Claims:1. A system comprising:
a shaft; and
a journal bearing coupled to the shaft, wherein at least one of the journal bearing and the shaft comprises a base and at least one coating layer disposed on the base, wherein
the base comprises a heat-affected zone bonded to one layer of the at least one coating layer, wherein the heat-affected zone has a thickness less than 5 micrometers; and wherein
the one layer of the at least one coating layer has a coating thickness greater than 50 micrometers, density greater than 98 percent of a theoretical density of the one layer, and a dilution less than 0.5 volume % of the one layer.
2. The system of claim 1, wherein each of the base and the one layer of the at least one coating layer comprises a material composition comprising steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or any combinations thereof.
3. The system of claim 2, wherein the base comprises a journal bearing housing.
4. The system of claim 1, wherein the base comprises a base material composition comprising steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or any combinations thereof, and wherein the one layer of the at least one coating layer comprises a coating material composition comprising copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof.
5. The system of claim 4, wherein the coating material composition comprises a mixture of copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof.
6. The system of claim 4, wherein the one layer of the at least one coating layer comprises a gradient in the coating material composition along a direction perpendicular to the base.
7. The system of claim 1, wherein the base comprises a base material composition comprising copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof, and wherein the one layer of the at least one coating layer comprises a coating material composition comprising aluminum, tin, molybdenum disulfide, tungsten disulfide, graphite, a polymer, or a combination thereof.
8. The system of claim 7, wherein the base material composition further comprises steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys or any combinations thereof.
9. The system of claim 1, wherein the base comprises a base material composition comprising steel, and wherein the one layer of the at least one coating layer comprises a coating material composition comprising cobalt-based wear resistant alloys, nickel-based super alloys, chromium carbide, nickel, or any combinations thereof.
10. The system of claim 9, wherein the coating material composition comprises a mixture of cobalt-based wear resistant alloys, nickel-based super alloys, chromium carbide, nickel, or any combinations thereof.
11. The system of claim 10, wherein the one layer of the at least one coating layer comprises a gradient in the coating material composition along a direction perpendicular to the base.
12. The system of claim 1, wherein the base has a first hardness and the one layer of the at least one coating layer has a second hardness less than the first hardness.
13. An internal combustion engine comprising the system of claim 1.
14. A system comprising:
a shaft; and
a journal bearing coupled to the shaft, wherein the journal bearing comprises a base; a first coating layer disposed on the base; and a second coating layer disposed on the first coating layer, wherein
the base comprises a journal bearing housing comprising a base material composition comprising steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or any combinations thereof;
the first coating layer comprises a first coating material composition comprising copper, zinc, lead, tin, antimony, or any combinations thereof; and the second coating layer comprises a second coating material composition comprising aluminum, tin, molybdenum disulfide, tungsten disulfide, graphite, a polymer, or a combination thereof, and wherein
the base comprises a heat-affected zone bonded to the first coating layer, wherein the heat-affected zone comprises a thickness less than 5 micrometers; and
the first coating layer has a coating thickness greater than 50 micrometers, density greater than 98 percent of a theoretical density of the first coating layer, and a dilution less than 0.5 volume % of the first coating layer.
15. The system of claim 14, wherein the first coating layer comprises a gradient in the first coating material composition along a direction perpendicular to the base.
16. A method comprising:
forming one layer of at least one coating layer having a coating thickness greater than 50 micrometers, density greater than about 98 percent of a theoretical density of the one layer, and a dilution less than 0.5 volume % of the one layer, on a base of at least one of a journal bearing and a shaft of a system, using a friction surfacing process, wherein
the base comprises a heat-affected zone having a thickness less than 5 micrometers, bonded to the one layer of the at least one coating layer.
17. The method of claim 16, wherein forming the one layer of the at least one coating layer comprises forging and traversing a rotating cylinder on the base, wherein the rotating cylinder comprises a coating material composition of the one layer.
18. The method of claim 17, wherein forming the one layer of the at least one coating layer comprises forming a gradient in the coating material composition of the one layer, along a direction perpendicular to the base, wherein the rotating cylinder comprises a mixture of copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof.
