US3350759A

US3350759A - Process for making a spark plug

Info

Publication number: US3350759A
Application number: US302385A
Authority: US
Inventors: Antunes Manoel Jose
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-08-15
Filing date: 1963-08-15
Publication date: 1967-11-07
Anticipated expiration: 1984-11-07

Description

Nov. 7, 1967 M. J. ANTUNES 3,350,759

PROCESS FOR MAKING A SPARK PLUG Filed Aug. 15, 1963 INVENTOR. MANOEL JOSE ANTUNES ATTORNEYS 2 Sheets-Sheet 1 Nov. 7, 1967 Filed Aug. 15. 1963 M. J. ANTUNES PROCESS FOR MAKING A SPARK PLUG FIGS 2 Sheets-Sheet 2 92 INVENTOR. MANOEL JOSE ANTUNES 9;; JAM

ATTORNEYS United States Patent ()fifice 3,35%,759 Patented Nov. 7, 1967 3,350,759 PROCESS FOR MAKENG A SPARK PLUG Manuel .los Antunes, Rua Felix Eacheeo 93,

Rio de Janeiro, Brazil Filed Aug. 15, 1963, Ser. No. 362,385 2 Claims. (Ci. 29-25.12)

This invention relates generally to spark plugs for internal combustion engines, and more particularly to an improved process for making such spark plugs and the product thereof.

Presently the trend in manufacture of high combustion engines is to produce engines with higher and higher coinpression ratios. These require a perfect sealing of the central electrode of the spark plugs used therein. To obtain an adequate seal that will prevent high pressure leakage, the spark plug makers have been forced to produce the center electrode, the inner conductor, and the terminal of the spark plug in separate or multi-step operations and to seal these parts to the bore of the spark plug insulator by a complex glass sealing process as for example, those described in Patents 2,449,403 and 2,459,852. These methods of fabricating and sealing the central electrode are expensive because of the number of steps required and the materials used.

It is a primary object of the present invention to overcome the above stated disadvantages of the conventional methods of sealing spark plugs and, in particular, to utilize the metal from which the inner conductor of a spark plug is formed to seal itself during its formation, thus avoiding the need for additional sealing materials and additional process steps to obtain an adequate seal.

It is another important object of the present invention to provide an improved process for fabricating spark plugs in which the inner conductor alone, or the inner conductor and exposed terminal, are cast by injecting molten material at high pressure into the bore of the insulator, the solidification of the metal resulting in a contraction, or shrinkage, which tightly bonds the inner conductor to a spiral or helical channel in the insulator bore and thus provides a pressure-tight seal for the center electrode and inner conductor.

It is a further object of the invention to provide an improved process of fabricating spark plugs as briefly outlined above, wherein the inner conductor and exposed center terminal are integrally formed in one piece, and the multi-step conventional processes for forming and sealing the central electrode, inner conductor and central terminal are replaced by a single, elficient, and inexpensive operation.

Another object of the invention is to provide an improved spark plug having an integrally united central electrode, inner conductor'and central terminal well sealed to the insulator and formed as a product of the process briefly described above.

Still another object of the invention is to provide an improved process for forming a complete spark plug in which the inner conductor, central terminal and outer shell are simultaneously formed by high pressure injection molding in one operation.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both 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 specific embodiments when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the several figures and in which:

FIG. 1 is a longitudinal axial section of an insulator used in the improved process according to the invention;

FIG. 2 is a similar axial section showing the insulator capped by a mold and supported for injection casting of the inner conductor and central terminal;

FIG. 3 is an axial section similar to FIG. 1 showing the insulator removed from the mold after completion of the molding step which forms the inner conductor and central terminal;

FIG. 4 is an enlarged fragmentary sectional view of a portion of the insulator after the inner conductor has been cast;

FIG. 5 is a perspective view of a central electrode used in the process according to the invention;

FIG. 6 is an axial sectional View similar to FIG. 1 of a modified insulator;

FIG. 7 is a fragmentary sectional view similar to FIG. 2 showing a modified mold;

FIG. 8 is a sectional view similar to FIG. 2 but of a modified mold for simultaneously casting an inner conductor and an outer shell about an insulator to form a complete spark plug;

FIG. 9 is an elevation partly in axial. section of a finished spark plug molded in the apparatus of FIG. 9; and

FIGS. 10 and 11 are views respectively similar to FIGS. 8 and 9 but showing modified molding apparatus and the completed spark plug obtained therein.

