DE102009023818A1 - Antifriction bearing comprises components arranged under a bearing ring and roller body that rolls off on the bearing ring, where one of the components is equipped on its surface with a coating, which consists of a nickel-alloy - Google Patents

Abstract

The antifriction bearing comprises components arranged under a bearing ring and roller body that rolls off on the bearing ring. One of the components is equipped on its surface with a coating with a thickness of 2 mu m. The coating consists of a nickel-alloy and is produced by chemical deposition process. The component exists out of base material and the coating is directly applied on the base material. The coating process is carried out by immersion in a nickel bath and the coating has a hardness of 50-55 HRC. An independent claim is included for a method for the production of a component for antifriction bearing.

Description

The The invention relates to a rolling bearing comprising a plurality of components, including at least one bearing ring and rolling elements, which roll on the at least one bearing ring.

at the optimization of the service life of rolling bearings at the same time Reducing the failure rate is known to be the surfaces to handle components of rolling bearings. Such treatments can be coatings or chemical reactions at the Surface, through which, for example, the tribological Improves behavior, changes the adhesion of additives, the attack of harmful substances on the steel decreases or with their help unwanted surface irregularities made even or eligible for a license become. Some variants should also be used under extreme load conditions special damage such as cold welding or seizing prevention. A well-known method for refining the surface of components of rolling bearings is, for example, the burnishing. This is done by immersing the component in burnishing baths a protective layer on the ferrous surface of the formed respective component. It creates a thin layer on the surface, which has mixed oxides. The layer thickness is in the range of a few microns and uses a volume fraction of the base material, so that the components largely dimensionally stable stay. A burnishing layer mainly serves to extend the service life of the rolling bearing under unfavorable operating conditions. Against chemical attacks and continuous high mechanical loads Known burnishing coats offer only limited protection. Especially in the combination of several unfavorable conditions in the Use of rolling bearings can be achieved by a blackening the components depending on the operating parameters only a minor Increased service life compared to rolling bearings observe with unbrushed components. One reason for this is that the browning has only a part of the properties for a universal surface treatment are desirable.

at the selection of suitable surface treatments various desirable protective properties ideally be combined in one layer. For example, the layer should be protect against cold welding of the components, due to unfavorable load and lubrication conditions occur between the individual components of the bearings can. In addition, it is advantageous if the protective layer has a high chemical resistance and low permeability offers to eliminate disturbing environmental influences. These are not just corrosive environments or indiffusion damaging elements such as hydrogen, but also attacks of components of lubricating oils such as EP additives, Phosphorus and sulfur compounds, as well as acids. Furthermore would a protective layer with low friction and good oil adhesion have a positive effect on the running properties of the rolling bearing. An improvement of the surface structure, especially in Connection with the operations of the initial running of the Camp, should also be reached.

In order to the protective layer permanently performs its protective function, it must also be resistant to abrasion and scratching and resistant to rolling, d. H. during operation of the rolling bearing do not peel off, which occurs especially with thick protective layers. Thick layers have besides the problem of dimensional stability also the disadvantage that in case of flaking due to the sizes of the released particles consequential damage occur. Furthermore, it is necessary from process engineering Reasons to choose a coating method, the characterized by cost and time efficiency. With known blacking methods Large systems and long process times are required which leads to high production costs. Typically they are Times in the actual Brünierbad between 15 and 40 minutes as well Temperature-related very high energy costs to produce the burnishing layers required.

A in comparison to immersion in purely chemical baths complex but frequently used coating method is the electrolytic coating with externally initiated Current flow. This is technically due to the required electrical contacting with mass parts and high quality standards not cost feasible. Furthermore Hydrogen is formed during electrolysis, which develops over a longer period of time Process duration disadvantageous to the material properties of the rolling bearing components would affect. The hydrogen problem is in the purely chemical deposition also available, but much lower pronounced. In the electrolytic coating is also no form fidelity achieved, since the layer thickness in particular due to of different structure on edges, curves and heels is subject to undesirable fluctuations. In that sense, ideally a protective layer can be chosen that deals with an alternative Apply coating method.