19. The method of claim 17, wherein forming the one layer of the at least one coating layer comprises forming a gradient in the coating material composition of the one layer, along a direction perpendicular to the base, wherein the rotating cylinder comprises a mixture of aluminum, tin, molybdenum disulfide, tungsten disulfide, graphite, a polymer, or any combinations thereof.
The method of claim 16, further comprising machining the formed one layer of the at least one coating layer for altering the coating thickness, a surface texture, or a combination thereof of the one layer.
, Description:BACKGROUND
[0001] This invention relates generally to coatings of journal bearing systems, and more particularly to friction surfacing coatings of journal bearing systems.
[0002] Sliding-type journal or engine bearings are typically used in combustion engine applications, for example, for journaling a shaft of the engine. Typical engine bearings and shafts have arcuate steel backing onto which one or more layers of other softer or harder materials are applied. The steel backing provides structural rigidity to the bearings and shaft whereas the coatings are required to provide a low friction sliding surface, acceptable wear, corrosion, cavitation, embedability, fatigue and seizure-resistance, and acceptable conformability to the bearings and shafts.
[0003] Generally, methods such as sputtering, electrochemical deposition, electroless plating, spraying, are used for providing multilayered coatings on the steel backing of bearings and shafts. However, methods such as electrochemical deposition, electroless plating, and spraying may not provide required density of the coatings and hence may compromise on the tough ness and fatigue resistance of the coating layers. Sputtering is an expensive method known to provide very thin coating layers. Therefore, sputtering may not be used to provide the required thickness of some of the coating layers.
[0004] Further, a mechanical joint is provided between the coated bearing and housing, resulting in a poor heat transfer during operation of the journal bearings. Furthermore, there is a possibility of failure of the journal bearings due to fretting between the bearing and the housing because of dirt/soot accumulation between the bearing and the housing.
[0005] Therefore, there is a need for an enhanced coating for a journal bearing.
BRIEF DESCRIPTION
[0006] Embodiments of the invention are directed towards systems including the coated journal bearings or shafts and an efficient method of coating.
[0007] In one embodiment, a system is disclosed. The system includes a shaft and a journal bearing coupled to the shaft. At least one of the journal bearing and the shaft includes a base and at least one coating layer disposed on the base. The base includes a heat-affected zone bonded to one layer of the at least one coating layer. The heat-affected zone has a thickness less than 5 micrometers. The one layer of the at least one coating layer has a coating thickness greater than 50 micrometers, a density greater than 98 % of a theoretical density of the one layer, and a dilution less than 0.5 volume % of the one layer.
[0008] In one embodiment, a system is disclosed. The system includes a shaft and a journal bearing coupled to the shaft. The journal bearing includes a base, a first coating layer disposed on the base, and a second coating layer disposed on the first coating layer. The base includes a journal bearing housing including a base material composition having steel, titanium, or a combination thereof. The first coating layer includes a first coating material composition having copper, zinc, lead, tin, antimony or combinations thereof. The second coating layer includes a second coating material composition having aluminum, a polymer, or a combination thereof. The heat-affected zone is a part of the base and is bonded to the first coating layer. The heat-affected zone has a thickness less than 5 micrometers. The first coating layer has a coating thickness greater than 50 micrometers, a density of greater than 98 % of a theoretical density of the first coating layer and a dilution less than 0.5 volume % of the first coating layer.
[0009] In one embodiment, a method is disclosed. The method includes forming at least one coating layer on a base of at least one of a journal bearing and a shaft of a system. One layer of the at least one coating layer is formed using a friction surfacing process, thereby limiting a thickness of a heat-affected zone of the base to less than 5 micrometer. The one layer of the at least one coating layer has a coating thickness greater than 50 micrometers, a density greater than 98 % of theoretical density of the one layer, and a dilution less than 0.5 volume % of the one layer.
DRAWINGS
[0010] These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.
[0011] FIG. 1 is a schematic cross-sectional view of a system including a journal bearing and shaft according to an embodiment of the present invention;
[0012] FIG. 2 is an illustration of a friction surfacing method according to an embodiment of the present invention;
[0013] FIG. 3 is a schematic cross-sectional view of a system including a base and different coating layers according to an embodiment of the present invention;
[0014] FIG. 4 is a schematic cross-sectional view of a pin tool according to an embodiment of the present invention; and
[0015] FIG. 5 is a schematic cross-sectional view of a pin tool according to another embodiment of the present invention.
