US2774812A - Hermetically sealed electric terminal - Google Patents

Description

United States Patent HERMETICALLY SEALED ELECTRIC TERMINAL Richard U. Clark, West Acton, Mass.

Application April 27, 1953, Serial No. 351,317

6 Claims. (Cl. 174-153) The present invention relates to electrical terminals and lead-ins and the like, and pertains more particularly to improved hermetically sealed terminals and the methods of making and assembling the same.

Prior terminals or lead-in bushings have broken down or have otherwise proven unsatisfactory under severe service conditions due to impacts or shocks, atmospheric conditions of wide ranges of temperature, humidity, and pressure conditions, as well as due to excessive heating and stresses in tie associated equipment. Other contributing causes of failure have been attributed to damage due to faulty and improper installation, subjection to higher voltage and amperage conditions than the ratings for which the terminals were designed, and due to numerous other factors.

These and other difliculties have been either completely or largely overcome by my improved terminal constructions, the relative arrangement and installation of the component parts and the improved methods and materials utilized in their manufacture and assembly. In its simplest form my improved terminal comprises essentially a metal electrode or central stud and a surrounding tubu lar metal shell between which is squeezed in a novel relationship a resilient plastic insulating cup or insert having high dielectric strength and resistance to heat. The metal stud may preferably be barbed and provided with enlargements on its shank as well as a recess or re-entrant space having a relatively sharp knife edge at the mouth of the recess. The metal shell may be similarly provided with a sharp chamfer or knife edge which cuts into the plastic insert in a manner which improves the hermetic seal. The insert may preferably be formed of a plastic material having high insulation resistance, extremely low moisture adsorption, cold flowing and memory shrinkage characteristics such as for example Teflon, or tetrafluoroethylene. The completed terminal acquires exrtemely high hermetic sealing properties by initially pre-assembling the insert in the shell, then inserting the stud part way into the insert causing large distortion of the same, permitting the latter to relax and accelerating its partial return by heating before completion of the assembly, all preferably done within a vacuum.

it is accordingly a major object of the present invention to provide an improved terminal construction which is readily capable of providing hermetic sealing by the use of improved materials and methods which are reasonable in cost, fool-proof in application and which stand up longer and more satisfactorily under severe operating conditions. it is a further object to provide terminal constructions of improved semi-resilient high resistance type which more readily retain their hermetic sealing properties and maintain their high insulating characteristics under severe conditions of ultra high 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 assembly, preferably within a vacuum, and sub- 2,774,812 Patented Dec. 18, 1956 sequently 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 properties.

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 barbed metallic electrode stud;

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;

Fig. 5 is a similar sectional view of a modified form of the terminal assembly mounted within an extruded hole in a panel; and

Fig. 6 is a modified form of electrode stud.

Referring to Fig. l the stud 6 comprises a cylindrical metallic shank portion 6a, preferably of metal having good electrical conducting qualities, having a reduced diameter neck portion 6b. The lower end of the stud 6 is provided with integral barbed portion 60 and a pointed term nal barb 6e intermediately connected by a short neck portion ed. A flanged metallic tube having a tubular wall 6g and a flange 6] is forced down along the shank do on which it fits tightly extending partially over the neck portion 612. The tubular wall 6g is of an axial length which exposes a portion of the main shank 6a above the flange 63 to provide an upper electrical terminal and also exposes a portion of the neck portion 6b adjacent the bulb portion 60. The flange 6 and the tube g may be sweated upon the shank 6a, or alternatively these parts may be formed integrally with each other. The lower end of the wall 6g is internally ground with a chamfer or bevel to provide a sharp knife edge 6h.

