ROLLING ELEMENT BEARING WITH IMPROVED ROLLING CONTACT SURFACES

Abstract: A rolling element bearing comprises an inner ring, an outer ring and a series of rolling elements the rolling surface of which is in contact with the raceway surfaces of both rings, and possibly at least one flange the surface of which is in slidable contact with the end surface of a roller element, at least one of these surfaces (8) being provided with a topography comprising recesses (13) which are generally isolated from each other by lands (14) and which may contain a lubricant. The recesses have a maximum size of 100 micrometer in a direction parallel to the surface in question.

Description: Rolling element bearing with improved rolling contact surfaces The invention is related to the field of rolling element bearings which comprise an inner ring, an outer ring and a series of rolling elements, a surface of which is in contact with a surface of both rings, at least one of these surfaces being provided with a topography comprising recesses which are generally isolated from each other by lands and which may contain a lubricant. A bearing of this kind is known from JP-A-05240254. Said known bearing provides an improved lubricant film building capability, which is probably a result of the oil trapped in the surface recesses. Said recesses, which are stated to be smaller than the rolling contact surface area, have a diameter size of about 165 micrometer. Moreover, the pits cause the effective contact area to be smaller, as opposed to "smooth" surfaces. As a result, the wear rate in such bearings will be smaller. The object of the invention is to obtain a better lubricant film building capability at the raceways. This object is achieved in that the recesses have a maximum size of 100 micrometer in a direction parallel to the surface in question. The recesses with such maximum size appear to behave as pockets which are flattened during overrolling, resulting in an extra amount of lubricant being expelled and fed into the contact as an EHL (elasto-hydrodynamic lubrication) lubricant film. Thereby, the rolling surfaces will be separated already at a lower speed. Preferably, the average size of the recesses in a direction parallel to the surface is 50 micrometer. Further, the recesses may have a maximum depth of 4 micrometer; preferably, the recesses have an average depth of less than 0,5 micrometer. The depth preferred is about 0,2 μm. Apart from the size of the recesses, it appears that the geometry thereof is also of importance for obtaining a good lubricant film at low speeds. In particular, it appears to be advantageous in case, in a cross section, the average angle defined by the intersection of the wall of a recess and the adjacent surface is less than 4 degrees; preferred is an average angle of less than 2 degrees. Thereby, an improved lubrication may be obtained in combination with improved fatigue life properties. The average surface area may be more than 150 μm. In this respect, it is preferred furthermore that the recesses are spherically shaped. A spherical geometry provides a well defined recess, having the required lubricant holding capacity and providing the possibility to locate the recesses close to each other in a non-overlapping way, thus maintaining lands which isolate the recesses from each other. Such recesses may be obtained by a peening operation. The minimum average diameter may be 14 μm. According to a first possibility, the topography comprising recesses may be applied to at least one of the rolling surfaces of the rolling elements, and/or at least one of the raceways of the rings. The topography in a direction transverse with respect to the direction of rolling may be varying. For instance, the depth and/or the density of the recesses (number of recesses per unity of surface area) may be varying. This embodiment of the rolling bearing according to the invention is in particular useful in the case of varying lubrication requirements. According to a second possibility, the topography comprising recesses may be applied in a roller bearing wherein at least glass beads are used in the shot peening operation. The invention is furthermore related to a method for manufacturing a rolling element or a ring for a bearing as described before, wherein at least one of the rolling surfaces and the raceways is provided with a topography comprising recesses which are generally isolated from each other by lands and which may contain a lubricant, which topography in a direction transverse with respect to the direction of rolling is varying. Preferably, glass beads are used in the shot peening operation. The diameter of the glass beads should be about 200 micrometer. The invention will now be described further with reference to the figures. Figure 1 shows a cross-section through a single row cylindrical roller bearing. Figure 2 shows a detail of a surface of the bearing according to figure 1. Figure 3 shows a cross-section through said surface. The cylindrical roller bearing according to figure 1 comprises an outer ring 1, an inner ring 2 consisting of two halves 3, 4, as well as a series of cylindrical rollers 5. Both the outer ring 1 and the inner ring 2 have two integral flanges 6 respectively 7. Between these flanges, raceways 8 respectively 9 have been defined. The cylindrical rollers have flat end faces 10, which can slidably contact the facing surfaces 11 respectively 12 of the integral flanges 6 respectively 7. According to the invention, at least one of the surfaces of the rolling elements 5 and/or the rings 1 , 2 may be provided with a surface topography as shown in figure 2. The surface in question may be the rolling surface of the cylindrical rollers 5, their end faces 10, or the raceways 8, 9 and/or the facing surfaces 11, 12 of integral flanges 6, 7. As shown in figure 2 said topography of e.g. raceway 8 comprises a number of spherically shaped recesses 13, which may have varying dimensions. These spherically recesses 13 are e.g. obtained by means of shot blasting with glass beads. The recesses 13 are generally isolated from each other by means of lands 14 which are part of the raceway 8 in question. The recesses 13 constitute small pockets in which oil may be trapped. When a rolling element overrolls with the recesses 13, they are compressed somewhat, whereby the oil is expelled and a better lubrication is obtained. Figure 3 shows a cross-section of a recess 13. According to the invention, their maximum seize a in a direction parallel to the raceway 8 is 100 μm. Furthermore, their maximum depth is 4 μm. The average depth of the recesses is preferably 0.2 μm. In order to guarantee a smooth overrolling of the recesses 13 by the rolling elements, the average angle α defined by the intersection of the wall of the recess 13 and the adjacent land 14 is 2°.

