Abstract:
An apparatus for lighting an oxygen candle within a drum and for sealing the drum of an oxygen candle furnace. The apparatus includes a housing member for positioning the ignition assembly on a lid of the drum. The housing member having an upper portion, a lower portion and a borehole extending through the upper and lower portions. An ignition nail is placed in the borehole and housing member is structured to hold prevent the ignition nail from moving laterally, and to automatically align the nail with the oxygen candle within the drum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/406,783, filed Oct. 26, 2010, which is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The following description was made in the performance of official duties by employees of the Department of the Navy, and, thus the claimed invention may be manufactured, used, licensed by or for the United States Government for governmental purposes without the payment of any royalties thereon. 
    
    
     TECHNICAL FIELD 
     The invention is directed to an arrangement for igniting an oxygen candle furnace and also for providing a proper and long lasting seal for the furnace thereafter. 
     BACKGROUND 
     The use of chlorate candles, also known as oxygen candles, for generating and supplying oxygen to closed spaces is well known. An example of a known oxygen candle furnace arrangement is illustrated in U.S. Pat. No. 3,385,672, which outlines various elements of an oxygen candle furnace, such as the hollow metal drum within which the candle burns. The hollow metal drum is typically covered with a metal lid which has a sealing gland thereon. The sealing gland helps to seal and maintain the integrity of the furnace. However, the patent does not describe or illustrate elements of the “sealing gland” fitting. 
       FIG. 1  is an exploded view of the typical prior art sealing gland  10 . As shown, the sealing gland  10  includes a brass bulkhead fitting  25  having two threaded sections  20  and  40 , separated by a hexagonal middle section  30  that may be gripped with a wrench during installation. The hexagonal middle section  30  also provides a bearing surface for fastening to the lid  15  of an oxygen candle furnace. The sealing gland  10  may be secured to the lid  15  by a washer and nut on the underside of the lid. As shown in  FIG. 1 , inside the sealing gland is a small brass washer  50 , a coil of heat-resistant fiberglass yarn  55 , and a brass ferrule  60 . A brass compression nut  70  is threaded over the top portion of the bulkhead fitting. The coil of fiberglass yarn  55  rests on the washer  50 , and is compacted by the nut  70  and ferrule  60 . In operation, the fiberglass yarn  55  is located below the lid and within the furnace. 
       FIG. 1  also shows a borehole  80  through which an igniter nail extends. The fiberglass yarn  55  is intended to prevent combustion products from escaping the furnace via the borehole  80 . Because the diameter of the borehole  80  is significantly wide, as compared to the diameter of the igniter nail, the fiberglass yarn  55  provides friction to secure the igniter nail in place and to restrict lateral movement thereof, before and during oxygen production. However, the fiberglass yarn  55  deteriorates due to high temperatures and exposure to combustion products. The location of the fiberglass yarn  55  within the furnace also contributes to its deterioration. The sealing gland  10  is not easily maintainable and difficult to support logistically. As the yarn deteriorates the passageway though the borehole  80  opens up. Thus, the bulkhead fitting does not function as a sealing gland, and does not securely hold the igniter nail. Smoke freely escapes the furnace through the opening. When this happens, operators are forced to bend the nail to hold it in place, which is undesirable as a bent nail is difficult to use for ignition, and often damages the oxygen candle. Alternatively, an external device, such as a binder clip may be used to secure the nail, which is also undesirable because typically, the igniter nail is not securely supported. Catastrophic failures of furnaces have been recorded when an improperly secured nail has fallen through a deteriorated sealing gland and has been consumed in the furnace, allowing a release of hot combustion products through the breach in the lid. Thus, it is desired to have a more secure means of holding the ignition nail and sealing an oxygen candle furnace arrangement. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention is a furnace arrangement. The furnace arrangement includes a drum defining a furnace area within. The furnace arrangement also includes a lid for covering the drum, the lid having an opening in a substantially central portion of the lid. In this aspect the furnace arrangement also includes an ignition assembly extending through the lid. The ignition assembly includes a housing member having, an upper portion above the lid, a lower portion extending through the lid, and a borehole extending from the upper portion to the lower portion of the housing member. The lower portion includes a lower threaded outer surface for securing the housing member to the lid. The upper portion includes a threaded hole within, wherein the threaded hole intersects and is substantially perpendicular to the borehole. The housing also includes a ball plunger assembly having a threaded outer surface threadingly mating within the threaded hole of the upper portion of the housing member, the ball plunger assembly further including a spring loaded ball plunger biased in a direction substantially parallel to the threaded hole of the upper portion. In this aspect, the ignition assembly further includes a nail having a head end and a pointed end, the nail extending through the borehole of the housing in an orientation so that the nail head is within the furnace area and the pointed end is above the lid, wherein the ball plunger contacts the nail and is biased to lock the nail within the borehole. 
