Method for producing a bearing component, and bearing component

Abstract

A method for producing a bearing component includes providing a bearing component blank with an iron-based metal substrate, hardening the metal substrate, treating the metal substrate by an alkaline treatment bath in a region to form an iron oxide-based blackening layer as a conversion layer with an initial layer thickness (db) on the region, and rolling a spherical body over the region to compress the conversion layer in the region to form a bearing component with a protective layer having a final layer thickness (de) that is less than 95% of the initial layer thickness (db). The spherical body may be a component part of a hydrostatic finish rolling tool or a hydrostatic deep rolling tool. The spherical body may include a hard metal or a ceramic.

Claims

1. A method for producing a bearing component comprising: providing a bearing component blank with an iron-based metal substrate; hardening the metal substrate; treating the metal substrate by an alkaline treatment bath in a region to form an iron oxide-based blackening layer as a conversion layer with an initial layer thickness (db) on the region; and rolling a spherical body over the region to compress the conversion layer in the region to form a bearing component with a protective layer having a final layer thickness (de) that is less than 95% of the initial layer thickness (db).

2. The method of claim 1, wherein the spherical body is a component part of a hydrostatic finish rolling tool or a hydrostatic deep rolling tool.

3. The method of claim 1 wherein the spherical body comprises a hard metal or a ceramic.

4. The method of claim 1 wherein the protective layer has a protective layer hardness that is at least 150 percent of a conversion layer hardness of the conversion layer.

5. The method of claim 1, wherein the bearing component has an internal stress (σe) greater than 500 megapascals in the region of the protective layer.

6. The method of claim 1, wherein the spherical body is rolled over the region without slip.

7. The method of claim 1, wherein the bearing component blank comprises a blank geometry and the bearing component comprises a final geometry.

8. The method of claim 1, wherein the step of rolling a spherical body over the region to compress the conversion layer comprises applying a pressure greater than 2000 megapascals to the conversion layer with the spherical body.

9. The method of claim 1, wherein a diameter of the spherical body is greater than 3 mm.

10. The method of claim 1, wherein a diameter of the spherical body is greater than 13 mm.

11. The method of claim 1, wherein the final layer thickness is less than 1.8 micrometers.

12. The method of claim 1, wherein the final layer thickness is less than 1.0 micrometers.

13. The method of claim 1, wherein a surface roughness of the region has a mean peak to valley height that is less than or equal to 1.40 micrometers.

14. The method of claim 13, wherein the surface roughness of the region has a mean peak to valley height that is less than or equal to 1.0 micrometers.

15. The method of claim 8, wherein the pressure is greater than 5000 megapascals.

16. The method of claim 8, wherein the pressure is greater than 7000 megapascals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features, advantages and effects of the disclosure will become apparent from the following description of preferred illustrative embodiments. In the drawings:

(2) FIG. 1 shows a schematic view of the machining of a bearing component blank to produce the bearing component;

(3) FIG. 2 shows a schematic detail view of the overrolling of the bearing component blank;

(4) FIG. 3 shows boundary zone influencing by the overrolling of the bearing component blank;

(5) FIG. 4 shows internal stresses in the bearing component after overrolling;

(6) FIG. 5 shows a flow diagram of the method; and

(7) FIG. 6 shows a schematic section through a rolling bearing.

DETAILED DESCRIPTION

(8) FIG. 1 shows schematically a bearing component 1 and a bearing component blank 2 as the method for producing the bearing component 1 is carried out. FIG. 1 is divided into two sections I and II, wherein section I shows the bearing component blank 2, and section II shows the bearing component 1. In particular, bearing component 1 is the product of the machining of the bearing component blank 2 in accordance with the method.

(9) The bearing component blank 2 comprises a substrate 3, wherein the substrate 3 is a hardened metal substrate 3, e.g. a steel. In particular, it is also possible for the metal substrate 3 to be some other iron-based metal alloy. Here, the hardened metal substrate 3 forms a cylindrical shape. A conversion layer 4 in the form of a blackening layer is formed on the surface of the substrate 3, in particular on the lateral cylinder surface of the metal substrate 3. Based on the substrate 3 made of steel, the conversion layer 4 is here formed from a mixed iron oxide. The conversion layer 4 has a thickness, wherein this thickness forms the initial layer thickness d.sub.b. The initial layer thickness d.sub.b is greater than 1.5 micrometers and, more specifically, greater than 0.5 micrometer. The metal substrate 3 and the conversion layer 4 together form the cylindrical bearing component blank 2, which has a diameter dr.

(10) The bearing component blank 2 is overrolled by means of a rolling tool 5. The rolling tool 5 has a ball 6, which is in direct contact with the conversion layer 4 and thus with the bearing component blank 2. The rolling tool 5 is designed as a hydrostatic rolling tool 5 and has a hydrostatic telescopic compensator 7. The rolling tool 5 subjects the bearing component blank 2 to a force F, wherein the conversion layer 4 is compacted to give the protective layer 8 by being subjected to the force F in this way.

