Welding process for parts of water storage tank of liquid cooling system

Abstract

The invention discloses a welding process for parts of a water storage tank of a liquid cooling system, suspension liquid is needed during welding, the suspension liquid is prepared from deionized water, citric acid monohydrate, nitric acid, hydrofluoric acid, precipitated barium sulfate micro powder, magnesium fluoride micro powder and composite corrosion inhibition dispersion premixed liquid, and the welding process comprises the steps that the parts of the water storage tank are tailor-welded and subjected to electrolytic polishing; argon is filled for closed welding; a suspension and a stainless steel grinding needle are injected into the cavity, and alternating magnetic force polishing is conducted; and discharging waste liquid, and performing high-pressure washing and neutralization. According to the method, a fluid physical network with yield stress is constructed, and a high-viscosity state is maintained in a static non-working area to shield and protect a base material; in a closed weld zone, a magnetic field drives a grinding needle to generate mechanical shearing force to shear and dilute fluid, targeted release of acid liquor softens oxide skin, physical stripping is completed by combining inorganic micro powder friction, and fixed-point removal of blind zone welding spots and synchronous protection of base metal in a non-working zone are achieved.

Description

Technical Field

[0001] This invention relates to the field of liquid cooling system manufacturing and surface treatment technology, specifically to a welding process for parts of a water storage tank in a liquid cooling system. Background Technology

[0002] Austenitic stainless steel water tanks in liquid cooling systems typically require welding assembly during manufacturing. Under the high temperature of welding, a dense layer of metal oxide scale, or weld spots, will form on the surface of the weld and its heat-affected zone. These weld spots are mainly composed of iron and chromium oxides. If they are not thoroughly removed, they can easily cause local pitting corrosion during subsequent operation of the equipment, leading to coolant leakage and seriously affecting the service life of the system. In order to ensure the surface smoothness and corrosion resistance of the inner cavity of the water tank, pickling passivation or electrolytic polishing processes are commonly used in industrial production to treat the inner wall.

[0003] As water storage tank designs become more compact and complex, many cavities develop closed blind areas that are difficult to access directly after the final sealing weld. Since the tank is already in a closed or semi-closed state at this point, conventional surface treatment processes face significant limitations. Traditional free pickling solutions flow uncontrollably within the cavities, failing to effectively target and remove weld spatter with high concentrations. Instead, strong acid comes into contact with and damages the polished base material in non-working areas, causing severe over-corrosion and resulting in overall surface roughening. Furthermore, conventional mechanical grinding methods are limited by the macroscopic dimensions of the tools and the angle of force application, making it impossible to effectively cut and peel into the narrow dead corners and blind areas inside the tank.

[0004] To overcome the spatial constraints of enclosed cavities, the industry has attempted to introduce magnetic polishing technology in conjunction with acidic grinding fluids for internal operations. However, existing fluids lack effective control over their rheological state. If conventional low-viscosity pickling solutions are used directly, the highly corrosive media will still diffuse throughout the cavity, leading to indiscriminate corrosion. If conventional thickeners are added to restrict acid flow, these conventional powders are prone to violent chemical reactions in highly oxidizing mixed acids containing hydrofluoric acid. The accompanying large amount of heat release and gas generation will quickly cause severe pressure build-up in the sealed water tank cavity, posing a very high risk of container rupture. At the same time, conventional organic corrosion inhibitors will rapidly oxidize and degrade in highly oxidizing concentrated nitric acid environments, making it difficult to penetrate deep into internal blind spots and dead zones for effective cutting and peeling. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a welding process for water storage tank parts in liquid cooling systems, solving the problem that simple mechanical polishing is insufficient to effectively cut and peel away internal blind spots and dead angles, resulting in cleaning dead angles and safety hazards.

[0006] An anti-fluoride oxidation suspension for water storage tanks in liquid cooling systems is made from the following raw materials in parts by weight: 49.5-60.5 parts deionized water; 2.0-2.5 parts citric acid monohydrate solid; 20.0-23.0 parts nitric acid with a mass fraction of 68%; 4.0-5.0 parts hydrofluoric acid with a mass fraction of 40%; 10.0-15.0 parts precipitated barium sulfate micro powder; 2.0-3.0 parts magnesium fluoride micro powder; and 1.5-2.0 parts composite corrosion-inhibiting dispersion premix.

[0007] By adopting the above technical solution, the interaction between precipitated barium sulfate micropowder and magnesium fluoride micropowder and the composite corrosion-inhibiting dispersion premix in an acidic aqueous phase establishes a mechanochemical synergistic linkage mechanism between conventional pickling and mechanical polishing. Therefore, the effect of accurately removing weld spots in blind areas and protecting the polished base material in non-working areas is achieved. Precipitated barium sulfate and magnesium fluoride, which are in a thermodynamically stable state, are introduced into the mixed acid. The inorganic powders in the aqueous phase are bridged with the polymer chain segments in the composite corrosion-inhibiting dispersion premix through intermolecular forces, forming a three-dimensional physical network with a specific yield stress, which exhibits Bingham fluid characteristics. Since the coordination state of barium sulfate and magnesium fluoride is saturated, no violent chemical reaction or gas generation occurs inside.

[0008] In the non-working area inside the water tank where there is no high-frequency mechanical disturbance, the yield stress of the suspension keeps it in a high-viscosity gel state, densely covering the polished base material surface, increasing mass transfer resistance, blocking the diffusion path of hydrogen ions and fluoride ions to the metal surface, and achieving dual protection of passivation and physical shielding for the normal base material in conjunction with corrosion inhibitors.

[0009] Driven by an alternating magnetic field, the external grinding media generates high-frequency mechanical shear force in the weld area. When the shear force exceeds the fluid yield stress, the suspension undergoes shear thinning behavior, the local three-dimensional physical network disintegrates, the viscosity drops sharply, and low-viscosity free nitric acid and hydrofluoric acid are released in a local narrow space. Hydrofluoric acid polarizes and cuts the metal oxygen bonds of the weld oxide scale to complete chemical softening, while nitric acid provides a high oxidation potential to maintain the passivation tendency of the metal matrix.

