837 shows
another form of plate specimen in which the holes are dispensed with,
the ends being held in the machine by friction clips, as shown. These
specimens are more easily prepared, and from the absence of holes may be
made of a very narrow strip of plate.
[Illustration: Fig. 2836.]
[Illustration: Fig. 2837.]
"In Fig. 2837 the jaws or forked arms of the shackle are closed to form
a rectangular ring, as shown in section in the figure. Two of the
interior faces are tapered inwards to the same angle as the back of the
wedges or clips _a a´_, which are perfectly smooth and free to slide
upon the inclined or tapered surfaces of the shackles. The faces of the
wedges, however, which come in contact with and grip the specimen to be
tested, as _b_, are fluted or grooved, so that the friction of the edges
against the specimen is much greater than against the inside surfaces of
the shackles. The result of the arrangement is, that when the shackles
are pulled, the wedges _a a´_ are tightened against the specimen with a
degree of force proportionate to the load on the specimen, which is
prevented from slipping through the clips by the 'bite' of their fluted
faces. The grooves on the faces of the clips need not be deep--a depth
of a little more than 1/16, with about the same distance apart,
answering well for ordinary loads. With deep grooves and a wider pitch
apart, the danger of the specimen breaking in the clips is increased.
The inclination of the backs of the wedges _a a´_ to the faces may be at
an angle of 5 or 6 degrees. When the taper is too small, the removal of
the halves of the specimen after breaking is sometimes difficult, while
on the other hand, when too great, the specimen is apt to slip between
the wedges while being tested. The wedges exert a very considerable
outward pressure, and the jaws of the shackles must be made strong
enough to resist any strain likely, under extreme conditions, to fall on
them, otherwise they will speedily become unfit for use. In securing a
specimen care must be taken that its axis is in the direct line of
strain, and the opposite clips should be driven in equally so that the
stress may act fairly upon it. Parallel planed strips of metal, without
any enlargement at the ends, may be tested in these friction clips,
though, of course, there is a chance of the specimen breaking within
them. Turned specimens may also be held by such clips; as also may
rough, unturned round and square bars, an advantage when it is desired
to immediately ascertain approximately the strength of metal samples."
Open fires for hand forging purposes are mainly of two classes, those
having a side and those with a bottom or vertical blast.
[Illustration: Fig. 2838.]
Fig. 2838 represents a side draft forge. F is the fireplace, usually
from 3 to 5 feet long, T is the tuyère through which the blast enters
the fire, B being the blast pipe. To prevent T from being burned away it
is hollow as at S, and two pipes P and P´ connect to the water-tank W,
thus maintaining a circulation of water through S; V is simply a valve
or damper to shut off the supply of air from the tuyère; D is the
opening to the chimney C.
The side blast, though not so much used as in former years, is still
preferred by many skilful mechanics, on the ground that it will give a
cleaner fire with less trouble. The method of accomplishing this is to
dig out a hole in the fire bed and fill it in with coked coal, which
will form a drain through which the slag or clinker may sink, instead of
remaining in the active fire and obstructing the blast.
In cases where the fire requires to be built farther out from the
chimney wall than the location of the tuyère permits, it may be built
out as follows:--
[Illustration: Fig. 2839.]
[Illustration: Fig. 2840.]
A bar B, Fig. 2839, is placed in the tuyère hole and supported at the
other end at P. The coal is well wetted and packed around and above the
bar, which is then pulled out endwise, leaving a blast hole through the
coal, as is shown in the end view Fig. 2840.
[Illustration: Fig. 2841.]
Fig. 2841 represents a patent tuyère of vertical or bottom draft, in
which the blast passes through pipe A and circulates around B, finding
egress at C into the fire. C is hollow and receives water from the tank
F by the pipe D. The steam generated in the nozzle C is conveyed to the
tanks by the pipe E.
Figs. 2842 and 2843 represent a blacksmith's forge, for work up to and
about 4 inches in diameter. It consists of a wind-box A, supported on
brickwork which forms an ash-pit G beneath it. To this box is bolted the
wind-pipe B, and at its bottom is the slide E. In an orifice at the top
of A is a triangular and oval breaker D, connected to a rod operated by
the handle C. This rod is protected from the filling which is placed
between the brickwork and the shell F of the forge by being encased in
an iron pipe I. The blast passes up around the triangular oval piece D.
The operation is as follows: when D is rotated, it breaks up the fire
and the dirt falls down into the wind-box, cleaning the fire while the
heat is on. At any time after a heat the slide E may be pulled out,
letting the slag and dirt fall into the ash-pit beneath. It is a great
advantage to be able to clean the fire while a heat is on without
disturbing the heat.
[Illustration: Fig. 2842.]
[Illustration: Fig. 2843.]
Blacksmiths' anvils are either of wrought iron steel faced, or of cast
iron steel faced, the faces being hardened. It is sometimes fastened to
the block by spikes driven in around the edges. A better plan, however,
is to make the block the same size as the anvil, and secure the latter
by two bands of iron and straps, as shown in Fig. 2844, because in this
way the block will not come in the way of arms or projecting pieces that
hang below the anvil. The square hole is for receiving the stems of
swages, fullers, &c., and for placing work over to punch holes through
it, and the round is used for punching small holes.
The proper shape for blacksmiths' tongs depends upon whether they are to
be used upon work of a uniform size and shape, or upon general work. In
the first case, the tongs may be formed to exactly suit the special
work. In the second case, they must be formed to suit as wide a range of
work as convenient.
Suppose, for example, the tongs are for use on a special size and shape
of metal only; then they should be formed so that the jaws will grip the
work evenly all along, and therefore be straight along the gripping
surface. It will be readily perceived, however, that if such tongs were
put upon a piece of work of greater thickness, they would grip it at the
inner end only, and it would be impossible to hold the work steady. The
end of the work would act as a pivot, and the part on the anvil would
move about. It is better, therefore, for general work to curve the jaws,
putting the work sufficiently within the jaws to meet them at the back
of the jaw, when the end will also grip the work. By putting the work
more or less within the tongs, according to its thickness, contact at
the end of the work and at the point of the tongs may be secured in one
pair of tongs over a wider range of thickness of work than would
otherwise be the case. This applies to tongs for round or other work
equally as well as to flat or square work.
