Designs and variants

SKF composite dry sliding thrust washers (table 1) provide a cost-effective and space-saving solution for axial location. Both, PTFE and POM composite thrust washers are suitable where oscillating and rotational movement can occur. These washers are punched from the composite material and have as standard a hole to take a pin or screw to prevent the washers from rotating on their seat.

PTFE composite thrust washers

SKF PTFE composite thrust washers (fig. 1) are self-lubricating as well as maintenance-free and provide a long service life due to low friction. Despite of their compact design, these washers can accommodate heavy axial loads and are suitable for relatively slow rotational or oscillating movements. They also have good dimensional stability and thermal conductivity.

PTFE composite washers consist of a sheet steel backing on which a 0,2 to 0,4 mm thick porous layer of tin/bronze is sintered (fig. 2). Furthermore, by a rolling process the pores of the sintered layer are filled with a mixture of PTFE (polytetrafluoroethylene) and molybdenum disulphide additives. This additional 5 to 30 μm thick running-in layer provides an optimum combination of the mechanical properties of the sintered tin/bronze and the good sliding and lubricating properties of the PTFE mixture.

Running-in period
During a short running-in period, minute amounts of the PTFE material from the running-in layer are transferred to the counter surfaces. After this transfer has taken place, the characteristics low friction and wear properties of these washers are reached.

POM composite thrust washers

SKF POM composite thrust washers have pockets in the sliding surface (fig. 3), which serve as grease reservoirs and should be filled with grease prior to installation. This makes these washers suitable for applications that require minimal maintenance under difficult operating conditions, for example in contaminated environments where lubricant cannot be supplied continuously or frequently. Despite of their compact design, POM composite washers can accommodate heavy axial loads and are less sensitive to misalignment. They are suitable for slow rotational or oscillating movements.

POM composite bushings consists of a sheet steel backing on which a 0,2 to 0,4 mm thick layer of tin/bronze is sintered. The principal characteristic of these bushings is their relatively thick (0,3 mm) covering layer of acetal resin (POM – polyoxymethylene) with additives. This covering layer has pockets to retain grease and is firmly attached to the sintered tin/bronze layer (fig. 4).
The thickness of the covering layer makes these bushings less sensitive to misalignment and the edge loading associated with that misalignment.

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