Patent Publication Number: US-6703578-B2

Title: Exothermic reactions and methods

Description:
This is a continuation of U.S. application Ser. No. 08/846,285, filed Apr. 30, 1997, now U.S. Pat. No. 6,553,911 which is incorporated herein by reference in its entirety. 
    
    
     DISCLOSURE 
     This invention relates generally to Exothermic Reactions and methods, and more particularly to apparatus and methods for initiating self propagating exothermic reactions. 
     BACKGROUND OF THE INVENTION 
     Examples of self propagating exothermic reactions are found in the CADWELD® process and the Thermit® process. CADWELD® is a trademark of Erico International, Inc., Solon, Ohio, U.S.A., and Thermit®) is a trademark of Th. Goldschmidt AG, Essex, Germany. Exothermic 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 supplies 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 molten copper has a higher density than the slag and is usually directed by a mold to join or weld copper to copper or steel to steel. The aluminum oxide slag is removed from the weld or joint 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 fuze brazing material, for example. 
     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. Once the reaction has begun it becomes self sustaining and requires no further energy to proceed to completion. There are numerous combinations of reductant metals and transition metal oxides that can react exothermically. These reactions and the energy required to initiate these reactions vary greatly depending on the properties of the reactants and the localized conditions. Two common mixtures are combinations of copper oxide and aluminum, and iron oxide and aluminum. This invention is concerned with the initiation of exothermic reactions, and apparatus or packaging for utilizing such reactions. 
     Currently the most common way of making welds or joints with the CADWELD® process involves the use of split graphite molds. The conductors or items to be joined are thoroughly cleaned and then placed in the appropriate location to project into a weld chamber in the graphite mold. The molds may include a crucible above the weld chamber connected to the weld chamber by a tap hole. 
     The mold is then securely closed and locked usually with a toggle clamp, and a metal disk is positioned in the crucible over the tap hole. An appropriate amount of exothermic material is emptied into the crucible on top of the disk, and the traditional starting powder or material, which is essentially a much finer exothermic material, is sprinkled over the top of the welding material. The mold cover is then closed and the reaction initiated through the use of a flint ignitor. 
     The starting powder or material sprinkled on top of the exothermic material has a lower ignition temperature and is easily ignited by the flint gun while the flint gun cannot normally ignite the exothermic material directly. When the exothermic material is ignited, the molten metal phase separates from the slag and melts through the metal disk. The molten metal then is directed via the tap hole to the weld chamber and the conductors to be joined. Once the metal has solidified the mold is opened and the slag is separated from the weld joint. The mold is cleaned and readied for reuse for the next connection. 
     Because of the starting powder&#39;s low ignition temperature and deficiencies 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 ignitors. Such efforts pre seen, for example, in prior U.S. Pat. Nos. 4,881,677, 4,879,952, 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. 
     The packaging of the system is also important. Many such applications are performed outdoors or in the field, and portability and ease of use is important. For example, no one wants to carry around a car battery to use as an ignition system. Also, the system should be capable of use with few light weight, easily used and cleaned or preferably disposable components. 
     An ignition system for such materials should be able to produce about thirty (30) joules of energy. The system should require no special shipment classification or labeling which is now required in some jurisdictions with certain starting powders or materials. The system components should be user friendly to the point of being easily carried and operable with only one hand. The system should be readily transportable to difficult working ares or confined or cramped spaces. The system components should weigh less than 1.5 kgs or about the weight of a partially full attache case. As important, the ignition must be reliable and repeatable without requiring frequent new batteries or a frequent recharge, and must be economic to make and use. 
     It would also be advantageous if the ignition system did not use wires or projecting wires to which a power source needs to be connected. Power may be connected to such wires by allegator clips, for example, one for each wire. The wires tend to get bent, dislodge, catch on things, or broken off and may easily short. Many times lack of reliability is simply a faulty clip or clip connection, and this usually requires some probing or testing or repositioning of the clips or wires before the problem is even located. It would be desirable if no wires were used and a proper connection could be made with a single clip. 
