Mechanical Drives and Bearings Flashcards

What is the main advantage of a helical gear over a spur gear?

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.

When checking a roller chain drive for wear, at what percentage of elongation should the chain typically be replaced?

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.

What causes fretting corrosion on a bearing's outer race in its housing?

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.

In a worm gear drive, which component is typically the driving member?

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.

What is the purpose of a flexible coupling in a drive system?

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.

What type of lubrication regime provides a full oil film separating bearing surfaces with no metal-to-metal contact?

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.