A PROCESS FOR MANUFACTURE OF IMPROVED LADLE BRICK, A NOVEL COMPOSITION OF BRICK FOR VAD LADLE AND THE BRICK OBTAINED
THEREOF
FIELD OF INVENTION
The present invention relates to magnesia refractories for use in linings of steel-making vessels. More particularly the present invention relates to a process for manufacture of improved ladle bricks for VAD ladle, specifically, to a brick composition for lining a converter used for the smelting of molten steel and the brick used in lining structure.
BACKGROUND ART
The magnesia carbon bricks have a wide range of applications that include LD converter wear lining, VAD / LF ladle slag areas, ladle bottom impact UHP / EBT-EAF slag line and hotspot areas. The variety of magnesia carbon bricks offered includes normal density magnesia carbon bricks, metal line magnesia carbon bricks for steel ladles and slag line magnesia carbon bricks for steel ladles.
The lining of metallurgical vessels in particular for converters in the steel industry usually consists of basic refractory materials and is often subject to very severe operating conditions due to the combined effect of very high temperatures, thermal and mechanical stresses, and chemical attack. The principal basic materials used for fired magnesia bricks (of high MgO content) subsequently impregnated with tar or carbonaceous material, and tar bonded magnesia bricks (of high MgO content), which may be subsequently tempered.
Of these two materials the first are bricks in which magnesia grains of high purity form strong ceramic bonds by sintering at high temperature They have great mechanical strength but suffer in use from brittle fracture in layers mainly parallel

to the hot face of the brick, in spite of the impregnation with carbonaceous material, and this damage may even occur in the course of the first heating-up of the lining to its operational temperature.
When the second of the above-mentioned materials, i.e. tar bonded unfired magnesia bricks, are used, particular care has to be taken during the heating-up period of a new lining, because of transient mechanical weakening of the brick in a temperature range up to 500 degree Celsius when the tar undergoes a process of thermal cracking Moreover, the desired ceramic bonding of the magnesia grains by sintering in situ is substantially delayed, which is thought to be due to interference by the intergranular deposits of carbon in the brick For these reasons, such bricks are subject to strong wear.
RUSSELL PEARCE HEUER, in a British published Patent document GB991103 discloses a refractory composition comprises calcined magnesia, 1-25 weight per cent of hard pitch having a melting point of at least 250 DEG F. and a bonding agent made effective by the presence of water. Bonding agents specified are sulphuric acid, magnesium sulphate, sulphite paper waste, starch, dextrine and gum tragacanth. Refractory bricks may be prepared by tempering the above composition with water, pressing at least 5000 p.s.L, and drying preferably in an atmosphere of carbon dioxide.
TOSHIBA CERAMICS CO, in a Japanese published Patent document JP186259 discloses a refractory material comprising 70 to 99wt.% of the magnesia sources and 1 to 30wt.% of graphite are combined with 0.1 to 10 pts wt of a foaming agent of 1 to 20um average particle diameter. Further, 100 pts wt of the resultant composition are mixed with 1 to 10 pts wt of one or more of metallic Al, Mg and Si and the material is molded and dried.
VEITSCHER MAGNESITWERKE AG in a British published Patent document GB1137143 discloses a fired magnesite brick contains 2-5% by wt. Fe2O3

calculated free of ignition losses, wherein the Fe2O3, CaO and S1O2 components are almost completely combined to dicalcum silicate and dicalcium ferrite, and the ceramically-bonded brick is impregnated with a carbon carrier. The brick may have the composition by weight: MgO 84-95%; SiO2 1-2%; Fe2O32-5%; CaO 2^ 8% and not more than 1 % of other constituents. The raw materials, preferably of grain size below 500A, may be sinter-burned, formed into bricks and subsequently vacuum impregnated with tar to give a brick having a residual porosity of not greater than 2% by volume for use in lining vessels in steel manufacturing processes which use oxygen.
RDCIS had introduced in-situ spinel forming castable in working lining of bottom
and metal zone in VAD ladle at ASP. This has shown a remarkable improvement
I in the lining life of these zones of the ladle from 25-30 heats to ~200 heats with
intermediate repairs. However, in slag zone MgO-C bricks of SAIL-25 quality was in use and a life of only 10-12 heats was obtained under existing operating conditions of ASP. Such a low life of slag zone caused frequent cold repairs of ladles and leads to poor availability of ladles. This has also increased chances of thermal shock failure of monolithic lining. It was, therefore, felt necessary to develop a suitable composition of Magnesia-carbon (MgO-C) bricks to enhance the lining life of slag zone of steel ladie.
The improvement in the slag zone lining life was envisaged by developing improved ladle brick composition replacing the existing SAIL-25 quality. The bricks were manufactured at Ranchi Road refractory Plant of M/s BRL as per formulation of RDCIS and tried for performance evaluation in VAD ladles of ASP. Maximum lining life of 20 heats achieved at ASP

