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Heissen Riyadhovic101724017


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Introduction:

Pengecoran Logam (Metal casting) merupakan metode

pembentukan material yang di kenal paling tua.Casting/Pengecoran berarti menuangkan logam cair ke dalamcetakan dengan bentuk rongga yang akan dibuat,danmemungkinkannya untuk kembali mengeras(solid). Ketika telah padat, benda logam yangdiinginkan diambil keluar dari cetakan baik

dengan memecahkan cetakan ataumengambil cetakan terpisah. Objek atau materialyang dipadatkan disebut casting. Keuntungan dari pengecoranlogam (casting) adalah memungkinkan produksi pada banyakbentuk objek dengan murah. Keuntungan lainnya adalahmemungkinkan pembentukan objek lebih presisi yang tidakdapat di produksi dengan metode lainnya.Cetakan tempat logam di tuangkan terbuat dari bahan yangtahan terhadap panas. Pasir merupakan bahan yang palingbanyak digunakan karena memiliki heat resistancy yang tinggi.


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Foundry or casting is the process ofproducing metal/alloy component parts ofdesired shapes by pouring the molten

metal/alloy into a prepared mould (of thatshape) and then allowing the metal/alloy to

cool and solidify. The solidified piece ofmetal/alloy is known as a CASTING.


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Casting Terms:

1. Flask: yaitu sebuah bingkai yang terbuat dari kayu

atau logam sebagai tempat cetakan di bentuk.Tergantung pada posisi flask pada strukturcetakan, oleh karena itu flsk memiliki berbagai

sebutan yaitu drag - lower molding flask, cope -upper molding flask, cheek - intermediatemolding flask.

2. Pattern (pola): replika dari objek akhir yang akan

dibuat. Rongga cetakan (mold cavity) dibuatdengan bantuan pattern.

3. Parting line: yaitu garis pemisah antara dua flask

pada catakan.


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4. Core: Sebuah bagian terpisah dari cetakan, terbuatdari pasir dan umumnya dipanggang, yangdigunakan untuk membuat

bukaan dan berbagai bentuk rongga dalam coran.5. Pouring basin: Sebuah

rongga berbentuk corong kecil di bagian atas daricetakan dimana logam cair dituangkan.

6. Sprue: Bagian di mana logam cair, dari Pouringbasin mencapai rongga

cetakan. Berfungsi mengontrol aliran logamke cetakan.

7. Runner: Saluran yang di lewati logam cair dari Sprueke Gate.


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8. Gate: Sebuah saluran yang dilalui logamcair memasuki rongga cetakan.

9. Chaplets: digunakan untuk mendukung core didalam rongga cetakan untuk mengurus beratcore sendiri danmengatasi kekuatan metallostatic.

10. Riser: Sebuah kolom logam cairyang ditempatkan dalam cetakan untuk menjagakesetabilan coran (casting) karena menyusut dan

membeku. Juga dikenal sebagai feed head. 11. Vent: katup atau bukaan kecil pada cetakan

untuk memfasilitasi aliran udara dan gas.


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Basic Features:

Pattern and Mould A pattern is made of wood or metal, is a replica of the

final product and is used for preparing mould cavity.

Mould material should posses refractorycharacteristics and with stand the pouringtemperature.

When the mold is used for single casting, it made ofsand and known as expendable mold.

When the mold is used repeatedly for number ofcastings and is made of metal or graphite are calledpermanent mould.

For making holes or hollow cavities inside a casting,coresmade of either sand or metal are used.


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Melting and Pouring:

Several types of furnaces are available formelting metals and their selection depends onthe type of metal, the maximum temperaturerequired and the rate and the mode of molten

metal delivery. Before pouring provisions are made for the

escape of dissolved gases. The gating systemshould be designed to minimize the turbulent

flow and erosion of mould cavity.The otherimportant factors are the pouring temperatureand the pouring rate.


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Solidification and Cooling: The properties of the casting significantly

depends on the solidification time cooingrate.

Shrinkage of casting, during cooling of

solidified metal should not be restrainedby the mould material, otherwise internalstresses may develop and form cracks incasting.

Proper care should be taken at the designstage of casting so that shrinkage canoccur without casting defects.


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Removal, Cleaning, Finishingand

Inspection:

After the casting is removed from the mould

it is thoroughly cleaned and the excessmaterial usually along the parting line andthe place where the molten metal waspoured, is removed using a potable grinder.

