A COMPOSITION FOR MAKING HIGH ALUMINA BRICKS WITH HIGH THERMAL
SHOCK RESISTANCE AND VOLUME STABILITY, BRICKS MADE THEREFROM
AND A PROCESS FOR PRODUCING THE SAID BRICKS
FIELD OF THE INVENTION
The present invention relates to refractory lining of roof in Electric Arc Furnaces (EAF).
More particularly, the present invention relates to a composition for producing improved
High Alumina bricks having high Thermal Shock Resistance combined with high volume
stability and high refractoriness suitable for use as refractory lining of roof in Electric Arc
Furnaces (EAFs).The invention also relates to the said bricks produced from the said
composition. The invention further relates to a process for producing said bricks. The
invented bricks have particular application in Alloy Steels Plant (ASP) of Steel Authority
of India Limited (SAIL).
BACKGROUND OF THE INVENTION
Alloy Steels Plant (ASP) is found to have faced problem with poor performance of EAF
Roof Refractories. Sometimes, this poses problem in maintaining an uninterrupted and
continuous operation of even one EAF for SMS production due to unplanned shut down
of furnace for roof changing. Average lining life of roof is about 100 heats. For
maintaining a steady production in SMS, ASP needs to have a consistent EAF roof
performance of about 150 heats.
To circumvent this problem, the applicant had initiated a research project for
development of high alumina roof bricks with high thermal shock resistance combined
with high volume stability suitable for use as roof lining of electric arc furnaces. The
design of roof and operating conditions demand refractory bricks having a combination
of high thermal shock resistance and high volume stability. The present invention has
led to a successful development of a High Alumina (80% Al2O3), high Thermal Shock
Resistant roof bricks with high volume stability and high refractoriness.
PRIOR ART
Following prior art patent references in the field are mentioned:

US 3378385 (1968) disclosed a ceramically bonded high alumina refractory made from
a batch comprising essentially of fused alumina grain containing Titania, finely divided
chrome sesquioxide and finely divided non-fused high alumina refractory material.
US 3377178 (1968) disclosed a ceramically bonded brick made from a batch consisting
essentially of co-burned Al2O3-Cr2O3 grain, finely divided chrome sesquioxide and finely
divided high alumina material.
US 3888687 (1975) disclosed an improved alumina-chrome refractory composition of
Tubular Alumina, calcined alumina, chromic oxide, phosphate compound, bentonite and
water.
US 4126474(1978) disclosed an improved alumina or alumina-silicate refractory for
lining aluminium melting furnaces and other containers for molten aluminium including
0.5-30% by wt of BaSO4. The addition of BaSO4 to a phosphate-bonded or phosphate
free plastic, ramming mix, brick, mortar or castables eliminate metal penetration and
reduces dross and metal adherence.
US 4290814(1981) disclosed a ceramically bonded brick made from a batch consisting
essentially of fused zirconia-mullet grain or fused zirconia-alumina grain, chromic oxide
and high alumina material.
US 4792538(1988) disclosed a chrome-alumina refractory brick prepared by pressing
and firing a mixture consisting of about 15-90% by wt. of chrome-alumina grain, 5-25%
by wt of chromium oxide, upto 30% of zirconia containing grain and balance alumina.
No prior published document is found which discloses any technology for high alumina
bricks with high thermal shock resistance, high refractoriness and high volume stability
suitable for use as refractory lining of roof in electric arc furnaces.
OBJECTS OF THE INVENTION
The main object of the invention is to provide for a composition for making High Alumina
bricks having high Thermal Shock Resistance, high refractoriness and high volume
stability suitable for use as refractory lining of roof in Electric Arc Furnaces (EAFs).
Another object of the present invention is to providefor refractory bricks made from the
said composition.