[0010] Barium sulfate and magnesium fluoride have a Mohs hardness lower than that of austenitic stainless steel base material but higher than that of softened oxide scale. Inorganic micro powders moving at high speed with fluid eddies act as flexible micro abrasives to perform friction cutting on loose oxide scale, peel off blind area attachments, and do not produce mechanical scratches on the underlying bright substrate. Citric acid then complexes the free metal ions to prevent secondary hydrolysis and redeposition.

[0011] Preferably, the composite corrosion-inhibiting dispersion premix is ​​made from raw materials comprising the following parts by weight: 65.0-75.0 parts of deionized water; 10.0-15.0 parts of polyethylene glycol 400; and 15.0-20.0 parts of hexamethylenetetramine solid. At room temperature, deionized water and polyethylene glycol 400 are added to a reaction vessel and mixed evenly. Hexamethylenetetramine solid is then slowly added, and mechanical stirring is started at a speed of 300-500 rpm. The temperature is slowly raised to 40-45°C and stirred at a constant temperature for 40-50 minutes. The mixture is then cooled to room temperature to obtain the final product.

[0012] By adopting the above technical solution, polyethylene glycol 400 is used to premix hexamethylenetetramine, which slows down the oxidative degradation rate of organic amine corrosion inhibitors in a strong oxidizing environment, maintains the chemical activity of the corrosion inhibitor during the polishing cycle, and ensures its continuous passivation protection of the substrate in non-target areas.

[0013] A welding process for parts used in water storage tanks of liquid cooling systems, employing the aforementioned anti-fluoride oxidation suspension for water storage tanks of liquid cooling systems, includes the following steps: S1. Weld the main shell, side wall fittings and first side end cover of the austenitic stainless steel water tank together, leave the second side end cover unwelded, keep the cavity semi-open, inject electrolytic polishing liquid for electrolytic polishing, clean and blow dry. S2. High-purity argon gas is introduced into the inner cavity of the water storage tank for replacement, and laser sealing welding is performed on the retained parts under the protection of argon gas. S3. Deionized water, citric acid monohydrate solid, nitric acid, hydrofluoric acid, precipitated barium sulfate micro powder and magnesium fluoride micro powder are added to the reaction vessel and slurryed under high shear. Then, composite corrosion inhibitor dispersion premix is ​​added and mixed evenly to obtain a suspension. S4. Inject the suspension into a closed water tank to immerse the closed weld, insert a stainless steel grinding needle, install a micro-pressure one-way exhaust valve at the injection port, and then perform alternating magnetic polishing. S5. Discharge the suspended waste liquid and stainless steel grinding needles, perform high-pressure water washing and anhydrous sodium carbonate aqueous solution circulation neutralization and rinsing of the inner cavity, and finally rinse with pure water and dry with hot air.

[0014] By adopting the above technical solution, the process achieves a balance between overall internal smoothness and localized weld spot removal by using electrolytic polishing to establish an initial bright surface and alternating magnetic polishing with a rheological suspension. In S3, high-shear pulping ensures uniform dispersion of inorganic micropowder to form thixotropy. In S4, the alternating magnetic field drives the movement of stainless steel grinding needles, providing macroscopic mechanical force to break the yield stress of local fluids and trigger the targeted cleaning mechanism. The micro-pressure one-way exhaust valve releases trace amounts of reactive gas from the parent material, preventing pressure accumulation and rupture of the sealed container. In S5, the fluid kinetic energy of the high-pressure water jet breaks through the yield stress of the residual suspension again, causing the gel-like powder network adhering to the blind area to disintegrate. Combined with sodium carbonate to neutralize residual acid, inorganic particles and residual acid are discharged, eliminating the risk of pipeline blockage and corrosion after the equipment is put into operation.

[0015] Preferably, the specific process parameters for S1 are as follows: the electrolytic polishing solution is a phosphoric acid-sulfuric acid type electrolytic polishing solution; the temperature is controlled at 55–65°C; the applied DC voltage is 10–15V; and the current density is controlled at 10–20A / dm³. 2 The electropolishing time is 5-8 minutes; the specific implementation method of S2 is as follows: high-purity argon gas with a purity ≥99.999% is continuously introduced through the side wall fitting at a flow rate of 10-15 L / min, and the gas is continuously purged for 3-5 minutes; the specific preparation method of S3 is as follows: deionized water and citric acid monohydrate solid are added to a high-shear reactor with a polytetrafluoroethylene liner and stirred until completely dissolved; under the condition of maintaining the temperature at 20-30℃ with jacket circulating water cooling, nitric acid and hydrofluoric acid are slowly added dropwise in sequence; the high-shear disperser is turned on and the speed is set to 1500-2000 rpm, and barium sulfate micro powder and magnesium fluoride micro powder are slowly added while stirring, and high-shear pulping is continued for 25-30 minutes; within 15-30 minutes before the planned polishing operation. Add the composite corrosion inhibitor dispersion premix to the reactor and stir at 300 rpm for 5 minutes to mix evenly; the specific implementation parameters of S4 are as follows: the amount of stainless steel grinding needles added is 5% to 8% of the inner cavity volume of the water storage tank; the opening and closing pressure difference of the micro-pressure one-way exhaust valve is set to 0.01 to 0.03 MPa; the alternating magnetic field speed is set to 1500 to 2500 rpm, and the operation is carried out for 1 to 8 minutes at an ambient temperature of 20 to 35℃; the specific rinsing process of S5 is as follows: use a tubular high-pressure nozzle to extend into the water storage tank and rinse the inner cavity with high-pressure deionized water of 0.3 to 0.5 MPa for 2 to 3 minutes; pump in an anhydrous sodium carbonate aqueous solution with a mass concentration of 2.0% to 3.0% for 3 minutes of circulation rinsing; finally, blow dry with hot air at 60 to 80℃.

[0016] By adopting the above technical solutions, the system stability is improved by precisely controlling the process parameters. The high-shear pulping time and speed parameters ensure that the powder is fully dispersed to form a uniform physical network. The premixed liquid is added 15 to 30 minutes before polishing and is prepared on the spot. The kinetic time difference is used to avoid the risk of oxidation failure of the corrosion inhibitor when it is placed in concentrated nitric acid for a long time. The opening and closing pressure difference of the exhaust valve of 0.01 to 0.03 MPa takes into account the working state of the internal fluid micro-positive pressure and the safety of the container against pressure stagnation. The high-pressure flushing of 0.3 to 0.5 MPa provides sufficient fluid shear force to overcome the adhesion caused by the thixotropic recovery characteristics and achieve efficient cleaning and obstacle removal of the cavity.

