RU2263564C1 - Steam plasmotron - Google Patents

Abstract

FIELD: plasma technology, possibly plasma cutting, surfacing, metallurgy, plasma chemistry and so on.

SUBSTANCE: steam plasmotron includes housing. In housing electrode holder with electrode secured to it is placed. Nozzle is secured to housing with gap relative to electrode for forming arc generation chamber. Cooling system in the form of ducts and branch pipes is provided in housing. Plasmotron also includes water supply branch pipe with regulation unit; steam generator having heating member, mounted on non-working end of plasmotron and coupled with arc generation chamber and with cooling system. In order to improve strength of nozzle and electrode and to increase cutting speed due to intensified heat removal out of them, nozzle is provided with protection cover mounted with gap relative to nozzle. Gap value at working end of nozzle is sufficient for cooling in steam generation mode. Outlet of gap is turned to working zone of plasmotron. At inlet of gap there is capillary-porous structure having water supply and steam discharge ducts and connected with heat removal gap at working end of nozzle. Electrode is provided with capillary-porous structure having water supply and steam discharge ducts and arranged inside it.

EFFECT: improved strength of nozzle and electrode, increased cutting speed.

4 cl, 2 dwg

Description

The invention relates to mechanical engineering, in particular to plasma technology, and can be used in various technological operations: plasma cutting, welding, surfacing, metallurgy, plasma chemistry.

When designing plasmatrons, the two most important problems are: ensuring the durability of the elements in contact with high-temperature plasma, and reducing harmful emissions arising during the operation of the plasma torch while maintaining high technological parameters, such as metal cutting speed.

Known plasma torch with water cooling PVR - 402 [TU 16-739.083-76] for air-plasma cutting, including a housing with a water cooling system installed in it with channels for supplying and discharging water, an electrode holder with a cathode and a nozzle with a protective casing and rubber o-rings between the protective cover and the nozzle.

Despite the presence of water cooling, the resistance of the nozzle and electrode of this plasma torch is insignificant (about two hours) due to their ineffective cooling due to the formation of film boiling due to large heat fluxes (about 10 W / m ² ) and, as a result, a decrease in heat transfer from due to the formation of a vapor film.

In addition, when the plasma torch operates, a large number of emissions occur, in particular harmful nitrogen oxides, the generation of which occurs in the low-temperature zone of the plasma. It is not possible to reduce the low-temperature zone of the plasma by increasing the current density (by increasing the compression of the plasma) due to poor cooling of the nozzle and its rapid failure.

A disadvantage of the design of the known plasmatron is also almost instantaneous failure of the rubber bands under the influence of high temperatures, which leads to failure of the plasmatron itself.

In the air plasma torch PMR-74 [G.N.Shirshov, V.N.Kotikov "Plasma cutting", Leningrad, 1987], which includes a housing with a water cooling system located in it with channels for supplying and discharging water with a nozzle with a protective casing located with a gap relative to the latter, and an electrode holder with an electrode and an insert with tangential channels for swirling water, in the gap between the nozzle and the protective casing.

In this plasmatron, air emissions are significantly reduced due to the creation of a protective water curtain, which traps nitrogen oxides and at the same time more intensively cools the nozzle. The design does not contain o-rings between the nozzle and the protective casing, which increases its reliability in operation

But, despite the presence of a water curtain of the working zone of the plasma torch, environmental friendliness is not ensured during the operation of the plasma torch, significant safety measures are required (intensive ventilation of the working zone, capture and neutralization of emissions).

In addition, the cooling of the nozzle and electrode is also not efficient enough due to the formation of vapor films in the cooling region of the nozzle and electrode.

A large amount of water is required to operate the plasma torch.

Closest to the claimed technical essence and the achieved result is a steam-water plasmatron (RF patent No. 2041039), using water vapor as a working fluid. The steam-water plasmatron contains a housing, an electrode holder installed in it with an electrode fixed therein, a nozzle mounted on the housing with a gap relative to the electrode forming an arc-forming chamber, a cooling system in the form of channels, nozzles and a nozzle cooling jacket in the housing, a water supply nozzle with a regulating device as well as a steam generator with minimal thermal effect on the nozzle channel, since it is fixed on the non-working end of the plasma torch and a heating element mounted on the steam generator. The heating element is equipped with a power source with a current regulator. A temperature sensor connected to a current regulator is installed on the arc-forming chamber.

Fixing the steam generator on the non-working end of the plasma torch (outside the arc chamber), connecting it in series with the plasma torch cooling system, supplying a water supply regulator and current regulator made it possible to obtain a plasma-forming body in the form of dried steam, in which there are no water droplets in the arc forming chamber for all plasma torch power levels.

