Note: Descriptions are shown in the official language in which they were submitted.
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PLASMA WELDING TORCH
Technical Field
The invention relates to a plasma welding torch.
Background of the Invention
In known such welding torches the outlet port which extends in
the zone of the tapering section of the electrode is provided
with a cylindrical zone which is immediately adjacent to the
chamber and which is followed downstream by a tapering section
extending up to the orifice. The interior wall of the tapering
section of the outlet port, however, is provided with a cone
angle which is considerably larger than that of the conical end
of the electrode.
Despite the convergence of the plasma jet by the geometry of the
outlet port and the electrode, a very considerable divergence of
the plasma jet and thus a relatively large arc spot is observed
on the workpiece to be machined in such known welding torches.
This leads to a mostly undesirable increase of the zone of the
workpiece which is subjected to the heat, and frequently leads
to warping of the same, particularly when relatively thin
sheet-metal parts are to be processed.
The large arc spot also causes a high thermal stress on the
plasma torch, which as a result of the high temperatures must be
cooled respectively well. As this can be brought about already
at relatively small outputs of the plasma torch only with water
flowing through cooling ports, respectively unwieldy designs are
obtained for the plasma welding torch. This leads to the
disadvantage, however, that it is not possible to work on
workpieces that have a more complex shape, and it is
particularly not possible to work at locations where T-seams are
to be produced, and that it is already necessary to take into
account the welding with such plasma torches in the design of
the workpiece.
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As a result of the formed larged arc spot, it is also necessary
to work with conventional plasma welding torches from a very
small distance from the workpieces, thus increasing the stress
on the torch and subjecting it to high wear and tear.
A further disadvantage of known plasma torches is also that as a
result of the very high thermal stress on the plasma torch it is
not possible to have high outputs and the torches can therefore
only be operated with not more than approx. 100A. At higher
strengths of current the plasma arc begins to burn between the
electrode and the wall of the chamber of the outlet port of the
plasma torch and from its free face side in the zone of the
outlet port to the workpiece, which leads to a practically
immediate destruction of the plasma torch.
It is only possible to work with relatively low welding speeds
of not more than 25 mm per second or 30 mm per second with the
known plasma welding torches, as otherwise the plasma arc would
bend too strongly and begin to jump or even disintegrate.
Sununary of the Invention
It is the object of the present invention to avoid this
disadvantage and to provide a plasma welding torch of the kind
mentioned above which is also suitable for higher outputs and is
,characterized by a high service life.
This is achieved in accordance with the invention in a plasma
welding torch comprising, a non-consumable electrode arranged in
a chamber provided in the torch and having a free flat end face
extending substantially perpendicularly to a longitudinal axis
of the electrode and having a diameter of 15% to 35% of the
maximum diameter of the electrode, an inlet port leading to the
chamber for delivering a plasma gas thereto, an outlet port
leading from the chamber to an orifice at an outer end of the
outlet port, the outlet port having an interior wall, the
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electrode having a free tapering end section reaching at least
to the outer end of the outlet port, and the interior wall of
the outlet port being spaced from, and surrounding, the free
tapering end section of the electrode and extending to the
orifice substantially parallel to the tapering end section of
the electrode, and at least three further ports evenly
distributed along a circumferential line concentrically
surrounding the outlet port, the further ports being open to the
ambient atmosphere, leading from the chamber to the orifice,
having a smaller cross section than the outlet port, and having
axes forming generatrices of a convex surface of a cone whose
axis extends coaxially to the axis of the outlet port, the cone
and the outlet port having a common apex spaced in front of the
orifice a distance of 3 mm to 8 mm.
The proposed measures ensure that the plasma gas emerging from
the outlet port keeps the plasma jet of the torch together, or
constricts it, outside of the outlet port. This is caused by the
fact that the plasma gas emerges substantially along the
envelope of a cone having a specific wall thickness and that
thus turbulences are substantially avoided. This leads to a
respectively small arc spot on the workpiece and to a
concentration of the energy on a very small zone. This also
allows guiding the plasma torch at a higher distance,from the
workpiece and, as aresult of the higher energy density on the
workpiece, also processing it with a higher rate of feed.
