US2944325A - Method of making hermetically sealed electric terminals - Google Patents

Description

Richard U. Clark INVENTOR ATTO RN EY R. U. CLARK Jury 12, 1960 METHOD OF MAKING HERMETICALLY SEALED ELECTRIC TERMINALS Original Filed April 27, 1953 heating before completion of Patented July 1.2, 1960 Unite States Patent Qfice METHOD OF MAKING HERMETICALLY SEALED y ELECTRIC-TERMINALS Richard U. Clark, 4 Orchard Drive, West Acton, Mass.

Ori inal application Apr. 27 1953 Ser. No. 351,317, nw Patent No. 2,774,s12,datea Dee 1s, 1956. D1- vided and this application Dec. 6, 1956, Ser. No. 626,647

3 Claims. (Cl. 29e-155.55)

tributing causes of failure have been attributed to darnag'e dueto faulty land improper installation, subjection to higher voltage and amperage conditions than the ratings for which the terminals were designed, and due 'to'.nu

merous other factors. h

l These and .other difficulties have been either comy pletely or largely overcome by my improved methods of making such terminal constructions, the relative arrangement and installation of the component parts and the improved methods and materials utilized in their manufacture and assembly. In itssimplest form my improved terminal comprises essentially a metal yelectrode or central stud and a surrounding tubular metal shell between Vwhich is squeezed inV a novel relationship a` resilient `plastic insulating cup or insert having high dielectric strength and resistance to., heat. l vThe metal stud may `preferably be barbed andproyided [with enlargements on its shank as well as a recess orrrejentrant space having a relatively sharp knife edge at the mouth of the recess. The metal shell may b e similarly-provid'edwith a sharp chamfer orxknife -edge which cuts 'intb `the plastic insert in a manner rwhich improves the hermetic seal. The insert may preferably be formed of a plastic material having high insulation resistance, extremelyl low moisture adsorption, cold flowing and memory shrinkage characteristics such as for example Teflon, or tetrafluoroethylene. The completed terminal acquires extremely high hermetic sealing properties by initially pre-assembling the insert inthe shell, then inserting the stud part way into the insert causing large'distortio'n ofthe same, permitting the latter to relax and accelerating its partial return by the assembly, all preferably done within a vacuum.

Itis accordingly a major object of the present invention to provide an improved method of making a terminal construction which is readilyvcapable o'f providing hermetic sealing by the use of limproved materials and methods which are reasonable 'in cost, fool-proof in application and which stand up longer and Vmore satisfactorily under severe operating conditions. It is a further object to' providefimpr'oved methods of making terminal constructions of improved semi-resilient high Vresistance type Vwhich more readily retain their hermetic sealing properties and maintain their high insulating characteristics under severe conditions of ultrahigh frequencies,

extremes in temperatures and pressures, as well as to withstand sudden impacts and shocks. A further object resides in an improved method of forming and assembling the plastic insert by initial heating and stretching, then cutting, forming and assembling, preferably Within a vacuum, and subsequently re-heating the entire assembly to accelerate its return and filling of the spaces within the terminal due to the memory characteristics of the material by which it derives its high hermetic sealing propcrties.

Other objects and advantages of the present invention reside in the improved methods and details of making the components and their assembly, and these and other objects and advantages will become apparent to, those skilled in the art after reading the following description `taken in conjunction with the accompanying drawings, forming a part hereof,.in which:

Fig. 1 is a detail view of the barbedr metallic electrode' stud;V

Fig. 2 is a similar View of the plastic insert;

Fig. 3 is a like view of the metallic shell;

Fig. 3A is a sectional view of a modified metallic shell;

Fig. 4 is a` sectional view of the terminal assembly comprising the components shown in Figs. 1, 2 and 3;

neck portion 6d. A flanged metallic tube having a tubular wall 6g and a fiange f is forced down along the vshank 6a on which it fits tightly extending partially over the neck portion 6b. The tubular wall 6g is of an axial length which exposes a portion of the main shank 6a above the flange f to provide an upper electrical terminal and also exposes a portion of the neck portion 6b adjacent the bulb portion 6c. The flange 6f and the tube 6g maybe sweated upon the shank 6a, or alternatively these parts may be formed integrally with each other. The lower en d ofthe wall 6g is internally ground with, a chamfer or bevel to provide a sharp knife edge 6h.

