MP 1st Module Notes

8/10/2019 MP 1st Module Notes

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MODULE 1S4 MECHANICAL


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STIST DEPT OF MECHANICAL KSC

1ANUFACTURING PROCESS S4M 2 13 SCHEME

MODULE 1

1. Write short notes on Metal Casting

Virtually nothing moves, turns, rolls, or flies without the benefit of cast metal

products. The metal casting industry plays a key role in all the major sectors of

our economy. There are castings in locomotives, cars trucks, aircraft, office

buildings, factories, schools, and homes.

Metal Casting is one of the oldest materials shaping methods known. Casting

means pouring molten metal into a mold with a cavity of the shape to be made,

and allowing it to solidify. When solidified, the desired metal object is taken out

from the mold either by breaking the mold or taking the mold apart. The solidified

object is called the casting. By this process, intricate parts can be given strength

and rigidity frequently not obtainable by any other manufacturing process. The

mold, into which the metal is poured, is made of some heat resisting material.

Sand is most often used as it resists the high temperature of the molten metal.

Permanent molds of metal can also be used to cast products.

2. List the advantages and limitations of Metal casting process.

Advantages

The metal casting process is extensively used in manufacturing because of its

many advantages.

a)

Molten material can flow into very small sections so that intricate shapes can

be made by this process. As a result, many other operations, such as

machining, forging, and welding, can be minimized or eliminated.

b) It is possible to cast practically any material that is ferrous or non-ferrous.

c) As the metal can be placed exactly where it is required, large saving in weight

can be achieved.

d) The necessary tools required for casting molds are very simple and

inexpensive. As a result, for production of a small lot, it is the ideal process.


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e)

There are certain parts made from metals and alloys that can only be processed

this way.

f)

Size and weight of the product is not a limitation for the casting process.

Limitations

a)

Dimensional accuracy and surface finish of the castings made by sand casting

processes are a limitation to this technique. Many new casting processes have

been developed which can take into consideration the aspects of dimensional

accuracy and surface finish. Some of these processes are die casting process,

investment casting process, vacuum-sealed molding process, and shell

molding process.

b) The metal casting process is a labor intensive process.

3. Explain the important terms in Metal casting.

Flask: A metal or wood frame, without fixed top or bottom, in which the mold

is formed. Depending upon the position of the flask in the molding structure, it is

referred to by various names such as drag lower molding flask, cope uppermolding flask, cheekintermediate molding flask used in three piece molding.

Pattern: It is the replica of the final object to be made. The mold cavity is made

with the help of pattern.

Parting line: This is the dividing line between the two molding flasks that

makes up the mold.

Molding sand: Sand, which binds strongly without losing its permeability to

air or gases. It is a mixture of silica sand, clay, and moisture in appropriate

proportions.

Facing sand: The small amount of carbonaceous material sprinkled on the inner

surface of the mold cavity to give a better surface finish to the castings.


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Core: A separate part of the mold, made of sand and generally baked, which is

used to create openings and various shaped cavities in the castings.

Pouring basin: A small funnel shaped cavity at the top of the mold into which

the molten metal is poured.

Sprue: The passage through which the molten metal, from the pouring basin,

reaches the mold cavity. In many cases it controls the flow of metal into the mold.

Runner: The channel through which the molten metal is carried from the sprue

to the gate.

Gate: A channel through which the molten metal enters the mold cavity.

Chaplets: Chaplets are used to support the cores inside the mold cavity to take

care of its own weight and overcome the metallostatic force.

Riser: A column of molten metal placed in the mold to feed the castings as it

shrinks and solidifies. Also known as feed head.

Vent: Small opening in the mold to facilitate escape of air and gases.

4. Explain the different steps in Sand Mould Casting.

There are six basic steps in making sand castings:

1. Patternmaking

2.

Core making

3. Molding

4. Melting and pouring

5. Cleaning

Pattern making

The pattern is a physical model of the casting used to make the mold. The mold

is made by packing some readily formed aggregate material, such as molding


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sand, around the pattern. When the pattern is withdrawn, its imprint provides the

mold cavity, which is ultimately filled with metal to become the casting. If the

casting is to be hollow, as in the case of pipe fittings, additional patterns, referred

to as cores, are used to form these cavities.

