Efficient hot galvanizing process

Abstract

The invention relates to the field of chemistry, and discloses an efficient hot galvanizing process which comprises the following steps: degreasing: degreasing a workpiece at 40-50 DEG C by using a degreasing agent, and meanwhile, assisting in degreasing by adopting ultrasonic vibration or mechanical stirring; acid pickling is conducted, specifically, the degreased workpiece is subjected to acid pickling at the temperature of 20-30 DEG C through an acid pickling solution containing 15-25% of hydrochloric acid and 0.5-1% of a hydrogel acid mist inhibitor; three-stage countercurrent rinsing is adopted, and the workpiece obtained after acid pickling is washed with water; assistant plating: dipping the washed workpiece in a plating assistant at 60-70 DEG C for 3-8 minutes, and carrying out assistant plating treatment; and hot dipping. By adding the hydrogel acid mist inhibitor, volatilization of hydrochloric acid is inhibited, acid mist emission is reduced, pollution to the workshop environment and the corrosion risk to equipment are reduced, the three-stage countercurrent rinsing process is adopted, the washing efficiency is improved, and the water consumption is reduced while it is guaranteed that residual acid liquid on the surface of a workpiece is cleaned away.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, specifically to an efficient hot-dip galvanizing process. Background Art

[0002] As an important process widely used in the protection of steel products, hot-dip galvanizing plays a crucial role in many industries such as construction, transportation, and electricity. With the acceleration of the global industrialization process and the continuous improvement of the requirements for product quality and service life, the hot-dip galvanizing process faces an urgent need for continuous upgrading. In the current environment that emphasizes sustainable development, hot-dip galvanizing not only needs to ensure that the coating has good protective performance, but also needs to achieve energy conservation, emission reduction, and pollution reduction during the production process to conform to the environmental protection concept. At the same time, with the continuous innovation of materials science and mechanical manufacturing technology, higher standards are also put forward for the hot-dip galvanizing process in terms of improving production efficiency and meeting the needs of diverse workpieces.

[0003] In the traditional process, a large amount of acid mist is emitted during the pickling process, which causes serious damage to the workshop environment and equipment. The water consumption for water washing is large, and the wastewater discharge is large, thus polluting the environment and affecting the environmental protection performance. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides an efficient hot-dip galvanizing process to solve the problems that in the traditional process, a large amount of acid mist is emitted during the pickling process, the water consumption for water washing is large, and the wastewater discharge is large, thus polluting the environment and affecting the environmental protection performance.

[0005] To achieve the above purposes, the present invention is realized through the following technical solutions: The efficient hot-dip galvanizing process includes the following steps: S1. Degreasing: Degrease the workpiece with a degreasing agent at 40 - 50°C, and at the same time, use ultrasonic vibration or mechanical stirring to assist degreasing; S2. Pickling: For the degreased workpiece, use a pickling solution containing 15% - 25% hydrochloric acid and adding 0.5% - 1% hydrogel acid mist inhibitor to pickle at 20 - 30°C; S3. Water washing: Adopt three-stage countercurrent rinsing to wash the pickled workpiece; S4. Fluxing: Immerse the water-washed workpiece in a fluxing agent at 60 - 70°C for 3 - 8 minutes to perform fluxing treatment; S5. Hot-dip galvanizing: Melt the zinc liquid to 450 - 470°C through an intermediate frequency induction furnace, and use a sling to immerse the fluxed workpiece into the zinc liquid at a speed of 50 - 100 mm / s for hot-dip galvanizing; S6. Passivation: Use a passivation solution to passivate the hot-dip galvanized workpiece at 30 - 40°C; S7, Surface treatment: For the passivated workpieces, an environmentally friendly rust preventive oil is applied at a workpiece surface temperature of ≤ 50 °C, and then dried by hot air circulation at 60 - 80 °C for 5 - 10 minutes.

[0006] By adopting the above technical solution, the volatilization of hydrochloric acid is inhibited, the acid mist emission is reduced, the pollution to the workshop environment and the corrosion risk to the equipment are lowered, the water washing efficiency is improved, while ensuring the residual acid liquid on the workpiece surface is washed away, the water consumption is reduced, and further the waste water emission is decreased, realizing the improvement of environmental protection performance in the production process, and solving the problems of large acid mist emission, large water consumption for water washing, and large waste water emission in the pickling process of the traditional process, thus causing environmental pollution and affecting the environmental protection performance.

[0007] Preferably, the degreasing treatment time in S1 is 5 - 15 minutes, the Fe concentration of the pickling solution in S2 < 80 g / L, the pickling time is 10 - 30 minutes, and a fiberglass pickling tank is used. 2+

[0008] Preferably, the first tank of the three - stage countercurrent rinsing in S3 is circulating water with a conductivity < 500 μS / cm, the last tank is deionized water with a conductivity < 10 μS / cm, and the single - tank dipping time is 2 - 5 minutes.

[0009] Preferably, the hot dip plating time in S5 is determined according to the workpiece characteristics, the plating lifting speed is 60 - 120 mm / s, air cooling is carried out for 10 - 20 seconds after plating lifting, and then water cooling is carried out in a water cooling tank with a water temperature of 20 - 30 °C until ≤ 60 °C. The workpiece characteristics include workpiece thickness and material. The flow rate of the zinc bath into which the workpiece is immersed is 0.2 - 0.5 m / s. The pH value of the passivation solution in S6 is 4.8 - 5.2, the passivation treatment time is 20 - 60 seconds. What components does the environmentally friendly rust preventive oil in S7 include, the coating thickness is 1 - 3 μm, and the contact angle of the workpiece surface after oil coating > 90°.

[0010] Preferably, the zinc bath comprises the following raw materials by mass percentage: 5% - 11% aluminum, 0.5% - 3% magnesium, 0.01% - 0.1% rare earth, 0.1% - 0.5% silicon, and the balance is zinc.

[0011] Preferably, the preparation method of the zinc bath is: S501. Add zinc to an intermediate frequency induction furnace by mass percentage. When the zinc melts into a solution at a temperature of 450 - 470 °C, add aluminum, magnesium, and silicon, and at the same time perform stirring at a stirring speed of 100 - 200 rpm for 15 - 30 minutes to form a mixed solution; S502. Mix rare earth and zinc in a ratio of 1:9 - 11 by mass, heat to 600 - 700 °C, and at the same time stir at a stirring speed of 150 - 250 rpm for 30 - 45 minutes to make a zinc-rare earth master alloy; S503. Add the zinc-rare earth master alloy to the mixed solution and continue stirring for 10 - 20 minutes to evenly disperse the zinc-rare earth master alloy in the mixed solution to obtain a zinc solution.

[0012] Preferably, the fluxing agent comprises raw materials in the following mass percentages: zinc chloride 8% - 15%, ammonium chloride 7% - 12%, alkyl polyglycoside 3% - 8%, modified cellulose 2% - 5%, hexamethylenetetramine 0.5% - 2%, sodium benzoate 0.3% - 1%, citric acid 1% - 3%, ascorbic acid 0.1% - 0.5%, and the balance is deionized water. The modified cellulose comprises hydroxypropyl methylcellulose.

[0013] Preferably, the preparation method of the fluxing agent is as follows: S401. Add deionized water to a reaction kettle with a stirring device by mass percentage, perform stirring at a speed of 80 - 150 rpm, and then successively add zinc chloride and ammonium chloride, and stir for 10 - 15 minutes to completely dissolve them; S402. Then add alkyl polyglycoside and modified cellulose, continue stirring for 15 - 20 minutes, after they are fully dispersed, add hexamethylenetetramine, sodium benzoate, citric acid, and ascorbic acid, and continuously stir for 20 - 30 minutes to uniformly mix all components to obtain the fluxing agent.

[0014] Preferably, the passivating solution comprises raw materials in the following mass percentages: sodium molybdate 8% - 12%, sodium tungstate 3% - 6%, aminotrimethylenephosphonic acid 1.5% - 3%, citric acid 0.8% - 1.5%, polyethylene glycol 0.1% - 0.5%, sulfuric acid 0.5% - 1.2%, and the balance is deionized water.

