A hot-dip galvanizing sheet scatter coating process

Abstract

This invention discloses a bulk coating process for hot-dip galvanized sheets, belonging to the field of metal surface treatment and coating technology. The process includes the following steps: S1, shot blasting; S2, surface cleaning; S3, surface treatment; S4, water washing; S5, rust prevention treatment; S6, paint spraying; S7, leveling treatment; and S8, curing. This invention utilizes a three-stage pretreatment process of shot blasting, immersion washing, and rust prevention, combined with paint spraying, to achieve integrated cleaning and passivation based on shot blasting activation. This generates a crystalline zinc phosphate conversion film, followed by the formation of a Ti / Zr-Si hybrid passivation film using a chromium-free composite passivation solution, constructing a "double conversion film" layer. This process effectively protects the zinc layer and maintains its cathodic protection function while significantly improving coating adhesion and overall corrosion resistance. It is also environmentally friendly and efficient, making it particularly suitable for large-scale coating of hot-dip galvanized radiators for power equipment with high corrosion resistance requirements.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating technology for metal surfaces, and particularly to a hot-dip galvanized sheet bulk coating process. Background Technology

[0002] Hot-dip galvanizing is a common anti-corrosion treatment for metal components. The zinc layer formed by high-temperature immersion galvanizing provides cathodic protection for the substrate. However, hot-dip galvanized workpieces often have defects such as zinc nodules, oxide scale, residual flux, and white rust on their surface. In addition, the zinc layer is smooth, resulting in poor adhesion when directly coated, and it is prone to peeling and flaking.

[0003] Existing technologies mostly employ direct coating or a single shot blasting / cleaning pretreatment, which has the following shortcomings: 1. Shot blasting alone cannot completely remove white rust and trace amounts of oil stains; 2. Single pickling can easily lead to excessive corrosion of the zinc layer; the lack of targeted rust prevention transition links makes it easy for secondary rust to occur during the coating interval.

[0004] Existing processes are insufficient to meet the dual requirements of long-term corrosion protection and heat dissipation in highly corrosive environments (such as marine atmosphere, industrial acid mist, and high humidity). There is an urgent need for a new coating process that takes into account zinc layer protection, surface purification, and improved coating adhesion. Summary of the Invention

[0005] The purpose of this invention is to provide a hot-dip galvanized sheet bulk coating process that can significantly improve the coating adhesion of radiator workpieces and endow them with active self-healing and high heat radiation performance.

[0006] This invention is implemented as follows: a hot-dip galvanized sheet bulk coating process includes the following steps: S1. Workpiece preparation: Select radiator workpieces that are not passivated after hot-dip galvanizing, and remove obvious zinc nodules, burrs and large impurities from the surface. S2. Shot blasting: The workpiece is shot blasted until the surface of the workpiece is rough and uniform and there is no obvious oxide scale and flux residue. Then, compressed air is used to blow it. S3. Inner layer conversion of zinc phosphate: Immerse the workpiece in the zinc phosphate conversion treatment solution and gently move it up and down to stir until there are no white spots on the surface of the workpiece. S4. Water washing: Place the soaked workpiece into a water washing tank for water washing to remove residual treatment solution from the surface. S5. Outer passivation: Immerse the washed workpiece in the composite passivation solution, treat at room temperature for 3 to 5 minutes, and then dry with hot air. S6. Enhancement treatment: Immerse or spray the workpiece that has been treated in step S5 into the dispersion liquid, treat at room temperature for 2 min to 4 min and then dry with hot air. S7. Coating with primer: The workpiece that has completed step S6 is coated with primer, intermediate coat and topcoat in sequence using an automatic coating equipment. S8. Leveling treatment: After the paint is applied, the workpiece is leveled. S9. Curing: Transfer the leveled workpiece to a curing oven for curing. After curing, allow it to cool naturally to room temperature to obtain the finished product.

[0007] A further technical solution of the present invention is: in step S2, quartz sand or glass beads are used as abrasives, and the particle size of the abrasives is 0.6mm to 0.8mm.

