US2926269A - Rotating anode x-ray tubes - Google Patents

Description

Feb. 23; 1960* D. A. G. BROAD' 2,926,269

ROTATING ANODE X-RAY TUBES 7 Sheets-Sheet 1 Filed Feb. 18. 1957 BY wwxdhv knlw MIA 5% Feb. 23, 1960 D. A. G, BROAD ROTATING ANODE X-RAY TUBES I 7 Sheets-Sheet 2 Filed Feb. 18. 1957 Feb. 23, 1960 D. A. G. BROAD ROTATING ANODE X-RAY TUBES 7 Sheets-Sheet 3 Filed Feb. 18. 1957 D. A. G. BROAD ROTATING ANODE X-RAY TUBES Feb. 23, 1960 Filed Feb. 18'. 1957 '7 Sheets-Sheei 4' Fig.5.

.Illill. Ill-I r 0 4 l Jw B) M a D. w-MMM 4 mam/57's Feb. 23, 1960 D. A. G. BROAD ROTATING ANODE X-RAY TUBES '7 Sheets-Sheet 6 Filed Feb. 18. 1957 Feb. 23, 1960 D. A. e. BROAD 2,926,269

ROTATING ANODE X-RAY TUBES Filed Feb. 18. 1957 I 7 Sheets-Sheet 7 M/VE/VTOE b man-1L ML 5r EM 5WWMMM ATTOE/VEX,

U ir SW P m Q 2,926,269 I G A QDE; A? T E Donald Anthony Gifford Broad, Cirton, Cambridge, Eng- "land, assignorto National Research Development Corr t d n an a q por t q 9 Gr a Claims priority, application Great Britain eb u ry 2 1956 7 Claims. (Cl. 313 -60) This invention relates to X-ray tubes with rotating anodes, and has for an object to provide an" improved design of tube in which more than one output'wm w maybe provided, each of wh'ch js Qasily accessible to a variety of X-ray diffraction cameras and spectrdm; eters as those inja modern vertically mounted stationary anode tube. i

Where a precession camera is being used, the minimum of obstruction by the tube casing and associated parts is highly desirable if a wide-angle X-ray diffraction pattern is to be produced. Furthermore, ,ifhbstruction is kept to a min um a roun he h ad c 'the bea d win ows a e ov de Q res te 9 e ca in 19 pass two beams simultaneously, two specimeu'sjriiay he examined at a time. Thus, in the field of protein erystal lography the invention permits the simultaneous use of o m r e p e /a s gn c m ra pe t g a nrecess on angles of 20? on opposite sides of the tube without any obstruction.

Conversely, where specimens have molecules of high molecular weightsay, greater thhhZjOflOOIjas in some proteinslow precession angles and low collimator apertures call for minimum vibration. One feature of the invention is an arrangement of tube in vibration iskept to a minimum.

Furthermore, stray energetic electrons, representing a considerable fraction of the total power input to the tube, are scattered from the rotor, andin order toprevent them from heating the casing in the tubilthey are absorbed in a cooled metal block surrounding the cathode system close to the rotor. This .block forms a part of the electron focusing system. The electron bombard; ment of the cooled block causes hydrocarbon and silicone oil molecules absorbed on the surface oflthle metal to decompose and form a very thin ,but strouglylt adherent layerofcarbonaceous matter which is extremely difficult to remove save by abrasion or the use of concentrated hydrofluoric acid. It is desirable for the electrical stability of the tube to remove thislayer about every 2000 operational hours and it is difiicult to dotthis in situ without contaminating thebody of the wtubeby acidvapour's or abrasive materials. h

The present invention accordingly further aims at facilitating the servicing of the rotor and block {by mounting oneor both of these components on ,a separate and detachable carrier plate which closes clearance aperture in the front wall of the casing. A vaeuum seal is located bet en h ar e Plat en 'the said t ea wall around the said aperture. {The carrier plate can then be removed together with .the rotor as ,a unit. When, as is preferred,,the cooled block isIalsoattached to the carrier plate the' c asingabove thelfdfi r ex} tended upwards by an amount equal tojth'e depth ofjhe coo e toa l w h c ri iplt t be i be dr withdrawal in order to disengage thefb o'm the cathode system. This arrangementallows plug-1n conisw e s 1 e? t ru e 9991??? witi d he 2,926,269 Patented Feb. 23, 1960 2 the assembly may be withdrawn after the coolant has been drained with the minimum of inconvenience.

