The Sliding Frictional Properties of Untreated and Extrusion-Exploded Wheat and Rice Straw

Knowledge about the frictional characteristics of materials is required for equipment design, either to exploit the friction or to overcome it. This paper deals with studying the coefficients of sliding friction of non-treated and extrusion-exploded wheat straw and rice straw on mild steel and aluminum surfaces and the effects of several factors, including the moisture content (at five levels 35, 45, 55, 65, and 75%), normal pressure (at the following five levels: 2, 4, 6, 8, and 10 kPa), and length (at the following five levels: 30, 60, 90, 120, and 150 mm). Through the use of a statistical analysis method, we found that the moisture content, normal pressure, and interactions between them had statistically significant effects on the coefficient of sliding friction ( p < 0.01). The coefficient of sliding friction was much larger than that of rice straw on both contact surfaces, and the coefficient values of both straw samples on the aluminum surface were notably higher than those on mild steel. A significantly higher value was found for the coefficient of sliding friction of extrusion-exploded straw compared with that of untreated straw on both surfaces. As the normal pressure increased from 2 to 10 kPa, the coefficient of sliding friction decreased first, and then increased sharply, finally fluctuating slowly for both kinds of straw and on both tested surfaces, with the maximum value was observed at a normal pressure of 6 kPa. When the length increased from 30 to 150 mm, a slightly linear upward trend was observed for the coefficient of sliding friction of untreated wheat straw, and the coefficient of sliding friction of untreated rice straw initially increased and then decreased.