A Primer on Ferrous Foundry Practice & Metallurgy by Rajendra Prasad.G.M. - HTML preview

PLEASE NOTE: This is an HTML preview only and some elements such as links or page numbers may be incorrect.
Download the book in PDF, ePub, Kindle for a complete version.

INTRODUCTION

I deliver lectures on the following topics for practicing foundrymen, design

engineers and some engineering college teachers.

The topics I handle are:

1) Metallurgy for Non-Metallurgists.

2)Methoding of Steel and S.G. Iron castings

3)Steel and S.G. Iron foundry practice.

As is my wont I start my classes by asking a very ,very simple question.

“ WHAT IS ENTROPY” Believe me till date, in my last 35 years, I have not

met a person who has given the CORRECT answer including most of my

teachers. The word entropy has got philosophical overtones.

Invariably the answer given was / is ENTROPY IS DEGREE OF DISORDER

Or ENTROPY IS DEGREE OF RANDOMNESS. As far as I am concerned

they are not only silly answers but WRONG answers.

The word “ENTROPY” comes from 2nd law of Thermodynamics, which in turn

had it’s origin in Physics.

The above kind of answers are like saying that man is “SICK”. Sick of what ?

Has got AIDS, cancer, arthritis, ulcer etc.

Above answers for ENTROPY are so slimy and slippery, you can never make

use of it. Besides that Thermodynamics is a QUANTIFIABLE Science and not

a QUALITATIVE SCIENCE.

If a Mechanical, Metallurgical and a Chemical engineer, who studies

THERMODYNAMICS as a part of HIS course, is unable to define ENTROPY,

properly, he is not an engineer worth his salt.

Before I explain ENTROPY to you, let me tell you categorically, in

unambiguous terms, with out any vestige of doubt, ENTROPY decides your

growth, development and progress. Man who taught me ENTROPY is not an

ENGINEER or SCIENTIST but A FINANCE MAN by name JEROMY

RIFKIN. JEROMY RIFKIN wrote a book entitled “ENTROPY—A WORLD

VIEW.”

It is out of print now. Those of you who would want to get this book now, will

have to look for those groups who are in the business of selling old books in

USA.

(IT IS ORIGINALLY PRINTED BY BANTOM BOOKS,USA )

Let us get into explanation of ENTROPY.

In 1970-75, there was a motorbike called “ JAWA”, it used to give a mileage or

Should I call it a kilometreage of 25km per litre of petrol.

There after came a motorbike called as ‘RAJDOOT’, which used to give us a

mileage of 45 Km per litre of petrol.

Then came a motorbike called ‘YAMAHA-CRUX’ Which gives a mileage of

9

74 Km per litre of petrol.

Now let us look at it this way, in a matter of 15 years mileage went up from

25 Km to 74 Km per litre of petrol. HOW MUCH MORE IT CAN GO ?

Now a days there are vehicles which claim a mileage of 110 Km per litre.

Now we have come from 25 to 110 Km per litre of petrol. It is almost 4 times

the Our first value of 25 Km per litre of petrol.

One litre of petrol has 9100 Kilocalories of heat energy. First law of

thermodynamics states that energy can neither be created nor destroyed, it can

only be converted from one form to another.

If we convert 9100 KCal of heat energy to work energy, for a weight of 150 Kg

(100 Kg-motor-bike weight + 50 Kg is the man’s weight ) One litre of petrol

should give 180 Km per litre at 100 % efficiency.

.

Let us look at one vehicle after an other.

JAWA--------180—25 = 155 Km

Total available energy is 180 Km per litre of petrol.

What is made use of is only 25 Km.

Achievable energy – achieved energy = A MEASURE OF ENTROPY

180 Km –25 Km = 155 Km (unachieved energy) ENTROPY—JAWA.

180 Km –45 Km = 135 Km (unachieved energy)ENTROPY----RAJDOOT

180 Km –74 Km = 106 Km (unachieved energy)ENTROPY-----CRUX

180 Km –110 Km = 70 Km (unachieved energy) ENTROPY----PRESENT

DAY VEHICLES.

If you look at the UNAVAILABLE ENERGY, it has come down from 155 Km

to 70 Km. THIS IS ENTROPY.IS’T THIS A PROGRESS AND

ADVANCEMENT. IT IS THIS ENTROPY,WHICH SETS US THE

DIRECTION IN WHICH WE CAN PROGRESS.

IN OTHER WORDS,WHAT WAS HITHERTO UNAVAILABLE ENERGY

IS CONVERTED TO AVAILABLE ENERGY.REDUCING ENTROPY IS

EQUIVALENT TO IMPROVEMENT IN ENERGY EFFICIENCY.

Now do you understand that ENTROPY is not a slippery or a slimy term like

DEGREE OF DISORDER OR DEGREE OF RANDOMNESS. It is a perfectly

a quantifiable term.

