The grinding wheel is also called a bonded abrasive. The grinding wheel is a bonded abrasive that consolidates ordinary abrasives into a certain shape (mostly circular with a through hole in the center) and has a certain strength. It is generally composed of abrasives, binders and pores. These three parts are often called the three elements of bonded abrasive tools. According to different classifications of binders, the common ones are ceramic (bond) grinding wheels, resin (bond) grinding wheels, and rubber (bond) grinding wheels. The grinding wheel is the most commonly used and widely used type of abrasive tools. When used, it rotates at high speed and can be used for rough grinding, semi-finish grinding and grinding of the outer circle, inner circle, flat surface and various profiles of metal or non-metal workpieces. Fine grinding as well as grooving and cutting off, etc.
Grinding wheels are the most important type of abrasive tools in grinding processing. The grinding wheel is a porous body made by adding a binder to the abrasive, compacting, drying and roasting. Due to different abrasives, binders and manufacturing processes, the characteristics of grinding wheels vary greatly, which has an important impact on the processing quality, productivity and economy of grinding. The characteristics of the grinding wheel are mainly determined by factors such as abrasive, particle size, binder, hardness, structure, shape and size.
There are many types of grinding wheels. 1. According to the abrasives used, it can be divided into ordinary abrasives (corundum, silicon carbide, etc.) grinding wheels and natural abrasive superabrasives and (diamond, cubic boron nitride, etc.) grinding wheels; 2. According to the shape, it can be divided into flat grinding wheels, bevel grinding wheels, Tubular grinding wheels, cup-shaped grinding wheels, disc-shaped grinding wheels, etc.; 3. According to the binder, they can be divided into ceramic grinding wheels, resin grinding wheels, rubber grinding wheels, metal grinding wheels, etc.
The characteristic parameters of the grinding wheel mainly include abrasive, particle size, hardness, bond, shape, size, etc. Since the grinding wheel usually works at high speed, a rotation test (to ensure that the grinding wheel will not break at working speed) and a static balance test (to prevent machine tool vibration during operation) should be performed before use. After a grinding wheel has been in operation for a period of time, it should be dressed to restore grinding performance and correct geometry.
The grinding wheel is a circular bonded abrasive tool with a through hole in the center made of abrasives and binders. The characteristics of the grinding wheel are determined by factors such as abrasive, particle size, hardness, bond, shape and size, which are introduced below.
Abrasive is the main raw material for making grinding wheels, and it is responsible for cutting work. Therefore, the abrasive must be sharp, have high hardness, good heat resistance and a certain degree of toughness.
Granularity and its selection
The particle size of the grinding wheel refers to the size of the abrasive particles. There is an inverse relationship between the “mesh” and “grain size” of the grinding wheel. The larger the “mesh”, the smaller (the finer) the particle size.
External grinding wheel
Refers to the size of the abrasive particles. Particle size is divided into two categories: abrasive grains and micro powder. Abrasives with particle sizes greater than 40 μm are called abrasive grains. Classified by the screening method, the particle size number is expressed by the number of holes per inch of the sieve through which the abrasive particles pass. For example, a 60# abrasive grain means that its size is just enough to pass through a screen with 60 holes per inch. Abrasives with particle sizes less than 40 μm are called micropowder. Use microscopic measurement method to classify, use W and the number after it to indicate the particle size number, and the value after W represents the actual size of the micropowder. For example, W20 indicates that the actual size of the micropowder is 20μm.
Abrasive particle size
Mainly related to processing surface roughness and productivity. When rough grinding, the grinding allowance is large and the required surface roughness value is large, so coarser abrasive grains should be selected. Because the abrasive grains and pores are large, the grinding depth can be larger, and the grinding wheel is less likely to get clogged and heat up. When fine grinding, the margin is small and the roughness value is required to be low, so finer abrasive grains can be selected. Generally speaking, the finer the abrasive grains, the better the grinding surface roughness.
