Engineering materials laboratory manual

Apparatus used: Winch crab apparatus, weights. These are classified as:. Single purchase Winch crab. Double purchase Winch Crab. Single Purchase Winch Crab :- It consists of two parallel spindles, upper one called effort spindle and lower one is called as load spindle. One effort spindle a small touched wheel pinion is mounted in such a way that pinion and a lever is attached to apply the effort.

On load spindle, a large toothed wheel known as spur wheel is mounted in such a way that pinion meshes with it. Both the spindles are suitably mounted on a rigid frame. A rope is wound round the cylinder while load is attached on the other end,. Suppose, lever arm is rotated by one revolution. Double Purchase Winch Crab :- In this case to obtain velocity ratio compound gear train is used, because intermediately gears are compound wheel mounted on the same shaft. Other arrangements are similar to that of single purchase winch crab.

Therefore No. And no. For single winch crab:. Load W. P in Nt. For double winch crab:. Conclusion: Hence the winch crab is studied. Aim: To study t h e torsion testing m a chine and perform the torsion test. Apparatus used: A torsion testing machine, twist meter for measuring angles of twist and a steel rule and calipers or micrometer.

Theory: A torsion test is quite instrumental in determining the value of modulus of rigidity of a metallic specimen. The value of modulus of rigidity can be found out thought observations made during the experiment by using the torsion equation.

Aim : To study the Rock w ell Hardness t e sting machine and perform the Rock w e ll hardness test. Apparatus: R o ckwell Hardness testing machine, s p ecimen of m ild steel or other mater i al. Theory: Hardness represents the resistance of m a ter i al surface to abrasion, scratching and cutting, hardness after gives clear indication of strength. In all h a rdness tests, a define force is mechanically applied on the piece, va r ies in size and shape for different tests. Com m on indentors a r e made of hardened steel or dia m ond.

It differs only i n dia m eter and material of the indentor and t h e applied force. Here the indentor has a dia m ond cone at the tip and applied force is of kgf. Steel indentor at 60kgf. Various scales in Rock w e ll hardness test are given belo w : -. Type of. Di m ension. Position on dial. Kind of material. Cone, 12 0 o. Much harder such as carburized steel, cemented carbides.

Ball, 1. Soft steels, copper, aluminum,brass, grey cast iron. Cone, o. Hard steels, Ti, W, Va, etc. Insert ball of dia. Make the spec i men surface c l ean by remov i ng dust, dirt, oil and grease etc. Make contact b etween the specimen surface and the ball by rotating the jack adjusting wheel.

Push the required button for loading. Pull the load release lever wait for mini m u m 15 second. The load will automatically apply gradually. Re m o ve the specimen from support table and locate the ind e ntation so made. Repeat the entire operation, 3-times.

Observation and Calculations: Following observation are recorded are from a test on steel specimen using a hardened steel ball as indentor. Aim: To study the Brinell Hardness testing machine and the Brinell hardness test.

Need an account? Click here to sign up. Download Free PDF. Laboratory Manual for Engineering Properties of Foods. Teferra PhD. A short summary of this paper. Download Download PDF. Translate PDF. Tadesse F. Some of the Exercises may be added in the future in line with the laboratory capacity development. Currently there are no equipments that can be used for the measurement and testing of thermal, electrical, dielectric and acoustical properties of foods and related other parameters.

Table of Contents List of Figures Volume and Density Estimation of size of particulate foods Estimation of shape roundness of food particles Viscosity determination of liquid and pasty foods Volume and Density 1. In the SI system, the unit of volume is m3. It is an important quality attribute in the food industry. It appeals to the eye, and is related to other quality parameters.

For instance, it is inversely correlated with texture. In this method, volume of food materials can be measured by pycnometers specific gravity bottles or graduated cylinders.

The volume of a sample can be measured by direct measurement of volume of the liquid displaced by using a graduated cylinder or burette. The difference between the initial volume of liquid in a graduated cylinder and the volume of liquid with immersed material gives us the volume of the material. That is, the increase in volume after addition of solid sample is equal to the solid volume. Most commonly used fluids are water, alcohol, toluene, and tetrachloroethylene.

For displacement, it is better to use a non-wetting fluid such as mercury. Coating of a sample with a film or paint may be required to prevent liquid absorption. The most commonly used gases are helium and nitrogen. Volume is determined based on the ideal gas law. Rapeseeds are commonly used for determination of volume of baked products such as bread.

