Project Report on Crown Shrinkage Final

8/18/2019 Project Report on Crown Shrinkage Final

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IPL's major OEM customers include Hyundai Motor Company, Maruti,

Ashok Leyland, TATA Motors, Eicher Motors, Simpsons & Co., TAFE, Mahindra

& Mahindra, Greaves, KOEL, Hindustan Motors, Indian Railways, etc.,

In addition to the OEM segment, IPL continues to be a leading company inthe domestic Replacement market. IPL products are the preferred choice of the

most of the re-conditioners in India. IPL continues to make impressive strides in

the export market and is among the top exporters of auto components in the

country.

IPL and its subsidiary companies have posted a combined turnover of over

$350 Million USD during 2010-2011 and is poised for an exponential growth.

1.2 Group Overview

An amalgamation is a huge conglomerate comprising of 52 companies and

20,000 strong workforces with offices and manufacturing facilities spread across

the country. The Amalgamations group is one of the India's largest light

engineering groups with established presence in diverse businesses such as auto

components, engines, tractors, cutting tools, paints, agricultural implements,

distribution and variety of service industries and exports, plantations, batteries,

security printing, book selling, pesticides, advertising and communication,

warehousing and goods transportation, bus body building, retreating and a range of

trade and distribution services.

Through their diverse product and service portfolio, the group touches

millions of people every day ranging from farmers to business tycoons. Whatstarted off with Simpsons & Co, today, Amalgamations is a huge conglomerate

comprising of 52 companies and 20,000 strong workforces with offices and

manufacturing facilities spread across the country.

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The group is known for its devotion to values, strict adherence to highest

quality standards in their products and services, responsible corporate governance

and business ethics.

1.3 Mission Statement

To be a Technology Leader, delivering to our customers as a high Quality of

Product and Service. This will be achieved through constant Innovation of all

products and processes making us a natural first choice to our customers. The

company was able to achieve consistent growth and industry leadership through its

visionary and qualitative response to the changing consumer and market demands.

1.4 Quality System

Professional project management mechanism designed to identity possible

defects during the initial phases of development.

Suppliers are committed to stringent quality standards to ensure the

company gets high quality raw materials and components.

Strong vendor development programs to enhance the quality of our vendors.

Customer recognition and host of honors and awards for maintaining

outstanding quality is the proof of our commitment to progress through the

path of quality.

At all IPL locations, systems and procedures based on TPM, TQM and lean

manufacturing procedures are used to ensure that quality levels are on par

with the best in the world. All plants of IPL are TS 16949 and ISO 14001certified.

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CHAPTER 2

INTRODUCTION

2.1. Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas

compressors and pneumatic cylinders, among other similar mechanisms. It is the

moving component that is contained by a cylinder and is made gas-tight by pisto n

rings. In an engine, its purpose is to transfer force from expanding gas in the

cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the

function is reversed and force is transferred from the crankshaft to the piston for

the purpose of compressing or ejecting the fluid in the cylinder.

Pistons are cast from aluminium alloys. For better strength and fatigue life,

some racing pistons may be forged instead. Early pistons were of cast iron, but

there were obvious benefits for engine balancing if a lighter alloy could be used.

To produce pistons that could survive engine combustion temperatures, it was

necessary to develop new alloys such as Y alloy and Hiduminium, specifically for

use as pistons.

Fig.2.1 Piston Casting

CROWN

SKIRT

INSERT

PAD

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The pouring temperature can range greatly depending on the casting

material; for instance zinc alloys are poured at approximately 700 °F (371 °C),

while Gray iron is poured at approximately 2,500 °F (1,370 °C).

Permanent mold casting is metal casting process that employs reusablemolds ("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 aluminium, magnesium, and copper

alloys. Other materials include tin, zinc, and lead alloys and iron and steel are also

cast in graphite molds. Typical parts include gears, splines, wheels, gear housings,

pipe fittings, fuel injection housings, and automotive engine pistons.

2.4 Melting

The process includes melting the charge, refining the melt, adjusting the

melt chemistry and tapping into a transport vessel. Refining is done to remove

deleterious gases and elements from the molten metal to avoid casting defects.

Material is added during the melting process to bring the final chemistry within a

specific range specified by industry and/or internal standards. Certain fluxes may

be used to separate the metal from slag and/or dross and degassers are used to

remove dissolved gas from metals that readily dissolve certain gasses. During the

tap, final chemistry adjustments are made. Several specialised furnaces are used to

melt the metal. Furnaces are refractory lined vessels that contain the material to be

melted and provide the energy to melt it. Modern furnace types include electric arcfurnaces (EAF), induction furnaces, cupolas, reverberatory, and crucible furnaces.

