Bluing device

Abstract

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

Description

Technical area

[0001] The present invention relates to a bluing device according to the preamble of patent claim 1. Furthermore, the present invention relates to a method for bluing a bearing component according to the preamble of patent claim 9. Technical background

[0002] Coating and surface finishing processes for bearing components, particularly bearing rings, include black oxide coating, in which a black iron oxide conversion layer is formed on the steel surface of the bearing component. For large bearing rings, a rotational black oxide coating process can be used. This process involves suspending a large bearing ring with its axis horizontal above the fluid containers, i.e., with its axis of rotation in the horizontal plane. The ring is in constant rotation and is partially immersed in the fluid containers. A conveyor system moves the ring from container to container until the entire processing process, which comprises approximately 15 stations, is completed. Since the fluid containers are too small to immerse the entire ring, it is usually only immersed to a depth of 1 / 3 to 1 / 4 of its diameter.

[0003] One to three of the containers contain a bluing fluid. This fluid can be a water-based salt mixture. The bluing fluid preferably has a temperature of up to 150 °C. At this temperature, a good reaction between the bluing fluid and the ring surface can be achieved.

[0004] When a segment of the ring is immersed in the bluing liquid and the ring is rotated, the bluing liquid wets its entire surface. When the ring surface wetted with bluing liquid moves into the air zone, i.e. the area outside the bluing liquid, the hot bluing liquid evaporates some of its water content and thereby increases its chemical concentration. This effect is undesirable because, particularly when combined with an occurring drop in temperature, it increases the aggressiveness of the surface attack. For smaller rings, i.e. in particular rings less than 2 m in diameter, this effect is only minimal due to the rapid rotation because each section of the ring is very quickly re-immersed in the bluing liquid. For very large rings, however, the problem is significant. Furthermore, the bluing liquid film must never break up because otherwise it will form strong, irreversible stains.

[0005] To control these effects, water has been continuously added to the surface of the bearing ring via spray nozzles, for example, at very high rotation speeds. This system has proven effective for diameters up to 2.5 m.

[0006] The requirement for black oxide coating of, for example, main shaft bearings or rotor bearings of wind turbines leads to the need to carry out rotational black oxide coating or other partial immersion processes on even larger rings, if possible up to 4.0 m or even beyond.

[0007] During rotational bluing, however, the massive and heavy steel ring, which can weigh several tons, never reaches bath temperature. The ring cannot be preheated above the degreasing temperature (approx. 70 °C minus the cooling losses in the air zone). Preheating in hot water would be limited to 100 °C and would have a very negative passivating effect on the surface, leading to stains and reduced bluing ability as well as a thinner layer. It would also carry the risk of corrosion. In the bluing bath itself, the ring cannot heat up to a temperature similar to the bluing bath (approx. 140-150 °C) because the bluing time of, for example, 40 minutes per bath with, for example, a 3 / 4 air zone is not sufficient for this. It should be noted that the surface of heavy rings during rotational bluing always remains cooler than the bluing liquid, as the steel core draws heat energy inwards at a considerable rate.

[0008] To ensure a correct bluing reaction without microstructural defects in the substrate (which are potentially damaging to a bearing's raceway), it is critical that the temperature of the bluing fluid is precisely controlled and maintained at or very close to its boiling point. The workpiece temperature only influences the result if it has the potential to significantly influence the fluid and lower the fluid temperature. However, a correct fluid temperature will produce a correct bluing result even on a surface 20-30°C colder if the fluid temperature is kept stable. In the bluing fluid tank, provided large volumes are used, intensive fluid movement and powerful, rapidly regulating electric heating elements can keep the fluid temperature stable, even when a ring with a lower temperature is immersed.However, this only applies up to a certain workpiece weight. If the ring size and thus the ring weight are so high that the system is overloaded, especially if the permissible area-related power at the heating elements or the energy conductivity of the fluid is not yet reached without a sufficient temperature profile, this can lead to insufficient heating of the bearing ring surface and thus to an insufficient temperature of the fluid reacting with the steel at the interface, and possibly even damage to the blacking system itself.

[0009] For very large rings, the air zone remains a critical point, as already described above. Even if the rotation speed is set to maximum, it must still remain below the speed at which centrifugal forces would cause droplets to spin off. The residence time of a workpiece surface element in the air zone during rotation is very high for large bearing rings, which has two disadvantages. First, undesirable ring cooling instead of heating occurs in the air zone, so the larger the air zone, the lower the remaining ring temperature.However, especially for extremely large and heavy rings, which have a general and serious heating problem, the air zone is actively enlarged, not only because of the geometric limitations of the container, but also to avoid thermal instability of the liquid in the container, which further lowers the ring temperature and exacerbates the liquid film problem.