All measurements are done until the constant weight is reached between the consecutive measurements. Figure Typical solid displacement method for volume measurement The densities of the seeds are calculated from the measured weight of the seeds and volume of the container. Then, the sample and rapeseeds are placed together in the container. The container is tapped and the surface is smoothed with a ruler.

Tapping and smoothing are continued until a constant weight is reached between three consecutive measurements. Clean the food samples by washing and cutting of the tips stems and roots. Measure volume of water in a graduated cylinder about half of its maximum volume and record it as V1; carefully read to the meniscus Figure Here the pull of gravity against the molten metal is much greater. The basic principle of arc welding is shown in Figure1. However the basic elements involved in arc welding process are shown in Figure2.

Most of these processes use some shielding gas while others employ coatings or fluxes to prevent the weld pool from the surrounding atmosphere. The basic principle of arc welding 11 Channel for cable 1 Switch box.

The basic elements of arc welding Arc Welding Equipment Arc welding equipment, setup and related tools and accessories are shown in Figure. However some common tools of arc welding are shown separately through Figure. Few of the important components of arc welding setup are described as under. Arc welding power source Both direct current DC and alternating current AC are used for electric arc welding, each having its particular applications.

DC welding supply is usually obtained from generators driven by electric motor or if no electricity is available by internal combustion engines.

For AC welding supply, transformers are predominantly used for almost all Arc-welding where mains electricity supply is available. They have to step down the usual supply voltage volts to the normal open circuit welding voltage volts. The following factors influence the selection of a power source: a.

Type of electrodes to be used and metals to be welded b. Available power source AC or DC c. Required output d.

Duty cycle e. Efficiency f. Initial costs and running costs g. Available floor space h. Versatility of equipment 2. These are insulated copper or aluminum cables. Electrode holder Electrode holder is used for holding the electrode manually and conducting current to it. These are usually matched to the size of the lead, which in turn matched to the amperage output of the arc welder. Electrode holders are available in sizes that range from to Fig.

Electrode Holder Amps. Welding Electrodes An electrode is a piece of wire or a rod of a metal or alloy, with or without coatings. An arc is set up between electrode and workpiece. Welding electrodes are classified into following types- i Consumable Electrodes a Bare Electrodes Fig. Parts of a electrode b Coated Electrodes ii Non-consumable Electrodes a Carbon or Graphite Electrodes b Tungsten Electrodes Consumable electrode is made of different metals and their alloys.

The end of this electrode starts melting when arc is struck between the electrode and workpiece. Thus consumable electrode itself acts as a filler metal.

Bare electrodes consist of a metal or alloy wire without any flux coating on them. Coated electrodes have flux coating which starts melting as soon as an electric arc is struck.

This coating on melting performs many functions like prevention of joint from atmospheric contamination, arc stabilizers etc. Non-consumable electrodes are made up of high melting point materials like carbon, pure tungsten or alloy tungsten etc. These electrodes do not melt away during welding. But practically, the electrode length goes on decreasing with the passage of time, because of oxidation and vaporization of the electrode material during welding.

The materials of non-consumable electrodes are usually copper coated carbon or graphite, pure tungsten, thoriated or zirconiated tungsten. Hand Screen Hand screen used for protection of eyes and supervision of weld bead. Chipping hammer Chipping Hammer is used to remove the slag by striking.

Wire brush Wire brush is used to clean the surface to be weld. Earth Clamp Fig. Chipping Hammer Fig. Wire Brush 8. Protective clothing Operator wears the protective clothing such as apron to keep away the exposure of direct heat to the body. Safety Recommendations for ARC Welding The beginner in the field of arc welding must go through and become familiar with these general safety recommendations which are given as under.

The body or the frame of the welding machine shall be efficiently earthed. Pipe lines containing gases or inflammable liquids or conduits carrying electrical conductors shall not be used for a ground return circuit All earth connections shall be mechanically strong and electrically adequate for the required current.

Welding arc in addition to being very is a source of infra-red and ultra-violet light also; consequently the operator must use either helmet or a hand-shield fitted with a special filter glass to protect eyes 3.

