BEARING MATERIAL, BEARING AND METHOD

Abstract

A bearing material for a bearing element (e.g., a crankshaft bearing) and a method of making a bearing material are disclosed. The bearing material includes a polyamide-imide plastics polymer material functionalised with hydrocarbon groups. In one example, the method includes preparing a polyamide-imide polymer material and, when the polyamide-imide polymer material reaches a predetermined molecular weight, adding a hydrocarbon-containing reactant to a reaction mixture containing the polyamide-imide polymer material to form a bearing material comprising a polyamide-imide plastics polymer material functionalised with hydrocarbon groups. In another example, the method includes mixing a polyamide-imide plastics polymer with a catalyst to form a reaction mixture, and adding a hydrocarbon-containing reactant to the reaction mixture to form a bearing material comprising a polyamide-imide plastics polymer material functionalised with hydrocarbon groups.

Claims

1. A bearing material, comprising: a polyamide-imide plastics polymer material functionalised with hydrocarbon groups.

2. The bearing material according to claim 1, wherein more than 90% of the hydrocarbon groups are aliphatic hydrocarbon groups.

3. The bearing material according to claim 1, wherein more than 90% of the hydrocarbon groups are unbranched hydrocarbon groups.

4. The bearing material according to claim 1, wherein an average chain length of the hydrocarbon groups is between 6 and 21 carbon atoms.

5. The bearing material according to claim 1, wherein a molar ratio of hydrocarbon groups with reactive functionality to repeat units in each molecule of the polyamide-imide plastics polymer material is between 0.2 and 0.02.

6. A bearing element, comprising: a bearing-surface layer comprises a bearing material, the bearing material including a polyamide-imide plastics polymer material functionalised with hydrocarbon groups.

7. The bearing element according to claim 6, wherein the bearing-surface layer further comprises particles of one or more other materials within a matrix of the bearing material.

8. A method for making a bearing material comprising the steps of: preparing a polyamide-imide polymer material; and when the polyamide-imide polymer material reaches a predetermined molecular weight, adding a hydrocarbon-containing reactant to a reaction mixture containing the polyamide-imide polymer material to form a bearing material comprising a polyamide-imide plastics polymer material functionalised with hydrocarbon groups.

9. The method according to claim 8, wherein the hydrocarbon-containing reactant is a fatty acid or a fatty amine.

10. The method according to claim 8, wherein the hydrocarbon-containing reactant contains an epoxide functional group.

11. The method according to claim 8, wherein an average chain length of the hydrocarbon-containing reactant is between 6 and 21 carbon atoms.

12. The method according to claim 8, wherein the hydrocarbon-containing reactant is added in a quantity such that a molar ratio of the hydrocarbon-containing reactant to repeat units in each molecule of the polyamide-imide polymer material is between 0.2 and 0.02.

13. A method for making a bearing material comprising the steps of: mixing a polyamide-imide plastics polymer with a catalyst to form a reaction mixture; and adding a hydrocarbon-containing reactant to the reaction mixture to form a bearing material comprising a polyamide-imide plastics polymer material functionalised with hydrocarbon groups.

14. The method according to claim 13, wherein an average chain length of the hydrocarbon-containing reactant is between 6 and 21 carbon atoms.

15. The method according to claim 13, wherein the hydrocarbon-containing reactant is added in a quantity such that a molar ratio of the hydrocarbon-containing reactant to repeat units in each molecule of the polyamide-imide polymer material is between 0.2 and 0.02.

16. The method according to claim 15, wherein the molar ratio is between 0.1 and 0.05.

17. The method according to claim 13, wherein the hydrocarbon-containing reactant is a fatty acid or a fatty amine.

18. The method according to claim 13, wherein the hydrocarbon-containing reactant contains an epoxide functional group.

19. The bearing material according to claim 2, wherein the hydrocarbon groups include branched hydrocarbon groups and unbranched hydrocarbon groups, and wherein more than 70% of the hydrocarbon groups are the unbranched hydrocarbon groups.

