term paper gear imran khan

7/30/2019 Term Paper Gear Imran Khan

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This is to certify that

Of ,

(

Enrollment no. has done

bonafide

work on the project

under my guidance superbly.

Date:_02/11/2012 ___________________


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(Teacher In-charge)


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Apart from the efforts of me, the success of any projectdepends largely on the encouragement and guidelines of

many others. I take this opportunity to express my gratitude

to the people who have been instrumental in the successful

completion of this project.

I would like to show my greatest appreciation to the

respected TEACHER IN-CHARGE. I cant say thank you

enough for his tremendous support and help. Without his

encouragement and guidance this project would not have

materialized.

The guidance and support received from my family and

friends who helped me in making this project a success. I am

grateful for their constant support and help.


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CONTENTS-

1.Introduction2.Gears: An Historical Note

Importance of Clock

Influence on Bicycles

Industrial Revolution And Gears

3.Comparison with Drive Mechanism

4.Terminology in gear technology5.Various types of gears

External v/s Internal gears

Spur

Helical

Skew gears

Double helical Bevel

Hypoid

Crown

Worm

Non-circular

Rack and pinion

Epicyclic

Sun and planet

Cage gear

6.Sprockets


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7.Backlash

8.Shifting of gears

Manual transmission

Automatic transmission

9.Derailleur gear

10. Hub gear

11. Tooth profile

12. Involute gears

13. Gear materials

14. Gear train15. Gear box

16. Uses of gears

17. Gears applications


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Introduction

A gear is a rotating machine part having cut teeth, orcogs,which meshwith another toothed part in order to transmit torque. Twoor more gears working in tandem are called atransmissionand canproduce a mechanical advantage through a gear ratio and thus maybe considered a simple machine. Geared devices can change thespeed, torque, and direction of a power source. The most commonsituation is for a gear to mesh with another gear, however a gear canalso mesh a non-rotating toothed part, called a rack, therebyproducing translation instead of rotation.

The gears in a transmission are analogous to the wheels in a pulley.An advantage of gears is that the teeth of a gear prevent slipping.

When two gears of unequal number of teeth are combined amechanical advantage is produced, with both the rotational speedsand the torques of the two gears differing in a simple relationship.

In transmissions which offer multiple gear ratios, such as bicycles and

cars, the term gear, as in first gear, refers to a gear ratio rather thanan actual physical gear. The term is used to describe similar deviceseven when gear ratio is continuous rather than discrete, or when thedevice does not actually contain any gears, as in acontinuouslyvariable transmission.

The earliest known reference to gears was circa A.D. 50 by Hero ofAlexandria but they can be traced back to the Greek mechanics ofthe Alexandrian school in the 3rd century B.C. and were greatly

developed by the Greek polymath Archimedes (287

212B.C.). The Antikythera mechanism is an example of a very early andintricate geared device, designed to calculate astronomical positions.Its time of construction is now estimated between 150 and 100 BC.
http://en.wikipedia.org/wiki/Transmission_(mechanics)http://en.wikipedia.org/wiki/Transmission_(mechanics)http://en.wikipedia.org/wiki/Transmission_(mechanics)http://en.wikipedia.org/wiki/Simple_machinehttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Translation_(physics)http://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Pulleyhttp://en.wikipedia.org/wiki/Pulleyhttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Translation_(physics)http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Simple_machinehttp://en.wikipedia.org/wiki/Transmission_(mechanics)


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Gears: An Historical Note

Gears have existed since the invention of rotating

machinery. Because of their force-multiplying properties,early engineers used them for hoisting heavy loads such asbuilding materials. The mechanical advantage of gears wasalso used for ship anchor hoists and catapult pre-tensioning.

Early gears were made from wood with cylindrical pegs for

cogs and were often lubricated with animal fat grease. Gearswere also used in wind and water wheel machinery for

decreasing or increasing the provided rotational speed forapplication to pumps and other powered machines. An early

gear arrangement used to power textile machinery isillustrated in the following figure. The rotational speed of awater or horse drawn wheel was typically too slow to use, soa set of wooden gears needed to be used to increase thespeed to a usable level.

An 18th Century Application of Gears for Powering Textile Machinery


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The industrial revolution in Britain in the eighteenth centurysaw an explosion in the use of metal gearing. A science of

gear design and manufacture rapidly developed through thenineteenth century.

Today, the most significant new gear developments are inthe area of materials. Modern metallurgy has greatlyincreased the useful life of industrial and automotive gears,and consumer electronics has driven plastic gearing to new

levels of lubricant-free reliability and quiet operation.

Gears are about as old as any of the machinery of mankind. The

oldest machine is the potter's wheel. At first time over 3000 years ago

primitive gears first meshed with each other and transmitted rotary

motion.

In the fourth century, BC Aristole wrote about wheels using friction

between smooth surfaces to transmit motion. The earliest gears were

of wooden and had teeth of really engaging pins. The early Greeks

made use of metal gears with wedge shaped teeth. The Romans

made considerable use of gears in their mills. In middle age stone

gears were used in Sweden.


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Water wheels were used to convert energy of moving water into

energy that would power machines. Wooden gears connected water

wheels to machines that would grind wheat and hammer metals.

Gears mesh with each other toothed machine parts, its mechanicaltransmission and the mechanical application of the field is extremelybroad. Modern gear technology has been achieved: the gear moduleO.004 ~ 100 mm; gear diameter from 1 mm to 150 m; transmissionpower up to the 100 thousand kilowatts; speed up to hundreds ofthousands of r / min; maximum peripheral speed of 300 m / sec. Thecomposition generally gear teeth, alveolar, French side addendumcircle, tooth root circle, base circle, pitch circle. Gear can beClassified by gear shape, tooth shapes, tooth surface. Such as geartooth profile, including tooth profile curve, pressure angle, toothheight, and deflection. On the above mentioned involute gear, it isrelatively easy to manufacture, so the modern use of gears, theinvolute gear absolute majority, while the cycloid gear and the circulargear is seldom used.

Gear manufacturing gear materials and heat treatment process onthe weight of the carrying capacity and size have significant influence.