An alternative system in which the carrier plate is not first lifted before withdrawal, involves retraction of the cathode system and its relocation on accurate register surfaces. This "system is less desirable since the alignment of the cathode shield With thecooling .bloc'l; cannot be observed'visually. r

"Th esent invention, stated generally, is a rotary anode X-ray tube comprising a single or free-standing hollow pressure-tight casing carrying the anode assentbly, 'incln'ding'a fluid-cooled [rotor journalled therein, and housing the cathode system. The cathode system is carried on a metal support column .Within the casing and terminating vclosejto the anode. .The said casing has connectionsfo'r acooling fluid circulating pump and a vacuum pump at or near its end remote from the'anode rotor. The space surrounding the tube from the table in which it is mounted to the point of emergence of the X-ray beams is entirely free from obstruction radially outwards from the. tube throughout 360.

Windows for the emergence of X-rays are preferably located in the casing in such positions that they view the focus of the incident electron beam from four directions. Thus, they view a line focus endwise or sidewaysfand compass an angle of emergence ofX-ray between 201 and '10? from the plane'tangential'to'tlie rotor surface at: thefocus;

'Advantageously, the vibration inherent in the drive to the rotor is balanced out by locating the motor on the lower part ofithe casing, and mountinglthe'latter by a'suspension which absorbs lateral vibration. The mass ofithecasing audits contents is made approximately equal to that of the motor, whilst the lengthwise forces due to inequalities in the driving belt are taken'through the casing-itself, and cancel each other out. r

Practical embodiments of'the"inve'ntion will now b particularly described with reference'to the'accoinpany ing drawings in which: i

Figure 1 is 'a fragmentary exploded perspective view of the upper part of a first form of tubecasing with'the carrier plate, rotor, and block detachedj" T Figures 2 and'3a're side and'frontelevations respec- V ppe p of the tube;

-Fi'gure4"is a'vertical'section, on the line IV-IV of Figurefifwith some parts broken away; *Figure 5 is a viewsim'ilar to Figure 3 but with belt""cover removed;

" Eigureifi is asectional plan on the .1ine.VI- VI-of iiFigure 7 is a section through a detail on the line' igure 8 is a section of a detail on the line VIIIVI1I of Figure 6; i Figure 9 is an enlarged view of part of Figure 4 sh'owi'nglthe upper end ofthe casing and therotor "fFigu're "10'is a view similar to Figure 4 of a'modified constrhctiouoftube; "Figure 11 is a fragmentary front elevation of the tube 0r igure-'10; and 1 2 is a"fragmentary plan view of Figure 11.

fi s a embly u es 1- Thecasing 1 is pressure-tight and, of rectangular crossection,"'andis mounted in any convenient manner-"id e. horizontal bench o'r'table 2, through an opening 3 in which"'it'extends vertically from a mainheader 4 below the bench. The header 4 is connected to a conventional vacuum pump (not shown) and also serve's asa foundatio n fo an electric motor 5 for driving the water-cooled em r'sth reuglrap n 7 m pulleys s, i

The rotor 6 is cup-shaped and is carried in bearings 10 (Figure 4) in a boss 11 formed integrally on the inner surface of a carrier plate 12, and having an oil trap groove 11a around its outer circumference. Similar grooves 6a are formed around the internal cylindrical wall of the rotor. The plate 12 is rectangular, of the same width as the front wall 1a, and of a depth suflicient to extend from the level of the top 1b of the casing to a point below the level of the bottom edge of a hollow copper block 13. This block consists of an inner cylindrical liner 14, concentric with and surrounding the electron emitting end of the cathode system 15, and an outer rectangular block 16. The space 17 between the liner 14 and block 16 is closed at the top and bottom and constitutes a water jacket which is divided by a helical baffle 18. The top surface of the block 13 is saddleshaped, as seen at 13a in Figures 4 and 5, and is apertured in four places 19 to permit passage of anX-ray beam to each of four windows 20, one in each wall of the casing 1.

