TECHNICAL FIELD OF THE INVENTION
This invention relates generally to refractory lining in electric arc furnace. More particularly the
present invention relates to an improved magnesia carbon brick for use as refractory lining of an
electric arc furnace and a method of manufacturing said magnesia carbon brick.
BACKGROUND AND THE PRIOR ART
Magnesia carbon bricks are used as refractory lining of Electric Arc Furnace. The major area of
concern is 'hot spot' area of lining near the electrodes. In hot spot area of EAF the gap between
electrode and the refractory lining is quite low. Due to faster rise in temperature near electrodes,
the slag becomes more fluid and highly corrosive which causes faster wear out of the refractory
lining.
Some of the prior arts in the present field of invention are as follows:
US8,093.169 disclose a magnesia-carbon based sleeve brick for steelmaking converters, which
is obtained by adding, to a refractory raw material mix containing 60 to 95 mass % of
a magnesia raw material and 5 to 20 mass % of graphite, a metal powder of one or more selected
from the group consisting of Al, Si, Mg, Ca, Cr and an alloy thereof, in an amount of greater than
3 to 6 mass %, and an organic binder, in addition to 100 mass % of the refractory raw material
mix, and subjecting the resulting mixture to kneading, forming and heat treatment, wherein the
sleeve brick is used under a condition that a thickness thereof is set at 70 mm or less. This makes
it possible to prevent cracking which would otherwise occur in the sleeve brick itself, to allow
the sleeve brick to have enhanced durability. One or more selected from the group consisting of
B, B.sub.4C, MgB.sub.2, CaB.sub.6, and CrB may be further added in an amount of 0.1 to 3
mass %, in addition to 100 mass % of the refractory raw material mix, to enhance strength and
oxidation resistance and further enhance the durability. The magnesia raw material may
comprise a first particle fraction having a particle diameter of greater than 10 to 500 .mu.m and
occupying 20 to 50 mass % in the refractory raw material mix, and a second particle fraction
having a particle diameter of 10 .mu.m or less and occupying 5 mass % or less in the refractory
raw material mix, to additionally enhance corrosion resistance and thermal shock resistance.
US8.030,235 provides a magnesia-carbon brick comprised of about 50 to about 95% by
weight magnesia and about 1 to about 20% by weight carbon, with or without metallic
additions, such that the chemical analysis of the mixture of aggregates used in the brick will
comprise, by chemical analysis, about 2 to about 15% SiO.sub.2, about 3 to about 50%
Al.sub.20.sub.3, and about 50 to about 95% MgO.
US4,747,985 provides a method for the manufacture of a magnesia-carbon brick comprising the
steps of: a. preparing a mixture comprising: 1. burned magnesite 2. carbon 3. binder solution
comprising 3.1 pre condensed novolak resin 3.2 solvent for the novolak resin 4. a hardener for
the resin b. pressing a brick from the said mixture.
Although there are large numbers of magnesia carbon bricks but the problem of reliability and
long life which is vital to refractory lining persists. An improvement in the quality of magnesia
carbon bricks will enhance furnace lining life, which in turn will lead to improvement in furnace
availability, reduction in overall refractory consumption & cost, better productivity and other
operational benefits. The present invention therefore provides for an improved magnesia carbon
brick for use as refractory lining of an electric arc furnace and a method of manufacturing said
magnesia carbon brick.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known
art.
Another object of the present invention is to provide an improved magnesia carbon brick for use
as refractory lining of an electric arc furnace
Another object of the present invention is to provide a method of manufacturing magnesia
carbon brick for use as refractory lining of an arc furnace.
Another object of the present invention is to provide for Higher thermal conductivity.
Yet another object of the present invention is to provide for improved corrosion and erosion
resistance.
These and other advantages of the present invention will become readily apparent from the
following detailed description.
SUMMARY OF THE INVENTION
There is provided an improved refractory lining in electric arc furnace.
According to one embodiment of the present invention, there is provided an improved magnesia
carbon brick for use as refractory lining of an electric arc furnace, said magnesia carbon brick
comprising:
Magnesia (coarse) having particle size ranging from 3mm to 5mm and about 23-25% by weight;
Magnesia (middle) having particle size ranging from 1mm to 3mm and about 25-27% by weight;
Magnesia (fine) having particle size ranging from 0 to 1mm and about 35-37% by weight;
Magnesia (microfine) having particle size ranging below 0.063mm and about 13-15% by weight;
Graphite about 13.5-15.5% by weight;
Aluminium powder about 1.5-2% by weight; and
Pitch about 6-7% by weight.
