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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , Properties, Composition, and Industrial Application of Engineering Materials: Metals-Ferrous: Tool steels, and stainless steels. Non-ferrous /metals: aluminum alloys. Ceramics- Glass, optical fiber glass, ceramets., Composites- Fiber reinforced composites, Metal matrix Composites. Smart materials- Piezoelectric materials,, shape memory alloys, semiconductors, and super-insulators., Metal Joining Processes: Soldering, Brazing and Welding: Definitions. Classification and methods of soldering,, brazing, and welding. Brief description of arc welding, Oxy-acetylene welding, Introduction to TIG welding and, MIG welding., Heat Transfer Applications: Review of modes of Heat Transfer; Automobile Radiators; Condensers and, evaporators of refrigeration systems; Cooling of Electrical and Electronic Devices; Active, Passive, and Hybrid, Cooling., , Q. Define engineering materials? What are ferrous and non-ferrous metals with examples?, Materials are the solid substances which are used for various applications. These materials possess different, properties. The metals are classified into two categories. Ferrous & non ferrous metals., , FERROUS METALS, , NONFERROUS METALS, , Ferrous metals contain iron as constituent, Ferrous metals are attracted by Magnets, They are much denser than non-ferrous metals, Pig iron , Wrought iron ,Cast iron, Mild Steel, Alloy, steels, Tool steels, Stainless steel, etc, Cost Less, , They do not contain iron as constituent, Non-Ferrous metals are not attracted by Magnets, They are much lighter than ferrous metals, Copper and its alloys, Brass, Bronze, Lead and its, alloys, Aluminum alloys ,Nickel and its alloys, Cost More, , Q.Explain composition, properties, applications of Ferrous metals:, Sl. Metals, No, 1, Pig iron, , 2, , Wrought, Iron, , 3, , Cast Iron, , 4, , Gray Cast, iron, , 5, , White Cast, iron, , Composition, , Properties, , Applications, , 92% iron, 3-4% carbon, Small amount of sulphur,, manganese, phosphorous, other, impurities, 99.5% iron, 0.05-0.25% carbon,, Small amount of sulphur,, manganese, phosphorous,, silicon, 90-92% iron, 2-4.5% carbon, 13% silicon, Small amount of, sulphur, manganese,, phosphorous, , Rich in carbon, very hard, and more brittleness, , Forging basic tools, for, making wrought iron, cast, iron and steel., , Soft, ductile, High, elasticity and better tensile, strength., , Decorative applications like, fences, gates, railings,, balcony, etc, , More brittle, low melting, point, Good fluidity,, castability, Machinability,, Good resistance to wear, and deformation, Good castability, good, machinability, vibration, damping characteristics,, good fatigue resistance., Extremely hard, brittle and, wear resistance., , Automotive engine blocks,, gears, flywheels, brake, discs, frames, body machine, bases etc, , 90-92% iron, 3-3.5% carbon,, 1.3-3.3% silicon,Small amount, of sulphur, manganese,, phosphorous, 90-92% iron, 1.8-3.6% carbon,, 0.5-2% silicon,Small amount of, sulphur, manganese,, , Dept. of Mechanical Engg., BKIT, Bhalki,, , Automotive engine blocks,, gears, flywheels, brake, discs, frames, body machine, bases etc, Mill liners, railroad shoes, hot blasting nozzles, , car, wheels, sprockets, rolling, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 1

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , 6, , Malleable, cast iron, , 7, , Ductile cast, iron, , phosphorous, 90-92% iron, 2-3% carbon, 0.61.3% silicon, Small amount of, Sulphur, manganese,, phosphorous, 90-92% iron, 3.2-4.2% carbon,, 1.1-3.5% silicon, Small amount, of Sulphur, manganese,, phosphorous, , Castability, moderate, strength, toughness,, corrosion resistant shock, resistant., Good machinability,, strength, shock resistant., , mill, crushers, pulverizes., Connecting rods, joint, yokes, gears, crankshaft,, hubs, flanges and heavy, duty applications., Roll punches, dies, sheet, metal works., , Q. Classify and explain various types of Steel (10 m), 1, , STEELS:, Low carbon, steel /Mild, Steel (MS), , 2, , Medium, carbon steel, , 3, , High carbon, steel, , 4, , Tool steel:, High Speed, Steel (HSS)., , 5, , Stainless, steel, , 95-98% iron, 0.03-0.25%, carbon, small amount of, Sulphur, nickel, manganese,, phosphorous, chromium, copper, etc., 95-98% iron, 0.25-0.59%, carbon, Small amount of, Sulphur, nickel, manganese,, phosphorous, chromium, copper, 95-98% iron, 0.6-1% carbon,, and Small amount of Sulphur,, nickel, manganese,, phosphorous, chromium, copper, 14-22% tungsten, 3-5%, chromium, 0.7-0.8% carbon, 1-2% vanadium 5-10% cobalt,, Molybondum, and vanadium., 11-25% chromium,, 8% nickel, 0.03% Carbon, small amount of nickel, silicon,, Molybondum., , More malleable & ductile,, less strength, Poor surface, hardness, wear resistance., good machanabity,, formability characteristics,, Balance between strength, and ductility bit stronger,, wear resistant., , Small gears, screws, nails,, nuts, rivets, pins small, forgings, body