WO2008089316A2

WO2008089316A2 - Resistor igniter for weld metal material

Info

Publication number: WO2008089316A2
Application number: PCT/US2008/051286
Authority: WO
Inventors: Fady Alghusain
Original assignee: Erico International Corporation
Priority date: 2007-01-19
Filing date: 2008-01-17
Publication date: 2008-07-24
Also published as: WO2008089316A3

Abstract

An igniter for particulate weld metal material includes a resistor, and a pair of conductive leads connected to the resistor. The resistor is located in or above the weld metal material. An electrical current is provided to the resistor to overload the resistor and cause it to structurally break apart, such as by exploding, spewing hot resistor material into and/or on the weld metal material, igniting the weld metal material. Weld metal produced by the exothermic reaction of the weld metal material is used to weld together two or more pieces of metal, ends of metal bars, thereby electrically and/or mechanically joining the bars together. The igniter may be including in a weld metal package that includes the particulate weld metal material. The package may be a sealed package, with parts of the conductive leads protruding from the package.

Description

RESISTER IGNITER FOR WELD METAL MATERIAL

BACKGROUND OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates generally to welding apparatus and methods, and more particularly to apparatus and methods for forming weld connections, and for initiating self-propagating exothermic reactions, such as in the process of forming the weld connections.

DESCRIPTION OF THE RELATED ART

[0002] Exothermic welding has become recognized as a preferred way to form top quality high ampacity, low resistance electrical connections. [0003] Exothermic welded connections are immune to thermal conditions which can cause mechanical and compression joints to become loose or corrode. They are recognized for their durability and longevity. The process fuses together the parts or conductors to provide a molecular bond, with a current carrying capacity equal to that of the conductor. Such connections are widely used in grounding systems enabling the system to operate as a continuous conductor with lower resistivity.

[0004] Examples of self propagating exothermic reactions for exothermic welding are found in the CADWELD process and the THERMIT process. CADWELD is a trademark of ERICO International Corporation, Solon, Ohio, U.S.A., and Thermit is a trademark of Th. Goldschmidt A G, Essex, Germany. Exothermic welding mixtures are basically a combination of a reductant metal and usually a transition metal oxide. An example is aluminum and copper oxide, which upon ignition supply enough heat to propagate and sustain a reaction within the mixture. It is usually the molten metal product or the heat of this reaction, which is then used to produce a desired result. The CADWELD process produces, for example, a mixture of molten copper and aluminum oxide or slag. The higher density of the molten copper causes separation from the slag, with the molten copper usually directed by a mold to join or weld copper to copper, copper to steel, or steel to steel. The aluminum oxide slag is removed from the weld connection and discarded. Another common mixture is iron oxide and aluminum. Where only the heat of the reaction is used, the heat may be used to fuse brazing material, for example.

[0005] The exothermic reaction produces a large amount of heat. The most common way to contain the reaction, and to produce the weld or joint, has been to contain the reaction in a split graphite mold. A particulate welding material is placed in the mold, and a starting powder is ignited to initiate an exothermic reaction in the material. When the exothermic material is ignited, molten metal is produced that is used to join to produce the joint in a chamber of the mold.

[0006] As suggested by the above, exothermic mixtures of this type do not react spontaneously and need a method of initiating the reaction. This initiation method involves generating enough localized energy to enable the reaction to begin. One method of initiating reaction is that described above, use of a starting powder and an ignition source such as a flint igniter. However, because of the starting powder's low ignition temperature and difficulties in handling and shipping, much effort has been made to find a reliable and low cost alternative ignition system for the exothermic material. A number of electrical systems have been devised which range from simple spark gaps to bridge wires or foils, to much more esoteric devices such as rocket igniters. Such efforts are seen, for example, in prior U.S. Patent Nos. 4,881 ,677, 4,879,452, 4,885,452, 4,889,324 and 5,145,106. For a variety of reasons, but primarily because of power requirements, dependability, and cost, such devices have not succeeded in replacing the standard starting powder/flint gun form of initiating the self-propagating exothermic reactions. Another electrical ignition system is the system disclosed in U.S. Patent No. 6,553,911 , owned by the assignee of this application, which is incorporated herein by reference in its entirety. [0007] Accordingly, it will be appreciated that improved welding apparatus and methods would be desirable.

