1. Causes of Temperature Variations in Electrophoretic Bath Liquid
1. Energy Conversion During Electrophoresis: During the electrocoating process, some electrical energy is converted into heat, causing the bath liquid temperature to rise. Additionally, mechanical friction from equipment like stirring pumps and circulation pumps generates heat, further increasing the bath temperature.
2. Environmental Factors: Seasonal and ambient temperatures directly affect bath liquid temperature. In summer, high temperatures cause the bath liquid to heat up more easily, while in winter, low temperatures may cause the bath liquid to fall below the ideal range.
3. External Heat Transfer: The temperature of workpieces, added paint, and pure water can influence the bath liquid temperature. For instance, cold workpieces or low-temperature paint and water can lower the bath temperature.
4. Equipment Heat Exchange: Operating heat exchange equipment can cause corresponding changes in the bath liquid temperature.
Causes of High Bath Liquid Temperature:
1. Process Parameter Settings:
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High Voltage or Current: Excessive voltage or current generates excessive heat during electrophoresis, causing a rapid rise in bath temperature.
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Long Electrophoresis Duration: Prolonged electrophoresis accumulates heat beyond the cooling system’s capacity.
2. High Environmental Temperature: Poor ventilation or heat dissipation in the workshop during summer leads to elevated bath temperatures as the liquid absorbs ambient heat.
3. Insufficient Cooling System: Inadequate or underperforming cooling systems (e.g., high cooling temperature, insufficient flow, or inadequate heat exchange area) fail to regulate bath temperature effectively.
Causes of Low Bath Liquid Temperature:
1. Low Environmental Temperature: Excessive cold input from low-temperature paint, water, or workpieces, combined with poor workshop insulation, results in high heat loss.
2. Insufficient Heating Rate: Inadequate heat exchanger area (e.g., due to blockages), low hot water temperature, or insufficient flow prevent the bath from reaching the required temperature.
2. Impact of Temperature on Electrocoating Quality
Effects of Low Temperature:
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Poor Coating Quality: When the bath temperature falls below 15°C, deposition decreases, resulting in a thinner film, reduced gloss, and poor coverage.
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Appearance Defects: Low temperatures increase paint viscosity, making it difficult to eliminate bubbles generated during electrodeposition. High surface tension and poor wettability at low temperatures can lead to defects like pinholes.
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Throw Power Changes: Low temperatures may increase throw power, but film thickness and quality are difficult to maintain.
Effects of High Temperature:
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Rough Coating Film: When the temperature exceeds 35°C, the film deposits too quickly, leading to a rough surface and potential wavy buildup after baking.
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Poor Bath Stability: High temperatures accelerate solvent and additive evaporation, causing bath liquid degradation and reduced stability.
Optimal Temperature Range:
The recommended bath liquid temperature during production is 26–34°C, which ensures good coating appearance and appropriate film thickness. During extended downtime, the temperature can be lowered to 20–25°C.
3. Solutions for Low Bath Liquid Temperature
Heating Measures:
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For large electrophoretic baths, use a hot-cold thermostat exchanger with dual heating and cooling functions and automated control for precise temperature regulation.
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Install a plate heat exchanger in the main circulation system of the electrophoretic bath to heat the liquid using hot water.
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If the main circulation heat exchanger’s power is insufficient, install electric heating tubes or hot water heat exchange tubes in the UF (ultrafiltration) tank to heat the UF liquid, which then flows back to the main bath to raise its temperature.
Process Parameter Optimization:
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At low temperatures, moderately increase the electrophoretic voltage to enhance deposition, but avoid excessive voltage to prevent other issues.
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Increase solvent content to reduce bath liquid viscosity and promote film deposition.
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Bath Liquid Circulation and Monitoring: Ensure uniform temperature distribution through the bath circulation system.
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Regularly monitor bath liquid temperature using thermometers or temperature probes and adjust heating equipment as needed.