KYAMBOGO UNIVERSITY

FACULTY OF ENGINEERING

DEPARTMENT OF MECHANICAL AND PRODUCTION

NAME: ORTEGA IAN

REG NO: 11/U/11049/EMD/PD

COURSE: BACHELOR OF ENGINEERING IN MECHANICAL AND

MANUFACTURING ENGINEERING.

COURSE UNIT: MATERIALS SCIENCE, ME 212

COURSE CODE: BEMME

TASK: PRACTICAL REPORT

ACADEMIC YEAR: 2014/15

LECTURER: MR. GIDONGO FRANCIS

TITLE: A Practical Report About the Preparation of Specimens and Study of micro-structure

of white heart malleable cast iron in particular and eight other given metals and alloys.

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Table of Contents

DECLARATION ............................................................................................................................................... 4

ACKNOWLEDGMENT: .................................................................................................................................... 5

DEDICATION .................................................................................................................................................. 6

1.0 INTRODUCTION ................................................................................................................................. 7

2.0 TITLE .................................................................................................................................................. 7

3.0 OBJECTIVES OF THE STUDY ............................................................................................................... 7

3.1 Main Objective: ............................................................................................................................. 7

3.2 Specific Objectives: ....................................................................................................................... 7

4.0 EQUIPMENTS USED IN THE PREPARATION ....................................................................................... 7

5.0 ABRASIVE CUT-OFF MACHINE ........................................................................................................... 8

5.1 Construction .................................................................................................................................. 8

5.2 Structure of the Abrasive Cut-Off Machine .................................................................................. 8

5.3 Operation ...................................................................................................................................... 9

6.0 GRINDER POLISHER APPARATUS..................................................................................................... 10

6.1 Construction ................................................................................................................................ 10

6.2 Structure of a Grinder Polisher Apparatus.................................................................................. 10

6.3 Operation .................................................................................................................................... 10

6.4 Precautions ................................................................................................................................. 11

7.0 POWDER DRIVEN WET GRINDING MACHINE .................................................................................. 11

7.1 Construction ................................................................................................................................ 11

7.2 Structure of a Wet Grinding Machine ......................................................................................... 12

7.3 Installing the Abrasive Belt ......................................................................................................... 12

7.4 Operation .................................................................................................................................... 12

7.5 Precautions ................................................................................................................................. 13

8.0 CHEMICALS (ETCHANTS) USED IN MICRO-EXAMINATION OF METAL ............................................ 13

9.0 PREPARATION OF THE SPECIMEN FOR MICRO-EXAMINATION ...................................................... 13

9.1 Precautions to be observed in the process of Preparation of the Specimen ............................. 14

10.0 EQUIPMENT USED IN THE MICRO-EXAMINATION OF METALS SPECIMENS AFTER PREPARATION.

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10.1 The Metallurgical Microscope .................................................................................................... 15

10.1.1 Main Parts ............................................................................................................................... 15

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10.1.2 Working Details ....................................................................................................................... 15

10.1.3 Precautions ............................................................................................................................. 16

11.0 MICRO-EXAMINATION PROCESS ......................................................................................................... 16

12.0 RECOMMENDATIONS...................................................................................................................... 21

13.0 CONCLUSION ................................................................................................................................... 21

References .................................................................................................................................................. 21

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DECLARATION I, Ortega Ian declare that the contents of this report are a product of my work and efforts in

partial fulfillment for the award of a Bachelors Degree in Mechanical and Manufacturing

Engineering.

Signed: ..

Date: ..

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ACKNOWLEDGMENT: First and foremost, I thank my lecturers; Mr. Francis Gidongo and Mr. Kakebe for their special

guidance in the course of this practical. In a similar manner, I convey my heartfelt gratitude to

my fellow students for their team work and wish to acknowledge the tremendous support of

everyone at the department.

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DEDICATION I dedicate this report to my dear parents and guardians. Finally, to everyone with whom we

performed this practical, I dedicate this report to you.