DETAILED DESCRIPTION
[0016] Aspects of the present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
[0017] In the following description, whenever a particular aspect or feature of an embodiment of the invention is said to comprise or consist of at least one element of a group and combinations thereof, it is understood that the aspect or feature may comprise or consist of any of the elements of the group, either individually or in combination with any of the other elements of that group.
[0018] In the following specification and the claims that follow, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
[0019] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” or “substantially,” may not be limited to the precise value specified, and may include values that differ from the specified value. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
[0020] An aspect of the present invention is directed to a coating for a journal bearing system. Journal bearing systems may be used in different types of engines such as, for example, internal combustion engines and reciprocating engines. Failure of engine journals and journal bearings can affect operation of the engines. Journal and bearing damage may occur due to fatigue, wear, corrosion, embedability, seizure and cavitation.
[0021] FIG. 1 is a schematic representation of a system 100 in accordance with some embodiments of the present invention. The system 100 includes a journal (alternatively referred to as shaft) 110 and a journal bearing 120 coupled to the shaft 110. As used herein, the phrase “journal bearing 120 coupled to the shaft 110” means that the journal bearing 120 and the shaft 110 operate as a pair during the operation of the system 100 and does not necessarily indicate any physical bonding between the journal bearing 120 and the shaft 110. At least one of the journal bearing 120 and the shaft 110, includes a base 130 and at least one coating layer 140 disposed on the base 130. The base 130 includes a heat-affected zone 150 bonded to one layer of the at least one coating layer 140 at an interface 132 of the base 130 and the one layer 140. The heat-affected zone 150 has a thickness less than 5 micrometers. A coating thickness of the one layer 140 is greater than 50 micrometers. A density of the one layer 140 is greater than 98 % of a theoretical density of the one layer 140. A dilution of the one layer 140 is less than 0.5 volume percent (%) of the one layer. As used herein, a “dilution of the one layer 140” is an inclusion of any impurity, such as, for example, any other material other than the coating material of the one layer 140.
[0022] Some aspects of the present invention is related to a method of forming the at least one coating layer 140 on the base 130 of at least one of the journal bearing 120 and the shaft 110 of the system 100. In some embodiments, on layer 140 of the at least one coating layer 140 is formed, using a friction surfacing method. Coatings formed using a friction surfacing process facilitates to limit the thickness of the heat-affected zone 150 of the base 130 to less than 5 micrometers.
[0023] Hardness and toughness of the base 130 and the one layer of the at least one coating layer 140 may vary depending on the applications, for example, depending on whether the one layer 140 is applied to the journal 110 or the journal bearing 120. In one embodiment, for the journal 110, the one layer 140 may include a harder material than the material of the base 130. For example, the base 130 may include a hard material including steel, and the coating layer 140 may include a harder material including StellitesTM. In some embodiments, the base 130 has a first hardness and the one layer 140 has a second hardness less than the first hardness. Non limiting examples of the material of the base 130 may include steel, StellitesTM, titanium, or any combinations thereof. Non-limiting examples of the material of the one layer 140 may include bronze, leaded bronze, aluminum-based alloys, and copper-based alloys. In certain embodiments, the base 130 has a first toughness and the one layer 140 has a second toughness less than the first toughness.
[0024] Referring to FIG. 2, a perspective view of a friction surfacing apparatus 200 is illustrated according to some embodiments of the present invention. The friction surfacing apparatus 200 includes a movable pin tool 210. In the illustrated embodiment, the pin tool 210 has a substantially cylindrical, rod-like shape. The pin tool 210 may be a solid rod or may be partially or entirely hollow. The pin tool 210 can have any diameter depending on the application and apparatus specifications. In some embodiments, the diameter of the pin tool 210 is in a range from about 0.50 mm to about 50 mm.
