Preparation method of high-cleanliness stainless steel three-way pipe fitting

Abstract

The invention provides a preparation method of a high-cleanliness stainless steel three-way pipe fitting, and relates to the technical field of stainless steel pipe fitting manufacturing. The preparation method of the high-cleanliness stainless steel three-way pipe fitting comprises the steps that raw materials are selected, food-grade austenitic stainless steel plates or pipes are selected as the raw materials, such as 316L stainless steel and 304L stainless steel, the chemical components of the stainless steel need to meet the relevant requirements of food contact materials in stainless steel and heat-resistant steel plates and steel strips for pressure-bearing equipment GB / T24511-2017, it is ensured that the content of nickel, chromium and other elements reaches the standard, and the requirement for high-cleanliness stainless steel three-way pipe fitting is met; and the pollution risk of the material to a fluid medium is reduced. Through a series of processes such as laser cutting, hot extrusion forming, electrochemical polishing, pickling passivation and ultrasonic cleaning, internal defects and surface impurities of the pipe fitting are effectively eliminated, the inner wall of the pipe fitting is low in roughness and high in cleanliness, the high-cleanliness requirement of the industries such as food and pharmacy for fluid conveying components can be met, and the fluid pollution risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of stainless steel pipe fitting manufacturing technology, specifically to a method for preparing a high-cleanliness stainless steel tee pipe fitting, which is particularly suitable for industries with extremely high hygiene and safety requirements such as food, pharmaceuticals, and cosmetics, and is used in the production and manufacturing of high-cleanliness pipeline connection components in fluid transportation systems. Background Technology

[0002] In industries such as food, pharmaceuticals, and cosmetics, fluid transport systems place extremely high demands on the cleanliness, corrosion resistance, and safety of pipe fittings. Stainless steel tee fittings, as critical connecting components in piping systems, directly impact fluid quality and product safety due to their cleanliness. Traditional methods for manufacturing stainless steel tee fittings have several drawbacks. Molding process defects: Some parts are made using casting processes, which can easily produce internal defects such as air holes and sand holes. Residual impurities are difficult to remove, affecting the cleanliness of the pipe fittings. When cold extrusion or welding is used, stress concentration is likely to occur, which can cause cracks in the pipe fittings during use and reduce their service life.

[0003] Insufficient surface treatment: Conventional surface polishing is difficult to achieve high cleanliness requirements, and there are tiny pits or scratches on the inner wall of the pipe fittings, which can easily breed bacteria and residual dirt; pickling and passivation processes may leave chemical residues, which can contaminate the fluid medium.

[0004] Weak cleanliness assurance: During the production process, from raw material processing to finished product packaging, there is a lack of systematic cleanliness control measures. For example, dust in the processing environment and contaminants brought in by operators may reduce the final cleanliness of the pipe fittings.

[0005] Therefore, developing a method to overcome the above problems and produce stainless steel tee fittings that meet food-grade high cleanliness standards is of great practical significance. Summary of the Invention

[0006] (a) Purpose of the invention This invention aims to provide a method for preparing high-cleanliness stainless steel tee fittings. By optimizing the molding process, improving the surface treatment technology and strengthening clean production control, a stainless steel tee fitting with a dense internal structure, high surface smoothness, no impurity residue, and meeting food-grade safety standards is prepared, solving the problems of insufficient cleanliness and unstable quality in traditional preparation methods.

[0007] (II) Technical Solution To achieve the above objectives, the present invention provides a method for preparing a high-purity stainless steel tee fitting, specifically comprising the following steps: Raw material selection: Food-grade austenitic stainless steel plates or pipes, such as 316L and 304L stainless steel, are selected as raw materials. Their chemical composition must meet the relevant requirements for food contact materials in GB / T24511-2017 "Stainless Steel and Heat-Resistant Steel Plates and Strips for Pressure Equipment" to ensure that the content of elements such as nickel and chromium meets the standards and reduce the risk of material itself contaminating fluid media.

