Magnesium smelting workshop steel structure multi-layer anti-corrosion fireproof coating system and construction method

Abstract

The invention discloses a multi-layer anti-corrosion fireproof coating system for a steel structure of a magnesium smelting workshop and a construction method, which are used for solving the problem of steel structure protection in a severe environment in which high temperature, strong corrosion (such as HF and SO2) and fire risk coexist. The system consists of four layers, namely a zinc-rich primer (60-80 microns, the zinc content of more than or equal to 80% and containing a silane coupling agent), an epoxy closed transition layer (20-30 microns), a fireproof coating layer (thin type 3-7 mm / thick type 15-25 mm) with built-in alkali-free glass fiber gridding cloth and a corrosion-resistant surface layer (150-200 microns), wherein the corrosion-resistant surface layer contains calcium fluoride or phenolic aldehyde modified components. In the construction process, 1000-1500W laser rust removal is adopted to replace sand blasting, and gridding cloth laying by a wet laying method and a layered curing process are combined, so that the durability, the fire endurance and the adhesive force of the coating are remarkably improved, the construction cost is reduced by 15-20%, and the coating is particularly suitable for steel structure protection transformation of high-altitude and existing magnesium smelting workshops.

Description

Technical Field

[0001] This invention relates to the field of industrial steel structure corrosion and fire protection technology, specifically to a multi-layer anti-corrosion and fireproof coating system and construction method for steel structures in high-temperature, highly corrosive, and high-altitude operation scenarios in magnesium smelting workshops. Background Technology

[0002] Due to the characteristics of the production process, magnesium smelting workshops face multiple harsh operating conditions: On the one hand, during the smelting process, SF6, used as a protective gas, is prone to decomposition at high temperatures to produce HF, a highly acidic gas. Fuel combustion and raw material impurities release corrosive gases such as SO2 and HCl. At the same time, the high temperature (50-100℃) and high humidity environment accelerates the electrochemical corrosion of the steel structure. On the other hand, magnesium powder is flammable and fuels have a high volatile content, resulting in an extremely high fire risk. The steel structure must have sufficient fire resistance. In addition, after the workshop is built, the steel structure is mostly located at high altitudes (such as columns and beams), making it difficult to implement traditional pretreatment methods such as sandblasting and rust removal, further increasing the difficulty of coating construction.

[0003] In existing technologies, the coating of steel structures in magnesium smelting workshops mostly adopts a two-layer structure of "single anti-corrosion coating + fireproof coating", which has the following drawbacks:

[0004] Insufficient corrosion resistance: Conventional epoxy coatings have poor resistance to HF and SO2 penetration, and the coating is prone to pinholes and cracks. The corrosion protection life is usually only 3-5 years, requiring frequent maintenance.

[0005] Poor compatibility between fire retardancy and corrosion resistance: Fire retardant coatings (especially thick ones) are mostly inorganic base materials, which have weak adhesion to organic anti-corrosion coatings and are prone to delamination and peeling.

[0006] Poor construction adaptability: Sandblasting cannot be used to remove rust from high-altitude steel structures, resulting in insufficient adhesion between the coating and the substrate; thick fireproof coatings are prone to dripping during application and cracking after curing.

[0007] High cost: Frequent maintenance leads to increased total cost, and the use of expensive materials such as carbon fiber mesh in some solutions further increases the economic burden.

[0008] For example, patent CN108753246A proposes an anti-corrosion and fireproof coating for industrial steel structures, which adopts an "epoxy primer + intumescent fireproof coating + fluorocarbon topcoat" structure. However, it is not designed for highly corrosive gases such as HF in magnesium smelting workshops, and it does not solve the problems of high-altitude rust removal and fireproof coating flow. Patent CN110256789B discloses an anti-corrosion coating containing glass flakes, but it does not combine fireproof function, and sandblasting pretreatment is still required during construction, making it unsuitable for existing high-altitude steel structures.

[0009] Therefore, there is an urgent need to develop a coating system and construction method that combines strong corrosion resistance, high fire resistance, adaptability to high-altitude construction, and economy to meet the special needs of magnesium smelting workshops. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-layer anti-corrosion and fireproof coating system and construction method for steel structures in magnesium smelting workshops. Through multi-layer functional collaborative design, targeted material selection and process optimization, it solves three core problems: strong corrosion, fire risk and high-altitude construction.

