US2519872A - Electrical contact composition or the like - Google Patents

Description

Aug. 22, 1950 G. BELLOWS, JR

ELECTRICAL CONTACT COMPOSITION 0R LIKE Filed Nov. 19. 1946 Figi Invento Guy Bel lows JT; by www@ His ,Achter-weyv Patented Aug. 22, 1950 ELECTRICAL CONTACT COMPOSITION R THE LIKE Guy Bellows, Jr., Erie, Pa., assignor to General Electric Company, a corporation of New York Application November 19, 1946, Serial No. 710,843

(Cl. 200-166l 11 Claml.

My invention relates generally to electric circuit makers and breakers and more particularly to the contact materials employed in the cooperating contacts of relays designed for intermittent or vibratory opening and closing duty.

In electric contactors and relays, particularly of the class such as the Tirrill type of voltage regulating relays, a serious disadvantage has been encountered in the short life customarily obtained with the use of silver or silver alloys for the contact materials. In addition, these materials are subject to welding and tend to accumulate an insulating surface on the contact faces due to products of the arc formed between contacts over a long period of operation, resulting in a poor quality of regulation and erratic operation.

It is an object of my invention to provide an improved voltage regulating relay of the highspeed vibratory type.

It is a further object of my invention to provide contact materials for an electric relay which will be relatively free from wear and which functions, during operation, to produce a minimum of arcing and resultant contact burning.

It is another object of my invention to provide a pair of contacts for a voltage regulating relay in which the voltage regulating characteristics of the relay are improved by reduction in arcing voltage across the contacts, and which are easily manufactured and require a minimum of maintenance.

In accordance with a preferred embodiment of my invention, I provide a vibratory relay having a light-weight balanced armature member pivoted for vibrating motion under the influence-of a magnetlzing solenoid and a biasing spring. The use of the light-weight balanced armature member eliminates the necessity for special antivlbration mountings of the relay, as well as reducing the inertia of the moving armature, thereby resulting in faster and smoother operation and improved voltage regulation of the dynamo-electric equipment to which it is operatively connected. I have found that the use of a stationary contact consisting of a carbon and cadmium composition provides distinct advantages in that the contact is not subject to wear to the same extent as pure carbon or graphite, and in addition the carbon-cadmium combination embodies superior arc-quenching qualities, Lthereby reducing the burning of the contacts and poibility of destructive welding of the contacts. For the movable contact, I prefer to employ a sliver alloy which may be one of the group of silver-cadmium-nickel alloysl which are well known as contact materials in the electrical art. For example, the silver-cadmium-nickel alloy disclosed in Patent 2,080,811 granted to K. L Emmert on May 18, 1937, has proved very satisfactory as a. material for the moving contact of this relay.

My invention'will be more clearly understood by reference to the accompanying drawing in which Fig. 1 illustrates a side view partially in section of a vibratory-type relay constructed in accordance -with my invention; Figs. 2 and 3 show characteristics of the arc voltage appearing across the contacts of the relay of Fig. 1 using different materials for the stationary and movlng contacts; Fig. 4 shows a preferred form of construction of the stationary contact, and Fig. 5 shows the moving contact of the relay of Fig. 1.

Referring to Fig. 1, I have shown a vibratory type of relay, although it should be understood my invention is not limited to this specific type of device, having a frame member I which may be formed from a flat metal blank and adapted at one end for mounting a magnetic pole piece 2 around which is disposed the magnetizing coil or solenoid 3. shown in cross section. The frame I has an upwardly extending bifurcated support II in which is mounted the pivot 5 for supporting the light-weight balanced armature member 6. At the right end of the armature member 6 a magnetic piece l is arranged for co-operation with the pole piece 2 so as to be under the influence of the magnetic eld produced by the solenoid 3. A tension spring 8 is attached to the armature 6 to the left of the pivot 5, as viewed in Fig. l, and opposes the magnetic force exerted -on the armature member due to energization of the coil 3. Also mounted rigidly on the left end of the armature member 6 is the movlng contact 9 which, as shown in detail in Fig. 5, may be a simple, fiat blank of silver-cadmiumnickel alloy. Electrical connection between the moving contact 9 and the frame of the relay is made by the ilexible conductor I0 which is electrically connected to the moving contact 9 by means oi' the bolt II, and to the relay frame by means of the bolt I2. The stationary contacts I3 and Il are supported on a pair of extending arms I5 of the frame I and are rigidly held in spaced relationship by means of the long adjusting stud I6 upon which are mounted a pair of blocks of insulating material I'I and I8, respectively. I'he ilxed contact, I4 for example, is provided with a threaded stud I9, as shown in Fig. 4, and a working surface or contact face 20 is inserted in the head of the stationary contact I4, which assembly may be accomplished by forcing the contact face 20 into a cylindrical bore in the head I4 under pressure. The contact face 20, in accordance with my invention, is preferably a compositionof carbon and cadmium, such as a carbon or graphite rod which has been impregnated or treated with cadmium until the composition approximates 60% carbon or graphite and 40% cadmium. However, the exact proportions of the two constituents are not critical and a 50%-50% composition has been found equally satisfactory. Another method is the sintering of a mass of powdered graphite and powdered cadmium in the proper proportions. The contact material may then be shaped into disks or buttons which are assembled into the face Iof the stationary contact I4 with a forced t as previously described.