     SUMMARY OF THE INVENTION 
     The exothermic materials reaction initiation system includes a power source for producing a voltage spike or surge and an ignitor comprising two strips of metal foil separated by a layer of insulation. The ignitor includes one or more strategically shaped and placed distortions in the form of one or more punched holes. It has been discovered that a relatively low voltage spike applied to the foil strips will create a spark plasma of sufficient shape and projection to ignite substantially adjacent exothermic mixture and have the reaction propagate to completion. The hole is formed by a small conical tip punch. The conical tip shapes the hole like a horn and the through opening at the small end of the horn acts as a vent. 
     The power source may be a battery powered capacitor discharge unit which will create the voltage to be delivered to the metal foil strips by two electrodes forming the opposite gripping surfaces of a spring clothespin type clip which is simply clamped on a projecting end of the metal foil strip with one foil strip in contact with one electrode. This maintains the required polarization. The battery or batteries may be relatively small, easily replaced, and rechargeable. The capacitor discharge unit need only create a voltage for about thirty (30) joules for most applications, and this is sufficient to create the shaped and vented spark plasma at the disruption or hole. 
     The ignitor unit is preferably thin strips of conductive foil which are separated by a thin layer of paper insulation adhered to the foil with thin layers of adhesive so that the layers do not readily separate and no air gaps or bubbles occur. Preferably the insulation extends beyond the foil, particularly at the ends so that no spark-overs occur at the edges or at a location other than at the strategically positioned disruption. The adhesive may be conductive to enhance current flow through the metal foil. The entire assembly including the conductive foil, the adhesive and the insulation may be only a few mils in thickness, and the strip assembly may be bent, folded or even twisted to some degree without damage to its integrity and purpose. 
     The selection of the metal or type of foil depends to some degree on the application. Since the shaped and vented plasma creating spark discharge at the disruption involves some controlled metal splatter and fusion of the foil, and since the ignitor in some applications will be consumed or partially consumed by the reaction, it is important that the metal of the foil be compatible with the reaction. Thus for copper welding, copper would be a suitable foil material. The paper and adhesive are also selected so as not to contaminate the exothermic process. 
     Although the ignitor assembly has many applications in connection with reusable crucibles and molds designed to contain and direct the reaction and the products of the reaction, a preferred form is built into a self contained and expendable package of exothermic material. The package may be positioned on a reusable or expendable mold, and the ignitor assembly may be unfolded or bent to extend or project from the package. The ignitor is connected to the power source, and the reaction initiated. A disk in the bottom of the package is fused by the reaction, and the molten metal formed runs into a reusable or expendable mold. The power source is then disconnected and the package discarded when cooled. 
     In some embodiments, the ignitor may include two or more holes or spark plasma creating disruptions. If the holes are of the same size, they will fire essentially concurrently. Such ignitors may be used for large volumes of exothermic materials to obtain multiple point ignition. If the holes vary in size, sequential ignition can be obtained. Multiple hole ignitors may also be used for larger charges or redundancy. 
     In addition to the ignitor and methods of making the ignitor, the invention also relates to the methods of ignition disclosed, as well as the applications and packages for utilizing the ignitor, all of which economically eliminate the use of the starting powder and materials, and the flint gun ignitor. 
