Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1996-11-15
1998-07-14
Simmons, David A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562722, 2282629, 445 7, B32B 3114, H01T 2102
Patent
active
057798427
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the formation of an erosion resistant coating on a pre-selected area of a spark plug electrode, for example the tip of one or more electrodes of a spark plug for use in an internal combustion engine. The invention also provides a spark plug in which one or more electrodes are provided with a tip coated in accordance with this method.
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 at the electrode tips an erosion resistant material. One suitable material is platinum, but any material which is more resistant to erosion than INCONEL metal (alloy of 9% by wt Fe, 15% Cr and 76% Ni) may be used. INCONEL metal is a material that is conventionally used for spark plug electrodes and the name INCONEL is a registered trademark.
2. Discussion of Related Art
It is known from U.S. Pat. No. 4,180,220 to apply the platinum or other erosion resistant material using a spherical body of platinum which is welded onto the respective base electrodes. However these spheres are necessarily of small size and therefore difficult to handle. Similar methods are known using platinum discs rather than spheres. It is also known from U.S. Pat. No. 4,705,486 to weld a strip of platinum ribbon to the electrode. It is also known from European patent application number 90912755.7 to form a pellet of erosion resistant material on the tip of an electrode by welding a wire to the tip and severing the wire, and then to carry out successively a coining operation to flatten the pellet and a second welding process to force the pellet into the material of the electrode.
In all these methods it has proved difficult to protect a large area of electrode with the erosion resistant material.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of manufacturing a spark plug electrode which is coated in a pre-selected area with an erosion resistant material, which method including the steps of: coated, a web which contains the erosion resistant material and which carries a thermally decomposable and/or volatilisable adhesive on one surface, so that the web adheres to the electrode; cause the adhesive to decompose and/or volatilise so that the adhesive is substantially eliminated from the electrode/web combination, and to fuse at least some of the erosion resistant material so that it bonds to the electrode.
By applying the erosion-resistant material to the electrode in the form of a web it is possible to control the area of application and the thickness of the coating. The process facilitates the coating of large areas of an electrode.
It is preferred that the web is provided on a reel, and that the web is cropped (cut) to separate the part of the web that is adhered to the electrode from the remainder of the web on the reel. The cropping step may be carried out at any stage of the process, but it is preferred that the cropping is carried out after step a) and before the heating step.
The web may have an adhesive coating on only one surface, or the web may have an adhesive coating on more than one surface. It is also possible for the web to have adhesive distributed throughout its structure so that cutting or breaking the web provides fresh adhesive surfaces where the web has been cut or broken. Preferably the web is relatively thin; however the web may be of any preferred dimensions. For example the web may comprise a rod which has adhesive distributed throughout its length so that one end of the rod may be brought into contact with an electrode, for example the tip of a centre electrode of a spark plug, so that it adheres to the centre electrode. The rod may then be cut so as to leave a disc adhered to the centre electrode for the heating stage b). For convenience hereinafter the invention will be described in terms of the use of a thin, flexible web with one adhesive coated surface and one non adhesive coated surface.
The web
REFERENCES:
patent: 5348215 (1994-09-01), Rafferty et al.
patent: 5578365 (1996-11-01), Kume et al.
McDonald, Robert J., "Metal Powders -Their Role in Brazing is characterized by flexibility and freedom to select a wider range, as to both performance and cost, of filler metal compositions", Welding Journal, vol. 50, pp. 327-331, May 1971.
Fawcett Nigel
Knowles Richard
Ford Global Technologies Inc.
Gray Linda L.
Malleck Joseph W.
Simmons David A.
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