[0008] A further technical solution of the present invention is: in step S3, the zinc phosphate conversion treatment solution in step S3 is prepared from the following components in parts by mass: Industrial phosphoric acid, 30-50 parts; Zinc source, 1-3 parts; Sodium nitrate accelerator, 10-20 parts; Corrosion inhibitor, 5-10 parts; Nonionic surfactant, 1-2 parts; The remainder is water.

[0009] A further technical solution of the present invention is: in step S4, the washing tank is equipped with a filter device with a filtration accuracy of ≥50μm, and the pH value in the washing tank is 5 to 7.5.

[0010] A further technical solution of the present invention is: in step S5, the pH value of the composite passivation solution is 2.5 to 4.0, and the composite passivation solution is prepared from the following components in parts by mass: Titanium compounds, 2-10 parts; Inorganic silicon compound, 5–20 parts; Tannic acid or phytic acid, 10-25 parts; Silane coupling agent, 10-20 parts; Cerium nitrate, 0.1–0.5 parts; Corrosion inhibitor, 5-10 parts; The remainder is water.

[0011] A further technical solution of the present invention is that the titanium compound is selected from at least one of fluorotitanic acid, fluorotitanate, or an organic complex of titanium; The inorganic silicon compound is selected from silica sol or nano-silica.

[0012] A further technical solution of the present invention is: the dispersion in step S6 is composed of the following components in parts by mass: Silane-modified hexagonal boron nitride, 0.5–3 parts; Polyvinylpyrrolidone or polyoxyethylene octylphenyl ether, 5 to 20 parts; Ethanol or isopropanol, 50-150 parts; KH-570 or KH-550, 1 to 5 portions; The remainder is water; Furthermore, the pH value of the dispersion is adjusted to 6.5–8.5.

[0013] A further technical solution of the present invention is: in step S7, the primer is a zinc plating primer, the intermediate paint is an epoxy resin paint, and the topcoat is an acrylic polyurethane paint.

[0014] A further technical solution of the present invention is: in step S8, the leveling temperature is 25℃~35℃, and the leveling time is 5min~10min.

[0015] A further technical solution of the present invention is that the interval between the completion of the reinforcement treatment and the start of the paint coating of the workpiece shall not exceed 4 hours.

[0016] The beneficial effects of this invention are: 1. By combining physical roughening through shot blasting with chemical purification through zinc phosphate inner layer transformation, white rust and trace amounts of oil are precisely removed, resulting in a zinc layer thinning of <0.3μm. Combined with a subsequent Zr / Ti-Si-Ce hybrid outer layer, a double protective layer is formed, fully preserving the cathodic protection function of the zinc layer. The composite passivation solution contains... When the coating is damaged, ions can migrate to the defect site and generate... / The deposition process endows the coating with active self-healing ability, greatly extending the finished product's resistance to neutral salt spray.

[0017] 2. In this invention, the 30-40 μm roughness formed by shot blasting provides a strong physical adhesion force to the paint film. Meanwhile, the silane coupling agent in the h-BN nano-anchoring layer reacts with the hydroxyl groups in the Zr / Ti-Si-Ce passivation layer at one end and cross-links with the organic coating at the other end. Simultaneously, the h-BN nanosheets themselves are embedded in the interface, forming a nanoscale "mechanical interlock." This structure results in a paint film adhesion strength ≥7.5 MPa under pull-out test and a cross-cut adhesion test grade of 0.

[0018] 3. In this invention, hexagonal boron nitride (h-BN) inherently possesses high thermal conductivity and high infrared emissivity. Through silane pre-modification and process control, this invention ensures its uniform anchoring on the workpiece surface, increasing the infrared emissivity of the heat sink surface to 0.95–0.97. In practical applications, this characteristic can reduce the temperature rise of power equipment by 8–12°C, effectively extending equipment lifespan by more than 20%, a technical effect that traditional single anti-corrosion coatings cannot achieve. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the present invention; Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0022] This invention provides a hot-dip galvanized sheet coating process, aiming to solve the problems of poor coating adhesion, easy damage to the zinc layer during pretreatment, or poor rust prevention transition in existing technologies. This process significantly improves the overall corrosion resistance of the coating through a synergistic pretreatment of shot blasting, surface treatment, and passivation sealing, combined with spray coating. Its core innovation lies in forming a three-layer composite film structure: 1. Zinc phosphate inner membrane This achieves a metallurgical bond with the zinc layer and provides a barrier protection; 2. Zr / Ti-Si-Ce hybrid passivation outer layer film enhances corrosion resistance and self-healing function; 3. The h-BN nano-anchoring layer improves the adhesion of the paint film through mechanical interlocking and chemical anchoring, while also improving heat dissipation performance.

