Electric citrcuit protection device having electrical parts ultrasonically joined using a brazing alloy

Abstract: An electric conductor assembly comprising: an electrically conductive contact having a i constituent comprising a non-alloying material and further comprising silver; and an electrically conductive contact carrier comprising a predominance by weight of nonferrous material, mechanically joined together at a particular location by the application of ultrasonic energy, brazing material being disposed between the contact and the carrier at the location where they are joined. The brazing material comprises at least two materials, with elemental copper being the largest single constituent of the brazing material, and the contact comprises serrations in the surface joined to the brazing material, said serrations being filled with excess silver from the contact, the brazing material forming a layer overlapping the serrations.

Description: This invention relates generally an electric circuit protection device having electrical parts ultrasonically joined using a brazing alloy, as defined in claim 1. Electric circuit protection devices, such as circuit breakers, for example, may be used to interrupt current flow relatively quickly to a circuit that is being protected by the protection device upon the occurrence of an overload, such as a fault. This has been referred to in the industry as tripping the breaker. Once the condition that gave rise to the trip has been corrected, the circuit breaker may be reset, such as by appropriately manipulating an operating handle in the case of a manually resettable circuit breaker. When a circuit breaker trips because of a dead short fault, it is believed that relatively large magnitudes of electric current may flow through the interruptible current path of a circuit breaker, so as to initiate the trip. However, the circuit breaker integrity must be maintained until it finally completes the trip. Moreover, because it is resettable, a circuit breaker must be capable of maintaining its integrity over its specified life, during which the circuit breaker may be subjected to multiple instances of tripping and resetting. The internal construction of a circuit breaker comprises various individual electric parts. Some of these parts are joined together by welding or brazing. A known method for joining certain parts comprises high temperature welding. An example of high temperature welding is resistance welding wherein pressure is applied to the parts at a location where they are to be joined, and welding current is passed through the location to create temperatures sufficiently high to cause a certain degree of localized material melting and flow migration between the parts so that upon termination of the welding current, the molten mass solidifies to create the joint. It is believed that the thermal effects of resistance welding may act on the parts in a manner that undesirably affects one or more physical properties of at least one of the parts being joined. One example of such a side effect comprises some annealing of all or a portion of a part. Another known method for joining certain parts comprises ultrasonic welding wherein pressure is applied to the parts at a location where they are to be joined, such as by clamping them in a suitable fixture in an ultrasonic welder. Ultrasonic energy is then applied to that location to create a certain upsetting and flow of material between the parts which ceases upon termination of the application of the ultrasonic energy, thereby creating the joint. It is believed that one advantage of ultrasonic welding is the elimination or at least attenuation of annealing of the parts being joined. In any particular application, it is believed that the choice of using either resistance welding or ultrasonic welding depends on the composition of the parts being joined. For example, in a circuit breaker application where an electric contact is to be joined to another electric part, such as a terminal or a movable contact arm or blade, if the contact comprises the combination of a refractory element, such as tungsten or molybdenum, and an electric conductor, such as silver or copper, and the other part comprises, either predominantly or exclusively, a non-ferrous electric conductor, such as copper, the disposition of an attachment agent on a face of the contact that is to be placed in intimate surface-to-surface contact with the non-ferrous conductor is generally believed to be suitable for high-temperature welding. The attachment agent should be compatible with the contact's conductor material; for example, being fine silver when the contact conductor comprises silver. It is believed, however, that such materials are inappropriate or at least not optimally suited for ultrasonic welding. It is also believed that refractory-based materials are at least generally not optimal candidates for the alloying that is necessary to create an acceptable joint by ultrasonic welding. US Patent No. 4,019,876 describes the assembly of a contact piece onto a carrier by ultrasonic welding, using an intermediate layer of cold-weldable metal foil. The present invention relates to a novel brazing material selection that provides for materials to be joined that previously have been believed to be inappropriate for satisfactorily joining parts by ultrasonic welding. Although the principles described herein are not necessarily limited to the joining of parts of an electric circuit protection device such as a circuit breaker, it is believed that these principles may provide significant advantages when used in a circuit