Excess ultra-violet light can cause an effect similar to sunburn on the skin of the welder 4. Gloves protect the hands of a welder. For overhead welding, some form of protection for the head is required 8. Leather skull cap or peaked cap will do the needful. Leather jackets and 1ather leggings are also available as clothes for body protection.

Welding equipment shall be inspected periodically and maintained in safe working order at all times. Arc welding machines should be of suitable quality. All parts of welding set shall be suitably enclosed and protected to meet the usual service conditions. S pieces by arc welding. S electrodes 3. Rough and smooth files. Protractor 3. Arc welding machine transformer type 4. Mild steel electrode and electrode holder 5. Ground clamp 6. Tongs 7.

Face shield 8. Apron 9. Chipping hammer. Marking 2. Cutting 3. Edge preparation Removal of rust, scale etc.

Try square leveling 5. Tacking 6. Welding 7. Cooling 8. Chipping 9. Cleaning Procedure: 1. The given M. S pieces are thoroughly cleaned of rust and scale. The two pieces are positioned on the welding table such that, they are separated slightly for better penetration of the weld.

The electrode is fitted in the electrode holder and the welding current is ser to be a proper value. The ground clamp is fastened to the welding table. Wearing the apron and using the face shield, the arc is struck and holding the two pieces together; first run of the weld is done to fill the root gap. Second run of the weld is done with proper weaving and with uniform movement.

During the process of welding, the electrode is kept at to from vertical and in the direction of welding. The scale formation on the welds is removed by using the chipping hammer. Filling is done to remove any spanner around the weld.

S pieces and by arc welding. The two pieces are positioned on the welding table such that, the two pieces overlapped one over the other as shown in drawing. Wearing the apron and using the face shield, the arc is struck and the work pieces are tack- welded at both the ends and at the centre of the joint. The alignment of the lap joint is checked and the tack-welded pieces are required. The two pieces are positioned on the welding table such that, the L shape is formed.

The tongs are made use of for the purpose. The alignment of the corner joint is checked and the tack-welded pieces are required. For individual establishment power is supplied through three phase two wire system. To give V, the neutral is earthed at to the domestic utilities; power is fed to kilo watt meter and then to distributes power along several circuits. It also protects these circuits from over load by safety devices like fuses or circuit breakers.

Fuses and circuit breakers 2. Electric switch 3. Plug 4. Socket out let 5. Lamp holder 6. Main switch 7. Replacing a fuse 2. Resulting a circuit beaker 3.

Resulting a switch or an out let 4. Ensure that the insulation of wire reaches up to accessory 2. Do not over tighten the screw 3. Ensure that the base wire is not touching any part of accessory. Every fitting or appliances must also be controlled by a switch. The switch should be on the line conductor 3. Every sub-circuit must have a separate fuse.

All the metals covering frames etc. A lamp actually work slike aheating element,exceptthat it gives of flight by becoming whiteh ot. The amount of powerit consume sisstamped on the bulb. The higher the wattage, brighterthe light. The bulbs have filaments made of tungsten. However, special bulbs are available with inside coating and filled with gas. Wires and Wire Sizes: A wire is defined asa bare or an insulated conductor consisting of one or several strands.

The wire may consist o f one or several twisted strands. A multi core conductor consists of several cores insulated from one another and enclosed in a common sheathing fig. Wires ize sare specified by diameter of the wire, using a stand ard wire gauge SWG , which also gives an ideao f the current carrying capacity.

Thespecification consist so fb ot htheno. Of strandsand the diameter of each wire in it. One way switch — 2 no. Two-pin plug socket-1no. Bulb holder-1no. Wire stripper 4. Tester 5. Hack saw 7. Fitting the wires 2. Connection of the bulb holder 3. Connection of plug socket 4. Connection of switch 5. Circuit connections 6.

Power from mains 7. Operation the bulb 8. Testing the plug socket. The outline wiring diagram marked on the wooden board and clips are nailed to the board following the diagram, six wire pieces are taken and insulation is removed at the ends by using wire stripper. A phase wire is connected to one point switch s1 and s2. The lower points of switches s1ands2 are connected to one point of bulb holder and one point of plug socket respectively.

Two neutral wires are taken and one in connected to the remaining point of the bulb holder. The other is connected to the remaining points of plug socket. After checking the proper circuit connections the power supply is given. Now the bulb is ready to glow bright and the plug socket is also ready with control. All the wire connections of the switches, bulb holder and sockets are tight.