     In another aspect, the invention is an ignition assembly for lighting an oxygen candle within a drum and for sealing the drum. The ignition assembly includes a housing member for positioning the ignition assembly on a lid of the drum. The housing member includes an upper portion for above the lid and a lower portion for extending through the lid. The housing also includes a borehole extending from the upper portion to the lower portion of the housing member. The lower portion includes a lower threaded outer surface for securing the housing member to the lid. The upper portion includes a threaded hole within, wherein the threaded hole intersects and is substantially perpendicular to the borehole. The housing also includes a ball plunger assembly having a threaded outer surface threadingly mating within the threaded hole of the upper portion of the housing member, the ball plunger assembly further including a spring loaded ball plunger biased in a direction substantially parallel to the threaded hole of the upper portion. In this aspect, the ignition assembly further includes a nail having a head end and a pointed end, the nail extending through the borehole of the housing in an orientation so that the nail head is below the pointed end, and wherein the ball plunger contacts the nail and is biased to lock the nail within the borehole. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
         FIG. 1  is a prior art illustration of a sealing gland; 
         FIG. 2  is a perspective illustration of an oxygen candle furnace having an ignition assembly, according to an embodiment of the invention; 
         FIG. 3A  is an isometric view of an ignition assembly according to an embodiment of the invention; 
         FIG. 3B  is a perspective illustration of the housing member of the ignition assembly, according to an embodiment of the invention. 
         FIG. 3C  is a perspective illustration of the housing member of the ignition assembly showing different dimensions, according to an embodiment of the invention. 
         FIG. 4  is a sectional view of an ignition assembly attached to the lid of an oxygen candle furnace, according to an embodiment of the invention; 
     
    
    
     DETAILED DESCRIPTION 
     The invention is directed to an arrangement for igniting an oxygen candle furnace, and for providing a proper and long lasting seal for the furnace.  FIG. 2  is a perspective illustration of an oxygen candle furnace  100  having an ignition assembly  300  according to an embodiment of the invention. The furnace is used to provide oxygen to closed spaces. The oxygen candle furnace may be used in different applications such as in submarines, airplanes, spacecrafts, and survival chambers in mines. 
     As shown in  FIG. 2 , the oxygen candle furnace  100  includes a hollow metallic drum or container  200 . Although  FIG. 2  shows the drum  200  being cylindrical, the drum may be any desired shape, so long as it accommodates all its internal elements. The drum  200  defines a furnace area therewith.  FIG. 2  also shows a lid  220  that covers and seals the drum  200 . The lid  220  may be removably attached to the drum  200 . Therefore, latching mechanisms around the circumference of the upper edge of the drum  200  and around the circumference of the lid  220  allow for securing the lid  220  to the drum  200 . These latching mechanisms also allow for the removal of the lid  220  from the drum  200 . The removal of the lid  220  allows for access to components on at the bottom surface of the lid, and also for easy access to components within the drum  200 . In another embodiment, the lid  220  may be hinged to the drum  200 . 
     The oxygen candle furnace  100  also includes an ignition assembly  300 , which as shown is attached to the lid  220  and extends through an opening in the lid  220 . The opening in the lid  220 , through which the ignition assembly  300  extends, may be located at a substantially central part of the lid.  FIG. 2  also shows an oxygen candle  250  within the drum. It should be noted that the candle  250  is only schematically illustrated. Oxygen candles  250  may typically be a chlorate candle or the like. The candles  250  may be about 11⅜ in to 11⅝ in high and have a diameter of about 6⅛ in. Within the drum  200 , oxygen candles  250  may be vertically stacked on top of each other. As shown by the dotted line and as will be outlined below, the candle  250  is vertically aligned with the ignition assembly  300 . 
       FIG. 3A  is an isometric view of an ignition assembly  300  according to an embodiment of the invention.  FIG. 3A  shows the ignition assembly  300  having a housing member  301  that provides support for the entire ignition assembly arrangement. The ignition assembly  300  also includes a safety plate  320 , first and second washers  330 , and a nut  340 .  FIG. 3A  also shows an igniter nail  350  extending through the housing member  301 , and a removable nail holder  360  for holding a pointed end of the nail  350 . A chain  365  attaches the removable nail holder  360  to the safety plate  320 . 
