Abstract:
A portion of a work-hardened essentially tubular work piece such as a metallic firearm cartridge case is annealed by contact with solid or granular tooling material which has been heated to a temperature approximately that of the appropriate annealing temperature, thereby reducing the possibility of overheating the work piece, and also thereby permitting the annealing of only that portion of the work piece contacted or in close proximity to the point(s) of contact.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/439,579, filed on Apr. 4, 2012 issued as U.S. Pat. No. 8,707,844 on Apr. 29, 2014, of which is incorporated herein in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is generally related to the field of annealing of work hardened cartridge casings. More specifically, the present invention is directed to annealing a cartridge casing by applying heat conductively to the casing. 
       BACKGROUND OF THE INVENTION 
       [0003]    Metals, such as copper and tin alloys, can become increasingly hard and inflexible due to stress introduced into the metal from physically shaping of the metal from bending, stamping, coining, punching, flattening, extruding, hammering, stretching and other conventional means of shaping metals. “Working hardening” from the shaping and reshaping of metals can result in metal fatigue ultimately resulting in failure of the metal. 
         [0004]    Work hardening is concern in the production and in particular the reloading and reuse of metal cartridge casings. A cartridge casing typically comprises a tubular casing having a closed end and an open end in which the bullet is seated. The metal surrounding the open “mouth” end of the casing must be sufficiently flexible such that mouth can be crimped against the bullet. The mouth must also flex outwardly during firing to seal against the chamber walls of the firearm to create a pressure tight seal for propelling the bullet. The shaping process for forming the tubular casing can harden the metal around the mouth preventing the mouth from properly flexing during loading or firing. In addition, many high power cartridges are necked such that the diameter of the mouth is reduced to less than the diameter of the closed “head” end of casing. The necking process can further harden the mouth of the casing. 
         [0005]    The flexing of the mouth and the rest of the casing during firing can also cause work hardening of the casing. As a result, casings that are recovered after firing and reloaded with a new bullet are typically harder than new casings. Moreover, the reloading process typically involves mechanical reshaping and re-crimping of the cartridge casing further hardening the cartridge casing. Similarly, spent cartridges are often reshaped to fit firearms that the cartridge was not originally manufactured to fit. In addition to being performed by individuals with little or no formal training, these reloaded or repurposed “wildcat” cartridges are largely unregulated for safety and effectiveness. 
         [0006]    Work hardening of the casing caused by initial manufacture and reloading can harden the mouth of the casing until the casing cannot flex to seal against the projectile or the chamber walls. A work hardened casing could fracture, rupture or otherwise mechanically fail, potentially causing injury to the shooter and/or damaging the firearm. 
         [0007]    Annealing is a common technique for counteracting the affects of work hardening that involves softening the metal by heating the metal into critical temperature range at which the stress caused by the shaping of the metal is released. The casing is then cooled with air or water. The casing must carefully be heated to a temperature sufficiently high enough to soften the metal for the stress to be released while less than a temperature where the metal becomes too soft and weaken the structural integrity of the casing. 
         [0008]    A related concern is that the metal of the rest of the casing and in particular at the head of the casing is typically harder than the metal at the mouth of the casing. The harder metal at the rear of the casing is necessary to prevent rupturing of the casing during firing and to direct the propellant gases against the bullet and down the barrel of the firearm. The annealing process can apply heat to more of the casing then the mouth portion potentially weakening the rear of the casing. In addition, even if heat is only applied to the portion of the casing to be annealed, the heat can often migrate along the length of the casing even though direct heat was only applied to a portion of the casing. 
         [0009]    A currently available technique for annealing the mouth portions of the casings comprises passing the mouth portion of the casing through at least one flame oriented to contact only the mouth portion. The casing is typically positioned on a moving structure such that the mouth of the casing remains in contact with the flame for a limited period of time to prevent heat migration throughout the casing. In addition to the inherent risk of having an opening flame in an ammunition loading area, a drawback of the approach is that the temperature of the flame is typically greater than the preferred annealing temperature creating a danger of overheating the mouth portion of the casing or causing rapid heat migration through the casing. Similarly, an open flame can heat the surrounding air causing convective heating of the casing including the head portion. In addition, flame size, shape, direction, closeness to the mouth portion, and heating time must all be exact to avoid either incomplete annealing or catastrophic case damage. These factors are commonly arrived at empirically, as it is obviously difficult to accurately measure the temperature of the cartridge case along its length in real-time under these conditions. 
