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“FAILURE ANALYSIS OF FLAT BELT CONVEYOR SHAFT ”

Updated: May 28, 2020

conveyor shafts, finite element analysis, failure analysis, fatigue testing.

The shafts which are used for transmission of power or torque between two moving elements of machines which are used in different applications in our industries and day to day life, to give an overview on the various possible types of failures of shafts and identifying reason of their failures.For this purpose some papers on failure of shafts have been reviewed in which mechanical properties, material structure, design and various methods of stress analysis have been considered as the primary parameters for their study.

The objective of present work is to study the various methodologies used for the shaft failure analysis and to choose best methodology suitable for the failure analysis of shaft used in conveyor belt for material handling.


Problem Statement.


“To identify the failure of flat belt conveyor shaft and the stresses generated on shaft.”

Description

A shaft is a rotating member usually of circular cross-section (solid or hollow), which is used to transmit power and rotational motion in machinery and mechanical equipment in various applications. Most shafts are subjected to fluctuating loads of combined bending and torsion with various degrees of stress concentration. For such shafts the problem is fundamentally fatigue loading. Failures of such components and structures have engaged scientists and engineers extensively in an attempt to find their main causes and thereby offer methods to prevent such failures

Material handling is a vital component of any manufacturing and distribution system and the material handling industry is consequently active, dynamic and competitive. Overhead belt conveyor is used for material handling purpose and hence it is very useful for any industry.


Project Objectives

1.To find the location of failure of test piece (shaft) subjected to sequence of stress amplitude.

2.To identify the basic root cause of shaft failure.

3.To identify the methods of reducing failure of shaft.

4.To implement best suitable method.


Components of Conveyor System

1.Gear Box

2.Motor

3.Driving Pulley

4.Stepped Shaft

5.Flat Belt

6.Bearing

7.Idler Roller


Background of failure analysis:-

Failure analysis is the process of collecting and analyzing data to determine the cause of a failure and how to prevent it from recurring. It is an important discipline in many branches of manufacturing industry. Such as the electronics industry where it is a vital tool used in the development of new products and for the improvement of existing products. However, it also applied to other fields such as business management and military strategy. Failure analysis and prevention are important functions to all of the engineering disciplines. The materials engineer often plays a lead role in the analysis of failures, whether a component or product fails in service or if failure occurs in manufacturing or during production processing. In any case, one must determine the cause of failure to prevent future occurrence or to improve the performance of the device, component or structure.

Failure analysis can have three broad objectives.

1. Determining modes

2. Failure Cause

3. Root causes.


Causes of Shaft failure

• Excessive corrosion and wear.

• Incorrect shaft size.

• Excessive stresses

• Material problems.

•Bending or deflection causing interference with stationary parts.


Theories of failure


1. Maximum principal stress theory - Good for brittle materials According to this theory when maximum principal stress induced in a material under complex load condition exceeds maximum normal strength in a simple tension test the material fails. So the failure condition can be expressed as


2. Maximum shear stress theory - Good for ductile materials According to this theory when maximum shear strength in actual case exceeds maximum allowable shear stress in simple tension test the material case. Maximum shear stress in actual case in represented as


3. Maximum normal strain theory This theory states that when maximum normal strain in actual case is more than maximum normal strain occurred in simple tension test case the material fails. Maximum normal strain in actual case is given by


Where E is Young's modulus of the material


4. Total strain energy theory - Good for ductile material According to this theory when total strain energy in actual case exceeds total strain energy in simple tension test at the time of failure the material fails. Total strain energy in actual case is given by,

5. Shear strain energy theory - Highly recommended According to this theory when shear strain energy in actual case exceeds shear strain energy in simple tension test at the time of failure the material fails.

Shear strain energy in actual case is given by,

Where G is shear modulus of the material


Method of finding root cause of failure

1.Visual inspection

2.Design standards of the shaft considering maximum bending and shear stress theory.

3.Theories of failure.

4.Finite element analysis of roller shaft using ANSYS software.


Tools used for shaft failure analysis

Non destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties

of a material, component or system without causing damage. The terms Non destructive examination (NDE), Non destructive

inspection (NDI) and Non destructive evaluation (NDE) are also commonly used to describe this technology.

