Examining the influence of injection speed and mould temperature on the tensile strength of polypropylene and ABS

This report is the final task of course “41738 Experimental Plastics Technology” in the three weeks period of June 2009 at DTU, IPL. The aim of this project has been to investigate the ultimate tensile strength behaviour of two different polymers, with different structural composition, by varying the injection speed and the mold temperature independently while keeping all other process parameters fixed. In addition the scaling from production of large to small geometries has been investigated by doing two parallel productions and test setups of respectively injection moulded and micro injection moulded specimens. After production and tensile testing the specimens were examined with a microscope to underpin conclusions from the tensile test data. It was experienced that the injection speed in general increased the the tensile strength by orienting the polymeric-chains lengthwise in the specimens and thus increasing the strength in the tensile strength. This observation was however disturbed by the test results for small ABS specimens where an increased injection speed in general meant lower tensile strength, which though can be explained by the extremely rapid cooling that the small specimens in general were subjected to. The influence of the mould temperature was generally less significant and usually lay within the uncertainty of the standard deviation, but can superficially be said to affect the semicrystaline PP in a way where higher mould temperature induce slightly higher tensile strength, which is seen as a consequence of the slower cooling speed and thus a longer crystalisation time that this implies. In relation to the amourphous ABS the influence of the mould temperature is found to be of an insignificant character.