STORAGE COMPONENT

Description

[0001] The present invention relates to a bearing component with a blackened layer according to the preamble of claim 1. Furthermore, the present invention relates to a method for manufacturing such a bearing component according to claim 6.

[0002] It is known to apply blackening coatings to bearing components, e.g., rolling bearing rings or rolling elements, to protect these components from various types of damage typical of rolling bearings and occurring on the surface. In this process, the iron surface of the bearing component is immersed in one or more oxidizing baths. This creates a conversion layer that is firmly bonded to the base material and does not substantially affect the dimensions of the bearing component. A bearing component of this type is known from DE 10 2011 006296 A1, according to the preamble of claim 1.

[0003] The wear resistance of such a bearing bluing is sometimes too low in very wear-intensive applications, so that the bluing is weakened or worn away even after a test run or break-in period, while in other, more favorable applications it remains durable for years. The observed wear of the layer is often related to sliding components. While the layer is only smoothed but not worn away in pure rolling contact, it can be removed very quickly in sliding contact because it has a lower hardness than the hardened bearing steel of the mating surface.

[0004] It is therefore an object of the present invention to provide a bearing component with increased wear resistance.

[0005] This problem is solved by a bearing component according to claim 1 and a method for manufacturing a bearing component according to claim 6.

[0006] In general, coatings can be favorably influenced by the incorporation of additional substances. Until now, it was known to produce a blackening layer on a bearing component and then apply another layer with various additives, such as tungsten compounds or polymers, to the blackening layer to reinforce it or provide additional properties. However, this has the disadvantage that the additional elements constitute a separate layer that is unable to improve the properties of the blackening layer itself, such as wear resistance.

[0007] However, the inventor has now discovered that it is possible to improve the properties of the bluing layer by alloying it. Such an alloy allows the properties of the layer formed during the bluing process to be adjusted, and in particular improved.

[0008] Therefore, a bearing component with a blackened coating is proposed. This bearing component can be, in particular, a component of a rolling or sliding bearing, such as a bearing ring or rolling element.

[0009] To provide a durable bluing layer, metallic elements are incorporated into its structure. These elements are not intended as a separate layer with their own properties; rather, they are directly embedded within the bluing layer, i.e., integrated into its structure. In this way, they adapt the properties of the bluing layer instead of adding further properties of the elements themselves.

[0010] By manufacturing the coating as an alloyed bluing layer, the metallic additives are essentially integrated along the radial extent of the bluing layer, or at least along a significant portion of it. In contrast to previous manufacturing processes, where additive elements are only present in the radial boundary regions of the bluing layer—that is, on the surface of the layer or in its open cavities and pores—the metallic additives used here are located along the radial extent of the bluing layer, i.e., within the layer structure and not just on the surface. In this way, the metallic additives contribute to an improvement in the properties of the bluing layer across its radial extent.

[0011] During the running-in period of rolling bearings, a blackening layer necessarily and intentionally loses approximately 50% of its oxidation depth, while the remaining 50% typically remains stable and provides long-term protection to the surface. Therefore, modifying the properties of the layer remaining after running-in only requires a change in the layer properties extending beyond 50% of the oxidation depth. While a change in the layer properties across the entire oxidation depth of the blackening layer is desirable and ideally present, it is not strictly necessary for improved durability of the layer.

[0012] According to one embodiment, the metallic additives are provided in a proportion of between 0.1 and 1%, in particular between 0.3 and 0.7% (mass percent), of the bluing layer. These low proportions of metallic additives ensure that they do not alter the overall properties of the bluing layer through their own material properties, but instead adapt the properties of the actual bluing layer. The mass percentages used are similar to various alloying element proportions in steel, where significant changes in properties are also achieved despite low concentrations well below 1%.

[0013] The low concentration of the additives allows for a resource-saving coating process without high chemical usage, significant losses, or high costs. Furthermore, maintenance of the bluing bath and analysis are also simplified.

