Sudy on the Molding Characteristics and Mechanical properties of Injection-molded Foaming Polypropylene Parts

摘要

This study investigates the molding characteristics and mechanical properties of injection-molded foaming polypropylene (PP)parts and coinjection-molding PP parts for foaming core material embedded in nonfoaming skin material.Effects of processing parameters including injection-velocity,metling tmperature,molde temperature and back pressure on part weight and part mechanicla properties including tensile strength,flexural strength and stifness are investigated.influence of part thickness and Foaming agent content on the degree of foaming is also studied.Based on the measured results,it was found that for thin-wall bending foam specimens with thickness,weight reductionis about 4-9(percent)whereas in the thick-wall bending foam specimens with 15 mm thickness,the reduction is approximately 43-50(percent).Part thickness is a dominant factor to determine the degree of foaming.For injection-molded foaming parts,part weight,tensile strength,determine the degree of foaming.For injection-molded foaming parts,part weight,tensile strength,flexural strength and stiffness decrease with increasing melt temperature,mold temperature and injection velocity,whereas they increase with increasing back pressure.Foaming results in weight reduction but it also reduces part mechanicla properties.The foaming agent content increases from 0.8 to 1.6(percent),teh mechanical properties reduces significantly.Moreover,the conjection-molding thin-wall parts process for foaming core material embedded in nonfoaming skin material results in a foam part with very good esthetics and higher tensilej strength than injection-molded foaming parts.Meanwhile,the foam core is well bonding to the nonfoam skin in the coinjection-molding parts.The presetn investigation provides a molding guideline for injeciton-molded foaming parts and coinjection-molding parts to achieve a specific objective of part quality.