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Special CastingBy S K Mondal1Shell MouldingThe sand is mixed with a thermosetting resin is allowed to come in contact with a heated metal pattern (2000C).A skin (shell) of about 3.5 mm of sand and plastic mixture adhere to the pattern.Then the shell is removed from the pattern. The cope and drag shells are kept in a flask with necessary backup material and the molten metal is poured into the mold.It is a process in which, the sand mixed with a thermosetting resin is allowed to come in contact with a heated pattern plate (2000C), this causes a skin (shell) of about 3.5 mm of sand/plastic mixture to adhere to the pattern. Then the shell is removed from the pattern. The cope and drag shells are kept in a flask with necessary backup material and the molten metal is poured into the mold.

This process can produce complex parts with good surface finish 1.25 m to 3.75 m, and dimensional tolerance of 0.5 %. A good surface finish and good size tolerance reduce the need for machining. The process overall is quite cost effective due to reduced machining and cleanup costs. The materials that can be used with this process are cast irons, and aluminum and copper alloys.

2Can produce complex parts.A good surface finish and good size tolerance reduce the need for machining.Materials can be cast: CI, Al and Cu alloys.Shell moulding process

Molding Sand in Shell Molding The molding sand is a mixture of fine grained quartz sand and powdered bakelite. Cold coating and Hot coating methods are used for coating the sand grains with bakelite.Cold coating: quartz sand is poured into the mixer and then the solution of powdered bakelite in acetone and ethyl aldehyde are added. (mixture is 92% quartz sand, 5% bakelite, 3% ethylaldehyde )Contd The molding sand is a mixture of fine grained quartz sand and powdered bakelite. There are two methods of coating the sand grains with bakelite.Cold coating method and Hot method of coating.In the method of cold coating, quartz sand is poured into the mixer and then the solution of powdered bakelite in acetone and ethyl aldehyde are added.The typical mixture is 92% quartz sand, 5% bakelite, 3% ethylaldehyde.5Hot coating: the mixture is heated to 150oC 180oC prior to loading the sand. In the course of sand mixing, the soluble phenol formaldehyde resin is added. The mixer is allowed to cool up to 80 90o C. Hot coting gives better properties to the mixtures than cold method.During mixing of the ingredients, the resin envelops the sand grains and the solvent evaporates, leaving a thin film that uniformly coats the surface of sand grains, thereby imparting fluidity to the sand mixtures.

In the method of hot coating, the mixture is heated to 150oC 180oC prior to loading the sand. In the course of sand mixing, the soluble phenol formaldehyde resin is added. The mixer is allowed to cool up to 80 - 90 .This method gives better properties to the mixtures than cold method.

6AdvantagesDimensional accuracy.Smoother surface finish. (Due to finer size grain used)Very thin sections can be cast.Very small amount of sand is needed.Shell-mould castings are generally more dimensionally accurate than sand castingsA smoother surface can be obtained in shell castings. This is primarily achieved by the finer size grain used.Very thin sections (up to 0.25 mm) of the type of air-cooled cylinder heads can be readily made by the shell moulding because of the higher strength of the sand used for moulding.Very small amount of sand needs to be used.

7LimitationsExpensive pattern Small size casting only.Highly complicated shapes cannot be obtained.More sophisticated equipment is needed for handling the shell moldings.The patterns are very expensive and therefore are economical only if used in large-scale production. The size of the casting obtained by shell moulding is limited. Highly complicated shapes cannot be obtained.More sophisticated equipment is needed for handling the shell moldings such as those required for heated metal patterns.

8ApplicationsCylinders and cylinder heads for air- cooled IC enginesAutomobile transmission parts.Piston ringsIES 2010Consider the following advantages of shell mould casting:1. Close dimensional tolerance.2. Good surface finish.3. Low cost.4. Easier.Which of these are correct?(a) 1, 2 and 3 only (b) 2, 3 and 4 only(c) 1, 2 and 4 only (d) 1, 2, 3 and 4Ans. (c)10IES-1996Consider the following ingredients used in moulding:1.Dry silica sand2.Clay3.Phenol formaldehyde4.Sodium silicateThose used for shell mould casting include(a) 1, 2 and 4 (b) 2, 3 and 4 (c) 1and 3 (d)1, 2, 3 and 4Ans. (c)11IES-2005In shell moulding, how can the shell thickness be accurately maintained?(a) By controlling the time during which the pattern is in contact with mould (b) By controlling the time during which the pattern is heated(c) By maintaining the temperature of the pattern in the range of 175oC 380oC(d) By the type of binder usedAns. (a)12IES-2006Shell moulding can be used for:(a)Producing milling cutters(b)Making gold ornaments(c)Producing heavy and thick walled casting(d)Producing thin casting

