THE FLAME AND ITS MANAGEMENT.
Before attempting to light the gas the operator must be sure that all
the air is exhausted from the tubes. Otherwise the flame will go back
and explode in the tubes or fire trap. To be sure of this the beginner
must test the gas. A handy test tube can be made by capping one end of a
piece of ½-inch pipe, which should be about 6 inches long. To test the
gas, first open wide the gas cock M on the generator, Fig. 1. Then open
the gas cock _f_ on the mixing fork and let the gas displace the air in
the tubes, which it will do in about one minute. Then invert the test
tube, Fig. 20, and hold it over the blow pipe tip for a moment until the
gas has displaced the air in the tube. Then quickly place your thumb
over the opening of the test tube, which will keep the gas from
escaping. Close the gas cock _f_ on the mixing fork, then take the test
tube to one side away from the generator, still keeping it inverted, and
bring it close to a lighted match or candle. It will light with a pop,
and if it is free from air it will burn quietly down in the tube until
the gas is exhausted. Continue to test the gas in this manner until it
burns as described, when it may be safely lit at the jet without fear of
its burning back. This precaution is necessary only after opening the
generator for some purpose.
[Illustration:
_Fig. 20.—Method of Testing Gas._
]
Regulating Volume and Pressure.
This generator evolves gas under a greater pressure than can be used on
most work, and for this reason the flame will at first be long, noisy
and unsteady, as shown in A, Fig. 21, but, as there are two cocks, the
volume and pressure can be regulated to the requirements of the work at
hand. Now, to note the peculiarities of this flame, we will close the
gas cock _f_ on the mixing fork until the flame is about 3 inches long.
It will be of a pale reddish color and will burn steadily. The inner
flame is not as yet very well defined. Then open the air cock _g_
slowly, and when sufficient air has been admitted the flame will be seen
to shoot out suddenly and then shorten to about 1¾ or 2 inches in
length. It will be smooth, compact, and will have the appearance of
darting rapidly. If the correct quantity of air has been admitted the
inner flame, as shown in B, Fig. 21, will then be plainly seen, and its
apex, which is the point of greatest heat, will be blue. This inner
flame is known as the nonoxidizing flame, and is the flame with which
the fusing is done.
[Illustration:
_Fig. 21.—Flames Under Different Pressures._
]
The outer flame will change to a bluish color. Its temperature is low,
and its effect on the lead is to coat the metal with a heavy blue oxide,
under which the lead runs but does not unite. To demonstrate this, bring
the point of the inner or nonoxidizing flame to bear on a piece of sheet
lead. It will fuse bright and clean and will have a circle of gray oxide
around it. Then quickly remove the flame and the spot will remain
bright. Now, again bring the flame to bear on the same piece of lead,
keeping the point of the inner flame at least ¾ inch away from the lead.
It will melt and flow together, but will be covered with a coat of gray
oxide and the union will not be perfect. Slowly withdraw the flame, and
before the flame is entirely removed the spot will be heavily coated
with a thick blue oxide, under which the lead will not unite. C, in Fig.
21, shows the appearance of the flame when too much air has been
admitted and it is on the point of going out from lack of gas.
The proper way to use the gas is to open wide the gas cock M on the
generator, and do any regulating of the flame with the gas cock _f_ on
the mixing fork. These cocks should have pieces of heavy wire brazed or
soldered lengthwise of the handles, Fig. 16, _h_ and _i_, so as to form
lever handles. This will allow the gas and air cocks to be closed or
opened by gently tapping the levers _h_ and _i_, which is the only way
that a slight variation can be had, for if you try to regulate them with
the finger you will constantly open or close them too much, and the
result is that in adding air too much is always admitted, which will
blow out the flame, making it necessary to turn off the air and light
the jet again, and many times this operation will have to be repeated
before the flame is correctly adjusted.
It must be remembered to always turn on and light the gas before
admitting any air, and when through with the flame the air must be
turned off first, then the gas. If this operation is reversed an
explosive mixture of gas and air would form in the tube and would spoil
the tube, if nothing worse.
Study the Flame Well.
The beginner should study the flame until perfectly familiar with the
color and form of the proper flame. One of the greatest troubles that
the beginner will have with the blow pipe is the inability to regulate
the flame to the requirements of the work. For instance: A flame that
would work nicely on 12-pound sheets would burn holes in 4-pound sheets
before you had time to touch the lead with the inner flame. For that
reason three different sizes of tips should be used. On a 2-pound sheet
the smallest, or 1-32, tip should be used, and the flame before reducing
should not be longer than ¾ inch, and when reduced the inner flame can
hardly be distinguished, but you can easily tell when it touches the
lead by the metal fusing bright. If it is desired to fuse 12-pound
sheets the 2-32-inch tip should be substituted, and it would be found
necessary to have the jet of gas about 3 inches long, which, when
reduced, would be about 2 inches long and would show the inner flame
very distinctly.
The only way to determine the size of the flame necessary is by
experimenting with it. It will also come with experience. The flame
should be reduced to a size that will not melt the lead as soon as it
touches it. Rather, it should be in such condition that the lead would
have to be heated first and let the fusing come gradually. In that way
it can be determined just what sized drop is required, and also plenty
of time is allowed to place it just where it is wanted—particularly on
upright seams and _imperatively_ on inverted seams.
It is not necessary to be so particular on horizontal seams, as on seams
in that position you are assisted by gravity. The lead drop that is
melted from the upper lap cannot do otherwise than unite with the under
lap. It must be remembered that in starting a seam you have cold lead to
fuse, and after the first drop is started the lead in its vicinity will
be heated almost to the melting point, and you will probably be
surprised to see the lead run at the approach of the flame for the next
application.
Do Not Hurry.
The point to be taught here is that you must not attempt to hurry this
work or holes will surely be burned in the sheets, which oftentimes
makes difficult work to patch. The old adage, “haste makes waste,” can
well be applied to lead burning. Sufficient time must be allowed for one
drop to set before attempting to place the next drop. Time spent on
practicing at the bench is time well spent, as many little details that
cannot be brought to the beginner's attention here will be learned in
that way and stored in his mind for future application.