US2624008A - High-vacuum seal - Google Patents

Description

William M. Hickom.

W. M. HICKAM HIGH-VACUUM SEAL Filed Dec. 6, 1949 Dec. 30, 1952 WITNESSES:

Patented Dec. 30, 1952 UNITED STATES PATENT F F ICE HIGH-VACUUM SEA'L William M. ,Hickam, Pittsburgh, Pa ass ignorrto WestinghouseEle'ctric Corporation, Eastfittfs- ,burgh, 3a., a; ,oorporation of Pennsylvania Applicationwecember 6, 1949, SerialJNo. 131,409

11 Claims.

trhisinuention relate enerally ti -7 aihiah vacuumzseal, :and,.1more particularly, ;to argaslget type seal for maintainin l w pr ssur insid an evacuatedeontainer, such as. "f or -example,;a; mass spectrometertube. Theinvention isd scribed applied toa massspectrometertubeot metal wall construction,;,a;metal construction being used for reasons. of strength. ID-he; invention, howeven is not restricted to metal since it is ,usefuljor; tubes having glasswalls, or ,iorother :typesof vacuous electrical. apparatus, such :asthermionie orzeleetronsdischarge -;apparatus :in general.

;Heretofor.e, .in :the operation of .a mass aspece trometerztube,;oonsiderable. difficultyhas been-encountered becauselofthe necessity forheating .the tube, either for the purpose of degasifyingit preparatory to introduction-of. a new. sample in the. ion;source, or for-preventing :the occurrence of ;col d;spots. Molecules .of thesample emanating. fromrthei-ion souroe'tend to accumulate on thesercoldspots and, therefore, prevent attainmentofza. eonstant.1 fiow.rate;of za aseous sampl and accura e analysi Mole ules r main on the col spots after r moval of th sample, evacuation of i zhfii tube :introduction :of a new ample thu ivinarise .179 back rou d neak whieh interfer withthezan lrsisiof the. new sam- D1 andzwhieh e a ionlvb easily liminated :excent by :aricolon es zhake-out o th :tub

(The n eessaryheating of :the wall gives 9 .3. to; difiicultieswith respeetztosthe sealinama e ial which usually comprises wax, rubber, ior @ther lowzmeltin rpointplastic materialslieatinssof ours tends to. melt the wax 0 r bber ;-and eausebreakdown. of thewseal. Wax seal ar adesirable. :because of Ltheease of meltin :an :selidi ficationv thereof which readily. permits -rperiedi removal of the electrodes for ;cleaning.. Such cleaning is p necessary since the reaction :which occur in :the pr sence of th '.fi1.ament :formin par of theion. source causes an in la in ifilm to :form on :thezflflitQdGs which affectsthe :elecri a hfl dqis as mak errati ::nerformaneao thezmasstfspectliemetentuhe. I ni-the-use of glass tubes w th u aTWa W s i a :seal; :removakof the-electr d may be acco l shed .rs le -y r-by cracking the walls which can bedone-onlybya-n x e en ede a b ower.

, lnathe past, in view of thehighwacuum required in certain types of electrQhicetubes.itihas been-attempted to insuremaintenance of :such hi h v cuum :by- ;.comp1ete1y surrounding -:the ev e a itu e by a zseeendt b nd evacuatin the space hetween the .;respective walls thereof. Such ce nstruet on, however; has .been sioundz..un-

desirable not only because of the suhstantial e2;- pense involved in providing an additional tube, but because of the difiiculty in providing elec trode leads and-pumping .leads throu gh the walls of both tubes-also because of the difficulty in maintaining the respective seals.

An object of the present invention is to provide a high vacuum seal which is devoid of the above mentioned .disadvantagesof common types of seals.

A more specific object of this invention is to provide-a hi h va u s a hi partieularly su a e or in a ning a h g va uum in an evacuated container, such as, for examplaa mass spectrometertube, andwhieh permits easy ac.- .cess to the electrode system located in the con.- tainer.