Furnace choice is dependent on the alloy system quantities produced. For ferrous

materials EAFs, cupolas, and induction furnaces are commonly used.

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2.5 Degassing

In the case of aluminium alloys, a degassing step is usually necessary to

reduce the amount of hydrogen dissolved in the liquid metal. If the hydrogen

concentration in the melt is too high, the resulting casting will be porous as the

hydrogen comes out of solution as the aluminium cools and solidifies. Porosity

often seriously deteriorates the mechanical properties of the metal. An efficient

way of removing hydrogen from the melt is to bubble argon or nitrogen through

the melt. To do that, several different types of equipment are used by foundries.

When the bubbles go up in the melt, they catch the dissolved hydrogen and bring it

to the top surface. There are various types of equipment which measure the amountof hydrogen present in it. Alternatively, the density of the aluminium sample is

calculated to check amount of hydrogen dissolved in it. In cases where porosity

still remains present after the degassing process, porosity sealing can be

accomplished through a process called metal impregnating.

Fig.2.1 Rotary degasser for molten aluminium alloy

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2.6 Heat treatment

Heat treatment is a group of industrial and metalworking processes used to alter the

physical, and sometimes chemical, properties of a material. The most common

application is metallurgical. Heat treatments are also used in the manufacture ofmany other materials, such as glass. Heat treatment involves the use of heating or

chilling, normally to extreme temperatures, to achieve a desired result such as

hardening or softening of a material. Heat treatment techniques include annealing,

case hardening, precipitation strengthening, tempering and quenching. It is

noteworthy that while the term heat treatment applies only to processes where the

heating and cooling are done for the specific purpose of altering properties

intentionally, heating and cooling often occur incidentally during other

manufacturing processes such as hot forming or welding.

Fig.2.2 Heat treatment of piston casting

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2.7 Finishing

The final step in the process usually involves machining the component in

order to achieve the desired dimensional accuracies, physical shape and surface

finish. 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 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. 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 introductionof 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.

Fig.2.3 Machined piston casting

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CHAPTER 3

LITERATURE SURVEY

3.1 TYPICAL DIE TEMPERATURES AND LIFE FOR VARIOUS CASTMATERIALS

John L., Jorstad et al [1], "Aluminum Future Technology in Die Casting".

Table 3.1 Typical die temperatures and life for various cast materials

Description Zinc Aluminium Magnesium Brass(leaded yellow)

Maximum die life 1,000,000 100,000 100,000 10,000

[number of cycles]

Die temperature [C° (F°)] 218 (425) 288 (550) 260 (500) 500 (950)

Casting temperature 400 (760) 660 (1220) 760 (1400) 1090 (2000)

[C° (F°)]

3.2 Chvorinov ’s Rule

Giesserei et al [2], "Theory of the Solidification of Castings".

Chvorinov's Rule is a mathematical relationship first expressed by Nicolas

Chvorinov in 1940, that relates the solidification time for a simple casting to

the volume and surface area of the casting. In simple terms the rule establishes thatunder otherwise identical conditions, the casting with large surface area and small

volume will cool more rapidly than a casting with small surface area and a large

volume.

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The relationship can be written as:

Where t is the solidification time, V is the volume of the casting, A is the surface area of

the casting that contacts the mold, n is a constant, and B is the mold constant. The mold

constant B depends on the properties of the metal, such as density, heat capacity, heat of

fusion and superheat, and the mold, such as initial temperature, density, thermal

conductivity, heat capacity and wall thickness. The S.I. units of the mold constant B are

. According to Ask eland, the constant n is usually 2, however Degarmo claims itis between 1.5 and 2.The mold constant of Chvorinov's rule, B, can be calculated using

the following formula:

Where

Tm = melting or freezing temperature of the liquid (in Kelvin)

To = initial temperature of the mold (in Kelvin)

ΔT s = T pour − T m = superheat (in Kelvin)

L = latent heat of fusion (in [J.Kg −1])

k = thermal conductivity of the mold (in [W.m −1.K −1)])

ρ = density of the mold (in [Kg.m −3])

c = specific heat of the mold (in [J.Kg −1.K −1])

ρm = density of the metal (in [Kg.m −3])

cm = specific heat of the metal (in [J.Kg−1.K −1])

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It is most useful in determining if a riser will solidify before the casting, because if the

riser solidifies first then defects like shrinkage or porosity can form.

