JPH11285832A - Plasma torch and its parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the plasma torch which can be inserted into a narrow place and easily cools a nozzle. SOLUTION: A cap 11 is covered on an outside of a nozzle 9 having an arc blowing hole 19, a water jacket region 27 is formed between the nozzle 9 and the cap 11. The cap 11 has a cap base part 1A having a prescribed outer diameter and extending in a torch axial direction, a cap tip part 1C having a roughly fixed prescribed diameter smaller than the cap base part extending in a torch axial direction and a cap tapered part 1B connecting both parts 1A, 1B. The cap tip part is small to be inserted into a narrow place. The nozzle 9, same as the cap, has a nozzle base part having a prescribed outer diameter and extending in a torch axial direction, a nozzle tip part having a roughly fixed prescribed diameter smaller than the nozzle base part extending in a torch axial direction and a nozzle tapered part 1B connecting both parts. An outer peripheral face of the nozzle 9 is roughly parallel to an inner peripheral face of the cap 11, a water jacket region 27 is not narrowed up to a nozzle tip, the nozzle 11 is cooled well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a torch for plasma processing such as plasma arc welding.

[0002]

2. Description of the Related Art A "pencil-shaped" plasma welding torch having an elongated conical tip, such as a sharpened pencil tip, is known so that it can be inserted even into a narrow place (for example, a real pencil). Kaihei 4-108976).

[0003]

During the plasma processing, the electrodes and nozzles at the tip of the torch are at the highest temperature, and thus are consumed much. Therefore, liquid cooling of the electrode and the nozzle is generally performed. In particular, since the nozzle generates a large amount of heat and has a large size as compared with the electrode, a large coolant flow path is required. However, since the conventional pencil-type torch becomes thinner toward the tip, the cooling liquid passage for the nozzle must be similarly designed to be thin. Therefore, it is difficult to sufficiently cool the nozzle.

Accordingly, it is an object of the present invention to provide a plasma torch which can be inserted into a narrow place and can easily cool a nozzle.

[0005]

A plasma torch according to the present invention includes a nozzle having an arc outlet and a cap which is placed outside the nozzle and forms a water jacket region around the nozzle. The cap has a predetermined outer diameter and a cap base end extending in the torch axis direction, and a cap distal end having a substantially constant outer diameter smaller than the cap base end and extending in the torch axis direction, It has a cap taper portion connecting the cap base end and the cap tip.

[0006] The outer shape of the plasma torch is largely determined by the outer shape of the cap. However, in the plasma torch of the present invention, since the tip of the cap is thinner than the base end, it can be inserted into a narrow place as in the case of a conventional pencil torch. It is possible. In addition, the outer diameter of the tip of the cap does not taper toward the tip like a pencil-type torch, but is kept almost constant. It is easier to secure than a pencil torch.

For the purpose of securing the water jacket area, the nozzle also has a constant outer diameter and a nozzle base end extending in the torch axial direction, and a substantially constant outer diameter smaller than the nozzle base end. It is desirable to comprise a nozzle tip portion extending in the axial direction, and a nozzle taper portion connecting the nozzle base end portion and the nozzle tip portion. Since the outer shape of the nozzle is essentially the same as the outer shape of the cap, the outer peripheral surface of the nozzle is substantially parallel to the inner peripheral surface of the cap. No. Therefore, it is possible to cool the nozzle well.

[0008] The outer periphery of the nozzle is a water jacket. However, since a gas flow path usually exists inside the nozzle or at the base end of the base end of the nozzle, the water jacket and the gas flow path are connected to each other. Therefore, a structure for isolating is required. In this case, if the base end of the nozzle has a constant outer diameter as described above, a cylindrical body is externally fitted to the base end of the nozzle having the constant outer diameter in an intimate manner via an O-ring or the like. With a simple structure, the water jacket and the gas flow path can be reliably separated.

