ROLLING BEARING, PARTICULARLY HYBRID ROLLING BEARING FOR REFRIGERANT COMPRESSOR

Abstract

A rolling bearing having an inner raceway and an outer raceway and a plurality of rolling elements arranged therebetween. The rolling bearing is media-lubricated or oil-free lubricated. The lubricant forms an elasto-hydrodynamic lubricant film between the rolling elements and the raceways. At first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid, preferably an oil-based preservative fluid. Also, a refrigerant compressor having such a rolling bearing.

Claims

1: A rolling bearing comprising: an inner raceway, an outer raceway, and a plurality of rolling elements arranged therebetween, wherein the rolling bearing is media-lubricated or oil-free lubricated, wherein the lubricant forms an elasto-hydrodynamic lubricant film between the rolling elements and the raceways, wherein at first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid, and wherein the protective fluid is a polar substrate with polar heads and non-polar tails, and wherein the polar heads are adapted to bond to the bearing surface and the non-polar tails prevent elements to come into contact with the bearing surface.

2: The rolling bearing according to claim 1, wherein the protective fluid is water/humidity repellent.

3: The rolling bearing according to claim 1, wherein the rolling bearing is media-lubricated with pure refrigerant or a refrigerant mixture forming the elasto-hydrodynamic lubricant film.

4: The rolling bearing according to claim 1, wherein the rolling bearing is lubricated by means of an ultra-thin lubrication film arranged between the rolling elements and the raceways.

5: The rolling bearing according to claim 1, wherein the protective fluid is a preservative fluid with anticorrosion additives.

6: The rolling bearing according to claim 8, wherein the protective fluid is a polar substrate with polar heads and non-polar tails, and wherein the polar heads are adapted to bond to the bearing surface and the non-polar tails prevent elements to come into contact with the bearing surface.

7: The rolling bearing according to claim 1, wherein the polar substrate is a detergent, a dispersant or an inhibitor.

8: A rolling bearing comprising: an inner raceway, an outer raceway, and a plurality of rolling elements arranged therebetween, wherein the rolling bearing is media-lubricated or oil-free lubricated, wherein the lubricant forms an elasto-hydrodynamic lubricant film between the rolling elements and the raceways, wherein at first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid, and wherein at least one raceway is made from a hardened corrosion-resistant steel, having a corrosion resistance with a pitting potential of at least 25 mV higher than the stainless steel reference (AISI 440C) according to ASTM G61-86.

9: The rolling bearing according to claim 1, wherein at least one rolling element is made from silicon nitride (Si.sub.3N.sub.4).

10: The rolling bearing according to claim 1, wherein the rolling elements are guided by means of a cage.

11: A media lubricated machine comprising at least one rolling bearing: an inner raceway, an outer raceway, and a plurality of rolling elements arranged therebetween, wherein the rolling bearing is media-lubricated or oil-free lubricated, wherein the lubricant forms an elasto-hydrodynamic lubricant film between the rolling elements and the raceways, and wherein at first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid and wherein the protective fluid is a polar substrate with polar heads and non-polar tails, and wherein the polar heads are adapted to bond to the bearing surface and the non-polar tails prevent elements to come into contact with the bearing surface.

12: The rolling bearing according to claim 1, wherein the protective fluid is an oil-based preservative fluid.

13: The rolling bearing according to claim 4, wherein the ultra-thin lubrication film defines a lubrication film thickness that is less than three hundred nanometers (300 nm).

14: The rolling bearing according to claim 13, wherein the lubrication film thickness is less than one hundred nanometers (100 nm).

15: The rolling bearing according to claim 13, wherein the lubrication film thickness is less than thirty nanometers (30 nm).

16: The rolling bearing according to claim 7, wherein the protective fluid comprises at least one of overbased sulfonates, amides, imides and Zn-naphentate.

17: The rolling bearing according to claim 10, wherein the cage is made from a fiber-enforced material.

18: The rolling bearing according to claim 10, wherein the cage is made from glass-fiber-enforced PEEK.

19: The rolling bearing according to claim 10, wherein the cage is made from carbon fiber-enforced PEEK.

20: The media lubricated machine according to claim 11, wherein the protective fluid is an oil-based preservative fluid.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0056] In the following, the present invention will be described by means of embodiments shown in the figures. The shown embodiments are exemplarily, only, and are not intended to limit the scope of protection. The scope of protection is solely defined by the attached claims.

