Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to processing a workpiece with a beam of
charged particles. More particularly, the invention relates to performing
operations such as welding, cutting, melting, vaporizing, heating, machining
or other processing steps with a beam of charged particles, as an electron
beam, produced by a machine having a vacuum chamber (sometimes called "beam
column") which, during operation, is evacuated and moved relative to the ma-
terial or workpiece processed.
The invention relates to the problem of sealing the vacuum chamber
which is movable in respect to the workpiece. It is known from United States
patent 3,136,882, to seal the beam exit opening of the vacuum chamber of an
electron beam welding machine relative to a workpiece by a compressible rub-
ber sealing ring pressed against and sliding on the workpiece surface. A
gap between two workpiece parts to be Joined by welding and the weld seam
produced by the machine is covered by an adhesive tape. A channel-shaped
metal member is attached with adhesive tapes to the rear side of the work-
piece to seal the gap at the beam exit side of the workpiece.
A further known technique for sealing a movable vacuum chamber
relative to a workpiece is to use a pressure stage seal, i.e. to use a num-
ber of concentric zones of gradually increasing vacuum from the atmosphere
to the inner vacuum chamber in which the beam gun is located.
It is further known from British patent 1,292,338j German patent
18 05 719, French patent 69 36 856 to form a flexible seal for a vacuum
chamber of electron beam (E.B.) welding machines by means of a suspension of
magnetizable particles in carrier fluid such as silicon oil. The suspension
is brought in a quasi-elastic state by means of a periodically varied uni-
directional magnetic field.
A problem, which is common to all known sealing systems of this
type is to provide proper sealing at the region of the seal, where the work-
piece zone to be processed by the beam enters the vacuum chamber and/or at
the region of the seal where the zone of the workpiece which has been pro-
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cessed by the beam, leaves the vacuum chamber. The term "processing zone"
is used in the following for both the zone of the workpiece to be processed
by the beam and the zone of the workpiece which has been processed by the
beam, since both the zone to be processed and the zone already processed may
create sealing problems. The zone to be processed often includes a gap or
other structural features through which air can enter the vacuum chamber,
and the processed zone, e.g. a welding bead, is generally rough and hot and
may protrude over the adjacent portions of the workpiece surface.
Thus, the main problem dealt with by this invention is the sealing
of a vacuum chamber which houses a beam gun or generator and is relatively
movable with respect to a workpiece, specifically to provide an appropriate
sealing in respect to the processing zone of the workpiece.
A further object of the invention is to provide a sealing system
which affords proper sealing between a vacuum chamber in respect to a rough,
hot, uneven or other surface difficult to seal by means of the known sealing
systems.
According to the present invention, there is provided a sealing
system for a vacuum chamber of a machine arranged to mount on a workpiece
for processing said workpiece with a beam of charged particles produced by a
beam gun mounted within said vacuum chamber, said vacuum chamber being arrang-
ed to mount to said workpiece in a manner to allow relative movement with
respect to the workpiece and having a beam exit opening surrounded by a cir-
cumferential seal formed by an annular end portion of said vacuum chamber and
arranged to cooperate with an opposed surface of said workpiece, said seal
and said chamber moveable along said workpiece surface, said seal having a
radial sealing width between said beam exit opening and the surrounding
environment, for sealing said beam exit opening against said surface such that
said relative movement of said chamber with said seal with respect to said
workpiece can take place while securing a path of high flow resistance across
said seal from said surrounding environment to said vacuum chamber, said
workpiece being processed while moving relative to said vacuum chamber, where-
in said seal includes an entrance section through which a portion of saidworkpiece to be processed enters said chamber radially with respect to said
seal for processing by said beam and an ex:it section through which a process-
ed workpiece portion, which has a hot and relatively uneven surface compared
to the unprocessed portion of said workpiece, leaves said chamber radially
with respect to said seal characterized in that for improving the flow
resistance of said seal, said seal has a greater radial width in the region
of at least one of said entrance or exit sections of said seal than at other
circumferential points.
