The Study on Optimum Thickness of Thermocouple Used for Measuring the Grinding Temperatures of Brittle Materials

The grinding temperatures were measured with half-cylindrical thermocouple which made by grinding method and measrued with foil thermocouple which made by rolling method respectively when grinding brittle granite with an Al2O3 wheel. Experimental results include average grinding zone temperatures and grains’ temperatures were analysed. The deviation of average grinding zone temperatures measured by them were within 6%. The foil thermocouples do not easily to lap due to the brittleness of the workpiece which usually makes the joint of thermocouples disconnected. But half-cylindrical thermocouples are more convenient to be prepared and be used than foil ones. However, the periodic “flash” impulses which reflect the grains’ temperature measured by half-cylindrical thermocouple were about 51% lower than the others. According to time constant, the thickness of the thermocouple less than 0.007mm is a necessary condition for measure the grains’ temperatures without distortion. The half-cylindrical thermocouple is too thick to have a momentary response time thus makes it out of the measurement accuracy range when it is used to measure the temperature of the grains. Therefore, foil thermocouple has an optimum thickness of 0.007mm is suitable for measuring the grains’ temperature while half-cylindrical thermocouple with average thickness less than 0.12mm is suitable for measuring the average grinding zone temperature.