Aluminium removes Oxygen.
FeSi +FeMn are also deoxidizers.
Mischmetal consists of Ce, La etc & they are very strong sulphide &oxide
formers. Hence they reduce Sulphur ,which improves % E, % RA etc
Calcium Silicide can act as a sulphur reducer & since it has low melting
point, it can take out inclusions while it is floating up.
FeSiZr is also a deoxidizer & grain refiner.
ROASTED or DRY MAGNESITE SAND is a wonderful material.
57
It has a very low density & a melting point of 2800 degrees. Hence it is
totally unaffected by the liquid steel, IT SIMPLY FLOATS UP LIKE A
ONE WAY LIFT,IN THE PROCESS COLLECTS LOT OF INCLUSIONS,
& CLEANS UP THE METAL OF LOT OF INCLUSIONS.SO MUCH SO
THAT YOUR % E & %RA GO UP BY 2 TO 3%.
Salem ,in TAMILNADU ,is a place where you get this Magnesite in plenty.
% of ADDITIONS.
Al----- 1.0 Kg per ton of Steel.
Mischmetal—0.10 % of total metal.
FeSiZr 0.05 %
CaSi 0.10 %
Magnesite Sand 1.0 Kg per ton.
These additions are made into to the FIRST STREAM OF LIQUID METAL
WHICH FALLS INTO THE LADLE. This avoids any burn-out of any
addition as some of them are highly reactive( if put to pre-heated empty
ladle).
In steels ,grain boundary is stronger than grain. Hence total grain boundary
length should be as long as possible, or in other words GRAINS SHOULD
BE AS SMALL AS POSSIBLE. That is the reason we always ask for FINE
GRAINED STEELS. This can be achieved by the addition of a small amount
of FeTi or FeZr.( 0.05 % to 0.10 %)
In Steels, you have two BIG enemies. They are S & P. They go to the Grain
boundary & make it weaker and also make the alloy less tougher.
That is lower % E & % RA. That is the reason why all steels specify
S & P as 0.04 % MAX.
Attempts can be made in Steels to reduce these rogue elements in steels.
(Excepting FREE CUTTING STEEL where % S is kept high)
DEPHOSPHORISATION needs the following conditions.
1) High Basicity.
2)Oxidizing condition.
3) Low temperature.
For HIGH basicity, use SODA ASH or SODIUM CARBONATE, say 5.0 Kg
per ton of Steel (in ladle).There will be some pollution problem, so have
exhaust fans installed.
For Oxidizing Condition, do not deoxidize the metal in the furnace at all.
For the 3 rd condition, pour the metal into ladle at least 30 to 40 degrees
less than pouring temperature.
Take the metal back to ladle. REMOVE the slag.
DESULFURIZATION needs the following conditions.
1)High Basicity.
2)REDUCING CONDITION.
3) High Temperature.
58
FOR condition 1) follow the same procedure you followed in the FIRST case.
For 2) deoxidize the metal in furnace itself thoroughly
For 3) take temperature to the pouring temperature
POUR the metal into ladle
Take the metal back to the furnace, remove the slag &then pour the alloy in the
normal way.
As regards Basic slag, DO NOT WORRY. Your lining is any way BASIC.
I have done DESULFURISATION for S.G. Iron in a SILICA (Acidic) lined
crucible. As the time of residence of slag in the crucible was so short, we had no
problem what so ever.
Instead of specified 0.04 max for both S&P, even if you bring it down to 0.03 %
you stand to gain in terms of Higher % E & % RA. Your quality of Steel will
be appreciated by the customer. You are likely to become A FAVOURED
SUPPLIER OF QUALITY STEEL CASTINGS.
Do not be too generous with Al, if the residual Al content is more, it will form
Aluminium Nitride, which goes to GRAIN BOUNDARY & make your steel
brittle.
If your alloy has got elements like Mn, Cr, Si (on the higher side) which are
prone to oxidation loss, do not allow the liquid metal to become GASSY at
all. Like a priest goes on throwing flowers on the deity, you also keep throwing
ALUMINIUM PELLETS into liquid metal so that metal does not get oxidized
at all.
For Mechanical testing, there are Standards like ASTM( American),
BS( British), IS ( Indian ),JIS (Japan ),GOST (Russian) & DIN (German).
