Presentation on theme: "MOULDING SAND Granular particles from the breakdown of rocks by frost, wind, heat and water currents Complex Composition in different places At bottom."— Presentation transcript:
MOULDING SAND Granular particles from the breakdown of rocks by frost, wind, heat and water currents Complex Composition in different places At bottom and banks of rivers - mainly silica (86 to 90%); Alumina (4% to 8 %); Iron oxide (2 to 5%) with oxides of Ti, Mn, Ca. etc. NITC
NATURAL SAND, called Green sand. Only water as binder; can maintain water for long time SYNTHETIC SAND.- (1)GREEN and (2)DRY types (1) Artificial sand by mixing clay free sand, binder(water and bentonite) Contains New silica sand 25%; Old sand 70%; bentonite 1.5%;moisture 3% to 3.5% (2) New 15%; Old 84%; bentonite and moisture 0.5 % each NITC
DRY SAND- for moulding large castings. Moulds of green sand dried and baked with venting done. Add- cow dung, horse manure etc. LOAM SAND- mixture of clay and sand milled with water to thin plastic paste. Mould made on soft bricks. The mould dried very slowly before cast. For large regular shapes- drums, chemical pans etc. FACING SAND- used directly with surface of pattern; comes in contact with molten metal; must have high strength, refractoriness. Silica sand and clay without used sand- plumbago powder, Ceylon lead, or graphite used. Layer of 20 to 30 mm thick--- about 10% to 15% of whole mould sand NITC
BACKING SAND- old used moulding sand called floor sand black in colour. Used to fill mould at back of facing layer. Weak in bonding strength SYSTEM SAND- used in machine moulding to fill whole of flask. Strength, premealibility and refractoriness high PARTING SAND- used for separating boxes from adhering, free from clay CORE SAND- for making cores. Silica sand with core oil (linseed oil, rosin, light mineral oil, binders etc) SPECIALISED SANDS - like CO 2 sand, Shell sand, etc for special applications Mould washers- slurry of fine ceramic grains applied on mould surface to minimize fusing NITC
ADV - Acid Demand Value Defined as the property of a sand or additive to affect the cure process as a function of the materials acidity or basicity on the pH scale.
MOULDING SAND- PROPERTIES Green Strength- Adequate strength after mixing, and plasticity for handling Dry Strength- After pouring molten metal, adjacent surface loses water content. Dries. Dry sand must have enough strength to resist erosion Hot Strength- Strength at elevated temperature after evaporation of moisture Permeability- Permeable or porous to permit gases to escape. Ability of sand moulds to allow the escape of gases NITC
Thermal stability- Rapid expansion of sand surface at mould-metal interface. May crack. Results in defect called SCAB Refractoriness- Ability of sand to withstand high temperature Flowability- Ability to flow & fill narrow portions around pattern Surface finish- Ability to produce good surface finish in casting Collapsibility- Allow easy removal of casting from mould Reclamation- Should be reusable and reclaimable NITC
FURNACES Proper selection depends on: Composition and melting point of alloy to be cast Control of atmospheric contamination Capacity and rate of melting required Environmental considerations- noise, pollution Power supply, availability, cost of fuels Economic considerations-initial cost, operating cost, maintenance cost etc. CUPOLAS (> 50 T, VERTICAL, HIGH RATES ) ELECTRIC FURNACES INDUCTION FURNACES NITC
FOUNDRIES From Latin word- fundere (meaning melting & pouring) Pattern & Mould making- automated, computer integrated facilities- CAD/CAM Melting, controlling composition & impurities, pouring- Use of conveyors, automated handling, shakeout, cleaning, heat treatment, inspection, etc. NITC
CUPOLA * CHARGE PASSES DOWNWARDS UNDER GRAVITY * MEETS FLOW OF HOT GASES MOVING UPWARDS * CONTINUOUS IN OPERATION.Vertical steel shell, lined with fire bricks..Base on four steel columns.Hinged doors in the base plate to remove residue at the end of melt..Air blast through tuyeres (number on size).Through charging door, coke, pig iron, scrap & lime stone charged..Cold & Hot blast cupolas.
TOWER FURNACE TO MELT ALUMINIUM & alloys 3 main sections- charging elevator, melting unit, holding furnace (Cylindrical rotary unit). Automatic controls Grate above burners supports solid charge Molten charge runs down
REVERBERATORY FURNACE Small units (50kg) for melting non ferrous metals, large (about 25T) 10 T capacity to melt iron AIR FURNACE: One type of RB- to melt cast iron for roll mill rolls, malleable castings, 15 T capacity – Charge out of contact with fuel, less sulphur absorbed, long melting time enables control of composition, large size scrap handled. Lump coal, pulverised fuel, oil used to fire. Solid coal burnt in a grate