US2820087A - Seals between metal conductors and ceramic insulators - Google Patents

Description

G. D. SUTER Jan. 14,'1958 SEALS BETWEEN METAL CONDUCTORS AND CERAMIC INSULATORS Filed June 22, 1953 f r r 32:31. W A I. l MWI/Ichi@ Illy] J @Enmwmmll* O Zw 3,

,INI/ENTOR. Casonas. D. Slg-rea BY` MA1 mM 4 rag? AT-roanex United States Patent O SEALS BETWEEN METAL CONDUCTORS AND CERAMIC INSULATORS George D. Suter, Wauwatosa, Wis., assignor to Globe Union Inc., Milwaukee, Wis., a corporation of Delaware Application June 22, 1953, Serial No. 363,243

3 Claims. (Cl. 174-152) This invention relates to improvements in pressure resistant seals between metal conductors and dielectric materials such as seals for the center electrodes of spark plugs, terminals for sealed transformers and condensers, leads for headers for vacuum tubes, feed-through bushings, and any other usage of seals between metal and dielectric material.

Seals of this type are made between glass and metal and require close balance between the coefficients of expansion of both metal and glass. This balance cannot be done without the use of carefully selected, metallurgically controlled metals and specially prepared mixtures of glass, both of which are often so costly as to be impractical for commercial purposes. Even with care in the selection of the metal and glass, the so-called chemical bond between glass and metal will not withstand mechanical shock and abrupt changes in temperature and pressure.

It is the object of this invention therefore to provide a pressure resistant glass seal for conductors or other metal members which is free of the above mentioned disadvantages and drawbacks and can be made from inexpensive, common glass adjoining inexpensive, common metals.

This object is obtained by securing a metallic cup made of common cold rolled steel to a metal conductor or part so that the cylindrical Wall of the cup spacedly encircles such metal conductor and its other wall is welded or otherwise sealed thereto. Such conductor and cup are then imbedded in a body of common glass so that the glass enters the cup between the cylindrical wall and conductor. The seal may be made by forcing the common glass, while plastic, in between such cup and such conductor. As cooling takes place, the cup, having a higher coeflicient of expansion than the common glass, will contract radially and squeeze the glass against the conductor, thus establishing and maintaining a pressure resistant seal therebetween. The seal thus made will endure during all uses where operating temperatures are not high enough to expand the cup an amount suliicient to lessen such seal holding pressure. Because of this method of holding the glass tight against the metal, it is not necessary to balance the physical characteristics of the metal and glass so as to have comparatively like coetlicients of expansion. Hence, expensive metals and glass need not be employed. The metal of the cup and the metal conductor may be common cold rolled steel which is cheap and easily formed and machined into the proper shape. Likewise, common glass tubing of the cheaper grades may be used to form the body of the glass seal.

The novel features, which are considered characteristie of the invention, are set forth with particularity in the appended claims,

The invention itself, however, both` 2,820,087 Patented Jan. 14, 1958 ICC as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specic embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is an exploded isometric view of a spark plug insulator, center electrode, and seal forming parts embodying the present invention;

Fig. 2 is a View in vertical section of such spark plug insulator with such electrode and parts assembled prior to completing the seal;

Fig. 3 is a view similar to the View of Fig. 2 showing the completed seal;

Fig. 4 is a fragmentary view partly in vertical section and partly in side elevation of a modified form of center electrode seal forming parts embodying the present invention;

Fig. 5 is a view in vertical section of a spark plug insulator with the modified form of electrode of Fig. 4 assembled and sealed therein;

Fig. 6 is a view in vertical section of a spark plug insulator and another modified form of electrode and seal embodying the present invention; and

Fig. 7 is a View in vertical section of a feed-through bushing embodying the present invention.

Referring to the drawings by reference numerals, the pressure resistant seal embodying this invention, for the sake of illustration, is shown incorporated between a spark plug insulator 10 and a center electrode. The insulator is of standard construction made of ceramic material and has an upper bore 12 connected to a smaller lower bore 14 to form a shoulder 16 therebetween. ln the example shown in Figs. l to 3, inclusive, the center electrode has a lo-wer erosion resistant or sparking portion 1S connected to a stud or terminal mounting portion 2t) by a conductor 24. At its upper end the stud has a ange 21 which in assembled condition seats on the iusulator 1t). The lower end of the stud 20 is cup-shaped with the walls of the cup forming a band 22. The conductor 24 is press fitted in a hole in the stud 2E) and is held within and spaced from such band. Such conductor may also be Welded to the stud. The opposite end of the conductor 24 is spot wel-ded to the upper end of the ysparking portion 18, thereby making a unitary center electrode. It is advisable to provide on the stud 29 knurling 26 or the like to be gripped by the seal and restrain such stud against rotation. For purposes hereinafter explained, it is also desirable to provide reductions in the diameter of the stud 20 such as the grooves 2%, or a standard thread cut in the outer wall of the stud 2li.

