US3290472A

US3290472A - Electric current collecting element

Info

Publication number: US3290472A
Application number: US465556A
Authority: US
Inventors: Robert H Savage
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-06-21
Filing date: 1965-06-21
Publication date: 1966-12-06
Anticipated expiration: 1983-12-06
Also published as: CH459330A; FR1483421A; DE1564011B2; DE1564011A1; GB1141474A; JPS4630537Y1

Description

Dec. 6, 1966 R. H. SAVAGE ELECTRIC CURRENT COLLECTING ELEMENT Filed June 21. 1965 /n van/0r Haber) H. Savage,

His Afro/06V- United States Patent 3,290,472 ELECTRIC CURRENT COLLECTING ELEMENT Robert H. Savage, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed June 21, 1965, Ser. No. 465,556 Claims. (Cl. 200-166) This invention relates to contact elements for the collection and delivery of current in electrical devices both by the mechanism of make-and-break contact and by sliding contact.

Contact carbon brushes for the collection and delivery of electrical current are most commonly employed, because of the natural lubricating qualities thereof. However this material, usually graphite, has the disadvantage .that it is quickly subject to substantial wear in use and also shows higher electrical contact resistance than do the metals copper, silver, gold, palladium and platinum. Various attempts have been made to offset the abnormal wear of carbon brushes by impregnating graphitic carbon with inclusions of metals (i.e. copper or silver), by the addition of solid lubricant materials (i.e. molybdenum disulfide), and by the incorporation of organic compounds into the contact body. The purposes for the various modifications to carbon brushes differ, but all achieve substantially the same object; to wit, reduction of the wear rate. This reduction may be effected either through direct lubricant action or by reduction of electrical erosion through improved current conduction.

Metal contacts used either as make-and-break elements or as sliding conductors have the disadvantage that, because the contact is unlubrioated, consequent welding occurs between the contact element and the surf-ace. Also lack of lubrication may lead to arcing, which in turn creates regions of roughness in the metal surface, thereby precipitating further arcing in an autodestructive manner. Metal contact elements, while they are operating satisfactorily, have the distinct advantage of being excellent conductors of electricity.

Therefore, it is the prime object of this invention to provide a composite contact element combining the advantage of both metal construction and lubricant construction.

It is another object of this invention to provide a contact element usable either in a make-and-break electrical current-carrying capacity or as a sliding contact, the construction thereof combining a highly effective electrical conductor in the form of .a metal shell having a core consisting of a low adhesion electrically conductive material, which will neither stick to the surface from which current is being collected by sliding contact nor evaporate or splash under the difficult electrical disturbances characteristic of the make-and-break processes.

It is still another object to provide a composite makeand-break contact element having a metal outer wall and a core of electrically conducting lubricant material disposed to make contact (on closing) with a movable portion of a juxtaposed contact surface, whereby after an initial contact is made with the conducting lubricant core, the dwell period of the electrical contact occurs with contact between the metal portion of the contact surface and the metal wall of the composite element.

These and other objects may be attained in the practice of this invention by the construction of small metal contact elements having a large portion of the cross section thereof composed of an electrically conducting lubricating material. The construction can be effected either by providing -a recess in a metal contact, which recess is then provided with the lubricant core by pressing a rod of the lubricant material therein, or by a more commercially practical method; that is, filling a metal cylinder 'ice with the electrically conducting lubricant core material, plugging the ends of the cylinder, swaging the composite to a reduced diameter, and then finally, drawing the structure into small wire of the requisite composite cross-section. Once drawn into wire it is expedient to cut the wire in appropriate lengths as required. The more common metals to be employed as the thin outer contacting wall of the composite construction are copper and silver, alalthough other metals may be employed. The contacting core material may, for example, be graphite, molybdenum disulfide (modified to render it electrically conductive), mixtures of silver and graphite.

The exact nature of this invention will be more readily apparent from consideration of the following specification relating to the annexed drawing in which:

FIG. 1 is a small composite contact button having a metal wall and a graphite core;

FIG. 2 shows a short length of composite wire construction having a bevelled contact face;

FIG. 3 composed of FIGS. 3a, 3b, and 3c schematically illustrates steps of production by which the composite wire construction shown in FIG. 2 may be produced;

FIG. 4 schematically illustrates the use of the contact element shown in FIG. 1 as a make-and-break element, and

FIG. 5 shows the application of the composite structure shown in FIG. 2 in conjunction with a timing disk employed as a motor control.