Thus, the edge of said vacuum chamber or the wall dividing two
pressure stages in the direction of a relative movement with respect to work-
piece may be extended, so that the restricted flow passage for the air is
made longer, which always exits to a greater or lesser extent across the
seal.
A further important aspect of the invention is to provide a special
-~ sealing section with a box-shaped casing which forms in fact some sort
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of extension of the ~c~ng-z~n~ and which comprises some kind of package or
other means which is able to conform to an uneven surface of the workpiece
and to provide the necessary sealing.
C The casing may comprise a brush-like bundle of metal wires, e.g.
brass wires, which are pressed with their one end against the workpiece sur-
face by a spring or similar device while on each side of the brushlike pack-
; ing of wires preferably two pads of a deformable or pliable material are
provided, e.g. a fabric of felt or fleece of mineral fibers, as asbestos or
glass or ceramic fibers.
Another approach is to fit one or a number of subsequent rollers
rotably mounted in the casing. The axial ends of each roller abut tightly
against the sidewalls of the casing, its lower portion bears in a sealing
relationship on the surface of the workpiece, and the periphery of the rol-
ler, e.g. on the opposite side of the workpiece, slides tightly and sealing-
ly on the casing or some other sealing element.
A chainlike or tracklike device (i.e. a track used in a heavy
tractor) may be used instead of the rollers ~ust mentioned.
Still another approach would be a bed of particular or granular or
powder material instead of the brass wire packing, said bed being replen-
ished at the inner end and, if desirable, taken off at the outer end and if
desired, recycled. The bed may consist of steel granules or sand.
A thermoplastic material may be used to smooth the surface and to
alleviate the sealing.
Another approach is to apply a material which forms a continuous,
elastic or pliable body, or can be brought in the form of such a body upon
application, to the processing zone before it passes through the sealing
zone, so that it conforms to the rough surface or surface features and forms
an intermediate layer having a relatively smooth surface which can be easily
sealed by a conventional sealing system, as a lip seal. This material forms
- 30 in fact also an extended sealing zone. The material is pressed firmly
against the rough or uneven or slotted surface to be sealed and conforms to
the surface features because of its pliability, softness or elasticity. It
conforms smoothly and tightly to the sliding or rolling seal of the mobile
vacuum chamber. The intermediate material can be taken off from the work-
piece surface at an area, where it has been released by the sealing system,
i.e. where the sealing zone has slid or rollen over the material.
In a specific embodiment, the material is then collected and re-
cycled through a vacuum lock to that side of the moving seal, at which the
material is applied. ~he vacuum lock may be a simple hole in a wall of the
vacuum chamber which is sealed by the material pressed through.
The material may be e.g. a band, strip or cord of very soft rubber
;~ with a central or inner textile band for reinforcement. Alternatively, the
material may be applied in the state of a powder, liquid or dough to the
surface to be sealed and then by change of temperature transformed to a con-
tinuous, solid and elastic state so that it can be easily removed (stripped)
from the workpiece behind the sealing zone. The material may comprise a
high proportion of a material of high atomic number, as lead, to provide for -
the necessary X-ray sealing. This is a desirable but not necessary feature,
and other materials can be used, e.g. a band or cord of asbestos fibers, if
the X-ray sealing is provided by other means.
The problem of preventing X-rays from escaping from the inner of
the vacuum chamber through the sealing zone to the outside should be taken
care of in any sealing system used with a charge to particle beam machine.
A further important embodiment of the invention comprises a com-
- bination of a pressure stage seal with a lip seal arrangement, e.g. a system
wherein the edge of one or each pressure stage of a pressure stage seal is
provided with a flexible lip seal member to enhance the sealing and to re-
duce the leakage.
Further objects, features and advantages of the invention will be-
come apparent when reading the following description of specific, non-limit-
~ 5
ing embodiments.