[0010] Second, the liquid film entrained by the ring cools more rapidly in the comparatively longer air zone, but the liquid continues to react. A significant temperature imbalance and an increase in the concentration of the blackening liquid can promote microstructural attack and surface cracking in the steel substrate. While an added water spray device can keep the surface moist and prevent this overconcentration, it further contributes to the temperature drop. Below a certain temperature level of the ring surface, it can no longer be assumed that the liquid in the immersion zone has a constant temperature. Instead, the liquid near the surface and reacting with the surface is cooled by the ring and reacts well below its boiling point, jeopardizing the correct result. The larger and heavier the ring becomes, the more serious this imbalance becomes.

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

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

[0013] The bluing device for bluing a bearing component, in particular a bearing ring, or any other component of a rolling or plain bearing, comprises at least one container with a bluing fluid. Furthermore, the bluing device comprises a holding device designed to hold the bearing component. The holding device can, for example, comprise a plurality of holding elements, e.g., rollers, clamps, supports, or the like, capable of holding the bearing component. Furthermore, the holding device is designed to move the bearing component held by it into and / or out of the container in order to at least partially immerse the bearing component in the bluing fluid. This movement can occur either as a vertical movement of the bearing component or, in the case of rotational bluing, as a rotational movement of the bearing component, as explained in more detail below.

[0014] This holding device can, for example, depending on the size of the burnishing device and the bearing component, be part of a settling rack or settling bogie. Such a rack or bogie can be suspended from a system's transport carriage into corresponding receptacles in the edge of the burnishing tank. The transport carriage can then alternately serve several settling racks (product carriers) located in the system simultaneously and in cycles. For rings that are particularly large in relation to the system, the holding device can be part of the transport carriage itself, so that the transport carriage is in continuous contact with the bearing components throughout the entire processing. This reduces the possible system throughput but increases the upper size limit.

[0015] To avoid the aforementioned problems that occur when the bearing component is too cold, the bluing device comprises an induction heating device with at least one inductor, wherein the inductor is designed to heat the bearing component, in particular a surface of the bearing component, by means of an inductive coupling before immersion in the bluing liquid and / or during the bluing process. In this context, "before immersion in the bluing liquid" or "during the bluing process" can be understood to mean that at least that part of the surface of the bearing component that is to be immersed in the bluing liquid subsequently, or at least shortly thereafter, is heated by the inductor.

[0016] In particular, it is sufficient to heat only the outer surface areas of the bearing component and not the core. Heating the core would only be an unnecessary waste of energy and would lead to higher costs and longer cooling times. An inductor is generally particularly well suited to focusing the energy input on areas close to the surface.

[0017] In one embodiment, a temperature sensor can be used. This can measure the surface temperature of the bearing component, particularly in a non-contact manner. Based on this measurement, the induction heater or inductor can be controlled to reach and maintain a target temperature. The temperature sensor can be an infrared temperature sensor, for example.

[0018] The induction heater advantageously heats the bearing component to achieve the most constant surface temperature possible. The surface temperature is advantageously selected to be sufficiently high so that the surface can react well and properly with the bluing fluid. At the same time, the surface temperature should not be too high, as otherwise the applied bluing fluid will evaporate in the air zone of the rotational bluing process, causing the surface to dry out. This can, as already described above, lead to irreversible staining within the bluing layer.

[0019] The surface temperature can preferably be between 98 °C and 150 °C, and should be below 200 °C. The bearing steel from which the bearing component can be made is usually hardened and tempered, but its structure remains unchanged and stable in any case up to at least 150 °C, and for many bearing types even up to 200 °C.

[0020] According to one embodiment, a spray device can be provided, which is designed to spray water or another water-containing liquid onto the surface of the bearing component in the air zone above the bluing liquid container. In this way, the water evaporating from the bluing liquid film can be compensated. This avoids the above-described disadvantages of an increase in the concentration of the bluing liquid. The spray device can be combined with the induction heating device or can be arranged near the induction heating device.