Thus, to describe in greater detail the invention illustrated in the drawings, the small composite contact button 10 shown in FIG. 1 was converted from a metal contact button by providing recess 11 therein and then force-pressing tight-fitting carbon rod 12 into the recess. As a result a composite construction having a cross-section is produced containing a large percentage of low adhesion material to serve in the requisite lubricant capacity for the metal shell disposed in contact with the surface from which current is being collected. The action of forcing the tight-fitting graphite rod 12 into the recess 17 insures a good electrical contact between the graphite core and metal shell 13. As indicated above, the metal wall 13 is preferably constructed of copper or silver, although other metals or alloys may be employed.

Similarly in FIG. 2 the composite current collecting wire element 16 consists of metal wall, or shell, portion 17 serving as a good electrical conductor and enclosing the sidewall area of the electrically conductive lubricant core 18. Another particularly important advantage of employing metal as the outer wall consists in the ease With which attachment can be made thereto by mechanical means, as by soldering or welding. The outside diameter of the wire is, of course, a matter depending upon the particular application; however, wire sizes in the range of from about 10 to 60 mils are suitable for the practice of this invention. Preferably, the ratio of the radius of the lubricant core to the thickness of the metal wall will be within the range of from about 20:1 to 1:1. Expressed another way, the ratio of the cross-sectional area of the lubricant core to the cross-sectional area of the metal wall would be in the range of from about 400:1 to 1:1.

The choice of the core material to be used is controlled by relatively simple criteria. Thus, the core material must be free of corrosive impurities (nor may it itself be corrosive) such as will cause deterioration of the metallic wall portion enclosing it; the core material in its compacted state should have a coefiicient of friction against itself or against copper or silver of less than about 0.5 (preferred range about 0.05 to about 0.25), and it should have electrical resistivity of less than 10 ohm-centimeter.

Examples of core materials meeting these criteria are graphitic carbon, graphitic carbon mixed with silver or copper, graphitic carbon mixed with solid lubricants, such as molybdenum or tungsten disulfide, and electrically conductive molybdenum disulfide or tungsten disulfide.

Referring to FIG. 3, process steps for preparing the composite wire element shown in FIG. 2 are illustrated. First, a tubular body or billet 20 (FIG. 3a) is prepared comprising tube 21, filled with compressed powder, or granular material 22, to form a core. The filler material, as for example graphite, is retained within tubular body 20 during the subsequent swaging and drawing operations by the end caps or

plugs

23, 24, which are welded (or otherwise fixedly secured) to tube 21. The billet 20 is next swaged to drawing size, after which the composite body of reduced diameter so produced is subjected to successive wire drawing stages as shown in FIGS. 3b and 3c to produce composite wire of the ultimate small diameter. In reducing the tube and its core from its original size to wire size, approximately a 90% reduction in size may advantageously be employed. Then, the composite wire so produced may be cut into such varied lengths as may be required.

As an illustration of the manner in which the composite contact elements forming this invention may be employed, reference is made to FIGS. 4 and 5. Thus, in FIG. 4 a make-and-break device is shown employing the contact button element shown in FIG. 1 afiixed to flexible spring-like arm 31. Motor panel 32 is activated in response to the demands of timer mechanism 33, such as may be employed in an automatic washing machine. Timer 33 receives power from the l10-volt power source, which services motor panel 32. Upon demand from timer 33 solenoid 34 is actuated pulling the flexible member 31 toward it. During this movement core 12 of element 10 contacts the depressible contact 36 of a stationary contact forcing contact 36 inwardly against the action of spring 37, which is located in recess 38 of metal stationary contact 39. In this manner initial electrical contact (making) occurs between core element 12 and depressible contact 36. Thereafter, as contact 36 is forced inwardly, the annular metal portion 13 of composite contact element 10, which encloses core 12, is brought into contact with the face of stationary contact 39. Because of its lower electrical resistance this metal shell then assumes the function of conducting most of the current through the switch. With the make-andbreak switch closed the requisite power is provided to motor panel 32. As dictated by timer 33, breaking of the circuit occurs with the annular metal portion 13 of composite contact element 10 moving away from the face of stationary element 39 without causing arcing, because of the continued electrical contact between core 12 and depressible element 36. By the use of such construction, it is possible to employ the core 12 to effect the makeand-break functions, while the dwell time of switch closure occurs with metal-to-metal contact.

The structures shown in FIGS. 1 and 2 are interchangable for the purpose of collecting current and it is to be understood that applications illustrative of the one structure are also illustrative of the other.

In FIG. 5, by way of example, the rotating disk 41 schematically represents part of a timing mechanism such as is conventionally employed in an automatic washer (not shown). The composite wire contact element illustrated in FIG. 2 is shown in juxtaposition to rotating disk 41. Sliding contact element 42 is held in fixed position so that, as disk 41 rotates, the timing islands 43 are brought into contact with element 42. The disk 41 is itself electrically nonconductive, while the timing islands 43 are electrically conductive. The arc length of the individual islands 43 in conjunction with the rate of rotation of disk 41 determines the period of time during which some given automatic operation is conducted by the machine, because of the completion of an electric circuit through ring contact 44, lead 46, the particular island 43 and the sliding contact 42. Interruptions in motor operation occur when the electrically nonconducting portions of disk 41 are rotated into juxtaposition with the sliding contact elements 42.

