Claims:WE CLAIM:

1. High Alumina bricks for use as refractory lining of Reheating Furnace Hearth comprising:

Andalusite (Coarse) having particle size up to 3 mm and about 17–25% by weight,

Brown Fused Alumina (BFA) (Coarse) having particle size ranging from 8 to 30 mesh and about 22–28% by weight,

Fused Mullite (Coarse) having particle size up to 2 mm and about 17–23% by weight,

White Fused Alumina (WFA) (Fines) having particle size below 140 mesh and about 5–

9% by weight,

Calcined Alumina (Fines) having particle size below 0.044 mm and about 7–11% by weight,

Plastic Clay (Fines) having particle size below 0.074 mm and about 9–13% by weight, Raw Kyanite (Fines) having particle size below 0.074 mm and about 4–6% 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 as liquid binder for wet mixing.

2. High Alumina bricks as claimed in claim 1, wherein said Andalusite comprises

Al2O3 (Min.), % 57
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

3. High Alumina bricks as claimed in anyone of claims 1 and 2, wherein said Brown

Fused Alumina (BFA) comprises

Al2O3 (Min.), % 95
SiO2 (Max.), % 1.0
Fe2O3 (Max.), % 0.50
TiO2 (Max.), % 3.2
CaO (Max.), % 0.60
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.93
Free Iron (Max.), % 0.10 (With total Fe2O3 – 0.5% Max.)

4. High Alumina bricks as claimed in anyone of claims 1 to 3, wherein said Fused

Mullite comprising

Al2O3 (Min.), % 70
SiO2 (Max.), % 29
Fe2O3 (Max.), % 1
Na2O (Max), % 0.60

5. High Alumina bricksas claimed in anyone of claims 1 to 4, wherein said White Fused

Alumina (WFA) comprising

Al2O3 (Min.), % 99
Fe2O3 (Max.), % 0.10
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.80

6. High Alumina bricks as claimed in anyone of claims 1 to 5, wherein said Calcined

Alumina comprising

0

7. High Alumina bricks as claimed in anyone of claims 1 to 6, wherein Plastic Clay comprising said

Al2O3 (Min.), % 37
Fe2O3 (Max.), % 2.5

PCE (Ort.), Min. 32
Moisture (Max. after drying at 110 for 24 hrs.), % 12
Material should be free from calcerious & ferrogeneous impurities &

free silica on physical verification having sinterability and plasticity.

8. High Alumina bricks as claimed in anyone of claims 1 to 7, wherein said Raw

Kyanite comprising

Al2O3(Min.), % 37
Fe2O3 (Max.), % 1.8
PCE (Min.), Ort. 33
PLC (at 14500C/2 Hrs.) (Min.), % + 4

9. High Alumina bricksas claimed in anyone of claims 1 to 8 wherein saidFeldspar

comprising

Al2O3 (Min.), % 16
SiO2 (Max.), % 70
Fe2O3 (Max.), % 1
Melting point (0C) 1000 – 1260

10. High Alumina bricks as claimed in anyone of claims 1 to 9, having maximum Abradability Index (A.I.) of 45 (A.I. as per B.S.1902: Section 4.6:1985) coupled with Refractoriness under load (RUL) of minimum 16000 C ( ta, as per IS:1528 Part II).

11. High Alumina bricks as claimed in anyone of claims 1 to 10, having high thermal shock resistance of 50 cycles (By Air Quenching) as well as high volume stability by way of Repeat Permanent linear change after reheating (Repeat PLCAR) comprising:

Repeat PLCAR, %, At 15000C fa 1stpLCAR: ± 0.50

3 hours (PLCAR as per IS: 1528, 2nd PLCAR: ± 0.30

Part VI) 3rd PLCAR: ± 0.10

, Description:HIGH ABRASION AND THERMAL SHOCK RESISTANT ALUMINA BRICKS FOR REFRACTORY LINING OF REHEATING FURNACE HEARTH (UP TO 11000 C)

FIELD OF THE INVENTION

The present invention relates to refractory lining of pre-heating zone hearth of reheating furnace. More particularly, the present invention is directed to providing an improved alumina bricks with minimum 70% Alumina having high abrasion resistance combined with high Thermal shock Resistance suitable for use as refractory lining of pre-heating zone hearth (up to 11000 C) of reheating furnace such as in Merchant mill of Durgapur Steel Plant (DSP) of Steel Authority of India Limited (SAIL).