[0011] I. Coating System Design

[0012] The coating system of the present invention consists of four layers from bottom to top, each layer having complementary and synergistic functions, as detailed below:

[0013] Zinc-rich primer layer: As the underlying rust-preventive base, a solvent-based epoxy zinc-rich primer (zinc content ≥80%) is used. Through the sacrificial anodic protection of zinc powder and the physical barrier effect of a dense zinc salt layer, oxidation of the steel structure substrate is prevented. Adding 2%-5% silane coupling agent significantly improves adhesion to the substrate, solving the problem of peeling caused by incomplete high-altitude rust removal with traditional zinc-rich primers; the solvent-based system avoids the bubbling risk caused by incomplete moisture evaporation in water-based coatings in high-temperature workshops.

[0014] Epoxy Sealing Transition Layer: Addressing the poor compatibility between zinc-rich primers (low polarity) and fire-retardant coatings (inorganic substrates), an E-44 epoxy resin-based transition layer is designed. This layer can penetrate into the tiny pores of the zinc-rich primer while simultaneously providing a polar surface for the upper fire-retardant coating, increasing interlayer adhesion by 30%-50% and effectively preventing delamination.

[0015] Fire-retardant coating layer: Thin / thick fire-retardant coatings are selected according to the load-bearing requirements of the steel structure. The key innovation lies in embedding 8-12 mesh alkali-free glass fiber mesh.

[0016] The mesh fabric acts as a "skeleton" to support the fireproof coating and solves the problem of dripping when applying a thick coating (especially for vertical steel columns);

[0017] The fiber structure disperses the stress generated by temperature changes, inhibiting cracking after curing;

[0018] Alkali-free glass fiber has a temperature resistance of ≥200℃, which is compatible with the high-temperature working conditions in magnesium smelting workshops. Moreover, its cost is only 1 / 5 to 1 / 8 of that of carbon fiber mesh, thus balancing performance and economy.

[0019] Corrosion-resistant surface coating: Three differentiated formulations were designed to address the highly corrosive gases present in magnesium smelting workshops.

[0020] Formula A (Epoxy-Glass Flakes): Add 5%-8% calcium fluoride, which can react with HF to generate stable CaF2·2H2O, enhancing the resistance to HF corrosion; the "maze effect" of glass flakes blocks gas permeation, making it suitable for normal temperature ranges;

[0021] Formula B (Modified Epoxy-Phenolic): After phenolic modification, the temperature resistance is improved to 120℃, and graphite powder assists in heat dissipation, making it suitable for high-temperature environments near the melting zone.

[0022] Formula C (polyurea): gel time < 5 min, fully dry in 1 h, suitable for emergency repairs, with good elasticity to adapt to slight deformation of steel structures and reduce cracking.

[0023] II. Innovation in Construction Methods

[0024] Addressing the construction challenges of existing high-altitude steel structures, the core innovations of this invention's construction method are as follows:

[0025] Laser rust removal + spot grinding replaces sandblasting: Utilizing a 1000-1500W air-cooled handheld laser rust removal machine, weighing only 5-10kg, suitable for high-altitude operations, with a rust removal efficiency of 0.5-1m. 2 / h, combined with localized grinding using an 80-120 grit resin abrasive wheel, to achieve a surface roughness of Ra20μm, meeting the coating adhesion requirements. Compared to sandblasting, it requires no large equipment, produces no dust pollution, and causes less damage to the substrate (laser power is controllable);

[0026] "Wet laying method" for laying mesh cloth: immediately after applying the first coat of fireproof coating, lay the mesh cloth and press it in with a scraper until it is completely saturated to ensure that the mesh cloth and the coating are tightly bonded and to avoid air bubbles; lay adjacent mesh cloths at a 90° angle to further enhance the resistance to deformation.

[0027] Layered curing control: Strictly control the curing interval of each layer (zinc-rich primer 4-6h, transition layer 24h, fire retardant coating 24h per coat, anti-corrosion surface layer 4-6h) to avoid coating blistering caused by solvent retention; for polyurea coatings, control the construction time after mixing to ≤10min to ensure curing quality;

[0028] Targeted testing and maintenance: Regularly test the pH value of the anti-corrosion surface and reapply it in time; strengthen the corners (rounded corner mesh cloth + 20% thicker coating) to solve the problem of easy corrosion and cracking in weak areas.

[0029] III. Beneficial Effects

[0030] Excellent performance: corrosion resistance life ≥ 8 years (traditional solutions 3-5 years), fire resistance limit 0.5-3 hours (meeting the needs of different load-bearing structures), coating adhesion ≥ 4MPa, and can withstand high temperatures of 50-120℃ and strong corrosive gases such as HF and SO2.

