Rolling bearings for refrigerant compressors, especially hybrid rolling bearings

Abstract

A rolling bearing having an inner raceway and an outer raceway and a plurality of rolling elements arranged between the inner raceway and the outer raceway. The rolling bearing is medium-lubricated or oil-free lubricated. The lubricant forms an elastic hydrodynamic lubricant film between the rolling elements and the raceway. When the rolling bearing is used for the first time, at least one surface of the rolling bearing is coated with a protective fluid, preferably, the protective fluid is an oil-based anti-corrosion fluid. In addition, a refrigerant compressor having such a rolling bearing.

Description

Technical Field

[0001] The present invention relates to a rolling bearing, in particular a hybrid rolling bearing, and to a refrigerant compressor comprising such a hybrid rolling bearing. Background Art

[0002] Rolling bearings and in particular hybrid rolling bearings are often used in very demanding environments, for example, in applications with reduced lubrication conditions and / or in applications with high speeds and / or high temperatures. In hybrid roller bearings, the bearing rings and the roller elements are made of different materials. Typically, the (bearing) rings are made of steel and the rolling elements are made of ceramic materials. With increasing severity of the operating conditions (for example, heavier loads combined with higher temperatures, thinner lubricating films and / or poor lubrication conditions), the bearing assembly may suffer from surface initiated fatigue, the so-called micropitting. Even if micropitting is not necessarily the main failure mode, it may promote / accelerate the appearance of other failures such as indentations, surface initiated spalling and seizure.

[0003] Micropitting is therefore one of the mechanisms leading to life-limiting bearing wear. One way to mitigate the effects of micropitting is to ensure that the rolling contact surfaces in the bearing are always separated by a lubricating film of sufficient thickness.

[0004] This is not feasible in ultra-thin lubricant film thickness (UTFT) applications. UTFT applications in rolling element bearings are those conditions when the surfaces separated by the lubricant film are compromised by:

[0005] The lubricant has a low viscosity, i.e. the dynamic viscosity of the fluid is on the order of 1 cSt and below, and / or

[0006] Lubricant starvation is a condition where the available lubricant layer in the rolling contact inlet does not guarantee a fully flooded condition in the bearing.

[0007] In both cases, the total lubricant layer thickness at the contact surface is limited to 300 nm or less. This can happen because: the bearing is lubricated with grease (limited release of lubricant), or the lubricant evaporates before reaching the contact (volatile fluid), or the lubricant supply by the lubrication system is limited.

[0008] Furthermore, many of these UFT applications use medium lubrication (e.g. pure refrigerant lubrication, oil-refrigerant mixture lubrication, fuel (kerosene, diesel, gasoline, natural gas, alcohols) lubrication) and / or grease in combination with the medium. Water lubrication is excluded. For pure refrigerant lubrication, the resulting lubricant film thickness is even significantly less than 300 nm, more often less than 100 nm, and typically in the range of 30 nm.

[0009] The main failure mode of these rolling bearings is wear assisted by corrosion. Wear (solid-to-solid contact enhanced by corrosion) can change the raceway profile, increase clearance, and cause local stress concentrations that can develop spalling. Another important failure mode of these bearings is solid contamination. Since these applications operate at very thin film thicknesses (e.g., less than 300nm to 200nm), any solid particles (debris, sand, oil soot, etc.), even very small solid particles, will cause damage to the contact surface and change the topography, disrupting the film-building ability of the original surface. Excessive contamination may also produce high friction that will hinder / block the bearing from rotating, and may cause fractures in the cage or seizures in the raceways and rolling elements.

[0010] Therefore, in the prior art, it has been proposed to use surface engineering techniques and to provide as equal a roughness as possible of the raceways of the bearing rings and the roughness of the rolling elements in order to reduce micropitting and improve the wear and fatigue life of the bearing. This is based on the understanding that in the presence of sliding and in the absence of full-film lubrication, the rougher rolling contact surface will impose load microcycles on the smoother opposing rolling contact surface. Unfortunately, in practice, even in ordinary steel-steel bearings, the raceways of the bearings are usually somewhat rougher than the rolling elements. In hybrid rolling bearings, the difference between the roughnesses is even greater.

