Patent Publication Number: US-2004045446-A1

Title: Air core cookware

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an Air Core™ cooking vessel, specifically, to a cooking vessel having a double-layered structure that preserves heat and traps moisture during cooking.  
       [0003] 2. Description of the Related Art  
       [0004] Various types of cooking vessel are known and used in a kitchen. Such cooking vessel is made of one or more layers of stainless steel and has a single-layered bottom. The single layered bottom is good for directly transmitting heat to the food contained in the vessel, but also causes burning of the food when carefully not attended to.  
       [0005] To solve the above problems, a cooking vessel having a double-layered structure has been proposed for preventing burnt food and to improve food flavor. One such ideas is published in Korean Utility Laid-Open Publication No. 85-7307, which teaches that paraffin is injected between a space provided by a double-layered structure and an air hole is established thereon.  
       [0006] Moreover, a pot of a double-layered structure and a pot having a double-layered structure into which a working fluid is injected are taught by Japanese Laid-Open Publication No. 56-169825.  
       [0007] Instead of charging the space with paraffin, a structure into which a fluid of heat-medium is injected and sealed is disclosed in Korean Laid-Open Publication No. 97-4035.  
       [0008] In such pots having the above-mentioned structures of the related arts, the gap between the double-layer are filled with heat media to provide even-heat distribution and to save heat energy. Unfortunately, the structures of the related arts are filled with the heat medium substances and have to be sealed to prevent the substances from leaking out, resulting in the difficulties in manufacturing the cookware.  
       SUMMARY OF THE INVENTION  
       [0009] Accordingly, the present invention is directed to a cooking vessel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
       [0010] The object of the present invention is to provide a cooking vessel having a double-layered structure, which provide even heat distribution and preserves heat for a longer period of time.  
       [0011] Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
       [0012] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a cooking vessel comprises an inner shell having an open region having a bottom surface which extends upwardly to terminate at a top flange, a portion of the top flange forming an inner rim and an outer rim, the inner rim having a radius less than the radius of the outer rim, the outer rim formed substantially above the inner rim; an outer shell having an open region having a bottom surface which extends upwardly to terminate at an outwardly projecting bottom flange, the bottom flange having a length less than the length of the top flange; an inner space formed in an area between the inner shell and the outer shell and at least partially contains a heat conduction medium, the inner space formed by disposing the inner shell into the open region of the outer shell, wherein outer edges of the top flange is interlocked to outer edges of the bottom flange and substantially flattened to hermetically seal the inner space.  
       [0013] According to one aspect of the present invention, the wall space between the outer and inner shells contains air as its primary heat conduction medium. Alternatively, the wall space defined by the outer and inner shells contains a chemical, such as silicon oil, as its primary heat conduction medium.  
       [0014] According to another aspect of the present invention, a heat transfer plate is affixed to and in contact with an outer bottom surface of the outer shell. Preferably, the heat transfer plate is bonded to the base of the vessel by high impact. By bonding the plate by high impact, the vessel is more durable than if it was affixed by a brazing method because water that can cause rust and damage the cooking vessel is kept out of the area where the heat transfer plate is affixed.  
       [0015] In addition, the cooking vessel comprises an inner lid adapted to cover an open region of the inner shell and a portion of the inner rim. The inner lid comprises a disk having a diameter sufficiently large to cover the opening of the inner shell, and a ring having a flange coupled to the disk and circumferentially covering outer edges of the disk. The disk is preferably made of tempered glass but could also be made of stainless steel, aluminum and aluminum alloy.  
       [0016] The inner rim can also be shaped in a groove-like manner to fit the ring attached to the outer edges of the disk and to trap moisture. When moisture evaporates from cooking, the groove-like inner rim collects a pocket of moisture. The collected moisture acts as a seal, preventing additional moisture and heat from leaving the open region of the inner shell where the food is being cooked.  
