US3087289A

US3087289A - Method of processing articles or materials in a continuous flow operation

Info

Publication number: US3087289A
Application number: US18637A
Authority: US
Inventors: William J Helwig
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1959-03-05
Filing date: 1960-03-30
Publication date: 1963-04-30
Anticipated expiration: 1980-04-30
Also published as: US3057130A; BE588321A; DE1117782B

Description

April 30, 1963 w. J. HELWIG 3,087,289

METHOD oF PROCESSING ARTICLES oE MATERIALS IN A CONTINUOUS FLOW OPERATION Original Filed March 5, 1959 3 Sheets-Sheet 1 Mir/4mm Kun/M Pam@ MIF

Aprll 30, 1963 w. J. HELWIG 3,087,289

METHOD OF PROCESSING ARTICLES OR MATERIALS IN -A CONTINUOUS FLOW OPERATION Original Filed March 5, 1959 5 Sheets-Sheet 2 April 30, 1963 w. .1. HELWIG 3,087,289

METHOD OF' PROCESSING ARTICLES OR MATERIALS IN A CONTINUOUS FLOW OPERATION Original Filed March 5, 1959 3 Sheets-Sheet 5 INV NTOR. Ma/@WJ f/W/a United States Patent 9 Claims. (Cl. 53-9) This invention relates to an appara-tus for and method of processing articles, s-uch as electron tubes, and in particular is concerned with an improved method of and apparatus for heat treating and/or vacuum processing work-pieces fed in a continuous flow.

This application is -a division of my copending application, Serial No. 800,357, filed March 5, 1959, now Patent Num-ber 3,057,1'130.

While the invention will be described in an environment having. utility in evacuating and sealing electron tubes, it is not limited to such utility. Indeed, an apparatus and method incorporating the invention has utility in a wide range of applications involving the vacuum and/ or heat treatment of articles and materials in a continuous flow operation.

4One type of apparatus employed on a relatively large scale for processing electron tubes to provide an evacuated and sealed envelope is known as a Sealex machine. This type of machine includes two turrets, on one of which a stern wafer is sealed to a bulb of an electron tube, and on the other of which the envelope `formed by the stem and bulb is evacuated through an exhaust tubulation, and the tubulation is pinched ofi.

This type of apparatus is characterized by several objectiona'ble features. One of such objectionable features resides in a discontinuity in the processing. Such discontinuity arises as a consequence of the need to transfer 'workpieces from one to the other of the aforementioned two turrets. Such transfer usually is effected manually and involves a time interval, during which the workpieces are removed from machine control. Not only does this time interval represent an undesirable time delay in tube manufacture, lbut it is accompanied by risks of tube damage incidental to tube handling and iby the expense of operator attendance.

In addition to the aforementioned discontinuity in operation, Sealex machines are accompanied by the disadvantage that the evacuating operation is effected under conditions wherein the outer wall of the tube envelope undergoing evacuation 4is subjected to atmospheric pressure. Since the tube envelope is usually heated during the evacuating operation by heating means directed to driving out occluded gases from the tube elements, the glass of the envelope is raised to a temperature that may be high enough to set strains therein, in response to stresses produced by the pressure differential on the outer and inner walls of the envelope. Such strains Imay pro-` duce cracks in the tube envelope, thereby destroying further yutility of the tube. Furthermore, the pressure differential referred to produces objectionable suck-in of the portion of the exhaust tubulation softened for pinch-off.

In .the evacuation and sealing ofthe envelopes of certain tube types provided with exhaust tubulations, the foregoing objectionable features of Sealex machines, in respect of discontinuity and pressure differential, have been toleratedV in View of the relatively high speed of processing .that such machines provide.- However, cer-tain other tube types having no exhaust tubulations in the envelopes thereofH and requiring sealing -ofenvelope parts after evacuation, cannot be processed by Sealex machines.

F or processing such other tube'types, use has been made Patented Apr. 30, 1963 of a bell jar type of enclosure within which the envelope parts of a tube are placed. While this type of processing avoids the pressure differential characteristic of Sealex machines in that the entire space within the bell jar enclosure is evacuated, thus equalizing the pressure on the inner and outer surfaces of the envelope parts, it is subject 4to a discontinuity of an even more serious kind than that associated with Sealex machines. Consequently, the bell jar type of processing device does not lend itself to efficient mass production of electron tubes.

Accordingly, it is Kan object of the invention to provide an improved method and apparatus :for vacuum and/ or heat processing workpieces in a continuous flow operation.

`It is a further purpose to provide an evacuating and sealing apparatus which includes a structure defining a continuous flow path 4therethrough for articles, such as electron tube workpieces to' be processed, and wherein the flow path has an ambient for avoiding objectionable suck-'in of a softened seal region.

Another .object is to provide a method of and apparatus for first evacuating a space defined by loosely pos-i-tioned envelope parts arid then sealing .the par-ts, in an operation involving continuous travel of the parts in a predetermined path, for increasing the efficiency and speed of .tube manufacture.

A further aim is to provide means defining a predetermined path `of Itravel of tube envelope parts, wherein the path is characterized by a convex temperature profile extending Ifrom one end of the path to the other, for providing relatively low temperature at the path ends to facilitate loading and unloading parts at such ends, and a relatively high temperature at a region intermediate the ends of the path, for sealing said parts together;

Another purpose is to provide means defining a path having a convex temperature gradient and a concave gas pressure gradien-t therealong, for facilitating a continuous evacuating and sealing operation.

