DE2152094A1 - Heating system for an electron beam furnace - Google Patents

Description

Patent attorneys Dipl.-Ing. F. Weickmann, 2152094

Dipl.-Ing. H, Weickmann, Dipl.-Phys. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber

8 MUNICH 86, POST BOX 860 820

MÖHLSTRASSE 22, NUMBER 4 «39 21/22

<983921/22>

AIR REDUCTION COMPANY, INCORPORATED

150 East 42nd Street, New York, N.Y., V. St. A.

Heating system for an electron beam furnace

The invention relates generally to electron beam furnaces and, more particularly, to an improved heating system in one such furnace.

Electron beam furnace in a variety of designs are particularly useful for processing many metals, alloys or other materials, e.g. in the Cases in which high degrees of purity are achieved by degassing or avoiding a reaction with oxygen and nitrogen can be achieved. Another area of application of electron beam furnace arises in cases where a substrate has to be coated by evaporation and condensation of a material is. Electron beams are particularly useful for material heating, insofar as it is through their Application is possible to introduce heat locally into a melt.

Electron beam furnaces typically contain one evacuated container, a heating system with one or more electron beam guns and associated deflectors for the guidance and focusing of the respective electron beam and a container for the to be processed or processed molten material.

Depending on the particular type of processing being carried out, the container for the molten material have a variety of shapes «In a case where it is desired to use the material contained in the container evaporate and then condense on a suitably supported substrate to allow the To coat substrate, a typical container consists of an upright crucible with an open top. Electron beam heating makes it possible to cool the crucible itself. This can cause a skin to become solidified form molten material between the crucible and the molten material. This skin protects the purity of the molten material and makes the use of refractory linings for the crucible structure unnecessary.

Another type of material processing or processing is the cleaning of metals and alloys the molten material or alloy is passed through a shallow hearth. Because the material surface is simultaneously exposed to a vacuum and electron beam heating, v ^ ele volatile impurities and trapped gases are removed from the molten material, creating a major effect purified product is obtained.

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Other forms of containers that can be used in materials processing include tundishes, gutters, and ladles for the transfer of molten material between different locations. The electron beam heating can thereby are used to keep the material in such containers in a molten state.

During the processing of the molten material in an electron beam furnace, the vaporized material can cause ionization problems or even the various parts The electron beam gun overpowering its operation is affected. Otherwise, condensed materials can flake off the cool surfaces of the vacuum container as well as the splashing and splattering of the molten material from the crucible also the operation of the elec- ' affect the electron beam cannon. If you arrange the electron beam cannon below the container in which the molten Material is contained, and one uses transverse magnetic fields to deflect the electron beam a curved path of 180 ° or an even greater one Angle, so is the contamination and short-circuiting reduced to a minimum value in the case of the electron beam gun.

The heating of large surfaces in electron beam furnaces can be effected by applying a large number of Electron beam guns with separate deflection fields for any electron beam is used. If the furnace container is relatively large, this may not be a significant problem. If, however, the space concerned is a factor, the arrangement of devices for generating can run transversely Magnetic fields close together become extremely difficult due to mutual interference and Distortion of the fields.

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During the processing of molten material in an electron beam furnace as well as during the evaporation of the material in question Material, a significant amount of vaporous material can be generated. The amount of such material typically has its maximum in the area immediately above the molten target area. Accordingly is it is undesirable to have devices for generating transverse magnetic fields for deflecting the electron beam directly arrange above the respective melted target area. The reason for this is that the production The pole pieces or other devices used in the magnetic fields are susceptible to being condensed by the vaporous material to become heavily coated, with the possibility of a disadvantageous resultant therefrom Effect on the shape or configuration of the magnetic field. In addition, such condensate can peel off lead to renewed contamination of the melt.

