Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a refractory ceramic moulding
having an impregnation which at least partially fills the
open pore volume.
Impregnation with petroleum products such as tar or pitch
have long been known. It serves primarily to increase the
resistance of the refractory ceramic products in question to
infiltration or resistance to agressive slag. In order to
carry out the impregnation, the impregnation medium is
heated beyond its melting point by a heating apparatus to
obtain a specific vi,scosity so that the pore system can
subsequently be effectively filled with pitch or tar by a
vacuum/pressure method. ~
The disadvantages of this are, on the one hand, the -
impregnation temperatures needed and the subsequent
tempering of the impregnated mouldings at above 300C to
eliminate volatile constituents. Furthermore, the volatile
constituents constitute a major polluting factor.
A method of impregnating ceramic chimney pots is known from
German Patent 3704020, using a silicon impregnating agent to
` which methyl cellulose has been added, the impregnatir.g
agent being introduced into the open pore volume of the
chimney pot by a process of immersion which is only
selective from the outside to a depth of penetration of a
few millimetres.
Apart from the fact that silicon impregnation for refractory
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ceramic par~s such as are used in secondary meta]lurgy, for
example, does not give adequate temperature resistance the
selective filling of the pores would wash out in the short
or long term and the components would then be exposed once
more to the direct action of slag for example.
The aim of the invention is therefore to provide a possible
means of impregnating refractory ceramic mouldings having
open pores, which is not only easier than the known tar
and/or pitch impregnation but at the same time will cause
less damage to the environment.
The invention is based on the knowledge that the industrial
engineering process hither to used in the art
(liquidification of an impregnating agent in order to
introduce it into the open pores and then harden the
impregnating agent in the pores) can be achieved not only by
the use of temperature control but also by a totally
different, i.e. mechanical/physical method. - -
A slip having thixotropic properties can, in fact, be
changed into a more!or less viscous condition ~ in the cold
state~ - like heated pitch, for example. Depending on the
choice of the components for the slipj its viscosity can be
lowered to such a degree that it will fill the open pores
more or less completely and, after a suitable
mechanical/physical agitator unit has been switched off -
the slip will solidify again as a result of its thixotropic
properties and reliably seal the pores.
The thixotropic slip will be selected on the basis of the
following criteria:
- The particle size of the solid component of the
slip must be adapted to the size of the pores which
are to be filled, i.e. it must be smaller. In the
preferred rangej the average particle size of the
solid component of the slip should be at most 1/5 and ~-
preferably at most 1/10 of the average diameter of the
open pores of the moulding. The finer the slip
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ma~erial, ~he more completely it is able Lo fill even
small pores. It is therefore proposed, in a preferred
embodiment, that the particle size of the s]ip
particles should be adjusted to be less than 1/10 of
the average pore diameter. Thus, with an average pore
diameter of 30 microns, for example, the solid
component would then have a particle size of less than
3 microns.
The solid component is preferably a ceramic component
which itself has a high fire resistance. When a basic
product is impregnated the filling material will be a
basic one and when an acidic product is filled the
slip component will be acidic. Micronised corundum or
finally divided magnesite may be mentioned by way of
example. Of course, amphoteric substances may also be
used.
For the preparation of the slip this will contain, in
addition to the solid component, a framework forming
and/or liquid component which is preferably a resin,
e.g. a phenolic resin. The resin simultaneously
introduces a carbon component into the slip which will
crack when the impregnated moulding is subsequently
heat treated at 150 to 200 ~, for example, so as to
form a carbon framework for the refractory ceramic
particles which will have the effect of further
increasing the stability of the impregnating medium.
The most general embodiment of the invention is described by
the feature of claims 1 and 7.
The solid content of the impregnating agent should be at
30 least 40% by weight. The higher this content, the greater
the level of filling of the pores.
The slip preferably contains an additive to reinforce the
thixotropic properties. Such additives includej for --
example, methyl cellulose as well as other wetting agents
such as alkyl-aryl-polyoxyethanol.
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The proposal according to the invention has a number of
advantages, namely:
- The impregnation may be carried out ~in the cold
state~, i.e. at room temperature, for example. This
will save the energy costs which are necessarily
incurred, for example, by the melting of tar and
pitch.
- The impregnating agent may contain highly
refractory ceramic components which have better heat
properties and better resistant to infiltration than
tar or pitch. -
- There is absolutely no need for the tempering which
is necessary after impregnation according to the prior
art in order to evaporate any volatile components. In
any case, the products are dried at temperatures not
exceeding 200C in order to expell the liquid
components or promote the carbonising of the
carbon-contain~ing component so as to form a
stabilising carbon framework. However, this process
could also be carried out ~in situ~ during subsequent
use.
- The impregnating method proposed does not produce
any environmentally harmful emissions. -
The mechanicallphysical agitator means envisaged for --
liquifying the thixotropic slip may for example consist of
mechanical vibrators or ultrasound equipment. Thus, the
products to be impregnated might be placed, for example, in
a vessel filled with the slip. Subsequently, either the
whole apparatus is vibrated or the slip is acted upon by
ultrasound equipment so that in either case the thixotropic
structure of the slip is broken down and the slip is able to
penetrate into the open pores. The impregnating process may ~ i !:
be additionally aided by a pressure/vacuum device such as is
already known in the art.
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Further feat.ures of t:he invention will become apparent from
the features of the sub-claims and the other documents of
the application.
The invention can be applied to all types of refractory
products, for example in the field of sliding plates, ladle
bricksj bricks for the slag area of metallurgical vessels,
tank blocks used in glass manufacturing, etc.
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