[0031] Highly adaptable to construction: Suitable for existing high-altitude steel structures, no sandblasting required, lightweight equipment, safe and convenient high-altitude operations; solves the problems of fireproof coating dripping and cracking;

[0032] Excellent economic performance: The total cost is 15%-20% lower than the traditional solution (sandblasting + carbon fiber mesh + conventional coating), the maintenance cycle is extended, and the long-term economic benefits are significant.

[0033] Environmentally friendly and safe: Laser rust removal generates no dust, and the coating uses low-VOC solvents, meeting environmental protection requirements; no open flame is required during construction (except for local repairs), reducing the risk of fire in magnesium smelting workshops. Detailed Implementation

[0034] The coating system and construction method of the present invention are described in detail below through six specific embodiments. Each embodiment is designed for different areas of the magnesium smelting workshop (conventional area, near-smelting area, emergency repair area) and steel structure types (load-bearing columns, non-load-bearing beams, high-altitude platforms).

[0035] The following six embodiments are designed for different working areas in the magnesium smelting workshop (conventional low temperature zone, near-smelting high temperature zone, emergency repair zone) and different functional steel structures (non-load-bearing beams, load-bearing columns, high-altitude maintenance platforms, smelting furnace support steel frames, temporary maintenance supports, and old coating renovation steel components). They are designed in combination with the differences in coating system parameters and construction processes, and all meet the core requirements of "corrosion protection life ≥ 8 years, fire resistance limit meets the standard, and high-altitude construction adaptability". In addition, each embodiment reflects targeted optimization in material selection and process details.

[0036] Example 1: Non-load-bearing steel beams in the conventional area of ​​a magnesium smelting workshop (temperature ≤ 60℃, fire resistance limit 0.5h)

[0037] 1.1 Operating Background

[0038] The steel beam is located in an auxiliary area of ​​the workshop, far from the smelting furnace. It mainly bears its own weight and minor maintenance loads. The ambient temperature is stable between 35-60℃, and the SF6 leakage concentration is low (HF content ≤0.1mg / m³). 3 However, it is susceptible to SO2 (fuel combustion products) and water vapor erosion, so both basic corrosion protection and low cost must be considered.

[0039] 1.2 Coating system parameters (from substrate outwards)

[0040]

[0041] 1.3 Construction Process Details

[0042] S1 Surface Pretreatment: A 1000W air-cooled handheld laser rust removal machine (weighing 5kg, compatible with high-altitude telescopic poles) is used, with a laser power of 150W / mm. 2 The scanning speed was 8 mm / s. After rust removal, the surface was purged with 0.5 MPa high-pressure air. The weld seams were lightly ground with an 80-grit resin grinding wheel. The final surface roughness Ra = 22 μm, and the oil content was 3 mg / m³. 2 (Detection by solvent wiping method).

[0043] Application of S2 zinc-rich primer: Mix base material and zinc powder at a ratio of 1:2.5, add 3% KH-550, mechanically stir for 15 minutes and then cure for 10 minutes; use high-pressure airless spraying (nozzle diameter 0.2 mm, pressure 15 MPa), wet film thickness 80 μm, cure at 25℃ for 4 hours, and the average dry film thickness is 61 μm.

[0044] S3 transition layer construction: E-44 epoxy resin and T31 are mixed at a ratio of 7:1. After stirring evenly, the mixture is applied by roller within 20 minutes. The wet film thickness is 30μm. The mixture is cured at 25℃ for 24 hours, and the dry film thickness is 21μm.

[0045] S4 fire-retardant coating application: The first coat is sprayed with a wet film thickness of 4mm. Immediately lay the mesh cloth (cut the corners to R=10mm rounded corners), flatten it with a scraper until it is completely saturated, and cure at 25℃ for 24 hours; the second coat is sprayed with a wet film thickness of 4mm. After curing for 24 hours, lightly grind the surface. The average dry film thickness is 3.1mm.

[0046] S5 anti-corrosion surface coating construction: After mixing all components of formula A, grind them to a fineness of 45μm, and apply with high-pressure airless spray (pressure 12MPa). The first wet film thickness is 120μm and it is cured for 4 hours. The second wet film thickness is 125μm and it is cured for 4 hours. The average dry film thickness is 152μm.

