EP2024526A1

EP2024526A1 - Method for producing a rolling bearing component and rolling bearing component

Info

Publication number: EP2024526A1
Application number: EP07722403A
Authority: EP
Inventors: Werner Trojahn; Silke RÖSCH
Original assignee: Schaeffler KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2006-05-19
Filing date: 2007-05-10
Publication date: 2009-02-18
Also published as: DE102006023690A1; WO2007134571A1; RU2446227C2; AU2007252142A1; CN101448968A; AU2007252142B2; US8499458B2; RU2008146496A; JP2009537334A; BRPI0711934A2; CN101448968B; KR20080110686A; US20090310898A1

Abstract

A method for producing a rolling bearing component with a carbon gradient, at least in the region of its outer layer, wherein molten metal is sprayed onto a carrier in a spraying process, the carbon content of the metal to be sprayed on being varied during the spraying operation.

Description

Name of the invention

Method for producing a rolling bearing component and rolling bearing component

description

Field of the invention

The invention relates to a method for producing a rolling bearing component with a given at least in the region of its boundary layer carbon gradients.

Background of the invention

Rolling bearings are known to consist of at least two components, namely one or more rings, between which the rolling elements, such as rollers run. Usually, such rotationally symmetrical rolling bearing components are produced by machining, for example from case hardening steel, wherein rings or rollers are either turned out of a bar or forged by a bolt. In order to produce a defined hardness in the region of the surface layer, a gradient structure is set by a carburization treatment, within which a heat treatment process is used. driving in the boundary layer carbon is enriched. Optionally, a carbonitriding, ie a nitrogen enrichment in the region of the surface layer done. This surface layer becomes hard after the carburizing treatment due to the at least 0.6% enriched carbon and the optionally additionally enriched nitrogen, the hardness is usually 58 HRC or more in rolling bearing rings. The non-enriched core remains softer according to the original composition, depending on the starting material used, the hardness is between 20 and 45 HRC. Thus, for example, the ring produced contains a tough core and a hard roll-over outer layer, which is also still under positive pressure compressive stresses.

Due to the stresses of such a rolling bearing component, however, high carburizing depths of more than 2 mm are required, for example, during case hardening, which require a heat treatment time of several hours, depending on the particular material selected. This is a considerable amount of time associated with this treatment step, which also has an adverse effect on the manufacturing cost.

Summary of the invention

The invention is therefore based on the problem of specifying a method in which at least one carbon-rich, a carbon gradient-pointing edge layer can be produced without time-consuming carburizing.

To solve this problem, it is provided in the method according to the invention that molten metal is sprayed onto a carrier in a spraying process, the carbon content of the metal to be sprayed being varied during the spraying process. Unlike rolling bearing components according to the invention, the rolling bearing component according to the invention is no longer machined from a homogeneous material and then subjected to a corresponding hardening treatment; instead, according to the invention, the surface layer, which usually forms the rolling bearing bearing surface, is produced in a metal spraying process. In such a spray-compacting process, in a gas atomizer, a molten metal in an inert gas stream is atomized into spherical droplets. The gas quickly chills the metal droplets to a temperature between the liquidus and solidus temperatures, often even slightly below the solidus temperature. The thus cooled drops move at high speed and have a doughy consistency. If the drops now hit a surface at high speed, for example a carrier ring or the like used to produce the component, they compact because of their inherently high kinetic energy. It forms a high-density composite material. The production of non-dense and low-pore metal layers with a homogeneous structure and a high density is possible by spray compacting. According to the invention, the carbon content of the metal to be sprayed is now varied during the spraying process to produce the carbon gradient within the sprayed-on metal layer which extends radially in the conventional rotationally symmetrical rolling bearing components. That is, depending on the desired carbon gradient, the carbon content of the sprayed viscous metal is arbitrarily changed during the spraying process. After the edge layer is sprayed successively layer by layer, this inevitably results in a changing depending on the variation of the carbon content carried carbon content also within the finished edge layer. This means that as a result of the production according to the invention in a spray-compacting process with a varying carbon content, the finished rolling bearing component inherently has an arbitrarily adjustable carbon gradient which can be adapted to the requirements, at least in the region of the surface layer. Thus, the very time-consuming in the prior art heat treatment for Aufkoh- completely eliminated. The always performed heat treatment of the rolling bearing component is thus only dependent on the component dimension and thus the weight, but no longer dependent on the thickness of an edge layer to be modified.

