The atomic number of copper is 29, the density is 8.92g/cm3, the melting point is 1083.4℃, has good thermal and electrical conductivity, but in the humid air, the surface of copper metal and oxygen chemical reaction, Cu2(OH)2CO3, that is, copper green, usually in the cable production plant copper oxidation more than show the surface black, It is the existence of oxidation phenomenon on the surface of copper conductor of cable that troubles many cable enterprises.

In our daily production observation and a large number of data research, we found that through better selection of copper rod, effective control of drawing process and emulsion concentration and temperature, passivation treatment of copper conductor stranded or stranded copper wire surface, and subsequent process optimization treatment, the quality of cable copper conductor can be effectively controlled to prevent its oxidation, which will greatly improve work efficiency and reduce rework frequency. Thus achieve the beneficial effect of reducing the cost and improving the internal product quality.

Cable copper conductor

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

In principle, cable copper mainly includes physical methods to prevent the contact between copper and humid air, cathodic protection REDOX method to prevent the oxidation of copper conductor, chemical methods to produce passivation film on the surface of copper conductor to prevent oxidation, or spray special liquid on the surface of the conductor to protect.

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

Most of our cable enterprises basically purchase copper, and most of them tend to ignore the control of the transport process before the copper rod enters the factory. In southern Jiangxi and coastal areas (Jiangsu and Zhejiang provinces, Fujian and Guangdong provinces), the summer is long and rainy, and the copper rod is transported to the company by heavy trucks. According to the author's understanding, many cable enterprises have not established corresponding transport standards for copper rod suppliers, packaging standards for summer rainy days and other systems. This often makes the surface of the copper rod intact without oxidation and black when the copper rod supplier delivers the goods, and the surface of the copper rod black when it reaches the cable enterprise users, bringing unnecessary trouble.

Copper rod into the factory inspection basically in accordance with GB/T 3953-2009 or cable enterprise enterprise standard, there are strict procedures. Storage of copper rod general cable enterprises are placed in the warehouse, general enterprises have more strict storage management methods, in copper rod storage, especially in summer rainy days, must be covered with plastic sheet or plastic film copper rod, with z.u simple physical barrier method to prevent the contact system of copper rod and humid air, and this point is often ignored by cable enterprises. When using copper rods in the workshop, we must check whether there is black phenomenon by naked eye one by one, and control it from the source of production.

1.2 Control of copper rod drawing process

This stage takes the power cable z.u commonly used 8mm copper rod as an example. Now, when drawing wire, the continuous annealing of copper is generally used. It is necessary to go through the process of laying off, drawing and annealing, cooling, drying and winding, and select the mold of the corresponding specifications.

Check the concentration of the emulsion before starting, to ensure that the concentration is qualified, in the process of pay-off, should keep the pay-off tension stable, uniform, not excessive fibrillation (fibrillation is inevitable), the operator should pay close attention to the annealing temperature changes in the process of wire drawing, conductor hardening, elongation becomes smaller, conductor DC resistivity increases, wire drawing wait ring copper conductor surface should not have residual emulsion. Here, the operator needs to be identified by the naked eye, sealed with transparent plastic film after drawing the foot plate, stored in a dry environment for circulation, but most cable enterprises because of the trouble of copper wire wrapped film and omit the film wrapping process. The surface temperature of freshly drawn coil conductors is higher than room temperature, and there is a potential risk of oxidation in rainy season.

1.3 Copper wire stranding (bunching) and chemical crosslinking extrusion process

Take copper wire stranding as an example, during the conductor stranding process, each single wire is stranding in regular or irregular ways, after the action of each die, the temperature of the copper conductor after the die is much higher than that before the die, especially the pressed conductor, sector conductor, and the frame stranding machine currently has no online annealing or cooling device, so the outer layer of the copper conductor is easy to oxidize, before stranding, Select the appropriate stranding mold, pressing wheel and wire-setter, adjust the tension of wire receiving and pay-off. After the equipment is adjusted, the operator shall observe the surface finish of the copper wire on the hanging plate and the copper wire in the center of the pay-off stand to ensure that there are no obvious black spots before starting the machine.

General cable enterprises will apply antioxidant in the twisting process (frame winch, cage winch), the formulation of antioxidant is about 0.3% benzotriazole alcohol solution, the operation method is to blend antioxidant into industrial alcohol, drip into the copper wire with infusion hose, drip standard to just infiltrate the copper wire, to avoid too little local potential oxidation or too much waste phenomenon. After all the anti-oxidation work is ready and secure, start the machine again.

The receiving coil should be ensured to be dry, and the receiving coil should be filled and sealed with transparent plastic film. In the same way as copper wire drawing, many cable enterprises also omit this step. If this step causes oxidation of copper conductor, the impact on low-voltage cable is still low, and on ultra-high-voltage cable, the impact is unimaginable. After the copper conductor has been drawn, twisted and stored, the metal copper lattice has been basically stable. Chemical crosslinking means that XLPE is uniformly extruded on the copper conductor under the conditions of crosslinking agent, antioxidant and coupling agent. Before starting the pay-off tray full of copper conductors, adjust the pay-off tension to ensure smooth operation of the device.

Ii. Summary

Almost all cable plants in our country are faced with the oxidation of copper conductors, based on the chemical properties of copper, in order to maintain the reducibility of copper. In daily production, the following measures can reduce the probability of copper conductor oxidation by adopting Guangdong Pearl River wire and cable:

1) Select high quality metal copper rod, standardize the supplier's transportation and delivery process and system, adopt transparent plastic film sealing measures after the copper rod arrives at the company, and adopt transparent plastic film sealing measures after the copper conductor is drawn and stranded;

2) Adopt appropriate copper wire drawing process, check anneal parts of wire drawing machine regularly, give priority to drawing oil containing antioxidant, check emulsion concentration regularly, and replace in advance before expiration of shelf life;

3) Passivation technology is adopted in the stranded and extruded insulation process of copper wire;

4) Establish quality awareness and strengthen business training to make the operators of the above processes aware of the adverse consequences caused by copper wire oxidation.