METAL CASTING

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METAL CASTING
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Some basics - you had in Foundry

• Sand casting.
• Steps
• 1.Mechanical Drawing of the part
• 2. Making pattern- about pattern material.
• 3.Making cores- if needed
• 4.Preparing drag and cope. (Setting the core,
  positioning etc.)
• 5.Removal of pattern
• 6Assembling cope and drag
• 7.Pouring- factors, method, etc.
• 8.Casting removed
• 9.Trimming etc.
• 10. READY FOR SHIPMENT

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1.Mechanical Drawing of the part2. Making
pattern- about pattern material.3.Making cores-
if needed4.Preparing drag and cope. (Setting
the core, positioning etc.)5.Removal of
pattern6Assembling cope and drag7.Pouring-
factors, method, etc.8.Casting
removed9.Trimming etc.10. READY FOR SHIPMENT
Some basics you had in Foundry
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CASTING

• 
  FUNDAMENTALS Basically involves
• i. Pouring molten metal into a mould
  patterned after the part to be made WITHOUT
  TURBULANCE , SERIES OF EVENTS TAKES PLACE
• INFLUENCE SIZE, SHAPE, UNIFORMITY
  OF THE GRAINS FORMED,
• AND THUS THE OVERALL PROPERTIES.
• ii. Allow it to cool HEAT TRANSFER
  DURING SOLIDIFICATION
• iii. Remove from the mold INFLUENCE OF
  THE TYPE OF MOULD MATERIAL
• SIMILARITY WITH POURING
  CAKE MIX INTO A PAN

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POURING CAKE MIX INTO A PAN (MOULD) BAKING
IT SELECT THE KIND AND SIZE OF PAN, CONTROL
THE COMPOSITION OF THE MIX, CAREFULLY POUR
THE MIX, SET THE PROPER BAKING TEMPERATURE,
SET THE TIMER FOR PROPER BAKING TIME,
LEAVE THE CAKE IN THE MOULD FOR A CERTAIN
AMOUNT OF TIME BEFORE REMOVING. 
(CASTING OF PLASTICS CERAMICS - DIFFERENT)
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Knowledge of certain fundamental relationships is
essential to produce good quality economic
castingsThis knowledge helps in establishing
proper techniques for mould design and casting
practice. Castings must be free from defects,
must meet the required strength, dimensional
accuracy, surface finish
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Outline of production steps in a typical sand
casting operation

• 
  - pattern making
• 
  - Core making
• 
  - Gating system

Moulding
Mould
Sand
Melting
Pouring
casting
Heat Treat
Clean
Inspect
Furnaces
Solidification
Shakeout
Addl. Heat Treatment

Defects, pressure tightness, dimensions
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• ADVANTAGES OF CASTING PROCESS
• Process is cheap
• More suitable for mass production
• Most suitable for manufacturing
  complex/complicated/intricate shaped products.
• Large parts weighing several tonnes and also
  small components weighing a few grams can be
  cast.
• No limitation on the size of component.
• Directional properties absent in castings.
  Components with uniform properties as well as
  with varying properties at different locations
  can be cast.
• By use of cores, saving in machining of holes
  achieved.
• Internal stresses are relieved during
  solidification in many types of castings.
• Even some materials which cannot be made by other
  processes made by casting eg. Phosphor-Bronze.

NIT CALICUT
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• DISADVANTAGES
• Cast product properties inferior in many cases
  when compared with other manufacturing processes.
• Elevated temperature working in castings, as
  material has to be melted.
• Thin section limitations exist.
• For number of components very small, casting not
  preferred.

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• SIGNIFICANT FACTORS-
• TYPE OF METAL,
• THERMAL PROPERTIES OF BOTH THE METAL AND MOULD,
• GEOMETRIC RELATIONSHIP BETWEEN THE VOLUME AND
  SURFACE AREA ,AND
• SHAPE OF MOULD.

