Abrasives - Natural abrasives

Natural abrasive materials of industrial importance are diamond, corundum, emery, garnet, and flint.

Diamond is a mineral composed of crystalline carbon. It is the hardest of all known abrasive materials. Depending on certain qualities, diamonds are divided into technical and jewelry. Of all the mined diamonds, only about 20 percent goes to jewelry: the bulk is consumed by industry. For some types of instruments, only clean crystals of the correct shape are required without any defects and inclusions. The mass of diamonds is determined in carats. One carat is equal to 0.205 grams.

Corundum is a rock consisting of crystalline aluminum oxide with a small admixture of minerals and quartz chemically associated with it. The color of corundum depends on the impurities it contains. There are many varieties of corundum in nature, including noble ones - ruby and sapphire.

Emery is the third hardest material. This is a rock in which corundum and magnetite are mixed with some other minerals. Typically, emery contains about 30 percent corundum.

Garnet - garnets include a group of minerals from the class of silicates having a common structural and chemical formula AI₂B₃ (SiO₄).

Flint is a homogeneous dense rock, consisting of a cryptocrystalline mass of silica (chalcedony) and microscopic grains of quartz with an admixture of clay and other substances. In the abrasive industry, only the purest varieties of this material are used.

Artificial abrasives

Synthetic diamond is obtained from graphite at high pressures and temperatures. In terms of performance, it often surpasses natural diamonds, and its cost is much less. Synthetic diamonds have been produced in the Soviet Union on an industrial scale since 1959. The technology was developed by Soviet scientists. The production of synthetic diamonds is several times higher than the production of natural industrial diamonds.

Elbor is cubic boron nitride. Synthesized at high pressure and temperature. Chemical formula BN. Elbor combines high hardness and heat resistance, twice the heat resistance of diamond. Chemically inert to iron and iron-based alloys. These qualities make CBN indispensable in the processing of high-hard steels and alloys, which are poorly or not processed at all by conventional abrasive and diamond tools. Elbor was created by Soviet scientists. The economic effect from the use of elbor at the enterprise is on average 10 rubles per 1 carat of the tool.

Boron carbide - obtained in an electric furnace from technical boric acid and petroleum coke. The formula of crystalline boron carbide is B₄C.

Silicon carbide is a chemical compound of silicon with carbon SiC. Formerly called carborundum.

Electrocorundum is an artificial abrasive material, which is obtained by melting alumina raw materials in electric arc furnaces, followed by crystallization of the melt. Depending on the content of alumina and melting technology, normal electrocorundum, white and alloyed - chromium, titanium, zirconium are produced. Monocorundum and spherocorundum are also produced. The first is small single crystals of corundum, the second is hollow corundum spheres.

An old recipe from the "Book of Recent Recipes 1899"

... “Two parts by weight of Portland cement and one part of finely ground quartz are kneaded in water until a liquid mushy mass is obtained, which is then poured into the appropriate molds of the required sizes and dried for 12 days.

When the mass prepared in this way dries, it is removed from the mold and immersed for some time in a solution of equal parts of copper sulphate and zinc sulphate; in this solution, all the pores of the molded mass are filled, and the stone acquires the properties of the best natural whetstone or polishing stone.

What abrasives to choose?

Each type of abrasive material has its advantages and disadvantages. Incorrect selection of abrasive material for processing the product can lead to negative consequences. For example, diamond abrasives process steel and hard alloys well, but diamond easily penetrates into the surface structure of steel, caricature it (i.e., saturates the material with itself) - and already this steel begins to work like a file. Selection of an abrasive for work is made individually. It is desirable to carry out tests on experimental samples.

When repairing a measuring tool, various finishing powders and pastes are used. White electrocorundum is used for fine-tuning KMD. It is also used for the preparation of repair plates. To finish the caliper tool, you can use diamond, elbor paste, silicon carbide or titanium carbide. The base of the height gauge is adjusted with electrocorundum. Micrometers and all tools with carbide measuring surfaces are repaired with diamond pastes. When repairing the wear of a micrometer screw, a polishing paste is used ... and so on.

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