[0057] The figures show:

[0058] FIG. 1: a schematic drawing of a refrigerant compressor comprising a hybrid roller bearing according to a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0059] In the following same or similar functioning elements are indicated with the same reference numerals.

[0060] FIG. 1 shows a sectional view of a refrigerant compressor 1 having an electric motor 2 which drives a shaft 4. The shaft 4 is radially supported by a set of roller bearings, particularly hybrid roller bearings, 10-1, 10-2, which are arranged on both sides of the motor 2. Further, the shaft 4 is axially and radially supported by a plurality of ball bearings, particularly hybrid ball bearings, 20-1, 20-2, 20-3. The ball bearings 20 are preferably angular contact ball bearings, which are enabled to support axial and/or radial forces, but may be any other type of ball bearing. The roller bearings 10 may be any kind of roller bearing, e.g. a cylindrical roller bearing, a spherical roller bearing, a tapered roller bearing or a toroidal roller bearing or combinations thereof.

[0061] Each roller bearing 10 comprises an inner ring 12 having a raceway 13, an outer ring 14 having a raceway 15, and rollers 16 having raceways 17, which are arranged therebetween. The rollers 16 are further guided by means of a cage 18, which is preferably made from a glass-fiber enforced PEEK material. However, any other fiber-enforced material e.g. a carbon fiber material, may be used for the cage.

[0062] Analogously, each ball bearing 20 comprises an inner ring 22 having a raceway 23, an outer ring 24 having a raceway 25, and balls 26 having surfaces 27, arranged therebetween. Also, the balls 26 are guided by means of a cage 28, which is preferably made from a glass-fiber enforced PEEK material. However, any other fiber-enforced material e.g. a carbon fiber material, may be used for the cage.

[0063] Further, it should be noted that the ball bearings shown in FIG. 1, have a contact angle of 25 to 30, but it is also possible to use ball bearings having contact angles in the range of 0 to 45. Optionally, the ball bearing 20 has an osculation , which ranges between 1.02 and 1.1, wherein is defined as

[00002]$=\frac{2.Math.r_{i,e}}{D_w},$

with ri,e being me raceway radius of the inner raceway or the outer raceway, and Dw being the diameter of the ball. The proposed osculation gives a balance between low friction forces at the surface and high contact stresses, so bearing life is optimized.

[0064] As is further shown in FIG. 1, the rolling bearings 10, 20 are lubricated by lubrication means 30, 32, which are adapted to provide a lubricant to the rolling bearings 10, 20. Since the device shown in FIG. 1 is a refrigerant compressor, it is preferred to use the refrigerant itself or a refrigerant/oil mixture as lubricant. This has proven to improve heat transfer in the condensers and the evaporator heat exchangers. Eliminating oil lubricant also eliminates the need for oil maintenance and oil cost.

[0065] Unfortunately, the used refrigerant, e.g. R134a, R1233zd, R1234ze, or R515B produces a very aggressive environment which results in an increased corrosion risk for the bearings. Consequently, any deteriorating influences to the rolling bearing, even before first use, is to be avoided. Therefore, before first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid, preferably an oil-based preservative fluid. The protective fluid covers at least one of the functional surfaces of the bearing and protects the bearing from any deteriorating influence and chemical attack. Thereby, the protective fluid ensures that the surface of the bearing is, as much as possible, undamaged before the bearing is used for the first time.

[0066] Water/humidity is one of the main reasons for corrosion. In combination with the used refrigerant, water/humidity may generate corrosive elements or other substances which increase the corrosion risk. Consequently, the protective fluid coating may be water/humidity repellent or even hydrophobic, so that water or humidity does not get into contact with the media which is used for lubrication.

[0067] The protective fluid itself is a preservative fluid with anticorrosion additives. The anticorrosion additive or the protective fluid is preferably a polar substrate with polar heads and non-polar tails, wherein the polar heads are adapted to bond to the bearing surface and the non-polar tails prevent elements to come into contact with the bearing surface. The polar substances have the further advantage that the physical and chemical properties of the polar substance support that that the protective fluid coating is re-established, in case the coating is washed off the bearing to some extent.

