Extrusion refers to the process of forcing material through a nozzle or die in order to produce parts with a constant desired cross section. This process is widely used in the food industry, and the development of extrusion technology has been regarded as the most significant achievements in food process engineering.

The process of plastic extrusion requires the use of screws. These screws primarily melt or plasticate polymers by introducing energy into the material by shearing it. This shearing process is essentially achieved by “stretching” the polymer material, while the screw flights allow for the transport of the polymer material through the cylinder while generating pressure and improving pressure.

Top screw speed refers to the highest motor speed divided by the reduction ration, which is determined by the gearbox and occasionally, the pulley sets. The average speed for most extruders is in the region of 100 revolutions per minute (rpm), while twin-screw extruders for rigid PVC pipes, PVC profiles and PET sheets run more slowly at less than 30rpm.

You can measure the rpm of your screws by having the motor run and accessing it manually or by reading the motor nameplate and extrapolating the rpm from the motor speed and reduction ration.

High speed may reduce thickness control and risk mechanical problems and increase production costs without increasing production value to the same degree. Optimum speed is more valuable than maximum speed, as maximum speed is only a mathematical concept whereas optimum takes several aspects, including sales, thickness control and overheating into account.  In contrast, if the screws are too slow, and it could result in poor melt quality, unstable output and large temperature differentials in the extrudate. The larger the extruder, the more complicated this problem becomes.

Plastic & Chemical Trading,  together with international partner KraussMaffei Berstorff, delivers world-class plastics, injection moulding, and extrusion solutions.

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