Method for blackening rolling bearing rings

Abstract

A method for preparing rolling bearing rings for an alkaline bluing process, wherein an alkaline and acid-free aqueous adhesive foam mixture containing sodium hydroxide is applied to the rolling bearing rings for cleaning purposes, wherein the adhesive foam mixture is sprayed onto the rolling bearing rings, wherein the consistency of the adhesive foam mixture is adjusted so that the adhesive foam mixture adheres firmly to the rolling bearing rings without running or dripping off due to gravity, wherein an exposure time is allowed, then the adhesive foam mixture is removed from the rolling bearing rings and the rolling bearing rings are then subjected to an alkaline bluing process, wherein lanolin adhering to the rolling bearing rings is removed with the aid of the adhesive foam mixture.

Description

[0001] The invention relates to a method for blackening rolling bearing rings.

[0002] During the bluing process for rolling bearing rings, especially large ones with an outer diameter of at least one meter, intermediate storage or transport is usually necessary, for example, from the production site to a bluing facility. To prevent corrosion during these waiting periods, it is common practice to apply a corrosion inhibitor to the bearing rings, thus preserving them. This preservation can be achieved, for example, by spraying a preservative oil onto the rings. Since large bearing rings are very expensive, a film-forming agent such as lanolin is typically added to the preservative oil, creating a durable protective film on the rings and thus minimizing the risk of corrosion.

[0003] For the bluing of rolling bearing rings, an alkaline bluing process has proven effective, as it does not attack the rings or cause grain boundary damage. Such a process produces a very thin bluing layer and is known, for example, from DE 10 2007 061 193 A1. While the hot degreasing performed in the known bluing process can remove a number of corrosion inhibitors from the surface of the rolling bearing rings, the alkaline hot degreasing is not sufficiently effective if film-forming agents have been added to the corrosion inhibitor, meaning that the preservative film is not adequately removed. The film-forming agents cannot be sufficiently removed with alcohol or acetone either, contaminating the bluing baths and disrupting the bluing process.

[0004] In principle, it is possible to include pickling steps in the bluing process to remove the protective film. However, these pickling steps are so aggressive that they attack the steel surface of the bearing rings, leading to grain boundary damage.

[0005] DE 602 07 723 T2 discloses a liquid degreasing composition comprising an aqueous nitric acid solution containing: at least a first emulsifying non-ionic surfactant consisting of a polyethoxylated fatty alcohol, and at least a second wetting non-ionic surfactant consisting of an ethylene oxide / propylene oxide copolymer.

[0006] WO 2007 / 033 761 A1 discloses an aqueous cleaning agent for hard surfaces, which is applied to the surface to be cleaned by means of a spray dispenser in the form of a foam, and which contains a fatty alcohol sulfate and / or a fatty acid sarcosinate as well as isopropanol and butyl glycol. The agent can be used in a process for streak-free cleaning of hard surfaces, in particular glass.

[0007] GB 1 162 039 A discloses a method for cleaning an open surface with harmful cleaning compositions containing eye, nose, and skin irritants. The method comprises mixing a foamable cleaning composition containing harmful chemicals such as alkalis, mineral acids, sulfamic acid, or strongly basic amines with at least 90% by volume of a gas, applying the resulting foam to the open surface to be cleaned, and rinsing the surface to remove the remaining foamed cleaning composition.

[0008] DE 10 2012 213 317 A1 discloses a bluing process in which the bearing component to be blued is first degreased.

[0009] EP 1 121 690 B1 discloses a degreasing composition comprising a base, a saturated or unsaturated polyoxyethylated fatty alcohol, a copolymer of ethylene oxide and propylene oxide and water, wherein the base is an OH selected from the range of 0.1 to 1.5 mol. - -ion ​​concentration, wherein the saturated or unsaturated polyoxyethylated fatty alcohol is present in a concentration selected from the range of about 0.01 to about 1.5 wt% and wherein the copolymer of ethylene oxide and propylene oxide is present in a concentration selected from the range of about 0.025 to about 1.5 wt%.