IDEALLY SPEAKING IF ENTROPY BECOMES ZERO,SYSTEM CANNOT

BE IMPROVED UPON FURTHUR.THAT IS THE DEAD-END.

Now let us talk of ENTROPY OF DEED. This is the difference between what

You are capable of achieving and what are you actually achieving. If this

happens to be negative, then there is ENTROY at play and you have ample

scope to improve on your achievement. Thus reducing ENTROPY.

This can be partly achieved by employing the principles of “OPERATIONAL

RESEARCH”, a subject in MANAGEMENT and MATHAMATICS. This is a

10

A case of “OPTIMISATION”

ENTROPY OF THOUGHT: Here you have no one to guide you, except

your own EFFORTS towards SELF-IMPROVEMENT.

Every day identify some thing about which you don’t know anything.

Animals can’t do this, only HUMAN BEINGS can do it. Then, is it not the time

you started? There is a saying “WHERE THERE IS A WILL,THERE IS A

WAY”

You know as to how much weight you can lift.

You know as to how much you can eat.

You know as to how far you can see.

You know as to from how far you can hear.

BUT DO YOU KNOW AS TO WHAT YOUR MIND CAN DO OR CAN NOT

DO ? HENCE THINK INTENSELY.

Now you will realise what is the POTENTIAL of MIND.

My dear friend you have only one OPTION,THINK—THINK INTENSELY.

To close this chapter, I will give you an other example on ENTROPY.

If you have a savings bank account in a bank with cheque facility, willy-nilly,

you have to keep a minimum balance of Rs 1000. If you have a balance of

Rs 20000 in your account, you can withdraw only Rs 19000 and leave Rs 1000

untouched. Don’t you think that THIS Rs 1000 is ENTROPY as it is your

money and yet it is not available to you.

Before I close, I want to tell you some thing.

Any subject ( CURRICULAM) will have about 15 chapters.---100 %

In examination they give about 8 Questions covering about 10 chapters—66 %

You are asked to answer 5 Questions, if all of which will fetch FULL MARKS

You will get 100 %----------------------------------for 33 % of the subject

If you are a just first class student ( 60 % )-----for 20% of the subject.

THINK & REFLECT ON IT.

TOPICS COVERED

1. PATTEREN

2. METHODING

3. MELTING

4. SAND PLANT

5. MOULDING

6. MOULD FINISHING

7. POURING

8. KNOCK OUT

9. FETTLING

10. HEAT TREATMENT

11. INSPECTION & TESTING

12. MANAGEMENT & LAYOUT

13. FERROUS METALLURGY

11

ABBREVIATIONS USED

UTS

ULTIMATE TENSILE STRENGTH IN

Kg / mm2

YS

YIELD STRENGTH IN Kg / mm2

%E

PERCENTAGE ELONGATION

%RA

PERCENTAGE REDUCTION IN

AREA

BHN

BRINNEL HARDNESS NUMBER

Ra

ROCKWELL HARDNESS-A Scale

Rc

ROCKWELL HARDNESS-C Scale

Mc

MODULUS OF THE CASTING

Mf

MODULUS OF THE FEEDER

Mn

MODULUS OF THE NECK

B.C.C

BODY CENTERED CUBE

F.C.C

FACE CENTERED CUBE

B.C.T

BODY CENTERED TETROGONAL

DEGREES

DEGREES CENTIGRADE

M.P

MELTING POINT

Cp

SPECIFIC HEAT

L.H

LATENT HEAT

K

THERMAL CONDUCTIVITY

Dm

DECIMETRE ( 100 mm )

Psi

POUNDS PER SQUARE INCH

TOUGHNESS

HIGHER VALUES OF %E,%RA

&IMPACT STRENGTH

IMPACT STRENGTH STRENGTH OBTAINED ON HIGHER

RATE OF LOADING

A

ANNEALING

N

NORMALIZING

AQ

AIR QUENCHING

OQ

OIL QUENCHING

WQ

WATER QUENCHING

T

TEMPERING

12

Metals can be Rolled, Forged & Cast.

When your mother takes a dough of wheat flour and water, gives a round shape

with a wooden round piece, it is ROLLING

When a blacksmith heats a long piece of metal and hammers it, it is called

FORGING.

During Chrismas and Makara Sankranthi, people distribute toy like things

made of sugar to children. A slurry of sugar and water or milk is made and this

slurry is poured into wooden dies(whose inside shapes can be a horse, elephant

or any shape of your choice).This slurry is allowed to dry for while in the die

itself for while till it attains some amount of strength for handling, there after

it is dried in SUN LIGHT so that it becomes strong enough. Here a liquid

sugar syrup has become solid.

Now let us see the differences between Rolling, Forging and Casting.

