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
Depending on the requirement and place of use there are several types of Gears.
Types of Gears
This is the case when we have to transmit power between two parallel shafts.
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, as shown in image. Power transfer capacity of double helical gear is more than simple helical gear.
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).
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.
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, as shown in figure.
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 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.