       [0017] The flange formed on the bottom portion of the ring slides downward into the open region of the inner shell, and it is another means of ensuring that moisture and heat stay inside the cooking vessel.  
       [0018] Additionally, the cooking vessel comprises an outer lid that fits over the outer rim of the inner shell and the inner lid. The outer and the inner lid define an air gap space therebetween for trapping heat. The air gap, like the inner space, is a way of trapping heat and moisture, and distributing heat evenly and optimally.  
       [0019] Preferably, a means gauging temperature is installed on the outer lid. More preferably, the temperature gauge is affixed on the protruding knob. The temperature gauge informs the user when to turn off the stove and let the cooking vessel utilize the heat trapped in the vessel to finish the cooking.  
       [0020] When the heat conduction medium, such as silicon oil is contained in the wall space defined by vertical cylindrical walls of the outer and inner shells, the amount of silicon oil stored in the wall space is approximately 55 to 75%, and more preferably about 65%, by volume.  
       [0021] According to another aspect of the present invention, the cooking vessel further comprises a guard ring disposed in a lower proximity of the wall space around a circumference of the first heat conduction plate. Preferably, the guard ring has an L-shaped cross section. Alternatively, the guard ring has a U-shaped cross section.  
       [0022] According to another aspect of the present invention, the outer edges of the top flange are first welded to the outer edges of the bottom flange, and then interlocked and substantially flattened to form an interlocking joint. Preferably, the outer edges are welded in a seamless matter to prevent water from entering into the inner space formed in between the inner and outer shell.  
       [0023] According to another aspect of the present invention, the outer edges of the bottom flange is rolled at least one time, at about a 360 degree angle, interlocked with the top flange and substantially flattened to form an interlocking joint.  
       [0024] According to another aspect of the present invention, a pressure control element is installed on the outer shell. Preferably, a pressure relief valve is installed near one of the handles.  
       [0025] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0026] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
     [0027]FIG. 1 is a perspective view of the cooking vessel according to the present invention;  
     [0028]FIG. 2 is a cross-sectional view of a first embodiment of the cooking vessel according to the present invention;  
     [0029]FIG. 3 is a cross-sectional view of a second embodiment of the cooking according to the present invention;  
     [0030]FIG. 4 illustrates an enlarged cross-sectional view of the interlocking joint according to the second embodiment of the present invention;  
     [0031]FIG. 5 is illustrates an enlarged cross-sectional view of the interlocking joint according to the third embodiment of the cooking vessel according to the present invention;  
     [0032]FIG. 6 illustrates the process of welding the top flange of the inner shell to the bottom flange of the outer shell; and  
     [0033]FIG. 7 is illustrates an enlarged cross-sectional view of the interlocking joint and the welding point according to the fourth embodiment of the cooking vessel according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0034] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
     [0035]FIG. 1 is a perspective view of the cooking vessel  100  according to a preferred embodiment of the present invention. The cooking vessel  100  generally comprises an open region  10  for receiving and cooking food contained therein, an inner lid  20  for substantially covering the vessel  10  and a thermal insulating cover  30  disposed above the inner lid  20  and covering the open region  10  of the cooking vessel  100 .  
     [0036]FIG. 2 is a cross-sectional view of the cooking vessel  100  having at least a double-layered structure according to the present invention. According to the preferred embodiment, the inner lid  20  is constructed with a dome-shaped disk  21  of which edge is surrounded by a safety ring  22  preferably made of stainless steel or other suitable materials. The safety ring  22  is attached to the edges of the disk  21 , thereby preventing damages to the disk  21 . Additionally, an inner lid flange  33  that slides into an open region of an inner shell is formed on the safety ring. However, the inner lid  20  may be used without the ring  22 . Preferably, the disk  21  is made to form a slight convexed surface with respect to the vessel  10  of the cookware.  
     [0037] The disk  21  of the inner lid  20  is preferably made of tempered glass of approximately  4  mm thick. Alternatively, the disk  21  may be made of stainless steel, aluminum, aluminum alloy or other suitable materials known to one of ordinary skill in the art.  
