METHOD OF MANUFACTURING A STRIP FOR A BEARING

Abstract

A method of manufacturing a strip for a bearing may comprise roll-bonding a bearing layer comprising a tin-free aluminium alloy directly to a base layer to form a bimetal and heat-treating the bimetal at a temperature below a recrystallization initiation temperature of the aluminium alloy. A strip for a bearing manufactured using the method, and a bearing having a strip manufactured using the method, are also provided.

Claims

1. A method of manufacturing a strip for a bearing, the method comprising: roll-bonding a bearing layer comprising a tin-free aluminium alloy directly to a base layer to form a bimetal; and heat-treating the bimetal at a temperature below a recrystallization initiation temperature of the aluminium alloy.

2. A method according to claim 1, wherein the bimetal is heat-treated at a temperature less than 250° C.

3. A method according to claim 1, wherein a thickness reduction of the aluminium alloy during roll-bonding is at least 40%.

4. A method according to claim 1, wherein the aluminium alloy is substantially free of any soft phase elements.

5. A method according to claim 1, wherein the aluminium alloy comprises at least 90 wt % Al.

6. A method according to claim 1, wherein the aluminium alloy comprises: between 0.5 wt % and 2.0 wt % Mn; and between 0.5 wt % and 2.0 wt % Mg.

7. A method according to claim 6, wherein the aluminium alloy comprises: between 0.8 wt % and 1.4 wt % Mn, and between 0.8 wt % and 1.3 wt % Mg; and wherein the aluminium alloy comprises at least one of: about 0.6 wt % Si; about 0.8 wt % Fe; between 0.05 wt % and 0.25 wt % Cu; about 0.25 wt % Zn; about 0.1 wt % Ti; about 0.05 wt % Ga; about 0.05 wt % V.

8. A method according to claim 6, wherein the aluminium alloy comprises: between 1.0 wt % and 1.5 wt % Mn, and between 0.8 wt % and 1.3 wt % Mg; and wherein the aluminium alloy comprises at least one of: about 0.3 wt % Si; about 0.7 wt % Fe; about 0.25 wt % Cu; about 0.25 wt % Zn.

9. A method according to claim 1, wherein the aluminium alloy comprises between 1.0 wt % and 1.5 wt % Mn.

10. A method according to claim 1, wherein a bearing comprising the strip, at a load of 110 MPa, has a fatigue test pass rate of at least 90%.

11. A method according to claim 1, wherein a bearing comprising the strip has a fatigue load of at least 120 MPa.

12. A method according to claim 1, wherein a hardness loss of a bearing comprising the strip after 500 hours in a soak test at 160° C. is less than 20%.

13. A strip for manufacturing a bearing manufactured according to the method of claim 1.

14. (canceled)

15. A strip for a bearing, the strip comprising: a base layer; and a bearing layer comprising a tin-free aluminium alloy, wherein the bearing layer is directly roll-bondable to the base layer to form a bimetal; wherein the bimetal is heat-treatable at a temperature below a recrystallization initiation temperature of the aluminium alloy, so that a bearing comprising the strip satisfies at least one of the following: at a load of 110 MPa, a fatigue test pass rate of at least 90%; a fatigue load of at least 120 MPa; a hardness loss after 500 hours in a soak test at 160° C. is less than 20%.

16. The strip for a bearing according to claim 15, wherein the bimetal is heat-treated at a temperature less than 250° C.

17. The strip for a bearing according to claim 15, wherein the aluminium alloy is substantially free of any soft phase elements.

18. The strip for a bearing according to claim 15, wherein the aluminium alloy comprises at least 90 wt % Al.

19. The strip for a bearing according to claim 20, wherein the aluminium alloy comprises: between 0.5 wt % and 2.0 wt % Mn; and between 0.5 wt % and 2.0 wt % Mg.

20. A strip for a bearing, the strip comprising: a base layer; and a bearing layer comprising a tin-free aluminium alloy, wherein the bearing layer is directly roll-bondable to the base layer to form a bimetal; wherein the bimetal is heat-treatable at a temperature below a recrystallization initiation temperature of the aluminium alloy.

21. The strip for a bearing according to claim 20, wherein the bimetal is heat-treated at a temperature less than 250° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In order that the present invention may be more fully understood, some example embodiments of the present invention will now be described by way of illustration only with reference to the accompanying drawings, in which:

[0077] FIG. 1 shows a cross section through part of a bimetal bearing utilising a strip manufactured by a method embodying the present invention;

[0078] FIG. 2 shows a micrograph of a strip manufactured by a method embodying the method of the present invention;

[0079] FIG. 3 shows a flow diagram of a method embodying the present invention;

[0080] FIG. 4 provides the results of a high-cycle fatigue test for four batches of preferred example strips manufactured by a method embodying the present invention, a baseline tin-containing aluminium alloy strip of the prior art, and a tin-free aluminium alloy strip heat-treated at 300° C. for comparison;

[0081] FIG. 5 provides the results of a bearing fatigue load test for preferred example bearings comprising strips manufactured by a method embodying the present invention;

[0082] FIG. 6 provides the results of a staircase fatigue load test for preferred example bearings comprising strips manufactured by a method embodying the present invention; and

[0083] FIG. 7 provides the results of a hardness loss test for a preferred example bearings comprising at least one strip manufactured by a method embodying the present invention.

