Patent Publication Number: US-9410784-B1

Title: Initiator assembly with gas and/or fragment containment capabilities

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/779,057 filed Feb. 27, 2013, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/604,255 filed Feb. 28, 2012 entitled “Initiator Assembly With Gas And/Or Fragment Containment Capabilities”. The disclosure of the above-referenced patent applications are incorporated by reference as if set forth in their entirety herein. 
    
    
     FIELD 
     The present disclosure relates to an initiator assembly having gas and/or fragment containment capabilities. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Certain initiators for energetic materials must meet the MIL-DTL-23659 standard, which requires that the initiator assembly be exposed to a relatively large amount of electrical power (i.e., 20 amps @ 440 VAC) for an extended period of time (i.e., 5 minutes) without causing initiation of the initiator assembly&#39;s output charge. Exposure of the initiator assembly to such large amounts of electrical power can cause the initiator assembly&#39;s input charge, typically formed of a secondary explosive, to “cook off”. The standard requires that the initiator assembly be constructed such that cook-off of the input charge not cause subsequent energetic initiation (i.e., combustion, deflagration, detonation) of the initiator assembly&#39;s output charge. Heretofore, the initiator assemblies that we know of that are compatible with the MIL-DTL-23659 standard must have an external vent that permits gases generated by the input charge as it cooks-off (and fragments of the initiator assembly) to be vented from the interior of the initiator assembly. 
     It can be desirable at times to position an initiator assembly within the propellant of a motor (e.g., rocket). For such initiators to also comply with the MIL-DTL-23659 standard, the initiator assembly cannot leak or eject materials or energy that might possibly initiate the motor propellant. Additionally, such an initiator assembly is preferably relatively small, produces a consistent output, and should not generate casing fragments or solid by-product that could impede proper function of the motor valves. 
     Accordingly, there remains a need in the art for an improved initiator assembly that is suited for use in the propellant of a motor. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present teachings provide an initiator assembly that includes an initiator and a containment shell. The initiator has an initiator housing, an initiator device mounted inside the initiator housing, and an input charge that is formed of an energetic material. The initiator device is configured to initiate at least one of a combustion event, a deflagration event and a detonation event in the input charge. The containment shell is coupled to the initiator housing and defines a space into which gas and/or particles are ejected from the initiator housing if the initiator device is not activated and the input charge is cooked off. The containment shell is configured such that the gas and/or the fragments produced when the input charge is cooked off is/are contained within the initiator assembly. 
     In another form, the present teachings provide an initiator assembly that includes an initiator and a containment shell. The initiator has an initiator housing, an initiator device mounted inside the initiator housing, and an input charge that is formed of an energetic material. The initiator device is configured to initiate at least one of a combustion event, a deflagration event and a detonation event in the input charge. The containment shell is coupled to the initiator housing and defines a space into which gas and/or particles are ejected from the initiator housing if the initiator device is not activated and the input charge is cooked off. The space is sized such that the gas and/or the fragments produced when the input charge is cooked off is/are contained within the initiator assembly. 
     In still another form, the present teachings provide an initiator assembly with an initiator and a containment shell. The initiator has an input charge that is formed of an energetic material and is configured to initiate a detonation event in the input charge. The containment shell is coupled to the initiator housing and defines a space into which gas and/or particles are ejected from the initiator housing if the initiator device is not activated and the input charge is cooked off. The containment shell is configured such that the gas and/or the fragments produced when the input charge is cooked off is/are contained within the initiator assembly. 
     In yet another form, the present teachings provide an initiator assembly with an initiator and a containment shell. The initiator has an input charge that is formed of an energetic material and is configured to initiate a detonation event in the input charge. The containment shell is coupled to the initiator housing and defines a space into which gas and/or particles are ejected from the initiator housing if the initiator device is not activated and the input charge is cooked off. The space is sized such that the gas and/or the fragments produced when the input charge is cooked off is/are contained within the initiator assembly. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a perspective view of an initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 2  is a longitudinal section view of the initiator assembly of  FIG. 1 ; 
         FIG. 3  is a perspective view of a second initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 4  is a longitudinal section view of the initiator assembly of  FIG. 3 ; 
         FIG. 5  is a longitudinal section view of a third initiator assembly constructed in accordance with the teachings of the present disclosure′ 
         FIG. 6  is a section view taken along the line  6 - 6  of  FIG. 5   
         FIG. 7  is a perspective view of a fourth initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 8  is a longitudinal section view of the initiator assembly of  FIG. 7 ; 
         FIG. 9  is a perspective view of a fifth initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 10  is a longitudinal section view of the initiator assembly of  FIG. 9 ; 
         FIG. 11  is a perspective view of a sixth initiator assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 12  is a longitudinal section view of the initiator assembly of  FIG. 11 ; and 
         FIG. 13  is a section view taken along the line  13 - 13  of  FIG. 12 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2  of the drawings, an initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The initiator assembly  10  can include an initiator  12  and a containment structure  14 . 
