The operations of combing and splitting as performed in both the
breaker and finisher card are obviously due to the circular movement
of the pins since all these (with the single exception of those in
the draw-head mechanism of certain finisher cards) are carried on the
peripheries of rotating rollers. In the draw-head mechanism, the
pins move, while in contact with the fibres, in a rectilinear or
straight path. In the machines which fall to be discussed in this
chapter, viz., the "drawing frames," the action of the pins on the
slivers from the finisher card is also in a straight path; as a
matter of fact, the draw-head of a finisher card is really a small
drawing frame, as its name implies. Moreover, each row or rather
double row, of pins is carried separately by what is termed a
"faller." The faller as a whole consists of three parts:
1. A long iron or steel rod with provision for being
moved in a closed circuit.
2. Pour or six brass plates, termed "gills" or
"stocks," fixed to the rod.
3. A series of short pins (one row sometimes about
1/8 in. shorter than the second row), termed gill or
hackle pins, and set perpendicularly in the above
gills.
The numbers of fallers used is determined partly by the particular
method of operating the fallers, but mostly by the length of the
fibre. The gill pins in the fallers are used to restrain the
movements of the fibres between two important pairs of rollers.
There are actually about four sets of rollers from front to back of
a drawing frame; one set of three rollers constitute the "retaining"
rollers; then comes the drawing roller and its large pressing roller;
immediately after this pair is the "slicking" rollers, and the last
pair is the delivery rollers. The delivery rollers of one type of
drawing frame, called the "push-bar" drawing frame, and made by
Messsrs. Douglas Fraser & Sons, Ltd., Arbroath, are seen distinctly
in Fig. 17, and the can or cans into which the slivers are
ultimately delivered are placed immediately below one or more
sections of these rollers and in the foreground of the illustration.
The large pressing rollers, which are in contact with the drawing
roller, occupy the highest position in the machine and near the
centre of same. Between these rollers and the retaining rollers are
situated the above-mentioned fallers with their complements of gill
pins, forming, so to speak, a field of pins.
Each sliver, and there maybe from four to eight or more in a set, is
led from its sliver can at the far side of the machine to the sliver
guide and between the retaining rollers. Immediately the slivers
leave the retaining rollers they are penetrated by the gill pins of
a faller which is rising from the lower part of its circuit to the
upper and active position. Each short length of slivers is
penetrated by the pins of a rising faller, these coming up
successively as the preceding one moves along at approximately the
same surface speed as that of the retaining rollers. The sheet of
pins and their fallers are thus continuously moving towards the
drawing rollers and supporting the slivers at the same time. As each
faller in succession approaches close to the drawing rollers, it is
made to descend so that the pins may leave the fibres, and from this
point the faller moves backwards towards the retaining roller until
it reaches the other end ready to rise again in contact with the
fibres and to repeat the cycle as just described. It will thus be
seen that the upper set of fallers occupy the full stretch between
the retaining rollers and the drawing rollers, but there is always
one faller leaving the upper set at the front and another joining
the set at the back.
[Illustration: Fig. 17 Push-bar drawing frame]
The actual distance between the retaining rollers and the drawing
rollers is determined by the length of the fibre, and must in all
cases be a little greater than the longest fibre. This condition is
necessary because the surface speed of the drawing roller is much
greater than that of the retaining rollers; indeed, the difference
between the surface speeds of the two pairs of rollers is the actual
draft.
Between the retaining and drawing rollers the slivers are embedded
in the gill pins of the fallers, and these move forward, as mentioned,
to support the stretch of slivers and to carry the latter to the nip
of the drawing rollers. Immediately the forward ends of the fibres
are nipped between the quickly-moving drawing rollers, the fibres
affected slide on those which have not yet reached the drawing
rollers, and, incidentally, help to parallelize the fibres. It will
be clear that if any fibre happened to be in the grip of the two
pairs of rollers having different surface speeds, such fibre would be
snapped. It is to avoid this rupture of fibres that the distance
between the two sets of rollers is greater than the longest fibres
under treatment. The technical word for this distance is "reach."
On emerging from the drawing rollers, the combed slivers pass
between slicking rollers, and then approach the sliver plate which
bridges the gap between the slicking rollers and the delivery rollers,
and by means of which plate two or more individual slivers are
diverted at right angles, first to join each other, and then again
diverted at right angles to join another sliver which passes
straight from the drawing rollers and over the sliver plate to the
guide of the delivery rollers. It will thus be seen that a number of
slivers, each having been drawn out according to the degree of draft,
are ultimately joined to pass through a common sliver guide or
conductor to the nip of the delivery rollers, and thence into a
sliver can.
The push-bar drawing illustrated in Fig. 17, or some other of the
same type, is often used as the first drawing frame in a set. With
the exception of the driving pulleys, all the gear wheels are at the
far end of the frame, and totally enclosed in dust-proof casing. The
set-on handles, for moving the belt from the loose pulley to the
fast pulley, or _vice versa_, are conveniently situated, as shown,
and in a place which is calculated to offer the least obstruction to
the operative. The machines are made with what are known as
"two heads" or "three heads." It will be seen from the large
pressing rollers that there are two pairs; hence the machine is a
"two-head" drawing frame.
The slivers from the first drawing frame are now subjected to a
further process of doubling and drafting in a very similar machine
termed the second drawing frame. The pins in the gills for this
frame are rather finer and more closely set than those in the first
drawing frame, but otherwise the active parts of the machines, and
the operations conducted therein, are practically identical, and
therefore need no further description. It should be mentioned,
however, that there are different types of drawing frames, and their
designation is invariably due to the particular manner in which the
fallers are operated while traversing the closed circuit. The names
of other drawing frames appear below.
Spiral or screw gill;
Open link chain;
Rotary;
Ring Carrier
Circular.
For the preparation of slivers for some classes of yarn it is
considered desirable to extend the drawing and doubling operation in
a third drawing frame; as a rule, however, two frames are considered
sufficient for most classes of ordinary yarn.