PLAIN / PIN BARREL TYPE EXTRUDERS VENT / VACUUM TYPE EXTRUDERS, DUAL EXTRUDERS FOR CO-EXTRUSION

PRODUCT INTRODUCTION

The pins, made from special steel, eliminate a problem which leads to a noticeable drop in throughput and extruder quality in the operation of large, conventional cold-feed extruder. Due to temperature and viscosity differences, where no material exchange occurs between neighbouring compound layers, »islands« form in the rotating flow between the screw flights. These layers insulate themselves from one another, thus preventing proper mixing of the extruder.

The pins (see diagram) which are inserted through the barrel from the outside, divide the flow of rubber, invert it and mix the layers with one another. This results in the formation of permanent new surfaces and leads to an intensive exchange of materials and heat. In order to ensure optimal mixing throughout, the first pin row is situated at a point where the filling process has definitely been completed. As the pins nearly extend to the screw core, gaps have been cut in the screw flights at the corresponding positions.

In most cases the screw of Extruder is made of nitrided steel although for some applications other special steels may also be used. In order to better protect the highly stressed external surfaces of the screw flights from wear, for example when abrasive compounds are processed, these may be coated with extremely hard armour plating. The barrels are equipped with replaceable liners which can be treated with an abrasion-resistant coating if required.

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