Mechanical Power Transmission and Lubrication Flashcards

A motor turning at 1,750 RPM has a 4-inch pulley that drives an 8-inch pulley. What is the speed of the driven shaft?

Answer: 875 RPM

Driven RPM = Driver RPM × (Driver diameter ÷ Driven diameter) = 1,750 × (4 ÷ 8) = 875 RPM. A larger driven pulley turns more slowly.

A 20-tooth driver gear meshes with a 60-tooth driven gear. Ignoring losses, what happens to the output compared with the input?

Answer: Speed is cut to one-third, torque triples

The gear ratio is 60:20, or 3:1. The output turns at one-third of the input speed, and because power is conserved, the output torque is three times higher.

What is a common result of over-greasing a rolling-element bearing?

Answer: Overheating from churning of excess grease

Too much grease gets churned by the rolling elements. This creates friction and heat, which can break down the grease and blow out the seals. Over-greasing is a leading cause of bearing failure.

Which property of a lubricant describes its resistance to flow?

Answer: Viscosity

Viscosity measures how thick a lubricant is, or how much it resists flowing. It is the most important property to consider when choosing an oil for an application.

When aligning two shafts joined by a flexible coupling, what are the two basic types of misalignment a technician checks for?

Answer: Angular and parallel (offset)

In parallel (offset) misalignment, the shaft centerlines are parallel but displaced from each other. In angular misalignment, the centerlines meet at an angle. Both must be corrected to prevent bearing and coupling wear.

What is the common rule of thumb for V-belt deflection when checking tension?

Answer: 1/64 inch per inch of span

A widely used guideline is about 1/64 inch of deflection for each inch of span between the pulley centers. A belt that is too loose slips and glazes; a belt that is too tight overloads the bearings.