[0017] This invention provides a welding process for parts of a water storage tank in a liquid cooling system. It has the following advantages: 1. This invention constructs a Bingham fluid physical network with yield stress by adding precipitated barium sulfate and magnesium fluoride micropowder to mixed acid and cooperating with a composite corrosion-inhibiting dispersion premix. In the static non-working area, the fluid network relies on the yield stress to cover the surface of the base material, blocking the mass transfer of acid to prevent corrosion of the normal base material. In the weld area, the alternating magnetic field drives the grinding needle to generate mechanical shear force exceeding the yield stress, causing the fluid to undergo local shear thinning, releasing free acid to chemically soften the oxide scale, and relying on the mechanical friction force of the inorganic micropowder to complete the physical peeling.

[0018] 2. The precipitated barium sulfate and magnesium fluoride selected in this invention have thermodynamic stability in a strongly oxidizing mixed acid environment, overcoming the defect that conventional fumed silica thixotropic agents easily react with hydrofluoric acid to generate gas, causing container rupture. At the same time, polyethylene glycol is used to coat hexamethylenetetramine to form a premixed solution, which is prepared and used immediately within a specified time before polishing. The kinetic time difference is used to delay the oxidative degradation of organic corrosion inhibitors in concentrated nitric acid, maintaining the chemical stability of the formulation during the polishing cycle.

[0019] 3. After the polishing operation of this invention is stopped, the remaining suspension recovers its viscosity due to thixotropy and adheres to the blind area of ​​the inner wall. It is then rinsed with high-pressure deionized water at 0.3 to 0.5 MPa. The mechanical shear force provided by the water jet can break through the yield stress of the residual fluid again, causing the high-viscosity powder network to disintegrate and transform into a low-viscosity state. Combined with the acid-base neutralization effect of sodium carbonate aqueous solution, the inorganic particles that have lost physical adhesion and the residual acid liquid are smoothly discharged with the water flow, eliminating the risk of pipeline blockage and corrosion when the liquid cooling system is put into operation later. Attached Figure Description

[0020] Figure 1 This is a step diagram of the present invention; Figure 2 This is a perspective view of the water storage tank of the present invention; Figure 3 This is a side view of the water storage tank of the present invention.

[0021] The components are: 1. Main housing; 2. Side wall fittings; 3. First side end cap; 4. Second side end cap. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described 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.

[0023] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0024] Nitric acid, CAS number 7697-37-2, has a mass fraction of 68%. Hydrofluoric acid, CAS No. 7664-39-3, mass fraction 40%; Citric acid monohydrate, CAS No. 5949-29-1; Hexamethylenetetramine, CAS No. 100-97-0; Polyethylene glycol 400, CAS No. 25322-68-3, has an average molecular weight distribution range of 380 to 420. Precipitated barium sulfate, CAS No. 7727-43-7, with a D50 particle size distribution between 0.5μm and 1.5μm and a Mohs hardness of 3.0 to 3.5; Magnesium fluoride, CAS No. 7783-40-6, D50 particle size distribution between 1.0μm and 2.0μm, Mohs hardness of 4.0 to 4.5; Anhydrous sodium carbonate, CAS No. 497-19-8; The stainless steel grinding needle is made of SUS420 martensitic stainless steel, cylindrical in shape, with a diameter of 0.5mm to 1.0mm and a length of 3mm to 5mm, and is magnetically conductive. High-purity argon gas, purity ≥ 99.999%; Deionized water, conductivity <5μS / cm.

[0025] Preparation Example 1: This preparation example provides a method for preparing a composite corrosion-inhibiting dispersion premix, including the following steps: At room temperature, 75.0g of deionized water and 10.0g of polyethylene glycol 400 were added to a reaction vessel and mixed evenly. Then, 15.0g of hexamethylenetetramine solid was slowly added, and mechanical stirring was started at 300rpm. The temperature was slowly raised to 40℃ and stirred at a constant temperature for 40 minutes. After cooling to room temperature, a transparent and viscous composite corrosion-inhibiting dispersion premix was obtained.

[0026] Preparation Example 2: This preparation example provides a method for preparing a composite corrosion-inhibiting dispersion premix, including the following steps: At room temperature, 70.0g of deionized water and 12.5g of polyethylene glycol 400 were added to a reaction vessel and mixed evenly. Then, 17.5g of hexamethylenetetramine solid was slowly added, and mechanical stirring was started at 400 rpm. The temperature was slowly raised to 42°C and stirred at a constant temperature for 45 minutes. After cooling to room temperature, a transparent and viscous composite corrosion-inhibiting dispersion premix was obtained.

[0027] Preparation Example 3: This preparation example provides a method for preparing a composite corrosion-inhibiting dispersion premix, including the following steps: At room temperature, 65.0g of deionized water and 15.0g of polyethylene glycol 400 were added to a reaction vessel and mixed evenly. Then, 20.0g of hexamethylenetetramine solid was slowly added, and mechanical stirring was started at 500 rpm. The temperature was slowly raised to 45°C and stirred at a constant temperature for 50 minutes. After cooling to room temperature, a transparent and viscous composite corrosion-inhibiting dispersion premix was obtained.

