Chapter X.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
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.
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.
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.
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 multiplerubber 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.
Fig. 1.—Embossing MachineFig. 2.—End View
Fig. 1.—Embossing Machine
Fig. 1.—Embossing Machine
Fig. 2.—End View
Fig. 2.—End View
Fig. 3.—Embossed Water-Marked Effect on Middle stripeFig. 4.—At Top, Cord Used by Acrobats; At Bottom, Exercise Cord In Two Colors
Fig. 3.—Embossed Water-Marked Effect on Middle stripe
Fig. 3.—Embossed Water-Marked Effect on Middle stripe
Fig. 4.—At Top, Cord Used by Acrobats; At Bottom, Exercise Cord In Two Colors
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 aroundcam-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.
Fig. 5.—At Bottom. Flat Braid Contracted; At Top, the Same Braid Before ContractionFig. 6.—At Bottom, Braided Frill; At Top, the Same Frill Before Contraction
Fig. 5.—At Bottom. Flat Braid Contracted; At Top, the Same Braid Before Contraction
Fig. 5.—At Bottom. Flat Braid Contracted; At Top, the Same Braid Before Contraction
Fig. 6.—At Bottom, Braided Frill; At Top, the Same Frill Before Contraction
Fig. 6.—At Bottom, Braided Frill; At Top, the Same Frill Before Contraction
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.
The sizes of cords are determined by the Birmingham wire gauge as follows (Diameters in decimal parts of an inch):
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.
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.