components., , More strength, longer life,, wear resistant, superior, surface hardness, brittle., , Springs, wires, hacksaw, blades, chisels, hammers,, drills, taps, discs etc., , Machined components,, rods, axles, crankshafts., , Toughness, hot strength., Cutting tools for metal, red hardness up to a cutting operations. drill, bits, lathe tools, milling, temperature of 620C., cutters, reamers, Kitchen utensils, food, Corrosion resistant, High, processing, architectural, oxidation resistance, self, applications, surgical, healing., instruments, shafts shaving, blades, heat exchangers,, marine applications, sprigs, , Discuss important Alloy Steels:, 1.Chromium steel: Chromium improves corrosion resistance, harden ability, toughness, provides resistance to, abrasion, resistance to heat and causes improvement in cutting ability. It finds its application in balls, rollers and, races for bearings, armor plate, safes, and cutting tools. A Chromium addition of 4% to 1% carbon steel can, render it useful in making permanent magnets., 2.Manganese steel: Manganese improves strength, hardness, toughness. It is a de-oxidizer and provides high, strength at elevated temperatures. It contains usually over 1.5% Manganese, 0.4 to 0.55%carbon. Its application, includes axles gears, shafts, etc. A special alloy steel called Mangalloy which consists of 11 to 15%. Manganese, and o.8 to 1.25% carbon is a non-magnetic steel with anti-wear properties, abrasion resistant and heavy impact, resistant. This is why it is used in rock crushers, mining cement mixtures, crawler treads for tractors, etc., Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 2

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , 3.Molybdenum steel: Molybdenum increases tensile strength and creep strength at high temperature, increases, wear resistance, heat resistance and corrosion resistance and provides the ability to deep harden. Molybdenum, alloys are used in high temperatures heating element, forging dies, extrusions, radiation shields, etc Sprayed, coatings of molybdenum alloys are used in automotive pistons to improve wear and reduce friction., 4.Tungsten steel: Tungsten increases strength, hardness, toughness, provides shock resistance to softening at high, temperatures, and wear resistance. The Tungsten alloys (Tungsten carbide) is used in industrial cutting tools. The, high melting point of tungsten makes it a good material for rocket nozzles. Hastelloy and Stllite which are, superalloys containing tungsten is used in the blades of a turbine., 5.Invar steel: which consists of 36% Nickel and 64% iron has very less co-efficient of expansion and is therefore, used in measuring instruments, clock pendulum, etc., , COMPOSITION, PROPERTIES, APPLICATIONS OF NONFERROUS METALS:, 1, , Copper, , 99.3% minimum copper, content, , 2, , Brass, , Alloy of copper and zinc,, 5-45% of zinc, small, amount of lead, tin, silicon, etc., , 3, , Bronze, , 88% copper, 11% tin,, small amount of, phosphorous, lead etc., , 4, , Alumin 91.2 - 97.6% aluminum,, um alloy small amount of, chromium, copper, iron,, magnesium, manganese,, silicon., , Light material, easy machinable,, High electrical conductivity,, reflectivity, and corrosion, resistance, light weight and high, strength-to-weight ratio, , 5, , Lead, alloys, , 1-6% antimony, tin, iron,, small amount of copper,, zinc, silver, arsenic, or, traces of nickel., , Malleable, ductile, corrosion, resistant, heavy, poor conductor, and poisonous in nature., , 6, , Nickel, alloys, , 3% Nickel and 0.2 to, 0.35% carbon., , High strength, toughness,, excellent corrosion resistance,, good machining properties, good, electrical, magnetic properties., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Pure copper is very ductile and, weak, Corrosion resistant,, malleable, good conductor of heat, and electricity. Properties of, copper are improved by adding, alloying element and metal, working., , Electrical wires, cables,, refrigeration tubing, Utensils,, injectors, valve bodies, heat, exchangers, pump bodies and, fittings,, , Corrosion resistant, malleable, good, conductor of heat and electricity., Properties of copper are improved, by adding alloying element and, metal working., , Utensils, injectors, valve, bodies, heat exchangers, taps,, pump bodies and fittings,, electrical wires, cables, nuts,, refrigeration tubing. bolts,, Wires, rods, sheets, springs,, bellows, clutch discs, valve, parts electrical contacts, pump, casings, marine, condensers,, Aircrafts, automotives,, spacecrafts, marine, electrical,, fire fighting applications,, mirrors, reflectors etc, , Soft, corrosion resistant, better, hardness and fatigue, good, conductor of heat and electricity., , Electrical fuses, connectors, for lead–acid batteries boiler, plugs, electrodes, high, voltage power cables, fusible, alloys, radiation shield etc., Locomotive forgings, axles,, piston rods, parts of a ship., Aerospace, power generation,, petrochemical applications,, electroplating etc., , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 3

