Title of Invention

A COVERING AGENT FOR FORMING A TOP SLAG ON A STEEL MELTING BATH AND METHOD OF PRODUCTION THEREOF

Abstract The invention relates to a covering agent for a top slag of a metallic melt bath in a metallurgical vessel, in particular used in the steel industry, containing a material which melts on the melt bath and performs metallurgical work, wherein the material substantially comprises granules which have been rendered porous and the porosity of which is such that, at the melt bath temperature, a molten layer of liquid slag is formed on the melt bath, and a thermal barrier layer of the granules is formed above the molten layer of liquid slag. In addition, the invention relates to a process for producing the covering agent and to its use.
Full Text The invention relates to a covering agent or a covering
material for covering the exposed surface of a metal
melt bath in an open metallurgical vessel, in
particular in steel making in the pig iron and
secondary metallurgy sector and the continuous casting
thereof, in order to form a top slag. Moreover, the
invention relates to the use of the covering agent.
The melt bath in open metallurgical vessels used in the
steel industry, for example in continuous-casting
tundishes, is usually covered with a covering agent or
covering material which melts and forms what is known
as the top slag. The top slag ensures a liquid
protective layer on the metal bath surface, which is
intended to perform metallurgical work for, for
example, the oxidic purity level by, for example,
preventing gases from being taken up out of the
atmosphere and absorbing non metallic inclusions from
the melt.
Top slag agents for covering a melt bath generally have
a melting point that is typically 150°C below the
liquidus temperature of the melt, so that they melt a
short time after being applied.
The composition of the top slag depends on the
requirements of the metallic melt bath. For steel
making, it is mostly basic covering agents based on
calcium aluminate, e.g. C12A7 (12 CaO • 7 Al2Q3) that are
used. These may, for example, be mixtures or melt
products from an Al2O3 carrier, such as bauxite or
alumina and a CaO carrier, such as limestone, calcined
lime or dolomite. However, it is also possible, for
example, to use continuous-casting powders as a mixture
of SiO2, CaO, Al2O3, fluorine or soda components or
vanadium slag-forming agents.


The liquid slag layer dissipates large quantities of
heat outward from the melt bath and therefore causes
high heat losses. To prevent this, a thermal barrier
agent is applied as a coating to the slag. The thermal
barrier agents should not melt at the melt bath and
slag melt temperatures and should be sufficiently inert
or nonreactive for them not to participate in the
metallurgical work. By way of example, one thermal
barrier agent used is biogenic silica in the form of
rice husk ash. Furthermore, granulated spray-dried
granules which are in the form of hollow minispheres
are used.
In practice, the metal melt is generally first of all
covered with the top slag agent; then, the thermal
barrier agent is added to the molten top slag. The
combination of top slag plus thermal barrier agent is
also known as a "sandwich covering".
One drawback of this known sandwich covering method
with thermal barrier is that two different agents have
to be used. Two products have to be kept in stock, and
it must be ensured that they are not used in the wrong
order on site. Another drawback is that reactions still
occur between the dry, more solid thermal barrier agent
and the liquid top slag, and these reactions have an
adverse effect on the metallurgical work of the top
slag. By way of example, SiO2 from the rice husk ash
can be taken up by the top slag until the saturation
limit is reached, with the result that the top slag
releases oxygen to the metal melt, something which the
top slag is actually supposed to prevent.
Melts in metallurgical casting ladles are often also
covered with thermal barrier agents. The melt bath
surface of a casting ladle is covered with the thermal
barrier material, for example at the end of the
metallurgical work, thereby reducing the thermal
losses.

In some cases, a thermal insulation is even applied
before the metallurgical work has ended, for example if
relatively long transfer or standing times are intended
from tapping to the next treatment stage. In this case,
the thermally insulating covering may have to be
removed again by slag removal prior to the next
treatment stage, since it would impede the subsequent
metallurgical work of a top slag applied subsequently.
This measure requires additional outlay, considerably
delays

