Transfer zone at the doffer


Fig. 22 – Transfer of fibers from the main cylinder (T) to the doffer (A)

The arrangement of the clothing between the main cylinder and the doffer is not, as might have been expected, a stripping arrangement, but a carding arrangement. This is the only way to obtain a condensing action and finally to form a web. It has both advantages and disadvantages. The advantage, is that an additional carding action is obtained here. This is important, since the processing of the fibers differs somewhat from processing at the flats.

A disadvantage to be noted is the formation of hooks at this point. Before transfer, some of the fibers remain caught at one end on the teeth of the main cylinder (Fig. 22, T). During transfer, the other ends of the projecting fibers are caught by the clothing of the doffer and taken up. Since, however, the velocity of the main cylinder is much higher than that of the doffer, the teeth of the cylinder wire (T) smooth out the fibers in the direction of rotation, whereby the rear ends of the fibers remain caught on the teeth of the doffer (A).

By this means, they form hooks at their ends. In the web, and then in the card sliver, most of the fibers in the strand possess trailing hooks. However, aside from the serious disadvantage of hook formation, the carding effect mentioned is also produced here, since either the main cylinder clothing rakes through the fibers caught in the doffer clothing, or the doffer clothing rakes the fibers on the main cylinder. Neps can still be disentangled here, or non-separated neps disentangled during the next passage through the flats  [11, 14].

The intensity of carding (as at other carding positions) is here dependent upon  [14]:

  • type of clothing;
  • geometry of the teeth;
  • number of teeth per surface;
  • distance between the carding surfaces;
  • speed relationships;
  • sharpness of the clothing;
  • degree of wear of the clothing.

The diameter of the cylinders is also relevant. Large diameters imply a large contact surface at the working positions and thus, in addition to improvement of the transfer factor, longer raking of the raw material by the clothing.