The spindle and flier of the jute roving-frame are, with the exception of their dimensions, exactly the same as those employed in the cotton trade. Here, however, the parts are larger and stronger, as befits the heavier fibre to be treated. The number of spindles in a frame may be either few or many, ranging between 24 and 64 to each frame. A common size contains 56 spindles ; and as there is required a gill to each spindle, and eight gills form the complement of each carriage, there are consequently 7 carriages in a frame of 56 spindles.
The spindles a, with their fliers b on the summit, are arranged in two rows in a vertical position in front of the frame, as shown in section in Fig. 869. The spindles are actuated by gearing at the foot, and make about 600 rev. a minute. The arms of the flier are tubular, the rove, after leaving the drawing-rollers, being conducted downwards through them to the extremity of the arm, whence, passing through an eye or curl, it is wound upon the bobbin.
The bobbin is driven by gearing similar to that which turns the spindles, but of which it is quite independent. The course of its revolution is in the same direction as the flier, and either flier or bobbin may be arranged to lead. As a rule, it is the former that takes precedence, with the bobbin following. The twist imparted to the reve should not be more than is necessary to secure its coher ence when being drawn from the bobbin in the subsequent process. Assuming a case in which the frame is arranged for the flier to lead, and supposing that one turn a minute is sufficient for the roving being produced, with the spindles making 600 rev. a minute, the fol lowiug conditions require to be observed. The drawing-roller must be arranged to deliver 1 in. for each rev, of the flier, and the speed of the bobbin must be retarded, as compared with the spindle, to a degree sufficient to enable it to wind up the quantity of roving delivered by the drawing-rollers. In this case, the roller delivers 600 in. a minute, the spindle and flier make 600 rev, a minute, and the shank of the bobbin c, which is shown by the dotted vertical lines, is 5 in. in circumference. Dividing the number of in. (600) delivered by the roller by the winding sur face (5 in.) = 120, then 600 — 120 = 480, is the speed at which the bobbin is required to run to wind up the 600 in. But this is not a
constant rate : every layer of roving wound upon the bobbin enlarges the circumference of the winding surface. If the bobbin were to remain constant, the roving would be rapidly attenuated, or so over-run as to be broken in every case long before the bobbin could be filled. These results are obviated by means of differential driving-gear, the essential parts of which are seen in Figs. 869, 870. The roving is first wound upon the bare shank of the bobbin in an even layer, and each succeeding one upon that which has gone before, until the bobbin is filled. This is accomplished by mount ing the bobbins on a lifting-rail d, whose traverse extends downwards to d', by which means, the bobbins c are moved upwards and downwards through the same space, and the rove is placed in even layers by the flier. The deposit of each layer of rove upon the bobbin increases the cir cumference of the winding surface of the bobbin, but the drag which this would cause is prevented, by the speed of the bobbin being accelerated in exact proportion to its increased winding surface, so that it still continues to take up only the 1 in.
delivered for each rev. of the flier. This accele ration of the speed is caused by a projection attached to the lifting-rail, which is so arranged as to release a catch each time the rail arrives at the top and bottom of its traverse. The regulating motion is obtained from a bowl or pulley B, Figs. 869, 870, having a leather face, which is made to revolve by frictional contact between two flat, circular, iron discs e, rotating in opposite directions.
In commencing to fill a set of bobbins, the friction-bowl B occupies the position shown by the dotted lines at A (Fig. 870), which is its starting-point. Each time that a catch is released, either at top or bottom of the traverse, the bowl, with the shaft on which it is fixed, is allowed to slide outwards a little from the centre of the two discs e, whereby its speed is increased, and. that of the bobbin correspondingly accelerated, for each additional layer of rove that the bobbin receives ; and when the bowl has arrived at the position B (Fig. 870), the bobbin has attained its maximum speed, is filled, and is then ready for doffing. When the frame is arranged so that the bobbin leads, these movements are reversed.