Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Patent
1992-03-05
1993-01-12
Ramsey, Kenneth J.
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
445 7, 228160, H01T 2102
Patent
active
051793130
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the formation of an erosion resistant tip on an electrode, for example on one or both electrodes of a spark plug for use in an internal combustion engine; to an electrode having a tip formed by this process and to a spark plug in which either one or both electrodes are provided with tips formed in accordance with this process.
2. Description of the Prior Art
In order to achieve greater spark plug life and/or to allow the area of the electrode to be reduced to produce more efficient ignition, it is desirable to place and the electrode tips an erosion resistant material One suitable material is platinum, but any material which is more resistant to chemical erosion than Inconel may be used. Inconel is the conventional material used for spark plug electrodes and the name Inconel is a Registered Trade mark.
It is known from U.S. Pat. No. 4 810 220 to apply the platinum or other erosion resistant material using a sphere which is welded onto the respective base electrodes. However these spheres are necessarily of small size and therefore difficult to handle. Similar methods using platinum discs rather than spheres are also known. It is also known from U.S. Pat. No. 4 705 486 to weld a strip of platinum ribbon to the electrode.
In all these methods, it has proved difficult to ensure the necessary penetration of the platinum metal into the substrate to ensure that the platinum tip remains in place under service conditions.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a process for applying an erosion resistant tip to an electrode, wherein the erosion resistant material is supplied in the form of a continuous wire, the end of the wire is welded to the electrode, the wire is severed at a predetermined distance from the weld to leave a pellet welded to the electrode, a coining operation is carried out to flatten the pellet onto the electrode and finally a second welding operation is carried out during which pressure is applied to the pellet to force the pellet into the material of the electrode.
The erosion resistant material is preferably platinum, and a grain stabilised platinum is particularly suitable.
The welding operations are preferably carried out by electrical resistance welding. The first welding operation is preferably carried out under conditions such that the weld formed is just sufficient to retain the wire secured to the electrode whilst the end of the wire is severed to separate the pellet from the remainder of the wire and during a subsequent coining operation.
The leading end of the wire is preferably pointed or tapered so as to form a contact area with the electrode which is smaller than the cross-sectional area of the wire. This can normally be accomplished by leaving the end of the wire "as sheared".
It is advantageous for the first welding operation to produce a minimum welded area, because when the second welding operation takes place the flow path for the welding current will be smaller, thus producing a higher temperature which allows some melting of the electrode so that the pellet can be pressed into the material of the electrode.
Where the electrode is the centre electrode of a spark plug, the electrode is preferably machined in a subsequent stage so that the exposed end of the electrode is entirely covered by the erosion resistant material.
Where the electrode is the side electrode of a spark plug, the tip material preferably lies substantially flush with the electrode material following the second welding operation.
According to a second aspect of the invention, there is provided an electrode to which an erosion resistant tip has been applied by the method set forth above. The electrode may be the centre electrode or the side electrode of a spark plug, and the invention extends to a spark plug which has a so-formed electrode tip on either or both electrodes.
The erosion resistant tip is preferably of platinum.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic elevational
REFERENCES:
patent: 3868530 (1975-02-01), Eaton et al.
patent: 4073425 (1978-02-01), Bollian
patent: 4699600 (1987-10-01), Kondo
patent: 4700103 (1987-10-01), Yamaguchi et al.
patent: 4803395 (1989-02-01), Matesco
patent: 4810220 (1989-03-01), Moore
patent: 4826462 (1989-05-01), Lenk
Eves Terence J.
Margetts Jeffrey W.
Palmer Graham E.
Ford Motor Company
Malleck Joseph W.
May Roger L.
Ramsey Kenneth J.
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