Process of coating iron or steel with molten zinc

Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. It can be identified by the crystallization patterning on the surface (often called a "spangle").[1]

Galvanized steel can be welded; however, one must exercise caution around the resulting toxic zinc fumes. Galvanized fumes are released when the galvanized metal reaches a certain temperature. This temperature varies by the galvanization process used. In long-term, continuous exposure, the recommended maximum temperature for hot-dip galvanized steel is 200 °C (392 °F), according to the American Galvanizers Association. The use of galvanized steel at temperatures above this will result in peeling of the zinc at the inter-metallic layer[citation needed]. Electrogalvanized sheet steel is often used in automotive manufacturing to enhance the corrosion performance of exterior body panels; this is, however, a completely different process which tends to achieve lower coating thicknesses of zinc.

Like other corrosion protection systems, galvanizing protects steel by acting as a barrier between steel and the atmosphere. However, zinc is a more electropositive (active) metal in comparison to steel. This is a unique characteristic for galvanizing, which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of 5 mm, above which electron transfer rate decreases).

Process

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edit

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The process of hot-dip galvanizing results in a metallurgical bond between zinc and steel, with a series of distinct iron-zinc alloys. The resulting coated steel can be used in much the same way as uncoated.

A typical hot-dip galvanizing line operates as follows:[2]

• Steel is cleaned using a caustic solution. This removes oil/grease, dirt, and paint.
• The caustic cleaning solution is rinsed off.
• The steel is pickled in an acidic solution to remove mill scale.
• The pickling solution is rinsed off.
• A flux, often zinc ammonium chloride is applied to the steel to inhibit oxidation of the cleaned surface upon exposure to air. The flux is allowed to dry on the steel and aids in the process of the liquid zinc wetting and adhering to the steel.
• The steel is dipped into the molten zinc bath and held there until the temperature of the steel equilibrates with that of the bath.
• The steel is cooled in a quench tank to reduce its temperature and inhibit undesirable reactions of the newly formed coating with the atmosphere.

Lead is often added to the molten zinc bath to improve the fluidity of the bath (thus limiting excess zinc on the dipped product by improved drainage properties), help prevent floating dross, make dross recycling easier and protect the kettle from uneven heat distribution from the burners. Environmental regulations in the United States disapprove of lead in the kettle bath. Lead is either added to primary Z1 grade zinc or already contained in used secondary zinc. A third, declining method is to use low Z5 grade zinc.[3]

Steel strip can be hot-dip galvanized in a continuous line. Hot-dip galvanized steel strip (also sometimes loosely referred to as galvanized iron) is extensively used for applications requiring the strength of steel combined with the resistance to corrosion of zinc, such as roofing and walling, safety barriers, handrails, consumer appliances and automotive body parts. One common use is in metal pails. Galvanised steel is also used in most heating and cooling duct systems in buildings

Individual metal articles, such as steel girders or wrought iron gates, can be hot-dip galvanized by a process called batch galvanizing. Other modern techniques have largely replaced hot-dip for these sorts of roles. This includes electrogalvanizing, which deposits the layer of zinc from an aqueous electrolyte by electroplating, forming a thinner and much stronger bond.

History

[

edit

]

In 1742, French chemist Paul Jacques Malouin described a method of coating iron by dipping it in molten zinc in a presentation to the French Royal Academy.

In 1772, Luigi Galvani (Italy), for whom galvanizing was named, discovered the electrochemical process that takes place between metals during an experiment with frog legs.

In 1801, Alessandro Volta furthered the research on galvanizing when he discovered the electro-potential between two metals, creating a corrosion cell.

In 1836, French chemist Stanislas Sorel obtained a patent for a method of coating iron with zinc, after first cleaning it with 9% sulfuric acid (H2SO4) and fluxing it with ammonium chloride (NH4Cl).

Specification

[

edit

]

A hot-dip galvanized coating is relatively easier and cheaper to specify than an organic paint coating of equivalent corrosion protection performance. The British, European and International standard for hot-dip galvanizing is BS EN ISO 1461, which specifies a minimum coating thickness to be applied to steel in relation to the steels section thickness e.g. a steel fabrication with a section size thicker than 6 mm shall have a minimum galvanized coating thickness of 85 µm.

Further performance and design information for galvanizing can be found in BS EN ISO 14713-1 and BS EN ISO 14713-2. The durability performance of a galvanized coating depends solely on the corrosion rate of the environment in which it is placed. Corrosion rates for different environments can be found in BS EN ISO 14713-1, where typical corrosion rates are given, along with a description of the environment in which the steel would be used.

See also

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References

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En

Zar®

Galvanized Steel Grating as Platform Grating for Airports

Galvanized grating, also called galvanized steel gratinggalvanized steel grating or galvanized steel bar grating, refers to the steel bar grating made of mild carbon steel through hot dipped galvanized surface treatment.

