Plasma torch

In a plasma torch, the contact surface (61) between the nozzle (6) and the swirler (5), the contact surface (4b) between the swirler (5) and the insulating cylindrical body (4), the contact surface between the insulating cylindrical body (4) and the electrode (3), and the contact surface (3a) between the electrode (3) and the electrode table (2) are arranged in line from the nozzle (6) to the torch body (1). The inner diameter (d1) of the portion of insulating cylindrical body (4) positioned in contact with the flange (31) of the electrode (3) is smaller than the inner diameter (d2) of the flat surface (4b) of insulating cylindrical body (4) which is in contact with the end of swirler (5). An upper stepped chamber (65) or an upper tapered chamber (66) can be formed in the cylindrical portion (62) of the nozzle (6) above the swirler (5) which upper chamber has a diameter larger than that of the swirler (5) to permit easy removal of the swirler (5) from the cylindrical portion (62).

FIELD OF THE INVENTION 
The present invention relates to a plasma torch for use in cutting or 
welding metallic material. 
BACKGROUND ART 
A conventional plasma torch comprises a torch body, an electrode table, an 
electrode, an insulating cylindrical body, a swirler and a nozzle as the 
main component elements thereof, the plasma torch being constituted by 
simply fastening the outer surface of the electrode table to the nozzle in 
the above-described sequential order and by inserting the thus-fastened 
elements into the torch body. Another known example is constituted in such 
a manner that a cap is fitted to the outer surface of the leading portion 
of the plasma torch and thereby the same is protected. Another known 
example is constituted in such a manner that the insulating cylindrical 
body and the swirler are integrally molded (for example, see Japanese 
Patent Utility Model Laid-Open No. 63-19978). Since the conventional 
plasma torches have been respectively constituted in the above-described 
simple manner, they can easily be manufactured. However, there arises the 
following problems when they are used: 
(1) The insulating cylindrical body can be broken. 
(2) The contact part between the electrode table and the electrode can be 
melted. 
The reason why the above-described problems take place will be specifically 
described with reference to a plasma torch shown in FIG. 5. When the 
plasma torch is used, its electrode 3, which is one of the consumables, 
must be exchanged on occasion. In a case where the electrode 3 is mounted, 
a cap 7 is screwed so as to cause the electrode 3 to be fitted to the 
outer surface of an electrode table 2 via an insulating cylindrical body 4 
and a nozzle 6. At this time, the force applied to the cap 7 acts on an 
outer peripheral portion 42 of the insulating cylindrical body 4. However, 
an inner peripheral portion 41 of the insulating cylindrical body 4 gives 
the electrode 3 the insertion force. That is, shearing force is generated 
in the insulating cylindrical body 4. Since the insulating cylindrical 
body 4 is usually made of ceramic, it has a disadvantageous point in that 
it is too weak against an impact or an excessively large stress, though it 
has satisfactory heat resistance. Therefore, the insulating cylindrical 
body 4 will be gradually broken, causing the force with which the 
electrode 3 is brought into contact with the electrode 3 to be reduced. As 
a result, there arises a problem in that a defective electrical connection 
(that is, defective contact) takes place and thereby the contact part 3b 
can be melted. 
The nozzle of the plasma torch is, as shown in FIG. 6, arranged in such a 
manner that a small hole 11 for jetting out plasma arcs is formed at the 
central portion of the substantially conical leading portion thereof. 
Furthermore, a swirler 5 for introducing an operating gas in the form of a 
swirling flow or an axial flow into a portion between the electrode 3 and 
the nozzle 6 is fitted within a hole formed in a cylindrical portion 62 so 
that the electrode 3 is held via the swirler 5 and the insulating body 4. 
Since the electrode 3 and the nozzle 6 of the plasma torch consume whenever 
the plasma arc generates, they must be exchanged when they reach the limit 
in terms of the use. In this case, since the swirler 5 can be further 
used, it is again used after it has been removed from the consumed nozzle 
6. However, as for the nozzle 6, only a small gap, to which the swirler 5 
can be fastened while preventing looseness, is permitted to be present in 
the hole formed in the cylindrical portion of the nozzle 6 through the 
overall length thereof. Therefore, when the consumed nozzle 6 is 
decomposed, it takes too much time to complete an operation of removing 
the swirler 5 from the nozzle 6. Usually, although the electrode 3 and the 
insulating body 4 can easily be removed from the nozzle 6, the swirler 5 
is left in the nozzle 6 in a state in which the same is fastened there. 