The method according to the invention therefore makes use of the advantages of the spray method, which is highly flexible with regard to the composition of the metal layer and thus the adjustment of the physical, chemical and mechanical properties of the metal layer, after the composition of the metal layer, in particular with respect to the individual mechanical, physical and chemical properties determining components can vary almost arbitrarily. That is, the starting materials used by the house, hence the molten metal, can be selected depending on the required properties. In addition, the variation of the carbon content according to the invention takes place within the test procedure, so that a further degree of freedom is given in the method according to the invention.

Various approaches are available for altering the carbon content during the spraying process. According to a first alternative of the invention, for varying the carbon content, carbon is introduced into the melt from which the sprayed-on metal is drawn off. This can be done, for example, in the form of a carbon wire, which is wound into the melt and dissolves there, or by means of a carbon powder blown into the melt. In this embodiment of the invention, therefore, the melt itself is enriched with carbon, wherein the carbon content can be varied in any way by appropriate variation of the amount of eingespultem carbon wire or injected carbon powder. The increasing accumulation of the metal to be sprayed, that is to say the molten steel, inevitably leads to the growth of a layer which has a different carbon content than the layer underneath, if the spraying process continues which is so enriched in the carbon content that the desired carbon content is achieved, as it should be present after carburizing.

As an alternative to introducing the carbon into the melt, ie the melt stock itself, it is possible to inject a carbon powder into the spray cone of molten material to vary the carbon content. The injected high-purity carbon powder is taken along by the metal droplets entrained at high speed in the inert gas stream and the gas stream itself and in this way integrated into the surface layer. Again, the carbon content of the sprayed metal is varied by the addition of carbon powder in the spray cone, where the variation of the carbon content can be extremely fast vonzufatten since the injected carbon powder amount can ultimately be varied arbitrarily and at any time, with the change directly to the Carbon content of the sprayed layer affects.

Another process alternative involves the use of two or more melts with different carbon contents, which are mixed together to form the melt from which the sprayed metal is withdrawn. The two melts, which can be taken off from separate melt containers, are fed to a distributor, which can be an integral part of the spray unit, where they are mixed together in any desired mixing ratio between 100% of the first melt and 100% of the second melt. Consequently, therefore, any desired carbon content between the minimum carbon content of one melt and the maximum carbon content of the other melt can be achieved by mixing technology. A further method alternative according to the invention envisages spraying two or more melts with different carbon contents using two or more separate spraying devices, wherein the spraying cones overlap and the discharge quantities of the spraying devices are varied. Here, for example, a low-carbon steel is sprayed on via a first spraying device, and a steel with a high carbon content via a second spraying device. The spray cones preferably completely overlap, so they are completely sprayed together when sprayed simultaneously. As a result, the sprayed melts can also be mixed with one another as desired. If only the first spraying device is operated, only the metal which can be sprayed on it is applied. If the second spraying system is increasingly switched on, depending on its spraying power, the carbon content of the finally produced boundary layer, which consists of a mixture between the two starting melts, increases, whereby the spraying control can be such that as far as the second spraying device is switched on is reduced, the first sprayer in its spraying performance. The carbon content can obviously be varied in any manner between the minimum carbon content of the first melt and the maximum carbon content of the second melt. Here too, any desired carbon gradients can be generated over the sprayed-on layer, which, as will be discussed below, does not necessarily have to be just the boundary layer.

As the carrier gas for spraying the molten metal, nitrogen or a nitrogen-enriched gas is preferably used. This can simultaneously nitrogen enrichment of the sprayed metal layer can be achieved according to a carbonitriding, so that even for this no longer separate treatment step after Sprühkompaktierverfah- ren is required. An expedient development of the invention envisages injecting one or more hard materials in powder form, in particular for forming a wear-resistant edge layer on the component in the spray cone, which are then incorporated into the sprayed-on metal layer. The hard materials may be carbides, nitrides or oxides, which are conveyed in powder form into the spray cone and should have a very fine grain size of 1 nm to 200 μm. As a result, in addition to the increase in hardness by the carbon content and the wear can be reduced.

The molten metal can be sprayed according to a first embodiment of the invention on a carrier in the form of a prefabricated part, in particular in the form of a tube or a rod made of a curable material, which part is then an integral part of the produced rolling bearing component. Here, therefore, a prefabricated carrier, which may have been subjected to a first shaping, is used. As such a carrier as described a rod or a pipe made of a correspondingly curable material can be used as well as this prefabricated part already the essential contour of the finally manufactured rolling bearing component, for example, an inner or outer ring may have or is dimensioned accordingly. In such a case, the prefabricated endkontumahe part is applied to a reusable carrier, which holds it during the spraying process and from which it can be removed.

