Selection of grinding wheel in grinding process

2019-01-29 15:57 Source:未知 Writer: admin
Selection of grinding wheel in grinding process
1 Material Classification
In grinding process, grinding wheel is made by mixing abrasive and binder in proper proportion, pressing, drying and sintering. It is mainly composed of abrasive particles, binders and voids. The abrasive grain is equivalent to the cutting edge of the cutting tool and plays the role of cutting. The binding agent fixes the position of each abrasive grain and supports the abrasive grain. The voids are helpful for cutting and heat dissipation.
The working characteristics of grinding wheels are measured by several factors, such as abrasive, particle size, binder, hardness, structure strength, shape and size. All kinds of characteristics have their application scope.
Abrasive is the main material of grinding wheel. When grinding, it needs strong friction, extrusion and high temperature. Therefore, there are certain requirements for the performance and composition of the abrasive: if the hardness is higher than the hardness of the workpiece, the remaining metal can be cut off. It also has higher strength and toughness. Under the action of external force, it produces the ability to resist cracking, and has high thermal and chemical stability. At high temperature, maintaining physical properties is conducive to reducing cutting deformation and good chemical stability, so as not to adhere to the workpiece, protect the workpiece, do not occur chemical reaction, delay the passivation of grinding wheel, prevent blockage of air holes, improve the cutting ability and prolong service life.
2. Main Composition of Grinding Wheel
The types of grinding wheels for grinding are generally divided into three categories: corundum, carbide and superhard abrasives.
(1) The main component of corundum is alumina, which is suitable for grinding materials with high tensile hardness, such as various steels. It is further subdivided into: brown corundum, white corundum, chromium corundum, single crystal corundum, microcrystalline corundum, etc., with good cutting performance and good "self-sharpening".
(2) Carbides are classified into black silicon carbide and green silicon carbide, with black and green colors respectively.
(3) Superhard abrasive is a new type of abrasive developed recently, which can be divided into artificial diamond and cubic boron carbide. Artificial diamond takes graphite as raw material. Its cutting edge is very sharp and its cutting performance is excellent, but its price is expensive. It is suitable for processing high hardness materials, such as hard alloy, optical glass and so on. The hardness of cubic boron oxide is slightly lower than that of diamond, which has good grinding performance, stable thermochemical performance and high grinding efficiency.
3 binder has great influence on the life of grinding wheel
The grinding wheel is grinded in high speed rotation, and it works under the conditions of high temperature, high pressure, strong impact load and strong corrosive grinding. The bonding of abrasives must be firm, which requires a higher requirement for the use of grinding wheel. It can be roughly divided into the following categories:
(1) Ceramic adhesives: It has stable physical and chemical properties, more voids, can better maintain the geometric shape of grinding wheel, cold, hot, dry and wet can adapt, and not afraid of water, oil, acid and alkali erosion, low price, widely used. Be careful not to use too fast.
(2) Binder: It has a high bonding degree, can be used to manufacture thin-section grinding wheel, and has a certain elasticity and good polishing performance, but its heat resistance is poor. It burns itself first at high temperature. Sand grains are easy to fall off, self-sharpening is good, grinding efficiency is high, but it is easy to lose the correct shape. In addition, resin bond has poor alkali resistance and wears quickly under the action of alkaline cutting fluid. Strength decreases in humid environments. Therefore, the storage period of grinding wheel should not exceed one year.
(3) Rubber binder: It has high elasticity and good yield of grinding wheel. Especially at high temperature, it is easy to produce deformation, not easy to burn workpiece and has good polishing effect. Small pore, less void, compact organization, good grinding wheel shape. However, rubber binder has poor heat resistance, oil resistance and moisture resistance, and the storage life of grinding wheel should not exceed two years.
(4) Binder of magnesite: Binder of magnesite has low strength, good self-sharpening of grinding wheel, less heat in grinding and poor water resistance, so it is only suitable for dry grinding.
(5) Reinforcing resin binder and reinforcing rubber binder: Adding high strength polyester plastics and other materials into resin binder or rubber binder enhances bonding strength and improves the degree of anti-cracking of grinding wheel.
4 Requirements for Grinding
The hardness of grinding wheel refers to the degree of firmness of bonding abrasive particles. The firmer the bonding is, the harder the grinding wheel is. It is suitable for grinding soft workpieces. On the contrary, the soft grinding wheel should grind the workpiece with high hardness and high surface finish. General selection principles: brown corundum, with high hardness and toughness, is suitable for grinding metals with high tensile strength, such as carbon steel, alloy steel, bronze, etc. White corundum: good self-sharpening, small grinding force and heat, suitable for grinding hardened steel, high carbon steel, gears, thin-walled parts, etc. Chromium corundum: Good toughness and hardness, suitable for grinding high-speed steel, manganese steel, cutting tools, etc. Single crystal corundum and microcrystalline corundum: Hardness, toughness and strength are good, suitable for grinding stainless steel, bearing steel, ductile iron and so on. Black silicon carbide and green silicon carbide: brittle, high hardness, suitable for grinding brass, cemented carbide tools, optical glass, etc. Cubic boron carbide and synthetic diamond: high hardness, good wear resistance, suitable for grinding tough and sticky materials, gemstones and jades, etc.
5. Structures and strengths have higher requirements for grinding wheels
Tight organization, easy to maintain the geometric shape of the grinding wheel, ensure high grinding accuracy, prolong the service life of the grinding wheel. It can bring cutting fluid or air into the grinding zone together, reduce grinding heat and improve grinding efficiency, but it can make grinding wheel wear fast and shorten its life.
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