Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a liquid-cooled plasma
torch with transferred arc, its coolant, current and gas being
guided to the ignition and main electrode via ignition electrode
and main electrode lances consisting of coaxial tubes.
Plasma torches of this kind are known, for example,
from German OS 29 00 330, their main components consisting
essentially of a torch jacket with nozzles r a main electrode lance
with a main electrode and an ignition electrode lance with an
ignition electrode.
According to the state of the art all three aforenamed
components are as such structural units electrically insulated
from one another with their own water cooling. Both the ignition
electrode lance as well as the main electrode lance are liquid-
cooled, each lance consisting of tubes arranged coaxially to one
another. The end face of the outer tube o the ignition electrode
lance Eacing the ignition electrode is closed, this outer tube
accommodating the ignition electrode. The inner tube o~ the
ignition electrode lance leaves a gap towards the end wall of the
outer tube or the ignition electrode, the connection for the
coolant between the central bore of the inner tube and the
annular channel between the inner and the outer tube being
established through this gap. The current is guided via the outer
tube to the ignition electrode.
The outer tube of the ignition electrode lance is guided
via electrically insulating spacers or sleeves in the inner tube
of the main electrode lance. The ignition plasma gas is conducted
via the annular channel resulting between the outer tube of the
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ignition electrode lance and the inner tube of the main electrode
lance to the ignition electrode and the enclosing, nozzle-shaped
central bore of the main electrode.
According to the state of the art, a main electrode
lance consisting of three coaxially arranged tubes is used to
cool the main electrode. Through this an output and return
annular channel is provided for the coolant diverted at the inner
end wall of the main electrode. Depending on the design of the
connection between the electrode and the lance, the current can
be supplied to the main electrode via the inner and/or outer tube
of the main electrode lance. Electric insulation between the
outer tube of the main electrode lance and the inner tube of the
torch jacket and the nozzle is carried out by means of spacers in
the manner described above with respect to the front electrode
lance. The main plasma gas is also conducted in a corresponding
manner in the region between the main electrode and the nozzle.
Plasma torches known according to the state of the art
have the drawback that they are structurally verv expensive and
the heat losses along their jacket surface are relatively high.
It is therefore desirable to further develop the plasma
torch described at the beginning in such a way that its
construction can be simplified, that the heat losses occurring
hitherto can be reduced and that better efficiency can be
achieved.
The present invention provides a liquid-cooled plasma
torch with transferred arc, its coolant, current and gas being
guided to the ignition and main electrode via ignition electrode
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lances and main electrode lances consisting of coaxial tubes,
characterized by a common cooling circuit for the ignition
electrode lance and main electrode lance. Not only can this
advantageously result in a cost saving for tubes and seals~ but
the entire supply of cooling water to the plasma torch is
simplified considerably. ~oreover, the aiameter of the plasma
torch shaft can be kept substantially smaller, this corresponding
to a direct reduction in the torch jacket surface affected by the
outside temperature, i.e. the heat losses of the jacket are
reduced and the efficiency of the torch is improved. A smaller
diameter of the torch shaft also permits greater universality
with respect to the possibilities for using and installing plasma
torches in vessels of various types and sizes, for example ln a
smelting furnace, a ladle, a tundish or a vacuum installation.
Further developments of the inventive thought are
described in the sub-claims. Since the ignition electrode lance
is sealed vis-à-vis the coolant chann~ls and electrically
insulated vis-à-vis the main electrode lance or main electrode,
the ignition gas can be guided directly into the ignition electrode
lance, whereby it is simultaneously cooled from the outside. The
main electrode and ignition electrode lances preferably comprise,
all told, only three tubes arranged coaxially to one another,
whereby the coolant is guided in the interconnected annular
channels between the outer tube and the centre tube on the one
hand and between the centre tube and the inner tube on the other
hand. This thus takes into consideration the fact that the main
electrode is the structural member requiring the greatest cooling.
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The main electrode current is thereby guided via the outer tube
and the ignition electrode current is guided via the inner tube.
So that the inner tube is adequately cooled despite the
insulating hose that is pulled over it from the outside, an
accordingly thin-walled insulating hose is selected w~ich should,
however, preferably be resilient and unaffected by high tempera-
tures. One or a plurality of sleeves are used to centre the
ignition electrode lance.
The centre tube is continued in the area of the main
electrode by an essentially annular deflecting member which at
the end face leaves open a connection between the coolant annular
channels lying on either side thereof. The centre tube, the
aforenamed deflecting member and the s:Leeve for centering the
ignition electrode lance are thereby made of non-conductive
material, preferably plastic. This pr~3vents a reduction in the
contact resistance between the ignition and m~in electrode
possibly caused by the coolant. On the other hand, the ignition
electrode and the gas nozzle into which the cylindrical interior
of the ignition electrode lance merges is electrically conductive.