SUMMARY OF THE INVENTION

[0008] According to aspect of the invention, a method of igniting weld metal material includes electrically overloading a resistor of an igniter, causing the resistor break apart, sending out hot material of the resistor that ignites the weld metal material. [0009] According to another aspect of the invention, a weld metal package for exothermic welding includes a container, a particulate weld material inside the container, and an igniter at least partially in the container, wherein the igniter includes a resistor and a pair of conductive leads connected to the resistor. [0010] According to yet another aspect of the invention, an igniter for weld metal material includes a resistor and conductive leads electrically coupled to the resistor. The conductive leads may be rigid metal rods, which may be bent. The conductive leads may be covered with insulation.

[0011] According to still another aspect of the invention, a weld metal package for exothermic welding includes: a container; a particulate weld material inside the container; and an igniter at least partially in the container. The igniter includes a resistor and a pair of conductive leads connected to the resistor. [0012] According to a further aspect of the invention, a welding apparatus includes: a graphite mold; a particulate weld metal material in a chamber of the mold; and an igniter at least partially within the mold. The igniter includes: a resistor above or at least partially within the weld metal material; and conductive leads electrically coupled to the resistor.

[0013] According to a still further aspect of the invention, a method of joining metal pieces includes the steps of: electrically overloading a resistor of an igniter, causing the resistor break apart, sending out hot material of the resistor to initiate an exothermic reaction in particulate weld metal material to produce molten metal; and directing the molten metal into contact with ends of the metal pieces. [0014] To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS [0015] In the annexed drawings, which are not necessarily to scale: [0016] Fig. 1 is an oblique view of an igniter in accordance with an embodiment of the present invention;

[0017] Fig. 2 is an oblique view illustrating a first step of a first ignition process using the igniter of Fig. 1 ;

[0018] Fig. 3 is an oblique view illustrating a second step of the first ignition process using the igniter of Fig. 1 ;

[0019] Fig. 4 is an oblique view illustrating a first step of a second ignition process using the igniter of Fig. 1 ;

[0020] Fig. 5 is an oblique view illustrating a second step of the second ignition process using the igniter of Fig. 1 ;

[0021] Fig. 6 is an oblique cutaway view of a first embodiment welding apparatus using the igniter of Fig. 1 , in accordance with an embodiment of the present invention;

[0022] Fig. 7 is an oblique, partial cutaway view of a welding material package using the igniter of Fig. 1 , in accordance with an embodiment of the present invention;

[0023] Fig. 8 is a side view of another welding material package using the igniter of Fig. 1 , in accordance with an embodiment of the present invention; and

[0024] Fig. 9 is an exploded view showing a weld assembly that used the welding material package of Fig. 8.

DETAILED DESCRIPTION

[0025] An igniter for particulate weld metal material includes a resistor, and a pair of conductive leads connected to the resistor. The resistor is located in or above the weld metal material. An electrical current is provided to the resistor to overload the resistor and cause it to structurally break apart, such as by exploding, spewing hot resistor material into and/or on the weld metal material, igniting the weld metal material. Weld metal produced by the exothermic reaction of the weld metal material is used to weld together two or more pieces of metal, ends of metal bars, thereby electrically and/or mechanically joining the bars together. The igniter may be including in a weld metal package that includes the particulate weld metal material. The package may be a sealed package, with parts of the conductive leads protruding from the package. [0026] Fig. 1 shows an igniter 10 used for igniting particulate weld metal material. The igniter includes a resistor 12, and a pair of conductive leads 14 and 16 for coupling the resistor to a voltage supply. A resistor, as the term is used herein, is defined as a manufactured resistance device having an insulator covering. [0027] The resistor 12 is configured to structurally break apart when electrically overloaded as part of its intended use. The intended structural failure of the resistor 12 when overloaded may cause an explosion of the resistor 12, in the sense that the overheating and failure of the resistor 12 is accomplished by forcibly spewing hot material out. As explained in greater detail below, the hot material is used to ignite a particulate weld metal material, to initiate an exothermic reaction that produces molten weld metal. Most resistors are manufactured to have a voltage and/or a current rating. Sufficiently overcoming the rating(s) will cause the resistor to explode. The explosion can cause, for example: hot material to be sent out from the explosion; one or more high energy sparks directed to the weld material; release of sound energy; expulsion of burning pieces of the conductive leads and/or burning components of the resistor (which may vary depending on what kind of material the resistor is made of, such as carbon, metallic films, and/or mixtures of any suitable materials); and/or any combination of these.

