LASER REBUILDING OF ENGINE EXHAUST VALVES

The study presents the results of tests concerning laser rebuilding of worn exhaust valve faces of combustion engines. Materials that are used for pad welding were reviewed and analyzed from the angle of their usability for pad welding of valve faces. The material that was selected was a powdered cobalt alloy (stellite). Subsequently, there was conducted a selection of the pad welding process parameters, taking into account, among other things, the heat capacity of valves being rebuilt. Rebuilding of worn out valves was realized and the properties of obtained layers were subject to evaluation. It was found, among other things, that it was necessary to make machining undercuts at the point of the valve face in order to locate the pad welded stellite layer properly. In the case of valves made of H9S2 steel, it was found that it was necessary to preheat the valves so as to eliminate cracks in the layer being pad welded. Microscopic analyses of the structures of layers rebuilt with the use of stellite as well as microhardness tests confirmed the possibility of the application of laser pad welding in order to rebuild worn out valve faces.