US3337676A - Electron beam melting apparatus - Google Patents

Description

I fr 4 Aug. 22, 1967 s w H, Y TAL 3,337,676

' ELECTRON BEAM MELTING APPARATUS Filed April 2, 1964 a Sheets-Sheet 1 Si'e hen W H Yih Royal H.D1'm1'c'k IN V EN TORS 22, 1967 s. w. H. YIH ETAL ELECTRON BEAM MELTING APPARATUS Filed April 2, 1964 s Sheets-Sheet 2 A118. 2, 1967 s. w. H. YIH ETAL 3,337,576

ELECTRON BEAM MELTING APPARATUS Filed April 2, 1964 I 3 Sheets-Sheet 5 Shephen W HfYl'h Royal H. Dimick IN V EN TORS BY @491 @M flgeni" United States Patent 3,337,676 ELECTRQN BEAM MELTING APPARATUS Stephen W. H. Yih and Royal H. Dimick, Albany, 0reg., assignors to Web Chang Corporation, New York, N.Y., a corporation of New York Filed Apr. 2, 1964, Ser. No. 356,853 6 Claims. (Cl. 13--31) This invention relates to apparatus for melting materials by electron bombardment in a vacuum, and has for its primary objective the provision of such apparatus which is characterized by affording greater economy and efliciency of operation by reducing the requirements of the vacuum pumping system, by the protection of the high voltage power supply against insulation breakdown, by extending the life and reducing the maintenance of the electron source by protection against spatter and other contamination, and by affording operation under a wider latitude of control conditions, as compared with corresponding apparatus of the prior art.

Another important object of the present invention is the provision of apparatus of the class described in which a plasma gun is utilized as a rich source of electrons.

The foregoing and other objects and advantages of this invention will appear from the following detailed description, taken in connection with the accompanying drawings in which:

FIG. 1 is a foreshortened fragmentary view in side elevation, partly in section, showing schematically an electron beam melting apparatus embodying the features of the present invention;

FIG. 2 is a fragmentary view in side elevation, partially sectioned, showing details of construction of the plasma gun and deflection assembly of FIG. 1;

FIG. 3 is a fragmentary view in side elevation, partially sectioned, showing details of construction of the plasma gun control mechanism of FIG. 1;

FIG. 4 is a fragmentary view, partially sectioned, of the plasma gun control mechanism as viewed from the top in FIG. 3;

FIG. 5 is a fragmentary view in side elevation, partially sectioned, showing further details of construction of the plasma gun component;

FIG. 6 is a sectional view taken along the line 6-6 in FIG. 5 and illustrating the manner of adjustment of the plasma gun;

FIG. 7 is a sectional view taken along the line 7--7 in FIG. 2; and

FIG. 8 is a schematic representation of a modified form of electron control.

Referring principally to FIG. 1 of the drawings, the apparatus is shown to include a housing 10 provided with an intermediate transverse wall 12 dividing the housing into a melt chamber 14 and an electron acceleration chamber 16. An opening 18 is provided in the top of the melt chamber for the passage downwardly therethrough of an elongated rod 20 of stock material to be melted. It will be understood that appropriate seal-ing means (not shown) is interposed between the opening and the melt stock to provide a vacuum type seal therebetween. In addition, conventional means (not shown) is provided for rotating the rod 20 on its longitudinal axis during melting.

Vertically below the melt stock opening is an opening 22 in the bottom Wall of the housing, mounting therein an elongated hollow crucible 24 for receiving the material melted from the melt stock. The crucible preferably is provided with a retractable piston 26 by which to provide for the continuous collection of melted material in the crucible, as is well known in the art. A deflecting coil 28 preferably surrounds the crucible adjacent the bottom wall of the housing, for the purpose of directing an electron beam into the crucible.

A conduit 30 communicates the melt chamber with vacuum pumping equipment (not shown) capable of reducing the pressure in the chamber to a value below the glow discharge condition within the chamber.