BACKGROUND OF THE INVENTIONAND PRIOR ART

DSP was facing problem of low refractory lining life of merchant mill reheating furnace preheating zone hearth. Sometimes, this poses problem in maintaining an uninterrupted and continuous operation due to billet pile-up inside the furnace and unplanned shutdown. For maintaining a steady production in merchant mill, DSP need to have consistent furnace hearth life of about a year. DSP also intends to reduce cost for its pre- heating zone hearth refractory of the reheating furnace of Merchant mill.

To circumvent this problem, RDCIS (Research and Development Centre for Iron and Steel) of Steel Authority of India (SAIL) took up a project jointly with DSP and SRU, IFICO for development of high alumina refractory which has lower cost as compared to existing refractory and can be manufactured using in-house refractory manufacturing facility at IFICO plant of SRU. Developmental work carried out at RDCIS&IFICO led to the development of a High Alumina (70% Al2O3, min.) High Abrasion resistant and High Thermal Shock Resistant bricks for preheating zoneof reheating furnace hearth with high strength.

A few prior patents are known to exist in the fields which are given herein by reference:

US3615775A (1970) discloses a high alumina refractory composition comprising Al2O3, MgO and Cr2O3. The said refractory microscopically characterized by coarse alumina grains.

US3953563A (1970) discloses a method for producing high alumina refractory material (bricks) containing more than 50% by wt. alumina. The moist refractory starting material is pressed into bricks, dried and hydrothermally bound. The principal binding agent used is finely divided activated alumina alone or together with slaked lime, slaked magnesia and finely divided silicon dioxide. The hydrothermal treatment essentially converted all the activated alumina into boehmite.

US3378385 (1966) discloses a ceramically bonded, high alumina refractory bricks made from a batch consisting essentially of fused alumina grain containing titania, finely divided chrome sesquioxide, and finely divided non-fused high alumina refractory material.

US3841884A (1973) discloses a high alumina refractory of improved resistance to deformation at high temperature and resistance to slag penetration made with coarse fraction containing calcined flint clay and a fine fraction of fine silica, and fine alumina.

US3421917 (1966) discloses aluminosilicate refractory brick prepared from aluminosilicate grogs and bond clays.

CA872289 (1971) discloses high alumina refractory brick.

US3403213A (1966) discloses electric furnace having refractory brick containing at least

50% fused grain.

EP 0311553 discloses a chromia– alumina refractory brick prepared by pressing and firing a mixture of 15-90 % of fused chromia – alumina grain, 5 – 25% chromic oxide, a zirconia – containing grain up to 30 % and the balance alumina.

OBJECTS OF THE INVENTION

The basic object of the invention is directed to provide High Alumina (70% Al2O3, min.) bricks having high abrasion resistance and high Thermal shock Resistance suitable for use as refractory lining of pre-heating zone hearth (up to 11000C) of Reheating furnace.

Another object of the invention is to provide refractory bricks which would ensure Refractoriness under load (RUL) of minimum 1600O C (ta, as per IS: 1528 Part II) coupled with Abradability index (A.I.) of maximum 45 (A.I. as per B.S.1902:Section4.6:1985).

A further object of the invention is to provide refractory bricks with minimum thermal shock resistance of 50 cycles (By Air Quenching) of said 70% Alumina bricks.

SUMMARY OF THE INVENTION

The basic aspect of the invention is to provide High Alumina (70% Al2O3, min.) bricks for use as refractory lining of pre-heating zone hearth (up to 11000C) of Reheating furnace, comprising:

Andalusite (Coarse) having particle size up to 3 mm and about 17–25% by weight,

Brown Fused Alumina (BFA) (Coarse) having particle size ranging from 8 mesh to 30 mesh and about 22–28% by weight,

Fused Mullite (Coarse) having particle size up to 2 mm and about 17–23% by weight,

White Fused Alumina (WFA) (Fines) having particle size below 140 mesh and about 5–9

% by weight,

Calcined Alumina (Fines) having particle size below 0.044 mm and about 7–11% by weight,

Plastic clay (Fines) having particle size below 0.074 mm and about 9–13% by weight, Raw Kyanite (Fines) having particle size below 0.074 mm and about 4–6% by weight, Feldspar (Fines) having particle size below 0.074 mm and about 4–6% by weight, Molasses of about 2.5–4% by weight as liquid binder for wet mixing.

