Polishing equipment

Abstract

A polishing device (1) for polishing a bearing component (2), in particular a bearing ring, is disclosed, the polishing device (1) having a container (6) containing a polishing liquid (8) and a holding device (4), the holding device (4) being designed to hold the bearing component (2) and to move it into and / or out of the container (6) in order to at least partially immerse the bearing component (2) in the polishing liquid (8), the polishing device (1) comprises an induction heating device (10) with at least one inductor (10), wherein the inductor (10) is designed to heat the bearing component (2) by inductive coupling before immersion in the polishing liquid (8) and / or during a polishing operation.

Description

Technical Field

[0001] The invention relates to a polishing device according to the preamble of claim 1. The invention also relates to a method for polishing a bearing component according to the preamble of claim 9. Background Art

[0002] The coating and surface finishing methods of bearing components, especially bearing rings, include polishing, in which a black iron oxide conversion layer is formed on the steel surface of the bearing component. In the case of large bearing rings, a rotational polishing method can be used, in which the large bearing ring is suspended with its horizontal axis above a liquid container, i.e., with its axis of rotation in a horizontal plane. The ring is constantly rotated and partially immersed in the liquid container. A transport system transports the ring between containers until the entire processing operation, which includes about 15 stations, is completed. Since the liquid container is too small to immerse the entire ring, usually only 1 / 3 to 1 / 4 of its diameter is immersed.

[0003] The polishing liquid is present in one to three containers. This polishing liquid can be a water-based salt mixture. The polishing liquid is preferably at a temperature of up to 150° C. At this temperature, a good reaction of the polishing liquid with the ring surface can be achieved.

[0004] When a section of the ring is immersed in the polishing liquid and the ring rotates, the polishing liquid wets its entire surface area. When the surface of the ring wetted by the polishing liquid moves into the air zone, i.e. the area outside the polishing liquid, the hot polishing liquid evaporates some of its water content, thereby increasing its chemical concentration. This effect is undesirable because, in particular with the occurrence of a temperature drop, it increases the aggressiveness of the surface erosion. In the case of smaller rings, i.e. in particular rings with a diameter of less than 2 m, due to the rapid rotation, this effect occurs only to a small extent, since every part of the ring is immersed back into the polishing liquid very quickly. However, in the case of very large rings, the problem is considerable. Furthermore, the polishing liquid film must not be broken, otherwise noticeable irreversible spots will form.

[0005] In order to control these effects, the surface of the bearing ring has hitherto been continuously replenished with water, for example by nozzles, at very high rotation rates. Such a system has been found to be effective up to a diameter of 2.5 m.

[0006] For example, the requirement to polish the main shaft bearings or rotor bearings of wind turbines has led to the need for spin polishing or other partial immersion methods for even larger rings (up to 4.0 m or even higher if possible).

[0007] However, in the case of spin polishing, a heavy steel ring weighing several tons may never reach bath temperature. The ring cannot be preheated above the degreasing temperature (about 70°C minus cooling losses in the air zone). Preheating in hot water would be limited to 100°C and would passivate the surface in a very unfavorable way, leading to spots and a weaker polishing ability, as well as thinner layers. It also carries the risk of corrosion. In the polishing bath itself, the ring cannot be heated to a temperature similar to that of the polishing bath (about 140-150°C), because a polishing time of, for example, 40 minutes / bath (with, for example, 3 / 4 air zone) is not sufficient for this. It should be noted here that in spin polishing, the ring surface of the heavy ring essentially always remains cooler than the polishing liquid, because the core of the steel absorbs thermal energy inwards with considerable intensity.