[0028] Example 1: This example provides a welding process and targeted weld spatter removal method for parts used in liquid cooling system water tanks. (Refer to the attached document.) Figure 1 -Appendix Figure 3 This includes the following steps: The main shell (1), side wall fittings (2), and first side end cap (3) of the austenitic stainless steel water storage tank are welded together, while the second side end cap (4) is left unwelded, keeping the cavity semi-open. An auxiliary cathode is inserted into the inner cavity of the water storage tank, and a phosphoric acid-sulfuric acid type electrolytic polishing solution is injected. The temperature is controlled at 55°C, a DC voltage of 10V is applied, and the current density is controlled at 10A / dm³. 2 Electropolishing for 5 minutes; drain the electrolyte, rinse the inner cavity with room temperature tap water and deionized water in sequence until neutral, and blow dry with compressed air; High-purity argon gas with a purity ≥99.999% is continuously injected into the inner cavity of the water storage tank at a flow rate of 10L / min for 3 minutes; under argon protection, the second side end cap is aligned with the port and laser-sealed. 60.5 parts by weight of deionized water were added to a high-shear reactor lined with polytetrafluoroethylene, and 2.0 parts by weight of citric acid monohydrate solid was added and stirred until completely dissolved. Under the condition of maintaining the temperature at 20°C by jacket circulating water cooling, 20.0 parts by weight of 68% nitric acid and 4.0 parts by weight of 40% hydrofluoric acid were slowly added dropwise. The high-shear disperser was turned on and the speed was set to 1500 rpm. 10.0 parts by weight of precipitated barium sulfate micro powder and 2.0 parts by weight of magnesium fluoride micro powder were slowly added while stirring, and high-shear slurrying was continued for 25 minutes. 15 minutes before the planned polishing operation, 1.5 parts by weight of the composite corrosion inhibitor dispersion premix obtained in Preparation Example 1 were added to the reactor and stirred at 300 rpm for 5 minutes to mix evenly to obtain a suspension. Inject the above suspension into a closed water tank, ensuring the liquid level completely submerges the final closed weld; add a stainless steel grinding needle, with the amount added at 5% of the inner volume of the water tank; install a sealing plug with a micro-pressure one-way exhaust valve at the external injection port of the water tank, setting the opening and closing pressure difference of the exhaust valve to 0.01MPa; fix the water tank on the worktable of the alternating magnetic polishing machine, set the alternating magnetic field speed to 1500rpm, and run it for 1 minute at an ambient temperature of 20℃; Stop the alternating magnetic field, open the sealing plug, and pour out the suspended waste liquid and stainless steel grinding needle; use a tubular high-pressure nozzle to insert into the water storage tank and flush the inner cavity with 0.3MPa high-pressure deionized water for 2 minutes; pump in an anhydrous sodium carbonate aqueous solution with a mass concentration of 2.0% and circulate it for 3 minutes; finally, rinse with deionized water 3 times and blow dry with 60℃ hot air.

[0029] Example 2: This example provides a welding process and targeted weld spatter removal method for parts used in liquid cooling system water tanks, including the following steps: The main shell (1), side wall fittings (2), and first side end cap (3) of the austenitic stainless steel water storage tank are welded together, while the second side end cap (4) is left unwelded, keeping the cavity semi-open. An auxiliary cathode is inserted into the inner cavity of the water storage tank, and a phosphoric acid-sulfuric acid type electrolytic polishing solution is injected. The temperature is controlled at 60°C, a DC voltage of 12V is applied, and the current density is controlled at 15A / dm³. 2 Electropolishing for 6 minutes; drain the electrolyte, rinse the inner cavity with room temperature tap water and deionized water in sequence until neutral, and blow dry with compressed air; High-purity argon gas with a purity ≥99.999% is continuously injected into the inner cavity of the water storage tank through the side wall fittings at a flow rate of 12L / min for 4 minutes; under argon protection, the second side end cap is aligned with the port and laser-sealed. 55.0 parts by weight of deionized water were added to a high-shear reactor with a polytetrafluoroethylene liner, and 2.2 parts by weight of citric acid monohydrate solid were added and stirred until completely dissolved. Under the condition of maintaining the temperature at 25°C by jacket circulating water cooling, 21.5 parts by weight of 68% nitric acid and 4.5 parts by weight of 40% hydrofluoric acid were slowly added dropwise. The high-shear disperser was turned on and the speed was set to 1800 rpm. 12.5 parts by weight of precipitated barium sulfate micro powder and 2.5 parts by weight of magnesium fluoride micro powder were slowly added while stirring, and high-shear slurrying was continued for 28 minutes. 20 minutes before the planned polishing operation, 1.8 parts by weight of the composite corrosion inhibitor dispersion premix obtained in Preparation Example 2 were added to the reactor and stirred at 300 rpm for 5 minutes to mix evenly, thus obtaining a suspension. Inject the above suspension into a closed water tank, ensuring the liquid level completely submerges the final closed weld; add a stainless steel grinding needle, with the dosage calculated as 6.5% of the water tank's inner volume; install a sealing plug with a micro-pressure one-way vent valve at the external injection port of the water tank, setting the vent valve's opening and closing pressure difference to 0.02 MPa; fix the water tank on the worktable of an alternating magnetic polishing machine, set the alternating magnetic field speed to 2000 rpm, and run it for 3 minutes at an ambient temperature of 25°C; Stop the alternating magnetic field, open the sealing plug, and pour out the suspended waste liquid and stainless steel grinding needle; use a tubular high-pressure nozzle to insert into the water storage tank and flush the inner cavity with 0.4MPa high-pressure deionized water for 2.5 minutes; pump in an anhydrous sodium carbonate aqueous solution with a mass concentration of 2.5% and circulate it for 3 minutes; finally, rinse with deionized water 3 times and blow dry with 70℃ hot air.