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , Polymers: A polymer is a large molecule made up of chains or rings of linked repeating subunits, which are, called monomers. polymer comes from the Greek word poly-means "many" and mer means "parts" Ex. many, synthetic organic materials used as plastics and resins., Sl.no. Thermosetting plastic, , Thermoplastic polymer, , 1, , Always remain in a permanent solid state, , Can be remelted back into a liquid, , 2, , Used for sealed products due to their resistance, to deformation., , Used for plastic bags or high-stress mechanical, parts., , 3, , Enhances chemical resistance, heat resistance, and structural integrity., , High strength, shrink-resistance and easy, bendability., , 4, , Advantages, • More resistant to high temperatures than, thermoplastics, • Highly flexible design, • Thick to thin wall capabilities, • Excellent aesthetic appearance, • High levels of dimensional stability, • Cost-effective, , Advantages, • Highly recyclable, • Aesthetically-superior finishes, • High-impact resistance, • Remoulding/reshaping capabilities, • Chemical resistant, • Hard crystalline or rubbery surface options, • Eco-friendly manufacturing, , 5, , Disadvantages, • Cannot be recycled, • More difficult to surface finish, • Cannot be remoulded or reshaped, , Disadvantages, • Generally, more expensive than thermoset, • Can melt if heated, , Ceramics: Ceramics are compounds between metallic and nonmetallic elements for which the inter-atomic, bonds are either ionic or predominantly ionic. The term ceramics comes from the Greek word keramikos which, means ‘burnt stuff’., Types & applications of ceramics: Ceramics greatly differ in their basic composition. The properties of ceramic, materials also vary greatly due to differences in bonding, and thus found a wide range of engineering applications., Based on their composition, , Based on their application, , Oxides, Carbides, Nitrides, Sulphides, Fluorides, , Glasses, Clay products, Refractories, Abrasives, Cements, , Optical fiber glass: Optical fiber uses light to carry voice and data messages. The inner core is made, of glass or plastic, and the cable is lighter in weight and less bulky than copper wiring. Optical fiber can be used, over great distances or for shorter runs as well. It can carry a tremendous amount of data at very high speeds., Advantages of Glass Optical Fiber:, Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 4

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , 1.Glass optical fiber enables you to use a photoelectric sensor in areas where you wouldn’t normally be able to, use them. The sensors are available with a wide range of housings, mounting styles, and features for your specific, application., 2.Glass fiber cables can be used in high-temperature applications like furnaces, ovens, and condensers in large, engines, and they can also be used in extremely low temperature areas such as cold storage warehouses., 3.Since glass cores are efficient at transmitting light and allow for significantly higher transfer speeds, glass, optical fibers can be used over long sensing distances., 4.Even more, glass fiber optic cables are optimized for small spaces and small targets. They can be used with both, visible red and infrared light and are compatible with a long list of fiber heads., Ceramets: are combination of ceramics and metals in order to get the ceramic available to bear hightemperature and uneasy to be broken. The cermets with ceramic-base are classified into 3 categories:, 1.Oxidize-base cermets,. used as the missile nozzle insert, crucible of melting metals & metallic cutting tools., 2. Carbide-base cermets, used as cutting tools, high-temperature bearing, sealing ring,drawing die sleeve and, turbine blade etc, 3. Nitride-base cermets ,taking TiN,BN,SIN and TaN as substrates with high hardness, thermal vibration, resistance and good high-temperature creep etc performances .which are rarely used, , What are composites? Write the classifications of composites?(8m), Composites: A composite is a structural material that consists of two or more combined constituents that are, combined at a macroscopic level & are not soluble in each other.Ex: Plywood, Car rubber tyre, Cutting tools., Classification of composite materials:, , Q. Explain the classifications of composites with their suitable examples? (10M), 1.Polymer Matrix Composite (PMC):It is the material consisting of a polymer (resin) matrix combined with, a fibrous reinforcing dispersed phase. Polymer Matrix Composites are very popular due to their low cost and, simple fabrication methods., PMC- Typical properties: Low cost., High tensile strength, Good abrasion resistance;, , High stiffness, Good corrosion resistance, , High Fracture Toughness, Good puncture resistance, , The main disadvantages of Polymer Matrix Composites (PMC) are:, Low thermal resistance, , High coefficient of thermal expansion, , Polymer Matrix Composites (PMC) are used for manufacturing: Secondary load-bearing aerospace structures,, boat bodies, canoes, kayaks, automotive parts, radio-controlled vehicles, sport goods (golf clubs, skis, tennis, racquets, fishing rods, bullet-proof vests and other armor parts, brake and clutch linings., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 5

