Electroless plating
Electroless plating refers to the use of reducing agents to chemically reduce metal ions in the solution to the surface of catalytically active parts without the passage of external current to form metal Coating process. In mechanical maintenance, electroless nickel plating is the most practical. The biggest feature of electroless plating is the strong dispersion of the plating solution. All parts that come into contact with the plating solution are covered with metal coatings of basically equal thickness. The coating has a good appearance, is dense, and is corrosion-resistant.
1. Introduction to electroless plating technology
1. Principle
The principle of chemical immersion plating (referred to as electroless plating) technology is: electroless plating is a process that does not require Electricity, based on the principle of redox reaction, uses a strong reducing agent in a solution containing metal ions to reduce the metal ions into metal and deposit them on the surface of various materials to form a dense coating. Commonly used solutions for chemical plating: chemical silver plating, nickel plating, copper plating, cobalt plating, nickel phosphorus plating solution, nickel phosphorus boron plating solution, etc.
2. Characteristics of electroless plating
Electroless plating is electroless deposition of coatings. Select a suitable electroless plating solution, remove oil stains from the surface of the workpiece to be plated and put it directly into the plating solution. Just determine the immersion plating time according to the set thickness. Generally, as long as there is a plastic or polytetrafluoro container, the heating method is flexible, and there is a water boiling device (such as steam, oil furnace, gas)! Among the coatings obtained by these three methods, there is no obvious difference in the bonding strength and hardness of most metal coatings! The advantages of electroless plating are: (1) The process is simple and has a wide range of adaptability. It does not require power supply or anode production, and can be operated by general operators. (2) The bonding strength between the coating and the substrate is good. (3) The yield is high, the cost is low, the solution can be recycled, and there are few side reactions. (4) Non-toxic and environmentally friendly. (5) The investment is small, just a few hundred yuan for equipment, and the results are quick.
Chemical plating is not as fast as electroplating and brush plating! The former has a flexible anode shape and is particularly suitable for local plating and workpiece repair; the latter has relatively high requirements for anode material and shape, can obtain thick coatings, and is suitable for mass production. However, both electroplating and brush plating require electrodeposition coating! It requires equipment worth tens of thousands to tens of thousands of dollars and the process is complex. Electroplating, brush plating of copper, zinc, silver, etc. use cyanide poison to varying degrees. The treatment of the three wastes is troublesome and costly!
2. Application of electroless plating technology
Application of electroless plating on the surface of metal materials
Non-precious metal substrates such as aluminum or steel materials can be electroless nickel plated Technical protection and the avoidance of using difficult-to-machine stainless steels to improve their surface properties. Relatively soft, non-wear-resistant substrates can be given a hard, wear-resistant surface with electroless nickel plating. In many cases, there are many advantages to using electroless nickel plating instead of hard chrome plating. Especially for internal coatings and complex-shaped parts, as well as hard chromium layers that require post-plating machining. Electroless nickel plating is used on some substrates to make them easier to braze or to improve their surface properties.
1. Electroless nickel plating Because the electroless nickel plating layer has excellent comprehensive physical and chemical properties such as uniformity, hardness, wear resistance and corrosion resistance, this technology has been widely used abroad. The proportion of electroless nickel plating used in various industries is roughly as follows: aerospace industry: 9%; automobile industry: 5%; electronic computer industry: 15%; food industry: 5%; machinery industry: 15%; nuclear industry: 2% ; Petrochemical industry: 10%; Plastic industry: 5%; Power transmission: 3%; Printing industry: 3%; Valve manufacturing industry: 17%; Others: 11%.
For example, chemical nickel plating on the inner surface of the brass tube of the condenser of a power plant can greatly improve the corrosion resistance and extend the service life of the condenser tube; nickel plating on aluminum alloy can improve the hardness and protection of the aluminum alloy. performance. Improve the surface properties of aluminum alloys and expand the application scope of aluminum alloys.
2. Electroless nickel alloy plating
(1). Nickel-phosphorus binary alloy coating: hardness HV550~600, good conductivity! Good weldability and corrosion resistance, used for IC top covers, lead frames, molds, buttons, etc.;
(2). High phosphorus nickel alloy coating, non-magnetic, widely used in electronic instruments, semiconductor electronic equipment Shielding layer against electromagnetic interference, etc.
(3). Nickel-boron-phosphorus ternary alloy, coating hardness HV680, used for piezoelectric ceramic electrodes, transmission devices, and valves.
(4). Nickel-B-W hardness HV800, electronic molds, contact materials, etc.
(5). The 45# steel gear surface is brush-plated with nickel-phosphorus and nickel-cobalt alloy metal, which can significantly improve the contact surface and fatigue life of the 45# steel gear.
3. Electroless plating Silver is mainly used in solder joints of electronic components and printed circuit boards to improve the corrosion resistance and conductivity of products. It is also widely used in various decorations, such as assembly cups, high-end travel mugs, fasteners, etc. Beryllium bronze is widely used in the communications industry. In order to further improve the elastic conductivity of beryllium bronze, beryllium bronze can be plated with silver.
Application of electroless plating on the surface of non-metallic materials
Non-conductors can be plated with one or several metals using electroless nickel plating, both in terms of decoration and function (such as electromagnetic interference shielding) Part is important. Many engineering plastics have been considered as substitutes for metals on many occasions. Some of them have good high temperature resistance. All of these plastics are lighter than metal and more corrosion-resistant, including polycarbonate, polyaryl ketone ether, polyetherimide resin, etc. Where conductivity or electrical shielding is required, the plastic needs to be metallized, and electroless nickel plating can be used to achieve this purpose.
1. Silver, copper, and nickel plating on the surface of nylon: For example, electroless nickel, silver, and copper plating on the surface of nylon are used to replace metal or decoration; a new process of electroless plating is used to plate pure silver on special On the nylon base cloth, the nylon cloth has good anti-electromagnetic radiation performance.
2. Surface decoration plating of plastic workpieces, such as buttons, fasteners on vehicles, protective plates, etc. Using electroless plating is simple and convenient and can meet the needs of the market.
3. Chemical copper plating on polypropylene fibers can be used for industrial filtration and protection in chemical, pharmaceutical, textile and other industries. Polypropylene nonwoven copper-plated composite materials increase the conductivity of polypropylene materials and can eliminate the hazards of static electricity. They can be used It has broad application prospects in the manufacture of anti-static protective clothing packaging materials, decorative materials, etc.
4. Chemical immersion copper plating: Using high-strength plastic copper plating instead of metal copper can achieve the same surface properties and effects as copper. It is less difficult than casting and forging processes, and reduces equipment investment and saves money. Lots of copper. High-strength plastics are plated with metal, which can improve the anti-aging properties of plastics and eliminate the electrostatic dust collection effect of plastics.