[0008] Material cutting and forming: Based on the specifications and dimensions of the tee fittings, laser cutting technology is used to precisely cut stainless steel plates or pipes, ensuring dimensional accuracy within ±0.1mm and reducing subsequent processing allowances.

[0009] The hot extrusion molding process involves heating the stainless steel material after blanking to 950-1050℃ and extruding it in a special mold. This allows the material to flow fully under high temperature and pressure, eliminating internal pores and loose structures, and forming a dense tee pipe blank. During the hot extrusion process, the extrusion speed is controlled at 5-10mm / s and the pressure is 80-120MPa to ensure that the wall thickness of the formed pipe is uniform and the deviation does not exceed ±0.05mm.

[0010] Heat treatment: The formed tee pipe blank is solution treated by heating to 1050-1100℃ and holding for 1-2 hours, and then rapidly cooled (e.g., by water cooling) to eliminate processing stress, improve the corrosion resistance and toughness of the material, refine the grains, and improve the overall performance of the pipe.

[0011] Rough machining: High-precision CNC machine tools are used to rough machine the heat-treated pipes, turning and milling the outer surface and connection ports of the pipes to remove excess machining allowance, so that the outer diameter, wall thickness and port size of the pipes initially meet the design requirements, and the machining accuracy is controlled within ±0.2mm.

[0012] Internal wall polishing: The inner wall of the pipe fitting is polished using an electrochemical polishing process. The pipe fitting is used as the anode and immersed in a specialized polishing solution (the main components of which include phosphoric acid, sulfuric acid, chromic anhydride, etc., mixed in a specific ratio). The solution is applied for 15-25 minutes at a voltage of 8-12V and a temperature of 45-55℃. Through electrochemical corrosion, the microscopic protrusions on the inner wall of the pipe fitting are preferentially dissolved, resulting in a smooth and clean surface. The inner wall roughness Ra value is reduced to below 0.2μm.

[0013] Pickling and passivation: The polished pipe fittings are immersed in a pickling and passivation solution composed of nitric acid (15-20% by volume) and hydrofluoric acid (1-3% by volume) at a temperature of 40-50℃ for 10-15 minutes to remove oxide scale, oil and other impurities from the surface of the pipe fittings and form a dense passivation film on the surface to improve the corrosion resistance of the pipe fittings. After pickling and passivation, the pipe fittings are repeatedly rinsed with deionized water until the pH value of the rinsing water is neutral to ensure that there are no chemical residues.

[0014] Cleaning treatment: After pickling and passivation, the pipe fittings are transferred to a cleanroom (cleanliness level of ISO 5 or above). Ultrasonic cleaning equipment is used with deionized water as the cleaning medium. The pipe fittings are cleaned for 20-30 minutes at a frequency of 40-60kHz and a temperature of 30-40℃ to remove residual microparticles and impurities. After cleaning, the surface moisture of the pipe fittings is immediately wiped dry with a lint-free cloth and then dried with hot air (temperature controlled at 60-80℃) to ensure that the surface of the pipe fittings is dry and free of moisture residue.

[0015] Quality Inspection: Visual inspection: Use visual inspection and a magnifying glass (10-20x) to check the surface of the pipe fittings to ensure that there are no defects such as scratches, pits, oxidation and discoloration, and that the surface is smooth, flat and uniform in color.

[0016] Dimensional inspection: Using measuring tools such as vernier calipers and micrometers, the outer diameter, wall thickness, length, and port dimensions of the pipe fittings are accurately measured to ensure that the dimensions meet the design requirements.

[0017] Cleanliness testing: The cleanliness of the pipe fittings is tested using a particle counter, requiring that the number of particles ≥0.5μm in the air does not exceed 1000 per cubic meter; the surface of the pipe fittings is tested for microorganisms by wiping, and the total number of colonies should meet the food-grade hygiene standards (e.g., ≤10CFU / cm²).

