Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an internally cooled
roller for a continuous casting plant, in particular a supporting
and guide roller, this having a casing of copper or alloys that
surrounds a core of ferrous material and which is joined to said
core, and with a wearing layer that surrounds this casing, and to
a process for producing this.
In continuous-casting plants, the rollers, in
particular the driven rollers that are directly adjacent to the
casting die, are exposed to a great deal of wear that is caused
by the hot billet. For this reason, over the course of time,
many attempts have been made to optimize the wear resistance of
these rollers.
Japanese document Sho-52-40608 describes an internally
cooled continuous casting roller with a core, a casing that
surrounds the core, and a wearing layer casing -that surrounds the
casing. The casing around the core is o copper, copper-nickel
alloy, a copper-aluminum alloy, or aluminum. The wearing layer
or casing is OI steel or cast iron and is joined to the inner
casing, in particular, by shrink fitting.
This document describes the basic construction, which
involves enclosing the core of a continuous casting roller with
a casing of copper and then protecting this against wear by means
of a second casing; however, thermal conductivity is reduced by
the steel or cast casing that is of lower thermal conductivity
than copper. In addition, the thickness of the walls, which is
required for reasons of strength and is needed to shrink the steel
or cast casing into place, also has a negative effect on thermal
conductivity.
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German disclosure document DE 26 36 199 Al describes a
process for producing quenched and drawn rollers wi-th a
protective layer for continuous casting plants. The protective
layer of a chromium-nickel alloy is applied by spraying and then
sintered. Finally, the protective layer is machined mechanically
to a final dimension of at least 1 mm.
The disadvantage of metalliæing protective layers is
their low adhesion, since these are only cramped mechanically to
the roughened surface of the basic material. In addition, these
layers cannot be applied at an even wall thickness, so that
secondary processing is required.
A newer patent specification, DE 37 35 38~ Cl,
describes an internally cooled roller with a wearing layer -that
is applied by buildup welding. The wearing layer is arranged on
a casing of iron rods and interposed welding fillers, the iron
rods covering open cooling channels that are machined into a
core. The wearing layer is, if necessary, applied in several
layers and then machined.
According to the invention, two layers with a total
thickness of approximately 5 to 8 mm are applied/ on the one
hand to avoid the welding material mixing with the casing, and,
on the other hand, to maintain a required 2 mm final machining
allowance.
All of the proposaIs des~ribed-abo~e-ent~iT the common
disadvantage that the transfer of heat from the billet to the
cooling agent is reduced by the thickness and poor thermal
conductivity of the wearing layer.
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It is the task of the present invention to create an
internally cooled, dimensionally stable, roller for a continuous
casting plant, which has high resistance to wear and, at -the same
time, good thermal conductivity, and to describe a process for
producing such a roller.
According to one aspect of the present invention -there
is provided an internally cooled roller for a continuous casting
plant, said roller comprising a casing of copper or alloys that
surrounds a core of ferrous material and which is joined to said
core, and with a wearing layer that protects the casing, wherein
the wearing layer consists of an in-termedia-te layer that is of a
thermal conductivity that is lower -than that of copper that is
applied to the casing and a-t least one covering layer that is
applied -to the intermedia-te layer by means oE build~p welding~
According to a further aspect of the present inven-tion
there is provided a process for preparing an internally cooled
roller as defined above, comprising applying an intermediate layer
by galvanic means to -the casing of copper or copper alloy and
applying at least one covering layer to the intermediate layer by
resistance roller seam buildup welding.
In some preferred embodiments: the intermediate layer
is of nickel and is applied by galvanic means; the thickness of
the intermediate layer is 0.3 to 1 mm; the covering layer that is
applied by resistance roller seam buildup welding is of a
thickness of at least 1 mm~ in particular from 0.2 to 0.5 mm;
the covering layer is of an Ni-Cr-B alloy; the cov~ring layer
comprises a mechanically resistant material, the covering layer
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is formed in several layers; the roller is a supporting or guide
roller.
The process is characterized in that an intermediate
layer is applied by galvan.ic means to the casing tha-t is of
copper or a copper alloy, and then at least one covering layer
is applied to the intermediate layer by resistance roller seam
buildup welding.
According to the present invention, the intermediate
layer, particularly such a layer of a galvanically applied
nickel layer, makes it possible to provide the copper casing with
a covering layer applied by buildup welding. The nickel, layer is
from 0.3 to 1 mm thick and is of a lower thermal conduc-tivity
than the copper casing. This layer prevents the loss o~ heat
through the copper casing during weldi.ng and thereby permits
complete fusion of the welding material and welding to the inter-
mediate layer. The use of a resistance roller seam buildup
welding process provides covering layers, in particular of
Ni-Cr-B alloys as a wearing layer with great adhesion on the
basic material, and also permits thicknesses of less than 1 mm.
In this method, it is also possible to incorporate mechanically
resistant materials such as wolfram carbide in the welding
substance in order to increase the wear resistance of the layer.
Rollers produced by the process according to the
present invention are distinguished, over all, by great thermal
conductivity and resistance to thermal shock because of the small
coating thicknesses of the nickel and wearing layers, outstanding
wear resistance that results from the layer applied by buildup
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welding, and great dimensional stability, which results Erom the
core that is of ferrous material.
Patent DD 225 334 Al describes a process and an
apparatus for resistance roller seam buildup welding with
additional materials, in particular metal powders (e.g., nickel-
chromium-boron-silicon alloys) to strengthen or clad s-tructural
elements (e.g., steel cylinders). However, the direct coating
of non-ferrous metals, in particular copper or copper alloys, is
neither described nor possible. In addition, the specification
contains no indications of coating thicknesses of less than 1 mm
that can be achieved.
The present invention is described below on the basis
of the drawing appended hereto.
Figure 1 shows a longitudinal section through a roller
with a helical channel for a cooling agent. Essentially, this
roller consists of a core 1 that is of Eerrous material, a
casing 2 of copper or a copper alloy that surrounds the core 1,
and a wearing layer that surrounds the casing 2. The wearing
layer consists of an intermediate layer 3 of nickel, which is
applied, in particular, by galvanic means to the casing 2, and a
coating layer 4 that is applied by buildup welding. The casing 2
is joined so as to be a snug fit, in particular by way of shrink
fitting, to the core 1. In addition, the casing 2 is secured by
welding 6 to the core 1 at least on one edge 5. A channel 7 for
a cooling agent is machined into the surface of the core 1 in
the form of a single or multi-start helical groove in the
longitudinal direction L of the core 1. The channel 7 for the
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cooling agent is covered by the tubular casing 2. Within the
area of the edges 5 of the casing 2, the cooling channel 5 is
connected through radial bores 8 to cooling agent connectors 9.
The cooling agent connectors 9 are arranged concentrically on
the core 1 and the journal that is adjacent thereto.
The present invention has been described on the basis
of a roller with a single layer covering layer 4; however, with
a covering layer that is applied by resistance roller seam
buildup welding it is possible to apply several layers for an
overall thickness that is, at the same time, less. Because the
concept of the present invention relates to coating the copper
casing, it can also be used for solid copper rollers without a
core.
