FACE SEAL

Abstract: A seal assembly (2) for sealing the area between a stationary member and a rotatable member includes first and second mating metal seal rings (6, 8). The substantially flat sealing surface (9) of the first metal seal ring (6) is constructed of a harder material relative to the sealing surface (10) of the second metal seal ring (8). Additionally, the sealing surface (10) of the second metal seal ring (8) is geometrically dissimilar to the substantially flat sealing surface (9) of the first metal ring (6). The dissimilar hardnesses and dissimilar geometries result in enhanced performance and durability of metal face seals.

Description: Description FACE SEAL Technical Field This invention relates generally to a metal to metal seal assembly and more particularly to a pair of metal seal rings with dissimilar geometry and dissimilar hardnesses on the sealing surfaces of the metal seal rings to increase the durability of the metal seal faces . Background Art The present invention has particular application to the earthmoving and heavy equipment machine field, wherein seals are operated in highly destructive or abrasive environments. The invention has particular application to the use of wheels on large off-road machines such as trucks. The present invention also has application to track rollers, final drives, and other components of track-type machines. The problem of short bearing life in wheel axles on trucks and in track rollers assemblies of track-type machines is one that has continuously plagued the industry for some time. Such machines typically operate in environments that are highly destructive to seals and consequently to the underlying bearings. One approach to this problem is the metal type seals disclosed in U.S. Pat. No. 5,553,931, which issued September 10, 1996, to Diekevers et al . and was assigned to the assignee hereof. These type metal seals and subsequent improvements have greatly improved track roller bearing life. These seals, while satisfactory for the normal operation of the average track-type machine or truck is found to have some drawbacks when applied to large high speed trucks and track machines. For example, when the seal diameter gets large, the surface velocity at the seal face increases, increasing heat and radial force problems. One problem with prior art metal to metal seal assemblies involves wear patterns. Wear patterns can develop such that the seal surface migrates in the radial direction, which can unbalance the seals. When the seal becomes unbalanced, the force on the seal will either increase or decrease, depending on the location of the sealed fluid. Eventually, the force will either exceed the maximum allowed value or fall below the minimum allowed value for the seal. The former results in leakage from damage to the seal faces, and the latter results in leakage from insufficient loading to hold the fluid. An additional problem with too low of a loading is that dirt and abrasives can enter at the seal face, thereby damaging the bearings . Wear patterns can also develop in which the seal face wears non-uniformly in the radial direction. This results in leakage from damage to the seal faces. Damage to the seal faces is accelerated by the presence of dirt and grit on the seal face. The increased coefficient of friction with high face loads and/or high sliding speeds further exacerbates the problem. The present invention is directed to overcoming one or more of the problems as set forth above . Disclosure of the Invention In one aspect of the invention, a durable metal seal assembly is provided having a first metal seal ring with a substantially flat sealing surface having a first pre-determined hardness and a predetermined width. A second metal seal ring has a sealing surface that mates with and rotates relative to the flat sealing surface. The sealing surface of the second metal seal ring has a second pre-determined hardness that is lower than the surface hardness of said first metal seal ring and a pre-determined width that is narrower than the width of said first metal seal ring. In another aspect of the invention, a method for making a pair of metal seal rings with dissimilar geometry and dissimilar hardnesses on the sealing surfaces of the metal seal rings is disclosed. Brief Description of the Drawings FIG. 1 is a cross-sectional view of a portion of one of the seal assemblies of the present invention; FIG. 2 is a cross-sectional view of a portion of an alternate embodiment of the present invention; FIG. 3 is a diagrammatic sectional view of an axle assembly incorporating the subject invention; and FIG. 4 is a diagrammatic sectional view of a portion of one of the seal assemblies of the present invention in rotation. Best Mode for Carrying Out the Invention The term "metal", as used herein means materials which include, but is not limited to, steel, metal carbides, metal nitrides, metal borides, diamond-like carbon containing compounds, ceramics, metal-ceramic composites and combinations thereof. The term "thermally spraying", as used herein means the thermal spray techniques such as, oxyacetylene torch thermal spray, gas stabilized plasma