Yoke roller bearing is a kind of rolling bearing and is one of the widely used components in modern machinery. It relies on rolling contact between the main elements to support the rotating parts. Most yoke roller bearings are now standardized. The yoke roller bearing has the advantages of small torque required for starting, high rotation accuracy, and convenient selection.
Bearing rubbing injury caused by slippage of yoke roller bearing is a common form of damage. Do you know what slippage of yoke roller bearing is? Why does the yoke roller bearing slip? What measures can be taken to prevent the yoke roller bearing from slipping? Today, let’s share related content.
What is yoke roller bearing slippage?
When the bearing is working, the rollers should perform pure rolling motion on the inner and outer raceways. If the drive roller cage is required to have enough drag force, its resistance can be overcome. When the drag force of the roller is not enough to overcome the resistance, at this time, in addition to rolling, there will be some slippage, and this difference in running speed relative to the inner ring (or outer ring) is called slippage.
What are the factors that cause the yoke roller bearing to slip and rub?
Slippage of the yoke roller bearing is a necessary condition for rubbing the bearing, but slippage may not necessarily cause surface rubbing. Some factors that cause the yoke roller bearing to slip and rub, such as the vibration of the shaft and the alternating load, generate a force that can tear the lubricating oil film and cause rubbing on some areas of the working surface.
Slip damage is the result of material transfer due to the interaction of the uneven rough surface of the metal after the lubricating oil film is destroyed. Some materials are “smeared” to form pits; while the more smeared parts protrude above the original surface. In addition, some parts of the working surface are scratched, which is closely related to the degree of alternating load and damage to the oil film. In severe cases, due to the excessive frictional heat generated between the rollers and the inner ring, the inner ring expands and the radial clearance is reduced, resulting in the bearing being stuck.
Anti-skid measures of yoke roller bearing
1. Reduce the number of rollers and reduce the diameter of the rollers
The roller is held by the rotating ring, and when the strength allows, its weight is reduced to achieve the purpose of reducing inertial resistance. It becomes very important to prevent and reduce slippage. This measure is relatively simple and can be achieved only by reducing its number and diameter. In aero-turbine engines, due to the small external load, contact fatigue is not the main damage factor of the rollers. According to the conventional standard, the bearing size allowance is still large. It is generally believed that the number of rollers is reduced by 50%, and the contact fatigue life of the bearing is still not affected after the diameter is reduced by 25%.
2. Select a reasonable structure and reduce the weight of the cage
In addition to reducing its weight as far as the strength allows, the cage should also consider its own characteristics, such as resonance, high-speed rotation resistance, etc. should be avoided.
The cage guidance method is also a very important factor in high-speed bearings. If the unbalance of the cage is properly controlled, the cage is changed from outer guidance to inner guidance, which is also very beneficial to reduce slippage. Because of the relative movement between the cage and the guide surface of the bearing due to the outer guide, the lubricating oil film forms a viscous resistance, while the inner guide is the opposite, and the viscous force of the lubricating oil 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-the-ring oil supply is to take away the heating of the bearing, while minimizing additional losses caused by agitation. Another example is to change the outer ring belt rib to the inner ring belt rib, which can undoubtedly reduce the resistance of stirring.
4. Using hollow roller preload bearing
Hollow roller preloaded bearings preload all rollers so that all areas are slip-free. Due to the wide operating speed and temperature range of the turbine engine rotor bearing, the selection of the appropriate preload should be prudent. Even at very low applied loads, excessive preload can still cause premature failure of the rollers. A common form of failure is bending fatigue.
5. Using elliptical bearings
The use of elliptical bearings is the most common form of anti-skid, and there are generally two types of structures: double-lobed and three-lobed. Take the double-lobed elliptical bearing as an example. Generally, the outer diameter of the outer ring is elliptical, and the inner diameter (raceway) of the outer ring and the bearing seat are all circular. After assembly, the outer ring raceway becomes an ellipse, that is, the rollers are preloaded. 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 gravity load of the rotor on the lowermost rollers, the rollers at 90° to the left and right are also preloaded by a certain amount, so that the number of rollers under load increases to About 60% of the total number of rollers. Therefore, increasing the drag force is beneficial to prevent the rollers and cages from slipping. However, the method of giving the ovality will reduce the fatigue life of the bearing, so it is necessary to consider the selection of the optimal ovality in use.
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