December 2012 Archives

Electroless Plating

Electroless plating is also called chemical plating. Unlike the electroplating where metal is deposited on objects by reduction precipitation using a DC current, this method uses chemical reduction agents to plate, and therefore does not require DC power sources, cathodes, or anodes. One of such platings is Displacement Plating. It is also called Immersion Plating, and the plating layer is obtained by displacement reaction caused by differential in ionization tendency by simply immersing in the plating solution. Zincate treatment used as a pre-process for aluminum plating belongs to this category. In a case of electroless plating using hypophosphite as the reduction agent, Nickel-Phosphorus (Ni-P) alloy plating is obtained, and Nickel-Boron (Ni-B) alloy plating if boron compounds are used. There are Nickel, Cobalt, Palladium, Copper, Silver, and Gold for electroless platings, though the ones that are put to practical industrial uses are Nickel, Copper, and Gold platings.

Electroless nickel plating -1

Nickel-Phosphorus (2~15%) alloy plating which is a representative of the electroless platings is valued high and utilized in a various application fields due to its excellent mechanical, electrical, and physical properties with its ability to uniformly coat complex shaped components. The properties are shown in [Table] below.

[Table] Physical properties of Nickel-Phosphorus Alloy Plating

The standards define industrial nickel plating and nickel electroforming for the purposes of corrosion reistance, wear resistance, and overlay build-up on steel and nonferrous metals.

(1) Classification and applications

[Table 1] shows the classification and applications of industrial nickel plating and nickel electroforming.

[Table 1] Classification and applications of industrial Ni plating and Ni electroforming

(2) Quality

Appearances, surface roughness, thickness, hardness, wear resistance, and other required qualities of plating and electroforming are to be determined by the agreements of the involved parties.

(3) Adhesion characteristics

Tested by grinding test method, chisel driving test method, thermal test method, or tensile test method.

(4) Symbols and names of plating and electroforming

●Ep-Fe*, M/E-Ni, M, 500±10/1G, 2G（1.6 μm Ra）

Industrial nickel plating on steel surface: 500±10μm, base metal and plating are to be ground finished to a surface roughness of 1.6μm Ra.
M: machining on base metal, E-Ni: industrial nickel plating, 1G: machining before plating, 2G: grinding after plating, Ra: Center line average roughness.

●Ef/Ni, b, 100±10/

Ef: Electroforming, Ni: Nickel, b: Gloss type electroforming

●Ep-AL*/Ni, 100±10, ICr, 10/G, （0.4μmRa）

Ep: Electroplating, AL: Aluminum alloy A5052S, Ni: Nickel plating 100±10μm, ICr,10: 10μm Industrial chrome plating, /G: Grinding finish after plating

Other characteristics of the functional platings are as follows.

(1) Flame retardancy

In general, plastics are not heat resistant, but application of metalic plate coatings on plastics improve weaknesses against heat. Concurrently, the platings give electric conductivity, antimicrobial property, contamination resistance, decorative effects, and extended life.

(2) Sea water corrosion resistance

This relates to anti-corrosiveness in sea water or the salts, a characteristic required for marine vessel parts, submarine communication equipment, construction machinery, and coastal region communication equipent, etc. In general, cadmium plating is used for the corrosion prevention, but for the equipent requiring high reliability such as relays for undersea communication lines, tin-lead alloy plating, gold plat

(3) Carburizing prevention

Parts that are used in rotating applications have increased hardness by carburizing process in order to improve wear resistance. The carburizing is a process of diffusing carbon onto the surface of low carbon steel, enebling the steel to be heat treatable. In such cases, applying copper plating on sections where carbon diffusion penetration is unwanted the carburization can be prevented.

(4) Realism・reproducibility

This is a characteristic of being able to reproduce the original faithfully. This high reproducibility is achieved by the use of thick platings and electro-forming. Elecro-forming is used to faithfully reproduce artist's renditions of crafts, Buddhism equipment, and reliefs. In industrial applications, electro-formings are in active usage for production of electromagnetic waveguides, metal bellows, blades for electric razors, as well as copper, silver, nickel electro-forming are used on stampers for records and CDs.

Chemical properties of the functional plaring are as follows

(1) Chemical resistance

A characteristic that is resistant to chemicals. This is required on various tubs, agitators, valves, flanges, pumps used in the chemical industry, and lead plating, tin-lead alloy plating, electroless nickel plating are utilized. Platinum plating is used on electrodes.

(2) Contamination prevention

This property prevents scales from adhering to liquid contacting surfaces on chemical reaction vessels. Electroless nickel plating is widely used for this sinc it has this characteristic as well as chemical resistance characteristic.
In the ornamental products field, chrome plating is used on A refrigerator handles and etc. due to the plating's characteristics of preventing microbial propagation and soiling.

(3) Antibacterial property

It is known that bacterial growth is quite slower, or even become ectinct, on metal surfaces compared to plastic and natural fabric surfaces. Utilizing this characteristic, silver plating is applied on flatware such as knives and folks, and copper plating is applied on fibers for sox to terminate Trichophyton for athlete's foot prevention.

(4) Printing durability

This is a characteristic indispensable for obtaining clear printing results. This characteristic is always required for printing cylinders and rollers.
When the chrome plating is applied on offset and gravure printing cylinders and rollers, not only clear printing can be obtained but many benefits are obtained such as the equipment service life can be extended, corrosion by ink can be prevented, ink removal becomes easy, surface wear when scraping the ink can be prevented, and only requiring plating removal and replating when the printing plates are to be regenerated.