Mild carbon steel provides an economical, high strength for uses in most industrial and commercial applications. And hot dipped galvanized surface treatment supplies excellent corrosion resistance performance for durability.

Steel grating is available in various material, such as stainless steel, aluminum, and galvanized steel. Among them, the galvanized steel grating is the most cost effective and economical type with long service life and high load. And it is the most widely used in both industrial, commercial and residential applications.

GDS-01: Galvanized grating.

GDS-02: Serrated galvanized grating.

GDS-03: Bearing bars of galvanized steel grating.

GDS-04: Twisted bars of galvanized steel grating.

Technology

• Welded galvanized grating. The cross bars are welded onto bearing bars with the high pressure resistance welding machine and then cutting, banding, surface treatment.
• Press-locked galvanized grating. The cross bars are pressure locked onto the bearing bars with grooving and then welding and hot dipped galvanizing.

Features & Characteristics

• High strength. The strength and the toughness are much higher than cast iron. Can be used for terminals, airport and other large-span and heavy loading condition.
• Hot-dip galvanized treatment. Good rust-proof property, maintenance-free replacement.
• Anti-theft design. The cover and the frame is joint with hinge offering security, safety and open convenience.
• Savings investments. Large-span. Less lost for heavy load compared with cast iron products. Cost can be saved for the risk of being stolen or crushing one if cast iron is uses.
• Aesthetic outlook. Simple lines and silver appearance meeting the modern trend.
• The best drainage. Leakage area of 83.3 percent, more than twice of cast iron products.

Applications

Galvanized grating are designed and manufactured for various industrial and civil constructions in city road, gardens, yard, airport, railway and industrial engineering.

• Hot dip galvanized steel grating is the best choice for steel platforms in airports. Grating with 30 × 3 mm thick load bearing bars with a pitch of 30 mm and traverse bars at 50 mm or 100 mm is the suitable one.
• Steel grating, with robust design and spanning abilities, is very strong and safe for the support of floors and elevated walkway. It can be used for ceiling, interior decoration, platform aisle, ventilation windows, (Wells), advertising plaque and other construction.
• Widely used in the petrochemical industry, power plants, waterworks, sewage treatment plants, municipal works, sanitation projects in areas such as platforms, corridors, bridge, ditch cover, covers, ladders, fences, rails, and so on.

Resources

Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. It can be identified by the crystallization patterning on the surface (often called a "spangle").[1]

Galvanized steel can be welded; however, one must exercise caution around the resulting toxic zinc fumes. Galvanized fumes are released when the galvanized metal reaches a certain temperature. This temperature varies by the galvanization process used. In long-term, continuous exposure, the recommended maximum temperature for hot-dip galvanized steel is 200 °C (392 °F), according to the American Galvanizers Association. The use of galvanized steel at temperatures above this will result in peeling of the zinc at the inter-metallic layer[citation needed]. Electrogalvanized sheet steel is often used in automotive manufacturing to enhance the corrosion performance of exterior body panels; this is, however, a completely different process which tends to achieve lower coating thicknesses of zinc.

Like other corrosion protection systems, galvanizing protects steel by acting as a barrier between steel and the atmosphere. However, zinc is a more electropositive (active) metal in comparison to steel. This is a unique characteristic for galvanizing, which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of 5 mm, above which electron transfer rate decreases).

Process

[

edit

]

The process of hot-dip galvanizing results in a metallurgical bond between zinc and steel, with a series of distinct iron-zinc alloys. The resulting coated steel can be used in much the same way as uncoated.

A typical hot-dip galvanizing line operates as follows:[2]

• Steel is cleaned using a caustic solution. This removes oil/grease, dirt, and paint.
• The caustic cleaning solution is rinsed off.
• The steel is pickled in an acidic solution to remove mill scale.
• The pickling solution is rinsed off.
• A flux, often zinc ammonium chloride is applied to the steel to inhibit oxidation of the cleaned surface upon exposure to air. The flux is allowed to dry on the steel and aids in the process of the liquid zinc wetting and adhering to the steel.
• The steel is dipped into the molten zinc bath and held there until the temperature of the steel equilibrates with that of the bath.
• The steel is cooled in a quench tank to reduce its temperature and inhibit undesirable reactions of the newly formed coating with the atmosphere.

