main report fettling 03

8/2/2019 Main Report Fettling 03

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Seminar on

FELTTING OF CASTING, INSPECTIONS & CASTING DEFECTS

Submitted In partial fulfillment of Bachelor of Engineering Technology

Degree of the Jodhpur National University, jodhpur.

Guide By: Submitted By:

Mr. Pawan Gupta Patel Chintan

Department of Mechanical Engineering

Faculty of Engineering & technology

Jodhpur National University

Jodhpur(Raj.)

2011-12


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FACULTY OF ENGINEERING & TECHNOLOGY,

JODHPUR NATIONAL UNIVERSITY, BORANADA. JODHPUR (RAJ.): 342001

CERTIFICATE

This is to certify that the seminar report summited by Mr.

PATEL CHINTAN s/o DEVENDRABHAI (roll no:- 08ET405036) towards

the partial fulfillment of the requirements for the Degree of Bachelor of

Technology in Mechanical Engineering (Fourth year) of Jodhpur National

University is record of work of carried out by him under my supervision and

guidance. The work submitted has in my opinion reached a level required for

being accepted for examination.

APPROVED BY: GUIDED BY:

HOD of Mechanical

Prof. S.N.Garg Mr. Pawan Gupta


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Acknowledgement

Apart from the efforts of me, the success of any seminar depends largely on the

encouragement and guidelines of many others. I take this opportunity to express

my gratitude to the people who have been instrumental in the successful

completion of this seminar.

I would like to show my greatest appreciation to Shri. Pawan Gupta(Asst.prof) I

cant say thank you enough for his tremendous support and help. I feel motivated

and encouraged every time I attend his meeting. Without his encouragement and

guidance this seminar would not have materialized.

The guidance and support received from all the members who contributed and

who are contributing to this seminar, was vital for the success of the seminar. I

am grateful for their constant support and help.

PATEL CHINTAN

B.Tech 4th Year

Mechanical Engineering

JNU. JodhpurDate :-

Place :- Jodhpur


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TABLE

TITAL PAGE NO

1.FETTLING & CLEANING OF CASTING 1

1.1 SHAKING OF MOULD

1.2 CLEANING OF CASTING

1.2.1 KNOCKING OF DRY SAND CORES

1.2.2 REMOVEAL OF GATES & RISERS

1.2.3 REMOVEAL OF FINS & UNWANTED

PROJECTIONS

1.2.4 CLEANING & SMOOTHEN CASTING

1.2.5 REPAIRING THE CASTING

1

1

2

2

2

3

5

2.CASTING DEFECT

2.1 INTRODUCTIONS

2.2SHRINKAGE DEFECT

2.3 GAS POROSITY

2.4 COLD SHOT DEFECT

2.5 HOT TEARING DEFECT

2.6 MISRUNS DEFECT

2.7 METAL PENETRATIONS

11

11

12

12

13

13

14

14

3.INSPECTIONS OF CASTING

3.1 VISUAL SURFACE

3.2 DIMENSIONAL INSPECTIONS

3.3 NON DESTRUCTIVE TESTING

3.4 DESTRUCTIVE TESTING

15

15

16

18

26

4. CONCLUSION

30

5. REFERENCE

31


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LIST OF FIGURES

FIGURE NAME PAGE NO

1.1 METAL ARC WELDING

1.2 TIG PROCESS

1.3 MIG PROCESS

1.4 SUBMERAGE ARC WELDING

1.5 ATOMIC HYDROGEN WELDING

1.6 TERMIT WELDING

1.7 BRAZE WELDING1.8 METAL SPRAYING

5

6

7

7

8

8

911

2.1 SHRINKAGE DEFECT

2.2 GAS POROSITY

2.3 COLD SHUT DEFECT

2.4 HOT TEARING

2.5 MISRUNS

2.6 METAL PENETRATIONS

12

13

13

14

14

14

3.1 VISUAL SURFACE

3.2 RADIOGRAPHY

3.3 MAGNETIC PATICAL

INSPECTIONS

3.4 LIQUID PENETRANT TESTING3.5 ULTRASONIC TESTING

3.6 TENSILE TESTING

15

19

21

2324

27


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INTRODUCTION

1.0: Abstract

Casting is a manufacturing process by which a liquid material is usually poured into a

mold, which contains a hollow cavity of the desired shape,and then allowed to solidify,

this solidify part is known as Casting.Casting is most often used for making complex

shapes that would be otherwise difficult or uneconomical to make by other

methods. Metal casting involves pouring molten metal into a mould containing a cavity

of the desired shape to produce a metal product. The casting is then removed from the

mould and excess metal is removed, often using shot blasting, grinding or welding

processes. The product may then undergo a range of processes such as heat treatment,

polishing and surface coating or finishing.

The different techniques have been designed to overcome specific casting problems or

to optimize the process for specific metals, product designs and scales or other

operational considerations such as automation. All casing processes use a mould, either

permanent or temporary, which is a negative of the desired shape. Once the metal is

poured and has solidified it forms the positive shape of the desired product. Processes

differ in the number of stages that are required to produce the final casting. The process

uses a permanent mould negative to produce the final casting positive. Processes, such

as sand mouldingand shell casting, use a temporary mould negative which is typically

produced using a permanent pattern or die positive. Investment casting and lost foam

casting techniques use a temporary mould negative that is build around a temporary

pattern positive. For repetitive work, patterns are often produced using a permanent

mould or die negative.


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1.FETTLING AND CLEANING OF CASTINGS[BOOK 1]

1.1 Shaking of Moulds[BOOK 1]

After the metal has solidified and cooled in the sand mould, the casting is knocked out

by breaking the mould. It is essential to ensure that the castings are removed from the

mouldas early as possible for economic reasons. Premature withdrawal may, however,

give rise to distortion, cracks and a chilling effect and cause rejections. It is, therefore,

advisable to establish temperatures at which castings of each type, alloy composition or

complexity are to be withdrawn from mould sand sent for shake out. Suggested

temperatures at which steel castings can be withdrawn from moulds are shown below:

(i) Simple castings of uncritical nature and uniform sections: 900C.

(ii) Parts within even wall thickness; cast with chills: 600C.

(iii) Castings with critical shapes, prone to warping or cold cracking; subjected to

variable impact loads: 300C.

(iv) Thin-walled casting shaving abrupt changes in sections: 100C.

The moulds may either be broken manually on the pouring floor itself or transferred

to a separate shakeout station. In the latter case the mould is dumped on the shakeout

where it is rapidly jarred so that the sand falls through a grate or screen either into a pit

or on a belt conveyor arranged below the floor. The casting and moulding boxes remain

on the grate and are removed from there. Shaking maybe done either manually or

mechanically, but generally. mechanical shake-outs are used for large-scale work. In

the manual type, a stationary grating is mounted and the moulds break when dropped

over the grating. The mechanical units consist of a perforated plate or heavy mesh

screen fixed to a vibrating frame. The screen is vibrated mechanically, producing a

jarring action and causing quick separation of sand from other parts.

