US3592987A

US3592987A - Gettering arrangements for vacuum-type circuit interrupters comprising fibers of gettering material embedded in a matrix of material of good conductivity

Info

Publication number: US3592987A
Application number: US714197A
Authority: US
Inventors: Joseph Lempert; Gerald R Kotler
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1968-03-19
Filing date: 1968-03-19
Publication date: 1971-07-13
Anticipated expiration: 1988-07-13
Also published as: BE729723A; CH493924A; DE1910633A1; FR2004231A1

Abstract

To provide a gettering action in relatively high-power vacuumtype circuit interrupters, an active gettering material, such as titanium, tantalum, columbium, zirconium, tungsten or molybdenum is incorporated in the electrode structures or interior elements of a vacuum-type circuit interrupter, so as to be subjected to the heat of the arc, which is established during circuit interruption. By the raising of the temperature of the gettering materials, or agents, their gas-absorption characteristics are activated. The gettering materials are incorporated as filaments, or rods, either disposed randomly, or in parallel alignment in a matrix of good conducting material, such as copper or silver, in the contact portions, so as to be subjected to the heat of arcing.

Description

United States Patent 2,121,180 6/1938 Vatter Joseph Lempert Pittsburgh, Pa.;

Gerald R. Kotler, Oak Park, Mic 714,197 Mar. 19, 1968 July 13, 1971 Westinghouse Electric Corporation Pittsburgh, Pa.

Inventors Ap No. Filed Patented Assignee GET'I'ERING ARRANGEMENTS FOR VACUUM- TYPE CIRCUIT INTERRUPTERS COMPRISING FIBERS OF GETTERING MATERIAL EMBEDDED IN A MATRIX OF MATERIAL OF GOOD References Cited UNITED STATES PATENTS ZOO/144 (.2)

2,794,885 6/1957 Jennings 200/144 (.2)

3,158,719 11/1964 Polinko, Jr. et a1. ZOO/144 (.2)

3,270,172 8/1966 Chubb ZOO/144(1) 3,379,846 4/1968 Wood eta]. 200/144 (.2) FOREIGN PATENTS 351,131 6/1931 Great Britain................ ZOO/144(2) 403,937 4/1932 Great Britain .2)

Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorneys-A. T. Stratton, C. L. McHaIe and W. R. Crout ABSTRACT: To provide a gettering action in relatively highpower vacuum-type circuit interrupters, an active gettering material, such as titanium, tantalum, columbium, zirconium, tungsten or molybdenum is incorporated in the electrode structures or interior elements of a vacuum-type circuit interrupter, so as to be subjected to the heat of the arc, which is established during circuit interruption. By the raising of the temperature of the gettering materials, or agents, their gas-absorption characteristics are activated. The gettering materials are incorporated as filaments, or rods, either disposed randomly, or in parallel alignment in a matrix of good conducting material, such as copper or silver, in the contact portions, so as to be subjected to the heat of arcing.

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PATENTED JUL] 3 I97! SHEET 2 [IF 3 FIG.|3.

FIG.IO.

FIGS.

GETTERING ARRANGEMENTS FOR VACUUM-TYPE CIRCUIT INTERRUPTERS COMPRISING FIBERS OF GETTERING MATERIAL EMBEDDED IN A MATRIX OF MATERIAL OF GOOD CONDUCTIVITY BACKGROUND OF THE INVENTION The present invention relates to gettering arrangements in vacuum-type circuit interrupters for maintaining the pressure within such an interrupter at the desired low level over a prolonged period. Successful operation of a vacuum-type circuit interrupter depends to an important extent upon the maintenance of a very low pressure within the interrupter. If the static pressure within the interrupter is allowed to Auerbach exceed a value of about Torr for devices of usual dimensions, the dielectric strength of the vacuum becomes impaired, and, as a result, the likelihood of a breakdown between the parts of the interrupter greatly increases. In addition, if any significant amount of gas is present in the interrupter for an appreciable period, it tends to be adsorbed by, or react with the surfaces of the device, and a high voltage breakdown is more likely to be initiated from a relatively dirty surface, such as this, than from a gas-free surface.

Moreover, an excessive pressure within the interrupter can seriously impair the ability of the interrupter to perform its intended interrupting operation. In this regard, the usual vacuum-type circuit interrupter comprises a pair of separable contacts disposed within an evacuated envelope. Circuit interruption is initiated by separating these contacts, thus establishing an arc across the resulting gap. Assuming that the circuit is an altemating-current circuit, the arc maintains itself until about the time a natural current zero is reached. The are then vanishes, and the usual recovery voltage transient begins building up across the gap, in some cases approaching a peak value of twice normal system voltage. If the interruption is to be a successful one, the vacuum interrupter must have a sufficiently high dielectric strength during buildup of the recovery voltage transient to prevent the transient or the subsequent peak AC voltages which are impressed across the interrupter from breaking down any of the electrically stressed gaps of the interrupter. I

Any significant amount of free gas present inside the interrupter, or on the surfaces of the interrupter during this interval, could interfere with establishment of the required dielectric strength across the stressed gaps of the interrupter, and the recovery voltage transient would breakdown these gaps. Accordingly, it is highly desirable to minimize the amount of gases present within the interrupter, and to maintain the pressure at a low level, preferably below l0 Torr.