Added to this is the requirement that the layer is deposited without cracking and that the component is to be completely enveloped. Otherwise, the corresponding layer does not form a perfect chemical protective barrier against the environmental influences, which in turn would reduce the shelf life. In addition, it would be desirable if the layer has readily moldable and non-brittle properties, so that an additional smoothing of the surface of the component occurs through the application of the layer provides. This smoothing can already occur when applying the layer, or only during operation under load by a leveling effect in the run-in phase. This is especially the case when the layer reaches a slight leveling effect in the sub-micron range already during the application and can then be rolled flat under load. It is also desirable that the layer does not contain any reactive iron, otherwise there would be no complete separation of the steel surfaces of the components from each other. High ferrous, excluding iron oxide, coatings would not provide reliable protection against cold welding of the components. In addition, the layer should have a long service life under rolling bearing conditions and do not reject the lubricant used.

It is therefore an object of the invention, a rolling bearing with at least a coated component and a method for coating the Specify component, bringing as many of the above properties let realize.

The device-related task is through a rolling bearing with the features of claim 1 solved. The procedural The object is achieved by a method having the features of the claim 7 solved. Further advantages and refinements of the rolling bearing and the method are the subject of each dependent Dependent claims.

According to claim 1 is a rolling bearing, comprising several components, including at least one bearing ring and rolling elements on to roll the at least one bearing ring specified. At least one of the components is coated with a thickness in the range of 2 microns or less provided, the coating a Contains nickel alloy. This means that the layer thicknesses also slightly, ie in the sub-micron range, thicker than 2 microns can be. However, the layer thicknesses should be preferably 1 to 2 microns. Indicated here is one each average layer thickness, because additional fluctuations in the sub-micron range contribute to the flattening of the surface of the component. In this respect, a layer with a layer thickness of 2 microns certainly in some areas, for example, 2.2 microns be thick, in other areas again only 1.8 microns. Indeed also have layers from a thickness of 0.5 microns already advantageous properties. Layers between 2 μm and 5 microns, at lower load even up to 10 microns also have comparable advantageous properties, However, there is the tolerance class of rolling bearing components the coating already impaired and the coating time and manufacturing costs increase without significant gain. Furthermore It is desirable to soften, which compared to the base material Insert layer in such a limited thickness that it under Rolling load although the surface smoothes, But it does not contribute to impressions or Walkeffekten in the Order of microns comes. Prefers the coating consists of a nickel alloy.

It has been found that straight coatings of nickel alloys, which are known to be usable with much larger layer thicknesses, often 15 to 50 microns, but generally up to 300 microns, for coating metallic articles, with the unusually small layer thickness in the range of 2 microns or below fulfill a majority of the properties and requirements described above. Thus, nickel alloys can be crack-free and non-porous, thus dense. Chemical nickel layers have residual compressive stresses up to 50 N / mm ² up to a limit of about 50 μm, which is beneficial for the tightness. The chemical resistance of the nickel layer is very high against most substances except oxidizing acids. Therefore, a closed layer provides extremely high protection against chemically aggressive substances.

The Layer can also be absolutely consistent in consistent Apply thickness. The components can therefore be completely uniformly and geometrically independent. For example, this is not true for chromium in the selected layer thickness range possible, so there due to defects, thickness variations and the natural microcracking no chemical barrier would be formed. It turned out that on nickel alloys based coatings even with complex component geometries such as Bearing rings with high homogeneity the layer thickness and almost linear time-layer thickness course can be deposited are, the fluctuations compared to the desired ones Target layer thicknesses are in practical execution only in the range of less than 10%. By the hardness of the nickel alloy leaves to realize a long service life under rolling bearing conditions. Flaking is associated with the small layer thickness excluded with the high adhesiveness and sufficient formability. The adhesion arises through a combination of metallic and mechanical bond with diffusion exchange.

coatings same material class with layer thicknesses in the range of 10-300 microns would be next to the tolerance class change when forming the layer and a life-shortening walkthrough Relatively short running time of rolling bearings for detachment tilt from the surface, reinforced from 50 microns due to unfavorable layer-internal stress direction, so that the protective effect would no longer exist and the bearing sustainable would be harmed.

