Most of the industrial machines use the round-shaped drive belts for the power transfer. They are often a few millimetres in diameter, and made of thermoplastic elastomer, especially polyurethane. Their production process requires the bonding step, which is often performed by butt welding, using the hot plate. The authors took an effort to design the automatic welding machine. This action demands the hot plate welding process analysis, which consists in describing the dependency between technological parameters (temperature, pressure force, time) and the quality of the joint. To analyse this process in a proper way, it is necessary to describe the physical phenomena in the material during temperature and force impacts. In this case the research of thermomechanical properties of the belts is needed. The paper shows results of some preliminary research of the thermomechanical properties of the polyurethane. This research allows to predict the material reaction to increased temperature and force during hot plate welding.