US2228384A - High-voltage discharge tube - Google Patents

Description

Jan. 14, 1941. BQUWERS ETAL 2,228,384

HIGH-VOLTAGE DISCHARGE TUBE Filed Aug. 1, 1938 2 Sheets-Sheet 1 ITTORIYIY- 14,v1941- A. BOUWERS ETAL 2,228,384

I HIGH-VOLTAGE DISCHARGE TUBE I Filed Aug. 1, 1938 2 Sheets-Sheet 2 w'w mm -M&8:'% Mam ArTok/MK Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE hoven, Netherlands,

assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application August 1,

1938, Serial No. 222,524

In Germany August 20, 1937 11 Claims.

Our invention relates to high-voltage discharge tubes, and more particularly to X-ray tubes.

In order to shockproof such tubes various constructions have been proposed. For example, in one construction an X-ray tube is arranged within a sheet metal protective shield, which surrounds the ends of the tube with considerable air space and is grounded during the operation of the tube. In such a construction the air between the tube ends and the protective shield serves as the only insulation, and to reduce this air space and thus decrease the size of the construction, it has been proposed to insert a partition of insulating material, or to replace the air with an oil filling. In a still further construction means are provided to prevent this air space from becoming electrostatically charged, and for this purpose it has been proposed to provide the inner surface of the portion of the protective shield adjacent the tube ends with a conductive layer which is electrically connected to the high-tension parts surrounded thereby, and to provide the external surface with a conductive layer which is grounded during operation of the tube. In constructions of the above types, however, the shockproof tube is of considerable weight and size, which hinders the handling thereof, and the use of an oil filling has several disadvantages.

In the shockproof X-ray tube described in U. S. Patent #2,119,069 .to Bouwers, the intermediate air spaces have been completely eliminated by applying a body of solid insulating material directly to the glass envelope portion of the tube, with the interposition of an insulating cement. In such cases it is possible for the outer surface of this insulating body to be coated with a conductive layer adapted to be grounded when the tube is in use.

Shockproof constructions of the above types have the additional disadvantage that rather complicated means must be provided to remove the heat developed in the tube during operation. More particularly, when using protective shields separated from the tube by an air space, a stream of cooling air is usually passed through this space, and for this purpose an electrically-operated fan is frequently built into the protective shield. When a protective shield engages the tube without intermediate space, as in the above-mentioned patent, cooling means of this type cannot be used, but instead a cooling fluid is circulated through a passage-way in the high-tension cable, a cavity in the anode, and out through another passageway of the cable, in order to remove the heat developed at the target surface. Such a construction, in addition to the difliculties accompanying the use of a cooling fluid such as water, is rather complicated. Only in small tubes of very low power can artificial circulating cooling be entirely dispensed with.

The main object of our invention is to overcome the above difficulties, and to produce a shockproof tube of very small size and weight without reducing the safety of the tube or the power which can be used.

A further object of the invention is to eliminate a circulating cooling fluid and the attending accessories.

A still further object of the invention is to prevent the insulating protective shields and envelope portions from being unduly heated in order that the design of such members will not be handicapped by heating problems.

Further objects of the invention will appear as the description progresses.

In accordance with the invention we use a shockproof construction in which the end portions of the tube are surrounded by insulating protective shields without intermediate air spaces, and provide means to prevent these shields as well as the insulating envelope portions from being unduly heated.

However, the heat due to energy losses in the tube-which in a normally-heated diagnostic tube may have an average value of about 100 watts as calculated over a whole working period, or an instantaneous value above 20 kw.must be removed from the tube. For this purpose we employ a combination of structural features which are more or less known per se, but which have never been combined to obtain the results aimed at by the present invention.

More particularly, we use an anode of the socalled heavy type, i. e. one in which a highlyrefractory impact disc or target is secured to a massive body of a metal of good heat conductivity. such as copper, through which the heat produced at the target is immediately distributed. To facilitate the removal of heat from the anode we provide the same with a surface of high heatradiating capacity, for instance, we blacken a large part i. e. at least 75 sq. cms., of the sheath surface of the anode.

