casting process report by savan

Kautilya Inst. Of Tech. & Engg. Jaipur

A Training Report (Submitted for the partial fulfillment of Bachelor of Technology in MECHANICAL ENGG. Rajasthan Tech. Univ.-Kota)

Submitted By GHADIYA SUGNESHKUMAR (B.Tech. VIIth semester)

Submitted To: Mr. Mukul Sharma Training Co-ordinator

Head of the Department: Mr. K.K Khatri

2010-2011 Department of Mechanical Engineering KAUTILYA INSTITUTE OF TECHNOLOGY AND ENGINEERING Sitapura, Jaipur

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Kautilya Inst. Of Tech. & Engg. Jaipur

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: Mr. Mukul Sharma TRAINING CO-ORDINATOR, (MECH. ENGG. DEPT.)

SUBMITTED BY: Ghadiya Sugnesh G. MECHANICAL ENGG.

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Kautilya Inst. Of Tech. & Engg. Jaipur

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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Kautilya Inst. Of Tech. & Engg. Jaipur

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

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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 5

Kautilya Inst. Of Tech. & Engg. Jaipur

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 16 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 6

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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 90012000 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 2.2.4 Centrifugal casting 2.2.5 Plaster-mould casting 2.2.6 Permanent-mold casting 2.2.7 Squeeze 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. 13

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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.

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2.2.2 Investment Casting

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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Kautilya Inst. Of Tech. & Engg. Jaipur

2.2.4 Centrifugal casting 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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2.2.5 Plaster-mould casting 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.

2.2.6 Permanent-mold casting 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.

2.2.7 Squeeze casting 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. The squeeze casting process is easily automated to produce near-net to net shape high-quality components. 18

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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 3.1.2.1 Solid or single piece pattern. 3.1.2.2 Split pattern or two-piece pattern 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

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3.1.2.1 Solid or single piece pattern. 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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3.1.2.4

Match plate pattern 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.

3.1.2.5

Gated Pattern 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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3.1.2.6

Skeleton Pattern 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.

3.1.2.7

Pattern with Loose – Pieces 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). 23

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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. 28

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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. 29

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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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Kautilya Inst. Of Tech. & Engg. Jaipur

 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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Kautilya Inst. Of Tech. & Engg. Jaipur

 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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Kautilya Inst. Of Tech. & Engg. Jaipur

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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Kautilya Inst. Of Tech. & Engg. Jaipur

 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.

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Kautilya Inst. Of Tech. & Engg. Jaipur

The 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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Kautilya Inst. Of Tech. & Engg. Jaipur

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

O

temperature of 1000 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

thermocouples.

The

is heating

monitored chamber

by 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 lightgauge 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 the first is being melted down, and pre-heated with off-gas from the active shell. Other 36

Kautilya Inst. Of Tech. & Engg. Jaipur

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 oxygenfuel 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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Kautilya Inst. Of Tech. & Engg. Jaipur

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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Kautilya Inst. Of Tech. & Engg. Jaipur

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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Kautilya Inst. Of Tech. & Engg. Jaipur

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 40

Kautilya Inst. Of Tech. & Engg. Jaipur

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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Kautilya Inst. Of Tech. & Engg. Jaipur

 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. 42

Kautilya Inst. Of Tech. & Engg. Jaipur

 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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Kautilya Inst. Of Tech. & Engg. Jaipur

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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