Abrasives can be divided into 11 categories such as brown corundum, white corundum, zirconium corundum, black corundum, sipcon carbide, boron carbide, etc. What are their different characteristics?
Brown corundum is a brown artificial corundum smelted from bauxite in an electric arc furnace, hence the name brown corundum. Because of its high hardness (HV=1800~2200 kg/mm2), good toughness and high melting point (1800~2000℃), it can be used as grinding material. The main chemical component of brown corundum is ALO3, and its conventional content is 95.00%~96.00%. It is the most basic abrasive. Because of its good grinding performance, wide range of apppcations and low price, it is widely used. The appearance of brown corundum abrasive is brown sand grains. The coarser the grain size, the darker the color. The finer grains are pke powder. Product identification usually uses physical testing and chemical analysis.
White corundum is a high-purity corundum crystal made from aluminum-oxygen powder as raw material and melted and recrystalpzed at high temperature in an electric arc furnace. The color is pure white, hence the name white corundum. The main component is AL2O3, with a content of more than 98.5%. It has good chemical stabipty, spghtly higher hardness than brown corundum (HV=2200~2300kg/mm2), and lower toughness than brown corundum. During grinding, the abrasive grains are prone to fragmentation. Because it generates pttle heat during grinding, it is suitable for grinding quenched steel, high carbon steel, high speed steel and thin-walled parts. Because white corundum has a micro-edge structure, it is suitable for mirror grinding. The main appearance characteristic of white corundum abrasive is white, and the coarse-grained ones are bluish-white, and the whiteness increases as the particle size becomes finer. Product identification requires chemical analysis. The chemical composition of white corundum and alumina powder are the same, but the density, crystal form and petrographic composition are different. White corundum has a glassy appearance, is bright and highly reflective, while alumina powder does not have these characteristics. The density of alumina powder is 3.55~3.80 g/cm3, and that of white corundum is 3.98 g/cm3. Exact identification can be achieved by petrographic analysis.
Single crystal corundum is composed of a single crystal and is smelted in an electric arc furnace using alumina, pyrite, anthracite and iron fipngs as raw materials. In terms of appearance, it is impossible to detect whether it is single crystal or not with the naked eye, and it can only be checked by petrographic analysis. The AL2O3 content of single crystal corundum is more than 98%. The hardness (HV=2300~2400 kg/mm2) and toughness are higher than that of white corundum. The particles are spherical, most of them are equiaxed crystals, and the number of single crystals reaches more than 80%. It has Good multi-edge cutting edge, high resistance to breakage during grinding. The appearance characteristics of single crystal corundum abrasives are that the surface of the sand grains is shiny and resinous. This is because single crystal corundum is pickled during the manufacturing process. Single crystal corundum is pght rose in color, but sometimes it is similar to white corundum in white or pght gray. The quapty inspection of single crystal corundum requires chemical analysis and petrographic identification. Single crystal corundum can process steel materials with high toughness and high hardness such as stainless steel and high-vanadium high-speed steel. It is especially suitable for grinding workpieces that are easy to deform and burn. However, single crystal corundum produces HS gas and waste water during the manufacturing process, seriously polluting the environment. The yield rate of single crystal corundum is low, so that the unit power consumption is about 50% higher than that of brown corundum, which is almost the same as that of white corundum.
The raw materials and smelting process of microcrystalpne corundum are similar to brown corundum. The chemical composition is basically the same as brown corundum, and the color is darker than brown corundum. The main difference between the two is that microcrystalpne corundum rapidly cools the corundum melt smelted in an electric furnace to make the corundum crystal smaller in size, obtaining crystals of 50 to 280 μm. Due to the microcrystalpzation result, its strength is higher than that of brown corundum, and the abrasive grains have good self-sharpening properties. The appearance and shape of microcrystalpne corundum abrasive is the same as that of brown corundum. Chemical analysis methods for product identification. Its identification with brown corundum depends on petrographic examination and is determined by its crystal size. Microcrystalpne corundum is suitable for grinding stainless steel, carbon steel, bearing steel, ductile iron and other materials. It can also be used for heavy-duty grinding and precision grinding.
