Investment molding 3 ceramic molding 4 plaster

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Unformatted text preview: estment molding 3. Ceramic molding 4. Plaster molding 5. Graphite molding Classification of the casting processes 1. Sand casting 2. Permanent - mold casting (metal mold) 3. Die casting 4. Rapid solidification processing 5. Centrifugal casting 6. Injection casting 7. Suction casting 8. Cold crucible casting Shell Molding - fine grained sand - thermosetting resin binder (phenol formaldehyde) - catalyst hexa-methylene tetramine (CH2)6N4 -> NH3 - stearic acid (reduce friction) h_1 formaldehyde phenol Loam Molding Plaster casting Au, Ag, Cu, Al-alloys Plaster: slurry of plaster of paris (gypsum)+ water Antioch process: slurry of plaster of paris (gypsum)+ water + talc + sodium silicate + asbestos + sand Advantage: permeability Setting of plaster: hydration CaSO4.1/2 H2O + H2O = CaSO4.2H2O+ heat drying: 160-230oC CaSO4.2H2O--> CaSO4.1/2 H2O--> CaSO4 (anhydrous calcium sulfate) Calcium sulfate Investment casting alloys for medical application, sculptors, jewelry Pattern and gating systems: Wax, plastic, tin Refractory slurry: binder + alumina+silica+Zr-silicate steps: - preparation of pattern and gating system - welding / assembling - precoating and sand blasting - investing - dewaxing & preheating - firing binders: ethylsilicate, Mg-phosphate, gypsum Si(OC2H5)4+4H2O=H4SiO4+4C2H5OH drying in air for 8 h H4SiO4 (orthosilicate)= 2H2O+SiO2 Graphite mold casting features - Ti-alloys, brass, bronze can be cast - expendable mold: 30% binder (pitch+Carbonaceous cement+starch+water) + 70% graphite grains is molded by squeezing around the pattern. dried and fired in reducing atmosphere - permanent mold: solid block of graphite is machined - coating: ethyl silicate deposits silica- to prevent oxidation Permanent mold casting mold material: grey CI, steel, bronze features - permanent metal mold (5-100,000 cycles) - Al, Mg, Zn, Pb, cast iron, Cu-alloys can be cast - coating (refractory, C-shoot by acetylene flame) mold life and casting ejection become easier good surface finish castings carburetor, hydraulic brake cylinders, gears, vacuum pump cylinders Die casting or pressure die casting - similar features as permanent mold casting - molten alloy is forced to fill the mold cavity under high pressure (1000-100,000 psi) - option: hot chamber- or- cold chamber steps: - cleaning the mold by brushing/ air blasting and maintain proper operating temperature - painting refractory wash/ blacking by C-deposition from oil or gas-flame on mold wall - insertion of core (if any), closing of mold, - pouring of metal and solidification - ejection of casting from the mold Centrifugal casting - economical for tubular cast...
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This note was uploaded on 10/11/2012 for the course MINING 101 taught by Professor K.dey during the Spring '11 term at Indian Institute of Technology, Kharagpur.

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