A further object of this invention s .to provide a gasket type seal-for a high vacuum tube. such as ,a mass spectrometer tube, whihmaintains, for long periods of time, extremely low pressures within the tube overa wide temperature range and permits the entire .system to be operatediathigh,temperatures without detrimentally affectinggthe seal.

:I a corda cewith the b e t .1 pr vide a vacuum chamber having .two sections. fl he :line o t e iunet o -onl is eur oun by a intermediate pressure chamber viorined between ,the innerchamber and aprojection-on the flanges of the two 'pa tso e m nu-m chamber- The novel features that ,eon-sideryoharacteristic of myv invention areset forthwith ,particularity in :the appended claims. The invention itself, however", both ,asto its organization and. itsmethod of operation together with additional objects and advantages thereof will hest be understood from the following description-of alspecific embodiment when read in connection with the accompanyingorawing, in whichthe single figure is a longitudinal, cross-sectional viewof aportion of aim as s spectrometer tube adjacent the .ion source and embodying {a seal inaccordance-with the teachingS-Qf the present invention.

The apparatus sh wn i -th -.d ;a i e. nelude a fixed tubular section I and; a -removahl etuhular section :2 of a portion or iextensionwof a n ags spectrometer tube that surrounds an ion source 3. The tube is preferably made of metal-such as -stainless steel, Monel metal, iconel prhth suitable y-e etaLa thQugh .it shouldbelunderstood at i -m y:;bemade,.instead,;oe. 1ass, ceramic'or other. suitablematerial. {I-hestop por tion of z eetioni hasga;,disk=shapedzend wallwz brazed, welded, or otherwise permanently connected in an air-tight seal to the tubular section 2. A seal 4 is provided between the lower end portion of section 2 and a shoulder portion formed on the inner wall of section 5. This seal is made of material that will withstand heat normally applied to these sections, preferably gold in the shape of wire, since gold anneals at relatively low temperatures, that is, in the neighborhood of 200 C., and since portions thereof can be joined together very simply by heating such as by means of a torch. Other metals, such as aluminum or copper, may be used instead, but these have a higher coefficient of expansion than that of the metal sections l and 2, and, therefore, may not match the coefiicient of these sections as well as gold will. As the gold becomes hardened, as most metal seals do from continued operation, it is an easy matter to raise the temperature sufficiently to effect softening or annealing thereof.

Integrally secured to section 2 is an annular flange having extending therefrom and integrally secured thereto a skirt or cylindrical outer wall member 6 terminating at the lower end thereof with a sealing shoulder for accommodating a seal 1 preferably of rubber or other plastic material having relatively low melting temperature. The upper portion of fixed section I is of reduced thickness and terminates in a sealing edge which engages seal I. An intermediate pressure chamber i2 is formed between the wall of section I and the wall of section 2 adjacent to the seal 1. Since the intermediate pressure region is at approximately mm. high pressure, it is a poor conductor of heat. Substantially all of the heat from the interior of the high vacuum chamber reaching the seal '1 will be conducted through the thin wall portion on movable section 2 at the top of the intermediate pressure chamber l2 and through the wall portion of section i at the bottom of the immediate pressure chamber I2. Since both skirt 5 and the upper portion of section I are substantially thinner than the portions of sections I and 2 forming the inner wall of the tube, they restrict conduction of heat from the inner walls of the tube to seal 7. To prevent heating of rubber seal I, cooling coils 8 are provided on the respective outer wall portions for conducting a. cooling fluid,

such as water, to dissipate the heat as it is conducted along these thin sections.

The outer seal 1 need not be made of rubber. It may be made of gold'or any other material, which would be suitable in the seal 4. The flanges must then be machined with greater accuracy, because a variation of greater than 0.001 inch may make one of the two metal seals defective.

To join the two sections l and 2 tightly and maintain pressure on the seals, there is provided a plurality of bolts, such as the bolt 9, whose lower ends are welded or otherwise secured to the metal'base 5a of the section I of the spectrometer tube, and whose upper threaded ends extend through holes in the annular flange 5. Nuts [0 are screw threaded to the upper ends so that by tightening the nuts, sections l and 2 are brought tightly together so as to compress seals 3 and 1.