Ans. (d)13IES 2007Which of the following are employed in shell moulding?1. Resin binder 2. Metal pattern 3. Heating coilsSelect the correct answer using the code given below:(a)1 and 2 only(b)1 and 3 only(c)2 and 3 only(d)1, 2 and 3Ans. (d) Shell moulding employed heated (1500C) metal pattern with resin binder.14IAS-2007The mould in shell moulding process is made up of which of the following?(a)Gypsum + setting agents(b)Green sand + clay(c)Sodium silicate + dried sand(d)Dried silica + phenolic resinAns. (d)

15IAS-1999Match List I (Moulding Process) with List II (Binding Agent) and select the correct answer using the codes given below the lists:List I List IIA.Green sand1. SilicateB.Core sand2. OrganicC.Shell moulding 3. ClayD.CO2 process 4. Plaster of Paris5. PlasticCodes:A B C DA B C D(a)3251(b) 3 2 4 1(c) 2 35 4 (d)2 3 4 5

Ans. (a) Organic i.e. oil; Plastic i.e. resin; Plaster of Paris never used for casting. 16Investment CastingInvestment casting process or lost wax processBasic steps:1.Produce expendable wax, plastic, or polystyrene patterns.2.Assemble these patterns onto a gating system3.Investing or covering the pattern assembly with refractory slurry4.Melting the pattern assembly to remove the pattern material5.Firing the mould to remove the last traces of the pattern material6.Pouring molten metal7.Knockout, cutoff and finishing.The root of the investment casting process, the cire Perdue or "lost wax" method dates back to at least the fourth millennium B.C. The artists and sculptors of ancient Egypt and Mesopotamia used the rudiments of the investment casting process to create intricately detailed jewelry, pectorals and idols. The investment casting process also called lost wax process begins with the production of wax replicas or patterns of the desired shape of the castings. A pattern is needed for every casting to be produced. The patterns are prepared by injecting wax or polystyrene in a metal dies. A number of patterns are attached to a central wax sprue to form a assembly. The mold is prepared by surrounding the pattern with refractory slurry that can set at room temperature. The mold is then heated so that pattern melts and flows out, leaving a clean cavity behind. The mould is further hardened by heating and the molten metal is poured while it is still hot. When the casting is solidified, the mold is broken and the casting taken out.

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Fig. Investment flask-casting procedureCeramic Shell Investment CastingIn ceramic shell investment casting a ceramic shell is built around a tree assembly by repeatedly dipping a pattern into a slurry (refractory material such as zircon with binder).After each dipping and stuccoing is completed, the assembly is allowed to thoroughly dry before the next coating is applied. The basic difference in investment casting is that in the investment casting the wax pattern is immersed in a refractory aggregate before dewaxing whereas, in ceramic shell investment casting a ceramic shell is built around a tree assembly by repeatedly dipping a pattern into a slurry (refractory material such as zircon with binder). After each dipping and stuccoing is completed, the assembly is allowed to thoroughly dry before the next coating is applied. Thus, a shell is built up around the assembly. The thickness of this shell is dependent on the size of the castings and temperature of the metal to be poured.After the ceramic shell is completed, the entire assembly is placed into an autoclave or flash fire furnace at a high temperature. The shell is heated to about 982 to burn out any residual wax and to develop a high temperature bond in the shell. The shell molds can then be stored for future use or molten metal can be poured into them immediately. If the shell molds are stored, they have to be preheated before molten metal is poured into them.

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IES 20092 marks

AdvantagesTight dimensional tolerancesExcellent surface finish (1.2 to 3.0 m )Machining can be reduced or completely eliminatedHigh melting point alloy can be cast, almost any metal can be castAlmost unlimited intricacyLimitationsCostly patterns and mouldsLabour costs can be highLimited sizeApplicationsAerospace and rocket components. Vanes and blades for gas turbines.Surgical instrumentsIES 2011The proper sequence of investment casting steps is :(a) Slurry coating pattern melt out-Shakeout Stucco coating(b) Stucco coating Slurry coating Shakeout Pattern melt out(c) Slurry coating Stucco coating Pattern melt out Shakeout(d) Stucco coating Shakeout Slurry coating Pattern melt outAns. (c)

