Experimental assessment of polymer slippers for oil-hydraulic axial piston machines, based on efficiency, film-thickness, contact-temperature, geometry and wear

The slipper–swashplate contact is a performance-, lifetime-, and efficiency-critical interface in hydraulic pumps, that is typically made from toxic leaded non-ferrous metal alloys that promote oil ageing and corrosion. This work is the first to experimentally compare carbon-fiber-reinforced PEEK as an alternative for highly loaded oil-hydraulic slippers. For this, friction, leakage, efficiency, contact temperature and pressure, film thickness, micro-motion, geometry, and wear are evaluated using new methods for direct friction-force, film-thickness, slipper-spin, and contact-temperature measurement. It is shown that for identical geometry, polymer slippers achieve efficiencies comparable to non-ferrous metal slippers at both 40 °C and 60 °C. Under full load and 60 °C oil temperature, the slipper contact temperature remains about 85 °C, well below the glass-transition temperature. SEM/ EDX analyses reveal that the polymer forms a stable transfer film, yielding non-critical wear coefficients on the order of 10 − 10 mm 3 /Nm. However, spatially resolved wear, contact-pressure, and geometry-dependent leakage measurements show that direct geometry transfer is not feasible. The high polymer deformation results in an unfavorable contact pattern that blocks slipper spin and increases film thickness, leakage, and local wear. As countermeasures, the load-carrying pattern, hydrostatic balance ratio, and sealing land width are discussed.