US2752532A

US2752532A - dussaussoy etal

Info

Publication number: US2752532A
Authority: US
Publication date: 1956-06-26
Anticipated expiration: 1973-06-26

Description

June 26, 1956 P. DussAUssoY ErAL 2,752,532

MANUFACTURE PROCESS OF TUBES OR VACUUM ENVELOPES Filed Jan. 17, 1951 2 Sheets-Sheet 1 l/V VE/VTORS June 26, 1956 P. DUssAussoY ETAL 2,752,532

MANUFACTURE PROCESS oF TUBES 0R VACUUM ENvELoPEs Filed Jan. 17, 1951 2 sheets-sheet 2 /IV V/VTORS ,1D/@w25 .ox/SSA asso y, MA x/ME 6R V07',

l ArroR/VEY MANUFACTURE PROCESS F TUBES OR VACUUM ENVELOPES Pierre Dussaussay and Maxime Grivot, Paris, France, assrgnors to Compagnie Generale de Telegraphie Sans Fii, a corporation of France Application .l'anuary 17, 1951, Serial No. 206,347

lairns priority, application France March 4, 1950 8 Claims. (Cl. S16-19) The invention relates to tight and permanent joints, and more particularly to vacuum tight joints designed for the manufacture of hermetically closed envelopes and especially those of radio and television tubes, gas tubes and similar devices. It aims more particularly at joints between parts placed end to end, of the same or of different materials, but offering practically the same coefficient of expansion.

The technical progress in radio-electricity, involving the use of higher and higher frequencies, imposes on the manufacturers of electronic tubes very strict conditions of geometric precision in the assembling of the electrodes, the position of which should be all the more rigorously determined and maintained as the lengths of the wave decrease.

On the other hand, the use of very high frequencies imposing special conduction conditions, often makes necessary the use of metals which are very good conductors in the making of the tight envelope. This case arises particularly when the envelope forms part of a resonator.

The conventional method which consisted of melting the end of one of the parts in order to solder it to the other part of the envelope, can no longer satisfy these conditions for the relatively high melting temperature of the metal causes a dangerous alteration of the electrodes, or else reacts on their positioning. Since the heating operation was made when the cathode was in an enclosure still lled with air, the oxidation of said cathode was always detrimental, and it caused large losses. Besides, the fact itself of using the ends of the parts of the envelope involved relative displacements of the electrodes supported by these parts, and changed their geometry.

If, in order to reduce the temperature, one resorted to the contrivance of an enamel rim between the parts to be hermetically united, one nevertheless always had to effect the fusion of this rim, introducing a collapse of the parts and a disturbance of the spacings of the electrodes, and subjecting, on the other hand, the cathode in the air to the danger of oxidation.

The present invention has as its object a new method for making stable and vacuum-tight joints, no longer having the above-mentioned defects and permitting of manufacturing the tubes with a minimum waste, and offering all the guarantees of positioning and quality of the electrodes. l

The invention is directed to an industrial method permitting the tight joining of parts made of materials with very high melting points, and particularly ceramic parts either among themselves, or with parts made of metals which are good conductors.

Furthermore, the invention permits of Sealing the glass parts without their edges being subjected to `a temperature causing their deformation; and in a general way, the invention permits of joining parts of whatever nature, without attaining the state of softening.

The invention also permits of maintaining a high vacuum inside of the enclosure during the thermic phase,

nited States Patent lice and of thus preventing any oxidation or alteration of the electrodes.

The invention permits of industrially making electronic or similar tubes for very short waves, of a very reduced size, satisfying all the required conditions.

Finally, the invention permits of effecting tubes made entirely or partially of ceramics or of glass, in which the tight joints serve as lead-in current conductors.

According to the invention, the surfaces of the parts designed to be placed in contact, after having undergone a suitable machining, are coated with a thin layer of silver closely adhering to the support and in tight contact with it. This silver coating is then polished as carefully as possible, preferably to an optical polish. The parts are then applied one against the other so as to form the closed vessel which is then subjected to the pumping operation until a high vacuum is obtained. The tightness while cold already secured from the contact between the optically polished coatings, concurrently with the effect of outer pressure owing to the vacuum, makes this operation possible. The completely emptied tube is then subjected to a heat treatment having the effect of bringing the joint between the silver coatings to a temperature which transforms it into a permanent seal, free from oxides, by molecular diffusion between the two parts under the combined effect of the heating and the pressure. This operation is assured by any suitable means, and preferably inside the degassing oven; and the thermic application is controlled so that the support-parts do not reach the state of softening. The cold-tight opticallypolished contact is thus transformed into a permanent joint, without the intermediary silver layer, nor its supports, undergoing a softening effect, and thus without risk of deformation by the action of the external pressure.