In an advantageous embodiment of the Er The coating is produced by a chemical deposition process. It is possible to deposit layers containing nickel alloys both electrolytically and chemically. Due to the disadvantages of the electrolysis described above, however, in the case of rolling bearing components, the chemical deposition method, in particular due to its currentless feasibility, to be preferred. Due to the unnecessary electrical contact, the surface of the components, for example, in their free movement in drums or Umlaufgestellen completely coat. In electrolytic processes, an electrical contacting of the surface would be required, so that no coating could take place at the contact point. A complete protective layer would not be possible. Even visually, such a surface would have defects due to the incomplete coating. Furthermore, the electrolytic nickel layer has properties which are less favorable for the rolling bearing application than those of a chemically generated nickel layer. The hardness of a nickel-phosphorus layer can be adjusted to 52 HRC, for example, and is thus softer than the heat-treated bearing steel with nevertheless good bearing capacity. Galvanically deposited nickel has only one third of this hardness and can be used, for example, as an adhesion-promoting intermediate layer.

A tempering of the layers produced is not required, since a further increase in hardness to approximate the bearing steel is not desirable. Furthermore, annealing would change the microstructure of the nickel-phosphorus layer. An X-ray amorphous deposited layer would become crystalline and ferromagnetic upon annealing by formation of Ni ₃ P crystals, which would degrade the properties of the layer.

• – Entfettung des Bauteils,
• – Dekapieren des Bauteils und
• – Aufbringung der Beschichtung.

According to claim 7, a method for producing a component for a roller bearing according to one of claims 1 to 6 is specified, comprising the following method steps:

• - degreasing of the component,
• - picking the component and
• - Application of the coating.

The initial degreasing of the component is required, around the surface of disturbing elements, separating layers and clean contaminants before applying the coating. Especially at the desired low layer thickness in the range of 2 microns or less, impurities would be the protective effect endanger the layer.

Would after degreasing the component immediately with the application of the coating continued, so would possibly the Problem revealed that the coating process is not everywhere would use the surface of the component simultaneously. In this case would be at an appropriately selected Coating time the layer thickness at the different points the surface fluctuate greatly, so that in the desired low layer thickness in the range of 2 microns or less no closed coating of the component would be expected. The expected time differences in the beginning of the reaction result among others from partial separation layers, from invisible oxides on the partially still passive surface and in addition from different pH values on the surface of the component, which individually change the reaction rate. These effects, however, can be achieved by pickling (surface acidification) of the component before beginning the coating or completely eliminate. When decorating it is a comparison for pickling shortened process, its short duration and low aggressiveness for activation and acidification the surface is sufficient, but not yet detectable attacks. After the appropriate preparation of the component by Degreasing and pickling and the associated rinsing operations the actual coating is applied.

In an advantageous embodiment of the method, the component for applying a coating in a coating bath for immersed for about 5 to 12 minutes. Already after 5 minutes can be realize a layer thickness in the range of about 1 micron. Compared to the production of burnishing layers is the Coating time consequently significantly reduced and thus more time-effective feasible. Together with the lower energy input, resulting from a single nickel-phosphorus bath at about 90 ° C compared with several burnishing baths at about 140 ° C results, the coating is cheaper and more environmentally friendly feasible.

In an advantageous embodiment of the method, the degreasing of the component and the application of the coating take place at almost the same temperature, which is above the room temperature. The coating is applied by default at elevated temperatures. This may possibly lead to the surface heating in the coating bath being carried out at different speeds in the case of complex geometries of the components, resulting in a different reaction rate. Also, the parameters of the growing layer can be adversely affected if the surface temperature does not correspond to the target from the beginning. Furthermore, the coating bath temperature may fluctuate undesirably due to the workpiece heating requirement. However, if the degreasing of the components is already carried out at the same temperature as the subsequent coating, for example as alkaline hot degreasing at about 80-90 ° C, the component is already close to the reaction temperature at the beginning of the actual coating, which positively influences the process flow of the coating and the ability to plan the exact layer thickness.

