The reason for the blackening of
Copper Wire is caused by many factors, not only the formulation problem, but also the state of the copper wire itself, the rubber processing technology, the rubber vulcanization process, the cable structure, the sheath rubber formula, the production environment, etc. Related factors.
Causes the blackening of the copper wire
1. The area of the wire drawing emulsified oil pool is small, the return pipe is short, and the sealing is caused, resulting in slow heat dissipation, resulting in high temperature of the emulsion oil.
2. It is caused by the annealing of copper wire.
1 The continuous cooling water is usually tap water and ground water. Because the water quality varies from place to place, the water quality of some areas is lower, only 5.5~5.0 (normally 7.0~7.5), the original emulsion is resistant. The oxidized oil film is washed away, and the annealed copper wire is easily oxidized and blackened;
2 The finished copper wire drawn by the ordinary wire drawing machine is annealed on another annealing line, the cooling water is not used with anti-oxidant, the anti-oxidation time is short, and the blackening phenomenon will soon occur;
3, some old factories use annealing cylinders to anneal, so the following reasons will also cause oxidation and blackening:
1 The annealing cylinder nut is not tightened, and the air leaks after the carbon dioxide or high-purity nitrogen is washed out;
2 The temperature of the copper wire exiting the cylinder is too high, exceeding 30 °C;
3 brushed emulsion is not maintained enough, the pH value is too low;
These conditions are more common in summer when the temperature is high. The emulsion will be worn out constantly. When the temperature is high, the loss will be faster. If the new crude oil is not replenished in time, the fat content is small, and the temperature is high. The temperature of the emulsion may also exceed 45 ° C, which is likely to cause oxidation blackening.
4. In another case, since high-speed wire drawing is generally used at present, the speed is increased, and the relative heat dissipation time is reduced, which brings a certain space and time for oxidation. Therefore, it is recommended that manufacturers pay more attention to the fat content of the emulsion, the use temperature, the pH value, etc., the bacteria in the spring yellow mold rain season can be quickly propagated, the fungicide can be used, and the antioxidant can be used in the summer to solve the oxidation and blackening. And other issues.
the reason
1 The deformation of the finished mold is too small
2The outer and front of the mold insert are not sealed.
Solution
Add a rubber pad in the direction of the exit of the finished mold, and then screw the finished mold to solve the problem of oil leakage. The deformation of the finished mold is too small, which is a common mistake. The single-mode deformation needs a minimum amount of deformation, and the generated pressure can be greater than the yield limit of the metal. Only plastic deformation can be achieved, the size can be stabilized, and the single-line surface is There will be light from the cold pull.
Causes the coil to black out
We often use a variety of products that use coils, such as motors, hearing aids, remote control toys, wireless chargers, power switches, computers, etc. The blackening of the coil is due to the oxidation of the copper wire, the main material of the coil is basically used. Copper wire, and the metal will oxidize, so we will see the coil black.
1. Technical reasons
In the past, most domestic manufacturers used universal copper rods with a copper content of 99.95%, but even so, there is oxygen in the copper. Because copper itself is not oxygen-free copper, the surface of copper is inevitably exposed to air and oxidized during processing.
Nowadays, the advanced production technology of oxygen-free copper and the oxygen-free copper production technology developed by the country have been introduced in the country, which has made the whole copper wire industry use oxygen-free copper, which has undoubtedly greatly improved the blackening problem of copper wire.
However, due to the processing of the
Copper Rod, especially the use of the toughening process, and the storage conditions of the finished copper core are not good, the copper wire itself will still be slightly oxidized.
2, the material problem of the insulation layer
Insulating varnish can be divided into five categories: impregnating varnish, enameled wire lacquer, covering lacquer, silicon steel lacquer and anti-corona lacquer. The impregnating varnish is used as an immersion treatment motor and an electrical coil. The impregnating varnish can play the role of filling gaps and micropores in the insulation system, and form a continuous paint film on the surface of the impregnated material to bond the coil into a solid whole, effectively improving the integrity, thermal conductivity and moisture resistance of the insulation system. Properties of dielectric, dielectric strength and mechanical strength.
Secondly, it also plays a role in heat dissipation. When the insulating varnish is saturated, the dried coil can be regarded as a whole, and the heat of the inner and outer layers can be easily transmitted, thereby functioning to dissipate heat.
At present, China's impregnating varnish and insulating oil production process, preparation method and formulation technical data are still relatively backward. The production and processing of impregnating lacquer basically only plays a short-term role, and the phenomenon of falling and failure will occur after a long time.