         [0010]    A related drawback is that a single flame will not evenly heat the case around its entire circumference, leading to uneven metal hardness in the area to be annealed. As a result, the cartridge are commonly rotated within the flame to apply the heat around the entire circumference of the casing. Certain currently available methods utilize multiple flames at different orientations or rotate the casing within the flame area to evenly heat the casing around the mouth portion. Both remedies significantly increase the complexity of the process and the likelihood of failure. 
         [0011]    Other approaches to annealing only the mouth portions of the casing include dipping the casing into a molten solution, such as molten metal or chemical salts. However, these approaches typically leave solidified residue on the casing, which can render the case unusable or toxic depending on the molten material used. Similarly, the molten solution itself is often cost prohibitive and can produce toxic fumes. In addition, the solution often requires frequent regeneration or replacement and can often corrode the casing. 
         [0012]    Other even less satisfactory annealing processes have been tried, including dipping the cartridge case into molten metal such as lead, or into molten chemical salts intended for specialized heat-treatment and surface-preparation of metals. In the former example, the molten metal tends to wet the surface of the cartridge case brass, leaving behind a solidified residue which makes the case unusable. In the latter example, the salts are usually highly toxic, via either skin contact or the breathing of heated fumes, or both; and many such salts have proven corrosive to the brass cartridge case material. Further, such salts are expensive and have a limited useful life, requiring frequent regeneration or replacement. 
         [0013]    As the currently available annealing processes are often dangerous and difficult to control or repeat, there is a need for an effective means of annealing the mouth portions of casing. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention is directed an annealing system and related method of using that anneals the cartridge casing primarily through conductive heat transfer. The annealing system generally comprises a heat transfer element that directly contacts the mouth portion of the casing to transfer heat directly to the portion of the casing to be annealed. The heat transfer through conduction is more rapid and efficient than through convection or other heat transfer means. As such, the heat transfer element can be maintained at a temperature proximate to the effective annealing temperature for the metal used in the casing lowering the likelihood of overheating the casing or avoiding heating more of the casing then intended. In one aspect, the heat transfer element can be pre-formed to match the shape of the portion of the casing to be annealed in order to maximize contact between the heat transfer element and the casing to maximize the heat transfer from the heat transfer element to the casing. In another aspect, the heat transfer element can comprise a plurality of shape adapting structures that move or flex to conform to the shape of the casing to maximize contact between the heat transfer element and the casing. 
         [0015]    In an embodiment of the present invention, an annealing system can comprises a heating element and a heat transfer element comprising a plurality of shape adapting structures, wherein the shape adapting structures comprise plurality of granules. The granules can comprise metal shot, ceramic beads, sand or other packable spherical elements capable of being heated to the annealing temperature. The granules can be positioned in a bath and heated by the heating element to a temperature proximate to the annealing temperature. The mouth portion of the casing can be inserted into the bath to anneal the mouth portion. The granules can be sized and/or loosely packed such that the granules can move to conform to the shape of the mouth portion and conductively transfer heat around the circumference of the mouth portion. 
         [0016]    In another embodiment of the present invention, the shape adapting structures can comprise a plurality of fingers. The fingers are heated by the heating element and can be arranged in a generally tubular configuration for receiving the mouth portion of the casing between the fingers. In this configuration, the fingers cooperate to contact the mouth portion around the entire circumference of the mouth portion. The fingers can flex to conform to the shape of the casing to maximize contact between the fingers and the casing. 
         [0017]    In yet another embodiment of the present invention, the heat transfer element can comprise a conductive block defining an axial cavity for receiving the mouth portion of the casing. The axial cavity can be pre-formed to match the shape of the casing so as to provide continuous heat around the circumference of the casing. 
