The reason for the copper wire itself is in the 1950s and 1960s. Most domestic manufacturers use ordinary copper rods with a copper content of 99.99%, all of which are oxygenated copper rods. The production method is that copper ingots are heated and then rolled in multiple passes. After the black copper rod is made, the copper rod is made into a relatively thin copper wire through large, medium and small pulling. Because copper itself is not oxygen-free copper, oxidation will inevitably occur on the surface of copper wire during processing. In the 1980s, the advanced production technology of oxygen-free copper rods was introduced in China, as well as the production technology of oxygen-free copper rods developed in China, which made the whole wire and cable industry use oxygen-free copper rods, which is undoubtedly improved. The problem of blackening of copper wire. However, due to the processing of the copper rod, especially the mastery of the toughening process and the poor storage conditions of the processed copper wire core, the copper wire core itself has been slightly oxidized, which is also one of the reasons for the blackening of the copper wire.
Reasons for rubber formulation In the 1950s, rubber insulation was formulated with natural rubber and styrene-butadiene rubber. Since the insulating rubber is in direct contact with the copper wire, sulfur cannot be used directly as a vulcanizing agent, and even a small amount of sulfur will make the copper wire black. Some compounds that can decompose free sulfur must be used, such as the aforementioned accelerator TMTD, vulcanizing agent VA-7, and some vulcanization accelerators must be used to improve the vulcanization speed and degree of vulcanization to ensure the physical and mechanical properties of the insulating rubber. and electrical performance. However, in terms of elasticity, strength and permanent deformation of insulating rubber, it is not as good as rubber with sulfur (if the blackening of copper wire is not considered). Decades of practice have confirmed that TMTD cannot solve the problem of blackening of copper wires. In addition, the insulating rubber should have various colors. Red, blue, yellow, green and black are the basic colors. The appearance of these colors will also make the rubber sticky and the copper wire black. The main fillers in the formula are light calcium carbonate and talcum powder. Due to the price, some manufacturers use calcium carbonate and talcum powder which are especially cheap in order to reduce costs. These fillers have coarse particles, large free alkali content and impurities. Therefore, the physical and mechanical properties are relatively poor, the electrical properties are not good, and it is easy to cause the copper wire to turn black. Some factories use active ultrafine calcium carbonate to improve the physical and mechanical properties of insulating rubber, and most active calcium is treated with stearic acid, which is also the reason for the blackening of copper wires. The use of vulcanizing agent VA-7 can improve the blackening of copper wires, but due to insufficient vulcanization, the permanent deformation of the rubber is large, which will cause the rubber to become sticky. Especially after adding the accelerator ZDC, the vulcanization speed is increased. In order to prevent scorch, the accelerator DM is also added to delay the scorch time. From the structure of the accelerator ZDC, a metal zinc is placed between the two connected sulfurs in the TETD structure. H5C2>N-C-S-S-C-N< H5C2 H5C2 is very close, and it is impossible to avoid the blackening of copper wire with a structure similar to thiuram in the formula. It may take a little longer, but it has not been fundamentally solved.
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