[0025] The pin tool 210 may be coupled to a drive mechanism (not shown), such as, for example, a spindle. The drive mechanism may be operable for rotating the pin tool 210 about an axis 212 of the pin tool 210. Typically, the pin tool 210 is rotated at a speed in a range from about 100 revolutions per minute (rpm) to about 100,000 rpm during the friction surfacing process. Rotation of the pin tool 210, in conjunction with a forging load imposed between the pin tool 210 and the base 130, provides a combination of frictional heat and thermo-mechanical work. As a result, the pin tool 210 is subjected to frictional heat to a temperature below its melting point causing plasticization and deposition of material of the pin tool 210 to the surface of the base 130. The amount of material deposited by the pin tool 210 may be dependent on the rotational speed of the pin tool 210, the feed rate of the pin tool 210, and the traverse speed of the friction surfacing apparatus 200. The pin tool 210 may be made of a material that is same as, similar to, or dissimilar from a material of the base 130. For example, if the base is made of a metal or metal alloy, the pin tool 210 can be made of the same metal or metal alloy, or similar metal or metal alloy, or dissimilar material that provides a desired characteristic when the pin tool material is deposited on the base 130.
[0026] During operation, the pin tool 210 is fed at a desired feed rate while rotating the pin tool 210 and traversing it along the base 130. In some embodiments, the feed rate may range from about 2 millimeters per minute (mm/minute) to about 100 mm/minute. It should be noted that the feed rate of the pin tool 210 may vary based upon pin tool material(s) and the material(s) of the base 130.
[0027] During operation, a temperature of a tip of the pin tool 210 is maintained at a range in which the pin tool material is substantially plastic. For example, the temperature of the tip of the pin tool 210 may be maintained in a range from about 800° C to about 1000° C for copper and copper alloys; from about 875° C to about 1075° C for different steels and nickel alloys, and from about 1100° C to about 1300° C for titanium and titanium alloys.
[0028] As the pin tool 210 is traversed along the base 130, the plasticized metal, metal alloy, or other material of the pin tool 210 is transferred, forming a deposit (coating) of the pin tool material on the surface of the base 130. The pin tool 210 is substantially continuously fed along the surface of the base 130 such that the pin tool material is coated on the surface of the base 130. The pin tool 210 may be traversed along the surface of the base 130 at a rate that is sufficient to deposit a desired amount of material on the surface of the base 130. For example, in some embodiments, the pin tool 210 may traverse along the surface of the base 130 at a rate in a range of from about 2 mm/minute to about 400 mm/minute.
[0029] A continuous forging action on the pin tool 210 improves the mechanical bond between the deposited pin tool material and the base 130, refines the microstructure of deposited pin tool 210 material, and minimizes any flash during operation.
[0030] The localized plastic deformation of the pin tool 210 results in a crystalline microstructure and very low porosity. In some embodiments, relatively thick coatings may be disposed using the friction surfacing methods as compared to some other standard coating methods, such as, for example, sputtering. For example, thickness greater than 50 micrometers may be achieved by the friction surfacing method by a single pass. In some embodiments, the thickness of the coating material may further be increased at a single location on the base 130, by performing multiple passes of the pin tool 210. The pin tool 210 composed of similar or dissimilar materials may be subjected to sequential passes to form a monolithic or graded coating. In some other embodiments, linear, angular and/or contoured coating may be formed.
[0031] In accordance with the embodiments of the present invention, the friction surfacing apparatus 200 may be used to deposit similar or dissimilar material on a wide variety of base materials, such as cobalt-based alloys, titanium alloys, iron based alloys (including steel), copper-based alloys, aluminum-based alloys and the like. The exemplary journal and journal bearings may be suitable for any applications that include, but not limited to, turbo-machinery applications, such as gas turbine, steam turbine, and aircraft engines.
[0032] The exemplary friction surfacing method described herein provides benefits including: 1) minimal solidification cracking, porosity, or segregation; 2) a fine, hot-worked metallurgical structure; 3) mechanical properties of the deposited or bonded zone material that are equivalent to or better than the base material; 4) lower heat input to the base material that helps to reduce residual stresses and distortion and does not adversely affect the structure and properties of the base material and 5) ability to tailor the local chemistry, metallurgical structure, and mechanical properties of specific areas or coating of the components.
