Thermal Methods of Change of FormSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Other Permanent Mold CastingsSlide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Chapter 9 IT 208 1Thermal Methods of Change of FormChapter 9Chapter 9IT 2082CompetenciesIdentify the unique characteristics for each casting processDescribe the Investment Casting processList the advantages of Investment Casting over Sand CastingDescribe how to select a casting processIdentify a given casting process as either expendable mold or permanent moldChapter 9IT 2083Thermal Methods of Change of FormMetal Casting: Solidification of molten metal poured into a mold or injected into a die.4 Most Popular Casting Processes:•Sand casting•Investment casting•Permanent mold casting•Die castingChapter 9IT 2084Thermal Methods of Change of FormSAND CASTING (Expendable Mold classification) – mold is produced around a pattern that is withdrawn to leave a cavity. Used only once and must be broken up to free the solidified casting There are two significant restrictions on the shape of an object that can be sand cast.•There must be a plan that will become the plane of separation for the two halves of the mold•The pattern should slip cleanly out of the sand without disturbing the sand.Chapter 9IT 2085Thermal Methods of Change of FormImportant factors in casting operations:•The flow of the molten metal into the mold cavity•Heat transfer during solidification and cooling of the metal in the mold (The metal grain sizes are smaller near the mold than in the center)•Influence of the type of mold material•Solidification of the metal from its molten stateChapter 9IT 2086Thermal Methods of Change of FormParts of a Sand Casting:Pattern is the shape that is to be cast, about which the Mold is made. Mold is the container into which liquid metal, plastic, or other material is poured in making a casting. The Cope is the top half of the casting flask. The Drag is the bottom part of the flask. Pouring Basin - Molten metal is poured through a pouring basin (cup) and flows through the gating systemChapter 9IT 2087Thermal Methods of Change of FormSprue - vertical channel through which the molten metal flows downward into the mold Runners - channel to carry molten metal from sprue to gateGates - portion of the runner through which the molten metal enters the mold cavity, traps contaminate, prevents gas buildup and provides for ease of separationRiser (Feeder head) – let out trapped air, reservoirs to supply the molten metal necessary to prevent shrinkage during solidification.Chapter 9IT 2088Thermal Methods of Change of FormProcedureSand is MulledThe pattern is place flat side down on a smooth surfaceThe empty drag is placed around itPattern is dusted with dry parting sandMulled sand is riddled into the drag and tamped about the patternAfter complete packing around pattern, the bottom of drag is screeded Packed drag is carefully lifted from the patter and invertedThe cope is similarly made with cores forming the sprue and riser for filling Cope is placed atop drag and secured if necessaryMold is ready to pour.Chapter 9IT 2089Thermal Methods of Change of FormMelting and pouringCharge - the mixture of alloying elements that will be at the specified composition upon meltingFluxes - various compounds that can be mixed with the metal to react with the meltMelt - the molten metal that will be used to produce the castingTapping - when melt reaches proper temperature, method used to extract the metal from furnacePouring - transferring the tapped material to the castingChapter 9IT 20810Thermal Methods of Change of FormCasting techniques:Mulling is the mixing of the sand with the bonding agent. Riddling is the sifting of the sand into the flask. Green-sand casting uses water as the bonding agent for the sand. When the water dries out, the mold falls apart. Shell molds use a resin or other organic bonding agent and are baked to harden the mold. Since they do not dry out, they last a long time.Chapter 9IT 20811Thermal Methods of Change of FormCasting Alloys •Cast steels - readily welded to build up components of unusually large size and complexity•Railroad equipment (wheels, truck, frames, couplers)•Construction and mining equipment•Metal working machineryChapter 9IT 20812Thermal Methods of Change of FormWhite cast irons - hard and brittle, wear resistant parts (virtually unmachineable except by grinding)•Grinding balls•Liners for ore-crushing mills•Some agricultural machinery partsGray Iron - (low cost) is preferred choice in all fields where ductility and high strength are needed•Weights•Motor gears•Pump and pipe fitting•Machine tool bases (damping capacity)Chapter 9IT 20813Thermal Methods of Change of FormINVESTMENT CASTING (Expendable Mold)Lost wax– Pattern made of wax or polystyrene. Dipped into refractory material, then wax is melted out and metal is poured in. Advantages of investment casting versus sand are greater detailed parts, better surface finish, less machining, less tool wear.Chapter 9IT 20814Thermal Methods of Change of FormFull-mold – lost-form/expanded polystyrene/evaporative patter – pattern is made of expanded polystyrene rather than wax. Stryrofoam is vaporized and molten metal takes its place. •Minimum wall thicknesses - are 2.5 mm•Tolerances - can be held to .3 % on dimensions•Surface finish - can be held from 2.5µm to 25µm (0.1µin to 1.0 µin) rms. •Size limits- are from 400 g (1 lb) to several tons. No draft allowance is required. •Typical materials - aluminum, iron, steels, nickel alloys, copper alloys. •Types of parts - pump housings, manifolds, and auto brake components.Chapter 9IT 20815Thermal Methods of Change of FormPlaster Mold – investment material is plaster, works only with plastics or low-melting-point nonferrous metals or alloys. In plaster mold casting, a plaster, usually gypsum or calcium sulfate, is mixed with talc, sand, asbestos, and sodium silicate and water to form a slurry. This slurry is sprayed on the polished surfaces of the pattern halves (usually brass). The slurry sets in less than 15 minutes to form the mold. The mold halves are extracted carefully from the pattern, and then dried