A further object is to provide an evacuating and sealing apparatus having a structure including a rectilinear tube and heating and evacuating means distributed along the length thereof to provide a temperature an-d degree of evacuation within the tube having a gradient rising from one end of .the tube to -an intermediate portion thereof, and falling from said intermediate portion to the other end of the tube, for facilitating not only a continuous processing of workpieces carried through said tube, from one end thereof to the other, .but also the loading and unloading of the workpieces at the tube ends.

A further object is to provide an evacuating and sealing apparatus having path-determining means responsive in enlargement ,to increasing temperatures to provide increased access of said parts to an evacuating means at relatively high temperatures.

Another purpose is to provide a rectilinear tubular evacuating oven and a workpiece carrier made of such materials that the inner diameter of said oven is enlarged at a region of maximum temperature while the carrier is substantially free from enlargement transversely of the tube, to facilitate evacuation of a space defined by said carrier in the aforementioned region. Another purposeV is to provide an evacuating system lwherein two or more evacuating means overlap in a region where the lowest gas pressure is desired.

Another aim of the invention is to provideV an evacuating and sealing apparatus having a structure defining a rectilinear path therethrough, and including Work carriers adapted to close effectively from the ambient atmosphere, regions of said path, for facilitating the evacuation of electron ytube envelope workpieces carried through the aforementioned regions.

One embodiment of the invention selected for illustrative purposes only, zcomprises a structure including a vertically supported metal tube having a predetermined inner diameter and a plurality of aperture groups spaced axially thereof. The tube is embraced at regions including at least one aperture group by duct means communicating with an evacuating means. The two aperture groups adjacent to the opposite ends of the metal tube are each associated with an evacuating means having a capacity of gas conductance that is appreciable in relation to the gas conductance through open ends of the tube to the two aperture groups aforementioned. Several groups of apertures in an intermediate portion of the tube are connected to a third evacuating means of greater eiciency than the rst named evacuating means. Thus, the latter evacuating means may comprise mechanical vacuum pumps, while the third means may constitute oil diffusion pumps backed up by mechanical pumps.

To further increase the efficiency of the evacuation of the intermediate portion of the tube in the embodiment referred to, a first chamber embracing several groups of apertures is connected to an oil diffusion pump backed up by a mechanical pump, while a second chamber within the rst chamber embraces at least one group of apertures of said several groups and is connected to an independent oil diffusion pump backed up by a mechanical pump. In this way, the gas pressure differential within and outside of the inner chamber is reduced for increased eiciency of evacuation of the portion of the tube embraced by the inner chamber.

The foregoing combination of evacuating means provides a gas pressure gradient in the metal tube which is concave in profile, that is, the gas pressure in the portion of the tube embraced by the aforementioned inner charnber is lowest and increases toward both ends of the tube. In the embraced portion of the tube, therefore, maximum evacuation of an envelope defined by workpieces takes place, and accordingly, the parts are sealed in this portion to preserve the aforementioned maximum evacuation.

For heating the interior of the metal tube -to provide predetermined heat zones for degassing, cathode activation and sealing, a system is provided having a moderate heating capacity in relation to the portion of the metal tube embraced by the outer evacuating chamber aforementioned, and excluding the portion embraced by the inner chamber, and an appreciably high heating capacity adjacent to the last named tube portion. The inner chamber is spaced along the axis of the metal tube from both ends of the outer chamber, and the outer chamber is disposed intermediate the tube ends. In this way, the temperature gradient, from one end of the metal tube to the other, is substantially convex in profile, so that an intermediate portion of the tube is at sealing temperature and the ends of the tube are relatively cool for convenient loading and unloading of the workpieces.

To reduce gas conductance from the ends of the tube to the several pumping regions, a novel carrier for workpieces is provided having one or more spaced wafers of a diameter to provide a relatively small clearance iit with the inner wall of the metal tube adjacent to the cooler end portions thereof. In this way, when the metal tube is fully occupied by work carriers, interior portions along the length of the tube are appreciably blocked against passage of gas admitted from the external atmosphere.

An important feature of the invention resides in appropriate selection of materials for the metal tube and work carrier wafers, so that the metal tube may have an appreciable coeticient of expansion causing its inner diameter to enlarge at the hotter intermediate portion thereof, while the wafers do not enlarge appreciably. Thus, the annular spacing between the inner wall of the tube and the periphery of -a wafer is enlarged at the intermediate portion of the tube where evacuation is most ecient. This enlarged space facilitates evacuation of envelope workpieces supported on the work carriers.

Work carriers of the type referred to may be loaded continuously in tandem relation into the lower end of the metal tube, either manually or mechanically, to assure a predetermined rate of travel of previously loaded carriers through the tube. This rate is related to the capacities of the evacuating means and heating means, and must be sufliciently slow to assure desired evacuation of envelope parts on the carriers and desired sealing of the parts after evacuation. y

Carriers with evacuated and sealed electron tubes emerging from the upper end of the metal tube may be 4removed manually or mechanically.

