Basic oxygen furnace is well known in the art of steel making. B.O.F. is normally
lined with magnesia carbon refractory. Maintenance for long life of the lining at a
reasonable cost is one of the main problems in the industry. Patching mass is
used to install the mass in worn out portion of B.O.F. lining to prolong B.O.F. life.
To make it compatible with magnesia carbon lining, patching mass is generally
made with magnesia and carbon based material.
Magnesia, is of high purity and mostly sea water based or natural source having
more than 98% purity is used for B.O.F. lining. In conventional patching mass
also this type of magnesia is used for compatibility. Carbon used is mostly of
pitch or resin material. They impart corrosion resistance of the material and to
some extent flow of the mass. Conventional patching mass on analysing found to
contain minimum 80% of MgO and 12% to 16% of C.
Deltailed properties are given below:

Hot patching mass has been widely used to repair the bottom and impact area of
charge side of BOF. At present, the hot patching mass is either imported or partly
supplied by one or two indigenous suppliers. In a campaign life of 1000 heats,
approximately 10 - 12 T of patching mass is being used. But in near future, with
adoption of programmed patching technique for increasing lining life, there will be
quantum jump in the requirement of hot patching mass in Indian steel plants.
Main object of the invention is to prepare a magnesia based patching mass
composition to restrict the import of the same, from indigenous raw materials.
Other object is to utilise impure magnesia to produce a compatible form of
patching mass with the magnesia carbon lining of B.O.F. Other object is to
produce a patching mass having good corrosion resistivity and having a good
flow characteristic.
Considering the demand of magnesia based patching mass in the repairing of
B.O.F. furnace in steel industry, we have developed a process for preparing
magnesia based patching mass from an impure form of magnesite having high
iron content as available in Almora magnesite with proper selection of carbon in
the form of liquid tar and pitch.
It is the first time that patching has been made by using high iron content
magnesia. For that, grains have been selected of hard fired nature with high bulk
density and granulometry have been selected by choosing coarser and finer
fractions than the middle fractions to impart flowability in the mass. Because of
the high impurity, tar and pitch have been so selected that grains are coated with
carbon thoroughly to retard the reactivity of the grains. Additionally, pitch of low
softening point with high fixed carbon have been identified for better adhesion of
grains, low spalling of material because of high carbon content and high
corrosion resistance of the material. Finely grained pitch should be used in the
mass to impart better distribution of carbon and better adhesivity of the material.
The invention therefore provides a process for preparing a magnesia based
patching mass for repair of Basic Oxygen Furnace from magnesite with high iron
content which comprises selecting Almora magnesia, Tar and soft pitch in the
following proportion and sizing :
In which Finer fractions of Almora Magnesia first weighed and taken in the mixer
and then the finer pitch fractions were weighed and mixed with the above
magnesia finer and separately coarser fraction of magnesia grains were weighed
and in it liquid tar added and mixed thoroughly and then the two parts were mixed
together in a mixer and then mixing was done at least for 5 minutes until a
homogenous mass is produced. The mixed mass is discharged and stored in
airtight condition.
Quality of Almora magnesia is such that it can not be used directly for brick
manufacture as total amount of impurities like SiO2, AI2O3, Fe2O3 etc. is about
12%. However, presence of CaO and Fe2O3 contaminants help in adherence over
hot magnesia bricks or MgO-C brick surface coated by slag containing CaO, SiO2
and Fe2O3.
Tar is used as an intermediate binder between magnesia and pitch. Purpose of
tar is to coat the grains of magnesia uniformly so that finer grains of magnesia
and pitch powder can stick to the coated grains of magnesia. This enhances the
fluidity of the ultimate mass and uniform distribution of finer grains and pitch. The
better this distribution the better shall be the corrosion resistance of the material
because of uniform distribution of pitch. This also enhances the fired density of
the material.
Granulometry of Magnesia materials is important factor to control the bulk density
of developed mass. Coarser i.e. (-6 + 30) BSS and finer fractions (-150 BSS)
should be maximise with minor middle fraction i.e. (-30+150) BSS to impart high
B.D. in the material, which will retard the oxidation rate of carbonaceous material
and thereby helping in setting of material. Otherwise, carbon will burnt up and
porous structure appear and will be easily worn out by metal and slag.
Similarly, highly sintered and dense grain should be selected for making of this
mass because of its comparatively inactive nature and this also helps in using
lower amount of binder in the material because of low porosity.
Tar should be so selected that its oil content does not go out very quickly and
leads to drying of material. Then it can not be used for patching. Oil in tar should
be properly selected and preferably it should contain between 0.5 to 1% of
anthracene oil i.e., Distillation range >270° C - 360°C - 30% min.
Higher the softening point of pitch, lesser is the wettability of it. Hence, pitch of
low softening point should be selected. It also imparts god fusibility of the material
and helps in sticking. But low soft. Pt. Pitch has the disadvantage of generally low
fixed carbon. Therefore, soft pitch should be so selected that it contains high
fixed carbon. High fixed carbon helps in reducing the corrosion of the material
and also imparts good density in the mass.
Following non-limitative examples are given to elucidate the invention:
In these examples raw materials used are of following composition :-
Finer fractions of Almora Magnesia first weighed and taken in the mixer and then
the finer pitch fractions were weighed and mixed with the above magnesia finer
and separately coarser fraction of magnesia grains were weighed and in it liquid
tar added and mixed thoroughly and then the two parts were mixed together in a
mixer and then mixing was done at least for 5 minutes until a homogenous mass
is produced. The mixed mass is discharged and stored in airtight condition.
Physico-chemical properties are as follows :
Hardening time 5 min. 10min. 9 min.
Flowability 130 min. 110 min. 100 min.
So, the best properties obtained by using the granulometry and composition
shown in Example 1 has been selected and tried. Based on the performance, the
final composition has been arrived at.
Granulometry of the ingredients are measured by conducting the sieve analysis
according to standard BSS method. Granulometry is measured by doing sieve
analysis and whether proper granulometry is achieved or not is measured by
doing loose bulk density of different fractions of material in measuring cylinder.
WE CLAIM :
1. A process for preparing a magnesia based patching mass composition for
repair of Basic oxygen furnace from magnesite with high iron content
characterized by selecting Almora magnesia, tar and soft pitch in the following
proportion and sizes.