[0015] Preferably, the preparation method of the passivating solution is as follows: S601. Add deionized water to a corrosion-resistant liquid preparation tank by mass percentage, then add sodium molybdate and sodium tungstate, and perform stirring at a stirring speed of 100 - 180 rpm for 15 - 20 minutes to fully dissolve them; S602. Then add aminotrimethylenephosphonic acid and citric acid, continue stirring for 20 - 30 minutes, add polyethylene glycol, stir for 10 - 15 minutes, and adjust the pH value of the solution to 4.8 - 5.2 with sulfuric acid to obtain the passivating solution.

[0016] The present invention provides an efficient hot-dip galvanizing process, which has the following beneficial effects: 1. By adding a hydrogel acid mist inhibitor, the present invention inhibits the volatilization of hydrochloric acid, reduces the acid mist emission, decreases the pollution to the workshop environment and the corrosion risk to equipment. By adopting a three-stage countercurrent rinsing process, the water washing efficiency is improved. While ensuring the removal of residual acid solution on the surface of the workpiece, the water consumption is reduced, and thus the wastewater emission is decreased. By controlling the zinc solution preparation and hot-dip galvanizing process, the generation of zinc fume is reduced. An environment-friendly rust preventive oil is selected for surface treatment, comprehensively reducing the generation of pollutants, making the hot-dip galvanizing production more green and sustainable, and meeting the current environmental protection requirements.

[0017] 2. Through elements such as aluminum, magnesium, rare earth, and silicon in the zinc solution, the present invention makes the microstructure of the zinc layer dense. The protective film formed by aluminum and the cathodic protection of magnesium synergistically enhance the corrosion resistance. Rare earth refines the grains, improving the strength and toughness. Silicon improves the fluidity of the zinc solution to ensure the integrity of the coating, enhancing the protective performance of the coating and significantly extending the service life of the workpiece in a harsh environment.

[0018] 3. The present invention synergistically removes the oxide film on the surface of the workpiece through zinc chloride and ammonium chloride. Alkyl polyglycoside enhances the wettability of the fluxing agent, enabling the fluxing agent to better penetrate into the tiny pores of the workpiece. Modified cellulose thickens and forms a protective film on the surface of the workpiece. Hexamethylenetetramine prevents the workpiece from being corroded during the fluxing process. Sodium benzoate adjusts the pH value and complexes impurities. Citric acid removes impurities and promotes the fluxing reaction. Ascorbic acid stabilizes the chemical properties of the fluxing agent, thereby efficiently cleaning and activating the surface of the workpiece, enhancing the fluxing effect, ensuring that the zinc solution can evenly and firmly adhere to the surface of the workpiece during hot-dip galvanizing, improving the coating quality and stability, and reducing the defective rate.

[0019] 4. The present invention reacts sodium molybdate and sodium tungstate with the zinc layer in an acidic environment to form a composite passivation film with protective properties, improving the corrosion resistance and wear resistance of the zinc layer. Amino trimethylene phosphonic acid chelates metal ions, promotes the formation of the passivation film and enhances its bonding force with the zinc layer. Citric acid adjusts the pH value of the passivation solution, removes impurities, and helps to form a high-quality passivation film. Polyethylene glycol reduces the surface tension of the passivation solution, enhancing the flexibility and scratch resistance of the passivation film. Sulfuric acid adjusts the pH value and promotes the passivation reaction, thereby generating a passivation film on the surface of the zinc layer, enhancing the protective performance and appearance quality of the hot-dip galvanized workpiece, and extending the service life of the product.

[0020] 5. By using auxiliary means to shorten the time for degreasing, the three-stage countercurrent rinsing reduces the water consumption for water washing, and the hot-dip galvanizing precisely controls the speed and time. Each process is closely connected, improving the production efficiency, reducing the production time and energy consumption per unit product. Moreover, the high-quality coating quality reduces the defective rate, decreasing the rework and scrap costs caused by product quality problems, further enhancing the competitiveness of the enterprise and occupying an advantageous position in the market competition. Brief Description of the Drawings

[0021] Figure 1 The figure is a flowchart of the method for the high-efficiency hot-dip galvanizing process proposed by the present invention. Detailed Embodiments

[0022] Next, in combination with the drawings of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0023] Please refer to the attached Figure 1 , the embodiments of the present invention provide a high-efficiency hot-dip galvanizing process, including the following steps: S1. Degreasing: Degrease the workpiece with a degreaser at 40 - 50°C, and at the same time use ultrasonic vibration or mechanical stirring to assist degreasing; the degreasing time in S1 is 5 - 15 minutes.

[0024] Specifically, a biodegradable degreaser mainly composed of a biosurfactant (such as rhamnolipid, sophorolipid, etc., with a mass ratio of 3% - 10%) is selected, and is combined with an alkaline auxiliary agent (such as sodium carbonate, with a mass ratio of 2% - 5%) and a buffer agent (such as sodium silicate, with a mass ratio of 1% - 3%). Place the workpiece in a corrosion-resistant degreasing tank, which can be made of polypropylene (PP) or stainless steel. Inject the prepared degreaser into the tank, and turn on the heating device to keep the temperature stable at 40 - 50°C. At the same time, turn on the ultrasonic generator, set the frequency at 20 - 40 kHz, utilize the cavitation effect of ultrasonic waves, or turn on the mechanical stirring device, with the rotation speed controlled at 50 - 100 rpm, to accelerate the emulsification and peeling of the degreaser on the oil stain on the workpiece surface. The degreasing time depends on the severity of the oil stain on the workpiece surface, generally controlled at 5 - 15 minutes. The workpiece can be taken out for observation every 2 - 3 minutes until there is no oil stain residue on the workpiece surface, showing a uniform metallic luster.

[0025] The temperature range of 40 - 50°C can not only ensure the activity of the biosurfactant in the degreaser, effectively reduce the surface tension of the solution, enhance the emulsification ability of the oil stain, but also avoid the decomposition of the degreaser caused by too high temperature, affecting the degreasing effect. Ultrasonic vibration or mechanical stirring to assist degreasing can break the solution boundary layer, make the degreaser more evenly contact the workpiece surface, accelerate the oil stain detachment speed, thereby shortening the degreasing time and improving production efficiency. The treatment time of 5 - 15 minutes can not only ensure the complete removal of the oil stain, but also will not cause unnecessary corrosion or damage to the workpiece due to too long treatment time.

[0026] S2. Pickling: The degreased workpieces are pickled in a pickling solution containing 15%-25% hydrochloric acid and added with 0.5%-1% hydrogel acid mist inhibitor at 20-30°C; the Fe 2+ concentration in the pickling solution in S2 < 80 g / L, the pickling time is 10-30 minutes, and a fiberglass pickling tank is used.

[0027] Specifically, in a corrosion-resistant fiberglass pickling tank, a hydrochloric acid solution with a mass fraction of 15%-25% is prepared and added with 0.5%-1% hydrogel acid mist inhibitor. The degreased workpieces are slowly placed into the pickling tank with a special lifting tool to ensure that the workpieces are completely immersed in the pickling solution. The circulating filtration system is turned on to make the pickling solution circulate continuously to avoid uneven local concentration. At the same time, the temperature control system is turned on to maintain the temperature stably at 20-30°C. During the pickling process, the workpieces are taken out every about 5 minutes to observe the pickling effect. If there are local unwashed areas, an acid-resistant plastic brush can be used to dip in the pickling solution for manual auxiliary cleaning. The Fe2+ concentration in the pickling solution is monitored in real time using chemical analysis methods or on-line monitoring instruments. When the Fe2+ concentration is close to 80 g / L, part of the old pickling solution is discharged in time and new prepared pickling solution is added to maintain the pickling ability of the pickling solution. The pickling time is generally controlled within 10-30 minutes, and the specific time is determined according to the rust degree of the workpieces. Workpieces with less rust can be cleaned in about 10 minutes, while those with severe rust need to be extended to 30 minutes.