1.2 Cleaning Of Castings [BOOK 1]After the casting is extracted from the mould, it is no longer fit for use as such, as it has

sprue, risers, etc. attached toit. Besides, It is not completely free of sand particles. This

operation of cutting off the unwanted parts, and cleaning and finishing the casting is

known as fettling. The fettling operation may be divined dinto different stages:

(1) knocking out of dry sand cores;

(2) removal of gates and risers;

(3) Extraction of fins and unwanted projections at places where the gates and risers

have been removed and also elsewhere;

(4) cleaning and smoothening the surface; and

1


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(5) repairing castings to fill up blowholes, straightening the warped or defomied

Casting.

1.1.1 Knocking Out of Dry Sand Cores[BOOK 1]

Dry and cores may be removed by rapping or knocking with an iron bar. For quick

knocking. pneumatic or hydraulic devices may be employed. These devices, besides

knocking the cores, also help in cleaning and smoothening die casting.

1.1.2 Removal of Gates and Risers [BOOK 1]

The choice of method for removing gates and risers from the castings depends upon the

size and the shape of the casting and the type of the metal. The options for such work

are:

(i) knocking off or breaking with a hammer. Which is particularly suited in case

of grey iron castings and other brittle metals.

(ii) sawing with a metal cutting saw. Which may be a band saw circular saw. or a

power hacksaw (a metal band saw of the "do-all type is considered

suitable for steel, malleable iron, and nonferrous castings);

(iii)flame cutting with oxyacetylene gas is generally adopted for ferrous metals,

specially for large-sized castings where the risers and the gates are very

heavy;

(iv)using a sprue cutter for shearing of the gates;

(v) employing abrasive cut-off machines, which can work with all metals but are

specially designed for hard metals. Which are difficult to saw or shear.

(vi)Plasma arc cutting is now being increasingly used to cut sprue sand risers of

plate-shaped castings with a view to eliminate the manual operation of

burning off and to make the work fast, clean and accurate, by using a

programmable robot for holding and manipulating the castings.

1.1.3 Removal of Fins and Unwanted Projections[BOOK 1]

The operation of removing unwanted metal fins, projections, etc. from the surface of

the casting is called snagging. While snagging, care must be exercised to see that a

proper casting contour is followed and too much metal is not removed.

'The methods for snagging include:(i) using grinders of pedestal, bench, flexible shaft, or swing-frame type;

(ii) chipping with hand or pneumatic tools;

(iii) gouging and flame-cutting;

(iv) removing metal by arc-air equipment; and

(v) filing.


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2

1.1.4 Cleaning and Smoothening Castings[BOOK 1]

In as-cast state, castings often have sand particles adhering to their surface in a fused

form. When the castings are heat treated, a scale is also formed on the surface. In order

that the casting surface be clean and smooth, the adhering sand particles and the scale

have to be removed. The various methods available for this purpose are now described

briefly.

1.Tumbling[BOOK 1]

The castings to be cleaned are put in a large steel shell or barrel. which is closed at its

ends by cast iron lids. The barrel is supported on horizontal trunnions and is rotated ata speed varying from 25-50 rpm. Along with the castings, small pieces of white iron

called "stars" are also charged to help complete the cleaning and polishing operations.

When the barrel is rotated, it causes the castings to tumble over and over again,

rubbing against each other. Thus, by continuous peening action, not only do the

castings get cleaned and polished but also the sharp edges and fins get eliminated and

the internal stresses in the castings arc relieved. When the band is charged, care should

be taken to ensure that the castings are packed tight enough to prevent any breakage.

At the same time these should not be so tight as to prevent the relative motion of the

adjacent pieces. The capacities of tumbling barrels may vary from 1-12 cum. The

limitation of this process is that heavy castings cannot be charged with small ones of

fragile nature. Generally, small sized castings. which are not fragile in nature, are best

suited for tumbling.

2.Tumbling with Hydroblast [BOOK 1]

In this method, the barrel is not horizontal but is arranged obliquely at an angle of

about 30. One end of the barrel, which is at a higher level than the other, may be kept

open to enable observation of the cleaning process. When the castings are tumbled., a

high velocity stream of water and sand is blasted on the castings at a velocity of about

6000 metres per minute. This action results in more efficient cleaning and polishing,

and the tumbling time is also considerably reduced. The method is better adapted tononferrous castings since ferrous ones tend to get corroded due to water treatment. The

base of the barrel is perforated to facilitate removal of the sand-and-water mixture. For

large castings, hydroblasting chambers are used. The castings are placed on a slowly

rotating table and a high velocity stream is emitted from an adjustable nozzle.

3.Cleaning with Compressed Air Impact (Sand Blasting)[BOOK 1]

A high velocity stream of compressed air along with abrasive panicles is directed by

means of a blast gun against the casting surface. The blast gun is designed to convey

air at high velocity into a mixing chamber. The abrasive is fed into this chamber

through a side tube by suction feed, gravity feed, or direct pressure.


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3

Generally, in the ease of small guns, the abrasive is drawn in the mixing chamber due tovacuum created by the passage of high velocity air. The abrasive used is either sand or

steel grit, From the mixing chamber. airborne sand particles are directed towards the

casting. Figure shows a compete sand blasting arrangement which has a manually

operated blast pipe.

The blasting operation is generally carried out in special cabinets or rooms where the

operator directs the blast against the castings to be cleaned. The discharged sand drops

through a perforated floor from where it is conveyed to the moulding hop for re use.

The small sized castings are cleaned in cabinets equipped with windows through which

the operator can manipulate the gun and direct the blast. While working, the operator

must be thoroughly protected against harmful dust He should wear large Faber gloves,protective clothing on the body, and an air pressurised helmet. Unlike tumbling, the

sand blasting method can be adopted for both fragile and large-sized castings. The

method is also more efficient and ensures good polish.

4.Cleaning with Mechanical Impact (Shot Blasting) [BOOK 1]

Instead of using air pressure for hurling the abrasive grit towards the casting,

centrifugal force may be exerted by means of an impeller wheel. The abrasive applied

in this case is steel shots. As die shots move from the hub of the impeller towards the

periphery, their velocity gets accelerated and they finally leave the impeller at a very

high velocity hitting the casting surface with enormous impact. Large cleaning units

may be equipped with one or more blasting impellers strategically positioned at

different places all around the casting. The casting may also be mounted on a rotating

table. In sonic units, the castings am tumbled and at the same time the abrasive is hurled

towards them. In a monorail type shot blast, the castings are carried by a power

conveyer into machine from one side and taken out from the otherside.

5. Arc-air Process[BOOK 1]

This method involves arc heating of the casting surface and blowing off the melted

metal with compressed air. The projections or surface imperfections are heated by the

arc so that they reach the molten state when the air simultaneously blows them away,leaving behind a clean and smooth surface. The process is used on large castings in

steel foundries. The equipment is portable and comprises a gun which is equipped for

producing the arc and blowing the air.

6.Pickling[BOOK 1]

It essentially involves cleaning of casting surface by dilute acid treatment. The castings

are suspended by means of nickel-plated steel or monel metal hooks, into a pickling

tank containing equal part of hydrofluoric acid and sulphuric acid, or only


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4

sulphuric acid for about four hours. The tank is made of mild steel plates but is linedwith lead sheets on the inner walls. The castings are then washed with plain water in a

washing tank and they arc further immersed in a neutralising tank, containing 10%

solution of washing soda, preferably maintained at about 75 c .The castings are once

again rinsed in plain water and dried. The pickling treatment is a cheap and yet

effective method of dislodging sand. scales or tentacles of metal and producing clean

and bright surface on iron and steel castings.