[0011] In order to provide a hybrid rolling bearing having an extended service life and improved corrosion resistance and micropitting resistance even after running-in, it is also proposed to provide at least one of the rolling elements of the hybrid rolling bearing with an increased surface RMS roughness R q2,N , the RMS roughness R q2,N Significantly higher RMS roughness R than other rolling elements q2,iWhen at least one rolling element with increased roughness contacts the raceway, the higher roughness value R of the at least one rolling element q2,N Allowing ( / causing) wear to increase. Even though increased wear should generally be avoided, the anticipated wear according to the invention also smooths out indentations ( / indentations / notches / nicks) in the raceways (that occur during the service life of the bearing). This in turn reduces the overall corrosion of the hybrid bearing and extends the service life of the bearing.

[0012] However, it has proven disadvantageous that during transportation or installation of the rolling bearing, the precision machined surface may be damaged and / or the intentionally designed roughness of the surface may be degraded, for example due to mishandling or corrosion. This in turn degrades the corrosion resistance and micropitting resistance of the bearing and ultimately its service life.

[0013] It is therefore an object of the present invention to provide a rolling bearing, in particular a hybrid rolling bearing, which can be used in ultra-thin lubricating film thickness applications, in particular for refrigerant compressor devices, and which has improved and protected corrosion and micropitting resistance. Summary of the invention

[0014] This object is solved by a hybrid rolling bearing and a refrigerant compressor comprising such a bearing according to patent solution 1.

[0015] In the following, a rolling bearing, in particular a hybrid rolling bearing, is proposed, which includes an inner raceway and an outer raceway and a plurality of rolling elements arranged therebetween. The rolling bearing may be a hybrid ball bearing with balls as rolling elements or a hybrid roller bearing with rollers as rolling elements, wherein the hybrid rolling bearing has an outer raceway and an inner raceway made of bearing steel and rolling elements (balls or rollers) made of ceramic material.

[0016] In order to provide a rolling bearing with an extended service life and improved corrosion resistance and micropitting resistance even after running-in, the inventors have found that for rolling bearings that are medium-lubricated or oil-free lubricated during use (wherein the lubricant forms an elastic hydrodynamic lubrication film between the rolling elements and the raceway), it is crucial to avoid any deteriorating effects on the rolling bearing even before the first use. Therefore, a rolling bearing is proposed, wherein, when the rolling bearing is used for the first time, at least one surface of the rolling bearing is coated with a protective fluid, and the protective fluid is preferably an oil-based anti-corrosion fluid. The protective fluid covers at least one of the functional surfaces of the bearing and protects the bearing from any chemical attack. Thereby, the protective fluid ensures that the surface of the bearing is as undamaged as possible before the bearing is used for the first time.

[0017] It is therefore particularly advantageous if the protective fluid coating is water / humidity repellent, or even hydrophobic, so that water / humidity does not come into contact with the medium used for lubrication. Typically, lubricants are used in medium-lubricated bearing applications, which have an even higher corrosive impact when in contact with water / humidity. Therefore, any water / humidity exposure should be avoided, which can be achieved by coating the bearing with a water-repellent or hydrophobic coating fluid.

[0018] According to another preferred embodiment, the medium-lubricated bearings are lubricated by pure refrigerant or refrigerant-oil mixtures. Refrigerants and refrigerant-oil mixtures can be aggressive and / or easily decompose and form acids. Such refrigerant substances are even more aggressive when combined with moisture / humidity. Therefore, bearings operating in a refrigerant-lubricated environment need to be additionally protected, which is accomplished by an additional protective fluid coating. Any slight damage to the surface during installation or transportation may result in a shortened life. Even in a refrigerant-lubricated environment, a protective fluid coating can avoid such damage, thereby increasing the service life of the bearing. Typically, refrigerants such as R134a, R1233zd, R1234ze or R515B can be used.

[0019] Another challenge of medium-lubricated bearings is that the medium usually provides only an insufficient lubricating film. Therefore, for rolling bearings (especially hybrid rolling bearings) that are lubricated by means of an ultra-thin lubricating film arranged between the rolling elements and the raceways (wherein the lubricating film thickness is less than 300 nm, preferably less than 100 nm, most preferably less than 30 nm), an additional protective fluid coating is advantageous.

[0020] Advantageously, the protective fluid coating with anti-corrosion additives remains on the bearing during use because the substance does not react with the medium (lubricant / refrigerant). Moreover, the protective fluid coating can protect the bearing surface from the corrosive effects of the medium (lubricant / refrigerant) by maintaining an additional protective coating on the bearing surface, which in turn improves bearing performance. Another advantage is that the additional coating can increase the thickness and / or continuity of the lubricating film in ultra-thin lubricating film applications.

