Reconditioning crankshafts of car engines by air‐plasma spraying

Abstract

At present, there are a large number of methods available for reconditioning worn crankshafts of car engines in car repair plants. The authors believe that the most efficient methods are those which enable the surface of crankshafts to be built up without melting the base. One of these methods is air-plasma spraying. The use of plasma torches with magnetic arc stabilisation and the application of powder feeders with built-in pneumatic vibrators (Authors cert No. 1799230, USSR) has made it possible to increase greatly the service properties of plasma coatings. The service life of shafts is increased mainly by ensuring a high strength of bonding the coating with a parent metal, which should be uniform over the entire surface of sprayed pins and should equal 30-40 MPa. One of the factors reducing the strength of crankshafts is the stress concentration formed at the fillet and edges of holes in pins of oil channels. This leads to failure of components of the crank of journals in these areas. When reconditioning crankshafts by spraying, it is recommended to displace the fillet into the journal to reduce the stress concentration and prevent damage of the coating in these zones (Fig. 1). In the presence of an unloading groove in the journal, the stresses in the fillet zone are distributed more uniformly. The tests show that the depth of the fillet should be (0.01—0.015) df, but for single-row carburettor engines