[0030] Example 3: This example provides a welding process and targeted weld spatter removal method for parts used in liquid cooling system water tanks, including the following steps: The main shell (1), side wall fittings (2), and first side end cap (3) of the austenitic stainless steel water storage tank are welded together, while the second side end cap (4) is left unwelded, keeping the cavity semi-open. An auxiliary cathode is inserted into the inner cavity of the water storage tank, and a phosphoric acid-sulfuric acid type electrolytic polishing solution is injected. The temperature is controlled at 65°C, a DC voltage of 15V is applied, and the current density is controlled at 20A / dm³. 2 Electropolishing for 8 minutes; drain the electrolyte, rinse the inner cavity with room temperature tap water and deionized water in sequence until neutral, and blow dry with compressed air; High-purity argon gas with a purity ≥99.999% is continuously introduced into the inner cavity of the water storage tank through the side wall fittings at a flow rate of 15L / min for 5 minutes; under argon protection, the second side end cap is aligned with the port and laser-sealed. 49.5 parts by weight of deionized water were added to a high-shear reactor with a polytetrafluoroethylene liner, and 2.5 parts by weight of citric acid monohydrate solid were added and stirred until completely dissolved. Under the condition of maintaining the temperature at 30°C by jacket circulating water cooling, 23.0 parts by weight of 68% nitric acid and 5.0 parts by weight of 40% hydrofluoric acid were slowly added dropwise. The high-shear disperser was turned on and the speed was set to 2000 rpm. 15.0 parts by weight of precipitated barium sulfate micro powder and 3.0 parts by weight of magnesium fluoride micro powder were slowly added while stirring, and high-shear slurrying was continued for 30 minutes. 30 minutes before the planned polishing operation, 2.0 parts by weight of the composite corrosion inhibitor dispersion premix obtained in Preparation Example 3 were added to the reactor and stirred at 300 rpm for 5 minutes to mix evenly, thus obtaining a suspension. Inject the above suspension into a closed water tank, ensuring the liquid level completely submerges the final closed weld; add a stainless steel grinding needle, with the amount added at 8% of the inner volume of the water tank; install a sealing plug with a micro-pressure one-way vent valve at the external injection port of the water tank, setting the opening and closing pressure difference of the vent valve to 0.03 MPa; fix the water tank on the worktable of an alternating magnetic polishing machine, set the alternating magnetic field speed to 2500 rpm, and run it for 8 minutes at an ambient temperature of 35°C; Stop the alternating magnetic field, open the sealing plug, and pour out the suspended waste liquid and stainless steel grinding needle; use a tubular high-pressure nozzle to insert into the water storage tank and flush the inner cavity with 0.5MPa high-pressure deionized water for 3 minutes; pump in an anhydrous sodium carbonate aqueous solution with a mass concentration of 3.0% and circulate it for 3 minutes; finally, rinse with deionized water 3 times and blow dry with 80℃ hot air.

[0031] Comparative Example 1 differs from Example 2 in that barium sulfate powder and magnesium fluoride powder are not added in step three, and water is used to make up the corresponding weight proportions, while the rest are the same.

[0032] Comparative Example 2 differs from Example 2 in that in step three, precipitated barium sulfate powder and magnesium fluoride powder are replaced with equal parts by weight of fumed silica, while the rest are the same.

[0033] Comparative Example 3 differs from Example 2 in that magnesium fluoride powder is not added in step three, and water is used to make up the corresponding weight parts, while the rest are the same.

[0034] Comparative Example 4 differs from Example 2 in that the composite corrosion-inhibiting dispersion premix is ​​not used in step three. Instead, hexamethylenetetramine solid, with a mass equivalent to that contained in the premix, is directly added to the reaction vessel along with nitric acid and hydrofluoric acid. All other aspects are the same.

[0035] Comparative Example 5 differs from Example 2 in that stainless steel grinding needles are not used in step four, and the alternating magnetic polishing machine is not started for processing. Instead, the samples are simply soaked for the same amount of time. All other steps are the same.

[0036] Test Example 1 uses an MCR302 rotational rheometer equipped with a coaxial cylindrical testing system, and the test temperature is kept constant at 25℃. Take an appropriate amount of each group of test solutions and put them into the test cylinder. Let it stand for 5 minutes to eliminate the shear history during sample addition. The shear rate range is set to 0.1 s. -1 up to 1000s -1 Data points were collected using a logarithmic distribution, and the corresponding changes in shear stress and apparent viscosity were recorded. In the first stage, a low shear rate was applied and maintained for 60 seconds, and the initial viscosity was recorded. The second stage involves a sudden jump to a high shear rate, which is maintained for 60 seconds, and the viscosity is recorded after shear thinning. In the third stage, the viscosity was restored to a low shear rate and maintained for 120 seconds, and the viscosity recovery process and recovery rate were recorded.

[0037] Table 1. Rheological property parameters of each tested fluid

[0038] According to the data in Table 1, the suspensions of Examples 1 to 3 all exhibited significant yield stress, and the yield stress increased with the increase of the mass fraction of inorganic filler. At low shear rates, the initial viscosity of the examples was at a high level, indicating that they could maintain a stable physical network structure under static or very low disturbance conditions. When the shear rate suddenly increased to 1000 s⁻¹, the viscosity of the examples was significantly lower. -1 When the high shear force was removed, the apparent viscosity of each embodiment rapidly decreased to an extremely low level, exhibiting strong shear thinning behavior; after the high shear force was removed, the viscosity recovered to more than 84% within 120 seconds, demonstrating good thixotropy.

[0039] Inside the water tank, on the surface of the polished base material in the non-working area, the suspension is in a static state. Due to its yield stress and high initial viscosity, the high-density inorganic powder forms a dense three-dimensional network through intermolecular forces and the bridging effect of polyethylene glycol 400. This network, like a solid gel, physically covers the metal surface, blocking the mass transfer and diffusion paths of highly corrosive hydrogen ions and fluoride ions, thus forming a static physical shielding protection for the base material in the non-working area. In the closed weld area, the alternating magnetic field drives the high-speed movement of the magnetic needle, generating a high-frequency microscopic shear force much greater than the yield stress. Under the action of this shear force... The suspension rapidly undergoes shear thinning, instantly tearing apart the original physical network; low-viscosity free nitric acid and hydrofluoric acid are precisely released in a localized, extremely small space, targeting and corroding the oxide scale at the weld; the pure aqueous acid solution in Comparative Example 1 lacks rheological regulation, does not possess yield stress and shear thinning characteristics, and cannot form a physical protective layer, which would lead to uncontrolled uniform corrosion throughout the entire cavity in practical applications; the thixotropic viscosity recovery capability further ensures that the residual liquid can still maintain a certain suspension stability after the polishing operation, and can prevent inorganic powder from hardening in the blind area when combined with subsequent high-pressure water washing.

[0040] Test Example 2: Prepare 4 sets of acid-resistant polytetrafluoroethylene rigid containers, each with a volume of 500mL, and assemble a high-precision digital pressure sensor with a range of 0-1.0MPa and a precision gas collection bag. Inject 350 mL of the suspension to be tested into each group of containers, and quickly tighten the sealing cap to ensure good airtightness of the device; Each set of test devices was placed in a constant temperature water bath at 25℃ and left to stand for 24 hours. The pressure changes inside each group of containers were continuously recorded using a data acquisition instrument, with data recorded every hour. After 24 hours, gas samples were collected from each group of gas collection bags and qualitative analysis was performed using a Fourier transform infrared spectrometer.

