Grinding wheels are also called fixed abrasive tools. The grinding wheel is a fixed shape (mostly circular with a through hole in the center) of ordinary abrasives that are consolidated into a certain shape by a bonding agent, and has a certain strength. It is generally composed of abrasives, binders and pores. These three parts are often referred to as the three elements of a consolidated abrasive. According to the different classification of bonding agents, the common ones are ceramic (bonding) grinding wheels, resin (bonding) grinding wheels, and rubber (bonding) grinding wheels. Grinding wheels are the most widely used type of abrasive tools. They rotate at high speed during use. They can rough, semi-finish and grind the outer circle, inner circle, flat surface and various shapes of metal or non-metal workpieces. Fine grinding, slotting and cutting, etc.
The Chinese name of the grinding wheel is divided into natural abrasive super-hard abrasive shape, beveled grinding wheel, cylindrical grinding wheel. Attribute Abrasive, particle size English name Grinding Wheel
Table of Contents
▪ Abrasive selection
▪ Granularity and its choice
4 Abrasive particle size
▪ Hardness and its choice
▪ Shape size and its choice
5 Installation and use
6 Handling and storage
7 Safety requirements
Grinding wheel is the most important type of abrasive tool in grinding process. The grinding wheel is a porous body made by adding a bonding agent to the abrasive, and then compacting, drying and roasting. Due to the difference in abrasives, bonding agents and manufacturing processes, the characteristics of grinding wheels are very different, which has an important impact on the quality of grinding, productivity and economy. The characteristics of the grinding wheel are mainly determined by factors such as abrasive, particle size, bonding agent, hardness, organization, shape and size.
There are many kinds of grinding wheels. According to the abrasives used, it can be divided into ordinary abrasive (corundum and silicon carbide, etc.) grinding wheels and natural abrasive super-hard abrasives and (diamond and cubic boron nitride, etc.) grinding wheels; according to the shape, it can be divided into flat grinding wheels, beveled grinding wheels, cylindrical grinding wheels, Cup-shaped grinding wheels, dish-shaped grinding wheels, etc.; according to the bond 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, bonding agent, shape, size and so on. Since the grinding wheel usually works at high speed, it is necessary to carry out a rotation test (to ensure that the grinding wheel will not break at the working speed) and a static balance test (to prevent vibration of the machine tool during work) before use. After working for a period of time, the grinding wheel should be trimmed to restore the grinding performance and the correct geometry.
The grinding wheel is a round consolidated abrasive tool with a through hole in the center made of abrasive and bonding agent. The characteristics of the grinding wheel are determined by factors such as abrasive, particle size, hardness, bonding agent, shape and size, and are introduced as follows.
Selection of abrasive
Abrasive is the main raw material for making grinding wheels, it is responsible for cutting work. Therefore, the abrasive must be sharp, have high hardness, good heat resistance and certain toughness.
Granularity and its choice
Refers to the size of abrasive particles. The particle size is divided into two types: abrasive particles and fine powder. For large particle size.
Cylindrical grinding wheel
Abrasives smaller than 40μm are called abrasive grains. It is classified by the sieving method, and the particle size number is expressed by the number of holes per inch of the length of the screen through which the abrasive particles pass. Such as 60 # abrasive grains means that its size can pass every inch of length.
Super hard abrasive
There is a 60-hole screen on the degree. For abrasives with a particle size of less than 40μm, it is called micropowder. Use microscopic measurement method to classify, use W and the following number 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 powder is 20μm.
Abrasive particle sizeedit
Mainly related to surface roughness and productivity. In rough grinding, the grinding allowance is large and the required surface roughness value is larger, so coarser abrasive grains should be used. Because the abrasive grains are coarse and the pores are large, the grinding depth can be larger, and the grinding wheel is not easy to block and generate heat. In 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 choice
The hardness of the grinding wheel refers to the firmness of the abrasive particles and the adhesive on 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, and the hardness of the grinding wheel is hard, which means that the abrasive grains are more 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”. Choosing the hardness of the grinding wheel is actually choosing the self-sharpening of the grinding wheel. It is hoped that the sharp abrasive grains will not fall off too early, nor should they not fall off after being dull. . The general principle of choosing 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, in order to make the blunt abrasive particles fall off in time, thereby exposing new abrasive particles with sharp edges and corners (ie self-sharpening), soft grinding wheels are used. The former is because when grinding soft materials, the working abrasive grains of the grinding wheel wear very slowly and do not need to be detached too early; the latter is because when grinding hard materials, the working abrasive grains of the grinding wheel wear faster and require faster Update. In order to ensure the precision and roughness of grinding, a slightly harder grinding wheel should be used for fine grinding. When the workpiece material has poor thermal conductivity and is prone to burns and cracks (such as grinding cemented carbide, etc.), the selected grinding wheel should be softer.