Core making

Cores are forms, usually made of sand, which are placed into a mold cavity to

form the interior surfaces of castings. Thus the void space between the core and

mold-cavity surface is what eventually becomes the casting.

Molding

Molding consists of all operations necessary to prepare a mold for receiving

molten metal. Molding usually involves placing a molding aggregate around a

pattern held with a supporting frame, withdrawing the pattern to leave the mold

cavity, setting the cores in the mold cavity and finishing and closing the mold.

Melting and Pouring

The preparation of molten metal for casting is referred to simply as melting.

Melting is usually done in a specifically designated area of the foundry, and the

molten metal is transferred to the pouring area where the molds are filled.

Cleaning

Cleaning refers to all operations necessary to the removal of sand, scale, and

excess metal from the casting. Burned-on sand and scale are removed to improved

the surface appearance of the casting. Excess metal, in the form of fins, wires,

parting line fins, and gates, is removed. Inspection of the casting for defects and

general quality is performed.


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5. What is mean by Pattern? What are the functions of 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. The costs

of the pattern and the related equipment are reflected in the cost of the casting.

The use of an expensive pattern is justified when the quantity of castings required

is substantial.

Functions of the Pattern

1. A pattern prepares a mold cavity for the purpose of making a casting.

2.

A pattern may contain projections known as core prints if the casting

requires a core and need to be made hollow.


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3.

Runner, gates, and risers used for feeding molten metal in the mold cavity

may form a part of the pattern.

4.

Patterns properly made and having finished and smooth surfaces reduce

casting defects.

5.

A properly constructed pattern minimizes the overall cost of the castings.

6. Write short notes on Pattern Materials

Patterns may be constructed from the following materials. Each material has its

own advantages, limitations, and field of application. Some materials used formaking patterns are: wood, metals and alloys, plastic, plaster of Paris, plastic and

rubbers, wax, and resins. To be suitable for use, the pattern material should be:

1.

Easily worked, shaped and joined

2. Light in weight

3. Strong, hard and durable

4.

Resistant to wear and abrasion

5.

Resistant to corrosion, and to chemical reactions

6. Dimensionally stable and unaffected by variations in temperature and

humidity

7.

Available at low cost

The usual pattern materials are wood, metal, and plastics. The most commonly

used pattern material is wood, since it is readily available and of low weight. Also,

it can be easily shaped and is relatively cheap. The main disadvantage of wood is

its absorption of moisture, which can cause distortion and dimensional changes.

Hence, proper seasoning and upkeep of wood is almost a pre-requisite for large-

scale use of wood as a pattern material.


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7. Explain Pattern Allowances.

Pattern allowance is a vital feature as it affects the dimensional characteristics of

the casting. Thus, when the pattern is produced, certain allowances must be given

on the sizes specified in the finished component drawing so that a casting with

the particular specification can be made. The selection of correct allowances

greatly helps to reduce machining costs and avoid rejections. The allowances

usually considered on patterns and core boxes are as follows:

1.

Shrinkage or contraction allowance

2.

Draft or taper allowance

3. Machining or finish allowance

4.

Distortion or camber allowance

5.

Rapping allowance

Shrinkage or Contraction Allowance

All most all cast metals shrink or contract volumetrically on cooling. The metal

shrinkage is of two types:

i. Liquid Shrinkage: it refers to the reduction in volume when the metal

changes from liquid state to solid state at the solidus temperature. To

account for this shrinkage; riser, which feed the liquid metal to the casting,

are provided in the mold.

ii.

Solid Shrinkage:it refers to the reduction in volume caused when metal

loses temperature in solid state. To account for this, shrinkage allowance

is provided on the patterns.

Draft or Taper Allowance

By draft is meant the taper provided by the pattern maker on all vertical surfaces of the pattern

so that it can be removed from the sand without tearing away the sides of the sand mold and


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without excessive rapping by the molder.Figure shows a pattern having no draft allowance

being removed from the pattern. In this case, till the pattern is completely lifted out, its sides

will remain in contact with the walls of the mold, thus tending to break it .Second figure is an

illustration of a pattern having proper draft allowance. Here, the moment the pattern lifting

commences, all of its surfaces are well away from the sand surface. Thus the pattern can be

removed without damaging the mold cavity.

Machining or Finish 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
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molding and casting used viz. hand molding or machine molding, sand casting or

metal mold 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.