DETAILED DESCRIPTION

[0084] FIG. 1 shows a part of a bimetal bearing 100 comprising: a backing or base layer 102, a bearing layer 104 of a soft phase-free aluminium alloy, and a polymer overlay or running layer 106.

[0085] The base layer 102 is made from steel and may optionally comprise up to about 1 wt % copper. The bearing 100 does not comprise an interlayer, as the aluminium alloy of the bearing layer 104 is roll bonded directly to the steel of the base layer 102.

[0086] A surface of the bearing layer 104 of the strip may be coated 306 with a polymer overlay 106. The strip may be bent to form at least a portion of a bearing, such as a half shell of the bimetal bearing 100 shown in FIG. 1.

[0087] Suitable polymer overlays 106 may be as described in GB0822346A. The polymer overlay 106 may comprise polyimide/amide plastics and/or fluoropolymer.

[0088] The aluminium alloy is a standard, commercially available aluminium alloy of the wrought aluminium-manganese family. Suitable alloys include A3003, A3004, and A3104. The elemental compositions of these suitable standard alloys are shown in Table 1.

TABLE-US-00001 TABLE 1 elemental compositions of A3003, A3004, and A3104. A3003 A3004 A3104 Aluminium (Al) balance balance balance Manganese (Mn)  1.0-1.5 wt % 1.0-1.5 wt %  0.8-1.4 wt % Magnesium (Mg) — 0.8-1.3 wt %  0.8-1.3 wt % Silicon (Si)  0.6 wt %  0.3 wt %  0.6 wt % Iron (Fe)  0.7 wt %  0.7 wt %  0.8 wt % Copper (Cu) 0.05-0.2 wt % 0.25 wt % 0.05-0.25 wt % Zinc (Zn) 0.10 wt % 0.25 wt % 0.25 wt % Titanium (Ti) — — 0.10 wt % Gallium (Ga) — — 0.05 wt % Vanadium (V) — — 0.05 wt % Residuals 0.15 wt % 0.15 wt % 0.15 wt %

[0089] The wt % content of the various elements is the wt % content of the relevant element in the final aluminium alloy as applied to a sliding element component (a bearing for an engine or motor) rather than the wt % content of the initial mixture used to form the aluminium alloy.

[0090] Some suitable techniques for measuring the wt % content of the various elements of the aluminium alloy, where present, that are referred to in the present specification comprise the following: [0091] (i) X-Ray Fluorescence spectroscopy (XRF); and [0092] (ii) Optical Emission Spectroscopy (OES).

[0093] The skilled person will be aware that there will be other suitable techniques for measuring the wt % of the various elements of the final aluminium alloy as applied to a bearing to ensure that they are present in the aluminium alloy with the specified content.

[0094] FIG. 2 shows a micrograph of a strip forming at least a portion of the bimetal bearing 100 of FIG. 100, showing the aluminium alloy in the bearing layer 104 after roll-bonding directly to a low-carbon steel base layer 102. The aluminium alloy in the bearing layer 104 comprises no directional weak phases, because it does not contain tin or any other soft phase elements.

[0095] FIG. 3 shows a flow diagram of a method 300 embodying the present invention. In a first step, a suitable tin-free aluminium alloy is roll-bonded directly to a steel base layer 102 to form a bimetal strip. The roll-bonding of the bimetal results in a minimum thickness reduction of the aluminium alloy of 50% so as to provide sufficient bond strength between the aluminium alloy bearing layer 104 and the steel base layer 102. In particular, the thickness reduction may be between 50% and 60%.

[0096] While a higher thickness reduction typically results in better bond strength, it can be difficult to achieve very high thickness reductions (e.g. above 55%, or above 60%) without impacting on other properties of the strips/bearings. The achievable thickness reduction will depend on the rolling mill used—a higher aluminium alloy thickness reduction is achieved on a 3-high rolling mill than a 4-high rolling mill. For a 4-high rolling mill, a thickness reduction of at least 50%, preferably of 50 to 60%, is preferable and achievable.

[0097] The roll-bonded bimetal strip is then heat-treated 304, in air, for one to fifteen hours, preferably for eight to twelve hours, at a temperature of 200° C., which is below the recrystallization initiation temperature of the aluminium alloy. As such, the microstructure of the aluminium alloy is not recrystallized, so that the adhesion of the bearing layer to the base layer is not jeopardised, and the strengthening/hardening from cold working in the aluminium alloy is retained. If the same bimetal strip were heat-treated at a temperature of 300° C., the aluminium alloy would recrystallize, which would result in a significant drop in hardness.

