US3156811A

US3156811A - Gaseous sealing means in an apparatus for working materials by a beam of charged particles

Info

Publication number: US3156811A
Application number: US235214A
Authority: US
Inventors: Frank W Barry
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1962-11-05
Filing date: 1962-11-05
Publication date: 1964-11-10
Anticipated expiration: 1981-11-10
Also published as: NL299874A; DE1298850B; GB1069791A; BE638949A; CH433526A

Description

l ml 3;. 3 j btrmm nuuw Nov. 10, 1964 F. w. BARRY 3,156,811

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OF CHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet l IN VEN TOR.

ATTUQNEYS mm v Nov. 10, 1964 F. w. BARRY 3,156,811

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OF CHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 2 FIG. 2

Nov. 10, 1964 F w BARRY 3,156,811

GASEOUS SEALING MEAIiS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OF CHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 3 FIGB 210 l mu" 1/ 2oo 22s uz AMA Nov. 10, 1964 F. w. BARRY 3,156,311

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OF CHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 4 United States Patent 3,156,811 GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM 0F CHARGED PARTICLES Frank W. Barry, Manchester, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Nov. 5, 1962, Ser. No. 235,214 22. Claims. (Cl. 219121) This invention relates to the working of materials, for example, drilling, welding or surface treating, by means of a beam of charged particles or the like. In the apparatus to be described a precisely focused beam of electrons impinges upon the material to be worked and the energy thereof works the material.

Among the advantages of using an electron beam or the like are inertialess control and great energy concentration. The chief disadvantages include the tendency for an electron beam to scatter and attenuate upon contact with air or other material.

One obvious means for avoiding such attenuation and scattering is to enclose the electron beam generator and the material to be worked in a vacuum. This approach, however, entails obvious disadvantages. First, there is a serious work size limitation imposed by the dimensions of an evacuated work chamber. Secondly, rapid vaporization of the material being worked is encountered and the vaporized work material is deposited on the inside of the apparatus with a cloud of vaporized material causing some attenuation of the beam.

In order to avoid the last-mentioned difliculty, the work may be enclosed in an inert atmosphere to minimize vaporization of the material being worked. It will be apparent however, that any environmental gas will cause attenuation of the electron beam in proportion to the pressure of the gas. To minimize such attenuation, two devices have been utilized in the past.

First, the work chamber has been sealed oil. from the evacuated vessel which contains the electron beam. This approach necessitates the provision of a window in the path of the beam which window is nonporous to an environmental gas at roughly atmospheric pressure but which is transparent with respect to the electron beam. It has been found that a window material meeting the former requirement will so attenuate the beam as to require an economically prohibitive power input to operate the beam generator. Moreover, the window material itself will vaporize on contact with the beam at the power levels required to work materials.

A second device which has been utilized to minimize beam attenuation comprises a so-called dynamic pressure stage-stretch. A small diameter bore is provided interconnecting an evacuated beam chamber and a work chamber and the pressure stage stretch minimizes attenuation of the beam in passage through the bore. The stretch includes a system of pressure cascade chambers of increasmg gas pressures which are arranged in series in the direction of beam and also includes fine aligned apertures so that only a fraction of the total pressure difference will be effective to cause the work chamber gas to enter each successive chamber. The electron beam can be conducted through these apertures and thus, stage by stage, from that portion of the evacuated chamber containing the beam generator into chambers of progressively higher gas pressure and finally into the work chamber. This approach has been used in the art of electron microscopy but like the electron beam window approach, it causes excessive attenuation of the beam at the relatively high energy concentrations required for working materials. Further,

3,156,811 Patented Nov. 10, 1964 extensive pumping means are required to maintain the low pressures in the various pressure chambers.

The general object of the present invention is to prevent gas adjacent a workpiece from flowing into an evacuated beam vessel or chamber by means of a stream of sealing gas discharged adjacent the vessel or chamber opening.

Another object is to so direct a stream of sealing gas that a stream of relatively low total pressure can be used to prevent workpiece environmental gas from flowing into an evacuated beam vessel, thus minimizing leakage of the sealing gas into said vessel.

Another object is to achieve a pressure gradient across a stream of sealing gas by turning the same just prior to discharge from a supply passageway, thus further minimizing the leakage of sealing gas into the vessel.

Still another object is to achieve a more pronounced pressure gradient across a stream of sealing gas by the use of a convergent-divergent nozzle to achieve supersonic flow adjacent a vacuum vessel opening thus realizing a lower pressure in that region of the sealing gas stream and thus minimizing still further the leakage of sealing gas into the vessel.

Still another and a more specific object is to provide a gaseous seal across an evacuated vessel opening by directing a stream of sealing gas across a beam, the attenuation of the beam due to the sealing gas being minimized by the low total pressure of the gas and the short path of the beam in traversing the gas stream.

Still another specific object is to provide a gaseous seal around the periphery of a vessel opening by directing a stream of sealing gas generally radially outwardly with respect to the beam and adjacent a workpiece.