Further features and advantages of the invention will become apparent as the present description of an embodiment thereof proceeds,

In the drawing, to which reference is now made for a consideration of an embodiment of the invention, by way of example,

FIG. 1 is an enlarged view in elevation, partly broken away, of envelope workpieces that may be processed by an apparatus according to the invention;

FIG. 2 is a partly sectional schematic elevational view of an apparatus embodying the invention;

FIG. 3 is an enlarged fragmentary view, partly in section, of the loading and retaining mechanism employed in association with the apparatus shown in FIG. 2;

FIG. 4 is an enlarged sectional View in elevation of a work carrier and bafe used in the operation of the apparatus shown in FIG. 2;

FIG. 5 is an enlarged sectional view in elevation of the structure of a portion of the apparatus depicted in FIG. 2;

FIG. 6 is an enlarged sectional view taken in the general direction of arrow A shown in FIG. 5;

FIG. 7 is a perspective structural view of the apparatus shown schematically in FIG. 2 with certain parts, shown in FIG. 2, omitted in the intere-sts of clarity;

FIG. 8 is an enlarged sectional view taken along the line 8 8' of FIG. 5;

FIG. 9 is a fragmentary perspective view of a portion of the radiant heating means;

FIG. 10 is a schematic view of an actuating system that may be employed in connection with the loading mechanism shown in FIG. 3;

FIG. 1l shows an enlarged fragmentary elevation of a portion of the processing tube of the apparatus shown in FIGS. 2, 5 and 7, and depicts one of several similar sets of openings in the processing tube; and

FIG. l2 shows an enlarged fragmentary elevation of the processing tube and depicts another set of openings therein.

The workpieces lto be processed by the apparatus of the invention may comprise a metal bulb 10 made of steel, for example, and an electron tube mount including a stem wafer 12, made of a ceramic, such as Forsterite, having lead wires 14 extending therethrough, as shown in FIG. l. A ring 16 of brazing material made of an alloy, such as Nioro solder, known in the trade, is disposed adjacent to the periphery of the wafer 12, and the end of the bulb 1i), closed by loosely positioning the wafer :12 thereon, The periphery of the wafer 12 may have a coating 18 thereon, made of molybdenum, for example.

A processing of the described workpieces by the apparatus, according to the invention, involves evacuating the envelope loosely defined by the wafer :12 and the bulb 110, degassing metal components of the electron tube shown in FIG. 1, activating a cathode, -not shown, inconporated in the electron tube aforementioned, and sealing the periphery of the wafer 12 to the inner wall of the bulb 10.

When the bulb 10 and wafer `12 are in the loosely assembled position shown in FIG. 1, su'icient communica- -tion between the space dened by the bulb and Wafer, and the exterior is provided, so that when the parts referred to are placed in an ambient of reduced gas pressure, the gas pressure within the space aforementioned is reduced correspondingly. Furthermore, in the position shown, a

apar/,289s

of the bulb le, to provide a hermetic seal therebetween when the solder is cooled to hardness.

For accomplishing the foregoing vacuum processing and heat treatment of the electrontube vvorkpieces` de scribed, an apparatus is provided includinga tube 20de-- iining a path of travel for the workpieces fromone endof the tube to the other in a continuous flow, as shown in FIGS. 2, and 7. The tube 20 is approximately ten feet long. The apparatus includes `a plurali-tyof combined carriers and baffles 22, one of whichisshownina FIG. 4. Each carrier includes-a cylindrical portion 24, having openings 26 and extending from one` sideof a bafe disc 28 defining two flanges or baffles 30 and 31,

and a supporting recess 32, on which the electronV tubey The workpieces shown in FIG. l' are adapted to rest; cylindrical portion 24 surrounds thezworkpieces, and the bale disc 2S provides `a cavity 33 into which the lead wires 14 of workpieces supported in a lower carrier-may.r extend. A plurality of carriers are adapted to be receivedt in tube 2i) in tandem relation.

The carriers 4are preferably made ofv a materialwhich exhibits a small heat retaining property. Thus, if. the

specific heat of the carriers is relatively small, the carriers will cool rapidly and assume substantially roonr temperature when unloaded Ifrom tube 20. When the composition of. `the carriers 22 is cold rolled steel and` their structure is as shown in FIG. 4, their heat retaining property is sufciently small'to permit convenient unloading thereof, after passage through theheat zonesV to be described at a rate to be specified herein.

Work carriers 22 may. be fed successively into the lower open end of tube 20, shown in FIG. 3,- either manually or mechanically. The rate of feed should besuch as to assure suflicient time for several processing-elements disposed outside of and extending along the-tube, to operate on the workpieces. In one example, to be described, this rate is one carrier per minute.

In the example shown -in FIGS. 2, 5 and 7, the processing tube 20 is disposed in vertical position. Consequently, the combined weight of the carriers previouslyy loaded into the tube will rest on the lowermost carrier. To support the column of carriers in tube 20, between loading operations, a stop structure is provided, asA shown in FIG. 3, comprising a pin 34 urged by a spring'36 into distended position through the wall of tube 20-and into the path of travel of carriers therein. A head 3-8 on the pin determines its maximum distended position. The portion of the pin 34 extending into the tube 20* is bev,-

eled on its lower side, so that a forceful extension of a.

carrier 22 into the lower open end 40 ofthe tube will cause the flange 30 on the carrier to bear against the bevelled side of pin 34, thereby causing the pin to retract against spring 36 and permitting the flange 30 to pass upwardly beyond lthe pin. As soon as the flange 30 clears the pin 34, the pin is free 4to spring out'to distended position, for engaging the underside of flange 30 and restraining falling movement lat the carrier 22.

