US 3162749 A
Description (OCR text may contain errors)
' Dec. 22, 1964 A. A. PERACCHIO JET VALVE PRESSURE STAGING DEVICE Filed Dec. 31, 1962 2 Sheets-Sheet 1 Dec. 22, 1964 A. A. PERACCHIO 3,162,749
JET VALVE PRESSURE STAGING DEVICE Filed Dec. :51, 1962 2 Sheets-Sheet 2- Wae/f P/ECE CZ WWW United States Patent Ofiice 3,162,749 Patented Dec. 22, 1964 3,162,749 JET VALVE PRESSURE STAGING DEVICE Aldo A. Peracchio, Wapping, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Dec. 31, 1962, Ser. No. 248,315 8 Claims. (Cl. 219121) My invention relates to working materials with a beam of charged particles. More particularly, my invention is directed to permitting a beam of charged particles, which is generated in a first low pressure chamber, to impinge upon a workpiece which is located in a region where the ambient pressure is relatively high.
While not limited thereto, my invention is thought to have particular utility when used in conjunction with an electron beam machine. Electron beam machines, as they are commonly known, are devices which use the kinetic energy of an electron beam to work a material US. Patent No. 3,009,050, issued November 14, 1961, to K. H. Steigerwald, discloses such a machine. These machines operate by generating a highly focused beam of electrons which is caused to impinge upon a workpiece. The electron beam is a welding, cutting and machining tool which has practically no mass but which has high kinetic energy because of the extremely high velocity imparted to the electrons. Transfer of this kinetic energy to the lattice electrons of the workpiece generates higher lattice vibrations which cause an increase in temperature within the impingement area sufiicient to accomplish work.
In apparatus, such as electron beam machines, which use beams of charged particles to perform work, the elements which emit or otherwise cause production of the particles which comprise the beam are highly susceptible to damage. For example, the electrons which form the working beam in an electron beam machine are emitted by a filament which is heated to an extremely high temperature. Any oxygen in the chamber where the filament is located will cause almost instantaneous oxidation and failure of said filament. Thus, it is required that the filament be located in an evacuated chamber. If the filament is located in an evacuated chamber, it has, in the prior art, followed that the workpiece must also be located in an evacuated chamber. Because there are practical limitations on the size of the evacuated work chamber and further because of the time-consuming operation of pumping down the work chamber for each new workpiece, it obviously would be highly desirable to locate the workpiece outside of the vacuum.
If the workpiece is positioned outside of the vacuum, means must be provided to bring the beam, without attenuation, out of the low pressure chamber in which it is generated. This presents a second problem coincident with the above-mentioned oxidation danger which, of course, arises because of the leakage of gas up the beam path. In applications where it is desired to weld, drill or perform other operations that require high beam power density, any gas molecules present in the path of the beam will interact with the beam and substantially attenuate the beam intensity through scattering caused by collisions between the gas molecules and the beam particles. Therefore, in order to minimize this undesirable attenuation, the length of the beams path along which there is a heavy concentration of gas molecules must also be minimized. In the prior art, various schemes have been tried to overcome these two aforementioned problems. However, to date, only moderate success has been achieved and this only by the use of cascaded vacuum systems utilizing large capacity, high speed vacuum pumping apparatus. An example of this approach is illustrated in the above-mentioned Steigerwald patent. A further variation of the cascaded vacuum system is the use of a pressure stretch such as that disclosed in US. Patent No. 2,640,948, issued June 2, 1953, to E.. A. Burrill.
My invention overcomes the above-stated problems and produces better and more efiicient operation than previously obtainable by providing novel apparatus for permitting a beam of charged particles to be brought out of a low pressure chamber to a region of relatively high pressure.
It is therefore an object of my invention to provide communication between a low pressure chamber and a region of relatively high pressure.
It is another object of my invention to bring a beam of charged particles out of a region of low pressure to a region of higher pressure with a minimum amount of attenuation.
It is still another object of my invention to perform work with a beam of charged particles at atmospheric pressure without damage resulting to the beam-generating apparatus.
These and other objects of my invention are accomplished by novel apparatus wherein a beam of charged particles is generated in an evacuated chamber and then accelerated through an aperture where it impinges upon a workpiece which is positioned in a region of high ambient pressure. The particularly novel feature of my invention comprises means for inducing a flow deflection, away from the beam axis, of the gas which attempts to rush into the evacuated chamber through said aperture.
My invention may be better understood and its numerous advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various figures and in which:
FIGURE 1 is a sectional view of a first embodiment of my invention.
FIGURE 2 is a cut-away view of a second embodiment of my invention.
FIGURE 3 is an enlarged partial view of the embodiment of FIGURE 2.
