The atomic number of metallic copper is 29, the density is 8.92g/cm3, and the melting point is 1083.4 ℃. It has good thermal conductivity and conductivity. However, in humid air, the surface of metallic copper reacts with oxygen to produce Cu2 (OH) 2CO3, that is, copper green. Usually, the surface of copper oxidation in cable production plants is blackened. It is this phenomenon of surface oxidation of cable copper conductor that puzzles many cable enterprises.

Through daily production observation and a large amount of data investigation, 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 bundle stranded copper wire surface, optimization treatment of subsequent processes and other means, the quality of cable copper conductor will be effectively controlled, oxidation will be prevented, work efficiency will be greatly improved and rework frequency will be reduced, So as to achieve the beneficial effect of reducing cost and improving internal product quality.

Cable copper conductor

1、 Anti oxidation control of copper conductor in wire and cable production

In principle, metallic copper for cables mainly includes physical methods to prevent copper from contacting with humid air, cathodic protection oxidation-reduction method to prevent copper conductor oxidation, chemical methods to produce passive film on the surface of copper conductor to prevent oxidation, or spraying special liquid on the surface of conductor for protection.

1.1 transportation, inspection and storage of copper rods before entering the plant

Most cable enterprises in China basically purchase copper, while most enterprises often ignore the control of the transportation process of copper rods before entering the plant. In Jiangnan and coastal areas (Jiangsu, Zhejiang, Fujian and Guangdong), the summer is long and rainy, and the copper rods are basically transported to the company by heavy trucks. According to the author's understanding, many cable enterprises have not formulated corresponding transportation specifications for copper rod suppliers and packaging specifications in rainy days in summer, This often makes the copper rod surface intact without oxidation and blackening when delivered by the copper rod supplier, while the copper rod surface blackening occurs when it reaches the users of cable enterprises, 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, with strict procedures. Generally, cable enterprises store copper rods in warehouses. Generally, they have strict storage management methods. When storing copper rods, especially in rainy days in summer, they must cover the copper rods with plastic cloth or plastic film, and use z.ui simple physical barrier method to prevent the contact between copper rods and humid air, which is often ignored by cable enterprises. When receiving copper rods in the workshop, make sure to visually check whether there is blackening one by one, and control it from the source of production.

1.2 control of copper rod wire drawing process

At this stage, the 8mm copper rod commonly used in power cable z.ui is taken as an example. Nowadays, continuous annealing copper drawing is generally used in wire drawing. It needs to go through the processes of setting out, wire drawing and annealing, cooling, drying and wire take-up. The mold of corresponding specification must not be too small. If it is too small, it will force the lattice variation of metal copper and aggravate the sharp rise of metal temperature.

Check the concentration of emulsion before startup to ensure that the concentration is qualified. In the process of setting out, keep the setting out tension stable and uniform without excessive vibration (vibration is inevitable). During wire drawing, the operator should pay close attention to the change of annealing temperature. After wire drawing, the conductor hardens, the elongation decreases, the DC resistivity of the conductor increases, and there should be no residual emulsion on the surface of copper conductor when wire drawing is waiting to form a circle. Here, the operator needs to identify it with his naked eyes, After drawing the footwall, it is sealed with transparent plastic film and stored in a dry environment for circulation. However, most cable enterprises omit the film wrapping process because of the trouble of copper wire film wrapping. The surface temperature of the conductor just drawn into a circle is higher than the room temperature, and there will be a potential risk of oxidation in rainy season.

1.3 copper wire stranding (bundle stranding) and chemical crosslinking extrusion process

Take copper wire stranding as an example. In the process of conductor stranding, each single wire is strangled by regular stranding or irregular stranding. Under the action of each die, the temperature of the copper conductor after passing the die is greatly higher than that before passing the die, especially the compacted conductor and fan-shaped conductor. At present, there is no on-line annealing or cooling device in the frame strander, so the outer layer of the copper conductor is easy to oxidize. Before stranding, select the appropriate stranding die, compactor and wire arranger, Adjust the take-up and pay off tension. After the equipment is adjusted, the operator shall visually observe the surface finish of the hanging coil copper wire and the central copper wire of the pay off frame to ensure that there are no obvious black spots, and then start the machine.

Generally, cable enterprises will apply antioxidant in the stranding process (frame stranding machine and cage stranding machine). The antioxidant formula is about 0.3% benzotriazole alcohol solution. The operation method is to integrate the antioxidant into industrial alcohol and drip it into the copper wire with an infusion hose. The dripping standard shall be just soaked into the copper wire, so as to avoid too little local potential oxidation or too much waste. Start up and operate after all anti-oxidation work is well prepared.

If the cable reel is filled with transparent film, it will not affect the sealing of the high-voltage cable, which is the same as that of the high-voltage cable. After drawing, stranding and storage of copper conductor, the lattice shape of metal copper has been basically stable. Chemical crosslinking means that XLPE is evenly extruded on the copper conductor under the conditions of crosslinking agent, antioxidant and coupling agent. Adjust the tension of the retractable line before starting the wire tray with copper conductor, so as to ensure the smooth operation of the equipment.

2、 Summary

Almost all cable factories in China are faced with the problem of copper conductor oxidation. In terms of the chemical characteristics of metal copper, it is necessary to maintain the reducibility of metal copper. In daily production, the following measures are taken to reduce the probability of copper conductor oxidation:

1) Select high-quality metal copper rod and standardize the supplier's transportation and delivery process and system. After the copper rod arrives at the company, transparent plastic film sealing measures shall be taken. After the copper conductor is drawn and twisted, transparent plastic film sealing measures shall be taken;

2) Adopt appropriate copper wire drawing process, regularly check the annealing parts of the wire drawing machine, give priority to the wire drawing oil containing antioxidant, regularly check the emulsion concentration, and replace it in advance before the expiration of the warranty period;

3) Passivation treatment technology is adopted for copper wire stranding and Extrusion insulation processes;

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.