In Tensile Testing Specimen, ASTM wants L / d =5.0, DIN wants L / d = 10.00.
DIN specifications are so stringent, that if you can satisfy DIN Standards, you
can satisfy any other Standard.
May be that is the reason when you think of CARS what comes to your mind is
BENZ,AUDI,BMW,PORCHE & VOLKSWAGON do you know what is the
common factor in all these. They are all GERMAN CARS.
After having finished with STEEL MAKING IN FOUNDRY, let us go to
S.G.IRON
These days S.G. Iron is becoming very popular because of it’s versatility.
S.G.IRON is a CAST IRON. You will get to know the details of
difference between Steel & Cast irons.
Simply put, if STEEL is like a HOUSING COLONY developed by a CITY
DEVELOPMENT AUTHORITY, CAST IRON is like a SLUM.
But Cast irons also have their UTILITY where TOUGHNESS &STRENGTH
together are not deciding criteria.
S.G.IRON is closer to Steel, in orderliness, than Grey or White cast irons.
S.G. Iron stands for SPHEROIDAL GRAPHITIC IRON.IT IS ALSO
59
CALLED NODULAR IRON.
S.G. Iron has a normal composition of 3.8 % C,2.7 % Si, 0.30 % Mn
& 0.03 % S
Metallurgy of Steel, Grey iron, White iron &S.G Iron will be talked in greater
detail later when we discus Metallurgy.
It is generally, unusual to talk of FOUNDRY PRACTICE before talking of
METALLURGY.
Generally, people have a perception that Metallurgy can’t be understood,
so you mug it up, pass the exam & forget about it.
I will try, for all I am worth, to make you UNDERSTAND Metallurgy the
same way you are getting to know Foundry
Until then please take my statements as they are told.
This book will have about 100 pages of written matter & about 60 drawings.
By the time you finish this book you will feel comfortable & confident
about FERROUS METALLURGY & FOUNDRY PRACTICE.
There is a diagram called Fe-C diagram. From this diagram you get to know
that up to 2.0 % C, it is called STEEL & beyond 2.0% C ,it is called CAST
IRONS.
In cast irons we have grey, malleable, compacted, white & S.G irons.
They are called by different names because of different phases. It is this
phase difference which is responsible for different behaviour of each alloy.
S.G.IRON OR NODULAR IRON
S.G. iron is made in an Induction furnace with a lining of SILICA RAMMING
MASS.
In this furnace we put a charge of steel, pig iron, S.G. iron returns( GATES
&FEEDERS),Fe-Si etc.
Here we melt the alloy the way we melted steel.
In Fe-C diagram you also see a point called 4.3 % C. This point is called
Eutectic Point at 1130 degrees. Any alloy which has less then 4.3 is called
HYPOEUTECTIC CAST IRONS.AN ALLOY WHICH HAS MORE THAN
4.3 is called HYPEREUTECTIC CAST IRONS.
S.G. Iron is a hypereutectic iron. Otherwise most of the irons we deal with are
hypoeutectic irons.
In S.G. Irons we maintain a C % of 4.4 or 4.5.The Carbon we are talking of is
no different from GRAPHITE you get in a PENCIL used for WRITING.
The Si that we have in S.G Iron is provided in 3 stages.
1) Liquid metal in Induction Furnace--- 1.3%
2)From Fe-Si-Mg treatment----------------- 0.7 %
3)From Inoculation-------------------------- 0.7 %
Total Si content of the alloy----------- 2.7 %
When we finish melting, the liquid metal will have about 4.0 %C & 1.3 % Si.
If the S is more than what is required, metal is treated with soda ash to remove
60
S. This has already been explained in STEEL MELTING.
S.G .Iron ladle looks different from a steel ladle. S.G. Iron ladle will have a
WELL to place Fe-Si-Mg lumps. It is because of Mg vapour in liquid metal
surface tension of the melt is increased, which does not allow Graphite to
take any shape other than a SPHEROIDAL SHAPE.
Mg has a boiling point of 1107 degrees. while our pouring temperature is
1380 to 1400 degrees.
Fe-Si-Mg lumps are placed in the WELL & covered with M.S. borings or
a thin M.S. plate. Liquid metal from the Furnace is poured over it.
