THE DRAWING MACHINE.
(207) The slivers produced on the carding engine, although, as
previously noted, composed of approximately parallel fibres, are
not perfectly laid in that way. If, however, they are subjected to
a pull in a longitudinal direction they easily assume the parallel
position. Even slivers produced on a combing machine, in which the
fibres are, as has been observed, in much better order than when
treated in a carding engine, are improved by being subjected to this
drawing action. The net result of the process is an improvement in the
strength of the resultant thread. Not only is it essential to improve
the parallelisation of the fibres in the sliver, but it is equally
desirable to produce a sliver of even weight and thickness. As it
leaves the carding or combing machine the sliver is not so regular in
weight as is requisite, and if this irregularity were allowed to go
uncorrected a yarn of varying thickness would eventually be spun. It
is true that the variations are not serious in amount, but they are of
sufficient importance to render it desirable to correct them. Again,
it is necessary to reduce these irregularities in order to facilitate
future manipulation, and, generally speaking, the proper conduct of the
drawing process is of prime importance to successful spinning.
(208) The essential feature in a drawing machine or frame is, of
course, the mechanism by which the extension or drawing of the sliver
is effected. As it is necessary to pass the material continuously
through the machine while reducing it to parallel order, the use of
rollers becomes imperative. These are arranged in pairs, one above the
other, and there are four pairs arranged in parallel lines with each
other, as shown in Fig. 124. That illustration is a transverse section
of the drawing frame as made by Mr. S. Brooks, Figs. 123 and 125
being respectively end and front views of the same machine. The lower
rollers are borne, as shown, by brackets =B= fastened to a longitudinal
beam =C=, known as the “roller beam.” They are made in sections and
are coupled throughout the length of the frame, so as to form four
continuous “lines,” which are driven from one end of the machine.
Each set of four lower and four upper rollers constitutes a “head,”
and there are usually from two to four heads in a machine. The lower
rollers are made of a special class of wrought iron, very fine and
clear in the grain, and are accurately turned throughout, being formed
with two or three bosses to each head. They are also fluted with fine
flutes in a longitudinal direction, great care being taken to ensure
the flutes being smooth and quite free from anything likely to catch
the cotton. The upper rollers are made of cast-iron, and are placed on
the top of the lower lines, against which they are constantly pressed
by means of the hooks =D= and weights =E=, the former passing over
the arbors of the rollers. The arbors of the top rollers engage with
grooves in the roller brackets, and the rollers are thus prevented from
moving laterally, although they have freedom of vertical movement. Bars
forming caps for the arbors of the top rollers are fitted, being known
as “cap bars.” It is the practice to form the top rollers with as many
bosses as there are on the bottom rollers in each head, and of a length
corresponding to that of the latter. Thus if, in each head, the bottom
rollers had three bosses the top rollers would be formed to correspond,
and the slivers to be drawn would be passed between them. In this case
the head would be said to be one of three “deliveries,” and a machine
is usually described as being one of so many heads of a certain number
of deliveries. It will be easily understood that the top rollers are
not positively driven, but derive their motion by frictional surface
contact with the lower set. The top rollers are accurately turned, and
are usually covered with a specially-prepared soft leather, formed
into a sheath, which can be drawn over the boss of the roller. Special
care is taken in forming these coverings, so that they have no extra
thickness at their joints, and, after they are drawn on to the rollers,
the latter are subjected to a rolling and pressing action, which beds
the leather firmly and ensures the roundness of the roller. The mode
of preparing the rollers will be described in full in Chapter XIV.
It is now almost the universal practice to use the loose boss top
roller invented by the late Mr. Evan Leigh, and illustrated in Fig.
126 in longitudinal section and elevation. Its advantages are many,
and arise from the lessened friction consequent upon the more perfect
lubrication, which is also obtained with a smaller quantity of oil.
[Illustration: FIG. 126. J.N.]
(209) The rollers are driven from the end of the machine in the way
shown in Fig. 123 in end elevation. They may be arranged with all their
driving wheels at one end of the frame, or may be—as is the case in
Messrs. Howard and Bullough’s machine—driven at both ends. That is to
say, the driving of the first and fourth rollers may be effected at
the gearing end of the machine, while that of the intermediate lines
is obtained at the other end. It will be, perhaps, as well to say that
the first line here means the back rollers, and the fourth the front.
