DE1940040A1 - Plasma torch - Google Patents

Description

194QQ40

Patent attorney Dlpl.-Ing. R. BeetzU. Dipl.-Ing. Lamprecht Ql -14.82? P (14.828h) 6.8.1969

MCkidiM 22, SMlnKicNrtetl. 1·

H IT A CH I, LTD. / T ο k i ο (Japan)

Plasma torch

The invention relates to a Piasra burner, in particular a burner, the abrasion resistance of the cathode and the nozzle for an active gas as a working gas is improved.

Plasma jets are used on a large scale in the most diverse Fields of technology used e.g. B, to Fusion cutting and welding of various workpieces, for coating metallic or ceramic Material by spraying, for chemical reactions »as Light and heat sources,

Have the plasma jets used for these purposes a relatively large heat capacity, and the electrodes in the burner to generate such a plasma

81- (Item 19 »O43) * - Hd-r (7)

Beams are of a very high temperature during operation exposed. Especially at the arc focal point of the The cathode and its vicinity often have a temperature of more than 1000 ° C.

To prevent oxidation of the electrodes often non-oxidizable gases such as argon, nitrogen, hydrogen or the like as working gas for generation a plasma jet is used. These non-oxidizable However, gases are generally very expensive, be it that way Procedure is uneconomical, especially if the generated Plasma jet is used for fusion cutting and welding, since it consumes a lot of working gas.

For this reason, attempts have recently been made to use an oxidizable gas such as air or the like as a working gas. In particular, it has become known, on the one hand, to manufacture the electrodes, especially the cathodes, from a material that is very resistant to oxidation even at high temperatures, and, on the other hand, to use a small amount of inert gas to shield the cathode surface and thereby protect the cathode from the Protect working gas that contains air or other active gas. The latter known burner will be explained in more detail with _{reference to FIG. 1 1 of the drawing.}

In the known burner, current is supplied from a direct current source 10 via a current supply line 11 to a cathode 12. After passing through a channel 23, electrons emitted by the cathode 12 hit the; Inner wall of a channel 2h formed in an anode 13. is. The anode 13 is connected to the power source via a power supply line 1A in order to complete the circuit su.

The cathode 12 is carried by a holder 15 which is fastened to a non-conductive housing 16 by screws. Between the cathode 1Ί 'and a nozzle 17 there is a spacer: T8 made of a heat-resistant oxide. "The nozzle 17 is electrically isolated during operation of the burner, and it also has the channel 23 already described. The distaiizstück 18 made of oxide has a continuous still enkannl 25 · The end of the channel 25 facing the cathode 12 has a smaller diameter," while the other end opens into the channel 23 has the larger diameter. Gas inlet pipes 29 and 30 for supplying different gases are attached to the housing 10 at its rear end, and gas inlet slots 26 and 27 'connected to the gas inlet pipes 29 and JO ' serve for introducing the various gases into the step channel 25 According to FIG. 2, which shows a cross section along line-XI-II of FIG. 1, the gas inlet slots 26 are formed tangentially to the circumference of the cathode end surface 20 and open into the narrower section of the channel 25 in the plane which coincides with the cathode end surface 20. The gas inlet slits 27 run similarly tangential to the circumference of the channel 25 open out he in the further section of the channel 25.

In the known plasma torch just described, an inert gas such as argon or the like is fed to the carbon fiber inlet tube 29 and the gas inlet slots 26 on the end face of the cathode. This inert gas forms a very fast helical (helical) flow across the cathode end face so that it acts as its shield.

An active working gas such as air or the like becomes

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fed through the other gas inlet roller 30 and via the Gas inlet slots are introduced into the channel 25 where the active Gas has a helical flow in the same direction how the flow of the inert gas forms, and the active and the inert gas are mixed together in channel 23 in the nozzle, through the opening at the front end of the Brenner to exit.

In such a known plasma torch, the working gas, which forms a strong helical flow, has a low pressure at its axis center, and this low pressure region enables an arc to be easily ignited by itself as well as reducing damage to the inner wall of the torch. Cool inert gas is constantly blown through the inlet slots 2.6 to the end face 20 of the cathode during operation; this inert gas prevents the active gas from penetrating to the cathode end face 20 to a certain extent. This has the great advantage that the cathode end face can be effectively protected by a relatively small amount of inert gas.

Nevertheless, in such a known plasma torch, the flow of the active gas is prevented to the electron emission surface of the cathode or the The arc discharge stabilization is insufficient to operate the torch long enough Amount of the expensive inert gas that is required as a protective gas is relatively large.