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• SOLIDIFICATION OF METALS
• AFTER POURING MOLTEN METAL INTO MOULD, SERIES OF
  EVENTS TAKES PLACE DURING SOLIDIFICATION AND
  COOLING TO AMBIENT TEMPERATURE.
•  
• THESE EVENTS GREATLY INFLUENCE THE SIZE, SHAPE,
  UNIFORMITY OF THE GRAINS FORMED, AND THUS THE
  OVERALLL PROPERTIES.
•  

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Volumetric variation from Liquid through
Solidification and then to ambient temperature
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The liquid Metal has a Volume "AIt
solidifies to solid with a new volume "B"The
solidified casting further contracts (shrinks) 
through the cooling process to Volume "C"
Three Stages of Contraction (Shrinkage)
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COOLING CURVE

• For pure metal or
  compound

TEMPERATURE
Cooling of Liquid
Latent heat of solidification given off during
freezing- At constant temperature
Freezing begins
Freezing ends
Liquid Solid
Cooling of solid
Liquid
Solid
TIME, log scale
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COOLING CURVE
And FOR ALLOYS Alloys solidify over a range of
temperatures Begins when temp. drops below
liquidous, completed when it reaches
solidous. Within this temperature range, mushy or
pasty state. Inner zone can be extended
throughout by adding a catalyst.- sodium,
bismuth, tellurium, Mg (or by eliminating
thermal gradient, i.e. eliminating convection.
(Expts in space to see the effect of lack of
gravity in eliminating convection) (refresh
dendritic growth- branches of tree, interlock,
each dendrite develops uniform composition, etc)

• For Binary solid solutions

TEMPERATURE
Freezing with drop in temperature
TIME, log scale
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The ambient temperature is always in a state of
transition Minor variations in volumetric
displacement are negligible, compared to the
variations that occur from "A" to "B" and lastly
to "C".
B
A
C

A
B
C
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STRUCTURE

• FOR PURE METALS
• At the mould walls, metal cools rapidly.
  Produces solidified skin or shell (thickness
  depends on composition, mould temperature, mould
  size and shape etc)
• These of equiaxed structure.
• Grains grow opposite to heat transfer through the
  mould
• These are columnar grains
• Driving force of the heat transfer is reduced
  away from the mould walls and blocking at the
  axis prevents further growth

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Development of a preferred texture - for pure
metal at a cool mould wall. A chill zone close
to the wall and then a columnar zone away from
the mould.

• Solidified structures of metal - solidified in a
  square mould
• (a). Pure metal
• (b). Solid solution
• (c). When thermal gradient is absent within
  solidifying metal

Three basic types of cast structures- (a).
Columnar dendritic (b). equiaxed dendritic
(c). equiaxed nondendritic
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Size and distribution of the overall grain
structure throughout a casting depends on rate
direction of heat flow(Grain size influences
strength, ductility, properties along different
directions etc.)CONVECTION- TEMPERATURE
GRADIENTS DUE TO DIFFERNCES IN THE DENSITY OF
MOLTEN METAL AT DIFFERENT TEMPERATURES WITHIN THE
FLUID - STRONGLY EFFECTS THE GRAIN SIZE. Outer
chill zones do not occur in the absence of
convection
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DIRECTIONAL SOLIDIFICATION
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LIKE A PRESSURISED SYSTEM
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MOULDING BOARDFLASKSHOWELDRAW
SPIKERIDDLESLICKRAMMERLIFTERSTRIKE-OFF
BARTROWELS GATE CUTTER BELLOWSSPRUE PINS
VENT ROD ..

• MOULDERS
• TOOLS
• AND
• EQUIPMENT

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b
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e
d
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Making a Core (a). Ramming Core Sand. (b).
Drawing the core box (c). Baking in an oven (d)
Pasting the core halves
(e). Washing the core with refractory
slurry
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• Make the pattern in pieces, prepare the core.
• Position the drag half of pattern on mould board
  in the drag half of flask
• Prepare the drag half of mould, roll drag over,
  apply parting sand, place the cope half of
  pattern and flask, ram and strike off excess sand
• Separate flasks, remove patterns, cut sprue, set
  core in place, close flask
• Now after clamping, ready fro pouring.

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THREE BOX MOULDING PROCEDURELOAM MOULDING
USING LOAM SAND