U.S. patent application number 10/472609 was filed with the patent office on 2004-05-27 for ceramic moulded body.
Invention is credited to Meier, Peter, Pischek, Stefan, Wikelmann, Manfred.
Application Number | 20040100003 10/472609 |
Document ID | / |
Family ID | 7694038 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040100003 |
Kind Code |
A1 |
Pischek, Stefan ; et
al. |
May 27, 2004 |
Ceramic moulded body
Abstract
The invention relates to a ceramic moulded body, the surface of
which is at least partly covered by a steel cladding, whereby the
steel cladding is at least partly coated with a fire-resistant
material on the surface thereof not covering the moulded body.
Inventors: |
Pischek, Stefan;
(Honigsberg, AT) ; Wikelmann, Manfred; (Krefeld,
DE) ; Meier, Peter; (Marktredwitz, DE) |
Correspondence
Address: |
WALKER & JOCKE, L.P.A.
231 SOUTH BROADWAY STREET
MEDINA
OH
44256
US
|
Family ID: |
7694038 |
Appl. No.: |
10/472609 |
Filed: |
September 19, 2003 |
PCT Filed: |
July 30, 2002 |
PCT NO: |
PCT/EP02/08439 |
Current U.S.
Class: |
266/286 |
Current CPC
Class: |
B22D 41/50 20130101 |
Class at
Publication: |
266/286 |
International
Class: |
C21B 007/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 2, 2001 |
DE |
10137758.4 |
Claims
1. Ceramic form (1), whose surface (9, 13, 15) is covered at least
sectionally with a steel covering (5), where the steel covering (5)
is covered, at least sectionally, in that part of its surface not
covering the form (1), with a scale-inhibiting substance (7).
2. Ceramic form (1) according to claim 1, as pouring spout for
metal casting.
3. Ceramic form (1) according to claim 2, as an interchangeable
pouring spout.
4. Ceramic form (1) according to claim 1, for a sliding value
system.
5. Ceramic form (1) according to claim 1, the steel covering (5) of
which rests directly on the surface (13) of the ceramic form
(1).
6. Ceramic form (1) according to claim 1, the steel covering (5) of
which is a sheet of steel.
7. Ceramic form (1) according to claim 1, the steel covering (5) of
which envelops the ceramic form (1) along its outer circumferential
surface (13).
8. Ceramic form (1) according to claim 6, the steel covering (5) of
which envelops the ceramic form (1) under pre-stress tension.
9. Ceramic form (1) according to claim 1, the scale-inhibiting
substance of which is a metal or metallic compound.
10. Ceramic form (1) according to claim 1, with a scale-inhibiting
substance in the form of a sheet (7) or a layer applied to the
steel covering (5).
11. Ceramic form (1) according to claim 1, the scale-inhibiting
substance of which consists of aluminum or an aluminum
compound.
12. Ceramic form (1) according to claim 1, the scale-inhibiting
substance (7) of which is sprayed onto the steel covering (5).
13. Ceramic form (1) according to claim 1, the scale-inhibiting
substance (7) of which forms a gas-tight seal with respect to the
covered surfaces of the steel covering (5).
Description
[0001] The invention concerns a ceramic form (workpiece), in
particular a form made of a refractory ceramic material. Due to
their fire-resistant properties, ceramic forms made of a refractory
ceramic material can be used for applications where they are
exposed to high temperatures, for example above 500.degree. C., and
even far higher.
[0002] For example, ceramic forms are used in metal casting, for
instance as the pouring spout in sliding gate systems; for example,
in continuous metal casting. Although the invention is not limited
to the application of ceramic forms for a pouring spout (nozzle/tap
hole) in sliding gate systems, it will be described hereinafter
using such an application by way of example.
[0003] In metal casting, pouring spouts (also called nozzles or tap
holes) in slide gate valve systems serve to convey the melt, for
example molten steel, from the ladle into the intermediate
container ("tundish") or from the tundish into the ingot mold. For
the necking down of the metal stream in these slide gate valve
systems, the pouring elements can be designed in the form of "top
hats" (plate with integral spout) or as interchangeable pouring
spout. With the interchangeable spout, the spout is a part separate
from the slide gate valve system, and thus interchangeable.
