1. Blackening is a common method of metal heat treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. When the appearance requirements are not high, blackening treatment can be used. The surface of steel parts is blackened, and some are also called bluish. Bluing treatment is a kind of chemical surface treatment, its main function is to form a dense oxide film on the surface of the workpiece, prevent corrosion and rust of the workpiece, and improve the wear resistance of the workpiece. It is only a surface treatment and will not damage the internal structure. To produce any effect, it is not heat treatment, which is fundamentally different from quenching. The commonly used methods of blackening treatment are traditional alkaline heating blackening and room temperature blackening that appear later. However, the normal temperature blackening process is not very effective for low carbon steel. The main components of the blackening solution are sodium hydroxide and sodium nitrite. The temperature tolerance required for blackening is relatively large, and a good surface can be obtained between 135 and 155 ° C, but the time required is somewhat long.
2. Electroplating - Plating gold, silver, copper, tin, nickel, chromium and other metals on the workpiece as required, the appearance is the color of the plated metal, and the salt spray test is more than 24 hours.
Electrogalvanizing is a traditional metal coating treatment that provides basic corrosion resistance to metal surfaces.
Cadmium plating: Cadmium plating is an anodic coating, mainly used for technical anti-corrosion. The main advantage is good brazing and suitable contact resistance. Due to its good lubricating properties, cadmium plating is often used in aviation, aerospace, navigation, and radio and electronic products. The coating plays a dual role of mechanical and chemical protection for the steel substrate, so its anti-corrosion performance is much better than that of the zinc coating. The cost of cadmium plating is high (about 5 times that of galvanized), which is serious for environmental pollution, so it is not recommended to be used, and galvanized is usually used instead.
Hot-dip galvanizing: The molten metal reacts with the iron substrate to produce an alloy layer, thereby bonding both the substrate and the coating. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. Hot-dip galvanizing has good corrosion resistance, sacrificial protection for steel substrates, high weather resistance, and salt water erosion resistance. It is suitable for chemical plants, refining plants, and coastal and offshore operating platforms.
Hot-dip aluminized steel: hot-dip aluminized steel has both the high strength of the steel substrate and the corrosion resistance, wear resistance, and high temperature resistance of the aluminum layer. Its corrosion resistance is 5-10 times that of galvanized steel, and it is resistant to sulfide and In terms of heat and corrosion resistance, its performance is better than 18-8 stainless steel, and it can withstand high temperatures of 600 degrees, which has obvious economic benefits.
3. Coating - apply paint (colored paint, dacromet) on the workpiece as required, the appearance is silver, black, colorful, and the salt spray test is more than 240 hours.
Dacromet: The appearance of Dacromet coating is uniform silver gray. The coating contains 80% thin zinc flakes and aluminum flakes, and the rest is chromate. It has excellent properties, such as strong corrosion resistance, Electro-galvanizing increased by 7-10 times, salt spray test > 500 hours, no hydrogen embrittlement, especially suitable for high-strength stressed parts, such as high-strength bolts used in subway projects, high heat resistance, heat resistance and stability of 300 degrees, It also has the advantages of high permeability, high adhesion, high friction reduction, high weather resistance, high chemical resistance stability and no environmental pollution.
PTFE: The anti-sticking effect of PTFE coating is very significant, it is the most heat-resistant substance among all fluoropolymers, and it can resist almost all chemical substances. Very low coefficient of friction and excellent wear resistance and good chemical stability. The operating temperature of PTFE coating can reach up to 300 degrees, and its application thickness is usually 25-75 microns.
Xylan: Xylan coating is a kind of fluoropolymer. Most Xylan coatings contain PTFE and other lubricating ingredients, and are generally applied in the form of thin films for the surface treatment of various metal components and fasteners. It has good lubricity, wear resistance, corrosion resistance, high friction reduction and high heat resistance. It also has the advantages of unique non-stickiness, high chemical resistance stability and no environmental pollution.
4. Phosphating——It is a process of chemical and electrochemical reactions to form a phosphate chemical conversion film. 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 Use lubricated. 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.