RELAXATION OF RESIDUAL STRESSES DURING COOLING OF A WORKPIECE WITH A COATING APPLIED BY CENTRIFUGAL INDUCTION SURFACING METHOD

As a result of a theoretical analysis of the cooling process of parts with deposited coatings applied by the method of centrifugal induction surfacing, the patterns of formation of residual stresses are established, taking into account relaxation. It is shown that a decrease in the cooling rate after surfacing makes it possible to reduce the level of residual stresses due to the relaxation phenomenon. Calculation relations are derived that allow predicting the permissible value of residual stresses depending on the required adhesive strength. As the analysis of the ratios obtained shows, the reduction of residual stresses in the resulting coatings due to their relaxation can be achieved by reducing the cooling rate or, accordingly, increasing its time. In the technological process of induction surfacing, a two-stage cooling mode of the workpiece was used; at the first stage, cooling is carried out at the maximum possible rate. If the temperature stresses reach the maximum allowable value τmax, the pairing condition for the transition from the previous cooling stage to the next one is the equality τmax = τi, where τi is determined from the equations derived in the work. In this case, one should be guided by the observance of the condition τi < τc, where τc is the theoretical adhesive strength of coatings in the absence of residual stresses. An example of the practical use of the twostage cooling after the process of applying coatings by centrifugal induction surfacing on the bushings of tamping blocks of a STS track machine is given.