(11) To overroll the bearing component blank 2, the bearing component blank 2 is set in rotation, wherein the rotation takes place with a speed. In particular, the speed is adjustable. During the rotation of the bearing component blank 2, the rolling tool 5 is moved in a feed direction 9. By virtue of the movement of the rolling tool 5 in the feed direction 9 during the rotation of the bearing component blank 2, a surface of the bearing component blank 2 is traversed by means of the ball 6. As an adjustable measure in the method for producing the bearing component 1, the feed f.sub.w, in particular, must be specified, wherein the feed f.sub.w can be adjusted by the combination of the speed and the feed direction 9 or feed rate.

(12) The overrolling of the bearing component blank 2 compacts, smoothes and hardens the conversion layer 4. The overrolled conversion layer 4 forms the protective layer 8. The protective layer 8 has a thickness, wherein this thickness forms the final layer thickness d.sub.e. The final layer thickness d.sub.e is less than 80% of the initial layer thickness d.sub.b. While the conversion layer 4 of the bearing component blank 2 is deformable and sensitive to shocks, the protective layer 8 is non-deformable and insensitive to shocks. The protective layer 8 is thus formed by the compacted conversion layer 4.

(13) To produce the protective layer 8 from the conversion layer 4, the bearing component blank 2 is overrolled, wherein overrolling takes place with suitable parameters that are required to achieve the desired material properties during overrolling. In FIGS. 2 to 4, achievable properties of the bearing component 1 are illustrated with the corresponding parameters.

(14) FIG. 2 shows a detail of the conversion layer 4, of the protective layer 8 and of the ball 6. The conversion layer 4 has a rough surface, wherein this rough surface has deep notches and pits 10. After overrolling, the protective layer 8 formed has a relatively smooth surface with a lower roughness. The ball 6 subjects the surface of the bearing component blank 2 to a force F in the region of the conversion layer 4. In particular, the force F is greater than 5000 megapascals.

(15) During overrolling in the corresponding region, there are number of prevailing stresses within the bearing component blank 2 and/or the bearing component 1. One stress that may be mentioned is the tensile stress 11, which is oriented substantially in alignment with the surface, i.e. with the conversion layer 4 or protective layer 8. The compressive stress 12 is opposed to the force F. Areas of plastic deformation 13 are furthermore entered in this figure, and lines of equal equivalent stress 14 are indicated, wherein these have a similar contour.

(16) Three diagrams are depicted in the right-hand part of FIG. 2, wherein diagram 15 shows the equivalent stress σ.sub.v versus the distance Z from the surface, diagram 16 shows the internal stress σ.sub.e versus the distance Z from the surface and diagram 17 shows the hardness HU versus the distance Z from the surface.

(17) It can be seen in diagram 15 that the equivalent stress σ.sub.v in relation to the distance Z from the surface assumes a relatively complex profile. Here, the equivalent stress σ.sub.v should be considered relative to a flow stress σ.sub.f. In the region of the surface, the equivalent stress σ.sub.v is somewhat lower than the flow stress σ.sub.f. With increasing distance Z from the surface, the equivalent stress σ.sub.v is greater than the flow stress σ.sub.f, wherein, as the distance Z from the surface increases further, the equivalent stress σ.sub.v falls below the flow stress σ.sub.f again and approaches a minimum value. The region of the distance from the surface at which the equivalent stress σ.sub.v is greater than the flow stress σ.sub.f represents an ideally elastic region, wherein the region in which the equivalent stress σ.sub.v is less than the flow stress σ.sub.f represents a really plastic region.

(18) Diagram 16 indicates the internal stress σ.sub.e relative to the distance Z from the surface. Here, it is apparent that the internal stress σ.sub.e from the surface into the interior of the bearing component 1 is always negative and, from a starting value, falls further and assumes a minimum, wherein the internal stress σ.sub.e approaches 0 from this minimum. The point of maximum internal stress σ.sub.e is therefore at a certain distance from the surface.

(19) Diagram 17 shows the hardness HU versus the distance Z from the surface. In addition, a basic hardness HU.sub.G is indicated as a comparison value. At the surface of the bearing component 1, the hardness is identical with the basic hardness HU.sub.G, wherein, from there, the hardness HU increases with increasing distance from the surface and tends toward a maximum, wherein, from this maximum onward, the hardness HU tends back toward the basic hardness HU.sub.G.

(20) FIG. 3 shows several diagrams 18, 19, 20 for the surface roughness P of the protective layer 8 obtained by rolling the conversion layer 4 with different forces F. Diagram 18 shows the surface roughness P along a feed path L.sub.F. Overrolling at ten megapascals results in a mean peak to valley height of 1.40 micrometers.