White light inspection, pressure test,magnetic particle inspection, radiographictest, ultrasonic inspection etc. are used


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Schematic diagram of casting

mould:


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STEPS INVOLVED IN MAKING A

CASTING:

1. Make the pattern out of Wood , Metal or Plastic.2. Prepare the necessary sand mixtures for mould and core making.

3. Prepare the Mould and necessary Cores.4. Melt the metal/alloy to be cast.5. Pour the molten metal/alloy into mould and remove the casting from

the mould after the metal solidifies.6. Clean and finish the casting.

7. Test and inspect the casting.8. Remove the defects, if any.9. Relieve the casting stresses by Heat Treatment.10. Again inspect the casting.11. The casting is ready for shipping.


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Advantages of metal casting:

Casting is one of the most versatilemanufacturing process.

Casting provides the greatest freedom ofdesign in terms of shape, size and the productquantity.

Casting imparts uniform directional propertiesand better vibration capacity to the cast parts.

Casting produces machinable parts. Shapes difficult and uneconomic to obtain

otherwise may be achieved through castingprocess.

( Contd..)


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A product may be cast as one piece, there byeliminating the need of metal joining processes.

Very heavy and bulky parts which are otherwisedifficult to get fabricated may be cast.

Metals (like cast iron) dificult to be shaped by

other manufacturing processes may be cast. Casting can be designed for equal distribution of

loads and for minimum stress concentration inorder to achieve more strength and increased

service life.

Casting process can be mechanised and usefully

employed for mass production of components.


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Limitations of casting: Dimensional accuracy and surface finish of the

castings made by sand casting processes are alimitation to this technique.

Many new casting processes have been developed

which can take into consideration the aspects ofdimensional accuracy and surface finish.

Some of these processes are die casting process,

investment casting process, vacuum-sealedmolding process, and shell molding process.

The metal casting process is a labor intensiveprocess


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Applications of Casting:

Transportation vehicles

Turbine vanes

Power generators

Railway crossings

Agricultural parts

Aircraft jet engine parts

Sanitary fittings

Communication, Construction and AtomicEnergy applications, etc..


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Different Sections in Foundry:

1) Pattern making2) Sand mixing & preparation

3) Mould and core making

4) Mould assembly & handling5) Melting

6) Pouring

7) Shaking out8) Fettling & finishing

9) Heat treatment

10) Inspection & testing


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Raw Materials for

Foundry:1) Metals and alloys.

2) Fuels (for melting metals).3) Fluxes.


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Metals and alloys commonly

used in Foundries:

1. Ferrous2. Non-Ferrous

FERROUS:

a. Cast ironsb. Steels

NON-FERROUS:a. Copper alloys

b. Aluminium alloys

c. Magnesium alloys

d. Zinc alloys

e. Nickel alloys


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Fuels for Melting Metals:

1. Coal

2. Coke

3. Gas4. Oil

5. electricity


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Fluxes:

A flux is a low melting point material.

When heated up, it melts and combines withash, viscous slags, sand, metallic oxides etc., and

makes a fluid and easy flowing slag. This slag being lighter comes on to the surface

of the molten metal from where it can be easily

skimmed, tapped or removed before pouring themetal into the mould.

Slag protects molten metal from furnaceatmosphere.


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Refractories:

o Refractories are heat resistant materials.

o They can withstand high temperatures withoutbeing fused.

o Crucibles and furnace sides and bottomscontaining molten metal are made up ofrefractories.

o These are used as ladles for pouring metal intothe mould.

o Refractories constitute furnace walls and roofand thus minimize heat losses.

d i


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Core and core prints:

Castings are often required to have holes, recesses, etc. of

various sizes and shapes. These impressions can be obtained by using cores.

So where coring is required, provision should be made tosupport the core inside the mold cavity.

Core prints are used to serve this purpose.

The core print is an added projection on the pattern and itforms a seat in the mold on which the sand core rests duringpouring of the mold.

The core print must be of adequate size and shape so that itcan support the weight of the core during the castingoperation.

Depending upon the requirement a core can be placed


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Pattern having core prints.


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Pattern Making:

A Pattern is a model or the replica of theobject to be cast.

Except for the various allowances a patternexactly resembles the casting to be made.

A pattern is required even if one object has tobe cast.


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Functions of Patterns:

A Pattern prepares a mould cavity for thepurpose of making a casting.

A Pattern may contain projections known ascore prints if the casting requires a core andneed to be made hollow.

Patterns properly made and having finished

and smooth surfaces reduce casting defects.

Properly constructed patterns minimizeoverall cost of the casting.


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Selection of Pattern

Materials:

The following factors assist in selectingproper pattern material:

No. of castings to be produced.

Dimensional accuracy & surface finish.

Shape, complexity and size of casting.

Casting design parameters.

