SINTERED FRICTION MATERIAL FOR A FRICTION LINING

Abstract

A sintered friction material comprises a metallic matrix and granular constituents embedded in the matrix. The metallic matrix comprises a copper base alloy. The friction material is characterized in that the granular constituents comprise at least one sintered cemented carbide in a proportion of up to 9 weight percent, based on the total weight of the friction material. Furthermore, a friction body, in particular for clutches and brakes, that comprises a friction lining with at least one layer made of the sintered friction material, and a method for the production of a friction lining with the sintered friction material are described.

Claims

1. A sintered friction material comprising a metallic matrix and granular constituents embedded in the matrix, the metallic matrix comprising a copper base alloy, wherein the granular constituents comprise at least a sintered cemented carbide in a proportion of up to 9 weight percent, based on the total weight of the friction material.

2. The friction material according to claim 1, wherein the sintered cemented carbide is contained in a proportion of 0.2 to 9 weight percent, based on the total weight of the friction material.

3. The friction material according to claim 1, wherein the sintered cemented carbide has a grain size in a range of 1 to 200 μm.

4. The friction material according to claim 1, wherein the sintered cemented carbide has a primary grain size in a range of 1 to 15 μm.

5. The friction material according to claim 1, wherein the sintered cemented carbide comprises a metallic binder selected from the group consisting of iron, cobalt, nickel, chromium, molybdenum, aluminum, and combinations thereof.

6. The friction material according to claim 5, wherein the binder is an alloy of iron, chromium, and aluminum.

7. The friction material according to claim 1, wherein the sintered cemented carbide comprises 70 to 95 weight percent of tungsten carbide (WC) and 5 to 30 weight percent of a metallic binder, each based on the total weight of the sintered cemented carbide.

8. The friction material according to claim 7, wherein the sintered cemented carbide comprises 83.5 to 88% WC, 9 to 11% Fe, 2.5 to 4% Cr, and 0.5 to 1.5% Al, each based on the total weight of the sintered cemented carbide.

9. A friction body including a friction lining, comprising at least one layer made of the sintered friction material according to claim 1.

10. The friction body according to claim 9, characterized in that the friction lining comprises at least one basic layer and one outermost friction layer arranged on the basic layer, the friction layer being formed by the sintered friction material made according to claim 1.

11. A method for the production of a friction lining comprising at least one layer made of a sintered friction material according to claim 1, in which a powder blend is provided, scattered onto a carrier or pressed into a friction foil, and subsequently sintered, the powder blend containing a copper base alloy and granular constituents, wherein the powder blend contains a sintered cemented carbide powder in a proportion of up to 9 weight percent, based on the total weight of the powder blend.

12. The method according to claim 11, wherein the powder blend has the following composition: 60 to 91.8 weight percent of a copper base alloy; 0 to 25 weight percent of further metals or metal alloys; 5 to 15 weight percent of graphite; 3 to 10 weight percent of granular constituents, except sintered cemented carbides, selected from metal oxides, carbides, nitrides, and borides; 0.2 to 9 weight percent of a sintered cemented carbide powder; and 0 to 15 weight percent of further additives selected from adhesion promotors, solders and fluxes; all powder constituents together being 100 weight percent.

13. The sintered friction material according to claim 1 configured for use in a friction lining for a friction body running in oil.

Description

DESCRIPTION OF THE DRAWINGS

[0020] Further features and advantages of the present invention are disclosed in the following description of preferred embodiments in conjunction with the drawing, which are, however, not to be understood as limiting. In the drawing:

[0021] FIG. 1 is a graph showing the friction behavior of friction materials comprising various proportions of sintered cemented carbide.

DETAILED DESCRIPTION

[0022] To produce a friction lining made of a sintered friction material, a powder blend is provided that contains a copper base alloy, preferably a brass alloy, and granular constituents. Optionally, further metals or metal alloys such as copper or iron can be added in small proportions. Preferably, the copper base alloy and the other metals or metal alloys have a melting point (solidus temperature) of more than 800° C., particularly preferably more than 900° C., and thus do not melt under the selected sintering conditions and form the metallic matrix of the sintered friction material.

[0023] The other granular constituents comprise in particular one or more metal oxides, carbides, nitrides or borides, preferably aluminum oxide and/or silicon dioxide, optionally also in the form of mineral additives such as corundum or quartzite.

[0024] The powder blend may contain further additives, including graphite used for building structure a tribologically efficient surface layer, as well as adhesion promoters, solders, and fluxes. In particular metals and metal alloys having a lower melting point than the matrix-forming copper base alloy that can be present in the liquid phase at the selected sintering temperatures and contribute to the integral bonding of the constituents of the friction material to each other and the carrier material are used as adhesion promotors and/or solders. Metal halides can be used as fluxes.

[0025] According to the invention, the powder blend for the production of a sintered friction lining contains a sintered cemented carbide powder in a proportion of up to 9 weight percent, preferably 0.2 to 9 weight percent.

[0026] The copper base alloy is preferably a tin bronze, a brass alloy, a copper-tin-zinc alloy or a copper-titanium alloy.

[0027] It is especially preferred that the copper base alloy is a brass alloy. The brass alloy can have a copper content in a range of 70 to 90 weight percent and a zinc content of 10 to 30 weight percent. Preferably, the content of the copper base alloy, in particular brass, is up to 90 weight percent of the powder blend. Brass alloys have a very good resistance, in particular to EP additives used as oil admixtures.