Still another specific object is to provide a mechanical seal around the periphery of a gaseously sealed vessel opening whereby to reduce still further the leakage of sealing gas into the vessel.

The drawings show four embodiments of the invention and such embodiments will be described, but it will be understood that various changes may be made from the constructions disclosed, and that the drawings and de scription are not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawings:

FIG. 1 is a schematic cross sectional view of one embodiment of my invention wherein a two dimensional rectangular passageway directs a supersonic stream of sealing gas into a beam chamber generally transversely with respect to the beam and which stream is shown recaptured in a supersonic diffuser.

FIG. 2 is a schematic cross sectional view of a second embodiment of my invention wherein an annular passageway directs the sealing gas int-o a beam chamber generally obliquely with respect to the beam, said sealing gas being ultimately discharged into the environmental gas surrounding the workpiece.

FIG. 3 is a schematic cross sectional view of a third embodiment of my invention wherein an annular passageway directs the supersonic stream of sealing gas generally radially outwardly with respect to the beam directly into the environmental gas.

FIG. 4 is a schematic cross sectional view of a fourth embodiment of my invention, similar to that depicted in FIG. 3 but also including a mechanical seal around the beam.

Gaseous Seal Across Beam, Closed Loop System, FIG. 1

Referring to FIG. 1, a beam generator 10 is shown emitting a beam along an axis 12, which beam is concentrated by a focusing means 14, 14 to be passed through a small vessel opening 16 into a beam chamber 18 and thence through a second opening 20, aligned with the vessel opening 16, to impinge on a workpiece 50 supported on a table or other work supporting or holding means 51. It should, of course, be understood that beam generator is shown schematically. For a complete disclosure of a state-of-the-art electron beam generator of the type being employed in commercially available welding and cutting machines and typical of those with which this invention is intended for use, reference is made to US. Patent No. 2,987,610, issued June 6, 1961, to K. H. Steigerwald. As explained above, it is an object of this invention to obviate the necessity of utilizing an evacuated work chamber, such as chamber 24 of FIG- URE 1 of the Steigerwald patent, when working materials with an intense beam of charged particles.

Although the focusing means shown comprises a magnetic lens, any suitable focusing means may be employed. For example, a series of electric lenses comprising an electrostatic focusing system is also within the scope of this invention.

That part of the beam generator 10 from which the beam emanates is contained in an evacuated vessel 22 connected by piping means 24 to a high vacuum pump 26. The pump 26 is capable of maintaining a pressure on the order of 10- Torr in the evacuated vessel 22.

Although the vessel opening 16 is shown in the evacuated vessel 22 said opening may be defined in the last chamber in a pressure stage stretch if both this invention and a stretch were to be combined in one apparatus.

Interposed between the workpiece 50 and the evacuated vessel 22, and attached to the latter in the schematic view of FIG. 1 is a housing means 30 comprising internally

opposed wall surfaces

32 and 34. The

surfaces

32 and 34 are arranged in inner to outer order with respect to the vessel opening 16 and at least partially define a gas supply passageway 33. An inlet end of the passageway 33 is connected by piping to a pressurized source of sealing gas 28 and the outlet end 17 thereof is connected to and communicates with the beam chamber 18.

Said housing means also comprises the internally

opposed wall surfaces

42 and 44 arranged in inner to outer order with respect to the vessel opening 16. The

surfaces

42 and 44 at least partially define a return passageway 43 for the sealing gas, the inlet end 19 of the return passageway outlet communicating with the opposite side of the beam chamber 18. The outlet end of the return passageway 43 may be connected to the source 28 by piping means 46 as illustrated.

As shown the housing 30 is subadjacent the evacuated vessel 22 but this arrangement is intended to be merely exemplary and the vessel 22 should be taken as representative of any chamber or series of chambers the outermost of which is in communication with the workpiece environment through an opening such as 16 and which is at some pressure less than that of the workpiece environmental gas.

The supply passageway 33 may take various forms but is shown as being generally rectangular whereby conveniently to illustrate two dimensionally the flow of sealing gas therein. As shown in FIG. 1 the supply passageway 33 turns the stream of sealing gas generally toward the vessel opening 16 by means of the generally concave outer wall surface 34. In turning the stream a pressure gradient is achieved thereacross, the lower pressure resulting in that part of the discharged stream adjacent the vessel opening 16.

In order to reduce still further the pressure of the Sealing gas in the area of the vessel opening 16 a nozzle is preferably employed to increase the velocity of the stream. As shown a supersonic nozzle means is utilized, the wall surfaces 32 and 34 cooperating to define convergent and divergent sections and a throat therebetween. The pressurized source of sealing gas 28 is effective to provide for supersonic flow at least in the divergent passageway section downstream of the throat 40 and across the beam chamber 18. As is also illustrated in FIG. 1 the discharged stream is oriented generally transversely with respect to the beam to provide a gaseous seal across the vessel opening 16 and thus to prevent leakage of environmental gas into the vessel.