The use of silver films is particularly advantageous in all cases in which the parts of the joint are made of materials which do not diffuse one into the other by molecular diffusion, or do so at too high temperatures, at the risk of causing the softening, and thus prohibitive deformations of these parts. In certain cases, especially when one has to do with parts in which the silver can diffuse directly at a temperature lower than that of the softening of the parts, oneV could use, without thereby departing fromthe scope of the invention, a single silver film, covering only one of the parts, the other remaining bare and receiving of course, the appropriate polishing. The molecular diffusion will thus be produced between the layer of silver and the polished surface of the bare part. In general, this layer of silver will be placed on the part offering the least affinity for molecular diffusion, and particularly on the ceramic part in case of a ceramicmetal joint, or on the metal in case of a metal-glass joint, etc.

For the silver, any other substance may be substituted, preferably non-oxidizing, which satisfies the conditions of close adhesion to the support, forming a tight and continuous film and lending itself to an optical polishing and to molecular diffusion at relatively low temperatures, and particularly that of the degassing, lower than those causing the state of softening of the component parts.

Instead of placing the parts end to end and reconciling; their expansion coefficients, one could, according to one variant of the invention, also give them a concentric arrangement and thus be able to use parts having different coefficients and working at radial compression.

For the silver one could substitute gold or platinum, both of these metals perfectly satisfying tne above-stated characteristics, and furthermore lending themselves to a molecular diffusion which assures the joint, at temperatures very much below those of their softening, and consequently lending themselves to a heat treatment transforming the tight contact into a seal not necessitating an exact control of the heating Vmeans, which is Aof particular interest in the use of ovens for this purpose.

According to one variant of the invention, the surfaces designed to come into contact, after having been carefully prepared so as to conform or adjust perfectly to one another, are cleaned and receive the silver by painting, in the colloid form mixed with a small amount of enamel powder serving as a glue; this deposit is then subjected to a suitable heat treatment process.

According to another variant of the invention, thc metallic coating could be effected by electrolytic deposit, indicated especially when it is a question of metallic supports.

lt is very useful, for the polishing, to anneal the glass parts in order to annul the internal tensions which exist in the glass, and which may, at the moment of heat treatment designed for the sealing, cause detachments between the parts, thus compromising the tightness of the joint. This annealed effect is often obtained before by the baking of the silver-enamel layer, described above, if the temperature of this baking, as well as its length, correspend to the annealing conditions for the glass in question.

The envelope effected according to the invention will be characterized by the presence of a thin layer of silver or of another equivalent metal, extending over the whole section of the joint, between the different parts and more particularly in contact with its ceramic or glass parts.

The opposite optically polished surfaces being in general more extended than the seal proper limited to the intimate contact, the envelope will offer in addition the characteristic particularity of the presence of a glittering surface in the vicinity of the seal, owing to the fact that the heat treatment regulated well below the softening temperature, has not altered the state of this surface.

lf the silvered surface exceeds the joint proper, outside of the enclosure, it will in time lose its glittering appearance because of the oxidation of the silver, but will nevertheless retain its polished appearance.

The finished envelope will be also characterized by the fact that the edges of the parts in tight contact, and more especially of the glass parts, have kept their initial shape, the heat treatment not having made them pass into the viscous state; in particular they retain their sharp edges due to their surfacing. These parts also retain the sharp and weil-pronounced angles between their edges.

The tube made according to the invention can have terminals or equivalent external means of connection, joined to the silver layer of Ythe joint, between the parts made of insulating substance.

An oscillograph tube made according to the invention will have a terminal glass plate supporting the fluorescent screen, sealed by the silver hlm to the body of the envelope, and this film will be extended onto the outer wall in such a way as to engage there the current Contact, as on thc inner part, so as to join this contact to the conducting coating inside of the tube.

Other modes of manufacture and assembling electron discharge tubes will be described in detail in the text which follows.

