US2308968A

US2308968A - Spark plug crimping method and apparatus

Info

Publication number: US2308968A
Application number: US393789A
Authority: US
Inventors: Douglas W Gregory
Original assignee: Firestone Tire and Rubber Co
Current assignee: Bridgestone Firestone Inc
Priority date: 1941-05-16
Filing date: 1941-05-16
Publication date: 1943-01-19
Anticipated expiration: 1960-01-19

Description

Jan. 19, 1943. D, w, GREGORY 2,308,968

SPARK PLUG CRIMPING METHOD AND APPARATUS Filed May 16, 1941 HTZI 117i.

I2b u ATTORNEYS Patented Jan. 19, 1943 UNITED STATES PATENT OFFICE SPARK PLUG CRIlWPlN G METHOD AND APPARATUS Douglas W. Gregory, Trenton, Mich., assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio Application May 16, 1941, Serial No. 393,789

2 Claims.

' Heretofore the metal shells of spark plugs have been crimped into engagement with the porcelain in two steps. The first crimping action is effected by a die having aconcave or arcuate work engaging face which engages the-end of a metal shell and bends it inwardly to cold form a convex peripheral radius on the shell. Next a second die, similarly constructed, is engaged with the metal shell end, the shell being heated to semi-plasticity by electrical current flowing therethrough, and with pressure being applied thereto, said shell collapses to seal upon the gasket and porcelain. In this practice it has been customary to use conforming cold and hot crimp dies. Both dies have to be machined very accurately to insure good contact and prevent arcing and burning at points of poor contact with the shell when sealing a specific size plug. Obviously alarge number of dies must be provided to seal the various sizes of spark plugs and the maintenance of the dies is quite costly. The hot crimping operation requires rather high pressures because the conforming hot die provides a rather large contact area for flow of electricity between the die and shell, which of course reduces the current density and tends to keep the section of the shell to be crimped and the gasket contiguous to it cool and rigid. High pressures are very apt to result in cracking of the insulators which in turn makes the plugs defective regardless of the effectiveness of the seal. Furthermore using the old practice it was required to keep the crimp section relatively cold to prevent the annealing of the soft metal having low recalescence used in making gaskets. Regardless of this, such gaskets annealed in service under modern high temperature operating conditions.

The general object of thi invention is to overcome the foregoing and other objections to previous types of spark plugs shell crimping operations and to provide novel crimping apparatus adapted to make improved seals at the upper ends of spark plugs.

Another object of the invention is to reduce the number of failures in the metal shell occurring during the crimping operation and to reduce the number of dies required in crimping a variety of sizes of spark plugs.

Another object of the invention is to reduce the crimping pressure required and to provide crimping dies that are easily and inexpensively produced and maintained.

Further objects are to seal spark plugs at higher temperatures than those used heretofore and to use gasket materials which are adapted to withstand high temperatures without annealing. The foregoing and other objects will be manifest as the specification proceeds.

In the accompanying drawing:

Figure l is a vertical section of a spark plug,

" shown at the end of the centering operation in the assembly thereof;

Figure 2 is a vertical section of the spark plug and crimping apparatus of the invention, the spark plug being shown before and during engagement with the crimping apparatus; and

Figures 3 and 4 are detail sections of further crimping apparatus of the invention in its initial and final engagement, with the spark plug of Figure 2 to complete the sealing thereof.

Referring in detail to the accompanying drawing, a spark plug I0 is shown therein, which spark plug mainly comprises a metal shell H and a porcelain [2. Initially the porcelain, which has an upper shoulder l2 and a lower shoulder I2 is seated on a gasket l3 which is carried on a shoulder I4 formed at the lower portion of the metal shell. An upper gasket 15 is carried on the upper portion of the porcelain l2 and both gaskets l3 and [5 are deformed and the porcelain is centered in the shell by a centering die l6 that is mounted by suitable means (not shown) and moved downwardly thereby to engage with the upper gasket l5 and move it and the porcelain l2 downwardly. This action distorts the gaskets l3 and I5 on the shoulders l2 and l2 of the porcelain and centers same in the metal shell, The gaskets are made from a metal such as native lake copper, silver-copper, copper-nickel, or mild steel, all of which have a relatively high recalescence or annealing temperature so that they do not anneal readily when in service. Gaskets may be made of relatively hard metals, rather than from soft metals such as copper, since they are hot worked in accordance with the present invention whereas in previous spark plug sealing practice the final working was done at low temperatures. Then too, the gasket materials named hereinabove are relatively soft at high temperatures so that they can be compressed around the porcelain without injuring same.

