0
0
Abstract: The multi-objective function and quasi-dynamic analysis model are used to optimize the design of high-speed and long-life sealed bearings. After installation, under the mechanical environment conditions, all indicators of functional adaptability meet the requirements of the national standard.
The sealing of rolling bearings is one of the necessary conditions for the simplification, miniaturization and light weight of mechanical equipment. High-quality sealed bearings should have good grease storage, dust-proof and low-temperature rise performance, and also have a long service life. For these four indicators, the technical solutions adopted are often beneficial to one of them, but unfavorable to the other, which restrain each other. Therefore, the high reliability quality of sealed bearings should be considered comprehensively. In this paper, the design of high-speed sealed bearings is discussed.
1 Design principles
1.1 Structural design of bearing
Taking the sealed bearing with sealing rings on both sides as an example, when the non-contact structure with rubber sealing ring is adopted, the space occupied by the sealing ring itself is larger than that of the dust cover. If allowed, the width of the inner and outer rings of the bearing should be widened, which can increase the effective sealing space, which is conducive to heat dissipation, and can be filled with grease accordingly, which is convenient for improving the bearing life. The non-assembly chamfer of the bearing is smaller than the conventional design, and r can be taken as 0.3, which is convenient to improve the dustproof performance of the sealed bearing and reduce its grease leakage rate. The selection of bearing clearance is usually based on the third set of clearance specified in the national standard or even larger, which is beneficial to the high-speed performance of the bearing.
1.2 Design of the sealing structure
The design principle of the sealed bearing is to ensure that the sealing space is the largest after the sealing ring is installed on the base bearing. This is restricted by many factors, for example, the minimum width of the sealing groove of the outer ring is generally 0.5mm; the minimum distance between the cage and the inner diameter of the sealing ring is not less than 0.3mm, etc.
Under the premise of ensuring the machining accuracy, the inner ring without groove double-lip sealing ring is selected, which is economical and can achieve better sealing performance.
1.3 The design of the cage In order to adapt to high-speed performance, a solid riveted cage is used, which has sufficient strength, light weight, and good wear resistance. At the same time, considering the convenience of lubrication and heat dissipation of the sealed bearing, try to do as much as possible under the condition that the strength of the cage allows. Thin, in order to reduce the cage volume and increase the effective sealing space. At the same time, when the radial load is large, the speed of the high-speed bearing steel ball changes greatly, and the pocket can be designed into an elliptical shape, which can not only increase the annular gap between the pocket and the ball, and make it easier for the grease to pass through the pocket Therefore, the cage can be effectively cooled, and the weakening of the strength of the side wall of the pocket and the axial instability of the cage can be avoided. The selection of the guide clearance and pocket clearance of the cage is larger than that of the conventional bearing design, which is beneficial to the lubrication and heat dissipation of the bearing.
1.4 Screening of lubricating grease and determination of filling amount
Bearings with fixed seals cannot be re-lubricated, so the service life of the bearing is often determined according to the life of the lubrication. Under certain conditions, it is likely that grease determines bearing life. Therefore, the determination of grease and its filling amount is very important.
The grease with high consistency is selected, and the bearing grease and dustproof performance are better, but the viscous resistance torque increases and the temperature rises during operation. If the consistency of the grease is too low, the fluidity is large and it is easy to leak. Based on the special requirements of high-speed and long-life sealed bearings, lithium-based or silicon-based high-temperature greases with high consistency should be used to meet the requirements for life reliability and sealing performance.
In principle, the grease filling amount of the sealed bearing accounts for 30% to 50% of the effective sealing space of the bearing, because the grease leakage of the sealed bearing increases with the increase of the grease filling amount. After the agitation of the rolling element and the cage, after the grease in the cavity reaches a saturated state, the excess grease leaks out. When the amount of grease filling is too small, it is difficult to ensure the lubrication life of the bearing.
