Measurement of the Fineness of Powdered Materials

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Abstract
The paper describes in detail the methods of analysis at present available for measuring the fineness of powdered materials used in engineering and industrial processes. Definitions of particle size and shape are discussed, and examples are given of the size-distribution curves for typical industrial powders. Sieving or screening is used for the size grading of the comparatively coarse particles, and processes involving motion in a fluid for particles smaller than the limit of sieving. The theory of sieving and the relationship between particle size and sieve aperture are discussed. The equivalent sizes of round, square, and slotted apertures have been measured and results are given. The motion of irregularly shaped particles in a fluid is briefly described, and a method is given for calculating the falling velocity of such particles when the fluid flow round the particles is turbulent. The procedures used for the fineness analysis of sub-sieve particles are: elutriation by means of air or water, sedimentation, hydrometer readings, and the obscuring of a beam of light by dilute suspensions of the particles. Each of these processes is fully described, and the respective merits and disadvantages discussed. Tables of the nominal apertures of all the standard sieve series in industrial use, and a bibliography of about 150 references are included in the paper.

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