[0018] Pressure resistance test: Perform a water pressure test on the pipe fittings. After filling the pipe fittings with water, slowly increase the pressure to 1.5 times the design pressure and hold the pressure for 5-10 minutes. Check the pipe fittings for any leakage, deformation, or other phenomena to ensure the sealing and pressure resistance of the pipe fittings.

[0019] Packaging and Storage: In a cleanroom, qualified pipe fittings are vacuum-packed with food-grade plastic film to prevent contamination during transportation and storage. Packaged fittings are then stored in a dry, clean environment, avoiding contact with corrosive substances.

[0020] (III) Beneficial Effects This invention provides a method for preparing a high-purity stainless steel tee fitting. It has the following beneficial effects: 1. The preparation method of this high-cleanliness stainless steel tee pipe fitting involves a series of processes such as laser cutting, hot extrusion molding, electrochemical polishing, pickling and passivation, and ultrasonic cleaning. This effectively eliminates internal defects and surface impurities in the pipe fitting, resulting in low inner wall roughness and high cleanliness. This meets the high cleanliness requirements of fluid transport components in industries such as food and pharmaceuticals, and reduces the risk of fluid contamination.

[0021] 2. The preparation method of this high-purity stainless steel tee pipe fitting involves selecting high-quality food-grade stainless steel raw materials and combining hot extrusion molding and solution treatment processes to make the internal structure of the pipe fitting dense, eliminate stress concentration, improve the strength, toughness and corrosion resistance of the pipe fitting, extend the service life of the pipe fitting, and reduce maintenance and replacement costs during use.

[0022] 3. The preparation method of this high-purity stainless steel tee fitting clearly defines the parameters of each production stage, such as the temperature, pressure, and speed of hot extrusion, and the voltage, time, and temperature of electrochemical polishing, which facilitates quality control during the production process and ensures the stability and consistency of product quality.

[0023] 4. The preparation method of this high-cleanliness stainless steel tee pipe fitting strictly controls the use and residue of chemical agents during pickling, passivation and cleaning processes, and uses deionized water for cleaning to ensure that the pipe fitting is free of harmful chemical residues, meets food-grade safety standards, and reduces environmental pollution. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of a method for preparing a high-purity stainless steel tee fitting according to the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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. Example 1:

[0026] like Figure 1 As shown in the figure, this embodiment of the invention provides a method for preparing a high-purity stainless steel tee fitting, which specifically includes the following steps:

[0027] S1: Raw material selection: 316L stainless steel pipes that meet food-grade standards are selected, and their chemical composition is tested and meets the requirements of GB / T24511-2017.

[0028] S2: Blanking and forming: The stainless steel pipe is cut into appropriate lengths using a laser cutting machine, then heated to 980℃, and hot extruded in a special mold at an extrusion speed of 8mm / s and a pressure of 100MPa to obtain the tee pipe blank.

[0029] S3: Heat treatment: Heat the blank to 1080℃, hold for 1.5 hours, and then cool with water to complete the solution treatment.

[0030] S4: Rough machining: The pipe fittings are rough machined using CNC machine tools to make the pipe fittings initially meet the design requirements.

[0031] S5: Inner wall polishing: The pipe is used as the anode and immersed in the polishing solution. It is then subjected to 10V voltage and 50℃ temperature for 20 minutes to reduce the inner wall roughness to 0.18μm.

[0032] S6: Pickling and passivation: Immerse the pipe fittings in the pickling and passivation solution at 45°C for 12 minutes, and then rinse with deionized water until the pH value is neutral.

[0033] S7: Cleaning treatment: In an ISO 5 cleanroom, use ultrasonic cleaning equipment at a frequency of 50kHz and a temperature of 35℃ for 25 minutes, followed by hot air drying.

[0034] S8: Quality Inspection: After inspection of appearance, dimensions, cleanliness and pressure resistance, all indicators meet the requirements.

