RU2777038C1 - Gas-discharge cathode-beam gun - Google Patents

Abstract

FIELD: electronics and electrical engineering.

SUBSTANCE: invention relates to electronics and electrical engineering in the field of heat treatment of metals for the purpose of their vacuum melting, evaporation, deposition, welding, cutting, for additive technologies. The gas-discharge electron-beam gun consists of a gas-discharge chamber, a cathode with a spherical emission surface, and a hollow anode. A spark-suppressing layer is deposited on the inner surface of the hollow anode in the region of the geometric proximity of the cathode with a spherical emission surface. Under the beam guide there is a vestibular evacuation chamber containing an annular system of evacuation nozzles.

EFFECT: increasing reliability, the possibility of implementing long-term technological processes, expanding the functionality of an electron beam gun to provide program-controlled heating modes in accordance with specified requirements.

1 cl, 4 dwg

Description

The invention relates to electronics and electrical engineering in the field of heat treatment of metals for the purpose of their vacuum melting, evaporation, deposition, welding, cutting, for additive technologies, and can be used in automated technological processes for aerospace, shipbuilding and automotive, railway transport, engine - and mechanical engineering.

Electron-beam technologies allow achieving breakthrough results. Of particular note:

- electron beam melting, which is currently widely used in the production of high-purity steels, as well as in the metallurgy of titanium and other refractory and reactive materials;

- electron beam welding, which provides dagger penetration with a very narrow and deep seam with a minimum heat-affected zone of reactive alloys (titanium, zirconium, niobium, molybdenum);

- electron beam sputtering, deposition using electron beam evaporators.

Electron-beam technologies for melting, welding and spraying are implemented using various types of electron guns. In the present invention, we are talking about a gas-discharge electron beam gun (GRELP).

In the information field, there are many varieties of GRELP, in the basic design of which there are the following mandatory elements:

- gas discharge chamber;

- cathode with spherical emission surface;

- hollow anode;

- high-voltage current lead;

- water rheostat;

- high voltage insulator;

- beam guide;

- system of focusing coils;

- system of deflecting coils;

- plasma gas supply system;

- water cooling system;

- flange.

The work of GRELP is based on the following phenomena and processes, which are accompanied by problems that need to be addressed.

In GRELP, ion-electron emission is used, when the energy that causes the emission of electrons is transferred by positive ions bombarding the cathode.

With a gradual increase in voltage under the action of the field, the electrons move towards the anode, and positive ions towards the cathode, but some of the charged particles fall on the walls, some recombine. Recombination of ions and electrons - the formation of neutral atoms or molecules from free electrons and positive atomic or molecular ions; the reverse process of ionization.

Starting from a certain voltage, almost all the charges that are born in the space between the electrodes fall on them. In this case, the current reaches saturation, and its value is determined by the rate of ionizing processes. Such a process is called a non-self-sustained discharge, since when the external ionizer is turned off (in our case, these are natural factors), the current will not flow between the electrodes.

In order for the discharge to become independent, i.e. able to exist in the absence of an external ionizer, it is necessary that as a result of the development of the initial avalanche, at least one secondary electron capable of creating a new avalanche should appear. The transition of a non-self-sustained discharge to an independent one is called an electrical breakdown of a gas; this transition occurs at a breakdown voltage (discharge “ignition” voltage).

With an increase in the working pressure in the gun to the level of 0.01 ... 0.1 mm Hg. and when a high voltage (1...30 kV) is applied, a high-voltage glow discharge (HTR) develops in the interelectrode gas space.

In the process of processing the product with the help of the GRELP in the normal mode of the VTR, there is a harmful phenomenon of the ascent of positive ions knocked out from the surface of the product by fast electrons and accelerated towards the cathode of the GRELP, as a result of which the service life of the cathode is significantly reduced.

There are two modes of glow discharge: normal and abnormal. The anomalous glow discharge mode is actively used in devices for ion-plasma deposition of thin-film coatings. In the anomalous region, with an increase in the external current, both the current density and the potential drop increase. An increase in the space charge is accompanied by a decrease in the width of the so-called dark space. With a further increase in current, the cathode heats up, and thermionic emission under conditions of high field strength begins to prevail over ion-electron emission. There is a sharp drop in voltage, and the discharge can turn into a spark.

The spark discharge significantly reduces the service life of the GRELP electrodes, in particular, the hollow anode; causes a temporary failure in the operation of the GRELP, which requires its restart and re-bringing to the operating mode. As a result, the technological process performed by GRELP becomes intermittent, and its result loses the required properties.