Although the curved supersonic stream of gas permits very low pressures to be achieved in the flow adjacent the vessel opening 16 it is a necessary adjunct to such flow that compression and expansion waves will appear therein. These waves, or pressure disturbances, will be propagated across the stream and some of the beneficial effects of the high speed low pressure supersonic flow will be lost if any compression waves cross the stream upstream of the vessel opening 16. In this embodiment, the compression waves are formed only downstream of a junction 35 on the outer wall surface 34. The compression Waves necessarily formed on the generally concave turning surface 34 are postponed by means of an upstream part of said surface which is substantially straight and which is located between the throat 40 and the junction 35. Downstream of the junction, the surface 34 is arcuate so as to facilitate the formation of compression waves thereon, the initial such wave being formed at the junction 35. With the design Mach No. a known factor, the initial compression Wave will be propagated from the junction 35 and will form a known angle with the surface 34. Thus, the junction 35 can be and is located such that the initial compression wave passes downstream of the vessel opening 16. The initial such Wave is indicated generally in FIG. 1 by the broken line 37 originating at 35 and extending angularly downstream therefrom.

Successive compression waves will of course be formed on the arcuate part of the surface 34 downstream of the junction 35 as a resulting of the concave curvature of the part. These compression waves define areas of successively increasing pressure and thus tend to further accentuate the pressure gradient across the sealing gas discharged into the beam chamber 18.

As a result of the convex curvature of the inner surface 32 downstream of the throat 40 expansion waves will be formed thereon. The effect of such Waves on the pressure at the opposite side of the passageway is not as deleterious as would be the effect of compression waves crossing the passageway. Thus, the inner wall surface 32 is preferably convex from the throat 40 to the outlet 17 of the supply passageway 33 as shown in FIG. 1. At the downstream edge 38 of the inner wall surface 32, a plurality of expansion waves will be formed defining areas of successively decreasing pressure. The net effect of all of said expansion waves is to further accentuate the pressure gradient across the sealing gas in the beam chamber 18.

The inlet 19 of the return passageway 43 is preferably of slightly larger cross section than 'the outlet 17 of the supply passageway 33 and is preferably stepped inwardly with respect to said outlet 17 as shown in FIG. 1. In this manner use is made of the additional expansion at the edge 38 and the pressure of the sealing gas adjacent the vessel opening 16 is further reduced.

By appropriate choice of a sealing gas source pressure, the pressure at the second opening 20 can be made approximately equal to the pressure of the workpiece environmental gas thus minimizing mixing of said environmental and sealing gas. The supersonic stream of sealing gas will thus block any flow of environmental gas into the evacuated vessel while the pressure gradient across the said stream permits leakage of sealing gas into the evacuated vessel to be minimized and the capacity of the high vacuum pump 26 to be substantially reduced. As a result of the supersonic flow phenomenon produced by the expansion surface or diverging wall 32 and the substantially converging wall or compression surface of wall 34 downstream of junction point 35, the flow cross section along the beam axis 12 will be as follows: The expansion waves emanating from the surface 32 and particularly from adjacent the upstream lip 38 of opening 16 provide a continually decreasing pressure region in a downstream direction (right to left in FIGURE 1). Thus the beam initially penetrates the cross flow in an area which is at a pressure not substantially higher than that existing in the area 16, which, as stated above, is maintained at a relatively low pressure by a vacuum pump 26. For the foregoing reason and since, as is well known, a fluid flowing at supersonic velocity has difficulty following sharp expansion surfaces or corners such as that presented by the upstream lip 38 of opening 16, there will be little flow upwardly into region 16. The foregoing phenomenon is explained in US. Patent No. 2,811,828, issued to G. H. McLafferty on November 5, 1957. Progressing downwardly along the beam axis 12 from lip 38 to the region of opening 20, the pressure will on the average progressively increase. A relatively high pressure in the region of opening results from the continued increase of pressure in the cross-flow stream resulting from the shock waves formed on and moving from left or right from junction point on wall 34 across the opening 20 and along wall 44. The relatively high pressure in the region of opening 20 caused by these shock waves will prevent gas from without the casing from flowing upwardly through opening 20.

The above-described pressure gradient along the beam axis from lip 38 to opening 20 caused by the expansion and compression waves in the supersonic flow creates, in the manner explained, a relatively high pressure in the region of opening 20. Due to this high pressure, some of the gas being pumped through the cross-flow orifice system will be forced downwardly through opening 20. The amount of gas Which will bleed out through opening 20 is, of course, determined by the pressure in the crossflow orifice which pressure, as is well known in the art, is a function of the pressure of the source 28. Rather than detrimental, this inherent loss of gas out through opening 20 provides an extremely beneficial self-cleaning effect for the opening. That is, in the prior art, attempts at bringing a working beam out of an evacuated container have been plagued with difiiculties caused by splatter from the workpiece rapidly causing clogging of the beam exit hole. With this invention, the bleed or selfcleaning gas flow through opening 20 tends to force debris rising from the beam impingement point on workpiece away from opening 20. This bleed flow also precipitates an added advantage of preventing contamination of the work since, if an inert gas is used in the system, the surface of the workpiece will be blanketed, as is done in tungsten inert gas welding, with such gas.