[0028] The hydrochloric acid concentration of 15%-25% can effectively control the pickling speed while ensuring good dissolution ability for rust (main components Fe2O3, Fe3O4, etc.), avoiding over-corrosion of the workpieces. Adding hydrogel acid mist inhibitor can form a protective film on the surface of the pickling solution, inhibit the volatilization of hydrochloric acid to produce acid mist, improve the working environment, and reduce the harm of acid mist to equipment and operators. The temperature range of 20-30°C can not only ensure the chemical reaction rate between hydrochloric acid and rust, but also avoid the aggravation of hydrochloric acid volatilization and acid mist pollution caused by too high temperature. Fe 2+ The control standard of concentration < 80 g / L is because when the Fe 2+ concentration is too high, the activity of the pickling solution decreases, the pickling effect becomes poor, and it may cause over-corrosion on the surface of the workpieces, affecting the quality of the workpieces. The pickling time of 10-30 minutes is the best range obtained by comprehensively considering production efficiency and workpiece quality on the basis of ensuring complete removal of rust products.

[0029] S3. Water washing: The pickled workpieces are washed with water by three-stage countercurrent rinsing; in S3, the first tank of the three-stage countercurrent rinsing is circulating water with a conductivity < 500 μS / cm, the last tank is deionized water with a conductivity < 10 μS / cm, and the single-tank immersion time is 2-5 minutes.

[0030] Specifically, a three-stage countercurrent rinsing process is adopted, using three corrosion-resistant PP material water washing tanks arranged in a stepped manner. The first tank is filled with circulating water, and its conductivity is monitored by a conductivity meter to ensure that the conductivity < 500 μS / cm. It is mainly used to initially rinse off most of the residual acid solution and impurities on the surface of the workpiece; the middle tank is used for further cleaning; the last tank uses deionized water treated by ion exchange resin with a conductivity < 10 μS / cm to thoroughly wash off the trace acid solution and impurities remaining on the surface of the workpiece, ensuring that the pH value of the residual acid solution on the workpiece surface ≥ 5.5. The pickled workpieces are successively placed in the three tanks for immersion cleaning, and the immersion time for each tank is 2 - 5 minutes. During the cleaning process, the workpieces can be appropriately shaken or swung to enhance the cleaning effect. Regularly detect the conductivity and pH value of the water in each tank. When the conductivity of the water in the first tank is close to 500 μS / cm or the pH value is too low, discharge part of the water in the first tank and supplement fresh circulating water; the deionized water in the last tank is regularly replaced to ensure that the water quality meets the requirements. If the spray water washing method is adopted, a resistivity meter is installed at the outlet of the last tank to monitor the resistivity of the dripping water after water washing in real time, ensuring that it > 10 kΩ·cm.

[0031] The three-stage countercurrent rinsing process can save water to the greatest extent while ensuring the cleaning effect. The first tank uses circulating water with a conductivity < 500 μS / cm, which can initially remove a large amount of impurities and acid solution, reducing the subsequent cleaning difficulty; the last tank uses deionized water with a conductivity < 10 μS / cm, which can ensure that the surface of the workpiece reaches a nearly impurity-free clean state, providing an excellent base for the subsequent fluxing process. The single-tank immersion time of 2 - 5 minutes is sufficient to thoroughly wash away the residual substances on the surface of the workpiece by water. By regularly detecting the water quality parameters and timely replacing or supplementing water, the stability of the water washing effect can be ensured, preventing incomplete cleaning of the workpiece due to water quality deterioration and affecting the subsequent process.

[0032] S4. Fluxing: The workpieces after water washing are fluxed by immersing them in the fluxing agent at 60 - 70 °C for 3 - 8 minutes; specifically, the fluxing agent is added to a stainless steel fluxing tank with a stirring device, the stirring device is turned on, and the rotation speed is controlled at 80 - 150 rpm to fully mix all components evenly, and the pH value of the fluxing solution is adjusted to 5.0 - 6.5 with a pH regulator (such as dilute hydrochloric acid or sodium hydroxide solution). The workpieces after water washing are quickly placed into the fluxing tank with a lifting tool to ensure that the workpieces are completely immersed in the fluxing solution. During the immersion process, the workpieces can be appropriately shaken to ensure that the fluxing solution evenly covers. The immersion time is 3 - 8 minutes, which is adjusted according to the surface area to volume ratio of the workpiece. For workpieces with a larger surface area and thinner thickness, the immersion time can be appropriately shortened to about 3 minutes; for workpieces with a larger volume and complex shape, it needs to be extended to 8 minutes. The Zn 2+ concentration in the fluxing solution is monitored in real time by a conductivity meter. When the Zn 2+ concentration is lower than 80 g / L, an appropriate amount of zinc chloride is added; when the Zn 2+When the concentration is higher than 120 g / L, it can be adjusted by dilution or replacing part of the fluxing solution. At the same time, since water will continuously evaporate during the fluxing process, deionized water needs to be replenished regularly to maintain the liquid level stability.

[0033] The fluxing temperature of 60 - 70 °C can improve the activity of each component in the fluxing solution, promote its chemical reaction with the workpiece surface, and form a more solid protective film. The impregnation time of 3 - 8 minutes is determined considering the production efficiency on the premise of ensuring that the fluxing solution fully acts on the workpiece surface to form a complete protective film. Control Zn 2+ The concentration of 80 - 120 g / L can ensure the activity and stability of the fluxing agent, and guarantee the consistency of the fluxing effect.

[0034] S5. Hot dip galvanizing: The zinc liquid is melted to 450 - 470 °C by an intermediate frequency induction furnace, and the fluxed workpiece is immersed in the zinc liquid at a speed of 50 - 100 mm / s using a lifting tool for hot dip galvanizing; the hot dip galvanizing time in S5 is determined according to the workpiece characteristics, the lifting speed is 60 - 120 mm / s, and after lifting, it is air-cooled for 10 - 20 seconds, and then enters a water-cooling tank with a water temperature of 20 - 30 °C for water-cooling until ≤60 °C. The workpiece characteristics include the workpiece thickness and material, and the flow rate of the zinc liquid into which the workpiece is immersed is 0.2 - 0.5 m / s.

[0035] Specifically, an automated lifting tool is used to uniformly immerse the fluxed workpiece into the zinc liquid at a speed of 50 - 100 mm / s. The immersion time is determined according to the workpiece characteristics such as thickness and material. For example, for a workpiece with a thickness of δ (mm), the immersion time is approximately δ × (2 - 3) s / mm. The lifting speed is controlled at 60 - 120 mm / s. After lifting, it is first air-cooled in the air for 10 - 20 seconds to reduce the workpiece surface temperature to 300 - 350 °C, and then enters a water-cooling tank with a water temperature of 20 - 30 °C for water-cooling until ≤60 °C. The plating bath adopts a two-zone heating structure, which is divided into a preheating zone and a heat preservation zone, and a flow guide plate is installed to keep the zinc liquid flow rate at 0.2 - 0.5 m / s, ensuring that the coating thickness uniformity error < 5%.

[0036] The zinc liquid temperature of 450 - 470 °C can ensure that the zinc liquid has good fluidity, enabling the zinc liquid to quickly and uniformly cover the workpiece surface. At the same time, it is conducive to the alloying reaction between zinc and the workpiece surface, forming a firm coating. The immersion speed of 50 - 100 mm / s and the lifting speed of 60 - 120 mm / s can not only make the workpiece fully contact the zinc liquid but also avoid uneven coating due to too fast or too slow speed. The control of the temperature and time of air-cooling and water-cooling helps to control the crystallization process of the coating and obtain good tissue structure and performance. The two-zone heating structure and flow guide plate design of the plating bath can optimize the zinc liquid flow state, make the zinc liquid act uniformly on the workpiece surface, and improve the coating uniformity.

