An Investigation of the Centrifugal Casting of Paraffin Wax in the Laboratory and in Microgravity

Stober, K.J., Wanyiri, J., Sanchez, A., Hooper, M., Mazumder, M., Jiwani, S., Waft, C., Lifson, M., Joseph, C., and Wood, D., "An Investigation of the Centrifugal Casting of Paraffin Wax in the Laboratory and in Microgravity," AIAA 2019-4012, AIAA Propulsion and Energy Forum, Indianapolis, IN, August 2019


This paper describes the results of numerous laboratory-based studies as well as an initial
parabolic aircraft microgravity flight studying the relationship between rotation rate and the
ability of the working fluid to form a smooth annulus for the purposes of producing paraffin fuel grains for hybrid rockets. A multi-step research plan is discussed which aims to elucidate the challenges associated with centrifugal casting in the space environment. With the small satellite form factor in mind, a miniaturization of the casting process was successfully carried out which sought to minimize size, power, and cost. A 12V, 2A, Arduino-controlled DC brushed motor proved sufficient for casting 2 in. diameter fuel grains. The miniaturization of the centrifugal casting process is a critical step towards on-demand production of paraffin fuel grains for in-space hybrid propulsion systems and continued efforts are required to further qualify paraffin for this application. 

Three working fluids were used: paraffin wax (approximately C32H66), SAE 5W-30 motor
oil, and dyed water, in order to understand the dependence upon fluid properties. Rotation
rates of 460, 480, and 600 RPM were required to reliably form a smooth annulus in a 1g
environment in water, oil, and liquid paraffin, respectively, for working fluid outside diameters
of 1.75-2 in. A rotation rate of roughly 555 RPM was the lowest tested and consistently yielded a smooth annulus of water with 1.75 in. outside diameter and 3 in. length in the microgravity environment, but further short- and long-term microgravity testing is planned in order to determine the minimum required rotation rate under these conditions.

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