[0021] According to another preferred embodiment, the protective fluid is an anti-corrosion fluid with an anti-corrosion additive. The anti-corrosion additive is physically or chemically bound to the bearing surface and protects the bearing from deteriorating influences such as chemical attack.

[0022] Such an anti-corrosion additive or protective fluid itself may be a polar substance ( / polar substrate) having a polar head and a non-polar tail, wherein the polar head is adapted to bind to the bearing surface and the non-polar tail prevents elements from contacting the bearing surface. Another advantage of polar substances is that the physical and chemical properties of polar substances support re-establishment of the protective fluid coating in the event that the coating is washed off the bearing to some extent.

[0023] In general, the mechanism of these anti-corrosion additives is relatively simple. Anti-corrosion additives are molecules with long alkyl chains and polar groups that can be adsorbed on metal surfaces to form a densely packed hydrophobic layer. The adsorption mechanism can be based on the physical or chemical interaction of polar anti-corrosion additives with metal surfaces.

[0024] Advantageously, the polar material is a detergent, dispersant or inhibitor, wherein the corrosion protection fluid preferably comprises overbased sulfonates, amides, imides and / or zinc naphthenates.

[0025] It is known to use, for example, petroleum sulfonates, which are byproducts of the production of white oils by treatment with oleum. The resulting acid tar contains long-chain alkylarylsulfonic acids which can be neutralized with alkali. In water-based metal working fluids, engine oils and rust inhibitors, sodium sulfonates with low molecular weights (less than about 450) are often used as low-cost emulsifiers and detergents with additional anticorrosive properties. Sulfonates with higher molecular weights are known to be highly effective corrosion inhibitors, especially when based on divalent cations such as calcium, magnesium and barium. Due to toxicological and ecotoxicological considerations, the importance of barium compounds is decreasing.

[0026] In addition, composite alkylbenzenesulfonates (syntheticalkylbenzenesulfonates) can be preferably used due to their higher and more constant quality. They are the reaction products of specially designed monoalkylbenzenesulfonic acids (usually C24 alkyl groups) and dialkylbenzenesulfonic acids (usually two C12 alkyl groups) with alkali metal hydroxides and alkaline earth metal hydroxides.

[0027] A special group of synthetic sulfonates is the dinonylnaphthenesulfonates.

[0028] In addition to neutral or only slightly basic sulfonates, overbased sulfonates with a high alkaline reserve (TBN (Total Base Number) 100-400 mg KOH / g) also play an important role. They exhibit detergent properties and are able to neutralize acidic oxidation products.

[0029] Furthermore, many different long-chain carboxylic acid derivatives can be used, in which the carboxyl group acts as a polar moiety that can be easily adsorbed on metal surfaces.

[0030] Examples are salts of fatty acids such as lanolin (wool fat) and lanolin, which are highly polar due to the high content of hydroxyl and oxocarboxylic acids, most often in combination with sulfonates or oxidized paraffins ( / oxygenated paraffins).

[0031] Zinc naphthenate can be used in particular in lubricating greases.

[0032] Alkylated succinic acids, their partial esters and half amides are also considered to be highly effective and will not emulsify the corrosion protection additive even at very low treat rates of 0.01% to 0.05%.

[0033] 4-Nonylphenoxyacetic acid and its derivatives have similar properties.

[0034] Another widely distributed group is amides and imides, which are the reaction products of saturated and unsaturated fatty acids with alkylamines and alkanolamines. The most well-known products of this type are N-acylsarcosines, which show a strong synergistic effect with imidazoline derivatives. In addition, these additives have good water-repelling properties.

[0035] Furthermore, some special amine salts of monoalkyl partial phosphate esters or dialkyl partial phosphate esters exhibit excellent anti-corrosion properties in addition to their highly effective anti-wear properties.

[0036] Alternatively or additionally, vapor corrosion inhibitors (VCI) can be used, particularly for closed systems. These substances have a high affinity for metal surfaces and a relatively high vapor pressure to ensure their availability on parts that are in direct contact with lubricants in an unstable manner. The most commonly used product family for this application is amines. Morpholine, dicyclohexylamine and diethanolamine have been shown to be very effective for this purpose. Due to the toxicological problems of the nitrosamine formation potential of mainly secondary amines ( / secondary amines), these product parts will be replaced by tertiary amines ( / tertiary amines) (such as diethanol methylamine) and similar products. Another group of oil-soluble VCIs are low molecular weight carbonic acids (n-C8 to n-C10).

