A process for eliminating surface yellowing after low-temperature tempering of an engine crankshaft

Abstract

The application provides a process method for eliminating yellow spots on the surface of an engine crankshaft after low-temperature tempering, and comprises the following steps: S1, cleaning and drying treatment is performed on the surface of the crankshaft; S2, medium-frequency quenching treatment is performed on the crankshaft after the step S1; S3, cooling and low-temperature tempering treatment is performed on the crankshaft after the step S2; and S4, the crankshaft after the step S3 is soaked in cutting fluid, dried, and then soaked in rust inhibitor, so as to eliminate the yellow spots on the surface of the crankshaft after low-temperature tempering. The cutting fluid can quickly penetrate, emulsify and peel off the yellow spot layer. Compared with sand blasting and polishing, the method does not change the surface roughness of the crankshaft, does not introduce mechanical scratches, and does not relax the residual compressive stress.

Description

Technical Field

[0001] This invention relates to the field of engine component manufacturing and surface treatment technology, specifically to a process for eliminating yellow spots on the surface of an engine crankshaft after low-temperature tempering. Background Technology

[0002] The crankshaft is a key component in an engine that withstands complex alternating loads, and it is commonly manufactured from medium carbon steel or medium carbon alloy steel. Medium-frequency quenching and low-temperature tempering are common heat treatment processes to improve its surface hardness, wear resistance, and fatigue resistance. However, in actual mass production, after medium-frequency quenching (using quenching medium cooling) and subsequent low-temperature tempering, yellowish-brown spots (hereinafter referred to as "yellow spots") are very likely to appear on the crankshaft surface, especially at the fillets and journals.

[0003] The main components of yellow spots are: quenching medium residues, high-temperature alloy oxides, and trace amounts of organic carbonized film. Yellow spots can cause many problems: 1. Affects the reliability of testing. Yellow spots can mask microcracks on the crankshaft surface, leading to missed or misjudged defects in subsequent magnetic particle testing, thus creating significant quality risks.

[0004] 2. Affects appearance and coating effect. Severe yellowing reduces the appearance quality of the product and weakens the adhesion of subsequent rust inhibitors and coating layers.

[0005] 3. Difficult to remove. Traditional yellow stain removal processes all have obvious drawbacks: manual grinding is extremely inefficient and easily causes mechanical damage to sensitive areas with rounded corners; sandblasting changes the surface roughness of the crankshaft and may also destroy the beneficial residual compressive stress formed by medium-frequency quenching; pickling easily corrodes the workpiece substrate and also poses serious environmental hazards.

[0006] Therefore, the industry urgently needs to develop a yellow stain removal process that does not damage the surface quality of the crankshaft, does not change the residual stress field, and is environmentally friendly and efficient. Summary of the Invention

[0007] This invention addresses the problem that yellow spots easily form on the surface of crankshafts after medium-frequency quenching and low-temperature tempering, and that traditional removal methods can easily damage the workpiece or pollute the environment. It provides a process method for eliminating yellow spots on the surface of engine crankshafts after low-temperature tempering.

[0008] The technical method of the present invention is as follows: A process for removing yellow spots from the surface of an engine crankshaft after low-temperature tempering includes the following steps: S1. Clean and dry the surface of the crankshaft; S2. Perform medium-frequency quenching on the crankshaft after step S1. S3. Cool and perform low-temperature tempering on the crankshaft after step S2. S4. After the crankshaft has been treated in step S3, immerse it in cutting fluid, dry it, and then immerse it in rust inhibitor to eliminate the yellow spots on the surface of the crankshaft after low-temperature tempering.

[0009] In step S1, the cleaning is performed using an alkaline cleaning agent or a water-based cleaning agent; the drying is performed by air drying or hot air drying.

[0010] In step S2, the heating frequency of the medium-frequency quenching is 6-8 kHz, and the heating time is 8-12 seconds.

[0011] In step S3, the temperature is cooled to 100–150°C.

[0012] In step S4, the cutting fluid comprises 20-60% mineral base oil, 5-15% alcohols and / or alkanolamines, 5-15% carboxylic acids, 3-10% surfactant, and 5-30% water. A cutting fluid concentration of 8-15% is used in step S4. The immersion time in the cutting fluid is 3-5 minutes at room temperature. The rust inhibitor is a solvent-based or water-based rust inhibitor, and the immersion time is 2-4 minutes. After immersion, the rust inhibitor is allowed to drain naturally or centrifuged.

[0013] Optionally, the method further includes: after step S4, visually inspecting or wiping the crankshaft surface with a white cloth to confirm whether the yellow spots have been completely eliminated.

[0014] The beneficial effects of this invention are: I. Highly Effective Removal of Yellow Stains Without Damaging the Substrate: Using 8%–15% cutting fluid, rapid immersion and cleaning at room temperature for 3 minutes, combined with the synergistic effect of surfactants and penetrants, allows for rapid penetration, emulsification, and removal of the yellow stain layer. Compared to sandblasting and grinding, this method does not alter the crankshaft surface roughness, introduces mechanical scratches, or relaxes residual compressive stress.