     To the accomplishment of the foregoing and related ends, the invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of the power source and ignitor assembly; 
     FIG. 2 is a schematic illustration of the metal foil strips of the ignitor being assembled with the insulation therebetween; 
     FIG. 3 is a schematic illustration of the ignitor assembled but prior to the punching and shaping of the hole; 
     FIG. 4 is a schematic edge elevation illustration showing the conical tip punch about to enter the ignitor; 
     FIG. 5 is a similar schematic illustration showing the punch forming the hole; 
     FIG. 6 is a similar schematic illustration showing the shaped hole formed; 
     FIG. 7 is a schematic illustration of an ignitor with the hole more centrally positioned; 
     FIG. 8 is a schematic illustration of the fusion which takes place around the hole in an intermediate phase of the ignition; 
     FIG. 9 is a schematic illustration of the spark plasma energy created showing the conical shape of the energy plasma on one side and the venting plasma on the other; 
     FIG. 10 is another somewhat larger view showing the shape of the spark plasma, the venting plasma and the fusion taking place, all immersed in an exothermic reaction mixture; 
     FIG. 11 is an exploded view of the ignitor assembly of the present invention extending diametrically through a disposable container or crucible to be positioned on a reusable mold; 
     FIG. 12 is a section through the assembly of FIG. 11; 
     FIG. 13 is a view of the ignitor extending through the wall of a reusable mold and crucible; 
     FIG. 14 illustrates the ignitor positioned beneath a hinged lid of a reusable mold and crucible; 
     FIG. 15 illustrates the ignitor positioned between a lid of the type used with one or more fume and particle collecting filters; 
     FIG. 16 illustrates the ignitor used with a disposable mold and crucible; 
     FIG. 17 is a perspective view of a squib-like container of exothermic material with the ignitor extending through the end; 
     FIG. 18 is a diametric section of the container of FIG. 17; 
     FIG. 19 is an illustration of a smaller shaped squib being used to ignite a larger reaction; 
     FIG. 20 is a view of an expendable package but with the ignitor not immersed in the exothermic material but being generally parallel to the top or lid and the spark plasma generating hole being substantially adjacent the top surface of the material; 
     FIG. 21 is a sectional view of another type of expendable package used with another type of disposable mold; 
     FIG. 22 is an illustration of a large crucible with three ignitors positioned above and substantially adjacent the top surface of the exothermic material; 
     FIG. 23 is an illustration like FIG. 22 but showing a single ignitor with plural holes; 
     FIG. 24 is a schematic illustration of a plural hole ingitor with holes of common size; 
     FIG. 25 is a similar schematic illustration of a plural hole ignitor with holes of ascending size; and 
     FIG. 26 is a schematic illustration of another form of ignitor which may also be used where redundancy is desired. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, there is illustrated generally at  30  a capacitor discharge unit for creating the voltage/joule surge or spike for firing the ignitor assembly  32  for the exothermic material. The capacitor discharge unit  30  includes one or more batteries  33  connected to an inverter or oscillator  34  which converts the DC current of the batteries to a high frequency AC current. The output of the inverter then passes through a step-up transformer  35  which steps-up the voltage. The higher voltage AC current is then passed through a rectifier  36  which may be full wave or half wave to convert the AC current back to DC current. The DC current then charges the capacitor  37 . When a switch  38  is closed, a voltage surge or spike is created between the leads  39  and  40 . The switch  38  may be a mechanical or solid state switch, and if the latter, the switch may closed by gate firing circuit  41 . The leads  39  and  40  shown schematically are connected to half-round projecting electrodes  43  and  44 , respectively, extending transversely on the interior of the jaws of a spring-loaded clothespin or alligator clip shown generally at  46 . 
     Referring now additionally to FIGS. 2-6, it will be seen that the ignitor assembly  32  comprises two conductive metal foil strips  50  and  51  separated by a layer of insulation  52 . The method of making the ignitor is sequentially illustrated in FIGS. 2-5. Since the ignitor is normally going to be consumed in the exothermic reaction, it is important to select materials for the ignitor which are compatible with the exothermic reaction materials. In the CADWELD process where copper conductors are being welded, the preferred metal foil material is copper. The preferred insulating material may be paper, and the entire thickness of the assembly may be only a few mils. It will be appreciate, however, that for other applications other metals or conductive foils may be employed together with other insulating strips. 
