STABILIZATION OF GREEN SAND SYSTEM FOR

MOULDING WITH CURRENT PRODUCT MIX

A dissertation submitted to National Institute of Technology, Jamshedpur in partial

fulfillment of the requirement for the award of the degree of

MASTER OF TECHNOLOGY

In

FOUNDRY TECHOLOGY

By

SHUBHAM SINGH RAJPUT

Registration No. 2015PGMMFT09

UNDER THE ESTEEMED GUIDANCE OF

Prof. Chandra Shekhar Choudhary

Associate Professor

Metallurgical & Materials

Engineering Department

National Institute of Technology

Jamshedpur

Mr. Madhu Bojja

AGM, Foundry Div.

TATA MOTORS

Jamshedpur

DEPARTMENT OF METALLURGICAL & MATERIALS ENGINEERING

NATIONAL INSTITUTE OF TECHNOLOGY

JAMSHEDPUR – 831014

JUNE 2017

Department of Metallurgical and Materials Engineering

NATIONAL INSTITUTE OF TECHNOLOGY

JAMSHEDPUR – 831014 INDIA

CERTIFICATE

This is to certify that thesis entitled “Stabilization of green sand system for moulding

with current product mix” being submitted by Shubham Singh Rajput to the National

Institute of Technology, Jamshedpur, for the award of the degree of MASTER OF

TECHNOLOGY in FOUNDRY TECHNOLOGY is a record of bonafide work carried

out under my supervision and guidance. I have examined the thesis and certify it worthy of

acceptance.

Mr. Madhu Bojja Shubham Singh Rajput

(AGM, Foundry Division, TATA MOTORS) 2015PGMMFT09

Dr. Ranjit Prasad Prof. Chandra Shekhar Choudhary

(HOD, MME) (Associate Professor, MME)

National Institute of Technology

Jamshedpur

BONAFIDE CERTIFICATE

This is to certify that the project entitled “STABILIZATION OF GREEN SAND

SYSTEM FOR MOULDING WITH CIRRENT PRODUCT MIX” is a bonafide record

of the work done by SHUBHAM SINGH RAJPUT (2015PGMMFT09) in partial

fulfillment of the requirements for the award of the Master degree in METALLURGICAL

AND MATERIALS ENGINEERING with specialization in “FOUNDRY

TECHNOLOGY” of the NATIONAL INSTITUTE OF TECHNOLOGY,

JAMSHEDPUR, during the year 2015-2017.

-------------------------------- ----------------------------

Prof. Chandra Shekhar Choudhary Dr. Ranjit Prasad

Signature of internal supervisor Signature of Head of Department

with Date and Official Seal

------------------------------------- ------------------------------

Signature of Internal Examiner Signature of External Examiner

iii

ACKNOWLEDGEMENT

The work presented in this master’s thesis is the result of collaboration between TATA

MOTORS, Jamshedpur and NATIONAL INSTITUTE OF TECHNOLOGY, Jamshedpur.

To start with, I am obliged to TATA MOTORS, Jamshedpur for considering me eligible

for internship in their prestigious organization. I would like to express my thankfulness to

Mr. Madhu Bojja for handing me over a project which enhanced my knowledge and

outlook manifold. His constant involvement coupled with his motivation led to the fine

completion of my project. I am also extremely indebted to Mr. B.C. Ghosh, who guided me

and carefully instructed me throughout the course of a whole year. Without his help, my

project would not have seen the light of day.

I humbly appreciate all other supporting staff at the Foundry Lab who paid heed to and

answered my queries related to the industry and made my experience in the plant a safe,

memorable and enjoyable one.

I express my deep sense of gratitude to, Mr. Chandra Shekhar Choudhary Associate

professor, Department of Metallurgical And Materials Engineering, NIT, Jamshedpur, for

their kind co-operation and support which I got during this work.

I express my sincere thanks to all my respected faculty members of Metallurgical And

Materials Engineering Department, National Institute of Technology, Jamshedpur

Last but not the least, I thank my parents and my fellow classmates who have always been

supportive and advised me to follow the right path and helped me make correct decisions

for my career.

Place: Jamshedpur Shubham Singh Rajput

iv

ABSTRACT

This project deals with the defects occurring in different product which are manufactured at

TATA motors and a practical approach to eliminate these defects, so that percentage of

rejection can be minimize and efficiency of plant can be increased. In TATA motors

different products like cylinder block CB6BT, cylinder head, gear box are manufactured in

foundry division, even in completely controlled process, defect in casting are observed and

hence casting process is also known as process of uncertainty which challenges explanation

about the cause of casting defects. Mainly cylinder block CB6BT has higher percentage of

rejection. There are mainly two defects in CB6BT due to which large numbers of castings

are rejected namely sand fusion & metal penetration which contribute nearly 40 – 50 % of

total defects. In 2015-16 rejection is 4.81% and during June 2017 to January 2017 rejection

percentage is higher (4.2% - 9.7%). Sand fusion and metal penetration are undesirable

since it results in reduction in the strength of the casting and bad finish of the casting

surface due to which the fettling department had to perform shot blasting for longer

duration to improve surface finish which is waste of time as well as money and also

product doesn’t meet desirable specification which are given by the customer. More than

hundred parameters are responsible for these defects and hence it is difficult to control

defect during casting. Therefore, these two defects and different properties of sand like

moisture content, active clay, etc. and the method to calculate them have been studied in

depth and grading of these defects have been done. We had approached in a well ordered

manner like detailed analysis of major defects & determine all causes, selection of root

cause, identify the solution and then implement them, if defects are eliminated then we had

made standard for that parameters, and if not, select the other cause. As we know only one

or two parameters are not responsible for defects, there are many, that’s why a balanced

between these parameters is necessary. Hence, we are able to minimize the defects and

achieve lower rejection percentage (5.22 %) than targeted which is 5.3 %.

v

TABLE OF CONTENTS

Page No.

Acknowledgement iii

Abstract iv

Table of Contents v

List of Figures ix

List of Table xi

CHAPTER- 1: INTRODUCTION 1

CHAPTER- 2: LITERATURE REVIEW

2.1 Basic of Casting

2.1.1 Casting

2.1.2 Pattern

2.1.3 Common Pattern Materials

2.1.4 Pattern Allowances

2.1.5 Core and Core Box

2.1.6 Mould

2.2 Moulding Sand

2.2.1 Silica Sand

2.2.2 Binder

2.2.3 Moisture

2.2.4 Additives

2.3 Properties of Moulding Sand

2.3.1 Refractoriness

2.3.2 Permeability

2.3.3 Cohesiveness

2.3.4 Green Strength

2.3.5 Dry Strength

2.3.6 Flowability or Plasticity

3

3

3

3

3

4

4

5

5

5

7

7

8

8

8

9

9

9

10

10

vi

2.3.7 Collapsibility

2.4 Schematic Sketch of Foundry Layout

2.5 Sand Casting Process

2.6 Defects In Casting

2.6.1 Defects Caused by Pattern and Moulding Box Equipment

2.6.2 Defects Due To Improper Moulding and Core

Material (Improper Sand Conditions)

2.6.3 Defects Caused By Moulding, Core Making, Gating, Etc.

2.6.4 Defects Occuring While Closing & Pouring Molds

2.6.5 Defects Caused By Molten Metal

2.6.6 Defects Occurring During Fettling

2.7 Foundry Division at Tata Motors

2.7.1 Foundry Lab

2.7.2 Pattern Shop

2.7.3 High Pressure Moulding Line

2.7.4 Dispatch Line

2.8 Rejection of Casting

2.8.1 Total Rejection for CB6BT

2.8.2 Total Rejection for CBCMVR

2.8.3 Total Rejection for 6BT Head Euro-III-4-Valve

2.8.4 Total Rejection for 6BT Head 2-Valve

2.8.5 Total Rejection for Gear Box 1150 Rear

2.9 Manufacturing Process of CB6BT

2.10 Literature Review

2.11 Sand Fusion

2.11.1 Causes

2.12 Metal Penetration

2.12.1 Causes

10

11

12

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14

16

19

20

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vii

CHAPTER- 3: EXPERIMENTAL INVESTIGATION

3.1 Methodology Used

3.2 Grading of Defects

3.2.1 Level 1

3.2.2 Level 2

3.2.3 Level 3

3.2.4 Level 4

3.2.5 Level 5

3.3 Data Collection

3.3.1 Data Collected at Shot Blasting Point

3.3.2 Data Collected at Foundry Lab

3.4 Tests Done at Foundry Lab

3.4.1 Preparation of standard test specimen

3.4.2 Test for Compactability

3.4.3 Test for Moisture Content

3.4.4 Test for Permeability

3.4.5 Green Strength (Compression, Tensile, Shear, Split)

3.4.6 Test for Shatter Index

3.4.7 Active Clay

3.4.8 Test for Volatile Matter 900 F(482 C)

3.4.9 Test for Loss on Ignition (LOI)

47

47

48

48

49

49

51

51

52

52

53

55

55

56

58

59

62

65

67

70

70

CHAPTER- 4: RESULT AND DISCUSSION

4.1 Sand Fusion and Metal Penetration with Different Parameters

4.2 Returned Sand Variation

4.3 Causes In Our Case and Steps Taken for Elimination of Defects

4.3.1 Extra Care is Taken In Handling of Core

4.4 Stabilization of Green Sand System

4.5 Prediction that Eliminate Defects

4.6 Comparison of Rejection

71

71

72

72

72

74

77

78

viii

CHAPTER- 5: CONCLUSION 80

REFERENCES 81

ix

List of Figure

FIG. NO. FIGURE CAPTIONS PAGE NO.

2.1 A Schematic Sketch Foundry Layout 11

2.2 A Schematic Diagram of Sand Casting

Process

12

2.3 Mismatch/Mould Shift 14

2.4 Casting with Flash Defect 15

2.5 Casting with Sand Drop Defect 17

2.6 Scab Defect 17

2.7 Casting with Metal Penetration 18

2.8 A schemati Hot Tear Defect 19

2.9 Porous Casting 22

2.10 A Schematic Diagram of Foundry Division

Product

23

2.11 A Schematic Diagram of Foundry Division 23

2.12 (a) Cope and (b) Drag Pattern for CB6BT

Block

26

2.13 EURO-II Core Assembly 26

2.14 Total Rejection Graph 28

2.15 Total Rejection For CB6BT 28

2.16 Total Rejection For CBCMVR 29

2.17 Total Rejection For 6BT Head Euro-III 4-

Valve

29

2.18 Total Rejection For 6BT Head 2-Valve 30

2.19 Total Rejection For GB1150 R 30

2.20 Manufacturing Process 31

2.21 Key Core CB6BT 32

2.22 Water Jacket With Base Core For CB6BT 32

2.23 Casting With Gating System 33

2.24 Shot Blasting 33

2.25 CB6BT with sand fusion 36

2.26 CB6BT with Metal Penetration Defect 40

x

3.1 A Schematic Procedure for Reducing

Casting Defects and Select Best Solution

47

3.2 Cope side of CB6BT with Level 1 49

3.3 Drag Side of CB6BT with Level 1 49

3.4 Cope side of CB6BT with Level 2 50

3.5 Drag side of CB6BT with Level 2 50

3.6 Cope side of CB6BT with Level 3 50

3.7 Drag side of CB6BT with Level 3 51

3.8 A schematic Cope Side of CB6BT with Level 4 51

3.9 Drag side of CB6BT with Level 4 52

3.10 Sand Rammer With Specimen Tube 56

3.11 (a) Tube Filler (b) Sand Rammer With

Compactabilty Tester

57

3.12 Permeabilty Meter 61

3.13 Motor Driven Universal Sand Strength

Machine (AFS)

63

3.14 Holders for Compression Strength Test 64

3.15 Holders for shear StrengthTest 64

3.16 Shatter Index Tester 66

3.17 Spot Test for End Point of Methylene Blue

Titration

68

3.18 Methylene Blue Active Clay Test Apparatus 69

4.1 Core dipped in wash for coating by hand 74

4.2 Man spraying wash on mould in moulding

line

74

4.3 Comparison of Total Rejection for all

product (a) Previous (b) Present

78

4.4 Comparison of Total Rejection for CB6BT

(a) previous (b) present

79

xi

List of Tables

Table No. Caption Page No.