U.S. Pat. No. 3,090,852 issued to Allan Greewood teaches the concept of employing a getter element that is operable, when heated to a predetermined temperature, to clean up gases present within the evacuated envelope of a vacuum-type circuit interrupter. For heating the getter element to the predetermined temperature during normal operation of the vacuum interrupter, he provides a saturable core of magnetizable material disposed about the circuit-interrupter conductor, and a secondary winding inductively coupled to the core. The getter element is electrically connected across the terminals of the secondary winding. The core has magnetization characteristics that causes saturation of the core to occur at a level of current through the conductor not substantially exceeding the rated continuous current of the interrupter. Also Australian Pat. No. 236,915 issued Apr. 14, 1960 to Kenneth William Brown teaches the concept of utilizing gettering materials within the contacts of a vacuum-type circuit interrupter. Brown utilizes zirconium, titanium and thorium as his getter materials.

SUMMARY or THE INVENTION According to the present disclosure, a suitable getter material, such as titanium, tantalum, columbium, zirconium, tungsten, or molybdenum is located in a strategic position within the evacuated envelope of the vacuum circuit interrupter, so as to be heated by the are, which is established during a circuit-interrupter opening operation. As a result, some of the getter material is evaporized and sputtered, and provides a layer of the fresh elemental gettering material on certain portions of the interior of the evacuated envelope. In one particular gettering arrangement, a disc of titanium, for example, is provided rearwardly of one of the separable contacts of a vacuum circuit interrupter. In another gettering arrangement, the gettering material is provided as a ring surrounding the contact of the interrupter. According to the present invention, the gettering material is provided in filamentary or columnar form and infiltrated with copper or silver to provide a mechanically high-strength contact material.

In still another form of gettering arrangement, the gettering material, in wire form, is compacted and infiltrated with a suitable metal, suchas copper or silver, of relatively high conductivity, so that the gettering material is immediately adjacent the established arc, and is evaporized and sputtered during the arc-interruption operation.

Accordingly, it is a general object of the present invention to provide an improved vacuum-type circuit interrupter in which improved gettering arrangements are provided.

Still a further object of the present invention is the provision of an improved vacuum-type circuit interrupter in which residual .gases are eliminated by interposing gettering materials at strategic locations within the vacuum interrupter envelope so as to be heated and sputtered during a normal circuit-interrupting operation, hence deposited on the interior walls of the interrupter to provide high speed gettering.

Still a further object of the present invention is to incorporate gettering materials in fiber form, within the contact structure so as to be subjected to the discharge effects associated with the arc and as a result deposited on the interior walls of the interrupter.

As well known by those skilled in the art, contact members for electrical circuit making and breaking devices should have low electrical resistance, low contact drop, resistance to sticking, wear resistance and low chopping current. Good conducting metals such, for example, as copper and silver which have relatively low melting points have poor wear resistance, and are not entirely satisfactory as contact members for continuous usage. Refractory metals such as tungsten, molybdenum, or tantalum, which have satisfactory resistance to wear and sticking, are generally poor conductors having a high contact drop and high electrical resistance. Contacts of these refractory metals because of their lower electrical and thermal conductance and lower vapor pressure are limited in the current they will interrupt by their tendency to reach very high temperatures where large and uncontrollable thermonic currents can be emitted. Higher vapor pressure materials operate at lower electrode temperatures because of vapor cooling as evaporation takes place.

It is a distinct purpose of the present invention to provide contact members for vacuum-type circuit interrupters in which the contact members will have a low resistance, low contact drop, resistance to sticking and wear, low chopping currents and yet will provide adjacent the arcing region gettering materials which will have a very rapid continuous pumping action to remove residual gases from the interior of the vacuum envelope, or gases which are released from the electrodes as a result of the erosion to the electrodes which occurs on interruption which, as mentioned may lead to dielectric breakdown.

Further objects of the invention will readily become apparent upon reading the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a vacuum-type circuit interrupter embodying one form of our device;

FIG. 2 is a considerably enlarged fragmentary view of one of the contacts utilized in the circuit interrupter of FIG. 3 is an alternate form of gettering arrangement associated with one of the contacts of the vacuum-type circuit interrupter, the view being taken partially in section along the line lIl-III of FIG. 4;

FIG. 4 is a top plan view of the contact structure illustrated in FIG. 3;

FIG. 5 illustrates a plurality of short fibers or wires of gettering metal;

FIG. 6 illustrates the fibers illustrated in FIG. 5 after they have been compressed into the form of a contact member;

FIG. 7 is a vertical sectional view taken through an induction heating furnace for infiltrating the gettering wire of FIG. 6 with an infiltrating good conducting material, such as copper or silver, in an evacuated environment or in a hydrogen environment;

FIG. 8 illustrates a modified type contact structure;

FIG. 9 illustrates a contact member made by infiltrating the compressed form of contact of FIG. 6 with a good conducting metal in the apparatus of FIG. 7;

FIG. 10 is an elevational view of a composite contact bar that has been formed in accordance with the principles of this invention, and cut into a plurality of contact members;

FIG. 11 is an enlarged view of a section of the contact surface of one of the contact members shown in FIG. 10;

FIGS. 12 and 13 illustrate different embodiments of the invention shown in FIG. 10;

FIG. 14 is a vertical sectional view taken through a modified-type of separable contact structure in which an arcinitiating region and an arc-running region is utilized, and the arc-running region is provided by a composite contact structure of the type illustrated in FIGS. 913 of the drawings;

FIG. 15 is a perspective view of the general type of contact structure illustrated in FIG. 14, wherein the arc is caused by magnetic action to rotate circumferentially about the arcrunning region,- which is made of the composite contact material incorporating a gettering element; and,

FIG. 16 illustrates contacts made by a sintering mixture of powder metal with a good conducting metal, heating taken place in a furnace of the type illustrated in FIG. 7 of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS When the electrodes of a vacuum switch are opened at the beginning of a given interruption, a metallic arc initiates between the separating electrodes, and serves as a vehicle for current conduction until the normal alternating current cyclic variation of current drops the magnitude of the current below the chopping current. At this value of current, the mechanisms which cause the arc to extinguish predominate over those, which sustain the arc, and it goes out. Because of the high-power density impressed on the electrodes during the conduction interval, substantial erosion takes place releasing gas adsorbed on the surface and contained within the volume of the electrode proper.

