casting process report by savan

Kautilya Inst. Of Tech. & Engg. Jaipur

A Training Report

(Submitted for the partial fulfillment ofBachelor of Technology in MECHANICAL ENGG.

Rajasthan Tech. Univ.-Kota)

Submitted ByGHADIYA SUGNESHKUMAR (B.Tech. VIIth semester)

Submitted To: Head of the Department:Mr. Mukul Sharma Mr. K.K KhatriTraining Co-ordinator

2010-2011Department of Mechanical Engineering

KAUTILYA INSTITUTE OF TECHNOLOGY AND ENGINEERINGSitapura, Jaipur

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KAUTILYA INSTITUTE OF TECHNOLOGY AND ENGINEERING, JAIPUR

A

REPORT ON PRACTICAL TRAINING TAKEN AT

Shining Engineers & Founders Pvt. Ltd. (In partial fulfillment of Award of Bachelor of Technology in MECHANICAL ENGG. Rajasthan Tech. Univ.-Kota)

SUBMITTED TO: SUBMITTED BY:Mr. Mukul Sharma Ghadiya Sugnesh G.TRAINING CO-ORDINATOR, MECHANICAL ENGG.(MECH. ENGG. DEPT.)

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To whom so ever It May Concern

This is certifying that the Practical Training Seminar Report entitled

“SHINING ENGINEERS & FOUNDERS PVT. LTD. RAJKOT,

GUJARAT” being submitted by Mr.Ghadiya Sugneshkumar G. (IVyr

B. Tech., VII Sem.) for the partial fulfilment of the requirement of the

Degree of Bachelor of Technology in Mechanical Engineering of

Kautilya Institute of Technology & Engineering & School of

Management, Jaipur is a record of the practical training taken by him.

(Internal Examiner) H.O.D (Mech.)Mr. Mukul Sharma Mr. K.K Khatri

(External examiner)

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AKNOWLEDGEMENT

I express my deep sense of gratitude to Mr. SANJAY BHAI

(H.O.D, SHINING ENGINEERS & FOUNDERS PVT. LTD )

for giving me a golden opportunity to pursue

My industrial training at SHINING, Rajkot ( Gujarat )

I owe my heartiest thanks to my training guide Mr. Brijesh sir for

giving me the opportunity to learn & understand the

practical implementation of academic studies. He is always there in the

hours of need. Here I express my sincere thanks to all other Colleagues of

Engineering department who extend their help in the

Understanding of the duties and responsibilities of the Dept.

Here I express my sincere gratitude to Mr. Nittin Goyal sir (Training and

Placement Officer of K.I.T.E. jaipur ) for his active cooperation and sincere

Advice in choosing the right company to pursue my training. He is not only

my guide but also my mentor.

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CONTENTS

Page No.

1. Introduction of Company 1

1.1. Company Profile 1

1.2. History of Company 1

1.3. Organization Chart

2. Introduction about Casting 2

2.1. Definition 2

2.2. Type of Casting 3

2.2.1 Sand Casting

2.2.2 Die casting

2.2.3 Investment Casting

2.2.4 Centrifugal casting

2.2.5 Plaster-mould casting

2.2.6 Permanent-mold casting

2.2.7 Squeeze casting

2.3 Advantages & Disadvantages

3. Casting Terminology 13

3.1 Pattern 13

3.1.1 Pattern Material

3.1.2 Type of Pattern

3.1.2.1 Solid or single piece pattern.

3.1.2.2 Split pattern or two-piece pattern

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3.1.2.3 Cope and Drag Pattern

3.1.2.4 Match plate pattern

3.1.2.5 Gated Pattern

3.1.2.6 Skeleton Pattern

3.1.2.7 Pattern with Loose – Pieces

3.1.3 Pattern Allowances

3.1.3.1 Shrinkage allowance

3.1.3.2 Draft allowances

3.1.3.3 Machining allowance

3.1.3.4 Distortion allowance

3.1.3.5 Rapping Allowance

3.2 Core

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3.2.1 Types of Core

3.2.1.1 Green sand core

3.2.1.2 Dry sand core

3.2.2 Core Print

3.2.3 Core Box

3.3 Mould

3.3.1 Type of Mould

3.3.1.1 Permanent mould

3.3.1.2 Temporary mould

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3.3.2 Moulding Sand

3.3.2.1 Properties of Moulding Sand

3.3.2.2 Sand Testing

4. Melting Equipment

4.1 Cupola Furnace

4.2 Electric Furnace

5. Melting & Pouring

5.1 Gating System

5.1.1 Runner & Sprue

5.1.2 Riser

6. Cleaning & Finishing.

7. Casting Defects

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1.1 INTRODUCTION OF THE COMPANY:

M/s Shining Engineers & Founders Pvt. Ltd. are capable and equipped with

all kind of manufacturing facilities to produce high quality of products under one roof.

The production unit consist melting furnace with controlled environment, conventional

& non-conventional to be assured about the good quality of products.

Spanned across 34,000 square meter area and environment friendly foundry

setup along with the full fledge testing facilities like instance lab, chemical lab,

standard room for inspection is the infrastructure that we have for high-quality product

manufacturing as well as quality assurance.

This is the core of quality and process improvement as well as the

infrastructure that can stand in the most demanding situations. This is what have gained

us strong client base.

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COMPANY PROFILE

1. Name of the company:

Shining Engineers & Founders Pvt. Ltd

2. Address:

Shining Engineers & Founders Pvt. Ltd.