3.1 Grading of Defects 48

3.2 Data Collected at Shot Blasting Point 53

3.3 Data Collected from Foundry Lab 54

4.1 Sand Fusion and Metal Penetration with

Different Parameters

71

4.2 Returned Sand Variation 72

4.3 Fundamental and Ideal Sand parameters of

prepared

75

4.4 (a) First Prediction (b) Second Prediction 76

4.5 (a) Third Prediction (b) Fourth Prediction 76

4.6 Prediction for A shift 76

4.7 Change in prediction for A shift 76

4.8 Values for A shift 77

4.9 Values for B shift 77

4.10 Values for C shift 77

5.1 Targeted and achieved value 80

xii

1

CHAPTER - 1.

INTRODUCTION

Castings play a very important role in manufacturing industry. Casting is mother process

major applications and uses of castings are in automobile industry, agricultural industry,

machinery etc. Casting is a 6000 year young process. Casting process is mentioned as

shilpashastra in several Sanskrit works and dhamatri (cupola), gharma aranmaya

(crucible), bhastri (blower) are the casting equipments mentioned in the Rig-Veda. The

major application of casting was in creating the God idols used for worshipping which can

be confirmed from the cast idols of Gods seen in our ancient temples. We hardly recognize

our daily close association with castings through these cast God idols we worship.

Cast Iron components are produced usually in large quantity by sand casting process and

give rise to thirty to forty different defects like sand and slag inclusion, blow holes, scab,

shrinkage etc. Sand fusion is a major defect and the mould material itself is responsible for

this defect. Component weakens because of sand inclusion and lack in properties like

soundness, high fluid pressure resistance, high bearing strength etc. and results in bad

surface finish. In a gray cast iron foundry, total rejection on an average is around 8 to 10

percent. Rejection due to sand fusion is about 30 to 40 percent of this amount that is 2 to 4

percent of the total rejection. This is a huge loss to the foundry considering wastage of the

large amount of heat energy in melting the material, remelting of scrap; handling and

inspection cost and has a demoralising effect on the employees. There are a large number

of parameters to be controlled while manufacturing the sand casting and are broadly

categorized as sand, moulding, melting and pouring parameters. Correct selection of

parameters responsible for sand fusion and metal penetration defect is very difficult task

and hence these defects are very difficult to control. In this work we had try to correct the

parameters and eliminate the defects.

2

The topic ‘stabilization of green sand system’ is being made the subject of this particular

study. As green sand system include sand and its properties, different additives and binder

and there amount which is been added. These are the main cause of defects that occur in

sand casting. The surface finish of a casting is dependent on the moulding process. The

mould materials as well as the moulding variables apart from other factors not related to

mould. The various factors are poor treatment of sand, use of different type of sand

particles used in moulding, accumulation of spend dead clay in the moulding sand, use of

badly compacted mould or cores due to sand moisture not thoroughly mixed or not

possessing sufficient flowability in clay bounded sand moulding, exceeding bench life of

sand moulds or sand cores, inadequate compaction of moulds or cores in normal moulding.

Pouring temperature of the molten metal to be poured into the mould. These are some of

the reasons for surface defects over castings.

In this particular session the problem of sand fusion and metal penetration is being

discussed in detail (how sand fusion and metal penetration occur and their causes). The

various possible factors for sand fusion, metal penetration and the practical ways to control

these factors are also discussed. Here, for controlling these defects there grading has been

done and data is collected. Further, for that particular day for which rejection/defects are

more all the properties, amount of additives and carbonaceous material for that casting are

compared with the properties and amount of additives, carbonaceous materials for casting

which have lower percentage of defects and then that particular parameter which is

different is varied so that defects are minimized. Various instruments/machines have been

used for calculating different properties of sand (moisture, active clay, permeability, GCS,

etc.). This particular study was conducted in TATA MOTORS, Jamshedpur.

3

CHAPTER - 2.

LITERATURE REVIEW

2.1 Basics of Casting

2.1.1 Casting

Casting process is one of the earliest metal shaping techniques known to human being. It

means pouring molten metal into a refractory mold cavity and allows it to solidify. The

solidified object is taken out from the mold either by breaking or taking the mold apart.

The solidified object is called casting and the technique followed in method is known as

casting process.

2.1.2 Pattern

A pattern is a model or the replica of the object (to be casted) with some allowances and/or

with core prints. It is embedded in molding sand and suitable ramming of molding sand

around the pattern is made. The pattern is then withdrawn for generating cavity (known as

mold) in molding sand. Thus it is a mould forming tool. When molten metal is poured into

the cavity, molten metal solidifies and produces a casting (product). A pattern prepares a

mold cavity for the purpose of making a casting. It may also possess projections known as

core prints for producing extra recess in the mould for placement of core to produce

hollowness in casting. The first step in casting is pattern making. The pattern is a made of

suitable material and is used for making cavity called mould in molding sand or other

suitable mould materials.

2.1.3 Common Pattern Materials

The common materials used for making patterns are wood, metal, plastic, plaster, wax or

mercury. The some important pattern materials are discussed as under.

4

2.1.4 Pattern Allowances

Pattern may be made from wood or metal and its color may not be same as that of the

casting. The material of the pattern is not necessarily same as that of the casting. Pattern

carries an additional allowance to compensate for metal shrinkage. It carries additional

allowance for machining. It carries the necessary draft to enable its easy removal from the

sand mass. It carries distortions allowance also. Due to distortion allowance, the shape of

casting is opposite to pattern. Pattern may carry additional projections, called core prints to

produce seats or extra recess in mold for setting or adjustment or location for cores in mold

cavity. It may be in pieces (more than one piece) whereas casting is in one piece. Sharp

changes are not provided on the patterns. These are provided on the casting with the help of

machining. Surface finish may not be same as that of casting. The size of a pattern is never

kept the same as that of the desired casting because of the fact that during cooling the

casting is subjected to various effects and hence to compensate for these effects,

corresponding allowances are given in the pattern. These various allowances given to

pattern can be enumerated as, allowance for shrinkage, allowance for machining, allowance

for draft, allowance for rapping or shake, allowance for distortion.

2.1.5 Core and Core Box

Cores are compact mass of core sand that when placed in mould cavity at required location

with proper alignment does not allow the molten metal to occupy space for solidification in

that portion and hence help to produce hollowness in the casting. The environment in

which the core is placed is much different from that of the mold. In fact the core has to

withstand the severe action of hot metal which completely surrounds it. Cores are classified

according to shape and position in the mold. There are various types of cores such as

horizontal core, vertical core, and balanced core.

Any kind of hollowness in form of holes and recesses in castings is obtained by the use of

cores. Cores are made by means of core boxes comprising of either single or in two parts.

Core boxes are generally made of wood or metal and are of several types. The main types

of core box are half core box, dump core box, split core box, etc.

5

2.1.6 Mould

A suitable and workable material possessing high refractoriness in nature can be used for

mould making. Thus, the mold making material can be metallic or non-metallic. For

metallic category, the common materials are cast iron, mild steel and alloy steels. In the

non-metallic group molding sands, plaster of paris, graphite, silicon carbide and ceramics

are included. But, out of all, the molding sand is the most common utilized non-metallic

molding material because of its certain inherent properties namely refractoriness, chemical

and thermal stability at higher temperature, high permeability and workability along with

good strength. Moreover, it is also highly cheap and easily available.

2.2 Moulding Sand

The general sources of receiving molding sands are the beds of sea, rivers, lakes, granular

elements of rocks, and deserts. Molding sands may be of two types namely natural or

synthetic. Natural molding sands contain sufficient binder. Whereas synthetic molding

sands are prepared artificially using basic sand molding constituents (silica sand in 88-

92%, binder 6-12%, water or moisture content 3-6%) and other additives in proper

proportion by weight with perfect mixing and mulling in suitable equipments.

The main constituents of molding sand involve silica sand, binder, moisture content and

additives.

2.2.1 Silica Sand

Silica sand in form of granular quarts is the main constituent of molding sand having

enough refractoriness which can impart strength, stability and permeability to molding and

core sand. But along with silica small amounts of iron oxide, alumina, lime stone,

magnesia, soda and potash are present as impurities. The silica sand can be specified

6

according to the size (small, medium and large silica sand grain) and the shape (angular,

sub-angular and rounded).

Effect of grain shape and size of silica sand

The shape and size of sand grains has a significant effect on the different properties of

molding and core sands. It determines the possibility of its application in various types of

foundry practice. The shape of foundry sand grains varies from round to angular. Some

sands consist almost entirely of grains of one shape, whereas others have a mixture of

various shapes. According to shape, foundry sands are classified as rounded, sub-angular,

angular and compound. Use of angular grains (obtained during crushing of rocks hard sand

stones) is avoided as these grains have a large surface area. However, a higher percentage

of binder is required to bring in the desired strength in the molding sand and core sand. For

good molding purposes, a smooth surfaced sand grains are preferred. Rounded shape silica

sand grain sands are best suited for making permeable molding sand. These grains

contribute to higher bond strength in comparison to angular grain. However, rounded silica

sand grains sands have higher thermal expandability and compactability than angular silica

grain sands. This is connected with the fact that the silica sand with rounded grains having

the greatest degree of close packing(contact surfaces between the individual grains) of

particles while sand with angular grains the worst. The green strength increases as the

grains become more rounded. As already mentioned above, the compactability increases

with rounded grains. The permeability or porosity property of molding sand and core sand

therefore, should increase with rounded grains and decrease with angular grains. Thus the

round silica sand grain size greatly influences the properties of molding sand. The

characteristics of sub-angular sand grains lie in between the characteristics of sand grains

of angular and rounded kind. Compound grains are cemented together such that they fail to

get separated when screened through a sieve. They may consist of round, sub-angular, or

angular sub-angular sand grains. Compound grains require higher amounts of binder and

moisture content also. These grains are least desirable in sand mixtures because they have a

tendency to disintegrate at high temperatures. Moreover the compound grains are cemented

together and they fail to separate when screened.

7

The grain size distribution has a significant effect on permeability. Silica sand containing

finer and a wide range of particle sizes will have low permeability as compared to those

containing grains of average fineness but of the same size i.e. narrow distribution. The

compactability is expressed by the green density obtained by three ram strokes. Finer the

sand, the lower is the compactability and vice versa. This results from the fact that the

specific surface increases as the grain size decreases. As a result, the number of points of

contact per unit of volume increases and this in turn raises the resistance to compacting.

The green strength has a certain tendency, admittedly not very pronounced, towards a

maximum with a grain size which corresponds approximately to the medium grain size. As

the silica sand grains become finer, the film of bentonite becomes thinner, although the

percentage of bentonite remains the same. Due to reducing the thickness of binder film, the

green strength is reduced. With very coarse grains, however, the number of grains and,

therefore, the number of points of contact per unit of volume decreases so sharply that the

green strength is again reduced. The sands with grains equal but coarser in size have

greater void space and have, therefore greater permeability than the finer silica sands. This

is more pronounced if sand grains are equal in size.

2.2.2 Binder

In general, the binders can be either inorganic or organic substance. In foundry shop, the

clay acts as binder which may be kaolonite, ball clay, fire clay, limonite, fuller’s earth and

bentonite. Binders included in the organic group are dextrin, molasses, cereal binders,

linseed oil and resins like phenol formaldehyde, urea formaldehyde etc. Organic binders

are mostly used for core making. Among all the above binders, the bentonite variety of clay

is the most common. However, this clay alone cannot develop bonds among sand grins

without the presence of moisture in molding sand and core sand.

2.2.3 Moisture

The amount of moisture content in the molding sand varies generally between 2 to 8

percent. This amount is added to the mixture of clay and silica sand for developing bonds.

8

This is the amount of water required to fill the pores between the particles of clay without

separating them. This amount of water is held rigidly by the clay and is mainly responsible

for developing the strength in the sand. The effect of clay and water decreases permeability

with increasing clay and moisture content. The green compressive strength first increases

with the increase in clay content, but after a certain value, it starts decreasing. For

increasing the molding sand characteristics some other additional materials besides basic

constituents are added which are known as additives.

2.2.4 Additives

Additives are the materials generally added to the molding and core sand mixture to

develop some special property in the sand. This reducing atmosphere results in any oxygen

in the poles becoming chemically bound so that it cannot oxidize the metal. It is usually

added in the molding sands for making molds for production of grey iron and malleable

cast iron castings. Sea coal is the fine powdered bituminous coal which positions its place

among the pores of the silica sand grains in molding sand and core sand. When heated, it

changes to coke which fills the pores and is unaffected by water: Because to this, the sand

grains become restricted and cannot move into a dense packing pattern. Thus, sea coal

reduces the mould wall movement and the permeability in mold and core sand and hence

makes the mold and core surface clean and smooth. Additives are added for gas cushion,

reduced atmosphere and improve collapsibility.