Too many load connections fr4om a single junction are avoided. All the wire connections of the switches, bulb holder and sockets be tight. In series connection if one bulb does not glow the bulb also does not glows. In parallel connection if one bulb does not glow the other bulb blows.

Materials required: PVC wire of sufficient length 5-no,Two-way switches, bulb holders, ceiling rose and bulb. Tools and equipment used: 1. Operations to be carried out: 1.

Connection of switches 4. Circuit-connection 5. Power from mains 6. Operating the lamp Procedure: A phase wire is taken and its one end is connected to the middle point of two — way switch, S1. While the other end is connected to the phase point of main supply. Another phase wire second wire is taken and used for connecting the lower points of the two switchesS1; S2. The third phase wire piece is taken and is connected between the middle point of S2 and one of the points o f the bulb holder.

A neutral wire piece is taken and its one end is connected to the remaining points of bulb holders, while the other end is connected to main supply. Now the glowing of the bulb is controlled by two way switches. All wire connections to the switches and bulb holders should be right.

Always red wire should be used for phase and black for neutral. Too many load connections from a single junctions are avoided 4. Switch should be connected in phase only. Result and conclusion: Stair case wiring i. Hacksaw 5. Wire stripper 6. Operating the lamp Procedure: Five phase wire pieces are taken and insulation is removed at the ends by wire stripper. The first phase wire is connected by seconds phase wire. One of it is connected to the main supply.

After checking the proper circuit connects the power supply is given to switches. Now the bulbs are ready to show bright and dim. Result: Controlling of two lamps by two independent switches located at two different places is done. A phase wire is connected to one point on the switch. The other point of the switch is connected to Choke. The other point of the Choke is connected to one point of the starter and the other point of l amp holder The other point of the lamp holder-1 is connected to one point of the Starter.

A neutral wire pieces taken and connected to one point of the lampholder The other point of the lamp holder-2 is connected to Remaining point of the Starter. After checking proper circuit connections the power supply is given. Now the lamp is ready to glow. All wire connections to the switches and bulb holders should be tight. The switches must be in off position before giving power supply Result: Operating the fluorescent lamp is done.

Wire stripper 8. Tester Operations to be carried out: 1. Another phase wire second wire is taken and used for connecting the upper points of the two switches S1 with middle point of switch S The third phase wire piece is taken and is connected between the upper point of S2 and one of the points of the bulb holder. Precautions: 5. Too many load connections from a single junctions are avoided 8.

Result and conclusion: GD wiring is done. The process is mainly used for the supply of drinking water and the drainage of waste water, sometimes mixed with waste floating materials in a living or working place. A plumber is someone who installs or repairs piping systems, plumbing fixtures and equipment such as valves, washbasins, water heaters, water closests, etc.

Thus it usually refers to a system of pipes and fixtures installed in a building for the distribution of water and the removal of waterborne wastes. The latin word plumbum, means metal lead pipe, is the origin for developing the term plumbing. Plumbing process was originated during the ancient civilizations such as the greek, Roman, Persian, Indian and Chinese civilizations as they developed public baths and needed to provide potable water, and drainage of wastes carried by water.

They are usually classified according to the material. They are also grouped as cast, welded, seamless, extruded, etc. For conveying large quantity of water, cast iron, steel or concrete pipes having large diameter are usually used. Galvanized iron pipes GI pipes are popular for medium and low pressure water supply lines. Plastic pipes are preferred for household uses at low pressure. Pipes are generally specified by their inner diameter Nominal diameter specified in inches.

Hence, the pipe fitting size is also based on this dimension. But for plastic pipes, this rule is not strictly followed because threading is not usually required for them. For engineering uses, along with the nominal diameter, the pipe thickness is also specified as light, medium or heavy.

Types of pipe joints: According to the pipe material, size and application, different methods are used to join pipes. The most common types of pipe joints are: 1. Screwed pipe joint — For GI Pipes 2. Welded pipe joint — for steel, copper, aluminum and lead pipes 3.

Flanged pipe joint — for cast iron and steel pipes 4. Soldered pipe joint — for brass and copper tubes 5. Glued or cemented pipe joint — for PVC pipes Pipes made of iron GI Pipes and brass of small and medium diameters 10 mm to mm are usually joined by screwing the pipe specials with internal or external threads.