1.1.5Repairing the Castings[BOOK 1]

Defects such as blowholes, gas holes, cracks, etc. may often occur in castings.

Sometimes the castings get broken, bent, or deformed during shake-out or because of

rough handling. Often the castings gets warped during heat treatment or while they cool

down in the mould- Such defective castings cannot be rejected outright for reasons ofeconomy. They are therefore repairs by suitable means arid put to use unless the defects

ire such that they cannot be remedied. The common methods of repair are now dealt

with.

1.Metal Arc Welding [BOOK 1]

Large-sized cracks, blowholes. and other imperfections can be rectified by metal are

welding. The area to be welded must first be cleaned by chipping, filing, gouging. or

grinding, then the joint must be accurately prepared and, if necessary, widened before

welding is commenced. Metals that can be welded by this method include almost all

cast metals, except magnesium. A proper selection of welding electrode is vital. A.C.

metal arc welding is most often selected for welding steel castings. The electrodes used

should preferably be coated so that a dense and strong joint is produced. D.C. arc

welding is preferred for welding cast irons and nonferrous metals as the polarity can be

changed and more heat can he obtained on either the electrode or the workpiece. as

desired. D.C. welding can thus give the lower electrode consumption, higher metal

deposition rates and smoother welds. It is also less dangerous, lie arc voltage used

bieing lower than in the case of AC. welding.

FIG 1.1 METAL ARC WELDING[REF 9]

2.Oxy-acetylene Gas Welding [BOOK 1]

This method, which is the least expensive and easily portable.is suitable where the

sections to be melded are not too heavy and where slower cooling rates arc required. for

instance, to prevent hardenable steels from getting hardened. Gas welding can easily

allow the use of a broad flame, which can pre-heat the area ahead of the section being

welded.


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5

This is not possible in are welding. The flame temperature is also lower than that of the

arc. so cooling rates are slow. The flame can be adjusted so as to make it oxidising,

reducing. or neutral. An oxidising flame is used for welding brasses and bronzes,

reducing flame for high carbon and alloy steels, nickel alloys, and other hard-facing

materials, and a neutral flame for low carbon steels. By using the proper technique,

almost all cast metals and alloys, except magnesium. can be gas welded. Liquefied

petroleum gas (L.P.G.) or natural gas is also used in place of acetylene where a broad

flame is desired.

3.Inert Gas Tungsten Arc Welding (TIG Process)[BOOK 1]

This process uses a non-consumable type of tungsten electrode together with a shield of

Men gas. such as helium and argon for protection of the welding zone. It is most

suitable for metals that tend to gel quickly oxidised, for instance. magnesium and

inagnesium alloys. It is also widely used for welding thin aluminium castings as also for

stainless sleek and alloys of copper and nickel.

FIG 2.2 TIG PROCESS[REF 9]

4.Inert Gas Metal Arc Welding (MIG Welding) [BOOK 1]

The electrode is made of metal similar to the work metal and is of the consumable type.

The method is very fast as electrode wire is automatically fed and inert gas protects the

metal from oxidation. The gases used are argon. nitrogen, and carbon monoxide. The

method is suitable for the repair and joining of large-sized steel castings and is

economical where high speed of operation is required.


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6

FIG 1.3 MIG PROCESS[REF 9]

5. Submerged Arc Welding[BOOK 1]

In this case, the entire welding action takes place beneath a granular mineral material

which acts as flux (Fig. 8.4). The electrode used is in bare form. The flow of current

melts the flux, spreading it over the weld zone and keeping the arc and weld metal

submerged. The metal is has completely protected from oxidation; besides, there is no

visible arc, sparks, spatter, or smoke. This enables use of heavy welding currents, high

welding speeds, deeper penetration, and superior quality of welds. The method is

unsuitable for repair work as it is basically a production process. but it is adopted for

building up large pressure vessels or structures by welding together smaller steel

castings.FIG 1.4 SUBMERGED ARC WELDING[REF 9]

6.Atomic Hydrogen Welding [BOOK 1]

A continuous stream of hydrogen is passed through the arc produced between two

tungsten electrodes. Due to the heat of the am, the gas dissociates from molecular to

atomic form. When the atoms of hydrogen strike the cooler work surface, they again

re-unite and emit an enormous amount of heat, thus melting the base metals that

need to be jointed. The heat input thus available is very high; hydrogen also acts

as ashield the action of atmospheric oxygen and nitrogen. Filler metal is fed

separately from a wire. This process is ideal for the repair welding of metal

moulds and dies made of alloy steels and is used for welding of thin casting in

stainless steel, aluminium alloy etc. It produes a very homogenous and smooth

joint with strength that equals that in the parent metal.


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7

FIG 1.5 ATOMIC HYDROGEN WELDING[REF 9]

7.Thermit welding[BOOK 1]

The high temperature required for melting metal to fill up the joint is

attained by employing an exothermic reaction. The method is more like a casting

process. It entails igniting in a crucible mixture of iron oxide and finely divided

aluminium in the ratio 3:1 and a special powder is used to ignite the mixture.

Due to the heat of ignition the mixture explodes at a temperature of about 1540c,

and pure iron with aluminium oxide as slag is produced:

8AL+ 3FE3O4 = 9FE + 4AL2O3

FIG 1.6 TERMIT WELDING[REF 9]

The joint crack or cavity to be filled is arranged in a sand mould with a proper

gating and feeding system and the metal from the thermit crubical is poured into

the mould. Pure metal occupices the space between the pieces to be jointed and

slag floats at the top. To enable preparations of the gating system, also in wax,

is attached. The whole assembly is embedded in moulding sand and the mould

inverted and heated to cause the wax and flow out, leaving the cavity around

the metal parts to be jointed as shown in fig.


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8

Thermit welding is employed for repairing large and heavy steel casting such as

steel mill rolls, ship stern frames, and gears . It is also used for the fabrication of

heavy units by joining relatively simple casting. The process is simpler, less time

consuming and cheaper then other methods and produces good strength and

better quality. Also, no stress relief is necessary as the cooling is very slow and

the operations it self relieves the stresses.

8. Flow welding[BOOK 1]

This entails melting the metal, in the same way as for casting purposes,

then continuously pouring the molten metal directly into the crack or cavity tobe filled, till the surrounding area also starts melting. This method is not much

favoured now as easier and quicker methods of welding are available.

9. Braze welding[BOOK 1]

This process is applied for such parts that tend to get distorted or

cracked when welded by other means. A lower heat is required as the base

metal is not actually melted and the bond is obtained only by diffusion. A

nonferrous copper base or silver base alloy which melts at a temperature above

430c is employed as filler metal. It is method may be used to make casting

watertight and to repair pipe sand pipe fittings fine cracks, crevices , porosity

etc.

FIG 1.7 BRAZE WELDING[REF 9]

10.Slodering[BOOK 1]

This is similar to brazing, the difference being in the filler metal; a tin lead

alloy which at a much lower temperature(below 430c) is preferred for soldering.

The process serves to fill up surface imperfections when high strength is not

required and porous areas in copper base alloy casting are to be made pressure

tight.