     The initiator  12  can generally include an initiator housing  20 , a plurality of first terminals  22 , an initiator device  24 , an input charge  26  and an output charge  28  and can be constructed in a manner that satisfies the MIL-DTL-23659 standard. One exemplary configuration for the initiator  12  is disclosed in U.S. Pat. No. 7,661,362, the disclosure of which is incorporated by reference as if fully set forth in detail herein. 
     Briefly, the initiator housing  20  can comprise a housing body  30  and a cover assembly  32 . The housing body  30  can be formed of any desired material, such as 304L stainless steel, Inconel or KOVAR®, for example. The cover assembly  32  can be welded to the housing body  30  to hermetically seal a space into which the initiator device  24 , the input charge  26  and the output charge  28  can be received. The first terminals  22  can be received in one or more seals (e.g., first seals  36 ) that in turn can be received in holes  38  in the housing body  30 . The first seals  36  can be formed of any suitable material, such as glass, and can sealingly engage the first terminals  22  and the housing body  30 . 
     The initiator device  24  can be any kind of device that is configured to initiate an energetic material, such as a secondary explosive, such as RSI-007 which is available from Reynolds Systems, Incorporated of Middletown Calif. Exemplary initiator devices can comprise an exploding foil initiator, an exploding bridgewire initiator, semi-conductor bridge devices, squibs, and thin-film initiators. In the particular example provided, the initiator device  24  comprises an exploding foil initiator, which may conventionally include a pair of initiator contacts (not specifically shown), which are electrically coupled to respective ones of the first terminals  22 , a bridge (not specifically shown), which is disposed between the initiator contacts, a barrel (not specifically shown), which is mounted over the bridge, and a flyer that may be expelled from the barrel when the initiator device  24  is activated due to conversion of the material that forms the bridge into a plasma. As those of skill in the art will appreciate, the flyer can impact against the input charge  26  to initiate the input charge  26  such that the input charge  26  releases energy in a desired manner. 
     In the particular example provided, initiator assembly  10  is configured to produce a pyrotechnic output that would be suitable for initiating combustion in the fuel of a rocket motor. The initiator device  24  can be configured to detonate the input charge  26  and energy released from the detonation of the input charge  26  can be employed to initiate combustion or deflagration of the output charge  28 , which can be formed of BKNO3. As those of skill in the art will appreciate, energy released during detonation of the input charge  26  can be attenuated by a barrier system  40  as is disclosed in detail in U.S. Pat. No. 7,661,362. 
     The containment structure  14  can comprise a containment shell  50 , a plurality of second terminals  52 , a plurality of second seals  54  and a connector circuit  56 . 
     The containment shell  50  can be formed of any appropriate material, such as 304L stainless steel, Inconel, or KOVAR®, for example, and can be shaped in any desired manner that may be suited to reduce the cost of the manufacture of the initiator assembly  10  and/or to facilitate packaging of the initiator assembly  10  into a device (e.g., a rocket motor). The containment shell  50  can be fixedly coupled to the initiator housing  20  and can define a void space  60  into which the first terminals  22 , the second terminals  52  and the connector circuit  56  can extend. The second terminals can be received in one or more of the second seals  54 , which can be received in a corresponding hole or holes  64  in the containment shell  50 , and the second seals  54  can sealingly engage the second terminals  52  and the containment shell  50 . The second seals  54  may be formed of any desired material, such as glass. If desired, the second terminals  52  can be configured such that the portion that extends through the second seals  54  into the void space  60  can be configured to buckle in the event that an axial load is applied to the second terminals  52  that would otherwise tend to urge the second terminals  52  in a direction away from the initiator  12 . One manner to promote the buckling of the second terminals  52  is to form a portion of the second terminals  52  that extends into the void space  60  such that the portion (in part or in its entirety) has a cross-sectional size (e.g., diameter) that is smaller than a portion that is located in a corresponding one of the second seals  54 . 