[0014] If additional elements were incorporated into a layer as "islands" to significantly alter the overall properties of the layer through their specific characteristics, several mass percentages of these additional elements would have to be introduced into the layer. Such massive island formations could disrupt the homogeneous properties of the layer, compromise its internal stability, and would require a high material input of additional elements in the coating process.

[0015] If additive elements are to be positioned not on top of a layer, but within a layer, it is therefore ideal if the additive elements are distributed within the layer through structural connections, for example in the crystal lattice structure, or through chemical reactions, and do not exist as isolated agglomerates. This is achieved by the bearing component described here. At the same time, incorporating the metallic additive elements into the basic structure of the layer makes it possible to achieve significant improvements in properties, even at very low concentrations.

[0016] According to another embodiment, the metallic additive elements are incorporated into the blackened layer with a radially increasing proportion.

[0017] Bluing is achieved by immersing the bearing component in one or more bluing baths. During immersion, iron and iron oxides contained in and on the component material, such as steel, are continuously dissolved, redeposited, and restructured. Unlike a two-layer coating, where a second layer is applied to the statically fixed first layer, in two-bath bluing, the second bath further re-modifies the already deposited first oxidation layer. The oxide layer becomes denser and more stable, and the proportion of free FeO decreases in favor of Fe3O4. The deeper the layer layers, the slower the re-modification process, until it ceases and usually reaches its final, desired oxidation state.

[0018] The metallic additives, which are applied to the bearing component, for example, using a pre-immersion solution, are not only embedded in the blackening layer but are also subject to a dissolution reaction. This means that during the restructuring of the area in which they are embedded, some of them can be lost back into the blackening bath.

[0019] If the bearing component is immersed again in a suspension containing metallic additives during the coating process, particularly between bluing baths, the concentration of these metallic additives increases again from the surface of the coating, and the metallic additives diffuse into the bluing layer that is still undergoing further transformation. This results in a concentration gradient, because the deeper a layer is, the less effectively it can be replenished with metallic additives. The final result is a bluing process with a measurable concentration gradient. The deepest areas of the layer have a lower concentration of metallic additives, increasing towards the surface. However, these metallic additives are not simply lying on the surface; rather, they are embedded within the bluing layer, predominantly in the upper regions, with an inward concentration gradient.

[0020] This differs from a conventional burnished surface, where additive elements merely lie on the surface and, at most, are pressed into it during operation or deposited in the outwardly open pores of the burnished layer. In contrast, the metallic additive elements in the bearing component proposed here are demonstrably incorporated into the microstructure of the burnished layer, with a maximum concentration near the burnished layer surface, but not above it.

[0021] According to another embodiment, the metallic additive elements are designed to adapt the properties of the bluing layer. As explained above, the properties of the additive elements are not used directly; rather, the metallic additive elements serve to adapt, and in particular improve, the existing properties of the bluing layer.

[0022] Tests have shown that the layer alloyed with metallic additives exhibits no relevant difference compared to a conventional blackened coating, neither in terms of color nor in the scanning electron microscopic surface structure or porosity. Corrosion protection was also identical within the limits of the test accuracy, as was friction. No significant difference in the wear pattern was observed in rolling contact tests. However, sliding tests revealed reproducible and significant differences between the bearing component described here and a bearing component with a conventional blackened coating.

[0023] It has been shown that the wear pattern for the bearing component described here was significantly reduced under all loads in the test setup used: at 0.9 GPa from 0.85 µm to 0.50 µm (-41%) at 1.1 GPa from 1.50 µm to 0.85 µm (-43%) at 1.4 GPa from 2.15 µm to 1.20 µm (-44%)

[0024] The following improvements to the alloyed bluing layer described here were observed in the investigation using nanoindentation tests compared to conventional bluing layers: Increase in hardness of the alloyed bluing on smooth polished surfaces to 227%; increase in hardness of the alloyed bluing on ground rough surfaces to 192%; increase in the modulus of elasticity on smooth polished surfaces to 220%; increase in the modulus of elasticity on ground rough surfaces to 229%

[0025] In summary, the bluing layer described here, alloyed with metallic additives, achieves twice the hardness, twice the modulus of elasticity, and half the sliding wear compared to conventional bluing layers. However, as already explained, the metallic additives do not create a separate layer; rather, the relatively low hardness and resistance of the "soft" bluing layer, which tends to wear quickly under sliding conditions, is doubled. The properties required for rolling contact remain unaffected.

