Load-dependent behavior in PTFE-glass slideways

Hysteretic behavior in the direction of sliding is investigated for kinematically constrained slideways, using a special system produced to study the limits of performance of thin-film polymer on glass bearings. A typical configuration for a superprecision instrument slideway using PTFE pads and a Zerodur counterface is shown to exhibit around 200-nm sliding hysteresis. Moreover, this value is strongly dependent on the total load on the bearing system. The pattern of dependence is consistent with an established model of contact under oblique forces, although the materials conditions at the interface are much more complex than those assumed in that model. Full isolation of these properties is not possible with the present experiments, but they indicate that die shear modulus of the interface layer is more than ten times greater than that of bulk polymer. (C) Elsevier Science Inc., 1997.