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How to avoid copper wire blackening?
Apr 23, 2018

Rubber sheathed cable is a flexible and movable cable product, which is used as a conductor, rubber insulation and rubber sheath. Generally, the rubber sheathed cables are composed of five types: general rubber flexible cable, electric welder cable, submersible motor cable, radio installation cable and photo light source cable.

After a period of use, the color of the copper wire is often blackened. The reason is found that the cause of black cabtyre cable wire has a lot of, in addition to materials and rubber related formula, but also with copper wire itself in the state, rubber processing, rubber vulcanization process, the structure of the cable, the sheath of rubber formulation and production environment, and many other factors.

Practice has proved that TMTD has no method to solve the problem of copper wire blackening. At the same time, the insulating rubber will have various colors, among which red, blue, yellow, green and black are the basic colors. These colors will cause the rubber to be sticky and the copper wire will be black. The main fillers in the recipe are light calcium carbonate and talcum powder, but are affected by price factors. Some manufacturers use low price calcium carbonate and talcum powder to reduce costs. These filler particles have a large amount of crude and free alkali and many impurities, so the physical mechanical properties are poor, the electrical properties are not good, and the copper wire is easily blackened. Some manufacturers use the active superfine calcium carbonate to improve the physical mechanical properties of the insulating rubber, while the active calcium is mostly treated with stearic acid, which is also the cause of copper wire blackening. The use of vulcanizing agent va-7 can improve copper wire blackening, but due to the lack of vulcanization, the permanent deformation of rubber will cause the rubber to be sticky. In particular, after the addition of ZDC, the curing rate was increased, and the promoter DM was added to delay the coke burning time. From the structure of the accelerator ZDC, a metal zinc is attached to the two connected sulfur in the TETD structure.

The catalysis and aging of copper are the important reasons for the adhesion of rubber. In the process of vulcanization, the copper from the contact with the rubber penetrated into the insulating rubber. The insulating rubber with a thickness of 1.0-2.0mm was 0.009-0.0027%. It is well known that even trace amounts of copper can have a great effect on the rubber, which is what we usually call the catalytic and aging of rubber. During the process of insulation vulcanization, a number of free sulfur and copper reactions were precipitated in the autumn lamb, forming an active copper group. In the aging process, the weaker -s-s-bond fracture, the formation of active copper - containing Cu-S-. The combination of the low molecular chain and the rubber action also reacts with the oxygen to destroy the long bond molecules of the rubber, making the rubber soft and sticky. French recurring problems in the study of sticky rubber institute pointed out: if the rubber contains harmful metals, such as copper, manganese and other heavy metal salts, so no matter which kind of accelerator, rubber sticky phenomenon happens.

The possibility of sulfur diffusion in cable sheath rubber was confirmed by the use of radioisotopes in the former Soviet union for the reasons for the permeation of the sulfur to the insulating rubber and copper wire in the rubber sheathed cables. Vulcanized rubber with natural rubber as base, under the temperature of 130-150 , the diffusion coefficient of the free sulphur is about 10-150 px2 / s. And in continuous vulcanization production workshop, vulcanized rubber sheath temperature keep between 185-200 , the sulfur diffusion coefficient is bigger.

The diffusion of free sulfur in the rubber sheath changes the structure of chulam rubber, which may form a polysulfide bond. The migration of polysulfide by chemical decomposition and combination, namely "chemical diffusion", not only changed the rubber insulation structure, reduce its heat resistance, and react with copper surface, form cuprous copper sulfide, the sulfide, lead to black copper wire. At the same time, copper sulfide and copper sulfide also accelerated the aging of rubber, which caused the rubber to be sticky.


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