Under electroplating (also called electroplating ) is the electrochemical deposition of metallic precipitates ( coatings ) on substrates ( objects). The history of electroplating, such as electroplating is colloquially known, dates back to the Italian physician Luigi Galvani, who discovered named after him galvanism on November 6, 1780.
When electroplating is passed through an electrolytic bath stream. At the positive pole (anode ) is the metal that is to be applied (eg, copper or nickel), the negative ( cathode ) of the object to be coated. The electric current thereby dissolves metal ions from the consumable electrode from and deposits them by reducing it to the workpiece. So the object is to be refined on all sides evenly coated with copper or another metal. The longer the object remains in the bath and the higher the electric current, the more the metal layer ( e.g., copper layer). In order to apply successfully conversation layers, the substrate must be pre-treated.
Strictly speaking, between the electroforming (also called electroforming ) is still the electrolytic production of metal objects, and the Galvanostegie (English electroplating ), the production of metallic coatings, distinguished. The term Galvanostegie has now been replaced almost entirely by the general term electroplating. Because fewer and fewer equestrian statues were needed, the electroforming was a bit more into oblivion, but experienced a renaissance in connection with the micro system technology, as a Mikrogalvanoformung, also called lithographically - galvanic Abformungstechnik. Another use of the electroforming mold during the injection molding of plastics.
Generally, a distinction is made between decorative and functional electroplating. The former is basically used for beautification of objects and must for this purpose have certain minimum technical characteristics. Examples of the decorative electroplating, the plating on plastics, chromium plating of steel tube furniture and motorcycles and the gold plating of jewelry and cutlery.
The functional electroplating is used for corrosion protection, wear protection, catalysis or improve electrical conductivity and the reduction of friction forces. Examples are zinc screws, the coating of machine components with hard chrome, the production of metal, usually nickel or platinum-containing catalysts for the chemical industry or fuel cells as well as the gold and silver plating of electrical contacts and smoothing, for example, medical supplies and materials. Electrical contacts - called pins - for different copper alloys are usually plated galvanically. To prevent materials of the base material to diffuse through the layer of tin, nickel or copper barrier layer is applied before tin plating, as a rule.
The optical media (CDs / DVDs ) in a press shop based on electroplating.
Electroplating in practice
Electroplating can be integrated into the production process of a metalworking company (operating electroplating) or as a service - that is, by production of commissioned works ( Electroplating ) - act. In a broader sense, anodising and other (mostly current-driven ) methods are called electroplating. In the Federal Republic of Germany there are an estimated 1500 electroplating operations.
Galvanic systems are a very long series of trays, under which, the various process steps sequentially in the rule. Modern systems are controlled more or less completely automatically. They are operated by Oberflächenbeschichtern. ( Previously known as " depositor " was a few years ago by " surface coaters " replaced)
Technically laboratory can nowadays be all common base materials made of metal, and most of the known dielectric / plastic coat. When plating on plastics / coating be produced industrially only two common methods of polymer coating have been established. Direktmetallisieren after the so-called Futuron process and the conventional process sequence on pickling activated electroless plating as a first metallic process level ( layer sequence: Vornickel, bright copper, bright nickel, chromium ) are here specifically to be found in the decorative segment. Especially in the automotive industry, one is forced by high quality features and demands of the manufacturer to deposit up to four different nickel layers in combination, to achieve optimum stability, function and appearance.
The quality of a workpiece is often determined by the gloss. Here, the luster of metallic layers is not readily with physical methods ( reflectance, etc.) can be determined. The so-called physiological impression of gloss of a metal layer may differ slightly from the defined physical property. Especially for decorative applications, it is of high importance. For a high gloss special brighteners are used in the various processes. It must be ensured that a high luster, the physical properties (eg electrical conductivity, hardness, solderability ) may change a layer.
Metal coatings can give objects shine and an impressive appearance. Thus, for example, cutlery, made of inexpensive metal, are coated with a more expensive metal. To Silver, for example, a spoon of nickel, the spoon is first cleaned and then connected to the negative pole of a voltage source. The spoon, then, is the cathode. The anode is a silver rod. Both electrodes are immersed in a silver nitrate solution. The positively charged silver ions will be attracted to the cathode, the spoon. There, they take electrons from the cathode to be thereby discharged and then settle as silver atoms on the cathode. Thus, the spoon is made of nickel coated with a thin silver layer. The reaction equations are:
Is a base material rough, the surface can be facilitated by appropriate selection of the galvanic method. The better technical term for leveling is the term micro- throwing power. This property is used, for example, in bearings, rollers or decorative applications (see also gloss).