[0028] In addition, the resistor 12 may contain metal particles that are used to aid in initiating ignition. Overloading and explosion of the resistor 12 may spew hot metal particles particulate weld metal material. The metal particles may melt as part of the overloading and explosion of the resistor 12. The added metal particles may be aluminum or copper particles, using materials that are the same as that of the molten weld metal to be formed. The added metal particles advantageously can provide multiple ignition points within particulate weld metal material to be ignited. In addition, having the material of the metal particles match that of the metal in the particulate weld metal material may result in a more homogenous chemical reaction. The result may be a faster and better quality chemical reaction of the particulate weld metal material. The added metal particles may be added to carbon or metal film parts of the resistor 12. These particles may be added without changing the resistance of the resistor 12, relative to a resistor of similar structure without added metal particles. [0029] The resistor 12 may be any of a variety of different types of suitable resistors. Examples of suitable resistor types include precision wirewound resistors, NIST standard resistors, power wirewound resistors, fuse resistors, carbon composition, carbon film resistors, metal film resistors, foil resistors, filament resistors and power film resistors. The resistor 12 may have a resistance that stays substantially the same as the current through the resistor 12 changes. That is, the voltage drop across the resistor 12 may be a substantially linear function of the current through the resistor 12.

[0030] The resistance of the resistor 12 may vary over a wide range of resistances, such as from 1 to 1000 ohms. The type and resistance of the resistor 12 may be selected depending upon the characteristics of the system for which it will be employed. Suitable equations for predicting the optimum resistance for use in two different classes of firing systems (constant voltage and capacitor discharge) can be derived according to the firing system available.

[0031] The conductive leads 14 and 16 may be rigid metal leads that emerge from opposite sides of the resistor 12. The leads 14 and 16 may be round steel rods with sufficient rigidity to maintain the resistor 12 at a desired location. The conductive leads 14 and 16 have 90-degree bends 18 and 20 to allow placement of the resistor 12 closer to or in particulate weld metal material to be ignited, while allowing free ends 22 and 24 of the leads 14 and 16 to protrude out of the side of a mold or package containing the weld metal material. The leads 14 and 16 may have dielectric coatings 25 and 26 over some of their lengths, to prevent shorting of the leads 14 and 16 through a graphite mold or a metal package in contact with the leads 14 and 16.

[0032] Figs. 2 and 3 illustrated one method of initiating ignition using the igniter 10. As is shown in Fig. 2, the igniter 10 is placed so that the resistor 12 is partially or fully within particulate weld metal material 30. The particulate weld metal material 30 may be a powderized or granulated mixture of a reductant metal and a transition metal oxide, for example a mixture of aluminum and copper oxide. [0033] An electrical unit 32 is used to send a current through the resistor 12 to overload the resistor 12. The electrical unit 32 may be any of various types of units for providing a voltage across the leads 14 and 16, and a current through the resistor 12. The electrical unit 32 may be a constant voltage unit or a capacitor discharge unit. An example of a suitable electrical unit 32 is the CADWELD PLUS control unit available from ERICO, Inc, of Solon, Ohio, USA. The CADWELD PLUS control unit has an output of 800 volts, which has been found suitable for overloading resistors in the 1-2 ohm range. A lower output voltage may require lower resistance in the resistor 12 in order to keep the output heat, spark, and energy released to the weld metal material sufficient to start ignition. The relationship between resistance, voltage, and current is provided by Ohm's Law: R=V/I, where R is the resistance, V is the voltage drop, and I is the current. Most resistors have voltage and current ratings. For a resistor having a 150-volt rating value, application of 200 volts may be amply sufficient to explode the resistor. No specific resistance value for the resistor 12 is required. Rather the resistance, the voltage, and the current are all interrelated. The current and the voltage applied across the resistor 12 to overload it may be a continuous steady value, or may involve a transient application of a voltage difference across the resistor 12.