To sum up, for high-speed and long-life sealed bearings, considering the high-speed performance and the benefit of bearing heat dissipation and dust-proof performance of the bearing, the lower limit of the amount of grease should be used, that is, 30% to 40% of the effective sealing space.
1.5 Selection of sealing gap The gap between the dust cover and the inner ring is directly related to the sealing performance. If the gap is too large, the sealing performance is not good, and it is easy to leak grease; but if the gap is too small, it will not only increase the difficulty of processing, but also cause the wear of the inner ring rib by the external abrasive medium; and for the use of sealed bearings, if the sealing There is an interference fit between the inner diameter of the ring and the outer diameter of the inner ring of the bearing, and the grease cannot leak out. Due to the large stirring resistance moment of the rolling element and the cage, the cavity will heat up sharply, which will bring more serious consequences. Through the grease test and analysis of the bearing, it is determined whether the selection of the bearing sealing clearance is appropriate.
1.6 If the grease filling of the sealed bearing is uneven, even if there is not much grease filling, it will be partially saturated and serious grease leakage will occur. Therefore, after filling the grease, it must be evenly greased, so that the grease is evenly filled between the steel ball and the channel.
1.7 Verification of the quasi-dynamic performance analysis of grease lubricated bearings Through multi-objective optimization design and quasi-dynamic analysis model, the quasi-dynamic analysis software of grease lubricated bearings is used to conduct heating, heat generation and Life and other performance analysis to verify the selection of bearing design parameters.
2 Design examples
2.1 Structural parameter optimization Take the design of a high-speed and long-life sealed ball bearing with an external dimension of 25 × 52 × 15 (dn value is 0.4 × 106 mm.r/min) as an example. Since the main engine requires good sealing performance of the bearing and high speed requirements, the non-contact sealing structure of the rubber sealing ring is adopted. The designed bearing adopts the fourth group of radial clearance, and the cage adopts the riveted form of solid elliptical pocket half cage. Under the premise of ensuring its strength, the diameter of the center circle of the pocket is moved outward, and the thickness of the side wall is only 2.7mm. Lithium-based high-temperature and high-speed grease is used, and the amount of grease filling accounts for 33% to 40% of the effective sealing space of the bearing. The main parameters of the optimally designed bearings are shown in Table 1. The first group in the table is the optimized design parameters for high-speed and long-life sealed ball bearings, and the second group is the optimized design parameters for conventional sealed ball bearings.
The design of this example bearing comprehensively considers the design concept of the high-speed and long-life sealed bearing described in this paper. It can be seen from Table 1 that the bearing radial clearance is 25-35 μm, which is much larger than the 5-20 μm usually selected for ordinary sealed bearings. The range of the cage pocket center circle is moved outward, the inner diameter of the cage is increased, the position of the outer ring sealing groove is moved outward, etc. are all measures to increase the sealing gap, which is convenient for grease storage and heat dissipation. The use of solid elliptical pocket half cage riveting to replace the traditional wave-shaped stamping cage can limit the limit speed of the bearing, so that the limit speed of the bearing can reach 16000r/min, and the dn value can reach 0.4×106mm.r/ min. At the same time, it does not reduce the service life of the bearing. The calculated fatigue life of the bearing can reach 1400h, which is a leap for the design of high-speed sealed bearings. It is verified that the scheme is feasible and has been used in production practice.
2.2 Bearing bench test results According to the requirements of the bench test program, the assessment tests were carried out on the bearing grease leakage testing machine, and the results were very satisfactory. %.
Another 4 sets of bearings have been tested for 500h bench life assessment respectively according to the requirements of the bench test program. During the whole test process, the bearing runs smoothly, the display of each instrument is accurate, the test data is reliable, and there is no abnormal phenomenon. After completing the 500h life test, there are no phenomena such as serious partial wear, slippage, obvious scratches and steel ball cat eye rings in the bearing channel, and the rotation is still flexible
