Plastic plating-how to classify electroplated coatings.
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It can be divided into protective coating. Protective-decorative coating, restorative coating, functional coating, etc.
(1) protective coating.
The coating that prevents the base metal from corrosion in the atmosphere or other environment is called a protective coating. For example, zinc, cadmium, tin and other coatings on iron and steel parts and zinc-based alloy coatings (zinc-iron, zinc-cobalt, zinc-nickel, etc.) belong to this kind of coating. Zinc plating is used to protect ferrous metal workpieces under general atmospheric conditions. This coating has a wide range of uses and accounts for more than 50% of electroplating production. It can be protected by cadmium plating in humid and oceanic atmosphere. Choose cadmium or cadmium-tin alloy for fastener protection. For example, high pressure gasket sealing and anticorrosion in chemical production. Tin coating has good corrosion resistance to organic acids, it not only has strong anti-rust, but also produces corrosion compounds that are harmless to human body, so it is widely used in food processing industry.
(2) Protective-decorative coating.
The coating which can not only prevent the matrix metal from corrosion but also has a beautiful coating is called protective decorative coating. Such as copper / nickel / chromium coating, nickel-iron / chromium coating, copper-tin / chromium coating on iron and steel parts. It requires that the coating is not only anti-corrosion, but also decorative. This kind of coating is often plated first "bottom", then "surface", and sometimes "middle layer". The reason for this is that it is difficult to find a single metal coating that can meet the dual requirements of protection and decoration at the same time. Although some coated metals have strong anti-corrosion ability, they can not maintain luster for a long time in the environment of use. In addition, although the anti-corrosion ability of some coated metals is poor, it can give the product a luster that lasts for a long time, and is not easy to wear. Therefore, make use of the advantages of multi-layer electroplating to match and use it to make up for the defects of each other. Such as copper / nickel / chromium coating, first copper plating as the bottom layer, and then nickel plating as the middle layer to improve corrosion resistance, the outer layer is a micro-blue bright chromium, has a good decoration. This kind of composite coating is mostly used in the exterior parts of instruments, cars and bicycles.
(3) repairable coating.
The coating that can thicken or restore the size of the locally worn workpiece locally or as a whole is called restorative coating. Some major mechanical parts, such as trains and cars. Large shafts, crankshafts and gears on petrochemical machinery can be repaired by electroplating to prolong service life, while deep well pump shafts can be repaired by electroplating hard chromium and iron plating.
(4) functional coating.
Functional coatings use a variety of mechanical, physical and chemical properties of coating metals to meet the needs of various occasions, according to the properties of coatings, they can be divided into the following main categories.
1 wear-resistant and antifriction coating. To increase its wear resistance by improving the surface hardness of products, hard chromium plating is often used in industry, such as the journal of various shafts and crankshafts, the roll surface of printing rollers, the inner wall of engine cylinder and piston ring, the inner cavity of stamping die, etc. Lead-tin alloy and lead-tin-copper alloy are used as antifriction coating for sliding contact surface to play the role of lubrication so as to reduce sliding friction.
(2) High temperature oxidation resistant coating. The parts that may be oxidized at high temperature (high temperature corrosion) are coated with high temperature anti-oxidation layer to improve the high temperature oxidation resistance of the parts surface. Some special purpose workpieces made of high melting point metal materials such as jet engine rotors and blades need to be plated with nickel and chromium. Platinum-germanium alloy plating; in some cases, composite coatings such as nickel-germanium oxide are also used. Nickel-alumina and so on to improve the high temperature oxidation resistance of metal materials.
3Magnetic coating. Magnetic materials are required for magnetic rings, magnetic drums, magnetic disks and magnetic film magnetic storage components in electronic computer equipment. The commonly used magnetic alloy coatings are cobalt-nickel, nickel-iron, nickel-phosphorus-cobalt and so on. At present, electroplating and electroless plating are often used to prepare magnetic materials to meet the requirements in this aspect. The magnetic property parameters of the coating can also be adjusted by changing the electroplating process parameters.
4solderable coating. Brazing is needed when some electronic components are assembled. In order to improve their weldability, tin, silver or tin-lead alloys are usually plated. Gold and so on all belong to this kind of coating. If wear resistance is required at the same time, silver-antimony alloy can be plated. Gold-cobalt alloy, gold-antimony alloy, etc.
There are many other functional coatings used in production practice. For example, in order to enhance the bonding of steel wire and rubber during hot pressing, brass (copper-zinc alloy) can be plated on steel wire; in order to improve the surface electrical conductivity, copper or silver can be plated, which not only requires good electrical conductivity, but also has certain wear resistance, it should be plated with gold or silver alloy; in order to resist the corrosion of sulfuric acid and chromic acid, lead can be plated. In order to prevent local Carburizing, copper plating and local nitriding should be plated with tin; in order to increase reflective ability, chromium, silver or high tin bronze can be plated; in order to extinct or absorb light energy into heat, black nickel and black chromium can be plated.
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