As an alternative to the use of a prefabricated carrier part, it is also possible to use a reusable carrier by default, onto which the metal is sprayed in order to form the entire component in the spraying process. In this embodiment of the invention, therefore, not only an edge layer in Sprühkompaktierverfahren is prepared, but the entire component, such as the inner or outer ring, itself. For this purpose, a reusable support, such as a ceramic or concrete pipe, is used, on the formation of the essential component body a melt of a composition, as they should just have this central component body, is sprayed. As described in the introduction, usually a case hardening steel is used. The carbon modification according to the invention then takes place to form the surface layer. In this way, the procedure is when the rolling bearing component is an inner ring whose rolling bearing bearing surface is the outer side. If the rolling bearing component is an outer ring, the carbonization according to the invention begins with the first spraying onto the reusable carrier, and the material is sprayed on to form the essential component body only after the inner boundary layer has been produced. If, in addition, an enriched outer edge layer is to be produced, a carbon addition according to the invention takes place again during the final spraying process at the end of the spraying process.

Thus, it is evident that in the method according to the invention a very high degree of flexibility, which allows the production of different in their composition and their properties rolling bearing components, with time-consuming heat treatment processes for carburizing or carbonitriding account advantageously. After completion of the rolling bearing component in the context of the method according to the invention, only a re-compaction of the residual porosity in the subsequent production steps such as forging and / or ring rolling, followed by a conventional heat treatment without time-consuming diffusion-controlled training of rolling bearing layer is required. When using preformed, preferably near-net shape blanks (prefabricated carriers), these post-processing steps can also be simplified.

In addition to the method according to the invention, the invention relates to a rolling bearing component, in particular in the form of a ring or a roller, which has at least one edge layer, which is formed by spraying a molten metal, and within the at least partially varies. The rolling bearing component is produced in particular by the method described in the introduction. The rolling bearing component itself can have a metallic prefabricated carrier, for example an end-to-valley ring or the like, on which the surface layer is formed. Alternatively, the rolling bearing component as a whole may be a spray-compacted component made entirely by spraying. Furthermore, at least in sections, one or more hard materials may be incorporated at least in the sprayed-on boundary layer, as there may also be an increased nitrogen content introduced during the spraying process.

Brief description of the drawings

Further advantages, features and details of the invention are described below with reference to embodiments with reference to the figures. The figures are schematic representations and show:

1 is a schematic diagram for explaining a first variant of the method,

2 shows a partial view of a rolling bearing component according to the invention, showing the carbon gradient,

3 is a schematic diagram for explaining a second variant of the method,

Fig. 4 is a schematic diagram for explaining a third variant of the method, and

Fig. 5 is a schematic diagram for explaining a fourth variant of the method. Detailed description of the drawings

Fig. 1 shows in the form of a schematic representation of a spraying device 1, by means of which the inventive method is feasible. The spraying device 1 comprises on the one hand the spray unit 2, furthermore a melt reservoir 3, in which a molten metal S is contained. Furthermore, a carrier gas supply 4, here a nitrogen supply, is provided. From the melt reservoir 3, molten metal to be sprayed is continuously withdrawn, which is sprayed in the form of smallest metal droplets 5 via the carrier gas in a spray cone 6 onto a carrier 7, in the example shown a tube made of a hardenable metal. The carrier 7 rotates and can be moved axially. With increasing rotation and spraying an ever thicker spray-compacted layer is formed on the carrier 7. In order to be able to vary the carbon content within the sprayed-on layer 8, carbon C is introduced into the melt S at the appropriate time in the example shown. This can be done by winding a carbon wire or by blowing carbon powder. The melt accumulates as a result of carbon, but necessarily so that the layer produced 8. While in the example shown in FIG. 1 is indicated that the carbon C is introduced directly into the melt reservoir 3, there is of course the possibility of this only in the Melt feed immediately before the spray unit 2 or in this self bring. In any case, the carbon C is introduced into the homogeneous melt in this embodiment.

