1. Types

Grains used for grinding and polishing tools can be broadly divided into (1) general grain and (2) extra-abrasive grain.
The materials used can be categorized (1) as alumina and silicon carbide, and (2) as diamond and cubic boron nitride, with further sub-categories according to differences in properties and structure. The grain categories here are coded according to JIS standards.

Features of abrasive grain

Abrasive Grain A

This is the most usable abrasive grain and it is used for the cut off wheel, free grinding wheel and for grinding general metallic material that strength tensile is high and it is comparatively extended since its toughness is high.

Abrasive Grain WA

Since the toughness of abrasive grain WA is less than the abrasive grain A and hardness is high, the abrasive grain itself is crushed during grinding work and sharp edges are newly and continuously made. As a result, this is suitable to light grinding for high strength tensile quenched steel, special steel, etc.

Abrasive Grain GA

Though the chemical composition of abrasive grain is the same as the abrasive A, this is suitable to the rough grinding of high strength tensile quenched steel, special steel, etc.

Abrasive Grain PA

This is the pink abrasive grain made by adding a little quantity of chromic oxide. Since the toughness is adequately adjusted, it is effective for preventing burn marks and suitable to tool grinding.

Abrasive Grain SA

This is the abrasive grain that releasing the boundary of crystal after hydrated collapse individually separates crystal. The toughness is top ranking among A-system abrasive grains for precision grinding. Consequently, this is suitable for grinding the intricate materials of stainless steel, super heat-resistant steel, etc., and cast iron, various quenched steels, etc., at a high efficiency rate.

Abrasive Grain KA

This abrasive grain contains titanium oxide more than A-acid grain and the toughness is high. Thus, it is suitable for free grinding and heavy load grinding of steel.

Abrasive Grain RG

This is the most complex oxide abrasive grain having strong and microstructure dendrite crystal which is made by melting and cooling under special condition after mixing zirconia of about 25% to alumina. Thus, it is suitable to remove flaw or scratch on steel billet and rolled steel of special steels except stainless steels by the super heavy grinding.

Abrasive Grain 6A

This is the sintered abrasive grain of column type. Since the toughness is extremely high though hardness is low, it is suitable to remove flaw scratch on steel billet and rolled steel of stainless steels by the super heavy grinding.

Abrasive Grain VA

This is the abrasive grain sintering the high purity alumina microstructure crystal in column type. The toughness is slightly lower even though it is more harder than abrasive grains 6A and RG. Therefore, the abrasive grains bite into hard material by heavy load grinding, thus improving efficiency of grinding.

Abrasive Grain HF

This is the abrasive grain mixing the zirconia of about 25% as well as abrasive grain RG. Since grain shape is sharper than the abrasive grain RG, it displays an excellent performance for deburring of cast iron and free grinding of steels.

Abrasive Grain HN

This is the abrasive grain mixing zirconia of about 40%. Since it has unique friability that occurs for anisotropic crystal, it displays an excellent performance for light grinding to work with the grinder such as portable grinder, offset grinder, etc.

Abrasive Grain C

This abrasive grain is harder than A-system abrasive grain and the toughness is low. It is suitable for grinding a soft and less-extension material and a hard easily broken material.

Abrasive Grain GC

This is as hard as the abrasive grain C, but its toughness is lower than that of abrasive grain C. Since each grain from is very sharp, it is suitable for grinding the crustaceous materials of non-ferrous metals and nonferrous materials for carbide, stone materials, etc., and the soft materials for aluminum, rubber, urethane, etc.

Mixing Abrasive Grain

Abrasive Grain made together with Cardner Co., associated

79A, 80A, 81A, 82A, 83A, 84A, 86A, 91A

Diamond Abrasive Grain

The diamond abrasive grain is divided into two (i.e. natural diamond and composite diamond). This is the hardest material in the world that knoop hardness is 7000 ~ 8000. It is suitable for grinding the crustaceous materials such as the nonferrous materials and non-ferrous metals for carbide, cermet, ceramics, glass, ferrite, stone, refractory materials, etc. However, this diamond abrasive grain is unsuitable for less carbon content of general steels since the abrasive grain is dipped because carbon that is the constituent of diamond abrasive grain will disperse into iron at a high temperature. Also, since it is weak for heat, oxidation occurs at 600 ~ 700℃ into air and its hardness is lost.

Abrasive Grain CBN

This is the cubic boron nitride abrasive grain and its hardness is next to that of diamond since Knoop hardness is 4700. CBN does not react with steel chemically since it differs from the diamond. Since temperature converting to soften hexagonal metal is high as 1400℃, it is suitable for grinding the quenched steel.

2. Grain size

(1) Grain size of grains for grinding wheels

1. Coarse particle grain size distribution

2. Fine particulate and sedimentation test method for general polishing (units: μm)

3. Fine particulate and dispersal test method for precision polishing (units: μm)

(2) Grain size of abrasives for abrasive cloth and sandpaper

1. Coarse particle grain size distribution

2. Fine particulate (P240–P1200) and dispersal test method (units: μm)

3. Fine particulate (P1500–P2500) and dispersal test method (units: μm)

(3) Grain Size of diamond and abrasive grain CBN