In the drawings:
Figure 1 a highly schematic part-sectional elevation of a portion
of an electron beam welding machine and a workpiece being welded;
Figure 2 is a schematic plan view of the sealing system of the
machine of Figure 1;
Figure 3A is a bottom view of a pressure stage sealing system ac-
cording to an embodiment of the invention;
Figure 3B is a sectional view along a line B-B in Figure 3A;
Figure 3C is a sectional view along a line C-C in Figure 3A;
Figure 4 is a perspectivic view of a portion of a sealing system
according to an embodiment of the invention;
Figure 5 is a cross-sectional view in a plane V-V of Figure 4;
Figure 6 is a sectional view of a preferred embodiment of a portion
of a pressure stage sealing system;
Figure 7 is a sectional view of another embodiment of a pressure
stage sealing system with additional elastic lip sealing elements;
Figure 8 is a sectional view of a sealing system for the beam exit
side of a workpiece welded by an electron beam;
Figure 9 is a schematic view, partially in section, of a proces-
sing zone entrance section of a sealing system according to a further embod-
iment of the invention;
: Figure 10 is a sectional view in a plane X-X of Figure 9;
Figure 11 is a simplified sectional view of the processing zone
exit section of a sealing system of the type shown in Figures 9 and 10;
Figure 12 is a sectional view of a modification of the sealing
system shown in Figures 4 and 5;
Figure 13 is a view of part of another modification of the sealing
system shown in Figures 4 and 5; and
Figure 14 is a front end view of the sealing systems of Figure 12
~L~ r!'S
and 13.
Figure 1 shows in a highly schematic manner an electron beam
(E.B.) welding machine 10 having a vacuum chamber 12 which is movable rela-
tive to a workpiece 14. The vacuum chamber 12 has a beam exit opening 16
(Figure 2) which is sealed against a surface 18 of the workpiece in a manner
to allow relative movement between the E.B. welding machine and the work-
piece. The workpiece shown consists of two plates 20, 22 which form a gap
24 ("processing zone") where the plates 20, 22 are to be joined by an elec-
tron beam 25 produced by a beam gun (not shown) located in a column section
26 of the vacuum chamber. The beam, which may be oscillated in a direction
transverse to the gap 24 fuses the workpiece material and forms a weld seam
r~ 28 which generally has an upper and lower weld bead 30 and ~, respectively,
which generally protrude somewhat above the essentially flat surface of the :
plates 20, 22 and have a rough and irregular surface. 3 ~
A filler or additional material in form of a wire or rod 3~may :
be supplied to the pool of molten material which is formed at the welding
site by the beam 25. ~ :
~: It is well known that a fairly high vacuum must be maintained in
; an inner portion 34 of the vacuum chamber in which the E.B. gun is housed
for propagation of the beam 25. The sealing system which is necessary for
maintaining this vacuum can be divided in several zones, which are marked
with roman numerals in Figures 1 and 2, namely:
I. A lateral section of the sealing system which provides for
sealing the beam exit opening 16 against the opposed workpiece surfacej
- II. A section through which a workpiece zone, which is to be pro-
; cessed by the beam enters the vacuum chamber ("processing zone entrance
section");
III. A zone through which the zone which has been processed by the
beam, leaves the vacuum chamber ("processing zone exit section")j
IV. A rear portion of the sealing system which provides for seal-
~ 9~s
ing the beam exit side (underside) of the workpiece; and
V. A lock section, if needed, for supplying the rod-shaped or
wire-shaped additional material 32 to the welding side.
The problem underlying the invention has been Just described with
reference to electron beam welding; however, similar problems exist when
other processing operations are to be formed by an electron beam or ion beam
machine having a mobile vacuum chamber which moves with respect to the work-
piece. Such operations are e.g. cutting, melting, vaporizing, heating, ma-
chining, engraving (e.g. printing cylinder). The invention is likewise ap-
plicable to such other operations, however, it will be described with refer-
ence to E.B. welding since this is one of the most common E.B. processing
operations.
The lateral sealing sections I pose the least problems, since the
workpiece surface will be generally smooth in this area. An elastic sealing
element as shown in United States-patent 3,136,882 or a pressure stage seal
will generally do the ~ob, however, an improved sealing arrangement for this
section will be described later.