While it is feasible to feed work carriers manually into the lower end portion `40 of the processing tube 20 at the required rate, it is preferable to utilize mechanical means for this purpose, in view of the appreciable weight of the column of work carriers wit-hin tube 20, and which requires lifting manually in a manual feed. A suitable mechanical system 37 I(FIG. 2) for feeding carriers into the lower end of tube 2,0 is shown in FIGS. 3 and l0. The system may include a piston 42 having an enlarged head portion 44 extending through an opening in Ia table 46 fixed as by welding to the lower end of processing tube Ztl. 'The piston 42 extends into a pneumatic cylinder 48 having an upper duct 50 communicating with the atmosphere, and a lower duct 52 communicating with a source ofA air under pressure, not shown, through a three-way valve 54. The valve S4 includes a valve member 56. having-a T-shapedchannel `58 and shown in a position wher in the channel provides communication between duct 52 and a duct @communicating with the atmosphere. Rotation of the valve member 56 in a counterclockwise direction, asviewed in FIG. l0, and lthrough anarc of 90,

will permit communication only between duct 52 and when the solenoid is-connected to a source of A.C. electrical energy, it retracts piston `66, therebyV actuating thev valve member-56to a position wherein the channel therein communicates withducts 52 and k62 and the source of air under pressure.l This causes the piston 42 and the piston head 44 to rise through table 461 for pushing a work carrier loaded" on the upper surface of the piston head, up intotube 20 :and toL a position wherein the iange v30 onsthe carrier is above pin34 forpreventing return downward movement ofthe loaded carrierV onv subsequent retraction of the` piston 42-and head 44.

For controlling the feed of work carriers into; the tube 20, at a, rateof.y say one carrier per minute, a switching arrangement (FIG. 10)' isprovided. across. the A.C. power line serving the solenoid 64. This. switchingv arrangement includes a switch 7-0, normally open, and adaptedto be closediby aca-m 72 having a switch closing. lobe 74. The cam is rotated` counterclockwise, as viewed in FIG. l0, on an axis 76 by a shaft 78 engaging the cam connected-to a motor. Ltrhrough a gear box 82,

to. provide a rate of" one rotation through 360 per' minute.

The lower end portion 40 of. processing-tube 20 has a portion of its Wall removed, as shown at 84, (FIG. 3). The removed portion includes an arc of atleast 180 to allow. a carrier-22 to be inserted` therein in coaxial and operating relation with respect to theA tube 20. The inserting operation is facilitated by the-fact that the upper surface ofcylinderhead 44 is flush with the upper surfaceoh table 46lbetween intermittent loading movements ofY the piston head. This facility in the inserting operation renders the use ofy manual means feasible. However, mechancial` means, not shown, may be used for inserting work carriers into the lower end of the processing tube.

For a reason tha-t will become apparent, the cylinder 4Sispreferably supported by table 46, by means of suitablebrackets 86, `88,v as shown in FIGS. 3 and l0. As has previously beenmentioned, the table, in turn, is supportingly fixed to the lower end' of the tube 20. As a consequence, axial expansions ofthe tube 20.will not effect the-flush position of the piston head' 44 with respect to the upper surface of table 46, which is important in facilitating loading of carriers into the tube.

As the work carriers 22 are raised in -tube 2t), the uppermost carrier'in the column will emerge from the upper end of the tube. The-emerging work carrier may be removed either manually or by mechanical means, not shown.

For suitably vacuum treating, the workpiece in the work carriers 22,` as the carrierstravel through the proc.- essing tube 20, suitable means are provided for producing a gas pressure gradient within tube 20 thatis concave in profile along thek tube. That is to say, the gas pressure at the open. ends of the tube 20 is atmospheric and decreases toward an intermediate portion of the tube 20, at which the pressure is sufficiently reduced for providing a desired ambient having a degree of evacuation required in the envelopes of the electron tube work*- ieces.

p The nieans for providing the aforementioned gradient in gas pressure comprises a system for producing Zones surrounding axially spaced portions of the tube 20, each having a desired pressure to produce the gradient referrea te. The wan of the 'tube 2e is provided with @pas ings at each z one f o'r equalizing thegas pressure each Zone and the interior of the adjacent tube portion. Adjacent the intermediate portion of the tuber20, two overlapping zones are provided for maximum evacuation of this portion.

Reference to FIGS, 2 and 5 reveals one specific form that the aforementioned pressure reducing means may assume. As shown in FIG. 2, two mechanical vacuum pumps 90, 92 are connected to

fittings

94, 96 embracing portions of the tube 20 adjacent to its ends and dening chambers or tanks 98, 100, respectively. The vacuum pumps referred to may be of the type known commercially as Kinney KDH65. Two sets of

openings

102, 104 in the wall of tube 20 provide communication between the chambers 98, 100, respectively, and the interior of the adjacent portions of the tube.

Each set of

openings

102, 104 comprises twenty-eight openings106 extending along the tube 20 a distance of about one and onehalf inches, as shown in FIG. 11. Each opening is about one quarter inch in diameter, and each set includes seven annular arrays of four openings each, the openings in each array being equidistantly spaced around the tube 20. Adjacent arrays are staggered circumferentially of the tube 20 to permit a grouping of the twenty-eight openings in a one and one-half inch length of the tube without appreciably weakening the tube, and for desired air ow conductance between the chambers 98, 100 and the interior of the adjacent portions of tube 20.

Pumps 90, 92 produce a degree of evacuation of chambers 98 and 100, and the interior of adjacent portions of the tube 20, that is dependent on several factors. These factors constitute the capacity of the pumps, the air ow conductance between the ends of the tube 20 and through the sets of

openings

102, 104 referred to, and the degree of blockage to such ow presented by the work carriers 22.