Referring now more specifically to FIGS. 1-5 of the drawing which illustrate the steps of the improved process, FIG. 1 shows a tubular insulator 10 which may be of any conventional shape and formed of porcelain, ceramics or other conventional spark plug insulator material. The insulator is provided with a non-conventional central bore having a smaller diameter in the lower portion 12 than in the upper portion 14, the two portions passing completely through the insulator axially thereof and being separated by shoulder 16. The upper portion of the bore during fabrication is formed with a spiral channel, or groove 18, for substantially its complete length and which, as illustrated in FIG. 4, may take the form of a threadlike groove having lower and upper, inclined,

plane sides

18a and 18b.

In the improved process it is preferred to utilize a conventional type center electrode shown at 26 (FIG. 5) but in which the head 22 is flattened, or pinched, so as to project a portion of the material diametrically of the electrode pin 20. The pin 20 is then inserted in the bore portion 12 of the insulator from the top, either by hand or automatically by machine, until the head 22 engages and rests on the shoulder 16 (see FIG. 2). The wall of the bore portion 12 preferably makes a close fit about the electrode 20, and when the electrode is supported by its head on shoulder 16 the lower end of the electrode projects slightly from the bottom of the insulator. As thus supported, the electrode is virtually centered. and an annular space surrounds the head 22 in the enlarged bore portion 14 for reception of metal flash during the injection of molten metal.

The assembled insulator and electrode 20 are then placed or moved by machine for support on a base structure 24 having a cavity 26 which closely approximates the external shape of the insulator but leaves an opening at the lower end for the protruding electrode 20 to be received without touching the base under pressure of the casting operation. The base cavity 26 is provided with a shoulder 28 which seats the lower end of the insulator to restrain the insulator from downward motion under the pressure of the casting or molding step to be described.

The upper portion of the insulator 10 is then surrounded by the

mold halves

30 and 32 having

conduits

34 and 36 respectively, for passage of a coolant such as Water at low temperature. The assembled mold halves provide a mold cavity 38 shaped in the form of a conventional spark plug terminal, such as that illustrated at a 44, FIG. 3, which has an exposed bulbous head with a cylindrical central portion and reversed conical upper and lower adjacent surfaces on a cylindrical neck and base with an enlarged flange 46 defined by the portion 48 of the mold cavity 38.

To form the inner conductor and terminal of the spark plug, molten metal is introduced into the die cavity 38 through the opening 39 under high pressure. The molten metal completely fills the bore portion 14 and thread groove 18, flashing around the head 22 of central electrode to form a primary seal at the shoulder 16 of the bore. The supply of molten metal is instantaneously cut off and the metal allowed to cool and solidify aided by water or other coolant passing through the

passages

34 and 36 in the directions of the arrows shown in FIG. 2.

During solidification, the metal shrinks and because of the difference in coefiicient of linear expansion of said metal as compared to that of the insulator 10, the metal will shrink more than the insulator and tend to separate considerably from the wall of bore 14 at its upper and lower ends but less at its center. In this way the solidified inner conductor 42, FIG. 3, will have shrunk inwardly from its ends toward its center to intimately bond to the surface interstices of the groove in the bore of the insulator. As illustrated in FIG. 4, the central portion of conductor 42 does not shrink materially and tightly bonds to both lower and

upper plane sides

18a and 18b of the thread-like channel in the central area 10a of the insulator. In shrinking, the metal of the upper portion of the conductor 42, in the insulator area 10b, separates slightly, as shown in exaggerated manner, from the upper Walls 18b of the thread groove, but shrinks tightly against the lower walls 18a to form a very tight seal. In the lower portion 100 of the insulator, corresponding to the lower portion of bore 14, the metal of the inner conductor 42 contracts upwardly into tight engagement with the upper plane surfaces 18b of the thread groove. Thus at least some portion of each increment of the entire length of the thread groove in bore portion 14 is tightly sealed by the solidified metal.

