Fractal prediction of frictional force against the interior surface of forming channel coupled with temperature in a ring die pellet machine

Abstract

For the biomass ring die pellet machine, the frictional force against the interior surface of the forming channel is the main cause for its frictional wear and also is key to the research of wear mechanism as well as its prediction. In this study, four ring die samples were used to measure and obtain data on their surface morphology. The fractal dimension D and fractal feature G were calculated using the Yardstick method, and lastly a fractal prediction model of sliding frictional force against the interior surface of forming channel was built, which was coupled with a fractal model of temperature distribution over friction surface. Numerical simulation, as well as friction-wear test were conducted to verify the accuracy of the model. The result showed that: when Ar < Arc, the slope of F was larger, which means the frictional force increased more rapidly, and the larger slope of FD represented a rapidly decreasing unit of frictional force. When true contact area Ar = 3.93%, Aa, FT, and FTD increased with the increase in temperature; FT increased rapidly at first and then gradually slowed down. When Ar was small, FTD increased sharply with the increase in temperature.