With the capacity `of the aforementioned pumps known, the air dow conductance and the degree of blockage to now may be controlled to provide a gas pressure in chambers 98, 100 and the adjacent interior regions of the tube 20, that is less than 1/0 mm. of mercury, and about 6 mm. of mercury. Thus, it has been found by applicant that a desired control of air ilow conductance is realized when tube 20 is provided with an inner diameter of 1.055 inches, when the portions of tube 20 having the sets of

openings

102, 104 are spaced approximately twenty inches from the adjacent ends of the tube, and when the clearance between the inner wall of the tube and the periphery of ange 20 on Work carriers iilling the tube is about 0.003 inch when cold. The gas pressure referred to is, of course, also dependent on the gas pressure in the portion of the tube 20 intermediate the chambers 98, 100:

For reducing the gas pressure in a relatively long intermediate portion of tube 20, a relatively large diameter chamber or tank 110 is provided which embraces the intermediate portion aforementioned, as shown in FIGS. 2 and 5. The tank 110 is cylindrical in shape and about four feet long and has a diameter of about one foot. End portions of the tank are hermetically sealed around the tube 20 by means of bellows 112, 114. The tank is supported by a bracket 116 resting on four legs, three of which 118, 120 and 122, are shown in FIG. 7. The tank 110 serves the two functions of providing a low gas pressure ambient about the aforementioned intermediate portion of tube 20, and of supporting -tube 20.

For providing the low gas pressure ambient referred to, which is approximately 0.0002 mm. of mercury, the tank is connected to an oil diffusion pump 124 backed up by a mechanical pump 126, by means of a high conductance duct 128, as shown in FIG. 2. The oil diffusion pump has a capacity of 500 liters per second, and may be of a commercially available type known by the designation CEC-MCSOGB The mechanical backup pump used, has a capacity of sixty-live cubic feet per minute, and islkrown commercially by the designation Kinney KHAGS.-

For providing communication between the low gas pressure ambient produced in tank 110, and the interior of the tube portion embraced by the tank, a plurality of sets of openings are provided in the wall of tube 20. One of two sets of openings shown schematically at 129, in FIG. 2, and of the type shown in FIG. 11 and comprising twenty-eight openings each, is disposed in the wall of each portion of the tube 20 located within the space defined by each of bellows 112, 114. Each set is spaced about thirty-five inches from the adjacent end of tube 20. An additional set of openings 131, also similar to the set shown, in FIG. 11, is spaced inwardly of tank 110 from opening set 129, a distance of about one foot. Further sets of openings 132, each comprising four openings spaced around tube 20, as shown in FIG. 12, each having a diameter of one quarter inch, are distributed between opening sets 130 and 131. The opening sets 132 are spaced about one and one-half inches from each other and from

sets

130, 131 axially of tube This arrangement of openings in the -wall of tube 20 assures a reasonably constant pressure within tank 110 of about 0.0002 mm. of mercury, even though workpieces located within the region of the tube 20 encompassed by the tank 110, may be releasing considerable quantities of gas.

However, the gas pressure in tank 110, and the interior portions of tube 20 to which communication is afforded by opening

sets

129, 130, 131 and 132 aforementioned, is not suiciently low to provide a desired evacuation of workpieces being processed. Therefore, a second tank 133 is disposed lwithin tank 110, and embraces a length of tube 20 having an axial extent of about one foot. The second tank, or inner vacuum chamber 133 is semicylindrical in shape and includes a dat side 134 removably iixed to the semi-cylindrical portion 136. The iiat side referred to is xedly supported on an air duct 138, which extends through and is hermetically sealed to the wall of the larger tank 110.

For evacuating the interior of the vacuum chamber 133 t0 a gas pressure of about 0.00001 mm. of mercury, the duct 138 is connected to an oil diffusion pump 140 backed up by a mechanical pump 142. The oil diiusion pump 140 has a capacity of three hundred liters per second and is of a type known commercially by the designation CEC-MCF300. The mechanical 'back-up pump is of a type available commercially under the designation Kinney KS13.

To provide communication between the vacuum chamber 133 and the interior of the portion of tube 20 which it surrounds, two sets of perforations '1414, 146 of the type shown in FIG. 11 are provided through the wall of the tube portion referred to. These two( sets of perforations are spaced about nine inches from each other, axially of tube 20. Intermediate perforation sets 144, 146, are provided three sets of openings 148 of the type shown in FIG. 12. The opening sets 148 are spaced about one and one-half inches `from each other axially of tube 20. These tive sets of openings in the tube portion embraced by the inner vacuum chamber 133 eii`ectively eliminate any appreciable pressure differential between the vacuum chamber and the space within the tube portion referred to. Thus, the pressure in this space is maintained reasonably constant at 0.00001 mm. of mercury, even though workpieces processed in thespacef evolve an appreciable quantity of gas.

It will be appreciated trom thek To this end the communicating withl the interior of the tube`20g"producev a gas pressure gradient within tube- 20"that is conc-ave Thus, at'the" ends of `the tube,A From the' ends ofthe tube, regions of progressively reduced gas pressure are in profile along the tube; the gas pressure is'atmospheric.

provided, until at the inter-mediate'portionf ofthe tube embraced by vacuum chamber 133, a gas pressure of about 0.00001 mm. of mercury is realized. Thispres-v sure gradient is obtained without closing the*v endslof `the tube 20. While the workcarriers 22 eiiect partial closure of the end portions of the tube, suicient clearance' between the' sides ofthe carriers and the inner wallV of the tube is found necessary for free travel ofthe-work' This clearance,- Vwhile expos-`v carriers through the tube. ing the interior of the tube'20 to atmospheric pressure, is insufficient, according to the invention, to preventV the high degree of evacuation'secured in an intermediate portion of the tube.

