CLIAMS:We Claim:
1. High Alumina bricks for use as refractory lining of roof of a Rotary hearth furnace, comprising:
Calcined Fire clay (Coarse) having particle size ranging from 2mm to 3 mm and about 15-17 % by weight,
Calcined Fire clay (Coarse)having particle size upto 2 mm and about 3-5 % by weight,
Andalusite (Coarse) having particle size upto 1 mm and about 30-35 % by weight,
Brown fused Alumina (Coarse) having particle size ranging from 0.5 mm to 0.25 mm and about 30-35 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 4-5 % by weight,
Raw Kyanite (Fines) having particle size below 0.074 mm and about 4-5 % by weight,
Plastic clay (Fines) having particle size below 0.074 mm and about 10-12 % by weight,
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 % as liquid binder for wet mixing.
2. High Alumina bricks as claimed in claim 1 wherein said Andalusite comprises
Al2O3- 57% Min;
Fe2O3 - 1% Max;
Specific Gravity– 3.0gm/cc Min.

3. High Alumina bricks as claimed in anyone of claims 1 or 2 wherein said calcined Alumina comprises
Al2O3– 99.5% Min of which a- 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.

4. High Alumina bricks as claimed in anyone of claims 1 to 3 wherein said Calcined Fire Clay comprising
Al2O3 – 36% Min. (acceptable upto 35% with rebate);
Fe2O3 – 1.8% Max (acceptable upto 2.5% with rebate);
PCE - Ort 31 ½ Min;
Water Absorption – 6% Max (acceptable upto 9% with rebate);
free from calcareous & ferruginous impurities, melted & siliceous lumps based on physical verification;
Moisture content being – 1% Max (For moisture above 1% pro-rata deductions will be made).
5. High Alumina bricks as claimed in anyone of claims 1 to 4 wherein said Brown fused Alumina comprising
Al2O3- 95% Min;
SiO2 - 1% Max;
Fe2O3 - 0.5% Max;
TiO2 - 3.2% Max;
CaO – 0.6% Max;
Specific Gravity – 3.93 Min;
Free Iron – 0.1% Max (with total Fe2O3 - 0.5% Max).

6. High Alumina bricks as claimed in anyone of claims 1 to 5 wherein said plastic clay fines comprising
Al2O3 – 37% Min (acceptable upto 35% with rebate);
Fe2O3 – 2.5% Max (acceptable upto 3% with rebate);
PCE – Ort 32 Min (acceptable upto Ort 31 ½ with rebate);
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.

7. The High Alumina brick as claimed in anyone of claims 1 to 6 having minimum thermal shock resistance of 30 cycles (as per small prism test under IS: 1528 Part III) coupled with Refractoriness under load (RUL) of minimum 1550 OC ( ta , as per IS: 1528 Part II).

8. The High Alumina brick as claimed in anyone of claims 1 to 7 having high volume stability by way of Repeat Permanent linear change (Repeat PLC) comprising:

Repeat PLC, %, At 1500 0C
1st PLC: ± 0.20
2nd PLC: - 0.15 to + 0.10
3rd PLC: ± 0.10

9. A process for the production of High Alumina Bricks as claimed in claims 1 to 8 comprising the steps of
A. dry mixing of all the coarse grains (0.25mm 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 (<0.044mm) 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 therefrom the said High Alumina Bricks.

10. A process as claimed in claim 9 comprising the 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.

11. A process as claimed in anyone of claims 9 or 10 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.
(iii) 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.

12. A process as claimed in anyone of claims 9 to 11 wherein said firing schedule of dried bricks comprises
(i) preheating of bricks at a rate of 5 to 7 0C per minute from ambient temperature to 300-400 0C.
(ii) heating up of bricks at 10-12 0C per minute from 400 to 800 0C;
(iii) firing of bricks at a much slow rate of 0.8 to 1.0 0C per minute from 800 to 1200-1300 0C to avoid cracking at this stage due to absence of sufficient bonding strength.
(iv) further firing at comparatively faster rate of 1.5 to 2 0C 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.

