US2449759A - Electrical seal - Google Patents

Description

2 Sheets-Sheet l f INVENTOR. cazrf ATTORNE v H. O. BARSCHDORF' ELECTRICAL SEAL Harry Haras' Sept. 2l? 1948.

Filed May 5, 1944 Mfness: 542ML um( Sept 21, 1948. H. o. BARscHDoRF 2,449,759

ELECTRICAL SEAL.

Filed May 5, 1944 2 Sheets-Sheet 2 HARRy afA/escf/@ORF INVEN TOR.

' Patented Sept. 21., 1948 Harryh 0. Barschdorf, Sprague Electric Adams, Mass., assigner to Company. North Adami,

Mass., a corporation of Massachusetts Application May 5. 1944. Serial No. 534,192

` 1o claims. (ci. 18a-365i This invention relates to improved electrical sealsyand more particularly refers to improved hermetic glass-to-metal seals.

Broadly speaking, the Aart of making seals be- 'tween glass and metal members has been practiced for some time. Unfortunately, however, the

efforts in the prior art to pro'duce permanent. hermetic glass-to-rnetal seals for assemblies likely to undergo wide temperature changes. Ihave been, for the most .part unsuccessful. One' type of seal proposed is described in U. S. Patent No. 189,778, in which a glass tube is placed in a molten bath of solder or other low-melting alloy andthe metal allowed to cool and solidify about this outer sui,- .iaces ci the glass tube. By thisV method, however, no drm and integral bond is formed between the glass and the rnetal.- Thereiore, the permanence ci the hermetic seal is limited, at best.

in general, it has been impossible to produce glassto-rnetal assemblies which withstand without rupture the eect of temperature changes, due to the vast dierence in the temperature coeihci'ents of expansion of the materials, the metal coemcient usually being 4 or more times as great as the glass cccmcient.I

llt is an object of this invention to overcome the foregoing disadvantages. A further Objectis to produce 1 a permanent, hermetic glass-to-metal seal." A still further object is to produce a permanent hermetic glass-to-metal seal capable ci v' withstanding temperature changes oi 160 C.

without rupture. A still further object is to loroduce a permanent hermetic glass-to-metal seal with a strain-absorbing iange incorporated therein. 'A still further object is to produce a permanently hermetically sealed .container i'or electrical equipment. A still further object is to produce a permanently hermetically sealed coutainefr for electrical condensers and related devices. Additional objects will become apparent said glass member. The invention is further prisiugr a glass member, on the outer surfaces o'fA concerned with a glass terminal cap seal comwhich is provided at least in par-t a thin, integral ly bonded metal layer, a metal cap member com-g prising a conical section and a cylindrical section, the edges of which,'not adjacent to the conical section, are provided with a radially extending lip, the cylindrical portion of said cap -being positioned about the metal surfaces of the glass member and being intersoldered therewith. '.ihe invention is further concerned with novel strainabsorbing members useful in producing glass-tof metal seais.l 4

lin its broadest aspect, the invention disclosed .herein is applicable in producing 'hermetic seals between metal surfaces and glass.. porcelain or other high-temperature inorganic insulators hy use' o'i strain-absorbing'iianses or members therebetween, to be hereinafter described. A consideration of the physical or structural conditions, as

' well as the electricaland chemical conditions, has

from a consideration of the following description andclaims.

"ihese objects are attained in accordance with the present invention wherein a strain-absorbing flange is introduced between the metal assembly and the glass assembly. Ina more restricted. sense, this invention is concerned with a glass-tometal seal comprising a metal surface, a conical metal ange whose 'radial elements are at an angle with respect to the planeof the metal surface. and a glass member, whose surface is Drovlded at least in part with an integrally bonded,

thin metal layer, said metal surface being soldered to said -ilange and said ange being soldered to said integrally bonded metal layer on indicated that a permanent seal 'betweeninsulators and metals can be achieved only by interpositioning sme Adevice therebetween, to eliminate extremeforces, tensile and/or compressive in nature, onthe relatively fragile glass or other cerc surface. This. however, cannot be realized simply-.by utilizing a relatively thick interlayer oi' solder, inorganic cement, etc., `between the members. According introduced a carefully and particularly designed metal stresses and strains due to unequal expansion and contraction without affecting the more delicate consti-tuents of the assembly.