[0047] S6 Inspection and Repair: Visually inspect for no missed coatings / bubbling; film thickness deviation ≤ ±5%; pull-off test: zinc-rich primer adhesion 5.2MPa, anti-corrosion surface layer adhesion 4.3MPa; one pinhole (0.3mm in diameter) is repaired with two coats of Formula A, and the coating passes the re-inspection after curing.

[0048] 1.4 Performance Verification

[0049] Corrosion resistance: No rust was observed after 1000 hours of neutral salt spray test (GB / T 10125-2021); HF gas immersion test (concentration 0.5 mg / m³) 3 300h coating without bubbling.

[0050] Fire resistance performance: Tested according to GB / T 9978.1-2021, the fire resistance limit is 0.6h, which meets the requirements for non-load-bearing structures.

[0051] Economic efficiency: The total cost is 22 yuan / m2 (including materials and labor), which is 18% lower than the traditional sandblasting + conventional coating solution.

[0052] Example 2: Load-bearing steel columns near the smelting area in a magnesium smelting workshop (temperature 80-100℃, fire resistance limit 2h)

[0053] 2.1 Operating Context

[0054] The steel column is located within a 3-meter radius of the smelting furnace, bearing the load from the workshop roof and equipment vibrations. The ambient temperature fluctuates greatly (80-100℃), and the concentration of HF, a decomposition product of SF6, is relatively high (0.3-0.5 mg / m³). 3 Furthermore, there is a risk of magnesium powder falling off, requiring high temperature resistance, high corrosion resistance, and high fire resistance.

[0055] 2.2 Coating System Parameters

[0056]

[0057] 2.3 Construction process details

[0058] S1 Surface Pretreatment: A 1500W air-cooled laser rust removal machine (8kg weight, equipped with an aerial work platform for assistance) is used, with a laser power of 200W / mm. 2 The scanning speed was 6 mm / s. Severely corroded areas were polished with a 100-grit resin grinding wheel, resulting in a final surface roughness Ra = 25 μm and an oil content of 2 mg / m³. 2 .

[0059] Application of S2 zinc-rich primer: Mix base material and zinc powder in a ratio of 1:2.8, add 4% KH-560, stir for 20 minutes and then cure for 15 minutes; apply with high-pressure airless spray (nozzle 0.25mm, pressure 18MPa), wet film thickness 95μm, cure at 25℃ for 5 hours, dry film thickness 72μm.

[0060] S3 transition layer construction: Mix E-44 and 650 polyamide at a ratio of 7:1, roll coat within 30 minutes, wet film thickness 38μm, cure at 25℃ for 24h, dry film thickness 26μm.

[0061] S4 fire-retardant coating application: First coat: wet film thickness 25mm, lay the first layer of mesh cloth (corner radius R=15mm), press flat and cure for 24 hours; Second coat: wet film thickness 25mm, lay the second layer of mesh cloth (crossed at 90°), cure for 24 hours; Third coat: wet film thickness 18mm, cure for 24 hours, total dry film thickness 18.5mm (lightly sand the surface).

[0062] S5 Anti-corrosion Surface Coating Application: After mixing component B of the formula, sand mill to a fineness of 40μm, apply with high-pressure airless spray (pressure 15MPa). The first wet film thickness is 140μm, cured for 5 hours; the second wet film thickness is 145μm, cured for 5 hours; the dry film thickness is 183μm. S6 Inspection and Repair: Film thickness deviation ≤ ±8%; zinc-rich primer adhesion 5.5MPa, anti-corrosion surface coating adhesion 4.6MPa; two localized thin coatings (170μm each) are applied for re-coating, and the coating is qualified after curing.

[0063] 2.4 Performance Verification

[0064] Temperature resistance: After being placed in a constant temperature chamber at 120℃ for 300 hours, the coating showed no cracking or discoloration; high temperature (100℃) + HF (0.5mg / m³) 3 After 200 hours of alternating testing, the coating remained intact.

[0065] Fire resistance performance: Fire resistance limit of 2.2h, meeting the design requirement of "2h fire resistance" for load-bearing columns.

[0066] Economic efficiency: Total cost 35 yuan / m 2 It reduces corrosion by 15% compared to traditional high-temperature anti-corrosion coating solutions.