Nexta tubular cold crimping die ll, which has a conical face, or work-engaging surface It, is

brought into engagement with the upper end 01' the metal shell II. The face I8 is formed at an angle of about 45 with the horizontal. This shape of the die face is advantageous in that it does not set up excessive compressive strains on the metal shell but gradually folds the upper end of the shell inwardly upon the gasket I5 as the die is moved downwardly upon the upper end of the metal shell. The shell and die are Positioned in (and the die moved by) any suitable means (not shown).

Finally a tubular hot crimping die I9; generally similar to the die I1, is brought into engagement with the upper portion of the metal shell II. The die' I9 is mounted on suitable means (not shown), and it and the shell II form terminals in an electrical circuit over which current may flow from any convenient source, whereby current flows between the die and the shell when they contact. Such current flow bring the end of the metal shell I I to a readily workable temperature very rapidly. The die I9 has a conical work engaging face 2| which is shown at an angle of 20 with the horizontal, but which may be at any angle to the horizontal appreciably smaller than that of the face of the die II. Any angle that is substantially less than 45", such as from about 5 to about 30, has been satisfactory for practice of the invention. Then, since the outer surface of the upper end of the shell I I is at an angle of about 45 with the horizontal, the face 2I first engages with only the upper edge of the shell (Figure 3), rapidly heats it to semiplasticity and folds it inwardly onto and around the gasket i5. shell comes into engagement with the die I9 as it moves downwardly and the gasket I5 is compressed inwardly and downwardly against the shoulder I2 of the porcelain I2.

The final position of the component spark plug parts is shown in Figure 4 and it is seen that the inner edge 22 of the crimped section is substantially closer to the porcelain than the inner surface 23 of the shell at the region of maximum distortion. The edge 22 of the crimped shell section entirely covers the gasket I5 and locks it between the porcelain insulator shoulder I2 and metal shell I I to form a very effective seal therebetween.

In general, by the gradual engagement of the die IS with the spark plug shell, higher sealing temperatures, lower compressive forces than those usually used, and the practical employment of gaskets which will not anneal in service result and effect a good seal of the spark plug. Also, a single die can be used with several sizes of spark Gradually more of the upper surface of the plugs and deviation of a spark plug shell from standard form will not prevent the formation oi a satisfactorily sealed spark plug therefrom. The working faces of the crimping dies are relatively easily and inexpensively maintained, especially in comparison with concave crimping dies previously used.

The detailed description of the particular embodiment of the invention illustrated and described herein is not to be construed as limiting the invention thereto. The invention includes all features of patentable novelty residing in the foregoing description and the accompanying drawing.

What is claimed is:

l. A method of forming spark plugs consisting of the steps of placing a gasket of metal havin a high annealing temperature in a metal shell and on an inner shoulder thereof, placing an insulator having an upper and lower shoulder in said shell and seating the lower shoulder of said insulator on said gasket, placing a gasket of material similar to that of the first-mentioned gasket on the upper shoulder of said insulator, centering the insulator and gaskets in the shell by means of a centering die, whereby the shell and insulator' is held in spaced relation; next, by a preliminary crimping operation and while the shell is at room temperature, turning the upper edge of said shell inwardly in closer association with the gasket carried on the upper shoulder of the insulator, then softening said shell by means of heat and completing the crimping operation of the upper edge 01' the shell, thereby anchoring the insulator firmly in said shell and forming an efi'ective seal between the insulator, the gasket and the shell.

2. Apparatus for crimping spark plug shells comprising an apertured die for cold crimping the upper edge of a spark plug shell to approximately the shape desired. said die having a lower corner defining said aperture, and a second aper tured die for hot crimping the partially crimped upper edge of a spark plug shell to its ultimate position, means for effecting electrical current flow between said spark plug shell and said second named die upon contact thereof, said last named die being beveled oil at an appreciably smaller angle to the horizontal than the said first named die whereby only a small contact area is initially obtained when it is engaged with a spark plug shell initially crimped by said first named die, to produce high density current flow between said second named die and spark plug shell.

DOUGLAS W, GREGORY.