Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

COMPOSITION FOR HIGH ALUMINA LOW CEMENT CASTABLE

STEEL AUTHORITY OF INDIA LIMITED, A GOVERNMENT OF INDIA ENTERPRISE, HAVING ITS ADDRESS AT RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL (RDCIS), DORANDA, RANCHI-834002, STATE OF JHARKHAND, INDIA

THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention
The present invention relates to a composition for high alumina low cement castable and application of the castable in blast furnace area.

Background of the Invention
Major performance indices of a blast furnace, such as productivity, coke rate, quality of hot metal, etc. are very much dependent on hot blast temperature. As the size of blast furnaces of the plant has increased, higher blast temperature has become essential. Design of stoves was also modified accordingly for this purpose. Presently, in the known art stoves are available to provide hot blast temperature of around 1200°C. However, in the attempts to increase the hot blast temperature beyond 1050°C, bottleneck was found as formation of red spot in compensator/ elbow/ blow pipe which eventually restrict the increase in hot blast temperature.
There are several patent publications such as CN101475390A that disclosed Al2 O3/ZrO2 refractory casting material made up of aggregate consisting of bauxite chamotte; powder consisting of silicon powder, rho-Al2O3 micro powder, sub-white corundum powder, alpha-Al2O3, zirconite powder, white slime, bauxite chamotte powder, high alumina cement, pure calcium aluminate cement; and additives consisting of sodium hexametaphosphate and water.
Indian patent application 202031008707 discloses a pre-cast block manufacturing of Vacuum Arc Degassing (VAD) ladle cover comprising white tabular alumina (WTA), silimanite sand, calcined alumina, fume silica, chromic oxide, high alumina cement as binder for wet mixing, sodium hexa meta phosphate (SHMP), and citric acid. This application uses chromic oxide to make the product suitable for operating condition of VAD ladle cover, however corrosion by slag and metal at high temperature is not addressed.
There has been a persistent need in the castables as refractory lining of compensator, elbow and blow pipe of blast furnace, to achieve high strength castable with resistance to corrosion from slag and higher hot strength by way of having required Hot Modulus Of Rupture (HMOR) coupled with required Cold Crushing Strength (CCS) and Bulk Density (BD) and without formation of red spot in compensator/ elbow/ blow pipe and without sacrificing much of the slag or metal corrosion resistance properties and for improving abrasion resistance, and volume stability of the castables, reducing downtime, ensuring economy in operations and enhancing productivity, coke rate, quality of hot metal.

Summary of the Invention
The present invention relates to a composition for a high alumina low cement castable. The composition comprises white tabular alumina (WTA) having particle size ranging from 3 mesh to -325 mesh in an amount in the range of 50 to 70 % by weight, silimanite sand having particle size upto 200 mesh in an amount in the range of 5 to 15 % by weight, stabilized zirconia having particle size below 40 mesh in an amount in the range of 6 to 12 % by weight, calcined alumina having particle size below 0.044 mm in an amount in the range of 13 to 23 % by weight, fume silica having particle size below 0.044 mm in an amount in the range of 3 to 7 % by weight, high alumina cement in an amount in the range of 4 to 6 % by weight, sodium hexa meta phosphate (SHMP) in an amount in the range of 0.07 to 0.18 % by weight, and citric acid in an amount in the range of 0.01 to 0.05 % by weight.
The present invention relates to a high alumina low cement castable. The castable is having high strength by way of hot modulus of rupture (HMOR) of minimum 90 at 1200ºC for 0.5 hour, high strength by way of cold crushing strength (CCS) of minimum 500 kg/cm2 at 110ºC/ for 24hrs and of minimum 1200 kg/cm2 at 1200ºC for 3hrs, high strength by way of bulk density (BD) of minimum 3.00 gm/cc at 110ºC for 24hrs and of minimum 2.90 gm/cc at 1200ºC for 3hrs. The castable has high volume stability by way of permanent linear change (PLC) of 0 to 0.20 % at 1200ºC for 3 hrs.

