Gears Ppt1

8/3/2019 Gears Ppt1

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8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


Power transmission is the movement of energy

from its place of generation to a location where

it is applied to performing useful work

A gear is a component within a transmission

device that transmits rotational force to another

gear or device

8/3/2019 Gears Ppt1


1. According to the position of axes of theshafts.

a. Parallel1.S pur Gear 2.Helical Gear 3.R ack and Pinion

b. IntersectingBevel Gear

c. Non-intersecting and Non-parallelworm and worm gears

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


Teeth is parallel to axisof rotation

Transmit power fromone shaft to another parallel shaftUsed in Electric

screwdriver, oscillatingsprinkler, windup alarmclock, washing machineand clothes dryer

8/3/2019 Gears Ppt1


Simplest of All gearsTeeth is parallel to axis

of rotationTransmit power from

one shaft to another parallel shaft High Efficiency &H

igh precision rating,hence they used for High S peed & HighLoad applications

8/3/2019 Gears Ppt1


Suitable for Low &

medium speed

applicationsRelatively high

ratio can be

achieved

Steel, bronze, castIron & Plastics

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


The teeth on helical gears are cut at an angle to the faceof the gear

Their contact ratio (the average number of teeth incontact at any one time) is therefore higher than that of

spur gears, which allows increased capacity (better loadsharing) and a smoother and quieter operation. This gradual engagement makes helical gears operate

much more smoothly and quietly than spur gears One interesting thing about helical gears is that if the

angles of the gear teeth are correct, they can bemounted on perpendicular shafts, adjusting the rotationangle by 90 degrees

8/3/2019 Gears Ppt1


Used in Automotive Gear boxes

8/3/2019 Gears Ppt1


Used in Automotive Gear boxes

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


To avoid axial thrust, two

helical gears of opposite

hand can be mounted side by

side, to cancel resultingthrust forces

Herringbone gears are

mostly used on heavymachinery.

8/3/2019 Gears Ppt1


Two Helical Gears with opposing helical anglesside by side

Axial Thrust gets cancelled.

They have two opposing tooth helix's on thecircumference. These opposing helix anglesenables this type of gear to nullify more axialloads.

Their load capacity is very high but manufacturingdifficulty makes them more costly.

These gears are used in cement mills and crushers.

8/3/2019 Gears Ppt1


Rack and pinion gears

are used to convert

rotation (From the

pinion) into linear

motion (of the rack)

A perfect example of thisis the steering system on

many cars

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


Bevel gears are useful when the direction of a shaft'srotation needs to be changed

They are usually mounted on shafts that are 90degrees apart, but can be designed to work at other

angles as well The teeth on bevel gears can be straight, spiral or

hypoid locomotives, marine applications, automobiles,

printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc.

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


Worm gears are used when large gear reductions are

needed. It is common for worm gears to have

reductions of 20:1, and even up to 300:1 or greater

Many worm gears have an interesting property thatno other gear set has: the worm can easily turn the

gear, but the gear cannot turn the worm

Worm gears are used widely in material handling and

transportation machinery, machine tools, automobilesetc

8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


8/3/2019 Gears Ppt1


Pitch surface: The surface of the imaginary rolling cylinder (cone, etc.) that the toothed gear may be considered to replace.

Pitch circle: A right section of the pitch surface. Addendum circle: A circle bounding the ends of the teeth, in a

right section of the gear .

Root (or dedendum) circle: The circle bounding the spaces between the teeth, in a right section of the gear .

Addendum: The radial distance between the pitch circle andthe addendum circle.

Dedendum: The radial distance between the pitch circle and

the root circle. Clearance: The difference between the dedendum of one gear

and the addendum of the mating gear .

8/3/2019 Gears Ppt1


Face of a tooth: That part of the tooth surface lying outside the pitch surface.

Flank of a tooth: The part of the tooth surface lying inside the pitch surface.

Circular thickness (also called the tooth thickness): Thethickness of the tooth measured on the pitch circle

Tooth space: It is the width of space between the tooth spaceand the tooth thickness along the pitch circle.

Backlash: The difference between the Tooth thickness of onegear and the tooth space of the mating gear .

Circular pitch (Pc) :

The width of a tooth and a space,measured on the pitch circle.

N

D P c

T

8/3/2019 Gears Ppt1


Diametral pitch (Pd): The ratio of the number of teeth of agear unit to pitch circle diameter . The diametral pitch is, bydefinition, the number of teeth divided by the pitch diameter . That is,

WherePd = diametral pitchZ = number of teethD = pitch diameter

Module (m): Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimeters; inthe former case the module is the inverse of diametral pitch.

m = D/Z

D

Z P d !

8/3/2019 Gears Ppt1


d = Diameter of the wheel

N1,Z

1=S peed of the Driver Gear

N2,Z2 =S

peed of the Driven Gear = Angular speed

velocity ratio (n) =

1

2

2

1

1

2

z

z

N

N !!

[

[

8/3/2019 Gears Ppt1


d = Diameter of the wheel

N1,Z

1=S peed of the Driver Gear

N2,Z

2=S peed of the Driven Gear

= Angular speed

velocity ratio (n) =

1

2

2

1

1

2

z

z

N

N !!

[

[

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Gears Ppt1