[0004] Ceramic forms in the shape of pouring spouts (nozzles) are
usually enclosed on their outer surfaces with a sheet-steel
covering. These help to improve the mechanical properties as well
as the chemical resistance of the spout. At the high temperatures
inherent in the casting process, the oxidizing atmosphere leads to
the formation of oxides (scale) on the surface of the steel
covering. This so-called scaling is due to the reaction of the
metal sleeve with the oxygen in the air. With iron materials, the
oxidation begins at above ca. 400.degree. C. and it becomes
especially active at temperatures above 600.degree. C. The
thickness of the scale layer increases with time and temperature.
Should the scale layer spall off, be removed by mechanical means,
or, as is usually the case under the stress of temperature changes,
develops cracks, the scaling of the steel sleeve increases
markedly. It can happen that the steel sleeve develops scale to the
extent that it can no longer perform its intended function of
improving the mechanical and chemical properties of the pouring
spout.
[0005] Although by adding special alloying elements to the steel of
the covering, such as create the forming of tightly adhering, dense
layers of scale, it has been possible to slow the speed of the
scaling process, such scale layers only possess low mechanical
strength, and they can be easily removed from the steel sleeve,
thereby exposing the unprotected underlying surface of the steel
sleeve to further scaling.
[0006] In practice, therefore, scaling has mostly been countered by
the use of buffer gases, especially argon, at high temperatures.
Such a gassing of the steel sleeve, however, is cumbersome and
expensive, and thus extremely uneconomical.
[0007] Moreover, argon gassing is not able to completely prevent
the scaling of the steel sleeve.
[0008] As a result, scaling of the steel sleeve occurs even with
argon gassing.
[0009] Where the scaling of the steel sleeve progresses too far,
and as a consequence it is no longer able to effectively protect
the ceramic form underneath, it then has become necessary to
replace the pouring spout together with the steel sleeve, even
though the ceramic form would permit a longer service life.
[0010] The invention has the objective of making available a
ceramic form with its surface covered, at least partially, by a
steel covering, that can be economically used, and on which the
steel covering undergoes reduced scaling, even at high
temperatures.
[0011] The invention arrives at the objective by means of a ceramic
form whose surface is at least partially covered by a steel
covering, where the steel covering, in that part of its surface
that is not covering the ceramic form, is at least partially coated
with a scale-inhibiting substance.
[0012] The reduction or prevention of scaling results in the
mechanical performance of the metal covering is maintained for a
longer time. This, in turn, means longer service life/durability
for the ceramic forms.
[0013] It has been found that the oxidation (scaling) of the steel
covering of a ceramic form, at those places where it is exposed to
high temperatures in an oxidizing atmosphere (for example, air),
can be effectively inhibited if the steel covering, at these
places, is coated with a scale-inhibiting substance. In this
connection, "scale-inhibiting" substances are understood to be
substances, which, based on their composition, possess a
comparatively higher resistance to scaling than the steel
covering.
[0014] Substances that may be used to inhibit scale formation are,
for example, metallic alumimum, chromium or silicon, or their
oxides (Al.sub.2O.sub.3, Cr.sub.2O.sub.3, SiO.sub.2), or other
alloys or compounds thereof, singly or in combination.
[0015] The steel covering may also be coated with a
scale-inhibiting substance in a manner such that, for example,
metallic chromium or aluminum are applied to the steel covering,
and are then "passivated" [[rendered passive]].
[0016] The scale-inhibiting substance can, for example, be applied
to the steel covering as a solid, and, in the case of a metallic
material, for example, as a sheet or plate. When sheeting is used,
they can be made to adhere to the steel covering by, for example,
welding or glueing them together. The sheet of scale-inhibitor can
also be applied to the steel covering by shrink- or press-fitting.
In particular, it is possible to arrange for the steel covering to
be covered by the scale-inhibiting substance in a manner such that
the steel covering, in those parts covered by the scale-inhibiting
substance, cannot come in contact with the surrounding gas
atmosphere. The lamination/coating, in other words, should be
gas-tight.
[0017] In using a scale-inhibiting substance in sheet form, the
facing surfaces of the scale-inhibiting sheet and the steel
covering can be made to exactly correspond dimensionally, so that
the scale-inhibiting sheet covers the entire surface of the steel
covering. It may suffice, on the other hand, for the
scale-inhibiting sheet to be attached in a gas-tight manner to the
steel covering just along its edges, perhaps by welding.