The return passageway 43 preferably comprises a supersonic diffuser means adapted to reduce the speed of the sealing gas and to thus reduce the pressure losses in conveying the gas back to the pressure source 28 through the piping means 46. This minimizes the task of the pumping means 28 and permits the use of a comparatively small pump or other pressurizing means. As shown in FIG. 1 the diffuser is formed by the opposing wall surfaces 42 and 44 of said housing 30 and preferably has an upstream convergent section and a downstream divergent section defining a throat 45 therebetween. The inlet 19 of the return passageway 43 comprises the inlet of the convergent section and an inner edge 39 of said inlet 19 is stepped inwardly as mentioned. By a series of oblique compression Waves in the convergent section the speed of the stream of sealing gas is reduced with a minimum loss in stagnation pressure thus permitting a relatively small pumping means as stated.

While the embodiment of FIGURE 1 has been described as a closed loop system, as will be obvious from the explanation of the embodiments of FIGURES 2 through 4 below, the sealing gas flowing in the cross-flow system may be dumped into the atmosphere downstream of the beam axis. That is, it may in some cases be desirable to eliminate the supersonic diffuser and dump the sealing gas into the atmosphere at some point downstream of the trailing edge of opening 20. The foregoing might be done, for example, when an inexpensive gas is utilized.

Gaseous Seal Across Beam, Open Loop System, FIG. 2

Referring to FIG. 2, a beam generator is shown emitting a beam of charged particles or the like along an axis 112. That part of the beam generator from which the beam emanates is contained in an evacuated vessel 122, which vessel is connected by means of a pipe 124 to a high vacuum pump 126 capable of maintaining a pressure on the order of 10- Torr in said vessel 122. The beam is concentrated by a focusing means 114 to be passed through a small vessel opening 116 and thence through a beam chamber 118 and through a second opening 120 to impinge on a workpiece 150. The beam chamber 118 is defined by a housing means attached to the vessels exterior and adjacent said vessel opening 116, said chamber being in communication with the vessel opening at its inner end and with the second opening 120 at its outer end.

The housing means 130 may be attached to the exterior of vessel 122 as shown and is disposed between the vessel opening 116 and the workpiece 150. Opposing wall surfaces 132 and 134 arranged in inner to outer order with respect to the vessel opening 116 at least partially define a passageway 133. The said passageway is represented in FIG. 2 as being annular in cross sectional shape but may take various other forms so long as the outlet thereof is peripherally arranged around at least a portion of the beam chamber 118.

One end of the annular passageway 133 is connected by means of an annular plenum 113 and a pipe 115 to a pressurized source of sealing gas 128, and the other end, defining an annular outlet 117, is connected to and communicates peripherally with the cylindrical beam chamber 118.

Still referring to FIG. 2, it will be seen that the passageway 133 turns a stream of sealing gas generally towards the vessel opening 116 by means of a generally concave downstream portion of the outer wall surface 134. In turning the stream a pressure gradient is achieved thereacross as previously mentioned, the lower pressure occurring in that part of the discharged stream adjacent the vessel opening 116.

In order to further reduce the pressure of said sealing gas in the area of the vessel opening 116 a supersonic nozzle is preferably employed to increase the velocity of the stream. As shown, the annular wall surfaces 132 and 134 cooperate to define convergent and divergent sec tions in the direction of flow and an annular throat therebetween. When such a nozzle is utilized the source of sealing gas 128 is at a pressure high enough to achieve supersonic flow at least in the divergent passageway section and in the beam chamber.

In this embodiment the discharged stream of sealing gas is directed generally obliquely with respect to the beam axis so as to have a component generally transverse with respect to the beam and a component directed outwardly through the second opening 120. Unlike the first mentioned embodiment of the invention in which the sealing gas is recaptured on the opposite side of the beam chamber, this embodiment requires a continuous source of sealing gas, this stream of said gas being ultimately discharged from the beam chamber through the second opening and into the workpiece environment gas as shown. The pressure rise due to obstruction of the flow of sealing gas by the environmental gas is utilized to prevent leakage of the environmental gas into the evacuated vessel.

Although the curved supersonic stream of sealing gas permits very low pressures to be achieved in the flow adjacent the vessel opening 116, it is a necessary adjunct to such a stream that compression and expansion waves will appear therein. As previously mentioned, these waves or pressure disturbances will be propagated across the stream and some of the beneficial effects of the high speed low pressure supersonic flow will be lost if any of the compression waves cross the stream upstream of the vessel opening 116. Therefore, in this embodiment as in the first mentioned embodiment of the invention, the compression waves are preferably formed only at and downstream of a junction 135 on the outer wall surface 134. The compression waves necessarily formed on the generally concave wall surface 134 are delayed by means of an upstream substantially straight part of said wall surface between the throat 140 and the junction 135. Downstream of said junction the wall surface 134 is arcuate so as to facilitate the formation of compression waves thereon. With the design Mach No. known, the initial compression wave will leave the surface 134 at a known angle therewith and the junction 135 is so located that said initial compression wave passes downstream of the vessel opening 116. Such a wave is indicated generally in FIG. 2 by the broken line 137 originating at the junction 135.

