The atomic number of metallic copper is 29, the density is 8.92g/cm3, the melting point is 1083.4°C, and it has good thermal conductivity and electrical conductivity, but in humid air, the surface of metallic copper reacts chemically with oxygen to form Cu2(OH)2CO3, which is patina , Usually copper oxidation in cable production plants shows black surface. It is the existence of this phenomenon of surface oxidation of copper conductors of cables that troubles many cable companies.

In our daily production observation and a large amount of data research, we found that through better copper rod selection, effective control of wire drawing process and emulsion concentration and temperature, passivation treatment of copper conductor stranded or bundled copper wire surface, subsequent process optimization treatment and other means , it will effectively control the quality of the copper conductor of the cable and prevent its oxidation, which will greatly improve the work efficiency and reduce the frequency of rework, thereby achieving the beneficial effects of reducing costs and improving internal product quality.

Cable copper conductor

1. Anti-oxidation control of copper conductors in the production process of wire and cable

In principle, metal copper for cables mainly includes physical methods to block copper from contact with humid air, cathodic protection redox method to prevent oxidation of copper conductors, chemical methods to produce passivation films on the surface of copper conductors to prevent oxidation, or spray special liquids on the surface of conductors to prevent oxidation. Protect.

1.1 Transportation, testing and storage of copper rods before entering the factory

Most cable companies in my country basically outsource copper, but most companies tend to ignore the control of the transportation process before copper rods enter the factory. When transporting to the company, the author understands that many cable companies have not formulated corresponding copper rod supplier transportation specifications, summer rainy packaging specifications and other systems, which often makes the copper rod surface intact without oxidation and blackening when the copper rod supplier delivers the goods. When it reaches the cable enterprise users, the surface of the copper rod appears black, which brings unnecessary trouble.

The incoming inspection of copper rods is basically in accordance with GB/T 3953-2009 or the enterprise standard of cable enterprises, and there are strict procedures. The storage of copper rods is generally placed in warehouses by cable companies. Generally, companies have stricter storage management methods. When copper rods are stored, especially in summer rainy days, they must be covered with plastic sheets or plastic films. Use z.ui The simple physical barrier method prevents the copper rod from contacting with humid air, which is often overlooked by cable companies. When receiving copper rods in the workshop, it is necessary to visually check whether there is any blackening phenomenon one by one, and control them from the source of production.

1.2 Control of copper rod drawing process

At this stage, the 8mm copper rod commonly used in power cables is taken as an example. Nowadays, continuous annealed copper wire is generally used for wire drawing. The mold must not be too small. If too small, it will force the lattice variation of the metal copper and aggravate the sharp rise of the metal temperature.

Check the concentration of the emulsion before starting the machine to ensure that the concentration is qualified. During the pay-off process, the pay-off tension should be kept stable and uniform without excessive vibration (chatter is inevitable). The operator should pay close attention to the change of the annealing temperature during the wire drawing process. After the wire drawing, the conductor hardens, the elongation becomes smaller, and the DC resistivity of the conductor increases. There should be no residual emulsion on the surface of the copper conductor when the wire is drawn into a loop. The operator needs to identify it with the naked eye, and seal it with a transparent plastic film after the wire drawing. It is stored in a dry environment and is to be circulated, but most cable companies omit the film coating process because of the troublesome copper wire coating film. The surface temperature of the conductor that has just been drawn into a loop is higher than room temperature, and there is a potential risk of oxidation in the rainy season.

1.3 Copper wire stranding (strand stranding) and chemical cross-linking extrusion process

Taking copper wire stranding as an example, in the conductor stranding process, each single wire is twisted in a regular or irregular manner. There is a great improvement, especially for compacted conductors, fan-shaped conductors, etc., and the frame stranding machine currently has no online annealing or cooling device, so the outer layer of the copper conductor is easily oxidized. , cable reel, adjust the tension of take-up and pay-off. After the equipment is adjusted, the operator visually observes the surface finish of the copper wire on the upper coil and the center copper wire of the pay-off frame to ensure that there are no obvious black spots, and then start the machine.

Generally, cable companies will apply antioxidants in the stranding process (frame stranding machine, cage stranding machine), and the formula of the antioxidant is about 0.3% benzotriazole alcohol solution. In the alcohol, use the infusion tube to drip into the copper wire. The dripping standard is based on the copper wire just soaked, so as to avoid the occurrence of too little local potential oxidation or too much waste. After all the anti-oxidation work is properly prepared, restart the machine. run.

Make sure that the take-up reel is dry at the take-up area. After the take-up reel is full, it is sealed with a transparent plastic film. It is the same as copper wire drawing. Many cable companies also omit this step. The impact of cables is still low, and for ultra-high voltage cables, the impact is unimaginable. After the copper conductor has been drawn, twisted and stored, the lattice morphology of metallic copper has been basically stable. Chemical cross-linking means that XLPE is evenly extruded on the copper conductor under the conditions of cross-linking agent, antioxidant, coupling agent, etc. Before starting the pay-off reel filled with copper conductors, adjust the tension of the take-up and pay-off to ensure the smooth operation of the equipment.

2. Summary

Almost all cable factories in my country are faced with the problem of copper conductor oxidation. From the chemical properties of metal copper, it is necessary to maintain the reducibility of metal copper. In daily production, the following measures of Guangdong Pearl River Wire and Cable can reduce the probability of oxidation of copper conductors:

1) Select high-quality metal copper rods, standardize the supplier's transportation, delivery process and system, take transparent plastic film sealing measures after the copper rods arrive at the company, and take transparent plastic film sealing measures after copper conductors are drawn and twisted ;

2), adopt the appropriate copper wire drawing process, regularly check the annealing parts of the wire drawing machine, give priority to the drawing oil containing antioxidants, regularly check the concentration of the emulsion, and replace it in advance before the expiration of the shelf life;

3), copper wire stranding, extrusion insulation process adopts passivation treatment technology;

4) Establish quality awareness and strengthen business training so that operators of the above processes are aware of the adverse consequences of copper wire oxidation.