METHOD FOR PRODUCING PLAIN-BEARING COMPOSITE MATERIALS, PLAIN-BEARING COMPOSITE MATERIAL, AND SLIDING ELEMENT MADE OF SUCH PLAIN-BEARING COMPOSITE MATERIALS

Abstract

A method for producing plain-bearing composite materials (30) is provided in which a bearing metal melt (14) is poured onto a belt material (6) of a steel and the composite material (25) of belt material (6) and bearing metal (14) is then subjected to a heat treatment. After the bearing metal (14) has been poured on, the composite material (25) is quenched, followed by an aging operation. A plain-bearing composite material (30) is provided, which has a carrier layer (32) of steel and a bearing metal layer (34) of a cast copper alloy, wherein the bearing metal layer has a dendritic microstructure.

Claims

1. A method for producing plain-bearing composite materials, a bearing-metal melt being cast onto a strip material made of a steel and the composite material consisting of the strip material and bearing metal then undergoing a heat treatment, wherein after the bearing metal has been cast, the composite material is quenched and then an aging process is carried out subsequently.

2. The method according to claim 1, wherein the aging process is carried out over four to ten hours at a temperature of between 350 C. and 520 C.

3. The method according to claim 2, wherein the aging process is carried out at a temperature of between 350 C. and 420 C.

4. The method according to claim 2, wherein the aging process is carried out at a temperature of between >420 C. and 520 C.

5. The method according to claim 1 wherein an austenitic steel is used as the steel.

6. The method according to claim 1, wherein a steel having a carbon content of 0.15% to 0.40% is used.

7. The method according to claim 1, wherein a bearing metal consisting of a copper alloy is cast.

8. The method according to claim 7, wherein the copper alloy is precipitation hardenable.

9. The method according to claim 7, wherein the copper alloy consists of a copper-nickel alloy, a copper-iron alloy, a copper-chromium alloy or a copper-zirconium alloy.

10. The method according to claim 1, wherein the quenching process begins immediately after the casting process.

11. The method according to claim 1, wherein the quenching process begins within 15 to 25 seconds after the casting process.

12. The method according to claim 1, wherein the composite material is quenched to a temperature T.sub.1 of from 150 C. to 250 C.

13. The method according to claim 1, wherein the quenching process is carried out at a quenching rate of from 10 K/s to 30 K/s.

14. The method according to claim 1, wherein the copper-nickel alloy is quenched at a quenching rate of from 15 K/s to 25 K/s.

15. The method according to claim 1, wherein the copper-iron alloy is quenched at a quenching rate of from 15 K/s to 25 K/s.

16. The method according to claim 1, wherein the copper-chromium alloy is quenched at a quenching rate of from 10 K/s to 20 K/s.

17. The method according to claim 1, wherein the copper-zirconium alloy is quenched at a quenching rate of from 10 K/s to 20 K/s.

18. The method according to claim 1, wherein the quenching is carried out by means of a quenching fluid.

19. The method according to claim 18, where a cooling oil is used for the quenching.

20. The method according to claim 1, wherein the quenching fluid is sprayed onto the rear side of the composite material.

21. A plain-bearing composite material comprising a steel substrate and a bearing-metal layer consisting of a cast copper alloy, wherein the bearing-metal layer has a dendritic microstructure.

22. The plain-bearing composite material according to claim 21, wherein the substrate has a hardness of from 150 HBW 1/5/30 to 250 HBW 1/5/30.

23. The plain-bearing composite material according to claim 21 wherein the bearing-metal layer has a hardness of from 100 HBW 1/5/30 to 200 HBW 1/5/30.

24. The plain-bearing composite material according to claim 21, wherein the bearing-metal layer has a tensile strength of from 380 MPa to 500 MPa.

25. The plain-bearing composite material according to claim 21, wherein the bearing-metal layer has a yield strength of from 250 MPa to 450 MPa.

26. The plain-bearing composite material according to claim 21, wherein the copper alloy is a copper-nickel alloy, a copper-iron alloy, a copper-chromium alloy or a copper-zirconium alloy.

27. The plain-bearing composite material according to claim 21, wherein the copper-nickel alloy comprises 0.5 to 5 wt. % nickel.

28. The plain-bearing composite material according to claim 21, wherein the copper-iron alloy comprises from 1.5 to 3 wt. % iron.

29. The plain-bearing composite material according to claim 21, wherein the copper-chromium alloy comprises from 0.2 to 1.5 wt. % chromium.

30. The plain-bearing composite material according to claim 21, wherein the copper-zirconium alloy comprises 0.02 to 0.5 wt. % zirconium.

