Induction Heating of Thermoplastic Materials by Particulate Heating Promoters

Abstract

Induction heating is a fast and selective heating method, which can also be applied to polymeric materials, even though these materials do not offer the required electrical or ferromagnetic properties. To compensate for this deficiency, polymeric matrixes (high density polyethylene and polyamide 6) were compounded with various ferromagnetic and electrically conductive particles. The experimental series included induction heating experiments of compounds with different particle materials and variable filler grades at two distinct frequency levels (430 kHz and 2500 kHz). A mechanical characterization of the compounds was performed to identify the influence of the particles on matrix properties. The heating experiments showed a significant temperature rise of the particle doped materials, when they were exposed to an alternating magnetic field. The temperature rise was observed with plates as well as with pellets. The heating effect was found to be dependent on the frequency and the particle material. The best results were obtained from ferromagnetic particles like iron and magnetite, whereas for example non-ferromagnetic carbon black could only be activated in pellet-shape at high magnetic field strength. To reach the melting temperature of the polymer within a maximum time frame of three minutes, the filler content of specific particles could be as low as 5 wt.%. The mechanical properties of the materials, such as tensile strength and stiffness were influenced only marginally, while the impact strength was reduced by the particles by up to 25%.