The stud 20, the band 22, and conductor 2d are preferably made from common cold rolled steel which is relatively inexpensive and easy to machine. However, it is advisable to make the sparking portion It of an alloy which will resist erosion due to the spark discharge. The band 22 provides the force for compressing the glass seal againstthe conductor. Hence, it must have suiiicient cross-sectional dimension. A cross-section which has a length of approximately 1/16 inch to 1A; inch and a wall thickness of approximately .025 inch has been found satisfactory. The inner wall of such band should be sufficiently spaced from the conductor 24 to permit the glass seal to form a cylindrical body about such conductor and within such band, the wall of which will be approximately .025 inch thick.

The glass seal is made from a glass tube 30 cut from a length of common glass tubing. There must be enough mass of glass in the tube 30 to completely fill the space above the shoulder 16 to a level slightly above the lower end of stud 20 (see Fig. 3) when such glass is compressed while in plastic state. yIn the size illustrated, the tube is approximately 11/16 inch long and has an I. D. of .167 inch and an O. D. of .188 inch. In order to prevent the glass while plastic from flowing into the lower bore 14, a ball-like ring 32 made of cold rolled steel has a close sliding fit on the sparking portion 18. With the glass tube 30 and ring 32 assembled thereon, the center electrode is inserted within the bore of the insulator to the position shown in Fig. 2. The entire assembly is then heated to a temperature of approximately l600 F. until the glass is plastic. While in such condition the connector 2t) is forced inwardly of the insulator 10 to flow thc glass into the confined seal 31 shown in Fig. 3 with the cup formed by the band 22 filled and with a thin layer between the knurling 26 and the walls of the bore 12. At such temperature the glass will bond or fuse to the ceramic insulator 10 to make a pressure tight joint therewith. However, the joint between the glass seal 31 and the conductor 24 will be maintained by the compressive force in band 22 as hereinafter explained.

Because it is practicaly impossible to gage the exact amount of glass which, when compressed into the seal 3l, will resist further movement of the center electrode just as the flange 21 seats on the insulator 10, a slight over amount is used so that advancement of the center electrode is stopped by the confined seal 31 before the flange 21 reaches the insulator 10. To seat the flange 21 the conductor 2f) is slightly collapsed between the flange 21 and its lower end. The grooves 28 or threads or other diameterreducing means facilitate such collapse. During the assembling process the sparking portion 18 has been projected out of the lower end of the bore 14. It may thereafter be cut off to the desired length.

The feature of this seal is the compressing of a surrounding body of glass against the conductor 24 by the metal band 22. This band, being made of cold rolled steel, has a coefficient of expansion which is greater than the coefiicient of expansion of the glass. Hence, as cooling takes place, the band contracts and continually cornpresses the glass into a tight joint with the conductor. There is also some compressive force created by the longitudinal contraction of the conductor 24 which keeps the joint between the glass seal 31 and the bottom of the stud tight.

It is not necessary that the band 22 be an integral part of the lower end of the stud 20. In the modification shown in Figs. 4 and 5 the center electrode has a sparking portion 4t) unattached to a stud 42. The upper end of the sparking portion 40 is enlarged and provided with a band 44. The stud 42 has a conductor 46 press-fitted in a hole in the end thereof (see Fig. 4). Such stud also has the usual flange 47 at its upper end, a lower knurled portion 48, and intermediate corrugations 50. In the assembly of this modification the sparking portion 40 is first seated within the lower bore 14 from the top of the insulator. The glass tube is then dropped in place and the stud 42 inserted in the upper bore 12. The conductor 46 is long enough so that when the tube 30 is melted to form the seal 31 the conductor 46 will be forced against the upper face of the sparking portion within the ring 44 and slightly sprung as shown. Asin the previous example, the glass will form a body surrounding the conductor 46 and encircled by the ring 44. Upon cooling. such ring will compress such body of glass against the conductor 46 to make and keep a tight seal therebetween.