[0041] Table 2. Data on pressure variation inside a sealed container over time.

[0042] According to the data in Table 2, the pressure increment of the suspensions in Examples 1 to 3 remained within 0.01 MPa during 24 hours of standing in a closed container, maintaining a relatively stable atmospheric pressure. The gas qualitative analysis results showed that the samples in the examples mainly contained trace amounts of acid mist and water vapor volatilized by heat, and no newly generated reaction gases were detected. Comparative Example 2 showed a rapid pressure increase trend in the early stage of standing, reaching 0.237 MPa after 4 hours, which eventually caused the container to exceed the sensor range and rupture. Infrared spectroscopy analysis confirmed that a large amount of silicon tetrafluoride was present in the gas collected in Comparative Example 2.

[0043] Based on the technical mechanism of this invention, the barium sulfate and magnesium fluoride selected in the examples exhibit extremely high thermodynamic stability in a mixed acid mixture of highly oxidizing concentrated nitric acid and highly corrosive hydrofluoric acid; due to Ba 2+ Mg 2+ SO4 2- and F - The coordination state of the powder is extremely saturated, and even in environments with high fluoride ion concentrations, no dissolution or redox reactions will occur. This chemical inertness ensures that the powder, suspended in a sealed water tank cavity that is prone to heating due to the accumulation of reaction heat, will not generate a large amount of gas due to its own chemical reaction. Comparative Example 2 uses conventional fumed silica as a thixotropic agent. Silica reacts violently with hydrofluoric acid in an aqueous solution to generate silicon tetrafluoride gas. This reaction not only destroys the physical structure of the rheological network, but the accompanying large amount of gas generation causes extremely serious pressure buildup problems in the sealed space. The test results of the examples demonstrate that the specific inert dual-powder compound is not only the key to constructing the rheological network, but also the core factor in avoiding the risk of gas generation and explosion during sealed pickling. Minor pressure fluctuations can be completely released through the design of a one-way exhaust valve, ensuring the absolute safety of welding of water tank parts and targeted removal of weld spots in industrial production.

[0044] Test Example 3: Each group of water storage tanks that have completed the full set of process treatments is mechanically cut open along the longitudinal centerline, and a sample with a size of 10mm×10mm is cut from the inner wall away from the closed weld area. The average surface roughness Ra of each group of samples was tested using a white light interferometer. Five different locations were randomly selected for scanning and measurement of each group of samples, and the average value was recorded. Each group of samples was connected to copper wires on the back and then cold-mounted and encapsulated with epoxy resin, leaving 1cm of the front side intact. 2 The working area is used as the test surface; Potentiodynamic polarization curves were tested using a three-electrode electrochemical workstation, with a saturated calomel electrode as the reference electrode and a platinum sheet as the auxiliary electrode. The test environment was a 3.5 wt% sodium chloride aqueous solution at room temperature. The working electrode was immersed in the test solution and left to stand for 30 minutes to obtain a stable open circuit potential. Then, a potentiodynamic scan was performed at a scan rate of 1 mV / s. The scan range was from -0.5 V at the open circuit potential to the potential point where pitting corrosion occurred due to a sharp increase in anodic current density. The polarization curve was recorded and the pitting breakdown potential Eb was extracted.

[0045] Table 3. Surface roughness and electrochemical pitting breakdown potential data of the bright area outside the weld seam.

[0046] According to the data in Table 3, the surface roughness of the non-weld bright area after treatment in Examples 1 to 3 changed very little, and the Ra value remained at around 0.15 μm after treatment, which was comparable to the level of the blank control group. Moreover, its pitting breakdown potential remained between 389 mV and 405 mV, and no obvious passivation film degradation phenomenon was observed. After treatment, the surface roughness of the sample in Comparative Example 1 increased sharply to 0.824 μm, and the pitting breakdown potential decreased significantly to 127 mV. After treatment, the roughness of the sample in Comparative Example 4 increased to 0.415 μm, and the breakdown potential decreased to 236 mV. The roughness and potential data of Comparative Example 3 were similar to those of the Examples.

[0047] Due to the lack of a rheological network constructed from inorganic micropowders, the conventional aqueous acid solution in Comparative Example 1 underwent unrestricted fluid convection throughout the entire internal cavity during equipment operation; the free-state strong acid directly contacted the substrate surface in non-operating areas, causing the dense passivation layer formed by previous electrolytic polishing to be peeled off over a large area and severely over-corroded, resulting in roughening of the substrate and a precipitous decrease in pitting corrosion resistance.

[0048] In the static non-working area, the embodiment can effectively block the diffusion and mass transfer of hydrogen ions and fluoride ions to the metal surface by means of a high-viscosity physical network; the Mohs hardness of precipitated barium sulfate and magnesium fluoride is lower than that of austenitic stainless steel matrix. In the fluid disturbance generated by the ambient magnetic field, these flexible micro abrasives will not cause mechanical cutting and micro-scratches to the underlying bright matrix, thus ensuring the optical smoothness of the original surface.

[0049] Comparative Example 4 data shows that, without the protection of a premixing process, directly adding hexamethylenetetramine corrosion inhibitor to a solution containing high concentrations of nitric acid and hydrofluoric acid results in a strong oxidizing environment that causes rapid oxidative degradation of organic amine corrosion inhibitor molecules. The ineffective corrosion inhibitor cannot form an effective adsorption protective film on the metal surface, leading to localized corrosion in non-working areas. This invention, through a composite corrosion-inhibiting dispersion premix formed by polyethylene glycol coating of hexamethylenetetramine, and the precise timing of its addition just before use, effectively maintains the chemical activity of the corrosion inhibitor during the polishing cycle. Combined with static physical shielding, this achieves complete protection of the substrate material in non-targeted areas.

