Workpiece with improved coating

Abstract

The invention relates to a metallic work-piece (2, 5, 6, 14, 20, 23) for a hydraulic device (1, 15). The workpiece (2, 5, 6, 14, 20, 23) comprises a coating layer (12), characterized in that the coating layer (12) contains Mo, in particular metallic Mo, with a weight fraction of at least 1%.

Claims

1. A hydraulic device comprising a part comprising at least in part a coating layer, wherein the coating layer consists of a weight content of Mo between 80% and 85%, a weight content of Ni between 3% and 4%, a weight content of Cr between 3% and 4%, a weight content of B between 3% and 4%, a weight content of Si between 3% and 4% and a weight content of Fe between 3% and 4%, and wherein the part is movably arranged relative to another part of the hydraulic device.

2. A part for a hydraulic device comprising at least in part a coating layer, wherein the coating layer consists of a weight content of Mo of at least 1%, a weight content of Fe between 75% and 90%, a weight content of C between 0.5% and 2% and a weight content of Mn between 3% and 7%, wherein the part is movably arranged relative to another part of the hydraulic device, wherein the part is in direct contact or in indirect contact with the another part, and wherein indirect contact means there is a layer of lubricant separating the part and the another part.

3. The hydraulic device according claim 1, wherein the coating layer is made from a spray material.

4. The hydraulic device according to claim 3, wherein the spray material comprises particles of sizes in a range from 1 μm to 25 μm.

5. The hydraulic device according to claim 1 wherein the coating layer is present at least at a contacting surface.

6. The hydraulic device according to claim 1, wherein the part is a swash plate, eccentric, piston, piston foot, cylinder, cylinder block, valve, valve plate, valve plate device, valve segment device, ring, liner, plate, bearing or bearing plate device.

7. The hydraulic device according to claim 6, wherein the part is configured for use in a fluid working machine.

8. The hydraulic device according to claim 1, further comprising a second part, the second part comprising at least in part a coating layer, wherein the coating layer consists of a weight content of Mo between 80% and 85%, a weight content of Ni between 3% and 4%, a weight content of Cr between 3% and 4%, a weight content of B between 3% and 4%, a weight content of Si between 3% and 4% and a weight content of Fe between 3% and 4%, and wherein the first part is movably arranged relative to the second part.

9. The part according to claim 2, where the weight content of Fe is between 80% and 85% and/or the weight content of C is between 1% and 1.5% and/or the weight content of Mn is between 4% and 6%.

10. The hydraulic device according to claim 1, wherein the part is in direct contact or in indirect contact with the another part, and wherein indirect contact means there is a layer of lubricant separating the part and the another part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings, wherein the drawings show:

(2) FIG. 1: a possible first embodiment of a fluid working machine comprising several parts, where some of those parts show a partial surface coating, in a schematic cross section;

(3) FIG. 2: a possible second embodiment of a fluid working machine comprising several parts, where some of those parts show a partial surface coating, in a schematic exploded view.

DETAILED DESCRIPTION

(4) In FIG. 1, a possible embodiment of a fluid working machine 1 is shown. In the present case, the fluid working machine 1 is of a hydraulic fluid pump type, where a tilted swash plate 2 (frequently addressed as “wobble plate”) is used for first converting a rotary movement 3 (indicated by arrow 3 around turning shaft 4) into an up-and-down movement of several pistons 5 that move in their respective cylindrical cavities 6. The cylindrical cavities 6 are arranged in a valve block 14 that remains stationary. By the up-and-down movement of the pistons 5, the volume that is enclosed by the pistons 5 and the cylindrical cavity 6 is repetitively expanding and contracting. Furthermore, fluid inlet channels 7 and fluid outlet channels 8 fluidly connect to the cylindrical cavities 6 with appropriately arranged check valves 9 arranged in the fluid channels 7, 8. As already mentioned, and as it is typical for a fluid working machine 1 of the embodiment shown, the valve block 14 remains (essentially) stationary. However, it is of course not ruled out that the fluid working machine 1 is used for mobile applications. Therefore, in the context of the present application “stationary” or “fixedly” are typically to be interpreted with respect to the imminent environment (for example with respect to the reference frame of a vehicle). As an additional remark, different designs apart from the presently shown design with check valves 9 are certainly possible as well. Just to name another possibility: a valve plate (valve plate device, valve segment, or the like) could be used additionally and/or alternatively.

