US1220886A - Tungsten contact-point. - Google Patents

Description

' UNITED s'rATEs PATENT OFFICE.

CABI. A. PFANsTIEHL, or WAUKEGAN, ILLINors, AssIGNoR 'ro PFANSTIEHL COMPANY,

A CORPORATION or DELAWARE. o

TUNGsTENcoNTAcr-Pomr.

Application filed April 1914. Serial No. 830,013.

Be it known that I, CARL A. 'PFANs'rmHL,

a citizen of the United States, residing at Waukegan, in the county of Lake and State of Illinois,.have invented certain new and useful mprovements in Tungsten Contact- Points, of which the following is a full,

clear, concise, andexact description, reference being had to the accompanying drawings, forming a part of this specification.

4My invention relates to a process for the production of tungsten electrical contacts and to the particular type of contact point produced by such process.

Metallic tungsten is one of the group of so-called rare metals. It'fuses o'nly at eX- tremely high temperatures. It does not readily oxidize or corrode in ordinary atmospheres. It is extremely hard, and can not be cut or worked-with ordinary tools.

Its properties are such as to make it admirably adapted for electrical contact points of electrical switchingmechanisms of various types,,but the high cost for the metal 25. itself, coupled with the difiiculties in working it into Shape for use, has greatly limited if not indeed practically prevented its applcation as a material from which to make electrical contact points- The process of my invention involves the Cutting of appropriate disks of tungsten from thelend of a rod whose cross-section corresponds substantially to that of the finished contact points. The tungsten disk thus madeis preferably attached to a base metal stem by means of a film or layer of gold,y silver or copper fused or welded both to the base metal stem and thetungsten of the contact point proper.

I have found that disks or ground from the end of a 'worked' or drawn tungsten rod in the manner hereinafter described arev far preferable for the purposes of electrical contacts to disks which arestamped or punched from a Sheet of tungsten, the reason being that the fiber or 40 of tungsten cut grain of a' sheet of 'metalllctungsten is parallel with the surfaceof the sheet so that the `specification of Letters Patent.

Patena Mar.` 27, 1917.

side of the wear of electrical sten rod, on the other hand, the grain is lengthwise of the rod and the disks cut from the end thereof, by the process hereinafter described, present the end of the grain of the tungsten as the contact circuits with the result that the wear upon the point is far more uniform than in the case of disks cut from sheet metal.

I have found also that the contact points thus cut from the end of a rod are far less subject to pitting due to the'arcing to which switch contact points are subjected than are points punched from sheettungsten and that the latter crumble away at the edges, whereas therel is little or no crumbling at the edge of my contact points when used under similar conditions.

The process of carrying out my invention as embodied in the machine for doing it, and the tungsten rod before being cut and disk after being cut, are illustrated in the accomgrain or fiber is subjected to the 'the contact points as mounted in panying drawings in which like. characters designatev like parts throughout, and inr which, l

Figure 1 illustrates the grinding or slitti'ng machine by means of which. the 'disks are cut from the end of a tungsten rod;

Fig. 2 illustrates a disk of tungsten;

Fig. 3 illustrates the disk of silver by means of which the disk of tungsten is fused to the head of the mounting stem shown in Fig. 4. V

Referring first to' Fig. 1, Iv have illustrated a rod of tungsten 20, which is preferab-ly of circular cross-section and of the diameter of the finished contact point. This tungsten rod is inserted in a closely-fitting hole 21 of the clamping frame 22, the clamping mechanism being provided with al movable clamping member 23 provided with a screwthreaded rod 24 upon which the clamping nut 25 may be turned to clamp the tungsten rod 20 in the end of he clamping member, as shown.

