enameled copper strip is one of the main raw materials for motors. The wire used for winding or coil is called magnet wire. There are many kinds of electromagnetic wires, according to the shape of their cross-sections, they can be divided into three types: round wires, flat wires and ribbon wires. The cross-sections of round and flat wires have uniform standard dimensions. The cross-section size of the ribbon conductor is according to the design requirements, and can be ordered with the wire manufacturer. According to the characteristics and uses of the insulating layer, the magnet wire can be divided into four categories: enameled wire, wrapped wire, inorganic insulated wire and special magnet wire.
1. Enameled wire
The enameled wire requires the paint film to be uniform, smooth, and completely covered (small number of pinholes). The diameter of the wire and the thickness of the paint film should comply with the national standards. The performance of enameled wire is determined by the paint film, and generally includes the following items:
(1) Mechanical properties. The paint film should be scratch-resistant, elastic, with appropriate softness and elongation, so as to ensure that the paint film can withstand friction, bending, stretching and compression during the winding, embedding, stretching, and shaping processes. Does not cause damage.
(2) Electrical performance. The main reason is that the breakdown voltage of the paint film should be high. For the enameled wire used for high-frequency and high-voltage motor windings, the paint film loss tangent is required to be small. For enameled wires with a diameter of 0.5 or less, the number of pinholes is a very important indicator to evaluate its electrical performance; many motor manufacturers have equipped with paint film continuity testers during the inspection of electromagnetic wires in the factory to check the number of pinholes .
(3) Thermal performance. Including the softening breakdown, thermal aging and thermal shock properties of the paint film. The softening and breakdown performance indicates the ability of the paint film to resist heat deformation under a certain pressure; the thermal aging performance reflects the ability of the paint film to retain a certain degree of elasticity after a short time of heat; the thermal shock performance reflects the paint film’s ability to be baked and dipped The ability of the paint film to withstand thermal shock (rapid cold, hot) without cracking during process or overload operation.
(4) Chemical properties. Indicates the ability of the paint film to withstand the corrosion of chemicals such as acid, alkali, salt spray, organic solvents or refrigerants.
- Winding wire
At present, the commonly used covered wires for motor windings mainly include glass filament covered wires and film covered wires. Glass-fiber covered wire is made of alkali-free glass filaments tightly wound on bare wires or enameled wires, and then dipped and baked by adhesive insulating varnish. The electrical and mechanical properties of glass fiber covered wire are better than enameled wire, and the heat resistance grade depends on the heat resistance of adhesive insulating varnish and enameled wire.
For glass-fiber covered wires, except that the dimensional tolerance shall not exceed the regulations, when the flat wire is bent at 180° on the wide surface, its insulation shall not fall off, crack, expose copper or paint, or break fibers; Insulation resistance and breakdown voltage.
Film wrapping wire has higher mechanical and electrical properties and is a very valuable wrapping wire. At present, there are glass fiber wrapped polyester film wrapping wire and polyimide film wrapping wire. The polyimide film wrapped wire can withstand high temperature, low temperature, and radiation; and it has good airtightness, electrothermal aging performance, and drag resistance; the slot space utilization rate is higher than that of glass wire. The glass-fiber-coated polyester film-wrapped wire has good electrical and mechanical properties, but the insulation layer is thicker.
- Inorganic insulated wire
Inorganic insulated wires for motor windings mainly include oxide film aluminum wires. It uses anodizing method to generate a dense aluminum oxide film on the surface of the aluminum wire. It has the advantages of thin insulating layer, good heat resistance, and radiation resistance; but the oxide film is porous, so the breakdown voltage is low; at the same time, bending resistance, scratch resistance, acid and alkali resistance are also poor.
Special magnet wire has insulation structure and performance suitable for special environment. For example, polyvinyl chloride insulated magnet wire and polyethylene insulated nylon sheathed magnet wire for submersible motor windings. The former has better water resistance, but the slot space utilization is low; it is easy to damage the insulating layer when winding the coil, and is used for general submersible motors. The latter has good water resistance, high mechanical strength of the sheath, but low slot space utilization, and is often used in water-filled submersible motors.