WO2016030258A1

WO2016030258A1 - Friction component

Info

Publication number: WO2016030258A1
Application number: PCT/EP2015/069086
Authority: WO
Inventors: Yuri KADIN; Xiao Bo Zhou
Original assignee: Aktiebolaget Skf
Priority date: 2014-08-28
Filing date: 2015-08-19
Publication date: 2016-03-03
Also published as: GB2529652A; GB201415191D0

Abstract

A friction component (1) for a clutch, the friction component (1) comprising a metal substrate (2) and a ceramic layer (3) thereon, said ceramic layer (3) comprising an outer facing friction surface (4) having pores (5) therein, wherein at least some of the pores (5) in said friction surface (4) are filled or partially filled with an elastomeric material (6).

Description

Friction Component

Technical Field The present invention relates to a friction component which may be used in frictional torque applications.

Background Friction torque is caused by the frictional force that occurs when two objects in contact move. It occurs, for example, when power from a wind turbine is transmitted to a gearbox via a friction disc. High friction torque is often required in such applications. Current friction discs comprise a cast iron substrate (or base) on which is fixed or bonded diamond particles or a ceramic layer. The outer facing surface of the bonded diamond particles or ceramic layer constitutes the friction face of the disc and will typically have a coefficient of friction (COF) of about 0.6 to 0.8. In use, the counter face of the friction disk is typically cast iron. The COF is derived from two mechanisms. First, adhesion between the bonded diamond particles or ceramic layer to the cast iron. Second, ploughing due to plastic deformation of the cast iron induced by the hard and sharp diamond or ceramic surface.

There is a need to further increase the power transmission capacity and/or reduce the size and weight of friction discs.

The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.

Summary of the Invention The present invention provides a friction component for a friction coupling, the friction component comprising a metal substrate and a ceramic layer thereon, said ceramic layer comprising an outer facing friction surface having pores therein, wherein at least some of the pores in said friction surface are filled or partially filled with an elastomeric material

Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

The outer facing friction surface (i.e. the working surface) of the friction component exhibits a high coefficient of friction. Accordingly, when used, for example, as a friction disc or plate, the friction component exhibits an improved power transmission capacity compared with prior art friction components. A higher power transmission capacity may allow the use of a smaller working surface area, which consequently reduces the component size and weight.

Furthermore, for the same power transmission capacity, the friction component may be of reduced size and/or weight compared with prior art friction components, typically at least 10% smaller and/or lighter.

The outer facing friction surface of the ceramic layer is porous. In practice, it is only a requirement that the surface region of the ceramic layer is porous. However, typically all or substantially all of the ceramic layer will be porous, not just the surface. At least some of the pores in the friction surface are filled or partially filled with an elastomeric material. Preferably, most if not substantially all of the pores in the surface are filled or partially filled with an elastomeric material. It is preferred if at least the surface of the ceramic layer is impregnated with the elastomeric material. The inventors have surprisingly found that, in use, the impregnated elastomer material forms a thin layer between the ceramic layer and a counter-face of the friction component, for example a metal or metal alloy counter-face, typically a steel or cast iron counter-face. Since the elastomeric material has a high coefficient of friction (COF typically up to 1 .5) in contact with steel, the coefficient of friction of the friction disc is higher than prior art friction components without the elastomeric impregnation (COF typically around 0.6 to 0.8).

The friction component comprises a metal substrate. The term "metal" as used herein encompasses an alloy. Examples include steel and cast iron.

In the ceramic layer, at least some of the pores in said friction surface are filled or partially filled with an elastomeric material. As noted above, typically the majority of the pores are filled or partially filled with an elastomeric material, more typically at least 95% of the pores are filled or partially filled with an elastomeric material.

The term "elastomeric material" used herein encompasses a polymer with

viscoelasticity (having both viscosity and elasticity).

The ceramic layer advantageously has a Vickers hardness at least five times greater than the hardness of the material forming the counter-face. The ceramic forming the ceramic layer typically contains particles having a diameter of from 5 to 150 microns, more typically from 15 to 75 microns. The particle sizes may be obtained, for example, by the use of sieves. The particle sizes can be measured by optical methods such as, for example, laser diffraction. Typically the majority of the ceramic forming the ceramic layer contains particles having diameters within these ranges, more typically substantially all of the ceramic forming the ceramic layer contains particles having diameters within these ranges.

The ceramic layer preferably has a thickness of at least 20 microns, more preferably from 100 to 500 microns. Thinner ceramic layers may contain inadequate levels of elastomeric material to sufficiently increase the coefficient of friction of the ceramic layer. Thicker ceramic layers may exhibit reduced structural integrity. The ceramic layer is preferably firmly bonded, adhered or fixed to the metal substrate.