Rolling and Forging are the operations made in solid state of Metal to

change the shape of the metallic piece into desired shape.

For example ,your M.S. sheet is a Rolled product, the steel hammer you use

for driving a nail into a wall is a Forged product. As these operations are done

in solid state, you can’t get complex shapes.

In casting, a metal is melted and poured into a container, whose shape it will

take. Remember your horse, elephant made out of sugar syrup.

In case of Casting, metal is melted and molten metal is poured into a

container Whose shape is pre-determined. This liquid metal is allowed to

solidify to become solid in the container.

Casting is an old art but an young Science. Even now there are several things

in castings about which we don’t know much.

So it is very essential to keep your mind openly open and keep thinking

When you keep your mind open and work, you will discover something

every day. Your life becomes exhilarating. For a person with job satisfaction

other things become insignificant.

Life is full of mysteries for a person who can think.

IT IS BELIEVED THAT THERE ARE ONLY 26 DISEASES FOR WHICH

EMPERICAL CURE IS KNOWN.REST IS ALL GUESS WORK.

INCIDENTALLY DO YOU KNOW THAT EVEN TO THIS DAY WE

DONOT KNOW THE EXACT CURE FOR “COMMON COLD”

THAT IS PROBABLY THE REASON FOR SAYING--------

COLD GETS CURED IN 7 DAYS TIME IF YOU TAKE MEDICINE,

COLD GOES AWAY ON IT’S OWN IN A WEEK’S TIME EVEN IF YOU

DONOT TAKE MEDICINE.

13

PATTERN

Patterns are replicas of component to be made with certain allowances.

You should also remember that your casting can only be as good as your

Pattern and certainly not better.

When you see a Brass tap ( a cast product) in your house, don’t you marvel

at it’s complexity and elegance.

3000 years back, our fore-fathers made statues of DANCING NATARAJA

out of metal, it was a cast product.

Patterns can be several types:

Solid pattern.

Split pattern.

Skeleton pattern.

Cored pattern

Cover cored pattern.

Patterns can be made of wood, metal polymer, plaster of Paris etc.

A pattern made by a pattern maker and a pattern designed by a Methods

engineer may look totally different. I would like to state in no uncertain terms,

that the fate and eventual cost of the casting, depends to a great extent on

Pattern design.

A pattern maker is only concerned with taking the pattern out of the mould.

( mould—British English & mold---American English )

Whereas a Methods Engineer takes a holistic view. His goal is a good casting.

In the process a Method’s Engineer’s pattern may altogether look different.

A Methods Engineer can be compared to a GYNECOLOGIST;

OBSTETRICIAN & PAEDIATRICIAN all packed in one.

Can you think of any of the above medical practitioners having a callous

attitude towards pregnant mother, growing foetus, or the baby after birth.

Similarly a Methods engineer, worth his salt, must envisage all the phases

a pattern or a casting goes through, identify probable problems which

are likely to manifest at various stages of Foundry operation.

In other words I am calling a” METHODS ENGINEER “ a complete foundry

man.

For all I am worth, to the best of my ability with a dash of divine intervention,

I hope I will able to do justice to the TASK on hand. Also familiarise you

with all facets of a foundry operation.

Your are probably feeling bit heavy. So let us digress a bit. There is a saying

“ IT TAKES ALL SORTS TO MAKE A WORLD “ How true. Remember

you are not a nonentity. Do you know why ? With out you this world of ours

will not be complete.

14

I need to tell you a story now. There was an Indian scientist by name

S.N.BOSE. He was a physicist and an young man. He wrote a paper on

Theoretical physics. Like any youngster, he wanted second opinion from an

other theoretical physicist. He sent his paper to none other than Einstein

himself. At that time Einstein was still in Germany. He did not know

English. A kind soul he was he got the paper translated to German. Read the

paper, made some corrections and published a paper jointly in the name of

BOSE & EINSTEIN. That paper was titled “ BOSE-EINSTEIN STATISTICS”

which is like a Bible for all Theoretical physicists even to this day. He

identified a particle in the process and he named the particles as “BOSANS”

after S.N.BOSE. What a commendable act of kindness.

Let us go to the other end of the Spectrum.

One Mr Chandrashekar ,again a physicist and a theoretical physicist. He

went to LONDON and delivered a lecture on ASTROPHYSCIS at ROYAL

SOCIETY. In the audience there was PROF EDDINGTON. EDDINGTON

was a NOBEL LAUREATE himself. He tore Chandrashekar into pieces.

A dejected, demoralised, demolished and depressed Channdrashekar left

the shores of BRITAIN once for all. He went to UNIVERSITY OF CHICAGO

in USA. Chandrashekar worked on Astrophysics. After full 50 years later

Chandrashekar got a NOBEL PRIZE for the same theory he had proposed

50 Years earlier at ROYAL SOCIETY OF LONDON.

To day there is what is called “CHANDRASHEKAR LIMIT” in Astrophysics.