It is desirable that the nozzle is long enough to be accommodated in a portion from the tip of the cap to the tapered portion.
As a result, the size of the replacement nozzle, the guide, and the electrode rod can be reduced, so that the running cost can be reduced. In this respect, the fact that the base end portion of the nozzle is thick as described above is advantageous in that the size of the most frequently replaced electrode rod can be particularly reduced. That is, if the base end of the nozzle is thick, it is possible to design such that the electrode pedestal extending from the base end of the torch enters into the thick base end. When such a design is employed, the electrode rod can be shortened by an amount corresponding to the fact that the electrode pedestal has entered the base end portion of the nozzle.

[0010] Other objects and solutions of the present invention will become apparent in the following description.

[0011]

FIG. 1 shows a cross section along a central axis of a plasma welding torch 1 according to one embodiment of the present invention.

First, the basic structure of the torch 1 will be described.

Although the torch 1 has a substantially cylindrical shape as a whole, when viewed from the point of the outer diameter, the base 1
A, tip 1C, and tapered portion 1B connecting both portions 1A, 1C
And can be divided into The proximal end 1A is a portion on the proximal end side of the torch 1 literally, and extends in the axial direction of the torch 1 while maintaining a large outer diameter. On the other hand, the tip 1C
Is a portion on the distal side of the torch 1 and is
A has a smaller outer diameter than A, and extends in the axial direction of the torch while maintaining the small outer diameter substantially constant. Further, the tapered portion 1B has an outer diameter reduced from the proximal end 1A to the distal end 1C, and connects the proximal end 1A and the distal end 1C.

The electrode rod 3 is located at the center axis position of the torch tip 1C.
Is arranged. The electrode rod 3 is made of a metal having good heat conductivity such as copper. A tip-shaped electrode 5 is fixed to a position to be a main arc discharge point at the tip of the electrode rod 3 by a method such as brazing or press fitting. Tip electrode 5
Is made of a metal having a high melting point and a low work function, such as tungsten.

The electrode rod 3 is housed inside a cylindrical guide 7. The inner peripheral surface of the guide 7 fits the outer peripheral surface of the electrode rod 3. A cylindrical electrode pedestal 17 extends from the center axis position in the torch base end 1A into the tapered portion 1C. The base end of the guide 7 is externally fitted to the front end of the electrode base 17. Further, the base end of the electrode rod 3 in the guide 7 abuts on the distal end surface of the electrode pedestal 17 and is fitted inside the distal end. With this structure, the electrode rod 3 is fixed at the center axis position of the torch tip 1C.

The outside of the guide 7 is covered with a cylindrical nozzle 9. The nozzle 9 is made of a metal having good heat conductivity such as copper. At the time of ignition, a high voltage for generating an arc discharge is applied between the nozzle 9 and the electrode rod 3. Nozzle 9
Is extended further forward than the electrode 5 at the tip of the electrode rod 3, and an arc outlet 19 for blowing out a main arc is opened at the center axis position. The tip of the electrode 5 is desired from the inside of the nozzle at the arc outlet 19. The above-mentioned guide 7 is made of a material having high heat resistance and electrical insulation such as ceramics, particularly a material which is resistant to thermal shock such as silicon nitride. Guide 7
Of the tip 3 extends slightly beyond the tip of the electrode rod 3, and only the head of the tip electrode 5 projects slightly beyond the tip of the guide 7. Therefore, the guide 7 surrounds almost all of the electrode rod 3, thereby completely eliminating the possibility of a pilot arc occurring between the electrode rod 3 and the nozzle 9, and the pilot arc is connected to the electrode 5 and the nozzle 9. Only occurs between

Although the inner peripheral surface of the nozzle 9 has a shape along the outer peripheral surface of the guide 7, a narrow gap 21 is provided between both surfaces. The gap 21 communicates with a gas supply path 23 formed on the base end side of the base end of the nozzle 9 and functions as a gas passage for sending gas toward the electrode 5. Guide 7
The tip part is a swirler and has a plurality of gas ejection holes 25 arranged around the electrode 5. The gas sent to the distal end of the guide 7 through the gas passage 21 is blown out toward the front of the electrode 5 as a swirling flow from the gas ejection hole 25. This gas swirling flow serves to stabilize the position of the main arc coming out of the tip of the electrode 5 so as to pass through the center of the arc outlet 19.

