WO2008068130A2

WO2008068130A2 - Rolling bearing with a surface coating

Info

Publication number: WO2008068130A2
Application number: PCT/EP2007/062252
Authority: WO
Inventors: Tim Matthias Hosenfeldt; Harald Meisel; Yashar Musayev; Roland Tap
Original assignee: Schaeffler Kg
Priority date: 2006-12-06
Filing date: 2007-11-13
Publication date: 2008-06-12
Also published as: DE102006057484A1; DE102006057484B4; WO2008068130A3

Abstract

In a rolling bearing comprising rolling elements (3), an outer ring (4), an inner ring (2), and a bearing cage (1), the bearing cage has a surface coating (7) made of metal-free amorphous hydrocarbon in order to reduce friction in relation to the remaining parts of the bearing and to minimize wear from abrasion. The remaining parts of the rolling bearing may be provided with a tougher surface coating (12) made of amorphous hydrocarbon comprising metal.

Description

Name of the invention

Rolling bearings with a surface coating

description

The present invention is in the field of surface coating for mechanical components that are subject to particularly high loads and concomitant wear.

Various methods and materials for surface coating of components are known, either chemically or physically only surface areas of a body are changed in their nature in order to meet higher demands or can be applied to a body additional materials that with firmly connect the body to be coated, share the mechanical properties substantially with the body, but bring about an improvement in the surface condition in terms of wear and / or friction reduction. Basically, the spraying of surface coatings as well as the burnishing and the application of layers in the PVD or PACVD coating process is known in this context.

In the simple spraying of surface layers there is a risk that the dimensional accuracy of the original component is lost or post-processing is required because of the significant layer thickness of the coating, on the one hand to ensure dimensional accuracy and on the other hand to ensure smoothing of the surface, so that corresponding mating surfaces with come into contact with the coated component, do not wear out unnecessarily. When browning an increase in surface hardness is achieved by the oxidation, but the design options for such a layer keep within narrow limits, so that many times the requirements that are placed on surfaces, can not be met with this technology.

With vacuum coating techniques, either as PVD (Physical Vapor Doposition) or as PACVD (Physically Assisted Chemical Vapor Diposition), a variety of coatings can be applied in freely selectable layer thicknesses under precisely controllable conditions. Apart from the composition of the coating, the thickness and the smoothness of the coating can also be adjusted well.

The invention relates specifically to a rolling bearing with a plurality of rolling elements and a cylindrical bearing cage.

In particular, such rolling bearings are exposed by the increasing stresses in current applications sometimes very high loads. This results in increased abrasion in the region of the bearing cage, especially at high rotational speeds and high rotational accelerations, where it comes into contact with the remaining parts of the bearing.

The invention is therefore based on the object to provide a rolling bearing of the type mentioned, which has a low friction, ideally associated with low abrasion at high speeds and spin accelerations.

The object is achieved according to the invention with the features of claim 1. Advantageous embodiments of the invention can be found in the dependent claims.

The invention further relates according to claim 17 to a bearing cage for a rolling bearing according to the invention and to a method according to claim 18 for producing a surface coating. The invention is based on the idea that by coating at least the inner and / or outer lateral surface of the bearing cage with a first surface coating of a metal-free amorphous hydrocarbon, the abrasion in the region of contact of the bearing cage with other parts of the bearing is minimized. This is a special property of the metal-free hydrocarbon layer which, while not able to develop its optimum properties in other areas of a bearing, is optimally applicable in the said area where high roll-over resistance is not required. This layer not only minimizes abrasion in the bearing cage, but also ensures that the friction is reduced and also the corresponding counter-body are only slightly stressed by the frictional load. This is easy to realize by the inventive nature of the surface coating on the one hand and on the other hand by the easy to achieve in this material low surface roughness.

In the stated area of use, the loads of the surface coating are not in the range of high compressive stresses but, in particular at high speeds and high accelerations of a bearing, the surfaces are rubbed against each other at high speed or great slippage occurs.

By using the material according to the invention, the abrasion, the friction as well as a noise development and, as a consequence of the friction reduction, also the frictional heat generated is kept low.

