Counting Methods

Counting methods work for single particles or on their projection [SALM07, p. 140]. A common procedure for counting abrasive grits is laser granulometry. Herein, a mixture of loose samples in a fluid medium flows through a ring. Laser light leads to different shadowing effects depending on the grit size. Commonly, three proportions of different grit sizes are measured, i. e. grit sizes of 10 % of biggest and of smallest grit proportion of the complete grit mixture and the size, which is 50 % of sample, in total 10, 50, 90 % [HORI10].

Especially for coarse diamond grits, the number of particles per carat (PPC) is an important characteristic. Coarser diamonds with high purity are used in electro­plated tools, rotary dressing tools or as so called “saw grits” in saw blades, circular saws, drill bits, wire saws, and milling tools, e. g. for stone cutting or drilling operations. Since PPC may vary if the average grit size is defined by the sieving method, significant variations in tool performance can occur [ENGL03]. Therefore, the number of particles per carat offers an additional measure for the consistency of the diamond batch [LIST08]. The PPC value can be obtained directly by weighing and counting or indirectly by two-dimensional digital image processing [LIST08].

2.9.1.4 Other Methods

Several more methods for particle size characterization exist, such as laser light diffraction, dynamic light scattering, photon correlation spectroscopy, Brownian motion turbidity, etc. [BENE10].

The size of microgrits can be analyzed by their electrical resistance as defined in the ANSI standard B74.10-2001 [UAMA09]. The underlying principle is that a particle causes a change in the strength of the current proportional to the particle volume [UAMA09]. Problems, however, arise for irregular grit shapes, which will be graded with finer sizes than by sedimentation methods.