Wednesday 17 February 2021

Design Properties for Engineers – Processing Temperatures of High Performance Polymers

In this blog post, I present to you the processing temperatures of high performance polymers for injection molding.

For processing of high performance polymers equipment is needed which is capable of dealing with temperatures up to 450°C for the plasticizing unit and 250°C for the moulding tool (oil heating).

The figure below shows the mould and processing temperatures of the most used high performance polymers, together with the processing shrinkage values.

Figure: processing temperatures of high performance polymers for injection molding

Important to note is that certain wall cross sections and flow length ratios need to be fulfilled. Polymers such as PAI have a high viscosity. Therefore, wall thicknesses below 1.5 mm should be avoided. A wall thickness of 1 mm is possible with unreinforced PEEK. In case the part has a wall thickness of 10 mm, additional ribs prevent sink marks.

Commodity and engineering plastics show high processing shrinkage values. However, with high performance polymers, shrinkage values are much lower compared to engineering and commodity plastics. PEEK shows shrinkage values below 2.5 %. In general, shrinkage is in flow direction lower than cross flow direction. Additionally, it is important to have sufficient draft angels (around 2°).

Furthermore, attention needs to be paid to the forming of weld lines in the cavity, since high performance polymers have a high viscosity and this may result in a lower strength at weld lines (less entanglements). 

Thank you for reading and #findoutaboutplastics

Herwig Juster

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[1] Sachtling Kunststoff-Taschenbuch

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