The substantial erosion of the interrupter electrodes is not confined to the interruption operation but also occurs when the contacts are closed under load to permit nonnal operation of the associated circuitry. The open position, which may be as much as one-half inch, has the dielectric strength to withstand the open circuit voltage. As the electrodes are closed, however, the gap length decreases to a value where arc-over occurs. The arc persists until the interrupter reaches the fully closed position, causing further erosion of the electrodes.

One of the principal problems associated with the manufacture of vacuum-tube interrupters concerns the quantity of gas evolved during an interruption. If the release of gas from the electrodes produces pressures in the micron range, when the interrupter is in the open position, a discharge will be initiated as soon as the dielectric strength of the vacuum dielectric is exceeded during the alternating current wave, and a restrike occurs, or indeed, no interruption takes place at all. Consequently, it is necessary to subject the components of the tube during interruption manufacture to very stringent outgassing procedures which are time consuming and expensive to insure an absence of restrikes and to produce the desired interruption reliability. The penalties for inadequate outgassing of the tube are severe. In the first place, failure of the tube to extinguish will cause premature tube failure due to the high loadings, which will melt and damage components of the tube. Secondly, it may also result in injury to the electrical equipment being protected by the vacuum switch.

Referring now to the vacuum interrupter of FIG. 1, there is shown a highly evacuated envelope 1 comprising a casing 2 of suitable insulating material, and a pair of metallic end caps 3 and 4 closing off the ends of the casing. Suitable seals 5 are provided between the end caps and the casing to render the envelope vacuum-tight. The normal pressure within the envelope 1 under static conditions is lower than 10 Torr. so that a reasonable assurance is had that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

Located within the envelope 2 is a pair of relatively movable disc-shaped contacts or electrodes 7 and 8 shown in full lines in their separated, or open-circuit position. When the contacts are separated, there is an arcing gap 9 located therebetween. The upper contact 7 is a stationary contact suitably secured to a conductive rod 10, which at its upper end is united to the upper end cap 3. The lower contact 8 is a movable contact joined to a conductive operating rod 11, which is suitably mounted for movement. The operating rod 11 projects through an opening 12 in the lower end cap 4, and a flexible metallic bellows 13 provides a seal about the rod 11 to allow for movement of the rod without impairing the vacuum inside the envelope 2. As shown in FIG. 1, the bellows 13 is secured in sealing relationship at its respective opposite 'ends to the operating rod 11 and to the end cap 4.

Coupled to the lower end of the operating rod 11, suitable actuating means (not shown) is provided for driving the movable contact 8 upwardly into engagement with the stationary contact 7 so as to close the interrupter. The closed position of the movable contact is indicated by the dotted line 14. The actuating means is also capable of returning the contact 8 to its illustrated solid-line open position so as to open the interrupter. A circuit-opening operation will, for example, entail a typical gap length, when the contacts are fully separated, of perhaps one-half inch.

The are (indicated at 15) that is established across the gap 9 between the electrodes, as the electrodes are opened and also when they are closed, vaporizes some of the contact material, and these vapors are dispersed from the arcing gap 9 toward the envelope 2. In the illustrated interrupter, the internal insulating surfaces of the casing 2 are protected from the condensation of arc-generating metallic vapor and particles thereon by means of a tubular metallic shield 16 suitably supported on the casing 2 and preferably isolated from both end caps 3 and 4. This shield 16 acts to intercept and to condense aregenerated metallic vapors before they can reach the casing 2. To reduce the chances for vapor bypassing the shield 16, a pair of end shields l7 and 18 are provided at opposite ends of the central shield 16.

The vacuum interrupter is an unusual electronic tube, inasmuch as normal operation of the interrupter, that is the normal service of opening and closing contacts, causes an unusual amount of electrode erosion. As mentioned previously the interrupter must be processed during manufacture so as to minimize the amount of gaseous contaminants dissolved in the electrode structure and adsorbed on the internal surfaces of the interrupter, since as explained previously, pressures of the order of a micron, even though of transient duration, can cause permanent failure of the tube and possible injury to associated circuitry.

It is well known that the speed of diffusion of gas molecules or atoms from a solid is proportional to the concentration of the gaseous species within the solid. For this reason it is very expensive and difficult during the fabrication of a vacuum interrupter to outgas the electrodes to the desired extent, which is to achieve a freedom of gaseous contamination of the order of 1 part per million. In conventional electronic tubes the outgassing is usually accomplished by heating the electrodes at a higher temperature than they are expected to encounter in service. Since gaseous diffusion is slower in the operation of the usual electronic tube than it is during exhaust due to the lower temperature and the low gas concentration gradients present in a well outgassed tube electrode, no difficulty with gas is usually encountered in service with conventional electronic tubes.

The contrary situation holds in a vacuum interrupter. The surface of the electrodes which melt in service necessarily reach higher temperatures than can be imposed during exhaust. The low concentration gradient which may be expected in a well outgassed part is of no assistance during interrupter operation since the forces which hold the gaseous contaminant within a solid or liquid no longer apply for that portion of the electrode material which is vaporized and deposited on neighboring parts of the tube. For this reason the extremely fast and instantaneous getter disclosed can be used to lower the cost of the tube manufacture substantially for the interrupters having low current ratings, and using the shielded getter electrode structures also disclosed can be used to increase rated current capabilities and to lower fabrication costs for tubes interrupting more than 8000 or 10,000 amperes.