Whatever be the system of driving adopted, the front roller is always
the primarily driven one, and for this course there are good reasons.
The thickness of the emerging sliver is determined by the relatively
superior speed of the front roller, which runs at a faster rate than
any of the others. Thus it becomes an easy matter to reduce the speed
of the remaining rollers, and this course is preferable to using a slow
running wheel as the driver from which higher velocities are to be
obtained.
[Illustration: FIGS. 123 AND 124. J.N.]
[Illustration: FIG. 125.]
Between the driver and driven roller a series of wheels are interposed,
which are used as change wheels, so as to allow of an easy adjustment
of the relative speeds of the whole series.
(210) The proper construction of a drawing frame turns largely upon the
consideration of a number of small points. In this, as in all other
machines used in the preparation of cotton, due regard must be had to
the material which is being treated. Especially is this the case in
drawing. The “staple” here plays an important part. If the distance
between the centres of each line of rollers exceeds that of the length
of the “staple” it is quite clear that no drawing worthy of the name
will take place. To draw anything one end of it must be firmly held,
and if the fibres could lie between two pairs of rollers without being
gripped by either it is obvious they would not be drawn. Thus the
distance between the centres of the rollers must be regulated to suit
the material being treated, and the roller bearings are arranged to
permit of that adjustment. This leads to the necessity, where very
short slivers are drawn, for the reduction of the diameter of the
rollers so as to permit of their being set in together more closely
than could otherwise be done. Thus East Indian cotton is best dealt
with by rollers of a small diameter set closely; while Sea Island or
Egyptian can be drawn by larger rollers set wider apart. The principle
underlying this practice has been indicated, but may be formally
stated. The necessity exists for the fibre being drawn to be held at
one end by one roller, while it is subjected at the other to the pull
of a faster running roller. It is therefore essential that the distance
between the centres of the rollers shall be such that the fibres are
sufficiently drawn without being subjected to overstrain, by which a
liability to rupture is incurred.
(211) It is the universal practice to effect the major part of the
drawing between the third and fourth rollers, the increase in speed
prior to that having been comparatively small. The exact speeds at
which the various lines run depend largely upon the material treated,
but a common acceleration is as follows: Assuming the first or back
roller to revolve at 100 times per minute, the second line would run
at 125, the third at 175, and the fourth at 275. The attenuation of
the sliver between the first and second line is only 25 per cent; that
between the second and third 40 per cent; and between the third and
fourth 57 per cent. Putting it in another way, assuming one foot of
sliver to have passed through the back rollers, it would become 15
inches long after passing the second roller; 21 inches as it leaves
the third roller; and 33 inches as it finally emerges from the front
roller. Thus, although the _percentage_ of increase between the third
and fourth is not largely in excess of that arising between the second
and third rollers, the actual increase is exactly twice as much. These
proportions are approximations to those which are actually employed,
but, as was said, much depends on the character of the material which
is being treated. In dealing with a soft elastic fibre like Sea Island
cotton, light weighting and an easy draught is possible, while, if a
harsh strong fibre is subjected to the same treatment there would be
little effect produced. It is therefore necessary to put additional
weight upon the rollers and thus increase their grip. A severe
treatment of this character, which would be fatal to a weak or fine
cotton, is beneficial to the coarser varieties, which can easily be
subjected to a coarser draught. All these are points which require
attention in practice, and careful observation will do more than many
instructions in giving the knowledge of the right course to pursue.
(212) Another point requiring close attention is the preservation of
absolute cleanliness. All cotton in its passage through the machines
used, gives off a certain quantity of loose, short fibre, to which the
name of “fly” is given. This is found all over the machine, and it
adheres to the rollers in considerable quantity. Unless it is removed
in some way it is apt to collect into thick pieces, or “slubs,” which
attach themselves to the sliver, and thus cause thick places. These,
of course, are perpetuated in every subsequent stage, and the removal
of the fly, therefore, becomes of great importance. To accomplish
this desirable end appliances known as “clearers” are fitted. These
are flannel-covered surfaces, either flat or cylindrical, which rest
upon the rollers. One common form is a plain, wooden cylinder covered
with rough flannel, which is placed upon, and rests between, two of
the lines of rollers, the rotation of which causes it to revolve. The
rougher surface of the flannel licks up the fly from the rollers, and
a periodical stripping is sufficient to keep the clearer effective. A
simpler and also a common arrangement consists of a strip of flannel
stretched within a cover and resting on the whole of the top rollers.