Distortion or Camber 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:

i.

Modification of casting design

ii. Providing sufficient machining allowance to cover the distortion affect

iii.

Providing suitable allowance on the pattern, called camber or distortion

allowance (inverse reflection)

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


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personnel practice involved. It is a negative allowance and is to be applied only

to those dimensions that are parallel to the parting plane.

8. Explain Core and Core Prints

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

shapes. These impressions can be obtained by using cores. So where coring is

required, provision should be made 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. A typical job, its pattern and the mold cavity with core and core

print is shown in Figure.


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9. Explain different types of patterns.

Patterns are of various types, each satisfying certain casting requirements.

1.

Single piece pattern

2. Split or two piece pattern

3. Match plate pattern


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Single Piece Pattern

The one piece or single pattern is the most inexpensive of all types of patterns.

This type of pattern is used only in cases where the job is very simple and doesnot create any withdrawal problems. It is also used for application in very small-

scale production or in prototype development. This type of pattern is expected to

be entirely in the drag and one of the surface is is expected to be flat which is

used as the parting plane. A gating system is made in the mold by cutting sand

with the help of sand tools. If no such flat surface exists, the molding becomes

complicated. A typical one-piece pattern is shown in figure

Split or Two Piece Pattern

Split or two piece pattern is most widely used type of pattern for intricate castings.

It is split along the parting surface, the position of which is determined by the

shape of the casting. One half of the pattern is molded in drag and the other half

in cope. The two halves of the pattern must be aligned properly by making use of

the dowel pins, which are fitted, to the cope half of the pattern. These dowel pins

match with the precisely made holes in the drag half of the pattern. A typical split

pattern of a cast iron wheel is shown below.


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10.

Explain the step by step procedure of Sand Mould Making.

The procedure for making mold of a cast iron wheel is shown in figure.

The first step in making mold is to place the pattern on the molding board.

The drag is placed on the board

Dry facing sand is sprinkled over the board and pattern to provide a non

sticky layer.

Molding sand is then riddled in to cover the pattern with the fingers; then

the drag is completely filled.

The sand is then firmly packed in the drag by means of hand rammers. The

ramming must be proper i.e. it must neither be too hard or soft.

After the ramming is over, the excess sand is leveled off with a straight bar

known as a strike rod.


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With the help of vent rod, vent holes are made in the drag to the full depth

of the flask as well as to the pattern to facilitate the removal of gases during

pouring and solidification.

The finished drag flask is now rolled over to the bottom board exposing

the pattern.

Cope half of the pattern is then placed over the drag pattern with the help

of locating pins. The cope flask on the drag is located aligning again with

the help of pins

The dry parting sand is sprinkled all over the drag and on the pattern.

A sprue pin for making the sprue passage is located at a small distance from

the pattern. Also, riser pin, if required, is placed at an appropriate place.

The operation of filling, ramming and venting of the cope proceed in the

same manner as performed in the drag.

The sprue and riser pins are removed first and a pouring basin is scooped

out at the top to pour the liquid metal.

Then pattern from the cope and drag is removed and facing sand in theform of paste is applied all over the mold cavity and runners which would

give the finished casting a good surface finish.

The mold is now assembled. The mold now is ready for pouring (see


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11.Explain the properties of moulding materials.

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.

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


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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.

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.


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12.Explain the composition of Moulding Sand

The main ingredients of any molding sand are:

Base sand,

Binder, and

Moisture

Base Sand

Silica sand is most commonly used base sand. Other base sands that are also used

for making mold are zircon sand, Chromite sand, and olivine sand. Silica sand is

cheapest among all types of base sand and it is easily available.

Binder

Binders are of many types such as:

1.

Clay binders,

2.

Organic binders and

3. Inorganic binders

Clay binders are most commonly used binding agents mixed with the molding

sands to provide the strength. The most popular clay types are:

Kaolinite or fire clay (Al2O32 SiO22 H2O) and Bentonite (Al2O34 SiO2nH2O)

Of the two the Bentonite can absorb more water which increases its bonding

power.

Moisture

Clay acquires its bonding action only in the presence of the required amount of

moisture. When water is added to clay, it penetrates the mixture and forms a


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microfilm, which coats the surface of each flake of the clay. The amount of water

used should be properly controlled. This is because a part of the water, which

coats the surface of the clay flakes, helps in bonding, while the remainder helps

in improving the plasticity.