31. The plain-bearing element comprising a plain-bearing composite material according to claim 21.

32. The plain-bearing element according to claim 31, wherein a sliding layer applied to the bearing-metal layer.

33. The plain-bearing element according to claim 32, wherein the sliding layer consists of a galvanic layer.

34. The plain-bearing element according to claim 33, wherein the galvanic layer consists of a tin-copper alloy, a bismuth-copper alloy or of bismuth.

35. The plain-bearing element according to claim 32, wherein the sliding layer consists of a plastic layer.

36. The plain-bearing element according to claim 32, wherein the sliding layer consists of a layer applied by means of PVD processes.

37. The lain-bearing element according to claim 32, wherein the sliding layer consists of a sputtered layer.

38. The plain-bearing element according to claim 32, wherein the plain-bearing element is formed as a plain-bearing shell, a valve plate or a sliding segment.

Description

[0093] Example embodiments will be explained in more detail below on the basis of the drawings:

[0094] FIG. 1 is a schematic illustration of the production method according to the prior art,

[0095] FIG. 2 is a schematic illustration of the method sequence according to the invention,

[0096] FIG. 3 is a schematic view of a strip casting system according to the invention,

[0097] FIGS. 4a and b are perspective views of two sliding elements,

[0098] FIG. 5 is a graphic illustration of the hardness as a function of the microstructure state for a comparative example,

[0099] FIG. 6 is a graphic illustration of the bearing-metal strength as a function of the microstructure state for the comparative example,

[0100] FIG. 7 is a graphic illustration of the hardness for examples 1 to 3 according to the invention,

[0101] FIG. 8 is a graphic illustration of the bearing-metal strength for examples 1 to 3 according to the invention,

[0102] FIG. 9 is an iron-carbon diagram of steel,

[0103] FIG. 10 is the status graph for the bearing-metal alloy CuNi2Si,

[0104] FIG. 11 is a micrograph of a cast microstructure,

[0105] FIG. 12 is a micrograph of a dendritic microstructure of a bearing-metal layer according to Example 1,

[0106] FIG. 13 is a micrograph of another dendritic microstructure of the bearing-metal layer according to Example 2,

[0107] FIG. 14 is a micrograph of another dendritic microstructure of the bearing-metal layer according to Example 3.

[0108] FIG. 2 is a schematic illustration of the method sequence according to the invention, in which the temperature T of the individual method steps is plotted against time t. For example, the melt is cast onto the steel strip material at a temperature T.sub.m of 1100 C. and then immediately afterwards the composite material is quenched to a temperature T.sub.1 of around 150 C. to 250 C. The quenching process lasts around t.sub.a=1 to 3 min. This is followed by the aging at a temperature T.sub.A of from 350 C. to 520 C. The total duration of the method t.sub.g2 is thus shorter than the method according to the prior art (see FIG. 1, t.sub.g1). The shorter process is due to the fact that the entire homogenisation annealing step (solution annealing) is omitted.

[0109] When using CuNi2Si, for example, the prior art requires heating times of e.g. several hours to reach the target temperature of 750 C. to 800 C. as well as holding times of several hours, after which the quenching takes place.

[0110] FIG. 3 is a schematic view of a strip casting system 1. In the unwinding station 2 there is a steel strip roll 3, from which the steel strip material 6 is unwound. In a subsequent profiling station 8, the two edges 9 of the strip material 6 are bent upwards. In a heating station 10, the strip material 6 is preheated to a temperature of up to T.sub.o=1050 C. by means of the heating elements 11 arranged above and below the strip material 6.

[0111] In the subsequent casting station 12, there is a melt container 13, in which the bearing-metal melt 14 is provided. In the casting station 12, the melt is cast onto the strip material 6. The composite material 25 produced is quenched in a quenching station 16 by means of the spray nozzles 17. The spray nozzles 17 are arranged below the strip material 6, and so the quenching fluid 18, which consists of cooling oil, is sprayed onto the rear side 26 of the composite material 25.

[0112] In the subsequent milling station 20, the bearing-metal surface is roughly milled away to remove the skin produced during casting or to level out the surface.

[0113] Next, the plain-bearing composite material 30 is wound up in a winding station 4. The edges 9 are used as spacers during the winding, and so the bearing-metal layer does not contact the rear side of the steel strip. This prevents the bearing metal and steel from adhering to one another. The edges 9 are not removed until later when the plain-bearing composite material is unwound again for further processing.

[0114] Next, the composite material roll 5 is brought to an aging station 24 where the final aging occurs in a bell furnace in order to set the desired mechanical properties in the bearing metal. The aging time is between 4 h and 10 h at temperatures of from 350 C. to 520 C.