Also supported within the melt chamber, by any suitable electrical insulation means, is a pair of laterally spaced vertical deflection plates 32, a pair of vertically spaced horizontal deflection plates 34 and a focusing coil 36. These are all arranged symmetrically with respect to a common horizontal axis which extends through the small opening 38 in an electrically conductive orifice plate 40 supported by the partition wall 12 but isolated electrically therefrom.

The electron acceleration chamber 16 of the housing contains the focusing coil 42 supported therein by any suitable electrical insulation means and arranged concentrically on the common horizontal axis previously mentioned. The outer end wall of the chamber 16 is formed in part by the plate 44 of electrical insulation material which, in turn, supports the orifice plate 46. The orifice 48 of this plate also is arranged concentrically about the common horizontal axis previously mentioned.

A conduit 50 communicates the electron acceleration chamber with vacuum pumping equipment (not shown) capable of reducing the pressure within the chamber to at least about 5 X 10* torr.

The orifice plate 40 is connected through the electrical conductor 52, suitably insulated from the housing at 54, to an appropriate source 56 of high voltage, low amperage electric supply. Exemplary of such supply is 10,000 volts at from zero to 500 amperes.

The orifice plate 46 is connected to a suitable source 58 of low voltage, high amperage electric supply, for example 30 volts at 100 to 500 amperes. 1

The vertical and horizontal deflection plates and focusing coils are connected in conventional manner to appropriately controlled sources of electric supply, as will be apparent to those skilled in the art.

Projecting outwardly from the acceleration chamber 16 and enclosing the orifice 48 therein, is an elongated plasma gun housing 60. A conduit 62 communicates said housing with vacuum pumping equipment (not shown) capable of reducing the pressure Within the housing from atmospheric down to about 5X10- torr. The rear end of the housing is closed by a plate 64 which slidably receives therethrough an elongated tubular member 66. This member terminates at its forward end in spaced relation to the orifice 48 and extends rearwardly through the plate 64. A conduit 68 extends through the tubular member and communicates at its rear end with a source (not shown) of argon or other suitable inert gas under pressure. The tubular member is made of electrically conductive material and is connected to the negative side of the electric supply 58 for the orifice plate 46.

For the purpose described in detail hereinafter, means is provided for moving the tubular member 66 longitudinally and rotationally relative to the orifice 48. In the embodiment illustrated, the means for moving the tubular member rotationally comprises a handle 70 secured to the tubular member and projecting radially therefrom. The means for moving the tubular member longitudinally comprises a pantograph assembly of the parallel links 72 and 74- which are connected together pivotally at one of their opposite ends by means of the control lever 76. One of the links 72 is connected pivotally to a hub extension 78 on the sealing plate 64 of the housing 60, and the other link 74 is conected pivotally to a collar 80 mounted for rotation in a longitudinally fixed position on the tubular member 66.

Certain perferred structural details of the assembly described hereinbefore are illustrated in FIGS. 2-7. Referring particularly to FIG. 2, the orifice plate 46 is cooled by the circulation of cooling liquid through the tube 82 mounted in surface contact therewith and arranged spirally about the orifice member 84 which provides the orifice 48 described hereinbefore. The orifice member 48 is mounted in an annular cooling member 86 supported by the orifice plate 46 and arranged for the circulation of cooling liquid therethrough.

The housing 60 for the plasma gun comprises an elongated glass or other electricaly non-conductive and nonmagnetic tube supported at its forward end on the orifice plate 46 by means of the assembly of the clamping ring 88. Interposed between the forward end of the glass tube 60 and the orifice plate 46 is the annular flange 90 of a tubular magnetic shield 92 of copper or other suitable material. The annular flange 90 is hollow, for the circulation of cooling liquid, and is spaced from the orifice plate 46 by means of the annular insulating block 94 of glass or other suitably non-conductive and non-magnetic material. These abutting surfaces are sealed for high vacuum by means of the interposed annular seals 96, 98, 100. The foregoing assembly is held together by means of the clamping screws 102.