13.Explain Shell Moulding Process

It is a process in which, the sand mixed with a thermosetting resin is allowed to

come in contact with a heated pattern plate (200 oC), this causes a skin (Shell)

of about 3.5 mm of sand/plastic mixture to adhere to the pattern.. Then the shell

is removed from the pattern. The cope and drag shells are kept in a flask with

necessary backup material and the molten metal is poured into the mold.

This process can produce complex parts with good surface finish 1.25 m to 3.75

m, and dimensional tolerance of 0.5 %. A good surface finish and good size

tolerance reduce the need for machining. The process overall is quite cost

effective due to reduced machining and cleanup costs. The materials that can be

used with this process are cast irons, and aluminum and copper alloys.


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Molding Sand in Shell Molding Process

The molding sand is a mixture of fine grained quartz sand and powdered

bakelite. There are two methods of coating the sand grains with bakelite. Firstmethod is Cold coating method and another one is the hot method of coating.

In the method of cold coating, quartz sand is poured into the mixer and then

the solution of powdered bakelite in acetone and ethyl aldehyde are added.

The typical mixture is 92% quartz sand, 5% bakelite, 3% ethyl aldehyde.

During mixing of the ingredients, the resin envelops the sand grains and the

solvent evaporates, leaving a thin film that uniformly coats the surface of sand

grains, thereby imparting fluidity to the sand mixtures.

In the method of hot coating, the mixture is heated to 150-180 o C prior to

loading the sand. In the course of sand mixing, the soluble phenol

formaldehyde resin is added. The mixer is allowed to cool up to 80 90 o C.

This method gives better properties to the mixtures than cold method.

14. Write short notes on Carbon Dioxide moulding.

In this process, the refractory material is coated with a sodium silicate-based

binder. For molds, the sand mixture can be compacted manually, jolted or

squeezed around the pattern in the flask. After compaction, CO 2 gas is passed

through the core or mold. The CO 2 chemically reacts with the sodium silicate to

cure, or harden, the binder. This cured binder then holds the refractory in place

around the pattern. After curing, the pattern is withdrawn from the mold.

The sodium silicate process is one of the most environmentally acceptable of the

chemical processes available. The major disadvantage of the process is that the

binder is very hygroscopic and readily absorbs water, which causes a porosity in

the castings.. Also, because the binder creates such a hard, rigid mold wall,


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shakeout and collapsibility characteristics can slow down production. Some of

the advantages of the process are:

A hard, rigid core and mold are typical of the process, which gives thecasting good dimensional tolerances;

good casting surface finishes are readily obtainable;

15.Explain Gating System.

The assembly of channels which facilitates the molten metal to enter into the mold

cavity is called the gating system. Alternatively, the gating system refers to allpassage ways through which molten metal passes to enter into the mold cavity.

The nomenclature of gating system depends upon the function of different

channels which they perform.

Down gates or sprue

Cross gates or runners

Ingates or gates

The metal flows down from the pouring basin or pouring cup into the down gate

or sprue and passes through the cross gate or channels and ingates or gates before

entering into the mold cavity.

Goals of Gating System

The goals for the gating system are

To minimize turbulence to avoid trapping gasses into the mold

To get enough metal into the mold cavity before the metal starts to solidify

To avoid shrinkage


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Establish the best possible temperature gradient in the solidifying casting

so that the shrinkage if occurs must be in the gating system not in the

required cast part.

Incorporates a system for trapping the non-metallic inclusions


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16.Explain different types of Gating System

The gating systems are of two types:

Pressurized gating system

Un-pressurized gating system

Pressurized Gating System

The total cross sectional area decreases towards the mold cavity

Back pressure is maintained by the restrictions in the metal flow

Flow of liquid (volume) is almost equal from all gates

Back pressure helps in reducing the aspiration as the sprue always runs full

Because of the restrictions the metal flows at high velocity leading to more

turbulence and chances of mold erosion

Un-Pressurized Gating System

The total cross sectional area increases towards the mold cavity

Restriction only at the bottom of sprue

Flow of liquid (volume) is different from all gates

aspiration in the gating system as the system never runs full

Less turbulence


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Pressurized Gating System

UnPressurized Gating System


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17.Explain the functions and design requirements of Riser.

