PREPARATORY MACHINES AND SPINNING-MACHINES.
Drawing.—The cotton, having been wrought by the carding-engine or other preparatory machine so as to form a continuous sliver or ribbon of sonic consistency, must next be converted into drawings. To obtain the utmost uniformity as regards thickness, several ribbons or slivers are combined by " doubling" and the fibres straightened out by stretching these ribbons. It is then made gradually thinner by continued stretching or "drawing," being at the same time slightly twisted, which gives it the requisite consistency of "roving." This, which may be considered as a preparatory yarn, is finally reduced to the fineness and firmness required by more forcible twisting or fine spinning.
Canal mere placing together of several ribbons or slivers as they come from a train of carding-machines is effected by the canal drawing-machine (ti. 37, fig. r). This machine contains two wooden bobbins, to be used alternately, upon which the narrow ribbons to be widened out are wound in regular layers. This is effected by alternately resting the bobbins with a suitable pressure upon two fluted rollers, which revolve uniformly around their axes and rotate the bobbin with a constant velocity.
regular combination of the ribbons to be doubled takes place upon an endless cloth running horizontally in a long box open on the top, the so-called " canal," at the end of a train of card ing-engines. It being improbable that in placing the ribbons together a somewhat thicker place in one will meet a similar thick place in all the others, but rather that the defective places of the separate slivers will vary in position in the finished ribbon, it is evident that the uniformity of the product as regards thickness is increased by this doubling process. The above-described doubling-machine is chiefly used in cotton-mills between the first and the second carding process, though sometimes after the com pletion of the latter.
Combined and machine belonging to this group is the drawing-machine (fig. 3), which, serving for the simultaneous doubling and stretching (drawing), finds quite general application in spinning the various textile fibres. The effective parts of the machine are rollers arranged in pairs, which catch the doubled ribbon and through their different velocities draw it out to five or six times its original length, thus stretching and straightening the fibres. The ribbons
thus manipulated are caught in sheet-iron cans, two of which are shown in the Figure. In spinning establishments producing yarns of high counts these machines are called "spreading-" or "drawing-frames," and, being generally used several times in succession to obtain the fibres in the com pletely stretched and uniform condition of the ribbon, the terms "first," " second," " third," etc., drawing, spreading, or slubbing are used.
long as the doubling and drawing proceed together the sliver retains sufficient tenacity to sustain without injury the operations of placing it in the can and of taking it out. If however, doubling is to be entirely omitted or is to be unequal to the drawing, the ribbon gradu ally becomes so tender that it may tear if means are not provided to increase its strength. The requisite strength is imparted by a temporary or permanent twisting of the ribbons, by which the fibres, being brought closer together, are more intimately intertwined and adhere more firmly. This bringing together of the fibres must, however, not be carried too far, as thereby a further drawing would be rendered difficult or impossible. The machines by means of which the drawing is effected simultaneously with a twisting to increase the consistency of the thread are called " rov of which there are two kinds, one for a temporary (" false") twist and the other for a permanent twist.
ROVi/T-MaChiite.—FigUre 2 (P. 37) exhibits a tem porary-twist roving-machine. Besides the ordinary drawing-frame, there is an apparatus which, after the ribbons or threads have been stretched, twists them alternately to the left and right, the action being similar to that of rolling a filament between the palms of the hands. This twisting apparatus consists, for each sliver, of an endless strip of leather stretched over two rollers, a leather-covered cylinder being pressed upon the strips in the centre of the upper one. These two mechanisms, having a con tinuous revolving motion, catch the ribbon between them and convey it from the drawing-frame to the tin can, while an alternate pushing back ward and forward in a longitudinal direction normal to that of the sliver effects the twisting of the sliver in alternate directions.