The casting process to build a combustion-driven actuator (CDA) with a necessary monoblock structure consists of three steps. First, the mold has to be prepared by connecting casting parts. Then, the silicone has to be mixed. Last, this mixture is injected into the mold and cured. Even though these steps seem to be simple, we will show a few tricks to increase your casting efficiency. Some of the preparation steps are also illustrated in the video below.
The mold we've created needs a few additional parts prior to casting. These parts will further help to prevent any dead zones, which would trap air (other preventive steps are explained in Step 3 – Mold Design).
Mix silicone according to the instructions given by your manufacturer, in our case Altropol (usually given at the end of each data sheet). Each system has its own monomer to cross linker ratio. Mix until a homogeneous material is obtained, either by hand or with a mixer. We also suggest you degas the mixture to decrease the amount of dissolved air. This helps to avoid entrapped air in the molds.
The figure below shows the previously mentioned silicone press (taken from Schumacher et al.). The syringes (50 mL) are filled with the uncured silicone mixture and then injected into the mold until the reservoir is full. When a tube connected to a vented hole starts to fill with silicone, a possible dead zone has been completely filled with silicone and that escape route is no longer needed. You can inject hot glue into the tubing to seal it so no more silicone escapes. (This technique is shown in the video below).
A few tricks: