Laying down of roving in the package is effected in parallel layers, i.e. each wrap is laid on the tube closely adjacent to the neighboring wrap (Fig. 80 and Fig. 81). In order to be able to wind over the whole length of the tube, the winding point must be continually shifted.
In principle, this is possible by adjusting the position of the press finger through raising and lowering the flyer or by up-and-down movement of the tube. However, the appropriate up-and-down movement of the flyer cannot be implemented in practice because it would result in continual variation of the spinning geometry – the inclination and length of the thread path from the drafting arrangement to the head of the flyer. The only practical method is the more complex continual raising and lowering of the packages together with the bobbin rail.
Since the first winding layer is formed on the bare tube, its diameter and hence its circumference (length of wrap) are both small. The second layer of wraps lies upon the first, i.e. the circumference of the wraps is already larger. However, since the individual wraps must be located very close to each other, so that the package takes up as much material as possible, the package (as a unit with a bobbin rail) must be moved more slowly for this second winding layer than for the first. For the third layer, it must be moved still more slowly, and so on. The speed of the bobbin rail, and also of the bobbin itself, must be continuously reduced.
A second change of movement is required insofar as the bobbin rail must perform continually shorter strokes. This is necessary because of the lack of end limitations in the form of flanges. If the stroke were held constant, i.e. the package ends were made straight, then the individual layers would fall away at the ends. In order to prevent such falling away, the ends are made conical, and consequently the stroke of the bobbin rail has to be reduced after each layer.
Fig. 80 – Build of roving bobbin in sections
Fig. 81 – Laying wraps next to each other
