If you were asked to design a simple circuit to blink an on/off turn signal, most likely you would reach for a micro or a low-cost 555. In thermomechanical designs, old cars used bimetallic stripes. Why? Because, initially, 555s and microcontrollers weren’t available. [Breaking Taps] NASA engineers were asked to create some special cooling chambers as part of a rocket design that was used for the Space Shuttle. Today you’d 3D print them, but in the 70s, that wasn’t an option. So, they used wax. In the video below, you can watch a video that shows the entire process including the building of a model engine.
You can use additional thin pipes brazed onto the engine. Additional thin pipes can be brazed on the engine. This method has several drawbacks, but it was used in early rocket engines. The cooling path being integrated into the rocket engine would be ideal. However, without 3D printing it appears difficult. But it’s not impossible.
This technique involves the use of wax and slots machined into the wax that will become the tubes needed. You then electroplate the material over the wax in order to create the outer shell. NASA actually used two steps of electroplating: a thin layer of copper to close the tube, and a thicker layer nickel to add strength. The combination is logical because copper survives contact better with the cryogenic fluid than nickel, but nickel has much greater strength. The wax is needed to create a conductive layer for electroplating. NASA used fine silver powder, but [Breaking Taps] Simply impregnate the wax with graphite. The wax can be difficult to remove but it is possible.
You might think that electroplating was one of the first techniques for additive manufacturing. In fact, printers have been made based upon the idea but are extremely slow. On the other hand, electroplating a plastic print takes less time and looks great, even if you wouldn’t use it for a rocket engine.