, Description:IMPROVED HIGH ALUMINA CASTABLE FOR MANUFACTURING PRE-CAST BLOCK FOR REFRACTORY LINING OF VAD LADLE COVER

FIELD OF THE INVENTION
The present invention relates to refractory lining of VAD ladle cover. More particularly, the present invention is directed to providing an improved Alumina ( 80% Min. Al2O3) castable for manufacturing of pre-cast block having high thermal shock resistance combined with high volume stability and high strength suitable for use as refractory lining of VAD ladle cover such as in Alloy Steels Plant (ASP) of Steel Authority of India Limited (SAIL).

BACKGROUND OF THE INVENTION
ASP was facing problem with poor refractory lining life of VAD ladle cover. Sometimes, this poses problem in maintaining an uninterrupted and continuous operation due to unplanned shut down.

To circumvent this problem, a project was taken up for development of improved quality refractory to enhance its lining performance in VAD ladle cover and which can be manufactured using in-house refractory manufacturing facility at IFICO plant of SRU.

Developmental work carried out at RDCIS & IFICO led to development of a High Alumina (min. 80% Al2O3), High Thermal Shock Resistant, Highly volume stable and High strength castable for manufacturing of pre-cast blocks for VAD ladle cover.

A few prior art patents exist in the field which are given herein by reference -
Indian Patent No. 195673 of SAIL discloses a high alumina self flow castable refractory composition and process wherein the composition is obtained of selective mix of Fused alumina 65% to 70% by wt Reactive alumina 15% to 18% by wt. Calcined alumina 2% to 5% by wt Micro fused silica 4% to 5% by wt and high alumina cement 1% to 4% by wt with particular distribution coefficient of grains.
CN104003741B discloses Tundish covering castable and preparation method wherein 30-50% of used high - residual alumina magnesite carbon brick regenerative particles and 20-40% of micro pore corundum particles are taken as aggregates.
US4570910A discloses a method of constructing a steel making ladle.
CA2049171A discloses a surface coating material for tundish and steel ladle containing a synthetic dolomite aggregate.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to provide High Alumina (80% Al2O3, min.) castable having high thermal shock resistance and high volume stability with high strength suitable for manufacturing of pre-cast blocks for refractory lining of VAD ladle cover.
Another object of the present invention is to provide refractory castable which would ensure thermal shock resistance at 10000C of minimum 40 cycles (By water quenching) coupled with high strength by way of having required Cold Crushing Strength (CCS).
A further object of the present invention is to provide refractory castable with high volume stability by way of having required Repeat Permanent Linear Change After Reheating (Repeat PLCAR) of said High Alumina castable.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to provide High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block for use as refractory lining of VAD ladle cover, comprising:
White Tabular Alumina (WTA) (Coarse + Middle) having particle size ranging from 3 mesh to 28 mesh and about 55–65 % by weight,
Silimanite Sand (Fines) having particle size up to 200 mesh and about 7–11 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 15–25 % by weight,
Fume Silica (Fines) having particle size below 0.044 mm and about 4–6 % by weight,
Chromic Oxide (Fines) having particle size below 0.044 mm and about 1–2 % by weight,
High Alumina Cement (Fines) as binder for wet mixing about 4–6 % by weight,
Sodium Hexa Meta Phosphate (SHMP) about 0.07–0.18 % by weight,
Citric acid about 0.01–0.05 % by weight.

A further aspect of the present invention is directed to said 80% (min.) Alumina castable for manufacturing of pre-cast block wherein said White Tabular Alumina (WTA) comprises
Al2O3 (Min.), % 99.3
Fe2O3 (Max.), % 0.13
Na2O+K2O (Max), % 0.60
Bulk Density (Min.) 3.55

A still further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Silimanite Sand comprises
Al2O3 (Min.), % 58
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

Yet another aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Calcined Alumina comprises
Al2O3 (Min.), % 99.5 [of which a- Al2O3 content is 90% (Min.)]
Fe2O3 (Max.), % 0.03
Na2O (Max), % 0.50
SiO2 (Max.), % 0.03
Specific Gravity (Min.) 3.90
Specific Surface Area (Max.), m2/gm 3

A further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Fume Silica comprises
SiO2 (Min.), % 98
Cfree (Max.), % 0.70
Al2O3 (Max.), % 0.30
Fe2O3 (Max.), % 0.10
Na2O (Max), % 0.20
K2O (Max.), % 0.30
B.D., kg/m3 250 – 350
L.O.I. (Max.), % 0.80