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9

11. EPOXY FILLER[BOOK 1]

Certain epoxy plastic filler can be used to fill up pinholes, blowholes, crack, etc.

and to impart enough strength to the casting. For good mechanical properties,

filler are also duly charged with metal powders to suit different cast metal. These

fillers are of two types ,viz. general purpose and fastcuring. The latter takes

hardly two hours to harden whereas the former takes longer. Smooth on

cement , which is a pasty mixture of iron filings in hardening agent, is also

widely used to repair iron casting.

12. STAIGHTENING[BOOK 1]

Deformed or warped casting can be straightened in a press by applying

pressure. This operations is possible only in the case of ductile material ,such as

steel, aluminium ,copper, and bronze. Generally , a hydraulic press along with

formed dies. Small casting can be straightened by hammering manually. Both

cold and hot pressing are used according to size and material of casting.

13. Metal Spraying [BOOK 1]

When the casting becomes undersized. it can be built up by providing a coat of metal in

die desired thickness by a metal spraying process. This isa simple and relatively

inexpensive way of forming a layer of metal on the cast surface. The sprayed metal may

be e her the same as the base metal or a dissimilar one. The deposited metal is taken in

wire form. The spray gun uses oxygen and acetylene to melt the wire and compressed

air to atomise the molten metal in the form of spray. All types of metals and alloys can

be sprayed. The bond obtained is of the mechanical type with negligible diffusion. The

joint between the parent metal and the sprayed metal is not as strong as that obtained by

welding or brazing. This technique is also used for providing an anticorrosive metal

layer on iron and steel castings. Figure explains the principle of metal spraying and Fig.

shows the set-up required for the process.

10


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FIG 1.8 METAL SPRAYING[REF 9]

2 CASTING DEFECTS [REF 8]2.1 Introduction:

A casting defect is an irregularity in the metal casting process that is undesired. Some

defects can be tolerated while others can be repaired otherwise they must be eliminated

or by changing the casting process. The defects 17ccurring in casting process mainly

are as below,

Shrinkage defect

Gas porosity

Hot tearing defect

Misruns defects

Metal penetrations defect

2.2Shrinkage defects [REF 8]

Shrinkage defects occur when feed metal is not available to compensate

forshrinkage as the metal solidifies. Shrinkage defects can be split into two different

types: open shrinkage defects and closed shrinkage defects. Open shrinkage defects are

open to the atmosphere, therefore as the shrinkage cavity forms air compensates. There

are two types of open air defects: pipes and caved surfaces. Pipes form at the surface of

the casting and burrow into the casting, while caved surfaces are shallow cavities that

form across the surface of the casting.Closed shrinkage defects, also known

as shrinkage porosity, are defects that form within the casting. Isolated pools of liquid

form inside solidified metal, which are called hot spots. The shrinkage defect usually

forms at the top of the hot spots. They require a nucleation point, so impurities and

dissolved gas can induce closed shrinkage defects. The defects are broken up

into macro porosity and microporosity (or micro shrinkage), where macro porosity can

be seen by the naked eye and micro porosity cannot.

11
http://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Shrinkage_(casting)http://en.wikipedia.org/wiki/Solidificationhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Nucleationhttp://en.wikipedia.org/wiki/Metal_castinghttp://en.wikipedia.org/wiki/Shrinkage_(casting)http://en.wikipedia.org/wiki/Solidificationhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Nucleation


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FIG 2.1 SHRINKAGE POROSITY[REF 9]

2.3 Gas porosity [REF 8]

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

occurs because most liquid materials can hold a large amount of dissolved gas, but the

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

it cools. Gas porosity may present itself on the surface of the casting as porosity or the

pore may be trapped inside the metal, which reduces strength in that

vicinity.Nitrogen, oxygen and hydrogen are the most encountered gases in cases of gas

porosity .In aluminum castings, hydrogen is the only gas that dissolves in significant

quantity, which can result in hydrogen gas porosity. For casting that is a few kilograms

in weight the pores are usually 0.01 to 0.5 mm (0.00039 to 0.020 in) in size. In largercasting they can be up to a millimeter (0.040 in) in diameter.

Gas porosity can sometimes be difficult to distinguish from micro shrinkage because

micro shrinkage cavities can contain gases as well. In general, micro porosities will

form if the casting is not properly risered or if a material with a wide solidification

range is cast. If neither of these are the case then most likely the porosity is due to gas

formation To prevent gas porosity the material may be melted in a vacuum, in an

environment of low-solubility gases, such as argon orcarbon dioxide, or under a flux

that prevents contact with the air. To minimize gas solubility the superheat temperatures

can be kept low. Turbulence from pouring the liquid metal into the mold can introduce

gases, so the molds are often streamlined to minimize such turbulence. Other methods

include vacuum degassing,gas flushing, or precipitation. Precipitation involves reactingthe gas with another element to form a compound that will form a dross that floats to

the top. For instance, oxygen can be removed from copperby addingphosphorus, or

aluminum orsilicon can be added to steel to remove oxygen. A third source consists of

reactions of the molten metal with grease or other residues in the mold.

12
http://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Hydrogen_gas_porosityhttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Superheatinghttp://en.wikipedia.org/wiki/Vacuum_degassinghttp://en.wikipedia.org/wiki/Gas_flushinghttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Phosphorushttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Hydrogen_gas_porosityhttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Superheatinghttp://en.wikipedia.org/wiki/Vacuum_degassinghttp://en.wikipedia.org/wiki/Gas_flushinghttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Phosphorushttp://en.wikipedia.org/wiki/Silicon


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FIG 1.2 GAS POROSITY[REF 9]

2.4 COLD SHOT DEFECT[BOOK 3]

These are external defects caused by two streams of metals that are too cold to

fuse properly; these can occur due to slow pouring ; poor design and small gate; and

can be controlled by the use of hotter metal using streamlined splines to give

smoother flow. In this defect small shot like spheres of metal are almost distinct

from casting.

FIGURE 1.3 COLD SHUT[REF 9]

2.5 Hot tearing[Book 3 ]

There are the crack having ragged edags due to tensile stress during

solidification. It is due to the discontinuity in the metal casting resulting from

hindered contraction,occurring just after the metal has solidfied. It is caused by

excessive mould hardness of ramming, high dry and hot strength , improper

metallurgical and pouring temperature control , provision of insufficient fillets or

brackets at the junctions of sections.

13


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Figure 1.4 Hot tearing[REF 9]

2.6 Misruns[BOOK 3]

Misruns may be present in the from of improperly filled corners and mouldcavities. There occur because of low pouring temperature, lack of fluidity of the

metal too small gates, too many resterictions in gating system etc. Another defect

called the cold shot occur when two cold streams of molten metal meet at the

junctions of a mould cavity and do not fuse together and thus the mould is not

properly filled with metal.

Figure 1.5 MISRUNS[REF 9]

2.7 Metal penetrations[BOOK 3]

It is refer to the conditions of penetrations of metal in the interstices of the

sand grains. It causes a fused aggregate of metal and sand on the surface of

casting which results in rough surface finish. It is caused by soft ramming , too

coarse mould and core sand , and excessive metal penetrations.

Figure 1.6 metal penetrations[REF 9]

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3. INSPECTIONS OF CASTING[REF 1]Inspections of casting aims at finding both surface and subsurface defects in the

casting. Inspections will ascertain the quality of the casting and result in their

acceptance or rejections. Inspections procedures and tests may be classed as

follows.

