Knowledge
2021-06-01 8672
Surface treatment and coating of rolled steel coil (plate)-JCG Industrial Co., Ltd. Manufacturing Factory
Surface treatment coating of cold rolled steel
The surface treatment process of cold-rolled section steel is divided into three stages: substrate treatment, anti-rust coating, surface coating and anti-corrosion treatment after damage on the construction site. To
The surface treatment and coating of cold-rolled steel, which is not a light-weight steel, shall be handled in accordance with the "Code for Construction of Building Steel Structures"
The cold-rolled steel plate should have been treated with anti-corrosion on the surface during the manufacturing process. However, on-site welding, mechanical cutting, and collision during construction are unavoidable in the construction site, which may easily cause corrosion on the section of the steel plate and damage to the galvanized layer on the surface. When these steels interact with the atmospheric environment, they often produce corrosion and cracks, which damage the safety and durability of the steel itself, and affect the appearance of cold-rolled steel sheets or the difficulty of subsequent surface treatment.
Commonly used anti-corrosion methods for cold-rolled steel structures
Surface treatment method of cold rolled section steel
The anti-corrosion coating of cold-rolled steel must undergo surface treatment before decontamination, degreasing, rust removal, and appropriate roughness to facilitate the adhesion of the coating.
The processing method is as follows:
1. Mechanical: sandblasting, steel brushing, grinding, solvent washing and steam degreasing, etc.
2. Chemical formula: treated with phosphate or chromate coating
Rust removal grade
1. The degree of surface corrosion of steel without surface treatment can be divided into A, B, C, D according to SIS-05-5900
The four levels are as follows:
Grade A: The surface of the steel is completely covered with an oxide layer, and there is no red rust or only a small amount of red rust.
Grade B: The surface of the steel begins to rust, part of the oxide layer peels off, and red rust appears.
Grade C: The steel surface has been rusted comprehensively, most of the oxide layer has been peeled off or loosened, and there are a few corrosion holes.
Grade D: The oxide layer is completely peeled off, and there are many corrosion holes on the surface of the steel, which is a severely corroded state.
2. According to the Swedish standard SIS-05-5900 rust removal degree classification.
3. SlS-05-5900 rust removal degree is divided into two categories:
(1) St rust removal grade [hand tools or electric grinders]:
St0: Steel surface without derusting treatment.
St1: Use a steel brush to do a slight overall brushing to remove floating rust and loosen the oxide layer. To
St2: Use manual, electric shovel, steel brush or grinder to remove the loose oxide layer, floating rust and other foreign objects, and then use a vacuum cleaner or compressed air or brush to remove the dust.
St3: Use electric appliances, steel brush or grinder to completely remove the loose oxide layer, rust and foreign matter and remove the dust, the surface should have metallic luster.
(2) Sa derusting degree grade [with sandblasting treatment]:
Sa0: Derusting treatment at the end of the surface.
Sa1: Lightly sandblasted to remove loose oxide layer, rust and foreign matter.
Sa2: Moderate sandblasting treatment to remove most of the oxide layer, rust and foreign objects, and remove the dust with a vacuum cleaner. The surface should have only tiny spots and foreign objects remaining. The surface after the treatment should be similar to white metal color, which is an anti-corrosion coating. Surface treatment required by installation engineering.
Sa2 1/2: Thorough sandblasting treatment, after treatment, 95% of the oxide layer, rust and foreign matter are removed, and the surface after removing the dust should be white metal color, which is the most common surface treatment requirement for anti-corrosion coating projects.
Sa3: Absolutely thorough sandblasting treatment, all oxide layers, rust and foreign matter are completely removed without leaving any tiny foreign matter. The surface after dust removal is uniform white metal color, which is the highest standard of surface treatment.
Surface roughness
The average surface roughness should generally be 25~75μm.
The surface roughness of sandblasting has a great influence on the anti-rust function of the coating film. When the roughness is large, it can increase the adhesion of the paint, but it also reduces the thickness of the coating film on the surface of the steel. It is easy to produce pinholes and reduce the paint film. The anti-rust ability; on the contrary, it reduces the adhesion of the paint. Therefore, the appropriate surface roughness must be selected according to the paint characteristics and the thickness of the paint film.
