Gear A gear is a rotating machine part having cut teeth or cogs which mesh with another toothed part in order to transmit torque Introduction Gears are the most common means used for power transmission ID: 293851
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Slide1
“IN THE NAME OF ALLAH, THE MOST BENEFICENT, THE MOST MERCIFUL”Slide2
Gear
A gear is a rotating machine part having cut
teeth
, or
cogs
, which
mesh
with another toothed part in order to transmit
torqueSlide3
Introduction
Gears are the most common means used for power transmission They can be applied between two shafts which are ParallelCollinearInclined at any arbitrary angleSlide4
Why
we use gearsIn order to avoid the slipping, a number of projections (called teeth) are provided on the periphery of the wheel which will fit into the corresponding recesses on the periphery of the other wheel.A friction wheel with the teeth cut on it is known as toothed wheel or
gear
.Slide5
Gear advantages
It transmits exact velocity ratioIt may be use to transmit large powerIt has high efficiencyIt has reliable(easy) servicesSlide6
Gear disadvantages
It costs expensive to manufactureAny type of error may cause vibrations and noiseIt requires suitable lubricant and reliable method of applying it, for proper operation of gear drives Slide7
Classification of toothed wheel on the basis of teeth
Parallel
Intersecting
Non-intersecting and non-parallel
.Slide8
1)PARALLEL:
These gears have teethparallel to the axis of the wheel.Slide9
2)INTERSECTING:
These gears are called bevel gears and the arrangement is known as
bevel gearing
.
The bevel gears
have their teeth inclined to the face of the bevel, in which case they are known as
helical bevel gears
.Slide10
3)Non intersecting & non parallel:A gear having teeth in such a way that its axis of rotation does not cross the length of teeth when extended
Slide11
NomenclatureSlide12
Pitch circle
It is the circle made by joining those points where two meshed teeth release each other Slide13
2
. Pitch circle diameter
.
It is the diameter of the pitch circle. The size of the gear is usually specified by the pitch circle diameter. It is also known as
pitch diameter
3.
Pitch point
.
Point where the line of action crosses a line joining the two gear axes
4.
Pitch surface
.
It is the surface of the rolling discs which the meshing gears have replaced at the pitch circleSlide14
5
. Pressure angle or angle of obliquity.
It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point.
6
.
Addendum
.
It is the radial distance of a
tooth from the pitch circle to
the top of the tooth
7.
Dedendum
.
It is the radial distance of a tooth from the pitch circle to the bottom of the toothSlide15
8
. Addendum circle.
It is the circle drawn through the top of the teeth and is concentric with the pitch circle.
9.
Dedendum
circle
.
It is the circle drawn through the bottom of the teeth. It is also called root circle.
10.
Circular pitch
.
It is the distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth.
Mathematically,
Circular pitch
=
D/T
where
D
= Diameter of the pitch circle, and
T
= Number of teeth on the wheel.Slide16
11.
Diametral pitch. It is the ratio of number of teeth to the pitch circle diameter in millimetres.Mathematically,
Diametral pitch=
T/D
12.
Module
.
It is the ratio of the pitch circle diameter in millimeters to the number of teeth.
It is usually denoted by
m
. Mathematically,
Module,
m
=
D
/
TSlide17
13
. Clearance.
It is the radial distance from the top of the tooth to the bottom of the tooth, in a meshing gear. A circle passing through the top of the meshing gear is known as
clearance circle
.
14
.
Total depth
.
It is the radial distance between the addendum and the
dedendum
circles of a gear. It is equal to the sum of the addendum and
dedendum
.Slide18
15
. Working depth.
It is the radial distance from the addendum circle to the clearance circle.
16.
Tooth thickness
.
It is the width of the tooth measured along the pitch circle.
17.
Tooth space
.
It is the width of space between the two adjacent teeth measured along the pitch circle.Slide19
18
. Backlash.
It is the difference between the tooth space and the tooth thickness, as measured along the pitch circle.
19.
Face of tooth
.
It is the surface of the gear tooth above the pitch surface.
20.
Flank of tooth
.
It is the surface of the gear tooth below the pitch surface.
21.
Top land
.
It is the surface of the top of the toothSlide20
22
. Face width.
It is the width of the gear tooth measured parallel to its axis.
23.
Profile
.
It is the curve formed by the face and flank of the tooth.
24.
Fillet radius
.
It is the radius that connects the root circle to the profile of the tooth.Slide21
25
.
Path of contact
.
