Method for manufacturing a bearing ring for rolling bearings having at least one raceway for rolling elements and device for carrying out the method

Abstract

The invention relates to a method for manufacturing a bearing ring for rolling bearings with an outer diameter of more than 500 mm, having at least one raceway (1) for rolling elements, wherein a pre-ring (101) is started, which consists of quenched and tempered steel with a carbon content of ≥ 0.4 wt.% or case-hardening steel, wherein the pre-ring (101) is heated to a first forming temperature (T1) which is between 1100 and 1300 °C, wherein the heated pre-ring (101) is subjected to ring rolling, wherein the rolled ring is subjected to a quenching and tempering heat treatment.To specify such a method by which the load-bearing capacity and service life of large slewing bearings is increased, it is proposed that the ring rolling is designed as a multi-stage ring rolling process, wherein the individual stages of the ring rolling process are carried out on ring rolling machines (301, 302) connected in series such that in a first ring rolling step (103) a ring blank with a substantially rectangular cross-sectional area is produced from the pre-ring (101) and in at least a second ring rolling step (200) the ring blank is subjected to profile rolling to produce a ring with a cross-section close to the final dimensions, wherein the heat treatment (201) is carried out on the ring with the cross-section close to the final dimensions, wherein a workpiece area forming the at least one raceway (1) is arranged in a near-surface edge region of the cross-section close to the final dimensions.

Description

[0001] The invention relates to a method for manufacturing a bearing ring for rolling bearings having at least one raceway for rolling elements and an outer diameter of more than 500 mm according to the preamble of claim 1, and to a device for carrying out the method.

[0002] European patent EP 1 358 953 B1 describes a ring rolling process with a forming roll and a mandrel for producing ring elements. The mandrel is rotatable about a first axis and the forming roll about a second axis. During the rolling process, the mandrel is pressed towards the forming roll by means of a receiving roll, which is rotatably arranged about a third axis that is substantially aligned with the first and second axes and is rotated as a result of its contact with the rotating mandrel.

[0003] European patent EP 1 024 914 B1 describes a rolling machine for forming an annular component. The rolling machine comprises a forming mandrel, a forming wheel, and two support rollers. Furthermore, two side control rollers are provided to act on the side surfaces of the annular component at a distance from the rolling shell, with the side control rollers being arranged between the support rollers in the overall volume surrounding their outer circumference.

[0004] Ring rolling for the production of ring blanks with a substantially rectangular cross-section is known from the prior art. "Substantially rectangular cross-section" means that the shape of the cross-section does not have to be exactly rectangular; in particular, the cross-sectional shape of the ring blank can have one or more rounded corner areas. This manufacturing process is described, for example, in Chapter 7.4 of the textbook "Massive Forming in a Nutshell" (ISBN: 978-3-928726-2-0). There, it is described that the pre-ring for ring rolling is heated to a temperature of 1200°C and that the ring rolling is carried out on an axial-radial ring rolling mill. This mill has conically shaped axial rolls for applying an axial rolling force to reduce the height of the ring-shaped workpiece, as well as a main roll and a mandrel roll for applying the radial rolling force.The radial rolling force reduces the wall thickness of the ring-shaped workpiece. The main roll acts on the outer circumferential surface, and the mandrel roll on the inner circumferential surface of the ring-shaped workpiece. After ring rolling, the ring blank undergoes further processing, which includes a heat treatment known as "FP annealing" or "isotherm annealing" and mechanical (machining) processing. FP annealing (FP stands for treatment to ferrite-pearlite microstructure) serves to create a uniform microstructure with good machinability.

[0005] In the manufacturing practice for rolling bearing rings of large slewing bearings, it is known to harden the raceways for the rolling elements, which are produced by machining the rolled ring blank, e.g., by induction hardening. When case-hardening steel is used as the material, the hardening is carried out by case hardening.

[0006] In the manufacturing process described above, the workpiece areas that form the raceways of the finished bearing ring after machining are located far from the surface of the ring blank. A disadvantage of this process is that these areas, which are far from the surface, exhibit low degrees of deformation due to the inherent limitations of the process. Furthermore, particularly in large ring cross-sections, these areas are only insufficiently tempered during heat treatment, as the necessary cooling and heating rates are not achieved in these regions. In large ring cross-sections, the limited thermal conductivity of these areas also leads to less effective quenching, which can result in adverse property changes such as material inhomogeneities and grain growth due to the longer dwell times at higher temperatures.These factors combine to result in unfavorable material properties in the workpiece areas far from the surface. This, in turn, leads to adverse properties of the rolling bearings, such as a reduced service life or reduced load-bearing capacity. The larger the ring cross-sections and the bearings themselves, the greater the adverse effects.