26GATE-2006An expendable pattern is used in(a) Slush casting(b) Squeeze casting(c) Centrifugal casting(d) Investment castingAns. (d)27GATE-2011 (PI)Which of the following casting processes uses expendable pattern and expendable mould?(a) Shell mould casting(b) Investment casting(c) Pressure die casting(d) Centrifugal castingAns. (b)28ISRO-2010Investment casting is used for(a) Shapes which are made by difficulty using complex patterns in sand casting(b) Mass production(c) Shapes which are very complex and intricate and can't be cast by any other method(d) There is nothing like investment castingAns. (a)29IES-1992The most preferred process for casting gas turbine blades is:(a)Die moulding(b)Shell moulding(c)Investment moulding(d)Sand casting

Ans. (c) 30JWM 2010Consider the following materials :1. Wax 2. Wood3. PlasticWhich of these materials can be used as pattern in investment casting process ?(a) 1, 2 and 3 (b) 1 and 2 only(c) 2 and 3 only (d) 1 and 3 onlyAns. (d)31IES 2010 Assertion (A): The investment casting is used for precision parts such as turbine plates, sewing machines etc.Reason (R): The investment castings have a good surface finish and are exact reproductions of the master pattern.(a) Both A and R are individually true and R is the correct explanation of A(b) Both A and R are individually true but R is NOT the correct explanation of A(c) A is true but R is false(d) A is false but R is trueAns. (a)32IES 2007Consider the following statements in respect of investment castings: 1. The pattern or patterns is/are not joined to a stalk or sprue also of wax to form a tree of patterns. 2.The prepared moulds are placed in an oven and heated gently to dry off the invest and melt out the bulk of wax.3.The moulds are usually poured by placing the moulds in a vacuum chamber. Which of the statements given above are correct?(a) 1 and 2 only(b) 1 and 3 only (c)2 and 3 only(d) 1, 2 and 3Ans. (c) The pattern or patterns is/are joined to a stalk or sprue also of wax to form a tree of patterns.33IES-2006Which of the following materials are used for making patterns in investment casting method?1. Wax 2. Rubber3. Wood 4. PlasticSelect the correct answer using the codes given below:(a) Only 1 and 3(b) Only 2 and 3(c) Only 1, 2 and 4(d) Only 2, 3 and 4Ans. (c) Wood cannot be used for patterns in investment casting as by heating wood cannot be liquefied.34IAS-1996Light and intricate parts with close dimensional tolerances of the order of 0.005 mm are produced by (a)Investment casting(b)Die casting(c)Centrifugal casting(d)Shell mould casting

Ans. (a)

35Permanent Mould CastingThe process in which we use a die to make the castings is called permanent mold casting or gravity die casting, since the metal enters the mold under gravity.Some time in die-casting we inject the molten metal with a high pressure. When we apply pressure in injecting the metal it is called pressure die casting process.Grey cast iron is used for mould material.In all the above processes, a mold need to be prepared for each of the casting produced. For large-scale production, making a mold, for every casting to be produced, may be difficult and expensive. Therefore, a permanent mold, called the die may be made from which a large number of castings can be produced. , the molds are usually made of cast iron or steel, although graphite, copper and aluminum have been used as mold materials. The process in which we use a die to make the castings is called permanent mold casting or gravity die casting, since the metal enters the mold under gravity. Some time in die-casting we inject the molten metal with a high pressure. When we apply pressure in injecting the metal it is called pressure die casting process.

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AdvantagesGood surface finish and dimensional accuracyMetal mold gives rapid cooling and fine-grain structureMultiple-use molds.

Permanent Molding produces a sound dense casting with superior mechanical properties.The castings produced are quite uniform in shape have a higher degree of dimensional accuracy than Castings produced in sandThe permanent mold process is also capable of producing a consistent quality of finish on castings.

37DisadvantagesHigh initial mold costShape, size, and complexity are limitedMold life is very limited with high-melting-point metals such as steel.Low melting point metals can be cast-Aluminum-Zinc-Magnesium alloys-Brass-Cast ironyield rate rarely exceeds 60%. but runners and risers can be directly recycled; 38ApplicationsPistons/cylinders/rodsGearsKitchenwareDie CastingMolten metal is injected into closed metal dies under pressures ranging from 100 to 150 MPa. Pressure is maintained during solidificationAfter which the dies separate and the casting is ejected along with its attached sprues and runners. Cores must be simple and retractable and take the form of moving metal segments

VideoDie casting machines can beHot chamberCold chamberHot chamber machines areGood for low temperature (approx. 400C)Faster than cold chamber machinesCycle times must be short to minimize metal contaminationMetal starts in a heated cylinderA piston forces metal into the dieThe piston retracts, and draws metal inMetal: Lead, Tin, Zinc

Hot ChamberCold chamber machinesCasts high melting point metals ( > 600C)High pressures usedMetal is heated in a separate crucibleMetal is ladled into a cold chamberThe metal is rapidly forced into the mold before it coolsCopper, Brass and Aluminium can cast.