[0034] Fig. 3 illustrates the ignition process of the igniter 10. The electrical unit 32 provides a voltage across the conductive leads 14 and 16, and a current through the resistor 12. This is sufficient to overload the resistor 12, and cause the resistor 12 to break apart, such as by exploding or otherwise spewing hot material 36 out into the weld metal material, indicated at reference number 38. The pieces of hot material 36 may be various bits of the resistor 12. The hot material pieces 36 may include any of the different materials of the resistor 12 and/or the leads 14 and 16. For instance, the hot material 36 may include the metal particles added to the resistor 12. The hot material 36 is hot enough, and carries enough energy, to ignite the weld metal material that it comes in contact with. This initiates an exothermic reaction in the weld metal material 30 as a whole. A molten weld metal is produced, which can be directed to flow into a place where a pair of to-be-joined metal pieces are located. This electrically and/or mechanically couples together the metal pieces. [0035] Fig. 4 and 5 shows an alternative configuration, where the resistor 12 is located above the particulate weld metal material 30 (Fig. 4). After activation of the electrical unit 32, the resistor 12 breaks apart and spews the hot material 36 down onto the particulate weld metal material 30 (Fig. 5), indicated at reference number 38. This initiates an exothermic reaction in the particulate weld metal material 30, to produce a molten weld metal. [0036] The igniter 10 may be used a number of configurations, in conjunction with a graphite mold, to produce a weld coupling together metal pieces. Fig. 6 shows a simple configuration, where the igniter 10 is part of a welding apparatus 40 utilizing a split graphite mold 42. The mold 42 includes an upper mold body section 44, a lower mold body section 46, and a mold cover 50. The metal pieces or items to be joined, such as bars 52 and 54, are thoroughly cleaned and then placed in the appropriate location to project into a weld chamber 56 defined by the body sections 44 and 46 of the mold 42. The upper mold body section 44 includes a crucible chamber 60 above the weld chamber 56, connected to the weld chamber 56 by a tap hole 62. The mold body sections 44 and 46 are then securely closed and locked usually with a toggle clamp, and a metal disk 64 is positioned in the crucible chamber 60 over the tap hole 62. An appropriate amount of the exothermic particulate weld metal material 30 is emptied into the crucible chamber 60 on top of the disk 64. The igniter 10 is position with the resistor 12 partially or fully in, or over, the weld metal material 30. The cover 50 is then closed, with portions of the conductive leads 14 and 16 protruding from an opening 66 between the cover 50 and the upper mold body section 44. The dielectric coatings 25 and 26 on the leads 14 and 16 prevent the graphite mold 42 from shorting the leads 14 and 16. The electrical unit 32 is then coupled to the leads 14 and 16.

[0037] The electrical unit 32 is activated, causing breakdown of the resistor 12 and initiation of the exothermic reaction in the weld metal material 30. When the exothermic material 30 is ignited, the molten metal phase separates from the slag and melts through the metal disk 64. The molten metal then is directed via the tap hole 62 to the weld chamber 56. There the conductors 52 and 54 are joined. Once the metal has solidified the mold body sections 44 and 46 are opened and the slag is separated from the weld connection. The mold 42 is cleaned and readied for reuse for the next connection.