[0033] With reference to FIGS. 1 and 2, the heat-affected zone 150 is defined as the portion of the base 130 that is affected by the process of providing the one layer of the at least one coating layer 140. When a friction surfacing method is used to provide the one layer 140 on the base 130, the heat-affected zone 150 is a top portion of the base 130 that is affected while providing the one coating layer 140. As used herein, a portion or zone of the base 130 is said to be “heat-affected” if any physical or chemical characteristics of the portion is changed to an extent greater than 5% when compared to remaining portion of the base 130 which is not affected by the coating process. The physical characteristics may include, for example, the structure, microstructure, and density of the heat affected zone. The chemical characteristics may include, for example, the material composition or the crystal structure of the heat affected zone.
[0034] The heat-affected zone 150 is formed by the heat and friction generated by the coating process of the pin tool 210 while depositing the one coating layer 140 on the base 130. Therefore, in some embodiments, the heat-affected zone 150 of the base 130 connects the base 130 to the one coating layer 140.
[0035] In some embodiments, the heat-affected zone 150 is a very thin layer of the base 130. This is particularly advantageous over a thicker heat-affected zone, as a thick heat-affected zone may include weak zones of coarse microstructure and low hardness, where failure may be initiated. Therefore, in some embodiments, a well-adhering and effective coating is provided on the base 130 without substantially changing the mechanical characteristics of the base 130 during the coating process. Therefore, a desired base material may be designed before-hand without the need to accommodate any further substantial changes during the process of coating. In some embodiments, a thickness of the heat-affected zone 150 of the base 130 is less than 5 micrometers. In some embodiments, the thickness of the heat-affected zone is less than 2 micrometers, and in certain embodiments, the thickness of the heat-affected zone 150 of the base 130 is less than 1 micrometer.
[0036] In some embodiments, a coating thickness of the one coating layer 140 is greater than 50 micrometers. In some specific embodiments, the coating thickness of the one coating layer 140 may be greater than about 75 micrometers. A coating thickness of the one coating layer 140 may be designed, such as, for example, to be greater than 100 micrometers, or greater than 500 micrometers, or greater than 1 millimeter, or greater than 2 millimeters depending on the application of the one coating layer 140.
[0037] In some embodiments, a density of the one coating layer 140 is greater than 98 % of a theoretical density of the one coating layer 140. As used herein, the “theoretical density” is the “true density” defined as the mass per volume of the material of the one coating layer 140, excluding all the pores. The theoretical density may further be calculated from the crystallographic data of the material composition of the one coating layer 140. In some embodiments, a crystal grain size of the one coating layer 140 that is obtained by the friction surfacing method, is greater than 1 micrometer.
[0038] In the friction surfacing method disclosed herein, a mechanical mixing or stirring between the base material and the coating material is substantially less compared to some other thick coating methods of coating, such as, for example, tungsten inert gas (TIG), plasma transferred arc (PTA) and other welding associated techniques. In some embodiments, the exemplary friction surfacing method results in minimal contamination of the one coating layer 140, compared to other coating processes. In some embodiments, a dilution (not shown in figures) of the one coating layer 140 is less than 0.5 volume% of the one coating layer 140. In certain embodiments, the dilution is less than 0.1 volume % of the one coating layer 140.
[0039] As discussed herein, in one embodiment, the base 130 and the one coating layer 140 are part of the journal bearing 120. In another embodiment, the base 130 and the one coating layer 140 are part of the journal 110. The base 130 and the one coating layer 140 are applicable for both high and low temperature applications.
[0040] FIG. 3 is a schematic illustration of the journal bearing 120 in accordance with one exemplary embodiment. In the illustrated embodiment, the journal bearing 120 includes a backing plate 160 which provides rigidity to the journal bearing 120. The backing plate 160 may be formed of a material, such as, for example, steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or combinations thereof. In some embodiments, the backing plate may be formed of a base material that includes steel, titanium, or a combination thereof. In some embodiments, the backing plate 160 may be a journal bearing housing that may have a circular or semi-circular shape to accommodate the journal 110 shown in FIG. 1.
