EXPERIMENTAL TESTING OF PLUNGER RECOVERY MODES BY COMBINED PROCESSING

Abstract

Stainless steel parts are widely used in milk processing equipment. The condition of these elements determines the operability of the equipment and the quality of the product. The most susceptible to wear are parts of the plunger type, the failure of which is by the loss of the cylindricity when changing geometric dimensions in longitudinal and cross sections. (Research purpose) The research purpose is developing a method for restoring cylindrical parts of the plunger type during combined processing; reducing the complexity of the restoration process and increasing the durability of the plunger (Materials and methods) Samples of 40Kh13 steel imitating the shape of a plunger with a diameter of 45 millimeters were studied. Three samples were produced with different pre-treatment: shot blasting, finishing turning and manual grinding. The study was as follow: initial measurement of the diameter in four sections at three levels; electric spark buildup, electromechanical processing and grinding before the preparing the working surface; measuring geometric parameters before and after each treatment; making slits for microstructural analysis, and measuring microhardness. (Results and discussion) As a result of the experiment and sample processing, there achieved an increase in diameter by 1.10 ± 0.08 millimeters when applying from 15 to 20 layers by the electric spark method with an electrode of the brand 308L-16. After deformation during electromechanical processing, the layer ranged from 0.36 ± 0.03 to 0.47± 0.07 millimeters, during grinding, the thickness of the final layer was from 0.04 ± 0.02 to 0.26± 0.02 millimeters. Measurements of the microhardness of the structural zones showed that the microhardness of the residual layer is 250-400 Vickers, the transition zone has a compacted structure and a hardness of over 550, and the core is 200-250. (Conclusions) Based on these data, the article proposes recommendations for the building of a compensation layer to restore the cylindrical working surface of the plunger type part.