Continuous casting-tundish technology

SO,WHAT IS STEEL?
 Steel is an alloy of iron and other elements,
including carbon. When carbon is the primary
alloying element, its content in the steel is
between 0.002% and 2.1% by weight. The
following elements are always present in
steel: carbon, manganese, phosphorus,
sulfur, silicon, and traces of oxygen, nitrogen
and aluminum

CONTINUOUS CASTING
 Continuous casting, also called strand casting, is
the process whereby molten metal is solidified into a
semifinished billet, bloom, or slab for subsequent
rolling in the finishing mills.

 Most basic metals are mass-produced using a
continuous casting process, including over 500
million tons of steel, 20 million tons of aluminum, and
1 million tons of copper, nickel, and other metals in
the world each year

 The continuous casting has several
configurations to produce the steel as vertical,
vertical with bending and curved type.
.

 Curved machines are used for the majority of steel
casting and require bending and / or unbending of
the solidifying strand.

WHAT DO WE DO UNTIL CONTINUOUS
CASTING ?
 Preparation the steel by adding some materials
within the different furnaces such as BOF,EAF.

BOF(BASIC OXYGEN FURNACE)
1.Molten pig iron from a blast furnace is poured into
a large refractory-lined container called a ladle
2.The metal in the ladle is sent directly for basic
oxygen steelmaking

3.Filling the furnace with the ingredients is called
charging. Molten iron from the ladle is added as
required by the charge balance. A typical chemistry
of hot metal charged into the BOS vessel is: 4% C,
0.2–0.8% Si, 0.08%–0.18% P, and 0.01–0.04% S.
4.The vessel is then set upright and a water-cooled
lance is lowered down into it. The lance blows 99%
pure oxygen onto the steel and iron. This melts the
scrap, lowers the carbon content of the molten iron
and helps remove unwanted chemical elements
5.Fluxes (burnt lime or dolomite) are fed into the
vessel to form slag, which absorbs impurities of the
steelmaking process

6.The BOF vessel is tilted
again and the steel is
tapped into a giant ladle.

ELECTRIC ARC FURNACE
Arc furnaces differ from induction furnaces in
that the charge material is directly exposed to
an electric arc, and the current in the furnace
terminals passes through the charged material.

SMELTING PROCESS OF ELECTRIC ARC FURNACE

THE MORTEN STEEL IS NOW IN LADLE
FURNACE
LADLE FURNACE
There is an important thing that should not
be forgotten!!!! Before the tapping from the
EAF or BOF to the LF, the LF has to be
preheated..

SO,WE ARE READY TO START TO THE
CONTINUOUS CASTING

THE BENEFITS OF CONTINUOUS CASTING
 Considerable energy savings
 Less scrap produced, i.e. improved yield
 Improved labor productivity
 Improved quality of steel
 Reduced pollution
 Reduced capital costs
 Increased use of purchased scrap when
output is maximized

1) The liquid steel comes from the steel plant in a ladle
2) From ladle it is tapped in a tundish

3) Liquid Steel is flowed through the nozzle to mould
from tundish. The flow rate through the nozzle into the
mould can be controlled by a stopper in the tundish
4) The mould is a rectangular copper box without a top
and a bottom
5) The outer shell is being ’grabbed’ by a driven roll just
beneath the mould, pulling a strand of steel out of the
mould.
6) The core of the strand, as it exits, is still liquid;
because of that, the strand proceeds through a
secondary cooling section
7) The strand is bent from the vertical plane to
horizontal plane using rolls

8) At the end of the cooling section the cross-section of
the strand is completely solidified, slabs are then
created by cutting the strand
9) These slabs are put in a tunnel furnace to let them
homogenize
10) After a while the slabs come out of the furnace;
subsequently they are rolled out, further cooled and
finally coiled

The tundish holds enough metal to provide a
continuous flow to the mold, even during an
exchange of ladles, which are supplied
periodically from the steelmaking process

 The shape of the tundish is typically rectangular, but
delta and "T" shapes are also common.
 Nozzles are located along its bottom to distribute
liquid steel to the molds

The tundish also serves several other key functions!!!
 Enhances oxide inclusion separation
 Provides a continuous flow of liquid steel to the mold
during ladle exchanges
 Maintains a steady metal height above the nozzles to
the molds, thereby keeping steel flow constant
 Provides more stable stream patterns to the mold(s)

 The tundish is a refractory-lined channel consisting
of an inlet and outlet sections and sometimes has
flow control devices, such as dams and weirs or a
baffle with holes, along its length.
DAM BAFFLE
WEIR

• A tundish may have a refractory-lined lid, and has
bottom ports that are assembled with slide gates or
stopper rods through which the melt is teemed into
the mold

THE USED DEVICES IN THE
TUNDISH
 IMPACT PADS: Designed to redirect steel upward
and outward for enhanced steel residence time in the
tundish and prevent short circuiting to the closest
strand(s)
 Also used for optimized drainage and yield
enhancement for multiple radical grade change
sequences

 BAFFLES: While in the tundishes, impurities (called
"inclusions") in the molten steel float to the top,
forming a "slag" layer of impurities, and the pure,
substantially "inclusion-free" metal exits from the
bottom
 Depending on the size of the tundish, and the flow
rate of molten steel, the molten steel may not always
have enough residence time in the tundish to permit
the impurities to float to the top.Therefore,the baffles
are used.