[0010] The invention is based on the objective of enabling bluing by means of an alkaline bluing process, even for rolling bearing rings that have been treated with a corrosion protection agent containing a film former such as lanolin.

[0011] This problem is solved by the combination of features of claim 1.

[0012] In the inventive method for preparing rolling bearing rings for an alkaline bluing process, an alkaline and acid-free aqueous adhesive foam mixture containing sodium hydroxide is applied to the rolling bearing rings for cleaning purposes. The consistency of the adhesive foam mixture is adjusted so that it adheres firmly to the rolling bearing rings without running or dripping off due to gravity, and a contact time is observed. Subsequently, the adhesive foam mixture is removed from the rolling bearing rings, and the rolling bearing rings are then subjected to an alkaline bluing process, in which the adhesive foam mixture removes any lanolin adhering to the rolling bearing rings.

[0013] The invention has the advantage that the rolling bearing rings are cleaned and degreased gently and thoroughly. Oils, greases, and other contaminants adhering to the rolling bearing rings are removed without damaging them.

[0014] The bearing rings can be made of steel. These bearing rings can be large, with an outer diameter of at least 1 m. Particularly with large bearing rings, only a small amount of the adhesive foam mixture is required, relative to the size of the bearing rings.

[0015] The adhesive foam mixture is sprayed onto the rolling bearing rings. This allows for quick and even application of the adhesive foam mixture with minimal effort.

[0016] The rolling bearing rings can rotate during the application of the adhesive foam mixture. This has the advantage that the entire surface of the rolling bearing rings is easily accessible and overhead work can be completely or largely avoided.

[0017] The adhesive foam mixture can be mechanically removed from the bearing rings. This allows the adhesive foam mixture, and with it the substances detached from the bearing rings, to be easily and efficiently removed from the process. Compared to washing, mechanical removal has the advantage of not generating a large quantity of contaminated material. For example, the adhesive foam mixture can be removed from the bearing rings by wiping. In particular, the bearing rings can be wiped dry.

[0018] The adhesive foam mixture can be used to remove lanolin adhering to the roller bearing rings. Lanolin can significantly interfere with an alkaline bluing process and contaminate the bath media, so removing the lanolin is highly beneficial for the subsequent bluing process.

[0019] In particular, an aqueous-based adhesive foam mixture can be applied. This has the advantage of high compatibility with the bath media of the subsequent bluing process, should the adhesive foam mixture not be completely removed from the rolling bearing rings. These residues can then be removed in the bluing baths.

[0020] Furthermore, the adhesive foam mixture can be alkaline. Besides its compatibility with the bluing baths, this has the advantage that the adhesive foam mixture does not attack the steel of the rolling bearing rings and does not cause grain boundary damage.

[0021] The adhesive foam mixture may contain anionic surfactants. It may also contain emulsifying surfactants. Furthermore, the adhesive foam mixture may contain polyhydric chiral alkanols. These serve as solvents, solubility enhancers, and promoters of water-in-oil emulsion.

[0022] Other possible ingredients include, for example, absorbents and release agents, sodium hydroxide, amino alcohols, or ethanolamines. These substances can achieve a variety of desired properties, such as delamination and cohesive failure of the films adhering to the rolling bearing rings, alkalization, corrosion protection, cleaning, and degreasing.

[0023] The invention is explained in more detail below.

[0024] The method according to the invention is primarily aimed at use with large steel rolling bearing rings that have an outer diameter of at least one meter. Such rolling bearing rings are used, for example, in rolling bearings for wind turbines.

