Transcript Slide 1

NITC
Some basics - you had in Foundry
Sand casting.
Steps:
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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
NITC
Some basics you had
in Foundry
1.Mechanical Drawing of the part
2. Making pattern- about pattern
material.
3.Making cores- if needed
1
3
2
3a
4.Preparing drag and cope.
(Setting the core, positioning etc.)
5.Removal of pattern
3c
3b
6Assembling cope and drag
4b
7.Pouring- factors, method, etc.
5a
4a
8.Casting removed
9.Trimming etc.
5b
6
8&9
10
10. READY FOR SHIPMENT
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
castings
This 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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Moulding
Sand
- pattern making
- Core making
- Gating system
Mould
Melting Pouring
casting Heat Treat
Furnaces Solidification
Shakeout
Clean
Inspect
Addl. Heat Treatment
Defects, pressure tightness, dimensions
Outline of production steps in a typical sand casting operation NITC
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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.
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NIT CALICUT
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
Three Stages of Contraction (Shrinkage)
The liquid Metal has a Volume
"A”
It solidifies to solid with a new
volume "B"
The solidified casting further
contracts (shrinks) through
the cooling process to Volume
"C"
COOLING CURVE
For pure metal or compound
T
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P
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R
A
T
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R
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Cooling
of Liquid
Freezing begins
Freezing ends
At constant
temperature
Cooling of solid
Liquid
Liquid
+
Solid
Solid
TIME, log scale
Latent heat of
solidification
given off
during
freezing-
COOLING CURVE
For Binary solid solutions
T
E
M
P
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R
A
T
U
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Freezing with drop in
temperature
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)
TIME, log scale
(refresh dendritic growthbranches of tree, interlock, each
dendrite develops uniform
composition, etc)
The ambient
temperature is
always in a state of
transition
*
A
B
C
Minor variations in
volumetric
displacement are
negligible,
compared to the
variations that occur
from "A" to "B" and
lastly to "C".
*
A
B
C
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
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
Atm.Pressure
Pouring basin
MOULD
SPRUE
GATE
LIKE A PRESSURISED SYSTEM
MOULDERS’
TOOLS
AND
EQUIPMENT
MOULDING BOARD
FLASK
SHOWEL
DRAW SPIKE
RIDDLE
SLICK
RAMMER
LIFTER
STRIKE-OFF BAR
TROWELS
GATE CUTTER
BELLOWS
SPRUE PINS
VENT ROD …..
a
c
b
d
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
e
1.
1
2.
3a
3.
2
4a
3b
4.
5.
4b
5
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.
THREE BOX MOULDING
PROCEDURE
LOAM MOULDING USING
LOAM SAND