A Technique for Predicting Molding Conditions which Result in Class A Surfaces for Glass Fiber Reinforced Polymers

Abstract

This work is a continuation of our modelling studies which are aimed at predicting the appearance of glass fiber reinforced polymers. The mathematical model which has been developed was presented earlier [2,3]. In this study, the following two parameters were evaluated: 1—The effective thickness of fiber strands which is different from their apparent thickness and is an indication of clustering (bundle formation) of the strands; and 2—The slope of surface deformation pertinent to smooth surfaces. From the experimental results, the effective thickness of fiber strands was determined to be 0.35 mm. This value does not appear to be dependent on the type of fibers, type of resin, or fiber content, within the range of the materials and molding conditions used in this study. To obtain a definition for surface smoothness, the slope of surface deformation (0) is related to the smoothness of the surface. It is found that 0 = 0.006 relates to smooth sur faces on glass fiber reinforced polymers. Applying the above two values along with our mathematical model, graphic relation ships are derived which can predict the thickness of the top layer needed to produce a smooth surface.