[0037] S6, Passivation: The workpiece after hot-dip plating is passivated with a passivation solution at 30 - 40 °C. The pH value of the passivation solution in S6 is 4.8 - 5.2, the passivation time is 20 - 60 seconds. What components does the environmentally friendly rust preventive oil in S7 include? The coating thickness is 1 - 3 μm, and the contact angle of the workpiece surface after oil coating > 90°.

[0038] Specifically, the workpiece after hot-dip plating is quickly put into the passivation tank. If spray passivation is used, a corrosion-resistant spray pump and nozzle are used to evenly spray the passivation solution on the surface of the workpiece, and the treatment time is 30 - 60 seconds. If immersion passivation is used, a stirring device is installed to ensure full contact between the passivation solution and the workpiece, and the treatment time is 20 - 40 seconds. The Zn concentration in the passivation solution is monitored by a conductivity meter. When the Zn 2+ concentration > 5 g / L, the ion exchange resin system is started to remove Zn in the solution 2+ to prevent it from affecting the quality of the passivation film. At the same time, the main salts (sodium molybdate, sodium tungstate) are replenished regularly, and the consumption rate of the main salts is about 0.5 - 1.0 g / L·h. 2+ The passivation temperature of 30 - 40 °C can ensure the smooth progress of the passivation reaction, and at the same time avoid the passivation film being too thick and easy to fall off due to too high temperature or incomplete reaction due to too low temperature. The treatment time of 30 - 60 seconds (spray type) or 20 - 40 seconds (immersion type) is determined in combination with the production efficiency on the premise of ensuring the formation of a complete and dense passivation film. Controlling the pH value of the passivation solution at 4.8 - 5.2 can optimize the progress of the passivation reaction and obtain the best passivation effect. Monitoring the Zn

[0039] concentration and dealing with it in time, as well as regularly replenishing the main salts, can ensure the stability of the passivation solution and the consistency of the passivation effect. 2+ concentration and dealing with it in time, as well as regularly replenishing the main salts, can ensure the stability of the passivation solution and the consistency of the passivation effect.

[0040] S7, Surface treatment: For the passivated workpiece, an environmentally friendly rust preventive oil is used for coating at a workpiece surface temperature ≤ 50 °C, and then dried by hot air circulation at 60 - 80 °C for 5 - 10 minutes.

[0041] Specifically, the environmentally friendly rust preventive oil is composed of 80%-90% base oil (such as mineral base oil, synthetic base oil, etc.), 5%-10% rust preventive additive (such as petroleum sulfonate, barium dinonylnaphthalene sulfonate, etc.), and 3%-5% surfactant (such as fatty acid polyoxyethylene ester, alkylphenol polyoxyethylene ether, etc.). The rust preventive oil is evenly coated on the surface of the passivated workpiece by roll coating or spraying, and the coating thickness is controlled within 1-3 μm. If roll coating is used, a precision roll coater is used, and the oil film thickness is precisely controlled by adjusting the roller gap and rotation speed; if spraying is used, a high-pressure airless spray gun is selected, and the spray gun pressure and spraying distance are adjusted to ensure uniform spraying of the rust preventive oil. When applying the oil, ensure that the surface temperature of the workpiece ≤ 50°C to avoid excessive evaporation of the rust preventive oil due to too high oil temperature, which affects the coating effect. After applying the oil, send the workpiece into a hot air circulation drying oven, set the temperature at 60-80°C, and the drying time is 5-10 minutes to allow the solvent in the rust preventive oil to volatilize fully, ensuring no oil stain adhesion on the surface. Use an infrared thickness gauge to detect the uniformity of the oil film, and require the deviation of the oil film thickness < ±0.5 μm. At the same time, use a contact angle measuring instrument to detect the contact angle of the workpiece surface after applying the oil, ensuring that it > 90°, so as to ensure that the workpiece has no rust after 3 months of outdoor storage.

[0042] The base oil provides the basic film-forming and lubricating properties for the rust preventive oil; the rust preventive additive can form an adsorption film or a chemical reaction film on the metal surface to prevent corrosive media such as oxygen and moisture from contacting the metal, improving the rust prevention performance; the surfactant can reduce the surface tension of the rust preventive oil, enabling it to spread and adhere better on the workpiece surface. An oil film thickness of 1-3 μm can provide sufficient rust protection without affecting the appearance and use performance of the workpiece. Controlling the surface temperature of the workpiece ≤ 50°C can ensure the coating quality and stability of the rust preventive oil. The hot air circulation drying temperature of 60-80°C and the drying time of 5-10 minutes can enable the solvent in the rust preventive oil to volatilize quickly and fully, forming a firm rust preventive film. By detecting the uniformity of the oil film and the surface contact angle, the coating effect of the rust preventive oil can be ensured, guaranteeing that the workpiece has good rust prevention performance.

[0043] The zinc bath includes raw materials with the following mass percentages: 5%-11% aluminum, 0.5%-3% magnesium, 0.01%-0.1% rare earth, 0.1%-0.5% silicon, and the balance is zinc.

[0044] Specifically, aluminum in the zinc bath can react preferentially with oxygen in the air on the surface of the zinc bath to form a dense aluminum oxide (Al2O3) protective film. This protective film effectively prevents the further oxidation of the zinc bath and reduces the loss of the zinc bath. During the hot-dip galvanizing process, aluminum atoms diffuse to the surface of the zinc layer and participate in the formation of zinc-aluminum intermetallic compounds, making the structure of the coating more dense, thereby improving the corrosion resistance of the coating and achieving the purpose of long-term protection of the workpiece.

[0045] Magnesium has strong activity. In the coating formed by hot-dip plating, magnesium can act as a sacrificial anode, preferentially lose electrons and undergo an oxidation reaction, playing a cathodic protection role for the zinc layer and the workpiece substrate. At the same time, magnesium interacts with elements such as zinc and aluminum, changing the microstructure of the coating, refining the grains, increasing the hardness and toughness of the coating, and enhancing the comprehensive performance of the coating.

[0046] Rare earth elements (such as cerium, lanthanum, etc.) have a microalloying effect in the zinc bath. They can adsorb at the grain boundaries, inhibit the growth of grains, refine the grains of the zinc layer, thereby increasing the strength and toughness of the coating. In addition, rare earth elements can also improve the fluidity and wettability of the zinc bath, enabling the zinc bath to cover the workpiece surface more evenly during hot-dip plating, reducing the occurrence of defects such as missing plating and zinc nodules, and improving the quality of the coating.

[0047] Silicon can reduce the surface tension of the zinc bath, improve the fluidity of the zinc bath, make the zinc bath more easily fill the micro-pores and depressions on the workpiece surface during hot-dip plating, and ensure the integrity of the coating. At the same time, silicon interacts with other elements, helping to adjust the microstructure of the zinc layer, further enhancing the corrosion resistance and wear resistance of the coating, and optimizing the performance of the coating.

[0048] Zinc, as the main component of the zinc bath, is the basis for forming the hot-dip galvanized layer. During hot-dip plating, the molten zinc undergoes a metallurgical reaction with the workpiece surface to form a firm zinc coating, providing basic protection for the workpiece and protecting the workpiece physically and electrochemically.

[0049] Through the synergistic interaction of aluminum, magnesium, rare earth, and silicon with zinc, aluminum and magnesium improve corrosion resistance, rare earth refines grains and improves quality, silicon optimizes fluidity and microstructure, and zinc, as the main body, bears the role of other elements, enabling the zinc bath to form a coating with good corrosion resistance, high hardness and toughness, uniform and dense on the workpiece surface during hot-dip plating, achieving efficient hot-dip galvanizing and extending the service life of the workpiece in various environments.

