433A Mechanical Drives and Bearings 2 — Questions and Answers
Question 1: What is the main advantage of a helical gear over a spur gear?
- Lower manufacturing cost
- Smoother and quieter operation under load (Correct answer)
- Ability to transmit motion at right angles
- No thrust load generated
Correct answer: Smoother and quieter operation under load
Helical gears have teeth cut at an angle to the gear axis, which means multiple teeth are in contact at any time. This gradual engagement produces smoother, quieter operation compared to spur gears.
Question 2: When checking a roller chain drive for wear, at what percentage of elongation should the chain typically be replaced?
- 1%
- 3% (Correct answer)
- 5%
- 10%
Correct answer: 3%
Industry standards recommend replacing roller chain when it has elongated by 3% of its original pitch length. Beyond this point, the chain will no longer properly engage the sprocket teeth.
Question 3: What causes fretting corrosion on a bearing's outer race in its housing?
- Over-lubrication of the bearing
- Insufficient interference fit allowing micro-movement (Correct answer)
- Excessive radial load on the bearing
- Using incompatible grease types
Correct answer: Insufficient interference fit allowing micro-movement
Fretting corrosion occurs when there is insufficient interference fit between the bearing outer race and housing, allowing tiny oscillating movements that abrade the surfaces and create rust-colored debris.
Question 4: In a worm gear drive, which component is typically the driving member?
- The worm wheel
- The worm (Correct answer)
- Either component can drive
- It depends on the gear ratio
Correct answer: The worm
The worm (screw-shaped gear) is the driving member in a worm gear set. Most worm gear sets are self-locking, meaning the worm wheel cannot drive the worm due to the high friction angle.
Question 5: What is the purpose of a flexible coupling in a drive system?
- To increase the torque capacity of the drive
- To accommodate minor shaft misalignment and absorb shock loads (Correct answer)
- To change the direction of rotation
- To provide a fixed connection between shafts
Correct answer: To accommodate minor shaft misalignment and absorb shock loads
Flexible couplings accommodate minor parallel, angular, and axial misalignment between connected shafts while also dampening vibration and absorbing shock loads during operation.
Question 6: What type of lubrication regime provides a full oil film separating bearing surfaces with no metal-to-metal contact?
- Boundary lubrication
- Mixed-film lubrication
- Hydrodynamic lubrication (Correct answer)
- Dry lubrication
Correct answer: Hydrodynamic lubrication
Hydrodynamic lubrication creates a full fluid film that completely separates the bearing surfaces, preventing metal-to-metal contact. This occurs when adequate speed, load, and lubricant viscosity are maintained.
433A Mechanical Drives and Bearings 2
What is the main advantage of a helical gear over a spur gear?