GB2024665A

GB2024665A - Spark plug electrode manufacture

Info

Publication number: GB2024665A
Application number: GB7829170A
Authority: GB
Original assignee: Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Motor Co Ltd; Ford Motor Co
Priority date: 1978-07-07
Filing date: 1978-07-07
Publication date: 1980-01-16
Also published as: GB2024665B

Abstract

A central electrode (7) for a spark plug is produced quickly and easily by forming a rod from a core of thermally conducting material, such as copper, and a sheath of refractory metal such as a nickel-chromium alloy, said sheath having an open end which projects beyond the adjacent end of the core, and spinning, peaning or otherwise mechanically working the end of the sheath to close the end around the core. <IMAGE>

Description

SPECIFICATION Spark plug electrode Description This invention relates to central electrodes for spark plugs.

One conventional type of central electrode for spark plugs comprises a core of thermally conducting metal, such as copper, and a sheath of refractory metal, such as a nickel-or chromium-nickel steel. Such electrodes can be produced by forming the core and sheath into a composite rod, removing the core from one end of the rod to form a recess, and sealing the end of the sheath for example by brazing. Brazing is however relatively difficult and expensive to perform.

According to the present invention there is provided a method of manufacturing a central electrode for a spark plug comprising the steps of forming a rod using a core of thermally conducting metal and a sheath of refractory metal, said sheath having an open end which projects beyond and adjacent end of the core, and physically working the said one end of the sheath to close the end of the sheath around the core.

The invention also includes a central electrode for a spark plug comprising a core of thermally conducting metal and a sheath of refractory metal, one end of the sheath having been physically worked to close the end of the sheath around the core.

Any suitable forming process may be used to close the end of the sheath around the core. Spinning or peaning are however preferred.

Conveniently, the rod is formed by inserting a strand of core material into a tube of the refractory material, severing the tube containing the strand to form a rod of desired length, and removing the terminal part of the strand from the said one end of the sheath, for example by drilling.

Desirably, the other end of the rod is formed into a head.

The core may be formed from any thermally conductive metal such as copper, brass, or siliver, or aluminium, and the sheath may be made from any refractory metal such as stainless steel, nickel, nickel-chromium alloys, or molybedenum. Other suitable materials will be known to those skilled in the art.

An embodiment of the invention will be described, by way of example only, with reference to the drawings in which: Figure 1 is a partial axial cross-section through a spark plug incorporating an electrode in accordance with the invention, Figure 2 is a side view of the central electrode of the spark.

Figure 3 is an axial cross-section through the central electrode of Figure 2 and Figure 4 is an end view of the electrode of Figures 2 or 3.

Referring to the drawings, the spark plug comprises a hollow metal body 1 adapted to be screwed into an opening in an engine block and having an integrally formed earth electrode 2. The body 1 receives an insulator 3 of ceramic material which is itself hollow. A conductor 4 extends through the centre of the insulator 3 from an exterior terminal 5 to a central chamber 6 which is packed with a particulate conductive material such as graphite 6a. An axially elongated central electrode 7 is mounted in the opposite end of the insulator 3 from the terminal 5 in electrical contact with the material in the central chamber 6. The central electrode projects from the end of the insulator 3 and its exterior end is spaced from the earth electrode 2 by a spark gap 8.

Referring to Figures 2, to 4, the central electrode 7 comprises a cylindrical copper core 8 in a tubular sheath 9 of a Nickel-chromium ailoy sold under the trade mark "Inconel". Such alloys typically have the following compositions by weight:- Nickel: at least 75% Chromium: 14to16% Iron 6to 8% Maganese 0.1 to 0.5% Silicon 0.1 to 0.5% Carbon 0.04to0.1% The central electrode 7 is formed by inserting a strand of copper wire having, for example, a diameter of about 1 .7mm, into a tube of the nickel-chromium alloy having an exterior diameter of, for example about 2.75mm. The resulting rod is then cut into lengths of, for example, about 25mm.The copper core is then drilled out of one end of the rod to a depth of about 2mm to leave a cylindrical recess in the end of the sheath 9. The end of the sheath is then physically formed by peaning or by a conventional spinning process so that the adjacent end of the core is enclosed by the sheath. Where a spinning process is used, the end of the sheath may initially be drawn into a conical configuration with, for example a 40 cone angle. Afacing tool may then be placed over the cone angle and a flat face spun onto the end of the electrode. If desired the end face of the sheath can be subjected to a grinding operation to flatten the face further.

The other end of the central electrode is formed into a head 10 in a conventional head die. The terminal part of the head is then crimpped to form a flat projection 12 having indentations 14 in each face.

The process for producing the central electrode is therefore simple and easily performed, involving only mechanical working of the electrode.

Claims

1. A method of manufacturing a central electrode for a spark plug comprising the steps of forming a rod having a core of thermally conducting metal and a sheath of refractory metal, said sheath having an open end which projects beyond the adjacent end of the core, and physically working the said one end of the sheath to close the end of the sheath around the core.

2. A method according to Claim 1 wherein the rod is formed by inserting a strand of cone material into a tube of the refractory mental, severing the tube containing the strand of cone material to form a rod of desired length and removing the terminal part of the strand from one end of the sheath by drilling.

3. A method according to Claim 1 or Claim 2 wherein the other end of the rod is formed into a head.

4. A method according to any one of Claim 1 to 3 wherein the said one end of the sheath is closed by rolling.

5. A method according to any one of Claim 1 to 3 wherein in said one end of the sheath is closed by peaning.

6. A method of manufacturing a central electrode for a spark plug substantially as described with reference to the drawings.

7. A central electrode for a spark plug comprising a core of thermally conducting metal and a sheath of refractory metal, one end of the sheath having been physically worked to close the end of the sheath around the core.

8. A central electrode for a spark plug substantially as described with reference to the drawings.

9. A spark plug incorporating a central electorde according to Claim 6 or 7 and produced by a method according to any one of Claims 1 to 6.

New claims or amendments to claims filed on 15th Oct. 1979 Superseded Claims 1 New or amended claims:

1. A method of manufacturing a central electrode for a spark plug comprising the steps of forming a rod having a core in the form of a shaft of thermally conducting metal and a sheath of refractory metal, said sheath having an open end which projects beyond the adjacent end of the core, and physically working the said core end of the sheath to close the end of the sheath around the core.