US2488200A - Rotating vacuum seal - Google Patents

Description

Nov. 15, 1949 G. A. JUHLIN ET AL 2,488,200

ROTATING VACUUM SEAL Filed May 24, 1947 J6 J H 20 E J 1 J6 5 25' ri 16' 22 f A 29 26 2 i -1 i i: 1 -1 f;

flo /2Z5? GusrAF A (/UHL/N (I've/4. A [444L655 Patented Nov. 15, 1949 ROTATING VACUUM SEAL Gustaf Adolf Juhlin, High Beck, Carrwood, Hale Barns, and Cyril Hubert Walker, Urmstron, Manchester, England, assignors to General Electric X-Ray Corporation, Chicago, 111., a corporationof New York Application May 24, 1947, Serial No. 750,314 In Great Britain July 1, 1946 The present invention relates in general to seals and sealing, and has more particular reference to the provision of means for sealing rotating, shaft-like members for the prevention of oil leakage along the member through a wall or journal in which the shaft-like member extends; and the invention has especial reference to the sealing of shaft-like members which extend through the walls of low pressure vessels, such as the envelopes of X-ray generators, particularly generators having rotating anodes driven by shaft means extending through an opening in the envelope and drivingly connected with drivi'ng means dispose-d outwardly of the envelope.

X-ray generators commonly comprise an electron emitting cathode element and a target'forming anode for receiving electrons emitted by the cathode. X-rays are produced in such a generatop as a result of electron impingement on the anode target. The anode and cathode, ordinarily, are enclosed within a sealed and evacuated en'- velope; in which the anode and cathode may operate under substantial-1y vacuum conditions. Provision for rotating the anode of an X-ray generator is frequently desirable so that the anode, at any instant, may receive electrons upon a portion only of the target area, the target being of annular configuration so that when rotated the target may be continuously moved to progressively' present adjacent sections thereof in position for electron bombardment, and thereby pre-. vent overheating of the target area. 'El'ectron bombardment of the target, of course, results in the creation of excessive heat at the electron receiving surface portions of the target area under electron bombardment;- and by progressively shifting the target area an opportunity is afforded for allowing each successively bombarded. portion of the target area to cool off before being again exposed to electron impingement when it is again presented in position to receive electrons during a successive rotationof the anode An important object of the present invention is to provide an X-ray generator having arotating: anode mounted within an evacuated envelope, including: shaft-like means. connected with the anode andextending outwardly of the; envelope for connection with anode: turning means, and an improved seal arrangement for sealing the opening, in the envelope walls, through. which the shaft-like means extends, against. fluid leakage along the shaft-like means and through said opening. a

Another important object is to provide animproved seal structure, particularly for vacuum, or

6- Claims. (01. 250'-148)' low pressure, vessels; a further object being to utilize a plurality of liquid seals in spaced apart, tandem arrangement along the shaft-like means in the envelope opening through which such means extends. In combination with pressure reducing means for exhausting the space around the shaft-like means, between the spaced liquid seals.

Another important object is to utilize a manometer seal, for shaft sealing purposes in a low pressure vessel; a further object being to utilizea manometer seal charged with fluid of high viscosity; a still further object being to arrange the manometer seal to minimize fluid movement therein through centrifugal action imparted by relative rotation of the sealed parts; and a still further object being to" limit the pressure differential on opposite sides of the seal to thereby maintain the length of the manometer seal legs within reasonable limits.

Another important object is to employ an atmospheric seal in combination with a manometer seal, as by arranging the manometer and atmospheric seals in series or tandem arrangement within the opening to be sealed aroundthe shaftl'ike member, with the atmospheric seal disposed in said opening outwardly of the manometer seal.

The foregoing and numerous other objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection withthe accompanying drawing, discloses a preferred embodiment of the-invention.

Referring to the drawings? The single figure of the drawings is a sectional view through an X-ray generator embodying the 7 present invention.

To illustrate the invention, the drawings show an electronic device comprising an X-ray generator it, although it will beunderstood that. the invention is not necessarily limited, in all of its aspects, to X-ray generators, someof the features of the present invention having general application wherever effective shait sealing functions are desired. The drawings, however, show that the generator It may comprise a sealed en'- velope l2 forming a target chamber l2 in which an electron emitting cathode I 3 maybe-mounted and enclosed. This cathode may be ofany preferred construction such as the electron emit ting' filament illustrated, such filament being suitably mounted and supported upon theenvelope and provided with leads preferably extending outwardly of the envelope for connection with an external source of filament energizing power, said leads extending through suitable lead seals on the envelope.

