24 Questions
What is the primary function of a power transmission system?
To transmit power from one mechanical element to another
Which of the following types of transmission systems is most suitable for high-speed applications?
Gear drives
What is the primary factor that determines the type of transmission system to be used?
All of the above
What is the purpose of friction in a belt drive system?
To act as a helpful agent
What is the term used to describe the portion of the belt that is in contact with the pulley surface?
Arc of contact
What is the term used to describe the pulley that supplies power to another mechanical element?
Driver
What is the unit of measurement for the tension in a belt drive system?
Newtons
What is the advantage of using a belt drive system over other types of transmission systems?
All of the above
What is a characteristic of an open belt drive?
The driven pulley rotates in the same direction as the driver pulley
What is a precaution to be taken in a cross belt drive?
The speed of the belt should be less than 15 m/s
What is a characteristic of a closed belt drive?
The driver and driven pulleys rotate in opposite directions
Which of the following is a disadvantage of a closed belt drive?
The life of the belt reduces due to the rubbing point
What is a characteristic of an open belt drive when the shafts are horizontal or inclined?
It is effective to transmit power
Which of the following belt materials is not commonly used?
Steel
What is an advantage of an open belt drive over a cross belt drive?
It requires less length of the belt
What happens to the belt in a cross belt drive at the point where it crosses?
It rubs against each other and there will be wear
What is the ratio of speed of driving to speed of driven in belt drives, considering the thickness of the belt?
n1/n2 = (d2 + t)/(d1 + t)
What is the effect of creep on power transmission in belt drives?
It reduces the power transmission.
What is the function of the idler gears in a simple gear train?
To provide intermediate gears between the driver and driven.
What is the advantage of flat belt drives over other types of belt drives?
They have a low running and maintenance cost.
What is the effect of slip on the velocity ratio of a belt drive?
It decreases the velocity ratio.
What is the arrangement of gears in a simple gear train?
Series arrangement of gears with intermediate gears.
What is the disadvantage of using flat belt drives for short centre distances?
They are not preferred for short centre distances.
What is the definition of a gear train?
Two or more gears that mesh with each other to transmit power from one shaft to another.
Study Notes
Power Transmission
- Rotating elements with mechanical energy need to be utilized at the required place by transmitting power from one shaft to another or from a prime mover to a machine.
Transmission System
- A system used to transmit power from one mechanical element to another mechanical element.
Types of Transmission Systems
- Belt drives
- Rope drives
- Chain drives
- Gear drives
Factors to Select Transmission System
- Distance between driver and driven pulley shaft
- Operational speed
- Power to be transmitted
Belt Drive
- Power is transmitted between parallel shafts
- Consists of two pulleys with an endless belt passed over them
- Rotary motion is transmitted from driving pulley to driven pulley
- Friction is a helpful agent in belt drives
Terminology of a Belt Drive
- Driver: supplies power to another mechanical element
- Driven: receives power from the driver
- Tight side: portion of the belt with maximum tension (denoted by T1 Newton)
- Slack side: portion of the belt with minimum tension (denoted by T2 Newton)
- Arc/Angle of contact: portion of the belt in contact with the pulley surface
Belt Materials
- Rubber
- Leather
- Canvas
- Cotton
- Steel
Classification of Belt Drives
- Open belt drive
- Closed belt drive
Open Belt Drive
- Both driver and driven pulleys rotate in the same direction
- Belt is passed over driver and driven pulleys
- Driver pulley pulls the belt from one side and delivers to the other side
- Tension is more on the lower side than the upper side
Cross Belt Drive
- Driven rotates in the opposite direction to that of the driver
- Belt rubs against each other at the point where it crosses, causing wear
- To avoid this, the speed of the belt should be less than 15 m/s
Comparison between Open Belt Drive and Closed Belt Drive
- Open belt drive: both driver and driven rotate in the same direction, no rubbing point, and requires less length of the belt
- Closed belt drive: driver and driven rotate in opposite directions, has a rubbing point, and requires more length of the belt
Velocity Ratio of Belt Drives
- n1/n2 = d2/d1 (speed of driving shaft to speed of driven shaft = diameter of driven pulley to diameter of driver pulley)
- When thickness of belt is considered: n1(d2 + t) / n2(d1 + t)
Creep and Slip
- Creep: relative motion between belt and pulley surface due to contraction and expansion of the belt
- Slip: relative motion between pulley and the belt passing over it
- Velocity ratio when slip is considered: n1 d2 / n2 d1 (100 - S), where S is the percentage slip
Idler Pulley, Stepped Pulley, and Fast and Loose Pulley
- Idler pulley: used to change the direction of the belt or to increase the arc of contact
- Stepped pulley: used when the centre distance between the pulleys is fixed
- Fast and loose pulley: used when the belt needs to be shifted from one pulley to another
Advantages and Disadvantages of Flat Belt Drives
- Advantages: low running and maintenance cost, possibility to transmit power over a moderately long distance, and efficient at high speeds
- Disadvantages: not preferred for short centre distance, belt joints reduce the life of the belt, and loss of power due to slip and creep
Gear Trains
- An arrangement of gears that mesh with each other to transmit power from one shaft to another
- Types: simple gear train (SGT) and compound gear train (CGT)
Simple Gear Train
- Arrangement of gears in series
- Intermediate gears are provided between the driver and driven gears
This quiz covers the basics of power transmission, including the types of transmission systems and their applications. It explains the concept of transmitting power from one mechanical element to another.
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