The figure shows a top-down view of an electrolytic cell, highlighting several of its fundamental components.
As previously discussed, the cathode (marked with a negative sign, –) consists of a motor shaft holding the part to be electroformed. This part is mounted on a rotating Plexiglas plate. The anode (marked with a positive sign, +) consists of a basket containing nickel pellets.
The two shades of green in the figure indicate the presence of two distinct tanks:
- a lower tank, which holds the bulk of the electrolyte volume. This tank typically contains only the liquid electrolyte along with the resistor(s) and temperature probe(s) that maintain a constant temperature.
- a smaller upper tank (usually there are 2 or 4), where the actual electroforming process takes place. Each of these tanks contains a basket with nickel pellets on one side (anode) and the part to be formed (e.g., metal master, metal mother, etc.) on the other side (cathode). Each anode and cathode is connected to the corresponding terminals of a dedicated power supply (generator).
To ensure proper operation, the electrolyte must circulate continuously. A pump draws electrolyte from the lower tank, pushes it through a filter unit, and directs it toward the central part of the anode basket, thereby supplying the upper tank. The electrolyte level in the upper tank is regulated by an overflow pipe (represented in the figure as a small circle at the top left of the small tank). If the pipe is removed, the electrolyte drains back into the lower tank. If inserted, the tank fills up to the height of the pipe, with any excess flowing back down into the lower tank.
The cell is designed so that, when the lid is closed, the anode and cathode are aligned face-to-face, separated by only a few centimetres. The front of the anode basket features a large circular opening covered by a fabric filter, matching the diameter of the part on the cathode.
It is crucial to understand that the anode, cathode, and electrolyte form part of a direct current (DC) circuit. If any one of these components is disconnected, the current flow is interrupted. For example, opening the lid of a cell during operation causes the ammeter (which measures current) to drop to zero, even though the voltmeter (which measures voltage) remains unchanged.
For electroforming to occur:
- the part at the cathode and the basket at the anode must both be fully submerged in the electrolyte.
- the part must be in contact with the motor shaft, which is connected to the negative terminal of the generator.
- the basket must be in contact with the positive terminal of the generator.
The generator typically consists of a high-capacity transformer and rectifier, delivering low-voltage direct current while supporting very high currents — often exceeding 150 A.
When the circuit is complete, voltage and current are proportional. However, their relationship is influenced by various factors, including the electrolyte’s density and temperature, the resistivity of the materials involved, and the size and resistance of both the anode and cathode.
Electrolytic cells