Shulou(Shulou.com)11/24 Report--

Among the many surface treatment processes, there is a process that can make the surface of the product black, rainbow or gray close to the metal color after treatment. This process is the phosphating process.

Phosphating treatment is a chemical reaction, forming a layer of film (phosphating film) on the surface of a surface treatment process.

Phosphating treatment process is mainly used on the metal surface, the purpose is also to provide a protective film for the metal surface, so that the metal is isolated from the air, to prevent corrosion; it will also be used for some products before painting, with this layer of phosphating film can improve the adhesion of the paint layer and corrosion resistance, improve the decoration to make the metal surface look more beautiful, and can also play a lubricating role in the cold working process of some metals.

After phosphating treatment, the workpiece will not oxidize and rust for a long time, so the application of phosphating treatment is very wide, and it is also a commonly used metal surface treatment process, which is more and more used in automobile, ship, machinery manufacturing and other industries.

However, phosphating treatment also has many disadvantages such as more solution sediment, rough surface, higher phosphating temperature, long time and higher cost.

In fact, the phosphating treatment process has been developed for a long time, it should be a modern metal surface treatment, the invention of an earlier time, its development has also gone through different periods.

In the United Kingdom in 1869, it was discovered that the phosphide film can be used on the surface of metal, which can effectively protect the metal from corrosion for a long time, and it was also patented at that time, which also laid the foundation for the technology and development of phosphide treatment.

From the beginning of the 20th century, phosphating treatment began to be used in industrial products, which also promoted the development and progress of phosphating technology, since then phosphating treatment has been rapidly developed and entered the practical application period.

In modern times, in order to meet various needs, the phosphating process is also constantly improving, mainly towards low temperature, low slag, environmental protection and non-toxic direction.

Under normal circumstances, after a surface treatment, a color is presented, but the phosphating treatment can be based on actual needs, by using different phosphating agents will present different colors, which is we often see phosphating treatment gray, color or black.

Iron phosphate after the surface will show rainbow color and blue, so it is also known as color phosphorus, phosphate solution is mainly molybdenum salt as raw material, will form a rainbow color phosphate film on the surface of steel materials, but also mainly used for coating the bottom layer, in order to achieve the corrosion resistance of the workpiece and improve the adhesion of the surface coating.

Zinc series phosphating color is gray, so it is called gray film phosphating, the main use of phosphating solution composed of phosphoric acid, sodium fluoride and emulsifier, will form a gray phosphating film on the surface of the workpiece, it is mainly for the coating bottom layer, and after the spray, spray paint or electrophoresis and other processes for combination.

The gray phosphating film itself also has certain corrosion resistance, so it can also be used as an anti-corrosion coating on the surface of the workpiece alone, mainly for some galvanized sheets, cold-rolled sheets, and aluminum sheets.

Manganese phosphating color is black or black ash, so also known as black phosphating, mainly using phosphating solution containing manganese ions, will form a layer of black phosphating film on the surface of the workpiece, it is also the best anti-rust performance of a kind of phosphating treatment, can be used as parts of long-term rust, but also the most widely used anti-rust phosphating.

Manganese phosphating will have a smaller friction coefficient than other phosphating, so black phosphating can be used for parts that often rub, which can effectively reduce friction, such as some automobile parts and some fasteners.

Phosphating treatment process The commonly used phosphating treatment process is to use chemical elements to react to form a film on the metal surface to prevent corrosion and priming, and these processes are mainly used in modern phosphating processes.

Degreasing and degreasing metal materials will come into contact with various oil stains or sweat stains during storage and processing, and these oil stains will also be mixed with various dust impurities and attached to the metal surface, which will not only affect the formation of phosphating, but also reduce the adhesion of phosphating film, corrosion resistance and appearance.

This requires cleaning the workpiece before phosphating. The common method is chemical method. Put the workpiece into a cleaning solution with strong acid heated to 80℃ for about 5 minutes. The grease is removed from the workpiece by reacting with strong acid.

Iron and steel in the process of processing will form a layer of oxide scale on its surface, there is water or corrosive liquid in the storage process will rust, these oxide scale and rust if not cleaned up, it will accelerate the corrosion of the workpiece.

Therefore, rust removal and oxide scale removal are also the main procedures before the workpiece is phosphated, which will affect the phosphating quality.

There are mechanical and chemical methods for rust removal and scale removal. Chemical methods are usually used. The workpiece is put into acid solution containing industrial hydrochloric acid and allowed to stand for about 30 minutes to complete rust removal and scale removal.

Phosphating process is the most important phosphating solution, different phosphating solution used will be different, the metal workpiece into the phosphating solution, there will be a chemical reaction between each other to generate an iron phosphate element, and will also produce hydrogen and oxygen.

This iron carbonate element will slowly crystallize and deposit on the metal surface. When this crystallization increases, it will form a piece on the metal surface to form a layer of phosphate film that is insoluble in water.

After the workpiece is put into the phosphating solution, it needs to be shaken for a few minutes, mainly in order to discharge the air and bubbles trapped in the groove of the workpiece. The phosphating time is generally determined according to the different workpiece structure, material and temperature, usually about 30 minutes.

Other processes Workpieces need to be washed after each process, mainly in order to clean off the chemical components remaining on the surface of the workpiece and successfully complete the next process.

After the workpiece is phosphorized and washed, it is necessary to dry the moisture on the surface, so that the entire phosphorization process is completed and it can be reprocessed or used.

Coating is a simple and practical method of modern metal corrosion protection treatment, phosphating treatment is the key process of its pretreatment, in addition to phosphating treatment process, the entire surface treatment coating industry has played a great role in promoting.

However, phosphating process is also facing many problems. It is necessary to improve the treatment process and develop towards energy saving, environmental protection, non-toxicity and efficiency improvement.

The picture in this article is taken from "1969 Mustang Restoration Part 27 How to Phosate and Oil restore your parts-Palmetto Enterprises" This article comes from Weixin Official Accounts: Manufacturing Principle (ID: zhizaoyuanli), Author: Lao Zheng

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