METHOD FOR PRODUCING A WATER-HYDRAULIC MACHINE

Abstract

A method for producing a water-hydraulic machine having a first member (1) and a second member (2) in sliding contact with a contact surface (3) of the first member (1), wherein the second member (2) comprises a surface made of a friction reducing plastic material and the contact surface (3) is a metallic surface, is disclosed. The machine should have a low risk of damages. To this end, the method includes the steps of using a first member (1) comprising a first part (4) having the contact surface (3) and a second part (5), using a high temperature hardening process at a temperature of at least 1000 C. to give a deep surface hardening of the contact surface (3) of the first part (4), machining of the first part (4) to the desired geometry, assembling the first part (4) and the second part (5) to form the first member.

Claims

1. A method for producing a water-hydraulic machine having a first member and a second member in sliding contact with a contact surface of the first member , wherein the second member comprises a surface made of a friction reducing plastic material and the contact surface is a metallic surface, characterized in that the method comprises the steps of: using a first member comprising a first part having the contact surface and a second part , using a high temperature hardening process at a temperature of at least 1000 C. to give a deep surface hardening of the contact surface of the first part machining of the first part to the desired geometry assembling the first part and the second part to form the first member.

2. The method according to claim 1, wherein the high temperature hardening process is carried out in the presence of nitrogen.

3. The method according to claim 1, characterized in that wherein a low temperature hardening process at a temperature of 550 C. or lower is used to give a final super hard contact surface of the first part.

4. The method according to claim 1, wherein at least the contact surface is polished.

5. The method according to claim 1, wherein the first part is chosen to have a smaller thickness than the second part.

6. The method according to claim 5, wherein the thickness of the first part is equal to or smaller than 10 mm.

7. The method according to claim 1, wherein the first part is chosen to be symmetric with respect to an axis located in the contact surface.

8. The method according to claim 7, wherein the first part is chosen to be symmetric with respect to a second axis located in the contact surface and being orthogonal to the first axis.

9. The method according to claim 1, wherein the first part is chosen to be of stainless steel.

10. The method according to claim 9, wherein the first part is chosen to be duplex steel or super duplex steel or 316 steel.

11. The method according to claim 2, wherein a low temperature hardening process at a temperature of 550 C. or lower is used to give a final super hard contact surface of the first part.

12. The method according to claim 2, wherein at least the contact surface is polished.

13. The method according to claim 3, wherein at least the contact surface is polished.

14. The method according to claim 2, wherein the first part is chosen to have a smaller thickness than the second part.

15. The method according to claim 3, wherein the first part is chosen to have a smaller thickness than the second part.

16. The method according to claim 4, wherein the first part is chosen to have a smaller thickness than the second part.

17. The method according to claim 2, wherein the first part is chosen to be symmetric with respect to an axis located in the contact surface.

18. The method according to claim 3, wherein the first part is chosen to be symmetric with respect to an axis located in the contact surface.

19. The method according to claim 4, wherein the first part is chosen to be symmetric with respect to an axis located in the contact surface.

20. The method according to claim 5, wherein the first part is chosen to be symmetric with respect to an axis located in the contact surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will now be described in more detail with reference to the drawing, which show:

[0021] Only FIGURE: A schematic flow diagram of the method.

DETAILED DESCRIPTION

[0022] The FIGURE shows schematically members of a water-hydraulic machine, more precisely a first member 1 in form of a swash plate and a second member 2 in form of a slide shoe. The invention can, however, be used in connection with another pairing of elements, for example cylinder drum and valve plate. The first member comprises a metallic contact surface 3. The second member 2 is in sliding contact with the contact surface 3. In order to be able to use water as hydraulic fluid, the second member 2 is provided with a coating of a friction reducing plastic material, for example Polyetheretherketon (PEEK) at least at the side facing the contact surface 3.

[0023] In order to keep the risk of damages of the contact surface 3 low, it is desired to make the contact surface 3 as hard as possible.

[0024] To this end, the first member 1 is designed to have two parts, namely a first part 4 having the contact surface 3 and a second part 5.

[0025] The first part 3 is symmetric at least with respect to a first axis of symmetry located in the contact surface. However, it is preferred that the first part 4 is symmetric with respect to a second axis of symmetry located in the contact surface as well and being orthogonal to the first axis of symmetry.

[0026] Furthermore, the first part 4 is chosen to have a smaller thickness than the second part 5. The thickness of the first part 4 is equal to or smaller than 10 mm.

[0027] Only the first part 4 is subjected to a hardening process at a temperature of at least 1000 C. and preferably in the presence of nitrogen. Such a hardening process is described in more detail in EP 2 841 617 B1. This process is abbreviated with high temperature hardening process 6.

[0028] During this high temperature hardening process 6 the first part 4 distorts. However, the distortion is small due to the symmetry.

[0029] In a machining step 7 the first part 4 is machined to the desired geometry. This means that some of the hardened surface layer of the first part 4 is removed.

[0030] In a following low temperature hardening process 8 the first part 4 is provided with a super-hard surface layer. The flow temperature hardening is performed at a temperature in the range of 450 C. to 550 C. The super-hard surface layer has a thickness of approximately 100 m and a hardness of 1000 HV (Vickers hardness) or more.

[0031] The low temperature hardening process 8 again leads to a distortion of the first part 4. However, this distortion is smaller than the distortion caused by the high temperature hardening process 6.

[0032] Following to the low temperature hardening process 8 the part 4 is polished in a polishing step 9. In the polishing step 9 part 4 is polished to required flatness tolerances. Due to the smaller distortions, polishing is sufficient to achieve the desired geometry.

[0033] After the polishing step 9 the first part 4 and the second part 5 are assembled, for example, by screws or glue. It is possible to use other assembly technics. Furthermore, in some cases it is not necessary to connect the two parts, e. g, when a pressure or a force produced by spring means acting on one of the two parts is sufficient to hold the two parts together. In this case it might be necessary to use something to align the two parts.

[0034] Achieved is a final product, i.e. the first member 1, having an exact geometry and a high surface hardness with a thickness of the hardened surface of approximately 50 m.

[0035] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.