When using an active gas as the working gas protection of the nozzle can be done by good cooling of the nozzle. However, more comprehensive protection of the nozzle is known by passing water through the nozzle

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0098 1.1AO-9 6.6

so st-flows that a helical flow of water on the inner surface the nozzle is formed (see. US Pat 2 906 858) 0 Using this procedure, the inner surface of the nozzle essentially completely - from corrosion by the active gas and before the heat of the plasma jet to be protected,

The invention is based on the object of a plasma torch indicate at the efrie small amount of an inert or neutral gas is used to shield the cathode, while an active gas such as air or the like is used as the main or working gas, by in particular, the section of the plasma torch located in the vicinity of the cathode is improved. In this way a lower erosion of the cathode is to be achieved, although air or another active gas than the arc discharge gas is used. In addition, the cathode surface should be covered by a smaller amount of inert gas than previously possible to be protected.

A plasma torch with a cylindrical housing, with a nozzle formed at the front end of the housing, with a cathode holder that has a cathode at one end and at the other end electrically isolated on the housing is attached so that the cathode is in a predetermined Distance from the nozzle is located ^ with a device for supplying working gas into the nozzle, so that a helical flow of the working gas arise in the housing and exit through the outlet opening of the nozzle can, with a device for applying a voltage to generate an arc discharge between the cathode and the nozzle or a suitable conductor in front of the nozzle, with protective gas inlet slots and with a device

0 0 981 1/0968 bad ofüginal

for supplying protective gas to the protective gas iiilaöschlitzen

is characterized according to the invention in that the front end of the Kathodeiihal age has a recess, its bottom surface with the electron emission surface the cathode is aligned so that the inert gas inlet cord is in Abstänien auf.dem extent of the recess closer to their Muzzle ends are arranged in the nozzle and open into the recess tangential to the circumference, and that the |. Diameter of the recess on hers > iündun / .seride smaller ■ than is at the section with the inert gas inlet slots,

The invention will be explained in more detail with reference to the drawing., It shows:

Fig. 1 is a longitudinal section through a known one Plasma torch;

Fig. 2 shows a cross section along line U-II. from Fig. U

Fig. 3 is a longitudinal section through a Ausführungsbeifi game of the plasma torch according to the invention;

FIG. 4 is a cross section along line IV-IV of FIG

Fig. 3;

Fig. 3 shows a cross section along line V-V of Fig. 3 »

6-8 show a longitudinal section through various modified ones Exemplary embodiments of the cathode holder according to the invention}

9 is a photograph of a longitudinal portion of FIG

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Cathode tip and its adjacent area to explain the degree of consumption of the cathode tip during operation of the plasma torch according to the invention;

Fig. 10 is a similar photograph for explaining the Degree of consumption of the cathode tip during the operation "of the well-known plasma torch;

Fig. 11 compares the curves of the consumption of the cathode tip in the plasma torch according to the invention and in the known plasma torch; and

Fig. 12 is a partial view, in longitudinal section, of the front end of the burner according to another embodiment the invention"

Figs. 1 and 2, which lines the known burner, are has already been explained above.

In Fig. 3 to 5 an embodiment of the plasma torch according to the invention is shown. The plasma torch has a housing 32 with a nozzle 31 at one end. A cathode holder 33 with a cylindrical insulating piece 48, which is located between the housing 32 and the cathode holder 33, is firmly attached in the housing 32. At the front end of the holder 33 opposite the nozzle 3 "! There is a recess "} h in the form of a truncated cone, the mouth end of which has a smaller diameter than the opposite bottom end. Inward to the bottom surface of the recess 34 • a cathode tip 3 "is embedded in such a way that at least the center of the bottom surface of the recess has an electron

009811/0968. bad original

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emission area 35 forms. At the rear end of the cathode holder 33 there is an inlet pipe 37 for the supply of protective gas and an inlet 38 for the supply of cooling water, the pipe 37 and the inlet 3 $ being connected to a protective gas duct 39 and a cooling water duct 40, respectively, both of which are located in the cathode holder 33 are located·. The protective gas channel 39 has protective gas inlet slots 4i which open into the recess 3A. The shielding gas inlet ports are formed such that they are tangentially separated to the side wall of the ψ recess 3h open and a predetermined distance from the bottom of the recess 34, as shown in FIG. It can be seen, so that a strong helical flow of the protective gas 3k in the recess be formed can if the protective gas is introduced.

