DE1190112B - Device for generating a high current strength electron beam and method for heating and melting by means of such a device - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

HOIj

German KI .: 21g -21/01

Number: 1190 112

File number: St 16459 VIII c / 21 g

Filing date: May 9, 1960

Open date: April 1, 1965

The invention relates to a device for generating a high electron beam Amperage for heating and melting metals, consisting of one in the form of an annular Loop arranged around the axis of the bundle cathode, one axially spaced concentrically to this arranged acceleration electrode and one at a more negative electrical potential than that Cathode lying focussing electrode between the cathode and the acceleration electrode, which deflects the electrons towards the beam axis. The invention also relates to a method for heating and melting by means of such a device.

Although a large number of measures and devices for generating electron beams which are known both for general use and for special fields of application are absent in certain areas, e.g. B. in the field of melting and casting of metals Electron bombardment, practically useful and well suited methods and devices. Although the Invention and the great advantages of which are set out below on the basis of a casting process, it is by no means restricted to a certain area.

It is an electron gun for generating two in approximately the same direction Electron beam known. This surrounds that generated by the external electron source Electron beam generated by the inner electron source like a hose. This well-known Electron gun is not for use in electron beam melting furnaces suitable because the cathode is in no way protected from ion bombardment or vapor deposition is. Ion bombardment and vapors precipitating on the cathode will reduce their service life and thus the life of the electron gun significantly reduced, d. h., the The cathode had to be changed frequently. However, a cathode change is required when using electron guns extremely disadvantageous in melting furnaces, as this even interrupts a melting process can entail and the previous melt must be discarded. Also would have to when the cathode is changed, the vacuum in the furnace is canceled, so that considerable dead times the consequence would be.

The aim of the present invention is, inter alia, to improve the known electron beam generation while avoiding the above disadvantages.

The invention consists in that one with the device for generating an electron beam high amperage and method
for heating and melting by means of a
such device

Applicant:

Stauffer Chemical Company, New York, N.Y.

(V. St. A.)

Representative:

Dipl.-Ing. Dr. jur. V. Busse, patent attorney,

Osnabrück, Möserstr. 20/24

Named as inventor:

Charles W. Hanks, Orinda, Calif. (V. St. A.)

Claimed priority:

V. St. v. America June 5, 1959 (818 306)

Focusing electrode combined into a structural unit and lying on the same potential as this Shielding electrode which directs the emitted electrons away from the beam axis onto the focusing electrode deflects out, enclosing the cathode over the greater part of its cross-sectional circumference and thereby partially electrical against the accelerating electrode and against the molten metal mechanically shields outgoing steam jets.

According to an advantageous embodiment of the device, the focusing electrode is movable, preferably in the axial direction, attached to the shielding electrode. This is the location of the focal point of the electron beam adjustable along the loop axis.

The shielding electrode advantageously consists of a solid body with an annular recess, in which the cathode is arranged.

In various applications it is extremely beneficial to have electrons coming from a variety of directions to direct on a limited area, both from the point of view of the eventual to be preserved Electron energy as well as various side effects of the converging trajectory. An example this is the vacuum melting of metals by electron bombardment. In this example, a The metal block is continuously melted and a molten pool of this metal is heated at the same time.

509 537/295

3 4

The method of heating and melting with- cathode 16 in the recess 14 of the annular means of a device according to the invention consists of electrode 13 are suitable in the drawing in that the melting material is used in particular in the form of insulating means, not shown. The association Rod coaxially to the loop-shaped recess 14 is made somewhat re-entrant by method and the electrodes in the direction of the bundle 5 a protruding lip 17 is provided, the off-axis to the focal point or to the focal surface danger on the radially inward side of the is moved so that the melt is arranged in the focal point recess 14 and to the outside or in the focal surface of the conically extending and here part of the recess in the Electron beam heated and melted underside of the shielding electrode 13 covers. Inner will. 10 half of this covered part of the recess 14 is

