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Basic characteristics of roller plating

Electroplating is very important in the surface treatment of metal parts. By coating a layer of anti-corrosion layer on the metal surface, the anti rust performance of the product can be greatly improved, the service life can be increased, and the appearance can also be increased. There are various electroplating processes, and the conventional anti-corrosion performance can range from 48 hours to 120 hours. If combined with sealing treatment, it can also be improved to a certain extent, which can meet the requirements of various usage scenarios, such as ordinary household hardware, automotive parts industry, outdoor equipment, door and window accessories, etc,

Due to the hazards of the galvanizing process, automated operations are particularly important for protecting workers and the environment. For some products that are relatively small and do not require very high surface requirements, we generally use rolling plating, which not only liberates workers' manual operations but also increases work efficiency through automated assembly lines. Moreover, the output of rolling plating is very large, and the surface quality obtained is uniform, especially for fasteners. ordinary hardware supports generally use rolling plating technology.

1. Roll plating is carried out inside a drum

The biggest difference between rolling plating and hanging plating on small parts is that it uses a drum, which is a feeding device that carries small parts to be plated during the continuous rolling process. A typical drum has a hexagonal prism shape and is placed horizontally. One side of the drum wall panel has an opening, and a certain number of small parts are loaded into the drum through the opening during electroplating, and then the drum door is covered to seal the opening.

The drum wall panel is covered with many small holes, which are necessary for the conduction of current between the parts and the anode during electroplating, the renewal of the solution inside and outside the drum, and the discharge of exhaust gas. The cathode conductive device inside the drum is threaded out of the central shaft holes on both sides of the drum through copper wire or rod, and then 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 inside the drum by their own gravity. The rolling plating of small parts is carried out in such a device.

The structure, size, dimensions, rotational speed, conductivity, and porosity of the drum are all related to the production efficiency and coating quality of the rolling coating. So, the drum is one of the key areas of research in the entire rolling plating technology.

2. Roll plating is a process in which small parts are continuously rolled over

During rolling plating, small parts are not stationary inside the drum, but rather roll continuously as the drum rotates. The specific situation of this rolling to a certain part is: one moment it is buried inside the entire stacked part, and another moment it flips over to the outer surface. Repeat this process until the entire electroplating process is completed.

3.So, why keep the small parts rolling inside the drum?

(1) Ensure that each component is evenly coated. 

Small parts are stacked together inside the drum, and some of them are distributed inside the stacking body, called inner layer parts; The other part is distributed on the outer surface of the pile, called the surface part (as shown in Figure 1). During rolling plating, the main metal ions actually only reduce to form a metal coating on the surface of the surface parts, while the inner parts are only affected by the shielding and obstruction of the surface parts, with current passing through and almost no electrochemical reaction occurring. So, in order to have the opportunity to be plated, the inner layer parts need to be flipped out from the inside of the pile to become surface layer parts. And the surface parts cannot stay for a long time. After electroplating for a while, they become inner parts again due to the rotation of the drum. In this way, only by constantly rolling the small parts can the inner and surface parts be constantly changed and transformed, ultimately ensuring that each part has a chance of uniform plating.    

(2) Avoid blackening or burning surface parts.

 If small parts remain stationary inside the drum without rolling, using a very low current density may cause a shortage of metal ions near the surface parts and result in a "burning" phenomenon. Especially for the surface parts that are close to the drum wall panel, the current entering the drum from the holes will be obstructed, causing it to concentrate on the narrow surface of the part next to the holes, resulting in the burning of the coating and leaving black eye spots, known as "drum eye marks". At this point, the small parts roll inside the drum, similar to stirring the plating solution or moving the cathode. If there is no solution stirring or cathode movement during hanging plating, the upper limit of current density is not easy to increase, and the deposition rate of the coating is also difficult to accelerate.

4.The current required for small parts during rolling plating is transmitted indirectly. 

When hanging plating, the current required for the parts is directly transmitted by the hanging device, and the parts are in close contact with the hanging device without any medium in between. Therefore, the current transmission of hanging plating is smooth, the contact resistance is small, and the current obtained by each component is basically not different due to transmission problems. However, during roll coating, the parts are pressed as a whole onto the cathode conductive device inside the drum, and only a very small number of parts are directly connected to the cathode conductive device, while the vast majority can only be connected to the cathode through stacking and overlapping parts. So, the cathode conductive device inside the drum can only first deliver current to the parts in direct contact with itself, and then these parts can be delivered to other parts, and transmitted one by one between other parts. This is the indirect conductive method of rolling plating. This indirect conductive method is undoubtedly another important feature of electroplating. It mainly relies on indirect conduction between parts rather than direct contact between parts and the cathode, so the contact resistance of parts during rolling plating is correspondingly increased compared to hanging plating.