         [0018]    In one aspect, the heating element can be sized to directly contact the entire portion of the casing to be annealed maximizing the rate of heat transfer into the portion to be annealed. As the heating transfer to the casing is primarily conductive, the risk of inadvertently heating the head portion of the casing is lessened. Moreover, as only the mouth portion is directly heated, the heat transfer through the casing toward the head portion can be more accurately controlled. 
         [0019]    A method of annealing a mouth portion of a cartridge casing, according to an embodiment of the present invention, can comprise providing a heat transfer element conformable to the mouth portion of the cartridge casing. The method can further comprise heating the heat transfer element to a predetermined temperature. The method can also comprise inserting the mouth portion of the cartridge casing into the heat transfer element such that the heat transfer element contacts the casing around the circumference of the mouth portion. The method can further comprise transferring heat through the heat transfer element into the mouth portion of the cartridge casing for a predetermined period of time. Finally, the method can comprise removing the mouth portion of the casing from the heat transfer element and cooling the casing. 
         [0020]    The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the invention. The figures in the detailed description that follow more particularly exemplify these embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention can be completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a cross-sectional side view of a two typical metallic firearm cartridge casings useable with the present invention. 
           [0023]      FIG. 2  is a cross-sectional side view of an annealing system having a heat transfer element comprising a quantity of granular material, according to an embodiment of the present invention. 
           [0024]      FIG. 3  is a cross-sectional side view of an annealing system having a heat transfer element comprising a plurality of flexible fingers, according to an embodiment of the present invention. 
           [0025]      FIG. 4  is a cross-sectional side view of the annealing system depicted in  FIG. 3 , wherein a cartridge casing is inserted into a cavity defined by the plurality of flexible fingers. 
           [0026]      FIG. 5  is a cross-sectional side view of an annealing system having a heat transfer element comprising a conductive block with a pre-formed cavity, according to an embodiment of the present invention. 
           [0027]      FIG. 6  is a cross-sectional side view of the annealing system depicted in  FIG. 5 , wherein a cartridge casing is inserted into the pre-formed cavity. 
           [0028]      FIG. 7  is a cross-sectional side view of an annealing system having a heat transfer element comprising a quantity of granular material, according to an embodiment of the present invention. 
           [0029]      FIG. 8  is a representative chart illustrating the differences in hardness across a manufactured then annealed cartridge casing, a shot then annealed cartridge casing, an un-annealed cartridge casing, according to an embodiment of the present invention. 
           [0030]      FIG. 9  is a representative chart illustrating the temperature gradient across a heating element, according to an embodiment of the present invention. 
       
    
    
       [0031]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0032]    As shown in  FIG. 1 , a conventional cartridge casing  10  generally comprises a tubular casing  12  having a closed “head” end  14  and an open “mouth” end  16 . The casing  10  can further comprise a necked portion  18  such that the diameter of the mouth end  16  of the tubular casing  12  is less than the diameter of the head end  14 . The cartridge casing  10  can comprise a metal such as a copper, brass, tin, aluminum and other metals and alloys used to form cartridge casings  10 . Similarly, the casing  10  can comprise any conventional ammunition size. The general description of the casing  10  is not intended to be limiting, but to assist in the description of the present invention. 
         [0033]    As shown in  FIGS. 2-7 , an annealing system  20 , according to an embodiment of the present invention, can comprise a heating element  22  and a heat transfer element  24 . The heating element  22  can comprise a coil shape, as shown in  FIG. 2 , an elongated shape, as shown in  FIGS. 3-6 , a ring shape, as shown in  FIG. 7  or other conventional heating element. In one aspect, the heating element  22  can comprise a conventional resistive heating element. 
         [0034]    The heating element  22  is adapted to heat the heat transfer element  24  to within a predetermined temperature range corresponding to the annealing temperature of the metal used for the casing  10 . In one aspect, the heating element  22  can heat the heat transfer element  24  to a temperature between 400 to 800° F. for brass casings  10 . 
