Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2001-05-09
2002-10-15
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S297000, C384S298000
Reexamination Certificate
active
06464396
ABSTRACT:
BACKGROUND
The invention relates to a rolled-up plain bearing bush made of a metal/plastic composite plain bearing material with a wall thickness of at least 0.75 mm, which can be pressed into a bearing opening to create a force fit, with a metallic backing and a sliding surface.
Such bearing bushes are known, for example, from GB 15 92 341 and have been marketed for a long time by the Applicant under the trade name PERMAGLIDE P10. These bearing bushes have a steel backing and a bronze layer sintered porously to it. A mixture consisting of 80 percent PTFE by volume and 20 percent lead by volume is introduced into the porously sintered bronze layer to form the sliding layer, where this sliding layer is thicker than the porous bronze layer and thereby coats it completely.
Rolled bearing bushes produced in this way, the composition of whose sliding layer has been developed in different ways, admirably fulfil the requirements for tribological properties in a plain bearing.
However, it has been shown, particularly in motor vehicle applications and as part of the ongoing efforts to reduce weight in this area, that the weight of a large number of plain bearing bushes has a cumulative negative effect. A further disadvantage of known bushes can be seen in the fact that especially in winter operation, when the motor vehicle is exposed to corrosive media, such as road salt, the steel backing of the plain bearings corrodes.
A generic bearing bush is known from JP-A-61-13025. This bush comprises a steel backing, a thin perforated plate which is completely coated with a binder or adhesive material, which can also contain PFA. A plastic sliding material with fillers is impregnated onto the perforated plate and into the apertures of the perforated plate. The adhesion of the plastic sliding material to the perforated metal is problematic, which is why the binder or adhesive material has to be used. This is expensive.
SUMMARY
The object of the present invention is to avoid the disadvantages described previously, specifically high weight, corrosion and poor adhesion of the plastic sliding material.
This object is achieved by the plain bearing bush described at the beginning, in which the metal backing consists of aluminum alloy and the sliding layer consists of a section of stretched mesh strip made of aluminum alloy and a mixture consisting of a plastic sliding material and necessary fillers to improve thermal conductivity and tribological properties which is introduced on the section of stretched mesh strip and into the apertures of the stretched mesh strip, and wherein the sliding layer and the backing are bonded together by means of an additional layer of PFA located between the sliding layer and the backing.
The plain bearing bush possesses sufficient wall thickness that it can be pressed into a bearing opening to form a force fit and in operation it is seated in the bearing opening such that it cannot shift and/or rotate. The plain bearing bush according to the invention is distinguished by unusually low weight. As a result of the metallic backing being formed from aluminum alloy, preferably high strength, salt-water resistant aluminum alloy, preferably from wrought aluminum alloy, there are no more problems with respect to corrosion of the backing.
Starting with the known steel/plastic composite plain bearing material named at the beginning, it would not have been possible to replace the steel backing layer with an aluminum backing, because aluminum would become fluid at the sintering temperatures for the porous bronze layer.
As a result of the sliding layer comprising a section of an aluminum stretched mesh strip with undercuts in the direction of material thickness, the mixture of plastic sliding material and fillers adheres extremely well, without the need for an adhesion promoter. There are no signs of separation.
A foil-like plain bearing material was already known from EP 0 193 214, consisting of an stretched mesh strip which was coated with a mixture of plastic sliding material and fillers. However, this foil-like plain bearing material was suitable only for manufacturing bushes for relatively low loads and with a thickness of 0.5 mm and less.
The Norton-Pampus Company has already proposed applying a PTFE film to a steel backing. But this does not meet the object underlying the present invention.
With the present invention it was recognized that as the result of the combination of a backing consisting of an aluminum alloy and a sliding layer of the described composition, which are bonded to each other by means of a layer of PFA between them, a plain bearing bush can be produced suitable for creating a force fit, which is also noteworthy for its extremely lightweight and, with regard to evidence of corrosion, proves to be far less problematic than steel/plastic composite bearing materials.
In a preferred embodiment, the plastic-based mixture contains 30 to 90 percent by volume, preferably 40 to 80 percent by volume, PTFE as the plastic sliding material. In addition to PTFE, additional plastic components, such as for example, PFA, PVDF, etc., can be provided. The mixture can additionally contain from 10 to 60 percent by volume of a filler. It has proven to be particularly advantageous if the mixture contains 10 to 30 percent by volume of a metallic filler, preferably in the form of lead. Ten to 30 percent by volume of the mixture can also be made up of a fibrous filler.
The low mass per unit area of the metal/plastic composite plain bearing material forming the bush proves to be especially advantageous, being between 0.19 and 0.77 g/cm
2
at a wall thickness of 0.75 mm to 3.0 mm. It must be pointed out that a metal/plastic plain bearing material, as it was described previously, is regarded independently as such as the basis of the invention.
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Encyclopedia der technischen Chemie, 4. Aufl., Bd. 20 (1981) Verlag Chemie GmbH, Weinheim, Seite 536.
Becker Karl
Schubert Werner
Footland Lenard A.
KS Gleitlager GmbH
Young & Basile PC
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