Description of Invention
The present invention relates to high alumina (75% Al2O3, min.) low cement castable having high strength combined with high volume stability for use as refractory lining of compensator, elbow and blow pipe of blast furnace. The present invention provides refractory castable with high strength by the way of having required hot modulus of rupture (HMOR) coupled with having required cold crushing strength (CCS) and bulk density (BD). The present invention relates to refractory castable with high volume stability by way of having required permanent linear change (PLC).

In an embodiment, the present invention relates to a composition for a high alumina low cement castable. The composition comprises white tabular alumina (WTA) in an amount in the range of 50 to 70 % by weight, silimanite sand in an amount in the range of 5 to 15 % by weight, stabilized zirconia in an amount in the range of 6 to 12% by weight, calcined alumina in an amount in the range of 13 to 23% by weight, fume silica in an amount in the range of 3 to 7% by weight, high alumina cement in an amount in the range of 4 to 6% by weight, sodium hexa meta phosphate (SHMP) in an amount in the range of 0.07 to 0.18% by weight, and citric acid in an amount in the range of 0.01 to 0.05% by weight.

In another embodiment, the composition for the high alumina low cement castable comprises white tabular alumina (WTA) having particle size ranging from 3 mesh to -325 mesh and in an amount of 50 to 70 % by weight, silimanite sand having particle size upto 200 mesh in an amount of 5 to 15 % by weight, stabilized zirconia having particle size below 40 mesh and in an amount in the range of 6 to 12 % by weight, calcined alumina having particle size below 0.044 mm and in an amount in the range of 13 to 23 % by weight, fume silica having particle size below 0.044 mm and in an amount in the range of 3 to 7 % by weight, high alumina cement in an amount in the range of 4 to 6 % by weight, sodium hexa meta phosphate (SHMP) in an amount in the range of 0.07 to 0.18 % by weight, and citric acid in an amount in the range of 0.01 to 0.05 % by weight. The high alumina cement (Fines) can be used as binder for wet mixing.

In an aspect, white tabular alumina (WTA) comprises minimum 99.3% Al2O3, maximum 0.13% Fe2O3, maximum 0.60% Na2O+K2O, and having bulk density of minimum 3.55.

In another aspect, silimanite sand comprises minimum 58% Al2O3, 1% Fe2O3, and having a minimum of 3.00 specific gravity.
In another aspect, stabilized zirconia comprises minimum 94% ZrO2 + HFO2, 3.30 to 4.20% CaO, maximum 0.15% Fe2O3 and maximum 0.30% TiO2.
In another aspect, calcined alumina comprises minimum 99.5% Al2O3, maximum 0.03% Fe2O3, maximum 0.50% Na2O, maximum 0.03 % SiO2, and having minimum 3.9 specific gravity and maximum 3 m2/gm specific surface area.
In another aspect, fume silica comprises minimum 98% SiO2, maximum 0.70 % free carbon, maximum 0.30% Al2O3, maximum 0.10 % Fe2O3, maximum 0.50 % Na2O + K2O and having bulk density of 250 to 350 kg/m3 and a maximum of 0.80% loss of ignition (L.O.I.).
In another aspect, high alumina cement comprises minimum 70% Al2O3, maximum 0.30% Fe2O3, maximum 29% CaO and maximum 0.30% SiO2.
In another aspect, sodium hexa meta phosphate comprises minimum 65% P2O5.
In another aspect, citric acid is having minimum of 99.5% purity.

The stabilized zirconia in the composition of the present invention imparts high strength and excellent abrasion resistance against the high temperature and high-speed air flow through the compensator, elbow and blow pipe of blast furnace.

In another embodiment, the present invention relates to a high alumina low cement castable. The castable is having minimum of 75% Al2O3, minimum of 6.5% ZrO2, maximum of 0.6% Fe2O3 and maximum of 1.5% CaO.

In an aspect, the high alumina low cement castable is used as refractory lining of compensator, elbow and blow pipe of blast furnace.