SUMMARY OF THE INVENTION
Accordingly, the present invention discloses a process for manufacture of improved ladle brick, a novel composition of brick for VAD ladle, specifically, to a brick for lining a converter used for the smelting of molten steel.
Therefore such as disclosed herein there is a process for the manufacture of improved ladle bricks for VAD ladle comprising the steps of : selecting proper size fractions and quality of coarse, medium and fine grains of magnesia; selecting of purer grade of Carbon and using high softening point carbon additive as per partial replacement of antioxidant; mixing the fines of the components separately; Dry mixing of coarse, medium and fines together in a mixer; Adding Phenol formaldehyde resol type liquid resin binder as per requirement (around 4%) and mixing for 4-5 minutes; Curing the mixture; Forming the bricks by pressing the mix in the brick moulds at a specific pressure by a press; Heat treatment of bricks in a tempering kiln.
Also disclosed herein a brick composition for lining a converter consisting essentially of, in weight percent, about 92% (Min) MgO, about 1.0% (Max) SiO2, about 2.0% (Max) CaO, about 4.0 to 4.5 % (Min) AI2O3 and about 0.5% (Max) Fe2O3 alongwith around 4% Phenol formaldehyde resol type liquid resin as binder for the mixture.
As per another object of the present invention there is provided a composition wherein the harmful effect of SiO2 present in principal source of magnesia e.g sea water magnesia or fused magnesia is controlled by restricting CaO / SiO2 molar ratio to > 2.
As per another exemplary object of the present invention, to improve the slag corrosion resistance around 50 % fused magnesia of 300 p.m crystal size in the MgO-C brick's is used in the formulation to improve it's slag corrosion resistance.

As per an exemplary embodiment of the present invention there is provided a new carbonaceous binder in the brick composition as a partial replacement of antioxidant to impart soft bonding in the brick matrix.
As per another object of the present invention the slag corrosion resistance of the bricks are improved by around 15% with respect to the regular used bricks with the use 97% pure carbon graphite.
As per another object of the present invention the new carbonaceous binder, so selected, has been introduced in the brick formulation imparts soft bonding between MgO and graphite.
As per another object of the present invention there is provided a process for manufacturing of improved ladle bricks, which is simple, easy having readily available components, and have an enhanced performance and is long lasting compared to other available bricks.
These together with other objects of the invention, along with the various features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a block diagram showing the function of the different ingredients in MgO-C brick as per the present invention.

FIG. 2 is a graph showing the test results and relation / analysis between bulk density and antioxidant addition as per the present invention.
FIG. 3 is a graph showing the test results between apparent porosity after coking at 1000 degree Celsius and antioxidant addition as per the present invention.
FIG. 4 is a graph showing the test results between hot modulus of rupture and antioxidant addition as per the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
There are four basic ingredients for making magnesia carbon bricks, viz. magnesia, graphite, anti-oxidants and liquid resin as binder. Liquid pitch is also used as a substitute of liquid resin as binder in some places. The quality and quantity of the raw materials used in the brick formulation varies from manufacturer to manufacturer and greatly influence the properties and performance of the MgO-C brick in actual use. In order to improve the quality of existing MgO-C bricks of SAIL - 25 specifications being used in slag zone of steel ladle as ASP, an improved brick composition has been formulated and disclosed herein.
The Previously proposed compositions have many disadvantages, which may be clear from the description, fn order to simulate the properties of developed bricks with the conventional MgO-C bricks, 100 kg batches were made in a commercial mixer at Ranchi Road Refractory Plant (RRRP) and standard bricks were made following the above process chart. All the batches contained same aggregate (fused MgO + sea water MgO and total carbon 12%). In the soft bonding batches, special carbon additive was added to the tune of 1% replacing antioxidant partly. Samples of different sizes were then drawn from those bricks by cutting using diamond cutter. The coked properties of the bricks are more relevant to operating condition of steel ladle than properties as such. Hence the concept of evaluation of brick properties after coking was adapted in the