(5) Based on the repetitive expansion and contraction of the fluid volume enclosed by the cylindrical cavities 6 and the pistons 5, fluid will be pumped from a low pressure reservoir 10 to a high pressure reservoir 11 (presently not shown in detail), when rotary action is performed on the rotating shaft 4. Such a device is as such known in the state of the art.

(6) The invention lies in the surface coating 12 (indicated by hatched areas) that is arranged on parts of the pistons 5 (cylindrical part), parts of the inside walls of the cylindrical cavities 6, parts of the surface of the swash plate 2 and parts of the surface of the contacting balls 13 that are arranged on the lower parts of the pistons 5, where the contacting balls 13 are designed to be in driving contact with the swash plate 2.

(7) It is to be understood that (at least part of) the gist of the invention lies in the various parts that show a surface coating as discussed later on and the surface coating itself.

(8) It has to be also understood that the various surface coatings 12 can of course be applied to different parts and/or for different embodiments of the fluid working machine 1 as well. In particular, when additionally and/or alternatively to the presently shown check valves 9, a valve plate (or similar device) is used, additional and/or other surface parts should preferably show a surface coating (while some surface parts might not need a surface coating any more).

(9) Furthermore, such appropriately coated parts can be used for different machinery as well. To just name a few examples from the technical field of hydraulics: the parts could be used for hydraulic pumps, for hydraulic motors, for combined hydraulic pumps/motors, for fluid working machines (pumps, motors, combined pumps and motors) of various designs like a tilted plate type; a type with a twistable tilted plate; a fluid working machine using an eccentric that is driving piston feet; a fluid working machine with a rotating cylinder block; a fluid working machine with a valve plate (or a similar device); and so on (where a fluid working machine showing a combination of the aforesaid and possibly even more features is possible as well). Surface coatings in the presently shown embodiment have a thickness of some 200 μm (where some variations can of course occur). Furthermore, it is usually not too problematic if the surface coatings 12 show some variations with respect to their thickness. For example, a nominal surface thickness of (let's say) 200 μm show some variations between 190 μm and 210 μm or even 180 μm to 220 μm without resulting in any noticeable adverse effects (at least usually).

(10) The surface coating 12 is presently applied using a plasma spraying technique, a method that is well known in the state of the art. Presently, for plasma spraying particles of a size of some 10 μm are used (with some variations of ±5 μm). However, the invention is not limited to such sizes and/or to a plasma spray coating method. Essentially all coating techniques can be used likewise, in particular HVOF-techniques (high velocity oxy fuel spraying). Additionally and/or alternatively, particles of a different size can be used as well.

(11) In the present embodiment plasma spraying is based on an arc formation between an anode and a cathode, which leads to the ionisation of a reaction gas, forming a plasma. The coating material is introduced into the plasma and melted due to the high temperature it experiences by those conditions. However, the exact details can vary, of course.

(12) The surface coatings 12 of some surface areas of some parts of the fluid working machine 1 are only applied on those surface parts, where a high probability of a sliding contact between two different parts is present (i.e. such surface areas, where during use of the fluid working machine a relative movement between two different surface parts will usually take place).

(13) In the present embodiment, the surface coatings 12 are therefore limited to the upper side of the swash plate 2 (neighbouring the pistons 5 and the block in which the cylindrical cavities 6 are arranged). On this surface side of the swash plate 2, contacting balls 13 that are arranged on the lower side of the various pistons 5 are in driving contact with the (turning) swash plate 2. Furthermore, the lower half spheres of the contacting balls 13 show a surface coating 12 as well. It is easily understandable that by the surface coatings 12 on the upper side of the swash plate 2 and on the lower spherical half of the contacting balls 13 all surface parts of the contacting balls 13 of the swash plate 2 that can come into sliding contact with each other during normal operation conditions of the working machine 1 show a surface coating 12 in between. Therefore, only a sliding contact between surface coatings is present here (where, of course, a dry sliding without any hydraulic oil can occur in certain operating conditions, like in a malfunction of an oil pump, under severe load and/or in very adverse operating conditions and/or when the fluid working machine has just been started and the oil circuit has been not yet been fully established).

(14) Nevertheless, due to the surface coatings 12, even when dry friction between the contacting surfaces occurs, a lower friction and a lower wear occurs as compared to the case, where no surface coating is present and the (typically metal) parts 2, 13 are in direct contact with each other.

