DYNAMIC AND STATIC WALL FRICTIONS FOR BULK SOLIDS

Wall friction is a critical material characterization parameter to understand when designing mass flow bulk solids storage and handling equipment such as silos/bins and hoppers. There are two wall friction coefficients, namely kinematic (dynamic) and static, to consider, each of which can be measured using standardized test methods. While kinematic wall friction is commonly of more interest for design purposes, static friction is also required for certain applications, such as after material has been held at rest (i.e., not flowing) in storage. This study compares the results of both dynamic and static friction measurements for three bulk solids materials on various wall liners. The results showed that the static wall friction coefficient measured was not consistently higher than the dynamic coefficient as expected. Reasons for this difference are outlined, and the dependence on the material and wall