A model and its experiment using compressed cold air to clean the active surface of a grinding wheel during sharping of a hob cutter

The removal of chips, which is produced during the grinding process and forms, among other things, cloggings on the grinding wheel active surface (GWAS), is key to extending wheel life and achieving low surface roughness. Currently, as a result of the minimum quantity lubrication (MQL) method of delivery coolant into the cutting zone, the support of chips removal with a stream of cooled compressed air (CCA) is becoming particularly important. Among other things, the angle of the CCA jet delivery nozzle with respect to the GWAS is responsible for the removal efficiency, which has to be considered individually for each grinding process variation, and experimental tests alone do not give an idea of the CCA jet flow. In the present study, a numerical flow analysis (using the computational fluid dynamics method) of cooled compressed air in the grinding zone during the sharpening of a hob cutter face was carried out. The results of the numerical simulations were verified experimentally by determining the percentage of the grinding wheel clogging Z%. The experimental results confirmed the conclusions from the numerical analysis regarding the most favorable angle of the CCA nozzle. The Z% = 5.3 clogging index obtained when grinding with the CCA nozzle set at an angle of 45° is 2.5 times lower than the Z% = 13.5 index determined for the most favorable setting of the MQL nozzle. Simultaneous delivery of CCA and air-oil aerosol using the MQL-CCA method resulted in the lowest Z% = 2.5, comparable to the Z% = 2.0 obtained for a grinding wheel operating under cooling conditions with a water-based oil emulsion delivered by the flood method (WET).