[0021] This has the advantage of keeping the surface of the bearing component moist at all times. The boiling point of the undiluted blackening fluid is preferably in the range of 140°C–150°C, as it contains a high salt load. The added water spray dilutes this solution to a lower boiling point, but with a sensible dosage, does not result in a pure water film, which would already boil at 100°C. Thus, the heating temperature of the induction heater can be set to a liquid film between 98°C and 150°C, which, together with the water spray, is adjusted to a surface that does not dry out. The exact temperature can be set individually depending on the type of bearing component, e.g., depending on the shape and / or material. It is also possible to preheat the water or aqueous medium used for spraying.

[0022] According to a further embodiment, the induction heating device is arranged outside the burnishing fluid, in particular in the area of ​​the described holding device. In the case of rotation burnishing on a transport carriage, the transport carriage can have rollers for holding and rotating the ring, including a corresponding drive, optionally a water spray device, and at least one inductor. All components are preferably installed in the air and are not submerged. In the case of rotation burnishing on a set-down bogie, the bogie can have rollers for holding and rotating the ring, including a corresponding drive, and at least one inductor.

[0023] The induction heater or inductor is preferably arranged spatially in the direction of rotation close to the re-immersion area. This arrangement has the advantage that the bearing component can be heated to the required temperature immediately before immersion in the blackening liquid. This ensures that the surface of the bearing component is at the correct temperature to react with the blackening liquid. Furthermore, the arrangement of the inductor in the immediate vicinity of the re-immersion area prevents the heating from resulting in unwanted evaporation of the liquid film. In the air area, too, the surface of the bearing component should be prevented from cooling down too much to ensure a proper reaction between the bearing component and the blackening liquid. Therefore, if necessary, an additional inductor can be provided closer to the immersion area.Its power setting can be different, for example, lower, than the existing inductor. The additional inductor can also be coupled to another temperature sensor.

[0024] The inductor is typically small compared to the bearing component, e.g., the bearing ring, so it only covers a small segment of the bearing component. To heat the surface of the entire bearing component, rotation can be added, either by rotating the bearing component or by rotating the inductor around the bearing component.

[0025] With appropriate pretreatment and consideration of the drying issue, it would be possible to preheat an entire ring using induction preheating and then completely immerse it in the process with a horizontal or vertical axis. For reasons of cost-effectiveness, rotational burnishing is usually preferred over full immersion in oversized containers for large rings requiring this type of preheating.

[0026] According to a preferred embodiment, the holding device is therefore designed to rotate the bearing component such that the bearing component can be moved in sections along the at least one inductor or through the inductor and through the container. To rotate the bearing component, the holding device can, for example, have a motor drive.

[0027] As already explained, the inductor can be arranged above the container. The inductor can consist of two hinged halves which, when closed, enclose the bearing ring cross-section on all sides. By moving along the inductor or through the inductor, the bearing component or its surface is heated and then directly immersed in the bluing liquid. Preferably, the holding device is designed to continuously rotate the bearing component. In this case, the holding device can preferably rotate the bearing component so quickly that bluing liquid remains on the bearing component even in the air zone and does not dry out. This has the effect that the bearing component behaves almost as if it were always immersed in the bluing liquid, although its surface elements move out of the bluing liquid and back in again.As already described above, additional wetting with water may be possible. Additional wetting with heated bluing fluid, especially with lower concentrations, via tubes without fine atomization is also possible.

[0028] The rotation speed is preferably determined by the ring diameter, the immersion depth, and the centrifugal forces. It can be selected at a maximum speed, i.e., just below the speed at which liquid droplets would be thrown off the surface. For example, the bearing component, or a specific section of the bearing component, can be immersed in the blackening fluid between 3 and 15 times per minute.

[0029] It may be sufficient to rotate the bearing component using a single inductor. However, multiple inductors can also be used, preferably arranged evenly around the bearing component, preferably outside the container and preferably not submerged. This can ensure uniform heating of the bearing component. Furthermore, it can prevent excessive cooling in the air zone and excessive surface cooling due to thermal energy migrating into the bearing component core.

[0030] In particular, the holding device is designed to rotate the bearing component in a vertical plane, i.e. with a horizontal axis of rotation. The holding device can have a plurality of support rotary rollers which are designed to support and rotate the bearing component. For example, a transport carriage or a set-down frame or set-down bogie, as used to date, can be used as the holding device and supplemented with the induction heating device. The induction heating device can be installed within the transport carriage housing or within the set-down bogie. Preferably, the inductor is arranged close to the supporting rotary rollers of the holding device, e.g. behind them as seen in the direction of rotation. The induction heating device can be integrated into the holding device.

