Vibratory Sifter Analysis to Support Extraterrestrial Surface Systems
Cameron K. Turner
University of Washington, Seattle; NASA Glenn Space Academy 2011
Allen Wilkinson, Ph.D.
NASA Glenn Research Center
Many systems and processes that utilize granular materials depend on specific particle size distributions to operate correctly. Extraterrestrial regolith can be integrated into in-situ resource utilization processes, but first methods for efficiently sorting that regolith must be established. This study examines the effectiveness of a vibratory sifter to separate granular materials based on particle size. The sifter has two layers of sieves so that the material left between the two screens should be within a known range of sizes. In order to get material to pass through the screens both high and low frequency vibrations are used. A device known as a Vibrasonic imparts supersonic vibrations directly to the screen, while an un-balanced rotary motor imparts larger and lower frequency vibrations to the entire sifter. The system was optimized by varying the type and amount of lunar simulant that was added, how often and in what configuration the different vibrations were powered, and the magnitude of low frequency vibrations. The data gained from the testing includes accelerations caused by the vibrations, the mass of the simulant that passes, or fails to pass, through each sieve, the energy consumption of the induced vibrations, and qualitative video. The sifter will be judged on both its mass to energy efficiency, and the accuracy of the mass measurements based on standard particle distribution curves for the various simulates. During the testing, some key observations were gathered from the videos that show the behavior of the soil inside the sifter including that the Vibrasonic affects the soil near the edges of the sifter the most, and that the soil tends to collect to the side of the ejection spout. Currently, data gathered from the first round of testing is undergoing processing. Future work will be focused on determining the optimal operating conditions for the vibratory sifter based on those initial tests as well as other tests that may be deemed necessary. The vibratory sifter will then be compared to other sifting systems to determine the system best suited for extraterrestrial incorporation.
Purpose and Background
The mechanics of granular materials, such as soils, are primarily governed by the particle size distribution of the sample, which holds true for extraterrestrial regolith. The ability to efficiently and accurately determine the particle size distribution plays a key role in understanding the processes of evacuation, traction, and material flowability. Furthermore, it is often the case that a sample containing only a narrow particle size range is desired from an extraterrestrial surface comprised of a large range of particle sizes. For either of these applications, it is important to reach a full understanding of how granular sifting equipment functions in a variety of conditions, especially since surface samples will be collected using automated or robotically controlled equipment. With this understanding, equipment and instrumentation can be properly designed to gather samples and measure particle size distributions, or to control the size range used in some process like a fluidized bed reactor that can produce water and oxygen.
Research Tasks and Goals
This project, led by Dr. Allen Wilkinson, aims to gather information on the performance of vibratory sifters used to separate granular materials into categories based on particle size. The sifter, which is illustrated in Figure 1, is produced by Russell Finex, and will be tested first in a 1G environment. Future research should be oriented towards testing the equipment in reduced gravities.
Granular material is loaded into the top of the sifter, and is then sorted with wire meshes of varying sizes. Unbalanced weights on a rotary motor can be adjusted to cause variations in the horizontal and vertical vibrations. Vertical vibrations help the particles fall through the sieves, while the horizontal vibrations are most useful for dispelling larger unwanted particles out the side of the sifter. A feature known as Vibrasonic can also be used to excite the material through the screens. The free parameters of interest include:
- Amount of soil loaded into the sifter
- Time until more soil is added
- Number of times soil is loaded
- The effect of using Vibrasonic
- How the motor is weighted
- Type of granular simulant loaded
During the test it will be important to note the patterns of the granular materials in the sifter, the qualitative effect of the unbalanced motor, and the degree of blinding that occurs. Additionally, the outputs of the testing will include:
- The efficiency based on how much soil failed to be sifted correctly
- The total time required
- The total energy consumed
- The raw amount of the particle sizes of interest recovered
- Frequency and amplitude data recovered from accelerometers
Based on these outputs, the correct set of operating parameters that should be adopted for various environments will be determined. In general, the granular material should be sorted quickly, with minimal energy, and minimal waste.