Successive compression waves formed on the arcuate part of the wall surface 134 define areas of successively increasing pressure and thus tend to further accentuate the pressure gradient across the sealing gas discharged into the beam chamber 118. As is well known such a succession of oblique compression waves is to be preferred over a single normal shock at the opening 120 because of the low pressure recovery characteristic of the latter.

Further in accord with the presently preferred practice, the inner wall surface 132 in the divergent section of the passageway 133 is of convex curvature so that expansion waves will be formed thereon. As in the FIG. 1 embodiment, the said inner wall surface is preferably convex from the throat 140 to the outlet 117 as shown. At the downstream edge 138 of said surface 132 a plurality of expansion waves will necessarily be formed each of which defines an area of successively decreasing pressure. The net effect of all of said expansion waves is to further accentuate the pressure gradient across the sealing gas discharged into the beam chamber 118.

Gaseous Seal Around Beam, Open Loop System, FIG. 3

Referring now to FIG. 3, a beam generator 210 is shown emitting a beam of charged particles or the like along an axis 212. The part of the beam generator from which the beam emanates is contained in an evacuated vessel 222, which vessel is connected by means of a pipe 224 to a high vacuum pump 226 capable of maintaining a pressure on the order of Torr in said vessel 222. The beam is concentrated by a focusing means 214 to be passed through a small vessel opening 216 to impinge on a workpiece 250 which workpiece is held in closely spaced relationship to said vessel opening by a table 251 or the like.

Attached to the vessel 222 an forming a part thereof which defines the vessel opening 216 is an inner annular housing member 218. Said member has a cylindrical bore forming the opening 216 and includes an inner wall surface 232. An outer annular housing member 220 defines an outer wall surface 234 of a gas supply passageway 233.

One end of the annular passageway 233 is connected to a pressurized source of sealing gas 228 by the piping 215 and the other end, comprising an outlet 217, is defined by a downstream edge 236 of the outer wall surface 234 and a downstream edge 238 of the inner surface 232. Said outlet 217 is adapted to discharge sealing gas around the periphery of the beam and radially outwardly with respect thereto adjacent a workpiece 250.

Unlike the first and second mentioned embodiments in which the discharged gas is directed into the path of the beam, this embodiment operates not unlike an ejector in that the discharged gas creates a low pressure about the periphery of the opening 216 and in the space between said opening and the workpiece without crossing the beam itself. This embodiment, like that of FIG. 2,

requires a continuous source of sealing gas, there being no provision for recovering the gas as in the first mentioned embodiment of FIG. 1.

Referring more specifically to the passageway 233, the outer wall surface 234 is preferably concave at a downstream portion to turn the stream of sealing gas generally towards the vessel opening 216 and to thereby achieve a pressure gradient across the discharged stream at the outlet 217. In turning the stream towards the vessel opening the lower presure results in that part of the stream closest to the vessel opening 216, the space between said vessel opening and the workpiece 250 providing a means for communication between said stream and opening.

In order to further reduce the pressure of the sealing gas in the area of flow which is in communication with the vessel opening, a nozzle is preferably employed to increase the velocity of the stream. The presently preferred practice is to use a supersonic nozzle means, the wall surfaces 232 and 234 cooperating to define convergent and divergent sections and a throat 240 therebetween. The source of sealing gas 228 is at a high enough prsesure to achieve supersonic flow downstream of the throat 240 in the divergent passageway section and downstream of the outlet 217 into the space between the workpiece 250 and the lower end portion of the outer annular member 220, both of which elements cooperate to form a continuation of the passageway 233. This space or passageway continuation is not unlike the beam chamber 218 in the previous embodiment, FIG. 2, the stream of discharged gas being oriented generally obliquely as it enters said space and then discharged outwardly into the environmental gas as it leaves the space. Thus, the device is similar to the previous embodiment in that a pressure rise is achieved in obstruction of the flow of sealing gas by the workpiece environmental gas. Unlike the previous device, however, this embodiment does not require the stream to cross the beam and so avoids all beam attenuation due to the sealing gas stream.

Although the curved supersonic stream of sealing gas permits very low pressures to be achieved in the area of flow which is in communication with the vessel opening, it is a necessary adjunct to such a stream that compression and expansion waves will appear therein. These waves, or pressure disturbances, are propagated across the stream and some of the beneficial effects of the high speed low pressure supersonic flow will be lost if any compression waves cross the stream upstream of that part of the flow which is in communication with the vessel opening 216. Therefore, in the present embodiment, as in the previously mentioned devices, the compression waves are preferably formed only downstream of a junction 235 on the outer wall surface 234. The compression waves necessarily formed on the generally concave surface 234 are delayed by means of an up stream part of the wall surface which is substantially straight and which extends between the throat 240* and the junction 235. Downstream of said junction the outer Wall surface 234 is arcuate os as to facilitate the formation of compression waves thereon. With the design Mach. No. known, the initial compression wave leaves the wall surface 234 at a known angle therewith and the junction 235 is so located that said wave passes downstream of the area of said sealing gas stream which is in communication with the vessel opening 216. The broken line 237 originating at 235 and extending across the stream to the workpiece 250 represents such an initial wave.

