NITC. Some basics - you had in FoundrySand casting. Steps: »1.Mechanical Drawing of the part »2. Making pattern- about pattern material. »3.Making cores-

NITC

Some basics - you had in Foundry

Sand casting.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 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

Some basics you had in Foundry

1

4a

32

5b 6 8&9 10

5a4b

3b 3c3a

CASTINGCASTING FUNDAMENTALS 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 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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Outline of production steps in a typical sand casting operation

- pattern making - Core making - Gating system

Moulding

Sand Mould

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.

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CA

LIC

UT

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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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CA

LIC

UT

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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

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"

Three Stages of Contraction (Shrinkage)

COOLING CURVE For pure metal or compound

TEMPERATURE

TIME, log scale

Freezing begins Freezing ends

Liquid

Liquid

+

SolidSolid

Cooling of Liquid

Cooling of solid

Latent heat of solidification

given off during

freezing-

At constant temperature

COOLING CURVE For Binary solid solutions

TEMPERATURE

TIME, log scale

Freezing with drop in temperature

And FOR ALLOYS:Alloys solidify over a range of temperaturesBegins 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)

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".

A

C

B

B

C

A

*

*

STRUCTURE

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FOR PURE METALSFOR 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

Solidified structures of metal - Solidified structures of metal - solidified in a square mouldsolidified in a square mould

(a). Pure metal(b). Solid solution(c). When thermal gradient is absent

within solidifying metal

Development of a preferred texture Development of a preferred texture - for pure metal at a cool mould wall. - for pure metal at a cool mould wall.

A chill zone close to the wall and then a columnar zone away from the mould.

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 convectionOuter chill zones do not occur in the absence of convection

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DIRECTIONAL SOLIDIFICATION

Atm.Pressure

Pouring basin

MOULD

GATE

SPRUE

LIKE A PRESSURISED SYSTEM

MOULDING BOARDFLASKSHOWELDRAW SPIKERIDDLESLICKRAMMERLIFTERSTRIKE-OFF BARTROWELS GATE CUTTER BELLOWSSPRUE PINS VENT ROD …..

MOULDERS’

TOOLS

AND

EQUIPMENT

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

edc

ba

1. Make the pattern in pieces, prepare the core.

2. Position the drag half of pattern on mould board in the drag half of flask

3. 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

4. Separate flasks, remove patterns, cut sprue, set core in place, close flask

5. Now after clamping, ready fro pouring.

2

3b

4a

1

3a

4b

5

THREE BOX MOULDING PROCEDURE

LOAM MOULDING USING LOAM SAND