Abstract:
An exothermic cord, foil, or ribbon is produced by first cold drawing individual round wires of the constituent materials under a cover gas. The cold drawing operation yields a clean surface that is free of oxidation and other contaminants. Next, the constituent wires are brought together and twisted, cold drawn, swaged, and/or friction welded to create a unitary cord exhibiting intimate contact between the constituent materials. The unitary cord may then be used directly or further shaped to a desired form and/or thickness. By controlling the size ratio between the cross-sections of the constituents, a degree of control can be exercised over the exothermic reaction characteristics. The unitary cord, once formed, can be coated with braze and/or flux materials to aid in a subsequent joining operation. Multiple cords can be woven together to form a cloth structure. The exothermic assembly can be applied in the field of gaskets to permanently affix opposing surfaces together, such as affixing a cylinder head in an operative position over a cylinder block.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This invention claims priority to U.S. Provisional Application No. 60/667,999 filed Apr. 4, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to an improved method of forming exothermic materials for various applications, and for use of exothermic material to permanently seal a cylinder head to a block in an internal combustion engine.  
         [0004]     2. Related Art  
         [0005]     Reactive multilayer foils and coatings are used in a wide variety of applications requiring the generation of intense, controlled amounts of heat in a planar region. Such structures conventionally comprise a succession of substrate-supported layers that, upon appropriate excitation, undergo an exothermic chemical reaction that spreads across the area covered by the layers and thus generate precisely controlled amounts of heat. Such exothermic chemical materials are particularly useful as sources of heat for specialized welding, soldering, and brazing operations. However, they can also be used in other applications requiring controlled local generation of heat, such as primers for incendiary devices.  
         [0006]     Reactive multilayer materials permit exothermic reactions with controlled and consistent heat generation. The basic driving force behind such reactions is a reduction in atomic bond energy. When the reactive materials are ignited, the distinct layers mix atomically, generating heat locally. This heat ignites adjacent regions of the structure, thereby permitting the reaction to travel the entire length of the structure, generating heat until all the material is reacted.  
         [0007]     In addition to reactive coatings, efforts have been made to develop free-standing reactive layers by cold rolling. Nickel-Aluminum multilayer reactive foils have been formed by cold-rolling bi-layer sheets of Ni and Al, followed by repeated manual folding and repeated cold rolling. After the first bi-layer strip is rolled to half its original thickness, it is folded once again to regain its original thickness and to double the number of layers. This process is repeated many times.  
         [0008]     The fabrication of rolled foils is time consuming and difficult. The rolling passes introduce lubricating oil and other contaminants, such that the surfaces of the rolled materials must be cleaned after every pass. In addition, the manual folding of sheet stock does not easily lend itself to large-scaled production. When many metal layers are rolled at once, these layers can spring back, causing separation of the layers and degradation of the resulting foil. Such separations also permit undesirable oxidation of interlayer surfaces and impedes unification of the layers by cold welding.  
         [0009]     Accordingly, there is a need for improved methods of fabricating reactive multilayer structures, particularly for large-scale production applications.  
       SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0010]     The invention comprises a method for producing a multi-stranded exothermic assembly of the type for propagating an exothermic reaction between the strands in response to an initial thermal impulse. The method comprises the steps of providing elongated first and second wires of respective constituent metallic materials each having a generally round cross-section, cold drawing the first and second wires through respective reduction dies in a non-oxidizing atmosphere, bringing the first and second wires into contact with one another in a non-oxidizing atmosphere, and simultaneously plastically deforming the first and second wires together into a unitary cord so that the surfaces of the first and second wires are pressed into contact to facilitate a sustained propagating exothermic reaction in response to an initiating thermal impulse.  
         [0011]     According to another aspect of this invention, a one-time use gasket is provided of the type for sealing a cylinder head to a cylinder block in an internal combustion engine. The one-time use gasket comprises a sheet-like body, at least one cylinder bore opening formed in the body, and at least one fluid flow passage formed in the body. The fluid passage is isolated from the cylinder bore opening. The body is fabricated from a reactive multi-stranded exothermic assembly of the type for propagating an exothermic reaction in response to an initiating thermal impulse. The heat produced during the exothermic reaction is sufficient to metallurgically fuse the cylinder head to the cylinder block while maintaining fluidic isolation between the cylinder bore opening and the fluid flow passage.  