As has been indicated previously herein, the tank 110 not only serves to produce a zone of desired low gas pressure, but also provides support -for the processing tube 20. The tank 110 is well suited to serve a support function, since it is ruggedly supported on bracket 116,' as previously described,

The tube 20 is supported at end portions of tank 110by means ofthe bellows 112, 114 previously referred to. Thebellows include sleeves 160, 162'which fixedly en-l gage the outer surface of the t be 20. The corrugated cylindrical bellows

bodies

164, 166 `are fixed at one end thereof, las yby brazing or welding, to the peripheries of

sleeves

160, 162. The other ends of the cylindrical bellows are fixed suitably to edges definingopenings in the end walls of tank 110, as bybrazing or welding. v The bellows bodies may be -made `of'a material, such as 'stain-l less steel, and the thickness/of the side walls of the

bodies

164, 166 may be from twenty to thirty rnil-s, if the bellows alone are relied upon to support the tank 110.

'In additionto supporting the tank 110', the 'bellows 112, 114 exert-a tensile `force on the portion of tube 20 extendingV therebetween. This tension isV desirable t prevent buckling or other deformation of'tube 20l in response to relatively high processing temperatures.

if desired, the suppo-rting function of the bellows 112, 114l may 'be supplemented by an additionalV structure. This additional structure includes three-armed spiders 168, 1.70 iixedly clamped around. portions of tube spaced from the -bellows referred to, Compression springs 172, 1.73 bear against the outer `surfaces of the end walls of tank 110 and the arms of the two spiders aforementioned. The springs are guided by

rods

174, 175 which are'freely movable through the spider arms. lf this additional support andtensioning structure is used, the material of the bellows bodies may have a reduced thickness of ten mils, for example.

In addition to providing an evacuated ambient for evacuating the enclosurefformed by envelope workpieces, it is also desirable to heatthe workpieces` iirst to dgas the material of the workpieces and activate a. cathode included within the envelope workpieces, and iinally. to seal the envelope workpieces to preserve the evacuated space therein. To this end a heating system is provided foregoing that-the-` pressure dierential between the interior of tanks 1101 To preserve this pressure dif and embrace the tube 20- foregoing that-v 10ja temperatureV gradient along thev This adapted to. produce tube 201that-is: substantially. convex in profile.

assuresv that .theworkpieces are graduallyv raised. to a sealingltemperature through a. gradient at.;whichoutgassing. and cathode activationtake-.place `priorxio sealing, and

which gradually-is reducedltolroom: temperature toavoid objectionable. strains inl the workpieces.A

The heatingsystem` referred toA includes radiantl heat producing structuresy 176,1 177 spacedalong the 17 8i' positioned between thev radiantr heating-structures 176', 177'.I Eachwoffheat-radiating structurescornprises; 182 rma-de. of'aninsulatingfrnateriah such asAlundum4 asshown. ind-716895,A 8f-andi9.` The insulating-members -180',. 182.l ribs 184,' defining; a .plurality of two semi-cylindric-allyinsulatingmembers 180;;

in-"heatin'g structure 177 is/lalso connected to .a suitable source of-electricalfpowerthrough leads l1194,' 196.

Each' of theradiantheatingA strluctures-176, 177, also includes: two concentric and radially spaced'iheatk re. flectingcyl-inders-198', 200 rnadeof a-highly heat're- -iiectingmater-ial, suchl as stainless-steel;

The temperature producedwit-hi-n tube 20l by the radiant heatingstructureslf, 177`A energizedjby azsixty cycle"v commercial current,L is about 800 This-tern-` peratureappearsina region'relativelyy close to the ends ofthe inner vacuum chamber;133rfanddecreases Vtowards the remote 'endsoflthe #heating structures aforementioned This gradient is* produced; partly' as a'consequence of heat ygenerated byn the radio frequency heating structure 178 surrounding-'a portion offtube 20'intermediate the radiant heatingl structures 17-6, 17 7 i The radio frequency-heating structure 178 corn-prises a tubular coil`202,l made Aofan electrically conductive material, such as copper, embracinga portionl of tube 20,- including opening sets"1'44,'- 146 and 148 `rin the tubefwall, insuitablespacedrelation-to the tube. The endsoftthe coil 2,02 pass through theiiat side 134 of the vacuum chamber 1313, and through'thesidewall oftank 110, by means of radio frequency energy'feed-throughvconnectiorr`204, showninFIGS. 5 and 6. This feed-through connection,l as shown in FIG. 6, includes-coaxial ducts 206", 208, made of electrically conductive material, such as copper andsupportedby; a body ofcompressible insulating material 210; The material 210' is A compressed in the annular space between ducts 206and 208-.by a plug 212A of insulating'rnaterial, xed tothe body 214 defining duct 206, by two screwsA 216; The feed-through connector referredto, is hermetically sealedthrough the walls ofthe tanks and 133by'engagements involving contacts between the tanksand the'outer duct member 206. This duct'mernberv is'operatediat RF ground, not'only to permit direct contact with the tanks 110 and -173, but to avoid'ob'jectionable reactance effects with the tanks aforementioned;

Inner duct 208 is connected to an RF source-217having frequency of ab'outfourV hundred kilbcycles and a power output-of abouttwo kilowatts;

The coaxial ducts` 2,06k and 208, andthe coil 202 are hollow, toallow' a cooling' fluid from a source 2 17`to liow therethrough.