The quality of the material of the gear will directly affect the stabilityduring use, more use of carbon steel in the early gears, As thedevelopment of science gear has slowly changed from metal gearplastic gear. Because the plastic gear more lubricity and wearresistance. It can reduce noise, lower costs, reduce the friction.Plastic gears are commonly used materials: POM, PTFE, Pa, etc.

As the gears and other mechanical parts widely used, the network

also appears more and more mechanical parts trading platform, themore famous may be Ecplaza, SeekPart, Commercial Place and soon .

Importance of clocks
http://www.seekpart.com/http://www.seekpart.com/


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Later metal clock gearing also became important. Clocks and

watches were made that showed accurate time. Later mechanical

clocks also started in Europe and were invented by monks. The first

mechanical clock was made of escapement device and had a set of

tooth gearing.

Influence of Bicycles in Gear Evolution

The history of cycling has had an immense influence on the

technologies and industries. The story of bicycle starts in 1817 when

Baron Won Drais of Baden invented a 'running machine' to help himmove more quickly around his forests. Then after there were many

changes that took place in improving the make up and usage of

bicycles.

Development of chain drive was an added advantage. Leonardo Da

Vinci had developed an idea of chain and cog in the fifteenth century.

It took years to implement on this idea and make it a practical aspect

of bicycle design. Later gear was invented and was an added

advantage to the bicycle design.

Gears allowed the cyclist to pedal at a comfortable and efficient rate

especially while travelling uphill or downhill. Paul de Vivie of French

was a passionate advocate of cycling. He rode his first high wheelerat the age of 28, sold his silk business and started a bike shop.

Industrial Revolution and Gears


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Wooden gears were used all over the world by the eighteenth

century. They were used in gristmills, textile mills and steel mills. The

use of electric motors and steam engines created a considerable

need of the gears. Few years later gears were widely used in all parts

of the world in a wide number of industries. Gears were alsopreeminent for scientists who required more accurate clocks and

using gears they made clocks with more accuracy, one of them was

pendulum clock.

The industrial revolution in Britain in the eighteen-century saw an

explosion in the use of metal gearing. A science of gear design and

manufacture rapidly developed through the nineteenth century.

Today, the most significant new gear developments are in the area of

materials. Modern metallurgy has greatly increased the useful life of

industry and automotive gears. Along with this consumer electronics

have driven plastic gearing to new levels of lubricant free reliability

and quiet operation. Gears are also used in many machines that we

use in our homes. The washing machines and electric drills are someof the machines that have gears.

Comparison with drive mechanisms

The definite velocity ratio which results from having teeth gives gears

an advantage over other drives (such as traction drives and v-belt) inprecision machines such as watches that depend upon an exactvelocity ratio. In cases where driver and follower are in closeproximity gears also have an advantage over other drives in thereduced number of parts required; the downside is that gears aremore expensive to manufacture and their lubrication requirementsmay impose a higher operating cost.


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Terminology in Gear Technology

Active Profile - Active profile refers to the part of the gear tooth thatin actual comes in touch with the profile of its mating toothsomewhere along the line of action.

Addendum - Addendum is radial or the perpendicular distance that ismeasured between the tip of the teeth and pitch circle.

Arc of Action - Arc of action is the arc of a pitch circle via which the

tooth moves from the time it first makes any contact with a matingteeth till the time the contact with mating tooth stops.

Axial Pitch - Axial Pitch is referred to as the distance measured in anaxial plane surface between two corresponding and adjacent toothprofiles.

Backlash - Backlash is the point of measure of the quantum of width


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of a tooth space by which it exceeds the thickness of the engagingtooth on pitch circles.

Base Circular Thickness - Base circular thickness is the length ofarc on a base circle between two involute curves resulting in the

profiles of a tooth.

Base Radius - Base radius refers to the radius of the circle, theinvolute is generated from here only.

Basic Rack - Basic Rack is there for every pair of a conjugateinvolute profile. This basic rack is essentially the profile of theconjugate gear that has infinite pitch radius.

Circular Pitch - Circular Pitch means the distance along the pitchcircle or a pitch line, in between corresponding profiles of teeth thatare placed adjacently.

Circular Thickness - Circular thickness is the length of an arc on apitch circle that is in between the two sides of the gear tooth.

Contact Ratio - Contact ratio is the ratio formed by the arc of actionto a circular pitch.

Conjugate Action - Conjugate Action is a smooth type of drivingaction which produces a constant and uniform angular velocity in adriven member.

(D)

Dedendum - Dedendum refers to the perpendicular or radial distancecovered between a pitch circle and the tooth space's bottom portion.

Diametral Pitch - Diametral pitch refers to a ratio that is formed bythe number of teeth to the number of inches in a pitch diameter. Therelation is fixed between a diametral pitch (P) and a circular pitch (p),denoted by p=p/P.


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Double-Helical Gear - Double Helical Gear is the gear of a cylindricalform that has two sections of teeth, one is at the right hand and theother is on the left hand, They engage in tandem with the teeth of anidentically designed mating gear.

(E)Effective or (Active) Face Width - This is in actual the width of aface which comes in touch with a mating gear.

Equal-Addendum Teeth - This is the teeth of two Gears that areengaged and having similar addendum.

External Gear - External Gear is the gear that has a teeth formed ona outer surface of a cylinder or even a cone.

(F)Face Advance - Face advance refers to the distance on a pitch circlewhich a gear tooth travels from the time when at one end the pitchpoint contact is made till at the other end another pitch point contactis made.

Face Contact Ratio - Face contact ratio refers to the contact ratiomade in an axial plane. It also refers to the ratio of the face width toan axial pitch. In case of bevel and hypoid gears, it refers to the ratioof face advance to a circular pitch.

Face Width - Face width is the length of a teeth in an axial plane.

Fillet Curve - Fillet curve refers to a tooth profile's concave portion,

where it is able to join the bottom of a tooth space.

(G)Gear Blank - Gear Blank is the work piece which is applied formanufacturing a gear, before there is machining the gear teeth.

Gear Center - Gear center is the center of pitch circle.


