Communication cable in the transmission of high-frequency signals, conductors will produce skin effect, and with the increase in the frequency of the transmitted signal, the skin effect is more and more serious. The so-called skin effect refers to the transmission of signals along the outer surface of the inner conductor and the inner surface of the outer conductor of a coaxial cable when the frequency of the transmitted signal reaches several kilohertz or tens of thousands of hertz.
In particular, with the international price of copper soaring and copper resources in nature is becoming more and more scarce, so the use of copper-clad steel or copper-clad aluminium wire to replace copper conductors, has become an important task for the wire and cable manufacturing industry, but also for its promotion with the use of a large market space.
But the wire in the copper plating, due to pre-treatment, pre-plating nickel and other processes, as well as the impact of the plating solution, easy to produce the following problems and defects: wire blackening, pre-plating is not good, the main plating layer off the skin, resulting in the production of waste wire, material waste, so that the product manufacturing costs increase. Therefore, it is extremely important to ensure the quality of the coating. This paper mainly discusses the process principles and procedures for the production of copper-clad steel wire by electroplating, as well as the common causes of quality problems and methods of solution. 1 Copper-clad steel wire plating process and its causes
1. 1 Pre-treatment of the wire
First, the wire is immersed in alkaline and pickling solution, and a certain voltage is applied to the wire (anode) and the plate (cathode), the anode precipitates a large amount of oxygen. The main role of these gases are: one, violent bubbles on the surface of the steel wire and its nearby electrolyte plays a mechanical agitation and stripping effect, thus promoting the oil from the surface of the steel wire, accelerate the saponification and emulsification process of the oil and grease; second, because of the tiny bubbles attached to the interface between the metal and the solution, with the bubbles and steel wire out, the bubbles will be adhering to the steel wire with a lot of oil to the surface of the solution, therefore, on the The bubbles will bring a lot of oil adhering to the steel wire to the surface of the solution, thus promoting the removal of oil, and at the same time, it is not easy to produce hydrogen embrittlement of the anode, so that a good plating can be obtained.
1. 2 Plating of the wire
First, the wire is pre-treated and pre-plated with nickel by immersing it in the plating solution and applying a certain voltage to the wire (cathode) and the copper plate (anode). At the anode, the copper plate loses electrons and forms free divalent copper ions in the electrolytic (plating) bath:
Cu – 2e→Cu2+
At the cathode, the steel wire is electrolytically re-electronised and the divalent copper ions are deposited on the wire to form a copper-clad steel wire:
Cu2 + + 2e→ Cu
Cu2 + + e→ Cu +
Cu + + e→ Cu
2H + + 2e→ H2
When the amount of acid in the plating solution is insufficient, cuprous sulphate is easily hydrolysed to form cuprous oxide. The cuprous oxide is trapped in the plating layer, making it loose. Cu2 SO4 + H2O [Cu2O + H2 SO4
2 The causes of quality problems in the copper plating process and their solutions
2. 1 The influence of pre-treatment of the wire on the plating layer The pre-treatment of the wire is very important in the production of copper-clad steel wire by electroplating. If the oil and oxide film on the surface of the wire is not completely eliminated, then the pre-plated nickel layer is not plated well and the bonding is poor, which will eventually lead to the main copper plating layer falling off. It is therefore important to keep an eye on the concentration of the alkaline and pickling liquids, the pickling and alkaline current and whether the pumps are normal, and if they are not, they must be repaired promptly. The common quality problems in the pre-treatment of steel wire and their solutions are shown in Table
2. 2 The stability of the pre-nickel solution directly determines the quality of the pre-plating layer and plays an important role in the next step of copper plating. Therefore, it is important to regularly analyse and adjust the composition ratio of the pre-plated nickel solution and to ensure that the pre-plated nickel solution is clean and not contaminated.
2.3 The influence of the main plating solution on the plating layer The plating solution contains copper sulphate and sulphuric acid as two components, the composition of the ratio directly determines the quality of the plating layer. If the concentration of copper sulphate is too high, copper sulphate crystals will be precipitated; if the concentration of copper sulphate is too low, the wire will be easily scorched and the plating efficiency will be affected. Sulphuric acid can improve the electrical conductivity and current efficiency of the electroplating solution, reduce the concentration of copper ions in the electroplating solution (the same ion effect), thus improving the cathodic polarisation and the dispersion of the electroplating solution, so that the current density limit increases, and prevent the hydrolysis of cuprous sulphate in the electroplating solution into cuprous oxide and precipitation, increasing the stability of the plating solution, but also reduce the anodic polarisation, which is conducive to the normal dissolution of the anode. However, it should be noted that high sulphuric acid content will reduce the solubility of copper sulphate. When the sulphuric acid content in the plating solution is insufficient, copper sulphate is easily hydrolysed into cuprous oxide and entrapped in the plating layer, the colour of the layer becomes dark and loose; when there is an excess of sulphuric acid in the plating solution and the copper salt content is insufficient, the hydrogen will be partially discharged in the cathode, so that the surface of the plating layer appears spotty. Phosphorus copper plate phosphorus content also has an important impact on the quality of the coating, the phosphorus content should be controlled in the range of 0. 04% to 0. 07%, if less than 0. 02%, it is difficult to form a film to prevent the production of copper ions, thus increasing the copper powder in the plating solution; if the phosphorus content of more than 0. 1%, it will affect the dissolution of copper anode, so that the content of bivalent copper ions in the plating solution decreases, and generate a lot of anode mud. In addition, the copper plate should be rinsed regularly to prevent the anode sludge from polluting the plating solution and causing roughness and burrs in the plating layer.
Through the processing of the above-mentioned aspects, the adhesion and continuity of the product are good, the quality is stable and the performance is excellent. However, in the actual production process, there are many factors affecting the quality of the plating layer in the plating process, once the problem is found, it should be analysed and studied in time and appropriate measures should be taken to solve it.