03 SAND AND FURNACES

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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. Addcow 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 CO2 sand, Shell sand, etc
for special applications
Mould washers- slurry of fine ceramic grains applied on
mould surface to minimize fusing
NITC
About MOULDING SAND
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NATURAL SAND
SYNTHETIC SAND.- GREEN and DRY
DRY SAND
LOAM SAND
FACING SAND
BACKING SAND
SYSTEM SAND
PARTING SAND
CORE SAND
SPECIALISED SANDS
Mould washers
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
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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, pouringUse 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 sectionscharging 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
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