USE OF A WIRE MESH

UTILISATION D'UN TREILLIS DE FIL METALLIQUE

English Abstract

The invention relates to the use of a wire mesh coated with a material that
can be burnt out for the production of gas flush elements, notably to form a
porous network inside a ceramic matrix material after said coating material
has burn out.

French Abstract

L'invention concerne l'utilisation d'un treillis de fil métallique enrobé d'un matériau pouvant être consumé par le feu pour la fabrication d'éléments de type tampon poreux; notamment pour former un réseau de pores à l'intérieur d'une matériau matriciel céramique, après combustion complète dudit matériau d'enrobage.

Claims

6
Use of a Wire Mesh
Claim
1. Use of a wire mesh coated with a material which can be
burned out, and fabricated as a self-supporting formed
body in the production of ceramic gas purging elements
for forming a network of pores within a ceramic matrix
material after burning out said coating material.

Description

CA 02278473 1999-07-16
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DID 13940
Use of a Wire Mesh
Specification
The invention refers to the use of a wire mesh being coated
by a material which can be burned out, and being fabricated
as a self-supporting formed body.
Such a wire mesh, which, for instance, is plastic-coated, is
known for constructing fences, for example.
By the present invention a totally different use of such a
wire mesh is presented, that is for the production of
ceramic gas purging elements and in this for forming a
network of pores within a ceramic matrix material after
burning out said coating material.
Several techniques are known for producing such refractory
ceramic gas purging elements, mostly in the form of discrete
gas purging plugs. Particularly, this concerns the formation
of pores or channels through which a treating gas may be
injected into the molten metal by the gas purging plug.
Basically, three different types of such gas purging
elements are known, that ist:
1. gas purging plugs with undirected porosity
2. gas purging plugs with directed porosity
3. so-called gas purging plugs with slitlike channels.

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The invention is directed to the second group.
It can be gathered from the DE 195 04 941 A1 that gas
purging plugs are known, wherein the gas passage channels
are formed with the aid of a three-dimensional network
structure wich is produced within the monolithicly cast
refractory workpiece with the aid of a tensioning device.
The production of that gas purging plug is described as
relatively expensive.
Also, the same document refers to known purging plugs
according to DE-OS 38 23 897, wherein threads or stripes are
inserted into a casting mould, also with the aid of a
tensioning device, which can be pulled out or burned out
after the formed piece having set.
The technology describe above for forming channels of pores
within refractory gas purging elements has been accepted,
particularly for the following reasons: the channels
(channels of pores) resulting after burning out the threads
or strips mostly consisting of plastic may only have a
relatively small cross section (diameter), a maximum cross
section of 1 mm being envisaged in most cases. With larger
cross sections the risk of infiltration of molten metal
increases considerably. However, plastic threads or strips
having such small cross sections have only an insufficient
inherent stability so that they have to be arranged in said
tensioning devices. Then, they are cast around mostly with a
refractory casting material. After the refractory material
is set the plastic inserts are burned out later in tempering
necessary anyway in most cases and/or burning the gas
purging element.
On the other hand, the invention provides a substantial
technical improvement in that said tensioning devices may be
omitted.

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It sticks to the technology of channel formers which can be
burned outs however, no threads or strips of plastic only
but wire meshes being coated by a material which can be
burned out are used, which have a considerable inherent
stability corresponding to the stability of the metallic
basic body and, accordingly, need no or no considerable
additional anchorage.
If, for example, the wire mesh is fabricated having a
cylindrical shape, it is simply placed on the bottom of a
mould for a gas purging plug and subsequently cast around
(cast over) with a refractory material. After setting and
removing the mould the gas purging plug may be tempered
and/or burned to eliminate the coating material which can be
burned out so that annular channels result around the "wire
ropes", along which the treating gas can be transported
through the gas purging body.
It is evident that by selecting appropriate, mostly metallic
materials with very small diameters (cross sections) a wire
mesh having an appropriate inherent stability may be
produced, which is sufficient to keep the formed body stable
in shape while casting over the ceramic material. The
coating material may be applied in a thin to very thin
layer. It may consist of plastic but also of wax, paraffin
or like materials which can be burned off.
Also with respect to the shape of the cross section of the
individual wires, the idea of the invention is not subject
to limitations. Wires having circular cross sections,
angular cross sections or the like may be used.
Also, the geometry of the workpiece is almost arbitrary. So,
in addition to the cylindrical shape mentioned above the
wire mesh may have the shape of a cone or a truncated cone.
Cylinder-like shapes having angular cross sections are
conceivable as well; but also formed bodies having a semi-

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circular cross section, an L-shaped or a U-shaped cross-
section are part of the concept of a "formed body"
(workpiece)~ there is only the requirement that it is self-
supporting, if it is placed upon a bottom, for example, and
that also during the further production process for said
ceramic gas purging plugs.
The coated wire meshes can be used not only for the
production of cast gas purging plugs of course they can
also be employed when the ceramic material is pressed.
With respect to the concrete geometry the term "wire mesh"
allows any embodiment. So, the wire mesh and thus the later
structure of the channel system of pores may have a net-like
shape. But also main wires (main channels) extending more or
less coaxially to each other are conceivable as well, which
are connected by individual transversal channels
(transversal wires).
A coiled shape of individual wires, possibly on a basic body
of wires, is conceivable as well.
Of course, several wire meshes of said type can be
fabricated side by side or coaxially.
The wire mesh can be used not only in the area of discrete
gas purging elements but also in the area of monolithic gas
purging elements (gas purging devices). So, it may be
inserted into the hearth bottom of an electric furnace and
cast around with a monolithic ceramic mass.
Necessary gas supply elements are associated in an actually
known manner.
The wire thickness (width, length or diameter) is typically
0,1 to 1,0 mm. The coating may have a very small diameter
(thickness), in order to impede an infiltration of molten

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metal after its removal (for example by chemical reaction,
fusing or burning out). The thickness may be smaller than
0, 3 mm, also smaller than 0, 1 mm. With a small slit width a
relatively large cross section of purging is obtained
because of the ring channel structure of the channels.