Method for checking pickling burn of bg801 bearing part

Abstract

The application discloses a pickling burn inspection method based on a BG801 bearing part, which sequentially performs the processes of oil removal and degreasing, hot water cleaning, flowing cold water washing, pickling, flowing cold water washing, brightening, flowing cold water washing, neutralization, flowing cold water washing, rust prevention and naked eye observation, and special degreasing liquid, pickling liquid, brightening liquid, neutralization liquid and rust prevention liquid formulas suitable for the material characteristics of the BG801 are matched, and the temperature, time length and operation requirements of each process are clear. The application can make the surface of the BG801 bearing part uniform color development, the color difference between the burn area and the normal matrix is clear, the slight pickling burn which cannot be identified by the conventional process can be stably detected by the naked eye, the detection precision is high, the pickling corrosion amount is controllable, the subsequent processing and use performance of the part are not damaged, the problem that the conventional bearing steel pickling process is not suitable for the BG801 material is solved, and the strict quality control demand of the aviation bearing can be met.

Description

Technical Field

[0001] This invention relates to a method for inspecting pickling burns on BG801 bearing parts. Background Technology

[0002] Aviation bearings, primarily including main shaft bearings for aircraft engines and crucial bearings for helicopter transmission systems, are among the core components of aircraft. Due to their unique applications and harsh operating environments, aviation bearings must meet stringent requirements for high precision, high speed, high temperature, long lifespan, and high reliability, with the defect control standards for main shaft bearings being the most stringent. BG801 material is a martensitic gear steel obtained by adding 0.5% tungsten to CSS-42L steel, possessing excellent high-temperature performance and high strength and toughness. After carburizing, a sample with a theoretical carburized layer depth of 1.3mm can achieve a rotational bending fatigue strength of 850MPa at 500℃, making it an important candidate material for high-end aviation bearings. Acid pickling burn inspection is a routine process for verifying surface quality and identifying grinding burns after grinding of bearing parts. Currently, the pickling inspection process for conventional bearing steels such as GCr15, 9Cr18Mo, and 8Cr4Mo4V is relatively mature. However, the composition system of BG801 material differs significantly from that of conventional bearing steels. Using existing pickling solutions and processes for conventional bearing steels results in issues such as parts failing to properly color the surface and color development not meeting the judgment standards. In particular, it is difficult to detect minor pickling burns. If parts with minor burns proceed to subsequent processes, it can lead to premature fatigue spalling during bearing service, significantly reducing bearing life and failing to meet the quality control requirements for aerospace bearings. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for inspecting pickling burns on BG801 bearing parts. By using pickling solutions, clarifying solutions, and matching pickling processes adapted to the characteristics of BG801 material, the method achieves effective color development on the surface of BG801 bearing parts, can reliably detect minor pickling burns, has high detection accuracy, and does not damage the subsequent processing and use performance of the parts.

[0004] To achieve the above objectives, this invention provides a method for inspecting pickling burns on BG801 bearing parts, comprising the following steps: Step 1: Degreasing. Place the bearing parts in the degreasing solution and shake them to soak. The degreasing solution is prepared by 4wt% anhydrous sodium carbonate, 3wt% trisodium phosphate, 2wt% sodium hydroxide and the balance deionized water. The soaking temperature is 75℃~95℃ and the soaking time is ≥2min. Step 2: Hot water cleaning. Use hot water at 75℃~85℃ to clean the bearing parts for 1~2 minutes. Step 3: Rinse with running cold water for 30-60 seconds; Step 4: Pickling. Place the bearing parts in the pickling solution and pickle with shaking at room temperature for 40-60 seconds until the surface of the bearing parts turns black. The pickling solution is prepared from 20wt% HNO3, 5wt% HF, 3wt% FeCl3 and the balance deionized water. Step 5: Rinse with running cold water for 30-60 seconds; Step 6: Illumination. Place the bearing parts in the illumination solution and shake and soak for 20-30 seconds at room temperature. The illumination solution is prepared by 5 wt% HCl and the remainder deionized water. Step 7: Rinse with running cold water for 30-60 seconds; Step 8: Neutralization. Place the bearing parts in the neutralization solution and immerse them at room temperature for 30-60 seconds. The neutralization solution is prepared by 5 wt% anhydrous sodium carbonate and the remainder water. Step 9: Rinse with running cold water for 30-60 seconds; Step 10: Rust prevention. Place the bearing parts in a rust-preventive solution and immerse them at room temperature for 1-2 minutes. The rust-preventive solution is prepared from 2 wt% anhydrous sodium carbonate, 10 wt% sodium nitrite, and the remainder water. Step 11: Visual inspection. Place the pickled bearing parts under light for visual inspection.

