Advantages and Disadvantages of Roll Plating

author: YITECH

2025-02-26

The invention of roller plating solved the problem of low electroplating efficiency of small parts and improved the surface quality of plated parts. However, due to the change in the way parts are plated, roller plating will inevitably have defects, such as long electroplating time and reduced dispersion ability of the plating solution. Therefore, only by fully understanding these advantages and disadvantages can roller plating better serve production.

Advantages and Disadvantages of Roll Plating

Advantages of Roll Plating

Compared with Hanging Plating of Small Parts, the advantages of Roll Plating are mainly reflected in the following aspects.

1. Save labor and improve labor productivity

Roll plating brings a large number of small parts together for electroplating, eliminating the cumbersome hanging, saving labor and improving labor productivity. This is the biggest advantage of Roll Plating compared with Hanging Plating of Small Parts. For example, a factory rolls bright nickel on ￠5mm×5mm iron screws, using a GD-10 roll plating machine, operated by one worker, and the output per shift is about 70-80kg. The factory initially adopted the copper wire bundling hanging plating method, and one worker produced a maximum of 5-6kg per shift. If the output per shift is 70-80kg, about 8-12 workers are required.

For example, in recent years, the automated roll plating technology has developed rapidly, realizing the full automation and unmanned operation of the entire production process from loading to unloading, which really maximizes the superiority of high labor productivity of roll plating. Practice has proved that it is precisely because barrel plating has replaced the backward production method of small parts rack plating that the large-scale industrial production of small parts has been realized. Therefore, the invention and wide application of barrel plating is a major leap in the development of small parts electroplating technology!

2. Good surface quality of plated parts

During barrel plating, due to the mutual polishing between parts, coarse crystals cannot grow on the surface of parts, so the obtained coating is delicate, soft, uniform in color, and has a high surface finish. For example, galvanizing of plumbing pipe clamps and elbows (malleable cast iron parts) is a case where such parts can be barrel plated or rack plated, but the surface quality of barrel plated parts is much better than that of rack plating.

For example, high-quality barrel nickel-plated small screws have a delicate and smooth surface. Grasping them in your hand and rubbing them gently gives people a silky and comfortable feeling; while the effect of copper wire bundling and rack plating will be greatly reduced.

3. Small fluctuation of coating thickness

The fluctuation of coating thickness reflects the closeness of the coating thickness between parts. The small fluctuation of coating thickness indicates that the coating thickness of each part is close to each other. During roller plating, small parts are turned from the inner layer to the surface layer in the drum for a while, and then turned from the surface layer back to the inner layer. When turning to the surface layer, the parts are plated normally, and when turning back to the inner layer, the electrochemical reaction basically stops. When electroplating is just started, there are always some parts that have more chances to turn to the surface layer, so they have more chances to be plated and thicker coatings; while other parts have fewer chances to turn to the surface layer, so they have fewer chances to be plated and thinner coatings. However, as the electroplating time increases, the probability of different parts turning in and out gradually becomes equal, and the coating thickness of each part gradually approaches, and the fluctuation of coating thickness gradually decreases. In addition, the various effects on different parts in the drum are gradually equalized, and the surface quality of each part gradually tends to be the same.

When small parts are hang-plated, due to the different plating conditions (such as hanging positions) of different parts, the current distribution is uneven, and the coating thickness of each part varies greatly. For example, the same part on a hanger, whether it is hung in the middle or on the edge, on the upper layer or on the lower layer, will have different results in the thickness of the coating due to the influence of the metal tip effect.

4. Small footprint

Because barrel plating processes scattered parts in a centralized manner, it increases the carrying capacity of the plating tank for parts, so compared with the rack plating that processes the same number of parts, the footprint is greatly reduced, which is precious today when land resources are increasingly scarce. Moreover, the more parts are processed, the more obvious this advantage of barrel plating is.

For example, an iron washer with a diameter of ￠50mm and an inner hole of ￠22mm is galvanized. This part can be barrel plated or rack plated. If barrel plating is used, using a GD-20 type roller, the solution volume is generally about 400L, and the entire barrel plating machine occupies about 0.7 square meters. At this time, the equipment can process about 20kg of parts at a time. However, if rack plating is used, the same solution volume and equipment footprint can only process about 2.3kg of parts at a time. If 20kg of parts are to be processed at a time, it will take about 8 to 9 times the floor space of barrel plating.