Another object of the invention is to provide for refractory bricks which would ensure
minimum thermal shock resistance of 50 cycles (By Air Quenching) coupled with
Refractoriness under load (RUL) of minimum 1550OC ( ta, as per IS:1528 Part II).
A further object of the invention is to provide for refractory bricks with high volume
stability by way of having required Repeat Permanent linear change after reheating
(Repeat PLCAR) of High Alumina bricks.
Another object of the invention is to provide for a process for producing the said
refractory bricks.
A further object of the invention is to provide for lining of roofs in electric arc furnaces
made from the said bricks.
DESCRIPTION OF THE INVENTION
The present invention provides for a composition for makingHigh Alumina bricks with
high thermal shock resistance, volume stability and high refractorinessfor use as
refractory lining of roof of Electric Arc Furnaces (EAFs)comprising:
Andalusite (Coarse) having particle size ranging from 1mm to 3mm and about
18-25 % by weight,
White Tabular Alumina (WTA) (Coarse) having particle size upto 2.5 mm and
about 13-18 % by weight,
Fused Mullite (Coarse) having particle size upto 2 mm and about 18-22 % by
weight,
Calcined Bauxite (Coarse & Fines) having particle size ranging from 0.074 mm to
1 mm and about 20-25 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 6-10 %
by weight,
Plastic clay (Fines) having particle size below 0.074 mm and about 8-14 % by
weight,

Feldspar (Fines) having particle size below 0.074 mm and about 4-6 % by
weight,
Molasses (Specific gravity- 1.1 to 1.2) of about 2.5-4 % by weight and aqueous
slurry of Plastic clay (Specific gravity- 1.1 to 1.2) of about 2-3 % as liquid binder
for wet mixing.
According to the invented composition–
Said Andalusite comprises
Al2O3- 57% Min;
Fe2O3 - 1% Max;
Specific Gravity– 3.0gm/cc Min.
Said calcined Alumina comprises
Al2O3– 99.5% Min. of which α- Al2O3 content is 90% Min;
Na2O – 0.5% Max.
Fe2O3 – 0.03% Max.
SiO2 – 0.03% Max.
Average Particle Size d50 – 5.5 micron Max.
Specific Gravity – 3.9 Min.
Specific Surface Area – 3.0 m²/gm Max.
+325 mesh (ASTM Tyler) – 1.5% Max.
Said White Tabular Alumina (WTA) comprises
Al2O3 – 99.3% Min.
Fe2O3 – 0.13% Max.
Na2O+K2O – 0.60% Max.
Bulk Density – 3.55 gm/cc Min.
Said Fused Mullite comprises
Al2O3- 70% Min.,
SiO2 - 29% Max.,
Fe2O3 - 1% Max.,
Na2O – 0.6% Max.;

Said plastic clay comprising
Al2O3 – 37% Min.,
Fe2O3 – 2.5% Max.,
PCE – Ort 32 Min.,
Moisture – 12% Max after drying at 110°C for 24 Hrs;
free from calcerious & ferrogeneous impurities & free silica based on physical
verification having sinterability and plasticity.
Said Calcined Bauxite comprises
Al2O3 – 87% Min.,
Fe2O3 – 2% Max.,
Na2O+K2O – 0.30% Max.,
SiO2 – 6% Max.,
TiO2 – 4% Max.,
MgO – 0.4% Max.,
CaO – 0.4% Max.,
Bulk Density – 3.20 gm/cc Min.;
Said Feldsparcomprises
Al2O3- 16% Min.,
SiO2 - 70% Max.,
Fe2O3 - 1% Max.,
Melting point – 10000C – 12600C
Another aspect of the invention is to provide for the refractory bricks made from the said
composition. The said High Alumina brickshave a minimum thermal shock resistance of
50 cycles (By Air Quenching) coupled with Refractoriness under load (RUL) of minimum
15500C (ta, as per IS:1528 Part II) and high volume stability by way of Repeat
Permanent linear change after reheating (Repeat PLCAR) comprising:


A further aspect of the invention is to provide for a process for the production of said
High Alumina Bricks which comprises the steps of
A. dry mixing of all the coarse grains (0.5mm to 3.0mm) taken together in a
mixture for 5 to 7 minutes.
B. Addition of a liquid binder comprising of Molasses (Specific gravity- 1.1 to
1.2) of about 2-3 % by weight and aqueous slurry of Plastic clay (Specific
gravity- 1.1 to 1.2) of about 2-3 % to the dry mix
C. thereafter wet mixing for 8 to 10 minutes.
D. addition of all the fines (<0.074mm) to the resultant mix and then final
mixing for 12 to 15 minutes to get the green mixture; and
E. subjecting the green bricks thus obtained to firing such as to thereby obtain
there from the said High Alumina Bricks.
The said process comprises the further steps of
(i) pressing the mixture obtained in step (D) in hydraulic press at a specific
pressure of 1.0 to 1.1 ton/cm2 to form the green bricks at steps using an
optimum plurality of de-airings to avoid lamination in bricks;
(ii) subjecting pressed bricks to air drying for 24-32 hours followed by further
drying in Tunnel drier at 110 0C for 20-24 hours;
(iii) Firing of bricks maintaining desired firing schedule to obtain bricks with
high thermal resistance coupled with Refractoriness under load and
volume stability.
According to the invented process aid mixing/addition sequence of raw material
ingredients comprises of :