[0025] Bluing large rolling bearing rings requires a bluing system with large baths, which is often not available directly at the production site. Therefore, transporting the rolling bearing rings to the bluing system is usually necessary. Furthermore, handling large rolling bearing rings is considerably more complex than handling small bearing components, resulting in frequent waiting times between different production steps. To prevent corrosion of the rolling bearing rings during transport and storage, they are coated with a highly adhesive film of corrosion inhibitor. For this purpose, a film-forming agent such as lanolin is added to a conventional corrosion inhibitor, such as a preservative oil, and the rolling bearing rings are then sprayed or coated with this mixture. The treated rolling bearing rings are then transported to the bluing system.

[0026] Upon arrival at the bluing line, the rolling bearing rings are either temporarily stored or pre-treated for bluing. Pre-treatment for bluing takes place immediately before the bluing process, as the bearing rings lose their corrosion protection during this stage, and corrosion must be prevented. During pre-treatment, the bearing rings are individually placed in a holder and set into rotation around their axis. The slowly rotating bearing rings are then sprayed with a water-based adhesive foam mixture. This can be done, for example, using a hand-held or machine-operated spray gun. The adhesive foam mixture can also be applied in other ways. However, a container to hold the bearing rings is not required.Furthermore, only a small amount of the adhesive foam mixture is required, just enough to completely coat each rolling bearing ring. The consistency of the adhesive foam mixture is formulated so that it adheres firmly to the rolling bearing rings and does not run or drip off due to gravity. Even a very low surface energy of the rolling bearing ring does not cause the adhesive foam film to dewette.

[0027] The adhesive foam mixture is water-based, not solvent-based. Therefore, it is compatible with the bath media used in the bluing process and can be rinsed off completely. Furthermore, the adhesive foam mixture is alkaline and non-corrosive. It contains no acid, as this would attack the steel of the bearing rings and cause grain boundary damage.

[0028] The adhesive foam mixture contains a number of other ingredients besides water and foaming agent: One ingredient is anionic surfactant, for example sodium dodecyl poly(oxyethylene) sulfate. The concentration of this ingredient can range from 1 to 15% by mass.

[0029] Another ingredient is an emulsifying surfactant, such as coconut fatty acid monoethanolamide. The concentration of this can range from 1 to 15% by mass.

[0030] Furthermore, chiral alkanols can be included in the adhesive foam mixture as solvents, solubility improvers, and water-in-oil emulsion promoters. 1,2-Propanediol is particularly suitable for this purpose. The concentration can range from 1 to 20% by mass.

[0031] Furthermore, adsorbents and release agents may be included for film delamination, cohesion disruption, and adsorption. These can be, for example, magnesium silicate or soft silica derivatives. The concentration of silica or magnesium salts can range from 1 to 6% by mass.

[0032] Furthermore, the adhesive foam mixture contains sodium hydroxide for alkalization, corrosion protection, cleaning, and degreasing. In an alkaline bluing process, at least some of the bluing baths typically also contain sodium hydroxide. For a pH value of 13.0 to 13.5, the sodium hydroxide concentration can be 0.5 to 2% by mass.

[0033] Finally, the adhesive foam mixture may contain small amounts of amino alcohols or ethanolamines. These are completely rinsed off before reaching the nitrite baths of the bluing process to prevent the formation of nitrosamines from amines and nitrite. For example, monoethanolamine, diethanolamine, and / or triethanolamine may be present. The total concentration of ethanolamines can range from 4 to 12% by mass. Monoethanolamine acts as an alkaline enhancer of the hydroxide action. Diethanolamine acts as a solvent and emulsifier. Triethanolamine acts as a corrosion inhibitor.

[0034] The adhesive foam mixture has a density of less than 1 g / cm³ in its unfoamed state. 3 , especially from 0.96 to 0.98 g / cm³ 3 , and is almost odorless and irritating, but not toxic, so the necessary safety precautions when using the adhesive foam mixture are not particularly elaborate.