Successive compression waves formed on said arcuate part of the wall surface 234 define areas of successively increasing pressure as mentioned and thus tend to further accentuate the pressure gradient across the sealing gas discharged into the space between the workpiece 250 and the member 220.

Further in accord with the presently preferred practice, the inner wall surface 232 in the divergent section of the passageway 233 is of convex curvature so that expansion waves will be formed thereon. At the downstream edge 238 of said surface a plurality of expansion waves will necessarily be formed each of which defines an area of successively decreasing pressure. The net efiect of this wave pattern will further accentuate the pressure gradient across the sealing gas discharged into the space between the workpiece and the annular housing member 220.

Gaseous Seal and Mechanical Seal Around Beam, FIG. 4

FIG. 4 shows an apparatus for working materials by means of a beam of charged particles or the like similar in most respects to that illustrated in FIG. 3, a gaseous seal being provided around the beam. In addition to the gaseous seal, however, a mechanical seal 252 is also provided around the beam and is disposed between the gaseous seal and the beam.

According to presently preferred practice the mechanical seal is of resilient material and takes an annular shape with a center hole 254 of slightly larger size than the vessel opening 216. An outer circumference 256 of the seal is of roughly the same diameter as the circular edge 238a of the inner wall surface 232a. The said seal 252 is or may be fixedly attached, adjacent its center hole, to the lower end portion of the inner annular member 218a. The outer circumference 256 of the seal rests on the upper face of the workpiece 250 and being resilient is well adapted to conform to any uneveness in the face of the workpiece. The seal is held in contact with the workpiece at least partly by reason of the difference in pressure across said seal, the static pressure of the sealing gas stream past the seal necessarily exceeding the very low pressure in the evacuated vessel 222.

As will be noted, parts generally similar to corresponding parts of the embodiment of FIG. 3 have here been given like reference numerals and such parts will not be described in detail. Of the corresponding parts only the inner and outer

annular members

218a and 220a differ in any material respect. The inner member 218a is not directly attached to the vessel 222, and the outer member 220a is slidably received by said vessel as shown.

It is characteristic of a flexible mechanical seal such as 252 that optimum sealing can only be achieved within a narrow range of angular positioning of the seal with respect to the workpiece face. This characteristic has the effect of making the distance between the face of the workpiece and the lower end portion of the annular member 218a a critical dimension. Not only must the workpiece 250 be in closely spaced relationship with the

housing members

218a and 220a, but the said workpiece must not be so close thereto as to impair the etiiciency of the seal.

Accordingly, biasing means are provided which hold the inner and

outer members

218a and 220a in a relatively fixed relationship to the workpiece 250. As shown the biasing means comprise a spring 258 acting between the exterior of the vessel 222 and an upper end portion 221a of the outer member 220a, which member is fixedly attached to the inner member 218a. In operation, the use of the spring 258 makes the positioning of the workpiece 250 with respect to the beam generating apparatus 200 less critical. The operator merely sets the workpiece close to the apparatus and the spring 258 will position the outer and

inner members

220a and 218a in the optimum position for efficiently sealing the opening 216 from both the environmental gas and the sealing gas.

Further in the present embodiment, a second mechanical seal 260 is required because of the movable connection between the vessel 222 and the outer annular member 220a. The inner annular member 218a, in conjunction with the vessel 222, defines the beam opening 216, which opening is at very low pressure and therefore requires sealing at any connection where inward gas leakage is likely to occur. The slidable connection between the vessel 222 and the member 220a is therefore fitted with a bellows type seal 260 as shown in FIG. 4.

Finally, the relative motion between the apparatus 200 to which the source is attached and the

annular housing members

218a and 220a requires a flexible hose or the like 262 connecting the source'of sealing gas 228 to the piping 215a and the passageway 233a.

The invention claimed is:

1. Apparatus for working materials by means of a beam of charged particles comprising:

means for generating a beam of charged particles;

a vessel containing at least a portion of said beam generating means, said vessel defining an opening for transmission of said beam;

means for creating and maintaining a first relatively low pressure in said vessel;

means for directing the beam out of said vessel through said opening so that the beam will impinge on a material to be worked located outside of said vessel in a region where the environmental gas is at a second pressure greater than the said first pressure;

a source of gas under pressure; and

means connected to said pressurized source of gas for generating a supersonic stream of gas and establishing a pressure gradient between said vessel opening and the environmental gas in the region of the material to be worked, said means thereby effecting passage of said beam from said vessel opening without material attenuation thereof.

2. The apparatus of claim 1 wherein the means for establishing a pressure g adient comprises:

means defining a gas supply conduit having a throat therein for acceleration of gas flowing therethrough to supersonic velocity, said conduit being connected at one end to said pressurized source of gas and having an outlet portion arranged to discharge a supersonic stream of gas adjacent said vessel opening.

