Note: Descriptions are shown in the official language in which they were submitted.
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Tra.nslated Text of WO 00/29146 (PCT/EP99/08442) with Amended
Pages and Clal>las Incorporated Therei.n
Mold Plate of a Continuous Caszing PlanG
The present invention relates zo a mold plate of copper for a
continuous casting plant, comprisirlg a working surface facing a
metal melt or a (partially) solidified metal strand during
operation of the continuous casting plant and comprising at leasc
one cooling surface contaczing a cooling medium during operation
of the conLinuous casting plant, wherein the mold place has a
heat conductivity and extends along a mold length in the casting
direction.
Such a mold plate is k.nown, for example, from EP 0 149 734 A1.
The mold plat.es have in their upper area a reduced heat
conductivity and a greater thermal resistance chan in the lower
area.
When caszing metal, in particular, steel, by continuous casting,
a high wear occurs on zhe mold places. Accordingly, the working
surface of zhe mold plate must be refinished from time to time
after a number of ladles which number depends on the conditions
of use of the mold plate. When doing so, the thickness of the
mold plate continuously decreases.
In order to cast high-quality steel strands, the t.emperaLure of
the working surface must be within a predetermined range.
Moreover, the thickness of the mold plate must be within a
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permissible thickness range which is greater than the minimum
thickness required for mechanical reasons.
The application of layers, in particular, of nickel layers, onto
mold plates as such is already known. For example, reference is
being had to WO 97/12708 and Herrmann, "Handbook on Concinuous
Casting", Aluminium-Verlag, Dusseldorf, 1980. zn the prior art,
a nickel layer is however applied to the working surface of zhe
mold plate. It serves primarily for reducing the mold wear
during continuous casting.
It is an objecz of the presenz invention co develop a mold place
of che aforemenLioned kind such that it can be refinished more
often than was possible in the past when a minimally permissible
copper wall thickness has already been reached.
This object is solved in chac onco zhe cooling surface at least
in one portion thereof a layer with a heat conductivity is
applied and in that the layer heat conductivity of the layer is
smaller than the heat conductivity of the mold plate, that che
layer is substantially comprised of nickel, and that the layer is
a layer that is applied currencless onto the cooling surface in a
nickel bath.
It is particularly advantageous when the layer is comprised
substantially of nickel because the thermal expansion coefficient
of nickel is smaller than the thermal expansion coefficient of a
conventional mold plate of copper. The nickel layer is
preferably deposized currenciess onco the cooling surface of the
mold plate in a nickel bath with additives. This is so because
in this situation, concour-sharp coazings of the cooling surface
are possible. Moreover, the layer thickness is very uniform and
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the heat conductivity of the layer is considerably smaller than
that of nickel applied by electroplating. Independent of the
coating process, the layer heat conductivity should be
maximally 10 % of the heat conductivity of the copper of the
mold plate.
The insulating properties of the layer are even better when the
layer is comprised of five to twenty percent of phosphorus and
otherwise - aside from contaminants - of nickel. This is so
because in this case, the layer heat conductivity is less than
3 % of the heat conductivity of the mold plate made of copper.
The cooling surface can be formed as a cooling groove arranged
on a back side that is located opposite the working surface or
a cooling bore closed relative to the back side that is located
opposite the working surface.
The cooling groove has a bottom surface and sidewalls. The
layer can be applied only onto the bottom surface and/or also
onto the sidewalls, as desired.
When the layer extends from an upper edge, viewed in the
casting direction, across a layer length and the layer length
is smaller than the mold length, the temperature distribution
across the mold length can be influenced. The layer length is
at least 100 mm, preferably between 300 mm and 500 mm.
Alternatively, the layer can also extend over the entire mold
length.
In one aspect, the present invention provides a mold plate of
copper of a continuous casting plant, comprising a working
surface facing during operation of the continuous casting
plant a metal melt or a (partially) solidified metal strand
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and at least one cooling surface contacting during operation of
the continuous casting plant a cooling medium, wherein the mold
plate has a heat conductivity and extends in a casting
direction across a mold length, wherein on the cooling surface,
at least on one portion, a layer with a layer heat conductivity
is applied and in that the heat conductivity of the layer is
smaller than the heat conductivity of the mold plate, in that
the layer is substantially comprised of nickel, and in that the
layer is a layer applied currentless onto the cooling surface
in a nickel bath.
Further advantages and details result from the following
description of an embodiment in connection with the drawings.
In a basis illustration, it is shown in:
Fig. 1 a continuous casting mold in operation;
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Fig. 2 a decail of the mold plate with cooling elements;
Fig_ 3 a coating method; and
Fig. 4 a further detail of the mold plate with cooling bores.