[0050] Test Example 4: Using wire cutting equipment, each group of water storage tanks that have completed the weld spot removal process is longitudinally cut along the closed weld of the second side end cover to obtain a semi-circular sample containing the inner weld and heat-affected zone. A large amount of coolant is introduced during the cutting process to prevent secondary oxidation. The semi-circular ring sample was placed in an ultrasonic cleaning tank filled with anhydrous ethanol and ultrasonically cleaned at a frequency of 40 kHz for 5 minutes to remove the cutting debris and residual coolant adhering to the surface. After removal, it was dried with cold air. The lightness L value of the heat-affected zone of the weld in the blind area of ​​the inner wall of the sample was measured using a spectrophotometer. The measuring aperture was set to 4 mm and the light source was D65. Eight test points were randomly selected along the weld direction for each group of samples. The L value after treatment was recorded. At the same time, the L value of the original weld area without weld spot removal treatment was measured as the reference before treatment, and the L value of the bright base material area after standard electrolytic polishing was measured as the target reference. The oxide scale removal rate is calculated using the formula: (L value after treatment - L value before treatment) / (Standard L value of the parent material - L value before treatment) × 100%.

[0051] Table 4. Data on brightness L* values ​​and oxide scale removal rates before and after treatment of closed weld areas.

[0052] According to the data in Table 4, the oxide scale removal rate of Examples 1 to 3 all reached over 92%, and the L value of the closed blind weld after treatment was very close to the standard value of the bright base material, indicating that the stubborn heat-affected oxide scale inside the blind weld was completely removed. In Comparative Example 5, under the condition of only static soaking with chemical agents without the intervention of alternating magnetic field and magnetic needle, the oxide scale removal rate was only 6.98%, and the weld spot was basically not damaged. Comparative Example 1 used conventional pickling solution without the addition of inorganic powder combined with magnetic grinding, and the removal rate was 68.61%. In Comparative Example 3, the magnesium fluoride micro powder was removed from the formula and only barium sulfate was retained, and the removal rate remained at 83.26%.

[0053] Comparative Example 5 data conversely confirms that under static conditions, the yield stress of the suspension restricts the mass transfer of hydrogen and fluoride ions, and the high-viscosity physical network is not broken, thus preventing active corrosion of the metal surface. In the example, an alternating magnetic field drives a large-sized stainless steel grinding needle to generate high-frequency impacts in the weld area. This macroscopic mechanical shear force breaks through the yield stress of the fluid, triggering shear thinning. The spatial physical network is torn at the tip of the magnetic needle, and the free nitric acid and hydrofluoric acid encapsulated inside are targeted and released in the narrow local space of the weld. The hydrofluoric acid polarizes and cuts the Fe-O and Cr-O bonds in the oxide scale to complete chemical softening, while the nitric acid provides a high oxidation potential to maintain the passivation tendency of the matrix.

[0054] Based on chemical softening, the suspended powder plays a physical peeling role as a flexible micro abrasive. Comparative Example 1 lacks micron-sized inorganic powder, and the magnetic needle with a macroscopic size alone cannot effectively cut the oxide scale deep into the micro-pits. Moreover, the diffusion of free acid in the entire cavity leads to insufficient concentration of active material in the blind area, resulting in low overall peeling efficiency. Comparative Example 3 lacks magnesium fluoride and relies solely on precipitated barium sulfate with a Mohs hardness of 3.0 to 3.5. Due to the low hardness of barium sulfate, its cutting force on the softened dense oxide layer is insufficient. This example introduces magnesium fluoride with a Mohs hardness of 4.0 to 4.5, filling the gap between barium sulfate and austenitic stainless steel base material in terms of hardness gradient. The barium sulfate and magnesium fluoride micro powder, moving at high speed with the fluid vortex, act as kinetic micro abrasives, continuously frictionally cutting the softened loose oxide scale and completely peeling it off from the underlying matrix. The peeled metal ions are then complexed with citric acid, avoiding secondary hydrolysis and deposition, and finally achieving efficient cleaning of the blind area of ​​the closed cavity.

[0055] Test Example 5: Collect 500 mL of mid-stage rinse water samples from the drain outlet at the bottom of the water tank using a clean polyethylene sampling bottle, and seal and store in the dark. The turbidity of each group of water samples was measured using a portable scattering light turbidimeter. The instrument zero point was calibrated with deionized water before each measurement. Each group of water samples was measured in parallel three times and the average value was taken. Take 100 mL of water sample and filter it through a polyethersulfone microporous membrane with a pore size of 0.22 μm under vacuum to remove solid suspended particles in the water and collect the clear filtrate. The filtrate was analyzed using an ion chromatograph equipped with an anion exchange column, with a sodium carbonate-sodium bicarbonate mixed solution used as the eluent, and the mass concentrations of fluoride and sulfate ions in the filtrate were determined.

[0056] Table 5. Test data on anion concentration and turbidity in the final rinsing solution.

[0057] According to the data in Table 5, the concentrations of fluoride ions and sulfate ions in the final rinsing solutions of Examples 1 to 3 were all at extremely low levels, and the turbidity test value dropped to below 1.0 NTU, with all indicators approaching the background value of deionized water. However, a high concentration of fluoride ions and sulfate ions was still detected in the last rinsing solution of the low-pressure rinsing control group, with a turbidity value as high as 16.74 NTU, indicating that there were still a lot of inorganic powder and acid residues in the cavity.

[0058] After the alternating magnetic polishing operation is completed, the external magnetic field is removed. The residual suspension inside the water tank reconstructs a three-dimensional physical network in a very short time by relying on the interaction force between polyethylene glycol and powder. The viscosity recovers, and a retention layer with high yield stress is formed in blind areas such as closed welds and side wall pipe connections. The fluid shear force generated by conventional gravity drainage or low-pressure water flow of 0.15MPa is lower than the yield stress of the retention layer and cannot destroy the powder network, resulting in inorganic particles and encapsulated residual acid being trapped in the dead corners of the inner cavity.

