Note: Descriptions are shown in the official language in which they were submitted.
~2~
.
GRANUL~R, PLASl`IC, CARBON CONTAINING
REFRACTORY COMPOSITION_ _
The invention relates to a granular, plastic, carbon
containing refractory composition for the lining of vessels
for liquid steel.
The refractory lining of steel transport ladles and casting
ladles has to withstand wear requirements which have recently
become more and more difficult to meet. Downstream continuous
casting or metallurgical treatment processes carried out in the
ladles such as desulphurization or dephosphorization often
require very high temperatures oF the melts as well as longer
residence times J having a highly adverse ef-fect on the refractory
lining; for this reason, conventional lining materials such as
acid clay sands, fire clay or bauxite can be used to a limited -
extent only.
In order ~o meet these higher requirements it has become
common use to line ladles with magnesia, magnesia chrome or
dolomite bricks. However, the specific material properties of
these basic bricks, in particular their high dilatation~ high
heat conductivity and low thermal shock resistance require a
very careful, time-consuming and expensive installation. It is
therefore the aim to reduce the lining time for such vessels
by using basic refractory masses.
The steel industry applies various types o~ lining equipment
such as slingers or automatic ladle lining machines which
automatically introduce and su~ficiently compact the refractory
masses .
In the slinger process, the refractory mass leaves the end
of the conveyor belt with high speed and is introduced ~rom the
upper end of the ladle downwards between a template and the
permanent or insulating lining which has in most cases been
preserved. Due to the high throughput, th0 lining time can be
.
,,
~ 8~
shortened consiclcrably. I-lowever, uniEorlll comp.lc-tlrlg cal1not be
achieved with t}liS met}1ocl, as coarse grail1 clusters are
frequently formed due to grain rebouncl and scgregation,
resulting in an ulleven lining structure.
With ladle ramming machines, the ramn~ing process which is
conventionally done by hand can be automated. The material
having a consistency suitable for ramming is fed directly
before the over-mounted pneumatic ramming device and compacted
continuously. This process allows a controlled and automatic
consolidation and reduces the lining time to about 10 to 20
percent of the time required for manual ramming. Contrary to
the lining work performed by slingers, grain segregation can
be avoided with this method.
The ramming mixes from basic materials with a conventional
inorganic bonding such as silicateS sulphate, phosphate or
chromate which have so far been tested in the automatic ramming
process have not rendered satisfactory results. These types
of masses, being characterized by a high degree of dilatation,
exhibit pronounced gaps in bonding in the course o~ the
heating-up process; this deficiency is due to a weakening of
the chemical bond while the ceramic bond does not yet exist,
and will often cause the mass to peel off during operation.
Infiltration of steel and slag also has an adverse effect on
the exposed mass layers and promote the tendency towards peeling.
Furthermore, the setting of such ramming mixes neecls much time
and energy. Chemical consolidation of the mass should have at
least to some extent been effected before the template can be
removed. The subsequent cLryillg period o-f I or 2 days is
extremely energy-intensive as at least one temperature level
has to be maintained by means of gas burners or the like in
order to achieve the final strength.
Refractory ramming mixes which contain liquid tar or pitch
as plastifying additives have also turned out insatisfactory
. . .
results as the smoke they develop dur iTlg drying excl~ldes the
use of such additives for envirollmental reasons.
~ ccording to DE-A 2 806 506, magnesia carbon bricks are
manufactured by mixing 70 to 95 parts of sin-tered magnesia having
an MgO content in excess oE 90 percent by weight with 5 to 30
parts of carbon such as graphite; after adding 2 to 6 percen-t
by weight of Novolak phenolic resin solution (related to the
weight of the magnesia-carbon mixture) and 8 to 20 percent by
weight of hardener (related to the weight of the Novolak phenolic
resin) bricks are formed from the mixture and dried. This
mixture which has been designed for brick manufacturing only,
cannot be used as a ramming mix as it is not stable for
storage ln the unshaped state.