[0115] The plain-bearing composite material 30 thus produced is then processed further. For example, plain-bearing shells can be produced therefrom by deformation. FIG. 4a shows a sliding element 40 in the form of a plain-bearing shell 42. The plain-bearing shell 42 comprises a steel substrate 32, a plain-bearing metal layer 34 and a sliding layer 36. The structure of the valve plate 44 shown in FIG. 4b has a steel back 32 together with the bearing-metal layer 43 produced according to the invention. In such applications, a sliding layer 36 is generally not included for stress reasons. The thickness D.sub.1 may be between 1.5 mm and 8 mm. The bearing-metal thickness D.sub.2 is from 0.5-3.0 mm.

Comparative Example

[0116] A plain-bearing composite material consisting of C22+CuNi2Si was produced, the production method according to DE 10 2005 063 324 B4 being carried out as follows: [0117] casting [0118] homogenisation annealing at T=700 C. over 5 h [0119] rolling [0120] recrystallisation annealing at T=550 C. over 3 h [0121] levelling (rolling step involving low deformation (max. 5%) used to adjust the hardness of steel and bearing metal within a defined window).

[0122] FIG. 5 shows the hardness values for the steel and the bearing metal following casting, homogenisation annealing, recrystallisation annealing and levelling.

[0123] At the end of the production method, the plain-bearing composite material has a steel hardness of 138 HBW 1/5/30 and a bearing-metal hardness of 100 HBW 1/5/30. FIG. 6 shows the corresponding strength values. The electrical conductivity is stated in IACS units.

Examples According to the Invention

[0124] If higher strengths of both steel and bearing metal are required for certain applications, i.e. applications in which the main requirements are resistance to wear and fatigue, this can be achieved by the method according to the invention. The method according to the invention was also carried out on the same materials: steel C22 and bearing metal CuNi2Si: [0125] bearing-metal melt cast onto a steel strip, T.sub.m=1100 C., [0126] material quenched from 1100 C. to 300 C. i.e. 800 C. in 0.6 min, corresponding to a quenching rate of 22 K/s.

[0127] After casting, the steel is quenched from the austenite area (see FIG. 9) by the rapid cooling and hardened.

[0128] After the rapid solidification (see FIG. 10) and due to the high cooling rate, the bearing metal CuNi2Si, applied in liquid form, is present as a supersaturated -mixed crystal, has low strength and very high elongation at break values (see FIG. 8, Cast state).

[0129] Afterwards, the plain-bearing composite material does not undergo any homogenisation annealing, but rather undergoes aging at temperatures of 380 C./8 h (example 1), 480 C./4 h (example 2) or 480 C./8 h (example 3), i.e. aging in the two-phase area of the CuNi2Si alloy (see FIG. 10), as a result of which nickel silicides form in the -mixed crystal, leading to a significant rise in the hardness of the bearing metal. Although the hardnesses of the steels reduce slightly as a result, they remain considerably higher than in the comparative example (see FIG. 7).

[0130] FIG. 8 shows the corresponding strength values.

[0131] FIG. 11 is a micrograph of the cast state of the bearing-metal layer 34 following the quenching process according to the invention. As a result of the rapid solidification (quenching), the microstructure has a highly pronounced dendritic structure and is present as a supersaturated mixed crystal.

[0132] FIG. 12 is a micrograph of the bearing-metal layer 34 following aging according to example 1.

[0133] FIG. 13 is a micrograph of the bearing-metal layer 34 according to example 2. The stems of the dendrites extend perpendicularly to the plane of the substrate 32 and precipitates have formed in the matrix of the bearing metal, which lead to increased hardness.

[0134] FIG. 14 is a micrograph of the bearing-metal layer 34 according to example 3.

LIST OF REFERENCE SIGNS

[0135] 1 strip casting system [0136] 2 unwinding station [0137] 3 steel strip roll [0138] 4 winding station [0139] 5 composite material roll [0140] 6 steel strip material [0141] 8 profiling station [0142] 9 edge [0143] 10 preheating station [0144] 11 heating element [0145] 12 casting station [0146] 13 melt container [0147] 14 bearing-metal melt [0148] 15 solidified bearing-metal layer [0149] 16 quenching station [0150] 17 spray nozzle [0151] 18 quenching fluid [0152] 20 milling station [0153] 24 aging station [0154] 25 composite material [0155] 26 rear side of the composite material [0156] 30 plain-bearing composite material [0157] 32 substrate [0158] 34 bearing-metal layer [0159] 36 sliding layer [0160] 40 plain-bearing element [0161] 42 plain-bearing shell [0162] 44 valve plate [0163] D.sub.1 steel layer thickness [0164] D.sub.2 bearing-metal layer thickness [0165] T.sub.0 preheating temperature [0166] T.sub.M melt temperature [0167] T.sub.1 temperature following quenching [0168] T.sub.A aging temperature [0169] t.sub.A quenching time [0170] T.sub.G1 total duration of the method according to the prior art [0171] t.sub.G2 total duration of the method according to the invention