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Gear Ratio - Gear ratio is the ratio of the number of tooth in matinggears.

Groove Depth - Groove depth is the depth of clearance groove

between the helices of two helical gears.

Groove Width - Groove width refers to clearance groove betweenthe helices of two helical gears.

(H)Helical Gear - A type of cylindrical gear that has helical teeth.

Helical Rack - A type of rack that has teeth obliquely placed to thedirection of motion.

Helix Angle - It refers to the angle formed between a tangent to ahelix and the element of a cylinder.

Herringbone Gears - Herringbone is a type double helical gear, withno clearance groove.

Hub Diameter - Hub diameter refers to the diameter of a central partof the gear body that encloses the bore and extends the web, spokes,or the body.

(I)Inside Cylinder - Inside cylinder is the surface which coincides withthe top of a of teeth of an gear of the nature internal cylindrical.

Interference - It refers to any type of contact made between themating teeth at any other point than that made along the line ofaction.
http://www.gearshub.com/helical-gears.htmlhttp://www.gearshub.com/helical-gears.html


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Internal Diameter - It is basically the diameter of a circle thatconsists of the top of teeth ofinternal gears.

Involute Curve - This is very important term and is referred to as thecurve described by the end of a line which is unwound from a circle's

circumference. Base circle is the circle from where the said line isunwound.

(L)Lead - Lead is the axial advance made by the helix for one completeturn. This is typified in the threads of a cylindrical worm or in teeth ofhelical gears.

Lead Angle - The angle formed between a tangent to a pitch helixand the rotational plane.

Length of Action - It is the distance measured on an involute line ofaction via which the point of contact travels during the action of toothprofiles.

Line of Action - It is the path of contact in case of involute gears. Astraight line that passes via the pitch point and tangent to the base

circles of two mating gears.

(M)Modified Addendum Teeth - It refers to teeth of two engaging gears,one or sometimes both of which have addendum that arenonstandard.

Modified Contact Ratio - It is the contact ratio of improvised tooth

surfaces.

(N)Normal Helix - It refers a helix on a pitch cylinder which is normal toa pitch helix.
http://www.gearshub.com/internal-gears.htmlhttp://www.gearshub.com/internal-gears.html


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Normal Plane - The plane that is perpendicular to a straight line orthat forms a tangent to the curved line.

Normal Pressure Angle - It is the pressure angle in a plane which is

normal to the pitch line element.

Normal Tooth Profile - Normal tooth profile is the outline takingplace by the intersection of a tooth surface and a plane which isperpendicular to a pitch line element.

(O)Outside Diameter of Gear - It is essentially the diameter of a circle,

comprising the top of the teeth of an external type of gear.

Operating Pitch Diameters - It is the diameter of the circle on agear. It is proportional to the gear ratio and the centerdistance(actual) at which there will be operation of the gear pair.

Operating Pressure Angle - Operating pressure angle isascertained by the center distance at which the gears operate.

Outside Helix Angle - This is the helix angle formed on the outsidecylinder.

(P)Pinion - Pinion is a gear where number of teeth is small. In two gearsthat mesh together one with that has the smaller number of teeth isknown as pinion.

Pitch, Circular - It is the distance measured on the circumference ofa pitch circle between the corresponding points of teeth that areplaced adjacently.

Pitch Circle - It is the circle via which the pitch point have its centeron axis of a gear.


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Pitch Cylinder - Pitch cylinder is an imaginary cylinder drawn in a ina gear which rolls without any slip on a pitch cylinder or a pitch planeof the other gear.

Pitch Helix - Pitch helix is formed as a result of the intersection of the

thread or surface of a helical tooth with a pitch cylinder.

(R)Rack, General - A gear that has its teeth spaced along a straight line.It is perfect for straight-line motion.

Root Circle - The circle comprising the bottom of tooth spaces.

Root Cylinder - An imaginary cylinder which is tangent to the bottomof tooth spaces in a cylindrical type of gear.

Root Radius - Refers to the radius of a root circle.

(S)Single-Helical Gears - Helical gears that has teeth of on one handon each of the gear.

Spur Rack - A rack that has a straight teeth and at 90 degree to thedirection of motion.

Surface of Action - An imaginary surface where a contact takesplace between two of the engaging tooth surfaces.

(T)Tangent Plane - It refers to the plane tangent formed at the tooth

surface at the line of contact.

Tolerance, Tooth Alignment - It is the maximum permissible amountof variation in tooth alignment. Values are normal to the surface oftooth.

Tooth Bearing - The part of the tooth surface that actually comes in


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touch.

Transverse Circular Thickness - It refers to the thickness of thecircular tooth in the plane of rotation.

(U)Undercut - A sort of condition that is generated in gear teeth when apart of the fillet curve is lying inside of a line. It is drawn as a tangentto a true involute form at its lowest point. Undercut may be introducedfor facilitating the process of finishing.

(W)Whole Depth (total depth) - It is the radial distance between an

outside circle and a root circle.

Working Depth - It is the extent of greatest depth to which a tooth ofa gear can move into the tooth space of the mating gear.

(Z)Zone of Action - It the area (rectangular) in a plane of action. It isrestricted by the length of action or the face width.

The automobile transmission allows selection between gears to givevarious mechanical advantages.


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An external gearis one with the teeth formed on the outer surface ofa cylinder or cone. Conversely, an internal gearis one with the teethformed on the inner surface of a cylinder or cone. For bevel gears, aninternal gear is one with the pitch angle exceeding 90 degrees.

Internal gears do not cause direction reversal

Spur gearsorstraight-cut gearsare the simplest type of gear.They consist of a cylinder or disk with the teeth projecting radially and

although they are not straight-sided in form, the edge of each tooth isstraight and aligned parallel to the axis of rotation. These gears canbe meshed together correctly only if they are fitted to parallel shafts.
http://en.wikipedia.org/wiki/File:Spur_Gear_12mm,_18t.svghttp://en.wikipedia.org/wiki/File:Inside_gear.pnghttp://en.wikipedia.org/wiki/File:Spur_Gear_12mm,_18t.svghttp://en.wikipedia.org/wiki/File:Inside_gear.png


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Helicalor "dry fixed" gears offer a refinement over spur gears.The leading edges of the teeth are not parallel to the axis of rotation,but are set at an angle. Since the gear is curved, this angling causesthe tooth shape to be a segment of a helix. Helical gears can bemeshed in a parallelorcrossedorientations. The former refers towhen the shafts are parallel to each other; this is the most common

orientation. In the latter, the shafts are non-parallel, and in thisconfiguration are sometimes known as "skew gears".

