SACA Mechanical Power Transmission 2

Question 1

What is 'mechanical advantage' in a gear system and how is it calculated?

Accepted Answer

The ratio of output torque to input torque, equal to the gear ratio — a higher gear ratio produces proportionally more torque at lower speed

Answer

The ratio of output speed to input speed, indicating how much the gear system increases rotational velocity

Answer

The efficiency of power transmission, expressed as (output power / input power) × 100%

Answer

The ratio of driver gear teeth to driven gear teeth, indicating the direction of rotation

Question 2

In belt drive systems, what is the difference between a 'timing belt' and a 'V-belt', and when is each preferred?

Accepted Answer

Timing belts use positive tooth engagement for synchronous, no-slip drive; V-belts rely on friction wedging for torque transfer and allow slip under shock loads

Answer

Timing belts use friction for torque transmission; V-belts use positive engagement teeth — timing belts are used for high-torque drives

Answer

V-belts are used with metal pulleys; timing belts require plastic pulleys only

Answer

Timing belts need lubrication; V-belts are maintenance-free

Question 3

What is a 'flexible coupling' used for when connecting a motor shaft to a gearbox or machine?

Accepted Answer

To accommodate minor shaft misalignment and absorb vibration/torsional shock between connected shafts

Answer

To allow controlled slippage between motor and load during overload, protecting the motor from damage

Answer

To change the rotation direction between motor and driven shaft

Answer

To connect shafts of different diameters without requiring adapters

Question 4

What is 'bearing preload' in precision machine tools, and why is it applied to angular contact bearings?

Accepted Answer

Applying a controlled axial compressive force on bearings to eliminate clearance and improve stiffness, accuracy, and load capacity under combined loads

Answer

Applying initial load on bearing mounting bolts to prevent vibration loosening during operation

Answer

Lubricating bearings before installation to prevent dry start damage when the machine first runs

Answer

Increasing bearing radial clearance to compensate for thermal expansion at operating temperature

Question 5

What is a 'torque limiter' (slip clutch) in mechanical power transmission and what does it protect against?

Accepted Answer

A device that disconnects or slips at a preset torque level, protecting connected machinery from damage during jam, impact, or stall conditions

Answer

A device that gradually increases motor starting torque to prevent belt slippage during startup

Answer

A gearbox with adjustable gear ratios for variable torque/speed output from a fixed-speed motor

Answer

A coupling that reverses rotation direction when torque exceeds a threshold, preventing reverse loading

Question 6

What does 'L10 bearing life' (or 'B10 life') specification mean and how is it calculated?

Accepted Answer

The number of operating hours (or revolutions) at which 10% of a batch of identical bearings would be expected to fail

Answer

The bearing life in years for 10 continuous hours of operation per day

Answer

The maximum ambient temperature of 10°C below rated temperature that extends bearing life

Answer

The bearing rating when loaded to 10% of its basic dynamic load capacity