[0037] According to a further preferred embodiment, the bearing is an angular contact ball bearing having a contact angle between 10° and 40°, in particular an angular contact ball bearing having a contact angle between 15° and 30°.

[0038] The bearings may also comprise more than one row of rolling elements or may be arranged in groups, for example: pairs of bearings arranged back-to-back or face-to-face. In the case where the bearings are also angular contact ball bearings, it is further preferred that the contact angles are identical. As another alternative, the contact angles may also be different, wherein in particular the contact angle of the first of the two ball bearings is between 10° and 20° and the contact angle of the second of the two ball bearings is between 21° and 35°.

[0039] If the bearings are arranged in pairs, it is further preferred that the two bearings are configured to provide an axial clearance with zero measured load and zero installed load, wherein the axial clearance is between -5 μm and 40 μm if the inner diameter of the inner ring is less than or equal to 80 mm; the axial clearance is between -5 μm and 50 μm if the inner diameter (of the inner ring) is greater than 80 mm and less than or equal to 180 mm; and the axial clearance is between -5 μm and 70 μm if the inner diameter (of the inner ring) is greater than 180 mm. Alternatively, the axial clearance may be defined based on the pitch diameter of the rolling elements, such that: if the pitch diameter of one of the two bearings is less than or equal to 100 mm, the axial clearance is between -5 μm and 40 μm; if the pitch diameter of one of the two bearings is greater than 100 mm and less than or equal to 200 mm, the axial clearance is between -5 μm and 50 μm; and if the pitch diameter of one of the two bearings is greater than 200 mm, the axial clearance is between -5 μm and 70 μm.

[0040] Thereby, the clearance is determined before the bearing is used for the first time. It is further preferred that two rolling bearings are paired to form a synchronized set.

[0041] According to a further preferred embodiment, the rolling bearing is designed for high rotational speeds between 2500 rpm and 25000 rpm or for ndm values ​​between 500000 / 60 s and 1500000 mm / 60 s, wherein the ndm value is the product of the rotational speed and the pitch circle diameter.

[0042] In case the roller bearing is a hybrid roller bearing, it is further preferred that at least one of the rolling elements of the hybrid roller bearing has an increased surface RMS roughness R q2,N , the RMS roughness R q2,N Significantly higher RMS roughness R than other rolling elements q2,i When at least one rolling element with increased roughness contacts the raceway, the higher roughness value R of the at least one rolling element q2,N Allowing ( / causing) wear to increase. Even though increased wear should generally be avoided, the anticipated wear according to the invention also smooths out indentations ( / indentations / notches / nicks) in the raceways (that occur during the service life of the bearing). This in turn reduces the overall corrosion of the hybrid bearing and extends the service life of the bearing.

[0043] Another advantage of at least one rolling element with increased roughness is that contamination particles can be received within the rough surface of the at least one rolling element. Thus, contamination particles that are known to damage the raceways and / or rolling elements of the rings can be filtered out, which also increases the wear and corrosion resistance of the bearing.

[0044] It is thus proved that if the increased RMS roughness R of at least one rolling element q2,N RMS roughness R of the rest of the rolling elements q2,i Advantageously, it is 10 to 25 times higher. Such a high roughness allows excellent smoothing results.

[0045] According to another preferred embodiment, the increased roughness R of at least one rolling element q2,N Higher than the roughness R of the raceway q1 It is further preferred that the roughness of the remaining rolling elements is lower than the roughness of the raceway, wherein the roughness R of the raceway of the hybrid ball bearing is q1 Roughness R of the rest of the ball q2 2 to 5 times, preferably 2.5 to 4 times, higher and / or the roughness R of the raceway of the hybrid roller bearing q1 Roughness R of other rollers q2 1.2 to 4 times higher, preferably 1.5 to 3 times higher.

[0046] In contrast to recent efforts to provide hybrid rolling bearings having substantially identical raceway roughness values ​​and rolling element roughness values, the inventors surprisingly discovered that the wear caused by micropitting and corrosion of the hybrid rolling bearing can be significantly reduced if the roughness of the contact surface of the hybrid rolling bearing (especially when in new condition) is engineered to be within the predefined boundaries mentioned above.

[0047] By providing a hybrid rolling bearing engineered to have the above defined parameters, the ceramic rolling elements reduce boundary friction and optimize running-in. In addition, under poor lubrication and contamination conditions, the proposed ceramic rolling elements inhibit damage mechanisms. In addition, strict control of the roughness of the formation helps to establish a lubricating film and improve running-in as well as the establishment of a protective fluid coating.