development of this brick. The coking was done at 1000 degree Celsius for 2 hours. The properties of special carbon additive is given below:
The properties of Special Carbon Additive are as under :-
Softening Point - 230-240 degree Celsius
Granulometry < 0.4 mm Min. 90%
< 0.080mm Min.50%
Coking value - 80-90 (%)
B[a]P content - 300-350 (ppm)
Processing and manufacturing
Optimization of granulometry and composition is done by selecting proper size fractions and quality of coarse, medium and fine grains of magnesia. The proper size fractions is done by the conventional known processes. The crystal size of MgO in sea-water magnesia is around 100 um whereas crystal size of fused magnesia normally varies from 300 - 800 ^m. It was therefore proposed to use around 50 % fused magnesia of 300, fj.m crystal size in the MgO-C brick's formulation to improve it's slag corrosion! resistance.
The purest level of Carbon is selected as additive with the properties as disclosed above. It has been seen experimentally that the slag corrosion resistance is improved by around 15% when purity level of graphite is increased from 95 to 98% fixed carbon level. It is therefore, proposed to use 97% fixed pure carbon graphite. It is reported in literature that the graphite available at Tamilnadu mines is having the highest fixed carbon graphite of crystalline nature is available in India. The high softening point carbon additive is used as per partial replacement of antioxidant.

Thereafter the fines of the magnesia, metallic aluminium as antioxidant & special carbon additive is mixed separately, followed by dry mixing of coarse, medium and fines together in a mixer for 2-3 minutes. The harmful effect of SiO2 present in principal source of magnesia e.g seawater magnesia or fused magnesia is controlled by restricting CaO / S1O2 molar ratio to > 2. At this molar ration C2 S is formed which has a high melting point (m.p) and does not form any low eutectic with MgO.
A new carbonaceous binder in the brick composition is introduced as a partial replacement of antioxidant to impart soft bonding in the brick matrix. Phenol formaldehyde resol type liquid resin binder is used as per requirement (around 4%) and is added to the mixture and mixing is carried out for 4-5 minutes. The mixture is then cured for 24 hours at normal /room temperature.
The cured mixture is thereafter taken up for the brick formation by pressing the mix in the brick moulds at a specific pressure of around 1000 kg/cm2 in a press. The art of brick formation as carried out is the conventional process with a pressure of 1000 kg/cm2 . The formed bricks are then heat treated at 250-300 degree Celsius for 48 hours in a tempering kiln.
Laboratory Studies
In order to simulate the properties of developed bricks with the conventional MgO-C bricks, 100 kg batches were made in a commercial mixer at Ranchi Road Refractory Plant (RRRP) and standard bricks were made following the above process chart. All the batches contained same aggregate (fused MgO + sea water MgO and total carbon 12%). In the soft bonding batches, special carbon additive was added to the tune of 1% replacing antioxidant partly. Samples of different sizes were then drawn from those bricks by cutting using diamond cutter. The coked properties of the bricks are more relevant to operating condition of steel ladle than properties as such. Hence the concept of evaluation

of brick properties after coking was adapted in the development of this brick. The coking was done at 1000C for 2 hours. The effect and result of soft bonding are as follows:
Effects
Strengthening of binder structure by softening and migration into Pores during heat up
Softening of carbon additive before coking
More flexible, anisotropic and graphitizable coke structure
Results
Improvement in bulk density of the bricks from 2.95 to 2.96/cc Reduction in coked porosity from 12.8 to 10.0%
Though the HMOR values decreased from 140 to 100kg/cm2 due to soft bonding nature of carbon additive and decrease in content of antioxidant, but improves stress absorbing structure of refractories. This in turn reduces the generation of microcracks due to alternate heating and cooling of lining of ladle during circulation. And thereby improves slag corrosion resistance of developed bricks.
Improves hot erosion resistance
Higher oxidation resistance due to uniform distribution of carbon and anisotropic and graphitizable nature of coke structure
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Innovative featuresThe slag zone, bricks of steel ladles are mainly; affected due" to high corrosive nature of slag which is in contact at highjtemperature and for a longer time duringthe processing of steel in LF7VADA/0D. Fused magnesia of higher crystal size of¦ ¦ • • i300 |am was used to the tune of 50% in the MgO-C brick's formulation to improve it's slag corrosion resistance.The carbonaceous binder has been introduced in the brick formulation to impart soft bonding between MgO and graphite. Since carbon additive prevent slag penetration through the porous structure of biicksahd thereby improves the slag corrosion resistance. Several trials were conducted with improved quality MgO-C bricks manufactured¦ - ;¦ — > ¦ |at RRRP and procured by Alloy Steef plant (ASP) based on the developed¦¦¦¦¦-¦¦• ^specification as given in the comparative table below. The lining life of 20 heats 1 i or more is achieved against the existing life 10-12 heats with the existing qualitybricks. Product Comparison Chemical Composition Existing Quality Superior Quality
MgO (%), Min. (Loss free Basis) 90.0 92.0
SiO2 (%), Max. 2.0 1.0
CaO (%), Max 2.0 2.0
CaO/SiO2 >2: * ....