3, the problem of use
In the process of using coil copper wire, we often have such problems: collision friction; slower rinsing, a large amount of moisture in contact with the coil; lubrication with waste engine oil, causing damage to the conductor surface and insulation layer; Causing conductor oxidation;
4, copper wire annealing process
Copper wire annealing refers to a metal heat treatment method in which the copper wire is slowly heated to a certain high temperature for a certain period of time and then cooled at a corresponding speed.
The copper wire annealing process can reduce hardness, improve machinability, eliminate residual stress, stabilize size, reduce deformation and crack tendency, refine grains, adjust microstructure, and eliminate tissue defects. However, once the temperature is higher than 50 °C in the production process, the specified pumping time is insufficient, the SO content is high, and the imperfection of the shielding gas will cause insufficient annealing, and the copper wire will be easily blackened after a period of time.
The blackening of the coil copper wire is caused by many factors, not only the above four problems, but also related to the state of the copper wire itself, the coil processing technology, the vulcanization process, the structure of the coil, the formulation, the coil production environment and many other factors. .
The reason why the copper cable of the rubber cable is black
The blackening of the copper wire of the rubber cable is caused by many factors, not only the formulation problem of the rubber, but also the state of the copper wire itself, the rubber processing technology, the rubber vulcanization process, the cable structure, the sheath rubber formula, and the production. The environment is related to many factors.
1. Analysis of the causes of rubber sticky and blackening of copper wire
1.1 The reason for the copper wire itself
In the 1950s and 1960s, most domestic manufacturers used ordinary copper rods with a copper content of 99.99%, all of which were aerobic copper rods. The production method was that after the copper ingots were heated, the black copper rods were obtained after multiple calendering. After the large, medium and small pull, the copper rod is made into a relatively thin copper wire. Because copper itself is not oxygen-free copper, it is inevitable that oxidation will occur on the surface of the copper wire during processing.
In the 1980s, the country introduced advanced production technology of oxygen-free copper rods and domestically developed oxygen-free copper rod production technology, which made the entire wire and cable industry use oxygen-free copper rods, which is undoubtedly improved copper. Silk blackening problem. 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 core, the copper core itself has been slightly oxidized, which is one of the reasons for the blackening of the copper wire.
1.2 Reasons for rubber formula
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 directly used as a vulcanizing agent, that is, the use of a small amount of sulfur also causes the copper wire to be blackened. Some compounds that can decompose free sulfur, such as the accelerator TMTD and vulcanizing agent VA-7 mentioned above, must be used together with some vulcanization accelerators to increase the vulcanization speed and vulcanization degree to ensure the physical and mechanical properties of the insulating rubber. And electrical performance. But from the elasticity, strength and permanent deformation of the insulating rubber, it is not as good as the rubber with sulfur (if the copper wire is not considered black). Decades of practice have confirmed that TMTD cannot solve the blackening problem of copper wire.
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 cause the rubber to stick and the copper to black. The main fillers in the formula are light calcium carbonate and talc. Due to the price, some manufacturers use calcium carbonate and talc which are particularly cheap in order to reduce the cost. These filler particles are coarse and free of alkali and impurities. Many, so the physical and mechanical properties are relatively poor, the electrical performance is not good, it is also easy to cause the copper wire to black.
Other plants use active ultra-fine calcium carbonate to improve the physical and mechanical properties of the insulating rubber, and most of the active calcium is treated with stearic acid, which is also responsible for the blackening of the copper wire. The use of vulcanizing agent VA-7 can improve the blackening of copper wire, but due to insufficient degree of vulcanization, the permanent deformation of the rubber is large, which will cause the rubber to become sticky. In particular, after the addition of the promoter ZDC, the vulcanization rate is increased, and in order to prevent scorch, a promoter DM is added to delay the scorch time.
From the structure of the promoter ZDC, it is indirectly a metal zinc in the two connected sulfur in the TETD structure, the structural formula is SS H5C2 ‖ ‖ H5C2 > NCS-Zn-SCN < H5C2 H5C2 and TETD structure SS H5C2 ‖ ‖ H5C2 >NCSSCN < H5C2 H5C2 is very close. It is impossible to avoid the blackening of the structure similar to thiram in the formula. The blackening time may be slightly longer, but it is not fundamentally solved.
2, from the analysis of wire and cable structure
2.1 Catalytic aging of copper is an important cause of rubber stickiness.
The test of the former Soviet Cable Science Research Institute proved that copper infiltrates into the insulating rubber from the contact with the rubber during the vulcanization process, and the insulating rubber with a thickness of 1.0-2.0 mm contains 0.009-0.0027% of copper. It is well known that trace copper has a great destructive effect on rubber, which is the catalytic aging of rubber by heavy metals.