By the time you pour about 50 to 100 Kg of liquid metal vaporisation of
Mg starts. From the practice, I am familiar with, in less than 6.0 minutes
the entire 1000 Kg of metal has to be emptied to hand ladles( WHERE
1.0% Fe-Si is added as an INOCULANT --which gives about 0.7 % Si)
to moulds. If the pouring is delayed all the Mg vapour will escape &
we do not get S.G. Iron. This is called FADING. The iron so obtained after
fading is called COMPACTED GRAPHITIC IRON. It is inferior to
S.G. Iron, but Superior to grey iron. All said & done we didn’t get what we
wanted.
It was at this point an Idea occurred to me. If Mg vaporisation reaction is
delayed I can save on Fe-Si-Mg & also delay the pour out time.
What I did was a simple experiment & it turned out to be effective also.
The well of the preheated ladle was cooled with compressed air. Fe-Si-Mg
lumps were dumped into the well. The top of Fe-Si-Mg was covered with
Sodium Silicate Sand. This sand cover became rock-like( because of heat)
subsequently the sand cover was pierced with 30 mm M.S. rod with a
sharp point at the end. On pouring the liquid metal over it, unlike before
no reaction started till the ENTIRE 1000 Kg of metal was poured.
There after I had to wait for 1.0 minute for a minor explosion to occur.
As 1000 Kg of metal was above Fe-Si-Mg, FERROSTATIC HEAD
had increased, obviously our fading time got delayed.
As we were already equipped for emptying the entire 1000 Kg in less than
6.0 minutes. Now for the same fading time, my consumption of Fe-Si-Mg
came down FROM 18 Kg per ton of melt TO 12 Kg per ton of melt.
A Savings of 33 % in consumption( 7 % Mg content in Fe-Si-Mg) occurred.
After I explained what I did, it does not sound out of the ordinary or anything
special.
All that it requires is “WANTING TO DO SOME THING DIFFERENTLY”
NEVER BE AFRAID OF FAILURES.ONLY A PERSON WHO ATTEMPTS
TO SOME THING, FAILS & SUCCEEDS.
SAVINGS THAT ACCRUED WAS A SAVINGS OF 33 % Fe-Si-Mg PER
MONTH WHICH WAS ONE MONTH’S WAGE BILL.
Even to this day when I see people making S.G. Iron as though it is steel or
Grey Iron as regards to feeding & gating, not having a proper ladle, having
61
open feeders like you have in steel &grey iron.
I have already given the details feeding S.G. Iron.
WE INDIANS HAVE SERIOUS PROBLEM IN SAYING “ I DON’T KNOW”
AWARENESS of IGNORENCE is the BEGINNING OF LEARNING.
Let me confess something to you, even to this day I am a computer illiterate.
Like it is said NECESSITY is the MOTHER OF INVENTION.
Once I decided to write THIS BOOK I LEARNT HOW TO WORK ON
“ M S WORD”
Please remember RICHARD FYNMMAN’SAYINGS.
Once entire 1000 Kg is poured out, how to check whether what you have got is
S.G. Iron or not. For every hand ladle I used to pour a pencil of the metal.
whose diagram is provided. On a grey iron cube, if you hit with a STEEL ROD
the sound you get is TUN ( METALLIC SOUND),if you did the same thing
with S.G. Iron ,sound you get is TUNG ( Slightly less metallic sound) & if you
did the same thing with a GREY IRON ROD, sound is TUCK(non metallic)
Let us look at the specification of S.G. Iron & grey Iron.
Kg / mm2
% E
Grey iron
25 to 30
1 to 2
S.G Iron IS 1865-
1968
80 Minimum
2 minimum
70
3
60
5
50
7
42
12
37
17
S.G. Iron IS 1865-
1991
MPa min
% E min
900
2
800
2
700
2
600
3
500
7
450
10
400
15
400
18
350
22
( 1.0 Kg / mm2 = 10.20 MPa)
In case of a grey iron all the Graphite are interconnected & it is a path of
62
least resistance. So the metallic matrix hardly contributed to strength.
(An artistic impression of interconnection is provided)
Now do you realise how superior is S.G. Iron compared to Grey iron.
There is an other variety of S.G. Iron called ”AUSTEMPERED S.G.IRON.”
It is cooled from 930 degrees to about 500 degrees in a SALT BATH &
held there for the transformation to complete (Bainite)
2
This alloy gives you a strength of 120 Kg / mm & % E of 1 to 3.
