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How To Avoid Copper Wire Blackening With Rubber Sheath Cable
Apr 02, 2018

Rubber sheathed Cable is a flexible and movable cable product, which is composed of many strands of thin copper wire as conductor, and rubber insulation and rubber sheath are outsourced.


Usually, the rubber sheath cable mainly includes general rubber sheath soft cable, welding machine cable, submersible motor cable, radio installation cable and photographic light source cable. After the use of a period of time, rubber sheath cable copper wire color tends to black.


The reason found: There are many reasons for the rubber sheath cable blackening, in addition to the rubber material formulations, but also with the copper wire itself in the state, rubber processing technology, rubber vulcanization process, cable structure, sheath rubber formulations and production environment and many other factors. The Fifties or sixties of the 20th century, most of our domestic manufacturers are using ordinary copper rods (copper content of 99.99%, are oxygen copper rods), production methods are ingots after heating by a number of pressure delayed black copper rods, in large, medium and small pull after the copper rod made of a relatively fine brass wire.


Because copper itself is not oxygen-free copper, in the process of copper wire surface will inevitably occur oxidation. The 1980s, the introduction of advanced oxygen-free copper rod production technology in China, as well as the domestic self-developed oxygen-free copper rod technology, so that the entire wire and cable industry began to use oxygen-free copper rods, greatly improved the problem of copper wire blackening.


However, due to the processing of copper rods, especially the mastery of the toughening process and the poor storage of copper core, the copper core surface is slightly oxidized. The 1950s, rubber insulation using natural rubber and styrene-butadiene rubber and formula. As the insulating rubber is directly in contact with the copper wire, sulfur can not be used as vulcanizing agent, even if the use of very little sulfur will make copper wire black, so we have to use some can decompose free sulfur compounds, such as accelerator TMTD, vulcanizing agent VA-7, but also with curing accelerator to improve vulcanization speed and degree of vulcanization, Ensure the physical and mechanical properties and electrical properties of the insulating rubber.


But from the angle of elasticity, strength and permanent deformation of insulating rubber, the rubber with sulphur is the best (regardless of copper wire blackening). Practice proves: TMTD can't solve the problem of copper wire blackening. At the same time, insulating rubber will have a variety of colors, of which the red, blue, yellow, green, black is the basic color, these colors will make the appearance of rubber sticky and copper wire black. The main filler in the formula is light calcium carbonate and talcum powder, but influenced by price factors, some manufacturers use low price calcium carbonate and talcum powder in order to reduce the cost. 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. Some manufacturers use active superfine calcium carbonate to improve the physical mechanical properties of insulating rubber, while 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.


Viewed from the structure of the Promoter ZDC, it is indirectly a metal zinc in the two connected sulfur in the tetd structure. The catalysis and aging of copper are the important reasons of rubber sticky. The former Soviet Union cable Science Research Institute Test proves: In the vulcanization process, the copper from contact with the rubber into the insulating rubber, 1.0-2.0mm thickness of insulating rubber copper 0.009-0.0027%. As we all know, even trace copper will have a great damage to the rubber, which is what we usually call the heavy metal on the rubber, the catalysis, aging. During the process of insulation vulcanization, the reaction of free sulfur and copper is formed in the autumn Lamb, which forms the active copper-containing group. In aging, the weak-s-s-bond breaks, forming active copper-containing cu-s-. The combination of this low molecular chain and the role of rubber also reacts with oxygen, damaging the long bond molecules of rubber, making the rubber soft and sticky.


The French Rubber Institute in the study of the issue of Sticky reproduction, said: If the rubber contains harmful metals, such as copper, manganese and other heavy metal salts, then no matter what kind of promoter, will occur rubber sticky phenomenon. In view of the reasons for the permeability of sulfur to insulating rubber and copper wire in rubber sheath cable, former Soviet scientists used radioisotope to confirm the possibility of sulfur diffusion in cable sheath rubber. The diffusion coefficient of free sulfur is about 10-6cm2/s at 130-150 ℃ temperature in the vulcanized rubber base of natural rubber.


In the production workshop of continuous vulcanization, the temperature of vulcanization sheath rubber is kept between 185-200 ℃, which makes the sulfur diffusion coefficient larger. The diffusion of free sulfur in the rubber sheath changes the structure of the autumn lamb rubber and may form multiple sulfur bonds. These sulfur compounds through chemical decomposition and combination of migration, that is, "chemical diffusion", not only changed the insulation rubber structure, reduce its heat resistance, but also with the copper surface reaction, forming copper sulfide, cuprous sulfide, resulting in copper wire blackening.


At the same time, copper sulfide and cuprous sulfide also accelerated the aging of rubber, resulting in rubber sticky.


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