WO1998041771A1

WO1998041771A1 - Track and/or hinge pin having improved abrasion, corrosion and galling resistance

Info

Publication number: WO1998041771A1
Application number: PCT/US1998/002472
Authority: WO
Inventors: Peter W. Anderton; Chuong Q. Dam; Gary K. Shearburn; Dennis R. Shookman
Original assignee: Caterpillar Inc.
Priority date: 1997-03-19
Filing date: 1998-02-06
Publication date: 1998-09-24

Abstract

An abrasion, corrosion and galling resistant pin (10) comprises a cylindrical shape, an outer surface (50), a first end portion (20), a second end portion (30) and a middle portion (40). The pin (10) also comprises a first bearing surface (22) defining the first end portion (20) and a second bearing surface (32) defining the second end portion (30). An abrasion resistant coating (60) is deposited on at least one of the first bearing surface (22) and the second bearing surface (32). The coating (60) is selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof.

Description

TRACK AND/OR HINGE PIN HAVING IMPROVED ABRASION. CORROSION AND GALLING RESISTANCE

Technical Field

The present invention relates generally to track pins used in track bushings for linking track links in the endless track of a track-type machine, and hinge pins used in hinge joints of loader linkage mechanisms, and more particularly to a track pin and/or hinge pin having a coated surface for improved abrasion, corrosion and galling resistance.

Background Art

The track pins used in the bushings for linking the track links in the endless track of a track type machine, such as an earthmoving machine for example, are subjected to a very severe operating environment. The end portions of a track bushing and the inner surface of the track bushing adjacent its two end portions are the main bearing surfaces that respectively slide against a track seal and a track pin. The end portions of the track bushing slide against a seal lip of a mechanical face seal, or a track seal. The track seal keeps oil from leaking out of the pin joint. After prolonged use, dirt and debris particles eventually get trapped under the seal lip and wear grooves into the bushing ends. Once the dirt gets into the joint, during operation, dirt and debris particles tend to work their way into the clearance between the track pin and the bushing and eventually wear the outer surface of the track pin and/or the inner surface of the track bushing. Further, due to the high loads being applied to the joint assembly, the oil gets sgueezed out of clearance between the pin and bushing, creating an oil-starved situation. The respective surfaces get hot due to friction and this situation results in metal-to-metal transfer between the track pin and the track bushing, a phenomenon called "galling". In fact, it is observed that during "galling", metal from the track pin is transferred and welded on to the bushing.

It is desirable to provide a track pin that has a very hard, highly corrosion resistant coating that protects the track pin from abrasion, corrosion and galling. It is also very desirable to provide a track bushing having a hard coating on its inner surface so as to prevent galling. It is also desirable to generally improve the surface finish of the aforementioned bearing surfaces of a track pin and track bushing so that they are more resistant to friction and wear. It is further desirable to prevent abrasion, corrosion and galling in the hinge mechanisms of loader linkages which use similar pin and bushing arrangements. The present invention is directed to overcome one or more problems of heretofore utilized track pins and other hinge pins for various track-type and wheeled machines.

Disclosure of the Invention

In one aspect of the present invention, an abrasion, corrosion and galling resistant pin is disclosed. The pin comprises a cylindrical shape, an outer surface, a first end portion, a second end portion and a middle portion. The pin also comprises a first bearing surface defining the first end portion and a second bearing surface defining the second end portion. An abrasion resistant coating is deposited on at least one of the first bearing surface and the second bearing surface. The coating is selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof.

In another aspect of the present invention, a track pin for an endless track of a track-type machine is disclosed. The track pin comprises a cylindrical shape, an outer surface, a first end portion, a second end portion and a middle portion. The track pin also comprises a first bearing surface defining the first end portion and a second bearing surface defining the second end portion. A chromium nitride coating is deposited on the first bearing surface and the second bearing surface.

In yet another aspect of the present invention, in a pin having a cylindrical shape, an outer surface, a first end portion, a second end portion and a middle portion, a first bearing surface defining the first end portion and a second bearing surface defining the second end portion, an improvement is disclosed. The improvement comprises depositing an abrasion resistant coating on at least one of the first bearing surface and the second bearing surface, the coating being selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof.

Brief Description of the Drawings

FIG. 1 is a side view of a preferred embodiment of a track pin of the present invention.