It is generally more difficult to provide for proper sealing in
section II since the processing zone which enters the vacuum chamber through
this section may comprise a gap, such as the gap 24 formed by the opposed
front edges of the plates 20 and 22, which makes sealing more difficult.
In section III it is still more difficult to provide for the prop-
er sealing because of the irregular surface features of the welding beads.
Since a substantial portion of the beam 25 emerges from the beam
exit side of the workpiece, the rear side sealing section IV must be con-
structed so that it is not damaged by the beam.
The lock for the filler material 32 at sealing section V may be
provided by an elastic sealing element or a pressure stage seal and, pref-
erably, by a combination of both.
One of several measures which, according to the invention, can be
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'iL~L~9~!~5
taken individuall~ or in combination is to broaden or extend the width of
the sealing system in the processing zone exit region and/or the processing
zone entrance region. Thus, for example the edge of the vacuum chamber of
the wall dividing two pressure stages is broadened or extended in the direc-
tion of relative movement with respect to the processing zone of the work-
piece so that the restricted flow passage for the air is made longer.
Figures 3A and 3B show a vacuum chamber having a sealing system
with two pressure stages and a processing zone exit region ~ devised ac-
cording to the concept ~ust described. The pressure stage sealing system com-
prises an inner wall 40 separating the inner vacuum chamber 34 from an an-
nular intermediate vacuum chamber 42 having an outer wall 44 separating the
intermediate vacuum chamber 42 from the surrounding atmosphere. At the pro-
cessing zone exit side, where the upper weld bead 30 leaves the vacuum cham-
ber, the wall 40 comprises a portion 40a of enlarged width. The wall 44
comprises a similar portion 44a, the width of which being extended in the
direction of relative movement with respect to the welding bead 30. The
front end of the enlarged wall sections 40a, 44a which is shown in Figure
3A, may form a channel-shaped slot 40b, 44b (Figure 3C) to accommodate the
front end to the protruding upper weld bead 30.
The inner chamber 34 and the intermediate chamber 32 are connected
to appropriate vacuum pump systems 46, 48 respectively, as known in the art.
To provide a proper seal at the processing zone entrance section,
the gap 24 may be sealed with two tapes 50 made of metal foil and secured
with an adhesive to the workpiece. A sealing system 52 similar to that
just described may be provided at the beam exit side of the workpiece. A
preferred alternative of a sealing system for the rear of the processing
zone, which is welded by the beam, will be described below with reference
to Figure 8.
Figures 4 and 5 show another embodiment of the processing zone
exit section of a sealing system according to the invention. As shown, a
wall 60 of a vacuum chamber is provided with a box-shaped extension 62 which
forms an exit section for the weld bead 30. The wall 60 with the box-shaped
extension 62 may replace extended wall portions 40a and/or 44a of the embod-
iment of Figure 3, or may be the sole wall separating the vacuum chamber 34
from the surrounding atmosphere.
The box-shaped extension 62 comprises two intermediate walls 64,
66 which divide the space within the box 62 into a center compartment and
two lateral compartments. The center compartment comprises a brush-like
bundle of metal wires 68 which are pressed with their one end against the
weld bead by a spring 70. The lateral compartments each comprise a pad 72
of a deformable or pliable material, e.g. a fabric or felt or fleece of min-
eral fibers, as asbestos or glass fibers.
The lower end portions of side walls 62A of the box-shaped exten-
sion 62 and of the intermediate walls 64, 66 may be tapered away from the
pads 72 as shown in Figure 5 to allow some spreading of the pads 72 at the
surface of the workpiece.
On both sides of the box-shaped extension 62, the wall 60 is pref-
erably provided with a lip seal arrangement 74 which considerably reduces
the leakage through the narrow gap 75 which is present in all conventional
20 pressure stage sealing systems. The sealing arrangement 74 comprises an
elongated, strip-shaped sheet member 76 of elastic material, preferab~y syn-
thetic rubber, and a film 78 of a low friction material, e.g. of poly-
tetrafluorethylene or a similar polymeric material. The lip seal 76-78 is
pressed against the surface of the workpiece by a spring-loaded metal ledge
80. The rubber sheet 76 may comprise an end portion of increased thickness
ad;acent to the box-shaped extension 62 as shown.