[0005] As a further provision of the present invention, in step eleven, the visual inspection is performed while the bearing parts are wet, the minimum illuminance of the inspection environment is 2153 Lux, and the visual inspection is completed within 2 hours after the start of pickling and corrosion.

[0006] As a further feature of the present invention, the corrosion amount of the bearing parts in the pickling process of step four is controlled to be 1μm~2μm.

[0007] The beneficial effects of this setup are as follows: Firstly, the principle of this technical solution is that HNO3 and HF in the pickling solution have acidic and strong oxidizing properties, and FeCl3 also has strong oxidizing properties. Therefore, during the pickling process, not only can the substrate be decomposed, but some carbides can also be oxidized. The working principle of the pickling solution is as follows: 4Fe + 10H + +NO3 — =4Fe 2+ +NH4 + +3H2O Fe2O3+6H + =2Fe 3+ +3H2O Cr2O3 + 6H + =2Cr 3+ +3H2O Fe3W3C+16H+ +12NO3 — =3Fe 3+ +3H2WO4+CO2+9NO↑+4NO2↑+5H2O, This solution utilizes the acidic oxidation of nitric acid and hydrofluoric acid, along with the auxiliary oxidation of ferric chloride, to not only uniformly etch the steel substrate but also effectively decompose tungsten-based special carbides such as Fe3W3C. This completely solves the problem that traditional pickling formulas for bearing steels like GCr15, 9Cr18Mo, and 8Cr4Mo4V cannot properly develop the color of BG801 material. After treatment, a uniform and stable gray-black base is formed on the surface of the part, with color fully meeting the criteria for burn inspection, filling the technological gap in the pickling burn detection of BG801 aerospace bearing steel. Through a combined process of acid pickling and hydrochloric acid clarification, the clarification solution dissolves the metal salts and oxide deposits generated on the surface after pickling, precisely highlighting the structural differences between the burned area and the normal substrate, creating a clearly distinguishable color difference. Compared to the limitations of traditional processes that cannot detect minor grinding burns, this method can visually detect minor tempering burns and softening defects in the subsurface layer, effectively avoiding missed detections. It prevents damaged parts from entering subsequent processes, preventing premature fatigue spalling of bearings due to burn areas becoming fatigue sources during service, directly ensuring the bearing's design life. The acid pickling etching depth is strictly controlled within the range of 1μm to 2μm, removing only a very thin surface layer of the part, without altering its dimensional accuracy, geometric tolerances, or surface roughness. The grinding process only needs to leave a corresponding trace allowance to meet the final dimensional requirements. Furthermore, this etching depth is much smaller than the carburized layer depth of BG801 material, without disrupting the hardness gradient and effective hardened layer depth of the carburized layer, fully preserving the material's high-temperature strength, impact toughness, and rotational bending fatigue performance. The detection process will not negatively impact the subsequent processing and service performance of the part. The entire process, from solution ratios and temperatures to time and operating methods, is quantitatively controlled. It also includes solutions for analyzing the causes of common anomalies such as over-pickling, insufficient corrosion, and surface spots, along with rapid elimination methods. On-site operators can quickly adjust process parameters based on actual conditions, reducing the risk of batch quality accidents. The complete hot water washing, flowing cold water washing, neutralization, and rust-preventing post-treatment processes thoroughly remove acid and alkali residues from parts surfaces, preventing secondary corrosion. The entire process can be directly integrated into the post-grinding inspection stage of bearing mass production lines, meeting the batch production control requirements of aerospace bearings. Grinding burns are one of the core causes of early bearing failure under high-temperature, high-speed conditions. This method significantly improves the consistency of BG801 bearing quality by effectively detecting burn defects at all levels. Bearing parts that pass this inspection can avoid contact fatigue failure caused by burns under harsh conditions such as high-speed, high-temperature, and alternating loads in aero-engine spindles and helicopter transmission systems, effectively extending the mean time between failures (MTBF) of bearings, improving the operational safety and reliability of aerospace equipment, and meeting the core quality requirements of high reliability and long service life for aerospace products.Parts treated and rust-proofed using this method have no corrosive residue or foreign matter adhering to their surface. They can be directly connected to subsequent processes such as fine grinding, ultra-precision machining, assembly, oiling, and packaging without the need for additional cleaning procedures. This method will not adversely affect the subsequent machining accuracy, assembly fit accuracy, or lubrication performance, and can be seamlessly integrated into the existing bearing manufacturing process. Attached Figure Description