According to Fig. 1, a continuous casting plant has mold places 1
made of copper. Each mold plate 1 has a working surface 2 which
extends in the casting direction x across a mold length L.
During operazion of the conLinuous casting plant, a metal melt 3,
in general, a steel melc, is located between the working surfaces
2. The metal melt 3 solidifies gradually to a meral scrand 4
which is removed in the casting direction x from the mold plates
1.
For a controlled solidificazion of the mezal melt 3 to a metal
strand 4, a considerable energy quantity, che so-called casting
heat, must be removed via the mold plates 1. For the purpose of
removing the casting heac, the mold places 1 have according to
Fig. 2 cooling surfaces 5 which contact a cooling medium, for
example, water (not illustrated) during operation of the
continuous casting mold. The cooling surfaces 5 are arranged on
the backside 6 which is positioned opposite the working surface
2. They are open toward the backside 6. They are moreover
formed as cooling grooves 5.
As already menzioned, the mold plate 1 is comprised of copper.
Ic has therefore a high heat conductivity W of, for example,
approximately 377 W/mK. In order to impart to the mold plate 1 a
greater thermal resistance, or a reduced total heat conductivity,
a layer 7 is applied onto che cooling surfaces S. This layer 7
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has a heat conductivity S which is considerably smaller than the
heat conductivity W of the copper plate.
According to the embodiment, the layer 7 is comprised
substanzially of nickel, having a phosphorus conzents of 5$ to
20 t. Preferably, the phosphorus contents is between 9t and 14
a, for example, 10 $ to 12 t. The heat conductivity of the layer
can be further reduced in that, in addition to zhe phosphorus
added to the nickel bath, also up to 30 t silicon carbide is
added. Otherwise, the layer 7 contains only minimal
conzaminants.
Preferably, the layer 7, as illustrated schematically in Pig_ 3,
is applied in that the mold plate 1 is introduced into a nickel
bath 8. Here, the layer 7 is applied currentless onto the
cooling surfaces 5. Such a nickel layer 7 has a layer heat
conductivity S which is, for example, approximacely only 5 W/mK.
The layer 7 has a layer thickness d which is, of course,
dependent on the residence cime of the mold plare 1 in the nickel
bath 8. By means of conventional nickel baths 8 layer
thicknesses d chac are between 40 pm and 80 m, for example, 60
m, can be applied to the coating surfaces 5. In a special
nickel bath 8 it is however also possible to apply a layer 7
having a layer thickness d of up to 200 m_
In principle, it is also possible to coat the backside 6
completely. Technically, this is the simplest approach.
However, ic is also possible to provide the backside 6, before it
is being coated with a layer 7, with a protective layer and to
apply che nickel layer 7 only onto the porcions that are not
covered.
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For example, che cooling grooves 5 have boctom surfaces 9 and
sidewalls 10 while between the cooling grooves 5 stays 11 are
arranged. 1t is, for example, possible to apply the layer 7 only
onto the bottom surfaces 9. However, it is also possible to
apply che layer 7 onto the bottom surfaces 9 and the sidewalls
10. Finally, it is also possible to apply the layer 7 over the
entire surface area, i.e., onto che bottom surfaces 9 and the
sidewalls 10 of the cooling grooves 5 as well as onco che
intermediacely positioned stays 11. According to Fig. 2, the cwo
lefc cooling grooves 5 are completely coated while only the
bottom surfaces 9 of the cwo right cooling grooves 5 are coated.
It is furthermore possible that the layer 7 extends over che
encire mold length L. This is the case for the oucer cooling
channels in Fig. 2. Alternatively, the layer 7 can extend from
the upper edge 12 only across a layer length 1 when viewed in the
casting direction x, wherein the lengch 1 is smaller than the
mold length L. The layer length 1 is preferably between 300 mm
and 500 mm, at least however 100 mm. This is the case for the
inner cooling channels in Fig. 2.
The mold plate 1 according to Fig. 4 differs from the mold place
1 according to Fig. 2 in thac, instead of the cooling grooves 5
which are open toward the backside 6, cooling bores 5' are
provided. In this case, the cooling bores 5' are also provided
with the iayer 7 wherein, as before, alternatively a complete or
only a partial coating over the length of the cooling bores 5' is
possible.
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Lisc of Reference Numerals
1 mold plate
2 working surface
3 metal melt
4 metal strand
cooling surfaces/cooling grooves
51 cooling surfaces/cooling bores
6 backside
7 layer
8 nickel bach
9 boLLom surface
sidewalls
11 stays
12 upper edge
d layer thickness
1, L lengths
N, S, W conductivicies
x casting direction
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