Machine Design & Shop Practice_MSDP (PDF)

 The amount of the offset is usually 0.2% (0.002 in./in. of strain) for steel,  RECALL FOR ELEMENTS IN aluminum, and magnesium alloys.  MACHINE DESIGN & SHOP PRACTICE_MSDP (VIT_01)...

 The amount of the offset is usually 0.2% (0.002 in./in. of strain) for steel,  RECALL FOR ELEMENTS IN aluminum, and magnesium alloys.  MACHINE DESIGN & SHOP PRACTICE_MSDP (VIT_01)  Elastic limit is the maximum stress to which standardized test specimen  Stress or unit stress, s, is measured may be subjected without a in pounds or kips per square inch permanent deformation. (psi or ksi) A kip is the same as 1000 lb. ( a  Proportional limit is defined as the contraction of kilo-pounds) stress at which the stress-strain curve deviates from a straight line. Strain means the deformation per unit gage length, in. per in.  Modulus of elasticity (E) is the proportionality constant in tension. It Ultimate stress or tensile strength, is the slope of the straight part of the the highest point on the stress-strain stress-strain curve. It is a measure curve, is the maximum load divided of stiffness. by the original area before straining occurs.  Factor safety (better be called design factor) N is a number that is  Yield point (YP) the stress at which a divided into a criterion of strength in low or medium carbon steel order to obtain a design criterion. undergoes a marked elongation (Factor of safety has been called without an increase in load. "factor of ignorance")  Yield strength is the stress for a  Computed or nominal stress is a specified deviation from the straight stress computed from a stress part of the stress-strain curve. equation.  Age hardening (precipitation hardening) occurs in some metals,  Charpy test is one in which a notably certain stainless steel, specimen, supported at both ends aluminum, and copper alloys, at as a simple beam, is broken by the ambient temperature after solution impact of a falling pendulum. The heat treatment, the process being energy absorbed in breaking the one of a constituent precipitating specimen is a measure of the impact from solid solution. Where used, the strength of the metal. consequences, include increased strength and hardness, decreased ductility. Aging at moderately  Cold shortness is brittleness of elevated temperature expedites the metals at ordinary or low process and is called artificial aging. temperatures.  Alloy is a substance with metallic  Cold working is the process of properties composed of two or more deforming a metal plastically at a elements of which at least one is a temperature below the metal. recrystallization temperature and at a rate to produce strain hardening. Cold-drawn steel is frequently used  Alloying elements in steel are because it increases strength and usually considered to be the metallic  machinability, and improves surface elements added for the purpose of finish. It reduces ductility. modifying the properties. Commercial amounts of cold working of steel are of the order of  Anisotropy is the characteristic of 10-20%. exhibiting different properties when tested in different directions (as  Damping capacity is the ability of a tensile strength "with the grain" or material to absorb or damp "across the grain"). vibrations, which is a process of absorbing kinetic energy of vibration owing to hysteresis. The absorbed  Brittleness is a tendency to fracture energy is eventually dissipated to without appreciable deformation. the surroundings as heat. At a  particular stress level, cast iron is a may take an occasional much better damping material than exceptionally high load without steel. breaking.  Decarburization is a loss of carbon  Elasticity is the ability of a material to from the surface of steel, occurring be deformed and to return to the during hot rolling, forging, and heat original shape. Stress is proportional treating, when the surrounding to strain only during an elastic medium reacts with the carbon (as deformation. oxygen and carbon combining).  Embrittlement involves the loss of ductility because of a physical or  Ductility is that property that permits chemical change of the material. permanent deformation before fraction in tension. There is no  Free carbon is that part of the absolute measure of ductility, but the carbon content of steel or iron that is percentage elongation and the in the form of graphite or temper percentage reduction of area are carbon. used as indices; the higher these indices, the more ductile the material  Hard drawn is a temper produced in is said to be. Ductility is the opposite a wire, rod, or tube by cold drawing of brittleness, but there is no sharp division line. For purposes of  Homogeneous material (have definition, homogeneity) has the same structure at all points. (Steel consists  it is frequently assumed that: Ductile of randomly oriented iron crystals of material →Elongation greater than different sizes, with other matter in 5% in 2-in. gage. between and is thus not homogeneous.  Brittle material →Elongation less than 5% in 2-In. gage. Ductility is  Isotropic materials have the same frequently a valuable property properties in all directions. (Wood because, by virtue of it, a member has a grain; rolled steel is not  isotropic.  