Claims:WE CLAIM:

1. A magnesia based composition of spray mass used for making working lining in Tundish steel vessel characterized in that Dunite (Foresterite - MgO, SiO2) is incorporated with dead burnt magnesia (DBM) therewith.

2. A composition as claimed in claim 1, wherein the proportion of Dunite is 10 to 50% by wt. in the composition with particle size of 0.15 to 0.75 mm.

3. A composition as claimed in claims 1 and 2, wherein the proportion of Dunite is 50% by wt. in the composition with particle size between 0.15 to 0.75 mm.

4. A composition as claimed in claims 1 and 3, wherein raw Dunite is used without further processing of the material into the developed composition.

5. A composition as claimed in claims 1 to 4, wherein the Dunite is obtained from the own in-house stock.

6. Working lining composition for Tundish Spray mass to be used in Tundish vessel using dead burnt magnesia and in that Dunite is incorporated in the composition.

Dated this 26th day of March, 2018
, Description: DEVELOPMENTOF DUNITE BASED TUNDISH SPRAY MASS

FIELD OF THE INVENTION
This invention relates to Tundish spray mass. This invention particularly relates to magnesia based Tundish spay mass where Dunite is used as a component in the composition for making the working lining in the Tundish steel vessel.

BACKGROUND OF THE INVENTION:
Tundish is generally a steel vessel which is lined with several layers of refractory. A permanent lining, generally of high alumina low cement castable, serves as an inner lining to protect the Tundish shell. The permanent lining is coated with a wearable and disposable lining of Magnesia boards or Basic Spray Mass which is called working lining. The working lining is in direct contact with the molten metal in the Tundish. Slag present in the steel reacts with the working lining and corrodes the working lining. If working lining is a basic in nature then the reaction is minimum as the slag is basic in nature. Generally MgO based minerals are used as raw materials in the manufacturing of Tundish spray mass as slag is basic in nature.
One of the SAIL Units is having vast stock of Raw Magnesite (MgCO3) and Raw Dunite. Both Magnesite and Dunite are Magnesia (MgO) bearing mineral. Dunite is a natural Forsterite –Serpentine or olivine group’s of mineral. Chemical Composition of Dunite is: MgO - 48%, SiO2- 39%, Fe2O3 -10.0% and rest is impurities like Al2O3, CaO etc. Dunite is a low cost raw material and readily available as it does not require any calcinations like dead burning. So for better utilization of Dunite, this work was taken.

OBJECT OF THE INVENTION

The object of the invention is to develop a magnesia based composition of spray mass used for working lining in Tundish steel vessel where Dunite can also be used as one of the major raw material along with DBM.

The other object of the invention is to suitably utilize in-house stock of Dunite.

Another object of the invention is to use different percent of Dunite in the composition of tundish spray mass.

A further object of the invention is to manufacture the Tundish spray mass economically using Dunite.

DETAIL DESCRIPTION OF THE INVENTION
According to the invention there is provided a magnesia based composition of spray mass used for making working lining in Tundish steel vessel wherein Dunite (Forsterite - MgO, SiO2) is incorporated with dead burnt magnesia (DBM) therewith.
The proportion of Dunite can be in the range of 10 to 50% by wt. in the composition with coarser particle size between 0.15 to 0.75 mm.
In one embodiment of the invention the proportion of Dunite is up to 50% by wt. of the composition with coarser particle size between 0.15 to 0.75 mm.
In another embodiment of the invention Dunite is used without further processing.
In another embodiment of the invention Dunite is sourced from the own in-house stock.
Tundish spray mass is widely used material in Tundish working lining for continuous casting process. Magnesia based Spray mass is used in Tundish working lining. Generally raw Magnesite (MgCO3) is used for source of Magnesia (MgO) for producing spray mass composition. Raw magnesite is required calcinations to decompose to Magnesium Oxide (MgO) and Carbon Di-oxide (CO2). After calcinations, Raw Magnesite becomes Dead Burnt which is called Dead Burnt Magnesia (DBM). DBM contains about 80-90% MgO, rest is SiO2 and other impurities depending upon the source. DBM is a widely used raw material for manufacturing of Spray Mass composition.
Dunite is another Magnesia (MgO) bearing raw material. Dunite is a natural Forsterite –Serpentine or olivine group’s of mineral. The major chemical composition of Dunite is MgO and SiO2. Dunite is a mineral which is abundantly available in one of SAIL unit. Chemical Composition of Dunite is: MgO - 48%, SiO2- 39%, Fe2O3 -10.0% and rest is impurities like Al2O3, CaO etc. Dunite is a low cost raw material and readily available as it does not require any calcinations like dead burning. The knowledge of incorporating of Dunite along with DBM in the spray mass composition is not available in the literature. Incorporation of Dunite up to certain percentage in the composition will reduce the raw material cost of spray mass.
DBM of chemical composition: MgO - 91.0%, SiO2 – 6.5%, CaO - 1.7% and Fe2O3 – 0.5 and minor ingredients are mixed together as par following Table 1. The particle size of DBM is taken from 0 – 0.75 mm range. For better particle size distribution, particle of DBM can be added in to two groups – one is up to 0-0.15 mm which is called fines and another one is 0.15 – 0.75 mm which is called coarser size particle. But in case of Dunite particles, only coarser Dunite is added.