A corresponding coating of the mating surfaces, for example, the inner surface of the outer ring in the area where it touches the bearing cage or the outer surface of the inner ring, also in the region of contact, is thus no longer necessary, so that in the design of these components to other stipulations can be optimized. The same applies to the design of the rolling elements, which come into contact with the cage to an even lesser extent, in particular in the case of a needle bearing.

Thus, the advantage of the coating according to the invention lies in the fact that with the choice of a surface coating of a single moving parts of the bearing, the interaction with the other parts can already be optimized without their nature would have to be set.

The life of the bearing is increased by the described design, without the need for the construction of the bearing components unusual components would have to be used. Instead, conventional bearing steels such as preferably 16MnCr5 or C45, but also steels such as 100 Cr6, 16 MnCrδ, C45, 31 CrMoV9, 80 Cr2 or the like can be used.

An advantageous embodiment of the invention provides that the first surface coating contains at most 16 atomic% of hydrogen.

Due to the low hydrogen content of at most 16%, the adsorption tendency of the surface coating to a metallic counter-body is kept low, ensures a high abrasive wear resistance and a high chemical resistance and ensures a high hardness / modulus ratio. Otherwise, the amorphous hydrocarbon layer consists of SP ² and SP ³ -hybridized carbon, wherein preferably process-related impurities of less than 1 atom% are maintained.

The surface coating is advantageously applied in a thickness range of between 0.5 and 4 .mu.m, whereby on the one hand the dimensional stability of the coated component is obtained, on the other hand a sufficiently thick layer is applied, and with suitable coating methods such as, for example, the PVD and PACVD method Even when coating such smoothness, that is low surface roughness can be maintained that subsequent processing of the surface coating is unnecessary. Non-metallic atoms, such as, for example, silicon, fluorine or oxygen atoms, may be incorporated individually or in combination in the surface coating in order to further stabilize the layer.

For the construction of a particularly resistant and durable layer can be advantageously provided that the bearing cage is provided under the first surface coating with an adhesion promoting layer of a metal, a metal alloy or a boride, a carbide, a nitrite or a silicide of a transition metal.

The substances mentioned, in particular metals but also borides, carbides, nitrides and suicides, adhere particularly well to a metallic base body and are also very hard in the case of the borides, carbides, nitrides and suicides of the transition metals. It is thus achieved a reliable connection of the coating with the base body, wherein the transition of the material hardness from the base body on the bonding layer for surface coating should be done in several stages.

This is advantageously further supported, in that the bearing cage is provided under the first surface coating with an intermediate layer in the form of a metal-containing hydrocarbon layer.

Straight metal-containing hydrocarbon layers have a high degree of toughness at relatively high hardness, which qualifies them as a transition layer between the particularly hard surface coating and the base body.

Advantageously, tungsten, titanium, cadmium, tantalum, germanium, chromium, nickel or a combination of these metals can be used as metal components of the metal-containing intermediate layer.

In addition, advantageously, the intermediate layer as a component of a non-metal oxygen, fluorine, silicon or nitrogen atoms or a combination contain these substances. As a result, the coating properties (friction reduction, wear resistance adjustment, improvement of the oxidation resistance, etc.) can be optimized accordingly.

In an embodiment of the entire rolling bearing, in addition to the surface coating of the bearing cage, the remaining parts can be coated in a favorable manner. The coating of rolling elements, inner ring and outer ring of the bearing must, however, withstand different loads than those of the bearing cage. In particular, it must be able to roll over with high loads.

The invention therefore advantageously provides that the rolling elements have at least in the region of their running surface a surface coating of a metal-containing amorphous hydrocarbon, and / or that the outer ring at least in the region of its tread has a likewise designed Oberflächenbe- layering and / or that optionally also the inner ring of the rolling bearing at least in the region of the tread carries a coating of a metal-containing amorphous hydrocarbon. The running surface is understood to be that region of the surfaces of the individual bearing components which are potentially exposed to a roll-over load.

As already described above, no special precaution must be taken in the coating of these components (rolling elements, outer ring, inner ring of the bearing) because of possible contact with the bearing cage, since the corresponding parts of the bearing cage are already provided with a surface coating, which is also the counter body protects against excessive wear. For this reason, in the coating of the rolling elements, the inner and outer ring no compromises must be made in this regard and the rollability may be in the foreground.