Do you see the extreme contrast between EINSTEIN & EDDINGTON.

Now back to work.

15

METHODING OF CASTINGS

Methoding of castings is the HEART & SOUL of making a sound CASTING.

As I have already told you Foundry is an old art but young science.Till1939

castings were made by trial and error method. What we call FEEDERS now

were called RISERS because workers used to see the way liquid metal was

raising in the mould. The name RISERS got stuck, but to-day it is an

inappropriate word. FEEDER is the appropriate word

Let us understand the word FEEDER. When we heat any thing it expands.

When a metal is melted, it takes the heat in 3 stages. 1) Solid state,

Mass x Cp1 x (melting point – room temperature)-Sensible Heat, 2) Melting

(Solid to Liquid ) Mass x Latent Heat At it’s Melting point, this is called as

Latent Heat, 3) Mass x Cp2 x ( pouring temperature—melting temperature)-

Super Heat. To give you an example, Pure Iron melts at 1539 degrees.

But you can not pour at 1539 degrees as it will become solid while pouring

itself, so we give an additional heat to this liquid so that the metal remains

above 1539 degrees till the cavity in the mould is filled & metal takes the shape

of the casting. So we pour our metal at about 1640 degrees. As we all know

when ever some thing is heated it expands, as we have put in 3 different heats

namely Sensible Heat, Latent Heat & Super Heat-there is a great deal of

expansion. While cooling, loss of Super Heat leads to Liquid – Liquid

Shrinkage, the loss of Latent Heat leads to Solidification Shrinkage.

While loosing Sensible Heat, it occurs in Solid state, hence to counter

the contraction the Pattern in made bigger to accommodate that contraction.

We need a Reservoir of liquid metal to compensate for other two shrinkages.

That comes from FEEDERS.

Imagine a CONE solidifying and a ROD solidifying. Would there be any

difference. In a Cone solidification starts from the tip and gradually

solidification moves towards the base of the cone. This pattern of solidification

is called DIRECTIONAL SOLIDIFICATION. Where as in a ROD ,there is a

concurrent solidification taking place across the length of the rod. This kind of

solidification that takes place in a rod is not conducive to a SOUND CASTING.

Where as THE SOLIDIFICATION PATTERN that takes place in a CONE is

conducive to a SOUND CASTING.

SO THE METHOD OF MAKING ANY CASTING SOLIDIFY LIKE A

CONE TOWORDS THE FEEDER,LEADS TO A SOUND CASTING.

IN ONE WORD THIS IS THE CRUX OF “ METHODING”

This is achieved by making use of temperature gradients which result in

Directional Solidification. By this we are making all the SHRINKAGE

move out of the casting and go to feeder where a reservoir of liquid metal

is available to compensate for the shrinkage which otherwise would have

have occurred in the casting it self. This process of taking this shrinkage

16

from casting into a feeder is called Directional Solidification. The

Engineering of this is called METHODING.

In 1939,one person by name CHEVERINOV came up with an equation,

Called CHEVERINOV’S EQUATION. It looked like this:

2

2

2

2

2

t = 0.75 x V x Q x S / (SA) x T x k x D x Cp

Where t = Solidification time

V = Volume of the liquid metal

Q = Heat content of the metal

S = Density of the metal

SA = Surface area through which heat content of the liquid metal was

lost to facilitate solidification

T = Solidification temperature

K = Thermal conductivity of mould material

D = Density of mould material

Cp = Specific heat of mould material

There are some terms which need further explanation.

Q-Heat content of Metal.

= Weight of metal x Specific heat (Cp1) x ( Melting point – Room temp ) ----1

= Weight of metal x Latent heat (at melting point )---------------------------------2

= Weight of metal x Specific heat ( Cp2) x( Pouring temp---Melting point )----3

The sum of 1+2+3 = Total amount of heat required till pouring temp

Specific heat is the amount heat required to raise the temp of a unit

mass(weight) by 1degree centigrade—calories / gram/ degree C

This specific heat is not a constant figure.

Imagine that you are climbing 1000 steps to reach a temple, you will climb first

50 steps easily with out getting tired. There are after raising each and every step

needs an extra effort. We human beings being intelligent we rest for a while and

start climbing again. Even the people who built the steps provide what is called

“LANDING” for resting.

But metals have no such advantage. The extra effort(heat) needed to raise the

the temp by every 1 degree keeps raising.

For the most part, Cp of pure metals at room temp are available in

Physical constants tables. But Cp at higher temp are not available at all even

for pure metals and for ALLOYS it is not available at all.

Then again we have Cp1 and Cp2.If Cp1 itself is not known properly what to

talk of Cp2.

