compression moulding

impact benefit from having a compression moulder available, with a variety of mould shapes available.

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compression molding - Plexiglass sheets colored

compression moulding

Compression moulding is a method of forming plaques from polymer in the  form of pellets or powder by the application of heat and pressure. The raw plastic is pressed at high temperature for a set period of time to create a plaque. It is an ideal method for creating test samples of material.

impact have years of experience in pressing different materials, and the equipment is ideal for making small scale sample plaques. These samples can then be assessed through tests such as tensile, flex, impact, FNCT and weathering.

how compression moulding works

A metal frame of required dimensions and thickness is filled with a measured quantity of polymer and sandwiched between two polished metal plates. The assembly is loaded in a compression press, pre heated to the required temperature. The platens are closed and required pressure is applied for the specified time period. The press is then cooled at a controlled rate. On completion of the cycle the frame assembly is taken out, disassembled and the plaque separated from the frame.

Compression moulding is fundamental to any plastics testing laboratory. It produces plaques with no internal stress or orientation which may affect the test results. It is useful for R&D work especially when the material available is scarce.

impact have a compression press with platen size 450mm x 450mm capable of delivering low pressure (5bar) and high pressure (100bar). Our experts can control the rate of cooling which is essential factor in controlling the crystallinity of polymers.  impact are UKAS accredited for ISO 293 and ISO 295. We can press wide range of plaques from 1mm to 20mm thick and have good experience of producing laminates and composite materials using compression pressing.

compression moulding machine
compression moulding machine - semi positive

semi positive moulding

Compression moulding is relatively simple way of pressing plaques from which test specimens can be machined out of. However it is difficult to press plaques of thickness greater than 10mm due to formation of internal voids, warpage and uneven shrinkage.

impact has developed their own method of pressing thick plaques using semi positive moulding. An insulated mould filled with required amount of polymer and is covered with polished plates on top and bottom. In the compression press, after allowing the polymer to sufficiently melt, the pressure is gradually applied and controlled during the cooling cycle. This prevents voids, uneven shrinkage and warpage. Our plaques are even tested using ultrasound for voids.

We can press plaques up to 30mm thick and 155mm x 155mm size or 230mm x 230mm sizes. Some of our customers use our plaques as control material or calibrant for their thickness measuring equipment.

sample preparation

full list of tests