The corresponding coating of one or more of these components with a metal-containing amorphous hydrocarbon creates a very tough and yet resistant well-adherent and hard layer, so that the resulting rolling bearing, depending on the stresses to which it is exposed, even at high speeds with low wear can withstand high mechanical loads.

Depending on the selected surface coating technology, either the corresponding running surface of a component or all or certain surfaces of the component as a whole can be coated exclusively.

As a metal component, the respective consisting of a metal-containing amorphous hydrocarbon surface coating tungsten, titanium, cadmium, germanium, chromium, tantalum or nickel or a mixture of some or all of these ingredients.

The invention further relates to a special bearing cage, which is coated as described above and is provided for the construction of a corresponding rolling bearing.

An inventive method for producing a roller bearing provides that the first surface coating, consisting of a metal-free a morphine hydrocarbon layer by means of a PVD or PACVD method is applied. This technology can also be used to apply a corresponding primer layer and / or an intermediate layer. This has the advantage that the component which is to be coated, for example the bearing cage, can be left in a corresponding coating chamber, while the coating parameters and the substances which are to be incorporated into the layer or from which the individual layers consist a specific time schedule can be changed. As a result, the thicknesses of the individual layers, that is to say the adhesion-promoting layer, the intermediate layer and the surface coating, can be set very precisely and the adhesion between the individual layers is also optimized. The same applies accordingly for the application of the metal-containing amorphous hydrocarbon layers on the inner ring, the outer ring and the rolling elements of the rolling bearing.

In the following the invention will be shown by means of an embodiment in a drawing and described below. It shows

Figure 1 in cross section the structure of a roller bearing;

FIG. 2 schematically shows the cross section and structure of a surface coating of a bearing cage;

FIG. 3 is a schematic cross-sectional view of the structure of the surface coating of an outer ring.

In Figure 1, the bearing cage with 1, the inner ring with 2, a rolling element with 3 and the outer ring with 4. The outer surface of the bearing cage carries the reference numeral 5 and faces the outer ring 4, while the inner circumferential surface carries the reference numeral 6 and the inner ring 2 faces.

In the example shown, the bearing cage 1 is continuously provided with a surface coating of a metal-free amorphous hydrocarbon both on the outer lateral surface 5 and on the inner lateral surface 6.

This coating is shown by way of example in FIG. 2 in more detail. There is denoted by 1 of the main body of the rolling bearing cage. The first surface coating 7 is formed by a metal-free amorphous hydrocarbon layer as stated above, while the intermediate layer 8 is a metal-containing hydrocarbon layer. In addition, an adhesion-promoting layer 9 is provided which consists of a metal or, for example, a carbide of a transition metal and is arranged directly on the base body 1.

The main body 1 consists of a conventional bearing steel. Here comes z. As a case hardened steel such. For example, 16MnCr5 or C45. Conceivable, however, would be other steels such as 100 Cr6.

The base body 1 can also be hardened, whereby care should be taken when applying the laminations that the tempering temperature of the base body is not exceeded.

In the figure 3 the structure of the coating of a rolling element, an outer ring or an inner ring of the rolling bearing according to the invention is shown by way of example, wherein the special case of an outer ring 4 is shown in more detail.

The main body of the outer ring 4 carries a surface coating 12, which consists of a metal-containing amorphous hydrocarbon. This choice of material ensures a high degree of toughness and thus the ability to roll over the entire configuration.

For adhesion promotion, an adhesion-promoting layer 10 is provided on the base body 4, which in its construction or its nature may correspond to that of the adhesion-promoting layer 9.

Between the primer layer 10 and the surface coating 12, an intermediate layer 11 may be provided, which should be located between the properties of the base body 4 and those of the surface coating 12 in terms of hardness and toughness, in order to provide suitable between them, while the surface coating 12 reliably to support. In the rolling bearing described is achieved according to the invention with low friction and wear, along with low temperature increase at high speeds and spin and also with a reduced noise in addition that high mechanical loads can be absorbed. In particular, by dividing the requirements between the bearing cage on the one hand and the other parts of the bearing optimum performance is achieved with little effort.