Claims: C l a i m s 1. Rolling element bearing, comprising an inner ring (2), an outer ring (1) and a series of rolling elements (5) a surface (10) of which is in contact with a surface (8, 9, 11, 12) of both rings, at least one of these surfaces (8-12) being provided with a topography comprising recesses (13) which are generally isolated from each other by lands (14) and which may contain a lubricant, characterized in that the recesses (13) have a maximum size of 100 micrometer in a direction parallel to the surface (8-12) in question. 2. Rolling element bearing according to claim 1, wherein the average size of the recesses (13) in a direction parallel to the surface (8-12) is 50 micrometer. 3. Rolling element bearing according to claim 1 or 2, wherein the recesses (13) have a maximum depth of 4 micrometer. 4. Rolling element bearing according to claim 1 or 2, wherein the recesses (13) have a maximum depth of less than 0,5 μm. 5. Rolling element bearing according to claim 1, 2, 3 or 4, wherein the recesses (13) have an average depth of 0,2 micrometer. 6. Rolling element bearing according to any of the preceding claims, wherein, in a cross section, the average angle α defined by the intersection of the wall of a recess (13) and the adjacent surface (8) is less than 5 degrees. 7. Rolling element bearing according to any of the preceding claims, wherein, in a cross section, the average angle α defined by the intersection of the wall of a recess (13) and the adjacent surface (8) is less than 2 degrees. 8. Rolling element bearing according to any of the preceding claims, wherein the average surface area of the recesses is more than 150 μm. 9. Rolling element bearing according to any of the preceding claims, wherein the minimum diameter of the recesses is 14 μm. 10. Rolling element bearing according to any of the preceding claims, wherein the recesses (13) are spherically shaped. 11. Rolling element bearing according to claim 10, wherein the recesses (13) are obtained by a peening operation. 12. Rolling element bearing according to any of the preceding claims, wherein at least one of the rolling surfaces of the rolling elements (5) and or at least one of the raceways (8, 9) of the rings (1, 2) is provided with a topography comprising recesses which are generally isolated from each other by lands (14) and which may contain a lubricant. 13. Rolling element bearing according to claim 12, wherein the topography in a direction transverse with respect to the direction of rolling is varying. 14. Rolling element bearing according to claim 13, wherein the depth and/or the density of the recesses (13) (number of recesses per unity of surface area) is varying. 15. Rolling element bearing according to claim 12, 13 or 14, wherein the number of recesses is not more than 200 per square millimetre. 16. Roller bearing according to any of claims 1-15, wherein at least one of the rings (8, 9) comprises an integral flange (6, 7), and the rollers (50 have an end face (10) which slidably contacts the facing support surface (11, 12) of said flange (6, 7), at least one of the end surface (11, 12) of said flanges (6, 7) and the end faces (10) of the rollers (5) being provided with a topography comprising recesses (13) which are generally isolated from each other by lands (14) and which may contain a lubricant. 17. Method for manufacturing a rolling element (5) or a ring (8, 9) for a bearing according to any of the preceding claims, wherein the surface of a rolling element respectively a ring (8, 9) is treated by means of a shot peening operation. 18. Method according to claim 17, whereby glass beads are used in the shot peening operation. 19. Method according to claim 18, wherein the diameter of the glass beads is about 200 micrometer.

Inventors: DE VRIES ALEXANDER JAN CAREL, LUGT PIETER MARTIN, OLSCHEWSKI ARMIN HERBERT EMIL, TRIPP JOHN HOWARD, DE VRIES, ALEXANDER, JAN, CAREL, LUGT, PIETER, MARTIN, OLSCHEWSKI, ARMIN, HERBERT, EMIL, AUGUST, TRIPP, JOHN, HOWARD
Applicants: LUGT PIETER MARTIN, OLSCHEWSKI ARMIN HERBERT EMIL, SKF IND TRADING & DEV, TRIPP JOHN HOWARD, VRIES ALEXANDER JAN CAREL DE, DE VRIES, ALEXANDER, JAN, CAREL, LUGT, PIETER, MARTIN, OLSCHEWSKI, ARMIN, HERBERT, EMIL, AUGUST, SKF INDUSTRIAL TRADING & DEVELOPMENT COMPANY B.V., TRIPP, JOHN, HOWARD
Application year: 1998
Main classification: F16C33
IPC codes: F16C33