By way of non-limiting examples, and in order to illustrate the numerous possible applications of the method according to the invention, there have been shown on the accompanying drawings several embodiments or types of vacuum enclosures made according to this method.

Figure l is a vertical sectional view of a sealed disk triode of the so-called light-house-tube type, the walls having parts ot glass and parts of metal; Fig. 2 is an enlarged fragmentary portion of the structure; Fig. 3 is a vertical sectional view showing the application of the invention to a tube structure where the walls are formed from ceramic material; Fig. 4 shows in longitudinal section a television-oscillograph cathode ray tube made according to conventional methods; Fig. 5 isla longitudinal sectional view of a television oscillograph-cathode ray tube manufactured according to the method of this invention; Fig. 6 shows the application of the method of the invention to the manufacture of a conventional electron discharge tube; and Fig. 7 is a vertical sectional view showing the assembly, according to the invention, of an exterior anode type of tube.

In the example of the invention as applied to a lighthouse-tube such as that shown in Fig. l, the method of the invention permits of obtaining a great precision, because of the fact that the seals are made metal on metal, without the interposition of oxides. The dilerent elements of this tube are: a base of pressed glass A, bearing the cathode block G; a cupel B in metal welded to the glass, for example in dilver p coppered or silvered (dilver being an alloy, corresponding to Kovar, of iron, nickel and cobalt); a glass ring C; a metallic disk grid support D; another glass ring E; finally, an anode-holder part F, for example of the same metal as the part B.

The edges of all these parts, in 1, 2, 3, 4, 5, 6, 7, 8, 9, and 1t) are perfectly dressed by line emery wear on a metallic plane; a subsequent cleaning removes all trace of abrasive and grease from these surfaces, which are then covered by brush with a tine layer of metal in the colloid state, for example colloid silver containing a very small proportion of powdered enamel. This done, the different parts are tired in the furnace at a temperature generally between 450 degrees and 750 degrees C., for a suitable time, variable, moreover, with the baking temperature. A final surfacing, consisting of friction on a cloth polisher smeared with polishing paste permits of reaching a degree of polishing suitable for the layers of colloid metal.

It sutiices therefore, to align the diierent elements thus prepared one against the other in complementary relation, to make the vacuum in the enclosure formed by this juxtaposition (the external atmospheric pressure sutlicing to maintain the various parts firmly applied the ones against the others), and finally, to bake the whole at about 450-500 degrees C. for at least an hour. After cooling, an extremely strong enclosure is obtained, comprising live perfectly tight sealings.

The sealing operation is more clearly disclosed in Fig. 2, showing on a very much enlarged scale, the joint between the parts A in glass and B in metal of Fig. 1. 1B and 1A represent in Fig. 2 the thin layers of silver adhering solidly and tightly to the surface of these opposite parts and forming there a continuous lm. Their thickness will vary for example between 0.2 and 3 hundredths of m./m. depending on the number of layers applied. These layers are optically polished and their close contact keeps the vacuum. The envelope can be exhausted to a high vacuum. subjected to heating inside of an oven, this contact is transformed into a seal by the phenomenon of molecular migration between the two films, when the temperature has reached to around 450 degrees C. During this transformation the joint is subjected to the outer atmospheric pressure, and it completely retains its solid structure without reaching the viscous state, and consequently continues to support the vacuum.

This relatively low temperature of molecular diffusion assures a relatively large margin of safety before reaching the point of softening of the glass, which is located at around 530 degrees C., which is very advantageous in the case of glassrparts; and this temperature is thus a 'good deal lower than that of metal deformation, which is practically the same as its melting point and is located for silver, at around 950 degrees C. Thus one runs no risk of softening the parts in contact and one is completely able to assure this heat operation in the oven which serves for the degassing, and to combine it with the degassing operation without being obliged to carefully regulate the temperature of the oven.

It is to be noted that the fraction PO inside the space of the surface of the layer 1A, which extends beyond the joint proper at the interior of which the two lms are closely bound together by forming a homogeneous layer. The interior extension of the joint will retain its opticallypolished appearance. In fact, since the seal is produced at a temperature considerably below than that of melting for silver, its surface will not undergo any alteration and will keep the glittering appearance.