Best Mode for Carrying; Out the Invention

Referring to FIG. 1, a track pin 10 for a bushing for an endless track of a track-type machine is shown. The track pin 10 comprises a first end portion 20, a second end portion 30 and a middle portion 40. The track pin 10 also comprises a cylindrical shape and an outer surface 50. The track pin 10 further comprises a first bearing surface 22 defining the first end portion 20 and a second bearing surface 32 defining the second end portion 30. The track pin 10 still further comprises an abrasion resistant coating 60 deposited on at least one of first bearing surface 22 and second bearing surface 32. The coating 60 is selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof.

In the preferred embodiment of the present invention, coating 60 has a thickness desirably in the range of about 0.0005 mm to about 0.01 mm, and preferably, in the range of about 0.001 mm to about 0.005 mm. A thickness less than 0.0005 mm is undesirable because the coating tends to wear too soon. A thickness greater than 0.01 mm is undesirable because the coating can spall, resulting in premature wear. It is further preferred that the coating have a uniform thickness of about 0.0025 mm and a macroparticle size desirably no greater than 2 μm and preferably no greater than 1 μm. It is desirable to deposit the coating on each of the first and second bearing surfaces for a linear length of at least 50%, more desirably at least 30% and preferably in the range of about 15% to about 25%, of the total length of the pin in order to obtain superior abrasion and galling resistance. It is understood that when each coated bearing surface represents 50% of the total axial pin length, essentially the entire pin outer surface acts as the coated bearing surface. The total length of the pin is the sum total of the lengths of the first portion, the second portion and the middle portion. In the preferred embodiment, the coating is deposited by vapor deposition techniques and is preferably deposited on both the first bearing surface and the second bearing surface to get maximum corrosion and galling resistance.

In the preferred embodiment, the coating is deposited on both bearing surfaces and it is preferred that the total coated bearing area of the pin be at least 30% of the total outer surface area. This is desirable to obtain at least a 100% increase in the galling resistance.

In the preferred embodiment of the present invention, the coating 60 is desirably, selected from one of chromium nitrides and chromium carbonitrides, or mixtures thereof. Preferably, the coating is chromium nitride. CrN is preferred because it has been observed during performance tests that the abrasion, corrosion/erosion and galling resistance is much superior as compared to other coatings.

The coating is deposited desirably, by any one of the vapor deposition techniques, such as physical vapor deposition, chemical vapor deposition and arc vapor deposition. In the preferred embodiment of the present invention, the chromium nitride coating 60 is deposited by arc vapor deposition process which comprises the following steps: An arc source is provided. The arc source is adapted to impart a positive charge on the vapor generated. A negative bias voltage of about 50 volts is applied to the race substrate by a voltage source. A vapor deposition coating 60 is deposited on the track pin bearing surfaces. Such coating methods are well known to those skilled in the art of vapor deposition coating.

However, during arc vapor deposition, macroparticles having a size in the range of 0.01 μm to 0.05 μm are often produced in the vapors and these macroparticles may detrimentally affect the coating surface. Thus as an alternative, the above process may be improved in order to reduce the amount of macroparticles in the coating, such macroparticles being at least 0.01 μm in size, by providing a metallic wire mesh, preferably stainless steel having a preselected opening size desirably in the range of about 0.22 mm to about 0.86 mm, and preferably, of about 0.47 mm. The wire mesh is positioned in between the arc source and the substrate to be coated, say, the first bearing surface 22 for example, preferably at a distance of at least 15 mm from surface 22. A negative bias voltage of about 50 volts is applied to the wire mesh by a voltage source. The arc source provides a current in the range of about 50 Amps to about 250 Amps and imparts a positive charge on the macroparticles present in the vapor generated. The positively charged macroparticles are entrapped on the negatively biased wire mesh.

In another embodiment of the invention, an improvement in a pin is disclosed. In a pin of the type previously described in Fig. 1, the improvement comprises depositing an abrasion resistant coating on at least one of the first bearing surface and the second inner bearing surface. The coating is selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof. Preferably, the coating is CrN.

In yet another embodiment, a track pin has an outer diameter in the range of about 50 mm to about 100 mm and a length in the range of about 250 mm to about 500 mm. Each of the first and second bearing surfaces have an axial length in the range of about 50 mm to about 125 mm. Each of said first and second bearing surfaces have a chromium nitride coating deposited thereon by physical vapor deposition. The coating has a thickness in the range of about 0.001 mm to about 0.005 mm. The size of macroparticles on the coating is no greater than 1 μm. In tests, this track pin exhibits at least 100% greater galling resistance than a non-CrN coated track pin and consequently, higher service life.

