A large number of tests at home and abroad show that: the machining quality of cage, ferrule and steel ball has different degrees of influence on bearing vibration. The processing quality of steel ball has the most obvious effect on bearing vibration, followed by the processing quality of ferrule, the most important influence. The factors are the roundness, waviness, surface roughness, and surface scratching of steel balls and ferrules.
The most prominent problem in China's steel ball products is the large dispersion of vibration values and serious surface defects (single point, group point, pit, etc.). Although the surface roughness, size, shape, and error are not lower than the level outside the circle, the joints The rear bearing has a high vibration value, and even produces a strange sound. The main problem is that the waviness is not controlled (no standard, no suitable test and analysis instrument), and the vibration resistance of the machine tool is poor, and there are problems with the grinding wheel, grinding disc, coolant, and process parameters. On the other hand, it is necessary to improve the level of management and avoid problems such as bumps, scratches, burns, etc., at any time.
For the ferrules, channel waviness and surface roughness are the most serious ones that affect bearing vibration. For example, when the roundness of the inner and outer channels of small and medium deep groove ball bearings is greater than 2 μm, it will have a significant impact on the bearing vibration. When the internal and external channel waviness is greater than 0.7 μm, the bearing vibration value increases with the increase of the waviness, and the channel seriously bruises. It can increase the vibration by more than 4dB, and even make a strange sound.
Whether it is a steel ball or a ferrule, waviness arises from grinding. Although superfinishing can improve the waviness and reduce the roughness, the most fundamental measure is to reduce the waviness during the grinding process and avoid randomness. There are two main ways to deal with bumps: First, reduce the vibration when grinding the super-finish on the rolling surface, and obtain good surface processing shape accuracy and surface texture quality. In order to reduce the vibration, the super-abrasive machine must have good vibration resistance. Other important structural parts are shock-absorbing. The whetstone oscillation system of ultra-precision machine tools has good anti-vibration performance; to increase the grinding speed, 6202 electric spindles are commonly used in foreign 6202 outer raceways, and the grinding speed is 60m/s or more. It is generally much lower and is mainly limited by the performance of the main shaft and the main bearing. In high-speed grinding, the grinding force is small, the grinding layer is thin, and it is not easy to burn. It can also improve the machining accuracy and efficiency. It has a great impact on low-noise ball bearings; the dynamic and static stiffness of the spindle and its speed characteristics on low-noise ball bearings Grinding vibration has a great influence. The higher the stiffness, the less sensitive the grinding speed is to the change of the grinding force and the smaller the vibration of the grinding system. To improve the rigidity of the spindle bearing, a random dynamic balancing technique is adopted to increase the vibration resistance of the grinding spindle. Sex. Abroad grinding head vibration speed (such as Gamfior) is about one-tenth of the domestic general spindle; improving the cutting performance and dressing quality of grinding wheel stone is very important. The main problems of China's current gravel wheel oil stone are poor homogeneity of the organizational structure, which seriously affects the quality of ultra-low-noise Ball Bearing
grinding; adequate cooling, improves the filtering accuracy; improves the feeding resolution of the fine feed system, reduces the feed inertia; reasonable grinding super processing Process parameters and processing procedures are important factors that cannot be ignored. Grinding allowance should be small, form and position tolerances should be strict, the outside diameter of medium and small-sized ball bearings should not be superfinished, and rough grinding should not be separated to ensure good surface quality.
The second is to improve the accuracy of the machining plane, reduce the errors in the grinding process, reconstruct the outer diameter and the end surface is the positioning benchmark in the grinding process. The error re-transformation of the ultra-smooth OD to the channel is indirectly transmitted by the OD on the groove grinding, and the groove grinding on the error of the super retransmission. If the workpiece is scratched during the transfer process, it will be directly reflected on the raceway machining surface, affecting the bearing vibration. Therefore, the following measures must be taken: to improve the accuracy of the positioning datum surface shape; to pass the process smoothly, without scratching; the shape error of the blank shape can not be too large, especially when the remaining volume is small, excessive error will cause the final grinding and superfinishing The shape accuracy at the end has not been improved to the final quality requirements, which seriously affects the consistency of the processing quality.
