What is barrel plating?

Barrel plating and The biggest difference in rack plating of small parts is that it uses a roller, which is a material holding device that carries the small parts to be plated during the continuous tumbling process. The typical roller is in the shape of a hexagonal prism and placed horizontally. One side of the wall of the drum is open, a certain number of small parts are loaded into the drum from the opening during electroplating, and then the drum door is covered to close the opening. There are many small holes on the wall of the drum. During electroplating, the current between the parts and the anode is conductive, and the solution inside and outside the drum is connected. Renewal and exhaust gas must pass through these small holes. The cathode conductive devices in the drum are passed through the central shaft holes on both sides of the drum through copper wires or rods, and then respectively fixed on the conductive feet of the left and right wall panels of the drum. The parts are naturally connected to the cathode conductive device in the drum by their own gravity. Barrel plating of small parts is carried out in such a device. Many factors such as the structure, size, size, rotation speed, conduction mode and opening rate of the drum are related to the production efficiency of barrel plating and the quality of the coating. Therefore, the drum is one of the focuses of the entire barrel plating technology research.

Barrel plating is The small parts are constantly tumbling in the process

When barrel plating , The small parts are not stationary in the drum, but they must roll continuously with the rotation of the drum. This kind of tumbling is specific to a certain part: it is buried inside the entire stacked part for a while, and then turned to the outer surface for a while. This repeats until the end of the entire barrel plating process.

So, why Want to keep small parts tumbling in the drum?

(1) Ensure that each part can be evenly plated. Small parts are stacked together in the drum, some of which are distributed inside the stack, called inner parts; the other part is distributed on the outer surface of the stack, called surface parts (as shown in Figure 1) . During barrel plating, the main metal ions are actually only reduced on the surface of the surface parts to form a metal coating, while the inner parts are affected by the shielding and shielding of the surface parts and only current passes through, but almost no electrochemical reaction occurs. Therefore, in order to have the opportunity to be plated, the inner layer parts need to be turned out from the inside of the stack to become surface layer parts. The surface parts cannot stay for a long time. After the electroplating process is carried out for a while, they become inner parts again by the rotation of the drum. In this way, only by constantly rolling small parts, can the inner and surface parts be continuously changed and converted, and ultimately ensure that each part has the opportunity to be evenly plated.

(2) Avoid “burning” or “scorching” of surface parts. If the small parts are in a static state without rolling in the drum, the use of a small current density may cause the lack of metal ions near the surface parts and cause “scorching”. Especially the surface parts close to the wall of the drum will hinder the current entering the drum from the holes, and concentrate on the narrow surface of the parts close to the holes, causing the coating to burn and leave black eye spots, the so-called so-called “Cylinder eye print”. At this time, the effect of the small parts rolling in the drum is similar to the stirring of the rack plating solution or the movement of the cathode. If there is no effect of stirring the solution or moving the cathode during rack plating, the upper limit of the current density is not easy to increase, and the deposition rate of the coating layer is also difficult to increase.

When barrel plating The electric current required by small parts is transmitted in an indirect way.

When plating , The current required by the parts is directly transmitted by the hanger, and the parts are in close contact with the hanger without any medium in between. Therefore, the current transmission of rack plating is stable, the contact resistance is small, and the current obtained by each part is basically not different due to transmission problems. However, during barrel plating, the parts are integrally pressed on the cathode conductive device in the drum, and there are only a few parts directly connected to the cathode conductive device, and most of them can only be connected to the cathode by stacking and overlapping parts. Therefore, the cathode conductive device in the drum can only deliver the current to the parts that are in direct contact with itself, and then can transmit the current from these parts to other parts, and transfer them one by one between other parts. This is barrel plating. The indirect conduction method. This indirect conduction method is undoubtedly another important feature of barrel plating. Because it mainly relies on the indirect conduction between the parts and the parts, rather than the direct contact between the parts and the cathode, the contact resistance of the parts during barrel plating is correspondingly higher than that of rack plating