Moreover, substantially lower wear and tear of the torch is
obtained and it is also possible to work with a higher current
load, e.g. with 1000A.
Furthermore, it is also possible to omit water cooling of the
welding torch which would be required in many cases, e.g. in
pulsed operation as is required in overhead welding or in some
types of steel, and is mandatory in conventional welding torches
in such cases. The system can make do with cooling produced by
the plasma gas flowing into the chamber.
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The thermal stress as compared with conventional welding torches
is also substantially lower when operating the welding torch in
accordance with the invention with flow plasma, i.e. with a
continuously flowing plasma, so that the efforts for water
cooling can be reduced dramatically and the welding torches per
se can thus be built with a substantially smaller size. This
allows working with the welding torches in accordance with the
invention at locations which formerly were inaccessible for
conventional plasma welding torches as a result of their size
which was caused by cooling.
The plasma gas emerging from the orifice of the outlet port
ensures as a consequence of the conical shape of the gas
envelope a very favourable constriction of the plasma by the
ambient air despite the deceleration at its outer side, and thus
ensures a very small size of the arc spot produced on the
workpiece. This considerably reduces the danger of warping.
By avoiding the divergence of the plasma jet as occurs in
conventional welding torches and as a result of the fact that
the plasma jet does not touch the welding torch, it is possible
to work with substantially higher welding speeds of 300 mm per
second and more without any jumping of the plasma occurring on
the workpiece. A working position of the welding torch in
accordance with the invention can also be provided in which said
plasma torch is inclined in the feeding direction, so that the
orifice of the outlet port is leading in the feeding direction.
Moreover, the distance between the orifice of the outlet port
and the workpiece, which formerly had to be set very precisely
in known torches to mostly 2.5 mm to 3 mm, is uncritical in the
welding torches in accordance with the invention and can also
fluctuate between 2 mm and 6 mm, for example. As a result, the
time consumed during the dressing and the setup of the
workpieces to be welded can be reduced considerably.
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In one embodiment of the present invention, the tapering end
section is cone-shaped, the cone angle being between 15 and
25 . This leads to the advantage of a very precise guidance of
the plasma gas jet, with the same accelerating towards the
5 orifice of the outlet port as a result of the reduction of the
free cross section between the electrode and the wall of the
outlet port.
In another embodiment of the present invention, the torch has a
peak-to-valley height of the tapering end section of the
electrode of the outlet port and of the further ports not
exceeding l m.
These measures moreover lead to a very stable root of the arc at
the electrode in applications where the workpiece to be machined
is connected to a pole of a current source, and heat can be
favourably discharged from the same. This leads to only very low
wear and tear of the electrode.
In a known plasma torch its electrode is held in a chamber for
plasma gas, e.g. argon, helium, hydrogen, etc., and penetrates
the same, with said chamber being provided with an inlet port
and an outlet port which is provided on one face side of the
plasma torch with an orifice and the transition from the chamber
to the outlet port is disposed in the zone of the minimum
distance between the electrode and a wall encompassing the same
in the zone adjacent the orifice of the plasma torch. The outlet
port is enclosed in sections by further ports which have a
smaller diameter as compared with the outlet port, are open at
the face side of the plasma torch comprising the orifice of the
outlet port, and are in connection with the chamber. In the
known case only two additional ports are provided whose axes
extend parallel to one another and to the axis of the outlet
port.
Although plasma gas can be guided into the zone of the arc spot
with this known torch, there is only a rather reduced screening
against the access of oxygen. Moreover, the additional ports
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practically contribute nothing to an improved constriction of
the plasma, so that the mentioned problems in this connection
are substantially maintained.
