The main methods for preventing oxidation of rubber-sheathed cable conductors

Copper is the main raw material in the cable industry, but it is easily oxidized into black CuO by oxygen in the air under acidic conditions. When there is a water film or water droplets on the surface of the copper conductor, due to the presence of a large amount of dust in the atmosphere, such as smoke, coal, vehicle exhaust, chlorides and other acid, alkali and salt particle dust, these harmful substances dissolve in the water film or water droplets and can form an electrolyte. This will intensify the oxidation discoloration of copper conductors.

General-purpose rubber-sheathed cables use category 5 copper conductors as the conductive core. During their production process, it is often found that the copper conductors oxidize and discolor, which seriously affects the quality of the products and has become a long-standing technical problem for many domestic cable manufacturers. Below, Zhujiang Cable takes the production of general-purpose rubber-sheathed cables as an example to explore how to prevent the oxidation of rubber-sheathed cable conductors.

Transportation, inspection and storage of copper rods before they enter the factory

Most cable enterprises in our country should choose high-quality metal copper rods for copper use, standardize the transportation and delivery processes and systems of suppliers, and the inspection of copper rods upon entry to the factory shall be carried out in accordance with GB/T 3048.2 or the enterprise standards of cable enterprises. Copper rods can be stored by covering them with plastic sheeting or plastic film, and simple physical barrier methods can be used to prevent the copper rods from coming into contact with moist air. When the workshop takes out copper rods, it is essential to visually inspect each copper rod roll for any blackening to control the production from the source.

2. Control of the copper rod wire drawing process

The drawing of 0.4mm single wire generally adopts large and small copper drawing machines with continuous annealing, and it needs to go through processes such as wire laying, wire drawing and annealing, cooling, drying and winding. First of all, a suitable mold should be selected. It must not be too small; otherwise, it will force the lattice variation of the metal copper and accelerate the sharp rise in metal temperature. Secondly, before starting the machine, check the pH level of the emulsion to ensure it is an alkaline solution. At the same time, antioxidants should be added to the wire drawing oil to form a passivation film on the surface of the copper conductor and prevent oxidation. When laying out the wires, keep the tension stable and uniform, and avoid excessive vibration. During the wire drawing process, the operator should ensure an appropriate water level height, guarantee uniform annealing degree, and avoid insufficient or excessive annealing. When winding the wire, there should be no residual liquid on the surface of the copper conductor. A dry felt (replaced frequently) can be placed in front of the winding to ensure the dryness of the single wire. Finally, after drawing the lower coil, seal it with transparent plastic film and store it in a dry environment for circulation. Otherwise, due to the high surface temperature of the conductor, there is a risk of oxidation with moist air.

3. Copper wire stranding (bundle stranding) and extrusion process of insulating rubber and sheath rubber

Take copper wire stranding as an example. During the stranding process, the copper lattice structure of the metal changes after passing through each die. Under the action of strong external force, the temperature of the copper conductor after passing through the die is significantly higher than that before passing through the die. Therefore, the outer layer of the copper conductor is prone to oxidation. Therefore, during the twisting process, the antioxidant can be dropped into the copper wire using an infusion hose. The drop standard should be just enough to wet the surface of the copper wire to avoid local oxidation due to too little or waste due to too much. After all the anti-oxidation preparations are in place, the machine can be started and operated. The winding point should ensure that the winding reel is dry. After the winding reel is full, it should be sealed with transparent plastic film.

Before extruding and insulating the conductor, polyester tape should be longitudinally wrapped or wound to prevent substances in the rubber insulating material from corroding the conductor. During the extrusion process of insulating rubber and sheathed rubber, it is necessary to prevent water from entering the thread ends to avoid oxidation and blackening of the thread ends. In our daily production observations, we have found that by choosing copper rods, effectively controlling the wire drawing process and the concentration and temperature of the emulsion, the annealing process, the passivation treatment of the surface of the conductor twisted or bundled copper wire, and preventing water from entering the wire ends, in addition, the workshop operators should establish a quality awareness, strengthen business training, and be able to clearly recognize the adverse consequences brought about by the oxidation of copper wire. Only by strictly controlling the quality can the quality of copper conductors in cables be effectively controlled, preventing their oxidation, which greatly improves work efficiency, reduces the frequency of rework, and thus achieves the beneficial effects of cost reduction and improvement of the intrinsic product quality.