U.S. patent number 3,710,170 [Application Number 05/071,556] was granted by the patent office on 1973-01-09 for x-ray tube with rotary anodes.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Rudolf Friedel.
United States Patent |
3,710,170 |
Friedel |
January 9, 1973 |
X-RAY TUBE WITH ROTARY ANODES
Abstract
An X-ray tube has a rotary anode which is a compound body with
parts of heavy metal and graphite, the focal point path lying upon
the heavy metal. The invention is particularly characterized by the
provision of at least one graphite part at the heavy metal part
outside of the focal point path.
Inventors: |
Friedel; Rudolf (Erlangen,
DT) |
Assignee: |
Siemens Aktiengesellschaft
(Erlangen, DT)
|
Family
ID: |
5747955 |
Appl.
No.: |
05/071,556 |
Filed: |
September 11, 1970 |
Foreign Application Priority Data
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Oct 11, 1969 [DT] |
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P 19 51 383.8 |
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Current U.S.
Class: |
378/125;
378/144 |
Current CPC
Class: |
H01J
35/108 (20130101) |
Current International
Class: |
H01J
35/10 (20060101); H01J 35/00 (20060101); H01j
035/10 () |
Field of
Search: |
;313/330,352,355 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lake; Roy
Assistant Examiner: Hostetter; Darwin R.
Claims
I claim:
1. In an X-ray tube, a rotary anode having an axle, a rotary plate
of heavy metal carried by said axle and receiving the focal point
path of the X-ray tube, and at least one graphite part applied to
said heavy metal plate outside of the focal point path.
2. An X-ray tube in accordance with claim 1, wherein graphite parts
are applied only to the underside of the part consisting of heavy
metal.
3. An X-ray tube in accordance with claim 1, wherein the graphite
parts are soldered by a layer of soldering.
4. An X-ray tube in accordance with claim 1, wherein the heavy
metal part has bore holes, several graphite parts having the shape
of plugs being fixed in said bore holes.
5. An X-ray tube in accordance with claim 4, wherein the bore holes
have rounded ends.
6. An X-ray tube in accordance with claim 1, wherein the heavy
metal part has annular grooves extending concentrically to its
rotary axis, the graphite part consisting of graphite rings
inserted into said grooves.
7. An X-ray tube in accordance with claim 6, wherein said graphite
rings are divided radially into segments.
8. An X-ray tube in accordance with claim 1, wherein the graphite
part consists of strips mounted as radial cooling ribs upon the
underside of the heavy metal part.
9. An X-ray tube in accordance with claim 1, wherein the entire
underside of the heavy metal part is covered by the graphite part
consisting of a plate.
10. An X-ray tube in accordance with claim 2, wherein graphite
parts are additionally applied to the upper side of the part
consisting of heavy metal.
11. An X-ray tube in accordance with claim 9, wherein the graphite
parts have concentrical and/or radial cutouts.
12. An X-ray tube in accordance with claim 1, wherein the heavy
metal part has the shape of a rotary anode plate.
13. An X-ray tube in accordance with claim 1, wherein the heavy
metal consists of molybdenum.
14. An X-ray tube in accordance with claim 3, wherein the layer of
soldering consists of the eutectic of zirconium and tungsten.
15. An X-ray tube in accordance with claim 3, wherein the layer of
soldering consists of an alloy containing 70 percent zirconium and
30 percent molybdenum.
16. An X-ray tube in accordance with claim 3, wherein the layer of
soldering consists of the eutectic of molybdenum and molybdenum
carbide.
17. An X-ray tube in accordance with claim 1, wherein the heavy
metal part consists of molybdenum and wherein the graphite parts
are fixed to the heavy part by heating to a temperature of
2200.degree.C.
18. An X-ray tube in accordance with claim 3, wherein the surfaces
of the graphite parts which are to be soldered are initially coated
with a layer of zirconium carbide, tantalum carbide or hafmium
carbide.