An inlet pipe 42 for introducing working gas is provided on the other surface of the housing 32 and connected to an annular channel 43 for the working gas which is formed in the housing 3 ² at a distance from the mouth end of the recess 3k in the nozzle 31. Working gas inlet slots 45 are connected to the annular channel 43 and open into a cavity kk in the housing 32. The working gas inlet slots 45 are tangential to the inner side wall of the housing 32 (see. Fig. 4), so that a helical flow of the working gas in the same direction as the helical flow of the protective gas in the cavity 44 in front of the recess 34 can form when the working gas flows into this. Another channel 47 is located axially in the wall of the housing 32, one end of which is connected to the cooling water channel 40 via a slot 49 which is located in the cylindrical insulating piece 48. The other end of channel 4? is connected to a Kühlwasserkreislaufkaixal 50, which the inner wall of the nozzle 31 at the front end of the

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Housing 32: surrounds. ■ * A KühlwasserauslaßrpHr 51, which with the circulatory channel 50 is connected, is located outside of the housing 32 at the front end thereof.

If the plasma torch described is in accordance with the invention is used as a non-transfer burner, the Cooling water inlet 38 at the rear end of the cathode holder 33 also as a connection for connection to the negative pole a power source, while the cooling water outlet pipe 51 at the front end also as a connection for connection with the positive pole of the power source is used. When the cooling water flows through the cooling water system and at the same time the cooling water inlet and the outlet pipes to the outlet speaking poles of the power source are connected, with the working gas through the working gas inlet pipe 42 flows, an arc discharge occurs between the cathode 35 and the inner surface of the nozzle 31 such as. described above ;; ignited so that the working gas is heated, ionized and strong, is converged to form a plasma jet 52 ^ the emerges from the nozzle 31.

When the plasma torch is used as a transfer torch becomes, an arc discharge between a suitable Conductor (not shown) on the front of the nozzle 31 and the cathode 35 is generated.

When an active gas such as air or the like is used as the working gas for this burner, an inert gas such as argon is introduced into the recess 3 ^ through the shielding gas inlet slots At, so that a helical flow; of the protective gas can arise in the recess 3h.

0 09811/0968

From the foregoing description it should be apparent that the plasma torch according to the invention provides significantly more effective protection of the cathode from corrosion by the active gas than the known plasma torch described above. This is achieved primarily because of a predetermined distance ⁵ between the protective gas inlet slots kl , and the electron emission surface 35 does not disturb the helical flow of the protective gas, even if a certain unevenness of the catholic tip 36 is present at the beginning or is caused later.

For example, if air is the working gas and argon is the Protective gas used in the known plasma torch according to FIG. 1 to generate a plasma jet is the Consumption of the cathode tip so that the strong helical Flow of the working gas and the protective gas the arc focal point essentially in the center of the electron emission surface hold, so that a strong erosion takes place in this section of the electron emission surface, which is exposed to the focal point, and a bulge arises around the ablated area.

If the protective gas is introduced in such a way that it touches the end surface of the cathode, as is the case with the known burner, the ablated area and the bulge, which are created in the electrode emission surface as just described, disrupt the helical flow of the protective gas , which in turn causes the arc focal point to move continuously on the electron emission surface of the cathode. This constant movement of the Bpgenprennflecke leads on the other hand to an increase in the ablation and Jd ^ i ¹ Atjrab; a, iie}> uiig at the

009811/0968

nenenii ssionsaberfläche, so that a greater perturbation of the Lielical flow of the protective gas the result; 1st what the inert gas has a greater effect on the electron emission surface meets. The cathode is therefore heavily consumed by the inert gas.

In contrast to this, in the plasma torch of FIG. 1 according to the invention by the formation of a space between the electron emission surface of the cathode and « the protective gas inlet slots are essentially avoided, that the helical flow of the protective gas is "disturbed, even if a certain amount of erosion and a bulge are present at the beginning or later in the electron emission surface the cathode are formed, so that the risk of an increase in the ablation and the The bulge in the electron emission surface, as in the known plasma torch, is extremely small. that the inert gas atif the electron emission surface reaches the cathode is considerably reduced.

The second reason for the extraordinarily good protection of the cathode through the design according to the invention is due to the fact that the smaller diameter of the Recess 3 ^ at the mouth end compared to Diameter of the recess 3 ^ at its section with the Inert gas inlet slots a more effective convergence of the Protective gas than with the known plasma torch, resulting in great stabilization of the arc discharge.