(15) The big advantage of the presently used surface coating 12 is that it is essentially lead-free, i.e. that (apart from some residual contaminations) the surface coating does not contain any lead.

(16) As a remark it should be noted that it is even sufficient that the top surface of the swash plate 2 shows only a ring-like coating so that a sliding contact between the contacting balls 13 and the swash plate 2 is only established with surface parts, showing a surface coating. However, applying only a ring on top of the swash plate is usually comparatively difficult to achieve. Therefore, it is usually cheaper to coat the complete top surface of the swash plate 2. Likewise, additional surface parts of the various parts that are shown in FIG. 1 could be covered with a surface coating as well (to name an example, the pistons 5 could be “completely covered” with a surface coating).

(17) As can be seen from FIG. 1, surface coatings 12 are also applied on the (outer) cylindrical surfaces of the pistons 5 and on the (inner) cylindrical surfaces of the cylindrical cavities 6. As it is easily understandable, here a sliding movement between the contacting surfaces of the pistons 5 and the cylindrical cavities 6 occurs when the pistons 5 are moving up and down under typical operating conditions of the fluid working machine 1.

(18) Presently, two specific embodiments of surface coatings 12 have been investigated and measured, and the results have been compared to presently used surface coatings, comprising a bronze layer with a lead content.

(19) In particular, as substance 1 a material with the content formula Mo25 (NiCrBSiFe) was used, while as substance 2, a material with the content formula Fe16Mo2C0.25Mn was used.

(20) The surface coating was applied with a nominal thickness of 200 μm. This was compared to a lead-containing bronze, as it is available in the state of the art. The lead-containing bronze was also applied with a nominal thickness of 200 μm.

(21) All surface coatings have been applied on a C22 steel substrate according to DIN EN 10083-2, consisting of pearlite and ferrite phases. The hardness of the substrate was given by 195±4 HV0.2, and the flatness was quoted to be 13.38±1.08 μm. Measurements showed that the roughness of the respective coatings after lapping is according to table 1.

(22) TABLE-US-00001 Rpk/μm Rk/μm Rvk/μm Lead-containing 0.503 ± 0.013  1.17 ± 0.013 0.666 ± 0.014 bronze Substance 1 0.136 ± 0.007 0.664 ± 0.01   1.57 ± 0.079 Substance 2 0.457 ± 0.016 1.858 ± 0.031 2.356 ± 0.128

(23) When measurements were performed, the micro hardness measurements (HV0.2) on the basis of a metallographic cut was 126 for the reference lead-containing bronze layer, while for substance 1 the micro hardness was approximately 500 HV0.2 and for substance 2 the micro hardness was approximately 460 HV0.2. Likewise, the adhesive strength of the thermally sprayed coatings was measured to be 37 N/mm.sup.2 for substance 1 and 41 N/mm.sup.2 for substance 2.

(24) The seizure test (coefficient of friction against time) showed a coefficient of friction of approximately 0.11 after 60 sec. of test run for both substances (substance 1 and 2) which is almost the same as for lead-containing bronze according to the state of the art (0.11 after 60 sec. as well).

(25) Finally, the critical contact pressure to the end of the seizure test is even advantageous over lead-containing bronze. While the lead-containing bronze layer showed a critical contact pressure of 650 N/mm.sup.2, substance 1 showed a critical contact pressure of 1250 N/mm.sup.2, while substance 2 showed a critical contact pressure of 1070 N/mm.sup.2.

(26) In short, it can be seen that the presently investigated materials, both containing molybdenum to a certain relevant extent, show even mechanical advantages over presently used lead-containing bronze. The advantage of environmental friendliness due to the absence of lead is of course obvious.

(27) As already mentioned above, the afore described and/or presently suggested surface coatings 12 can be advantageously used for other surfaces, parts, devices, surface parts, fluid working machines and/or so on. Therefore, to elucidate the present invention and its advantages and applicability in more detail, in the following, a second possible embodiment of a fluid working machine 15 will be described with reference to FIG. 2. In particular, some kind of a “combination” of the embodiments of a fluid working machine 1 according to FIG. 1 and of a fluid working machine 15 according to FIG. 2 is possible as well (in particular by combining certain features), although this is not explicitly described. Such a “combination” is of course not limited to the presently shown and described embodiments of a fluid working machine 1, 15.