[0050] The preparation method of the zinc bath is as follows: S501. Add zinc to the intermediate frequency induction furnace according to the mass percentage. When the zinc melts into a solution at a temperature of 450 - 470 °C, add aluminum, magnesium, and silicon, and at the same time carry out stirring at a stirring speed of 100 - 200 rpm for a stirring time of 15 - 30 minutes to form a mixed solution; S502. Mix rare earth and zinc in a mass ratio of 1:9 - 11, heat to 600 - 700 °C, and at the same time stir at a stirring speed of 150 - 250 rpm for 30 - 45 minutes to make a zinc-rare earth master alloy. S503. Add the zinc-rare earth master alloy to the mixed solution and continue stirring for 10 - 20 minutes to make the zinc-rare earth master alloy evenly dispersed in the mixed solution to obtain the zinc bath.

[0051] Specifically, zinc ingots with a purity of ≥99.9% are selected, accurately weighed according to a predetermined mass percentage, and then added into an intermediate frequency induction furnace. The power supply of the furnace is turned on, and a heating program is set to slowly heat the zinc ingots to 450 - 470 °C. During this process, the temperature is precisely monitored using the temperature control system equipped with the furnace to ensure that the temperature fluctuation range is controlled within ±2 °C. When the zinc is completely melted into a solution state and the temperature is stable, aluminum blocks (purity ≥99.7%), magnesium pellets (purity ≥99.5%), and silicon powder (purity ≥99%) are sequentially added into the zinc liquid. Meanwhile, the stirring paddle installed in the furnace is started, and the stirring speed is set between 100 - 200 rpm, and the stirring time lasts for 15 - 30 minutes. During the stirring process, the flow state of the zinc liquid can be observed through the observation window or online monitoring equipment to ensure that all raw materials are fully and evenly mixed to form a uniformly composed mixed liquid.

[0052] An appropriate amount of rare earth metals (such as cerium, lanthanum, etc., purity ≥99%) and zinc ingots are weighed and placed in a special melting crucible according to a mass ratio of 1:9 - 11. The crucible is placed in a resistance furnace, and the heating temperature is set to 600 - 700 °C, and the heating rate is controlled at 10 - 15 °C / min. When the temperature reaches the set value, the stirring device in the crucible is used to stir at a stirring speed of 150 - 250 rpm for 30 - 45 minutes. During the stirring process, the intermediate alloy is periodically sampled and detected using a spectral analyzer to ensure that the content deviation of rare earth elements in the intermediate alloy is controlled within ±0.005% to ensure the stable quality of the intermediate alloy.

[0053] After the zinc-rare earth intermediate alloy is prepared and passes the inspection, it is slowly added to the previously prepared mixed liquid. The stirring device is started again to stir at a speed of 100 - 150 rpm for 10 - 20 minutes to evenly disperse the zinc-rare earth intermediate alloy in the mixed liquid. After the stirring is completed, a small amount of zinc liquid can be taken for metallographic analysis or composition detection to confirm that the rare earth elements are evenly distributed, thereby obtaining zinc liquid that meets the requirements.

[0054] The flux includes raw materials with the following mass percentages: zinc chloride 8% - 15%, ammonium chloride 7% - 12%, alkyl polyglycoside 3% - 8%, modified cellulose 2% - 5%, hexamethylenetetramine 0.5% - 2%, sodium benzoate 0.3% - 1%, citric acid 1% - 3%, ascorbic acid 0.1% - 0.5%, and the balance is deionized water. The modified cellulose includes hydroxypropyl methyl cellulose.

[0055] Specifically, zinc chloride is one of the main active components in the flux. It can chemically react with the oxides on the workpiece surface to form volatile chlorides, thereby removing the oxide film on the workpiece surface and providing a clean metal surface for hot-dip plating. At the same time, zinc chloride can form a zinc salt film on the workpiece surface, reduce the surface tension between the zinc bath and the workpiece, promote the spreading and wetting of the zinc bath on the workpiece surface, improve the hot-dip plating effect, and ensure uniform adhesion of the coating.

[0056] Ammonium chloride and zinc chloride act synergistically to further enhance the ability to remove oxides on the workpiece surface. Ammonium chloride decomposes during heating to produce ammonia (NH3) and hydrogen chloride (HCl) gases. HCl can react with metal oxides to accelerate the dissolution of the oxide film. In addition, ammonium chloride can also adjust the pH value of the flux, maintain the stability of the flux system, optimize the fluxing environment, and improve the fluxing effect.

[0057] As a non-ionic surfactant, alkyl polyglycoside has good wettability and dispersibility. It can reduce the surface tension of the flux solution, enable the flux to better penetrate into the tiny pores and defects on the workpiece surface, enhance the contact and adsorption between the flux and the workpiece surface, improve the uniformity of the flux coverage on the workpiece surface, and ensure the consistency of the fluxing effect.

[0058] Taking hydroxypropyl methylcellulose as an example, the modified cellulose plays a thickening and stabilizing role in the flux. It can increase the viscosity of the flux solution, prevent the precipitation of solid particles in the solution, and maintain the uniformity of the flux components. At the same time, the modified cellulose can form a protective film on the workpiece surface, enhance the bonding force between the flux and the workpiece, and improve the stability of the flux performance and the durability of the fluxing effect.

[0059] Hexamine is a corrosion inhibitor. During the fluxing process, it can form an adsorption film on the workpiece surface to inhibit the corrosion of the workpiece in the acidic fluxing environment. Especially in the presence of acidic components such as zinc chloride and ammonium chloride, hexamine can effectively protect the workpiece substrate, reduce the occurrence of excessive corrosion, protect the workpiece substrate, and improve the quality of the workpiece.

[0060] Sodium benzoate has a certain buffering effect. It can adjust the pH value of the flux solution to keep it within a suitable range, ensuring the stability of each component in the flux. At the same time, sodium benzoate can undergo a complexation reaction with metal ions, further enhancing the cleaning and activation of the workpiece surface, optimizing the chemical environment of the flux, and improving the fluxing effect.

[0061] Citric acid, as an organic acid, has the ability to complex metal ions. It can complex with metal impurity ions (such as Fe 3+Form stable complexes with (such as etc.), reduce the influence of impurity ions on the pickling effect, and improve the purity and stability of the pickling agent. In addition, citric acid can also adjust the pH value of the pickling agent, promote the pickling reaction, and achieve the effect of improving the quality and efficiency of the pickling agent.

[0062] Ascorbic acid has reducibility and can prevent certain components in the pickling agent from being oxidized in the pickling agent, maintaining the chemical stability of the pickling agent. At the same time, ascorbic acid can chemically react with the metal surface to form a thin film with a certain protective effect, enhancing the binding force between the pickling agent and the workpiece, and improving the antioxidant performance and pickling effect of the pickling agent.

[0063] Deionized water, as the solvent of the pickling agent, can dissolve various solutes such as zinc chloride and ammonium chloride, making the components of the pickling agent evenly dispersed in the solution to form a stable system. At the same time, deionized water can adjust the concentration of the pickling agent, ensure that the pickling agent exerts the best pickling effect within a suitable concentration range, and provide a uniform dispersion medium and concentration adjustment for the components of the pickling agent.

[0064] The unique molecular structure of hydroxypropyl methylcellulose endows it with good thickening, suspending and water retention properties in the pickling agent. It can form a uniform and certain-thickness protective film on the surface of the workpiece, enhance the adhesion between the pickling agent and the workpiece, prevent the pickling agent from drying too quickly on the surface of the workpiece, extend the action time of the pickling agent, and achieve the improvement of the adhesion performance and the durability of the action effect of the pickling agent on the surface of the workpiece.

[0065] Through the cooperation of each raw material, zinc chloride and ammonium chloride are responsible for removing the oxide film on the surface of the workpiece and adjusting the pH value, alkyl polyglycoside enhances wettability, modified cellulose stabilizes the solution and enhances adhesion, hexamethylenetetramine protects the workpiece substrate, sodium benzoate and citric acid adjust the pH value and complex impurities, and ascorbic acid has antioxidant properties. Deionized water, as the solvent, enables each component to work together to effectively clean, activate and protect the surface of the workpiece, improves the quality and efficiency of subsequent hot-dip plating, and ensures that the workpiece can obtain a uniform and firm coating after hot-dip plating.