This measure alone would not suflice for attaining the objects of the invention, because the anode must be capable of assuming the necessary operating temperature without unduly heating the tube walls and other parts of the tube. More particularly, although a heavy anode, in comparison with known anodes constituted by a disc or a club-shaped tungsten part cooled by radiation, can be said to be cold, its operating temperature with practically serviceable proportioning and a manner of loading normally existing in a diagnostic tube, is still so high, for example about 500" C., that the insulating protective parts and the insulating parts of the tube wall would be incapable of withstanding this temperature.

In accordance with the invention we overcome the above difliculty by using a tube envelope having a metal portion which opposes the whollyblackened part of the sheath surface of the anode in good heat-transferring relationship. This metal portion, which is preferably of ferrochrome, is insulated from the anode and the cathode of the tube to withstand high tension, and may be grounded when the tube is in use. We arrange this metal portion in good heat receiving relationship with the anode whereby heat received by radiation from the anode, is readily transmitted through this portion and is dissipated to parts of a stand, if provided, or to a radiator mounted on or forming part of this portion. Thus, the metal portion, as distinguished from a glass envelope portion which would absorb heat but would not transmit it readily, remains comparatively cold. For example, with an anode temperature of 500 C. such a metal envelope portion would not be heated to a temperature above C.

To prevent undesired heat transfer from the anode, we so connect the anode to the end of the tube and use an external supply conductor of such poor heat conductivity that the quantity of heat conducted away thereby is very small in comparison with the quantity of heat radiated by the anode to the metal wall portion. If the anode is mechanically connected to the metal portion, which would constitute an indirect connection to the tube end, we make this connection of good heat conductivity.

By using the combination of the above means, we ensure that substantially all the heat developed in the anode during operation is radiated to the metal envelope portion, and is dissipated to the sides of the tube, whereas only a comparatively small amount of this heat reaches the high-tension insulating protective shields, insulating envelope portions, and the external metal parts which are at electrode potential. As the hightension supply cables are secured to the protective shields, the very small amount of heat which still reaches the tube ends by radiation, or by conduction through the anode lead, is readily removed. If, in an extreme case, there should be any danger of the above parts reaching an undesired high temperature, a small fan may be provided, but in no case is it necessary to use air conduits, elastic water tubes or other complicated cooling means because only a low percentage of the entire heat loss is concerned. As a result, the protective parts and the connections of the cables may be of very simple construction.

To further protect the anode end, or both ends, of the tube against heat radiated from the electrodes, we may use one or more screens arranged in the vacuum space.

To decrease the mechanical load upon the in sulating envelope portions we may support the anode or the cathode or both from transverse insulating members which are secured to the metal envelope portion. It is thus possible to construct a tube in which a metal envelope portion and the transverse members form a unitary structure enclosing a. central space, on which the electrodes are located. With such a construction the imulating envelope end portions in which the supply eonductorsaresealedserveonlytosecureacloaed envelope and are protected from external contact by means of protective hoods.

The transverse insulating members may be made ofaceramicmaterialcapableofwitlmtandinga high temperature. Furthermore, these members are preferably made of a material which, in addition to being a good electrical insulator. also has good thermal conductivity. By using smh materials, these transverse members are cooled by the transfer of heat to the metal envelope portion and thus undesired heating of the tube ends by radiation is prevented.

In order that the invention may be clearly understood and readily carried into effect, we shall describe the same in more detail with reference to the accompanying drawings, in which:

Figure 1 is a partly-scctionized view of an X-ray tube according to the invention, and

Figurezisasectionizedviewwithcertainparts omitted of an X-ray tube according to another embodiment of the invention.

The x-ray tube shown in Fig. i has an envelope comprising a cylindrical-shaped flanged metal member I, for instance of ferrochrome, which is hermetically fused at 02 and G8 to two vitreous end portions 2 and 3. Supported in a manner latertobedescribedisananodel,ofoopper, about 60 mm. long and of an outside diameter of about 55 mm. Anode 4 is provided with a tungsten target 5, and its sheath surface I, which has anareaofabout 100sq.cms.,isofgoodhatradiating properties. For this purpose the surface is blackened. for instance by applying thereto a thin coating of chromium and thereafter oxidising the chromium.