[0023] A hot-dip galvanized sheet bulk coating process includes the following steps: (1) Workpiece preparation: Select a radiator workpiece that has not been passivated after hot-dip galvanizing (material Q235, zinc coating thickness approximately 85μm). Remove zinc nodules, burrs, and large impurities from the workpiece surface to provide a smooth surface for subsequent processing. Unpassivated workpieces ensure that the chemical conversion solution can directly act on the zinc layer, improving adhesion.

[0024] (2) Surface roughening treatment: Use quartz sand or glass beads with a particle size of 0.6mm to 0.8mm as abrasive to shot blast the workpiece for 3min to 8min until the workpiece surface is uniformly rough, the roughness Ra value reaches 30μm to 40μm, and there is no obvious oxide scale and flux residue. Then, use compressed air to blow it.

[0025] The impact of high-speed abrasives thoroughly removes white rust (basic zinc oxide), welding scale, and residual flux (such as ammonium chloride) generated during storage and transportation on the surface of the galvanized layer, providing a clean zinc layer surface for subsequent chemical conversion. (3) Inner layer conversion of zinc phosphate: Immerse the workpiece in the zinc phosphate conversion solution and gently stir it up and down. Treat at room temperature for 5 to 6 minutes until there are no white spots on the workpiece surface and an in-situ layer with a thickness of 1 to 3 μm is formed. Inner membrane.

[0026] The zinc phosphate conversion treatment solution is prepared from the following components in parts by mass: Industrial phosphoric acid, 30-50 parts; Zinc source, 1-3 parts; Sodium nitrate accelerator, 10-20 parts; Corrosion inhibitor, 5-10 parts; Nonionic surfactant, 1-2 parts; The remainder is water. The pH of the treated solution is 1.8–2.5.

[0027] This step utilizes an acidic treatment solution to induce a micro-dissolution reaction with the zinc layer. While removing trace amounts of oil and oxide film from the surface, it also induces in-situ nucleation and growth of zinc phosphate crystals on the zinc layer surface by increasing the interfacial pH, forming a dense inner film that is metallurgically bonded to the substrate. The film thickness is precisely controlled between 1-3 μm, providing both barrier protection and avoiding excessive consumption of the zinc layer (thinning <0.3 μm), thus preserving the cathodic protection function of the zinc layer. Sodium nitrate in the treatment solution accelerates film formation, corrosion inhibitors prevent localized over-corrosion, and surfactants improve wettability to ensure uniform film formation for complex structures. The absence of white spots on the surface at the treatment endpoint indicates that the original white rust has been completely converted.

[0028] (4) Water washing: After the workpiece has been soaked, put it into a water washing tank equipped with a filter device with a filtration accuracy of ≥50μm for water washing until the pH value of the workpiece surface is stable at 6.5 to 7.5.

[0029] After treatment with acidic zinc phosphate solution, a strongly acidic liquid remains on the workpiece surface. If it is directly introduced into the next step of composite passivation solution with a pH of 2.5–4.0, the interface pH value will fluctuate drastically, resulting in uneven formation and a loose structure of the outer passivation film. By washing with water, the surface pH value is precisely controlled to a neutral range of 6.5–7.5, creating ideal pH gradient conditions for the uniform film formation of the outer passivation solution in the next step.

[0030] The filtration device is included to prevent contamination by impurity ions and ensure the quality of water washing.

[0031] (5) Zr / Ti-Si-Ce hybrid outer layer passivation: The workpiece after water washing is immersed in the composite passivation solution, treated at room temperature for 2 min to 4 min and then dried with hot air; a Zr / Ti-Si-Ce hybrid outer layer film with a thickness of 0.5 μm to 2 μm is formed.

