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05
2025
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09
Powder Coating System Design for Metal Home Appliances
Author：
Chuangzhi Coating
Metal home appliances (such as refrigerator side panels, washing machine casings, and air conditioner outdoor units) have both "functional" and "aesthetic" requirements for coatings: they need to meet performance standards such as fingerprint resistance, impact resistance (≥50kg·cm), and salt spray resistance (≥500 hours), while ensuring uniform coating color (color difference ΔE≤1.0). Powder coating has become the preferred process for metal home appliance coating due to its advantages of zero VOC emissions, high material utilization rate (≥95%), and stable coating performance. A powder coating system suitable for metal home appliances must be designed around three cores: "adaptation to home appliance characteristics, precise process parameters, and balance between environmental protection and efficiency". As a professional manufacturer of coating line equipment, we provide full-process customized solutions from system architecture and module design to intelligent optimization.
1. Core Principles of System Design: Adapting to Home Appliance Characteristics
The diversity of metal home appliances (large size differences, complex structures) determines that system design must follow the principles of "flexibility and refinement":
- Size Adaptation: For workpieces of different sizes such as refrigerator side panels (2000×800mm) and washing machine inner tubs (diameter 500mm), an "adjustable conveyor track" (width 500-1500mm adjustable, load capacity ≥50kg/m) is used, combined with a liftable spray gun rack (height 300-2000mm adjustable) to avoid equipment idleness;
- Structure Compatibility: For air conditioner outdoor unit grilles (hollow rate ≥30%) and refrigerator door handles (special-shaped parts), a "zoned spraying strategy" is designed - reciprocating machines are used for spraying flat areas (speed 5-10m/min), and 6-axis robots (repeat positioning accuracy ±0.1mm) are used for touch-up spraying in special-shaped areas to ensure no spraying dead corners;
- Batch Adaptation: It supports switching between "multi-variety small-batch" and "large-batch standardized" production. The system presets more than 200 process recipes (such as "refrigerator white paint" and "washing machine champagne gold"), and the changeover time is ≤15 minutes, meeting the flexible production needs of home appliance enterprises.
2. Core Module Design: Full-Process Performance Guarantee
A. Pretreatment Module: Laying the Foundation for Coating Adhesion
Most metal home appliance substrates are cold-rolled steel plates or aluminum alloys. Pretreatment needs to solve "oil stain removal" and "surface activation":
- Process Design: A six-stage process of "pre-degreasing → main degreasing → water washing → phosphating → passivation → drying" is adopted. Pre-degreasing uses a low-temperature alkaline cleaning agent (40-50℃, pressure 0.2MPa) to remove surface oil; main degreasing is upgraded to high-temperature and high-pressure (55-65℃, pressure 0.4MPa), combined with a chelating degreaser to dissolve stamping oil; phosphating uses a zinc-based phosphating solution (film weight 2-4g/m²) to improve coating adhesion (cross-cut test grade 0); finally, hot air drying (80-100℃, 15 minutes) ensures the surface moisture content ≤0.5%;
- Equipment Adaptation: The tank body is made of 316L stainless steel (acid and alkali corrosion resistance), equipped with a combination of "rotating spray arm + fixed nozzle". For home appliance corners (such as refrigerator door seal grooves), the spray angle is set to 45° to ensure no liquid accumulation; an online bath concentration monitor (accuracy ±0.1%) adjusts in real time to avoid parameter fluctuations.
B. Electrostatic Powder Spraying Module: Precise Control of Coating Quality
The spraying module is the core that determines coating uniformity and needs to adapt to the "large-area flat + small-size special-shaped" structural characteristics of home appliances:
- Spraying Equipment: For flat areas, a combination of "reciprocating machine + electrostatic spray gun" is used. The spray gun spacing is 300-500mm, powder output is 80-120g/min, and voltage is 60-80kV, ensuring the dry film thickness is 60-80μm (deviation ≤±5μm); for special-shaped areas, robots are equipped with "fan-shaped nozzles" (atomization angle 60-90°), and 3D visual scanning (accuracy ±0.5mm) is used to generate paths. For hollow areas of air conditioner grilles, the "low-pressure thin spraying" mode (voltage 40-50kV) is activated to avoid powder accumulation;
- Powder Supply System: A "central powder supply tank + diverter valve" design is adopted. A single powder supply tank has a capacity of 500L and supports simultaneous powder supply for 2-4 spray guns. The fluidization air pressure is 0.05-0.1MPa to ensure uniform powder fluidization (no agglomeration); an "automatic mixing device for new powder + recycled powder" (ratio 3:7) is equipped to increase the material utilization rate to 98%.