Welding is used to make permanent joint of medium and large diameter steel pipes. The flanged are screwed to the pipe for smaller diameter but made integral for large diameters. Pipes of copper and brass are usually joined by soldering. PVC poly Vinyl Chloride pipe is the most popular choice in plastic group.

It is rigid and uses thread and solvent weld glue connections. It also can be heat fused. PVC pipes are available in various pressure ratings for water supply, and is a very choice for landscape irrigation. The reasons for the popularity are the economy, no corrosion and easiness to work.

CPVC is a different type of plastic, which has an extra chlorine atom in the compound, can be used for the hot water supply, and in industry. To join plastic pipes, gluing or cementing method is used. Solvent cement is the gluing material and it partially melts the surface of the plastic pipe to make the joint. As the glue evaporates within two minutes, a strong joint is obtained. The functions of pipe fittings can be broadly classified as: 1. To join two or more pipe lines together 2. To effect change in diameter or direction 3.

To close the end of a pipe line The most common types of screwed pipe fittings used in galvanized iron GI pipe lines and plastic PVC pipe lines are shown in Figure 1 I to A brief description of these fittings is given below 1. Coupler coupling : Two pipe lines of equal diameter and in axial alignment can be joined by a coupler coupling. It is a short sleeve with internal thread. Reducer coupler Reducer coupling : This is a coupler to join two pipe lines of different diameters in axial alignment.

Internal threads are provided on both ends. An elbow brings twice the head loss than a bend. The two ends of the bend are externally threaded.

The ends are internally threaded for fitting the pipe lines. Tee: This pipe special is used to make a branch connection of same diameter to the main pipe line at right angle. A Tee is internally threaded and it connects three ends of pipes.

Reducer Tee: This is a pipe special similar to Tee used to take a branch connection of reduced diameter from the main pipe line. The threads are provided internally, Close nipple: A nipple is a short straight piece of pipe with external thread on both ends. A close nipple is the shortest one of this category with external thread for the full length. They are used to join two internally threaded pipe specials and valves.

Short nipple: A short nipple has the same shape and function of a close nipple, but it has a short unthreaded portion at the middle of its length for gripping.

Short nipple with hexagonal grip: This nipple has an additional hexagonal nut shape at the middle portion for easy screwing with spanner. It is similar to an ordinary short nipple, except that difference. Hose nipple: A hose nipple is used to connect a hose flexible pipe-usually plastic or rubber to a pipe line.

One end of the hose-nipple has a stepped taper to fit the hose, while other end has thread. Signature of the Staff in charge Name: …………………………….. Date: …………. Signature of Head of the Department 3. Preparation of specimen for Metallographic examination of different engineering materials. To report microstructures of plain carbon steel, tool steel, gray C. Heat treatment: Annealing, normalizing, hardening and tempering of steel. Metallographic specimens of heat treated components to be supplied and students should report microstructures of furnace cooled, water cooled, air cooled, tempered steel.

Students should be able to distinguish the phase changes in a heat-treated specimen compared to untreated specimen. To study the defects of Cast and Welded components using Non-destructive tests like: a Ultrasonic flaw detection b Magnetic crack detection c Dye penetration testing.

PART — B 5. Tensile, shear and compression tests of steel, aluminum and cast-iron specimens using Universal testing machine 6. Torsion Test on mild steel bar.

Bending Test on steel and wood specimens. Izod and Charpy Tests on mild steel and aluminum specimen. To study the wear characteristics of ferrous and non-ferrous materials under different parameters. Fatigue Test demonstration only. Basic Mechanical Engineering 2.

Machanics of Materials 3. I Specimen and to train on Brinell, Rockwell and Vicker's hardness tests. Engineering Knowledge: Apply basic knowledge of science, mathematics and engineering fundamentals in the field of Mechanical Engineering to the solution of complex engineering problems PO2. Problem Analysis: Identify, formulate, review research literature and analyze complex mechanical engineering problems by using basics principles of science, mathematics and engineering for reaching substantiated conclusions.

Conduct Investigations of Complex Problems: Design and conduct experiments using research-based knowledge and methods including design of experiments, analyze, interpret the data, and synthesis of the information to provide the results with valid conclusion. Modern Tool Usage: Create, Select and apply appropriate techniques, resources, and modern engineering and software tools including prediction and modeling to complex mechanical engineering activities with an understanding of the limitations.

