15.8 Bearings and Seals Flashcards
What is the primary function of bearings in a turbine engine?
To support the main engine rotor.
What types of bearings are commonly used in gas turbine rotors?
Ball and roller bearings.
List the forces that act on the rotor during engine operation.
- Weight forces caused by the rotor
- Gas forces from the gas flow
- Shock forces caused by turbulence and impact of landing
- Gyroscopic forces during changes in aircraft direction
- Imbalance forces of the rotor components
What are the two main types of forces that bearings must withstand?
Axial and radial forces.
What are the advantages of anti-friction bearings?
- Offer little rotational resistance
- Facilitate precision alignment of rotating elements
- Are relatively inexpensive
- Are easily replaced
- Withstand high momentary overloads
- Are simple to cool, lubricate, and maintain
- Accommodate both radial and axial loads
- Are relatively resistant to elevated temperatures
What is a significant disadvantage of anti-friction bearings?
Tendency to fail without warning and vulnerability to foreign object matter.
What is the function of a fixed bearing in a bearing system?
Supports the rotor in the radial direction and fixes the rotor in the axial direction.
What does a floating bearing allow for in a bearing system?
Transmits only radial forces and can move in an axial direction.
What is the purpose of a triple-bearing system?
To minimize the expansion of the shaft end.
Describe the typical construction of a ball bearing.
The outer race is bolted to the bearing support and the inner race is installed on the rotor shaft.
How do roller bearings differ from ball bearings?
Roller bearings have a larger working surface and are better equipped to support radial loads than thrust loads.
What is the role of oil-dampened bearings?
To reduce dynamic loads from the rotor to the case.
What are the two methods of lubrication for bearings?
- Direct lubrication method
- Under-race lubrication method (indirect lubrication method)
In which lubrication method is oil sprayed directly onto the bearings?
Direct lubrication method.
What is the advantage of the under-race lubrication method?
Removes more heat than the direct lubrication method.
What is the function of oil seals in bearing housing?
To prevent oil leakage and deliver oil for lubrication.
What are the two types of oil seals mentioned?
- Labyrinth seal
- Thread (helical) seal
What is a characteristic of carbon seals?
They are usually spring-loaded and prevent oil from leaking along the shaft.
Fill in the blank: A floating bearing is usually a _______.
roller bearing.
True or False: A labyrinth seal relies solely on reverse threading to stop oil leakage.
False.
What is the typical temperature range that bearings can reach due to bearing loads?
200 °C to 260 °C (392 °F to 500 °F).
What is the main purpose of the bearing support housing?
To carry the radial and axial loads of the rapidly rotating rotor.