     Thin layer of paper insulation serves two purposes. It provides an insulating barrier between the two strips of copper foil and also provides a deflective barrier for both heat and energy once the ignitor is fired or the reaction initiated. The outer foil layers  50  and  51  are joined to the intermediate insulating layer of thin paper by a minimal amount of conductive adhesive which may be placed on the interior of the copper foil strips. The adhesive enables the copper strips to be firmly attached to the paper while eliminating air gaps, and the conductive nature of the adhesive enhances current flow lengthwise of the metal foil strip. The foil layers and the insulation may be passed through the nip of rolls, for example, to ensure the proper adhesion and elimination of air gaps as seen in FIG.  2 . When the layers of the ignitor are assembled as seen in FIG. 3, the insulation  52  preferably projects slightly beyond the ends of the foil strips, such projections being shown at  55  and  56 . The projections are shown somewhat exaggerated in the schematic illustrations and may be only a small fraction of an inch or a few millimeters. 
     Once the ignitor is assembled as seen in FIG. 3, a disruption is formed in the ignitor to provide a source of energy discharge. This disruption is in the form of a conical hole which is formed by punch  58  having a relatively sharp conical tip  59 . 
     As seen in FIG. 5, the punch enters the strip and the tip  59  projects through the strip assembly to project slightly from the other side as seen at  60 . As seen in FIG. 6, when the punch is withdrawn, there is formed a hole  62  in the strip ignitor which has the conical configuration of the punch. The hole on one side has a large end  63  and on the other side has a small or vent end  64 . The hole passes completely through the strip assembly, and the hole formed is shaped like a horn flaring to the large end  63 . 
     The hole may be located at any desired point along the strip, and in the form seen in FIG. 6 is located at one end. In FIGS. 7,  8  and  9 , the hole shown at  66  is located in the center of the strip end-to-end and midway between the lateral or side edges. Also, as hereinafter described, more than one hole may be employed, and the size of the hole may vary. The hole illustrated is not to scale, and the diameter of the large end of the hole may vary from a fraction of a millimeter to about 2 millimeters. The cone angle may also vary from that illustrated to obtain the conical or horn configuration which provides a shaped spark plasma. Being a punched perforation, the hole has characteristics of punching which distorts the linear nature of the assembly providing slightly folded or jagged edges and an attenuated insulation at the hole. 
     When the reaction is to be initiated and the ignitor strip assembly  32  fired, it is connected to the capacitor discharge unit  34  simply by clamping the clip  46  on the projecting end of the ignitor assembly. Upon release of the capacitor energy, the initiation of the exothermic reaction occurs within milliseconds. Although the precise mechanics of the phenomena are not known, it is believed that the phenomena may be expressed by the following sequence of events, and as particularly illustrated in FIGS. 7,  8 ,  9  and  10 . 
     In the ignition sequence, the energy is released from the capacitor and into the two copper strips  50  and  51 , each receiving one pole of the discharge, i.e. one negative and one positive. 
     The conical hole  66  through the foil and paper strip assembly acts as a disruption or a point of resistance and begins to heat rapidly; so rapidly, that there is essentially no time for the heat to dissipate to the surrounding materials. Eventually enough heat is available to cause a rapid melting of the entire thin 360° edge of the foil at the edge of the conical hole. This occurs according to I 2 R where I is the current push and R is the resistance. The molten edge in the intermediate phase as seen at  68  in FIGS. 8 and 10 increases the resistance thereby increasing the speed of further heating. The melting of the copper occurs at 1083° C. 
     The phenomena occurs in such a short time that the molten phase is unable to move, and the continued heating forces the molten copper to vaporize. This occurs for copper at in excess of 2571° C. The gas phase increases the resistance in the localized area even further. 
     The vapor begins to expand but continues to draw current until it begins to draw an electric arc. The arc or spark plasma may obtain temperatures in excess of 5000° C. The electric arc-or spark forces the gas phase to a point of ionization which will begin to reduce the resistance very quickly which further increases the amount of current moving into the area. 
