Gears And its types

KUMARAGURU COLLEGE OF TECHNOLOGY
P15CCT104 - INTEGRATED MECHANICAL DESIGN
GEARS
Presented By,
RAGHUL S(17MCC006)

TABLE OF CONTENTS
 Introduction
 General Nomenclature
 Types Of Gears
 Gear Materials
 Gear Tooth Failure

INTRODUCTION:
 A gear is a wheel with teeth that mesh together with
other gears.
 Transmit motion by engaging teeth
 Two or more meshing gears, working in a
sequence, are called a gear train
 Used to change,
 Speed
 Torque
 Direction

Face Width:
 The Face width of a gear is the length of teeth in an
axial plane.
Pressure Angle ( α ):
 Pressure angle is the leaning angle of a gear tooth, an
element determining the tooth profile.
Whole depth:
 The distance from the top of the tooth to the root; it is
equal to addendum plus dedendum or to working depth
plus clearance.
Working depth:
 Depth of engagement of two gears, that is, the sum of
their operating addendums.

Pitch circle:
 A Pitch circle is the curve of intersection of a pitch
surface of revolution and a plane of rotation.
Outside diameter:
 Diameter of the gear, measured from the tops of the
teeth.
Root diameter :
 Diameter of the gear, measured at the base of the tooth.
Clearance:
 Distance between the root circle of a gear and the
addendum circle of its mate.

Addendum:
 Radial distance between the pitch diameter and the
outside diameter.
Addendum circle:
 Coincides with the tops of the teeth of a gear and is
concentric with the standard pitch circle.
Dedendum:
 Radial distance from the depth of the tooth trough to the
pitch surface.
Dedendum Circle:
 The circle touching the bottom of the spaces between
the teeth of a gear wheel.

TYPES OF GEAR:
 Spur Gear
 Helical Gear
 Bevel Gear
 Worm Gear
 Rack And Pinion
 Herringbone Gear

SPUR GEAR:
 Most commonly used Gear type.
 Teeth are parallel to the axis of the gear.
 Transmit power from one shaft to other parallel
shaft.

Advantage:
Low Cost
Ease of manufacture
Availability
Disadvantage:
Only works with mating gear
Axis of each gear must be parallel
Applications:
Washing Machines, Rolling Mills, Marine
Engines.

HELICAL GEAR
 Teeth are at an angle to the gear axis
 This gradual arrangement makes helical gear
operate much more smoothly and quietly than spur
gear
 Can transmit power between Right angle or Parallel
Axis

Advantage:
Smooth and quiet due to gradual tooth
engagements
Parallel to perpendicular shaft arrangement
Disadvantage:
Difficult to Manufacture
Cost is High
Resulting axial thrust component
Applications:
Fertilizer industries, Printing industries, earth
moving industries, Conveyors, Elevators

BEVEL GEAR:
 Usefull when the direction of shaft location has to
be changed.
 Mounted on shaft that are 90deg apart, can also be
designed to work in other angles.
 Teeth can be straight, Spiral or Hypoid

Advantage:
Operate on Shafts intersecting at an Angle.
Sliding friction will be low.
Disadvantage:
Assembled with respective shaft precisely.
At high speed it will produce noise.
Applications:
Textile Machine, Sewing Machine.

WORM GEAR:
 Used when large Gear Reduction is needed.
 Have good intersecting property.
 Used widely in material Handling and transportation
machinery, machine tools etc…

Advantage:
Higher speed reduction could be secured;
speed reduction could be secured up to 300:1
Worm and worm gears operate silently
Disadvantage:
Manufacturing cost is high as compared with
manufacturing cost of bevel gear
Worm and worm gear set will have heavy
power losses.
Efficiency will be low
Applications:
 Tuning Instruments, Lifts/Elevators.

RACK AND PINION:
 Convert Rotational to Linear motion
 Round Gear – Pinion
Flat or Straight Gear – Rack
 Best example is Car Steering System.