The water-cooled block 13 is attached to the back face of the carrier plate 12 and is detachable therewith when servicing is required. Cooling water is supplied to the jacket 17 through an inlet port 21 in the front of the block 16 and exhausted through an outlet port 22. These ports register with respective ducts 23, 24 formed by grooves machined in the thickness of the plate on the front surface thereof and covered by flush-fitting plates 25, 26 respectively. Into each duct opens .a T- branch 27, 28 of a corresponding union 29, 30 to be more fully described below. Each union serves to connect main riser and return pipes 31, 32 respectively both with the block jacket 17 and with the rotor coolant injection head 33 details of which are given later.

In order to permit insertion or withdrawal of the rotor 6 and block 13 into or from the casing 1, the front wall 1a is apertured at 34, leaving a roughly pear-shaped opening around which runs a shallow groove 35 which accommodates a resiliently deformable sealing element of known material. The back surface of the carrier plate 12 and the front surface of the front casing wall 1a are rendered as flat as is conveniently possible so that the inequalities to be absorbed by the seal 35 are reduced to a minimum. The carrier plate 12 is shown as being secured by studs at 36, at the top of the casing 1, and by a tongue and groove joint 37, 38 along the bottom edge of the plate 12, the groove 38 being formed in a transverse locating strip 39 secured to the front face of the front wall In of the casing 1 (see Figure 1). Steady blocks 40 are formed integral .with this strip 39 at each end thereof and are drilled vertically to allow the insertion, with radial clearance, of the upper ends of the main riser and return coolant pipes 31, 32. Lateral location of the bottom edge of the carrier plate 12 is ensured by the short parallel portions 34a at the bottom of the opening 34 between which the sides of the block 13 fit closely.

The upper ends of the main riser and return coolant pipes 31, 32 carry plugs or nozzles 41, 42 respectively (see Figures 1 and 6). These nozzles are shaped to enter corresponding sockets 43, 44 in the union blocks 29, 30, these sockets containing captive sealing rings 45 which are resiliently compressed by the nozzles 41, 42 as they enter the sockets. This arrangement enables the coolant circuit to be broken on lifting the carrier plate 12 prior to its bodily removal from the front of the tube casing 1. The sockets 43, 44 in the union blocks 29, 30 are continued up through the blocks and terminate in nipples 46 to which are connected flexible coolant pipes 47 leading to and from the rotor coolant injector head 33.

As seen best in Figure l, the height of the opening 34 in the front wall 1a of the casing 1 is greater than the overall height of the top of the rotor 6 above the bottom of the cooled block 13 by at least the vertical CTI distance through which the block must be raised to clear the tip of the cathode system 15. The rotor and block assembly can thus be detached from the casing by undoing the top screws 36, sliding the plate 12 upwards to disengage first the tongue 37 from the groove 38 and then the block 13 from the cathode system 15. During this movement, the plug and socket connections 41, 43 and 42, 44 in the coolant circuit are separated.

When the block 13 is clear of the cathode system 15, the rotor and block can be drawn out as a unit for servicing or replacement of worn parts without disturbing any of the high tension components or the main vacuum circuit. For remounting, the reverse procedure is followed.