[0066] The preparation method of the pickling agent is as follows: S401. Add deionized water to the reaction kettle with a stirring device according to the mass percentage, carry out stirring at a rotation speed of 80 - 150 rpm, and then sequentially add zinc chloride and ammonium chloride, and stir for 10 - 15 minutes until they are completely dissolved; S402. Then add alkyl polyglycoside and modified cellulose, continue to stir for 15 - 20 minutes until they are fully dispersed, and then add hexamethylenetetramine, sodium benzoate, citric acid, and ascorbic acid, and continuously stir for 20 - 30 minutes to make each component evenly mixed to obtain the pickling agent.

[0067] Specifically, a stainless-steel reactor equipped with a stirring device is selected to ensure that the interior of the reactor is clean and free of impurities. Deionized water is accurately measured and added to the reactor according to a predetermined mass percentage. The stirring device is turned on, and the rotation speed is set to 80 - 150 rpm to form a stable vortex of deionized water inside the reactor. Then, accurately metered zinc chloride (analytical grade) is slowly added to the water, and continuous stirring is carried out during the addition process. The stirring time is controlled within 10 - 15 minutes. During this period, the dissolution of zinc chloride can be observed through the observation window to ensure that zinc chloride is completely dissolved. After the zinc chloride is dissolved, ammonium chloride (analytical grade) is added in the same manner, and stirring is continued for 10 - 15 minutes to completely dissolve the ammonium chloride in the deionized water to form a homogeneous solution.

[0068] Alkyl polyglycoside (industrial grade) is slowly added to the above solution while maintaining the stirring speed at 80 - 150 rpm, and the stirring time is continued for 15 - 20 minutes. During this process, a surface tensiometer can be used to monitor the change in the surface tension of the solution to ensure that the alkyl polyglycoside is fully dispersed and the surface tension of the solution is reduced. Then, pretreated modified cellulose (such as hydroxypropyl methylcellulose, which needs to be fully swollen in an appropriate amount of deionized water before use) is added, and stirring is continued for 15 - 20 minutes to uniformly disperse the modified cellulose in the solution, and the viscosity of the solution increases. Subsequently, hexamethylenetetramine (analytical grade), sodium benzoate (analytical grade), citric acid (analytical grade), and ascorbic acid (analytical grade) are added in sequence. After each raw material is added, continuous stirring is carried out for a period of time, and the total stirring time is controlled within 20 - 30 minutes. During the stirring process, the pH value, conductivity and other parameters of the solution can be sampled and detected regularly to ensure that all components are fully mixed and a plating assistant with stable performance is obtained.

[0069] The passivation solution includes the following raw materials in mass percentages: sodium molybdate 8% - 12%, sodium tungstate 3% - 6%, aminotrimethylenephosphonic acid 1.5% - 3%, citric acid 0.8% - 1.5%, polyethylene glycol 0.1% - 0.5%, sulfuric acid 0.5% - 1.2%, and the balance is deionized water.

[0070] Specifically, sodium molybdate is the key film-forming substance in the passivation solution. In an acidic environment, sodium molybdate can react chemically with the zinc coating to form a passivation film containing molybdenum oxides (such as MoO3) on the surface of the zinc layer. This passivation film has good corrosion resistance and can effectively block the contact between corrosion media such as oxygen and moisture and the zinc layer, improving the corrosion resistance of the zinc coating and extending the service life of the workpiece.

[0071] Sodium tungstate and sodium molybdate work together to form the passivation film. During the passivation process, sodium tungstate can form a composite oxide film (such as MoO3-WO3-ZnO) with sodium molybdate to enhance the density and hardness of the passivation film. This not only improves the corrosion resistance of the passivation film, but also improves the wear resistance of the passivation film, further optimizes the performance of the passivation film, and enhances its protective effect.

[0072] Aminotrimethylenephosphonic acid is an organic phosphonic acid compound with strong chelating ability and can bind to metal ions (such as Zn 2+ 、Mo 6+ , W 6+ The aminotrimethylenephosphonic acid can form a stable complex with zinc (such as zinc oxide, zinc sulfate, etc.), promote the formation of the passive film, and inhibit the generation of pores in the passive film. At the same time, aminotrimethylenephosphonic acid can enhance the bonding force between the passive film and the zinc coating, making the passive film more firmly attached to the surface of the zinc layer, thus improving the quality and adhesion of the passive film.

[0073] Citric acid has multiple functions in the passivation solution. First, as an organic acid, it can adjust the pH value of the passivation solution and provide a suitable acidic environment for the passivation reaction. Secondly, citric acid has the ability to complex metal ions and can form complexes with impure metal ions in the solution, reducing the impact of impurity ions on the quality of the passivation film and improving the purity of the passivation solution. In addition, citric acid can also promote the formation of the passivation film, making the passivation film more uniform and dense, optimizing the chemical properties of the passivation solution, and improving the performance of the passivation film.

[0074] As a nonionic surfactant, polyethylene glycol can reduce the surface tension of the passivation solution, allowing the passivation solution to spread and infiltrate the zinc coating surface better. This helps to form a uniform passivation film and reduce defects and pinholes in the passivation film. At the same time, polyethylene glycol can form a protective film on the surface of the passivation film, improve the flexibility and scratch resistance of the passivation film, and improve the surface quality and comprehensive performance of the passivation film.

[0075] Sulfuric acid is used to adjust the pH value of the passivation solution to keep it within the range of 4.8-5.2. In this pH range, sodium molybdate, sodium tungstate and other ingredients can react chemically better to form a high-quality passivation film. Sulfuric acid also participates in the formation of the passivation film, and works synergistically with other ingredients to enhance the corrosion resistance and adhesion of the passivation film, thereby controlling the pH of the passivation solution and promoting the passivation reaction.

[0076] Deionized water, as the solvent of the passivation solution, can dissolve various solutes such as sodium molybdate, sodium tungstate, aminotrimethylenephosphonic acid, etc., so that the components of the passivation solution are evenly dispersed in the solution to form a stable system. At the same time, deionized water can adjust the concentration of the passivation solution to ensure that the passivation solution has the best passivation effect within the appropriate concentration range, thereby providing a uniform dispersion medium for the components of the passivation solution and regulating the concentration.

[0077] Through the combination of various raw materials, sodium molybdate and sodium tungstate form a passivation film with protective properties. Amino trimethylene phosphonic acid and citric acid regulate the chemical environment, promote film formation, and enhance the bonding force. Polyethylene glycol improves the surface properties, and sulfuric acid adjusts the pH value. Deionized water enables the components to work synergistically, jointly achieving the formation of a uniform, dense passivation film with good corrosion resistance, adhesion, and comprehensive properties on the surface of the zinc coating, further enhancing the protective performance and appearance quality of the hot-dip galvanized workpiece.

[0078] The preparation method of the passivation solution is as follows: S601. By mass percentage, add deionized water to a corrosion-resistant liquid preparation tank, and then add sodium molybdate and sodium tungstate, and conduct stirring at a stirring speed of 100 - 180 rpm for 15 - 20 minutes to fully dissolve them; S602. Then add amino trimethylene phosphonic acid and citric acid, continue stirring for 20 - 30 minutes, add polyethylene glycol, stir for 10 - 15 minutes, and adjust the pH value of the solution to 4.8 - 5.2 with sulfuric acid to obtain the passivation solution.

[0079] Specifically, select a corrosion-resistant polypropylene (PP) material liquid preparation tank. After cleaning the liquid preparation tank, accurately measure deionized water and add it to the liquid preparation tank according to the predetermined mass percentage. Then, slowly add accurately measured sodium molybdate (analytical pure) and sodium tungstate (analytical pure) to the deionized water, and at the same time, start the stirring paddle installed in the liquid preparation tank, set the stirring speed to 100 - 180 rpm, and the stirring time to 15 - 20 minutes. During the stirring process, the dissolution of sodium molybdate and sodium tungstate can be observed through the observation window or online monitoring equipment to ensure that the two raw materials are fully dissolved in the deionized water to form a uniform solution.

