FR2920434A1 - Solid lubricant composition for roller bearing, comprises a mixture of a thermoplastic polymer powder and oil, where the mixture includes grease - Google Patents

Abstract

Solid lubricant composition for roller bearing, comprises a mixture of a thermoplastic polymer powder and oil, where the mixture includes grease. An independent claim is included for roller bearing comprising a fixed body and a rotating body forming a rolling space between them, in which rolling bodies are arranged to allow relative rotation of the body, where the: rolling space includes solid lubricant formed after heating the solid lubricant composition; and lubricant is in contact with the roller body, and at least on a part of their periphery.

Description

1

The invention relates to a solid lubricant composition for the bearing space of a bearing, and to such a bearing whose running space comprises a solid lubricant formed after heating such a composition.

In some applications, for lubricating the bearing space of the bearings, it is known to use a solid lubricant conventionally produced by disposing and then heating a composition comprising a mixture of a thermoplastic polymer powder and an oil.

Indeed, the oil required for lubrication is then trapped in the polymer matrix. In addition, during the operation of the bearing, the oil is supplied by bleeding as close as possible to the rolling contacts, and this by limiting the risk of ejection of the oil outside the running space.

Depending on the application envisaged, there are a large number of compositions which differ in the type of oil used and / or in the nature of the polymer and / or in the mass ratio between the oil and the polymer.

In a conventional manner, the composition is produced by mixing at room temperature the polymer powder and the oil in the desired proportions so as to obtain a more or less homogeneous fluid. The running space is then filled with the mixture and then heated, for example by induction, so that the lubricant cures in said space.

However, the solid lubricant compositions according to the prior art have two problematic limitations. The first concerns the tendency of the mixture to be decanted, in particular by migration of the oil because of its great difference in density with the polymer, which induces a significant loss of oil. In addition, the storage of the mixture then poses a problem, in particular requiring permanent mixing.

The second limitation relates to the implementation of the composition in the running space. Indeed, the composition being essentially liquid, 2

its casting requires the implementation of a tool for sealing before heating, said tool being specific for each bearing geometry.

In addition, the composition being liquid, it can not be positioned in the running space before heating, which requires a total filling of said space to ensure lubrication closer to the rolling contacts. This results in a lack of modularity in the geometry of the solid lubricant obtained, as well as an increase in the friction-induced torque of the rolling bodies which are enclosed in the polymer matrix.

Solid lubricant compositions comprising a mixture of a thermoplastic polymer powder and a grease are also known.

However, the solid lubricants obtained with these compositions are not entirely satisfactory in terms of lubrication and induce an increase in the torque which is important.

Indeed, the trapping of the oil in the grease soap is not optimal relative to its bleeding to feed the rolling contacts. In addition, the presence of soap increases the frictional torque of the rolling bodies enclosed by the solid lubricant.

The object of the invention is to overcome the aforementioned limitations by proposing in particular a solid lubricant composition which, in combination with optimized lubrication and a limited increase in torque, has improved resistance to settling and a pasty consistency.

For this purpose, and according to a first aspect, the invention provides a solid lubricant composition for the bearing space of a bearing, said composition comprising a mixture of a thermoplastic polymer powder and an oil, the mixture further comprising a grease.

According to a second aspect, the invention proposes a rolling bearing comprising a fixed member and a rotating member forming between them a running space in which rolling bodies are arranged to allow the relative rotation of said member, said bearing space comprising a lubricant solid formed after heating such a composition, said lubricant being provided to be in contact with the rolling bodies, at least over a portion of their periphery.

Other features and advantages of the invention will appear in the following description of various embodiments.

The invention relates to a rolling bearing, in particular a bearing, comprising a fixed member and a rotating member forming between them a running space in which rolling bodies are arranged to allow the relative rotation of said members.

A rolling bearing according to the invention finds particular application in the automotive field, especially in gearboxes, in flywheels with fixed hub, in the clutch stops, and in industry in general, particularly for guiding an oscillating element relative to a fixed structure.

In order to lubricate the rolling contacts, the running space comprises a solid lubricant which is intended to be in contact with the rolling bodies, at least over part of their periphery.

The solid lubricant is formed from a composition which is introduced into the running space and then heated to solidify it. The solid lubricant composition comprises a blend of a thermoplastic polymer powder and a liquid oil.

Indeed, by heating, the polymer powder will fuse to create a matrix in which the oil is trapped. The polymer will then behave like a sponge inside which the oil is bonded by Van der Walls forces. Then, as the bearing is used, the bonds holding the oil to the polymer will be broken which will release the oil and therefore effectively lubricate the bearing throughout its use.