Referring now to FIGURE 1, there is shown an electron beam machine comprising an electron beam column indicated generally at 10. In this column are located means, such as those shown in the above-mentioned Steigerwald patent, for generating an extremely high energy electron beam. Column 10 is evacuated by thirdstage pump 12. The beam generated in column 10 passes down a conduit 14 which is located between the coils of a magnetic lens assembly 16. The function of lens assembly 16 is to focus the beam at the workpiece which is positioned at a desired distance below the lens. Upon emerging from conduit 14, the beam passes through -a chamber 18 which forms the second stage of a three-stage cascaded vacuum system. Chamber 18 is evacuated by a second-stage pump 20. The beam exits from chamber 18 through second-stage probe 22 and then passes through chamber 24 of the first stage. Chamber 24 is evacuated by first-stage pump 26. The beam leaves chamber 24 through an orifice 28. After passing through orifice 28 the beam strikes workpiece 30 where, in accordance with its parameters as set by the operator, it performs the desired type of work. Workpiece 30 is positioned upon a movable table 32 and is thus movable in respect to the beam axis. As should be obvious to those skilled in the art, the distance between orifice 28 and workpiece 30 must be kept as small as possible to minimize scattering or attenuation of the beam due to collisions between the charged particles and molecules of air.
Because of the large pressure drop across orifice 28, the ambient air is induced to flow up into the electron beam machine. The novel feature of my invention consists of means for turning this air. which flows into the evacuated column through orifice or nozzle 28, away from the beam axis thus minimizing both leakage into the region of column where the beam of charged particles is generated and also the length of the path of the beam along which there is a heavy concentration of air molecules which would cause attenuation of the beam. To accomplish the foregoing, my invention utilizes the bistable valve principle. A passage 38 is formed in the bottom wall 34 of the first-stage chamber 24. Passage 38 terminates in an opening 36 which is in communication with the ambient air. Passage 38 may be tapered at its other end to form a nozzle or jet valve 40 having its longitudinal axis perpendicular to the beam axis. Nozzle 40 is shaped and sized so that the flow discharging therethrough may be either sonic or supersonic depending upon the particular application. The bistable valve operates on the principle that there are two stable modes of flow for a given geometric configuration as, for example, the one shown in FIGURE 1. The two stable flow modes for the air entering the evacuated regions through orifice 28 are straight through into probe 22 or to the side between wall 41 and airfoil shaped member 42. The position or path which the flow assumes depends on whether or not a side flow is induced in passageway 38 and through nozzle 40. If, as in the embodiment of FIGURE 1, such a side flow is induced, the main flow through orifice 28 will be turned and will pass between wall 41 and member 42. Thus, the main flow will be deflected away from probe 22. By virtue of this deflection of the main flow, the second-stage probe 22 only feels the static pressure in chamber 24 and does not feel the dynamic pressure created by the main stream. It is apparent from the foregoing that the second-stage probe 22 is not subjected to the total pressure head and consequently the air weight fiow at this point is not as high as it would be without my invention. As a result of the reduction of weight flow at second-stage probe 22, the required capacity for second-stage pump is significantly reduced. This affords a substantial savings in cost, consumption of power, and the like. The use of this jet valve deflection also permits close spacing of probe 22 to orifice 28 and this close spacing, in turn, greatly reduces beam attenuation since the beam has a much shorter distance to travel through partially evacuated or unevacuated regions.
Referring now to FIGURES 2 and 3, there is shown a second embodiment of my invention wherein the deflection of the gas attempting to flow into the evacuated electron beam machine is achieved by an aerodynamic nozzle pressure staging device. In FIGURES 2 and 3, the charged particle generator, like that discussed above in relation to the embodiment of FIGURE 1, incorporates a staged vacuum system comprising first-stage chamber 24, second-stage chamber 18, and the beam forming column 10 which functions as the third stage. As in the embodiment of FIGURE 1, the ambient air in the region of workpiece attempts to rush into the evacuated region through orifice 28.
As is well known in the art, when air rushes through an orifice with very low downstream static pressure, the flow will be supersonic and behave as a free-stream jet discharging into a large chamber. Because of the low downstream static pressure, the air will compress and expand in a predetermined pattern causing shock waves and expansion waves to be formed. As a result of this wave pattern, a series of minimum pressure points are established. By locating a second-stage probe, such as 22, at one of these points of minimum pressure, the mass flow into a second-stage chamber may be decreased. This manner of locating successive probes at minimum pressure points in a free jet flowing into a cascaded vacuum system has previously been utilized as shown in US. Patent No. 2,899,556, issued August 11, 1959, to E. Schopper et al. My invention constitutes an improvement over the prior art in that it deflects the flow entering a low pressure chamber through an orifice away from the axis of the second-stage probe and in so doing can produce a lower pressure at the tip of the probe than previously obtainable.