3.3 Minimization of defects in aluminium alloy castings using sqcChokkalingam, B., and Nazirudeen et al [3] , “Analysis of casting defe ct through defect

diagnostic approach” .

3.4 Shrinkages

The following points describe how shrinkages occur in castings

Shrinkage occurs during solidification as a result of volumetric differences

between liquid and solid state. For most aluminium alloys, shrinkage duringsolidification is about 6% by volume.

Lack of adequate feeding during casting process is the main reason for shrinkage

defects.

Shrinkage is a form of discontinuity that appears as dark spots on the radiograph.

It assumes various forms, but in all cases it occurs because the metal in molten state

shrinks as it solidifies, in all portions of the final casting.

By making sure that the volume of the casting is adequately fed by risers,

Shrinkage defects can be avoided.

By a number of characteristics on radiograph, various forms of shrinkages can be

recognized.

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3.5 Types of shrinkages:

(1) Cavity

(2) Dendritic

(3) Filamentary

(4) Sponge types

3.5.1 Shrinkage Cavity

The following points explain how shrinkage cavity occurs in castings are: It appears in areas with distinct jagged boundaries.

When metal solidifies between two original streams of melt coming from

opposite directions to join a common front.

It usually occurs at a time when the melt has almost reached solidification

temperature and there is no source of supplementary liquid to feed possible

cavities.3.5.2 Dendritic Shrinkage

This type of shrinkage can be identified by seeing distribution of very fine lines

or small elongated cavities that may differ in density and are usually unconnected.

3.5.3 Filamentary Shrinkage

This type of shrinkage usually occurs as a continuous structure of connected lines of

1. Variable length

2. Variable width

3. Variable density

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3.5.4 Sponge Shrinkage

Sponge shrinkage can be identified from areas of lacy texture with diffuse

outlines.

It may be dendritic or filamentary shrinkage. Filamentary sponge shrinkage appears more blurred as it is projected through the

relatively thick coating between the discontinuities and the film surface.

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CHAPTER 4

MATERIALS AND METHODS

4.1 Process flow for the manufacturing a piston

Manufacturing a piston through casting in aluminium foundry has

consist of various steps are as follows:

MELTING OF ALUMINIUM ALLOY

TREATMENT OF ALLOY

PREPARATION OF DIE

INSERTS FROM PREHEATING OF INSERT FERROUS FOUNDRY

INSERTS DIPPED IN BONDING BATH

INSERTS PLACED IN DIE AND METAL POURED IN TO DIE

FETLING

HEAT TREATMENT OR AGE HARDENING

SENT TO M/C SHOP FOR MACHINING

Fig.4.1 Process flow in Aluminiumfoundry

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4.2 Melting of Aluminium alloy

There are two types of furnaces for melting the aluminium alloy. They

are tower furnace and rotary furnace. These furnaces are oil burn furnace. The

oil is preheated to 90°C.this furnaces are used to melt the aluminium ingot oneton per hour. It consists of two chambers. They are namely holding chamber

and melting chamber.

Table 4.1 Tapping Temperature of Aluminium Alloys

Aluminium Alloys Tapping temperatures

IP101 (LM-13) 760-800°C

IP 102 (3L33) 750-800°C

IP 123 (M142) 780-800°C

IP 104 (HE) 800-820°C

4.2.1 Conditions for melting

Holding chamber is preheated till it reaches 600°Cand then slag is removed

from the chamber walls. Ingot and returns are charged as per the charge mix.

Then it is allowed to melt until it reaches 700°C. Then the Phos-copper and

magnesium is added and at last coverall flux is added.

Remove dross and close the furnace and switch on the holding chamber

burner and allow them to reach 760-800°C.

Check the metal level and send the chemistry sample to laboratory. After

receiving the chemistry approval tapping temperature is checked.

.

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Table 4.2 Material Composition of LM-13 alloy for piston castings

4.3 Treatment of alloy

The purpose of this step is to remove the hydrogen gas, moisture content,

dirt and to achieve grain refinement by adding nucleant and degasser flux andcover flux. It is then stirred by the automation technique and passing nitrogen

(N2) gas. The whole process will be carried out for 30 minutes.

