Study of Shrinkage of Thermoplastics in Injection Molding

Abstract The article is devoted to problem of plastic materials deformation in process of production by injection molding. The stages of plastic processing are considered, including heating, melting, mold filling and subsequent solidification. The main types of shrinkage and key ways of measuring it are described. A series of experiments using polypropylene, high-density polyethylene and two modifications of polyvinyl chloride are carried out. The influence of processing temperature regimes and rheological characteristics of materials on final dimensional parameters of products has been investigated. Correlation dependences between coefficient of thermal expansion, range of working temperatures of mold and yield index for each type of polymer have been established. The optimum technological modes providing minimum geometrical deviations of finished parts have been revealed. The results of study can be used to improve technological processes and increase accuracy of manufacturing polymer products of complex configuration.