BELT DRIVEBELT DRIVE1.1. A belt is a looped strip of flexible A belt is a looped strip of flexible

material, used to mechanically link two material, used to mechanically link two or more rotating shafts. or more rotating shafts.

2.2. They may be used as a source of motion, They may be used as a source of motion, to efficiently transmit power, or to track to efficiently transmit power, or to track relative movement. Belts are looped relative movement. Belts are looped over pulleys. over pulleys.

3.3. In a two pulley system, the belt can In a two pulley system, the belt can either drive the pulleys in the same either drive the pulleys in the same direction, or the belt may be crossed, so direction, or the belt may be crossed, so that the direction of the shafts is that the direction of the shafts is opposite. opposite.

Open belt driveOpen belt drive

Cross belt drive.Cross belt drive.

Belts on a Yanmar 2GM20 marine Belts on a Yanmar 2GM20 marine diesel enginediesel engine

FLAT BELTFLAT BELT

VEE BELTVEE BELT

TIMING BELTTIMING BELT

ROUND BELTROUND BELT

Advantages of belt driveAdvantages of belt drive They are simple. They are economical.They are simple. They are economical. Parallel shafts are not required. Parallel shafts are not required. Overload and jam protection are provided. Overload and jam protection are provided. Noise and vibration are damped out. Machinery Noise and vibration are damped out. Machinery

life is prolonged because load fluctuations are life is prolonged because load fluctuations are cushioned (shock-absorbed). cushioned (shock-absorbed).

They are lubrication-free. They require only low They are lubrication-free. They require only low maintenance. maintenance.

They are highly efficient (90–98%, usually 95%). They are highly efficient (90–98%, usually 95%). Some misalignment is tolerable. Some misalignment is tolerable.

They are very economical when shafts are They are very economical when shafts are separated by large distances. separated by large distances.

Disadvantages of belt driveDisadvantages of belt drive The angular-velocity ratio is not necessarily The angular-velocity ratio is not necessarily

constant or equal to the ratio of pulley diameters, constant or equal to the ratio of pulley diameters, because of belt slip and stretch. because of belt slip and stretch.

Heat buildup occurs. Speed is limited to usually Heat buildup occurs. Speed is limited to usually 7000 feet per minute (35 meters per second). 7000 feet per minute (35 meters per second). Power transmission is limited to 370 kilowatts Power transmission is limited to 370 kilowatts (500 horsepower). (500 horsepower).

Operating temperatures are usually restricted to –Operating temperatures are usually restricted to –31 to 185°F (–35 to 85°C). 31 to 185°F (–35 to 85°C).

Some adjustment of center distance or use of an Some adjustment of center distance or use of an idler pulley is necessary for wear and stretch idler pulley is necessary for wear and stretch compensation. compensation.

A means of disassembly must be provided to A means of disassembly must be provided to install endless belts.install endless belts.

Chain driveChain drive Chain drive is a way of transmitting mechanical Chain drive is a way of transmitting mechanical

power from one place to another. power from one place to another. It is often used to convey power to the wheels of It is often used to convey power to the wheels of

a vehicle, particularly bicycles and motorcycles. a vehicle, particularly bicycles and motorcycles. It is also used in a wide variety of machines It is also used in a wide variety of machines

besides vehicles.besides vehicles. Most often, the power is conveyed by a roller Most often, the power is conveyed by a roller

chain, known as the drive chain, passing over a chain, known as the drive chain, passing over a sprocket gear, with the teeth of the gear meshing sprocket gear, with the teeth of the gear meshing with the holes in the links of the chain. with the holes in the links of the chain.

The gear is turned, and this pulls the chain The gear is turned, and this pulls the chain putting mechanical force into the systemputting mechanical force into the system.. ..

Roller chain and sprocketRoller chain and sprocket

PROBLEMPROBLEMFollowing are the details of a crossed belt drive. Calculate the Following are the details of a crossed belt drive. Calculate the

lengthlengthof the belt?of the belt?

Diameter of the driverDiameter of the driver :: 200 mm200 mmDiameter of the followerDiameter of the follower :: 400 mm400 mmCenter distance of the driveCenter distance of the drive :: 2m 2mSpeed of the driverSpeed of the driver :: 400 rpm400 rpmAngle of contactAngle of contact : : 197.3 197.3

Determine the length of the belt.Determine the length of the belt.Solution:Solution:D1 = 200 mmD1 = 200 mmD2= 400 mmD2= 400 mmC = 2mC = 2mN1 = 400 rpmN1 = 400 rpmLength of the belt = L =2C+ П / 2 (D1+ D2) + (D1+ D2) / 4CLength of the belt = L =2C+ П / 2 (D1+ D2) + (D1+ D2) / 4C

= (2x2) + П / 2 (0.2+ 0.4) + (0.2+ 0.4) / 4x2= (2x2) + П / 2 (0.2+ 0.4) + (0.2+ 0.4) / 4x2= 4.99 m= 4.99 m

Possible QuestionsPossible QuestionsShort Answer QuestionsShort Answer Questions

1.1. Differentiate between open belt and crossed belt Differentiate between open belt and crossed belt drive.drive.

2.2. What are the commonly used materials for flat belts?What are the commonly used materials for flat belts?

3.3. List out the applications of belt drives.List out the applications of belt drives.

4.4. What do you mean by slip in a belt drive?What do you mean by slip in a belt drive?

5.5. Differentiate between belt drive and chain drive.Differentiate between belt drive and chain drive.

Long Answer QuestionsLong Answer Questions1.1. Explain with neat sketch, the types of various flat Explain with neat sketch, the types of various flat

belt drives.belt drives.

2.2. List out the advantages and disadvantages of belt List out the advantages and disadvantages of belt drives.drives.

3.3. Compare flat belt and V belts.Compare flat belt and V belts.

4.4. Briefly explain chain drives.Briefly explain chain drives.