2.3 Properties of Moulding Sand

2.3.1 Refractoriness

Refractoriness is defined as the ability of molding sand to withstand high temperatures

without breaking down or fusing thus facilitating to get sound casting. It is a highly

important characteristic of molding sands. Refractoriness can only be increased to a limited

extent. Molding sand with poor refractoriness may burn on to the casting surface and no

smooth casting surface can be obtained. The degree of refractoriness depends on the SiO2

i.e. quartz content, and the shape and grain size of the particle. The higher the SiO2 content

9

and the rougher the grain volumetric composition the higher is the refractoriness of the

molding sand and core sand. Refractoriness is measured by the sinter point of the sand

rather than its melting point.

2.3.2 Permeability

It is also termed as porosity of the molding sand in order to allow the escape of any air,

gases or moisture present or generated in the mould when the molten metal is poured into

it. All these gaseous generated during pouring and solidification process must escape

otherwise the casting becomes defective. Permeability is a function of grain size, grain

shape, and moisture and clay contents in the molding sand. The extent of ramming of the

sand directly affects the permeability of the mould. Permeability of mold can be further

increased by venting using vent rods.

2.3.3 Cohesiveness

It is property of molding sand by virtue which the sand grain particles interact and attract

each other within the molding sand. Thus, the binding capability of the molding sand gets

enhanced to increase the green, dry and hot strength property of molding and core sand.

2.3.4 Green Strength

The green sand after water has been mixed into it, must have sufficient strength and

toughness to permit the making and handling of the mould. For this, the sand grains must

be adhesive, i.e they must be capable of attaching themselves to another body. Therefore,

sand grains having high adhesiveness will cling to the sides of the molding box. Also, the

sand grains must have the property known as cohesiveness i.e. ability of the sand grains to

stick to one another. By virtue of this property, the pattern can be taken out from the mould

without breaking and also the erosion of mould wall surfaces does not occur during the

flow of molten metal. The green strength also depends upon the grain shape and size,

amount and type of clay and the moisture content.

10

2.3.5 Dry Strength

As soon as the molten metal is poured into the mould, the moisture in the sand layer

adjacent to the hot metal gets evaporated and this dry sand layer must have sufficient

strength to its shape in order to avoid erosion of mould wall during the flow of molten

metal. The dry strength also prevents the enlargement of mould cavity cause by the

metallostatic pressure of the liquid metal.

2.3.6 Flowability or Plasticity

It is the ability of the sand to get compacted and behave like a fluid. It will flow uniformly

to all portions of pattern when rammed and distribute the ramming pressure evenly all

around in all directions. Generally sand particles resist moving around corners or

projections. In general, flowability increases with decrease in green strength, an, decrease

in grain size. The flowability also varies with moisture and clay content.

2.3.7 Collapsibility

After the molten metal in the mould gets solidified, the sand mould must be collapsible so

that free contraction of the metal occurs and this would naturally avoid the tearing or

cracking of the contracting metal. In absence of this property the contraction of the metal is

hindered by the mold and thus results in tears and cracks in the casting. This property is

highly desired in cores.

11

2.4 Schematic Sketch of Foundry Layout

Fig. 2.1 A Schematic Sketch Foundry Layout

12

2.5 Sand Casting Process

Pattern with mould box Spray/Wash/Facing Sand Moulding Sand

Cope & Drag Gatting Elements

Extra Sand Removed Sprue & Riser Pin Ramming

Molten Metal Poured & Casting

Fig. 2.2 A Schematic Diagram of Sand Casting Process

13

2.6 Defects In Casting

Under normal conditions, like all metallurgical products, casting also contain certain

imperfection which contribute to a normal quality variation. Such imperfection are taken as

defects or flaws when they affect the appearance or the satisfactory functioning of the

casting and the casting in turn do not come up to the quality and inspection standards being

applied. Defective casting offers an ever-present problem to the foundry industry,

Defective casting account for the normally higher losses incurred by the foundry. Casting

defects are usually not incidents; they occur because some steps in the manufacturing cycle

does not get properly controlled and somewhere goes wrong. A defect may be te result of a

single clearly defined cause or a combination of factors, in which box necessary preventive

measured are more obscure. Close control and standardization of all aspects of

manufacturing techniques offers the best defense against the occurrence of defects in

castings.

Classifications of Defects

Logically classification of casting defects presents great difficulties because of the wide

range of contributing cause; however a rough classification may be made by grouping the

defects under certain broad type of origin such as:

Defects caused by pattern and moulding box equipments.

Defects due to improper molding and core making material.

Defects due to improper sand mixing and distribution.

Defects caused by molding, core making and gating, etc.

Defects due to improper mold drying and core baking.

Defects occurring while closing and pouring the molds.

Defects caused by molten metal.

14

2.6.1 Defects Caused by Pattern and Moulding Box Equipment

Mismatch or Mould Shift

It produce a casting which does not match at the parting line. Fig. 2.3 Shows mould

shift.

There is mismatching of top and bottom parts of the casting at the mould joint

Causes

Worn or loose dowels in the pattern made in halves.

Faulty resting of top and bottom halves of pattern mounted on plates.

Fig. 2.3 Mismatch/Mould Shift

Fin, Flash and Strain

Fins, flash and strain usually occur at the parting line and result in excess metal

which has to be ground off. Flashes or fins commonly appears along the mould

joint at the place where the mould halves do not fit together properly because of

much wear of the flask halves or improper fastening of the cope to the drag.

Straining or movement of the mould makes a casting appreciably thicker than the

pattern. Fig. 2.4 shows flash defect.

15

Causes

Bottom boards are too flexible.

Pattern plates are not sufficiently rigid to keep straight during ramming.

Pattern having insufficient taper and thus requiring excessive rapping for their

withdrwal from sand results in fins at the joints.

Top part box inadequately weighted, that permit (cope) to lift slightly, when

poured, thereby causing flash along mould joint.

Fig. 2.4 Casting with Flash Defect

Crush

It is the displacement of sand while closing a mould, thereby deforming mould

surface.

A crush shows itself as an irregular sandy depression in the casting.

Causes

Excessive weighting of the green sand mould (cope portion).

Core print too small for the core or vice-versa.

Careless assembly of moulding box and cores.

16

2.6.2 Defects Due To Improper Moulding and Core Material (Improper

Sand Conditions)

Blowholes

Blowholes are smooth, round holes. If visible on the surface of a casting are called

open blows. Whereas those occurring below the surface of casting and not visible

from outside are termed as blowholes. They may occur in cluster or there may be

one large smooth depression, these are entrapped bubblers of gas with smooth

walls. Entrapment of air resulting due to pouring of liquid metal takes the form of

rounded contours or spherical cavities. Surface blows or inter granular cavities

appear in cope of the mould.

Causes

Excess moisture in the moulding sand.

Low permeability and excessive fine grain sands.

Rusted and damp chills, chaplets, core neither properly baked nor adequately

vented.

Extra hard rammed sand.

Drop

A drop occurs when cope surface cracks and break, thus the pieces of small sand

fall into the molten metal. Fig. 2.5 shows casting with sand drop defect.

Causes

Low green strength (owing to less, mulling time, moisture or clay content).

Low mold hardness (soft ramming).

17

Fig. 2.5 Casting with Sand Drop Defect

Scab

It occurs when a portion of the face of a mold lifts and metal flows underneath in

thin layer. In other words, liquid metal penetrates behind the surface layer of sand.

Fig. 2.6 showing scab defect.

Causes

Too fine sand, low permeability, high moisture content.

Uneven mold ramming, less fluidity producing local heating.

Fig. 2.6 Scab Defect

18

Pin-holes

Pinholes result when the hydrogen present in liquid metal evolves due to less

solubility during solidification resulting in triangular appearances, prevalent mostly

in thinner castings which are revealed after machining.

Causes

High moisture content, sand containing gas generating ingredients.

Metal mould reaction.

Metal Penetration and Rough Surface

Metal penetration is a condition in which the metal or metallic oxides have filled

the voids between the sand grain without displacing them. In general terms, true

penetration implies an openness of the mould surface. Fig. 2.7 shows metal

penetration.

Causes

High permeability, large grain size.

Low dry strength of sand, soft ramming.

Fig. 2.7 Casting with Metal Penetration

19

Hot Tears

Immediately after solidification, metals having low strengths; if at this stage, solid

shrinkage of the casting develops sufficiently high stresses, the metal fails with a

resulting hot tears. Fig. 2.8 shows casting having hot tear.

Fig. 2.8 Hot Tear Defect

Causes

Very hard ramming and therefore excessive mold hardness.

Insufficient collapsibility of core or of portion of mold.

Too much shrinkage of metal while solidification.

Faulty design causing some portion of casting to be restrained while cooling.

High sulphur content, too low pouring temperature.

2.6.3 Defects Caused By Moulding, Core Making, Gating, Etc.

Hot Tears, Shifts, Fin and Flash, Crush which are discussed above

Cold Laps (shuts) Misrun

If the molten metal is too cold or casting section is too thin (section sensitivity),

entire mould cavity may not be filled during pouring before the metal starts

solidifying and the result is misrun.

20

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

two steams of metals which are too cold, physically meet in the mould cavity but do

not fuse together, they develop cold shut defect.

Causes

Too cold molten metal, too thin casting.

Too small gates, less fluidity.

2.6.4 Defects Occuring While Closing and Pouring the Molds

Mismatch, Misrun, Cold shuts, Crush are dicussed above.

Inclusion

Any separate undesirable foreign material present in the metal of a casting is known

as inclusion. An inclusion may be:

Oxides, slag, dirt, etc., which enter the mould cavity along metal during pouring.

Such inclusion should be skimmed off before poring metal into the mold cavity.

Sand cracked and broken from gating system, mold cavity, core. Sand sinks in

molten light metal and causes sand cavity in the drag whereas in heavier metal sand

either floats to the cope surface of the casting or becomes entrapped within the

casting itself.

2.6.5 Defects Caused By Molten Metal

Misrun, Cold shuts, Hot Tears are discussed above

Cut and Wash

Molten metal as it flows over the mould and core surface, erodes the same and

results in cut and wash.

21

The place from where the sand has been cut or washed is occupied by molten metal

and thus an excess metal appears on the casting surface in the form of rough spots,

these spots are scab.

Causes

Soft ramming, insufficient draft on pattern.

Insufficient bonded or overbaked cores, improper gating system.

Fusion

Sand may fuse and stick to the casting surface with the result rough glossy

appearance.

Causes

Lack of refractoriness of sand, too high molten metal temperature.

Faulty gating system.

Gas porosity, Gas holes

Gas porosity differs from blowholes which results due to the moulding sand having

low permeability, excessive moisture or having been rammed too hard.

Gas porosity is caused by the gases absorbed by the molten metal. The main gases

dissolved by practically all metal are, oxygen, nitrogen, hydrogen. Hydrogen is

responsible for gas porosity. Fig. 2.9 show porous casting.

As molten metal solidifies, many small voids distributed quite uniformly

throughout the metal are found and it is known as pin hole porosity.

Causes

Hydrogen or sulphur dioxide dissolved in molten metal.

Excessive high pouring temperature, low permeability

22

Fig. 2.9 Porous Casting

Swell

A swell is an enlargement of the mould cavity (hence that of the casting) due to

molten metal pressure on the wall and the sides.

Causes

Soft ramming, low mould strength.

Mould being not adequately supported.

2.6.6 Defects Occurring During Fettling

Sand and scale not properly removed from casting surface to be machined.

Sand not properly removed from cavity where oil is to be circulated.

Crack caused in brittle casting by too heavy grinding.

Chisel mark left on the castings.

2.7 Foundry Division at Tata Motors

Foundry division is the heart of Tata Motors as most of the products are manufactured here

only, and after that their respective assembly is done. Different products like cylinder block

(CB6BT) which is mainly consumed by Cummins, cylinder head, Gear Box are

manufactured under foundry division as shown in fig. 2.10.

23

Foundry Division Products

Cylinder Block Cylinder Heads Gear Box

CB6BT CBCMVR 497 CMVR 6BT CRDi Rear Front Intermediate

EURO-I EURO-II EURO-III EURO-I EURO-II

Fig. 2.10 A Schematic Diagram of Foundry Division Product

Foundry division have mainly 4 section namely foundry lab, pattern shop, high pressure

moulding line, dispatch line as shown in fig. 2.11.

Foundry Division

Foundry Lab Pattern Shop HPML Dispatch Line

Lab 1 Lab 2 CAD/CAM Quality Pattern Sec.