According to US-A 4 102 694, a mass consisting of l00 parts
by weight of a powdsry refractory material, 4 to 40 parts by
weight of a solid or liquid coal tar pitch or petroleum pitch
and, if necessary, 0.5 to 5 parts by weight of a mineral powder
such as a coke powder or fibrous material and, if necessary,
0.1 to 10 parts by weight of a thermosetting synthetic resin,
is mixed with 10 to 30 parts by weight of a liquid oil such as
mineral oil to form a pumpable slurry for repairing the lining
of blast furnaces. This mix, havi.ng a mushy consistency, is not
suitable for ramming or the like as it is not self-supporting
and does not have enough stability after removal of the template.
An object of the prescnt invention is the development of
a granular, plastic, carbon containing refractory composition
having a shelf life of two months or more, which can be
introduced in ladles or other vessels for liquid steel and
which can be compacted by means of manual or automatic ramming,
slingering or vibrating, and during heating-up of which
smoke formation can largely be avoided.
.~ . i
.. ~ .
'~ , .
~ 3~
This and othcl~ ol)jects are ,'lChieVed l~y the l)resellt illVelltiOll
~ith a compositioll comL)Iising a granlllated re~ractory matcrial,
1 to ~0 percent by weigllt, preEerably ~ to 10 percent by weight
of a solid carbon carrier such as graphite, carbon black, ground
coke powder, crushed carbon electrodes and the like or mixtures
thereof, and 2 to 7 percent by weight of a s~able, thermosetting
synthetic resin free of hardener, preferably a phenolic resin
of the type Novolak.
Accordin~ to one embodiment of the invention, the synthetic
resin can be present in a solid, finely ground form, preferably
having a grain size below 0.2 mm, with more than 50 percent by
weight of the synthetic resin having a grain size below 0.06 mm.
For bringing ~he composi~ion into a plastic state suitable for
compacting by ramming, slingering or vibrating, the addition
of a plasticizer is recommended. Such plasticizer can be a
liquid aliphatic hydrocarbon such as a naphthenic or para~fin-
base oil or silicone fluid. The plasticizer can be admixed to
the dry, granular composition before starting the lining
procedure. However, in order to avoid manipulation on site,
2 to 7 percent by weight of plasticizer should favourably ~e
admixed during manufacturing, and the mass should be supplied
in a plastic state.
According to another embodiment of the invention, the
synthetic resin can be dissolved in a non-aqueous solvent such
as ethylene glycol or polyethylene glycol. In this case, the
solvent also acts as a plasticizer.
The composition according to the presellt invention exhibits
an organic bond which is achieved by the use of a stable
duroplastic material i.e. a thermosetting synthetic resin, in
particular a phenolic resin, preferably of the type Novolak,
avoiding the adclition of a hardener. This phenolic resin can be
modified e.g. with natural resins. Surprisingly, the composition
according to the present invention cures at elevated temperatures
without needing a hardener.
.,`'~
-- 5
This organic bond has tl~e advantage that the nlass will
hardly react during stora~e so that a shelf life of at least
2 to 3 months and more ~can be obtained, whereas liquid synthetic
resins, e.g. resols, can tend to cross-link reactions and to
chelate formation during storage or curing. This is due to
speciically acting catalysts (in particular bivalent metal
ions such as ~Ig, Ca, Cd, Mn) which might be provided by the
refractory material.
Contrary to a liquid synthetic resin, a synthetic resin such
as phenolic resins provides a higher amount o~ residual carbon
in the composition. A lining made of a composition according to
the present invention will therefore develop a stronger carbon
skeleton during operation, so that higher strengths at ope~ating
temperatures can be reached. Furthermore, masses which contain
synthetic resins of the phenolic resin type rather than liquid
synthetic resins will be subject to less dehydration during
heating-up; this is of importance for refractory base materials
which are not resistant to hydration.