In an aspect, the high alumina low cement castable is having high strength by way of minimum hot modulus of rupture (HMOR) at 1200ºC for 0.5 hour of 90.

In another aspect, the high alumina low cement castable is having high strength by way of cold crushing strength (CCS) of minimum 500 kg/cm2 at 110ºC/ for 24hrs and of minimum 1200 kg/cm2 at 1200ºC for 3hrs.

In yet another aspect, the high alumina low cement castable is having high strength by way of bulk density (BD) of minimum 3.00 gm/cc at 110ºC for 24hrs and of minimum 2.90 gm/cc at 1200ºC for 3hrs.

In yet another aspect, the high alumina low cement castable is having high volume stability by way of permanent linear change (PLC) of 0 to 0.20 % at 1200ºC for 3 hrs.

In another embodiment, the present invention relates to a process for preparing a high alumina low cement castable. The process comprises dry mixing a composition comprising white tabular alumina (WTA) in an amount of 50 to 70% by weight, silimanite sand in an amount of 5 to 15% by weight, stabilized zirconia in an amount of 6 to 12% by weight, calcined alumina in an amount of 13 to 23% by weight, fume silica in an amount of 3 to 7% by weight, high alumina cement in an amount of 4 to 6% by weight, sodium hexa meta phosphate (SHMP) in an amount of 0.07 to 0.18% by weight, and citric acid in an amount 0.01 to 0.05% by weight for around 10 minutes to obtain a dry mixture; adding water slowly into above mixture and again mixing for another 5 minutes; casting the mixture in steel moulds and keeping the casted moulds undisturbed for minimum 24 hours; de-moulding the casted moulds and air drying for 24 hours; and
drying the castables in an oven at 110°C for 24 hours to obtain high alumina low cement castable.
The high alumina low cement castable of the present invention facilitates increase in hot blast temperature, provides high speed air flow through the compensator, elbow and blow pipe of blast furnace, improves metal corrosion resistance properties and improves abrasion resistance, provides high strength and high-volume stability to the refractory lining of compensator, elbow and blow pipe of blast furnace.

Examples
Examples are set forth herein below and are illustrative of different amounts and types of reactants and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other amounts and types of reactants and reaction conditions than those used in the examples, and the resulting devices various different properties and uses in accordance with the disclosure above and as pointed out hereinafter.
EXAMPLE I - Composition of High Alumina (75% Al2O3, min.) castable
The starting batch composition for producing a high alumina low cement castable is given in Table 1:
Table 1: Batch Composition for High Alumina (75% Al2O3, min.) low cement castable
Raw Material %
1. WTA (Coarse+ Middle+ Fines) 50 – 70
2. Silimanite Sand (Fines) 5 – 15
3. Stabilized Zirconia (Fines) 6 – 12
4. Calcined Alumina (Fines) 13 – 23
5. Fume Silica (Fines) 3 – 7
6. High Alumina Cement 4 – 6
7. SHMP (Sodium HexaMetaPhosphate) 0.07–0.18
8. Citric acid 0.01 – 0.05

Details of different components of raw materials in a batch have been given in following Table 2.
Table 2: Details of each of the components of the present composition for high alumina low cement castable
1. White Tabular Alumina (WTA):
Al2O3 (Min.), % 99.3
Fe2O3 (Max.), % 0.13
Na2O+K2O (Max), % 0.60
Bulk Density (Min.) 3.55

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

3. Stabilized Zirconia:
ZrO2 + HFO2 (Min.), % 94
CaO, % 3.30 – 4.20
Fe2O3 (Max.), % 0.15
TiO2 (Max.), % 0.30

4. Calcined Alumina:
Al2O3 (Min.), % 99.5
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. Fume Silica:
SiO2 (Min.), % 98
Cfree (Max.), % 0.70
Al2O3 (Max.), % 0.30
Fe2O3 (Max.), % 0.10
Na2O + K2O (Max), % 0.50
B.D., kg/m3 250 – 350
L.O.I. (Max.), % 0.80

