The weld lines that occur in injection mouldings are critical areas on which depends on the strength of the mouldings. The flow of the material in the injection mould takes place through the gate and then gradually in the mould cavity. Depending on the shape of the formed object, the weld line may or may not occur. In the case of spreading of plastic streams or bypassing obstacles in the form of cores in the mould, the joining lines run down. Most often, the strength of the moulded part is the lowest in these areas and the resulting lines can cause cracking. The aim of the research presented in the publication was to evaluate the properties of particular parts of mouldings obtained from an experimental injection mould equipped with 4 weld line areas. The tests were performed using the method of thermal analysis by Dynamic Mechanical Analysis DMA. Tensile tests were performed on the parts with weld areas and the maximum crack force was determined. The morphology of the obtained fractures was observed using an optical microscope.

The parameters of the injection moulding process have a significant influence on the properties of the moulded parts. Selection of appropriate injection conditions (e. g. the injection temperature, mould temperature, injection and holding pressure, injection speed) contributes to the productivity and energy consumption of the injection moulding process as well as to the quality of the moulded parts. The aim of this study was to evaluate the influence of injection moulding parameters on properties of poly(ethylene) mouldings. Regranulate obtained from recycled film, which is a mixture of low-density poly(ethylene) and linear low-density poly(ethylene), was used for testing. Samples in the form of standardised tensile bars of type A1 were produced by injection moulding. A Krauss-Maffei KM65-160C4 injection moulding machine was used for this purpose. Variable parameters of the this process used in the study were: injection speed, mould temperature and holding pressure. The results of tensile strength tests of the obtained samples are presented. The weight and dimensions of mouldings from four different regranulates were also investigated. The effect of injection moulding conditions on the properties of poly(ethylene) mouldings was shown in the investigations. The mass of poly(ethylene) mouldings is dependent on the holding pressure.