To maintain the jaw pressure of the tongs upon the work, a ring is
employed, the tong ends being curved to prevent the ring from slipping
off.
After a piece of work has left the fire it should, if there are scales
adhering upon it, have them cleaned off before being forged, for which
purpose the hammer head or an old file is used, otherwise the forging
will not be smooth, and the scale will be hammered into the surface.
This will render the forging very hard to operate upon by steel cutting
tools, and cause them to dull rapidly. For the same reason it is proper
to heat a finished forging to a low red heat and pass a file over its
surface, which will leave the forging soft as well as free from scale. A
forging should not be finally finished by being swaged or forged after
it has become black hot, because it produces a surface tension that
throws the work out of true as the metal is cut away in finishing it.
Work to be drawn out is treated according to the amount of elongation
and reduction of diameter required. Thus, suppose a piece of square work
to require to be drawn out, then it is hammered on its respective sides,
being turned upon the anvil so that each successive side shall receive
the hammer blows. It is essential, however, that the piece be forged
square, or in other words, that during the forging the sides be kept at
a right angle one to the other, or else the work will hammer hollow, as
it is termed; that is to say, the iron will split at the centre of the
bar, which occurs from its being forged diamond-shaped instead of
square. If a piece required to be forged diamond-shaped, it must be
forged square until reduced to such dimensions as will leave sufficient
to draw out while altering its form from the square to the
diamond-shape.
In very small work, which is more apt to hammer hollow than large work,
the end of the piece is left of enlarged size, as shown in the figure,
the strength of the enlarged end serving to prevent the hammering
hollow, which usually begins at the end of the piece; the end is in this
case forged last. In the case of round work the same rule holds good,
inasmuch as that a round bar may be forged smaller to some extent,
either by hammer blows or by swaging, but if the forging by hammer blows
be excessive, hammering hollow is liable to ensue.
The blacksmith's set of chisels consists of a hot chisel for cutting off
hot iron, a cold chisel for cutting cold metal, a hardy, which sets in
the square hole in the anvil, [C]-chisels, which are curved somewhat
like the carpenter's gouge, and a cornering or [V]-chisel, in which the
cutting edges are at a right angle one to the other.
[Illustration: Fig. 2844.]
The hot chisel has its edge well curved in its length, and is kept cool
by lifting it from the work after each hammer blow, and by occasionally
dipping it in water. Lifting it also prevents it from wedging in the
work. The cold chisel is tempered to a blue, and answers virtually to
the machinist's chisel. The hardy is used for small work, which is laid
upon it and struck with the hammer. The [C]-chisel is used, not only in
curved corners, but also to cut off deep cuts, answering, like the cape
or cross-cut chisel of the machinist, to relieve the corners of the hot
chisel. The cornering chisel is used for square corners, situated so
that the hot chisel cannot be used. The blacksmith's punch is made well
taper, so that it shall not wedge in the hole it produces.
For large holes a small punch is first used, and the hole enlarged in
diameter by driving in punches of larger diameter. If this swells the
work at the sides, it is forged down while the punch is in the hole.
The first blow given to the punch is a light one, so as to leave an
indentation that will mark the location, and enable its easy correction
if necessary. The blows delivered after the correct location is indented
are quick and heavy; but a piece of soft coal is inserted and the punch
placed on top of it, the gases formed by the combustion of the coal
serving to prevent the punch from binding in the hole. Between the blows
the blacksmith lifts the punch and moves the handle part of a lateral
rotation, which prevents it from becoming fast in the hole. The punch
should not be suffered to get red hot, but must be removed and cooled, a
fresh piece of green soft coal being inserted in the hole just previous
to the punch. If the punch is allowed to become as heated as the work,
the end will "upset" or swell and become firmly locked. Should the punch
lock in the hole a few blows will usually loosen it, but in extreme
cases it is sometimes necessary to employ another punch from the
opposite side of the work. Unless in very thin work, the hole is punched
half way from each side, because by that means a short stout punch may
be used.
It is obvious that when the hole requires to be bell-mouthed or of any
other form, the punch must be made to correspond.
The tools employed by the blacksmith, other than tongs, hammers,
chisels, and punches, are composed mainly of "fullers" and "swages" of
various kinds. The fuller is essentially a spreading tool, while the
swage may be termed essentially a shaping one.
[Illustration: Fig. 2845.]
In Fig. 2845, for example, let A represent an end view of an anvil, B
the bottom, and C the top fuller, and the effects of blows upon C will
be mainly to stretch the piece in the direction of its length without
swelling it out sideways.
[Illustration: Fig. 2846.]
[Illustration: Fig. 2847.]
[Illustration: Fig. 2848.]
[Illustration: Fig. 2849.]
If the work requires to be swelled sideways we turn the fuller the other
way around, as in Fig. 2846, in which it is supposed that one side of
the work is to be kept flat, hence no bottom fuller is employed. The
action of a fuller may be increased in the required direction by leaning
in the direction in which we desire to drive the iron; thus, suppose we
require to spread the end of a rectangular bar from the full lines to
the dotted ones in Fig. 2847 and the first fuller across the piece as at
A, Fig. 2848, and then spread out the end by fullering, as in Fig. 2849,
inclining the fuller in the direction in which we desire to forge the
iron.
[Illustration: Fig. 2850.]
It is the roundness of the face of the fuller that serves to control the
direction in which it will drive the iron, since the curve acts somewhat
on the principle of a wedge. Suppose, for example, that the faces were
flat, as in Fig. 2850, and the iron would spread in both directions, the
same as though the hammer were used direct, and if the work were
intended to be kept parallel it would frequently require to be turned on
edge to forge down the bulge that would form on the edge.
[Illustration: Fig. 2851.]
Fullers are, however, also used as finishing tools for curves or
corners, an example being given in Fig. 2851, which represents a fuller
applied to finish the round corner of a collar.
[Illustration: Fig. 2852.]
[Illustration: Fig. 2853.]
[Illustration: Fig. 2854.]
For finishing plane surfaces the flatter shown in Fig. 2852 is employed,
W representing the work. For inside surfaces the flatter requires to be
offset, as in Fig. 2853, in which L represents a link whose face A may
be flattened by the flatter F. There is a tendency in this case for the
flatter to tip or cant; and to avoid this and regulate the flatter upon
the work, a side foot is sometimes added, as at A in Fig. 2854.