[0031] According to a further embodiment, the inductor is adapted to the shape of the bearing component. This can ensure uniform heating of the bearing component, since the inductor can have the same distance at all heating points on the bearing component due to the adaptation to the shape of the bearing component. In this way, the surface of the bearing component is heated evenly. The inductor can, for example, be designed similarly to an inductor in induction hardening systems. It can, for example, be made of two halves that can be opened and closed, for example, using a pneumatic or electric cylinder. The inductor can be moved away from the bearing component, e.g. pivoted, in order not to hinder smaller rings with a diameter of less than 2.5 m, which do not require the additional heating by the inductor.This allows the device to be used for both large rings with induction heating and smaller rings without induction heating. The induction heating device can thus be flexibly and variably activated, switched on, or deactivated.

[0032] According to a further embodiment, the inductor is adapted 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] According to a further aspect, a method for browning a bearing component, in particular a bearing ring, is proposed, the method comprising: holding the bearing component and moving the bearing component into a container with browning liquid and / or out of the container in order to at least partially immerse the bearing component in the browning liquid, heating the bearing component by means of an inductive coupling before immersion in the browning liquid or during the browning process by means of an induction heating device with at least one inductor.

[0034] According to a further embodiment, heating the bearing component comprises preheating the bearing component to a pretreatment temperature and / or postheating it to a posttreatment temperature. In particular, the pretreatment temperature and / or the posttreatment temperature can be below the tempering temperature. This can provide the advantage that the same device and the same method used for blackening the bearing component can also be used for thermal pretreatment and / or posttreatment of the bearing component. In this case, for example, the bearing component is no longer immersed in a blackening liquid after heating, but instead the bearing component can only be heated to the posttreatment temperature, for example to relax the near-surface microstructure or to implement a required hydrogen deembrittlement.

[0035] For certain steel grades, such as some case-hardening steels, or after heat treatments such as carbonitriding, it may be advisable to perform an additional thermal treatment prior to blackening to reduce the risk of microstructural damage and cracking during blackening. If the plant is equipped with inductors, such thermal pretreatment can be carried out in special insulated containers within the plant, for example, when using offset bogies.

[0036] Further advantages and advantageous embodiments are set forth in the description, the drawings, and the claims. In particular, the combinations of features set forth in the description and the drawings are purely exemplary, so the features may also be present individually or in other combinations. Short character description

[0037] The invention will be described in more detail below with reference to exemplary embodiments illustrated in the drawings. The exemplary embodiments and the combinations shown in the exemplary embodiments are purely exemplary and are not intended to define the scope of the invention. This scope is defined solely by the appended claims.

[0038] It shows: Fig. 1: a schematic view of a bluing device for bluing a bearing component. Detailed description of the invention

[0039] In the following, identical or functionally equivalent elements are identified by the same reference symbols.

[0040] Fig. 1 shows a burnishing device 1 for burnishing a bearing component 2. The bearing component 2 can be a bearing ring as shown in Fig. 1, but can also be any other type of bearing component, e.g. a sleeve, that is to be burnished.

[0041] The bearing component 2 is held by a holding device 4. For this purpose, the holding device 4 can have holding elements, preferably driven support rotation rollers. Fig. 1, two holding elements are provided, which are designated as a holding device 4. The holding device 4 serves to partially immerse the bearing component 2 into a container 6 containing browning fluid 8 and to move it out of this container 6. This partial immersion is advantageously supplemented by a rotational movement of the bearing component 2. The holding elements serve not only to hold the bearing component 2, but also to rotate the bearing component 2. In Fig. 1 this rotation is indicated by the arrow.

[0042] By rotating the bearing component 2, its surface is continuously immersed in the bluing liquid 8 and then moved out of it again. However, due to the short residence time of the bearing component 2 in the bluing liquid 8, the bearing component 2 cannot be sufficiently heated by the temperature of the bluing liquid 8 alone to ensure a proper reaction of the surface of the bearing component 2 with the bluing liquid 8.

[0043] For this reason, an induction heating device 10 is provided, which has at least one inductor. Fig.In Figure 1, the induction heating device with the inductor is schematically illustrated as a single element with the reference numeral 10 for the sake of simplicity. The inductor is implemented as a coil that forms an inductive coupling with the bearing component 2, thereby heating it. Although only a single inductor 10 is shown, multiple inductors 10 may also be provided, which may be arranged circumferentially around the bearing component 2, outside the container 6, in order to heat the bearing component 2 evenly.

