Effect of Weld Lines on the Injection Moulding of Structural Foams. II Mechanical Properties

Abstract

The effect of weld lines on the mechanical properties of structural high density polyethylene foams was studied. Injection moulding was used to produce foams using azodicarbonamide in single and double gated moulds where shot size, injection speed, and flow direction were changed. The mechanical response of the foams was characterized in tensile and shear tests. Density reduction, decreasing injection speed, and the presence of the weld line were found to reduce both tensile and shear moduli, as well as tensile strength, break strain and toughness. The lost of mechanical properties can be related to lower skin thickness and incomplete bonding at the weld line. Simple correlations are also presented to predict moduli and strength of these foams.