- Welcome to YOCH Bearing!
- 0086-531-85866205
- 0086-16653196205
- market@yochibearing.com
The Role Of Phosphate Coating
Causes Of Common Faults Of Construction Machinery In Winter Construction
17/04/2024Intermediate Bearing Maintenance And Installation Technology
19/04/2024The paintable phosphating film is porous, uniform and fine, and the paint penetrates into the pores to increase the adhesion of the coating. At the same time, the modified low-zinc film can resist the corrosion during the electrophoresis process of electrophoretic paint and enhance the electrophoresis effect. These are all beneficial to improving the corrosion resistance of the phosphating film + organic coating of the coating product. The corrosion resistance of the steel surface after phosphating is 2 times higher than that of direct coating without phosphating. The effects of phosphate coating on coating are as follows.
- Improve the paintability of metal surfaces
The paintable phosphating film is porous, uniform and fine, and the paint penetrates into the pores to increase the adhesion of the coating. At the same time, the modified low-zinc film can resist the corrosion during the electrophoresis process of electrophoretic paint and enhance the electrophoresis effect. These are all beneficial to improving the corrosion resistance of the phosphating film + organic coating of the coating product. The corrosion resistance of the steel surface after phosphating is 2 times higher than that of direct coating without phosphating. The effects of phosphate coating on coating are as follows.
① Provide protection between processes to avoid secondary rust.
②Prevent chemical reaction between the coating film and the substrate.
③Slow down coating damage and the spread of rust under the coating, improving the corrosion resistance of the entire coating system and product service life. If the metal is directly coated, when the coating is damaged, micro-battery corrosion will occur there. Due to the conductivity of the metal and the capillary phenomenon between the coating and the substrate, the electrolyte under the coating will be sucked out, and the corrosion will spread in all directions. Spreads, causing corrosion under the film and blistering of the coating. It is different if there is a phosphating film on the metal. The corrosion is limited to the damaged area. This is because the metal surface is isolated by the non-conductive phosphating film, and the phosphating film is firmly attached to the substrate, preventing electrolyte lateral expansion, so it can effectively inhibit subfilm corrosion.
Therefore, the phosphating film has become an indispensable and good base layer for the coating. No phosphating or poor phosphating effect cannot guarantee the coating quality.
- Improve metal surface functionality
①As the surface layer of cold processing such as carbon steel wire drawing, cold stamping and cold extrusion of steel plates and steel pipes, cold forming of metal blanks, etc., it improves the ductility, friction reduction, lubricity, demolding properties, etc. of the metal. For example, the stamped parts are not phosphated, and even when the stamping force is small (8. 6 t) and the section reduction rate is small (εF =20%), serious scratches still appear on the surface of the stamped parts. After the steel plate is phosphated, the pressure required for stamping is smaller and it can withstand an increase in the section reduction rate, which is good for stamping. When the phosphating film is thickened, the stamping surface is still good despite the large stamping force (63.5t) and high section reduction rate (εF=80%).
②As a wear-resistant and anti-rust layer on the surface of metal workpieces. Such as auto parts (screws, bolts), molds, moving bearing parts (valves, piston rings, gears, valve lifters, etc.), hydraulic parts (solenoid valves), pump parts (stator, oil pan), magnetic parts (TiFeB ) and other phosphating treatments can play a role in wear resistance and rust prevention. Examples are as follows.
a. Car tire screws and bolts are phosphated with medium temperature zinc to improve the wear resistance of the threads (unphosphated threads are easy to wear and cannot be used) and achieve the purpose of rust prevention (neutral salt spray test 72h).
b. The service life of the steel die can be extended to more than 10,000 times after phosphating.
③ Increase the insulation of metal materials. Examples are as follows.
a. The silicon steel sheets used in motors and transformers are phosphated to improve electrical insulation (insulation resistance up to 5×107 Ω, breakdown voltage 240~380V) and heat resistance (small space factor).
b. There is a polycrystalline iron fiber used as a filler material in the manufacture of absorbing coatings because it has good electromagnetic properties. However, the surface resistivity of polycrystalline iron fiber is very low. It forms a conductive network inside the coating, reflects electromagnetic waves, and also affects the surface resistivity of the coating, which will affect the wave absorption performance. In order to increase the resistivity of the polycrystalline iron fiber surface, it must be phosphated and its specific saturation magnetization is required to be guaranteed. It is suitable to use magnetic phase iron-based phosphating (both zinc and manganese are non-magnetic phases).
- Improve the performance of metal cutting tools
After metal cutting tools (such as high-speed steel twist drills, etc.) are phosphated (thermal phosphating), the service life (2 to 3 times) and corrosion resistance (18 times or more) can be significantly increased. The reasons are as follows.
① The phosphating film has poor thermal conductivity and is difficult to heat up the cutting edge of the tool, thereby increasing the life of the cutting tool.
②Phosphating film can improve the lubrication conditions of the tool surface. Therefore, phosphated tools are most suitable for processing cast iron or workpieces with poor cooling conditions.
- Improve the heat treatment effect of metal
Phosphating film has the function of absorbing laser light. Phosphating treatment before laser quenching of alloy cast iron increases the laser absorption rate of the workpiece surface, and the quenched surface hardness is high (HRC 50). - Improve the adhesion of rubber pressing parts
The unphosphated rubber of steel parts (easy to remove oil and rust) has poor adhesion between the rubber and the substrate. The workpiece is treated with zinc-based phosphating, which can significantly improve the adhesion of rubber pressing parts. - Enhance the bonding strength of composite metal sheets
When manufacturing composite metal sheets (steel sheets, galvanized sheets, etc.), phosphating the surface of the sheet and then pasting it with a plastic sheet or PVC colored film can enhance the bonding strength between the metal sheet and the surface material and improve the shear strength of the composite metal sheet. . - Eliminate the corrosiveness of coating contact with different material workpieces
The mixed assembly of two coated workpieces of different materials will cause metal contact corrosion problems. For example, when workpieces are assembled with steel/galvanized steel or steel/aluminum rods, electrochemical corrosion will occur at the contact points between them, resulting in severe peeling of the coating film. If different materials are phosphated before painting, contact corrosion can be eliminated and the adhesion of the coating film can be improved. - Improve the plating properties of electroplated reworked parts
Some electroplated reworked parts (angle steel, etc.) have rough surfaces due to repeated stripping, and their electrical conductivity has deteriorated (iron elements have decreased and carbon elements have increased), making it difficult to plating. If phosphorus is pre-deposited before electroplating, the wet plating properties will become better and the coating will be uniform.