[0041] In some embodiments, the backing plate 160 is provided with a coating layer 170. In some embodiments, the backing plate and the coating layer 170 have same material composition. The thickness of the coating layer 170 may be adjusted as required for particular applications. Another coating layer 180 may be disposed on the coating layer 170. In some embodiments, the coating layer 170 may not be used and the coating layer 180 may be disposed directly on the backing plate 160. The coating layer 180 may have a different material composition than the backing plate 160 or the coating layer 170. The coating layer 180 may aid in shock absorption of the shaft or bearing component and may further act as a back-up for a top-most layer. Further, another coating layer 190 may be provided on the coating layer 180.
[0042] With reference to FIGS. 1 and 3, in some embodiments where the backing plate 160 and the coating layer 170 have the same material composition, the base 130 illustrated in FIG. 1 would be equivalent to the backing plate 160 of FIG. 3, and the one layer of the at least one coating layer 140 would be equivalent to the coating layer 170. The heat-affected zone 152 of the backing plate 160 is equivalent to the heat-affected zone 150 of the base 130. In some embodiments, the backing plate 160 and the coating layer 170 may include a material composition having steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or combinations thereof. In some other embodiments, the backing plate 160 and the coating layer 170 may include a material composition that includes steel, titanium, or a combination thereof.
[0043] In some embodiments, the thickness of the coating layer 170 may be in a range from about 1 mm to about 3 mm. In some specific embodiments, the thickness of the coating layer 170 is in a range from about 1.5 mm to about 2.5 mm. In certain embodiments, the thickness of the coating layer 170 is about 2 mm.
[0044] Referring again to FIGS. 1 and 3, in some embodiments, a combination of the backing plate 160 and the coating layer 170 is equivalent to the base 130, the coating layer 180 is equivalent to the one layer of the at least one coating layer 140, and the heat-affected zone 154 is equivalent to the heat-affected zone 150. In some of these embodiments, the coating layer 170 includes a base material composition that includes steel, titanium, cobalt-based alloys, titanium-based alloys, nickel based alloys, or combinations thereof. In some specific embodiments, the coating layer 170 includes a base material composition that includes steel, titanium, or a combination thereof. In such embodiments, the coating layer 180 may include bronze or leaded bronze composition. In some embodiments, the coating layer 180 may include a coating material composition that includes copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof. In certain other embodiments, the coating material composition includes cobalt-based wear resistant alloys, such as for example StellitesTM, nickel-based super alloys, such as for example, InconelTM, chromium carbide, nickel, or combinations thereof. In some other embodiments, an amount of tin present in the coating material composition of the layer 180 is limited to less than 15 volume% of the coating layer 180. In some embodiments, the coating layer 180 includes a gradient in the coating material composition along a direction perpendicular to the heat-affected zone 154.
[0045] In some embodiments, the thickness of the coating layer 180 may be in a range from about 0.1 mm to about 1 mm. In some specific embodiments, the thickness of the coating layer 180 is in a range from about 0.3 mm to about 0.8 mm. In certain embodiments, the thickness of the coating layer 180 is about 0.6 mm.
[0046] In some embodiments, the coating layer 180 is equivalent to the base 130, the coating layer 190 is equivalent to the coating layer 140, and the heat-affected zone 156 is equivalent to the heat-affected zone 150 of the base 130. In some specific embodiments, the coating layer 190 includes a softer material composition compared to the coating layer 180. In certain embodiments, the coating layer 190 is referred to as an “overlay coating” and may have lesser thickness compared to the coating layer 180. In one embodiment, the coating layer 190 may include an aluminum-based or copper-based alloy material. In certain embodiments, the coating layer 190 includes an aluminum-based material, such as, for example an aluminum-tin-copper alloy. In some embodiments, an amount of tin present in the coating material composition of the coating layer 190 is limited to less than 15 volume% of the coating layer 190.
[0047] In such embodiments, where the base 130 is equivalent to the coating layer 180, the coating layer 180 may include a base material composition that includes copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or combinations thereof. The coating layer 190 may include a coating material composition that includes aluminum, tin, molybdenum disulfide, tungsten disulfide, graphite, a polymer, or a combination thereof. The overlay coating layer 190 may include for example, a polymer such as polytetrafluoroethylene (PTFE) having low friction characteristics. In other embodiments, other polymer materials such as ultra-high molecular weight polyethylene (UHMWPE), polyether ether ketone (PEEK), nylon, polyimides such as VespelTM, or any combinations thereof may also be used. In some embodiments, the polymers disclosed hereinabove may be used along with suitable reinforcements.
