Black oxidation deplating and re-coating method for surface of metal part

Abstract

The invention discloses a black oxidation deplating and re-coating method for the surface of a metal part. The method comprises the following steps: preparing a coating layer cleaning agent; testing calibration of the sample piece along with the furnace; carrying out deplating test on the bearing body; re-coating the metal part; cleaning (flowing clear water at room temperature for 10-20 minutes), hot cleaning (warm water at 60-80 DEG C for 10-20 minutes) and dewatering (hot air blowing at 105 DEG C for 10-20 minutes) are sequentially carried out; and performing rust prevention (spraying a thin oil film on low-viscosity anti-rust oil), packaging (a dust-free woven cloth / paper lining and a damping foam layer outer lining) and warehousing after the inspection is qualified, and scrapping if the inspection is unqualified. By standardizing the process, the treatment efficiency and quality are improved, uniform adhesion of the coating is ensured, the anti-rust performance is enhanced, and the service life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of steel surface treatment technology, specifically relating to a method for removing and recoating black oxide plating on the surface of metal parts. Background Technology

[0002] Blackening, also known as boiling blackening, involves a chemical solution reacting with the workpiece material to form a coating. After oxidation, the film thickness is 1μm±0.5μm, with no significant impact on part dimensions and precision. Black anodizing coating is mainly used for precision parts in engineering machinery, electrical appliances, power and medical equipment, textile printing and dyeing, automotive industry, chemical equipment, shipbuilding, and mold industry, as well as protective and decorative workpieces that cannot be replaced by other coatings. Currently, in bearings, it is mainly used in wind turbine generator transmission systems, and in some methods to improve the appearance quality of bearings. Its film has good wear resistance, a glossy black color, and is extremely aesthetically pleasing.

[0003] The principle of blackening oxidation reaction: Iron parts are heated in a high-concentration solution of a strong oxidizing agent, and a dense protective film of iron oxide (Fe3O4) is formed under the catalytic action of a catalyst. The coating component, iron oxide, is non-toxic and does not pollute the environment.

[0004] The key to achieving a dense and smooth surface of iron(III) oxide on steel lies in selecting a suitable strong oxidizing agent. A strong oxidizing agent consists of a strongly alkaline reagent with a pH of 12-14 and a weakly alkaline reagent with a pH of 7-12. The strongly alkaline reagent acts as a strong oxidant, while the weakly alkaline reagent acts as a catalyst. An aqueous solution of these agents is used to treat the steel parts during the blackening process.

[0005] For coatings that do not meet technical requirements (such as insufficient thickness, color, resistance to oxalic acid, acetic acid and / or copper sulfate corrosion, incomplete surface coverage, or non-compliance with process specifications), direct scrapping would be costly and would result in a long production cycle. Therefore, the industry accepts one rework coating. One recoating should include a complete black oxidation process. If the recoating is still unqualified, it should be scrapped.

[0006] For recoating, the initial coating layer should first be removed. Since the black oxide layer on the surface is relatively thin, typically 1μm ± 0.5μm, boring is generally performed. This involves using oilstones (also called boring bars) embedded in the boring head for surface finishing. During boring, the workpiece is mounted on the boring machine table or in a fixture. The boring head with several oilstones is inserted into the machined hole and rotated by the machine spindle, making axial reciprocating motion. The oilstones contact the hole wall with a certain pressure, thus removing a very thin layer of metal.

[0007] Boring and grinding is a highly efficient machining method that achieves high precision, high surface quality, and long service life on workpiece surfaces. It can effectively improve dimensional accuracy, shape accuracy, and reduce Ra value, but it cannot improve the positional accuracy of holes and other surfaces. For some complex bearing parts (such as those with oil grooves, threaded holes, or oil inlet / outlet ports), boring and grinding also cannot fully perform the machining, potentially leaving residual original coating layers in certain areas, leading to uneven coating in later stages. Boring and grinding relies on restoring the original metallic color to the surface, resulting in poor reliability. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for removing and recoating black oxide plating on the surface of metal parts, so as to improve the surface properties of metal parts.