[0038] Fig. 7 shows an alternative configuration, a sealed crucible assembly package 70. The crucible assembly package 70 is a self-contained weld material and igniter package that may be used with the mold 40 (Fig. 6) or another suitable mold. The crucible assembly package 70 includes a container 71 that has a container body 72 with side walls 74 and a fusible bottom 76. The container body 72 may be made of steel or another suitable material. A refractory material 80, such as a graphite foil, lines the side walls 74 of the container body 72. The refractory material 80 protects the side walls 74 from the heat generated by reaction of the exothermic weld material 30 that is within the container body 72. [0039] The igniter 10 is positioned such the resistor 12 is in or above the particulate weld metal material 30. The leads 14 and 16 rest on a top edge 86 of the container body 72. A cover 88 of the container 71 engages the top edge 86 of the container body 72, sealing the weld material 30 and part of the igniter 10 within the container 71. The leads 14 and 16 are between the top edge 86 and the cover 88, with portions of the leads 14 and 16 protruding out from the container 71. The dielectric coatings 25 and 26 on the leads 14 and 16 prevent the cover 88 and/or the container body 72 from electrically shorting the leads 14 and 16. Alternatively, the cover 88 and the top edge 86 may be configured to prevent electrical contact with one or both of the leads 14 and 16.

[0040] An adhesive may be used to secure the cover 88 to the top edge 86 and the leads 14 and 16. The cover 88 prevents the particulate weld material 30 from leaving the container 71 prior to initiation of a reaction to form a weld connection. In addition the cover 88 prevents ingress of dirt, moisture, or other contaminants into the container 71 , and in particular into the weld material 30. The cover 88 may include a metal foil, a plastic such as MYLAR, or a metallized plastic film. [0041] Reaction of the weld material 30 produces heat, as discussed above. The refractory material 80 protects the side walls 74 of the container body 72 from being ruptured, perforated, or from otherwise failing as a result of the heat produced by the reaction of the weld material 30. However, at least part of the fusible bottom 76 of the container body 72 is not protected by the refractory material 80. The partially- or fully-reacted weld material 30 possesses sufficient heat to rupture and/or melt the fusible bottom 76, allowing the molten reacted weld material 30 (also referred to herein as "weld metal") to exit the container 71 to form a weld connection below the bottom 76 of the container 71.

[0042] Further details regarding possible configurations for the container 72 may be found in Moore et al., U.S. Patent No. 6,835,910, which is incorporated herein by reference in its entirety. The Moore patent describes a container similar to the container 72, albeit with a different sort of igniter than the igniter 10. [0043] Fig. 8 shows a welding material package 100 that includes a container 102 made of an expendable material that is consumed by the exothermic reaction of the weld metal material 30 inside the container 102. The container 102 includes a conical container body 106 and a cover 108. The conical body 106 is sealed at a seam 110 at its bottom, leaving a flap of material 112 below the seam 110. This defines a chamber 114 within the container 102, where the particulate weld metal material 30 resides. The cover 108 is affixed to the conical body 106 along a top edge 118 of the conical body 106.

[0044] The igniter 10 is partially within the container 102, with the conductive leads 14 and 16 protruding out from the container 102 from between the cover 108 and the top edge 118 of the conical body 106. The resistor 12 is located within the container 102, located within or above the particulate weld metal material 30. The material of the conical body 106 and/or the cover 108 may be a plastic material, such as MYLAR. The plastic of the body 106 and/or the cover 108 may be a metallized film, such as with aluminum. Alternatively, the conical body 106 and/or the cover 108 may include a metal foil, such as an aluminum foil or copper foil. More broadly, the body 106 and the cover 108 may be made of suitable metals or non- metals. The conical body 106 and/or the cover 108 may be made of the same material, or of different materials. The body 106 and the cover may be made of flexible material, or may impart some rigidity to the cover 108. [0045] At least part of the container 102 may be consumed during the reaction of the weld metal material 30. The conical body 106 and/or the cover 108 may be burned, vaporized, and/or melted during the exothermic reaction. This allows the molten weld metal produced by the reaction of the particulate weld metal material 30 to break through the container 102. The container 102 may be fully or partially consumed by the exothermic reaction. The materials of the container 102 may be part of a vapor, may melt and enter into the molten weld metal, or may be dross or a crust on the top of the molten material.