Accordingly, the present invention provides a covering agent for forming a top slag on a steel
melting bath, which melts on the melting bath and performs metallurgical work, characterised
in that (a) it consists of granular material which has been made porous, the grains of which
have a porosity of 5 to 70 vol. %, (b) the granular material consists of calcium aluminates with
the following chemical analysis: CaO/AI2O3 of 0.25 to 1.5, preferably of 1.0 to 1.5, wherein up
to 15 mass % of secondary phases, particularly MgO and/or MgOSiO2 and/or TiO2 and/or
Fe2O3 and/or alkalis, may selectively be included, so that (c1) its melt has a chemical and
mineralogical composition required for the metallurgical work, (c2) it forms both the slag melt
and also thereover, as a result of the grains being made suitably porous, a thermal insulation
layer on the steel bath.
The present invention also provides a method for producing a covering agent as described in
the preceding paragraph, wherein fine-particle mineral raw materials,such as herein
described, for producing the specified calcium aluminates for a top slag, which react with one
another at high temperatures and which ensure in the mixture the following chemical
analysis:CaO/AI2O3 of 0.25 to 1.5, particularly of 1.0 to 1.5, are mixed and heated to a
temperature, dependent on the mol ratio of CaO/AI2 O3 until they react, wherein a) at least one
said raw material is used which is dehydrated and/or calcined and in the process releases
water vapour and/or gaseous products,b) the mixture is mixed with a binder.such as herein
described, capable of burning out, to form a shapeable material, c) the shapeable material
is shaped into granular product, particularly granulated into granules or pelletised into pellets,
d) the granular product is heated to a temperature,depending on the type of the binder, such
that the binder burns out, pores are produced by means of dehydration and/or calcination,
and then a ceramic bond and/or a sintered bond of the raw materials is produced.

The invention therefore relates to a covering agent in
grain form, the melt of which has a chemical and
mineralogical composition required for the
metallurgical work, and which forms both the slag melt
and, above it, as a result of the grains being rendered
suitably porous, a thermal barrier layer on a metallic
melt bath.
Consequently, the top slag material according to the
invention has the synergistic function of also acting
as a thermal barrier agent by virtue of the grains
having a suitable thermally insulating porosity as a
result of having been rendered porous.
If the slag material which has been rendered porous in
accordance with the invention is applied to the
metallic melt bath, a predetermined part of the
material of the coating, which is in direct contact
with the melt bath surface and forms a molten layer of
slag, melts. Above this is dry, solid slag material
which has been rendered porous in a loose bulk bed,
while both slag melt and slag material that has been
rendered porous are present in a transition region. The
thermal barrier results substantially from the grain
porosity and the spaces between the grains of the top
slag material (intergrain volume) of the bulk bed.
The quantity of top slag material to be applied depends
on the metallurgical work required and on the desired
thermal insulation.
One particular further synergistic effect of the top
slag material according to the invention results from
it being possible for elements or substances of the top
slag melt which are consumed by the metallurgical work
automatically to be topped up from the transition
region material and/or the material of the thermal
barrier layer above.

If the levels of a certain constituent in the slag melt
become depleted, a concentration drop results, and this
is compensated for by the constituent being topped up
from the unmelted material. This automatically produces
optimum conditions for the metallurgical work in the
long term.
The invention is therefore taking a completely new
route to ensuring the thermal insulation which,
moreover, results in a surprisingly large number of
benefits. By way of example, there is no longer . any
problem with filled casting ladle which have to wait
for relatively long periods of time initially only
being provided with a thermally insulating covering of
the top slag material according to the invention,
without significant quantities of liquid slag being
produced. Only at a later stage is the thermal barrier
material melted to form the top slag for the
metallurgical work. This eliminates the need to remove
thermal barrier agent prior to the metallurgical work,
as was hitherto necessary.
The top slag material which has been rendered porous in
accordance with the invention can be produced, for
example, by using at least one starting material which
releases gaseous substances and thereby produces pores
during dewatering or calcining reactions. It is
preferable for milled top slag raw materials, for
example top slag raw materials which have been milled
to at relatively low temperatures and allows bodies of a
defined grain size to be produced from the mixture in a
pelletizing or granulating device, e.g. on a
granulating plate or in a granulating drum. The bodies
or pellets or granules are heat-treated in such a
manner that the binder is burnt out, the raw materials
are dewatered and/or calcined and ceramic bonding
and/or sintered bonding is produced. After cooling,
solid pellets or granules with pores which have been

introduced by dewatering and/or burning out and/or
calcining are obtained.
Binders which are preferably used include water, water
glass, synthetic resins, sulfite waste liquor,
phosphate compounds and/or calcined lime.
According to one particular embodiment of the
invention, organic combustibles which produce porosity
by being burnt out are added to render the binder/raw
material mixtures porous. These agents for rendering
the mixture porous, such as paper fibers, sawing chips,
sawdust, wood chips, styropor granules or the like, are
used in particular if the starting raw materials
produce few if any pores when they are burnt.

