(261e) On-Line Particle Size Distribution Analyser

Approximately 30% of the chemicals produced in the world are in the form of powder and nearly all aspects of the technology related to their manufacture, handling or application at some stage require a knowledge of the particle size. The quest for a knowledge of particle size has led to the development of a large number of particle sizing techniques. Allen (1997) cites over 50 methods for particle size analysis based on a variety of principles with different degrees of sophistication. Typical drawbacks include cost, complicated use, the inability to handle relatively large samples (> 2 g) thus giving rise to representation problems or the requirement for special sample preparation prior to analysis.

This paper describes the design and development of a spring particle size analyser, which overcomes most of the problems associated with the above conventional techniques. It also reports the results of a series of experiments relating to the evaluation of its performance. The system comprises a close-coiled spring that is partly filled with the powder under test. It works on the basis of the fact that when the spring is stretched and agitated, the particle size of the powder discharged from the spring coils is equal to the spring's openings. The weight of the powder discharged is measured and particle size distribution (PSD) is then provided as a plot of percentage mass of discharged powder versus the corresponding particle size. With current configurations, the technique is evaluated against a range of powders with different shape and flow characteristics in the size range 30 - 1200 micron. The data are compared against those obtained using sieves in terms of reproducibility, resolution and cross correlation.