A metal cap 11 is provided on the outer periphery of the nozzle 9.
Is covered. A protective cover 13 is further placed outside the base end of the cap 11. The cap 11 covers a portion including the distal end 1C, the tapered portion 1B, and a part of the proximal end 1A of the torch 1. Therefore, the outer shape of the torch 1 described first is reflected in the outer shape of the cap 11. That is, the proximal end of the cap 11 extends in the axial direction while maintaining a substantially constant large outer diameter, and the distal end extends in the axial direction while maintaining a substantially constant outer diameter clearly smaller than the proximal end,
The outer diameter of the tapered portion connecting the two portions is reduced from the base end to the distal end. The inner peripheral surface of the cap 11 also has a shape substantially parallel to the outer peripheral surface.

The nozzle 9 is accommodated in a portion from the tip of the cap 11 to the tapered portion. The size of the nozzle 9 is naturally smaller than that of the cap 11, and the water jacket region 27 is provided between the outer peripheral surface of the nozzle 9 and the inner peripheral surface of the cap 11.
Are formed. The water jacket region 27 covers almost the entire outer peripheral surface of the nozzle 9 (except for a part of the base end and the tip). The outer shape of the nozzle 9 substantially inherits that of the cap 11. That is, the proximal end of the nozzle 9 extends in the axial direction while maintaining a substantially constant large outer diameter, and the distal end extends in the axial direction while maintaining a substantially constant outer diameter that is clearly smaller than the proximal end. Are connected by a tapered portion. Therefore, the outer peripheral surface of the nozzle 9 and the inner peripheral surface of the cap 11 are substantially parallel. This means that the nozzle 9 is located in the range of the torch tip 1C.
Means that the area of the water jacket region 27 is secured substantially constant. In other words, the water jacket does not become thinner as it approaches the tip of the torch.

At the base 1A of the torch, there is a cylindrical member 29 having an outer diameter substantially the same as the inner diameter of the cap 11, and a male screw 29A is formed on the outer peripheral surface of the cylindrical member 29.
A female screw 11A is formed on the inner peripheral surface of the base end of the cap 11, and the female screw 11A is screwed into the male screw 29A of the cylindrical member 29, whereby the cap 11 is attached to the torch 1. The cap 11 connects the nozzle 9, the guide 7 and the electrode rod 3 inside the cap 11 to the electrode pedestal 17 on the torch 1.
It also plays the role of pressing and fixing. Therefore, when the cap 11 is removed from the cylindrical member 29, the set of the nozzle 9, the guide 7 and the electrode rod 3 can be easily removed by pulling out the set from the electrode base 17. Since the nozzle 9, the guide 7, and the electrode rod 3 are consumables, they are replaced as needed.

The inner peripheral surface at the distal end of the cylindrical member 29 is in contact with the outer peripheral surface at the proximal end of the nozzle 9, and O-rings 31 are interposed at the contact portions on both surfaces. The O-ring 31 allows the gas supply path 2 existing on the base end side of the base end of the nozzle 9.
3 and the water jacket region 27 present on the outer periphery of the nozzle 9 are completely isolated. In the wall of the cylindrical member 29, a water supply path 33 for supplying cooling water to the water jacket area 27 on the outer periphery of the nozzle 9 and a water discharge path 35 for discharging cooling water from the water jacket 27 are provided. They are formed symmetrically with respect to the central axis. The joint water channel 37 is connected to the base end of the water supply channel 33, and the water discharge channel 3
5 has a drainage channel 3 for guiding cooling water out of the torch.
9 is connected.