Lead is often added to the molten zinc bath to improve the fluidity of the bath (thus limiting excess zinc on the dipped product by improved drainage properties), help prevent floating dross, make dross recycling easier and protect the kettle from uneven heat distribution from the burners. Environmental regulations in the United States disapprove of lead in the kettle bath. Lead is either added to primary Z1 grade zinc or already contained in used secondary zinc. A third, declining method is to use low Z5 grade zinc.[3]

Steel strip can be hot-dip galvanized in a continuous line. Hot-dip galvanized steel strip (also sometimes loosely referred to as galvanized iron) is extensively used for applications requiring the strength of steel combined with the resistance to corrosion of zinc, such as roofing and walling, safety barriers, handrails, consumer appliances and automotive body parts. One common use is in metal pails. Galvanised steel is also used in most heating and cooling duct systems in buildings

Individual metal articles, such as steel girders or wrought iron gates, can be hot-dip galvanized by a process called batch galvanizing. Other modern techniques have largely replaced hot-dip for these sorts of roles. This includes electrogalvanizing, which deposits the layer of zinc from an aqueous electrolyte by electroplating, forming a thinner and much stronger bond.

History

[

edit

]

In 1742, French chemist Paul Jacques Malouin described a method of coating iron by dipping it in molten zinc in a presentation to the French Royal Academy.

In 1772, Luigi Galvani (Italy), for whom galvanizing was named, discovered the electrochemical process that takes place between metals during an experiment with frog legs.

In 1801, Alessandro Volta furthered the research on galvanizing when he discovered the electro-potential between two metals, creating a corrosion cell.

In 1836, French chemist Stanislas Sorel obtained a patent for a method of coating iron with zinc, after first cleaning it with 9% sulfuric acid (H2SO4) and fluxing it with ammonium chloride (NH4Cl).

Specification

[

edit

]

A hot-dip galvanized coating is relatively easier and cheaper to specify than an organic paint coating of equivalent corrosion protection performance. The British, European and International standard for hot-dip galvanizing is BS EN ISO 1461, which specifies a minimum coating thickness to be applied to steel in relation to the steels section thickness e.g. a steel fabrication with a section size thicker than 6 mm shall have a minimum galvanized coating thickness of 85 µm.

Are you interested in learning more about Electro galvanized welded wire mesh? Contact us today to secure an expert consultation!

Further performance and design information for galvanizing can be found in BS EN ISO 14713-1 and BS EN ISO 14713-2. The durability performance of a galvanized coating depends solely on the corrosion rate of the environment in which it is placed. Corrosion rates for different environments can be found in BS EN ISO 14713-1, where typical corrosion rates are given, along with a description of the environment in which the steel would be used.

See also

[

edit

]

References

[

edit

]

En

Zar®

Galvanized Steel Grating as Platform Grating for Airports

Galvanized grating, also called galvanized steel grating or galvanized steel bar grating, refers to the steel bar grating made of mild carbon steel through hot dipped galvanized surface treatment.

Mild carbon steel provides an economical, high strength for uses in most industrial and commercial applications. And hot dipped galvanized surface treatment supplies excellent corrosion resistance performance for durability.

Steel grating is available in various material, such as stainless steel, aluminum, and galvanized steel. Among them, the galvanized steel grating is the most cost effective and economical type with long service life and high load. And it is the most widely used in both industrial, commercial and residential applications.

GDS-01: Galvanized grating.

GDS-02: Serrated galvanized grating.

GDS-03: Bearing bars of galvanized steel grating.

GDS-04: Twisted bars of galvanized steel grating.

Technology

• Welded galvanized grating. The cross bars are welded onto bearing bars with the high pressure resistance welding machine and then cutting, banding, surface treatment.
• Press-locked galvanized grating. The cross bars are pressure locked onto the bearing bars with grooving and then welding and hot dipped galvanizing.

Features & Characteristics

• High strength. The strength and the toughness are much higher than cast iron. Can be used for terminals, airport and other large-span and heavy loading condition.
• Hot-dip galvanized treatment. Good rust-proof property, maintenance-free replacement.
• Anti-theft design. The cover and the frame is joint with hinge offering security, safety and open convenience.
• Savings investments. Large-span. Less lost for heavy load compared with cast iron products. Cost can be saved for the risk of being stolen or crushing one if cast iron is uses.
• Aesthetic outlook. Simple lines and silver appearance meeting the modern trend.
• The best drainage. Leakage area of 83.3 percent, more than twice of cast iron products.

Applications

Galvanized grating are designed and manufactured for various industrial and civil constructions in city road, gardens, yard, airport, railway and industrial engineering.

• Hot dip galvanized steel grating is the best choice for steel platforms in airports. Grating with 30 × 3 mm thick load bearing bars with a pitch of 30 mm and traverse bars at 50 mm or 100 mm is the suitable one.
• Steel grating, with robust design and spanning abilities, is very strong and safe for the support of floors and elevated walkway. It can be used for ceiling, interior decoration, platform aisle, ventilation windows, (Wells), advertising plaque and other construction.
• Widely used in the petrochemical industry, power plants, waterworks, sewage treatment plants, municipal works, sanitation projects in areas such as platforms, corridors, bridge, ditch cover, covers, ladders, fences, rails, and so on.

Resources

For more 2x2" galvanized welded wire mesh rollinformation, please contact us. We will provide professional answers.