[0068] Further, using pure refrigerant and/or a refrigerant/oil mixture as lubricant, leads to ultra-thin lubrications film thickness (UTFT) conditions due to the refrigerant providing an elasto-hydrodynamic lubrication film with a thickness of less than 200 nm, preferably less than 100 nm, most preferred less than 30 nm. Since these applications work with very thin film thicknesses (e.g. less than 200 nm) any solid particle (debris, sand, oil soot, etc.) even the very small ones can produce damage in the contact surfaces and can modify the topography disrupting the film build-up capability of the original surface. Excessive contamination, which is also an issue in refrigerant lubricated rolling bearing, can also generate high friction forces that will hinder/block the rotation of the bearing and can produce fractures in the cage or seizure in the raceways and rolling elements.

[0069] Advantageously, the protective fluid coating with anticorrosion additives is left on the bearing in use, as the substances do not react with the media-lubricant/refrigerant. To the contrary, the protective fluid coating may protect the bearing surfaces from the corrosive influence of the refrigerant by maintaining an additional protective coating on the bearing surface, which in turn enhances the bearing performance. A further advantage is that the additional coating may increase the thickness and/or continuity of the lubrication layer in ultra-thin lubrication film applications.

[0070] Further, in order to improve the wear and fatigue life of rolling bearings used in the refrigerant compressor, it has already been common knowledge to use a hardened high nitrogen stainless steel, e.g. VC444 steel, and silicon nitride rolling elements for the hybrid rolling bearing.

[0071] Additionally, micropitting and corrosion induced wear of a hybrid rolling bearing may be significantly reduced if the roughness of at least one rolling element is significantly higher than the roughness of the remaining rolling elements. The higher Rq2,i roughness value of the at least one rolling element allows for an increased wear when the at least one rolling element with the increase roughness contacts the raceways. Even if increased wear should in generally be avoided, the intended wear smooths out indentations in the raceways which occur during the service life of the bearing. This also reduces the overall corrosion of the bearing and prolongs the service life of the bearing.

[0072] The steel used for the rings and the raceway is preferably a hardened corrosion resistant steel, e.g. VC444 steel, another example is DIN X30CrMoN15-1 (AMS 5898). In general the hardened corrosion-resistant bearing steel for UTFT conditions refers to a bearing steel with an after-heat-treatment hardnessHRC 58 and/or fracture toughness of at least 14 MPa m (ASTM-E399-12). It is further preferred, if the corrosion resistance has a pitting potential bigger or equal to +25 mV higher than the stainless steel reference (AISI 440C) according to ASTM G61-86. After heat treatments the ring raceways 13, 15, 23, 25 are machined to dimensions, and the desired roughness is adjusted. The heat treatment usually comprises one of more of the following steps:

[0073] Austenitising at 1000 C. to 1150 C.;

[0074] Gas quench;

[0075] Subzero treatment at 40 C. to 150 C.;

[0076] Tempering to certain temperatures for different dimensional stability properties.

[0077] Table 1 shows one example of the covered steel: DIN X30CrMoN15-1 (AMS 5898), compared with the reference steel AISI 440 C. It is further shown that different tempering temperatures give different dimensional stability properties for the same corrosion resistant steel.

TABLE-US-00001 TABLE 1 Example of corrosion resistant steel parameters Pitting Potential relative to Steel reference, [mV] Tempering Hardness DIN X30CrMoN15-1 +25 At 400 C. to 58 HRC 550 C. DIN X30CrMoN15-1 +375 At 150 C. to 58 HRC 240 C. AISI 440C 0 Min. of ~204 C. 58 HRC

[0078] Preferably the rolling bearings 10, 20 are hybrid rolling bearings, wherein the rolling elements, namely the rollers 16 and the balls 26, are Silicon Nitride Balls/Rollers (Si3N4): The rolling elements 16, 26 are made by most stringent ceramic quality control and grade and have to pass ASTM F2094 or ISO 26602 class I and II with rolling element grade equal or better than G10.

[0079] Besides the roughness difference as mentioned above, the inventors have further found that it is preferred to adjust the combined roughness of raceways and rolling elements of the hybrid rolling bearings 10, 20 used for applications operating under UTFT conditions to predetermined ranges. It has been proven that hybrid rolling bearings 10, 20 having the roughness values as listed below are particularly resistant to corrosion induced wear even in UTFT conditions:

[0080] For the hybrid ball bearings 20, the following values apply:

[0081] the combined surface RMS roughness Rq of raceways and the remaining balls is R.sub.q410.sup.9(1000d.sub.m).sup.0.55 [meter], and the combined surface RMS roughness Rq of raceways and the at least one ball with the increased roughness is R.sub.qf*410.sup.9(1000d.sub.m).sup.0.55 [meter], with 2f12, wherein Rq is defined as R.sub.q={square root over (R.sub.q1.sup.2+R.sub.q2.sup.2)};