[0046] The package 100 optionally may have refractory material liner similar to the refractory material 80 (Fig. 7), such as a graphite foil liner, that protects portions of the conical body 106 from being consumed during the exothermic reaction of the weld metal material 30. The refractory material liner may have a conical shape. The liner may advantageously provide a fixed shape to the package 100 and may aid in directing flow of molten metal produced by the exothermic reaction of the weld metal material.

[0047] Referring now in addition to Fig. 9, the package 100 may be used as part of a weld assembly 120, using a mold such as the mold 42, similar to the mold 42 shown in Fig. 6. The package 100 may be placed in the crucible chamber 60, with the conductive leads 14 and 16 protruding from the crucible chamber 60. [0048] Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

CLAIMSWhat is claimed is:

1. A weld metal package for exothermic welding comprising: a container; a particulate weld material inside the container; and an igniter at least partially in the container; wherein the igniter includes a resistor and a pair of conductive leads connected to the resistor.

2. The package of claim 1 , wherein the resistor has a resistance of at least 1 ohm.

3. The package of claim 1 , wherein the container includes a container body and a cover connected to the container body; and wherein portions of the leads protrude from the between the cover and the container body.

4. The package of claim 3, wherein the leads are rigid metal rods with bends in them.

5. The package of claim 1 , wherein the resistor is above the particulate weld metal material.

6. The package of claim 1.wherein the resistor is at least partially in the weld metal material.

7. The package of claim 1.wherein the particulate weld metal material includes a mixture of a reductant metal and a transition metal oxide.

8. The package of claim 1 , wherein the resistor contains metal particles.

9. The package of claim 8, wherein the metal particles include at least one of copper particles or aluminum particles.

10. A welding apparatus comprising: a graphite mold; a particulate weld metal material in a chamber of the mold; and an igniter at least partially within the mold; wherein the igniter includes: a resistor above or at least partially within the weld metal material; and conductive leads electrically coupled to the resistor.

11. The welding apparatus of claim 10, wherein the resistor and the weld metal material are enclosed in a container; and wherein portions of the leads protrude from the container.

12. The welding apparatus of claim 11 , wherein the leads are rigid, bent metal rods.

13. The welding apparatus of claim 10, wherein the weld metal material includes a mixture of a reductant metal and a transition metal oxide.

14. The welding apparatus of claim 10, wherein the resistor is fully within the weld metal material.

15. The package of claim 10, wherein the resistor contains metal particles.

16. The package of claim 15, wherein the metal particles include at least one of copper particles or aluminum particles.

17. A method of joining metal pieces, the method comprising: electrically overloading a resistor of an igniter, causing the resistor break apart, sending out hot material of the resistor to initiate an exothermic reaction in particulate weld metal material to produce molten metal; and directing the molten metal into contact with ends of the metal pieces.

18. The method of claim 17, wherein the electrically overloading the resistor includes electrically overloading the resistor while the resistor is at least partially in the weld metal material.

19. The method of claim 18, wherein the electrically overloading the resistor includes electrically overloading the resistor while the resistor is fully in the weld metal material.

20. The method of claim 17, wherein the electrically overloading the resistor includes electrically overloading the resistor while the resistor above the weld metal material.

21. The method of claim 17, wherein the directing includes directing the molten metal includes directing the molten metal into a chamber of a graphite mold where the ends of the metal pieces are located.

22. The method of claim 17, wherein the electrically overloading the resistor includes electrically overloading a resistor in an upper chamber of a graphite mold; and wherein the directing the molten metal includes directing the molten into a lower chamber of the graphite mold.

23. The method of claim 17, wherein the electrically overloading occurs while the resistor and the particulate weld metal material are in a package.

24. The method of claim 17, wherein the electrically overloading includes activating an electrical unit that is coupled to conductive leads of the igniter that are in turn electrically connected to the resistor.

25. The method of claim 24, wherein the conductive leads are rigid metal rods.

26. The method of claim 17, wherein the electrically overloading the resistor includes exploding the resistor.

27. The method of claim 17, wherein the electrically overloading the resistor includes spewing the hot material from the resistor.