The ceramic layer may be applied, for example, using a thermal spray technique and/or a sintering technique. Thermal spray techniques suitable for use in the present invention include, for example, plasma spraying and high velocity oxygen fuel (HVOF) spraying. Such techniques are known in the art.

Prior to applying the ceramic layer, the surface of the metal substrate is preferably roughened in order to enhance adhesion between the metal substrate and the ceramic layer. Roughening may be carried out, for example, using sand blasting and/or grit blasting. Such techniques are known in the art.

Impregnation of the ceramic layer with the elastomeric material may be carried out, for example, by injection moulding, hot pressing, hot dipping and/or vacuum impregnation. Such techniques are known in the art. Alternatively, monomers may be impregnated into the ceramic layer, which are then polymerised to form the elastomeric material in situ. The impregnated elastomeric material may be vulcanised. On impregnation of the elastomeric material into the ceramic layer, a layer of elastomeric material may form on the surface of the ceramic layer. This layer of elastomeric material may be removed.

The majority of the pores preferably have a diameter of from 0.1 to 100 microns, more preferably from 1 to 10 microns. Typically, substantially all of the pores have a diameter in this range. The pore sizes may be measured, for example, using a mercury porosimeter.

As noted above, the substrate preferably comprises steel or cast iron. The mechanical properties of steel and cast iron make them particularly suitable for use in a friction component, for example a friction disc or plate. Furthermore, a ceramic layer may adhere strongly to a steel or cast iron substrate. The porosity of the ceramic layer in the friction surface is preferably from 1 to 25%, more preferably from 2 to 10%. The porosity may be measured using a porosimeter, such as, for example, a Micromeritics mercury porosimeter. Porosimetry involves the intrusion of a non-wetting liquid at high pressure into a material using a porosimeter. The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid's surface tension. Lower porosities may result in the ceramic layer having

unfavourably low levels of elastomeric material impregnated therein. This may result in the friction component exhibiting a low coefficient of friction. Higher porosities may reduce the structural integrity of the ceramic layer, thereby reducing the working lifetime of the friction component.

The term ceramic as used herein encompasses inorganic non-metallic materials such as metal oxides, nitrides, carbides and carbonitrides, and also ceramic-metal composite materials.

The ceramic layer preferably comprises one or more of Al₂0₃, Cr₂0₃, WC, SiC, TiC, Cr₃C₂, Mo₂C, TiN and/or Si₃N₄. Such materials may be easily applied to the metal substrate, exhibit strong adhesion to the metal substrate and exhibit a high coefficient of friction. These materials are also capable of having favourable levels of elastomer material impregnated therein.

In another aspect, the ceramic layer may comprise a cermet (i.e. a ceramic-metal composite material), for example a WC/Co, Cr₃C₂/NiCr or AI₂0₃/NiCrAIY cermet.

The elastomeric material preferably has a coefficient of friction of up to 1 .5, more preferably from greater than 0.8 to 1 .5. This may increase the coefficient of friction of the outer facing friction surface. The elastomeric material preferably comprises one or more of nitrile butadiene rubber (NBR) and hydrogenated nitrile butadiene rubber (HNBR). Such materials exhibit favourable coefficients of friction and may be easily impregnated into the pores of the ceramic layer.

In a preferred embodiment, the ceramic layer comprises WC and the elastomeric material comprises NBR, more preferably hydrogenated nitrile butadiene rubber (HNBR). Such a combination provides a particularly high coefficient of friction, and the friction component therefore exhibits a particularly improved power transmission when used in a clutch. The friction component preferably further comprises an adhesion promoter between the ceramic layer and the metal substrate. Such an adhesion promoter serves to reduce delamination of the ceramic layer from the metal substrate, thereby increasing the working lifetime of the friction component. Such adhesion promoters may be disposed on the metal substrate using techniques known in the art. The adhesion promoter preferably comprises one or more of Cr, Ni, Ti, Co and/or W. Such species are particularly suitable for promoting adhesion between the ceramic layer and the metal substrate.

The friction component may be a friction disc, friction gear or friction plate.

In a further aspect, the present invention provides a clutch comprising a friction component as described herein. A clutch is a mechanical device that engages and disengages the power transmission, for example from a driving shaft to a driven shaft.

Brief description of the drawings

The invention will now be described with reference to the following non-limiting Figure, in which:

Figure 1 shows a first embodiment of a friction component in accordance with the present invention. Detailed description

Referring to Figure 1 , there is shown a cross-section of a friction component 1 , for example a friction disc or plate, according to the present invention comprising a metal substrate or base 2 and a ceramic layer 3 thereon. The ceramic layer 3 comprises an outer facing friction surface 4 having pores 5 therein. The pores 5 are filled with an elastomeric material 6. The friction component 1 may find application as a friction disc in a clutch, for example when power from a wind turbine is transmitted to a gearbox via a friction disc. High friction torque is required in such an application.

