THE INFLUENCE OF THE MANUFACTURING PROCES S ON CREEP AND WEAR PROPERTIES OF UHMWPE

The creep and wear behaviour of pressed UHMWPE and extruded UHMWPE was compared, taking Chirulen(R) and extruded UHMWPE of the Lennite(R) ty pe as examples. Using the ring-on-disc test, the wear and deformation volumes per 360 000 cycles were determined. The static tests were perf ormed at surface pressures of 5,62 MPa and 9,37 MPa, while the test du ration was 41.86 and 100 hours, respectively. The surface pressures re sult from the axial forces of 900 N and 1500 N, respectively, and a ri ng surface analogous to the DIN 58 835 and ISO 6474 standards. Between conventionally pressed and the extruded UHMWPE material differences o f up to 350 % in the sums of wear and deformation were found. It was n oted that already at low surface pressures the extruded UHMWPE is more susceptible to creep deformation than is the conventionally pressed m aterial, and that this effect dramatically increases at high surface p ressures.