Fig.V 2 shows the insert 7 Iwhich may preferably be formed of Teflon (tetrafluoroethylene) or a similar plastic composition material having a memo'ry characteristic. I have found Teflon highly satisfactory for the insert of my improved seal, this material withstanding compression pressures of several thousand p.s.i. under which it may distort due to its cold flowing qualities upto about 35% fro'm which it may relax vto under a 15% distortion when most of the distorting pressure is relieved. The material used has very high insulation resistance and pratically Zero moisture adsorption, having a practical range of hardness of from 55 to 70 durometer scale. The insert is preferably made from tubing or tubular sto'ck of an outside diameter slightly greater than that of the flange 7c. The tubing is then heated to from 26910 400 degrees F. and stretched in the manner of an elastic cord while heated. The plastic insert 7 ls permitted to cool and is cut or formed to provide the flange 7c and preferably Vformed as a flanged tube with a tubular wall 7a, having a central bore 7b and an integral flange or shoulder 7c, The bo're 7b is preferably of lesser, diameter than the outside diameter ofthe portions 6c, 6e and 6g of thestud 6 which is forced within the bore 7b. Similarly the outside diameter'a is slightly greater than the bore 8b of the metallic sleeve 8 into which the insert 7 lis also forced. All of these parts are dimensioned to take the maximum advantage of the shrinkage or memory characteristics of the particular material of which the insert is formed.

Fig. 3 shows the tubular metal shell component 8, which may preferably be formed of brass or other metal having a tubular wall 8a, with a central bore 8b and an integral flange 8c, which may have an outside diameter approximatelythe same as that of the flange or shoulder 7c. The lower terminal is preferably bevelled to form the sharp knife edge 8d. In Fig. 3A there is shown a mo'diiied form of the shell component, identified by the numeral 9, having a similar wall 9a, internal bore 9b, flange 9c, and knife edge 9d, but with its bore 9b provided with an extra internal sharp edge annular ring 9e. This helps to push the plastic insulator insert 7 in so it can be bored or sliced into by the tubular stud extension 6g provided with the internal knife edge chamfer 6h.

The terminal lis preferably assembled as follows: After the insert 7 has been cut and formed as described above and has been permitted to become cooled i-tV preferably is in :the shape shown in Fig. 2, with the exception of course that for purposes of convenience it has been illustrated to a greatly enlarged scale, as have the other components in each of the figures. The insert 7 is then forced into the shell or sleeve 8, when making the terminal assembly of Fig. 4, until the bottom of the flange or .shoulder 7c rests against the tiange or shoulder 8c of the shell 8. The barbed electrode 6 is then forced into the central hole or bore 7b of the insert 7 about half way. The barb-like point 6e and the rounded cylindrical bulb or enlargement 6c, as well as the electrode tube 6g, expand the insert 7 which has considerable cold flow. In the case of the double knife edged shell 9 the electrode 6 is forced in far enough so that the annu- ,.lar inner ridge 9e in the shell is opposite the space between the end 6h of the electrode tube 6g and the squared end of the inner barb or enlargement 6c, or opposite the necked portion 6b of the electrode stud. The material of the insert 7 is then allowed to Vrelax for several hours at room temperature, or preferably at an elevatedv sand p.s.i. which may distort it up to about 35% from which it may relax or return to under of the initial distortion when it is relieved of most of the distorting pressure. Y

By thus partially assembling the terminal and waiting a few hours or more while it relaxes at room tempera- `ture the hole 7b in the insert gradually becomes small again and starts to curl around the knife edge 6h and back up into the tube 6g. As stated above this waiting time may be shortened materially by the secondary heating of the assembly which considerably accelerates the relaxation and return of the plastic material off the insert.

The electrode 6 then is pushed all the way into the insert 7, while the latter is disposed within the shell 8, causing the lower end of the insert 7 where it expands beyond the end of the shell 8 to curl outwardly slightly and eventually, as it shrinks back, to cut itself into a tapered joint conformation against the knife edge 8d, which joint con-tact remains and retains itself under a reasonable amount of shrinkage tension. In this relationship the inner bulb 6c is positioned so as to expand the insert 7 at the knife edge 8d and the adjacent portions 6d and 6e form a connection point. This iinal insertion of the electrode 6 tothe point at which vits flange 6j' bottoms against the insert flange 7c, is preferably Vdone in a vacuum, such asin an evacuated assembly The insert mayV Vbe initally compressed under pressures of several thou- `known and acceptable methods.

tank, receptacle or the like. The flange 7c is compressed in this assembling operation between the flanges 6f and 8c and after the insert 7 relaxes and returns to its maximum, under the influence of its extreme memory characteristics, and the assembly assumes the relative relationship shown in Fig. 4in which it forms the completed terminal. The slicing into or cutting back of the insert material against the sharp knife edges 6h and 8d which it bites into under its shrinkage tension forms what amounts :to a ground joint providingboth internal and external seals against the tube walls 6g and 8b respectively which takes care of all expansion and contraction of the metal components under the temperature changes to which they may be subjected and which results in a terminal of extremely high hermetic sealing properties. The improved terminal when made with a brass or like shell 8 can be soldered or welded into a panel, header or like part. Other metals than brass could of course be used which would be desirable for welding. Relatively high temperature solders are preferable and where the electrode shell is a separate piece it would preferably be sweated on. In the completed terminal, as shown in Fig. 4, the upstanding shank 6a and the exposed neck and lower barb 6d and 6e form the connection points to which the conductors maybe attached by any of the The barb end may be made having other configurations such as ball shapes or hollow-ended for roll-back'after assembly.