       FIG. 3B  is a perspective sectional illustration of the housing member  301  shown in  FIG. 3A , according to an embodiment of the invention. The housing member  301  includes an upper portion  303  and a lower portion  305 , with a borehole  370  extending in the Y direction from the upper portion  303  through to the lower portion  305 . The borehole  370  is provided to accommodate the igniter nail  350 . As shown, the borehole  370  has an upper portion diameter D U  and a lower portion diameter D L , with the lower portion diameter D L  being larger than the upper portion diameter D U . According to this embodiment, when an igniter nail  350  is inserted, both upper and lower portions accommodate the igniter nail  350 . The upper portion diameter D U  prevents lateral movement of the nail  350 . (As outlined below, the lower portion diameter D L  may also prevent lateral movement of the nail  350 .) The nail has a width d, which is almost equal, but slightly smaller than the diameter D U  of the borehole in the upper portion  303 . The difference in diameters allows the nail  350  to have a substantially exact fit in the upper portion of the borehole  370 . This substantially exact fit prevents lateral movement in the X direction, with respect to the borehole  370 , when the nail is inserted into the borehole  370 . The slightly larger lower portion diameter D L  accommodates for gripper marks near the head of most types of nails. These gripper marks are produced during the manufacturing of the nails and result in a slightly increased diameter, larger than d, near the head of the nail. This slightly increased nail diameter may be almost equal, but slightly smaller than the diameter D L  of the borehole in the lower portion  305 , thereby preventing lateral movement of the nail  350 . The larger diameter D L  of the lower portion  305  also makes it easier for a user to insert the igniter nail  350  into the housing  301  because as outlined below, the pointed end of the nail  350  is first inserted into the lower portion  305 , then through the upper portion  303 . 
     It should be noted that according to another embodiment of the invention, the diameters D U  and D L  may be the same. According to this embodiment the borehole  370  is constant along the length of housing  301 . The difference in diameters allows the nail  350  to have a substantially exact fit in the upper and lower portions of the borehole  370 . This substantially exact fit prevents lateral movement in the X direction. 
       FIG. 3B  also shows the upper portion  303  having a threaded hole  372  extending in the X direction. As shown, the threaded hole  372  is substantially perpendicular to, and intersects with the borehole  370 .  FIG. 3B  also shows a ball plunger assembly  380 , which is disposed within the threaded hole  372 .  FIG. 3B  also illustrates a cylindrical coil  375  inserted into the threaded hole  372 . The ball plunger assembly  380  is then threaded onto the cylindrical coil  375 , within the hole  372 . The cylindrical coil  375  may be a screw-lock HELI-COIL® in which one of the loops of the cylindrical coil is hexagonal instead of round. According to this embodiment, when the ball plunger assembly  380  is threaded onto the cylindrical coil  375 , the hexagonal loop bites into the outer surface of the ball plunger assembly body  380 , preventing the ball plunger assembly  380  from freely rotating. The cylindrical coil  375  may be made from a steel alloy that is resistant to corrosion and galling, such as for example NITRONIC 60®. According to another embodiment of the invention, the ball plunger assembly  380  may be threaded directly onto the surface of the threaded hole  372 , without a cylindrical coil. 
     As shown, the ball plunger assembly  380  includes a round-nose plunger  382  that is biased in direction X towards the borehole  370 .  FIG. 3B  also shows a biasing member  384 , such as a spring, pushing the round-nose plunger towards the borehole  370 .  FIG. 3B  shows the round-nose plunger  382  disposed within the borehole  370 . When the igniter nail  350  is inserted into the borehole  370 , because of the biasing arrangement, nail  350  pushes the plunger  382  back out of the borehole  370 . However because of the spring biasing, the round-nose plunger  382  maintains contact and pushes against the nail  350 , thereby preventing the nail from moving in the Y direction, without user intervention. 
     The lower portion  305  of the housing includes a threaded outer surface  306 , which as outlined below, and illustrated in  FIG. 4 , is used to secure the housing to the lid  220 . It should be noted that the elements of the housing member  301  may be any desired material that provides the strength and the heat resistance suitable for use in the oxygen candle furnace. According to an embodiment of the invention, the housing is a brass material, but may alternatively be a metal such as stainless steel or the like, so long as the material is sufficiently heat and corrosion resistant. 
       FIG. 3C  is an illustration of the housing member  301 , showing possible dimensions, according to an embodiment of the invention. As shown, the housing member  301  has a diameter of D 1  at the top of the upper portion  303  of the housing  301 , and a diameter of D 2  at the bottom of the lower portion. The housing member  301  also has an upper portion length of L U  and a lower portion length of L L .  FIG. 3C  also shows a threaded diameter of D T  for the threaded hole  372 .  FIG. 3C  also shows the aforementioned borehole diameters D U  and D L . 