Scrap & Furnace HPML Core Mfg. & Assembly Fettling Shot Blasting Inspection

Fig. 2.11 A Schematic Diagram of Foundry Division

24

2.7.1 Foundry Lab

In lab there are different instrument/machine which are used for measuring different

properties of sand. This is most vital process as one can identify the causes which are

responsible for any defects, or if there is any variation in properties of sand which can

affect the casting can be determined here, like if moisture content will vary we can check

and quantify that change, in lab only. We can check the consistency of the prepared green

sand and determine if the green sand has the physical and chemical properties to produce

good castings. Poor quality sand can lead to a number of casting‐related defects. To ensure

the properties necessary to avoid casting defects and produce the quality we desire

consistently throughout the entire green sand system. Foundry lab test green sand daily for:

Compactibilty

Moisture

Specimen weight

Permeability

Green compression strength.

Dry compression strength

Methylene blue clay content

Total combustibles (LOI)

Volatiles at 900F (482C)

Shatter Index

Weight Tensile Strength

Different instruments like three ram machine, machine which is used for calculating green

compression strength and shear strength, for calculating shatter index, etc., are available in

the lab. Scrap which is used for making molten metal are also tested in lab, because for

every product there is particular range of different constituent in that scrap, example

percentage of phosphorus should not be more than 0.15% in scrap.

25

2.7.2 Pattern Shop

In pattern shop, patterns for different casting are available. If, any alternation or changes

are needed in pattern are done in pattern shop. Mainly cast iron pattern are used in Tata

Motors. Fig shows cope and drag for CB6BT. Apart from pattern shop under this shed we

have cad/cam section which plays an important role in providing different drawings of

casting with different views and necessary locations of casting with the help of which

inspection can be done easily. Inspection and quality control section view all the casting, if

there is any defect which cannot be tolerated casting will be rejected, and hence they have

the data for rejected casting.

2.7.3 High Pressure Moulding Line

All the casting process is done under this shed. HPML reduces man work and their

involvement and hence increases the efficiency of plant. Scrap is collected over here and

with the help of furnace it is converted into molten metal. On the other side in HPML sand,

binder (bentonite), additives (lustron) are mixed with water in correct proportion with the

help of mixture, and correct amount of these are maintained with the help of computerized

system. Now, pattern (Fig. 2.12 (a) Cope and (b) Drag Pattern for CB6BT Block) for

respective casting is loaded and with the help of belt drive mixture (sand, bentonite and

lustron) is send for filling the mould box which is fitted with the respective pattern and

ramming is done, both cope and drag are loaded in a plate and this plate do 180 degree

rotation. If cope is been fitted with the mould box sand filling, removal of extra sand,

ramming will be done simultaneously plate will do 180 degree rotation and drag will be

filled by sand and ramming will be done and cope will move forward, where wash is apply

so that molten metal will not penetrate into the mould or to improve collapsibility. At this

place each and every casting is given specific number and date. Then vents are provided

and core, chaplet, etc., are assembled in assembly line, then cope and drag will be fitted

together and finally molten metal is poured. Now this will be collected at the dispatch line

at fettling point. On the other side in HPML core are like inlet valve, outlet valve, inner

water jacket, outer water jacket, base core, key core, etc., are

26

(a) Drag

(b) Cope

Fig. 2.12 (a) Cope and (b) Drag Pattern for CB6BT Block

manufactured. Here, for manufacturing of core, sand is mixed with mill scale, hexamine,

resin. There percentage will vary from core to core, basically core box method is used.

Fig. 2.13 EURO-II Core Assembly

27

Base core are manufactured by cold box process. After this core are dipped in wash and

baked in furnace. In HPML there are different section where assembly of respective core is

done like for EURO-II head, base core, inlet, exhaust, water jacket are assembled. EURO-

II core assembly is shown in fig. 2.13. There is one section where inspection of heads are

done with the help of boroscope.

2.7.4 Dispatch Line

At dispatch line, first section is fettling section where casting arrives after pouring of

molten metal and solidification is done. Here, casting have gating system like sprue, riser

fuse with it, which has to be removed, this is done in fettling section and some casting

specially CB6BT castings are sent out for fettling. Now, another section is shot blasting

section, here castings in which sand firmly adhere to the casting is treated, sometimes on

consumer demands. Mainly blocks and sometimes heads are shot blasted (3-4 mm diameter

hardened steel balls are bombarded on the casting with the help of pressure). Further,

castings are inspected with the help of boroscope, and if required grinding is done. After

this castings are placed for inspection and if casting is passed it is ready to dispatch.

2.8 Rejection of Casting

In every foundry the main aim is to minimize the rejection of casting, indirectly to reduce

the defects. Rejection data of Tata Motors is given below. Below graph (fig.2.14) tells the

rejection of casting from 2010 to 2016 yearly and for 2016 month wise. For 2016 rejection

percentage is targeted for less than or equal to 3.5 which is shown by red color in graph.

But except for the month of may and june rejection percentage is higher than targeted

percentage and also for january 2017. This means that defects in the casting are more

during these month.

28

Fig. 2.14 Total Rejection Graph

2.8.1 Total Rejection For CB6BT

Fig. 2.15 Total Rejection For CB6BT

Fig. 2.15 shows total rejection for CB6BT. It can be observe from graph that except for the

month of may and june rejection percentage are higher than targeted . We can observe that

in CB6BT rejection is mainly due to defects namely sand fusion and metal penetration.

2.8.2 Total Rejection For CBCMVR

Fig. 2.16 shows total rejection graph for CBCMVR. We can observe that except for the

month of april rejection percentage is lower than targeted percentage

29

Fig. 2.16 Total Rejection For CBCMVR

. 2.8.3 Total Rejection For 6BT Head EURO-III 4-Valve

Fig. 2.17 Total Rejection For 6BT Head Euro-III 4-Valve

Fig. 2.17 shows total rejection for 6BT Head Euro-III 4 valve. We can observe from graph

that except for the month of june, july, september, october rejection percentage are higher

than targeted rejection percentage.

2.8.4 Total Rejection For 6BT Head 2-Valve

Fig. 2.18 shows graph of rejection for 6BT Head 2 valve. We can observe from graph that

for the month of april, july, august, november rejection percentage are higher than targeted

percentage. There is problem of jamming in heads due to which rejection percentage is

higher.

30

Fig. 2.18 Total Rejection For 6BT Head 2-Valve

2.8.5 Total Rejection For Gear Box 1150 Rear

Fig. 2.19 Total Rejection For GB1150 R

Fig. 2.19 shows rejection for GB 1150 R. We can observe from graph that for all months

rejection percentage are lower than targeted rejection percentage.

From above we can conclude that if we can minimize the jamming in heads and defects

namely sand fusion and metal penetration mainly in CB6BT we can minimize the rejection

percentage. This is the aim of my thesis to reduce sand fusion and metal penetration.

31

For eliminating sand fusion and metal penetration in casting, mainly in CB6BT we should

know its process of manufacturing from scrap to casting because sometimes defects may

occur due to wrong process or wrong habit (it include handling of core, applying wash, in

assembly line, etc.).

2.9 Manufacturing Process of CB6BT

Fig. 2.20 shows whole manufacturing process from scrap to casting for all the products.

But we had discus only CB6BT.

Fig. 2.20 Manufacturing Process

Firstly, raw material like metal for making molten metal, sand, bentonite, lustron for

making mould and mill scale, resin, hexamine for making core are purchased from vendor

32

and are placed at their respective place. Sample is collected and tested in lab. Now, scrap is

melted with the help of furnace and molten metal is ready for pouring at HPML.

On the other side, sand, bentonite, lustron are mixed in correct proportion with water with

the help of mulling machine, and sample of this mixture also is collected by lab person and

test for different properties like moisture, permeability, etc,. On the other section core for

CB6BT namely key core (fig. 2.21), base core, water jacket (fig. 2.22) are made then

pattern (fig. 2.12), core, mould are assembled at moulding assembly point, then molten

metal is poured, after solidification casting is taken out in which sprue, riser are fused (fig.

2.23) which are removed at the fettling point, then for good surface finish shot blasting (fig.

2.24)is done and grinding is also done if necessary, after inspection it is ready to dispatch.

Fig. 2.21 Key Core CB6BT

Fig. 2.22 Water Jacket With Base Core For CB6BT

33

But, during inspection it is found that rejection of a block is due to metal penetration and

sand fusion.

Fig. 2.23 Casting With Gating System

Fig. 2.24 Shot Blasting

Defects In Block

In block defects like blow hole, crush, scab, sand fusion, metal penetration are found. But,

percentage of sand fusion and metal penetration are higher.

2.10 Literature Review

We cannot eliminate defects theoretically as in practical we have to eliminate defects with

more constraints like we cannot change the whole process, we cannot take steps which are

34

expensive (we can use zircon sand instead of green sand for elimination of defects but it is

costly). Though this project is completely practical, some of research papers are discuss

below.

Meredith (1996) [4] explained the effect of variables and its control to produce defect free

castings. According to him, amount of ramming, jolting, squeezing, type of sand etc.

decides the compaction density of green sand, which is checked and controlled in terms of

mould hardness. He also observed that the strength of resin bonded sand is much more than

green sand thus will help in reduction of sand inclusion. According to Kumruoglu et al.

(2008), [5] moulding and melting parameters like amount of sand ramming, specifications

of the mould wall, type and quality of sand used, rate of metal pouring and its temperature

etc. important for getting good quality sand casting.

Deshmukh et al. (2009) [8] have discussed the problems like sand cut, wash, erosion etc.

which give rise to sand inclusion defect. The paper highlighted possible causes like

insufficient cohesive strength of sand, poor gating, defective drying of mould and core,

improper casting and mould design, poor green strength, improper alignment of mould

halves, careless pattern removal, failure to use nails and gaggers, poor condition of pattern,

varying strengths developed in different layers of mould. The precautions like gating

system redesign and relocation, mould cavity reinforcing, timely mould repair and due care

while moulding, provision of more draft, provision of aligning devices, correct pattern

stripping, use of nails and gaggers etc. should be taken to avoid the sand inclusion defect.

According to Brieger (2011), [6] sand inclusion is a result of breakage of core, feeder etc.

because of high compressive force, during complex shaped casting production. Woldert

(2011) [7] stated that the proper quality of moulding sand can be obtained by maintaining

the specific values of sand parameters like loss on ignition(LOI), sand temperature, residual

dust content etc. He related the quality of casting surface and binder consumption with

sand quality. Use of Furan resin sand moulds is suggested for getting high sand strength to

large size casting moulds which will avoid sand inclusion defect.

35

Studies have been performed to understand both qualitatively and quantitatively the

factors that cause burn-on and metal penetration. Svoboda [9] showed that burn-on

and penetration are caused by a combination of three modes. The first such mode is

liquid-state penetration of metal into the inter-granular voids of the mold. Liquid-state

penetration is governed by capillary forces and head height pressure: when the head

height pressure is greater than the surface tension resistive force, metal can penetrate into

the mold. The second mode of penetration is vapor-state penetration into the mold. The

metallic vapor penetrates the mold and subsequently condenses into liquid and then

solidifies. The solidified metal changes the surface tension properties, thereby aiding in

further liquid-state penetration described as the primary mode of penetration. The third

mode found by Svoboda is chemical reaction penetration, where complex oxides are

formed by the alloying elements, mold washes, and sand. Svoboda suggested methods of

reducing void sizes and changing chemistries of washes and sands to reduce the instances

of penetration and burn-on defects.

2.11 Sand Fusion

Fusion is a surface defect having a rough glossy appearance related to penetration of the

metal oxides acting as a flux on the sand. Many metal oxides, including iron oxides, have

an affinity for sand and react with it at relatively low temperature. When the oxides is

absorbed by the sand, the resulting fusion may merely create a hard cake or fused layer

which peel away from the casting leaving a smooth finish. If, however, the oxides remain

in contact with and are part of the metal casting surface, the fusion of oxides and silica

result in the rough glassy finish which require additional cleaning. It should be noted that

if the fused oxide-silica system continues and penetrate into the sand surface it is termed as

metal penetration. Fig. 2.25 shows CB6BT with sand fusion.

36

2.11.1 Causes

Casting and Pattern Design

Since fusion is a high temperature chemical reaction, the speed of reaction increases

as temperature increases. A design which create an unusually high temperature in

any part of core or mould will produce maximum fusion tendencies.

Fig. 2.25 CB6BT with sand fusion

Pattern Equipments

Pattern equipments so constructed as to promote uneven or soft ramming, modifies

the metal-sand relationship. This tends towards either high oxides formation or

greater metal penetration. These construction may be improper location of parting

line so as to induce soft ramming, improper location of sprue, riser and runner.