Riser is a source of extra metal which flows from riser to mold cavity to

compensate for shrinkage which takes place in the casting when it startssolidifying. Without a riser heavier parts of the casting will have shrinkage

defects, either on the surface or internally.

Risers are known by different names as metal reservoir, feeders, or headers.

Shrinkage in a mold, from the time of pouring to final casting, occurs in three

stages.

1.

during the liquid state

2. during the transformation from liquid to solid

3. during the solid state

First type of shrinkage is being compensated by the feeders or the gating system.

For the second type of shrinkage risers are required. Risers are normally placedat that portion of the casting which is last to freeze. A riser must stay in liquid

state at least as long as the casting and must be able to feed the casting during this

time.

Functions of Risers

Provide extra metal to compensate for the volumetric shrinkage Allow mold gases to escape

Provide extra metal pressure on the solidifying mold to reproduce mold

details more exact

Design Requirements of Risers

1.

Riser size: For a sound casting riser must be last to freeze. The ratio of(volume / surface area)2of the riser must be greater than that of the casting.


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However, when this condition does not meet the metal in the riser can be

kept in liquid state by heating it externally or using exothermic materials

in the risers.

2.

Riser placement: the spacing of risers in the casting must be considered by

effectively calculating the feeding distance of the risers.

3.

Riser shape: cylindrical risers are recommended for most of the castings as

spherical risers, although considers as best, are difficult to cast. To

increase volume/surface area ratio the bottom of the riser can be shaped as

hemisphere.

18.Explain Directional Solidification

The solidification process begins at the mold-metal interface, meaning the entire

outer skin of the casting, the energy transfer continues through the layer of solid

metal toward the mold material. As the energy is traveling in one direction the

solidification process is traveling in the opposite direction.

Logically, thin sections of castings will solidify before thick sections of the

casting, as the volume of metal is decreasing in relation to the percentage of metal

that has solidified, a source of liquid metal has to be drawn upon to keep the

casting dimensionally accurate. The source of liquid metal is from the Risers that

act as reservoirs to feed the casting during the solidification phase.

Essentially there will always be a cavity defect, but the idea is to position thedefect in the riser not the casting itself. This is accomplished by gate and runner

placement such that the thinnest sections cool first and the placement of the risers

ensure a source of molten metal.

In closing the process of "Directional Solidification" is accomplished by orienting

the Sprue, gates, runners, pattern and risers such that the thinnest sections through

thickest are forming a wedge that ends with the riser(s) being the thickest section


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19.Explain the different methods of testing moulding sand.

The moulding sand after it is prepared should be properly tested to see that require

properties are achieved. Tests are conducted on a sample of the standard sand.

The moulding sand should be prepared exactly as it is done in the shop on the

standard equipment and then carefully enclosed in a container to safeguard its

moisture content.

Sand tests indicate the moulding sand performance and help the foundry men in

controlling the properties of moulding sands. Sand testing controls the moulding

sand properties through the control of its composition.

The following are the various types of sand control tests:

1. Moisture content test

2. Clay content test

3. Grain fitness test


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4. Permeability test

5. Strength test

6. Refractoriness test

7. Mould hardness test

Moisture content test:

Moisture is the property of the moulding sand it is defined as the amount of water

present in the moulding sand. Low moisture content in the moulding sand does

not develop strength properties. High moisture content decreases permeability.

Procedures are:

1. 20 to 50 gms of prepared sand is placed in the pan and is heated by an

infrared heater bulb for 2 to 3 minutes.

2. The moisture in the moulding sand is thus evaporated.

3. Moulding sand is taken out of the pan and reweighed.

4. The percentage of moisture can be calculated from the difference in the

weights, of the original moist and the consequently dried sand samples.

Percentage of moisture content = (W1-W2)/(W1) %

Where, W1-Weight of the sand before drying,

W2-Weight of the sand after drying.


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Clay content test:

Clay influences strength, permeability and other moulding properties. It is

responsible for bonding sand particles together.

Procedures are:

1. Small quantity of prepared moulding sand was dried

2. Separate 50 gms of dry moulding sand and transfer wash bottle.

3. Add 475cc of distilled water + 25cc of a 3% NaOH.

4. Agitate this mixture about 10 minutes with the help of sand stirrer.

5. Fill the wash bottle with water up to the marker.

6. After the sand etc., has settled for about 10 minutes, Siphon out the water

from the wash bottle.

