Ball joint which is resistant to wear and high temperatures, and method for manufacturing the ball joint

Abstract

A spherical ball joint has an outer ring 2 of a nickel based material with a carbonitriding layer on a spherical inner surface 2a sliding on an inner ring 3 of a cobalt-based or nickel-based material

Description

Title: Ball joint which is resistant to wear and high temperatures, and method for manufacturing the ball joint Technical field of the invention The present invention relates to the field of ball joints and, more particularly, to the field of the composition of the inner and outer rings of ball joints. More precisely, the invention relates to the reduction of the wear of a ball joint by exploiting a particular composition of the outer ring of a ball joint. The invention also relates to a support system for supporting an engine on its housing, and to the method for manufacturing such a ball joint and such a support system. A support system comprises conventional ball joints and / or shackles incorporating ball joints for supporting the engine in its housing. These components are generally made of a nickel or cobalt alloy, which are materials resistant to the high temperatures generated by the combustion of the combustion chamber of the engine. The ball joints allow the support system to be flexible during thermal expansions of the engine. A ball joint comprises an inner ring and an outer ring respectively comprising an outer surface and an inner surface in contact with one another. The synergy between the inner ring and the outer ring nevertheless has limited advantages in terms of high temperature, since there is wear of the materials of the rings over time. The outer ring of the ball joint may be a component added onto the support system and fastened by any suitable means, for example by a nut or by crimping, or may else be formed directly in the support system. Prior art Up until now, to limit the wear of the ball joints, an inner ring comprising a cobalt alloy and an outer ring comprising a nickel alloy have conventionally been used. The combination of these materials allows good sliding behaviour of one ring with respect to the other. However, the wear still remains too high for this assembly and therefore necessitates regular maintenance of the engine support system, which generates costs. Summary of the invention The invention thus aims to significantly reduce the wear due to the friction between the rings of a ball joint and makes it possible to increase the fatigue life of the components. One subject of the invention is a ball joint comprising an outer ring and an inner ring respectively comprising a spherical inner surface and a spherical outer surface in contact with one another. Said outer ring comprises a nickel-based material and an outer layer obtained by carbonitriding at least the inner surface of said outer ring, and said inner ring comprises a cobalt-based or nickel-based material. With such a combination of materials, the wear caused by friction of the outer and inner rings of the ball joint is reduced. Advantageously, the outer ring comprises an outer surface radially opposite the inner surface, said outer surface of the outer ring being obtained by carbonitriding at least the inner and outer surfaces. Advantageously, the outer ring is made of a nickel-based alloy, in particular of formula NiCrl9Fel8Nb. According to one embodiment, the inner ring is made of a cobalt-based alloy, in particular of a cobalt alloy of formula CoCr29W5. Alternatively, the inner ring may be made of a nickel-based alloy, in particular of a nickel alloy of formula NiCrl9Fel8Nb and comprises a cobalt-based coating, said coating being positioned over all or part of the outer surface of the inner ring. Preferably, the inner ring is a solid-type ring made of cobalt alloy or nickel alloy. The term "solid-type ring" is understood to mean a ring whose shape is obtained by machining with material removal (turning, grinding) from tubes, bars or forged and / or rolled blanks. Advantageously, the outer layer of the outer ring has a thickness of between 2 pm and 20 pm, preferably between 5 pm and 10 pm. According to one embodiment, the inner ring comprises a bore radially opposite the spherical outer surface and said ball joint comprises a sleeve which 3 is mounted in the bore of the inner ring and comprises an outer surface radially in contact with the bore. The sleeve may comprise a nickel-based material, more particularly an alloy of formula NiCrl9Fel8Nb. Another subject of the invention is a method for manufacturing a ball joint as defined above. The method comprises at least the following steps: - step of providing an outer ring comprising a nickel-based material, and an inner ring comprising a cobalt-based or nickel-based material, - step of carbonitriding at least the inner surface of the outer ring, - step of assembling the outer ring with the inner ring. Advantageously, the method comprises, before the step of assembling the outer ring with the inner ring, a step of treating the inner ring, said inner ring comprising an outer surface covered entirely or in part with a cobalt-based coating, preferably an alloy of formula CoCr29W5. Brief description of the figures Other aims, features and advantages of the invention will become apparent upon reading the following description, which is given purely by way of non-limiting example and with reference to the appended drawings, in which: [Fig 1] illustrates a ball joint according to one exemplary embodiment of the invention; [Fig 2] is a front view of the ball joint of Figure 1; [Fig 3] is a