Views: 2 Author: Site Editor Publish Time: 2022-11-15 Origin: Site
Phosphating is a commonly used pretreatment technology. In principle, it should belong to chemical conversion film treatment. It is mainly used for phosphating on the surface of steel, and non-ferrous metals (such as aluminum and zinc) can also be phosphating. Phosphating is a process in which chemical and electrochemical reactions form a phosphate chemical conversion film, and the formed phosphate conversion film is called a phosphating film. The purpose of phosphating is mainly to provide protection for the base metal and prevent the metal from being corroded to a certain extent; it is used as a primer before painting to improve the adhesion and anti-corrosion ability of the paint film layer; it can reduce friction in the metal cold processing process Lubrication.
Phosphating is a commonly used pretreatment technology. In principle, it should belong to chemical conversion film treatment. It is mainly used for phosphating on the surface of steel, and non-ferrous metals (such as aluminum and zinc) can also be phosphating.
Phosphating is a process in which chemical and electrochemical reactions form a phosphate chemical conversion film, and the formed phosphate conversion film is called a phosphating film.
The purpose of phosphating is mainly to provide protection for the base metal and prevent the metal from being corroded to a certain extent; it is used as a primer before painting to improve the adhesion and anti-corrosion ability of the paint film layer; it can reduce friction in the metal cold processing process Lubrication.
The phosphating treatment process has been applied in industry for more than 90 years and can be roughly divided into three periods:
1. The period of laying the foundation for phosphating technology
Phosphating film is used as an anti-corrosion protective film for steel. The earliest reliable record is the patent obtained by Charles Ross in England in 1869. Since then, the phosphating process has been used in industrial production. In the long years of nearly a century, phosphating treatment technology has accumulated rich experience and made many important discoveries. During World War I, the development center of phosphating technology was transferred from the United Kingdom to the United States.
2. The period of rapid development of phosphating technology
In 1909, T.W. Coslet of the United States dissolved zinc, zinc oxide or zinc phosphate in phosphoric acid to make the first zinc-based phosphating solution. This research result has greatly promoted the development of phosphating process and broadened the development prospect of phosphating process. The Parco Power researched and developed by Parker Antirust Co., Ltd. formulated the phosphating solution, which overcomes many shortcomings and increases the phosphating treatment time to lho. In 1929, the Bonderizing phosphating process shortened the phosphating time to 10 minutes. In 1934, the phosphating treatment technology achieved a revolutionary development in the industry, that is, the method of spraying the phosphating solution onto the workpiece was adopted.
3. The period of widespread application of phosphating technology
After World War II, there were few breakthroughs in phosphating technology, but steady development and improvement. Phosphating is widely used in anti-corrosion technology and metal cold deformation processing industry. The important improvements in phosphating treatment technology in this period mainly include: low-temperature phosphating, various methods of controlling the weight of phosphating film, and high-speed phosphating of continuous steel strip. At present, the research directions in the field of phosphating technology are mainly focused on improving quality, reducing environmental pollution, and saving energy.
Using formula analysis technology in China, we can analyze the main components and trace main formula of high-quality phosphating solution.
⒈Classification according to phosphating treatment temperature
⑴High temperature type
The treatment time at 80-90°C is 10-20 minutes, and the thickness of phosphating film is 10-30g/m2. The ratio of free acidity to total acidity is 1: (7-8)
Advantages: The film has strong corrosion resistance and good bonding force.
Disadvantages: long heating time, large solution volatilization, high energy consumption, many phosphating deposits, unstable free acidity, uneven crystal thickness, and less application.
⑵Medium temperature type
50-75°C, treatment time 5-15 minutes, phosphating film thickness 1-7 g/m2, solution free acidity to total acidity ratio is 1: (10-15)
Advantages: stable free acidity, easy to master, short phosphating time, high production efficiency, corrosion resistance is basically the same as high-temperature phosphating film, and has many applications.
⑶ low temperature type
30-50℃ saves energy and is easy to use.
⑷ normal temperature type
10-40°C Normal (low) temperature phosphating (in addition to adding oxidizing agent, but also adding accelerator), time 10-40 minutes, the ratio of free acidity to total acidity of the solution is 1: (20-30), and the film thickness is 0.2- 7 g/m2.
Advantages: no heating required, less drug consumption, and stable solution.
Disadvantages: long processing time and complicated solution preparation.
2. Classification according to the composition of phosphating solution
⑴ Zinc phosphating
⑵ Zinc-calcium phosphating
⑶ iron phosphating
⑸Composite phosphating Phosphating solution is composed of zinc, iron, calcium, nickel, manganese and other elements.
⒊Classified by phosphating treatment method
⑴ chemical phosphating
The workpiece is immersed in the phosphating solution, and the phosphating is realized by chemical reaction, which is widely used.
⑵ Electrochemical phosphating
In the phosphating solution, the workpiece is connected to the positive electrode, and the steel is connected to the negative electrode for phosphating.
4. Classification according to the quality of phosphating film
⑴Heavyweight (thick film phosphating) The film weight is above 7.5 g/m2.
⑵ Sub-heavyweight (membrane phosphating) membrane weight 4.6-7.5 g/m2.
⑶ lightweight (thin film phosphating) film weight 1.1-4.5 g/m2.
⑷ Sub-lightweight (extra-thin film phosphating) film weight 0.2-1.0 g/m2.
⒌Categorized by construction method
⑴ impregnation phosphating
Suitable for high, medium and low temperature phosphating Features: Simple equipment, only need heating tank and corresponding heating equipment, it is best to use stainless steel or rubber-lined tank, stainless steel heating pipes should be placed on both sides of the tank.
⑵ Spray phosphating
It is suitable for medium and low temperature phosphating process, and can process large-area workpieces, such as automobiles, refrigerators, and washing machine shells. Features: Short processing time, fast film forming reaction, high production efficiency, and the phosphating film obtained by this method has dense, uniform, thin film and good corrosion resistance.
⑶ brush phosphating
When the above two methods cannot be implemented, use this method, operate at normal temperature, easy to paint, and can remove rust. After phosphating, the workpiece will dry naturally and have good antirust performance, but the phosphating effect is not as good as the first two.