In order to achieve a very substantial protection of the
workpiece heated in the zone of the arc spot against the access
of air, the torch has at least three further ports evenly
distributed along a circumferential line concentrically
surrounding the outlet port, the further ports being open to the
ambient atmosphere, leading from the chamber to the orifice,
having a smaller cross section than the outlet port, and having
axes forming generatrices of a convex surface of a cone whose
axis extends coaxially to the axis of the outlet port, the cone
and the outlet port having a common apex spaced in front of the
orifice a distance of 3 mm to 8 mm.
This also ensures that plasma gas which emerges with a very
considerable speed through the further ports cools the immediate
surroundings of the arc spot and thus prevents a higher thermal
stress of the workpiece and thus also any warping of the same,
particularly when workpieces made of thin sheet metal are
concerned. Moreover, the constriction of the plasma is improved
by the proposed measures, as a result of which the arc spot can
be kept particularly small, which again increases the energy
density on the workpiece and allows saving energy. In addition,
it is possible to work with respectively high feed speeds due to
the high energy density. A relatively large depth of the weld
seam is still possible.
The invention is now explained in closer detail by reference to
the enclosed drawings.
Brief Description of the Drawings
Fig. 1 shows a sectional view through a plasma welding torch in
accordance with the invention;
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Fig. 2 shows a sectional view through the coolant chamber;
Fig. 3 shows a sectional view through the centering sleeve and
Fig. 4 schematically shows a plasma welding torch in accordance
with the invention with a workpiece.
Detailed Description of the Invention
In the plasma welding torch 11' a holding part 18' of an
electrode 19' is formed by a collet chuck which is made from an
electrically well-coanducting material. This collet chuck is held
in the usual manner in a receiver 44 which is screwed into a
contact part 45.
Said contact part 45 is provided with a coolant chamber 46 which
is connected with a connecting opening 48 by way of a radial
port 47. Said connecting opening 48 is in alignment with the
contact pins when the plasma welding torch 11' is mounted in a
holder (not shown).
An adjusting nut 49 is provided for tensioning and loosening the
collet chuck 18', which nut rests on the upper face side of the
receiver 44 by way of a seal 50, thus preventing any leakage of
coolant. Receiver 44 also rests on the contact part 45 by way of
a seal 51 in order to seal the coolant chamber 46.
For the purpose of further sealing the coolant chamber of the
contact part 45, an 0-ring 52 is provided which is placed in a
groove of a bore 53 which is penetrated by the receiver 44.
In order to secure the axial adjustment of the electrode 19'
during the tensioning of the collet chuck 18', the adjusting nut
49 is provided with a continuous threaded bore 90 into which a
stop 91 is screwed which engages into the collet chuck 18'. Said
stop 91 is provided with a smooth head 94 in which a circular
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groove has been machined for receiving an 0-ring 95 which is
used for sealing the interior of the collet chuck 18'.
In order to secure the position of the stop 91, which is
adjustable by means of a screwdriver inserted into the face-side
slot 93, a counternut 92 is provided which simultaneously
ensures a torsionally rigid connection between the stop 91, on
which the electrode 91' rests, and the adjusting nut 49.
As a result of the stop 91 it is ensured that during the
tensioning of the collet chuck the electrode 19' can no lonber
be moved by the collet chuck towards an orifice part 15' which
can be used for different purposes as an anode, because the
adjusting nut 49 rests on the face side of the contact part 45
and the orifice part 15' is fixed with respect to the same.
The contact part 45' which is used for making the contact with
the electrode 19' is inserted into an intermediate part 55 by
interposing a seal 54 and rests on the same. The intermediate
part 55 is made of an electrically insulating material such as
ceramics. Said annular intermediate part 55 defines a chamber
27' which is connected by way of a radial port 56 with a
connecting opening 57.