The electron beam is advantageously mounted on the cathode 16; based on the reasons for this measure of the ring-shaped electrodes of takme are listed below. The two Conical surfaces with different opening angles, the position 14 is arranged on that side of the electrode borders, with the generatrix of the inner lying on the outside seen in the radial direction. On the Cone in one below the end of the melting material and 15 electrode 13 is a focusing ring 18 by means of BoI above the melting point lying on the zen 19, which axis through slots in the ring 18 cut while the cutting line is stuck between and screwed into the electrode 13, the generatrices of the inner cone and the axially moveable attached. This focus ring 18 generating the outer cone a focal surface depends on the electrode 13 at its outer boundaries, that descends with the surface of the enamel mold and thereby determines with the lip 17 collapses. together an outlet opening 20 for the electrical

The present invention not only creates a gap between the recess 14 and the exterior very intensive electron beam bombardment of one of the shielding electrode 13. Immediately below desired, limited area which is located substantially from the shielding electrode 13 is a Be radiation origin removed, scored. By means of the acceleration electrode 21, which is preferably with vergence of the bombarding electrons it is also provided with a rounded outer edge and as makes it possible to melt the material to be melted and to form a ring which is below the shielding level to heat the weld pool. electrode 13 is arranged and is located in the radial direction

Further details of the invention result device further outward than the lip 17 extends. with reference to the drawing, in the exemplary embodiment 30. It can be seen that illustrated in the described are. In particular, the width of the opening 20 is below the annular formation not only a circular ring shape, but also a shielding electrode 13 by the acceleration elliptical shape and the like to understand forms. electrode 21 is reduced because this is within the The same also applies to the conical shape of the electron focusing ring 18 radially less than this Ray, with which all converging figures to be 35 the lip 17 is removed. For the acceleration standing are. electrode 21 can use suitable fasteners

Fi g. 1 shows schematically an oblique view of a device to be provided, e.g. B. can, as shown in the drawing

Device for generating electron radiation is shown, on the inner circumference of the loading

including the achieved converging electrode acceleration electrode 21 a cylindrical edge

electron beam paths, 40 are provided in part, which is located within the

F i g. Fig. 2 is an elevation of a device for shielding electrode 13 extends. Suitable coolants

Melting with the help of a converging elec-

electron beam as provided in an electron element of the device. The acceleration

jet melting furnace can be used, inclination electrode 21 is preferably with a cooling

F i g. 3, a cross-section along the line 3-3 of 45 tube 22, which is attached below the electrode.

F i g. 2 is ordered by a preferred embodiment and with it in good heat-conducting relationship

the device. bond to which the scattered electrons,

In Fig. 1 is the device 11 for generating which bombard the acceleration electrode,

of an intense electron beam only schematically dissipate the heat generated. Similar cooling devices

indicated. It creates the hollow cone-shaped elec- 50 can also be used for the focusing ring and

electron beam 12. The electron beam can also be provided for the electrode 13, whether-

at some distance from the radiation source, normally only the accelerating elec-

focused. trode is heated so much during operation that

As shown in FIG. 2 and 3 shows that the removal of larger amounts of heat is necessary.

Electron gun is a ring-shaped 55 borrowed.

mige shielding electrode 13, which in plan is a For operation of the electron beam generating device

Circular shape, an elliptical shape or the like. May have. direction, the cathode 16 is directed to the emission

There are a relatively large number of possi- ble temperatures by being heated by an external

borrowed figures for the plan shape of the electron energy source a current through the cathode 16

Beam generating device, and the expression ⁶ <> lets flow, which for the sake of simplicity in the drawing

"Ring-shaped" is therefore not shown in the following for any of these reasons. The desired electrical

different forms used. The shielding acceleration and deflection field is

electrode 13, which in the following for the sake of simplicity put a voltage between the electrode 13 and

is considered to be circular, has generated the acceleration electrode 21 on it. In the

Underside a trough or recess 14. In this drawing, this is indicated by a battery 23,

Well is an electron-emitting cathode whose negative pole with the electrode 13 and their

16 arranged, which with the electrode 13 does not have a positive pole with the acceleration electrode 21

has electrical contact. To attach the connected. The connecting lines are with

24 designated. Since the focusing ring 18 is in electrical contact with the electrode 13, the Focusing ring at the same potential as electrode 13. If desired, the cathode 16 can be brought to a potential between that of the electrode 13 and that of the accelerating electrode 21 is so that the electrode

