CLIAMS:We Claim:
1. Magnesia carbon brick suitable for impact area of steel ladles comprising:
magnesia carbon having incorporated with Alumina rich spinel comprising:
Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

2. Magnesia carbon bricks as claimed in claim 1 wherein the Magnesia carbon bricks incorporating said Alumina rich spinel are obtained of :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS

3. A ladle with improved impact resistance characteristics comprising:
a bottom layer region obtained of magnesia carbon bricks having incorporated with Alumina rich spinel as claimed in anyone of claims 1 or 2 and
side wall layers obtained of MgO-C.

4.A process for the manufacture of Magnesia carbon bricks for impact area of steel ladles comprising obtaining said bricks selectively involving :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS
Alumina rich spinel comprising

Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

5. A process as claimed in claim 4 comprising
(i) providing raw material ingredients of selective specification and grain size distribution comprising
said magnesia grains:79-87 wt%,
said spinel: 3-5wt%,
said aluminium metal powder: 1.5-2wt%,
said graphite: 5-10wt%; and
said resin: 3.75-4wt%;
for mixing the ingredients in a high intensive mixer, wherein
(a)said spinel and aluminium metal powder are premixed with microfines (<0.1mm) of magnesia;
(b) premix of magnesia, spinel and aluminium metal powder is mixed with magnesia grains (3-4.5mm, 1-3mm, 0-1mm) and graphite in said high intensive mixer; and
(c) said resin which is phenol formaldehyde liquid resin is added in two stages over premix of magnesia, spinel, aluminium metal powder and magnesia grains (3-4.5mm, 1-3mm, 0-1mm) in the said rotating high intensive mixer, and continuing the mixing process for specific time of 25-30 minutes.
(ii) Collecting the mix thus prepared in steel container and ageing for 18-24 hours;
(iii) manufacturing of bricks using said aged mix obtained in step (ii) with optimum specific pressure of 1500-2000kg/cm2 in an automatic type hydraulic press;
(iv) curing the bricks so produced in tunnel kiln for 200-2200C for 8 hours;
(v) cooling the cured bricks and sorting out good bricks for use in lining impact area of ladle.

6. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 5 wherein said specified amount of spinel and mixing sequence is used for making the bricks adapted for controlled expansion of brick during operation in ladle.

7. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 6 wherein said specified amount, type and size of antioxidant is used as per the defined mixing sequence for high hot strength.

8. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 7 wherein said specified grain size distribution is used for achieving high density and low porosity.

9. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 8 wherein said selective specification of magnesia and its chemical purity is maintained to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area.

Dated this the 18th day of February, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

,TagSPECI:FIELD OF THE INVENTION

The present invention relates to improved quality magnesia carbon bricks for Impact area of steel ladles and a process for its manufacture. More particularly, the present invention is directed to provide improved quality magnesia carbon bricks for impact area of steel ladles by addition of a particular variety of spinel along with changes in graphite content, antioxidant content and granulometry so as to produce MgO-C bricks having highly resistant to thermal shock, resistant to slag corrosion and have high hot strength as well as impact strength favouring higher straight life and campaign life of steel ladle.

BACKGROUND OF THE INVENTION

In Iron & Steel Industry, manufacturing processes has changed significantly due to the rising demand of quality steel in the market. Plants have been modernized with addition of secondary steel making facilities to meet the stringent quality requirement of newer grades of steel.

Refractories in secondary steel ladle are subjected to severe operating conditions like impact of liquid steel from BOF tapped at high temperature, thermal shock, abrasion with molten metal due to stirring during gas purging, localized heating in slag zone due to arcing, corrosion with slag, thermo mechanical stress etc.

Based on the operating environment of different areas, the ladle lining is divided in 3-4 zones. These are bottom, bottom impact area, metal zone and slag zone. Earlier only magnesia carbon bricks were being used. Later on, alumina magnesia carbon(AMC) bricks were introduced in bottom impact area as performance of magnesia carbon bricks were not adequate (30-35 heats) to achieve higher straight life as well as total campaign life.