         [0012]     According to yet another aspect of this invention, a method for establishing a fluid-tight seal between opposing surfaces having formed therebetween at least two discrete flow passages, is provided. The method comprises the steps of forming a gasket from a reactive multi-stranded exothermic assembly of the type for propagating an exothermic reaction in response to an initiating thermal impulse, forming at least two spaced and isolated flow passages in the gasket for conducting fluid material between the two opposing surfaces, aligning the openings in the gasket with the flow passages in the opposing surfaces, compressing the gasket between the opposing surfaces, initiating a propagating exothermic reaction in the gasket body, melting the opposing surfaces in response to the heat generated during the exothermic reaction, and metallurgically fusing the opposing surfaces together while permitting fluid exchange between the isolated flow passages.  
         [0013]     The subject invention, as expressed through these various methods and apparatus, provides an exothermic cord, foil, ribbon or cloth produced in a manner that is particularly conducive for large-scale production applications. Utilizing commercially available wire products, the subject intention allows an exothermic assembly to be produced at lower cost as compared with prior art exothermic foils and the like. The subject methods enable substantially faster throughput of finished product. By controlling the size ratio between the cross-sections of the constituents, a degree of control can be exercised over the exothermic reaction characteristics and, therefore, tuned to particular applications. Accordingly, the subject invention provides a lower cost, higher production rate technique for creating reactive multi-layer assemblies for use in any of the known applications, including welding, soldering, brazing, and as primers for incendiary devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These and other features and advantages and applications of the present invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0015]      FIG. 1  is a simplified cross-sectional view of a prior art internal combustion engine having a traditional gasket positioned in the interface between the cylinder head and cylinder block;  
         [0016]      FIG. 2  is a cross-sectional view as in  FIG. 1 , but showing an exothermic gasket assembly disposed in the region once occupied by the prior art gasket in preparation for an exothermic reaction which will result in permanent attachment of the cylinder head to the cylinder block;  
         [0017]      FIG. 3  is a view as in  FIG. 2 , but showing the cylinder head permanently affixed to the cylinder block following the exothermic reaction;  
         [0018]      FIG. 4  is a simplified schematic view showing the formation of the subject exothermic assembly in a cold-drawing operation on bulk wires;  
         [0019]      FIG. 5  is a cross-sectional view of a single wire taken generally along lines  5 - 5  of  FIG. 4 ;  
         [0020]      FIG. 5A  is a cross-sectional view of an alternative cross-section of a single wire, with representative bundled wires shown in phantom;  
         [0021]      FIG. 6  is a cross-section of the cord taken along lines  6 - 6  of  FIG. 4 ;  
         [0022]      FIG. 7  is an end view of a completed exothermic ribbon as taken along lines  7 - 7  of  FIG. 4 ;  
         [0023]      FIGS. 8A and 8B  are simplified views showing an exothermic assembly disposed between two substrates in the sequence of before and then during a welding or joining operation;  
         [0024]      FIG. 9  is a simplified schematic view as in  FIG. 4  but showing an optional application of a braze or other coating material applied to the cord and beneficial in a later joining application;  
         [0025]      FIG. 10  is a schematic view as in  FIG. 4  yet showing another method of tightly bundling the wires through a twisting operation to form the exothermic cord;  
         [0026]      FIG. 11  is yet another alternative method of tightly packing the wires by rotary swaging;  
         [0027]      FIG. 12  is an illustrative cross-sectional view of the swaging die taken generally along lines  12 - 12  of  FIG. 11 ; and  
         [0028]      FIG. 13  is still another alternative method of tightly combining the wires using an ultrasonic friction welding technique.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a prior art engine assembly is shown in  FIG. 1  including a cylinder head  10  affixed to a cylinder block  12  via head bolts  14 . A gasket  16  is disposed between the head  10  and block  12 , clamped under pressure from the head bolts  14 . The gasket  16  seals the internal pressure and fluids cycling within the cylinder bore to prevent leakage and maximize combustion efficiency.  
         [0030]     In some engine applications, it may be desirable to permanently seal the cylinder head  10  to the cylinder block  12  without the aid of a gasket  16 . Reminiscent of prior art fixed head engines, in which the cylinder head and cylinder block form one inseparable unit, an engine assembly thus formed has the advantage of eliminating the expense of a gasket  16  and its vulnerability as a leak path over time. However, sealing a cylinder head  10  to a cylinder block  12  without the aid of a gasket  16  is a very difficult undertaking because there are many flow passages  17  which must be sealed. For example, liquid coolant and liquid oil are routed in respective passages  17  between the cylinder head  10  and the cylinder block  12  for proper lubrication and cooling. There are also sometimes passages provided for valve train components. The cylinder bore itself can even be considered a flow passage If these passages are not independently sealed in isolation from one another, then the engine will leak fluids and there can be contamination between the various fluids and passages.  