[0008] In order to achieve a correct polishing reaction without microstructural defects in the substrate (which are potentially harmful to the raceways of the bearing), it is important to accurately control the temperature of the polishing liquid and keep it at or very close to the boiling point. The workpiece temperature will affect the result only if it has the opportunity to significantly affect the liquid and reduce the liquid temperature. On the contrary, if the liquid temperature remains stable, the correct liquid temperature can produce a correct polishing effect even on surfaces that are 20-30°C lower. In the polishing liquid container, assuming a high volume size, strong liquid movement and high performance, a fast-adjusting electric heating element can keep the liquid temperature stable even if a ring with a relatively low temperature is immersed. However, this only applies to a certain workpiece weight. If the size of the ring and therefore the weight of the ring is too high, so that the system becomes overloaded, especially when the permissible power per unit area in the heating element or the ability of the liquid to transfer energy is still reached without sufficient temperature distribution, this may lead to insufficient heating of the bearing ring surface, resulting in insufficient temperature for the liquid to react with the steel at the interface, and even possible damage to the polishing system itself.

[0009] In the case of very large rings, the air zone is still a critical point, as already mentioned above. Even if the rotation speed is set to a maximum value, it must remain below the speed at which the centrifugal forces cause the droplets to be centrifuged off. In the case of large bearing rings, the residence time of the workpiece surface elements in the air zone during rotation is very high, which has two disadvantages. Firstly, an undesirable cooling of the ring instead of heating occurs in the air zone, so that the remaining ring temperature decreases with increasing size of the selected air zone. However, especially in the case of very large and heavy rings, which have widespread and severe heating problems, the size of the air zone is actively increased, not only because of the geometrical limitations of the container, but also in order to avoid thermal instabilities of the liquid in the container, but this further reduces the ring temperature and aggravates the liquid film problem.

[0010] Secondly, the liquid film entrained by the ring cools more significantly in the relatively long air zone, but the liquid continues to react. Significant temperature imbalances and increased polishing liquid concentrations promote microstructural erosion and surface cracks in the steel substrate. Added water spray equipment keeps the surface wet, preventing this excessive concentration, but further helps to reduce the temperature. At a certain temperature level below the ring surface, it can no longer be assumed that the liquid in the immersed zone will have a constant temperature; instead, the near-surface liquid that reacts with the surface is cooled by the ring and reacts at well below its boiling point, which jeopardizes the correct results. The larger and heavier the rings become, the more severe this imbalance becomes.

[0011] It is therefore an object of the present invention to provide an improved method of polishing large bearing components. Summary of the invention

[0012] This object is achieved by a polishing device according to claim 1 and a polishing method according to claim 9 .

[0013] A polishing device for polishing a bearing component, in particular a bearing ring, or any other component of a roller bearing or a sliding bearing, comprises at least one container for containing a polishing liquid. In addition, the polishing device comprises a holding device designed to hold the bearing component. The holding device may comprise, for example, a plurality of holding elements, such as rollers, clamps, ports, etc., which are capable of holding the bearing component. In addition, the holding device is designed to move the bearing component it holds into and / or out of the container so as to at least partially immerse the bearing component in the polishing liquid. This movement can be achieved as a vertical movement of the bearing component, or in the case of rotary polishing, as a rotary movement of the bearing component, which will be described in detail below.

[0014] The holding device can be, for example, part of a supporting frame or a rotating supporting frame, depending on the size of the polishing device and the bearing component. Such a frame or rotating frame can be suspended in a corresponding receptacle on the edge of the polishing container by a trolley, which is part of the device. The trolley can then alternately serve a plurality of supporting frames (article carriers) present in the device simultaneously and in a cycle. In the case of particularly large rings compared to the device, the holding device can be part of the trolley itself, so that the trolley remains in uninterrupted contact with the bearing component during the entire treatment. This reduces the possible device throughput, but increases the upper size limit.

[0015] In order to avoid the above-mentioned problems which occur when the bearing component is too cold, the polishing apparatus comprises an induction heating device having at least one inductor, wherein the inductor is designed to heat the bearing component, in particular the surface of the bearing component, by inductive coupling before immersion in the polishing liquid and / or during the polishing operation. "Before immersion in the polishing liquid" and "during the polishing operation" in this context may be taken to mean that at least a part of the surface of the bearing component which is immersed in the polishing liquid subsequently or at least in the near future is heated by the inductor.

