Experimental Studies on the Influence of Electrochemical Dimensional Processing on the Surface Fatigue of Rolls in Rolling Machines

Abstract

The state of surface layer in large part determines the performance characteristics of products, especially those operating at high contact loads, and in particular of rolls in rolling machines. As a rule, grinding is the final processing of rolls, but high specific work and high local heating in the cutting area lead to the appearance of a large variety of defects in the surface layer of the machined part. Subsequent electrochemical dimensional processing can significantly reduce their number. This article presents the results of comparative tests for surface fatigue of samples made of alloy steel 9Cr2MoV. The sequence of samples preparation for experimental studies is considered, they underwent a cycle of heat treatment according to a single standard mode, which made it possible to obtain a martensitic structure in the presence of inclusions of small carbides. Then the samples were ground to the height of irregularities Ra = 0.3-0.2 microns. Some of the ground samples were subjected to electrochemical dimensional processing at rational modes, when 0.2 mm thick metal layer was removed per side in the time equal to 0.5 min. The result was practically flaw-free surface with the microroughness height Ra = 0.25-0.18 microns. The sample tests for surface fatigue were carried out on a two-contact roller machine under rolling conditions with relative slip between the sample surface and pressure rollers at the peripheral speed of sample rotation 1.3 times lower than the circumferential speed of pressure roller rotation. The analysis on the contact stress diagram of the samples showed that higher resistance to fatigue fractures is observed in the samples after electrochemical dimensional processing. The number of cycles at which the limit of material contact endurance occurs for these samples is almost twice as large as for the samples after grinding.