power transmission (rotational power) belt drives chain drives gear drives

Power transmission Power transmission (rotational power)(rotational power)Belt drivesChain drivesGear drives

A belt drive is a method of transferring rotary motion

between two shafts(attached with pulleys).

It is a looped strip of flexible material, used to

mechanically link two or more rotating shafts..

Belt drives may be used as a source of motion, to

efficiently transmit power, or to track relative

movement.

Generally belt drives are friction drives.

Simple belt drive systemSimple belt drive system

ApplicationApplicationWhere the rotational speeds are

differentDistance between the shafts is

highMotion or power that needs to be

transmitted to more number of applications

Types of beltsTypes of beltsFlat belt

V belt

Round belt

Timing belt

Pictorial view of beltsPictorial view of belts

Round belt

Pictorial viewPictorial view

Pictorial viewPictorial view

Materials used for belt Materials used for belt drivesdrivesOak tanned leather – fairly stiff Chrome leather belt – for oil and

steam environmentFabric belts - (Canvas or cotton

duck)Rubber belts – layers of fabric

impregnated with rubber or vulcanized rubber

Types of Belt drivesTypes of Belt drivesOpen belt driveCrossed belt drive

Open belt driveOpen belt drive

Crossed belt driveCrossed belt drive

TerminologyTerminologyLength of the beltVelocity ratioSlipTight side and slack sideLength of the beltAngle of contactRatio between the belt tensionsPower transmitted

Ratios b/w belt tension and Ratios b/w belt tension and PowerPower R= T1/T2 =eµθ

T1 = Tension in the tight side

T2 = Tension on the slack side

µ= coefficient of friction

θ= angle of contact

Power transmitted P = (T1-T2 )V V= velocity of the belt V= πd1 * N/60 m/s

Merits of belt drive Merits of belt drive mechanismmechanism

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. Noise and vibration are damped out.

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

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

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

Demerits of belt driveDemerits of belt driveNon compactConstant velocity cannot be

obtainedSlippage Not applicable for heavy loads

Real time applicationsReal time applicationsLathe , drilling and sewing

machinesCompression systems AutomobilesWater systemsPower generation unitsAir conditioning systems

ExampleExample

An engine running at 300 rpm drives a line shaft by means of belt drive. The engine pulley is 600mm in diameter and the pulley on the shaft is 400mm in diameter. Determine the speed of the line shaft.(assume no slip).

ExampleExampleFollowing details of the cross and open

belt driveDiameter of the driver= 300mmDiameter of the follower = 600mmCenter distance of the drive is =3mtsSpeed of the drive is = 500rpmAngle of contact = 195.6 °Determine the length of the belt

required for both of the drive systems

ExampleExampleFor the example in the previous

slide the tension on the tight side is 1.3KN and the coefficient of friction between the pulley is 0.25 find the power capacity of the drive.

CHAIN DRIVESCHAIN DRIVES

Animated viewAnimated view

ApplicationsApplicationsWhere slippage needs to be

reduced to a considerable amount

Initial torque developed is moreContinuous drive systemsSmaller center distanceAgro machinery ,

automobiles,cranes

Gear systemsGear systemsMachine elements that transmit

the motion and power between the rotating shafts by means of successively engaging teeth .

Compact than the other drive systems

More accurate power transmission

Less slippage or little backlash

Common forms of gear Common forms of gear configurationconfigurationGears for connecting parallel

shaftsGears for connecting intersecting

shaftsGears for connecting neither

parallel nor intersecting shafts

Gear types for connecting Gear types for connecting parallel shaftsparallel shaftsSpur gears (internal and

external)Parallel helical gearsRack and pinion arrangement

Spur gearSpur gear

Helical gear Helical gear

Herring bone gear Herring bone gear

Rack and pinion Rack and pinion

Gears for connecting Gears for connecting interesting shaftsinteresting shaftsStraight bevel gear

Neither interesting nor Neither interesting nor parallelparallel

NomenclatureNomenclature

TerminologiesTerminologiesPitch circle Tooth spaceAddendum circle BacklashRoot circle Circular pitch Addendum Diametral pitch Dedundum ModuleClearance Face of the tooth Flank of tooth Tooth space Tooth thickness or circular thickness

Velocity ratio of the Gear Velocity ratio of the Gear DriveDriveAngular speeds of two gears

◦ω1 = 2π N1

◦ω2 = 2π N2.

Peripheral velocity of the Driver gear Vp = ω1 d1 /N1 = π d1N1 = ω2d2 /N2 = π d2N2

Velocity ratio = n= ω1/ ω2=N1/N2

Gear trainsGear trainsA combination of two or more

gears for transmission of energy.Size /number of teeth makes a

speed change(reduction or increment).

Preferred when large speed change is required in a compact space.

Types of gear trainsTypes of gear trainsSimple gear train Compound gear train Planetary gear train

Simple gear train Simple gear train

Compound gear train Compound gear train

Velocity ratio of Gear Velocity ratio of Gear trainstrains

ω1 = angular velocity of Gear 1 ω2 = angular velocity of Gear 2 ω3 = angular velocity of Gear 3 N1= speed of gear 1 N2 = speed of gear 2 N3 = speed of gear 3 T1= teeth of gear 1 T2= teeth of gear 2 T3= teeth of gear 3 ω1/ ω2= N1/N2 = T2/T1; ω2/ ω3 = N2/N3 =T3/T2 ω1/ ω3= ω1/ ω2 * ω2/ ω3 = N1/N2* N2/N3 = T2/T1* T3/T2

Planetary gear trainPlanetary gear trainAlso termed a epicyclical gear

Gears in real time Gears in real time application application AutomobilesMachine systemsPumping systemsMachine toolsTiming and related equipments

Merits and DemeritsMerits and DemeritsMerits:CompactnessGreater speed amplification and

reduction of speedsLess slipDirect contact with the driver

Merits and DemeritsMerits and DemeritsDemeritsWear and tearRequired coolant for reduction of

heat developedBack lash Noise and vibration