[0016] In particular, it may be sufficient to heat only the outer surface area of ​​the bearing component and not the core. Heating the core would be an unnecessary waste of energy and would lead to higher costs and longer cooling times. Inductors are generally particularly suitable for focusing the energy input onto a near-surface area.

[0017] In one embodiment, a temperature sensor can be used. This can measure the surface temperature of the bearing component, in particular contactlessly. Based on this measurement, the induction heating device or the inductor can be controlled in order to obtain and maintain a target temperature. The temperature sensor can be, for example, an infrared temperature sensor.

[0018] Advantageously, the induction heating device heats the bearing component so that a substantially very constant surface temperature is obtained. Advantageously, the selected surface temperature is high enough so that the surface can react effectively and appropriately with the polishing liquid. At the same time, the surface temperature should not be too high, because otherwise the applied polishing liquid evaporates in the air region of the spin polishing and the surface dries out. As already mentioned above, this can lead to irreversible spots in the polishing layer.

[0019] The surface temperature may preferably be between 98° C. and 150° C. and should be below 200° C. The bearing steels from which bearing components can be produced are usually already hardened and annealed, but their microstructure remains unchanged and stable in any case up to at least 150° C. and in the case of many bearing types even up to 200° C.

[0020] In one embodiment, a spraying device can be provided, which is designed to spray water or other aqueous liquid onto the surface of the bearing component in the air zone above the polishing liquid container. In this way, water evaporating from the polishing liquid film can be compensated. This can avoid the above-mentioned disadvantages of increased polishing liquid concentration. The spraying device can be combined with the induction heating device, or can be arranged close to the induction heating device.

[0021] This has the advantage that the surface of the bearing component always remains wet. The boiling temperature of the undiluted polishing liquid is preferably in the range of 140°C-150°C, since it contains a high content of salt. The added water jet dilutes this solution to a lower boiling point, but in the case of a reasonably adjusted amount, does not produce a pure water film that already boils at 100°C. The heating temperature of the induction heating device can therefore be adjusted to a liquid film between 98°C and 150°C, which is established together with the water jet onto the non-drying surface. The exact temperature can be adjusted individually depending on the type of bearing component, for example depending on the shape and / or material. In addition, the water or aqueous medium used for the jet can also be preheated.

[0022] In another embodiment, the induction heating device is arranged outside the polishing liquid, in particular in the region of the holding device. In the case of rotary polishing on a trolley, the trolley can have rollers for holding and rotating the ring and corresponding drives, optional water jets and at least one inductor. All components are preferably in the air zone and are not immersed. In the case of rotary polishing on a rotating support frame, the rotating frame can have rollers for holding and rotating the ring and corresponding drives and at least one inductor.

[0023] The induction heating device or the inductor is preferably arranged spatially close to the re-immersion area in the direction of rotation. The advantage of this arrangement is that the bearing component can be heated to the required temperature immediately before being immersed in the polishing liquid. It can thus be ensured that the surface of the bearing component has the correct temperature to react with the polishing liquid. In addition, arranging the inductor in the immediate vicinity of the re-immersion area prevents heating from causing unwanted evaporation of the liquid film. Likewise in the air region, the surface of the bearing component should be prevented from cooling too significantly, so that a correct reaction between the bearing component and the polishing liquid can be ensured. Therefore, if necessary, an additional further inductor can be arranged closer to the immersion area. Its power setting can be different, for example lower than that of the already existing inductor. The further inductor can also be coupled to another temperature sensor.

[0024] In terms of its size, the inductor is usually small compared to the bearing component (e.g. a bearing ring), so that it only covers a small subsection of the bearing component. In order to heat the surface of the entire bearing component, rotation can therefore be added, either rotation of the bearing component or movement of the inductor around the circumference of the bearing component.

[0025] With proper pretreatment and consideration of drying issues, induction preheating can be used to preheat the entire ring before full immersion via a horizontal or vertical axis. For reasons of economic feasibility, where such preheating of large rings is required, preference is usually given to spin polishing rather than full immersion into an oversized vessel.

