BEARING ASSEMBLY

Abstract

A bearing assembly, particularly refrigerant lubricated bearing assembly, having at least an inner ring and an outer ring, which are rotatable to each other. At least one bearing ring is made from a nitrogen-alloyed stainless steel having a nitrogen (N) content of more than 0.6 wt.-%. A method for manufacturing such a bearing ring is also provided.

Claims

1. A refrigerant lubricated bearing assembly, comprising: at least an inner ring and an outer ring, which are rotatable to each other, wherein at least one of the inner ring and the outer ring is made from a nitrogen-alloyed stainless steel having a nitrogen content of greater than zero point six (0.6 wt. %) weight percent.

2. The bearing assembly of claim 1, wherein the nitrogen content is in the range of zero point four to two (0.4 to 2.0 wt. %) weight percent.

3. The bearing assembly of claim 1, wherein a lubricant is encompassed between the inner ring and the outer ring, and wherein the lubricant comprises a refrigerant.

4. The bearing assembly of claim 1, wherein the bearing assembly is a rolling hearing, and wherein the inner ring and the outer ring define a rolling chamber in which a set of rolling elements are housed.

5. The bearing assembly of claim 1, wherein at least one of the inner ring and the outer ring is heat treated.

6. The bearing assembly of claim 5, wherein the at least one of the inner ring and the outer ring is at least one of quenched, deep-frozen, and tempered.

7. A refrigerant lubricated bearing assembly, comprising: an inner ring and an outer ring, the inner ring and the outer ring being rotatable relative to each other; wherein at least one of the inner ring and the outer ring is made from a nitrogen-alloyed stainless steel having a nitrogen content of more than zero point six (0.6 wt. %) weight percent; wherein the bearing assembly is a roller bearing; and wherein the inner ring and the outer ring define a rolling chamber therebetween in which a set of rolling elements is housed.

8. The bearing assembly of claim 7, wherein the nitrogen content of the nitrogen-alloyed stainless steel is less than two (2.0 wt. %) weight percent.

9. The baring assembly of claim 1, wherein the nitrogen content of the nitrogen-alloyed stainless steel used for the bearing assembly is between zero point six to two (0.6 to 2.0 wt. %) weight percent.

10. The bearing assembly of claim 7, wherein the nitrogen content of the nitrogen-alloyed stainless steel is between one point two to one point eight (1.2 to 1.8 wt. %) weight percent.

11. The bearing assembly of claim 10, wherein the nitrogen content of the nitrogen-alloyed stainless steel is between one point four to one point six (1.4 to 1.6 wt %) weight percent.

12. The bearing assembly of claim 11, wherein the nitrogen content of the nitrogen-alloyed stainless steel is one point fifty-five (1.55 wt %) weight percent.

13. The bearing assembly of claim 12, further comprising a lubricant located between the inner and the outer ring, the lubricant being a refrigerant.

14. The bearing assembly of claim 12, further comprising a lubricant located between the inner and the outer ring, the lubricant containing a refrigerant.

15. A system for manufacturing a bearing assembly, comprising: wherein at least one component of the bearing assembly is made from a nitrogen-alloyed stainless steel having a nitrogen content of more than zero point six (0.6 wt. %) weight percent.

16. The system of claim 15, further comprising a vacuum chamber configured to apply a heat treatment to the at least one component of the bearing assembly.

17. The system of claim 16, wherein the vacuum chamber encloses a nitrogen atmosphere having a gas pressure between zero point one and zero point five (0.1 and 0.5 bar) bar.

18. The system of claim 17, further comprising an induction hardening apparatus configured to apply a heat treatment to the at least one component of the bearing assembly.

19. The system of claim 18, wherein the hardening apparatus is configured to apply the heat treatment using an austenitisation temperature of between one thousand forty and eleven hundred (1040° C. to 1100° C.) degrees Celsius for between five to forty five (5 to 45) minutes, wherein the hardening apparatus is configured to convert the nitrogen-alloyed stainless steel from being ferritic to austenite during the heat treatment.