When the nozzle 6 in the above-described state is turned upside down and a 
small shock is applied to it, the swirler 5 can sometimes be removed from 
the nozzle 6. However, the swirler 5 cannot always be removed if the 
cylindrical portion 62 of the nozzle 6 is deformed or small dust is caught 
at a space between the swirler 5 and the nozzle 6 during the removal 
movement of the swirler 5. In a case where the swirler 5 cannot be removed 
even if the shock is given to the nozzle 6, the nozzle 6 must be cut to 
take the swirler 5. Therefore, there arises a problem in that the 
above-described nozzle cutting work causes the work for 
assembling/disassembling the plasma torch to take too much time. 
Accordingly, a first object of the present invention is to provide a plasma 
torch having an insulating cylindrical body which cannot be easily broken 
and having a contact part between the electrode table and the electrode 
which cannot easily be melted. Furthermore, a second object of the present 
invention is to provide such a plasma torch having an improved structure. 
A third object of the present invention is to provide a plasma torch 
having a swirler which can easily be removed from the nozzle at the time 
of disassembling the plasma torch. 
SUMMARY OF THE INVENTION 
In order to achieve the first object, a plasma torch according to the 
present invention is constituted in such a manner that: the electrode 
table 2 has a flange 21 on the outer surface thereof; the electrode 3 has, 
on the outer surface of the end portion thereof which confronts the 
electrode table 2, a flange 31 which is positioned in contact with the 
surface of the flange 21 adjacent to the nozzle 6; the end surface of the 
insulating cylindrical body 4 adjacent to the electrode table 2 is 
positioned in contact with the surface of the flange 31 adjacent to the 
nozzle 6 and the insulating cylindrical body 4 has a stepped portion 4b in 
its portion adjacent to the nozzle 6; the end surface of the swirler 5 
adjacent to the electrode table 2 is positioned in contact with the 
surface of the stepped portion 4b of the insulating cylindrical body 4 
adjacent to the nozzle 6; and the end surface of the swirler 5 is 
positioned in contact with a nozzle directional inner side surface 61 of 
the nozzle 6 (see FIG. 1). An inner diameter d1 of the insulating 
cylindrical body 4 of a surface which is positioned in contact with the 
flange 31 of the electrode is smaller than an inner diameter d2 of the 
radially extending annular portion 4b of the insulating cylindrical body 
4, which is positioned in contact with the swirler 5. 
In order to achieve the second object, an inner cap 7 has a first end 
portion which circumscribes the nozzle 6 and a second end potion which is 
secured to the outer surface of the torch body 1. An outer cap 8 has a 
first end portion which circumscribes the inner cap 7, and a second end 
portion which is secured to the outer surface of the torch body 1. An 
assist gas passage 82 is formed between the caps 7 and 8, and an assist 
gas jetting hole 81 is formed in an end portion of the cap 8 (see FIG. I). 
The insulating cylindrical body 4 and the swirler 5 can be integrally 
molded. 
In order to achieve the third object, a first hole or chamber 64 is formed 
in the cylindrical portion 62 of the body of nozzle 6 such that the wall 
surface of the chamber 64 confronts the whole or a part of the outer wall 
surface of the swirler 5 when the swirler 5 is placed in the cylindrical 
portion 62 of the nozzle 6, and a second hole or chamber 65 is formed in 
the cylindrical portion 62 of the body at a position between the top end 
portion of the first chamber 64 and the top end portion of the cylindrical 
portion 62, the second chamber 65 having a diameter which is larger than 
that of the first chamber 64. A tapered chamber 66, the larger end of 
which is placed at the top end portion of the cylindrical portion 62, can 
be formed instead of the second chamber 65 (see FIGS. 3 and 4). 
As a result of the thus-arranged structure, the contact surfaces of the 
above-described elements are arranged in line running from the nozzle 6 to 
the torch body 1. Therefore, the insertion force applied in a direction 
from the nozzle 6 to the electrode table 2 becomes substantially the 
compressive stress in the abovedescribed elements. As a result, although 
the insulating cylindrical body 4 can be broken, it cannot easily be 
broken in comparison to the conventional structure. As a result, melting 
of the contact surface 3a due to the defective contact between the 
electrode 3 and the electrode table 2 can be prevented. On the other hand, 
the contact force between the electrode 3 and the electrode table 2 is, as 
can be understood from the above-made description, substantially the same 
as the insertion force applied via the nozzle 6. As a result, further 
reliable contact can be realized at the contact surface 3a so that the 
prevention of melting can be further completely performed. 
