During the roasting process, various mineral components interact with each other. Under the same roasting temperature, atmosphere and pressure conditions, some only partial melting. After cooling, the molten binder becomes a vitreous body, which is evenly distributed around the abrasive particle and consolidates the abrasive particle. For the binder whose refractoriness is lower than the firing temperature, it becomes a firing binder. If the refractoriness is higher than the roasting temperature, it becomes a sintering binder. A binder whose refractoriness is close to or equal to the firing temperature becomes a semi-sintered binder.
(1) Binder for corundum abrasives
Roasting binder is mainly used for corundum abrasives, which have a wide variety of commonly used clay-feldspar (K2O·Al2O3·SiO2) and clay-feldspar - boron glass (K2O·Al2O3·B2O3·SiO2).
The ratio of clay-feldspar binder is 20%~50% for clay and 50%~80% for feldspar. Among them, the viscosity content below 30% is the sintering binder, and the high content is the sintering binder. The refractoriness of the binder increases with the increase of clay content and decreases with the increase of feldspar content. The clay-feldspar binder has low cost and can meet the performance requirements of general corundum abrasives, but it cannot manufacture abrasive tools with coarse particle size and soft hardness.
The boron glass in the clay-feldspar-boron glass binder has a refractoriness of 640~690℃, which is a strong flux accelerator. The boron-containing binder is a sintered binder, which has large fluidity, good high temperature wettability and strong reaction ability, and is conducive to improving the strength of abrasive tools. It is mostly used to improve the strength of abrasive tools and coarse-grained and soft-grade hardness abrasives, high-speed grinding wheels and super-hard abrasives with less binder dosage.
(2) Bonding agent for silicon carbide abrasive tools
SiC abrasives are commonly used as sintered bonds. SiC is decomposed into C and Si at high temperature, and the decomposition is intensified with the increase of the liquid phase of the binder. When the oxygen is insufficient, it will produce "black heart" waste products, the refractoriness of the sintered bond is higher than the firing temperature, and the bond only produces a small amount of liquid phase and sintering. The small amount of C decomposed by the particles is oxidized and a SiC film is formed on the surface of the SiC particles to prevent further decomposition of SiC. The fluidity, reactivity and high temperature wettability of the sintered bond are poor. Its grinding tools have low porosity, poor grinding efficiency, and easy to burn the workpiece, and are mostly used for SiC grinding tools with high hardness.
The commonly used bonding agents for SiC abrasives are clay-feldspar-quartz, clay-feldspar-quartz-talc, clay-feldspar-boron glass, etc. The raw material ratio of clay-feldspar quartz binder ranges from 15% to 30% for quartz, 40% to 65% for feldspar, and 20% to 35% for clay, most of which are sintered binders. The sintered binder is brittle, and the grinding tool is suitable for grinding hard workpieces. Clay-feldspar - quartz-talc binder is a sintered binder, mainly used in the manufacture of SiC abrasives above the hardness level, with a large acid-base ratio, and a strong ability to resist "black heart" and prevent abrasives from redness. The strength of the clay-feldspar-boron glass bond is high, suitable for manufacturing 60m/s high-speed SiC grinding wheel, this kind of bond is a sintered bond, the acid-base ratio is large, the product is not easy to produce "black heart" phenomenon.
(3) Binder for diamond and cubic boron nitride abrasive tools
Due to the poor thermal stability of diamond and cubic boron nitride, the ultra-hard abrasive binder must be fired at a lower temperature, and the low temperature firing of low melting binder has the following characteristics.
① Low temperature firing of low melting bond can save fuel cost and reduce the firing cycle.
② Can improve the quality of abrasive tools, reduce waste. Low temperature firing can avoid diamond, cubic boron nitride high temperature thermal stability is poor
③ The low-melting binders at room temperature are clay-feldspar-boron glass-fluorite, boron glass-quartz - corundum powder - solid water glass, clay - boron-containing needle bottle glass, clay - feldspar - window glass.
The glass materials commonly used in diamond abrasive binding are SiO2·ZnO·B2O3 series glass, Na2O·Al2O3·B2O3·SiO2 series glass, SiO2·Al2O3·TiO2·BaO·B2O3 series glass, Cubic boron nitride abrasive commonly used glass material SiO2·B2O3·Na2O·PbO·ZnO series glass, due to the softening temperature of sodium borosilicate glass is low, high strength, good chemical stability, so often selected for diamond and cubic boron nitride ceramic bonding base glass, and then according to the binder low melting point, low expansion. High strength and good wettability require the addition and adjustment of other ingredients. Now, the use of glass-ceramics as a bonding agent of glass materials for the manufacture of diamond and cubic boron nitride abrasives. Glass-ceramics include silicate, aluminosilicate, fluorosilicate, borate and other glass-ceramics. Among them, fluoro-silicate glass-ceramics are commonly used as bonding agents. It is based on the MgO· Al2O3-sio2 system, adding strong co-solvent fluorine and potassium to reduce the melting humidity and crystallization temperature of fluoro-silicate glass-ceramics, so that it can reach the low melting point required by superhard material bonding agents.