Manufacturing of AMC bricks along with magnesia carbon bricks in the same shop with limited presses hampers tonnage production as erosion of mould liner plate of press is much more compared to magnesia carbon bricks. Need was felt to develop an improved quality of magnesia carbon bricks for bottom impact area which will perform similar to AMC bricks so that higher straight life and campaign life of steel ladle can be achieved.

Refractory bricks used in bottom impact area have to withstand the impact of stream of liquid steel tapped directly from BOF. This also creates severe thermal shock in bricks. The bricks should be able to resist corrosive attack of left over slag after casting of steel for some time before dumping of slag. Therefore, bottom impact bricks should be dense, highly resistant to thermal shock, resistant to slag corrosion and should have high hot strength as well as impact strength.

US 5344802 disclosed a refractory mix and resultant shapes formed by burning the mix, the mix comprising a magnesia-alumina spinel grain containing at least 27% MgO by weight, a fused magnesite grain, and up to 10% by weight alumina, it being possible to substitute a sintered magnesite grain for up to 50% by weight of the fused magnesite grain.

US 4389492 disclosed a spinel-magnesia basic brick composition containing spinel clinker and magnesia clinker wherein pulverized iron oxide by additional weight mixing ratio is mixed or special magnesia clinker is substituted for magnesia clinker instead of addition of iron oxide. This invention relates to bricks and particularly spinel-magnesia bricks available for use in rotary cement kilns.

US 4126479 disclosed a magnesium aluminate spinel-bonded refractory which does not exhibit undue expansion (due to the reaction of magnesia and alumina to form magnesium aluminate spinel) between the raw, compacted state and the fired, ceramically bonded state when fired to a temperature of 1400C used. More specifically, the alumina used has an average particle size of less than 5, preferably less than 2, microns, and a specific surface of less than 30 m.sup.2 /g, preferably about 5 m.sup.2 /g (i.e., the small crystallites or particles are dense and do not have a high surface area, as do finely divided active alumina).

During past few years magnesium aluminate (MgAl2O4) spinel is being used as alumina system. It improves the slag corrosion resistance of high alumina refractories by trapping bivalent and trivalent ions of slag and is widely used in monolithic steel ladles. Similarly, it has been found that presence of spinel in MgO-C refractories improves slag coating on working surface of the brick by trapping bivalent and trivalent ions of slag into its structure. Optimum addition of spinel reduces brick porosity and improves strength after coking.

There has been thus a need in the art to developing magnesia carbon refractory bricks for application in steel making particularly for bottom impact area of steel ladles and accordingly developmental work has been carried out to improve the required properties by suitable modifications of batch composition and addition of spinel.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide improved quality spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles and a process for its production.

A further object of the present invention is directed to alumina rich spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles which is dense, highly resistant to thermal shock, resistant to slag corrosion and should have high hot strength as well as impact strength.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles using particular variety of spinel is added along with changes in graphite content, antioxidant content and granulometry so as to produce MgO-C bricks to achieve desired properties.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles to ensure higher straight life and campaign life of steel ladle.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles wherein a specified amount of spinel and mixing sequence was used for making these bricks for controlled expansion of brick during operation in ladle.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles wherein a specified amount, type and size of antioxidant is used as per the defined mixing sequence for high hot strength.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles wherein a specified grain size distribution is used for achieving high density and low porosity.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles wherein a specific type of magnesia and chemical purity has been used to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area.

A still further object of the present invention is directed to spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles wherein premix of magnesia, spinel and aluminium metal powder is mixed with specific magnesia grains size and graphite in a high intensive mixer.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided Magnesia carbon brick suitable for impact area of steel ladles comprising:
magnesia carbon having incorporated with Alumina rich spinel comprising:
Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

A further aspect of the present invention is directed to said Magnesia carbon bricks wherein the Magnesia carbon bricks incorporating said Alumina rich spinel are obtained of :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS

Yet another aspect of the present invention is directed to a ladle with improved impact resistance characteristics comprising:
a bottom layer region obtained of magnesia carbon bricks having incorporated with Alumina rich spinel as described above and
side wall layers obtained of MgO-C.