[0008] Figure 1 This is a flowchart of an embodiment of the present invention; Figure 2 This is a diagram showing the bearing parts before pickling, according to an embodiment of the present invention. Figure 3 This is the state of the bearing parts after pickling according to an embodiment of the present invention. Figure 1 ; Figure 4 This is the state of the bearing parts after pickling according to an embodiment of the present invention. Figure 2 . Detailed Implementation

[0009] The first embodiment of the pickling and burning inspection method for BG801 bearing parts of this invention has the following steps: Figure 1 As shown: Follow these steps in sequence: Step 1: Degreasing and preparation of degreasing solution: Take 4% anhydrous sodium carbonate, 3% trisodium phosphate, and 2% sodium hydroxide by mass fraction, add deionized water to make up the balance, and stir until the solutes are completely dissolved. Immerse the BG801 bearing parts to be inspected in the degreasing solution, controlling the solution temperature at 75℃~95℃. During immersion, continuously shake the parts to ensure that all surfaces of the parts are in full contact with the degreasing solution; the immersion time should be no less than 2 minutes to thoroughly remove oil and machining residue from the surface of the parts.

[0010] Step 2: Hot water cleaning. Transfer the degreased bearing parts to hot water at 75℃~85℃ and clean for 1~2 minutes to remove the degreased liquid adhering to the surface of the parts.

[0011] Step 3: Rinse with running cold water. Place the parts that have been cleaned with hot water under running cold water for 30 seconds to 1 minute to thoroughly remove any alkaline residue from the surface. At the same time, allow the parts to cool to room temperature to avoid introducing them into the subsequent pickling solution and affecting the solution stability.

[0012] Step 4: Pickling. Prepare the pickling solution: By mass fraction, take 20% HNO3, 5% HF, and 3% FeCl3, add deionized water to make up the balance, stir evenly, and let stand until the solution is stable. Under room temperature conditions, immerse the bearing parts in the pickling solution, continuously shaking the parts up and down during the pickling process to ensure that all surfaces are evenly contacted with the acid solution; control the pickling time to 40~60s, and observe until the overall surface of the parts turns black and presents a uniform gray-black or dark gray color before removing them. In this step, the corrosion of the parts by the pickling process is controlled to 1μm~2μm through experimental testing; when formulating the grinding process parameters, this amount of corrosion from pickling must be considered, and a corresponding dimensional allowance must be reserved to ensure that the dimensions of the parts still meet the tolerance requirements after pickling.

[0013] Step 5: Rinse with running cold water. Immediately place the acid-washed parts under running cold water for 30 seconds to 1 minute to quickly rinse away any residual acid on the surface, terminate the acid-washing reaction, and avoid excessive corrosion.

[0014] Step Six: Clarification. Prepare the clarification solution: Take 5% HCl by mass fraction, add deionized water to make up the balance, and stir well. Under room temperature conditions, immerse the parts in the clarification solution, shake and soak for 20-30 seconds to dissolve the metal salt deposits formed on the surface after pickling, so that the surface color is uniform and the boundaries of the burn area are clear.

[0015] Step 7: Rinse with running cold water. Place the cleaned parts under running water and rinse for 30 seconds to 1 minute to remove residual hydrochloric acid and dissolved products from the surface.

