When silicon carbide material is heated to 1300℃ in air, a layer of silica protective film is generated on the surface of its silicon carbide crystal. When the temperature reaches above 1627℃, the silica protective film starts to break down, and the oxidation of silicon carbide intensifies. Therefore, 1627℃ is the high temperature of silicon carbide in the presence of oxidizing agents.
At normal temperature, industrial silicon carbide like green silicon carbide powder is a semiconductor with impurity conductivity. The electrical conductivity of high-purity silicon carbide abrasive decreases with increasing temperature, and the conductivity performance of impurity-containing silicon carbide varies depending on its impurities. Another electrical property of silicon carbide is electroluminescence, and practical devices have been developed.
Physical and mechanical properties
Density: The particle density of various silicon carbide crystal forms is very close, generally considered to be 3.20g/mm³. The natural packing density of silicon carbide abrasive is between 1.2~1.6g/mm³, which depends on the particle size number, particle size composition, and particle shape.
Hardness: The Mohs hardness of silicon carbide is 9.2, the Vickers microhardness is 3000~3300Kg/mm², the Knoop hardness is 2670~2815Kg/mm², and the hardness is high.
The thermal conductivity of silicon carbide products such as black silicon carbide powder is very high, with a small coefficient of thermal expansion and high resistance to thermal shock, making it a good refractory material.
The soft hardness of a grinding wheel indicates that the grinding abrasive is easy to fall off. The hard hardness of a grinding wheel indicates that the abrasive is not easy to fall off. The hardness of the grinding wheel and the hardness of the abrasive are two different concepts. The significant difference between grinding and cutting is that the grinding wheel is self-sharpening. Choosing the hardness of the grinding wheel is actually choosing the self-sharpness of the grinding wheel, hoping that the sharp abrasive will not fall off.
The hardness of the grinding wheel refers to the degree of difficulty of the silicon carbide abrasive particles on the surface of the grinding wheel falling off under external force. When choosing the hardness of the abrasive tool, it is mainly based on the properties of the workpiece material and the grinding method. A single type of abrasive can be made into grinding wheels of different hardness, which is mainly determined by the role and quantity of the bonding agent and the manufacturing process of the grinding wheel.
The general principles are as follows
When grinding hard materials, the abrasive is easy to become blunt. In order to make the blunt abrasives fall off in time, softer abrasives should be selected.
When grinding soft materials, the abrasive is not easy to become blunt. In order to prevent the unsharpened particles from falling off too early, harder abrasives should be selected, such as silicon carbide abrasives.
When grinding non-ferrous metal materials that are very soft and hard (such as aluminum and copper), in order to avoid the clogging of the abrasive tool, softer abrasives should be used.
If the linear speed of the grinding wheel is low, a harder grinding wheel should be used; if the linear speed is high, a softer grinding wheel should be used. If the contact area between the grinding wheel and the workpiece is large, a softer grinding wheel should be selected; if the contact area is small, a harder silicon carbide grinding wheel should be used.
When grinding workpieces with low thermal conductivity, easy deformation, and scorching, a softer grinding wheel should be selected.
When dry grinding, in order to reduce heat generation and prevent scorching the workpiece, the hardness of the abrasive tool should be 12 lower than that of the wet grinding. When the grinding efficiency is high, softer grinding wheels can be selected. When the surface roughness requirements are low, harder grinding wheels can be selected.