[0048] According to another preferred embodiment, the rolling bearing has a degree of oscillation Φ in the range between 1.02 and 1.1, wherein Φ is defined as where r i,e is the raceway radius of the inner or outer raceway and Dw is the diameter of the rolling element. The proposed closeness strikes a balance between low friction and high contact stress at the surface, thus optimizing the bearing life.

[0049] It is further advantageous that at least one component of the proposed rolling bearing (e.g., raceway and / or rolling element) is made of a hardened corrosion-resistant steel having a pitting potential of at least 25 mV higher than the stainless steel reference (AISI 440C) according to ASTM G61-86. Additionally or alternatively, the steel used has a heat-treated hardness of ≥58 HRC and / or a fracture toughness of at least 14 MPa m1 / 2 (see ASTM-E399-12).

[0050] In the case where the rolling bearing is a hybrid rolling bearing, it is preferred that at least one rolling element of the hybrid rolling bearing is made of silicon nitride (Si3N4). This, combined with the selected corrosion resistance of the steel mentioned above, allows low wear to develop in the hybrid rolling bearing, since the wear in this case depends on the steel hardness and the chemical aggressiveness of the environment (corrosion assisted wear).

[0051] According to another preferred embodiment, the rolling elements of the proposed rolling bearing are guided by means of a cage, which is preferably made of a fiber-reinforced material, preferably glass-fiber-reinforced PEEK or a carbon fiber material. The fiber-reinforced material of the cage prevents the cage from breaking in a heavily polluted environment.

[0052] Preferably, the cage has at least one cage cell adapted to accommodate at least one rolling element, wherein the at least one cage cell has an annular shape. The annular shape of the cage cell can support the performance of the bearing under poor lubrication conditions.

[0053] All these features alone or in combination ensure a long duration of rolling bearings, in particular hybrid rolling bearings, even under the specific conditions of ultra-thin lubricating film thickness conditions. This would not be achievable without the above features.

[0054] Another aspect of the invention relates to a refrigerant compressor comprising at least one rolling bearing as described above.

[0055] Further advantages and preferred embodiments are disclosed in the description and in the drawings.It should also be noted that a person skilled in the art may combine the presented features in a manner other than indicated without extending the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Hereinafter, the present invention will be described by means of the embodiments shown in the accompanying drawings. The embodiments shown are only exemplary and are not intended to limit the scope of protection.

[0057] The accompanying drawings show:

[0058] Figure 1 : Schematic diagram of a refrigerant compressor including a hybrid roller bearing according to a preferred embodiment.

[0059] 1Refrigerant compressor

[0060] 2 Electric motors

[0061] 4 Compressor shaft

[0062] 10Hybrid roller bearings

[0063] 12Inner ring of hybrid roller bearing

[0064] 13 Raceway of the inner ring of a hybrid roller bearing

[0065] 14 Outer ring of hybrid roller bearing

[0066] 15 Raceway of outer ring of hybrid roller bearing

[0067] 16 rollers of hybrid roller bearings

[0068] 17 Roller raceway of hybrid roller bearing

[0069] 18 Cage for hybrid roller bearings

[0070] 20 Hybrid ball bearings

[0071] 22 Inner ring of hybrid ball bearing

[0072] 23 Inner ring raceway of hybrid ball bearing

[0073] 24 Outer ring of hybrid ball bearing

[0074] 25 Raceway of outer ring of hybrid ball bearing

[0075] 26 balls for hybrid ball bearings

[0076] 27 Surface of the ball of the hybrid ball bearing

[0077] 28 Cage for hybrid ball bearings

[0078] 30, 32 Lubrication parts DETAILED DESCRIPTION

[0079] In the following, identical or similar functional elements are denoted by the same reference numerals.

[0080] Figure 1 A cross-sectional view of a refrigerant compressor 1 is shown, which has an electric motor 2 driving a shaft 4. The shaft 4 is radially supported by a set of roller bearings (particularly hybrid roller bearings) 10-1, 10-2 arranged on both sides of the motor 2. In addition, 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 bearing 20 is preferably an angular contact ball bearing capable of supporting axial forces and / or radial forces, but can be any other type of ball bearing. The roller bearing 10 can be any type of roller bearing, for example, a cylindrical roller bearing, a spherical roller bearing, a tapered roller bearing, a toroidal roller bearing or a combination thereof.