The glass part A as well as the metal part B, not having been subjected to the deformation temperature, Will completely retain their initial shape and will in particular retain the sharp angle tp caused by the initial machining; and the silver film will also retain its mechanical resistance. The geometry of the tube will undergo no alteration in the course of the sealing.

Since the heating operation is made while the electrodes are in the high vacuum, no alteration, and particularly not their oxidation occurs.

No oxidation is to be feared either, of the internal walls of the metallic parts of the envelope of oxidizable metals, such as copper. This is especially advantageous in electron discharge tubes designed for centimetrical waves and of which the metallic walls form part ofthe resonant cavities. Even a supercial oxidation introduces losses in such tubes which compromise the operation, because of the pellicular effect of the conduction. For its part, the silver joint not being subject any trace of oxidation, does not risk offering a resistance to the surface currents.

Instead of giving a plane shape to the contact surfaces, in numerous cases, in order to facilitate the manufacture, they will be given a slight curvature. The surface of one of these parts will be convex, the surface of the other will offer a complementary concave profile taking on exactly the profile of the first part. These profiles are obtained by friction (as well during the griding operation as during the polishing) against a suitable body of spherical shape. This latter will in most cases be driven by a rotary movement.

in the example of manufacturing the vacuum tube shown in Fig. 3 the different elements of the wall are described successively as a base-cupel H in tight ceramic, bearing the cathode block G; a cupel I and a disk I also of tight ceramic; and finally a cupel of tight ceramic K bearing the anode L of dilver p. The edges of these parts, 11, 12, 13, 14, and 16 are silvered according to the process described above; on the other hand, the cupel I as well as the disk l' are silvered on part of their surface to serve as current lead-in conductors, appearing for example, in the form of coaxial conductors; finally the traversing conductors M from the cathode block G are metallic, whereas the exhaust tube N is of glass. The assembling of the tube is accomplished as in the case of Fig. l.

The method of the invention finds a particularly interesting application in the construction of television cathode oscillographs, the making of which is quite delicate, especially when the tube is to have a large diameter.

In these tubes, in fact, of which Fig. 4 shows one section, it is necessary to have a post-accelerating electrode generally made up of a colloid graphite layer O placed on the inner wall of the enlarged part of the tube, this layer being brought to the high tension potential by the intermediary of a metallic traversing conductor P.

in the example of manufacture according to the method of the invention of an oscillograph tube, shown in Fig. 5, the end-plate Q serving as viewing screen is covered over on its periphery, at 17, with a thin layer of polished silver; likewise, the edge of the bulb R at 18 is covered with a similar layer of silver, a layer which extends onto a part of the wall, toward the inside at 19 and toward the outside at 2t); finally the colloid graphite O is deposited on the inner wall 21 and also partially covers the silver layer 19.

After assembling the mirror Q and the bulb R, and then baking, a tight sealing without deformation is ob- Cil tained; the silver circumference of the end of the bulb, as all around the screen, constitutes an integral part of the accelerating electrode and serves at the same time as metallic traversing conductor for this electrode.

Furthermore, the luminescent layer deposited at 22 on the internal surface of the mirror Q cannot be negatively charged, since it is joined by the peripheral silver layer 17 to the post-accelerating anode itself. In addition, the mirror Q can be perfect, for it can be optically surfaced, which is not of negligible interest in projection tubes.

Fig. 6 deals with the manufacture of a conventional tube by the method of this invention. The base S and the flask T are as hereinbefore, silver-plated on their 'edges at 23 and 24, edges which may be of polished spherical surfaces, which facilitates the obtaining of a suitable optical polish when it is a question of using flat pressed bases.

Finally, Fig. 7 shows the construction, by the method of the invention, of an external anode tube. The space of this tube is made up successively of the anode U, which may be of copper, to which there will be united a part U in the shape of a ring of dilver P metal brazed at u onto the body of the anode; by an insulating part V, of tight ceramic, profiled in such a fashion that it increases the lines of leakage; by a metal ring, W, of dilver p"; and finally by a base-cupel X of tight ceramic supporting, with W, the grid and cathode G.

The edges of the different parts are rectified, silverplated, then polished, at 25, 26, 27, 7.8, 2S? and 3f), and then assembled and sealed as in the preceding forms of the invention.

