Enamelled Copper Magnet Wire

Magnet wire, the wire wound into motors, transformers, coils and loudspeakers, is copper wire with a very thin layer of insulation. Despite the name, the "enamel" is not glass but a polymer film. The usual process runs in one continuous line: the wire is annealed to make it soft and flexible, passes through a bath of enamel, a polymer such as polyurethane, polyester, polyamide or polyimide dissolved in solvent, then through a die that leaves only a thin even layer, and up through a vertical oven that first drives off the solvent and then cures the film. One coat is too thin, so the wire goes round many times, building the insulation up layer by layer.