Thus, the processes taking place in GRELP are accompanied by problems:

1) bombardment of the cathode with ions knocked out from the surface of the workpiece (reducing the life of the cathode);

2) spark interelectrode discharges (reduce the resource of the hollow anode, reduce the functionality of the GRELP).

Two inventions should be considered as prototype devices that are similar in design.

The invention RU 2400861 C1 (18.08.2009) contains the basic elements listed above with a distinctive feature in the design of the gas discharge chamber, which contains an annular slotted plasma-forming gas swirler in order to improve the focusing properties of the gun using gas dynamic effects.

The closest prototype is the invention of RU 2323502 C1 (03.07.2006), which proposes high power and reliability GRELP, achieved by optimizing the geometric parameters of the electronic system and controlling the passage of the electron beam (EB) in the beam guide. The design proposed by the authors also contains the basic elements, supplemented by the EC control system.

The disadvantages of the mentioned inventions is the lack of constructive solutions to combat the upward flow of positive ions from the product to the cathode of the metal product evaporated during heating, as well as to protect the hollow anode from destruction caused by interelectrode spark discharges, which results in the need for new solutions to increase the life of the GRELP and its functionality.

The task to be solved by the present invention is to introduce fundamental improvements in the design of the GRELP, providing a comprehensive solution to increase the reliability resource of both the gun itself and its functionality to provide complex program-controlled heating modes in strict accordance with the specified requirements.

This task is achieved in that the gas-discharge electron-beam gun consists of a gas-discharge chamber, a cathode with a spherical emission surface, a hollow anode, water cooling, a high-voltage current supply, a water rheostat, a high-voltage insulator, a beam guide, focusing coils, deflecting coils, a flange, a spark suppression layer on the inner the surface of the hollow anode in the region of geometric proximity of the cathode with a spherical emission surface located under the beam guide of the vestibule evacuation chamber containing an annular system of evacuation nozzles.

A distinctive feature of the present invention is a comprehensive solution for improving the design of the GRELP, which can be applied and adapted to most modern GRELP with an obligatory positive effect, integrally expressed both in increasing the reliability resource of the gun itself and its functionality.

In FIG. 1 shows a schematic diagram of GRELP.

In FIG. 2 shows the main unit of the GRELP, in which the electron beam is formed.

положительными ионами металла

In FIG. 3 shows the process of ionization-recombination of neutral particles

positive metal ions

In FIG. 4 shows the organization of vestibular pumping in GRELP.

The schematic diagram of the proposed GRELP is shown in Fig. 1, where the following designations are accepted:

1 - gas discharge chamber;

2 - cathode with a spherical emission surface;

3 - hollow anode;

4 - spark suppression layer;

5 - plasma gas;

6 - plasma-forming zone;

7 - water cooling;

8 - high-voltage current lead;

9 - water rheostat;

10 - high voltage insulator;

11 - beam guide;

12 - focusing coils;

13 - deflecting coils;

14 - electron beam (EB);

15 - vestibular evacuation chamber (VOK);

16 - annular system of exhaust nozzles;

17 - flange;

18 - heated section of the metal.

The gas-discharge chamber 1 is the central element of the GRELP design, in which cathode 2 with a spherical emission surface and a hollow anode 3 are located. zone 6. The gas discharge chamber 1 is provided with water cooling channels 7. In the upper part of the structure there is a high-voltage current lead 8, which, through a water rheostat 9 and a high-voltage insulator 10, provides a negative high voltage to the cathode 2. The cathode 2 and the hollow anode 3 provide the conditions for generating the emission of EP 14 further formation of which occurs in the beam guide 11 located below the gas discharge chamber 1. The beam guide 11 contains a system of focusing 12 and deflecting 13 coils. Under the beam guide 11 there is a vestibule evacuation chamber 15, containing an annular system of evacuation nozzles 16. The installation of the GRELP structure on the seat is provided using a flange 17. Setting the system of focusing 12 and deflecting 13 coils of the GRELP ensures focusing of the EB on the heated area of the metal 18.