(In case of S.G. Iron, Graphite Spheroids are separate & are not connected
in any way. Hence, the Matrix has a greater role to play in UTS , % E.
As Graphite nodules are ROUND , they reduce the Stress Concentration
factor a great deal & results in enhanced Strength & % Elongation.)
63
SAND PLANT & SAND PREPARATION
Sand used for building purpose looks reddish in colour. This reddish colour
comes from the presence of Fe2O3.( red oxide of Iron—which we use as paint)
This Fe2O3 is an impurity. This leads to lowering of refractoriness or Melting
point of sand. Hence such sands are not suitable for a STEEL FOUNDRY.
Originally sands used for STEEL FOUNDRIES are SEA sands like COCHIN,
MANGALORE,NELLORE SANDS.
The above sands are almost 99.9 % pure SILICA –SiO2. Therefore these sands
have adequate refractoriness to be suitable for STEEL FOUNDRY.
The word sand does not mean silica sand. It is only a size gradation Viz.
Boulder, gravel, sand & flour etc. you can have GOLD sand also.
Green sand mould made of sand, Bentonite &Water is the cheapest moulding
medium. Retrieval of sand for further use is maximum. Way back in 1980,the
landed cost of Mangalore sand in Bangalore was Rs 120 per ton ,where as the
cost of sand was only Rs 20 per ton. To day I am told that the landed cost of
sand is about Rs 1000 per ton. So reclaiming of sand becomes all the more
important.
Normal metal to sand ratio is 1:5. If I were to run a foundry of my own, I would
use 1part fresh sand, 1part reclaimed sand & 3 parts even construction sand as it
does not come in contact with metal anyway, provided it is coarser to allow
moisture to escape.
In a Green sand mould, I compare WATER with a COBRA. If cobra had an
escape route it would escape without biting any body, but if it’s escape route is
blocked, it will bite some body. The situation of WATER in mould is no
different. It WANTS to get away from HOT METAL as water vapour. So
we should provide a PATH for it to get away. This path is defined by
PERMEABILITY of sand. Imagine permeability as voids in sand mould which
are interconnected.
Technical requirement of Silica Sand :
Chemical composition----
Silica ( SiO2)---- 96 % min.
Iron oxide ( Fe2O3)--- 1.0 % Max.
Aluminium Oxide ( Al2O3) --- 1.5 % max.
CaO +MgO--------------------- 0.75 % max.
Na2O +K2O--------------- 1.0 % max.
Loss on ignition------- 0.75 % max
The above sand would have adequate refractoriness to withstand the
temperature of 1640 degrees of molten metal.
64
The generally acceptable sand shapes are major portion of rounded and a minor
portion of sub-angular.
Average Grain size of Sands:
1) Coarse sand------ 0.70 mm to 0.35 mm,
2) Medium sand---- 0.35 mm to 0.23 mm,
3) Fine sand------- 0.23 mm to 0.125 mm.
Medium Sands are best suited for STEEL FOUNDRY PRACTICE for making
moulds & cores. These sands have good Permeability, which helps in escaping
of moisture as steam. As the surface area is also less, it consumes less of binder.
They are amenable to reclamation & reuse.
Grain size terminology which is in vogue,
Coarse sand--------- 22 # to 44#
Medium sand-------- 40# to 60#
Fine sand------------ 60# to 100#
You are probably wondering as to what is this #.It is called a Mesh. You go
home & ask your mother as to what she does to wheat flour after Wheat has
been converted to flour. She SIEVES to separate FINES from COARSE flour.
These sieves are designated by sieve size. If 1.0 inch ( 25.4 mm) length is
divided into 10 equal parts. Each part measures 2.54 mm. If a SQUARE is made
out of this, it becomes a square of 2.54 mm x 2.54 mm. It is called 10 MESH or
10 #. If 25.4 mm is divided into 60 equal parts, it will become 0.423 mm. A
sieve with SQUARES of 0.423 mm x 0.423 mm is called a 60 MESH or
60#. More is the NUMBER finer the material.
Bonding Clays for Foundry Sands :
All clays( the material a POT maker uses is also a CLAY) can be classified as
Hydrous Alumina Silicates with a particle size of 0.01 microns (0.00001 mm)
to 20 microns(0.02 mm). They have a unique property of becoming plastic-
PASTY when wet & hard when dried. The Chemical name of these clays
is MONTMORRILLONITES. These are called BENTONITES in every day
parlance. There are two kinds of Bentonites: Sodium based & Calcium based.
