US3053214A - Fixture for furnace brazing spark plugs - Google Patents

Description

p 1962 E. w. PIERCE 3,053,214

FIXTURE FOR FURNACE BRAZING SPARK mugs Filed Aug. 6, 1954 l \\\Zi H 5 a! 62212711 .Pzleme Attorney- United States Patent M 3,053,214 FIXT FOR FURNACE BRAZING PARK PLUGS Earl W. Pierce, Flint, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Aug. 6, 1954, Ser. No. 448,3tlil 1 Claim. (Cl. 1l3--99) This invention relates to a fixture for furnace brazing spark plugs and more particularly to an angle type shielded plug having brazed interconnections between the several metal sections of the shell. This application is a c0ntinuation-in-part of my application Ser. No. 406,171 filed January 26, 1954, now Patent 2,875,365.

In the manufacture of angle type spark plugs for aviation use, the shell, the metal structure surrounding the plug insulator and serving as the electrical shield for the plug, is necessarily formed of at least two parts. One part is positioned about that portion of the insulator in which the electrode is located. The second part is positioned about the cable receiving portion of the insulator which extends angularly from the electrode portion.

Such shell construction is commonly obtained in the art by brazing or welding the two tubular shell sections together using various saddleshaped butt type joints or matching 45 angle butt type joints. It has been found that such butt joints frequently fail under the vibration and shock encountered in field use as well as in the course of normal handling for the reason that it is extremely difiicult to obtain a uniform and efficient weld or braze on a long joint-line such as results from this method of production. At the same time, the absence of a uniform and continuous braze or weld results in the incomplete electrical sealing of the plug with the result that the plug produces intolerable electrical interference with the other electrical and communications equipment. Likewise, 45 angle construction requires that the plug have available on the engine a relatively large head room, the height of the plug from the engine exterior surface, a condition which is usually non-existent in aviation usage. Additionally, by reason of the difficulties pointed out above, the assembly of each plug is a difiicult and expensive hand operation which is obviously not adapted for high volume production requirements.

It is therefore the object of my invention to provide a simple and inexpensive fixture for enabling high volume production of angle type spark plugs.

To attain this objective, I provide a spark plug shell formed of a plurality of telescoping sections which are furnace-brazed to provide high strength lap joints, the brazing operation being facilitated by means of a steel supporting structure in which a plurality of plugs are supported in such maner as to be out of direct contact there- Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a prefered form of the present invention is clearly shown.

In the drawing:

FIGURE 1 is a plan view with parts broken away of the brazing fixture and spark plug assembly of my invention.

FIGURE 2 is an enlarged sectional view taken on line 2,2 of FIGURE 1 showing the details of construction of the brazing fixture and spark plug assembly of my invention.

Referring now to the drawing and more particularly to FIGURE 2, there is shown an angle type spark plug ll. Plug 11 comprises a cylindrical main portion or shell 3 having a longitudinal bore 5 therein, the upper portion 7 thereof being counterbored to form a shoulder 9. The edge of shoulder 9 is beveled to provide a conical seating ledge 11 having an axis coincident with the axis of 3,fi53,2l4 Patented Sept. 11, 1962 shell 3. The bottom portion 13 of shell 3 serves as the outer or ground electrode and is annular in configuration. Seating ledge 1]. acts both to support the spark plug insulator with its tip end concentric with the outer electrode 13 and as an abutment for establishing a seal between the insulator and the shell 3.

Shell 3 is provided with an annular groove 15 on its outer surface adjacent shoulder 9 to enable a gas-tight seal between the shell and insulator by means of the Cico weld process wherein, under the influence of axial pressure and electrical heating, the shell is thermoplastically collapsed in the annular thin wall section of groove 15 to clamp the insulator on ledge 11.

The upper end of shell 3 adjacent groove 15 is necked down to provide a shoulder 17 on which a metal mounting pad 19 is telescopically positioned. Pad 19' serves to provide the means for mounting the assembled plug in the engine and at the same time provides an extension of the shell 3 for shielding the plug.

The metal plug body and electrical shielding of plug 1 is completed by means of the metal shield cap 21 and shield sleeve 23, these elements being shown as telescopically fitted to each other and to pad 19. The body portions 3, 19, 21 and 23 are securely attached to each other by brazing to form a single unitary structure. In assembling the plug, the telescoping surfaces are coated with a copper brazing paste which, upon brazing, forms a uniform and substantially perfect seal between the lapped surfaces of the several body portions or with a fluxing paste alone in which case a copper, or other suitable metal, wire ring is applied at each joint. Though both the braze paste and the flux ring combination are satisfactory and may be described as brazing materials, I prefer to use a copper wire ring and flux at each of the joints.