The nozzle effect of the gas nozzle is favoured in that the
corresponding ignition gas guide channels are guided conically
outwards, preferably in the form of a plurality of individual
bores that are brought together again in the area of the main
electrode or the outlet.
The gas nozzle and the main alectrode are connected to
one another via an annular insulating sleeve, whereby this sleeve
can be made from a plastic unaffected by high temperatures, from
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a pressure liquid sealed ceramic or from a composite material
made from a plastic, a metal and a ceramic. The insulating hose
overlaps and seals the gas nozzle and part of the insulating
sleeve in order to improve the liquid insulation. The tightness
to the liquid is optimized by the O-ring seal provided between
the outer surface of the gas nozzle and the inner surface of the
insulating sleeve and which lies in a corresponding groove of the
gas nozzle. The main electrode itself has a cup-shaped design and
is connected in electrically conductive manner to the outer tube.
an O-ring seal is inserted between these parts for the purpose of
tightness to the liquid. An additional O-ring seal is provided
in the overlapping area of the insulating sleeve and the main
electrode.
It has proved advantageous to manufacture the inner tube
and/or the gas nozzle from coppe.r. The ignition electrode should
consist of tungsten, whereby for reasons involving manufacturing
technology the upper conical portion of the ignition electrode can
be cast round with copper and the relevant ingot forms the gas
nozzle.
To achieve an as laminar flow as possible in the flow
channels for the ignition gas, the lower portion of the inner tube
is widened conically and the conical form is adapted to the
adjacent bores.
An exemplary embodiment of the present in~ention is
illustrated in the drawings and is explained in greater detail
herebelow. The drawings show in
Figure 1 a plasma torch according to the invention in
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longitudinal section, and
Figure 2 an enlarged illustration of the fastening of
the ignition electrode in longitudinal section.
The main components of the plasma torch include an
ignition or auxiliary electrode 11, a main or nozzle electrode 12
and a nozzle 13, each of which are electrically insulated from one
another.
The upper, conical end 11' of the, in cross-section,
circular ignition electrode 11 is embedded in a gas nozzle 14
which in turn is fastened to an ignition lance which, unlike the
known plasma torches, comprises only a single tube 16. The lower
region of the cylindrical interior or hollow 17 of the tube 16
adjacent the gas nozzle 14 merges into a conical enlargement ].~
with the angle of taper ~. The gas nozzle 14 has a plurality of,
for example, ten bores or through holes 19 uniformly distributed
over the circumference. The axes oE the bores 19 are arranged on
an ~imaginary) conclcal surface (19') in such a way that the ends
of the bcres 19 facing the tube 16 are closer together than the
ends facing the ignition electrode 11 and the ends of the bores
facing the tube 16 all lie within the hollow section of the
conical enlargement 1~. The cone angle of the (imaginary) conical
surface 19' is identified in Figure 2 as ~. The inner tube 16
is preferably manufactured from copper, whereas the ignition
electrode 11 is made of tungsten. It is hereby possible to pre-
fabricate the ignition electrode 11 to a semifinished product as
follows. The ignition electrode 11 is semifinished to a rod with
a cone 11' having an angle of taper and in the casting process it
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is subsequently cast round with copper in the dimensions required
for the gas nozzle 14. The thus manufactured semifinished product
is finished by preparing the bores 19 and is connected to tube 16.
The position of the area cooled by the gas flow and the intensity
of cooling are determined by the angle of inclination (= half the
angle of taper ~1 of the bores 19 in the ~as nozzle 14. The area
of the gas nozzle facing the tube 16 is cooled more intensely than
of the area facing the ignition electrode 11 due to the proximity
of the bores 19. Accordingly, the angle of taper ~ of the upper
conical portion lli of the ignition electrode 11 is selected such
that the entire section of the connection between the gas nozzle
14 and the ignition electrode 11 is used uniformly for current
transmission and thermal conduction.
The gas nozzle 14 is surrounded on the outside by one
end of an electrically insulating sleeve 20. The other end of
the insulating sleeve 20 surrounds a cylindrical flange 21 of the
main electrode 12. The gas nozzle 14 and the main electrode 12
with its flange 21 are kept at a distance by the annular
projection 22 on the inside of the sleeve 20. The insulating
sleeve 20 accordingly serves as a mechanical connecting member
between the gas nozzle 14 and the main electrode 12 and causes
the ignition electrode 11 to be positioned exactly with respect to
the main electrode 12. The insulating sleeve 20 preferably
consists of a plastic unaffected by high temperatures and/or of a
pressure liquid sealed ceramic or of a composite material of
plastic, metal and ceramic.