The types of inorganic insulators which may be employed with good results in producing the seals of the invention are many. Outstand-r ing 'hermetic seals have been obtained using thin or thick walled tubes of eIectricaVPyreX, a boro' silicate glass? Also :satis-factory are ceramic materials generally. suchas non-porous steatites. porcelains, etc.r

The metals to which the seals are joined, an'd the insulators thereby attached, are not limited, except that it is preferable that they may be readilyrsoldered. "MoneP metal, tinned metals,

copper, aluminum. zinc, lead, silver, terneplate tand other metal surfaces may be employed. In zgeneral. the metal surfaces to which the seals are 'joined are part oi a container of some type :lor

equipment' requiring hermetic sealing from the eiects of corrosive atmospheres. humidity. etc. For example, they may be the ends of glass tube -to the invention, there is.

member whose `function. is to absorb .c'an-type containers for condensers,

2,386,628, patented fuses with the glass means for producing on or the tops of networks,

enclosed condensers and resistors,

etc.

The first step in the production of the seals described herein is the preparation of a thin metal layer on a .part of 'the surface of the glass or other insulating nontallic member. This thin metal layer is preferably bonded to the glass by a minute interlayer of lead oxide or other common medium,

which may chemically react with the glass to pro- Such a layer and interlayer and the formation thereof is 'described in detail in co--pending application Serial No. 445.609, filed on June 3, 1942, by M. Nazzewski.V now Patent No. October 9, 1945. Briefly, the process comprises heatlng"the glass member to a temperature approximating the melting point of the metal or alloy to be deposited thereon-and spraying the molten metal or alloy (preferably 97.5% lead and 2.5% silver) onto the glass surface, causing formation of lead oxide to some degree in transit. The lead oxide apparently interto form an integral chemical bond therewith and with the unoxidized portion jof the sprayed metal. The thin metal layer thus duce a lead glass.

` `formed is readily soldered to, and acts to some degree as a strain-absorbing layer and permanently maintains its bond to the glass.

However. it is to be understood that other the glass a bonded metal layer may be used. if so desired. For example. cathode sublimation of a metal on a heated glass surface maybe employed.

Reference is made to in which: v

Figure l represents the cross-section of a terthe appended drawings minal-to-container seal,

f Figure 2 'represents the cross-section of a terminal end seal, and

Figure 3 represents the cross-section of another terminal end seal.

Referring more spe iically to Figure i, a thickwalled glass insulator is shown passing through a metal surface and sealed thereto in accordance with thel invention. Such a terminal device is useful in high-voltage electrical equipment, where a conductor is led through the insulating tube as one terminal. v

In this figure, l represents a thick-walled cylindrical tube of electrical Pyrex through which passes a conductor It, and upon the surface of which is deposited or otherwise applied a thin metal band i i, preferably in an integral chemically bonded relationship therewith. The thickness of this metal layer is greatly enlarged for the sake' of clarity. I6 represents a terneplate metal sheet, which has been punched to form a hole for the glass tube and then the edges crimped into a position Il, which may be represented as a. groove into which the outer edge of a ange I2 fits, therefore being concave with respect to the flange.

The strain-absorbing flange I2, according to l one of the preferred embodiments of the invention comprises a conical section. whose inner lip I3 is radially turned inwardly until parallel with the axis ofthe cone, thus forming a cylinder.

I'he angle between the elements of the cone I2 and the plane of the metal sheet I6 is represented by I and is advisably at least 45 degrees, and

. preferably 50 degrees or somewhat greater. The

axis of the tube I0 is preferably perpendicular to the plane of the metal sheet I6.

The flange I2 may be produced from deep drawing steel.- In the device illustrated its thickness is from .010" to about .012, although, for larger or smaller glass tubes and terminals. this range of values may be varied tofit the physical requirements of the flange. Other metals or alloys may be used for the flange.

The flange I2 is soldered to sheet Il by solder I1; and it is soldered to layer II by solder Il.