The principle of operation of GRELP is as follows. The cathode 2 and the hollow anode 3 are located in the gas discharge chamber, the geometric shape and mutual arrangement of which provide the primary focusing of the formed EC 14. The necessary conditions for the formation of the EC 14 are the supply of high voltage to the cathode 2 through the high-voltage current lead 8 and the plasma-forming gas (hydrogen) 5 into the gas-discharge chamber 1. The pressure of the plasma-forming gas determines and allows you to adjust the power of the EA 14. The generated EA 14 is controlled in the beam guide 11 by means of the focusing 12 and deflecting 13 coils. The active spot of the EA is focused on the heated area of the metal 18. The heat dissipation of the power dissipated on the structural elements of the GRELP is provided by the water cooling system 7. The body of the GRELP is fixed on the working chamber, in which the technological process is carried out, using the flange 17.

The remaining elements of the presented scheme, namely, the vestibule evacuation chamber 15, the annular system of evacuation nozzles 16, the spark suppression layer 4, are the subject of the present invention and are described below.

The main GRELP unit in which the electron beam is formed is shown in Fig. 2.

на электроды ГРЭЛП вдоль осевой линии зажигается ВТР; образуются положительные ионы

, которые начинают бомбардировать катод 2, и в результате γ-процессов образуются быстрые электроны пучка

(область а). Быстрые электроны пучка

, сталкиваясь с нейтральными частицами

становятся причиной появления новых ионов

и медленных электронов

(область б). В области б показаны два варианта траектории быстрых электронов

. Некоторая часть возникших ионов захватывается электрическим полем и устремляется к катоду 2. Некоторые из них на своем пути испытывают перезарядку, в результате которой образуются быстрые нейтральные частицы

, движущиеся к катоду (область в). Бомбардировка катода продолжается уже не только ионами

(область а), но и быстрыми нейтральными частицами

(область в), в результате чего возникают новые быстрые электроны

, и мощность ЭП 14 возрастает. Таким образом, на выходе полого анода 3 из плазмы 6 ВТР образуется ЭП 14. The cathode 2 and the hollow anode 3 surround the plasma zone 6. The plasma gas (hydrogen) 5 is fed through the anode channel into the plasma zone, the pressure of which determines the power of the formed EP 14. After applying a high accelerating voltage

VTR is ignited on the electrodes of the GRELP along the center line; positive ions are formed

, which begin to bombard cathode 2, and as a result of γ-processes, fast beam electrons are formed

(region a). Fast beam electrons

colliding with neutral particles

give rise to new ions

and slow electrons

(area b). Area b shows two variants of the trajectory of fast electrons

. Some of the ions that have arisen are captured by the electric field and rush to the cathode 2. Some of them experience a recharge on their way, as a result of which fast neutral particles are formed

moving towards the cathode (region c). The bombardment of the cathode continues not only with ions

(region a), but also by fast neutral particles

(region c), resulting in new fast electrons

, and the power of the EP 14 increases. Thus, at the exit of the hollow anode 3 from the HTS plasma 6, an EC 14 is formed.

притягиваются к аноду, компенсируя заряд ушедших быстрых электронов пучка

.The concave plane of the cathode 2 and the shape of the hollow anode 3 provide the initial electronic focusing of the formed EP 14 in the lower hole of the anode. Some of the ions moving in the vicinity of the EP are attracted to the EP; along with electronic focusing, ionic focusing takes place around the electron beam. slow electrons

are attracted to the anode, compensating for the charge of the departed fast beam electrons

.

нагреваемого металла, которые, благодаря ионной фокусировке, проникают в плазмообразующую зону 6 и присоединяются к процессу бомбардировки катода 2 наряду с положительными ионами

и нейтральными частицами A, провоцируя изменение его эмиссионных характеристик и эксплуатационный износ.In the process of heating a metal with the help of GREL, along with ion-electron emission, there is another source of charged particles that has a harmful effect on the operation of GREL. During heating by an electron beam, metal particles evaporate and undergo collisions with electrons emanating from the GRELP. In sufficiently high-energy collisions, electrons are knocked out of these particles, as a result of which positively charged ionic particles appear in the evaporation zone.

heated metal, which, due to ion focusing, penetrate into the plasma-forming zone 6 and join the process of cathode bombardment 2 along with positive ions

and neutral particles A, causing a change in its emission characteristics and operational wear.

Cathode 2 and anode 3 are elements that ensure the quality of processes in the plasma zone 6. They are subject to the greatest wear and determine the reliability resource of the GRELP.

The subjects that provide an increase in the reliability and functionality of the GRELP are the following elements of its design:

- vestibular evacuation chamber (VOK);

- spark suppression layer (IPS) in the area of small interelectrode gaps.

Moreover, the FOC is designed to increase the reliability resource, and the IPS, along with reliability, provides the extended functionality of the GRELP.

