1.What are the core material requirements for electrical enclosures?
Corrosion Resistance: The enclosure must withstand environmental moisture (such as humidity from kitchen appliances, rain and snow from outdoor distribution boxes), oil (such as from kitchen appliances), and mildly corrosive gases (such as from industrial workshops). This prevents steel plate corrosion, which could lead to structural failure or electrical leakage.
Workability: Enclosures often have complex shapes (such as folded edges, grooved doors, and internal brackets), requiring stamping, bending, and welding processes. The material must exhibit good plasticity and weldability.
Economical: Electrical appliances (especially household appliances) are mass-produced, requiring cost-effective materials that are superior to more expensive materials like stainless steel.
Foundation Strength: The enclosure must support the weight of internal components (such as circuit breakers and transformers within the control cabinet) and resist deformation under external forces (such as collisions during transportation and installation).
2.What are the typical application scenarios of galvanized sheets in household appliance boxes?
Refrigerators/Freezers:
The exterior casing (doors and side panels) is typically made of electrogalvanized (EG) steel. The electrogalvanized layer is thin (typically 5-10μm) and smooth (Ra ≤ 0.8μm), making it easy to color-coat or powder coat (with strong coating adhesion), meeting the refrigerator's "white/colored appearance + rust-free" requirements. Internal non-exterior components, such as the evaporator bracket and base plate, can be made of lower-cost hot-dip galvanized (GI) steel (with a zinc layer of 10-20μm), focusing on corrosion resistance and supporting strength.
Washing Machines:
The exterior casing (especially the metal casing of drum washing machines) needs to withstand moisture and minor vibrations during washing. Hot-dip galvanized (GI) steel is typically used. The zinc layer is thicker (15-25μm), offering superior corrosion resistance compared to electrogalvanized steel and resisting cracking during stamping (excellent plasticity). For a more aesthetically pleasing appearance, some high-end washing machines use electrogalvanized steel followed by a mirror coating for the front door panels. Air Conditioners:
Indoor unit casings (panels and bottoms) often use electrogalvanized steel sheets with a powder coating for aesthetic appeal. Outdoor unit casings (for protection against rain, sun, and wind) require enhanced corrosion resistance and are typically treated with hot-dip galvanized steel sheets (zinc layer ≥ 20μm), or even hot-dip galvanized steel sheets with a phosphating treatment, to prevent rust from long-term outdoor exposure (especially in humid coastal areas).
Microwave Ovens/Water Heaters:
The casings are often small and require lightweight and easy processing. Thin-gauge electrogalvanized steel sheets (0.3-0.5mm thick) are commonly used. They resist breaking when bent, and the surface treatment makes them suitable for the oily, dirty environments of kitchens (the coating is easy to clean).
3.What are the applications of galvanized steel sheets in industrial/commercial electrical enclosures?
Distribution Boxes/Control Cabinets:
Outdoor or workshop enclosures need to withstand long-term moisture and impact. Hot-dip galvanized steel (GI, with a zinc layer of 25-40μm) or galvanized aluminum-magnesium steel (GLAM, an alloy coating containing aluminum and magnesium elements) are commonly used. GI offers 3-5 times the corrosion resistance of standard hot-dip galvanized steel and is even more scratch-resistant (due to a higher coating hardness), making it suitable for use in highly corrosive environments such as chemical plants and coastal areas. The enclosure frame supports internal components, so high-strength galvanized steel (such as Q355 hot-dip galvanized steel) with a thickness of 1.5-3mm is often used to ensure structural rigidity. Server Cabinets/Charging Pile Enclosures:
Server cabinets must balance heat dissipation and dust protection. Side panels and door panels are typically constructed of hot-dip galvanized sheet metal with punched holes (punched galvanized sheet metal resists rusting and is superior to ordinary cold-rolled sheet metal). Charging pile enclosures (for outdoor installation) must be UV-resistant and temperature-resistant. Hot-dip galvanized sheet metal with a weather-resistant coating (the zinc layer acts as a base for corrosion protection, while the coating protects against UV degradation) is used to prevent cracking and rusting caused by prolonged exposure to the sun.
4.What are the "Material Selection Points" for Galvanized Sheets for Electrical Boxes?
Galvanizing Type: Electrogalvanizing (EG) vs. Hot-Dip Galvanizing (GI):
Electrogalvanizing: Suitable for exterior parts (e.g., refrigerator housings)-the surface is smooth and easy to paint, but the zinc layer is thin (limited corrosion resistance), requiring a coating.
Hot-Dip Galvanizing: Suitable for structural/outdoor parts (e.g., outdoor distribution boxes)-the zinc layer is thick and corrosion-resistant, providing short-term rust protection without a coating, but the surface is slightly rough (phosphating is required before painting).
Zinc layer thickness: Match the environmental corrosion level:
Low-corrosion environments (e.g., indoor control cabinets, washing machine interiors): 10-20μm zinc layer (electrogalvanizing or thin hot-dip galvanizing);
Medium-corrosion environments (e.g., kitchens, general outdoor use): 20-30μm zinc layer (hot-dip galvanizing);
High-corrosion environments (e.g., coastal areas, chemical plants): 30μm or greater zinc layer (thick hot-dip galvanizing or galvanized aluminum-magnesium plate). Baseboard strength: Select based on the load-bearing requirements of the enclosure:
Lightweight enclosures (such as microwave oven housings): Ordinary low-carbon steel baseboard (Q235), thickness 0.3-1mm;
Heavyweight enclosures (such as server cabinets and large control cabinets): High-strength baseboard (Q355), thickness 1.5-4mm, to prevent deformation under load.
Surface condition: Impacts subsequent processing and appearance:
Enclosures requiring painting/powder coating: Choose oil-free, oxidation-free galvanized sheet (such as passivated electro-galvanized sheet) to avoid oil contamination that may affect coating adhesion.
Enclosures subject to frequent welding: Choose hot-dip galvanized sheet with low zinc brittleness (such as hot-dip galvanized sheet with a zinc-iron alloy coating) to reduce pores caused by zinc evaporation during welding (the zinc layer of ordinary hot-dip galvanized sheet evaporates easily during welding, requiring controlled welding current).
5.What are the "precautions" for galvanized sheet metal processing in electrical box?
Stamping/Bending: Preventing Zinc Delamination:
When bending galvanized sheet (e.g., bending the edge of a box), control the bend radius (usually ≥ 2 times the sheet thickness) to avoid sharp bending that can crack the zinc layer (especially for hot-dip galvanized sheet with thick zinc coatings). Stamping dies should be polished to a smooth surface to minimize scratches from friction between the die and the sheet (scratches can expose the base plate and cause rust).
Welding: Controlling Zinc Evaporation and Porosity:
When welding galvanized sheet (e.g., splicing box frames), the zinc layer (melting point approximately 420°C) tends to evaporate before the steel layer (melting point 1538°C), generating zinc vapor that can cause weld porosity. Low-current, short-time welding parameters (e.g., CO2 gas shielded welding) should be used, or the zinc layer in the weld area should be removed (e.g., by grinding) before welding. After welding, clean spatter around the weld and reapply anti-corrosion paint to prevent rust from damage to the zinc layer in the heat-affected zone.
Surface Treatment: Improving Coating Adhesion:
If the cabinet requires coating (such as powder coating or color coating), surface pretreatment is required. Electrogalvanized steel can be directly phosphated (forming a phosphate film to enhance coating adhesion). Hot-dip galvanized steel, due to the presence of an oxide layer on the surface, requires pickling and passivation (removing the oxide layer and forming a passivation film) to prevent blistering and peeling of the coating.