Abnormal Conditions and Solutions for Electrocoating (23 Issues) - II

I. Overview

Many abnormal issues in the electrocoating system can be addressed by identifying the causes through daily and periodic monitoring and analysis of the bath solution, thereby resolving coating film abnormalities. Since the actual conditions of each electrocoating line vary, the elimination method is usually adopted to troubleshoot problems. The following analysis and treatment suggestions serve as general operational guidelines.

II. Methods for Handling Abnormal Conditions

(I) Clarify the Problem

1. Distinguish whether the problem occurs in the system or on related surfaces.
2. Determine the type of issue and whether it affects all workpieces.
3. Identify if the problem affects the entire workpiece or consistently occurs at the same location.
4. Ascertain the timing of the problem.
5. Understand the persistence of the problem—whether it occurs frequently, occasionally, or is related to changes in certain factors.

(II) Identify the Cause of the Fault

1. Analyze common causes of the fault and check for any changes in the production line.
2. Judge if there is a correlation between the bath solution parameters and the problem symptoms.
3. Inspect mechanical aspects, and test whether equipment, instruments, and electrophoretic production line devices are operating normally.
4. Verify process compliance—check for any operations that violate processes or procedures.
5. Confirm if there are changes in the quality of pretreatment.

(III) Determine Adjustment Measures

1. Clarify which variables can be quickly measured on the line.
2. Identify which variables can be measured with minimal interruption to production.
3. Know which variables need to be measured in the laboratory.
4. Judge if technical support from suppliers is required for parameter measurement.

(IV) Implement Adjustment Measures

Each variable needs to be tested to eliminate or confirm potential solutions. If multiple solutions exist, they should be verified one by one. If no solution is found, re-clarify the problem before further handling.

(V) Follow-Up

Determine constant variables to prevent the problem from recurring. Maintaining detailed records enables rapid response to future similar issues.

(VI) Preventive Measures

1. Ensure the normal operation of electrocoating equipment, and conduct regular maintenance or cleaning annually.
2. Maintain stable pretreatment processes and control pretreatment quality.
3. Keep all parameters of the electrophoretic bath solution within the process-specified range.

III. Specific Abnormal Conditions and Solutions

7. Decrease in Ash Content (P/B Ratio) (Accompanied by Increased Coating Gloss, Tendency for Pinholes, Cratering, and Orange Peel)

• Insufficient addition of color paste: Adjust the feeding ratio of emulsion to color paste and increase the amount of color paste added.
• Poor bath solution circulation causing gravitational sedimentation of pigments: Check the circulation function of the equipment and whether the circulating spray pipeline is blocked, and modify the circulation equipment; confirm the bath solution circulation status by testing the solid content of the upper and lower layers of the bath solution.

Note: Sustained low ash content in the electrophoretic bath solution will reduce the corrosion resistance of the coating film.

8. Increase in Ash Content (P/B Ratio) (Accompanied by Rough Coating Film)

• Excessive addition of color paste: Adjust the feeding ratio of emulsion to color paste and increase the amount of emulsion added.

9. Decrease in Solvent Content (Poor Coating Leveling, Coating Pinholes, and Decreased Thickness)

• Excessive volatilization loss due to high bath solution temperature and high ambient temperature: Check if the paint solution temperature is within the required range and add solvent to adjust the solvent content.
• Excessive leakage of UF solution: Check the ultrafiltration system for leaks.
• Excessive volatilization loss due to overly high spray pressure in UF solution cleaning: Adjust the spray pressure.
• Insufficient solvent replenishment: Increase the amount of solvent replenishment.

10. Increase in Solvent Content (Increased Coating Thickness, Decreased Breakdown Voltage, and Decreased Throw Power)

• Excessive solvent addition: Stop solvent addition and monitor changes in solvent content.
• Excessive addition of original paint and high solid content: Reduce the amount of original paint added or stop replenishment.
• Large production volume and rapid bath solution renewal leading to solvent accumulation: Discharge the ultrafiltrate appropriately and monitor the solvent content.

