Magnetic wire insulation coatings

NEMA also has developed standards and specified test methods for magnet wire insulation coatings. A summary of these materials, properties, and standards may be found in Appendix C. 

Polyvinyl Aldehyde 1940 H VG VG VG VG Most molding pro-cesses Used for coatings and magnet wire insulation, interlayer of safety glasses... 

Dual Constructions. In addition to the "basic" magnet wire insulations in which the conductor wire is coated with a single enamel, there are a number of cases where two different enamels are used one overcoated over the other. Examples include polyurethane-base insulation overcoated with poly(vinyl butyral) or with nylon, or polyester-base insulation overcoated with nylon or with polyamide imide. 

Polyvinyl formal (PVF) is used to manufacture magnetic wire insulation as well as metal coatings and can linings. The quantities of PVF used are small and thus is a minor use for VAM. 

Table 10.8 shows electric strengths. Table 10.9 shows volume resistivities, Table 10.10 shows dielectric constants, and Table 10.11 shows dissipation factors for coatings using most of the available resins. Magnet wire insulation is an important use for organic coatings. National Electrical Manufacturer s Association (NEMA) standards and manufacturers trade names for various wire enamels are shown in Table 10.12. This information can be used to guide the selection of coatings. However, it is important to remember the aforementioned warnings about blends of various resins and the effects on performance properties.

Formulated with pigments, like graphite and carbon black [232] or metal powders [233,234], conductive films were obtained at low cost, used as electromagnetic shielding layers or for capacitive energy-storing inductive coils, when coated on an insulated magnet wire. 

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. 

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. 

The commonly-used term for wire that is used to make electromagnets, but is itself non-magnetic, is magnet wire it is an excellent conductor with a thin coating of insulation. 

Electrical properties of organic coatings vary by resin (also referred to as polymer) type. When selecting insulating varnishes, insulating enamels, and magnet wire enamels, the electrical properties and physical properties determine the choice. 

Uses. Polyimide coatings are used in electrical applications as insulating varnishes and magnet wire enamels in high-temperature, high-reliability applications. They are also used as alternatives to fluorocarbon coatings on cookware, as shown in Fig. 10.5. 

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