(195c) Vibro-Spring Particle Sizer

Powder technology is a very important field in the world today. In fact over, 75% of all materials processed in industry are in particulate form, and knowledge of particle size is important to the manufacture, handling and application of many of these powders. (Merkus, 2009)

Several hundred instruments have been developed for the measurement of particle size distribution. Widely used techniques include microscopy, sieving and laser diffraction. However, the majority are either expensive, not robust, require complicated operating procedures or capable of handling only small amount of samples as a result raising sample representative problems.

In 1996, Mahgerefteh et al. developed a novel Spring Particle Sizer which overcomes most of the problems associated with conventional techniques. In the most basic form, the instrument comprises a horizontally held closed coil helical spring partly filled with powder; the size of the discharged particles is directly related to the spring extension.

The results of experimental investigations carried out on the Spring Particle Sizer are described. This task also includes a search for an optimal spring design in terms of uniform spring opening. The development of methodologies for characterising the spring performance in terms of uniform openings and reproducibility using image analysis is also considered. Test results are presented based on springs supplied by three different manufactures each fabricated to produce uniform extension. These investigations revealed that out of the three manufacturers, one (Airedale Ltd), produced the best performance when compared to sieves. However, these springs cannot be fabricated in a reproducible manner hence compromising the commercial potential.

A number of methodologies are presented in pursuit of obtaining sample mass within the sping in-situ to produce particle size distribution data. Data relating the pressure drop versus air flow rate are presented to deduce the mass of particles within the spring from the minimum fluidisation velocity. A viable correlation between the minimum fluidization velocity and the mass was not obtained. Thus, a more direct measurement approach is investigated, with the aid of a strain gauge.

Finally, the designs and development of a hand-held model of spring particle sizer is described next. Calibrations and performance evaluations are carried out using powder samples with different characteristics. The results show a close correspondence with sieve data, and thus the establishing the device's potential for quality control assessment in the powder industry.

References

1. Mahgerefteh H and Shaeri A Vibro-Spring Particle Size Analyser, PhD Thesis, University College London, 1996.

2. Merkus H.G. Particle Size Measurements: Fundamentals, Practice, Quality Series, Particle Technology Series, Vol 17, XII, p.536, Springer, 2009