The rearward end of the glass tube 60 is closed by the plate 64 (FIG. 3) which is secured across said open end by means of the annular centering wedge joints 104, 106 on the glass tube 60 and clamping collar 108, respectively, the latter being secured to the end plate by means of the screws 110. A vacuum tight seal between the abutting surfaces of the glass tube and end plate is provided by the annular sealing ring 112.

The tubular member 66 of the plasma gun includes a pair of concentrically arranged tubes 114 and 116 (FIGS. 4 and of copper or other non-magnetic material supported in spaced relation to provide an annular chamber 118 therebetween for the passage of cooling liquid. The outer one 114 of these pairs of tubes supports at its forward end a plug 120 provided with an axial bore in which the forward end of the gas supply tube 68 is supported. The rearward end of the outer tube 114 is sealed to a plug 122, as is the rearward end of the inner tube 116 of the pair. A stepped bore in the plug 122 provides a forward annular chamber 124 communicating with the space 118 between the pair of tubes, and a rearward chamber 126 communicating with the interior of the inner tube 116 of said pair.

Conduits 128 and 130 (FIG. 3) communicate said forward and rearward chambers in the plug 122 to a supply and drainage, respectively of a source of cooling liquid. The forward end of the inner tube 116 terminates rearwardly of the forward plug 120, to provide for communication of the annular space 118 between the pair of tubes with the interior of the inner tube 116, to accommodate said circulation of cooling liquid. The forward end of the inner tube 116 terminates rearwardly of the forward plug 120, to provide for communication of the annular space 118 between the pair of tubes with the interior of the inner tube 116, to accommodate said circulation of cooling liquid.

The outer tube 114 of the plasma gun is shielded by the encircling tube 132 of glass or other non-conductive and non-magnetic material. The tube is supported at its forward end by reception over the forward plug 120.

The tube 132 extends slidably through the closure plate 64 at the rear end of the glass tube housing 60 for the plasma gun, and a vacuum tight seal is provided therebetween by means of the annular seal 134. The rearward end of tube 132 is supported on the forward end of the plug 122. Thus, the assembly of tubes 114, 116 and 132 may be moved longitudinally and rotationally with respect to the closure plate, by means of the controls previously described.

A spider member 136 (FIGS. 2 and 7), having a central opening 138 freely receiving the glass tube 132 therethrough, is provided with a plurality of radiating fingers 140 which engage the glass tube housing 60, for supporting the forward portion of the plasma gun assembly.

The forward plug 120 is counterbored inwardly from its forward end and threaded for reception of the threaded shank of the adapter plug 142. The forward end of the adapter plug is provided with a tapped bore disposed off center with respect to the axis of the plug and this tapped bore communicates through the offset bore 144 extending rearwardly through the adapter plug, with the gas supply tube 68. The tapped bore in the adapter plug receives the threaded end of the elongated stinger tube 146 which extends forwardly toward the orifice member 84.

The purpose of the offset tapped opening in the adapter plug 142 is to provide adjustment of the bore of the stinger tube 146 relative to the bore 48 of the orifice member 84. Thus, referring to FIG. 6, rotation of the plasma gun assembly by means of the control handle 70 causes rotation of the bore of the stinger tube in a circle whose center is offset from the axis of the bore 48 in the orifice member, as indicated by the arrow. The degree of offset of the bore of the stinger tube thus may be varied to control the electron flow through the orifice. In this regard, electrons are produced by causing an electric arc discharge between the forward end of the stinger tube and the orifice member, to effect ionization of the inert gas being forced through the tube 68. 7

An electron emission control coil 148 surrounds the housing 60 of the plasma gun, adjacent the forward end of the stinger tube 142, and is connected to a controlled source of electric potential for focusing the beam through the aperture 48, as is well known.

The forward portion of the plasma gun assembly is provided with an electric shield in the form of a plurality of circumferentially spaced rods 150 supported by the longitudinally spaced rings 152 supported freely on the plasma gun tube assembly.