AdvantagesExtremely smooth surfaces (1 m)Excellent dimensional accuracyRapid production rateBetter mechanical properties compared to sand castingIntricate parts possibleMinimum finishing operationsThin sections possibleLimitationsHigh initial die costLimited to high-fluidity nonferrous metalsPart size is limitedPorosity may be a problemSome scrap in sprues, runners, and flash, but this can be directly recycledApplicationsCarburettorsAutomotive partsBathroom fixturesToys

Common metalsAlloys of aluminum, zinc, magnesium, and leadAlso possible with alloys of copper and tin

IES 2011Consider the following advantages of die casting over sand casting :1. Rapidity of the process2. Smooth surface3. Strong dense metal structureWhich of these advantages are correct ?(a) 1, 2 and 3(b) 1 and 2 only(c) 2 and 3 only(d) 1 and 3 onlyAns. (b)51IES-2009Which of the following are the most suitable materials for die casting?(a)Zinc and its alloys(b) Copper and its alloys(c)Aluminium and its alloys(d)Lead and its alloys

Ans. (d)52JWM 2010Assertion (A) : In die casting method, small thickness can be filled with liquid metal.Reason (R) : The air in die cavity trapped inside the casting causes problems.(a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is true

Ans. (b) Because of high injection pressure may cause turbulence and air entrapment, leads to porosity.53IES-2005Which one of the following processes produces a casting when pressure forces the molten metal into the mould cavity?(a)Shell moulding (b)Investment casting(c)Die casting (d)Continuous casting

Ans. (c)54IES-2006In which of the following are metal moulds used?(a)Greensand mould(b)Dry sand mould (c)Die casting process (d)Loam moulding

Ans. (c)55IES-1995Assertion (A): An aluminium alloy with 11 % silicon is used for making engine pistons by die casting technique.Reason (R): Aluminium has low density and addition of silicon improves its fluidity and therefore its castability.(a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is true

Ans. (a)56IES-1995Match List I with List II and select the correct answer taking the help of codes given below the lists:List IList II (Products)(Process of manufacture)A.Automobile piston in aluminium alloy1. Pressure die-castingB.Engine crankshaft in spheroidal graphite iron2. Gravity die-castingC.Carburettor housing in aluminium alloy3. Sand castingD.Cast titanium blades4. Precision investment casting5. Shell mouldingCode:ABCDABCD(a)2315(b)3215(c)2134(d)4123

Ans. (a)57IAS-2007Consider the following statements:1.Zinc die castings have low strength.2.In the die casting process, very thin sections or complex shapes can be obtained easily.Which of the statements given above is/are correct?(a)1 only (b)2 only(c)Both 1 and 2(d)Neither 1 nor 2

Ans. (b)58IAS-1996Assertion (A): Die casting yields a product of good accuracy and finish.Reason (R): Low melting alloys used in die casting. (a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is trueAns. (b)59IES 2011Consider the following statements :1. Hot chamber machine is used for casting zinc, tin and other low melting alloys.2. Cold chamber machine is used for die casting of ferrous alloys3. Rapid cooling rate in die casting produces high strength and quality in many alloys.Which of these statements are correct?(a) 1, 2 and 3 (b) 1 and 2 only (c) 2 and 3 only (d) 1 and 3 only

Ans. (d) Cold chamber machine is used for die casting of NOT ferrous alloys. Copper, Al etc.

60GATE-2007Which of the following engineering materials is the most suitable candidate for hot chamber die casting?(a)Low carbon steel(b)Titanium(c)Copper(d)TinAns. (d)61IES-1995Assertion (A): Aluminium alloys are cast in hot chamber die casting machine.Reason (R): Aluminium alloys require high melting when compared to zinc alloys.(a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is trueAns. (d) As Liquid aluminium attack goose neck material, Hot chamber process is not used, cold chamber process is used.62GATE -2009 (PI)Hot chamber die casting process is NOT suited for(a) Lead and its alloy(b) Zinc and its alloy(c) Tin and its alloy(d) Aluminum and its alloyAns. (d) Due to the reaction with goose neck materials.63Centrifugal CastingProcess: Molten metal is introduced into a rotating sand, metal, or graphite mould, and held against the mould wall by centrifugal force until it is solidifiedA mold is set up and rotated along a vertical (rpm is reasonable), or horizontal (200-1000 rpm is reasonable) axis.The mold is coated with a refractory coating.During cooling lower density impurities will tend to rise towards the center of rotation.