Another thinner cylindrical member 41 is arranged at the center axis position of the torch in the inner space of the cylindrical member 29. The above-described cylindrical electrode pedestal 1 is attached to the tip of the cylindrical member 41.
7 is fixed by screwing. As described above, the electrode rod 3 is attached to the tip of the electrode pedestal 17. Inside the electrode rod 3, an elongated cavity is formed from the base end to the position on the back side of the electrode 5. . A water supply pipe 43 for guiding cooling water from outside the torch into the torch is inserted into the inside of the cylindrical member 41 and the electrode base 17. A thin needle pipe 45 is attached to the tip of the water supply pipe 43, and the needle pipe 45 is inserted deeply into the cavity of the electrode rod 3 to a position near the back side of the electrode 5. A gap 47 is provided between the inner peripheral surface of the cavity of the electrode rod 3 and the outer peripheral surface of the needle pipe 45, and the gap 47 is formed from the distal end to the proximal end while cooling water cools the electrode rod 3. It becomes a cooling water passage for flowing. Outer peripheral surface of water supply pipe 43, cylindrical member 41 and electrode pedestal 17
Gaps 49 and 51 are also provided between the gap 4 and the inner peripheral surface of the gap.
Reference numerals 9 and 51 serve as cooling water channels for sending the cooling water coming out of the electrode rods 3 to the joint water channel 37. A plurality of shortcut holes 53 communicating the inside of the water supply pipe 43 and the outer gap 51 are opened at a position slightly upstream of a connection point with the needle pipe 45 at the distal end of the water supply pipe 43. A gap 49 between the cylindrical member 41 and the water supply pipe 43 is connected at a base end thereof to an inlet of the above-described joint water passage 37, and communicates with the above-described water supply passage 33 to the water jacket region 27.

Of the above basic structures, the following four structures are particularly noteworthy. The first is the outer shape of the torch 1 and the shapes of the cap 11 and the nozzle 9. The second is the shape of the nozzle 9, the guide 7, the electrode rod 3, and the electrode pedestal 17 and the positional relationship between them. The third is the structure and positional relationship between the tip of the guide 7 and the tip of the electrode rod 3. The fourth is a cooling water piping structure. Hereinafter, each point will be described in detail.

As shown in FIG. 1, the outer shape of the torch 1 is
It reflects the outer shape of the cap 11, and includes a base end 1C having a substantially constant large outer diameter, a distal end 1C having a substantially constant small outer diameter, and a tapered portion 1B connecting both parts. Have been. Since the outer diameter of the torch tip 1C is small, the work can be performed by inserting the tip 1C into a narrow place. Moreover, since the torch tip 1C, that is, the tip of the cap 11, does not become thinner as approaching the tip as in a conventional pencil-type torch, it extends while maintaining a constant outer diameter. The area does not become extremely narrow at the tip. And cap 1
The outer shape of the nozzle 7 housed inside 1 also has a cap 11
Is inherited, and the outer peripheral surface of the nozzle 9 and the inner peripheral surface of the cap 11 are substantially parallel. As a result, the water jacket region 27 on the outer periphery of the nozzle 9 is secured with a constant area at any place of the nozzle 9, so that the nozzle 9 can be sufficiently cooled.

The proximal end 1A of the torch, that is, the proximal end of the cap 11 has a large outer diameter, and various electrical and mechanical structures for supplying power and supplying / discharging the cooling water are packed therein. Have been. For example, the cylindrical member 29 having the water supply channel 33 and the drain channel 35 and the electrode base 17 are connected to the torch base end 1.
A. The tip of the cylindrical member 29 and the tip of the electrode pedestal 17 project into the tapered portion 1B, and a set of the nozzle 9, the guide 7, and the electrode rod 3 is attached thereto. Therefore, the nozzle 9 which is a replacement part
The length of each of the guide 7 and the electrode rod 3 may be shorter than the total length of the tapered portion 1B and the tip 1C of the torch 1.