Hardness and its selection
The hardness of the grinding wheel refers to how firmly the abrasive grains and adhesive adhere to the surface of the grinding wheel. The hardness of the grinding wheel is soft, which means that the abrasive grains of the grinding wheel are easy to fall off; the hardness of the grinding wheel is hard, which means that the abrasive grains are difficult to fall off. The hardness of the grinding wheel and the hardness of the abrasive are two different concepts. The same abrasive can be made into grinding wheels with different hardnesses, which mainly depends on the performance and quantity of the bond and the manufacturing process of the grinding wheel. The significant difference between grinding and cutting is that the grinding wheel has “self-sharpening properties”. Choosing the hardness of the grinding wheel is actually choosing the self-sharpening property of the grinding wheel. It is hoped that the sharp abrasive grains will not fall off too early, nor will they not fall off after being blunted. . The general principle for selecting the hardness of the grinding wheel is: when processing soft metals, in order to prevent the abrasive from falling off prematurely, use a hard grinding wheel. When processing hard metals, a soft grinding wheel is used in order to quickly shed the blunt abrasive grains and expose new abrasive grains with sharp edges and corners (i.e., self-sharpening). The former is because when grinding soft materials, the working abrasive grains of the grinding wheel wear very slowly, and there is no need to break away too early; the latter is because when grinding hard materials, the working abrasive grains of the grinding wheel wear faster and require faster removal. renew. When fine grinding, in order to ensure grinding accuracy and roughness, a slightly harder grinding wheel should be used. When the workpiece material has poor thermal conductivity and is prone to burns and cracks (such as grinding carbide, etc.), the grinding wheel selected should be softer.
Grinding wheel structure wear resistance
The structure of the grinding wheel refers to the proportional relationship between the volumes of the three parts of the grinding wheel: abrasive grains, binder, and pores. It is usually classified by the percentage of the grinding wheel volume occupied by the abrasive grains. The grinding wheel has three organizational states: tight, medium, and loose; it is subdivided into No. 0-14, a total of 15 levels. The smaller the tissue number, the greater the proportion of abrasive grains, and the tighter the grinding wheel; conversely, the larger the tissue number, the smaller the proportion of abrasive grains, and the looser the grinding wheel.
Shape size and selection
According to the machine tool structure and grinding processing needs, grinding wheels are made into various shapes and sizes. The outer diameter of the grinding wheel should be selected as large as possible to increase the peripheral speed of the grinding wheel, which is beneficial to improving grinding productivity and surface roughness. In addition, if the stiffness and power of the machine tool permit, if you choose a grinding wheel with a larger width, you can also achieve the effect of improving productivity and reducing roughness. However, when grinding highly heat-sensitive materials, in order to avoid burns and burns on the workpiece surface If cracks occur, the width of the grinding wheel should be appropriately reduced.
Install and use
1. Before installation and use, the grinding wheel must be visually inspected to see if it has cracks or damage, and the grinding wheel should be struck with a wooden hammer. The sound should be crisp. Before use, a rotation test should be carried out in accordance with the GB/T2493 standard. Otherwise, use is strictly prohibited. .
2. Before installation, the spindle speed of the machine tool must be checked and must not exceed the working speed marked on the grinding wheel.
3. Only special nut wrenches are allowed to be used to fasten the grinding wheel, and they must be tightened symmetrically and gradually in sequence on both sides of the spindle. The nuts should be tightened appropriately. It is prohibited to use supplementary clamps or knocking tools.
4. Turn off the coolant to avoid imbalance of the grinding wheel.
5. The cooperation between the grinding wheel aperture, the grinding wheel spindle and the chuck should comply with the GB4674 standard.
6. The newly installed grinding wheel must be idling at working speed with a protective cover: no less than 2 minutes for a grinding wheel with an outer diameter <400 mm, and no less than 5 minutes for a grinding wheel with an outer diameter ≥ 400 mm. When idling , the operator should not stand in front of the grinding wheel or in the tangential direction.