In Steel foundry, Sodium based Bentonites are used. As these have a
combination of high bonding strength, high durability & resistance to heat
expansion defects.
Bentonite absorbs WATER which is 13 % of it’s own original volume.
Sand needs water to WET the sand surface & it is of the order of 1.9 % of
sand weight. This water is called TEMPER WATER. 8.0% Bentonite needs
8.0 x 0.13 =1.04 % water.
Water absorbed by for PEAK STRENGTH by different additives is,
ADDITIVES % water absorbed by each % of additive,
65
A) Wood Flour 0.275
B) Corn Flour 0.325
C) Cereals 0.135
D) Sea coal 0.060
E) Silica Flour 0.33
The Total Amount of Water required is :
1) Weight of Sand ------------------ a Kg
2) Weight of Bentinite ------------ b Kg
3) Weight of Wood Flour ------ c Kg
4) Weight of Corn Flour ------- d Kg
5) Weight of Cereal --------------- e Kg
6) Weight of Sea Coal ----------- f Kg
7) Weight of Silica Flour ----- g Kg
The Total Water required for PEAK STRENGTH is :
1.9 % x a + 13 % x b + 0.275 % x c + 0.325% x d + 0.135% x e + 0.06% x f +
0.33% x g.
As regards to amount of additions, it depends on ADDITIONAL properties
required.
While moulding use 25 % to 30 % NEW SAND as FACING SAND &
the rest is Backing Sand.
For Good Permeability, Sand should be of 40 to 60 # ( Facing Sand )
Sodium Bentinite---- 4 to 6 %
Cereals ( Starch or Dextrine ) -- 0.5 to 0.75 %
Water --------------------- 2.8 to 3.2 %
Preparation of Sand : There are TWO methods of preparing Sands.
1) MULLING.
2) MIXING.
Let us understand the difference between these two.
When your mother wants to make “Chapathis “ what does she do. She takes
wheat flour & puts a small amount of water or may be some amount of milk.
( Incidentally do you know when only Milk is put , Chapathis remain softer for
a longer period ) Then she SQUEEZES them together & it becomes a DOUGH.
With it she makes Chapathis. Similar is the condition in applying a Paste of
Bentonite (Smearing ) on every Grain of Sand. This is called Mulling.
For this purpose you have TWO Rollers(which are rotating) in a MULLER,
To begin with mull Sand and tempered water, this wets the sand surface , then
add Bentonite and it’s water requirement and mull. In the process of mulling
Sand + water + bentonite get SQUEEZED between bottom plate of the muller
& bottom of rollers. Subsequently you make your other additions and
corresponding water & mull. The similar process of mulling is followed
with Sand and Sodium Silicate.
66
Now let us look at MIXING. If your mother wants to make Ghee rice or Lemon
rice, she mixes the ghee or masala into cooked rice so delicately that the cooked
RICE grains do not BREAK. This is called Mixing. This process is adopted in
foundries, where the BINDER is a LIQUID. Such as OIL,SHELL RESIN,
NO-BAKE etc.
Normal green (WET) strength of your SAND –MIX is about 6 to 10 psi.
(POUNDS PER SQUARE INCH). When you want to get your TWO
WHEELER tyres filled with AIR, you go to a PETROL BUNK & get them
filled with air. While getting them filled, you say 30 in the FRONT & 35 in the
BACK. What do these 30 &35 indicate. They are 30 psi & 35 psi.
If you want to check the adequacy of green strength, there are equipments
available. If you want to do it manually, take a hand-full of green sand in your
palm & squeeze it into a shape of “ MODAK “. Holding the bottom of the
sample in your palm, BREAK the TOP of the sample with your THUMB. On
looking at the sample, if you NOTICE your FINGER PRINTS on the sample &
sand grains at the EDGE OF BROKEN SURFACE are intact (NOT FALLEN
DOWN) then the you can conclude that green strength is adequate.
Dry strength of this sand can be around 150 psi. If you do not have an oven to
dry the mould, you can even SKIN DRY the surface with L.P.G Flame at LOW
intensity so as to remove MOISTURE only & not burn away your additions
like DEXTRINE etc.
When you want to make a green sand mo