For another example, a standard part is zinc-plated by roller, with a daily output of 10 tons and two-shift production. The production line requires about 10 electroplating stations, plus other auxiliary stations, worker operation area and non-operation area reserved, and the entire production line can be controlled within 20×3m. However, if rack plating is used to achieve the same output, it may take several times or even dozens of times more space than roller plating.

Defects of roller plating

Compared with rack plating, the plating method of roller-plated parts has changed significantly:

Rack plating is carried out when the parts are individually packaged, while roller plating is carried out when the parts are concentrated and sometimes connected and separated, resulting in a mixing cycle of parts in this process;
Rack plating is carried out when the parts are fully exposed, while roller plating is carried out in a closed drum (although there are holes on the wall plate) with a low solution concentration. The change in the way parts are plated brings two major defects to roller plating, namely the defects caused by the mixing cycle and the structural defects of roller plating. The two major defects have a serious impact on the improvement of roller plating production efficiency and product quality, and the advantages of roller plating cannot be fully utilized.

1. Defects caused by mixing cycle

The mixing cycle refers to the time required for the part to turn from the inner layer to the surface layer and then from the surface layer back to the inner layer during roller plating. It is caused by the use of rollers to make small parts roll continuously. Due to the existence of the mixing cycle during roller plating, the parts cannot be plated all the time like during rack plating. When they are located on the surface layer, they can be plated normally, but when they are located in the inner layer, the electrochemical reaction basically stops. In this way, the effective plating time of the parts during roller plating cannot be guaranteed. In order to achieve the required coating thickness, the time of the entire electroplating process can only be extended. This is one of the important reasons why roller plating takes longer than rack plating.

For example, a galvanized part with a coating thickness of 5µm requires about 10 minutes for rack plating, but if it is roller plating, it may take 30 to 40 minutes or even longer. Explain this phenomenon from the perspective of the mixing cycle. If the effective plating time of the parts is to be guaranteed to be 10 minutes, the entire roller plating time may be several times due to the influence of the mixing cycle.

2. Structural defects of barrel plating

The parts of the rack plating are completely exposed to the plating solution, and there is no barrier between the parts and the anode, so the transmission of substances in the solution is not affected in any way. However, the parts of the barrel plating are enclosed in a porous barrel, and there is an additional barrier between the parts and the anode, the barrel wall plate, compared with the rack plating. Therefore, the resistance to the transmission of substances is greater than that of the rack plating. Therefore, compared with the rack plating, the coating deposition speed of barrel plating is slow, the dispersion ability and deep plating ability of the plating solution are reduced, and the tank voltage is higher. These defects caused by the closed structure of the barrel can be called structural defects of barrel plating.

(1) Slow coating deposition speed

During barrel plating, the metal ions consumed in the barrel are difficult to be replenished in time from the fresh solution outside the barrel, resulting in a decrease in the metal ion concentration in the barrel. It is difficult to increase the upper limit of the current density and accelerate the coating deposition speed. This is another important reason why barrel plating takes longer than rack plating.

(2) Decreased dispersibility and deep plating ability of the plating solution

After the start of roller plating, the concentration of conductive ions in the solution in the drum decreases, and the fresh solution outside the drum cannot be replenished in time, so the resistivity of the solution increases, the current distribution on the cathode surface becomes uneven, the dispersibility of the solution decreases, and the uniformity of the coating thickness on the surface of the parts deteriorates. Therefore, roller plating is difficult to be suitable for parts with high precision requirements for coating thickness (especially needle shafts).

In addition, because it is difficult to use a large current density and the secondary current distribution on the cathode surface is uneven, the current density in the low area of the parts is small. When it is lower than the lower limit, the coating will not be deposited or the deposited coating does not meet the requirements. Therefore, the deep plating ability of the roller plating solution will also decrease, and the coating quality of the low area of the roller plated parts (especially deep holes and blind holes) is often unsatisfactory.

(3) The tank voltage is high, the power loss is large, and the tank liquid temperature rises quickly

The closed structure of the roller increases the resistance of the roller plating solution. In order to achieve the required current density, a higher voltage is often required to increase the driving force for the roller plating process. Therefore, the tank voltage of roller plating is often higher than that of rack plating, which increases the power loss. The large solution resistance will lead to a faster rise in the temperature of the tank solution.