     The increase in current to the vapor region produces increased heating or super heat to the expanding vapor which forces the vapors to expand rapidly producing a resultant shock wave of spark plasma which is shown schematically as the top cone  70  in FIGS. 9 and 10. In such Figures, the ignitor is immersed in exothermic material which may be in the granular form illustrated at  72  on both sides of the ignitor. The conical shock wave, however, expands with reduced force due to the presence of the smaller or vent hole in the other or opposite side of the ignitor. This vent or smaller end of the hole produces a somewhat smaller spark plasma seen at  74  reducing the extent and force of the shock wave cone  70  thus reducing the disturbance of any surrounding or close-by exothermic material  72  prior to the initiation of the reaction. A force too extensive and too sudden may literally remove or blow away some types of exothermic material from the heat of the spark plasma. 
     The shock wave carries molten copper such as seen at  76  in FIG. 10 from the molten circumference  68  of the conical hole. The molten copper  76  spreads outwardly from the circumference of the conical hole while the vent hole provides the spark plasma  74  and the energy transfer in the opposite direction. The combination of the super heated vapor, the molten copper release in the shock wave, and the drawing of the electrical arc provide a substantial broadcast of energy and a multi-point ignition of the exothermic material  72 . 
     Referring now to FIGS. 11 and 12 there is illustrated a utilization of the ignitor of the present invention in exothermic welding apparatus such as the CADWELD process for welding bar or cable to each other, for example. The apparatus illustrated in FIGS. 11 and 12 comprises an expendable crucible or container  80  and a two part reusable mold shown generally at  81 . The mold assembly  81  is horizontally split as seen at  82  into upper and lower mold parts  83  and  84  made of a refractory material such as graphite. The parting faces have recesses which form sleeving passages  85  and  86  which lead to an enlarged weld chamber  87 . The mold assembly parts may be clamped together at the parting plane and opened by a suitable toggle clamp assembly, not shown. 
     The upper mold part  83  is provided with a recessed seat  89  axially aligned with a smaller and vertical tap hole  90  which communicates with the weld chamber  87 . The sleeving passages are adapted to receive cable or rod ends, which project into the welding chamber and which are to be welded together by the apparatus and process illustrated. 
     The expendable package  80  includes a correct amount of exothermic material seen at  92  in FIG.  12 . That exothermic material is supported on a metal disk  93  which closes hole  94  in the bottom of the package, and which hole is aligned with the tap hole  70  when the package is assembled with the mold. The expendable package is in the form of a refractory cylindrical container  95  and a lid or top  96  having a central vent hole  97 . The interior of the package provides a crucible chamber  99  which terminates in conical seats at the bottom, the lowermost of which supports the metal disk  93 . 
     Extending diametrically through the top of the generally cylindrical package or container is an ignitor assembly strip  32  which includes the shaped hole  62  in the upper center of the exothermic charge  92 . The ignitor assembly extends through vertical slits  101  and  102  in the wall of the package, and the end  103  projects substantially beyond the outside of the package. The upper level of the exothermic charge seen at  104  is above the ignitor strip  32  so that the hole  62  is immersed in the upper portion of the exothermic material. The expendable package  80  of FIGS. 11 and 12 contains the precise amount of exothermic material, and the components of the package may be formed from a variety of refractory materials such as a fired ceramic, molded sand, or glass, for example. The package after use is disposable. The container may be formed with the ignitor assembly in place, filled with the requisite amount of exothermic material and then closed by the lid  96  to form the completed package. The extended end  103  of the ignitor may simply be folded flat against the wall of the package and the entire assembly wrapped. 
     When in use, the package is simply unwrapped and placed in the seat  89 , and the ignitor end  103  caused to project radially as shown. The clip  46  of FIG. 1 is then attached to the projecting end  103 . When the exothermic reaction is initiated, it will start at the top of the charge of the material and move downwardly fusing the disk  93  to permit the molten metal formed to run into the weld metal chamber  87  welding the end of the cables or rods together. Any slag formed by the reaction rises to the top and may be removed from the weld. When the package cools, the package is simply discarded, and the mold parts  83  and  84  are opened for removal of the welded cable or rods. The mold parts are cleaned for reuse with another disposable package. 
     In the embodiment of FIG. 12, the ignitor extends diametrically completely through the charge of exothermic material and is immersed therein. There are, however, a number of ways in which the ignitor may be positioned with respect to the exothermic material contained in the crucible, whether it be a disposable package or a reusable mold. 