         [0031]     The subject invention overcomes these issues in the manner shown in  FIGS. 2 and 3  in which an exothermic assembly, generally indicated at  18 , is strategically routed around all of the various passages, as well as the combustion chambers. The strategically routed exothermic assembly  18  can be in the form of a continuous, snake-like ribbon of material laid in a course, or formed into a sheet-like or cloth-like body member similar in appearance to modern gasket bodies. With the cylinder head  10  firmly held in compression as suggested by the force arrows, the exothermic assembly  18  is ignited to accomplish a weld of the cylinder head  10  to the cylinder block  12  and thus form a fully sealed, integral engine assembly without the use of a gasket  16 . Although  FIG. 2  does not show continued use of the head bolts  14 , it may be desirable to retain use of some or all of the head bolts  14  for added integrity.  
         [0032]     An energy source, such as the representative match  20  shown in  FIG. 2 , ignites an exposed wick portion  21  of the exothermic assembly  18 , thus initiating a propagating exothermic reaction between its interstitial layers. As an alternative to the match  20 , an electric sparking device, laser beam, or other device capable of producing the requisite thermal impulse can be used. Because the exothermic assembly  18  has such large interfacial areas between alternating layers of the constituent materials (typically Ni and Al), ignition from the flame source  20  causes the atoms or molecules of the constituent materials to rapidly mix and combine in a highly exothermic reaction. Once the heat is generated locally at the ignition point, it is conducted along the assembly  18  and initiates additional mixing, thereby sustaining the reaction. The speed at which the reaction front proceeds depends upon the physical properties of the constituent materials and how they are arranged. The reaction front causes atoms to diffuse normal to the layers themselves, with heat being conducted parallel to the layers.  
         [0033]     In addition to joining a cylinder head  10  to a block  12  using the exothermic assembly  18 , it is possible to permanently seal other components in an internal combustion engine using these techniques. For example, the engine exhaust ports can be permanently sealed to the exhaust manifold, the intake ports can be permanently sealed to the intake manifold, or any of the various covers or housings can be fixed in a permanently sealed condition. Anywhere a gasket has been used in the past, and even in non-automotive applications, the component parts can instead be permanently fixed and sealed using the exothermic assembly  18  and techniques here described.  
         [0034]     The exothermic assembly  18  thus applied to permanently seal engine components can be accomplished using prior art type exothermic materials. However, the invention also contemplates a novel technique for producing an exothermic assembly  18  using bulk wires of constituent materials, as shown in  FIG. 4 . As mentioned above, the constituent materials can be Ni and Al or alloys thereof, but other materials can be used as well, including titanium-aluminides and the like. In fact, any of the currently known and available materials used in reactive multilayer foil applications may be used in the context of this invention.  
         [0035]     In  FIG. 4 , bulk wires of commercial grade Ni  22  and Al  24 , for example, are readily available from numerous commercial sources. These bulk wires  22 ,  24  are typically formed with a generally round cross-section. These commercially available wires  22 ,  24  are first cold-drawn (below 100° C.) through respective reducing dies  26 . The bulk wires  22 ,  24  may be of any effective size, but diameters in the range of 50 microns have proven satisfactory. This first drawing operation, conducted under a cover gas (such as nitrogen or argon), removes all oxides and other contaminates from the wires  22 ,  24 , thus providing clean surfaces that are suited for an exothermic reaction.  
         [0036]     As shown in  FIG. 5 , the first draw dies  26  may simply reduce the original diameter of the bulk wires, thus resulting in a smaller circular cross-section. However, the dies  26  can alternatively impart a full or partial geometric shape to the wires  22 ,  24 , such as shown in  FIG. 5A . In this example, the first dies  26  impart a hexagonal cross-section to the wires  22 ,  24  which may aid in better nesting and increased surface contact as represented by the phantom adjacent wires. Of course, other wire shapes are possible.  