breaker, especially one where one of the parts to be joined predominantly comprises a refractory material. It is believed that one advantage is that improved integrity, and hence useful life, of a circuit breaker is attainable, enabling a tripped breaker to be reset multiple times after having been subjected to relatively large magnitude fault currents that have caused multiple tripping events. The present invention accordingly provides an electric conductor assembly comprising an electrically conductive contact having a constituent comprising a non-alloying material and further comprising silver and an electrically conductive contact carrier comprising a predominance by weight of non-ferrous material. The contact and the carrier are mechanically joined together at a particular location by the application of ultrasonic energy. Brazing material is disposed between the contact and the carrier at the location where they are joined. The brazing material comprising at least two materials, with elemental copper being the largest single constituent of the brazing material. The contact comprises serrations in the surface joined to the brazing material, said serrations being filled with excess silver from the contact. The brazing material forms a layer overlapping the serrations. In particular, the brazing material consists of substantially 80 parts elemental copper by weight, substantially 15 parts elemental silver by weight, and substantially 5 parts elemental phosphorus by weight. The non-alloying material may comprise a refractory material. Any such refractory material may be selected from the group consisting of silver tungsten, silver tungsten carbide, copper tungsten, copper tungsten carbide and silver molybdenum. The refractory material preferably makes up at least about 35% by weight of the contact. In an embodiment of the invention, the contact comprises the non-alloying material and the carrier comprises copper as the non-ferrous material. The present invention also provides an electric circuit protection device comprising an interruptible current path for interrupting current flow to a load including trip means for tripping the interruptible current path upon occurrence of a load fault. The current flow path comprises an electric conductor assembly according to the present invention. The foregoing, along with additional features, and other advantages and benefits of the inventions, will be seen in the following description and claims which are accompanied by drawings and disclose preferred embodiments of the inventions according to the best mode contemplated at this time for carrying out the inventions. Brief Description of The Drawings Figure 1 is an elevation view, schematic in nature, illustrating a stage in the manufacture of the inventive structure. Figure 2 is an elevation view, schematic in nature, illustrating a further stage in the manufacture of the inventive structure. Figure 3 is an elevation view, schematic in nature, of an embodiment of the present invention. Figure 4 is an elevation view of a portion of a circuit breaker mechanism containing a contact arm assembly that includes a refractory-based contact joined to a two-piece contact arm in accordance with the present invention. Figure 5 is a view in the direction of arrows 5-5 in Figure 4. Figure 6 is a view in the direction of arrows 6-6 in Figure 5 of one of the two contact arm pieces by itself. Figure 7 is a view substantially in the direction of arrows 7-7 in Figure 4. Figure 8 is a top view of Figure 4. Figure 9 is an enlarged photomicrograph of a cut-away cross section through an actual joint between a contact and a contact arm created in accordance with the present invention. Figure 10 is an enlarged photomicrograph of a cut-away cross section through another actual joint between another contact and another contact arm created in accordance with the present invention. Figure 11 is an enlarged view, generally within the area 11 of Figure 10, that has been enhanced in brightness and contrast to show a particular feature. Description of the Invention One application of the invention is presented by the following specific example of the joining of one part of a circuit protection device to another, the example showing the joining of a contact to a contact arm of a circuit breaker, which may include insulated case and molded case circuit breakers that are well known. Figures 1 to 3 show a contact, designated by the reference numeral 10, and a contact arm, designated by the reference numeral 12. An exemplary contact 10 is a part having, for example, a silver-infiltrated refractory composition, silver-infiltrated tungsten or silver-infiltrated molybdenum. An exemplary contact arm 12 is a part of substantially elemental copper. A brazing alloy designated by the reference numeral 14 for use in joining the two parts 10, 12 comprises an alloy consisting of 80 parts elemental copper, 15 parts elemental silver, and 5 parts element phosphorus, all by weight. It may be advantageous for the brazing alloy to be applied to a face of the silver-infiltrated refractory contact in an inert atmospheric oven (the oven not being shown in the drawing). After this joining of parts 10 and 14 (Figure 1), they are allowed to cool. The face of contact 10 that contains the brazing alloy is then disposed in surface-to-surface contact with the copper contact arm 12 in an ultrasonic welder 16. In Figure 2, the parts are held clamped in the welder and suitable pressure and ultrasonic energy are applied to the clamped region to create a certain upsetting and cross-flow of materials between the intimately contacting