That, is to be explained in more detail _o A fluid stroni striämii-. Along the wall surface which it touches. If so de? _rl pi5climesser of the recess at its mouth end in the wese ^ tüjiGhejiig same as the diameter of the recess

_BATH

its section is where the protective gas inlet slots are present, as in the known plasma torch according to FIG. 1, the shielding gas is distributed at the mouth end of the recess in the circumferential direction of the end face of the cathode holder, so that the protective gas greatly reduces its protective effect after leaving the recess.

In contrast, according to the invention, the smaller diameter of the recess at its mouth end is used for F Reduction of the distribution of the protective gas in the circumferential direction the end face of the cathode holderβ and increases the Helical flow of the protective gas at the mouth end of the recess. This enables a greater convergence of the protective gas and fixing the arc focal point to a predetermined one Place on the electron emission surface of the Cathode to give a very stable discharge. Furthermore, due to the increased helical flow of the protective gas the impingement of the active gas on the electron emission surface the cathode is greatly reduced, which also helps a lot to protect the cathode «

. Using Fig. 6-8, the longitudinal section should now be

various shapes of the front end of the cathode holder are explained according to the invention.

In the embodiment shown in Fig. 3, the recess Jk at the front end of the cathode holder has the shape of a truncated cone * the diameter of which decreases linearly from the bottom to the mouth end, but the recess Jk can also take a different course.

According to FIGS. 6 and 7, the recess Jk can have a rare wall 53 which is curved inwards or outwards.

009811 ■: / 0 9S8

Optionally, the recess 3 ^ according to FIG · 8, a mouth end with the same diameter as the opposite end have, but an orifice plate is $ k attached to the MUndungsende, which has in the middle a narrow hole "These optional facing en From filhrungs forms of Recesses have essentially the same function as in the exemplary embodiment of FIG. 3.

Fig. 9 shows a longitudinal section through the front end of Kathodenhalterβ according to the invention, while Fig. 10 is a similar view of the front end of the known plasma torch darstelltι both FIG _e are illustrative of the consumption of the cathode.

The operating values for the associated plasma torches are given in Table 1 below

Table 1

Burner according to the known burner invention (Fig. 9) (Fig ^.: TO)

Arc current (A) ■ 300 300

Shielding gas », (ΐ / πι ± η) N_s 7 - Art 14

Working gas' (l / min) Lmfti 65 Luftι 5k

Operating time (h) 12 12

¥ © rlcstoff was feeid® Br «n-

Me - a «f too M: Fifc: S

From the table above it can be seen that the burner according to the invention used nitrogen as protective gas, the flow rate of which was half that of the known burner, while the flow rate of air as the working gas was 10 5b greater than that of the known burner * Despite such Unfavorable working conditions for the burner according to the invention compared to the known burner, the consumption of the cathode tip after .12 hours of operation for the burner according to the invention (Fig. P 9) was significantly less than for the known burner {Fig. 10).

11 shows the dependence of the consumption of the cathode on the operating time for the burners of FIG. 9 (according to the invention) and FIG.

The operating conditions for each burner were! Inert gas F ₂ 10 l / NTiN, work Gass air 6'Q l / m ± n _t Bog © nPOWER 300 A. ¥ ie in FIG. 11 can be seen, the consumption of the Kathod @ j3spitze at the plasma torch according to the invention only about 1 / 6 as big as the well-known plasma torch. ^J

The life of the entire burner essentially depends from the service life of the cathode »therefore mean these figures that by the invention the The service life of the burner can be increased substantially by six times compared to the known burners.

Furthermore, according to the invention, ® ± n UmlikätlmT water-

strow along dar - Ziraexif lttehe d «r, .Diia · etrife # w, tsnu dwßjh. the opening "the bus © ββ initiated« rdesj iaffäsr fl®s «aaetrafel v®n ©

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The inner wall of the nozzle is protected from damage by the water film; step next to it, still to be explained Benefits on.

FIG. 12 shows schematically in longitudinal section the nozzle of an exemplary embodiment of the plasma torch according to FIG Invention in which a helical stream of water flows along the inner wall of the nozzle as mentioned above.

The embodiment of Fig. 12 has an inlet pipe 61 extending outwardly from the housing JZ for introducing water into the nozzle, an annular water circulation channel 62 in the housing 32 which is connected to the water inlet pipe 61 via a channel 6j, and water inlet slots 6k _$ which open into the nozzle 31 tangentially to its inner edge. .