Rotor coolant circuit (Figure 9) The anode rotor 6 is carried on a hollow shaft 48 which is integral with the driven pulley 9. The rotor has a flanged hub portion 49 which surrounds with clearance the outer surface of the boss 11 and has a number of radial grooves 50 machined on the rear surface thereof. These grooves are closed, to form coolant flow channels, by a cup-shaped baffle 51 bolted to the rear surface of the rotor hub 49. The side wall 52 of the baflle is of greater internal diameter than the central part of the hub 49, and of less external diameter than the rim of the hub flange 49a. The latter carries a copper sleeve 53 the outer cylindrical surface of which constitutes the anode surface. The rear end of this copper sleeve is closed by a back cover plate 54 which lies behind, and clear of, the baffle 51 so as to leave a coolant flow space 55 between them.

Through the pulley 9 and the tubular shaft 48 passes, with clearance, a water injector tube 56, the inner end thereof being located in a synthetic resin plastic hearing bush 57, preferably of a phenolic resin, secured in the baflle 51 and forming a liquid seal between the tube and the baffle. A small cone 58 is fixed in the back cover plate 54 on the rotor axis, whilst the bearing bush 57 is pressed into a conical boss 59 in the baffle 54. The two cones 58, 59 constitute water deflectors. The outer end of the water injector tube 56 is anchored in a central socket 60 in the hollow head 33, and an external water inlet connection 61 opens through the wall of the central socket 60. The connection 61 is coupled by a hose 47 to the water flow pipe hose union 29 (Figure 5). The hose is preferably of metal-braided flexible plastic.

The injector head 33 has an outer annular compartment 62 to which is sealed a short, stepped water return tube 63 the larger diameter portion of which is engaged by a water seal 64 within a cavity 65 in the pulley 9 whilst the smaller diameter portion fits into another synthetic resin plastic bush 66 which is tight in the tubular shaft 48 but which embraces the return tube 63 with the freedom of a bearing bush. A bleed hole 67 in the return tube 63 allows coolant to seep between the tube and the bush to act as a lubricant. A return connection 68 (Figure 5) opens into the compartment 62 and is connected by a hose 47 to the return pipe hose union 30 (Figure 5). The flow and return connections 61, 68 are rigid, ahdembrace an abutment or steady 69 secured in a bridge piece 70 bolted to the rotor chamber cover plate 12. The injector head 33 has a plane outer end face which bears against a corresponding internal surface of the bridge piece 70 which takes the axial reaction thrust on the water injector tube 48 as cooling water flows into the rotor 6 between the cup-shaped bafile 51 and the back cover plate 54. The steady 69 acts as a stop preventing rotation of the head 33 by frictional drag from the rotor, and at the same time accommodates within an axial counterbore spring-loaded carbon brush 71 which bears on the face of the pulley 9 and earths it. v

Since the end wall of the head 33 and the coacting fast f e b g P ece 70 are normal to the axis of the shaft-48, no lateral restr'aintis imposed thereby onthecoolant injector unit. Similarly, the stop 69 acts in a purely circumferential direction, so that the injector unit is entirely self centering. At the same time it is compact,

with a minimum of external projection.

Vacuum seal for rotor (Figure 9) During operation of the tube, the casing 1 is continuously evacuated through the trunk 4 by a high vacuum pump (not shown) of known design. Whilst the joints in the casing itself can, by careful attention to detail in design and construction, be rendered reasonably leakproof, leakage past the rotor bearing is more difficult to overcome. Nor is the. problem confined to rotating anode X-ray tubes.

Attempts have been made to solve the problem by the use. of a rubber or like elastomer ring embracing a smooth shaft, but difficultly is frequently experienced in maintaining the efiiciency'of such seals over periods comparable with the working life of the other parts of the equipment. The term rubber as used herein is intended to cover both natural and .synthetic rubber and like elastomer sealing materials. Loss of efficiency seems to be primarily caused by a sudden rapid deterioration of the surface of the rotary shaft where it is engaged by the rubber ring. This deterioration is noticed even on hardened shaft surfaces, and several factors appear to contribute towards it.