A variety of gases are released during opening and closing of electrodes including hydrogen carbon monoxide (CO), and carbon dioxide (C0,). These gases are eliminated, according to the present invention, by a getter such as titanium or zirconium. As shown in FIG. 1, and in the enlarged view of FIG. 2, there is provided a disc of gettering material on the rear side of one or both of the separable contacts 7, 8. The result of such a construction is a vacuum interrupter l which will provide a high-speed gettering to increase vacuum-switch reliability. Fast gettering is obtained by providing a fresh surface of sputtered getter material 21 as a result of each individual interruption, when the need for high-speed gettering is at its maximumQIn the following discussion of the disclosed principles of the invention, titanium will be used as an example of a suitable gettering material 21. Other materials, however, such as tantalum, columbium, zirconium, are particularly appropriate for use in this application. Tungsten and molybdenum may also be used.

FIG. 2 shows the general design of an electrode structure used successfully in a vacuum circuit interrupter. This electrode structure successfully interrupted over 1,200,000 integrated amperes in life testing. Pressures were substantially lower than those experienced with the same electrodes without the provision for high-speed titanium gettering element 2].

The general objective of the construction illustrated in FIG. 2 is to locate the titanium disc 20 in a region of the vacuum interrupter where it will participate in the discharge action 15. The sputtering of titanium, resulting from the exposure of titanium to the general discharge associated with a given interruption or electrode closing, will produce freshly deposited titanium 21 on the internal shield 16 and other surfaces of the vacuum interrupter, thus making available a large area clean fresh titanium surface, which has a very high gettering speed as a result of its large area and its initial cleanliness and freedom from adsorbed gases. High-speed gettering action not only takes place on the internal surfaces of the interrupter but also during the transit of the titanium ions and atoms to the walls of the vacuum interrupter.

The mechanism of gettering of the sputter ion deposited titanium film is complex and depends on the type of gas being gettered. The hot fresh deposited titanium surface reacts instantaneously with the ambient gas fonning stable chemical compounds, such as titanium oxides and nitrides with oxygen and nitrogen gases respectively. 'Ion burial plays an important role in pumping hydrogen and noble gases, while other mechanisms allow removal of complex molecules, such as the hydrocarbons.

An extremely important feature of the disclosed means of gettering is that a fresh clean uncontaminated gettering surface 21 is provided with each closing or opening operation. In conventional electronic tubes gettering is obtained by deposition of a film of getter material such as barium on an interior wall of the tube. The customary service of a getter layer tends to slow down the gettering action with time since the more exposed portions of the surface quickly get saturated with gas as the gettering action proceeds. Further gettering takes place as a result diffusion of the gaseous contaminant to the interior of the getter layer, an inherently slow process. Ti and Zr films also have similar characteristics which quickly slow down the speed of gettering as the gettering proceeds.

In certain electron tubes filaments of zirconium are heated to temperatures of the order of 850 C. for use as getters. It is still necessary for a diffusion process to occur to permit the gaseous contaminant to combine with getter material in the interior of the wire, after the surface layer has reacted with gas. Furthermore such getter wire structures are usually small in area to minimize power dissipation and thus have relatively slow gettering speeds.

Thus in an application where fast gettering is imperative if it is to be useful, the disclosed automatic mechanism for providing fresh unexposed films of the gettering material as required over a large internal area of the interrupter, and as a result accomplishing a very high speed of gettering, is extremely advantageous. The fact that additional mechanisms for gettering are available as a result of the combination of the gaseous contaminant with ions and atoms in transit from the getter reservoir to the interior walls of the interrupter is an important plus feature, which makes the disclosed structure an even more significant advance over the state of the art.

Regardless of the specific mechanisms involved, it is an experimental fact that the gettering action resulting from participation by the titanium surfaces 22 in the discharge 15 associated with the interruption, produces a drastic reduction in the pressures that are built up within the vacuum switch 1 as the result of circuit interruptions and are extinctions.

According to the present disclosure, it is intended to include locating the titanium and/or other gettering metal 20 selected in an area of the vacuum interrupter, which is exposed to the sputtering discharge action 15. Suitable areas include the condensing shield 16 and the end shields 17, 18, as well as the electrodes 7, 8. Specifically excepted would be areas of the vacuum interrupter, which would throw the active gettering metal onto the glass 2, since this would affect the dielectric strength of the envelope 2, and lead to premature breakdowns. Also specifically excepted is the portion of the electrode structure which makes contact when the electrodes are in the closed position. The excepted sections of the electrode structure include surface .t" of FIG. 2, surface 8' of FIG. 3 and 19 of FIG. 14. We prefer to use copper and copper alloys, such as copper bismuth, as the material for the direct contact to the arc 15 to avoid electrode sticking problems in the contact region, and to provide low chopping currents. The main objective in the placement of the gettering material 20 is to maintain a reservoir, or supply of gettering material 21 to supply fresh material as required.

The rate of erosion of the electrodes 7 and 8 exposed to the full'arc l5, and hence the rate of gas evolution from them is a function of the interruption current. A very advantageous feature of the disclosed method is that the amount of titanium 21 sputtered from the surfaces 22 is also proportional to the current being interrupted. Thus, the disclosed principle has a selfcompensating feature, which increases the gettering capability in proportion to the gettering requirement.

FIGS. 3 and 4 illustrate a modified type of electrode construction 24 in which a ring of titanium or zirconium 25 is brazed on the rear side of the butt-type contact 8'. Tests on this construction consisted of a series of direct-current interruptions at 200 amperes in a demountable tube. During the first run, the test electrodes were outgassed by connecting the switch to an exhaust system, and in subsequent runs, the system was sealed off from the pumps, and observations made as to the rate of rise of pressure as a function of the number of interruptions. In the vast majority of tests on electrode structures and materials which did not utilize getter materials, a significant pressure rise was noted as a function of the number of interruptions applied once the switch 1 was sealed off. The demountable tube was, in fact, used to assess the relative quantity of gas held in different electrode materials. In the case of both tests with titanium 21 participating in the discharge, a significant drop in pressure was noted as a function of the number of interruptions for the tests with the switch sealed off, contrary to experience when no getter materials were employed as part of the electrode structure.

