Gear | Definition, Advantages, Disadvantages, Types, Applications

What is a Gear?

A Gear is a machine component, which is used to transmit mechanical power from one shaft to the other by successively engaging its teeth.

Gears are one of the most used method of mechanical power transmission in the machines. Power transmission by the gears have almost 100% efficiency.

Advantages of Gear drive

• It is positive drive hence velocity remains constant
• Provisions for changing velocity ratios can be made with the help of gear box
• Its efficiency is very high
• It can be used even for low speeds
• It can transmit high torque values
• It is compact in construction

Disadvantages of Gear drive

• They are not suitable when shafts are distant
• At high speeds noise and vibration happens
• It requires lubrication
• It has no flexibility

Reasons of Gear failure

There are following reasons of Gear failure.

• Abrasive wear
• Corrosive wear
• Initial pitting
• Destructive pitting
• Scoring

Depending on the requirement and place of use there are several types of Gears.

Types of Gears

1. Parallel shafts

This is the case when we have to transmit power between two parallel shafts.

• Spur gears

Spur Gears are used for the power transfer in the shafts which are parallel to each other. They have straight teeth as shown in above image.

• Spur rack and pinion

The long bar shown in the image is known as rack and the gear is known as pinion. We know that in a gear meshing, generally small Gear is known as Pinion but why the single Gear used here is known as Pinion.

The reason is we consider the Rack as a very large Gear with infinite diameter so that it looks almost straight and hence the other gear than rack is known as pinion.

• Helical gears or helical spur gears

   

Helical gears are almost same as spur gears but they have inclined teeth for uniform and silent teeth meshing. Power transmitting capacity of helical spur gears is more than that of normal spur gears.

• Double helical gears

The the helical gears some unbalanced force remains in the system due to inclined teeth so, to balance that unbalanced force we use double helical gears which has inclined teeth in both the directions.

One should note that there is a gap between two sets of inclined teeth. Power transfer capacity of double helical gear is more than simple helical gear.

• Herringbone gears

There is only one difference between double helical and Herringbone gears. Herringbone gears do not have any gap between inclined teeth (as shown in figure).

2. Intersecting shafts

This is the case when the shafts (between which the power is to be transmitted) are mutually intersecting.

• Spiral bevel gears

Spiral bevel gears are used for power transmission in the shafts which are perpendicular to each other. Due to spiral teeth they provide uniform and silent teeth engagement. It has more power transmitting capacity than zero bevel gears.

• Zero bevel gears

Zero bevel gears or simply Bevel gears have straight teeth. The teeth engagement not as uniform and smooth as in spiral bevel gears.

3. Skew shafts

This is the case when the shafts (between which the power is to be transmitted) are non-parallel and non-intersecting.

• Cross helical gears

Cross helical gears are used for non parallel and non intersecting shafts.

• Worm gears

Some times this type of gear arrangement is also known as worm and wheel. Here the long rod having spiral is the worm. We should note one thing that worm can rotate the Gear but reverse is not true.

• Hypoid gears

Hypoid gears as same as spiral bevel gears but the only difference is that the center line of both the shafts do not intersect in Hypoid gears. Alternatively we can say that there is some eccentricity in the center line of the shafts in the Hypoid gear arrangement.

Image sources:

Spur gear: Attribution: By Inductiveload – Self-madeiThe source code of this SVG is valid.This vector image was created with Inkscape., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2628658

Rack and pinion: Attribution: By OSHA Directorate of Technical Support and Emergency Management – Point of Contact Between a Rack and Pinion. The original uploader was Brian0918 at English Wikipedia., Public Domain, https://commons.wikimedia.org/w/index.php?curid=186765

Helical gears: Attribution: By user:Sador – Own work/Création personnelle, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=113510

Herringbone gear: Attribution: By Andy Dingley (scanner) – Scan from Bentley (1918) Sketches of Engine and Machine Details, London, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7653373

Spiral bevel gears: Attribution: By Myriam Thyes – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4078185

Worm gears: Attribution: By User:Catsquisher – User:Catsquisher, Public Domain, https://commons.wikimedia.org/w/index.php?curid=12858338

Hypoid gears: Attribution: By Hapesoft – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7916301