Question: What is the maximal aspect ratio (Length/Inner diameter) of the smallest capillary cavity possible? For example, is it possible to produce a silicone body with an inner hole of 0.1mm diameter 5mm long?
Answer: The maximum aspect ratio for molding is dependent on the properties of the material, geometry of the part, and the strength of the core. The greater aspect ratios combined with higher viscosity materials increased the risk of core deflection and loss off concentricity. A capillary tube with an inner through hole diameter of 0.1mm at 5mm long may be possible depending on tolerances by using low viscosity material and a core held in tension while a blind hole would not be possible using compression or injection molding. Extrusion may be more practical for regular cross sections to make longer sections and then cut to length.