Member I extends from the cathode end of the tube to a point beyond the blackened sheath surfacetsothatthissurfacehasametalenvelope portion arranged opposite it throughout its extension without intermediate members. The metal member I can be grounded when the tube is in use.

A layer 1 of X-ray absorbent material, such as lead, surrounds the central portion of metal member I and serves to absorb undesired X-rays, whereas the x-rays emitted by target I can emerge through a glas window 8 hermetically sealed In member I and a corresponding aperture in lead layer 1.

Surrounding lead layer I is a metal protective sheath 0 which comprises two parts which are held together by screws (not shown) and has a tubular portion III. It will be noted that the ends of sheath 9 are in contact with metal portion I, whereas the two parts of this sheath are clamped together and in contact with the lead layer I. The layer I may consist of a metal composite having a low melting point, such as Woods metal and be castintothespacebetweenthetubewall I and the radiator 8 so as to form a binder between these parts.

The blackened surface 6 readily radiates the heat developed at the anode during the operation ofthe tube, andthemetalparts I, I andO,which are in good heat transferring relationship with each other, satisfactorily trannnit the heat absorbed by them so that the anode temperature remains at a comparatively low value, for example 500C. Forexamplainthecaseofananode temperature of 470 C., a heat radiation of 1.3 watts per sq. cm. of the sheath surface can be obtained. Hence the sheath surface 8, which has a surface area of about 100 sq. cms., can radiate continuously 130 watts at this temperature. This heat is readily dissipated by the sheath 9, and in some cases as shown, the protective sheath 9 may be provided with cooling fins 33 in order to further assist in the dissipation of heat. Furthermore, the sheath 9 may be secured to a suitable stand, a portion of which is shown at 95 to which the heat would be dissipated.

The vitreous portions 2 and 3 are covered by protective hoods II and I2 respectively of a material of high insulating properties, for example molded synthetic resin. Hood I2 comprises an internal member I3 which fits over portion 3, and an external member I5 having a projection portion I4 to which a high-tension supply cable 31 is secured. Similarly hood II comprises an internal member I3, and an external member I5 to which a high-tension cable 18 is secured.

As it is difficult, for manufacturing reasons, to give the vitreous portions 2 or 3 such an accurate shape that they will fit into members I3 and I3 without intermediate air space, a layer I8 of a hardened insulating cement, for example lead oxide, molding asphalt, or sealing wax, is provided to prevent the presence of air spaces.

Members I5 and I5 are mechanically secured to the metal member I so as to be either rotatable or stationary with respect to this member. For this purpose member I may be tapped for receiving screws I! (as shown at the lower end of member I) so that the member I5 is rigidly connected to member I. Alternatively, the screw ends may be located in a circular guide groove 49, as shown at the upper part of the figure, i. e. so that member I5 may be rotated on the member I3. Instead of being directly connected to the metal member I, members I5 and 15 may be either rigidly or rotatably connected only to metal sheath 11 which embraces metal member I, or they may not engage these metal parts at all.

Members I5 and I5 may be provided on their outer surface with a conductive coating which is connected to metal parts, I, I and '9, and may be grounded when the tube is in use. This connec tion may be effected by metal members 'I'I carried by members I5 and I5 and bearing upon the metal portion I. However, if the insulating hoods II and I2 are sufficiently thick such protective measures are unnecessary.

In the construction shown in Fig. i, the metalglass seals 62 and and insulating protective hoods II and I2 are not heated to an undesirable temperature because substantially all the heat developed in anode 4 is radiated to metal member I and dissipated thereby. Furthermore, the connection of the anode to the tube end is such as to prevent conduction of heat to the hoods. For this purpose anode 4 is supported by a thin-walled metal tube I9, for example of ferrochrome, having a wall thickness of about 0.5 mm. This tube, which is a poor heat-conductor, is not secured to glass part 2, but its upper end is secured to a metal insert mounted in a transverse disc 28 of ceramic insulating material, which is preferably a good heat-conductor, for example the material known under the registered trade-mark Calit," which is a pure iron free magnesium-silicate.

Disc 20 is secured to metal member I by a screw 18, so that any heat that may still be conducted through tube I9 as well as the radiant heat absorbed by disc 20 will readily pass to the member I. Insert 98 is connected through a thin conductor 2I to a small disc 26, for instance ferrochrome, hermetically sealed in vitreous portion 2 and connected to a conductor I8 of the hightension cable I8. As a result of this arrangement the anode end of the tube is always maintained at a low temperature.

