Effects of Interfacial Structure and Molding Condition on the Injection Welding Strength of Polyamide

Abstract

The effects of injection-molding conditions and interfacial structures on the shear welding strength of polyamide material were investigated and the following main results have been obtained. (1) Variations of the first injection-molding speed and temperature exert an influence on the welding strength when the secondary injection-molding temperature T2 is low (below T2=265°C), but the influence vanishes when T2 is higher than 285°C. (2) Under any first injection-molding condition, the welding strength intensifies with the increase of secondary injection-molding temperature, and the highest welding strength reaches 45 MPa, which is almost the same as that of the non-welding base material. (3) It greatly influnences the welding strength that a trans-crystal which is perpendicular to the welding interface is formed in secondery molding. When T2 is higher that 285°C the trans-crystal layer is formed in the whole welding interface and a stable high welding strength may be obtained. Above results show that it is possible to obtain a high shear welding strength close to that of base material by controlling welding conditions in the injection welding method applied in the present research.