A still further aspect of the present invention is directed to a process for the manufacture of Magnesia carbon bricks for impact area of steel ladles comprising obtaining said bricks selectively involving :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS
Alumina rich spinel comprising

Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

A still further aspect of the present invention is directed to a process comprising
(i) providing raw material ingredients of selective specification and grain size distribution comprising
said magnesia grains: 79 to 87 wt%,
said spinel: 3-5wt%,
said aluminium metal powder: 1.5-2wt%,
said graphite: 5-10wt%; and
said resin: 3.75-4wt%;
for mixing the ingredients in a high intensive mixer, wherein
(a)said spinel and aluminium metal powder are premixed with microfines (<0.1mm) of magnesia;
(b) premix of magnesia, spinel and aluminium metal powder is mixed with magnesia grains (3-4.5mm, 1-3mm, 0-1mm) and graphite in said high intensive mixer; and
(c) said resin which is phenol formaldehyde liquid resin is added in two stages over premix of magnesia, spinel, aluminium metal powder and magnesia grains (3-4.5mm, 1-3mm, 0-1mm) in the said rotating high intensive mixer, and continuing the mixing process for specific time of 25-30 minutes.
(ii) Collecting the mix thus prepared in steel container and ageing for 18-24 hours;
(iii) manufacturing of bricks using said aged mix obtained in step (ii) with optimum specific pressure of 1500-2000kg/cm2 in an automatic type hydraulic press;
(iv) curing the bricks so produced in tunnel kiln for 200-2200C for 8 hours;
(v) cooling the cured bricks and sorting out good bricks for use in lining impact area of ladle.

A still further aspect of the present invention is directed to a process of manufacturing spinel added magnesia carbon bricks wherein said specified amount of spinel and mixing sequence is used for making the bricks adapted for controlled expansion of brick during operation in ladle.

A still further aspect of the present invention is directed to a process of manufacturing spinel added magnesia carbon bricks wherein said specified amount, type and size of antioxidant is used as per the defined mixing sequence for high hot strength.

A still further aspect of the present invention is directed to a process of manufacturing spinel added magnesia carbon bricks wherein said specified grain size distribution is used for achieving high density and low porosity.

A still further aspect of the present invention is directed to a process of manufacturing spinel added magnesia carbon bricks wherein said selective specification of magnesia and its chemical purity is maintained to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area.

The objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure: 1: is the schematic sectional view of the steel ladle showing Lining design of 300T steel ladle at BSL with improved quality spinel added magnesia carbon bricks according to the present invention for bottom striking (impact pad) area.

Figure: 2: is the graphical presentation showing the comparison of performance of steel ladle lining life with conventional AMC bricks in bottom impact area and Spinel added MgO-C bricks (1st Repair life) according to the present invention.

DETAILED DESTRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to provide improved quality spinel added magnesia carbon bricks suitable for bottom impact area of steel ladles and a process for its production which would provide magnesia carbon bricks which is dense, highly resistant to thermal shock, resistant to slag corrosion and should have high hot strength as well as impact strength resulting in higher straight life as well as total campaign life. This is achieved by way of the present invention by using particular variety of spinel added along with changes in graphite content, antioxidant content and granulometry wherein a specified amount of spinel and mixing sequence was used for making these bricks for controlled expansion of brick during operation in ladle and a specified grain size distribution is used for achieving high density and low porosity.

Thus to improve the performance of impact area of steel ladles a special quality of MgO-C bricks have been developed by addition of a particular variety of spinel along with changes in graphite content, antioxidant content and granulometry.
These bricks were manufactured along with existing quantities of MgO-C bricks for other areas of steel ladles. Bricks were manufactured at captive brick plant at the applicants’ Refractory Unit at Ranchi Road.
Thus according to the present invention a process of manufacturing spinel added magnesia carbon bricks in which input materials of specified quality/chemical composition was used.
Spinel is incorporated in magnesia carbon bricks for use in impact area of ladle. Spinels of different varities (stochiometric, alumina rich, magnesia rich) and sizes are available. A specific variety of spinel and of specified size was used for proper incorporation in magnesia carbon bricks. A specified amount of spinel and mixing sequence was used for making these bricks for controlled expansion of brick during operation in ladle. A specified amount, type and size of antioxidant was used as per the defined mixing sequence for high hot strength. A specified grain size distribution was used for achieving high density and low porosity. Magnesia used for magnesia carbon bricks can be of different varieties (Fused, Sintered, dead burnt). A specific type of magnesia and chemical purity has been used to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area. Combination of all these ingredients as per a specified proportion and grain size distribution have resulted development of special quality of magnesia carbon brick which has given superior performance in bottom impact area of steel ladle.