     The connector circuit  56  can be configured to electrically couple the first and second terminals  22  and  52  to one another and as such, any suitable electric conductors can be employed. In the particular example provided, the connector circuit  56  comprises a low-inductance flex circuit  70  that is soldered to the first and second terminals  22  and  52 . As used herein, the term “low-inductance” means an inductance of less than 250 nano-Henries (nH), preferably less than or equal to 50 nH and more preferably less than or equal to 30 nH. The inductance can be measured when power that is configured to cause the initiator  12  to operate is transmitted through the connector circuit  56 . In the particular example provided, the containment structure  14  (including the flex circuit  70 ) adds an inductance of about 15 to 25 nano-Henries to the inductance of the initiator  12 . As will be appreciated, the flex circuit  70  can be a flexible flat cable (FFC), a ribbon cable, or a flexible plastic substrate (e.g., polyimide, polyester ether ketone (PEEK)) having one or more conductive elements coupled thereto. In the particular example provided, the flex circuit  70  comprises a flexible plastic substrate onto which a conductive foil is deposited or adhered. The conductive foil can be etched to remove undesired material to thereby form the individual conductive elements. 
     The connector circuit  56  can be configured to permit the electrical connection between the first and second terminals  22  and  52  to be verified before the containment shell  50  is fixedly coupled to the initiator  12 . In the example provided, the flex circuit  70  is relatively longer than a span between the first and second terminals  22  and  52  so as to provide slack in the flex circuit  70  that permits the containment shell  50  to be separated from the initiator  12  by a distance that permits a tool (e.g., continuity tester) to be coupled to the first terminals  22 . As will be appreciated, the slack in the flex circuit  70  also permits the coupling (e.g., soldering) of the flex circuit  70  to either the first terminals  22  or the second terminals  52 . 
     In the example provided, the containment shell  50  can be fixedly coupled to the initiator  12  after the flex circuit  70  is fixedly and electrically coupled to the first and second terminals  22  and  52 . For example, the containment shell  50  can be laser welded to the initiator housing  20  to hermetically seal the void space  60 . 
     In the event that the initiator assembly  10  is subjected to a relatively large amount of electrical power over an extended period of time (as is required in the electric cook-off test in MIL-DTL-23659), the initiator assembly  10  may heat in response to receipt of the electric energy and may cause the input charge  26  to cook-off (i.e., decompose, combust or deflagrate). Gases created as the input charge  26  cooks-off may cause failure of one or more of the first seals  36 , so that fragments of the initiator  12  and by-products created as the input charge  26  cooks-off are contained in the void space  60 . Moreover, the additional volume provided by the void space  60  effectively reduces the internal pressure within the initiator assembly  10  (once one or more of the first seals  36  have failed) so that the risk of failure of the second seals  54  is effectively eliminated. 
     The containment shell  50  can have a void space  60  that can have a volume that is between 15 cc and 1 cc, such as a volume between 10 cc and 5 cc or 1 cc, or a volume between 5 cc and 1 cc. We have found that sizing the containment shell  50  such that the void space  60  has a volume between 10 cc and 5 cc (e.g., a volume of 5 cc) provides sufficient additional volume to ensure that any gas, fragments or energy that exits the initiator  12  as a result of a failure of one or more of the first seals  36  during cook-off of the input charge  26  remains completely contained in the initiator assembly  10 . As will be appreciated, however, the volume of the void space  60  can be tailored to the needs of a specific initiator, which could vary depending on the material used for the input charge  26  and the size of the input charge  26 . Additionally, space constraints for packaging the initiator assembly  10  would typically warrant the sizing of the volume of the void space  60  in as small a manner as possible, such as about 1 cc. 
     Additionally, it may be beneficial in some situations to include electrical insulation on one or more of the internal surfaces in the initiator assembly  10 . The electrical insulation may help to prevent grounding between the containment shell  50  and one or more of the second terminals  52 , for example. The electrical insulation can comprise one or more insulating materials (e.g., films, sleeves, discs, tapes) that can be mounted to the rear surface  80  of the initiator  12 , the inside diameter of the containment shell  50 , and any shoulders or end faces of the containment shell  50 . In the particular example provided, a unitarily formed insulation shell  82  is mounted within the containment shell  50  and an adhesive tape  84  formed of polyimide (e.g., Kapton®) is mounted to the rear surface  84  of the initiator  12 . 
