Experimental Investigation of Rotational Molding and the Characterization of Rotationally Molded Polyethylene-Parts

Abstract

Abstract An experimental study of the rotational molding of polyethylene parts is presented. Specific attention is given to heating and cooling of the molding cycle and to the micro structuring and bulk characteristics. Experimental measurements of the heatup of the oven at the startup of the process is presented. The heatup of different molds in the oven is then measured and interpreted in terms of heat conduction theory and the Fourier number αt/L2. In the experiments, thick aluminium molds heated up more slowly than thinner steel molds. The cooling characteristics of mold subject to different quenching conditions were compared with water showers inducing the most rapid cooling followed by fan blowing and the slowest being in quiescent air. The order of cooling of the different molds studied followed the same order as their rates of heating as would be expected from the theory of heat conduction. Polyethylene parts formed in the molds were found to be crystalline, without orientation and to possess large spherulites. The size of the spherulites and the level of the crystallinity was highest where the cooling rate was the lowest. Uniformity of part thickness and warpage were measured. Warp age correlated with rapidity of cooling rate. This suggested a mechanism of thermal quench stresses.