[0035] S9: Packaging and Storage: Vacuum packaged in a cleanroom and stored in a dry environment. Example 2:

[0036] like Figure 1 As shown in the figure, this embodiment of the invention provides a method for preparing a high-purity stainless steel tee fitting. The raw material selection is: food-grade 304L stainless steel sheet is used as the raw material.

[0037] Material cutting and forming: After laser cutting, the sheet is heated to 1020℃ and hot extruded at an extrusion speed of 6mm / s and a pressure of 90MPa.

[0038] Subsequent steps: Refer to the heat treatment, rough machining, inner wall polishing, pickling and passivation, cleaning treatment, quality inspection, packaging and storage steps of Example 1. Each parameter is finely adjusted according to the actual situation. The final tee fitting also meets the food-grade high cleanliness standard.

[0039] 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 alterations 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 method for preparing a high-purity stainless steel tee fitting, comprising the following steps: S1: Food-grade austenitic stainless steel sheets or pipes are selected as raw materials, and the chemical composition of the raw materials meets the requirements for food contact materials in GB / T24511-2017. S2: The raw material is cut using laser cutting technology, and the dimensional accuracy is controlled within ±0.1mm. Then the cut material is heated to 950-1050℃ and hot extrusion molding is carried out at 80-120MPa pressure and 5-10mm / s extrusion speed to form a tee pipe blank. S3: The tee fitting blank is subjected to solution treatment, heated to 1050-1100℃, held at the temperature for 1-2 hours, and then rapidly cooled. S4: Use high-precision CNC machine tools to rough machine the solution-treated pipe fittings, and control the machining accuracy within ±0.2mm; S5: The inner wall of the pipe is polished using an electrochemical polishing process. The pipe is used as the anode and immersed in a polishing solution containing phosphoric acid, sulfuric acid, and chromic anhydride. It is then subjected to an electric current treatment for 15-25 minutes at a voltage of 8-12V and a temperature of 45-55℃ to reduce the roughness Ra value of the inner wall of the pipe to below 0.2μm. S6: Place the polished pipe fittings into a pickling and passivation solution consisting of 15-20% nitric acid and 1-3% hydrofluoric acid by volume, immerse at 40-50℃ for 10-15 minutes, and then rinse with deionized water until the pH of the rinsing water is neutral. S7: Transfer the pickled and passivated pipe fittings to an ISO 5 or higher cleanroom, use an ultrasonic cleaning device with a frequency of 40-60kHz and a temperature of 30-40℃, clean with deionized water for 20-30 minutes, wipe dry with a lint-free cloth and dry with hot air at 60-80℃ after cleaning. S8: The pipe fittings are subjected to appearance inspection, size inspection, cleanliness inspection and pressure resistance inspection in sequence. Among them, the cleanliness inspection requires that the number of particles ≥0.5μm in each cubic meter of air does not exceed 1000, and the total number of microbial colonies is ≤10CFU / cm². The pressure resistance inspection involves pressurizing the pipe fittings to 1.5 times the design pressure and holding the pressure for 5-10 minutes. S9: Vacuum-pack qualified pipe fittings with food-grade plastic film in a cleanroom and store them in a dry, clean environment.

2. The method for preparing a high-purity stainless steel tee fitting according to claim 1, characterized in that: The food-grade austenitic stainless steel is 316L or 304L stainless steel.

3. The method for preparing a high-purity stainless steel tee fitting according to claim 1, characterized in that: The rapid cooling method is water cooling.

4. The method for preparing a high-purity stainless steel tee fitting according to claim 1, characterized in that: The polishing solution contains phosphoric acid, sulfuric acid, and chromic anhydride mixed in a specific ratio.

5. The method for preparing a high-purity stainless steel tee fitting according to claim 1, characterized in that: If any of the quality inspection items fails to meet the requirements, the pipe fitting shall be reworked and re-inspected.

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