[0015] II. Wide process window and low energy consumption: 3-minute short cleaning time, high production efficiency, suitable for large-scale assembly line operation.

[0016] 3. Significantly improves the reliability of non-destructive testing: After removing the yellow spots, the surface cleanliness of the crankshaft meets the requirements of magnetic particle testing, avoiding missed crack detection caused by yellow spots.

[0017] IV. Environmentally friendly process and low cost: It does not use strong acids, strong alkalis or organic solvents, the cleaning wastewater is easy to treat, and the cutting fluid can be recycled. Attached Figure Description

[0018] Figure 1 A flowchart of the process method of this invention. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a process for eliminating yellow spots on the surface of an engine crankshaft after low-temperature tempering, such as... Figure 1 As shown, it includes the following steps: S1. Clean and dry the crankshaft surface.

[0021] In this embodiment, cleaning and drying processes are used to remove impurities from the crankshaft surface.

[0022] In this embodiment, an alkaline cleaning agent or a water-based cleaning agent is used for cleaning. The alkaline and water-based cleaning agents can be commercially available in the art, and their function is to remove oil stains and other impurities from the crankshaft surface.

[0023] For example, the cleaning temperature is 25–70℃, and the cleaning time is 3–5 minutes. For example, the temperature is 55℃, 60℃, or 65℃.

[0024] In this embodiment, drying is carried out by natural air drying or hot air drying to ensure that the crankshaft surface is free of oil and moisture.

[0025] In this embodiment, the crankshaft may be one or more of 42CrMo, 40Cr, 35CrMo, 45 steel, 50Mn, QT700-2, QT800-2, and QT900-2.

[0026] S2. Perform medium-frequency quenching on the crankshaft after step S1.

[0027] In this embodiment, the heating frequency of the medium-frequency quenching is 6–8 kHz, and the heating time is 8–12 seconds. For example, the heating frequency is 6.5 kHz, 7 kHz, or 7.5 kHz, and the heating time is 9 seconds, 10 seconds, or 11 seconds.

[0028] S3. Cool and perform low-temperature tempering on the crankshaft after step S2.

[0029] In this embodiment, the temperature is cooled to 100–150°C. For example, the cooling can be achieved by spraying a quenching fluid or by natural cooling. The quenching fluid spraying time is 8–10 seconds, and the quenching medium is a polymer quenching fluid. Common polymer quenching fluids in the art can be used.

[0030] In this embodiment, the low-temperature tempering treatment temperature is 165–175°C, and the low-temperature tempering treatment time is 180–240 minutes. For example, the low-temperature tempering treatment temperatures are 166°C, 170°C, and 172°C, and the low-temperature tempering treatment times are 200 minutes, 210 minutes, 220 minutes, and 230 minutes.

[0031] S4. After the crankshaft has been treated in step S3, immerse it in cutting fluid, dry it, and then immerse it in rust inhibitor to eliminate the yellow spots on the surface of the crankshaft after low-temperature tempering.

[0032] In this embodiment, the cutting fluid effectively dissolves or disperses the yellow stains formed during tempering, while also providing lubrication and cleaning. The cutting fluid comprises 20-60% mineral base oil, 5-15% alcohols and / or alkanolamines, 5-15% carboxylic acids, 3-10% activator, and 5-30% water. The mineral base oil is a hydrotreated heavy cycloalkane petroleum distillate. The carboxylic acid includes one or more of dicarboxylic acids, acetic acid, propionic acid, and butyric acid. The alcohols and / or alkanolamines include one or more of triethanolamine, N-methyldiethanolamine, 1-amino-2-propanol, 2-aminoethanol, 2-amino-1-butanol, ethoxylated C16-18-ol, and C18-unsaturated alcohols. The activator is sodium petroleum sulfonate. Here, the hydrotreated heavy cycloalkane petroleum distillate includes mineral oil and an extract containing less than 3% DMSO.

[0033] In this embodiment, a cutting fluid with a concentration of 8% to 15% is used. For example, 9%, 10%, or 11%.

[0034] In this embodiment, the soaking time is 3 to 5 minutes, and the soaking temperature is room temperature.

[0035] In this embodiment, the rust inhibitor is a solvent-based or water-based rust inhibitor, and commercially available solvent-based or water-based rust inhibitors can be used. The soaking time is 2-4 minutes, followed by natural drainage or centrifugal drying. The rust inhibitor can form a protective film on the crankshaft surface, further removing residual yellow stains and preventing rusting during subsequent storage.

[0036] In this embodiment, the method further includes: after step S4, visually inspecting or wiping the crankshaft surface with a white cloth to confirm whether the yellow spots have been completely eliminated.

[0037] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0038] The present invention will be described in detail below through embodiments and experimental examples. However, these are merely examples and do not limit the present invention in any way.

[0039] Example 1 This embodiment provides a process for eliminating yellow spots in crankshafts after medium-frequency quenching and low-temperature tempering using cutting fluid. The crankshaft material is 42CrMo. The specific steps are as follows: Step 1: Clean the crankshaft surface and let it dry.

[0040] The spray cleaning pressure is 0.3-0.6 MPa, the concentration of commercially available alkaline cleaning agent is 1%-3%, the spray angle is 45°-90°, and the product is air-dried after cleaning.