[0080] Add accurately weighed amino trimethylene phosphonic acid (industrial grade) and citric acid (analytical pure) to the above solution in sequence, keep the stirring speed at 100 - 180 rpm, and the stirring time at 20 - 30 minutes. During this process, a potentiometric titrator can be used to monitor the potential change of the solution to ensure that amino trimethylene phosphonic acid and citric acid fully complex with the metal ions in the solution. Then, add an appropriate amount of polyethylene glycol (the molecular weight is selected according to actual needs, such as PEG - 600), and continue stirring for 10 - 15 minutes to evenly disperse the polyethylene glycol in the solution. Finally, slowly adjust the pH value of the solution to 4.8 - 5.2 with concentrated sulfuric acid (98%). During the adjustment process, insert a precision pH meter into the solution to monitor the pH value change in real time, add sulfuric acid while stirring to ensure that the pH value rises evenly until the target pH value range is reached to obtain a qualified passivation solution.

[0081] The following is a further introduction in combination with specific embodiments: Example 1: High-efficiency hot-dip galvanizing process, including the following steps: S1. Degreasing: Degrease the workpiece with a degreasing agent at 45°C, and at the same time, use ultrasonic vibration or mechanical stirring to assist degreasing; S2. Pickling: For the degreased workpiece, use a pickling solution containing 20% hydrochloric acid and adding 0.75% hydrogel acid mist inhibitor to pickle at 25°C; S3. Water washing: Adopt three-stage countercurrent rinsing to wash the pickled workpiece; S4. Fluxing: Immerse the water-washed workpiece in a fluxing agent at 65°C for 5.5 minutes for fluxing treatment; S5. Hot dip galvanizing: Melt the zinc liquid to 465°C through an intermediate frequency induction furnace, and use a lifting tool to immerse the fluxed workpiece into the zinc liquid at a speed of 75 mm / s for hot dip galvanizing; S6. Passivation: Use a passivation solution to passivate the hot-dip galvanized workpiece at 35°C; S7. Surface treatment: For the passivated workpiece, use an environmentally friendly rust preventive oil to coat when the surface temperature of the workpiece ≤ 50°C, and then dry it through hot air circulation at 70°C for 7.5 minutes.

[0082] The degreasing time in S1 is 10 minutes, and the Fe 2+ concentration in the pickling solution in S2 < 80 g / L, the pickling time is 20 minutes, and a pickling tank made of fiberglass reinforced plastic is used.

[0083] In S3, the first tank of the three-stage countercurrent rinsing is circulating water with a conductivity < 500 μS / cm, the last tank is deionized water with a conductivity < 10 μS / cm, and the single-tank immersion time is 3.5 minutes.

[0084] The hot dip galvanizing time in S5 is determined according to the workpiece characteristics, the plating lifting speed is 90 mm / s, after lifting plating, air cooling is carried out for 15 seconds, and then it enters a water cooling tank with a water temperature of 25°C for water cooling to ≤ 60°C. The workpiece characteristics include workpiece thickness and material. The zinc liquid flow rate when immersing in the zinc liquid is 0.35 m / s. The pH value of the passivation solution in S6 is 5, and the passivation treatment time is 40 seconds. What does the environmentally friendly rust preventive oil in S7 include? The coating thickness is 2 μm, and the contact angle of the workpiece surface after oil coating > 90°.

[0085] The zinc liquid includes raw materials with the following mass percentages: 11% aluminum, 3% magnesium, 0.1% rare earth, 0.5% silicon, and the balance is zinc.

[0086] The preparation method of the zinc liquid is: S501. Add zinc to the intermediate frequency induction furnace according to the mass percentage. When the zinc melts into a solution at a temperature of 460°C, add aluminum, magnesium, and silicon, and at the same time, carry out stirring with a stirring speed of 150 rpm and a stirring time of 23 minutes to form a mixed liquid; S502. Mix rare earth and zinc in a ratio of 1:10 by mass, heat to 650 °C, and stir at a stirring speed of 200 rpm for 38 minutes to make a zinc-rare earth master alloy. S503. Add the zinc-rare earth master alloy to the mixed solution and continue stirring for 15 minutes to evenly disperse the zinc-rare earth master alloy in the mixed solution to obtain a zinc solution.

[0087] The flux includes raw materials in the following mass percentages: zinc chloride 15%, ammonium chloride 12%, alkyl polyglycoside 8%, modified cellulose 5%, hexamethylenetetramine 2%, sodium benzoate 1%, citric acid 3%, ascorbic acid 0.5%, and the balance is deionized water. The modified cellulose includes hydroxypropyl methylcellulose.

[0088] The preparation method of the flux is as follows: S401. Add deionized water to a reaction kettle with a stirring device according to the mass percentage, stir at a speed of 125 rpm, and then sequentially add zinc chloride and ammonium chloride and stir for 12.5 minutes to completely dissolve them. S402. Then add alkyl polyglycoside and modified cellulose, continue stirring for 17.5 minutes, after they are fully dispersed, add hexamethylenetetramine, sodium benzoate, citric acid, and ascorbic acid, and continuously stir for 25 minutes to mix all components evenly to obtain the flux.

[0089] The passivation solution includes raw materials in the following mass percentages: sodium molybdate 12%, sodium tungstate 6%, aminotrimethylenephosphonic acid 3%, citric acid 1.5%, polyethylene glycol 0.5%, sulfuric acid 1.2%, and the balance is deionized water.

[0090] The preparation method of the passivation solution is as follows: S601. Add deionized water to a corrosion-resistant liquid preparation tank according to the mass percentage, then add sodium molybdate and sodium tungstate, and stir at a stirring speed of 140 rpm for 17.5 minutes to fully dissolve them. S602. Then add aminotrimethylenephosphonic acid and citric acid, continue stirring for 25 minutes, add polyethylene glycol, stir for 12.5 minutes, and adjust the pH value of the solution to 5 with sulfuric acid to obtain the passivation solution.

[0091] Example 2: The difference between this example and the above Example 1 is as follows: The zinc solution includes raw materials in the following mass percentages: aluminum 5%, magnesium 0.5%, rare earth 0.01%, silicon 0.1%, and the balance is zinc.

[0092] The flux comprises raw materials with the following mass percentages: zinc chloride 8%, ammonium chloride 7%, alkyl polyglycoside 3%, modified cellulose 2%, hexamethylenetetramine 0.5%, sodium benzoate 0.3%, citric acid 1%, ascorbic acid 0.1%, and the balance being deionized water. The modified cellulose includes hydroxypropyl methylcellulose.

[0093] The passivation solution comprises raw materials with the following mass percentages: sodium molybdate 8%, sodium tungstate 3%, aminotrimethylenephosphonic acid 1.5%, citric acid 0.8%, polyethylene glycol 0.1%, sulfuric acid 0.5%, and the balance being deionized water.

[0094] Example 3: The difference between this example and Example 1 above is that: The zinc solution comprises raw materials with the following mass percentages: aluminum 8%, magnesium 1.75%, rare earth 0.055%, silicon 0.3%, and the balance being zinc.

[0095] The flux comprises raw materials with the following mass percentages: zinc chloride 11.5%, ammonium chloride 10.5%, alkyl polyglycoside 5.5%, modified cellulose 3.5%, hexamethylenetetramine 1.25%, sodium benzoate 0.65%, citric acid 2%, ascorbic acid 0.3%, and the balance being deionized water. The modified cellulose includes hydroxypropyl methylcellulose.

[0096] The passivation solution comprises raw materials with the following mass percentages: sodium molybdate 10%, sodium tungstate 4.5%, aminotrimethylenephosphonic acid 2.25%, citric acid 1.15%, polyethylene glycol 0.3%, sulfuric acid 0.85%, and the balance being deionized water.