Swages are shaped according to the kind of work they are to be used for.
[Illustration: Fig. 2855.]
[Illustration: Fig. 2856.]
Fig. 2855, for example, represents a top and bottom swage for rounding
up iron. For general work the recesses or seats of such swages would be
made considerably oval, as in Fig. 2856, the work being revolved
slightly after each blow. This capacitates one swage for different sizes
of iron. When, however, a swage is to be used for one particular size
only, its cavity may be made more nearly a true half circle and may
envelop one half the diameter of the work, so that when the top and
bottom swages meet, the work will be known to be of the required
diameter without measuring it. If the seat were made a true half circle
it would lock upon the work, preventing the smith from revolving it and
making it difficult to remove the swage.
[Illustration: Fig. 2857.]
If the conditions are such that a swage must be used to perform forging
rather than finishing, its seat should be [V]-shaped and not curved.
Suppose, for example, that a piece of iron, say, 6 inches in diameter,
required a short section to be forged down to a diameter of 3 inches,
then the swages should be formed as in Fig. 2857, because otherwise the
effects of the blow will act to a certain extent to force the iron out
sideways, for reasons which will be explained presently.
[Illustration: Fig. 2858.]
[Illustration: Fig. 2859.]
[Illustration: Fig. 2860.]
In some cases, for small work, the upper swage is guided by the lower
one: thus, in Fig. 2858 is a swage for a cross piece, and the outside of
its base is squared and fits easily within the upper part of the lower
one shown in Fig. 2859. For very small work, on which the hand hammer
is sufficiently heavy to perform the swaging, a spring swage may be use:
thus, in Fig. 2860 is a swage for pieces of 3/8, 5/16, and 1/4 inch in
diameter, and having a square stem fitting into the square hole in the
anvil. Fig. 2861 represents a spring swage for a pin having a collar,
and it may be observed that the recess to form the collar must be
tapered narrowest at the bottom, so that the top swage will readily
release itself by the force of the spring, and so that the work may
easily be revolved in the lower one. A similar tool is shown in Fig.
2862, designed for punching sheet metal cold, the die D being changeable
for different sizes of punches P.
[Illustration: Fig. 2861.]
[Illustration: Fig. 2862.]
[Illustration: Fig. 2863.]
For large hand-made forgings the swage block, such as in Fig. 2863, is
employed, S representing a stand for the block, whose dimensions are
larger than the block, so that the latter may be rested on its face in
the stand when the holes are to be used.
[Illustration: Fig. 2864.]
Fig. 2864 represents a swage block mounted on bearers, so that it may be
revolved to bring the necessary cavity uppermost.
[Illustration: Fig. 2865.]
[Illustration: Fig. 2866.]
[Illustration: Fig. 2867.]
Swages for trip hammers or for small steam hammers are for work not
exceeding about 4 inches in diameter, made as in Fig. 2865, the weight
of the top swage being sufficient to keep the two closed as in the
figure; for larger sizes the bottom swage fits to the anvil, and the top
one is provided with a handle, as in Fig. 2866, B representing the anvil
block, S´ the bottom, and S the top swage, having a handle H. The flange
of the bottom swage is placed as in Fig. 2867, so as to prevent the
swage from moving off the anvil block when the work is pushed through it
endways. Obviously such swages are employed when the part to be swaged
is less in length than the width of the hammer or of the anvil face.
If the hammer and anvil face is rounded as in Fig. 2868, or if dies thus
shaped are placed in them, their action will be the same as that of the
fuller, drawing the work out lengthways, with a minimum of effect in
spreading it out sideways.
Detached fullers, such as shown in Figs. 2869 and 2870, are, however,
used when the section to be acted upon is less in length than the hammer
face.
In the case of trip hammers, steam hammers, &c., blocks fitted to the
hammer and anvil block may take the place of detached swages and
fullers. Thus, in Fig. 2871 is represented the hammer and anvil block
for flat work, the corners being made rounded, because if left sharp
they would leave marks on the work. The blocks or dies A and B are
dovetailed into their places, and secured by keys K; hence they may be
removed, and dies of other shapes substituted.
When the work is parallel it may be forged to its finished dimensions by
forming in the lower die recesses whose depth equals the required
dimensions. Thus, in Fig. 2872 the recess A in the lower die equals in
depth the depth A of the work, while the depth of the recess B in the
die equals the thickness of the bar; hence by passing the work
successively from A to B, and turning it over a quarter turn, it will be
made to finished size, when the faces C D of the dies meet.
For this class of work the recesses must obviously be made in the lower
die, because it would be difficult to hold the work upon the lower die
in the proper position to meet a recess cut in the upper one: and,
furthermore, the recesses in the die should be wider than the work, to
avoid the necessity of holding the work exactly straight in the recess,
and keeping it against the shoulder or vertical face of the recess. If,
however, the work is to be made taper, we may obviously make the recess
taper, so as to produce smooth work, the die recess being made to be of
the correct depth for the smallest end of the work.
[Illustration: _VOL. II._ =EXAMPLES IN STEAM HAMMER WORK.= _PLATE XV._
Fig. 2868.
Fig. 2869.
Fig. 2870.
Fig. 2871.
Fig. 2872.
Fig. 2873.
Fig. 2874.
Fig. 2875.
Fig. 2876.
Fig. 2877.
Fig. 2878.]
When the shape of the work is such that it cannot be moved upon the die
during the forging, the operation is termed stamping, or if the hammer
or upper die falls of its own weight it is termed drop forging, and in
this case the finishing dies are made the exact shape of the work, care
being taken to let the work be enveloped as much as possible by the
bottom die, so that the top one shall not lift it out on its up stroke.
In forging large pieces from square to round we have several important
considerations. In order to keep the middle of the work sound, it must
be drawn square to as near as possible the required diameter before the
finishing is begun. During this drawing-down process the blows are heavy
and the tendency of the work is to spread out at the sides, as in Fig.
2873.
When the work is ready to be rounded up it is first drawn to an octagon,
as shown in Fig. 2874, so as to bring it nearer the work, nearer to
cylindrical form. The corners are then again hammered down, giving the
work sixteen sides, the work during this part of the process being moved
endways, as each corner is hammered down. The blows are during this part
of the forging lighter, but still the tendency is to spread the work out
sideways. The final finishing to cylindrical form is done with light
blows, the work being revolved upon the anvil without being moved
endways, so that a length equal to the width of the anvil is finished
before the work is moved endways to finish a further part of the length.
