Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to electric heat conductors,
their method of manufacture and components incorporating the
heat conductors and the method of manufacture of the components.
In conventional wear parts, e.g. parts in the form of
sliding plates for gate valves on containers for metal melts
according to Swiss Patent No. 444,390, a metal resistance wire
is embedded or moulded in the part to serve as a heat conductor.
German Patent No. 402,861 discloses, by way of example, a process
for the production of heating elements from silicate materials
containing carbon. In this process the red-hot basic part is
exposed to a stream of oxygen which oxidises the carbon on the
surface to carbon dioxide and after this oxygen treatment the
surface is provided with an enamel coating which renders the
element airtight. In this way the carbon exposed to the oxygen
in the air is preserved. German Patent No. 82,455 discloses a
process for the production of heating rods, in which ~e principal
constituents are silicon and carbon, and which are obtained by
heating carbon-containing members in a bed which produces silicon
vapour, so that various parts of the member to be treated are
embedded in various bed mixtures in order to produce varied
silicon content at various points.
The object of the present invention is to provide an
electric heat conductor which when used in wear parts, particu-
larly those made from refractory concrete, make it possible to
heat these wear parts for a relatively long time to relatively
high temperatures of, for example, 1500C, so that these wear
parts can be used in gate valves in which the steel melt can
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be effectively prevented from freezing so that the gate valve
can be used for multiple pourings.
According to one aspect of the present invention, an
electric heat conductor suitable for embedding or moulding in re-
fractory parts such as wear parts made from refractory concrete
whirh come into contact with melt metal, for example plates or
housings of gate valves, comprises approximately 50 to 70%, pre-
ferably approximately 60%, graphite (e.g. natural graphite com-
prising crystal platelets of some tenths of a millimeter in size),
approximately 2 to 10%, preferably approximately 8% Si metal powder
and approximately 10% binding pitch.
A heat conductor of this type is not solid even at
1500C but remains soft. Thus it cannot crack, is not affected by
expansio~ and contraction of the plate material and constantly
absorbs thermal variations in length and volume. The conductor
can be set so that an optimum specific resistance of 0.05 Ohm.cm
can be achieved. The ma~mum current density should not exceed
30 A/cm . The heating capacity can be 1.5 to 2kW. The heat con-
ductor is refractory and thus a refractory component of the wear
part. Thus simple production of a refractory member with electrical
resistance heating for relatively high temperatures is possible,
whereas this was not possible in earlier metal resistance wires.
No thermal tension occurs in the wear parts which can be heated.
With the graphite content the conductivity of the heat
conductor can be altered, the Si metal dust improves the oxidation
stability since it holds off oxygen from the graphite, and the
binding pitch, apart from its binding function, also
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serves to set the heat resistance at the most uniform current
density.
According to a further aspect of the present invention,
the electric heat conductor has a content of approximiately 5
to 20~, preferably 10~, anhydrous clay. The anhydrous wind-
dried plastic binding clay improves the workability of the heat
conductor.
Preferably the heat conductor also comprises approxi-
mately 5 to 20%, and preferably 10~, SiC powder which provides
an optimum strength characteristic.
According to a further aspect of the present invention,
there is provided a method of manufacturing a heat conductor of
the type described above wherein initially the quantities of
Si metal powder and powdered or liquid binding pitch and
optionally clay and/or SiC powder are mixed together and then
the quantity of graphite is added to the mixture. This method
has been found to provide the best possible conductivity of the
heat conductor.
In use, the electric heat conductor of the present in-
vention is embedded or moulded in a wear component, preferablymade from refractory concrete, wherein the component is adapted
for use in the discharge region of a gate valve of containers
for a metal melt such as steel, the component being in the
form of plates or housing with the heat conductor made from
an electric heat conductor of the type described above.
The heat conductor may be preformed and isostatically
pressed before insertion into passages in the body of the
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wear component. Alternatively, the material from which the
heat conductor is to be made may be introduced into passages
formed within the body of the wear component and cured therein.
A heat conductor may be located within an A12O3 ceramic pipe.