4.4 Preparation of die

The die is cleaned and air blowed to the die cavity. The die is preheated

by using LPG burner and then it is coated. The preheating of die is to attain the

temperature of about 225°C - 250°C. The coating material is prepared by adding

6kgs of Die coat 140, 5kgs of Ivaplast-k and 5litres of sodium silicate in 10

litres of water and stirred. The dust and slags present in the die cavities and air

vents are cleaned.

CHEMICALS COMPOSITION (%)

MINIMUM MAXIMUMAluminium 83 85Silicon 11.0 13.0Magnesium 0.80 1.50Copper 0.70 1.50

Nickel 0.70 1.30Ferrous 0.80Manganese 0.45Zinc 0.50

Lead 0.10Tin 0.20Unlisted impurities (including pb + sn) 0.15Phosphorous 15ppm 100ppm

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4.5 Preheating of insert

Ni-resist piston inserts are found near the top of a piston, where piston

rings (compression rings and oil control rings) are located. This section of the

piston is grooved for the insertion of these rings. The Ni-resist piston insert is

generally cast into the piston to protect the first ring groove, but a second Ni-

resist piston insert may also be cast in after the second ring groove. They place

the inserts into piston molds and pour molten aluminium into the molds. The

piston inserts bond with the aluminium, and become one with the solidified

diesel engine piston. It is preheated in induction oven at 250°C. It is preheated

inorder to avoid insert hole defect in the piston.4.6 Insert dipped in bonding material 3L33

After preheating the insert it is dipped in LM-6 (3L33). The

chemical compositions of LM-6 are

Table 4.3 Material composition of 3L33 (IPL 102) for insert bonding

CHEMICALS COMPOSITION (%)

MINIMUM MAXIMUM Aluminium 83.0 85.0

Silicon 10.0 13.0

Magnesium 0.50

Copper 0.50

Nickel 0.80

Manganese 0.50

Zinc 0.10

Tin 0.05

Lead 0.10

Titanium 0.20

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The purpose of dipping insert in 3L33 is to increase the bonding strength of the

insert with the LM-13 alloy.

4.7 Insert placed in die and metal pouring in to die

The filter and dipped insert is placed in a die and then the molten metal

(LM-13) is poured in to die. The water is circulated around the die and

solidification takes place. After solidified for 120secs the casting is made ready

and immediately quenched in water. The runner and riser in the piston casting is

fetled off. The filter is used to increase the flow of molten metal properly and to

filter the inclusion materials and micro inclusion in the molten material.

4.8 Heat treatment or Age hardening

Heat treatment is the process which is used to increase the hardness and

physical strength of the casting. Heat treatment is carried out based on the

hardness required. It is usually carried out for 6-8 hours based on the material.

Heat treatment will be carried by heating the casting for about 200-240°C by

using electric furnace. It is then send to machine shop for further machining.

Fig.4.2 Piston casting after machining

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CHAPTER 5

CROWN SHRINKAGE DEFECT

5.1 Major defects in casting

There are various defects in casting are Cold shut

Gas porosity or Skirt porosity

Inclusion

Wall thickness variation

Crown shrinkage

5.1.1 Cold Shut

If molten metal is too cold or casting section is too thin, entire mold

cavity may not filled during pouring before the metal starts solidifying and the

result is misrun. Besides, misrun is often the result of interrupted flow of metal

from ladle into the mold.

If the molten metal enters mold cavity through two or more ingates or

otherwise if two streams of metal which are too cold, physically meet in the

mold cavity but do not fuse together, they develop cold shut defect.

Fig.5.1 Cold shut defect in piston casting

Cold Shut

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Causes:

a) Too cold molten metal

b) Too thin casting section

c) Too many restriction in the gating system

d) Metal lacking in the fluidity

5.1.2 Inclusion:

Any separate undesired foreign materials present in the metal of the

casting are known as inclusion. An inclusion may be oxides, slag, dirt etc.which enters the mold cavity along with the molten metal during pouring. Such

inclusion should be skimmed off before pouring the molten metal into the mold

cavity.

Remedies:

1) Proper molding

2) Molding sand should possess adequate hot strength.

3) Skimming off or screening of molten metal before pouring.

Fig.5.2 Inclusion defect in piston casting

Inclusion

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5.1.3 Gas Porosity or Skirt Porosity

Gas porosity is the formation of bubbles within the casting after it has cooled.