1t is advisable that the layer II, flange I2 and metal IG be readily soiderable. If they are not readily soiderable, a layer of metal which is may be applied thereto.' For example. they may be Y tinned. either by the electro-tinning or dip-tinning methods, with excellent results.

According to another preferred embodiment of the invention, the various components of the assembly are first affixed into their ultimate positions by suitable blocks. clamps. etc. Following this. ajgas torch flame is applied to the portions of the flange I2 and metal sheet I6 to be soldered. Solder is then applied and fills the concavity between the outer conical edge of the flange I2 and the crimped portion I4. The torch is then applied to the upper and inwardly curved lip of the flange Il, without heating the metal layer II to any great extent. Solder is then applied and flows into the channel between the flange and the metal layer. Often the first heating of the divergent endl of the flange is sufficient to cause enough heat transmission to the convergent end lto permit soldering without additional heating.

The so-formed hermetic seal may then be used as a. terminal for an electrical condenser or network. as indicated by I9 which represents an electrical lead.

In soldering the extremity of the flange to the metal layer I I, most satisfactory results have been obtained by restricting the flow of the solder so that it ,does not extend to the edges of the metal layer' ii'. It is advisable for the minimum distance between the solder and the metal layer edge to be at least in the case of tubes of 1/2" outside diameter or less and correspondingly vgreater in the case of tubes of larger outside diameter. This figure applies' for both thin and thick-walled tubes. although with the former, the minimum distance is somewhat more critical.

Referring now to Figure 2, an end cap seal for a glass terminal is illustrated in cross-section. The glass tube might be the end of the tube shown in Figure 1, for example, in a condenser assembly.

The glass tube .30 is composed of' electrical Pyrex rial, the end thereof being preferably ground to a plane perpendicular to the axis of the tube. A thin metal layer 3l is positioned upon the outer cylindrical surface of the extremity of the tube. This layer preferably adheres to the glass by an integral chemical bonding, as heretofore described.

The metal cap 32 is a preferred embodiment of the invention and is hermetically sealed to the tube end as hereinafter described. Geometrically. the cap 32 comprises a cylindrical section l5, slightly larger in diameter than the glass tube, the lower edges of which are turned or pressed into a radially extending lip 4I, a conical frustum 33, and a p ,lane surface 34 defining the outer extremity of the cone frustum. A hole is provided in the center of the plane surface 3l, through which terminal lug 31 is riveted. and electrical lead 40 is extended. The angle 42 between the cone elements and the axis oi' the tube should generally -be no more than 4B degrees and preferably about 30 degrees. The riveted lug 31, the

by solder 3l at any time convenient to the assemor a similar inorganic insulating matebly of .the apparatus. For example, the soldering may take place following impregnation of an electrical condenser whose terminals are produced in accordance with the invention.

The cap 32l and the metal layer 3i may be intersoldered by solder 39. It is preferable to rapidly heat the portion of the cap to be soldered to the metal layer, as for example, by use of a torch flame. The heating should be uniform about the circumference of the cap and need not be appreciably higher than the-solder melting point.

As in the case of the seal illustrated in Figure 1, the. solder 39 should be limited in its now so as not to reach any edges of the metal layer 3| 'I'he minimum distance between the solder 39 and the edge of. the metal layer 3l is preferably at least 1%" when the outside diameter of the tube 30 is 1/2" or less, and correspondingly greater when the outside diameter of the tube is greater than 1/2.

The cap, by virtue of its design, will substantially absorb the expansion difference between the metal components and the glass component, when the seal is produced as indicated. It is preferably pressed from deep drawing steel .sheets of about .010" to .012" in thickness, al-

though greater or smaller thicknesses may successfully be employed. It may be electroor diptinned to facilitate soldering. This is, of course, also applicable with respect to the lug el and lead t0.

The terminal lug 3l may be replaced by a nut and bolt combination, a plug-in assembly or other common type of electrical connector.