[0026] In a preferred embodiment, for this reason, the holding device is designed to rotate the bearing part so that the bearing part can be moved along the at least one inductor or through the inductor and through the container segment. In order to rotate the bearing part, the holding device can have a motor drive, for example.

[0027] As already explained, the inductor can be arranged above the container. The inductor can consist of two foldable halves, which in the closed state surround the cross section of the bearing ring on all sides. Due to the movement along or through the inductor, the bearing component or its surface is heated and then directly immersed in the polishing liquid. The holding device is preferably designed to continuously rotate the bearing component. In this case, the holding device can preferably rotate the bearing component quickly enough so that the polishing liquid remains on the bearing component even in the air zone and does not dry out. This has the effect that even if the surface elements of the bearing component are moved into and back out of the polishing liquid again, the bearing component behaves roughly as if it is always immersed in the polishing liquid. As already mentioned above, wetting with water is also possible. Additional wetting with heated polishing liquid, in particular also with a lower concentration of polishing liquid, can also be carried out through a tube without fine spraying.

[0028] The rotation speed is preferably determined by the ring diameter, immersion depth and centrifugal force, and can be selected to be at a maximum value just below the speed at which droplets would be thrown off the surface. For example, the bearing component or a specific portion of the bearing component can be immersed in the polishing liquid at 3x to 15x / minute.

[0029] Rotating the bearing component by means of a single inductor may be sufficient. However, a plurality of inductors may also be used, which are preferably arranged evenly around the bearing component, preferably outside the container, and preferably not immersed. This ensures uniform heating of the bearing component. Furthermore, this prevents excessive cooling in the air zone and excessive surface cooling due to the migration of heat energy to the core of the bearing component.

[0030] In particular, the holding device is designed to rotate the bearing component in a vertical plane, i.e. about a horizontal axis of rotation. The holding device can have a plurality of supporting rotating rollers, which are designed to support and rotate the bearing component. For example, a trolley or a supporting frame or a rotating supporting frame used hitherto can be used as a holding device and can be supplemented by an induction heating device. The induction heating device can be installed in the trolley housing or in the rotating supporting frame. The inductor is preferably arranged close to the load-bearing rotating rollers of the holding device, for example beyond these load-bearing rotating rollers in the direction of rotation. The induction heating device can be integrated in the holding device.

[0031] In another embodiment, the inductor is matched to the shape of the bearing component. This can ensure uniform heating of the bearing component, because by adjusting the shape of the bearing component, the inductors can have equal spacing at all heating points of the bearing component. In this way, the surface of the bearing component is heated uniformly. The inductor can be designed, for example, similar to the inductor in an induction hardening device. For example, it can be made of two halves, which can be opened and closed, for example by a pneumatic cylinder or an electric cylinder. The inductor can be moved away from the bearing component, for example pivoted, so as not to interfere with smaller rings with a diameter of less than 2.5m, which do not require additional heating by the inductor. In this way, the device can be used for large rings with induction heating as well as for small rings without induction heating. The induction heating device can therefore be activated / switched on or off in a flexible and variable manner.

[0032] In another embodiment, the inductor is matched to the shape of the bearing component. This has the advantage that the inductor can optimally heat the bearing component or the surface of the bearing component.

[0033] On the other hand, a method for polishing a bearing component, in particular a bearing ring, is proposed, wherein the method comprises: holding the bearing component and moving the bearing component into and / or out of a container containing a polishing liquid so as to at least partially immerse the bearing component in the polishing liquid, and heating the bearing component by inductive coupling with the aid of an induction heating device having at least one inductor before immersion in the polishing liquid or during the polishing operation.