The clamping member is provided with a switching mechanism. In atung-- gage 26, the thiclmess `tion shown v20 when the rod abutment to stop i the hole through the'gage member 2d 32 adapted Operating lever 36 is The entire clamplng mechanism as thus far described is mounted 'upon a carriage to slide in a .T-shaped slot 33 formed in the base`of the cutting' machine. .A rack 34 mounted upon the carriage coperates with a pinionv 35 -to advance the carriage with its clamping mechanism whenever the manipulated, the mothrough the erank tion being' transmitted pin 38 arm 37, which is provided with a riding in the'slot 489 of the lever 36, which in turn is pivoted at 40, as illustrated.

may be swung down to the posi- Mount'ed upon the common base plate 410 is the rotatable spindle 42 of the grinding i head, provided with. rollers or ball bearings an inch ,in thickness,

mounted in the frame 48. A belt runs over the pulley 44 to rotatethe spindle`42, upon the end ofwhichis mounted the vslitting wheel 45. This slittingwheel is preferably not much more than one one-hundredth of tween the metal disks 46 and/47, these disks extending near but not quite to the perphery of thev slitting' wheel 45.

.The slitting Wheel islrotated at high' speed to cut the disks -from the end of the tungsten red-20. The operation ofl this part of the mechanismemployed in -carrying out my process involves the adjustment of the rod of tungsten within the clamping meohanism, as shown in the vdrawings, whereupon the lever 36 is lmanipulated to force the end of the rod of tungsten against the periphery of the slitting wheel., The pressure is continued until the wheel has cut or ground its way through the tungsten. The tungsten disk thus'cut from the end ofthe rod is retained in the hole in the end 27 of'the gage 26 until the side of the slitting wheel has passed shown inFig. 1, and

'and T support it bef entirely across the face of the disk, as a result of which the bur which would otherwise be formed at one side of the tungsten disk is entirely rernoved` When a. disk has thus been cut from the end of the rod the carriage is withdrawn, due to the pull of the retracting spring 48. Thereupon, the handle 31 of the stoprnechanism is depressed to ;permit the finished 'tungsten disk to drop from the hole in the. end 2,7 of the gage- .piece 26.; The nut 25 is then'tur'nedto the naedeee containing the carborundum grain or crystals is then vulcanized to form a hard Vulcanite wheel in which the grain or crystals are firmly embedded. ll have found it'preferable to employ carborundum dust of from 60 to 100 mesh, and llthave found it desirable also to add to the unvulcanized rubber mixture a sufiicient percentage of sodium silicate to assure the production of a hard and tough wheel after the vulcanizing operation has been performed.

The vulcanite carborundum. wheels above described may be made extremely thin and can be satisfactorily operated without breaking when held between clamping disks, as rovidedfalso that the spindle upon 'which t e wheel is mfounted is providedlwith closely-adjusted bearings, and provided also that the entire mechanism is so strongly and firmly constructed as to avoid chatter or vibration.

After the tungsten end of the rod as above described, they must be thoroughly cleaned and freed from any film of oxid. This is done by treating the disks in a hot bath of solution ,of caustic .potash or soda, whereupon they are ready to the clean stemsof base shank 51 through lthe hole of a contact lspring or lever,

'whereupon 'the shank may be riveted to secure the stem and its tungsten contact face securely in place.

While-l havedescribed my invention in connection with the use of tungsten di'slrs, f do not wish to be limited to the use of pure tungsten, for the reason that tungsten al'- loyed with certain other rare metals can advantageously be substituted for pure tung-v sten. Small percentag'es lof molybdenum, for example, may he alloyed with the tiingsten with results in some instances .better than those secured from the use of substantially pure tungsten..

ll do not wish, therefore, to he limited to disks are cut from the I the precise details herein described,l but tends perpendicularly to'the impact' face of 10 claim as my nvention: the contact. I

1. A make and break electrical contact of In Wtness 'whereof, I hereunto Subscribe davrn ltungsten in whch the grn or fiber my name this 24th day of Marchl A'. D. 1914. 5 o t e tungsten exten s er en icularl to the contact face" P P Y CARL A. PFAN TIEHL.

2. An electrical make and break contact Witnesses: sawed from the end of a tungsten rod, so A. G. MCCALEB, that 'the Jfiber or grain of the tungsten ex- ALBIN C. AHLBERG.

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