US2793282A - Forming spherical bodies by electrons - Google Patents

Description

K. H. STEIGERWALD 2,793,282

FORMING SPHERICAL BODIES BY ELECTRONS" May 21, 1957 3 Sheets-Sheet 1 Filed Nov. 28, 1951 Jill/DING min/41 Irwin 5n" May 21, 1957 K. H. STEIGERWALD FORMING SPHERICAL BODIES BY ELECTRONS 3 SheetsSheet 2 Filed Nov. 28, 1951 I Q I I @000! may; 7

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FORMING SPHERICAL scams BY ELECTRONS' Filed Nov. 28; 1951 United States Patent FORMING SPHERICAL BODIES BY ELECTRONS Karl Heinz Steigerwald, Mosbacli, Germany, assignor, by mesne assignments, to Carl Zeiss, Heidenheim (Brenz), Wurttemberg, Germany Application November 28, 1951, Serial No. 258,673 Claims priority, application Germany April 13, 1951 3 Claims. (Cl. 219-69) My invention relates to a novel apparatus for and methods of producing balls having a diameter of the order of millimeters to tenths of millimeters, and more par.- ticularly relates to apparatus for and methods of using the energy of an electron stream for this purpose.

In my copending application Serial No. 258,671, filed November 28, 1951, I have described in detail an arrangement for controlling an electron beam so as to produce a long distance to the focus plane. I have found as therein described that by a proper control of an electron stream, I can produce a suflicient current density thereof to heat objects to a temperature at'which the material becomes fluid and will flow.

In general my invention contemplates impinging such an electron beam on objects and transferring the kinetic energy of the electrons to the objects causing the object to soften sufficiently to flow into spherical forms without causing any rise in temperature in the adjacent region of the object.

In another form of my invention, I impinge electrons on the object with such force that the object, after being melted, explodes and forms a number of smaller objects of spherical shape.

Accordingly, an object of my invention is to provide apparatus for and methods of utilizing the energy of an electron beam to form spherical objects having diameters of the order of one millimeter to tenths of a millimeter.

A further object of my invention is to provide novel means for utilizing an electron beam to form minute particles from larger objects. I

Still another object of my invention is to provide a novel arrangement of an electron stream for transferring the energy therefrom to objects.

These and other objects of my invention willbe more clearly understood from the detailed description of my invention which is to follow in which:

Figure 1 is a cross sectional view of one embodiment of my invention.

Figure 2 is a cross section of a modified form of my invention in which a plurality of electron beams are impinged on an object; and

Figure 3 is a further modification of my invention in which a plurality of electron sources are employed for producing electron beams reacting on objects.

In the drawing, the electron gun 11' comprising a tubular housing made of any suitable metal is mounted on an insulator 12 with a suitable rubber ring washer 14. Mounted within the tubular housing 11 is a cathode 15 of any suitable electron emitting material'such'as tungs'ten. Leads 16 and 17 extending from the cathode are connected to any suitable source of direct current voltage supply such as battery 18 operating normally at a potential of four volts and supplying approximately four amperes.

Also mounted within the electron gun 11' in any suitable manner is a control electrode 19 having its upper portion 20 in the form of a cylinder and having an integral extension 21 of conical construction with an opening at its apex 22. A further integral extension 23 of the control electrode is cylindrical in shape.

The control electrode is connected over the conductor 24 to a potential source. The cathode is maintained at a potential of approximately 50,000 volts with respect to ground, and the control electrode is maintained over conductor 24 to a higher negative potential than the cathode by approximately to 300 volts. These voltages may be suitably regulated in any well known manner.

It will be noted that the electron emitter 15 protrudes through the apex opening 22 of the sonically shaped extension 21 of the control electrode 19. In practice, I have found that the cathode is preferably of hairpin shape having a wire diameter of 0.15 mm. For my purposes, I have found that the electron emitter should protrude beyond the opening 22 at the apex of the cone 21 by a distance substantially equal to the diameter of the wire for reasons which will be more clearly understood from the description which is to follow.

The cone section 21 of the control electrode may comprise a preferably six in number of conical sectors 25, insulated from each other. Each sector is maintained at suitable potential between each other and cathode of the order of 500 volts. 7

It will of course now be understood that the voltages of each of these sectors with respect to ground remain of the order of S0,000 volts.

To maintain these potential differences between the sectors, individual conductors corresponding to 24 are connected to each of the sectors 25 each having predetermined potentials applied thereto. Correspondingly, the cylindrical section 23 is also connected over its individual conductor corresponding to conductor 24 for applying a predetermined voltage thereto.

The cylindrical sections 23 may be also formed of a plurality of sectors, insulated from each other and each maintained at suitable potentials with respect to each other.