     [0038] A handle  23  is attached to the center of the dome-shaped disk  21  by, for example, piercing the central portion of the disk  21 . Alternatively, the handle  23  may be affixed to the disk  21  by using adhesives or other fasteners.  
     [0039] The thermal insulating cover  30  is preferably made of a stainless steel plate being about 0.5 to 0.7 mm thick, and preferably about 0.6 mm thick, and has a dome like figure. The insulating cover  30  and the inner lid  20  form a horizontal air gap  26  which acts as an insulating layer to trap and hold heated air therein. As a result, once the heat source is removed from underneath the cooking vessel  100 , the air gap  26  and the inner space  16  filled with a heat conduction medium  34  insulate the inner shell  12  from outside and reduce heat loss, thus keeping the food contained in the inner shell  12  warm for a long period of time. More importantly, the structure of the present invention allows the food to be cooked even after removing the cooking vessel from the heat source.  
     [0040] Alternative to a single sheet structure, the cover  30  may comprise a plurality of layers of stainless steel and/or aluminum for increased durability and preservation of heat. In the thermal insulating cover  30 , a knob  32  is attached to the center of the thermal insulating cover  30 . In the present invention, the knob  32  may include a built-in temperature gauge for measuring the inside temperature of the cookware. The temperature gauge provides the user with information as to when it is time to remove the cooking vessel  100  from the heat source once a desired temperature has been reached.  
     [0041] The cooking vessel  100  according to the present invention includes an outer shell  11  and an inner shell  12  disposed adjacent the outer shell. Edges or flanges of the outer and inner shells are jointly curled and substantially flattened to form an interlocking joint  17 .  
     [0042] As a result, an inner space  16  filled with a heat conduction medium  34  is provided between the outer and inner shells  11  and  12 . The inner space as well as the heat conduction medium  34  is not in fluid communication with outside air.  
     [0043] In a first embodiment the present-invention, the inner space  16  filled with ambient air during the manufacturing process. In such embodiment, air serves as the primary heat conduction medium  34 .  
     [0044] In the preferred embodiment, the distance between the outer and inner shells  11  and  12  are approximately 15 to 25 mm, and preferably about 20 mm. Preferably, the outer and inner shells  11  and  12  are made of such materials as AIS1304 stainless steel that has a thickness of about 0.6 mm. Alternatively, instead of using a single-layered stainless steel, a multiple-layered composite materials may be used. Typically, three or more layered stainless steel or combination of stainless copper and steel are preferred.  
     [0045] In another embodiment of the cooking vessel  100 , the inner space  16  is at least partially filled with silicon oil up to 55 to 90% by volume. Preferably, the silicon oil is filled up to about 65% of the inner space  16  to accommodate for increased pressure in the inner space  16 . For example, while cooking, the pressure of the inner space  16  varies from 200 mmAG to 600 mmAG due to expansion of the silicon oil.  
     [0046] Referring to FIG. 2, there is provided a heat conduction plate  14  placed between the outer and inner shells  11  and  12 . The first heat conduction plate  14  is preferably made of an aluminum disk, copper or other suitable materials known to one of ordinary skill in the art. The heat conduction plate  14  is preferably affixed to the inner bottom surface of the outer shell. The heat conduction plate  14  is about 1.5 to 2.5 mm thick, and preferably about 2 mm thick. To provide speedy transmission of heat to the food contained in the cooking vessel  10 , the heat conduction plate  14  also makes contact with the outer bottom surface of the inner shell  12 . Due to the presence of the heat conduction plate  14 , there is no inner space  16  between the bottom of the inner shell  12  and that of the outer shell  11 ; alternatively, a heat conductive plate  14  having a fluid path is placed between the outer and inner shells  11  and  12 .  
