METHOD OF ULTRASONICALLY JOINING TWO ELECTRICALLY CONDUCTIVE PARTS

Description

Field Of The Invention

[0001] This invention relates generally to the ultrasonic joining of electrically conductive materials. More specifically, it relates to the realization that by selecting certain brazing materials, ultrasonic welding can be used to join two diverse electrically conductive materials, which it is believed, have been previously considered incompatible for joining by ultrasonic welding to create a joint that can withstand electric current faults, such as occur in circuit breakers.

Background Of The Invention

[0002] 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.

[0003] 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 interruptable 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] WO-A-93/11550 discloses a contact with a silver contact base which is soldered to a contact carrier by means of a silver intermediate layer and a solder. The solder is in the form of a platelet, comprising a copper-silver alloy, which is provisionally fastened or tacked to the intermediate silver layer using ultrasonic welding prior to soldering the contact to its carrier.

[0008] US-A-4 019 876 discloses an electrical contact element which is produced by ultrasonically welding one or more contact pieces onto a carrier. An intermediate layer is interposed between the contact piece and the carrier prior to welding to assist in the welding to contact pieces which are made of a material which is otherwise difficult to weld. The contact piece comprises cadmium oxide in a matrix of silver, the carrier comprises brass and the intermediate layer comprises aluminium foil.

Summary of the Invention

[0009] The present invention relates to a novel method which provides for materials that previously have been believed to be inappropriate for satisfactorily joining parts by ultrasonic welding.

[0010] 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 believe 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.

[0011] One aspect of the present invention relates to a method of mechanically joining two electrically conductive parts, the method comprising the steps of:- providing first and second electrically conductive parts which are to be joined by a brazing material to establish electric conductivity between them, a constituent of the first part comprising a non-alloying material and the second part comprising a predominance by weight of non-ferrous material.

[0012] The method further comprises the steps of joining the brazing material to the first part by heating in an inert atmospheric oven; allowing the brazing material and the first part to cool; disposing the face of the first part that contains the brazing material in surface-to-surface contact with the second part; and joining the two parts by the application of ultrasonic energy. The brazing material comprises at least two materials, with elemental copper being the largest single constituent of the brazing material by weight.

[0013] The brazing material may comprise at least 50% elemental copper by weight.

[0014] In particular, the brazing material may consist of substantially 80 parts elemental copper by weight, substantially 15 parts elemental silver by weight, and substantially 5 parts elemental phosphorus by weight.

[0015] Preferably, the non-alloying material comprises a refractory material, which may be selected from the group consisting of silver tungsten, silver tungsten carbide, copper tungsten, copper tungsten carbide and silver molybdenum.

[0016] The refractory material may be selected to comprise at least about 35% by weight of the first part.

[0017] The non-ferrous material may be copper.

[0018] The foregoing, along with additional features, and other advantages and benefits of the invention, will be seen in the following description and claims which are accompanied by drawings and disclose certain embodiments of the invention.

Brief Description Of The Drawings

[0019] 

Figure 1 is an elevation view, schematic in nature, illustrating a stage in the inventive method.

Figure 2 is an elevation view, schematic in nature, illustrating a further stage in the inventive method.

Figure 3 is an elevation view, schematic in nature, of parts that have been joined by the inventive method.

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

[0020] 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.

[0021] A brazing alloy designated by the reference numeral 14 for use in joining the two parts 10, 12 comprises at least two materials, one of the two materials being elemental copper, with the elemental copper being the largest constituent of the brazing material. One example of a suitable brazing material is an alloy consisting of 80 parts elemental copper, 15 parts elemental silver, and 5 parts element phosphorus, all by weight.

[0022] The brazing alloy is 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Figures 4 to 8 illustrate a portion of a circuit breaker mechanism including an actual contact 10 joined to a contact arm 12. 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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" (3.175 mm x 7,14375mm) and 1/8" X 9/32". 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).

[0032] 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.

[0033] 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	132	62
	40Ag60W	B75	14.0	55
	35Ag65W	B85	14.5	51
	25Ag75W	B90	15.5	45
	45Ag50W5C	B50	10.6	40
Sliver Tungsten Carbide	65Ag35WC	B55	11.5	55
	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	14.5	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

[0034] While the present inventions have 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 and preferred embodiments. Accordingly, the claimed inventions are intended to encompass various modifications and arrangements that are within the scope of the claims.

Claims

1. A method of mechanically joining two electrically conductive parts (10, 12), the method comprising the steps of:-

providing first and second electrically conductive parts (10, 12) which are to be joined by a brazing material to establish electric conductivity between them, a constituent of the first part comprising a non-alloying material and the second part comprising a predominance by weight of non-ferrous material;

   characterised in that the method further comprises the steps of:

joining the brazing material (14) to the first part (10) by heating in an inert atmospheric oven;

allowing the brazing material and the first part to cool;

disposing the face of the first part that contains the brazing material (14) in surface-to-surface contact with the second part ; and

joining the two parts by the application of ultrasonic energy,

further characterised in that
   the brazing material comprises at least two materials, with elemental copper being the largest single constituent of the brazing material by weight.

