The processes of electroplating

Dr. Galva®
2023-05-10 13:33:00 / Guides / Comments 0

In the following section, the different processes of electroplating are presented, including the basic working utensils for the individual methods. In general, a distinction is made between three different electroplating processes, namely barrel electroplating, pin/tampon electroplating and bath electroplating.


The procedures at a glance

A distinction is made between 3 processes for the electrodeposition of metals. These are bath electroplating, pin electroplating (or tampon electroplating) and barrel electroplating. Each of these processes has its advantages and disadvantages.

Procedure Advantages Disadvantages
Bath plating
  • automatic sequence of the galvanisation process
  • layer thicknesses of a few micrometres to several millimetres can be achieved
  • powerful power supply unit required
  • large containers necessary
  • large amount of electrolyte
  • impractical for plating small parts
Pen plating / Tampon plating
  • galvanising of large surfaces feasible
  • power supply unit with low power necessary, because current only flows at small contact point
  • small amount of electrolyte needed
  • only low layer thicknesses achievable, thus hardly any corrosion protection
  • electroplating process is not automated
  • very time-consuming
  • strenuous
Barrel plating
  • excellent for plating small parts
  • relatively uniform coating due to continuous rotation
  • electroplating process runs automatically
  • quick to fill
  • powerful power supply unit necessary
  • large containers essential
  • large amount of electrolyte
  • workpieces receive small impact marks
  • a certain number of pieces is necessary so that the workpieces are permanently contacted, or a suitable drum size

The bath electroplating process

Bath electroplating is a method in which the workpiece to be electroplated and the anode are immersed in an electrolyte. In addition, a current flow is generated so that metal is deposited on the workpiece.

Bath electroplating is a process that is frequently used in industry. As a rule, workpieces are chrome-plated, gold-plated or nickel-plated in tanks of enormous size. For this purpose, racks are often used on which the parts to be plated are suspended. In order to increase the possible current density and thus faster deposition, a bath movement is a good solution here. This can be done by air injection, pumping or even moving the rack.

Advantageously, the process is easy to carry out and large current flows can be generated, so that deposition of thick metal layers is also possible. A disadvantage is that large quantities of electrolyte are required to fill the baths. For this reason, bath electroplating is only suitable for smaller parts in the private or hobby sector.

Basic equipment required

To carry out the bath electroplating process, a controllable direct current source, a tank or container and connecting cables are required.

The power source can be, for example, a laboratory power supply unit, with both a volt and ampere display, i.e. voltage and current. The tank should be large enough to completely immerse the object to be electroplated. It should be made of an alkali-resistant and acid-resistant material; in addition to plastic containers, glass containers are also very suitable. They also need cables to connect the power supply to both the anode and the workpiece. To avoid confusion, always use a red cable for the (+) pole and a black cable for the (-) pole.

Anode surface

As a general rule, the surface area of the anode should be as large as the surface area of the workpiece to be electroplated. If, on the other hand, the surface area of the anode is too small, it is possible that the layers will be deposited unevenly.

This effect occurs because the current is not distributed evenly in the electrolyte (scattering) and this takes the shortest path. Thus, the current is higher in the area of the shortest path and the layer is deposited thicker here. The anode shape and arrangement must also be suitable so that the current can be distributed evenly.

A larger anode does not have a negative effect on the result. However, due to an unfavourable anodic current density (anodic efficiency), a stronger passivation (depending on the electrolyte) can take place, which reduces the current flow. If this is the case, the anode should be cleaned.

Arrangement of the anodes

With regard to the anode arrangement, it should be noted that the workpiece to be electroplated should be evenly surrounded by anodes all around. This ensures that the layers are deposited evenly. At least they should be present on two sides if possible.

If it is not possible to achieve such an arrangement of anodes, an even coating of the workpiece can be achieved by continuous turning. It is also important that the distance between the anode and the workpiece is as large as possible.

The anode and the workpiece occupy a position opposite each other. More metal is deposited on the front side of the workpiece than on the rear side. The workpiece should be rotated at regular intervals. Two anodes and the workpiece are in the tank. Note that both anodes should be connected to the same power supply. The workpiece is placed centrally, between the two anodes. This ensures a more even deposition.

