Hot dip galvanizing pre-treatment

The surface of steel materials and parts cannot be directly hot-dip galvanized because foreign matter, such as oxide scale, oil stains, processing chips and dust, is easily generated or adhered to during processing, storage and transportation. Appropriate surface treatment is required. The quality of the pre-galvanizing treatment of steel parts has a great impact on the quality of the galvanized layer, so it should be highly valued. The process steps of pre-galvanizing treatment are: degreasing → water washing → pickling and rust removal → water washing → solvent plating → drying. 1. Degreasing and degreasing
This process is mainly used to remove grease and other water-insoluble substances adhering to the surface of the workpiece to avoid affecting the effects of rust removal, solvent main plating and hot-dip galvanizing. Here are several ways to remove oil.

①Chemical degreasing method ②Electrodegreasing method

③Acidic degreasing method ④Ultrasonic degreasing method

⑤Biological degreasing and oil removal method

2. Inspection of degreasing cleaning effect

After cleaning metal materials, the cleanliness requirements are determined based on the properties of the parts or the requirements of the processing technology. The following three methods are generally used to check cleanliness, and they are relatively simple and feasible.

①Visual inspection method ②Wiping method ③Water film rupture method

3. Remove old paint

The paint film on the surface of steel parts is damaged due to poor coating or transportation, or is aged and damaged during use. When it is necessary to hot-dip galvanizing again, the old paint should be removed.

Commonly used methods for removing old paint include mechanical, flame and chemical methods.

4. Pickling and rust removal

In hot-dip galvanizing of steel parts, the commonly used acids are mainly hydrochloric acid and sulfuric acid.

The purpose of pickling is to remove rust, but not to corrode the steel matrix. Excessive pickling will roughen the surface of steel parts, thus affecting the quality of hot-dip galvanizing. Therefore, acid solution is usually added to inhibit corrosion inhibitors during pickling. In corrosive environments, adding a small amount of this substance can effectively inhibit the corrosion of steel parts.

Pickling precautions:

①Control the concentration of pickling solution ②Keep the pickling solution clean

③Control the temperature ④Stir appropriately ⑤Pay attention to the washing procedure

5. Washing

The water washing process after alkali washing and pickling is mainly used to remove impurities that adhere to the workpiece after alkali washing and pickling to prevent cross-contamination and bring them into the main plating agent of the next process. There are two ways to wash with water:

①Immersion washing ②Spray washing

In some related domestic enterprises, the practice of recycling clean water is adopted, that is, a conductivity measuring instrument is installed in the pickled water tank to monitor the acidity of the water. When the acidity reaches a certain value, the solenoid valve will automatically open and pump the water to In the cleaning tank after alkali cleaning, clean water is injected into the cleaning tank after pickling at the same time, so that the water consumption can be reduced to the minimum, and the effect of less sewage discharge and low water consumption can be achieved.