Study On Injection Process Of Polypropylene

In order to development of new products and offer technology support for customers, injection molding process and CAE technology application was studied in this thesis.Six kinds of polypropylene, which were produced by Yansan Petrochemical Corporation, were used in this thesis. The processing properties of polypropylene were studied by methods of melt flow rate, gel permeation chromatography (GPC), Brabender torque rheometer and PVT-100 analyzer. The results showed that these polypropylene samples presented feasible relative molecular mass, suitable distributions and good fluid properties. The analysis of thermogravity and differential scanning calorimetry (DSC) were used to analyze the thermal degradation temperature, melting point, crystallization temperature, ejection temperature and glass-transition temperature of polypropylene. According to the results, the feasible range of processing temperature and mold temperature were 175~325℃and 30~110℃respectively. The upper limit ejection temperature was about 113~128℃. The effect of process parameters on fluid property was studied by analysis of spiral lengths of PP samples. It was shown that the spiral lengths increased in different degree with an increase in melt temperature, injection pressure and injection rate. Polarized optical microscopy (POM) was used to analyze the effect of injection molding process parameters on morphologies of polypropylene. The results showed that the thickness of skin layer increased with an increase in melt and mold temperature, on the other hand, the thickness of skin layer appeared to be almost unaffected by changing injection pressure. With different process, the polypropylene samples were molded to analyze the influence of process parameters on the property of the production. On condition that the mold cavity was filled, lower melt temperature should be adopted to improve the property of the production. Experimental results showed that the increasing of holding pressure could improve tensile yield strength and impact strength. The shrinkage decreased with increasing of hold pressure and injectionrate. The mold temperature could promote the bending strength and tensile strength, but shrinkage also increased. The effect sequence of the process parameters was gotten by orthogonal design method, which could direct customers to determine the important parameters firstly according to their specific demands. Through injection molding computer aided engineering (CAE) analysis, the injection molding condition of writing case was optimized. It had been proved that a viable process condition was: injection time 1~4s, injection pressure 44.3~46.1MPa, holding time 21.4 s, holding pressure 36.0MPa, temperature of cooling water 25℃and flow rate of cooling water 10L/min.