When the roller bearing is working, the stick performs pure rolling motion on the inner and outer ring raceways, so the bracket driving the roller needs to have enough drag force to overcome the resistance. If the drag force is not enough to overcome the resistance, then the roller will slide on the raceway, resulting in a speed difference, that is, slipping. So what should I do when the roller bearing slips?

How to deal with roller bearing slippage:

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%. Many engines have adopted this measure. For example, the main bearing of the Spey engine is this type, not only the rollers are obviously sparse, but also small in size.

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. A typical hollow roller, with a ratio of OD to ID of 2, should have bore bending stress below 25,000 psi; concentricity of the inner and outer diameters should be maintained at 0.005 mm.

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. Taking the double-lobed elliptical bearing as an example, talk about its structure and anti-skid mechanism. This kind of bearing generally has an oval outer ring outer diameter, and the outer ring inner diameter (raceway) and 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 lowermost rollers being subjected to the gravity load of the rotor, the rollers at 90° to the left and right are also preloaded with a certain amount of preload, so that the number of rollers under load increases to About 60% of the total number of rollers (roller bearings generally bear about 20% of the total number of rollers under load). 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 ovality in use.