1) Visual surface inspections for foundry defects

2) Dimensional Inspections

3) Non Destructive type

4) Destructive type

3.1 Visual surface:[REF 1]

Visual inspection refers to an NDT method which uses eyes, either aided or non-aided todetect, locate and assess discontinuities or defects that appear on the surface ofmaterial undertest (Fig).Ifis considered as the oldest and cheapest NDT method. It isalso considered as one of the most important NDT method and applicable at allstages of construction or manufacturing sequence. In inspection of any engineeringcomponent,

if visual inspectional on is found to be sufficient to reveal the required informationnecessary for decision making, then other NDT methods may no longer considerednecessary.

FIG 3.1 VISUAL SURFACE[REF 1]

Visual inspection is normally performed by using naked eyes. Its effectivenessmay be improved with the aid of special tools. Tools include fiberscopes, borescopes,magnifying glasses and mirrors. In both cases, inspections are limited only to areasthat can be directly seen by the eyes. However, with the availability of moresophisticated equipment known as borescope, visual inspection can be extended to coverremote areas that under normal circumstances cannot be reached by naked eyes.Defects such as corrosion in boiler tube, which cannot be seen with naked eyes caneasily be detected and recorded by using such equipment.


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15

Although considered as the simplest method of NDT, such an inspection must be carriedout bypersonnel with an adequate vision. Knowledge and experience related tocomponents are also necessary to allow him to make correct assessment regarding the

status of the components.

Advantages:

Cheapest NDT method

Applicable at all stages of construction or manufacturing Do not require extensive training Capable of giving instantaneous results

Limitation:

Limited to only surface inspection Require good lighting Require good eyesight

3.2Dimensional Inspections [REF 2]

Dimensional control is usually required for all types of

castings. Sometimes it is not so critical but at other times it may be vital. When

precision castings are produced by processes such as investment casting, shell

moulding and die casting, dimensions Trod to be closely checked. Initially, when the

castings are made from a new pattern, a few sample castings are first made which are

carefully checked with the drawings to ensure that the sizes obtained conform to those

specified and will be maintained within the prescribed tolerances in the lot under

production. On testing of the sample lot, deviations from the blueprint are rectified on

the pattern equipment. When the castings are found to be consistently within the

tolerances, spot checks, together with a regular check of the patterns and dies being

used, may be sufficient. In the case of the jobbing type of foundry, each casting

produced may be different and, therefore, according to the customer's requirements,

each one may have to be thoroughly inspected for dimensional variations. Dimensional

inspection of castings may be conducted by various methods:

3.2.1 Standard Measuring Instruments to Check the Sizes[REF 2]

Instruments such as rule, vernier callipers,vernier height gauge, vernier depth

gauge, micrometers, scribing block, combination set, straight edge, squares. spirit level,

and dial indicator are commonly used. For high precision castings or after machining,

more advanced measuring instruments, such as auto-collimator, comparator, ultrasonic

instruments tor measuring wall thickness and projection instruments are also required.

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3.2.2 Templates and Contour Gauges for the Checking of Profiles, Curves, and

Intricate Shapes [REF 2]

Templates act as time-saving aid in measurement and facilitate the

entire job. These can be easily prepared in mild steel or brass sheet by marking out, and

cutting and finishing the profile that is required to be checked on the castings.

3.2.3 Limit Gauges [REF 5]

For toleranced dimensions on casting produced on a repetitive basis, limit

gauges are usually. The type of limit gaugesthe plug, ring, snap, plate, etc.depends

on the shape of the parameter to be checked. Periodical checking and maintenance of

limit gauges is very important

3.2.4 Special Fixtures [REF 3]

Special fixtures are required to be designed and used where dimensionscannot be conveniently checked by using instruments, for instance, during the checking

of locations, relative dimensions, centre-to-centre distance, angularity of surfaces, and

so on.

3.2.5Coordinate Measuring and Marking Machine (CMM) [REF 5]

This machine is very useful for measurement and inspection of

uneven, undulated, irregular, or curved surfaces which cannot be conveniently or

accurately checked by other measuring tools or instruments. The accuracy of

measurement of these machine ranges from 0.01 mm to 0.05 mm. Besides measuring, it

can be used for marking purposes also in all three dimensions on metallic or non-metallic surfaces. Measurement and marking are accomplished easily without errors in

reading in all three dimensions. Once the machine is set, all measurements can be

carried out in a programmed sequence automatically. The machine in reality is a multi-

axial device providing measurement of output of position and displacement sequentially

without a need for changing tools.

The machine essentially consists of a touch probe, usually having a ruby tip, which is

mounted on a horizontally sliding arm, movable vertically along a column. The column,

is fixed to a base which in turn is held on a large accurately machined granite surface

plate and is movable in a direction perpendicular to the direction of be movement of

arm. Thus, the probe is capable of being moved along all three u for carrying out

measurement of different surfaces of a workpiece. The sliding movements of arm and

column are performed with great precision and are read on m electronic digital read out

unit, attached to the machine. When marking is to be lone on surfaces, a scriber is used

in place of a probe. A larger variety of probes, scribers and other accessories are

available to enable the machine to be highly flexible and accurate in operation. The

movements along the three axes may be manual or motorised. The machine can be

further equipped with a small computer system for processing the data obtained from

measurement and for storing and retrieving the same. A special software is also

available with the computer so that measurement and inspection of different types of

surfaces can be carried out automatically without the need for manual control.17


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The drawing data from CAD station an be also transmitted to this machine by inter-

linking the two systems with the actual value of dimensions. A printer can also be

provided with the computer for producing & hard copy of the inspection report.

The CMM machines are now getting increasingly popular in inspection departments

attached to tool rooms, pattern and die shops, foundry and forging shops, press shops,welding and structural shops and plastic and glass parts manufacturing units. The

appraisal of surface roughness or finish is required in addition to the dimensional

measurement. Surface roughness is expressed as a number (in microns), which is an

arithmetical average of the heights of the peaks and depths of the valleys on a casting

surface above and below a mean line within a specified sampling length. IS: 3073-1967

provides a method for assessing the surface roughness by this system. The approximate

values for different types of castings are specified

Surface roughness is evaluated approximately, as is usually

sufficient for castings, by surface roughness comparison standards, where the given cast

surface is compared visually or with the aid of a magnifying lens with a set of standards

duly marked with varying surface roughness values. For finished surfaces and moreprecise measurements, electrical type of direct reading, surface measuring instruments

or profilometers, such as Talysurf, are used.

3.3 Non destructive testing[REF 6]

Non-destructive testing (NDT) is a noninvasive technique for determining the integrityof a material, component or structure. Because it allows inspection without interferingwith a product's final use, NDT provides an excellent balance between quality controland cost-effectiveness.

The main goal of NDT is to predict or assess the performance and service life of acomponent or a system at various stages of manufacturing and service cycles. NDT isused for quality control of the facilities and products, and for fitness or purposeassessment (so-called plant life assessment) to evaluate remaining operation life of

plant components (processing lines, pipes and vessels).

NDT inspection of industrial equipment and engineering structures is important inpowergeneration plants, petroleum and chemical processing industries, and transportationsector. State-of-the-art methodology is applied to assess the current condition, fitness-for-service, and remaining lifeof equipment. NDT inspection provides basic datahelping to develop strategic plans for extending plant life.

