Magnet wire

Copper wire ( copper wire ) is a copper wire which has been coated during manufacture with an electrically insulating lacquer layer. The thickness and weight of the enamel insulation is very low compared to other insulating materials having equivalent effect. This wire is therefore preferably used for the construction of electric coils, transformers and machinery.

Other applications are soldered jumper wires and the manufacture of high-frequency braided.

By using enamelled copper wire, the mechanical size of electrical machines is reduced in a favorable manner, with the added yield further spatial -saving effects by the concentration of the electric and magnetic fields in a smaller space. Ultimately, this reduction in size results in shorter conduction paths also in energy savings for the same power output. See also winding technology.

The classification of enamelled wires is done by by the International Electrotechnical Commission (IEC) created standards 60317 and 60851st wires are classified according to temperature index ( continuous use temperature ), breakdown voltage and thermal shock behavior.

Wire enamels are solutions of polymers in most cresolic solvent mixtures. All wire enamels are painted on special wire enamelling and baked at 300-600 ° C. The solvents are evaporated and burned catalytically. The heat is used to heat the plant. The polymers crosslink and form insoluble films. When brazing - already stripped with a blade or sandpaper - enamelled copper wire, small amounts of highly toxic toluene -2 ,4 -diisocyanate can be released, so extraction will be required in commercial workplaces, private one should ventilate well.

In order to obtain smooth, concentric and non-porous films, enamelled wires are usually 6-20 times painted and baked. As a rule of thumb, that the paint film makes up about 10 % of the weight of the enamelled copper wire. The resulting increase in diameter is referred to as gain.

Polyurethane enamelled wires are soldered, which means they can be soldered without prior removal of the paint. The soldering process requires temperatures > 340 ° C; while the polyurethane film decomposes instantaneously due to the low thermal resistance of the urethane group. It caused harmful gases.

For winding wires in coils, transformers, relays and motors coatings have prevailed with polyesterimides as film formers. Depending on the composition and selection of the raw films having different thermal, mechanical and dielectric properties can be obtained. Polyesterimides are made from ethylene glycol, THEIC, dimethyl terephthalate, Trimelitsäureanhydrid, Diaminodiphenlymethan in a polycondensation reaction. Commercially available polyester-imides have Hydroxidmassenverhältnis between 100 and 300 mg / g and a molar mass lower than 5000 g.mol -1. They are supplied in a solvent mixture as approximately 40 % solutions. Polyesterimides the wire enamels are most commonly used in Europe. Polyester-imide enamelled wires are only partially, solderable then if but only above 450 ° C.

For coils with high altitude stresses and / or at high frequencies (for example, switching power supply transformer), it is common that made ​​with enameled wire windings additionally to soak in impregnating varnish under vacuum and dry to avoid pre-discharges in air spaces and thus the dielectric strength in the to increase continuously.

For self-supporting coil bonding wire is used. Meanwhile paint consists of a temperature-resistant insulation and base of an adhesive by heating, often attending polymerized top layer.

For negligence in the processing, electrical breakdown or due to prolonged pre-discharges in air spaces, however, the enamel insulation may be damaged, it arises from adjacent layers of wire winding short one. Due to the induced current in the resulting short-circuit turn the insulating varnish is further destroyed by the heat, so spread the winding shorts and the bare wires eventually form a short circuit.