(i) Dry mixing of all the said coarse grains taken together in a mixer for 5 to 7
minutes.
(ii) Addition of liquid binder comprising a mixture of Molasses (Specific gravity-
1.1 to 1.2) of about 2-3 % by weight and aqueous slurry of Plastic clay
(Specific gravity- 1.1. to 1.2) of about 2-3% by weight to the dry mix;
(iii) Wet mixing for 8 to 10 minutes;
(iv) Addition of all the fines to the resultant mix and then final mixing for 12 to 15
minutes to get the green mixture.
Said firing schedule of dried bricks comprises:
(i) Preheating of bricks at a rate of 5 to 70C per minute from ambient
temperature to 300-400 0C.
(ii) heating up of bricks at 10-120C per minute from 400 to 800 0C;
(iii) Firing of bricks at a much slow rate of 0.8 to 1.00C per minute from 8000C
to 1200-13000C to avoid cracking at this stage due to absence of sufficient
bonding strength.
(iv) Further firing at comparatively faster rate of 1.5 to 20C per minute up to
1550 0C.
(v) Allowing soaking time for 12 to 18 hours at the highest temperature to
obtain bricks with required properties.
The batch composition for producing the High Alumina Bricks and the processfor the
production of the same are given in the following illustrative example:
Example:
In manufacturing of improved High Alumina bricks according to the present invention,
different high Alumina and Alumino-Silicate raw materials in different size fractions are
mixed in required proportions with the addition of required binder which is a mixture of
molasses and plastic clay slurry in required consistency. During mixing a particular
sequence of addition and mixing time is followed to obtain optimum coating of granular
materials and fines to make a homogeneous mix. After mixing Pressing of the mixture
in hydraulic press at a specific pressure of 1.0 to 1.1 ton/ cm2 and the green bricks are
formed at steps using an optimum plurality of de-airings to avoid lamination in bricks.
Then the pressed bricks are allowed for air drying for 24-32 hours. After proper air

drying further drying is done in Tunnel drier at 1100C for 20-24 hours. The bricks are
then fired in Tunnel kiln at 15500C with total heating cycle of 6 to 7 days in which
soaking is provided for 12 to 18 hours. Firing is an important step which is done in a
controlled manner following an optimum rate and time schedule of heating up. Improper
firing leads to firing cracks and thereby causes high rejection of bricks. Considering the
composition and granulometry of the developed formulation of the bricks, following firing
schedule is followed:
(i) Preheating of bricks at a rate of 5 to 70C per minute from ambient temperature to
300-400 0C.
(ii) Heating up of bricks at 10-120C per minute from 400 to 8000C.
(iii) Firing of bricks at a much slow rate of 0.8 to 1.00C per minute from 8000C to
1200-13000C to avoid cracking at this stage due to absence of sufficient
bonding strength.
(iv)Further firing is done at comparatively faster rate of 1.5 to 20C per minute up to
15500C.
(v) Soaking time is provided for 12 to 18 hours at the highest temperature.
Batch Composition of invented High Alumina bricks for Electric Arc Furnace
(EAF)
The present invention is to provide High Alumina bricks with higher Thermal shock
resistance; high Refractoriness under load and higher volume stability suitable for use in
Electric Arc Furnace (EAF). The starting batch composition for producing such bricks is
given in Table 1:
Table 1: Batch Composition of High Alumina bricks



Details of different Raw Materials, Additives and Binder are given below:
Andalusite:
Al2O3- 57% Min;
Fe2O3 - 1% Max;
Specific Gravity– 3.0gm/cc Min.
CalcinedAlumina:
Al2O3– 99.5% Min of which α- Al2O3 content is 90% Min;
Na2O – 0.5% Max
Fe2O3 – 0.03% Max
SiO2 – 0.03% Max
Average Particle Size d50 – 5.5 micron Max
Specific Gravity – 3.9 Min
Specific Surface Area – 3.0 m²/gm Max.
+325 mesh (ASTM Tyler) – 1.5% Max.
White Tabular Alumina (WTA):
Al2O3 – 99.3% Min.
Fe2O3 – 0.13% Max.
Na2O+K2O – 0.60% Max.
BulkDensity – 3.55 gm/cc Min.
FusedMullite:
Al2O3- 70% Min;
SiO2 - 29% Max;