A third modification is known as “Ermen’s revolving clearer,” and is
an endless band of flannel passed over two rollers fixed in the cover.
The lower part of the band rests upon the top rollers, and the clearer
is slowly traversed, so as to remove the fly and convey it to the upper
part of the case when the band is turned up. Here an oscillating comb
is placed, and scrapes up the fly into small rolls, which can easily
be removed periodically. A further form of clearer is made by Messrs.
Dobson and Barlow. It consists of two wooden rollers sustained in a
frame which is hinged at one end. One of the rollers which presses
upon the back rollers is suitably driven so as to take up the fly
from the first and second pair. The other roller is loose upon its
spindle, which is much smaller than the bore of the roller, so that the
revolution of the front rollers causes it to rotate at a speed somewhat
below that of the rollers. Both of the wood cylinders are covered with
flannel, and thus take up the fly with very great ease. It was found
by practice that the positive driving of the back clearer effectually
cleaned the first two sets of rollers, while a similar procedure with
the front clearer did not lead to the same result. By allowing the
latter to be frictionally driven, the rollers can be kept clean without
difficulty. To strip the clearers they only require raising, when the
fly can be readily removed.
(213) A reference to Figs. 123 and 125 will show that extending along
the frame is a shaft having a hand-wheel at the end, and a number of
worms keyed on it. The latter gear into worm wheels, on the axes of
which cams are fixed by which a bar—through which the weight-rods
pass—is lifted. As the rods have a loop at their upper end which cannot
pass through the holes in the bar, it is clear that the elevation of
the latter will also raise the weights. In this way the pressure on
the rollers is relieved. This is of value when the frame is stopped
for any prolonged period, as the maintenance of the pressure during
that time results in the formation of flat places on the rollers, which
are detrimental to good work. It is undesirable to put on or take off
the weight suddenly, and some makers prefer to use a simple lifting
appliance by which each weight can be released singly.
(214) The important features in connection with the roller portion of
the mechanism are—first, their perfect finish; second, the adoption of
such diameters and distances as are suitable for different lengths of
staples; third, their effectual cleansing; and, fourth, the regulation
of their velocity so as to suit the material being dealt with.
(215) It was pointed out in paragraph 207 that there are certain
irregularities in the size of the slivers, as obtained from the carding
engine. Up to the present the machine has been considered as though
each sliver was treated separately, a course which would result in
the delivery of a sliver longer than, but possessing the same defects
as, the original one. That this must be so is apparent, unless some
provision is made for the acceleration of the speed of delivery when a
thin place was passing, or its retardation when a thick place occurred.
It therefore becomes necessary to find a method of rectifying these
defects, and it is obtained by passing several slivers through the
machine simultaneously. Reference is now more particularly made to
Fig. 123, which shows the mode pursued clearly. A number of full cans
from the carding engine—up to eight—are placed behind each delivery,
and the slivers they contain are combined and passed through the
rollers together. Before passing on to consider the exact effect of
this arrangement, a few words may be said as to the method of feeding
the cans to the machine. As each can contains approximately the same
length, it follows that, the rate of passage being the same throughout
the machine, they would all become empty at practically the same time.
This implies the necessity for the attendant to remove the cans and
piece up the new slivers all along the frame almost simultaneously.
This is practically impossible, and it is therefore highly desirable
that there should be an arrangement adopted which would enable the cans
to be substituted at different times along the frame. In a little but
valuable work, “Progress in Cotton Carding,” the late Mr. F. A. Leigh,
of Boston, U.S.A., makes the following remarks: “If there are 10 pounds
(or 1,000 yards), say, in a full can, instead of putting them all up
full at first, it is better to put them up at back of drawing in four
sections, say:—
4 or 6 cans 4 or 6 cans 4 or 6 cans 4 or 6 cans
------------- ------------- ------------- -------------
2-1/2lbs. 5lbs. 7-1/2lbs. 10lbs.
