The so-called electroplating come to light in the real work ust as its name implies. But how many people really understand it?
Electroplating is by using use electroanalysis to make metal or alloy materials scale on the surface of products, and form an even, compact, adhering metal layer. It has been widely use in many place in society, for example: machine, light industry, electronic, navigation, chemical industry, metallurgy and other industries, the main purpose are:
A. To improve the corrosion resistance of the metal parts.
B. Improve the protective and decorative property of metal products.
C. Repair the size of metal parts.
D. To give special properties to some products and fittings, for example: copper plating and silver plating can improve conductivity while nickel plating can improve magnetoconductivity.
Below is regular knowledge before electroplating.
Treatments before electroplating are: grinding and polishing, deoiling, rust removing, activating, and pretreatment of hard electroplating metal.
I. Grinding and polishing: sand blasting, burnishing, polishing, chemical polishing, electrochemical polishing.
1. Sand blasting: to use compressed air to spray sand on the surface of work piece, and use the impact of sand to clean or decorate the surface of work piece:
1. Improve the roughness of the surface of work piece, to increase adhesive force.
2. Remove burr, iron dross, sinter, impurity on work piece.
3. Mat finish before milky chrome plating.
2.Burnishing: to use the sharp angle of the polishing wheel to cut the metal surface, to remove iron dross and level metal surface.
3.Polishing: further smoothen surface of work piece, it is for preparation before plating or finishing after plating.
4.Chemcial polishing: to put work piece in solution with assist of outer power.
5. Electrochemical polishing: put work piece in water, connect electricity in the solution to improve the smoothness and gloss of the surface of metal surface.
II. Usually, there are three deoiling methods, they are: organic solvent deoiling, chemical deoiling, electrochemical deoiling.
1. Organic solvent deoiling: put work piece into organic solvent deoiling, until oil is totally wash out. For example: gas, toluene, alcohol.
2. Chemical deoiling: use alkali solutions saponification to oil to wash saponifiable oil.
3. Electrochemical deoiling: faster than chemical deoiling, it is more effective in deoiling, metal part can deoil in negative or positive pole, but please decide electrolyzing deoiling technique according to the material, character, demand of the metal piece.
III. Chemical rust removing before plating is use chemical or electrochemical reaction, to get rid of thick millscale and bad surface substance on the surface of the work piece. It is one of the important technique in plating techniques. According to the property of the object, rust removing can be separated into: regular etching, bright etching, and strong etching.
. Activation is to remove the thin oxide film on the metal surface in weak etching agent, to expose the metal surface of the work piece, actually, activation is weak etching. It is the final procedure of electric plating.
Dark nickel is also called normal nickel, the electrolyte consists of nickel sulfate, sodium chloride and boric acid, it can be separated into pre nickel plating and normal nickel plating. And the former has neutral electrolyte and acid electrolyte.
2. Semi-bright nickel plating
Semi-bright nickel plating is based on dark nickel, and add small quality additive which has good leveling ability, will not increase plating stress and not contain sulfur, to form semi-bright electrolyte. Semi-bright nickel plating usually use as the basic plating layer of double layer or triply layer nickel plating, to increase the electrochemical protective function of the metal.
3. Bright nickel plating
Bright nickel plating electrolyte need to add two kinds of brighteners, it can directly make mirror-like plating layer, which is of good ornamental. Two comprehensive cleaning methods:
1. Low current intensity electrolytic cleaning
2. Chemical synthetical deposit cleaning
Because the properties of the plating work piece is various, so the plating solution is different too. For example: alloy plating kind, gold imitation layer, copper zinc alloy, lead zinc alloy, nickel iron alloy, zinc nickel alloy, chemical nickel plating, chemical copper plating etc, and also plastic plating, i.e., ABS plastic plating. Their electrolytes are not the same.
After treatment of electroplating: passivation, coating, sealing, rendering and dehydrogenation.
1. Passivation: through chemical or electrochemical treatment, to create a thick and stable film on the surface of the metal plated layer, the usual passivation methods are:
Chemical passivation
Electrochemical passivation.
For example the passivation treatment of zinc plating layer can be separated into: colored passivation, blue-white passivation, black passivation and etc. Colored passivation solution has low content, medium content, and high content. The technique process of low content chromic acid colored passivation is:
Polishing cleaning colored passivation washing hot water washing drying
Blue-white passivation can be achieved in two ways:
1. Five colored passivation film blanching;
2. Low chromium white passivation.
2. Coating: for silver and gold imitation plating parts, to smear or soak a transparent organic film, to prevent or prolong the plating layer change color.
3. Sealing: to improve the corrosion resisting ability of work piece in opened air. By using physical, chemical or electrochemical methods, to cover a film on the surface or medium plating layer.
4. Rendering: it has chemical, electrochemical, and heat treatment methods, to decorative the work piece.
Dehydrogenation: eliminate the hydrogen embrittlement of the plating layer and the metal, usually zinc plating, hard chromium plating need to carry out Dehydrogenating. It is cause by acid washing, cathodic electrolyzing deoiling and electroplating. The Dehydrogenation temperature should be kept in 200230, and last for 4 hours.
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