[0007] The object of the invention is to provide a method for manufacturing a bearing ring for rolling bearings with an outer diameter of more than 500 mm, comprising at least one raceway for rolling elements, which increases the load-bearing capacity and service life of large rolling bearings. The object of the invention is also to provide a device for carrying out the method according to the invention.

[0008] With regard to the method, this problem is solved by a method with the features specified in the independent method claim. With regard to the apparatus, this problem is solved by a device with the features specified in the independent apparatus claim. Advantageous embodiments are described in the dependent claims, the following description, and the drawings.

[0009] The inventive method for manufacturing a bearing ring for rolling bearings with an outer diameter of more than 500 mm, having at least one raceway for rolling elements, comprises the following process steps, which are known from practice and from the aforementioned textbook “Massivumformung kurz und bündig” (ISBN: 978-3-928726-2-0) in Chapter 7.4: - It is assumed that a pre-ring is made of heat-treated steel with a carbon content of ≥ 0.4 wt.% or case-hardening steel, - wherein the pre-ring is heated to a first forming temperature which is between 1100 and 1300 °C, - wherein the heated pre-ring is subjected to ring rolling, - whereby the rolled ring is subjected to a heat treatment.

[0010] The term "pre-ring" refers to a workpiece as described in Chapter 7.4.3 of the aforementioned textbook "Mass Forming in a Nutshell," namely a circular disc-shaped workpiece with a hole in the center. The pre-ring can be produced, for example, in a forming process using open-die forging, as described in Chapter 7.4.3 of the same textbook. Open-die forging can include the process steps of upsetting, rounding, and punching.

[0011] To produce a bearing ring for large rolling bearings with an outer diameter greater than 500 mm from a ring blank with a substantially rectangular cross-section, manufactured according to the state of the art by ring rolling and heat-treated, the ring blank is subjected to machining according to the state of the art. The desired final shape of the bearing ring, with its at least one rolling element raceway, is thus produced by removing material. The rolling element raceway(s) are then subsequently hardened to achieve the required service life.

[0012] This manufacturing method for bearing rings of large rolling bearings is associated with the disadvantages already mentioned at the outset. These disadvantages are avoided by the method according to the invention.

[0013] The method according to the invention is characterized in that the ring rolling is designed as a multi-stage ring rolling process, wherein the individual stages of the ring rolling process are carried out on ring rolling machines connected in series such that in a first ring rolling step a ring blank with a substantially rectangular cross-sectional area is produced from the pre-ring and in at least a second ring rolling step the ring blank is subjected to profile rolling to produce a ring with a cross-section close to the final dimension, wherein the heat treatment is carried out on the ring with the cross-section close to the final dimension, wherein a workpiece area forming the at least one raceway is arranged in a near-surface edge region of the cross-section close to the final dimension.

[0014] In the inventive process, the workpiece areas located in the near-surface edge region of the near-net-shape cross-section, which form the raceways on the finished bearing ring, exhibit high degrees of deformation because these workpiece areas are subjected to significant deformation during profile rolling. Due to the increased local degree of deformation in the workpiece area that forms the rolling element raceway on the finished bearing ring, dynamic and metadynamic recrystallization processes are repeatedly carried out in this workpiece area during deformation. This allows a very small grain size to be achieved in this workpiece area. This small grain size contributes significantly to increasing the bearing service life.

[0015] Furthermore, the workpiece areas located in the near-surface edge region of the near-net-shape cross-section exhibit a much finer-grained microstructure than the more distant workpiece areas exposed by machining in the prior art manufacturing process, because the heat treatment acts directly on the workpiece areas that will later form the raceways. According to the invention, adverse material inhomogeneities and adverse grain growth are avoided because the quenching acts directly on the near-surface workpiece areas of the near-net-shape ring, and therefore no longer residence times of the microstructure at higher temperatures occur.

[0016] The material structure resulting from the inventive process exhibits an advantageous fine grain. Subsequent hardening of the raceway(s) results in improved hardness values ​​and more uniform case hardening depths.

[0017] As a result, the inventive method leads to bearing rings for large rolling bearings that have a high load-bearing capacity and meet very high service life requirements.

[0018] According to one embodiment of the inventive method, the first ring rolling step and the at least one second profile rolling step are carried out in a single heat, i.e., without reheating before the second profile rolling step. This results in a particularly economical manufacturing process because intermediate heating of the ring blank with its substantially rectangular cross-section between the first ring rolling step and the at least one additional profile rolling step is avoided. Likewise, this results in an overall short manufacturing process for bearing rings of large slewing bearings.