Cylinders or tubes, such as l l, are provided for connection to a vacuum pump (not shown) for maintaining the space within sections l and 2 at low vacuum pressure, usually of the order of 10 mm. Hg. The intermediate vacuum chamber 12, made vacuum-tight by seals 4 and l, is

connected by means of a tube l3 to a low-vacuum pump of the high vacuum pump (not shown) and is preferably maintained at an intermediate pressure of the order of 10- mm. Hg. Thus, since there is a considerably smaller difierential of pressure, between the interior of the tube and intermediate chamber I2 than between the interior and the surrounding atmosphere outside of the tube, there will be less tendency toward leakage through seal 4. Furthermore, since the portion of section 2 below flange 5 is surrounded by vacuum, heat will be readily conducted along the inner wall rather than across the intermediate vacuum chamber [2.

In operation, the multi-section tube is assembled as follows: Removable section 2 is placed over fixed section I. Suflicient rubber or other plastic material is provided to form seal 6 so that it will contact both the removable and fixed sections 2 and l before the gold gasket or seal 4 makes contact. Therefore, the rubber gasket 1 is under some compression before the gold gasket 4 is sealed. Pressure is then applied to these two seals by tightening nuts [0. The intermediate pressure chamber is then evacuated to approximately 10 mm. Hg through tube or pipe I3 while the high pressure chamber of the mass spectrometer tube is evacuated through cylinder 1 I to approximately 10"' mm. Hg.

While I have illustrated and described a certain specific embodiment of my invention, it will be apparent that this is by way of illustration only, and that various changes and modifications may be made within the contemplation of my invention and within the scope of the following claims.

I claim as my invention:

1. An evacuated container comprising a pair of metal tubes, a seal comprising a gold ring for joining said tubes for forming a continuous envelope, an extension integrally formed on and extending outwardly from one of said tubes in the vicinity of said seal, a second extension integrally formed on the other of said tubes and surrounding a portion thereof in spaced relationship, a second seal comprising a plastic material for sealing the ends of said respective extensions in a gastight manner so that said extensions and a portion of said other tube form an airtight enclosure, said enclosure being evacuated to lesser degree than the space enclosed by said tubes.

2. Apparatus recited in claim 1 wherein said second seal consists of plastic material of relatively low melting point and wherein said extensions are of lesser thickness than said tubes so as to restrict conduction of heat from said tubes to said plastic seal.

3. Electrical vacuous apparatus comprising a fixed metallic tubular member having an inner shoulder adjacent one end thereof and a removable metallic tubular member whose end is fitted against said shoulder, a metallic sealing material at said shoulder for providing a gastight joint between said members, said fixed member having an outwardly extending portion in spaced relationship to and surrounding a portion of said removable member, said removable member having an integral flange and a depending skirt extending from said flange which surrounds a portion of said removable member, a second seal of plastic material for sealing the end of said skirt to the end of said outwardly extending portion, thereby providing a small airtight enclosure, said skirt and outwardly extending portion being of lesser degree than the space defined by said tubular members.

5. A mass spectrometer tube comprising electrode means, said tube being made of metal and. including aifixed tubular portion having an inner shoulder and a removable tubular portion whose end is seatedon said shoulder, a seal in the iormi of a gold wire between said shoulder and end,

said fixed tubular portion having an integral extension surrounding, in spaced relationship, the