NDT life extension and life assessment services include:

Equipment integrity analysis Corrosion monitoring of structures and equipment

Corrosion damage evaluation Fatigue and creep damage prediction Fitness-for-service evaluation

18


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The long list of NDT methods and techniques includes: radiographic testing (RT),ultrasonic testing (UT), liquid penetrant testing (PT), magnetic particle testing (MT),eddy current testing (ET), visual testing VT as well as leak testing LT, acousticemission AE, thermal and infrared testing, microwave testing, strain gauging,holography, acoustic microscopy, computer to mography, non-destructive analyticalmethods, non-destructive material characterization methods and many more.

The major four (or basic) NDT methods, which are largely used in routine services toindustryare:

Liquid penetrant testing

Magnetic particle testing

Radiography Ultrasonic testing

3.3.1 Radiography[REF 6]Radiography is an NDT method, which uses penetrating radiation. It is based ondifferential absorption of radiation by the part under inspection. In this inspection thesource of radiation can be from radioactive sources, typically Irridium-192, Cobalt-60,Caesium-137, which emit gamma rays orfrom a specially built machine that can emitX rays. The former is known as gamma radiography whereas the latter is referred asX ray radiography. Table I presents major radioisotope sealed sources largely used ingamma radiographic testing.

There are many methods of NDT, but only a few of them examine the volume ofa specimen; some only reveal surface-breaking defects. One of the best established andwidely used NDT methods is radiography the use of X rays and gamma rays to

produce a radiograph of a specimen, showing any changes in thickness, defects (internaland external), assembly details etc.

Radiographic testing (RT) method can be used in civil engineering equipmentsnotably to verify the integrity of pre-stressed wires in a pre-stressed concrete structure

by using radioisotope sealed sources, X ray machines or linear accelerator. Table Ipresents the main radioisotope sealed sources used for gamma radiography. Figure 9shows a typical set up in radiographic testing and figure 10 presents a radiographicimage of a metallic structure.

FIG 3.2 RADIOGRAPHY[REF 2]

19


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During the radiography X rays or gamma rays penetrate through material underinspection. While traversing through the material, these radiations experiencemodification by the internal structure of the material through absorption andscattering processes. If the internal structure is homogeneous, the absorption andscattering processes would be uniform throughout the material and radiations thatescape from the material would be of uniform intensities.

These radiations are then recorded by a suitable recording medium, typicallyradiographic film. When the film is processed, a uniform dark image will appearon the film that indicates the homogeneity of the material tested. The situation isdifferent for cases of materials containing discontinuities or different in thickness. Ingeneral, the absorption of radiation by a material depends on the effective thicknessthrough which the radiations penetrate.

Discontinuities such as cracks, slag inclusions, porosity, lack of penetration and lack offusion reduce the effective thickness of the material under test. Thus, the presence ofsuch discontinuities causes radiations to experience less absorption as compared with

those in areas with discontinuity. As a result, in areas containing discontinuities moreradiations escape, recorded by the film and forming a dark image that represents theinternal structure of the material.

The appearance of radiographic images depends on the type discontinuities encounteredby the radiation. Cracks for example will produce a fine, dark and irregular line, whereasporosities produce dark round images of different sizes.

Some discontinuities that presence in a material such as tungsten inclusion in steel has ahigher density than its surrounding. In this case, the effective thickness that needs to

be traversed by radiation is somewhat greater. In other words, more radiation isabsorbed in this area as compared with other areas. As a result the intensity of

radiation that escaped after traversing this area will be lesser than that for other areasgiving a lighter image bearing the shape of tungsten inclusion inside the material.

Radiography is widely used throughout the industry. Its capability to produce two-dimensional permanent images makes it as one of the most popular NDT methodsfor industrial application. However, radiation used for radiography presents a

potential hazard to radiographers as well as members of public. Due to itshazardous nature, the use of radiation, including for industrial radiography isstrictly controlled by Regulatory Authorities.

Almost all countries throughout the world have their own Regulatory Body thatregulates the use of radiation. Requirements imposed by the Authority upon the use of

this method make it as one of the most expensive NDT method.

Advantages and limitations of this method are as follows:

Advantages

Applicable to almost all materials Produce permanent images that are readily retrievable for future reference Capable of detecting surface, subsurface and internal discontinuities

Capable of exposing fabrication errors at different stages of fabrication Many equipment are portable

20


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Limitations Radiation used is hazardous to workers and members of public

Expensive method (cost of equipment and other accessories related toradiation safety are relatively expensive)

Incapable of detecting laminar discontinuities

Some equipment are bulky For X ray radiography, it needs electricity Require two sides accessibility (film side and source side)

Results are not instantaneous. It requires film processing, interpretation and evaluation Require highly trained personnel in the subject of radiography as well as radiationsafety.

Organizations applying this method need to be licensed and subjected tovarious rule and regulation.

3.3.2Magnetic partical inspections:[REF 4]

Magnetic particle testing (MT) is a NDT method that utilizes the principle of

magnetism. Material to be inspected is first magnetized through one of many waysof magnetization. Once magnetized, a magnetic field is established within and in thevicinity of the material. Finely milled iron particles coated with a dye pigment are thenapplied to the specimen. These magnetic particles are attracted to magnetic fluxleakage fields and will cluster to form an indication directly over the discontinuity.They provide a visual indication of the flaw.

The presence of surface breaking and subsurface discontinuity on the materialcauses the magnetic field to leak and travel through the air. Such a field is calledleakage field. When magnetic powder is sprayed on such a surface the leakage fieldwill attract the powder, forming a pattern that resembles the shape of the discontinuity.

This indication can be visually detected under proper lighting conditions

FIG.1.3 Magnetic field lines and magnetic particles influenced by a crack.[REF 4]

There are many methods of magnetizing materials. The use of permanent magnet is oneof the ways of magnetization. However, in many cases the use of electromagnet isconsidered as a more superior and effective way of magnetization. Another way ofcreating magnetic field in a material is by the use of coil carrying current.

21In this way, a longitudinal magnetic field would be able to be established in long items


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such as bars and cylinders. Circular magnetic field on the other hand is produced byallowing current flowing along the cylindrical material. Induction of magnetic fieldinto the material to be inspected can be achieved by the use of either alternating current(AC) or direct current (DC). In general the use of DC would produce magneticfield deeper below that surface that allow subsurface discontinuity to be detected.

Discontinuities can be best detected when the direction of magnetic field isperpendicular. The chance of detection reduces as the angle between the magnetic fieldand the plane of defect decreases.

When the angle between the magnetic field and the plane of defect is zero, i.e. themagnetic field is parallel with the plane of defect then the chance of detection becomeszero.