Fig. True centrifugal castingPropertiesThe mechanical properties of centrifugally cast jobs are better compared to other processes, because the inclusions such as slag and oxides get segregated towards the centre and can be easily removed by machining. Also, the pressure acting on the metal throughout the solidification causes the porosity to be eliminated giving rise to dense metal.No cores are required for making concentric holes in the case of true centrifugal casting.AdvantagesFine grained structure at the outer surface of the casting free of gas and shrinkage cavities and porosityFormation of hollow interiors in cylinders without coresCan produce a wide range of cylindrical parts, including ones of large size.Good dimensional accuracy, soundness, and cleanlinessThere is no need for gates and runners, which increases the casting yield, reaching almost 100 %.

LimitationsMore segregation of alloy component during pouring under the forces of rotationContamination of internal surface of castings with non-metallic inclusionsInaccurate internal diameter Shape is limited.Spinning equipment can be expensivePoor machinability Common metalsIronsteelstainless steelalloys of aluminium, copper, and nickelGATE-2002In centrifugal casting, the impurities are(a)Uniformly distributed(b)Forced towards the outer surface(c)Trapped near the mean radius of the casting (d)Collected at the centre of the castingAns. (d) 71GATE-1993Centrifugally cast products have(a)Large grain structure with high porosity(b)Fine grain structure with high density(c)Fine grain structure with low density(d)Segregation of slug towards the outer skin of the casting

Ans. (b)72GATE -2008 (PI)In hollow cylindrical parts, made by centrifugal casting, the density of the part is(a) maximum at the outer region(b) maximum at the inner region(c) maximum at the mid-point between outer and inner surfaces(d) uniform throughout Ans. (a)73IES-2008Which of the following casting processes does not /do not require central core for producing pipe?1.Sand casting process2.Die casting process3.Centrifugal casting processSelect the correct answer using the code given below:(a)1 and 2(b)2 only(c)2 and 3(d)3 only

Ans. (d) The basic process is:1.A mold is set up and rotated along a vertical (rpm is reasonable), or horizontal (200-1000 rpm is reasonable) axis.2.The mold is coated with a refractory coating.3.While rotating molten metal is poured in.4.The metal that is poured in will then distribute itself over the rotating wall.5.During cooling lower density impurities will tend to rise towards the center of rotation.6.After the part has solidified, it is removed and finished.Properties: 1.The mechanical properties of centrifugally cast jobs are better compared to other processes, because the inclusions such as slag and oxides get segregated towards the centre and can be easily removed by machining. Also, the pressure acting on the metal throughout the solidification, causes the porosity to be eliminated giving rise to dense metal.2.Up to a certain thickness of objects, proper directional solidification can be obtained starting from the mould surface to the centre.3.No cores are required for making concentric holes in the case of true centrifugal casting.4.There is no need for gates and runners, which increases the casting yield, reaching almost 100%.

74IES-2009Which one of the following casting processes is best suited to make bigger size hollow symmetrical pipes?(a)Die casting(b)Investment casting(c)Shell moulding(d)Centrifugal casting

Ans. (d)

75IES 2007Which one of the following is the correct statement?In a centrifugal casting method(a)No core is used(b)Core may be made of any metal(c) Core is made of sand(d)Core is made of ferrous metal

Ans. (a)76IES-1998Poor machinability of centrifugally cast iron pipe is due to(a)Chilling(b)Segregation(c)Dense structure(d)High mould rotation speed

Ans. (c)77IES-2009Which of the following are the most likely characteristics in centrifugal casting?(a)Fine grain size and high porosity(b)Coarse grain size and high porosity(c)Fine grain size and high density(d)Coarse grain size and high densityAns. (c)Advantages of centrifugal castingFine grained structure at the outer surface of the casting free of gas and shrinkage cavities and porosityFormation of hollow interiors in cylinders without coresLess material required for gate

78IES 2007Match List I with List II and select the correct answer using the code given below the Lists:List IList II(Casting Process)(Principle)A.Die casting1.The metal solidifies in a rotating mouldB.Investment casting2.The pattern cluster is repeatedly dipped into a ceramic slurry and dusted with refractoryC.Shell moulding3. Molten metal is forced by pressure into a metallic mouldD.Centrifugal casting4. After cooling, the invest is removed from theCasting by pressure jetting or vibratory cleaningCode:ABCDABCD (a)2134(b)3421 (c)2431(c) 3124