(21) Diagram 19 illustrates the surface roughness P along the feed path L.sub.F for a bearing component overrolled with a force F of twenty megapascals. This results in a mean peak to valley height of 1.28 micrometers. Diagram 20 illustrates the surface roughness P for a bearing component 1 overrolled at 40 megapascals, illustrated along the feed path L.sub.F. A mean peak to valley height of 0.98 micrometers is obtained for the protective layer 8. Here, it is apparent that the surface roughness P, more specifically the mean peak to valley height, decreases as the force F increases.

(22) Diagram 18a shows the profile of the internal stress versus the distance Z from the surface for the force F of ten megapascals, while diagram 18b shows the hardness HU for overrolling with the force F of ten megapascals. Diagram 19a shows the internal stress for a force F of twenty megapascals, and diagram 20a shows the internal stress for a force F of 40 megapascals. Here, it is apparent that, as the force F increases, the internal stress also increases, wherein, as the force F increases, the maximum of the internal stress also shifts into the interior of the bearing component 1 and/or of the protective layer 8.

(23) Diagram 19b shows the hardness HU for the force F of 20 megapascals, while diagram 20b shows the hardness HU for the force F of 40 megapascals. Here, it is apparent that, as the force F increases, the hardness HU increases, and, as the force F increases, the maximum of the hardness HU shifts into the interior of the bearing component 1 and/or of the protective layer 8.

(24) FIG. 4 shows the internal stresses σ.sub.e versus the distance Z from the surface for different diameters of the ball 6. Diagram 21a illustrates the internal stress for a force F of ten megapascals at a diameter of the ball 6 of three millimeters. Diagram 21b illustrates the internal stress σ.sub.e for a force F of 10 megapascals at a diameter of the ball 6 of six millimeters, and FIG. 21c illustrates the internal stress σ.sub.e for a force F of 10 megapascals at a diameter of the ball 6 of 13 millimeters. Here, it is apparent that with the same force F of 10 megapascals and an increase in the diameter of the ball 6, there is a shallower gradient of the internal stress σ.sub.e in the case of small distances Z from the surface, and the decline from the maximum of the internal stress σ.sub.e is shallower in the case of larger diameters.

(25) FIG. 5 shows schematically a sequence of the proposed method as an illustrative embodiment. In a production step 100, a metal substrate 3 is produced from an iron-based metallic material. Here, the production step 100 can comprise turning, honing, milling, calking and/or forming the material to give the metal substrate 3. The metal substrate 3 is then hardened. In a passivation step 200, the hardened metal substrate 3 is provided with a conversion layer 4. For this purpose, the metal substrate 3 is treated in an alkaline solution, wherein the surface of the metal substrate 3 is converted into a metal oxide, which forms the conversion layer 4. Here, the metal substrate 3 with the conversion layer 4 forms the bearing component blank 2. In an overrolling step 300, the bearing component blank 2 is overrolled, at least in a region of the conversion layer 4. In particular, only sections of the bearing component blank 2 are overrolled, e.g. only the running surface of a rolling bearing ring or the rolling surfaces of a rolling element. In the overrolling step 300, the conversion layer 4 is compacted to give the protective layer 8, wherein the bearing component blank 2 is transformed into the bearing component 1 by the overrolling step 300.

(26) FIG. 6 shows schematically a section through a rolling bearing 22. The rolling bearing 22 comprises an inner ring 23 and an outer ring 24. The inner ring 23 and the outer ring 24 are arranged concentrically with respect to one another and can be rotated relative to one another so as to be rotatable about a common axis A. A plurality of rolling elements 25 is arranged between the inner ring 23 and the outer ring 24. The inner ring 23, the outer ring 24 and the rolling elements 25 each form a bearing component 26. The bearing components 26 each have the protective layer 8 on their surface. The inner ring 23 and the outer ring 24 each have the protective layer 8 on the raceway, wherein the raceway has and/or forms a rolling surface for the rolling elements 25. The rolling elements 25 have the protective layer 8 on the entire rolling surface, wherein the entire surface of the rolling elements 25 is covered by the protective layer 8 for the rolling elements 25, which are spherical in this case.

REFERENCE NUMERALS

(27) 1, 26 bearing component 2 bearing component blank 3 metal substrate 4 conversion layer 5 rolling tool 6 spherical body or ball 7 telescopic compensator 8 protective layer 9 feed direction 10 pits 11 tensile stress 12 compressive stress 13 deformation 14 equivalent stress 15 diagram 16 diagram 17 diagram 18a,b diagram 19a,b diagram 20a,b diagram 21a,b,c diagram 22 rolling bearing 23 inner ring 24 outer ring 25 rolling element I first section II second section d.sub.b initial layer thickness d.sub.f diameter F force f.sub.iv feed d.sub.e final layer thickness σ.sub.v equivalent stress Z distance from the surface σ.sub.e internal stress HU hardness σv equivalent stress σ.sub.f flow stress HU.sub.G basic hardness L.sub.F feed path A axis P surface roughness