[0009] To achieve the above objectives, the present invention provides the following technical solution, comprising the following steps: Step 1: Prepare the coating cleaning agent; Step two: Conduct on-site inspection and calibration tests on the sample parts. Step 3: Perform a deplating test on the bearing body; Step four: Apply a recoating to the metal parts; Step 5: Clean the metal parts. Rinse the black oxidized parts with running water at room temperature for 10-20 minutes. Step 6: Perform hot cleaning on the metal parts, using warm water at 60-80℃ for 10-20 minutes; Step 7: Dehydrate the metal parts by blowing them with hot air at 105℃ for 10-20 minutes; Step 8: Inspect the metal parts. If the inspection is qualified, proceed to the next step of rust prevention, packaging, and warehousing. If they are still unqualified, they shall be scrapped. Step 9: Apply rust prevention to the metal parts by spraying a thin layer of low-viscosity rust-preventive oil onto the surface of the parts. Step 10: Package the metal parts, using clean fabric / paper as a protective inner lining and a shock-absorbing foam layer as a protective outer lining. Step 11: Put the metal parts into storage by placing them in the designated storage locations according to the corresponding procedures.

[0010] As a further improvement of the present invention, the specific steps for preparing the coating cleaning agent in step one are as follows: prepare a 0.1 mol / L dilute hydrochloric acid solution according to the ratio of 8.33 ml of analytical grade concentrated hydrochloric acid per liter of aqueous solution.

[0011] As a further improvement of the present invention, the specific steps for the calibration test of the in-furnace inspection sample in step two are as follows: the undamaged sample used for inspection with the same process as the bearing parts is used to measure the thickness D1, D2, D3, ..., Dn of the black oxide coating at multiple locations using a film thickness gauge, and the average thickness result is output in μm; Immerse the sample in cleaning solution for 10 seconds to remove the surface coating, rinse with running water, and dry. The thickness of the black oxide coating layer on the sample was measured again at multiple locations using a film thickness gauge, d1, d2, d3, ..., dn. The average thickness result was output in μm. Calculate the dissolution rate: , in μm / s.

[0012] As a further improvement to the present invention, the specific steps of the bearing body deplating test in step three are as follows: The thickness of the black oxide coating layer on the bearing at multiple locations (H1, H2, H3, ..., Hn) is measured using a film thickness gauge, and the average thickness result is output in μm. Calculate cleaning time: Unit s The bearing components were placed in a freshly prepared 0.1 mol / L dilute hydrochloric acid solution for corrosion time. Then, remove it, wash it with running water, and dry it. The metal parts are then baked. The bearing parts are placed at a high temperature of 120℃ and a high pressure of 3.5MPa steam for dehydrogenation treatment, which is a preheating treatment for black oxidation to improve the activation energy of molecules on the workpiece surface.

[0013] As a further improvement of the present invention, the specific method for recoating the metal parts in step four is as follows: After adjusting the process according to the corresponding technical requirements, the bearing parts are immersed in a black oxidation solution reaction tank for black oxidation. The temperature of entering the tank is 120-125℃, the temperature of exiting the tank is 125-130℃, and the processing time is 40-50 minutes.

[0014] The beneficial effects of this invention are: 1) High adaptability, capable of handling various complex structural parts, especially suitable for difficult-to-machine areas such as oil grooves and threaded holes; 2) Controllable precision, achieving quantitative deplating through film thickness measurement and dissolution rate calculation, overcoming the subjectivity of boring and grinding relying on manual judgment; 3) Improved efficiency, the entire deplating process takes only tens of seconds to several minutes, far lower than the time cost of boring and grinding. Subsequent steps, by optimizing cleaning parameters and strictly controlling recoating process conditions, further ensure the stability of the surface quality of the parts, reducing rework rate and scrap risk. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process for removing and recoating plating in this invention; Figure 2 This is a schematic diagram of the process for stripping and recoating plating involving boring and grinding; Figure 3 This is an image showing the appearance of the plating removal and recoating process in this invention; Figure 4 This is an image showing the appearance of a decoating and recoating process involving boring and grinding. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the embodiments shown in the accompanying drawings.