Advantage:
Rack and pinion gives easier and more
compact control over the vehicle
Cheap, Compact, Robust.
Disadvantage:
The rack and pinion can only work with certain
levels of friction.
Applications:
Rack Elevators, Steering.

HERRINGBONE GEAR:
 Two helical gears that have been placed side by
side.
 Referred to as “double helical”.
 No thrust loading on the bearings

Advantage:
The double helical form balances the inherent
thrust forces.
Efficient transfer of torque and smooth motion
at very high rotational velocities.
Disadvantage:
High cost due to special gear shaping
equipment and special cutting tools.
Applications:
Used in Heavy Machinery.

GEAR MATERIALS:
 Numerous nonferrous alloys, cast irons, powder-
metallurgy and plastics are used in the manufacture
of gears.
 Steels - commonly used - high strength-to-weight
ratio and low cost.
 Plastics - cost or weight is a concern - Reduce
repair cost.

GEAR TOOTH FAILURE:
 Gear failure can occur in various modes.
 Care has to be taken to avoid such failures
 Types of Gear Tooth Failure:
 Scoring Failure
 Wear Failure
 Pitting Failure
 Plastic Flow
 Tooth Fracture

SCORING FAILURE:
 Occurs Due to Lubrication failure in Contact region
and metal to metal contact.
 Welding and tearing action resulting from metallic
contact removes the metal.
 Types of Scoring:
 Initial Scoring
 Moderate Scoring
 Destructive Scoring

Initial Scoring:
 Occurs by High spots left by previous machine.
 Lubrication failure at this point leads to Scoring
 Scoring stops when temperature, load and speed
remains unchanged.

Moderate Scoring:
 Occurs After initial scoring if the load, speed or oil
temperature increases, the scoring will spread over
to a larger area.
 Progresses at tolerable rate.

Destructive Scoring:
 If the load, speed or oil temperature
increases appreciably, then severe scoring sets in
with heavy metal will occur.
 Predominant over Pitch line since the lubrication
is least at that region.

WEAR FAILURE:
 Wear is a kind of tooth damage where a layers of
metal are removed more or less uniformly from the
surface.
 Tooth Thins and get weakened.
 Cause of gear tooth wear is
 Adhesive Wear
 Abrasive Wear
 Corrosion Wear

Adhesive Wear:
 Hard to detect.
 Occurs from start since the rate of wear is low.
 When the load and speed of operation are more
than mild wear conditions, moderate wear takes
place with higher rate.
 Occurs over long Period.

Abrasive Wear:
 Reason for the failure of open gearing and closed
gearing of machine operated in Abrasive materials.
 Depending on the size, shape and concentration of
the abrasives the wear will change.

Corrosion Wear:
 Due to the chemical action of the lubricating oil or
the additives.

PITTING FAILURE:
 Surface fatigue failure of the gear tooth.
 Occur due to repeated loading of tooth surface and
contact stress.
 Pit is formed.
 Impact load resulting from pitting may cause failure.
 Types of Pitting
 Initial Pitting
 Progressive Pitting

Initial Pitting:
 Small pits of 25 to 50 μm deep are formed just
below the pitch line.
 the load gets distributed over a larger surface area
and stress comes down.
 Common with medium hard Gears.

Progressive Pitting:
 High load and corrective action of initial pitting
leads to Progressive Pitting.
 Pitting begins on the tooth flanks near the line
along the tooth passing through the pitch point.
 Very rare in tooth Face.

PLASTIC FLOW:
 Occurs due to sliding action of Gear.
 Surface deformation Occurs due to yielding of
surface.
 But occurs only in heavy loading Case.

TOOTH FRACTURE:
 Dangerous kind of gear failure leads to disablement
of drive and frequently to damage of other
components.
 Occurs over a long a period of time.
 Tooth failure may result low-cycle fatigue, Repeated
cyclic load

Gears And its types

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