20. The system of claim 19, further comprising a quenching apparatus configured to convert a matrix of the nitrogen-alloyed stainless steel of the at least one component of the hearing assembly from austenite to martensite during a quenching step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. At least one of the embodiments of the present invention is accurately represented by this application's drawings which are relied on to illustrate such embodiment(s) to scale and the drawings are relied on to illustrate the relative size, proportions, and positioning of the individual components of the present invention accurately relative to each other and relative to the overall embodiment(s). Those of ordinary skill in the art will appreciate from this disclosure that the present invention is not limited to the scaled drawings and that the illustrated proportions, scale, and relative positioning can be varied without departing from the scope of the present invention as set forth in the broadest descriptions set forth in any portion of the originally filed specification and/or drawings. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

[0038] The figure shows:

[0039] FIG. 1: a flow diagram of a preferred embodiment of a method for manufacturing a bearing component according to the present invention.

[0040] In the following same or similar functioning elements are indicated with the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Certain terminology is used in the following description for convenience only and is not limiting. The words “right,” “left,” “up,” and “down” designate the directions as they would be understood by a person facing in the viewing direction unless specified otherwise. At least one of the embodiments of the present invention is accurately represented by this application's drawings which are relied on to illustrate such embodiment(s) to scale and the drawings are relied on to illustrate the relative size, proportions, and positioning of the individual components of the present invention accurately relative to each other and relative to the overall embodiment(s). Those of ordinary skill in the art will appreciate from this disclosure that the present invention is not limited to the scaled drawings and that the illustrated proportions, scale, and relative positioning can be varied without departing from the scope of the present invention as set forth in the broadest descriptions set forth in any portion of the originally filed specification and/or drawings. The words “outer” and “inner” refer to directions away from and toward, respectively, the geometric center of the specified element, or, if no part is specified, the geometric center of the invention. The terms “downward” and “upward refers to directions above and below the referenced component, respectively, unless specified otherwise. Those of ordinary skill in the art will appreciate from this disclosure that when a range is provided such as (for example) an angle/distance/number/weight/volume/spacing being between one (1 of the appropriate unit) and ten (10 of the appropriate units) that specific support is provided by the specification to identify any number within the range as being disclosed for use with a preferred embodiment. For example, the recitation of a percentage of copper between one percent (1%) and twenty percent (20%) provides specific support for a preferred embodiment having two point three percent (2.3%) copper even if not separately listed herein and thus provides support for claiming a preferred embodiment having two point three percent (2.3%) copper. By way of an additional example, a recitation in the claims and/or in portions of an element moving along an arcuate path by at least twenty (20°) degrees, provides specific literal support for any angle greater than twenty (20°) degrees, such as twenty-three (23°) degrees, thirty (30°) degrees, thirty-three-point five (33.5°) degrees, forty-five (45°) degrees, fifty-two (52°) degrees, or the like and thus provides support for claiming a preferred embodiment with the element moving along the arcuate path thirty-three-point five (33.5°) degrees. The language “at least one of ‘A’, ‘B’, and ‘C’,” as used in the claims and in corresponding portions of the specification, means “any group having at least one ‘A’; or any group having at least one ‘B’; or any group having at least one ‘C’; —and does require that a group have at least one of each of ‘A’, ‘B’, and ‘C’.” More specifically, the language ‘at least two/three of the following list’ (the list itemizing items ‘1’, ‘2’, ‘3’, ‘4’, etc.), as used in the claims, means at least two/three total items selected from the list and does not mean two/three of each item in the list. The term “interior”, as used in the claims and corresponding portions of the specification means the area proximate to the center of the invention. The term “exterior” similarly defines the area not in proximity to the center of the invention. Additionally, the words “a” and “one” are defined as including one or more of the referenced items unless specifically stated otherwise. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import.

[0042] FIG. 1 is a flow diagram depicting preferred steps of a preferred embodiment of a method for manufacturing a bearing assembly or a bearing component, wherein at least one component of the bearing assembly is made from a nitrogen-alloyed stainless steel having a nitrogen content which is higher than 0.6 wt. %. Such a nitrogen-alloyed stainless steel is preferably used in bearing assemblies which operate in aggressive environments, e.g. in refrigerant lubricated bearings.