These may create small pockets of sand which are difficult to ram to proper density,

inadequate draft. This makes some pattern difficult to ram to proper hardness. Such

patterns are difficult to get at and the lack of draft forces the molder to soft ram in

order to avoid tearing up the sand when drawing the pattern.

37

Flask Equipment

Design and construction of flask equipment (size, proper placement of gates) which

promote uneven or soft ramming should be avoided.

Excessive cope height has a direct effect on metallostatic pressure and therefore,

upon the tendency towards fusion. This cause of penetration has increased in recent

years as the tendency to a universal flask size has increased.

Gating and Riser

The location of gates and riser which promotes localized overheating of the sand

has a direct effect upon the rate of the chemical reaction which is fusion. A sprue or

riser too close to the vertical surface not only creates soft spot but unusually high

sand temperature in these areas. The high temperature increases the rate of reaction

between metal oxide and sand.

Anything that causes excessive pressure increases the degree of contact between

metal and sand and there by converts a normal peel to a fused surface. Cope height

and pouring height (distance from ladle to mould) are obvious example. Slow

pouring type gates prolong the time of heating the mould, thereby increasing the

degree to which the sand is heated. This promotes fusion.

Incorrect gating ratio (sprue, runner, gate) permits metal oxidation during pouring,

increases the amount of oxide on the surface. As such, it increases the amount of

fusion product to be found on the casting surface.

An oversize riser neck which overheats the sand will increase the rate of fusion.

This, combined with the heat of riser itself often explains the fusion found near the

base of live riser.

A pouring cup or sprue, designed so as to cause aspiration of air creating oxidized

metal, has the same effect as of incorrect gating ratio since more metal oxides

promotes a greater fusion product.

38

Moulding Sand

A low sintering point or low fusion point of the sand grains indicates that they are

already fluxed. As result, further fluxing with metal oxide during pouring is easier

and quicker. In some cases, the sintering point is so low that fusion in the absence

of metal oxides occurs. In this case, it os doubtful whether or not such fused sand

would adhere to the casting. The presence of metal oxide on the casting surface is

probably necessary to develop the adherence defined as a fusion defect.

Any sand condition which promotes, excessive porosity of the mould surface can

cause fusion. Low density sand caused by improper distribution of the grains

increase the ease with which the metal oxide can adhere to the surface. Such low

density sand is also characteristic by low flowability and high permeability since

density and permeability are related.

Insufficient carbonaceous materials permit rapid metal oxide formation to takes

place. There must be enough of these materials to hold a reducing atmosphere down

to the temperature below which fusion cannot occur. Unfortunately, too much

carbonaceous materials may increase the demand for water and the excessive water

will more than offset the advantage of the higher carbon.

Core Practice

Too low sintering point of sand grains. Soft rammed cores.

Grain size is too large or improper distribution in uncoated cores.

A rough or porous core surface permits ready access to the metal oxides. The

surface of a core is usually the densest. If the surface is rough, abraded, or loose, an

abnormal fusion or penetration can result.

Insufficient or incorrect coating on those core designed for dipping or washing

permits penetration into the more open core body. Underbaked core may have a

weak skin or they may be such as to provide a high gas pressure during pouring.

A broken or disturbed core wash due to rough handling or handling while the core

wash is still wet exposes an open grain for fusion.

39

Insufficient penetration of the core wash can be due to grain size that is too fine or

incorrect Baume of wash and the type of wetting agent used.

Low hot strength of the core permits a break down of the core surface which is

conducive to metal oxide formation and fusion. The low strength may be because

the binder is too low in hot strength or the binder content is too low.

Dipped or sprayed cores that are not redried cause high moisture. The high

humidity atmosphere in the mould during pouring increases the rate of oxidation

and metal oxide formation.

Moulding and Pouring Practice

Soft or uneven ramming, uneven or insufficient or spraying of cores may lead to

fusion.

Excessive use of parting compounds and washes may cause trouble in one or two

ways. Liquid parting in excessive quantities weakens the mould surface and

promotes boiling action and erosion.

Excessive pouring height and temperature will overheat the sand, especially when

aggravated by any of the design practice. The higher sand temperature in turn aid in

reaching the required reaction temperature for fusion at the interface of mould and

metal.

2.12 Metal Penetration

Metal penetration is a condition in which the metal or metallic oxides have filled the voids

between the sand grain without displacing them. In general terms, true penetration implies

an openness of the mould surface. There are also occasion when apparent penetration occur

even with the dense surface such as from high pressure squeeze, shell core and moulds. It

should be noted that the definition also include the penetration of metal oxides. There has

been adequate demonstration of the fact that some penetration takes place as a movement

of metal oxides rather than of molten metal. It is important to recognize that metal also at

elevate temperature do have a measurable rate of oxidation when exposed to oxidizing

40

atmosphere. Some penetration defects can be shown to occur after metal has solidified but

still at an elevate temperature. The role of oxide penetration is one of the explanation for

these case in which metal appears to penetrate the minor porosity of the mould under

conditions which obviously are beyond the capability of metal fluidity. Studied have been

performed to understand both qualitatively and quantitatively the factors that cause metal

penetration. It is caused by three modes. The first such mode is liquid state penetration of

metal into inter granular voids of mould. Liquid state penetration is govern by capillary

forces and head height pressure: when head height pressure is greater than surface tension

resistive force, metal can penetrate into the mould. The second mode is vapor state

penetration into the mould. The metallic vapors penetrate into the mould and subsequently

condense into the liquid and then solidifies. The solidified metal changes the surface

tension property, thereby aiding in further liquid-state penetration described as the primary

mode of penetration. The mode is chemical reaction penetration, where complex oxides are

formed by the alloying element, mould wash, sand. Fig. 2.26 showing CB6BT with metal

penetration.

Fig. 2.26 CB6BT with Metal Penetration Defect

2.12.1 Causes

Casting and Pattern Design

Design is a contributing factor where sharp corners or protruding section are

necessary or sand section is necessary and surrounded by a heavy metal section.

41

These design permits a concentration of heat which ultimately destroy the normal

properties of the mould or core. Preliminary collapse of the surface permits ready

access to the metal or metal oxides. Some design require the use of special sand

such as zircon, olivine in order to develop resistance to excessive temperature.

Pattern Equipment

Pattern equipment constructed so as to promote uneven or soft ramming has a direct

effect upon the penetration problem by promoting an openness or mould porosity.

The most common errors in this respect are as follow

Improper location of the pattern on the plate results in sand pockets which are

difficult to ram. This may be a case of mounting the pattern too close to the flask

wall or mounting too many pattern on a single plate.

Improper location of sprue, riser and runner. It is common to have penetration and

swell on the same casting since the cause is the same.

Inadequate draft of less than 1.5 degree can result in a torn surface which permits

ready penetration of metal or metal oxides even in a mould f adequate overall

density.

Pattern equipment constructed to permit excessive metallostatic pressure is

illustrated by the effect of vertical versus horizontal mounting of a pattern. The

increased pressure imposes greater loads in the sand and may require special sand

or more dense moulding to offset the penetration pressure.

Flask Equipment

Design and construction of flask equipment which promotes uneven or soft

ramming may be a cause of flask distortion.

Excessive cope height. Penetration is always related to both resistance and pressure.

A mould which is adequate for low metal pressure may easily penetrate if the

pressure is increased. The pressure is related to metal density and cope height (a

42

heavy metal, such as steel, produces greater metal pressure than a light metal such

as aluminum for the same sprue height).

Gating and Riser

Location of gates and riser which promotes localized overheating of the sand leads

to premature destruction of the mould surface. This permits ready access to the

metal, or to metal oxides formed at elevated temperature. The following are typical

of this.

A sprue or riser too close to the mould surface creates a definite hot spot which is

aggravated by a tendency to soft ram in the same spot.

Anything which causes excessive pressure of metal during pouring will act to

promote penetration especially if the pressure is accompanied by high temperature.

Slow pouring retards solidification and, therefore, acts to prolong the time during

which the sand is exposed to high temperature.

Incorrect ratio of sprue, runner, gates, permitting metal oxidation during pouring

increases the amount of metal oxides and introduce fluxing action. Any part of the

gating system can be the cause unless all sections are full of metal at all time. The

so called pressure-ratio gating system minimizes problems because all sections are

full and oxygen has a minimum opportunity to contact the metal. Any form of

turbulence will increase the rate of oxidation. A non turbulent flow is therefore

desirable especially with metals showing a rapid rate of oxide formation.

An oversize riser neck which overheats the sand is a common problem. It is the

result of using a long connecting neck which freezes unless it is made oversize.

When lack of feeding results from faulty neck design, it is better to shorten the neck

to prevent freezing rather than making it oversize. The smaller neck has advantage

of reduce heating of the sand plus the reduced cost of chipping and grinding.

A pouring cup or sprue designed sa as to permit aspiration of air creating oxidized

metal, is a common cause of turbulence which promotes penetration by building up

the metal oxide film on the molten metal.

43

Moulding Sand

Any condition that promotes excessive porosity of the mould surface tends towards

penetration. In this regards, it must be recognized that porosity is a mould condition

and those inherent features of the sand which make it difficult to mould on the

equipment available are pertinent factors.

Improper distribution of sand grains may cause low density mould.

Low flowability and/or mouldability is related to many factors. It must be

remembered that the type of moulding must be considered. It is not possible to refer

to a single property of flowability since each moulding method applies energy

differently. What is best flowability for one type may be less desirable for an

entitrely different piece of equipment. The aspects of interest are as follows.

Moisture segregation will lead to poor mouldability and penetration in all type of

moulding. It is to be avoided because it is the cause of many other defects such as

blow holes, scabs, and inclusion, and is the result of poor mixing.

Poorly aerated sand is often a variation of moisture segregation. The sand grains

leaving the muller may be already premoulded which reduces the ability to be

mould under normal conditions. Such prearrangement of the sand grains can be

broken by some of riddling or aeration.

Insufficient coating of shell snad permits penetration of shell moulds by the simple

mechanism of localized low strength and open grain.

Excessive mould permeability is another way of saying open grain. Permeability

and density are function of each other. Low density is the same as high permeability

and vice-versa.

Insufficient carbonaceous material permits excessive metal oxide formation. It also

allow the oxide to wet the sand grain and penetrate easily. Oxidation of a casting

surface is exothermic promoting localized heating.

44

Core Practice

A grain size which is too large or improperly distributed in uncoated core is related

to moulding sand. It applies only to uncoated cores because it is assumed that a

wash, dip, or coating will conceal any openness in the core proper.

Soft rammed cores are of the same undesirable nature as soft rammed moulds. They

are often the most vital factor in this type of penetration. The actual openness of the

core or mould must be related to the potential density and the moulding process.

A rough or porous core surface creates the problem by its very nature. When the

metal or metal oxide wets such a surface, it can penetrate. This is especially true

where pressure is involved, such as in heavy metalsection, expansion metals (gray

ion) cast in permanent moulds. The rough or open surface is commonly related to

one of the following factors.

Insufficient or incorrect coating permits the penetration to occur because such a

coating is unable to protect the relatively open core underneath. Obviously, the

more open the core, the greater must be the care to protect it with adequate and

proper core wash, dip or coating.

Underbaked core can cause penetration from the gases and steam generated during

pouring.

A partially disintegrated core due to overbaking likewise produces a weak surface.

This may be simple miscalculation of the proper baking time ore temperature. It

may be related to an improper mix in the oven (large and small cores on the same

cycle) or poor heat distribution in the oven. Oven temperature indicator may be

faulty. Another common cause is a solid large core which overbakes on the surface

while the center is coming up to temperature. In large cores this can be avoided by

use of coke centers or other lightening techniques so the core can be removed

before the surface is destroyed or weakened to a low scratch hardness reading.

Core that have picked up moisture during store. It is particularly troublesome in

cores because the excessive moisture is not readily apparent. The core may look dry

and still carry a high moisture on the surface. It can usually be noticed by a scratch

hardness test on the suspected core.

45

Insufficient absorption of the core wash will allow direct penetration or will permit

the coating to peel away exposing the open grain core underneath. Such a peel also

act to promote boiling and penetration from the cause. Such insufficient penetration

is usually the result of: very fine grain size; incorrect Baume of wash.

Low hot strength due to sufficient clay in the wash or to a low binder content from

the use of too much solvent leads to penetration. Poorly cleaned and finished cores

provide penetration in a direct manner. Inspection of such core would prevent this

from occurring.

A dirty core box has a direct effect upon sand sticking to the box leaving an open

surface on the core. A good core has a smooth dense surface. Such a good surface is

important but is impossible with a dirty box.