However, in the known design of the plasma torch, its most heat-loaded zones are not sufficiently cooled: the nozzle channel and the thermochemical insert due to the fact that they are located far from their cooling zones, as a result, despite the good thermal conductivity of copper, a sufficiently intense heat removal from them is not provided.

All this to a certain extent limits the current density of the plasma arc and thus does not allow to achieve high technological parameters, for example, high speed plasma cutting and does not provide sufficient resistance of the nozzle and electrode.

The basis of the invention is the task of increasing the resistance of the nozzle and electrode and increasing the cutting speed by intensifying heat removal from them while maintaining the environmental cleanliness of the cutting process.

The problem is solved in that, in a steam-water plasma torch, including a housing, an electrode holder installed therein with an electrode fixed thereto, a nozzle mounted on the housing relative to the electrode with a gap forming an arc-forming chamber, a cooling system in the form of channels and nozzles in the housing, a nozzle for water supply with a regulating device, as well as a steam generator with a heating element, mounted on the inactive end of the plasma torch and connected to the arc-forming chamber and to the cooling system, the nozzle is supplied with a protective cover installed with a heat-removing gap relative to the nozzle, while the value of the heat-removing gap at the working end of the nozzle is sufficient for cooling in the vaporization mode, the output of the heat-removing gap faces the working area of the plasma torch, and a capillary-porous structure with water-supplying and steam-removing channels is installed at its entrance associated with the heat sink gap at the working end of the nozzle, and the electrode is equipped with a capillary-porous structure with a water supply and steam channels located inside it.

Wherein:

- in the heat sink at the working end of the nozzle, the outer surface of the nozzle and the inner surface of the cover facing it are made rough;

- capillary-porous system made in the form of a copper mesh;

- the plasma torch body is grounded.

Providing the nozzle with a protective cover installed with a heat-removing gap relative to the nozzle so that the size of this gap at the working end of the nozzle is sufficient to cool it in the vaporization mode, and reversing the exit of the gap to the working zone of the plasma torch allows the heat transfer from the working zone of the nozzle to be maximized by reducing the thermal resistance of the heat-removing section by reducing its length and using the latent heat of vaporization (provided it is cooled in the vaporization mode)

The introduction of a capillary-porous structure with water supply and steam removal channels associated with a heat sink at the working end of the nozzle made it possible to intensify the heat sink from the side surface of the nozzle and the inner surface of the casing, and, on the other hand, to ensure uninterrupted supply of coolant to the heat sink gap directly adjacent to to the most heat-loaded section of the nozzle facing the working area of the plasma torch. In addition, an annular steam jacket emerging at the exit of the heat sink gap protects the steam-water plasma from contact with air, thereby preventing the formation of nitrogen oxides during operation of the plasma torch.

The execution of the outer surface of the nozzle, located in the heat-conducting gap at its working end and rough inner surface of the cover facing it, made it possible to intensify the cooling process by increasing the actual contact surface in the liquid-solid system, improving the wettability of the surfaces of the heat-removing gap compared to a smooth surface, excluding film boiling.

The implementation of the capillary-porous structure in the form of a copper mesh provided intensive heat dissipation due to the high thermal conductivity of copper in the absence of corrosion.

Grounding of the plasma torch case provided on the one hand the worker’s safety against electric shock, and on the other hand provided the possibility of automating the plasma processing process by creating a duty arc mode.

In Fig.1 presents a steam-plasma torch in the context;

figure 2 is a section of a plasma torch with a heat sink gap adjacent to the working area, in section.

The steam-water plasma torch includes a housing 1, a pipe 2 for supplying distilled water to the plasma torch with a valve 3 in it regulating the water supply to the plasma torch, and a current lead 4 connected to the electrode holder 5 installed in the housing 1. The electrode holder 5 is electrically connected to the copper electrode 6 by means of a nut 7 and a thermochemical insert is pressed into it 8. Inside the electrode holder 5, a water supply pipe 9 is installed with a gap for cooling the electrode 6 and water and steam collectors (not shown in the drawing). Outside the electrode 6, a plasma-forming gas swirl 10 and an insulating sleeve 11 are mounted, which together with the insulating sleeve 12 centers the electrode 6 relative to the copper nozzle 13 with the plasma-forming channel 14. In the housing 1, channels 15 and 16 are made for supplying water and discharging the two-phase mixture, respectively. The plasma forming channel 14 is made in the form of a central through hole.