The tube has a cathode structure which comprises an apertured cup-shaped focussing device 22 enclosing a filament 23, and which is supported by a thin-walled metal tube 25. Tube 25 is mounted in an insulating disc 24, which is similar to disc 28 and similarly secured to the metal part I. so that only a negligible quantity of heat will be conducted from the cathode to the cathode end of the tube.

As shown insulating discs 28 and 24 are provided with apertures I0, and with concentric grooves or corrugations to improve the insulating character of their surface and to avoid flashing-over along this surface.

It will be noted that metal member I forms with the insulating discs 29 and 24 an independent central chamber in which the electrodes are arranged. This chamber is not sealed from the remaining space of the tube but is connected thereto through apertures III. Thus, the vitreous portions 2 and 3 through which the supply conductors are passed in an air-tight manner, serve solely for sealing-in these conductors and for electrically insulating them from the metal portion I, and do not serve to support the electrodes. Furthermore, they are not subjected to an undesired degree of heat.

One end of filament 23 is connected through a supply conductor 21 to a metal ring 29 which is sealed at one end to vitreous portion 3. The other end of the filament is connected through a conductor 28 to a cup-shaped metal contact 30 sealed through a vitreous ring 3I to ring 29. Ring 29 is embraced by a contact bush 32 molded in member I5, whereas a contact plug 33 carried by member I5 engages contact 38. The bush 32 is electrically connected to a tubular conductor 34, and plug 33 is secured to a central conductor 35. Conductors 34 and 35 are insulated from each other by an intermediate tubular rubber piece 36 and pass on with the'latter into the high-tension cable 31, whichis provided with a woven metal covering 80.

To avoid flashing-over between the parts under tension, for instance ring 29 and member I, along the separating surface of the parts I5I3 and '|3'|5, these parts are provided, as shown in the drawings, with interfitting concentric extensions and recesses 9|. In this manner a long leakage path is obtained from the high-tension parts along the separating surface to the external surface of the hoods II and I2.

As stated the insulating disc 20 protects the anode end of the tube against direct radiation of heat from the anode. To prevent this disc from being heated by the extreme heat radiated from the anode, a metal screen 38 is provided, which screen absorbs a considerable part of the thermal rays which would otherwise strike this disc. Screen 38, which may be made of copper, has a flanged end secured between the flange of metal portion I and the disc 20. Thus, screen 38 is in good heat transferring relationship with metal part I and consequently is cooled thereby.

The surface of the screen 38 which is nearer the anode and the surface of the anode which is nearer to the screen 38 may also be blackened in order to assist in the transmissiorf'oi' heat from the anode to the metal member I via the screen 38.

We have found that the invention makes it possible to construct diagnostic X-ray tubes of normal power whose length is only half and weight is less than one third that of present day X-ray tubes. More. particularly the tube shown in Figure 1 may have a length of about 35 cms. and a weight or about 6 kg., and is capable of being loaded to 6 kw. with a voltage of 100 kv.

The X-ray tube illustrated in Pig. 2 has an envelope comprising a cylindrical-shaped metal wall portion 4| whose ends are fused at N and .4 to glass portions 42 and 43. Hermetically sealed into portion 4| is a window 44 of X-ray transmitting material which serves to allow for the exit of X-rays.

The tube also comprises a copper anode 45, which carries a tungsten target 4|, is provided in themanner described above with a blackened sheath surface 41, and is supported by a thinwalled metal tube 48 from a copper member 4!. Secured to member 4! is a ring 66 of ferrochrome whose edge is fused to portion 42 to form a metalglass seal 94.

Tube 48, similar to tube is of Fig. l, is a poor heat conductor, and m the member 4! has a comparatively highthermal capacity, this member does not quickly acquire a high temperature. As a result the upper or anode end 01' the tube is always maintained at a suiilciently low temperature when the tube is in use. Thus it is possible, in a manner similar to that set forth with reference to Fig. l, to provide the X-ray tube with insulated protective hoods (not shown) and without using circulating cooling means.