The Engineer and Society: Apply reasoning informed by contextual knowledge to assess societal, health, safety, legal and cultural issues and the consequent responsibilities relevant to the professional mechanical engineering practice. Environment and Sustainability: Understand the impact of the professional engineering solutions in societal and environmental contexts, and demonstrate the knowledge of, and need for sustainable development.

Ethics: Apply ethical principles and commit to professional ethics and responsibilities and norms of the engineering practice. Individual and Team Work: Function efficiently as an individual and as a member or leader in diverse team, and in multidisciplinary settings PO Communication: Communicate effectively on complex mechanical engineering activities with engineering community and with society at large, such as, being able to comprehend and write effective reports and design documentation, make effective presentation, and give and receive clear instruction PO Life-Long Learning: Recognize the need for, and have the preparation and ability to engage in independent and lifelong learning in the broadest adapt to emerging field of context of technological change.

Title Page no. All the students are expected to come to the lab, with shoe, uniform etc. For each lab class, all the students are expected to come with observation note book, record note book, pencil, eraser, sharpener, scale, divider, graph sheets etc.

While coming to each laboratory class, students are expected to come with the observation book for the class. All the students are expected to complete their laboratory work including calculations and get it corrected in the laboratory class itself. Therefore, students are expected to handle the instruments with utmost care during the experiment. It includes the study of the microstructure of metals, the space arrangement of the atoms, heat treatment and examination by X-rays.

It is possible to determine the grain size and the size, shape and distribution of various phases and inclusions which have a great effect on the mechanical properties of the metal. The microstructure will reveal the mechanical and thermal treatment of the metal, and it may be possible to predict its expected behavior under a given set of conditions.

In comparison with biological type, the metallurgical Microscope differs in the manner by which the specimen is illuminated. Since the metallographic sample is opaque to light, the sample must be illuminated by reflected light. Some of this incident light reflected from the specimen surface will be magnified in passing through the lower lens system, the objective, and will continue upward through the plane glass reflector and be magnified again by the upper lens system, the eye piece.

The initial magnifying power of the objective and the eyepiece is usually engraved on the lens mount. When a particular combination of the object and eye piece is used at the proper tube length, the total magnification is equal to the product of the magnification of the objective and the eye piece.

The maximum magnification obtained about X. The principal limitation is the wavelength of visible light, which limits the resolution of fine details in the metallographic specimen. Under certain circumstances, high-velocity electrons behave like light of very short wave length. The electron beam has associated with it a wavelength nearly times smaller than the wavelength of visible light, thus increasing the resolving power tremendously.

Since metallographic specimens are opaque to an electron beam, it is necessary to prepare a thin replica of the surface to be studied.

The specimen is polished and etched by following normal metallographic practice. It is then placed on a hot plate with small pellet of suitable plastic on the etched surface. As the temperature rises, the plastic begins to flow and pressure is applied to ensure intimate contact between the plastic and surface.

After cooling the replica is carefully peeled -off. The disk is then placed over the opening in the specimen holder, which is inserted in the column of the instrument. The electrons emitted by a hot tungsten filament cathode are accelerated, to form a high-velocity beam, by the anode.

This beam is concentrated on the replica by the condensing lens. Depending upon the density and the thickness of the replica at each point, some of the electrons are absorbed or scattered while the remainder passes through. The magnetic field of the objective lens focuses and enlarges the electron beam that has passed through the replica. Some of the electrons in this image are brought into a second focus on a fluorescent screen by the projector lens.

It has magnification range of to X which may be extended to X with accessory lenses. Although in principle, the Electron Microscope is similar to the Light Microscope; its appearance is very much different.

It is much larger because of the highly regulated power supplies that ay needed to produce and control the electron beam. The entire system must be kept pumped to a high vacuum since air would interfere with the motion of the electrons. Sampling: The choice of a sample may be very important. If a failure is to be investigated, the sample should be chosen as close as possible to the area of failure and should be compared with one taken from the normal section.

If the material is soft like non-ferrous metals and non-heated-treated steels, the section may be obtained by manual hack sawing. If the materials are hard, the section may be obtained by an abrasive cut-off wheel. Rough grinding: whenever possible the specimen should be of a size that is convenient to handle. It is continued until the surface is flat and free from nicks, burs, etc. And all scratches due to the hacksaw or cut-off wheel are no longer visible.