The atoms of the metal are BOUND or BONDED by a FORCE. For our

17

convenience sake ,let us assume that each atom of metal is BOUND BY

A SPRING with another atom of metal. On heating the strength of the spring

strength deceases. Here (1) is called SENSIBLE HEAT.

LATENT HEAT is the amount of heat required to CONVERT one unit mass

of metal from SOLID TO LIQUID at it’s MELTING TEMPARATURE.

For pure metals this data is available. Alloys do not melt at ONE temp

rather OVER A RANGE OF TEMPERATURE. Here we do not know the

Latent Heat. Now do you see in what sort of unchartered territory we are

working in.

We virtually know nothing.

ON SEVERAL OCCASSIONS I HAVE FELT THAT WE METALLURGISTS

OR FOUNDRYMEN ARE NEITHER SCIENTISTS NOR ENGINEERS.

When solid becomes liquid several bonds(springs in our case) are broken and

hence liquid has a mobility which solids didn’t have.

Information :Even in liquids all the bonds are not broken. That is the reason

why it can be held in a container, but once you cross BOILING POINT all the

bonds are broken and alloy becomes a GAS. Can you imagine holding a gas in

an open container.

1) SENSIBLE HEAT- room temperature to melting point.

2)LATENT HEAT- at the melting point itself.

3) SUPER HEAT- from melting point to pouring temperature.

THE SUM OF 1+2+3 is the heat required to bring the metal to a temp where

it can be poured into a container called MOULD.

Here I need to clarify a point, that is A SINGLE METAL (GOLD) is pure

metal. But the moment we put some other element(ALL ELEMENTS ARE

PURE) into a pure metal it becomes AN ALLOY.

Look at the RING you have on your finger, though we call it a GOLD RING,

in actuality it is a GOLD ALLOY RING.

Pure Gold (24 carat ) is too soft and hence to give it some strength, we add

small amount of COPPER or SILVER. Now your GOLD ALLOY RING is 22

carat.

Most of us have a misconception about the amount heat required to bring the

metal to pouring temp.

For example Iron has a melting point of 1539O C

Copper------do--------------1083O C

Aluminium-----do----------660O C

Hence we conclude that heat required to melt one unit weight of Fe > that of

Copper > that of Aluminium .

Nothing is farther from truth.

Let us say we pour our metals at a superheat ( melting temp + 100) degrees.

IRON AT 1539 +100 = 1639 O C

COPPER AT 1083 + 100 =1183 O C

18

ALUMINIUM 660 + 100 = 760 O C

Now look at the amount of heat required to raise temp to a super heat of 100 O C.

IRON ----349 KILOCALORIES PER Kg

COPPER—186 KILOCALORIES PER Kg

ALUMINUM 281 KILOCALORIES PER Kg

Hence heat required by Fe> Al >Cu

This is all because of combination of specific heats and latent heats.

So make sure you don’t fall into this trap.

Now let us take a look at the some of the constants in CHEVERINOV’S

EQUATION about which we are not certain.

Q---heat content of metal. Do we know Cp, LH and Melting point to any degree

of certainty. NO. WE DON’T.

Cp –Specific heat of pure metals at high temp are not known, where is the

question of knowing Cp of Alloy either at room temp or at high temperature ?

LH—Alloys do not solidify at ONE temp But over a range of temp, so we are

not sure of latent heat of alloys.

Melting Point—Since alloys solidify over a range of temp, which temp do we

take? HIGHEST,AVERAGE or LOWEST. We don’t know.

Then coming to MOULD MATERIALS, we may know their Thermal

conductivity and specific heat at room temp, but temp at which HEAT IS

EXTRACTED( during solidification mould temp is not ROOM TEMP.) we do

not know these values.

WITH SO MANY UNKNOWNS OR NOT-SURE-OF PARAMETERS how

can we use this EQUATION with any degree of confidence.

There appeared a person in early 1960’s who simplified our problem a great

deal. His name is R.WLODAWER.

Before we discuss Wlodawer’s equation, let us have bit of a breather.

In early 70’s a movie came whose name was SIDDHARTHA .Do not get

confused this SIDDHARTHA with GOWTHAMA BUDDHA. He is different.

It is a story of a young man who leaves his home and family on a quest for

the truth. Embarking on a journey that takes him from the austerities of

renunciation to the profligacy of wealth. That leads him through the range

of human experiences from hunger and want, to passion, pleasure, pain,

greed, yearning, boredom, love, despair and hope. A journey that finally

leads him to a RIVER, where he gains PEACE AND EVENTUALLY

WISDOM.

This classic is written by HERMANN HESSE, a NOBEL laureate in

Literature.

In this book SIDDHARTHA was asked several times about what he can do.

19

His answer was always, I CAN WAIT,I CAN FAST & I CAN THINK.

(DOES THAT MEAN WE DON’T OR CAN’T DO ANY OF THESE).

