Effects of pipe angular velocity and oven configuration on tube temperature distribution in the radiative heating of PVC pipes

Several manufacturing processes in polymer industry aim at obtaining products by deforming preforms or sheets after a heating process. A thorough knowledge of the operating parameters of such heating processes is fundamental to fulfill the often high production requirements with the least energy consumption and to avoid unacceptable defects in the final product. A common example of such an application is the end-forming process of polyvinyl chloride (PVC) tubes, which are enlarged at one end in order to allow pipes connections. The heating phase which comes before the deformation process is usually carried out in ovens equipped with short wave infrared lamps; to ensure uniform heating, pipes rotate with a given angular velocity, which represents a fundamental parameter for the success of the whole manufacturing process. In this work, a transient analysis of the radiative heat exchange between rotating PVC pipes and infrared lamps in an oven for end-forming process has been conducted by means of a finite element model, in order to investigate the influence of cylinder angular velocity on the temperature distribution in the tube. Local view factors have been calculated for different oven configurations and have been expressed as a function of angular velocity, allowing pipe rotation to be simulated as a time-dependent boundary condition, instead of using a moving mesh. Simulations were carried out for different tubes geometries and angular velocities and results were compared with the case of a uniformly irradiated tube in terms of temperature displacement. For a given oven configuration, the results obtained by the numerical model can be used to find a critical angular velocity over which further increase does not lead to appreciable improvements in temperature evenness. The effect of the lamps’ relative position was also investigated, showing a significant influence on critical angular velocities obtained. The model realized represents a potential tool to characterize the end-forming process in terms of critical angular velocity, leading to reductions in machine set-up time and product waste due to thermal failure.