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Barrels

The extruder cylinders are subject to considerable wear, depending on the process. In the case of co-rotating twin screw extruders, generally shorter cylinder segments 3 to 6 D in length are used. Also 8 or 10 D for certain special tasks, such as the degassing of large quantities of volatile components.

Over time, diverse wear protection systems have been developed. It should be noted here that, in most processes, cylinder cooling is required. This cooling is carried out for intensive heat transfer mostly by means of impulsive water injection into a cooling circuit.

This creates additional cylinder material requirements. In the area of cooling, a ductile material is required, as an excessively rigid material could crack due to thermal stresses.

In principle, there are therefore three possible versions for barrel design:

A: Barrels without cooling

It is possible to use a fully hardened material. This version is often used in combi barrels, i.e. barrels with a side opening to connect a side feeder and generally a top opening for simultaneous venting.

B: Barrels with an inliner

The wear protection and cooling functions are separate. The housing can generally be reused if, due to wear, the inliner must be changed. The advantage of this design is the large variety of materials that can be used for such inliners. For example, high-alloy steels, chrome steels and materials produced using powder metallurgy on nickel or cobalt-base alloys with interlayer hardening components.

C: Barrels with a directly bonded protective layer

This also includes, in the simplest case, a nitrided layer on the bearing surface of the extruder screw. This is extremely hard but relatively thin so there is limited wear protection before the wear increases rapidly at the softer base material. The advantage of nitrided barrels is their good dry running properties.
It is also possible, for example, to use an HIP process to apply a high wear-resistant hardening component layer to the bearing surface.

 

We carry out a precise analysis of the extrusion process in order to select the optimum solution for the relevant zone, together with our customers. The entire tribological system, with process parameters, product and wear combination, is taken into account. This is ImproveXtrusion.