The average pass rate and the lowest pass rate of the quality inspection of the grinding wheel products in the past 6 years Major quality problems and their hazards
1. Unsatisfactory Swing Strength Rotary strength refers to the ability of the grinding wheel to resist cracking under the action of centrifugal force, reflecting the tensile stress of the grinding wheel. It is a very important indicator for the manufacture and use of the grinding wheel. In order to ensure the safe use of the grinding wheel, the standard classifies the unsatisfactory slewing strength as a "fatal defect", that is, "a defect that is dangerous or unsafe to the user or the device". The sampling inspection scheme is that the number of samples is n=10, the number of receptions is Ac=0, and the number of rejections is Rc=1; that is, the rotation strength of 10 grinding wheels must be all qualified, and if one piece fails, it is judged as unqualified. The quality inspections over the years have found that the rotational strength of the fiber reinforced resin sheet grinding wheel and the é’¹-shaped grinding wheel is not ideal, and some are lower than the maximum working speed, and some ruptures when the speed of the slewing test is not reached; some also reach the test speed but cannot It will rupture after 30s. The unsatisfactory ratio of the rotation strength is 7.1% to 18.7% (see Table 2 for details).
When the fiber reinforced resin sheet grinding wheel and the é’¹-shaped grinding wheel are used, most of them are hand-held cutting and grinding, and the distance between the operator and the grinding wheel is relatively close. Therefore, once the rotating strength is poor, the grinding wheel is broken during the cutting or grinding process, which is liable to cause personal injury or death.
2. The static balance is unqualified: the grinding wheel is an inhomogeneous object. When the grinding wheel rotates, the vibration is caused by the center of mass and the center of rotation do not coincide. This state is called the imbalance of the grinding wheel. Wheel imbalance can bring a lot of harm:
Acting on the grinding machine bearing, causing the main shaft to vibrate and accelerate the wear of the grinding machine spindle;
The additional increase of the rotary stress on the grinding wheel reduces the rotational strength and may even cause it to rupture upon rotation;
The vibration of the grinding wheel and the workpiece system is intensified, which is manifested by the occurrence of vibration marks on the surface of the workpiece to be processed, and the machining accuracy and surface roughness are deteriorated;
Affect the uniformity of the self-sharpening of the grinding wheel, so that the grinding wheel wears unevenly.
The static balance of the grinding wheel is also one of the main quality indicators reflecting the intrinsic characteristics and performance of the grinding wheel. The static balance failure is classified as “heavy defect†in the standard, that is, “seriously reduce the product performance and have a serious impact on the performance of the machined parts. Defects". In the spot check, the static balance is not qualified as shown in Table 2, one of which
A fiber-reinforced resin sheet grinding wheel with a diameter of 400 mm and a linear speed of 70 m/s has a standard static imbalance value of ≤13 g, but the actual measurement exceeds 18 g. The vibration of such a grinding wheel during use is conceivable.
3. Unsatisfactory hardness: The hardness of the grinding wheel refers to the resistance of the bonding agent to resist the detachment of the abrasive particles from the surface of the grinding wheel under the action of external force, or the ease of detachment of the abrasive particles from the surface of the grinding wheel. Hardness can correctly 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 the hardness of the grinding wheel:
Uniformity of hardness (the difference between the maximum and minimum values ​​of the hardness values ​​of each point measured) shall comply with the standards;
The compliance requirement of the hardness, that is, the average value of the hardness (the arithmetic mean of the measured values ​​of the hardness of each measuring point) is within the allowable range specified by the standard. The proportion of unqualified hardness is also quite high. For example, the hardness of the flat grinding wheel is less than 20% of the total unqualified (see Table 2).
4. The hole diameter is unqualified: the inner hole of the grinding wheel is the installation reference, and the hole diameter of the grinding wheel is unqualified and listed as “heavy defect†in the standard. When the diameter of the grinding wheel is large, the grinding wheel is eccentric after installation, which makes the grinding wheel unbalanced. When rotating at high speed, it will aggravate the vibration, affect the quality of the grinding process, and even cause the grinding wheel to rupture and the equipment to be damaged. If the hole diameter is too small, the grinding wheel cannot be installed and cannot be used. If it is forcibly installed, the spindle will be scratched, and the grinding wheel may be caused to be dark, which may cause the grinding wheel to break during operation and easily cause an accident. As shown in Table 2, the case where the aperture is unqualified is the most serious in the spot check. The total number of unqualified flat wheels is 16.7%, accounting for 58.2% of the total unqualified grinding wheels.
5. Marking error: The grinding wheel mark indicates the basic performance of the grinding wheel and plays an important role in guiding the user's use. It cannot be ignored. Flag errors are listed as "heavy defects" in the standard. There are many problems in the logo, some of the logos are incomplete; some of the logos are wrong; even deliberately shoddy, fake, and fraudulent use of trademarks, causing confusion, affecting the use of users, harming their interests, and may lead to major accidents.
6. End face runout and radial runout failure: End face runout and radial runout failure will cause yaw and affect balance performance when the grinding wheel rotates, which will adversely affect the machine tool and workpiece, so it should be controlled within the allowable range. .
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