The particularity of wire processing industry makes its requirements for copper plating process different from that of conventional copper plating of steel parts. Therefore, how to choose a copper plating process suitable for wire processing is a very important issue.
Usually, the basis for selecting the electroplating process is the first requirement of the coating product itself. That is, the product is processed first, and then electroplating. Such as thickness, brightness, hardness and dispersion ability. Some also have requirements for current efficiency and deposition speed. Then look at the pre-plating layer, intermediate coating and surface coating of the required copper plating.
The characteristic of wire processing and electroplating is that the wire processing and electroplating process are sometimes carried out simultaneously. That is, some are first drawn and then plated, and some are first plated and then drawn. Even the electroplating of the finished wire is carried out under the traction of the take-up machine. In addition to the requirements for the coating layer according to the different uses of the wire, the selected process should also consider the adaptability of the electroplater to factors such as the running speed of the wire, the number of traction heads, and the length of the processing line.
For CO2 gas shielded welding wire, due to the strict limit on the amount of copper adhesion on the welding wire, for example, the copper content per unit volume should be within 0.52 (mass fraction) of the solder, which is a very thin coating, and the chemical immersion method is used. Replacement copper plating can meet the requirements, but due to the traditional method used in China to replace copper plating, its bonding force and coating color can not meet the product requirements. And in practice, the process of first dip plating and then drawing is adopted, so that the copper layer is extended and thinned during the drawing to meet the product requirements. In this method, the coating layer is often peeled off and the bottom is exposed. Therefore, it is very important to choose a copper plating process with good bonding force and ductility for gas shielded welding wire.
Before there is a new process that can make the finished wire successfully electroless copper plating at one time, it is still only possible to use the process of first drawing to the middle wire diameter, then copper plating and then drawing into the finished product. Suitable for this process should be cyanide copper plating or matt acid copper plating. Because cyanide is too toxic, it has been rarely used in the metallurgical wire processing industry. At present, the more popular method is still to thicken the copper after chemical immersion copper and then draw. The thickened copper plating used is acid copper plating or pyrophosphate copper plating. In the flat wire processing industry, chemical copper plating is also often used.
The traditional replacement copper plating uses the process of copper sulfate plus sulfuric acid. Only a very thin coating can be replaced in a very short period of time. When the copper plating is thickened on it, the bonding force is not strong. If the immersion time in this chemical displacement plating is too long, not only will the thickness of the coating not be increased, but the coating will become loose and porous, the iron matrix will be corroded, and the strength of the wire will be greatly reduced. The improved method is to add additives with surface retardation to the replacement copper plating solution, so that the replacement process can be carried out in an orderly manner. The ideal additive also has a certain brightening effect.
For wire products that require a certain thickness or even a thicker coating, be very careful with the replacement coating. For thick copper plating, a reliable process should still be electrochemical pre-plating, at least until there is no primer process that can be reliably adapted to the plating of thick copper layers. Mature pre-plating processes include cyanide copper plating nickel plating and high P ratio pyrophosphate copper plating. Weighing various advantages and disadvantages, in the wire drawing and electroplating industry, it is better to use nickel plating as a pre-plating base. For thicker copper plating, acid sulfate copper plating can be used. This is because after process adjustment, acid copper plating can meet the requirements of high-speed electroplating. The current density can reach 30-50A/dm2, which greatly improves the deposition rate. In contrast, cyanide copper plating is not suitable for use due to environmental pollution problems, and pyrophosphate copper plating is not only expensive because of its complex composition, but also unsuitable for working under high current. The test shows that in the high-speed electroplating in acid copper plating, when the current density increases, the deposition rate of the coating also increases at the same time, and the approximate relationship is shown in Table 1.