Patent Publication Number: US-2016223260-A1

Title: Heating furnace

Description:
TECHNICAL FIELD 
     The present invention relates to a heating furnace. 
     BACKGROUND ART 
     Patent Document 1 discloses a heat treatment furnace. The heat treatment furnace includes a furnace body opening downward and a floor body closing the lower opening of the furnace body. The furnace body and the floor body form a furnace chamber. Shelves are provided in the furnace chamber. Workpieces are mounted on the shelves. Hot air circulation devices are disposed on the outer periphery of the furnace body at two positions along the circumferential direction. The hot air circulation devices horizontally send hot air into the furnace chamber. Each of the hot air circulation devices communicates with the inside of the furnace chamber. Each of the hot air circulation devices has an opening. The opening faces the workpieces inside the furnace chamber. The hot air fed into the furnace chamber from each of the hot air circulation devices is circulated in the circumferential direction in the furnace chamber between the hot air circulation devices. A sand discharge mechanism is disposed on the floor body. The sand discharge mechanism discharges sand falling from the workpieces in the furnace chamber to the outside of the furnace chamber. The heat treatment furnace described in Patent Document 1 makes it possible to reduce variation in quality between workpieces. The heat treatment furnace also makes it possible to reduce the loss of energy. The heat treatment furnace also makes it possible to shorten the time required for the whole heat treatment including a soaking time. The heat treatment furnace achieves elongation of the durability thereof. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Patent Application Laid-open No. 2006-200823 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, disadvantageously, the heat treatment furnace disclosed in Patent Document 1 fails to sufficiently reduce variation in temperature among various points inside the furnace chamber. That is, in the heat treatment furnace disclosed in Patent Document 1, temperatures often largely differ from each other among various points inside the furnace. 
     The present invention solves such a problem. An object of the present invention is to provide a heating furnace that reduces variation in temperature among various points inside a furnace chamber. 
     Solutions to the Problems 
     A heating furnace of the present invention will be described with reference to drawings. In this column, reference signs in the drawings are used in description for the purpose of facilitating understanding of the contents of the invention. Thus, there is no intention to limit the contents to the illustrated range. 
     In order to solve the above problem, according to an aspect of the present invention, the heating furnace includes a furnace body  10 , a workpiece loading unit  12 , a hearth  14 , and hot air supply devices  20 ,  24 . The furnace body  10  forms a furnace chamber  40 . The furnace body  10  has workpiece passing openings  70 ,  72 ,  74 ,  76 . The workpiece loading unit  12  is arranged inside the furnace chamber  40 . The hearth  14  faces the furnace chamber  40 . The workpiece loading unit  12  is placed on the hearth  14 . The hearth  14  rotates to allow the workpiece loading unit  12  to rotate inside the furnace chamber  40 . The hot air supply devices  20 ,  24  are arranged inside the furnace chamber  40 . The hot air supply devices  20 ,  24  send out hot air inside the furnace chamber  40 . Tubular partitions  28  are arranged inside the furnace chamber  40 . The tubular partitions  28  divide the furnace chamber  40  into an inner space  110  and an outer space  112 . The workpiece loading unit  12  is arranged in the inner space  110 . The hot air supply devices  20 ,  24  are arranged in the outer space  112 . Each of the tubular partitions  28  has a furnace chamber inside communication portion  130  and a furnace outside communication portions  132  or  134 . The furnace chamber inside communication portion  130  allows the inner space  110  and the outer space  112  to communicate with each other. The furnace outside communication portions  132 ,  134  allow the inner space  110  and the workpiece passing openings  70 ,  72 ,  74 ,  76  to communicate with each other. 
     Workpieces  200  are placed on the workpiece loading unit  12  through the workpiece passing openings  70 ,  72 ,  74 ,  76 , and the furnace outside communication portions  132 ,  134 . The workpiece loading unit  12  rotates inside the furnace chamber  40 . Along with the rotation of the workpiece loading unit  12 , the workpieces  200  also rotate inside the furnace chamber  40 . While the workpieces  200  are rotating inside the furnace chamber  40 , the hot air supply devices  20 ,  24  send out hot air inside the furnace chamber  40 . The hot air flows to the inner space  110  through the furnace chamber inside communication portion  130  while flowing in the outer space  112 . Even when hot air that has previously flown into the inner space  110  loses its thermal energy by heating the workpieces  200 , hot air flowing into the inner space  110  thereafter compensates the lost thermal energy. Since the lost thermal energy is compensated, it is possible to reduce variation in temperature among various points inside the furnace chamber. 