 DAMS: This device helps to modifying the inside
bottom surface of a tundish for continuous casting
molten steel to minimize turbulence thereby reducing
gas bubble and slag entrainment during continuous
casting of steel, especially when initially filling of the
tundish.
DAM

 Thermocouple: It reads the steel bath temperature in
real time at a fixed location inside the tundish.
 Diffusers: During operation the Tundish Gas Diffuser
will help reduce "dead" areas within the tundish and
provide a more stable steel temperature in the tundish
bath

 Stoppers: This is used to control the molten steel
flow from the tundish to the mold

 Slide Gates: Tundish gates are provided with 3
plates in order to avoid the movement of the
subentry shroud in the mould during the flow control
by throttling.

 Metering Nozzle: Key features of nozzle changer
systems include:
1) Improved casting operator safety
2) Enables longer casting sequences
3) Improved metallurgical quality
4) Flexibility

 Submerged Entry Nozzle: These refractories are
subjected to severe operating conditions such as
thermal shock,molten steel erosion,and slag attack.
Upper Nozzle

THE IMPORTANCE OF TUNDISH
 The melt remains in the tundish for a relatively short
time, reflecting the continuous nature of tundish
operation
 Thus, the major refining reactions such as deoxidation
and desulfurization are carried out in the ladle.
The goals of a tundish are to
minimize heat loss, deliver the
melt evenly into molds, minimize
the formation of macro inclusions,
and
maximize their removal.

INCLUSIONS AND DEFECTS
 Non-metallic inclusions are a significant problem in
cast steels
 The mechanical behavior of steel is controlled to a
large degree by the volume fraction, size,
distribution, composition and morphology of
inclusions and precipitates, which act as stress
raisers
 The inclusion size distribution is particularly
important, because large macro inclusions are the
most harmful to mechanical properties.

 The ductility and durability are significantly impaired
by large-sized, non-metallic inclusions in steel.
The samples of inclusions are shown above

 Non-metallic inclusions in steel are of two kinds, and
each has its different mode of formation.
1. one is indigenous oxide inclusions which form by
deoxidation of the steel melt.
2. The other kind is exogenous inclusions, which form
by reoxidation of deoxidized steel melt by air or by
the entrained slag into the melt during the melt
transfer from ladle to mold.
INDIGENOUS EXOGENOUS

DEFECTS IN STEEL PRODUCTS
Flange
Cracked Cans
Slag spots on
cold rolled
sheet
Line defect on
cold rolled sheet

THE FOLLOWING FACTORS NEED PARTICULAR
ATTENTION IN MAKING A TUNDISH EFFECTIVE
FOR REDUCING MACRO INCLUSIONS:
#1. Steady state period of casting requires:
 Melt flow with less turbulence along the tundish
flux/melt interface
 No short circuiting of melt flow from the inlet section
to the exit (tundish nozzle)
 Minimal dead volume for the melt in the tundish
 Sufficient residence time for the melt to promote
flotation
 An argon gas shrouding pipe or long nozzle for ladle
melt discharge into the tundish
 Thermal insulation and protection against reoxidation
by argon gas injection with lid or a tundish flux cover

#2. Non-steady state period of casting requires:
 Prevention of slag carry over by vortexing and
draining from the ladle to the tundish
 The above slag carry over issue also applies to
tundish to mold transfer
 Suppression of turbulence caused by impinging melt
stream to the tundish at the ladle opening
 Sustaining an inert atmosphere at ladle opening and
ladle change
 Active compensation for temperature drop

 The tundish can be designed according to the
following conditions:
• The amount of the production:The volumes of ladle,
BOF,EAF
• The various of the production (bloom, billet, slab)
• The number of the strands
• The features should be placed to float the inclusions
from the morten steel to the slag( dams, baffles,weirs )
• The control of melt temperature to an appropriate level
for feeding into the mold
• The control of flow rates ( nozzle port(s), slide gates,
stopper rods )
• The adjustment chemical compositions

 Various technologies such as a long nozzle or an
inert gas shrouding pipe have been implemented to
reduce air reoxidation and slag emulsification.
 Tundish thermal state during continuous casting as
function of heat losses through the tundish shell,
insulation of the steel bath and temperature.