Fig. 2 shows the insert 7 which may preferably be formed of Teflon (tetrafluoroethylene) or a similar plastic composition material having a memory 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 up to about 35% from which it may relax to under a 15% distortion when most of the distorting pressure is relieved. The material used has very high insulation resistance and practically zero moisture adsorption, having a practical range of hardness of from 55 to 70 durometer scale, A. The insert is preferably made from tubing or tubular stock of an outside diameter slightly greater than that of the flange 7c. The tubing is then heated to from 200 to 400 degrees F. and stretched in the manner of an elastic cord while heated. The plastic insert 7 is permitted to cool and is cut or formed to provide the flange 7c and preferably formed as a flanged tube with a tubular wall 7a, having a central bore 7b and an integral flange or shoulder '76. The bore 711 is preferably of lesser diameter than the outside diameter of the portions 60, 6e and 6g of thestud 6 which is forced within the bore 7b. Similarly the outside diameter 7a is slightly greater than the bore 8b of the metallic sleeve 8 into which the insert 7 is alsoforced. 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 80, which may have an outside diameter approximately the same as that of the flange or shoulder 70. The lower terminal is preferably bevelled to form the sharp knife edge 8d. In Fig. 3A there is shown a modified 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 is preferably assembled as follows: After the insert 7 has been cut and formed as described above and has been permitted to become cooled it 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 70 rests against the flange 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 62 and the rounded cylindrical bulb or enlargement 60, 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 annular inner ridge 9e in the shell is opposite the space between the end 611 of the electrode tube 6gand the squared end of the inner barb or enlargement 60, or opposite the necked portion 612 of the electrode stud. The material of the insert 7 is then allowed to relax for several hours at room temperature, or preferably at an elevated temperature which may be at or about the distortion temperature, or preferably to above the initial distortion temperature of from 200 to 400 degrees F. when the tubing was first heated and stretched. The plastic material of the insert 7 has considerable memory and tends to return or shrink back almost to its original shape, or about 85% return thereto. The insert may be initially compressed under pressures of several thousand p. s. i. which may distort it up to about from which it may relax or return to under 15% of the initial distortion when it is relieved of most of the distorting pressure.

By thus partially assembling the terminal and waiting b a few hours or more while it relaxes at room temperature 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 of 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 contact 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 final insertion of the electrode 6 to the point at which its flange 6f bottoms against the insert flange 7c, is preferably done in a vacuum, such as in an evacuated assembly tank, receptacle or the like. The flange 7c is compressed in this assembling operation between the flanges 6 and 3c 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. 4 in 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 shrinkagetension forms-what amounts to a groundjoint providing both 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 sol ders 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 may be attached by any of the known and acceptable methods. 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 ltlb 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 flanged 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 finally 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 of other satisfactory metals may be utilized. The flange 6f and the tube shell 6g may be soldered or sweated upon the shank 6a of the electrode or these portions may be formed or cut as integral portions of the electrode as illustrated in the modified form of Fig. 6, terminating in a ball end 116 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 terminals are capable of being produced in a wide variety of sizes to suit individual requirements.

As indicated above Teflon, or tetrafluoroethylene is ideally suited for the insert but other plastic materials having the desired characteristics may be used. The improvedterminal has very low power losses even when used at ultra-high frequencies and when assembled in an evacuated tank as described, it maintains good hermetic scaling properties over a temperature range of from -l00 degrees F. and lower up to +550 degrees F.

Other forms and modifications of the present improved terminal, as well as the methods utilized in its manufacture and assembly, which occur to those skilled in the art after reading the foregoing description are intended to come within the scope and spirit of the present invention as more particularly set forth in the appended ciaims, in which I claim:

1. In combination, in an electrical terminal, a flanged metallic electrode, a flanged tubular insert of plastic material having cold flow properties and a flanged outer metallic shell, said shell, said insert and said stud proportioned for nesting assembly, said outer shell having an inwardly disposed knife edge end portion, said electrode having an enlargement thereon spaced from the flanged portion and an intermediate outwardly disposed knife edged tubular section arranged so that with said insert disposed within said outer shell insertion of said electrode within said insert causes distortion and cutting of said insert around the knife edge end portion of said shell by the said enlargement of said electrode and embedment of the stud tubular knife edge into said insert wall to provide an hermetically sealed terminal.