In the present illustrations however, the conical portions and the cylindrical portions are unitary members maintained at a common potential.

As will be seen, the cathode 15 protrudes beyond the conically shaped control electrode 21 by a distance equal to the diameter of the emitter wire. Adjacent to the electron emitter 15 there exists as is well known in the art, a space charge. The equipotential lines produced by the potential between the control electrode and anode assume the shapes shown by the lines 27, 27'.

It will be seen from Figure 1 that the equipotential lines follow the values of their adjacent electrodes.

The 50,000 volt equipotential line which is at the cathode or electron emitter potential follows generally the form of the cylindrical electrode 23 and the conical electrode 21. In Figure l, the line closest to the cathode has a slight hump 27" adjacent the space charge zone at the cathode tip. The negatively charged electrons in the space charge Zone are pulled out by this shape of the potential line. The equipotential lines thereafter rapidly straighten out this hump and assume complete convex forms as shown at 27*. The curvature of these lines further away from the cathode become straightas at 27 "and then concave as at 27.

Because these potential lines apply an accelerating force to the electrons in a direction normal to the potential, the electron beam is at first widened as at 32' and then accelerated inwardly slowly as at 32" by the potential lines 27 to produce a large distance to the focal plane.

It will of course be understood that the equipotential lines in Figure 1 necessarily are not shown in their true dimensions as this is not possible in illustrating the principal functions of these lines.

Preferably the cross section of the electron beam should be circular. This is determined by the shape of the cathode, the space charge adjacent thereto and the shape and potentials of the' various conical sectors 25. If because of an unsymmetrical shape of the electron emitter, the cross sectional area of the electron stream in the first instance is elliptical, I have found that by a proper distribution of potentials applied to the individual conical sectors, I can reconstruct the cross sectional shape of the electron stream to .restore it to a circle.

Thus for example, in the case .of an original elliptically shaped electron stream, I would increase the relative potential of those sectors opposite the long axis of the conical shaped electron stream causing the long axis to be reduced. I also decrease the potential of the sectors opposite the small axis of the sectors which enlarges the small axis and restores the cross sectional circular shape of the electron stream. By use of potential distributions between the sectors which are not chosen symmetrical to the optical axis, one can also secure deflections of the electron beams direction.

It will, of course, be understood that in referring to an increase or decrease of potentials at the conical sectors, I am here referring to the relative voltages with respect to each other.

The diameter of the electron stream at its widest point is between 0.5 to 1.5 mm. For the smaller diameter of electron stream, that is, 0.5 mm., the focal point of the electron stream will be approximately cm. from the electron emitter, whereas for the electron stream having a diameter of 1.5 mm. the focal point will be 30 cm. from the emitter.

As the potential between the electron emitter and the control electrode increases, the diameter of the cross section through the electron stream adjacent the cathode decreases and the length to the focusing plane of the electron stream correspondingly decreases. As a result the current density increases until a critical point is reached. A further increase in the potential difference between the electron emitter and the control electrode withdraws the hump 27" from the space charge region and the current density decreases.

I have given below a table in which such relative values are set forth. It Will be understood, however, that these values are not exactly reproduced but are given solely for purposes of illustration.

It will be noted that the anode 11 is grounded in any suitable manner as, for example, in the illustration here shown through the grounded base member 11'. The member 11 carries the entire electron gun. The entire mechanism including the base 11 and the electron gun construction hereinafter described is evacuated in any suitable manner.

The electron beam 32, as described hereinabove, has been provided with a long focal point located in the region 65. Mounted within the evacuated chamber is a rod 67 having a plurality of grooves 66. The rod 67 protrudes through the walls of the chamber and is connected to an operating handle 68 which permits the insertion and removal of the rod. In order to maintain vacuum within the chamber, gasket means 69 and 70 are provided of any well known construction such as rubber.

The rod 67 extends through a chamber 72 and gasket member 73. The chamber 72 is connected over the passageway 74 to an evacuating pump. In order to insert members to be treated, the rod 67 is drawn to the right until the grooves 66 are exposed on the outside of the chamber 72 and the material 75 to be treated is then in serted in the grooves.

It will of course be understoodthat the rod is sufiiciently long so that the stop 76 at the left end of the rod will hit the wall of the chamber only after all of the grooves have been exposed.

With this construction, it is now possible to slide the rod without disturbing the vacuum in the evacuated chamber. With the rod in the position shown, the article 76' is in the focal region of the electron beam.

The object or articles to be treated which may be of A1203 crystalline in construction, may have previously been broken up into small particles of millimeter size by any well known means and had assumed irregular shapes as shown at 75. When now the object in its groove is brought into the focal region of the electron stream, the material is brought to a fluid state in a matter of seconds. Due to the surface tension, the fluid material now flows into a ball or spherical form as shown at 76'.