(28) In FIG. 2, a second possible embodiment of a fluid working machine 15, comprising a rotatable cylinder block 14, is shown in a schematic exploded view. For the sake of clarity, some parts are not shown and/or are not shown in detail. Furthermore, for the sake of simplicity, identical reference numerals are used for parts that are similar in function. Therefore, an identical reference numeral does not necessarily imply that the respective parts are identical in function and/or have the same design in both embodiments.

(29) According to the embodiment of FIG. 2, a fluid working machine 15 with a rotatable cylinder block 14 (as indicated by rotating arrows 16) is suggested that shows several surface coatings 12.

(30) In operation, the cylinder block 14 is rotated under the action of a turning shaft 4. Turning shaft 4 and cylinder block 14 are, for example, connected in a torque proof manner, using corresponding protrusions and indentations (for example in toothed wheel like manner). To “compensate” for the now-rotating cylinder block 14 (as compared to the embodiment of FIG. 1), the tilted plate 18, on which the piston feet 17 of the pistons 5 rest (in FIG. 2 only a single piston 5 is shown for simplicity), is now arranged fixedly (i.e. not rotating). This does not necessarily rule out that the angle of the tilted plate 18 can possibly be changed during operation.

(31) When the rotating cylinder block 14 rotates, the pistons 5 are carried along together with the rotating cylinder block 14. Therefore, the piston feet 17 slide along the tilted plate 18 and move up-and-down due to the inclination of the tilted plate 18. Therefore, the pistons 5 move back and forth in their respective cylindrical cavities 6 that are arranged inside the cylinder block 14. This translates into an internal volume of a repetitively changing size that can be used for pumping hydraulic fluid and/or for transforming pressure energy into a movement (similar to the embodiment of a fluid working machine 1 according to FIG. 1).

(32) As a consequence of the rotation of the cylinder block 14, the outer circumferential surface 19 of the cylinder block 14 shows a surface coating 12, since the outer circumferential surface 19 of the cylinder block 14 is in sliding arrangement with a corresponding supporting surface (not shown). Of course, the outer circumferential surfaces of the pistons 5 and the inner circumferential surfaces of the cylindrical cavities 6 show surface coatings 12 as well (necessitated by the sliding contact between the cylindrical cavities 6 and the pistons 5).

(33) In the presently shown embodiment, the cylindrical cavities 6 are designed as simple through bores. It is easy to understand that such a design is particularly simple to manufacture. Therefore, “on top” of the cylinder block 14, a bearing plate 20 is arranged. The bearing plate 20 is fixed in a torque proof (and fluid tight) manner to the cylinder block 14. Thus, the bearing plate 20 rotates together with the cylinder block 14 (as indicated by rotating arrow 16). To realise a simple but effective torque proof connection between the cylinder block 14 and the bearing plate 20, protruding pins 21 that fit into corresponding holes 22 are presently used (of course, different arrangements can be used as well). The bearing plate 20 shows several openings 24, that are typically in fluid connection with the cylindrical cavities 6, but do not have the same cross sections as the cylindrical cavities 6.

(34) On the surface side of the bearing plate 16, lying opposite to the cylinder block 14 (and neighbouring the valve plate 23), a valve plate 23 is arranged. The neighbouring surfaces of the bearing plate 20 and of the valve plate 23 are in sliding contact with each other. Consequently, the respective surfaces are provided with surface coatings 12.

(35) The valve plate 23 is fixedly arranged (i.e. it is not rotating together with the cylinder block 14 and/or the bearing plate 20). As indicated in FIG. 2, the valve plate 23 also shows several openings 25.

(36) The openings 25 in the valve plate 23 and the openings 24 in the bearing plate 20 are designed and arranged in a way that they “mimic the behaviour” of active and/or passive valves when the cylinder block 14/bearing plate 20 rotates with respect to the valve plate 24, so that a pumping behaviour and/or a motoring behaviour of the fluid working machine 15 is realised. Such a design is known as such in the state-of-the-art and presently not further described for brevity.

(37) Thanks to the various surface coatings 12 on the various surface parts of the various parts of the fluid working machine 15, a reliable and wear resistant fluid working machine 15 with a long lifetime and comparatively low friction can be realised.

(38) 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.