Usually, to combat the pollution of the process medium in the working chamber, where the process of heating and evaporation of the metal by means of the EA, pumping is provided, however, it may not be effective enough due to the technological impossibility of concentrating its influence in the zone of the EA itself.

In order to compensate for the wear of the cathode caused by the bombardment of the evaporated metal by positive ions, a fundamental additional module was introduced into the design of the GRELP - the vestibule evacuation chamber, the purpose of which is the targeted removal of positive ions of the evaporated metal from the ion focusing area. The presence of a FOC is taken into account when developing and adjusting the focusing and deflecting systems. In other words, equipping the GRELP FOC is a complex solution that cannot be implemented as a mechanical addition. The design of the FOC is due to the following processes taking place in the vicinity of the EP.

положительными ионами металла

показан на фиг. 3, где 19 – область ионизации; 20 – область рекомбинации. Часть близко расположенных к оси ЭП положительных ионов испаряемого металла

притягивается к оси ЭП, в результате чего претерпевают рекомбинацию и становятся нейтральными металлическими частицами

. В свою очередь, удаленные от оси ЭП положительные ионы испаряемого металла

слабо притягиваются к оси ЭП и ускоренно устремляются к катоду. Часть из них рекомбинируют на пути к катоду, а часть, самых удаленных, продолжает приближаться к катоду. Положительные ионы металла, оказавшиеся в пространстве ЭП, наиболее активно взаимодействуют с быстрыми электронами ЭП

. Они рекомбинируют, становятся нейтральными частицами и, опять соударяясь, с быстрыми электронами становятся положительными ионами металла. Таким образом, в пространстве ЭП циклически воспроизводится процесс ионизации-рекомбинации положительными ионами металла, поэтому перемещение испаренных частиц металла в пространстве ЭП не существенны.The process of ionization-recombination of neutral particles

positive metal ions

shown in FIG. 3, where 19 is the ionization region; 20 - region of recombination. Part of the positive ions of the evaporated metal close to the EP axis

is attracted to the EP axis, as a result of which they undergo recombination and become neutral metal particles

. In turn, the positive ions of the evaporated metal

are weakly attracted to the EB axis and rapidly rush to the cathode. Some of them recombine on their way to the cathode, while some of the most distant ones continue to approach the cathode. Positive metal ions that find themselves in the EP space most actively interact with fast electrons of the EP

. They recombine, become neutral particles and, again colliding with fast electrons, become positive metal ions. Thus, in the EP space, the process of ionization-recombination by positive metal ions is cyclically reproduced, so the movement of evaporated metal particles in the EP space is not significant.

, оказавшихся в непосредственной близости ЭП; 24 – разгонная траектория положительных ионов металла

, 25 – экстрагирующая траектория положительных ионов металла

.The organization of vestibular pumping in GRELP is shown in Fig. 4, where 21 is the region of cyclic ionization-recombination, the processes in which obey the model in Fig. 3; 22 – EA scanning axes; 23 - the trajectory of positive metal ions

, caught in the immediate vicinity of the EP; 24 - accelerating trajectory of positive metal ions

, 25 – extracting trajectory of positive metal ions

.

, потерянных в окрестностях ЭП, ограниченных пространством ВОК, в результате сканирования или случайного вылета из зоны ЭП.In FIG. 4 shows the behavior of charged and neutral particles

lost in the vicinity of the EF, limited by the FOC space, as a result of scanning or accidental departure from the EF zone.

, находящиеся в непосредственной близости с ЭП, притягиваются ЭП, двигаясь с ускорением, и вступают в рекомбинацию с быстрыми электронами

ЭП, не успевая набрать больших скоростей. В то же время удаленные от оси ЭП положительные ионы металла

имеют большие разгонные траектории 24 и набирают значительные скорости, устремляясь по дуге одновременно к оси ЭП и к катоду.As can be seen from FIG. 4, positive metal ions

, which are in close proximity to the EP, are attracted by the EP, moving with acceleration, and enter into recombination with fast electrons

EP, not having time to gain high speeds. At the same time, positive metal ions remote from the EP axis

have large accelerating trajectories 24 and gain significant speeds, rushing along the arc simultaneously to the axis of the electric beam and to the cathode.

