Effects of surface roughness on friction coefficient of plate bricks (Part 1) - Sliding characteristics at room temperature

Slide gate valve within a continuous casting system is composed of a couple of nozzle plate bricks, and controls molten steel flow rate. The slide gate valve adjusts flow rate by varying the gate size with shifting the overlapped nozzle plate bricks. Steady and efficient operation of the slide gate valve deeply depends upon the endurance strength and the sliding performance of nozzle plate brick surfaces. Therefore, we performed some experiments to elucidate the effects of surface roughness on frictional force with using the ground or sand blasted alumina-carbon bricks with different surface finishing roughness at room temperature. The results indicate that the case of sand blasted plate bricks could be operated under less frictional force conditions than the case of ground plate bricks, and this means that it would be possible to prolong the lives of slide gate valves by finishing the nozzle plate brick surfaces in the optimum surface roughness. Under the condition of optimum surface roughness, the plate brick surface mainly contacts at the convex portions of alumina grits, but these contacting spots were lubricated well by the solid lubricant trapped at concave carbon-matrix pits on their surfaces.