In the embodiment shown, water is forced into the circulation channel 62 via the inlet pipe 6V and then fed in through the inlet slots 6k to generate a helical water stream 6'5 which flows in close contact with the inside of the nozzle. When this water flow reaches the nozzle outlet, it emerges in the form of an outwardly diverging water jet 66 together with the plasma jet 52.

The embodiment shown in Fig. 12 has the following advantages; '.'. - - ... "-. .--- ι '

1. The inner surface of the nozzle can be effectively cooled without affecting the arc discharge, and the nozzle can from thermal or chemical damage

009811/0968

be protected by the very hot plasma jet, so that the life of the nozzle is increased considerably.

2. The outer edge of the plasma jet is strongly cooled, so that a stronger pinch effect occurs and thus the plasma jet has a higher energy density.

3 "Toxic NO ₂ gas that is produced when using

^ Air or any other fluid that contains oxygen and / or ™ nitrogen, which is created as working gas, can be easily removed. Oxygen or nitrogen are reacted with nitrogen or oxygen in the atmosphere when heated in the plasma jet when it leaves the nozzle, so that gaseous NO is formed, which is further oxidized to NO ,, gas. The gaseous NO generated in this way. is water-soluble and can therefore be easily absorbed by the water jet 66 emerging from the nozzle

H. If the plasma jet is used to cut up work pieces or to process them in some other way, then the work pieces are prevented from being subject to a so-called L · ^w shoulder deformation "which would otherwise occur Interface of the work piece could occur. When a Plasma jet is used to cut a metallic workpiece by melting it, the material becomes of the workpiece in the vicinity of the interface heated to a very high temperature, so that the metal is melted in cross section so that a rounded The end surface is what is called "shoulder deformation". With the known plasma torches, this "shoulder deformation" is very difficult to prevent, while it is easy to prevent due to the water flow that occurs together with the plasma jet (see FIG. 12)

009811/0968

can be prevented so that the separated workpieces to have a smooth interface »

As already mentioned, the plasma torch according to the invention can work well for many hours, whereby only a small amount of inert or neutral gas how nitrogen is used as a protective gas, while air or another active gas is used as the working gas. Through this will be the cost of the working gas so far the use of plasma beams * for processing various Workpieces or as a light and heat source have prevented, decreased considerably. In this way the invention allows greater use of plasma jets in engineering. ·

Claims (1)

Claims i 1, plasma torch, with a cylindrical housing, with a nozzle formed at the front end of the housing, with a cathode holder that holds a cathode at one end and is attached to the housing at the other end in an electrically insulated manner located at a predetermined distance from the nozzle, with a P Means for supplying working gas into the nozzle, so that a helical flow of the working gas can arise in the housing and exit through the outlet opening of the nozzle, with a device for applying a voltage to produce an arc discharge between the cathode and the nozzle or a suitable one Head in front of the nozzle, with protective gas inlet slots and with a device for supplying protective gas to the protective gas inlet slots, thereby g eke η η ζ β ic H η et that the front end of the cathode holder (33) has a recess (3 * 0, the bottom surface with the Elektronemisslonsoberflache (35) of the cathode (.36) is aligned that the inert gas inlet slot (4i) at intervals on the The circumference of the recess is arranged closer to its mouth end in the nozzle (31) and opens into the recess tangentially to its circumference, and that the diameter of the recess at its mouth end is smaller than at the section with the protective gas inlet slots (Fig. 3 - 5) · 2. Plasma torch according to claim 1, characterized in that » that the recess (34) is tapered so that you Continuous diameter: vosi d © r - B © d @ siÖlle & @ zum Mtin.- · end of application decreases (Fi ^, 3 »6, 7) · © 08 t.t / 09S8 3. Plasma torch according to claim 2 * characterized in that that the side wall of the recess (3 * 0 is a conical surface is (Fig. 3), **. Plasma torch according to Claim 2, characterized in that that the side wall of the recess (3 * 0 a rotational is hyperboloid (Figures 6, 7). 5β plasma torch according to claim 1, characterized in that that the recess (3 * 0 carrying end of the cathode holder (33 ') has an opening (5 * 0, the diameter of which smaller than that of the recess, so that the diameter the recess at the mouth end is smaller than in any other section (Fig. 8). 6. Plasma torch according to claim 1, characterized by a device (61, 63, 62) for generating a helical Water flow (65) on the inner surface of the nozzle (31) between the outlet opening of the nozzle and the working gas inlet slots (45) (Fig * 12). 009811/0968