The angled teeth engage more gradually than do spur gear teethcausing them to run more smoothly and quietly. With parallel helicalgears, each pair of teeth first make contact at a single point at oneside of the gear wheel; a moving curve of contact then growsgradually across the tooth face to a maximum then recedes until theteeth break contact at a single point on the opposite side. In spur

gears teeth suddenly meet at a line contact across their entire widthcausing stress and noise. Spur gears make a characteristic whine athigh speeds. Whereas spur gears are used for low speed applicationsand those situations where noise control is not a problem, the use ofhelical gears is indicated when the application involves high speeds,large power transmission, or where noise abatement is important.
http://en.wikipedia.org/wiki/File:Helical_Gears.jpg


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The speed is considered to be high when the pitch line velocityexceeds 25 m/s.

A disadvantage of helical gears is a resultant thrust along the axis ofthe gear, which needs to be accommodated by appropriate thrustbearing and a greater degree of sliding friction between the meshing

teeth, often addressed with additives in the lubricant.

For a 'crossed' or 'skew' configuration the gears must have the samepressure angle and normal pitch, however the helix angle and

handedness can be different. The relationship between the two shaftsis actually defined by the helix angle(s) of the two shafts and thehandedness, as defined

E= 1+ 2 for gears of the same handedness

E= 1 2 for gears of opposite handedness

Where is the helix angle for the gear. The crossed configuration isless mechanically sound because there is only a point contactbetween the gears, whereas in the parallel configuration there is a

line contact.

Quite commonly helical gears are used with the helix angle of onehaving the negative of the helix angle of the other; such a pair mightalso be referred to as having a right-handed helix and a left-handedhelix of equal angles. The two equal but opposite angles add to zero:the angle between shafts is zero that is, the shafts are parallel.Where the sum or the difference (as described in the equationsabove) is not zero the shafts are crossed. For shafts crossedat rightangles the helix angles are of the same hand because they must addto 90 degrees.


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Double helical gears, orherringbone gear, overcome the problemof axial thrust presented by "single" helical gears by having two setsof teeth that are set in a V shape. Each gear in a double helical gearcan be thought of as two standard mirror image helical gears stacked.This cancels out the thrust since each half of the gear thrusts in theopposite direction. Double helical gears are more difficult to

manufacture due to their more complicated shape.For each possible direction of rotation, there are two possiblearrangements of two oppositely-oriented helical gears or gear faces.In one possible orientation, the helical gear faces are oriented so thatthe axial force generated by each is in the axial direction away fromthe center of the gear; this arrangement is unstable. In the secondpossible orientation, which is stable, the helical gear faces are
http://en.wikipedia.org/wiki/File:Herringbone_gears_(Bentley,_Sketches_of_Engine_and_Machine_Details).jpg


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oriented so that each axial force is toward the mid-line of the gear. Inboth arrangements, when the gears are aligned correctly, the total(ornet) axial force on each gear is zero. If the gears becomemisaligned in the axial direction, the unstable arrangement generatesa net force for disassembly of the gear train, while the stable

arrangement generates a net corrective force. If the direction ofrotation is reversed, the direction of the axial thrusts is reversed, astable configuration becomes unstable, and vice versa.

Stable double helical gears can be directly interchanged with spurgears without any need for different bearings.

A bevel gear is shaped like a right circular cone with most of itstip cut off. When two bevel gears mesh their imaginary vertices mustoccupy the same point. Their shaft axes also intersect at this point,forming an arbitrary non-straight angle between the shafts. The anglebetween the shafts can be anything except zero or 180 degrees.Bevel gears with equal numbers of teeth and shaft axes at 90degrees are called miter gears.

The teeth of a bevel gear may be straight-cut as with spur gears, or

they may be cut in a variety of other shapes. Spiral bevel gearteethare curved along the tooth's length and set at an angle, analogouslyto the way helical gear teeth are set at an angle compared to spurgear teeth. Zerol bevel gearshave teeth which are curved along theirlength, but not angled. Spiral bevel gears have the same advantagesand disadvantages relative to their straight-cut cousins as helical
http://en.wikipedia.org/wiki/File:Gear-kegelzahnrad.svghttp://en.wikipedia.org/wiki/File:Gear-kegelzahnrad.svghttp://en.wikipedia.org/wiki/File:Gear-kegelzahnrad.svghttp://en.wikipedia.org/wiki/File:Gear-kegelzahnrad.svg


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gears do to spur gears. Straight bevel gears are generally used onlyat speeds below 5 m/s (1000 ft/min), or, for small gears, 1000 r.p.m

Hypoid gears resemble spiral bevel gears except the shaft axes donot intersect. The pitch surfaces appear conical but, to compensatefor the offset shaft, are in fact hyperboloids of revolution. Hypoidgears are almost always designed to operate with shafts at 90degrees. Depending on which side the shaft is offset to, relative to theangling of the teeth, contact between hypoid gear teeth may be evensmoother and more gradual than with spiral bevel gear teeth. Also,the pinion can be designed with fewer teeth than a spiral bevel pinion,

with the result that gear ratios of 60:1 and higher are feasible using asingle set of hypoid gears. This style of gear is most commonly founddriving mechanical differentials; which are normally straight cut bevelgears; in motor vehicle axles.
http://en.wikipedia.org/wiki/File:Sprocket35b.jpg


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Crown gearsorcontrate gearsare a particular form of bevel gear

whose teeth project at right angles to the plane of the wheel; in theirorientation the teeth resemble the points on a crown. A crown gearcan only mesh accurately with another bevel gear, although crowngears are sometimes seen meshing with spur gears. A crown gear isalso sometimes meshed with an escapement such as found inmechanical clocks.
http://en.wikipedia.org/wiki/File:Crown_gear.png


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Worm gearsresemble screws. A worm gear is usually meshed witha spur gear or a helical gear, which is called the gear, wheel, orwormwheel.

