Technical reasons: In the past, most domestic manufacturers used universal copper bars, and the copper content could reach 99.95%. However, even today, this O still exists in copper. The reason is that copper itself is not oxygen-free copper, and the surface of copper will inevitably contact with air and be oxidized during processing. Up to now, domestic advanced oxygen-free copper production technology and self-developed oxygen-free copper production technology have been introduced, which makes the whole copper wire industry use oxygen-free copper, which undoubtedly greatly improves the blackening problem of copper wire. However, due to the processing of copper rod, especially the application of toughening technology, and the poor storage conditions of finished copper wire core, the copper wire itself will still be slightly oxidized.
Insulation material: Insulation paint can be divided into five categories: impregnating paint, enameled wire paint, covering paint, silicon steel sheet paint and anti-corona paint. Among them, impregnating varnish is used to impregnate the coils of motors and electrical appliances. Impregnating paint can fill the gaps and micropores in the insulation system, and form a continuous paint film on the surface of the impregnation, so that the coil can be bonded into a solid whole, effectively improving the integrity, thermal conductivity, moisture resistance, dielectric strength and mechanical strength of the insulation system.
Secondly, it also plays the role of heat dissipation. If the insulation paint is dipped, the dried coil can be regarded as a whole, and the heat of the inner and outer layers is easy to conduct, which plays a role in heat dissipation. At present, the production technology, preparation method and patent formula technical data of impregnating varnish and insulating oil in China are still relatively backward, and the impregnating varnish produced and processed basically only plays a short-term role, and will fall off and fail after a long time.
Problems in use: In the process of using coil copper wire, we often encounter such problems as collision and friction, slow cleaning, coil contact with a lot of water, lubrication of waste oil, resulting in conductor surface residue and insulation damage, and conductor oxidation in subsequent processing.
Copper wire annealing process: copper wire annealing refers to a kind of metal heat treatment in which copper wire is slowly heated to a certain high temperature, kept for a period of time, and then cooled at a corresponding speed. Copper wire annealing can reduce hardness, improve machinability, eliminate residual stress, stabilize size and reduce deformation and crack tendency. Refine grain, adjust structure and eliminate structural defects. However, once the temperature is higher than 50℃ in the production process, the stipulated vacuumizing time is not enough, the SO2 content is high, and the protective gas is impure, which will lead to insufficient annealing, and the copper wire will be prone to blackening after a period of time.
The blackening of coil copper wire is caused by many factors, not only the above four factors, but also the state of copper wire, coil processing technology, vulcanization technology, coil structure, formula, coil production environment and many other factors.
Some metals are easily oxidized if left in the air for a long time, so it is recommended to put pure copper in a dry and sunny place.