After that replace with the full 10 pounds (or the 1,000 yard) cans,
and they will continue to empty in rotation, all full cans having the
same length. The tender [minder] will know exactly where to find them.”
(216) The diminution of the irregularities in the slivers is most
important. The plan pursued is to pass several slivers through the same
set of rollers, and deliver the combined sliver at the front of the
machine. The number of slivers which are combined varies considerably
according to the practice of different spinners, but is not more than
eight. Now, if it be assumed that an irregularity of 40 per cent
existed in one sliver, and that it was drawn simultaneously with five
others in which that irregularity did not exist, the latter would be
reduced to one-sixth, or 16-2/3 per cent. It is, however, the custom
to “put up,” or feed, the slivers so obtained to another head of the
machine, and subject several of them to a second or even a third
drawing. Assume, therefore, that four of the partially drawn slivers
were fed and again drawn. The irregularity would be reduced to 1-2/3
per cent, and a further drawing would again reduce it. The figures
given are hypothetical, and it is not likely, of course, that only one
sliver would be irregular in thickness, but the example serves to show
the principle. The number of “doublings” given to the sliver is arrived
at by multiplying the number of ends passed through at each drawing.
Thus, in the case stated, the doublings are 6 × 4 × 4 = 96, and it can
be easily seen that any difference in substance which existed at first
would be very speedily rectified, and would not be of much moment by
the time the finished sliver was produced.
(217) The number of times the material is passed through the machine
and the draught to which it is subjected varies, as was shown, with
the class of cotton treated. Thus, the harsh, wiry varieties of cotton
stand more drawing, but if well drawn will spin fairly well into
weft, which does not receive so much twist as warp, and should be
full bodied. How much any class of cotton should be doubled and drawn
is a matter to be determined by practice only, and even then great
variations in the course pursued will occur. The one thing which must
be remembered is that as soon as an even sliver is produced further
drawing is unnecessary, and only results in a diminution of the
strength of the spun yarn.
(218) A necessary corollary to the process of doubling slivers is the
provision of means whereby the passage of all the combined slivers is
ensured throughout their entire length. Assuming, for instance, that
eight ends were being passed through the machine, and one of them
from some cause failed, it is clear that the delivered sliver would
be diminished in thickness one-eighth. Of course the attendant would
rectify this at the earliest moment, but, in the interim, a large
amount of the thin sliver might have been produced. In order to avoid
this serious evil, it is the practice to fit all machines of this class
with a detector motion, which operates on the failure of any of the
ends. Referring now to Fig. 123, it will be seen that, after passing
through the guide-plate =F=, the sliver is conducted over the end of
the short lever =G=, which oscillates on a knife-edge bearing. The end
over which the sliver passes is hollowed out, and is highly polished,
while the other end—which is slightly heavier—is beneath a curved
guide-plate, shown in section. The lever =G= is balanced so that the
pressure of the sliver during its passage is sufficient to keep the
spoon-shaped end down, while, on the breakage or failure of the sliver,
the lever oscillates on its bearing. A reference to Fig. 124 will show
that a shaft =H=, driven from the main shaft, as shown, has on it an
eccentric, to which the rod =I= is attached. This rod is attached to a
bell crank lever =J=, on the shaft =K=, which is oscillated, and thus
gives a reciprocal movement to the levers =L=, carrying a square bar. A
bell crank lever =M= is also placed upon the shaft =H=, and ordinarily
engages with a snug on the stop rod =N=. The latter has a helical
spring attached, which always tends to pull it longitudinally, and when
it is released, to throw over the strap from the fast to the loose
pulley.
(219) Assuming now that one of the slivers has failed, its spoon lever
will oscillate and its weighted end will fall. It thus comes in the
path of the reciprocating bar in the lever =L=, which is prevented
from completing its traverse. The result is that the lever =M= is
oscillated and the stop rod =N= released, so that the spring named at
once throws the strap on to the loose pulley and stops the machine. As
the reciprocations of =L= are very rapid, no considerable length of
the sliver can pass without causing the stoppage of the machine. The
attendant is compelled to piece up the broken end, and “single” is thus
prevented.
