Electromagnetic wire must meet the requirements of various applications and manufacturing processes. The former includes its shape, specifications, the ability to work at high temperatures in the short and long term, and in some cases at high speeds to withstand strong vibration and centrifugal forces, corona and breakdown resistance at high pressures and chemical resistance. Special atmospheric corrosion, etc.; the latter includes the requirement to be subjected to stretching, bending and abrasion during winding and embedding, as well as to swelling and corrosion during immersion and drying.
Electromagnetic wires can be classified according to their basic composition, the conductive core and the electrical insulation layer. Generally, they are classified as enamelled, wrapped, enamelled wound or inorganically insulated wires according to the insulation material used for the electrical insulation layer and the manufacturing method.
Enameled wire is made by coating the conductor with a corresponding varnish solution, then curing and cooling the varnish by solvent evaporation. Enameled wire can be classified as polyester enameled wire, polyesterimide enameled wire, polyamideimide enameled wire, polyimide enameled wire, polyesterimide/polyamideimide enameled wire, corona-resistant enameled wire, oil-based enamel, acetal enamel, polyurethane enameled wire, etc. Sometimes they are also classified according to the specificity of their application, such as self-adhesive enameled wire and refrigerant-resistant enameled wire.
In the early days, the enameled wire was an oil-based wire made of tung oil and other materials. The coating film had poor abrasion resistance and could not be used directly in the manufacture of motor coils and windings, requiring the use of cotton yarn wrapping layers. Later, polyvinyl acetal enameled wire was introduced and its mechanical properties were greatly improved, so it could be used directly for motor windings and was called high-strength enameled wire.
With the development of weak current technology, self-adhesive enameled wire emerged, which can be used to obtain coils with better integrity without impregnation and baking. However, it has poor mechanical strength and can only be used for micro motors and small motors. In addition, to avoid the trouble of removing the varnish first during the soldering process, a straight solder enameled wire was developed whose varnish would fall off in a high-temperature tinning bath, thus making it easy to solder copper wire.
As the application of enameled wire became more widespread, the requirements became more stringent and composite enameled wire was developed. The inner and outer enamels consist of different polymer materials, e.g. polyesterimide/polyamideimide enameled wire. Wrapped wire is an important variety of winding wire. The early use of cotton and silk, known as yarn-wrapped wire and silk-wrapped wire, was used in electric motors and appliances. Due to the large insulation thickness and low heat resistance, most of them have been replaced by enameled wire. Currently it is only used as high frequency winding wire. In medium and large winding wires, when the heat resistance is high and the mechanical strength is high, glass fiber covered wires are also used and equipped with suitable adhesive coatings in the manufacturing process.
It still occupies a considerable place in the wound wire and is mainly used in oil-immersed transformers. The oil-paper insulator formed in this case has excellent dielectric properties, is inexpensive and has a long life.
In recent years, the development of film-wrapped wire is relatively rapid, mainly polyester film and polyimide film-wrapped wire.
Z recently, there also exists mica tape coated polyester imide film wrapped copper flat wire for wind power generation.
Inorganic insulated wires are usually coated with inorganic insulating varnish when the heat resistance level exceeds the limits of organic materials. Existing inorganic insulated wires can be further classified into glass-film wires, oxide film wires and ceramic wires.