Of course, the binders which are burnt out also produce
additional pores, so that the level of pores can be
controlled by the addition of binder, the choice of
starting materials which can be dewatered and/or
calcined and/or the combustibles.
It is preferable to produce pellets or granules with
grain sizes of between 1 and 50 mm, in particular
between 3 and 20 mm, in which case it is advantageous,
with regard to the grain size distribution, to use
grain fractions that are as narrow as possible, so that
as much air as possible is present in the grain pockets
in the packed bed of grains on a melt bath or on the
slag melt, thereby further increasing the thermal
insulation.
It is expedient for the pellets or granules in the
material in grain form to have a porosity of 5 to 70%
by volume, in particular from 2 0 to 60% by volume.
Preferred bulk densities of the top slag material
according to the invention are between 0.2 and
1.6 kg/dm3, in particular between 0.3 and 1.3 kg/dm3.
Basic top slag agents which have been rendered porous
for steel making based on calcium aluminates in the
following ratio:
CaO/Al2O3 from 0.25 to 4, in particular from 1.0 to
1.5
are particularly suitable. Up to 15% by mass of
auxiliary phases may be present. These auxiliary phases
include, for example, MgO and/or MgOSiO2 and/or TiO2
and/or Fe2O3 and/or alkali metals.
According to a further embodiment of the invention, top
slag material according to the invention is produced by
adding an expanding agent and water or a foaming agent

and water to the raw material mixture, so that the
mixture is expanded or foamed, thereby producing pores.
Then, the expanded or foamed mixture can be burnt and
broken up to the desired grain size after cooling.
As an alternative to a foaming agent, it is also
possible for a prefoamed foam to be admixed to the dry
mixture or an aqueous mixture.

These production processes likewise allow a
predeterminable or controlled porosity to be achieved
in a simple way; it is also possible to select a
combination of these processes with the production of
pores by means of combustibles and calcining.
The production of a top slag product according to the
invention is explained in more detail on the basis of
the following example.
A shapeable mixture with a CaO/Al2O3 ratio of 1.14 was
produced from raw bauxite and limestone flour each
having a fineness of quantity of binder was set to be such that it was
possible to produce granules with a grain size fraction
of between 5 and 20 mm on a granulating plate.
. The granules were heated to 1250°C in such a manner
that the binder was burnt out, the bauxite and
limestone components were calcined and the calcined
grains were ceramically bonded.
The result after cooling was a free-flowing top slag
material which was in grain form and had been rendered
porous, comprising calcium aluminate in approximately
the starting composition in terms of Al2O3 and CaO and
the starting. grain fraction, which it was possible to
pack down and dispatch.
Once applied to a steel melt bath in a continuous-
casting tundish, a molten slag layer, a transition
region and a thermally insulating bulk layer were
produced on top of one another. The thermal insulation
was comparable to that provided by conventional thermal
barrier agents. The metallurgical work performed by the
slag was likewise excellent and in particular more
durable than in the case of the conventional slag of
the same sandwich covering. This evidently resulted
from materials which had been consumed during the
metallurgical work in the slag being topped up from the

thermally insulating granules above the slag and from
chemical reactions between the top slag and the thermal
barrier agent being avoided.
It is within the scope of. the invention for top slag
material that has not been rendered porous and is known
per se to be combined with top slag material according
to the invention that has been rendered porous, the two
materials as far as possible having an identical or
similar, i.e. metallurgically equivalent, composition,
by the melt bath first of all being covered with the
known top slag material that has not been rendered
porous; this material melts very quickly. Then, top
slag material according to the invention is applied to
the slag melt; this top slag material according to the
invention substantially only has

a thermally insulating effect and can also be used to
top up substances which have been consumed in the slag
melt. In this case - as with the "mono-covering"
according to the invention as described above - the
thermal insulation can be deliberately set by selecting
the grain fraction and/or the porosity in the material.
This is possible, for example, by combining different
grain size fractions and/or different porosities in the
material.