surfaces. The application of ultrasonic energy is then ended or terminated to stop the cross-flow. The joined parts are finally removed from the welder to yield the finished assembly shown in Figure 3. The joint that has been created is believed to be capable of withstanding relatively high electric current densities that occur in a circuit breaker upon occurrence of a circuit fault that causes the breaker to trip. Moreover, it is believed that the joint has been created with little or essentially no degradation in the physical properties, such as hardness, of the joined materials. Moreover, the beneficial use of a refractory based contact has been advantageously retained. While a specific composition for the brazing alloy has been given in the example just described, it is believed that satisfactory results may be obtained with somewhat different compositions. It is believed that one consideration for the brazing alloy is that it comprise at least two elemental materials and that the major constituent be an abundance of elemental copper over any other constituent material. Ultrasonic welding machines for performing the joining that is the subject of the present invention are commercially available. They can be selected and set to meet specified performance criteria to accomplish part joining in accordance with relevant specifications, such as current carrying capacity, trip time, etc. Examples of suitable ultrasonic welders are: Sonobond Model No. MH-1545, available from Sonobond Ultrasonics Company, 200 East Rosedale Ave., Westchester, Pennsylvania 19380; and ATE Ultraweld 20 System available from American Technology Equipment, Inc., 25 Controls Drive, Shelton, Connecticut 06484. Figures 4 to 8 illustrate a portion of a circuit breaker mechanism including an actual contact 10 joined to a contact arm 12 according to the present invention. Contact arm 12 forms a carrier for the contact by an illustrative two-piece construction, comprising a first contact arm piece 12A and a second contact arm piece 12B. Contact 10 is joined to the distal end of contact arm 12, creating a contact arm assembly 13. The two pieces 12A, 12B are essentially mirror images of each other. As shown by Figure 6, confronting portions of each piece 12A, 12B proximate the distal end of contact arm 12 comprises respective zones 16 where they are joined directly together. Such joining may be accomplished by ultrasonic welding or brazing. Proximate to zones 16, the joined pieces 12A, 12B form a bifurcation. Proximate the distal end of this bifurcation which is proximate zones 16, each piece 12A, 12B has an abutment 18 whose free end is adapted to abut, but at the minimum at least closely confront, the free end of the opposite abutment 18. At the proximate end of contact arm 12, each piece 12A, 12B has a lobe 20 that, in the completed circuit breaker, defines an axis 22 about which contact arm assembly 13 executes swinging motion. Further portions of the mechanism shown in Figures 4, 7 and 8 comprise a load terminal 24, a flexible connector, or braid 26 and a bi-metal 28. Load terminal 24 is adapted to be mounted on a casing (not shown) of a circuit breaker, for example by a fastener, such as a headed screw, whose shank is passed a hole in the casing and threaded into an extruded hole 30 in the load terminal. The end of terminal 24 designated 24A leads to a load circuit (not shown). The end designated 24B provides a cantilever mounting for bi-metal 28. Bi-metal 28 comprises a nominally flat strip having a relatively higher expansion side 28A and a relatively lower expansion side 28B. The distal end of bi-metal 28 and one end of braid 26 are joined together, such as by brazing. The opposite end of braid 26 is joined, by brazing for example, to contact arm 12 distally proximal to a lobe 20 of one of the two pieces 12A, 12B, the one piece being 12A in the example depicted. When a finished circuit breaker containing the mechanism just described is in its "on" position, contact 10 has direct contact with another contact that is connected to a line terminal (not shown). Hence a complete circuit exists from that line terminal and its associated contact, through contact 10, contact arm 12, braid 26, and bi-metal 28, to load terminal 24. One type of fault condition that should cause the circuit breaker to trip is due to thermal energy input to bi-metal 28 sufficient to warp the bi-metal to an extent that causes operation of a trip mechanism (not shown). As a result, contact arm assembly 13 swings in the sense of arrow 29 in Figure 4 to separate contact 10 from the line terminal contact that it had been engaging. This breaks the continuity through the circuit breaker between the line terminal and load terminal 24, causing the circuit breaker to operate to "tripped" condition. Figures 4 and 6 show adjoining flat rectangular surface areas 32 of contact arm pieces 12A and 12B. Contact 10 has a rectangular surface area 34 of slightly larger overall area than the combined surface areas 32. Joining of surface area 34 to the surface areas 32 is advantageously accomplished by the present approach. The occurrence of a fault that should trip the circuit breaker may create relatively large current densities through the joint between contact 10 and contact arm 12. The present approach is believed to aid in better maintaining the integrity of the joint under such high stress conditions. This is important where small areas are involved. Although general principles of the invention are not intended to necessarily be limited to particular interface areas, it is believed that interface areas less than about 1/4" X 