Patent Publication Number: US-2006016524-A1

Title: Annealing system for ammunition casings using induction heating

Description:
RELATED APPLICATION  
      The present application is based on, and claims priority to the Applicant&#39;s U.S. Provisional Patent Application 60/509,676, entitled “Annealing System For Ammunition Casings Using Induction Heating,” filed on Oct. 8, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to the field of annealing systems for ammunition casings. More specifically, the present invention discloses an annealing system for ammunition casings using induction heating.  
      2. Statement of the Problem  
      One of the time-consuming and costly steps in ammunition manufacturing is the annealing process. Annealing is necessary to reduce work hardening caused by various forming steps during manufacturing. The conventional approach has been to anneal brass in batches in a pit furnace. Each batch typically takes many hours (e.g., about eight hours) to ensure that the inner-most parts in the pit furnace reach the annealing temperature. Batch processing limits through-put and makes it more difficult to efficiently integrate the annealing process with the other steps in the manufacturing process that are designed for steady production over the work day.  
      The long processing times required for annealing with a pit furnace also promote oxidation of the brass. In some cases, an inert gas is introduced to reduce oxidation. However, in any case, the parts must be washed in sulfuric acid after annealing to remove oxidation. Product losses of up to 1% by weight are common. In addition, the effort and expense of handling sulfuric acid and disposing of the resulting waste products can be significant.  
      Furthermore, the large size and thermal mass of a conventional pit furnace cause wide variations in the annealing times and temperatures that parts experience based on their locations within the pit furnace. Those parts closest to the heating elements in the pit furnace are annealed at higher temperatures and for a longer time than parts located away from the heating elements. This results in wide variations in part quality because it is nearly impossible to control variations in hardness.  
      Finally, conventional pit furnaces require large amounts of electricity and are not very energy efficient. For example, one type of conventional pit furnace requires 45 KW of electricity. The entire thermal mass of the pit furnace and its contents must be heated to the annealing temperature and held at this temperature for many hours. At the end of the annealing cycle, the pit furnace must be allowed to cool over a significant period of time, and all of this thermal energy simply dissipates into the ambient environment. Therefore, a need exists for an annealing system for brass ammunition casings that addresses these shortcomings. It should be expressly understood that the term “casings” should be broadly construed in the present application to include cups and other forms of work in progress.  
      Prior Art.  
      The prior art in the field also includes the following:  
                                                       Inventor   Patent No.   Issue Date                          Distler   2,907,858   Oct. 6, 1959           Carbo   2,937,017   May 17, 1960           Carbo   3,005,894   Oct. 24, 1961           Armstrong   3,829,650   Aug. 13, 1974           Mucha et al.   4,090,698   May 23, 1978           Pryor et al.   4,494,461   Jan. 22, 1985           Pryor et al.   4,594,117   Jun. 10, 1986           Pryor et al.   4,638,535   Jan. 27, 1987                      
 
      Mucha et al. disclose a system for inductively heating elongated work pieces, such as shell casings. Two multi-turn induction heating coils are axially aligned. The work pieces pass in sequence along a passage through both heating coils. An indexing system is used to maintain spacing between work pieces.  
      Distler discloses another example of a system for treating shell casings using induction heating.  
      The Carbo patents disclose a system for hardening shell casings that uses a bonnet-type induction heating coil.  
      Armstrong discloses another example of a system for hardening shell casings using an induction heating tunnel. The patents issued to Pryor et al. are only of passing interest.  
      Solution to the Problem.  
      Nothing in the prior art discussed above shows an annealing system for annealing in which brass ammunition casings pass in series through a rotating tube within a solenoid induction coil. This approach produces a continuous stream of annealed parts more rapidly with uniform hardness characteristics and minimal oxidation. In addition, the solenoid induction coil generates heat only in the area of the casings, which significantly reduces electrical consumption.  
     SUMMARY OF THE INVENTION  
      This invention provides an annealing system for brass ammunition casings using induction heating. In particular, casings are continuously fed in series through a rotating tube within a solenoid induction coil.  
      These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention can be more readily understood in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a cross-sectional diagram of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Turning to  FIG. 1 , a cross-sectional view is shown of the present invention. A continuous series of brass cartridge casings are fed from the left side of the drawing by means of a dual belt feed system  10 . Other types of feeder mechanisms could be readily substituted. The feed rate of the casings can be monitored by an encoder  12 .  
      The casings are heated to the annealing temperature by induction of eddy currents as they pass along the central axis of the solenoid induction coil  30 . For example, an induction coil with a length of about 24 inches and a power rating of approximately 10 kilowatts is sufficient to anneal a stream of typical casings in about 10 to 15 seconds. The solenoid induction coil  30  has a generally helical winding surrounding a hollow central passageway extending along the central axis of the induction coil  30 .  
      A rotating quartz tube  20  is used as a conduit for the casings as they pass through the induction coil  30 . Quartz is relatively chemically inert and has a high melting point. Other materials with suitable physical properties could be readily substituted, such as a ceramic material. Preferably, the quartz tube  20  extends along the central axis within the passageway of the induction coil  30  so that the casings within the tube  20  pass along the most concentrated region of the electromagnetic field created by the induction coil  30 . The quartz tube  20  preferably has an inside diameter slightly larger than the outside diameter of the casings. This maintains a uniform alignment of the casings roughly parallel to the longitudinal axis of the tube  20 .  
      As shown in  FIG. 1 , the quartz tube  20  is supported at one end by a mounting collet  24  attached to a drive tube  22  driven by a motor (not shown). Rotation of the tube  20  about its longitudinal axis achieves a number of objectives. First and foremost, it helps to prevent casings from sticking to the wall of the tube or to one another, thereby keeping the casings moving along the length of the tube. It also helps to ensure even heating and annealing by tumbling the casings radially as they slide along the tube. Optionally, additional steps can be taken to prevent contact welding between adjacent casings. For example, glass marbles or other suitable insulating spacers can be inserted between the casings. A slight taper (e.g., approximately 0.002 inches per inch) can be ground into the inside diameter of the quartz tube  20  to help ensure relative movement between adjacent casings.  
      An infrared probe  40  monitors the temperature of the casings emerging from the quartz tube  20 . This temperature sensor  40  can be used to regulate the power output of the induction coil, and thereby control the annealing temperature of the casings.  
      The present invention uses less electrical energy than a conventional pit furnace of comparable capacity. A 45 KW pit furnace running on an eight-hour cycle consumes more energy in the first two hours than a 10 KW induction coil in the present system consumes in the full eight hours. After the pit furnace comes up to full temperature, it will cycle on and off for the remaining six hours at about 40% of its full load rating, thus consuming additional electrical energy. In contrast, the present system requires far less electrical energy by heating only the brass cups and the adjacent region within the quartz tube. Each part receives the same amount of energy to exactly the same depth, thereby assuring uniform hardness. A very large portion of this thermal energy can be reclaimed by means of a heat exchanger and used in the subsequent acid etching process.  
      The rapid annealing times achieved by the present invention allow only minimal oxidation of the parts. In turn, this allows the use of a much milder acid wash and results in almost no loss of weight by the parts. For example, a relatively dilute solution of phosphoric acid can be employed in place of sulfuric acid.  
      The present system also allows on-demand annealing instead of batches once a day. This allows both the pre-annealing and post-annealing processes to be performed on a continuous basis. This simplifies scheduling and reduces lead times between operations in the manufacturing process.  
      The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims.