US1089907A - Electrical contact. - Google Patents

Description

W. D. coounen.

ELECTRICAL CONTACT.

nrmoumurnnn DEO.17, 1912.

1,089,907. ente Mar,10,191L

W esses: Inventor":

g William DCOoIid e,

m 3 WM W His fitter-neg.

' Schenectady, county In apparatus of complete making and breaking ,o

I once of material from UNITED STATES WILLIAM D. COOLIDGE, 0F SCHE PATENT clamor..-

l a CTADY, NEW YORK, ASSIGNOR TO GENERAL -ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

' ELEcrnrcAL'coNrAcr.

Original application filed larch 20, 1912,

To all whom it may concern: Be it known that I, WILLIA'M'D. CooLmcn,

a citizen. of the of Schenectady, State of New York, have invented certain new and useful Improvements in Electrical Contacts, set forth in my application, Serial No. 685,113, filed March 20, 1912, of which this is a division.

M invention relates to electrical contacts, particularly for rheotomes or other vibratory circuit making and breaking devices, ordinarily used as sparking or ignlting contacts for gas-edgines, as circuit controllers for regulators, and for other like purposes. this character, vibratory contact terminals of expensive metals, such as platinum and iridium, have heretofore been used, and it was found that these contacts deteriorated and became destroyed, so as to be unfit for further paratively' short time. The contacts were found toblacken and pit ,1 their contacting surfaces became hammering action and by the formation of irregular and variably distributed small pro to the transfer-' tuberances due, probably,

the cathode to the anode, whereby the normal distance between the contacts was were often formed between the two contacts. It was also found that the accidental wetting of the contacts with oil seriously interfered with their operation. In addition to this, the materials heretofore used for vibra tory contactsare softened by the heat of the sparks passingbetween them, to such an extent as to cause welding, or incipient weldin Iibratory contacts are. largely used in regulators of the kind known as Tirri'll regulators, and the use of platinum or'iridium, or platinum-iridium, or silver, for the contacts, results in rendering'the regulators inoperative within a comparatively short time, because these regulators depend for their successful operation upon the Periodical or circuits by thecontacts. The normal space Specification of Letters Patent.

United States, residing at use, within a comdeformed by, the continuous reduced and bridges a circuit between contacts.

longer life than contacts Patented Mar. '10, 1914.

Serial No. 685,113. Divided and this application-filed December 17, 1912. Scrial No. 737,214.

the contacts is between 1/32 inch and 1/100 inch, and this space is reduced by i the formation of protuberances on one or both contacting surfaces to such extent that the sparks between them are frequently maintained during the periods of the breaks, so that no real break of circuit takes place, but only an irregular and insufficient increase of resistance. The deformation of the contact surfaces, due to the hammering action, has a like result, and all these variable deformations result in a variation of the number of points of actual physical contact, whereby the transition resistance is irre ularly varied.

y invention is designed to .overcome these difliculties and it consists broadly in make and break contacts of metallic tungsten, preferably in the wrought or malleable form.

It is a well-known fact that tungsten,

when heated to redness in air, is 'soon covered with a layer of oxid which is practically an insulator, especially in the cold state, and this property of tungsten would seem to make this material unfit for use as But I that this is not so, and that by reason of the light powdery or flocculent condition of the oxid, the same is shaken off almost as quickly as it is formed, so that vibratory contacts of tungsten, and especially. of wrought or malleable tungsten, can be used with great advantage.

I have tacts made of tungsten, while theoretically not absent, is pract'cally insignificant; that the normal distance between the contacts remains sensibly constant during a long period; that no welding or incipient welding of the contacts occurs, and that the presence of oil on the contact surfaces does not interhave found by experiment fere with their operation. In consequence of these properties of tungsten which I have ascertained by long continued experiments, contacts of this material have a very much made of any other material known to me, or of any material that has heretofore been used.

conditions and wit-h the same number of makes and breaks, were found to have become so badly pitted, consumed and deformed as to be unfit for further use.

One of a pair of contacts is usually mount-v ed on a resilient support, such as a spring, and the other to a rigid support, and the joinder between the contacts and supports should. be very intimate so that the contacts will not become loose by the hammering action to which they are subjected. I secure this result either by fusing to one face of the tungsten contact a backing of a rather bulky iece of 'a metal of superior conductivity For heat and electricity, such as copper, silver or gold, and fasten the backing to a spring or rigid support by screws or other mechanical means; or I interpose the backing of superior conductivity between the contact and the support by fusion to both,

-that is to say, by using the backing as a solder. In either case. the heat generated in the contact is carried away rapidly. A new and improved process of thus joining tungsten contacts to their supports is hereinafter fully described, but no claim is herein made for the same, since that invention is claimed in my aforesaid original application Serial Number 685,113, filed March 20, 1912, of which this is a division.

Tungsten cannot be joined satisfactorily -to other metals by soldering in-the ordinary manner. This difiiculty is apparently due to the ease with which a thin film ofoxid forms on the surface of the tungsten. The

soldering metal either will notstick or when apparent adhesion has been produced'I find ing metal breaks away as though the tungsten" broke away from the film of oxid. The joinder of tungsten contacts or other bodies of tungsten to the backing of the metal of superior conductivity is, however, successfully accomplished by causing melted copper. silver or gold to flow over the tungsten surface in an atmosphere of hydrogen, as-

more specifically hereinafter set fort In the accompanying drawings, Figure 1'" shows aform of mold suitable for holding the contacts during the process of heating hydrogen; Fig. 2 shows the 'partsof a con'- tact before attaching; Fig. 3 illustrates the completed contact; Fig. 4 illustratesan apparatus by which a tungstein contact is directly attached to a spring or other support; Fig. 5 illustrates another modificationaccording to which a body of copper is cast directly into'contact with a piece of tungsten; Fig. 6 shows a machined contact at between the holes in tached to a support, and Fig. 7 illustrates coopertaing 'rheotome or spark contacts.

'In carrying out the process as above outlined, I find'it highly desirable to completely remove from the surface of the tungsten body all the loosely adherent metal or oxid which I findis left by the preliminary process of shaping the tungsten/ Unle'ss this is done, I find that in some cases the tungsten may be torn away from its backing or support at this loosely adherent surface layer, part of which'will be found clinging to the copper or other metal used as solder. .In order to remove this surface layer I prefer to bring the body of tungsten into contact with melted nitrite of sodium or potassium for a few seconds or with hot caustic potash or caustic soda solution for a longer time.

This leaves a perfectly bright surface of solid metal.

When it is desired to fasten a small disk of tungsten to a tack or support of steel, which may then be conveniently riveted or otherwisefastened to terminal supports, as

shown in Fig. 7, the operation may be carried out as follows: The parts particularly used for building up the contact are shown in Fig. 2. An iron or steel tack isplaced in a holder or mold 1 shown in Fig; 2, which may consist of graphite, magnesia, fire clay,

alumina or other refractory material. As

illustrated by a portion of the holder 1 broken away, the shank 2 of the tack is inserted'in a holeso that the tack is supported by the shoulder 3 and centered by its shank. A plate of copper 4 is placed upon the tack, and disk 5 of tungsten is placed upon the copper, the three .parts being thus properly held in position. The connecting channels 6 the mold are provided for the purpose of allowin the circulation of hydrogen during the su sequent heating process. Only a few holes have been indicatedbut of course as many as desired may be used with a single holder. The holder with the parts ofthe contact thus assembled is then placed in a suitable furnace and heated in a hydrogen atmosphere to a temperature above the melting point of copper.

A porcelain tube furnace, with hydrogen I passed through the tube, is suitable for this purpose. Under these conditions in the absence of oxygen the copper will wet the surface of the tungsten, so as to form a continuous metallic ,union between the tungsten and the steel. When1removed'from the furnace and allowed to cool the tungsten and steel will be found as be intimately'united ya backing or layer-of copper as indicated in Fig. 3. v I

, In some cases, as when joining the tung sten contact directly to a steel spring, it is convenient to carry out the heating operation with an electrie are as shown in Fig. 4. In this case the spring 7 is held-in a clamp teat 12 and the hand 636,270, filed metallic jaws 9 ofwhich hold the 8, the

heat from it so as to spring and abstract e jaws 9 may be tightened by The tungsten contact 11 is a teat 12 which passes through A small body of coper such as the copper wire 13 is introduced in close proximity to'the spring and tungsten contact. The spring and contact thus assembled are placed in a container 14 open at the bottom and supplied with a stream of hydrogen gas through a tube 15. An

operation.

the strap 10. provided with a hole in the spring.

are fed by a suitable source of current such then drawn between the electrode 17, thereby heating the tungsten contact to the melting point of copper at which temperaturethe melted copper will be drawn into the contracted space under the tungsten disk by capillary forces. ence of hydrogen as a battery 16, is

wets the contiguous surfaces of tungsten and steel in the contracted space thereby making a continuous metallic junction between the contact and the spring. Of course, in the same manner that steel is joined to tungsten, other metals such as nickel, cobalt, platinum, molybdenum, or even another body of tungsten, may be joined to tungsten. attach tungsten to platinum, gold as the soldering metal.