[0019] In practice, intermediate heating between the first and at least one subsequent rolling step cannot always be avoided. It is particularly important to ensure that the workpiece is not overheated before the first ring rolling step, as overheating leads to excessive scale buildup, grain boundary oxidation, and carbon erosion in the near-surface areas of the workpiece, resulting in detrimental material properties. Therefore, it is not always possible to heat the workpiece to a sufficiently high temperature before the first rolling step to maintain a sufficiently high temperature for the subsequent profile rolling step.

[0020] According to one embodiment of the method according to the invention, it is therefore provided that after the first ring rolling step the ring blank is reheated to a temperature ≥ 1100 °C and ≤ 1300 °C. This ensures that the workpiece has an optimal rolling temperature during profile rolling.

[0021] Reheating can take place in a continuous furnace, a chamber furnace, or a bogie hearth furnace. The reheating furnace can simultaneously be used as a material buffer if further processing in the second rolling step is delayed for operational reasons, or if the profile rolling step takes longer than the heating time required to reach the necessary rolling temperature during reheating.

[0022] According to one embodiment of the inventive method, the reheating of the ring blank takes a period of ≤ 60 minutes. It has been shown that this relatively short period is sufficient to bring the workpiece homogeneously to the rolling temperature required for profile rolling. This short reheating time ensures a fast manufacturing process with a short cycle time.

[0023] According to one embodiment of the method according to the invention, the reheating is carried out in a chamber furnace or a continuous furnace. Particularly with ring blanks of large dimensions (e.g., in the range of 4 m to 8 m outer diameter) or with large-volume workpieces, the use of continuous furnaces can be uneconomical due to the required furnace size. In such cases, it is more economical to carry out the reheating in a chamber furnace.

[0024] According to one embodiment of the method according to the invention, the profile rolling process for producing a ring with a cross-section close to the final dimensions is designed as a multi-stage rolling process comprising several contouring steps. The desired final shape or contour of the bearing ring is thus achieved by stepwise profile rolling in individual partial steps. For example, when producing bearing rings with a complex shape and / or multiple rolling element raceways, it can be advantageous to divide the required overall forming of the ring blank with its essentially rectangular cross-section into several partial profile rolling steps.

[0025] In principle, the individual partial profile rolling steps could be carried out in separate ring profile rolling mills. However, it is more cost-effective to perform the individual partial profile rolling steps on the same rolling mill, changing the profile rolls between each step.

[0026] According to one embodiment of the method according to the invention, the at least one raceway on the ring with the near-net-shape cross-section is produced by machining and subsequently hardened. This machining process requires the removal of very little material to achieve the final shape of the raceway and the desired surface roughness. Therefore, very little scrap is generated and machining times are reduced.

[0027] The degree of deformation achieved according to the invention is at least three times that achievable according to the prior art in the areas near the raceway. Due to the high degrees of deformation to which the workpiece area forming the raceway is subjected during the manufacturing process, and due to the heat treatment directly applied to this workpiece area, very good mechanical and technological properties can be achieved in the basic microstructure and, in particular, in the areas near the raceway. Higher hardness values ​​and more uniform case depths are achieved after raceway hardening. Investigations have shown that the bearing rings produced using the method according to the invention have a 63.3% smaller mean grain size (22 µm) in the areas near the raceway compared to bearing rings produced according to the prior art (60 µm).The invention thus leads to a significant reduction in the average grain size, which promotes higher hardness values ​​and more uniform hardening depths.

[0028] According to one embodiment of the inventive method, the ring blank is subjected to profile rolling in the second ring rolling step. Using a profiled rolling tool, a multiple ring is produced, which has at least one parting line. The multiple ring is separated in the parting line into at least two individual rings with cross-sections close to the final dimensions. This results in a particularly efficient manufacturing process with a significantly increased output of rings with cross-sections close to the final dimensions. The number of bearing rings that can be produced in a given period is multiplied, meaning the productivity of the production plant increases significantly. The manufacturing costs per bearing ring are correspondingly reduced significantly.

[0029] The device for solving the aforementioned technical problem and for carrying out the method according to the invention is characterized in that it has two ring rolling machines connected in series, wherein a first of the two ring rolling machines is set up to produce a ring blank with a substantially rectangular cross-sectional area, wherein a second of the two ring rolling machines has profile rollers for producing a ring with a cross-section close to the final dimension, and wherein a device for heat-treating the ring with the cross-section close to the final dimension is provided.

[0030] According to one embodiment of the device according to the invention, a reheating device is provided in which the ring blank can be heated to a temperature of ≥ 1100 °C and ≤ 1300 °C after the first and before the second ring rolling step.

[0031] According to one embodiment of the device according to the invention, the reheating device is designed as a chamber furnace or as a continuous furnace.