Upon cooling of the metal in the bore of the insulator, the latter may be removed from the support 24 and the mold halves and 32 to yield the product, illustrated in FIG. 3, in which the inner conductor 42 and external terminal 44 are integrally united to the center electrode 20. The shoulder 46, formed in the mold cavity portion 40, is tightly shrunk and solidified against the upper edge of the insulator to seal the bore at that point while a primary seal is obtained by the flash metal injected around the head 22 of the electrode in the area of the bore shoulder 16. In addition, the above described shrinkage in two directions in the spiral channel 18 tightly seals the inner conductor 42 for the entire length of the channel in bore portion 14, so that the single injection operation and the use of only the metal of the inner conductor, without other sealing materials, serves to effectively seal the electrode, the inner conductor and the terminal against high pressure leakage through the bore of the insulator.

In molding the inner electrode according to the above described process any suitable metal may be utilized, for example, substantially pure aluminium or nickel, or alloys thereof, zinc alloys, steel, and others. The molten metal is preferably injected at very high pressure, a suitable pressure having been found to be about 50008000 p.s.i. when forming the inner conductor to a center electrode having a diameter of approximately /8 of an inch and a length of about 1 inch. The shrinkage and resultant bonding of the cast metal is due to the difference in the coefficient of thermal expansion of the porcelain insulator from that of the casting metal. The coefiicients of thermal expansion (linear expansion per 1 F.) for the named metals are approximately: aluminum, 14.2 10 nickel, 7 10 carbon steel, 5.57.2 10 and porcelain 2 10 in temperature. The ratio of linear contraction of any of the above metals to that of porcelain is adequate to provide for considerable shrinkage and to thereby affect the tight seal and bonding to the spiral groove in the wall of the bore of the insulator.

The injection of the metal under high pressure is nearly instantaneous. The metal of inner conductor 42 is allowed to cool and solidifies in approximately 10-15 seconds at which time the mold may be removed. The water cooling of the mold aids in conducting heat away from the injected metal and materially increases the speed of its solidification. If a poor grade of porcelain or ceramics is used, making the insulator prone to fracture under the shock of injection of metal at fusion temperature, the insulator may be pre-heated before injection of the metal into the bore of the insulator.

In FIG. 6 is shown a modified insulator 10 in which the spiral thread groove 18 is replaced by a spiral groove 48 having a semicircular or ellipsoidal cross section. In such a spiral groove the solidifying metal will again contract toward the lower or upper sides of the groove and, because of the curved shape of the groove, a complete locking of the solidifying metal to the wall will result, further improving the seal.

In FIG. 7 is disclosed a modified embodiment of the mold in which the mold halves 50 and 52 are provided with a cavity 54 shaped to form a terminal in the form of a threaded stud, the bottom portion 56 of the cavity having a shape which will form a nut-like base on said terminal stud. The mold cavity has an opening 58 for entrance of the injection material.

While the process for making the spark plug as thus far described is concerned solely with the formation of the integral electrode, conductor and terminal, it is also contemplated that simultaneously with the formation of these portions of the spark plug, an outer metal shell including a cylindrical metal sleeve and an outer electrode may be injection molded at the same time. US. Patent No. 3,077,649 discloses a process for injection molding of the outer shell and outer terminal, and the process fully described therein, which will not be repeated here, is contemplated to be combined with the process for forming the center electrode and center terminal, above described, by a suitable modification of the mold parts so that both the internal and external conductor (shell) of the spark plug may be simultaneously injection molded in and about the insulator in one operation.