[0035] After applying the adhesive foam mixture to the bearing rings, a dwell time of several minutes, typically 2 to 10 minutes, is allowed. For example, the dwell time can be 5 minutes. The adhesive foam is then mechanically removed from the bearing rings, for example, by wiping. Wiping can be done with a dry, soft cloth. For automated wiping, elastic wiper lips or sponge-like structures can be used, which are shaped to fit the bearing rings and are guided over their surface. Wiping removes oil, grease, and other contaminants from the bearing rings along with the adhesive foam mixture. The contaminated cloth can be discarded or processed separately. The wiper lips can be cleaned with a water jet.

[0036] The described procedure has the advantage that only a comparatively small amount of the adhesive foam mixture is required to clean large rolling bearing rings, which can have an outer diameter of more than one meter. Furthermore, it ensures that the adhesive foam mixture and substances detached from the rolling bearing ring are removed from the process and do not enter the cleaning baths or the baths of the bluing system. This prevents contamination of the baths and recontamination of the rolling bearing rings.

[0037] After treatment with the adhesive foam mixture, the rolling bearing rings are thoroughly cleaned and degreased and can be blued in a manner known per se. For example, the blued process described in DE 10 2007 061 193 A1 can be used. The relevant disclosure is incorporated into the present application by reference to DE 10 2007 061 193 A1. In the aforementioned blued process, the prior cleaning with the adhesive foam mixture prevents contamination of the equipment, and a very good blued result can be achieved. A spotless and deep black blued layer with a thickness of approximately 1 µm is formed.

[0038] The adhesive foam mixture can also be used for cleaning and degreasing burnished rolling bearing rings. This can be advantageous if the burnished rolling bearing rings are subjected to a process step such as a thermal post-treatment known from DE 10 2012 215 591 A1. During thermal post-treatment, any remaining protective films on the rolling bearing rings can cause burn marks. These burn marks can be prevented if the rolling bearing rings are treated with the adhesive foam mixture before the thermal post-treatment.

[0039] The bluing layer is not noticeably damaged by treatment with the adhesive foam mixture within normal process times. With a bluing layer formed according to DE 10 2007 061 193 A1, the application of the adhesive foam does not lead to any visible damage to the bluing layer, nor to any damage detectable by measurements according to DIN 50938, nor to any attack on the underlying steel material, even after a 30-minute exposure time.

Claims

[1] Method for preparing rolling bearing rings for an alkaline bluing process, wherein an alkaline and acid-free aqueous adhesive foam mixture containing sodium hydroxide is applied to the rolling bearing rings for cleaning purposes, wherein the adhesive foam mixture is sprayed onto the rolling bearing rings, wherein the consistency of the adhesive foam mixture is adjusted so that the adhesive foam mixture adheres firmly to the rolling bearing rings without running or dripping off due to gravity, wherein an exposure time is allowed, the adhesive foam mixture is then removed from the rolling bearing rings and the rolling bearing rings are then subjected to an alkaline bluing process, wherein lanolin adhering to the rolling bearing rings is removed with the aid of the adhesive foam mixture. [2] Method according to claim 1, wherein the rolling bearing rings rotate during the application of the adhesive foam mixture. [3] Method according to any of the preceding claims, wherein the adhesive foam mixture is mechanically removed from the rolling bearing rings. [4] Method according to any of the preceding claims, wherein the adhesive foam mixture is removed from the rolling bearing rings by wiping. [5] Method according to any of the preceding claims, wherein an adhesive foam mixture is applied which contains sodium hydroxide in a concentration of 0.5 to 2% by mass. [6] Method according to any of the preceding claims, wherein an adhesive foam mixture containing anionic surfactants is applied. [7] Method according to any of the preceding claims, wherein an adhesive foam mixture containing emulsifying surfactants is applied. [8] Method according to any of the preceding claims, wherein an adhesive foam mixture containing chiral alkanols is applied. [9] Method according to any of the preceding claims, wherein an adhesive foam mixture is applied which contains adsorbent and release agent.