The input materials of specified quality/chemical composition used to produce the spinel added magnesia carbon bricks are as follows:

Table – 1: Specification of Magnesia used for brick making:

Properties Magnesia
Chemical Analysis (%)
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150

Table – 2: Typical Specification of Graphite:

Properties Specification (%)
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6

Table - 3 Typical properties of Resin used:
Properties Values
Type Resol
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)

Table – 4: Typical Specification of Aluminium metal powder:

Properties Specification (%)
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS

Table – 5: Typical Specification of Alumina rich Spinel (MgAl2O4):

Constituents Mass %
Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

The process of manufacturing spinel added magnesia carbon bricks according to the present invention comprising the steps of:
(i) Providing the input materials of specified quality/chemical composition as given in Table 1-5 above;
(ii) Mixing specified amount (79-87 wt%) of magnesia grains and specified amount (5-10wt%) of graphite and specified amount of phenol formaldehyde liquid resin (3.75-4wt%) with specified amount (3-5wt%) of spinel and specified amount(1.5-2wt%) of aluminium metal powder in a high intensive mixer wherein aluminium metal powder are premixed with microfines (< 0.1mm) of magnesia; and wherein phenol formaldehyde liquid resin is added in two stages in the rotating high intensive mixer, over premix of magnesia, spinel, aluminium metal powder and magnesia grains (3-4.5mm, 1-3mm, 0-1mm) and continuing the mixing process for specific time of (25-30 minutes).
(iii) Collecting the mix thus prepared in steel container and ageing for 18-24 hours;
(iv) manufacturing of bricks using aged mix obtained in step (ii) with optimum specific pressure of 1500-2000kg/cm2 in an automatic type hydraulic press;
(v) curing the bricks so produced in tunnel kiln for 200-2200C for 8 hours;
(vi) cooling the cured bricks and sorting out good bricks for use in lining impact area of ladle.

Four trials were conducted with these bricks in 300T Steel ladle at Bokaro Steel Limited, as per the lining design shown in accompanying Figure 1 showing the schematic sectional view of the steel ladle with Lining design of 300T steel ladle at BSL involving improved quality spinel added magnesia carbon bricks for bottom striking (impact pad) area produced according to the present invention.

By using these bricks in bottom impact area, straight life of 42, 48, 46 and 49 heats could be achieved. Finally, this has also helped to achieve campaign life of more than 100 heats in two ladles. In 3rd trial a new record life of 101 heats was achieved which is the highest steel ladle lining life in SMS-II,BSL with bricks of applicants Refractory Unit, Ranchi Road.

Accompanying Figure 2 showing graphically the comparison of performance of steel ladle lining life with conventional AMC bricks in bottom impact area vis-à-vis Spinel added MgO-C bricks (1st Repair life 42, 48, 46 and 49 heats) according to the present invention.

It is thus possible by way of the present invention to provide improved quality magnesia carbon bricks with spinel addition for refractory lining in bottom impact area of steel ladle which is dense, highly resistant to thermal shock, resistant to slag corrosion and should have high hot strength as well as impact strength resulting in higher straight life as well as total campaign life. This is achieved by way of the present invention by using particular variety of spinnel added along with changes in graphite content, antioxidant content and granulometry and required ingredients provided with selective proportions and mixing sequence to achieve desired end properties in such bricks.

We Claim:
1. Magnesia carbon brick suitable for impact area of steel ladles comprising:
magnesia carbon having incorporated with Alumina rich spinel comprising:
Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

2. Magnesia carbon bricks as claimed in claim 1 wherein the Magnesia carbon bricks incorporating said Alumina rich spinel are obtained of :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS

3. A ladle with improved impact resistance characteristics comprising:
a bottom layer region obtained of magnesia carbon bricks having incorporated with Alumina rich spinel as claimed in anyone of claims 1 or 2 and
side wall layers obtained of MgO-C.