3. The apparatus of claim 2 wherein the gas supply conduit defining means comprises:

housing means defining a first opening adjacent said vessel opening and a second opening spaced outwardly from said vessel opening and aligned there- With for passage of the beam therethrough, said housing means serving also to define a beam chamber between said first and said second openings and gas supply and exit passageways communicating respectively at their outlet and inlet ends with said beam chamber.

4. The apparatus of claim 3 wherein the outlet and inlet ends of said supply and exit passageways are respectively disposed in opposing relationship for the generally transverse flow of gas across said beam chamber.

5. The apparatus of claim 4 wherein said gas supply passageway comprises:

opposed inner and outer wall surfaces arranged in that order with respect to said vessel opening, said supply passageway extending upstream from said beam chamber in generally angular relationship with respect to the axis of a beam passing through said aligned openings, said inner and outer wall surfaces further serving to define said throat therebetween.

6. The apparatus of claim 5 wherein:

the outer wall surface of said passageway downstream of said throat comprises:

a generally concave portion adjacent the outlet end of said supply passageway for turning the gas entering said beam chamber from said supply passageway towards said exit passageway thereby generating compression waves in said supersonlc stream of gas; and i said inner wall surface of said supply passageway downstream of said throat comprises:

a generally convex portion adjacent the outlet end of said supply passageway to provide for the formation of expansion waves in the gas leaving said supply passageway, said expansion and compression waves establishing a pressure gradient across the stream of gas in the beam chamber, the lower pressure being adjacent said first opening.

7. The apparatus of claim 6 wherein the generally concave portion of said outer wall surface comprises:

a substantially straight wall segment adjacent said throat; and

an arcuate wall segment downstream of said straight part, oblique compression waves being formed in said gas at and downstream of the junction of said straight and arcuate segments, said junction being so located that the initial compression wave extends beyond the outlet end of said gas supply passageway and across the beam chamber downstream of said first opening.

8. The apparatus of claim 7 wherein said inner wall surface downstream of said throat further comprises:

a downstream edge adjacent said first opening which presents a sharp expansion angle to said supersonic stream of gas thereby further expanding the gas adjacent said vessel opening.

9. The apparatus of claim 8 wherein said exit passageway comprises:

inner and outer opposing wall surfaces defining a convergent-divergent passageway section in the direction of flow, said section serving to reduce pressure losses in the passageway gas.

10. The apparatus of claim 2 wherein the gas supply conduit defining means comprises:

housing means defining a first opening adjacent said vessel opening and a second opening spaced outwardly from said vessel opening and aligned therewith for passage of the beam therethrough, said housing means serving also to define a beam chamber between said first and second openings and a gas supply passageway communicating with said beam chamber, said passageway being arranged to extend upstream from said beam chamber in a direction generally oblique with respect to the axis of a beam passing through said aligned openings.

11. The apparatus of claim 10 wherein said gas supply passageway comprises:

opposed inner and outer wall surfaces defining a passageway which is annular in cross section and has its outlet end disposed about said beam chamber to communicate peripherally therewith, said inner and outer wall surfaces further serving to define said throat therebetween.

12. The apparatus of claim 11 wherein:

the outer wall surface of said passageway comprises:

a generally concave wall surface downstream of said throat for turning gas entering said beam chamber from said supply passageway thereby generating compression waves in said supersonic stream of gas; and

said inner wall surface of said supply conduit downstream of said throat comprises:

a generally convex portion to provide for the formation of expansion waves in the gas leaving said supply passageway, said expansion and and compression waves establishing a pressure gradient across the stream of gas in the beam chamber, the lower pressure being adjacent said first opening.

13. The apparatus of claim 12 wherein said generally concave portion of said outer wall surface comprises:

a straight part and an arcuate part downstream of said straight part, the junction of said straight and arcuate parts being so located that oblique compression waves are formed commencing at said junction with the 12 initial such wave extending across said beam chamber downstream of said vessel opening.

14. The apparatus of claim 13 wherein said convex inner wall surface further comprises:

a downstream edge adjacent said vessel opening which edge presents an abrupt convex turning angle to the gas leaving said passageway whereby to further expand the flow past said vessel opening and to thereby reduce the pressure of the gas and minimize leakage of the same into the vessel.

15. The apparatus of claim 2 wherein the gas supply conduit defining means comprises:

housing means defining a gas supply passageway connected with said pressurized source of gas and having an outlet portion arranged to establish a flow of gas which circumscribes a beam of charged particles passing through said vessel opening, said gas flow extending outwardly to the surface of the material to be worked thereby inhibiting flow of environmental gas to the region between said vessel opening and the area to be worked.

16. The apparatus of claim 15 further comprising:

a mechanical seal afiixed to housing means at a point between said vessel opening and the outlet end of said supply passageway and extending from said housing means to the surface of a material to be worked with the beam whereby said seal serves to isolate said vessel opening from said sealing gas thereby further minimizing leakage of said gas into said vessel.

