24 Questions
What is the primary purpose of a transmission system?
To transmit power from one mechanical element to another
What type of transmission system is used to transmit power between parallel shafts?
Belt drives
What is the factor that is NOT considered when selecting a transmission system?
Material of the pulley
What is the role of friction in a belt drive?
It is a helpful agent
What is the term used to describe the portion of the belt with maximum tension?
Tight side
What is the term used to describe the one which drives or supplies power to other mechanical element?
Driver
What is the angle of contact in a belt drive?
The portion of the belt which is in contact with the pulley surface
What is the primary function of a pulley in a belt drive?
To transmit rotary motion from one shaft to another
What is a characteristic of the open belt drive?
Both driver and driven pulleys rotate in the same direction
What is the primary reason for the wear of the belt in a cross belt drive?
Because the belt crosses and rubs against each other
What is a disadvantage of the closed belt drive?
Due to the rubbing point, the life of the belt reduces
What is the maximum speed of the belt recommended to avoid wear in a cross belt drive?
15 m/s
What is a characteristic of the closed belt drive?
Driver and driven pulleys rotate in opposite directions
What is the advantage of the open belt drive when the shafts are horizontal or inclined?
It is effective to transmit the power
Why does the open belt drive require less length of the belt compared to the closed belt drive?
Because the open belt drive does not have a rubbing point
What is a type of material that can be used to make a belt?
All of the above
What is the ratio of the speed of the driving pulley to the speed of the driven pulley in a belt drive, considering the thickness of the belt?
n1/n2 = (d2 + t)/(d1 + t)
What is the effect of creep on power transmission in a belt drive?
It reduces power transmission by reducing the speed of the driven pulley.
What is the purpose of the idler gear in a simple gear train?
To provide an intermediate gear between the driver and driven
What is the advantage of using 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 depends on the percentage of slip.
What is the purpose of a stepped pulley in a belt drive?
To provide a means of changing the speed of the driven shaft.
What is the disadvantage of using belt joints in a belt drive?
They reduce the life of the belt.
What is the definition of a gear train?
A system of gears that 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 explores the concept of transmitting mechanical energy from one element to another.
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