Dated this the 15th day of July, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION

The present invention relates to refractory lining of roof in Rotary Hearth Furnace. More particularly, the present invention is directed to providing an improved High Alumina bricks having high Thermal shock Resistance combined with high Refractoriness under load(RUL) as well as high volume stability suitable for use as refractory lining of roof in Rotary hearth furnace of sprung arch type such as in Wheel & Axle plant and a method of manufacturing said High Alumina brick.
BACKGROUND OF THE INVENTION
The roof lining design of Rotary hearth furnace in Wheel & Axle plant is of sprung arch type. The design of roof and operating conditions demand refractory bricks having a combination of high thermal shock resistance and high refractoriness under load (RUL). Earlier, Semi Silica bricks were being used for lining of furnace roof. Over the years, performance of roof lining has drastically deteriorated due to poor quality of bricks supplied by both imported and indigenous sources. Many a times, this led to poor performance of lining and dwindling stock of lining materials as well. The deterioration in quality is caused by poor availability of Pyrophilite which is one of the important raw materials that contributes most to attain above properties.
There has been thus a continuing need in the art to developing refractory bricks for roof lining of sprung arch type Rotary hearth furnace which would be made from alternative materials avoiding the quality and availability issues related to conventional semi silica bricks while ensuring required properties of high thermal shock resistance and high refractoriness under load (RUL) with desired life of the refractory lining.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide High Alumina bricks having high Thermal shock Resistance, high Refractoriness under load and high volume stability suitable for use as refractory lining of roof in Rotary hearth furnace and a process for its production.
A further object of the present invention is directed to provide said High Alumina bricks for refractory lining of roof in Rotary hearth furnace to circumvent the problem of inconsistent quality and supply of conventional Semi Silica brick by developing an alternate suitable quality of roof bricks in High Alumina quality, raw materials of which are widely available.
Another object of the present invention is to provide refractory bricks which would ensure minimum thermal shock resistance of 30 cycles (as per small prism test under IS: 1528 Part III) coupled with Refractoriness under load (RUL) of minimum 1550 OC ( ta , as per IS: 1528 Part II).
A further object of the present invention is to provide refractory bricks with high volume stability by way of having required Repeat Permanent linear change (Repeat PLC) of High Alumina bricks.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to provide High Alumina bricks for use as refractory lining of roof of a Rotary hearth furnace, comprising:
Calcined Fire clay (Coarse) having particle size ranging from 2mm to 3 mm and about 15-17 % by weight,
Calcined Fire clay (Coarse)having particle size upto 2 mm and about 3-5 % by weight,
Andalusite (Coarse) having particle size upto 1 mm and about 30-35 % by weight,
Brown fused Alumina (Coarse) having particle size ranging from 0.5 mm to 0.25 mm and about 30-35 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 4-5 % by weight,
Raw Kyanite (Fines) having particle size below 0.074 mm and about 4-5 % by weight,
Plastic clay (Fines) having particle size below 0.074 mm and about 10-12 % by weight,
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 % as liquid binder for wet mixing.
A further aspect of the present invention is directed to said High Alumina bricks wherein said Andalusite comprises
Al2O3- 57% Min;
Fe2O3 - 1% Max;
Specific Gravity– 3.0gm/cc Min.

A still further aspect of the present invention is directed to said High Alumina bricks wherein said calcined Alumina comprises
Al2O3– 99.5% Min of which a- 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.

