U.S. patent number 3,751,702 [Application Number 05/056,554] was granted by the patent office on 1973-08-07 for rotating anode x-ray tube.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Kurt Dietz.
United States Patent |
3,751,702 |
Dietz |
August 7, 1973 |
ROTATING ANODE X-RAY TUBE
Abstract
This invention relates to an X-ray tube of the rotating-anode
type which includes a disk which is resiliently mounted upon a
shaft and also contains an electron impinging portion thereupon.
The anode is provided with a plurality of recesses therewithin
which produces the advantages which will be hereinafter
summarized.
Inventors: |
Dietz; Kurt (Erlangen,
DT) |
Assignee: |
Siemens Aktiengesellschaft
(Erlangen, DT)
|
Family
ID: |
5740611 |
Appl.
No.: |
05/056,554 |
Filed: |
July 20, 1970 |
Foreign Application Priority Data
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|
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Jul 23, 1969 [DT] |
|
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P 19 37 351.4 |
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Current U.S.
Class: |
378/125; 313/149;
378/128; 313/40; 378/127; 378/144 |
Current CPC
Class: |
H01J
35/10 (20130101) |
Current International
Class: |
H01J
35/10 (20060101); H01J 35/00 (20060101); H01j
035/04 () |
Field of
Search: |
;313/60,40,41,149,330
;29/25.14 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kaufman; Nathan
Claims
I claim:
1. An X-ray tube having an anode comprising a ring-shaped disc
portion and rotating means extending through the center of said
disc portion and connected therewith, said disc portion receiving
electrons impinging upon it, said disc portion being provided with
outwardly extending recesses connected between the focal point path
and axle and which at least penetrate partially through the
thickness of the disc and thus the direct connection between the
axis of the disc and the electron impinging portion is
interrupted.
2. An X-ray tube as described in claim 1, said recesses passing
entirely through the disk portion.
3. An X-ray tube as described in claim 2, said recesses having the
form of a sun burst.
4. An X-ray tube as described in claim 3, said recesses being
alternate lateral cuts within said disk portion.
5. A rotating anode for an X-ray tube, as described in claim 1 a
securing ring member carried by said disk having an electron
impinging portion thereupon.
6. A rotating anode as described in claim 5, said recesses
extending to the edge of said disk and below said ring member.
7. A rotating anode as described in claim 6, said disk being made
of graphite and said ring being made of tungsten.
8. A rotating anode as described in claim 7, said disk having a
plurality of individual spaced members disposed thereupon.
9. A rotating anode as described in claim 6, said recesses
extending from the top and bottom of said disk.
10. A rotating anode as described in claim 9, said recesses
extending alternately from the top and bottom of the disk and
extending through at least half the thickness of the disk.
11. A rotating anode as described in claim 10, including additional
circumferential within said disk portion.
Description
DESCRIPTION OF THE INVENTION
Generally, in rotating anode X-ray tubes which are presently known
the electron impinging portion is placed at the greatest possible
distance from the center of rotation so that the surface of the
anode has the highest possible velocity at the point where the
electron beam impinges thereupon. This permits the anode to be
subjected to high load. As is also generally known, as the
impinging electrodes strike the electrode impinging portion, the
anode material heats up and expands. This, of course, will produce
mechanical strains with regard to the other portion of the anode
which are colder than the electrode impinging portion. Thus the
anode has a tendency to break. In addition, of course, when a
rotating anode ruptures the centrifugal force involved will cause
the broken parts to fly apart and thus further dangers are
produced. Where anodes are made of tungsten or molybdenum metal the
metal involved is very brittle if it is not heated to at least
200.degree. C. Where graphite anodes are used, their tensile
strength is very low even though they have high heat capacitance
and high ability to radiate heat.
In the anodes utilized heretofore, in order to increase the
strength of the anode, the heating stresses have been distributed
over longer time intervals so that the differences in thermal
expansion between portions of the anode subjected to electron
impingement and non-electron impingement do not exceed the stress
resistance of the material involved. In the case of known anode
materials the thermal conductivity is between 0.3 to 0.6 cm times
the square root of the time of loading in seconds. Thus, in one
second, a heat migration of a maximum of 3 - 6 mm is obtained. Thus
an anode of a radius of 5 cm requires 20 - 40 seconds before it is
warmer than 200.degree. C in all places. If the above limits are
exceeded, of course, the anode will rupture but this can also be
avoided if the entire thermal load is maintained below the breaking
limit. This causes the additional disadvantage, however, that the
exposure time must be lengthened. There is also a disadvantage
that, where high temperature differences are involved, warp of the
anode will occur making the anode unsuitable for proper use.
It has also been proposed to provide the electron impinging portion
of the anode upon the surface of the ring. By the use of a ring,
because the heat conduction paths are short, several of the
above-mentioned disadvantages have been avoided. However, the ring
only has a small surface area and therefore has poorer heat
conduction and heat radiation.
I have avoided the disadvantages of the prior structure by
providing a rotating anode which includes rotating means and a disk
portion which contains the electron impinging portion thereupon.
