Pattern making a pattern is an approximate replica of

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Unformatted text preview: making A pattern is an approximate replica of the exterior of the casting 2. Core making Cores (usually made of sand) are placed in to mold to form the interior surfaces of the casting 3. Molding involves placing a molding aggregate around a pattern, held within a supporting frame, withdrawing the pattern, setting the core, and closing the mold 4. Melting and pouring Lip, teapot, bottom pouring 5. Cleaning refers to removal of sand, scale and excess metal from the casting. Excess metal: fins, wires, parting line fins, gates Defective casting: salvaged by welding etc. Further processing: heat treatment, surface treatment, or machining Pattern allowances A pattern is made of wood, metal, plaster, plastics, wax etc. 1. Shrinkage allowance Solidification shrinkage (during solidification) Thermal contraction (liquidus - room temperature) (1/8)-(1/4) in./ ft for cast iron 2. Machine finish allowance depends on metal, casting design, method of casting and cleaning 1/8 in./ ft for cast iron 3. Pattern draft draft is the taper allowed on vertical faces of a pattern to permit its removal from the molding medium without tearing the mold cavity. 1/16 in./ft 4. Size tolerance The variation which may be permitted on a given casting dimension is called tolerance; difference between min & max dimension 1/16 in./ ft for cast iron 5. Distortion allowance To prevent distortion of large flat plate, dome or U-shape casting from a perfect/straight pattern, the patterns are intensionally distorted (“faked”) to produce castings with desired shape and size. Making a mold green sand molding pattern core molding aggregate (sand+clay+water) flask (drag-cheeks-cope) rammer (pin and butt end) chaplet/core prints downgate (sprue) ingate pouring cup/ basin riser facing sand (fine & clean) backing sand parting powder Cores Cores sand mixture: consist of sand grains and organic binders (linseed oil) mixture is rammed in a core box. Green cores are baked at 150-200oC; binder molecule polymerize in presence of O2 and harden Cores making machine: Jolt machine (used for ramming) Shell core machine (used for ramming and baking) Cores setting: Location of the core chaplets (radiator, double head, sheet metal, perforated) unsupported load = core buoyancy - core print support Core sand disposal: core sand should be separated from the molding sand Core knockout: burning, hammering, hydro-blasting Required properties of sand 1....
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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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