In a concrete process embodiment, the spraying process is started, for example, on the support 7, here as described, a pipe, for example made of a hardened steel, which is curable, first using the original melt S, ie without composition varied in carbon content. The melt S has, for example, the composition of a case steel, that is, the carbon content is less than 0.35%, alloying elements such as Cr (maximum 4%), Mo (maximum 2%), Ni and / or Mn (maximum 4%) and Si (maximum 1, 5) and other steel companions may be included. Using this original composition, a first layer 8a (see Rg. 2) which has a thickness of several millimeters, preferably at least 5 mm, is first sprayed on during the spraying process. Then, the carbon-enriched surface layer is formed in the spraying process, for which purpose, in order to increase the carbon content of the melt, the carbon C is introduced into the melt S as described. As a result, more carbon accumulates in the subsequently produced second boundary layer 8b, as shown in the basic diagram in FIG. There, the carbon content is plotted over the cross section through the two layers 8a, 8b, it being again pointed out that this is only a schematic diagram. The maximum carbon content present in the surface layer 8b corresponds to the desired carbon content, as is customarily present after a carburization step not required here.

The carrier 7 here forms an integral part of the produced rolling bearing component. In the example shown 7 individual rings are cut to form the rolling bearing component of the carrier, wherein Fig. 2 shows a sectional partial view of such a cut-length rolling bearing component 9, here in the form of a ring shows. Of course, it would be possible to use instead of a continuous tube and individual near-net shape prefabricated parts, here rings, but then arranged on a reusable carrier not shown here in turn and can be removed from this.

FIG. 3 shows a further variant for producing the layer having a carbon gradient. In the case of the spray device 1 shown here comprising a spray unit 2 and a melt reservoir 3 with the melt S of the original composition and a carrier gas feed 4, the addition of the carbon C takes place at the required time directly into the melting cone 6, where the injected carbon powder is immediately taken away by the metal droplets and the carrier gas (N ₂ ) leaving the spraying unit 2 at high speed and in the forming surface layer (FIG. According to embodiment of FIG. 2, the edge layer 8b) is stored. Here, too, it is possible first to form a first layer using the unchanged melt composition and to carry out the carbon enrichment at a later time. In this embodiment of the invention, an extremely rapid variation of the carbon content due to the direct introduction into the spray cone 6 is possible. In addition, wear-inhibiting hard materials in the form of the finest powdery oxides, carbides or nitrides could be introduced into the spray cone, which are incorporated into the layer 8b.

4 shows a further schematic diagram for explaining a further variant of the method. The spray device 1 shown here also comprises a spray unit 2 and a total of three melt reservoirs 3a, 3b and 3c. In the melt reservoir 3a in the example shown, a first melt Si with a low carbon content is present in the melt reservoir 3b is a melt S ₂ with a high carbon content. These melts are then poured alternately or simultaneously into the third melt reservoir 3c, where then either the pure melt S ₁ , the pure melt S ₂ or a mixed melt of the melts Si and S _{2 is} present. From this melt reservoir 3c, which need not be a large container, but may also be a small-sized distributor, the final aufzusprühende melt composition is now withdrawn and with the aid of the supplied via the carrier gas supply 4 inert gas over the melting cone. 6 sprayed. The carrier 7 in FIG. 4 is, for example, a reusable carrier, e.g. B. a ceramic or concrete pipe. On this, the entire rolling bearing component, here the ring, applied in Sprühkompaktierverfahren. For this purpose, an inner boundary layer is sprayed on, for example, in a first spray section exclusively using the melt S ₂ having the high carbon content, until the desired layer thickness has been reached. Then, the melt Si is increasingly mixed until the formation of the essential component body, the pure melt Si is sprayed. In order to form an outer carbon-enriched boundary layer, the proportion of melt S ₂ in the last spraying section is again increased to a maximum of 100%, so that the carbonaceous material is also formed there. Here, therefore, the entire rolling bearing component is manufactured in Sprühkompaktierverfahren, wherein in the example described, the inner and the outer surface layer have the carbon gradient. It is of course possible to design only the inner or the outer surface layer accordingly.

