Measurement of internal stresses in injection moulded parts

The purpose of this study was to determine the internal stress state in injection moldings made of high density polyethylene (PE-HD) and polypropylene (PP) and to register the influence on it of various processing parameters, it was envisaged that measurement would be carried out at the interference lines of the crystalline phase of the partly crystalline plastics. The basis for the experimental determination of internal stresses by means of diffraction and interference phenomena of X-rays is the fundamental equation of the X-ray stress measurement. The formation of internal tensile stresses near the sprue and internal compressive stresses at the edge is due to cooling processes in the molded part. Extending the cycle time for the PE-HD moldings assists the relaxation processes in the material, as does an increase in the cylinder temperature for the PP parts.