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
- Teeth will be straight in case of spur gear, hence designing and manufacturing of spur gear will be easy.
- Spur gear will be more efficient as compared to helical gear of similar size.
- There will not be any axial thrust force in case of spur gear because teeth are straight and parallel to the axis of gear.
- 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.
- In case of spur gear, bearing has to bear only radial load as axial thrust will not be there in spur gearing system.
- 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
- Helical gear will be more capable to handle the load as compared to the spur gear of similar module.
- 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.
- 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.
- 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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