The tendency to spread sideways is here unchecked, because the iron is
squeezed top and bottom only. We may check it to some extent, however,
by employing a bottom swage block, as in Fig. 2875, in which case the
contact of the swage and the work will extend further around the work
circumference than would be the case with a flat anvil. If we were to
use a top and a bottom swage, as in Fig. 2876, the circumferential
surface receiving the force of the blow will be still further increased,
but there will still be a tendency to spread at the sides, as at A B, in
Fig. 2876. A better plan, therefore, is to use a [V]-block with the
hammer, as in Fig. 2877, in which case the effects of the blow are felt
at A, B, and C, and the points A B of resistance being brought higher up
on the work, its tendency to spread is obviously diminished. By using a
top and bottom [V]-block, as shown in Fig. 2878, the effect will be to
drive the metal towards the centre, and, therefore, to keep it sound at
the centre, it being found that if the metal is swaged much without
means being taken to prevent spreading, it "hammers hollow," as it is
termed, or in other words, splits at its centre.
[Illustration: Fig. 2879.]
The points A B of resistance to the blow at C are higher and the
tendency to spread sideways is better resisted. For cutting off under
the steam hammer, the hack shown in Fig. 2879 is used, being simply a
wedge with an iron handle.
WELDING.--In the welding operations of the blacksmith there are points
demanding special attention: first, to raise the temperature of the
metal to a proper heat; second, to let the temperature be as nearly
equal as practicable all through the mass; third, to have the surfaces
to be welded as clean and free from oxidation as possible; fourth, have
the parts to be welded of sufficient diameter or dimensions to permit of
the welded joint being well forged.
The following remarks on the theory of welding are from a paper read by
Alexander L. Holley before the American Institute of Mining Engineers:--
"The generally received theory of welding is that it is merely pressing
the molecules of metal into contact, or rather into such proximity as
they have in the other parts of the bar. Up to this point there can
hardly be any difference of opinion, but here uncertainty begins. What
impairs or prevents welding? Is it merely the interposition of foreign
substances between the molecules of iron, or of iron and any other
substance which will enter into molecular relations or vibrations with
iron? Is it merely the mechanical preventing of contact between
molecules, by the interposition of substances? This theory is based on
such facts as the following:
"1. Not only iron but steel has been so perfectly united that the seam
could not be discovered, and that the strength was as great as it was at
any point, by accurately planing and thoroughly smoothing and cleaning
the surfaces, binding the two pieces together, subjecting them to a
welding heat, and pressing them together by a very few hammer blows. But
when a thin film of oxide of iron was placed between similar smooth
surfaces, a weld could not be effected.
"2. Heterogeneous steel scrap, having a much larger variation in
composition than these irons have, when placed in a box composed of
wrought-iron side and end pieces laid together, is (on a commercial
scale) heated to the high temperature which the wrought-iron will stand,
and then rolled into bars which are more homogeneous than ordinary
wrought iron. The wrought-iron box so settles together as the heat
increases that it nearly excludes the oxidizing atmosphere of the
furnace, and no film of oxide of iron is interposed between the
surfaces. At the same time the enclosed and more fusible steel is
partially melted, so that the impurities are partly forced out and
partly diffused throughout the mass by the rolling.
"The other theory is that the molecular motions of the iron are changed
by the presence of certain impurities, such as copper and carbon, in
such a manner that welding cannot occur, or is greatly impaired. In
favor of this theory it may be claimed that, say, 2 per cent. of copper
will almost prevent a weld, while, if the interposition theory were
true, this copper could only weaken the weld 2 per cent., as it could
only cover 2 per cent. of the surfaces of the molecules to be united. It
is also stated that 1 per cent. of carbon greatly impairs welding power,
while the mere interposition of carbon should only reduce it 1 per cent.
On the other hand, it may be claimed that in the perfect welding due to
the fusion of cast iron, the interposition of 10 or even 20 per cent. of
impurities, such as carbon, silicon, and copper, does not affect the
strength of the mass as much as 1 or 2 per cent. of carbon or copper
affects the strength of a weld made at a plastic instead of a fluid
heat. It is also true that high tool steel, containing 1-1/2 per cent.
of carbon is much stronger throughout its mass, all of which has been
welded by fusion, than it would be if it had less carbon. Hence copper
and carbon cannot impair the welding power of iron in any greater degree
than by their interposition, provided the welding has the benefit of
that perfect mobility which is due to the fusion. The similar effect of
partial fusion of steel in a wrought-iron box has already been
mentioned. The inference is, that imperfect welding is not the result of
a change in molecular motions due to impurities, but of imperfect
mobility of the mass--of not giving the molecules a chance to get
together.
"Should it be suggested that the temperature of fusion, as compared with
that of plasticity, may so change chemical affinities as to account for
the different degrees of welding power, it may be answered that the
temperature of fusion in one kind of iron is lower than that of
plasticity in another, and that as the welding and melting points of
iron are largely due to the carbon they contain, such an impurity as
copper, for instance, ought, on this theory, to impair welding in some
cases and not to affect it in others.
"The obvious conclusions are: 1st. That any wrought iron, of whatever
ordinary composition, may be welded to itself in an oxidizing atmosphere
at a certain temperature, which may differ very largely from that one
which is vaguely known as 'a welding heat.' 2nd. That in a non-oxidizing
atmosphere heterogeneous irons, however impure, may be soundly welded at
indefinitely high temperatures.
"The next inference would be that by increasing temperature we chiefly
improve the quality of welding. If temperature is increased to fusion,
welding is practically perfect; if to plasticity and mobility of
surfaces, welding should be nearly perfect. Then how does it sometimes
occur that the more irons are heated the worse they weld?
"1. Not by reason of mere temperature, for a heat almost to dissociation
will fuse wrought iron into a homogeneous mass.
"2. Probably by reason of oxidation, which, in a smith's fire
especially, necessarily increases as the temperature increases. Even in
a gas furnace a very hot flame is usually an oxidizing flame. The oxide
of iron forms a dividing film between the surfaces to be joined, while
the slight interposition of the same oxide, when diffused throughout the
mass by fusion or partial fusion, hardly affects welding. It is true
that the contained slag, or the artificial flux, becomes more fluid as
the temperature rises, and thus tends to wash away the oxide from the
surfaces; but inasmuch as any iron with any welding flux can be oxidized
till it scintillates, the value of a high heat in liquefying the slag is
more than balanced by its damage in burning the iron.