Adherence to the walls of the container is prevented because the electron beam being concentrated on the object, it does not heat the surrounding regions so that they remain substantially cold. Before any substantial heat transfer can occur the ball-like structures which have been formed have cooled and resolidified.

The particular crystalline construction of the end product may be controlled by the rate of cooling. Where it is desired to provide a single crystal, the article is cooled at a relatively low speed by slowly decreasing the electron stream. This may be done either by changing the electron volts or by a diaphragm which regulates the electron stream. Such a diaphragm is illustrated at 81 and consists as described in connection with my aforesaid application, of a hollow U-shaped member 82, a disk 83, with an interposed diaphragm 84 having a central opening at 85 through which the electron beam moves.

The member 81 is adjustably moved to control the electron stream by means of the screw members 86 and 87. The diaphragm here shown is positioned in a position corresponding to the focus plane described in my aforesaid copending application which is hereby made a point of this application. Inasmuch as every electron ray in the focus plane is reproduced in the image plane, I may adjust merely one of the adjusting screws 86, for example, or 87.

By moving the diaphragm to the left, for example, whatever portion of the electron stream is left exposed will form an image in the image plane of uniform intensity.

In this illustration, the object 76 will be in the plane corresponding to the image plane of my copending application, although the focus plane may alternatively be used.

The electron chamber is evacuated in any well known manner, as by means of any standard pump. If desired, in order to further control the rate of cooling, I may heat the supporting members in which the slots are formed and in which the members to be treated have .mm. or less.

Where it is desired to form an amorphous construction, that is to say to reconstruct the crystals into a large number of individual crystals, a more rapid cooling is required. In such a case, the electron stream is instantly out 01f afterthe material has been sufficiently caused to flow. For balls having a diameter of 0.1 mm., the cooling may be achieved in 0.1 second the heat being dissipated mostly by radiation and by conduction to the surrounding regions. With such rapid cooling, I will form minute balls having a number of individual crystals formed therein.

To further decrease the speed of cooling, I may, if desired, provide a saucer or well 51 which is filled with a cooling fluid such as oils which have low vapor pressure and will remain in a fluid condition in an evacuated chamber. Immediately after the object has been formed into a ball construction, the handle 68 is rotated through 180 and the object will then fall into the fluid located directly underneath, the remaining objects are prevented from falling since the rod in these other regions is mounted within the tubular members 52 and 53.

If I desire to further reduce the object to smaller sizes I may first melt the object in the manner described above to a fluid. For the melting, I require fifty microamperes and this is obtained by the particular potential of the control electrode with respect to the electron emitter. By decreasing this negative potential of the control elec trode to 250 volts, I increase the current of the electron stream to 300 microamperes. At this value I have found that the object will explode, breaking up into a number (100 for example) of smaller particles of still smaller diameter. As they fall, these particles are cooled and when they reach the base, are sutficiently cold to retain their shape.

Any well known shape or construction of the base may be employed for collecting these balls as, for example, making the base of the evacuated vessel conical in shape.

In Figure 2 I have shown a modified form in which the electron stream from a common source is split into a number of electron beams for impinging on ditferent areas of the article. In this construction, the electron beam 121 which has been formed in the manner described in detail hereinabove is interposed by barrier 122 which has been grounded in any suitable manner.

The upper end 123 of the plate 122 is of increased thickness so as to keep the electron stream from touching the plate 122. On both sides of the plate 122 are deflecting electrodes 124 and 125 each maintained at a positive potential of the order of 100 to 1000 volts with respect to ground. Control of these electrodes is obtained through the rods 126 and 127 which protrude through the walls 128 of the evacuated vessel and are provided with gaskets and insulators 129 and 130 for preventing a loss of vacuum. The electron stream is thus divided into two electron streams 131 and 132 having predetermined angles of deflection and pass between the deflecting plates 134 and grounded plate 135 and between the deflecting plate 136 and grounded plate 137. Plates 134 and 136 are supported on adjustable rods 141 and 142 respectively extending through the wall 128 of the evacuated vessel and mounted in insulators and gaskets 143 and 144.

The deflecting plates 134 and 136 will redirect electron beams 131 and 132 to impinge upon adjacent or opposite walls of the object 145 mounted on the carriage 146 of a construction similar to that shown in Figure 1.