A principal factor in seal deterioration under Vacuum conditions is the breakdown of the surface layer of the rubber sealing ring itself. Most commercially available rubber seal rings are made from a material having a fair percentage of carbon particles in the mass. This carbon initially holds an absorbed water film. As this evaporates under high vacuum conditions, rubber-to-metal contact ensues which results in localized heating and blistering of the rubber and roughening of the metal surface, since the lubrication between the rubber seal and the metal shaft is not in the nature of a true dynamic film, as is usual in air to oil seals. The evaporation of the oil film on the vacuum side at a greater rate than that at which it is replenished is thought to initiate breakdown.

The abrasive content of most commercial oil seals introduced to facilitate the bedding in of the seal on a soft shaft appears to make the above problems more acute.

Hence a further feature of the present invention is the use of sealing rings made from an elastomer material ferably a low coefficient of friction with steel. Preferred materials are hydrocarbon or chlorocarbon rubbers loaded with molybdenum disulphide or like anti-friction material, or alternatively, fluorocarbon rubbers having a naturally low coefficient of friction combined with high abrasive resistance.

Another factor is the degree of roughness of the shaft surface as presented to the stationary sealing ring, and this is divisible into two components-actual surface roughness and a virtual roughness due to radial vibration of the shaft, especially in high speed shafts running at, say, several thousand revolutions per minute. Substantial elimination of these components has been found to produce a marked prolongation in the life of the seal.

Hence, another feature of the present invention is a vacuum seal of the said rubber ring type in which the surface of the shaft is finished optically smooth and has a minimum eccentricity with respect to its axis of rotation, whilst the shaft is supported in one or more radially pro-stressed bearings having no ,play in the radial direction. Gyroscope grade ball bearings are preferred be cause of their high degree of accuracy and smoothness of running.

Figure 9 shows such a seal. The shaft 48 is a push fit within a sleeve 72 of high grade hardened steel such as is used for the manufacture of balls or rollers for bearings. The sleeve has reduced diameter end portions 73,

6 74, and a central seal portion- 75,, thQjSaidj-fifldS-Migg push fits in the inner races, of the respective gyroscope grade ball bearings 10.

The. external cylindrical surface of the seal portion 75, of the sleeve 72 is ground and polished to an optical finish, and both the ovality of the portion and its concentricity with the end portions '73, 74 are held to the closest precision instrument limits. The seal portion 75 is embraced by a pair of generally C-section elasticallydeformable sealing rings 76, 77 of known type, having V-shaped ridges 78 around their inner peripheries which bear radially inwards on the external surface of the seal portion 75. The material of these rings is a synthetic. rubber havinga minimum or preferably no abrasive particle content.

The rings 76, 77 face inwards towards each other and,

are axially separated by a thin spacer ring 79 which is gapped at one point 80 around its periphery, this gap. registering with a duct 81 in the boss 11 leading to a vacuum oil reservoir 82 mounted externally on the carrier plate 12 for the rotor 6. The reservoir 82 is mounted thereon by means of a threaded plug 83 which is counterbored from its inner threaded end to meet a diametral cross-bore 34 opening at its ends into a peripheral groove 85. This groove is in permanent communication with an outlet port 86 in the lower end of the reservoir 82, the upper end being closed by a vented filling plug 87. The walls of the reservoir are preferably of a transparent material so that the level of the vacuum oil therein can be seen. a

To fill the reservoir 82 a pump (not shown) is attached to the reservoir in place of the vented plug 87, and air is progressively withdrawn from the space between the sealing rings 76, 77 and from the duct 81 and reservoir 52 whilst oil is allowed to flow into the system to replace the extracted air, Air bubbles are thus eliminated, and the seal is full of oil.

Such a seal can be run for several hundred hours under high vacuum conditions without breakdown, thus pro longing by a considerable factor the length of Working life of the tube between successive overhauls. In practice, vacuum shaft seals according to the invention which were made from a normal commercial rubber mix and run on trued and polished shafts have operated at surface speeds at the seal of 750'ft./min. with lives of 300 hours average. On the other hand, seals that have been made from a carefully prepared mix have lived as long as 5000 hours without breakdown, indicating that average lives in excess of 1000 hours can be expected.