7. Dry the settled down sand.

8. The clay content can be determined from the difference in weights of the

initial and final sand samples.

Percentage of clay content = (W1-W2)/(W1) * 100

Where, W1-Weight of the sand before drying,

W2-Weight of the sand after drying.


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Grain fitness test:

The grain size, distribution, grain fitness are determined with the help of the

fitness testing of moulding sands. The apparatus consists of a number of standardsieves mounted one above the other, on a power driven shaker.

The shaker vibrates the sieves and the sand placed on the top sieve gets screened

and collects on different sieves depending upon the various sizes of grains present

in the moulding sand.

The top sieve is coarsest and the bottom-most sieve is the finest of all the sieves.In between sieve are placed in order of fineness from top to bottom.

Procedures are:

1. Sample of dry sand (clay removed sand) placed in the upper sieve

2. Sand is vibrated for definite period

3. The amount of same retained on each sieve is weighted.

4. Percentage distribution of grain is computed.

Permeability test:

The quantity of air that will pass through a standard specimen of the sand at a

particular pressure condition is called the permeability of the sand.

Following are the major parts of the permeability test equipment:

1. An inverted bell jar, which floats in a water.

2. Specimen tube, for the purpose of hold the equipment

3. A manometer (measure the air pressure)


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Steps involved are:

1. The air (2000cc volume) held in the bell jar is forced to pass through the

sand specimen.

2. At this time air entering the specimen equal to the air escaped through the

specimen

3. Take the pressure reading in the manometer.

4. Note the time required for 2000cc of air to pass the sand

5. Calculate the permeability number

6. Permeability number (N) = ((V x H) / (A x P x T))

Where,

V-Volume of air (cc)

H-Height of the specimen (mm)

A-Area of the specimen (mm2)

P-Air pressure (gm / cm2)

T-Time taken by the air to pass through the sand (seconds)

Strength test:

Measurements of strength of moulding sands can be carried out on the universal

sand strength testing machine. The strength can be measured in compression,

shear and tension.


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The sands that could be tested are green sand, dry sand or core sand. The

compression and shear test involve the standard cylindrical specimen that was

used for the permeability test.

a. Green compression strength:

Green compression strength or simply green strength generally refers to the

stress required to rupture the sand specimen under compressive loading. The

sand specimen is taken out of the specimen tube and is immediately (any delay

causes the drying of the sample which increases the strength) put on the

strength testing machine and the force required to cause the compression

failure is determined. The green strength of sands is generally in the range of

30 to 160 KPa.

b. Green shear strength:

With a sand sample similar to the above test, a different adapter is fitted in the

universal machine so that the loading now be made for the shearing of the sand

sample. The stress required to shear the specimen along the axis is then

represented as the green shear strength. It may vary from 10 to 50 KPa.

c. Dry strength:

This test uses the standard specimens dried between 105 and 1100 C for 2

hours. Since the strength increases with drying, it may be necessary to apply

larger stresses than the previous tests. The range of dry compression strengths

found in moulding sands is from 140 to 1800 KPa, depending on the sand

sample.

Steps involved are:

1. Specimen is held between the grips


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2. Apply the hydraulic pressure by rotating the hand wheel

3. Taking the deformation use of the indicators.

Refractoriness test:

The refractoriness is used to measure the ability of the sand to withstand the

higher temperature.

Steps involved are:

1. Prepare a cylindrical specimen of sand

2. Heating the specimen at 1500 C for 2 hours

3. Observe the changes in dimension and appearance

4. If the sand is good, it retains specimen share and shows very little

expansion. If the sand is poor, specimen will shrink and distort.

Mould hardness test:

Hardness of the mould surface can be tested with the help of an indentation

hardness tester. It consists of indicator, spring loaded spherical indenter.

The spherical indenter is penetrates into the mould surface at the time of testing.

The depth of penetration w.r.t. the flat reference surface of the tester.

Mould hardness number = ((P) / (D (D2-d2))

Where,

P- Applied Force (N)

D- Diameter of the indenter (mm)


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d- Diameter of the indentation (mm)

20.Explain Plaster Mould Casting.