As regards to conclusion I leave it to your own judgement ?

There is a SPIRITUAL classic called “I AM THAT” by Nisargadutt Maharaj.

This man was a carpenter and unlettered BUT a realised SOUL. When he

was asked a QUESTION about his impression of the WORLD. His answer

was whose world yours or mine. This statement made a deep impression on

me, made me to conclude that world is an illusion. Each person has his own

WORLD IN HIS MIND.

Now back to business.

Wlodawer came out with a concept called MODULUS. The word modulus

means VOLUME / SURFACE AREA.

Wlodawer’s premise is that since both mould and feeder are made of same

material, why bother about their physical properties.

So Wlodawer stated that Mf = 1.2 x Mc will give a sound casting.

For a feeder Sphere is the Best. As it has got lowest surface area for a given

volume. In other words a Sphere has got the highest modulus for a given

volume. But a spherical feeder has got moulding problems. The next best shape

is a CYLINDER.A cylinder has no mouldability problems.

When a feeder is kept on a casting, casting solidifies(shrinks) and results in a

vacuum and as a result of it metal is “SUCKED IN” from feeder to casting. As a

result volume of metal in feeder reduces. In the process a conical void is formed

in feeder. To begin with, surface area of top of the feeder is a circular. On

feeding the volume of feeder reduces and because of formation of a conical

void, surface area of feeder increases. Thereby Mf decreases.

When we start of with Mf = 1.17 x Mc, after complete solidification, Mf = Mc

as Mc is not changing and Mf is reducing because of increase of surface area

and decrease of volume. Thus he provided a safety factor of 0.03 i.e. 1.17+0.03

= 1.2 x Mc. There by at the end of solidification, Mf = 1.03 as against a Mc

of 1.0.This ensures a sound casting.(see figures in end)

In Wlodawer’s equation we are not dealing with any factor which we cannot

measure. We can measure volume and surface area. For the most part, that is all

required.

Mf ( volume / surface area of the cylinder ) = 1.2 x Mc ( volume / surface area

of the casting )

Let us take a cube as an example. volume of the cube of side ,say 200 mm is

3

equal to 200 x200 x 200 = 8000000 mm ,surface area is equal to

2

200 x 200 x 6 =240000 mm .Its modulus is 8000000 / 240000 = 33.33mm.

Let us look at the modulus of feeder. Mf = 1.2 x Mc.

20

Mf = 1.2 x 33.33 = 39.996 mm.

Here we have made a mistake. That is we have taken 6 surface areas for a cube.

But once we put a feeder, as there is no heat loss between casting and feeder

junction, we have only 5 cooling surfaces. Volume of cube being the same

3

2

i.e. 8000000 mm ,surface area reduces.200 x 200 x 5 = 200000 mm .

Now the Mc =8000000 / 200000 = 40 mm.

If Mc = 40 mm, Mf = 1.2 x 40 = 48 mm.

Now let us look at a cylindrical feeder.

3

Volume of a cylinder = 0.785 x d ( if h / d = 1.0 ) and it’s surface area is

2

2

equal to 0.785 x d ( top ) +3.14 x d ( sides).Bottom of the cylinder, as it is ,

sitting on the cube is a non-cooling area..

3

2

2

Now Mf = volume / surface area = 0.785 x d / 0.785 xd +3.14 x d = d/ 5

Mf = d / 5 = 0.2 d = 48 mm ( see above).

d = 48/ 0.2 = 240 mm dia.

3

i.e. for a cube of 200 x 200 x 200 =8000000 mm , you need a feeder of

240 mm dia and 240 mm height sand cylindrical feeder.

A cube of 200 mm side needs a feeder of 240 mm dia x 240 mm height.

Here there is a lacuna. If we deal in terms of mm(which are large numbers ) we

are likely to make mistakes, while dealing with large numbers.

Hence a simple solution is 10 mm = 1.0 cm,10 cm = 1.0 dm.

So we deal with decimetres. 1.0 decimetre = 100 mm. then calculation becomes

3

simple. For 200 mm x 200 mm x 200 mm =8000000 mm becomes ,

3

2dm x 2dm x 2 dm = 8 dm .Now compare the above values.

3

3

8000000 mm = 8 dm .The chances of your making mistakes are greatly

reduced.

So we deal with dm only. Not in cm or in mm.

3

3

1.0 dm = 8.0 kg. since the figure is on the higher side, we consider 1.0 dm =

7.8 kg while dealing with casting weight.7.6 kg while dealing with feeder

weight( liquid). You are already incorporating a safety factor.

3

( DENSITY OF STEEL FOR CASTING-----7.8 Kg / dm .)

( DENSITY OF LIQUID STEEL IN FEEDER----7.6 Kg / dm3)

Now to familiarise ourselves with calculations in dm, let us repeat the process.