[0082] the combined roughness skewness Rsk of raceways and all balls is R.sub.sk0, wherein R.sub.sk is defined as

[00003]$R_{s.Math.k}=\frac{R_{s.Math.k.Math.1}.Math.R_{q.Math.1}^3+R_{s.Math.k.Math.2}.Math.R_{q.Math.2}^3}{R_q^3};$

[0083] the combined roughness slope parameter Rqx of raceways and remaining balls is R.sub.qx8 [mrad], and the combined roughness slope parameter Rqx of raceways and the at least one ball with increased roughness is R.sub.qxf*8 [mrad], with 2f12, wherein Rqx is defined as

[00004]$R_{.Math.q.Math.x}=\frac{R_{.Math.q.Math.x.Math.1}+R_{.Math.q.Math.x.Math.2}}{2}.$

[0084] For the hybrid roller bearings 10, the following values apply:

[0085] the combined surface RMS roughness Rq of raceways and the remaining rollers is R.sub.q510.sup.8(1000d.sub.m).sup.0.2 [meter], and the combined surface RMS roughness Rq of raceways and the at least one roller with the increased roughness is R.sub.qf*510.sup.8(1000d.sub.m).sup.0.2 [meter], with 1.2f18, wherein Rq is defined as R.sub.q={square root over (R.sub.q1.sup.2+Rq.sub.2.sup.2)};

[0086] the combined roughness skewness Rsk of raceways and all rollers is R.sub.sk0, wherein R.sub.sk is defined as

[00005]$R_{s.Math.k}=\frac{R_{s.Math.k.Math.1}.Math.R_{q.Math.1}^3+R_{s.Math.k.Math.2}.Math.R_{q.Math.2}^3}{R_q^3};$

[0087] the combined roughness slope parameter Rqx of raceways and remaining rollers is R.sub.qx50 [mrad], and the combined roughness slope parameter Rqx of raceways and the at least one roller with increased roughness is R.sub.qxf*50 [mrad], with 1.2 18, wherein Rqx is defined as

[00006]$R_{.Math.q.Math.x}=\frac{R_{.Math.q.Math.x.Math.1}+R_{.Math.q.Math.x.Math.2}}{2}.$

[0088] By providing a rolling bearing with an additional protective fluid coating, a robust operation of rolling element bearings in media lubricated applications may be achieved. Media (refrigerant) lubricated bearings often suffer from being exposed directly to the process media, which in many cases has poor properties as a lubrication and does not prevent or even promotes corrosion. Fluids used in media lubricated applications can be corrosive by themselves or generate corrosive elements in combination with water/humidity, other substances or by aging. The protective fluid (e.g.: preservative including antirust additives) covers the functional bearing surfaces, protects them, and prevents the bearing surfaces from chemical attack. Possible additives contained by the preservative in order to protect the bearing surfaces are overbased sulfonates, amides and imides, and Zn-naphentate. These additives have polar heads which bond to the polar bearing surfaces and non-polar tails which prevent other polar elements to get in contact with the bearing surface.

[0089] The protective fluid covering the bearing surfaces should not be removed before mounting the bearing into the application. The specialized bearing treatment allows a reliable operation of rolling element bearings for such demanding applications (stiffness, simplicity, robustness, tight clearances, . . . ).

REFERENCE NUMBERS

[0090] 1 refrigerant compressor [0091] 2 electric motor [0092] 4 compressor shaft [0093] 10 hybrid roller bearing [0094] 12 inner ring of the hybrid roller bearing [0095] 13 raceway of the inner ring of the hybrid roller bearing [0096] 14 outer ring of the hybrid roller bearing [0097] 15 raceway of the outer ring of the hybrid roller bearing [0098] 16 roller of the hybrid roller bearing [0099] 17 raceway of the roller of the hybrid roller bearing [0100] 18 cage of the hybrid roller bearing [0101] 20 hybrid ball bearing [0102] 22 inner ring of the hybrid ball bearing [0103] 23 raceway of the inner ring of the hybrid ball bearing [0104] 24 outer ring of the hybrid ball bearing [0105] 25 raceway of the outer ring of the hybrid ball bearing [0106] 26 balls of the hybrid ball bearing [0107] 27 surface of the balls of the hybrid ball bearing [0108] 28 cage of the hybrid ball bearing [0109] 30, 32 lubrications means