Malleability is a material's susceptibility to extreme deformation  Izod test is a test in which a in rolling or hammering. specimen, supported at one end as  Mechanical properties are those that a cantilever beam, is broken by the have to do with stress and strain: impact of a falling pendulum. The ultimate strength and percentage energy absorbed in breaking the elongation, for example. specimen is a measure of the impact strength. impact values in the tables  Percentage elongation is the should be considered more extension in the vicinity of the qualitative than quantitative because fracture of a tensile specimen, the actual variation of samples from expressed as a percentage of the the same universe is quite wide. original gage length, as 20% in 2 in.  Killed steel is steel that has been  Percentage reduction of area is the deoxidized with a strong deoxidizing smallest area at the point of rupture agent, such as silicon or aluminum, of a tensile specimen divided by the in order to eliminate a reaction original area. between the carbon and oxygen during solidification. Ingots of killed  Physical properties exclude steel are sounder, containing fewer mechanical properties, and are other gas holes, and more homogeneous physical properties such as density, than non-killed or rimmed steel; conductivity, coefficient of thermal these are desirable characteristics expansion. for forgings and heavy rolled sections.  Plasticity is the ability of a metal to be deformed considerably without  Machinability is a somewhat rupture. In a plastic deformation, the indefinite property that refers to the material does not return to its relative ease with which a material original.shape can be cut.  Poisson's ratio is the ratio of the lateral strain (contraction) to the  longitudinal strain (extension) when which results in the optimum surface the element is loaded with a on rolled sheets. longitudinal tensile force.  Precipitation heat treatment brings  Solution heat treatment is the about the precipitation of a process of holding an alloy at a constituent from a supersaturated suitably high temperature long solid solution by holding the body at enough to permit one or more an elevated temperature, also called constituents to pass into solid artificial aging. In some alloys, solution and then cooling fast precipitation may also occur at enough to hold the constituents as a ambient temperatures, a process supersaturated solution. called aging. (Precipitation may occur with time.)  Stiffness is the ability to resist  Proof stress is that stress which deformation. It is measured by the causes a specified permanent modulus of elasticity in the elastic deformation of a material, usually range; the higher the modulus, the 0.01% or less. stiffer is the material.  Red shortness is a brittleness in steel when it is red hot.  Strain hardening is increasing the hardness and strength by plastic deformation at temperatures lower  Relaxation stresses are those not than the recrystallization range. due to applied loads or temperature gradients; they exist for various  Temper is a condition produced in a reasons, as unequal cooling rates, non-ferrous metal by mechanical or cold working, etc. thermal treatment.  Rimmed steel is incompletely deoxidized steel. Ingots of this steel  Toughness is the capacity of have a surface layer quite free of material to withstand a shock load slag inclusions and gas pockets, without breaking.  Transverse strength refers to the  Critical range has the same meaning results of a transverse bend test, the as transformation range. specimen being mounted as a simple beam; also called rupture  Drawing is often used to mean modulus. It is frequently applied to tempering, but this usage conflicts brittle materials, especially cast iron. with the meaning of the drawing of a material through a die and is to be  Work hardening is the same as avoided. strain hardening.  Graphitizing, and annealing process,  Wrought steel is steel that has been causes the combined carbon to hammered, rolled, or drawn in the transform wholly or in part into process of manufacture; it may be graphitic or free carbon; it is applied plain carbon or alloy steel to cast iron, sometimes to high- carbon steel.  Heat treatment is an operation or combination of operations involving  Hardening is the heating of certain the heating and cooling of metal or steels above the transformation an alloy in the solid state for the range and then quenching, for the purpose of altering the properties of purpose of increasing the hardness. the material. In the general case, hardening is any process of increasing the hardness of a metal.  Aging (and age hardening) is a change in a metal by which its structure recovers from an unstable  Malleablizing is an annealing or metastable condition that has process whereby combined carbon been produced by quenching or cold in white cast iron is transformed working. wholly or in part to temper carbon. Temper carbon is free (graphitic)  Annealing, a comprehensive term, is carbon in the form of rounded a heating and slow cooling of a solid nodules, characteristic forms in metal, usually done to soften it. graphitizing and malleablizing.  