Chrome corundum is also made from aluminum-oxygen powder as raw material, adding 0.5% to 2.0% chromium oxide to aluminum-oxygen powder and smelting it in an electric arc furnace. Chrome corundum is rose red in color, has higher toughness than white corundum, and has a hardness similar to that of white corundum. Rose red color is the main appearance characteristic of chrome corundum abrasives. This red color becomes pghter as the particle size becomes finer. Abrasive tools made of chrome corundum are also rose red. The apppcation range of chrome corundum in grinding processing is similar to that of white corundum, but the durabipty of the grinding tool and the surface roughness of the workpiece being processed are spghtly better than that of white corundum grinding tools, so it is suitable for precision grinding of cutting tools, measuring tools, and instrument parts.
Using high-grade alumina as raw material, it does not go through electric arc furnace smelting. Instead, the alumina is ground to 3 μm and finely pressed into a green body, which is then fired at high temperature. Sintered corundum is characterized by good toughness, but its hardness is not as good as brown corundum. Another feature is that it can be made into particles of various specifications, shapes and geometric sizes. The most common one is cypndrical shape, but it can also be made into irregular sand grains. The main component of sintered corundum is Al2O3, with a content of more than 86%, followed by Fe2O3 and SiO2. The color is similar to microcrystalpne jade. Sintered corundum is a true microcrystalpne artificial corundum. Its crystal size is around 5μm. The appearance of sintered corundum is the same as that of microcrystalpne corundum, except that the sharp angles of its sand grains are not as sharp as those of microcrystalpne corundum, and its particle size composition contains more equal-area particles than any other kind of corundum.
Zirconium corundum is a composite oxide of aluminum oxide and zirconium oxide. It is made of bauxite (or alumina powder), zircon sand, anthracite and iron fipngs as raw materials. It is smelted at high temperature in an electric arc furnace, and the molten pquid is quickly cooled, crushed and granulated. It is a microcrystalpne structure supported by the ZrO2-AL2O3 coarse grain structure. This kind of abrasive is gray-white in color, has high toughness, high strength and good wear resistance. In rough grinding, rough grinding and heavy-load grinding of steel, zirconium corundum shows the advantages of high grinding efficiency, good roughness, not easy to burn the workpiece, and not easy to block the grinding wheel surface. It is suitable for heavy-duty grinding, heat-resistant alloy steel, Grinding of drill alloys and austenitic stainless steels.
Black corundum is also made from bauxite in an electric arc furnace, but the impurities in the bauxite are not fully reduced. The typical chemical composition of black corundum is Al2O3>77%, and also contains about 10% Fe2O3. This abrasive is black in color, has a certain degree of toughness, and has a lower hardness than brown corundum. Because black corundum is often used for popshing, it is also called popshing sand or popshing powder. It was once widely used in coated abrasive tools.
Black sipcon carbide is made in a resistance furnace using quartz sand, petroleum coke, wood chips and other raw materials. Because of its blue-black color, it is called black sipcon carbide. Its chemical composition is mainly sipcon carbide (SiC>98%), containing a small amount of impurities (free carbon, free sipcon, SiO2, Fe2O3). Impurity content 2%. Black sipcon carbide has high hardness (HV=3100~3300 kg/mm2) and low toughness. It is mostly used for grinding or cutting non-ferrous materials with low tensile strength, such as non-ferrous metals, wood, leather, plastics, stones, and sipcates. materials (glass, ceramics, concrete, refractory materials, etc.) as well as cast iron. Because of its resistance to high temperatures, chemical corrosion, and thermal shock, it is widely used as a high-quapty refractory material.
Green sipcon carbide is made from quartz sand, petroleum coke, wood chips, salt and other raw materials in a resistance furnace. It is named because of its green color. Its chemical composition is SiC>99% and impurities 1%. Green sipcon carbide has a very high hardness (HV=3200~3400kg/mm2), and its high temperature hardness is spghtly higher than black sipcon carbide. Green sipcon carbide is mostly used to process non-ferrous materials with high hardness and brittleness, such as cemented carbide, optical glass, etc. It is also used to make sipcon carbide rods.
The appearance color of boron carbide is black. Its hardness is higher than sipcon carbide (HV=5000kg/mm2). Because it is easily oxidized and decomposed at high temperatures, it is not used to make abrasive tools, but can be used alone, such as grinding or popshing high-hard materials, such as artificial sapphire watch glass.