11. Excessively Thick Coating Film

• Low pH value of the bath solution: Adjust the pH value to within the required range.
• Low bath solution temperature: Adjust the bath temperature to the upper limit of the control range.
• Low solvent content in the bath solution: Replenish solvent appropriately.
• Low bath solution conductivity: Reduce the loss of UF solution.
• Low bath solution solid content: Increase the bath solution solid content to within the process specification range.
• Insufficient electrophoresis time: Extend the electrophoresis time.
• Low application voltage: Increase the electrophoresis voltage.
• Poor connection between the electrode plate and power supply, corroded electrode plates, blocked electrode cover diaphragm, or low anode solution conductivity: Inspect the electrode plates, electrode covers, and anode solution system, clean and replace them regularly to ensure good conductivity; increase the anode solution conductivity.
• Poor electrical connection of the coated workpiece: Clean the hangers to ensure good electrical connection of the coated workpiece.
• Long post-washing time with ultrafiltrate causing redissolution: Shorten the UF solution washing time.
• Too thick phosphating film with high resistance: Control the phosphating film thickness within the process range.
• Excessively high application voltage: Reduce the application voltage.
• Excessively high bath solution temperature: Adjust the bath temperature to the upper limit of the control range.
• Excessively high bath solution solid content: Reduce the amount of original paint replenishment.
• Excessively high solvent content in the bath solution: Discharge the ultrafiltrate appropriately and replenish with pure water.
• High bath solution conductivity: Discharge the ultrafiltrate appropriately and replenish with pure water.
• Excessively long electrophoresis time: Control the electrophoresis time.
• Excessively high anode solution conductivity: Discharge the anode solution and replenish with pure water.
• Uneven distribution of electrode plates leading to locally excessive film thickness: Adjust the distribution of electrode covers.
• Excessively large electrode area and imbalanced electrode ratio: Remove part of the anode if necessary.

12. Particles

• High bath solution pH value causing paint agglomeration into particles: Add neutralizer to control the bath solution pH value at the lower limit.
• Low bath solution pH value causing pigment precipitation: Discharge the anode solution to increase the bath solution pH value.
• Low solvent content in the bath solution reducing the water solubility of the electrocoat Replenish solvent to increase the bath solution solvent content.
• High pigment-to-binder ratio in the bath solution: Replenish emulsion to adjust the pigment-to-binder ratio to within the process range.
• Mixing of alkaline substances causing paint precipitation or agglomeration, forming sediment or particles: Strengthen pretreatment water washing, strictly prohibit the introduction of alkaline substances, and enhance the filtration of the electrophoretic bath solution.
• Poor bath solution circulation causing particle formation: Improve circulation efficiency and enhance filtration.
• Poor bath solution filtration effect or damaged filter bags: Enhance filtration.
• Contaminated workpieces entering the electrophoretic bath, poor post-phosphating water washing, or impurities/particles on the surface: Ensure the workpiece surface is clean, free of phosphating sludge, and prevent secondary contamination; install filters in the pre-electrophoresis pure water washing step to remove particles from the water.
• Dirty post-washing solution for the bath solution and poor filtration: Enhance filtration; it is recommended to use filter bags with a precision of 25 μm.
• Particulate contaminants falling onto the coating during drying: Clean the drying chamber and air filters.
• Dirty coating environment: Adjust the spray pressure.
• Power outage leading to long circulation stop time, followed by direct electrophoresis: Increase the bath solution solid content.
• Significant loss of ultrafiltrate leading to low MEQ: Eliminate ultrafiltrate loss and adjust by adding neutralizer (lactic acid).
• Damage to the FRP (fiberglass-reinforced plastic) of the electrophoretic tank causing redissolution of the electrophoretically deposited paint: Repair the FRP promptly.
• Poor water solubility of the replenished paint causing particles: Ensure the newly added paint is well-dissolved and neutralized, and check for particles.

Note: Hard particles with a rough hand feel on the surface of the dried electrocoating, or small visible prickly heat(1-3 mm in diameter), which are more severe on the horizontal surface than the vertical surface of the workpiece, are referred to as "particles" (a coating defect).