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The production process and some properties of enameled wire

Enameled wire is a main type of winding wire, which is composed of a conductor and an insulating layer. After the bare wire is annealed and softened,

It is painted and baked many times. However, it is not easy to produce products that not only meet the standard requirements, but also meet the customer requirements.

It is affected by the quality of raw materials, process parameters, production equipment, environment and other factors. Therefore, the quality characteristics of various enameled wires are different.

But they all have four major properties: mechanical properties, chemical properties, electrical properties, and thermal properties.

At present, the manufacture of magnetic components such as electronic transformers generally uses QZ polyester enameled wire to be wound, and then the coil is dipped in paint. If a self-bonding wire with a composite coating is used to wind the coil, it will change the traditional transformer manufacturing mode, instead of dipping varnish, only heat melting can make the coil into a whole, with certain mechanical properties And moisture-proof insulation performance. This can shorten the manufacturing cycle of magnetic components such as transformers and greatly improve the efficiency of mass production. Self-adhesive enameled wires are now mainly used in coils for micro motors, meters, and telecommunication equipment.

1. The characteristics of self-adhesive enameled wire and its bonding mechanism

General polyester enameled wire is a single-coated enameled wire. The polyester paint on the surface is a type of enameled wire paint made by the condensation polymerization of dimethyl terephthalate and polyol. Because polyester enameled wire has better resistance Thermal (Class B, Class F), electrical insulation, scratch resistance, and solvent resistance, so it has been widely used.

Composite coating enameled wire is the current development direction. From its insulation structure, it is an enameled wire composed of two or more varnish films. Self-adhesive enameled wire belongs to composite coating enameled wire, which is roughly divided into two types: self-adhesive polyester enameled wire and self-adhesive polyurethane enameled wire.

Self-adhesive polyester enameled wire is based on polyester enamelled round copper wire and coated with an adhesive paint layer. The self-adhesive paint is mainly composed of epoxy resin and phenolic resin dissolved in a solvent. The solvent is n-butanol and xylene. Mixed solvent is the main component, and the reaction mechanism is the same as epoxy paint.

Self-adhesive polyurethane enameled wire is a polyurethane-based enameled wire. Polyurethane paint has the following characteristics: (1) Good direct solderability. Because the polyurethane paint film decomposes at high temperatures and can act as a flux, it is not necessary to remove the paint film in advance. It can be soldered directly. (2) High frequency performance is good, and the dielectric loss tangent is relatively small under high frequency conditions.

2 Application analysis of self-adhesive enameled wire

3.1 Processability Self-adhesive enameled wire, like ordinary enameled wire, has better processability, which is measured from windability, formability, and insertability. Windability refers to the ability of the winding wire to resist mechanical damage and electrical damage during the process of winding the coil, and the coil is wound in the tightest and  conformable way. Formability refers to the ability to withstand bending and maintain the shape of the coil. When the formability is good, the shape will not change. After being removed from the winding machine, the coil can maintain various angles. The rectangular coil will not bulge into a barrel shape. The line will not jump out. Embeddedness refers to the ability to be embedded in a wire slot.

3.2 Compatibility

Compatibility of self-adhesive enameled wire with chemical composition and temperature index of other materials. Other materials used in products of magnetic components such as transformers: bakelite or metal frame, PTFE film or telephone paper (insulation layer), AF lead wire, etc., in terms of chemical composition and temperature index, they are all compatible with self-adhesive enameled wire Compatible.

3.3 Price

The price cost of self-adhesive enameled wire is an issue that must be considered in its application. The price trend of self-adhesive enameled wire and ordinary enameled wire is the same, the smaller the wire diameter, the higher the price. In the case of the same wire diameter (specification), the price of self-adhesive enameled wire is higher than that of ordinary enameled wire, but the self-adhesive enameled wire saves paint, man-hours, depreciation costs of dipping equipment, and production savings during its application. The benefits of the cycle are far greater than the price difference.

3.4 Spatial factors

The design of electronic instruments tends to be intensive and miniaturized, reducing the volume of the transformer and increasing the space factor of the winding are issues that must be considered when selecting the winding wire. For winding wires with the same conductor cross-sectional area, the space factor of the foil tape (planar transformer) is the highest, followed by the flat wire, and the round wire the smallest. Compared with ordinary round enameled wire, self-adhesive enameled wire does not reduce the winding volume, but in some cases, self-adhesive enameled wire can be used without the coil frame (inductance coil), which is beneficial to improve the product structure.

3.5 Temperature index and thermal performance

Generally, the winding wire with the corresponding temperature index is selected according to the allowable temperature rise of the transformer product or the highest hot spot index that may appear in the coil. The temperature index of self-adhesive polyester enameled wire is 130℃, and the temperature index of self-adhesive direct welding polyurethane enameled wire is 120℃. At present, the temperature index of enameled wire used in the manufacture of transformer products in our factory is 130℃, but  of them are low-power transformers, and the maximum temperature of working state is generally 70-80℃.