The Effect Of Processing Method On Foam Structure And Mechanical Property Of SCF Microcellular Parts

Today,we are facing problems of global energy crisis and environmental pollution.The existence of a large number of tiny bubbles in supercritical fluid(SCF)microcellular parts is able to reduce the use of raw materials and energy consumption.At the same time,compared with traditional products,some performance in aspects of microcellular products are more excellent.With unique advantages,the technology of microcellular foam,which has become a research hotspot,are faced with many problems and challenges.It is a problem waiting to be solved that how to form the high density and regular micro structure to obtain excellent mechanical properties.In this paper,the bubble structure in SCF microcellular injection molding parts was studied including conventional injection molding,high pressure injection molding and injection-compression molding.The main works are as follows:(1)We designed and manufactured an injection-compression mold which can be used to produce SCF microcellular products with 3 kinds of processing methods.Also,we simulated thermoplastic injection molding and microcellular injection molding using the commercial software Moldflow to evaluate performance of mold with polystyrene(PS).The results showed that a compression frame with spring and a movable cavity plate are keys to the mold design.Compared with thermoplastic injection molding,microcellular injection molding had a shorter filling time,lower melt front temperature and lower uniform pressure distribution after filling.(2)We studied the effects of SCF content,back pressure and pre-filling volume on foam structure of conventional injection molding SCF microcellular foam.The results showed that the SCF content,back pressure and pre-filling volume had an important influence on foam structure of the products.The bubbles on section of perpendicular to the flow direction are spheres or ellipsoids,while bubbles on section of along to the flow direction showed obvious shear effects.The foam structure at the beginning,middle and end along the flow direction was obviously inhomogeneous.(3)We studied the effect of holding pressure and holding time on the foam structure of high pressure injection molding SCF microcellular foam products.The results showed that there are highest bubble density and smallest bubble size when holding pressure is 600 bar and holding time is 5s.What's more,bubbles in parts of high pressure injection molding are circular whenever observed in the section of along to the flow direction or perpendicular to the flow direction.(4)We studied the influence of compression force and compression time on the foam structure of injection-compression molding parts.The results showed that there are highest bubble density and smallest bubble size when compression pressure is 400 bar and compression time is 5s.What's more,bubbles in parts of injection compression molding are circular whenever observed in the section of along to the flow direction or perpendicular to the flow direction.(5)Base the different foam structure of different foaming methods,we compared the cavity pressure and mechanical property.The results showed that the mechanical property in conventional injection molding,with the low cavity pressure,is poor.And,the mechanical property in high pressure injection molding,with higher cavity pressure,is higher.What's more,with highest cavity pressure,mechanical property in injection-compression molding is highest.