Moulding and Core Practice

Moulding practice is often the prime cause of soft mould penetration. It may be a question

of carelessness or improper correlation of the machine and the mould. For example, using

an undersized machine for large mould can easily create a built-in soft ram unless the

moulder substitute laborious tucking, peening, ramming to compensate.

Uneven or insufficient coating or spraying of core applies to the mould. Excessive

use of washes may cause trouble in one of the two ways. Liquid parting in

excessive quantities weakens the mould surface and promotes boiling action and

erosion. Low fusion, dry parting permit a fusion of sand grains which is often

confused with true penetration.

When the Baume for the type of coating used is too low, absorption of the wash

occur. As a result, the wash may peel, chip permitting both direct penetration and

boil penetration.

Any combination of hot and cold materials (cores, moulds, chaplets, chills, etc.) can

set up condensation deposits of water. These can cause a boil type penetration and

can vastly increase the rate of oxide formation and subsequently metal oxide

46

penetration. This is a common cause of this type of penetration and a predominate

cause of had mould penetration.

Pouring Practice

Excessively high pouring temperature has a double effect. In first place, they tend

to be fluid. In second place, they oxidize rapidly and increase oxide penetration.

There is also a secondary effect in which the unusually high temperature rapidly

destroys the core or mould surface.

Excessive pouring height, like excessive cope height, creates unusually high metal

pressure and force the metal or oxide into the mould pores. It, therefore, aggravates

all conditions previously described in moulding sand, core practice and moulding

practice.

47

CHAPTER - 3.

EXPERIMENTAL INVESTIGATION

3.1 Methodology Used

Fig. 3.1 A Schematic Procedure for Reducing Casting Defects and Select Best Solution

Fig. 3.1 Showing methodology used for reducing defects and selects the best solution.

Firstly, defects are detected which occurs in CB6BT like scab, blow hole, mould erosion,

sand fusion, metal penetration and among these, sand fusion and metal penetration are two

major defects due to which rejection of CB6BT is higher which is 4.2 % minimum to 9.7 %

maximum. Further, detailed analysis of these two defects has been done and various causes

which are responsible for these two defects are studied. Then, root cause is selected and

solution for that is identify and among various solutions best solution is implemented and if

after implementation defects are reduced then standards are made for that process.

48

3.2 Grading of Defects

Grading of defect is done at shot blasting point. After fettling section, castings, mainly

CB6BT comes for shot blasting so that its surface can be finish to a desired level. At shot

blasting hardened small (3 – 4 mm diameter) steel balls are bombarded on the casting in a

confined region. Numbers of rounds in shot blasting is directly proportional to percentage

of defect i.e. if percentage of sand fused with the casting is more then number of rounds in

shot blasting is more. On the basis of this fact grading has been done. Defects are graded as

level 1, level 2, level 3, level 4, and level 5. Table 3.1 shows grading of defects.

Levels Percentage of Defect Rounds Required In

Shot Blasting

Level 1 0 – 20 1

Level 2 21 – 40 2

Level 3 41 – 60 3

Level 4 61 – 80 4

Level 5 81 – 100 5

Table 3.1 Grading Of Defects

3.2.1 Level 1

If casting needs only one round in shot blasting for cleaning then it is categorized as level

1, and it has 0 – 20 % of defect (fusion or penetration of sand). Fig. 3.2 Shows cope side of

CB6BT with level 1, in which it had taken only one round in shot blasting for cleaning.

Fig. 3.3 shows drag side of CB6BT with level 1. These castings are hang on the hanger,

maximum of six can be hag and at a fixed interval it rotate so that another hanger with

casting can enter in a confined region. Time of rotation vary from 120 – 300 seconds. After

shot blasting grinding is also done if necessary.

49

Fig. 3.2 Cope side of CB6BT with Level 1

Fig. 3.3 Drag Side of CB6BT with Level 1

3.2.2 Level 2

If casting needs two rounds in shot blasting for cleaning then it is categorized as level 2,

and it has 21 – 40 % of defect (fusion or penetration of sand). Fig. 3.4 Shows cope side of

CB6BT with level 2, in which it had taken two rounds in shot blasting for cleaning. Fig. 3.5

shows cope side.

3.2.3 Level 3

If casting needs three rounds in shot blasting for cleaning then it is categorized as level 3,

and it has 41 – 60 % of defect (fusion or penetration of sand). Fig. 3.6 Shows cope side of

50

CB6BT with level 3, in which it had taken two rounds in shot blasting for cleaning. Fig.

3.7 show drag side.

Fig. 3.4 Cope side of CB6BT with Level 2

Fig. 3.5 Drag side of CB6BT with Level 2

Fig. 3.6 Cope side of CB6BT with Level 3

51

Fig. 3.7 Drag side of CB6BT with Level 3

3.2.4 Level 4

If casting needs four rounds in shot blasting for cleaning then it is categorized as level 4,

and it has 61 – 70 % of defect (fusion or penetration of sand). Fig. 3.8 Shows cope side of

CB6BT with level 4, in which it had taken four rounds in shot blasting for cleaning. Fig.

3.9 Drag side of CB6BT with Level 4.

Fig. 3.8 Cope side of CB6BT with Level 4

3.2.5 Level 5

If casting needs five rounds in shot blasting for cleaning then it is categorized as level 5,

and it has 81 – 100 % of defect (fusion or penetration of sand). At present we didn’t get any

52

castings having level 5 defects. But casting is an uncertain process in future we can get

that.

Fig. 3.9 Drag side of CB6BT with Level 4

3.3 Data Collection

3.3.1 Data Collected at Shot Blasting Point

Everyday ten castings are reviewed at shot blasting point and data of ten castings are

recorded as shown in table 3.2. For each and every product which has been made in

foundry division at Tata motors have particular date and number which was written on the

mould before pouring, with the help of which we can find the date at which metal is poured

and the number of that particular casting. In every foundry there are codes given for each

months. Example, if 12G16 is written on the casting it shows that particular product was

manufactured on July 12, 2016, and 331,123, etc,. Shows number of casting for that

particular batch.

In below figure, in block number column, the number of dots represents number of rounds

needed in shot blasting for cleaning. Example 7G16, 167 . represents that on July 13, 2016

casting poured on/ manufactured on July 7, 2016 having part number 167 arrived at shot

blasting point and it needed only one round in shot blasting for cleaning or it falls under

level 1 grade. If PREDICTED is written then it means that before it goes for shot blasting

53

only by seeing it, we had predicted the numbers of rounds needed for cleaning in shot

blasting. If predicted is followed by three dots then it means we had predicted that this

particular casting needs three rounds in shot blasting, it may also vary than actual numbers

of rounds. We had collected data for three months and almost every time our prediction is

right from this we can conclude that our grading is correct.

Table 3.2 Data Collected at Shot Blasting Point

3.3.2 Data Collected from Foundry Lab

Every day for each and every batch, sample is taken and different tests are done at foundry

lab. With the help of date of pouring and number, on the casting we can point out particular

casting properties which are tested by foundry man. At lab tests are done to calculate

permeability number, moisture percentage, GCS, active clay, shatter index, volatile matter,

54

compactness, weight tensile strength (WTS), loss on ignition (LOI). Table 3.2 shows data

collected at foundry lab in table format.

S.NO. BLOCK NO.

ITEM

BEFORE

NEW

SAND (Kg)

BENTONITE

(Kg)

LUSTRON

(Kg)

MIXING

TIME (s)

MOISTURE

%

PERM.

NO.

1 5G16,48 EIII 60 20+51 21 158 3.3 145

2 5G16,128 EIII 60 20+51 21 158 3.3 140

3 4G16,115 EIII 60 20+51 21 158 3.6 145

4 7G16,167 EII 60 20+51 21 163 3.9 135

5 7G16,302 EII 60 20+25 20 161 3.9 130

6 8G16,133,146 EIII 60 20+45 20 161 3.7 140

7 11G16,310 EIII 70 20+51 21 160 3.5 140

8 9G16,330,335 6BT 70 20+37 21 181 3.4 135

9 5G16,314 6BT 70 20+37 21 181 3.4 135

10 12G16,44 70 20+51 21 163 3.3 135

For all castings which are reviewed at the shot blasting point similar data is collected. Now,

we can compare the properties of castings having defects with castings having no defects

and from here we can predict the main cause for sand fusion and metal penetration.

S.NO. GCS

COMPACT

%

SHATTER

INDEX

SPLIT

STRENGTH

SP. WT.

(gms) LOI %

AL CLAY

% WTS VM

1 25 34 77 4.1 152

2 26.5 35 75 4 152 4 8 16

3 25 37 75 4 153 5 7.7 16

4 25.5 35 76 4.2 152 5.5 8.2 18 3.4

5 26 36 75 4.3 152

6 25.5 37 76 4.3 152 4.8 8.2 15 3.2

7 26 35 75 3.8 152 4.1 8.2 15 2.9

8 24 35 72 3.8 152 4.6 7.7 15 3.1

9 24 35 72 3.8 152 4.6 7.7 15 3.1

10 26 35 78 4.4 152 4.2 7.7 15

Table 3.3 Data Collected from Foundry Lab

55

3.4 Tests Done at Foundry Lab

Different tests are done at foundry lab and different properties are calculated. In this

section we will discuss about the importance of properties of sand. Metalcasters have two

primary reasons for green sand testing:

To check the consistency of the prepared green sand.

To determine if the green sand has the physical and chemical properties to produce

good castings.

Poor quality sand can lead to a number of casting-related defects. To ensure the

properties necessary to avoid casting defects and produce the quality we desire

consistently throughout the entire green sand system, metalcasting facilities need to

test their green sand daily.

Physical Tests For Moulding Sand

3.4.1 Preparation of standard test specimen

Procedure

It is necessary that the specimen be prepared under standard conditions. To get

reproducible ramming conditions, a laboratory sand rammer is used along with a specimen

tube. Fig. 3.10 shows the set up of laboratory sand rammer. The measured amount of sand

is filled in the specimen tube, and a fixed weight of 6.35 to 7.25 Kg is allowed to fall on the

sand three times from a height of 50.8 ±0.125 mm. The specimen thus produced should

have a height of 50.8± 0.8 mm. To produce this size of specimen usually sand of 145 to

175 g would be required.

56

Fig. 3.10 Sand Rammer With Specimen Tube

3.4.2 Test for Compactability

The purpose of this test is to determine the percentage decrease in the height of a loose

mass of sand under the influence of compaction (i.e., how resistant is it to squeeze and

compaction. The compactability test tells you how wet or dry the green sand is and helps

control the most common green sand defects. It is directly related to the performance of the

green sand in the molding operation and reflects the degree of temper of the green sand. It

indicates how a fixed volume of green sand will react to a fixed energy input (such as

mulling or molding). Metalcasters want to select a compactability level high enough to

avoid cuts and washes, friable broken edges, hard-to-lift pockets, cope downs, crushes,

penetration, burn on and erosion scabbing. Yet, compactability must be low enough to

avoid oversized castings (due to mold wall movement), shrinks, blows, pin holes, super

voids, poor finish, expansion defects, gas and rough surfaces, shakeout problems and high

ramming resistance.

57

The compactability test is carried out in conjunction with a Sand Rammer. This test

measures the decrease in height of a riddled mass of sand, 4¾ inches (120 mm) high, under

the influence of a standard compacting force. The Compactability tester consists of a scale,

graduated 0 – 65% in units of 5, which fits into the hole on top of the Standard Sand

Rammer, and a tube filler comprising a ¼” (6.35 mm) mesh screen and funnel mounted on

a cast base shown in fig. 3.11. .

Installation

(a) Place a precision specimen tube and pedestal cup in position on the sand rammer.

Mount the scale on the top of the rammer frame using the ¼” (6.35 mm) drilled hole.

(b) Using the weight lifting lever, raise the plunger of the rammer until the bottom face of

the ram end is level with the top edge of the specimen tube.

(c) Move the scale up or down until the zero is in line with the top of the plunger shaft.

Lock the accessory in position by means of the 3/16” Allen screw located on the right-hand

side of the top of the rammer.

(a) (b)

Fig. 3.11 (a) Tube Filler (b) Sand Rammer With Compactabilty Tester

58

Procedure

(a) Position a specimen tube and pedestal cup on the tube filler beneath the funnel outlet.

Pass the sand to be tested through the screen until the specimen tube is filled.

(b) Strickle the sand level with the top of the tube with the strike-off blade. Remove the

specimen tube and pedestal cup and place in position on the sand rammer.

(c) Lower the plunger gently onto the sand and ram with three blows. Read percentage

compactability as indicated by the position of the top of the plunger shaft on the scale.