[0081] 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 a raceway 17 and arranged between the inner ring 12 and the outer ring 14. The rollers 16 are also guided by means of a cage 18, which is preferably made of a glass fiber reinforced PEEK (polyetheretherketone) material. However, any other fiber reinforced material (e.g., a carbon fiber material) may be used for the cage.

[0082] Similarly, each ball bearing 20 comprises an inner ring 22 having a raceway 23, an outer ring 24 having a raceway 25, and a ball 26 having a surface 27 and arranged between the inner ring 22 and the outer ring 24. In addition, the ball 26 is guided by means of a cage 28, which is preferably made of a glass fiber reinforced PEEK material. However, any other fiber reinforced material (e.g., a carbon fiber material) can be used for the cage.

[0083] In addition, it should be noted that Figure 1 The ball bearing shown in has a contact angle of 25° to 30°, but ball bearings with contact angles in the range of 0° to 45° may also be used. Optionally, the ball bearing 20 has an osculation Φ in the range of 1.02 to 1.1, where Φ is defined as Among them, r i,e is the raceway radius of the inner or outer raceway, D w is the diameter of the ball. The proposed closeness strikes a balance between low friction and high contact stress at the surface, thus optimizing the bearing life.

[0084] Also like Figure 1 As shown in FIG. 1 , the rolling bearings 10 , 20 are lubricated by lubricating components 30 , 32 , which are suitable for providing lubricant to the rolling bearings 10 , 20 . Figure 1 The device shown in is a refrigerant compressor, so it is preferred to use the refrigerant itself or a refrigerant / oil mixture as the lubricant. This has been shown to improve heat transfer in the condenser and evaporator heat exchangers. Eliminating the oil lubricant also eliminates the need for oil maintenance and oil costs.

[0085] Unfortunately, the refrigerants used (e.g. R134a, R1233zd, R1234ze or R515B) create a very aggressive environment, which leads to an increased risk of corrosion of the bearing. Therefore, even before the first use, any deteriorating influences on the rolling bearing should be avoided. Therefore, before the first use of the rolling bearing, at least one surface of the rolling bearing is coated with a protective fluid, which is 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 influences and chemical attack. Thereby, the protective fluid ensures that the surface of the bearing is as undamaged as possible before the bearing is used for the first time.

[0086] Water / humidity is one of the main causes of corrosion. When combined with the refrigerant used, water / humidity may create corrosive elements or other substances that increase the risk of corrosion. Therefore, the protective fluid coating may be water / moisture resistant, or even hydrophobic, so that water or humidity does not come into contact with the medium used for lubrication.

[0087] The protective fluid itself is an anticorrosive fluid with an anticorrosive additive. The anticorrosive additive or protective fluid is preferably a polar substance ( / polar matrix) having a polar head and a non-polar tail, wherein the polar head is suitable for bonding to the bearing surface and the non-polar tail prevents (corrosive) elements from contacting the bearing surface. Another advantage of polar substances is that the physical and chemical properties of polar substances support the re-establishment of the protective fluid coating in the event that the coating is washed off the bearing to some extent.

[0088] Furthermore, the use of pure refrigerants and / or refrigerant / oil mixtures as lubricants results in ultra-thin lubricating film thickness (UTFT) conditions, since the refrigerant provides an elasto-hydrodynamic lubricating film with a thickness of less than 200 nm (preferably less than 100 nm, most preferably less than 30 nm). Since these applications operate at very thin film thicknesses (e.g., less than 200 nm), any solid particles (debris, sand, oil soot, etc.), even very small solid particles, may cause damage to the contacting surfaces and change the topography, disrupting the film build-up capability of the original surface. Another problem in refrigerant-lubricated rolling bearings is that excessive contamination may also produce high friction forces that will hinder / block the bearing rotation and may produce fractures in the cage or seizures in the raceways and rolling elements.

[0089] Advantageously, the protective fluid coating with anti-corrosion additives remains on the bearing during use because the substance does not react with the medium (lubricant / refrigerant). Moreover, the protective fluid coating can protect the bearing surface from the corrosive effects of the refrigerant by maintaining an additional protective coating on the bearing surface, which in turn improves bearing performance. Another advantage is that the additional coating can increase the thickness and / or continuity of the lubricating layer in ultra-thin lubricating film applications.

[0090] Furthermore, in order to improve the wear and fatigue life of rolling bearings used in refrigerant compressors, it is known to use rolling elements of hardened high nitrogen stainless steel (eg VC444 steel) and silicon nitride for hybrid rolling bearings.