Will pole pieces or other generating facilities a transverse magnetic field for deflecting an electron beam from one side of the area above the arranged offset from the melted target surface, the condensation problem mentioned above is reduced. Still it arises a restriction of the distance to the target material in which the deflecting devices are arranged by various factors can be. If the angle of incidence of the electron beam on the respective target area is too small, besides surface arrangements provided on the sides of the target surface in question, such as magnetic shields or components, the Block electron beam path. In addition, with a very small angle of incidence, the impact area is spread out on the target surface, which leads to ineffective heat transfer.

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The invention is accordingly based on the object to provide an improved electron beam furnace heating system. With the new heating system to be created, the room and the service is effectively used. Furthermore, the newly created heating system should be of minimal complexity and provide the ability to direct a plurality of electron beams along a curved path onto a target surface and to be able to control. After all, the new heating system to be created should be particularly suitable for heating large areas of molten material.

The object indicated above is achieved by the invention specified in claim 1.

The invention is explained in more detail below with reference to drawings.

Fig. 1 shows in an overall sectional view schematically a heating system constructed according to the invention.

FIG. 2 shows a view along the line 2-2 entered in FIG. 1.

3 and 4 show top views of different shapes for pole pieces in the heating system according to FIGS. 1 and 2.

The electron beam furnace heating system according to the invention contains generally an electron beam gun 11 for generating an electron beam. With the help of guidance systems 12, the electron beam hits a target surface 13 directed. The guide devices contain a pair of rod-shaped pole pieces 14 and 15, the longitudinal axes of which in a common plane and which are arranged so that they run a transversely in the electron beam path Generate magnetic field. The pole pieces are fed or excited by feeding devices 16. This creates a magnetic

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field of sufficient strength generated. By this magnetic field, the electron beam is deflected in such a way that it is on the same The side on which it entered the magnetic field. The magnetic field is also sufficient Strength that the electron beam in question is prevented from occurring behind a plane passing through the longitudinal axes the pole pieces runs.

The embodiment of the invention shown in FIG. 1 will be explained in more detail below. The electron beam furnace contains an evacuated container, part of which is indicated by 20. The molten target material 13 is in one Contain elongated container 17, which is cooled by a coolant circulating in passages 18. This forms A layer or skin 19 of solidified material forms between the molten material and the container walls. The container 17 is shown as a hearth into which molten material flows from a channel 21 (Fig. 2) at one end. The contents of the cooker in question are discharged at the other end through an opening 22 (FIG. 2). The amount of the molten material in the hearth can be regulated by an overflow (not shown). Other bodies devices for introducing molten material into the hearth and removing the material in question from the hearth can be such as tundishe, siphons or ladles. Between the entry and exit of the material in or out of the hearth the material in question flows slowly along the hearth. As a result, the material in question is very much the Exposed to vacuum environment in which the device shown is housed.

The illustrated hearth arrangement causes a large area of the molten material at a shallow depth during a exposed to vacuum for a long period of time. Such a one

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Arrangement is particularly useful in cleaning many types of steel and nickel-based alloys as well for most refractory metals, such as niobium »tantalum, titanium, zirconium and others» studies have shown that many purification reactions involving different evaporation properties or other types of degassing require residence times of tens of seconds during which the molten surface is exposed to very low pressures. In such cases the form shown is a long, rectilinear hearth with slowly flowing molten material is particularly advantageous. Electron beams are used to do this used to prevent solidification of the material on the hearth when the material in question flows along the hearth, and causing local areas of high heat, namely, to vaporize contaminants and thermal agitation to evoke.

In the device shown, a large number of electron beams are used to remove that located in the hearth 17 to heat molten target material 13. The electron beams are emitted by a large number of corresponding electron beam guns generated, of which only one electron beam gun 11 is shown. These electron beam guns are provided below the cooker 17 spaced apart from one another in the longitudinal direction thereof.

The electron beam guns can be formed by electron beam guns of any suitable type. A preferred one The form of an electron beam gun is shown in U.S. Patent 3,514,656. The details of such a Electron beam guns are in conjunction with the electron beam gun 11 shown in FIG. It should be understood that the other electron guns are of the same kind Can be construction.

