I. Concept of Galvanized Steel Sheet
Galvanized steel sheet is a processed coiled material featuring a zinc layer on the surface of a steel plate. Its core composition consists of a steel substrate and a zinc layer, with each component serving a distinct role:
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Steel Substrate: The foundational structure of the galvanized steel sheet, primarily categorized into three types based on processing methods and material properties:
- Cold-rolled steel plate (cold plate): Produced by cold rolling at room temperature, it boasts high dimensional accuracy, a smooth surface, and excellent formability, making it suitable for applications requiring precise shaping (e.g., electrical appliance shells).
- Hot-rolled steel plate (hot plate): Manufactured via hot rolling at high temperatures, it offers high strength and toughness, though its surface smoothness is slightly lower than that of cold plates. It is commonly used in structural components such as building frames.
- Alloy steel plate: A steel plate mixed with other alloying elements (e.g., manganese, chromium, nickel), it possesses specialized properties like high corrosion resistance, high temperature resistance, or high wear resistance. It is applied in scenarios with strict performance requirements, such as chemical equipment.
- Zinc Layer: A protective coating (attached) to the steel substrate’s surface, primarily formed through two mainstream processing methods: electro-galvanizing and hot-dip galvanizing. Its core function is to isolate the steel substrate from the external corrosive environment (e.g., air, water, chemicals), thereby preventing the steel from rusting and corroding.
II. Characteristics of Galvanized Steel Sheet
- Superior Corrosion Resistance: The zinc layer on the surface of galvanized steel sheet acts as a “protective barrier.” When exposed to the atmosphere, water, or various alkaline/acidic chemical substances (e.g., weak acids in rainwater, alkaline cleaning agents), the zinc layer (prioritizes) undergoes chemical reactions (e.g., oxidation, dissolution) instead of the steel substrate. Even if the zinc layer is slightly damaged, the remaining zinc can still form a galvanic cell with the steel, continuing to protect the steel from erosion. This characteristic significantly extends the service life of the steel, often making it 3-5 times longer than that of ungalvanized steel in outdoor environments.
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Excellent Mechanical Properties:
- High Strength: The steel substrate itself provides strong load-bearing capacity. For instance, hot-rolled galvanized steel sheets with a thickness of 3mm can withstand a tensile strength of 300-500MPa, meeting the load requirements of structural components like building roofs and container frames.
- Good Toughness: Galvanized steel sheet maintains good ductility and impact resistance even in temperature fluctuations (e.g., from -20°C to 60°C) or under sudden mechanical loads (e.g., slight collisions during transportation). It is not prone to brittle fracture, ensuring the material’s integrity and stability in practical use.
- Versatile Processability: Galvanized steel sheet can be easily processed using common metalworking techniques such as cutting, bending, stamping, and welding. For example, in the production of electrical appliance shells, it can be stamped into complex shapes through a stamping process; in the manufacturing of building doors and windows, it can be bent into specific angles to meet assembly requirements. This processability enables it to adapt to diverse product design needs.
- Cost-Effective Economy: Although the initial procurement cost of galvanized steel sheet is slightly higher than that of ungalvanized steel, its long service life reduces the frequency of maintenance, replacement, and repair. In the long run, the total life-cycle cost (including procurement, installation, and maintenance) is lower than that of ungalvanized steel. Additionally, the zinc layer processing technology is mature, and large-scale production further controls the manufacturing cost, making it a cost-effective metal material.
- Broad Application Scope: Relying on the above advantages, galvanized steel sheet is widely used in multiple fields, spanning construction, manufacturing, furniture manufacturing, and transportation. Specific application scenarios will be detailed in the “Application” section below.
III. Production Process of Galvanized Steel Sheet
The production of galvanized steel sheet mainly includes two core processes: electro-galvanizing and hot-dip galvanizing. The two processes differ significantly in principles, steps, and product performance, as shown in the following table:
| Process Indicator | Electro-Galvanizing Process | Hot-Dip Galvanizing Process |
|---|---|---|
| Core Principle | Utilizes electrochemical deposition: The steel plate (as the cathode) and a zinc plate (as the anode) are immersed in an electrolyte containing zinc ions. When an electric current is applied, zinc ions in the electrolyte move to the steel plate surface and are reduced to metallic zinc, forming a zinc layer. | Relies on high-temperature chemical reaction: After the steel plate is chemically cleaned (to remove oil, rust, etc.), it is immersed in a molten zinc solution (at a temperature of about 445-465°C). The iron in the steel and zinc undergo a chemical reaction to form a zinc-iron alloy layer, and a pure zinc layer is attached to the alloy layer surface. |
| Key Production Steps | 1. Pre-treatment: Degreasing (removing surface oil), pickling (removing rust), and activation (enhancing the adhesion of the zinc layer);2. Electroplating: Immersing the treated steel plate in the electrolyte and applying current for zinc deposition;3. Post-treatment: Passivation (improving the corrosion resistance of the zinc layer), drying, and trimming. | 1. Pre-treatment: Degreasing, pickling, fluxing (preventing the steel plate from re-rusting before entering the zinc solution);2. Hot-dip plating: Immersing the pre-treated steel plate in the molten zinc solution for a certain period (usually 3-5 seconds);3. Post-treatment: Cooling (air cooling or water cooling), shot blasting (smoothing the surface), and passivation. |
| Zinc Layer Thickness | Generally thin, ranging from 5-20μm (micrometers). It is suitable for scenarios with low corrosion resistance requirements. | Thicker, generally ranging from 50-150μm. The zinc-iron alloy layer enhances the bonding force with the steel substrate, providing stronger corrosion resistance. |
| Process Cost | Lower: The equipment investment is small, the production process is simple, and the energy consumption is low. | Higher: The equipment (e.g., high-temperature zinc melting furnace) has large investment, high energy consumption, and requires strict control of the molten zinc temperature. |
| Product Advantages | Smooth surface, high dimensional accuracy, and suitable for products with aesthetic requirements (e.g., household appliance shells). | Strong corrosion resistance, good wear resistance, and suitable for outdoor or harsh environment applications (e.g., building roofs, highway guardrails). |
| Typical Application Scenarios | Electrical appliance shells, furniture hardware, interior decoration materials. | Building structural components, industrial containers, oil tanks, transportation equipment (e.g., truck compartments). |
IV. Applications of Galvanized Steel Sheet
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Construction Field: Galvanized steel sheet is a staple material in the construction industry, mainly used in the following aspects:
- Roofs and Walls: Corrugated galvanized steel sheets (commonly known as “color steel tiles”) are widely used in factory workshops, warehouses, and temporary buildings. Their lightweight (about 10-15kg/m²) feature reduces the load on the building’s foundation and frame, while the excellent corrosion resistance ensures that the roof/wall remains free from rust for more than 10 years in outdoor environments.
