Most of the industrial machines use the belt transmission for the power transfer. These mechanisms often use the round belts with a few millimetres in diameter, which are made of the thermoplastic elastomers, especially the polyurethane. Their production process requires the bonding step, which is often performed by the butt welding, using the hot plate. To design the automatic welding machine in a proper way, the authors analyzed this process. The paper discusses the topic of butt welding of polyurethane drive belts by the hot plate method in the context of modelling the process of this technological operation. Based on the analysis of the butt welding process, a series of studies of the thermomechanical properties of the material from which the belt is made has been made, especially dynamic thermomechanical analysis and thermogravimetry. On the basis of their results there is possibility to determine the allowable values of welding temperature and viscosity of the material in the context of technological parameters of plasticizing operation.