Since titanium alloys mix rapidly with copper, it is necessary in fabricating the electrode assembly 24 not to expose the copper-titanium joint 26 to excessive temperatures. A lowmelting eutectic forms at 900 C. In fact, in fabricating the tube, the titanium disc 25 was joined to the copper 8' without solder by the simple expedient of heating the titanium-copper assembly 24 to 900 C. in vacuum, and allowing the eutectic, which forms at the interface, to effect the braze. Both of these two components of the electrode assembly 24 were outgassed at high temperature at pressures in the to 10 Torr range prior to the eutectic joining procedure described above. It is, however, important to design the interrupter tube so that temperature gradients cannot build up during the operation of the tube within its interruption ratings which well exceed the eutectic temperature. The high temperature solubility problem associated with the use of the copper-titanium structures does not exist with structures utilizing copper and tantalum, molybdenum or tungsten, since these refractory materials have an extremely low solubility for copper, and' vice versa. Thus copper casting techniques can be utilized when Ta, W or Mo mixtures with Cu are used as the getter reservoir material. Low alloying action between Cu, and Ta, W and Mo helps in keeping the conductivity of the copper high.

Nothing which has been said before should be interpreted as indicating that the gettering reservoir 21 needs to be a pure material. In some instances, it is desirable to use a composite metal structure consisting of two or more metals from the standpoint of increasing the heat dissipation efficiency of the electrode system. For example, a technique for taking advantage of the high thermal conductivity associated with copper, is to use molybdenum, tantalum or tungsten in either fine wire or powder form within a cast or sintered copper matrix as described hereinafter.

One advantage of the use of tantalum as the gettering material 21 is the fact that it is easier to outgas than copper. The recommended procedure for fabricating an electrode, consisting of tantalum, tungsten or molybdenum impregnated in copper is the following: Assume a 60 percent weight percent of the refractory metal. Using 2 to 5 mil tantalum wire, compress a conglomerate or ball of the wire into a small button 23, say, for example, 1 inch long and 1% inches in diameter, in a suitable fixture (not shown). Place the compressed fine wire button 23 in a degassed graphite crucible 28, as shown in FIG. 7, about 1 inches in diameter. Place the desired amount of copper 29 above the button 23 in the crucible 28. Bring the copper 29 to melt in vacuum using suitable techniques, such as radiofrequency heating. When the copper melts, it will impregnate the wire button 23 fully. Upon solidification, the desired composite electrode assembly 46 (FIG. 9) is obtained. By adjusting the percentage of getter material 21, and the location of this material within the tube 2, it is possible to arrange for the desired release of gettering material 21 as a function of the required rate of loading of the interrupter. The percentage of getter material 21 in a conducting matrix like copper, silver or gold can vary from 5 percent to 97 percent.

In addition to locating the gettering surfaces 22 in the manner indicated above, it can also be used as fabricated in the tantalum-copper mix 46, described above, to replace the outer spiral structure 32 illustrated in FIGS. 14 and 15. As set forth in U.S. Pat. No. 3,182,156, issued May 4, 1965 to Lee et 8.... al., the arc-initiating portion or annulus 19 may be formed of a low-chopping level metal or alloy, such as an alloy of Cu with tin, antimony, lead, zinc, bismuth and other metals. However the outer arc-running surface 32, of FIG. 14 may be adapted for high-current interruption, and according to the present invention can be fabricated using for example a tantalum copper getter electrode fabricated as described herein. The advantage of the use of such an electrode assembly is that the release of getter during operation of the interrupter permits substantially lower manufacturing costs as a result of the shorter less stringent exhaust schedules which can be employed in manufacturing the interrupter.

For interrupters having ratings in excess of 8000 or 10,000 amperes we prefer to use the structures shown in FlGS. 2 and 8 in which the getter reservoir is in a partially protected position. The spacing between the outer arc-running electrode 8 and the gettering reservoir 20 of FIG. 2 and the diameter and the thickness of getter reservoir 20 can be adjusted in the design of the interrupter electrode to release an amount of getter appropriate to the current being interrupted, and the quantity of gas which will be released in a given interruption.

It is a further purpose of the invention to embed refractory metals having good wear resistance and good resistance to sticking within a main base member of a good electrical conducting metal. lt is a purpose of the invention to locate the refractory metal 21 within the contact member 7, 8 so as not to interrupt the continuity of the electrical path through the good conducting metal.

The refractory gettering metals, which have been found to provide excellent wear resistance and resistance to sticking, are the gettering metals tantalum, tungsten and molybdenum, particularly in wire or rod form. The members are preferably of an elongated shape with any general cross section. A further characteristic which will be desirable in the refractory gettering members is the property of being wetted by molten good conducting metal and with a good bond being formed on solidification.

The main body of the contact members is composed of a good conducting metal such, for example, as copper and silver. The properties which are desirable for the main electrode body metals are good electrical conductivity. Copper and silver base alloys, while they may not have as good conducting characteristics as pure silver or copper, may be suitable for application in contact members, and it is contemplated to make use of them in this invention.

The copper and silver will not form a good alloy with tantalum, tungsten and molybdenum gettering materials, since these metals do not form solid solutions. Thus, it is not possible to alloy the good conducting metal with a refractory metal to secure a combination of their desirable properties. It is accordingly, necessary to mechanically intermingle selected shapes of each of these groups of metals and by proper casting or other uniting treatment, form a unitary contact member body.

