FIELD OF THE INVENTION
This invention relates to a protective coating for tundish working lining.
This invention further relates to a coating of Zircon based material on
MgObase tundish working lining, which is applicable in all those areas
where MgO based castablejspray massjvibro-mass are used in the
working face at high temperature.
BACKGROUND OF THE INVENTION
Tundish is a vessel lined with refractory, in which the molten steel is
metallurgically processed before pouring into the moulds. The properties
of a tundish working lining are that it should have low thermal
conductivity, which helps to reduce the rate of heat loss from the steel in
the tundish and provides a more uniform steel temperature entering the
mould which improves the steel quality, a low thermal conductivity also
prevents reaction between the acidic and basic lining due to low
temperature at the interface and aids in easy removal of steel skull due
to formation of weak, friable layer in the working lining near permanent
lining. The other important property is that the tundish lining should
have high resistance towards corrosion against metal and slag which
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helps to maintain steel clearliness and leads to high performance i.e.
long sequence casting. Due to an increased demand of high purity steel,
the interaction between tundish refractory lining and molten steel and
slag has become an important concern for steel manufacturers.
The purpose of tundish working lining is to maintain molten steel
cleanliness, to maintain steel temperature to protect permanent lining
and to allow easy removal of steel skull after casting.
All these requirements are achieved through proper design of working
lining material.
In the existing tundish lining practice, permanent lining is made up of 70%
Ah03 LowCement Castable & above it the working lining of DBMbased
DVM(Dry Vibratable Mass) having the following composition:
Oxide 010
MgO 70-90 approx
Si02 5-20 approx
Fe203 1-2.5 approx
CaO 1 approx
Ah03 0.15 approx
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At the application temperature the molten slag penetrates into the
working lining & subsequently corrodes the working lining thus reducing
the sequence length.
The interaction between slag & the refractory lining involves wetting,
penetration and reaction, which determines the service life of the working
lining and the quality of semi-processed products like slabs, billets and
blooms.
Therefore, the need exists to provide a suitable coating for the tundish
working lining which has a low thermal conductivity, so that the rate of
heat loss from the steel in the tundish is reduced, and for more uniform
steel temperature entering the mould which improves the quality of steel.
Further, the reaction between acidic and basic lining should be
prevented due to low temperature at the interface. Also, there should be
easy removal of steel skull due to formation of weak, friable layers in the
working lining near the permanent lining.
OBJECTS OF THE INVENTION
It is, therefore, an object of this invention to propose a protective coating
for tundish working lining, which is dense and hard and prevents the
-l(-
penetration of slag into the lining and improves its service life.
It is a further object of this invention to propose a protective coating for
tundish working lining, which has good adhesion property.
Another object of this invention is to propose a protective coating for
tundish working lining, which has low thermal conductivity, which
eventually improves the steel quality.
These and other objects and advantages of the invention will be apparent
from the ensuing description.
BRIEF DESCRIPTION OF THE INVENTION
Thus, according to this invention is provided a protective coating for
tundish working lining.
In accordance with this invention, a Zircon based protective coating is
developed which comprises 60% to 70% by weight of Zircon, 25% to 30%
by weight of Silica, a maximum of up to 0.75% by weight of 8203, 0.75%
to 1.25% by weight of Alumina, a maximum of up to 0.5% by weight of
Titania and a maximum of up to 1% by weight of ferric oxide, 0.75% to
1.25% by weight of calcium oxide and a maximum of 0.5% by weight of
Magnesium Oxide. The lining prevents the penetration of slag, thus
reducing further reaction leading to corrosion of the working lining. This
lining can be used as an effective top-coating on the MgO based tundish
working lining.
The invention will now be explained in greater detail with the help of the
following non-limiting example. However, this is only an exemplary
embodiment, without implying any limitation on the scope of the
invention.
Example
The followingcompounds were mixed in the proportions given:
Zr02 67 gms
Si02 28gms
8203 0.75 gms
Ah03 1 gm
Ti02 0.5 gms
Fe203 1 gm
CaO 1 gm
MgO 0.5 gms
The compounds were ground and mixed into a fine powder. This powder,
the coating composition was then mixed with water and organic binder
into a paste, ready for application to the tundish walls.
A cube shaped test sample MgO is prepared out of regularly used MgO
DVM(Dry Vibratable Mass). The Zircon based material is then made into
a paste by using suitable quantity of organic binder & water. A layer of
this paste is coated on the inside surface of the groove made in the cube.
Then it is heated at the operation temperature with plant slag of different
steel grade. The same experiment is conducted with a sample having no
coating and when compared it is found that in case of Zircon coated
sample, slag remains on the bottom and does not penetrate on the side
walls whereas in case of sample with no coating, slag penetrates deep
into the bottom and side wall of the refractory. This Zircon coating has a
very good adhesion on MgObased DVM.At the application temperature,
it forms a dense and hard coating which is impermeable to slag on the
tundish working lining. The coating increases the refractory service life
thus reducing specific refractory consumption and also prevents
refractory inclusion from the working lining to the steel. It will help in
increasing the production by reducing change over time for the tundish
and it will also significantly increase the steel cleanliness by preventing
inclusions from the refractory working face.

WE CLAIM:
1. A protective coating composition for tundish working lining
comprising
Zirconia
Silica
Borax
Alumina
Titania
Ferric Oxide
Calcium Oxide
Magnesium Oxide
60 to 70% by weight
25 to 30% by weight
upto 0.75% by weight
0.75 to 1.25% by weight
upto 0.5% by weight
upto 1% by weight
0.75 to 1.25% by weight and
upto 0.5% by weight.
2. The process as claimed in claim 1, wherein the protective coating
composition is converted into a paste by mixing with organic
binder and water.
3. A process for the preparation of a protective coating for tundish
working lining comprising mixing
Zirconia
Silica
Borax
60 to 70% by weight
25 to 30% by weight
upto 0.75% by weight
Alumina 0.75 to 1.25% by weight
Titania upto 0.5% by weight
Ferric Oxide upto I% by weight
Calcium Oxide 0.75 to 1.25% by weight and
Magnesium Oxide upto 0.5% by weight.
and converting it into a fine powder, followed by mixing the powder with
an organic binder and water to obtain the protective coating.