The contact force applied via the nozzle 6 sometimes generates internal 
stress, in addition to the compressive stress, depending upon the shape or 
the state of fitting of the elements. Even if the internal stress is 
generated, insertion force F can be made to be substantially pure 
compressive stress--.sigma. in each element by determining the inner 
diameter of the insulating cylindrical body 4. As a result, the 
above-described operation and effect can further be improved. 
The above-described structure of the plasma torch can be applied to a 
plasma torch provided with the caps 7 and 8 and having an assist gas 
jetting function and as well applied to a plasma torch arranged in such a 
manner that the insulating cylindrical body 4 and the swirler 5 are 
integrally molded. 
Furthermore, the interior opening of the cylindrical portion 62 of the 
nozzle 6 can have a stepped portion 54 or a tapered portion 66 for ease of 
removal of the swirler 5. The interior opening in the cylindrical portion 
62 of nozzle 6 can be in the form of a lower chamber 64 for holding the 
swirler 5 and an upper chamber connected to the lower chamber, with the 
diameter of the portion of the interior opening above the swirler 5 being 
enlarged with respect to the whole or a part of the swirler seat. The 
mounting/removing of the swirler can significantly easily be performed in 
comparison to the conventional structure. In particular, the removal of 
the swirler 5 from the nozzle 6 at the time of disassembling the plasma 
torch can be smoothly performed even if the cylindrical portion is 
deformed to some degree or small dust adheres to the inner surface of the 
cylindrical portion.

BEST MODE FOR CARRYING OUT THE INVENTION 
Best modes of a plasma torch according to the present invention will 
specifically be described with reference to the drawings. The best mode 
according to a first embodiment of the invention will be described with 
reference to FIGS. 1 and 2. The best mode according to the second and 
third embodiments of the invention will be described with reference to 
FIGS. 3 and 4. 
Referring to FIG. 1, an electrode 3 is fastened to the outer surface of the 
leading portion of an electrode table 2 included in a torch body 1. The 
lower or leading portion of the electrode table 2 has a flange 21 for 
enlarging the contact area between the electrode table 2 and the electrode 
3. The outwardly extending annular flange 21 at the upper end of the 
electrode 3 has an upper flat portion 3a, which confronts the flange 21, 
and a stepped portion 3b the outer cylindrical surface thereof. 
Furthermore, an insulating cylindrical body 4 is fastened to the outer 
surface of the electrode 3 in such a manner that the body 4 is brought 
into contact with the lower flat portion 3a on the underside of flange 31. 
In addition, by utilizing the stepped portion 4b formed on the outer 
surface of the insulating cylindrical body 4, a swirler 5 for generating a 
swirling gas is fastened to the above-described outer surface of 
insulating cylindrical body 4. Furthermore, a conical and cylindrical 
nozzle 6 is fastened to the outer surface of the swirler 5. The 
above-described elements are inserted into the torch body 1. As a result 
of the thus-arranged structure, an annular contact surface 61 between the 
nozzle 6 and the swirler 5, an annular contact surface 4b between the 
swirler 5 and the insulating cylindrical body 4, a lower annular contact 
surface 3a between the insulating cylindrical body 4 and the electrode 3, 
and an upper annular contact surface 3a between the electrode 3 and the 
electrode table 2 are arranged on a line running from the nozzle 6 to the 
torch body 1. As a result, insertion force acting from the nozzle 6 to the 
electrode table 2 becomes substantially only the compressive stress in the 
above-described elements. 
In order to cause substantially only compressive stress--.sigma. to be 
applied, the insulating cylindrical body 4 is arranged in such a manner 
that the outer surface of the cylindrical portion thereof which is below 
the stepped portion 4b for fastening the swirler 5 has an outer diameter 
d2 which is greater than the inner diameter d1 of the annular flat portion 
3a which confronts the flange 21 (See FIG. 1) of the electrode 2. That is, 
the structure is arranged such a relation of d2&gt;d1 is held. By providing 
this relationship of d1 and d2, the insertion force F becomes pure 
compressive force--94 in each element. 