[0032] The invention is explained in more detail below with reference to the figures. They show schematically: Fig. 1 a cross-section of a bearing ring for a large rolling bearing designed as a double-row tapered roller bearing according to the state of the art; Fig. 2a a ring blank with a substantially rectangular cross-section, obtained from the first ring rolling step of the inventive process; Fig. 2b a ring with a cross-section close to the final dimensions, obtained from the profile rolling step of the method according to the invention; Fig. 3 the inventive production of rings with a cross-section close to the final dimensions from a double ring produced by profile rolling; Fig. 4 a comparison of the prior art method for manufacturing a bearing ring for large rolling bearings with the method according to the invention; Fig. 5 opposite Fig. 4 modified process sequence of the inventive method with intermediate heating of the workpiece after the first ring rolling step and before the profile rolling step; Fig. 6 a device according to the invention for carrying out the method according to the invention.

[0033] In Fig. Figure 1 shows a cross-sectional view of a ring blank 2 for a bearing ring of a large rolling bearing designed as a double-row tapered roller bearing. The ring blank 2 has a substantially rectangular cross-section. This substantially rectangular cross-section is obtained by ring rolling on a radial-axial ring rolling machine, as described above. The substantially rectangular cross-section of the ring blank 2 is formed in Fig. 1 The contour K of the bearing ring to be produced is drawn.

[0034] According to the manufacturing process known from the prior art, the shape of the bearing ring is produced by machining the excess material of the ring blank 2. That is, the material of the blank 2 which is outside the Fig. The contour K shown in section 1 is removed by machining, for example by turning and / or milling, of the blank 2. This produces a large quantity of metal chips that must be disposed of. A bearing ring with the in Fig. The contour K shown in Figure 1 is also referred to in practice as a "nose ring". Such a bearing ring is frequently used in double-row tapered roller bearings. After machining the blank 2, the wedge flanks of the contour form the raceways of the bearing ring on which the rolling elements roll.

[0035] The workpiece areas that form the raceways 1 after completion of the machining of the blank 2 are located far from the surface O of the ring blank 2. As a result, these workpiece areas are only minimally deformed during ring rolling of the ring blank 2, because the greatest deformations of the ring blank 2, or in other words, the greatest degrees of deformation in the material of the ring blank 2, occur in the edge regions of the ring blank 2 (cf. Fig. 2a) The low degrees of deformation in the area of ​​the raceways 1 after machining result in the technical disadvantage that coarse grains and porosities are formed in the microstructure, which in turn leads to a deterioration of the mechanical properties of the raceways 1. This can negatively affect the load-bearing capacity and service life of the workpieces or the bearing ring.

[0036] The ring blank 2, with its essentially rectangular cross-section, undergoes a heat treatment after ring rolling and before machining. This heat treatment comprises heating and quenching the ring blank 2. A potential disadvantage is that the areas of the workpiece far from the surface, which form the raceways 1 of the bearing ring after machining, are not sufficiently tempered. Particularly with large cross-sections of the ring blank 2, the heat treatment in these areas is inadequate because, for example, the necessary cooling and heating rates are not achieved. With large cross-sections, the limited thermal conductivity of the material also results in less effective quenching of these areas, leading to adverse property changes such as...Material inhomogeneities and grain growth can occur due to longer residence times at higher temperatures. These mechanisms collectively lead to poorer material properties in areas of the ring blank 2 that are far from the surface. This results in adverse properties of the rolling bearing rings or bearings after machining, such as reduced service life and / or reduced load-bearing capacity. For example, mechanical damage to the raceways of the bearing rings can occur. The larger the bearings or the cross-sections of the ring blank 2, the greater the adverse effects.

[0037] In the Fig. 2a schematically shows which degrees of forming a ring blank 2 according to Fig. 1. After ring rolling, the component areas exhibit deformation. For clarity, only four areas with different deformation degrees U1, U2, U3, and U4 are distinguished. It is understood that a finer subdivision with significantly more than four deformation degrees would be possible, but this would lead to greater complexity in the diagrams. In reality, the component areas with different deformation degrees can transition seamlessly into one another.

[0038] In Fig. Figure 2a shows a legend to the right of the ring blank 2 with its essentially rectangular cross-section, displaying four areas with different hatching patterns. The hatching patterns U1, U2, U3, and U4 indicate the different degrees of deformation. U1 denotes the component area with the lowest degree of deformation, and U4 the component area with the highest degree. The following relationship holds true for the degrees of deformation: U1 ≤ U2 ≤ U3 ≤ U4.

