Auger pitch

The auger pitch can be either progressive, linear or degressive As the angle of pitch varies with the distance from the hub, differentiaton has to be made between the inner, the middle and the outer pitch angle. 

Cylindrical extrusion barrel. The extruders commonly in use nowadays are usually provided with a cylindrical extrusion barrel and accordingly also a cylindrical extrusion auger. The pressure build-up is achieved by extrusion augers with a degressive pitch, i.e. the pitch decreases in direction of material feed. 

Conical extrusion barrel. When using a conical extrusion barrel, the diameter of the auger is gradually reduced in the direction of feed, whereby the augers have a linear pitch. The pressure build-up is in this case generated by the conicity of the extruder barrel. An extrusion auger of pure conical design is however rarely employed nowadays. 

The extrusion augers are differentiated by their pitch, i.e. the pitch of a full spiral of 360°, as follows ... 

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