The friction component 1 comprises a metal substrate or base 2, which is formed from a steel or cast iron material. A ceramic layer 3 is provided on the surface of the metal substrate 2. An adhesion promoter (not shown) may be provided between the ceramic layer 3 and the metal substrate 2. Examples of adhesion promoters include one or more of Cr, Ni, Ti, Co and/or W. The ceramic layer 3 advantageously comprises tungsten carbide (WC). The ceramic layer 3 is porous, at least in the outer facing friction surface 4, and comprises pores 5. The outer facing friction surface 4 of the ceramic layer 3 is the working surface of the friction component 1 and, in use, contacts a counter-face (not shown). In Figure 1 , pores 5 are shown only in the region of the outer facing friction surface 4 of the ceramic layer 3. It will be appreciated that the pores 5 may extend into and throughout the ceramic layer 3. That is, typically all or substantially all of the ceramic layer 3 will be porous, not just the outer facing friction surface 4.

The pores 5 are filled with an elastomeric material 6, which is advantageously NBR or HNBR, preferably the latter. Such elastomers have been found to exhibit favourable coefficients of friction in combination with WC for a friction disc. Moreover, such elastomers 6 may be easily impregnated into the pores 5 of the ceramic layer 3.

The outer facing friction surface 4 (i.e. the working surface) of the friction component 1 is therefore formed of the WC ceramic layer 3 having pores 5 filled with the HNBR elastomeric material 6. The outer facing friction surface 4 exhibits a high coefficient of friction. In use, the impregnated elastomer 6 material forms a thin layer between the ceramic layer 3 of the friction component 1 and a counter-face, for example a steel or cast iron counter-face (not shown). Since the elastomeric material 6 has a high coefficient of friction (COF typically up to 1 .5) in contact with, for example, steel, the coefficient of friction of the friction disc is higher than prior art friction components without the elastomeric impregnation (COF typically around 0.6 to 0.8).

Accordingly, when used as a friction disc or plate, for example in a wind turbine, the friction component according to the present invention exhibits an improved power transmission capacity compared with prior art friction components. A higher power transmission capacity may allow the use of a smaller working surface area, which consequently reduces the component size and weight. The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

Claims

CLAIMS:

1 . A friction component for a clutch, the friction component (1 ) comprising a metal substrate (2) and a ceramic layer (3) thereon, said ceramic layer comprising an outer facing friction surface (4) having pores (5) therein, wherein at least some of the pores in said friction surface are filled or partially filled with an elastomeric material (6).

2. A friction component as claimed in claim 1 , wherein the metal substrate (2) comprises steel or cast iron.

3. A friction component as claimed in claim 1 or claim 2, wherein the porosity of the ceramic layer (3) in said friction surface (4) is between 1 and 25%.

4. A friction component as claimed in claim 1 or claim 2, wherein the porosity of the ceramic layer (3) in said friction surface (4) is between 2 and 10%.

5. A friction component as claimed in any one of the preceding claims, wherein the ceramic layer (3) comprises one or more of AI2O3, Cr₂03, WC, SiC, TiC, Cr₃C₂, Mo₂C, TiN and/or Si₃N₄.

6. A friction component as claimed in any one of the preceding claims, wherein the ceramic layer (3) comprises a cermet, preferably a WC/Co, Cr₃C₂/NiCr or AI₂0₃/NiCrAIY cermet.

7. A friction component as claimed in any one of the preceding claims, wherein the elastomeric material (6) has a coefficient of friction of up to 1 .5.

8. A friction component as claimed in any one of the preceding claims, wherein the elastomeric material (6) comprises one or more of nitrile butadiene rubber (NBR) and/or hydrogenated nitrile butadiene rubber (HNBR).

9. A friction component as claimed in any one of the preceding claims, wherein the ceramic layer (3) comprises WC and the elastomeric material (6) comprises hydrogenated nitrile butadiene rubber (HNBR).

10. A friction component as claimed in any one of the preceding claims, wherein the friction component further comprises an adhesion promoter between the ceramic layer (3) and the metal substrate (2).

1 1 . A friction component as claimed in claim 10, wherein the adhesion promoter comprises one or more of Cr, Ni, Ti, Co and/or W.

12. A friction component as claimed in any one of the preceding claims, which is a friction disc, friction gear or friction plate.

13. The friction component of any preceding claim, wherein the metal substrate (2) forms a wheel and the ceramic layer (3) is formed on the radially outermost surface thereof.

14. The friction component of any of claims 1 - 12, wherein the metal substrate forms a disc and the ceramic layer (3) is formed on one or both of the planar surfaces thereof.

15. A clutch comprising a friction component (1 ) as defined in any one of the preceding claims.