TWI Industrial Member Report Summary 552/1996
R J Wise
This report reviews the currently available welding techniques for plastics, current theories of welding and experimental details of polymer self-diffusion.
Welds in polymers are commonplace in the modern world, with many such joints being present in a typical motor car, gas or water pipeline and in plastic window frames.
The development of weld strength in polymers is believed to be due to the movement or diffusion of polymer chains across the weldline. During mechanical testing of welds, the strength of the joint is mainly due to polymer chains which have migrated across the weldline unravelling and being pulled out of one surface or the other. These concepts assume that the polymer chains are free to move or diffuse during welding, which generally means that the polymer must be above its softening point (T g) or melting point (T m). It also means that the two parts being welded must be in intimate contact to allow chains to pass from one side of the weldline to the other. In addition, sufficient time must be allowed for the polymer chains to move or diffuse a certain distance into the chains within the opposing part. These three considerations form the basis for the derivation of the welding parameters temperature, pressure and time.
- To review the current state-of-the-art and fundamental understanding of polymer welding.