[0034] In a further embodiment, the heating of the bearing component comprises preheating the bearing component to a pretreatment temperature and / or reheating to a posttreatment temperature. In particular, the pretreatment temperature and / or the posttreatment temperature may be lower than the annealing temperature. This may provide the advantage that the same apparatus and the same method used for polishing the bearing component may also be used for thermal pretreatment and / or posttreatment of the bearing component. In this case, for example, the bearing component is not immersed again in the polishing liquid after being heated, but the bearing component may only be heated to the posttreatment temperature, for example, to anneal the near-surface microstructure or to achieve the desired hydrogen de-embrittlement.

[0035] For certain steel types, such as some case-hardening steels, or after heat treatments such as carbonitriding, an additional heat treatment before polishing is recommended to reduce the risk of microstructural damage and cracks during the polishing operation. If the machine has an inductor, for example when a rotating support frame is used, this heat pretreatment can be performed in a special insulated container within the machine.

[0036] Further advantages and advantageous embodiments are detailed in the description, the drawings and the claims.In particular, the combinations of features specified in the description and the drawings are merely illustrative, so these features may also exist alone or in different combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be described in detail below by means of the working examples shown in the accompanying drawings. The working examples and the combinations shown in the working examples are purely illustrative and are not intended to limit the scope of protection of the present invention. This is limited only by the attached claims.

[0038] The accompanying drawings show:

[0039] Figure 1 is a schematic diagram of a polishing device for polishing a bearing component. DETAILED DESCRIPTION

[0040] Identical or functionally equivalent elements are denoted below by the same reference numerals.

[0041] Figure 1 A polishing device 1 is shown for polishing a bearing component 2. The bearing component 2 may be a bearing ring, such as Figure 1 shown, but could also be any other type of bearing component, such as a sleeve to be polished.

[0042] The bearing component 2 is held by a holding device 4. For this purpose, the holding device 4 can have holding elements, preferably driven supporting rotating rollers. Figure 1 In the embodiment, two holding elements are provided, which are designated as holding devices 4. The holding devices 4 serve to partially immerse the bearing component 2 into a container 6 containing a polishing liquid 8 and to move it back out of the container 6. Advantageously, this partial immersion is supplemented by a rotational movement of the bearing component 2. Here, the holding elements serve not only to hold the bearing component 2, but also to rotate the bearing component 2. In Figure 1 In , this rotation is indicated by the arrow.

[0043] By rotating the bearing component 2, its surface is continuously immersed in the polishing liquid 8 and moved back out of it again. However, due to the short residence time of the bearing component 2 in the polishing liquid 8, the bearing component 2 cannot be heated sufficiently by the temperature of the polishing liquid 8 alone to ensure the correct reaction of the surface of the bearing component 2 with the polishing liquid 8.

[0044] For this purpose, an induction heating device 10 having at least one inductor is provided. Figure 1 An induction heating device with an inductor is shown, which for simplicity is in schematic form as a single element with reference numeral 10. The inductor is implemented by a coil, which is inductively coupled to the bearing component 2 and thus heats the bearing component 2. Although only a single inductor 10 is shown, two or more inductors 10 may also be provided, which may be arranged around the circumference of the bearing component 2 outside the container 6 in order to heat the bearing component 2 uniformly.

[0045] Since the inductor 10 heats the bearing component 2 or its surface, the part of the bearing component 2 that is then moved into the container 6 and thus into the polishing liquid 8 can have a temperature that is only slightly different from the temperature of the polishing liquid 8. This firstly allows a correct reaction of the polishing liquid with the surface of the bearing component 2 and thus the formation of a correctly formed conversion layer, i.e. the polishing layer. Secondly, the heated surface of the bearing component 2 prevents the polishing liquid 8 from cooling down due to the immersion of the cold bearing component 2.