As shown the generator also comprises an anode 14 providing an annular target surface 15, said anode being preferably hollow to provide a chamber [6 therein and being mounted on a hollow shaft member I! which extends outwardly of the envelope through a preferably cylindrical sleeve-like envelope extension IS. The hollow shaft H at one end is sealed to the anode M in communication with the anode chamber l6; and a central pipe I9 is preferably mounted in concentric relationship within the hollow shaft ll so that by delivering a cooling fluid through the pipe 19 from outwardly of the envelope l2 and its extension l8, said fluid may be caused to circulate within the chamber NS for the purpose of cooling the anode and may pass thence outwardly of the envelope I2 and the sleeve-like extension I8 thereof through the hollow shaft l1, outwardly of the pipe IS. The present invention contemplates the application of sealing means 20 and 2| around the shaft l1 and within the envelope extension Is, the sealing means 20 being spaced with respect to the sealing means 2| and said envelope extension l8 forming a chamber l8 around the shaft l1 and between the seal means 20 and 2|. In the case of X-ray apparatus of the type in which the target I5 is adapted to be rotated from without the target chamber I2 by means of a shaft l'l extending through an aperture [8 in the wall of said chamber, and in some applications serving the additional purpose of affording facility for entry and exit of cooling medium for the target, it is usual for the degree of vacuum required in the target chamber to be of such high order that special sealing arrangements must be provided between the chamber wall I8 and the shaft I! in order to prevent ingress of unwanted gas or vapour.

The present invention consists broadly in combining a manometer or barometric-column type seal 20 with means for ensuring that the pressure difference to which the seal is subjected cannot exceed a predetermined value.

In practicing the invention there may be connected across the manometer seal 20, a pump 22, preferably of the diffusion or condensation type, having the characteristic that the pressure difference produced by said pump cannot exceed a predetermined amount. In this connection it is notable that diffusion pumps employing oil as working fluid are capable of producing a maximum pressure difference corresponding to an inlet pressure of the order of 10- mm. Hg, and an outlet pressure of the order of 0.4 mm. Hg, beyond which value the ump will cease to exert pumping effort. Accordingly, by employing such a pump in conjunction with a manometer seal as described the possibility of the pressure, across the manometer seal, being greater than, say 0.5 mm. Hg, in an extreme case, is precluded; and, in consequence, the manometer seal need only include relatively short manometer limbs or barometric column to accommodate the pressure difference involved.

Another feature of the invention resides in that, in utilizing amanometer seal 20, especially one charged with high viscosity fluid 23, to provide vacuum-tight sealing between a relatively stationary part and a rotatable part, such for example as between the wall I8 of a low pressure or evacuable vessel and a, shaft I! or other shaftlike member extending into said vessel, the (iividing wall 24 of the manometer, namely that which separates the manometer limbs or barometric columns, is arranged as part of, or to be secured to, the relatively rotatable part ll; such arrangement involves minimum tendency for rotary movement to be imparted to the sealing fluid 23, and thus minimization of the elfects of centrifugal force upon said sealing fluid. It will generally be desirable for said dividing wall 24 to be highly polished with a view to reducing friction with the sealing fluid which might otherwise give rise to rotation of said fluid and consequential unwanted centrifugal force effects. Advantageously, too, baflies may be interposed between the stationary and moving parts of the seal so as to minimize tendency for movement of the sealing fluid.

The invention also includes the combination of the two evacuable chambers 12' and I8, or equivalently an evacuated chamber subdivided into two compartments, which chambers or coinpartments are separated by the manometer seal 20, with the pump 22 of the condensation or diffusion type connected at inlet to one chamber or compartment l2 and at outlet to the other chamber or compartment l8 for limiting the pressure difierence between the chambers or compartments in the event of the development of fault. The chambers or compartments aforesaid may for example be constituted, one by the evacuable target chamber l2 of the X-ray apparatus of the rotating target type, and the other by the extension iii of the target chamber through which passes the shaft I! for rotating the target, and in some cases conveying cooling fluid into heat relation with the target. With the pump utilizing as its working fluid an oil of low vapour pressure, a pressure of 10- mm. Hg or lower can be maintained in the one chamber or compartment 12' while the pressure in the other chamber or compartment I8 is of the order of 0.02 mm. Hg or higher, the maximum permissible pressure difference between the chambers or compartments being limited to a value of the order of 0.5 mm. Hg.