At : - Shaper (Veraval),

Shaper GIDC,

Dist :- Rajkot

State :- Gujarat

3. Year of Establishment:

1968

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1.2 History and Development of Company

Founded in the year 1968, M/s Shining Engineers & Founders Pvt. Ltd. has its

strong hold on the Electric Motor Body and Cast Iron Castings. From its inception

company set its focus on producing high-quality cast iron casting parts.

Started with the production capacity of 100 MT/Month, company keeps capturing

the niche market while maintaining its strong focus on quality and process improvement.

With the efforts of the company promoters and their global team, company entered into

the global market in the year 1996 with its products in Electric Motor Components.

Today company is prominent supplier of electric motor housing and end-shield with a

range of 10 kg to 600 kg withthe1200MT/Month capacity.

Today company has shining share in export market of Electric Motor Housing and

End-Shield. Company started supply to leading OEM motor manufacturers like Siemens,

Demag Crains & Components.

With more responsible and committed approach towards quality and environment,

company validated, confirmed and certified the ISO 9001-2000 standards by RWTUV

Germany in the year 2003

To answer the ever growing requirements of customers, M/s Shining Engineers &

Founders Pvt. Ltd has tied up its activities with M/s D. N. Engineers, India, an ISO 9001-

2000 company. M/s D. N. Engineers aim to manufacture Motor Components and

Automobile parts. It supplies electric motor housing and its parts to OEM like ABB,

Bharat Bijlee, Siemens, Crompton Greaves and Eicher Motors Ltd.

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1.3 Organization Chart:

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2. Introduction about Casting

Casting is basically melting a solid material, heating to a special temperature, and

pouring the molten material into a cavity or mould, which is in proper shape. Casting has been

known by human being since the 4th century B.C.

Today it is nearly impossible to design anything that cannot be cast by means of one or

more of the available casting processes. However, as with other manufacturing processes, best

results and economy can be achieved if the designer understands the various casting processes

and adapts his designs so as to use the process most efficient.

2.1 Definition

In casting involves pouring a liquid metal into a mold, which contains a hollow cavity

of the desired shape, and then is allowed to solidify. The solidified part is also known as a

casting, which is ejected or broken out of the mold to complete the process. Casting is most

often used for making complex shapes that would be difficult or uneconomical to make by

other methods

2.2 Type of Casting

2.2.1 Sand casting

2.2.2 Die casting

2.2.3 Investment casting





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2.2.1 Sand casting

Sand casting is a flexible, inexpensive

process. Sand is used as the mold material. The

sand grains, mixed with small amounts of other

materials to improve the mold ability and

cohesive strength, are packed around a pattern

that has the shape of the desired casting. Products

covering a wide range of sizes and detail can be

made by this method. A new mold must be made

for each casting, and gravity usually is employed

to cause the metal to flow into the mold. As

shown below in figure steps of sand casing

The process of sand casting is very old going back to the Bronze Age; the technique has

changed very little since. It involves making a suitable void in compacted sand which is then

filled with molten metal. This process is best suited to large casting where surface finish is not

important or which will be machined later. Thin sections are not really suitable as the molten

material starts to cool before the mould is completely filled, forming “cold shuts”.

The first stage in sand casting is to make a pattern in wood or metal of the shape to be cast.

This pattern is made slightly larger to allow for shrinkage of the hot metal as it cools down

after casting. Any part that requires machining after casting would have a machining allowance

incorporated in the pattern. The pattern maker is a very skilled craftsman because as well as

making the pattern he must have a complete understanding of the actual process of casting. In

making the pattern he decides the way the item will be cast. Depending on the shape of the

item the pattern could be in one or several pieces. If the pattern is split the separate parts are

located together with metal pins or dowels. In deciding which way to cast a particular item the

pattern maker would consider several factors such as, which way up to cast it. Molten metal is

very heavy and most of the impurities in the metal float. When the metal is cast the impurities

get carried around the mould with the metal as they have a tendency to float they are likely to

be deposited in one place, either trapped by a narrowing in the shape or floating to the top of

the casting.

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2.2.2 Die casting

Die castings are among the highest volume, mass-produced items manufactured by the

metalworking industry. They can be found in thousands of consumer, commercial and

industrial products. Die cast parts are important components of products ranging from

automotive to toys. Parts can be as simple as a trowel handle or a complex engine block.

A versatile process for producing engineered metal parts, die

casting calls for forcing molten metal under high pressure

into reusable steel moulds. These moulds, called dies, can be

designed to produce complex shapes with a high degree of

accuracy and repeatability. Parts can be sharply defined,

with smooth or textured surfaces, and are suitable for a wide

variety of attractive and serviceable finishes.

Refinements are continuing in both the alloys used in die

casting and the process itself, expanding die casting applications into almost every known

market. Today’s die casters can produce castings in a variety of sizes, shapes and wall

thicknesses that are lightweight, strong, durable and dimensionally precise. The process has

been well researched and systematically quantified in terms of thermodynamics, heat transfer

and fluid flow. A new range of machine casting technologies such as squeeze casting and

semi-solid metal casting (SSM) are able to combine the near-net-shape benefits of traditional

die casting with innovative approaches to producing highly dense, heat-treatable parts.

The basic die casting process consists of injecting molten metal under high pressure into a steel

mould called a die. Die casting machines are typically rated in clamping tons equal to the

amount of pressure hey can exert on the die. Machine sizes range from 200 tons to 5,000 tons.

Regardless of their size, the only fundamental difference in die casting machines is the method

used to inject molten metal into a die.