LIST OF REFERENCE NUMBERS

1 camp cage

2 inner ring 3 rolling elements

4 outer ring

5 outer surface

6 inner lateral surface

7 Surface coating 8 Intermediate layer

9 adhesion layer

10 adhesion layer

11 interlayer

12 surface coating

Claims

claims

1. rolling bearing with a plurality of rolling elements (3), and a cylindrical bearing cage (1), characterized in that at least the inner and / or outer circumferential surface of the bearing cage with a first

Surface coating (7) is provided from a metal-free amorphous hydrocarbon.

2. Rolling bearing according to claim 1, characterized in that the first surface coating (7) contains at most 16 atomic% hydrogen.

3. Rolling bearing according to claim 1 or 2, characterized in that the first surface coating (7) has a thickness of at most 4 microns.

4. Rolling bearing according to claim 1 or one of the following, characterized in that the first surface coating (7) has a thickness of at least 0.5 microns.

5. Rolling bearing according to claim 1 or one of the following, characterized in that in the first surface coating (7) non-metallic atoms are stored except carbon and hydrogen.

6. rolling bearing according to claim 5, characterized in that the non-metallic atoms are formed by silicon atoms, oxygen atoms or fluorine atoms or a mixture of these types of atoms.

7. Rolling bearing according to claim 1 or one of the following, characterized in that process-related impurities amount to less than 1 atomic%.

8. Rolling bearing according to claim 1 or one of the following, characterized in that the bearing cage (1) under the first surface coating (7) with an adhesion-promoting layer (9) made of a metal, a metal alloy or a boride, a carbide, a nitrite or a silicide of a transition metal.

9. Rolling bearing according to claim 1 or one of the following, characterized in that the bearing cage (1) under the first surface coating (7) with an intermediate layer (8) is provided in the form of a metal-containing hydrocarbon layer.

10. Rolling bearing according to claim 9, characterized in that the metal component of the metal-containing intermediate layer (8) by tungsten, titanium, cadmium, tantalum, germanium, chromium, nickel or a combination of these metals is formed.

11. Rolling bearing according to claim 10, characterized in that the intermediate layer (8) contains as component oxygen, fluorine, silicon or nitrogen or a combination of these substances.

12. Rolling bearing according to claim 1 or one of the following, characterized in that the rolling bodies (3) at least in the region of the running surface have a surface coating (12) made of a metal-containing a-morphine hydrocarbon.

13. Rolling bearing according to claim 1 or one of the following, characterized in that an outer ring (4) of the rolling bearing at least in the region of the running surface has a surface coating (12) made of a metal-containing amorphous hydrocarbon.

14. Rolling bearing according to claim 1 or one of the following, characterized in that an inner ring (2) of the rolling bearing at least in the loading rich of tread has a surface coating (12) of a metal-containing amorphous hydrocarbon.

15. Rolling bearing according to one of claims 12, 13 or 14, characterized in that the surface coating (12) is provided from a metal-containing amorphous hydrocarbon exclusively in the region of the tread.

16. Rolling bearing according to one of claims 12 to 15, characterized marked, that the surface coating (12) of a metal-containing amorphous hydrocarbon as metal content tungsten, titanium, cadmium, germanium, chromium, tantalum or nickel or a mixture of these constituents.

17. bearing cage for a rolling bearing according to one of claims 1 to 16, characterized by a first surface coating (7) made of a metal-free amorphous hydrocarbon, at least in the region of its inner and / or outer circumferential surface.

18. A method for producing a roller bearing according to one of claims 1 to 16, characterized in that at least one surface coating (7, 12) by means of a PVD and / or PACVD coating method is applied to the bearing cage and / or the other components of the rolling bearing ,

19. The method according to claim 18, characterized in that prior to the application of the surface coating (7, 12) by means of a PVD and / or PACVD coating process, an adhesion-promoting layer (9,10) is applied.

20. The method according to claim 18 or 19, characterized in that between the adhesion-promoting layer (9, 10) and the first surface Chen coating (7, 12) by means of a PVD and / or PACVD coating method, an intermediate layer (8, 11) is applied.