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According to FIG. 1, the electron beam gun 11 includes a elongated emitter 23 for the generation of electrons. The emitter is preferably formed by a tungsten wire, which runs between support parts 24 and 25. A direct voltage is applied by devices not shown here the parts 24 and 25 applied, whereby the emitter 23 is traversed by a direct current. The current flow in question leads to increase the emitter temperature, whereby free electrons are generated.

The free electrons generated by the emitter 23 are reflected on three sides by a shaping electrode 26. The relevant electrode 26 is separated or insulated from the emitter support parts 24, 25 by insulating strips 27, 28. the The shaping electrode 26 has an elongated recess 29 through which the emitter 23 protrudes. If the shaping electrode by a suitable one not shown here Connection is held at the emitter potential, the electrons generated by the emitter 23 show the tendency to off the open end of the recess 29 to move out and away from the forming electrode 26.

ψ The recess 29 in the forming electrode 26 leaving the electrons are accelerated by an accelerating electrode 31 to an electron beam or electron beam and passed through a located in the relevant electrode 31 opening 32nd The acceleration electrode 31 consists of a plate with two right-angled projections 33 and 34, which are attached to suitable support devices, which are not shown in detail here. The plate is held at a potential which is significantly more positive than the emitter potential and the potential of the back electrode. This causes an acceleration of the electrons

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evoked. The result is a ribbon electron beam, i.e. an electron beam with an elongated cross-section, the is ideally a narrow rectangle, but approximates to a narrow oval. The electron beam points has a major axis plane that passes through the emitter.

The electrons of the electron beam leave the emitter 23 at an acute angle in the main axis plane. The axis the electron beam is indicated by the dash-dot line 36; this line represents the center of the ribbon beam. That of the normal orientation of the initial electron path deviating alignment of this electron path in relation to the emitter 23 is caused by the strong peripheral field, which is caused by the direct current flowing through the emitter. After exiting the anode opening 32, the electron beam 36 is deflected by approximately 90 ° on a curved path, specifically by means of a transverse magnetic field or magnetic transverse field. The relevant transverse magnetic field is in the initial path of the electron beam generated between two elongated rod-shaped pole pieces 37, only one of which is shown. The pole pieces run substantially parallel to the emitter 23 and parallel to each other; they are on both sides of the electron beam arranged parallel to its main axis plane. A magnet 38 and 38 extends between the upper ends of the pole pieces 37 A magnet 39 extends between the lower ends of the respective pole pieces 37. The two magnets are relative their polarities oriented in the same way; they are electromagnets attached to a suitable one, but not here The control circuit and supply source shown in more detail are connected. Field lines occur at the respective polarities which occur perpendicularly in the plane of the drawing. This results in an upward deflection of the electron beam 36 caused in the manner shown. From-

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effect of the magnetic field on the electron beam also brings a convergence of the opposite edges of the Electron beam with it, as indicated by the dashed lines 40. The electron beam in question} .- edges run towards each other in the plane of the curved path, taking into account that the electrons at the lower edge of the electron beam in the magnetic field caused by the pole pieces 37 along a larger one Track length are guided. For further details on the deflection and focusing of the electron beam, refer to refer to the aforementioned U.S. patent.

After leaving the electron beam gun 11 and after deflection The electron beam passes upwards by approximately 90 ° through an opening 41 in a vapor barrier 41. Even though the vapor barrier or vapor shield 42 is not always is necessary, however, it brings one in cases where a large amount of vaporous material is generated additional protection for the electron beam gun 11 with it. In addition to the vapor barrier 42, a separate one can also be used Pump system (not shown) in the lower part of the interior Oven can be provided in order to keep the electron beam gun 11 in a virtually vapor-free environment The life of the emitter of the electron beam gun is extended, and the quality of the electron beam is also increased improved when entering the upper part of the furnace chamber.