I have shown the vibratory relay in Fig. 1 as having a pair of stationary contacts I3 and I4 oppositely arranged so that electrical contact will be made between the moving contact 9 and one of the stationary contacts in both the energized and deenergized positions of the relay. In Fig. 1 the relay is shown in its energized or picked-up condition. It is customary in the application of a vibrating voltage regulating relay of this type to have the normally closed pair of contacts, in this case the lower contact I4 and the movable contact 9, placed in parallel with all or a portion of the generator field resistance, thereby short circuiting the field resistance in the normally closed position and causing the generator voltage to build up rapidly.

The normally open contacts, that is the stationary contact I3 and the movable contact 9, may be placed in series with a resistance which shunts the generator iield winding so that upon closure of these contacts, corresponding to a condition of a generator voltage in excess of the normal value, in addition to inserting resistance in the generator field circuit by the opening of the contacts 9 and I4, the eld excitation current will be partially diverted from the eld winding through the shunting resistance when the conacts 9 and I3 are closed. The generator field excitation is, therefore, quickly corrected, the corrective action taking place in both the energized and deenergized positions of the relay armature.

For some applications, the upper stationary contact I3 and its mounting assembly may be entirely eliminated and generator voltage controlled merely by opening and closing the eld resistance shunting circuit by means of the contacts 9 and I4. This single contact type is commonly used in automotive applications.

In order to allow for adjustment of the spaced relationship of the fixed contacts I3' and I4, the threaded studs of the fixed contacts are held in position by means of the self-locking nuts 2l and 22 which are provided with a knurled shank that is pressed into the insulating blocks I1 and I8. The bent-up terminal connectors 23 and 24 also assist in maintaining the nuts in locked position, thereby preventing the contact adjustment from working loose during relay operation.

In order to maintain the generator voltage constant, it will be understood from the foregoing description that the relay operates or vibrates continuously during generator operation, and that in some cases an appreciable amount of generator field circuit current is interrupted by the moving contact, thereby producing consider- 4 able arcing voltage across the contacts with a resultant tendency toward welding or sticking of the contacts as the deterioration of the contact surface increases.-

Reference should now be had to F18. 2 which shows the form of the voltage wave across the regulating contacts when silver or silver alloys are used for both the moving and stationary contacts of the relay. It will be seen that every time the contacts open the voltage across the contacts increases rapidly from zero to maximum which is inducive to destructive arcing between the contacts. In practicing my invention, I have found that by providing a silver-nickelcadmium alloy for the moving lcontact co-operating with the carbon-cadmium composition for the xed contact, oscillographic records showed the voltage wave shape across the contacts to be reduced to a rectangular wave of approximately 25% of the value shown inFig. 2.

As shown in Fig. 3, the voltage wave varies from a minimum of '75% to a maximum of 100% during the close-open cycle, an'd from this it can be seen that the voltage eiIective for arcing or burning is only 25% of that encountered with the silver alloy contacts as shown in Fig. 2. This also indicates that the contacts are never completely closed and that a certain amount of resistance remains in the field circuit. The operation of the relay thereby'approximates the characteristics of a carbon pile regulator under rapid application and release of pressure on the carbon pile. This results in an improved regulation of the field current in the regulated machine. Due to the well known arc-quenching characteristics of cadmium and carbon and the resultant decreased contact burning and wear with the contact materials used in my invention, I have found that where a contact lift of only about two hours of accelerated life test was obtained with the silver alloy contacts, when the combination of a silver alloy moving contact and the carboncadmium xed contact was employed, the relay operated successfully for over 250 hours of accelerated life test and in addition showed practically no wear of the contacts or evidence of destructive arcing or burning. The amount of cadmium impregnated in the carbon or graphite composing the working surface of the stationary contact is not particularly critical. but best results were obtained with a composition approximating 40 to 50% cadmium, with the balance being graphite or carbon.