A still further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Chromic Oxide comprises
Cr2O3 (Min.), % 98
Specific Gravity (Min.) 5.0
Solubility Insoluble in Water, alcohol and acetone
Colour Green

Yet another aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said High Alumina Cement comprises
Al2O3 (Min.), % 70
Fe2O3 (Max.), % 0.30
CaO (Max), % 29
SiO2 (Max.), % 0.30
Major Phase CA.CA2

A further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Sodium Hexa Meta Phosphate comprises
P2O5 (Min.), % 65
Grade LR

A still further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block wherein said Citric acid comprises

Purity (Min.), % 99.5
Grade LR

A further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block having thermal shock resistance at 10000C of minimum 40 cycles (By Water Quenching) coupled with high strength by way of Cold Crushing Strength (CCS) comprising:

C.C.S., kg/cm2, Min. At 1100C/ 24hrs. : 400
12000C/ 3hrs. : 800
14500C/ 3hrs. : 1000

A still further aspect of the present invention is directed to said 80% Alumina (min.) castable for manufacturing of pre-cast block having high volume stability by way of Repeat Permanent Linear Change After Reheating (Repeat PLCAR) comprising:

Repeat PLCAR, %, At 15000C for 3 hours (PLCAR as per IS:1528, Part VI)
1st PLCAR: ± 0.50
2nd PLCAR: ± 0.20
3rd PLCAR: ± 0.10

The objectives and advantages of the present invention are described hereunder in greater details with reference to the following accompanying illustrative example.

DETAILED DESCRIPTION, USEFULNESS & INDUSTRIAL APPLICABILITY OF THE INVENTION
The present invention is directed to provide improved High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block with High Thermal shock Resistance, high strength and high volume stability suitable for refractory lining of VAD ladle cover such as in Alloy Steels Plant (ASP) at Durgapur of Steel Authority of India Limited (SAIL) and in particular related to development of its formulation. The batch composition of the High Alumina castable for manufacturing of pre-cast block is illustrated with following example:
Example:
Batch Composition of invented High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block for VAD ladle cover
The present invention is directed to provide High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block with high high thermal shock resistance; high strength and higher volume stability suitable for use in VAD ladle cover. The starting batch composition for producing such castable for manufacturing of pre-cast block is given in TABLE I:
TABLE I: Batch Composition of High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block

Raw Material %
WTA (Coarse+ Middle) 55 – 65
Silimanite Sand (Fines) 9 – 11
Calcined Alumina (Fines) 15 – 25
Fume Silica (Fines) 4 – 6
Chromic Oxide (Fines) 1 – 2
High Alumina Cement 4 – 6
SHMP 0.07–0.18
Citric acid 0.01 – 0.05

Details of different components of raw materials in a batch have been given in following TABLE II.
TABLE II: Details of different Raw Materials, Additives and Binder
White Tabular Alumina (WTA):
Al2O3 (Min.), % 99.3
Fe2O3 (Max.), % 0.13
Na2O+K2O (Max), % 0.60
Bulk Density (Min.) 3.55

Silimanite Sand:
Al2O3 (Min.), % 58
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

Calcined Alumina:
Al2O3 (Min.), % 99.5 [of which a- Al2O3 content is 90% (Min.)]
Fe2O3 (Max.), % 0.03
Na2O (Max), % 0.50
SiO2 (Max.), % 0.03
Specific Gravity (Min.) 3.90
Specific Surface Area (Max.), m2/gm 3

Fume Silica:
SiO2 (Min.), % 98
Cfree (Max.), % 0.70
Al2O3 (Max.), % 0.30
Fe2O3 (Max.), % 0.10
Na2O (Max), % 0.20
K2O (Max.), % 0.30
B.D., kg/m3 250 – 350
L.O.I. (Max.), % 0.80

Chromic Oxide:
Cr2O3 (Min.), % 98
Specific Gravity (Min.) 5.0
Solubility Insoluble in Water, alcohol and acetone
Colour Green

High Alumina Cement:
Al2O3 (Min.), % 70
Fe2O3 (Max.), % 0.30
CaO (Max), % 29
SiO2 (Max.), % 0.30
Major Phase CA.CA2