Ans. (b)79IES-2000Match List I (Process) with List II (Products/materials) and select the correct answer using the codes given below the Lists:List I List IIA.Die casting 1. Phenol formaldehydeB.Shell molding 2. C.I. pipesC.CO2 molding 3. Non-ferrous alloysD.Centrifugal casting 4. Sodium silicateCodes:A B C D A B C D(a) 1 3 4 2 (b) 3 1 4 2(c) 3 1 2 4 (d) 1 3 2 4

Ans. (b) Phenol formaldehyde is as a resin.80IAS-2004Match List-I (Name of the Process) with List-II (Advantage) and select the correct answer using the codes given below the lists:List-I List-II(Name of the Process)(Advantage)A.Sand Casting1. Large cylindrical parts with good qualityB.Ceramic mold casting2.Excellent dimensional accuracy and surfacefinishC.Die casting3. Intricate shapes and close tolerance partsD.Centrifugal casting4. Almost any metal is cast and there if no limit tosize, shape and weight5. Good dimensional accuracy, finish and lowporosityCodes:A B C DA B C D(a) 2 3 5 1(b)4 123(c) 2 1 5 3 (d)4321

Ans. (d)

81Semi-centrifugal CastingCentrifugal force assists the flow of metal from a central reservoir to the extremities of a rotating symmetrical mold, which may be either expendable or multiple-useRotational speeds are lower than for true centrifugal castingCores can be used to increase the complexity of the product.Centrifugal force assists the flow of metal from a central reservoir to the extremities of a rotating symmetrical mold, which may be either expendable or multiple-useRotational speeds are usually lower than for true centrifugal casting, and it is not uncommon for several molds to be stacked on top of one another, being fed by a common pouring basin.The central reservoir acts as a riser and must be large enough to assure that it will be the last material to freeze. Since the lighter impurities concentrate in the center, the process is best used for castings where the central region will ultimately be hollow. Cores can be used to increase the complexity of the product.

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Fig. Semi-centrifugal castingIAS-2003Assertion (A): Semi-centrifugal casting process is similar to true centrifugal casting except that the central core is used in it to form inner surface.Reason (R): In semi-centrifugal casting process the axis of spin is always vertical(a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is true

Ans. (a)84CentrifugingUses centrifuging action to force the metal from a central pouring reservoir into separate mold cavities that are offset from the axis of rotation.Low speedMay used to assist in the pouring of investment casting trees.Uses centrifuging action to force the metal from a central pouring reservoir into separate mold cavities that are offset from the axis of rotation.Relatively low rotational speeds are required to produce sound castings with thin walls and intricate shapes.Centrifuging is often used to assist in the pouring of investment casting trees.In an adaptation of the process, pewter, zinc, or wax can be cast into spinning rubber molds to produce products with close tolerances, smooth surfaces, and excellent detail. These can be finished products or patterns for subsequent assembly onto the investment casting trees.

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Fig. Method of casting by the centrifuging processIES-2000Match List I (Type of casting) with List II (Working principles) and select the correct answer using the codes given below the Lists:List IList IIA.Die casting1. Molten metal is forced into the die under pressureB.Centrifugal casting2. Axis of rotation does not coincide with axis of mouldC. Centrifuging3. Metal solidifies when mould is rotatingD.Continuous casting4. Continuously pouring molten metal into mouldCodes:ABC DAB CD(a) 1 3 2 4 (b) 4 3 2 1(c) 1 2 3 4 (d) 4 2 3 1Ans. (a)87Dry Sand MoldingTo reduce gas forming materials air dried mould used.Types:1.Skin drying and2.Complete mold dryingWhen it is desired that the gas forming materials are lowered in the molds, air-dried molds are sometimes preferred to green sand molds. Two types of drying of molds are often required.1.Skin drying and2.Complete mold drying.In skin drying a firm mold face is produced. Shakeout of the mold is almost as good as that obtained with green sand molding. The most common method of drying the refractory mold coating uses hot air, gas or oil flame. Skin drying of the mold can be accomplished with the aid of torches, directed at the mold surface.

