Cautious about choosing needle roller bearing clearance

Cautious about choosing needle roller bearing clearance.

Carefully choose the bearing clearance

The needle roller bearing clearance is small. There is little relative movement between the inner and outer rings, which is good for the work of the rotor. This is very beneficial for machines that work steadily for a long time. But for the aero-engine with many working changes and starting after stopping just for more than ten minutes, it can not be equipped with the bearing with a small clearance.

The main shaft bearing of the aero-engine has a high DN value and a big heat generated by the friction during the operation. In addition, the heat transmitted by the environment (the engine chamber is at a high temperature) and the neighboring parts (turbine, corona, etc.) are comparatively big. As a consequence, it needs to take the heat by the lubricating oil. When it reaches a balance between the heat taken by the lubricating oil and the heat emitted from the bearing and sent from the outside, the bearing will be stable at a certain temperature.

The lubricating oil pump of the aero-engine is driven by the attached drive configuration of the motor. As the motor is stopped, the lubricating oil pump doesn't work, and no lubricating oil sprays to the needle thrust bearing, and the heat of the bearing cannot be taken away by the lubricating oil. However, on the other hand, when the motor is stopped, the most heat of the neighboring parts is sent to the bearing and transmitted to the outside through the receiver supporting the bearing. Therefore, after stopped, the temperature of the bearing keeps increasing rather than decreasing. And after increasing to a certain time, its temperature will decrease with the declined temperature of the rotor. As for the bearing installed near the turbine, the specialty is pretty outstanding. When the motor works, the high-temperature fuel gas flows through the turbine vanes and makes the temperature of vanes and corona all high. After stopped, because the vanes and corona are comparatively big and thick and the reserved heat is pretty much, the heat sent to the bear is much and keeps for a long time. Generally, the temperature will decrease after 30 to 40 minutes.

For some being developed motors, they are always stopped for some reasons and started again after adjustment and troubleshooting during debugging. As for these circumstances, if the interval time between stopping and starting again is about half an hour, it is exactly the time that the bearing is at the highest temperature.

When stopped, the direction of heat flow of the thrust needle roller bearing is from the axis to the inner ring and then from the outer ring to the receiver, so the temperature of the outer ring is higher than the inner. At this point, if the bearing clearance is pretty small, when started again, the roller will get stuck in the outer ring by the inner ring of the bearing and can not almost free rotate. Then it easily occurs that the inner ring of the bearing relative rotates at the axis or the outer ring do in the bearing block, which causes the excessive wear-out failure of the axis or bearing block and the inner or outer ring.

Summary

All in all, we should be careful to choose the bearing clearance to avoid damage to machines. Top-bearing is a professional needle bearing manufacturer and also provides needle rollers. If you need the products, welcome to contact us. E-mail: manager@www.top-bearing.com.cn

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