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , 2.Metal Matrix Composite (MMC):It is a material consisting of a metallic matrix combined with a ceramic, (oxides, carbides) or metallic (lead, tungsten, molybdenum) dispersed phase., MMC- Typical properties, High strength even at elevated temperatures, High stiffness (modulus of elasticity), Low coefficient of thermal expansion, , High thermal conductivity, High wear resistance, High thermal stability, , Excellent abrasion resistance, Good creep resistance, Low density, , 3. Ceramic Matrix Composite (CMC):It is a material consisting of a ceramic matrix combined with a ceramic, (oxides, carbides) dispersed phase. Ceramic Matrix Composites are designed to improve toughness of, conventional ceramics, the main disadvantage of which is brittleness., CMC-Typical properties, High strength even at elevated temperatures, High thermal shock resistance, High corrosion resistance at high temperatures, , High thermal stability, High stiffness, High toughness, , Excellent abrasion resistance, Good creep resistance, Low density, , Ceramic matrix composites are used for, Manufacturing combustion liners of gas turbine engines, hot gas recirculating fans, heat exchangers, rocket propulsion components, filters for hot liquids, gas-fired burner parts,, furnace pipe hangers, immersion burner tubes., Classification of composite materials II (based on reinforcing material structure):, , 1.Particulate Composites, Particulate Composites consist of a matrix reinforced by a dispersed phase in form of particles., ➢ Composites with random orientation of particles., ➢ Composites with preferred orientation of particles. Dispersed phase of these materials consists of twodimensional flat platelets (flakes), laid parallel to each other., 2. Fibrous Composites, ➢ Short-fiber reinforced composites. Short-fiber reinforced composites consist of a matrix reinforced by a, dispersed phase in form of discontinuous fibers (length < 100*diameter)., o Composites with random orientation of fibers., o Composites with preferred orientation of fibers., ➢ Long-fiber reinforced composites. Long-fiber reinforced composites consist of a matrix reinforced by a, dispersed phase in form of continuous fibers., o Unidirectional orientation of fibers., o Bidirectional orientation of fibers (woven)., 3. Laminate Composites: When a fiber reinforced composite consists of several layers with different fiber, orientations, it is called multilayer (angle-ply) composite., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 6

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , Q. What are Characteristics of Composites:, 1. Composites can be very strong and stiff, yet very light in weight, so ratios of strength-to-weight and, stiffness-to-weight are several times greater than steel or aluminum, 2. High specific strength and modulus, as well as high fatigue strength and fatigue damage tolerance, 3. Toughness is often greater., 4. Designable or tailorable materials for both microstructure and properties, 5. Production of both material and structure or component in a single operation - manufacturing flexible, netshape, complex geometry, 6. Corrosion resistance and durable, 7. Other unique functional properties - damping, low CTE (coefficient of thermal expansion), , Q. What are the advantages and dis-advantages of composites? (10), Advantages of composites, , Disadvantages of composites, , Higher directional mechanical properties, Higher toughness than ceramics and glasses, Easy to machine, Higher Fatigue endurance., Lower density (20 to 40%), Can combine other properties (damping, corrosion)., , Not often environmentally friendly., Low recyclability., Anisotropic properties., Can be damaged., Cost can fluctuate., Low reusability, Matrix degrades, , Q. Explain the various applications of composites? (8M), Applications: Aerospace, 1. A wide range of load-bearing and non-load-bearing components are used in both fixed-wing and rotary, wing aircraft., 2. Air frames, wing spars, spoilers, tail-plane structures, fuel tanks, drop tanks, bulkheads, flooring,, helicopter rotor blades, propellers, and structural component., 3. Pressured gas containers, domes, nose and landing gear doors, fairings, engine nacelles., 4. Air distribution ducts, seat components, access panels., 5. Modern light aircraft., 6. Rocket nozzles and re-entry shields., 7. Rocket motor casings and rocket launchers., Automotive Engineering, 1. Increasing interest in weight reduction in order to improvement in fuel economy, majority of automotive, applications involve glass-reinforced plastics for vehicle body moldings, panels and doors., 2. Selective reinforcement of aluminum alloy components for pistons and connecting rods., 3. Fuel tanks, disc brakes, brake parts, clutch plates, steering wheel, bumpers, radiator tanks support etc., Sports: Tennis rackets, cricket bats, golf clubs, fishing rods, boats, oars, archery equipment, canoes and canoeing, gear, surf boards, wind-surfers, skateboards, skis, ski-poles, bicycles, and protective equipment., General applications: Kitchen equipments, electrical equipments, motor-cycle crash helmets, television and, computer casings, and furniture., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 7