During the insulation vulcanization process, thiuram precipitates some free sulfur to react with copper to form active copper-containing groups CH3 │ CH2-CH-C-CH2- │ │ SS │ │ Cu Cu. In aging, weaker -SS- The bond breaks to form an active copper-containing group: Cu-S-, which acts with the rubber and simultaneously acts with oxygen to destroy the long bond molecules of the rubber, making the rubber soft and sticky, and is a combination of low molecular chains. The French Rubber Research Institute also pointed out that if the rubber contains harmful metals, such as heavy metal salts such as copper and manganese, rubber stickiness will occur regardless of the type of accelerator.
2.2 Migration of sulfur to insulating rubber and copper wire surface in rubber cable
The use of radioisotopes by former Soviet scientists confirmed the possibility of sulfur diffusion in cable sheath rubber. In natural rubber-based vulcanizates, the diffusion coefficient of free sulfur is about 10-6 cm 2 /s at a temperature of 130-150 ° C. In a continuous vulcanization plant, when the sheath rubber is vulcanized, the temperature is between 185 and 200 ° C, and the coefficient of diffusion is even greater.
Due to the diffusion of the free sulfur of the rubber sleeve, the structure of the thiura rubber is changed, and a polysulfide bond may be formed. These polysulfide compounds undergo migration by chemical decomposition and combination, that is, "chemical expansion." As a result of the migration, not only the structure of the insulating rubber can be changed, but also the heat resistance is lowered, and sulfur reacts with the copper surface to form copper sulfide and cuprous sulfide, resulting in blackening of the copper wire. In turn, the aging of copper sulphide and cuprous sulphide plus rubber leads to the occurrence of stickiness.
3. Reasons for processing technology
3.1 Reasons for rubber processing
In the insulation formula based on the combination of natural rubber and styrene-butadiene rubber, natural rubber needs to be plasticized to improve rubber plasticity. Some large plants use a mixer to masticate for production, and a small amount of chemical plasticizer, accelerator M, to increase plasticity. If the temperature of the mastication temperature and the raw rubber filter is not well controlled, a high temperature of 140 ° C or higher occurs, and when the raw rubber is placed on the open mill, it slowly passes through the drum, and the above accumulated rubber is exposed to the hot oxygen and the accelerator M at the same time. As a result, it will be found that the rubber surface is coated with a layer of oil. In fact, the rubber molecules are more severely broken by the chemical plasticizer, resulting in a softer and more viscous smaller molecular weight rubber.
Although the insulating rubber was later mixed with styrene-butadiene rubber, these small-molecular-weight natural rubbers were evenly dispersed in the rubber. After the rubber was extruded on the copper wire for continuous vulcanization, there may be no problem at that time. However, it has already laid a hidden danger for the rubber-bonded copper wire, that is to say, these small-molecular-weight natural rubber will first appear as a localized copper wire phenomenon.
The process of insulating rubber plus vulcanizing agents and accelerators is also very important. Some small factories add vulcanizing agent to the mill, that is, the tank containing the vulcanizing agent is poured into the middle of the drum, and there are many in the middle, and there are fewer on both sides. When the vulcanizing agent is eaten into the rubber, the number of turning the triangle is less, and the vulcanizing agent is unevenly distributed in the rubber. In this way, when the package is continuously vulcanized, the place where the vulcanizing agent is contained is likely to be blackened, and in the place where the blackening is long, the phenomenon of rubber-bonded copper wire may occur.
3.2 Causes of vulcanization of insulating rubber
In order to pursue production, some enterprises only have a continuous vulcanization pipe of 60 meters long, a steam pressure of 1.3Mpa, and a vulcanization rate of 120 m/min, so that the residence time of the insulating rubber in the pipe is only 30 seconds.
The rubber itself is a poor conductor of heat. The surface temperature of the insulated core is greater than 190 ° C. When the temperature is transferred to the inner rubber that is in contact with the copper wire, the copper wire absorbs heat, and the copper wire heats up to the temperature of the inner rubber. The vulcanized rubber wire core has already been vulcanized. In this way, the temperature of the inner rubber layer is relatively low, about 170 ° C, and the vulcanization tube is discharged only after a few seconds, and the cooling rubber is cooled and the wire is removed, and the insulating rubber is insufficiently vulcanized. In order to achieve sufficient vulcanization. The amount of accelerator TMTD (used as a vulcanizing agent) is as high as 3.4%. Excessive vulcanizing agent releases more free sulfur during the vulcanization process. In addition to the crosslinked rubber molecules, there is excess free sulfur. This is the reason for the blackening of the copper wire surface.
In short, to solve the problem of blackening of copper wire, the difficulty is still great. Every process from copper wire to rubber should be taken seriously, in order to achieve better results. The choice of glue and the use of the vulcanization system are still the key to the problem. The solution to this problem needs to go through the test of time.
June 23, 2023
