BEHAVIOR OF LUBRICATION LAYERS OF PLATENS IN ELEMENT TESTS

Abstract

The results of a series of direct shear tests on lubrication layers and other related tests performed to get a better insight into the methods of lubrication between the sand samples and the platens are described. The lubrication layers used consist of grease and latex disc. To get a good quality of lubrication, it is first needed that the grease has an enough resistance against squeezing out when compressed. The inclusion of fine solid fillers in the grease increases this resistance, while as a result lubrication when not squeezed out becomes less effective with the increase in the amount of fillers as well. The quality of lubrication depends on the following factors at least; (1) the quality of grease (the viscosity of the base silicone oil and the amount of fine solid fillers included in the grease), (2) the normal stress, (3) the composition concerning latex disc and silicone grease. For the lubrication at low normal stresses, the following composition may be recommended; (1) the grease should be composed of low viscosity silicone oil and an appropriate amount of fillers, and (2) a smooth surface should be facing the grease layer. For the lubrication at high normal stresses the following composition may be recommended; (1) the grease should be composed of high viscosity silicone oil and an appropriate amount of fine fillers, and (2) a composition with which stress concentrations in the grease layer are reduced. By using an appropriate method of lubrication the apparent angle of friction for a lubrication layer placed between a fine angular sand mass and a steel platen can be much smaller than 1 degree for normal stresses of 150∼670 kN/m² at least.