13 is kept at a negative potential with respect to the cathode and thus repels electrons. By the presence of a potential difference between the acceleration electrode 21 and the Electrode 13 is formed, especially between the outer end of the accelerating electrode 21 and of the lip 17 of the electrode 13, an electric field, the lines of force of which are indicated by the lines 26 in FIG the drawing are indicated. This field, which is indicated by the drawn field lines 26, is curved between the accelerating electrode 21 and the lip 17, thereby reducing that of the cathode 16 emitted electrons are forced, in accordance with the curvature of the lines of force to follow a curved path. The electrons emitted by the cathode 16 are from the With a positive voltage provided acceleration electrode 21 attracted, so that an electron beam 27 arises, that of the recess

14 in the electrode 13 flows to the outside. This electron beam 27 leaves the cathode 16 in a direction which leads substantially radially outward from it, and is through the field 26 of of the electrode 13 through the opening 20 downwards and then further against the axis 28 (FIG. 1) of the Directed electron gun. The degree of curvature or that of the electron beam The deflection given is by the size and curvature of the accelerating electric Field determined. The regulation of the acceleration voltage thus also enables the regulation of the Point of intersection of the electron beam 27 with the axis 28 of the electron beam generating device. As a further control for the electron beam path, the focusing ring 18 is adjustable mounted on the electrode 13 so that it is axially movable. Since the focusing ring 18 is electrical is connected to the electrode 13, creates a deeper position of the focusing ring with respect to the Electrode 13 creates a negative electric field along the outer periphery of the electron beam path goes deeper. By lowering the focusing ring 18, it is possible to reduce the radial deflection of the To enlarge the electron beam within the generating device.

Various effects, including space charge effects, are known to cause scattering of a high density electron beam. That generally speaks against that Reaching the maximum density of an electron beam at any distance from the source of the beam Period. In the present invention, the scattering of the electron beam as shown in FIG. 3 can be seen from the drawing does not entail any particular disadvantages, namely because the electron beam is generated along a circular ring and only at some distance from Point of origin is concentrated on one point, as it is e.g. B. can be seen from Fig. 2 of the drawing can. Although the cross-section of each electron beam emanating from a point on the cathode with increasing distance from the point of generation, as the scattering increases, the entire beam itself is focused as a whole, so that the scattered rays converge at a point of high density. This is best seen in FIG. 2 can be seen in the drawing, in which the delimitation of the electron beam by means of dashed lines is drawn from two opposite sides of the generating device and from what one can further see that the density of the electron beam in a focal plane which is from of the generating device is axially removed from the electron beam density in all others Areas is greatest. It depends on various factors, including the electron speed, that the converging ray can actually cross, as shown in FIG. 2 is shown or that, on the other hand, a more laminar flow of electrons in the vicinity of the focal plane of the beam exists.

The electron beam generated can be used for many purposes. So can z. B. at the focal surface 31, where the electron beam is its smallest diameter and thus the Maximum density achieved, an electron lens or the like. Are arranged through which the resulting Beam can be directed into an apparatus in which it is recycled. In conjunction with a such electron lens can e.g. B. also a closure against steam can be attached, so that no Gases or vapors from the recovery apparatus into the electron gun area can penetrate. It is particularly advantageous and expedient to use the generated Electron beam in connection with melting furnaces, as indicated in FIG. It can e.g. B. a Melting rod 32 can be provided which can be moved into the electron beam, e.g. B. along the axis of the beam generating device. Here the melting rod is progressively through the electron beam bombardment liquefies and flows down into a crucible 33 where the liquefied Metal is further bombarded and heated by the electron beam converging there. Of the The angle at which the electron beam converges in the direction of its focal plane 31 can easily be can be changed by moving the focus ring 18 of the generating device. This feature has particular advantages, as different uses have different angles of the Require ray convergence. So it is z. B. extremely desirable in the electron bombardment one Molten metal bath in an electron beam melting furnace for a large number of angles and Directions to ensure complete and even heating of the upper surface of the Melt bath can be achieved. The present electron gun is for one Such use is very suitable because, even if a melting rod or the like at any desired Place in the electron beam can be brought for the purpose of starting the melting of the in the melting furnace material introduced by the convergence of the electron beam generated here ensures bombardment of the entire surface of the molten metal in the crucible. Another significant advantage when using the electron beam generating device in electron beam

Melting furnace is the cathode's relative inadequacy for condensing metal vapor that propagates from crucible 33 toward the cathode.

