Gear Box & Its Maintenance

GEAR BOX & ITS MAINTENANCE

BY J I T E N KU M A R B I S WA L ,

GEAR

A machine element used to transmit motion and power between rotating shafts and by means of progressive engagement of projections called teeth.

WHY ???  To transmit torque/ power from one shaft to another shaft. Other commonly used power transmitting elements:  Belt drive

major limitation: Slippage 

Rope drive  Chain drive

major limitation: Discontinuous drive

To avoid slippage and discontinuity during power transmission, the best solution is gear drive.

 To get desired rotational speed  To change direction of rotation  Where distance between drive shaft and driven shaft is very small

FUNDAMENTAL OF GEARING The motion and power transmitted by gear is kinematically equivalent to that transmitted by friction wheel. Consider two circular wheels A & B mounted on two parallel shafts and the wheels are pressed against each other. When wheel A is rotated by shaft, it will rotate wheel B in opposite direction.

F=µRN

A

T

B

GEAR NOMENCLATURE

IMPORTANT TERMS Pitch circle: It is the imaginary circle that rolls without slip with a pitch circle of a mating gear.  Pitch Point: It is the point of tangency of two pitch circles and is on the line-of-centers. The pitch point of a tooth profile is at its intersection with the pitch circle.  Circular pitch: It is the distance measured on the circumference of the pitch circle from a point on the tooth to the corresponding point on the next tooth. Mathematically, circular pitch, Pc=∏D/T, 

where, D= P.C.D. T= No. of teeth

Module: It is the ratio of the pitch circle diameter in millimeters to the number of teeth. Mathematically, Module, m=D/T The recommended series of the modules in Indian standard are 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 32, 40, 50.  Backlash: It is the distance between the tooth space and the tooth thickness of mating gear as measured on the pitch circle. Purpose of backlash:  prevent gears from jamming together  making contact on both sides of their teeth simultaneously.  Lack of backlash may cause noise, overloading, overheating of the gears and bearings, and even seizing and failure. Excessive backlash is objectionable, particularly if the drive is frequently reversing, or if there is an overrunning load as in cam drives. Excess backlash causes noisy operation. 

 Pressure Angle: If a tangent is drawn to the involute profile of a tooth at any point on the curve, and if a radius line is drawn through this point of tangency connecting this point with the centre of the gear, then the acute angle included between this tangent and radial line is defined as pressure angle at that point. In gear design, the pressure angle is measured at the pitch point.

CLASSIFICATION OF GEARS According to the position of shafts:

 Parallel shaft: (i) Spur gear (ii) Helical gear (a) Single helical gear (b) Double helical gear & herringbone gear:

 Intersecting shaft: (i) Bevel gear (a) Straight bevel gear (b) Spiral bevel gear

 Non-intersecting and non-parallel shaft: (i) Hypoid gear: (ii) Worm gear

TYPES OF GEARS

NOMENCLATURE

Smaller Gear is Pinion and Larger one is the gear In most application the pinion is the driver, This reduces speed but it increases torque.

GEAR TRAIN

A system of gears which transmits motion from one shaft to another.

GEAR TRAINS

n5 N3 N1 N4  ( )(  )(  ) n1 N2 N4 N5

GEAR BOX

A set of assembled gears with its casing used for power and torque transmission.

CLASSIFICATION OF GEARBOX  Sliding mesh gearbox

 Constant mesh Gearbox

GEARBOX DESIGNATIONS

GEARBOX SELECTION

MAINTENANCE

MA

IN T

EN

AN

CE

Preventive Maintenance Predictive Maintenance Breakdown Maintenance

PREVENTIVE MAINTENANCE

 Alignment checking Axial alignment Radial alignment  Oil level checking & top-up  Lube oil analysis  Motor current check  Noise check

PREDECTIVE MAINTENANCE

 During running  Seal leakage  Bearing check Temperature Vibration  Oil level checking  Internal condition monitoring (LLF)

BREAKDOWN MAINTENANCE  Dye penetrant test

 Machining processes

CASE STUDY- FINES CONVEYOR GEAR BOX ELECON MAKE SCN 280  PROBLEM DEFINITION: Input play occurrence  OBJECTIVE: to check and correct input play  PROCEDURE:  Check for axial misalignment  Check for radial misalignment  Provide correction If axial, motor-gearbox base checking If radial, provide appropriate shim If play persists, install new I/P – O/P shaft Otherwise change gearbox.

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