A further aspect of the invention is directed to the said bricks wherein said Andalusite

comprises

Al2O3 (Min.), % 57
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

A still further aspect of the invention is directed to the said bricks wherein said Brown

Fused Alumina (BFA) comprises

Al2O3 (Min.), % 95
SiO2 (Max.), % 1.0
Fe2O3 (Max.), % 0.50
TiO2 (Max.), % 3.2
CaO (Max.), % 0.60
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.93
Free Iron (Max.), % 0.10 (With total Fe2O3 – 0.5% Max.)

Yet another aspect of the invention is directed to the said bricks wherein said Fused

Mullite comprises

Al2O3 (Min.), % 70
SiO2 (Max.), % 29
Fe2O3 (Max.), % 1
Na2O (Max), % 0.60

A further aspect of the invention is directed to the said bricks wherein said White Fused

alumina (WFA) comprises

Al2O3 (Min.), % 99
Fe2O3(Max.), % 0.10
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.80

A still further aspect of the invention is directed to the said bricks 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
Average Particle Size d50 (Max

µ 5.5
Specific Gravity (Min.) 3.90
Specific Surface Area (Max.), m2/gm 3
+325 mesh (ASTM Tyler) Max., 1.5

Yet another aspect of the invention is directed to the said bricks wherein said Plastic Clay

comprises

Al2O3 (Min.), % 37
Fe2O3(Max.), % 2.5
PCE (Ort.), Min. 32
Moisture (Max. after drying at 1100 C

for 24 hrs.), % 12
Material should be free from calcerious & ferrogeneous impurities

&free silica on physical verification having sinterability and plasticity.

A further aspect of the invention is directed to the said brickswherein said Raw

Kyanitecomprises

Al2O3(Min.), % 37
Fe2O3 (Max.), % 1.8
PCE (Min.), Ort. 33
PLC (at 14500C/2 Hrs.) (Min.),% + 4

A still further aspect of the invention is directed to the said brickswherein said

Feldsparcomprising

Al2O3 (Min.), % 16
SiO2 (Max.), % 70
Fe2O3 (Max.), % 1
Melting point (0C) 1000 – 1260

Yet another aspect of the present invention is directed to the said bricks wherein said

Molasses is having Specific gravity–1.1 to 1.2.

A further aspect of the present invention is directed to the said bricks having maximum Abradability Index (A.I.) of 45 (A.I. as per B.S.1902: Section 4.6:1985) coupled with Refractoriness under load (RUL) of minimum 16000 C (ta, as per IS: 1528 Part II) and minimum thermal shock resistance of 50 cycles (By Air Quenching).

A still further aspectof the invention is directed to the said bricks 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: ± 0.30

3rd PLCAR: ± 0.10

The invention is described hereunder in details with reference to the following illustrative example.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to provide improved High Alumina (70% Al2O3, min.) bricks with High Abrasion Resistance, High Thermal Shock Resistance and high Refractoriness under load suitable for refractory lining of pre-heating zone hearth (up to 11000 C) of Reheating furnace such as in Merchant mill of Durgapur steel plant (DSP) of Steel Authority of India Limited (SAIL) and in particular related to 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 improved High Alumina (70% Al2O3, min.) bricks according to the invention, different high Alumina and Alumino-Silicate raw materials in different size

fractions are mixed in required proportion with the addition of required binder i.e. molasses 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 1100 C for 20-24 hours. The bricks are then fired in Tunnel kiln at 15000 C 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 70 C per minute from ambient temperature to

300-4000 C.

(ii) Heating up of bricks at 10-120 C per minute from 400 to 8000 C.

(iii) Firing of bricks at a much slow rate of 0.8 to 1.00 C per minute from 8000 C to 1200-

13000 C 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 20 C per minute up to

15000 C.

(v) Soaking time is provided for 12 to 18 hours at the highest temperature.