Fe2O3 - 1% Max;
Na2O – 0.6% Max;
Plastic Clay:
Al2O3 – 37% Min
Fe2O3 – 2.5% Max
PCE – Ort 32 Min
Moisture – 12% Max after drying at 110°C for 24 Hrs;
Free from calcerious & ferrogeneous impurities & free silica based on physical
verification having sinterability and plasticity.
Calcined Bauxite:
Al2O3 – 87% Min.
Fe2O3 – 2% Max.
Na2O+K2O – 0.30% Max.
SiO2 – 6% Max.
TiO2 – 4% Max.
MgO – 0.4% Max.
CaO – 0.4% Max.
BulkDensity – 3.20 gm/cc Min.
Feldspar:
Al2O3- 16% Min;
SiO2 - 70% Max;
Fe2O3 - 1% Max;
Melting point – 10000C – 12600C.
Molasses
Specific Gravity > 1.4

Further aspect of the present invention is that the above components are added and
mixed in the order as indicated below:
Mixing sequence of ingredients
1. Dry mixing of all the said coarse grains taken together in a mixer for 5 to 7 minutes.
2. Addition of liquid binder which is a mixture of Molasses (Specific gravity- 1.1 to 1.2) of
about 2-3 % by weight and aqueous slurry of Plastic clay (Specific gravity- 1.1 to 1.2) of
about 2-3 % to the dry mix.

3. Then wet mixing for 8 to 10 minutes.
4. Addition of all the fines to the resultant mix and then final mixing for 12 to 15 minutes
to get the green mixture.
Properties of developed high alumina bricks are given in Table 2:

The invention also includes refractory lining of roofs in electric arc furnaces made from
the said bricks.
Although the invention described herein mentions various specific embodiments, it
could be possible for a person skilled in the art to develop other embodiments as well
beyond those disclosed herein with modifications. However, all such modifications are
deemed to be within the broad scope of thedisclosed invention claimed hereafter.

WE CLAIM:
1. A composition for making High Alumina brickswith high thermal shock resistance,
high refractoriness and high volume stabilitycomprising:
Andalusite (Coarse) having particle size ranging from 1mm to 3mm and about
18-25 percent by weight,
White Tabular Alumina (WTA) (Coarse) having particle size upto 2.5 mm and
about 13-18 % by weight,
Fused Mullite (Coarse) having particle size upto 2 mm and about 18-22 % by
weight,
Calcined Bauxite (Coarse & Fines) having particle size ranging from 0.074 mm to
1 mm and about 20-25 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 6-10 %
by weight,
Plastic clay (Fines) having particle size below 0.074 mm and about 8-14 % by
weight,
Feldspar (Fines) having particle size below 0.074 mm and about 4-6 % by
weight,
Molasses (Specific gravity- 1.1 to 1.2) of about 2.5-4 % by weight and aqueous
slurry of Plastic clay (Specific gravity- 1.1 to 1.2) of about 2-3 % as liquid binder
for wet mixing.
2. A compositionas claimed in claim 1, wherein said Andalusite comprisingAl2O3-
57% Min.,Fe2O3 - 1% Max., Specific Gravity– 3.0gm/cc Min.;
said calcined Alumina comprising Al2O3– 99.5% Min. of which α-Al2O3 content is 90%
Min.,Na2O – 0.5% Max.,Fe2O3 – 0.03% Max.,SiO2 – 0.03% Max., Average Particle Size
d50 – 5.5 micron Max.,Specific Gravity – 3.9 Min.,Specific Surface Area – 3.0 m²/gm
Max.+325 mesh (ASTM Tyler) – 1.5% Max.;