     Referring now to FIGS. 13 through 15 there is illustrated a number of ways in which the ignitor may be mounted with respect to the exothermic material contained in a crucible which forms part of a reusable mold. In FIGS. 13 through 15 the molds are vertically split, and each half of the mold contains the cavity and passage pattern illustrated in the form of generally semi-circular recesses. When the mold halves are clamped together, the complete mold assembly is formed. Each mold assembly includes a weld chamber  106 , sleeving passages  107  and  108 , a riser chamber  109  on top of the weld chamber, a tap hole  110  communicating with the bottom of crucible  111  and the riser or weld chamber, the latter including the conical seat at the bottom for the metal disk  112  closing the bottom of the crucible at the tap hole containing the charge of exothermic material  114 . In FIGS. 13 and 14, the top of the assembly is provided with a hinged refractory lid  116 . 
     In FIG. 13, the ignitor assembly shown generally at  32  extends through one wall only of the crucible chamber and through an insulator indicated at  118  which may be made of paper. The ignitor has a projecting end  119  extending from the exterior of the insulator and the hole or disruption  62  is below the level  120  of the exothermic material  114 . The ignition hole is nonetheless in the top center portion of the charge of exothermic material. 
     In FIG. 14, the ignitor  32  extends through insulator  122  which may be paper on the rim of the crucible beneath the hinged lid  116 . The ignitor assembly projects beyond the insulator as seen at  123  and is twisted at  124  so that the disruption or hole  62  is below the surface  120  of the exothermic material. In this embodiment, the ignitor assembly has at the projection as major horizontal plane rather than a vertical plane as seen in FIG.  13 . The ingitor strip assembly is, however, twisted so that at the hole or disruption  62  the major plane extends vertically. 
     In the reusable mold of FIG. 15, a lid  128  telescopes over the assembly and supports one or more filters  129  adapted to contain any fumes or other unwanted byproducts of the exothermic reaction. The charge of exothermic material  114  may nonetheless be ignited by the ignitor  32  extending through an insulator  131  between the filter containing lid  128  and the top rim of the crucible. The insulator  131  is stepped to provide the zigzag configuration shown to fit between the mold and lid. The ignitor may readily be bent to fit through the insulator and includes the projecting horizontal portion  132  and a twisted section  133  inside the insulator which enables the inner end to project downwardly in a different plane so that the hole or disruption  62  is below the level  120  of the exothermic charge. Fume containing filter units are sold by Erico International Corporation of Solon, Ohio, under the registered trademark EXOLON® which enables exothermic welding to be performed in sensitive or clean environments. 
     In any event, the ignitor of the present invention may readily be adapted to extend through the walls of reusable molds or between the lids and rims of the crucibles, and the insulators or packings illustrated not only readily support the ignition assemblies either projecting through the wall as seen in FIG. 13, or to be twisted to project from the rim down into the exothermic material. In each instance, the ignition is obtained by simply fastening the clip  46  to the projecting ends  119 ,  123  or  132 . 
     As illustrated in FIG. 16, the ignition assembly  32  projects through the wall  138  of a disposable or expendable mold  139 . The mold body may be made of a refractory material such as a ceramic, a bonded sand, or glass, for example, and includes an interior upper crucible chamber  140  and a lower weld chamber  141  with a shoulder  142  between such chambers supporting a metal disk  143  containing a charge  144  of exothermic material in the crucible chamber. The expendable mold is provided with a lid  146 . The bottom of the mold is provided with a keyhole sleeving passage  148 . The passage may accommodate the top of a rod  149  and a cable  150  to be welded thereto. 