Normalizing is the heating of an iron- transformation range, followed by base alloy to some 100°F above the any desired rate of cooling. transformation range with subsequent cooling to below that  Transformation range for ferrous range in still air at room temperature. metals is the temperature interval The purpose is to produce a uniform during which austenite is formed structure. during heating; it is also the temperature interval during which  Spheroidizing is any heating and austenite disappears during cooling. cooling of steel that produces a rounded or globular form of carbide. Typically, it is a prolonged heating at  Hardness of a material is the a temperature slightly below the measure of its resistance to transformation range, usually indentation, and is one of the most followed by slow cooling; or, for significant properties because, small objects of high-carbon steel, it properly interpreted, it says much may be prolonged heating about the condition of the metal. alternately within and slightly below the transformation range.  Brinell, Rockwell, Vickers, and Shore Scleroscope are the most common instruments used to determine  Stress relieving (thermal) is the hardness. heating of a metal body to a suitable temperature (generally just below the transformation range for steel,  Brinell hardness number (BHN) is say 1100-1200°F) and holding it at the load in kilogram divided by the that temperature for a suitable time area of the surface of the indentation (1 to 3 hours for steel) for the in square millimetres. purpose of reducing internal residual stresses  Hardenability is the capacity of steel. to through-harden when cooled from  Tempering is a reheating of above its transformation range. hardened or normalized steel to a temperature below the  Case hardening of iron base alloys factor of 4, and assuming that the is a process of surface hardening stress concentration factor K= 1, a whereby the surface or case is suitable diameter is to be substantially harder than the core or determined. Calculations are to be inside metal. based on a yield strength. Answer: 0.06 m  Carburizing is a process of adding carbon to the surface of steel by  Determine the size for the section of exposing it to hot carbonaceous a square bar which is to be held solids, liquids, or gases above the firmly at one end and is to support a transformation temperature. load of 3000 pounds at the outer end. The bar is to be 30 inches long  Pack (or box) carburizing and gas and is to be made from SAE 1045 carburizing are the common medium carbon steel with a yield methods of adding carbon. point of 60,000 psi. A factor of safety of 3 and a stress concentration factor of 1.3 are to be used.  In gas carburizing the part is heated Answer: 3 5/16 in. in carburizing gases, such as methane, ethane, propane, and  A lever secured to a 2-inch round CO2. shaft by a steel tapered pin (dimension d = 38 inch) has a pull of  In liquid carburizing the part is 50 pounds at a 30-inch radius from immersed in a molten salt bath that shaft center. Find S, the unit working imparts a case similar to that stress on the pin. obtained with gas or pack Answer: 6770 psi carburizing except that the case is thinner, usually not in excess of  A lever secured to a 50 mm round about 0.025 in. shaft by a steel tapered pin (d = 10 mm) has a pull of 200 newtons at a radius of 800 mm. Find S, the  A round steel bar of 300 Mpa yield working stress on the pin. Answer: strength, is to withstand a direct 40.6 Mpa tension of 200 KN. Using a safety  MB Grade, ASTM A227 (0.60-0.70 per cent carbon)  If a shaft of 50 mm diameter is to transmit power of 12 kilowatts at a  These spring steels are used for speed of 500 rpm, find the mean conditions of high stress, and shock diameter of the pin for a material or impact loadings. Answer: Alloy having a safe unit stress of 40 Spring Steels N/mm2 Answer: 12.09 mm  This very popular spring steel is  This is the most widely used of all used under conditions involving spring materials for small springs higher stresses than those for which operating at temperatures up to the high-carbon spring steels are about 250° F. Answer: Music Wire, recommended and is also used ASTM A228 (0.80-0.95 per cent where good fatigue strength and carbon) endurance are needed. Answer: Chromium Vanadium, ASTM A231  This general-purpose spring steel is commonly used for many types of  This stainless spring steel is very coil springs where the cost of music popular because it has the highest wire is prohibitive and in sizes larger tensile strength and quite uniform than are available in music wire. properties. Answer: Stainless Type Answer: Oil-Tempered MB Grade, 302, ASTM A313 (18 per cent ASTM A229 (0.60-0.70 per cent chromium, 8 per cent nickel): carbon)  These are important spring materials  This grade is used for general- because of their good electrical purpose springs where cost is the ar properties combined with their good most important factor. Although resistance to corrosion. Answer: increased use in recent years has Copper-base alloys resulted in improved quality, it is best not to use it where long life and  This material is the least expensive accuracy of loads and deflections and has the highest electrical are important Answer: Hard-Drawn conductivity of the copper-base alloys. It has a low tensile strength  and poor spring qualities but is titanium, columbium and aluminum extensively used in flat stampings in its composition make it a and where sharp bends are needed. precipitation-hardening alloy. Answer: Spring Brass, ASTM B 134 Answer: Inconel "X"(70 per cent (70 per cent copper, 30 per cent nickel, 16 per cent chromium, 7 per zinc) cent iron):  These are corrosion resistant,  This alloy is non-magnetic, corrosion withstand both elevated and sub-o resistant, has a high tensile strength zero temperatures, and their non- and is hardenable by precipitation magnetic characteristic makes them hardening at 900 degrees F. for 6 useful for such applications as hours. Answer: Duranickel (“Z” gyroscopes, chronoscopes, and Nickel)(98 percent nickel) indicating instruments Answer: Nickel-base alloys  This alloy, the first constant-modulus alloy used for hairsprings in  This material is quite similar to watches, is an austenitic alloy Monel except that the addition of the hardened only by cold-drawing and aluminum makes it a precipitation- cold-rolling. Answer: Elinvar(nickel, hardening alloy. Answer: "K" Monel iron, chromium) (66 per cent nickel, 29 per cent copper, 3 per cent aluminum)   This very popular constant-modulus  This is one of the most popular of alloy is usually formed in the 50 per the non-magnetic nickel-base alloys cent cold-worked condition and because of its corrosion resistance precipitation-hardened at 900 °F. for and because it can be used at 8 hours, although heating up to 1250 temperatures up to 700 degrees F. degrees F. for 3 hours produces Answer: Inconel (78 per cent nickel, hardnesses of 40 to 44 Rockwell C, 14 per cent chromium, 7 per cent permitting ne safe torsional stresses iron) of 60,000 to 80,000 pounds per squares of inch. This material is  This material is quite similar to ferromagnetic up to 400 degrees F; Inconel but the small amounts of abovem that temperature it becomes  non-magnetic. Answer: Ni-Span C  This popular alloy is relatively easy (nickel, iron, chromium, titanium) to fabricate and is used at safe torsional stresses of 40,000 to  This alloy, the first constant-modulus 60,000 pounds per square inch and alloy used for hairsprings in hardnesses of 30 to 36 Rockwell C. watches, is an austenitic alloy It is used principally in hardened only by cold-drawing and dynamometers, instruments, and cold-rolling. Additions of titanium, food-weighing scales. Answer: Iso- tungsten, molybdenum and other Elastic (nickel, iron, chromium, alloying elements have brought molybdenum): about improved characteristics and precipitation-hardening abilities.  This alloy, also known by the trade These improved alloys are known by names &J Alloy, Durapower, and the following trade names: Elinvar Cobenium, is a non-magnetic alloy Extra, Durinval, Modulvar and suitable for sub-zero temperatures Nivarox.onig st. Answer: Elinvar and temperatures up to about 1000 (nickel, iron, chromium) degrees F., provided that torsional stresses are kept under 75,000 pounds per square inch. It is  This very popular constant-modulus precipitation-hardened at 900 alloy is usually formed in the er 50 degrees F. for 8 hours to produce per cent cold-worked condition and hardnesses of 48 to 50 Rockwell C. precipitation-hardened at 900 The alloy is used in watch and degrees F. for 8 hours, although instrument springs. Answer: Elgiloy heating up to 1250 degrees F. for 3 (nickel, iron, chromium, cobalt): hours produces hardnesses of 40 to 44 Rockwell C, permitting safe torsional stresses of 60,000 to  This alloy is a non-magnetic, 80,000 pounds per square inch. This corrosion resistant material suitable material is ferromagnetic up to 400 for sub-zero temperatures and degrees F; above that temperature it temperatures up to about 750 °F, becomes non-magnetic. Answer: Ni- provided that torsional stresses are Span C (nickel, iron, chromium, kept below 75,000 pounds per titanium): square inch. It is precipitation-  hardened to produce hardnesses of  It is used for small ropes such as 48 to 50 Rockwell C and is used in sash cord and aircraft cord. Answer: watch and instrument springs. Cotton Answer: Dynavar (nickel, iron, chromium, cobalt):  These are offered for use where exposure to moisture, acids, or caustics is excessive.  