[0043] Recently, not only “classic” lubricants, such as grease or oil, have been used as lubricants for bearings, but also substances already present in the bearing assembly may be used. One of the main applications in this area are refrigerant lubricated bearings which are used in in compressors of cooling systems, e.g. in chillers or air condition systems, and are, for the sake of simplicity, lubricated by the refrigerant used in the cooling system itself. However, the refrigerant often contains harmful substances which increase corrosion. The reason for that is that refrigerants usually used in air conditioning chillers are not stable under all conditions. The molecules can break down and produce by-product compounds which are harmful to the bearings. The breakdown can be caused by heat, pressure or the presence of liquid contaminants that functions as catalysts or by the inherent chemical instability of the refrigerant.

[0044] The most damaging by-products are acids, in particular hydrofluoric acid (HF) and hydrochloric acid (HCl), which are very corrosive. HF and HCl are formed by fluorine and chlorine atoms contained in the refrigerant molecules. Of special concern are recently developed refrigerants such as R1234ze, R1233zd and R1234yf, which are formulated to break down easily in case they are leaked into the atmosphere where they can potentially cause environmental problems.

[0045] The nitrogen-alloyed stainless steel having a high nitrogen content of more than 0.6 wt. %, reduces the risk for corrosion, but has to be treated in a special way for providing both a high corrosion resistance as well as sufficient microstructural features for being useable in a bearing assembly at all. The reason for that is that the nitrogen content in the nitrogen-alloyed stainless steel does not only increase the corrosion resistance but also the brittleness of the component which has to be avoided in bearing assemblies under all circumstances.

[0046] Additionally, in the above mentioned applications in refrigerant lubricated bearings, often so called hybrid bearings are used, wherein the bearing rings are made from metal whereas the rolling elements are made from ceramic. In such bearings, brittleness is of special concern as the ceramic rolling elements have a higher hardness and therefore a higher impact on the “softer” metal rings. An increase brittleness of the metal rings e.g. due to the high nitrogen content in the nitrogen-alloyed stainless steels would also lead to an increased risk for damage.

[0047] For reducing the brittleness in general, and further to addressing the main disadvantages of the nitrogen-alloyed stainless steel having a high nitrogen content, namely porosity, softness and reduced toughness, the bearing component made form a nitrogen-alloyed stainless steel having a very high nitrogen content is subjected to a special heat treatment. In the following, a preferred embodiment of such an inventive heat treatment will be described with reference to FIG. 1. In general, the preferred heat treatment comprises a heating step, a subsequent quenching step, for reducing the porosity, followed by a deep-freezing step for reducing the softness and a final tempering step for increasing the toughness.

[0048] To the main steps in detail.

[0049] After having provided in step 100 a bearing component, particularly at least one bearing ring or at least one rolling element, made from a nitrogen-alloyed stainless steel having a nitrogen N content of more than 0.4 wt.-%, preferably a nitrogen content between 0.4 to 2.0 wt.-%, preferably be-tween 1.2 to 1.8 wt.-%, more preferred between 1.4 to 1.6 wt.-%, and most preferred 1.55 wt.-%, the bearing component is transferred to a vacuum chamber for the heat treatment (step 101). Alternatively, also other heat treatment methods, as for example an induction hardening apparatus, may be used.

[0050] In the described preferred embodiment of the heat treatment, the vacuum chamber is filled with a nitrogen atmosphere, wherein a gas pressure of the nitrogen is in the range between 0.1 and 0.5 bar, preferably 0.2 bar. The nitrogen content ensures that the usual nitrogen content loss during heat treatment in a vacuum chamber, which results in the above mentioned porosity, may be reduced. In the vacuum chamber, the heating step comprises a pre-heating step 102, during which the bearing component is pre-heated to austenitisation temperature, wherein the austenitisation temperature is in the range of 1040° C. to 1100° C.

[0051] The preheating may be performed in a single step or by multi steps (double steps) with equilibration at each step.