sectional view of the ball joint of Figure 1; and [Fig 4] illustrates the steps of the method for manufacturing a ball joint according to one mode of implementation of the invention. Detailed description of the invention Figures 1, 2 and 3 illustrate a ball joint 1 in a reference frame (X, Y, Z) according to the invention, comprising an outer ring 2 and an inner ring 3 which are coaxial along the axis X. As illustrated in Figure 2, the outer ring 2 comprises a concave spherical inner surface 2a or bore, an outer surface 2b radially opposite the inner surface 2a, and two opposite radial end faces (not referenced) axially delimiting the inner 2a and outer 2b surfaces. The inner ring 3 comprises a convex spherical outer surface 3b on which the inner surface 2a of the outer ring 2 is mounted, a cylindrical bore 3a radially opposite the outer surface 3b, and two opposite radial end faces (not referenced) axially delimiting the bore 3a and the outer surface 3b. The inner 2a and outer 3b surfaces of the outer 2 and inner 3 rings are in contact with one another and have a complementary shape. The outer ring 2 comprises a nickel-based material, particularly an alloy of formula NiCrl9Fel8Nb, and an outer layer obtained by carbonitriding at least its inner surface 2a. This outer layer has a thickness of between 2 pm and 20 pm, preferably between 5 pm and 10 pm. The outer surface 2b and the end faces of the outer ring 2 may also be treated by carbonitriding such that the outer ring 2 is entirely covered with the outer layer. The inner ring 3 comprises a cobalt alloy of formula CoCr29W5, or a nickel alloy of formula NiCrl9Fel8Nb and may in this case comprise a cobalt-based coating, particularly of formula CoCr29W5. The coating covers all of the outer surface 3b of the inner ring 3 or only a part. Sliding between the inner surface 2a of the outer ring, which comprises a carbonitriding layer, and the inner ring 3, which comprises a cobalt-based or nickel-based alloy, causes very little wear. In the exemplary embodiment illustrated, the ball joint 1 also comprises a sleeve 4 which is mounted in the bore 3a of the inner ring 3 and which forms the bore of the ball joint 1. The sleeve 4 has an annular shape. The sleeve 4 has an outer surface 4a radially in contact with the bore 3a of the inner ring 3. In a manner known per se, the sleeve 4 and the inner ring 3 are assembled together by radial interposition of an elastic retaining ring 5 inside grooves formed on the outer surface 4a of the sleeve 4 and on the bore 3a of the inner ring 3. The sleeve 4 comprises a nickel-based material, more particularly an alloy of formula NiCrl9Fel8Nb. In another embodiment, the ball joint 1 could be deprived of the sleeve 4. In the exemplary embodiment illustrated, the outer ring 2 of the ball joint 1 comprises a fastening flange 6 radially outwardly extending one of the 5 axial ends of the outer surface 2b. Alternatively, the outer ring 2 of the ball joint 1 could be deprived of the flange 6. The invention also proposes a method for manufacturing a ball joint 1 as described above. The method for manufacturing a ball joint 1 comprises at least three steps illustrated by Figure 4. The method first of all comprises a step El of providing an outer ring 2 comprising a nickel-based material, and an inner ring 3 comprising a cobaltbased or nickel-based material. Next, the method comprises a step E2 of carbonitriding the inner surface 2a of the outer ring 2. It is also possible to envisage carbonitriding the outer surface 2b and the end faces of the outer ring 2. This carbonitriding step E2 may, for example, comprise two substeps, a first case-hardening substep E3 and a second nitriding substep E4, which is carried out simultaneously or successively to the first substep E3 and in the same heat treatment cycle. A heat treatment cycle is characterized by raising the temperature from a low initial temperature to a high temperature, maintaining the high temperature, then lowering the temperature to a temperature close to the low initial temperature. For example, a heat treatment cycle corresponding to the step E2 of carbonitriding the inner surface 2a of the outer ring 2 starts with the first case-hardening substep E3, which uses acetylene to supply carbon, and continues with the second nitriding substep E4, which uses ammonia to supply nitrogen. The temperature of this heat treatment cycle may, for example, be between 400°C and 500°C and is maintained for the time necessary to achieve the desired carbon and nitrogen enrichment of the treated inner surface 2a. The carbonitriding step E2 ends with a rapid lowering of the temperature of the outer ring 2. The treated outer ring 2 is, for example, brought back down to ambient temperature. The carbonitriding treatment may last from 10 to 50 hours depending on the chosen thickness. Finally, the method comprises a step E5 of assembling the inner 3 and outer 2 rings together. Optionally, the method for manufacturing the ball joint 1 may further comprise a step E6 of treating the inner ring 3. During this step, the outer surface 3b of the inner ring 3 may be covered entirely, or only in part, with a cobalt-based coating, preferably an alloy of formula CoCr29W5. The present invention has been illustrated on the basis of a ball joint comprising an inner ring and an outer ring which is intended to be added onto 5 the associated support system. It would not be a departure from the scope of the invention if the outer ring of the ball joint were constituted directly by a component of the support system by machining to form the inner surface of said outer ring. 7

