Aug 102013
 

In my previous article, I explained worm gears with their advantages, disadvantages and applications. In this article, I will be giving you a brief introduction to spur gear.

Introduction:

Spur gear is the most common type of gear used. It is used for transmitting power between two parallel shafts.

In this type of gear, the teeth cut on the cylindrical face are parallel to the axis of the gear. You can understand this well by taking a look at the following image.

Spur Gear

Spur Gear

Though several types of profiles can be used for cutting teeth on a spur gear, we commonly use involute teeth profile. The gear found in the image above uses an involute tooth profile.

A spur gear drive is a combination of two spur gears properly meshed with each other. It is used for transmitting rotational motion between parallel shafts. It offers a definite velocity ratio. From my previous article about gears,

Velocity~ratio~=~{Angular~Velocity~of~Driving~Gear}/{Angular~Velocity~of~Driven~Gear}

Spur Gear Drive

Spur Gear Drive

If the driving gear is smaller the than the driven gear, then rotating velocity is reduced in the driven gear. If the driving gear is larger than the driven gear, rotational velocity is increased in the driven gear. If both the driving and driven gears have the same number of teeth, there is no change in the rotational velocity. In the image above, both the gears have the same number of teeth :) Hence, their velocity ratio is one and they rotate at same speeds.

In a spur gear drive, the smaller gear is called pinion and the larger one is called gear. When designing a spur gear drive, the pinion is made harder than the gear. This is because, the pinion has to run more no. of cycles when compared to the gear.

Materials used for making spur gears:

The following are some of the common materials used for making spur gears:

  1. Cast iron
  2. Steel (Plain Carbon, C45 and alloy steel)
  3. Bronze
  4. Nylon, Fibre Reinforced Plastics (FRP)

Modes of Failures in a Spur gear:

The following are some of the common modes of failure in a spur gear:

  1. Tooth Breakage (mostly because of fatigue loading)
  2. Surface Failures (Because of abrasion, pitting, seizure and scoring)

For a list of advantages, disadvantages and applications of spur gear, read this article.

Don’t forget to share your ideas by commenting on this article :)

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Written by

I am a mechanical engineer with a passion for technical stuff. I am the founder and former editor-in-chief of Mechteacher.com.

  • mayank

    sir,why spur gear produce more noise as compare to helical one,s

    • http://mechteacher.com/ Surjeet Sankararaj

      When two teeth on a spur gear system engage, sudden contact occurs. This produces huge noise.

      When two teeth on a rotating helical gear drive engage, the contact begins at one end and gradually grows, until both the teeth are in complete contact. This gradual engagement reduces noise and allows helical gears to operate smoothly.

      • srikant stnd

        nyltron gear is the material used for decreasing sound

  • phani

    there is no description about helical gears