The structure of the grinding wheel refers to the proportion of the three parts of the volume of the abrasive particles, the bonding agent and the pores that make up the grinding wheel. The classification is usually based on the percentage of abrasive particles in the volume of the wheel. The grinding wheel has three organizational states: tight, medium, and loose; it is subdivided into 0-14, a total of 15 levels. The smaller the organization number, the larger the proportion of abrasive particles, and the tighter the grinding wheel; on the contrary, the larger the organization number, the smaller the proportion of abrasive particles and the looser the grinding wheel.
Shape size and its choice
According to the structure of the machine tool and the needs of grinding processing, the grinding wheel is made into various shapes and sizes. Table 6 shows several commonly used wheel shapes, sizes, codes and uses. The outer diameter of the grinding wheel should be selected as large as possible to increase the circumferential speed of the grinding wheel, which is beneficial to improve the grinding productivity and surface roughness. In addition, under the conditions of machine tool rigidity and power permitting, if a larger width grinding wheel is selected, the effect of increasing productivity and reducing roughness can also be obtained, but when grinding materials with high heat sensitivity, in order to avoid burns and burns on the workpiece surface If cracks occur, the width of the grinding wheel should be appropriately reduced.
Installation and useedit
1. The grinding wheel must be visually inspected before installation and use, depending on whether it has cracks or damage, and hit the grinding wheel with a wooden hammer, the sound should be crisp. The rotation test should be carried out according to the GB/T2493 standard before use, otherwise, it is strictly prohibited to use 2. Before installation, the spindle speed on the machine must be checked, and it must not exceed the working speed marked on the grinding wheel. 3. Only special nut wrenches are allowed to tighten the grinding wheel, and must be symmetrically and gradually tightened on the opposite sides of the spindle. The tightening of the nut should be appropriate. It is forbidden to use supplementary fixtures or tapping tools. Turn off the coolant to prevent the grinding wheel from being unbalanced. 5. The diameter of the grinding wheel and the coordination of the grinding wheel spindle and chuck should comply with the GB4674 standard. 6. The newly installed grinding wheel must be in place In the case of the protective cover, idle at the working speed according to the following time: the grinding wheel with an outer diameter of less than 400 mm is not less than 2 minutes, and the grinding wheel with an outer diameter of ≥ 400 mm is not less than 5 minutes. When idling, the operator should not stand in front of the grinding wheel Or tangential direction. 7. Grinding wheels that are not specifically used for end grinding (such as parallel grinding wheels), and grinding wheels that are not specifically used for cylindrical grinding (such as bowl-shaped, cup-shaped grinding wheels) are also not allowed. Grind the outer circle of the grinding wheel 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 the thin-section grinding wheel and the cymbal-shaped grinding wheel, when cutting, such as excessive force , It is easy to cause the grinding wheel to stop and jam and break the grinding wheel, which will cause the grinding wheel to be damaged. When cutting the workpiece, multiple workpieces cannot be stacked and cut to prevent accidents.
Handling and storageedit
1. The grinding wheel is a fragile item and must be handled with care when handling to prevent cracking and damage.
2. The grinding wheel should be stored on the shelf or in the box to prevent moisture.
3. The resin bond grinding wheel should not be in contact with alkali substances. After being stored for more than one year, it must go through the rotation strength test again, and only qualified ones can use it.
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 for cutting off the grinding wheel shall not be less than one-fourth of the diameter of the installed grinding wheel.
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. The surfaces of the grinding wheel chuck should be smooth, free of sharp edges, and well balanced.
4. All rotating parts on the grinding machine, such as grinding wheels, motors, belt pulleys and workpiece headstocks, must be equipped with protective covers. The protective cover should be firm, and its connection strength shall not be lower than the strength of the protective cover.