Around the electron beam from its essentially vertically upward path into the upper part of the furnace chamber redirect down to the target surface 13 are the pole pieces 14 and 15 are provided. Corresponding pairs of Pole pieces 44, 45 and 46, 47 are used to reduce the electron beams which are generated by the other electron beam guns, as can be seen from FIG

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can be. As mentioned above, the electron beam deflected onto the surface of the molten material in the hearth at an angle which is preferably is between about 30 ° and about 60 ° relative to the vertical. An angle greater than 60 ° with respect to the vertical generally results in an electron beam spot that is spread out too widely. In addition, the electron beam can be in in this case act on arrangements along the sides of the cooker. An angle of incidence of less than 30 ° with respect to the vertical can result in an overly dense arrangement of the pole pieces in the area immediately above the hearth, i.e. in an area in which the slope it is undesirably large that condensate collects on the pole pieces.

The pole pieces 14 and 15 are fed so that a Magnetic field is generated, which runs transversely or transversely to the electron beam above the opening 41, from which the electron beam exits and enters the upper part of the electron beam furnace. The field includes a part of almost uniform field strength in the area immediately between the pole pieces. The field in question also includes upper and lower edge areas, in which the lines of flux extend outwardly away from the uniform area. In these areas, the Field strength decreases with distance from the uniform area. For the purposes of the present invention, the upper edge area can be ignored, since only the lower edge area in electron beams or the electron beams influenced.

The pole pieces are arranged at such an angle that the magnetic field generated by them deflects the respective electron beam back down onto the target material 13.

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That between the inclined rod-shaped pole pieces existing magnetic field is given by the feed device 16 such a strength that the electron beam is not in a penetrates a significant depth into the area lying directly between the pole pieces, but rather by an angle is deflected by about 140 °, completely or almost completely within the edge area of the field. The one in question The electron beam emerges on the same side of the magnetic field on which it entered the magnetic field | is. The magnetic field generated by the pole pieces thus acts in a similar way to an optical mirror.

The lines of force of the magnetic field which run between the pole pieces 14 and 15 can be seen from FIG. As can also be seen from FIG. 2, the deflection or deflection of the electrons in the respective electron beam takes place almost completely within the curve or edge region of the magnetic field which has been generated below the region lying directly between the pole pieces. Since the electrons on the outside of the curved path of the electron beam remain in the magnetic field for a longer period of time and pass through stronger magnetic field areas than the electrons to the ψ inner edge of the curved electron beam, a focusing effect can occur in the plane of the curved electron beam path. Under certain conditions the focusing effect can be so strong that a kind of nodal point with subsequent diffusion of the electron beam is created. By suitably setting the magnets close to the electron beam gun, a sufficiently compact electron beam cross section can be achieved, so that any tendency of the electron beam to show a scattering in the above-mentioned manner can be tolerated.

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The divergence of the electron beam is due to the outwardly bent lines of flux in the lower edge area of the magnetic field in the direction transverse to the plane of its curved path is amplified when the electron beam in question has the magnetic field leaves. This means that the electron beam deflected or deflected by the magnetic field in a lateral direction is defocused and that a larger impact dimension than is achieved in the flow direction on the target surface in the event that the electron beam would be directed over the same distance without deflection. However, this is tolerable, if the electron beam cross-section is kept compact by suitable adjustment of the magnets of the electron beam gun as mentioned above. Such a compact electron beam can by suitable arrangement and Feeding of the pole pieces 37 on the electron beam gun 11 be achieved.

The pole pieces 14 and 15 are supported by two pole piece attachments 51 or 52 supported. The pole piece approaches consist of one ferromagnetic material; theirs from pole pieces 14 and 15 opposite ends are in contact with the ends of the magnetic core 53 of an excitation coil 54. The excitation coil is through a supplied by the feed device 16 output suitable current.