Figure 6 shows a preferred embodiment of a sealing system, which
is a combination of a pressure stage seal and a lip seal arrangement, and
which is preferably used for sealing the vacuum chamber in the lateral sec-
tions I (Figure 2) and the portions of sealing sections II and III adjacent
_ g _
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the processing zone sealing sections. The pressure stage seal shown inFigure 6 comprises three walls 82, 84, 86 (similar to the sealing system
shown in Figure 3) which form an inner vacuum chamber 34 and two intermedi-
ate vacuum chambers 42a, and 42b. The lower edges of the walls 82, 84 and
86 end short of the surface of the workpiece forming small gaps 75a, 75b and
75c respectively. To reduce the leakage through each of these gaps, an ad-
ditional lip seal arrangement is provided to seal each of these gaps, the
lip seal arrangements being similar to the sealing arrangement 74 just de-
scribed in relation to Figures 4 and 5. Thus, each lip seal arrangement
comprises a flexible sheet 76 made preferably of synthetic soft rubber and
having a thickness of, say, 5 mm, and a film 78 of a low-friction material,
as polytetrafluorethylene. The strip-shaped structure formed by the sheet
76 and the film 78 is mounted, e.g. clamped, in an air-tight manner to the
respective wall while the other end portion is pressed by a series of
springs 88 against the workpiece; the springs being mounted between one leg
of an L-shaped ledge 90 having its other leg attached to the respective wall,
and a ledge 80 bearing against the rubber sheet.
The lip seal arrangement may be still further enlarged by provid-
ing two spaced rows of springs ô8a, 88b as shown in combination with wall
86 abutting the outer atmosphere; the other walls may also be provided with
such an enlarged lip seal arrangement.
The lip seal arrangements JUSt described with reference to Figure
6 can also be used in a sealing system having only a single wall which sep-
arates a high vacuum chamber from the outer atmosphere.
Figure 7 shows a more simple combination of a pressure stage seal-
ing system with a lip seal arrangement. The sealing system of Figure 7
corresponds essentially to that described with reference to Figure 6 with
the exception that the spring which presses the sealing lip consisting of
the rubber sheet 76 and the anti-friction film 78 against the workpiece sur-
face is omitted. In this case, the film 78 preferably ends at some distance
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before the free end of the rubber sheet or the film 78 is firmly attachedto the sheet 76.
Figure 8 shows a preferred embodiment of the sealing section IV
sealing the rear or beam exit side of the workpiece. The sealing section
shown in Figure 8 comprises a channel-shaped member 92 forming a chamber 94
at the rear side of the processing zone of the workpiece. An elastic seal
90 seals the chamber 94 against the outer atmosphere. The chamber comprises
two lateral portions 96 communicating with an exhaust tube 98 and a central
section lO0 of increased depth which containing a particulate material 102
which may be a metal powder or metal granulate and has the purpose of dis-
sipating the emerging portion of the electron beam 25 and/or preventing the
molten material from flowing out of the welding side. The material 102 may
be e.g. relatively coarse metal powder or metal granulate, or sand. The
body 92 is pressed by a plunger 106 against the rear side of the workpiece,
and spacer 104 may be provided at spaced locations along the length of the
body 92 to prevent the body from bending.
The sealing system shown in Figures 9 to 11 makes use of a mate-
rial which forms a continuous, elastic or pliable body, or can be brought in
the form of such a body upon application to the workpiece, to conform to the
surface features of the workpiece and form a seal with a relatively smooth
surface which can be easily sealed by a pressure stage seal and/or a lip-
seal.