This occurs because most liquid materials can hold a large amount of dissolved

gas, but the solid form of the same material cannot, so the gas forms bubbles

within the material as it cools. Gas porosity may present itself on the surface of

the casting as porosity or the pore may be trapped inside the metal, which

reduces strength in that vicinity. Nitrogen, oxygen and hydrogen are the most

encountered gases in cases of gas porosity. In aluminium castings, hydrogen is

the only gas that dissolves in significant quantity, which can result in hydrogen

gas porosity.

Remedies

Degassing of molten metal.

Pouring of molten metal above 730°C.

Gas Porosity

Fig.5.3 Gas porosity formed in the piston

5.1.4 Wall thickness variation

Wall thickness variation is the variation of boss thickness in the casting.

This is caused due to misalignment of die.

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5.2 REASON TO CHOOSE CROWN SHRINKAGE

The defects so far discussed are due to some of the causes shown above

and can be rectified. But the defect which is going be discussed does not havethe predictable causes. So the scope of the project is to determine the parameters

which influence the defect and possible suggestion to rectify it.

5.3. Crown shrinkage

Crown Shrinkage is the depression typically internal to the casting that is

caused by a molten island of material that does not have enough feed metal to

supply it. Shrinkage cavities are characterized by a rough interior surface. The

shrinkage causes due to the irregular solidification and improper water cooling

to the die.

Fig.5.4 Crown shrinkage visible after the felting process in piston casting

CrownShrinkage

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Fig.5.5 Crown shrinkage after the machining of piston casting

gjhghgghhhhghghgjj

CrownShrinkage

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5.4 Steps to determine the predominant causes for crown shrinkage

The crown shrinkage is the challenging dilemma in which the particular

deciding factor cannot be predicted. So, all the parameter influencing the

casting are considered and experimentally analyzed. Based on the experimentalanalysis probable causes for the crown shrinkage is determined. The steps

followed in the company are shown below.

Fig.5.6 Process flow to determine the root causes for crown shrinkage

Parameters influencing the casting

Experimental Analysing of the casting parameters

Probable inference from the experimentalanalysis for the crown shrinkage

Solution for the crown shrinkage

Reason to choose this solution

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5.5 Parameters influencing the castings

The various parameters influencing the castings are as follows

Pouring Metal temperature

Water cooling to die

Solidification timing

Die body temperature

Centre core temperature

Runner and riser design

Degassing of metal Air vent

5.5.1 Pouring Metal temperature

Pouring is a process by which molten metal is transferred to the

cast for cooling and solidification and thus be converted into final product.

Pouring temperature is the temperature to which the molten metal has to be

raised to before being poured into casts for cooling and setting. This pouringtemperature must also take into account the heat loss and caused due to the

transfer of metal through ladles, as a distance between furnace and cast has to

be covered and also due to the heat absorbed by ladles. However, due to

repeated exposure to high temperature of molten metal, these casts have a

limited life, or can be used for metals with low pouring temperature

requirements. Therefore one of the main requirements of the casting process isrefractoriness or in other words, the capability of cast to bear high temperatures

of the molten metal without undergoing any changes in its physical properties.

This is a very important requirement in alloys with high melting point such as

steel. However, this issue may be taken secondary in alloys with lower melting

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points. Where alloys with high melting point are being used, the moulds need to

be lined with an insulating material with refractory properties so that the mould

retains its shape and original characteristics. If the molten metal temperature is

below 720 °C else the cold shut is formed in the castings.

5.5.2 Water cooling to die

Water flow rate is defined by the limit: i.e., the flow of water of

fluid (V) through a surface per unit time (t). Since this is only the time

derivative of volume, a scalar quantity, the volumetric flow rate is also a scalar

quantity.

Table 5.1 Standard water flow rate to the die

WATERFLOW RATE

CASTING MODEL> 100

PISTONOUTER

DIAMETER

< 100 PISTONOUTERDIAMETER

CENTRECORE

4-6 Lt/min 3-4 Lt/min

PIN 2-3 Lt/min 2-2.5 Lt/min

DIE BODY 1-2 Lt/min 0.5-1 Lt/min

CROWN 2-3 Lt/min 2-2.5 Lt/min

5.5.3 Solidification timing

Casting Geometry, material and process determine the solidification time ofa casting. The rudimentary equations that are required to estimate the casting

solidification will be reviewed in this section. The occurrence of solidification

shrinkage defect, which is indicated by the relationship between temperature,

gradient and cooling rate, would also be looked at.