The location and shape of the pole pieces can depend on the particular furnace geometry can be changed accordingly to the desired electron beam spot size and the to achieve respectively desired deflection characteristics. The formation of condensate can be prevented by a low setting of the field strength if necessary, easily compensated. The actual distance of the pole pieces from the target face and from the electron beam source is by taking into account the desired angle of incidence of the electron beam and by

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the geometric distance between the target surface and the electron beam gun set. The depth of the pole pieces has no appreciable effect on the electron beam path The result is that the electron beam does not penetrate through the area between the pole pieces. The size of the However, opposing faces of the pole pieces determines the power that is required to produce the required Generate field strength. The required field strength depends of course on the electron beam gun power as well P as from the size of the deflection desired. The angle of the poles with respect to the horizontal depends on the angle between the entrance electron beam path and the desired Exit electron beam angle. Preferably runs a plane p which includes the longitudinal axes of the poles, approximately perpendicular to a plane which is defined by the entrance electron beam path and the exit electron beam path intersects and is perpendicular to one of these running plane. A shield 60 made of ferromagnetic Material prevents the field next to the coil 54 and the pole piece extensions 51 and 52 from the electron beam influenced.

To deflect the electron beam and make a scanning movement of the electron beam impact spot across the surface of the molten material 13 includes the guide means a suitable set of pole pieces 61 which cause an orthogonal deflection of the electron beam when this just emerges from the opening 41. Although the particular construction of the deflector 61 is not shown and may be any of a variety of suitable shapes, preferably becomes a deflector 61 used, which contains four electromagnetic coils in the manner of a magnetic relay, the axes of which are arranged so that

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they intersect and delimit a rectangular flat area. The coils have cores made of a material low magnetic resistance on. The respective cores are at their ends with the cores of the respectively immediately neighboring ones Coils in contact. A change in the supply of the coils leads to a change in the direction of the lines of force of the field generated by the coils, This results in a change in the size of the deflection of the electron beam,

Due to the outwardly bent lines of flux of the magnetic field generated by the pole pieces 14 and 15, an amplification occurs the deflection of the electron beam caused by the operation of the deflection device 61 on a perpendicular towards the poles axis. This means that there is a very large deflection area along the hearth available, as can be seen from FIG. In Fig. 6, the electron beams are all electron beam guns indicated by dashed lines. The impact surfaces on the target area are indicated by small ovals or circles on the Ends of the electron beams indicated. By appropriately spacing the electron beam guns and their deflection fields some overlap of the deflections of the electron beam spots for a desired redundancy in the Operation of the system can be achieved.

The depth at which the electron beam penetrates the area immediately between the pole pieces (this is the Area of uniform field strength ^ is limited to the depth which avoids an impermissible limitation of the size of the possible electron beam deflection. Incidentally, a excessively deep penetration make the electron beam too difficult to control. The field strength is accordingly of the magnetic field selected so that penetration of the electron beam through a plane is prevented,

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which runs between the longitudinal axes of the two pole pieces.

The configuration of the pole pieces 14 and 15 can thus be changed be that parts of these pole pieces are beveled inwardly towards each other. This can either be achieved by doing this be that additional two-pole 63 are used, as shown in FIG. 3, or that the pole pieces themselves one a suitable shape is given, as can be seen in FIG. By using this type of pole piece, an equal) more moderate field strength can be achieved, since in this case there is much less tendency for the field strength to reach the ends of the Remove pole pieces. The reason for this is that the Pole pieces at the respective ends have an increasingly smaller distance.

As can be seen from FIG. 2, an undesired one is created between the adjacent pole pieces of adjacent pole piece pairs Field generated. Accordingly, an undesirable field becomes between the pole pieces 15 and 44 and between the pole pieces 45 and 46 generated. Since the deflection of the electron beam takes place almost completely in the edge area of the respective main field. finds, the edges of the undesired fields generated in this way are "outside the path of the electron beams, and indeed at large deflection angles. So although undesirable fields are generated between adjacent pole pieces in adjacent pole piece pairs such undesired fields do not cause any adverse effect on the operation of the system.