"But it still remains to be explained why some irons weld at a higher
temperature than others; notably, white irons high in carbon, or in some
other impurities, can only be welded soundly by ordinary processes at
low heats. It can only be said that these impurities, as far as we are
aware, increase the fusibility of iron, and that in an oxidizing flame
oxidation becomes more excessive as the point of fusion approaches.
Welding demands a certain condition of plasticity of surface; if this
condition is not reached, welding fails for want of contact due to
mobility; if it is exceeded, welding fails for want of contact due to
excessive oxidation. The temperature of this certain condition of
plasticity varies with all the different compositions of irons. Hence,
while it may be true that heterogeneous irons, which have different
welding points, cannot be soundly welded to one another in an oxidizing
flame, it is not yet proved, nor is it probable, that homogeneous irons
cannot be welded together, whatever their composition, even in an
oxidizing flame. A collateral proof of this is, that one smith can weld
irons and steels which another smith cannot weld at all, by means of a
skilful selection of fluxes and a nice variation of temperatures.
"To recapitulate. It is certain that perfect welds are made by means of
perfect contact due to fusion, and that nearly perfect welds are made by
means of such contact as may be got by partial fusion in a non-oxidizing
atmosphere or by the mechanical fitting of surfaces, whatever the
composition of the iron may be within all known limits. While high
temperature is thus the first cause of that mobility which promotes
welding, it is also the cause, in an oxidizing atmosphere, of that
'burning' which injures both the weld and the iron. Hence, welding in an
oxidizing atmosphere must be done at a heat which gives a compromise
between imperfect contact due to want of mobility on the one hand, and
imperfect contact due to oxidation on the other hand. This heat varies
with each different composition of irons. It varies because these
compositions change the fusing points of irons, and hence their points
of excessive oxidation. Hence, while ingredients such as carbon,
phosphorus, copper, &c., positively do not prevent welding under fusion,
or in a non-oxidizing atmosphere, it is probable that they impair it in
an oxidizing atmosphere, not directly, but only by changing the
susceptibility of the iron to oxidation."
In welding steel to iron both are heated to as high a temperature as
possible without burning, and a welding compound or flux of some kind is
used.
In welding steel to steel the greatest care is necessary to obtain as
great a heat as possible without burning, and to keep the surfaces
clean.
An excellent welding compound is composed as follows: Copperas 2 ozs.,
salt 4 ozs., white sand 4 lbs., the whole to be mixed and thrown upon
the heat, as is done when using white sand as described for welding
iron. An equally good compound is made up of equal quantities of borax
and pulverized glass, well wetted with alcohol, and heated to a red heat
in a crucible. Pulverize when cool, and apply as in the case of sand
only.
A welding compound for cast steel given by Mr. Rust in the _Revue
Industrielle_ is made up as follows: 61 parts of borax, 20 parts of
sal-ammoniac, 16-3/4 parts of ferrocyanide, and 5 parts of colophonium.
He states that with the acid of this compound cast steel may be welded
at a yellow red heat, or at a temperature between the yellow, red, and
white heats. The borax and sal-ammoniac are powdered, mixed, and slowly
heated until they melt. The heating is continued until the strong odor
of ammonia ceases almost entirely, a small quantity of water being added
to make up for that lost by evaporation. The powdered ferrocyanide is
then added, together with the colophonium, and the heating is continued
until a slight smell of cyanogen is noticed. The mixture is allowed to
cool by spreading it out in a thin layer.
[Illustration: Fig. 2880.]
[Illustration: Fig. 2881.]
The lap weld is formed as follows: Suppose it is required to weld
together the ends of two cylindrical pieces, and the first operation is
to pump or upset the ends to enlarge them, as shown in Fig. 2880, so as
to allow some metal to be hammered down in making the weld without
reducing the bar below its proper diameter. The next operation is to
scarf the ends forming them, as shown in Fig. 2881, and in doing this it
is necessary to make the scarf face somewhat rounding, so that when put
together as in the figure contact will occur at the middle, and the weld
will begin there and proceed as the joint comes together under the blows
towards the outside edges. This squeezes out scale or dirt, and excludes
the air, it being obvious that if the scarf touched at the edges first,
air would be enclosed that would have to find its escape before the
interior surfaces could come together.
It is obvious, that if the two pieces require to weld up to an exact
length and be left parallel in diameter when finished an allowance for
waste of iron must be made; and a good method of welding under these
conditions is as follows:--
[Illustration: Fig. 2882.]
[Illustration: Fig. 2883.]
Let the length of the two pieces be longer than the finished length to
an amount equal to the diameter. Then cut out a piece as at A, in Fig.
2882, the step measuring half the diameter of the bar as shown. The
shoulder A is then thrown back with the hammer, and the piece denoted by
the dotted line B is cut off, leaving the shaft as shown in Fig. 2883.
The faces of the scarf should be somewhat rounding, so that when the
weld is put together contact will take place in the centre of the
lapping areas. Then, as the surfaces come together, the air and any
foreign substances will be forced out, whereas, were the surfaces hollow
the air and any cinder or other foreign substances would be closed in
the weld, impairing its soundness.
The lap of the two pieces, when scarfed in this manner, is shown in Fig.
2884.
[Illustration: Fig. 2884.]
To take the welding heat the fire should be cleaned out and clear coked
coal, and not gaseous coal, used. The main points in a welding heat are,
to heat the iron equally all through, to obtain the proper degree of
heat, and to keep the scarfed surfaces as free from oxidation, and at
the same time as clean, as possible.
To accomplish these ends the iron must not be heated too quickly after
it is at a good red heat, and the fire must be so made that the blast
cannot meet it at any point until it has passed through the bed of the
fire.
When the iron is getting near the welding heat it may be sprinkled with
white sand, which will melt over it and form a flux that will prevent
oxidation and cool the exterior, giving time to the interior to become
equally heated. The sand should be thrown on the work while in the fire,
as removing the work from the fire causes it to oxidize or scale
rapidly. The work should be turned over and over in the fire, the scarf
face being kept uppermost until the very last part of the heating, when
the blast must be put on full, the bed of the fire kept full and clear
so that there shall be sufficient bed to prevent the blast from meeting
the heat until it has passed through the glowing coals.
