What is gear – spur gear, bevel gear and helical gear

What is gear - spur gear, bevel gear and helical gear

Hello friends, all of us have been hearing and seeing about gear since childhood. Although gears are round in shape and have teeth, there are many types of gears, which are difficult to identify because gears are divided on the basis of their working mechanism.

So today I will tell you about different types of gears like “spur gear, bevel gear, helical gear, internal gear and rack pinion gear as well as sliding mesh gear, constant mesh gear and synchromesh gear” used in tractors. So that after understanding you can easily identify the gear.


What is gear ?

Gear is a rotary device and it is the very main part of the gear box of the tractor, which increases the power generated from the engine or the speed as per the requirement.

For example, if the farmer wants to run rotavator, then he should run on first or second gear of low speed. Because the power is more on this gear and the speed is less. Similarly cultivator, ambi plough and trolley have different speed.


Types of gear

What is spur gear ?

Spur gears are very common gears and are also quite simple. The teeth of the spur gear are straight and are parallel to the axis of the gear. Spur gears are the easiest to design and manufacture due to their simplicity.

What is spur gear

Spur gears are very efficient and generate more power. Spur gears run well at low to medium speeds, but also vibrate and make a lot of noise at high speeds.


What is bevel gear ?

These gears transmit motion from one shaft to another when their axes intersect, they are called ‘bevel gears’ and this arrangement is called ‘bevel gearing’.

The teeth of these gears such as spur gears may also be inclined towards the face of the bevel, in which case they are called ‘helical bevel gears’.

What is bevel gear

As shown in the arrangement of bevel gearing, the angle between the axis of rotation of the two shafts 90 degrees, which can range from 0 degrees to 180 degrees. But bevel gears which have 90 degree angle between their axis and speed ratio as unity are called ‘mitre gears’.

It can be seen from the figure that the gears are in the shape of a frustum of a cone. These gears are also used in differentials of automobiles.


what is helical gear ?

When the gears rotate in the shaft, the axes of rotation are neither parallel nor intersecting, so this type of gear is called ‘helical gear’. This arrangement is called ‘worm and worm wheel’.

what is helical gear

As shown in the figure. It should be noted that the teeth cut on the worm are continuous like the threads on a screw.

They are used for speed reduction. Usually the velocity ratio obtained in this case ranges from 10:1 to 100:1 but it can go up to 500:1 in a single reduction.


what is rack pinion gear ?

When a gear joins another gear in a straight line as shown in the figure, the combination thus formed is called a ‘rack and pinion arrangement’.

rack pinion gear

With the help of this arrangement, rotary motion can be converted into linear motion and vice versa. The rack is assumed to have an infinite radius. It is commonly used in lathes where the rack accelerates the saddle.


what is internal gear ?

what is internal gear

When the pinion moves rapidly inside the larger wheel, the larger wheel is called an internal gear or annular wheel. The internal gearing arrangement is shown in Fig. In internal gearing, the speed of the two gears is always the same as shown by the arrows in the figure.


According to gear speed

These can be divided into the following three types according to the gear speed.

  • Low Speed Gears – Gears whose speed is more than 3m/s are called ‘Low Speed Gears’.
  • Medium Speed Gear – The gear whose speed is more than 3m/s but less than 15m/s is called ‘Medium Speed Gear’.
  • High Speed Gear – The gears in which the speed is more than 15 m/s are called ‘high speed gears’.


According to the size of the gear teeth

straight teeth gear

In straight teeth gears, the teeth on the gear are parallel to the respective shaft axis as already discussed in the case of spur gears. Spur gears with straight teeth are not subject to any axial thrust and as such they are commonly used as sliding gears for speed change mechanisms in gear boxes for various applications such as lathe machines.


helical teeth gear

 The teeth in a helical teeth gear are inclined at a certain angle to the wheel axis. This angle is known as the ‘helix angle’ and generally ranges from 20° to 30° which can go up to 45° for very high speed helical thit gears.


herring bone teeth gear

In the case of herring bone teeth gears to neutralize axial thrust, the gear teeth are made helical to one-half of the gear width and on the other to half of the gear’s width. Therefore, they find their use where there is a possibility of axial thrust as in the case of turbines.


curved teeth gear

 In this case the gear teeth have a curved shape for reasons of achieving quiet and thrustless operation while transmitting heavy torque. The curved teeth gear has more contact than the straight helical teeth gear.

This type of gear is used where heavy torque has to be transmitted and due to noise reduction as can be seen in the assembly of crown wheel and pinion in an automobile.


Types of gear box in tractor

sliding mesh gear box

This is an outdated technology and as the name suggests, the gears are mounted on top of each other only then the gears shift. It is also called crush gear box because when the driver gear and the driven gear come in friction with each other, the gear changes take place. Hence it is also known as Crush Gear Box.

  • In the sliding mesh gear box, the gear box wears out while changing gears and the life of the gear box is reduced.
  • Sliding mesh gear box makes a lot of noise.
  • In sliding mesh gear box, the driver has to stop the tractor to change gears.


Constant Mesh Gear Box

This is a modern technology, in which all the gears are connected with each other. It has a special dog clutch mechanism and collar shift mechanism for changing gears. By this mechanism, these gears are shifted, due to which there is no friction in the gears and there is no noise while changing gears.

The main feature of the constant mesh gear is that the tractor can change gears while moving. This reduces fuel consumption and prolongs the life of the gearbox.


synchronous gear box

This is an advanced technology, in which a special synchronizer has been installed. Due to which when the driver changes gears, the gears shift like butter. In this, any gear can be easily shifted, when the tractor is running or stopped. That’s why it is called synchromesh gear box.



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