It should be here noted that the telescopic assembly of the shell portions 3, 19, 21 and 23 is formed by machining down the outer end surface of shell 3, cap 21 and sleeve 23. The inner end surface of pad '19 and cap 21 are correspondingly formed to permit the several body portions to be sleeved one within the other and form both a lap and butt joint between the several parts. Such construction results in a large surface area of contact between the parts which upon brazing forms a plurality of high strength joints. Likewise, the large surface area of the brazed joints assures the effective electrical shielding of the plug.

As is clearly shown on the'drawing, the cap 21 abuts the top of the insulator and cooperates with ledge l1 to clamp the insulator in the plug body and provide a gastight seal therebetween. The cap 21 is of such configuration as to provide, together with mounting pad 19, a side opening in the plug body in which sleeve 23 is adapted to be positioned, its axis extending transversely to the shell 3.

As is shown in FIGURE 2, a ceramic insulator Z5 having a center electrode 27 positioned therein, is mounted within the metal body by means of gaskets 49 and 53 in a manner fully described in my co-pending application Ser. No. 406,171, now Patent 2,875,365, in order to position the electrode concentric with the bottom portion of the shell 3. Insulator 25 is generally cylindrical in shape and has a generally tapered lower section 29 and a raised upper section 31. A tubular section 33 extends laterally from the raised section '31. Insulator 25 is provided with a substantially concentric bore 35 extending from the firing end'37 of section 29 to within the upper portion of raised section 31. A laterally extending bore substantially concentric with section 33 is provided to intersect the upper end of bore 35 and form a recess 39 in which a metal contact cap 41 is adapted to be po- 3 sitioned. A counterbore 43 is provided in section 33 to receive an insulated ignition cable 45.

The electrical connection between cable 45 and center electrode 27 is assured by inserting the inner end of the electrode into a corresponding opening in cap 41. The end of the electrode may be either threaded as shown or slotted to form either a threaded or a spring-like friction connection with the cap. The conductor 47 of cable 45 is retained in contact with the outer end of cap 41 in any of a number of ways which are well known in the art and form no part of the present invention. Any spaces in cap recess 39 and around electrode 27 are filled with a sodium silicate-kaolin type cement also well known in the art. The cement acts to both seal and retain the electrode in the insulator.

As described above, a gas-tight seal between the insulator and the shell 3 is obtained by applying pres sure to the shield cap 21 to collapse the thin wall portion in the annular groove 15. The cap 21 then acts to clamp the insulator on ledge 11 with the conical portion of the gasket 49 therebetween.

In order that the above described spark plug be practical from a production standpoint, it was necessary to devise some means for enabling furnace brazing of the assembled structure. I have found that a device of the type shown in FIGURES =1 and 2. was well suited for the purpose. The device of my invention comprises a channel-like frame 57 shown as consisting of an elongated base plate 59 to each side of which there is rigidly secured, as by a plurality of bolts 61, a co-extensive plate 63. The plates 59 and 63 are formed of any suitable heat-resistant metal alloy, i.e., a nickel-steel alloy, and are of sufficient thickness to enable the fixture to withstand brazing temperatures as high as 2200 F. without destructive warpage. Reinforcing plates 64 may be used on each end between the side plates 63 in order to give further strength to the frame.

Because of the fact that the brazing metal tend to volatilize on passage through the brazing furnace, it was found necessary to prevent metal-to-metal contact between the frame 57 and the plug :1 since such contacting portions would likewise be brazed together. I have discovered that the isolation of the plug 1 may be accomplished by using support members formed of non-metallic material, i.e., ceramics such as alumina or titania type materials, glass, etc.

As is clearly shown on FIGURE 1, the unbrazed plug assemblies 1 are positioned crosswise in the frame 57 with the firing end of each alternate plug on the same side. In this manner, a maximum number of plug assemblies may be loaded in a given length of frame. Each plug assembly is supported within the frame 57 by means of a ceramic supporting saddle 65 which is positioned in an aperture provided in the base plate 59. Each plug assembly is clamped between a pair of axially bored ceramic bushings 67 and 69 which are positioned in apertures provided in each side plate 63, the bushings being in axial alignment with each other and in the same axial plane as that of saddle 65. Clamping action is attained by means of a screw 71, one end of which is threaded for cooperation with a loosely-fitted nut 73 and is adapted to fit within the axial bore provided in the bushings. The other end of the screw 71 is separated from the threaded portion by means of a radially extending flange 74 and is adapted to fit within the axial bore of an annular ceramic disk 75.