Plaster mold casting is a metalworking castingprocess similar to sand casting

except the molding material isplaster of paris instead ofsand.Like sand casting,

plaster mold casting is an expendable mold process, however it can only be used

with non-ferrous materials. It is used for castings as small as 30 g (1 oz) to as

large as 45 kg (99 lb). Generally, the form takes less than a week to prepare.

Production rates of 110 units/hr can be achieved with plaster molds.

Parts that are typically made by plaster casting are lock components, gears,

valves, fittings, tooling, and ornaments.

First, the plaster is mixed and the pattern is sprayed with a thin film of parting

compound to prevent the plaster from sticking to the pattern. The plaster is then

poured over the pattern and the unit shaken so that the plaster fills any small

features. The plaster sets, usually in about 15 minutes, and the pattern is removed.

The mold is then baked, between 120 C (248 F) and 260 C (500 F), to remove

any excess water. The dried mold is then assembled, preheated, and the metal

poured. Finally, after the metal has solidified, the plaster is broken from the cast

part. The used plaster cannot be reused.

Plaster mold casting is used when an excellent surface finish and good

dimensional accuracy is required. Because the plaster has a low thermal

conductivity andheat capacity the metal cools more slowly than in a sand mold,

which allows the metal to fill thin cross-sections; the minimum possible cross-

section is 0.6 mm (0.024 in). This results in anear net shape casting, which can

be a cost advantage on complex parts. It also produces minimal scrap material.[3]
http://en.wikipedia.org/wiki/Metalworkinghttp://en.wikipedia.org/wiki/Castinghttp://en.wikipedia.org/wiki/Sand_castinghttp://en.wikipedia.org/wiki/Plaster_of_parishttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Near_net_shapehttp://en.wikipedia.org/wiki/Plaster_mold_casting#cite_note-3http://en.wikipedia.org/wiki/Plaster_mold_casting#cite_note-3http://en.wikipedia.org/wiki/Plaster_mold_casting#cite_note-3http://en.wikipedia.org/wiki/Plaster_mold_casting#cite_note-3http://en.wikipedia.org/wiki/Near_net_shapehttp://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Plaster_of_parishttp://en.wikipedia.org/wiki/Sand_castinghttp://en.wikipedia.org/wiki/Castinghttp://en.wikipedia.org/wiki/Metalworking


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The major disadvantage of the process is that it can only be used with lower

melting temperature non-ferrous materials, such as aluminium, copper,

magnesium, and zinc.The most commonly used materials are aluminium and

copper. The maximum working temperature of plaster is 1,200 C (2,200 F), so

higher melting temperature materials would melt the plaster mold. Also, the

sulfur in the gypsum reacts with iron, making it unsuitable for casting ferrous

materials.

Another disadvantage is that its long cooling times restrict production volume.

Plaster is not as stable as sand, so it is dependent on several factors, including the

consistency of the plaster composition, pouring procedures, and curing

techniques. If these factors are not closely monitored the mold can be distorted,

shrink upon drying, have a poor surface finish, or fail completely.

21.Explain Ceramic Moulding

The ceramic molding process is an easy production method which guarantees the

precision required, and also gives a good surface finish, using a high temperature

method to better structure and shape parts. This process also gives a low grade of

toleration and is not very expensive.

The patterns that ceramic mold uses areplaster,plastic,wood,metal,rubber,etc.

The pattern is the shape body of the desired part.

The ceramic molding process can be summarized in 7 steps:

Step 1: The pattern is designed with the materials already mentioned (plastic,

wood, metal, etc.). Many materials can be used as a pattern, because most of

them support the low temperature which is used in the Ceramic Molding

Process.
http://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Woodhttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Plasterhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Aluminium


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Step 2: The mix is injected into a binder.

Step 3: Part of some refractory ceramic powder is taken out, according to what

is needed.

Step 4: To the binder, there is added a special gelling, in order to be mixed.

Step 5: The slurry is put into the pattern.

Step 6: The slurry is heated to a high temperature, depending on what is

required.

Step 7: The slurry is allowed to cool and the process is done.

The principal characteristic of the molding process is that it produces very

accurate castings.

22.Explain Dry Sand Moulding

Dry sand molding is the green sand practice modified by baking the mold at 400-

600F (204-316C). Some foundries use dry sand molds to produce intricate parts

which are difficult to cast to exact size and dimensions. Molds are generally dried

(or baked) in large mold drying or with large mold heaters.