6. High Alumina Cement:
Al2O3 (Min.), % 70
Fe2O3 (Max.), % 0.30
CaO (Max), % 29
SiO2 (Max.), % 0.30

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

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

EXAMPLE II –
Process for preparing the High Alumina (75% Al2O3, min.) low cement castable
Before performing any test for refractory castable, proper sample preparation is required. For performing different tests mentioned below, samples i.e. castables of the present invention are prepared by casting method in cube shape (50mmx50mmx50mm) and bar shape (25mmx25mmx150mm) using suitable steel moulds.
 Similar environment (Mixing parameters, casting parameters, etc.) was maintained during sample preparation for all compositions.
 All the raw materials of each composition (Annexure I) were taken in appropriate proportions and dry mixed in a mixer for around 10 minutes.
 After that water was added slowly as per requirement and again mixed for another 5 minutes.
 After proper mixing, flow of castable of each composition was checked and then the green mix was cast in steel moulds.
 Casting environment (Temperature, vibration, etc.) was kept uniform for all the samples during preparation.
 The casted moulds were kept undisturbed for minimum 24 hours.
 Then de-moulding was done and samples were air dried for 24 hours.
 After that, samples were kept in an oven for drying at 110°C for 24 hours.
 Then required samples for evaluation after drying were kept in desiccators and rest samples were fired at 1200°C for 3 hours to evaluate fired properties (Fired BD, Fired CCS, HMOR & PLC).
EXAMPLE III – Fired properties Testing of the High Alumina (75% Al2O3, min.) low cement castable
The cube shaped samples obtained were used for testing of Bulk Density (BD), Cold Crushing Strength (CCS) and bar shaped samples used for testing of PLC, HMOR.
1. Bulk Density (BD):
BD = (Mass/Volume) gm/cc.
Mass was measured by weighing the sample (in gm). All the dimensions (Length, Breadth and Depth) of the sample was measured by slide calipers and volume was calculated as (LxBxD) cm3/cc.
2. Cold Crushing Strength (CCS):
CCS = (Total load applied/ Surface area) kg/cm2.
Total load applied was measured by CCS machine in kg. Dimensions (Length and Breadth) of the sample was measured by slide calipers and surface area was calculated as (LxB) cm2.
3. Permanent Linear Change (PLC):
PLC = % of permanent change of length after heating.
For PLC, length of the sample was measured by slide calipers before firing and as well as after firing at 1200°C. Then the % of difference of length of the sample was reported as PLC.
4. Hot Modulus Of Rupture (HMOR):
HMOR = (3WL/2BD2) kg/cm2
W= Total load applied in kg at elevated temperature;
L = Fixed Span of HMOR machine = 12.5cm,
B= Breadth,
D= Depth
Total load applied was measured by HMOR machine. Breadth and Depth of the sample was measured by slide calipers.
The Properties of high alumina low cement castable of the present invention are given below in Table 3.
Table 3: Properties of High Alumina (75% Al2O3, min.) low cement castable of the present invention
Parameters Value
Al2O3, %, Min. 75
ZrO2, %, Min. 6.5
Fe2O3, %, Max. 0.6
CaO, %, Max. 1.5
BD, gm/cc, Min. After, 110°C/ 24hrs. : 3.00
120°C/ 3hrs. : 2.90
CCS, kg/cm2, Min. After, 110°C/ 24hrs. : 500
1200°C/ 3hrs. : 1200
PLC, %, at 1200°C/ 3 hours, Max. 0 to + 0.20
HMOR, kg/cm2, at 1200°C/ 0.5 hour, Min. 90
Water required for casting, %, Max. 5.5

The Properties of conventional refractory castable earlier used for lining of compensator, elbow and blow pipe of blast furnace is given below in table 4.
Table 4: Specification of 92% Al2O3 containing conventional refractory castable
Parameters Value
Al2O3, %, Min. 92
Fe2O3, %, Max. 0.75
CaO, %, Max. 4.2
B.D., gm/cc, Min. After drying at 110°C/ 24hrs. : 2.85
C.C.S., kg/cm2, Min. After drying at 110°C/ 24hrs. : 600
After firing at 1550°C/ 3hrs. : 400 – 800
P.L.C., %, at 1550°C/ 3 hrs., Max. ± 0.80
Water required for casting, %, Max. 8