While our invention has been described in certain preferred embodiments, it is realized that modifications may be made and no limitations upon our invention are intended other than may be imposed by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope in abutting relationship, consisting of machining the opposed edges of the coacting parts to give them complementary surfaces enabling the parts to establish an accurate mating relation, coating at least one of the mating edges with a thin layer of a substance which adheres intimately and tightly to the surface of the said edge, said coating having the property of molecular diffusion under pressure in the material of the edge of the opposite mating part at a temperature lower than the deformation temperature of said joined parts, imparting to said coating and to the edge of the opposite mating part a polish of the character required for a vacuum-tight contact-joint, creating a high vacuum within said parts when in assembled mating relation with said polished edges in direct contact, and heating the zone of said contact while submitting the mating parts to pressure to seal the contacting intimately mating edges by the effect of their molecular diffusion in a solid state below the deformation temperature of the parts.

2. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope, as set forth in claim l, in which said polished coating is formed from metal.

3. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope, as set forth in claim l, in which both envelope parts to be joined are coated with a metal film adhering intimately and tightly to the envelope part, each film being polished, so as to form, when in mating contact, a high vacuum-tight joint.

4. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope, as set forth in claim 1, in which both envelope parts to be joined are coated with a silver film adhering intimately and tightly to the envelope, each film being polished, so as to form, when in mating contact, a high vacuum-tight joint.

5. A method of producing a vacuum tight sealed joint between parts of a hermetic envelope of an electron tube and similar device, consisting of machining the opposed edges of the envelope parts to give them complementary surfaces for establishing an accurate mating relation therebetween, coating each of said edges with a metal lm adhering intimately to the parts and having the property of mutual molecular diffusion in the solid state under pressure at the temperatures which are substantially lower than the temperatures at which the joined parts undergo deformation, polishing said lms to an optical degree, assembling said parts in mating relation to form a vacuum tight envelope, pumping out the envelope to high vacuum and, while the parts are compressed by the external air-pressure, submitting said envelope to degassing operation, the temperature of which is regulated to seal the contacting polished edges by the ettect of their molecular diffusion in a solid state below the deformation temperature of the parts.

6. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope as set forth in claim 5, in which the metal film with which the parts are coated consists of a thin layer formed by a mixture of colloidal silver and enamel in a paint-like state, and wherein the coated parts are initially heat treated by ring to form a solid coating prior to said polishing operation.

7. A method of producing a vacuum tight sealed joint between two parts of a hermetic envelope as set forth in claim 5, wherein at least one of the parts to be joined is of glass, and wherein the sealing of the hermetically mating optically polished metal coatings is secured by keeping the degassing temperature below the deformation temperatures range of the glass and Within the difusion temperatures range of said metal coatings.

8. A method of producing vacuum tight envelopes for electron tubes and similar devices comprising at least one glass part, consisting of machining the opposed edges of the` envelopeA parts to be joined, to give them complementary shapesfor establishing an accurate mating relation therebetween, coating each of said edges with a silver lm adhering intimately and tightly to the part, polishing said films to an optical degree, assembling said parts in mating relation to form a tight envelope with said silver film disposed between the parts, pumping out said envelope to high vacuum and, while the parts are compressed by the external air pressure, submitting said envelope to degassing operation and, during said operation, heating the contacting polished edges to seal them by the effect of their molecular diffusion, said heating operation being regulated to avoid the deformation of the envelope glass parts.

References Cited in the file of this patent UNITED STATES PATENTS 227,370 Man May l1, 1880 1,079,804 Sidon Nov. 25, 1913 2,099,531 Passarge Nov. 15, 1937 2,100,187 Handrek Nov. 23, 1937 2,133,492 Vatter Oct. 18, 1938 2,141,677 Zegenbein Dec. 27, 1938 2,229,436 Beggs Jan. 21, 1941 2,250,986 Dobke July 29, 1941 2,334,020 Miller Nov. 9, 1943 2,351,895 Allerding Ian. 20, 1944 2,450,130 Gordon et al Sept. 28, 1948 2,504,504 Despois Apr. 18, 1950 2,568,460 Nolte Sept. 18, 1951 FOREIGN PATENTS 579,191 Great Britain July 26, 1946 OTHER REFERENCES Principles of Radar, M. I` T. Radar School Staff, secondV edition (1946), McGraw-Hill Book Company, Inc., Chapter IV, pages 4-48.