Casting Manufacturing

1. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Purpose
Purpose of this document is to provide general information of foundry practices normally being followed
by Iron casting manufacturers globally.
Prepared By: A T Ansari

2. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Typical process flow for casting manufacturing
Prepared By: A T Ansari

3. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Various raw materials are being used in foundry processes to form
end result cast, our focus will be on major ones as listed below.
a. Pig iron Storage of Raw materials,
Raw material receipt & b. Steel Scrap Identification and
Receipt inspection: c. CRCA scrap traceability, receipt
d. Ferro alloys inspection facilities
e. Green Sand
f. Resin coated sand
Method of metallic pattern
Pattern and core box can be made by using various materials,
manufacturing, Life of
such as
Pattern and core box toolings made from
a. Metallic
making wooden & chemical
b. Wooden
compound. System of
c. Chemical compounds e.g. Araldite
tooling management.
What is core? ==> Core is a component made of molding
material, used to create desired cavity / intricate shapes in Where are the core
casting. Core can be also made up by using various materials & prints?
methods, major processes as listed below.
a. By use of metallic core box and resin coated sand – Tooling is Core box temperature,
heated, as soon as resin coated sand comes in contact of heat, HTS / LOI of resin coated
sand grains form a bounding in desired shape. sand
b. By CO2 Process – Uses proportionate mixture of raw silica
y p p
sand and sodium silicate, after ramming/shooting the mixture into
Ratio of Sodium silicate,
the core box CO2 is passed thru, here CO2 acts as catalyst and
vents and passing of CO2
sand bounded to form a core. Wooden tooling can be used in this
Core making
process.
c. By Cold box process – Uses proportionate mixture of raw
silica sand, part 1 (resin) and part 2 (hardener), Shoots this Ratios of resin and
mixture into core box and then Amine gas is passed thru, here hardener, type of Amine.
Amine gas acts as catalyst to form hardened and strengthen core
d. By No Bake process – Uses proportionate mixture of raw silica
sand, part 1 and part 2 (These part 1 and part 2 are not same as
Ratio of part 1 and part 2,
used in Cold box process, chemical composition is different),
air set time
Shoots this mixture into core box. This process is time based, after
some time core gets rock solid and can be ejected from core box.
Prepared By: A T Ansari

4. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
What is Mold? ==> A mold or mould is a hollowed-out block, a
framework or shape used to make an object of complementary Sand to metal ratio
shape from a liquid metal.
a. All the above mentioned processes in core making can be As applicable as per
utilized for molding also. above.
Molding
b. Green Sand Molding – This is most commonly used molding
process, the term "green sand" is known principally because of the
Moisture content, Green
moisture content within the sand. The sand undergoes a "mulling"
compression strength
process in which various clay and chemical additives that act as
(GCS),
binders are blended with the sand, which results in a compound
which is suitable for the sand molding process.
a. By using Cupola + Induction furnace – In this method melting is
Melting rate of cupola,
done in cupola and then metal transferred to electric induction
holding furnace capacity,
furnace, where liquid metal can be hold at required temperature
operating controls,
and necessary chemistry can be adjusted. This method is called
support facilities
as “Duplex Melting”.
Melting
b. By using Electric induction furnace – In this method melting is Frequency type, capacity,
done in induction furnace it self and ready material tapped for operating controls,
pouring if CI or given for Mg treatment if SGCI. support facilities
a. High sulphur generally occurs in metal melted in acidic cupolas,
which if not lowered, necessitates the use of increased amount of Sulphur content prior to
spheroidizing alloy. Desulphurization can be done by commonly desulphurization
used methods, s ch as
sed methods such as…
i. Injection of calcium carbide into the melt – The fine calcium
carbide is injected through a refractory tube, using dry nitrogen Ratio of Calcium Carbide
gas as the carrying agent. The calcium sulfide formed floats to the and Nitrogen gas
surface of the melt as readily removable dross.
Desulphurization
ii. Soda ash additions are also used to reduce sulphur levels. Ratio of Soda ash
iii. Lime is also used for desulphurization, alone or in conjunction
Ratio of Lime.
with other materials.
iv. Shaking ladle – A recent innovation, uses lime. Shaking the
Ratio of lime and ladle
ladle increases contact of lime and metal, resulting in sulphur
shaking time
levels reduced.
b. Desulphurization generally not required when “Electric Sulphur levels of metal
induction furnace” used for melting. from induction furnace
Holding and Chemistry a. Superheat the metal taken from cupola. Holding temperature, time
adjustment – Induction b. Adjust the chemistry required to achieve metallurgical and taken for chemistry
furnace physical properties. adjustment, deslagging
Prepared By: A T Ansari

5. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Why magnesium treatment: Ductile iron, also known as spheroidal
graphite (s.g.) iron or nodular iron, is made by treating liquid iron
of suitable composition with magnesium before casting. This
promotes the precipitation of graphite in the form of discrete
nodules instead of interconnected flakes. The nodular iron so Amount of metal to be
formed has high ductility, allowing castings to be used in critical treated in any type of
applications such as Crankshafts, steering knuckles, differential treatment.
carriers, brake callipers, hubs, brackets, valves, water pipes, pipe
fittings and many others.
Types of Mg treatment as mentioned below…
i. Sandwich method
Sandwich ladle: the treatment alloy is contained in a recess in the
Ratio of nodulizer and
bottom of a rather tall ladle and covered with steel scrap. The
steel punching
method is suitable for use only with treatment alloys containing
Magnesium Treatment less than 10%
ii. Tundish cover method
Tundish cover: this is a development of the treatment ladle in
Diameter of tundish hole
which a specially designed cover for the ladle improves Mg
recovery and almost eliminates glare and fume
iii. Plunging method
Plunger: the alloy is plunged into the ladle using a refractory
Plunging system.
plunger bell usually combined with a ladle cover and fume
extraction
iv. Mechanical feeder.
Cored wire treatment: wire containing Mg, FeSi, Ca is fed Diameter of wire and its
mechanically into liquid metal in a covered treatment ladle at a chemical composition
special station
Treatment in the mould (Inmold): MgFeSi alloy is placed in a
size of inmold chamber,
chamber
chamber moulded into the running system, the iron is continuously
amount of nodulizer
treated as it flows over the alloy
Why Inoculation - Although the magnesium treatment is
responsible for the development of spheroidal graphite, quality
ductile iron also requires use of inoculants. Inoculation or post-
inoculation refers to the practice of making addition to the melt
which will increase the number of spheroids formed during
solidification.
Inoculation The amount of inoculant needed is governed by several factors.
The following rules guide the use of inoculation:
Low carbon equivalent irons require greater amounts of inoculant.
Grey cast irons with less than 0.06% sulphur are difficult to
inoculate, specially formulated products may be required.
For a given iron, the thinner the section of casting, the greater the
inoculation required.
Prepared By: A T Ansari

6. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Electric melted irons require more inoculation than cupola melted
irons. Electric melting will also produce low sulphur contents. High
steel scrap charges will require more inoculation. Where
inoculated iron is held for more than a few minutes after
inoculation, there is a need of a higher level of treatment. It is
therefore difficult to give an accurate estimate of the amount of
inoculant which is required for every situation. In general,
inoculant additions of 0.1–0.5% by weight of metal will be
satisfactory for grey cast irons, higher additions are needed for
ductile (SG) irons. Care must be taken not to over-inoculate grey
irons, otherwise problems will arise with shrinkage porosity due to
too high a nucleation level. Many grades of inoculants contain
high Si content, so that by adding 0.5% of inoculant, the silicon
content of the iron will be raised by as much as 0.3%, this must be
allowed for by adjusting the Si analysis of the furnace metal.
The most widely used inoculation for ductile iron is ferrosilicon Size and quantity of
alloys. The most widely used grade is 85 percent silicon. inoculant
i. Ladle inoculation Inoculation in bottom of
Inoculation Conventional method where inoculant either kept in ladle before ladle or during tapping,
tapping or put in the ladle during tapping the metal from furnace. size and type of inoculant
ii. Stream inoculation
The inoculant used in late stream inoculators must have a number
of important features:
It must be a powerful inoculant. System of stream
It must be finely divided to ensure free-flowing properties and inoculation, size and type
rapid solution. of inoculation, start and
It must be very accurately graded, without superfine material end time of stream,
which would blow away, or large particles which jam the gate amount of inoculant
mechanism.
It must dissolve rapidly and cleanly to avoid the presence of
undissolved inoculant particles in the castings.
iii. Mold inoculation
There are several ways in which mould inoculation can be
Design for mold
performed: powdered inoculant can be placed in the pouring bush;
inoculation, size of mold
or it can be placed at the bottom of the sprue. A more reliable
inoculation
method is to use sachets or precast slugs of inoculant in the
pouring bush or in the running system
Pouring is activity to pour cleaned and inoculated liquid metal into Pouring temperature,
mold with specific temperature range within specific time. pouring time, deslagging
Natural cooling of casting for designed time is necessary to
Pouring and cooling achieve required hardness, microstructure and physical
properties.
Cooling time
The cooling time not only allows the castings to solidify completely
but also reduces internal stresses within the casting caused by
differential cooling of sections of varying thickness.
The shakeout separates the castings from the sand. It may be a
vibrating grid or a rotating drum, the latter also having a cooling
function since water is sprayed onto the sand in the drum. The
shakeout is provided with copious air extraction, to prevent dust
System of shake out and
Shake out & Knock out from entering the foundry. This also removes some fines from the
knock out
sand and so plays an important part in the control of the sand
system.
In knock-off or knock out casting separation done from runners
and riser.
Prepared By: A T Ansari

7. GENERAL DUCTILE IRON MANUFACTURING PROCESS
Process Process Description What to look for
Shot blasting comes under category of Abrasive Blasting, abrasive
material in this case is steel shots.
Abrasive blasting is the operation of cleaning or preparing a
surface by forcibly propelling a stream of abrasive material against
Shot blasting Cycle time
it. Usually explained as the use of a material against another
material to make it smoother, remove surface contaminants or to
roughen a surface. It is also the appropriate term for what is
known as glass bead blasting, sandblasting, sand carving,
sodablasting or shot blasting.
These are the common processes in any foundry. In these
Grinding, trimming processes fins and burrs removed from casting with help of bench Tools for fettling.
grinders and portable grinders.
Primary Inspection
This is a type of visual inspection and carried out immediately
after knock out, in some special cases it is done after shot blasting
also as defect are more visible after shot blasting.
Secondary Inspection
This is combination of visual and dimensional inspection after all
grinding and fettling, when casting is ready for dispatch or
machining.
Physical testing
Inspections
These are destructive tests, often for to saving the casting and
cost, these tests are done on test bars of same metal according to
applicable standards. Two main test which are generally
conducted are Tensile test and Impact test.
Non Destructive testing (NDT)
These are the tests carried out directly on the part without causing
any damage to casting or product. Major NDT techniques are
ultrasonic tests, Magnetic particle inspection and liquid penetrant
test.
Prepared By: A T Ansari