I. Composition of adhesive:
Resin binder for superhard abrasives is composed of thermosetting resin as binder and various fillers. The properties and dosage of each component have great influence on the physical properties, mechanical properties and grinding properties of the binder. Therefore, in order to achieve good use effect, it is necessary to choose the materials and properties of the machined workpiece. The binder must have the following properties: high strength, high heat resistance, appropriate hardness, low grinding consumption, high grinding efficiency, good surface roughness of the workpiece, economical filler, soluble in acid or alkali and easy to recover. Phenolic resin, epoxy resin, neophenol resin, polyurethane resin, polyimide resin, phenolic resin powder, etc. Widely used as a binder for superhard resin abrasives.
Second, the type of binder:
According to the types, it can be divided into inorganic binders and organic binders. Inorganic binders include ceramic binders, metal binders and magnesite binders. Organic adhesives include resin adhesives and rubber adhesives.
1, resin adhesive
It has good elasticity and polishing function, and the abrasive tool still has good self-sharpening, less blockage, less dressing, higher grinding efficiency, lower grinding temperature and high surface finish after molding, so it has a wide range of applications. Diamond abrasive and diamond abrasive combine to form resin bond, which is often used for semi-fine grinding and fine grinding of cemented carbide workpieces, steel-based cemented carbide workpieces and some nonmetallic materials. The resin bonded cubic boron nitride abrasive tool is mainly used for semi-fine grinding and fine grinding of high vanadium high-speed steel tools and tool steel, die steel, stainless steel and heat-resistant alloy workpieces. However, the resin binder has poor grip on abrasive and poor heat resistance, which leads to great wear of abrasive under high temperature grinding, especially under heavy load grinding. It is often improved by coating metal with abrasive.
2. Ceramic adhesive
The bonding strength of this binder to abrasive is better than that of resin. After the abrasive tool is formed, the surface of the workbench has good chip performance, is not easy to block, has sharp cutting, high grinding efficiency, small thermal expansion and easy control of machining accuracy, which is beneficial to the smooth grinding process. In the shaping and dressing of abrasive tools, it is relatively easy to operate, and is generally used for rough grinding, semi-fine grinding and large contact surface forming grinding. Ceramic bonding agent is a kind of bonding agent which is widely used. The stability of ceramic bonded diamond abrasive is good, and it has gained a good market and reputation in the field of ceramic bonded cubic boron nitride grinding wheel. When ceramic bond is combined with diamond abrasive, the difficulty coefficient is relatively large, which hinders the research and development of ceramic bond diamond grinding wheel.
3. Metal adhesive
Include bronze adhesive and electroplating adhesive. Electroplating adhesive is a kind of adhesive with high bonding strength. Usually, single or multiple layers of abrasive particles are electroplated on a metal substrate. The number of abrasive particles per unit area of the working surface of this bond tool is much higher than that of other bonds, and the abrasive particles are exposed on the surface of the bond, so the cutting is sharp and the grinding efficiency is high. However, due to the limitation of coating thickness, the overall service life of abrasive tools is not high, and they are generally used for special-purpose processing, such as abrasive tools for forming grinding, small grinding heads, nesting knives, electroplating reamers and files. With the continuous progress of technical level, the application of cubic boron nitride electroplated metal bond abrasives is expanding day by day, especially when machining small holes and cavities of various steel parts, which not only has high grinding efficiency and good economy, but also can obtain better shape accuracy. The bronze bonded abrasive tool is made of copper powder and tin powder as the main raw materials, supplemented by other materials to supplement and improve its performance, then added with abrasive and mixed evenly, and then put into the mold for pressing and sintering. This kind of abrasive tool has high bonding strength with abrasive particles, good wear resistance and little wear, so it has a long service life and can maintain a good shape, so it can bear a large load. But the disadvantages are poor self-sharpness, easy surface blockage and high fever, which is very difficult to finish. It is mainly used for rough grinding, fine grinding and cutting of nonmetallic materials such as glass, ceramics, stone, building materials, concrete and semiconductor materials, and a small amount is used for grinding cemented carbide and composite superhard materials, as well as forming grinding, honing and electrolytic grinding.
4. Electroplating adhesive
High strength, thin abrasive layer, high abrasive density, sharp grinding wheel surface cutting, high grinding efficiency, good economic benefits, no need for dressing, but short abrasive life. Electroplating binder is mainly suitable for making abrasive tools, small grinding heads, nesting knives, cutting knives, blades, electroplating reamers and high-speed grinding methods with complex shapes.
Third, the requirements of the binder:
The molecular weight of the adhesive should be moderate. In order to fully wet, the molecular weight is small, but the cohesion is weak. With the increase of molecular weight, the binding capacity is enhanced. However, when the molecular weight is too large, the surrounding cohesive force is too large to wet, which is easy to deform the green body. In order to help the movement of intramolecular segments, plasticizer should be added properly at this time to make the adhesive more flexible and easier to form while being easy to wet.
In order to ensure the quality of products, it is also necessary to prevent impurities from mixing into binders, raw materials and preparation procedures, resulting in harmful defects of products. In the preparation of raw materials, mechanical methods such as crushing and mixing are used to cooperate with binder and dispersant to realize dispersion, and agglomeration particles are not contained as much as possible. Binders are affected by the type and molecular weight, particle surface properties and solvent solubility. And is adsorbed on the surface of raw material particles, so that the agglomeration of powder raw materials can be prevented through the stereoscopic stability effect. In the molding process, the binder endows the raw materials with plasticity, has the function of water retention, and improves the strength and construction workability of the molded body. Generally speaking, the binder is decomposed and volatilized by heating during degreasing, because it hinders the sintering of ceramics. Therefore, it is necessary to choose organic materials that are easy to disperse and remove, and do not contain harmful inorganic salts and metal ions to ensure the quality of products.