Claims

1. Ball joint (1) comprising an outer ring (2) and an inner ring (3) respectively comprising a spherical inner surface (2a) and a spherical outer surface (3b) in contact with one another, characterized in that the outer ring (2) comprises a nickel-based material and an outer layer obtained by carbonitriding at least the inner surface (2a) of said outer ring (2), and in that the inner ring (3) comprises a cobalt-based or nickel-based material.

2. Ball joint (1) according to Claim 1, wherein the outer ring (2) comprises an outer surface (2b) radially opposite the inner surface (2a), said outer layer of the outer ring being obtained by carbonitriding at least the inner (2a) and outer (2b) surfaces.

3. Ball joint (1) according to either of Claims 1 and 2, wherein the outer ring (2) comprises an alloy of formula NiCrl9Fel8Nb.

4. Ball joint (1) according to any one of Claims 1 to 3, wherein the inner ring (3) comprises an alloy of cobalt of formula CoCr29W5.

5. Ball joint (1) according to any one of Claims 1 to 3, wherein the inner ring (3) comprises a nickel alloy of formula NiCrl9Fel8Nb, and comprises a cobalt-based coating, said coating being positioned over all or part of the outer surface (3b) of the inner ring (3).

6. Ball joint (1) according to any one of Claims 1 to 5, wherein the outer layer of the outer ring (2) has a thickness of between 2 pm and 20 pm, preferably between 5 pm and 10 pm.

7. Ball joint (1) according to any one of Claims 1 to 6, wherein the inner ring (3) comprises a bore (3a) radially opposite the spherical outer surface (3b), and said ball joint (1) further comprises a sleeve (4) which is mounted in the bore (3a) of the inner ring and comprises an outer surface (4a) radially in contact with said bore.

8. Ball joint (1) according to Claim 7, wherein the sleeve (4) comprises a nickel-based material, more particularly an alloy of formula NiCrl9Fel8Nb.

9. Method for manufacturing a ball joint (1) according to any one of Claims 1 to 8, characterized in that it comprises at least the following steps:- step (El) of providing an outer ring (2) comprising a nickel-based material, and an inner ring (3) comprising a cobalt-based or nickel-based material,- step (E2) of carbonitriding at least the inner surface (2a) of the 5 outer ring (2),- step (E5) of assembling the outer ring (2) with the inner ring (3).

10. Method for manufacturing a ball joint (1) according to Claim 9, comprising, before the step (E5) of assembling the outer ring (2) with the inner ring (3), a step (E6) of treating the inner ring (3), said inner ring (3) comprising 10 an outer surface (3b) covered entirely or in part with a cobalt-based coating, preferably an alloy of formula CoCr29W5.

Images