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

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

19. Abnormal Adhesion

• Contaminated phosphating film (e.g., fingerprints, stains): Prevent secondary contamination; strictly prohibit touching the phosphating film surface with bare hands.
• Abnormal pretreatment processes (e.g., poor degreasing, insufficient water washing, blue-tinted phosphating film, yellow rust spots): Adjust pretreatment processes to ensure adequate degreasing, sufficient water washing, uniform phosphating film, and no yellow rust or blue spots.
• Rust on the workpiece surface: Install a pre-cleaning process to remove rust from workpieces before they enter the pretreatment process.
• Bath solution contaminated by impurity ions (high conductivity), excessive solvent content in the bath solution, or low pigment content: Discharge ultrafiltrate and add deionized water; add color paste to increase the pigment-to-binder ratio.
• Excessively high application voltage or high bath solution temperature, causing local breakdown of the coating film: Reduce the application voltage and strictly prevent excessively small electrode spacing..

Note: Due to uneven conductivity of the workpiece surface or phosphating film, current density concentrates on areas with low resistance during electrocoating, leading to coating accumulation and adhesion in those areas. If the application voltage is too high (close to the breakdown voltage), local damage to the coating film may occur, also resulting in accumulated adhesion.

20. Reduced Throw Power

• Low application voltage: Increase the application voltage.
• Low solid content of the bath solution: Ensure the solid content of the bath solution is within the process-specified range.
• Blocked diaphragm of the anode cover (high resistance): Clean the anode cover or replace the diaphragm.
• Low conductivity of the anode solution: Replenish neutralizer to increase the conductivity of the anode solution.
• Excessively high bath solution temperature: Reduce the operating temperature of the bath solution.
• Unfavorable workpiece structure: Improve the workpiece structure if possible and open reasonable process holes.

Note: Under normal conditions, the inner cavity and interlayer surfaces of the workpiece can be coated with paint. In production, if the inner cavity cannot be coated or is only thinly coated, this phenomenon is called "reduced throw power".

21. Dry Paint Marks

• Excessively long time between workpiece removal from the bath and post-washing: Enhance on-tank spraying; the draining time from on-tank spraying to circulating ultrafiltrate washing should not exceed 60 seconds.
• Poor post-electrophoresis washing: Check for clogged nozzles or misaligned nozzle directions; appropriately increase the water washing volume and spray intensity.
• Excessively high bath solution temperature: Appropriately reduce the temperature and increase ambient humidity.

Note: Residues of bath solution adhering to the wet coating film after electrocoating are not completely removed by washing, resulting in stains on the dried coating surface. This defect is called "dry paint marks".

22. Bath Solution Foaming

• Air leakage at valves, connections, or pipelines on the suction side of pumps in the electrophoresis system: Inspect and repair pumps, valves, and pipelines in the system.
• Excessively large overflow height difference between the main tank and auxiliary tank, causing foaming: Adjust the height of the overflow weir to reduce the height difference (should not exceed 10 cm).
• Insufficient circulation, resulting in poor surface flow of the bath solution and difficulty in eliminating bubbles carried into the tank by the workpiece (leading to accumulation): Check the operating status of equipment in the circulation system and perform maintenance if necessary; tank transfer and cleaning may be required if necessary.

23. Step Marks

• Charged workpiece entry into the tank with slow line speed: Change to power-on after tank entry or reduce the number of anodes at the tank entry end.
• Abnormal production line shutdown during pretreatment or electrophoresis: Minimize abnormal shutdowns as much as possible.
• Uneven washing during pretreatment or electrophoresis: Check the direction and spray pattern of nozzles for pretreatment and electrophoretic water washing.

Note: Horizontal or step-like marks appearing on the electrocoating film, usually caused by inconsistent coating deposition rates during workpiece entry or shutdowns. This defect is called "step marks".