By the use of, among others, chromium, the surface of a steel workpiece can be hardened. The abrasion resistance and sliding properties improve significantly. Typical areas of application are the piston of a hydraulic or pneumatic cylinder.
In the electrochemical method, the base materials are exposed to an electric field. As an electric field is not uniform sets, but higher field strengths occur at sharp points or ends, it is at these points to increased deposition and thus to larger layer thicknesses.
Acid method show compared to the alkaline process usually on a much more uneven layer thickness distribution. Example: A sour galvanized iron pipe with diameter of 20 and a length of 100 mm will have at a layer thickness of 8 microns in the middle to the ends up to 20 microns. An alkaline galvanized pipe, however, a maximum of 10 microns.
A workpiece is constructed galvanogerecht by taking into account certain principles which favor the planned electroplating process and avoid potential problems.
- Through holes are cheaper than blind holes. The latter can, depending on the diameter and depth of the penetration and leakage of process fluids hinder or prevent (air bubbles). Late leakage of fluids from the blind holes complicates the rinsing and can cause subsequent corrosion.
- Rounded contours are cheaper than sharp-edged exterior and interior angles: Increased deposition ( up to ridge or bud formation ) at sharp outer edges. Decreased or no deposition on sharp internal angles.
- A through V- seam is cheaper than a lap joint or a spot-welded connection: When two surfaces are not tightly sealed, then the liquids are " held " by capillary action in the gap. The layer is destroyed again during drying by these liquids. The same applies to flaring and riveted joints.
- Faraday cage: For a all around closed workpiece with small openings to no electric field can result in the workpiece. In this area, only purely chemical processes act. Wherein an electro- chemical process, the penetration depth is usually equated with the opening, i.e., a tube having an inner diameter of 2 cm, a coating to reach to the depth of 2 cm into the tube.
- Choice of material: steels with high carbon content can degrade the adhesion of the layer. In high strength steel, there is the risk of embrittlement. Combinations of different materials on a workpiece can lead to problems, such as when there are various indications and contraindications are mutual in the pretreatment.
Design and material selection have very great influence on later electroplating process in relation to possible problems and economy. Therefore, an interdisciplinary approach should be chosen with new designs from the start.
Electroplating is named after the physicist Luigi Galvani, the discoverer of galvanic electricity. It is sometimes claimed that in ancient times through the gilding of objects was known by electroplating techniques. This could include some scientists called the " battery of Baghdad," have a bottle- like clay pot with a copper cylinder and an insulated therefrom by bituminous iron bar inside, which was found in 1936 near Baghdad served.
The quality assurance is in electroplating a very high place. It includes the constant analysis of the bath parameters, such as acidity and metal content, control the appearance and color of layers, layer thickness measurements by X-ray fluorescence, ultrasound, eddy current method, transfer method, but also reviews of the raw material.
Furthermore, are checked: surface roughness, hardness, adhesion strength and ductility of the layer, surface defects (such as pores, cracks ) and test the corrosion resistance by salt spray, condensed-water, Corrodkote exam, CASS test (acetic acid - saline).
The electrochemical properties of the electrolytes can be assessed by practical tests (eg Hull cell ) or comparative measurements ( cyclic voltammetry Haring Blum cell or ).
Other important points are within the electroplating wastewater treatment and environmental protection related to instruction in the handling of hazardous chemicals and laboratory work. The thickness of the resulting metal coating varies depending on the application: decorative coatings (eg gold or polished chrome ) often have layer thicknesses of less than 1 micrometer ( micron ), while functional layers are significantly thicker ( zinc or nickel for corrosion protection about 10 microns, hard chrome or nickel as mechanical functional layers ( for example, hydraulic cylinders ) usually 100-500 microns ).
Electroplating ( Overview )
This technically similar electroplating are each limited to specific substrates or coating materials and received by their specific names.
- Anodic oxidation ( For aluminum anodizing also )
- Chemical plating by potential difference ( electroless ) or reducing agents, see reduction.
- Coloring metal
- Pulsed electrodeposition
- On plastics
- PCB manufacturing
- Brush plating
- Dip method (formerly brewing process )
- Barrel plating
- Chrome plating
- Aluminum electrolytes
- Antimony electrolytes
- Lead electrolytes
- Bronze electrolytes
- Cadmium electrolytes
- Cobalt electrolytes
- Chromium electrolytes
- Iron electrolytes
- Gold electrolytes
- Copper electrolyte
- Manga electrolytes
- Brass electrolytes
- Nickel electrolytes
- Nickel -iron- electrolytes
- Palladium electrolytes
- Platinum electrolytes
- Silver electrolytes
- Bismuth electrolytes
- Tungsten electrolytes
- Zinc electrolytes