3.4.3 Test for Moisture Content

This test is used to determine the percentage of moisture in the molding sand. Moisture in

molding sand affects the plasticity of the clay bond, which controls most sand-related

defects. Moisture content of a green sand molding system is not an arbitrary number. It

must be maintained within a narrow range. The moisture content is affected by the

hydration of the binder composite, coating of the sand particles and muller efficiency with

regard to working and available bond. Moisture affects all other green sand properties and

is the most abused ingredient in green sand. The two major factors that affect moisture

requirement are the type and amount of clay and the type and amount of additives in the

green sand mix. Excess moisture will produce an oxidizing atmosphere in the mold,

promote excess gas evolution and lower permeability, cause high dry and hot strength,

reduce mold hardness and result in poor flowability of the sand. Insufficient water produces

dry friable green sand that is difficult to mold.

Procedure

The most accurate method of moisture determination is to dry out the sand and to note

weights before and after. The percentage of moisture can be calculated from the difference

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

Calculate the percentage moisture by the following formula:

59

Moisture, percent = 𝐴

𝐵 x 100

Where,

A = loss of weight of the sand sample in g on heating.

B = weight in g of the sand sample taken.

Fifty grams of tempered sand accurately weighed and placed in the pan. The timer for the

blower of the moisture teller is set for the required time to dry the sand (approximately 5

min) and air at 110°C is blown over and through the sand. The sand is dried after this and

weighed again. Note the difference in the initial and final readings and determine the

percentage of moisture in the sand. Make the determination on three separate samples and

take the average of three test results as the moisture content of the sand.

3.4.4 Test for Permeability

Permeability is defined as that physical property of the moulded mass of sand mixture

which allows gas to pass through it. It is determined by measuring the quantity of air that

passes through a given sample of sand in a prescribed time and under standard condition.

Important factors in regulating the degree of permeability include sand grain size, shape,

distribution and type, binder composite quantity and the density to which the green sand

has been rammed, and moisture content. Low permeability will lead to a smooth casting

surface finish, but also could cause blows, pinholes and expansion defects. High

permeability reduces gas pressure but can result in mechanical penetration and a rough

surface finish. To determine permeability the AFS Standard sand specimen of 5.08 cm (2

inches) diameter and 5.08 cm in height is prepared by ramming the required quantity of

sand in a smooth surface tube with three blows of standard rammer. This sand specimen is

placed in the mercury cup of the permeability meter. The air drum is raised to take 2000

cm3 of air in to the air drum which will be indicated by the graduation on it. The whole air

is then allowed to escape through the sand specimen with a pressure of about 10 g/cm3 and

the time is recorded.

60

The permeability number of the sand sample can be calculated from the following

equation:

P = 𝑉ℎ𝑝𝐴𝑡

Where,

P = AFS standard permeability number

V = Volume of air in cm3 = 2000 cm3

h = Height of specimen in cm = 5.08 cm (or, 2 inches)

A = Cross sectional area of specimen in cm2 = 20.268 cm2

p = Air pressure in g/cm2 = 10 g/cm2

t = Time in minutes

The above equation may be simplified as

P = 3007.2

𝑡

Where,

t = time in seconds.

This Permeability Meter employs the orifice method for the rapid determination of sand

permeability. Air at a constant pressure is applied to a standard test specimen (in a

specimen tube), and the drop in pressure is measured on a pressure gauge, which is

calibrated directly in permeability numbers. Fig. 3.12 showing permeability meter.

Procedure

(a) Switch on blower motor by moving toggle switch to the “ON” position. Allow the

motor to run for at least one minute in order to obtain a stable reading on the gauge.

61

Fig. 3.12 Permeabilty Meter

(b) Select the orifice required for the sand sample to be tested. The general rule for

determining the orifice required is :-

(i) If the permeability number of the sample is over 50, use the large orifice

marked ‘L’.

(ii) If the permeability number of the sample is under 50, use the small orifice

marked ‘S’.

(c) Place the specimen tube with the sand sample uppermost over the centre post of the

Permeability meter. Rotate the knurled ring of the centre post anti-clockwise to seal the

specimen tube.

(d) Place the lever on the left-hand side of the permeability meter body in the “CHECK”

(forward) position. Adjust the motor speed control rheostat to obtain a pressure reading of

exactly 100 mm or ‘O’ permeability on the pressure gauge.

(e) Move the lever to the “TEST” (rear) position, and read permeability from the

appropriate scale according to the orifice in use.

(f) Return lever to its “CHECK” position and confirm that a pressure of 100 mm is still

recorded. Release the specimen tube by rotating the knurled ring in a clockwise direction.

62

3.4.5 Green Strength (Compression, Tensile, Shear, Split)

The Universal Sand Strength Machine, together with the appropriate accessories, will

determine the compression, shear, tensile, and splitting strengths of moulding and core

making materials by means of dead weight loading. This machine consists of four major

parts: frame, pendulum weight, pusher arm and motor. The pusher arm is driven by a

geared motor mounted on the pusher arm and coupled to the hand wheel shaft. The

pendulum weight swings on ball bearings and can be moved by the pusher arm, via a test

specimen, from a vertical position, through 90°, to a horizontal position, with a consequent

increase of load on the test specimen. A magnetic rider is moved up a calibrated scale by

the pendulum weight and indicates the point at which specimen collapse occurs. The

machine is calibrated in lb/in2 for 2 inch diameter x 2 inch height standard sand specimens.

Automatic operation is by means of push button stop/start control and micro-switches as

follows :-

(a) Reverse switch. This reverses the machine after the specimen has collapsed.

(b) Stop switch. This stops the machine when it returns to the zero position.

(c) Limit switch. This comes into operation if the specimen fails to collapse,

returning the pusher arm automatically to zero.

The accessories required for the determination of shear, dry, tensile, transverse and

splitting strengths are described separately. Fig. 3.13 shows motor driven universal sand

strength machine (AFS).

Procedure

Green Compression Strength

(a) Place the compression heads in the position shown on the illustration.

63

Fig. 3.13 Motor Driven Universal Sand Strength Machine (AFS)

(b) Raise the weight arm slightly and insert an AFS standard 2 inch diameter x 2 inch

height test specimen between the compression heads so that the face that was uppermost in

the ramming operation is facing the right-hand compression head. Care should be taken not

to damage the specimen.

(c) See that the magnetic rider is resting against the pusher plate and that there is at least

0.25 inch clearance between the rubber bumper and the lug on the weight arm. If this

clearance is not sufficient it means that the specimen is smaller than the permitted tolerance

and should be discarded.

(d) Press the “START” button. When the specimen collapses the machine will reverse and

return to zero automatically.

(e) Record the reading shown on the lower edge of the magnetic rider, reading the scale

designated “Green Compression Strength”. Remove the sand from the compression heads.

Fig. 3.14 Holders for GCS.

Green compression strength indicates the maximum compression stress the sand mixture is

capable of sustaining and is used to control the rate of clay addition to the green sand

system. The degree of mulling, sand to metal ratio, clay content, compactability range and

additive type affect green compression strength. Low green compression strength provides

good flowability but can result in broken molds and poor draws. Indicators of low strength

64

are low clay content, dry sand and poor mulling. High green compression strength means

stronger molds but difficulty in shakeout, poor casting dimensions, poor flowability, high

ramming resistance and higher cost. High clay content is an indicator of high strength.

Fig. 3.14 Holders for Compression Strength Test

Green Shear Strength

(a) Place the shear test heads in the lower position in the machine, with the head having the

half round holder attached to it in the pusher arm.

(b) Raise the weight arm slightly and insert an AFS standard 2 inch diameter x 2 inch

height specimen between the heads. Ensure that the magnetic rider is resting against the

pusher arm and that there is 0.25 inch clearance between the rubber bumper and the lug on

the weight arm.

(c) Press the “START” button. When the specimen shears the machine will reverse and

return to zero automatically.

(d) Read the lower edge of the magnetic rider on the scale designated “Green Shear”.

Remove the sand from the shear heads as shown fig. 3.15.

Fig. 3.15 Holders for shear StrengthTest

65

Compression and Dry Shear Strength

(a) Place either the compression heads or the shear heads in the top position of the

machine. This position increases the load applied by a factor of 5.

(b) Prepare AFS standard 2 inch diameter x 2 inch height test specimens in the usual way

and dry in an oven at 110 °C for 2 hours.

(c) When cool, place in position between test heads and adjust clearance between rubber

bumper and lug on weight arm to approximately 0.5 inch using the adjusting screw in the

pusher arm.

(d) Press the “START” button. When the specimen collapses the machine will reverse and

return to zero automatically.

(e) Read the scale designated “Dry Compression” or “Dry Shear” according to the test

heads being used. Remove the sand from the compression or shear heads.

The dry compression strength test determines the maximum compression load a dry sand is

capable of sustaining. It indicates the resistance of the mold to stresses during pouring and

casting cooling and the ease of shakeout. The higher the dry compression strength, the

greater the number of hard lumps present at shakeout.

An increase in moisture content, the type and amount of clay, rammed mold density and

excessive moisture significantly affect dry compression strength. Low dry compression

strength means easy shakeout by loose friable sand, cuts and washes, burn-in, inclusions

and erosion. High dry compression strength leads to stronger molds, but difficulty in

shakeout, loss of return sand, cracks and hot tears.

3.4.6 Test for Shatter Index

This equipment is designed to allow the free fall of an AFS Standard 2 inch diameter x 2

inch height specimen of moulding sand from a height of 6 feet onto a steel anvil as shown

fig. 3.16. By measuring the degree of disintegration of the specimen the toughness or

plasticity can be determined. The cast iron base of the unit is machined to accept a 13.2

66

mm mesh BS sieve and retaining pan. Through the centre of this assembly passes a solid

steel anvil which is covered by a removable cap onto which the sand specimen falls. Rising

vertically from the rear of the base is a 7 foot steel tube which carries the ejector

mechanism for the sand specimens.

Procedure

(a) Prepare an AFS Standard 2 inch diameter specimen in a precision specimen tube and

record the weight of sand used to form the specimen.

(b) Position the tube containing the sand specimen in the ejector mechanism, beneath the

plunger, with the specimen in the lower part of the tube. Pull the handle of the mechanism

downwards, slowly and evenly, so that the plunger enters the specimen tube and ejects the

sand specimen without giving it any downward impetus.

Fig. 3.16 Shatter Index Tester

67

(c) The sand specimen should strike the anvil squarely in the centre. If it does not, check

that the base is set level. Remove anvil cap, carefully lift off sieve assembly and remove

sieve from pan.

(d) For convenience, weigh the sand in the receiver and calculate the weight of sand

remaining on the sieve, including the cone of sand on the anvil cap, by subtracting this

weight from the total weight of the specimen.

Shatter Index = 𝑊𝑡.𝑜𝑓 𝑠𝑎𝑛𝑑 𝑟𝑒𝑚𝑎𝑖𝑛𝑖𝑛𝑔 𝑜𝑛 13.2 𝑚𝑚 𝑚𝑒𝑠ℎ 𝑠𝑖𝑒𝑣𝑒

𝑇𝑜𝑡𝑎𝑙 𝑤𝑡.𝑜𝑓 (𝑠𝑎𝑛𝑑)𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 x 100

3.4.7 Active Clay

The methylene blue test determines the capacity of clay to absorb cations from a solution,

and thereby predict how the clay will react. Clay may be a component of a drilling fluid, a

binder in foundry sand, or a component in another application. This test is based on the

property of clays known as cation-exchange capacity; clays can exchange some of their

ions for the ions of certain other chemicals. The number of ions available for this exchange

varies with different clays. For example, Western Bentonite, has more base exchange

capacity than Southern Bentonite. However, only the reactive portions of clays are

involved in the cation exchange process.

In this test, the clay particles are coated with methylene blue, giving them a distinct color

until all ions available in the clay cation exchange process have been used. Excess

methylene blue remains unaffected in solution around the particles and forms a blue-green

tint that radiates from the darker spot, similar to a halo. Development of the halo shows that

the total absorption capacity of the clay has been reached, and is noted as the endpoint.

Shown in fig. 3.17.

The methylene blue test is a simple, fast test for measuring the amount of effective binder in

foundry molding sands. This test produces accurate, reproducible results in 10 to 15 minutes.

Only reactive portions of clay participate in the cation exchange process. Finely ground

68

seacoal, wood flour, or cereal does not absorb methylene blue. The cation exchange capacity of

clays is destroyed when clays are exposed to high temperature. The degree of destruction is

depends on the temperature and time that the clay is exposed. A decrease in cation exchange

capacity is accompanied by a proportional decrease in bonding capacity. The altered portion of

depends on the temperature and time that the clay is exposed. A decrease in cation exchange

capacity is accompanied by a proportional decrease in bonding capacity. The altered portion of

the clay cannot be rehydrated, and bonding capacity cannot be restored. Since clay is the only

ingredient in a sand mix with cation-exchange capacity, a precise measurement of this property

is also a measure of the amount of effective binder in the sand.