It is largely used for low-strength Answer: Polyvinyl plastics cores applications such as elevator ropes not used for hoisting, and for  It often referred to as WSC, consists stationary guy ropes. Answer: Iron of a multiple-wire strand that may be wire rope the same as one of the strands of the rope. It is smoother and more  It is used occasionally for elevator solid than the independent wire rope governor-cable rope and for certain core and provides a better support marine applications as life lines, for the rope strands. Answer: wire- clearing lines, wheel ropes and strand core rigging. Answer: Phosphor bronze wire rope  It is often referred to as IWRC, is a small 6 x7 wire rope with a wire- strand core and is used to provide  It is used primarily as hoist rope for greater resistance to crushing and passenger and freight elevators of distortion of the wire rope. For the traction drive type, an application certain applications it has the for which it was specifically advantage over a wire-strand core in designed. Answer: Traction steel that it stretches at a rate closer to wire rope that of the rope itself. Answer: The independent wire rope core  It is the type of wire rope core most widely used when loads are not too great.  The other term of precipitation Answer: Fiber: (manila or sisal) hardening is: Answer: Age hardening  It occurs in some metals, notably  It is a tendency to fracture without certain stainless steel, aluminum, appreciable deformation. Answer: and copper alloys at ambient Brittleness temperature after solution heat treatment, the process being one of  It is one in which specimen, a constituent precipitating from solid supported at both ends as a simple solution. Where used, the beam, is broken by the impact of a consequences include increased falling pendulum. The energy strength and hardness, decrease absorbed in breaking the specimen ductility. Answer: Age hardening is a measure of the impact strength of the metal. Answer: Charpy Test  The aging at moderately elevated temperature expedites the process  Is the brittleness of metals at and is called: Answer: Artificial Aging ordinary or low temperatures. Answer: Cold Shortness  A substance with metallic properties, compound of two or more elements  It is the process of deforming a of which at least one is metal. metal plastically at a temperature Answer: Alloy below the recrystallization temperature and at a rate to produce strain hardening. Answer: Cold  In steel are usually considered to be working the metallic elements added for the purpose of modifying the properties. BE. Answer: Alloying elements  Steel that is frequently used because it increases strength and  It is the characteristics of exhibiting machinability and improves surface different properties when tested in finish. Answer: Cold-drawn Steel different directions (as tensile strength " with grain" or "across the  Commercial amounts of cold grain"). Answer: Anisotropy working of steel are of the order of Answer: 10 to 20%  It is the ability of a material to absorb Embrittlement or damp vibrations, which is a process of absorbing kinetic energy  It is the part of the carbon content of of vibration owing to hysteresis. The steel or iron that is in the form of absorbed energy is eventually graphite or temper carbon. Answer: dissipated to the surroundings as Free Carbon heat. Answer: Damping Capacity  It is a temper produced in a wire,  It is a loss of carbon from the rod, or tube by cold drawing. surface of steel, occurring during hot Answer: Hard drawn rolling, forging, and heat treating, when surrounding medium reacts  Materials that have the same with the carbon (as oxygen and structure at all points. Answer: carbon combining). Answer: Homogeneous materials Decarburization  Materials that have the same properties in all directions. Answer: Isotropic  It the property that permits permanent deformation before  A test in which specimen, supported fracture in tension. Answer: Ductility at one end as a cantilever beam, is broken by the impact of a falling  The percent elongation for ductile pendulum. The energy absorbed in materials. Answer: greater than 5% breaking the specimen is a measure in 2-in. gage The percent elongation of the impact strength. Answer: Izod for brittle materials. Answer: less Test than 5% in 2-in. gage  It is the ability of a material to be  A steel that has been deoxidized deformed and to return to the with a strong deoxidizing agent such original shape. Answer: Elasticity as silicon or aluminum, in order to eliminate a reaction between the  It involves the loss of ductility carbon and oxygen during because of a physical or chemical solidification. Answer: Killed Steel change of the material. Answer:  It is somewhat indefinite property  It is the ability of the metal to be that refers to the relative ease with deformed considerably without which a material can be cut. Answer: rupture. In this deformation the Machinability material does not return to its original shape. Answer: Plasticity  The material's susceptibility to extreme deformation in rolling or hammering. Answer: Malleability  Are those that have to do with stress and strain: ultimate strength and percent elongation. Answer: mechanical properties  It is the extension in the vicinity of the fracture of a tensile specimen, expressed as a percentage of the original gage length as 20% in 2 in. Answer: percent elongation  It is the smallest area at the point of rupture of a tensile specimen divided by the original area.  Answer: percent reduction of area  It exclude mechanical properties, and are other physical properties such as density, conductivity, coefficient of thermal expansion. Answer: physical properties