1. Purpose: to standardize the production process, operation contents and methods
2. Scope: applicable to pre-treatment in plastic spraying workshop.
3. Process flow:
Degreasing (alkaline) → water washing → rust removal → water washing → neutralization → surface conditioning → phosphating → water washing → post phosphating treatment (spraying)
4. Operation content and key control points:
4.1 Workpiece framing: handle with care to prevent deformation of workpieces. The height shall not exceed the scope of solution blistering (the effect of oil removal and phosphating is better than that of regular oil removal and phosphating when products are placed in a disorderly frame, but adequate drainage shall be ensured)
4.2 Degreasing: (normal temperature)
4.2.1 Alkaline degreasing: it is mainly used to remove the oil stain on the workpiece surface, with good effect. PH value is 9-11 (extensive test paper), the total alkalinity is 45-60 points, and the soaking time is 15-20 minutes. The soaking time can be appropriately extended according to the oil stain attached to the workpiece.
4.3. Water washing: PH value 6-7 (extensive test paper). For the water washing after degreasing, when the workpiece is completely poured into the water, it should be shaken up, down, left and right for 2-3 minutes, so as to completely remove the non-ionic surfactant left on the surface of the workpiece from the previous process. Keep clear water overflow during cleaning.
4.4. Derusting: the purpose of hydrochloric acid derusting is to remove rust completely, and the surface shall be white and clean without pitting. This process also has a good function of removing oxide scale. The disadvantage is that hydrochloric acid is easy to volatilize, resulting in acid mist which is seriously harmful to human health and serious environmental pollution. Therefore, it is required to use PVC plastic plates to cover when not in use. PH value 1-2 (extensive test paper) The total acidity is 300-500 points, and the soaking time is 25-30 minutes.
4.5 Water washing: PH value 6-7 (extensive test paper). For the water washing after degreasing, when the workpiece completely invades the water, it should be shaken up, down, left and right for 2-3 minutes, in order to completely remove the chlorine ions left on the surface of the workpiece from the previous process to prevent damage to the bath solution from the next process. Keep clear water overflow during cleaning.
4.6 Neutralization: PH value is 7-10 (extensive test paper). For the water washing after rust removal, when the workpiece is completely immersed in water, it should be shaken up, down, left and right for 2-3 minutes, in order to completely remove the chlorine ions left on the surface of the workpiece from the previous process and completely neutralize them, so as to prevent the workpiece from rusting due to exposure to the air. When the PH value of the tank liquid is lower than 7 or it is seriously yellow, the tank liquid shall be replaced in time.
4.7. Surface conditioning treatment: The purpose of pH 7-9 (extensive test paper) is to promote phosphating to form a fine and dense phosphating film and speed up phosphating. To re prepare the meter, use 50-80 ℃ warm water to stir and dissolve the meter, and then put it into the tank liquid bell. The configuration ratio is 0.3%. Under normal conditions, the solution is milky white and weakly alkaline. When the PH value is lower than 7 or is seriously yellow, the tank liquid shall be replaced in time. The workpieces cleaned in the previous procedure shall be slowly put into the tank, and shall be taken out and put into the phosphating tank after shaking up and down for 20-30 seconds.
7.8 Phosphating (zinc series, normal temperature)
7.8.1 After adjusting the workpiece table, put it directly into the phosphating tank and shake it up and down, left and right for 2-3 minutes. If there is no bubble, put it into the tank bottom. Shake for more than 2 times in the midway to remove the air trapped in the workpiece groove.
7.8.2. Phosphating solution and accelerator shall be supplemented before each shift every day, and they shall be properly supplemented during production. The pH value is 2.5-3.5 (precision test paper). The total acidity is 25-35 points, and the free acid is 0.9-1.8 points. More than once a day shall be tested and relevant records shall be made.
4.8.3. It is better to add accelerant in small amount for many times. It is normal when the titration points are 2-5. When the phosphating film is yellow, add 0.4 g/l accelerant. When more white powder is adsorbed on the phosphating film and it is difficult to clean, add 2-3 g/l phosphating solution.
4.8.4 The phosphating time is 10-15 minutes. If there are workpieces with special structures and materials or the weather temperature is low, it can be extended to 20-40 minutes according to the actual situation.
4.9 Water washing: PH value 6-7 (extensive test paper). For the water washing after phosphating, when the workpiece completely invades the water, it needs to shake up, down, left and right for 2-3 minutes, so as to completely remove the zinc phosphate left on the surface of the workpiece from the previous process to prevent the workpiece from rusting. During the cleaning process, it is necessary to keep clear water overflowing.
5. Drying shall be carried out according to oven operation instructions
5.1 The workpieces after phosphating cleaning shall be dried in time and coated on the surface to prevent rust after being stained with water and damped. The color of the film shall be measured by visual inspection, which is normally gray to dark gray.
6. Application Form
6.1. Pharmaceutical addition record (XG-QR-DD-02)
1、 Problem handling: After phosphating, the surface of the iron piece turns white. The reason is that the sediment in the phosphating solution is on the surface of the iron piece. Treatment method: add hydrogen peroxide into the phosphating solution to precipitate and remove the sediment under the phosphating solution. Increase water washing after phosphating.
Local yellowing is caused by the rust on the surface of the iron piece.
Reasons: 1. After phosphating, the workpiece was not washed thoroughly. 2. The workpiece is complex and the water is not completely emptied.
Treatment: 1. Increase water washing, 2. Dry with hot water, and increase ventilation.