In an advantageous embodiment of the method is the pickling carried out with a dilute acid, this process step takes only a few seconds. Prefers may be an organic acid or carboxylic acid be used. This can, especially if the acidification in the foreground is, for example, a citric acid or tartaric acid. For additional distance By contrast, oxidic boundary layers, for example, are low concentrated (2-3%) sulfuric acid is recommended. Also, the same acid can be used in the chemical nickel bath is included. Chemical nickel baths usually have slightly acidic properties pH values of 4 to 5, whereupon the workpiece surface after the alkaline degreasing has to be prepared.

Thereby is achieved that, although the effects mentioned, to different Initiate the reaction at different points on the surfaces, be successfully eliminated, the surface of the component but not etched. An etching of the Surface of the component with grain boundary attack, pitting, Formation of soft unsustainable reaction layers or Dissolution of alloying elements would become to adversely affect rolling bearings. Preferably, the Dappling by immersing the component in the diluted Acid carried out for 3 to 5 seconds.

Further Advantages and embodiments of the invention will become apparent from the embodiment described below.

at the following comments on the essential properties the invention is irrelevant, whether it is radial, axial or linear bearings. It is also irrelevant What kind of rolling elements and bearing rings are. Thus, the main advantages of the invention, for example Apply to ball bearings, cylindrical roller bearings or tapered roller bearings. Also needle roller bearings can of the advantageous properties benefit of the invention. In addition, it does not matter if several Bearing rings or only one bearing ring (inside or outside) available is.

A Significant increase in effectiveness is achieved when all Components are coated and avoided being coated run against uncoated components. In particular, the protective effect Cold welding requires the coating of all sliding partners.

One Rolling bearing according to a preferred embodiment The invention has a bearing inner ring and a bearing outer ring on. The rolling bearing also has rolling elements on, between the bearing inner ring and the bearing outer ring are arranged and roll between the two bearing rings.

at the rolling bearing according to the described Embodiment are the bearing inner ring, the bearing outer ring and the rolling elements each with a nickel-phosphorus alloy coated. It is possible to also use the cage to provide the same coating when made of metal is. The thickness of the nickel-phosphorus layer is preferably 2 μm. Preferably, the nickel-phosphorus layer is on the Upper limit of medium phosphorous region formed, which is usually corresponds to a phosphorus content of 9 wt .-%. Other phosphorus shares, especially between 3 and 15 wt .-%, are also positive Properties can be used.

lower Phosphorus parts make the layer harder and more metallic. High levels of phosphorus lead to slower and nonlinear growth, are softer, offer more corrosion protection but at the same time poorer oil wettability. Farther Phosphorus has a decisive share in the protection against cold welding, which would not be the case with pure nickel layers. When Universal layer is suitable in consideration of the specific Advantages and disadvantages of a medium-phosphorous variant. While microphosphorus layers are microcrystalline, begins above a phosphorus content of about 8.5% of the amorphous area, which in its structure has special advantages in rolling bearings. Therefore, the universal nickel-phosphorus layer is preferred a phosphorus content of about 9% could be quite pronounced certain desired properties but also low or higher phosphorus.

alternative is it possible to have a nickel-phosphorus-boron coating or To make a nickel-boron coating, the comparable properties having.

In The nickel-phosphorus or nickel-boron alloys can also added additional substances in small quantities or be stored, for example, tungsten, molybdenum, cobalt and other. Solid lubricants such as PTFE would only be available if they were suitable adapted small particle size in question and reduce some benefits of the solid lubricant-free layer.