Experience indicates that the best steel for use as a shaft material in carrying out the present invention is a fine grain ball steel such as that known commercially as KB 839, which is hardened by mar-quenching, ground, honed, and finally lapped to mirror finish without visible scratches. Possible alternatives are metallic carbides and tungsten-nickel alloys such as that known by the registered trademark Stellite.

A suitable lubricant for a seal constructed in accordance with the invention has a base of a known vacuum coil or grease, such as apiezon, with the addition of a' long-chain aliphatic compound such as lithium stearate. Such a lubricant has a very low vapour pressure, whilst the aliphatic compounds may tend to remain in the seal longer than the base and so replace the initial water film, since they have an afiinity for the dewatered elastomer of, the seal ring.

Accessories The plate 12 carries a pair of ion gauges 88, 89 (Figures 1 and 5) for measuring the degree of vacuum in the casing 1. These are mounted close to the rotor 6, and one or both may use the rotor itself as the anode, so that early warning can be obtained of contamination of the cylindrical surface 53 of the rotor and incipient arc-over conditions.

1 Instead of two ion gauges 88, 89 one may be replaced by a metal evaporator. This enables the operator himself to apply a desired metal coating to the cylindrical rotor wall 53 to form the anode surface on the rotor 6 when vacuum conditions have been established in the tube. This method of applying an anode coating to a copper rotor 6 dispenses with the necessity for electroplating the rotor before assembly when radiations of a characteristic other than copper are required, and enables co'atings to be used which would normally be unstable in air, or which can be plated on only with difficulty.

The coating of the anode rotor in situ by an evaporation technique such as that suggested above has particular advantages where emission which is characteristic of a high vapour pressure metal is desired, but which it would be diflicult to obtain from a stationary anode tube owing to the high temperature generated in the anode-exceeding, say, 200 C.for a reasonable beam current. The coating thickness is of the order of 0.001 inch.

Examples of metals which can with advantage be thus evaporated onto the anode rotor fall into three main categories:

Difiicult to plate.

Plating technique unknown.

]Easier to evaporate than to plate.

Before the rotor surface can be thus coated, its surface must be prepared in order to provide the required degree of adhesion for the evaporated coating. Any known technique can be employed for this purpose such as bombardment thereof by hydrogen ions in a gas discharge. Evaporation is then carried out in vacuo.

An inspection window 90 (Figures 1 and 2) of lead glass is inserted in a side wall of the casing 1 at the level of the axis of the rotor to permit visual examination of the anode surface. An instrument panel 91 is mounted on the top of the casing 1 to carry, say, beam current and vacuum gauge milliameters 92, 93 and sundry telltales or controls 94. The instruments 92, 93 may be repeaters or the main instruments for the control of the tube.

A cover plate 95 (Figures 26) which encloses the whole of the front face In of the casing 1 including the belt 7 and flexible pipe connection 47, is held in position at its top end by nuts 96 on captive studs 97 and has a slot 99 opposite the transparent vacuum oil reservoir 82. A hole 100 (Figure 4) in the top of the cover permits access to the reservoir filling screw 87. A further aperture 101 opposite the front beam emission window 20 allows clearance for a beam shield 102 which projects forwards from the plate 12. A shutter (not shown) may be provided for each beam window 20 to stop unwanted emission.

A jockey pulley (not shown) can be arranged to bear against the slack side of the belt 7 which can operate a micro-switch for cutting off the tube should the belt be broken.

Modified assembly (Figures 10-12) Figures 10-12 illustrate an alternative construction to that shown in Figures 18. In this construction, the casing 1 is of generally circular section, and is supported with its axis vertical by means of a flange 103 which is screwed to the underside of a horizontal bench 3. Below the flange 103, the casing is apertured at 104 and a pipe connection 105 is brazed onto the casing for connection to a conventional vacuum pump (not shown). The mounting flange 103 also serves as a union between fiow and return pipes 31, 32 respectively of a water cooling circuit and corresponding connections 106, 107 to the water pump (not shown).