[0048] In some embodiments, the base 130 is equivalent to a combination of the coating layer 180 and the backing plate 160, without an intervening coating layer 170.
[0049] In some embodiments, the overlay coating layer 190 may have a thickness in a range from about 5 micrometers to about 200 micrometers. In some specific embodiments, the thickness of the coating layer 190 is in a range from about 10 micrometers to about 100 micrometers. In certain embodiments, the thickness of the coating layer 190 is in a range from 25 microns to about 75 microns. In some other embodiments, the thickness of the coating layer 190 is greater than 50 microns and less than 200 microns. Further, in some embodiments, the thickness of the coating layer 190 is greater than 75 microns and less than 200 microns.
[0050] In some embodiments of the invention, the journal bearing 120 includes the coating layers 170, 180, 190. In such embodiments, the coating layer 170 acts as the base. As disclosed, in some specific embodiments, the coating layer 170 includes a base material composition having steel, titanium, or a combination thereof. The coating layer 180 (also referred to as a first coating layer) is bonded to the coating layer 170 and includes a first coating material composition having copper, zinc, lead, tin, antimony, or any combinations thereof. In some embodiments, the coating layer 180 includes a gradient of copper, zinc, lead, or antimony along a direction perpendicular to the coating layer 170. In certain embodiments, the thickness of the coating layer 180 is greater than 50 micrometers. In certain specific embodiments, the thickness of the coating layer 180 is greater than 200 micrometers. The coating layer 190 (also referred to as a second coating layer) disposed on the coating layer 180, may include aluminum, tin, molybdenum disulfide, tungsten disulfide, graphite, a polymer, or any combinations thereof. The density of the coating layer 180 and the coating layer 190 may be greater than 98% of the theoretical densities of the respective layers. A dilution of the coating layers 180, 190 may be less than 5 volume% of the respective layers. In some embodiments, a thickness of the coating layer 190 may be in a range from about 25 micrometers to about 100 micrometers.
[0051] In some embodiments, the overlay coating layer 190 is configured to increase the conformability of the journal bearing 120. The conformability of the journal bearing 120 may be particularly beneficial in applications that are prone to misalignment of the journal 110 relative to the journal bearing 120 causing an effect commonly referred to as "edge loading." In addition, conformability of the journal bearing 120 facilitates to compensate for any imperfections of the journal 110 that may reduce the useful life of the journal bearing 120.
[0052] In some high temperature applications, the backing plate 160 or the coating layers 170 (if present), 180 (illustrated in FIG. 3) may be desirably composed of metals such as, for example, nickel-based steel, beryllium-copper alloy, beryllium-bronze alloy, thermoplastic materials, or any combinations thereof, which have properties such as fatigue-resistance, good spring properties, and strong mechanical strength. In some specific embodiments, the overlaying coating layer 190 may be composed of multi-layer composite material which provides good internal damping. For example, in a high temperature journal bearing application operating at a temperature greater than 1000 ºC, the overlaying coating layers 190 may be made of super alloys such as, for example, Ni-based metals, Rene or InconelTM sheets, or the like. In some embodiments, for the journal bearing 120, the overlaying coating layer 190 may include a softer material provided over a base which includes a hard material.
[0053] In some embodiments, the coating layers 170, 180, 190 may further be subjected to other post-coating treatments, such as, for example, machining to provide exact thickness, surface texture, or a combination thereof. For example, in some embodiments, the coating layers may have a higher thickness than desired and may be further ground to reduce thickness to the desired level. In some other embodiments, a rough surface may be obtained from the friction surfacing methods and then may be further subjected to polishing, and /or lapping to obtain a desired surface finish. In certain embodiments, the coating layer 190 may be deposited by a friction surfacing method. In such embodiments, the coating layer 190 may have a thickness greater than 100 micrometers and may be then machined to reduce the thickness to less than 100 micrometers.