     [0047] In the preferred embodiment, a heat transfer plate  15  is disposed below the bottom surface of the outer shell  11  preferably below the heat conduction plate  14 . Similar to the heat conduction plate, the heat transfer plate  15  is preferably made of an aluminum disk or other suitable materials known to one of ordinary skill in the art. The heat transfer plate  15  is about 2 to 4 mm thick, and preferably about 3 mm thick. The heat transfer plate  15  is securely affixed to the bottom of the outer shell  11  by brazing or other suitable method known to one of ordinary skill in the art. Preferably, the heat transfer plate is secured to the outer bottom surface of the outer shell  11  by bonding. More preferably, the base is bonded by high-impact.  
     [0048] Alternatively, if a braising or other similar method secures the heat transfer plate, a support cover covers the second heat conduction plate  15 . The support cover is attached to an outer bottom surface of the outer shell  11  fully surrounding and in contact with the second heat conduction plate  15 . The support cover is preferably made of the same material as that of the vessel  10  of the cooking vessel  100 . In particular, the support cover is made of AIS1304 stainless steel that has a thickness of about 0.5 mm. In the vessel, the heat conduction plate  14 , the bottom wall of the outer shell  11 , the heat transfer plate  15  and the support cover are in thermal communication with each other.  
     [0049] In the embodiment where the primary heat conduction medium  34  is air, the heat transfer plate  15  and the heat conduction plate  14  also serve to heat the inner space  16  of the cooking vessel  100 . Although most of the heat transmitted to the bottom of the outer shell  11  is conducted to the heat conduction plate  14 , the rest of the heat are transferred to the side walls of the outer and inner shells  11  and  12 , respectively. Then, the temperature of the air in the inner space  16  is gradually increased and the heat energy of the air is transmitted to the inner shell  12  and spread out throughout the entire wall of the inner shell  12 . Therefore, the temperature along the inner shell  12  is substantially constant at any region thereof. In other words, the temperature of the bottom of the inner shell  12  is about the same as that of the cylindrical wall.  
     [0050] The presence of air in the inner space  16  delays heat transfer between the sides of the outer and inner shells  11  and  12  as well as provides even heat distribution as the heat conducted through the outer shell  11  of the cooking vessel  100  primarily is not transferred to the inner shell  12  of the pot but is partially conveyed through the air.  
     [0051] The heat distributed uniformly in the inner shell  12  heats up the contents in the cooking vessel  100 . Once heated, the double-layered structure of the cooking vessel  100  according to the present invention maintains the trapped heat, even after the heat source is removed, for a prolonged period. The heat loss through the sidewalls of the inner and outer shells  11  and  12  are slowed due to the presence of air pockets.  
     [0052] Moreover, it is easy to preserve the heat inside the cooking vessel  100  as the lid  20  and the thermal insulating cover  30  stop the heat dissipating upward. The third air pocket  26  formed between the lid  20  and the insulating cover  30  traps heat therein and holds the temperature for an extended period of time.  
     [0053] Accordingly, the present invention prevents the food from being burnt or being partially heated, since the flame of heating source is not directed to the inner shell  12  and heat is not focused in any one region. In addition, the air stored in the inner space  16  acts as an insulator. Therefore, the food stays hotter for a longer period of time. Moreover, heat efficiency of the cooking vessel is improved.  
     [0054] In the first embodiment of the present invention, the inner rim  37  is shaped in a groove-like manner to fit the ring  22  attached to the outer edges of the disk  21  and to trap moisture. When moisture evaporates from cooking, the groove of the inner rim  37  collects a pocket of moisture. The collected moisture acts as a seal, preventing additional moisture from leaving the open region of the inner shell  39  where the food is being cooked.  
     [0055] Referring to FIG. 3, first, an inner shell  12  and an outer shell  11  which are preferably made of stainless steel having a predetermined strength are prepared so that the inner shell  12  is placed in an opening region of the outer shell. A heat conduction medium  34 , such as silicon oil, is then put into the outer shell  11 . Then, the inner shell  12  is placed therein to fill up the space between the outer and inner shells  11  and  12  with the heat conduction medium  34  occupying up to 65% by volume of the space  16 . If the cooking vessel  100  does not utilize silicon oil as its primary heat conduction medium  34 , then the inner shell is simply placed inside the outer shell  11  for further processing.  