     The above-described furnace chamber  40  desirably includes heat treatment chambers  46 ,  48 , heating chambers  50 ,  52 , and furnace chamber communication portions  54 ,  56 . The workpiece loading unit  12  and the tubular partitions  28  are arranged in the heat treatment chambers  46 ,  48 . The hot air supply devices  20 ,  24  are arranged in the heating chambers  50 ,  52 . The furnace chamber communication portions  54 ,  56  allow the heating chambers  50 ,  52  and heat treatment chambers  46 ,  48  to communicate with each other. Hot air passes through the furnace chamber communication portions  54 ,  56 . In this case, the furnace chamber inside communication portion  130  of each of the tubular partitions  28  desirably includes a hot air inflow portion  140  and a hot air replenishment portion  142 . The hot air inflow portion  140  faces the furnace chamber communication portion  54  or  56 . The hot air inflow portion  140  allows the inner space  110  and the outer space  112  to communicate with each other. The hot air replenishment portion  142  is arranged on the downstream side of the flow of hot air with respect to the hot air inflow portion  140 . The hot air replenishment portion  142  allows the inner space  110  and the outer space  112  to communicate with each other. 
     The hot air inflow portion  140  faces the furnace chamber communication portions  54  or  56 . Thus, a part of the hot air that has flown into the furnace chamber  40  directly flows into the inner space  110 . The thermal energy of the hot air is used for heating an article inside the inner space  110 . The other part of the hot air temporarily flows to the outer space  112 , and then flows into the inner space  110  through the hot air replenishment portion  142 . The hot air compensates the thermal energy in the inner space  110 . Accordingly, it is possible to reduce the loss of thermal energy caused by transfer of thermal energy of hot air to the furnace body  10 . 
     Alternatively, the above-described hot air replenishment portion  142  desirably includes an upstream opening portion  150  and a downstream opening portion  152 . The upstream opening portion  150  has a hole  158 . The hole  158  allows the inner space  110  and the outer space  112  to communicate with each other. The downstream opening portion  152  is arranged on the downstream side of the flow of hot air with respect to the upstream opening portion  150 . The downstream portion  152  has a hole  158 . The hole  158  allows the inner space  110  and the outer space  112  to communicate with each other. The opening area per unit area of the downstream opening portion  152  is larger than the opening area per unit area of the upstream opening portion  150 . 
     Since the opening area per unit area of the downstream opening portion  152  is larger than the opening area per unit area of the upstream opening portion  150 , a larger amount of hot air flows into the inner space  110  in the downstream opening portion  152  than the upstream opening portion  150 . Hot air is prevented from flowing into the inner space  110  on the upstream side of the flow of hot air. Therefore, it is possible to prevent the temperature of the workpiece  200  from unnecessarily increasing. 
     Alternatively, the above-described tubular partition  28  desirably further includes a hot air outflow portion  136 . The hot air outflow portion  136  is arranged on the downstream side of the flow of hot air with respect to the hot air replenishment portion  142 . The hot air outflow portion  136  faces the furnace chamber communication portion  54  or  56  together with the hot air inflow portion  140 . Hot air inside the inner space  110  flows out toward the furnace chamber communication portion  54  or  56  through the hot air outflow portion  136 . In this case, the heating furnace further includes heating devices  22 ,  26 . The heating devices  22 ,  26  are arranged inside the heating chambers  50 ,  52 . Each of the heating devices  22 ,  26  heats hot air that has flown out through the hot air outflow portion  136  and then flown into each of the heating chambers  50 ,  52 . 
     The hot air that has flown out through the hot air outflow portion  136  can be reused by heating hot air flown into the heating chambers  50 ,  52  by the heating devices  22 ,  26  and sending out the hot air into the furnace chamber  40  by the hot air supply devices  20 ,  24 . Accordingly, it is possible to more efficiently use the thermal energy for heating the workpiece  200  than when thermal energy is not reused. 
     Alternatively, the above-described tubular partition  28  desirably further includes a hot air guide portion  138 . The hot air guide portion  138  guides hot air fed into the heat treatment chamber  46  or  48  from the heating chamber  50  or  52  to the hot air inflow portion  140 . The hot air guide portion  138  guides hot air flowing out through the hot air outflow portion  136  to the heating chamber  50  or  52 . 