The use of the composite construction illustrated in FIG. 2 and described herein is of particular advantage because of the dual function exercised thereby. Because of the lubricating capacity of the core and its capacity for electrical conductivity it becomes feasible to employ the metal wall, which surrounds the core and provides structural integrity to the composite, in direct electrical contact with the surface thereby to more elfectively collect current therefrom.

Thus, by the use of the structures illustrated and described herein, a novel construction for a contact element has been provided and, in addition, processes for the production thereof. By successfully combining the necessary materials for the simultaneous exercise of lubrication and superior electrical conduction, the resulting construction is one of substantial utility. Obviously, modifications of the materials employed for the core and metal wall are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

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

1. A longitudinally-extending electric current collecting element having an exposed current collecting contact face, said element comprising:

(a) a longitudinally-extending core of low adhesion,

electrically conducting material, and

(b) an outer longitudinally-extending wall of metallic material having low electrical resistance enclosing said core over the sidewall area thereof,

(1) said element having as an exposed current collecting contact face an area of said low adhesion material surrounded by an area of said metallic material with the ratio of the area of low adhesion material to the area of metallic material being in the range of from about 400:1 to 1:1.

2. A current collecting element substantially as recited in claim 1 wherein the low adhesion material contains graphite.

3. A current collecting element substantially as recited in claim 1 wherein the low adhesion material contains a solid lubricant.

4. A current collecting element substantially as recited in claim 1 wherein the element is substantially cylindrical in configuration.

5. In a make-and-break switch for selectively interrupting and permitting the passage of electric current by the separation and approximation of first and second opposed, relatively movable contacts, the improvement comprising: (a) the first contact having a current collecting contact face comprising a concentration of low adhesion,

electrically conducting material circumscribed by a metallic rim having low electrical resistance with the ratio of the contact face area of low adhesion material to the contact face area of metallic material being in the range of from about 400:1 to 1:1, and

(b) the second contact having a portion thereof movable relative to the balance of said second contact and projecting toward said first contact,

(1) said moveable portion and said balance of said second contact being made of electrically conducting material and being in direct physical contact with each other,

whereby as said contacts are brought into juxtaposition, said low adhesion material forms an electrical contact with said movable portion before said metallic rim comes into contact with said balance of said second contact.

6. The improvement in make-and-break switches substantially as recited in claim 5 wherein the low adhesion material contains graphite.

7. The improvement in make-and-break switches substantially as recited in claim 5 wherein the low adhesion material contains a solid lubricant.

8. In an electrical current transmitting juncture comprising first and second juxtaposed contacting surfaces, said first surface being the current collecting face of a longitudinally-extending current collecting element and said first and second surfaces being adapted for movement relative to each other, the improvement wherein:

(a) the collecting element comprises a longitudinallyextending core and a longitudinally-extending metallic shell,

(1) said core containing a concentration of low adhesion, electrically conducting material,

(2) said metallic shell enclosing said core over the longitudinal wall area thereof, having low electrical resistance and having a maximum value for the cross-sectional wall area about equal to the cross-sectional area of said core, and

References Cited by the Examiner UNITED STATES PATENTS 1,986,222 1/1935 Sachs 200l66 2,499,420 3/1950 Sakatos 200166 2,888,740 6/1959 Danis 29420 References Cited by the Applicant UNITED STATES PATENTS 2/1948 SaWhill. 6/1959 Danis.

ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner.

Claims

1. A LONGITUDINALLY-EXTENDING ELECTRIC CURRENT COLLECTING ELEMENT HAVING AN EXPOSED CURRENT COLLECTING CONTACT FACE, SAID ELEMENT COMPRISING: (A) A LONGITUDINALLY-EXTENDING CORE OF LOW ADHESION, ELECTRICALLY CONDUCTING MATERIAL, AND (B) AN OUTER LONGITUDINALLY-EXTENDING WALL OF METALLIC MATERIAL HAVING LOW ELECTRICAL RESISTANCE ENCLOSING SAID CORE OVER THE SIDEWALL AREA THEREOF, (1) SAID ELEMENT HAVING AS AN EXPOSED CURRENT COLLECTING CONTACT FACE AN AREA OF SAID LOW ADHESION MATERIAL SURROUNDED BY AN AREA OF SAID METALLIC MATERIAL WITH THE RATIO OF THE AREA OF LOW ADHESION MATERIAL TO THE AREA OF METALLIC MATERIAL BEING IN THE RANGE OF FROM ABOUT 400:1 TO 1:1.