[0039] In the core area of ​​contour K, the ring blank 2 has according to Fig. 2a undergoes the least deformation and therefore exhibits the lowest degree of deformation U1. The largest area of ​​the ring blank 2 exhibits the second-lowest deformation, or the second-lowest degree of deformation U2. The second-highest degree of deformation U3 is present in a relatively narrow, band-shaped area. The highest degree of deformation U4 is present in the outer areas of the essentially rectangular cross-section of the ring blank 2. When the contour K is produced by machining the ring blank 2 after ring rolling, the component areas where degrees of deformation U3 and U4 are present are almost completely removed. What remains are raceways 1, which lie almost entirely within a material area that exhibits only the low degree of deformation U2.

[0040] Based on the Fig. 2a and Fig. 2b explains the inventive method for manufacturing a bearing ring having at least one raceway for rolling elements for large rolling bearings, i.e. for rolling bearings with an outer diameter of more than 500 mm. Fig. Figure 2a shows the ring blank 2 with the essentially rectangular cross-section obtained from the first ring rolling step 103 (see Figure 2). Fig. 4) of the method according to the invention. This first ring rolling step 103 is carried out according to the invention on a first ring rolling machine 301 (see Figure 4). Fig. 6) carried out. Schematically, in Fig. 2a, the solid line again shows the contour K of the later bearing ring. The ring blank 2 is then, according to the invention, a profile roller 200 (see Figure 2a). Fig. 4) on a second ring rolling mill 302 (see Fig. 6) is subjected to this process. In contrast to the prior art method in which the shape of the bearing ring (i.e., the contour K) is produced by machining the ring blank 2 with a substantially rectangular cross-section, according to the invention, a ring is produced by profile rolling 200 on a second ring rolling machine 302 which has a cross-section close to the final dimensions with respect to the bearing ring to be manufactured. That is, the bearing ring obtained after profile rolling 200 has a shape that already comes quite close to the contour K of the bearing ring. Fig. Figure 2b shows the ring with the near-final cross-section produced by the profile rolling step 200 of the manufacturing process according to the invention.

[0041] In Fig. Figure 2b clearly shows that the workpiece areas, which will later form the raceways 1 on the bearing ring, lie close to the surface, directly below the surface of the ring with the near-net-shape cross-section. High degrees of deformation are achieved in these workpiece areas during profile rolling step 200.

[0042] In Fig. 2b is - analogous to Fig. 2a - To the right of the ring with the near-net-shape cross-section, a legend is shown, displaying four areas with different hatching. The hatching U1', U2', U3', and U4' indicates the different degrees of deformation. U1' denotes the component area with the lowest degree of deformation, and U4' the component area with the highest degree. The following relationship applies to the degrees of deformation: U1' ≤ U2' ≤ U3' ≤ U4'. The degrees of deformation U1, U2, U3, and U4 are generally lower than the corresponding degrees of deformation U1', U2', U3', and U4' because the profile rolling process (200) adds another, additional deformation.

[0043] Fig. Figure 2b shows which workpiece areas exhibit which degrees of deformation U1' to U4' after profile rolling 200. The core area inside contour K represents the workpiece area that has undergone the least deformation overall and therefore has the lowest degree of deformation U1'. The workpiece area surrounding the area with degree of deformation U1' has the second lowest degree of deformation U2'. The workpiece area with the second highest degree of deformation U3' surrounds the workpiece area with degree of deformation U2'. The outer workpiece areas exhibit the highest degree of deformation U4'. The in Fig. 2b The lower raceway 1 of contour K of the bearing ring lies completely within the workpiece area that exhibits the greatest degree of deformation U4'. The in Fig. 2b upper raceway 1 of contour K of the bearing ring lies mostly in a workpiece area which has the second highest degree of deformation U3', and to a small extent in workpiece areas which have the highest degree of deformation U4'.

[0044] According to the invention, a high degree of local deformation is thus achieved in the workpiece area(s) that form the rolling element raceway 1 of the subsequently finished bearing ring. During deformation in this workpiece area(s), the material repeatedly undergoes dynamic and metadynamic recrystallization processes. This advantageously results in a very small grain size in this workpiece area(s), which significantly contributes to increasing the service life of the bearing ring and the entire rolling bearing.

[0045] The heat treatment of the bearing ring is carried out – deviating from the method known from the prior art – according to the invention on the part in Fig. The ring shown in Figure 2b has a cross-section close to its final dimensions. This ensures that the cooling and heating rates required for effective heat treatment act on the material in the near-surface areas. Even with large cross-sections, the near-surface workpiece areas are sufficiently quenched because thermal conductivity is no longer the limiting factor for quenching. Adverse property changes, such as material inhomogeneities and grain growth, are avoided by preventing longer residence times at higher temperatures. The material properties of the near-surface workpiece areas that form the subsequent raceways 1 are improved by the manufacturing process according to the invention. The rolling bearing rings or bearings produced by the manufacturing process according to the invention exhibit an increased service life and / or improved load-bearing capacity compared to the prior art.These positive effects of the manufacturing process according to the invention are also achieved with large ring cross-sections.