2.2.2 Investment Casting

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Investment casting (known as lost-wax casting in art) is a process that has been

practiced for thousands of years, with the lost-wax process being one of the oldest known

metal forming techniques. From 5000 years ago, when beeswax formed the pattern, to

today’s high technology waxes, refractory materials and specialist alloys, the castings ensure

high-quality components are produced with the key benefits of accuracy, repeatability,

versatility and integrity.

Investment casting derives its name from the fact that the pattern is invested, or

surrounded, with a refractory material. The wax patterns require extreme care for they are not

strong enough to withstand forces encountered during the mold making. One advantage of

investment casting is that the wax can be reused.

The process is suitable for repeatable production of net shape components from a

variety of different metals and high performance alloys. Although generally used for small

castings, this process has been used to produce complete aircraft door frames, with steel

castings of up to 300 kg and aluminum castings of up to 30 kg. Compared to other casting

processes such as die casting or sand casting, it can be an expensive process, however the

components that can be produced using investment casting can incorporate intricate contours,

and in most cases the components are cast near net shape, so requiring little or no rework

once cast.

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http://en.wikipedia.org/wiki/Sand_casting

http://en.wikipedia.org/wiki/Die_casting

http://en.wikipedia.org/wiki/Aluminium

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Beeswax


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Centrifugal casting consists of having sand, metal, or ceramic mold that is rotated at

high speeds. When the molten metal is poured into the mold it is thrown against the mold

wall, where it remains until it cools and solidifies. The process is being increasingly used for

such products as cast-iron pipes, cylinder liners, gun barrels, pressure vessels, brake drums

gears, and flywheels. The metals used include almost all castable alloys.

Because of the relatively fast cooling time, centrifugal castings have a fine gram size.

There is a tendency for the lighter non-metallic inclusions slag particles, and dross to

segregate toward the inner radius of the casting where it can be easily removed by

machining. Due to the high purity of the outer skin, centrifugally cast pipes have a high

resistance to atmospheric corrosion.

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Plaster-mold casting is somewhat similar to sand casting in that only one casting is

made and then the mold is destroyed, in this case the mold is made out of a specially

formulated plaster. 70 to 80% gypsum and 20 to 30% fibrous strengtheners. Water is added

to make a creamy s1urry. This process is limited to non-ferrous metals, because ferrous

metals react with sulphur in gypsum. The core boxes are usually made form brass, plastics, or

aluminium.


The process utilizes a metal casting die in conjunction with metal or sand cores.

Molten metal is introduced at the top of the mold that has two or more parts, using only the

force of gravity. After solidification, the mold is opened and the casting ejected. The mold is

re-assembled and the cyc1e is repeated. The molds are either metal or graphite and,

consequently, most permanent-mold castings are restricted to lower melting point nonferrous

metals and alloys.


Squeeze casting, also known as liquid-metal forging, is a process by which molten

metal solidifies under pressure within c1osed dies positioned between the plates of a

hydraulic press. Squeeze casting consists of metering liquid metal into a preheated, lubricated

die and forging the metal while it so1idifies. The load is applied shortly after the metal begins

to freeze and is maintained until the entire casting has solidified. Casting ejection and

handling are done in much the same way as in closed die forging.

The applied pressure and the instant contact of the molten metal with the die surface

produce a rapid heat transfer condition that yields a pore-free fine-grain casting with

mechanical properties approaching those of a wrought product.

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The squeeze casting process is easily automated to produce near-net to net shape

high-quality components.

2.3 Advantages & Disadvantages

2.3.1 Advantages

1 Complex shapes can be produced.

2 Minimal directional properties are obtained

3 Hollow sections can be produced

4 Very large part can be produced.

5 Metals that are very difficult to machine can be used to produce an object.

6 Cheapest method of fabrication

7 Casting with wide range of properties can be produce by adding various alloys

elements.

8 Almost all the metals and alloys and some plastics can be casted.

9 The number Of casting can be vary from very few to several thousands.

2.3.2 Disadvantages

1 Time required for the process of making casting is quite long.

2 Metal casting involving melting of metal which is high energy consuming process.

3 The working condition in foundries are quite bad due to heat, dust,fumes, slags etc.

Compare to other process.

4 Metal casting is still high labour-intensive compare to other process.

5 Productivity is less than the other automatic process. E.g. Rolling.

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3. Casting Terminology

3.1 Pattern

The pattern is the principal tool during the casting process. It is the replica of

the object to be made by the casting process, with some modifications. The main

modifications are the addition of pattern allowances, and the provision of core prints. If the

casting is to be hollow, additional patterns called cores are used to create these cavities in the

finished product. The quality of the casting produced depends upon the material of the

pattern, its design, and construction.

3.1.1 Pattern Material

There are many types of pattern material used in industries as:

1) Wooden 2) Metal

3) Plastic 4) Quick setting material.

3.1.1 Type of Pattern


3.1.2.2 Split pattern or two-piece pattern

3.1.2.3 Cope and Drag Pattern





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A single piece pattern is the simplest of all

forms. As the name indicates they are made of a single piece

as shown in fig. This type of pattern is used only in cases

where the product is very simple and can be easily withdrawn

from the mould. This pattern is contained entirely in the drag.

One of the surfaces is usually flat which is used as the parting

plane.

3.1.2.2 Split pattern or two-piece pattern.

This is the most common type of pattern for intricate castings. When the

contour of the casting makes its withdrawal from the mould difficult or when the depth of the

casting is too high, then the pattern is split into two parts. One part is contained in the drag

and the other in the cope. The split surface of the pattern is same as the parting plane of the

mould. The two halves of the pattern should

be aligned properly by making use of dowel

pins which are fitted to the top half.