end portion of said removable tube portion, an annular flange integrally formed on and surrounding said removable portion and having a depending skirt, a rubber seal between the ends of said skirt and of said extension thereby forming an air-tight, small intermediate chamber, cooling coils mounted on said skirt and on said extension adjacent said rubber seal to maintain the temperature of said rubber seal below a predetermined value, said intermediate chamber being evacuated to a less extent than said mass spectrometer tube so as to reduce the pressure differentials across said respective seals, a plurality of bolts having one end integrally secured to said fixed tubular portion and the other end threaded and extending through holes formed on said annular fiange, nuts on said threaded ends, the tightening of which simultaneously compresses both of said seals, tubular means formed on said fixed tubular portion for connection to a vacuum pump for evacuating said mass spectrometer tube, and second tubular means formed on said extension for connection to a fore pump for evacuating said intermediate chamber to a lesser extent than said mass spectrometer tube; whereby said removable portion is detachably secured to said fixed tubular portion in a vacuum-tight manner to permit access to said electrode means, and whereby the respective seal may be adjustably compressed by tightening of said nuts.

6. For use in sealing a two-piece vacuum chamber, the interior of which will be heated, the combination comprising a first seal at the inner edge of the line of junction between the two pieces of the vacuum chamber, said first seal being formed of a material having the resistance characteristics that enable it to withstand the heat to which the chamber is subjected, means forming a chamber around said first seal, said last named chamber having a second seal of a more easily compressible material, outlet connections in said last named chamber for evacuating it to a pressure between atmospheric and the pressure in the inner chamber, and connecting means for pressing said two pieces of said vacuum chamber together.

7. For use in sealing a two-piece vacuum chamber, the interior of which will be heated, the combination comprising a first seal at the inner edge of the line of junction between the two pieces of the vacuum chamber, said first seal being formed of a material having the resistance characteristics that enable it to withstand the heat to which the chamber is subjected, means forming a chamber around said first seal, said last named chamber having a second seal of a more easily compressible material, outlet connections in said last named chamber for evacuating it to a pressure between atmospheric and the pressure in the inner chamber, and connecting means for pressing said two pieces of said vacuum together so that said second seal is contacted by said two pieces when said first seal is contacted.

8. For use in sealing a two-piece vacuum chamber, the interior of which will be heated, the combination comprising a first seal at the inner edge of the line of junction between the two pieces of the vacuum chamber, said first seal being formed of a material having the resistance characteristics that enable it to withstand the heat to which the chamber is subjected, means forming a chamber around said first seal, said last named chamber having a second seal of a more easily compressible material, outlet connections in said last named chamber for evacuating it to a pressure between atmospheric and the pressure in the inner chamber, and connecting means for pressing said two pieces of said vacuum chamber together and cooling means for cooling the chamber adjacent said second seal.

9. For use in sealing a two-piece vacuum chamber, the interior of which will be heated, the combination comprising a first seal at the inner edge of the line of junction between the two pieces of the vacuum chamber, said first seal being formed of a material havingthe resistance characteristics that enable it to withstand the heat to which the chamber is subjected, means forming a chamber around said first seal, said last named chamber having a second seal of a more easily compressible material, outlet connection in said last named chamber for evacuating it to a pressure between atmospheric and the pressure in the inner chamber, and connecting means for pressing said two pieces of said vacuum chamber together and tubes on either side of said second seal for cooling said seal.

10. A two-piece vacuum chamber having an inner region of low pressure, a region of higher pressure, a first washer of heat-resistant material at the junction point between the two pieces between the regions of low and higher pressure, and a second washer of a plastic material between the two sections between the region of higher pressure and the outside of said chamber.

11. A two-piece vacuum chamber having an inner region of low pressure, a region of higher pressure, a first washer of heat-resistant material at the junction point between the two pieces between the regions of low and higher pressure, a second washer of a plastic material between the two sections between the region of higher pressure and the outside of said chamber, and means for exerting pressure to hold said two sections in contact, said last named means being arranged to compress said second washer before contacting said first washer.

WILLIAM M. HICKAM.

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

UNITED STATES PATENTS Number Name Date 1,643,216 Kramer Sept. 20, 1927 2,151,937 Rabuteau et al Mar. 28, 1939 2,443,237 Gaudenzi et al. June 15, 1948 2,467,730 Coltman Apr. 19, 1949 2,481,506 Gamertsfelder Sept. 13, 1949

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