In particular, the electrode 3 to be replaced most frequently can be quite short, in particular, as can be seen from FIG. 1, about the same as or slightly longer than the length of the torch tip 1C. . The main reason why the electrode rod 3 can be shortened in this way is that the tip of the electrode pedestal 17 protrudes largely to the vicinity of the entrance of the torch tip 1C. One factor that enables such a large protrusion of the electrode pedestal 17 is the shape of the cap 11 described above. As a second factor, the shape of the cap 11 is determined by the nozzle 9 and the guide 7.
Is also inherited. That is, the nozzle 9
Has a thin distal end that fits within the distal end 1C of the torch (cap 11), a base end that is clearly wider than this distal end, and a tapered portion that connects the two. The guide 7 also has a thin distal end, a thick proximal end,
And a tapered portion. The distal end of the electrode pedestal 17 enters the thick base end of the guide 7. By entering the guide 7 in this manner, the tip of the electrode pedestal 17 protrudes greatly, and as a result, the electrode rod 3 is shortened.

The nozzle 9 and the guide 7 are
Inheriting the above shape also gives rise to several other advantages: First, since the base end of the nozzle 9 maintains a constant outer diameter, the outer peripheral surface of the base end of the nozzle 9
The inner peripheral surface of the distal end portion of the cylindrical member 29 can be firmly adhered via the O-ring 31. As a result, the gas supply path 23 existing on the base end side of the base end of the nozzle 9 can be reliably isolated from the water jacket region 27 on the outer periphery of the nozzle 9. In addition, the base end of the nozzle 9 and the base end of the guide 7 maintain a constant outer diameter and inner diameter, and are fitted in a slightly fitted state. It is fitted outside with a good fit at the tip of the. As a result, the nozzle 9 and the guide 7 are reliably positioned and mounted coaxially with the electrode pedestal 17.

The electrode rod 3 has a flange 55 having a certain thickness near the base end thereof.
Are in contact with the distal end surface of the electrode pedestal 17. In addition, a portion 57 of the electrode rod 3 protruding from the flange 55 to the base end side is fitted into the inside of the distal end portion of the electrode pedestal 17. Thus, the electrode rod 3 is connected to the flange 55 and the base end 57.
Contacting the electrode pedestal 17 at both sides improves the electrical connection between the electrode rod 3 and the electrode pedestal 17. In addition, the flange 55 of the electrode rod 3 ensures the positioning of the electrode rod 3 with respect to the electrode pedestal 17 in the axial direction, and the electrode rod 3
Also prevents tilting. On the other hand, the base end portion 57 of the electrode rod 3 fitted into the electrode pedestal 17 ensures the coaxial positioning of the electrode rod 3 with respect to the electrode pedestal 17.

As shown, the flange 55 of the electrode rod 3 is located at a position near the entrance of the tapered portion of the nozzle 9 and the guide 7, in other words, at the most distal end position that can enter the nozzle 9 and the guide 7. ing. Of course, the electrode pedestal 17
Has also entered the nozzle 9 and the guide 7 up to the position 55 of this flange. In short, the flange 55 of the electrode rod 3 and the electrode pedestal 17 are arranged at a position on the distal end as much as possible in the torch. With such a design, the electrode rod 3 has a minimum length.

FIG. 2 is an enlarged cross-sectional view taken along the central axis, showing the vicinity of the distal end of the guide 7. FIG. 3 is a cross-sectional view taken along line AA of FIG. The cross section of FIG.
-Along line B.