Anti-rust coating for cold rolled steel
The cold-rolled formed steel sheet (sheet) of the cold-rolled steel structure is treated to prevent corrosion from being exposed to the atmosphere. The anti-corrosion technology often used: (1) hot dip plating (2) electroplating (3) thermal spraying (4) paint Painting and other methods. The above-mentioned coating or coating not only has the function of isolating the external environment, but also contains the cathodic anti-corrosion protection function of zinc element.
Hot dip galvanizing
The galvanizing hot dip method is divided into: pure zinc coating, zinc-iron alloy coating and zinc-aluminum alloy coating. The minimum amount of zinc coating should meet the relevant regulations of CNS or ASTM.
International Standard Specification for Galvanized Steel Products
The weight and thickness table of hot-dip galvanized(aluminum) steel
Specification of hot-dip galvanized (aluminum) required for structural load-bearing members
Hot-dip galvanizing specifications can be referred to in addition to ASTM in the United States CNS9278 、CNS6183 ; JIS G3141、 JIS G3350、JIS G3302、JIS G3317 、JIS G3321 、JIS G3312 之規定。
Electrogalvanizing
The coating of the galvanized steel sheet produced by the electro-galvanizing method can be divided into: pure zinc coating, zinc-nickel alloy coating and zinc-iron alloy coating.
The galvanized layer of electro-galvanized steel sheet is very thin. It is not recommended for buildings such as outdoor roofs and exterior walls.
Manufacturing methods: (1) Degreasing, cleaning, and pickling of steel; (2) Because the plating temperature is close to room temperature, it is called cold plating.
Spray galvanizing
Zinc is treated on the surface of steel by spraying technology. The spray gun uses zinc wire or zinc powder as the raw material, melts the zinc with a gas flame or electric arc, and sprays the zinc liquid on the surface of the steel with high-pressure gas. The thickness of the zinc layer varies from 30-300 μm, and it only relies on mechanical force to adhere to the steel surface.
The working method is suitable for handling larger components with simple shapes.
Coating galvanizing method
The coatings used for coating the steel surface are mostly zinc-rich paints. Zinc-rich paints are mixed with fine zinc metal powders in organic or inorganic bonding agents, which can be single-agent or multiple-agent paints. The zinc component should account for at least
92% by weight, approximately 62% by volume. The painting method can be brush or spray.
Surface coating of cold rolled steel
1. The galvanized cold-rolled steel has anti-rust function, and the surface is coated with beautiful and special requirements.
2. Surface coating is divided into primer, topcoat and backcoat.
The surface treatment process of cold-rolled section steel is divided into three stages: substrate treatment, anti-rust coating, surface coating and anti-corrosion treatment after damage on the construction site. To
The surface treatment and coating of cold-rolled steel, which is not a light-weight steel, shall be handled in accordance with the "Code for Construction of Building Steel Structures"
The cold-rolled steel plate should have been treated with anti-corrosion on the surface during the manufacturing process. However, on-site welding, mechanical cutting, and collision during construction are unavoidable in the construction site, which may easily cause corrosion on the section of the steel plate and damage to the galvanized layer on the surface. When these steels interact with the atmospheric environment, they often produce corrosion and cracks, which damage the safety and durability of the steel itself, and affect the appearance of cold-rolled steel sheets or the difficulty of subsequent surface treatment.
Commonly used anti-corrosion methods for cold-rolled steel structures
| Stage | Step | Principle and Function | Method |
| Substrate processing | Degreasing (removing oil and rust) | Remove die oil, machine oil, rust prevention | Cauterize |
| Washing | |||
| Electrolysis | |||
| Sandblasting | |||
| Remove rust, black skin (carbon black) and other impurities and oxides | Sandblasting | ||
| Pickling | |||
| Dilute acid wipe | |||
| Anti-rust surface treatment | Anti-rust coating | Electrochemical corrosion protection | Metal coating |
| mineral powder | |||
| Physical insulation | Chemical conversion coating | ||
| Seal coating | |||
| Surface coating | Coating | Protect the anti-rust layer |
Surface treatment method of cold rolled section steel
The anti-corrosion coating of cold-rolled steel must undergo surface treatment before decontamination, degreasing, rust removal, and appropriate roughness to facilitate the adhesion of the coating.