spray, water stabilized plasma spray, combustion thermal spray, and high velocity oxygen fueled spray (HVOC) . It must be understood that the thermal spray techniques are not limited to the above enumerated methods and that other alternative thermal spray techniques known to those skilled in the art may be employed. For example, water stabilized plasma spray techniques are disclosed in U.S. Pat. No. 4,338,509 issued to Bartuska et al . Also, U.S. Pat. No. 5,882,801 issued to Beardsley et al . and assigned to Caterpillar Inc. discloses plasma spray techniques. With reference to the drawings and more particularly FIGS. 1 and 2, the seal assembly 2 is comprised of first and second metal to metal seal rings 6,8 respectively. The metal seal rings are of generally annular or ring shape configuration. A first metal seal ring 6 has a flat sealing surface 9 of a pre-determined width. In alternate embodiments, FIGS. 1-4 depict flat sealing surface 9 opening outwardly at the radially innermost diameter 16. In the invention, the flat sealing surface 9 of the first metal seal ring 6 also has a first predetermined hardness since the hardness is also important characteristic of the first metal seal ring 6 in relation to the second metal seal ring 8. The flat sealing surface 9 of the first metal seal ring 6 has a hardness of greater than 65 as measured using a Rockwell C hardness scale. In the present invention, a second metal seal ring 8 has a sealing surface 10 of a predetermined width that is narrower than the width of the flat sealing surface 9. The second metal seal ring 8 has a sealing surface 10 that mates with and rotates relative to the flat sealing surface 9 of the first seal ring 6. The sealing surface 10 of the second metal seal ring 8 has a second pre-determined hardness that is lower than the surface hardness of flat sealing surface 9 of the first metal seal ring 6. As depicted in FIG. 3, in one embodiment, for example, the sealing surface 10 of the second metal seal ring 8 has an angled surface 11 extending from the sealing surface 10. The angled surface 11 has a degree of taper radially and axially inward in the range of between zero degrees and about ninety degrees . Turning to FIGS. 1, 2, and 4, in alternative embodiments of the present invention, the sealing surface 10 of the second metal seal ring 8 has a first angled surface 11 extending from the sealing surface 10 and a second angled surface 13 extending from the sealing surface 10. The angled surfaces 11, 13 have a degree of taper axially inward in the range of between zero degrees and about ninety degrees. In one embodiment, for example, the first seal member or ring 6 is formed from a durable material, preferably steel. The flat sealing surface 9 is composed of a material of a pre-established hardness. This hardness may be achieved by a unitary construction of the first metal seal ring 6, as depicted in FIG. 2. A variety of hard materials may be used to form the flat sealing surface 9 of the first metal seal ring 6. These hard materials may be in the overall composition of the first metal seal ring 6, as a unitary construction, or, alternatively, the hard material may be present only on the flat sealing surface 9 of the first metal seal ring 6. The hard material includes, but is not limited to, steel, metal carbides, metal nitrides, metal borides, diamond- like carbon containing compounds, ceramics, metal -ceramic composites and combinations thereof. In the preferred embodiment, for example, the hardness of the flat sealing surface 9 of the first metal seal ring 6 is achieved by coating a metal substrate 19, as depicted in FIGS. 1,3, and 4. A coating 22, having a pre-established hardness, is deposited upon the metal substrate 19. The composition of the coating 22 is preferably selected from the group consisting of metal carbides, such as tungsten carbide, chromium carbide, and the like. Alternatively, the coating 22 is selected from the group consisting of metal carbides, metal nitrides, metal borides, diamond-like carbon containing compounds and combinations thereof. The coating thickness on the flat sealing surface 9 of the first metal seal ring 6 should be fairly uniform. One can demonstrate uniform coating thickness through measurement by calipers, ball crater test, scanning electron microscopy measurements on a sample of selected cross sections or through the use of X-ray fluorescence. In the preferred embodiment, the coating 22 has a thickness in the range between about 200 microns and about 450 microns, preferably in the range between about 250 microns and about 300 microns. The coating 22 may be applied to a portion or the entire length of the flat sealing surface 9 of the first metal seal ring 6. In the preferred embodiment, the preferred coating is chromium carbide and is applied over the entire length of the flat sealing surface 9 of the first metal seal ring 6. Any coating technique may be used to deposit the coating 22 on the metal substrate. These include welding, cladding, and various vapor deposition techniques . The preferred chromium carbide coating is preferably deposited by a thermal spray deposition process. Preferably, high velocity