When the heat is taken from the fire it should meet the anvil with a
blow, the scarfed face being downwards, to jar off any dirt, cinder,
&c., and the scarf should be cleaned by a stroke or two of a wire brush.
But as every instant the iron is in the air it is both cooling and
oxidizing, these operations must be performed as quickly as possible.
The two scarfs being laid together as shown in Fig. 2884, the first
blows must be delivered lightly, so as not to cause the upper piece to
move, and as quickly as possible, the force of the blows being increased
regularly and gradually until the weld is sufficiently firm to hold well
together, when it may be turned on edge and the edges of the scarf
hammered to close and weld the seam. If this turning is done too soon,
however, it may cause the two halves to separate. When the weld is
firmly and completely made the enlarged diameter due to the scarfing may
be forged down, working the iron as thoroughly as possible.
[Illustration: Fig. 2885.]
[Illustration: Fig. 2886.]
To form the scarf of a ring or collar, one end is bevelled, as at B in
Fig. 2885 and after the piece is bent to a circle it is cut off and
bevelled as at A. When a slight band is to be welded, and it is
difficult to steady the ends to bring them together, a clamp may be used
to hold them as in Fig. 2886.
[Illustration: Fig. 2887.]
Fig. 2887 represents a tongue weld, and it is obvious that to insure
soundness the wedge piece should fit in the bottom of the split, which
may be well closed upon it by the hammer blows.
[Illustration: Fig. 2888.]
Fig. 2888 represents an example of a [V]-weld applied to welding up a
band that is to be square when finished, and as the lengths of the sides
must be equal when finished, the side on which the weld is made should
be made shorter, so that in stretching under the welding blows it will
be brought to its proper length. The [V] form of weld is employed
because it stretches less in welding than the lap weld. The [V]-piece to
be welded in should bear at the bottom of the [V], and the weld made by
fullering.
[Illustration: Fig. 2889.]
[Illustration: Fig. 2890.]
Welds of this kind are obviously most suitable for cases in which the
weld is required to influence the shape of the piece as little as
possible. The figures above, which are taken from _Mechanics_,
illustrate as an example the repairing of a broken strap for the beam of
a river steamboat. The crack is at A, Fig. 2889, and is held together by
a clamp as shown; a [V]-recess is cut out as in Fig. 2890, and this
recess is fullered larger, as in Fig. 2891. A [V]-block is then welded
in. The strap is then turned over a second [V]-groove, cut out and
fullered out, and a second [V]-piece welded in. By thus welding one side
at a time the welding is taken in detail as it were, and the blows can
be less heavy than if a larger weld were made at one heat, as would be
the case if but one [V] block were used. A similar form of weld may be
employed to form a square corner, as is shown in Fig. 2892, which is
taken from "The Blacksmith and Wheelwright." In this example the inside
corner is shown to have a fillet, which greatly increases the difficulty
of the job. The weld is made by first fullering the [V]-piece on the
sides and on the rounded corner and then laying the piece on the anvil
to forge down, the fullering leaving the finished job as in Fig. 2893.
[Illustration: Fig. 2891.]
[Illustration: Fig. 2892.]
[Illustration: Fig. 2893.]
[Illustration: Fig. 2894.]
[Illustration: Fig. 2895.]
When one piece has to be driven on to the other, the weld is called a
pump-weld, for which the ends should be rounded as in Fig. 2894, so that
they will meet at their centres, and will, when struck endways to make
the weld, come to the shape shown in Fig. 2895.
[Illustration: Fig. 2896.]
It is obvious that in this case the interior of the iron comes together
and is welded, and that dirt, &c., is effectually excluded; hence if the
iron is properly heated the weld may be as sound as a lap weld, and is
preferred by many as the sounder weld of the two. When a stem requires
to be welded to a large flat surface, the pump weld is the only one
possible, being formed as in Fig. 2896, in which the stem is supposed to
be welded to a frame. The plate is cupped as shown, and the metal being
driven up on the sides as much as possible, the stem overlaps well at C
B, so that it may be fullered there. The stem should first meet its seat
at A, so that dirt, &c., may squeeze out as the welding proceeds.
[Illustration: Fig. 2897.]
[Illustration: Fig. 2898.]
Figs. 2897 and 2898 represent an example of welding a collar on round
iron. The bar is upset so as to enlarge it at A, where the collar is to
be. The collar is left open at the joint, and while it is cold it is
placed on the red-hot bar and swaged until the ends are closed. The
welding of the whole may then be done at one heat, swaging the outside
of the collar first. Unless the bar is upset there would be a crack in
the neck B of the collar on both sides.
WELDING ANGLE IRON.--Let it be required to form a piece of straight
angle iron to a right angle.
[Illustration: Fig. 2899.]
The first operation is to cut out the frog, leaving the piece as shown
in Fig. 2899; the width at the mouth A of the frog being 3/4 inch to
every inch of breadth measured inside the flange as at B.
The edges of the frog are then scarfed and the piece bent to an acute
angle; but in this operation it is necessary to keep the scarfs quite
clean and not to bend them into position to weld until they are ready
for the welding heat; otherwise scale will form where the scarfs overlap
and the weld will not be sound.
The heat should be confined as closely as possible to the parts to be
welded; otherwise the iron will scale and become reduced below its
proper thickness.
The iron is then bent to the shape shown in Fig. 2900; and the angle to
which it is bent is an important consideration. The object is to leave
the overlapping scarf thicker than the rest of the metal, and then the
stretching which accompanies the welding will bring the two arms or
wings to a right angle.
[Illustration: Fig. 2900.]
It is obvious, then, that the thickness of the metal at the weld
determines the angle to which the arms must be bent before welding. The
thicker the iron the more acute the angle. If the angle be made too
acute for the thickness of the iron at the weld there is no alternative
but to swage the flange down and thin it enough to bring the arms to a
right angle. Hence it is advisable to leave the scarf too thick rather
than too thin, because while it is easy to cut away the extra metal, if
necessary, it is not so easy to weld a piece in to give more metal. In
very thin angle irons, in which the wastage in the heating is greater in
proportion to the whole body of metal, the width of the frog at A in
Fig. 2901 may be less, as, say, 9/16 inch for every inch of angle-iron
width measured as at B in the figure. For angles other than a right
angle the process is the same, allowance being made in the scarf-joint
and bend before welding for the stretching that will accompany the
welding operation.