The processing method is as follows:
1. Mechanical: sandblasting, steel brushing, grinding, solvent washing and steam degreasing, etc.
2. Chemical formula: treated with phosphate or chromate coating
Rust removal grade
1. The degree of surface corrosion of steel without surface treatment can be divided into A, B, C, D according to SIS-05-5900
The four levels are as follows:
Grade A: The surface of the steel is completely covered with an oxide layer, and there is no red rust or only a small amount of red rust.
Grade B: The surface of the steel begins to rust, part of the oxide layer peels off, and red rust appears.
Grade C: The steel surface has been rusted comprehensively, most of the oxide layer has been peeled off or loosened, and there are a few corrosion holes.
Grade D: The oxide layer is completely peeled off, and there are many corrosion holes on the surface of the steel, which is a severely corroded state.
2. According to the Swedish standard SIS-05-5900 rust removal degree classification.
3. SlS-05-5900 rust removal degree is divided into two categories:
(1) St rust removal grade [hand tools or electric grinders]:
St0: Steel surface without derusting treatment.
St1: Use a steel brush to do a slight overall brushing to remove floating rust and loosen the oxide layer. To
St2: Use manual, electric shovel, steel brush or grinder to remove the loose oxide layer, floating rust and other foreign objects, and then use a vacuum cleaner or compressed air or brush to remove the dust.
St3: Use electric appliances, steel brush or grinder to completely remove the loose oxide layer, rust and foreign matter and remove the dust, the surface should have metallic luster.
(2) Sa derusting degree grade [with sandblasting treatment]:
Sa0: Derusting treatment at the end of the surface.
Sa1: Lightly sandblasted to remove loose oxide layer, rust and foreign matter.
Sa2: Moderate sandblasting treatment to remove most of the oxide layer, rust and foreign objects, and remove the dust with a vacuum cleaner. The surface should have only tiny spots and foreign objects remaining. The surface after the treatment should be similar to white metal color, which is an anti-corrosion coating. Surface treatment required by installation engineering.
Sa2 1/2: Thorough sandblasting treatment, after treatment, 95% of the oxide layer, rust and foreign matter are removed, and the surface after removing the dust should be white metal color, which is the most common surface treatment requirement for anti-corrosion coating projects.
Sa3: Absolutely thorough sandblasting treatment, all oxide layers, rust and foreign matter are completely removed without leaving any tiny foreign matter. The surface after dust removal is uniform white metal color, which is the highest standard of surface treatment.
Surface roughness
The average surface roughness should generally be 25~75μm.
The surface roughness of sandblasting has a great influence on the anti-rust function of the coating film. When the roughness is large, it can increase the adhesion of the paint, but it also reduces the thickness of the coating film on the surface of the steel. It is easy to produce pinholes and reduce the paint film. The anti-rust ability; on the contrary, it reduces the adhesion of the paint. Therefore, the appropriate surface roughness must be selected according to the paint characteristics and the thickness of the paint film.
Anti-rust coating for cold rolled steel
The cold-rolled formed steel sheet (sheet) of the cold-rolled steel structure is treated to prevent corrosion from being exposed to the atmosphere. The anti-corrosion technology often used: (1) hot dip plating (2) electroplating (3) thermal spraying (4) paint Painting and other methods. The above-mentioned coating or coating not only has the function of isolating the external environment, but also contains the cathodic anti-corrosion protection function of zinc element.
Hot dip galvanizing
The galvanizing hot dip method is divided into: pure zinc coating, zinc-iron alloy coating and zinc-aluminum alloy coating. The minimum amount of zinc coating should meet the relevant regulations of CNS or ASTM.