88Slush CastingSlush casting is a variation of the permanent mold process in which the metal is permitted to remain in the mold only until a shell of the desired thickness has formed.The mold is then inverted and the remaining liquid is poured out.When the mold halves are separated, the resulting casting is a hollow shape with good surface detail but variable wall thickness.Frequently used to cast low-melting-temperature metals into ornamental objects such as candlesticks, lamp bases, and statuary.Slush casting is a variation of the permanent mold process in which the metal is permitted to remain in the mold only until a shell of the desired thickness has formed.The mold is then inverted and the remaining liquid is poured out.When the mold halves are separated, the resulting casting is a hollow shape with good surface detail but variable wall thickness.This process is frequently used to cast low-melting-temperature metals into ornamental objects such as candlesticks, lamp bases, and statuary.

89IAS-2004Which of the following are produced by slush casting?(a)Hollow castings with thick walls(b)Hollow castings with thin walls(c)Thin castings(d)Thick castings

Ans. (b)90IES 2011The method of casting for producing ornamental pieces are:(a) Slush and gravity casting(b) Pressed and slush casting(c) Gravity and semi permanent mould casting(d) Semi permanent mould and pressed casting

Ans. (a)91IES - 2012The process of making hollow castings of non-circular shape and desired thickness by permanent mould without the use of cores is known as(a) Die casting (b) Slush casting(c) Pressed casting (d) Centrifugal casting

Ans. (b) It is non-circular shape, centrifugal casting is not answer.92Squeeze CastingProcess:1.Molten metal is poured into an open face die.2. A punch is advanced into the die, and to the metal.3.Pressure (less than forging) is applied to the punch and die while the part solidifies. 4.The punch is retracted, and the part is knocked out with an ejector pin.Overcomes problems with feeding the die, and produces near net, highly detailed parts.The basic process is,1.Molten metal is poured into an open face die.2.A punch is advanced into the die, and to the metal.3.Pressure is applied to the punch and die while the part solidifies. This pressure is lower than normally required for forging.4.The punch is retracted, and the part is knocked out with an ejector pin.This method overcomes problems with feeding the die, and produces near net, highly detailed parts.

93IAS-2002Match List I (Casting Process) with List II (Applications) and select the correct answer using the codes given below the Lists:List I List II(Casting Process) (Applications)A.Centrifugal casting1.CarburetorB.Squeeze casting2.PipesC.Die Casting3.Wheels for automobiles4.Gear housingsCodes: ABCABC(a) 231(b) 413(c) 213(d) 431

Ans. (a)

94Single Crystal CastingThe process is effectively:Prepare a mold so that one end is a heated oven, and the other end chilled. The part should be oriented so that the cooling happens over the longest distance.Cast metal into the moldSolidification will begin at the chill plate. These dendrites will grow towards the heated end of the part as long dendritic crystals. The part is slowly pulled out of the oven, past the chill plate.Remove the solidified part.The process is effectively:Prepare a mold so that one end is a heated oven, and the other end chilled. The part should be oriented so that the cooling happens over the longest distance.Cast metal into the moldSolidification will begin at the chill plate. These dendrites will grow towards the heated end of the part as long dendritic crystals. The part is slowly pulled out of the oven, past the chill plate.Remove the solidified part.

95Creep and thermal shock resistance properties.Creep and thermal shock resistance properties.There are two variants to this technique,Directionally solidified - in this case the dendrites grow from the chill plate towards the other end.Single crystal - a helical constriction is used so that instead of parallel dendrites, only a single crystal is formed in the blade.

96

IES 20092 marksPlaster CastingProcess: A slurry of plaster, water, and various additives is additives is pouted over a pattern and allowed to set. The pattern is removed and the mould is baked to remove excess water. After pouring and solidification, the mould is broken and the casting is removed.Advantage: High dimensional accuracy and smooth surface finish, thin sections and intricate detail can produce.Limitations: Lower-temperature nonferrous metals only:Common metals: Primarily aluminium and copperPit MouldingThis method is used for very large castings and is done on the foundry floor.This method is used for very large castings and is done on the foundry floor.However, a pit dug in the floor acts as the lower flask (drag) and the top flask (cope) is placed over the pit to complete the assembly.The walls of the pit are brick-lined and plastered with loam sand and allowed to dry.Sometimes, for large and tall castings, the bottom of the pit is rammed with a 50 to 80 mm layer of coke to improve the permeability of the mould. Vent pipes are run from this layer to the surface (at the sides) and the coke is covered with blacking sand.