[0044] Because the inductor 10 heats the bearing component 2, or rather its surface, the section of the bearing component 2 that is subsequently moved into the container 6 and thus into the bluing fluid 8 can have a temperature that differs only slightly from the temperature of the bluing fluid 8. This allows, on the one hand, a proper reaction of the bluing fluid with the surface of the bearing component 2 and thus the formation of a correctly formed conversion layer, the bluing layer. On the other hand, the heated surface of the bearing component 2 prevents the bluing fluid 8 from cooling down due to immersion of a cold bearing component 2.

[0045] 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. This temperature sensor 12 can, in particular, be a non-contact temperature sensor, such as an infrared sensor. The temperature sensor 12 determines the temperature of the bearing component 12 or its surface, preferably shortly before the inductor 10. The inductor 10 can then be set based on the measured temperature and readjusted during operation so that it heats the surface of the bearing component 2 to a predefined temperature and keeps this temperature constant in the measurement range. In this way, for example, ambient temperature, spray water temperature,Spray water quantity, blackening bath temperature drift, and previous heating of the bearing component 2 must be taken into account, which can influence the current temperature of the bearing component 2 and therefore may require higher or lower inductive reheating of the bearing component 2.

[0046] In summary, the bluing device described here provides a simple way to perform rotational bluing, particularly for very heavy bearing components, in which a suitable surface temperature of the bearing component can be ensured for a proper temperature of the reacting bluing liquid boundary layer and thus for a desired reaction with the bluing liquid.

[0047] The blackening fluid could also react with the surface outside the desired reaction range for rolling bearings, forming a similarly black iron oxide layer. However, the associated microstructural damage, such as grain boundary cracks in the steel, would be unacceptable on rolling bearing raceways. Therefore, especially for large rolling bearing rings, it is crucial to maintain the temperature of the blackening fluid boundary layer on the reacting workpiece surface within the desired range using inductors. List of reference symbols 1 burnishing device 2 bearing component 4 Holding device / holding elements 6 browning fluid containers 8 Browning fluid 10 Induction heater / inductor 12 Temperature sensor

Claims

[1] Burnishing device (1) for burnishing a bearing component (2), in particular a bearing ring, wherein the burnishing device (1) has a container (6) with a burnishing 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 the container (6) and / or out of the container (6) in order to immerse the bearing component (2) at least partially in the burnishing liquid (8), characterized by that the bluing 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 means of an inductive coupling before immersion in the bluing liquid (8) and / or during the bluing process. [2] Burnishing device according to claim 1, wherein the induction heating device (10) is arranged outside the burnishing liquid (8). [3] Burnishing device according to claim 1 or 2, wherein the holding device (4) is designed to rotate the bearing component (2) such that the bearing component (2) can be moved in sections along or through the at least one inductor (10) and through the container (6). [4] Burnishing device according to claim 3, wherein the holding device (4) is designed to rotate the bearing component (2) in a vertical plane with a horizontal axis. [5] Burnishing device according to claim 3, wherein the holding device (4) has a plurality of support rotation rollers which can be arranged circumferentially around the bearing component (2) and are designed to support and rotate the bearing component (2). [6] Burnishing device according to one of the preceding claims, wherein the burnishing device (1) comprises a temperature sensor, in particular a contactless temperature sensor, which is designed to measure a 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] Burnishing device according to one of the preceding claims, wherein the at least one inductor (10) is adapted to the shape of the bearing component (2). [8] Burnishing device according to one of the preceding claims, wherein the inductor (10) is designed to heat a surface of the bearing component (2) to be burnished and is adapted to the shape of the surface of the bearing component (2) to be burnished. [9] Method for burnishing a bearing component (2), in particular a bearing ring, the method comprising: holding the bearing component (2) and moving the bearing component (2) into a container (6) with burnishing liquid (8) and / or out of the container (6) in order to at least partially immerse the bearing component (2) in the burnishing liquid (8), characterized by that the method further comprises heating the bearing component (2) by means of an inductive coupling before immersion in the bluing liquid (8) and / or during the bluing process by means of an induction heating device (10) with at least one inductor (10). [10] Method according to claim 11, wherein the heating of the bearing component (2) comprises preheating the bearing component (2) to a pretreatment temperature and / or postheating the bearing component (2) to a posttreatment temperature.

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