The pen or tampon plating process

If permanently mounted or large workpieces are to be electroplated, pin electroplating is best suited. For this purpose, a metal rod is used as the anode (+), at the tip of which there is either a cloth tampon or a sponge (for the sake of simplicity, we will only use the word tampon). The tampon is used to absorb the electrolyte and is completely soaked with the desired electrolyte. While the object to be electroplated is connected to the cathode (-), the workpiece is now contacted with the tampon in a circular motion. In this way, a current flow is made possible and after a few seconds a metal layer is deposited at the corresponding contact points.

The circular motion is very important because a high current flows on a small contact area. As soon as you stop on a spot with the tampon, the spot can become dull and can turn dark (burns), this effect runs faster the higher the current flow is. A little experience is needed here, but you will get it quite quickly. Moving the tampon back and forth is rather unsuitable, as the movement is briefly interrupted in between and burning can already occur at high current density.

The anode should preferably be made of inert materials such as platinum or graphite (and sometimes also stainless steel) or the material of the electrolyte used.

Basic equipment required

To carry out the process of pin or tampon electroplating or pin electroplating, a controllable direct current source, i.e. a controllable power supply unit with digital voltage and current display, a pin anode with anode holder (electroplating pin), a set of cables and a tampon or sponge are required. The pin anode (or the anode holder) must be connected to the (+) pole of the power supply unit using a cable. In addition, the anode must be fitted with a tampon or sponge so that the complete electroplating pin is ready for use. The workpiece itself is connected to the (-) pole as in the procedures explained above.

Sponge & Tampon

If sponges or tampons are used, they are attachments that absorb the electrolyte. This characteristic is indispensable because it must hold the electrolyte between the anode and the workpiece during the electroplating process and release the metal ions. Ideally, pad attachments for electroplating have a very high absorbency and are robust. Electroplating pads should also not be too thin, because otherwise there could be insulation effects due to high pressure at certain points and the electric current could not be passed on. A pad for electroplating should also not have external seams, as this could cause scratches on the metal.

Thickener or gel former

A thickener, also called a gel former, is a specific thickening agent. Thickeners are added to the electrolyte solution so that it becomes more viscous. There are special thickeners designed for the different galvanic electrolytes. If conventional agents are used or mixed in, the electrolyte usually becomes unusable. In principle, all types of electrolytes can be thickened with the help of galvanic gel formers. By thickening the electrolyte, it is ensured that the liquid does not drip, work can be done more cleanly and electrolyte can be used sparingly. However, the electrolyte should not be too thick.

To thicken an electrolyte, you should pour as much electrolyte as you expect to need into a container and add as much gelling agent while stirring evenly until the individually desired consistency or firmness is reached. Proceed carefully and slowly. Make absolutely sure that there is no excessive dust formation when using powder. If you have thickened the electrolyte too much, you can make it more liquid again by adding unthickened electrolyte.


The barrel plating process

The barrel plating process is ideal for electroplating large quantities of small parts, especially for parts that cannot be fixed on racks or can only be fixed with great effort. Basically, the electroplating process corresponds to that of bath electroplating, whereby the workpieces to be electroplated are placed loosely in a slowly rotating barrel. The workpieces are contacted with the aid of a centrally mounted contact rod, freely movable clappers (cables with conductive caps) or via suitable contact points in the drum wall; the drum is set in rotation with the aid of a motor. The resulting uniform movement ensures a relatively even coating of the small parts, but there are subtle differences, as the uncontrolled mixing means that individual parts are contacted for longer and thus receive a higher coating thickness, or this effect is also reversed (i.e. shorter contact time and lower coating thickness).

The advantage here is that it can be loaded quickly, as the parts are simply fed in loosely. The disadvantage is that the workpieces always get small impact marks because they are mixed with each other, so this process is less suitable for mirror finishes, but this is not important for screws etc. A minimum number of pieces is also necessary. Also, a minimum number of pieces is necessary to ensure that the parts are continuously contacted.

Basic equipment required

To carry out the barrel plating process you need a plating barrel. Besides a barrel, a gear motor and the mechanics are the basic components, together this is a barrel plating line. Just as for the bath electroplating process, a sufficiently strong controllable power supply unit and a set of cables are required.

Filling the electroforming barrel

As a general rule, the electroforming barrel should be filled with workpieces to a maximum capacity of between 40 and 50 percent. This ensures that the components can move freely; at the same time, jamming, jamming or even blocking is prevented. If this were to happen, no ideal coating and thus uniform electroplating could take place due to the contact points. It is essential to ensure that these also have contact with the contact pin.

Note: Balls are the optimal filling material because they cannot tilt, free movement is ensured as well as an ideal electroplating result.