- Doors and Windows: Galvanized steel sheets processed through stamping and bending are made into anti-theft doors, fire doors, and aluminum-plastic composite window frames. The material’s high strength prevents deformation, and the zinc layer avoids rusting caused by rainwater erosion.
- Structural Components: Hot-dip galvanized steel pipes and profiles are used as scaffolding, steel trusses, and curtain wall keels. In high-humidity environments (e.g., coastal areas), the thick zinc layer resists salt spray corrosion, ensuring the safety and stability of the building structure.Suggested Illustration 1: A real scene of a factory workshop with a corrugated galvanized steel sheet roof, with labels highlighting the “galvanized steel roof” and “corrosion resistance advantage.”
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Manufacturing Field: The manufacturing industry relies heavily on galvanized steel sheet due to its mechanical properties and corrosion resistance:
- Industrial Containers and Tanks: Galvanized steel sheets are welded into chemical storage tanks, water tanks, and grain storage bins. For example, a 500L chemical storage tank made of hot-dip galvanized steel can resist the corrosion of weak acid/alkali solutions, ensuring the safe storage of materials.
- Electrical and Electronic Products: Electro-galvanized steel sheets with smooth surfaces are used to make shells for refrigerators, washing machines, air conditioners, and distribution boxes. The thin zinc layer does not affect the appearance of the product, and it can prevent the shell from rusting due to internal moisture (e.g., condensation in refrigerators).
- Mechanical Parts: Small mechanical components such as gears, bolts, and springs are often galvanized to improve their corrosion resistance. For instance, galvanized bolts used in outdoor machinery (e.g., agricultural machinery) can avoid jamming caused by rust.Suggested Illustration 2: A close-up of an electrical distribution box shell made of galvanized steel, with annotations indicating “electro-galvanized layer” and “smooth surface for aesthetic design.”
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Transportation Field:
- Automotive Industry: Galvanized steel sheets account for 50-70% of the materials used in automobile bodies. For example, the outer panels (doors, hoods) and inner panels (floor panels, door inner panels) of cars use hot-dip galvanized steel sheets. The zinc layer prevents the car body from rusting due to rainwater, road salt (used for snow melting in winter), and other factors, extending the car’s service life.
- Logistics and Transportation Equipment: Truck compartments, container bodies, and railway freight car side panels are made of thick hot-dip galvanized steel sheets. These components are exposed to wind, sun, and rain for a long time, and the thick zinc layer ensures that they do not corrode even after years of use.Suggested Illustration 3: A side view of a container with a galvanized steel body, with a label explaining “hot-dip galvanized layer (100μm) for long-term outdoor anti-corrosion.”
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Furniture and Daily Necessities Field:
- Furniture Manufacturing: Galvanized steel sheets are used to make metal furniture such as office filing cabinets, storage shelves, and outdoor garden chairs. For example, outdoor garden chairs made of galvanized steel do not rust even when exposed to rain and sunlight, and they are easy to clean (just wipe with a damp cloth).
- Daily Necessities: Household items such as trash cans, laundry racks, and kitchen knife handles also use galvanized steel sheets. The zinc layer on the surface of these items prevents rust caused by contact with water, ensuring their durability.Suggested Illustration 4: A set of outdoor galvanized steel garden chairs placed in a courtyard, with a note stating “galvanized steel material, waterproof and rust-proof for outdoor use.”
V. Supplementary Notes: Maintenance and Environmental Protection of Galvanized Steel Sheet
- Daily Maintenance: To maximize the service life of galvanized steel sheet, avoid scratching the zinc layer with sharp objects during installation and use. If the surface is stained with dirt (e.g., dust, oil), clean it with a neutral detergent and a soft cloth; do not use strong acid/alkali cleaners, as they may corrode the zinc layer.
- Environmental Protection: The zinc used in the galvanizing process is a non-toxic and recyclable metal. Waste galvanized steel sheets can be recycled and reused through melting and reprocessing, which reduces resource waste and meets the requirements of green and sustainable development. However, during the galvanizing production process, enterprises need to treat waste water (e.g., pickling waste water) and waste gas (e.g., zinc fume) in accordance with environmental protection standards to avoid environmental pollution.