The application of MT involved the following sequence:

Pre-cleaning Magnetization Application of magnetic powder

Demagnetization

The advantages and limitations of using MT method are as follows:

Advantages Inexpensive

Equipment are portable Equipment easy to operate

Provide instantaneous results

Sensitive to surface and subsurface discontinuities

Limitations

Applicable only to ferromagnetic materials Insensitive to internal defects

Require magnetization and demagnetization of materials to be inspected Require power supply for magnetization

Coating may mask indication Material may be burned during magnetization

3.3.3 LIQUID PENETRANT TESTING [REF 3]

Liquid penetrant is an NDT method that utilizes the principle of capillaryaction in which liquid of suitable physical properties can penetrate deep intoextremely fine cracks or pitting that are opened to the surface without beingaffected by the gravitational force. Liquid penetrant testing (PT) methodconsists in depositing on the object surface of a special liquid, which will

be drawn into any surface defect by capillary action. A liquid with highsurface wetting characteristics is applied to the surface of the part andallowed time to seep into surface breaking defects (Fig.). Followingremoval of excess penetrant an

22

FIG. 3.4 Liquid penetrant testing principle[REF 3]


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application of a developer reverses the capillary action and reveals thepresence of the flaw so that it can be visually inspected and evaluated. ThePT method can be used on metallic parts of civil engineering equipments.Liquid penetrant inspection generally involved the following sequence:

Pre-cleaningAt this stage, surface of the inspected item is cleaned to avoid the presence of any dirt thatmay close the opening of discontinuity. Cleaning is accomplished by various

methods such as vapor cleaning, degreasing, ultrasonic cleaning etc.

Penetrant applicationOnce the surface is cleaned, penetrant either in the form of dye penetrant orfluorescence penetrant is then applied. The application of penetrant can be achievedeither by dipping, spraying or brushing depending on the nature or item to be inspected.This penetrant is then allowed to remain on the surface for some duration. Such durationis termed as a dwell time. During this period, if there is any discontinuity, penetrant will

penetrate deep into it.

Removal of excess penetrant

Excessive penetrant need to be removed from the surface to allow inspection to be made.Such removal can be achieved by applying water, proper solvent or emulsifierfollowed by water (depending on the type of penetrant used) on the surface. At thisstage, all unwanted penetrant will be removed from the surface, leaving only those trappedinside the discontinuity.

Developer applicationDeveloper is then applied to the surface of the inspected item. This developer either in theform of dry powder or wet developer acts as a blotting paper which draws penetrant out ofthe discontinuity.

In doing so, penetrant will bleed to form an indication whose shape depends uponthe type of the discontinuity presence in the material. Such an indication is recordedeither by the application of a special tape or by taking its photograph.

Post-cleaningApplication of penetrant and developer causes the surface to be contaminated.Thus, upon completion of the inspection, it is important for the item to be cleaned sothat no corrosive material remains on its surface that may affect its serviceability.

23

As for other NDT methods, liquid penetrant has its own advantages and limitations.


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Advantages: Simple to perform

Inexpensive Applicable to materials with complex geometry

Limitation Limited to detection of surface breaking discontinuity

Not applicable to porous material Require access for pre- and post-cleaning Irregular surface may cause the presence of non-relevant indication .

3.3.4ULTRASONIC TESTING [REF 6]

As the name implies, ultrasonic refers to an NDT method, which uses soundshaving frequencies beyond those audible by human ears. Sounds having frequencies

about 50 kHz to 100 kHz are commonly used for inspections of nonmetallic materials,whereas those with frequencies between 0.5 MHz up to 10 MHz are commonly used forinspections of metallic materials.

Ultrasonic testing (UT) method uses high frequency sound waves (ultrasounds) tomeasure geometric and physical properties in materials. Ultrasounds travel in differentmaterials at different velocities. The ultrasound wave will continue to travel throughthe material at a given velocity and does not return back unless it hits a

FIG.3.5. Principle of ultrasonic testing.[REF 1]

reflector. Reflector is considered any boundary between two different materials, or a

flaw. The ultrasound generator (transducer) emits waves and in the same positionreceives reflected sounds (if any). Comparing both signals (emitted and reflected) the

position of the defect and its size can be measured. The UT can be used on civilengineering equipments, outside metallic parts, to verify the granulation of roadcovering or of concrete.

High frequency sound waves are introduced into a material and they are reflected backfrom surfaces or flaws. Reflected sound energy is displayed versus time, and inspectorcan visualize a cross section of the specimen showing the depth of features that reflectsound.

24

As in the case of radiography, ultrasonic is an NDT method that is used for detectinginternal discontinuity. In ultrasonic inspection, sounds are generated by the usetransducers that are made of materials exhibiting piezoelectric effect. Materialsexhibiting piezoelectric effect are capable of converting electrical energy into sound


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energy and vise versa. Typical example of such a material is quartz. When a quartzcrystal is cut in certain orientation and thickness it is capable of generating soundsappropriates for ultrasonic inspections. Depending upon the orientation of crystalcutting, sounds generated by quartz can be of the longitudinal or transverse modes.Figure 10 shows ultrasonic testing in laboratory.

During the inspection, sound generated by a transducer is transmitted into thematerial to be inspected via couplant. This sound travels in the material with a speedthat depends on the type of material. For example, longitudinal waves travel atspeeds of 5960 m/s and 6400 m/s in steel and aluminum respectively. When there isno discontinuity in the material, sound continues to travel until it encounters the

backwall of the material.

At the backwall, sound is reflected and continues to travel until it reaches the transducer.At this transducer, piezoelectric converts sound energy into electrical pulse. The pulseis then amplified and presented on the screen as a backwall signal or backwall echo (Fig.12).

However, if there is a discontinuity in the material, a portion of sound energy is reflectedby this discontinuity whereas another portion continues to travel until it reaches backwalland reflected. Under these circumstances, a portion of sound that was reflected by thediscontinuity reaches the transducer first and followed by those reflected by the backwall. In both cases sound energies areconverted into electrical signals which then are displayed on the ultrasonic flawdetector screen as backwall signal and signal due to discontinuity. By properlycalibrating the equipment, both the position of discontinuity with respect to the

position of backwall and the size of discontinuity can be determined.

The fact that ultrasonic does not present any potential hazard to the operator makes this

method as a good competitor for radiography method. However, highly skillful andexperience operators are required to allow correct interpretation of the test results.Unlike in the case of radiography where the results are presented in the pictorial forms,results of ultrasonic inspections are purely in the form of electrical signal. Knowledgeabout the material, correct movement of the transducer and proper time base calibrationis absolutely necessary for correct assessment of the test results.

More sophisticated ultrasonic equipment is currently available which allowresults to be presented in 2D or 3D dimensions. This development provides greaterstrength to ultrasonic method in its rivalry against radiographic method.

The advantages and limitations of ultrasonic methods are as follows:

Advantages

Requires only one side accessibility Capable of detecting internal defect

Not hazardous Applicable for thickness measurement, detection of discontinuity, anddetermination of material properties

25 Can provide the size of discontinuity detected

Very sensitive to planar type discontinuity Suitable for automation Equipment are mostly portable and suitable for field inspection


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Applicable for thick materials

.Limitations

Not capable of detecting defect whose plane is parallel to the direction of sound beam Require the use of couplant to enhance sound transmission

Require calibration blocks and reference standards Require highly skillful and experience operator Not so reliable for surface and subsurface discontinuity due to interference betweeninitial pulse and signal due to discontinuity.

3.4 Destructive type[REF 7]

There are two type of the this part. It is also know as the mechanical

properties.

1) Tensile testing

2) Hardness testing

3.4.1Tensile testing [REF 7]

Most materials are generally supplied to a mechanical property specification. This

usually involves data on tensile strength and ductility. Tensile strength is a measure of thematerials ability to withstand a load under tension. Ductility is a measure of thematerials ability to be permanently stretched, again under tension.

