Abrasive grain is the main raw material for the production of Vitrified bonded abrasive wheels. It acts as a cutting edge during grinding. There are many factors affecting the quality of abrasive wheels, such as bonding agent, firing temperature, manufacturing process and so on. But the impact of abrasive grains such as brown fused alumina, white fused alumina on the quality of abrasives is the most critical factor.
The physical and chemical properties of abrasive grains have a great impact on the market manufacturing of abrasive wheels. For vitrified boneded grinding wheels, the wheels need to be sintered at high temperature. So the requirements for various indicators of abrasives are more stringent. The impact of abrasive grain properties on the manufacture and performance of vitrified bond abrasives is reflected in the following aspects:
1. Microhardness of abrasive grain:
The hardness of the abrasive is directly related to the grinding ability of the abrasive particles. The microhardness of the commonly used abrasives is as follows:
| Abrasive type | BFA | WFA | GC | C | PFA | SA | ZA | SG |
| Microhardness（Mpa） | 17640-21600 | 21600-22600 | 28400-29000 | 23700-24200 | 21600-22600 | 21600-23500 | 14700-21000 | 17600-21600 |
2. Brittleness of abrasive grain:
Grinding for different material substrates requires abrasive grit with different toughness. Generally speaking, abrasive grain with less brittleness are used for grinding larger grinding volumes. For example, waste grinding, cutting, grinding, etc. The brittle abrasive is suitable for fine grinding and smooth grinding.
3. Strength of abrasive grain:
Workpieces with higher strength need to be ground with higher strength abrasives. For example, fused aluminum oxide are suitable for stainless steel and ordinary carbon steel. Silicon carbide grit are suitable for ceramics, glass, titanium alloys and other materials.
4. Thermal stability of abrasive grain:
During the grinding process, the grinding contact surface will generate high temperature, and the abrasive grain can maintain certain physical and mechanical properties under the high temperature state before subsequent grinding can be performed. In the manufacturing process of vitrified bonded wheels, especially the firing process, better thermal stability helps the abrasive to maintain a stable crystal structure and physical properties.
5. Chemical stability of abrasive grain:
During the grinding process, the abrasive particle and the processing substrate cannot react chemically. It has to avoid the passivation of the abrasive particles and the blockage of the abrasive tool caused by the adhesion of chemical substances. Under the action of high-temperature sintering of vitrified wheels and low-melting substances of bonding agent, the abrasive grit cannot be decomposed, oxidized or other chemical properties are changed. Especially for easily decomposable abrasive grit such as silicon carbide grain, attention should be paid to the firing process and the composition of the binder.
6. Chemical composition and mineral composition of abrasive grain:
The chemical composition and impurities of the abrasive grit will affect the basic performance of the abrasive wheels and also affect the grinding performance of the abrasive tool. Impurities in the abrasive grit such as SiO2, Fe2O3 and magnetic substances will affect the production of vitrified bonded grinding wheels. There may be defects such as foaming, black center, crack, deformation, etc.
7. The hydrophilicity (wettability) of the abrasive grain:
In the mixing stage of vitrified grinding wheel production, the hydrophilicity of the abrasive grain will affect the distribution of the auxiliary materials and the bonding between the primary abrasive and the auxiliary materials. If the hydrophilicity of the abrasive is not high, the flow and distribution of the bond will be affected. In turn, it affects the bonding strength of abrasive particles and binders.
8. Abrasive particle Surface Morphology
If there are cracks and holes on the surface of the abrasive particles, it will affect the brittleness and strength of the abrasive wheels. The surface roughness of the abrasive grains also affects the bonding properties of the grains and the bond. Generally, abrasive grain with a rougher surface have a stronger bond.
9. Bulk density of abrasive grain:
The bulk density of the abrasive grain affects the bulk density of the pressed molding. Especially in the constant pressure forming process, it has a greater impact on the density, hardness and structure of the green embryo of the abrasive tool. The bulk density of the abrasive is determined by the production process of the abrasive, especially the crushing and grinding process and equipment. Ball mills, roller mills, Barmac, and jet mills produce abrasive particles with different bulk densities.
10. The particle size composition of the abrasive
The particle size distribution range of abrasives is wide. It will the grinding efficiency and surface roughness of abrasives. In addition, it will also affect the hardness stability of the ceramic abrasive tool, especially for the grinding wheel with finer grain size.
11. Magnetic content of abrasive grain
After the magnetic substance is sintered at high temperature, it will form nodes. These nodes are distributed on the surface and inside of the grinding wheel. Participating in grinding will deteriorate the surface quality of the workpiece, and may cause defects such as burns and scribe lines. In addition, nodes can also affect the appearance of vitrified bonded grinding wheels.