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , Smart materials: Smart materials, called also intelligent or responsive materials, are designed materials that, have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as, stress, temperature, moisture, pH, electric or magnetic fields, light, or chemical compounds., Output, Input, , Charge/ Current, , Magnetization, , Strain, , Temperature, , Light, , Electric Field, , Conductivity, Permittivity, , Electromagnetic, Effect, , Reverse, Piezoelectricity, , Ohmic Resistance, , Electro Optic, effect, , Magnetic, Field, , Eddy Current, Effect, , Permeability, , Joule Effect, Magnetostriction, , Magneto caloric, Effect, , Magnet oOptic effect, , Stress, , Direct Piezo, Electric Effect, , Villary Effect, , Elastic Modulus, , ThermoMechanical Effect, , Photo elastic, Effect, , Heat, , Pyroelectric, Effect, , Thermo, Magnetization, , Thermal, Expansion, Phase Transition, , Specific Heat, , Thermo, Luminescence, , Light, , Photo Voltaic, Effect, , Photo, Magnetization, , Photo-striction, , Photo-Thermal, effect, , Refractive, index, , Principle of piezoelectric effect: According to Newton's Law this force is equal to the product of the, acceleration and the seismic mass. By the piezoelectric effect a charge output proportional to the applied force is, generated. Since the seismic mass is constant the charge output signal is proportional to the acceleration of the, mass. Piezoelectric materials are materials that produce an electric current when they are placed under mechanical, stress. The piezoelectric process is also reversible, so if you apply an electric current to these materials, they will, actually change shape slightly (a maximum of 4%)., There are several materials that we have known for some time that posses piezoelectric property, including bone,, proteins, crystals (e.g. Quartz) and ceramics (e.g. Lead Zirconate Titanate)., Applications of piezoelectric effect:, 1.Computers: Inkjet printers, disk drives., 2. NASA Applications: Electro-optical Device Technologies, Precise positioning, Switches, 3. Multifunctional Membranes: Antennas, Reflectors, Smart skins, Tuning & positioning inflatable structures, 4. Biomedical: Portable Artificial organs, lightweight fetal heart monitor, Ultrasonic imaging Tissue engg., 5. Automotive: Fuel atomizer, air flow sensor, airbag sensors, seat belt buzzers, knock sensors., 6. Consumers: LPG stove lighters, cigarette lighters, speakers, telephones, quartz crystals in watches., , Shape Memory Alloys: A shape memory alloy (SMA, smart metal, memory metal, memory alloy, muscle, wire, smart alloy) is an alloy that "remembers" its original, cold‐forged shape: returning the pre‐ deformed shape, by heating., Types: The three main types of shape memory alloys are the copper-zinc aluminium-nickel, copperaluminium-nickel, and nickel-titanium (NiTi) alloys but SMA's can also be created by alloying zinc, copper,, gold, and iron., Applications of shape memory alloy:, , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 8

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , • Aircraft Boeing, General Electric Aircraft Engines, Goodrich Corporation, NASA, and All Nippon Airways, developed the Variable Geometry Chevron using shape memory alloy that reduces aircraft's engine noise., • Robotics There have also been limited studies on using these materials in robotics (such as "Roboterfrau Lara"),, as they make it possible to create very light robots. Weak points of the technology are energy inefficiency, slow, response times, and large hysteresis., • Medicine Shape memory alloys are applied in medicine, for example, as fixation devices for osteotomies in, orthopaedic surgery, in dental braces to exert constant tooth‐moving forces on the teeth and in stent grafts where, it gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature., , Conductor, Semi-conductors, Insulators:, Characteristics Conductor, , Semiconductor, , Insulator, , Definition, , A conductor is a material that, allows the flow of charge, when applied with a voltage., , A semiconductor is a material, whose conductivity lies between, conductor & insulator, , An insulator is a material, that does not allow the, flow of current., , Temperature, Dependence, , The resistance of a conductor, increases with an increase in, temperature., , Its decrease with increases in, temperature. Thus, it acts as an, insulator at