Methylene blue is added to this sample until saturation, noted by the dye halo surrounding

the solids suspension.

Fig. 3.17 Spot Test for End Point of Methylene Blue Titration

Procedure

1. Pipette 50 ml of deionized water into the Erlenmeyer flask. Obtain a representative sample

of foundry sand. Accurately weigh 5 g of this foundry sand. Place in the Erlenmeyer flask with

the water.

69

2. Shake or stir thoroughly for 10 to 15 minutes. As an option, boil the mixture for 5 minutes.

Add 1 ½ ml to 2 ml of 5N sulfuric acid and shake vigorously for 20 to 30 seconds.

3. Add methylene blue in 1 ml increments. After each addition shake the flask briefly. Using a

stirring rod, place a drop of the fluid on the filter paper. Note the volume of methylene blue

titrated. If the end point has not been reached, a purple circle will appear on the filter paper.

4. Continue titrating until a blue-green halo appears around the purple circle on the filter paper.

When the halo first appears, shake the solution for two minutes to make sure that all the

methylene blue has been absorbed by the binder.

5. After two minutes, place another drop of liquid on the filter paper. If the halo is still present,

the end point has been reached. If the halo disappears, add 1 ml methylene blue and repeat the

filter paper test until the halo remains after two minutes of mixing.

6. Record the volume of methylene blue used to reach the endpoint with the help of table given

in fig. 3.18 (b).

Fig. 3.18 (a) Methylene Blue Active Clay Test Apparatus (b) Table to Calculate Active

Clay

Above Fig. 3.18 (a) shows Methylene Blue Active Clay Test Apparatus.

70

3.4.8 Test for Volatile Matter 900 F(482 C)

This method is used to determine the amount of material in the system sand or additives

that will volatize at a temperature of 900F (482C). Results from this and the LOI test are

used hand in hand. Low combustibles (as determined by the LOI test) and volatiles lead to

lower cost and less moisture required but also can result in poor casting peel, poor finish

and poor shakeout. High combustibles and volatiles cause lower expansion but can result in

pinholes, smoke, blows, brittle sand, higher cost and higher moisture requirements.

3.4.9 Test for Loss on Ignition (LOI)

Loss on ignition measures the weight change of a sample, consisting of weight losses and

weight gains, when a sample is fired at 1,800F (982C). This includes weight loss due to

volatization of organics, removal of chemically bound water, dissocation of inorganic

compounds (with one or more components given off as a gas), and weight gain due to

oxidation reactions. Loss on ignition determines the total amount of combustible material

in the green sand. The green sand sample is fired at 1,800F until it reaches a constant

weight. The quantity of gas forming materials in the green sand will affect casting results.

A high LOI may produce gas defects such as pinholes, blows and scabbing. In steel

castings, a high LOI could lead to carbon pickup on the casting surface. A low LOI can

lead to poor casting peel and a rough casting surface finish.

Above tests are done for moulding sand, same tests can be done for core sand also with

same procedure.

71

CHAPTER - 4.

Result and Discussion

4.1 Sand Fusion and Metal Penetration with Different

Parameters

From above collected data, literature review and observation below table 4.1 can be formed

in which different parameters are considered with respect to sand fusion and metal

penetration.

Parameters Sand Fusion Metal Penetration

High Mold Strength

NO YES/NO

High Pouring Temperature

YES YES

High Pouring Time

YES YES

Optimum Pouring Height

NO NO

Less Carbonaceous Material

YES YES

Less Hot Strength (Low Bentonite)

LESS YES

High Porosity/Less Density

YES YES

Optimum Mold Wash

NO NO

High Permeability

YES YES

Table 4.1 Sand Fusion and Metal Penetration with Different Parameters

Example, if mould strength is high then there will be no sand fusion but metal penetration

may occur, as earlier we had discussed modes of metal penetration, and there we had

studied that metal can penetrate into dense mould also. Similarly, if permeability is high

then metal can easily penetrate into mould.

72

4.2 Returned Sand Variation

Returned Produced Strength Bentonite Moisture Temperature

Block Block

Euro-III 6BT

Head

Block

Bake Drum Block

Table 4.2 Returned Sand Variation

Above table 4.2 shows returned sand variation. As we know good amount of returned sand

is mixed with new sand , bentonite, etc., In this case we are considering production of

block, from above collected data and by observing this table is formed. Above table shows

that the product manufactured just before the block varies the properties of sand mixture

used in production of CB6BT block. Example, if Euro-III 6BT head is manufacture in

previous batch and in next batch block is produced then sand from which head is

manufactured is used in another batch in which block is manufactured for which same sand

will be treated as returned sand then its strength and moisture will be increased, for

compensating this we have to add less amount of bentonite.

4.3 Causes In Our Case and Steps Taken for Elimination of

Defects

4.3.1 Extra Care is Taken In Handling of Core

Causes

Below are the points collected from the causes discussed above.

73

A rough or porous core surface permits ready access to the metal oxides. The

surface of a core is usually the densest. If the surface is rough, abraded, or loose, an

abnormal fusion or penetration can result.

Insufficient or incorrect coating on those cores designed for dipping or washing

permits penetration into the more open core body. Underbaked core may have a

weak skin or they may be such as to provide a high gas pressure during pouring.

A broken or disturbed core wash due to rough handling or handling while the core

wash is still wet exposes an open grain for fusion.

Insufficient penetration of the core wash can be due to grain size that is too fine or

incorrect Baume of wash and the type of wetting agent used.

Low hot strength of the core permits a breakdown of the core surface which is

conducive to metal oxide formation and fusion. The low strength may be because

the binder is too low in hot strength or the binder content is too low.

Dipped or sprayed cores that are not redried cause high moisture. The high

humidity atmosphere in the mould during pouring increases the rate of oxidation

and metal oxide formation.

Steps Taken

Cores are handled with the help of machine instead of hands.

Spray is applied carefully on the moulds in the moulding line.

Cores are redried in the oven before they are used in assembly line.

Correct Baume is maintained.

Cores should not posses porosity.

Fig. 4.1 shows handling of core by hand which is replaced by machine, with which more

precisely wash or coating may be applied.

Fig. 4.2 shows man spraying wash on mould in moulding line. On man side wash is not

applied properly due to which defects occurs.

74

Fig. 4.1 Core dipped in wash for coating by hand

Fig. 4.2 Man spraying wash on mould in moulding line

4.4 Stabilization of Green Sand System

Green system includes sand, bentonite, lustron. If we can correctly control these three

parameters and process then defect free casting can be achieved. But, as we know casting is

a process of uncertainity so it is very difficult to say that for that particular product this

should be amount of bentonite or lustron because casting depends upon environment

condition also. It is seen that during rainy season sand fusion and metal penetration are

more as casting absorb moisture from environment. But, there is standard range for all

parameters which is shown in table 4.3.

75

Sand Parameters Tolerance Range Value Range

Active Clay Tolerance range Total range from established

mean level capacity of the

Clay.

7.8% to 8.5% depending on

the swelling Index or

bonding

Total Clay ± 0.20 the sum of the Active Clay

+ Dead Clay should

normally be 11% -12%

Volatile Matter Volatile Matter Should

normally be 60% - 70% of

the LOI

Loss on Ignition ± 0.15 5.5% - 6.0% - in

conventional lines 4.5 –

5.0% in high pressure lines

Moisture (at moulding

machine)

± 0.15 3.8% - 4.0% in

Conventional Lines

3.2% to 3.7% in High

pressure lines

Table 4.3 Fundamental and Ideal Sand parameters of prepared sand

In casting we know that one parameter is related to many properties, like if we increase

amount of bentonite strength increased, active clay increased, etc. Similarly, if we vary

lustron then volatile matter vary. Hence we that predicted different values of bentonite and

lustron for different product. Initially we had increased the amount of bentonite but active

clay goes beyond standard values then we had decreased it. In Tata Motors there are two

mixture, old and new and there are three shifts namely A, B ,C. It is not necessary that

every foundry should follow above standards it may vary from foundry to foundry. Below

tables shows some prediction. In which we had changed amount of bentonite, lustron and

new sand for old and new mixture, firstly it is predicted for only one shift later we had

decided for all shifts. Table 4.4 shows first prediction and second prediction, there is large

change in bentonite as in first prediction we are getting more active clay, that’s why its

amount is decreased. Some time amount of bentonite reaches to 60 kg also. We had

predicted and stabilize the green sand system which is shown in table. 4.6 prediction values

for A shift for both old and new mixer and table 4.7 shows changes made in the same.

76

(a) (b)

Table 4.4 (a) First Prediction (b) Second Prediction

Table 4.5 (a) Third Prediction (b) Fourth Prediction

Old Mixture New Mixture

Bentonite Lustron Bentonite Lustron

Block 57 kg 17 kg 46 kg 14 kg

Other 51 kg 17 kg 41 kg 14 kg

Head 40 kg 19 kg 32 kg 15 kg

Sand 51 kg 40 kg

Table 4.6 Prediction for A shift

Old Mixture New Mixture

Bentonite Lustron Bentonite Lustron

Block 50 kg 17 kg 40 kg 14 kg

Other 45 kg 17 kg 36 kg 14 kg

Head 35 kg 19 kg 28 kg 15 kg

Sand 60 kg 48 kg

Table 4.7 Change in prediction for A shift

Bentonite Lustron

Block 46 kg 18 kg

Others 44 kg 17 kg

Bentonite Lustron

Block 54 kg 17 kg

Others 46 kg 16 kg

Bentonite Lustron

Block 58 kg 19 kg

Others 45 kg 19 kg

Bentonite Lustron

Block 54 kg 16 kg

Others 44 kg 16 kg

77

4.5 Prediction that Eliminate Defects

Below tables shows the final predicted values of amount of bentonite, lustron, new sand

considering both old and new mixture and all shifts for block and other products with

which defects are eliminated.

Old Mixture New Mixture

Bentonite Lustron Bentonite Lustron

Block 49 kg 17 kg 39 kg 14 kg

Other 44 kg 17 kg 35 kg 14 kg

Head 37 kg 19 kg 30 kg 15 kg

Sand 50 kg 40 kg

Table 4.8 Values for A shift

Old Mixture New Mixture

Bentonite Lustron Bentonite Lustron

Block 51 kg 18 kg 41 kg 14 kg

Other 47 kg 18 kg 38 kg 14 kg

Head 37 kg 20 kg 30 kg 16 kg

Sand 45 kg 36 kg

Table 4.9 Values for B shift

Old Mixture New Mixture

Bentonite Lustron Bentonite Lustron

Block 50 kg 17 kg 40 kg 14 kg

Other 46 kg 17 kg 37 kg 14 kg

Head 38 kg 19 kg 30 kg 16 kg

Sand 49 kg 40 kg

Table 4.10 Values for C shift

78

4.6 Comparison of Rejection

Below graph shows the comparison between previous total rejection and current total

rejection after predicted values are applied

(a)

(b)

Fig. 4.3 Comparison of Total Rejection for all product (a) Previous (b) Present

From above we observe that rejection percentage decreased from month of January

(predicted values are applied from january).

Below graph shows comparison between total rejection for CB6BT previously and total

rejection for CB6BT currently. From below graph we can observe that rejection percentage

decreases after the predicted values are applied.

79

(a)

(b)

Fig. 4.4 Comparison of Total Rejection for CB6BT (a) previous (b) present

80

CHAPTER 5.

CONCLUSION

In the study of block CB6BT mainly have two defects are responsible for higher

percentage of rejection namely sand fusion and metal penetration. Hence, there causes are

studied and causes which are responsible in our study are considered. Here, practically

defects are eliminated as we know in industries we have to eliminate the defects under

many constraints like we canot change the whole process and we cannot implement the

steps which increases the cost to company. So, we have to find the best solution

considering all constraints.

For elimaination of these defects, we had made changes like in handling of core,

application of wash carefully, etc,. We had measure various properties of sand and data is

collected from lab, at shot blasting point. Data is compared and standard values are set for

different products considering all shifts which are discussed above. After implementation

we had observe that percentage of rejections for CB6BT and overall rejections are reduced

and we have achieved percentage of rejection lower than targeted value.

Product Targeted Achieved

CB6BT 5.3 5.22

All 4.2 4.13

Table 5.1 Targeted and Achieved Value

81

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