It is desirable that the` magnetic iiux produced by the coil 202 penetrate to the interior of the adjacent region of processing tube 20, To' this end, desirable flux cornmunication to the interior of the tubev 20 is provided, not only by opening sets 144', 146 and' 14S-in the tube wall, but also as a consequenceof the'non-magnetic material of" which the tubes is' made, andthe-thinness ofthe tube wall. Thus; the tube2'0l is made of a non-magnetic matube 204 within tank 110, and a radio lfrequency heating structureV terial, such as an alloy known in the trade as Inconel, and the wall thickness of the tube is about 0.035 inch. This composition of tube 20, the thinness of the wall thereof, and the

openings

144, 146 and 148, allow the RF fiux produced by coil 202 to extend into the interior of tube 20, and through openings 26 in the work carriers therein, for heating the workpieces by RF energy induced therein. The RF coil is adap-ted to produce an ambient in which the workpieces are raised to a temperature of about 950 C.

To confine the heat produced by coil 202 to a region relatively close to the tube 20 and remote from the walls of the vacuum chamber 133, two concentric and radially spaced heat shields 220, 222 are disposed in spaced relation around the coil 202. The shields referred to are made of a material having a high heat reflecting property, such as stainless steel.

It is preferable to employ an RF coil for heating the ambient of maximum evacuation, since the coil includes a relatively small mass that is more readily degassed than the radiant heating structures before referred to.

The material of the tube 20 and the composition of the work carrier 22 are such as to permit appreciable radial expansion of the tube 20 at the hottest region thereof, at which maxim-um evacuation of the workpieces is desired, while the carrier is free from appreciable radial expansion. This desirable result is obtained when the tube 20 is made of Inconel, as previously mentioned, and when the carrier is made of cold rolled steel.

The unequal expansions of the tube 20 and the carrier 22, referred to, due to the difference of coefficients of expansion of the materials used in tube 20 and the work carrier 42.2, enlarge the space between the inner wall of tube 20 and the peripheries of the

flanges

30, 31 of the carrier 22. This is desirable in that it reduces resistance to conduction of gas from a region between two carriers when such region is between two sets of openings in the tube wall. This reduction in flow resistance contributes to increased efficiency of the evacuating means at the region of the tube 20 where maximum efficiency is desired. At such regions of maximum efficiency the work receiving space may be considered to be defined in part by the |wall of the carrier and in part by the wall of tube 20. For example, the wall of the tube 20 complements the wall of the carrier at the regions of openings 26 thus fully enclosing the space receiving the workpiece.

However, the increase in the radial spacing produced between the inner wall of the tube 20 and the carrier 22 places a burden on the

flanges

30, 31 to prevent tilting of the carriers in the tube. This burden is successfully met by the axial displacement of the two anges referred to.

An important advantage of the processing apparatus described, is that it avoids suck-in of the sealing ring 16 when heated to melting temperature. This advantage occurs from the fact that the Nioro solder ring 16 is' raised to melting temperature only in the region of tube 20 encompassed by the vacuum chamber 133. The ring is cooled to hardness while in the portion of tube 20 surrounded by the radiant heating structure 176, which is a region surrounded by tank '110, and in which the degree of evacuation is sufficiently high to avoid suck-in of the solder material prior to its hardening.

It is preferable to commence operation of the apparatus with the tube full of carriers 22, preferably empty of workpieces. The presence of carriers throughout the tube will result in a partial closure of end portions of the tube to the atmosphere and improve efficiency of operation.

Before the first carrier with a workpiece is loaded, however, it is desirable to assure that the several zones along the tube 20 are heated to a specified temperature pointed out previously herein. This determination is made by inspecting the several thermocouples 224, shown in FIG. 7, and extending from the several heat zones along the tube 20 within

tanks

110 and 133, to the exterior of tank 110. Suitable gauges, not shown, are also 12". connected to the several zones along the tube Ztl, to provide an indication of the gas pressures therein, and should be examined before and during the operation of the apparatus, to assure that the gas pressures comply with the specifications set forth in the foregoing.

When operation of the apparatus is stopped, it is irnportant that no workpieces remain in the tube r20. This is because such remaining workpieces will be only partially processed on resumed operation of the apparatus. The effects of initial processing of workpieces remaining in the tube after stoppage of the apparatus will be lost. To meet this problem, it is desirable to load a sufficient number of empty carriers 22 into tube 20 prior to stoppage of the apparatus, to allow all carriers having workpieces therein, to be unloaded before operation of the apparatus is stopped. This expedient is also of advantage, in that the tube 20 will be full of work carriers, when operation is resumed, for improved efficiency of operation, as aforementioned.

What is claimed is:

l. Method of vacuum processing a workpiece comprising passing said workpiece through a tube having an open loading end and at least two apertures in the wall thereof spaced along said tube and from said loading end, producing a first space of relatively low gas pressure around a length of said tube having said two apertures, and producing a second space of yet lower gas pressure withinI said first space and around only a portion of said length having one of said apertures remote from said open end, whereby the gas pressure differential inside and outside of said second space is relatively small for efficient evacuation of said tube portion.