In order to secure the combined advantages of the good conducting metals, copper or silver, and the refractory metals, tungsten or molybdenum, it is proposed to make electrical contact members embodying elements of the refractory gettering metal in a parallel relation relative to the direction of currentflow and extending substantially entirely through a cast bonding base member composed of good conducting metal. In this way the continuity of the electrical path through the good conducting metal is not interrupted by the refractory gettering metal.

As set forth in U.S. Pat. merchandising 2,295,338, issued Sept. 8, 1942 to James K. Ely, and assigned to the assignee of the instant application, such a construction may be obtained by molding a plurality of refractory gettering rods of tantalum, tungsten, molybdenum, or other active gettering metals within a mold in which the base metal of copper or silver, or their alloys, is poured in molten form. In the examples which follow, the combination of Ag and W are used as examples. A preferred combination of materials is Cu and Ta. In addition while casting in hydrogen (H furnaces is used as an example of a possible technique, we prefer to fabricate electrodes in a vacuum furnace at pressures less than l Torr to avoid H contamination and the necessity of special outgassing procedures to eliminate the H which would be picked up in an H furnace operation.

Still another method for fabricating the improved contact structures of the present disclosure in which a gettering agent 21 is disposed in the vicinity of the contact surface to provide a continuous gettering action during arc interruption, is set forth in U.S. Pat; No. 3,254,189, issued May 31, 1966 to .I. Evanicsko, Jr. and Charles Deibet, and likewise assigned to the assignee of the instant application.

The present invention is concerned with an improvement in the method of fabrication of contacts in that the contact members 34 may have a considerably higher percentage of surface area and volume of the gettering metal 21. In more detail, with reference to FIGS. -13, an elongated composite mass or bar 35 made in accordance with principles of this invention, and comprising a plurality of elongated fibers or wires 36 of refractory gettering metal selected from the group of tantalum, tungsten, molybdenum and their alloys. The refractory fibers 36 are embedded in a matrix of good conducting metal 37 selected from the group of copper, silver and their alloys. The elongated composite bar 35 is cut into five sections, as seen in FIG. 10. Each of the three inner sections 34 has two contact surfaces 38 at its opposite ends. The outer sections 34 have finished contact surfaces 38 at their inner ends; but the refractory wires 36 must be machined off of the outer ends 39 before these contact members 34 are ready for use.

The elongated composite mass or bar 35 shown in FIG. 10 is formed by bunching together the elongated tantalum or tungsten refractory fibers or wires 36 and infiltrating the bunched fibers with the good conducting metal 37. The elongated refractory fibers 36 are bunched together in a generally parallel relationship. It is to be noted, however, that these refractory fibers 36 are randomly distributed in the bunch.

One method of fonning the contact members 34 is to bunch the elongated refractory fibers 36 in a generally parallel relationship; the spacing between the fibers being determined merely by contact of the fibers 36 with each other. The elongated bunched fibers 36 are then held together at various points along the elongated bunch by means of wire or fiber wrappings (not shown), or by any other suitable means. The bunched fibers 36 are then infiltrated by continuously running the bunch through a bath of molten infiltrant of good conducting metal 37 selected from the group of copper, silver and their alloys. The infiltrant 37 is allowed to cool and solidify, whereupon the composite bar 35 can be cut, as shown in FIG. 10, into individual contact members 34 by means of an abrasive wheel, or any other suitable tool. The refractory fibers 36 that protrude from the outer ends of the outer contact members 39 are then cut off with an abrasive tool, so that each of these outer contact members 39 will have a contact surface 38 at each end thereof.

FIG. 11 represents a view of one of the contact surfaces 38 of the contact members 34 of FIG. 10. In the particular contact surface shown in FIG. 11, refractory fibers 36 having a 0.005 inch diameter were used in fonning the contact mem bers 34. Although, as seen in FIG. 11, all of the tungsten fibers 36 do not necessarily engage another tungsten fiber at the contact surface, substantially all of these fibers 36 at some part during the length thereof in the original bundle from which the contact member was formed, engaged other fibers 36 so that the distribution of the wires 36 was determined merely by engagement of the fibers with each other. The weight ratio of silver to tungsten in the contact shown in FIG. 11 is about 25 percent silver to 75 percent tungsten. This ratio can be varied to other desirable percentages by varying the compactness of the tungsten fiber bundle, and/or by varying the diameter size of the tungsten fibers 36 used in the bundle.

Another method of making the contacts 34 shown in FIG. 10 is to place an amount of powdered or solid good conducting metal, selected from the group of copper, silver and their alloys, into a mold or container (not shown). A plurality of elongated refractory fibers 36, selected from the group of tungsten, molybdenum and their alloys, are then bunched together in a generally parallel relationship. The bunched wires 36 are placed into the container over the powder or solid good conducting metal. About 1 percent of powdered nickel may also be included with the good conducting metal. The assembly is then charged into a furnace at a temperature at which the good conducting metal is molten, for hydrogen approximately ll00 C. with a dry hydrogen atmosphere. The good conducting metal, aided by the wetting property of the nickel, is distributed by capillary action throughout the interstices between the refractory fibers 36. The assembly is then removed from the furnace and allowed to cool and harden. The hardened elongated composite mass or bar 35 is then removed from the mold or container, and sliced as seen in FIG. 10 to produce the individual contact members 34. As was previously described the refractory fibers 36 at the outer surfaces of the-outer contact members 39 are machined off of the outer contact surfaces to complete the manufacture of these outer contact members 39.