Thus comparing the properties of the cement castable of the present invention and conventional refractory castable earlier used as given in table 3 and 4 it can be inferred that the High Alumina (75% Al2O3, min.) low cement castable of the present invention ensure high strength by the way of having minimum Hot Modulus Of Rupture (HMOR) coupled with Cold Crushing Strength (CCS) and Bulk Density (BD) ensures and high volume stability by way of Permanent linear change (PLC).

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.
, Claims:

1. A composition for a high alumina low cement castable, comprising:
white tabular alumina (WTA) having particle size ranging from 3 mesh to -325 mesh in an amount in the range of 50 to 70% by weight,
silimanite sand having particle size upto 200 mesh in an amount in the range of 5 to 15% by weight,
stabilized zirconia having particle size below 40 mesh in an amount in the range of 6 to 12% by weight,
calcined alumina having particle size below 0.044 mm in an amount in the range of 13 to 23% by weight,
fume silica having particle size below 0.044 mm in an amount in the range of 3 to 7% by weight,
high alumina cement in an amount in the range of 4 to 6% by weight,
sodium hexa meta phosphate (SHMP) in an amount in the range of 0.07 to 0.18% by weight, and
citric acid in an amount in the range of 0.01 to 0.05% by weight.

2. The composition as claimed in claim 1, wherein said white tabular alumina (WTA) comprises minimum 99.3% Al2O3, maximum 0.13% Fe2O3, maximum 0.60% Na2O+K2O, and having bulk density of minimum 3.55.

3. The composition as claimed in claim 1, wherein said silimanite sand comprises minimum 58% Al2O3, 1% Fe2O3, and having a minimum of 3.00 specific gravity.

4. The composition as claimed in claim 1, wherein said stabilized zirconia comprises minimum 94% ZrO2 + HFO2, 3.30 to 4.20% CaO, maximum 0.15% Fe2O3 and maximum 0.30% TiO2.

5. The composition as claimed in claim 1, wherein said calcined alumina comprises minimum 99.5% Al2O3, maximum 0.03% Fe2O3, maximum 0.50% Na2O, maximum 0.03 % SiO2, and having minimum 3.9 specific gravity and maximum 3 m2/gm specific surface area.

6. The composition as claimed in claim 1, wherein said fume silica comprises minimum 98% SiO2, maximum 0.70 % free carbon, maximum 0.30% Al2O3, maximum 0.10 % Fe2O3, maximum 0.50 % Na2O + K2O and having bulk density of 250 to 350 kg/m3 and a maximum of 0.80% loss of ignition (L.O.I.).

7. The composition as claimed in claim 1, wherein said high alumina cement comprises minimum 70% Al2O3, maximum 0.30% Fe2O3, maximum 29% CaO and maximum 0.30% SiO2.

8. The composition as claimed in claim 1, wherein said sodium hexa meta phosphate comprises minimum 65% P2O5.

9. The composition as claimed in claim 1, wherein said citric acid having minimum of 99.5% purity.

10. A high alumina low cement castable comprising the composition as claimed in claim 1, is having high strength by way of minimum hot modulus of rupture (HMOR) at 1200ºC for 0.5 hour of 90.

11. The castable as claimed in claim 10, is having high strength by way of cold crushing strength (CCS) of minimum 500 kg/cm2 at 110ºC/ for 24hrs and of minimum 1200 kg/cm2 at 1200ºC for 3hrs.

12. The castable as claimed in claim 10, is having high strength by way of bulk density (BD) of minimum 3.00 gm/cc at 110ºC for 24hrs and of minimum 2.90 gm/cc at 1200ºC for 3hrs.

13. The castable as claimed in claim 10, is having high volume stability by way of permanent linear change (PLC) of 0 to 0.20 % at 1200ºC for 3 hrs.