[0017] Reference Figure 1 As shown, the method for removing and recoating black oxide plating on the surface of metal parts in this embodiment includes the following steps: Step 1: Prepare the coating cleaning agent; Step two: Conduct on-site inspection and calibration tests on the sample parts. Step 3: Perform a deplating test on the bearing body; Step four: Apply a recoating to the metal parts; Step 5: Clean the metal parts. Rinse the black oxidized parts with running water at room temperature for 10-20 minutes. Step 6: Perform hot cleaning on the metal parts, using warm water at 60-80℃ for 10-20 minutes; Step 7: Dehydrate the metal parts by blowing them with hot air at 105℃ for 10-20 minutes; Step 8: Inspect the metal parts. If the inspection is qualified, proceed to the next step of rust prevention, packaging, and warehousing. If they are still unqualified, they shall be scrapped. Step 9: Apply rust prevention to the metal parts by spraying a thin layer of low-viscosity rust-preventive oil onto the surface of the parts. Step 10: Package the metal parts, using clean fabric / paper as a protective inner lining and a shock-absorbing foam layer as a protective outer lining. Step 11: Warehouse the metal parts by placing them in designated storage locations according to the appropriate procedures. This process replaces traditional boring and grinding with chemical stripping, solving the problem of coating residue on complex structural parts. Taking the inner ring of a bearing with oil grooves as an example, traditional boring easily creates machining dead corners at the bottom of the oil grooves. However, this invention uses a solution immersion method to allow the cleaning agent to fully penetrate deep into the oil grooves, thoroughly removing residual agents in subsequent cleaning steps and ensuring uniform surface activation during recoating.

[0018] Furthermore, refer to Figure 1As shown, the specific steps for preparing the coating cleaning agent in step one are as follows: Prepare a 0.1 mol / L dilute hydrochloric acid solution according to the ratio of 8.33 ml of analytical grade concentrated hydrochloric acid per liter of aqueous solution. This step ensures the stable dissolving ability of the cleaning agent on the black oxide layer by precisely controlling the hydrochloric acid concentration (0.1 mol / L), avoiding the local residue problem caused by traditional boring and grinding relying on mechanical processing. This invention achieves precise control of the cleaning agent concentration through quantitative ratio (8.33 ml / L concentrated hydrochloric acid), laying the foundation for the controllability of the subsequent stripping process.

[0019] Furthermore, refer to Figure 1 As shown, the specific steps for the in-furnace inspection sample calibration test in step two are as follows: The undamaged sample used for inspection with the same process as the bearing parts is used to measure the thickness D1, D2, D3, ..., Dn of the black oxide coating at multiple locations using a film thickness gauge, and the average thickness result is output in μm; Immerse the sample in cleaning solution for 10 seconds to remove the surface coating, rinse with running water, and dry. The thickness of the black oxide coating layer on the sample was measured again at multiple locations using a film thickness gauge, d1, d2, d3, ..., dn. The average thickness result was output in μm. Calculate the dissolution rate: The unit is μm / s. This process simulates the actual stripping environment using samples collected in the furnace, and utilizes a film thickness gauge to measure at multiple points (d1 to Dn, d1 to dn) and calculate the average thickness. To ensure data representativeness, the calculation of the dissolution rate v enables quantitative control of the stripping process, solving the problem of poor reliability caused by the reliance on manual judgment (surface restoration of metal color) in the background technology, and making the stripping effect predictable and verifiable.

[0020] Furthermore, refer to Figure 1 As shown, the specific steps for the bearing body decoating test in step three are as follows: The thickness of the black oxide coating layer on the bearing is measured at multiple locations (H1, H2, H3, ..., Hn) using a film thickness gauge, and the average thickness result is output in μm. Calculate cleaning time: Unit s The bearing components were placed in a freshly prepared 0.1 mol / L dilute hydrochloric acid solution for corrosion time. Then, remove it, wash it with running water, and dry it. The metal parts are then baked. The bearing parts are placed at 120℃ and 3.5MPa high-pressure steam for hydrogen removal, serving as a preheating treatment for black oxidation and increasing the activation energy of molecules on the workpiece surface. This step calculates the bearing stripping time based on the dissolution rate v calibrated in step two, achieving personalized stripping control for different initial coating thicknesses. This is particularly suitable for bearings with complex structures such as oil grooves and threaded holes mentioned in the background technology. Chemical immersion ensures uniform contact of the cleaning agent with all surfaces, avoiding the problem of dead corner residue from boring and grinding. The subsequent 120℃ high-temperature, 3.5MPa high-pressure steam baking not only removes the risk of hydrogen embrittlement but also activates surface molecules, improving the adhesion of the recoated layer.