C. Curing Module: Ensuring Stable Coating Performance
Metal home appliance coatings need to be high-temperature resistant (e.g., oven casings need to withstand 200℃), so the curing module design must balance "rapid curing" and "performance compliance":
- Process Parameters: Adjust according to coating type - epoxy powder curing temperature is 160-180℃ (time 15-20 minutes), polyester powder is 180-200℃ (time 20-25 minutes); a "stepwise heating" curve (heating rate 5℃/min) is adopted to avoid coating blistering;
- Equipment Design: The curing oven adopts a "hot air circulation + zoned temperature control" structure, with a length of 20-30m, wind speed of 1-1.5m/s, and temperature difference ≤±3℃; natural gas is preferred for heating (energy consumption ratio 1:1.2), and a waste heat recovery device (30% energy saving) is equipped; a forced cooling area (wind speed 3m/s) is set at the outlet to cool the workpiece temperature to ≤40℃, avoiding scratches during subsequent handling.
D. Environmental Protection Recycling Module: Realizing Green Production
The environmental advantages of powder coating need to be enhanced through recycling systems:
- Two-Stage Recycling Design: The first stage uses a cyclone separator (separation efficiency ≥95%) to recover large-particle powder (particle size ≥50μm) for direct reuse in the powder supply system; the second stage uses a high-precision filter element (filtration accuracy 1-3μm) to capture fine powder (particle size ≤50μm), which is cleaned regularly and mixed with new powder for use;
- Waste Gas Treatment: Waste gas from the curing oven is discharged after adsorption by activated carbon (iodine value ≥800mg/g), with a particulate matter concentration ≤10mg/m³, meeting the GB 16297-1996 standard; the workshop is equipped with a dust concentration detector (alarm value <10g/m³) to eliminate safety hazards.
3. Intelligent Optimization: Improving System Operation Efficiency
Modern powder coating systems need to reduce operation and maintenance costs through intelligent design:
- Parameter Monitoring: A PLC+SCADA control system is adopted to collect more than 20 parameters in real time, such as spraying voltage, curing temperature, and powder recycling amount. Data is stored for ≥1 year, and automatic alarms are triggered in case of abnormalities (e.g., the conveyor stops when the curing temperature fluctuation exceeds ±5℃);
- Quality Traceability: Each home appliance workpiece is assigned a unique barcode, which is associated with pretreatment time, spraying operator, and test results, supporting full-process data query by scanning the code;
- Energy Consumption Optimization: Equipment power is automatically adjusted according to the production rhythm - some spray guns and heating tubes are turned off during low production capacity, reducing energy consumption by 25%; standby powder supply tanks are activated during high production capacity to avoid production suspension due to powder cutoff.
Application Case: Effectiveness of a Refrigerator Enterprise's System Design
After a large refrigerator enterprise adopted a customized powder coating system, key indicators improved significantly: the coating qualification rate increased from 88% to 99.2%, the material utilization rate increased from 90% to 97%, and the single-shift production capacity increased by 40%; due to environmental compliance (zero VOC emissions), it successfully passed the EU CE certification, and exports increased by 35%; the intelligent control system reduced operation and maintenance personnel by 30%, saving more than 2 million yuan in annual labor costs.
Conclusion
The design of powder coating systems for metal home appliances focuses on "adaptability" - it must not only fit the structural and performance needs of home appliances but also balance environmental protection, efficiency, and cost. As an equipment manufacturer, we can provide turnkey services from module selection to overall implementation according to the enterprise's product type (e.g., white goods, brown goods) and production capacity scale (50,000-500,000 units/year), helping home appliance enterprises achieve the dual goals of "green coating + quality upgrading".
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