The most common method used to determine tensile strength and ductility is thetensile test. This involves preparing a specially shaped standard test piece that has no

sudden changes in cross-sectional area and then pulling it carefully in one direction

with a continuously increasing load. The test-piece may be round or rectangular in

cross section, depending upon the shape of the bulk material; for

example, samples with rectangular cross sections are prepared from sheet material. In

both cases, the central portion of the test piece is reduced in section to form a gauge

length. The reduced section helps to ensure that fracture, when it occurs, does so

within the gauge length rather than within the grips where surface imperfections may

induce premature failure.

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FIG 3.6 TENSILE TESTING[REF 7]

The extension is measured and plotted against load producing a load / extension

curve, as illustrated in FIG.

The curve has several distinct sections.

0 A where the extension is linearly proportional to load. Point A is the limit ofproportionality.

A B extension non linearly proportional to load. The extension from

O B is elastic deformation, and point B is the elastic limit.

B C the extension is non linearly proportional to load, and is plasticdeformation uniformly distributed along the length.

C D extension is plastic but localised.

27

FIG 3.7 TENSILE TESTING

27

The point B is important as it marks the change from elastic to plastic behaviour. It can


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be difficult to locate on the curve, as the change can be gradual. To overcome this a point

is added to the curve at X. X is found by measuring a distance Y, along the extension

axis and drawing a line parallel to OA. The intersection of this straight line with the

curved line is not open to interpretation error. The generally used value for Y is 0.2% of

the original length under test.

The load L1 associated with X, divided by the original cross sectional area, gives the

0.2% proof stress for the material.

Similarly L2 divided by the original cross sectional area gives the tensile strength.

The elongation is given by the total extension divided by the original length (thegauge length) presented as a percentage.

It should be noted that stress is defined as the load per unit area(for example, expressed in units of MPa);

- strain is the extension of the gauge length divided by the original gauge length(expressed as a fraction).

In the linear elastic part of the load - extension curve, O A in there is negligible

change in the cross-sectional area of the sample, so we may say that the ratio of stress to

strain is a constant, that is :

stress / strain = a constant (E) , known asYoungs Modulus.

The springiness of a material (its stiffness) is indicated by its Youngs modulus. For

most aluminium alloys, irrespective of their metallurgical conditions, the value ofYoungs Modulus is close to 68 GPa ( for the special case of

lithium-containing alloys, where there is a significant increase in stiffness).

The part of the load-extension curve given by C D in represents

incipient fracture. Appreciable necking of the sample occurs, leading to fracture.

Note that a progressive reduction of cross-sectional area occurs in the necking region;

the stress (ie the load per unit area) continues to increase, even though the total load

decreases.

The ratio of the cross-sectional area of the fracture surface to that of the original

cross-sectional area is known as the reduction in area , usually expressed asa

percentage.

28

3.2.2 Hardness Testing[REF 7]


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Hardness testing is a relatively quick and easy way to assess the strength of a material

without the need to prepare tensile test samples. For example, it may be a convenient way

of investigating the progress of precipitation hardening.

The majority of commercial hardness testers force a small hard metal or ceramic

sphere, diamond pyramid or diamond cone into the body of the metal under test bymeans of an applied load, and a definite hardness number is obtained from thedimensions of the indentation so formed. In practice, the dimension of the indent is

referred to a set of values defined in a hardness index chart. Hardness then may be

defined as resistance to permanent deformation, and a hardness test can often be

considered as a rapid non-destructive estimation of the plastic deformation behaviour

of metals.

Small indenters are used for microhardness testing, with a special instrumentequipped with an optical microscope to view the micro-indent. This provides a very

valuable technique for investigation of the relative hardnesses of phases within a

microstructure.

Although the term hardness is a comparative consideration of great engineering

importance, it is not considered to be a fundamental property of matter. The index of

hardness is a manifestation of several related properties of the metal, which may well

include a combined effect of yield point, tensile strength, ductility, work-hardening

characteristics and resistance to abrasion.

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4.0 CONCLUSIONS

The biggest issue that was raised in the simulation of foundry problems was the lack of

consistent process information which appears to be inherent in the foundry industry.

The response from the foundry, although delighted by their reduction of scrap, was

disappointment in the inability of the software to predict the occurrence of the defects

or to define the conditions which caused the defects.

The main conclusions that can be drawn from this study are:

By using simulation software intelligently it is possible to help foundries reduce

scrap rates even for defects which cannot be predicted.

The boundary conditions used to represent the process at the foundry are of

extreme

importance and must be assessed critically.

The difference between changing boundary conditions in reality and static

boundary conditions in the models gave rise to some discrepancies and an

inability to predict some defects.

More work should be performed in defining the mechanisms and or new modelsfor a wider range of defects than is currently possible.

MAGMAsoft has been validated to be able to produce reliable simulation

results that actually reflect the real castingphenomena. The results signify the

validity of using MAGMAsoft to perform mold design and casting

processsimulation. The results of mold filling and solidification would be of

high fidelity that can be relied upon to make decisions on designing the mold,

feeder, sprue, runner and gating system as well as setting the casting process

parameters to achieve the desired casting quality. The success of this validation

alsoserves as a milestone to further utilize and explore the application of

MAGMAsoft not only on sand casting, but also on gravity die casting, lowpressure die casting and high pressure die casting

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REFERENCE

1) INTERNATIONAL ATOMIC ENERGY AGENCY, Guidebook on Non-destructiveTesting of Concrete Structures, IAEA Training Course Series No. 17 (2002).

2) INTERNATIONAL ATOMIC ENERGY AGENCY, Training Guidelines in Non-

destructive Testing Techniques 2002 Edition, IAEA-TECDOC-628/Rev. 1, Vienna

(2002).

3) INTERNATIONAL ATOMIC ENERGY AGENCY, Development of Protocols for

Corrosion and Deposit Evaluation in Pipes by Radiography, IAEA-TECDOC-1445,

Vienna (2005).

4) MALHOTRA, V.M., 1984. In Situ Non-destructive Testing of Concrete."American Concrete Institute (ACI), Publication SP-82. 1984, 825 pp.

5) MALHOTRA, V.M., AND SIVASUNDARAM, V., 1991. CRC Handbook onNon-destructive Testing of Concrete: Resonance Frequency Methods. CRC press,

editors, V.M. Malhotra, N.J. Carino, pp. 147-168.6) MINDESS, SIDNEY. 1991. CRC Handbook on Non-destructive Testing ofConcrete: Acoustic Emission Methods.CRC press, editors, V.M. Malhotra, N.J. Carino,

pp. 317-334.

7) Prepare by M.H.Jacobs interdisplinary research centre in material the university of

Birmingham,UK.

8)http://www.espint.com/engineering/technical-reference-

guides/default.aspx by dr.jerry thiel

9) Googleimage.com

BOOKS

1) PRINCIPLES OF FOUNDRY TECHNOLOGY BY P. L. JAIN

2) A TEXT BOOK OF FOUNDRY TECHNOLOGY BY O.P.KHANNA

3) PRODUCTIONS TECHNOLOGY BY R.K .JAIN

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http://www.espint.com/engineering/technical-reference-guides/default.aspx%20by%20dr.jerryhttp://www.espint.com/engineering/technical-reference-guides/default.aspx%20by%20dr.jerryhttp://www.espint.com/engineering/technical-reference-guides/default.aspx%20by%20dr.jerryhttp://www.espint.com/engineering/technical-reference-guides/default.aspx%20by%20dr.jerry

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