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1.0 INTRODUCTION This report covers a brief description of the preparation of specimens in the study of the

micro-structure of white heart malleable cast iron in particular, and in eight other given

metals and alloys.

2.0 TITLE Preparation of Specimens and Study of micro-structure of white heart malleable cast iron in

particular and eight other given metals and alloys.

3.0 OBJECTIVES OF THE STUDY

3.1 Main Objective: To examine the micro-structure of the material provided.

3.2 Specific Objectives: 1. To study the different types of equipment and materials used in the preparation of

specimens for macro and micro-examination of metal.

2. To study the construction and working details of a metallurgical microscope.

3. To learn the method of preparing specimens for micro-examination with a metallurgical

microscope.

4. To carry out the micro-examination of the micro-examination of the micro-structures of

the following metal and alloys. Brass, bronze mild steel grey cast iron, malleable cast

iron, high carbon steel which is what I examined in particular, spheroidal graphite, cast

iron and aluminum cast alloys.

4.0 EQUIPMENTS USED IN THE PREPARATION Abrasive cut-off machine

Wet-grinding apparatus

Grinder/Polisher apparatus

Polishing paste

Metallurgical microscope

Etchants

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5.0 ABRASIVE CUT-OFF MACHINE

5.1 Construction

This consists of a heavy base over which is provided a clamping device on one side and

the other side, a motor that revolves the spindle. The spindle is coupled to the motor and

the other end to an abrasive cutting wheel which is enclosed in a sheet metal house.

A continuous flow of coolant is sprinkled over the surface to be cut. The abrasive wheel

can be operated and pressed over the specimen to be cut along with the full spindle

assembly. A lever is provided to the spindle to press the abrasive wheel against the

spindle. The base is provided with ON/OFF switch.

5.2 Structure of the Abrasive Cut-Off Machine

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5.3 Operation Select the wheel with the right degree of hardness and roughness according to the

specimen to be cut. Make sure that the wheel has the correct diameter.

Mount the wheel and put the washer on both sides of the wheel before tightening it with

the help of the nut. The wheel should be tightened with great care as to avoid damage of

the grinding wheel. And check that the wheel does not revolve in an eccentric position.

After mounting the abrasive wheel properly, tighten the specimen in the vice provided on

the bed of the machine, start the machine and check that the coolant pump and its flow is

proper.

Bring down the abrasive wheel slowly and press it over the specimen gently. Press the

wheel till the specimen is completely cut.

5.4 Precautions While mounting the abrasive wheel, make sure that it is properly tightened and revolves

truly and smoothly.

While tightening the abrasive wheel, no under due pressure should be exerted otherwise

the wheel may get fractured.

Before starting operation on the machine, check that the coolant flow is available

properly.

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The specimen should be tightly held and in a proper position.

The abrasive wheel should not be pressed against the specimen with a jerk.

6.0 GRINDER POLISHER APPARATUS

6.1 Construction It has water attachment and polishing wheels for use with polishing cloths or adhesive

backed abrasive papers. The unit is available in twin wheel version. The driving plate is

connected to the motor by Z-section V-belts and pulleys. Driving plate and motor

bearings are lubricated for life and do not require routine maintenance. Grinding,

polishing and lapping wheel types and are simply placed on the driving plate.

6.2 Structure of a Grinder Polisher Apparatus

6.3 Operation The specimen after having been ground properly on the wet grinding apparatus is next

polished on the diamond polishing apparatus. An abrasive paste known as the diamond

abrasive paste is applied on the upper surface of the polishing cloth and the specimen is

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then held rigidly and rubbed on the polishing cloth in a circular motion. The specimen is

then cleaned with a cleaning agent and dried with soft cotton.

The specimen is then viewed under a microscope and if it still has not attained a mirror

like lustre on its surface, the rubbing operation is continued until the desired and required

surface finish is obtained.

6.4 Precautions During tightening of the polishing cloth, it has to be ensured that its top surface does not

have any wrinkles. Never rub the specimen on a dry polishing cloth.

During rubbing operations, no undue pressure is exerted on the specimen.