The disk is provided with recesses which at least penetrate
partially through the thickness of the disk and thus the direct
connection between the axis of the disk and the electron impinging
portion is interrupted. As a result the deformation stresses are
moderated because of the fact that the disk is now somewhat
resilient. Thus, substantially greater temperature differentials
can be utilized without fracture of the anode. On the other hand
the heat conductance and thermal capacity of the anode is retained
since a large heat conductance area is provided. Also the heat
radiating surface of the anode is increased so that faster cooling
thereof is provided.
The recesses can be made in various shapes as indicated in the
drawings. One of the preferred shapes is that of a sunburst. The
recesses can be cut into the disk by various ways including the use
of electron beams. Embossing systems can also be used. The part of
the anode which lies between the electron impinging portion and the
axis of rotation can also be given resilient properties by
providing the anode plate with recesses which lie on concentric
circles on the axis of rotation and extend from both the upper and
lower surfaces. Such a construction provides for a resilience
transverse to the radial direction. The recesses can also be cut
into the support as interrupted lines. If this structure is
utilized the adjacent recesses are so arranged that the parts which
remain are always located at the place where a recess is provided
in the adjacent circle to assure radial mounting.
The anodes can consist either of a homologous material such as
tungsten, tantalum or carbon. Or, alternatively, it is possible to
make the anodes of composite material. For example, a disk-shaped
graphite anode could be coated on the electron impinging portion
with a metal such as tungsten. It is also possible to insert a
metal ring into a graphite dish. A particularly good anode is
obtained if the graphite plate is first provided with spokes which
extend up to the edge thereof. The plate is then prestressed by
reducing its circumference. The groove for the insertion of the
ring is then provided and the ring introduced therein. After this
is done the stress on the plate is released and the ring is firmly
clamped into position.
The above sets forth the proposed objects and advantages of this
invention and a brief description thereof. Other objects and
advantages of this invention will become apparent to the reader of
this specification as the description proceeds.
The invention will now be further described by reference to the
accompanying drawings which are made a part of this
specification.
IN THE FIGURES
FIG. 1 is a side elevational view of an X-ray tube having the
rotating anode of this invention with portions of the anode plate
partially broken away to show details of construction.
FIG. 2 is a bottom plan view of the anode plate of the tube of FIG.
1.
FIG. 3 is a cross-sectional view of an anode plate of an
alternative form of this invention in which the plate consists of a
single material and the openings are arranged in the form of a
sunburst.
FIG. 4 is a top plan view of the anode plate shown in FIG. 3.
FIG. 5 is a view similar to that of FIG. 3 but showing a further
alternative form of this invention wherein the anode plate is of
heavy metal and the openings therewithin are concentric to one
another.
FIG. 6 is a top plan view of the form of invention shown in FIG.
5.
FIG. 7 is a top perspective view of a further alternative form of
this invention wherein the anode consists of individual
spoke-shaped members which are held together on the outer periphery
by a heavy metal rim which also constitutes the electron impinging
portion.
FIG. 8A is a fragmentary cross-sectional view of a portion of an
anode plate wherein the electron impinging portion lies on a thin
ring which is located on a graphite base and provided with
concentric annular grooves on the top and bottom.
FIG. 8B is a view similar to that of FIG. 8A but showing the
position of the annular grooves when differential heating is
applied to the anode plate.
FIG. 9 is an isometric view of a further alternative form of anode
plate and associated structure with portions thereof broken
away.
FIG. 10 is a top plan view of one of the sections of the anode
plate shown in FIG. 9.
The invention will be further described by reference to the
specific form thereof as shown in the accompanying drawings. In
this connection, however, the reader is cautioned to note that such
specific form of this invention as set forth in the specification
herein is for illustrative purposes and for purposes of example
only. Various changes and modifications could obviously be made
within the support and scope of this invention.
Now referring to the specific form of this invention as shown in
the drawings herein, there is shown in FIG. 1 an X-ray tube 2 which
is surrounded by a glass vacuum element 1. The cathode 3 is spaced
from the rotating anode 4. Cathode combination 3 includes mount 5
with shielding 6 covering the conventional cathode construction
(not shown). Anode 4 includes a rotor 7 which carries shaft 8 at
its upper end. Between elements 11 and 12 is clamped an anode plate
9. It is thus seen that when rotor 7 turns anode plate 9 will also
turn. Rotor 7 can, of course, be turned by a conventional stator
which which is placed on the outside of tube 2. The rotation can be
accomplished, for example, by complementary magnetic means arranged
upon the rotor and stator.
Referring specifically to anode plate 9 (which preferably has a
diameter of 100 mm) there is shown a graphite portion 10 which has
a preferred thickness of 15 mm. Shaft 8 passes through an opening
substantially centrally located within plate 9 and plate 9 is
clamped in position between elements 11 and 12. A ring 13 is
provided within a groove 14 located within anode plate 9. Ring 13
is preferably made of tungsten. The two concentric circles shown as
15 and 16 on ring 13 constitute electron impinging portions which
are the portion of the anode upon which the electron beam from the
cathode will impinge. It is noted that element 10 is provided with
a plurality of recesses 17 and 18 which are preferably in the form
of a sunburst and extend from the inner surface to the outer edge
of element 10. Thus element 10 includes a plurality of sectors 20
which are connected with one another through spoke elements 19.
