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Electroforming

Electroforming is the process of copying an object by electrode position of a metallic coating from which it is afterwards removed so that the finished product is a hollow shell. Alternatively, a metallic coating may be deposited on the exterior of a nonmetallic solid object.

First of all mold have to be produced from the model to be copied (a). That mold may consist of a nonmetallic substance or sometimes a low-melting-point alloy. Wax, celluloid is the suitable substance used for this purpose, which is poured over the model and is removed when it has set. For making of mold Gypsum plaster, gutta-percha and plastics are used rapidly. Plastics have an advantage of producing molds that have a long service life i.e. can be used a large number of times. Molds may comprise one, two or three parts depending on the complexity and shape of the model.

The next step consists in making the surface of the mold electrically conductive (b). This can be done by brushing it with fine graphite powder, or with metallic powder such as copper, suspended in a thin lacquer, very finely divided copper, silver or some other metal may be deposited by chemical reduction or by vaporization in a vacuum. A mold made of a metallic substance must be provided with a bond-breaking layer before electrolysis, so as to enable the electroformed shell subsequently to be stripped from the mold and not remain adhering to it. The electrode position of metallic coatings is done with the aid of direct current on the principle of electrolysis in an acid or an alkaline salt solution containing the metal to be deposited

The mold is connected to the negative pole and thus forms the cathode; the anode, connected to the positive pole of the current source, usually consists of a plate of the metal to be deposited and is gradually consumed (c). Various auxiliary techniques are applied to ensure that a uniform and smooth metallic coating is formed For E.g.: internal anodes, masking, etc. For smoothness, fineness and luster of the coating special additional substance should be used. When a coating of the desired thickness has been attained, the shell is rinsed, removed from the mold (d) and, if necessary, given a finishing treatment.

Electroforming is used for a variety of purposes: e.g., making copies of archeological or art objects, printing plates, metal master discs in the manufacture of phonograph records, embossing dies, templates, molds for casting, and many objects used in mechanical and electrical engineering.

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