[0046] In Fig. Figure 3 illustrates the inventive and efficient production of single rings with near-net-shape cross-sections from multiple rings produced by profile rolling, using the production of a double ring 700 as an example. The production of two outer rings 701 for large rolling bearings designed as single-row tapered roller bearings is shown as an example. Fig. 3 is from the left, which is from a first ring rolling step 103 (cf. Fig. 4) The resulting ring blank 2 with the substantially rectangular cross-section is fed in. The first ring rolling step 103 and the feeding of the ring blank 2 to the second ring rolling step 200 is described in Fig. Figure 3 is not shown for the sake of clarity. The ring blank 2 is then rolled into a double ring 700 in a second ring rolling step 200 using a cylindrical radial roll 600, a rolling tool designed as a profiled inner mandrel 601, and a pair of axial rolls 602. The cylindrical radial roll 600 forms a cylindrical outer surface of the double ring 700, which, after the division of the double ring 700, forms the respective cylindrical outer surface of the two outer rings 701. The profiled rolling tool 601 forms the respective rolling element raceway on the outer rings 701. The output of a production plant equipped in this way with a profiled rolling tool for the production of double rings and the productivity of the manufacturing process are doubled or increased.compared to the manufacturing process described at the beginning, which is known from the prior art and involves manufacturing a single ring by machining the shape of the bearing ring, significantly increased.

[0047] Instead of one in Fig. In addition to the three exemplary double rings shown, triple rings, quadruple rings, or other multiple rings can also be produced using appropriately designed profiled rolling tools. The productivity of the manufacturing process (measured in the number of rings produced per unit of time) thus increases accordingly.

[0048] In Fig. Section 4 compares the process sequence according to the prior art with the process sequence according to the invention. The process sequence according to the prior art comprises the following process steps: The process begins with a pre-ring 101, i.e., a perforated circular disk produced, for example, by open-die forging and punching from a pre-product cut from bar stock. The pre-ring 101 is heated to rolling temperature (heating 102). The heated pre-ring 101 is then subjected to ring rolling 103. Ring rolling 103 is typically carried out in a radial-axial ring rolling mill 301. The intermediate product obtained by ring rolling 103 is a ring blank 2 with a substantially rectangular cross-section (see Figure 102). Fig. 1) This ring blank 2 undergoes a heat treatment 104. During this process, the disadvantages mentioned above occur with regard to the workpiece areas far from the surface, which later form the raceways 1 of the bearing ring to be manufactured. After the heat treatment 104, the ring blank 2 undergoes extensive machining 105 to produce the final shape of the bearing ring. The raceways are also ground to achieve the desired surface roughness. The raceways are then hardened 106.

[0049] The inventive method also starts with a pre-ring 101, which, as in the prior art, is first heated to rolling temperature (heating 102). The diameter and height of the pre-ring, as well as the heating temperature and time, are determined. The heated pre-ring 101 is then formed into a ring blank 2 with a substantially rectangular cross-section by ring rolling 103. The ring rolling 103 is carried out, for example, as is known from the prior art, on a first ring rolling mill 301 designed as a radial-axial ring rolling mill. According to the invention, a further ring rolling step 200 is carried out after the ring rolling 103, on a second ring rolling mill 302. The second ring rolling mill 302 has profile rolls with which the ring blank 2 is formed into a ring whose contour K or shape already substantially corresponds to the desired final contour.The final shape of the bearing ring to be produced corresponds to the "ring with a near-net-shape cross-section". During profile rolling 200, near-surface workpiece areas are created that later form the rolling element raceways 1 on the finished bearing ring and exhibit a high degree of deformation. Due to the increased local degree of deformation in the workpiece area that forms the rolling element raceway 1 on the finished bearing ring, the material structure in this workpiece area repeatedly undergoes dynamic and metadynamic recrystallization processes during deformation. This results in a very small grain size in this workpiece area, which significantly contributes to increasing the bearing service life.

[0050] In the Fig. In the process sequence shown in Figure 4 according to the invention, the ring rolling 103 and the profile rolling 200 are carried out in the same heat, i.e., the workpiece is not subjected to reheating after the first ring rolling step 103 to bring it to a rolling temperature required for the profile rolling step 200. Such two-stage rolling in one heat is particularly fast, energy-efficient and cost-effective.