`In the modification shown in Fig. 6 the center electrode is a single piece electrode with the compressing band separate. The band is formed as a part of the member for sealing the lower bore 14. The center electrode consists of a sparking portion 60 attached and conductively connected to a stud 62 by a conductor 64 Welded to auch sparking portion and press-fitted in an opening in the lower end of such stud. The stud is provided with the usual flange 66 at its upper end, a reduced neck 68 intermediate its ends, and a knurled surface 70 at its lower end. A band 72 is formed as an integral extension of a ball-like member 74 which has a close slidable fit on the sparking portion 60 and seats against the shoulder 16. To make the seal, first the glass tube 30 and then the member 74 are slid over the lower end of the center electrode and such assembly placed in the insulator 10 as in the case of the first modification. The treatment thereafter is identical with that of the first modification with the result that the band 72 compresses the glass against the conductor 64 to maintain a tight joint therebetween during operating conditions.

ln the example of the glass seal shown in Fig. 7, a metal cup 76 is secured to a conductor 78 so that the band 80 of the cup spaced encircles such conductor in the same way as heretofore described in connection with the spark plug center-electrode seal. This conductor is mounted in a metal shell or bushing 82 which is threaded so that it may be rigidly secured to the casing of a sealed transformer or capacitor. Depending upon size limitations such shell may have a larger counterbore 84 to accommodate the metal cup 76. The glass is forced within the cup and the bore of the shell while in plastic condition as previously described. The conductor 78 and cup 76 may both be made of common cold rolled steel and the glass seal formed for common glass tubing. Two lengths of tubing may be used, one length being inserted from each end of the shell. The forming pressure is applied by plungers (not shown) which enter each end of the shell. The space left upon removal of such plungers after the glass is cooled is filled by a resin type insulating seal 86.

When a cup secured to the conductor is utilized to provide the encircling band, the seal takes place (it is be lieved) along both the surface of the conductor and the inner surface of the band. If the band is not attached (by a seal forming weld or the like) to the conductor, the seal takes place only on the surface of the conductor. In such instances the band must contain enough sectional area and the section of the glass between band and conductor must be small enough so that the force created by the contraction of the band will be sufficient to compress the glass against the surface of the conductor. In many applications where the pressures are not excessive, such seal will be effective. While operating temperatures are below the temperature at which the glass was pressed into the metal band, the force continually asserted by such band during operating condition will always be enough'to keep tight the joint between the conductor and glass.

While several embodiments of the invention are shown and described herein, it will be understood that this application is intended to cover such other changes or modiiications as come within the spirit of the invention or scope of the following claims.

I claim:

1. A pressure resistant seal for the center electrode of a spark plug comprising: a ceramic insulator having an upper bore connected to a smaller lower bore to form an upwardly facing shoulder therebetween; a unitary center electrode in said bore having, a lower portion of erosion resistant metal extending from above said shoulder through said lower bore, a terminal mounting portion of cold rolled steel in said upper bore and having a flange resting on the upper end of said insulator, the lower end of said terminal portion being cup-shaped with the walls of the cup forming a band slightly spaced from said upper bore, and a reduced diameter conductor of cold rolled steel attached to said cup-shaped end and to the upper end of said lower portion, said conductor being held within and spaced from said band; a ball-like ring of cold rolled steel having close sliding fit on said lower portion within said upper bore and resting on said shoulder; and a body of common glass compressed between said shoulder and ring and said cup-shaped end with said glass entirely filling said cup between said conductor and said band with a thin layer of said glass between said band and said upper bore, said glass being bonded to said insulator and pressed toward said conductor by said band.

2. The pressure resistant seal of claim 1 in which said band is substantially 1,66 to 1A of an inch wide with a thickness of approximately .O25 of an inch and the thickness of said glass between said conductor and said band is approximately .O25 of an inch.

3. The pressure resistant seal of claim 1 in which said terminal mounting portion has a reduced diameter section intermediate its ends and said mounting portion is slightly collapsed from normal.

References Cited in the le of this patent UNITED STATES PATENTS 1,184,813 Birdsall May 30, 1916 1,199,487 Newcomb Sept. 26, 1916 1,456,110 Mackay May 22, 1923 2,317,305 Schwartzwalder et al. Apr. 20, 1943 2,497,158 Dutterer Feb. 14, 1950

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