Finally, FIG. 5 shows a further basic illustration of a spraying device 1 for carrying out the method according to the invention. This comprises two separately operable spraying devices 2a, 2b, to each of which separate melt reservoirs 3a, 3b are assigned. A melt S ₂ having a low carbon content is present in the melt reservoir 3 a, and in the melt reservoir 3 b a melt S ₂ having a high carbon content. The two spray units 2a, 2b, which are supplied in the example shown here via a common carrier gas supply 4, are arranged such that their respective spray cones 6a, 6b overlap completely in the example shown in the vicinity of the carrier 7. Here, too, it is assumed that the carrier 7 is a reusable carrier in the form of a ceramic tube or the like. For example, if a ring with an inner and with an outer, a carbon gradient having edge layer prepared In the first instance, the spray unit 2b begins spraying the first layer consisting of the melt S ₂ having the high carbon content. After reaching a minimum layer thickness of a few millimeters, the spraying power of the spraying unit 2b is lowered continuously and the spraying device 2a is switched on and its spray power is increased continuously. The reduction and increase in the respective power is preferably synchronous, so that at any time a total spray power of 100% is given. The formation of the essential component body is sprayed with 100% melt Si, that is, the rolling body consists only of material from the melt Si. To form the outer surface layer, the process is then reversed again, that is, the spraying performance of the spraying unit 2a is continuously reduced, while that of the spraying unit 2b is continuously increased. The result is a ring or a tube with a curable hole, a less curable core and a re-curable outer surface layer.

Overall, the method according to the invention enables the simple generation of a carbon gradient structure in the region of inner or outer surface layers. A special carburizing step, which takes a long time, is no longer necessary. Likewise, this share of the production costs as well as the amount of distortion attributable to this heat treatment step is eliminated, so that the post-processing (grinding) is cheaper. Furthermore, in a ring rolling eliminates the otherwise always beginning Auslochen the inner Schmiedebutzens, which is about 25% of the ring weight. Finally, the overall production chain shortened considerably in time, since the otherwise normal way of rod / semi-finished product manufacturing in the steel mill, the sawing of the bolts forging and the carburizing process omitted. reference numeral

1 spraying device

2 spray unit

2a spray unit

2b spray unit

3 melt reservoir

3a melt reservoir

3b melt reservoir

3c melt reservoir

4 carrier gas supply

5 metal droplets

6 spray cones

6a spray cone

6b spray cone

7 carriers

8 layer δa layer

8b layer

9 rolling bearing component

S molten metal

Si melt

S ₂ melt

C carbon

N ₂ carrier gas

Claims

claims

Anspruch [en] A process for producing a rolling bearing component having a carbon gradient given at least in the region of its boundary layer, characterized in that molten metal is sprayed onto a carrier in a spraying process, wherein the

Carbon content of the aufzusprühenden metal is varied during the spraying process.

2. The method according to claim 1, characterized in that for varying the carbon content carbon is introduced into the melt, from which the sprayed metal is withdrawn.

3. The method according to claim 2, characterized in that the carbon is wound in the form of a wire in the melt or injected as a powder into the melt.

4. The method according to claim 1, characterized in that for varying the carbon content carbon powder is injected into the spray cone of molten metal.

5. Process according to claim 1, characterized in that two or more melts with different carbon contents are used which are mixed with each other to form the melt from which the sprayed metal is withdrawn.

6. The method according to claim 1, characterized in that using two or more separate spraying two or more melts are sprayed with different carbon contents, wherein the spray cones overlap and the

Discharge quantities of the sprayers are varied,

7. The method according to any one of the preceding claims, characterized in that is used as the carrier gas for spraying nitrogen or a nitrogen-enriched gas.

8. The method according to any one of the preceding claims, characterized in that in particular to form a wear-resistant edge layer on the component in the spray cone one or more hard materials are blown in powder form.

9. The method according to claim 8, characterized in that powders are used with a grain size of 1 nm to 200 microns.

10. The method according to any one of the preceding claims, characterized in that a prefabricated part, in particular a tube is used as a carrier, which part becomes an integral part of the manufactured rolling bearing component.

11. The method according to any one of claims 1 to 9, characterized in that the carrier is a wiederzuverendender carrier on which the metal is sprayed to form the entire component in the spray process.

12. Rolling bearing component, in particular in the form of a ring or a roller, characterized in that at least one edge layer (8b) is formed by spraying a molten metal (5) within the at least partially varies the carbon content, in particular produced by the method according to one of Claims 1 to 11.

13. rolling bearing component according to claim 12, characterized in that it comprises a metallic prefabricated carrier (7) on which the edge layer is formed.

14 rolling bearing component according to claim 12, characterized in that it is a spray-compacted completely manufactured in a spray process.

15. rolling bearing component according to one of claims 12 to 14, characterized in that at least in the sprayed-on edge layer (8b) at least partially one or more hard materials are stored superimposed.