Plating Classroom: Basic Characteristics of Roll Plating-B

So, why is it important to keep the small parts tumbling in the drum?

(1) To ensure that each part can be evenly plated. Small parts in the drum is stacked together, which part of the parts are distributed in the stack of the body of the interior, known as the inner layer of parts; the other part of the parts are distributed in the stack of the body of the outer surface, known as the surface layer of parts (as shown in Figure 1). When tumbling plating, the main metal ions actually only in the surface parts of the surface layer of the reduction of the formation of metal plating, and the inner layer of parts due to the shielding of the surface layer of parts, blocking and other effects of the only current through, but almost no electrochemical reaction occurs. Therefore, in order to have a chance to be plated, it is necessary for the inner parts to be turned out from the inside of the stack to become the surface parts. The surface layer parts cannot stay for a long time, and after plating for a while, they are turned into the inner layer parts by the rotation of the drum. In this way, the small parts can only be rolled over continuously to promote the inner parts and surface parts to change and transform, and ultimately ensure that each part has the opportunity to be plated uniformly.

(2) Avoid “blackening” or “scorching” of surface parts. If small parts are not tumbled inside the drum and are in a stationary state, the use of a small current density may result in a lack of metal ions in the vicinity of the surface parts and produce the phenomenon of “scorching”. Especially close to the drum wall plate of the surface parts, will make the current from the eyelet into the drum is impeded, and thus concentrated in the parts close to the eyelet part of the narrow surface, resulting in the plating layer burnt leaving black eyes, that is, the so-called “drum eye mark”. At this time, the role of small parts in the roller tumbling, similar to the hanging plating solution stirring or cathode movement. Hanging plating if there is no solution stirring or cathode movement, the upper limit of the current density is not easy to improve the plating deposition rate is difficult to speed up.

4. The current required for small parts in barrel plating is transmitted in an indirect way.

Hanging plating, the current required by the parts of the direct transmission from the hanging device, the parts and the hanging device in close contact, without any medium in the middle. Therefore, the current transmission of rack plating is smooth, the contact resistance is small, and the current obtained by each part is basically not different due to the transmission problem. However, when roll plating, the parts are pressed as a whole on the cathode conductive device inside the drum, and the cathode conductive device directly connected to the parts of only a very small part, and the vast majority of the parts can only be stacked through the overlap of the parts and cathode conduction. Therefore, the cathodic conductive device in the drum can only first of all the current to the parts in direct contact with their own parts, and then only by these parts to other parts, and other parts and parts between one by one to transmit down, this is the indirect conductive way of roll plating. This indirect way of conducting electricity is undoubtedly another important feature of roll plating. It is mainly by parts and parts of the indirect conductive, rather than parts of the direct contact with the cathode conductive, so the contact resistance of the parts of the roll plating compared to hanging plating increases accordingly.