Yet another aspect of the present invention is directed to said High Alumina bricks wherein said Calcined Fire Clay comprises
Al2O3 – 36% Min. (acceptable upto 35% with rebate);
Fe2O3 – 1.8% Max (acceptable upto 2.5% with rebate);
PCE - Ort 31 ½ Min;
Water Absorption – 6% Max (acceptable upto 9% with rebate);
free from calcareous & ferruginous impurities, melted & siliceous lumps based on physical verification;
Moisture content being – 1% Max (For moisture above 1% pro-rata deductions will be made).
A further aspect of the present invention is directed to said High Alumina bricks wherein said Brown fused Alumina comprises
Al2O3- 95% Min;
SiO2 - 1% Max;
Fe2O3 - 0.5% Max;
TiO2 - 3.2% Max;
CaO – 0.6% Max;
Specific Gravity – 3.93 Min;
Free Iron – 0.1% Max (with total Fe2O3 - 0.5% Max).

A still further aspect of the present invention is directed to said High Alumina bricks wherein said plastic clay fines comprising
Al2O3 – 37% Min (acceptable upto 35% with rebate);
Fe2O3 – 2.5% Max (acceptable upto 3% with rebate);
PCE – Ort 32 Min (acceptable upto Ort 31 ½ with rebate);
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.

A still further aspect of the present invention is directed to said High Alumina brick having minimum thermal shock resistance of 30 cycles (as per small prism test under IS: 1528 Part III) coupled with Refractoriness under load (RUL) of minimum 1550 OC ( ta , as per IS: 1528 Part II).

Yet another aspect of the present invention is directed to said High Alumina brick having high volume stability by way of Repeat Permanent linear change (Repeat PLC) comprising:

Repeat PLC, %, At 1500 0C
1st PLC: ± 0.20
2nd PLC: - 0.15 to + 0.10
3rd PLC: ± 0.10

A further aspect of the present invention is directed to a process for the production of High Alumina Bricks as described above, comprising the steps of
A. dry mixing of all the coarse grains (0.25mm 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 (<0.044mm) 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 therefrom the said High Alumina Bricks.
A still further aspect of the present invention is directed to said process comprising the 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.

Yet another aspect of the present invention is directed to said process 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.

A still further aspect of the present invention is directed to said process wherein said firing schedule of dried bricks comprises
(i) preheating of bricks at a rate of 5 to 7 0C per minute from ambient temperature to 300-400 0C.
(ii) heating up of bricks at 10-12 0C per minute from 400 to 800 0C;
(iii) firing of bricks at a much slow rate of 0.8 to 1.0 0C per minute from 800 to 1200-1300 0C to avoid cracking at this stage due to absence of sufficient bonding strength.
(iv) further firing at comparatively faster rate of 1.5 to 2 0C 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 objectives and advantages of the present invention are described hereunder in greater details with reference to the following accompanying illustrative example.

DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to provide improved High Alumina bricks with High Thermal shock Resistance, high Refractoriness under load and high volume stability suitable for refractory lining of roof in Rotary hearth furnace of Wheel & Axle plant and in particular related to process of manufacturing such improved High Alumina bricks and development of its formulation. The batch composition of the High Alumina Bricks and its method of production is illustrated with following 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 proportion 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 110 0C for 20-24 hours. The bricks are then fired in Tunnel kiln at 1550 0C 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 7 0C per minute from ambient temperature to 300-400 0C.
(ii) Heating up of bricks at 10-12 0C per minute from 400 to 800 0C.
(iii) Firing of bricks at a much slow rate of 0.8 to 1.0 0C per minute from 800 to 1200-1300 0C 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 2 0C per minute up to 1550 0C.
(v) Soaking time is provided for 12 to 18 hours at the highest temperature.

