A Powder Fed Plasma Transferred Arc Process for Hard Facing Internal Combustion Engine Valve Seats

A powder fed, microprocessor controlled plasma transferred arc (PTA) hard facing technique is described for facing valve seats. A comparison of this technique is made with the conventional oxy-acetylene flame welding process to show the differences in the metallurgical characteristics of the respective products. The merits of the PTA process are associated with a) its precision controllable heat source and lower energy consumption b) finer microstructure and narrower heat affected zone, c) its versatility for powders of different raw materials, d) higher volume production capability, and e) minimum raw material waste; however, it does not replace the flame welding process completely. The relative choice between the two processes will depend on investment costs, volume of production and metallurgical quality requirements of the final product. The present trend of increasing costs and shortages of strategic hard facing materials and needs for more hard faced valves for future engines make the PTA technique attractive for new demands in the automotive industry.