The detection of pinhole defects uses the principle of high-pressure discharge. The electromagnetic wire is brought into contact with a concave wheel under high pressure in a semi-envelope manner. When the coating thickness is insufficient or there are serious bare copper defects, the instrument will record the specific number of defects.
The causes of this defect can be basically attributed to two categories. One is the unsuitability of the copper material, that is, the formed wire core has a lot of burrs, which may be due to the raw material itself or the wire drawing process. The other reason may be uneven coating, impurities in the coating, the quality of the coating itself, and the drying process after coating.
As a motor manufacturer, we should pay special attention to this performance, because this defect can easily lead to inter-turn faults in the motor, seriously affecting the service life of the motor.
Introduction to continuous online testing of paint film
Some offline testing methods used in the past for continuous coating testing, such as voltage mercury method, Japanese brine method, and low-voltage electrolyte method, are not suitable for online testing of enameled wire during the production process.
Currently, the continuous online inspection system for enameled wire coating quality, widely used in most enameled wire manufacturers, is a non-contact detection method based on a DC high-voltage electric field sensor. Its basic principle is that a DC high-voltage circuit generates a high voltage and connects it to a cylindrical metal conductor within the high-voltage electric field sensor. This creates a high-voltage electric field inside the conductor. Driven by the take-up reel, the enameled wire passes through this high-voltage electric field at high speed. When the electric field strength is sufficiently high, a corona discharge is generated on the surface of the enameled wire. If an enameled wire with defects in its coating passes through this field, a leakage current due to partial discharge will form between the metal conductor, the enameled wire, and the take-up reel. By dynamically measuring the changes in this leakage current, the location and severity of defects in the enameled wire can be accurately measured and recorded.
When using this method for detection, the enameled wire and the sensor are not in contact throughout the process, so there is no additional damage to the enameled wire. This method is very suitable for online detection of enameled wires traveling at high speeds on production lines. Moreover, the metal conductor in the high-voltage electric field sensor is approximately cylindrical, and the electric field generated is basically the same in all directions. Therefore, the detection capability is basically consistent in all directions, resulting in high detection sensitivity and a low risk of missed or false detections.
Of course, users of electromagnetic wires can only use offline testing, that is, using a coating continuity tester. Compared with online testing equipment, because it is only a semi-enclosed state test, its ability to detect defects is slightly weaker. However, given the randomness of sampling, it can still basically qualitatively determine the performance compliance of the electromagnetic wire.
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