Type of molding materials.

The chance of repeat orders.

Nature of molding process.


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The pattern material should be:1. Easily worked, shaped and joined.

2. Light in weight.

3. Strong, hard and durable.

4. Resistant to wear and abrasion .

5. Resistant to corrosion, and to chemicalreactions.

6. Dimensionally stable and unaffected by

variations in temperature and humidity.

7. Available at low cost.


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Materials for making patterns:

a. Wood

b. Metal

c. Plasticd. Plaster

e. Wax.


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Types of Patterns:

1. Single piece pattern.

2. Split piece pattern.

3. Loose piece pattern.

4. Match plate pattern.

5. Sweep pattern.

6. Gated pattern.

7. Skeleton pattern8. Follow board pattern.

9. Cope and Drag pattern.


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(a)Split pattern

(b) Follow-board

(c) Match Plate(d) Loose-piece

(e) Sweep

(f) Skeleton pattern


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Fig: Single piece pattern


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Fig: split piece pattern


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Loose piece pattern:


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Fig: Match plate pattern


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CASTINGS

Gating system


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Fig: Cope and drag pattern

Moulding Materials


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Moulding Materials

Major part of Moulding material in sand casting are

1.70-85% silica sand (SiO2)2. 10-12% bonding material e.g., clay cereal etc.

3. 3-6% water

Requirements of molding sand are:

(a)Refractoriness(b) Cohesiveness

(c) Permeability

(d) Collapsibility

The performance of mould depends on following factors:(a) Permeability

(b) Green strength

(c) Dry strength


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Molding Material and Properties:

A large variety of molding materials is used infoundries for manufacturing molds and cores.They include molding sand, system sand or

backing sand, facing sand, parting sand, andcore sand. The choice of molding materials isbased on their processing properties. The

properties that are generally required inmolding materials are:


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1. Refractoriness:

It is the ability of the molding material to withstand high temperatures (experiencedduring pouring) with out

1. Fusion,2. Cracking, buckling or scabbing,

3. Experiencing any major physical

change. Silica sand have high refractriness.

2 Permeability:


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2. Permeability:

During pouring and subsequent solidification of a

casting, a large amount of gases and steam isgenerated.

These gases are those that have been absorbed bythe metal during melting, air absorbed from theatmosphere and the steam generated by themolding and core sand.

If these gases are not allowed to escape from themold, they would be entrapped inside the castingand cause casting defects.

To overcome this problem the molding materialmust be porous.

Proper venting of the mold also helps in escapingthe gases that are generated inside the mold cavity.

3 Green Strength:


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3. Green Strength:

The molding sand that contains moisture istermed as green sand.

The green sand particles must have the abilityto cling to each other to impart sufficient

strength to the mold. The green sand must have enough strength so

that the constructed mold retains its shape.

Green strength helps in making and handlingthe moulds.

4 Dry Strength:


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4. Dry Strength:

A mould may either intentionally be dried, or a

green sand mould may lose its moisture and getdried while waiting for getting poured or whenit comes in contact with molten metal beingpoured.

The sand thus dried must have dry strength to1. Withstand erosive forces due to

molten metal,

2. Withstand pressure of molten metal,3. Retain its exact shape,and

4. Withstand the metallostatic pressure

of the liquid material.

5 Hot Strength:


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5. Hot Strength:

As soon as the moisture is eliminated, the sandwould reach at a high temperature when the metalin the mold is still in liquid state.

The strength of the sand that is required to hold the

shape of the cavity is called hot strength.

In the absence of adequate hot strength, the moldmay

1. enlarge

2. break, erode or

3. get cracked.


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6. Collapsibility:

Collapsibility determines the readiness withwhich the molding sand,

1. Automatically gets collapsed after

the casting solidifies, and2. Breaks down in knock out and

cleaning operations.

If the mould or core does not collapse, itmay restrict free contraction of solidifyingmetal and cause the same to tear or crack.


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7. Flowability:

It is the ability of the molding sand to getcompacted to a uniform density.

Flowability assists molding sand to flow andpack all-around the pattern and take up therequired shape.

Flowability increases as clay and water

contents increase.


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8. Adhesiveness:

It is the property of molding sand owing towhich, it

1. Sticks with the walls of molding boxes,

2. Sticks with gaggers, and

3. Thus makes it possible to mold copeand drag.


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9. Fineness:

Finer sand mould resist metalpenetration and produce smooth castingsurfaces.

Fineness and permeability are in conflictwith each other and hence they must bebalanced for optimum results.


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Molding Sand Composition:

The main ingredients of any molding sand are:

Base sand,

Binder, and Moisture

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