In the operation of the apparatus described hereinbefore, let it be assumed for purposes of illustration that an elongated cast ingot 20 of a refractory metal projects downwardly into the melting chamber 14, as illustrated in FIG. 1, and is driven in rotation preparatory to melting. A control valve (not shown) for the inert gas is manipulated to provide a flow of the gas through tube 68 in the forward end of the stinger tube 146 and the vacuum pumping equipments are activated to reduce the pressures within the associated chambers, as previously described. Further, the appropriate source of electric supply are activated to provide the proper potentials to the orifice plates, emission control coil, focusing coils and deflection plates.

By manipulation of the pantograph control assembly, the plasma gun is moved longitudinally relative to the orifice plate 84 until an electric arc discharge therebetwcen is achieved. Ionization of the inert gas results in the flow of electrons through the orifice 48, and this beam may be adjusted by appropriate adjustment of lever 70 and coil 148. The electrons are focused and accelerated through the orifice 38 and then again focused and deflected appropriately by proper control of the vertical and horizontal deflection plates 32 and 34, respectively. The electron beam thus is deflected toward the collecting crucible 24 while simultaneously intercepting the path of the rotating melt stock 20. The lower end of the melt stock thus is heated to a temperature above the melting point of the stock, whereupon the molten metal falls by gravity into the crucible.

The electron beam also impinges upon the metal in the crucible, thereby maintaining a molten pool at the surface thereof. Thus, as the piston 26 is lowered continuously during the accumulation of molten metal in the crucible, non-volatile impurities are caused to remain selectively in the molten pool while volatile impurities are exhausted through the vacuum system, in manner well known in the art.

Adjustable control of the flow of electrons to the melting chamber may be achieved by various means other than the rotational adjustment of the stinger tube 146. For example, the stinger tube may be aligned axially with an orifice member provided with an iris type opening which may be adjusted in diameter over an operating range. Another form of control is illustrated in FIG. 8, wherein the stinger tube 146 is aligned axially with the orifice 43 as well as with a plurality of longitudinally spaced coaxial accelerating orifices 154 and focusing coils 156, with each successive orifice forwardly of the orifice plate 46 being connected to progressively increasing sources of potential 158. The crucible 24 is connected to a source 169 of still higher potential, and the orifice plate 46 is connected to source 162 of lowest relative potential.

The plasma gun operates in the mode of complete space charge neutralization, and therefore minimum radio frequency oscillations in the plasma is generated. Accordingly, insulation breakdown in the power supply is substantially eliminated.

The high voltage component of the apparatus is isolated and protected from gas bursts which frequently occur in the melting chamber, thus eliminating the necessity for controlling such burst while simultaneously eliminating damage to the high voltage component.

The source of electrons, being isolated from the melting chamber, remains clean and maintenance free since it is not subject to the deleterious effects of spatter and other contamination which heretofore has necessitated frequent rebuilding or replacement of components of the electron source. Accordingly, the plasma gun remains operable over much longer periods of time as compared with electron sources of the prior art.

The apparatus of this invention is capable of operation under unlimited conditions of power, since operation does not depend upon the former requirement of a plasma column around the melt stock. The present invention utilizes a plasma gun merely as a rich source of electrons, and the melting chamber constitutes a field free space, whereas apparatus of the, prior art utilizes the plasma of the melt at the electron source and the crucible to neutralize the space charge and increase the electron beam current.

The apparatus of the present invention also has the advantage of being capable of operation at higher pressures, and thus requires smaller and less expensive vacuum pumping equipment than apparatus of the prior art.

It will be apparent to those skilled in the art that various changes may be made in the details of construction described hereinbefore. For example, a gate valve 164 may be provided between the orifice plate 38 and coil 42 for releasably sealing the acceleration chamber 16 from the melting chamber 14, to facilitate maintenance of the components in the latter without losing the vacuum in the acceleration chamber. A plurality of plasma guns and associated deflection systems may be arranged concentrically about the melt stock rod 20, if desired. The melt stock rod may be fed in from the side rather than from the top, as shown, and means may be provided for feeding powder or other particulate material. These and other changes and additions may be made without departing from the spirit of this invention and the scope of the appended claims.

