The particularity of the wire processing industry makes the requirements of the copper plating process different from the conventional copper plating of steel parts. Therefore, how to choose a copper plating process suitable for wire processing is a very important subject. Generally, the basis for selecting the plating process is first of all the requirements of the plating product itself on the plating layer. That is, the product is processed first, and then electroplated. Such as thickness, brightness, hardness and dispersion ability. Some are right …
The particularity of the wire processing industry makes the requirements of the copper plating process different from the conventional copper plating of steel parts. Therefore, how to choose a copper plating process suitable for wire processing is a very important subject.
Generally, the basis for selecting the plating process is first of all the requirements of the plating product itself on the plating layer. That is, the product is processed first, and then electroplated. Such as thickness, brightness, hardness and dispersion ability. Some also have requirements for current efficiency and deposition speed. Then look at the required pre-plating, intermediate plating and surface plating of copper plating.
The characteristic of wire processing electroplating is that the wire processing and electroplating are sometimes carried out simultaneously. That is, some are drawn first and then plated, and some are plated and then drawn. Even the electroplating of the finished silk is carried out under the traction of the take-up machine. In addition to the requirements for the coating according to the different uses of the wire, the selected process also needs to consider the adaptability of the electroplater to the walking speed of the wire, the number of traction heads, and the length of the processing line.
For the CO2 gas shielded welding wire, due to the strict limit on the amount of copper adhesion on the wire, for example, the copper content per unit volume should be within 0.52 (mass fraction) of the solder, which is an extremely thin coating. The chemical immersion method is used. The replacement of copper plating can meet the requirements, but due to the traditional method of replacement copper plating currently used in China, its binding force and plating color can not meet the product requirements. And in practice, the process of first immersion plating and then drawing is used to make the copper layer stretch and thin during drawing to meet the product requirements. In this method, the coating is often peeled off and the bottom is exposed. Therefore, it is very important for the gas shielded welding wire to choose a copper plating process with good bonding force and ductility.
Before the emergence of a new process that enables successful one-time electroless copper plating of the finished wire, the process of first drawing to the middle wire diameter and then copper plating can be used to complete the finished product. Suitable for this process should be cyanide copper plating or matte acid copper plating. Because cyanide is too toxic, few people have adopted it in the metallurgical wire processing industry. At present, the more popular method is still to thicken the copper plating and then pull out after chemical copper immersion. The thickened copper plating used is acid copper plating or pyrophosphate copper plating. In the flat wire processing industry, copper plating is also used chemically.
The traditional replacement copper plating uses copper sulfate plus sulfuric acid. Only a very short period of time can be replaced by a very thin plating layer, when the copper plating is thickened on the top, the bonding force is not strong. If the immersion time in this chemical substitution plating is too long, it will not only increase the thickness of the coating, but also make the coating loose and porous, the iron matrix will also corrode, and the strength of the wire will be greatly reduced. The improved method is to add additives with surface blocking effect to the replacement copper plating solution to make the replacement process orderly. The ideal additive also has a certain brightening effect.
For wire products that require a certain thickness or even a thick coating, be very careful to use a replacement coating as a primer. At least until there is no reliable primer process for thick copper plating, for thick copper plating, the reliable process should still be pre-plated using electrochemical methods. The mature pre-plating process includes cyanide copper plating nickel plating and high P ratio pyrophosphate copper plating. Weighing various advantages and disadvantages, in the wire drawing electroplating industry, it is better to use nickel plating as a pre-plating primer. For thick 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 increases the deposition speed. In contrast, cyanide copper plating is not suitable for environmental pollution problems, and pyrophosphate copper plating is not only expensive due to its complex composition, but also not suitable for working under high currents. Tests have shown that in high-speed electroplating in acid copper plating, when the current density increases, the deposition rate of the coating also increases.