V - The magazine of the VOLLMER Group - 2019

100° C 200° C 300° C 400° C 500° C 600° C 1 HOTSPOT AND COOLING Grinding creates lots of heat. Especially in the hotspot, where the grinding wheel engages, temperatures can measure around 1000 °C (Image 1) . The consequences can include damage to the workpiece from grinding burns, extreme variation in size and changes to the grinding wheel geometry. Cooling lubricants are required to avoid this. Oils or emulsions are injected using nozzles (Image 2) and reach the hotspot via the grinding wheel's pores. There, they absorb the heat and remove it, together with chips and grinding dust. For the most effective operation possible, two things in particular need to be optimised: The coolant speed and the contact angle. OPTIMUM COOLANT SPEED As the cooling lubricant is transported to the hotspot, it has to have approximately the same speed as the grinding wheel, i.e. 80 to 110% of the cutting speed. An example: If a grinding wheel is running at 50 m/s, the coolant has to achieve 40–55 m/s. The coolant speed is regulated by the pressure at the nozzle outlet. The Bernie equation is used to calculate the required pressure: For oil: For water-based coolant: Required pressure in bar = 1 HOTSPOT A hot topic in the grinding world. We call the area with the highest temperatures the “hotspot”. 2 COOLING LUBRICANT is injected through nozzles. This lowers the temperature and also has a cleaning effect and reduces corrosion. 2 (speed in m/s ) 2 220 (speed in m/s ) 2 200 Required pressure in bar = 20 FEED