It should be pointed out that my invention is not limited solely to a vibrating voltage regulating relay but readily is applicable to other forms of circuit makers and breakers, such as simple contactors and relays, wherein it is desired to provide increased contact life and reduction of arcing voltage with the resulting improved operation and decreased maintenance.

From the foregoing description it will be seen that I have provided an improved combination of contact materials for the contacts of a vlbrating relay in which regulation is improved due to the reduction of arcing voltage, and also the life of the contacts is greatly prolonged during which the relay will operate satisfactorily with a minimum of maintenance and adjustment.

While I have shown and described my invention as applied to a particular system embodying various devices diagrammatically shown, it wi1l be lobvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover al1 such changes and modifications as fall within the true spirit and. scope of my invention.

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

1. In an electric circuit maker and breaker, a movable contact composed of an alloy of silver, nickel and cadmium, and a fixed contact consisting of a carbon and cadmium composition.

2. In an electric circuit maker and breaker, a movable contact composed of a silver-nickelcadmium alloy and a stationary contact having a Working surface composed of carbon impregnated with cadmium.

3.,In an electric relay, a pair ofy cooperating contact members comprising a movable contact composed of an alloy of silver, nickel and cadmium, and a xed contact consisting of at least 55% carbon, the balance being cadmium.

4. A pair of cooperating make-and-break contact members for a rapidly vibrating relay, one of which is composed of a silver-cadmium-nickel alloy and the other of which is composed of carbon impregnated with cadmium.

5. A pair of cooperating electrical contact members, one of which is a silver-nickel-cadmium alloy and the other of which is composed of carbon and cadmium in approximately equal proportions.-

6. In an electric regulating circuit maker and breaker having a movable balanced armature and electromagnetic means for effecting vibra.- tion of said armature, the combination of a movable electrical contact carried by said armature and composed of an alloy of silver, and a fixed electrical contact arranged for cooperation with said movable contact and having a contact face composed of a carbon-cadmium compound.

7. In a high speed vibratory regulating relay having a movable balanced armature and electromagnetic means for eiecting vibration of said armature, the combination of a movable electrical contact carried by said armature and composed of an alloy of silver, and a fixed electrical contact arranged for cooperation with said movable contact and having a contact face of carbon impregnated with approximately 40% cadmium.

8. In a high speed vibratory relay adapted for regulating operation and having a movable balanced armature and electromagnetic means for effecting vibration of said armature, the combination of a movable electrical contact carried by said armature and composed of an alloy of silver, and a fixed electrical contact arranged for cooperation with said movable contact and having a working surface consisting of approximately equal parts of cadmium and carbon.

9. In a high speed vibratory relay adapted to hold a generator voltage constant and having a light-weight balanced vibrating armature and electromagnetic means for eiecting vibration of said armature, the combination of a movable electrical contact carried by said armature and composed of a silver-cadmium-nickel alloy, and a pair of xed electrical contacts arranged for cooperation with said movable contact and having contact faces composed of a carbon-cadmium compound.

10. In a. high speed vibratory relay adapted for regulating action and having a light-weight balanced vibrating armature and electromagnetic means for effecting vibration of said armature, the combination of an electrical contact carried by said armature and composed of a silver-cadmium-nickel alloy, and a pair of xed electrical contacts arranged for cooperation with said movable contact and having working surfaces of carbon impregnated with cadmium.

11. In a vibrating voltage regulating relay having a light-weight balanced vibrating armature and electromagnetic means for eiecting vibration of said armature, the combination of an electrical contact carried by said armature and composed of a silver-cadmium-nickel alloy, and a pair of xed electrical contacts arranged for alternate cooperation with said movable contact and having contact faces consisting of at least 40% cadmium, the balance being carbon.

GUY BELLOWS, JR.

REFERENCES CITED The following references are of record in file of this patent:

UNITED STATES PATENTS Burrows Sept. 23, 1947

Claims (1)

1. IN AN ELECTRIC CIRCUIT MAKER AND BREAKER, A MOVABLE CONTACT COMPOSED OF AN ALLOY OF SILVER, NICKEL AND CADMIUM, AND A FIXED CONTACT CONSISTING OF A CARBON AND CADMIUM COMPOSITION.

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