Since only a very limited opening is provided for the electrons to exit from the emitting cathode surface and since this emitting surface is further away from the resulting electron beam path in the radial direction, the greatest possible protection for the cathode is achieved. So if z. B. in the space traversed by the electron beam generated there are gases or vapors and consequently ions are formed by the interaction of the electron beam and such gases and vapors, the cathode is thus completely protected from the decision by such ions. In the event that ions actually arise in the space below the electron beam generator, these ions would normally be attracted by the electrode 13 and, although they are repelled by the acceleration electrode 21, can partially migrate back along the electron beam path. In the present example, however, because of their greater mass, these ions are too sluggish to move on the strongly curved path towards the cathode and would at most strike against the focusing ring 18 or the electrode 13. In the area of electron emission, the field is such that ions which approach the generating device and come through the opening 20 are more attracted to the electrode 13 than to the cathode 16. The strong structural design of the electrode 13 enables it to be resolved by ions that actually pass through the opening 20 without material damage. One of the difficulties with high density electron beam sources is that their cathode is severely demolished by ions generated by the electron beam. In using these generating devices for electron beam melting furnaces , an even greater difficulty is that the cathode is occupied by metal, which significantly reduces its service life. By the present inven tion, these difficulties are almost completely overcome, since the likelihood of loading or the formation of a deposit on the cathode 16 is extremely low.

The following are some further details are given devices for dimensioning Elektronenstrahlerzeugungs-. In the embodiment according to FIG. 3 of the drawing , the shielding electrode 13 can have an inner diameter of 139.7 mm and, including the focusing ring, an outer diameter of approximately 209.6 mm. The recess 14 can have a radius of curvature of 9.5 mm in cross section , but has a curvature with a radius of 4.8 mm before and at the transition to the lip 17 , in the center of which the cathode 16 is arranged. In this embodiment, the focusing ring 18 can reach approximately 31.7 mm below the electrode 13 and the total depth of the recess 14 can be made approximately 19.1 mm . In this example, the accelerating electrode can be electrically grounded and a negative voltage of several thousand volts can be used for the electrode 13 and the focusing ring 18.

Here, it is possible to generate a high density electron beam that has a high electron velocity Has. Although the electron beam diverges in thickness, it converges in diameter, thereby becoming close to it To cross the focal surface and to generate an electron beam of very high density here. the In the exemplary embodiment cited, the focal surface can be approximately 305 mm below the electron beam generating device are provided. Further, if desired, a vapor blocking rack with a Electron lens can be provided, which is erected below the same, around a second electron beam focal surface which is further away from the generating device.

Claims (5)

Patent claims: 1. Apparatus for generating a high amperage electron beam for heating and melting metals consisting of an annular loop around the The cathode arranged around the bundle axis, one arranged at an axial distance concentrically to this Accelerating electrode and one at a more negative electrical potential than the cathode lying focusing electrode between the cathode and the acceleration electrode, which deflects the electrons towards the beam axis, characterized in that one with the focusing electrode to one structural unit united and at the same potential as this shielding electrode, which move the emitted electrons away from the beam axis towards the focusing electrode deflects, enclosing the cathode over the greater part of its cross-sectional circumference and they thereby against the acceleration electrode partially electrically and against from the molten metal mechanically shields outgoing steam jets. 2. Apparatus according to claim 1, characterized in that the focusing electrode (18) is movably attached to the shielding electrode (13), preferably in the axial direction. 3. Apparatus according to claim 1 or 2, characterized in that the shielding electrode (13) consists of a solid body with an annular recess (14) in which the cathode (16) is arranged is. 4. Method of heating and melting by means of a device according to one or more of claims 1 to 3, characterized in that the melt in particular Shape of a rod coaxial with the loop-shaped cathode and the electrodes in the direction of the The bundle axis is moved to the focal point or to the focal surface, so that the material to be melted heated in the focal point or in the focal surface of the conical electrode beam and is melted. 5. The method according to claim 4, characterized in that the electron beam, starting from the ring-shaped electrodes, from two conical surfaces of different opening angles is limited, with the generators of the inner cone in one below the end of the melting material and above the melting mold Intersect point on the axis, while the intersection line between generatrices of the interior Cone and generators of the outer 10 Cone delimits a focal surface which coincides with the surface of the enamel mold. Publications considered: German Patent No. 898 193. 1 sheet of drawings 509 537/295 p. 65 © Bundesdruckerei Berlin