[0091] Furthermore, wear caused by micropitting and corrosion of hybrid rolling bearings can be significantly reduced if the roughness of at least one rolling element is significantly higher than the roughness of the remaining rolling elements. When at least one rolling element with increased roughness contacts the raceway, the higher roughness value R of at least one rolling element q2,N Allowing ( / causing) wear to increase. Even though increased wear should generally be avoided, the expected wear also smoothes out indentations ( / notches / recesses / depressions) in the raceways (which occur during the service life of the bearing). This also reduces overall corrosion of the bearing and extends the service life of the bearing.

[0092] The steel used for the rings and raceways is preferably a hardened corrosion-resistant steel, such as VC444 steel, another example is DINX30CrMoN15-1 (AMS5898). Typically, hardened corrosion-resistant bearing steel for UTFT conditions refers to a bearing steel (ASTM-E399-12) having a hardness ≥HRC58 and / or a fracture toughness of at least 14MPam1 / 2 after heat treatment. It is further preferred if the pitting potential of the corrosion resistance is greater than or equal to +25mV higher than the stainless steel benchmark (AISI440C) according to ASTMG61-86. After the heat treatment, the raceways 13, 15, 23, 25 of the rings are machined to a certain size and the desired roughness is adjusted. The heat treatment generally includes one or more of the following steps:

[0093] Austenitizing at 1000°C to 1150°C;

[0094] Gas quenching (quench);

[0095] Subzero treatment at -40°C to -150°C;

[0096] Temper to a certain temperature for different dimensional stability properties.

[0097] Table 1 shows an example of a covered steel: DINX30CrMoN15-1 (AMS5898) compared to a benchmark steel AISI440C. It also shows that for the same corrosion resistant steel, different tempering temperatures lead to different dimensional stability properties.

[0098] Table 1 Examples of corrosion-resistant steel parameters

[0099]

[0100]

[0101] Preferably, the rolling bearings 10, 20 are hybrid rolling bearings in which the rolling elements (i.e., rollers 16 and balls 26) are silicon nitride (Si3N4) balls / rollers: the rolling elements 16, 26 are made through the most stringent ceramic quality control and grades and must pass ASTM F2094 or ISO 26602 Grade I and II and the rolling element grade is equal to or better than G10.

[0102] In addition to the roughness differences as mentioned above, the inventors have also found that it is preferred to adjust the combined roughness of the raceways and rolling elements of the hybrid rolling bearings 10, 20 for applications operating ( / running) under UTFT conditions to a predetermined range. It has been proven that hybrid rolling bearings 10, 20 having the roughness values ​​listed below are particularly resistant to corrosion-induced wear even under UTFT conditions:

[0103] For hybrid ball bearings 20, the following values ​​apply:

[0104] Combined surface RMS roughness of raceway and other balls q For R q ≤4×10 -9 (1000d m ) 0.55 [m], and the combined surface RMS roughness R of at least one ball and raceway having increased roughness q For R q ≤f*4×10 -9 (1000d m ) 0.55 [m], where 2≤f≤12, where R q is defined as

[0105] Combined roughness skewness of raceway and all balls R sk For R sk ≤0, where R sk is defined as

[0106] The combined roughness slope parameter R of the raceway and the remaining balls Δqx For R Δqx ≤8 [mrad] and having a combined roughness slope parameter R of at least one ball and raceway with increased roughness Δqx For R Δqx ≤f*8[mrad], where 2≤f≤12, where R Δqx is defined as

[0107] For hybrid roller bearings 10, the following values ​​apply:

[0108] Combined surface RMS roughness R of raceway and other rollers q For R q ≤5×10 -8 (1000d m ) 0.2 [m], and the combined surface RMS roughness R of at least one roller and raceway having increased roughness q For R q ≤f*5×10 -8 (1000d m ) 0.2 [m], where 1.2≤f≤18, where R q is defined as

[0109] Combined roughness deflection R of raceway and all rollers sk For R sk ≤0, where R sk is defined as

[0110] Combined roughness slope parameter R of the raceway and the remaining rollers Δqx For R Δqx ≤50 [mrad] and having a combined roughness slope parameter R of at least one roller and raceway with increased roughness Δqx For R Δqx ≤f*50[mrad], where 1.2≤f≤18, where R Δqx is defined as

[0111] By providing rolling bearings with an additional protective fluid coating, robust operation of rolling bearings in medium-lubricated applications can be achieved. Bearings lubricated by medium (refrigerant) are often exposed to direct exposure to process media, which in many cases have poor properties as lubricants and cannot prevent corrosion or even promote corrosion. The fluid used in medium-lubricated applications may be corrosive in itself, or produce corrosive elements in combination with moisture, other substances or through aging. The protective fluid (for example, a preservative including a rust-proof additive) covers the functional bearing surfaces, protects them, and prevents the bearing surfaces from being chemically attacked. In order to protect the bearing surfaces, the additives that the preservative may contain are overbased sulfonates, amides and imides, and zinc naphthenates. These additives have a polar head that binds to the polar bearing surface and a non-polar tail that prevents other polar elements from contacting the bearing surface.