In a convenient embodiment of the invention as applied to an X-ray apparatus of the rotatable target type, there is attached to the wall of the target chamber the tubular body l8, which is preferably of metal and through which passes the hollow shaft ll carrying the target and conveniently conducting cooling medium into and out of heat relationship with the target. The shaft [1 is suitably journaled, preferably in ballor roller-bearings 25 carried by the tubular body 18. The chamber [8 in the interior of the tubular body I8 is sealed from atmosphere, by the atmospheric seal means 2!, and from communication with the target chamber I2, by means of the manometer seal 20, in order to provide what is hereinafter referred to as the pump chamber H3. The atmospheric seal means aforesaid comprise two seals 26 and 21 accommodated in suitable housings attached to the interior of the tubular body. One of said seals 26 may for example comprise a gland packed with high viscosity low vapour pressure fluid 23 and utilizing a rubberlike sealing membrane 29 secured on the shaft I! and carrying a seal face bearing on a seal seat 30, on the sleeve l8, to minimize tendency of the sealing fluid to escape into the pump chamber. The other seal 2'! may be in the form of a gland packed with the high viscosity low vapour pressure fluid 28 and utilizing leather sealing mem- .5 brane 3| to minimize the escape of the sealing fluid to atmosphere, through the opening end of the extension l 8. Advantageously, a cavity formed between these two seals is filled with the high viscosity liquid 28 of low vapour pres sure. With the sealing arrangement described the pump chamber i8 is effectively sealed from atmosphere.

The manometer seal 20 is conveniently constituted by an annular receptacle for sealing fluid formedby an annular extension 32 attached to the internal surface of the tubular body [8, and an annular extension forming the partition 24, sealingl y attached to the outer surface of the shaft l1 and projecting into said annular receptacle 32 so as to subdivide the sealing fluid therein into two columns. As the sealing fluid for the manometer seal it is preferred to use a low viscosity liquid of low vapour pressure. For reasons hereinbefore referred to, the: dividing wall attached to the shaft is preferably highly polished, and stationary bafiles are interposed between said dividing wall and tubular body or tubular extension attached thereto.

The condensation type pump 22 is connected at its inlet to the target chamber [2' and at its outlet to the aforesaid pump chamber [8, between the manometer seal 2|] and the atmospheric seals aforementioned. In addition, a mechanical rotary pump 33 may be connected to the pump chamber to serve the dual purpose of removing any gas leakage past the atmospheric seals and of backing the condensation pump.

In normal operation the condensation and backing pumps maintain a pressure of the order of from 10- to 10* mm. Hg in the target chamber and a pressure of the order of from 0.04 to 0.1 mm. Hg in the pump chamber through which the target shaft extends, any leakage between the target chamber and pump chamber being prevented by' the manometer seal. Inasmuch as the condensation pump would cease to exert pumping effort in the event the pressure difference across the manometer seal exceeds a value of the order of 0.5 mm. Hg, adequate protection is afforded against possibiilty of breakage of the seal and discharge of sealing fluid into the target chamber, and in such manner as to obviatethe need for the manometer seal being constructed with relatively long limbs.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description; and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of demonstrating the invention.

The invention is hereby claimed as follows:

1. An X-ray generator comprising means forming a sealed and evacuated envelope having an opening, sleeve-like means forming an envelope extension sealed to said envelope at said opening and extending outwardly thereof, a cathode and a cooperating rotary anode mounted within the envelope, a shaft member drivingly connected with said anode and extending outwardly of the envelope through said opening and said envelope extension, primary seal means cooperatively connected with and within the extension and with said shaft member for sealing said shaft member within said extension, secondary sealing means disposed in said extension and around said shaft in spaced relation said primary sealing means, whereby to define av chamberwithin said extension, around said: shaft andbetween said primary and secondary sealing means, and exhaustmeans connected with. said chamber to maintain the same under predetermined low pressure conditions.

2. An X-ray generator comprising means forming a sealed and evacuated envelope having an opening, sleeve-like means: forming an. envelope extension. sealed: to said envelope at said opening and extending outwardly thereof, a cathode and a cooperating rotary anode mounted within the envelope, a shaftmember drivingly connected with said anode and extending outwardly of the envelope through said opening and. said envelope extension, primary seal. means cooperatively connected with and within the extension and with said shaft member for sealing said shaft member within said extension, secondary sealing means disposed in said extension and around said shaft in; spaced relation with said primary sealing means, whereby to define a chamber within said extension, around said shaft and between said primary and secondary sealing means, said secondary sealing means comprising". a pair of spaced apart shaft seals. defining a seal cavity therehetween within said extension and around said shaft, reservoir means to maintain a supply of liquid sealing medium in said cavity, and exhaust means connected with said chamber to maintain the same under predetermined low pressure conditions.

