Self-coating requires strict process management, and the process parameters should be adjusted regularly to ensure that the parameters are within a reasonable range. The common defects and prevention methods of self-coating are shown in the table below.
defect | reason | Prevention method |
Poor wet film adhesion | ①The solid content of the bath liquid is low ② The surface is not clean ③The carbide is not cleaned | ① Add self-coating ②Strengthen pre-treatment ③The carbide is not cleaned |
Particles attached to the coating | ① There are particles in the self-swimming bad liquid ②There is scum in the washed grain ③Poor stability of self-swimming bath ④ Low autophoresis activity ⑤New bath solution | ①Regularly use nylon net to fish out sundries ②Cycle filtration ③Replace part of the bad liquid ④ Add active agent ⑤ Construction after placing for a period of time |
poor coating adhesion | ① Degreasing and rust removal ② The residence time before entering the drying tunnel is too long ③The workpiece hangs ash and turns black ④ Improper chemical post-treatment | ① Strengthen the pre-treatment process ② After leaving the tank, it should enter the drying tunnel as soon as possible ③Control pickling time ④ Supplement post-treatment agent, adjust pH value |
The part of the workpiece has no coating film | ① Degreasing unclean ②The preprocessing time is too long ③The activity of the bath solution is low ④ The solid content of the bath is too low | ①Strengthen pre-treatment, increase pre-degreasing process if necessary ②Shorten the preprocessing time ③ Add active agent ④Supplementary self-coating |
Part of the wet film is washed off | ① The pH value of the bath solution is too high ②The workpiece is degreased and unclean ③Excessively high iron content in dregs | ①Supplementary hydrofluoric acid ② Strengthen the pre-treatment process ③ Add distilled water and self-coating |
nudity | oily, special | Enhanced pre-processing |
Coating appearance is poor | ① There is slag in the self-swimming, washing or post-treatment tank ② The pH value of the bath solution is too low .③ The iron content of the bath is too low ④ Self-swimming time is too long ⑤ Oxidation-reduction potential is too low | ①Cycle filter or use nylon net to remove scum ②Adjust the pH value ③Supplementary iron-containing active agent ④ Reduce self-swimming time ⑤ Control the amount of hydrogen peroxide added |
bubbling | ①High fluoride ion content ② High washing concentration of reaction water | ① reduce ② dilution |
Bite the bottom | ①Baking temperature is low or overbaked ② Poor coating adhesion | ①Control the baking process ② see related items |
defect | reason | Prevention method |
Corrosion resistance deteriorates | Reactive washing concentration is low | Increased concentration |
pinhole | ① The gas ion content is too high ②The temperature is too high | ① adjust ② reduce |
completely filmless | Bad liquid pollution | deal with |
coating thinning | ①Short coating time ② Poor stirring condition | ① extend ②Strengthen stirring |
thickened coating | ① Long painting time ② High iron content | ① shorten ② reduce |
