The rollers D E F take such firm hold of the yarn that it cannot slip, and they would continue to deliver the yarn on the floor, were there no beam to take it up. At this point, also, the yarn is protected against all risk of straining, the beam being driven by the friction-disc at such a rate only as is required to take up the yarn delivered by the rollers. A firm, hard beam being desira ble, it is obtained by the employment of a revolving presser-roller, in sizes td fit the various widths of beams.
The roller D is made to serve the purpose of the measuring-roller, and is made of iron. Formerly it was a hollow tin cylinder, placed near the roller g', and was liable to be easily damaged ; brought to the position shown in this frame, it adds to the facility of doffing, and, com bined with the improved self-adjusting marker, prevents a considerable amount of waste being made at the commencement of the beam, and enables the sizer to concentrate his attention upon the front of the head-stock, during the important operation of doffing.
The cylinder sizing-machine is, comparatively speaking, universal in the cotton trade, in those branches where the yarns are used in their grey state. There are a few exceptions, where, in the case of very flee yarns, it is thought prudent to retain the old system of dressing; but these eases are so rare that they do not call for remark.
The disadvantages that have been experienced in connection with the cylinder-machine have led to the invention of air drying-machines, in which a current of either hot or cold air is employed to extract the moisture. At their first introduction, these machines excited great anticipations, owing to the softness and pliability of the warps sized upon them. But a little experience soon demonstrated the existence of various weak points, especially a want of uniformity in drying, which revealed itself by the development of mildew in the warps. This arose chiefly in warps that had been sized during a very humid state of the atmosphere, it being found that in such a condition the drying power was greatly reduced. However strong the current may be, little more than mechanical impact could be obtained. This diffioulty proved insuperable in connection with cold-air machines, and they are now rarely found in the market. In hot-air ma chines, however, the case is dif ferent; they have been so far improved that, for some classes of work, they now obtain a pre ference over the cylinder drying frame.
The accompanying illustra tions, Figs. 560, 561, and 562, show elevation, plan, and cross section of the Bullough and Whitehead hot-air drying-ma chine. The only points requiring notice are those wherein it differs from the cylinder-machine, the creel, size-box, and head-stock being the same.
In air drying-machines, it is obvious that provision must be made for a much longer expo sure of the yarn to the heated atmosphere than is necessary in the cylinder-frame, where the yam comes into immediate con tact with the heated surfaces of the cylinder. It is also requisite that the heated atmosphere, when it has become surcharged with moisture, should be speedily and effectually withdrawn, be cause, when its power to absorb moisture has been exhausted, it is useless. This will necessarily require a supply of hot air which shall be constant and steady, to replace the saturated atmosphere withdrawn.
In the above machine, thee( conditions have been met by the following arrangements — Ir the largo chest forming the central part of the frame, km steam - cylinders T are laic parallel and near the bottom, al will be seen in the cross section each of these contains a series small air-pipes, into which air ii drawn by the fan T', revolvinf at 1300 rev. a minute. Th( cylinders T being filled vitt steam, the air, in its passage through the pipes, gets heated and, entering the hot-air chambers, follows the direction of the arrows, until it is carried out by the fan at the vent. The yarn, after its passage through the size-box, enters the drying chambers between the rollers RR' and passes through the hot air, over the cylinders, around the roller s', through the middle chamber u, then around the large roller at its extremity, through the chamber u', over and under the roller in prox imity to the fan, and, reversing its track, passes from the upper side, around the small roller at the opposite extremity, and thence back along the chamber, making its exit between the largo and small rollers in the line of the framing. The warp is opened by half of it passing over, and half under, the small rollers near the rods which further separate the threads, after which it passes upon the beam.