Other embodiment of the present invention provides a method of manufacturing magnesia
carbon brick for use as refractory lining of an arc furnace, said method comprising the steps of:
a. mixing magnesia (micro fine) having particle size ranging below 0.063mm and about
13-15% by weight and Aluminium powder about 1.5-2% by weight and keeping the
mixture formed separately;
b. adding magnesia (coarse) having particle size ranging from 3mm to 5mm and about
23-25% by weight and magnesia (middle) having particle size ranging from 1mm to
3mm and about 25-27% by weight to said mixture formed at step a;
c. mixing the mixture formed at step b for about two minutes;
d. adding 70% of pitch to the mixture formed at step c and mixing for 10 minutes.
e. adding Graphite about 13.5-15.5% by weight to the mixture formed at step d and
mixing for about seven minutes;
f. adding rest 30% of pitch, Magnesia (fine) having particle size ranging from 0 to 1mm
and about 35-37% by weight to mixture formed at step e and mixing for about 25
minutes;
g. hot pressing the mixture formed at step fusing a plurality of de-airings.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention relates to pitch bonded Magnesia Carbon bricks with higher
carbon for improved thermal conductivity and better corrosion resistance. The invention is in
particular related to process of manufacturing of pitch boded Magnesia Carbon bricks with
higher retained carbon and development of its formulation.
In pitch bonded magnesia carbon brick manufacturing, the raw materials like MgO of different
quality and size fractions, graphite, antioxidant and additives are mixed in required proportion
with molten pitch. The temperature of molten pitch is maintained at 170 - 180oC. During mixing
a particular sequence of addition and mixing time is followed to obtain optimum coating of
magnesia grains and graphite flakes by pitch and additives. After mixing, the mix is discharged
in a container. The temperature of mix is around 120±10oC. The mix is hot pressed at a specific
pressure of 2 Ton/cm2.
With the increase of carbon addition, thermal conductivity of magnesia carbon brick increases
further. This increased thermal conductivity helps in formation of viscous layer of slag on the
working lining surface which protects the lining from corrosion and erosion. Carbon content of
the brick is increased by addition of higher amount of graphite, but higher graphite makes the
mix inconsistent and pressing becomes difficult, because of the density difference of graphite
(~2.1 gm/cc) and magnesia(~3.4 gm/cc). Also during pressing, lamination occurs due to air
entrapment and poor flow of mix. This is more predominant in pitch bonded magnesia carbon
bricks. Higher carbon (12-16%) was accommodated by suitably modifying the granulometry and
amount of pitch addition. Further, sequence of addition of different ingredients and mixing time
was adjusted to achieve desired consistency of the mix.
These modifications along with optimized number of de-airing during pressing resulted in
production of bricks without lamination. The developed brick had a green bulk density of 2.96-
2.98 gm/cc, cold crushing strength of 474 - 496 kg/cm2 and coked apparent porosity of 11.5-
12.8%.
Batch Composition of invented Magnesia Carbon brick
The present invention is directed to Pitch bonded Magnesia Carbon brick with higher residual
carbon and having better corrosion and erosion resistance. The batch composition is given
below:
Magnesia ( Coarse) : 23-25% by weight
Magnesia ( Middle) : 25-27% by weight
Magnesia ( Fine) : 35-37% by weight
Magnesia (microfine) : 13-15 % by weight
Graphite : 13.5-15.5% by weight (additional)
Aluminium Powder : 1.5-2% by weight (additional)
Pitch : 6-7% by weight ( additional)
Properties of developed brick are given in Annexure I. Batch composition of invented Magnesia
Carbon brick is given in Annexure II and details of different components have been given in
Annexure IV.
Further aspect of invention is that the above components are added and mixed in the order as
indicated in Annexure III.
The present invention provides for:
a) The formulation of pitch bonded Magnesia Carbon brick with 14-16% carbon
b) Process of manufacturing pitch bonded Magnesia Carbon brick with 14-16% carbon
c) Achieving green bulk density of 2.96-2.98 gm/cc with 14-16% carbon
d) Achieving coked apparent porosity of 12% with high carbon
The synergic effect of the above features result in pitch bonded Magnesia Carbon brick with the
following advantages:
• Higher residual carbon
• Higher thermal conductivity
• Improved corrosion and erosion resistance
ANNEXURE -1: Properties of Pitch bonded Magnesia Carbon Bricks
ANNEXURE - II: Batch Composition of Magnesia Carbon brick
Ingredients Wt. %
Magnesia ( Coarse) : 23-25%
Magnesia (Middle) : 25-27%
Magnesia (Fine) : 35-37%
Magnesia (microfme) : 13-15 %
Graphite : 13.5-15.5% (additional)
Aluminium Powder : 1.5-2% (additional)
Pitch : 6-7% ( additional)
ANNEXURE - III: Mixing sequence for preparation of mix for Magnesia Carbon brick
i. Magnesia micro fines, and Aluminium powder are mixed and kept separately,
ii. Coarse & middle fractions of Magnesia are added in the mixer and mixed for 2
minutes,
iii. Addition of 70% of pitch to the mixer and mixed for 10 mins.
iv. Addition of Graphite and mixing for 7 min.
v. Addition of remaining 30% pitch, Magnesia fines and premix batch and mix for 25
mins.
vi. Discharge of mix from mixer for hot pressing
vii. Hot pressing the mix with 4 de-airings
ANNEXURE - IV: Details of different Raw Materials, Additives and Binder
Magnesia:
MgO 97 % min.
Fe203 0.2% max.
A1203 0.12% max.
Si02 0.35% max.
CaO 2.4% max.