The main electrode 12 has a central opening 23 which
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over a partial length, particularly in the area of the cylindrical
flange 21, forms an annular channel 24 with the outer surface of
the ignition electrode 11. The inside diameter of the annular
projection 22 equals the inside diameter of the flange 21
connected thereto or of the opening 23 of the main electrode 12.
The bore 19 outlets all lie within the area given by this
diameter.
Tube 16 is covered on its outside by a thin-walled,
resilient insulating hose 25 unaffected by high temperatures which
can be easily assembled and disassembled, this hose also annularly
enclosing the gas nozzle 14 and part of the insulating sleeve 20.
An electrically insulating coating can also be provided instead
of the insulating hose.
The main electrode 12 is connected to an outer
cylindrical part 26 in electrically conductive manner and to a
tube 28 in a pressure liquid sealed manner. An additional tube
27t which has a de~lecting member 29 ~at its lower end, is
arranged between tube 28 and tube 16.
Due to their coaxial arrangement, the tubes 16, 27, 28
will be referred to herebelow as inner tube 16, centre tube 27
and outer tube 28. The inner tube 16 with the gas nozzle 14
thereby constitutes the ignition electrode lance and these parts
together with the sleeve 20 and the centre and outer tubes 27 and
28 foxm the main electrode lance.
Sleeves 31 made of electrically insulating material and
provided with axially parallel openings serve to coaxially centre
the inner tube 16, the sleeves abutting on the one hand the
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insulating hose 25 and on the other hand the inner surface of the
centre tube 27.
The centre tube 27 as well as the deflecting member 29
connected thereto and the centering sleeves 31 are preferably made
of plastic which brings with it a saving in weight in addition to
electric insulation.
The gas for the ignition electrode 11 flows via the
symbolically indicated ignition gas connection 32, the hollow
space 17, the bores 19 and the annular channel 24. The ignition
electrode lance formed by the tube 16 is cooled internally by the
ignition plasma gas. If the ignition arc between the ignition
electrode 11 and the main electrode 12 is fired, the ignition
plasma gas emerges from the central bore 23 of the main electrode
12 as a plasma jet.
The gas for the main or power arc to be ired, which is
between the main electrode 12 and another pole, for example a
metal melt, flows via the symbolically indicated plasma gas
connection 33 and the annular channe1 34 formed on the one hand
by the outer surface of the outer tube 28 and the main electrode
12 and by the inner surface of the torch jacket and the nozæle 13
on the other hand.
An annular channel 35 or 36 for the flow-through of a
liquid coolant is respectively provided between the inner tube 16
and the centre tube 27 and between the centre tube 27 and the
outer tube 28. Both annular channels 35, 36 are joined together
between the deflecting member 29 and the face end of the main
electrode 12. The coolant likewise flows over the ignition
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electrode lance formed by the inner tube 16.
The ignition electrode 11 is electrically connected to
a pole of a current or voltage source (not illustrated~ via the
gas nozzle 14, the inner tube 16 and its symbolically indicated
current connection 37. The main electrode 12 is connected to
another pole of the current or voltage source via the outer tube
28 and its likewise symbolically indicated current connection 39.
To cool both the ignition electrode 11 and the main
electrode 12, a liquid coolant is introduced into the annular
channel 35 via the symbolically indicated coolant connection or
inlet 41 and fed back below the deflecting member 29 through the
annular channel 36 to the symbolically indicated coolant discharge
or outlet 43. The outer tube 28 guiding the current to the main
electrode 12 is thereby cooled internally by the flow of coolant.
Xn addition, the outer tube 28 is cooled by the cold main plasma
gas flowing to the main electrode 12 through the annular channel
34.
Seals in the form of O-rings are respectively provided
between the sleeve 20 and the gas nozzle 14 (O-ring 45) and the
cylindrical inner flange 21 of the main electrode 12 (O-ring 46
and between the outer flange 26 of the main electrode and the
outer tube 28 (O-xing 47) to seal the coolant circuit through the
annular channels 35, 36. The O-rings 45...47 are held in annular
groo~es, of which annular groove 48 in the gas nszzle 14 for
O~ring 45 and annular groove 49 in the sleeve 20 for O-ring 46
are illustxated by example.
In addition to the liquid coolant, the inner tube 16 is
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also cooled by the plasma gas flowing through its hollow space 17.
The plasma torch described is preferably operated as a
three-phase plasma torch. However, it can in addition also be
operated with direct and/or alternating current as described in
European OS 0 134 961 A2.
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