The coating is in each case closed around the respective component, that is to say the bearing rings and the rolling bodies. That is why it is necessary that Chemically deposit nickel-phosphorus layer. In principle, an electrolytic deposition of a nickel layer would be possible. However, in this case, due to the need for electrical contacting of the component, no closed layer around the component is possible. For the chemical deposition of the nickel layer, however, an alloying addition, as here in the exemplary embodiment sodium hypophosphite, which reacts out in the layer to form phosphorus, is necessary for effecting the electron exchange. The reduction of the metal ions takes place autocatalytically without electrolysis in a redox reaction, wherein the sodium hypophosphite is needed as a reducing agent for electron exchange. In the case of nickel-boron layers, this task is taken over by organic boranes or aminoboranes.

Corresponding nickel bath mixtures are available from various manufacturers and known prior art. Chemical nickel layers are made of DIN EN ISO 4527 seen. The advantageous properties of a chemical nickel layer with a layer thickness of 2 microns or less, especially in use for rolling bearing components, has not yet been recognized.

While In mechanical engineering far higher layer thicknesses to achieve certain effects were considered necessary, were thin nickel layers previously reserved for the sensor and data technology sector. These however, thin nickel layers are needed unalloyed without phosphorus content and are usually not separated from baths, but by sputtering or Applied by evaporation. In the rolling bearing could neither thick conventional nickel alloys still thin not wet-chemically applied layers are used. The advantages of the thin however, chemical nickel alloy are significant.

So can the nickel-phosphorus layer due to the chemical Separation process completely on the component of the bearing muster. The coating takes place crack-free and dense, so that the surface of the component completely against external Influences is protected. The nickel-phosphorus layer Consequently, despite the small thickness already forms a very effective chemical barrier to protect the surface of the component.

It is also at the selected layer thickness of 2 microns or less is not required on the surface of the Component an adhesion-promoting intermediate layer, for. B. galvanic nickel, to increase the adhesion of the nickel alloy, as required especially for thicker chemical nickel layers is. Adhere nickel-phosphorus layers of such low layer thicknesses without adhesion promoter directly on rolling bearing components from the known steel grades. Insofar is on a basic material of the Component no intermediate layer applied and the nickel alloy applied directly on the base material of the component. The basic material will typically be a bearing steel.

by virtue of Their metallic properties are the nickel-phosphor coating the rolling bearing components not oil repellent, so that a good lubrication of the resulting rolling bearing is possible. By the complete separation of the steel surfaces the rolling bearing components against each other through the nickel-phosphorus layers is a cold welding of the components together during the use of the rolling bearing excluded. by virtue of The small layer thickness of the nickel-phosphorus layer is also a tear off or flaking of the coating excluded. The surface achieves a quality improvement when entering by smoothing. Furthermore, the permissible operating temperature much higher than for example with a black finish and covers all needs with 350 ° C. Opposite the Burnishing is also significant that the chemical attack almost disappears on the substrate in the coating bath while he is carefully controlled in the blackening process got to.

to Preparation of the coating is first necessary to clean and degrease the corresponding component. Thereby become disturbing impurities and fat components eliminated the surface of the component, leaving the thin Nickel-phosphorus layer is homogeneously applicable. For nickel plating From surfaces it is known in advance an electrolytic Perform degreasing of the surface. This is however for the surface of rolling bearing components also not advantageous because of the hydroxidic grain boundary attack, so that a conventional degreasing at least with solvent or cold cleaners, preferably with alkaline hot degreasing, is used. Here it proves to be particularly advantageous if the degreasing already at the temperatures, where too the application of the nickel-phosphorus layer takes place takes place. In this case, the component is already at the coating temperature brought, so that quality-reducing temperature differences be avoided. This would otherwise be the case in particular the short coating times required due to the small layer thickness disadvantageous. Negative effects on homogeneity the layer thickness are avoided. The degreasing can for example be carried out at 90 ° C, which is a typical Temperature of a nickel bath corresponds.

