Ordinarily, the product of this frame is rove only ; but it is customary, when the yarns required do not exceed 400 yd. to the lb., to finish the operation in this frame, by giving the material the amount of twist that is necessary to impart the requisite strength, and constitute it yarn. By this means, one process is dispensed with.
Spinning.—The bobbins containing the rove are next carried to the spinning-frame, in which the latter is attenuated for the last time to any required degree, and receives the complement of twist which renders it yarn. Fig. 871 shows a section of this machine, which, in its essential parts, is the " throstle-frame " of the cotton trade. The details of size, &e., depend upon requirements ; but, for the average of jute yarns, v. frame providing 128 spindles, 64 on each side, may be considered of full dimensions. These are arranged in a single row, the pitch or distance between them being 3 in. A rack or creel, possessing as many pins as there are spindles in the frame, is supplied with the bobbins a, containing rove from the last frame. The strand of rove is conducted through an eyelet-guide b, to the retaining-rollers c, between which it passes to the binding-plate d, and over the con ductor e, to the drawing- and pressing-rollers f f', through the thread plate g, and around the leg of the flier, whence it passes upon the bobbin i. The retaining-rollers c are fluted, and thereby retain a more firm grip of the rove. As the latter is attenuated by the drawing rollers, it is slightly condensed by its passage over the binder-plate and conductor. The drawing-roller f is made of iron, and the pressing roller of wood, the latter being held in position by steel springs. The attenuation of the rove is accomplished by this pair of rollers being made to run at a considerably greater surface velocity than the retain ing-rollers : the higher the velocity, the greater is the attenuation, and the finer the yarn. The differences in the relative speeds are obtained by change-wheels, to suit the size of the yarn required. The rove con taining only one turn of twist per inch, when subjected to a draught of seven, almost loses its power of coherence, and would probably break, were it not for the service rendered by the binder-plate, in con solidating the somewhat loose form of the fibres, and the assistance of a similar kind derived from the con ductor, whilst the rove is on its passage to and through the drawing-rollers. Immediately on emerg
ing from the nip of these, it is twisted strongly by the rapidly-revolving spindle, which fixes it in the form it has to retain as a thread, and so completes the first stage of the manufacture. Maintaining the assumption that the rove was 294 yd. to the lb., a draught of 7 would yield a yarn of 2058 yd. to the lb., loss the small proportion that would be taken up by the twist which is imparted to the strand.
For the foregoing illustrations, and much valuable information, indebtedness is acknowledged to W. Fleming, of the Barrow Flax and Jute Works, and to the Institute of Mechanical Engineers.
Jute yarns receive their denomination from the weight of the " spyndle," which contains 14,400 yd. ; such a yarn as has been assumed to be passing through the series of machines described above would give 7 lb. to the spyndle, and hence would be known as "7-lb. yarn." The range of weights of yarn extends from if to 30 lb. a spyndle.
. Jute yarns, as such, are used for many purposes : twines, cords, ropes, covering telegraph-cables, wire-ropes, &c.
Manufacturing.—Having traced the raw material through the processes necessary to form it into yarn, it only remains to describe the weaving department, or the operations necessary to convert it into a textile fabric. As compared with the preceding, these are comparatively unimportant, and vary but little from the processes followed in other branches of weaving.
Jute differs from most other. textile fibres in being capable of use in the " green " or unsizcd condition for most of its purposes, though the finer Nos. of its warp yarns are usually sized.
The calculations for the manufacture of jute in the weaving department are based on the following table:— 90 in. = 1 thread = 2i yd.
120 threads = 1 cut = 300 „ 2 cuts = 1 heer = 600 „ 6 beers = 1 hasp = 3,600 „ 4 hasps = 1 spyndle = 14,400 „ This means that jute yarn is reeled on a reel of 90 in. circumference, and 1 rev. forms a thread; 120 threads are tied together, and make a cut; and so on throughout the table. As observed above, the fineness of the yarn is determined by the weight of the spyndle, and is spoken of as 6-, 7-, and 8-lb. yarn, or otherwise, as the case may be.