While assembling the polishing disc and the base plate, care should be taken.

7.0 POWDER DRIVEN WET GRINDING MACHINE

7.1 Construction Belt alignment Knob: Turning clockwise causes the belt to shift to the right, turning

counter-clockwise causes a shift to the left. Adjust as required to center the belt.

Belt Switch and Indicator Light:

Sink Water Knob: Controls the flow of water to the sink spout for specimen rinsing.

Belt water Knob: Controls the flow of water to the belt. It should be adjusted to supply

just enough water to keep the sample cool and flush the grinding residue away. Turn on

after the belt is running.

Flush Water Knob: Controls the flow of water to the belt chamber flushing system. Turn

on before starting the grinder and turn off after grinding has been completed.

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7.2 Structure of a Wet Grinding Machine

7.3 Installing the Abrasive Belt

Open the belt chamber door by turning the door release latch counter clockwise

and lowering the hinged door.

Release belt tension by pulling the handle forwards to stop.

Insert the belt.

Position the belt so that the arrow on the inside of the belt lies in the direction of

the pulley rotation.

Slide the belt over the ramped table, the drive pulley so that it is roughly centered.

Apply the belt tension by pushing belt release handle to the rear.

Adjust the belt by turning the motor on momentarily to determine stability of the

belt tension. If the belt craws to the right, turn the alignment knob counter

clockwise. If the belt craws to the left, the alignment knob should be turned

clockwise.

Close the belt chamber door and turn the latch clockwise to secure.

7.4 Operation Cut the specimen on an abrasive cut-off machine taking care that the two sides of the

specimen are cut parallel to each other, clean the specimen with a cleansing agent.

Turn on flush water

Turn on belt switch

Adjust belt alignment if required

Turn on belt water

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The operator (right handed stands in front of and slightly to the left of the belt station to

be used so that his arm is in line with the long axis of the belt. Left handed stands slightly

to the right of the belt Centre.

The belt water knob is adjusted to provide a light film on the moving belt surface. Too

much coolant reduces cutting rate because the specimen will ride over a film of water and

too little coolant will cause the specimen to heat.

The specimen is grasped firmly between fingers and moved from side to side across the

width of the belt to obtain the highest belt life.

Use the sink water to flush away residues before inspection of the specimen.

After grinding the specimen in one direction on the roughest grade, its direction is

changed through 90 degrees for the second grinding operation. The same procedure is

followed on other grade of grinding paper/belt.

The specimen is then cleaned properly with a cleansing agent and viewed under

microscope in case of scratches, depressions are visible. Repeat the grinding procedure

until when these scratches disappear.

7.5 Precautions The direction of the specimen should not change during grinding operation.

There should be a continuous supply of sprinkling water throughout the experiment.

8.0 CHEMICALS (ETCHANTS) USED IN MICRO-EXAMINATION OF METAL For iron and steels, 2ml of concentrated Nitric acid are mixed with 98ml of ethanol.

For brass, bronze and bearing metal, use 10gm of of distilled

water. (To be dissolved just before use)

9.0 PREPARATION OF THE SPECIMEN FOR MICRO-EXAMINATION Cut the specimen with an abrasive cut-off machine (if required)

Grind one face of the specimen on the wet-grinding apparatus. On each strip of grinding

paper, the specimen should be ground first in one direction for a few minutes and then in

the direction 90 degree to the previous one till the marks of grinding in the earlier

direction are completely wiped off.

While moving from coarse grinding paper to a fine grinding paper, the pressure applied

on the specimen during rubbing should be decreased gradually. The pressure on the

specimen while grinding on the finest grinding paper should almost be zero. Otherwise

there is a possibility of strip giving way. The water must flow during the rubbing

operation.

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Rub the specimen then on the diamond polishing apparatus after polishing cloth is

charged with polishing paste. The process of rubbing should be continued for 15 to 20

minutes to get a mirror like surface.

After rubbing the specimen on the diamond polishing apparatus, clean the surface with

cotton dipped in spirit or so followed by final cleaning with dry cotton.