3.1.2.3 Cope and Drag Pattern.

When very large castings are to be made the complete pattern becomes too

heavy to be handled by a single operator. Such a pattern is made in two parts which are

separately moulded in different moulding boxes. After

completion of the moulds, the two boxes are assembled to

form the complete cavity. One part is contained by the

drag and the other by the cope. Thus it is different from

split pattern in which both pieces are moulded separately

instead of being moulded in the assembled position.

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These patterns are made in two pieces. One piece

is mounted on one side and the other on the other side of a plate

called match plate. Gates and runners are also attached to the

plate along with the pattern. After moulding when the match plate

is removed a complete mould with gating is obtained by joining

the cope and drag together. The complete pattern with match

plate is entirely made of metal, usually aluminium for its light weight and machinability.

These are generally used for mass production of small castings with higher dimensional

accuracy. These patterns are mainly employed for machine moulding. Their construction cost

is high but the same is easily compensated by a high rate of production and greater

dimensional accuracy.


They are used for mass production of

small castings. For such castings multi-cavity moulds are

prepared, i.e. a single sand mould carriers a number of

cavities as shown in fig. Pattern for these castings are

connected to each other by means of gate formers. They

provide suitable channels or gates in sand for feeding the

molten metal to these cavities. A single runner can be

used for feeding all the cavities. This enables a considerable saving in moulding time and a

uniform feeding of molten metal.

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When the size of the casting is very large, but easy to shape and only a few

numbers are to be made, it is not economical to make a large solid pattern of that size. In

such cases a pattern consisting of wooden frame and strips is made called skeleton pattern. It

is filled with moulding sand and rammed properly. The surplus sand is removed by means of

a strickle. A skeleton pattern for a pipe is shown in figure.


Certain single piece patterns are made to

have loose pieces in order to enable their easy withdrawal

from the mould. These pieces from an integral part of the

pattern during moulding. After the mould is complete the

pattern is withdrawn leaving the pieces in the sand. These

pieces are later withdrawn separately through the cavity

formed by the pattern as shown in figure. Moulding with

loose piece is a highly skilled job and is generally

expensive.

3.1.3 Pattern Allowances

3.1.3.1 Shrinkage allowance

The pattern needs to incorporate suitable allowances for shrinkage; these are

called contraction allowances, and their exact values depend on the alloy being cast and the

exact sand casting method being used. Some alloys will have overall linear shrinkage of up to

2.5%, whereas other alloys may actually experience no shrinkage or a slight "positive"

shrinkage or increase in size in the casting process (notably type metal and certain cast irons).

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The shrinkage amount is also dependent on the sand casting process employed, for example

clay-bonded sand, chemical bonded sands, or other bonding materials used within the sand.

3.1.3.2 Draft allowances

The pattern needs to incorporate suitable allowances for draft, which means

that its sides are tapered so that when it is pulled from the sand, it will tend not to drag sand

out of place along with it. This is also known as taper which is normally between 1 and 3

degrees.

3.1.3.3 Machining allowance

The finish and accuracy achieved in sand casting are generally poor and

therefore when the casting is functionally required to be of good surface finish or

dimensionally accurate, it is generally achieved by subsequent machining. Machining or

finish allowances are therefore added in the pattern dimension. The amount of machining

allowance to be provided for is affected by the method of moulding and casting used viz.

hand moulding or machine moulding, sand casting or metal mould casting. The amount of

machining allowance is also affected by the size and shape of the casting; the casting

orientation; the metal; and the degree of accuracy and finish required.

3.1.3.4 Distortion allowance

Sometimes castings get distorted, during solidification, due to their typical

shape. For example, if the casting has the form of the letter U, V, T, or L etc. it will tend to

contract at the closed end causing the vertical legs to look slightly inclined. This can be

prevented by making the legs of the U, V, T, or L shaped pattern converge slightly (inward)

so that the casting after distortion will have its sides vertical.

The distortion in casting may occur due to internal stresses. These internal

stresses are caused on account of unequal cooling of different section of the casting and

hindered contraction. Measure taken to prevent the distortion in casting include:

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3.1.3.5 Rapping Allowance

Before the withdrawal from the sand mold, the pattern is rapped all around the

vertical faces to enlarge the mold cavity slightly, which facilitate its removal. Since it

enlarges the final casting made, it is desirable that the original pattern dimension should be

reduced to account for this increase. There is no sure way of quantifying this allowance, since

it is highly dependent on the foundry personnel practice involved. It is a negative allowance

and is to be applied only to those dimensions that are parallel to the parting plane.

3.2 Core

A core is a device used in casting and moulding processes to produce internal

cavities and re-entrant angles. The core is normally a disposable item that is destroyed to get

it out of the piece. They are most commonly used in sand casting, but are also used in

injection moulding.

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3.2.1 Types of Core

3.2.1.1 Green-sand core

Green-sand cores are not a typical type of core in

that it is part of the cope and drag, but still form an internal

feature. Their major disadvantage is their lack of strength, which

makes casting long narrow features difficult or impossible. Even

for long features that can be cast it still leave much material to be

machined. A typical application is a through hole in a casting.

3.2.1.2 Dry-sand cores

Dry-sand cores overcome some of the disadvantages of the green-sand cores.

They are formed independently of the mold and then inserted into the core prints in the mold,

which hold the core in position. They are made by mixing sand with a binder in a wooden or

metal core box, which contains a cavity in the shape of the desired core.

3.2.2 Core Print

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 to support 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 it forms a seat in

the mold on which the sand core rests during pouring of the mold. The core print must be of

adequate size and shape so that it can support the weight of the core during the casting

operation. Depending upon the requirement a core can be placed horizontal, vertical and can

be hanged inside the mold cavity.

