8 - Application of Fluids

Abstract

Most grinding is conducted either with water-based oil-in-water emulsion or with a neat mineral oil or neat synthetic oil using a low-pressure delivery system. The functions of a grinding fluid are introduced and typical systems for grinding fluid delivery are described. Grinding fluids provide bulk cooling and also process cooling. Effective fluid delivery is therefore important for reducing the risk of thermal damage. A grinding fluid is also important for reducing wheel wear and for improving grinding process efficiency. Another function is flushing swarf from the grinding area and maintaining low surface roughness. Oil and water-based emulsions are described and compared for their different behavioural properties. Alternative methods employed for fluid delivery include flood delivery, high-pressure jet delivery, low-pressure shoe delivery, mixed phase delivery, minimum quantity lubrication, mist delivery, cryogenic fluid delivery and ice–air blasting. The nature of the air barrier surrounding a grinding wheel is explored and the effects of fluid velocity and rate of flow are studied. Air scrapers are shown to assist fluid delivery by interrupting the air barrier. Useful flow is defined as a flow that actually enters the grinding contact as opposed to fluid simply delivered from a nozzle. Measurements and calculations are given to assist optimization of nozzle positions and pumping requirements. Alternative nozzle and jet types are described including the application of auxiliary nozzles. Nozzle calculations are provided together with numerical examples. Grinding fluid provides a substantial drag on the grinding spindle in high-speed grinding. Spindle power drag and grinding fluid delivery power are calculated with examples. Models of grinding fluid heat convection are given together with experimental results. References are given to previous work.