The Knowledge Of Electroplating Part 2

- Mar 16, 2018 -

The method of plating

Electroplating is divided into rack plating, barrel plating, continuous plating and brush plating, and is mainly related to the size and batch of parts to be plated. Hanging plating is suitable for general-sized products such as bumpers for cars, handlebars for bicycles, etc. Barrel plating is suitable for small parts, fasteners, washers, pins, etc. Continuous plating of wire and strip suitable for mass production. Brush plating is suitable for partial plating or repair. The plating solution is acidic, alkaline, and has an acidic and neutral solution with a chromium mixture. Regardless of the plating method used, plating tanks and hangers that are in contact with the plating product and the plating solution should have a certain degree of Universality.

The classification of plating

If the composition of the coating can be divided into a single metal plating, alloy plating and composite plating three types.

If classified by purpose, it can be divided into:

① Protective coating;

② Protective decorative coating;

③ Decorative coating;

④ Repair of coating;

⑤ Functional coating

Single metal plating

The single metal plating has a history of more than 170 years. 33 kinds of metals on the periodic table can be electrodeposited from aqueous solution. Commonly used are electroplating zinc, nickel, chromium, copper, tin, iron, cobalt, cadmium, lead, gold, silver and other l0 species. The plating layer formed by depositing two or more elements simultaneously on the cathode is an alloy plating layer. The alloy coating has the organizational structure and properties not possessed by a single metal coating, such as amorphous Ni-P alloy, Sn alloys not found on the phase diagram, and special decorative appearance, particularly high corrosion resistance and excellent weldability. , magnetic alloy plating and so on.

Composite plating

Composite plating is a process in which solid particles are added to the plating solution and co-deposited with the metal or alloy to form a metal-based surface composite material to meet specific application requirements. According to the classification of electrochemical properties between the plating layer and the base metal, the electroplating layer can be divided into two major categories, anode coating and cathode coating. When the potential of the plated metal with respect to the base metal is negative, when the corrosion micro cell is formed, the plated layer is an anode, so that the anode plated layer, such as the galvanized layer on the steel piece; and the potential of the plated metal with respect to the base metal is positive, When the corrosion micro cell is formed, the plating layer is a cathode, so it is called a cathode coating layer, such as a nickel plating layer and a tin plating layer on a steel piece.

According to the purpose of use can be divided into:

① Protective coating: as Zn, Ni, Cd, Sn and Cd-Sn plating, etc., as a corrosion-resistant coating and a variety of corrosive atmospheric environment;

② Protection. Decorative coating: such as Cu-Ni-Cr, Ni-Fe-Cr composite coating, both decorative and protective;

③ Decorative coating: as Au, Ag and Cu. Imitation gold plating, black chrome, black nickel plating, etc;

④ Reparative Plating: Electroplating, such as Ni, Cr, Fe layer is high cost to repair some of the wear member or machining tolerance member;

⑤ Functional Coating: such as Ag, Au and other conductive plating; Ni-Fe, Fe-Co, Ni-Co magnetic coating and the like; Cr, Pt-Ru and other high temperature oxidation resistant coating; Ag, Cr, etc. reflective coating; black chrome, Black nickel and other anti-reflective coating; hard chrome, Ni. Wear-resistant coating such as SiC; Ni. VIEE, Ni. C (graphite) anti-abrasive plating, etc.; Pb, Cu, Sn, Ag, etc. Welded coating; anti-carburizing Cu plating.

Electroplating power supply

Power composition

The main circuit mainly includes a main transformer, a power rectifying device, and some detection and protection devices. The main transformer in the electroplating power supply is the voltage required to reduce the AC power supply voltage to the plating process. The thyristor rectifier uses an industrial frequency (50Hz) transformer, and a high-frequency (10 to 50kHz) transformer is used in the high-frequency switching power supply. Detection devices include voltmeters, current transformers, and the like. The protection device is mainly used for overcurrent protection of power rectifier devices.

The control circuit mainly includes a trigger control circuit such as a thyristor or an IGBT, a soft start circuit of a power supply, an over-current and over-voltage protection circuit, and a power supply phase loss protection circuit.

Power Features

1. Energy-saving effect is good

Switching power supply adopts high-frequency transformers, which greatly improves the conversion efficiency. Under normal conditions, the efficiency of SCR equipment is increased by more than 10%. When the load rate reaches 70% or less, the efficiency of SCR equipment is increased by more than 30%.

2. High output stability

Due to the fast system response (microseconds), it is highly adaptable to network and load changes, and the output accuracy is better than 1%. The switching power supply has high working efficiency, so the control accuracy is high, which helps to improve product quality.

3. Easy to modulate output waveform

Because the operating frequency is high, the output waveform adjustment is relatively low in relative processing cost, and the output waveform can be changed in accordance with user's process requirements more conveniently. This has a stronger effect on improving work efficiency and improving the quality of processed products on the job site.

4. Small size and light weight

The volume and weight are 1/5-1/10 of the thyristor electroplating power supply, facilitating planning, expansion, movement, maintenance and installation.

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