absolute zero., , Insulator has very high, resistance but it still, decreases with, temperature., , Conductivity, , The conductors have very high, conductivity (10-7 Ʊ /m), thus, they can conduct electrical, current easily., , They have intermediate, conductivity ((10-7 Ʊ /m to 1013 Ʊ /m), thus they can acts as, insulator & conductor at different, conditions., , They have very low, conductivity (10-13 Ʊ, /m), thus they do not, allow current flow., , Conduction, , The conduction in conductors, is due to the free electrons in, metal bonding., , The conduction in semiconductor, is due to the movement of, electron & holes., , There are no free, electrons or holes thus,, there is no conduction., , Band gap, , There is no or low energy, gap between the conduction &, valance band of a conductor. It, does not need extra energy for, the conduction state., , The band gap of semiconductor, is greater than the conductor but, smaller than an insulator i.e. 1, eV. Their electrons need a little, energy for conduction state., , The band gap in insulator, is huge (+5 eV), which, need an enormous, amount of energy like, lightning to push, electrons into the, conduction band., , Resistivity, , Low (10-5 Ω/m), , Normal (10-5Ω/m to 105 Ω/m), , Very High (105 Ω/m), , Coefficient of, Resistivity, , It has positive coefficient of, resistivity i.e. its resistance, increase with temperature, , It has negative coefficient of, resistivity., , The coefficient of, resistivity of an insulator, is also negative but it has, very huge resistance., , Absolute Zero, , Some special conductors turn, , The semiconductors turn into, , The insulator’s resistance, , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 9

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, into superconductors when, supercooled down to absolute, zero while other have finite, resistance., Valence Electron, in Outer Shell, , Examples, , Application, , insulator at absolute zero., , increase when cooled, down to absolute zero., , 1 Valence electron in outer, shell., , 4 Valence electron in outer shell., , 8 Valence electron in, outer shell., , Gold, Copper, Silver,, Aluminum etc, , Silicon, Germanium, Selenium,, Antimony, Gallium Arsenide, (known as semi insulator),Boron, etc., , Rubber, Glass, Wood,, Air, Mica, Plastic, Paper, etc., , The metals like iron & copper, etc. that can conduct electricity, are made into wires and cable, for carrying electric current., , Semiconductors are used every, day electronic devices such as, cellphone, computer, solar panel, etc as switches, energy converter,, amplifiers, etc., , The insulators are used, for protection against, high voltages &, prevention of electrical, short between cables in, circuits., , M, METAL JOINING PROCESS: Metal Joining is defined as joining of two metal parts either temporarily or, permanently with or without the application of heat or pressure., 1. PERMANENT JOINT: 1.Welding 2. Brazing 3. Soldering. 4. Rivets, 2. NON-PERMANENT (TEMPORARY) Examples 1. Bolt& Nut, 2.Screw, 3. Clamping,4.Couplings,5.Joints, 3. SEMI-PERMANENT: Examples 1. Adhesive Bonding, 2.Glues, , The above processes are an important for the following reasons: 1. The product is impossible to manufacture as, a single piece.2.Easier & more economical to manufacture as individual components., Welding: is process of joining two materials (similar or dissimilar) by the application of heat with or without, the application of pressure and addition of filler material, Advantages: 1.Any metal/alloy can be welded, 2.Any shape of component can be generated, , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 10

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , 3.Strength of the joint will be the same as that of the base metal, 4.General welding equipment is not very costly., 5. Portable welding equipments can be easily made available., 6. Welding permits considerable freedom in design, Disadvantages / Limitations:, 1. Harmful radiation and fumes may be generated during the process, 2. Residual stresses may be setup in the welded joint, 3. Jigs, and fixtures may also be needed to hold and position the parts to be welded, 4. Edges preparation of the welding jobs are required before welding, 5. Skilled operator may be required, 6. Structure of the weld portion will differ from parent metal., Application: Fabrication of aircraft & automobile components, Bridges, Building structures, Ships, Pressure, vessel, pipes, etc., , Classification of Welding:, , AC Arc Welding, ➢, ➢, ➢, ➢, ➢, ➢, ➢, , DC Arc Welding, , Alternating Current (from Transformer), More efficiency, Power consumption less, Cost of equipment is less, Higher voltage – hence not safe, Not suitable for welding nonferrous metals, Not preferred for welding thin sections, ➢ Any terminal can be connected to the work or, electrode, , ➢, ➢, ➢, ➢, ➢, ➢, ➢, ➢, , Direct Current (from Generator), Less efficiency, Power consumption more, Cost of equipment is more, Low voltage – safer operation, suitable for both ferrous non