According to a modified process a mass of copper is cast into contact with the tungsten. Ordinarily copper by reason of its dissolved gases or other impurities willnot wet the surface of tungsten. Either the tungsten acts as a deoxidizer'with respect to the copper and becomes coated with oxid or dissolved oxids of copper lower the surface tension of copper relatively to tungsten. -I have found, however, that if the melted copper is treated previous to casting with a small quantity of an oxidizable boron material such as elemental boron, boron suboxid or boron carbid, which combines with the dissolved impurities, the copper will then wet and permanently adhere to the surface of the tungsten. This process of purifying copper is described in an application filed by E. WVeintraub, Serial Number June 30, 1911. Elemental boron and boron carbid are now well-known to chemists. Boron sub-oxid is the product of the reduction of boric anhydrid with magnesium at a temperature of1300 C. or higher. The reduction mass left after I prefer to use washing with dilute sulfuric acid is a brown powder. The treatment of the copper is carried out by adding 1/30 to 1/10 of 1% or more of boron or of a boroncompound containing an equivalent amount of boron in the reduced state while the copper is heated considerably above its melting point, say 1200 to 1300 C.- or higher. The copper cation and attachment The copper in the pres-' When it is desired tothus prepared is then cast into contact with the tungsten body which may for example be placed in the bottom of a magnesia or alumina crucible 18 as shown in Fig. 5, After cooling, the mass of copper and tungsten thus oined together is removed and the copper maybe machined so as to attach it in any approved manner to electrical apparatus. Fig. 6 is illustrative of a contact made in this way, the copper 19 being attached by means of a screw 20 to the supporting part 21 indicated by dotted lines.

- vAs a modification I may cause the purifiof copper to the tungsten body to take place in one operation- This may be done by tungsten, for example, In the bottom of acrucible as shown in Fig. 5, placing the boron material upon the tungsten and then adding copper. 'The contents of the'crucible. are then heated to a temperature several hundred degrees in excess of the melting point of copper. The exclusion of air during the heating process is not essential although desirable.

According to another modification the copper is caused to unite metallically with a tungsten body by heating to a temperature considerably above its melting point in a vacuum preferably to a temperature about 1 100 C. Under these conditions an oxid of tungsten cannot exist, the oxid at this temperature being dissociated into metallic tungsten and oxygen. The copper itsel appears to lose at least part of its dissolved gases. .The operation may be carried out by placing a body of tungsten and a quantity of copper in a crucible, as shown in Fig. 5, and heatingthe'crucible and its contents in a vacuum furnace such as shown in Arsem Patent No. 785,535. After being heated to the required temperature the copper and tungsten are simply allowed to cool in contact with each other. Upon removal from the'crucible, the copper may be machined. The tungsten terminal 22, Fig. 7 is attached to an armature 23, and cooperates with a stationary tungsten contact 24.

What I claim as new and desire to secure by Letterslfatent of the United States, is:

1. An electrical make-and-break contact of tungsten.

2. An electrical make-and-break contact of malleable tungsten.

' '3. An electrical make-and-break contact of tungsten, and a backing for the same of a metal of superior electric and thermal con ductivity intimately joined thereto.

4. An electrical make-and-break contact of tungsten integrally joined to a -metal backing of superior electric and thermal conductivity v 5. An electrical make-and-break contact of tungsten, a support for the samefland a contact backing of a metal of superior elecplacing the disk of a trio and thermal conductivity intervening In witness whereof, I have hereunto set .between the contact and support and intemy hand this 16th day of December, 1912 grally joined to both. 1

6. An electrical vibratory make and- WILLIAM COOLIDGE' v break contact of tungsten. Witnesses? 7. An electrical make-and-break impact HELEN ORroRD,

contact of tungsten. BENJAMIN B. HULL.

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