1. preface
The sealing of rolling bearings is one of the necessary conditions for the simplification, miniaturization and lightweight of mechanical equipment. High quality sealed bearings should have better performance of fat storage, dust prevention and low temperature rise, and also have a long service life. Therefore, the high reliability quality of sealed bearings should be comprehensively considered. This paper discusses the design of high speed seal bearing, and enumerates design examples to further illustrate the application of fatigue resistant seal bearing in practice
2. Design Principles
(1) structural design of bearings. Take the sealed bearing with two sides of the sealing ring outer size of 25x52x15 as an example, when the non-contact structure with rubber sealing ring is adopted, because the space occupied by the sealing ring is larger than that of the dust cover, the width of the inner and outer ring of the bearing should be widened when the host space allows, so as to increase the effective sealing space. It is conducive to heat dissipation and can be filled with more grease accordingly, so as to improve the bearing life. The non-assembly chamfer of the bearing is smaller than the conventional design, and r can be set to 0.3, which is convenient to improve the dustproof performance of the sealed bearing and reduce its fat leakage rate. The selection of bearing clearance is usually the third set of clearance specified in the national standard and even larger, which is conducive to the high-speed performance of bearings.
(2) the design of sealing structure. The design principle of sealing bearings is to ensure that the sealing space is maximum 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 0.5. The minimum distance between the inner diameter of the cage and the sealing ring is not less than 0.3. Under the premise of ensuring the machining accuracy, the choice of inner ring without groove double lip sealing ring, which is not only economic, but also can achieve better sealing performance.
(3) Design of cage. In order to adapt to the high speed performance, the solid riveted cage is adopted, which has sufficient strength and light weight, good wear resistance, and considering the lubrication and heat dissipation of the sealing bearing, as thin as possible under the condition of the cage strength allows, in order to reduce the cage volume and increase the effective sealing space. When radial load is larger at the same time, the speed of the high-speed bearing steel ball change is very big, can be designed to elliptic shape back pocket hole, both to add ring to the gap between the hole and the ball, make it easier for grease through hole, to maintain effective cooling, but also to avoid the pocket hole wall strength weakening and axial instability of cage. The selection of guide clearance and hole clearance of cage is larger than that of conventional bearing design, which is conducive to bearing lubrication and heat dissipation.
(4) the selection of sealed brigade. The gap between the dust cover and the inner ring is directly related to the sealing performance. The old is too large, the sealing performance is not good, easy to leak grease; However, the gap is too small, not only increases the processing difficulty, but also the external abrasive medium is easy to cause the inner ring edge wear; And for the use of sealed bearings, if the inner diameter of the sealing ring and the outer diameter of the bearing inner ring is interference fit, the grease leakage is not out, because the stirring resistance moment of the rolling body and the cage is very large, the cavity will rise sharply, bringing more serious consequences. Through the bearing grease test and analysis, to determine whether the selection of bearing seal clearance is appropriate.
(5) screening of grease and determination of grave grease t. The grease with high consistency is selected, and the bearing has better grease storage and dustproof performance, but the viscosity resistance moment increases and the temperature increases in its operation. If the consistency of fat is too low, the fluidity is large and it is easy to leak out. Based on the special requirements of high-speed fatigue resistant seal bearings, hammer or silicon based high temperature grease with high consistency should be used to meet the requirements of life reliability and seal performance. In principle, the grease filling t of the sealed bearing accounts for 3 ~ 5 of the effective sealing space of the bearing, because the grease filling of the sealed bearing increases with the increase of the grease filling amount. When the grease filling amount is too much, the grease in the cavity reaches the saturation state during the high-speed operation of the bearing due to the agitation of the rolling body and the cage, the excess grease leaks out. When the grease filling t is too little, it is difficult to ensure the lubricating life of the bearing.
In conclusion, for high-speed fatigue resistant sealing bearings, considering the high-speed performance and to be conducive to the heat dissipation of bearings and the dustproof performance of bearings, the lower limit of the amount of tomb fat should be used, that is, the effective sealing space.
3. Design Examples
(1) Structural optimization. Take the design of 25x52x15 high speed long life sealed ball bearings (dn value 0.4 x 106 or/ im n) as an example. Because the main engine requires good sealing performance of bearings, and high speed requirements, so the rubber seal ring non-contact seal structure. The cage is riveted in the form of solid elliptical pocket-hole semi-cage. Under the premise of guarantee period strength, the diameter of the central circle of the pocket-hole moves outward, and the thickness of the side wall is only 2.
- The use of high temperature and high speed grease of keng base, filling grease amount accounts for the effective sealing space of bearing 3 device ~ 4. The main parameters of the optimized bearings are shown in Table 1. In the table, the first group is the optimized design parameters for high-speed 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 high-speed fatigue resistant seal bearing described in this paper. It can be seen from Table 1 that the radial clearance of bearing is far larger than the range of ordinary seal bearing. The diameter of the center circle of the cage hole moves outward to increase the inner diameter of the cage: the position of the outer ring sealing groove moves outward to increase the sealing clearance, which is convenient for fat storage and heat dissipation. The maximum speed of the bearing can be increased effectively by replacing the traditional wave stamping cage with the solid elliptic pocket hole half-cage riveted form, and the maximum speed of the bearing can reach 1600 r/min and 0.4 x l06 nl.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 140h0, which is a leap forward for the design of high-speed sealed bearings.