     The ignitor assembly may be installed in the expendable mold during the forming process, or it may be -inserted subsequently through a formed slit. The interior of the ignitor assembly has the hole or disruption  62  positioned centrally in the upper center section of the exothermic charge, and the outer end of the ignitor assembly projects radially as indicated at  152 . For packaging and shipping, the ignitor may be folded or bent along the dotted line indicated at  153  to lie flush against the exterior of the wall of the mold. The ignitor may readily be bent without compromising its integrity. When the package is opened, the ignitor can simply be rebent to project in the manner illustrated. The package is positioned on the rod and cable, and the clip  46  is clamped to the projecting end of the ignitor assembly. The capacitor discharge unit when fired then ignites the exothermic material by causing the spark plasma ignition described above. The ignition of the exothermic material fuses the disk  143 , and the molten metal formed drops into the weld cavity to weld the two parts together. After the weld, the mold may be left in place or simply knocked off with a hammer. 
     The ignitor of the present invention may also be used with what is commonly called a squib. Squibs are sometimes referred to as small charges of exothermic material which are in turn used to ignite larger charges. The squib may shower molten metal spray on the surface of the larger exothermic charge which is sufficient to initiate the main exothermic reaction. One such squib is shown in FIGS. 17 and 18 at  160 . 
     The squib  16  comprises a disposable refractory cup-shaped container  161  which includes a cylindrical wall  162  and an end wall  163 . The container contains a charge  164  of exothermic material, and the rim or open end of the cup is closed by a thin metal foil cap  165 . The ignitor assembly  32  projects through the end wall  163 , and the hole or disruption  62  is embedded in the charge of exothermic material. The free or connection end  167  simply projects axially from the container through the wall  163 , and the clip  46  may readily be connected to the projecting end  167 . When the exothermic material is ignited, it will quickly burn through the cap  165  spewing or broadcasting molten metal and other products or the reaction which may then in turn be used to ignite a larger charge of exothermic material. 
     In FIG. 19 there is a larger charge of exothermic material seen at  170  contained in larger crucible  171 . A squib ignitor for such charge is shown generally at  172  and comprises a smaller charge of exothermic material in a shaped consumable container  174 , the bottom of which is closed by a thin metal foil cap  175 . The ignitor assembly  32  projects through the wall of the consumable container with the hole or disruption  62  being within the container. The projecting end  177  enables the capacitor discharge unit readily to be connected thereto with the clip  46 . When ignited, the contents of the shaped squid fuses the cap  175  and literally showers the top surface of the main quantity of exothermic material  170  with a super heated molten metal shower as indicated at  178 . This in turn ignites the larger quantity of exothermic material. 
     In FIG. 20 there is illustrated a charge of exothermic material indicated at  180  within an expendable crucible or container  181  supported on consumable disk  182 . The upper level of the charge  180  is at  183 . The ignitor assembly  32  for the exothermic material  180  is positioned principally in a horizontal plane and is folded in a zig-zag fashion seen at  185  and  186  to fit over the rim of the container and beneath the lid  187 . The ignitor is thin enough to be folded in the manner indicated without compromising either the ignitor or the connection between the container and its lid. The central portion of the ignitor may be bowed slightly downwardly as seen at  189  to position the hole  62  slightly above the level  183  and in the center of the charge. It is noted that the large end of the hole  62  is directed downwardly and is closely above or substantially adjacent and almost contiguous with to the top level  183  of the exothermic charge. The ignitor end  190  projects beyond the container to enable the capacitor discharge unit to be connected thereto. The spark plasma characteristics of the spark plasma discharge are sufficient to ignite the exothermic material even though the hole or disruption is not immersed in the material. 
     In FIG. 21 there is illustrated a disposable refractory container  192  which includes inclined metal guide sleeves  193  and  194  projecting into a weld chamber  195 . The sleeves enable cabling or rod of different sizes to be inserted for welding without regard to molten metal sealing. The top of the expendable mold includes an annular rim  196 , and the expendable container  197  is positioned on such rim. The container  197  is generally similar to the container  80  seen in FIG. 12, but includes a bottom annular spout or nozzle  198  adapted to project into the top of the mold  192 . An annular shoulder  199  surrounds the nozzle enabling the container  197  to be positioned on the mold as illustrated. Like the container  80 , the ignitor assembly  32  extends diametrically through the wall of the container and the hole or disruption  62  is positioned within the charge of exothermic material at the upper center. 