2. A method according to claim 1 in which the brazing material comprises at least 50% elemental copper by weight.

3. A method according to claim 2 in which 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.

4. A method according to any preceding claim, wherein the non-alloying material comprises a refractory material.

5. A method according to claim 4, wherein the refractory material is selected from the group consisting of silver tungsten, silver tungsten carbide, copper tungsten, copper tungsten carbide and silver molybdenum.

6. A method according to claim 4 or 5, wherein the refractory material is selected to comprise at least about 35% by weight of the first part.

7. A method according to any one of the preceding claims, wherein the second part (12) comprises copper as the non-ferrous material.

Ansprüche

1. Verfahren zum mechanischen Verbinden von zwei elektrisch leitenden Teilen (10, 12), wobei das Verfahren die folgenden Schritte umfasst:

Versehen eines ersten und eines zweiten elektrisch leitenden Teils (10, 12), welche verbunden werden sollen, mit einem Hartlot, um die elektrische Leitfähigkeit zwischen ihnen herzustellen, wobei ein Bestandteil des ersten Teils aus einem Nichtlegierungsmaterial besteht und das zweite Teil zu einem gewichtsmäßig überwiegenden Teil aus einem Nichteisenmaterial besteht;

   dadurch gekennzeichnet, dass das Verfahren ferner die folgenden Schritte umfasst:

Verbinden des Hartlotes (14) mit dem ersten Teil (10) durch Erhitzen in einem Ofen mit einer Schutzgasatmosphäre;

Abkühlenlassen des Hartlotes und des ersten Teils;

Bringen der Seite des ersten Teils, die das Hartlot (14) enthält, in eine Position der Anlage auf der ganzen Fläche an das zweite Teil; und

Verbinden der zwei Teile durch die Zuführung von Ultraschallenergie,

ferner dadurch gekennzeichnet, dass
   das Hartlot aus wenigstens zwei Werkstoffen besteht, wobei der gewichtsmäßig größte Einzelbestandteil des Hartlotes elementares Kupfer ist.

2. Verfahren nach Anspruch 1, wobei das Hartlot wenigstens 50 Gewichts-% elementares Kupfer enthält.

3. Verfahren nach Anspruch 1, wobei das Hartlot (14) aus im Wesentlichen 80 Gewichtsanteilen elementaren Kupfers, im Wesentlichen 15 Gewichtsanteilen elementaren Silbers und im Wesentlichen 5 Gewichtsanteilen elementaren Phosphors besteht.

4. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Nichtlegierungsmaterial aus einem Feuerfestmaterial besteht.

5. Verfahren nach Anspruch 4, wobei das Feuerfestmaterial aus der Gruppe gewählt ist, die aus Silber-Wolfram, Silber-Wolframkarbid, Kupfer-Wolfram, Kupfer-Wolframkarbid und Silber-Molybdän besteht.

6. Verfahren nach Anspruch 4 oder 5, wobei das Feuerfestmaterial so gewählt ist, dass es wenigstens ungefähr 35 Gewichts-% des ersten Teils umfasst.

7. Verfahren nach einem der vorhergehenden Ansprüche, wobei das zweite Teil (12) Kupfer als das Nichteisenmaterial umfasst.

Revendications

1. Procédé pour joindre mécaniquement deux parties (10, 12) conductrices de l'électricité, le procédé comprenant les stades de :

prévoir des première et seconde parties (10,12) conductrices de l'électricité qui doivent être jointes par une matière de brasage pour établir de la conductivité électrique entre elles, un constituant de la première partie comprenant une matière non alliée et la seconde partie comprenant une proportion prédominante en poids de matière non ferreuse,

   caractérisé en ce que le procédé consiste en outre :

à joindre la matière (14) de brasage à la première partie (10) en chauffant dans un four à atmosphère inerte ;

à laisser la matière de brasage et la première partie se refroidir ;

à disposer la face de la première partie qui contient la matière (14) de brasage en contact surface contre surface avec la seconde partie ; et

à joindre les deux parties par l'application d'une énergie ultrasonore,

   caractérisé en outre en ce que
   la matière de brasage comprend au moins deux matières, du cuivre élémentaire étant le constituant le plus grand en poids de la matière de brasage.

2. Procédé suivant la revendication 1, dans lequel la matière de brasage comprend au moins 50 % en poids de cuivre élémentaire.

3. Procédé suivant la revendication 2, dans lequel la matière (14) de brasage consiste sensiblement en 80 parties en poids de cuivre élémentaire, sensiblement en 15 parties en poids d'argent élémentaire et sensiblement en 5 parties en poids de phosphore élémentaire.

4. Procédé suivant l'une quelconque des revendications précédentes, dans lequel la matière non alliée comprend une matière réfractaire.

5. Procédé suivant la revendication 4, dans laquelle la matière réfractaire est choisie dans le groupe consistant en argent-tungstène, argent-carbure de tungstène, cuivre-tungstène, cuivre-carbure de tungstène et argent-molybdène.

6. Procédé suivant la revendication 4 ou 5, dans lequel la matière réfractaire est choisie de manière à représenter au moins 35 % en poids environ de la première partie.

7. Procédé suivant l'une quelconque des revendications précédentes, dans laquelle la seconde partie (12) comprend du cuivre comme matière non ferreuse.

Drawing