Control Method for Anti-oxidation of Copper Conductor of Cable

2017-04-25

Metal copper has an atomic number of 29, a density of 8.92g/cm3 and a melting point of 1083.4 ℃, and has good thermal and electrical conductivity. However, in humid air, the surface of metal copper chemically reacts with oxygen to generate Cu2(OH)2CO3, I .e. patina green. Usually, copper oxidation in cable manufacturers mostly shows blackening of the surface. It is the existence of this phenomenon of surface oxidation of cable copper conductors that troubles many cable enterprises.

In our daily production observation and a large number of data research, we found that through the selection of high-quality copper rods, effective control of wire drawing process and emulsion concentration and temperature, passivation treatment of copper conductor stranded or stranded copper wire surface, subsequent process optimization treatment and other means, can effectively control the quality of cable copper conductor, prevent its oxidation, will greatly improve work efficiency, reduce rework frequency, so as to achieve the beneficial effect of reducing cost and improving internal product quality. This article will take the Guangdong Pearl River wire and cable production as an example, from the copper rod to the production plant, storage, wire drawing, stranding, core storage to insulation extrusion, the effective control measures for each step are analyzed.

Cable copper conductor

Anti-oxidation Control of Copper Conductor in 1. Wire and Cable Production

In principle, there are mainly physical methods to block copper from contacting humid air, cathodic protection redox method to prevent oxidation of copper conductor, chemical method to produce passivation film on the surface of copper conductor to prevent oxidation, or to spray special liquid on the surface of conductor to protect it. Taking the production of Guangdong Zhujiang wire and cable as an example, the main method of anti-oxidation control in each process.

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

Most cable enterprises in our country basically purchase copper, while most enterprises often neglect the control of the transportation process of copper poles before entering the factory. In the south of the Yangtze River and coastal areas (Jiangsu, Zhejiang, Fujian and Guangdong), summer is long and rainy, and copper poles are basically transported to the company by heavy trucks. According to the author's understanding, many cable enterprises have not formulated corresponding copper pole supplier transportation specifications, summer rainy day packaging specifications and other systems, this makes it often appear that the surface of the copper rod is intact without oxidation and blackening when the copper rod supplier delivers the goods, while the surface of the copper rod is blackened when it reaches the users of the cable enterprise, which brings unnecessary troubles.

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 the warehouse by cable companies. General companies have stricter storage management methods. When copper rods are stored, especially in rainy summer, the copper rods must be covered with plastic sheets or plastic films, and the simplest physical barrier method is used to prevent the copper rods from contacting with humid air, which is often ignored by cable companies. When collecting copper rods in the workshop, it is necessary to check whether there is blackening phenomenon one by one and control it from the source of production.

Control of 1.2 copper rod wire drawing process

In this stage, the most commonly used 8mm copper rod for power cables is taken as an example. Nowadays, continuous annealed copper rod is generally used for wire drawing. It needs to go through the processes of setting-out, wire drawing and annealing, cooling, drying, wire taking-up, etc. It is preferred to select the mold of corresponding specifications. It must not be too small. If it is too small, it will force the crystal lattice of metal copper to change and aggravate the sharp rise of metal temperature.

Check the concentration of emulsion before starting up to ensure that the concentration is qualified. During the setting-out process, the setting-out tension should be kept stable and uniform without excessive vibration (vibration is inevitable). During the drawing process, the operator should pay close attention to the change of annealing temperature. After 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 the copper conductor when drawing is looped, after drawing the lower plate, it is sealed with transparent plastic film and stored in a dry environment to be circulated. However, most cable enterprises omit the film wrapping process because they think it is troublesome to wrap the film with copper wire. The surface temperature of the conductor that is just drawn into the loop is higher than the room temperature, and there is a potential risk of oxidation in case of rainy season.

1.3 copper wire stranding (bundle stranding) and chemical cross-linking extrusion process

Taking copper wire stranding as an example, in the process of conductor stranding, the monofilaments are stranded in regular stranding or irregular stranding. Under the action of each die, the temperature of the copper conductor after overmolding is greatly improved compared with that before overmolding, especially the compacted conductor, fan-shaped conductor, etc., and the frame stranding machine has no on-line annealing or cooling device at present, so the copper outer conductor is easy to oxidize, select the appropriate stranding die, tightening wheel and wire arrangement, adjust the tension of take-up and pay-off. After the equipment is adjusted, the operator shall visually observe the surface finish of the upper copper wire and the copper wire in the center of the pay-off frame to ensure that there are no obvious black spots, and then start the machine.

General cable enterprises will apply antioxidant in the stranding process (frame stranding machine, cage stranding machine). The formula of antioxidant is about 0.3% benzotriazole alcohol solution. The operation method is to blend antioxidant into industrial alcohol and drip into copper wire with infusion hose. The dripping standard is based on just infiltrating copper wire, so as to avoid too little local potential oxidation or too much waste. After all anti-oxidation work is prepared properly, start up the machine again.

The take-up place should ensure that the take-up reel is dry. After the take-up reel is full, it is sealed with transparent plastic film. Similarly to copper wire drawing, many cable enterprises also omit this step. If this step causes oxidation of copper conductor, the impact on low-voltage cables is still low, and on ultra-high voltage cables, the impact is unimaginable. After the copper conductor is drawn, stranded and stored, the metal copper lattice morphology has been basically stable. Chemical crosslinking means that XLPE is uniformly extruded on the copper conductor under the conditions of crosslinking agent, antioxidant, coupling agent, etc. Before starting the pay-off reel full of 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 our country are faced with the problem of copper conductor oxidation. From the chemical characteristics of copper metal, it is necessary to maintain the reducibility of copper metal. In daily production, the use of Guangdong Zhujiang wire and cable the following measures can reduce the probability of copper conductor oxidation:

1), select high-quality metal copper rod, standardize the supplier's transportation, delivery process and system, copper rod to the company, take transparent plastic film sealing measures, copper conductor drawing, stranding should take transparent plastic film sealing measures;

2), the use of appropriate copper wire drawing process, regular inspection of the annealing parts of the wire drawing machine, priority selection of antioxidant-containing wire drawing oil, regular inspection of emulsion concentration, the expiration of the shelf life must be replaced in advance;

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

4), establish quality awareness, strengthen business training to make the above process operators aware of the adverse consequences of copper wire oxidation.

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Control Method for Anti-oxidation of Copper Conductor of Cable

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