[0051] Following profile rolling 200, the ring with a near-net-shape cross-section undergoes a heat treatment 201. This process provides excellent tempering of the near-surface workpiece areas that will form the future raceways 1, because the heat treatment (heating and quenching) acts directly on these areas. Material inhomogeneities and undesirable grain growth are thus avoided.

[0052] After heat treatment 201, the final shape of the bearing ring is produced by machining operations 202, which may include turning, milling, and grinding. Since the ring to be machined already has a cross-section close to its final dimensions, only a very small amount of metal scrap is generated during machining operations 202 compared to machining operations 105 in the prior art manufacturing process. The rolling element raceways 1 are also produced during machining operations 202. These are then hardened in process step 203. Due to the fine-grained microstructure produced in the raceway area during the manufacturing process according to the invention, particularly high hardness values ​​as well as uniform and good case depths are achieved during hardening 203.

[0053] In Fig. 5 is opposite Fig. Figure 4 shows a modified sequence of the process according to the invention. The only difference is that an intermediate heating step 110 takes place between the first ring rolling step 103 and the profile rolling step 200. This heating is also referred to as reheating 110. It serves to heat the workpiece to the rolling temperature required for profile rolling before the profile rolling step 200. By providing a reheating step 110, process steps 101 to 103 on the one hand and 110 to 203 on the other hand can, in principle, be carried out at different plant locations.

[0054] In Fig. Section 6 describes in more detail an apparatus for carrying out the method according to the invention. The pre-ring 101 is heated to a first forming temperature T1 in a heating device 300 as part of a heating process 102. The heating device 300 can be, for example, a chamber furnace or a continuous furnace.

[0055] A first ring rolling mill 301 is arranged behind the heating device 300. It can be designed as a radial-axial ring rolling mill. In the first ring rolling mill 301, the pre-ring 101 is rolled out in a first ring rolling step 103 into a ring blank with a substantially rectangular cross-section.

[0056] At the in Fig.In the apparatus shown in Figure 6, a reheating device 400 or 401 is arranged downstream of the first ring rolling mill 301. This can be designed, for example, as a chamber furnace 400 or as a continuous furnace 401. In the reheating device 400, 401, the ring blank 2 is heated to a second forming temperature T2, which is required for the subsequent second ring rolling step 200. Downstream of the reheating device 400, 401, a second ring rolling mill 302 is arranged. On this second ring rolling mill 302, the ring blank with its substantially rectangular cross-section is rolled into a ring with a cross-section close to its final dimensions using profile rolls. The second ring rolling step 200 can comprise multi-stage profile rolling, in which case the second ring rolling mill 302 must be equipped before each rolling stage with profile rolls required for the forming operation to be carried out in the respective rolling stage.

[0057] Downstream of the second ring rolling mill 302, a heat treatment device 500 is arranged in which the ring, with a cross-section close to its final dimensions, undergoes a heat treatment 201. The heat-treated ring can then either be machined immediately to produce the desired final shape of the large rolling bearing ring, including the rolling element raceways 1 (machining 202), or the machining 202 of the heat-treated ring can be carried out at a later time, e.g., in a different area of ​​the plant or even in a different plant. Therefore, the devices with which the machining 202 is performed are not necessarily part of the device according to the invention. The same applies to the hardening device with which the rolling element raceways 1 are hardened following the machining 202 (process step 203).

[0058] As already described, the invention aims to perform the first ring rolling step 103 for producing the ring blank with a substantially rectangular cross-section and the second ring rolling step 200 for producing the ring with a cross-section close to the final dimensions by profile rolling in a single heat, i.e., without reheating after the first ring rolling step. However, this will not always be possible. If reheating 110 is necessary after the first 103 and before the second ring rolling step 200, the method according to the invention offers the possibility of effectively preventing undesirable grain growth by controlling the temperature during and between the rolling operations. By linking or connecting at least two rolling mills in series according to the invention, the holding time during reheating 110 can be kept so short that undesirably strong grain growth is avoided.

[0059] The following further advantages are achieved with the method and device according to the invention: - Improvement of the quality of the rings without changing the material or using cheaper material alternatives while maintaining the same quality. - Material savings and thus a switch to smaller pre-block diameters are possible (for rings with an outer diameter >3000 mm, the raw weight is reduced by up to 18%). This, in turn, allows for a higher overall degree of deformation, resulting in greater dynamic and metadynamic recrystallization processes and thus a very small grain size in these workpiece areas. Since this small grain size significantly contributes to increasing bearing life, it can be further extended. - Improved microstructure properties (grain sizes) in the area of ​​interest through near-net-shape heat treatment. - Lower energy consumption for heating, reshaping and heat treatment. - For rings made of heat-treated steels with an outer diameter >3000 mm, machining after profile rolling is reduced by up to 50%. This leads to significant reductions in manufacturing costs and production time per bearing ring.

