Process control of copper conductor antioxidation

Are you still confused for copper antioxidation when using copper wire drawing machine and cable making machine?

Check the whole process control of copper conductor antioxidation

We take the production of medium voltage power cables as an example, from the arrival of copper rods to the production plant, storage, wire drawing, stranding, inner core storage to insulation extrusion, and analysis of effective control measures for each step.

▎Anti-oxidation control of copper conductors in the production process of medium voltage power cables

In principle, the metal copper used for cables mainly includes physical methods to block copper from contact with moist air, cathodic protection redox method to prevent oxidation of copper conductors, chemical methods to produce passivation film on the surface of copper conductors to prevent oxidation, or spray special liquids on the surface of the conductors. protection. Take the production of medium voltage power cables as an example, the main method of anti-oxidation control in each process.

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

Most cable companies in China use copper outsourcing, but most companies often ignore the control of the transportation process of copper rods before they enter the factory. In the south of the Yangtze River and coastal areas (Jiangsu, Zhejiang, Fujian and Guangdong), the summer is long and rainy, and copper rods are basically passed by heavy trucks. Transported to the company, through the author's understanding, many cable companies have not formulated the corresponding copper rod supplier transportation specifications, summer rainy packaging specifications and other systems, which makes it often happen that the copper rod surface is intact without oxidation and blackening when the copper rod supplier delivers the goods. When it reaches the cable enterprise user, the surface of the copper rod appears black, which brings unnecessary trouble.

The inspection of copper rods in the factory is basically in accordance with GB/T 3048.2 or the corporate standard of cable enterprises, with strict procedures. The storage of copper rods is generally stored in warehouses by cable companies. Generally, companies have stricter storage management methods. When storing copper rods, especially in rainy summer, you must cover the copper rods with plastic sheeting or plastic film. The physical barrier method prevents the copper rod from contacting the humid air, which is often ignored by cable companies. When using copper rods in the workshop, it is necessary to visually inspect the copper rod rolls one by one for blackening, and control it from the source of production.

▶ Control of copper rod drawing process

At this stage, the most commonly used 8mm copper rod for power cables is taken as an example. Nowadays, continuous annealed copper rods are generally used for wire drawing, which needs to go through the processes of wire drawing, wire drawing and annealing, cooling, drying, and wire take-up. It is preferred to select the corresponding specifications The mold must not be too small. If it is too small, it will force the crystal lattice of the metal to mutate 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 (vibration is inevitable). The operator should pay close attention to the change of annealing temperature during the drawing process. After the wire is drawn, the conductor hardens, the elongation becomes smaller, and the DC resistivity of the conductor rises. When the wire is drawn, there should be no residual emulsion on the surface of the copper conductor. The operator needs to recognize it with naked eyes. After the wire is drawn, the bottom plate is sealed with a transparent plastic film. Stored in a dry environment, waiting for circulation, but most cable companies omit the filming process because of the trouble of copper wire coating. The surface temperature of the conductor that has just been drawn into a loop is higher than room temperature, which may potentially be oxidized in the rainy season.

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

Take copper wire stranding as an example. In the conductor stranding process, each monofilament is twisted in a regular or irregular twisting manner. After each compression mold, the metal copper lattice changes its structure, and under the action of strong external force , The temperature of the copper conductor after over-molding has been greatly increased compared with that before over-molding, especially compact conductors, sector conductors, etc., 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, and it is easy to oxidize before stranding. , Select the appropriate stranding mold, pinch wheel, and wire arranging device to adjust the tension of the wire take-up and pay-off. After the equipment is adjusted, the operator visually observes the surface finish of the copper wire on the upper plate and the center copper wire of the pay-off rack to ensure that there is no Obviously black spots, then start the machine.

Generally, cable companies will apply antioxidants in the stranding process (frame stranding machine, cage stranding machine). The formulation of the antioxidant is about 0.3% benzotriazole alcohol solution. The operation method is to incorporate the antioxidant into the industry. In the alcohol, use an infusion hose to drip into the copper wire. The dripping standard is based on the infiltration of the copper wire to avoid too little local potential oxidation or excessive waste. After all anti-oxidation work is prepared, restart the machine. Running.

The take-up place should ensure that the take-up reel is dry. After the take-up reel is filled, it is sealed with a transparent plastic film. This is the same as the copper wire drawing. Many cable companies also omit this step. If this step causes the copper conductor to oxidize, it will affect the low voltage. The impact of cables is still low, and for UHV cables, the impact is unimaginable. After the copper conductor is drawn, stranded, and stored, the metallic copper lattice shape is basically stable. Chemical cross-linking means that XLPE is uniformly 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 line to ensure the smooth operation of the equipment.

▎Summary

Almost all cable factories in our country are facing the trouble of copper conductor oxidation. From the perspective of the chemical properties of metal copper, it is to maintain the reducibility of metal copper. In daily production, the following measures can reduce the chance of copper conductor oxidation:

1) Choose high-quality metal copper rods, standardize the supplier's transportation and delivery procedures and systems. After the copper rods arrive at the company, adopt transparent plastic film sealing measures, and adopt transparent plastic film sealing measures after copper conductors are drawn and stranded;

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

3) The copper wire stranding and extruding insulation process adopts passivation treatment technology;

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