ferrous metals, preferred for welding thin sections, Positive terminal connected to the work, ➢ Negative terminal connected to the electrode, , ARC WELDING: Arc welding is the process of joining metal – steel in this case – using electricity. Rather, than most other formats, which generally use gas, this process uses electricity to create enough heat to melt the, metal and fuse it together during cooling. Here an electric arc is used as the heat source. An electric arc is a, continuous stream of electron flowing between two electrodes into a medium. This is used to melt the surface and, deposit the metal from the electrode resulting in a joint on cooling. In arc welding processes the power supply, Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 11

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , could be AC or DC, the electrode could be consumable or non-consumable and a filler material may or may not, be used., , GAS WELDING: Gas welding is a fusion welding process. Here the heat is generated by the combustion of, oxygen or air and a gas (such as acetylene, hydrogen, butane, methane petroleum gas, etc) is used to join metals., A strong flame is produced when the mixture of gases are ignited. This flame has a very high temperature which, melts and fuses the metal parts. The quantities of gases are to be regulated for controlling the weld flame. A filler, metal rod is used to supply molten metal at the joint. It is used for repair work, for joining thin walled parts of, steel and non-ferrous alloys.Two familiar fuel gases used in gas welding are:, ➢ Mixture of oxygen and acetylene gas – called oxy-acetylene welding process. (upto 3200oC), ➢ Mixture of oxygen and hydrogen gas – called oxy-hydrogen welding process.( 2500oC)., Oxy-acetylene Gas welding: When the acetylene is mixed with oxygen in correct proportion and ignited a, flame is produced. The flame will have a temperature of about 3200oC. A gas torch is used for the, purpose. Acetylene gas is let out through the torch and ignited first. The gas catches fire and a flame is, produced. Oxygen is then let out to sustain the flame. By regulating the control valves the quantities of, both the gases can be adjusted, so that the desired flame is produced., Acetylene gas has more available carbon (92.3 %) and hydrogen (7.7 %) by weight. The heat is released, when the carbon breaks away from hydrogen to combine with O2 and burn. The chemical reaction involved in, burning of acetylene is 2C2H2 + 5O2 = 4CO2 + 2H2O + Heat, Operation: The equipment consists of two large cylinders: one containing oxygen at high pressure and the other, containing acetylene gas. Pressure regulators are fitted on the respective cylinders to control the pressure of, the gas to the welding torch. A welding torch having controlling knobs which mixes both oxygen and, acetylene in proper proportions and burn the mixture. A spark ignites the mixture at its tip. The resulting, flame at the tip having a temperature of 3200oC which is sufficient enough to melt the work piece. A slight, gap usually exists between the two work piece, a filler metal is used to supply the additional material to fill, the gap., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 12

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , Advantages of Gas welding, 1. Process is simple, 2. Controlling temperature is easy., 3. Easy maintenance., 4. Equipment is portable., 5. Eliminates skilled operator, 6. Temperature of the flame can be controlled depending upon the type & thickness of the material., Disadvantages Gas welding, 1. Cannot be used for heavy section., 2. Flame temperature is less than the arc temperature., 3. Acetylene gas is highly explosive and expensive., Applications: For joining thin section. Most of the ferrous & non-ferrous can be gas welded. Automotive &, aircraft industries in sheet metal joining., TYPES OF GAS FLAMES: Flame is established by burning of the two gases mixture at the outlet of blow, pipe or torch. The proportion of gasses in the mixture is controlled by controlling the flow rate of each of the two, gasses. Here, it should be clear that burning of acetylene generates heat and oxygen only supports acetylene in, burning. Insufficient supply of oxygen leaves acetylene unburnt in atmosphere creating pollution and adding cost, of waste acetylene.Three types of flames can be produced. Fig. shows the types of flame., , 1.Neutral Flame : (Oxygen : Acetylene - 1:1):Approximate volumes of gases are in equal proportions., Temperature of the flame is about 3300oC. Flame is light blue in colour. It is surrounded by outer flame produced, by the combination of oxygen and Co, H2 in the inner zone. This type of flame does not bring about any chemical, , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 13