1 AI2O3l(%), Min 4.0 Min 4.0-4.5
Fe2O3(%),Max 1.0 0.5
Physical Properties (as received)
A. P. (%), Max 3.5 3.0
B.D. (g/cc), Min 2.95 2.96
CCS (kg/cm2), min 450 400
HMOR (kg/crn^), at 1400°C/^ hr, min In oxidizing atmosphere 100 100
Physical Properties (after coking at 1000°C/2hrs)
A. P. (%), Max — 10.0
Total Carbon — 10-12
Size Tolerance (Max) ± 1mm in all sides ± 1mm in all sides

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the

invention 8$ described herein may be made, none of which depart from the spirit or scope cf the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, sind alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
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We Claim :-
1. A process for the manufacture of improved ladle bricks for VAD ladle comprising the steps of :-
selecting proper size fractions and quality of coarse, medium and fine grains of magnesia;
selecting of purer grade of Carbon and using high softening point carbon additive as per partial replacement of antioxidant;
mixinc the fines of the components separately;
Dry m xing of coarse, medium and fines together in a mixer;
Adding Phenol formaldehyde resol type liquid resin binder as per requirement (around 4%) and mixing for 4-5 minutes;
Curing the mixture;
Forming the bricks by pressing the mix in the brick moulds at a specific pressure by a press;
Heat Ireatment of bricks in a tempering kiln.
2. The process for the manufacture of ladle bricks as claimed in claim 1 wherein, the 50% of grains of magnesia used is of 300 nm crystal size in the MgO-C brick's formulation to improve it's slag corrosion resistance.
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The process for the manufacture of ladle bricks as claimed in claim 1 wherein, the 97% pure grade of carbon graphite is used as per partial replacement of antioxidant.
4. The process for the manufacture of ladle bricks as claimed in claim 1
wherein, the brick composition consists essentially of, in weight percent, about
92% (Min) MgO, about 1.0% (Max) StO2, about 2.0% (Max) CaO, about 4.0 to
4.5 % (Min) AI2O3 and about 0.5% (Max) FeaOs , with respect to chemical
analysis of the magnesia grains on loss free basis.
5. The process for the manufacture of ladle bricks as claimed in claim 4
wherein, the ratio between the components CaO / SiO2 is maintained as greater
than or equal to 2.
6. The process for the manufacture of ladle bricks as claimed in claim 1
wherein, the dry mixing of the coarse is carried out for only 2-3 minutes.
7. The process for the manufacture of ladle bricks as claimed in claim 1
wherein, the curing of the mixture is done for 24 hours.
8. The process for the manufacture of ladle bricks as claimed in claim 1
wherein, the pressure applied for the pressing the brick moulds is around 1000
kg/cm2.
9. The process for the manufacture of ladle bricks as claimed in claim 1
wherein, the heat treatment is carried out at a constant temperature of 250-300°
C for 48 hours.
10. A brick composition for lining a converter as claimed in claim 4 wherein,
the ratio between the components CaO / SiO2 is maintained as greater than or
equal to 2.
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11. A brick manufactured using the process as claimed in any of the
preceding claims.
12. A process for the manufacture of improved ladle bricks for VAD ladle,
substantially as herein described with particular reference to the accompanying
drawings.
13. A brick composition for lining a converter, substantially as herein
described with particular reference to the accompanying drawings,.

The present invention relates to a process for the manufacture of improved ladle bricks for VAD ladle comprising the steps of selecting proper size fractions and quality of coarse, medium and fine grains of magnesia; selecting of purer grade of Carbon and using high softening point carbon additive as per partial replacement of antioxidant; mixing the fines of the components separately; dry mixing of coarse, medium and fines together in a mixer; adding phenol formaldehyde resol type liquid resin binder as per requirement (around 4%) and mixing for 4-5 minutes; Curing the mixture; forming the bricks by pressing the mix in the brick moulds at a specific pressure by a press; heat treatment of bricks in a tempering kiln.