[0098] The strip heat-treated in step 304 is bent 306 to shape so as to form at least a portion of a bearing, such as a bearing or half-bearing shell. A surface of the bearing layer 104 of the strip may be coated in step 308 with a polymer overlay 106. The step of coating 308 a surface of the bearing layer 104 may be carried out before the step of bending 306 the strip, or, more preferably, coating 306 of a surface of the bearing layer 104 may be carried out after the strip has been bent to shape, i.e. to form a half shell of the bimetal bearing 100.

[0099] FIGS. 4 to 7 show results from testing of strips and bearings manufactured by the method 300, having a low carbon steel base layer and a A3104 bearing layer.

[0100] FIG. 4 shows the results of high-cycle fatigue testing 400 for four batches of strips manufactured using the method 300 as compared to a strip manufactured by a method embodying the present invention, except that it was heat treated at 300° C., and a prior art tin/aluminium alloy strip. The high-cycle fatigue testing 400 was carried out on flat bimetal strip samples without polymer coating. “Dog bone” test specimens were used for the high-cycle fatigue testing on a Rumul Mikrotron test machine.

[0101] The high-cycle fatigue testing was carried out by repeatedly loading samples of strips at a stress amplitude (plotted on the left hand axis) for up to 50,000,000 cycles until failure. As shown by lines 402, 404, 406, and 408, the strips manufactured by methods embodying the present invention, could be loaded with significantly higher stress amplitudes than the sample 410 heat-treated at 300° C., and the prior art tin/aluminium alloy strip 412. The recorded average stress and cycles to failure are shown in Table 2.

TABLE-US-00002 TABLE 2 High-cycle fatigue testing results for four strips manufactured by a method embodying the present invention (RB330 Batch A to D—lines 402, 404, 406, and 408), a strip annealed at a higher temperature (RB330 300° C. anneal—line 410), and a strip comprising a portfolio AlSn alloy (Portfolio AlSn alloy—line 412). Cycles to Failure Recorded average stress in RB330 Batch A 343512 179.8865 308473 189.919 50000000 199.9894 40754 219.9939 102946 209.934 RB330 Batch B 591028 209.9 269470 229.9 595887 199.9 3441 220.0 321820 189.9 50000000 180.0 RB330 Batch C 164656 209.9 195833 219.9 119638 229.9 50000000 200.0 RB330 Batch D 180817 219.9 162104 229.9 4231 240.0 163514 210.0 418723 199.9 6888218 190.0 RB330 300° C. anneal 10809 174.4 7734 175.6 60000000 160.0 816242 169.9 Portfolio AlSn alloy 341700 139.2 6847200 131.2 50000000 122.7

[0102] FIGS. 5 and 6 show the results of bearing fatigue testing of bearings made from strips manufactured using the method 300. The bearing shells used in these tests have dimensions of typical passenger car connecting rod bearings. The bearings had a wall thickness of about 1.81 mm. The bearings used in the bearing fatigue load test shown in FIG. 5 were coated with a polymer overlay.

[0103] A typical prior art tin/aluminium alloy bearing may achieve a pass rate of about 80% at a load of 103 MPa. As shown in FIG. 5, the bearings made from the strips manufactured using the method 300 showed a 100% pass rate in the bearing fatigue testing 500 at a load of 110 MPa. Each sample 502 passed the bearing fatigue testing 500 at a load of 110 MPa.

[0104] Indeed, as shown in FIG. 6, for bearing fatigue testing 600 at loads above 110 MPa, the bearings made from strips manufactured using the method 300 passed 602 at loads of up to 131 MPa, and even at loads of 138 MPa, the bearings seized 604 but did not fail.

[0105] The results shown in FIG. 6 were obtained using a staircase method according to ISO 12107.

[0106] The surprisingly good properties of the bearings using strips manufactured by the method 300 are also shown in FIG. 7, which shows the results of a hardness loss soak test 700.

[0107] For the hardness loss soak test 700, bearings comprising strips, manufactured by a method embodying the present invention, but without an overlay coat, were soaked (heated at a constant temperature for a length of time) at 160° C. for up to 500 hours in air, so as to test the hardness durability of the bearing in an environment that is comparable to an engine application. The hardness before and after soaking was determined using a Vickers test according to ISO 6507. The bearings may or may not be sectioned prior to hardness testing.

[0108] Lines 702 and 704 show that two prior-art tin/aluminium alloy bearings showed hardness losses of about 28% and 21% after 500 hours, whereas the bearings 706 using strips manufactured by the method 300 showed hardness losses of about 15% after 500 hours.

[0109] Although described herein and illustrated in the drawing in relation to a half bearing shell, methods embodying present invention may equally be used to manufacture other sliding elements, including, for example, bushes, and engines comprising such sliding engine components.