A 200 mm x 200 mm x 200 mm cube will have a volume of 2 dm x 2 dm x

3

2

2dm = 8 dm . surface area = 5 x 2 dm x 2 dm = 20 dm .

3

Volume = 8 dm

2

Surface area = 20 dm

Modulus of casting = 8 / 20 = 0.4 dm i.e. Mc = 0.4 dm

Modulus of feeder = 1.2 x Mc = 1.2 x 0.4 = 0.48 dm *

( Remember we have taken only 5 surfaces into consideration as feeder is kept

21

on top surface area and hence it becomes a NON-COOLING AREA)

Let us have a cylindrical feeder whose diameter is d and whose height is also d

This we call h / d = 1.0. Now let us do the calculations.

2

Volume = pi / 4 x d x h ( where pi = 3.14)

2

Volume = 3.14 / 4 x d x d ( as we have assumed h / d = 1.0 and hence h = d )

3

Volume = 0.785 x d --------------(a)

2

Surface area = pi / 4 x d (top ) + pi x d x h (side)

2

2

Surface area = 3.14 / 4 x d + 3.14 x d .

2

2

Surface area = 0.785 x d + 3.14 x d .---------(b)

Mf = volume / surface area ------------------------------( a) / (b )

3

2

2

Mf = 0.785 x d / 0.785 x d +3.14 x d

2

2

Mf = 0.785 x d ( d ) / 0.785 x d ( 1+ 4) -------3.14 / 4 = 0.785

Mf = d / 5 = 0.2 x d

We have already calculated our Mf ( * ) which is 0.48 dm.

Mf = 0.2 x d = 0.48 dm

d = 0.48 / 0.2 = 2.4 dm which is equal to 240 mm ( which we had got earlier)

So a CUBE of 200 mm x 200 mm x 200 mm NEEDS a SAND

CYLINDRICAL FEEDER of 240 mm DIAMETER x 240 mm HEIGHT.

Now let us look at a feeder with a h / d = 1.5.

2

3

Volume = 0.785 x d x 1.5 d = 0.785 x1.5 x d

2

Surface area = 0.785 x d ( top) + 3.14 x d x 1.5d (side) ( bottom-non-cooling )

Mf = Volume / surface area

3

2

2

Mf = 0.785 x 1.5 x d / 0.785 x d + 3.14 x 1.5 x d

2

2

Mf = 0.785 x d x 1.5 x ( d) / 0.785 x d ( 1 + 4 x 1.5 )

Mf = 1.5 x d / ( 1 + 6) = d x 1.5 /7 = 0.214d

Mf = 0.214d ( h/ d =1.5)

If h / d = 1.0, Mf =0.2d

If h /d = 1.5, Mf = 0.214d

For the same Mf of 0.48dm,in case of h /d = 1.0, d = 0.48 / 0.2 = 2.4 dm

For h /d =1.0 feeder size is 240 mm dia x 240 mm height

Weight of liquid metal = 0785 x (2.4)3 x 7.6 = 82.47 Kg. ( *1)

For h /d =1.5, Mf = 0.48 =0.214d,

d = 0.48 / 0.214 = 2.2429 = 2.25 dm dia ---height =2.25 x 1.5 = 3.37dm

weight of liquid metal = 0.785 x(2.25)2 x 3.37 x 7.6 = 101.78 Kg (*2)

COMPARE ( *1) WITH (*2)---101.78 Kg—82.47 Kg = 19.31 Kg of

EXCESS metal is being consumed to cater to same MODULUS.

19.31Kgs ( excess metal) / 82.47Kgs (actual metal in h/d = 1.0)

22

23.4% Excess metal being used in h / d = 1.5 to cater to a same MODULUS

VALUE.

Hence always use h / d = 1.0 feeders only unless you have some genuine

constraints.

Let us look at it from a different angle.

3

3

Weight of Cube = 2 dm x 2 dm x 2 dm = 8 dm x 7.8 Kg / dm = 62.4 Kg.

Plain Carbon steel has liquid-liquid shrinkage( superheat ) + solidification

Shrinkage ( latent heat ) of 6.0 %.

i.e. 62.4 Kg x 0.06 = 3.744 Kg. This is the feed metal requirement to get a

sound casting.

Now let us look at 240 mm dia x 240 height feeder has 82.47 Kg of metal,

assuming that 10 % of the total metal is available for feeding the casting,

82.47 x 0.1 = 8.247 Kg are available, which is more than adequate.

Now let us look at 225 mm dia x 337 mm height feeder, it has 101.78 Kg

Of metal. Assuming that same 10 % metal is available for feeding the casting

To be sound, see how much metal we are getting. 101.78 x 0.1 = 10.1 kg.

