Nondestructive acoustic monitoring of the quality of sulfur-steeped superfinishing bars

Abstract

Steeping in sulfur is a common method of improving the performance of abrasive superfinishing tools made of silicon-carbide and electrocorundum micropowder with ceramic binder. The use of sulfursteeped abrasive tools reduces the grinding temperature and power, extends scorch-free operation, and improves surface quality on account of the reduced heat stress [1, 2]. Very strict requirements are imposed on the surface quality after superfinishing. Therefore, to obtain the required surface roughness, the quality and stability of the abrasive tool must be improved. Operational experience with steeped abrasive tools (bars) in superfinishing shows that their properties are not always stable. Often, the operating conditions must be corrected on switching to bars from a different batch, although they are made at the same enterprise, to the same specifications. This is probably due to excess pore filling in the tool, which impairs the removal of wear products from the cutting zone, with consequent soiling, and also to nonuniform steeping, with the formation of unsteeped regions that disrupt the operational rhythm [2]. Therefore, stable superfinishing calls for the development of more comprehensive requirements on the bars and for additional monitoring after steeping. Given the lack of equipment for nondestructive monitoring, firms generally rely on visual verification of the completeness and uniformity of steeping, with external inspection of the fracture surface on specially broken bars. The technological regulations do not provide standard methods for quality monitoring and estimation of the degree of sulfur steeping of the bars. In the present work, we consider the factors that influence the properties of steeped superfinishing bars, identify the most significant characteristics of the bars, and propose an optimal method for nondestructive acoustic monitoring. The hardness is generally considered in selecting abrasive tools for specific grinding operations. We define the hardness as the tool’s ability to resist disruption of the adhesion between abrasive grains and the binder. The hardness scale for abrasive tools makes allowance for the ratio of the quantity of abrasive and binder and also for the physicomechanical properties of the abrasive and binder and the characteristics of their contact zone [3]. The ratio of the components responsible for the adhesion between the abrasive grains—in other words, the hardness—is selected in the manufacture of abrasive tools on the basis of specialists' requirements regarding abrasive treatment. The hardness and related characteristics are presented in the relevant standards [3‐6].