[0112] The protective fluid covering the bearing surface should not be removed before mounting the bearing in the application. Special bearing treatments enable rolling element bearings to operate reliably for such demanding applications (rigidity, simplicity, robustness, close clearances…).

Claims

1. A rolling bearing, comprising: Inner raceway, Outer raceway, and A plurality of rolling elements are arranged between the inner raceway and the outer raceway, wherein the rolling bearing is medium-lubricated or oil-free lubricated, wherein: The lubricant forms an elastic hydrodynamic lubricant film between the rolling elements and the raceways, and wherein, When the rolling bearing is used for the first time, at least one surface of the rolling bearing is coated with a protective fluid or an additive, The protective fluid or additive is a polar substance having a polar head adapted to bind to the bearing surface and a non-polar tail that prevents elements from contacting the bearing surface.

2. The rolling bearing according to claim 1, characterized in that: The protective fluid is water / moisture resistant and / or hydrophobic.

3. The rolling bearing according to claim 1, characterized in that: The rolling bearing is lubricated with a pure refrigerant or a refrigerant mixture which forms an elastohydrodynamic lubricant film.

4. The rolling bearing according to claim 1, characterized in that: The rolling bearing is lubricated by means of an ultra-thin lubricating film arranged between the rolling elements and the raceway, and the thickness of the lubricating film is less than 300 nm.

5. The rolling bearing according to claim 1, characterized in that: The protective fluid is an anti-corrosion fluid with anti-corrosion additives.

6. The rolling bearing according to claim 5, characterized in that: The polar substance is a detergent, a dispersant or an inhibitor.

7. The rolling bearing according to claim 1, characterized in that: At least one raceway is made of a hardened corrosion resistant steel having a corrosion resistance having a pitting potential at least 25 mV higher than a stainless steel reference (AISI 440C) according to ASTM G61-86.

8. The rolling bearing according to claim 1, characterized in that: At least one rolling element is made of silicon nitride (Si3N4).

9. The rolling bearing according to claim 1, characterized in that: The rolling elements are guided by means of a cage.

10. The rolling bearing according to claim 1, characterized in that: The rolling bearing is a hybrid rolling bearing.

11. The rolling bearing according to claim 1, characterized in that: The protective fluid is an oil-based anti-corrosion fluid.

12. The rolling bearing according to claim 4, characterized in that: The thickness of the lubricating film is less than 100 nm.

13. The rolling bearing according to claim 12, characterized in that: The thickness of the lubricating film is less than 30 nm.

14. The rolling bearing according to claim 6, characterized in that The corrosion resistant fluid includes an overbased sulfonate, an amide, an imide and / or zinc naphthenate.

15. The rolling bearing according to claim 9, characterized in that: The cage is made of fiber-reinforced material.

16. The rolling bearing according to claim 9, characterized in that The cage is made of glass fiber or carbon fiber reinforced PEEK or carbon fiber material.

17. A medium-lubricated and / or oil-free machine, comprising at least one rolling bearing, the rolling bearing having: Inner raceway; Outer raceway; as well as A plurality of rolling elements are arranged between the inner raceway and the outer raceway, wherein the rolling bearing is medium-lubricated or oil-free lubricated, wherein: The lubricant forms an elastic hydrodynamic lubricant film between the rolling elements and the raceways, and wherein, When the rolling bearing is used for the first time, at least one surface of the rolling bearing is coated with a protective fluid or an additive, The protective fluid or additive is a polar substance having a polar head adapted to bind to the bearing surface and a non-polar tail that prevents elements from contacting the bearing surface.

18. The medium-lubricated and / or oil-free machine according to claim 17, characterized in that The machine is a refrigerant compressor.

19. The medium-lubricated and / or oil-free machine according to claim 17, characterized in that The rolling bearing is a hybrid rolling bearing.

20. The medium-lubricated and / or oil-free machine according to claim 17, characterized in that The protective fluid is an oil-based anti-corrosion fluid.

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