The electrode 6 cooling system available in the steam-water plasmatron includes the water supply pipe installed in the direction of the water and connected in series to the water supply pipe 2 to the plasma torch, a water supply control valve 3, a water supply pipe 9, a capillary-porous structure 17 with water supply channels 18 and 19, and steam outlet, respectively, installed inside the electrode 6, and the channel system of the electrode holder 5 associated with the steam generator 20.

The steam generator 20 is provided with a heating element 21 and a capillary-porous structure 22 located on the inner surface of the steam generator 20, with water supply and steam channels 23 and 24, respectively. The heating element 21 is made, for example, in the form of a spiral of nichrome, the terminals of which are connected to the power supply circuit 25 with a current regulator 26. Outside, the heating element 21 is covered by a casing 27

The cooling system of the nozzle 13 includes a pipe 2 for supplying water to the plasma torch, a valve 3 regulating the supply of water, a channel 15 for supplying water, a capillary-porous structure 28 with channels 29 and 30 for water supply and steam removal, respectively, installed at the inlet of the heat removal gap 31 between the nozzle 13 and the protective a cover 32, and a channel for diverting the two-phase mixture 16 to the steam generator 20. A protective cover 32 is mounted on the housing 1 with a sealing element 33.

At the non-working end of the steam generator 20, a start button 34 of the plasma torch with a sealing element 35 is fixed and closed by a cover 36. When using contact ignition, the steam generator 20 is spring-loaded with a spring 37. (In the case of the oscillatory version, positions 34 and 35 are absent).

The swirler 10 is connected to the arc forming chamber 38 formed in the gap between the electrode 6 and the nozzle 13. A temperature sensor 39 is installed on the housing 1, made in the form of a thermocouple connected to the power supply control system 40 of the heating element 21. The plasma torch housing 1 is equipped with a ground wire 41.

Steam-plasma torch works as follows.

The circuit 25 of the heating element 21 is supplied with electric current. Due to the heat released on the spiral, the plasma torch is heated to a temperature of 120-180 ° C. Upon reaching this temperature, measured by the sensor 39, the valve 3 opens, through the pipe 2 begin to supply distilled water to the cooling system of the plasma torch. Water enters the cooling systems of the nozzle 13 and electrode 6, including a pipe 2, a tube 9, a water supply channel 15 and a two-phase mixture removal channel 16, a capillary-porous structure 17 for cooling the electrode 6 with channels 18 and 19, a capillary-porous structure 28 for cooling the nozzle 13 with channels 29 and 30 and into steam and water collectors located inside the electrode holder 5 (not shown in the drawing).

In capillary-porous structures 17 and 28, water partially evaporates and enters a steam generator in the form of a two-phase mixture 20. In addition, part of the water from the capillary-porous structure 28 enters the heat-removing gap 31, where it evaporates and is discharged into the working zone of the plasma torch, while cooling the most the heat-loaded neck of the nozzle 13 and protecting the steam-water plasma from contact with air in the working area of the plasma torch. In the steam generator 20, the two-phase mixture is drained and in the form of dried steam through the steam collector of the electrode holder 5 and through the swirler 10 enters the plasma formation chamber 38.

When the duty arc contacts the workpiece 42, the power mode of the working arc is turned on and the work cycle of the technological process begins.

This ensures the stability of the nozzle and electrode due to the intensification of heat removal from them while maintaining the environmental cleanliness of the cutting process. In addition, by increasing the current density (which can be achieved by intensifying the heat sink), the cutting speed of parts increases.

Claims (4)

1. A steam-water plasma torch, including a housing, an electrode holder installed in it with an electrode fixed therein, a nozzle mounted on the housing relative to the electrode with a gap forming an arc-forming chamber, a cooling system in the form of channels and nozzles in the housing, a water supply pipe with a regulating device as well as a steam generator with a heating element mounted on the inactive end of the plasma torch and connected to the arc forming chamber and to the cooling system, characterized in that the nozzle is provided with a protective cover installed with a heat sink gap relative to the nozzle, while the size of this gap at the working end of the nozzle is sufficient for cooling in the vaporization mode, the gap exit faces the working zone of the plasma torch, and a capillary-porous structure with water and steam channels connected to the heat sink is installed at its entrance a gap at the working end of the nozzle, and the electrode is equipped with a capillary-porous structure with a water supply and steam channels located inside it. 2. The steam-water plasma torch according to claim 1, characterized in that in the heat sink at the working end of the nozzle, the outer surface of the nozzle and the inner surface of the cover facing it are made rough. 3. The steam-water plasmatron according to claim 1 or 2, characterized in that the capillary-porous structure is made in the form of a copper mesh. 4. The steam-plasma torch according to claim 1, characterized in that the plasma torch body is grounded.

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