Assessment of spray quality from an external mix nozzle and its impact on SQL grinding performance

• Characteristics of spray from an external mix SQL grinding nozzle are numerically modelled and experimentally validated.
• Significance of the droplet diameter and surface heat transfer coefficient influenced by atomising air pressure.
• Total wetting area by spray droplets is estimated and found to remarkably increase with both air pressure and fluid flow rate.
• SQL grinding performance is experimentally investigated at different air pressures and fluid flow rates.
• Results are correlated with the modelled characteristics of spray.

Spray quality is the critical factor which decides the efficacy of Small Quantity Lubrication (SQL) technology in a high specific energy involved machining process like grinding. Yet, the understanding about spray quality, the actual process mechanics and its effect on machining performance is inadequate. The present work is an attempt to establish a correlation between the spray input variables, quality of the spray and machining performance of SQL grinding through modelling and experiments. Using computational fluid dynamic techniques, the variation of droplet size, droplet velocity, number of droplets and heat transfer coefficient have been analysed at different input parameters and the computed trends have been verified and validated. CFD modelling of spray indicates that it is possible to produce aerosol medium with high heat dissipation ability at moderately high air pressure and low flow rate. It also shows that any increase in atomising air pressure favourably leads to notable increase in wetting area and also results in substantial enhancement in heat dissipation ability. Reduction of residual stress is thus remarkably good. On the other hand, grinding fluid flow rate, if increased, offers significantly better lubricity and reduces the grinding force which also reduces tensile residual stress. Short spell grinding test results are found to be in good agreement with CFD results.