International Standard Specification for Galvanized Steel Products
| Name | Hot-dip galvanized steel coil | ||||||
| specification | CNS 1244 2013 | JIS G 3302 2012 | ASTM A653M 2013 |
AS1397 | 2011 | ||
| Hot-rolled Base: SGHC SGHD SGH 340 400 440 490 540 |
Cold-rolled Base: SGCC SGCD 1~3 SGC 340 400 440 490 570 |
Hot-rolled Base: SGHC SGHD SGH 340 400 440 490 540 |
Cold-rolled Base: SGCC SGCD 1~3 SGC 340 400 440 490 570 |
DS DDS CS TYPE A, B, C FS TYPE A, B SS GRADE 33(230) 37(255) 40(275) 50(340)CLASS 1~3 80(550)CLASS 1~3 |
G1~G3 G250 300 350 400 450 550 |
DX51-52-53D S220GD (250 280 320 350 550) |
|
| Coating Mass |
Z08 Z27 Z09 Z30 Z10 Z35 Z12 Z37 Z14 Z45 Z18 Z50 Z20 Z55 Z22 Z60 Z25 |
Z08 Z10 Z12 Z14 Z18 Z20 Z25 Z27 Z35 Z37 Z45 Z60 |
Z90 Z120 Z180 Z275 Z305 Z350 Z450 Z500 Z550 Z600 |
Z100 Z200 Z275 Z350 Z450 Z600 |
Z100 Z140 Z200 Z225 Z275 Z350 Z450 Z600 |
||
The weight and thickness table of hot-dip galvanized(aluminum) steel
| Plating name | Minimum amount of coating | Coating thickness (single side) | ||
| Oz/ft2 (英制) |
g/m2 (公制) |
mils(英制) | mm(公制) | |
| Hot dip galvanized | ||||
| G40 Z120 | 0.40 | 120 | 0.34 | 0.008 |
| G60 Z180 | 0.60 | 180 | 0.51 | 0.012 |
| G90 Z275 | 0.90 | 275 | 0.77 | 0.019 |
| Hot dip 5% zinc aluminum ASTM A875 | ||||
| GF45 ZGF135 | 0.45 | 135 | 0.39 | 0.009 |
| GF60 ZGF180 | 0.60 | 180 | 0.53 | 0.013 |
| GF90 ZGF275 | 0.90 | 275 | 0.79 | 0.019 |
| Hot dip 55% zinc aluminum ASTM A792 | ||||
| AZ50 AZ150 | 0.50 | 150 | 0.80 | 0.0200 |
Specification of hot-dip galvanized (aluminum) required for structural load-bearing members
| Structural material requirements | Minimum amount of coating | ||
| Hot dip galvanized ASTM A653/M | Hot dip 5% zinc aluminum ASTM A875/M |
Hot dip 55% zinc aluminum ASTM A792/M |
|
Load-bearing member |
G60 Z180 | GF60 ZGF180 | AZ50 AZ150 |
| Non-bearing structure | G40 Z120 | GF45 ZGF135 | AZ50 AZ150 |
Electrogalvanizing
The coating of the galvanized steel sheet produced by the electro-galvanizing method can be divided into: pure zinc coating, zinc-nickel alloy coating and zinc-iron alloy coating.
The galvanized layer of electro-galvanized steel sheet is very thin. It is not recommended for buildings such as outdoor roofs and exterior walls.
Manufacturing methods: (1) Degreasing, cleaning, and pickling of steel; (2) Because the plating temperature is close to room temperature, it is called cold plating.
Spray galvanizing
Zinc is treated on the surface of steel by spraying technology. The spray gun uses zinc wire or zinc powder as the raw material, melts the zinc with a gas flame or electric arc, and sprays the zinc liquid on the surface of the steel with high-pressure gas. The thickness of the zinc layer varies from 30-300 μm, and it only relies on mechanical force to adhere to the steel surface.
The working method is suitable for handling larger components with simple shapes.
Coating galvanizing method
The coatings used for coating the steel surface are mostly zinc-rich paints. Zinc-rich paints are mixed with fine zinc metal powders in organic or inorganic bonding agents, which can be single-agent or multiple-agent paints. The zinc component should account for at least
92% by weight, approximately 62% by volume. The painting method can be brush or spray.
Surface coating of cold rolled steel
1. The galvanized cold-rolled steel has anti-rust function, and the surface is coated with beautiful and special requirements.
2. Surface coating is divided into primer, topcoat and backcoat.