Schaeffler North America


Extruder Gearbox

Valve unit for twin screw


Extruders are used for the conveying, compaction, degassing and homogenization of plastics in powder or granulate form that may be processed using stabilizers, parting agents, colouring agents and fillers. The processed plastic is then pressed by the extruder into the profiled die through a nozzle.

In this application, the extruder gearbox is subjected to high torques and high radial and axial loads; the gearbox must meet high requirements. Small centre distances are a feature of certain extrusion processes.

High power levels are therefore transmitted through compact gearboxes and the screw shafts are subjected to very high axial loads.

The figure shows the valve unit for an extruder gearbox produced by the company P.I.V.

The gear (a) transmits high torque levels to the split intermediate shaft (b). The torque is then transmitted via intermediate gears (c) to the screw drive shafts (d) which rotate in the same direction. The speed and torque on the intermediate shaft is compensated by means of a torsion shaft.

The high axial loads due to the extrusion process act on the screw drive shafts.


The bearings in the extruder gearbox are lubricated by oil. The requirements on these bearings are as follows:

  • they must have a life of 20 000 h to 30 000 h
  • they must operate reliably
  • they must transmit high radial loads
  • they must transmit high axial loads
  • they must run quietly

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