Worm-and-gear sets are a simple and compact way to achieve ahigh torque, low speed gear ratio. For example, helical gears arenormally limited to gear ratios of less than 10:1 while worm-and-gearsets vary from 10:1 to 500:1. A disadvantage is the potential forconsiderable sliding action, leading to low efficiency.

Worm gears can be considered a species of helical gear, but itshelix angle is usually somewhat large (close to 90 degrees) and its
http://en.wikipedia.org/wiki/File:Worm_Gear.gifhttp://en.wikipedia.org/wiki/File:Worm_Gear_and_Pinion.jpghttp://en.wikipedia.org/wiki/File:Worm_Gear.gifhttp://en.wikipedia.org/wiki/File:Worm_Gear_and_Pinion.jpg


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body is usually fairly long in the axial direction; and it is theseattributes which give it screw like qualities. The distinction between aworm and a helical gear is made when at least one tooth persists fora full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a'helical gear'. A worm may have as few as one tooth. If that tooth

persists for several turns around the helix, the worm will appear,superficially, to have more than one tooth, but what one in fact sees isthe same tooth reappearing at intervals along the length of the worm.The usual screw nomenclature applies: a one-toothed worm iscalled single threadorsingle start; a worm with more than one toothis called multiple threadormultiple start. The helix angle of a worm isnot usually specified. Instead, the lead angle, which is equal to 90degrees minus the helix angle, is given.

In a worm-and-gear set, the worm can always drive the gear.However, if the gear attempts to drive the worm, it may or may notsucceed. Particularly if the lead angle is small, the gear's teeth maysimply lock against the worm's teeth, because the force componentcircumferential to the worm is not sufficient to overcome friction.Worm-and-gear sets that do lock are called self locking, which canbe used to advantage, as for instance when it is desired to set theposition of a mechanism by turning the worm and then have the

mechanism hold that position. An example is the machine head foundon some types of stringed instruments.

If the gear in a worm-and-gear set is an ordinary helical gear onlya single point of contact will be achieved. If medium to high powertransmission is desired, the tooth shape of the gear is modified toachieve more intimate contact by making both gears partially envelopeach other. This is done by making both concave and joining them ata saddle point, this is called a cone-drive.

Worm gears can be right or left-handed following the longestablished practice for screw threads.


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Non-circular gears are designed for special purposes. While aregular gear is optimized to transmit torque to another engagedmember with minimum noise and wear and maximum efficiency, anon-circular gear's main objective might be ratio variations, axledisplacement oscillations and more. Common applications includetextile machines, potentiometer and continuously variabletransmission.
http://en.wikipedia.org/wiki/File:Rack_and_pinion_animation.gifhttp://en.wikipedia.org/wiki/File:Non-circular_gear.PNGhttp://en.wikipedia.org/wiki/File:Rack_and_pinion_animation.gifhttp://en.wikipedia.org/wiki/File:Non-circular_gear.PNG


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A rack is a toothed bar or rod that can be thought of as a sectorgear with an infinitely large radius of curvature. Torque can beconverted to linear force by meshing a rack with a pinion: the pinionturns; the rack moves in a straight line. Such a mechanism is used inautomobiles to convert the rotation of the steering wheel into the left-

to-right motion of the tie rod(s). Racks also feature in the theory ofgear geometry, where, for instance, the tooth shape of aninterchangeable set of gears may be specified for the rack (infiniteradius), and the tooth shapes for gears of particular actual radii thenderived from that. The rack and pinion gear type is employed ina rack railway.

In epicyclic gearing one or more of the gear axes moves.Examples are sun and planet gearing (see below) and mechanicaldifferentials.
http://en.wikipedia.org/wiki/File:Epicyclic_gear_ratios.png


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Sun and planet gearing was a method of converting reciprocalmotion into rotatary motion in steam engines. It played an importantrole in the Industrial revolution. The Sun is yellow, the planet red, thereciprocating crank is blue, the flywheel is green and the driveshaft is

grey.
http://en.wikipedia.org/wiki/File:Sun_and_planet_gears.gif


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A harmonic driveis a specialized gearing mechanism often usedin industrial motion control, robotics and aerospace for its advantagesover traditional gearing systems, including lack of backlash,compactness and high gear ratios.
http://en.wikipedia.org/wiki/File:Harmonic_drive_animation.gif


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A cage gear, also called a lantern gearorlantern pinionhascylindrical rods for teeth, parallel to the axle and arranged in a circlearound it, much as the bars on a round bird cage or lantern. Theassembly is held together by disks at either end into which the toothrods and axle are set.

SPROCKETS

A sprocket is a profiled wheel with teeth that mesh witha chain, track or other perforated or indented material. The name'sprocket' applies generally to any wheel upon which are radial

projections that engage a chain passing over it. It is distinguished

from a gear in that sprockets are never meshed together directly, anddiffers from a pulley in that sprockets have teeth and pulleys aresmooth.

Sprockets are used in bicycles, motorcycles, cars, tracked vehicles,and other machinery either to transmit rotary motion between twoshafts where gears are unsuitable or to impart linear motion to atrack, tape etc. Perhaps the commonest form of sprocket is found in
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the bicycle, in which the pedal shaft carries a large sprocket-wheelwhich drives a chain which in turn drives a small sprocket on the axleof the rear wheel. Early automobiles were also largely driven bysprocket and chain mechanism, a practice largely copied frombicycles.

Sprockets are of various designs, a maximum of efficiency beingclaimed for each by its originator. Sprockets typically do not havea flange. Some sprockets used with timings belts have flanges tokeep the timing belt centered. Sprockets and chains are also used forpower transmission from one shaft to another where slippage is notadmissible, sprocket chains being used instead of belts or ropes andsprocket-wheels instead of pulleys. They can be run at high speedand some forms of chain are so constructed as to be noiseless even

at high speed.