[0026] The alloyed blackening layer exhibits particularly improved properties in the presence of sliding components. Since many rolling bearings, depending on their design and application, exhibit varying degrees of sliding in addition to the rolling motion, the improved wear resistance during sliding movement is relevant for rolling bearings. Thus, blackening in rolling bearings can be used not only to improve the performance of the raceways, but also to make the sliding movement of the outer ring within the housing in floating bearings less prone to wear.

[0027] According to the invention, the metallic additive elements comprise titanium and / or titanium oxide and / or titanium iron oxide.

[0028] Blackening is achieved using Fe3O4 (magnetite), whose crystal structure has cubic symmetry. When selecting metallic additives, particular attention should be paid to adding or creating a compound as similar as possible to magnetite, especially one based on iron oxide. This compound should have approximately the same hardness and properties, but should not have a cubic lattice structure, but rather, for example, a trigonal one. If the additives have similar properties but a different lattice structure, the combination of these different structures leads to a new and inevitably slightly distorted arrangement. The disturbances in the lattice structure and the available slip planes can significantly alter the hardness and elastic modulus of the overall layer.The actual structure of a blackening coating described only in simplified terms as Fe3O4 is a significantly larger structural system approximating Fe11O16 and can therefore be effectively strained, particularly at the Fe vacancy, by the deposition of very small amounts of other related lattice structures. Similar effects can be measured from the combination of Fe3O4 with an excess of Fe2O3.

[0029] Ilmenite (FeTiO3), for example, can be used as an additive in the layered structure, as it possesses all the desired properties. It is black, as is typical for bluing. It has a similar Mohs hardness to magnetite. It is also an iron oxide. It has a trigonal structure and thus the potential to strain and harden a cubic layer within the lattice. It contains titanium, a readily detectable element that provides information about the ilmenite content of the layer. Since ilmenite uses only one iron atom in its structure, it cannot inhibit the parallel formation of Fe3O4 at any conceivable concentration. The excess oxygen from the nitrite in the bluing bath can always meet the ilmenite formation requirements.

[0030] Other mixed oxides are conceivable. Beyond ilmenite (FeTiO3), FeTiO4 (iron(II) titanate) and FeTiO5 are also possible in the bluing layer. Thus, in the presence of excess oxygen, in addition to the three iron oxides FeO, Fe2O3, and Fe3O4, a group of three iron-titanium oxides can be present: FeTiO3, FeTiO4, and FeTiO5.

[0031] Mixed oxides can preferably be combined with other mixed oxides. This ensures that, even if the oxygen ratio in the bluing bath is not precisely maintained, a closely related iron-titanium oxide is produced, instead of allowing the reaction to drift in undesirable directions. Each of the iron-titanium oxides is capable of structurally distorting the magnetite of the bluing layer.

[0032] Various titanium compounds can be used for pre-immersion. These are all water-insoluble, therefore a suspension for the metallic additives is created in the immersion bath by blowing in air, as is common practice, for example, in activations before phosphating (sometimes with other solids). Analogous to such an activation, at least one pre-immersion bath with an aqueous suspension is maintained in the coating system, into which the workpieces are immersed before the first bluing step and possibly repeatedly as a short interruption during the bluing process.

[0033] Titanium dioxide is an extremely cost-effective and non-toxic titanium compound with high global market availability. It is also inert and does not lead to any undesirable side reactions. When used in a suspension, there is no risk of inhalation. Suitable particle sizes are specified for preparing the suspension, in particular KA 100 (0.25–0.35 mm).