2. An electrical terminal comprising a metallic electrode having a transverse flange, a tubular insert having a transverse flange, said insert formed from plastic material having cold flow properties, an outer metallic shell having a transverse flange and a knife edge spaced therefrom, said electrode having an enlargement thereon remotely spaced from said flange, said insert disposed within said outer shell with said flanges adjacently disposed, said electrode disposed within said insert with said flanges adjacently disposed, and said insert distorted around the knife edge at the end of said shell remote from said flanges by the said enlargement of said electrode.

3. An electrical terminal comprising a metallic electrode having a flange, a tubular insert of plastic material having cold flow properties, said tubular insert having a flange, an outer metallic shell having a flange, said outer shell having a knife edge end portion remote from said flange, said electrode having an enlargement thereon spaced from said flange, said insert disposed within said outer shell with said flanges adjacently disposed, and said electrode disposed within said insert in such manner as to cause distortion and cutting of said insert around the knife edge end portion of said shell by the said enlargement of said electrode to provide an hermetically sealed terminal.

4. An electrical treminal comprising a metallic electrode having a flange, an outer metallic shell having a flange, said electrode having an enlargement thereon spaced from said flange, said electrode having a tubular wall forming a re-entrant space, said insert disposed within said outer shell with said flanges adjacently disposed, and said electrode disposed within said insert in such manner as to cause cold flow distortion of said insert around the end of said shell by the said enlargement of said electrode and cold flow of said plastic insert within said re-entrant space.

5. In combination, in an hermetically sealed electrical terminal for the support of a conductor through an opening in a panel, said panel having a tubular wall defining said opening, said tubular wall of said panel terminating in an inwardly disposed knife edge formed on said tubu-- lar wall of said panel at a portion spaced from the plane of said panel, a flanged tubular insert of a cold flowing distortable plastic material having a memory, said plastic insert disposed within said tubular wall opening in said panel, and a conductor stud having a barbed enlarged portion and a tubular re-entrant portion, said stud tubular portion having an outwardly disposed knife edge portion arranged in such manner that with said conductor stud inserted within said plastic insert a portion of said insert is distorted and flowed against the knife edge of said panel wall to form a seal thereagainst and a portion of said plastic insert is also caused to flow into said tubular re-entrant portion of said conductor stud due to the distortion and the memory of said plastic insert so as to efiect a seal against said knife edge of said tubular re-entrant portion of said conductor stud.

6. In combination, in an electrical terminal, a flanged metallic electrode, a flanged tubular insert of plastic material having cold flow properties and a flanged outer metallic element, said outer element, said insert and said stud proportioned for nesting assembly, said outer element having a tubular wall with an inwardly disposed annular knife edge intermediate its end portions, said electrode having an enlargement thereon spaced from its flanged portion and an intermediate outwardly disposed knife edged tubular section arranged such that with said insert disposed within said outer element insertion of said electrode within said insert causes distortion and cutting of said insert around the inwardly disposed knife edge portion of said tubular wall of said outer element by the enlargement of said electrode to provide an hermetically sealed terminal.

References Cited in the file of this patent UNITED STATES PATENTS 1,888,071 Case Nov. 15, 1932 1,983,347 Daley Dec. 4, 1934 2,286,829 Reid June 16, 1942 2,305,150 Fearon Dec. 15, 1942 2,387,630 Weakley Oct. 23, 1945 2,433,911 Johnston Jan. 6, 1948 2,498,644 Billings Feb. 28, 1950 2,510,358 Wolf June 9, 1950 2,606,849 Dantsizen Aug. 12, 1952 2,622,578 Vogel et al. Dec. 23, 1952 FOREIGN PATENTS 641,917 Great Britain Feb. 2, 1949 OTHER REFERENCES Electrical Manufacturing magazine, article by Alex. E. Javitz entitled Fluorocarbon resins appraised, Part I, Properties, pages 76-81, Aug. 1950. Part H, Applications, pages 80-85, Sept. 1950. (Copies of these magazines are in the Patent Oflice Library and photostats of these pages in Class 174-1106 in Division 69 of the Ofl'ice.)

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