# GEAR DEFINITION A gear is a rotating machine part having cut ...

IN THE NAME OF ALLAH, THE MOST BENEFICENT, THE MOST MERCIFUL 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 They can be applied between two shafts which are Parallel Collinear Inclined at any arbitrary angle Why we use gears

In 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. Gear advantages It It

It It transmits exact velocity ratio may be use to transmit large power has high efficiency has reliable(easy) services Gear disadvantages It costs expensive to manufacture

Any type of error may cause vibrations and noise It requires suitable lubricant and reliable method of applying it, for proper operation of gear drives Classification of toothed wheel on the basis of teeth (a) Parallel (b) Intersecting (c) Non-intersecting and non-parallel.

1)PARALLEL: These gears have teeth parallel to the axis of the wheel. 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. 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

Nomenclature Pitch circle It is the circle made by joining those points where two meshed teeth release each other 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 circle 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 tooth

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. 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 /T 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. 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.

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 tooth

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. 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. Angular frequency Measured in radians per second. 1RPM = / 30 rad/ second

It is denoted by Gear, wheel The larger of two interacting gears Pinion The smaller of two

interacting gears Line of action, pressure line Line along which the force between two meshing gear teeth is directed. Axis Axis of revolution of the gear; center line of the shaft

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 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 materials The metallic gears with cut teeth are commercially obtainable in cast iron, steel and bronze The nonmetallic materials like wood, raw hide, compressed paper and synthetic resins like nylon are used for gears, especially for reducing noise.

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 steel The phosphor bronze is widely used for worm gears in order to reduce wear of the worms

TYPES OF GEARS SPUR GEAR BEVEL GEAR External and internal gear WORM GEAR DIFFERENTIAL GEAR RACK GEAR PINION IDLER GEAR RATCHET

PLANETARY GEAR DISCRIBTION

SPUR GEAR: A gear wheel having radial teeth parallel to the axle. 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. 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 ) Application of Bevel gear

it is used in grain mill. it is used in power plant. it is used in Railway track inspection machine Bevel gear used in floodgate. 1.External vs. internal gears

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. 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 generator external gear in bicycle 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! ). Application of worm

gear worm drive used in controlling a gate Packaging Industries (Machines) Material Handling Equipments

Food Processing Machines Widely in Conveyor Systems 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 ) DEFINITION OF PINION GEAR PINION: A small cogwheel, the teeth of which fit into those of a larger gearwheel or those of a rack.

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 ) DEFINITION OF RATCHET RATCHET: A

toothed wheel or bar that catches and holds a PAWL, which thus prevents backward movement.

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. Definition of Pawl PAWL A mechanical

device allowing rotation in only one direction. Definition of Planetary gear PLANETARY GEAR:A device allowing several gears to "orbit"

about others ( very handy for robot turntables ) Planetary Gears are the latest type and used in Robotics Gear Manufacturing Hobbing

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 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. 1.backlash 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 reestablished. 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.

Problem#1 A helical cast steel gearwith 30 helix angle has to transmit 35kW at 1500r.p.m.If the gear has 24 teeth and the necessary module is 6mm.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. 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

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