[0034] Titanium dioxide is available in the rutile, anatase, and brookite structures, which are not equivalent in application. Industrially, the pigment is typically defined by its color strength and whiteness. Rutile is preferred for suspension, as it offers the highest color strength and is the most widely available structure. Therefore, a raw material with a color strength of at least 1280 is preferably defined for the pre-dipping process. Other raw material properties to be specified for successful application include, for example, the oil number (preferably max. 25 g / 100 g), the sieve residue 45 (preferably <0.015%), and the purity (preferably >98%).

[0035] Since titanium dioxide influences the oxidation behavior of iron, it can be preferentially used as a metallic additive. Titanium dioxide (TiO2) advantageously modifies the ionic diffusion of the oxygen anion (O₂) with iron and iron oxide. In this process, external Fe cation diffusion is replaced by internal O₂ anion diffusion. This means that the addition of TiO2 not only improves the diffusion capacity of the oxygen anion in the substrate and the blackening layer and supports layer formation, but also replaces the dominant ion transfer mechanism for the oxidation of iron with a more efficient one.

[0036] It was found that the incorporation of titanium compounds into the bluing layer follows a natural mass ratio. The bluing layer typically incorporates approximately 0.4–0.7% titanium. Even when the pre-immersion suspension is operated with a significantly increased titanium dioxide concentration, for example, twice the concentration, the same result is obtained. This is because the incorporation of titanium mixed oxides into the structural Fe11O16 matrix follows a specific ratio, just as a chemical reaction can only process certain proportions of the reactants. This fact allows for particularly simple and stable bath control of the pre-immersion suspension, as it can be operated with a concentration excess as a chemical reserve, and the same result is always achieved despite varying concentrations.

[0037] While the nominal ideal concentration of titanium dioxide in the pre-immersion suspension was set at 10 g / liter, the equally functional tolerance range could be set at 5-20 g / liter without any variation in results.

[0038] The temperature of the pre-immersion suspension does not affect the result. Room temperature as well as a heated, elevated temperature produce the same adhesive nucleation with the same intensity and similar adhesion. To ensure the process stability of the pre-immersion, in addition to a stable suspension achieved through continuous and sufficient air injection via nozzle pipes at the bottom of the tank for intensive circulation and suspension, attention should be paid to using demineralized water or other demineralized water, and to ensuring a sufficient immersion time for the workpieces in the suspension. A typical immersion time of 2 to 5 minutes is required for the initial adhesive nucleation on a bare steel surface. With an existing blackening layer, the surface energy and structure are altered, and the intermediate immersion cycles can be shorter.The possibility of shorter intermediate immersion processes prevents the core temperature of the workpieces from dropping significantly, which would lengthen the overall process.

[0039] According to a further aspect, a method for manufacturing a bearing component as described above is proposed. The method comprises the following steps: depositing metallic additive elements onto the bearing component and immersing the bearing component with the deposited metallic additive elements into a blackening solution, wherein the metallic additive elements are incorporated into the structure of the blackening layer and preferably over almost the entire radial extent of the blackening layer.

[0040] In particular, the addition of metallic elements can be achieved by immersion in a pre-diving solution. If titanium dioxide powder is used as the metallic element, it can be present as a suspension in the pre-diving solution with a particle size of 0.25–0.35 mm. As has been shown, approximately 10 g / liter is sufficient. Higher concentrations are possible, but not necessary.

[0041] Such a simple and cost-effective pre-dip solution can reliably produce an alloyed bluing that, despite a very low content of alloying elements (i.e., components of metallic additives), exhibits a doubling of its properties in several areas, as described above. This results in no premature loss of the bluing layer occurring in rolling bearing applications with high sliding loads when using such an alloyed bluing layer.

[0042] According to a further embodiment, the steps of attaching metallic additives and immersing in the bluing solution are repeated, with immersion in the bluing solution being the step following each attachment. Furthermore, prior to attaching the metallic additives, the bearing component can first undergo (multi-stage) degreasing and rinsing.