[0041] Step 2: Medium-frequency quenching and low-temperature tempering The crankshaft that has undergone medium-frequency quenching (heating frequency of 7kHz, heating time of 8 seconds) is then cooled to 100-150℃ by spraying quenching fluid for 10 seconds, followed by low-temperature tempering (170℃, 240 minutes) and cooling to room temperature.

[0042] Step 3: Coolant soaking and cleaning Prepare a cutting fluid comprising 50% mineral base oil, 10% alcohols and / or alkanolamines, 10% carboxylic acid, 10% activator, and 20% water. The mineral base oil is a naphthenic mineral oil or a hydrogenated heavy naphthenic petroleum distillate, in a mass ratio of 2:1. The carboxylic acid is a dicarboxylic acid. The alcohols and / or alkanolamines are triethanolamine, N-methyldiethanolamine, 1-amino-2-propanol, 2-aminoethanol, 2-amino-1-butanol, ethoxylated C16-18-ol, or C18-unsaturated alcohol, in a mass ratio of 2:2:1:1:3:2:1. The activator is sodium petroleum sulfonate. Then, dilute the stock cutting fluid with water to a 10% concentration. Immerse the crankshaft treated in step two in the 10% cutting fluid for 3 minutes.

[0043] Step 4: Hot air drying Dry with hot air for 15 minutes to ensure no water stains remain on the surface.

[0044] Step 5: Rust prevention treatment Soak the crankshaft in a commercially available water-based rust inhibitor for 3 minutes, then remove it and let it air dry naturally.

[0045] Step 6: Testing The treated crankshaft underwent visual inspection and fluorescent magnetic particle testing. The results showed that there were no yellow spots or cracks on the crankshaft surface, and the magnetic particle testing background was clear with no false indications.

[0046] Comparative Example Comparative Example 1 (The cutting fluid stock was diluted with water to a mass concentration of 5%, the cleaning time was 5 minutes, and the temperature was 50°C) The difference between this comparative example and Example 1 is that the cutting fluid concentration is 5%, the cleaning temperature is 50°C, and the cleaning time is 5 minutes. The results show that the yellow stain removal rate is approximately 85%, and a longer cleaning time or a higher concentration is needed to achieve complete removal.

[0047] Comparative Example 2 (Sandblasting treatment) The difference between this comparative example and Example 1 is that steps S2 and S3 were replaced with sandblasting (80-mesh white corundum, pressure 0.5 MPa). The results showed that the yellow stain removal rate was 95%, but the surface roughness of the rounded corners increased from Ra0.4 to Ra1.2, and the residual compressive stress test showed a relaxation of about 15%.

[0048] Table 1 As shown in Table 1, Example 1, at a cutting fluid concentration of 10%, achieved the removal of yellow spots without damaging the substrate, changing the roughness, or disrupting the compressive stress.

[0049] The method of this invention can be widely applied to the yellow stain removal process of various precision shaft parts such as crankshafts and camshafts after medium-frequency quenching, and is particularly suitable for the manufacturing of key engine components with high requirements for surface quality and fatigue life.

[0050] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for eliminating yellow spots on the surface of an engine crankshaft after low-temperature tempering, characterized in that, Includes the following steps: S1. Clean and dry the surface of the crankshaft; S2. Perform medium-frequency quenching on the crankshaft after step S1. S3. Cool and perform low-temperature tempering on the crankshaft after step S2. S4. After the crankshaft has been treated in step S3, immerse it in cutting fluid, dry it, and then immerse it in rust inhibitor to eliminate the yellow spots on the surface of the crankshaft after low-temperature tempering.

2. The process method according to claim 1, characterized in that, In step S1, the cleaning is performed using an alkaline cleaning agent or a water-based cleaning agent. Drying can be done by air drying or hot air drying.

3. The process method according to claim 1, characterized in that, In step S2, the heating frequency of the medium-frequency quenching is 6-8 kHz, and the heating time is 8-12 seconds.

4. The process method according to claim 1, characterized in that, In step S3, the temperature is cooled to 100–150°C.

5. The process method according to claim 1, characterized in that, In step S3, the temperature of the low-temperature tempering treatment is 165–175°C, and the time of the low-temperature tempering treatment is 180–240 minutes.

6. The process method according to claim 1, characterized in that, In step S4, the cutting fluid comprises 20-60% mineral base oil, 5-15% alcohols and / or alkanolamines, 5-15% carboxylic acid, 3-10% surfactant, and 5-30% water. In step S4, a cutting fluid with a concentration of 8-15% is used.

7. The process method according to claim 6, characterized in that, The cutting fluid soaking time is 3 to 5 minutes, and the soaking temperature is room temperature.

8. The process method according to claim 1, characterized in that, The rust inhibitor is a solvent-based or water-based rust inhibitor. The soaking time is 2 to 4 minutes. After soaking, it is allowed to drain naturally or centrifuged to dry.

9. The process method according to claim 1, characterized in that, The method further includes, after step S4, visually inspecting or wiping the crankshaft surface with a white cloth to confirm whether the yellow spots have been completely eliminated.

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