If 240 mm dia x 240 mm ht is giving 8.2 Kg as against a requirement of

3.8 Kg .A h /d = 1.5 feeder of 225 mm dia x 337 mm ht is giving 10.1 Kg

which is much more than adequate.

So I repeat use only h / d = 1.0 feeder only unless you have some genuine

constraint.

I am beginning to hear lot of alarm bells or shall I call them warning bells

ringing in your mind as to why we should we provide so much extra metal i.e.

8.2 Kgs as against a requirement of 3.8 Kg.

This doubt is perfectly understandable and valid too.

A FEEDER HAS TWO FUNCTIONS.

1) IT SHOULD SOLIDIFY AFTER THE CASTING HAS SOLIDIFIED.

2) IT SHOULD HAVE ADEQUATE FEED METAL TO GIVE A SOUND

CASTING.

A FEEDER HAS TO TAKE CARE OF BOTH THE CRITERIA.

IF YOU LEAVE OUT ONE AND TAKE CARE OF AN OTHER YOU

END UP WITH A DEFECTIVE CASTING.

I have gone through this experience with a non-weldable, defective, HCHCr—

2.0% C ,12 %Cr alloy. Only option left was to cut the casting with expensive

cutting electrodes rather than relatively cheaper OXYGEN-ACETYLENE gas.

When I realised my mistake I felt miserable.

SO I REPEAT YOU HAVE TO SATISFY BOTH ASPECTS.YOU HAVE

NO FREEDOM THERE. Treat this as a WARNING from a person who has

burnt his fingers once way back in 1979.

R.WLODAWER wrote a book on “ DIRECTIONAL SOLIDIFICATION

OF STEEL CASTINGS “Originally this book was written in GERMAN &

Subsequently translated to ENGLISH in 1966.I have been having this book

23

from 1978,but I can’t say with any degree of certainty that I have read every

thing in this book.

There are two kinds of castings---CHUNKY CASTINGS(thick) & RANGY

CASTINGS(thin). Example of chunky castings is a CUBE, for RANGY

CASTINGS is a plate casting. In chunky castings Vc>> surface area of castings.

In a rangy castings Vc<< surface area of castings. In chunky castings Modulus

is more important, in a rangy castings available metal is more important, like in

a PLATE. At the outset you have no means of knowing which is rangy or

chunky casting. Do your calculation for MODULUS &AVAILABLE

LIQUID METAL, which ever diameter of feeder satisfies both the

conditions, employ that feeder.

Wlodawer, in his book(page-149)writes an equation.

2

SOLIDIFICATION TIME IN MINUTES = 2.1( M in cm) FOR GREEN

SAND MOLDS.

John Nash ,a brilliant mathematician, got a NOBEL prize in

Economics. He had the habit of inventing or discovering things for himself,

including Pythagoras theorem.

Let me confess something to you today, I am against h / d = 1.5 feeder, but the

explanation I used to give till yesterday is different from what I have given

today. when I look back at my old explanation I feel silly. Because I had

ignored something which would have been obvious to any body, but not to

me .

AWARENESS OF ONE’S IGNORENCE IS THE BEGINNING OF LEARNING.

He who knows not, knows not that he knows not, is a fool, shun him.

He who knows not, knows that he knows not, can be taught, teach him.

He who knows, but knows not that he knows, is asleep, wake him.

He who knows, knows that he knows is a prophet, follow him.

Generally people write books on what they know.

But RICHARD FEYNMAN, a NOBEL LAUREATE IN PHYSICS WRITES

ABOUT WHAT HE DOES NOT KNOW IN HIS “THE FEYNMAN

LECTURES ON PHYSICS “which went on to become an international best

Seller.

1) Feynman says “I was born not knowing and have only had little time to

change that here and there” If this is not height of humility, what is?

2) Science is a way to teach how something gets to be known, what is not

known, to what extent things are known( for nothing is known

absolutely),how to handle doubt & uncertainty, what the rules of evidence

24

are, how to think about things so that judgements can be made, how to

distinguish truth from fraud.

3)Feynman talked of how to build an automobile smaller than a dot. It was

only after 20 years this field got it’s name “NANOTECHNOLOGY” so

Feynman

was

intellectual

father

of

legion

of

self-described

nanotechnologists.

4)Feynman believed in “great value of satisfactory ignorance & how doubt is

not to be feared but welcomed.”

5) Feynman was happy to embrace ignorance & doubt.

6) A colleague of Feynman & a scientist himself commented that when

some body does some thing new, we felt that we could have also done it, but

with Feynman we were never sure.

Extracted from “GENIUS-THE LIFE & SCIENCE OF RICHARD FEYNMAN”

BY JAMES GLEICK.

Let us get back to work.

Solidification time is dependent on rate of heat extraction by the moulding

medium.

Moulding material Solidification time of 150 mm dia STEEL sphere

Moulding material

Solidification time(in Minutes)

1

Copper chill mould