Having now described our invention and the manner in which it may be used, what we claim as new and desire to protect by Letters Patent is:

1. Electron beam melting apparatus, comprising (a) a housing adapted to be evacuated to sub-atmospheric pressure and arranged to contain a material to be melted, the housing including a receptacle for receiving the melted material,

(b) conduit means communicating the housing with a source of inert gas,

(c) electric arc discharge means in the housing remote from and independent of the receptacle and melted material therein for providing an electric discharge are in the path of inert gas emitted from the conduit means whereby to effect ionization of the inert gas and consequent production of electrons, and

(d) electron control means in the housing for controlling the number of electrons to the material to be melted.

2. Electron beam melting apparatus, comprising (a) a melting chamber adapted to be evacuated to subatmospheric pressure and arranged to contain a material to be melted,

(b) a gas tube housing adapted to be evacuated to sub-atmospheric pressure,

(c) an electrically conductive orifice member having an opening therethrough communicating the housing with the melting chamber,

((1) an electrically conductive tube in the housing terminating at one end adjacent the orifice member and adapted for connection at its opposite end to a source of inert gas under pressure,

(e) means connecting the orifice member and tube in series in an electric circuit of a source of electric potential with the orifice member being positive with respect to the tube, for providing an electric discharge are between said orifice member and tube whereby to effect ionization of the inert gas and consequent production of electrons, and

(f) means for directing said electrons in a beam through the opening in said orifice member and onto the material to be melted.

3. The apparatus of claim 2 wherein the melting chamber includes a receptacle vertically below the material to be melted for receiving the melted material, and the directing means includes deflection means for directing the electrons in the beam into said receptacle along a path of interception of the material to be melted.

4. The apparatus of claim 2 including control means operatively associated with the orifice member and gas tube for adjusting the gas number of electrons in the electron beam.

5. The apparatus of claim 2 including movable support means for the gas tube for moving the latter longitudinally and laterally with respect to the opening in the orifice member for adjusting the number of electrons in the electron beam.

6. The apparatus of claim 2 wherein the opening in the orifice member communicates the housing with the melting chamber through an electron acceleration chamber adapted to be evacuated to sub-atmospheric pressure, the acceleration chamber communicating with the melting chamber through an opening in a second orifice member connected to a source of electric potential which is positive with respect to the tube.

References Cited UNITED STATES PATENTS 2,934,665 5/1960 Ziegler 313-231 X 3,015,745 1/1962 Klein 313-231 X 3,210,454 10/1965 Morley 13-31 X 3,218,431 11/1965 Stauffer 219-121 3,271,556 9/1966 Harris 219-121 3,275,787 9/1966 Newberry 13-31 X 3,294,954 12/1966 Ramsey 219-121 X JOSEPH V. TRUHE, Primary Examiner.

Claims (1)

1. ELECTRON BEAM MELTING APPARATUS, COMPRISING (A) A HOUSING ADAPTED TO BE EVACUATED TO SUB-ATMOSPHERIC PRESSURE AND ARRANGED TO CONTAIN A MATERIAL TO BE MELTED, THE HOUSING INCLUDING A RECEPTACLE FOR RECEIVING THE MELTED MATERIAL, (B) CONDUIT MEANS COMMUNICATING THE HOUSING WITH A SOURCE OF INERT GAS, (C) ELECTRIC ARC DISCHARGE MEANS IN THE HOUSING REMOTE FROM AND INDEPENDENT OF THE RECEPTACLE AND MELTED MATERIAL THEREIN FOR PROVIDING AN ELECTRIC DISCHARGE ARC IN THE PATH OF INERT GAS EMITTED FROM THE CONDUIT MEANS WHEREBY TO EFFECT IONIZATION OF THE INERT GAS AND CONSEQUENT PRODUCTION OF ELECTRONS, AND

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