Another method of manufacturing the contact members 34 shown in FIG. 10 is to bunch the elongated refractory wires 36, selected from the group of tungsten, molybdenum and their alloys, together in a generally parallel but randomly distributed relationship, and insert this bunch into a mold or container. A good conducting metal 37 selected from the group of copper, silver and their alloys is then preheated to a molten condition, and poured into the mold or container to flow into the mold and fill the interstices between the tungsten wires 36. The assembly is then allowed to cool after which the hardened composite mass or bar 35 is taken from the mold or container and sliced as shown in FIG. 10.

FIGS. 12 and 13 illustrate different embodiments of the invention shown in FIG. 10. The parts in FIGS. 12 and I3 that correspond to like parts of FIG. I have the same reference characters as the like parts in FIG. 10 except that the like reference characters of FIG. 12 are primed and the like reference characters of FIG. 13 are double primed.

The contact members 34 as shown in FIG. 12 are formed by means of the same methods hereinbefore described with reference to the contact members 34 shown in FIG. 10, except that the bunched together elongated refractory metal fibers 36' are wrapped and secured together, prior to the infiltration with the conducting metal, with an elongated wire or fiber 40 selected from the group of tantalum, tungsten, molybdenum and their alloys. The wrapping fiber 40 forms a collar around the bundle of refractory wires 36 that gives additional strength to the contact members 34 and also serves as the securing means to secure the fibers'36' of the elongated bundle together during the manufacturing operation.

The contact members 34" shown in FIG. 13 are formed by means of the same methods hereinbefore described with reference to the contact members 34 shown in FIG. 10 except that, as can be seen in FIG. 13, the bundle of refractory fibers 36" comprises a plurality of refractory fibers that are braided or stranded into a cable prior to being infiltrated with the good conducting metal 37". The embodiment shown in FIG. 13 has particular significance in the method of manufacture wherein the bundle of refractory fiber is passed through the molten good conducting metal 37" during which operating the metal infiltrates into the bundle in the same manner previously described. During this operation the braid of the fibers 36" serves to hold the fibers together so that additional securing means are not needed.

Another embodiment of the device is shown in FIGS. 5, 6 and 9. FIG. 5 illustrates a pile 42 comprising a plurality of short lengths of refractory fibers or wires 43 selected from the group of tungsten, molybdenum and their alloys. These short fibers 43 are placed into a closed-type die, such as the type used in metal powder compaction, and pressure is applied to compact the short refractory fibers into the desired shape and density. FIG. 6 illustrates a compacted mass 44 formed from the short refractory fibers 43 shown in FIG. 5. The compacted mass 44 of refractory fibers (FIG. 6), after being removed from the die, is inserted into a container for infiltration. Prior to insertion of the compacted refractory mass 44 into the container, an infiltrant of good conducting metal 37 selected from the group of copper, silver and their alloys is deposited in the container in the form of a powder or a solid piece. The container is then charged into a furnace at a temperature above the melting point of the good conducting metal 37 and below the melting point of the refractory metal. At this temperature the good conducting metal 37 melts and is distributed by capillary action throughout the interstices between the refractory fibers 43. It may be desirable to put a small percentage of powdered nickel into the container with the good conducting metal so that the wetting property of the nickel will aid the capillary action. The mold is then removed from the furnace and allowed to cool whereupon the composition 44 solidifies. The composition is then ejected from the mold in the form of a contact member 46, as shown in FIG. 9.

Although the preferable method of forming the contact member 46 shown in FIG. 9 is to have the good conducting metal 37 in the container under the compacted mass 44 of refractory metal, it will be understood that the good conducting metal can be placed on top of the compacted mass 44, before the assembly is charged into the furnace so that the good conducting metal, when melted, will flow down through the compacted mass 44 to infiltrate into the openings within the mass 44.

The contact member 46 (FIG. 9) can be made in another manner by merely placing the compacted mass 44 (FIG. 6)

into a container and pouring molten good conducting metal selected from the aforementioned group into the container whereupon the good conducting metal will fiow down through the compacted mass 44 to infiltrate within the mass 44.

Another method of forming a contact member, such as the contact member 46, shown in FIG. 9, is to merely place the loose short fibers 43, shown in FIG. 5, into a container on top of a powdered or a solid piece of good conducting metal 37 selected from the group of copper, silver and their alloys, and charge the container into a furnace whereupon the good conducting metal melts and is infiltrated throughout the openings between the refractory fibers 43 forming a composition that is allowed to cool and solidify and is then ejected from the container as a finishedcontact member 46.

It is to be understood that the container used in molding the contact members shown in FIG. 9 can be of considerable depth to produce a composition, that is similar to that shown in FIG. 9, but which is much longer. The elongated composition can be sliced by means of an abrasive wheel, or other suitable tool into contact members 46 having the desired depth.

The short members 43 (FIG. of refractory metal that are used in manufacturing the finished contact members 46 (FIG. 9) can be ends of wires or chips, that might otherwise have been considered scrap. Thus, an advantage of this method of the compacted mass 44 (FIG. 6) is infiltrated. The refractory fibers, that are disposed throughout the finished contact member and at the contact surface in a random orientation, are effective in preventing thermal cracking of the contact under operation conditions.

The following are examples of contacts made in accordance with principles of this invention.

EXAMPLEI Pure tungsten fiber of wire, cleaned and straightened was obtained in 0.010 inch size. The fiber was wound on a two spindle spool to form an oblong coil about 4 inches long. Both coil ends were cut and the two halves were brought together to form a fiber bunch approximately five-eighths of an inch in diameter which bunch was then tightly wrapped with tungsten fiber. This bundle of fiber was positioned vertically in a ceramic crucible containing silver powder plus about 1 percent, by weight, of nickel. The assembly was charged into a furnace 41 approximately I l00 C. with a dry hydrogen atmosphere. At this temperature the molten silver, aided by the wetting property of the nickel, was distributed by capillary action throughout the interstices between the tungsten fiber 36. The assembly was then taken from the furnace and allowed to cool after which the composition was removed from the crucible 28. Separate contact elements or members were then obtained manufacture is that material that might otherwise have been wasted can be utilized in forming improved contact members 46.

