The role of cryolite in abrasives

I. As a Bond Modification Additive

• Lowering the sintering temperature: The melting point of cryolite is approximately 1,000°C. During the sintering process of grinding tools, it can form a eutectic with other bonds (such as the silicate components in ceramic bonds), significantly reducing the sintering temperature and energy consumption. Meanwhile, it avoids the strength degradation of abrasives (such as corundum and silicon carbide) due to excessive high-temperature decomposition.
• Improving bond fluidity: Molten cryolite can increase the fluidity of the bond, enabling it to wrap abrasive particles more uniformly. This enhances the forming density and structural strength of grinding tools, reduces porosity, and optimizes the wear resistance and impact resistance of grinding tools.
• Regulating the chemical properties of the bond: The fluoride ions (F⁻) in cryolite can react with metal oxides in the bond to form stable fluorides, improving the chemical bonding force between the bond and abrasives and enhancing the overall bonding strength of grinding tools.

II. Optimizing the Grinding Performance of Grinding Tools

• Promoting the discharge of grinding debris: During the grinding process, cryolite may decompose or soften due to frictional heat, forming lubricating substances to reduce the friction between abrasives and workpieces, lower the grinding temperature, prevent workpieces from burn or deformation due to overheating, and help grindings discharge smoothly to avoid wheel clogging.
• Regulating the self-sharpening property of grinding tools: The addition of cryolite can change the hardness and brittleness of the bond, making the grinding tool more prone to micro-cracking during grinding to expose new abrasive edges, maintaining the sharpness of the grinding tool (i.e., enhancing the "self-sharpening property"), which is particularly suitable for high-speed grinding or machining of hard and brittle materials.

III. Functional Applications in Special Grinding Tools

• Used in electrolytic grinding tools: Cryolite has certain electrical conductivity. In electrolytic grinding (a process combining electrochemical and mechanical grinding), it can be added to grinding tools as a conductive phase to promote the progress of electrolytic reactions, improve processing efficiency, and is commonly used for precision machining of difficult-to-machine materials such as hard alloys and semiconductor materials.
• Stability in high-temperature environments: Cryolite is not easy to decompose at high temperatures and can maintain certain chemical inertness, which can be used to prepare high-temperature resistant grinding tools (such as ceramic grinding tools) and is suitable for grinding operations under high-temperature working conditions, such as rough grinding of steel castings.

IV. Other Auxiliary Roles

• Improving the forming process of grinding tools: In the mixing stage of grinding tools, cryolite powder can be used as a dispersant to promote the uniform mixing of abrasives and bonds, reduce agglomeration, and improve the uniformity and compactness of green body forming.
• Regulating the thermal expansion coefficient of grinding tools: Cryolite has a low thermal expansion coefficient. After addition, it can reduce the overall thermal expansion rate of grinding tools, reduce deformation caused by temperature changes, and improve the dimensional stability of grinding tools in precision grinding.

Application Scenarios and Precautions

• Common applications: Cryolite is mainly used in ceramic bond grinding tools (such as grinding wheels and grinding blocks), some resin bond grinding tools, and special electrolytic grinding tools, suitable for processing materials such as cast iron, non-ferrous metals, glass, and ceramics.
• Dosage control: Excessive addition of cryolite may cause excessive softening of the bond, reducing the hardness and wear resistance of the grinding tool. Therefore, the addition ratio should be accurately controlled according to the abrasive type, processing requirements, and bond system (usually 5%–15% of the bond mass).