Cause analysis of bubble pinhole defect in local coating after cathodic electrophoresis:
Management impact
The cathodic electrophoresis bath management requires adding 4 kg of solvents per day under the conditions of production and non-production. Due to the National Day holiday, the solvents in the bath are not added as required, which results in the volatilization of solvents.”However, except for the problematic parts, there is no such phenomenon in the subsequent parts.”After consulting the technical personnel of the paint manufacturer, 30 kg of solvents and 5 kg of acid are added to the bath. There was no significant improvement. It is considered that during the holidays, the weather is too hot, the volatilization of solvents is Too large, and the addition of 30 kg of solvents is insufficient, which has not yet been solved. Defects should not be caused by insufficient solvents.
Cooling system
After inquiring the staff of the production workshop, the cooling system of the electrophoresis cell broke down during the holidays, which led to the increase of the bath liquid to 32 degrees C and a specific time to 35 degrees C. We think that the air bubbles Are produced in the tank liquid due to the increase of the temperature of the tank liquid, which results in the air contact between the horizontal face of the workpiece and the tank liquid when the workpiece is in the tank, leading to the isolation of the workpiece From the tank liquid, and the place with air bubbles has no film, which makes the film incomplete and glossy. Defoaming treatment was carried out for 2 hours after the tank liquid was stationary, and then products and specimens were made. When, normal production, the defect appeared again, only slightly more than before.”It is obvious that the high temperature of the tank liquid in a short period of time to produce air bubbles is only one of the reasons for the defect.
(iii) Equipment impact
Check the pump associated with the electrophoresis tank! No leakage was found in the tube. However, the working pressure of the circulating pump of tank liquid can not meet the technological requirements. The pipelines related to the circulating pump of tank liquid are checked one by Because the filter screen at the outlet of the electrophoresis tank at the front end of the auxiliary circulating pump of the electrophoresis tank is not installed, the metal filter and the pipeline are blocked, Result in a number of small air bubbles into the electrophoresis tank.
The temporary solution is to stop the operation of the pump, stop the main circulating pump of electrophoresis tank and the ultrafiltration circulating pump for two hours before production every day, and release the air bubbles after three days’ treatment; then clean up the metal filters And pipes to ensure the smooth flow of the tank liquid and the normal production.
Blockage of metal filters and pipes is one of the major causes of defects.
Solvent content electrophoretic paint contains water-soluble organic solvents, which play a solubilizing role. Compared with other coatings, the content of organic solvents is smaller, but it has a certain impact on film thickness and coating stability. Generally, it is required to be Solvent content in working fluid increases, film thickness increases, swimming permeability and breakdown voltage decreases, solvent content is low, film thickness decreases, and the appearance (smoothness) of the paint film becomes worse. The content of solvent In working fluid can be adjusted by adding solvent and replacing ultrafiltrate.
The time of electrophoretic coating in the electrophoresis tank is the time when the coated workpiece forms a film (electrified) under the working fluid level. The period is generally limited to about 3 minutes. The film thickness increases with the increase of swimming time. Appropriately increasing the voltage of the electrophoretic coating can reduce the time of the electrophoretic coating. And increase the time of the electrophoretic coating at a lower voltage to ensure the thickness of the film.
In the electrophoretic coating line, the electrophoretic coating voltage can control the film forming speed and deposition volume. Usually the working fluid temperature and the electrophoretic coating time are fixed. If the film thickness needs to be increased or decreased, it can be achieved by increasing In the continuous pipeline electrophoretic coating equipment, the voltage of the first electrified section is generally controlled below the lower limit of the working voltage, and the voltage of the second section is even slightly higher.
After electrophoresis, the cleaning coating is recovered and cleaned. When it comes out of the trough after electrophoresis, the surface of the coating is coated with working fluid which has not been coated. If it is dried directly, it will cause paint film defects, Such as spots, and waste if it comes out of the trough directly. In order to eliminate the drawbacks of the paint film and recover the working fluid, it is necessary to wash after electrophoretic coating. Cleaning after electrophoresis can be divided into two stages: Recovering the working fluid taken out: cleaning with ultrafiltration or deionized water at the outlet of the trough, and directly returning the washing liquid to the trough, preferably within 1 minute after the coating is discharged from the trough. Wash it with circulating ultrafiltration solution, usually 23 times, and finally rinse it with deionized water.
Ipoxy sealing primer is a two-component primer, which is prepared strictly according to 121 proportion before use. It is required to be uniformly and uniformly applied on the surface of concrete components without leakage brush. The following working procedure is carried out after 26 hours. Component A and B epoxy asphalt anticorrosive paint is formulated in strict accordance with 31 proportion. After mixing and stirring, it is applied on the surface of two-component epoxy sealing primer. The construction of required to be uniform and brushless. The thickness of the paint film reaches 100120m, and the next process is brushed after 1824h.
