Effects of Surface Roughness on Friction Coefficient of Plate Bricks (Part 2): Sliding Characteristics at Elevated Temperature

摘要

Slide gate valve within a continuous casting system controls molten steel flow rate by varying the gate size with shifting its overlapped nozzle plate bricks. The nozzle plate bricks with solid lubricant are operated under higher contact pressure and higher temperature. The anti-friction performance of the graphite in the solid lubricant varies with elevated temperature. This might change the effects of surface roughness on the friction coefficient. Therefore, we performed some experiments with the ground or sand blasted alumina-carbon plate bricks with different surface roughnesses under the conditions of 600 K and 800 K of the upper plate brick temperature. The results indicate that the rougher ground plate bricks are operated with the lowest friction coefficient through the test under the elevated temperature, because the solid lubricant trapped at grinding grooves on the rough ground surface were effectively supplied to the contacting surfaces. On the other hand, the friction coefficients of the sand blasted bricks increased by heating the surfaces. The surface can not be supplied enough solid lubricant on account of the volume decrease of the lubricant at concave carbon matrix for their oxidation. Consequently, the hard alumina grits on the surface frequently plough their surfaces and increase the friction coefficient.