Abrasive grains and powder for use in the manufacturing of bonded abrasives
The following data sheets are a compilation of the useful chemical and physical properties of the abrasive grains and powders for the production of bonded abrasives. These data sheets will simplify selection of the best grain or powder for a particular application. All of the values included herein are to be considered typical values, not specifications.
CHEMICAL ANALYSIS:
The chemical analysis reported have been obtained by standard chemical methods. These analyses are important to the user because they affect the properties of the products made from these grains or powders. The composition of silicon carbide abrasive used directly effects the toughness and efficiency of the finished bonded abrasive products. The toughness of aluminum oxide grain is, in part, a function of the amounts of other metal oxides present. Titania, Silica, Zirconia and Soda are of particular interest in this respect
CHEMICAL SYMBOLS:
The most frequently referenced chemical symbols appearing in these data sheets are:
Al | Aluminum | MgO | Magnesium Oxide |
Al₂ O₃ | Aluminum Oxide | Na₂ O | Sodium Oxide |
C | Carbon | Si | Silicon |
CaO | Calcium Oxide | SiC | Silicon Carbide |
Cr₂ o₃ | Chrome Oxide | SiO₂ | Silicon Oxide |
Fe | Iron | TiO₂ | Titanium Oxide |
Fe₂ O₃ | Iron Oxide | ZrO₂ | Zirconium Oxide
|
COLOR:
The color of the aluminum oxide is also a function of the metallic oxides present and their oxidation states. Some of the principal oxides which effect color are chromium, iron and titanium.
CRISTALLOGRAPHY:
The crystallographic descriptions have been verified by x-ray diffraction techniques. For abrasive use it is important that silicon carbide be in the hexagonal system, alpha silicon carbide. Beta of cubic crystalline silicon carbide is considerably softer and less stable and is unsuitable for bonded abrasive use. Silicon carbide grains are fragments of whole crystals or are single crystals themselves. Therefore, crystal size measurements of silicon carbide grains would be meaningless.
Aluminum oxide grains, however, are often composed of several small crystals cemented together by a matrix material. In general, the finer the crystal size, the tougher the abrasive grain. Petrographic thin sections of aluminum oxide grain, ground to 30 micron thickness, when observed through a polarizing microscope, will show this crystal structure. Average crystal size is measured and the amount of matrix material is estimated from these thin sections.
POROSITY:
Determinations of porosity (and related friability characteristics) are made using two primary analyses methods:
1. Individual pores are measured in thin sections of 14 or 16 grit abrasive grain obtaining an average pore size from which total pore volume is then estimated. It has been observed that grains with high pore volume and large pores fracture much more readily than do similar grains which are nearly solid.
2. Particle specific gravity is measured with a pycnometer to indicate the amount of porosity. The closer this value approaches absolute material specific gravity ( Sic = 3.23 ; Al₂ O₃ = 3.99 ), the fewer the material’s pores or voids.
HARDNESS:
Hardness is measured on individual grains buy the Knoop ₁₀₀ micro-hardness method. A comparison of Knoop ₁₀₀ hardness values and the more familiar Moh hardness values is present on the COMPARING HARDNESS TABLE.