The radial port 56 and a further radial port 47 are provided
with circular grooves 58 in which 0-rings 59 are arranged. They
are used for sealing the contact pin (not shown) which engages
in said ports, said contact pins are hollow arrangement and are
used simultaneously for the supply of cooling water or as a gas
supply line for the supply of a plasma gas such as argon,
helium, hydrogen, etc.
A distributor ring 159 is arranged in the chamber 27' which is
provided _ with bores 60 which are arranged in a manner
distributed over the circumference and whose diameters increase
in both rotational directions with an increasing angle enclosed
between said bores 60 and the radial port 56. An axial bore of
the distributor ring 159 forms a chamber 96 which is penetrated
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by the electrode 19'. An annular space 61 remains between the
inner wall of the intermediate part -S and the distributor ring
159 in which gas can be introduced through the connecting
opening 57 and the radial port 56.
The intermediate part 55 is supported by way of a seal 62 on a
further contact part 63 which is used for making the contact
with the orifice part 15' when it is used as an anode, e.g. when
the plasma torch is used for surface hardening. A clamping
sleeve 64 is screwed into an inner thread 65 in said further
contact part 63, with a seal 66 being interposed between the
contact part 63 and the face surface of the clamping sleeve 64.
The clamping sleeve 64 is provided in the zone of its one end
with a conical bearing surface 67 on which rests a diametrically
opposed conical jacket surface 68 of a head 69 of the orifice
part 15' which, like the clamping sleeve 64 and the further
contact part 63, is made from an electrically well-conducting
material.
The orifice part 15' is provided at its end averted from the
head 69 with a further head 70 which by interposing a seal 71
rests on a shoulder of the further contact part 63. The orifice
part 15' penetrates a coolant chamber 46 of the further contact
part 63.
The orifice part 15' is bored through in the axial. direction,
with a sleeve 73 made of an electrically insulating material
such as ceramics being inserted in said bore 72 and being
penetrated by the electrode 19'. An annular chamber which is
part of the chamber 96 and can be flowed through by the
introduced plasma gas such as argon, helium, hydrogen, etc.
remains between the interior wall of the sleeve 73 and the
electrode 19'.
Moreover, a centering sleve 74 is inserted in the bore 72 in the
zone which is close to the orifice of the orifice part 15',
which sleeve is shown in closer detail in fig. 3 and whose guide
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surfaces 75, which are provided on guide ribs 89, rests on the
jacket surface of the electrode 19'.
As is shown in fig. 2, the orifice part 15' is provided with
5 radially projecting guide ribs 76 which, as can be seen in fig.
2, extend from the orifice part 15' having an hexagonal cross
section up to the interior wall of the clamping sleeve 64 and
stand perpendicular to the axis of the radial port 47. The guide
ribs 76 extend away from the head 70 towards the head 69 of the
10 orifice part 15'#, with said guide ribs 76 ending before head
69, however, and thus providing a flow path (not shown) between
the head 69 and the end of guide ribs 76.
As a result, the coolant chamber 46, which on the one hand is
limited by the further contact part 63 and the clamping sleeve
64, is subdivided by the guide ribs 76.
The two coolant chambers 46 of the contact part 45 and the
further contact part 63 are mutually connected by way of a
transfer port 78.
Said transfer port 78 is substantially composed of axial bores
79 in the contact part 45, or the further contact part 63, and
radial bores 80 which are coaxial to the radial ports 47 and
open into the axial bores 79. The intermediate part 55 is
provided with a bore 81 which is in alignment with the axial
bores 79.
Seals 82 are provided in the zone of the bore 81 of the
intermediate part 55.
The two contact parts 45 and 63 are encompassed by rings 84 made
of an electrically insulating material or rest on collars 85.
As is shown in fig. 1, the interior wall 99 extends
substantially parallel to the conical end section of electrode
19' in the orifice zone 98 of the orifice part 151. This leads
to a conical shape of the outlet port 97 in this zone.
