What is the method of electroplating
Under Electroplating (also Electroplating called) is understood as the electrochemical deposition of metallic deposits (coatings) on objects. The history of electroplating, as electroplating technology is colloquially known, goes back to the Italian doctor Luigi Galvani, who discovered electroplating named after him on November 6th, 1780.
In electroplating, electricity is sent through an electrolytic bath. The metal to be applied (e.g. copper or nickel) is located on the positive pole (anode), and the object to be coated on the negative pole (cathode). The electrical current detaches metal ions from the consumption electrode and deposits them on the goods through reduction. The object to be refined is coated evenly on all sides with copper or another metal. The longer the object is in the bathroom and the higher the electrical current, the thicker the metal layer (e.g. copper layer) becomes.
Strictly speaking, there is still between electroplating (also Electroforming called), the electrolytic production of metallic objects, and the Galvanostegie (engl. electroplating), the production of metallic coatings. The term Galvanostegie is today almost entirely by the general term Electroplating been replaced. Because fewer and fewer equestrian statues were needed, electroplating was also somewhat forgotten, but experienced a small renaissance in connection with microsystem technology, namely as Micro electroforming, also called lithographic-galvanic molding technique. Electroplating is also used in mold construction for the injection molding of plastics.
A distinction is made between functional and decorative electroplating. The latter is mainly used to beautify objects and must have certain minimum technical properties for this purpose. Examples of the decorative electroplating are the plating of plastic, the chrome plating of tubular steel furniture and motorcycles and the gold plating of jewelry and cutlery.
The functional electroplating serves to protect against corrosion, wear protection, catalysis or to improve electrical conductivity. Examples of this are the galvanizing of screws, the coating of machine parts with hard chrome, the production of metallic, mostly nickel or platinum-containing catalysts for the chemical industry or fuel cells, and the gold and silver plating of electrical contacts. Electrical contacts - so-called pins - made of different copper materials are usually tin-plated by electroplating. In order to prevent substances of the base material from diffusing through the tin layer, a nickel or copper barrier layer is usually applied before tin-plating.
The production of optical data carriers (CDs / DVDs) in a press shop is also based on electroplating.
Electroplating in the world of work
Electroplating can be integrated into the production process of a metalworking company (Industrial electroplating) or as a service provider, d. H. Production of commissioned work (Contract electroplating), act. In a broader sense, anodizing systems and other (mostly electricity-driven) processes are also used as Electroplating designated. In the Federal Republic of Germany there are an estimated 1,500 electroplating companies.
Galvanic plants are usually a very long series of tanks in which the various process steps take place one after the other. Modern systems are controlled more or less completely automatically. They are served by surface coaters. (The previous term "electroplater" was replaced by "surface coater" a few years ago)
The training occupation of electroplating is the Electroplater. Electroplaters operate the electroplating systems, which are usually controlled automatically; Semi-skilled personnel are used to feed the systems (e.g. hanging up the parts, simple maintenance work). Advanced professions are Electroplater or Electroplating Technician, both aim at a function as department head or even operations manager. The technical college engineering course of the Surface technology also includes some electroplating technology.
There are technical schools for electroplating in Schwäbisch Gmünd, Nuremberg and Solingen.
Nowadays all common base materials made of metal as well as most known non-conductors / plastics can be coated in laboratory technology. In the case of plastic electroplating / coating, only two common methods of polymer coating have become established on an industrial scale. Direct plating according to the so-called Futuron process and the conventional process sequence activated by pickling, electroless plating as the first metallic process stage (layer sequence: pre-nickel, bright copper, bright nickel, chrome) are particularly found in the decorative segment. In the automotive industry in particular, high quality features and manufacturers' demands force you to deposit up to four different nickel layers in a composite in order to achieve optimum durability, function and appearance.
The quality of a workpiece is often determined by its gloss. It is particularly important for decorative applications. For a high gloss, special brighteners are used in the various processes. It must be ensured that a high gloss can change the physical properties (e.g. electrical conductivity, hardness, solderability) of a layer.
If a base material is rough, the surface can be leveled by a suitable selection of the galvanic process. This property is z. B. used in bearings, rollers or decorative applications (see also gloss).
By using z. B. Chromium, the surface of a steel workpiece can be hardened. The abrasion resistance and sliding properties improve considerably. Typical areas of application are the pistons of a hydraulic or compressed air cylinder.
In the electrochemical process, the base materials are exposed to an electric field. Since an electric field does not appear uniformly, but rather with higher field strengths at sharp-edged points or ends, the layer thicknesses will increase at these points. Acid processes generally show a significantly more uneven distribution of layer thicknesses than the alkaline process. Example: An acid-galvanized iron pipe with a diameter of 20 and a length of 100 mm will have a layer thickness of 8 µm in the middle at the ends of up to 20 µm. An alkaline galvanized pipe, on the other hand, does not exceed 10 µm.