My improved terminal is also adapted for use in an extruded hole in a panel 10 as illustrated in the assembly shown in Fig. 5. The panel 10 is preferably formed with a cylindrical wall portion 10a which is provided` ,with a knife edge 10b and the assembly of the terminal shown in this figure may preferably be the same as described above with the hole in the panel 10 being substituted for the shell-8 of the previous modification. My improved terminal is also applicable to manufacture in the eyelet type and it will be obvious that it may be assembled with a iianged and knife edge eyelet substituted for the extruded hole in the panel 10, with the eyelet soldered, welded or sweated into a hole in a panel or the like in a well known manner when iinally installed in the apparatus or terminal equipped unit. The electrode 6 and the shell 8 may preferably be formed of brass, with any suitable finish, or a number Vof other .satisfactory metals may be utilized. The llange 6i and the tube shell 6g may be solderedor'sweated upon the shank y6a of the electrode or` these portions may be `fortified or cut as integral portions of the electrodeas illustrated in the modified form of Fig.V 6, terminating in a ball end V11e suitable for wire wrapping and can be manufactured in a number of automatic machines now available for making similar small parts. It will be appreciated that my improved terminals will normally be considerably smaller than those which have been illustrated in the drawings which'have been made to greatly enlarged scales for convenience, and the ter- `rninals are capable of being produced in a wide variety proved terminal, which occur to those skilled in the art after reading the foregoing -description are intended to come within 4the scope and spirit of the present invennicnas more particularly set forth in the appended claims,

in which I claim:v

. l.. Themethod of making an hermetically sealed electrical terminal assembly within a tubular wall defining an opening comprising the steps of forming an insert from a cold flowing plastic material with an axial Ibore, said material having a restoring memory after distortion, inserting said plastic insert into said tubular wall opening, forming a metallic stud with a reduced diameter shank portion and a surrounding tubular portion defining an intermediate re-entrant space, placing said tubular wall, said insert and said stud in an evacuated assem-bly receptacle, inserting said metallic stud within said insert in such manner that the plastic material thereof is distorted and cold flowed into said re-entrant space within said tubular portion of said stud to form a seal thereagainst, and heating said assembly to accelerate the movement of said plastic material into said re-entrant space.

2. The method of producing an hermetically sealed electrical terminal within a flanged tubular shell comprising the steps of forming a sharp edge on said tubular shell facing away from the shell flange, forming a flanged axially bored insert of an insulating material of the class having memory characteristics such that after being distorted returns to its original shape, inserting said insert within said tubular` shell, forming a metallic stud having an enlarged terminal portion and a sharp edge portion facing said terminal portion, inserting the terminal portion of said stud axially through the bore of said insert under vacuum conditions within an evacuated assembly enclosure such that said stud causes displacement and distortion of said insert around the sharp edges of said shell and said stud with the flanges of said shell and said insert in pressing contact whereby as the material of said insert returns under said memory characteristics t'o shrink axially and expand laterally it flows against, and around, both said sharp edge portions against the restraint of said contacting anges forming hermetic seals thereagainst.

3. The method of hermetically sealing an electrical conductor within an opening in a panel and insulating said conductor from said panel; comprising the steps of forming said conductor with a flange at a first end portion, with an enlargement at its opposite end portion and with a knife edge tubular re-entrant portion intermediate said end portions; forming a flanged tubular insulating member with a central bore; forcing said anged insulating member into said panel opening until the ange of said member abuts said panel, adjacent said opening; forcing the enlargement end of said conductor through the axial bore of the flanged end of said insulating member under high mechanical pressure and under greatly reduced atmospheric pressure until the flange of said conductor meets the flange of said insulating member; and permitting said assembly comprising said Wall, said insulating member and said conductor to cool and relax while still under said mechanical pressure to thereby eect an hermetic seal between the insulating member and the edge of said panel opening and between said member and said conductor knife edge re-entrant portion.

v References Citedl in the le of this patent UNITED STATES PATENTS 2,538,808 Swiss Jan. 23, 1951 2,606,849 `Dantsizen Aug. 12, 1952 2,774,812 Clark Dec. 18, 1956 2,839,595' Felts June 17, 1958

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