After manufacturing, the improved bricks are installed at preheating zone hearth of reheating furnace of Merchant mill at Durgapur Steel Plant (DSP) of Steel Authority of India Limited (SAIL).

Batch Composition of invented High Alumina (70% Al2O3, min.) bricks for preheating zone hearth (Up to 11000 C) of reheating furnace

The invention is directed to provide High Alumina (70% Al2O3, min.) bricks with high Abradability Index (A.I.); high Thermal shock resistance; high Refractoriness under load (RUL) and higher volume stability suitable for use in preheating zone hearth (Up to 11000
C) of reheating furnace. The starting batch composition for producing such bricks is given in Annexure I:

Annexure I: Batch Composition ofHigh Alumina (70% Al2O3, min.) bricks

Raw Material %
Andalusite (Coarse) 17 – 25
BFA (Coarse) 22 – 28
Fused Mullite (Coarse) 17 – 23
WFA (Fines) 5 – 9
Calcined Alumina (Fines) 7 – 11
Plastic Clay (Fines) 9 – 13
Raw Kyanite (Fines) 4 – 6
Feldspar (Fines) 4 – 6
Molasses (Liquid Binder) 2.5 – 4

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

Andalusite:

Al2O3 (Min.), % 57
Fe2O3 (Max.), % 1
Specific Gravity (Min.) 3.00

Brown Fused Alumina (BFA):

Al2O3 (Min.), % 95
SiO2 (Max.), % 1.0
Fe2O3 (Max.), % 0.50
TiO2 (Max.), % 3.2
CaO (Max.), % 0.60
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.93
Free Iron (Max.), % 0.10 (With total Fe2O3 – 0.5% Max.)

Fused Mullite:

Al2O3 (Min.), % 70
SiO2 (Max.), % 29
Fe2O3 (Max.), % 1
Na2O (Max), % 0.60

White Fused Alumina (WFA):

Al2O3 (Min.), % 99
Fe2O3 (Max.), % 0.10
Na2O (Max), % 0.50
Specific Gravity (Min.) 3.80

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
Average Particle Size d50 (Max.), µ 5.5
Specific Gravity (Min.) 3.90
Specific Surface Area

(Max.), m2/gm 3
+325 mesh (ASTM Tyler)

Max., % 1.5

Plastic Clay:

Al2O3 (Min.), % 37
Fe2O3 (Max.), % 2.5
PCE (Ort.), Min. 32
Moisture (Max. after drying at 1100 C for

24 hrs.), % 12
Material should be free from calcerious & ferrogeneous impurities &

free silica on physical verification having sinterability and plasticity.

Raw Kyanite:

Al2O3 (Min.), % 37
Fe2O3 (Max.), % 1.8

PCE (Min.), Ort. 33
PLC (at 14500 C/2 Hrs.)

(Min.), % + 4

Feldspar:

Al2O3 (Min.), % 16
SiO2 (Max.), % 70
Fe2O3 (Max.), % 1
Melting point (0 C) 1000 – 1260

Molassess: Specific gravity–1.1 to 1.2

The Properties of developed bricks are given in Annexure III.

Annexure III:

Properties of Developed High Alumina (70% Al2O3, min.) bricks

Parameters Value
Al2O3, %, Min. 70
Fe2O3, %, Max. 2
P.C.E., O.C., Min. 36
C.C.S., kg/cm2, Min. 700
R.U.L., ta, 0C, Min. 1600
A.P., %, Max. 16
B.D., gm/cc, Min. 2.60
Repeat P.L.C.A.R., %, at 15000 C/3 hrs. 1st P.L.C.A.R.: ± 0.50
2nd P.L.C.A.R.: ± 0.30
3rd P.L.C.A.R.: ± 0.10
Abradability Index, Max. 45
Thermal Shock Resistance, Cycles, Min. B

Air Quenching 50

Although the invention is described with various specific embodiments, it may be possible for a person skilled in the art to develop other similar embodiments with some modifications. However, all such modifications are deemed to be within the scope of the present invention.

It is also to be understood that the following appended claims are intended to cover all of the generic and specific features of the embodiments described herein and those with
possible modifications.