         [0035]    The heat transfer element  24  is adapted to transfer heat conductively to any portion of the casing  10  contacting the transfer element  24 . In one aspect, the heat transfer element  24  needs only remain in contact with the casing  10  until the casing  10  is heated through the wall of the tubular casing  12  as the residual heat in the casing  10  will anneal the remaining portions of the casing  10  to be annealed. In one aspect, the casing  10  is maintained in contact with the heat transfer element  24  for about  3  seconds. 
         [0036]    As shown in  FIGS. 2 and 7 , the heat transfer element  24  can comprise a plurality of granules  26  and a container  28 . The granules  26  can comprise metal, ceramic, quartz sand, granite, silica, or other conventional heat transfer elements that can be formed into small grains. In one aspect, diameter of the granules  26  can be between 0.010 and 0.015 inches. In this configuration, the granules  26  can form a free flowing media that can quickly conform to the shape of the casing  10  when inserted into the granules  26  or fill in any holes left when the casing  10  is removed. Similarly, the granules  26  are sized to have improved thermal transmissivity to reduce formation of hotspots. 
         [0037]    As depicted in  FIGS. 2 and 7 , the container  28  comprises a circular cup shape for retaining the granules  26 , but can comprise any conventional shape capable of retaining the granules  26 . The container  28  also defines an opening  30  in the top of the container  28  through which the casing  10  can be inserted. In one aspect, the container  28  can further comprise a lid  30  for more efficient heating of the granules  26 . 
         [0038]    The container  28  can comprise a heat conductive material including, but not limited to, lead, iron, titanium or aluminum. As shown in  FIGS. 2 and 7 , in one aspect, the heating element  22  can be wrapped around the exterior of the container  28  to evenly heat the granules  26  within the container  28 . In another aspect, the heating element  22  can be inserted into the container  28  to heat the granules  26  directly. As shown in  FIG. 9 , in one aspect, the temperature gradient can be formed in the granules  26  wherein the coolest portion of the granules  26  is proximate the opening  30  and the hottest portion of the granules  26  is near the center of the container  28 . In this configuration, the hottest portion of the granules  26  will be proximate to the mouth portion  16  of the casing  10  when the casing  10  is inserted into the granules  26  while the coolest portion of the granules  26  will be proximate to the head portion  14  of the casing  10 . 
         [0039]    In operation, the mouth portion  16  of the casing  10  is inserted through the opening  30  and into the heated granules  26 . The granules  26  are loosely packed such that the granules  26  can conform to the shape of the casing  10 . The casing  10  is inserted to a predetermined depth  32  within the granules  26  corresponding to portion of the casing  10  to be annealed. A hardened portion  34  of the casing  10  corresponding to the portion of the casing  10  that must remain hardened is not inserted into the granules  26  and protrudes from the granules  26 . After heating, the casing  10  is removed allowing the granules  26  to fill in the hole left by the casing  10 . In one aspect, the casing  10  can be heated progressively as the mouth portion  16  of casing  10  is contacts the fingers  38 . In this configuration, the mouth portion  16  of the casing  10  is first heated by the fingers  38  as soon as the mouth portion  16  contacts the fingers  38 . 
         [0040]    As shown in  FIGS. 3 and 4 , the heat transfer element  24  can comprise a base  36  and a plurality of fingers  38  extending from the base  36 . The fingers  38  are arranged in a tubular configuration to define a cavity  40  between the fingers  38  for receiving the mouth portion  16  of the casing  10 . In one aspect, the base  36  and the fingers  38  can comprise a low-friction, heat conductive material including, but not limited to tungsten disulfide, tungsten carbide, boron nitride, molybdenum disulphide and other low-friction, heat conductive material or heat conductive material with a low friction coating. The heating element  22  can be inserted into or wrapped around the base  36 , which transfers heat from the heating element  22  into the fingers  38 . In one aspect, the heating element  22  can be arranged to create a temperature gradient in the fingers  38  in which the hottest portion of the fingers  38  is proximate to the base  36  while the coolest portion of the fingers  38  will be proximate the end of each finger  38  opposite the base. In this configuration, the hottest portion of the fingers  38  will be proximate to the mouth portion  16  of the casing  10  when the casing  10  is inserted into the fingers  38  while the coolest portion of the fingers  38  will be proximate to the head portion  14  of the casing  10 . 
