Upload
laura-willis
View
258
Download
10
Embed Size (px)
Citation preview
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