My improvement consists of shaping the outside wall of second-stage probe 22 and the inner wall 44 of a passage forming member 46, extending from the downstream side of orifice 28, to define a diverging nozzle 48. That is, probe 22 and wall 44 are shaped so that section 48, which they define, forms the divergent section of a convergent/divergent nozzle having its throat at orifice 28. By proper sizing and location of nozzle 48, as shown in FIGURES 2 and 3, and proper adjustment of the static pressure in first-stage chamber 24, flow is directed therethrough and a normal shock wave 50 is formed between second-stage probe 22 and inner wall 44 downstream of the tip 52 of probe 22. Thus, the shock is located as shown in FIG. 3 by proper matching of the design of nozzle 48 and the characteristics of pump 26. For a given design of nozzle 48, this matching is accomplished by varying the pump flow until the shock is located at the desired point. The normal shock wave drops the velocity of the air passing through nozzle 48 from supersonic to subsonic thereby realizing an increase in static pressure in first-stage chamber 24 while a very low static pressure is maintained just before tip 52 of probe 22. This affords an advantage over the prior art in that for a given static pressure in first-stage chamber 24, the static pressure just upstream of second-stage probe 22 is much lower than in a free jet type apparatus as exemplified by the above-mentioned Schopper et al. patent. This is due to the greater expansion or turning of the air passing through orifice 28 made possible by properly shaping the wall 44 instead of allowing the air to expand as a free jet whose surface pressure would be the static pressure in chamber 24. This lower static pressure therefore results in reduction of the weight flow to the second-stage chamber 18 and thereby permits a reduction in the size 0f second-stage pump 20. Conversely, if it is desired to maintain the size of pump 20 equal to that utilized in the prior art, then a significant reduction in first-stage pump size can be realized with this embodiment of my invention because there is a rise in pressure across the shock wave 50 which accomplishes some pumping action, thereby reducing the pumping requirement of the first stage pump. By proper design of probe 22 and wall 44, it is possible to reduce the size of both first and second-stage pumps as compared'to the pumps employed in the prior art devices and yet obtain the same overall performance.
While a preferred embodiment has been shown and described, various modifications and substitutions may be made without deviating from the scope and spirit of my invention. Thus my invention is described by way of illustration rather than limitation and accordingly it is understood that my invention is to be limited only by the appended claims taken in view of the prior art.
I claim: 1'
1. Apparatus for working materials with a beam of charged particles comprising:
a first chamber having a beam exit aperture,
means positioned in said first chamber for generating a beam of charged particles,
means for evacuating said first chamber,
means supporting a workpiece outside of said evacuated first chamber in a gaseous atmosphere,
means positioned adjacent the aperture in said first chamber for permitting passage of the beam from said first chamber to the workpiece region without material attenuation, and
means positioned between the termination of said passage permitting means and said workpiece for inducing a flow deflection away from the beam axis of the stream of gas which tends to flow into the evacuated first chamber from the region of the workpiece. 2. The apparatus of claim 1 wherein the means for inducing a flow deflection comprises:
means establishing a jet of deflecting gas which impinges against and thus turns said gas stream. 3. The apparatus of claim 2 wherein the means establishing the deflecting jet comprises:
means including at least a second chamber positioned between the termination of the passage permitting means and the workpiece, means aligned with said passage permitting means for permitting the beam to enter said second chamber, means in the wall of said second chamber lying adjacent the workpiece for permitting the beam to pass out of the second chamber to impinge upon the workpiece, means for evacuating said second chamber, means providing communication between the atmosphere surrounding the workpiece and the interior of said evacuated second chamber for inducing a flow of deflecting gas in said second chamber at an angle to the beam axis. 4. The apparatus of claim 3 wherein the means for inducing a flow of deflecting gas comprises:
a passageway through a wall of said second chamber, said passageway having its discharge end located in the second chamber, said discharge end having its longitudinal axis in angular relation to the beam axis.
5. The apparatus of claim 4 wherein the means for permitting the beam to enter the second chamber comprises:
a hollow probe positioned so as to be coaxial with the beam axis and extending into the second chamber to a point adjacent the means for permitting the beam to pass out of the second chamber.
6. The apparatus of claim 1 wherein the means for inducing a flow deflection comprises:
means including at least a second chamber positioned between the termination of the passage permitting means and the workpiece,
means aligned with said passage permitting means for permitting the beam to enter said second chamber,
an opening in the wall of said second chamber lying adjacent the workpiece for permitting the beam to pass out of the second chamber and impinge upon the workpiece,
means for evacuating said second chamber, and
means extending from said opening in the downstream direction of the gas entering the second chamber from the workpiece region through said opening for causing expansion of the entering gas.
7. The apparatus of claim 6 wherein the means for causing expansion of the gas comprises:
a contoured wall extending from said opening into said second chamber, said wall being coaxial with the beam.
8. The apparatus of claim 7 wherein the means for permitting the beam to enter the second chamber comprises:
a hollow probe extending into said second chamber to a position where it is coaxial with the beam and contoured wall whereby said probe and contoured wall together form a nozzle.
Steigerwald Feb. 18, 1958 Schopper et al. Aug. 11, 1959