MOULDING SAND

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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.

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• 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 1.5moisture 3 to 3.5

• (2) New 15 Old 84
• bentonite and moisture 0.5 each

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• 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

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• 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

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About MOULDING SAND

1. NATURAL SAND
2. SYNTHETIC SAND.- GREEN and DRY
3. DRY SAND
4. LOAM SAND
5. FACING SAND
6. BACKING SAND
7. SYSTEM SAND
8. PARTING SAND
9. CORE SAND
10. SPECIALISED SANDS
11. Mould washers

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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.
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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

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• 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

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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 (gt 50 T, VERTICAL, HIGH RATES)
• ELECTRIC FURNACES
• INDUCTION FURNACES

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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.

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• CRUCIBLE FURNACE

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OIL FIRED FURNACE
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CUPOLA CHARGE PASSES
DOWNWARDS UNDER GRAVITY MEETS FLOW OF HOT GASES
MOVING UPWARDS CONTINUOUS IN OPERATION.Vertica
l 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.
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TOWER FURNACETO MELT ALUMINIUM alloys3 main
sections- charging elevator, melting unit,
holding furnace (Cylindrical rotary unit).
Automatic controlsGrate above burners
supports solid chargeMolten charge runs down
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REVERBERATORY
FURNACE Small units (50kg) for melting non
ferrous metals, large (about 25T) 10 T capacity
to melt iron AIR FURNACEOne 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
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TYPICAL DIRECT ARC FURNACE
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A TYPICAL DIRECT
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