Bearings – Rotary bearing – Plain bearing
Patent
1995-12-08
1999-06-15
Jeffery, John A.
Bearings
Rotary bearing
Plain bearing
384279, 384902, 384911, 384908, F16C 3302, F16C 3318
Patent
active
059115149
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is concerned with plain bearings, in particular, oil lubricated bearings which require low friction, particularly static (break-away) friction.
Polytetrafluoroethylene (hereinafter referred to as "PTFE") has good tribological properties and is, therefore, often used as the lining material for a plain bearing. PTFE is, however, soft and weak and has an unacceptably high wear rate when used alone. Therefore, harder materials must be added to the PTFE lining to reduce wear and give an acceptable bearing life.
2. Description of the Related Art
Bearings are known which comprise a steel backing having a porous bronze sintered layer thereon and a lining layer infiltrated into pores of the sintered layer and standing proud of the sintered layer to provide a low-friction surface of the bearing. Such bearing layers comprise PTFE filled with either lead or molybdenum disulphide. However, these conventional materials tend to suffer from erosion effects when used under severe conditions in an oil-lubricated bearing. This is caused by cavitation brought about by the lubricating oil and results in the removal of the filled PTFE from the sinter by the action of the lubricating oil alone, without rubbing wear.
GB Patent Specification No 2,166,142B describes a bearing of this type in which an ionic fluoride, for example calcium fluoride, is included in the lining layer. This lining material shows enhanced cavitation erosion resistance while retaining desirable low friction properties. It is, however, desirable to provide a bearing of this type having even better erosion resistance properties.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1 and 2 show steps in the production of a bearing according to the invention. More specifically, FIG. 1 shows mush 13 in position on a sintered layer 14 which in turn is on a backing 12. FIG. 2 shows the same configuration as FIG. 1 but with paper 15 in position instead of mush 13.
FIG. 3 shows a bearing 10 after the mush or paper has been compressed into the pores 18 of the sintered layer 14 to form the lining 16.
FIG. 4 is an enlargement of the circle 4 in FIG. 3 and shows the pores 18, fibers 20 and filler 22.
DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENT
The invention provides a plain bearing 10, as shown in FIG. 1 comprising a metal backing, a sintered layer 12 on said metal backing 11, and a lining layer 13 infiltrated into pores of the sintered layer 12 but standing proud of the sintered layer 12 to provide a low-friction surface of the bearing 10, characterised in that said lining layer 13 comprises polytetrafluoroethylene including 2 to 10% by volume of fibrillated aramid fibres.
A plain bearing according to the invention exhibits higher cavitation erosion resistance than the above-mentioned known materials.
It is, of course, a well-known technique for reinforcing plastics materials to incorporate fibres therein. However, reinforcement of PTFE in plain bearings by this means has not been successfully utilised. This is because the common fibres which can stand the temperatures and pressures involved, such as glass, do not adhere to the PTFE so that there is no benefit from the incorporation of such fibres. Indeed, non-fibrillated aramid fibres do not provide any benefit. The invention is, however, based on the discovery that fibrillated aramid fibres do give an enhanced cavitation erosion resistance. It is summised that the fibrils embed themselves in the PTFE matrix and are difficult to pull out due to entanglements and the high aspect ratios thereof.
Preferably, the lining layer also contains a filler which may be present in up to 28% by volume. The filler may be, for example, calcium fluoride or polyphenyl sulphide. Preferably, the total of the filler and the fibres approximates to 20% by volume.
Alternatively, the filler may be a polymeric material selected from:
In order to improve the adhesion of the fibres, the lining layer may also include a further polymeric material which wets the fibres and is distribut
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Davies Glyndwr John
Johnston Janette
Moisey Philip
Jeffery John A.
Kaness Matthew A.
T&N Technology Limited
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