Bacic Propertities of Abrasive Grains

Abrasive grains are the main component of abrasive tools, and can be directly used for grinding and polishing. Abrasives, working as the main material in grinding a workpiece, should possess the following basic properties, i.e. hardness, toughness, strength, thermal stability and chemical stability to satisfy all needs of workpieces' processing.

1. Hardness 

Hardness is a basic capacity of abrasives. Since grinding is performed through abrasives' abrasion on the surface of the workpiece, thus the abrasives must be harder than the material.

Abrasives' hardness is effected by its chemical composition, integrity of crystalline structure , impurities in the crystal and so on, the differences of which also determine each kind of abrasive partially suitable for a particular application.

2. Toughness 

Abrasives' toughness refers to the ability of resistance to rupture in force or impact. Proper toughness can guarantee abrasives' cutting effect and generate new blading edge after passivation to keep its sharpness. If the hardness is higher, it will get damaged before fully coming into play. Abrasives' toughness, to a large extent, depends on its crystalline state (including defects such as cracks and porosity) and its size, macro geometrical shape and granulating method. Besides, particle shape also affects its toughness, so shape of abrasive volume shows higher toughness than flake or needle ones.

3. Mechanical Strength

Abrasives, influenced by the impact and high temperature in the repeated grinding process, will produce thermal stress. Therefore, grits must have a certain mechanical strength to ensure its cutting effect. Abrasives' mechanical strength is derectly connected with its material and crystal state. In general, the strength of aluminum oxide is higher than silicon carbide. For aluminum oxide, zirconia alumina shows the highest strength, and brown fused alumina is higher than white fused alumina. For silicon carbide, black silicon carbide shows higher strength than green silicon carbide. Abrasives of a complete monocrystalline shape is of high strength.

4. Thermal Stability

Because the temperature of the grinding zone is quite high (400~1000℃ usually), it requires abrasives maintain the necessary physical and mechanical properties in such cicumstance to keep its sharp cutting edges. Chemical reactions between

abrasives and workpiece should be avoided, as it may cause adhesion and proliferation which will make abrasive plug or rust, and finally reduce or lose cutting ability.

6. Fine Granulating Process

For the convenience of grinding, abrasives can better be ginded into even and regular grits with full size. Some materials with high hardness and toughness are not suitable for abrasive, such as tungsten carbide powder.