     Referring now to FIG. 22 there is illustrated a large crucible  171  containing a large charge of exothermic material  170 . The ignitor assembly shown generally at  200  includes three ignitor strip assemblies  201 ,  202  and  203  projecting through the wall  204  of the mold. The end of each assembly is provided with a hole or disruption as seen at  205 ,  206  and  207 , respectively. The ignitor strip assemblies are interconnected by a bus section  209  which has a projecting stem  210  to which the capacitor discharge unit may be connected. The disruptions or holes may be positioned substantially adjacent the top surface of the material or may be immersed in the material. If on top of the material, the large ends of the holes are facing downwardly. In any event, the ignitor of FIG. 22 provides a multi-point substantially concurrent ignition for the larger charge of exothermic material. 
     In FIGS. 23 and 24 there is illustrated another multi-point ignitor assembly  212 . The ignitor assembly  212  extends through opposite walls  213  and  214  of crucible  171  and projects from both as indicated at  215  and  216 , respectively. The ignitor is provided with three holes or disruptions  218 ,  219  and  220 , which are of the same size, and which are equally spaced from each other. In the embodiment of FIG. 23, the large end of the holes faces downwardly or towards the charge of exothermic material. The capacitor discharge unit attached to either projecting end of the ignitor assembly will provide three points substantially concurrent ignition for the exothermic charge  170 . 
     With additional reference to FIG. 24, it will be seen that by strategically placing more than one hole on the ignitor body, and by making the holes all have substantially identical characteristics including shape and size, sufficient energy can be applied to insure that each hole or site acts as a shaped spark plasma charge firing essentially simultaneously. However, with multiple point ignition such as illustrated in FIGS. 23 and 24, higher levels of energy are required since each site or hole utilizes an equal fraction of the energy. 
     In FIG. 25 there is illustrated an ignitor assembly  225  having three different sites or holes  226 ,  227  and  228 , which holes are not of the same size and characteristics. An ignitor such as seen in FIG. 25 may be utilized to provide a reliability factor. Thus, if the hole sizes and shapes differ, then the electrical resistance at each site or hole determines which site will draw the energy necessary for initiation. With the clip attached at the end  230 , the smaller hole site would normally fire first. The other shape charges or sites on the ignitor will remain intact without any energy discharge occurring. Therefore, the ignitor acts normally as a single site ignitor. However, if the discharge fails to ignite the exothermic material such as by disturbing the material as indicated above, the site which has discharged is sufficiently destroyed, and any contact between the two copper foils is eliminated. This site then is not capable of discharging a second time. However, the remaining sites are still intact and capable of discharge. The recharging of the capacitor and releasing the current into the ignitor assembly a second time will result in another site on the same ignitor discharging. Once again, the amount of resistance at each site determines which site discharges next. The sequence can continue until the ignitor is sufficiently destroyed or the exothermic reaction is initiated. 
     With reference to FIG. 26, there is illustrated another form of ignitor assembly shown at  232  which includes two holes seen at  233  and  234 . The holes  233  and  234  may have identical characteristics and shape. However, the foil layer facing the viewer is provided with a gap seen at  235 . The clip  46  of the capacitor discharge unit may be positioned on either end  237  or  238  to obtain discharge at the hole site. If the discharge at one hole fails to ignite the exothermic material, the clip is simply placed on the other end of the strip assembly, and the capacitor discharge refired. 
     It can now be seen that there is provided a low cost foil strip ignitor assembly for exothermic material with wide application to exothermic welding, casting and other uses. The ignitor may be part of reusable crucibles and molds, or expendable packages, containers and molds, or used in smaller squibs for igniting larger charges. The ignitor may be immersed in or substantially adjacent a charge of exothermic material. The ignitor eliminates the need for starting powders or materials and flint gun ignitors. 
     To the accomplishment of the foregoing and related ends, the invention then comprises the features particularly pointed out in the claims, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.