MOULDING SANDGranular 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 % eachNITC

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 sandNITC

BACKING SAND- old used moulding sand called floor sand black in colour. Used to fill mould at back of facing layer. Weak in bonding strengthSYSTEM SAND- used in machine moulding to fill whole of flask. Strength, premealibility and refractoriness highPARTING SAND- used for separating boxes from adhering, free from clayCORE SAND- for making cores. Silica sand with core oil (linseed oil, rosin, light mineral oil, binders etc)SPECIALISED SANDS - like CO2 sand, Shell sand, etc for special applicationsMould washers- slurry of fine ceramic grains applied on mould surface to minimize fusing NITC

About MOULDING SANDNATURAL SANDSYNTHETIC SAND.- GREEN and DRYDRY SANDLOAM SANDFACING SANDBACKING SANDSYSTEM SANDPARTING SANDCORE SAND SPECIALISED SANDS Mould washers

NITC

ADV - Acid Demand ValueDefined 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 handlingDry Strength- After pouring molten metal, adjacent surface loses water content. Dries. Dry sand must have enough strength to resist erosionHot 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 SCABRefractoriness- Ability of sand to withstand high temperatureFlowability- Ability to flow & fill narrow portions around patternSurface finish- Ability to produce good surface finish in castingCollapsibility- Allow easy removal of casting from mouldReclamation- Should be reusable and reclaimable

NITC

FURNACES Proper selection depends on:Composition and melting point of alloy to be castControl of atmospheric contaminationCapacity and rate of melting requiredEnvironmental considerations- noise, pollutionPower supply, availability, cost of fuelsEconomic considerations-initial cost, operating cost, maintenance cost etc.CUPOLAS (> 50 T, VERTICAL, HIGH RATES) ELECTRIC FURNACESINDUCTION FURNACESNITC

FOUNDRIESFrom 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

CRUCIBLE FURNACE

OIL FIRED FURNACE

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

TYPICAL DIRECT ARC FURNACE

A TYPICAL DIRECT