[0052] The pre-heating step 102 is followed by a so-called austenitisation step 103, during which the bearing component is held at the austenitisation temperature for a predetermined time, preferably 5 to 45 min. During the heating steps 102, and 103, the nitrogen-alloyed stainless steel structure is converted from being predominantly ferritic to mostly austenite.

[0053] Once, the bearing component has reached the required temperature, and the specified time (soaking time) has passed, the bearing component is quenched (step 104), immediately. Preferably, the quenching step 104 is performed by gas quenching, wherein helium or nitrogen or a mixture of helium and nitrogen is used. The gas quenching is preferably performed at a pressure in the range of 4 to 9 bar. During the quenching step, the nitrogen-alloyed stainless steel microstructure matrix is converted from austenite to mostly martensite. Before the component is removed from the quenching device, it is preferred that component's temperature is below 65-50° C.

[0054] For removing the residual austenite structure, and for reducing the softness of the bearing component made from the high nitrogen content nitrogen-alloyed stainless steel, the bearing component is subsequently subjected a deep-freezing step 105. Preferably, the deep-freezing step 105 is performed in a temperature range between −70° C. to −196° C. The holding time at this temperature is preferably between 15 min to 4 h. As the deep-freezing is intended to remove residual austenite it is further preferred that the deep-freezing is performed immediately after the quenching.

[0055] Optionally, after the deep-freezing step, the bearing component is brought to ambient temperature (step 106), or at least to temperatures below 40° C. This may be done passively by leaving the component at ambient temperature, or actively by subsequent optional tempering step(s). Alternatively, the step 106 is left out and the bearing component is subjected to the tempering steps (see below), directly after the deep freezing step 105.

[0056] Finally, for increasing the toughness of the steel, the bearing component is subject to a tempering step, preferably a plurality of tempering steps (steps 107 to 109), which increase the toughness of the nitrogen-alloyed stainless steel to such an extent that the nitrogen-alloyed stainless steel is usable for bearing applications.

[0057] As mentioned above, the tempering is a multi-step tempering, wherein e.g. in a first tempering step 107, the bearing component is heated to a temperature in the range of 160° C. to 240° C., and held at the temperature for 30 min to 4 h. After the first tempering step, the bearing component is brought back to ambient temperature, or at least, preferably passively, to temperatures below 40° C., in step 108. Optionally, the bearing component might be subjected to (deep-) freezing to temperatures between −70° C. to −196° C. After having reached ambient temperature, the bearing component is heated again, in a second tempering step 109, wherein the bearing component is heated to a higher temperature, preferably between 470° C. to 550°, and held at the temperature for 30 min to 4 h, again. After the second heating step 109, the bearing component is cooled to ambient temperature, or at least, preferably passively, to temperatures below 40° C., in step 110.

[0058] Dependent on the combination of mechanical, dimensional stability and corrosion resistance properties of the bearing component, also more or less than two tempering steps are possible.

[0059] In summary, due to the above described inventive heat treatment of the bearing component, it has become possible to use high nitrogen content nitrogen-alloyed stainless steel for bearing applications. Consequently, is has become possible to obtain both increased corrosion resistance and desired mechanical properties for bearing components in very aggressive environments, such as refrigerant lubricated bearings.

REFERENCE NUMERALS

[0060] 100 providing bearing component made from nitrogen-alloyed stainless steel with a nitrogen content between 0.6 wt. % and 2.0 w.t % [0061] 101 transferring the bearing component to heat treatment [0062] 102 pre-heating the bearing component to the austenitisation temperature in a single or double step, with equilibration at each step [0063] 103 austenitisation of the bearing component once it has reached the required temperature, and for a specified time (soaking time) [0064] 104 gas-quenching of the bearing component [0065] 105 deep-freezing of the bearing component [0066] 106 bringing the bearing component to ambient temperature [0067] 107 first tempering step—heating the bearing component to first temperature [0068] 108 bringing the bearing component to ambient temperature or at least to temperatures below 40° C. [0069] 109 second tempering step—heating the bearing component to second temperature [0070] 110 bringing the bearing component back to ambient temperature