To prevent the anode end of the tube from being deleteriously aflected by direct radiation of heat from the anode, a metal screen 50, which is similar to screen 38 of Fig. l, is supported from member 4|. Glass portion 42 and the metal-glass seal 94 are also prevented from being struck by thermal rays and electrons by an enlarged portion 5| of the member 49.

The X-ray tube also comprises a cathode structure having an apertured cup-shaped metal vessel 52 which is sealed to the glass part 43 to form a metal-glass seal 58, and which serves as a focusing device for the cathode rays. Within vessel 52 is a filament 53, and a tungsten plate 54 which pre- 45. vents axial exit of the X-rays. One end of filament 53 is connected through plate 54 to a supply lead 55, and its other end is connected to a supply lead 56 which passes through plate 54 in an insulated manner. Leads I5 and 54 are sealed in a pinch 51 forming part of glass portion 43.

At the rear of metal vessel 52 and supported thereby is a screen 59 which protects the seal Bl against bombardment by electrons. A metal ring ill secured to the metal part 4| together with a 65 bent-out edge 6| of screen 59 serve to protect the glass part 43 and the metal-glass seal 84 against radiation of heat and bombardment by electrons.

The ends of the tube may be provided in the so manner shown in Fig. l with protective bodies of insulating materials (not shown) to which are secured supply cables insulated to withstand high tension. These bodies may be secured to the metal part 4| either rigidly or rotatable in the o5 manner described in Fig. 1. Also the metal portion 4| may be covered with an X-ray-protecting layer and a metal sheath in the manner shown in Fig. 1.

The metal part 4| readily transmits the heat 70 received by radiation from the anode 45, and the ends of the tube are always maintained at a relatively low temperature because they are protected against thermal radiation, and the anode is connected to the anode and of the tube only through 78 the tube 48 which is of poor heat conductivity.

In order to maintain the temperature of the seals II and 44, as well as glass portions 42 and 43 as low as possible, the metal portion 4| is provided with thin elongated edges '4 and I which constitute an increased resistance to heat flow. 5 Thisisalsothecaseinldg. 1.

While we have described our invention in connection with specific examples and in connection with X-ray tubes, we do not wish to be limited thereto, but desire the appended claims to be 10 construed as broadly as is permissible in view of the prior art.

What we claim is:

1. An X-ray tube comprising an envelope having a metal portion and vitreous portions sealed 15 together, electrodes within said tube including a massive anode of a material of good heat conductivity, said anode being surrounded by said metal portion with its sheath surfacein good heat-radiating relationship therewith, members go of insulating material covering said vitreous portions, a current-conducting member electrically connected to said anode and passing through one of said members of insulating material, means including a coating of black material on at least as 75 sq. cms. of said sheath surface for transferring to said metal portion by radiation a major portion of the heat developed in said anode during the operation of the tube, and means to obstruct the transfer of heat from said anode to 80 said current-conducting member and members of insulating material.

2. An X-ray tube comprising an envelope having a metal portion and vitreous end portions, electrodes within said envelope including a mas- 5 sive anode of a good heat-conductive material, said anode being surrounded by said metal portion with its sheath surface in good heat-radiating relationship therewith, means to completely transfer to said metal portion the heat dissipated 40 from the anode during the operation of the tube, said means including a coating of a black material on the sheath surface of the anode, and supporting means for said anode, said latter means being within the envelope and directly 45 connected to said metal portion.

3. An X-ray tube comprising an envelope having a metal portion and vitreous end portions fused thereto, electrodes within said envelope including a massive anode of a good heat-conduc- 60 tive material, said anode being surrounded by said metal portion with its sheath surface in good heat-radiating relationship therewith, means to transfer to said metal portion by radiation a major portion of the heat developed in said anode during the operation of the tube including a coating of a material of good heat-radiating properties on at least 75 sq. cms. of the anode sheath surface, and means supporting said anode from said metal portion including a transverse memher of ceramic material.

4. An X-ray tube comprising an envelope having a metal portion and vitreous members fused thereto, electrodes within said envelope including a massive anode of a good heat-conductive B5 material, said anode being surrounded by said metal portion with its sheath surface in good heat-radiating relationship therewith, means to transfer to said metal portion by radiation a major portion of the heat developed in said anode during the operation of the tube including a coating of a material oi good heat-radiating properties on at least sq. cms. of the anode sheath surface, and means supporting said anode from said metal portion including a transverse mem- 7s ber of an insulating material of high heat conductivity.