     With reference to  FIGS. 3 and 4 , a second initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   a . The initiator assembly  10   a  is generally similar to the initiator assembly  10  of  FIGS. 1 and 2 , except that a) the initiator  12   a  is configured to produce an output that is discharged perpendicular to the longitudinal axis of the input charge  26 , b) the containment structure  14   a  comprises only a containment shell  50   a , and c) a portion of the containment shell  50   a  is integrally formed with a portion of the initiator housing  20   a . Those of skill in the art will appreciate that the particular orientation of the output of the initiator assembly  10   a  is merely exemplary and that the orientation may be changed as desired (e.g., to an orientation that is in-line with the longitudinal axis of the input charge  26 ). 
     The housing body  30   a  can be formed as two discrete components (i.e., a base structure  100  and a body structure  102 ) that can be welded together. The first terminals  22 , the first seals  36  and the initiator device  24  can be mounted to the base structure  100 . The body structure  102  can define a first body bore  104  and a second body bore  106 . The first body bore  104  can be configured to receive the base structure  100 , the initiator device  24  and the input charge  26 , while the second body bore  106  can be configured to receive the output charge  28 . 
     The containment shell  50  can comprise one or more chamber assemblies  110 . Each chamber assembly  110  can comprise a chamber  114 , a burst disc  116  and a chamber cover  118 . Each chamber  114  can be fixedly coupled to (e.g., integrally formed with) the body structure  102 . In the particular example provided, each chamber  114  is formed by a chamber bore  120 , which is formed into the body structure  102  radially outwardly of the first body bore  104 , and a communicating aperture  122  that couples the chamber bore  120  in fluid communication with the first body bore  104 . The burst disc  116  can be fitted into the communicating aperture  122  and can be configured to inhibit fluid communication between the chamber bore  120  and the first body bore  104  when a pressure in the first body bore  104  is less than a predetermined pressure. Alternatively, the burst disc  116  can be integrally formed with the body structure  102 . The predetermined pressure can be greater than the operational pressure of the initiator  12   a  (i.e., the internal pressure generated when the input charge  26  is initiated by activation of the initiator device  24 ) but less than the pressure that is required to cause failure of the first seals  36 . The chamber cover  118  can be welded to the chamber  114  to close (i.e., hermetically seal) the chamber bore  120  on a side of the chamber  114  that is opposite to the communicating aperture  122 . 
     While the communicating apertures  122  are depicted as being positioned proximate the inside edge  130  of the base structure  100 , it will be appreciated that the communicating apertures  122  can be positioned in any desired location so long as the burst discs  116  are exposed to the gas pressure generated when the input charge  26  cooks-off. 
     In the event that the input charge  26  cooks-off, gas pressure generated by the input charge  26  can cause the burst discs  116  to fail (e.g., burst) to couple one or more of the chamber bores  120  with the first body bore  104 . As the pressure at which the burst discs  116  fail is lower than the pressure required to cause failure of the first seals  36 , no fragments of the initiator  12   a  or by-products produced by the input charge  26  as it cooks-off are discharged from the initiator assembly  10   a.    
     The example of  FIGS. 5 and 6  is generally similar to the example of  FIGS. 3 and 4 , except that the body structure  102   b  and the chambers  114   b  are formed in two pieces and the burst discs are eliminated. More specifically, the chambers  114   b  and the body structure  102   b  can be defined by a housing structure  150  and a cover plate  152 . The housing structure  150  can be milled, cast or molded, for example, to define various pockets that correspond to the first body bore  104   b , the second body bore  106   b , the chamber bores  120   b , and optionally the communicating apertures  122   b . Alternatively, the communicating apertures  122   b  can be drilled through the material that is disposed between the chamber bores  120   b  and the first body bore  104   b . The cover plate  152  can be welded to the housing structure  150  to close the pockets so that only the first and second body bores  104   b  and  106   b  remain open (i.e., for receipt of the base structure  100   b  and the internal components of the initiator  12   b.    
     In the event that the input charge  26  cooks-off, gas pressure generated by the input charge  26  is transmitted through the communicating apertures  122   b  from the first body bore  104   b  to the chamber bores  120   b  and no by-products produced by the input charge  26  as it cooks-off are discharged from the initiator assembly  10   b.    
