High-frequency dielectric heating and the strength of flexible polymer seams

A theoretical model was developed to explain how the various high-frequency (HF) dielectric-heating (or HF welding) parameters affect the T-peel seam strength of thermoplastic polyurethane (TPU)-coated nylon fabric. The T-peel seam strength was sensitive to the welding temperature, welding time, pressure, and lap length. The HF (27.12-MHz)-induced interference problem was solved, which allowed the temperature to be measured at two-part welded joints and the influence of the welding temperature on the seam strength to be analyzed. The various processing parameters were simplified into two nondimensional factors: the damage factor characterizing the residual-stress-induced peel strength loss and the mixing factor characterizing the original peel strength induced by the mixing of the squeezed TPU coating at the end of the welded zone. The peel strength was assumed to be the difference between the original peel strength and the lost peel strength. The mixing factor played a more important role when the welding temperature and pressure were lower than a critical limit. When they were higher than this limit, the damage factor was more important. The mixing factor increased or remained constant with increasing lap length, while the damage factor decreased. This explains why the T-peel seam strength increased with lap length.