         [0037]     Once drawn through the first dies  26 , the wires  22 ,  24  are merged and drawn as a bundle through a second die  28  which squeezes the wires  22 ,  24  into a cord  30 . A representative cross-section of the chord  30  is shown in  FIG. 6  to illustrate that the surfaces of the wires  22 ,  24  have been brought into substantial contact with one another through plastic deformation so that a large interfacial surface area is established between the respective wires  22 ,  24 . Those skilled in the art will readily appreciate that the number of strands of wires  22 ,  24  can be varied substantially, and that the five strands shown in the figures are merely illustrative. On the minimum side, there must be at least two such wires  22 ,  24 , whereas there is not an effective maximum limit. Wire bundles with strand numbers in the 10&#39;s or 100&#39;s may be used.  
         [0038]     The cord  30  exiting the second draw die  28  can be used immediately in an exothermic reaction in the form thus created, or can be further shaped by progressive rolling dies  32  to create a ribbon similar to the configuration illustrated in  FIG. 7 . Alternatively, the cord  30  can be shaped into other designs or configurations and is not limited to the flat ribbon shape shown in  FIG. 7 . Likewise, it is not necessary that the resulting cross-section be continuous. Thus, the cord  30  can be shaped by any other means known to those skilled in the art, including stamping, further drawing, forging, and the like.  
         [0039]      FIGS. 8A and 8B  illustrate, in simplified terms, the sequence of welding upper  34  and lower  36  substrates using the exothermic assembly  18  ignited by a flame source  20 . Once ignited at the wick  21 , the exothermic reaction propagates along the assembly  18 , fusing together the opposing surfaces along the way.  
         [0040]      FIG. 9  illustrates a supplemental application technique of the subject forming process. The result is a slightly modified exothermic assembly  118 . Here, the constituent bulk wires  122 ,  124  are pulled through the first draw dies  126  as in the preceding embodiment, and then merged and pulled through the second drawing die  128  as in  FIG. 4 . The cord  130  emerging from the second draw die  128  is then directed to a coating operation where a braze material  138 , contained as a suspension or powder in a hopper  140 , is applied to the exterior surface of the cord  130  to thus encase the exothermic assembly  11 ′ for benefit in a later joining operation. Instead of the braze material  138 , other coatings can be applied, such as solder, flux, or other beneficial treatments. Once the sprayed material  138  is sufficiently solidified or dried, the exothermic assembly  118  is ready for use in any conceivable application (i.e., not limited to internal combustion engines).  
         [0041]      FIG. 10  illustrates yet another alternative forming technique for the exothermic assembly  218 . In this situation, the bulk wires  222 ,  224  are drawn through the first set of dies  226  and then brought together in a twisting device, generally shown at  242 . The twisting device  242  includes a collar  244  driven by a gear wheel  246  via a motor  248 . The twisting operation takes the place of the second draw die  228  as in  FIGS. 4 and 9 , to effectively bring the wires  222 ,  224  tightly together to form a bulk exotherm with good interfacial contact between the constituent wires  222 ,  224 . The resulting cord  230  of twisted construction is ready for use in an exothermic reaction, or can be coated with a braze material as described in the preceding example. Alternatively, the resulting cord  230  of twisted construction can be rolled or shaped using progressive rollers like that shown in  FIG. 4 , or other post-forming techniques, to achieve a desired shape in the resulting exothermic assembly  218 . In situations where it would be advantages to work with a sheet of exothermic material, a cloth may be readily formed by weaving or felting a number of exothermic cords.  
         [0042]      FIG. 11  illustrates the use of rotary swaging to assemble the reactants. In this example, the second die  328  is formed in sections  350  that can be separately actuated to “hammer” the bundle of wires  322 ,  324  into a tightly packed condition, as shown in  FIG. 12 . The swaging die  328  can be simultaneously rotated to impart a twist to the emerging cord  330  or simply allow the wires to remain parallel.  
         [0043]      FIG. 13  illustrates the use of ultrasonic welding for joining the reactants. Here, the second die  428  is vibrated at high frequency to surface weld the individual wires  422 ,  424  together. The die  428  may also be rotated to introduce a twist in the resulting cord  430  as in preceding examples.  
         [0044]     It will be appreciated that all of the various assembly techniques can be blended to form additional hybrid variations with the resulting exothermic assembly useful in any application in which prior art reactive multilayer foils and coatings have been used. Thus, while the invention has been described in an illustrative manner, it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.  
         [0045]     Obviously, many modifications and variations of the invention are possible in light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described.