99IES-1996Which of the following pairs are correctly matched?1.Pit moulding ..................For large jobs.2.Investment moulding ... Lost wax process.3.Plaster moulding Mould prepared in gypsum.(a)1, 2 and 3(b)1 and 2(c)1 and 3(d)2 and 3

Ans. (a)100Loam MouldingMoulding loam is generally artificially composed of common brick-clay, and sharp sand. Loam means mud.Loam Moulding is restricted to forms which cannot be cast conveniently in any other process. It is costly. In practice, loam Moulding is generally restricted to forms which cannot be cast conveniently in any other process. Moulding loam is generally artificially composed of common brick-clay, and sharp sand. It is costly. Loam means mud.

101IES-1997Which one of the following pairs is not correctly matched?(a)Aluminium alloy piston Pressure die casting(b)Jewellery.. Lost wax process(c)Large pipes ..Centrifugal casting(d)Large bells Loam moulding

Ans. (a)102GATE-1998List I List II (A)Sand casting (1)Symmetrical and circular shapes only(B)Plaster mould casting (2)Parts have hardened skins and soft interior(C)Shell mould casting (3)Minimum post-casting processing(D)Investment casting (4)Parts have a tendency to warp (5)Parts have soft skin and hard interior (6)Suitable only for non-ferrous metalsAns. (A) -4, (B) -6, (C) -2, (D)-3103GATE-1992Match the following moulding/casting processes with the product:Moulding/Casting processesProduct(A)Slush casting(P) Turbine blade(B)Shell moulding (Q) Machine tool bed(C)Dry sand moulding(R) Cylinder block(D)Centrifugal casting(S) Hollow castings like lamp shades(T) Rain water pipe(U) Cast iron shoe brakeAns. A S, B P, C R, D Tlush casting is casting which produce hollow castings like lamp shades.104GATE-1996List I List II(A)Rivets for aircraft body 1.Forging(B)Carburettor body 2.Cold heading(C)Crankshafts 3.Aluminium-based alloy(D)Nails 4.Pressure die casting5.Investment castingAns. (A) 3, (B) - 4, (C) - 1, (D) 2105IES-2003Match List I (Products) with List II (Casting Process) and select the correct answer using the codes given below the Lists:List IList II(Products)(Casting Process)A.Hollow statues1.Centrifugal CastingB.Dentures2.Investment CastingC.Aluminium alloy pistons3.Slush CastingD.Rocker arms4.Shell Moulding5.Gravity Die CastingCodes:A B C DA B C D(a) 3 2 4 5(b) 1 3 4 5(c) 1 2 3 4(d) 3 2 5 4Ans. (d)106IES-1993Match the items of List I (Equipment) with the items of List II (Process) and select the correct answer using the given codes.List I (Equipment) List II (Process)P - Hot Chamber Machine 1.CleaningQ - Muller 2.Core makingR - Dielectric Baker 3.Die castingS - Sand Blaster 4.Annealing5.Sand mixing(a)P-2, Q-1, R-4, S-5 (b)P-4, Q-2, R-3, S-5(c)P-4, Q-5, R-1, S-2 (d)P-3, Q-5, R-2, S-1

Ans. (d) Hot chamber machine is associated with die casting, Muller with mixing of sand, dielectric baker with core making and sand blasting with cleaning.107IAS-2004Match List-I (Name of the Casting Process) with List-II (Process Definition) and select the correct answer using the codes given below the lists:List-IList-II (Name of the Casting Process)(Process Definition)A.Die casting1.This process involves use of a mould made ofDried silica sand and phenolic resin mixtureB.Electroslag casting 2. In this process, molten metal is forced byPressure into a metal mouldC.Centrifugal casting 3. This process employs a consumable electrodeD.Precision casting 4. This process involves rotating a mould while the metal solidifies5. This process produces very smooth, highlyAccurate castings from both ferrous and nonferrous alloysCodes:A B C DA B C D(a) 5 4 1 2(b) 2 3 4 5(c) 5 3 4 2(d) 2 4 1 5

Ans. (b)

108GATE 2007 (PI)Match the lists

(a) P 4, Q 1, R 3, S 2 (b) P 2, Q 4, R 3, S - 1(c) P 3, Q 4, R 1, S 2 (d) P 3, Q 2, R 1, S - 4

Group-1Group-2P. Sand Casting1. Turbine bladesQ. Centrifugal Casting2. IC Engine PistonsR. Investment Casting3. Large bellsS. Die Casting4. PulleysAns. (c)109Q. NoOption1A2A3C4A5D6A7D8C9B10D11A12BQ. NoOption13C14D15D16B17B18B19D20A21AConventional Casting Process Ch-21Q. NoOption1D2C3C4B5C6A7D8C9B10DQ. NoOption11A12A13D14A15A16B17ASpecial Casting Process Ch-22