Why does the crossed cylindrical roller bearing slip? Reasons and anti-slip measures
Crossed roller bearings are one of the more commonly used rolling bearings. However, some people cause the bearing to slip during operation due to some reasons, which will affect the operation and work of the entire equipment. So, why does the crossed cylindrical roller bearing slip? How to prevent slipping?
Ⅰ. Causes of cross roller bearing slippage
Crossed cylindrical roller bearing Slippage of crossed cylindrical roller bearing seat is a necessary condition for scratching the bearing seat, but the occurrence of slipping does not necessarily cause surface scratching. For example, the vibration of the shaft and the alternating load produce a force that can tear the lubricating oil film and cause scratches on some areas of the working surface (the working surface of the drum and the inner ring raceway is more common). Therefore, it is conceivable that the slipping injury is the result of material transfer due to the interaction of the uneven metal surface after the lubricant film is destroyed. Some materials are "stained away" to form pits; while the more stained parts protrude above the original surface. In addition, some parts of the working surface are scratched, and some parts are not scratched, which is closely related to the alternating load and the degree of damage to the sleeve. In severe cases, excessive frictional heat is generated between the roller and the inner ring, which causes the inner ring to expand, reducing the radial clearance, and causing the bearing seat to jam.
Ⅱ. Cross roller bearing slip performance
When the bearing is working, the rollers should make pure rolling motion on the inner and outer ring raceways. If the drive roller cage is required to have enough drag force, it can overcome its resistance. When the roller drag force is not enough to overcome the resistance, at this time, in addition to rolling, there will be some sliding, and this relative The difference in the running speed of the inner ring (or outer ring) is the phenomenon of slipping.
Ⅲ. Anti-skid measures for crossed roller bearings
1. Reduce the number of rollers and roller diameter
The roller is moved by the rotating ring. When the strength permits, reduce its weight to achieve the purpose of reducing inertial resistance. It is very important to prevent and reduce sliding. In aero-turbine engines, due to the small external load, contact fatigue is no longer the main damage factor of the drum. According to the conventional standard, the bearing size tolerance is still large. It is generally considered that the number of rollers is reduced by 50%, and after the diameter is reduced by 25%, it still does not affect its contact fatigue life.
2. Choose a reasonable structure and reduce the weight of the cage
In addition to reducing its weight when the strength permits, the cage of cylindrical roller bearings should also consider its own characteristics, for example, should avoid its resonance and high-speed rotation resistance. The cage guidance method is also a very important factor in high-speed bearing housings. If the imbalance of the cage is properly controlled, the cage is changed from outer guidance to inner guidance, which is also very beneficial for reducing slippage. Because of the outer guidance, the relative movement between the cage and the guide surface of the bearing, the lubricating oil film forms viscous resistance, while the inner guide is the opposite, and the viscous force of the lubricating film between the cage and the guide surface becomes a drag force. In this way, the viscous resistance becomes the force that drags the cage to rotate. The difference between the two cannot be ignored.
3, oil supply under the ring
The advantage of using under-ring oil supply is that it takes away the heat of the bearing seat and at the same time makes the additional loss caused by stirring smaller. Another example is to change the outer ring belt ribs to the inner ring belt ribs, which undoubtedly can also reduce the resistance of mixing.
4. Adopting hollow roller preload bearing
Hollow roller preload bearing can apply preload to all rollers, so that all areas are not slipping. Due to the wide operating speed and temperature range of turbine engine rotor bearings, care should be taken to select an appropriate preload. Even under a very low external load, an excessive preload will still make the drum prematurely damaged. The common form of failure is bending fatigue.
5. Use oval bearings
Using elliptical bearing seat is a common form of non-slip, generally there are two kinds of knots, double-lobed and three-lobed. Take a double-lobed elliptical bearing as an example. Generally, the outer diameter of the outer ring of this type of bearing is elliptical, and the inner diameter (raceway) of the outer ring and the bearing seat seat are both circular. After assembly, the outer ring raceway becomes elliptical, that is, preload is applied to the drum. That is to say, the radial clearance between the roller and the raceway at the short semi-axis of the elliptical raceway is eliminated (interference is formed), and the roller is compressed. Therefore, in addition to the few rollers at the bottom being subjected to the gravity load of the rotor, the rollers at 90° to the left and right are also subjected to a certain amount of preload, thereby increasing the number of rollers bearing the load to the rollers. About 60% of the total (cylindrical roller bearings generally bear about 20% of the total number of rollers bearing load). Therefore, increasing the drag force is beneficial to prevent the roller and the cage from slipping. However, the method of giving the ovality will reduce the fatigue life of the bearing seat, so it is necessary to consider the selection of the appropriate ovality in use.
Ⅳ. Factors affecting the slippage of crossed roller bearings
1, inner ring speed
The inner ring speed is a big factor influencing the roller slip of the cross roller bearing. Roller slip rate is generated as the inner ring rotates, decreases with the increase of the pressure generated by the interference fit, and tends to stabilize with the increase of time, accompanied by fluctuations.
2, radial load
In the process that the roller slip rate decreases with the increase of radial load, the roller speed fluctuates, and the wave amplitude increases with the increase of time. After the bearing enters the steady state, the roller slip rate decreases with the increase of the radial load, and there is a non-linear relationship between the two.
3, gap
With the increase of the clearance ratio, the cage movement state tends to be disordered, resulting in an intensified collision between the roller and the cage pocket, and the force between the two increases, and the cage's hindering effect on the roller movement is strengthened and intensified. The roller is skidding.
4, friction factor
As the friction factor increases, the roller's slippage in the load-bearing area and non-load-bearing area is suppressed. This is because the friction between the roller and the inner and outer raceways in the load-bearing area is the driving force for the roller. When the friction factor between the two increases, the driving force increases and the roller is less likely to slip , The slip is suppressed; in the non-load-bearing area, the increase of the friction factor will increase the friction force of the outer ring raceway to the roller, that is, the driving force increases, and slipping is not easy to occur.
Know why the cross roller bearing slips, and deal with it according to the corresponding method, in order to better help the normal use of the cylindrical roller bearing and reduce the cost of its maintenance and replacement. In daily use, we must also take relevant anti-skid measures for cylindrical roller bearings.
Do you have any specific questions about the design or manufacture of Cross roller bearings or Rotary table bearings? Contact Yogie! Our sales engineers will work with you from start to finish to ensure that your project is completed to your requirements.
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