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Spur Gears, Helical Gears, Bevel Gears and Worm Gears

Gear Cases

A gear is a mechanical component with tooth members that transmit either power or motion between two shafts. The teeth of the gears mesh with each other without slipping. When two gears run together, the one with the larger number of teeth is called the gear and the one with smaller number of teeth is called as pinion irrespective of which is driving the other. When the larger gear drives the pinion, it increases the speed and decreases the torque. When the pinion drives the gear, it decreases the speed but increases the torque.

Why use Gears?

There are quite a few characteristics gears have that make them invaluable as machine components:

  • Gears are used to change the speed of machine and the torque
  • Gears can reverse the direction of rotation
  • Gears (e.g. bevel) can transfer rotation to a different axis
  • Gears can translate rotational into linear motion and linear motion into rotational motion

Classification of Gears

There are many types of gears available today. Following are the most popular gears. All these gears can be cast.

Spur Gears: Spur gears are the most common type of gears. Spur gears have the teeth cast straight and parallel to the axis of the shaft. The contact between the teeth is straight meshing. Spur gears are easy to design and cast, but are slightly noisy. They impose radial load on the bearings that are mounted between the gear and the shaft. They are primarily used where noise is not a primary constraint. Because of their simple design and working, spur gears are also called as slow gears. Automobiles are an example where spur gears are used.

Helical Gears: As the name implies, helical gears have teeth that are at an angle to the shaft. The shape of these teeth is in the form of a helix. Since they mesh with each other at an angle, their contact ratio is higher. Helical gears can therefore take higher loads than similarly sized spur gears. They can also run at a higher speed, and are smooth as compared to spur gears. In a helical gear, the angle of the helix on both the gear and the pinion must be of the same magnitude while being opposite in direction. On more positive aspect of helical gears is that their load is distributed over several teeth. This results in reduced vibration and gear wear. However, one limit of the helical gears is the thrust force that the helix form causes. Helical gears find applications in industrial applications, railway equipment, etc.

Worm Gears: Worm gears are gears whose teeth are cut at an angle on the rim, parallel to the axis of rotation. Worm gears are used to transmit power at 90° and where high speed and torque reductions are required. The shafts of worm gears lie in parallel planes and may be skewed at any angle between zero and a right angle. They are less noisy, free from vibration and give a smooth torque.

There are three types of worm gears:

Non-throated – this involves a straight worm without a groove machined around the circumference. A single moving point is what provides tooth contact, meaning this particular type of worm gear is subjective to high unit load wear and tear.

Single-throated – concave helical teeth are wrapped around the worm for line contact, meaning higher unit loads with less excessive wear.

Double-throated – usually called a cone of hourglass, this type has concave teeth on both the worm screw and the gear itself. Increasing the contact area in such a way allows for increased unit loads with lower wear and tear.

Worm gears find application in lifts, conveyor belts, etc.

Bevel Gears: The single most important use of bevel gears is to change the direction of the power by as much as 90 degrees. Theoretically, they can be used to change the direction of the torque in any angle, but practically they are used to change it mostly at right angles. Bevel gears are used to transmit motion between shafts that have intersecting but co-planar centre lines. Bevel Gears have conical blanks. They have teeth cut on the body, perpendicular to the axis of rotation and placed conically. The teeth of straight bevel gears are tapered in both thickness and the tooth height. A prime example of bevel gears is the hand held drill.

Bevel gears are also called as miter gears.

Gear Manufacturers in India

Gears are vital components of mechanical gadgets – almost all machines require them. Companies in America and Europe prefer getting gears manufactured in India due to cost effectiveness. Sound infrastructure, ease of transportation and a well established mechanical industry hubs in different parts of the country make India a viable option for outsourcing gears manufacturing.