17. The apparatus of claim 16 wherein said seal comprises a flexible annular member, wherein said housing means is adapted for movement toward and away from the material to be worked, and wherein a biasing means is provided for urging said housing means toward the material to be worked thereby maintaining the seal in effective sealing engagement between the housing means and the material being worked.

18. The apparatus of claim 15 wherein said gas supply passageway comprises:

opposed inner and outer wall surfaces defining a passageway arranged to discharge gas radially outwardly with respect to the axis of the beam, said inner and outer wall surfaces further serving to define said throat therebetween.

19. The apparatus of claim 18 wherein said gas supply passageway is annular in cross section and discharges a stream of gas peripherally around said vessel opening.

20. The apparatus of claim 19 wherein said gas supply passageway downstream of said throat comprises:

a pair of oppositely disposed wall surfaces being arranged in inner and outer order with respect to said vessel opening and being generally convex and concave respectively for the formation of expansion and compression waves in the gas discharge from said passageway.

21. Apparatus for transmitting a beam of electrons from a low pressure to a gaseous environment without material attenuation thereof comprising:

means for generating a beam of charged particles;

means for creating and maintaining a pressure less than atmospheric in said vessel;

means for directing the beam out of said vessel through said opening whereby the beam may impinge upon a material to be worked located outside of said vessel in a gaseous atmosphere where the pressure is greater than that maintained in said vessel;

21 source of gas under pressure;

housing means abutting said vessel and defining a first opening adjacent said vessel opening and a second opening spaced outwardly from said vessel opening and aligned therewith for passage of the beam there- 13 through, said housing means serving also to define a beam chamber between said first and second openings and a gas supply orifice in the wall of said chamber; and

means defining a gas supply passageway having its inlet end connected to said pressurized source of gas and having its outlet end connected to said supply orifice, said passageway having a throat therein for acceleration of gas flowing therethrough from said source to supersonic velocity, said passageway further being contoured downstream of said throat so as to impart a change in direction to the supersonic stream of gas and thereby generate compression and expansion Waves and establish a pressure gradient across the gas in the beam chamber, the lower pressure being adjacent said first opening.

22. Apparatus for Working materials by means of a beam of charged particles comprising:

means for generating a beam of charged particles;

means for directing the beam out of said vessel through said opening whereby the beam may impinge on the material to be worked located outside of said vessel in a gaseous atmosphere where the pressure is greater than that maintained in said vessel;

a source of gas under pressure;

means defining a gas supply passageway having a throat therein for acceleration of gas flowing therethrough to supersonic velocity, said passageway having its inlet end connected to said pressurized source of gas and having its outlet end arranged to discharge said supersonic passageway gas adjacent said vessel opening in such a manner that it circumscribes a beam passing through said vessel opening and impinging upon the material to be worked, said gas flowing outwardly to the surface of the material to be worked and having a pressure gradient thereacross whereby a low pressure region circumscribed by said gas is created between said vessel opening and the desired point of beam impingement on the material to be Worked.

References Cited by the Examiner UNITED STATES PATENTS 2,554,236 5/51 Bernard 219- 2,587,331 2/52 Jordan 21975 2,590,084 3/52 Bernard 21972 2,686,860 8/54 Buck et al 21975 2,769,079 10/56 Briggs 219-75 2,771,568 11/56 Steigerwald.

2,806,124 9/57 Gage 21975X 2,824,232 2/58 Steigerwald.

2,899,556 8/59 Schopper et a1.

2,907,704 10/59 Trump.

2,922,869 1/60 Giannini et al.

RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, Examiner.

Claims

1. APPARATUS FOR WORKING MATERIALS BY MEANS OF A BEAM OF CHARGED PARTICLES COMPRISING: MEANS FOR GENERATING A BEAM OF CHARGED PARTICLES; A VESSEL CONTAINING AT LEAST A PORTION OF SAID BEAM GENERATING MEANS, SAID VESSEL DEFINING AN OPENING FOR TRANSMISSION OF SAID BEAM; MEANS FOR CREATING AND MAINTAINING A FIRST RELATIVELY LOW PRESSURE IN SAID VESSEL; MEANS FOR DIRECTING THE BEAM OUT OF SAID VESSEL THROUGH SAID OPENING SO THAT THE BEAM WILL IMPINGE ON A MATERIAL TO BE WORKED LOCATED OUTSIDE OF SAID VESSEL IN A REGION WHERE THE ENVIRONMENTAL GAS IS AT A SECOND PRESSURE GREATER THAN THE SAID FIRST PRESSURE; A SOURCE OF GAS UNDER PRESSURE; AND MEANS CONNECTED TO SAID PRESSURIZED SOURCE OF GAS FOR GENERATING A SUPERONIC STREAM OF GAS AND ESTABLISHING A PRESSURE GRADIENT BETWEEN SAID VESSEL OPENING AND THE ENVIRONMENTAL GAS IN THE REGION OF THE MATERIAL TO BE WORKED, SAID MEANS THEREBY EFFECTING PASSAGE OF SAID BEAM FROM SAID VESSEL OPENING WITHOUT MATERIAL ATTENUATION THEREOF.