| Summary: | Bibliography: pages 93-94. === The elastohydrodynamic lubrication of polymeric piston seals in a water powered rockdrill has been modelled in this thesis. Current seal designs, consist of an Ultra High Molecular Weight Polyethylene (UHMWPE) ring, energised to remain in contact with the reciprocating piston, using a nitrile rubber o-ring. The design of the seals is such that they do not facilitate the formation of a lubricating film, and the high contact stresses at the seal face due to the seal pressure cause excessive wear of the seals. The elastohydrodynamic model is based on a numerical algorithm in which the elasticity equations for the seal deflection and the one dimensional lubrication equation have been solved simultaneously. The polymeric ring has been simplified due to its axisymmetry, and modelled in cross section as an elastic beam resting on a spring base, while the deformation of the o-ring has been considered independently since the moduli of the two materials differs by nearly two orders of magnitude. The o-ring was modelled using the non-linear Mooney-Rivlin constitutive equation implemented in the finite element code ABAQUS. With this model, the contact stresses existing between the o-ring and the back of the polymer seal have been determined for a range of o-ring squeezes and rubber hardnesses. The resultant lubrication and o-ring forces acting on the rectangular polymer seal have been used in a finite difference formulation of the seal (or beam on a spring base) to determine the seal deflection above the piston.
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