PR - 69 :- Study of Gears, Belts, stepper motor and Drive

 

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 gear. 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.

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.

Different Types and Applications of Gears

Internal Gear

These gears have teeth cut on the inside part of cones and cylinders and are 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.

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 opposite directions. It consists of the same hand helical gears at an angle of 45 degrees on the non-intersecting and non-parallel shafts. It is used for small power transmission.

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 a worm wheel. These two together on a non-intersecting shaft form worm gear. material is used for worm and a 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 an hourglass type which increases the contact ratio but reduces the production. 

Mitre Gear

These are basic bevel gears with a speed ratio of 1. The 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 angles other than 90° are called angular mitre gears.

Bevel Gear

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

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 zero l bevel gears.

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 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.

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.

Helical Gear

These gears 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.

Type of Gear	Characteristics
Spur	Most common type of gear Circular gear body Straight teeth cut or inserted parallel to the gear’s shaft Used for parallel axes configuration Mated with spur gears, internal gears, or gear racks High precision and efficiency (A) Easy to manufacture (A) Does not produce thrust force (A) Capable of handling high speed and high loads (A) Gear teeth experience high stress due to tooth design (D) Noise production during high speeds (D)
Helical	Circular gear body Teeth twisted at an angle around gear body Used for parallel axes configuration Available in right-hand and left-hand designs Available in single and double helical designs Gradual tooth engagement and less impact loading (A) Quieter, smoother operation (A) Capable of handling greater loads (A) Lower efficiency (D) Higher design complexity, greater cost of manufacturing (D) Single helical design products thrust force (D), double helical does not (A)
Bevel	Cone-shaped gear body Used for intersecting axes configuration Available in straight, spiral, and Zerol® bevel tooth designs Straight: simplest bevel gear design and easiest to manufacture (A); high impact, noise level, and stress (D) Spiral: gradual tooth engagement and less impact loading, noise, and vibration (A); higher design complexity and greater cost of manufacturing (D) Zerol®: Quieter and smoother than straight bevel, able to rotate in both directions unlike spiral bevel (A)
Worm	Pair comprised of a circular gear and a screw-shaped gear Used for non-parallel, non-intersecting axes configuration Large gear ratios and gear reduction (A) Quiet, smooth operation (A) Self-locking mechanism (A) Low transmission efficiency (D) Large amounts of friction (D)
Rack and Pinion	Pair comprised of a gear rack and cylindrical gear Used for parallel axes configuration Rack mated with spur or helical gear Converts rotational motion to linear motion or vice versa Simple design, easy to manufacture (A) Capable of handling greater loads (A) Transmission cannot continue infinitely in one direction (D) Large amount of backlash between mated teeth (D) Gear teeth experience high friction and stress due to tooth design (D)

Table 2 – Industries and Applications of Gears by Type

Type of Gear	Common Industries and Applications
Spur	Clocks Pumps Watering systems Household appliances Clothes washing and drying machines Power plants Material handling systems Aerospace and aircrafts Railways and trains
Helical	Same as spur gears but with greater loads and higher speeds (see above) Automobiles (transmission systems)
Bevel	Pumps Power plants Material handling systems Aerospace and aircrafts Railways and trains Automobiles
Worm	Instruments Lifts and elevators Material handling systems Automobiles (steering systems)
Rack         and       Pinion	Weighing scales Material handling and transfer systems Railways and trains Automobiles (steering systems)