EXPERIMENTAL INVESTIGATIONS OF GUIDE RINGS MADE OF UHMWPE AND PTFE COMPOSITE IN WATER HYDRAULIC SYSTEMS

In the present work two materials of guiding elements were tested in water hydraulic. The guide elements used for the test station were made of UHMWPE and PTFE filled with 23% of carbon powder and 2% of graphite powder (Kefloy-22). During investigations of hardness conducted for stuffing box packings in water hydraulic systems an analysis of proper selection of piston rod guiding elements has also been carried out phi 45 f7 ( R-a = 0.07/0.20 mu m, R-m = 2.5 mu m). Working piston rod made of chromium-nickel steel AISI 431 (Cr = 16.7%, Ni = 2.08%) has been used for investigations. Some of the guiding elements, after proper selection of the material, could be still used, despite damaged seal. The tests have been performed maintaining water pressure on the sealing at a level of p = 8 +/- 1 MPa and the average velocity of the piston rod of v 0.35 m/s. Water temperature during investigations was regulated within the range of T-min = 291 K and T-max = 305 K. Variable value of friction coefficient has been obtained for the guide rings made of PTFE composite with the change in piston rod velocity and friction force as a function of the velocity of single guide element made of Kefloy-22 after the distance of 15 000, 60 000 and 90 000 m. For the lifetime reaching friction distance of 200 km the guide rings can be used several times. Similar measurement has been performed for guide elements made of UHMWPE. The seals were disassembled during tests from the stuffing boxes. During assessment of the elements made of polyethylene with very high molecular mass ( UHMWPE) it was found that friction force (and the friction coefficient, respectively) after 108 000 cycles (i.e. 108 000 m), decreased only by 30%. It was also found that friction coefficent for UHMWPE mu(UHMWPE) has a continuous value within the range of applied velocity of v = 0.05 to 0.40 m/s. In order to determine friction coefficient mu(UHMWPE) the weight of the piston rod was calculated, whose mass m = 15.5 kg, thus pressing force N = 152 N. At the friction force for single guide element, after the distance of 3500 m, with F pr = 20 N value of ae UHMWPE = 0.26. However after 108 000 m of friction distance the friction coefficient ae UHMWPE = 0.20. It should be highlighted that these coefficients concern dry friction. Kefloy-22 can be successfully used for guide rings in water hydraulic systems. Application of guide rings made of UHMWPE has been estimated negatively. It has been revealed that there was not beneficial to produce the guide elements from this material despite the fact that UHMWPE has the lowest abrasive wear from all polymers. Problem occurred due to wear particles disturbing the work of the cylinder.