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Backlash

Backlash is the error in motion that occurs when gears changedirection. It exists because there is always some gap between thetrailing face of the driving tooth and the leading face of the toothbehind it on the driven gear, and that gap must be closed before forcecan be transferred in the new direction. The term "backlash" can also

be used to refer to the size of the gap, not just the phenomenon itcauses; thus, one could speak of a pair of gears as having, forexample, "0.1 mm of backlash." A pair of gears could be designed tohave zero backlash, but this would presuppose perfection inmanufacturing, uniform thermal expansion characteristics throughoutthe system, and no lubricant. Therefore, gear pairs are designed tohave some backlash. It is usually provided by reducing the tooththickness of each gear by half the desired gap distance. In the case

of a large gear and a small pinion, however, the backlash is usuallytaken entirely off the gear and the pinion is given full sized teeth.Backlash can also be provided by moving the gears farther apart. Thebacklash of a gear train equals the sum of the backlash of each pairof gears, so in long trains backlash can become a problem. Forsituations in which precision is important, such as instrumentation andcontrol, backlash can be minimised through one of several


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techniques. For instance, the gear can be split along a planeperpendicular to the axis, one half fixed to the shaft in the usualmanner, the other half placed alongside it, free to rotate about theshaft, but with springs between the two halves providing relativetorque between them, so that one achieves, in effect, a single gear

with expanding teeth. Another method involves tapering the teeth inthe axial direction and providing for the gear to be slid in the axialdirection to take up slack.


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Shifting of gears

In some machines (e.g., automobiles) it is necessary to alter thegear ratio to suit the task. There are several methods ofaccomplishing this. For example:

1. Manual Transmission2. Automatic Transmission3. Derailleur gear which are actually sprockets in combination with

a roller chain4. Hub gears (also called epicyclic gearing or sun-and-planet

gears)

MANUAL TRANSMISSION

A manual transmission, also known as a manualgearbox orstandard transmission (informally,a manual; standard, straight shift; stick (shift), (US); orstraight drive)is a type of transmission used in motor vehicle applications. Itgenerally uses a driver-operated clutch, typically operated by a footpedal(car) or hand lever(motorcycle), for regulating torque transferfrom the internal combustion engine to the transmission, and a gearstick, either operated by foot (as on a motorcycle) or by hand (as in a

car).

A conventional manual transmission is frequently the base equipmentin a car; other options include automated transmissions such asan automatic transmission (often amanumatic), a semi-automatictransmission, or a continuously variable transmission (CVT).
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AUTOMATIC TRANSMISSION

An automatic transmission (also called automatic gearbox) isone type ofmotor vehicle transmission that can automaticallychange gear ratios as the vehicle moves, freeing the driver fromhaving to shift gears manually. Most automatic transmissions have adefined set of gear ranges, often with a parking pawl feature thatlocks the output shaft of the transmission.
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Similar but larger devices are also used for heavy-duty commercialand industrial vehicles and equipment. Some machines with limitedspeed ranges or fixed engine speeds, such as some forklifts and lawnmowers, only use a torque converterto provide a variable gearing ofthe engine to the wheels.

Besides automatics, there are also other types of automatedtransmissions such as continuous variable transmissions (CVTs)and semi-automatic transmissions, that free the driver from having toshift gears manually, by using the transmission's computer to changegear, if for example the driver were redlining the engine. Despitesuperficial similarity to other transmissions, automatic transmissionsdiffer significantly in internal operation and driver's feel from semi-automatics and CVTs. An automatic uses a torque converter instead

ofclutch to manage the connection between the transmission gearingand the engine. In contrast, a CVT uses a belt or other torquetransmission schema to allow an "infinite" number of gear ratiosinstead of a fixed number of gear ratios. A semi-automatic retains aclutch like a manual transmission, but controls the clutch throughelectro hydraulic means.
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DERAILLEUR GEAR

Derailleur gears are a variable-ratio transmission systemcommonly used on bicycles, consisting of a chain,multiple sprockets of different sizes, and a mechanism to move thechain from one sprocket to another. Although referred to asgearsinthe bike world, these bicycle gearsare technically sprocketssincethey drive or are driven by a chain, and are not driven by one another.

Modern front and rear derailleurs typically consist of a moveablechain-guide that is operated remotely by a Bowden cable attached toa shiftermounted on the down tube, handlebarstem, orhandlebar.When a rider operates the lever while pedalling, the change in cabletension moves the chain-guide from side to side, "derailing" the chainonto different sprockets.
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HUB GEAR

Hub gears orinternal-gear hubs are gear ratio changingsystems commonly used on bicycles. Hub gear systems generallyhave a long and largely maintenance-free life though some are notsuitable for high-stress use in competitions or hilly, off-road

conditions.Many commuter or urban cycles such as European city bikes are nowcommonly fitted with 7-speed gear-hubs and 8-speed systems arebecoming increasingly available. Older or less costly utilitybicycles often use 3-speed gear-hubs, such as in bicycle sharingsystems. Many folding bicycles use 3-speed gear-hubs. Moderndevelopments with up to 14 gear ratios are available.
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Gear-hubs use internal planetary orepicyclic gearing.Unlike derailleur gears, where the gears and mechanism are exposedto the elements, hub gears and lubricants are sealed within the hub-shell of the bicycle's rear wheel.
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Profile of a spur gear

Undercut

A profile is one side of a tooth in a cross section between the outsidecircle and the root circle. Usually a profile is the curve of intersectionof a tooth surface and a plane or surface normal to the pitch surface,such as the transverse, normal, or axial plane.

The fillet curve (root fillet) is the concave portion of the tooth profilewhere it joins the bottom of the tooth space.

As mentioned near the beginning of the article, the attainment of a

non fluctuating velocity ratio is dependent on the profile of theteeth. Friction and wear between two gears is also dependent on thetooth profile. There are a great many tooth profiles that will give aconstant velocity ratio, and in many cases, given an arbitrary toothshape, it is possible to develop a tooth profile for the mating gear thatwill give a constant velocity ratio. However, two constant velocitytooth profiles have been by far the most commonly used in moderntimes. They are the cycloid and the involute. The cycloid was morecommon until the late 1800s; since then the involute has largelysuperseded it, particularly in drive train applications. The cycloid is insome ways the more interesting and flexible shape; however theinvolute has two advantages: it is easier to manufacture, and itpermits the center to center spacing of the gears to vary over somerange without ruining the constancy of the velocity ratio. Cycloidal
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gears only work properly if the center spacing is exactly right.Cycloidal gears are still used in mechanical clocks.