Magnetic Particle Inspection

Radiography

Liquid Penetrant Testing

Electromagnetic Inspection


MECHANICAL TESTING

1.Hardness testing

Different Methods of Hardness Testing: There are four typical methods for testing the hardness of metals. These are the sclerometer method introduced by Turner in 1896, the spectroscope method recently invented by Shore, the indentation test adopted by Brinell about 1900 and the drill test introduced by Keep a few years earlier.


2.Fatigue test

A method for determining the behavior of materials [18] under fluctuating loads. A specified mean load (which may be zero) and an alternating load are applied to a specimen and the number of cycles required to produce failure (fatigue life) is recorded. Generally, the test is repeated with identical specimens and various fluctuating loads. Loads may be applied axially, in torsion or in flexure. Depending on amplitude of the mean and cyclic load, net stress in the specimen may be in one direction through the loading cycle or may reverse direction. Data from fatigue testing often are presented in an S-N diagram which is a plot of the number of cycles required to cause failure in a specimen against the amplitude of the cyclical stress developed. The cyclical stress represented may be stress amplitude, maximum stress or minimum stress. Each curve in the diagram represents a constant mean stress. Most fatigue tests are conducted in flexure, rotating beam, or vibratory type machines. Fatigue testing is generally discussed in "Manual on Fatigue Testing,"

3. Impact Testing

Two standard tests, the Charpy and Izod, measure the impact energy (the energy required to fracture a test piece under an impact load) also called the notch toughness.

The Charpy test is the test to determine the resistance of a material against shocks. The test temperature is very important because the resistance does decrease with decreasing temperature. Impact testing fits into two main categories: (a) low velocity impact, and (b) high velocity impact . These two main categories lead to three main types of impact testing. Charpy impact testing and drop weight impact testing fall into the category of low velocity impact testing (here it should be noted that an impact test machine can be used for high velocity impact also. Ballistics impact testing falls into the category of high velocity impact testing. Technology has increased to the point that there are now sophisticated measuring devices for instrumented impact testing.






Summery

The various failure analysis of shafts mentioned above do not follow any specific approach. To analysis the root cause of failure it essential to follow various examinations and comparing the results. A mechanical shaft may fail due to several reason such as improper engineering design, chemical composition, negligence in operations and maintenance, welding repairing works. To overcome the above disadvantages precautions should be taken.

The heavy nip roller shaft failure analysis is to done by following methodology

1. Visual inspection of the failed component

2. Design standards of the shaft considering maximum bending and torsional theory.

3. Metallographic inspection of failed specimen.

4. Analyzing stress concentration at major step down.

5. Finite element analysis of roller shaft using ANSYS software.


Conclusion

  • To analysis root cause of failure it essential to follow various examinations and comparing the results.

  • After comparing the results of various methods, we concluded that the shaft get failed due stress concentration at major stepdown.

  • Therefore to avoid the failure of shaft at major stepdown we uses the methods of reduction of stress concentration i.e. fillet.

  • So we again did the analysis of shaft using ansys and concluded that stress concentration is under limit.

References

Devendra Kumar, R.K. Mandloi “Analysis & Prospects of Modification in Belt Conveyors - A Review” IJERA Vol. 3, Issue 1, January -February 2013, pp.581-587.

VINOD M. BANSODE, ABHAY A. UTPAT “Fatigue Life Prediction of A Butt Weld Joint In A Drum Pulley Assembly Using Non-Linear Static Structural Analysis” Dept. of Mechanical Engineering, College of Engineering, Pandharpur, India.

X. Oscar fenn Daniel, A. Hussain lal “Stress Analysis in Pulley of Stacker-Reclaimer by Using Fem Vs Analytical” Department of Mechanical Engineering, JJ College of Engineering and Technology, Tiruchirappalli. IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684, p-ISSN: 2320-334X PP 52-59.

Gys van Zyl, Abdulmohsin Al-Sahli “Failure analysis of conveyor pulley shaft” Materials and Corrosion Section, SABIC T&I, Jubail, Saudi Arabia ,Received in revised form 27 APRIL 2013


project coordinator-Mr. Akshay Anil Tanmor


THANK YOU


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