Rieter

Speed relationships

Index

One assembly, the flyer (spindle), is needed to twist the roving, but two assemblies are needed to wind it, namely, both the flyer and the bobbin. Winding is effected only when the difference between the speeds of these two assemblies is equal to the delivery speed. In terms of design, such a difference can be obtained very easily if one of the two assemblies does not rotate. Such a design, however, would impede the fulfillment of an additional task of the flyer, namely twisting of the roving. With a non-rotating flyer, there would be no turns in the product; with a nonrotating package, there would be too few – only one twist per wrap. A bobbin diameter of 106 mm leads to one twist per circumference (= 333 mm), i.e. only three twists per meter instead of the required 40-60 twists.

In order to fulfill both tasks, winding and controlled twisting of the roving to a selected degree, the two assemblies must have the same direction of rotation. However, the bobbin must rotate faster than the flyer or the flyer faster than the bobbin. This is referred to operations with a leading bobbin or with a leading spindle (flyer) (Fig. 82). A leading spindle has the advantage that, with a pre-set fixed spindle speed, the operation can be run with lower bobbin speeds – lower than the spindle speed.

Nevertheless, all modern short staple roving frame designs use the principle of the leading bobbin. It provides significant advantages, as follows:

  • Fewer roving breaks or faulty drafted places at the winding point, because the drive transmission path from the motor to the spindle is short, whereas that to the bobbin is long. Furthermore, the drive transmission to the bobbin includes a slip position, the cone belt transmission. When the roving frame is started, the spindle starts up immediately, but the bobbin follows with a delay. With a leading spindle, the roving would tear at the press finger, and a drafting fault at the finger would be created. With a leading bobbin, there are no such effects.
  • No unwinding of the layers. Unwinding of the roving would arise on a roving break with a leading spindle, because the roving is moved against air-resistance in the rotational direction of the bobbin. On the other hand, with a leading bobbin, the air-resistance tends not to lift the roving off the bobbin but rather to press it back against the bobbin.
  • Speed reduction with increasing package diameter. With a leading bobbin, the bobbin speed must be reduced slowly with increasing bobbin diameter, i.e. with increasing mass to be moved. This is advantageous in terms of power consumption. On the other hand, with a leading spindle, the bobbin speed must gradually be increased, which is not altogether sensible.

Fig. 82 – Winding on flyer bobbins; (a) with a leading bobbin; (b) with a leading spindle