Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
1999-09-14
2001-06-05
Fooftland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S132000, C384S322000, C384S462000, C384S477000, C384S478000
Reexamination Certificate
active
06241393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to greased mechanical components. More specifically, the invention relates to greased mechanical components which provide, by sliding friction, a translational or rotational guiding function, in continuous or reciprocating motion, and are designed to meet effectively the concerns of many industrial sectors with regard to simplifying lubrication and reducing the frequency of maintenance.
2. Description of the prior art
Grease-lubricated devices exist in which, by virtue of suitable sealing means, it is possible to make two mechanical parts rub against each other, even when they are subjected to very high loading stresses, with a very low coefficient of friction: examples of such devices are given in the article “Theory and industrial practice of friction” by J J. CAUBET, published by Dunod Technip, 1964, Chapter 13.
FR 910,999 of Oct. 2, 1962, and its patent of Addition FR 921,708 of Jan. 17, 1963, describe an embodiment of such a device in the case of self-aligning bearings for high loads.
Such devices, the technical effectiveness of which is recognized, do have, however, a major drawback associated with the complexity of their practical construction, which leads to high implementation costs incompatible with the current requirements of most of the industrial sectors in question.
One object of the present invention is therefore to provide a guiding device for mechanical members which makes it possible to dispense with the use of a sealing system.
Another object of the invention is to propose a device of the above kind which is effective and inexpensive in the field in question.
Further objects and advantages of the invention will appear on reading the description below.
SUMMARY OF THE INVENTION
The invention proposes a device for guiding mechanical members which consists of two parts intended to interact by sliding friction, one of the two parts, called the smooth part, having a smooth, functional, i.e. friction, surface and the other part, called the pierced part, having at least one functional, i.e. friction, surface, including emergent cavities intended to accommodate a grease of the lubricating-paste type and especially an EP grease (extreme-pressure grease) comprising a soap-type constituent, an oil-type constituent and an extreme-pressure additive, wherein the contact angle between said functional surface of said smooth part and said grease, measured at a temperature called the measurement temperature, which is 15°±5° C. below the temperature at which the onset of separation between said soap-type constituent and said oil-type constituent occurs and/or the onset of evaporation of said oil-type constituent occurs, is in the range from 20 degrees to 40 degrees and the material of said pierced part is such that the contact angle, measured at said measurement temperature, between said functional surface of the pierced part and said grease is in the range from 45 degrees to 75 degrees.
The term “EP grease”, denoting an extreme-pressure grease, is well known to those skilled in the art. The expression “extreme-pressure grease” should be understood to mean a grease capable of withstanding a high load without damage. Examples of such greases are lithium greases of the SNR-LUB EP Class NLGI 2 type, or those of the KLUBER CENTOPLEX GLP 402 NLGI 2 type, or lithium greases and solid lubricants of the KLUBER COSTRAC GL 1501 MG NLGI 2 type.
It should be noted that both the smooth part and the pierced part may each have a non-functional surface, but this is not obligatory.
The two parts—the smooth part and the pierced part—are intended to interact by sliding friction, translationally or rotationally, in continuous or reciprocating motion.
The shape of each of the two parts may be plane, cylindrical or spherical.
Although it is commonly employed by those skilled in the art, the concept of the contact angle of a drop of a liquid or viscous product placed on a solid surface is not the subject of standardization, nor even of a completely standardized method of measurement, most particularly when said product is a grease.
The experimental conditions under which the contact angle is measured are therefore given below.
Measurement of the contact angle according to the invention:
Firstly, the surface of the solid body on which it is desired to perform the measurement is cleaned and then a straight bead of grease is deposited thereon. Next, the part is heated until the temperature of its face in contact with the bead of grease reaches a value of 20±5° C. greater than the limit use temperature of the grease. It is maintained at this temperature for the time needed for the grease to become sufficiently liquid to start to spread out over the surface (approximately 90 seconds). Heating of the part is then stopped and it is left to cool. This has the effect of freezing the shape of the drop and allows measurement of its contact angle at room temperature.
Suitable materials for forming the smooth part according to the invention are chosen from steels, for example case-hardened, quench-hardened and ground steels, ground HF quench-hardened steels, steels that are hardened and then coated with hard chromium, nitrided steels and carbonitrided steels, chromium and nickel, as well as from among ceramic-coated steels.
It is necessary each time to measure the contact angle between the grease and the material that is to form the smooth part, which angle must be in the range from 20 degrees to 40 degrees, in order to determine whether this material is really appropriate according to the invention.
The material of which the pierced part is made may be a bulk material. This will usually be chosen from among polymer materials and copolymer materials. However, other materials could be suitable as long as their contact angle with the grease satisfies the specified conditions.
Suitable materials for making the pierced part according to the invention are chosen from polyimides, filled polyimides, for example graphite-filled polyimides, epoxy resins, filled epoxy resins, such as epoxy resins filled with molybdenum disulphide MoS
2
, polyacetal resins, polyethylene, substituted or unsubstituted fluorocarbons, and especially PFA (perfluoroalkoxy), polyethylene terephthalate, polyethersulphone, polyamides and polyetheretherketone.
It is also necessary each time to measure the contact angle between the grease and the material that is to form the pierced part, which angle must be in the range from 45 degrees to 75 degrees, in order to determine whether this material is really appropriate according to the invention.
The material of which the pierced part is made may also be a substrate covered with a coating. The coating is usually deposited as a thin film, generally having a thickness of approximately 5 &mgr;m to approximately 50 &mgr;m.
In this case, the substrate is any material, in bulk form or in the form of a thin rolled sheet, for example plain carbon steel, alloy steel, stainless steel, aluminum alloy, copper alloy, titanium alloy, etc.
The thin rolled sheet is advantageously produced in accordance with patent FR-B-2,693,520.
When the material of which the pierced part is made is a substrate covered with a coating, it is advantageously a steel which is prenitrided and then covered with a polymer.
The material of which the coating is made is then chosen from polymer materials and copolymer materials, especially from polyimides, filled polyimides, for example graphite-filled polyimides, epoxy resins, filled epoxy resins, such as epoxy resins filled with molybdenum disulphide MoS
2
, polyacetal resins, polyethylene, substituted or unsubstituted fluorocarbons, and especially PFA (perfluoroalkoxy), fluoroethylene or fluoropropylene, polyethylene terephthalate, polyethersulphone, polyamides and polyetheretherketone.
When the material of which the pierced part is made is a substrate covered with a coating, it is advantageously a steel that has been subjected beforehand to a surface hardening treatment. This surface hardening
Georges Etienne
Tourneux Daniel
Centre Stenhanois de Recherches Mecaniques Hydromechanique et Fr
Fooftland Lenard A.
Morgan & Finnegan , LLP
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