Saturday, 26 December 2015

SPUR GEAR BASICS, ADVANTAGE, DISADVANTAGE AND APPLICATIONS

SPUR GEAR BASICS, ADVANTAGE, DISADVANTAGE AND APPLICATIONS

Before understanding the concept of spur gear, we must understand the each term used in gear drive mechanism and we have already discussed it i.e. various terminology used in gear in our previous post i.e. gear terminology. So before going ahead, i will request to my readers to find out the gear terminology in our previous post.

So let us start our discussion about basics of spur gears

Spur gear will have a cylindrical shape, as shown in following figure, with straight teeth made parallel to the axis of gear. Spur gear teeth engagement will not be gradual but also one tooth of driving gear will mesh with tooth of driven gear each time and will produce noise and also deliver the impact load over the meshing teeth. Therefore spur gears are not preferred in driving mechanism of vehicle such as car. Helical gears are used in driving mechanism of vehicle in order to reduce the impact loading, noise and stress on gear teeth.

There are two types of spur gears used in industries i.e. external spur gear and internal spur gear. In case of external spur gear, teeth will be cut over the outside surface of cylinder with parallel to the axis and such type of spur gear is widely used in various applications in industries that we will discuss later.

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In case of internal spur gear, teeth will be cut over the inside surface of cylinder with parallel to the axis and such type of spur gears could be easily seen in planetary gear mechanism, we will also discuss the applications of internal spur gears in this post.


In order to secure the uniform motion and transmission of power between drive and driven member, surface of tooth of spur gear teeth will have an involute profile.
Following image, which is taken from arrowgear, indicates involute profile of gear meshing with each other where left gear is shown as driver member and right gear is displayed here as driven member.

Spur gears in meshing with each other, Source: Arrogear

Let us try to understand the involute profile of gear, suppose we have wrapped one string across the outer surface of one circle and now we are unwinding the string from circle. During unwinding of string from circle, consider the path created by one fixed point of string and that path created by fixed point of string will be considered as involute circle. A spur gear will have similar involute circle or profile that we have understood above.

Image courtesy: Google

Advantage of spur gears

There are following advantages of using spur gear as mentioned here
  1. Spur gears are simple and also easy to design and install in drive mechanism
  2. Spur gears are suitable to use if space restriction is there
  3. Power transmission efficiency in case of spur gear driving system will be quite good
  4. As we have discussed above, spur gear teeth made straight and parallel to the axis of the gear and therefore there will not be any issue of axial thrust and we can use ball bearings to install the spur gears in our drive mechanism.
  5. If we compare the spur gear with similar size of helical gear, we will observe that spur gears are quite more efficient as compared to helical gear
  6. Spur gears will have constant velocity ratio and they are quite reliable
  7. Spur gears are considered as member of positive transmission as there will not be any slippage, while belt drive will have issue of slippage.

Disadvantage of spur gears

There are following disadvantages of using spur gear as mentioned here
  1. Spur gear teeth engagement will not be gradual but also one tooth of driving gear will mesh with tooth of driven gear each time
  2. Spur gears will produce noise and also deliver the impact load over the meshing teeth
  3. Spur gears could not be used between to non-parallel shafts
  4. Spur gears driving mechanism are costly as compared with belt driving mechanism
  5. There will be additional stress over spur gear teeth
  6. Spur gears will not be preferred to use at high rpm as it will create more abnormal sound and hence if noise restriction is the main design criteria then we will not prefer to use spur gear
  7. Spur gears could not preferred for power transmission for larger distance

 

Applications of spur gears

There are wide applications of spur gears as mentioned below
  1. Spur gears are used Gear pump and gear motor
  2. Steel sectors, rolling mill, power unit and cement units
  3. Spur gears are also used in marine engines
  4. Gate controlling mechanism in port sectors
  5. Rack and pinion drive mechanism
  6. Spur gears are also used in film winding equipment, film cutting equipment, automatic packaging equipment, Printing equipment, film sealing equipment and hydraulic press.
There are various more applications of spur gears and i will request to my readers to provide their point of view in respect of applications by giving comment in comment box.

Do you have suggestions? Please provide by giving comment in comment box

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