Study On High Surface Finish Of SMC

Sheet molding compound (SMC) is a thermosetting material made of unsaturated polyester resin, organic additives, the initiator, calcium carbonate, thickener and chopped glass fibres strands that are mixed and form sheets. Compared with made by hand and other FRP molding processes, SMC is a bit more complex. Any change in the material or the producing parameter would influence the final product. Thus SMC asks for stabilities of the material and the producing parameter. China has joined WTO for 5 years, the competition in automobile have become fiercer. In order to decrease the oil consumption, and to decrease the environment pollution, low weight is an important way for automobile development, and to use FRP products is the effective method. Meanwhile, along with the SMC technology increasing progress and the market increasing expansion, the quite high outward appearance of SMC are requested in the more and more application fields. So how to decrease and even eliminate the curing shrinkage of unsaturated polyester and to improve the surface finish of SMC are important subjects to our composite material industry.We have researched contraction mechanism of self-made new low profile additive. Afterwards, we have major studied LPA, the initiator, MgO (thickener), CaCO₃ (filler) and the mould pressing technological parameter with emphasis influence to the surface finish of SMC product. The results show that SMC product has small shrinkage ratio and surface change luminously and smooth with the weight fraction of LPA increasing. When the weight fraction of LPA over 30, the surface finish of SMC product increased range reduces. The moderate weight fraction of dicumyl peroxide (DCP) used may improve the surface finish of SMC product. With the weight fraction of MgO increasing, the surface finish of product continuously increases by no means, but MgO has a best weight fraction. The surface finish of SMC product may improved by adding suitable weight fraction of CaCO₃ whose average grain diameter is smaller than 20μm. In the mould pressing technological parameter, mould temperature is more important influence than mould pressure and time to the surface finish of SMC product. The surface finish of SMC product fast increases with temperature from 130℃ to 140℃. When the temperature increases from 150℃ tol60 ℃, the surface finish of SMC has little increasing. It has a drop tendency, when the temperature is higher than 170℃.The effect of thickener and the initiator on the surface finish of low profile SMC product were studied by using the SPSS13.0 software and polynomial regression theories. The predicting formula on the surface finish of low profile SMC product was derived. The results show that the synergies have occurred among ingredients of low profile SMC. LPA efficiency is increasing with weight fraction of MgO increasing, the surface finish of low profile SMC product is improving; DCP content is smaller, the LPA has better thermal expansion efficiency and the surface finish of product is higher. We obtain predicting formula about the surface finish of...