An X-ray generator comprising means form.- ing a sealed and evacuated envelope having an opening, sleeve-like means forming an enveiope extension sealed to said envelope at said opening and extending outwardly thereof; acathode and a cooperating rotary anode mounted withinthe envelope, ashaft member drivingly connected with said anode and extending. outwardly of the envelope through said opening andsaid; envelope extension, primary seal means comprising a manometer seal cooperatively connected with and within the extension and with said shaft member for sealing said shaftmember within said extension, said manometer seal comprising a pair of annular members sealed respectively onsaid extension and on said shaft, one of said annular members forming an annular trough around said shaft and adapted to contain a liquid sealing medium, and the other of said annular members comprising a dependent rim in position submerged in said sealing medium, secondary sealing means disposed in said extension and around said shaft in spaced relation with said primary sealing means, whereby to define a chamber within said extension, around said shaft and between said primary and secondary sealing means, and exhaust means connected with said chamber to maintain the same under predetermined low pressure conditions.

4. An X-ray generator comprising means forming a sealed and evacuated envelope having an opening, sleeve-like means forming an envelope extension sealed to said envelope at said opening and extending outwardly thereof, a cathode and a cooperating rotary anode mounted within the envelope, a shaft member drivingly connected with said anode and extending outwardly of the envelope through said opening and said envelope extension, primary seal means comprising a manometer seal cooperatively connected with and within the extension and with said shaft member for sealing said shaft member within said extension, said manometer seal comprising means forming an annular trough on and within said extension in position encircling said shaft member and adapted to contain a liquid sealing medium, and means forming an annular dependent rim sealed on said shaft member in position to submerge in said sealing medium, secondary sealing means disposed in said extension and around said shaft in spaced relation with said primary sealing means, whereby to define a chamber within said extension, around said shaft and between said primary and secondary sealing means, and exhaust means connected with said chamber to maintain the same under predetermined low pressure conditions.

5. An X-ray generator comprising means forming a sealed and evacuated envelope having an opening, sleeve-like means forming an envelope extension sealed to said envelope at said opening and extending outwardly thereof, a cathode and a cooperating rotary anode mounted within the envelope, a shaft member drivingly connected with said anode and extending outwardly of the envelopethrough said opening and said envelope extension, primary seal means comprising a manometer seal cooperatively connected with and within the extension and with said shaft member for sealing said shaft member within said extension, said manometer seal comprising a pair of annular members sealed respectively on said extension and on said shaft, one of said annular members forming an annular trough around said shaft and adapted to contain a liquid sealing medium, and the other of said annular members comprising a dependent rim in position submerged in said sealing medium, secondary sealing means disposed in said extension and around said shaft in spaced relation with said primary sealing means, whereby to define a chamber within said extension, around said shaft and between said primary and secondary sealing means, said secondary sealing means comprising a pair of spaced apart shaft seals defining a seal cavity therebetween within said extension and around said shaft, reservoir means to maintain a supply of liquid sealing medium in said cavity, and exhaust means connected with said chamber to maintain the same under predetermined low pressure conditions.

6. An X-ray generator comprising means form ing a sealed and evacuated envelope having an opening, sleeve-like means forming an envelope extension sealed to said envelope at said opening and extending outwardly thereof, a cathode and a cooperating rotary anode mounted within the envelope, a shaft member drivingly connected with said anode and extending outwardly of the envelope through said opening and said envelope extension, primary seal means comprising a manometer seal cooperatively connected with and within the extension and with said shaft member for sealing said shaft member within said extension, said manometer seal comprising means forming an annular trough on and within said extension in position encircling said shaft member and adapted to contain a liquid sealing medium, and means forming an annular dependent rim sealed on said shaft member in position to submerge in said sealing medium, secondary sealing means disposed in said extension and around said shaft in spaced relation with said primary sealing means, whereby to define a chamber within said extension, around said shaft and between said primary and secondary sealing means, said secondary sealing means comprising a pair of spaced apart shaft seals defining a seal cavity therebetween within said extension and around said shaft, reservoir means to maintain a supply of liquid sealing medium in said cavity, and exhaust means connected with said chamber to maintain the same under predetermined low pressure conditions.

GUSTAF ADOLF JUHLIN. CYRIL HUBERT WALKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,328,286 McClave Jan. 20, 1920 1,931,706 Powell Oct. 24, 1933 2,002,917 Mendenhall et al. May 28, 1935 2,075,146 Sergeeif Mar. 30, 1937 2,215,449 Alexander et a1. Sept. 24, 1940 2,362,816 Harker Nov. 14, 1944

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