Figure 3 represents a Across-section of a modined cap and exemplifies one Vof the preferred embodiments of the invention. Due to. the nature of the production of insulating tubes of electricai Pyreia it is not uncommon for the outside diameter to vary by considerable amounts from piece to piece. To compensate for this variation in tube diameter, the cap shown in Figure 2 is produced with a modied cone frustum, the lower section of which is curved inwardly.

In Figure 3, the so modiiied cap is shown with thek cone frustum tid at an angle of no more than with respect to the axis of insulating ltube dii. The cylindrical portion 53 of the cap nts over the end of tube 50, co-axially with metal band 52, to which the cap is eventually soldered or otherwise bonded.

In the case of the modified cap of this iigure, the inner diameter of the cylindrical portion 93 may be somewhat greater than that of the cap shown in Figure 2, to permit use on all insulating tubes to which it is to be sealed. The lower portion 55 of the cone frustum is curved inwardly, thus providing amore nearly fiat inner surface which will bear on the tube end 5i. Thus, if the tube diameter is less than the prescribed value, the end 5| will not extend materialy beyond the cylindrical portion 53 of the metal cap. In this way uniform assembly heights may be produced. The inward curvature shown in Figure 3 may be defined, with reference to the conefrustum, as a l section of increasing divergence.

Having described illustrative applications of the stress-absorbing anges or caps of the invention, it is apparent thatseveral structural features. are important and should be incorporated therein for optimum results.

In the caseof a glass member protruding through a metal piece, these are:

1. The conical flange should be at an angle of at least 45 degrees with respect to the plane of the metal component:

6 i 2. The radially turned lip of the inner flange extremity must be substantially parallel to the metal layer and therefore to the glass tube; 3. The solder must not extend to any edge of the metal layer on the glass tube;

4. In producing the seal, the glass tube and metal layer thereon should not be deliberately preheated.

In the case of sealing a metal cap to a glass tube, these are:

1. 'I'he conical frustum of the cap should not be at an angle of more than about 45 degrees with respect to the axis of theglass tube;

, '2. Inproducing the seal, the glass tube and metal layer thereon should not be deliberately preheated;

3. The solder must not extend to the edges of the metal layer on the glass tube'.

The above principles need-not all be incorporated in an assembly, as they are optional, but superior results may ordinarily be obtained by following them. By proper application of these principles, outstandingly permanent,v hermetic glass-to-metal seals may be produced, a tremendous advancement over the fragile glass-tometal seals oi the prior art.

i The strain-absorbing flange and terminal caps are of particular value in producing hermetically sealed electrical condensers, networks, resistors. etc. In the case of a condenser, armatures separated by porous dielectric material may be placed in an open-ended metal container and a top therefor be produced with one or more glass-tube insulated terminals with strain-absorbing ilange and cap arrangements therein, the top or metal sheet being soldered to the body of the container. The sealing of the cap end maybe accomplished following impregnation and, if desired, polymerization, of the porous dielectric spacer with a liquid or resinous dielectric material. I

Likewise, the caps disclosed herein are of great value in sealing resistance elements in glass tubes, with a cap at each end acting as a terminal, a mounting piece and to protect the glass from physical damage. The seals produced between the cap and the glass tube are permanent, and hermetic, protecting the resistor from the eilects of corrosive and humid atmospheres and the like.

`It is to be understood that the instructions Vinents ofthis invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is'not limited to the specific embodiments hereof except as dened in the appended claims.

I claim:

1.v A ceramic cylinder havinga. metallic layer .circumferentially bonded to the surface thereof, Vsaid metallic layer being bonded to and circumferentially enclosedb'y a strain-absorbing flange comprising a conical frustum, oneend'of which provides 'a circular bandyadjacent the cylindervk and the opposite end oi which is bonded to a metal surface.

2. A 'ceramic cylinder having asoma-able nie--- thereof, said metallic aseo-,vso

tallic layer circumferentially and integrally bonded Sto the surface thereof, said metallic layer being hermetically soldered to and circumferentialiy enclosed by a strain-absorbing flange comprising a conical frustum of solderable metal, one end of which is shaped to provide a circular band adjacent the cylinder and the opposite end of which' is hermetically soldered to a solderable metal surface.

3. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having a metallic layer predominatingl in lead circumferentially and integrally bonded to the surface 4layer being hermetically soldered to and circumferentially enclosed by a strain-absorbing flange comprising a conical frustum of solderable metal, the convergent end of which is shaped to provide a circular band adjacent and approximately parallel to the surface of the aforesaid cylinder, and the divergent end of which is hermetically soldered to a solderable metal surface.

4. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having ferentially and integrally bonded tothe surface thereof, said metallic layer being hermetically soldered to and circumferentially enclosed by a strain-absorbing flange comprising a conical rustum of solderable metal, the convergent end of which is turned inwardly to provide` a circular band adjacent and approximately parallel to the surface of the aforesaid cylinder, and the diverent end of which is hermetically soldered to a circumferentially indented portion of a solderable metal surface.

5. A hermetically sealed electrical device com` prising a cylinder of heat-resistant glass having a metallic layer predominating in lead circumfertially and integrally bonded to the surface thereof, said metallic layer being hermetically soldered to and circumferentially enclosed by a strain-absorbing flange comprising a conical frusturn of solderable metal, the divergent end of which is extended to form a cylinder adjacent and approximately parallel to the surface of the aforesaid cylinder, and the convergent end of which i7s-her metically soldered to the terminal of an electrical lead.

6. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having a metallic layer predominating in lead circumferentially and integrallybonded to the surface thereof, said metallic layer being hermetically soldered to and circumferentially enclosed by a strain-absorbing flange comprising a conical frustum of solderable metal, the convergent end of which is turned inwardly to provide a circular band adjacent and approximately parallel to the surface of the aforesaid cylinder. and the divergent end of which is hermetically soldered to a circumferentially indented portion of a solderable metal surface, said metal surface being in a plane approximately perpendicular to the axis of the aforesaid glassl cylinder.

ya metallic layer predominating in lead circuina solderable metallic surface.

. '2. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having a solderable metallic layer circumferentially and integrally bonded to the outer cylindrical surface of one extremity of said lic layer being hermetically soldered to and cir cumferentially enclosed by a strain-absorbing flange comprising a conical metal, the divergent end of which-increases in divergence and is extended to form a cylinder adjacent and approxlmatelyparailel to the surface of the aforesaid cylinder, and the convergent end of which is hermetically soldered to an electrical lead. i t. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having a solderable metallic layer circumferentially and integrally bonded to the surface thereof, said metallic layer being hermetically soldered to and circumferentially enclosed bya strain-absorbing flange comprising a conical frustum of solderable rnetal. the convergent end of which is shaped to provide a circular band adjacent and approximately parallel to thesurface of the `aforesaid cylinder, and the divergent end of which is hermetically soldered to a solderable metal surface. 9. A hermetically sealed electrical device comprising a cylinder of heat-resistant glass having layer circumferentially and integrally bonded to the surface thereof, said metallic layerbeing hermetically soldered to and circumferentially enclosed by a. strain-absorbing flange comprising a conical frustum of solderable metal, the convergent end of which 'is turned inwardly to provide a circular band adjacent and approximately parallel to the surface of the aforesaid cylinder, and the divergent end of which is hermetically soldered to a circumferentially indented portion of a solderable metal e. 10. A hermetically sealed electrical `device com- 'prising a cylinder of heat-resistant glass having integrally bonded to the surface thereof, said metallic layer being hermetically soldered to and circumferentially enclosed by a strain-absorbing nge comprising a conical frustum of solderable metal, the divergent end of which is extended to form a cylinder adjacent and approximately par- 0 allel to the surface ofthe aforesaid cylinder, and

the convergent end of which is hermetically soldered to an electrical lead.

u HARRY O. BARSCImORF.

REFERENCES CITED ,The following references are of record in the ille of this patent: f

UNITED STATES PATENTS Number Name Date 1,564,690 xruh et al Dec. e, 1925 1,166,217 Jackson Dec. 28, 1915 4 2,053,765 Dana Sept. 8, i936 2,194,8 86 Dallenbach Mar. 26, 1940 glass cylinder, said metal-A frustum of solderable.

a solderable metallic layer circumferentially and

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