Making a Perforated Strip Requires High-Precision Mechanical Engineering

The electrodes of a nickel-cadmium cell include, among other things, a perforated strip of steel that forms a kind of pocket for the active material. These strips are made on specialized machines that combine the accuracy of a Swiss watch with the robustness of solid engineering.

The manufacturing of perforated strips is far from a sterile operation in which robotic arms move silently around and every once in a while, someone with a tablet comes in to check on them. It has much more in common with traditional mechanical engineering with a hint of tailoring. The strip, made from deep-drawing, ferritic low-carbon steel, must be perforated to enable the exchange of a certain amount of electrons between the positive and negative electrode that generates current. The strips are perforated by a set of thin needles that must be inserted into the special die by hand.

But the whole process starts by placing a coil of the non-perforated strip on a stand that is often nicknamed a film projector” because it largely follows the same basic principle. The strip goes through the machine to be wound on another coil; inside the machine, however, it is perforated by hundreds of thin needles set in a die about the size of a thimble. These needles are placed in the die with maximum precision, fixed, covered in special glue, and hardened in a kiln.

The resulting perforation tool then oscillates within the stand to create open surfaces on the strip. The perforation is immediately checked using light; while still inside the machine, the strip is illuminated so the operator can fine-tune the machine to ensure that the open area of the strip is within the required parameters. The mechanical movement of the strip under the perforation tool is provided by stepper motors; the winding is optimized so there is no need to tighten the finished coil.

The result of the whole process is a perforated strip with non-perforated edges that are used to create a plate filled with the active material. This is because the electrode plate consists of smaller plates, which are made by bending over the non-perforated edges of the strip and mechanically linking several strips together. The smaller plates are placed next to each other to create the larger electrode plate, which is then cut to the required size. 

Together with the separator, the complete set is stored in the cell case made from a special plastic, which is then filled with electrolyte and welded shut, together with the metal poles. Then the finished cell can become part of a battery that might operate in some of the most difficult environments on our planet, including at minus 50 degrees Celsius and in hot deserts.