WE CLAIM :
1. A covering agent for forming a top slag on a steel melting bath, which melts on the
melting bath and performs metallurgical work, characterised in that
a) it consists of granular material which has been made porous, the grains of which
have a porosity of 5 to 70 vol. %,
b) the granular material consists of calcium aluminates with the following chemical
analysis:
CaO/AI2O3 of 0.25 to 1.5, preferably of 1.0 to 1.5,
wherein up to 15 mass % of secondary phases, particularly MgO and/or MgOSiO2 and/
or TiO2 and/or Fe2O3 and/or alkalis, may selectively be included, so that
c1) its melt has a chemical and mineralogical composition required for the
metallurgical work,
c2) it forms both the slag melt and also thereover, as a result of the grains being
made suitably porous, a thermal insulation layer on the steel bath.
2. A covering agent as claimed in claim1, wherein it is available in a grain-size fraction
between 1 and 50 mm, particularly between 2 and 20 mm.
3. A covering agent as claimed in claiml or 2, wherein it is a product made of shaped
granules and/or is a pelletised product.
4. A covering agent as claimed in any of claims 1 to 3, wherein it is a granulated foam
product and/or an expanded, granulated product.
5. A covering agent as claimed in any of claims 1 to 4, wherein the grains have a porosity
produced by means of dehydration and/or calcination.


6. A covering agent as claimed in any of claims 1 to 5, wherein the grains have a porosity
produced by means of organic burning-out materials.
7. A covering agent as claimed in any of claims 1 to 6, wherein the grains have a porosity
of 20 to 60 vol. %.
8. A method for producing a covering agent as claimed in any of claims 1 to 7, wherein
fine-particle mineral raw materials,such as herein described, for producing the specified
calcium aluminates for a top slag, which react with one another at high temperatures and
which ensure in the mixture the following chemical analysis:
CaO/AI2O3 of 0.25 to 1.5, particularly of 1.0 to 1.5, are mixed and heated to a
temperature, dependent on the mol ratio of CaO/AI2 O3 until they react, wherein
a) at least one said raw material is used which is dehydrated and/or calcined and
in the process releases water vapour and/or gaseous products,
b) the mixture is mixed with a binder, such as herein described, capable of burning
out, to form a shapeable material,
c) the shapeable material is shaped into granular product, particularly granulated
into granules or pelletised into pellets,
d) the granular product is heated to a temperature,epending on the type of the
binder, such that the binder burns out, pores are produced by means of dehydration and/or
calcination, and then a ceramic bond and/or a sintered bond of the raw materials is produced.

9. A method as claimed in claim 8, wherein ground raw materials with grain sizes are used.
10. A method as claimed in claim 8 or 9, wherein water, water glass, synthetic resins,
spent sulphite liquor, phosphate compounds and/or burnt lime are used as binders.


11. A method for producing a covering agent as claimed in any of claims 1 to 7,
wherein fine-particle mineral raw materials, such as herein described, for producing the
specified calcium aluminates, for a top slag, which react with one another at high
temperatures and which ensure in the mixture the following chemical analysis:
CaO/AI2O3 of 0.25 to 1.5, particularly of 1.0 to 1.5, are mixed and heated to a
temperature, dependent on the mol ratio of CaO/AI2O3, until they react,wherein
a) the raw materials are mixed with water and a foaming agent and/or an
expanding agent and/or a foam, so that pores are introduced into the aqueous material, and
b) the material is burned until a ceramic bond and/or a sintered bond is produced.

12. A method as claimed in claim 11, wherein the burned product is comminuted and
graded.
13. A method as claimed in any of claims 8 to 12, wherein organic burning-out materials
are added to the mixture to make it porous.
14. A method as claimed in claim 13, wherein paper fibres, sawdust, sawmill waste, wood
chips and/or polystyrene granular material are admixed.
15. A method as claimed in any of claims 8 to 14, wherein raw materials of a grain size 90 urn are used.
16. A method as claimed in any of claims 8 to 15, wherein raw materials are used which
have up to 15 mass % of secondary phases.
17. A method as claimed in any of claims 8 to 16, wherein the secondary phases are MgO
and/or MgOSiO2, and/or TiO2 and/or Fe2O3 and/or alkalis.

18. A method as claimed in any of claims 8 to 17, wherein burning takes place at
temperatures up to 1250°C.
19. A method as claimed in any of claims 8 to 18, wherein dehydrating and/or calcining raw
materials are used.