said White Tabularalumina (WTA) comprising Al2O3–99.3%Min., Fe2O3–0.13% Max.,
Na2O+K2O – 0.60% Max., BulkDensity – 3.55 gm/cc Min. ;
said Fused Mullite comprising Al2O3-70% Min., SiO2 - 29% Max., Fe2O3 - 1% Max.,
Na2O – 0.6% Max;
said plastic clay comprising Al2O3–37% Min., Fe2O3 – 2.5% Max., PCE – Ort 32 Min.,
Moisture – 12% Max after drying at 110°C for 24 Hrs; free from calcerious &
ferrogeneous impurities & free silica based on physical verification having sinterability
and plasticity;
said Calcined Bauxite comprising Al2O3 – 87% Min., Fe2O3 – 2% Max., Na2O+K2O –
0.30% Max.,SiO2 – 6% Max.,TiO2 – 4% Max., MgO – 0.4% Max., CaO – 0.4%
Max.,Bulk Density – 3.20 gm/cc Min.,and
said FeldsparcomprisingAl2O3- 16% Min.,SiO2 - 70% Max.,Fe2O3 - 1% Max., Melting
point – 10000C – 12600C.
3. High Alumina Bricks with high thermal shock resistance, high refractoriness and
high volume stability made from the composition as claimed in claims 1 and 2.
4. High Alumina Bricks as claimed in claim 3, having minimum thermal shock
resistance of 50 cycles (By Air Quenching) coupled with Refractoriness under load
(RUL) of minimum 1550OC (ta , as per IS: 1528 Part II).
5. High Alumina Bricks as claimed in claims 3 and 4, having high volume stability by
way of Repeat Permanent linear change after reheating (Repeat PLCAR) comprising:

6. High Alumina bricks as claimed in any of the claims 3 to 5, having particular use
as refractory lining of roofs of Electric Arc Furnaces (EAFs).

7. A process for the production of High Alumina Bricks as claimed in claims 3 to 6,
comprising the steps of
A. Dry mixing of all the coarse grains (0.5mm to 3.0mm) taken together in a mixture
for 5 to 7 minutes.
B. Addition of liquid binder comprising of Molasses (Specific gravity- 1.1 to 1.2) of
about
2-3 % by weight and aqueous slurry of Plastic clay (Specific gravity- 1.1 to 1.2) of
about 2-3 % to the dry mix
C. Thereafter wet mixing for 8 to 10 minutes.
D. Addition of all the fines (<0.074mm) to the resultant mix and then final mixing for
12 to 15 minutes to get the green mixture; and
E. Subjecting the green bricks thus obtained to firing such as to thereby obtain there
from the said High Alumina Bricks.
8. A process as claimed in claim 7, comprising the further steps of:
(i) pressing the mixture obtained in step (D) in hydraulic press at a specific
pressure of 1.0 to 1.1 ton/cm2 to form the green bricks at steps using an
optimum plurality of de-airings to avoid lamination in bricks;
(ii) subjecting pressed bricks to air drying for 24-32 hours followed by further
drying in Tunnel drier at 110 0C for 20-24 hours;
(iii) Firing of bricks maintaining desired firing schedule to obtain bricks with
high thermal resistance coupled with Refractoriness under load and
volume stability.
9. A process as claimed in claims 7 and 8, wherein said mixing/addition sequence of
raw material ingredients comprising
(i) Dry mixing of all the said coarse grains taken together in a mixer for 5 to 7
minutes.
(ii) Addition of liquid binder comprising a mixture of Molasses (Specific gravity-
1.1 to 1.2) of about 2-3 % by weight and aqueous slurry of Plastic clay (Specific
Gravity - 1.1 to 1.2) of about 2-3% by weight to the dry mix;

(iii) Wet mixing for 8 to 10 minutes;
(iv) Addition of all the fines to the resultant mix and then final mixing for 12 to
15 minutes to get the green mixture.
10. A process as claimed in claims 6 to 9, wherein said firing schedule of dried bricks
comprising:
(i) Preheating of bricks at a rate of 5 to 70C per minute from ambient
temperature to 300-4000C.
(ii) heating up of bricks at 10-120C per minute from 400 to 8000C;
(iii) Firing of bricks at a much slow rate of 0.8 to 1.00C per minute from 8000C
to 1200-13000C to avoid cracking at this stage due to absence of sufficient
bonding strength.
(iv) Further firing at comparatively faster rate of 1.5 to 20C per minute up to
1550 0C.
(v) Allowing soaking time for 12 to 18 hours at the highest temperature to
obtain bricks with required properties.
11. Refractory lining of roofs in electric arc furnaces (EAF) made from the bricks as
claimed in claims 3 to 6.