After degreasing the surface of the component, a picking step is performed. The surface of the component is brought into contact with a weak acid bath for only a few seconds. This prevents the steel surface of the component from being etched, which occurs during conventional pickling or pickling operations. In the present embodiment, the Dekapierbad should only act on the surface separation layers. This is guaranteed in a bath time of 3-5 seconds. The picking is required to homogenize the surface of the component. Due to the small layer thickness of the subsequent coating with the nickel-phosphorus layer, it is necessary for the coating reaction to begin at the same time as possible at all points of the surface of the component. Otherwise, sufficient homogeneity of the layer thickness would not be guaranteed. The time differences in the beginning of the reaction mainly result from partial separation layers. Furthermore, surface oxides and differences in pH play a role. All of these influencing factors are sufficiently reduced by the pickling. Due to the short duration of the decanting bath and rinsing by dwell time-free diving, there is no appreciable cooling of the component after degreasing. Only on the surface of the component is slightly cooled, while the interior of the component remains at the coating temperature.

To Degreasing and pickling is the surface of the component prepared so far that the actual coating can be done. While layers of pure nickel merely electrolytically deposited what is in the present case due to the requirement the closed coating of the surface is not in Considering, a chemical deposition is required. to Ensuring electron exchange and enabling The chemical deposition is the use of an alloy material required. This is preferably sodium hypophosphite used, from the phosphorus in a proportion of z. B. 9 wt .-% in the layer intercalates. Alternatively, boron could also be used. to Application of the nickel-phosphorus layer is the component for immersed in a corresponding nickel bath for a certain time. The layer thickness is over the residence time in the bathroom exactly tunable. The deposition is purely chemical, so without external power without electrical contact.

by virtue of the low required layer thickness of the nickel-phosphorus layer result in process engineering compared to burnishing considerable Time advantages. So can be within a few minutes in the corresponding Nickel bath layer thicknesses of 2 microns realize without Interlayers should be required. In this case, rolling elements and bearing rings in drums or racks with the nickel-phosphorus layers be provided.

The resulting rolling bearing has one over conventional Rolling bearings without appropriate coating or only with rolling layers provided rolling bearings clearly increased service life. In addition, it is due to the small layer thickness The nickel-phosphorus layer does not require the shape and size modify the components compared to uncoated variants. Due to the pre-treatment by degreasing and pickling leave to coat components homogeneously. Overall, can be in comparison to known protective coatings on rolling bearing components a reduced process duration with simultaneously improved protective properties to reach.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - DIN EN ISO 4527 [0031]

Claims (14)

Rolling bearing, comprising a plurality of components, including at least one bearing ring and rolling elements, which roll on the at least one bearing ring, characterized in that at least one of the components is provided on its surface with a coating having a thickness in the range of 2 microns or less, wherein the coating contains a nickel alloy. Rolling bearing according to claim 1, wherein the coating produced by a chemical deposition process. Rolling bearing according to claim 1 or 2, wherein the Component consists essentially of a base material and the Coating is applied directly on the base material. Rolling bearing according to one of the claims 1 to 3, wherein the coating by immersion in a nickel bath has been de-energized. Rolling bearing according to one of the above claims, at the coating is closed around the component. Rolling bearing according to one of the above claims, at the coating has a hardness between 45 and 60, preferably 50 to 55, HRC. Method for producing a component for a Rolling bearing according to one of claims 1 to 6, comprising the following process steps: - degreasing of the component, - picking of the component and - Application of the coating. The method of claim 7, wherein the application the coating by chemical deposition in a coating bath he follows. Method according to claim 7 or 8, wherein the application the coating by immersing the component in the coating bath he follows. The method of claim 9, wherein a dipping time of the component in the coating bath is between 5 and 12 minutes. Method according to one of claims 7 to 10, in which the coating is carried out at a temperature above the room temperature is. Method according to one of claims 7 to 11, in which the degreasing by alkaline hot degreasing he follows. The method of claim 7 to 12, wherein the degreasing at a temperature equal to the temperature of the coating equivalent. Method according to one of claims 7 to 13, in which the pickling is done with an acid and few Seconds takes.