Method For Preventing Oxidation Of Conductor

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

In our daily production observation and a large amount of data investigation, we found that by means of high-quality copper rod selection, effective control of wire drawing process and emulsion concentration and temperature, passivation treatment of copper conductor stranded or bundle stranded copper wire surface, and optimization treatment of subsequent processes, 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. Taking the wire and cable production in Zhujiang, Guangdong Province as an example, this paper analyzes the effective control measures in each step from the arrival of copper rods at the production plant, storage, wire drawing, stranding, inner core storage to insulation extrusion.

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. Taking the production of wires and cables in Zhujiang, Guangdong Province as an example, the main methods of anti-oxidation control in each process are introduced.

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 The packaging specifications and other systems in rainy days in summer often make 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 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 production source.

1.2 control of copper rod wire drawing process

At this stage, the 8mm copper rod commonly used in power cable Z is taken as an example. Nowadays, continuous annealing copper drawing is generally used in wire drawing, which needs to go through the processes of setting out, wire drawing and annealing, cooling, drying and wire take-up. It is preferred to select the mold of corresponding specification, which 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. During setting out, keep the setting out tension stable and uniform without excessive vibration (vibration is inevitable). During wire drawing, the operator shall pay close attention to the change of annealing temperature. After wire drawing, the conductor hardens, the elongation decreases, and the DC resistivity of the conductor increases, There should be no residual emulsion on the surface of copper conductor during wire drawing, which needs to be identified by the operator with naked eyes. After wire drawing, it should be sealed with transparent plastic film and stored in a dry environment for circulation. However, most cable enterprises omit the film wrapping process because it is troublesome for copper wire to wrap film. The surface temperature of the conductor just drawn into a circle is higher than the room temperature, which may lead to potential oxidation risk 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 stranded 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, the frame strander has no on-line annealing or cooling device, so the outer layer of the copper conductor is easy to oxidize. Before stranding, Select the appropriate stranding die, pressing wheel and wire setter, and adjust the take-up and setting out tension. After the equipment is adjusted, the operator shall visually observe the surface finish of the hanging 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 antioxidants in the stranding process (frame stranding machine and cage stranding machine). The formulation of antioxidants is about 0.3% benzotriazole alcohol solution. The operation method is to integrate the antioxidants into industrial alcohol and drip them into copper wire with infusion hose. The dripping standard shall be just soaked copper wire, so as to avoid too little local potential oxidation or too much waste, After all anti-oxidation work is well prepared, start the machine for operation.

The take-up reel shall be dry. After the take-up reel is full, it shall be sealed with transparent plastic film, which is the same as copper wire drawing. Many cable enterprises also omit this step. If this step causes copper conductor oxidation, the impact on low-voltage cables is still low, and the impact on ultra-high voltage cables is unimaginable. 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 copper conductor under the conditions of crosslinking agent, antioxidant, coupling agent, etc. 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, standardize the supplier's transportation and delivery process and system, take transparent plastic film sealing measures after the copper rod arrives at the company, and take transparent plastic film sealing measures after the copper conductor is drawn and twisted;

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.