The degree of coarseness or fineness of a powder is differentiated and expressed by reference to the nominal mesh aperture size of the sieves used.
The terms used in the classification of powders are:
1. Coarse powder (10/44):
A powder all particles of which pass through a 10 no. sieve and not more than 40% by weight through 44 no. sieve.
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2. Moderately coarse powder (22/60):
A powder all particles of which pass through a 22 no. sieve and not more than 40% by weight through 44 no. sieve.
3. Moderately fine powder (44/85):
A powder all particles of which pass through a 44 no. sieve and not more than 40% by weight through a 85 no. sieve.
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4. Fine powder (85/120):
A powder all particles of which pass through a 85 no. sieve and not more than 40% by weight through a 120 no. sieve.
5. Very fine powder (120/350):
A powder all particles of which pass through a 120 no. sieve and not more than 40% by weight through a 350 no. sieve.
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6. Microfine powder (350):
A powder of which not less than 90% by weight of the particles pass through a no. 350 mesh.
7. Superfine powder:
A powder of which not less than 90% by number of the particles are less than 10 µm in size.