It is not difficult to see from the above analysis that the ultra-processed low-noise ball bearings made of high-performance, high-stability machine tools are most suitable for the super-processed low-noise ball bearings, which can avoid scratch damage, reduce transmission errors, eliminate manual factors, and improve processing efficiency and quality consistency. , Lower production costs and increase corporate profits.
How to reduce the ball bearing noise? The author believes that efforts should be made in the following two aspects: (1) Manufacturing process. Refined process, mainly refers to the process as short as possible, process consolidation, production without intermediate inventory, effectively reduce the impact of Low Noise Ball Bearing
process factors; production cleanliness, which is a systematic technology, including grinding fluid, ultra Semen, cleaning fluid, air, high pressure air, production environment and other technical processes; automation, automation from car processing to assembly, little or no people; scale, such bearings, especially silent ball bearings, must form a large scale Only in this way can we have the global market competitiveness.
(b) Equipment. High-speed grinding, spindle precision, stiffness, life, and a variety of perfect detection and protection performance play a major role in grinding precision and efficiency; grinder technology, foreign internal grinding machines generally have high-speed grinding, AC servo control, feed Resolution 0.25μ, fully automatic easy operation, self-diagnosis function, etc.; Ultra-precision technology, which is mainly represented by Japanese Osaka Seiki, unintentionally supporting two-station ultra-precision, and hydraulic centering four workers represented by German Tierenhaus. Ultra-precision two methods; online detection technology, since the 1980s, the Japanese bearing industry to actively measure the machine outside the feedback control of automatic grinding ultra-short line applications are the most common. The application of grinding super-auto lines constructed in this way in China is also relatively mature. At present, there are about 100 in China. With the continuous improvement of mainframe technology in advanced industrial countries, the line is more and more simple, gradually reducing or no active measurement and off-machine testing; centerless cylindrical grinder, round outside (KOYO, MIKROSA, etc.) universally adopted roller bearing grinding wheel spindle unit, with high Stiffness, high precision, long life, convenient loading and unloading, reliable use, etc.; bed with damping attenuation characteristics; feed using high-precision micro AC servo system, stable drive AC frequency conversion guide wheel adjustment system, can be equipped with online Random intelligent measurement can realize grinding of CBN grinding wheel, etc. It can realize automatic connection, roundness up to 0.3μm, size dispersion up to 3μm.
Surface grinders, foreign double-end (such as KOYO, Landis Gardner) surface grinder spindle are generally used high-precision, high-stiffness roller bearing spindle unit grinding wheel shaft system, oil mist lubrication. Taking Gardner technology as an example, the company has studied the production system equipment for more than 90 years and can grind bearings, ceramics, glass, rubber, plastics and other materials. The main technology is automatic dressing and compensation of grinding wheel. The feed of grinding wheel head is based on the coaxial structure of the screw shaft of the servo motor. The grinding wheel is synchronously fed inward and outward. The feeding accuracy can reach 0.25μm. The machine body is placed on two horizontal pads and balanced. On the device, the balancer has a self-balancing support rod, which can automatically adjust to a horizontal plane with two horizontal pads, so that the machine tool has a stable supporting effect. The balancer focuses on maintaining the concentricity of the grinding wheel shaft and increasing the dressing wheel interval time. There are rotary, reciprocating, penetrating and special four feed forms, which can use superabrasive grinding wheel, diamond grinding wheel and CBN grinding, high grinding precision, good stability, extremely long grinding wheel service life and convenient operation adjustment , According to the processing requirements, the abrasive, binder, and structure (circular, button, or link) can be specially formulated to achieve the best grinding effect with parallelism and flatness of 1μm.