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If the solidification order of distinct regions of a casting is to be determined

then the same Chv orinov’s principle can be used. In order to derive the equation

that would represent the solidification time of the simply shaped casting, the

assumptions made are: The mold is made semi-infinite (the effect which the finite thickness of

the mold has must be neglected), and the heat flow is unidirectional.

Over a range of considered temperature the properties of metal and mold

material are uniform (throughout the bulk), and remain constant.

The mold surface and the metal are in complete contact (there are no air

gaps).From the commencement to the end of solidification the metal-mold

interface temperature remains constant.

An equation between the heat that the casting gives up Qcast, and the heat that

the mould transferees Qmould, can give the solidification time. Here the casting

volume (representing the heat content) is represented by V and the cooling

surface area (through which heat is extracted), is represented by the A. Thecasting modulus is given by the ratio V/A.

Table 5.2 Solidification time for the Piston casting

SOLIDIFICATION TIME: 120 SECS

WATER STARTS TO FLOW

PARTS OF DIE DELAY RUN

CENTRE CORE10 SECS [WHEN

TIMER ON] 110 SECS

PIN 15 SECS 25 SECS

DIE BODY 70 SECS 50 SECS

CROWN 100 SECS 20 SECS

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5.5.4 Die body temperature

Die temperature has considerable influence role on the quality of die cast parts

and on the production cycle. Working with a die at excessively low temperature,

you can encounter the following problems:

• Difficult ejection;

• Piece contraction around pins;

• Bonding between metal and die;

• Unreliable casting dimensions;

• Incomplete filling.

On the other hand, if die temperature is too high there will be:

•Difficult casting expul sion (warping, gripping);

• Fast release lube degradation

• Longer cycle time

• Unreliable casting dimensions

As a result, the correct die temperature is crucial to obtain a smooth and high

level of productivity and to optimize the production cycle.

Thermal regulators are electrical-mechanical devices designed to regulate dies

temperature used during die casting production.

1) Improvement in the mechanical and strength characteristics of castings.

2) Potential boost in casting productivity by reducing cycle time.

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3) Extended die life.

4) Reduction of initial rejects.

Fig.5.7 Piston castings die (IPL 400)

5.5.5 Centre core of the die

Centre core is the interior part of the die which is responsible for the formation

of centre hollow part in the piston.

Fig.5.8 Centre core of the die (IPL 400)

Die body

Centre core

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Fig.5.9 Piston centre hollow section

5.5.6 Runner and riser design

A sprue is the passage through which liquid material is introduced into a mold.

During casting or molding, the material in the sprue will solidify and need to be

removed from the finished part. This excess material is also called a sprue. 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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Fig.5.10 Runner and riser position in piston casting

5.5.7 Degassing of metal

Fluxes composed of chlorine and fluorine containing salts are used for

degassing molten aluminium alloys. Degassing fluxes are commonly shaped inform of tablets. Degassing operation starts when a flux tablet is plunged by a

clean preheated perforated bell to the furnace bottom. The flux components

react with aluminium forming gaseous compounds (aluminium chloride,

aluminium fluoride). The gas is bubbling and rising through the melt. Partial

pressure of hydrogen in the formed bubbles is very low therefore it diffuses

from the molten aluminium into the bubbles. The bubbles escape from the meltand the gas is then removed by the exhausting system. The process continues

until bubbling ceases.

Runner

Riser

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5.5.7.1 Rotary degasser

In the rotary degassing method an inert or chemically inactive gas (Argon,

Nitrogen) is purged through a rotating shaft and rotor. Energy of the

rotating shaft causes formation of a large number of fine bubbles providingvery high surface area-to volume ratio. Large surface area promotes fast

and effective diffusion of hydrogen into the gas bubbles resulting in

equalizing activity of hydrogen in liquid and gaseous phases.

Rotary degasser allows achieve more complete hydrogen removal as

compared to the flux degassing.

Additionally rotary degasser does not use harmful chlorine and fluorine

containing salts.

Rotary degasser may also combine the functions of degassing and flux

introduction. In this case the inert gas serves as carrier for granulated flux.

The method is called flux injection.