The plasma torch shown in FIG. 1 is constituted such that a conical portion 
of inner cap 7 contacts the outer surface of the nozzle 6 adjacent the 
nozzle outlet while a cylindrical portion of the inner cap 7 is fastened 
to the outer surface of the torch body 1 by threaded joint 71. A conical 
portion of an outer cap 8 contacts the outer surface of the conical 
portion of inner cap 7 adjacent the outlet of nozzle 6 while a cylindrical 
portion of outer cap 8 is fastened to the torch body 1 by threaded joint 
80. A passage 82 for passing an assist gas is formed between the inner cap 
7 and the outer cap 8. The leading portion of the outer cap 8 has a jet 
hole 81 formed therein for the purpose of jetting out the assist gas 
against a portion of the workpiece to be machined. The assist gas is used 
for the purpose of shielding the plasma flow and the portion of the 
workpiece to be machined from the outside air at the time of performing 
the plasma machining work. Furthermore, referring to the drawing, "O" 
rings, magnets and the like are disposed in order to prevent an 
undesirable introduction of cooling water and to support the established 
inward or outward fastening of elements. In another embodiment of the 
invention, the swirler 5 and the insulating cylindrical body 4 are 
integrally molded. Therefore one pair of contact surfaces can be omitted 
from the structure, and the rigidity can be improved. Therefore, an effect 
can be obtained to prevent the breakage and to improve the efficiency in 
transmitting insertion force F. 
According to the above-described embodiments, the breakage of the 
insulating cylindrical body 4 can satisfactorily be prevented and melting 
due to the defective electrical connection between the electrode table 2 
and the electrode 3 can be prevented. 
Referring now to FIG. 3, the cylindrical portion 62 of the nozzle 6 of the 
plasma torch has a first, lower chamber formed therein for the purpose of 
fastening the swirler 5 and a second, upper chamber 65 formed therein in 
such a manner that the diameter of the upper chamber 65 is slightly larger 
than that of the first chamber 64. Specifically, the diameter of the first 
chamber 64 is larger than the outer diameter of the swirler 5 by about 
0.05 mm and the depth of the same is made to be about two-third of the 
length of the swirler 5 in its axial direction. As shown in FIG. 3, the 
length of the swirler 5 in its axial direction is less than the combined 
axial length (depth) of the first chamber 64 and the second chamber 65. 
The diameter of the second chamber 65 is made to be larger than the 
diameter the first chamber 64 by about 0.5 mm when measured at a position 
above the first chamber 64. 
When the nozzle 6 thus-constituted is turned upside down and a light shock 
is given to the same, the swirler 5 can easily be removed. Furthermore, 
the swirler 5 can significantly easily be fastened to the nozzle 6. 
FIG. 4 illustrates an alternative to the structure in which the first 
chamber 64 is formed in the inner surface of the cylindrical portion 62 of 
the nozzle 6, and a tapered chamber 66 is formed to extend from chamber 64 
to the open top end of cylindrical portion 62, with the larger end of 
chamber 66 being at the open top end of the cylindrical portion 62. The 
depth of the first chamber 64 is made to be about two-third of the length 
of the swirler 5 in its axial direction. Also in this case, the swirler 5 
can significantly easily be fastened/removed. 
According to the above-described embodiments, the swirler 5 can 
significantly easily be fastened/removed while accurately maintaining the 
concentricity between the electrode 3 and the nozzle 6 and the distance 
from the bottom end portion of the electrode 3 and an arc control portion 
of the nozzle 6. Therefore, the efficiency in the disassembling/assembling 
work can significantly be improved. Furthermore, the hole machining range 
in which a desired fitness accuracy must be established can be narrowed, 
causing the cost required to machine the nozzle to be reduced. 
Although the depth of the first chamber 64 to which the swirler 5 is 
fastened is made to be about two-third of the length of the swirler 5 in 
its axial direction, the present invention is not limited to this. The 
depth of the first chamber 64 may be in a range in which the swirler 5 can 
be correctly seated at a predetermined position. Also the diameter of the 
second chamber 65 shown in FIG. 3 and the larger diameter of the tapered 
chamber 66 shown in FIG. 4 may be properly determined. 
INDUSTRIAL APPLICABILITY 
According to the present invention, there is provided a plasma torch for 
preferably use in cutting or welding metallic material and from which a 
significant effect can be obtained since the contact portion between the 
electrode table and the electrode cannot easily be melted. Furthermore, 
the plasma torch according to the present invention is effective since the 
swirler can easily be removed from the nozzle at the time of disassembling 
the plasma torch.