The upper end of the tube casing 1 is sealed to a thick copper sleeve 13a which is surrounded by a water jacket 17a into which open the flow and return pipes 31, 32. This assembly of jacketed copper sleeve 13a, 17a constitutes a cooling block for absorbing stray recoil electrons from the anode. The upper end of the sleeve 1.3a projects into a drumlike chamber 108 sealed onto the sleeve with its axis horizontal and constituting a head for the X-ray tube. The flow and return pipes 31, 32 continue upwards at 31a, 32a from the top of the water jacket 17a and are bent around the chamber 108, being preferably at least partly embedded in the chamber wall.

The top edge of the copper sleeve 17a is notched in four equiangularly spaced places 19 which embrace corresponding window apertures 20 for the emergent X-rays. The anode rotor 6 is carried in bearings 10 housed in a central boss 11 on a front cover plate 12 of the anode chamber 108, and its cylindrical wall 53 runs close to the top edge of the copper sleeve 13a. The rotor 6 consists of a main flanged cup 49 the rear wall of which has a numbersay, six-of radial channels 50 machined therein. A shallow cupshaped baflle 51 is bolted to the back of the hub 49 to close the open sides of the channels 50 so that the latter form radial ducts, the side wall 52 of the baffle being of greater internal diameter than the external diameter of the hub 49, and of external diameter less than the internal diameter of the cylindrical copper wall 53 of the rotor so as to define a tortuous flow path (indicated by arrows) for the cooling water. A back cover plate 54 is mounted on the rear end of the copper wall 53 so as to leave a water space between its front surface and the back surface of the cup-shaped bafiie 51.

The rotor 6 is carried on a tubular shaft 48 mounted and vacuum-sealed in the manner shown in Figure 9. The end thrust on the coolant injector head 33 is taken by a circular plate 109 integral with a part-cylindrical bracket 110 bolted to the cover plate 12 by the flange 111. This bracket embraces, with normal working clearance, the lower half of the circumference of the rotor driving pulley 9 (here shown grooved) which is driven by a V-belt 7 from a motor (not shown) located above, and clear of, the tube casing 1, although it will be understood that, if preferred, the motor may be mounted at the lower end of the casing, as shown at 5 in Figure 4.

The rotor and water injector assembly can be removed as a unit for inspection and cleaning by removing the rotor chamber cover plate 12. There is a breakablev labyrinth-like vacuum seal 112 between the plate 12 and the casing 1 which is constituted by a synthetic resin plastic gasket, the opposed surfaces of the plate 12 and the casing 1 being complementarily grooved to give a serrated appearance to the gasket in radial section.

General may be spoiled. This is particularly evident when usingsmall collimator apertures at low precession angles of the camera.

is intended to run at fairly high speed-of the order of Careful attention to the dynamic balanceof the rotor 6 and the smoothness of the bearings 10, can do much to minimise vibration, but since the rotor 3000 r.p.m.-belt slap in the driving belt 7 will inevitably occur, and will be difficult to damp out.

The cathode system may be displaced to one side of the vertical axis of the casing 1.while the electron beam remains radial to the rotor 6. Thus, whenthis beam is horizontal, two lateral and one upper window only are possible, the latter being set normal to the upward emergent beam at the top of the casing. The cathode may be located so as to bombard any portion of the cylindrical wall 53 of the rotor, and may even be mounted vertically above the top of the casing to bombard the rotor 6 on its upper arci.e. either assembly described above may be inverted and suspended above the bench 3 at a convenient height, which may be adjustable. -An X-ray tube according to the present invention operating at 50 ma. and 35 kv. peak anode volts at 50 cycles with a rotor speed of 3000 rpm. has an output beam intensity times that of a standard modern stationary anode tube. By increasing the electron beam current to 120 ma. and operating at 35 kv.-, D.C., the output beam intensity is raised to 70 times. An X-ray examination requiring 200 hours continuous running with a stationary anode tube has been completed, using a tube according to the present invention, in 10 hours.