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3.2.3 Core Box

The most simple way to make dry-sand cores is in a dump core box, in which sand is

packed into the box and scraped level with the top. A wood or metal plate is then placed over

the box, and then the two are flipped over and the core segment falls out of the core box. The

core segment is then baked or hardened. Multiple core segments are then hot glued together

or attached by some other means.

There are many types of core box use in industries as :

half core box

dump core box

split core box

left and right core box

gang core box

strickle core box

loose piece core box

3.3 Mould

In sand casting, the primary piece of

equipment is the mold, which contains several

components. The mold is divided into two halves -

the cope (upper half) and the drag (bottom half),

which meet along a parting line. Both mold halves

are contained inside a box, called a flask, which

itself is divided along this parting line. The mold

cavity is formed by packing sand around the pattern

in each half of the flask. The sand can be packed by

hand, but machines that use pressure or impact ensure even packing of the sand and require

far less time, thus increasing the production rate. After the sand has been packed and the

pattern is removed, a cavity will remain that forms the external shape of the casting. Some

internal surfaces of the casting may be formed by cores.

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3.3.1 Type of Mould

3.3.1.1 Permanent mould casting

Permanent mold casting is metal casting process that employs reusable molds

("permanent molds"), usually made from metal. The most common process uses gravity to

fill the mold, however gas pressure or a vacuum are also used. A variation on the typical

gravity casting process, called slush casting, produces hollow castings. Common casting

metals are aluminum, magnesium, and copper alloys. Other materials include tin, zinc, and

lead alloys and iron and steel are also cast in graphite molds. Permanent molds, while lasting

more than one casting still have a limited life before wearing out.

3.3.1.2 Temporary Mould casting

This mould are destroyed at the time of removing casting from them.

There are many type of temporary mould which are mentioned below.

Type of Temporary Mould

Greensand mold –

Greensand molds use a mixture of sand, water, and a clay or binder. Typical

composition of the mixture is 90% sand, 3% water, and 7% clay or binder. Greensand molds

are the least expensive and most widely used.

Skin-dried mold –

A skin-dried mold begins like a greensand mold, but additional bonding materials are

added and the cavity surface is dried by a torch or heating lamp to increase mold strength.

Doing so also improves the dimensional accuracy and surface finish, but will lower the

collapsibility. Dry skin molds are more expensive and require more time, thus lowering the

production rate.

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Dry sand mold –

In a dry sand mold, sometimes called a cold box mold, the sand is mixed only with an

organic binder. The mold is strengthened by baking it in an oven. The resulting mold has

high dimensional accuracy, but is expensive and results in a lower production rate.

No-bake mold –

The sand in a no-bake mold is mixed with a liquid resin and hardens at room

temperature.

3.3.2 Moulding Sand

Molding sand is more than just sand. Typically it is a fine grade of sand (mine is 110

grit sand blasting sand), clay binder and something to moisten it. There are two types of

molding sand namely natural sand and synthesis sand.

3.3.2.1 Properties of Moulding Sand

A large variety of molding materials is used in foundries for manufacturing molds and

cores. They include molding sand, system sand or backing sand, facing sand, parting sand,

and core sand. The choice of molding materials is based on their processing properties. The

properties that are generally required in molding materials are:

Refractoriness

It is the ability of the molding material to resist the temperature of the liquid metal to

be poured so that it does not get fused with the metal. The refractoriness of the silica sand is

highest.

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Permeability

During pouring and subsequent solidification of a casting, a large amount of gases

and steam is generated. These gases are those that have been absorbed by the metal during

melting, air absorbed from the atmosphere and the steam generated by the molding and core

sand. If these gases are not allowed to escape from the mold, they would be entrapped inside

the casting and cause casting defects. To overcome this problem the molding material must

be porous. Proper venting of the mold also helps in escaping the gases that are generated

inside the mold cavity.

Green Strength

The molding sand that contains moisture is termed as green sand. The green sand

particles must have the ability to 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.

Dry Strength

When the molten metal is poured in the mold, the sand around the mold cavity is

quickly converted into dry sand as the moisture in the sand evaporates due to the heat of the

molten metal. At this stage the molding sand must posses the sufficient strength to retain the

exact shape of the mold cavity and at the same time it must be able to withstand the

metallostatic pressure of the liquid material.

Hot Strength

As soon as the moisture is eliminated, the sand would reach at a high temperature

when the metal in 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.

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Collapsibility

The molding sand should also have collapsibility so that during the contraction of the

solidified casting it does not provide any resistance, which may result in cracks in the

castings.Besides these specific properties the molding material should be cheap, reusable and

should have good thermal conductivity.

Thermal stability

Heat from the casting causes rapid expansion of the sand surface at the mould-metal

interface. The mould surface may crack, buckle, or flake off (scab ) unless the moulding sand

is relatively stable dimensionally under rapid heating.

3.3.1.2 Sand Testing

Moisture Content test

Moisture is an important element of the moulding sand as it affects many properties.

To test the moisture of moulding sand a carefully weighed sand test sample of 50g is dried at

a temperature of 1050 C to 1100 C for 2 hours by which time all the moisture in the sand

would have been evaporated. The sample is then weighed. The weight difference in grams

when multiplied by two would give the percentage of moisture contained in the moulding

sand. Alternatively a moisture teller can also be used for measuring the moisture content. In

this sand is dried by suspending the sample on a fine metallic screen and allowing hot air to

flow through the sample. This method of drying completes the removal of moisture in a

matter of minutes compared to 2 hours as in the earlier method. \

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Permeability test

The permeability number, which has no units, is determined by the rate of flow of air,

under standard pressure, through a 2 x 2-in. rammed AFS cylindrical specimen.