[0032] Specifically, the pH value of the composite passivation solution is 2.5 to 4.0, and the composite passivation solution is prepared from the following components in parts by mass: Titanium compounds, 2-10 parts; Inorganic silicon compound, 5–20 parts; Tannic acid or phytic acid, 10-25 parts; Silane coupling agent, 10-20 parts; Cerium nitrate, 0.1–0.5 parts; Corrosion inhibitor, 5-10 parts; The remainder is water.

[0033] In this step, the composite passivation solution used constructs a hybrid passivation film on the workpiece surface through the synergistic effect of multiple components, which has both density and self-healing function.

[0034] Specifically, titanium / zirconium compounds are hydrolyzed under acidic conditions to form / Colloidal deposition forms an inorganic framework, providing basic corrosion resistance for the film. At the same time, inorganic silicon compounds (such as silica sol or nano-silica) fill the pores of the framework, further improving the density of the film.

[0035] Tannic acid or phytic acid, as natural organic polyacids, can undergo complexation reactions with zinc ions and titanium / zirconium ions to form an organic-inorganic hybrid network, thereby enhancing the flexibility and adhesion of the film. Silane coupling agents act as "molecular bridges": one end connects to an inorganic surface (such as a zinc layer, etc.). The hydroxyl group of the substance (etc.) is condensed at one end, and the other end contains an organic functional group, which provides chemical bonding sites for the subsequent adhesion of organic coatings.

[0036] In particular, the introduction of cerium nitrate endows the film with the ability to actively repair micro-damage—cerium ions ( The coating is evenly distributed within the film layer. Once microcracks appear in the coating due to mechanical damage, corrosive media (such as...) can penetrate it. Infiltration causes a local increase in pH value. It will then migrate to the defect and hydrolyze to form insoluble substances. / The deposits actively seal microcracks, thereby inhibiting corrosion propagation.

[0037] Through the synergistic effect of the above components, this hybrid passivation film not only possesses excellent initial protective performance but also acquires the self-healing ability to actively repair micro-damage. The formed Zr / Ti-Si-Ce hybrid outer layer and the underlying zinc phosphate inner layer form a dense gradient film, which works synergistically to protect the zinc layer.

[0038] (6) h-BN reinforcement treatment: Immerse or spray the workpiece treated in step (5) with a dispersion containing silane pre-modified hexagonal boron nitride, treat at room temperature for 2 to 4 minutes, and then dry with hot air. The dispersion consists of the following components in parts by mass: Silane-modified hexagonal boron nitride, 0.5–3 parts; Polyvinylpyrrolidone or polyoxyethylene octylphenyl ether, 5 to 20 parts; Ethanol or isopropanol, 50-150 parts; KH-570 or KH-550, 1 to 5 portions; The remainder is water; Furthermore, the pH value of the dispersion is adjusted to 6.5–8.5.

[0039] Specifically, h-BN possesses a graphite-like layered structure with a large specific surface area for its nanoscale sheets (50–200 nm in diameter). When these sheets are adsorbed onto the passivation layer surface and dried, they form a rough nanoscale "anchoring layer." During subsequent coating, the organic paint penetrates into these nanoscale gaps, and after curing, forms a "hook-like" mechanically interlocking structure, greatly enhancing the adhesion of the paint film. Simultaneously, the h-BN nanosheets are pre-modified with a silane coupling agent, grafting organic functional groups onto their surface. The free silane coupling agent in the dispersion can react with the underlying passivation film at one end and cross-link with the organic paint film at the other, thus achieving chemical anchoring.

[0040] Furthermore, h-BN itself is a highly thermally conductive material with a high infrared emissivity. Anchoring it to the workpiece surface can increase the infrared emissivity of the heat sink from approximately 0.88 to over 0.95. This means the heat sink can more effectively transfer heat through thermal radiation, thereby reducing equipment temperature rise. Applying a weak magnetic field during processing can also align the h-BN sheets parallel to the surface, further enhancing thermal radiation efficiency.

[0041] Optionally, a weak magnetic field can be applied during the process to help h-BN achieve parallel orientation.