I claim:

1. A rotating anode X-ray tube comprising a single straight vacuum-tight casing; a cathode assembly projecting axially into said casing from one end; a cathode mounting on the casing at the said end; a fluid-cooled electron-absorbent block within said casing and surrounding with clearance the beam emitting end of the cathode assembly; a hollow anode rotor having coolant flow passages therein; a plate carrying said rotor and said cooled block; an aperture in a side wall of the casing adapted for the passage of said rotor and said cooled block; avacuum seal surrounding said aperture for engagement by said plate; means for detachably securing said plate to said casing so as to seal said aperture; a stationary coolant injector opening through said plate into the interior of said rotor; flow and return pipes for coolant fiuidcommunicating between said injector and a point adjacent said cathode mounting; coolant circuit connections in said plate to said flow and return pipes for supplying coolant to said block in parallel with said rotor; a vacuum connection opening into the interior of said casing adjacent the cathode mounting; means on said casing for driving said rotor; and a plurality of windows for emergent beams, said windows being located in said casing with their centres on a common plane normal to the mean axis of the cathode beam and substantially tangential to the cylindrical surface of the rotor.

2. An X-ray tube according to claim l'wherein the aperture in the casing is of sufficient extent toallow the plate to be moved parallel to the aXis of the cathode assembly until the end of the block remote from the anode surface is clear of the tip of the cathodeassembly.

3. An X-ray tube according to claim 2 wherein the coolant circuits for the rotor and the cooled block are commoned at two points on the plate, and the said points are connected to the corresponding sections of the circuit on the fixed part of the casing by separable connections.

4. An X-ray tube according to claim 3 wherein the aperture in the casing is narrower at the part which embraces the cooled block and the vacuum seal between thedetachable plate and the casing wall follows a contour which also narrows around this part of the aperture, the common points of the coolant circuits lying outside the line of the seal and being connected to the.

coolant space within the block by respective ducts formed in the thickness of the detachable plate and each crossing the line of the seal.

5. A rotating anode X-ray tube having a single straight vacuum-tight casing, a cathode assembly mounted in the lower end of said casing; a vacuum connection to the interior of said casing adjacent the point of entry of the cathode assembly; a hollow anode rotor journalled in said casing adjacent the emission end of said cathode assembly; a motor for driving said rotor mounted on the lower end of said casing; a stationary cooling fluid in jector communicating with the interior of the rotor; flow and return pipes passing along the casing wall between the injector and a location adjacent the vacuum connection; and a fluid-cooled electron absorbing block lining the walls of said casing at the level of the cathode focus ing system and the point of impingement of the cathode beam on the rotor.

6. An X-ray tube as claimed in claim 5 wherein the casing is provided with mounting means at a point intermediate the rotor and its driving motor.

7. A rotating anode X-ray tube comprising a single upright vacuum-tight casing; an electron gun assembly projectinginto said casing from the lower end thereof; a fluid-cooled electron-absorbing block lining the internal walls of the casing adjacent the electron gun; a hollow-walled cup-shaped rotor mounted for rotation about a horizontal axis in the upper end of said casing and means for circulating coolant fluid through said block a and the inter-wall space in said rotor including a stationary injector head having a pair of rigid external lateral projections constituted by coolant fluid flow and return connectors and a plane outer end surface normal to the axis of rotation of the rotor; a fixed stop member mounted on the casing between and engageable with both said projections to prevent rotation of the injector head r with the shaft, and a fixed abutment mounted externally in said casing to engage said plane end surface.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Taylor: A 5 kw. Crystallographic X -Ray Tube With a Rotating Anode, article in Scientific Instruments, vol. 26, July 1949, pages 225 to 229.

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