Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ROLL FOR METAL PROCESSING, IN PARTICULAR
A CONTINUOUS CASTING ROLL, and Method of Producing Such a Roll
The invention concerns a roll for metal production and/or
metal processing, especially a continuous casting roll, which
has a roll body made of metal and a coating of wear-resistant
material applied on the roll body, where the coating contains
electrodeposited nickel and where the surface of the coating
forms the working surface of the roll.
The strand guide rolls have a great deal to do with the
satisfactory operation of a continuous casting plant as well
as with the quality of the cast product and the economy of the
plant. The function of the strand guide rolls is to support,
guide, bend, and convey the solidified strand after it has
left the mold. In this connection, the roll bodies and the
bearings of the segmented rolls are subject to high thermal,
mechanical, and corrosive chemical stresses.
The thermal stress arises from direct contact of the
surface of the roll body with the cast strand, which has a
temperature of 800 C to 1,200 C. The mechanical stress is the
result of ferrostatic forces, bending and straightening
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forces, and drive forces that must be transferred from the
roll to the strand. In addition, the rolls are subject to
wear due to friction with the strand. Due to the large
amounts of cooling water that are needed and the high
temperatures in combination with aggressive chemical
compounds, which are introduced, for example, by the use of
casting flux, it is also necessary to take into account the
corrosion characteristics and the corrosion protection of the
materials and parts used for the roll.
It is well known that the rolls of a continuous casting
plant can be produced from a heat-treatable steel as the base
material (e.g., 21 CrMoV 511 V, 16 CrMo 44, 24 CrMo 5, and
S 355), which is capable of absorbing the high mechanical
stresses. However, this steel is usually less well suited for
permanently withstanding the thermal and corrosive chemical
stresses. To realize adequate resistance to high temperatures
and corrosive chemical effects as well, it is known that
buildup welding can be used to cover the surface of the roll
body with a soft martensitic material. However, this
technique is relatively cost-intensive.
A roll of this general type is known from EP 1 555 074 Al
and EP 1 468 761 Al. EP 1 582 279 Al describes a similar
solution. WO 96/02340 describes a casting roll that is
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furnished with an outer wear-resistant coating.
DE 40 27 225 C2 discloses a method for producing a
continuous casting roll that consists of a core of iron
material covered with a jacket of wear-resistant material. A
layer of copper or copper alloy is provided between the outer
jacket and the core of iron material. To optimize the thermal
conductivity of the roll, a nickel coating is electrodeposited
on the layer of copper. This intermediate nickel coating is
then covered with a wear-resistant cover layer of a nickel-
chromium-boron alloy by buildup welding.
US 5,161,306 also proposes the application of a wear-
resistant layer on a roll body that is coated with
intermediate layers; in this case, the wear-resistant layer
consists of chromium oxides (CrZ03).
US 2002/0056539 Al also proposes the application of a
wear-resistant layer on a continuous casting roll; in this
case, the wear-resistant layer is based on nickel and contains
carbon, chromium, and molybdenum.
Other rolls with various wear-resistant coating materials
are disclosed by JP62-183950 Al, JP62-230462 A, JP63-086856 A,
JP60-030560 A, JP59-129754 A, and JP62-207549 A.
The objective of the invention is to remedy the
disadvantages described above and to create a roll, especially
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a continuous casting roll, which has sufficient strength and
at the same time is capable of withstanding the thermal,
abrasive mechanical, and corrosive chemical stresses that
arise during the operation of the roll, with it being possible
to operate the roll for the longest time possible and with
little or no geometric change in the roll. At the same time,
it must be possible to produce the roll at low cost. A
further objective of the invention is to propose a
corresponding method for producing a roll of this description.
The solution to this problem by the invention is
characterized by the fact that, besides electrodeposited
nickel as the base material, the coating contains ceramic
particles, which are carbides of titanium (Ti), tantalum (Ta),
tungsten (W), zirconium (Zr), boron (B), chromium (Cr), and/or
silicon (Si), or oxides of aluminum (Al), chromium (Cr),
silicon (Si), beryllium (Be), or zirconium (Zr), where the
amount of ceramic particles in the nickel or nickel alloy is
15-40 vol.%, and preferably 25-30 vol.%.
The invention is thus novel in relation to previously
known solutions by virtue of the fact that the wear-resistant
coating, whose surface forms the working surface of the roll,
is applied by a galvanic, i.e., electrolytic, method.
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The thickness of the coating applied by the galvanic or
electrolytic process is preferably 0.01 mm to 10 mm, and
especially 0.05 mm to 2 mm.
In one embodiment of the invention, the coating consists
of pure nickel. However, it is preferred that the coating
contain other constituents besides nickel. Specifically,
these other constituents besides nickel can be, for example,
one or more of the constituents cobalt (Co), phosphorus (P),
iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), and
chromium (Cr).
In this connection, in a preferred embodiment, the
coating consists of a nickel-cobalt alloy in which ceramic
particles of silicon carbide are incorporated.
In accordance with a preferred embodiment, the particle
size of the ceramic particles is 1-5 pm. In another
embodiment, the ceramic particles are much smaller, namely, 10
nm to 1,000 nm.
In accordance with an advantageous embodiment of the
invention, not the least of the advantages realized in this
way is that the hardness of the surface of the coating is 300-
500 HV1 (Vickers hardness),and preferably 350-450 HV1.
A method for producing a roll for metal production and/or
metal processing, especially a continuous casting roll,
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, , . involves the following steps:
(a) production of a metal roll body;
(b) immersion of the roll body in an electrodeposition
bath;
(c) electrodeposition of a coating on at least part of
the surface of the roll body, where the coating consists at
least partly of nickel, and the surface of the coating forms
the working surface of the roll.
