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ITM UNIVERSEInstitute of Technology &

Management Universe

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SPECIMEN PREPARATION FOR

MICRO-EXAMINATION

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SAMPLE PREPARATION Microscopic examination begins with: 1) Cutting 2) Grinding 3) Belt Polishing 4) Paper Polishing5) Etching 6) Examination through microscope

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PROCESS:-

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SELECTING OF SPECIMEN FOR MICRO-EXAMINATION A larger body of metal may not be

homogeneous either in composition or crystal structure

A specimen approx. 20 mm diameter or 20 mm square in a convenient size to handle is cut parallel to the method of manufacturing by saw/abrasive cutter.

Very small specimens are difficult to polish & this can best be done by mounting them.

Mounting a specimen provides a safe, standarised & ergonomic way by which to hold a sample during grinding & polishing operations

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GRINDING THE SPECIMEN The surface of the metal or alloy may have

irregulurities which are to be removed before preparation of the specimen

The cut sample og metal or alloy is ground by using a suitable quality grinding wheel or by an emery paper polishing upon the irregularities present on the surface.

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BELT POLISHING After grinding operation is over the next step

is to polish the ground surface of the specimen since the observation of the microstructure is possible by reflection of the light rays in case of optical microscope.

For the reflection of the light to be possible the surface of specimen must be well polished so we first use the 30 to 40 aluminum oxide belt.

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BELT POLISHING MACHINE

Belt :- 100mm width x 1000mm lengthRotation :- 1400rpmSurface speed :- 760rpmMotor :- 750WPower :- 380V/50HZ

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PAPER POLISHING In this polishing require use of emery paper of

different grades such as 1/0, 2/0, 3/0, 4/0, an increasing number of zeros that indicates that fineness of abrasive particle on the paper increase.

The polishing is carryout manually on the ground surface of the specimen by selecting course grade paper by moving the specimen to and fro number of times in one direction.

The same surface is polished by the next grade emery paper by rotating the specimen through 90 degree in a way that the scratches of the previous grade are completely removed by new ones.

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DIFFERENT TYPES OF EMERY PAPER

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MIRROR POLISHING Once the paper polishing over mirror

polishing is done by using a wet polishing mill having special velvet cloth being rotated at high speed.

The specimen surface which is dry polished is kept in contact with the rotating cloth and special paste of alumina is poured while the cloth is rotated which range is 0.5 – 0.03 micrometer.

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MIRROR POLISHING MACHINE

Double Disc Polishing MachineModel -Single/Double DiscVariable SpeedDigital R.P.M DisplayDriven By AC MotorDouble Disc400 to 1400 R.P.M

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ETCHING THE SPECIMEN To obtain the visual difference between grain and

grains boundary under the microscope etching process is required.

In this process of etching a dilute acid or a chemical regent is applied on the polished surface of the specimen for about five to ten seconds.

After that the specimen is washed by flowing water sufficiently. Thus a depression of an atomic size is produced throughout the grains boundaries if the metal surface.

Because of this differential etching process, the light rays if microscope get reflected back with different intensities.

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EXAMINATION

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EXAMINATION After polishing, the specimen is examined

under the metallurgical microscope by placing it on its table.

Normal Carbon steel

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