1. Process flow

1.1 Degreasing(alkaline) → Water Rinsing → Rust Cleaning → Phosphating → Water Rinsing → Drying

1.2 Degreasing(acid) → Rust Cleaning → Water Rinsing → Phosphating → Water Rinsing → Drying

1.3 Grease and Rust Cleaning → Water Rinsing → Phosphating → Water Rinsing → Drying

2. Solution preparation (1 ton)

The weight ratio of phosphate coating agent and water is 1 : 9, that means there are phosphating solution of 100 kg and water of 900 kg in working solution of 1 ton. The pH of working fluid is 3 to 4.

3. Performance indicators

4. Detection method

4.1 Total acidity (points)

Taking 10 ml working fluid to the conical flask, and adding phenolphthalein indicator of 3 to 5 drops. Titrating above-mentioned solution by 0.1 M sodium hydroxide standard solution from colorless to red. The quantity (ml) of 0.1 M sodium hydroxide standard solution is called the points of total acidity.

4.2 Free acidity (points)

Taking 10 ml working fluid to the conical flask, and adding bromophenol blue indicator of 2 to 4 drops. Titrating above-mentioned solution by 0.1 M sodium hydroxide standard solution from yellow to blue. The quantity (ml) of 0.1 M sodium hydroxide standard solution is called the points of free acidity.

5. Additions and adjustments (1 ton)

After using a period of time, phosphating working solution will lose activity. When total acidity is normal, but free acidity is too low, phosphate coating agent can be added.

Theoretical calculations: Adding phosphate coating agent of 5 kg can improve one point of the points of free acidity, and 4.2 kg can improve a total acid points.