[0016] Step 8: Neutralization. Prepare the neutralization solution: Take 5% anhydrous sodium carbonate by mass fraction, add water to make up the balance, and stir until completely dissolved. At room temperature, immerse the parts in the neutralization solution for 30-60 seconds to neutralize any residual acidic substances on the surface of the parts, preventing acid residue from causing corrosion or affecting the subsequent rust prevention effect.

[0017] Step 9: Rinse with running cold water. Place the neutralized parts under running clean water and rinse for 30 seconds to 1 minute to remove any neutralizing solution residue from the surface.

[0018] Step 10: Rust prevention. Prepare the rust inhibitor solution: Take 2% anhydrous sodium carbonate and 10% sodium nitrite by mass fraction, add water to make up the balance, and stir until completely dissolved. At room temperature, immerse the parts in the rust inhibitor solution for 1-2 minutes to provide short-term rust protection for the parts surface and prevent rust from affecting the observation results during inspection.

[0019] Step 11: Visual inspection. After pickling and rust prevention, the bearing parts should be visually inspected while still wet. The inspection environment should be equipped with dedicated lighting fixtures to ensure a minimum illuminance of 2153 Lux on the inspection surface. After completion, the parts should be promptly removed from the pickling inspection process and proceed to subsequent treatments. Other general technical requirements for pickling inspections shall be implemented in accordance with JB / T2850.

[0020] After the process described in this embodiment, the surface of the BG801 bearing parts exhibits a uniform dark gray color, such as... Figures 2 to 4 As shown; if the part has grinding burns, the burned area will show a color that is significantly different from the normal substrate, which can be clearly distinguished by the naked eye. Even minor burns can be reliably detected.

[0021] The above examples are merely one preferred embodiment of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention are all included within the protection scope of the present invention.

Claims

1. A method for inspecting pickling burns on BG801 bearing parts, characterized in that, Includes the following steps, Step 1: Degreasing. Place the bearing parts in the degreasing solution and shake them to soak. The degreasing solution is prepared by 4wt% anhydrous sodium carbonate, 3wt% trisodium phosphate, 2wt% sodium hydroxide and the balance deionized water. The soaking temperature is 75℃~95℃ and the soaking time is ≥2min. Step 2: Hot water cleaning. Use hot water at 75℃~85℃ to clean the bearing parts for 1~2 minutes. Step 3: Rinse with running cold water for 30-60 seconds; Step 4: Pickling. Place the bearing parts in the pickling solution and pickle with shaking at room temperature for 40-60 seconds until the surface of the bearing parts turns black. The pickling solution is prepared from 20wt% HNO3, 5wt% HF, 3wt% FeCl3 and the balance deionized water. Step 5: Rinse with running cold water for 30-60 seconds; Step 6: Illumination. Place the bearing parts in the illumination solution and shake and soak for 20-30 seconds at room temperature. The illumination solution is prepared by 5 wt% HCl and the remainder deionized water. Step 7: Rinse with running cold water for 30-60 seconds; Step 8: Neutralization. Place the bearing parts in the neutralization solution and immerse them at room temperature for 30-60 seconds. The neutralization solution is prepared by 5 wt% anhydrous sodium carbonate and the remainder water. Step 9: Rinse with running cold water for 30-60 seconds; Step 10: Rust prevention. Place the bearing parts in a rust-preventive solution and immerse them at room temperature for 1-2 minutes. The rust-preventive solution is prepared from 2 wt% anhydrous sodium carbonate, 10 wt% sodium nitrite, and the remainder water. Step 11: Visual inspection. Place the pickled bearing parts under light for visual inspection.

2. The method for inspecting pickling burns on BG801 bearing parts according to claim 1, characterized in that: In step eleven, the visual inspection is carried out while the bearing parts are wet, the minimum illuminance of the inspection environment is 2153 Lux, and the visual inspection is completed within 2 hours after the pickling and corrosion begins.

3. The method for inspecting pickling burns on BG801 bearing parts according to claim 2, characterized in that: The pickling process in step four controls the corrosion of the bearing parts to within 1μm~2μm.

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