The grain size, shape and distribution of the foundry sand, the type and quantity of

bonding materials, the density to which the sand is rammed and the percentage of moisture

used for tempering the sand are important factors in regulating the degree of permeability. An

increase in permeability usually indicates a more open structure in the rammed sand, and if

the increase continues, it will lead to penetration-type defects and rough castings. A decrease

in permeability indicates tighter packing and could lead to blows and pinholes.

Clay Content Test

A known amount of dried molding sand mixed with a pyrophosphate solution is

stirred with a high-speed mixer for 5 min. Water is added to the top level line, and the

mixture is allowed to settle for 5 min. before the top 5 in. of the water is siphoned off. The

procedure is repeated until the water above the sample is clear. The sand then is dried, and

the weight loss is recorded as Clay.

Clay may contain active clay, dead clay, silt, seacoal, cellulose, cereal, ash, fines and

all materials that float in water. Only the active clay gives active bonding capacity to the

system.

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4. Melting Equipment

4.1 Cupola Furnace

A Cupola or Cupola furnace is a melting device used in foundries that can be

used to melt cast iron, ni-resist iron and some bronzes. The cupola can be made almost any

practical size. The size of a cupola is expressed in diameters and can range from 1.5 to 13

feet (0.5 to 4.0 m). The overall shape is cylindrical and the equipment is arranged vertically,

usually supported by four legs. The overall look is similar to a large smokestack.

The bottom of the cylinder is fitted

with doors which swing down and out to 'drop

bottom'. The top where gases escape can be open or

fitted with a cap to prevent rain from entering the

cupola. To control emissions a cupola may be fitted

with a cap that is designed to pull the gases into a

device to cool the gasses and remove particulate

matter.

The shell of the cupola, being usually made of steel, has refractory brick and

refractory patching material lining it. The bottom is lined in a similar manner but often a clay

and sand mixture ("bod") may be used, as this lining is temporary. Finely divided coal ("sea

coal") can be mixed with the clay lining so when heated the coal decomposes and the bod

becomes slightly friable, easing the opening up of the tap holes. The bottom lining is

compressed or 'rammed' against the bottom doors. Some cupolas are fitted with cooling

jackets to keep the sides cool and with oxygen injection to make the coke fire burn hotter.

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Operation

To begin a production run, called a 'cupola campaign', the furnace is filled

with layers of coke and ignited with torches. Some smaller cupolas may be ignited with wood

to start the coke burning. When the coke is ignited, air is introduced to the coke bed through

ports in the sides called tuyeres.

When the coke is very hot, solid pieces of metal are charged into the furnace

through an opening in the top. The metal is alternated with additional layers of fresh coke.

Limestone is added to act as a flux. As the heat rises within the stack the metal is melted. It

drips down through the coke bed to collect in a pool at the bottom, just above the bottom

doors. A thermodynamic reaction takes place. The carbon in the coke combines with the

oxygen in the air to form carbon monoxide. The carbon monoxide further burns to form

carbon dioxide. Some of the carbon is picked up by the falling droplets of molten steel and

iron which raises the carbon content of the iron. Silicon carbide and ferromanganese briquets

may also be added to the charge materials. The silicon carbide dissociates and carbon and

silicon enters into the molten metal. Likewise the ferromanganese melts and is combined into

the pool of liquid iron in the 'well' at the bottom of the cupola.

The

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operator of the cupola, the 'cupola tender', observes the amount of iron rising in the well of

the cupola. When the metal level is sufficiently high, the cupola tender opens the taphole to

let the metal flow into a ladle or other container to hold the molten metal. When enough

metal is drawn off the taphole is plugged with a refractory plug made of clay.

The cupola tender observes the iron through the sight glass for signs of slag

formation, which is normal. Most slags will rise to the top of the pool of iron being formed.

A slag tap hole, located higher up on the cylinder, and usually to the rear or side of the iron

taphole, is opened to let the slag flow out. The viscosity is low (with proper fluxing) and the

red hot molten slag will flow easily. Sometimes the slag which runs out the slaghole is

collected in a small cup shaped tool, allowed to cool and harden. It is fractured and visually

examined. With acid refractory lined cuploas a greenish colored slag means the fluxing is

proper and adequate.

After the cupola has produced enough metal to supply the foundry with its

needs, the bottom is opened, or 'dropped' and the remaining materials fall to the floor

between the legs. This material is allowed to cool and subsequently removed. The cupola can

be used over and over. A 'campaign' may last a few hours, a day, weeks or even months.

5 Electric Furnace

Electric furnace is used for heating purpose in various industrial production

processes. Electric furnaces are used where more accurate temperature control is required.

There are three types of electrical furnaces namely: (1) Induction Heating Furnace (2)

Resistance Heating Furnace and (3) Arc furnace depending upon the method of heat

generation.

Induction heating furnaces and arc furnaces are beyond the scope of this project

profile. The scope of this project profile is confined to the resistance heating furnace only. In

resistance heating furnaces, the resistance heating

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The heating elements used are Nichrome wire, Kanthal wire or Graphite rods depending

upon the temperature requirements. The unit proposed in this project profile envisages

manufacturing furnaces to a maximum

temperature of 1000O

C and only up to 50 kW

power rating. In this case, Kanthal wire is used.