The proposal of the invention is thus no longer aimed at
providing the base material of the strand guide roll with a
soft martensitic surface layer that is welded on, as in the
prior-art methods, but rather at applying a coating of nickel
or a nickel alloy by electrodeposition.
In this connection, it is advantageous if a large number
of rolls can be simultaneously coated in electrodeposition
baths, so that the product costs per roll remain low. In
addition, the thickness of the applied coating can be easily
defined and varied by the residence time of the rolls in the
electrodeposition bath.
The electrodeposited coating is thin and effectively
protects the base material of the roll from corrosive attack.
At the same time, the coating is very hard and has good
resistance to high temperatures and good resistance to
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, . ,
scaling. The wear resistance of the continuous casting roll
is reliably and inexpensively improved in this way. The
proposed rolls thus have a longer service life, which results
in a corresponding reduction of costs for the operator of a
continuous casting plant.
The drawings illustrate a specific embodiment of the
invention.
-- Figure 1 shows a schematic side view of a continuous
casting roll.
-- Figure 2 shows the detail Z from Figure 1.
-- Figure 3 is a schematic drawing of the setup of a
galvanic or electrolytic coating system with two continuous
casting rolls to be coated.
Figure 1 shows a continuous casting roll 1, which
consists of a roll neck 9, which is of no further interest in
the present discussion, and of a roll body 2, which in the
present embodiment is cylindrical. The roll body 2 has a
coating 3 of wear-resistant material, the structure of which
is illustrated in greater detail in Figure 2.
The coating 3 has a coating thickness D, which can be,
for example, 0.05 mm to 2.0 mm. The essential feature is that
the surface 4 of the coating 3 is the working surface of the
roll 1. In the case of a continuous casting roll, the working
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~ ^
surface has contact with the continuously cast strand, which
is still hot, and is thus subject to high thermal, mechanical,
and corrosive chemical stress.
The coating 3 consists of nickel or a nickel alloy, which
is applied to the roll body 2 galvanically (electrolytically)
(in this connection, see Figure 3).
To increase especially the mechanical and thermal
resistance of the surface 4 of the roll 1, the surface is
provided with a considerable proportion of ceramic particles 5
with a mean particle diameter d, which in one embodiment of
the invention can vary within the range of 1-5 pm. However,
an alternative embodiment provides for the use of
nanoparticles, i.e., the diameter d in this case is within the
range of 10 nm to 1,000 nm.
Figure 3 illustrates the basic procedure for producing
the continuous casting roll 1. It shows a coating bath 6 that
contains a suitable plating solution for electrodeposition.
The solution can be an acid, e.g., sulfuric acid (HZSO4). An
anode 7 is submerged in the bath. It consists of an ingot of
nickel and constitutes the consumable electrode. In the
example illustrated here, two rolls 1 are also submerged in
the coating bath. The roll necks 9, which are not to be
coated, are covered with covers (not shown). The two rolls 1
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., .
constitute the cathode 8. The anode 7 and cathode 8 are
connected to a direct current source 10, which can be
regulated or automatically controlled by means that are
already well known in themselves.
When the current flows, a metallic precipitate that
consists of nickel is electrochemically deposited on the
(uncovered) surface of the rolls 1. The electric current
removes metal ions from the consumable electrode 7 and
deposits them on the surface of the rolls 1 by reduction.
This causes the roll 1 to be coated uniformly and on all sides
with nickel. The longer the rolls 1 remain in the bath 6, the
thicker the coating 3 of nickel on the roll body 2 becomes.
The ceramic particles introduced in the coating make it
possible to optimize the mechanical/technological properties
of the nickel or nickel alloy coating for the each intended
application. In the present situation, it is desired that a
continuous casting roll be provided with a coating that is
chemically resistant and stable at high temperatures and has
very low wear rates when subjected to abrasive stress, but at
the same time can be economically processed during its
manufacture. For example, nickel compounds can be produced
that have an average hardness of 350-450 HV1 at room
temperature and can thus be worked with an acceptable degree
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, . , ` .
of effort and at the same time have low wear rates even at
higher temperatures.
Electrolytically produced metal alloy dispersions based
on nickel/cobalt, in which ceramic particles (preferably
silicon carbide) with a particle size of 1-5 pm or ceramic
nanoparticles with a size of 10 to 1,000 nm are incorporated,
are especially well suited for the proposed application.
The nickel that is used is preferably high-purity nickel
that has been compressively prestressed.
Preferably, therefore, an electrolytic surface treatment
of the roll body is carried out, in which a high concentration
of hard solid particles is incorporated in a ductile nickel
matrix. This combination imparts very good wear resistance to
the part to be protected, for the cast strand then no longer
runs directly on the metal of the metal matrix but rather on
the ceramic particles that protrude from the base contour of
the roll surface. This greatly reduces the abrasion of the
nickel and makes it possible to achieve the goal of coating
strand guide rolls for a long service life, i.e., for at least
years of use.
In this regard, it is also conceivable that several
coatings can be electrodeposited on the roll body, and it is
possible to apply the same coating material each time or to
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use different coating materials.
The continuous casting rolls can be used for all known
applications, i.e., especially in plants for the continuous
casting of carbon steel and stainless steel grades in ingots,
round bars, sections, slabs, and thin slabs. The roll
diameter (final diameter including the surface coating) of the
strand guide roll is usually in the range of 80-350 mm.
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List of Reference Symbols
1 roll (continuous casting roll)
2 roll body
3 coating
4 surface of the coating
ceramic particle
6 coating bath
7 anode (positive terminal)
8 cathode (negative terminal)
9 roll neck
direct current source
D thickness of the coating
d particle size of the ceramic particle
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