TWINES, CORDS AND LINES
There are many instances in which yarns made by the foregoing operations
are incorporated in twines, cords and ropes, while, on the other hand,
special types of machinery are utilized to manufacture certain grades of
such goods with an entirely different system of machinery. It is in
connection with the latter branch that this chapter will for the most
part treat, but, before dealing with these machines for specific
purposes, we might just say that there are huge quantities of yarn spun
by the methods already described, and the single yarn so spun is then
twisted so that the resulting compound may contain two single threads
twisted together, or any other greater number twisted either in one
operation, or two or more separate operations, to obtain the desired
type of cordage. In many cases the yarns have to be bleached before they
are twisted, and Fig. 28 illustrates the drying of bleached yarns.
[Illustration: FIG. 28
DRYING BLEACHED YARNS]
The terms twine, cord and rope all indicate to the textile technologist
a multiple structure, that is, an article in which two or more single
threads are united by the process known as doubling, folding or
twisting.
Thus, in the manufacture of twines, of which there is a great variety,
the process is a comparatively simple one. A number of bobbins are
arranged on pins in a creel somewhat similarly to those illustrated in
the spinning frame in Fig. 24. The requisite yarns, from 2, 3, 4 ... n
bobbins, for the type of twine in process are led from the bobbins
through an eye or guide or through a “register plate,” then between a
pair of drawing rollers, and thence to the flyer and spindle as in the
spinning operation. As the spindle and flyer rotate, the group of single
yarns are drawn through the guide or eye, or through the register plate
by the drawing rollers, and the necessary amount of twist applied before
the finished product is wound on to the bobbin. The amount of twist, or
the technical term “twist per inch,” is fixed by the speed of the
spindle and the delivery of the yarn by the drawing rollers. In other
words we have--
revs. per min. of spindle
───────────────────────────────── = the number of turns per
delivery of twine in in. per min. in. or the twist per in.
There is this difference between spinning and doubling or twisting; when
a thread breaks in spinning, the supply of yarn to the bobbin ceases,
and the production from that spindle stops until the broken thread is
repaired; on the other hand, when two or more threads are being twisted
together and wound on to a bobbin, it is evident that if one thread
breaks the supply is not stopped entirely, but the product is defective
because it is short of that yarn. In order to prevent the production of
faulty goods and to minimize waste, it is a common practice to introduce
delicate mechanical parts to such frames, the function of which parts is
to stop the delivery of yarn to any spindle in connection with which any
of the constituent threads are broken. A frame so fitted is said to have
an “Automatic Thread Stop Motion.”
In many cases the twines made by the above process are taken to another
machine in which a number of bobbins are again arranged on pins, the
twines passed under rollers and immersed in polishing mixtures of starch
or size contained in troughs or boxes. A quantity of the size adheres to
the twines as they pass through it, and revolving brushes are used to
remove the excess of size and to clean the twines. These operations are
repeated a few times and ultimately the twines so starched, cleaned and
polished are led over drying cylinders in front of which are placed
rollers covered with suitable material, usually coir yarns. These
rollers rotate at a high speed, and sometimes wax is applied to the coir
yarn-covered rollers, so that the twines are dried, polished and
finished simultaneously before they leave the hot cylinders to be wound
on to a second set of empty bobbins. This machine is usually termed a
“bobbin to bobbin polishing machine,” and the bobbins upon which the
twine is finally wound are frictionally driven because the delivery of
twine is constant. In this way the requisite finish or polish is applied
to the surface of the twine, and this gives the twine the smart
appearance which makes it quite attractive.
In the operation of twisting single yarns, that is, in the roving frame
and in the spinning frame, it is usual to impart what is known as a
“right twist.” Thus, if one looks down on a spinning or roving spindle
and the direction of rotation is clockwise, then the twist imparted is
right hand. On the other hand, if, when viewed from the same position,
the spindle rotates counter-clockwise, the definition is “reverse” or
left-hand twist. When two single threads of right-hand twist are
combined in twisting as in the formation of the above-mentioned twines,
it is usual for the doubling or twisting spindles to rotate
counter-clockwise. This is done for practical reasons which need not be
discussed here, but, although this is the usual way, there are cases in
the twisting of textile threads where two right-hand twists are combined
with the same direction of twist. Some such definition as the above will
help considerably to elucidate the structure of more complicated
multiple-twist cords.