The temperature is controlled using thermostats

and the temperature is monitored by

thermocouples. The heating chamber is

constructed by M. S. Sheets and channels and for

thermal Insulation, fire clay bricks and refractory

bricks are used

Operation

Scrap metal is delivered to a scrap bay, located next to the melt shop. Scrap generally

comes in two main grades: shred (white goods, cars and other objects made of similar light-

gauge steel) and heavy melt (large slabs and beams), along with some direct reduced iron

(DRI) or pig iron for chemical balance. Some furnaces melt almost 100% DRI.

The scrap is loaded into large buckets called baskets, with 'clamshell' doors for a base.

Care is taken to layer the scrap in the basket to ensure good furnace operation; heavy melt is

placed on top of a light layer of protective shred, on top of which is placed more shred. These

layers should be present in the furnace after charging. After loading, the basket may pass to a

scrap pre-heater, which uses hot furnace off-gases to heat the scrap and recover energy,

increasing plant efficiency.

The scrap basket is then taken to the melt shop, the roof is swung off the furnace, and

the furnace is charged with scrap from the basket. Charging is one of the more dangerous

operations for the EAF operators. There is a lot of energy generated by multiple tonnes of

falling metal; any liquid metal in the furnace is often displaced upwards and outwards by the

solid scrap, and the grease and dust on the scrap is ignited if the furnace is hot, resulting in a

fireball erupting. In some twin-shell furnaces, the scrap is charged into the second shell while

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the first is being melted down, and pre-heated with off-gas from the active shell. Other

operations are continuous charging - pre-heating scrap on a conveyor belt, which then

discharges the scrap into the furnace proper, or charging the scrap from a shaft set above the

furnace, with off-gases directed through the shaft. Other furnaces can be charged with hot

(molten) metal from other operations.

After charging, the roof is swung back over the furnace and meltdown commences.

The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to

bore into the layer of shred at the top of the furnace. Lower voltages are selected for this first

part of the operation to protect the roof and walls from excessive heat and damage from the

arcs. Once the electrodes have reached the heavy melt at the base of the furnace and the arcs

are shielded by the scrap, the voltage can be increased and the electrodes raised slightly,

lengthening the arcs and increasing power to the melt. This enables a molten pool to form

more rapidly, reducing tap-to-tap times. Oxygen is also supersonically blown into the scrap,

combusting or cutting the steel, and extra chemical heat is provided by wall-mounted

oxygen-fuel burners. Both processes accelerate scrap meltdown.

5. Melting & Pouring

Many foundries, particularly ferrous foundries, use a high proportion of scrap

metal to make up a charge. As such, foundries play an important role in the metal recycling

industry. Internally generated scrap from runners and risers, as well as reject product, is also

recycled. The charge is weighed and introduced to the furnace. Alloys and other materials are

added to the charge to produce the desired melt. In some operations the charge may be

preheated, often using waste heat.

In traditional processes metal is

superheated in the furnace. Molten metal is

transferred from the furnace to a ladle and held

until it reaches the desired pouring temperature.

The molten metal is poured into the mould and

allowed to solidify.

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5.1 Gating System

The gating system serves many purposes, the most important being conveying the

liquid material to the mold, but also controlling shrinkage, the speed of the liquid, turbulence,

and trapping dross. The gates are usually attached to the thickest part of the casting to assist

in controlling shrinkage. In especially large castings multiple gates or runners may be

required to introduce metal to more than one point in the mold cavity. The speed of the

material is important because if the material is traveling too slow it can cool before

completely filling, leading to mis-runs and cold shuts. If the material is moving too fast then

the liquid material can erode the mold and contaminate the final casting. The shape and

length of the gating system can also control how quickly the material cools; short round or

square channels minimize heat loss.

The gating system may be designed to minimize turbulence, depending on the

material being cast. For example, steel, cast iron, and most copper alloys are turbulent

insensitive, but aluminum and magnesium alloys are turbulent sensitive. The turbulent

insensitive materials usually have a short and open gating system to fill the mold as quickly

as possible. However, for turbulent sensitive materials short sprues are used to minimize the

distance the material must fall when entering the mold. Rectangular pouring cups and tapered

sprues are used to prevent the formation of a vortex as the material flows into the mold; these

vortices tend to suck gas and oxides into the mold. A large sprue well is used to dissipate the

kinetic energy of the liquid material as it falls down the sprue, decreasing turbulence. The

choke, which is the smallest cross-sectional area in the gating system used to control flow,

can be placed near the sprue well to slow down and smooth out the flow.

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5.1.1 Runner & Sprue

The molten material is poured in the pouring cup, which is part of the gating

system that supplies the molten material to the mold cavity. The vertical part of the gating

system connected to the pouring cup is the sprue, and the horizontal portion is called the

runners and finally to the multiple points where it is introduced to the mold cavity called the

gates. Additionally there are extensions to the gating system called vents that provide the

path for the built up gases and the displaced air to vent to the atmosphere.

The cavity is usually made oversize to allow for the metal contraction as it

cools down to room temperature. This is achieved by making the pattern oversize. To

account for shrinking, the pattern must be made oversize by these factors, on the average.

These are linear factors and apply in each direction. These shrinkage allowance are only

approximate, because the exact allowance is determined the shape and size of the casting. In

addition, different parts of the casting might require a different shrinkage allowance. See the

casting allowance table for the approximate shrinkage allowance expressed as the Pattern

Oversize Factor.

5.1.2 Riser

A riser, also known as a feeder, is a reservoir built into a metal casting mold to

prevent cavities due to shrinkage. Most metals are less dense as a liquid than as a solid so

castings shrink upon cooling, which can leave a void at the last point to solidify. Risers

prevent this by providing molten metal to the casting as it solidifies, so that the cavity forms

in the riser and not the casting. Risers are not effective on materials that have a large freezing

range, because directional solidification is not possible. They are also not needed for casting

processes that utilized pressure to fill the mold cavity. A feeder operated by a treadle is called

an under feeder.