[0028] In particular metals and metal alloys having a melting point (solidus) of less than 800° C. are used as adhesion promotors and/or solders. Examples of such metals and metal alloys are tin and copper alloys such as CuSn15. To avoid environmental and health damage during production and use of the sintered friction materials, no lead-containing additives are used.

[0029] Preferably, the powder blend for the production of the sintered friction material has he following composition:

[0030] 60 to 91.8 weight percent of the copper base alloy, in particular a brass alloy;

[0031] 0 to 25 weight percent of further metals or metal alloys, in particular iron and/or copper;

[0032] 5 to 15 weight percent of graphite;

[0033] 3 to 10 weight percent of granular constituents, in particular metal oxides, carbides, nitrides, and borides;

[0034] 0.2 to 9 weight percent of sintered cemented carbide powder; and

[0035] 0 to 15 weight percent of further additives such as adhesion promotors, solders, and fluxes, in particular metals or metal alloys with a melting point of less than 800° C.;

[0036] all constituents together being 100 weight percent.

[0037] The grain size of the powder made of the copper base alloy, in particular the brass powder, is preferably between 40 and 200 μm. Preferably, the sintered cemented carbide powder has a spherical grain shape and a grain size in a range of 15 to 55 μm. The grain size distribution of the other constituents is selected such that the powder blend forms a homogeneous, free-flowing blend.

[0038] A tungsten carbide bound in a FeCrAl binder is used as a sintered cemented carbide. The sintered cemented carbide powder is agglomerated and sintered, wherein the primary grain size of tungsten carbide in a range of 1 to 5 μm. Preferably, the carbide powder has the following composition: 83.5 to 88% tungsten carbide (WC), 9 to 11% iron, 2.5 to 4% chromium, and 0.5 to 1.5% aluminum. In general, sintered cemented carbide powders having a WC content of 75 to 95 weight percent and a metallic binder in a proportion of 5 to 25 weight percent are used. Apart from the binder made of a FeCrAl alloy mentioned above, cobalt and optionally nickel can also be used as binders.

[0039] To produce a friction lining using the scatter-sintering process, the powder blend is applied onto a cleaned planar carrier component made of steel and sintered onto the carrier component in a sintering and brazing process at a temperature of 800° C. to 840° C. Optionally, a thin layer of an adhesion promotor, in particular a hard solder such as CuSn15 and/or a soft solder such as tin, can be scattered onto the carrier component prior to application of the powder blend. Following sintering, the friction lining obtained can be compacted to the desired thickness in a compactor and provided with grooves. A porosity of the compacted friction lining is preferably set to approximately 10 to 40%. Subsequently, the component provided with the friction lining can be cold-formed to form the desired friction body and gas nitrocarburized to increase wear resistance.

[0040] The thickness of the friction lining is preferably in a range of 300 μm to several millimeters, preferably between 350 and 1,000 μm. Due to the high material costs of the sintered cemented carbide the friction lining on the friction body can also be formed as a multi-layer coating with at least one cost-effective basic layer on the carrier component containing no sintered cemented carbide, and a sintered cemented carbide-containing friction layer formed on the basic layer that is made of the friction material according to the present invention. The improved friction properties of the friction lining remain unchanged in the multi-layer structure. The basic layer and the friction layer made of the friction material according to the present invention are integrally bonded to each other due to the solder contained in the friction material.

[0041] The thickness of the friction layer made of the friction material according to the present invention is preferably at least 60 μm, and particularly preferably at least 75 μm. Preferably, the thickness of the friction layer is in a range of approximately 5 to 50% of the total thickness of the sintered friction lining.

[0042] By using the scatter-sintering process to produce a sintered friction lining further parameters affecting the friction behavior such as porosity, surface roughness, strength, and homogeneity of the friction lining can be set in a known manner. In particular, the sintering temperatures and the sintering periods can be selected depending on the shape and size of the component and the composition of the friction material.

[0043] It is particularly preferred that the friction lining thus produced is used in a friction body for clutches running in oil.

Examples 1 to 4

[0044] To produce sintered friction materials, powder blends having the composition stated in the following table are provided. The powder blends are scattered onto a planar steel sheet with a thickness of 1.2-2.2 mm and a diameter of 70 to 110 mm and kept at a temperature of 830 to 840° C. in the sintering furnace.

[0045] The friction linings made of the sintered friction materials that were thus obtained were compacted to a thickness of 450 to 500 μm, and the friction body was tested on a p-comp clutch and synchronizer test stand of the company Horbiger with steel as a friction surface counterpart. A sliding speed of 2 to 4 m/s with a compression of 2 to 4 MPa during oil flow at an oil temperature of 80° C. was selected. The development of the friction coefficient was determined via 10,000 successive shifts at various load levels.

[0046] FIG. 1 shows the development of the friction coefficient of the friction materials tested. The addition of sintered cemented carbide results in a friction coefficient that improved by up to 20%. The best results are achieved with a proportion of approximately 1 weight percent of sintered cemented carbide. Proportions of 0.5 and 9 weight percent sintered cemented carbide show comparable friction coefficients. However, friction materials with a high carbide content tend to fail at higher load levels due to fretting.

TABLE-US-00001 TABLE Composition of the friction materials (powder) Example 1 (Comparison) 2 3 4 [Weight [Weight [Weight [Weight Constituent percent] percent] percent] percent] Brass 68.5 68 67.5 61 Copper 9 9 9 8.5 Quartz 4.5 4.5 4.5 4.5 Graphite 5.5 5.5 5.5 5 Bronze 7.5 7.5 7.5 7 Tin 5 5 5 5 Sintered 0 0.5 1 9 cemented carbide