Batch Composition of invented High Alumina bricks for Rotary hearth furnace
Ingredients Weight (%)
Brown Fused Alumina Grains 30 - 35
Calcined Fire clay 18 - 22
Andalusite 30 - 35
Calcined Alumina 4 – 5
Raw Kyanite 4 - 5
Plastic Clay 10 - 12
Binder (Molasses + Plastic clay slurry) 4 - 6
The present invention is directed to provide High Alumina bricks with higher Thermal shock resistance; high Refractoriness under load and higher volume stability suitable for use in Rotary hearth furnace. The starting batch composition for producing such bricks is given in Annexure-I:
Annexure I : Batch Composition of High Alumina bricks

Details of different components of raw materials in a batch have been given in following Annexure II.
Annexure II: Details of different Raw Materials, Additives and Binder
Calcined Fireclay
Al2O3 – 36% Min. (acceptable upto 35% with rebate)
Fe2O3 – 1.8% Max (acceptable upto 2.5% with rebate)
PCE - Ort 31 ½ Min
Water Absorption – 6% Max (acceptable upto 9% with rebate)
Material should be free from calcareous & ferruginous impurities, melted & siliceous lumps on physical verification
Free Moisture – 1% Max (For moisture above 1% pro-rata deductions will be made)

Andalusite
Al2O3- 57% Min
Fe2O3 - 1% Max
Specific Gravity– 3.0gm/cc Min

Calcined Alumina
a- Al2O3 content – 90% Min
Al2O3– 99.5% 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

Plastic Clay
Al2O3 – 37% Min (acceptable upto 35% with rebate)
Fe2O3 – 2.5% Max (acceptable upto 3% with rebate)
PCE – Ort 32 Min (acceptable upto Ort 31 ½ with rebate)
Sinterability – Good
Plasticity – Good
Moisture – 12% Max after drying at 110°C for 24 Hrs
Material should be free from calcerious & ferrogeneous impurities & free silica on physical verification

BFA
Al2O3- 95% Min
SiO2 - 1% Max
Fe2O3 - 0.5% Max
TiO2 - 3.2% Max
CaO – 0.6% Max
Specific Gravity – 3.93 Min
Free Iron – 0.1% Max (with total Fe2O3 - 0.5% Max)

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 in Annexure III. The Properties of developed brick are given in Annexure IV.
Annexure III : Mixing sequence of ingredients

1. Dry mixing of all the coarse grains taken together in a muller mixture 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.
Annexure IV:
Properties of Developed High Alumina bricks
Chemical composition Value

Al2O3, % 62

Fe2O3, %, max.
1.5
Physical properties

B.D., g/cc, min. (IS: 1528, Part XII)
2.5
2.5
A.P., %, max. (IS: 1528, Part VIII)
18.0
CCS, kg/cm2, min. (IS: 1528, Part IV)
400
RUL, ta, 0C (IS: 1528, Part II)
1550
Repeat PLC, %, At 1500 0C / 2 hours,
(PLC will be done as per IS: 1528, Part VI)
1st PLC: ± 0.20
2nd PLC: - 0.15 to + 0.10
3rd PLC: ± 0.10
Th-Shock, Cycles, min,
12000C,Small Prism Test (IS: 1528, Part III, Small Prism Test)
30

Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

We Claim:
1. High Alumina bricks for use as refractory lining of roof of a Rotary hearth furnace, comprising:
Calcined Fire clay (Coarse) having particle size ranging from 2mm to 3 mm and about 15-17 % by weight,
Calcined Fire clay (Coarse)having particle size upto 2 mm and about 3-5 % by weight,
Andalusite (Coarse) having particle size upto 1 mm and about 30-35 % by weight,
Brown fused Alumina (Coarse) having particle size ranging from 0.5 mm to 0.25 mm and about 30-35 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 4-5 % by weight,
Raw Kyanite (Fines) having particle size below 0.074 mm and about 4-5 % by weight,
Plastic clay (Fines) having particle size below 0.074 mm and about 10-12 % by weight,
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 % as liquid binder for wet mixing.
2. High Alumina bricks as claimed in claim 1 wherein said Andalusite comprises
Al2O3- 57% Min;
Fe2O3 - 1% Max;
Specific Gravity– 3.0gm/cc Min.

3. High Alumina bricks as claimed in anyone of claims 1 or 2 wherein said calcined Alumina comprises
Al2O3– 99.5% Min of which a- 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.

