When the copper wire was made into the core wire and the shell, no oxidation was found. Why does copper wire always appear oxidation blackening after being processed into slingshot wire? That? ...
I used to work in a wire factory. There may be a preheating process to make the core wire and sheath, but that is only to increase the temperature of copper wire and increase the adhesion between copper wire and rubber mixture. The speed is usually very fast, otherwise it will burn out. When the wire is processed and wound, it needs to be baked (shaped) and then rewound (increased elasticity). The environmental temperature of the baking line is too high, and after a period of time, the copper wire will naturally oxidize 100%.