Mounting: Specimens that are small should be mounted to facilitate intermediate and final polishing. Wires, small rats, sheet metal specimen, thin sections, etc. Resins used- synthetic plastic material, bakelite molding powders, Lucite, etc. The process is repeated with and grit papers. Fine polishing: The time consumed and the success of fine polishing largely depends upon the care that was taken during the previous polishing steps.

The final approximation to a flat scratch free surface is obtained by use of a wet rotating wheel covered with a special cloth that is charged with carefully sized abrasives particles. Abrasives used aluminum oxide for ferrous and copper based materials, cerium oxide for Al, Mg and their alloys: diamond paste, chromium oxide and magnesium oxide. The choice of a proper polishing cloth depends upon the material being polished and the purpose of the metallographic study.

Examples are synthetic polishing clothes gravel and micro-cloth , broad cloth, billiard cloth, velvet cloth, canvas duck, etc. Etching: The purpose is to make visible the many structural characters tics of the metal or alloy. The process must be such that the various parts of the microstructure may be clearly differentiated.

This is accomplished by use of an appropriate reagent which subjects the polished surface to chemical action. The selection of the appropriate etching reagent is determined by the metal or alloy and the specific structure desired for viewing as follows: For ail low-alloy steels attacked by this reagent More dilute solution occasionally useful.

Does not reveal ferrite grain boundaries as readily as nital. Etching time a few seconds to one minute or more. Generally used to copper and many of its alloys Peroxide content varies directly with copper content of alloy to be etched immersion or swabbing for about 1-min. Fresh peroxide for good results. Ammonium persulfate Ammonium persulfate- l0g Water ml. Copper, brass, bronze, nickel silver, aluminum bronze Use either cold or boiling: immersion Palmerton reagent Chromic oxide g Sodium oxide- 15g Water -1,ml General reagent for zinc and its alloys Immersion with gentle agitation THEORY: In materials science, wear is the erosion of material from a solid surface by the action of another substance.

The study of the processes of wear is part of the discipline of tribology. There are five principal wear processes: 1. Adhesive wear 2. Abrasive wear 3. Surface fatigue 4. Fretting wear 5. Erosion wear The definition of wear does not include loss of dimension from plastic deformation, although wear has occurred despite no material removal.

Wear can also be defined as a process in which interaction of the surfaces or bounding faces of a solid with its working environment results in dimensional loss of the solid, with or without loss of material. Aspects of the working environment which affect wear include loads such as unidirectional sliding, reciprocating, rolling, and impact loads , speed, temperature, type of counter body solid, liquid, or gas , and type of contact single phase or multiphase, in which the phases involved can be liquid plus solid particles plus gas bubbles.

In the results of standard wear tests such as those formulated by the respective subcommittees of ASTM Committee G-2 , the loss of material during wear is expressed in terms of volume. The volume loss gives a truer picture than weight loss, particularly when comparing the wear resistance properties of materials with large differences in density.

Adhesive wear Adhesive wear is also known as scoring, galling, or seizing. It occurs when two solid surfaces slide over one another under pressure. Surface projections, or asperities, are plastically deformed and eventually As sliding continues, these bonds are broken, producing cavities on the surface, projections on the second surface, and frequently tiny, abrasive particles, all of which contribute to future wear of surfaces.

Abrasive wear When material is removed by contact with hard particles, abrasive wear occurs. The particles either may be present at the surface of a second material two-body wear or may exist as loose particles between two surfaces three-body wear. Surface fatigue Surface fatigue is a process by which the surface of a material is weakened by cyclic loading, which is one type of general material fatigue.

Fretting wear Fretting wear is the repeated cyclical rubbing between two surfaces, which is known as fretting, over a period of time which will remove material from one or both surfaces in contact. It occurs typically in bearings, although most bearings have their surfaces hardened to resist the problem. Another problem occurs when cracks in either surface are created, known as fretting fatigue. It is the more serious of the two phenomena because it can lead to catastrophic failure of the bearing.

An associated problem occurs when the small particles removed by wear are oxidized in air. The oxides are usually harder than the underlying metal, so wear accelerates as the harder particles abrade the metal surfaces further.