Manufacturing process of corundum grinding wheel: brown aluminum oxide grinding wheel is the most important type of abrasive tool in grinding. The grinding wheel is a porous body made by adding a binder to the abrasive, compacting, drying and firing. Due to different abrasives, bonding agents 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, bond, hardness, structure, shape and size. There are many types of grinding wheels.
Classification of brown fused alumina grinding wheel:
According to the abrasive used, it can be divided into ordinary abrasive (corundum and silicon carbide, etc.) grinding wheels.
According to the shape, it can be divided into flat grinding wheel, beveled grinding wheel, cylindrical grinding wheel, cup-shaped grinding wheel, dish-shaped grinding wheel, etc.; according to the bond, it can be divided into ceramic grinding wheel, resin grinding wheel, rubber grinding wheel, metal grinding wheel, etc. The characteristic parameters of the grinding wheel mainly include abrasive, particle size, hardness, bonding agent, tissue number, shape, size, linear speed, etc.
Since the grinding wheel usually works at high speed, a rotation test (to ensure that the grinding wheel will not break at the highest operating speed) and a static balance test (to prevent vibration of the machine tool during operation) should be carried out before use. After the grinding wheel has been in operation for a period of time, it should be dressed to restore the grinding performance and correct geometry.
From the shape, it is divided into flat grinding wheel, double-sided concave grinding wheel, double bevel grinding wheel, cylindrical grinding wheel, dish-shaped grinding wheel, bowl-shaped grinding wheel, and grinding wheels are made into various shapes and sizes according to the needs of machine tool structure and grinding processing. The outer diameter of the brown aluminum oxide grinding wheel should be selected as large as possible to increase the peripheral speed of the grinding wheel, which is beneficial to improving the grinding productivity and surface roughness. In addition, under the conditions of machine tool rigidity and power permitting, if a grinding wheel with a larger width is selected, the effect of increasing productivity and reducing roughness can also be achieved. However, when grinding materials with high heat sensitivity, in order to avoid burns and If cracks occur, the width of the grinding wheel should be appropriately reduced.
Brown fused alumina flat grinding wheels, brown aluminum oxide thin slice grinding wheels (resin flakes, rubber flakes), and brown fused alumina cymbal grinding wheels are products with a large quantity and a wide range, and are also the main varieties for quality spot checks. There are also many quality problems found in spot checks, mainly focusing on quality characteristics such as rotational strength, aperture, hardness, static balance, shape and position tolerances, and product marks.
Main quality problems and hazards of brown fused alumina grinding wheel:
1. Unqualified gyration strength
The slewing strength refers to the ability of the grinding wheel to resist cracking under the action of centrifugal force during the rotation of the grinding wheel, which reflects the tensile stress of the grinding wheel. It is a very important index in the manufacture and use of the grinding wheel. In order to ensure the safe use of the grinding wheel, the standard lists the unqualified slewing strength as a "fatal defect", that is, "a defect that is dangerous or unsafe to the user or to the equipment". The sampling inspection plan is that the number of samples is n=10, the number of acceptances Ac=0, and the number of rejections Rc=1; that is, the rotational strength of 10 grinding wheels must be all qualified, and as long as one piece is unqualified, it will be judged as unqualified. Quality spot checks over the years have found that the rotational strength of fiber-reinforced resin sheet grinding wheels and cymbal-shaped grinding wheels is not ideal, some are lower than the maximum working speed, and some break when they do not reach the specified rotational test speed; some have reached the test speed but cannot It breaks after 30 seconds.
2. Static balance failed
The grinding wheel is an inhomogeneous object. When the grinding wheel rotates, it causes vibration because its center of mass does not coincide with the center of rotation. This state is called the unbalance of the grinding wheel. Unbalanced grinding wheels can cause many hazards:
● It acts on the bearing of the grinding machine to cause the main shaft to vibrate and accelerate the wear of the main shaft of the grinding machine;
● It additionally increases the turning stress of the grinding wheel, reduces its turning strength, and may even cause it to break when turning;
● The vibration of the grinding wheel and the workpiece system is aggravated, which is manifested by the appearance of vibration marks on the surface of the processed workpiece, and the deterioration of the processing accuracy and surface roughness;
● It affects the uniformity of the self-sharpening of the grinding wheel and makes the grinding wheel wear unevenly.
The static balance of the grinding wheel is also one of the main quality indicators reflecting the internal characteristics and performance of the grinding wheel. Unqualified static balance is listed as a "serious defect" in the standard, that is, "severely reduces the performance of the product and has a serious impact on the performance of the processed parts. Defects". In the spot check, if the static balance is unqualified, for example, a fiber-reinforced resin sheet grinding wheel with a diameter of 400mm and a linear speed of 70m/s, the standard stipulates that the static unbalance value is ≤13g, but the actual measurement exceeds 18g. The vibration is predictable.
3. Unqualified hardness
Grinding wheel hardness refers to the resistance of the bond against the detachment of abrasive grains from the surface of the grinding wheel under the action of external force, or it is understood as the difficulty of detaching abrasive grains from the surface of the grinding wheel. Hardness can more accurately reflect the grinding performance of the grinding wheel, and is one of the important indicators to measure the quality of the grinding wheel. There are two requirements for the assessment of grinding wheel hardness:
● The uniformity of hardness (the difference between the maximum value and the minimum value of the hardness value of each point measured) must meet the requirements of the standard;
● The hardness compliance requirement, that is, the average value of the hardness (the arithmetic mean value of the hardness measured at each measuring point) must be within the allowable range specified in the standard. The proportion of unqualified hardness is also quite high. For example, the unqualified hardness of flat grinding wheels exceeds 20% of the total number of unqualified.
4. Aperture failed
The inner hole of the grinding wheel is the installation benchmark, and the unqualified hole diameter of the grinding wheel is listed as "heavy defect" in the standard. If the hole diameter is large, the grinding wheel will be eccentric after installation, which will make the grinding wheel unbalanced. When it rotates at a high speed, it will aggravate the vibration, affect the quality of the grinding process, and even cause the grinding wheel to break and damage the equipment. If the hole diameter is too small, the grinding wheel cannot be installed and cannot be used. If it is installed forcibly, the spindle will be scratched, and the grinding wheel may have hidden damage, which will cause the grinding wheel to break during operation, which may easily lead to accidents. As shown in Table 2, the unqualified pore size is the most serious in spot checks. Accounting for 16.7% of the total number of unqualified flat grinding wheels, accounting for 58.2% of the total number of unqualified cymbal grinding wheels.
5. Flag error
The grinding wheel logo indicates the basic performance of the grinding wheel, which plays an important role in guiding users to use and cannot be ignored. Flag errors are listed as "serious defects" in the standard. There are many problems in the signs, and some signs are incomplete; some logos have wrong content; they even deliberately shoddy, faked and faked trademarks, causing confusion for users, affecting use, damaging their interests, and may lead to major accidents.
6. Unqualified end runout and radial runout
Unqualified end runout and radial runout will cause the grinding wheel to deflect and affect the balance performance when it rotates, which will have a negative impact on the machine tool and the workpiece, so it should be controlled within the allowable range.