The thermoplastic polymer used may in particular be selected from the group comprising high density polyethylenes. In the case of a high temperature application, typically at a temperature above 135 ° C. and in particular of the order of 150 ° C., the polymer may be chosen from the group of polymers with a high melting point, including polypropylenes, polyamides, polyvinylidene fluorides.

Regarding the choice of oil, it is mainly dictated by the constraints of the intended application. Mineral, synthetic ester or perfluorinated oils can be conventionally used.

To stabilize the mixture over time and increase its viscosity, the invention provides for introducing into the mixture a fat. Indeed, it has been found that the fat plays the role of an emulsifier by improving the cohesion of the oil in its mixture with the polymer. In addition, the grease being pasty, its incorporation into the mixture allows an increase in viscosity so as to obtain a pasty mixture. Moreover, by their nature, the greases have good compatibility with oils.

Depending on the nature of the oil and that of the polymer, the characteristics of the grease used are chosen relative to its dual emulsifying function and increasing viscosity. In particular, the grease comprises an oil disposed in a soap, said oil being identical to or different from the oil introduced into the mixture. For example, one can use a metal soap grease and mineral oil, synthetic ester, perfluorinated or a mixture of mineral oils and perfluorinated (so-called hybrid fats).

Although the grease incorporated in the mixture does not have as its main function the lubrication of the running space, it can also be chosen to improve said lubrication in the application in question.

Improving the stability and the viscosity of the mixture is particularly advantageous with a mass percentage of fat in the mixture of between 3 and 30%, especially between 5 and 15%.

The mixture may also comprise, in percentage by mass: between 20 and 45% of thermoplastic polymer powder; - Between 30 and 70% of oil.

In particular, the following mass compositions give good results: 5% fat; 35-40% of polymer; - 60-55% oil.

The viscosity of the mixture obtained according to the invention allows its injection into the running space in the manner of a conventional lubricating grease. Thus, it is possible to position the mixture in said space at least partially around the rolling bodies, said mixture then being heated to obtain the solid lubricant. In an exemplary embodiment, the heating is carried out in an oven at a temperature between 150 ° C and 180 ° C.

Due to the pasty nature of the composition, the solid lubricant can only partially fill the running space, in particular said lubricant can occupy less than 60% of the free volume of the running space, for example of the order of 50 %, so as to limit the induced torque and to increase the service life. In particular, the solid composition can be positioned between the bodies 6

wheels to be in contact with both raceways while allowing the rolling bodies to turn freely.

Moreover, for industrial injection of the pasty mixture into the running space, it is no longer necessary to use a mold, and the standard grease dispensers can be used. However, since these feeders apply a high pressure on the mixture, it is desirable to use a polymer powder whose average particle size is reduced, for example less than 100 m, in particular of the order of 40 m. Indeed, with larger particle sizes ~ o, the easier ejection of the oil relative to the polymer tends to vary over time the percentage of oil in the injected mixture.

Claims (9)

A solid lubricant composition for the bearing space of a bearing, said composition comprising a mixture of a thermoplastic polymer powder and an oil, said composition being characterized in that the mixture further comprises a grease. 2. Solid lubricant composition according to claim 1, characterized in that the weight percentage of thermoplastic polymer in the mixture is between 20 and 45%. 3. Solid lubricant composition according to claim 1 or 2, characterized in that the mass percentage of fat in the mixture is between 3 and 30%. 4. Solid lubricant composition according to claim 3, characterized in that the mass percentage of fat in the mixture is between 5 and 15%. 20 5. Solid lubricant composition according to any one of claims 1 to 4, characterized in that the mass percentage of oil in the mixture is between 30 and 70%. Solid lubricant composition according to any one of claims 1 to 5, characterized in that the average particle size of the polymer powder is less than 100 m. 7. Solid lubricant composition according to any one of claims 1 to 6, characterized in that the thermoplastic polymer is selected from the group consisting of high density polyethylenes, polypropylenes, polyamides, polyvinylidene fluorides. 15 8. Rolling bearing comprising a fixed member and a rotating member forming between them a running space in which rolling bodies are arranged to allow the relative rotation of said member, said running space comprising a solid lubricant formed after heating a composition according to any one of claims 1 to 7, said lubricant being provided to be in contact with the rolling bodies, at least over part of their periphery. 9. rolling bearing according to claim 8, characterized in that ~ o lubricant occupies less than 60% of the free volume of the running space.