Types of Gears

What is A Gear?

To the question, what is a gear we can say that a gear is a kind of machine element which has teeth cut around a cylindrical or cone-shaped surface with equal spacing? They are used to transmit rotations and forces from the driving shaft to the driven shaft when a pair of these elements have meshed. There are different types of gears. They have a different basis of classification. The history of gears is old and is mentioned by Archimedes to be in use in ancient Greece in B.C.

Classification of Gears

All types of gears are given in the classification chart below.


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Gears can be classified as parallel shaft gears, intersecting shaft gears and non-intersecting non-parallel shaft gears depending on the position of their axes. Some important gears are given in detail below.


  1. Internal gear

  2. Screw gear

  3. Worm gear

  4. Mitre gear

  5. Bevel gear

  6. Spiral bevel gear

  7. Spur gear

  8. Gear rack

  9. Helical gear


  1. Internal Gear

These gears have teeth cut on the inside part of cones and cylinders and is used to pair with external gears. These are used in shaft couplings which are of gear types and planetary gear drives. Due to trimming problems and interference such as trochoid and involute, there lies one disadvantage with this gear, which is an unequal number of internal and external gears.

  1. Screw Gear

Screw gears or sometimes called crossed helical gears are helical gears used in motion transmission between non-intersecting shafts. In parallel shafts, the helical gears used have the same helix angle but in the opposite directions. It consists of the same hand helical gears in an angle of 45 degrees on the non-intersecting and non- parallel shafts. It is used for small power transmission.

  1. Worm Gear

It consists of two elements, a screw-shaped cut on the shaft called a worm and the other one is a mating gear called worm wheel. These two together on a non-intersecting shaft form worm gear. material is used for worm and soft one for worm wheels as it is necessary to reduce friction due to sliding contact of surfaces. They can have a cylindrical shape and also hourglass type which increases the contact ratio but reduces the production.

  1. Mitre Gear 

These are basic bevel gears with a speed ratio of 1.Direction of power transmission is changed by them without changing speed. They can be both straight and spiral. With spiral mitre gear thrust bearing is also used as it produces thrust force in the axial direction. Mitre gears with shaft angle other than 90° are called angular mitre gears.

  1. Bevel gear

These have a cone shape at its pitch surface and teeth are cut along the cone. They transmit force between two shafts which intersect at a point. Various kinds of bevel gears are helical bevel gears, spiral bevel gears, straight bevel gears, mitre gears, angular bevel gears, zerol gears, hypoid gears and crown bevel gears.

  1. Spiral Bevel gear

Bevel gears with curved tooth lines are called spiral bevel gears. They are superior to straight bevel gears in efficiency, strength, vibration and noise due to higher contact ratio but are difficult to produce. Since teeth are curved, it produces thrust force in the axial direction. These gears with zero twisting angles are called zerol bevel gears.

  1. Spur gear

Spur gears are included in the parallel shaft gear group. They are cylindrical gears having tooth lines straight and parallel to the shaft. Cylindrical gears are the gears with cylindrical pitch surfaces. In meshing pairs, the larger one is called gear and the smaller one is pinion. They achieve high accuracy and are relatively easy to produce.

  1. Gear Rack

A gear rack consists of same sized and shaped teeth cut at equal distances along a flat surface or a straight rod. It is a cylindrical gear having a radius of pitch infinity. It converts rotational motion into linear motion by meshing with a cylindrical gear pinion. Straight tooth racks and helical tooth racks are its broader classification.

  1. Helical Gear 

These gear can transmit high loads. They are very quiet and are cylindrical gear with winding tooth lines. Its two subdivisions are left-hand twist and right-hand twist.


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Uses of different type of gears are given below.

Application of Gears

Type of gear

Application

Worm gear

Instruments

Lifts and elevators

Material handling systems

Automobiles (steering systems)

Spur gear

Clocks

Pumps

Watering systems

Household appliances

Clothes washing and drying machines

Power plants

Material handling systems

Aerospace and aircrafts

Railways and trains

Bevel gear

Pumps

Power plants

Material handling systems

Aerospace and aircrafts

Railways and trains

Automobiles

Helical gear

Similar to spur gears but with greater loads and higher speeds.

Automobiles (transmission systems)

Rack and pinion

Weighing scales

Material handling and transfer systems

Railways and trains

Automobiles (steering systems)


FAQ (Frequently Asked Questions)

1. What is the principle of Gear?

Gears work on the principle of mechanical advantage. Mechanical advantage is the ratio of output force to input force in a system. In context to gears, the ratio of the final gear's speed to the initial gear's speed in a gear train known as gear ratio gives the mechanical advantage. Mechanical advantage is the reciprocal of velocity ratio.


Gear ratio = final gear's speed/initial gear's speed


Also, Gear ratio = number of teeth on the driving gear/number of teeth on the driven gear


For example,gear ratio = 10/40=0.25

Therefore, mechanical advantage=4.


2. How do gears increase speed?


Gears enhance the speed by their mechanism.

Two gears, one having more teeth than the other or it's a bigger-sized wheel when connected together, make the second one turn round much faster to keep up. So this arrangement makes the second wheel turns faster than the first one but with less force. A gearing change produces noticeable change on the vehicle. Swapping in taller rear gears helps to achieve some top-end speed making the vehicle move faster.