5/16" (6.35mm x 7.9375mm) are especially well-suited for successful joining, at least in the case of joining a contact to a contact arm in an electric circuit protection device like a circuit breaker. "Interface area" is understood to include the area where the actual joining takes place. Specific examples of interface areas that have been used in practice of the inventive principles are 9/16" X 5/32" (14.2875mm x 3.96875mm) and 1/8" X 9/32" (3.175mm x 7.14375mm). By gathering a contact in an ultrasonic welder, it is believed that the thickness of the contact may be any of a number of different thicknesses typically used for contacts. Examples of typical thicknesses may range up to about 3/16" (4.76mm). Figures 9 and 10 show two examples of actual joints created by use of the joining procedure. The contact arm comprises predominantly copper, with small amounts of iron and silicon. An example is Cu at least about 97-99%, Si 1% or less, and Fe 2% or less. The brazing alloy consists of substantially 80 parts elemental copper by weight, substantially 15 parts elemental silver by weight and substantially 5 parts elemental phosphorus by weight. The contact is 50% Ag and 50% WC by weight. The accompanying patent drawings of Figures 9 and 10 contain 50X photomicrographs. In each of Figures 9 and 10, it can be seen that brazing alloy 14 was joined to contact 10 before the ultrasonic welding of the contact to contact arm 12. Excess silver fills troughs of serrations in the contact. The brazing alloy appears as a layer overlapping the serrations, and the region of ultrasonic bonding is so labeled. It is believed that there is essentially complete bonding across the joint. Figure 10 shows evidence of "swirling" at the interface, which is believed to indicate relatively good quality. Figure 11 is believed to show the swirling in more detail. It is contemplated that the inventions are suitable for joining an electric conductor that is primarily copper to the following refractory-based materials: Silver-Tungsten; Silver Tungsten Carbide; Copper Tungsten; Copper Tungsten Carbide; and Silver Molybdenum. Of course, the relative percentages of the contact constituents may vary. Specific examples are given by the following table wherein hardness, density, and electrical conductivity data are representative. In the table, IACS refers to International Annealed Copper Standard. Class Composition % by weight Hardness (Rockwell) Density gm/cc Conductivity %IACS Silver Tungsten 50Ag50W B65 13.2 62 40Ag60W B75 14.0 55 35Ag65W B85 14.5 51 25Ag75W B90 15.5 45 45Ag50W5C B50 10.6 40 Silver Tungsten 65Ag35WC B55 11.5 55 Carbide 60Ag40WC B65 11.7 50 50Ag50WC B80 12.2 47 40Ag60WC B95 12.7 43 35Ag65WC B100 12.9 34 Copper Tungsten 50Cu50W B65 11.9 50 40Cu60W B80 12.8 47 30Cu70W B90 13.9 46 25Cu75W B95 4.5 44 20Cu80W B100 15.2 40 Copper Tungsten Carbide 50Cu50WC B95 11.0 45 Silver Molybdenum 50Ag50MO B75 10.1 52 45Ag55MO B80 10.1 48 40Ag60MO B85 10.1 45 35Ag65MO B87 10.0 42 30Ag70MO B90 10.0 39 While the present invention has been described with reference to the embodiments as currently contemplated, it should be understood that the invention is not intended to be limited to the described embodiments. Accordingly, the claimed invention encompasses various modifications and arrangements that are within the scope of the claims.

Claims: An electric conductor assembly (10, 12, 14) comprising: an electrically conductive contact (10) having a constituent comprising a non-alloying material and further comprising silver; and an electrically conductive contact carrier (12) comprising a predominance by weight of non-ferrous material, mechanically joined together at a particular location by the application of ultrasonic energy, brazing material (14) being disposed between the contact (10) and the carrier (12) at the location where they are joined, with elemental copper being the largest single constituent of the brazing material, characterised in that the contact comprises serrations in the surface joined to the brazing material, said serrations being filled with excess silver from the contact, the brazing material forming a layer overlapping the serrations; and in that the brazing material (14) consists of substantially 80 parts elemental copper by weight, substantially 15 parts elemental silver by weight, and substantially 5 parts elemental phosphorus by weight. An electric conductor assembly according to claim 1, wherein the non-alloying material comprises a refractory material. An electric conductor assembly according to claim 2, wherein the refractory material is selected from the group consisting of silver tungsten, silver tungsten carbide, copper tungsten, copper tungsten carbide and silver molybdenum. , An electric conductor assembly according to claim 2 or 3, wherein the refractory material makes up at least about 35% by weight of the contact (10). An electric conductor assembly according to any one of claims 1 to 3, wherein the contact (10) comprises the non-alloying material and the carrier (12) comprises copper as the non-ferrous material. An electric circuit protection device comprising an interruptible current path for interrupting current flow to a load including trip means for tripping the interruptible current path upon occurrence of a load fault, characterised in that the current flow path comprises an electric conductor assembly (10, 12, 14) according to any one of claims 1 to 5.

Inventors: NEWLAND CHARLES ALLEN, NEWLAND, CHARLES ALLEN
Applicants: SIEMENS ENERGY & AUTOMAT, SIEMENS ENERGY & AUTOMATION, INC.
Application year: 1998
Main classification: H01H11
IPC codes: H01H11, H01H1