33

http://www.substech.com/dokuwiki/doku.php?id=argonhttp://www.substech.com/dokuwiki/doku.php?id=nitrogenhttp://www.substech.com/dokuwiki/doku.php?id=nitrogenhttp://www.substech.com/dokuwiki/doku.php?id=argon


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CHAPTER 6

EXPERIMENTAL ANALYSIS

6.1 Reason to choose experimental analysis than computerization

Analyses through computer softwares such as CFD, Autocast are choosed only

when the particular parameter affecting defect is known. Not only because of

this reason but also analysis of solidification, heat transfer rate through CFD

takes long duration. Upon changing the parameters in CFD would take more

duration. So we decided to analysis the casting parameters experimentally. In

experimental analysis, changing of input parameters is possible, through which

the main parameter causing crown shrinkage can be determined.

6.2 Experimental analysis of the casting parameters

6.2.1 Iteration No.1

The experiment was carried out to determine the inference for the crown

shrinkage in piston castings. The parameters influences the castings such as

water flow rate, water inlet temperature to the die, water outlet temperature

from the die, die body temperature, centre core temperature; crown temperature

was observed and recorded to find the reason for the crown shrinkage. The

castings are marked as a sample and followed for machining and inspection.

Annexure I is the first experiment done to determine the parameter

affecting crown part. Annexure I gives the various reading regarding the piston

manufacturing such as water inlet temperature, water outlet temperature from

the die, die body temperature, centre core temperature, crown temperature. But

the clear inference is not obtained from the experiment. The activities such as

air blown to die cavities and white and black coatings are observed during the

experiment.

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We found the particular causes .So we changed the variable input

parameters of castings such as solidification timing, sleeve size, pouring metal

temperature, centre core and die at three stages of temperature.

6.4 Iteration No. 2

As already explained, the first variable which is changed is die body and

centre core temperature of the die. The readings at a definite interval of time i.e.

at different stages. Then the pistons are cross sectioned perpendicular to the axis

and observed the shift of shrinkage towards the riser. Based on the shift of the

shrinkage, the inference for the crown shrinkage is obtained.

Table 6.1 Die at low temperature

S.No

CENTRE CORE

CAVITY 1ST CAVITY 2ND

Units ℃ ℃ 1 65 602 73 763 80 834 88 875 90 95

Based on the above table 6.1, it is clear that the center core temperature shouldnot be maintained at the range between 65 ℃ -100℃ . Let us discuss what would

happen if the centre core temperature maintained beyond this value.

Die at low temperatureTime: 11:10am

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Table 6.2 Centre core of die at Medium temperature

Table 6.3 Centre core of die at high temperature

Die at high temperatureTime: 12:40pm

Die at Medium temperatureTime: 11:40pm

S.No

CENTRE CORE

CAVITY 1ST CAVITY 2ND

Units

1 172 1782 177 2103 177 2134 208 2065 172 191

S. No

CENTRE CORE

1ST CAVITY 2ND CAVITY

Units ℃ ℃ 1 180 2102 220 2263 224 2284 231 2345 232 238

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6.5 Iteration No.3

6.5.1 Riser Sleeve

Riser sleeves are strong, low-density, tube sleeves of insulating refractory

material. They are specifically designed to promote efficient feeding of

aluminium castings. The excellent insulation value of keeping metal in the riser

liquid longer.

Benefits

Sleeve withstands rough handling and moulding

Increased casting yield

Reduced metal treatment costs

Reduced riser contact area

Reduced casting cleaning costs

Low smoke and fume

Sleeves are easily cut to special heights

There are three types of sleeve used such as 4, 4A, 4C based on the inner

diameter and taper angle of sleeve. The riser sleeves are made up of ceramic

material to withstand the heat (i.e. the riser sleeve maintains molten metal in

liquid state for long duration to feed the metal to casting).

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Fig.6.1 Riser Sleeve size 4

Fig.6.2 Riser sleeve size 4A

Fig.6.3 Riser sleeve size 4C

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Fig.6.4 Drafting of (a) Riser sleeve size 4, (b) Riser sleeve size 4A, (c) Riser

sleeve size 4C

An experiment made by using the riser sleeve size 4 as shown in fig.6.4 (a) and

then by using the riser sleeve size 4A as shown in fig.6.4 (b) and finally

experiment conducted by using the riser sleeve size 4c as shown in fig.6.4 (c)

From this experiments the shrinkage shift from the crown surface of the piston

to the riser.

The increase in sleeve size decreases the crown shrinkage in piston castings.

But it affects the yield of molten aluminium alloy. So, the standard sleeve size 4

is used to make the yield improvement in the molten aluminium alloy.