B203 0.03% max.
CaO : Si02 5 min.
Bulk sp.gravity 3.4 gm/cc min.
Av. Crystal size 100 micron min.
Graphite
Fixed Carbon 96% min.
Volatile matter 2% max
Moisture 0.5% max.
Non graphitized carbon 0.5% max
Size distribution
-100 mesh 30%(min.)
- 72 mesh 60% (min.)
-60 mesh 80% (min.)
+ 44 mesh 7% (max)
Aluminum Powder
Al 99.5% min.
Si 0.15% max.
Fe 0.40% max
Size 0 - 074 mm with limit
+ 200 mesh 20 % (min)
+ 150 mesh 0.5% (max.)
Pitch
Softening Point 95 - 98 oC
Coking Residue 50 - 52%
Benzene Insoluble 28 - 30 %
Quinolene Insoluble 4-6%
Beta Resin 21 -23%
Moisture 0.5% max
Distillation Range
0-300oC Nil
300-360 oC 0.5% max
Although the embodiments herein are described with various specific embodiments, it will be
obvious for a person skilled in the art to practice the embodiments herein with modifications.
However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and
specific features of the embodiments described herein and all the statements of the scope of the
embodiments which as a matter of language might be said to fall there between.
WE CLAIM:
1. An improved magnesia carbon brick for use as refractory lining of an electric arc furnace,
said magnesia carbon brick comprising:
Magnesia (coarse) having particle size ranging from 3 mm to 5 mm and about 23-25% by
weight;
Magnesia (middle) having particle size ranging from 1 mm to 3 mm and about 25-27%
by weight;
Magnesia (fine) having particle size ranging from 0 to 1 mm and about 35-37% by
weight;
Magnesia (microfine) having particle size below 0.063 mm and about 13-15% by weight;
Graphite about 13.5-15.5% by weight;
Aluminium powder about 1.5-2% by weight; and
Pitch about 6-7% by weight.
2. The magnesia carbon brick as claimed in claim 1 wherein all said magnesia consist of
minimum 97% of MgO, maximum 0.2% of Fe203, maximum 0.12% of A12O3, 0.35%
ofSiO2 CaO and maximum 0.03% of B2O3.
3. The magnesia carbon brick as claimed in claim 1 wherein all said magnesia having
minimum CaO : SiO2 ratio of 5.
4. The magnesia carbon brick as claimed in claim 1 wherein all said magnesia having
minimum Bulk specific gravity of 3.4 gm/cc.
5. The magnesia carbon brick as claimed in claim 1 wherein all said magnesia having
minimum average Crystal size of 100 micron.
6. The magnesia carbon brick as claimed in claim 1 wherein said graphite consisting
minimum 96% of fixed Carbon, maximum 2% of Volatile matter, maximum 0.5% of
Moisture and maximum 0.5% of Non graphitized carbon.
7. The magnesia carbon brick as claimed in claim 1 wherein said aluminium powder
consisting minimum 99.5% of Al; maximum 0.15% of Si and maximum 0.40% of Fe.
8. The magnesia carbon brick as claimed in claim 1 wherein said pitch consisting Coking
Residue around 50 - 52%, Benzene Insoluble around 28 - 30 %, Quinolene Insoluble
around 4 - 6 %, Beta Resin around 21 - 23 % and maximum Moisture of 0.5%.
9. A method of manufacturing magnesia carbon brick for use as refractory lining of an arc
furnace, said method comprising the steps of:
a. mixing magnesia (micro fine) having particle size below 0.063mm and about 13-15%
by weight and Aluminium powder about 1.5-2% by weight and keeping the mixture
formed separately;
b. adding magnesia (coarse) having particle size ranging from 3mm to 5mm and about
23-25% by weight and magnesia (middle) having particle size ranging from 1mm to
3mm and about 25-27% by weight to said mixture formed at step a;
c. mixing the mixture formed at step b for about two minutes;
d. adding 70% of pitch to the mixture formed at step c and mixing for 10 minutes.
e. adding Graphite about 13.5-15.5% by weight to the mixture formed at step d and
mixing for about seven minutes;
f. adding rest 30% of pitch, Magnesia (fine) having particle size ranging from 0 to 1mm
and about 35-37% by weight to mixture formed at step e and mixing for about 25
minutes;
g. hot pressing the mixture formed at step fusing a plurality of de-airings.
10. Method as claimed in claim 9 wherein said hot pressing is done at a specific pressure of
around 2 Ton/cm2.
11. A magnesia carbon brick for use as refractory lining of an electric arc furnace as herein
described and illustrated with reference to the description read in conjunction with the
tables.
12. A method of manufacturing magnesia carbon brick for use as refractory lining of an arc
furnace as herein described and illustrated with reference to the description read in
conjunction with the tables.

ABSTRACT

This invention relates generally to refractory lining in electric arc furnace. More particularly the
present invention relates to a magnesia carbon brick for use as refractory lining of an electric arc
furnace and a method of manufacturing said magnesia carbon brick. It provides for higher
residual carbon, higher thermal conductivity and an improved corrosion and erosion resistance.