Copper wire enamelling

The three-component cyanate/maleimide/epoxide compositions are mainly used as polymer matrix in copper clad laminates and in carbon fiber composites for engineering purposes. High heat resistance, water and solvent resistance, mechanical and impact strength is claimed. A composition for copper wire enamelling [121] and a resin for electric motor coil windings impregnation were described [107]. 

Isophthahc acid is also used in formulations for adhesives, inks (qv), wire enamels, and dental materials (qv). Copper isophthalate [10027-31-3] is an ingredient in algicides and fungicides (98). 

To fulfil the above requirements the material inputs for the motor, such as stampings, steel, enamelled copper wire, insulations and varnishes, bearings, enclosure materials and hardware must be subjected to a series of acceptance tests according to norms and standard specifications. For example, enamelled copper wire used... 

Copper and its compounds have many important uses in modern society. For example, copper wiring is used in electrical equipment. Copper is also used to make many alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals. The most familiar alloys of copper are probably brass and bronze. Many compounds of copper are commercially important, too. They are used as coloring agents in paints, ceramics, inks, varnishes, and enamels. 

Winding of copper wire, most often insulated with enamel. 

Table 1. Properties of wire enamels coated on copper wire ...

Polyesters modified with diimidodicarboxylic acids derived from aliphatic diamines and trimellitic anhydride have been patented, like methylene-N,N-bis-trimellitimide, made from hexamethylenetriamine [82], or the 1,4-dimeth-ylaminocyclohexane derivative [83]. The diacid obtained from trimellitimide, made from the anhydride and dry ammonia, complexed with a divalent metal, e.g., Zn, Co and others, is used in the preparation of a poly(ester-imide), described as giving a wire enamel with good flexibility on copper wire [84]. 

The poly(ester-imide) resins prepared world-wide in large tonnage are used for formulating wire enamels, which are coated using continuous working enameling machines and round and rectangular copper wires by repeated application. Commercially available poly(ester-imide) based wire enamels use cresol, also known also as cresylic acid, as solvent. Other solvents have no economical importance nowadays (see discussion below). 

The water based poly(ester-imide) wire enamel from Table 3 has the same resin composition as the cresol free solvent based resin 2. It can be seen that the mechanical and thermal properties of the water based varnish are inferior to the noncresylic product. It was also found that minor amounts of drawing agent residues from copper wire manufacturing were highly detrimental to the surface quality of the enameled wires. 

Besides the manufacturing of enameled wires in a conventionally way, starting from copper wire and a solvent-based varnish, other technologies have been developed. 

Solderable wires are used in telecommunications and the construction of analytical instruments, but they are becoming more and more common in small motors and dry-type transformers. The special characteristic of solderable wire enamels is the direct soldering. When the enameled wire is dipped in a solder bath at temperatures above 350 °C the coating melts and leaves the bare copper wire, avoiding the need for elaborate mechanical or chemical removal of the enamel. This characteristic achieved in solderable poly(ester-imide) by a special polymer composition and in polyurethane based wire enamels is due to the thermally reversible splitting of the polyurethane group. Nevertheless, good thermal stability is necessary and product temperature indexes >155 are required. For temperature indexes of 130, simply polyurethane wire enamels were used. 

Miscellaneous Extrusion-Applied Polymers. As mentioned earlier, there is a tendency to develop solventless magnet wire enamel formulations, and extrudable polymer systems would fulfill that requirement. There have been reports about extrusion of thin coatings of polyesters over copper wire. At this point, the state of the art allows extrusion of thin insulating films only with thermoplastic materials. The reliable extrusion of uniform and concentric insulating films of approximately 0.001-0.002 in. wall thickness is already an improvement over the more traditional extrusions of polyethylene, poly(vinyl chloride), and several fluoropolymers in much greater wall thicknesses. Because cross-linked insulation is ultimately required for most magnet wire applications, further materials development needs to be done to provide polymer compositions that are both extrudable as thin films and can be cross-linked in an economical process suitable for large-scale industrial application. 

Helmholtz coils consist of two identical rings made of nonmagnetic material, which are placed parallel to each other. The coils may have several hundred turns of enameled copper wire. When direct current is allowed to pass through the coils, a homogeneous magnetic field is produced. The greatest... 

Fine metal wires may be directly integrated into the fabric or yam stracture. In some applications, there is a need to insulate the wires. This can be achieved by the application of an insulated coating. For example, Elektrisola Feindraht (2014) markets enamelled copper wire with coatings of polyurethane, polyesterimide, poly-amidimide and polyimide. 

Before the Second World War, the standard insulation for wire used in telecommunications in the UK was waxed acetylated cotton, the conductor being tinned copper wire, while for tropical use the conductors were oleo-resinous enamelled copper wire. Jumper wire had braided wool insulation. 

Two coils vere wound continuously in four layers on one leg of the magnetic core, each coil consisting of 172 turns of No. 24 AWG enameled copper wire. To prevent penetration and corrosion of the laminations the entire core and coil were protected by a thin coat of baked epoxy resin. One coil was used as a primary, or current-carrying winding the second coil, as a voltage winding,... 

It is important to check the compatibility of the pressure sensitive adhesive with the magnet wire used to be sure that there is no deterioration of the wire enamel and reduction of dielectric strength. High sulphur and chlorides will adversely affect the copper wire especially in the presence of humidity and polution. 

This can be confirmed by simply pressing the tips of an ohmmeter at two points on the surface of any bare ferrite lying around in the lab. Further, if we are trying to rely on the enamel coating of a typical copper magnet wire to protect from shorts, we should know that the coating is considered to be just operational/functional insulation, and is not considered to be even basic insulation. 

Cadmium is used industriadly as a protective coating for iron, steel, and copper by electroplating. Cadmium sulfide and sulfoselenide are used as pigments in plastics, enamels, and paint. It may also serve as an alloy with copper for coating telephone cables, trolley wires, and welding electrodes. The stearate is used as a stabilizer in plastics, and cadmium electrodes are found in alka-... 

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