The welding blows should be light and quick, while during the scarfing
the scale should be cleaned off as soon as the heat leaves the fire, so
that it will not drive into the metal and prevent proper welding. The
outside corner should not receive any blows at its apex; and as it will
stretch on the outside and compress on the inside, the forging to bring
the corner up square should be done after the welding.
[Illustration: Fig. 2901.]
The welding is done on the corner of an angle block, as in Fig. 2901, in
which A is the angle iron and B the angle block.
[Illustration: Fig. 2902.]
To bend an angle iron into a circle, with the flange at the extreme
diameter, the block and pins shown in Fig. 2902 are employed. The block
is provided with the numerous holes shown for the reception of the pins.
The pins marked 1 and 2 are first inserted and the iron bent by placing
it between them and placed under strain in the necessary direction. Pins
3 and 4 are then added and the iron again bent, and so on; but when the
holes do not fall in the right position, the length of the pin-heads
vary in length to suit various curves.
To straighten the iron it is flattened on the surface A and swaged on
the edge of the flange B, the bending and straightening being performed
alternately.
[Illustration: Fig. 2903.]
When the flange of the angle iron is to be inside the circle, as in Fig.
2903, a special iron made thicker on the flange A is employed. The
bending is accomplished, partly by the pins as before, and partly by
forging thinner, and thus stretching the flange A while reducing it to
its proper thickness.
TO FORGE A BOLT BY HAND.--The blanks for bolts must be cut off
sufficiently long to admit of one end being upset to form the head, the
amount of this allowance, obviously, being determined by the size of the
head.
[Illustration: Fig. 2904.]
[Illustration: Fig. 2905.]
Fig. 2904 is a side view, partly in section, and Fig. 2905 a top view of
an anvil block for upsetting the ends of blanks to form the heads of
bolts. The stem fits into the square hole of the anvil. The tongue is
pivoted as shown in the top view to two lugs provided on the block; upon
the tongue rests a steel pin whose length determines the height to which
the blank will project above the top of the block, and, therefore, the
amount or length of blank that will be upset to form the head, this
amount being three times the diameter of the bolt for _black heads_.
[Illustration: Fig. 2906.]
[Illustration: Fig. 2907.]
The hole for the blank is made about 1/64 inch larger in diameter than
the designated size of the bolt, to permit of the easy extraction of the
blank after it is upset, this extraction being accomplished by striking
the end of the tongue with the hammer. If the block is made of cast iron
the upper end of the hole will become worn after forging five hundred or
six hundred bolts, leaving the bolts with a rounded neck, as at C C in
Fig. 2906; a steel block, however, will forge several thousand bolts
without becoming enlarged.
An excellent plan is to provide the block with removable dies, such as
at _d_ _d_ in Fig. 2907, which are easily renewed, a number of such dies
having different diameters of bore fitted to the same block.
When the bolt end is sufficiently reset or enlarged to form the head it
is laid in a bottom swage, containing three of the six sides of the
hexagon, and a hammer blow on the uppermost part of the end forges a
flat side. After each blow the work is revolved one-sixth of a
revolution, and as the angles of the swage are true they obviously true
the angles of the bolt head. After the head has been roughed down it is
necessary to flatten it again under the head and on the end, for which
purpose it may be placed in the heading block shown in Fig. 2904, after
which the sides of the head may be finished and the cupping tool for
chamfering the head applied.
The bolt may require passing from the heading tool to the swage several
times, as forging it in one direction spreads it in another.
[Illustration: Fig. 2908.]
In shops where bolt-making is of frequent occurrence a special
bolt-making device is usually employed. It consists of an oliver or foot
hammer, having two hammers and an anvil; in the square hole at one end
of the anvil fits a hardy or bottom chisel, such as shown in Fig. 2908,
for cutting up the bar or rod iron into bolt blanks; A is the anvil, H
the hardy, and G a gauge to determine the length cut off the rod R to
form a blank. An upsetting or heading device corresponding to that in
Fig. 2907 is provided, and at the other end of the anvil is the swage
for forming the bolt head.
The object of having two hammers is that one may be used for the
upsetting of the blank and the other for the swage. The swaging hammer
is provided with a hole and set-screw to receive top swages, and bolt
hammers are adjustable for height so that they may be set so that their
faces will meet the work fair.
[Illustration: Fig. 2909.]
[Illustration: Fig. 2910.]
[Illustration: Fig. 2911.]
Figs. 2909 to 2911 represent front, side, and top views of Pratt &
Whitney's portable bolt-forging device. It is provided with an elevating
screw that permits the employment of a single bolster-pin for all
lengths of bolt for a given diameter, instead of requiring a separate
pin for each different length of bolt. In the figures, A is a frame
carried upon wheels, and to which is pivoted at C C the jaw D. The
bolt-gripping dies are shown at E F. A treadle G is pivoted at H, and
acts upon the lower end of D, causing the die F to grip or release the
bolts, as may be required. The bolster-pin rests upon the end of the
screw I, which enters at its foot a split nut J, which is caused to grip
and lock the screw by operating the nut of the bolt K that passes
through the split of the nut. L is a spring that lifts the treadle when
it is relieved of the pressure of the operator's foot.
At M is a leather washer to protect the nut J from the scale that falls
from the forging. The operation is as follows:--
The nut K is released and the screw I operated to suit the length of
bolt required. Then J is caused to clamp the screw by operating the nut
K. The blank for the bolt is placed in the dies resting on the
bolster-pin, which in turn rests upon the end of the screw I. The
treadle G is depressed, and the bolt blank clamped between E and F. The
helper then with the sledge upsets the blank end to form the bolt head,
and the blacksmith forges it to shape in the former bar B, which is
provided with impressions for the form of head required, these
impressions being of varying sizes, as shown. The device is so strongly
proportioned as to be very solid, and is found to be a most useful
addition to the blacksmith's shop.
[Illustration: _VOL. II._ =EXAMPLES IN HAND FORGING.= _PLATE XVI._
Fig. 2917.
Fig. 2918.
Fig. 2919.
Fig. 2920.
Fig. 2921.
Fig. 2922.
Fig. 2923.