Raw Material Particle size %
Dead Burnt Magnesia 0-0.75 mm 42-85
Raw Dunite 0.15 -0.75 mm 10-50
Binder% Fines 4.0 – 5.50
Fibre% - 2.0 – 3.50
Additives% Fines 0.50 -1.25
Table -1: Percentage of raw materials and other ingredients
Spraying and sticking of Magnesia–Dunite powder after mixing with only water is not sufficient. Many other ingredients (minor ingredients) in small quantity are required to add with dry MgO powder and dry Dunite powder. Paper pulp fibre is added along with main constituent of spray mass to make porous structure. Clay as plasticizer is added in the composition to get more plastic property for easy transportation through the rubber hose pipe during spraying. Sodium silicate is generally added as setting agent during the process of heating of Tundish spray mass.
All the raw materials mentioned in Table-1 are mixed together varying the Dunite and DBM fraction in required quantity like with 10, 20, 30, 40 And 50% Dunite with DBM and minor ingredients. Mixing was done for 5 minutes in laboratory mixer at medium speed for homogeneous mixing. In an inhomogeneous mixing, fractional density will vary from point to point in proportion to the local composition.
Sample is prepared after mixing of another 5 minutes with 10 -15% water in the same mixer although spraying will be done as par actual water requirement. Physical properties are checked after firing at 1550° C for 2 hours in laboratory high temperature furnace.Bulk Density at 1550° C decreases a little with increasing percentage of Dunite. Higher BD does not improve the performance of the spray mass. Moderate BD is desirable for easy de-skulling after casting end. The CCS value is required to such level so that it is able to sustain its own shape till the liquid metal pouring in to the tundish. Shrinkage depends on particle size distribution of a Refractory body as sintering depends on surface area of the particles.
After firing at 1550° C for 2 hrs. Dunite and DBM produces a chemical reaction between the components giving Periclase (MgO) and Forsterite (MgO, SiO2) phase formation. Forsterite is a low melting compound compare to Periclase.
The composition and amount of the newly formed minerals depend on the fineness of particles and amount of Dunite in the compositions.
From XRD results, it is found that the peak intensity of Forsterite is increased with increasing percentage of Dunite. Peak intensity of Forsterite is increasing with increasing of fineness of Dunite particle with same Dunite content. Peak intensity of periclase decreases with increase of Dunite fines and high percentage of Dunite in the composition. Hence during the developmental process Dunite (0.15 – 0.75 mm) was added in coarser form in formulation of Spray mass.
USEFULNESS OF THE INVENTION
Dunite can be incorporated in the form of coarser particle. Dunite incorporation in the formulation of spray mass will reduce the cost of spray mass. Percentage of Dunite may be added according to the casting duration and process requirement of a particular plant.
Any spray mass producer including SAIL Refractory Unit can use this invention for manufacturing of Tundish Spray mass.
INDUSTRIAL APPLICABILITY
SAIL Refractory unit including SRCL, Salem and any spray mass manufacturer in India and abroad can use this invention.
Although the invention described herein mentions a few embodiments, it could be possible to those skilled in the art to develop other similar embodiments as well beyond those disclosed herein with modifications. However, all such modifications are deemed to be within the scope of the invention claimed herein.