[0059] The embodiment uses high-pressure deionized water at 0.3MPa to 0.5MPa with a tubular nozzle for rinsing. The high-pressure water jet provides great fluid kinetic energy and macroscopic shear force. This high-intensity mechanical disturbance instantly breaks through the yield stress of the residual suspension, triggering the shear thinning effect again. The dense powder network attached to the inner wall disintegrates, changing from a high-viscosity gel state to a low-viscosity fluid state, losing its physical adhesion to the metal surface. Subsequently, the pumped-in anhydrous sodium carbonate solution eliminates the chemical activity of residual nitric acid and hydrofluoric acid through acid-base neutralization reaction, converting the highly corrosive fluoride ions into a soluble state. The disintegrated precipitated barium sulfate, magnesium fluoride microparticles, and neutralization products lose their suspension support in the low-viscosity aqueous phase and are completely discharged from the semi-open cavity along with the rinsing water flow. The synergistic obstacle removal mechanism of fluid mechanics and thixotropic materials ensures that the liquid cooling system's water tank has no hidden dangers of particle blockage and pitting corrosion before being put into use.

[0060] 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 fluoride-resistant suspension for use in water storage tanks of liquid cooling systems, characterized in that, The anti-fluoride oxidation suspension is made from raw materials comprising the following parts by weight: 49.5-60.5 parts deionized water; 2.0-2.5 parts citric acid monohydrate solid; 20.0-23.0 parts nitric acid with a mass fraction of 68%; 4.0-5.0 parts hydrofluoric acid with a mass fraction of 40%; 10.0-15.0 parts precipitated barium sulfate micro powder; 2.0-3.0 parts magnesium fluoride micro powder; and 1.5-2.0 parts composite corrosion-inhibiting dispersion premix.

2. The fluoride-resistant suspension for a water storage tank in a liquid cooling system according to claim 1, characterized in that, The anti-fluoride oxidation suspension interacts with the composite corrosion-inhibiting dispersion premix in an acidic aqueous phase through the interaction of the precipitated barium sulfate micropowder and the magnesium fluoride micropowder.

3. The fluoride-resistant suspension for a water storage tank in a liquid cooling system according to claim 1, characterized in that, The composite corrosion-inhibiting dispersion premix is ​​made from raw materials comprising the following parts by weight: 65.0-75.0 parts deionized water; 10.0-15.0 parts polyethylene glycol 400; and 15.0-20.0 parts hexamethylenetetramine solid.

4. A welding process for parts of a water storage tank in a liquid cooling system, wherein an anti-fluoride oxidation suspension for a water storage tank in a liquid cooling system is provided according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Weld the main shell (1), side wall fittings (2) and first side end cap (3) of the austenitic stainless steel water storage tank, leave the second side end cap (4) unwelded, keep the cavity semi-open, inject electrolytic polishing liquid for electrolytic polishing, clean and blow dry. S2. High-purity argon gas is introduced into the inner cavity of the water storage tank for replacement, and laser sealing welding is performed on the retained parts under the protection of argon gas. S3. Deionized water, citric acid monohydrate solid, nitric acid, hydrofluoric acid, precipitated barium sulfate micro powder and magnesium fluoride micro powder are added to the reaction vessel and slurryed under high shear. Then, composite corrosion inhibitor dispersion premix is ​​added and mixed evenly to obtain a suspension. S4. The suspension is injected into a closed water tank to immerse the closed weld, a stainless steel grinding needle is inserted, and after installing a micro-pressure one-way exhaust valve at the injection port, alternating magnetic polishing is performed. S5. Discharge the suspended waste liquid and stainless steel grinding needles, perform high-pressure water washing and anhydrous sodium carbonate aqueous solution circulation neutralization and rinsing of the inner cavity, and finally rinse with pure water and dry with hot air.

5. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific process parameters for S1 are as follows: the electrolytic polishing solution is a phosphoric acid-sulfuric acid type electrolytic polishing solution; the temperature is controlled at 55-65℃; the applied DC voltage is 10-15V; and the current density is controlled at 10-20A / dm³. 2 The electropolishing time is 5 to 8 minutes.

6. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific implementation method of S2 is as follows: high-purity argon gas with a purity ≥99.999% is continuously introduced through the side wall fitting at a flow rate of 10-15L / min, and the gas is continuously purged for 3-5 minutes.

7. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific preparation method of S3 is as follows: Deionized water and citric acid monohydrate solid are added to a high-shear reactor with a polytetrafluoroethylene liner and stirred until completely dissolved; under the condition of maintaining the temperature at 20-30°C by jacket circulating water cooling, nitric acid and hydrofluoric acid are added dropwise in sequence; a high-shear disperser is turned on and the speed is set to 1500-2000 rpm, and barium sulfate micro powder and magnesium fluoride micro powder are slowly added while stirring, and high-shear pulping is continued for 25-30 minutes; 15-30 minutes before the planned polishing operation, the composite corrosion inhibitor dispersion premix is ​​added to the reactor and stirred at 300 rpm for 5 minutes to mix evenly.

8. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific preparation method of the composite corrosion inhibitor dispersion premix is ​​as follows: at room temperature, deionized water and polyethylene glycol 400 are added to a reaction vessel and mixed evenly. Hexamethylenetetramine solid is slowly added, and mechanical stirring is turned on with a speed of 300-500 rpm. The temperature is slowly raised to 40-45℃ and stirred at a constant temperature for 40-50 minutes. After cooling to room temperature, a transparent and viscous composite corrosion inhibitor dispersion premix is ​​obtained.

9. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific implementation parameters of S4 are as follows: the amount of stainless steel grinding needles added is calculated as 5% to 8% of the inner volume of the water storage tank; the opening and closing pressure difference of the micro-pressure one-way exhaust valve is set to 0.01 to 0.03 MPa; the rotation speed of the alternating magnetic field is set to 1500 to 2500 rpm, and it is run for 1 to 8 minutes at an ambient temperature of 20 to 35℃.

10. The welding process for a water storage tank part in a liquid cooling system according to claim 4, characterized in that, The specific rinsing process of S5 is as follows: a tubular high-pressure nozzle is inserted into the water storage tank, and the inner cavity is rinsed with high-pressure deionized water at 0.3-0.5 MPa for 2-3 minutes; an anhydrous sodium carbonate aqueous solution with a mass concentration of 2.0%-3.0% is pumped in and circulated for 3 minutes; finally, hot air at 60-80℃ is introduced to dry it.

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