2. Method of vacuum treating a workpiece comprising placing the workpiece in a carrier having one coefficient of expansion and dening a workpiece retaining space, transporting said carrier through a tubular member having a different coefficient of expansion from said one coefficient of expansion in a path having regions of decreasing gas pressures, and successively increasing the spacing between said carrier and said tubular member as said carrier traverses said regions.

3. Method of vacuum treating a workpiece comprising transporting said workpiece in a predetermined direction through regions of decreasing gas pressures in a carrier having a workpiece receiving space defined by a wall, moving said carrier in one direction in a transporting operation, said regions being defined by walls and moving said last walls in a direction normal to said one direction through a distance inversely related to the magnitude of said gas pressure for efficient evacuation of said space.

4. Method of evacuating a predetermined first region communicating with and surrounded by a second region, comprising reducing the gas pressure in said second region including said first region to a predetermined value, and further reducing the gas pressure in said first region while preserving the gas pressure in said second region at said predetermined value.

5. Method of vacuum treating a workpiece comprising moving said workpiece through a path having an environment of successively spaced regions of decreasing gas pressure, and increasing the exposure of said workpiece to said environment as said workpiece moves through said regions of decreasing gas pressure.

6. Method of joining in a seal, adjacent portions of envelope parts having a softening response to a predetermined temperature, said method comprising transporting said envelope parts in loosely assembled envelope relation in a first path having a heat gradient from room temperature to said predetermined temperature, then transporting said envelope parts in said relation in a second path constituting a continuation of said first path and having said predetermined temperature distributed substantially uniformly therealong, whereby said adjacent portions are softened and joined in a seal, and maintaining substantially the entire of said second path in an ambient of sub- 13 stantially uniform evacuation, for preserving said seal from a harmful pressure differential while said adjacent portions are at sealing softness.

7. Method of evacuating and sealing electron tube workpieces, comprising continuously feeding said work-pieces in tandem relation in a predetermined path, reducing the gas pressure in the ambient of said path to provide a concave pressure gradient along said path wherein the ends of said path are at atmospheric pressure and an intermediate portion of said path is at a desired reduced gas pressure for evacuating said workpieces and while in communication with said ends, and increasing the temperature in said ambient to provide a convex temperature gradient along said path wherein the ends of said path are at substantially room temperature and said intermediate portion is at a temperature for sealing said workpieces, whereby said workpieces are evacuated and sealed in a continuous operation.

8. Method of joining in a seal, adjacent portions of envelope parts having a softening response to a predetermined high temperature and a hardening response to a predetermined low temperature, said method comprising moving said envelope parts with said portions in loosely adjacent relation in a iirst path having an evacuated arnbient at said high temperature, for evacuating a space defined by said parts and joining said parts in a soft seal, and then moving said joined parts in a second path extending from said first path and in a second ambient having an increasing gas pressure gradient and a temperature gradient decreasing from said high temperature to said low 14 temperature, said temperature gradient and said pressure gradient being so related that said seal is progressively hardened to prevent migration of the seal region in response to an increasing pressure differential between said space and said second ambient produced by increasing gas pressure in said second ambient.

9. The method of evacuating and sealing electron tube workpieces, comprising the steps of continuously feeding said workpieces in succession along a predetermined path, reducing the gas pressure from atmospheric pressure in regions along said path to a region along said path of minimum gas pressure, and increasing the gas pressure along said path from said minimum to atmospheric pressure, applying heat to said workpiece along said path and increasing said heat in steps from room temperature to a maximum temperature at the point of minimum gas pressure for sealing said workpiece after evacuation thereof and thereafter decreasing the temperature in steps along said path to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,956,737 Walker et al May 1, 1934 2,343,104 Williams Feb. 29, 1944 2,380,903 Ray July 31, 1945 2,507,817 Ropp et al May 16, 1950 2,528,680 Berch Nov. 7, 1950 2,532,315 Johnson et al Dec. 5, 1950 2,780,043 Hensgen Feb. 5, 1957

Claims

8. METHOD OF JOINING IN A SEAL, ADJACENT PORTIONS OF ENVELOPE PARTS HAVING A SOFTENING RESPONSE TO A PREDETERMINED HIGH TEMPERATURE AND A HARDENING RESPONSE TO A PREDETERMINED LOW TEMPERATURE, SAID METHOD COMPRISING MOVING SAID ENVELOPE PARTS WITH SAID PORTIONS IN LOOSELY ADJACENT RELATION IN A FIRST PATH HAVING AN EVACUATED AMBIENT AT SAID HIGH TEMPERATURE, FOR EVACUATING A SPACE DEFINED BY SAID PARTS AND JOINING SAID PARTS IN A SOFT SEAL, AND THEN MOVING SAID JOINED PARTS IN A SECOND PATH EXTENDING FROM SAID FIRST PATH AND IN A SECOND AMBIENT HAVING AN INCREASING GAS PRESSURE GRADIENT AND A TEMPERATURE GRADIENT DECREASING FROM SAID HIGH TEMPERATURE TO SAID LOW TEMPERATURE, SAID TEMPERATURE GRADIENT AND SAID PRESSURE GRADIENT BEING SO RELATED THAT SAID SEAL IS PROGRESSIVELY HARDENED TO PREVENT MIGRATION OF THE SEAL REGION IN RESPONSE TO AN INCREASING PRESSURE DIFFERENTIAL BETWEEN SAID SPACE AND SAID SECOND AMBIENT PRODUCED BY INCREASING GAS PRESSURE IN SAID SECOND AMBIENT.