4.A process for the manufacture of Magnesia carbon bricks for impact area of steel ladles comprising obtaining said bricks selectively involving :
Magnesia:
MgO 95-98
CaO 1-3
SiO2 0.2-0.8
Fe2O3 0.15-0.22
Al2O3 0.7-0.14
B2O3 ,max. 0.01-0.04
Bulk density (g/cm3), min 3.4-3.55
Avg. crystal size (micron), min 70-150
Graphite:
Fixed Carbon(min)
NGC(max)
Volatile matter(max)
Moisture(max) 94-96
0.30-0.60
1.5-2.5
0.4-0.6
Resin:
Non-volatile matter (%) 68-72
Fixed carbon (%) 35-40
Viscosity (cp), at 250C 250-300
Sp.Gravity at 200C 1.17-1.19
pH at 200C 6.5-7
Moisture Content (%) 8-10
Free Phenol (%) 14 (± 2)
Free Formaldehyde (%) 0.8 (± 0.2)
Aluminium metal powder:
Material
Al (by difference)min
Fe
Si
Size Atomized Aluminium Powder
97-99.5
0.35-0.40
0.10-0.15
80%(min) pass through 200 mesh BSS
Alumina rich spinel comprising

Al2O3 85-90
MgO 5-10
CaO 0.60-0.70
SiO2 0.70-0.80
Na2O 0.35-0.40
Fe2O3 0.45-0.55
Particle size 100% below 45m (0.045mm)

5. A process as claimed in claim 4 comprising
(i) providing raw material ingredients of selective specification and grain size distribution comprising
said magnesia grains:79-87 wt%,
said spinel: 3-5wt%,
said aluminium metal powder: 1.5-2wt%,
said graphite: 5-10wt%; and
said resin: 3.75-4wt%;
for mixing the ingredients in a high intensive mixer, wherein
(a)said spinel and aluminium metal powder are premixed with microfines (<0.1mm) of magnesia;
(b) premix of magnesia, spinel and aluminium metal powder is mixed with magnesia grains (3-4.5mm, 1-3mm, 0-1mm) and graphite in said high intensive mixer; and
(c) said resin which is phenol formaldehyde liquid resin is added in two stages over premix of magnesia, spinel, aluminium metal powder and magnesia grains (3-4.5mm, 1-3mm, 0-1mm) in the said rotating high intensive mixer, and continuing the mixing process for specific time of 25-30 minutes.
(ii) Collecting the mix thus prepared in steel container and ageing for 18-24 hours;
(iii) manufacturing of bricks using said aged mix obtained in step (ii) with optimum specific pressure of 1500-2000kg/cm2 in an automatic type hydraulic press;
(iv) curing the bricks so produced in tunnel kiln for 200-2200C for 8 hours;
(v) cooling the cured bricks and sorting out good bricks for use in lining impact area of ladle.

6. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 5 wherein said specified amount of spinel and mixing sequence is used for making the bricks adapted for controlled expansion of brick during operation in ladle.

7. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 6 wherein said specified amount, type and size of antioxidant is used as per the defined mixing sequence for high hot strength.

8. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 7 wherein said specified grain size distribution is used for achieving high density and low porosity.

9. A process of manufacturing spinel added magnesia carbon bricks as claimed in anyone of claims 4 to 8 wherein said selective specification of magnesia and its chemical purity is maintained to achieve high spalling resistance and slag corrosion resistance property required for bottom impact area.

Dated this the 18th day of February, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: MAGNESIA CARBON BRICKS SUITABLE FOR IMPACT AREA OF STEEL LADLES AND PROCESS FOR ITS MANUFACTURE.
The present invention relates to providing improved quality magnesia carbon bricks suitable for Impact area of steel ladles and a process for its manufacture. More particularly, the present invention is directed to provide improved quality magnesia carbon bricks for impact area of steel ladles by addition of alumina rich spinel along with changes in graphite content, antioxidant content and granulometry so as to produce MgO-C bricks having highly resistant to thermal shock, resistant to slag corrosion and have high hot strength as well as impact strength favouring higher straight life and campaign life of steel ladle.