19. An X-ray tube in accordance with claim 3, wherein the soldering
consists of zirconium or hafmium.
Description
DESCRIPTION OF THE INVENTION
This invention relates to an X-ray tube with rotary anodes, the
anode being a compound body with parts of heavy metal and graphite,
the focal point path lying upon the heavy metal.
X-ray tubes with such anodes are used due to the high specific heat
and the good ray emitting capacity of graphite in order to produce
higher loads.
Anodes containing graphite and now used as rotary anodes for X-ray
tubes consist of a graphite disc the surface of which at least in
the area of the focal point path is coated with a layer of heavy
metal. Such layers are produced, for example, by steaming, spraying
or by pyrolytic decomposition of compounds. The layers must be thin
in order to be able to operate effectively and to utilize the
technological data. Such layers have, however, the drawback that
they are destroyed when tungsten is used, forming a carbide.
Furthermore, carbide layers are brittle and have bad heat
conductivity, so that they are not adequate for the high heat
exchange requirements of modern high output X-ray tubes. On the
other hand, graphite has the drawback that it is difficult to
eliminate gas from the large graphite volume due to its porosity.
There is the danger that the anode will develop gas during
subsequent operation. On the other hand, graphite can easily
evaporate in case of high voltage impacts or small graphite parts
can be torn off in high electrical field, as the result of which
arc-like discharges are produced causing disturbance in cathode
emission and finally destroying the X-ray tube. Furthermore, the
mechanical strain upon graphite is very high due to revolving
speeds up to and over 10,000 per min. and accelerations of 200 to
300 revolutions per sec.sup.2. When graphite is selected it is
necessary above all that it should have good strength. This means,
however, that it is necessary to accept worse thermic properties
and worse elasticity.
An object of the present invention is to eliminate these drawbacks
of prior art constructions.
Other objects will become apparent in the course of the following
specification.
In the accomplishment of the objectives of the present invention it
was found desirable to make the compound body out of a disc-shaped
heavy metal part wherein the graphite parts are applied outside of
the focal point path. Thus an anode is produced, the carrying
structure of which consists of a disc of heavy metal upon which
graphite parts are provided which absorb and emit heat received by
the plate from the focal point path. Then the anode is highly
loaded for a short time period, since the heat transfer from the
focal point path takes place faster due to high heat conductivity.
On the other hand, there is also good continuous load capacity,
since heat can be removed permanently from the graphite parts due
to high heat and radiation capacity.
As compared to prior art X-ray tubes the present invention attains
substantially the following advantages:
1. The short time load capacity corresponds at least to those of
the usual heavy metal plates.
2. The long term load capacity is improved due to the additional
heat capacity and radiation of graphite. Heat radiation can also
exceed that of plates consisting solely of graphite due to
different arrangement possibilities of the graphite parts and the
heat conductivity through the metal.
3. The support of the plate consists of heavy metal so that when
graphite is selected and its properties are considered it is not
necessary to consider its strength.
4. The construction of the present invention provides a larger
graphite surface relatively to volume than is the case in known
graphite plates. This improves not only radiation but also
degassing.
5. Graphite parts can be applied to the side of the anode plate
which is away from the cathode, so that these parts are located
outside of the direct high voltage field extending between the
anode and the cathode.
In accordance with an embodiment of the present invention which is
preferred due to its high efficiency, the anode consists of a heavy
metal plate shaped in a manner known per se and consisting of
molybdenum to which has been alloyed 5 percent tungsten, the plate
having along the focal point path a covering layer of tungsten and
10 percent rhenium. Bore holes having a diameter of 5 to 35 mm. are
provided from the lower side in this plate, their depth being about
5 mm. in case of a plate thickness of 10mm. It is also possible to
use diameters which are smaller than 5mm., but then increased
operational effort is necessary as related to effectiveness which
is also increased. The upper limit of the size of the diameter of
the bore holes and their depth is provided by the size of the anode
plate, its diameter and thickness. Graphite bodies are soldered
into the bore holes; they fill the holes to the greater extent and
their top can coincide with the plate surface or, depending upon
space conditions, they can project above the plate surface to the
extent of 25 mm. or more. The extending part can have a different
shape than that of the bore hole, it can be conical, etc. The
extending parts can be also varied in length, for example, they can
be shorter at the edges of the plate than at its middle; such
variations can facilitate ray emission and be useful and necessary
for geometrical reasons.
