As a result of heat treatment, ceramic bonds form two types: fusible (vitreous) and sintered (porcelain). After cooling down, melting bonds turn into glass-like, sintering ones are only partially melted and become close to porcelain in their composition. As a result of processing, the ceramic bond acquires such properties as water resistance, fire resistance, chemical and mechanical resistance. Different abrasive materials require different heat treatment.
Abrasive tools based on aluminum oxide (electrocorundum) are made on fusible bonds, and those made of silicon carbide are made on sintered bonds. Fusible bonds provide greater abrasive tool strength than sintered bonds. The disadvantages of the sintered bond are its brittleness and reduced bending strength. However, both bonds are considered to be hard. Under the hardness of the abrasive tool is understood, the ability of the bond to resist the tearing of abrasive grains from the working surface under the action of external forces.
Various raw materials are used for the production of ceramic binders: refractory clays, feldspars, wollastonite, boron and borlithium glasses, silica, lithium-containing materials (petalite, lithium manganate, molybdenum, etc.). All materials used in the production of binders are pre-dried, ground to a given coarseness (usually less than 100 microns) and mixed in various proportions. In order to increase plasticity, adhesives such as dextrin, soluble glass, etc. are added to the ceramic mass. Masks for abrasive tools are produced depending on the purpose of their use. Ceramic bond is marked with the letter K and has additional alphabetic and numeric designations. All bond varieties have additional indexing. For example, fusible ceramic binders have Russian marking K1, K5, K8.
Ceramic bond with silicon carbide powder is the most common, and is used to make most of the tools used for industrial grinding applications. The composition of the bond includes refractory clay, feldspar, talc, chalk, quartz and liquid glass. In Russia such clay grades as Latnenskaya, Polozhskaya, Novorayskaya are most commonly used. At the same time, the maximum effect is given by the use of coal clay or a mixture of refractory clay and coal-humus substances, which provide maximum strength. These types of raw materials give the binder additional porosity of the structure due to the burnout of carbon and organic impurities. This reduces the amount of carbon and in the final product, increases its strength. To improve wetting of silicon carbide grains with the binder, the method of coating the grains with fine powders, glasses of different composition is also used, as a result of which films are formed on the surface of silicon carbide grains, which, interacting with the binder, contribute to increasing the strength of the tool. In some cases, various modifiers, in particular so-called boron-containing fluxes, are used to increase the strength of such a bond. Manganese sulfate and manganese carbonate may be added to the bond as “modifiers” in amounts up to 2% of the total mass, which also contributes to increasing the strength and hardness of such bonds.
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Examples of ceramic bonded products used for knife sharpening include “Profile” stones based on silicon carbide. They demonstrate a good hardness of the bond and confidently cope with any steel.Also ceramic bond is used in the American Boride stones series T2, which are made on the basis of aluminum oxide and demonstrate a very high hardness of the bond. They also work on any steel, quickly remove metal, are productive and have a long service life. We will tell you more about these stones in a separate article.
