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

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

1. Decrease in pH Value (Accompanied by Decreased Film Thickness, Increased MEQ Acid Value, and Increased K Value)

• Anode solution leaking into the bath solution: Check if the inlet and outlet water are normal, if the anode membrane is damaged, and if the anode solution conductivity is within the process range.
• Excessive addition of neutralizer: Stop adding neutralizer, monitor the pH value at any time, increase the frequency and volume of anode solution discharge, and control the anode solution conductivity at the lower limit of the process range.
• Excessively high conductivity of the anode solution: Check for discrepancies between the actual anode solution conductivity and the displayed value, and if automatic water replenishment is normal; if the anode solution conductivity cannot be controlled automatically, manually discharge the anode solution and replenish with pure water, while monitoring the anode solution conductivity.
• Introduction of acidic substances: Control the water quality and cleaning effect of pre-electrophoresis water washing, as well as the dripping pH value of workpiece hangers.

Note: Under the above conditions, the pH value can be increased by adding original paint with a high pH value and increasing the discharge of ultrafiltrate, while simultaneously testing the MEQ value and conductivity.

2. Increase in pH Value (Usually Accompanied by Increased Film Thickness, Tendency for Pinholes, Decreased Ultrafiltration Permeability, and Decreased MEQ Acid Value)

• Excessive discharge or accidental loss of anode solution: Reduce anode solution discharge, appropriately increase the anode solution conductivity, and check for leaks in the circulation pipeline.
• Excessive discharge or accidental loss of ultrafiltrate (UF) solution: Stop discharge, monitor the pH value and MEQ value, and check for leaks in the ultrafiltrate-related pipeline.
• Introduction of alkaline substances during pretreatment: Strengthen water washing, control the dripping pH value and conductivity within the process range; adjust the nozzles for pre-electrophoresis water washing to prevent alkaline solution from being carried over; check if the overhead chain and hangers carry alkaline solution.

3. Decrease in Conductivity (Accompanied by Decreased Film Thickness and Decreased Electrodeposition Efficiency)

• Excessive discharge of UF solution (including accidental loss of UF solution): Stop UF solution discharge, monitor conductivity, and eliminate faults causing accidental loss.
• Too low solid content: Replenish the solid content to within the process range.
• Excessive discharge or loss of anode solution: Reduce anode solution discharge and check for leaks in the relevant pipeline.
• Malfunctioning instruments: Calibrate the instruments and electrodes in a timely manner.
• Low detection temperature: Conduct detection at 25°C.

4. Increase in Conductivity (Accompanied by Increased Film Thickness; Increased current density leading to defects such as pinholes, messy water marks, mesh patterns, and coating film cracking)

• Insufficient discharge of UF solution: Accelerate the discharge of UF solution and check the ultrafiltration permeation rate.
• Low pH value of the bath solution: Discharge the anode solution to increase the bath solution pH value, and discharge the UF solution simultaneously.
• Too high solid content: Stop adding the original paint.
• Excessively high conductivity of the replenished pure water: Ensure the conductivity of pure water is ≤10 μs/cm.
• High content of impurity ions carried over from pretreatment: Control the workpiece dripping conductivity to be ≤30 μs/cm.
• Excessive dissolution of the phosphating film during electrophoresis: Select a phosphating agent with a high P ratio and good alkali resistance.
• Malfunctioning measuring electrode: Calibrate the electrode constant or replace the electrode.
• Low detection temperature: Conduct detection at 25°C.

5. Decrease in Solid Content (Accompanied by Decreased Film Thickness, Decreased K Value, and Increased UF Solution Permeability)

• Failure to add the original paint on time and in the required quantity: Replenish the original paint in a timely manner according to consumption.
• Imbalanced return of the post-washing system to the electrophoretic bath, leading to increased bath solution volume: Control the liquid level of post-washing and the amount returned to the electrophoretic bath.
• Loss of bath solution: Check for leaks in the system, especially whether the bath solution remains in the reserve tank after tank transfer.
• Too high bath solution level: Control the amount of pure water replenishment and the reflux rate of washing water.

Note: Under the above conditions, if the tank capacity allows, the solid content can be restored by adding the original paint; if the bath level is too high, it may be necessary to discharge part of the UF solution.

6. Increase in Solid Content (Accompanied by Increased Film Thickness, Increased K Value, and Decreased UF Solution Permeability)

• Excessive addition of the original paint: Reduce the amount of original paint added or stop replenishment according to consumption.
• Insufficient replenishment of pure water into the tank: Replenish the required amount of pure water.
• Loss of ultrafiltrate leading to decreased electrophoretic bath level: Identify the cause of the loss and resolve it promptly.