[0043] An exemplary process with several pre-diving, intermediate, and bluing processes can proceed as follows: Degreasing, cleaning, and rinsing of the material surfaces, if necessary with additional activation aids. Pre-immersion in a titanium dioxide suspension, which can be kept at room temperature as well as at elevated temperature. Transfer to the first bluing bath. Optionally, an interruption during the first bluing process, e.g., after 10 minutes, for re-quenching and intermediate immersion in the same titanium dioxide suspension, with immediate removal and further bluing. After completion of the first bluing process, quench in the coolest possible water. Pre-immersion in another titanium dioxide suspension, which can be kept at room temperature as well as at elevated temperature. This can be a second pre-immersion tank to avoid obstructing the equipment. Transfer to a second bluing bath. Optionally, an interruption during the second bluing process, e.g.,After 10 minutes, the piece is quenched and immersed again in the same titanium dioxide suspension, immediately lifted out and the bluing process continued. After completion of the second bluing, it is quenched in the coolest possible water, followed by various cold and hot rinsing baths, and then treated with dehydrating fluid and preservative oil.

[0044] The process can be extended, if necessary, to include a third immersion tank, a third bluing bath, and a third quenching rinse.

[0045] Compared to a modified blackening system typically used in the rolling bearing industry for tribological two-bath blackening, alloy blackening requires only two additional tanks. These tanks, apart from air injection, do not require any special equipment, in particular no heating or cooling systems, no protective covers, and no high-grade materials. The activation of these additional tanks can be selectively enabled or disabled in the process program for the individual workpiece type, without any adjustments or modifications being necessary between batches of alloyed and unalloyed blackening.

[0046] The aforementioned immersion tanks can contain a titanium dioxide-water suspension in which the TiO2 is kept in suspension by continuous air injection. When the bearing component is immersed in this suspension, its surface is seeded with titanium dioxide. The component is then transferred directly, without rinsing, to the first bluing bath. There, the immediate layer reaction takes place using the titanium dioxide present. As is known from seeding during phosphating, this seeding does not detach from the surface when the component is transferred directly, while intermediate rinsing steps are avoided. Excess titanium dioxide that may dissolve during immersion in the bluing bath is lost to the bluing bath sludge and is not harmful. It has been observed that titanium dioxide cannot be kept in suspension in the boiling bluing bath but precipitates immediately. This precipitate can then be disposed of along with the bluing bath sludge.

[0047] Thus, the bluing bath is in no way contaminated or degraded and can be used for normal bluing at any time, without the resulting layer containing any titanium. This has the advantage that the same bluing bath can be used for different bluing processes, with or without metallic additives from a previous pre-immersion step. Depending on the product and other requirements, the same system can therefore alternately produce unalloyed tribological bluing layers or alloyed tribological bluing layers without these processes interfering with each other.

[0048] In tribological rolling bearing bluing, as described here, the total bluing time is distributed across several bluing steps. For particularly long bluing times in a single bath, the process is typically interrupted by an intermediate quenching in a water bath to saturate oxygen-affine elements and reactivate the surface. Therefore, as described above, a separate pre-immersion in a titanium dioxide suspension, or another pre-immersion solution with added metallic elements, can be performed before each bluing bath and each bluing step. This does not complicate or delay the coating process. This intermediate immersion leads to a re-enrichment of the surface of the bearing component to compensate for titanium dioxide losses and restore the natural titanium content of the layer, which is approximately 0.5%.

[0049] The characteristics described in connection with the process also apply to the bearing component and vice versa.

[0050] Further advantages and advantageous embodiments are specified in the description, the drawings, and the claims. In particular, the combinations of features specified in the description and the drawings are purely exemplary, so that the features may also exist individually or in different combinations.

[0051] The invention will now be described in more detail with reference to exemplary embodiments illustrated in the drawings. These exemplary embodiments and the combinations shown in them are purely illustrative and do not define the scope of protection of the invention. The scope of protection is defined solely by the appended claims.