20. The bearing material according to claim 4, wherein the average chain length of the hydrocarbon groups is between 8 and 18 carbon atoms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawing, in which;

[0061] FIG. 1 is a schematic diagram of a half-shell of a plain bearing.

DETAILED DESCRIPTION

[0062] FIG. 1 shows a half shell 2 of a cylindrical sliding bearing comprising a strong backing 4 of steel, a bearing lining layer 6, comprising a layer 8 of a copper-based alloy or an aluminium-based alloy bonded to the backing and a nickel diffusion barrier, or interlayer, 10, and a plastics, polymer-based overlay layer 12 embodying the present invention bonded to the lining layer. In other embodiments of the invention the overlay may be bonded directly to the backing, and the lining layer omitted, depending on the compatibility of the materials used and the intended use of the bearing.

[0063] The overlay layer, or sliding layer, comprises a modified PAI resin matrix embodying the invention and fabricated as described below. The PAI matrix may incorporate filler materials as follows.

[0064] As in prior-art polymer bearings, the sliding layer material may optionally include or incorporate at least one solid lubricant. Suitable solid lubricants include: metal sulphides with layered structures; graphite; hexagonal boron nitride (h-BN); molybdenum disulfide (MoS.sub.2); tungsten disulphide (WS.sub.2) or PTFE. One or more of these materials may be used in a sliding layer. Other suitable materials are envisaged and will be readily apparent to the skilled person.

[0065] As in prior-art polymer bearings, the sliding layer material may also include harder particles in powdered and/or flaked form. This may provide improved wear resistance. The harder particles may include, in any suitable combination, one or more different types of hard particle. Some suitable hard particles include nitrides, carbides, borides, oxides, and metal powders. Other suitable materials are envisaged and will be readily apparent to the skilled person.

[0066] The total thickness of the sliding layer material is between about 3 m, or 6 m, and about 14 m. A preferred thickness of the sliding layer material for bearing elements embodying the present invention is between about 8 m and about 12 m, or particularly preferably in the range 9 m to 11 m.

[0067] A conventional PAI polymer for a bearing material is formed by the copolymerisation of polyamide imide monomers such as trimellitic anhydride and methylene diamine. These monomers are mixed in known manner, in combination with suitable solvents and catalytic materials, to allow the monomers to copolymerise. An initial polymerisation step produces a polymer which may be applied to the surface of a bearing element, for example by spraying, and cured to form a thermoset PAI bearing layer. This process is described in the prior art, such as in patent publications WO 2004/113749 and GB 2521004A.

[0068] In a preferred embodiment of the present invention, this prior art process is modified by performing the copolymerisation route as usual and, at a time when the PAI polymer chains in the reaction mixture have reached a predetermined average molecular weight, adding under nitrogen a hydrocarbon-containing reactant containing hydrocarbon functional groups. The hydrocarbon-containing reactant will react with the polymer chains so that hydrocarbon groups with reactive functionality bond to the polymer chains at a proportion of available reaction sites. The quantities of reactant are controlled so that the addition of the hydrocarbon-containing reactant functionalises the polymer chains at a desired proportion of the potential reaction sites on the polymer chains.

[0069] The resulting polymer may be applied to the surface of a bearing element, for example by spraying, and cured to form a thermoset PAI bearing layer, as is known in the art.

[0070] In another preferred embodiment of the present invention, the prior art copolymerisation process is performed as usual to produce conventional PAI polymer. The conventional PAI is heated under nitrogen together with a solvent and a catalyst, so that the PAI is dissolved in the solvent. A hydrocarbyl-containing reactant is then added dropwise to the reaction mixture.

[0071] The resulting polymer may be applied to the surface of a bearing element, for example by spraying, and cured to form a thermoset PAI bearing layer, as is known in the art.

[0072] In a preferred example, PAI modified with various proportions (mol %) of hydrocarbon functional groups were prepared by the Synthesis by Functionalisation of PAI synthesis route set out above.

