Water-based Insulating Varnish for Painted Winding Wire This is a type of magnet wire widely used in the manufacturing and production of low-voltage products. A key performance characteristic of this magnet wire is its coating durability—specifically, it involves checking the number of pinholes in the coating over a standardized sample size. To measure pinhole density, a specialized coating durability tester is used. The lower the pinhole count, the better the quality of the wire's coating.

　　Inspecting pinhole defects relies on the basic principle of high-pressure discharge, where electromagnetic wire is brought into semi-linear contact with a concave wheel charged at high voltage. When the coating film is too thin or exhibits obvious bare-copper defects, the equipment automatically records the exact number of defects detected.

　　The causes of these defects can essentially be categorized into two main types: first, the unsuitability of the copper material itself, resulting in excessive burrs on the formed wire cores—this could stem from issues with the raw material or arise during the entire metal drawing process. The second factor may involve uneven coating application, the presence of impurities in the paint, the quality of the paint itself, or even variables like inadequate drying after coating.

　　As a motor manufacturer, you should pay particular attention to this feature, as such defects can easily lead to motor stalling—commonly resulting in failures—and significantly impact the motor's lifespan.

　　Detailed Introduction to Continuous Online Monitoring of Coating Films

　　Previously, offline inspection methods such as the working voltage liquid method, the Japanese water method, and the low-voltage lithium battery electrolyte method were used for coating film durability testing, but none of these approaches are suitable for online monitoring of the insulation varnish in enameled winding wires during the production process.

　　Currently, most electromagnetic wire manufacturers utilize an online monitoring system for the continuous inspection of enamel coating integrity in enameled winding wires. This system employs a non-contact inspection method based on DC high-voltage field sensors. The principle behind it is as follows: a DC high-voltage power supply circuit generates a steady DC voltage, which is then applied to a cylindrical metallic conductor embedded within the high-voltage field sensor. This setup creates a strong electric field inside the cylindrical conductor. As the enameled winding wire moves through this high-voltage field—driven by the winding mechanism—the water-based enamel coating rapidly traverses the electric field. When the electric field strength becomes sufficiently high, corona discharge begins to occur on the surface of the water-based enamel coating. If the coating contains defects, these imperfections will allow partial discharges to pass through, resulting in a leakage current between the metallic conductor, the coated wire, and the winding mechanism itself. By dynamically and precisely measuring changes in the leakage current, the system can accurately detect and map both the location and severity of defects in the water-based enamel coating of the enameled winding wire.

　　When using this method for inspection, the water-based varnish coating on the winding wire and a portion of the sensor remain completely isolated throughout the process. This ensures that no additional damage is inflicted on the water-based varnish insulation, making it ideal for real-time monitoring of water-based varnished winding wires moving rapidly along production lines. Additionally, the metallic conductor in the high-voltage electric field sensor is nearly cylindrical, resulting in an electric field that remains essentially uniform across all directions. As a result, the inspection capability is consistently reliable across different orientations, delivering high accuracy and minimizing the risk of false positives or negatives.

　　Of course, users of electromagnetic wire can rely only on offline inspection—specifically, using a coating durability tester—and compare it with an online monitoring device. While the detection capability for identifying defects is slightly weaker when dealing with only semi-linear conditions, the occasional nature of sampling still allows for a reliable assessment of whether the electromagnetic wire meets functional requirements.