3. Defects caused by indirect conduction

(1) The indirect conduction method of roller plating makes the contact resistance of the parts (i.e. the resistance of the metal electrode) larger than that of rack plating, so the tank voltage increases accordingly. This is another reason for the high tank voltage of roller plating.
(2) The parts are constantly rolling in the drum, which makes the contact between the parts and the cathode sometimes good and sometimes bad, which will inevitably cause the defect of unstable current transmission in roller plating.
(3) The distance between the parts in the drum and the cathode is different, so the distribution of current on each part is also quite different. The current of the parts close to the cathode is large, and vice versa.

4. Defects in current density control

Compared with the independent parts in rack plating, the parts in roller plating are overlapped and shielded with each other, and the shapes of the parts in roller plating are varied, and the opening rate of the roller is also different. Therefore, it is difficult to determine the effective area of the parts when they are plated, and it is also difficult to quantitatively control the current density on the surface of the parts. This brings great inconvenience to roller plating production.

In addition, barrel plating also has defects such as rapid changes in plating solution components, large amounts of solution carried out, and limited shapes, sizes, and coating thickness of parts. Moreover, due to the above defects, the requirements for barrel plating equipment are much more complicated than those for rack plating. In particular, the requirements for the core component of barrel plating equipment, the barrel, are higher. How to select the appropriate barrel structure, shape, specification, size, speed, conductive method, and barrel wall opening according to the specific situation in production is the key to improving barrel plating production efficiency, improving coating quality, and stabilizing production.

After fully understanding the advantages and disadvantages of barrel plating, we can take advantage of it and avoid disadvantages, take advantage of its strengths and avoid disadvantages, give full play to its advantages and reduce its adverse effects in production. For example:

1. In reducing the impact of mixing cycle :

The use of slender barrels can shorten the mixing cycle of parts, thus shortening the electroplating time and reducing the fluctuation of coating thickness.
Selecting the appropriate barrel shape, size, speed, and loading capacity can minimize the impact of the mixing cycle.
Selecting a suitable roller plating method (such as vibration plating) according to the specific conditions of the parts is an effective measure to reduce the impact of the mixing cycle.

2. Improving the structural defects of roller plating

The structural defects of roller plating are caused by the closed structure of the roller, which increases the resistance to the transfer of substances in the solution. Therefore, improving the closed structure of the roller to reduce this resistance is the key to improving these defects. For example:

The opening rate of the injection molding roller is greatly improved. For example, it can be increased by about three or four times compared with the round hole roller. The increase in the roller opening rate reduces the resistance to the transfer of substances during roller plating, and the structural defects of roller plating are greatly improved.
The jet liquid flow roller plating technology is an important part of the reform of traditional roller plating. It uses a circulating pump to force the fresh solution outside the roller into the roller, so that the consumed metal ions can be replenished in time, which can increase the production capacity of roller plating by 2 to 3 times, and can greatly reduce the difference in plating thickness inside and outside the holes of pinhole parts.
Vibration plating completely breaks the closed structure of the drum, eliminates the difference in ion concentration inside and outside the drum, and fundamentally improves the structural defects of drum plating. When plating needle-shaped, small, thin-walled, easily scratched, easily deformed, and high-precision parts, it has incomparable advantages over traditional drum plating. Practice has proved that the invention and wide application of vibration plating is another major leap in the development of small parts electroplating technology!

3. In the development of special additives for drum plating
The development and application of special additives for drum plating with excellent performance have greatly improved the production efficiency and coating quality of drum plating. For example, the use of drum plating nickel additives with excellent performance, the current used is even twice that of the normal case, and the plating time is greatly shortened; the use of deep hole nickel plating additives, the plating solution has excellent deep plating ability, so that the problem of in-hole plating of deep hole and blind hole parts such as battery shells is better solved.

DongGuan YiTai Electronic Technologies Co.,Ltd

DongGuan YiTai Electronic Technologies Co.,Ltd is a manufacturing service provider located in Dongguan, China.

YiTai specialized in CNC turning machining and sheet metal fabrication mainly. As a member of Hung Mou Group, we focus on the overseas marketing development. And based on our parent company’s manufacturing capability and resources, YiTai also expended machining services such as die casting, injection molding, aluminum profile extrusion, 3D printing, which are committed to providing customers with one-stop purchasing services and experience.

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