CORDS.--In the manufacture of cords, three or more twines are combined.
Thus, if three twines, each of reverse or left-hand twist and made from
two single yarns of right-hand twist, are combined together by a further
process of twisting, it is usual to apply a right-hand twist to these
three two-ply twines. When treated in this way, the finished article is
termed a cord which is “cable laid.” And, in general, in the twisting of
such cords, each successive twisting operation is in the opposite
direction to that which immediately preceded it.
Whip-cords, fishing lines and window-blind cords are typical of this
structure which, in general, involves the use of complicated machinery
or else a long rope walk. The single yarns are first made into twines
and finished as already described; afterwards the necessary number of
twines to form the cable-laid cord are united.
The operation is a costly one when compared with the simpler process of
twine making, but the cable-laid cord is a much more handsome product
than the twine, and is admirably adapted for purposes where a smart
compact and ornamental structure is desired or necessary.
BOX CORD.--Box cord is a very simple form of cordage, the method of
manufacture being quite different from that of the foregoing laid cords.
In the box-cord process there are two distinct groups of twisting
operations conducted simultaneously. The single threads, of which there
may be from two to eight, receive the necessary additional twist by a
corresponding number of flyers which differ in shape, however, from the
ones in roving and ordinary spinning in that they are known as enclosed
flyers. While these individual threads are being twisted, the several
yarns converge towards, and pass direct to, the eye of another enclosed
flyer which completes the process by twisting the component threads in
the opposite direction to that imparted to the single threads by the two
to eight different flyers. It should be mentioned that the building of
the completed box-cord on the bobbin is accomplished by suitable
mechanism attached to the flyer.
The machine is comparatively simple, and the attendants need little
experience beyond that of detecting broken threads and repairing them.
It need hardly be pointed out that the omission of a thread from the
requisite number in the group for the finished cord is a fault the
prevention of which constitutes one of the chief duties of the
attendant. The finished product is termed two-ply, three-ply, ...
eight-ply box-cord according to the number of single yarns which are
utilized. Practically all classes of fibre are used in the manufacture
of these goods, and this method of twisting is largely adopted for the
making up of comparatively light cords from fairly heavy sizes of yarn.
The product is used extensively for tying boxes and large packages and
thus serves the purpose of a light rope which is a more expensive
article.
PLAITING OR BRAIDING.--Special classes of lines and cords are now made
on a machine of an ingenious design. One of the advantages of this
machine is the fact that great lengths of line can be made; indeed,
there is practically no limit to the length which may be made beyond
that of the difficulty of handling the huge size of the finished
product.
The machine, which is complicated and costly in its upkeep, is used
extensively for the production of log lines, sash cords, and a large
variety of blind cords. The requisite number of threads for the cord are
wound on a suitable number of bobbins, and the latter are placed in
carriers in the machine. The yarns or twines are passed over or across
each other in such a way that they are locked in position and in the
well-known plaited form which is characteristic of this class of goods.
This scheme of interlocking is formed by an even number of groups of
threads, usually eight or more, and the movements of these groups, or
rather the bobbins which contain them, are practically identical with
the familiar “grand-chain” in circle dances practised by children and
also by grown-up persons. Alternate bobbins move sinuously round a
circle in one direction, while the remaining alternate bobbins move
similarly in the opposite direction. Each bobbin passes those in the
other group first on the left and then on the right of a circle whose
path is the centre of the two sinuous paths described by the two sets of
bobbins.
The continuous movements of the two sets of bobbins in each machine form
the elegant cord which, when plaited, passes through a guide eye in the
centre of the circle but in a higher plane. From this eye the cord rises
to a pair of hauling-winch pulleys around which it passes a few times
forming the figure 8. Finally, the cord passes between a pair of
delivery rollers into a large box at the back of the machine. The
hauling-winch pulleys and the drawing rollers, which combined give the
necessary firmness, are driven positively and accurately so that their
surface speeds may coincide with the amount of cord which is formed at
the guide eye.