Various high melting metals or their mixtures, preferably
zirconium-molybdenum or zirconium-tungsten-eutectic are suitable as
solder. Good soldering can be also produced with a autectic of
molybdenum and molybdenum-carbide. The soldering can take place in
a known manner by adding a powder mixture corresponding to the
desired composition to the part to be soldered and providing the
heating. When a molybdenum body is used, the molybedenum-molybdenum
carbide-eutectic solder can be also produced without a special
solder. It is merely necessary to place the graphite parts into the
desired position and then heat to about 2200.degree.C. At this
temperature soldered eutectic is formed at the places of
contact.
When an X-ray tube is operated high anode temperatures and high
differences in temperature take place in the anode. Even if the
heavy metal and the used graphite had the same thermic coefficients
of expansion, -- which, however, is never the case for the wide
temperature range from about 0.degree.C to 2500.degree.C, --
thermic tensions occur in the anode due to different temperatures.
This results in great danger to solder connections between heavy
metal and graphite primarily due to shearing and traction tensions.
Graphite itself has only small resistance to shearing and traction,
but good pressure resistance. These difficulties are also
eliminated by the present invention. The fixing of the graphite
part takes place, for example, in molybdenum at the solidification
temperature of the solder being used. Since molybdenum has a
greater thermic expansion coefficient than graphite, parts of
graphite are firmly held under pressure after further cooling
(co-called shrinking process). Since the soldering surface is
spaced from the location where heat of the focal point path is
produced, the melting temperature of the solder is not reached in
operation. Thus no shearing and traction tensions occur at the
soldering surface, but only pressure tensions, so that the strength
of the connection is very good. In addition, the solder improves
the heat contact and thus heat transmission from heavy metal to
graphite.
When proper composition is used, the diffusion of carbon into the
heavy metal is also prevented. Solder suitable in this connection
may be zirconium carbide, tantalum carbide, hafmium carbide, etc.
When Zr or Hf are used a diffusion preventing layer is produced by
itself at the contacting surface with carbon (graphite, etc.)
during the heating, i.e., soldering.
It is possible to avoid the boring of a large number of holes if
grooves are bored concentriclaly about the axis of rotation upon
the underside of the metal plate, these grooves being filled with
suitable graphite rings. These rings can be radially divided to
improve the soldering connection. A construction having radial
cooling ribs is produced by applying strip-shaped graphite parts
with their narrow sides in radial direction to the underside of the
plate; these parts can be also divided.
When sufficiently balanced thermic expansion properties have been
provided, it is possible to solder a graphite disc having a
thickness of about 1 mm. to 10 mm. to the underside of the plate,
so that the entire surface of the plate will be covered. The
reliability of the solder connection in case of thermic alternate
stresses is increased by providing the graphite plate with radial
and/or concentric recesses. It is also possible to provide
structural parts increasing the surface, such as ribs, etc. In case
of X-ray tubes wherein only small amounts of stray electrodes, etc.
strike the surface directed toward the cathode and which do not
have to be operated with very high voltages, the upper parts of the
anodes can be additionally provided with graphite parts to further
increase heat emission.
The invention will appear more clearly from the following detailed
description when taken in connection with the accompanying drawing
showing by way of example only, preferred embodiments of the
inventive idea.
In the drawing:
FIG. 1 is a perspective view of an X-ray tube the anode of which
has been broken off to show graphite parts soldered in bore holes
upon its underside.
FIG. 2 is a section through an anode the underside of which
contains graphite rings in concentrical grooves.
FIG. 3 is a bottom view of an anode wherein the rings of FIG. 2 are
provided with radial interruptions.