Industrial Applicability The present invention is particularly useful for improving the abrasion, corrosion and galling resistance of track pins used in bushings for linking the track links for an endless track of a track type machine, such as an earthmoving machine for example. The present invention is also useful for making various types of hinge joint pins for loader linkage mechanisms such as hydraulic buckets, shovels and the like for various earthworking machines such as excavators, dozers and the like. The present invention is expected to increase the useful service life of these track pins due to at least a 100% increase in galling resistance.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

Clai s

1. An abrasion, corrosion and galling resistant pin (10) , comprising: a cylindrical shape, an outer surface (50) a first end portion (20) , a second end portion (30) and a middle portion (40) ; a first bearing surface (22) defining said first end portion (20) and a second bearing surface (32) defining said second end portion (30) ; and an abrasion resistant coating (60) deposited on at least one of said first bearing surface (22) and said second bearing surface (32) , said coating (60) being selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof .

2. A pin (10), as set forth in claim 1, wherein said abrasion resistant coating (60) is of chromium nitride.

3. A pin (10), as set forth in claim 1, wherein said coating (60) has a thickness in the range of about 0.0005 mm to about 0.01 mm.

4. A pin (10), as set forth in claim 3, wherein said coating (60) has a thickness in the range of about 0.001 mm to about 0.005 mm.

5. A pin (10) , as set forth in claim 4, wherein said coating (60) has a thickness of about 0.0025 mm.

6. A pin (10) , as set forth in claim 1, wherein each of said first and second bearing surfaces

(22,32) extend for an axial length of at least 50% of the total length of said pin (10) .

7. A pin (10), as set forth in claim 6, wherein each of said first and second bearing surfaces

(22,32) extend for an axial length of at least 30% of the total length of said pin (10) .

8. A pin (10), as set forth in claim 7, wherein each of said first and second bearing surfaces

(22, 32) extend for an axial length in the range of about 15% to about 25% of the total length of said pin (10) .

9. A pin (10), as set forth in claim 1, wherein said first and second bearing surfaces (22,32) cumulatively represent at least 30% of said outer surface (50) of said pin (10) .

10. A pin (10) , as set forth in claim 1, wherein said abrasion resistant coating (60) is deposited by vapor deposition techniques.

11. A pin (10) , as set forth in claim 1, wherein said pin (10) is a track pin for an endless track of a track-type machine.

12. A pin (10), as set forth in claim 1, wherein said pin (10) is a hinge pin for a loader linkage mechanism.

13. A pin (10), as set forth in claim 1, wherein the size of macroparticles on said coating (60) is no greater than 2 ╬╝m.

14. A pin (10), as set forth in claim 13, wherein the size of macroparticles on said coating (60) is no greater than 1 ╬╝m.

15. A pin (10), as set forth in claim 1, wherein said first and second bearing surfaces (22,32) extend for an axial length of at least 30% of the total length of said pin (10) , said bearing surfaces (22,32) are coated with chromium nitride coating and said pin (10) possesses at least a 100% increase in galling resistance.

16. A track pin (10) for an endless track of a track-type machine, comprising: a cylindrical shape, an outer surface (50) , a first end portion (20) , a second end portion (30) and a middle portion (40) ; a first bearing surface (22) defining said first end portion (20) and a second bearing surface (32) defining said second end portion (30) ; and chromium nitride coating (60) deposited on said first bearing surface (22) and said second bearing surface (32).

17. A track pin (10), as set forth in claim 16, wherein said track pin (10) has an outer diameter in the range of about 50 mm to about 100 mm, a length in the range of about 250 mm to about 500 mm, first and second bearing surfaces (22,32) extending in an axial direction from said first and second end portions (20,30) respectively, each of said first and second bearing surfaces (22,32) having an axial length in the range of about 50 mm to about 125 mm, and each of said first and second bearing surfaces (22,32) having a chromium nitride coating (60) having a thickness in the range of about 0.001 mm to about 0.005 mm.

18. A track pin (10) , as set forth in claim 17, wherein the size of macroparticles on said coating

(60) is no greater than 1 ╬╝m.

19. In a pin (10) having a cylindrical shape, an outer surface (50) , a first end portion (20) , a second end portion (30) and a middle portion

(40) , a first bearing surface (22) defining said first end portion (20) and a second bearing surface (32) defining said second end portion (30) , an improvement, comprising: depositing an abrasion resistant coating

(60) on at least one of said first bearing surface (22) and said second bearing surface (32) , said coating (60) being selected from the group consisting of chromium nitrides, chromium carbonitrides, and mixtures thereof.

20. A pin (10), as set forth in claim 19, wherein said abrasion resistant coating (60) is of chromium nitride.

21. A pin (10) , as set forth in claim 20, wherein said coating (60) has a thickness in the range of about 0.0005 mm to about 0.01 mm.