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As is shown in particular in fig. 4, the tip of electrode 19' is
flattened off at its free end and projects from the free face
side of the orifice part 15'.
The electrode 19' is arranged conically at its two ends and, if
required, can be turned over after its removal and be
re-inserted. Only when the electrode 19' is worn off at both of
its ends it will be necessary to rework the electrode 19' in
order to enable its use again.
The orifice part 15' is provided in the zone of its head 69 with
further ports 102 which concentrically encircle the outlet port
97 having the shape of the envelope of a cone and axes of said
further ports 102 form the generatrices of a convex surface of a
cone whose axis extends concentrically to the axis of the outlet
port 97. The cone angle of the axes of the further ports 102 is
larger than the cone angle of the outlet port 97, thus leading
to a common point of intersection of the axes of the further
ports with the generatrices of the outlet port 97 having the
shape of the envelope of a cone. Said point of intersection is
preferably located 6 mm to 8 mm before the free face side of the
orifice part 15'.
The additional ports 102 extend from the chamber 96 right up to
the free face side of the orifice part 15' where they are open
and therefore are provided with cold plasma gas in operation
which thus also contributes to the cooling of the orifice zone
of the orifice part 15'. This is particularly relevant when the
orifice part 15' is switched as an anode and an arc burns in the
zone of the outlet port 97 between the electrode 19' which is
switched as a cathode and therefore plasma emerges from the
orifice 16'.
The two contact parts 45 and 63 and the intermediate part 55 are
mutually connected by means of screws (not shown) and represent
connecting parts which ensure a modular arrangement of the
plasma welding torch 11'. This module comprises not only the
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orifice part 15' which can be connected as an electrode, but
also the non-consumable electrode 19' including its holding part
18', as a result of which the entire plasma producer can be
exchanged as a single component.
During operation a gas such as helium, argon, hydrogen or the
like is blown into the chamber 27' or 96 and an arc is ignited
between the electrode 19' and the workpiece 83 which, like the
electrode 19', is connected to a DC power source (not shown). In
conjunction with the nozzle opening 16' provided at the end of
the outlet port 97, a plasma jet is formed between the tip of
the electrode 19', which - as can be seen from fig. 4 - is
flattened off, and the workpiece, with which two workpieces can
be welded together.
Since the plasma gas emerges from the outlet port 97 in form of
an envelope of a cone, this gas jet in the form of an envelope
of a cone acts in a constricting manner on the plasma and guides
the same. This only leads to a small arc spot on the workpiece
83 to be processed. Consequently, the thermal stress on the
immediate surroundings of the weld seam to be produced remains
small.
The plasma gas emerging at a high speed through the further
ports 102 prevents any divergence of the plasma jet emerging
from the orifice 16' as a result of the friction of the ambient
air which is substantially stationary. Moreover, both the
geometry of the outlet port 97 which has the shape of an
envelope of a cone as well as the cold plasma gas emerging from
the further ports 102 and also approximately having the shape of
the envelope of a cone act in a constricting manner upon the
emerging plasma jet. This leads to a very high energy density on
the workpiece to be processed. As a result, a high working speed
can be achieved with a relatively low input of energy and the
thermal stress on the workpiece is limited to a very small area.
This is particularly relevant in the processing of thin-walled
workpieces or sheet metal in view of avoiding warping phenomena.
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Since in the application as illustrated in fig. 4 the ard or the
plasma only burns between the flattened tip of the electrode 19'
which projects from the face side of the orifice part 15' and is
connected in most welding applications as a cathode, there is no
direct-stress on the orifice part 15' by the plasma, thus
leading to a considerably lower thermal stress on this part as
compared with conventional plasma welding torches where the
orifice part is also used for guiding the plasma.
Moreover, the distance between the free face side of the orifice
part 15' and the workpiece 83 can fluctuate within wide margins
and can be chosen considerably larger as was possible in
previous plasma welding torches and can be 2 mm to 6 mm for
example.