Figures 9 and lO show an embodiment of such a sealing system use-
ful for the processing zone entrance side of the sealing system of a E.B.
welding machine. The sealing system is adapted to seal a relatively wide
and irregular gap 24 between opposed front surfaces of two workpiece por-
tions to be joined by E.B. welding. The sealing system 134 of Figure 9 com-
prises a two-stage sealing arrangement of the type described with reference
to Figures 6 or 7 on both sides of the workpiece. To provide for sealing
the gap 24, a sealing material, e.g. a preheated thermoplastic polymeric
39?i~5
material, is introduced (poured or in~ected) in a liquid or plastic state
into the gap 24 and smoothed at the upper and lower side by smoothing plates
or shoes ]38 (or rollers). The material is chosen such that it attains a
highly viscous or solid elastic state within the gap by cooling and/or
polymerizing, the state being such that the material can be removed in the
form of a continuous body or band 140 from the gap after having passed the
sealing zone. The material may be removed from the gap by an appropriately
driven take-up reel, as described below with reference to Figure 11, or by
a pair of rollers 139 in which case it may be recycled through a lock system
142 to the atmosphere, where it is again liquified by application of heat in
a supply container 144, so that it can be applied again through a nozzle
136.
The material may comprise elongated flexible fibers e.g. polyester
or glass fibers, or similar reinforcement materials to enhance the tear
strength and the continuity of the applied material so that the band 140
does not rupture during removal from the gap 24. The workpieces preferably
form a wedge-shaped gap 24 as shown in Figure 10.
Figure 11 shows an embodiment of a processing zone exit section of
the sealing system of an E.B. welding machine comprising a vacuum chamber
with a wall 114. A cord or band 112 of glass or mineral fibers such as as-
bestos is used to smo~then the rough surface portion comprising the weld
bead 30 of the weld seam. The workpiece with the weld bead 30 moves in the
direction of an arrow 120 relative to the wall 114. The band 112 is deliv-
ered from a supply reel 122 rotably supported by means not shown within the
vacuum chamber 34 and passes below a sealing system 110 which includes a
box-shaped extension 115 of the wall 114. The bottom side of the box-shaped
extension 115 is formed by a flexible sheet 128 of a low-friction material
such as polytetrafluorethylene which is pressed by springs 130 against the
band 112 and the workpiece surface. The band 112 smoothes the uneven sur-
face features, so that the flexible film or sheet 128 can provide a seal
- 12 -
with low leakage rate. The band 112, after having passed through the seal-
ing system, is taken up by a take-up reel 124. The band 112 may be impreg-
nated with a liquid or greasy substance of low vapor pressure such as a
heat-resistant silicone compound to enhance the sealing properties. The
band 112 may be recirculated as shown in Figure 9.
Figure 12 shows a further alternative of a sealing system which
is preferably used in the processing zone exit section. The overall system
may be similar to that shown in Figures 4 and 5 with the exception that the
wire bundle 68 in the middle compartment of the box-shaped extension is re-
placed by one or several rollers 150 having a surface layer 152 of a pliable
or resilient material such as a metal felt. The rollers bear sealingly
against the surface of the workpiece 154 which may include a weld bead 30
which is accommodated by the resilient layer 152. The axial ends of each
roller abut tightly against the side walls of the box 62' and the periphery
of the roller on the opposite side of the workpiece slides tightly and seal-
ingly on the inner side of a top wall of the box or other sealing element,
e.g. a lip seal 156. If several successive rollers 150, 150', 150" are used,
exhaust tubes schematically shown by arrows 158 may be connected to the
space between two successive rollers to provide some kind of pressure stage
seal.
The embodiment of Figure 13 differs from that shown in Figure 12
mainly in that two rollers 150a, 150b supporting an endless loop 152' of an
elastic or pliable material are used instead of a roller 150. The loop 152'
may be comprised of a metal fiber felt or a fabric of asbestos or mineral
fibers, preferably impregnated with a low vapor pressure liquid or grease
such as a silicon compound. The pair of rollers 150a, 150b with the track-
like endless loop or band 152' operates in a similar fashion to a roller
150, 152 of Figure 12. The system of Figure 13 provides, however, a leakage
path of increased length as compared with the roller 150. Of course, two or
more pairs of rollers may be used in succession.
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