Rieter

Covers

Index

The pressure roller covers are made of synthetic rubber. The cover in the form of a short tube is fitted onto the bearing sleeve with a certain degree of pretension and glued in position, an operation that has to be performed with the greatest care. There are different ranges of hardness:

  • soft: 60°-70° Shore
  • medium hard: 70°-90° Shore
  • hard: over 90° Shore

Covers of less than 60° Shore are not usually of any use, since they are unable to recover from the deformation resulting from the contact pressure during a revolution of the roller. Soft covers have a larger contact surface, and therefore enclose the fiber bundle more fully, thus providing more effective guidance. However, they also wear rather more quickly and have a greater tendency to form laps due to the fulling effect. Harder covers are therefore used wherever possible. This is the case, for example, at the drawframe infeed. Here a compact, unified fiber bundle with a slight twist, requiring no increased guidance, is fed in. However, increased control of this nature is an advantage at the delivery end, where only few fibers remain in the bundle and these have a tendency to drift apart. Covers with approx. 80°-85° Shore are therefore usually used on the back rollers and 63°-67° Shore on the front rollers. Harder covers are also chosen at the front, i.e. at the delivery end, for coarser yarns and manmade fiber yarns due to wear (also due to the higher tendency to lap formation in the case of man-made fibers). Since the covers wear, they have to be ground on special grinding machines from time to time (after some 3 000 - 4 500 operating hours). The reduction in diameter should be some 0.2 mm, and the covers should never be ground to a total thickness of less than 3.5 mm.