Specifically, in the form of invention shown in FIGS. 1 and 2 there
are a total of nine sectors 20 formed within member 10. Since ring
13 must be held securely in position it has a diameter of about 1
mm, smaller than that of the recess in which it is clamped. The
ring 13 is then held in position by pressure. An additional holding
action is provided in that the edge 21 of ring 13 is inclined
outwardly toward shaft 8 and the upper diameter of ring 13 is
larger than the lower diameter. A preferred manner of inserting
ring 13 into groove 13 is to reduce the circumference of body 10 so
that the ring 13 can be inserted despite its smaller inside
diameter. Such a method can be easily accomplished by the
utilization of a band which can be tightened by imposing pressure
around the circumference of the disk. Once the ring has been
inserted the band can then be released so that spokes 19 can spring
outwardly and will insure the proper support of ring 13.
In order to produce a beam between anode and cathode high voltage
is applied to lines 22, 23, 24 and element 25. The heating voltage
for the cathode within screen 6 is connected between line 23 and
one of lines 22 and 24. Thus there is produced two spaced electron
beams which are adapted to individually strike impinging portions
15 and 16 which lie on the surface of ring 13. In the preferred
modification shown paths 15 and 16 are concentric to one another
and differ by their inclination with respect to the axis of
rotation of the anode plate with elements 16 being inclined
outwardly by 17.5.degree. with respect to the perpendicularity of
the axis of rotation and the inner portion 16 is inclined outwardly
by 10.degree..
In operation the device of FIGS. 1 and 2 produces generation of
X-rays which then strike ring 13 along the electron impinging
portions. The tensile and shear stresses which occur by reason of
the electron impingement are taken up by recesses 17 and 18 which
are provided in anode plate 9 and these stresses will then be
eliminated by reason of the provision of the structure shown. In
addition, of course, the fact that element 10 is made of graphite
radiates the heat far better than any metallic element.
In FIGS. 3 and 4 there is shown an alternative structure of the
anode disk portion. Here a plate 26 is provided which is equivalent
in function to anode 9. Plate 26 consists of molybdenum and is
coated with a 1.5 mm thick layer of an alloy of 90 percent tungsten
and 10 percent rhenium along the electron impinging portions 27 and
28 which correspond to electron impinging portions 15 and 16 in
FIG. 1. It is noted that there are provided 12 recesses in plate 26
which between them define spoke members 30 and these elements
permit the differential expansion forces to be converted to bending
forces and thus will note cause the disk to fracture.
In FIGS. 5 and 6 there is a further alternative structure of anode
plate 9 shown. Here the analogous plate is designated 31 and
consists of an allow which contains 0.1 percent yrridium plus 99.9
percent tungsten. This plate is 4 mm thick and contains 4
concentric rows of recesses 32, 33, 34 and 35 which have a width of
3 mm. The parts between the recesses then act as holding spokes.
The electron impinging portion is indicated by reference character
36 and is inclined 12.degree. downwardly with respect thereto
perpendicular to the axis of rotation. Thus, again, the tensile and
shear stresses produced during operation of the anode involved are
converted into flexural stresses.
A further alternative construction shown in FIG. 7 includes a
mounting plate 38 which includes a plurality of elements 39 which
become wider from the axis of rotation toward the edge and are
spaced from one another through slots 40. These elements 39 are
held together by the ring 42 which is clamped around their lateral
edges. In this construction it is noted that the electron impinging
portion lies upon the outer element of ring 41 and the cathode 42
is placed on the side of the anode 37. Thus the electron impinging
in the direction shown by the arrow 43 in FIG. 7 produces a beam of
X-rays 44.
In FIGS. 8A and 8B there is shown a construction which can be
provided in order to save weight. In such a construction the ring
could be easily deformed reversibly during heating upon production
of the beam, thereby making the anode angle smaller. Thus there are
produced not only tensile forces in a radial direction but also a
bending force in the mount 46 which is made of graphite. In order
to avoid breaking of mount 46 a plurality of annular grooves 47 and
48 are cut therewithin and are staggered with respect to one
another on the upper and lower sides. Thus, when stresses are
produced which lead to bending stresses grooves 47 then close
somewhat at their upper end and grooves 48 widen somewhat at their
lower end.
This position is shown in FIG. 8B.
In FIGS. 9 and 10 a further alternative construction is shown
wherein the anode plate is composed of individual members 49-54
which are held to one another in pie-sliced relationship by ring
55. Each of these members 49-54 are provided with a plurality of
recesses which extend transversely from either end. Element 54 is
specifically shown in FIG. 10 and includes the recesses 57-60 which
extend alternatively from opposite sides. It is obvious that this
construction of members 49-54 will hold ring 55 resiliently on
shaft 56. Here the electron impinging portion is also an outer
periphery of ring 55 and the electrons are produced from coil 61 of
cathode 62.
The foregoing sets forth the manner in which the objects of this
invention are achieved.
* * * * *