As shown in the figure below, it is a sensor coil used in the medical industry. The skeleton is made of aluminum. The diameter of the enameled wire is 0.1mm. The customer requires the arrangement to be neat and free of winding defects. The company has carefully evaluated the specific requirements of the customer, because the winding process and winding are considered. After the completion of the structure, the self-adhesive enameled wire process was adopted, and the self-adhesive coil winding machine was further optimized. The project was successfully completed. At the same time, some experience was summarized and shared with the public during the process.
In recent years, due to self-adhesive support, self-adhesive coils do not need to be dipped in the later stage, which is convenient for industrialization. They have been widely used in deflection coils of precision instruments, combined coils in micro motors, and micro coils in sensors.
Self-adhesive enameled wire has become the main wire type used in the coil winding process due to its excellent heat resistance, insulation, adhesion durability, easy forming, simple winding process and other advantages. After the self-adhesive coil is formed, it is required that the DC resistance of the coil is good, the inductance performance is stable, the wiring is neat and not scattered, the surface is smooth and there is no gap, and the appearance is beautiful.
In addition, the coil needs to maintain a certain shape during use, which requires that the bonding strength of the coil does not decrease over time under different environments. In the winding process, especially for enameled wires below 0.1mm, there are often scattered, overlapping, loose and other phenomena. The factors that affect the winding quality are mainly considered from the enameled wire, winding equipment and tooling:
1 The influence of enameled wire on winding quality
The surface paint layer of the self-adhesive enameled wire is divided into two parts: a primer layer and a self-adhesive layer. The primer layer functions as an insulating layer and protects the internal copper core. The self-adhesive layer mainly plays the role of bonding and forming. The primer layer is formed mainly by dipping and baking, which is generally baked after two to three dipping. Both the primer and topcoat materials need to be filtered to filter gels and mechanical impurities. The solvent formula is reasonable, so that the wire coating can be cured smoothly without defects such as uneven thickness and bubbles. The uniformity, fluidity, and adhesion of the primer make the final film thickness uneven.
Take ELEKTRISOLA Ф0.06ABP15 self-adhesive wire as an example. The outer diameter is between Φ0.072mm and Φ0.075mm. According to actual experience, during winding, the wire spacing needs to be set higher than the diameter of the enameled wire. Enameled wire with a core material of Φ0.06 mm, and the spacing between the wires should be at least 0.08 mm. According to the bonding method, self-adhesive enameled wires are mainly divided into hot air, heating furnace, and alcohol bonding (soluble in absolute ethanol). Alcohol bonding is to directly bond self-adhesive enameled wires with industrial absolute ethanol (industrial alcohol, ethanol content is higher than 99%) when winding the coil. The limitation is mainly that alcohol has a swelling effect on self-adhesive materials, and there is excessive alcohol volatile concentration. High risk of spontaneous combustion or explosion, hot air or heating furnace method is convenient for mass production and automatic control. Therefore, the mainstream self-adhesive methods are mainly hot air, heating furnace and other heating methods. For thermal curing methods such as hot air and heating furnaces, the temperature of the heating process, the temperature gradient and the uniformity of the temperature have an important influence on the bonding performance of the winding. The bonding effect of self-adhesive enameled wire is mainly because the curing of self-adhesive paint is a staged polymerization process, at this time, the self-adhesive layer exists in the form of prepolymer. When the self-adhesive enameled wire is being wound, it needs to be heated (usually heated by hot air) to make it secondary polymerization and deep curing, so as to achieve the purpose of firm bonding.