The invention relates to a covering agent for a top
slag of a metallic melt bath in a metallurgical vessel,
in particular used in the steel industry, containing a
material which melts on the melt bath and performs
metallurgical work, wherein the material substantially
comprises granules which have been rendered porous and
the porosity of which is such that, at the melt bath
temperature, a molten layer of liquid slag is formed on
the melt bath, and a thermal barrier layer of the
granules is formed above the molten layer of liquid
slag. In addition, the invention relates to a process
for producing the covering agent and to its use.

Documents:

01085-kolnp-2005-abstract.pdf

01085-kolnp-2005-claims.pdf

01085-kolnp-2005-description complete.pdf

01085-kolnp-2005-form 1.pdf

01085-kolnp-2005-form 3.pdf

01085-kolnp-2005-form 5.pdf

01085-kolnp-2005-international publication.pdf

1085-KOLNP-2005-AMANDED CLAIMS 1.1.pdf

1085-KOLNP-2005-AMENDED CLAIMS.pdf

1085-kolnp-2005-assignment.pdf

1085-KOLNP-2005-CANCELLED PAGES.pdf

1085-KOLNP-2005-CORRESPONDENCE-1.1.pdf

1085-kolnp-2005-correspondence-1.3.pdf

1085-KOLNP-2005-CORRESPONDENCE.1.2.pdf

1085-kolnp-2005-correspondence.pdf

1085-KOLNP-2005-DESCRIPTION (COMPLETE) 1.1.pdf

1085-KOLNP-2005-DESCRIPTION (COMPLETE).pdf

1085-KOLNP-2005-EXAMINATION REPORT REPLY RECIEVED 1.1.pdf

1085-kolnp-2005-examination report.pdf

1085-KOLNP-2005-FORM 1-1.1.pdf

1085-KOLNP-2005-FORM 1.pdf

1085-kolnp-2005-form 13-1.1.pdf

1085-KOLNP-2005-FORM 13.pdf

1085-kolnp-2005-form 18-1.1.pdf

1085-kolnp-2005-form 18.pdf

1085-KOLNP-2005-FORM 2-1.1.pdf

1085-KOLNP-2005-FORM 2.pdf

1085-kolnp-2005-form 3-1.1.pdf

1085-KOLNP-2005-FORM 3.pdf

1085-kolnp-2005-form 5.pdf

1085-KOLNP-2005-FORM-27.pdf

1085-kolnp-2005-gpa.pdf

1085-kolnp-2005-granted-abstract.pdf

1085-kolnp-2005-granted-claims.pdf

1085-kolnp-2005-granted-description (complete).pdf

1085-kolnp-2005-granted-form 1.pdf

1085-kolnp-2005-granted-form 2.pdf

1085-kolnp-2005-granted-specification.pdf

1085-kolnp-2005-intenational publication.pdf

1085-kolnp-2005-international preliminary examinary report.pdf

1085-kolnp-2005-international search report.pdf

1085-kolnp-2005-other patent document.pdf

1085-KOLNP-2005-OTHERS 1.1.pdf

1085-KOLNP-2005-OTHERS.pdf

1085-kolnp-2005-others1.2.pdf

1085-KOLNP-2005-PA.pdf

1085-KOLNP-2005-PCT PRIORITY DOCUMENT NOTIFICATION.pdf

1085-KOLNP-2005-PETITION UNDER RULE 137.pdf

1085-kolnp-2005-reply to examination report-1.1.pdf

1085-KOLNP-2005-REPLY TO EXAMINATION REPORT.pdf

1085-kolnp-2005-translated copy of priority document.pdf


Patent Number 248154
Indian Patent Application Number 1085/KOLNP/2005
PG Journal Number 25/2011
Publication Date 24-Jun-2011
Grant Date 22-Jun-2011
Date of Filing 07-Jun-2005
Name of Patentee REFRATECHNIK HOLDING GMBH
Applicant Address ADALPEROSTRASSE 82, 85737 ISMANING
Inventors:
# Inventor's Name Inventor's Address
1 KOSLOWSKI, WOLFGANG LAVATERSTRASSE 3, 81739 MUNCHEN
2 ACKERMANN, ANDREAS DONNERSBERGERSTRASSE 22, 80634 MUNCHEN
PCT International Classification Number B22D 11/111
PCT International Application Number PCT/EP2003/010807
PCT International Filing date 2003-09-29
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 102 59 335.3 2002-12-18 Germany