[0067] Example 3: High-altitude maintenance platform in magnesium smelting workshop (temperature ≤60℃, fire resistance limit 1h, requires frequent stepping)

[0068] 3.1 Operating Context

[0069] The platform is located on the top of the workshop and is used for equipment maintenance. It must withstand the loads of personnel and tools (≤5kN / m). 2 The ambient temperature is 30-60℃, and there is dust and occasional SF6 leakage (HF≤0.2mg / m³). 3 The coating needs to be wear-resistant and impact-resistant, and it needs to be easy to apply at high altitudes.

[0070] 3.2 Coating System Parameters

[0071]

[0072] 3.3 Construction process details

[0073] S1 Surface Pretreatment: 1200W laser rust removal machine (weight 6kg, with telescopic operating frame), laser power 180W / mm 2 The scanning speed is 7 mm / s, and the platform surface is lightly ground with a 90-mesh resin grinding wheel, resulting in a surface roughness Ra = 23 μm and an oil content of 2.5 mg / m². 2 .

[0074] Application of S2 zinc-rich primer: Mix base material and zinc powder in a ratio of 1:2.6, add 3.5% KH-550, stir for 18 minutes and cure for 12 minutes; apply with high-pressure airless spray (nozzle 0.22mm, pressure 16MPa), wet film thickness 88μm, cure at 25℃ for 4.5h, dry film thickness 66μm.

[0075] S3 transition layer construction: Mix E-44 and T31 at a ratio of 7:1, apply by roller within 25 minutes, wet film thickness 33μm, cure for 24 hours, dry film thickness 23μm.

[0076] S4 fire-retardant coating application: First coat: wet film thickness 7mm, lay 12-mesh mesh (platform edge R=12mm rounded corner), press flat and cure for 24 hours; Second coat: wet film thickness 7mm, cure for 24 hours, dry film thickness 5.2mm (lightly grind surface).

[0077] S5 anti-corrosion surface coating construction: Formula A with 2% alumina wear-resistant powder, sand-milled to a fineness of 42μm, high-pressure airless spraying (pressure 16MPa), the first wet film thickness is 160μm, cured for 5h, the second wet film thickness is 165μm, cured for 5h, and the dry film thickness is 203μm.

[0078] S6 Inspection and Repair: Adhesion test (zinc-rich primer 5.3MPa, surface layer 4.5MPa); Abrasion test (GB / T1768-2021) 500 revolutions with no exposed substrate; One edge thin coating (190μm) was successfully repaired.

[0079] 3.4 Performance Verification

[0080] Impact resistance: No cracks were observed in the 50cm drop hammer test (GB / T 1732-2020);

[0081] Practicality: After a year of frequent foot traffic by maintenance personnel, the coating showed no wear or peeling.

[0082] Example 4: Steel frame supporting a magnesium smelting furnace (temperature 90-110℃, fire resistance limit 2.5h, strong vibration)

[0083] 4.1 Operating Context

[0084] The steel frame directly supports the smelting furnace and bears the weight of the furnace body (≥10kN / m). 2 Vibration during the smelting process (amplitude ≤ 0.5 mm), ambient temperature 90-110℃, and high HF concentration (0.4-0.6 mg / m³) 3 It requires high temperature resistance, high earthquake resistance, and strong corrosion resistance.

[0085] 4.2 Coating System Parameters

[0086]

[0087] 3.3 Construction process details

[0088] S1 Surface Pretreatment: 1500W laser rust removal machine (equipped with an aerial work platform), laser power 250W / mm 2 The scanning speed is 5 mm / s. Welds and corners are finely ground with a 120-grit resin grinding wheel, achieving a surface roughness Ra = 28 μm and an oil content of 1.5 mg / m³. 2 .

[0089] Application of S2 zinc-rich primer: Mix base material and zinc powder in a ratio of 1:3.0, add 5% KH-560, stir for 25 minutes and cure for 20 minutes; apply with high pressure airless spray (nozzle 0.3mm, pressure 20MPa), wet film thickness 110μm, cure at 25℃ for 6 hours, dry film thickness 81μm.

[0090] S3 transition layer construction: Mix E-44 and T31 at a ratio of 7:1, apply two coats within 30 minutes (each with a wet film thickness of 22μm), for a total wet film thickness of 44μm, cure for 24 hours, and achieve a dry film thickness of 31μm.

[0091] S4 fire-retardant coating application: First coat: wet film thickness 28mm, lay the first layer of mesh cloth (corner radius R=20mm), press flat and cure for 24 hours; Second coat: wet film thickness 28mm, lay the second layer of mesh cloth (crossing at 90°), cure for 24 hours; Third and fourth coats: wet film thickness 20mm each, cure for 24 hours per coat, total dry film thickness 22.3mm.