As mentioned earlier, the composition is given the
plasticicity required for installation by adding 2 - 7 percent
by weight, preferably 3 to 6 percent by weight of an in particular
oily plasticizer or an equivalent amount of a non-aqueous
solvent if a dissolved synthetic resin is used. The composition
has a granular and slightly moist consistency. If the mass is
compacted by ramming, the amount of plasticizer added should be
in the lower range of the above mentioned quantity, for slingering
in the medium range and for vibrating in the upper range. It can
be expected that due to the additiorl of oil or glycol the
composition according to the present invention will tend to
less grain segregation during slingering than conventional
masses.
The green strength exhibited by the composition according
to the invention is high enough that the template can be removed
~,
" 'i;
.
~'
: '
: 1~ 8 ~3 ~
immediately after compacting. This property also makes it
suitable f~r being compacted with ramming machines working
with a local templa~e-like device such as a link belt which
travels along with the rammer.
The refractory base material mos~ suitable for the composition
according to the present invention is a sintered and/or fused
magnesia, preferably having an ~IgO content above 85 percent
by weight. Other re~ractory base materials having a sufficiently
high resistance to erosion can also be used. Among these are
spinel (such as magnesium aluminium spinel), magnesium silicate
material ~such as forsterite or olivine), zircon (zirconium
silicate), corundum, alumina or andalusite. In a manner known
per se, the refractory material is suitably applied in a grain
size providing for a relatively high packing density.
In order to reduce the effect of wetting by the melt or by
slags which might be present, the composition also contains a
solid carbon carrier in the form of graphite, carbon black,
ground coke powder, crushed carbon electrodes, breeze and the
like or mixtures thereof, providing a high content of residual
carbon.
In carbon bonded masses, the frequently occurring oxidizing
atmospheres can cause the strength values to drop due to carbon
consumption. In these cases, the mass should contain l to 7
percent by weight o~ an antioxidant which can be a metal powder
such as aluminiwll, silicium, magnesium or alloys, and/or a
finely ~round carbide such as silicium carbide or boron carbide.
The metal oxides resulting from oxidation of these substances
will prevent oxidation of the carbon which is essential for
maintaining the bond and for protecting the lining against
steel and slag infi]tration. The use of such substances as
antioxidants is well known. Antioxidants are not required in
installation areas which are not exposed to oxidation.
~ ' ' "
. . .
~8~3~
-- 7
'I`lle follo~ing exa~ )les show the compollents of a number o~
ready-for-use compositions according to the present invention.
'I`h~se compositions have a shelf liEe o~ approximately 3 mon~hs
and are characterized by a very good resistance to melts and
slags, low ~:ilatation and very good thermal shock resistance.
E x a In p 1 e l:
sin~ered magnesia with 97 percent by weight of MgO and
0.2 percen~ by weight of Fe2O3 3 - 5 mm 10% by weight
" 1 - 3 mm 36~ by weight
0.1 - 1 mm 15 ~ by weight
0 - 0.1 mm 22~ by weight
Novolak 4 ~ by weight
graphite 3 ~ by weight
carbon black 2 ~ by weight
magnesium powder s ~ by weight
silicone fluid 3 % by weight
: E x a m p 1 e 2:
sintered magnesia with 86 percent by weight of MgO and
3.5 percent by weight of Fe2O~0 - 3 mm 81 ~ by weight
Novolak 5 % by we.ight
carbon black 5 % by weight
silicium carbide SiC S ~ by weigh-t
parafin-base oil 4 % by weight
E x a m p 1 e 3:
zircon ZrSiO~ 0 - 5 mm 84 % by weight
crushed carbon electrodes 0 - 0.2 mm 8 ~ by weight
solution consis-ting of
37.5 percent by weight o-~ Novolak and
62.5 percent by weight of etllylene glycol 8 ~ by weight