[0097] Table 1: Comparison Example 1 Example 2 Example 3 Standard value Time to corrosion appearance (h) 1600 1000 1250 800 <![CDATA[Wastewater discharge (m 3 )]]> 5 3 4 10 <![CDATA[Acid mist concentration (mg / m 3 )]]> 20 10 15 50 <![CDATA[Zinc fume concentration (mg / m 3 )]]> 10 5 7.5 15 Hardness (HV) 175 135 150 110 In the above table, the comparison is made with the zinc layer of the workpiece galvanized by the traditional galvanizing process. It can be seen from Table 1 that different contents of aluminum, magnesium, rare earth, silicon, and zinc in the zinc solution can affect the microstructure of the zinc layer. Aluminum can form a dense protective film, improving corrosion resistance and hardness. Magnesium acts as a sacrificial anode to enhance protection and improve the organizational structure. Rare earth refines the grains, increasing strength and toughness and optimizing the characteristics of the zinc solution. Silicon reduces the surface tension, ensuring the integrity of the coating, and synergistically improving the comprehensive performance. Zinc serves as the basis to carry the functions of other elements, achieving improvements in performance such as corrosion resistance and hardness. Moreover, through the three-stage countercurrent rinsing process, the water consumption is reduced, and thus the wastewater discharge is decreased. The hydrogel acid mist inhibitor inhibits the acid mist volatilization, affects the acid mist concentration, optimizes the zinc solution preparation and hot-dip galvanizing process, reduces the excessive evaporation of the zinc solution, and lowers the zinc fume concentration, thereby enhancing the environmental protection performance, reducing environmental pollution, and at the same time reducing the cost investment of enterprises in environmental protection treatment, making the hot-dip galvanizing production more green and sustainable.

[0098] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill 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 present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An efficient hot-dip galvanizing process, characterized in that, It includes the following steps: S1. Degreasing: Degrease the workpiece with a degreasing agent at 40 - 50 °C, and assist degreasing with ultrasonic vibration or mechanical stirring simultaneously; S2. Pickling: For the degreased workpiece, use a pickling solution containing 15% - 25% hydrochloric acid and adding 0.5% - 1% hydrogel acid mist inhibitor to pickle at 20 - 30 °C; S3. Water washing: Adopt three - stage countercurrent rinsing to wash the pickled workpiece; S4. Fluxing: Immerse the water - washed workpiece in a fluxing agent at 60 - 70 °C for 3 - 8 minutes for fluxing treatment; S5. Hot - dip galvanizing: Melt the zinc liquid to 450 - 470 °C by an intermediate - frequency induction furnace, and use a sling to immerse the fluxed workpiece into the zinc liquid at a speed of 50 - 100 mm / s for hot - dip galvanizing; S6. Passivation: Use a passivation solution to passivate the hot - dip galvanized workpiece at 30 - 40 °C; S7. Surface treatment: For the passivated workpiece, use an environmentally friendly rust - preventive oil to coat when the surface temperature of the workpiece ≤ 50 °C, and then dry it by hot - air circulation at 60 - 80 °C for 5 - 10 minutes.

2. The high-efficiency hot-dip galvanizing process according to claim 1, wherein: The degreasing time in S1 is 5 - 15 minutes, and the Fe concentration of the pickling solution in S2 2+ 2+ is < 80 g / L. The pickling time is 10 - 30 minutes, and a fiberglass-reinforced plastic pickling tank is used.

3. The high-efficiency hot-dip galvanizing process according to claim 1, wherein: In the three - stage countercurrent rinsing in S3, the first tank is circulating water with a conductivity < 500 μS / cm, the last tank is deionized water with a conductivity < 10 μS / cm, and the single - tank immersion time is 2 - 5 minutes.

4. The high-efficiency hot-dip galvanizing process according to claim 1, characterized in that: In S5, the time for hot - dip galvanizing is determined according to the workpiece characteristics. The lifting speed is 60 - 120 mm / s. After lifting, air - cool for 10 - 20 seconds, and then enter a water - cooling tank with a water temperature of 20 - 30 °C to water - cool until ≤ 60 °C. The workpiece characteristics include workpiece thickness and material. The flow rate of the zinc liquid into which the workpiece is immersed is 0.2 - 0.5 m / s. In S6, the pH value of the passivation solution is 4.8 - 5.2, the time for passivation treatment is 20 - 60 seconds. In S7, what the environmentally friendly rust - preventive oil includes, the coating thickness is 1 - 3 μm, and the contact angle of the workpiece surface after oil coating > 90°.

5. The high-efficiency hot-dip galvanizing process according to claim 1, characterized in that: The zinc liquid includes the following raw materials by mass percentage: aluminum 5% - 11%, magnesium 0.5% - 3%, rare earth 0.01% - 0.1%, silicon 0.1% - 0.5%, and the balance is zinc.

6. The high-efficiency hot-dip galvanizing process according to claim 5, characterized in that: The preparation method of the zinc liquid is as follows: S501. Add zinc to the intermediate - frequency induction furnace according to the mass percentage. When the zinc melts into a solution at a temperature of 450 - 470 °C, add aluminum, magnesium, and silicon, and simultaneously perform stirring with a stirring speed of 100 - 200 rpm and a stirring time of 15 - 30 minutes to form a mixed solution; S502. Mix rare earth and zinc in a mass ratio of 1:9 - 11, heat to 600 - 700 °C, and simultaneously stir at a stirring speed of 150 - 250 rpm for 30 - 45 minutes to make a zinc - rare earth master alloy; S503. Add the zinc - rare earth master alloy to the mixed solution and continue to stir for 10 - 20 minutes to make the zinc - rare earth master alloy evenly dispersed in the mixed solution to obtain the zinc liquid.

7. The high-efficiency hot-dip galvanizing process according to claim 1, characterized in that: The flux comprises raw materials in the following mass percentages: zinc chloride 8%-15%, ammonium chloride 7%-12%, alkyl polyglycoside 3%-8%, modified cellulose 2%-5%, hexamethylenetetramine 0.5%-2%, sodium benzoate 0.3%-1%, citric acid 1%-3%, ascorbic acid 0.1%-0.5%, and the balance being deionized water. The modified cellulose includes hydroxypropyl methylcellulose.

8. The high-efficiency hot-dip galvanizing process according to claim 7, wherein: The preparation method of the flux is as follows: S401. Add deionized water into a reaction kettle with a stirring device according to the mass percentage, carry out stirring at a rotation speed of 80-150 rpm, and then sequentially add zinc chloride and ammonium chloride, and stir for 10-15 minutes until they are completely dissolved; S402. Then add alkyl polyglycoside and modified cellulose, continue stirring for 15-20 minutes until they are fully dispersed, add hexamethylenetetramine, sodium benzoate, citric acid, and ascorbic acid, and continuously stir for 20-30 minutes to make each component evenly mixed, thus obtaining the flux.

9. The high-efficiency hot-dip galvanizing process according to claim 1, wherein: The passivation solution comprises raw materials in the following mass percentages: sodium molybdate 8%-12%, sodium tungstate 3%-6%, aminotrimethylenephosphonic acid 1.5%-3%, citric acid 0.8%-1.5%, polyethylene glycol 0.1%-0.5%, sulfuric acid 0.5%-1.2%, and the balance being deionized water.

10. The high-efficiency hot-dip galvanizing process according to claim 9, characterized in that: The preparation method of the passivation solution is as follows: S601. Add deionized water into a corrosion-resistant liquid preparation tank according to the mass percentage, then add sodium molybdate and sodium tungstate, and carry out stirring at a stirring speed of 100-180 rpm for 15-20 minutes until they are fully dissolved; S602. Then add aminotrimethylenephosphonic acid and citric acid, continue stirring for 20-30 minutes, add polyethylene glycol, stir for 10-15 minutes, and adjust the pH value of the solution to 4.8-5.2 with sulfuric acid to obtain the passivation solution.

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