Typical Shapes of Powder Grains

Fig. 5 When calibrating a sieve mesh with trapped irregularly shaped grains, a subset of powder grains is obtained that can be used to generate a shape description of the powder grains. (From Ref. l) (A) Profiles of typical sand grain trapped in a sieve mesh (B) length and width distributions of sand grains trapped in a sieve mesh and (C) elongation ratio (shape) distribution for sand grains trapped in a sieve mesh.

Manufacture.The following method is typical An oven is constructed with stones in the shape of a well. The inside diameter of the oven is determined so that the hemp caules can be easily inserted. At first some of the hemp caules are ignited and thrown into the oveii, and then the remainder of the caules are heaped on the fire step by step at intervals so that the material thrown in at first does not become ash. Finally, water is poured on the hemp to extinguish the fire. The hemp coal thus produced is dried by itself from the remaining heat. Finally it is crushed to a fine powder and sieved to remove coarse grains and foreign matter. 

Figure 3.4. The operative aperture size in a sieve can be measured by examining powder grains which have been trapped in the apertures, a) Comparison of the aperture size distribution of a sieve as determined ftom direct examination of the sieve surface, trapped spherical glass beads, and trapped irregularly shaped sand grains, b) Profiles of typical sand grains trapped in the sieve mesh, c) Length and width distributions of two sets of 100 sand grains trapped in the mesh of the sieve, d) Shape distribution of the sand grains of (c).

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