[0092] S5 anti-corrosion surface coating construction: Formula B with 1% nitrile elastomer, sand milled to a fineness of 38μm, high-pressure airless spraying (pressure 18MPa), first wet film thickness 160μm, cured for 6h, second wet film thickness 165μm, cured for 6h, dry film thickness 202μm.

[0093] S6 Inspection and Repair: Film thickness deviation ≤ ±7%; zinc-rich primer adhesion 5.8MPa, surface layer 4.8MPa; vibration test (10Hz, amplitude 0.5mm, 24h) coating no cracking.

[0094] 4.4 Performance Verification

[0095] Temperature and vibration resistance: After 300 hours of alternating testing at 110℃ and vibration (0.5mm amplitude), the coating remained intact.

[0096] Corrosion resistance: HF (0.6 mg / m³) 3 After soaking for 400 hours, no bubbling or rust was observed.

[0097] Fire resistance: Fire resistance limit of 2.6h, meeting the furnace body support requirement of "2.5h fire resistance".

[0098] Example 5: Temporary maintenance support for magnesium smelting workshop (emergency repair, construction time ≤ 8h)

[0099] 5.2 Coating System Parameters

[0100]

[0101] 5.3 Construction process details

[0102] S1 Surface Pretreatment: A 1000W portable laser rust removal machine (weighing 5kg, single-person handheld operation) is used, with a laser power of 120W / mm. 2 Scanning speed 10mm / s (priority efficiency), rust removal only on rusted areas; unrusted old paint layers (if intact) are lightly roughened with sandpaper. Final surface roughness Ra = 18μm, oil content 4mg / m². 2 (Quickly wipe with ethanol).

[0103] Application of S2 Zinc-Rich Primer: Mix the quick-drying epoxy zinc-rich primer with a base material to zinc powder ratio of 1:2.4, add 3% KH-550, stir for 10 minutes, and then apply directly by brushing (no curing required, suitable for urgent applications). The wet film thickness is 80μm, and it can be cured quickly at 25℃ for 1.5h, resulting in a dry film thickness of 60μm.

[0104] S3 transition layer construction: Mix fast-drying E-44 epoxy resin and fast-curing amine agent at a ratio of 7:1, stir evenly and apply by roller within 10 minutes, with a wet film thickness of 30μm, cure at 25℃ for 3 hours, and a dry film thickness of 20μm.

[0105] S4 fire retardant coating application: Apply a wet film of 4mm thick quick-drying thin intumescent fire retardant coating, immediately lay down an 8-mesh mesh (quickly cut the edges to rounded corners), flatten with a scraper, and cure at 25℃ for 3.5 hours to a dry film thickness of 3mm (no need for secondary spraying, shortening the time), and lightly grind off any surface dust.

[0106] S5 anti-corrosion surface coating construction: Mix formula C with isocyanate prepolymer and polyetheramine at a ratio of 45:30, add catalyst and stir for 30 seconds. Apply one coat within 5 minutes using a small high-pressure airless sprayer (pressure 20MPa). The wet film thickness is 190μm. Allow it to dry completely at 25℃ for 1 hour, resulting in a dry film thickness of 150μm.

[0107] S6 Inspection and Repair: Simplify the inspection process, focusing on visual inspection for no missed coatings or runs; use a thickness gauge to quickly check 3 points (deviation ≤ ±10%) for film thickness; if there is a missed coating at one corner, manually apply Formula C, and it will be qualified after curing in 30 minutes. The total construction time is 7.5 hours, which meets the 8-hour emergency requirement.

[0108] 5.4 Performance Verification

[0109] Fast drying performance: The entire process can be completed and put into use within 8 hours, with no softening or peeling of the coating;

[0110] Short-term corrosion protection: 70℃ + SO2 (concentration 0.3mg / m³) 3 After being placed in the environment for 30 days, the coating showed no rust.

[0111] Practicality: The temporary support can withstand a 2kN load, and the coating is free from cracks and wear, meeting the needs of temporary use for 3 months.

[0112] Example 6: Refurbishment of old coated steel components in a magnesium smelting workshop (original coating partially cracked, fire resistance rating 1.5h)

[0113] 6.1 Operating Context

[0114] The steel component is an old steel beam that has been used in the workshop for 5 years. The original coating (single epoxy anti-corrosion coating + thin fireproof coating) has developed localized cracks (crack width ≤ 0.2mm) and corner corrosion. It needs to be partially refurbished without interrupting production. The ambient temperature is 40-70℃ and the HF concentration is 0.2-0.3mg / m³. 3 The core requirement is that the old coating is compatible with the new coating and that local construction does not affect surrounding equipment.