     [0056] Additionally, a inner portion of the top flange  35  forms an inner rim  37  and an outer portion of forms an outer rim  37 .  
     [0057] The inner and outer shells  12  and  11 , when overlapped, are constructed and designed to provide a vertical and bottom space. The vertical and bottom space are collectively referred to in this specification as the inner space  16 . Initially, the top flange  36  of the inner shell  12  and bottom flange  38  of the outer shell  11  are made to assist the downward curling of the edges; therefore, the top flange  35  of the inner of the inner shell  12  extends farther out than that of the bottom flange  38  of the outer shell  11 , as shown in FIG. 3. Alternatively, if the upward curling is desired, the bottom flange  38  of the outer shell  11  extends farther than the top flange  35  of the inner shell  12 .  
     [0058] Referring to FIG. 4, the outer edges of a top flange  35  is interlocked with the outer edges of a bottom flange  38  and substantially flattened to form an interlocking joint  17 . In particular, the interlocking joint  17  is formed by jointly curling the longer top flange  35  of the inner shell with the shorter bottom flange  38  of the outer shell, at about the same axis. The top flange  35  is rolled at about 360 degrees one time, about the same axis, and the bottom flange  38  is rolled about half as much as the top flange  35 , both flanges forming a hook-like shape and interlocked with one another. The two flanges are then substantially flattened together to form an interlocking joint  17 . The interlocking joint  17  prevents the heat conduction medium  34  in the inner space  16  from escaping even when the cooking vessel  100  is subjected to intense heat that causes high pressure in the inner space  16 . More importantly, when the two flanges are formed into an interlocking joint  17 , it prevents water from seeping into the inner space  16 ; therefore, substantially reducing the risk of explosion.  
     [0059] To further reduce the risk of explosion, in the first embodiment of the present invention as shown in FIG. 2 a pressure control element  40  is installed on the outer wall  11 . Preferably, the pressure control element  40  is installed near one of it handle.  
     [0060]FIG. 5 illustrates an enlarged cross-sectional view of the interlocking joint  17  according to the third embodiment of the cooking vessel according to the present invention. In this embodiment, the bottom flange  38  is rolled about one time; the top flange is rolled one and a half time, at about a 360-degree angle, and substantially flattened to form an interlocking joint  17 . The additional fold is another means of sealing the inner space  16 .  
     [0061]FIG. 6 illustrates the process of welding the top flange of the inner shell to the bottom flange of the outer shell.  
     [0062] To prevent the passage of fluid in and out of the inner space and to prevent the buildup of pressure, the flanges of the cooking vessel are electrically welded at a welding point W 1 . The top flange  35  and the bottom flange  41  are placed between an upper electrode pole  40  and a lower electrode pole  41  of an electric welding machine  42 . The cooking vessel  100  is then rotated with respect to the upper electrode pole  40  and the lower electrode pole  41 .  
     [0063] Alternatively, another way of seamlessly welding the top flange  35  to the bottom flange  41  is by first embossing a surrounding edge of the top flange  35  to form a protrusion of a predetermined height and utilizing an electric pole and electric plate style welding machine.  
     [0064]FIG. 7 is illustrates an enlarged cross-sectional view of the interlocking joint  17  and the welding point W 1  according to the fourth embodiment of the cooking vessel  100  according to the present invention. The top flange  35  is seamlessly welded to the bottom flange  38 , rolled at about the same degree as the first embodiment and substantially flattened to form an interlocking joint  17 .  
     [0065] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and equivalents.  
     [0066] The invention finds its industrial application in the fabrication of vessels for cooking, in particular multilayered cooking vessels.