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , change in the molten metal. This type of flame is used for welding mild steel, cast iron, copper aluminium and, stainless steel. This is the correct flame for welding., 2.Oxidising Flame : (Oxygen : Acetylene - 1.5:1) After establishing neutral flame, if the oxygen content, is further increased the resulting flame is oxidising in nature.The flame will be small short cone, dark blue in, colour and more pointed than in the first case. The outer envelope is much shorter than the first.The temperature, rise is as high as 3480oC.The excess oxygen at high temperature tends to combine with many metals to form hard,, brittle low strength oxides. This type of flame finds limited use in welding.A slightly oxidising flame is used in, welding copper base alloys, zinc base alloys., 3.Reducing flame : (Oxygen : Acetylene - 1:1.5)After establishing neutral flame, if the volume of, acetylene gas is increased then the resulting flame is reducing in nature. The outer flame envelope is longer than, that of neutral flame and is usually much brighter. A reducing flame does not completely consume the available, carbon, therefore the temperature is lower and the un-consumed carbon is forced into the molten metal. A, reducing flame ensures the absence of oxidation, metals that tend to absorb carbon should not be welded with this, flame. Ex. Non-ferrous, high carbon steels. A carburizing flame contains excess acetylene than a reducing flame., , INERT GAS SHIELDED WELDING (TIG AND MIG): In any type of welding we require flux to, avoid oxidation of weldment to maintain proper strength of the joint. In this regard, to keep the atmospheric air, away from the welding pool, inert gases like argon, helium, carbon dioxide, are used for surrounding the arc to, keep atmosphere away. It not only results in production of sound weld but also enables welding of such metals, which are otherwise difficult to weld. Important techniques of this type of welding are Tungsten Inert gas and, Metal inert gas welding., , TIG Welding :This is similar to arc welding. Additionally, it requires a cylinder of inert gas, valve, pressure, regulator and hose pipe with sprayer to spray inert gas in the welding pool. A non-consumable tungsten electrode, is used to establish arc. Sometimes inert gas sprayer is also mounted in the electrode holder. As per the, requirement additional filler metal can be provided from the outside to make up the joint. This is suitable for, welding of most of the metal and alloys except lead and zinc due to their very low melting point. TIG welding is, suitable for high quality welding., , TIG Welding/ Gas Tungsten Arc Welding (GTAW), , MIG Welding, , MIG Welding: This is similar to TIG welding. At the place of non-consumable tungsten electrode, a, consumable metal electrode is used in the form of continuously fed metal wire. The electrode wire and inert gas, are fed through welding gun. Only DC is recommended for this type of welding giving positive polarity to, electrode wire. Feeding speed of electrode wire is adjusted according to the welding speed. This is used for the, Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 14

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ELEMENTS OF MECHANICAL ENGG. (21EME15) MODULE-2 NOTES, ENGINEERING MATERIALS, JOINING PROCESS, HEAT TRANSFER APPLICATIONS, , welding of carbon steel, low alloys steel, stainless steel and alloys of the metal exhibiting resistance to heat. IG, may be preferable for thicker material and for fill passes in thick-wall pipe welds. MIG welding can be used on all, thicknesses of steels, on aluminium, nickel, and even on stainless steel, etc., , Q.Differentiate between Welding, Soldering and Brazing., Welding, , Soldering, , Brazing, , Strength of a welded joint may be, more than the strength of base metal., , These are weakest joint. Use to, make electrical contacts generally., , These are stronger than soldering, but weaker than welding., , Temperature ranges from 5000-60000c, , Temperature ranges from 150-3500c, , ranges from 4500c to 9000c, , Work piece to be joined need to be, heated till their melting point., , No need to heat the work pieces., , Work pieces are heated but below, their melting point., , Mechanical properties of base metal, may change at the joint due to heating, and cooling., , No change in mechanical properties, after joining., , May change in mechanical, properties of joint but it is almost, negligible., , Heat cost is involved and high skill, level is required., , Cost involved and skill requirements, are very low., , Cost involved and sill required are, in between others two., , Heat treatment is generally required to, eliminate undesirable effects of, welding., , No heat treatment is required., , No heat treatment is required after, brazing., , No preheating of work piece is, required before welding as it is, Carried out at high temperature., , Preheating of work pieces before, Soldering is good for making good, quality joint., , Preheating is desirable to make, strong joint as brazing is carried, out at relatively low temperature., , Dept. of Mechanical Engg., BKIT, Bhalki,, , Dr.Rajashekar Matpathi, M.E, Design ,Ph.D, , 15