[0115] 6.2 Coating System Parameters

[0116]

[0117] 6.3 Construction process details

[0118] S1 Old Coating Pretreatment: Wipe the surface of the old coating with a neutral coating cleaner (avoid corroding the intact coating). Widen cracks along the cracks with 120-grit sandpaper (extending 50mm in length and 0.5mm in width). For rusted areas (approximately 20%), use a 1200W laser rust removal machine (power 180W / mm). 2 Rust removal was performed at a scanning speed of 7 mm / s. Intact old coating surfaces were lightly roughened with 80-grit sandpaper (roughness Ra = 20 μm). The final oil content was ≤3 mg / m³. 2 .

[0119] S2 Zinc-Rich Primer Application: Apply epoxy zinc-rich primer only to areas with rust and old coating removal (to save materials and avoid waste from full coating). Mix base material and zinc powder in a 1:2.5 ratio, add 3% KH-550, wet film thickness 85μm, cure at 25℃ for 5h, dry film thickness 65μm, overlap width with surrounding intact old coating ≥100mm (to avoid joint cracking).

[0120] S3 transition layer construction: Roller coat the entire surface with a mixture of E-44 epoxy resin and T31 (7:1), wet film thickness 38μm, focus on applying an extra coat at the overlap of the old coating and the new primer (to enhance the connection), cure at 25℃ for 24h, dry film thickness 25μm.

[0121] S4 fire retardant coating application: Low-viscosity fire retardant coating is sprayed on the entire surface. For the cracked areas of the old coating, the first wet film thickness is 8mm. A 10-mesh mesh is laid (covering the cracked area and a 50mm radius around it). The mesh is then flattened with a scraper until the coating penetrates into the cracks (to repair defects) and cured for 24 hours. The second wet film thickness is 7mm, and the coating is cured for 24 hours. The total dry film thickness is 6mm. The surface is then lightly sanded to remove dust.

[0122] S5 anti-corrosion surface coating construction: After mixing formula A, sand it to a fineness of 45μm (low viscosity for easy coverage), and spray the entire surface with high pressure airless spray (pressure 15MPa). The first wet film thickness is 140μm (focus on covering the old coating interface), and it is cured for 5 hours. The second wet film thickness is 145μm, and it is cured for 5 hours. The dry film thickness is 182μm, and the overlap width with the surrounding unrenovated components (if any) is ≥150mm.

[0123] S6 Inspection and Repair: Focus on inspecting the adhesion at the overlap of old and new coatings (pull-out method ≥4.2MPa); for crack repair areas, use penetrant testing (no crack residue) to apply a thin coat (170μm) to 3 corners and edges, and it is qualified after curing.

[0124] 6.4 Performance Verification

[0125] Compatibility: No delamination or cracking was observed at the overlap between the old and new coatings after one year of storage;

[0126] Corrosion resistance: 70℃ + HF (0.3mg / m³) 3 After 1000 hours of environmental testing, the coating showed no blistering or rust, and no recurrence of old cracks.

[0127] Fire resistance: Fire resistance limit of 1.6h, which meets the design requirement of "1.5h fire resistance" for the renovated components, and the construction process did not affect the normal production of the workshop.

