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Wednesday, 24 June 2015

GEAR CLASSIFICATION

Hello once again!!!

After studying various posts based on the maintenance of conveyor belt "CONVEYOR BELT HOT SPLICING", I was thinking to start discussion and few posts basically based on the gear and gear box maintenance. 

If you want to know the complete mechanism and terminology as well as maintenance procedure of gear and gear boxes, this post will be the important key for you.

We will discuss various types of gear, characteristics of each gear and its maintenance aspects here.

Let us think what types of gears are normally used in industries.

Spur Gear

In case of spur gear, as shown in figure, teeth will be straight as well as parallel to the axis of shaft. Such types of gears are basically used to transmit the energy and motion between two parallel shafts.

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Spur gear: Characteristics

  1. Teeth will be straight in case of spur gear, hence designing and manufacturing of spur gear will be easy.
  2. Spur gear will be more efficient as compared to helical gear of similar size.
  3. There will not be any axial thrust force in case of spur gear because teeth are straight and parallel to the axis of gear.
  4. Easy to assemble as such type of gears do not produce axial thrust force, hence ball bearings will be the best selection for spur gears.
  5. In case of spur gear, bearing has to bear only radial load as axial thrust will not be there in spur gearing system.
  6. Spur gear system will provide approximate 75 % efficiency.

Helical gear

In case of helical gear, as shown in figure, teeth will not be parallel to the axis of the gear but also teeth will be inclined to the axis of the gear wheel i.e. teeth will be cut at an angle with the axis of the gear wheel and that is called as helix angle. On the basis of helix hand we decide type of helical gear i.e. right hand helical gear and left hand helical gear.

Helical gear: Characteristics

  1. Helical gear will be more capable to handle the load as compared to the spur gear of similar module.
  2. Helical gears are preferred to use for smoother operation i.e. silent operation because in case of helical gear engagement of teeth will be gradually with sliding contact.
  3. Helical gears are preferred where vibration is the main design criteria as vibration in case of helical gear trains will be less as compared to the spur gear train.
  4. In case of helical gear, teeth engagement will be sliding contact type, hence there will be produced axial thrust force in case of helical bearing. Hence single helical gear will impose radial load as well as axial thrust load over bearing, hence thrust bearing or roller bearings are preferred for helical gear arrangement. Roller bearing or thrust bearing will be best selection for application with helical gear.

Herringbone gear

Herringbone gear is also called as double helical gear as it indicates assembly of two helical gear of having opposite hand i.e. if one helical gear is of left hand helix then other gear should be right hand helix. Both gears must be placed side by side and that’s why axial thrust will be counter balanced, hence there will not be any thrust load over bearing.

Bevel Gear

Bevel gears are basically used for transmitting power between two shafts those are intersecting and co-planer. Bevel gears are used at right angle however such gears might be used at any angle but the common angle is right angle.

In case of bevel gear, teeth will be cut along a pitch line. Bevel gears are classified basically in two types, i.e. straight bevel gear and spiral bevel gear.

Straight bevel gear

Having straight teeth as shown in figure, manufacturing of straight bevel gear is quite easy as compared to the spiral bevel gear and will have reduction ratio approximate 1:5.

Spiral Bevel gear

In Spiral bevel gear, teeth will not be straight but also teeth will be curved as shown in figure. Spiral bevel gear teeth will provide better surface contact and gradual engagement and hence spiral bevel gear will yield better strength, contact ratio and reduction ratio as compared to similar size of straight bevel gear. 


Spiral bevel gear will provide smoother and silent operation as teeth engagement will be gradual.

Miter gear

Miter gear is also a type of bevel gear with reduction ratio 1:1 i.e. speed will not be reduced and gears will be used at right angle. 

Planetary gear

Planetary gear system consist three basic component as shown in figure.

  • Sun
  • Ring gear or internal gear
  • Planet gears and its carrier or arm
Reduction ratio of planetary gear system is quite high hence it is preferred to use where design is compact but required reduction ratio is high and that is the reason that planetary gear is used as key member for automatic transmission system. Planetary gear system will provide approximate 65 % efficiency.

Worm gear

Worm gearing system is preferred where high reduction is required at an angle of 900. In case of worm gear, one gear will have screw threads and that is the reason that we prefer such gearing system to transmit the power at right angle with silent operation as well as vibration free.

Screw gear

Screw gear is basically a helical gear that will transmit the motion from one shaft to another shaft and both shafts will not be parallel and non-intersecting. Such gears are not preferred for transmitting higher load.

Rack and Pinion

Rack and pinion gearing system will have two basic components i.e. rack gear and pinion. Rack gear will have straight teeth and we can assume rack gear as a portion of a gear of infinite diameter. Pinion gear will be simple spur gear with sufficient hub diameter. Rack and pinion gearing system is used for converting linear motion to rotary motion and vice-versa. 

Internal Gear

As name indicates internal gear will have teeth on the inner surface. We have already seen such gear above in case of planetary gear system i.e. ring gear.

External gear

As name indicates external gear will have teeth over its outer surface.
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