[0073] The quantites and molar ratios of the synthesis constituents are set out below.

Example 1: 5 Mol % Dodecylamine

[0074]

TABLE-US-00001 Mr Molar (g/mol) ratios PAI 372.37 1 Dodecylamine 185.35 0.05

Example 2: 10 Mol % Dodecylamine

[0075]

TABLE-US-00002 Mr Molar (g/mol) ratios PAI 372.37 1 Dodecylamine 185.35 0.10

Example 3: 20 Mol % Dodecylamine

[0076]

TABLE-US-00003 Mr Molar (g/mol) ratios PAI 372.37 1 Dodecylamine 185.35 0.20

Example 4: 5 Mol % Octylamine

[0077]

TABLE-US-00004 Mr Molar (g/mol) ratios PAI 372.37 1 Octylamine 129.24 0.05

Example 5: 10 Mol % Octylamine

[0078]

TABLE-US-00005 Mr Molar (g/mol) ratios PAI 372.37 1 Octylamine 129.24 0.10

Example 6: 20 Mol % Octylamine

[0079]

TABLE-US-00006 Mr Molar (g/mol) ratios PAI 372.37 1 Octylamine 129.24 0.20

[0080] The hydrocarbyl-containing reactants are believed to react with the PAI polymer molecules so that the resulting polymer chains are functionalised with the entire hydrocarbyl-portion of the reactant molecule. Thus, when octylamine was used as the hydrocarbon-containing reactant, it is believed that, on average, the PAI chains become functionalised with octyl-functional groups with a length of eight carbon atoms. Likewise, when dodecylamine was used as the hydrocarbon-containing reactant, it is believed that, on average, the PAI chains become functionalised with dodecyl-functional groups with a length of twelve carbon atoms.

[0081] Samples of the resulting modified polymers were analysed using nuclear magnetic resonance spectroscopy (NMR) to confirm functionalisation, and by gel permeation chromatography (GPC) to confirm molecular weight increase compared to unfunctionalised PAI

[0082] NMR and GPC measurements confirmed that functionalisation of the PAI material had been successfully achieved.

[0083] Contact angle analysis confirmed that oil wettability (oleophilicity) increased with an increasing degree of functionality. Contact angle measurements conducted with motor oil on 5 mol % and 10 mol % dodecyl-functionalised PAI are set out in Table 1, below.

TABLE-US-00007 TABLE 1 Contact Angle Results Coating oleophilicity Contact Contact increasing angle angle Increased wetting Sample name AVG 1 AVG 2 of motor oil MAHLE 47 47 Reference 5% Dodecyl 44 44 10% Dodecyl 35 35

[0084] Wear testing showed that 5 mol % dodecyl-functionalised PAI exhibited similar wear behaviour (measured by volume loss in mm.sup.3) to conventional PAI. The 10 mol % dodecyl-functionalised PAI exhibited slightly higher volume loss than the 5 mol % sample, but samples of PAI functionalised with both 5 mol % and 10 mol % dodecyl-functional groups exhibited suitable low wear behaviour.

[0085] Stribeck curves, plotting friction coefficient against sliding speed, for several samples of each type of bearing material were then prepared. In each case, the lubricated sliding of a steel journal against each bearing material was tested, and particular attention was paid to the running in phase of sliding and the steady state phase, which was reached after about 250 sliding cycles (rotations). Stribeck Curve testing of the samples showed a positive trend towards lower coefficients of friction as the proportion of functionalisation was increased. In particular for the 10% dodecyl-functional material lower coefficients of friction were observed at lower speeds at fewer cycles than the standard PAI polymer. This suggests that functionalisation improves the sliding surface and helps to achieve hydrodynamic lubrication at lower speeds than typically observed for conventional PAI polymer coatings. This suggests that the hydrocarbon-functionalised materials will perform better at start up, as lower frictions may be achieved much more quickly and steady state conditions may be reached quickly and possess lower frictions which will extend the bearing life.