The operating life of clothing is quoted in terms of the total throughput of material. For the cylinder it normally lies between 300 000 and 600 000 kg, but it can be higher in some circumstances.
Such quantities of material represent a huge number of fibers, which have to be processed by the individual tooth points. Processing therefore considerably wears down the teeth – they become rounded at the top and lose their aggressiveness. The direct result is a continuous increase in the nep content of the sliver (b).
The points must therefore be sharpened from time to time, in order to give a better shape to the edges by grinding them. Each new grinding operation reduces the number of neps, but the level never returns to that prior to the previous grinding. As Fig. 135 illustrates, the lower nep limit increases noticeably from “a” to “b”.
The deterioration in quality from one grinding interval to the next arises from the fact that the teeth are ground down to successively lower heights, the lands at the teeth points become steadily larger, and softer metal layers are gradually exposed. The following grinding intervals are currently in use:
| Cylinder | Flats | |
|---|---|---|
First grinding after [kg] | 80 000 - 150 000 | 80 000 - 150 000 |
Each additional grinding after [kg] | 80 000 - 120 000 | 80 000 - 120 000 |
The interval is best selected depending on the mills nep limit (c). Since the doffer clothing works much less than that of the cylinder, it should be ground only half as often, or even less frequently, except when man-made fibers are being processed: grinding should then be carried out more often but more lightly. The clothing on the licker-in should not be ground; it should be renewed after a throughput of 100 000 - 200 000 kg.
Fig. 135 – Increase in neps between grinding periods: A, number of neps in the web; B, grinding interval; b, general rise of the lower nep level; c, mills limit for neps