     The dimensions may vary according to specific applications. For example, according to one embodiment D 1  may be about 1.0 in to about 1.5 in, and D 2  may be about 0.6 in to about 0.90 in. According to this embodiment, the upper portion length L U  may be about 0.6 in to about 0.90 in, and the lower portion length L L  may also be about 0.6 in to about 0.90 in. According to this embodiment, the threaded hole diameter D T  may be about 0.213 in to about 0.319 in. The borehole diameter D U  may be about 0.125 in to about 0.187 in, and the borehole diameter D L  may be about 0.176 in to about 0.264 in. According to one specific embodiment, D 1  may be about 1.25 in, and D 2  may be about 0.75 in. According to this specific embodiment, the upper portion length L U  may be about 0.75 in, and the lower portion length L L  may also be about 0.75 in. According to this specific embodiment, the threaded hole diameter D T  may be about 0.266 in. The borehole diameter D U  may be about 0.156 in and the borehole diameter D L  may be about 0.22 in. 
       FIG. 4  is a sectional view of the ignition assembly  300  attached to the lid  220  of an oxygen candle furnace  100 , according to an embodiment of the invention. As shown, the upper portion  303  of the housing  301  is positioned above the lid  220  and the lower portion  305  extends through the lid  220  and into the furnace area. The lower portion  305  extends through a lid opening  222  that as outlined above may be located at a substantially central portion of the lid. The lid opening  222  has a diameter that allows the lower portion  305  to be pushed through the opening  222 , and secured to the lid  220  with a nut  340 , as outlined below. According to another embodiment, the opening  222  may have a threaded perimeter that threadingly mates with the threaded outer surface  306  of the lower portion. 
     When the housing  300  is attached to the lid  220  as shown in  FIG. 4 , the safety plate  320  is positioned above the lid  220 , with the safety plate having a top surface that abuts against the upper portion  303  of the housing. Also shown, a first of the washers  330  is sandwiched between the safety plate  320  and the lid  220 .  FIG. 4  also shows a baffle  230  positioned below the lid  220  for providing a thermal protective layer. During operation, the oxygen candle material sprays, and the baffle  230  is included to receive the hot material, significantly reducing the temperature of the lid, preventing injury and degradation of the lid. The fastening arrangement also includes the nut  340  which is fastened around the threaded outer surface  306  of the lower portion  305 . The second washer  330  is sandwiched between the nut  340  and the baffle  230 . This arrangement secures the housing  301  to the lid  220 . 
       FIG. 4  shows the igniter nail  350  with the pointed end  352  extending through the lid  220  and positioned above the lid, and the head end  354  below the lid. In operation when a candle is to be ignited, a user may remove the lid  220 . The igniter nail is then inserted via the pointed end  352  into the borehole of the housing. When the pointed end  352  of the nail  350  is pushed through the upper portion of the housing, the nail holder  360  may be placed over the pointed end, thereby providing a means for a user to grip and to manipulate the nail. As outlined above with respect to  FIG. 3B , when the igniter nail  350  is inserted into the borehole  370 , the round-nose plunger  382  pushes against the nail  350 , thereby preventing the nail from moving in the Y direction, without user intervention. The location of this mechanism for holding the nail in place, i.e., the ball plunger assembly  380 , which is outside of the furnace, is advantageous because it is away from the direct heat dissipated by the furnace. This arrangement including the ball plunger assembly  380 , significantly outlast the fiberglass arrangement  55  of the prior art, shown in  FIG. 1 , only failing after the spring  384  has endured hundreds of thousands of cycles. Note that the illustration of  FIG. 4  shows the ball plunger assembly  380  going into the page. 
     The oxygen candle  250  may be lit when the lid  220  is properly secured to drum  200 . A user may use the nail holder  360  to move the igniter nail  350  down in the Y direction into contact with the oxygen candle  250 , wherein chemicals on the head end  354  of the nail react to ignite the candle  250 . As outlined with respect to  FIG. 2 , and as shown in  FIG. 4 , the igniter nail  350  is vertically aligned with the candle  250 , so the downward Y-direction movement automatically brings the nail head into contact with the candle. Additionally, as outlined above, because of the respective diameters D U  and d of the upper borehole  370  and the nail  350 , there is also no lateral movement of the nail  350  in the X direction. 
     After the candle is lit, the user may move the nail  350  upwards in the Y direction until the head end  354  abuts against the nut  340 , covering the borehole  370 , thereby sealing the furnace  100 . Thus, the combination of the narrow borehole  370  having diameters (D U , D L ) outlined above, and the proximity of the nail head  354  with respect to the borehole  370 , and also the adhesion of reaction products to the nail head, all contribute to sealing the furnace, preventing almost all the smoke from escaping the furnace. Furthermore, even if the plunger fails during oxygen generation, the small borehole diameters (D U , D L ) substantially prevent the escape of combustion products. Again, when the user releases the nail holder, the round-nose plunger  382  pushes against the nail  350 , thereby preventing the nail from moving in the Y direction. 
     What has been described and illustrated herein are preferred embodiments of the invention along with some variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention, which is intended to be defined by the following claims and their equivalents, in which all terms are meant in their broadest reasonable sense unless otherwise indicated.