[0042] It should be noted that the workpiece after reinforcement treatment should be dried with hot air at 80℃~110℃ to form a stable gradient composite film with a total thickness controlled below 6μm.

[0043] (7) The workpiece that has undergone reinforcement treatment is coated with primer, intermediate paint and topcoat in sequence using an automatic coating equipment. Specifically, the primer is a zinc-plating primer (such as epoxy zinc-rich primer), the intermediate paint is an epoxy resin paint (such as epoxy micaceous iron oxide intermediate paint), and the topcoat is an acrylic polyurethane paint.

[0044] The interval between the completion of the reinforcement treatment and the start of the paint coating should not exceed 4 hours to prevent the h-BN anchoring layer from being contaminated or failing due to moisture absorption.

[0045] (8) After the paint coating is completed, the workpiece is leveled at 25℃~35℃ for 5min~10min. Leveling allows the wet paint film to spread more evenly, eliminates defects such as flow marks and orange peel generated during the paint coating process, and allows the solvent to partially evaporate.

[0046] (9) Transfer the leveled workpiece to a curing oven for curing (usually between 120℃ and 160℃, depending on the specific paint). After curing, allow it to cool naturally to room temperature to obtain the finished product.

[0047] The technical solution of the present invention will be described below by way of example, with reference to specific process parameters and operating steps. Example 1

[0048] A hot-dip galvanized sheet bulk coating process includes the following steps: S1. Workpiece preparation: Select a transformer fin radiator that has not been passivated after hot-dip galvanizing (material is Q235, average zinc layer thickness is 85μm), and use an angle grinder to grind away zinc nodules and welding spatter burrs from the edges.

[0049] S2. Shot blasting: The workpiece is fed into a tracked shot blasting machine, using 0.6mm quartz sand as the abrasive, and shot blasted for 5 minutes. After treatment, the surface roughness Ra value is measured to be 35μm, and no oxide scale or flux residue is observed by the naked eye. Then, the surface dust is blown away with 0.6MPa clean compressed air.

[0050] S3. Inner layer conversion of zinc phosphate: Prepare zinc phosphate conversion treatment solution: Add 40g of industrial phosphoric acid, 2g of zinc oxide, 15g of sodium nitrate, 8g of sodium molybdate corrosion inhibitor, 1.5g of OP-10 emulsifier, and add pure water to 1L. Stir well and adjust the pH to 2.0 with phosphoric acid or sodium hydroxide.

[0051] The workpiece was immersed in the treatment solution and shaken up and down at room temperature for 5.5 minutes. The white spots on the surface were observed to be completely dissolved, and the water film remained continuous. A uniform inner film was formed, and the film thickness was observed to be approximately 2 μm using a scanning electron microscope. The zinc layer thinning was measured to be 0.2 μm using a magnetic thickness gauge.

[0052] S4. Water Washing: Place the workpiece in a water washing tank equipped with a 50μm precision bag filter and a circulating water flow rate of 2m³ / h. 3 / h. Control the pH of the final stage water washing tank to 7.0. After rinsing for 2 minutes, remove the workpiece and test the wetting solution on the workpiece surface with precision pH test paper; the pH value is 6.8.

[0053] S5. Outer passivation: Prepare composite passivation solution: Add 6g of fluorotitanic acid, 40g of silica sol, 36g of phytic acid, 15mL of KH-560 silane coupling agent, 0.3g of cerium nitrate, and 8g of sodium molybdate corrosion inhibitor in sequence. Add pure water to 1L, stir evenly, and adjust the pH value to 3.2 with sodium carbonate or acetic acid.

[0054] The workpiece was immersed in the passivation solution and treated at room temperature for 4 minutes to ensure uniform film formation of the internal layers. After removal, it was allowed to drip dry for 30 seconds. X-ray fluorescence spectroscopy (XRF) determined that the thickness of the Zr / Ti-Si-Ce hybrid outer layer film was approximately 1.5 μm.