The principles of my invention will be readily understood from the following description of the production of a spark plug as shown on the drawing. The several metal parts of spark plug body 3, 19, 21 and 23, are accurately machined so that their several seating and wall surfaces are concentric and true with the longitudinal axis of shell 3 as well as being so dimensioned as to fit together telescopically, sleeve 23 being at a predetermined angle to shell 3. The angle type ceramic insulator 25 is then molded of a suitable heat resisting powder following which the molded blank is fired to sinter it into a composite fused body. The metal gaskets 49 and 53 are then positioned on the bottom and top portions, respectively, of the upper portion 31 of the insulator 25. Upon turning down these gaskets as described in my co-pending application, the insulator is positioned in the shell 3 with the conical portion of the gasket 49 squarely on ledge 11 thus positioning the center electrode concentric with the firing end of shell 3. The remaining body parts are then telescopically assembled on the shell and the assembly is ready for placement in a brazing furnace at about 2000 F the interlocking surfaces of the several parts having been previously coated with a flux, a copper wire ring being applied at each joint.

Upon positioning the saddle 65 and bushings 67 and 69 in the frame 57, the spark plug is located between the bushings and on the saddle. The expansion member, screw 71, is then positioned between the side plates 63 and the cap 21 with the threaded follower, nut 73, abutting the ceramic bushing and with the head or flange 74 abutting the ceramic disk 75 which is interposed between the cap 21 and the screw. Upon threading the follower 73 off of screw 71, the plug body portions are tightly forced together. The frame 57 is then passed through the brazing furnace where the temperature is such as to fuse the brazed metal. Upon cooling, the brazed sections are securely interconnected to form a strong, completely shielded, unitary spark plug body.

The gas-tight seal of the insulator 25 within shell 3 is then accomplished by mounting the plug 1 in a jig for supporting the shell 3 while passing an electric current therethrough at the same time that axial pressure is applied to shield cap 2 1. A spacer gasket 55 may be used on top of cap 53 when necessary. Contact cap 41 is then inserted into recess 39 and center electrode 27 is threaded into an opening therein. All spaces in recess 39 and about electrode 27 are then filled with a silicate base cement to seal the electrode in the insulator and fix the elements in position to form the completed and compensated plug 1.

From the above description, it can be seen that I have provided a simple and integrally formed shielded angletype spark plug by a method of fabrication which permitts the plug to be readily formed on a production basis.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted as may come within the scope of the claim which follows.

I claim:

A fixture for use in furnace brazing spark plugs having a metal body formed of a plurality of separate portions comprising a metal frame having side and bottom portions, a ceramic saddle positioned in an aperture in said bottom portion for supporting said body out of metal contact with said frame, a ceramic bushing positioned in an aperture provided in each side portion of said frame, said bushings being in axial alignment with each other and in the same axial plane as that of said saddle, a screw positioned on one of said bushings positioned in the side of said frame with the threaded end in a bore formed therein, a threaded follower on said screw in abutment with said bushing, a flange on said screw between said follower and the end of the screw adjacent the body and a ceramic disk positioned on said screw in contact with said flange for contact with the body.

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) UNITED STATES PATENTS 2,443,574 Burns June 15, 1948 1 51 79 A1 d M 29 193,2 2,464,574 g l Mali 1949 2 195 314 ggg M2; 2 1940 214799325 De g- 1949 2,209,709 Weatherhead July 30, 1940 216181234 Armaccst 1 1952 2,295,996 Lauffenburger Sept. 15, 1942 5 2,633,116 Ingram 1953 Eve eflt Aug 3, Duck et y 2,332,360 Wakefield 061, 19, 1943 2,820,286 Andrus Jail 1958 2,335,343 Sendzimir NOV. 2, 1943 FOREIGN PATENTS 2,352,857 Nachemov July 4, 1944 2,366,164 Weick et v11. Jan. 2, 1945 10 260,746 Great W? 11, 1926 2,389,597 Ciprian-i 6161 Nov. 27, 1945 Great m? 17: 1944 2 433 339 Brown Dec. 30, 1947 586,325 Great f 1947 2,435,448 Kraeft et a1. Feb. 3, 1948 115,784 Austr'aha 26, 1942 2,437,209 Rabezzana Mar. 2, 1948

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