FIG. 4 is a bottom view of an anode having radially applied
strip-like cooling ribs of graphite.
FIG. 5 is a section through an anode the underside of which is
completely covered by a graphite part.
FIG. 6 is a section through an anode which additionally is also
provided with a graphite part upon its upper side.
FIG. 1 shows a glass bulb 1 of a rotary anode X-ray tube 2. The
bulb 1 has at one end the cathode 3 and at the other end the anode
4. The cathode 3 consists of a cover 5 which contains in a lug 6
the actual glow cathode (not shown) of standard construction. The
anode 4 includes in a manner which is also known, the rotor 7
carrying by its axle 8 the actual compound anode 9 which is held
firmly by a screw 10. The anode 9 consists of a metal body 11 of an
alloy of molybdenum and 5 percent tungsten. The two focal point
paths 12 and 13 extend downwardly at different inclinations
relatively to the vertical line of the axle 8 and are located upon
a coating 14 consisting of an alloy of tungsten and 10 percent
rhenium, the coating having a thickness of 1 mm.
The underside of the metal part 11 which has a thickness of 10
millimeters is provided with bore holes having a depth of 4
millimeters in which graphite parts 15 are soldered. The solder is
the eutectic obtained from molybdenum and zirconium. The actual
solder is indicated in the drawing by thicker lines enclosing the
bore holes and is designated by the numeral 16.
X-rays are produced in a known manner by providing high voltage
between one of the conduits 17, 18 and 19 and the anode stem 20 and
by providing heating voltage between one of the conduits 17 and 18
and the conduit 19 for the glow cathodes located in the lug 6.
Electrons proceeding from the glow cathode then strike one or both
of the focal point paths and produce X-rays. As is known, a great
deal of heat appears as a by-product. This heat is conducted in the
metal part 11, accumulated in the graphite parts 15 and then
removed as rays.
FIG. 2 shows a plate 21 consisting of molybdenum the underside of
which is provided with annular grooves extending concentrically to
the axis of rotation. Graphite rings 22, 23 and 24 are soldered
into these grooves. As in the construction of FIG. 1, in this
construction also heat transmission takes place through the
graphite parts 22, 23 and 24.
This construction is again changed into that of FIG. 3 showing an
anode plate 25 consisting of molybdenum and provided with annular
grooves 26, 27 and 28. Sector-shaped parts of graphite rings are so
introduced into these grooves that radial interruptions are
provided, which are spaced from each other in the individual rings.
The graphite parts of the outer groove 26 are indicated by the
numeral 29 in the drawing, those of the middle groove 27 with the
numeral 30 and those of the inner groove 28 with the numeral 31.
The soldering takes place by heating to a temperature of about
2200.degree.C. A mixture of molybdenum and molybdenum-carbide power
is additionally introduced between the ring pieces.
FIG. 4 shows a plate 32 of a rotary anode, the plate having a
thickness of 10 millimeters. Strip-like graphite parts 33 are
provided on the underside of the plate 32 as radial cooling ribs.
For this purpose corresponding radial grooves are milled wiich are
three to 5 millimeters deep, so that the graphite parts 33 having a
width of 10 millimeters can be soldered into these grooves and
still project outwardly to the extent of 10 to 20 millimeters. This
construction also has good capacity for heat absorption and heat
reflection.
FIG. 5 shows an anode molybdenum plate 34 which is 8 millimeters
thick and at the underside of which a graphite body 35 having a
thickness of 6 millimeters is soldered by a soldering layer 36
consisting of Zr/Mo.
FIG. 6 shows an anode plate 37 to the underside of which has been
soldered a graphite body 38 of tungsten. Furthermore, the plate 37
has upon its upper side a surface limited by the inner edge of the
focal point path 42 which is deepened and which contains a graphite
body 43 soldered therein. This construction provides a better heat
transmission upwardly. Furthermore heat capacity is enlarged by an
increase of graphite bodies.
* * * * *