Pre-painting process guide
First, the process: degreasing → water washing → phosphating → water washing → drying → painting.
Second, the tank preparation (calculated in 1M2 tank)
1. Degreasing tank: add the designed volume of water in the tank, heat to about 45 °C, then open the spray pump to add 20~25Kg PA30-SM degreaser, test the free alkalinity, and heat to 50~65 °C Put into use.
2, washing: ordinary tap water.
3, phosphating tank: add a design volume of water in the tank, open the spray pump to add PA377-400 phosphating solution 16~20Kg, the amount of liquid alkali, the test free acidity should be within the process range, the temperature rises to 35~50 °C Put into use.
4, washing: ordinary tap water.
5, drying:
6, painting:
Third, tank management
1, degreasing tank
Regular test of free alkalinity should be greater than 11 points (generally 11 to 18 points, the free alkalinity can be lower according to the actual sheet oil stain), when low, degreaser should be added, when it is 1M3 tank, add Kg Free base rose by 3 to 4 points. Adhere to regular process changes.
Free alkalinity test: take 10ml bath, add 50ml distilled water, 1-2 drops of phenolphthalein indicator, 0.1N HCL standard droplets, red → colorless as the end point, the number of milliliters of HCL standard solution is the free alkalinity point .
2. Phosphating tank
Regular test of free acidity should be in the range of -1.0~0.5 points. When the pH is low, add phosphating solution. When it is 1M3 tank, add 5Kg free acidity to increase by about 0.2 points. It is recommended to take continuous dripping after experience. This saves and stabilizes the quality. Adhere to regular process changes.
Free acidity test: take 50ml bath, bromophenol blue indicator 3~5 drops, 0.1N NaOH standard droplets, yellow→purple as the end point, the consumption of NaOH standard solution is the number of free acid points (when adding bromine When the phenol blue indicator is purple, it is titrated with 0.1N HCL standard solution, the end point is purple→yellow, and the number of milliliters of the consumed HCL standard solution is both the negative value of free acidity).
Fourth, the process parameter table
Station name
Processing temperature
Processing time
control parameter
Test frequency
Degreasing
45~60°C
90~180 seconds
Free alkalinity: 11~18 points
Once/shift
Washed
Normal temperature
30~150 seconds
Overflow washing
Phosphating
35~50°C
90~180 seconds
Free acidity: -1.0~0.5 points
Once / 2 hours
Washed
Normal temperature
30~150 seconds
Overflow washing
V. Maintenance item list
Station name
Maintenance item
frequency
Maintenance
Degreasing
conventional
1 time / day
Check the liquid level to remove foreign matter
Nozzle
1 time / week
Remove and clean
Bath
1 time / season (or according to pollution)
Clean the tank and replace the bath
Washed
conventional
1 time / day
Check the liquid level to remove foreign matter
Nozzle
1 time / week
Remove and clean
Bath
1 time / day (or according to pollution)
Clean the tank and replace the bath
Phosphating
conventional
1 time / day
Check the liquid level to remove foreign matter
Nozzle
1 time / week
Remove and clean
Bath
1 time / season
Clean the tank and replace the bath
Heat exchanger
1 time / season
2~5% dilute nitric acid cleaning
Washed
conventional
1 time / day
Check the liquid level to remove foreign matter
Nozzle
1 time / week
Remove and clean
Bath
1 time / day
Clean the tank and replace the bath
Six, common faults and troubleshooting
6.1 degreasing tank
Common malfunctions
cause
Method of exclusion
Poor degreasing ability
Low concentration
Add degreaser
Low temperature
increase temperature
Solid fat can not be removed
Low temperature
Increase temperature or pre-erase
The bath turns black and the surface slick
Excessive oil content in the bath
Change bath
6.2 phosphating tank
Common malfunctions
cause
Method of exclusion
Phosphating film is evenly yellowed
Low concentration
Supplemental phosphating agent
Low temperature
increase temperature
Stop line
Reduce stop line
Phosphating film is too thick, hanging ash
Low concentration
Natural consumption or dilution with water
Free acidity is too high
Neutralization with alkali
High temperature
Reduce the temperature
Stop line
Reduce stop line
Membrane difference at normal parameters
Bath aging
Change bath
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