[0021] Furthermore, refer to Figure 1 As shown, the specific method for recoating the metal parts in step four is as follows: After adjusting the process according to the corresponding technical requirements, the bearing parts are immersed in a black oxide solution reaction tank for black oxidation. The tank entry temperature is 120-125℃, the tank exit temperature is 125-130℃, and the processing time is 40-50 minutes. This recoating process ensures a dense and uniform formation of the iron oxide film by precisely controlling the temperature range of entering (120-125℃) and exiting (125-130℃) and the processing time of 40-50 minutes. This solves the problem of substandard surface performance caused by uneven coating in the background technology, and improves the wear resistance and decorative properties of the metal parts.

[0022] In summary, this invention employs a chemical stripping and recoating process, replacing traditional mechanical boring and grinding through a complete workflow of "cleaning agent preparation - furnace sample calibration - bearing body stripping - recoating - cleaning and inspection." This solution solves the problems of coating residue on complex bearing parts (such as those with oil grooves and threaded holes), as well as the poor reliability and low efficiency of boring and grinding. It achieves uniform removal and precise recoating of coatings on metal parts, significantly improving the surface performance stability of products and reducing rework rates and production costs.

[0023] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for black oxide stripping and recoating the surface of a metal part, characterized by: It comprises the following steps: Step one, preparation of coating layer cleaning agent; Step two, calibration test of in-furnace inspection sample; Step three, bearing body stripping test; Step four, re-coating of metal parts; Step five, cleaning of metal parts, flowing clean water to clean the black oxidized parts at room temperature for 10-20 minutes; Step six, hot cleaning of metal parts, 60-80℃ warm water cleaning for 10-20 minutes; Step seven, dehydration of metal parts, 105℃ hot air blowing for 10-20 minutes; Step eight, inspection of metal parts, qualified for rust prevention, packaging, and warehousing, if still unqualified, scrap treatment; Step nine, rust prevention of metal parts, spraying a thin layer of oil film on the surface of the parts with low viscosity rust preventive oil; Step ten, packaging of metal parts, dust-free cloth / paper as protective lining, shock-absorbing foam as protective outer lining; Step eleven, warehousing of metal parts, placing the parts in the designated storage location according to the corresponding procedure.

2. The method of black oxide stripping and recoating of metal parts according to claim 1, characterized in that: The specific steps of preparing the coating layer cleaning agent in step one are as follows: preparing a 0.1 mol / L dilute hydrochloric acid solution according to the ratio of 8.33 ml of analytical pure concentrated hydrochloric acid per liter of water solution.

3. The method according to claim 1 or 2, characterized in that: The specific steps of calibration test of in-furnace inspection sample in step two are as follows: measuring the thickness of the black oxide coating at multiple positions D1, D2, D3, …, Dn of the undamaged sample for inspection with the same process as the bearing parts using a film thickness gauge, outputting the average thickness result in units of μm, Soaking the sample in the cleaning agent for 10 seconds to remove the surface coating, cleaning with flowing water, and drying; Measuring the thickness of the black oxide coating at multiple positions d1, d2, d3, …, dn of the sample again using a film thickness gauge, outputting the average thickness result in units of μm, The dissolution rate was calculated as: in μm / s.

4. The method of black oxide stripping and recoating of metal parts according to claim 3, characterized in that: The specific steps of bearing body stripping test in step three are as follows: measuring the thickness of the black oxide coating at multiple positions H1, H2, H3, …, Hn of the bearing using a film thickness gauge, outputting the average thickness result in units of μm, Calculated cleaning time: in s The bearing parts are placed in a new prepared 0.1 mol / L dilute hydrochloric acid solution for corrosion time After that, the product is taken out, washed with flowing water and dried. Then, baking the metal parts, placing the bearing parts in 120℃ high temperature, 3.5MPa high pressure steam baking, hydrogen removal treatment, black oxide preheating treatment, and improving the activation energy of the surface molecules of the workpiece.

5. The method of black oxide stripping and recoating of metal parts according to claim 4, characterized in that: The specific way of re-coating of metal parts in step four is as follows: adjusting the process according to the corresponding technical requirements of the bearing parts, immersing the parts in the black oxide solution reaction tank for black oxidation, tank temperature 120-125℃, tank temperature 125-130℃, and treatment time 40-50 minutes.

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