in which finer fractions of Almora magnesia first weighed and taken in the
mixer and then the finer pitch fraction were weighed and mixed with the above
magnesia fines and separately the coarser fraction of magnesia grains and
liquid tar are mixed thoroughly and then the two parts are mixed together
thoroughly in a mixer for at least 5 minutes till a homogenous mass is
produced which was then discharged from the mixer and stored in airtight
condition.
2. A process for preparing magnesia based patching mass composition as
claimed in claim 1 in which the particle size of the magnesia should be such
that coarser i.e. (-6+30) B.S.S. and finer fraction (-150 BSS) is taken in
maximum with a minor quantity of middle fraction i.e. (-30+150BSS) to impart
high bulk density in the product which will retard the oxidation rate of
carbonaceous material and help in setting of material.
3. A process for preparing magnesia based patching mass composition as claimed in claim 1
in which A1 mora magnesia is taken in the following proportion and sizes.

4. A process for preparing magnesia based patching mass composition as claimed in claim 1
in which Almora magnesia contains impurities to the extent of 12% max.
5. A process for preparing magnesia based patching mass composition as claimed in claim
3in which the impurities are, SiO:. CaO. FejCh, ANOj and are present in the following
proportion

6. A process for preparing magnesia based patching mass composition as claimed in claim 1
in which MgO present in Almora Magnesia is about 90 - 92%.
7. A process lor preparing magnesia based patching mass composition as claimed in claim 1
in which tar is so selected that its oil content does not vary quickly and contains between
0.5 to 1% of anthracene oil, distillation range >270°C - 360T - 30% min.
8. A process for preparing magnesia based patching mass composition as claimed in claim 1
in which pitch should be so selected that it should have low softening point and high
percentage of fixed carbon to impart corrosion resistivity of the product.
9. A process for preparing magnesia based patching mass composition as
claimed in claim 1 in which the pitch used in the invention has the following
characteristics
Soft Point 78 - 83°C
Fixed Carbon (%) 45
Ash 0.5
Benzene Insuluble 23
Quinolene Insoluble 6
10. A process for preparing magnesia based patching mass composition as
claimed in claim 1 in which the tar used has the following characteristics
Pitch - 55%
Oil - 45%
Viscosity - 2.5Angular at 55°C
11. Magnesia based patching mass composition for repair of Basic Oxygen
Furnace from magnesite with high iron content whenever prepared by the
process as claimed in claim 1.
12. A process for preparing magnesia based patching mass composition for
repair of Basic Oxygen Furnace from magnesite with high iron content
substantially as herein described and ascertained.

Invention provides a process for preparing a magnesia based patching mass
composition for repair of Basic oxygen furnace from magnesite with high iron
content which comprises selecting Almora magnesia, tar and soft pitch in the
following proportion and sizes.

in which finer fractions of Almora magnesia first weighed and taken in the mixer
and then the finer pitch fraction were weighed and mixed with the above
magnesia fines and separately the coarser fraction of magnesia grains and
liquid tar are mixed thoroughly and then the two parts are mixed together
thoroughly in a mixer for at least 5 minutes till a homogenous mass is produced
which was then discharged from the mixer and stored in airtight condition.