The distal end 7A of the guide 7 extends further forward than the distal end of the electrode rod 3 as described above.
Only protrudes forward beyond the guide tip 7A. As a result, a pilot arc is generated only between the electrode 5 and the nozzle 9. In order to obtain this advantage, the head of the electrode 5 does not necessarily have to protrude beyond the guide tip 7A, and the electrode 5 head is at the same position as the guide tip 7A or slightly recessed. Some designs are possible in some cases. Further, the guide tip 7A does not necessarily need to extend beyond the electrode rod 3, and a design in which the guide tip 7A is at the same position as or slightly recessed from the tip of the electrode rod 3 is also possible in some cases.

The guide tip 7A also functions as a swirler as described above. The structure of the swirler will be described in detail below. In this embodiment,
The guide 7 has a swirler distal end 7 and a proximal end 7B.
Are integrally formed as a single component, but the swirler distal end portion 7A can be separated from the proximal end portion 7B, and the guide 7 may be formed of two components. .

A portion 7 of the guide 7 on the proximal side from the distal end portion 7A.
B has an outer diameter slightly smaller than the inner diameter of the nozzle 9 as described above, and forms a gas passage 21 between its outer peripheral surface and the inner peripheral surface of the nozzle 9. On the other hand, the outer peripheral surface of the guide distal end portion 7A protrudes outward stepwise from the base end side portion 7B, and is in close contact with the inner peripheral surface of the nozzle 9. Four gas introduction grooves 61 communicating with the gas passage 21 are formed in an axially extending portion of the guide distal end portion 7A that protrudes outward. The four gas ejection holes 25 are formed in the radial direction so as to communicate with the four gas introduction grooves 61, respectively, and these gas ejection holes 25 surround the electrode 5 near the electrode 5. Open in position. As shown in FIG. 3, the gas ejection holes 25 are oriented so as to eject gas substantially tangentially to the space 63 around the electrode 5, so that a high-speed gas swirling flow is generated around the electrode 5. Will be done. As a result, the flow velocity of the gas swirling flow at the position of the electrode 5 is higher than that of the conventional torch in which the gas swirling flow is generated at a position deeper than the electrode, so that the pilot arc is swept away by the gas flow. The effect of shifting to the main arc and the effect of stabilizing the main arc with the gas swirling flow are further improved. Such an advantage is attributable to the fact that the guide tip 7A, which is a swirler, is arranged near the electrode 5, but the main factor that allows the guide tip 7A to be arranged near the electrode is the guide 7 Is to use a ceramic material such as silicon nitride which is strong against thermal shock.

FIG. 4 schematically shows the piping structure of the cooling water of the torch of FIG. 1 for easy understanding.

A part of the cooling water from the water supply pipe 43 enters the electrode rod 3 through the needle pipe 45 and flows through the flow path 47 between the needle pipe 45 and the electrode rod 3 from the distal end to the proximal end. To cool the electrode rod 3 and then
7 to a water jacket region 27 around the nozzle to cool the nozzle 9. The remaining cooling water from the water supply pipe 43 passes through the shortcut hole 53 and is supplied to the water supply pipe 4.
The fluid flows out to the flow paths 51 and 49 on the outer periphery of the nozzle 3, thereby bypassing the electrode rod 3 and flowing to the water jacket region 27 on the outer periphery of the nozzle to cool the nozzle 9. The area of the shortcut hole 53 is determined in consideration of the calorific value of the nozzle 9 and the electrode bar 3 such that the distribution ratio of the amount of cooling water to the nozzle 9 and the electrode bar 3 substantially matches the ratio of the calorific value between the two. . For example, nozzle 9
Is about four times as large as that of the electrode rod 3, the total area of the shortcut holes 53 is 3 to 3 times the cross-sectional area of the needle pipe 45.
It may be set to about 5 times (for example, the needle pipe 4
(3-5 short-cut holes 53 having the same diameter as 5). With such a structure, even if the electrode rod 3 is designed to be thin, the nozzle 9 can be sufficiently cooled. If the electrode rod 3 can be designed to be thinner without lowering the cooling capacity, the torch tip 1C can be designed to be thinner, and a torch capable of working in a narrower place can be provided.

