US 1658713 A
Description (OCR text may contain errors)
Feb. 7, 1928. 1,658,713
T. s. FULLER ELECTRICAL CONTACT Filed Oct- 30. 1923 Inventor: Truman '61",
"Us Attorney- Patented Feb. 7, 1928.
UNITED STATES PATENT OFFICE.
TRUMAN S. FULLER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COIPANY, A CORPORATION 01 NEW YORK.
Application filed October 30, 1923. Serial No. 671,785.
The present invention relates to electrical make and break contacts, as for example, the vibratory contacts in an ignition system for an internal combustion engine.
5 When refractory metals such, for example, as tungsten or molybdenum are utilized as tips for make and break contacts, the pellets of refractory metal between which the en'- cuit is broken have been secured by a layer 1 of copper to a base or tack of steel, or other metal suitable for riveting, which solidly binds the tip of refractory metal to the base to make a unitary structure. As described in Coolidge Patent 1,181,741, of May 2, 191$,
the brazing of the tip and base by copper 1s carried out by interposing copper as a thm plate between the contact tip and the base and then melting the copper in a hydrogen atmosphere.
Althoug copper is entirely satisfactory to produce a strong joint, great care must be exercised not to permit any excess of copper to remain on the contacting face or on the sides of the contact disk of refractory metal as this will cause arcing at the contacts during subsequent operation accompanied by overheating and burning of the contact points. This tendency of copper to cause arcing when present upon the contacting surfaces necessitated a separate grinding operation in the manufacture of make and break contacts. But even a careful removal of copper from the contact disk did not always obviate the dangerof arcing, as copper sometimes worked through cracks in the contact disk to the contact face and caused arcing.
I have discovered that when the brazing metal in an electrical contact is constituted by a suitable alloy of silver and copper that no arcing occurs when the brazing alloys remain on the face of the contact disk, or creeps on the contact face during operation of the contact.
The accompanying drawing illustrates a contact embodying my invention, Fig. 1 showing the parts before assembly, and Fig. 2 the completed contact.
Although the base whereby a contact is attached may consist wholly of soft metal, as silver-copper alloy in the present instance, I shall describe my invention as applied to the manufacture of contacts having a base of other metal.
Referring to the drawing, the disk 1 of silver-cop er alloy is interposed between the contact disk 2 and the stem or support 3. The silver alloy may contain from about 15 to 28 per cent copper, the lower content of copper of this range being preferred. The contact disk may consist of tungsten, molybdenum, or other refractory metal. The base 3 ordinarily consists of soft steel, but to advantage may consist of copper or bronze which have a higher heat conductivit than steel. The contact parts thusassemb ed are heated to the melting point of the brazing materials while held on a suitable form or support, preferably consisting of graphite in a furnace provided with an atmosphere of filling of hydrogen, as described in Coolidge Patent 1,181,741.
The silver-copper alloy readily wets' both the tip of tungsten or other refractory metal and the base of iron or steel in the presence of a reducing gas. The mechanical properties of the completed contact containing an interjacent brazinglayer of silver-copper alloy are substantially the same as a contact containing a brazing film of copper while as already indicated no grinding or other finishing step is required to remove excess brazing material, and no difficulty is experienced by brazing metal working through cracks of the contact disk to the face of the contact.
What I claim as new and desire to secure by Letters Patent of the United States, is,
1. An electrical make and break contact comprising a contact head having a substantially fiat surface and a parallel, substantially flat backing therefor consisting of an alloy of silver and copper, said backing being joined to said head by fusion.
2. An electrical make and break contact comprising a contact head of refractory metal, a base and an alloy of silver and copper uniting said head and base by fusion said alloy consisting largely of silver and containing not more than 28% of copper.
3. An electrical make and break contact comprising a contact head of refractory metal having a substantially flat surface, a base consisting of cuprous metal, said base having a substantially flat surface, and an alloy of silver and copper interposed between said flat surfaces to unite said head and base. 4. An electrical make and break contact comprising a. contact head of n0n-arcing,'1-efractory material and a backing material consisting of an alloy of 85 to 72% parts silver and about 15 to 28 per cent copper.
5. An electrical make and break contact comprising a head of tungsten, a base of 10 copper and an interjacent layer of silvercopper alloy containing at' least about 72 parts silver. I
In witness whereof, I have hereunto set my hand this 29th day of October, 1923.
TRUMAN S. FULLER.