Sodium Hexa Meta Phosphate (SHMP):
P2O5 (Min.), % 65
Grade LR

Citric acid:
Purity (Min.), % 99.5
Grade LR

The Properties of developed brick are given in TABLE III.
TABLE III:
Properties of Developed High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block
Parameters Value
Al2O3, %, Min. 80
Cr2O3, %, Min. 2
Fe2O3, %, Max. 2
B.D., gm/cc, Min. 2.50
C.C.S., kg/cm2, Min. At, 1100C/ 24hrs. : 400
12000C/ 3hrs. : 800
14500C/ 3hrs. : 1000
Repeat P.L.C.A.R., %, at 15000C/3 hrs. 1st P.L.C.A.R.: ± 0.50
2nd P.L.C.A.R.: ± 0.20
3rd P.L.C.A.R.: ± 0.10
Thermal Shock Resistance at 10000C, Cycles, Min. (By Water Quenching) 40

After manufacturing of pre-cast blocks with developed castable, the blocks were installed in VAD ladle cover of Alloy Steels Plant (ASP) at Durgapur of Steel Authority of India Limited (SAIL).

Although the invention described herein is with various specific embodiments, it can be possible to modify those embodiments by a person skilled in the art. However, all such modifications are deemed to be within the scope of the claims herein appended.

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Claims:WE CLAIM:

1. High Alumina (80% Al2O3, min.) castable having high thermal shock resistance, high strength and high volume stability for manufacturing of pre-cast block for use as refractory lining of VAD ladle cover, comprising:
White Tabular Alumuna (WTA) ( Coarse + Middle) having particle size ranging from 3 mesh to 28 mesh and about 55–65 % by weight,
Silimanite Sand (Fines) having particle size upto 200 mesh and about 7–11 % by weight,
Calcined Alumina (Fines) having particle size below 0.044 mm and about 15–25 % by weight,
Fume Silica (Fines) having particle size below 0.044 mm and about 4–6 % by weight,
Chromic Oxide (Fines) having particle size below 0.044 mm and about 1–2 % by weight,
High Alumina Cement (Fines) as binder for wet mixing about 4–6 % by weight,
Sodium Hexa Meta Phosphate (SHMP) about 0.07–0.18 % by weight,
Citric acid about 0.01–0.05 % by weight.

2. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in claim 1, wherein said White Tabular Alumuna (WTA) comprises
Al2O3 (Min.), % 99.3
Fe2O3 (Max.), % 0.13
Na2O+K2O (Max), % 0.60
Bulk Density (Min.) 3.55

3. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 or 2, wherein said Silimanite Sand comprises
Al2O3 (Min.), % 58
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

4. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 3, wherein said Calcined Alumina comprising
Al2O3 (Min.), % 99.5 [of which a- Al2O3 content is 90% (Min.)]
Fe2O3 (Max.), % 0.03
Na2O (Max), % 0.50
SiO2 (Max.), % 0.03
Specific Gravity (Min.) 3.90
Specific Surface Area (Max.), m2/gm 3

5. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 4, wherein said Fume Silica comprising
SiO2 (Min.), % 98
Cfree (Max.), % 0.70
Al2O3 (Max.), % 0.30
Fe2O3 (Max.), % 0.10
Na2O (Max), % 0.20
K2O (Max.), % 0.30
B.D., kg/m3 250 – 350
L.O.I. (Max.), % 0.80

6. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 5, wherein said Chromic Oxide comprising
Cr2O3 (Min.), % 98
Specific Gravity (Min.) 5.0
Solubility Insoluble in Water, alcohol and acetone
Colour Green

7. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 6 wherein said High Alumina Cement comprising
Al2O3 (Min.), % 70
Fe2O3 (Max.), % 0.30
CaO (Max), % 29
SiO2 (Max.), % 0.30
Major Phase CA.CA2

8. High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 7, wherein said Sodium Hexa Meta Phosphate comprising
P2O5 (Min.), % 65
Grade LR

and Citric acid comprising
Purity (Min.), % 99.5
Grade LR

9. The High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 8, having thermal shock resistance of minimum 40 cycles at 10000C (By Water Quenching) as well as high strength by way of Cold Crushing Strength (CCS) comprising:

C.C.S., kg/cm2, Min. At 1100C/ 24hrs. : 400
12000C/ 3hrs. : 800
14500C/ 3hrs. : 1000

10. The High Alumina (80% Al2O3, min.) castable for manufacturing of pre-cast block as claimed in anyone of claims 1 to 9 having high thermal shock resistance of 40 cycles (By Water Quenching) and high strength by way of Cold Crushing Strength (CCS) as well as high volume stability by way of Repeat Permanent Linear Change After Reheating (Repeat PLCAR) comprising:

Repeat PLCAR, %, At 15000C for 3 hours (PLCAR as per IS:1528, Part VI)
1st PLCAR: ± 0.50
2nd PLCAR: ± 0.20
3rd PLCAR: ± 0.10