         [0041]    In operation, the mouth end  16  of the casing  10  is inserted into the cavity  40  to the predetermined depth  32 . The fingers  38  are adapted to flex to maintain contact with the casing  10  along the length of the casing  10  inserted into the cavity  40 . The fingers  38  are arranged around the circumference of the cavity  40  to contact and heat the entire periphery of the casing  10 . 
         [0042]    In one aspect, each finger  38  can further comprise a protrusion  42  extending radially inward into the cavity  40 . The protrusions  42  cooperate to engage the mouth end  16  of the casing  10  when the casing  10  is inserted to predetermined depth  32 . 
         [0043]    In another aspect, each  FIG. 38  can further comprise an angled edge  44  for guiding the mouth end  16  of the casing  10  into the cavity  40 . 
         [0044]    As shown in  FIGS. 5 and 6 , the heat transfer element  24  can comprise a conductive block  46  defining a cavity  48  for receiving the mouth portion  16  of the casing  10 . The cavity  48  can be pre-formed to correspond to the size and shape of the mouth portion  16  of the casing  10 . In one aspect, the conductive block  46  can comprise a low-friction, heat conductive material including, but not limited to tungsten disulfide, tungsten carbide, boron nitride, molybdenum disulphide and other low-friction, heat conductive material or heat conductive material with a low friction coating. The heating element  22  can be inserted into or wrapped around the conductive block  46  to transfer heat through the block  46  into cavity  48 . In one aspect, the heating element  22  can be arranged to create a temperature gradient in the cavity  48  in which the hottest portion of the cavity  48  is in the center of the conductive block  46  while the coolest portion of the cavity  40  will be proximate the opening in the block  46 . In this configuration, the hottest portion of the cavity  48  will be proximate to the mouth portion  16  of the casing  10  when the casing  10  is inserted into the cavity  48  while the coolest portion of the cavity  48  will be proximate to the head portion  14  of the casing  10 . 
         [0045]    In operation, the mouth end  16  of the casing  10  is inserted into the cavity  48 . The cavity  40  is sized such that only the casing  10  can only be inserted into the cavity  48  up to the predetermined depth  32  while the hardened portion  34  of the casing  10  protrudes from the conductive block  46  and remains unheated. In one aspect, the casing  10  can be heated progressively as the mouth portion  16  of casing  10  is inserted into the cavity  48 . In this configuration, the mouth portion  16  of the casing  10  is first heated by the conductive block  46  as soon as the mouth portion  16  enters the cavity  48 . 
         [0046]    As shown in  FIG. 7 , in one aspect, the heat transfer element  24  can further comprise a thermocouple  50  for monitoring the temperature of the heat transfer element  24 . The measured temperature can be used to insure the temperature of the heat transfer element  24  does not exceed the threshold temperature of the metal of the casing  10  where the casing  10  becomes over-softened. 
         [0047]    As shown in  FIGS. 1-7 , a method of annealing a mouth portion  16  of a cartridge casing  10 , according to an embodiment of the present invention, can comprise providing a heat transfer element  24  conformable to the mouth portion  16  of the cartridge casing  10 . In an embodiment, the heat transfer element  24  can be pre-formed to correspond to the mouth portion  16  of the casing  10 . The method can further comprise heating the heat transfer element  24  with a heating element  22  to a predetermined temperature. The method can also comprise inserting the mouth portion  16  of the cartridge casing  10  into the heat transfer element to a predetermined depth  32  such that the heat transfer element  24  contacts the casing  10  around the periphery of the mouth portion  16 . The method can further comprise transferring heat through the heat transfer element  24  into the mouth portion  16  of the cartridge casing  10  for a predetermined period of time. Finally, the method can comprise removing the mouth portion  16  of the casing  10  from the heat transfer element  24  and cooling the casing  10 . In an embodiment, the casing  10  can be cooled with a liquid or air. 
         [0048]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and described in detail. It is understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.