A workpiece is designed to be suitable for electroplating by taking certain principles into account, which favor the planned electroplating process and avoid possible problems.
- Through holes are cheaper than blind holes. Depending on the diameter and depth, the latter can hinder or prevent the penetration and leakage of the process fluids (air bubbles). Delayed leakage of liquids from the blind holes complicates the flushing processes and can lead to subsequent corrosion.
- Rounded contours are cheaper than sharp-edged outer and inner angles: Increased separation (up to the formation of burrs or buds) on sharp outer edges. Decreased or no deposition at sharp interior angles.
- A continuous V-seam is cheaper than an overlap joint or a spot-welded connection: If two surfaces are not welded tightly, the liquids are "held" in the gap by means of capillary action. The layer is destroyed again by these liquids when it dries. The same applies to flanges and riveted connections.
- Faraday cage: If the workpiece is closed all around and the openings are too small, no electrical field can arise in the workpiece. Only purely chemical processes are effective in this area. In an electrochemical process, the depth of penetration is usually equivalent to the opening; i.e., for a pipe with an inside diameter of 2 cm, a coating to the depth of 2 cm in the pipe is achieved.
- Material selection: Steels with a high carbon content can impair the adhesion of the layer. With high-strength steel there is a risk of embrittlement. Combinations of different materials on a workpiece can lead to problems, e.g. B. if there are different indications and a mutual contraindication in the pretreatment.
The design and choice of materials have a major impact on a subsequent electroplating process in terms of potential problems and cost-effectiveness. For this reason, an interdisciplinary working method should be chosen from the start when designing new products.
Electroplating is named after the physicist Luigi Galvani, the discoverer of galvanic electricity.
It is assumed, however, that gold plating of objects with the help of electroplating was already known in antiquity . According to some scientists, the so-called "Battery of Baghdad" - a bottle-like clay vessel with a copper cylinder and an iron rod inside that is insulated by bitumen - that was found near Baghdad in 1936, could have served this purpose.
Quality assurance has a very high place in electroplating. This includes the constant analysis of bath parameters, such as acid and metal content, control of the appearance and color of the layers, layer thickness measurements by means of X-ray fluorescence, ultrasound, eddy current processes, and stripping processes. But also checking the raw material.
The following can also be checked: surface roughness, hardness, adhesive strength and ductility of the layer, surface defects (e.g. pores, cracks) and testing of corrosion resistance by means of a salt spray test, condensation water climate, Corrodkote test, CASS test (acetic acid salt solution).
The metal-separating properties of the electrolytes are measured using the Hull cell.
Other important points within electroplating are wastewater treatment and the associated environmental protection, instruction in handling hazardous chemicals and working in the laboratory. The resulting metal coating is usually only very thin.
Electroplating process (overview)
Footnotes and individual references
- ↑ H.-G. Bachmann; G. Bachmann: Surface gilding: old and new techniques. In: Chemie in our Zeit 23 (1989), No. 2, pp. 46-49
- Thomas W. Jelinek: Practical Electroplating: An Instructional and Manual. 5th edition Leuze (Galvanotechnik textbook series), Saulgau / Württ. 1997, ISBN 3-87480-108-X
- Bernhard Gaida: Electroplating technology. Leuze, Saulgau / Württ. 1996, ISBN 3-87480-114-4
- Bernhard Gaida: Introduction to electroplating: Basics of chemical, electrochemical, physical and electrotechnical terms. Leuze, Saulgau / Württ. 1999, ISBN 3-87480-143-8
- Bernhard Gaida: Electroplating questions and answers: for self-study and school use. Leuze, Saulgau / Württ. 1989, ISBN 3-87480-049-0
- Wolfgang Autenrieth techniques of etching and the fine printing process - tips, tricks, recipes and instructions - an alchemistic workshop book. Almost 100 pages of which are online. Some tips on galvanic etching processes and recipes for stealing copper
- BGI 790-016: Electroplating and anodizing: BG / BGIA recommendations for risk assessment according to the Hazardous Substances Ordinance 10/2006. Download from http://www.arbeitssicherheit.de
- Fraunhofer IPA layer technology
- Animation of a galvanization
- Federal Association of Electroplaters
- Specialist book publisher for electroplating
- Central Association of Surface Technology
- German Society for Electroplating and Surface Technology V.
- cathodic corrosion protection in electroplating (pdf)
Categories: Coating | Electrochemistry
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