oxygen fuel (HVOC) is used to apply the chromium carbide coating because it produces very low porosity coatings. Such thermal spray deposition coating methods are generally known in the art . Control of some or all of the physical properties of the coating and coated substrate other than thickness are also important to producing a highly reliable and cost effective component. For example, coating adhesion, coating hardness, surface texture, and frictional coefficients are some of the physical properties that should be monitored. As previously stated, the coating hardness is an important characteristic of the flat sealing surface 9 of the first metal seal ring 6 in relation to the sealing surface 10 of the second metal seal ring 8. The applied coating 22 has a hardness of greater than 65 as measured using a Rockwell C hardness scale. In an alternative embodiment, for example, the flat sealing surface 9 of the first metal seal ring 6 may not utilize a coating to achieve the hardness desired. The first metal seal ring 6 in FIG. 2 is of unitary construction. In FIG. 2, an embodiment of the present invention, the flat sealing surface 9 of the first metal seal ring 6 is ceramic. In the present invention, the second seal member or ring 8 is formed from a durable material, preferably a metal -ceramic composite. The sealing surface 10 is composed of a material of a pre- established hardness with the hardness being less than that of the flat sealing surface 9 of the first seal ring 6. This hardness may be achieved by the overall composition of the second metal seal ring 8, as depicted in FIGS. 1-4. A variety of materials may be used to form the second metal seal ring 8. These materials include, but are not limited to, steel, metal carbides, metal nitrides, metal borides, diamond-like carbon containing compounds, ceramics, metal -ceramic composites and combinations thereof. In the preferred embodiment, the second metal seal ring 8 is a metal-ceramic composite, preferably a nickel- chromium cast alloy. It is the difference in hardness of the sealing surfaces 9,10 that provides the beneficial wear patterns of the seal assembly 2. The metal seal ring assembly 2 of this invention produces a pressure balanced effect whereby the pressure of the sealing fluid would be nearly equally distributed. Turning to FIG. 3, in the static assembled condition of the seal assembly 2, resilient load rings 20,21 are adapted to contact one of the seal rings 6,8. In the assembled condition of the seal assembly 2 the load rings 20,21 are adapted to flex to promote sealing. The frame 24 acts as a support for the assembly. In FIG. 4, the seal assembly 2 is depicted while the first metal seal ring 6 mates with and rotates relative to the second metal seal ring 8. It can be noted that the sealing surface 10 may move along the length of the sealing surface 9 while in rotation. Industrial Applicability Wear patterns can develop in seal assemblies, which wears the seal face non-uniformly in the radial direction. This invention decreases wear by utilizing different hardnesses and different geometry on the seal face. During use of the seal assembly 2 as set forth in FIGS. 1-4, the flat sealing surface 9 of the first metal seal ring 6 is pressed against sealing surface 10 of the second metal seal ring 8. The sealing surface 10 may migrate along the length of the first metal seal ring 6 while the first metal seal ring 6 mates with and rotates relative to the second metal seal ring 8. The angled surface geometry in tandem with the different hardnesses of the materials on the sealing surfaces increase the life of the seal . The substantially flat sealing surface 9 of the first metal seal ring 6 is harder than the sealing surface 10 of the second metal seal ring 8. The sealing surface 10 is also tapered in the range of between zero and about 90 degrees. As the flat sealing surface 9 mates and rotates relative to sealing surface 10, the greater hardness of the flat sealing surface will press against sealing surface 10 and cause the tapered sealing surface 10 to wear away while still maintaining the sealed condition. Additionally, the metal seal ring assembly 2 of this invention produces a pressure balanced effect whereby the pressure of the sealing fluid would be nearly equally distributed. It is apparent that the improved seal of the present invention provides effective sealing in wheels on large off-road machines or like structure over relatively wide ranges of deflection and reduces loss of lubricant from the seal, thereby prolonging the effective life of sealing elements. In view of the above, it is readily apparent that a metal seal assembly with dissimilar hardnesses and dissimilar geometry is provided that is economical to produce and effective to increase the life of a seal, even when used in harsh operating conditions. Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims: Claims 1. A metal seal assembly (2) comprising: a first metal seal ring (6) having a substantially flat sealing surface (9) , said flat sealing surface (9) having a first pre-determined hardness and a pre-determined width; a second metal seal ring (8) having a sealing surface (10) that mates with and rotates relative to said flat sealing surface (9) , said sealing surface (10) of said second metal seal ring (8) having a second pre-determined hardness that is lower than the surface hardness of said first metal seal ring (6) , said sealing surface (10) having a pre- determined width that is narrower than the width of said first metal seal ring (6) . 2. The metal seal assembly (2) as in claim 1, wherein said sealing surface (10) of said second metal seal ring (8) has an angled surface (11) extending from said sealing surface (10) . 3. The metal seal assembly (2) as in claim 2, wherein said angled surface (11) has a degree of taper in the range of between zero degrees and about ninety degrees . 4. The metal seal assembly (2) as in claim 3, wherein said second metal seal ring (8) of said sealing surface (10) has a second angled surface (13) extending from said sealing surface (10) . 5. The metal seal assembly (2) as in claim 4, wherein said second angled surface (13) has a degree of taper in the range of between zero degrees and about ninety degrees . 6. The metal seal assembly (2) as in claim 1, wherein said hardness of said flat sealing surface (9) of said first metal seal ring (6) is greater than 65 as measured using a Rockwell C hardness scale. 7. The metal seal assembly (2) as in claim 1, wherein said sealing surface (10) of said first metal seal ring (6) is metal carbide. 8. The metal seal assembly (2) as in claim 7, wherein said sealing surface (10) of said first metal seal ring (6) is chromium carbide. 9. The metal seal assembly (2) as in claim 1, wherein said sealing surface (10) of said first metal seal ring (6) is ceramic. 10. The metal seal assembly (2) as in claim 1, wherein said sealing surface (10) of said second metal seal ring (8) is nickel chromium cast alloy. 11. A metal seal assembly (2) comprising: a first metal seal ring (6) having a substantially flat sealing surface (9) , said sealing surface having a pre-determined width and a coating (22) thereon of a first pre-determined hardness; a second metal seal ring (8) having a sealing surface (10) that mates with and rotates relative to said substantially flat sealing surface (9) of said first metal seal ring (6), said sealing surface (10) of said second metal seal ring (8) having a pre-determined width that is narrower than the width of said substantially flat sealing surface (9) of said first metal seal ring (6) , said sealing surface (10) of said second metal seal ring (8) having a second pre-determined hardness that is lower than the surface hardness of said coating of said first metal seal ring (6) . 12. The metal seal assembly (2) as in claim 11, wherein said sealing surface (10) of said second metal seal ring (8) has an angled surface (11) extending from said sealing surface (10) . 13. The metal seal assembly (2) as in claim 12, wherein said angled surface (11) has a degree of taper in the range of between zero degrees and about ninety degrees . 14. The metal seal assembly (2) as in claim 13, wherein said sealing surface (10) of said second metal seal ring (8) has a second angled surface (13) extending from said sealing surface (10) . 15. The metal seal assembly (2) as in claim 14, wherein said second angled surface (13) has a degree of taper in the range of between zero degrees and about ninety degrees . 16. The metal seal assembly (2) as in claim 13, wherein said hardness of said flat sealing surface (9) of said first metal seal ring (6) is greater than 65 as measured using a Rockwell C hardness scale. 17. The metal seal assembly (2) as in claim 11, wherein said thickness of said coating (22) is in the range of between about 200 and 450 microns. 18. The metal seal assembly (2) as in claim 16, wherein said thickness of said coating (22) ranges is in the range of between about 250 and 300 microns. The metal seal assembly (2) as in claim 16, wherein said coating (22) is metal carbide. 19. The metal seal assembly (2) as in claim 18, wherein said coating (22) is chromium carbide. 20. The metal seal assembly (2) as in claim 10, wherein said sealing surface (10) of said second metal seal ring (8) is nickel chromium cast alloy. 21. A method for making a metal seal assembly (2), comprising: preparing a first metal seal ring (6) having a substantially flat sealing surface (9) , said sealing surface having a first pre-determined hardness and a pre-determined width; depositing a coating (22) on said flat sealing surface (9) of said first metal seal ring (6) using a deposition process; and preparing a second metal seal ring (8) having a sealing surface (10) that mates with and rotates relative to said flat sealing surface (9) of said first metal seal ring (6) , said sealing surface (10) of said second metal seal ring (8) having a second pre-determined hardness that is lower than the surface hardness of said first metal seal ring (6) and a pre-determined width that is narrower than the width of said first metal seal (6) .

Inventors: HOEFFT THOMAS M, SEITZMAN LARRY E, HOEFFT, THOMAS, M., SEITZMAN, LARRY, E.
Applicants: CATERPILLAR INC, CATERPILLAR INC.
Application year: 2000
Main classification: F16J15
IPC codes: F16J15