Gears

ByAknath Mishra

What is Gear?

Power TransmissionPower transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.

Types of transmission elements:-

Transmission by Belts. Transmissions by ropes. Transmission by gears.

Involute & Its Properties• Tooth profile 1 drives

tooth profile 2 by acting at the instantaneous contact point K.

• N1N2 is the common normal of the two profiles.

• N1 is the foot of the perpendicular from O1 to N1N2

• N2 is the foot of the perpendicular from O2 to N1N2.

Properties-

• The tooth profile can be generated accurately using a simple straight-sided cutter.

• The error in the center distance does not disturb the conjugate action.

• The condition for inter mating series of gears is automatically satisfied.

• The same cutter can be used to cut addendum modified gears.

• The direction of normal force at the point of contact remains the same as the gears rotate.

• The ratio is given by base circle or pulley diameter ratio.

the transmission ratio between two involute gears is not sensitive to the center distance modification.

Gear Terminology.

Types of Gears1. Spur Gear2. Helical Gear3. Herringbone Gear4. Worm Gear5. Bevel Gear: a) Straight b) Spiral6. Hypoid Gear7. Pinion & Internal Gear8. Rack & Pinion9. Planetary Gears Arrangement

1. Spur Gear-Spur gears are 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 is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts.

2. Helical Gear-Helical 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 causes the tooth shape to be a segment of a helix. Helical gears can be meshed in a parallel or crossed orientations.

3. Herringbone Gear-It is a special type of gear which is a side to side combination of two helical gears of opposite hands. From the top the helical grooves of this gear looks like letter V. Unlike helical gears they do not produce an additional axial load.

4. Worm Gear-Worm Gears are right angle drives providing large speed ratios on comparatively short center distances from 1/4” to 11”. When properly mounted and lubricated they function as the quietist and smoothest running type of gearing.

5. Bevel Gear: Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped. Bevel gears are most often mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The pitch surface of bevel gears is a cone.a) Straight-Straight bevel gears have conical pitch surface and

teeth are straight and tapering towards apex. b) Spiral-Spiral bevel gears have curved teeth at an angle

allowing tooth contact to be gradual and smooth.

6. Hypoid Gear-Hypoid Gears Are a Subtype of Bevel Gears. However Bevel gears have a limitation i.e. they can only be used in systems where the input and output shafts are in the same plane. To overcome this problem, a special type of gear called the hypoid gear is used.

7. Internal Gear-An Internal Gear may be described as the opposite of an external gear in that the teeth point towards rather than away from the center, and addendum and dedendum take reverse positions.

8. Rack & Pinion-A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion.

9. Planetary Gears- Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear.

Nomenclature of Gear Tooth

What is Gear Box.

A gear box is a mechanical method of transferring energy from one device to another.The Gear box used to change the speed, direction and torque of mechanical energy.

Different types of Gear Boxes.

Offset Gearbox Sequential Gearbox Planetary Gearbox

Bevel Gearbox

Cycloidal Gearbox Helical Gearbox

Function of Gearbox.

• A gearbox is precisely bored to control gear and shaft alignment.

• It is used as a housing/container for gear oil.• It is a metal casing for protecting gears and

lubricant from water, dust and other contaminants.

Applications of Gearbox.Type of Industry Commonly used Gear Boxes

1 Cement 1.Parallel shaft gear box.2.Bevel Epicyclical gear box.3.Bevel Helical gear box.

2 Ferrous metal 1.Planetary gear box.2.Pinion gear box.3.Reduction gear box.

3 Non-ferrous metal 1.Planetary gear box.2.Reduction gear box.3.Worm reduction gear box.

4 Paper 1.Sha mounted gear box.2.Spur gear box.3.Helical gear box.

5 Sugar 1.Planetary gear box.2.Helical gear box.

6 Automobile 1.Continuously variable gear box.2.Automatic gear box.3.Manual gear box.

ComparisonsType

Normal Ratio Range

Pitch Line Velocity (m/s)

Efficiency Range

Spur 1:1 to 6:1 25 98-99%

Helical 1:1 to 10:1 50 98-99%

Double Helical 1:1 to 15:1 150 98-99%

Bevel 1:1 to 4:1 20 98-99%

Worm 5:1 to 75:1 30 20-98%

Crossed Helical 1:1 to 6:1 30 70-98%

References• en.wikipedia.org/wiki/Gear• Analytical Mechanics of Gears by Earle Buckingham• Standard Handbook of Machine Design, by Shigley, Mischke,

and Brown

Thank you.

Details & queries - aknath_mishra@rediffmail.com