[0018] An alternative version may have the scale-inhibiting
substance applied to the steel covering as a liquid, for example,
by brushing or spraying (e.g. with flame or plasma sprayers), or by
having the steel covering impregnated with the liquid, with the
liquid subsequently converted into a solid which coats the steel
covering in a tight bond.
[0019] The scale-inhibiting substance may also be applied to the
steel covering in powder form, and is subsequently tightly bonded
with the steel covering.
[0020] It is generally sufficient to apply the scale-inhibiting
substance to the steel covering in a thickness up to 1 mm, for
example, in a thickness between 0.1 and 0.7 mm, or 0.2 and 0.5
mm.
[0021] As discussed earlier, the ceramic form can in particular be
a ceramic pouring spout as an interchangeable spout, in the
continuous casting of metals, and the following description will be
based, by way of example, on such a discharge nozzle.
[0022] The surface of the steel covering facing the ceramic pouring
spout can lie directly on the surface of the ceramic spout, and the
steel covering may, for example, by applied by shrinking a previous
heated steel sheet.
[0023] In one embodiment, the steel covering wraps around the outer
surface of the spout. A version such as this is known in the
present state of the art. Since the outer circumferential surface
(surface) of the spout is usually formed with rotational symmetry,
the steel covering can, in this case, be wrapped around the spout
in the form of a sleeve.
[0024] The facing surfaces of the steel covering and the ceramic
spout may be made to be matching in a way such that they come to
lie against each other over their entire surfaces. In this case,
the parts of the spout's surface that are covered by the steel
covering are directly covered by the surface of the steel covering
facing the spout. The mechanical strength of the ceramic spout can
be enhanced by having the steel covering pre-stressed in its seat
against the spout, for example by shrink-fitting. Alternatively,
the steel covering may be provided for with only its edges in
contact with the ceramic spout. The contact zone between the steel
covering and the ceramic spout may be made gas-tight.
[0025] Further features of the invention may derive from the
subclaims and other application documents.
[0026] There follows an expanded description of an illustrative
version of a ceramic form according to the application, using the
appended, highly schematized figure. Here, FIG. 1 shows a ceramic
form in the shape of a spout for continuous metal casting, in a
lateral cross section.
[0027] The pouring spout 1 consists of a ceramic form 3, covered in
part by a steel covering 5. The steel covering 5 is covered in part
by a scale-inhibiting substance 7.
[0028] The ceramic form 3 has rotational symmetry around its
longitudinal axis L. Also with rotational symmetry around its
longitudinal axis L, it has on its interior a channel 2 for the
passage of the molten metal. An upper cylindrical section A of the
ceramic form 3 adjoins below it a downward conically tapered
section B, followed by another cyclindrical section C, and finally
a conically tapering section D. The ceramic form 3 consists of a
standard refractory ceramic material. A top face 9 of the ceramic
form 3 has a recess 11.
[0029] On its outer circumferential surface 13, the ceramic form 3
is covered in part by the sleeve-shaped steel covering 5, which
consists of sheet steel. The steel covering 5 lies fully against
the outer circumferential surface 13. It starts at the upper edge
13o of the outer surface 13 and ends at a distance from the lower
edge 13u of the outer surface 13 in the region of section D. That
part of the circumferential surface 13 which extends in the area of
section D from the lower end of the steel covering 5 to the lower
edge 13u is identified with the reference 13f; it is the only
section of the outer surface 13 that is not covered by the steel
covering 5.
[0030] Moreover, the upper face 9 and the bottom face 15 of the
ceramic form 3 are not covered by the steel covering 5.
[0031] The section of the steel covering 5 which covers section D
of the ceramic form is covered by a scale-inhibiting aluminum layer
7. This aluminum layer 7 is placed (by shrink-fitting) as a sleeve
over the steel covering 5, and forms a tight bond with it. This
section represents the contact surface with a submerged entry
nozzle or tapping spout, and is subject to the strongest oxidation.
Accordingly, in this description of an illustrative embodiment, it
is only this section of the steel covering 5 that is encased by a
scale-inhibiting substance.
* * * * *