It is the path traced by the point of contact of two teeth from the beginning to the end of engagement.Slide22
Angular frequency
Measured in radians per second.1RPM = π / 30 rad/secondIt is denoted by “ω”Slide23
Gear, wheel
The larger of two interacting gearsSlide24
Pinion
The smaller of two interacting gearsSlide25
Line of action, pressure line
Line along which the force between two meshing gear teeth is directed. Slide26
Axis
Axis of revolution of the gear; center line of the shaftSlide27
Application of Gear
· Defense
·
Fertilizer Industry
·
Food Processing
·
Marine
·
Paper
·
Turbine Plant
·
Aluminum
·
Chemical
·
Grinding Mills
·
Hot and Cold Rolling
·
Movable bridge
·
Petroleum
·
Plastics
·
Rubber
·
Sugar
·
Stamping Presses
·
Wind Turbines
·
Surface Mining
·
Petrochemical
·
Rubber Plants
·
Sponge Iron
·
Material Handling
·
Earth Moving Industry
·
Aviation Industry
·
Cement Plant
·
Coal Plants
·
Construction Machinery
·
Elevator Industry
·
Medical Industry
·
Micro Assembling
·
Power Industry
·
Printing Industry
·
Railway Industry
·
Steel Plants
Slide28
Gear Materials
The material used for the manufacture of gears depends upon the strength and service conditions like wear, noise etc.The gears may be manufactured from metallic or non-metallic materialsThe metallic gears with cut teeth are commercially obtainable in cast iron, steel and bronzeThe nonmetallic materials like wood, raw hide, compressed paper and synthetic resins like nylon are used for gears, especially for reducing noise.Slide29
Gear Materials
The cast iron gears with cut teeth may be employed, where smooth action is not important.The steel is used for high strength gears and steel may be plain carbon steel or alloy steelThe phosphor bronze is widely used for worm gears in order to reduce wear of the wormsSlide30
TYPES OF GEARS
SPUR GEARBEVEL GEARExternal and internal gearWORM GEARDIFFERENTIAL GEAR
RACK GEAR
PINION
IDLER GEAR
RATCHET
PLANETARY GEARSlide31
DISCRIBTION
SPUR GEAR: A gear wheel having radial teeth parallel to the axle.Slide32
Application Spur Gear
Spur Gear and Plastic Spur Gears used in a film winding component.Spur Gears used in automatic packing machine.Spur Gears are used in the film-cutting component.Slide33
BEVEL GEAR
A gear wheel meshed with another so that their shafts are at an angle less than 180 degrees ( LEGO size 90 degree with 14 teeth ) Slide34
Application of Bevel gear
it is used in grain mill.it is used in power plant.it is used in Railway track inspection machineBevel gear used in floodgate.Slide35
External Gear
An external gear is one with the teeth formed on the outer surface of a cylinder or cone.
internal gear
internal gear is one with the teeth formed on the inner surface of a cylinder or cone.
1.External vs. internal gearsSlide36
Application of internal & external gear
(hub gear) internal gear used in bicycle and bikes.internal gear used in internal gear pumps.used in wind turbine generatorSlide37
external gear in bicycle Slide38
DEFINITION OF WORM GEAR
WORM GEAR: A short rotating screw that meshes with the teeth of another gear. As a worm gear is an inclined plane, it will be the driving gear in most cases ( THE LAW OF THE WORM! ). Slide39
Application of worm gear
worm drive used in controlling a gatePackaging Industries (Machines)Material Handling Equipments Food Processing Machines Widely in Conveyor SystemsSlide40
DEFINITION OF RACK GEARS
RACK GEAR: A toothed bar into which a "pinion," ( worm gear spur etc ) meshes. ( LEGO® size 1 x 4 with 10 teeth )Slide41
DEFINITION OF PINION GEAR
PINION: A small cogwheel, the teeth of which fit into those of a larger gearwheel or those of a rack.Slide42
DEFINITION OF IDLER GEAR
IDLER GEAR: A gear wheel placed between two other gears to transmit motion from one to the other. It does not alter the speed of the output, but it does alter the direction it turns. ( ODD number =reverse rotation, EVEN number = same rotation )Slide43
Definition of Ratchet
RATCHET: A toothed wheel or bar that catches and holds a PAWL, which thus prevents backward movement.Slide44
The ratchet is really another form of gearing. Unlike gears which can be used to speed up or slow down movement, the ratchet can only be used to slow things down and it happens in a very jerky manner. Below and opposite is an explanation of how they work.
Slide45
Definition of Pawl
PAWL A mechanical device allowing rotation in only one direction.Slide46
Definition of Planetary gear
PLANETARY GEAR:A device allowing several gears to "orbit" about others ( very handy for robot turntables )Slide47
Planetary
Gears are the latest type and used in RoboticsSlide48
Gear ManufacturingSlide49
Hobbing is a
machining process for making gears, splines, and sprockets on a hobbing machine, which is a special type of
milling machine
. The teeth or
splines
are progressively cut into the
workpiece
by a series of cuts made by a
cutting tool
called a
hob
. Compared to other gear forming processes it is relatively inexpensive but still quite accurate, thus it is used for a broad range of parts and quantities.
It is the most widely used gear cutting process for creating spur and helical gears\and more gears are cut by
hobbing
than any other process since it is relatively quick and inexpensive.
Hobbing
Slide50
Gear Shaping Operation - Gear shaping process makes use of a hardened pillion as a cutter, ground with top rake and clearance. Referring to, gear shaping cutter 1 receives reciprocating movement (in the direction of arrow 1) which is the principal movement. The cutter reciprocates like the cutting tool in a standard shaper but at a rate of 50 to 450 strokes per minute.
Slide51
Defects in gear
In mechanical engineering, backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established. For example, in a pair of
gears
, backlash is the amount of clearance between mated gear teeth.
Theoretically, the backlash should be zero, but in actual practice some backlash must be allowed to prevent jamming. It is unavoidable for nearly all reversing mechanical couplings, although its effects can be negated. Depending on the application it may or may not be desirable. Reasons for requiring backlash include allowing for
lubrication
, manufacturing errors,
deflection
under load and
thermal expansion
.
1.backlashSlide52
Problem#1
A helical cast steel gearwith 30 helix angle has to transmit 35kWat 1500r.p.m.If the gear has 24 teeth and the necessary module is6mm.If tangetial tooth load is 3100N.Determine
1.the pitch diameter and face width for 20
fulldepth
teeth.
The static stress for cast steel may be taken as 56Mpa.The width
of
facemay
be taken as 3 times the normal pitch.
2.What would be the end thrust on the gear?
The tooth factor for 20 full depth
involute
gear may be taken as
.154-(.912/Te), where Te represents the equivalent number of
teeth.Slide53
Problem#2
A triple threaded worm has teeth of 6mmmodule and pitch circle diameter of 50mm.Ifthe worm gear has 30 teeth of 14.5 and the coefficient of friction of the worm gearing is .05 Find 1.The lead angle of the worm, 2.Velocity ratio, 3.Centre distance