(220) The sliver may, however, fail between the drawing rollers and the
delivery can, and it is therefore necessary to provide a means whereby
the machine can be arrested in this event also. In its passage to the
can the sliver is collected by a trumpet-mouthed tube and carried over
another spoon lever =O=, balanced and borne exactly as the lever =G=.
The failure of the sliver is followed by the fall of the inner end
of =O=, which comes in the path of the lever =P=, to which a lateral
reciprocal motion is given from the shaft =H=, as shown. This results
in the stoppage of the machine exactly as in the case of the back
stop-motion.
(221) After passing the detector lever, the sliver goes through another
tube and is compressed by the calender rolls =Q=, driven as shown in
Fig. 124. These give the sliver more cohesion, and slightly flatten
it, after which it is treated by the coiler head =R=, which is of
the same construction as that employed on the carding engine, and is
driven by the gearing indicated in Fig. 123. Some makers provide a
full can stop motion, which operates when the can gets quite filled
with cotton. There is a danger, if the attendant is careless, of it
becoming jammed under the coiler plate and serious damage occurring. In
order to obviate this, a thin plate is fitted below the coiler plate,
thus forming a sort of false bottom. This is weighted suitably for
various strengths of slivers, it being desirable to press the sliver
to a certain degree in order to get as great a length in each can as
possible. The amount of this pressure is, of course, variable, and care
must be taken not to make it too great. When the loose plate is raised
it lifts a vertical stop which comes in front of a lever coupled to the
front end of a lever corresponding to =P=, in Fig. 124, and the motion
of the latter is arrested as before, with the same result. This is the
arrangement used by Messrs. Platt Brothers and Co., Limited.
(222) It sometimes happens that a sliver in coming out of the can
will be formed into a knot, or loop, which, when it comes into the
guide plates, =F=, cannot pass through the holes in the latter. The
result is, that the sliver is broken and requires re-piecing. Now, it
is desirable to prevent the breakage of the sliver when possible, and
the case named is met by Mr. Brooks by the use of the motion shown in
detail separately. The bar fixed in =L= oscillates under a catch lever
=S=, which is balanced by the plate =F=, so as to be raised above the
path of =L=. When, however, a knot occurs, the plate =F= is drawn
inward, and the catch lever =S= brought in the way of the bar in =L=,
the oscillatory movement of the latter being arrested. The machine is
thus stopped, as in the cases previously named. In order to make this
movement more sensitive, the plate =F= is balanced by the weighted
lever fixed on the same rod on which =F= oscillates, the weight being
adjustable to suit different strengths of sliver.
(223) Messrs. Howard and Bullough have for some years made an
application of electricity to this machine for the purposes of stop
motions. Their arrangement is shown in Fig. 127, in transverse section.
The machine is practically divided into two pieces, which are joined
together, but have pieces of some insulating material introduced into
the joint. One half of the machine thus constitutes one pole, and is
connected to the battery, or dynamo, by the rod =R=; and the other
half being the other pole, also coupled to the battery by the rod
=O=. The sliver, as it passes to the back roller, goes between two
rollers =S T=, which are coupled to the positive and negative poles
respectively. The lower roller is fluted and is the full length of the
machine, while the upper roller is only long enough for two slivers.
Failure of an end is followed by the contact of the two rollers, thus
establishing the circuit and causing a current to pass through the
magnet =X=, which attracts the catch =Z=. The latter engages with a
constantly revolving cam and thus stops the latter, this being followed
by the release of the knocking-off lever. The lapping of a sliver in
passing through the drawing rollers causes the top front roller =H=,
which is coupled to one pole, to engage with a pin =L=, connected to
the other, and so stop the machine. The breakage of the sliver before
reaching the calender rollers =N K=, is followed by the establishment
of contact between them, with the usual result. Over filling of the can
lifts the tube plate in the coiler =O=, and completes the circuit with
the same result. The use of electricity in this connection has greatly
simplified the machine, and has proved to be a great success.
[Illustration: FIG. 127. J.N.]
(224) It only remains to be said that the diameter of the front roller
is from 1 inch to 1-3/8 inches, according to the work required, and the
speed at which it is run, from 290 to 450 revolutions per minute.