_Embossing Webs—Type of Construction and Design for Which Process is
Adapted—Braiding Flat Elastic Fabrics, Plain Cords for Athletics and
Airplanes, and Fancy Cords—How Sizes Are Indicated—Difference Between
Woven and Braided Effects_
The embossing of classic fabrics is a form of elaboration which is not
adapted for long stretch webs.
It has been confined mostly to goods of short stretch, suitable for use
in the manufacture of suspenders. In long stretch webs the patterns
will not stand out prominently for any length of time. After repeated
stretchings and wear, they lose much of the desirable sharpness of
detail, and become flat and indistinct. Twills and loose weaves of a
similar character should be avoided for embossing. The best results are
obtained on firm, closely woven plain webs which take the impress of the
design with clearness and retain it for a greater length of time.
DESIGNS SUITABLE FOR EMBOSSING
In planning such work it is well to avoid designs which run for any great
length with the warp, and to select effects where the general run of the
design is at an angle to the direction of the warp threads, rather than
with them. This will prolong the life of the figure.
The process is similar to that used in embossing paper and leatheroid
goods. The machine must be heavy and made to stand considerable pressure.
It should be run slowly so as to allow the goods to get sufficient heat
while in contact with the embossing roll. The webs should pass through
a steam softening process just ahead of the embossing. This steaming is
done by having a perforated steam pipe confined in a covered box, the web
passing through slots at either side. It puts the goods in condition to
receive and retain the impress of the figure.
EMBOSSING MACHINE
Figs. 1 and 2 show a machine used for embossing elastic fabrics. It
consists chiefly of a heavy frame A, a case hardened steel roll B on
which the design has previously been engraved, and a hard paper roll C.
The engraved steel roll B is heated with steam and may be subjected to
heavy pressure by turning the hand wheels D.
When putting in a new design and accompanying paper roll, it is necessary
to run the machine empty for a few hours, gradually applying the pressure
at the hand wheels in order to mesh the design into the paper roll so as
to get a strong impress on the goods. When moire-antique or water effects
are desired, the embossing rolls are engraved with straight lines of the
desired distance apart, and the goods are fed into the machine after
passing over irregularly formed rollers, which prevent them from going
through the machine straight. Fig. 3 is an example of this effect, with
the gros grain in the middle water-marked, and bordered with a fancy
effect not embossed.
BRAIDING ELASTIC FABRICS
The braiding of elastic fabrics is a simple process when compared with
weaving. It does not lend itself to any great variety of fancy effects,
but a great variety of elastic goods are braided, which serve many
purposes. Round cords are made in sizes from a single strand of rubber
thread, such as is used for the protection of eye glasses, to the
covering of multiple rubber threads for making a cord which may be one
inch or more in diameter. Some of these cords are used by professional
athletes in acrobatic work. Large quantities of heavy cord are now used
for shock absorbers in the manufacture of airplanes, and they are much
used for corset laces and doll cords.
[Illustration: Fig. 1.—Embossing Machine]
[Illustration: Fig. 2.—End View]
[Illustration: Fig. 3.—Embossed Water-Marked Effect on Middle stripe]
[Illustration: Fig. 4.—At Top, Cord Used by Acrobats; At Bottom, Exercise
Cord In Two Colors]
The braiding machines are small and compact, and are generally operated
in gangs on benches. One operator can care for many machines, as they
stop automatically when a thread breaks. Each machine may consist of a
variable number of spool carriers, according to the character of the
work they are engaged on. Carriers are made to travel around cam-like
grooves formed in the bed of the machine, being operated by a chain of
gears which propel them around a predetermined course. Gears and slots
are so arranged that the carriers are made to cross and recross each
other in their passage, so that the various threads of yarn carried are
plaited around the strands of rubber. The spools used on the carriers are
specially designed, and have a series of notches on the upper end, into
which a stop will drop upon the breaking of any of the different covering
threads, automatically stopping the machine.
The rubber is carried on a beam such as is used in weaving. These beams
are grooved on either side for receiving friction cords or belts, on
which are hung weights so as to govern the let-off of the beams and keep
the rubber at a high tension. The beams are hung on brackets underneath
the machines. If cords are being made, the rubber is delivered through a
central hole in the bed of the machine and fed up so that the covering
threads may be plaited around it. As there is no friction on the rubber
threads delivered in this manner (like the friction in weaving caused
by the repeated passage of the reed), the rubber can be worked at the
highest possible tension without fear of chafing or breaking, and
economical results in this respect are obtainable.