5. An X-ray tube comprising an envelope having a metal portion and vitreous end portions sealed thereto, electrodes within said envelope including a massive anode of a material of good heat-conductivity, said metal portion surrounding said anode and being in good heat transferring relationship with the sheath surface thereof, means to transfer to said metal portion the major portion of the heat developed in said anode during operation of the tube, and means to support said anode from said metal portion including a transverse member of insulating material of high heat conductivity provided with corrugations.

6. An X-ray tube comprising an envelope having a metal portion and vitreous end portions sealed thereto, electrodes within said envelope including a massive anode of a material of good heat conductivity, said metal portions surrounding said anode and being in good heat transferring relationship with the sheath surface thereof, means to facilitate the transfer of heat from said anode to said metal portion including a coating of a black material on the sheath surface of the anode, and means to obstruct the transfer of heat from the anode to the adjacent vitreous portion including a metal screen secured to said metal portion.

7. An X-ray tube comprising an envelope having a metal portion and vitreous end portions, means to insulate said end portions comprising members of insulating material fitting over the end portions and insulating filling material between said members and vitreous portions, electrodes within said envelope including a massive anode of a material of good heat conductivity, said metal portion surrounding said anode and 40 being in good heat-receiving relationship with the sheath surface therewith,-means to facilitate the transfer of heat from said anode to said metal portion including a coating of a black material on the sheath surface of the anode, and means 45 to obstruct the transfer of heat from the anode to the adjacent vitreous end portion and insulating member.

8. An x-ray tube comprising an envelope having a central metal portion and vitreous end por- 50 tions fused thereto, a member of insulating material covering each of said vitreous portions to shockproof the tube, electrodes within; said envelope including a massive anode of a material of good heat conductivity, said metal portion sur- 55 rounding said anode and being in good heat receiving relationship with the sheath surface thereof, means to increase the heat radiating properties of the sheath surface of the anode, a

transverse member of an electrical-insulating material of good heat conductivity-secured to said metal portion and carrying said anode, and

, means to prevent the transfer of heat from said anode to the adjacent vitreous end portion, said latter means including said transverse member.

9. An X-ray tube comprising an envelope having a central metal portion and vitreous end portions, an anode within said envelope, said anode being of good heat-conductive material, a cathode within said envelope, a contact member carried by each of said vitreous end portions, a current conductor of poor heat conductivity connecting said anode to one of said contact members, said metal portion surrounding said anode and being in good heat-receiving relationship with the sheath surface of the anode, and means to facilitate the dissipation of heat by radiation from said anode to said metal portion including a coating of black material on the sheath surface of the anode.

10. An X-ray tube comprising an envelope having a metal central portion and vitreous end portions, a member of insulating material fitting over each end portion to insulate the same, electrodes within said envelope including an anode body of a material of good heat conductivity, a contact member at the vitreous end portion adjacent the anode, a current lead of poor heat conductivity connected between said anode body and said contact member, said metal portion surrounding said anode and being. in good heat-receiving relationship with the sheath surface thereof, means to facilitate the transfer of heat from said anode to said metal portion including a coating of a black material on the sheath surface of the anode, and means to obstruct the radiation of heat from the anode to the adjacent vitreous end portion.

11. An X-ray tube comprising an envelope having a metal portion and a vitreous end portion fused theretopelectrodes within said envelope including an anode of a good heat-conducting material and having a cylindrical sheath surface, said anode being surrounded by said metal portion with its sheath surface in good heat-radiating relationship therewith, a contact member carried by said vitreous end portion, an electric connection between said anode and said contact member, said connection having a low heat-conductivity to obstruct any appreciable transfer of heat from said anode to said contact member and vitreous portion, and means to completely transfer to said metal portion by radiation a major portion of the heat dissipated from said anode during the operation of the X-ray tube, said latter means including a coating of black material on the major portion of the sheath surface of the anode.

ALBERT BOUWERS. ADRIANUS VERHOEFF.

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