Check under microscope, if the surface appears to be bright and does not show a line or

spots, that would show that the specimen has been ground properly and is ready for

etching.

9.1 Precautions to be observed in the process of Preparation of the

Specimen The direction of the specimen should not change during grinding.

There should be a continuous supply of the sprinkling water throughout the

grinding operation.

During tightening of the polishing cloth (on the diamond polishing apparatus) it

should be ensured that its top surface does not have any wrinkles.

During rubbing operation no undue pressure should be exerted on the specimen.

Apply polishing paste frequently on the polishing cloth.

Keep the polishing surface and the metallurgical microscope covered, after use.

Do not scratch microscope lenses.

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10.0 EQUIPMENT USED IN THE MICRO-EXAMINATION OF METALS

SPECIMENS AFTER PREPARATION.

10.1 The Metallurgical Microscope

10.1.1 Main Parts Vertical Arm: Is the main casting and constitutes the main body of the microscope. It

supports all the other parts of the microscope and is fixed on the base.

Turret heat arrangement: Is fixed in front of the arms and houses the objective lenses

of varying magnification. The turret can be rotated to bring any of the objectives into

viewing position to change the magnification.

Coarse adjustment Knob: Is circular in shape and is fixed on the lower portion of the

arms and over the base. It is primarily used for rough focusing of the specimen.

Fine adjustment Knob: Is also circular in shape and its function is to finely adjust the

view which had already been roughly focused by the coarse adjustment knob.

Multistage table: Is located in between the base and the objectives and is fixed in front

of the arm. It holds the specimen to be viewed.

Eye Piece: Is a small lens fitted in the rubber packings and placed at an angle on the top

the microscope for viewing for viewing the specimen.

Base: is the lowest portion of the microscope which supports all other parts.

10.1.2 Working Details The prepared specimen is placed on the multistage table.

The turret can be rotated to bring any one of the objectives into view to change the

magnification.

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The light is switched on and the adjustment of the lenses is made by coarse adjustment

and fine adjustment knobs. A clear image of the structure of metal is obtained by

adjusting the lenses by lit and trial methods.

The image is properly magnified so as to see the microstructure clearly.

The microstructure obtained is compared with standard photomicrographs of metals and

alloys.

The microstructure in some microscopes can be photographed by special arrangements

provided there in the identification of metals and alloys.

10.1.3 Precautions

Clean the lenses properly before viewing the specimen.

Place the specimen on the multistage table gently.

Operate the adjustment knobs slowly (without jerk)

Do not scratch microscope lenses.

11.0 MICRO-EXAMINATION PROCESS Treat the specimen with an etchant which is applied with cotton and rubbing carried out

for some time.

The specimen is then cleaned with dry cotton and viewed under microscope (100 and 200

magnifications)

If the specimen shows grooves or pits and white portion contains lines it means that the

specimen has been etched properly.

If the desired result is not obtained, continue rubbing using etchant and viewing specimen

under microscope till desired results and are obtained.

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Microstructure of Brass

Microstructure of Spheroidal Graphite cast iron

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White Heart Malleable Cast Iron (White-Ferrite)

Mild Steel (Black/dark-pearlite and white/light-ferrite)

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High Carbon Steel

High Speed Steel

Pearlite (laminated) and cementite (light) at crystal boundaries. The minor is assumed

cementite (iron carbide) and the major is martensite.

White Cast Iron (White Cementite and black pearlite)

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Grey Cast Iron (Graphite Flakes in a Matrix of Pearlite)

Microstructure of Bronze

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12.0 RECOMMENDATIONS 1. I recommend that the administration should always maintain and repair worn out

machines in the workshop.

2. The University administration should procure new machines and meet the

standards of students.

3. More materials should be readily availed in the workshops.

13.0 CONCLUSION The methods of preparing a specimen for micro-examination were successfully learnt.

The micro examination on the above metals was successfully carried out and clearly

observed.

References Lecture Notes

Internet

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