In FIG. 8 is shown one embodiment of mold apparatus capable of combining the injection molding of the inter nal conductor and outer shell in one operation. The mold halves 60, 62 are similar to

mold parts

30, 32, above described, except that they are lengthened to surround the entire insulator 74 as a core. Additional and connected cavities referenced as the shell cavity 64, are formed in

mold parts

62, 64 suitable to form shell 80, FIG. 9, having a lower portion with external threads and tightly shrunk about the insulator ribs 76. The mold parts are supported on base 66 having a central cavity 68 with outwardly flared walls which closely support the lower portion of insulator 74. A metal sleeve 70 also supports the insulator as a central core in mold cavity 64, while a metal strip 72 is supported adjacent the sleeve in a channel in base 66.

Parts

70 and 72 are similar to the corresponding sleeve and outer electrode described in Patent 3,077,649. When molten aluminum, or other metal, is injected into

mold cavities

38 and 64 simultaneously through opening 39 and a second opening, not shown, the inner conductor 42, central terminal 44, outer shell and outer electrode 72, FIG. 9, are simultaneously formed and in the completed electrode shell 80, sleeve 70 and outer terminal 72 are integrally united.

FIG. 10 illustrates another modified mold apparatus wherein mold halves 60, 62 are again used substantially without change but the base 84 is provided with a slot 86 positioned to cast the outer terminal of the spark plug directly without using sleeve 70 and metal strip 72 of FIG. 8. The resultant spark plug, cast in the FIG. 10

apparatus, is shown in FIG. 11 as having outer terminal 92 molded integrally With sleeve 90 and simultaneously with inner conductor 42 and central terminal 44. The outer electrodes 72, 92, FIGS. 9 and 11 may be bent to underlie the central electrode, as shown in broken lines, after the spark plug is removed from the mold.

It is apparent from the above that many changes in the size, shape and form of the structure and parts fabricated by the process may be made, as well as in the materials and molds used for casting of the described parts. The casting is not limited to a vertical direction and the mold may be cooled by air fins rather than water ducts. Accordingly, it is contemplated that the invention shall be limited only by the scope and spirit of the appended claims.

What is claimed is:

1. A method of making a spark plug having a terminal at its upper end, comprising the steps of:

fabricating an insulator having a central bore that is smooth at its lower end and having a spiral channel in its wall for a substantial portion of its length and terminating at its upper end, placing an electrode in the unchanneled portion of the bore, and 5 injecting molten material under high pressure into said bore to form an inner conductor, through a set of dies including a mold cavity which forms the terminal protruding from the upper end of said bore. 2. A method of making a spark plug according to 10 claim 1 including water cooling said dies as part of the operation.

References Cited UNITED STATES PATENTS 15 1,347,367 7/ 1920 Gerbaud 22202 1,362,773 12/1920 Brewster 22-202 2,400,917 5/ 1946 Corbin 22-202 X 3,077,649 2/1963 Muniz 22202 20 WILLIAM I. BROOKS, Primary Examiner.

Claims

1. A METHOD OF MAKING A SPARK PLUG HAVING A TERMINAL AT ITS UPPER END, COMPRISING THE STEPS OF: FABRICATING AN INSULATOR HAVING A CENTRAL BORE THAT IS SMOOTH AT ITS LOWER END AND HAVING A SPIRAL CHANNEL IN ITS WALL FOR A SUBSTANTIAL PORTION OF ITS LENGTH AND TERMINATING AT ITS UPPER END, PLACING AN ELECTRODE IN THE UNCHANNELED PORTION OF THE BORE, AND INJECTING MOLTEN MATERIAL UNDER HIGH PRESSURE INTO SAID BORE TO FORM AN INNER CONDUCTOR, THROUGH A SET OF DIES INCLUDING A MOLD CAVITY WHICH FORMS THE TERMINAL PROTRUDING FROM THE UPPER END OF SAID BORE.