TO INDICATE THE VOLUME AND THE NUMBER OF
THE STRANDS OF THE TUNDISH
 This exactly belongs to the amount and various of
factory production
 The number of molds is usually 1 or 2 for a slab
caster, 2 to 4 for a bloom caster, and 4 to 8 for a
billet caster
BLOOM SLAB

1) ANCHORING SYSTEM
 The anchoring system is done to be hold the
permanent lining slightly to the tundish.
 This anchors are assembled
to the tundish walls at certain
distances by welding

2) INSULATION MATERIAL
 The ceramic fiber panel is used due to its low thermal
conductivity and low heat storing between the tundish
wall and permanent lining.
 These may be showed according to the production
conditions and the volume of tundish

THE PLACEMENT OF NOZZLES AND STOPPERS
 Before the permanent lining process is begun, the
nozzles should be positioned to the outlet points at
the bottom of the tundish
 These devices are used to control the fluid flow from
the tundish to the mold.
 The used of these may be showed difference
according to the various of production and the
production conditions

3) PERMANENT LINING
 The permanent refractory lining made of aluminous-siliceous
refractory concrete may be made of
refractory bricks or may be a cast or rammed
monolithic lining or a combination of the two.
 The expected properties from the permanent lining
are showed on following:
 Almostly zero cement should be
 The particule distribution of admixture should be
lower
 These may be lowest bonded cement according to
the production and the materials

 The hot ratios of expansion of the components
should be close as material properties
 The high resistance against the high temperature,
wear and impact
 The application of this lining should be easy

 The permanent lining is generally made of high
alümina refractory(%70-%93) and is the thickest part
of the tundish lining. This lining has a low reactivity
with magnesia materials to form a surface working
layer.
 Aluminous-siliceous refractory concretes proved the
best in the second layer.
 These are the materials that contain cement binder
usually aluminate cement, which imparts hydraulic
setting properties when mixed with water
 The most common binder used in castables is HAC
(high alumina cement)

 Other binders that are often used include hydratable
aluminas and colloidal silica
 When the working temperature is increased,the
Al2O3 content should be increased.Because of this,
the thermal conductivity and flexibilty.
 These monolithic castables should be dried, sintered,
and preheated before being put in service to prevent
explosion spalling

• CAC in castables: The refractory concretes are
divided into 4 main groups:
1) Conventional Cement Castables,CCC,high cement
contents(>20% CAC)
2) Low Cement Castables,LCC (6-15%)
3) Ultra Low Cement Castables (<6%)
4) Cement Free Castables/No Cement Castables,
NCC (<1,5%)

 Here the permanent lining may show severe damage
by cracking
 Mechanical failure of the permanent lining occurs in
the transition zone between the inlet port and the
plain side wall of the bath.

 Cracks propagate through the whole thickness of the
permanent lining and are penetrated by hot metal up
to the cold end.
 This crack formation increases the probability of
failure during breaking out of the working lining.

 To reduce cracking and to avoid the delamination
quoted above, calculations with an additional
expansion allowance were performed with a
preheating up to 1100°C on the hot face.

 In conclusion, A longer heat penetration period leads
to a more homogeneous temperature distribution at
the moment of the thermal shock and this
circumstance decreases thermomechanical load in
the transition zone.

THE APPLICATION OF PERMANENT
LINING
 After the nozzles (SEN, metering nozzle or slide
gates) are placed to the bottom of the tundish based
on the production conditions, this application is done
 After the former is positioned into the tundish,the
lining process is begun.
 The mix that was prepared
before is filled between
the former and the tundish
walls

 The former is observantly vibrated till the end of the
installation
 However,this process is done as soon as the bubbles
are seen over the the permanent layer. The reason of
this is that the binders within the solidified mix rise up
through the layer and cause the micro and macro
cracks in the process.Therefore,the vibration process
should be done carefully.

4) THE PLACEMENT OF TUNDISH
DEVICES
 The placement of tundish devices (ımpact pads,
baffles, weirs, dams) is the most important section
for tundish design.Because,the non-metallic
inclusions can be moved away from the liquid steel
and added to the slag layer with using of this
devices.
 In this way, the clean steel can be occured.

 The placement or building with burnt MgO bricks of
impact pad is done firstly.
Burnt MgO Bricks

 By the last decade, testing and use of incidence ‘pot’
known under the name TURBOSTOP was accepted.
 The quite good conditions for rectifying flow in the
tundish were provided with its installation.

