Discussion on the control method of anti-oxidation of cable copper conductor

preface

Metal copper atomic number is 29, belonging to the transition metal, density is 8.
92g/cm3, melting point 1083.
4 °C, with good thermal and electrical conductivity, but in the humid air metal copper surface and oxygen chemical reaction, the formation of Cu2 (OH) 2CO3, that is, patina, usually in the cable production plant copper oxidation shows the surface blackening, it is the existence of this copper conductor surface oxidation phenomenon, plague many cable companies
.

In our daily production observation and a large number of data investigations, 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 stranding or stranded copper wire surface, follow-up process optimization treatment, etc.
, will effectively control the quality of cable copper conductors, prevent their oxidation, greatly improve work efficiency, reduce the frequency of rework, so as to achieve the beneficial effect
of reducing costs and improving intrinsic product quality.
In this paper, the production of medium-voltage power cables will be used as an example, from the arrival of copper rods to the production plant, storage, wire drawing, stranding, core storage to insulation extrusion, and the effective control measures at each step are analyzed
.

First, the anti-oxidation control of copper conductors in the production process of medium voltage power cables

In principle, the metal copper for cables mainly has physical methods to block the contact between copper and humid air, cathodic protection redox method to prevent copper conductor oxidation, chemical method to produce a passivation film on the surface of the copper conductor to prevent oxidation, or spray special liquid on the surface of the conductor for protection
.
Taking the production of medium voltage power cables as an example, the main method
of anti-oxidation control in each process.

1.
1 Transportation, testing and storage of copper rods before entering the factory

Most of China's cable enterprises with copper basic purchase, and most enterprises often ignore the control of the transportation process before the copper rod enters the factory, in the south and coastal zone (Jiangsu, Zhejiang, Fujian and Guangdong) summer is longer and rainy, copper rod is basically transported to the company by heavy truck, through the author understands, many cable companies have not developed the corresponding copper rod supplier transportation specifications, summer rainy weather packaging specifications and other systems, which makes often appear copper rod suppliers when the surface of the copper rod is intact without oxidation blackening, When it reaches the cable enterprise user, the surface of the copper rod is blackened, which brings unnecessary trouble
.

The inspection of copper rods into the factory is basically in accordance with GB/T 3048.
2 or cable enterprise standards, and there are strict procedures
.
The storage of copper rods is generally placed in the warehouse, the general enterprise has more strict storage management methods, in the copper rod storage, especially in the summer rainy days, must be covered with plastic sheet or plastic film, with the simplest physical barrier method to prevent the copper rod and humid air contact system, and this point is often ignored
by cable companies.
When receiving copper rods in the workshop, it is necessary to visually check whether there is blackening phenomenon by naked eye one by one copper rod rolls, and control
them from the source of production.

1.
2 Control of copper rod wire drawing process

At this stage, the most commonly used 8mm copper rod of power cables is an example, now the continuous annealed copper pulling is generally used when drawing wire, it is necessary to go through the process of paying, wire drawing and annealing, cooling, drying, receiving and other processes, the first choice is to select the mold of the corresponding specifications, must not be too small, such as too small will force the lattice of metal copper to change, aggravate the sharp rise
of metal temperature.

Check the concentration of emulsion before starting, to ensure that the concentration is qualified, in the process of paying, should keep the pay-off tension stable, uniform, not excessive chatter (chatter is inevitable), the operator should pay close attention to the change of annealing temperature during the wire drawing process, the conductor hardens after wire drawing, the elongation becomes smaller, the DC resistivity of the conductor rises, there should be no residual emulsion on the surface of the copper conductor when the wire drawing is waiting for the circle, here the operator needs to be visually identified, sealed with a transparent plastic film after the wire drawing disc, stored in a dry environment, to be circulated, However, most cable companies omit the film wrapping process
because of the trouble of copper wire wrapping film.
The surface temperature of the freshly drawn conductor is higher than room temperature, which is a potential risk
of oxidation during the 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, each monofilament is twisted in a regular twisting or irregular stranding, etc.
, after each pressing die metal copper lattice changes the structure, under the action of strong external force, the temperature of the copper conductor after the mold is greatly improved than before the mold, especially the tight conductor, sector conductor, 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, before stranding, select the appropriate stranding mold, pressing wheel, wire arranger, adjust the tension of 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 copper wire in the center of the pay-off frame to ensure that there are no obvious black spots, and then starts the machine
.

General cable companies will apply antioxidants 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 integrate the antioxidant into the industrial alcohol, with the infusion hose dripping into the copper wire, the drop standard is just infiltrated with the copper wire, to avoid too little local potential oxidation or too much waste phenomenon, after all anti-oxidation work is prepared securely, then start the operation
.

The take-up should ensure that the take-up reel is dry, after the take-up reel is full, sealed with a transparent plastic film, the same as copper wire drawing, many cable companies also omit this step, if this step causes copper conductor oxidation, the impact on low-voltage cables is still low, for ultra-high-voltage cables, the impact is unimaginable
.
After the copper conductor is drawn, stranded and stored, the metal copper lattice form has been basically stable
.
Chemical crosslinking is to uniformly squeeze XLPE on the copper conductor under the conditions of crosslinker, antioxidant, couplant and so on
.
Before starting the pay-off reel filled with copper conductors, adjust the retract and pay-off tension to ensure smooth operation of the equipment
.

II.
Summary

Almost all cable factories in China are facing the problem of copper conductor oxidation, from the metal copper chemical characteristics, is to maintain the reduction of metal copper
.
In daily production, the following measures can reduce the chance of oxidation of copper conductors:

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

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

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

4) Establish quality awareness, strengthen business training, and let the operators of the above processes understand the adverse consequences
of copper wire oxidation.

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