4. High Alumina bricks as claimed in anyone of claims 1 to 3 wherein said Calcined Fire Clay comprising
Al2O3 – 36% Min. (acceptable upto 35% with rebate);
Fe2O3 – 1.8% Max (acceptable upto 2.5% with rebate);
PCE - Ort 31 ½ Min;
Water Absorption – 6% Max (acceptable upto 9% with rebate);
free from calcareous & ferruginous impurities, melted & siliceous lumps based on physical verification;
Moisture content being – 1% Max (For moisture above 1% pro-rata deductions will be made).
5. High Alumina bricks as claimed in anyone of claims 1 to 4 wherein said Brown fused Alumina comprising
Al2O3- 95% Min;
SiO2 - 1% Max;
Fe2O3 - 0.5% Max;
TiO2 - 3.2% Max;
CaO – 0.6% Max;
Specific Gravity – 3.93 Min;
Free Iron – 0.1% Max (with total Fe2O3 - 0.5% Max).

6. High Alumina bricks as claimed in anyone of claims 1 to 5 wherein said plastic clay fines comprising
Al2O3 – 37% Min (acceptable upto 35% with rebate);
Fe2O3 – 2.5% Max (acceptable upto 3% with rebate);
PCE – Ort 32 Min (acceptable upto Ort 31 ½ with rebate);
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.

7. The High Alumina brick as claimed in anyone of claims 1 to 6 having minimum thermal shock resistance of 30 cycles (as per small prism test under IS: 1528 Part III) coupled with Refractoriness under load (RUL) of minimum 1550 OC ( ta , as per IS: 1528 Part II).

8. The High Alumina brick as claimed in anyone of claims 1 to 7 having high volume stability by way of Repeat Permanent linear change (Repeat PLC) comprising:

Repeat PLC, %, At 1500 0C
1st PLC: ± 0.20
2nd PLC: - 0.15 to + 0.10
3rd PLC: ± 0.10

9. A process for the production of High Alumina Bricks as claimed in claims 1 to 8 comprising the steps of
A. dry mixing of all the coarse grains (0.25mm 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 (<0.044mm) 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 therefrom the said High Alumina Bricks.

10. A process as claimed in claim 9 comprising the 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.

11. A process as claimed in anyone of claims 9 or 10 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.
(iii) 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.

12. A process as claimed in anyone of claims 9 to 11 wherein said firing schedule of dried bricks comprises
(i) preheating of bricks at a rate of 5 to 7 0C per minute from ambient temperature to 300-400 0C.
(ii) heating up of bricks at 10-12 0C per minute from 400 to 800 0C;
(iii) firing of bricks at a much slow rate of 0.8 to 1.0 0C per minute from 800 to 1200-1300 0C to avoid cracking at this stage due to absence of sufficient bonding strength.
(iv) further firing at comparatively faster rate of 1.5 to 2 0C 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.

Dated this the 15th day of July, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT
TITLE: HIGH ALUMINA BRICKS FOR REFRACTORY LINING OF ROOF OF ROTARY HEARTH FURNACE AND PROCESS FOR ITS PRODUCTION.
The present invention relates to providing High Alumina Bricks for refractory lining of roof in Rotary Hearth Furnace having high Thermal shock Resistance combined with high Refractoriness under load(RUL) as well as high volume stability suitable for use as refractory lining of roof in Rotary hearth furnace of sprung arch type such as in Wheel & Axle plant and a method of manufacturing said High Alumina brick. The High Alumina Bricks according to the invention are having minimum thermal shock resistance of 30 cycles (as per small prism test under IS: 1528 Part III) coupled with Refractoriness under load (RUL) of minimum 1550 OC ( ta , as per IS: 1528 Part II) and high volume stability by way of Repeat Permanent linear change (Repeat PLC) comprising: Repeat PLC, %, At 1500 0C of 1st PLC: ± 0.20; 2nd PLC: - 0.15 to + 0.10; 3rd PLC: ± 0.10.