Rieter

The doffing operation

Index

It would appear logical to arrange the  clothing of the  cylinder and doffer in the  doffing configuration relative to each other. In practice, however, they are actually arranged in the carding configuration (Fig. 115). This clothing arrangement is essential because the web that is finally delivered must be cohesive and therefore the fibers must be interlaced with each other and condensed. Compared with the doffing configuration, the carding configuration at this point is disadvantageous in some respects. One disadvantage is that the desired fiber parallelization achieved on the main cylinder largely disappears again, since a degree of random orientation is necessary to form a web and to doff it.

Another is the undesirable bending of the fiber ends which occurs here, because the cylinder has to give up the fibers to the doffer clothing, during which a certain degree of sweeping through the fiber fleece takes place. In the course of this step, the fibers are caught as hooks on the points of the clothing. Accordingly

  • over 50% of the fibers in the web exhibit trailing hooks(at the rear end as viewed in the direction of material flow);
  • about 15% have leading hooks;
  • another 15% have double hooks and
  • only a small proportion are delivered without hook deformation of any kind.

A third disadvantage, namely the poor efficiency of fiber transfer from the cylinder to the doffer, is in practice more an advantage than a disadvantage. Of course, it is a fact that the fibers rotate with the main cylinder about 5 to 10 (15) times (!) before passing to the doffer, but it is also a fact that this results in some important improvements:

  • it is an additional carding point;
  • the fiber-to-fiber blending effect increases, i.e.
  • a high degree of intermingling results there, which is important, e.g. for man-made fiber/cotton blending);
  • it produces good diagonal and short-term regularity.

The carding configuration implies that it is more or less a matter of chance which of the two clothing surfaces will finally carry along any individual fiber. However, this operation favors the cylinder clothing, as the flats push the fibers vigorously into the cylinder clothing, and as the cylinder clothing has more points, both facts increase the retaining effect.

As mentioned above, the result is a poor transfer factor. However, certain provisions can influence the latter positively, mainly by:

  • coordinating the clothing of both assemblies accordingly;
  • the choice of a proper relationship of the peripheral speeds;
  • providing for small distances between cylinder and doffer.

A reduction of the spacing between the two assemblies, e.g. from 0.18 mm to 0.08 mm results, for example, in a 100% improvement in the transfer factor.

Fig. 115 – Clothing configuration between main cylinder and doffer