     With reference to  FIGS. 7 and 8 , a fourth initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   d . The initiator assembly  10   d  can comprise an initiator  12   d , which can be generally similar to the initiator  12  of  FIGS. 1 and 2 , and a containment structure  14   d  having a containment shell  50   d , a first ferrule  200 , a plurality of second terminals  52 , a wire cable  202  and a second ferrule  204 . The containment shell  50   d  can be formed of a material and/or in a manner that permits the containment shell  50   d  to expand. In the particular example provided, the containment shell  50   d  is an expandable bag that is formed of a suitable material, such as aramid fiber (e.g., KEVLAR®). The first ferrule  200  can couple a first end of the containment shell  50   d  to the rear surface of the initiator  12   d . The second terminals  52  can couple the first terminals  22  to corresponding conductors in the wire cable  202 . The wire cable  202  can extend through the containment shell  50   d  and can be configured to couple to a fire set for activating the initiator  12   d . The second ferrule  204  can couple the second end of the containment shell  50  to the wire cable  202 . 
     In the event that the input charge (not specifically shown) cooks-off, gas pressure generated by the input charge can cause failure of one or more of the first seals  36 . Fragments of the initiator  12   d , along with by-products produced when the input charge cooks-off are contained in the containment shell  50   d , which can expand as necessary to ensure that no by-products produced by the input charge as it cooks-off or initiator fragments are discharged from the initiator assembly  10   d.    
     With reference to  FIGS. 9 and 10 , a fifth initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   e . The initiator assembly  10   e  is generally similar to the initiator assembly  10  of  FIGS. 1 and 2 , except that the housing body  30   e  of the initiator housing  20   e  has a threaded portion  250  that is configured to be mounted in the wall (not shown) of a container that stores a fuel propellant (rather than within the fuel propellant itself). As in the example of  FIGS. 1 and 2 , the containment shell  50   e  is configured to fit within available space in the device to which the initiator assembly  10   e  is mounted. It will be appreciated that an in-wall mounting configuration of the initiator assembly  10   e  eliminates issues with the venting of the initiator assembly into the propellant of a motor. Configuration of the initiator assembly in this manner may be desirable when through-wall initiation is permissible and it would be undesirable to discharge initiator fragments and/or by-products produced if the input charge  26  of the initiator assembly  10   e  should cook-off into a space in which the initiator assembly  10   e  is mounted (typically an environment with electronics that may be react poorly to introduction of gases or fragments into the environment). 
     With reference to  FIGS. 11 through 13 , a sixth initiator assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   f . The initiator assembly  10   f  can comprise an initiator  12   f , a containment structure  14   f  and a connector interface  300 . The initiator  12   f  can be generally similar to the initiator  12  of  FIGS. 1 and 2 . The containment structure  14   f  can comprise a containment shell  50   f , a plurality of second terminals  52 , and a wire harness  302 . The containment shell  50   f  can be a generally tubular structure that can surround the wire harness  302 . The containment shell  50   f  can be configured to contain any fragments and energy that are generated by the initiator  12   f  if the input charge  26  cooks-off, and can direct gas produced by the input charge  26  as it cooks-off to a desired area that can be located remotely from the propellant of the motor. 
     The connector interface  300  can be configured to fixedly and sealingly couple the initiator  12   f  to the containment structure  14   f  and can comprise a first connector portion  310  and a second connector portion  312 . The first connector portion  310  can be fixed to the initiator housing  20   f . In the particular example provided, the first connector portion  310  is integrally formed with the initiator housing  20   f . The second connector portion  312  can be fixedly and sealingly coupled to the containment shell  50   f . The second connector portion  312  can have a plurality of third terminals  320 , which can matingly engage the first terminals  22  and the second terminals  52  to thereby electrically couple the first terminals  22  to the wire harness  302 . The second connector portion  312  can define a plurality of vent apertures  330  that couple at least one of the first connector portion  310  and the initiator housing  20   f  in fluid connection with the containment shell  50   f.    
     In the event that the input charge  26  cooks-off, gas pressure generated by the input charge  26  can cause failure of one or more of the first seals  36 . Relatively large fragments of the initiator  12   f  (i.e., fragments that are too large to fit through the vent apertures  330  in the second connector portion  312 ) can be contained between the initiator housing  20   f  and the containment structure  14   f , whereas smaller fragments of the initiator  12   f , along with by-products produced when the input charge  26  cooks-off can be transmitted through the vent apertures  330  into the containment shell  50   f  where they can be directed to a desired area should they flow out of the distal end of the open containment structure  14   f.    
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.