Although in this illustration I have shown the deflectors as plates, it will now be apparent that I may replace the plates 124 and 125 by a single flaring tubular member with a barrier rod extending through it. The deflecting plates 134 and 136 would then comprise a single deflecting plate which is a sector of a doughnut shaped member. The ground plates 135 and 137 would similarly form a single plate also of a sector of a doughnut shape. Between the single plate formed by 134 and 136, and the single plate formed by electrodes by 135 and 137, the electron beam now in the form of a paraboloid envelope would be deflected as a continuous beam impinging in a continuous ring over the upper surface of the object l45.

6 In the above construction, the plate 122 would be supported on a rod 147 extending to the wall 128 and which in turn may carry the grounding wire. The single construction formed by the plates and 137 could either be similarly supported or on the same rod.

In Figure 3 I have shown a still further modification in which I employed two separate electron streams 201 and 202 each formed by its own or individual electron source. Here as in the previous modification, the construction of the source including the electron emitter, the accelerators and anode are the same as previously described. The electron vessels 203 and 204 are arranged to meet in a common chamber 205 into which the rod 206 carrying the articles to be treated are seated. The construction and operation here are similar to that described in previous figures, the advantage residing in the impinging on the articles by independent electron streams at adjacent or opposite areas.

Although I have described the electron stream in simple form here, it will now be apparent that I may utilize an electron system with an optical system of the type described in my above referred to co-pending application.

In this construction I would use optical lenses or focusing means in the optical system for controlling the dimensions of the parameters of the electron stream and therefore the current densities that I may explain.

In some instances, depending upon the type of material, it may be desirable .to impinge the electron beam on the article in an intermittent fashion. In such a case I can control the electron beam at the source cutting it on and off at any desired rate. It is then possible to increase the current density of the electron stream and regulate the heat distribution to the object.

From the above description it will be apparent that I can, through a proper arrangement of the deflecting electrodes and the potentials applied thereto produce an electron beam which can be rotated as in an oscilloscope or can take any desired path. In this manner a number of objects can be successively treated.

A substantial deflection of the electron beam may also be achieved in the modification shown in Figure 2 by varying the potentials applied to the deflecting plates 134 and 136.

In this manner I may melt only a desired portion of the object to form any desired shape at that portion without aifecting the remaining portions. It is also possible by a predetermined control of the size of the electron beam and the manner of impingement on the objects not only to form spherical shapes but also other irregular shapes or alternatively thereto drill holes in the objects as described in my co-pending application.

As further described in my co-pending application referred to above, I may instead of using an evacuated vessel as herein described for illustrating my invention, employ a gas filled tube and utilize ions for performing my operation. In such a construction I would utilize the ions for treating the objects as the electrons are used in the present illustration. The ions would then be formed in a separate gaseous tube mounted within the electron tube.

The generation of the ions in such a case are made in a manner now well known in the art and are directed into the evacuated chamber through an opening just large enough to permit the passage of the ions and small enough to prevent any substantial escape of gas.

Provision must then be made to maintain vacuum in the evacuated section.

I claim:

1. An evacuated vessel having an electron emitter, means adjacent said electron emitter for focussing the electron beam from said electron emitter to increase the current density thereof, means for placing objects to be melted by said electron beam in the plane of maximum current density of said electron beam, said focusing means providing a density of the electron beam at the araaaaz 7 point of impingement of said objects so as to cause the objects to be split into a number vof smaller objectssaid second mentioned means being movable in a transverse direction with respect to saidelectron beam in said evacuated vessel with substantially no loss of vacuum.

2. An evacuated vessel comprising an electron emitter for generating an electron beam, means for energizing said electron beam to 50,000 electron volts and higher, means adjacent said electron emitter for focusing the electron beam from said electron emitter to increase the current density thereof, means for placing objects to be melted by said electron beam in the plane of maximum current density .of said electron beam, electrons from said emitter when focused and impinged on said objects by said focusing means having a density such that the object is split into a number of smaller objects, said second mentioned means being movable in a transverse direction with respect to, said electron beam in said evacuated vessel with substantially no loss oi vacuum.

3. In an electron tube, a source of electrons for gencrating .an electron beam, conductive plates positioned in the path of said electron beam and connected to ground to produce an electrical .field configuration to thereby split said electron beam into a plurality of beams, a carrier member for supporting articles to be treated by said electrons, means for energizing said electrons .to 50,000 electron volts and higher, and means for impinging said electron beams on a single article on said carrier member to melt and form said article into spherical form said electron tube being evacuated and said article carrier being movable in said .electron tube with no loss of vacuum.

References Cited in the file of this patent UNITED STATES PATENTS 2,128,58l Gardner Aug. 30, 1938 2,267,714 Borries Dec. 30, 1941 2,267,752 Ruska et al. Dec. 30, 1 941 2,345,080 Von Ardonne Mar. 28, 1944

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