7. Grinding wheels that are not specifically used for end face grinding (such as parallel grinding wheels) must not be ground with the end face of the grinding wheel. Grinding wheels that are not specifically used for cylindrical grinding (such as bowl-shaped or cup-shaped grinding wheels) cannot be used for grinding with the cylindrical surface of the grinding wheel. Grind to prevent the grinding wheel from breaking.
8. When the grinding wheel is grinding the workpiece, it is prohibited to push the workpiece with a lever to increase the pressure on the grinding wheel.
9. For thin slice grinding wheels and cymbal-shaped grinding wheels, if you use too much force during cutting, the grinding wheel may stop and get stuck and the grinding wheel may be broken, causing damage to the grinding wheel. When cutting workpieces, do not stack multiple workpieces for cutting to prevent accidents.
Transportation and storage
1. The grinding wheel is a fragile item and must be handled with care when handling to prevent cracking and damage.
2. The grinding wheels should be stored on shelves or in boxes to prevent them from getting wet.
3. Resin bonded grinding wheels should not be in contact with alkali substances. After being stored for more than one year, they must pass the rotational strength test again and only those that pass the test can be used.
1. The diameter of the grinding wheel chuck shall not be less than one-third of the diameter of the installed grinding wheel. The diameter of the grinding wheel chuck used for cutting off the grinding wheel shall not be less than one quarter of the diameter of the grinding wheel being installed.
2. For any form of grinding wheel chuck, the diameter of the left and right parts and the radial width of the pressing surface must be equal.
3. Each surface of the grinding wheel chuck should be smooth, without sharp edges, and well balanced.
4. All rotating parts on the grinding machine, such as grinding wheels, motors, pulleys and workpiece headstock, must be equipped with protective covers. The protective cover should be strong and its connection strength should not be lower than the strength of the protective cover.
Grinding wheel forming process
The grinding wheel forming process is to mix the abrasive and the binder and put it into the mold, spread the material evenly, and then run the equipment to press down. When the pressure reaches the predetermined value, hold the pressure for a period of time, then release the pressure and return, and the ejection cylinder will The finished product is ejected. The processing of grinding wheels can be divided into two methods. One is the hot pressing method, which is to press and sinter the abrasives by hot pressing. This method is suitable for small grinding wheels, requires small tonnage of equipment, and has better precision in producing grinding wheel discs. , the grinding wheel has high strength and long service life; the second method is the cold pressing method, which is to press the abrasive into shape by cold pressing and then sinter it. This method has a simple process, long mold life, and a mass production cycle It has high short-term efficiency and low production cost. It is suitable for processing large grinding wheels and requires large tonnage of equipment.
1. Ingredients: Weigh the various raw materials required according to the formula requirements.
2. Mixing: The process of mixing abrasives and other various materials into molding materials in order and time according to process requirements.
3. Forming: The process of using a grinding wheel forming hydraulic press and a mold to press the molding material into a grinding wheel blank of the required shape.
4. Drying: It is divided into natural drying in natural environment and artificial drying using artificial heating, as well as continuous drying using both.
5. Firing: In this process, the ceramic grinding wheel is called sintering; the resin grinding wheel is called hardening; the rubber grinding wheel is called vulcanization. The entire process is completed by curve changes of heating, constant temperature, and cooling.
6. Processing: The process of using a lathe or grinder to process the outer circle, plane, and aperture of the burned embryo into finished products. Some also need to fill holes, infiltrate sulfur, penetrate wax, etc.
7. Inspection and stamping: The appearance, size, hardness, balance, strength, etc. of the product must be strictly inspected to ensure that it meets the requirements of the standard. Qualified products shall be stamped with the seal required by the standard and printed in batches. Product certification.
8. Packaging and storage: Qualified products are packaged as required and then stored in storage.