[0055] S6. Enhancement treatment: Preparation of h-BN dispersion: Weigh 2g of silane-modified hexagonal boron nitride nanosheets (average particle size 100nm, pre-modified with KH-570), 5g of KH-570 silane coupling agent, add to 993g of pure water, stir magnetically for 30 minutes, adjust pH to 7.0 with dilute ammonia water to obtain a dispersion containing 0.2wt% h-BN and 0.5wt% silane coupling agent.

[0056] The workpiece is immersed in the dispersion solution using an dip-coating method and kept at room temperature for 3 minutes. During this time, electromagnets are placed on both sides of the tank to apply a weak magnetic field of 0.1T to assist in aligning the h-BN sheets parallel to the workpiece surface. After removal, the workpiece is allowed to drip dry.

[0057] S7. Coating: Within 2 hours of completing the reinforcement treatment, hang the workpiece on the automatic coating line. The coating line speed is 1.5m / min, and epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate coat, and acrylic polyurethane topcoat are applied sequentially. Flash-dry for 5 minutes between each coat.

[0058] S8. Leveling treatment: After the paint is applied, the paint is placed in a leveling room at a temperature of 28℃ and a relative humidity of 60% for 8 minutes.

[0059] S9. Curing: Place the workpiece into a curing oven and bake at 140℃ for 30 minutes. Remove it and let it cool naturally to room temperature to obtain the finished product.

[0060] The performance test results of Example 1 are shown in Table 1. Example 2

[0061] This embodiment is basically the same as Embodiment 1, but some process parameters are adjusted to demonstrate the process tolerance of the present invention. A hot-dip galvanized sheet bulk coating process includes the following steps: S1. Workpiece preparation: Same as in Example 1.

[0062] S2. Shot blasting: Using 0.8mm glass beads as abrasive, shot blasting was performed for 6 minutes, and the surface roughness Ra value reached 38μm.

[0063] S3, Inner layer conversion of zinc phosphate: The composition of the treatment solution is the same as in Example 1, the pH is adjusted to 2.3, the treatment time is 6 min, an inner layer film of about 2.5 μm is generated, and the zinc layer is thinned by 0.3 μm.

[0064] S4. Water washing: Same as in Example 1, the surface pH is 7.2 after water washing.

[0065] S5. Outer layer passivation: The composition of the treatment solution is the same as in Example 1, the treatment time is 5 min, and a Zr / Ti-Si-Ce film with a thickness of about 1.2 μm is generated.

[0066] S6. Enhancement treatment: Apply by spraying. The h-BN dispersion composition is the same as in Example 1. Use an air spray gun to spray evenly until the workpiece surface is completely wetted. Keep at room temperature for 2 minutes without applying a magnetic field.

[0067] S7. Drying: Dry with hot air at 100℃ for 10 minutes. The total thickness of the composite film is about 4.8μm, and the total thinning of the zinc layer is 0.6μm.

[0068] S8. Spray painting: The interval time is controlled within 3 hours, and the rest is the same as in Example 1.

[0069] S9. Leveling treatment: Leveling temperature 32℃, leveling time 6min.

[0070] S10, Curing: Same as in Example 1.

[0071] The performance test results of Example 2 are shown in Table 1.

[0072] Comparative Example 1 Select bulk hot-dip galvanized sheet workpieces from the same batch and treat them using conventional pickling and rust removal processes. A bulk hot-dip galvanized sheet coating process includes the following steps: S1. Workpiece preparation: Select a transformer fin radiator that has not been passivated after hot-dip galvanizing, and grind away zinc nodules and welding spatter burrs from the edges and corners.

[0073] S2. Pickling treatment: Immerse the workpiece in a 5% hydrochloric acid solution and treat at room temperature for 5 minutes to remove surface oxide scale and white rust.

[0074] S3. Water washing: Place the pickled workpiece in a clean water tank and wash for 2 minutes to remove residual acid from the surface.

[0075] S4. Passivation treatment: Immerse the workpiece in hexavalent chromium passivation solution (chromate passivation solution) and treat at room temperature for 1 minute.

[0076] S5. Washing and drying: After the passivated workpiece is washed with water, it is dried with hot air.

[0077] S6. Spray coating: The workpiece is coated sequentially with epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and acrylic polyurethane topcoat using automatic spray coating equipment.

