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2020-10

Selection of copper-clad steel plating process

The special nature of wire processing requires different copper plating processes than those used for conventional steel parts. Therefore, selecting a suitable copper plating process for wire processing is a crucial issue. The choice of electroplating process usually depends primarily on the requirements for the coating of the product itself. That is, the product is processed first, then electroplated. For example, thickness, brightness, hardness, and dispersion ability. Some also have requirements for current efficiency and deposition rate. Then there is the required pre-plating, intermediate plating, and surface plating. The characteristic of wire electroplating is that the wire processing and electroplating processes are sometimes carried out simultaneously. That is, some are plated after drawing, and some are drawn after plating. Even the electroplating of finished wires is carried out under the traction of the wire-taking machine. The selected process, in addition to the requirements for the coating according to the different Applications of the wire, must also consider the adaptability of the electroplating process to factors such as the wire running speed, the number of traction heads, and the length of the processing line. For CO2 gas-shielded welding wires, due to the strict limitation on the amount of copper attached to the welding 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, i.e., displacement copper plating, can meet the requirements. However, due to the traditional displacement copper plating method currently used in China, its bonding strength and coating color cannot meet the product requirements. In practice, the process of first immersion plating and then drawing is adopted, so that the copper layer is expanded and thinned during drawing to meet the product requirements. This method often results in coating peeling and base metal exposure. Therefore, selecting a copper plating process with good bonding strength and ductility is crucial for gas-shielded welding wires. Until a new process that enables successful one-time chemical copper plating of finished wires appears, the process of drawing to an intermediate wire diameter, copper plating, and then drawing into a finished product can only be used. Cyanide copper plating or dull acid copper plating should be suitable for this processing process. Due to the high toxicity of cyanide, it is rarely used in the metallurgical wire processing industry. The currently more popular method is still chemical immersion copper plating followed by thickening copper plating and then drawing. The thickening copper plating used is acid copper plating or pyrophosphate copper plating. The chemical method is also mostly used for copper plating in the flat wire processing industry. Traditional displacement copper plating uses a process of copper sulfate plus sulfuric acid. Only a very thin coating can be displaced in a very short time, and the bonding strength is not strong when the copper is thickened on top. If the immersion time is too long in this chemical displacement plating, not only will the coating thickness not increase, but the coating will also become loose and porous, and the iron substrate will also be corroded, greatly reducing the wire strength. The improved method is to add additives with surface retarding effects to the displacement copper plating solution to make the displacement process proceed 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, the use of displacement plating as a base layer must be very careful. At least until a reliable base plating process suitable for thick copper plating is available, for thick copper plating, the reliable process should still be electrochemical pre-plating. Mature pre-plating processes include cyanide copper nickel plating and high P ratio pyrophosphate copper plating. Weighing the various advantages and disadvantages, nickel plating is better as a pre-plating base in wire drawing electroplating. The thickening copper plating can use acid sulfate copper plating. This is because, after process adjustment, acid copper plating can meet the requirements of high-speed electroplating. The current density can reach 30-50 A/dm2, greatly increasing the deposition rate. In comparison, cyanide copper plating is not suitable due to environmental pollution problems, while pyrophosphate copper plating is not suitable for high-current operation due to its complex composition and high cost. Tests show that in high-speed electroplating in acid copper plating, when the current density increases, the deposition rate of the coating also increases simultaneously, and the approximate relationship is shown in Table 1.

2020-10-30

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12

2021-01

Culture - Warm congratulations to Xinying FC on winning the 2020-2021 Leqing City Five-a-Side Football League C-League Championship

  Hearty congratulations to Xinying FC on winning the championship of the Yueqing City 2020-2021 five-a-side C-league    

2021-01-12

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