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Castings of large or medium size and of complex configuration such as frames,

engine cylinders, rolls, large gears and housings are often made using the dry sand

technique. Both ferrous and nonferrous metals are cast in this type of mold.

Advantages

Dry sand molds are generally stronger than green sand molds and therefore can

withstand much additional handling.

Better dimension control than if they were molded in green sand.

The improved quality of the sand mixture due to the removal of moisture can

result in a much smoother finish on the castings than if made in green sand molds.

Where molds are properly washed and sprayed with refractory coatings, the

casting finish is further improved.

Disadvantages

This type of molding is much more expensive than green sand molding and is not

a high-production process. Correct baking (drying) times are essential.

23.Write short notes on Chills.

A chill is an object used to promote solidification in a specific portion of ametal

casting mold.Normally the metal in the mold cools at a certain rate relative to

thickness of the casting. When the geometry of the molding cavity prevents

directional solidification from occurring naturally, a chill can be strategically

placed to help promote it. There are two types of chills: internal and external

chills.
http://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Mold_%28manufacturing%29http://en.wikipedia.org/wiki/Directional_solidificationhttp://en.wikipedia.org/wiki/Directional_solidificationhttp://en.wikipedia.org/wiki/Mold_%28manufacturing%29http://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Metal_casting


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Types

Internalchills are pieces of metal that are placed inside the molding cavity. When

the cavity is filled, part of the chill will melt and ultimately become part of thecasting, thus the chill must be the same material as the casting. Note that internal

chills will absorb bothheat capacity andheat of fusion energy.

Externalchills are masses of material that have a high heat capacity andthermal

conductivity.They are placed on the edge of the molding cavity, and effectively

become part of the wall of the molding cavity. This type of chill can be used to

increase the feeding distance of a riser or reduce the number of risers required.

Materials

Chills can be made of many materials, including iron,copper,bronze,aluminium,

graphite,andsilicon carbide.Other sand materials with higher densities, thermal

conductivity or thermal capacity can also be used as a chill. For example,

chromitesand orzircon sand can be used when molding withsilica sand.

24. List the essential requirements of Core.

There are seven requirements for core

1. In the green condition there must be adequate strength for handling.

2.

In the hardened state it must be strong enough to handle the forces ofcasting; therefore the compression strength should be 100 to 300 psi (0.69

to 2.07 MPa).

3. Permeability must be very high to allow for the escape of gases.

4.

As the casting or molding cools the core must be weak enough to break

down as the material shrinks. Moreover, they must be easy to remove

duringshakeout.
http://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Heat_of_fusionhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Bronzehttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Graphitehttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Chromitehttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Zirconhttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Permeationhttp://en.wiktionary.org/wiki/shakeouthttp://en.wiktionary.org/wiki/shakeouthttp://en.wikipedia.org/wiki/Permeationhttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Zirconhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Chromitehttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Graphitehttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Bronzehttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Heat_of_fusionhttp://en.wikipedia.org/wiki/Heat_capacity


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5.

Good refractoriness is required as the core is usually surrounded by hot

metal during casting or molding.

6.

A smoothsurface finish.

7.

A minimum generation of gases during metal pouring.

25.What is Chaplets?

Cores are usually supported by two core prints in the mold. However, there are

situations where a core only uses one core print so other means are required to

support the cantilevered end. These are usually supplied in the form of chaplets.

These are small metal supports that bridge the gap between the mold surface and

the core, but because of this become part of the casting. As such, the chaplets

must be of the same or similar material as the metal being cast. Moreover, their

design must be optimized because if they are too small they will completely melt

and allow the core to move, but if they are too big then their whole surface cannot

melt and fuse with the poured metal. Their use should also be minimized because

they can cause casting defects or create a weak spot in the casting. It is usually

more critical to ensure the upper chaplets are stronger than the lower ones because

the core will want to float up in the molten metal.
http://en.wikipedia.org/wiki/Refractorinesshttp://en.wikipedia.org/wiki/Surface_finishhttp://en.wikipedia.org/wiki/Surface_finishhttp://en.wikipedia.org/wiki/Refractoriness

MP 1st Module Notes

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