An undercut is a condition in generated gear teeth when any part ofthe fillet curve lies inside of a line drawn tangent to the working profileat its point of juncture with the fillet. Undercut may be deliberately

introduced to facilitate finishing operations. With undercut the filletcurve intersects the working profile. Without undercut the fillet curveand the working profile have a common tangent.

Involute Gear

The involute gear profile is the most commonly used systemforgearing today. In an involute gear, the profiles of the teethareinvolutesof a circle.(The involute of a circle is the spiraling curvetraced by the end of an imaginary taut string unwinding itself from thatstationary circle called the base circle.)

In involute gear design contact between a pair of gear teeth occurs ata single instantaneous point (see figure at right). Rotation of the gearscauses the location of this contact point to move across therespective tooth surfaces. The path traced by this contact point isknown as the Line of Action (also called Pressure Line or Line ofContact). A property of the involute tooth form is that if the gears aremeshed properly, the line of action is straight and passes throughthe Pitch Point of the gears. When this is true, the gears obey theFundamental Law of Gearing:

The angular velocity ratio between two gears of a gearset mustremain constant throughout the mesh.

This property results in smooth transmission of power without speedor torque variations as pairs of teeth go into or come out of mesh.

The Pressure Angle is the acute angle between the line of action anda normal to the line connecting the gear centers. The pressure angleof the gear is a function of the involute tooth shape and pairs of gearsmust have the same pressure angle in order for the teeth to meshproperly.
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While any pressure angle can be manufactured, the most commonstock gears have a 20 pressure angle, with 14 and 25 pressureangle gears being much less common.

[2]Increasing the pressure

angle increases the width of the base of the gear tooth, leading togreater strength and load carrying capacity. Decreasing the pressure

angle provides lower backlash, smoother operation and lesssensitivity to manufacturing errors.

[3]

Wooden gears of a historic windmill

Numerous nonferrous alloys, cast irons, powder-metallurgy andplastics are used in the manufacture of gears. However steels aremost commonly used because of their high strength to weight ratio
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and low cost. Plastic is commonly used where cost or weight is aconcern. A properly designed plastic gear can replace steel in manycases because it has many desirable properties, including dirttolerance, low speed meshing, and the ability to "skip" quitewell.

[19]Manufacturers have employed plastic gears to make

consumer items affordable in items like copy machines, opticalstorage devices, VCRs, cheap dynamos, consumer audio equipment,servo motors, and printers.

The module system

Countries which have adopted the metric system generally use themodule system. As a result, the term module is usually understood tomean the pitch diameter in millimeters divided by the number of teeth.When the module is based upon inch measurements, it is known asthe English moduleto avoid confusion with the metric module.Module is a direct dimension, whereas diametral pitch is an inversedimension (like "threads per inch"). Thus, if the pitch diameter of agear is 40 mm and the number of teeth 20, the module is 2, whichmeans that there are 2 mm of pitch diameter for each tooth.

Gear Train

A gear train is formed by mounting gears on a frame so that theteeth of the gears engage. Gear teeth are designed to ensure thepitch circles of engaging gears roll on each other without slipping, thisprovides a smooth transmission of rotation from one gear to thenext.

[1]

The transmission of rotation between contacting toothed wheels canbe traced back to the Antikythera mechanism of Greece and

the South Pointing Chariot of China. Illustrations by the renaissancescientist Georgius Agricola show gear trains with cylindrical teeth.The implementation of the involute tooth yielded a standard geardesign that provides a constant speed ratio.
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Some important features of gears and gear trains are:

The ratio of the pitch circles of mating gears defines the speedratio and the mechanical advantage of the gear set.

A planetary gear train provides high gear reduction in a compactpackage.

It is possible to design gear teeth for gears that are non-circular,yet still transmit torque smoothly.

The speed ratios ofchain and belt drives are computed in thesame way as gear ratios. See bicycle gearing.

A machine consists of a power source and a power transmissionsystem, which provides controlled application of the power. Merriam-Webster defines transmissionas: an assembly of parts including thespeed-changing gears and the propeller shaft by which the power istransmitted from an engine to a live axle. Often transmission referssimply to the gearbox that uses gears and gear trains to

provide speed and torque conversions from a rotating power sourceto another device.

In British English the term transmission refers to the whole drive train,including gearbox, clutch, prop shaft (for rear-wheel drive), differentialand final drive shafts. In American English, however, the distinction ismade that a gearbox is any device which converts speed and torque,whereas a transmission is a type of gearbox that can be "shifted" todynamically change the speed: torque ratio, such as in a vehicle.

The most common use is in motor vehicles, where the transmissionadapts the output of the internal combustion engine to the drivewheels. Such engines need to operate at a relatively high rotationalspeed, which is inappropriate for starting, stopping, and slower travel.The transmission reduces the higher engine speed to the slowerwheel speed, increasing torque in the process. Transmissions are
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also used on pedal bicycles, fixed machines, and anywhere elserotational speed and torque needs to be adapted.

Often, a transmission will have multiple gear ratios (or simply"gears"), with the ability to switch between them as speed varies. Thisswitching may be done manually (by the operator), or automatically.

Directional (forward and reverse) control may also be provided.Single-ratio transmissions also exist, which simply change the speedand torque (and sometimes direction) of motor output.

In motor vehicle applications, the transmission will generally beconnected to the crankshaft of the engine. The output of thetransmission is transmitted via driveshaft to one or more differentials,which in turn drive the wheels. While a differential may also providegear reduction, its primary purpose is to change the direction of

rotation.
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EXPLANATION

Early transmissions included the right-angle drives and other gearing

in windmills, horse-powered devices, and steam engines, in supportofpumping, milling, and hoisting.

