The difference between the European P-grading system (number has a P in front of the number) and the more common ANSI or CAMI standard is that the European number is based on the number of openings if the width of the wire mesh was eliminated from the calculation. For example, a 120 grit particle is approxmiately 105 microns in size, whereas, a 1200 grit particle has a particle size of 2.5 microns. Thus larger grits numbers would represent smaller or more openings in a mesh screen and thus would correlate to smaller sized particles. Roughly speaking, grit size represents the number of wires or mesh of wires per a specified area. Grit size would refer to the size of the particle if it were classified or sized with mesh screens. Typically 60 or 120 grit sizes have been found to be the most useful grain sizes for metallographic grinding with zircon.įor metallographic abrasives the particle size is typically classified by grit size or average particle size in microns. ![]() It is a very tough abrasive, so it lasts longer, however it is generally not as hard or sharp, and thus requires higher pressures to be effective. Zircon, or zirconium silicate, is another less common abrasive used for coarse grinding. For metallographic applications, polycrystalline diamond is recommended as a rough polishing abrasive. Although diamond would be ideal for coarse grinding, its price makes it a very inefficient grinding material for anything except for hard ceramics. It has a cubic crystal structure, and is available as a natural or an artificial product. Is the hardest material known to man (mHV). Note that larger coated or bonded grit sizes of alumina are commercially available, however they are not ideal for metallographic applications because they become dull, resulting in lower cut rates and higher surface and subsurface damage. Unlike SiC, alumina breaks down relatively easily to submicron or colloidal particles. Alumina abrasives are used primarily as a final polishing abrasive because of their high hardness and durability. It exits in either the softer gamma (mohs 8) or harder alpha (mHV) phase. 150x)Īlumina is a naturally occurring material (Bauxite). SEM micrograph of 600 grit SiC Abrasive Paper (original mag. ![]() Note that coated abrasives are not quite coplanar, thus SiC papers produce the maximum efficiency (cut rate, stock removal and minimal damage) because new abrasive is exposed as the old abrasive breaks down. This is achieved by aligning the abrasive particles approximately normal to the backing. For metallographic preparation, SiC abrasives are used in abrasive blades and for coated abrasive grinding papers ranging from very coarse 60 grit to very fine 1200 grit sizes.īonded or coated abrasive papers of SiC are designed so that the abrasive will have a large number of cutting points (negative abrasive rank angle). SiC is an excellent abrasive for maximizing cutting rates while minimizing surface and subsurface damage. It is also somewhat brittle, and therefore it cleaves easily to produce sharp new edges (self sharpening). It is an ideal abrasive for cutting and grinding because of its hardness and sharp edges. ![]() ![]() It has a hexagonal-rhombohedral crystal structure and has a hardness of approximately 2500 HV. SiC is a manufactured abrasive produced by a high temperature reaction between silica and carbon. The following are the most common metallographic abrasives:
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