[0078] S7. Leveling treatment: After the paint is applied, let it stand for 8 minutes in a 28℃ leveling room.

[0079] S8. Curing: Place the workpiece into a curing oven and bake at 140℃ for 30 minutes. Remove it and let it cool naturally to room temperature to obtain the finished product.

[0080] The performance test results of Comparative Example 1 are shown in Table 1.

[0081] Comparative Example 2 The process of this invention is employed, but the h-BN reinforcement treatment step is omitted, to verify the necessity of the h-BN layer. A hot-dip galvanized sheet bulk coating process includes the following steps: S1. Workpiece preparation: Select 10kV transformer radiators that have not been passivated after hot-dip galvanizing from the same batch, and grind away zinc nodules and welding spatter burrs from the edges and corners.

[0082] S2. Shot blasting and roughening: 0.6mm quartz sand is used as abrasive. Shot blasting is performed for 5 minutes to achieve a surface roughness Ra value of 35μm. Then, 0.6MPa compressed air is used to blow away the floating dust.

[0083] S3. Zinc phosphate inner layer conversion: Prepare zinc phosphate conversion treatment solution (per 1L): 40g industrial phosphoric acid, 2g zinc oxide, 15g sodium nitrate, 8g sodium molybdate corrosion inhibitor, 1.5g OP-10 emulsifier, add pure water to 1L, and adjust pH to 2.0. Immerse the workpiece in the treatment solution, and shake it up and down at room temperature for 5.5 minutes until no white spots appear on the surface. An inner layer film of approximately 2μm is formed, and the zinc layer is reduced by 0.2μm.

[0084] S4. Intermediate control of water washing: Place the workpiece in the water washing tank, control the pH value of the final water washing tank to 7.0, and the pH value of the surface after water washing to 6.8.

[0085] S5. Zr / Ti-Si-Ce self-healing outer passivation: Prepare a composite passivation solution (per 1L): 6g fluorotitanic acid, 40g silica sol, 36g phytic acid, 15mL KH-560 silane coupling agent, 0.3g cerium nitrate, 8g sodium molybdate corrosion inhibitor, and add pure water to 1L, adjusting the pH to 3.2. Immerse the workpiece in the passivation solution and treat at room temperature for 4 minutes. Remove and drip dry, forming a Zr / Ti-Si-Ce film with a thickness of approximately 1.5μm.

[0086] S6. Drying: Place the workpiece in an oven and dry with hot air at 100℃ for 10 minutes. The total thickness of the composite film is approximately 3.5μm, and the total thinning of the zinc layer is 0.5μm.

[0087] S7. Spray coating: Within 2 hours after drying, spray the workpiece with epoxy zinc-rich primer, epoxy micaceous iron oxide intermediate paint and acrylic polyurethane topcoat in sequence.

[0088] S8. Leveling treatment: After the paint is applied, let it stand at 28℃ for 8 minutes.

[0089] S9. Curing: Bake at 140℃ for 30 minutes, then cool naturally.

[0090] The performance test results of Comparative Example 2 are shown in Table 1.

[0091] Table 1: Performance Test Table The test results above show that: Compared to Comparative Example 1, the zinc layer thinning amount in this embodiment is significantly lower than that of the traditional process, thus better preserving the cathodic protection function of the zinc layer. Regarding adhesion, the pull-off adhesion of this embodiment is significantly improved, achieving the optimal level in the cross-cut test, which is significantly better than the traditional process. In terms of salt spray resistance, the time for red rust to appear in this embodiment is significantly extended, and the corrosion width after cross-cutting in the salt spray test is significantly reduced, confirming the effectiveness of Ce... 3+ The invention exhibits a self-healing effect. Furthermore, the infrared emissivity of the embodiments of the present invention is significantly improved, resulting in a noticeable temperature reduction effect.

[0092] Compared to Comparative Example 2, the embodiments of the present invention are comprehensively superior to the process without the h-BN layer in terms of adhesion, salt spray resistance, and heat dissipation performance. The significantly improved adhesion demonstrates the dual enhancing effect of the h-BN nano-anchoring layer through "mechanical interlocking + chemical anchoring." The significantly improved infrared emissivity and temperature drop indicate that the introduction of the h-BN layer not only enhances adhesion but also unexpectedly brings significant heat dissipation gains, achieving a synergistic effect of "1+1>2".