[0052] It shows: Fig. 1 : a schematic diagram of a process for manufacturing a bearing component.

[0053] In the following, identical or functionally equivalent elements are marked with the same reference symbols.

[0054] Fig. 1 Figure 1 shows a possible schematic sequence of a process for manufacturing a bearing component 1 with a blackening layer 10. The bearing component 1 is shown here as an example of a rolling bearing ring, but any other bearing component, for example a rolling element, can also be provided with such a blackening layer 10.

[0055] The bearing component 1 is first immersed in a pre-immersion solution 2 containing metallic additives. These metallic additives can be, for example, titanium dioxide, which is present in a titanium dioxide suspension in the pre-immersion solution 2. By immersing the bearing component 1 in the pre-immersion solution 2, the metallic additives are deposited on the surface of the bearing component 1, as exemplified here by spheres 4.

[0056] The bearing component 1 is then transferred to a bluing bath 6. In this bath, the surface of the bearing component is transformed into a bluing layer 8. This process involves the dissolution of iron and iron oxides contained in the material of the bearing component 1, followed by their continuous redeposition and restructuring. The metallic additive elements 4, which are already deposited on the bearing component 1, are incorporated into the bluing layer 8. In particular, the metallic additive elements are embedded within the structure of the bluing layer 8.

[0057] The pre-immersion and bluing process in the pre-immersion solution 2 and the bluing bath 6 can be repeated as often as desired, preferably two to three times. Furthermore, the bearing component 1 can be quenched after each bluing bath 6.

[0058] After completion of the bluing process, a bearing component 1 is obtained, which has a homogeneous alloyed bluing layer 10. The metallic additive elements 4 are embedded in this layer over its entire radial extent and are not identifiable as separate elements. Only a possible excess of additive elements could manifest as a local concentration peak, but this would not be functionally detrimental. The metallic additive elements 4 primarily serve to adapt the properties of the bluing layer 8 and do not contribute any properties of their own.

[0059] This alloyed bluing layer 10 makes it possible in particular to improve the properties of a bluing layer with regard to wear resistance and degree of wear. Reference symbol list

[0060] 1 Bearing component 2 Pre-immersion solution 4 Metallic additives 6 Bluing solution 8 Bluing layer 10 Alloyed bluing layer

Claims

1. Bearing component (1) having a burnishing layer (10), characterized in that additional metallic elements (4) are incorporated in the structure of the burnishing layer (10), where the additional metallic elements (4) include titanium and / or titanium oxide and / or titanium iron oxide.

2. Bearing component according to Claim 1, wherein the additional metallic elements (4) are provided with a proportion between 0.1% and 1%, in particular between 0.3% and 0.7%, of the burnishing layer (10).

3. Bearing component according to either of the preceding claims, wherein the additional metallic elements (4) are incorporated in the burnishing layer (10) with a proportion that rises radially outward.

4. Bearing component according to any of the preceding claims, wherein the additional metallic elements (4) are designed to adjust the properties of the burnishing layer (10).

5. Bearing component according to any of the preceding claims, wherein the bearing component (1) is a rolling bearing ring or a rolling element.

6. Method of producing a bearing component (1) according to any of the preceding claims, wherein the method comprises the steps of: adding additional metallic elements (4) to the bearing component (1) and immersing the bearing component (1) with the added additional metallic elements (4) into a burnishing solution (6), where the additional metallic elements (4) are incorporated in the structure of the burnishing layer (10), where the additional metallic elements (4) include titanium and / or titanium oxide and / or titanium iron oxide.

7. Method according to Claim 6, wherein the additional metallic elements (4) are added by immersion into a preliminary immersion solution (2).

8. Method according to Claim 6 or 7, wherein the steps of the adding of additional metallic elements (4) and immersing into the burnishing solution (6) are repeated, where the adding is followed by immersing into the burnishing solution (6).