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Various reasons of copper wire blackening in rubber sheath cable
Apr 11, 2018

Copper Wire blackening reason is caused by a variety of factors, not only the rubber formula, but also with the copper wire itself in the state, rubber processing technology, rubber vulcanization process, cable structure, sheath rubber formula, production environment and many other factors. 1 analysis of the causes of the rubber sticky and copper wire blackening 1.1 copper wire itself causes in the 20th century 50-60, most domestic manufacturers are using ordinary copper rods, copper content of 99.99%, are oxygen copper rods, production methods are ingots heated by a number of pressure delayed black copper rods, after large, medium and Fine wire the copper rods into a relatively fine brass wire. Because copper itself is not oxygen-free copper, in the process of copper wire surface inevitably appear oxidation. To the 20th century 80 's, the domestic introduction of oxygen-free copper rod advanced production technology, as well as the domestic development of the anaerobic copper rod production technology, so that the entire wire and cable industry are used oxygen-less copper rod, which is undoubtedly to improve the copper wire blackening problem. 


However, because of the processing of copper rods, especially the process of toughening and processing of good copper core storage conditions are not good, so that the copper core itself has a slight oxidation, which is one of the reasons copper wire blackening. 1.2 Reasons for the rubber formula 20th century 50, rubber insulation are made of natural rubber and styrene-butadiene rubber and formula. Because the insulating rubber is directly in contact with the copper wire, sulfur can not be used as a vulcanizing agent directly, that is, the use of very little sulfur will make copper wire black. It is necessary to use compounds that can decompose free sulfur, such as the accelerator TMTD and vulcanizing agent VA-7 mentioned earlier, as well as some vulcanization accelerators to improve the vulcanization speed and vulcanization, and to ensure the physical and mechanical properties and electrical properties of the insulating rubber. But from the elastic, strong and permanent deformation of insulating rubber, it is better to add a sulphur rubber (if copper wire blackening is not considered). Decades of practice have proved that TMTD can not solve the problem of copper wire blackening. In addition, insulating rubber to have a variety of colors, red, blue, yellow, green, black is the basic color, these colors will also promote the appearance of rubber sticky and copper wire black. The main filler in the formula is light calcium carbonate and talcum powder, because of the price of the relationship, some manufacturers in order to reduce costs, with a very cheap price of calcium carbonate and talcum powder, these filler particles coarse, free alkali content of large, impurities, so the physical mechanical properties are poor, electrical performance is not good, but also easy to cause copper wire blackening. There are also plants with active superfine calcium carbonate to improve the physical and mechanical properties of insulating rubber, and 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 the copper wire blackening, but due to the degree of vulcanization is not enough, the permanent deformation of the rubber, will cause the rubber hair sticky. In particular, after adding the promoter ZDC, the vulcanization speed is increased, in order to prevent Coke burning, the promoter DM should be added to delay the burnt time. From the structure of the Promoter ZDC, it is indirectly a metal zinc in the two connected sulfur in the tetd structure, the structure is as follows: s S h5c2‖‖h5c2 >n-c-s-zn-s-c-n< h5c2 h5c2 and tetd structural type S H5C2‖‖H5C2 >n-c-s


-s-c-n< h5c2 H5c2 is very close, in the formula can not avoid and autumn lamb similar structure copper wire blackening may be a little longer, but not fundamentally resolved. 2 analysis of the structure of wire and cable 2.1 The catalytic aging of copper is an important reason for the rubber sticking. The former Soviet Union cable Science Research Institute test has proved that: in the vulcanization process copper from contact with rubber into the insulating rubber, 1.0-2.0mm thickness of insulating rubber with copper 0.009-0.0027%. It is well known that trace copper has a great destructive effect on rubber, which is what we usually call a heavy metal-catalyzed aging of rubber. In the insulation vulcanization process, the autumn lamb precipitates several free sulfur and the copper reaction, forms the active copper-containing group: Ch3│ch2-ch-c-ch2-││s S││CU cu in the aging, the weaker-s-s-bond breaks, forms the active copper-containing base: cu-s-, it with the rubber function, simultaneously with the oxygen function, destroys the rubber the Long-bond molecules, which make rubber soft and sticky, are combinations of low molecular chains. 


The French Institute of Rubber Research on the issue of Sticky reproduction also pointed out: if the rubber contains harmful metals, such as: copper, manganese and other heavy metal salts, then regardless of the type of promoter, will occur rubber sticky phenomenon. The migration of sulfur to insulating rubber and copper wire surface in 2.2 rubber sheathed cables the possibility of sulfur diffusion in cable sheath rubber was confirmed by the use of radioisotope by former Soviet scientists. The diffusion coefficient of free sulfur is about 10-6cm2/s at 130-150 ℃ temperature in the vulcanized rubber base of natural rubber. Continuous vulcanization production plant, vulcanization sheath rubber, temperature between 185-200 ℃, this diffusion coefficient is greater. Because of the diffusion of free sulfur in the rubber sheath, the structure of the autumn lamb rubber is changed, and the sulfur bond may be formed. These sulfur compounds are chemically decomposed and combined to achieve migration, i.e., "chemical diffusion". As a result of the migration, not only can change the structure of insulating rubber, reduce its heat resistance, and sulfur and copper surface reaction, forming copper sulfide and cuprous sulfide, resulting in copper wire blackening. 


In turn, copper sulfide and cuprous sulfide accelerate the aging of rubber, and lead to the occurrence of sticky phenomenon.


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