[0093] Comparison between Example 1 and Example 2: In Example 2, the performance index decreased slightly but remained at a high level despite some fluctuations in process parameters, indicating that the process of the present invention has a wide process window and is suitable for different production conditions.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hot-dip galvanized sheet bulk coating process, characterized in that, Includes the following steps: S1. Workpiece preparation: Select radiator workpieces that are not passivated after hot-dip galvanizing, and remove obvious zinc nodules, burrs and large impurities from the surface. S2. Shot blasting: The workpiece is shot blasted until the surface of the workpiece is rough and uniform and there is no obvious oxide scale and flux residue. Then, compressed air is used to blow it. S3. Inner layer conversion of zinc phosphate: Immerse the workpiece in the zinc phosphate conversion treatment solution and gently move it up and down to stir until there are no white spots on the surface of the workpiece. S4. Water washing: Place the soaked workpiece into a water washing tank for water washing to remove residual treatment solution from the surface. S5. Outer passivation: Immerse the washed workpiece in the composite passivation solution, treat at room temperature for 3 to 5 minutes, and then dry with hot air. S6. Enhancement treatment: Immerse or spray the workpiece that has been treated in step S5 into the dispersion liquid, treat at room temperature for 2 min to 4 min and then dry with hot air. S7. Coating with primer: The workpiece that has completed step S6 is coated with primer, intermediate coat and topcoat in sequence using an automatic coating equipment. S8. Leveling treatment: After the paint is applied, the workpiece is leveled. S9. Curing: Transfer the leveled workpiece to a curing oven for curing. After curing, allow it to cool naturally to room temperature to obtain the finished product.

2. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S2, quartz sand or glass beads are used as abrasives, and the particle size of the abrasives is 0.6 mm to 0.8 mm.

3. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S3, the zinc phosphate conversion treatment solution described in step S3 is prepared from the following components in parts by mass: Industrial phosphoric acid, 30-50 parts; Zinc source, 1-3 parts; Sodium nitrate accelerator, 10-20 parts; Corrosion inhibitor, 5-10 parts; Nonionic surfactant, 1-2 parts; The remainder is water.

4. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S4, the washing tank is equipped with a filter device with a filtration accuracy of ≥50μm, and the pH value in the washing tank is 5 to 7.

5.

5. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S5, the pH value of the composite passivation solution is 2.5 to 4.0, and the composite passivation solution is prepared from the following components in parts by mass: Titanium compounds, 2-10 parts; Inorganic silicon compound, 5–20 parts; Tannic acid or phytic acid, 10-25 parts; Silane coupling agent, 10-20 parts; Cerium nitrate, 0.1–0.5 parts; Corrosion inhibitor, 5-10 parts; The remainder is water.

6. The hot-dip galvanized sheet bulk coating process according to claim 5, characterized in that, The titanium compound is selected from at least one of fluorotitanic acid, fluorotitanate, or an organic complex of titanium; The inorganic silicon compound is selected from silica sol or nano-silica.

7. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, The dispersion in step S6 is composed of the following components in parts by mass. composition: Silane-modified hexagonal boron nitride, 0.5–3 parts; Polyvinylpyrrolidone or polyoxyethylene octylphenyl ether, 5 to 20 parts; Ethanol or isopropanol, 50-150 parts; KH-570 or KH-550, 1 to 5 portions; The remainder is water; Furthermore, the pH value of the dispersion is adjusted to 6.5–8.

5.

8. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S7, the primer is a zinc plating primer, the intermediate paint is an epoxy resin paint, and the topcoat is an acrylic polyurethane paint.

9. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, In step S8, the leveling temperature is 25℃~35℃, and the leveling time is 5min~10min.

10. The hot-dip galvanized sheet bulk coating process according to claim 1, characterized in that, The interval between the completion of the reinforcement treatment and the start of the paint coating process shall not exceed 4 hours.

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