[0060] The method and device according to the invention can be used particularly advantageously in the applications mentioned below: 1. Near-net-shape rolling of so-called nose rings of moment bearings; 2. Near-net-shape rolling of support and retaining rings of moment bearings; 3. Near-net-shape rolling of outer rings of single-row tapered roller bearings; 4. Near-net-shape rolling of inner rings of single-row tapered roller bearings; 5. Near-net-shape rolling of nose rings for three-row roller slewing rings.

[0061] All of the above-mentioned bearings can be used, for example, in the following technical application areas: - In wind turbines, for example, as blade bearings, rotor bearings or azimuth bearings; - As triple-row roller slewing rings; typical applications include excavators, cranes and open-pit mining, wind turbines and antennas. Other fields of application include, for example, steelworks technology and general mechanical engineering; - As tapered roller bearings, e.g. in the field of wind turbines; - As moment bearings, e.g. as rotor bearings for wind turbines. Reference symbol list 1 career 2 ring blanks 101 preliminary round 102 Warming 103 first ring rolling 104 Heat treatment 105 machining 106 degrees of hardness 200 second ring rolling step 201 Heat treatment 202 machining 203 hardnesses 300 Heating device 301 first ring rolling mill 302 second ring rolling mill 303 profile rollers 400 Reheating device (chamber furnace) 401 Reheating device (continuous furnace) 500 Heat treatment device 600 outer roller 601 profiled inner mandrel 602 Axial roller pair 700 double ring 701 Outer ring T1 forming temperature K contour Surface

Claims

Method for producing a bearing ring for rolling bearings with an outer diameter of more than 500 mm, having at least one raceway (1) for rolling elements, wherein a pre-ring (101) is started, which consists of quenched and tempered steel with a carbon content of ≥ 0.4 wt.% or case-hardening steel, wherein the pre-ring (101) is heated to a first forming temperature (T1) which is between 1100 and 1300 °C, wherein the heated pre-ring (101) is subjected to ring rolling, wherein the rolled ring is subjected to quenching and tempering heat treatment, characterized in that the ring rolling is designed as a multi-stage ring rolling process, wherein the individual stages of the ring rolling process are carried out on ring rolling machines (301, 302) connected in series,that in a first ring rolling step (103) a ring blank with a substantially rectangular cross-sectional area is produced from the pre-ring (101) and in at least a second ring rolling step (200) the ring blank is subjected to profile rolling to produce a ring with a cross-section close to the final dimensions, wherein the heat treatment (201) is carried out on the ring with the cross-section close to the final dimensions, wherein a workpiece area forming the at least one raceway (1) is arranged in a near-surface edge region of the cross-section close to the final dimensions. Method according to claim 1, characterized in that the first ring rolling step (103) and the at least one second ring rolling step (200) are carried out in one heat. Method according to claim 1, characterized in that after the first ring rolling step (103) the ring blank is reheated (104) to a temperature ≥ 1100 °C and ≤ 1300 °C. Method according to claim 3, characterized in that the reheating (104) of the ring blank takes a period of time of ≤ 60 minutes. Method according to one of claims 3 to 4, characterized in that the reheating (104) is carried out in a chamber furnace (400) or in a continuous furnace (401). Method according to one of the preceding claims, characterized in that the profile rolling (200) for producing a ring with a cross-section close to the final dimension is designed as a multi-stage rolling process which includes several contouring steps. Method according to one of the preceding claims, characterized in that the at least one raceway (1) is produced on the ring with the cross-section near the end dimension by machining and is subsequently hardened. Method according to one of the preceding claims, characterized in that the ring blank is subjected to profile rolling in the second ring rolling step (200), in which a multiple ring is produced with the aid of a profiled rolling tool, which has at least one parting plane, wherein the multiple ring is separated in the parting plane into at least two single rings with a cross-section close to the end dimension. Device for carrying out a method according to claims 1 to 8, characterized in that the device has two ring rolling machines (301, 302) connected in series, wherein a first of the two ring rolling machines (301) is set up to produce a ring blank with a substantially rectangular cross-sectional area, wherein a second of the two ring rolling machines (302) has profile rolls (303) for producing a ring with a cross-section close to the final dimension, wherein a device (500) is provided for heat treatment (201) of the ring with the cross-section close to the final dimension. Device according to claim 9, characterized in that a reheating device (400; 401) is provided in which the ring blank can be heated to a temperature of ≥ 1100 °C and ≤ 1300 °C after the first (103) and before the second ring rolling step (200). Device according to claim 10, characterized in that the reheating device (400; 401) is designed as a chamber furnace (400) or as a continuous furnace (401).

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