Although the preferred embodiment of the present invention has been described above, the above-described embodiment is an exemplification for describing the present invention, and is not intended to limit the scope of the present invention only to this embodiment. Without departing from the spirit of the invention, those skilled in the art
The present invention can be implemented in various other forms in which various modifications, improvements, modifications, simplifications, and the like are added to the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along a central axis of a plasma welding torch according to one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along the line BB of FIG. 3, showing the vicinity of a guide tip of FIG. 1 in an enlarged manner.

FIG. 3 is a transverse sectional view taken along the line AA of FIG. 2;

FIG. 4 is an explanatory view schematically showing a piping structure of cooling water of the torch of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 torch 1A torch base end 1B torch taper 1C torch tip 3 electrode rod 5 chip-shaped electrode 7 guide 9 nozzle 11 cap 13 base end protection cover 15 tip protection cover 17 electrode pedestal 19 arc outlet 21 gas passage 23 gas Supply path 25 Gas injection hole 27 Water jacket area 29 Cylindrical member 31 O-ring 33 Water supply path 35 Drainage path 37 Joint pipe 39 Drainage pipe 41 Cylindrical member 43 Water supply pipe 45 Needle pipe 47, 49, 51 Gap (cooling water flow path) 53 Shortcut Hole 55 Flange of electrode rod 57 Base end of electrode rod 61 Gas introduction groove 63 Space near electrode

Continued on the front page (72) Inventor Yosuke Imai 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture, Komatsu Seisakusho Laboratories (72) Inventor Toru Shiina 1200, Manda, Hiratsuka-shi, Kanagawa Prefecture Komatsu Seisakusho Research Laboratories (72) Invention Person Hiroshi Aoyama 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture, Komatsu Ltd.

Claims (6)

[Claims] 1. A nozzle having an arc outlet, and a cap which is placed over the outside of the nozzle and forms a water jacket region on an outer periphery of the nozzle, wherein the cap has a predetermined outer diameter. A cap base end extending in the torch axis direction; a cap tip end having a substantially constant outer diameter smaller than the cap base end and extending in the torch axis direction; the cap base end and the cap tip end; A plasma torch having a cap taper portion connecting the two. 2. A nozzle base end having a constant outer diameter and extending in the torch axial direction, and a nozzle having a substantially constant outer diameter smaller than the nozzle base end in the torch axial direction. The plasma torch according to claim 1, further comprising: a nozzle tip that extends, and a nozzle taper that connects the nozzle base and the nozzle tip. 3. The plasma torch according to claim 1, wherein the nozzle is housed in a portion of the cap from the tip portion of the cap to the tapered portion of the cap. 4. A nozzle base end having a constant outer diameter and extending in the nozzle axis direction; a nozzle tip end having a substantially constant outer diameter smaller than the nozzle base end and extending in the nozzle axis direction; A nozzle for a plasma torch, comprising: a nozzle taper portion connecting the nozzle base end portion and the nozzle tip portion. 5. A cap base end having a predetermined outer diameter and extending in the torch axis direction; a cap tip end having a substantially constant outer diameter smaller than the cap base end and extending in the torch axis direction. A cap having a cap taper portion connecting the cap base end portion and the cap tip portion is accommodated in the cap so that the nozzle axis coincides with the torch axis, and can be attached to the plasma torch. 4. The nozzle for a plasma torch according to 4. 6. A cap for a plasma torch which is placed over a nozzle having an arc outlet and forms a water jacket region on an outer periphery of the nozzle, and has a predetermined outer diameter and extends in a torch axial direction. A base end portion of the cap, a tip end portion of the cap having a substantially constant outer diameter smaller than the base end portion of the cap and extending in the torch axis direction, and a cap taper portion connecting the base end portion of the cap and the tip end portion of the cap. For a plasma torch.