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6 Cleaning & Finishing.

Cleaning

After degating, sand or other moulding media may adhere to the casting. To

remove this the surface is cleaned using a blasting process. This means a granular media will

be propelled against the surface of the casting to mechanically knock away the adhering sand.

The media may be blown with compressed air, or may be hurled using a shot wheel. The

media strikes the casting surface at high velocity to dislodge the molding media (for example,

sand, slag) from the casting surface. Numerous materials may be used as media, including

steel, iron, other metal alloys, aluminum oxides, glass beads, walnut shells, baking powder

among others. The blasting media is selected to develop the color and reflectance of the cast

surface. Terms used to describe this process include cleaning, blasting, shot blasting and sand

blasting.

Finishing

The final step in the process usually

involves grinding, sanding, or machining the

component in order to achieve the desired

dimensional accuracies, physical shape and surface

finish.

Removing the remaining gate

material, called a gate stub, is usually done using a

grinder or sanding. These processes are used

because their material removal rates are slow enough to control the amount of material.

These steps are done prior to any final machining.

After grinding, any surfaces that require tight dimensional control are

machined. Many castings are machined in CNC milling centers. The reason for this is that

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these processes have better dimensional capability and repeatability than many casting

processes. However, it is not uncommon today for many components to be used without

machining.

A few foundries provide other services before shipping components to their

customers. Painting components to prevent corrosion and improve visual appeal is common.

Some foundries will assemble their castings into complete machines or sub-assemblies. Other

foundries weld multiple castings or wrought metals together to form a finished product.

More and more the process of finishing a casting is being achieved using

robotic machines which eliminate the need for a human to physically grind or break parting

lines, gating material or feeders. The introduction of these machines has reduced injury to

workers, costs of consumables whilst also reducing the time necessary to finish a casting. It

also eliminates the problem of human error so as to increase repeatability in the quality of

grinding. With a change of tooling these machines can finish a wide variety of materials

including iron, bronze and aluminium.

7 Casting Defects

Flash

This casting shows a very common defect, flash. This is where the mold

somehow separated enough to allow metal between the halves, along the parting line. (See

also the trivet for more flash.) You can see the inside circle here is nearly completely filled in

with flash. Fixing flash is no problem as it's usually less than 1/8" thick (unless something

really bad happened) so can be broken off with a hammer or pliers. A file will take it down to

the parting line. Causes include letting the mold dry out; the clay in the sand shrinks resulting

in a gap between the halves. In the pictured case, it was left out overnight.

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Mold Shift

This is due to operator error: not aligning the mold correctly.

Most flasks have alignment pins to prevent this, but I never installed

them on my 6x6 set so I have to guess at it.

Porosity

This is an investment casting. Different from sand casting, but defects still happen all

the same. In this case, it was either gas or slag (but the area doesn't have the right appearance

for slag). Come to think of it, it could be gas from the mould, but that's just a thought. In any

case, the area in question is on the right, where it looks rough (the area on the left appears to

be a broken section of the mould, which might've contributed to the next listed defect). There

are actually a few pinholes which you can see light clear though in the porous area.

Slag Inclusions

During the melting process, flux is added to remove the undesirable oxides and

impurities present in the metal. At the time of tapping, the slag should be properly removed

from the ladle, before the metal is poured into the mould. Otherwise any slag entering the

mould cavity will be weakening the casting and also spoiling the surface of the casting.

Gas pockets

Gas pockets come from gas dissolving in the melt then coming out when it

solidifies. This usually manifests itself as a rough surface on areas exposed to air or pockets

of varying size in the cross-section of the metal. Gas comes from melting too long or heating

too hot, 'stewing' the metal using an unusually oxidizing or reducing flame in the furnace,

getting water in the melt, and the alignment of the Moon with the Earth and Sun. A good

idea is to recycle scrap into ingots as a first step since the scrap might be wet, oily or painted

and will add gas to the melt. The gas comes out in the ingots, not your casting.

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Swell :

Under the influence of metallostatic forces, the

mould wall may move back causing a swell in the

dimensions of the casting. As a result of the swell, the

feeding requirements of the casting increase which should

be taken care of by the proper choice of risering. The

main cause of this defect is improper ramming of the mould.

Drop:

An irregularly shaped projection on the cope surface of a casting is called a drop.

This is caused by dropping of sand from the cope or other overhanging projections into the

mould. An adequate strength of the sand and the use of gaggers can help in avoiding the

drops.

Misrun:

Many a time, the liquid metal may, due to insufficient superheat,

start freezing before reaching the farthest point of the mould cavity. This

defect is called Mis-run.

Hot tears:

Since metal has low strength at higher temperatures, any

unwanted cooling stress may cause the rupture of the casting. The better

design of casting avoids this defect.

Cold shut:

For a casting with gates at its two sides, the misrun may show up at the centre of the

casting due to non fusion of two streams of metal resulting in a discontinuity or weak spot in

casting.Above two defects are due to lower fluidity of the molten metal or small thickness of

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the casting. The fluidity of the metal can be increased by changing the composition of molten

metal or raising the pouring temperature. The other causes for these defects are large surface

area to volume ratio of the casting, high heat transfer rate of the mould material and back

pressure of the gases entrapped in the mould cavity due to inadequate venting.

References

1 ) Manufacturing Technology - R. K. Rajput

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casting process report by savan

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