Microplasma-sprayed multilayer coatings for electric heating elements

The paper presents new results on the application of microplasma spraying (MPS) for manufacturing electric heating elements (EHEs) consisting of a St3 steel plate (the substrate) with a sprayed electrically insulating Al₂O₃ sublayer (400±50 μm thick) and TiO₂ electric heating tracks (4 mm width; 150±50 μm thickness). Measurements of the temperature of the multilayer coating with a thermal imager enabled determination of the temperature distribution over the surface of the EHE. The electric strength and conductivity tests showed the efficiency of the sprayed EHEs up to a temperature of 200°C. The results of analysis of the causes of material losses during MPS of electric heating tracks (TiO₂) are presented, and the optimal parameters for efficient MPS of coatings in the form of narrow tracks on steel substrates are determined. Using regression analyses, the equation for the influence of MPS parameters on the coating transfer efficiency (CTE) is obtained. Process parameters such as the electric current and the plasma-forming gas flow rate have been found to have the greatest influence on the CTE. In the experiment, a high efficiency of the sprayed material during MPS of electric heating tracks of TiO₂ powder was established (the maximum CTE reached 89%), which indicates the prospects for using MPS technology in the production of EHEs for DC electric heating and for maintaining the temperature of product surfaces up to 200°C.