Most modern gearboxes are used to increase torque while reducingthe speed of a prime mover output shaft (e.g. a motor crankshaft).This means that the output shaft of a gearbox will rotate at a slowerrate than the input shaft, and this reduction in speed will producea mechanical advantage, causing an increase in torque. A gearboxcan be set up to do the opposite and provide an increase in shaftspeed with a reduction of torque. Some of the simplest gearboxesmerely change the physical direction in which power is transmitted.

Many typical automobile transmissions include the ability to selectone of several different gear ratios. In this case, most of the gearratios (often simply called "gears") are used to slow down the outputspeed of the engine and increase torque. However, the highest gearsmay be "overdrive" types that increase the output speed.
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It provides structural support for the shaft bearings. This in turnhelps in gear loading.

It transfers the reaction of mechanical rotation (torque) to theother supporting structure of the gearbox or drive elements.

It prevents the lubricant from spreading and also prevents theunwanted particals from coming inside.

It provides the safety provision and reduce the noise intensity.

It also reduces the amount of heat that generates due to theinternal friction.

It increases the external and visual qualities of the gearbox.


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Gearboxes have found use in a wide variety of different

often stationary

applications, such as wind turbines.

Transmissions are also usedin agricultural, industrial, construction, mining and automotive equipment. In addition to ordinary transmission equipped with gears, suchequipment makes extensive use of the hydrostatic drive andelectrical adjustable-speed drives.

Today there is vast application of gears in every industry. It is themost common device for transmitting power in mechanicalengineering. Gears are an important component of small butcomplicated machines like clock to large kiln and mill drive system.The gears form an essential part in running of various machines andautomobile.

There are variety of gears available that are used in differentindustries according to the specific requirements. These gears can beclassified under automotive gears, mining gears, marine gears, windturbines, bicycle gears, mill heads, instrumentation gears, conveyor

system and more.

The basic function of the gear is to alter the rotational speed, poweror torque and direction between input and output shaft. Torque is themeasure of force required to produce torsion and rotation about anaxis. When a large gear drive is coupled with a smaller gear drive, thetorque is reduced and the speed of the rotation is increased. Differentarrangement of the gears can also be used for enhancement ofpositioning system.
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Automotive Gears

Automotive Industry require automotive gears for high torque capacityand to convert mechanical energy smoothly and noiselessly. The typeof automotive gears used are Manual transmission, Semi automatictransmission and Automatic transmission.

Marine GearsMarine uses gears in various vessels like fast ferry boats, luxuryyachts, frigates and work boats etc. These marine gears are usuallymore powerful and they meet critical applications. Types of marinegears used are Planetary Gears, Worm Reduction Gears and HelicalGears.


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Agricultural GearsAgricultural Gears are widely used in the agro industry.Agricultural Automotive Gears are used in processes like

tilling, seeding, ploughing, irrigation, pest and insectcontrol etc. The agriculture vehicle, tractor also make useof these agricultural gears in its mechanism. Usually SpurGears, Helical Gears, Worm Gears and Sprockets are used.

Conveyor SystemsGears are also used in Conveyor Systems foroptimizational of mechanical energy. With the help ofgears, goods are transported from one place to anotherthrough belts.

Mill HeadsFew of the gears are used for mill heads in cement plants,sugar mills, sag mills, tube mills, coal mills, sponge ironplants, gold mine sand many more. These gears are Girth

Gears, Spur Gears, Face Gears, Spiral Bevel Gears andHelical Gears.

Mining GearsDifferent types of gears are used in mining industry tokeep the machines run efficiently by power transmission inboth above and underground operations. Types of

gearboxes used are Bevel Gear , Helical Gear, RightAngle Gear, Parallel Shaft Gear, Planetary Gear andWorm Gear.
http://www.gear-gears.com/girth-gears.htmlhttp://www.gear-gears.com/girth-gears.htmlhttp://www.gear-gears.com/bevel-gears.htmlhttp://www.gear-gears.com/girth-gears.htmlhttp://www.gear-gears.com/girth-gears.htmlhttp://www.gear-gears.com/bevel-gears.htmlhttp://www.gear-gears.com/girth-gears.htmlhttp://www.gear-gears.com/girth-gears.html


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Power StationPower Station make use of high quality and high precisiongears for the use in power generation equipment and

machines. They are used for for high speed application.The gears that are usually used are Parallel ShaftGears and Planetary Gears.

Wind TurbineThe wind turbine makes use of gears to make the slowblades rotate faster. Types of gearbox used are Planetary

Gearbox, Helical Gearbox and Worm Gearbox.
http://www.gear-gears.com/axle-positioning-gears.html#parallel-shafthttp://www.gear-gears.com/axle-positioning-gears.html#parallel-shafthttp://www.gear-gears.com/axle-positioning-gears.html#parallel-shafthttp://www.gear-gears.com/axle-positioning-gears.html#parallel-shaft


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I. www.geartechnology.com/II. www.gear-tech.com/

III. www.zakgear.com/IV. gltrs.grc.nasa.gov

V. www.qtcgears.com

VI. www.sdp-si.com/d785/html

VII. www.gearinfo.com/Gear-Technology.htmlVIII. www.geartechnology.in/

IX. metalgear.wikia.com/wiki/Solid_Eye_(technology)

X. en.wikipedia.org/wiki/Gears
http://www.geartechnology.com/http://www.geartechnology.com/http://www.geartechnology.com/http://www.gear-tech.com/http://www.gear-tech.com/http://www.gear-tech.com/http://www.gear-tech.com/http://www.gear-tech.com/http://www.qtcgears.com/http://www.qtcgears.com/http://www.qtcgears.com/http://www.sdp-si.com/d785/htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.gearinfo.com/Gear-Technology.htmlhttp://www.geartechnology.in/http://www.geartechnology.in/http://www.geartechnology.in/http://www.geartechnology.in/http://www.gearinfo.com/Gear-Technology.htmlhttp://www.sdp-si.com/d785/htmlhttp://www.qtcgears.com/http://www.gear-tech.com/http://www.geartechnology.com/

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