[0054] Even though the backing plate 160 and the coatings layers 170, 180, 190 are illustrated as planar surfaces, in some embodiments; the backing plate 160 may have other shapes. A coating surface of the backing plate 160 may have different shapes, such as, for example, an outer arcuate convex surface (not shown) and an inner arcuate concave surface (not shown). The coating layers 170, 180, 190 described herein may be applied to the concave surfaces of the backing plate 160.
[0055] FIG. 4 shows a schematic sectional view of the pin tool 210 used to provide at least one coating layer 140 (illustrated in FIG. 1) on the base 130 in accordance with another exemplary embodiment. In the illustrated embodiment, the pin tool 210 is designed to include two or more different materials 214, 216 that are disposed during the coating process. The materials 214 and 216 may be any desired combinations of the materials, such as, for example, soft and hard materials; hard particles in soft or hard materials; solid lubricants in soft or hard materials. An example of a soft material may include copper. An example of a hard material may include StellitesTM. Non-limiting examples of the hard particles may include chromium carbides, chromium borides, tungsten carbides, StellitesTM powders. Non-limiting examples of the solid lubricants may include molybdenum disulfide, tungsten disulfide. A desired mixture of the material 214, 216 is deposited on predefined locations of the base 130 by rotating the pin tool 210. The rotation of the pin tool 210 may also be controlled to deposit different amounts of the materials 214, 216 depending on the application. While the illustrated embodiment shows only two materials 214, 216 to be deposited as a mixture, one skilled in the art would be able to envision additional materials depending on the application.
[0056] FIG. 5 is a schematic cross sectional view of the pin tool 210 in accordance with another exemplary embodiment. The pin tool 210 is configured to form the one layer 140 (illustrated in FIG. 1) having a graded compositional variation along a direction perpendicular to the base 130. Specifically, amount of the materials 214, 216 is graded in the pin tool 210 in a direction along the axis 212 that is perpendicular to the base 130 on which the coating is to be deposited. This may result in a gradient in composition of the one coating layer 140 that is deposited from the pin tool 210. Thus, in some embodiments, the coating material composition of the one coating layer 140 (shown in FIG. 1) includes a gradient along the direction perpendicular to the base 130. In certain embodiments, the pin tool 210 includes a mixture of copper, zinc, nickel, lead, antimony, aluminum, tin, molybdenum disulfide, or any combinations thereof.
[0057] In some embodiments, the coating layer 190 includes a graded aluminum-based alloy. In some other embodiments, the coating layer 190 includes a combination of a polymer with a solid lubrication material, such as for example, molybdenum disulfide and tungsten disulfide. In certain other embodiments, the solid lubricant materials may be graded along the thickness of the coating layer 190. In some embodiments, the coating layer 190 includes a double layer with an aluminum-based layer (including aluminum or aluminum-based alloy) and a polymer layer including a solid lubricant over the aluminum-based layer.
[0058] In conventional journal bearings, coating layers are mechanically inserted into the housing, in the form of a bushing. Mechanical joints are used between the housing and the coating layers, which may hinder heat dissipation leading to increased temperature build up at certain parts of the bearing. Certain common solid lubricants, such as, for example, tin and some polymers, used in low temperature applications, have low melting point, that may demand operation of the bearing at low temperatures. Embodiments of the present invention disclose an exemplary friction surface coating process, which facilitates to eliminate use of mechanical joints and thereby enabling higher heat transfer between parts and higher operating temperatures. Further, there can be a significant equipment and material cost benefit in using friction-surfacing methods, because there is no need to use expensive arcing or melting equipment, and further, loss of the coating material is very minimal.
[0059] Further, in conventional journal bearings, it is common for contaminants or debris to come in contact with the journal bearing. There are high chances of debris, such as for example, metal or soot deposition in-between the housing and the bushings of the journal bearings. In accordance with the embodiments of the present invention, the exemplary friction surface coating prevents formation of such gaps, thereby preventing deposition of debris. Furthermore, energy consumption during coating process employing a friction surfacing technique, is less, (for example, less than 10 %) compared to conventional coating methods.
[0060] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.