The efficiency of the FOC in providing cathode protection is determined by the number of evaporated metal particles captured by the annular system of exhaust nozzles, which are rapidly moving towards the cathode. The annular system of pumping nozzles consists of several radially oriented cylindrical steel tubes, the inlets of which are beveled, as shown in Fig. 4. Equal depressions are applied to the outlet ends of the nozzles (a differential system of depressions), which ensure pumping out at the molecular level in the WOC (in the aggregate 10 ^-4 ... 10 ^-5 MPa). The number N and the diameter d of the nozzles in combination with the rarefaction P at the outlet ends determine the efficiency E of the WOC pumping system:

In order to increase the efficiency of the nozzles, their ends are made beveled, as shown in Fig. 1. If we take into account that one of the most important parameters of the GRELP is the distance to the treated surface, then it becomes obvious that the peripheral evaporated positive metal ions can accelerate to high velocities by the time they enter the beam guide, and the kinetic energy they have achieved when colliding with the cathode can contribute a significant contribution to the reduction of the cathode resource. Therefore, WOK is an effective means of increasing the resource of GREL in general.

The wear of both electrodes (cathode 2 and hollow anode 3) is due to another circumstance that occurs in the operation of GREL. Structurally, both of these electrodes, having a huge potential difference (30...60 kV), are located very close (5...8 mm) in the region of the plasma-forming zone 6, therefore, the instability of the plasma-forming zone can cause random sparking interelectrode breakdowns. Special means of protecting high-voltage power sources make it possible to exclude a fatal outcome caused by spark breakdowns, however, the pauses required to restore the nominal operating mode of the HRP can radically narrow down the set of technological processes that it can safely ensure. Therefore, IPS 4, deposited on the inner surface of the hollow anode 3 in the area of a dangerous structural arrangement close to the cathode 2, is interesting not only in terms of increasing the reliability of the GRELP, but also its wide functionality.

There are ways to deal with the described interelectrode spark discharges. In high-voltage power supplies, protection against short circuits (short circuit) on the load is provided. It provides an instant voltage drop of the source. This saves the GRELP from complete failure, however, the formation of the EP is temporarily interrupted. Since when using a short-circuit-protected power source, a spark discharge is a self-terminating phenomenon, the conditions for the formation of an electric field are restored in the GRELP: the high-voltage power source resumes its operation upon elimination of the short circuit. However, as already mentioned, the resumption of the VTR takes time, and this time determines the duration of technological pauses in the processing of the product. If the requirements provide for a controlled uniform or programmatically variable effect of the ED on the surface of the product, then one of the existing ways to reduce the duration of technological pauses is to use high-frequency power supplies (HFPS), which significantly increases the cost of the installation as a whole.

The present invention proposes a method for effective suppression of interelectrode spark discharges without the use of expensive RFID by deposition of a ceramic coating on the inner wall of the anode in the area of small interelectrode gaps. Aluminum oxide (Al ₂ O ₃ ) or zirconium dioxide (ZrO ₂ ) (the main parameters of which are shown in Table 1), etc. can be used as a ceramic coating.

Table 1

Parameter _{Al2O3 _ ZrO2} Electrical strength, kV/mm ten >10 Melting point, °C 2072 2715 Vickers hardness, GPa 19…21 12…13 Crack resistance, MPa ⋅ m ^1/2 3…3.5 8…10

The ceramic coating of the inner surface of the hollow anode implements the functions of the spark suppression layer 4.

The advantages of the proposed device: the inclusion of a vestibular evacuation chamber and a spark suppression layer in the design of the GRELP is proposed as a comprehensive solution to increase the reliability resource of both the gun itself and its functionality to provide complex program-controlled heating modes in strict accordance with the specified requirements without the use of expensive HFIP.

Technical result:

- multiple increase in the reliability resource of GRELP;

- the possibility of implementing long-term technological processes;

- reduced requirements for the quality of power supplies;

- expanding its functionality to provide complex program-controlled heating modes in strict accordance with the specified requirements.

The described method for increasing the reliability and functionality of the GRELP has been implemented and implemented with a positive result in PJSC Elektromekhanika, Rzhev, Tver Region. RF.

Claims (1)

SUBSTANCE: gas-discharge cathode-beam gun, containing a gas-discharge chamber, a cathode with a spherical emission surface, a hollow anode, water cooling, a high-voltage current lead, a water rheostat, a high-voltage insulator, a beam guide, focusing coils, deflecting coils, a flange, characterized in that it contains a spark suppression layer on the inner surface hollow anode in the region of geometric proximity of the cathode with a spherical emission surface, as well as vestibular evacuation chamber located under the beam guide, containing an annular system of evacuation nozzles.

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