(a) b (c)

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Circular truncated cone

Volume: V=1/3 π (r 12+r 1r 2+ r 22)h

Table 6.4 Volume of molten metal consumed by riser sleeve

6.7 Experiment done by varying pouring metal temperature Next variable parameter is pouring metal temperature. Although the

pouring metal temperature does not plays predominant role because the pouring

metal temperature is already maintained at a range between 730°C -740°C. But

certain times this plays a role because there may be chance of temperature get

reduced below 730°C so it is account.

Fig.6.5 Piston casting cross section sample when pouring metaltemperature is about 740°C

Riser sleeve size spec. Volume of molten metal in sleevein mm 3

4 1,54,901

4A 2,01,146

4C 2,00,501

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Fig.6.6 Piston casting cross section sample when pouring metaltemperature is about 720°C

6.7.1 Result

Based on the fig.7.9, fig.7.10 it gets cleared that there is no probability of

crown shrinkage based on the pouring metal temperature. But if the pouring

metal temperature below 700°C to 650°C, then the crown shrinkage would

takes place. It is quite impossible in the company because there is a temperature

indicator which would indicate the temperature of pouring metal temperature by

dipping the thermocouple. So, parameter pouring metal temperature is neglected

in case of crown shrinkage.

6.8 Experiment done by varying solidification time

Casting Geometry, material and process determine the solidification time of

a casting. In simple terms the Chvorinov's rule establishes that under otherwise

identical conditions, the casting with large surface area and small volume willcool more rapidly than a casting with small surface area and a large volume.

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Fig.6.7 Piston casting cross section sample when solidification time90secs is given


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CHAPTER 7

RESULTS AND DISCUSSIONS

7.1 RESULTS

7.1.1. CENTRE CORE TEMPERATUREFrom iteration No.2, we found that there is an effect of centre core

temperature towards the shifting of shrinkage from the crown to riser. Based on

the three stages of the centre core temperature cross sectioned piston it may be

concluded that the centre core temperature should not be maintained at very low

temperature. It should be maintained at the optimum level of 200°C-288°C. But

it cannot be concluded that the crown shrinkage is only due to the centre core

temperature. So the experimental analysis was made for other variable

parameters such as sleeve size, pouring metal temperature, solidification timing.

Fig.7.1 Cross section of 2 nd cavity piston casting at low centre core temperaturewith gross crown shrinkage

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Fig 7.2 Cross section of 2 nd cavity piston casting at medium centre coretemperature

Fig.7.3 Cross section of 2 nd cavity piston casting at high centre coretemperature

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7.1.2 Riser Sleeve size

From iteration No.3, we found that the effect of increase in size of

riser sleeve would increases the shifting of shrinkage from crown to the riser of

the piston casting. So, the size of sleeve size is indirectly proportional to theoccurrence of crown shrinkage i.e. if the size (diameter) of sleeve is greater,

then the probability of occurring of crown shrinkage in the riser. Otherwise, the

increase in volume consumed reduces the chance of shrinkage formation in the

piston casting crown surface.

Fig.7.4 Piston casting Cross section with 4 riser sleeve size

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Fig.7.5 Piston casting Cross section with 4C riser sleeve size

7.1.3 POURING METAL TEMPERATURE

From the iteration No.4, it is clear that there is no effect of pouring metaltemperature towards the crown shrinkage.

Fig.7.6 Piston casting cross section sample when pouring metal temperature isabout 740°C and 720°C respectively.

7.1.4 SOLIDIFICATION TIMEFrom the iteration No.5, it is clear that there is no effect of Solidification time

towards the crown shrinkage by varying solidification time to 90 secs, 120 secs

and 150 secs.

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CHAPTER 8

CONCLUSION

Parametric study for the crown shrinkage in piston casting has been

studied and following were observed:

1. When the centre core temperature is low (65-175°C) the shrinkage is formed

at the crown of piston casting, if it is at medium temperature (175-195 °C)

then the shrinkage is shifted from the crown to riser.

2. When the volume of the riser sleeve increases the crown shrinkage moved

away.

3. There is no relation with respect to the pouring metal temperature.

4. There is no relation with respect to the solidification time.

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CHAPTER 9

SCOPE FOR THE FURTHER STUDY

To set the temperature sensor probe for indicating the centre core temperature ofthe die.

Other parameters such as Solidification time and pouring metal temperature can be widened to study the crown shrinkage formation.

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Documents

Project Report on Crown Shrinkage Final