Claims

1. A multi-layer anti-corrosion and fireproof coating system for steel structures in a magnesium smelting workshop, characterized in that, From the inside out, the steel structure substrate includes the following coating structure: Zinc-rich primer layer: using solvent-based epoxy zinc-rich primer, with a dry film thickness of 60-80μm, a zinc content ≥80% in the dry film, and 2%-5% silane coupling agent added as an adhesion promoter; Epoxy sealing transition layer: made by mixing E-44 epoxy resin and amine curing agent at a 7:1 mass ratio, with a dry film thickness of 20-30μm, used to enhance the compatibility and adhesion between the primer and the fire-retardant coating layer; Fire-retardant coating layer: using a thin-film intumescent fire-retardant coating... Fire retardant coating (dry film thickness 3-7mm, fire resistance limit 0.5-1 hour) or thick non-intumescent fire retardant coating (dry film thickness 15-25mm, fire resistance limit 2-3 hours), wherein 1-2 layers of 8-12 mesh alkali-free glass fiber mesh are embedded in the fire retardant coating layer, with the texture directions of adjacent meshes intersecting at 90° and the overlap width ≥50mm; Anti-corrosion surface layer: selected from one of the following three formulations, dry film thickness 150-200μm: A. Epoxy-glass flake coating: containing 35 parts by weight of epoxy resin E-44, 2 A. 0-25 parts 400-mesh glass flakes, 8 parts rutile titanium dioxide, 10 parts 325-mesh talc, 15 parts polyamide curing agent (type 650), 10 parts xylene-butanol mixed solvent (1:1), 1 part KH-550 coupling agent, 0.5 parts silicone defoamer, 0.5 parts acrylate leveling agent, and additionally add 5%-8% 325-mesh calcium fluoride powder; B. Modified epoxy-phenolic coating: containing 30 parts phenolic modified epoxy resin, 10 parts 300-mesh graphite powder, and 15 parts 300-mesh glass flakes. Flakes, 5 parts zinc oxide, 10 parts 2123 type phenolic resin, 8 parts T31 amine curing agent, 15 parts cyclohexanone-toluene mixed solvent (1:2), 1 part KH-560 coupling agent, 1 part fumed silica anti-settling agent; C. Polyurea coating: containing 45 parts MDI type isocyanate prepolymer, 30 parts polyetheramine D2000, 5 parts titanium dioxide, 8 parts 100 mesh hollow glass microspheres, 2 parts conductive carbon black, 0.5 parts dibutyltin dilaurate catalyst, 0.5 parts UV-531 ultraviolet absorber.

2. The coating system according to claim 1, characterized in that, The alkali-free glass fiber mesh has a tensile strength ≥1000N / 50mm and a temperature resistance ≥200℃. It should be rinsed with clean water and dried before use.

3. A construction method applicable to the coating system of claim 1, characterized in that, Includes the following steps: S1: Surface pretreatment: Use a 1000-1500W air-cooled handheld laser rust removal machine to remove rust from the steel structure surface, with a laser power of 100-300W / mm. 2 Scan at a speed of 5-10 mm / s to remove scale, rust, and old paint; after high-pressure air purging, wipe with anhydrous ethanol to ensure oil stains are ≤5 mg / m³. 2 For severely rusted areas, use 80-120 mesh resin grinding wheels to polish the surface to achieve a surface roughness Ra≥20μm; S2: Apply zinc-rich primer layer: Mix epoxy zinc-rich primer base material with zinc powder, add 2%-5% silane coupling agent, stir evenly and mature for 5-30 minutes; apply by high-pressure airless spraying or brushing, wet film thickness 80-110μm, cure at room temperature for 4-6 hours. S3: Apply epoxy sealing transition layer: Mix E-44 epoxy resin and amine curing agent at a mass ratio of 7:1, apply by roller, wet film thickness 30-45μm, cure at room temperature for 24 hours; S4: Apply fire-retardant coating and lay mesh: Apply the fire-retardant coating in layers according to the selected thin or thick type. The wet film thickness of each coating is 4-30mm. Lay the mesh and press it into the coating. Each layer should be cured for 24 hours. Finally, lightly grind the surface. S5: Apply anti-corrosion surface coating: Select formula A, B or C according to the ambient temperature, and apply in layers using high-pressure airless spraying. Each layer has a wet film thickness of 120-165μm, and each layer is cured at intervals of 4-6 hours. The total dry film thickness is 150-200μm. S6: Coating Inspection and Repair: Conduct visual inspection, film thickness inspection and adhesion inspection, and repair defective areas accordingly.

4. The construction method according to claim 3, characterized in that, In step S1, during laser rust removal, the surface temperature of the steel structure must be at least 3°C ​​higher than the dew point temperature, the relative humidity of the environment must be ≤85%, and the temperature must be 5-40°C.

5. The construction method according to claim 3, characterized in that, In step S4, the mesh fabric is cut into rounded corners and laid out, and the thickness of the fireproof coating at the corners is increased by 20%.

6. The construction method according to claim 3, characterized in that, In step S5, after the application of formula A, the coating surface should be tested with pH test paper every 3 months. If the pH is less than 5, it should be recoated in time.

7. The construction method according to claim 3, characterized in that, When working at heights, use 3-5m telescopic painting poles in conjunction with brushing or rolling. For areas that are difficult to reach, set up mobile scaffolding or use aerial work vehicles.

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