Inspection Standards and Methods of Industrial Bearing Products
1.1 Dimensional precision of finished bearing products
Dimensional precision is one of the main inspection items of finished bearing products, the maximum enclosed contour and the minimum circumcircle are required, thus the center and diameter of the circumcircle are obtained at last. For dimensional precision of inner and outer rings of finished bearing products, it would influence not only radial internal working clearance of the bearing, but also working performance of the host, and even service life of the bearing.
1.2 Rotating precision of finished bearing products
Rotating precision is a main inspection item of finished bearing products. At the time of installing the finished bearing products, the radial run-out at connection place of the bearing and the installation parts could be offset mutually, thus improving installation precision of such parts greatly. Therefore, there is a very high requirement for rotational precision of bearing. In the meantime, hole-boring precision of precision jig boring machine, precision of abrasive wheel axes of precision grinder, and quality of cold-rolled strips are all closely related with rotational precision of bearing.
1.3 Radial internal clearance of finished bearing products
Radial internal clearance is a main indicator for inspection of finished bearing products. Since the bearings are for different purposes, the internal clearance selected also differs greatly. Therefore, during the process of modern industrial production, radial internal clearance of finished bearing products has been greatly used as indicator for quality control standard, in inspection and supervision of finished products and other fields. So it can be seen that, inspection of the internal clearance is an important item for inspection of finished bearing products.
1.4 Rotational flexibility and vibration noise of finished bearing products
Since the bearing is subject to pressure and stress during operation, so there are high and even hardness characteristic, high elastic limit and relatively high compressive strength requirements for finished bearing products. Therefore, during rotation, a benign bearing should work briskly without blockage. For effective control of vibration noise of the bearing, corresponding measures shall be taken for vibration noise of bearing generated from improper installation.
1.5 Residual magnetic intensity of finished bearing products
Residual magnetic intensity is one of the inspection items of finished bearing products since there would be residual magnetism during the operation. This is because that two electromagnetic cores shall not be correlated, so they shall operate independently. In the meantime, the core of the electromagnetic coil is treated as a mechanical component, whereas the coil is not.
1.6 Surface quality of finished bearing products
Surface quality is also one of the inspection items of finished bearing products, therefore, corresponding quality inspection shall be performed regarding surface roughness, various cracks, various mechanical injuries and quality, etc. For non-conforming bearings, they can’t be used, but shall be returned to the manufacturer for rework. Once used, they would result in many mechanical injuries toward the equipment.
1.7 Hardness of finished bearing products
Hardness of bearing is a main quality indicator. Since the steel ball rotates in the spherical channel, it also has a certain centering effect at the same time, therefore, the bearings with non-conforming hardness shall not be put into use.
2.1 Traditional method
Traditional inspection method of finished bearing products is the manual inspection method, where, working condition of the bearings inside the machinery equipment would be roughly judged by some experienced workers touching with hands or listening with ears. However, with rapid development of industrial manufacturing industry nowadays, there are many shortcomings in using traditional method, and in the meantime, the faults can’t be effectively excluded timely in a manual way. Therefore, the tradition method has been rarely used nowadays.
2.2 Temperature inspection method
Temperature inspection method of bearings is a method using temperature-sensitive equipment to make accurate evaluation of service life of the bearings and make correct judgment of the faults. Temperature inspection of the bearings is very sensitive to changes in load, speed and lubrication, etc. of the bearings, and is mostly used in rotation part of machinery equipment, playing the main role of bearing, fixation and lubrication. Therefore, temperature inspection method is one of the common methods.
2.3 Acoustic emission inspection method
The bearings would have fatigue and failure after a long time of operation, which is manifested by pits on bearing contact surface. Acoustic emission inspection method is to judge condition of the finished products by collecting these signals. This method is equipped with many advantages such as short response time to acoustic emission signal, rapid reflection of failures, real-time display and positioning of fault points, etc., therefore, acoustic emission technology has been widely used in inspection of bearings.
2.4 Pressure wave inspection method
Pressure wave inspection method is an important method for early fault detection of finished bearing products. During the operation process, since the ball track, cage and other parts of the bearings are subject to constant abrasion, therefore, it has become a common inspection method of bearings by receiving the fluctuation signal to analyze and judge these information.
2.5 Vibration diagnosis technology
During working, periodic pulse signal is the key to inspection of bearings by vibration diagnosis technology. Cracks of bearings are mainly due to hidden danger from poor processing, where, during the use with high intensity, the defective areas would have cracks and even fracture, thus resulting in disintegration of bearings. Fault of the finished bearing products is judged by receiving and analysis of signal. It is very convenient to use this method to inspect the equipment installation and operation, therefore, this is also one of the common methods for inspection of finished bearing products.
3.1 Quality inspection items
Since the bearings are of very many varieties and greatly different purposes, and each quality characteristic also has different importance in various bearings, therefore, it becomes particularly important to make optimized processing of the functions of the inspection items of finished bearing products. As we all know, functional test itself belongs to a destructive test, therefore, there would be a certain damage to the bearings when making incoming inspection, process inspection and finished products inspection. When making scientific and effective quality inspection scheme, making quality characteristic requirement for a specific product, and setting the measurement precision, the precision requirement and measurement cost of the inspected object shall be mainly taken into consideration. It can be known from basic theory for signal analysis that, a vibration signal must include time domain indicator and frequency domain indicator, and the influence of processing process and various processes on various quality characteristics of the product shall also be understood.
3.2 Quality inspection methods
Regarding the development status and requirements of the bearing industry in China at present, a series of evaluation criteria are required in order to select the optimal scheme from many feasible design schemes. In this paper, quality inspection items of finished bearing products are relatively elaborated in details, including the quality inspection modes, quality inspection items and quality inspection methods. The needs for development of bearing industry in China could be met only by making constant enrichment and modification.
With rapid development of science and technology as well as increasingly improved people’s living standards in China, various kinds of machines exist with people’s life, of which bearing plays an important role. Quality of bearings can be guaranteed if packaging of the ex-factory bearings is intact. Since bearing is mainly used as a machinery part for supporting the rotation axis, therefore, at the time of working, it will bear radial and axial loads from the axis, and rotate with the axis at high speed. At present, there are mainly two inspection methods of finished bearing products: one hundred percent inspection and sampling inspection. The judgment criteria are different in accordance with the mechanical performance, importance and inspection period, etc. Quality inspection items of the products are mainly determined according to the quality characteristics, but each product is equipped with quality characteristics in multiple aspects. In order to give maximum play to performance of the bearings, the bearings shall be inspected regularly as a preventive measure.