The process of doubling ends with the last drawing frame, but there
still remains a process by means of which the drafting of the
slivers and the parallelization of the fibres are continued. And, in
addition to these important functions, two other equally important
operations are conducted simultaneously, viz., that of imparting to
the drawn out sliver a slight twist to form what is known as a
"rove" or roving, and that of winding the rove on to a large rove
bobbin ready for the actual spinning frame.
The machine in which this multiple process is performed is termed a
"roving frame." Such machines are made in various sizes, and with
different types of faller mechanism, but each machine is provided
for the manipulation of two rows of bobbins, and, of course, with
two rows of spindles and flyers. These two rows of spindles, flyers,
and rove bobbin supports are shown clearly in Fig. 18, which
represents a spiral roving frame made by Messrs. Douglas Fraser &
Sons, Ltd., Arbroath.
Each circular bobbin support is provided with pins rising from the
upper face of the disc, and these pins serve to enter holes in the
flange of the bobbin and thus to drive the bobbin. The discs or
bobbin supports are situated in holes in the "lifter rail" or
"builder rail" or simply the "builder"; the vertical spindles pass
through the centre of the discs, each spindle being provided with a
"flyer," and finally a number of plates rest upon the tops of the
spindles.
[Illustration: FIG. 18 ROVING FRAME _By Permission of Messrs.
Douglas Fraser & Sons, Ltd_.]
A roving machine at work is shown in Fig. 19, and it will be seen
that the twisted sliver or rove on emerging from the drawing rollers
passes obliquely to the top of the spindle, through a guide eye,
then between the channel-shaped bend at the upper part of the flyer,
round the flyer arm, through an eye at the extreme end of either of
the flyer arms, and finally on to the bobbin. Each bobbin has its
own sliver can (occasionally two), and the sliver passes from this
can between the sides of the sliver guide, between the retaining
rollers, then amongst the gill pins of the fallers and between the
drawing (also the delivery) rollers. Here the sliver terminates
because the rotary action of the flyer imparts a little twist and
causes the material to assume a somewhat circular sectional form.
From this point, the path followed to the bobbin is that described
above.
As in all the preceding machines, the delivery speed of the sliver
is constant and is represented by the surface speed of the periphery
of the delivery rollers, this speed approximates to about 20 yards
per minute. The spindles and their flyers are also driven at a
constant speed, because in all cases we have--
spindle speed = delivery x twist.
There is thus a constant length of yarn to be wound on the rove
bobbin per minute, and the speed of the bobbin, which is driven
independently of the spindle and flyer, is constant for any one
series of rove coils on the bobbin. The speed of the bobbin differs,
however, for each complete layer of rove, simply because the
effective diameter of the material on the bobbin changes with the
beginning of each new layer.
The eyes of the flyers always rotate in the same horizontal plane,
and hence the rove always passes to the bobbins at the same height
from any fixed point. The bobbins, however, are raised gradually by
the builder during the formation of each layer from the top of the
bobbin to the bottom, and lowered gradually by the builder during
the formation of each layer from bottom to top. In other words, the
travel of the builder is represented by the distance between the
inner faces of the flanges of the rove bobbin.
[Illustration: FIG. 19 ROVING FRAME FAIRBAIRN'S ROVING FRAME IN WORK]
Since every complete layer of rove is wound on the bobbin in virtue
of the joint action of the spindle and flyer, the rotating bobbin,
and the builder, each complete traverse of the latter increases the
combined diameter of the rove and bobbin shaft by two diameters of
the rove. It is therefore necessary to impart an intermittent and
variable speed to the bobbin. The mechanism by means of which this
desirable and necessary speed is given to the bobbin constitutes one
of the most elegant groups of mechanical parts which obtains in
textile machinery. Some idea of the intricacy of the mechanism, as
well as its value and importance to the industry, may be gathered
from the fact that a considerable number of textile and mechanical
experts struggled with the problem for years; indeed 50 years
elapsed before an efficient and suitable group of mechanical parts
was evolved for performing the function.
The above group of mechanical parts is known as "the differential
motion," and the difficulties in constructing its suitable gearing
arose from the fact that the speed of the rove passing on to the
various diameters must be maintained throughout, and must coincide
with the delivery of yarn from the rollers, so that the attenuated
but slightly twisted sliver can be wound on to the bobbin without
strain or stretch. The varying motion is regulated and obtained by a
drive, either from friction plates or from cones, and the whole gear
is interesting, instructive--and sometimes bewildering--two distinct
motions, a constant one and a variable one, are conveyed to the
bobbins from the driving shaft of the machine.
The machine illustrated in Fig. 18 is of special design, and the
whole train of gear, with the exception of a small train of wheels
to the retaining roller, is placed at the pulley end--that nearest
the observer. The gear wheels are, as shown, efficiently guarded,
and provision is made to start or stop the machine from any position
on both sides. The machine is adapted for building 10 in. X 5 in.
bobbins, i.e. 10 in. between the flanges and 5 in. outside diameter,
and provided with either 56 or 64 spindles, the illustration showing
part of a machine and approximately 48 spindles.
The machines for rove (roving frames) are designated by the size of
the bobbin upon which the rove is wound, e.g. 10 in. x 5 in. frame,
and so on; this means that the flanges of the bobbin are 10 in.
apart and 5 in. in diameter, and hence the traverse of the builder
would be 10 in. The 10 in. x 5 in. bobbin is the standard size for
the ordinary run of yarns, but 9 in. x 4-1/2 in. bobbins are
used for the roves from which finer yarns are spun. When the
finished yarn appears in the form of rove (often termed spinning
direct), as is the case for heavier sizes or thick yarns, 8 in. x 4
in. bobbins are largely used.
Provision is made on each roving frame for changing the size of rove
so as to accommodate it for the subsequent process of spinning and
according to the count of the required yarn; the parts involved in
these changes are those which affect the draft gearing, the twist
gearing, and the builder gearing in conjunction with the automatic
index wheel which acts on the whole of the regulating motion.