[0046] In order to heat the bearing component 2 to the correct temperature, i.e. not too hot and not too cold, a temperature sensor 12 can be provided. The temperature sensor 12 can in particular be a contactless temperature sensor, such as an infrared sensor. The temperature sensor 12 determines the temperature of the bearing component 12 or its surface, preferably just upstream of the inductor 10. The inductor 10 can then be set based on the measured temperature and readjusted in continuous operation so that it heats the surface of the bearing component 2 to a predetermined temperature and keeps it constant within the measuring range. In this way, for example, the ambient temperature, the spray water temperature, the spray water amount, the drift of the polishing bath temperature and the previous heating of the bearing component 2 can be taken into account, which can influence the current temperature of the bearing component 2 and thus require a higher or lower inductive reheating of the bearing component 2.

[0047] In summary, the polishing apparatus described herein provides a simple method for performing spin polishing, in particular for very heavy bearing components, wherein a suitable surface temperature of the bearing component can be ensured to obtain the correct temperature of the reactive polishing liquid interface layer and thus obtain the desired reaction with the polishing liquid.

[0048] Polishing liquids can also react with surfaces outside the desired reaction range of roller bearings and form the same black iron oxide layer, but the associated microstructural damage, such as grain boundary cracks in steel, is unacceptable on roller bearing raceways. Therefore, maintaining the temperature of the polishing liquid interface layer at the reactive workpiece surface by means of an inductor within the target range is particularly important for large roller bearing rings.

[0049] Reference numerals list

[0050] 1 Polishing equipment

[0051] 2 Bearing components

[0052] 4 Holding device / holding element

[0053] 6 Polishing liquid container

[0054] 8 Polishing liquid

[0055] 10 Induction heating device / inductor

[0056] 12 Temperature Sensor

Claims

1. A polishing device (1) for polishing a bearing component (2), in particular a bearing ring, wherein the polishing device (1) comprises a container (6) for containing a polishing liquid (8) and a holding device (4), wherein the holding device (4) is designed to hold the bearing component (2) and to move it into and / or out of the container (6) so that the bearing component (2) is at least partially immersed in the polishing liquid (8), It is characterized in that The polishing apparatus (1) comprises an induction heating device (10) having at least one inductor (10), wherein the inductor (10) is designed to heat the bearing component (2) by inductive coupling before immersion in a polishing liquid (8) and / or during the polishing operation.

2. The polishing device according to claim 1, wherein: The induction heating device (10) is arranged outside the polishing liquid (8).

3. The polishing device according to claim 1 or 2, wherein: The holding device (4) is designed to rotate the bearing component (2) so that the bearing component (2) can be moved sectionally along the at least one inductor (10) or through the inductor and through the container (6).

4. The polishing device according to claim 3, wherein: The holding device (4) is designed to rotate the bearing component (2) in a vertical plane about a horizontal axis.

5. The polishing device according to claim 3, wherein: The holding device (4) has a plurality of supporting rotating rollers which can be arranged around the circumference of the bearing component (2) and are designed to support and rotate the bearing component (2).

6. Polishing apparatus according to any one of the preceding claims, wherein: The polishing device (1) comprises a temperature sensor, in particular a contactless temperature sensor, which is designed to measure the surface temperature of the bearing component (2) outside the container (6), and wherein the induction heating device (10) is designed to heat the bearing component (2) based on the measured temperature.

7. Polishing apparatus according to any one of the preceding claims, wherein: The at least one inductor (10) matches the shape of the bearing component (2).

8. Polishing apparatus according to any one of the preceding claims, wherein: The inductor (10) is designed to heat the surface of the bearing component (2) to be polished and is matched to the shape of the surface of the bearing component (2) to be polished.

9. A method for polishing a bearing component (2), in particular a bearing ring, wherein: The method comprises: holding a bearing component (2) and moving the bearing component (2) into and / or out of a container (6) containing a polishing liquid (8) so as to at least partially immerse the bearing component (2) in the polishing liquid (8), The method further comprises heating the bearing component (2) by inductive coupling by means of an induction heating device (10) having at least one inductor (10) before immersion in the polishing liquid (8) and / or during the polishing operation.

10. The method according to claim 9, wherein: The heating of the bearing component (2) comprises preheating the bearing component (2) to a pretreatment temperature and / or reheating the bearing component (2) to a posttreatment temperature.

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