Shaeri, Ali; (1997) Vibro-spring particle sizer. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This work reports the design and development of a novel technique for particle size distribution analysis of powders particularly in the 75-1000 μm size range. The instrument comprises a horizontally held close-coiled helical spring that is partly filled with the powder under test. The principle of operation is based on the simple fact that when the spring is stretched along its length and vibrated in the vertical direction using simple harmonic motion, the particle size of the powder discharged from the spring coils is directly related to the spring extension. Data on the particle size distribution is provided as a simple plot of percentage mass of powder discharged at a given spring extension versus the corresponding particle size. Early on in the study, it is shown that although the spring linear extension is the most important parameter in determining the particle size, measurements with a high degree of resolution also require a knowledge of the spring shape and its vertical deflection during vibration. The above is addressed by developing a comprehensive analytical technique based on visco-elasticity. The model takes into account the effect of the presence of the 'vibro-fluidised' powder on the spring vibration characteristics and predicts the system's response in terms of size measurement from a knowledge of a number of readily available input parameters. Data are reported in conjunction with a variety of different size and shape particles including sand, glass Ballotini, coal, and alumina in the range 30 - 1000 μm with a typical resolution of ±15 μm. The effect of particle shape on the system's response is investigated by electron microscopy studies. The results show that the actual size measured is the minimum particle dimension. This information is in turn used to derive an appropriate correction for correlating the results from the current technique to those obtained from sieves.

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