THE VARIOUS OF TUNDISH DESIGNS
 The main points to improve tundish configuration are:
 increase minimum residence time
 get similar minimum residence times between all the
strands
 increase plug volume fraction
 increase mixing volume fraction
 decrease dead volume fraction

1) The Baffles Configuration:
 The hole angles of the baffles are important to move
away the non-metalic inclusions to the slag
 However,the only baffles don’t indicate the expected
effect regarding the non-metallic inclusions

2) The Baffles-The Dams Configuration
 As mentioned above,the dams help to minimize
turbulence thereby reducing gas bubble and slag
entrainment during continuous casting of steel.
 The shape and arrangement of dams and baffles has
also an affect on the thermal conditions prevailing in
the tundish.

 Depanding on tundish interior geometry, there are
zones of diverse flow intensities within the tundish:
- Active area
- Stagnant area( dead region )
 Dead zones result in a less homogeneous metal, and
also reduce the effective capacity of the tundish.

Configuration 1 Configuration 2
Regarding temperature yield,when low dams were
considered temperature at outer strands were around 3ºC
lower than the ones obtained at inner strands. This fact was
attributed to the lower velocities reached at bottom region
near the dams in configuration 1 and configuration 2

3) The Baffles-The Dams-The Diffusers Configuration:
 The diffusers will help reduce "dead" areas within the
tundish and provide a more stable steel temperature in
the tundish bath
 This device is used in the configurations which we can’t
find the solutions regarding reducing the dead zones.

4) The Weirs-The Dams Configuration:
 The weirs are located in the upper part of the tundish.
 The weir prevents liquid metal from flowing
continuously across the surface of the molten metal,
while allowing liquid flow beneath the weir.
WEİR
DAM

The differences can be seen with water modelling

 The height of the tundish and the steel velocity are
other properties to obtain the clean steel to prevent
the dead zones

The outlet temperature of
the melt is seen reduced
with the increase in the bath
height as in previous cases
due to increase in the heat
transfer area.
It is also observed that
with the increase in the
bath height, bluish
coloured cooler regions
shift towards the top
free surface and inlet
side with the increase in
the bath height, due to
recirculating and
reversing flow.

 Casting flow rate has a big influence on the structure
of flow and the steel turbulence intensity in the
tundish. The higher casting flow rate, the lower part
of dead zones in the volume of liquid steel.

 In conclusion,the best design should have the
baffles, the dams and the diffusers.Because,the
more wear are seen especially in the configuration
having the weirs and the zones combined the side
tundish walls with the weirs will be done more wear.
Therefore:

5) THE WORKING LINING
 A working lining layer is mostly made of magnesia
mixture that is wet applied through gunning in
succesive steps by 20mm layers up to requested on
walls and slag line(60-80 mm thickness)
 With their usage the use of monolithic isolation mixes
started to be even more important,because
compared to brick lining isolated tundish had better
isolation properties,which bettered the thermal
balance
 It has a higher thermal expansion coefficient

 From tundish lining is expected:
 Decrease of thermal loses by long sequences
 Better turn of tundish
 Longer life time and decrease in maintenance costs
of refractories
 Simple drying and heating
 Easy tapping and decrease of waste volume
 Better lining integrity-increased purity of steel
 Simple and quick installation
 Decreased specific consumption upon a ton of steel
 It shouldn’t include the asbestos

 The working lining is installed over permanent lining
to provide thermal insulation and keep the steel shell
temperature below its critical temperature range
throughout the operating campaigns of a tundish
The refractory material of the
working face in contact with
the steel melt should be high in
MgO, with a minimum amount
of reducible binder to prevent
oxidation of Al in the melt.

 The working tundish lining refractory composition
further includes a binder based on silicates or
phosphates; a plasticizer which enhances adherence
of the composition when applied to the permanent
lining; a bond stabilizer; a homogenizer; and in
certain cases, a small amount of a wetting/foaming
agent
 The corrosion of the working lining in molten slags
depends strongly on the viscosity of slag and also
the basicity gap between the refractories and the
slags.

 When slag penetrates into pores of common plaster
with high- MgO content, the phases such as
monticellite and merwinite develop around MgO
grains and provide continuous dissolution of MgO
grains during steel-making process.
 Replacing part of the magnesia of plaster by
chromite or olivine is promising for decreasing the
hot corrosion.
 This is because the basicity gap between introduced
plasters and tundish slag decreases and also causes
the formation of phases with high melting point on
the surface of primary grains of MgO and decreases
the dissolution of plaster in the slag. Therefore, the
life time of these plasters is increased to higher
sequences.

THE APPLICATION OF THE WORKING LINING
 Magnesia mixture with various additives is spread on
basis permanent lining with temperature up to 100̊C
in thickness 60-80mm.
 In generally,the amount of water added into the
mixture is % 18-25.

 The tundish lining is preheated before putting into
operation usually to temperature 1100-1200 ̊C

The tundish is ready for continuous
casting

Continuous casting-tundish technology

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