Fig. 2924.
Fig. 2925.
Fig. 2926.]
[Illustration: Fig. 2912.]
[Illustration: Fig. 2913.]
[Illustration: Fig. 2914.]
[Illustration: Fig. 2915.]
[Illustration: Fig. 2916.]
To forge a turn buckle, such as in Fig. 2912, we bend two rings, such as
in Fig. 2913, and weld into the open ends a piece as shown in Fig. 2914,
on the opposite side a recess A, Fig. 2915, is cut out to receive a
second piece, which being welded in the work appears as in Fig. 2916,
and the end may be drawn taper. Two such pieces welded together
obviously complete the job.
Fig. 2917 represents a yoke for the slide valve of a steam engine or a
locomotive, which may be forged by either of the following methods:
Fig. 2918 represents a stem A welded into the bar B, which may be bent
to the required rectangle and welded at the ends.
A second method is to jump the stem D and split it open as in the side
view in Fig. 2919. The bar E is forged with a projecting piece to go in
the split of D, and after the weld is made, bar E is drawn to size as
shown, leaving the two projections _x_ where the corners are to come,
which is necessary in order to have sufficient stock to bring the
corners up square. The ends of E are split open as in the end view at F,
and a piece G is then welded to F.
In a third method the end of the stem is rounded for the weld, as shown
in Fig. 2920. The ends of the bar J are then split open and piece K
welded on.
It is to be observed with reference to the two last methods that in
hammering to forge the weld the frame is closed, so that after welding
the swaging to finish may be carried on until the frame is brought to
square, and any superfluous metal may be cut away; whereas if the kind
of weld is such as to stretch the sides, it may happen that to get a
sound weld will stretch the side welded too long and throw the frame out
of shape.
Suppose, for example, that a scarf weld were made on the side of the
yoke opposite to the stem, and if, in welding, the scarf is hammered too
much, it would draw it out too much and throw the whole frame out of
shape, as in Fig. 2921, so that the welded side would require to be
jumped to bring it back to the proper length again.
A fourth method is to take a piece of iron and punch a hole in it, and
then split it open up to the hole, as in Fig. 2922, and by opening out
the split form the stem and part of the frame out of the solid, forging
the remainder of the frame by the plan described for either the second
or third methods.
A fifth method is to make the weld of the stem as in Fig. 2923, then
forge out the bar B, leaving projections _x_ _x_ to bring the corners
_y_ _y_ up square, and after bending to shape and squaring up to weld in
a piece C.
A sixth method is to form the band first as in Fig. 2924, form the stem
as in Fig. 2925, and weld as in Fig. 2926.
[Illustration: Fig. 2927.]
[Illustration: Fig. 2928.]
[Illustration: Fig. 2929.]
Figs. 2927, 2928, and 2929 represent a method of forging a fifth wheel
for a vehicle. A rectangular piece of Norway iron is fullered to form
the recess at C in Fig. 2927. Holes are then punched at _h_ and splits
are made to the dotted lines shown in the figure. The ends are then
opened out, forming a piece such as in Fig. 2928. The letter A
represents the same face of the work in all the figures, being the edge
in Fig. 2927, and the top face after the ends are opened out. The four
arms may then be dressed to shape, the two lower ones being drawn out
and threaded before being finally closed to shape. A piece may then be
welded on one end, as at B, to complete the circle.
[Illustration: Fig. 2930.]
[Illustration: Fig. 2931.]
[Illustration: Fig. 2932.]
To forge a double eye, such as in Fig. 2930, we may take a piece of
sufficient size and fuller at _a_ _a_, Fig. 2931; a hole is then punched
at _b_, and it is then split through to the dotted line in Fig. 2931,
and opened out as in Fig. 2932, and then forged to shape.
[Illustration: Fig. 2933.]
BENDING.--Fig. 2933 represents a tool for bending pieces of small
diameter to a short curve, either when cold or heated. In bending hot
iron it is advantageous to confine the heat as closely as possible to
the part to be bent, as a more true bend may then be obtained.
[Illustration: Fig. 2934.]
[Illustration: Fig. 2935.]
[Illustration: Fig. 2936.]
As an example in bending, let it be required to bend a straight shaft
into a crank shaft, and the following method (from "The Blacksmith and
Wheelwright") is pursued. The shaft is first bent as in Fig. 2934. The
piece is next bent as in Fig. 2935, and finally as in Fig. 2936, the
corners A A and B B corresponding in all the figures.
[Illustration: Fig. 2937.]
BLACKSMITH'S BENDING BLOCKS.--In cases where a great number of pieces of
the same size and shape are required to be bent during the forging
process, a great deal of time may be saved and greater accuracy secured
in the work by the employment of bending devices. Thus, in Fig. 2937 is
shown at A a clip requiring to be bent to the shape at B. A pair of
tongs is provided with a hole at C to receive the stem of the clip, and
the jaw D is made of the necessary width to close the ends of the
forging upon. It is obvious that the hole C being in the middle of the
width of the tong jaw, the wings will be equidistant from the pin.
Figs. from 2938 to 2943 represent bending devices.
[Illustration: Fig. 2938.]
[Illustration: Fig. 2939.]
[Illustration: Fig. 2940.]
[Illustration: Fig. 2941.]
Figs. 2938, 2939, and 2940, represent a "former" for a stake pocket for
freight cars. A is a cast-iron plate having a projection B, around which
the stake pocket C is bent. D is fast upon A, and affords a pivoted
joint for the bending levers E F. The work is placed in the former as
shown in Fig. 2939, and levers E F are swung around to the position
shown in Fig. 2938. To enable the work to be put in and taken out
rapidly and yet keep it firmly against the end of B, a hand-piece G is
used as in Fig. 2940, its form being more clearly shown in the enlarged
Fig. 2941. Sufficient room is allowed between B and D to admit the work,
and the end of the piece G, which is pressed in the direction denoted by
the arrow in Fig. 2940, forcing the work against B. A number of the
pieces are piled on the fire so as to heat them sufficiently fast to
keep the former at work, and the bottom piece is the one taken out.
The corners of the work are by this process brought up square and the
faces are kept out of wind. The surface A forms a level bed. These
advantages will be readily appreciated by all smiths who have had
comparatively thin work to bend to a right angle in the ordinary way.
[Illustration: Fig. 2942.]