A modification of the device shown in FIGS. 5, 6 and 9 comprises the introduction of a portion of the refractory metal in powder form along with the refractory metal fibers. Up to 80 percent of the weight of refractory metal selected from the group of tantalum, tungsten, molybdenum and base alloys thereof may be comprised of powdered refractory metal of approximately l00 mesh fineness, the balance being fibers of refractory metal, all being more or less homogeneously admixed and then compacted in the same manner hereinbefore described into a slug or mass similar to the slug 44 seen in FIG. 6, except that the slug comprises the compacted fibers and powder. The compacted slug or mass 44 is then infiltrated with a molten good conducting metal selected from the group of copper, silver and base alloys thereofin the same manner as from this elongated composition by slicing the composition in the manner shown in FIGS. l0, l2 and 13. One of these contact elements was then machined to a fz-inch diameter and a .4-inch height. The composition of this contact element-as to silver-to-tungsten ratio was determined by area measurements on a metallographically polished cross section. Because of the fixed diameter of the refractory tungsten wire, the area percentage is also the volume percentage and this area percentage was determined simply by counting the wires within a fixed diameter circle. The results indicated that this particular contact element had a tungsten volume percentage of 62 percent, the remaining 38 percent being the silver infiltrant. These figures convert to a weight percentage ratio of 25 percent silver- 75 percent tungsten.

EXAMPLE ll Another contact element or member was made in the same manner in which the contact element discussed in Example I was made except that the tungsten fibers 36 were of a 0.005 inch diameter. The resultant contact element was found to have a 20 percent silverpercent tungsten weight percentage ratio.

EXAMPLE "I Tungsten fiber 36 having a 0.010 inch diameter was cut up into short lengths similar to that shown in FIG. 5. These short lengths of fiber were poured into a cavity that has been machined in a block of graphite which cavity was 1 inch deep and had a %-inch diameter. Powdered silver was placed on top of the short tungsten fibers, and the assembly was charged into a hydrogen atmosphere furnace for one hour at 1 C. This allowed the silver to melt and completely infiltrate the tungsten fibers. The assembly was then removed from the furnace, and allowed to cool. The contact element was removed from the cavity and machined to a thickness of one-fourth of an inch and a diameter of one-half inch. The composition of this contact member was determined by measuring its density of water displacement, and converting this figure to composition, with the assumption that the member was 100 percent dense. The result showed that the contact element had a weight ratio of 80 percent silver-20 percent tungsten.

EXAMPLE IV Tungsten fiber 36 having a 0.005 inch diameter was cut into short lengths similar to that shown in FIG. 5. These short lengths were charged into a closed-type die having a z-inch diameter die cavity and compacted with a load of tons. The compacted mass was then removed from the die and it was found that this mass had a height of about one-half of an inch and the tungsten fibers occupied about 65 percent of the volume of the mass. The short tungsten wires interlocked very nicely, resulting in a strong compact mass which retained its shape. The compacted mass was then infiltrated with silver by placing it on top of a 4.0 gram silver disc within a cavity in a graphite block. The assembly was charged into a hydrogen atmosphere furnace for 30 minutes at l150 C. The assembly was then removed and allowed to cool. The hardened contact member was removed and machined to the desired size for test purposes. The composition of this contact member was determined by measuring the density of the member of water displacement, and converting this figure to composition, within the assumption that the contact member was 100 percent dense. Results showed that the contact member to have a weight ratio of percent silver-75 percent tungsten.

FIG. 16 illustrates using particles ofa gettering material 21 interspersed with particles of good conducting material 37, and heated in a furnace to melt the lower-melting good conducting material 37. The resulting contact is hence fabricated by powder metallurgical techniques.

From the foregoing description it will be apparent that there has been provided improved gettering arrangements for vacuum type circuit interrupters involving improved electrode assemblies, and contact structures in which the gettering material is disposed in the vicinity of the arcing region to receive the heat therefrom and thus to cause the vaporization and spattering of gettering material upon interior parts of the evacuated envelope of the vacuum-type circuit interrupter.

Although there has been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the inventlon.

We claim as our invention:

1. An alternating-current circuit interrupter of the vacuum type comprising, in combination:

a. an evacuated envelope;

b. a pair of separable contacts disposed within the evacuated envelope;

c. gettering means disposed within the evacuated envelope disposed in near proximity to the region of arcing between said separable contacts, whereby the effect of the arc is to cause vaporization and sputtering of the getter material; and,

d. the gettering means being incorporated in one of the contacts as a plurality of metallic fibers embedded in a matrix of metal of good conductivity.

2. The combination of claim 3, wherein the fibers have a random distribution at the contact surface.

3. The combination of claim 1, wherein the fibers are disposed in generally parallel relationship.

4. The combination of claim 3, wherein the fibers are selected from the group consisting of titanium, tantalum, columbium, zirconium, tungsten and molybdenum, and the matrix of metal is selected from the group consisting of copper, silver and base alloys thereof.

Claims

1. An alternating-current circuit interrupter of the vacuum type comprising, in combination: a. an evacuated envelope; b. a pair of separable contacts disposed within the evacuated envelope; c. gettering means disposed within the evacuated envelope disposed in near proximity to the region of arcing between said separable contacts, whereby the effect of the arc is to cause vaporization and sputtering of the getter material; and, d. the gettering means being incorporated in one of the contacts as a plurality of metallic fibers embedded in a matrix of metal of good conductivity.