[Illustration: Fig. 5.—At Bottom. Flat Braid Contracted; At Top, the Same
Braid Before Contraction]
[Illustration: Fig. 6.—At Bottom, Braided Frill; At Top, the Same Frill
Before Contraction]
FLAT BRAIDS
Where flat braids are made the rubber threads are passed separately
through different holes in the machine bed and the yarn is braided in
and out between these threads, binding them together side by side so
that they are flat as in a woven fabric. By this method each of the
different covering threads passes from one side of the flat web to
the other, giving them a diagonal direction across the fabric. This
diagonal crossing and recrossing of the covering threads allows for the
introduction of different colors, which produce a plaid-like effect.
In making the flat braid, when the individual rubber threads pass through
the separate holes on the outer part of the bed plate of the machine,
they all gather to one common center after they are through. This causes
the rubber threads, when they are at a very high tension, to draw at a
very acute angle at the edge of the hole, which necessitates running them
at a lower tension than is desirable for economy. It also introduces a
liability to break under the strain. In some mills this is cared for
by passing each thread over a small case hardened steel roller, thus
avoiding the friction at the edge of the hole.
SIZES OF CORDS
The sizes of cords are determined by the Birmingham wire gauge as follows
(Diameters in decimal parts of an inch):
Size 1 .300
Size 2 .284
Size 3 .259
Size 4 .238
Size 5 .220
Size 6 .203
Size 7 .180
Size 8 .165
In sizing or measuring the cord, it is passed easily into the gauge, so
that it hugs the sides without crowding. Any cords made heavier than a
No. 1 are designated by fractions of one inch in eighths.
It becomes necessary in making heavy round cords, such as are used by
athletes and in the manufacture of airplanes, to have a very durable
covering over the strands of rubber. Such a covering is put on by using
double deck machines, where above the regular machine there is another
bed plate having a second set of carriers which travel around the braided
fabric coming up from the lower deck. In such cases the inner covering is
generally a cheap coarse material, while the upper deck of carriers braid
the outer covering around it, which is of a higher grade material, often
a highly glazed polished thread.
Machines are made of a variable number of carriers to suit goods of
different character that are required. Provision is made to carry
the rubber beam in hanging brackets underneath the machine, which
are of sufficient strength and firmness to carry the maximum weight
necessary for governing the rubber tension. Above the machine there is a
gear-driven take-up shaft, on which are tension rolls to govern the feed
of the goods when braiding. The speed of these rolls can be regulated by
change gears of various sizes. The goods are then fed on a belt-driven
spool. On the very heavy goods it is necessary to pass them through other
press rolls to prevent any slipping back when feeding from the braiders.
FANCY BRAIDED CORDS
The wide range of goods of this character, covering so many varied uses,
makes it impracticable to particularize on any special construction. In
the making of braids and Vienna cords, the general methods are much the
same as those described for braiding the round cords, except that the
travel of the carriers is different and the strands of rubber are fed
up singly, instead of in a group, so that the carriers may pass in and
out between them. A different machine is required for the various widths
and number of strands of rubber used. Two carriers are required for each
strand of rubber used and one over. For example, an eight strand braid
requires 17 carriers, while a 10 strand requires 21, and so on. The width
of the braid may be further regulated by the contraction of the goods
determined upon and provided for in the take-up; also by the size and
character of the material used for covering.
On account of the diagonal formation of the covering threads when
braiding, it will be seen that variable contraction of the web will
produce variable widths. This is not so with a woven elastic fabric,
inasmuch as the weft lies straight across the web and therefore the same
width is maintained whether it is stretched or otherwise. In braiding,
the threads move both across and lengthwise of the fabric, taking the
place of both warp and filling, therefore increased contraction, no
matter whether it is produced from the use of heavier rubber, or changed
material or take-up, results in greater width, inasmuch as the lengthwise
position of the threads is brought into a new position which is more of a
crosswise formation.
This diagonal lay of the covering threads opens up possibilities for very
effective plaid effects, but this is the limit of color elaboration. A
fancy frill effect may be obtained by the omission of rubber threads at
the outer edges.