• Surface tech­niques for screws

Special hardfacing for rubber extruders

In a large number of cases, hard facing with conventional coating materials, such as stellite, has not proved successful.

During rubber processing, a very high surface pressure occurs between the screw flight and the barrel wall. This is caused by unequal force balances when the usually only slightly pre-tempered rubber strips are drawn in.

The resulting compressive stress, also known as sigma stress, far exceeds the limits of stellite.

Sometimes an armoured screw with stellite has only half the service life of a normal nitrided screw.
For this reason, we use a nitrided armour material.

This material already has a basic hardness of approx. 50 HRC after welding and is then nitrided.
The support effect resulting from the high base hardness in relation to the nitrided layer significantly improves the wear behaviour compared to normally nitrided screws.