Analysis of the Causes of Inductance Coil Blackening

Analysis of the Causes of Inductance Coil Blackening

Common Applications of Coils in Daily Life The most common coil applications in daily life include motors, inductors, transformers, and loop antennas. During use, we often encounter the problem of coil blackening. Simply put, the cause of blackening is the oxidation of copper wires, and metal oxidation leading to blackening is a common problem in the industry. However, the specific causes of copper wire oxidation and improvement methods are complex and require targeted solutions. Dongguan Fuying Electronics has been engaged in coil manufacturing for more than 20 years and has accumulated rich experience in coil design, production, and fault troubleshooting. Next, we will explain the causes of coil blackening in detail.

1. Reasons Related to Copper Smelting Processes In the past, some manufacturers used general-purpose copper rods with a copper content of up to 99.95%. However, even so, there were still 0.05% impurities in the copper, and the surface of the copper was inevitably exposed to air during processing, leading to oxidation. With the advancement of domestic copper smelting technology, oxygen-free copper is now widely used in China, which has greatly improved the problem of copper wire blackening. However, due to the processing of copper rods, especially poor annealing processes and improper storage conditions for finished copper wire cores, the copper wires themselves will still have slight oxidation.

2. Problems with the Insulation Layer of Copper Wires Copper wire insulation paints can be divided into five categories: impregnating paints, enameled wire paints, covering paints, silicon steel sheet paints, and anti-corona paints. Among them, impregnating paints are used for impregnating and treating motor and electrical appliance coils. Impregnating paints can fill the gaps and micro-pores in the insulation system, form a continuous paint film on the surface of the impregnated material, and bond the coils into a solid whole, effectively improving the integrity, thermal conductivity, moisture resistance, dielectric strength, and mechanical strength of the insulation system. Secondly, they also play a role in heat dissipation. When the insulation paint is fully impregnated, the dried coil can be regarded as a whole, and the heat from the inner and outer layers can be easily conducted, thus dissipating heat. At present, the production processes and preparation methods of impregnating paints and insulating oils used by some manufacturers are still relatively backward, and the impregnating paints produced are prone to falling off and failing after a long time.

3. Issues with the Usage Environment During the use of copper wires in coils, problems such as collisions and friction, slow flushing, extensive contact of water with the coils, and the use of waste motor oil for lubrication often occur. These cause residues on the surface of the conductor and damage to the insulation layer, leading to conductor oxidation during subsequent processing.

4. Copper Wire Annealing Processes Copper wire annealing is a metal heat treatment process in which copper wires are slowly heated to a certain high temperature, kept at that temperature for a certain period, and then cooled at a corresponding speed. Copper wire annealing can reduce hardness, improve machinability, eliminate residual stress, stabilize dimensions, reduce the tendency to deformation and cracking, refine grains, adjust the structure, and eliminate structural defects. However, according to Fuying Coil's experience, if the temperature exceeds 50°C when taking the copper wires out of the tank during production, the specified air extraction time is insufficient, the SO₂ content is high, or the protective gas is impure, the annealing will be insufficient, and the copper wires will easily turn black after a period of time.