This serves to ensure that the heat conductor will have a uni-
form cross-section. In addition, the ceramic pipe serves to
protect the heat conductor against oxidation and also to pro-
vide protection against breaking of the heat conductor rods.
The ceramic pipe may also be protected against oxida-
tion by surrounding it by a plastic foil made from polyamideor polyester.
It should be noted that an optimum heating effect can
be achieved with the heat conductor when it is arranged in the
form of straight unbent rods. For this reason, a wear com-
ponent in the form of a slide plate preferably has at least
two parallel embedded heat conductor rods with a diameter of
preferably between approximately 5 and 10 mm, the working sur-
face being located between the heat conductor rods and the rods
being located at a distance preferably from approximately 10
to 30 mm from the discharge opening.
The wear component may be in the form of a housing
characterized by having several heat conductor rods distributed
about the periphery thereof and extending substantially axially
of the housing. Again, the heat conductor rods are preferably
straight. The heat conductor rods of the wear component
preferably project approximately 20 to 50 mm from the wear
component so that it is possible to locate the electrical
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connections externally of the wear components so that they
can be cold.
The electrical connections are preferab~y arranged
over an area of 1 to 5 cm2 on the surface of the projecting
part of the preformed heat conductor rods so as to prevent
overheating.
The wear component is preferably impregnated with a
tar which provides additional protection against oxidization.
The wear component is burned before its first use.
According to a further aspect of the present invention
there is provided a process for the production of a wear
component wherein a proportion of the material capable of
vibration and made from chemically or hydraulically setting
refractory concrete, produced for example on the basis of
tabular alumina with cement, is introduced into a mould,
vibrated and a groove or passage is formed therein, the heat
conductor is then introduced into the groove or passage as
a shapeless material or as a preformed heat conductor element,
optionally after being introduced into an A1203 ceramic pipe
and optionally surrounded by a plastic foil, and then the
second proportion of the refractory concrete material is put
into the mould and vibrated to compress it, hardened and then
optionally impregnated with tar and/or burnt.
According to yet another aspect of the present inven-
tion, a process for the production of a wear component in-
cludes the steps of arranging preformed isostatically pressed
elements, optionally after insertion in an A12O3 ceramic pipe
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and optionall~ after surrounding with a plastic foil, in a
mould in the position they are to take up in the moulded
product and then a material which is capable of being vibrated
and which is made from chemically or hydraulically setting
refractory concrete, produced for example on the basis of
tabular alumina with cement, is introduced into the mould,
vibrated, compressed and hardened and optionally impregnated
with tar and/or burnt.
The invention will be more clearly understood after
reference to the following detailed specification read in
conjunction with the drawings wherein,
Fig. 1 is a diagrammatic representation of a slide
plate of a gate valve in horizontal seciton;
Fig. 2 is a diagrammatic pictorial representation of
a housing with heat conductor elements located therein;
Figs. 3a and 3b are partially sectioned end views of
a wear component illustrating alternative methods of forming
the current connections.
The sliding plate 4 shown in Fig. 1 has two straight
conductor rods which are parallel to the longitudinal edges
and to each other and which are accommodated in A1203 ceramic
pipes 1, the ends of which project from the sliding plate 4.
Between the heat conductor rods 2 are the discharge opening
6 and the working surface 9 of the sliding plate 4. In each
opening of the ceramic pipes 1 the current supply 5 is led
to cap-shaped dlectrical connections 3 which are let into the
heat conductor 2.
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In a housing 7, which is a wear part, the heat con-
ductor rods 2 extend substantially in the axial direction, i.e.
with only a slight inclination which is between the inclina-
tion of the inner surface of the housing and that of the
outer surface thereof. These heat conductor rods 2 are
equally straight and are held in ceramic pipes 1, the ends of
which project from the housing 7 where the current is supplied
as shown in Fig. 1. In the illustrated example four heating
rods 2 each offset by 90 are arranged in the wall of the
housing 7.
Fig. 3a shows in detail the arrangement of the electri-
cal connection 3 to the current supply 5 which has already been
described in connection with Fig. 1.
Fig. 3b shows in detail a current connection 3 of a
heat conductor 2 which is inserted in a passage 8 without a
special ceramic pipe 1.