Another advantage of the present system remains in that in the event that additional power is required, a separate and redundant system on the opposite side Side of the cooker. This doubles the heating power. In addition,

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if necessary, two electron guns do the same thing Pair of pole pieces for deflecting their electron beams use as this in conjunction with pole pieces 46, 47 is shown on the right-hand side of FIG.

From the foregoing it should be seen that the invention provides an improved heating system in an electron beam furnace has been created. The invention is particularly applicable in cases where in connection with a large number of electron beams is a relatively large surface to be heated and in which the electron beams are to be guided over the surface in question. The invention enables those provided for the generation of deflection magnetic fields To arrange pole pieces close to each other without

this has an adverse effect on the operation of the system. The system is also simple and reliable operational.

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Claims (11)

Claims Heating system for an electron beam furnace, with an electron beam gun for generating an electron beam, with guide devices which allow the electron beam to be directed onto a target surface and which have two rod-shaped pole pieces whose longitudinal axes lie in a common plane and generate a transverse magnetic field in the electron beam path, and with feeding devices for magnetic excitation of the | Pole pieces, characterized in that the pole pieces (14, 15) generate such a strong magnetic field that the electron beam emerges on the same side of the magnetic field on which it enters this magnetic field. 2. System according to claim 1, characterized in that the magnetic field strength is selected so high that it is prevented that the electron beam occurs behind a plane which runs through the longitudinal axes of the pole pieces (14,15). 3. System according to claim 1 or 2, characterized in that the feed devices (16,53,54,52,60) such . Magnetic field strength can cause a change in direction of the electron beam takes place at an angle between about 105 ° and about 165 °. 4. System according to one of claims 1 to 3, characterized in that that to change the direction of the electron beam emerging from the magnetic field, the guide devices (12) Allow to change the angle at which the electron beam enters through the pole pieces generated magnetic field occurs. 209817/0994 5. System according to claim 4, characterized in that the angle changing guide devices (12) a Cause change in more than one level. 6. System according to one of claims 1 to 5, characterized in that that the pole pieces (T4,15) are almost parallel to each other get lost. 7. System according to one of claims 1 to 6, characterized in that that at least a part of each pole piece (14,15) is arranged so that it is to the corresponding part of the other pole piece (15,14) is inclined inward, in such a way that the space between the pole pieces (14,15) to the one immediately above the target area (13) the lying area is narrowed. 8. System according to one of claims 1 to 7, characterized in that that the feed means an electromagnetic coil (54) with a core (53) low magnetic Resistor, means (52) for providing a low reluctance magnetic flux path from the Ends of the core (53) towards the pole pieces (14,15) and a magnetic shield (60) between the coil (54) and the electron beam path. 9. System according to claim 8, characterized in that the means defining the electron beam path contain two upstanding lugs (52) of low reluctance material, one Define the flux path from the ends of the core (53) to the ends of the pole pieces (14,15) and that the magnetic shield (60) is provided between at least some of the respective approaches and the electron beam path. 209817/0994 10. System according to one of claims 1 to 9, characterized in that a further electron beam gun is provided, which is arranged so that it emits an electron beam in the magnetic field on the same Side on which the electron beam occurs, which is generated by said electron beam gun (11), that the feed devices generate a magnetic field of such strength that that by the further electron beam gun ^ generated electron beam experiences such a deflection, that it emerges on the same side of the magnetic field on which it enters the magnetic field, and that the relevant one The electron beam is prevented from occurring behind a plane defined by the longitudinal axes of the pole pieces runs. 11. System according to one of claims 1 to 10, characterized in that that the plane common to the longitudinal axes of the pole pieces (14,15) runs approximately perpendicular to a plane, which is the angle between the entrance and exit electron beam paths intersects and the plane containing such paths is approximately perpendicular. 209817/0991 Blank page