     The hot air guide portion  138  of the tubular partition  28  prevents hot air fed into the furnace chamber  40  and hot air guided to the heating chamber  50  or  52  from slowing their flow velocities each other. As a result, hot air more smoothly flows than when the hot air guide portion  138  is not provided. 
     Further, the above-described heating furnace desirably further includes a flow end wall  34 . The flow end wall  34  is arranged between the inner peripheral surface of the furnace chamber  40  and the tubular partition  28 . The flow end wall  34  blocks hot air. 
     Since the flow end wall  34  blocks hot air, the hot air totally flows into the inner space  110  before reaching the flow end wall  34 . When the hot air totally flows into the inner space  110 , the velocity of flow of hot air inside the inner space  110  becomes higher than when hot air does not totally flow into the inner space  110 . The increase in the velocity of flow results in an increase in the heat transfer coefficient of hot air in a place where the velocity of flow increases. Further, the increase in the heat transfer coefficient makes it possible to efficiently compensate thermal energy. 
     Further, the above-described flow end wall  34  is desirably arranged on the downstream side of the flow of hot air with respect to the furnace outside communication portions  132 ,  134 . In this case, the workpiece loading unit  12  rotates in a direction of the flow of hot air. 
     When the flow end wall  34  is arranged on the downstream side of the flow of hot air with respect to the furnace outside communication portions  132 ,  134 , rise in the temperature of the workpiece  200  placed on the workpiece loading unit  12  through the workpiece passing openings  70 ,  72 ,  74 ,  76  and the furnace outside communication portions  132 ,  134  is accelerated. 
     The above-described heating furnace desirably further includes passage forming tubes  30 ,  32 . The passage forming tubes  30 ,  32  are arranged between the furnace outside communication portions  132 ,  134  and the workpiece passing openings  70 ,  72 ,  74 ,  76 . The passage forming tubes  30 ,  32  form passages. 
     When the passage forming tubes  30 ,  32  are arranged between the furnace outside communication portions  132 ,  134  and the workpiece passing openings  70 ,  72 ,  74 ,  76 , it is possible to reduce the amount of hot air flowing through the outer space  112  and then flowing out of the furnace body  10  through the workpiece passing openings  70 ,  72 ,  74 ,  76 . The reduction in the amount of hot air makes it possible to reduce the loss of thermal energy caused by hot air flowing out of the furnace. 
     The above-described workpiece loading unit  12  desirably includes shelves  80 ,  84  and direction guide bodies  86 ,  88 . The direction guide bodies  86 ,  88  are arranged at the position nearer the rotation center of the hearth  14  than the shelves  80 ,  84 . The direction guide bodies  86 ,  88  guide the flow of hot air in the inner space  110  to the rotation direction of the hearth  14 . 
     Since the flow of hot air is guided to the rotation direction of the hearth  14 , the hot air heats the workpiece  200  while flowing in the inner space  110 . Accordingly, it is possible to efficiently transfer thermal energy to the workpiece  200  from the hot air. 
     Effect of the Invention 
     As described above, according to the heating furnace of the present invention, it is possible to reduce variation in temperature between various points inside the furnace chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a heating furnace according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along line A-A of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a furnace body according to an embodiment of the present invention. 
         FIG. 4  is a cross-sectional view taken along line B-B of  FIG. 2 . 
         FIG. 5  is a cross-sectional view of a workpiece loading unit according to an embodiment of the present invention. 
         FIG. 6  is a perspective view of a tubular partition according to an embodiment of the present invention. 
         FIG. 7  is a cross-sectional view taken along line C-C of  FIG. 1 . 
         FIG. 8  is a conceptual diagram illustrating the tubular partition with inlet passage forming tubes and outlet passage forming tubes attached thereto according to an embodiment of the present invention. 
     
    
    
     EMBODIMENT OF THE INVENTION 
     Hereinbelow, an embodiment of the present invention will be described with reference to the drawings. In the following description, identical components are designated by identical reference signs. The identical components have identical names and functions. Thus, detailed description thereof will not be repeated. 
     [Configuration of Heating Furnace] 
     The configuration of a heating furnace according to the present embodiment will be described with reference to  FIGS. 1 and 2 . The heating furnace according to the present embodiment is provided with a furnace body  10 , a workpiece loading unit  12 , a hearth  14 , a hearth supporting unit  16 , a hearth rotating unit  18 , a lower hot air supply device  20 , a lower heating device  22 , an upper hot air supply device  24 , an upper heating device  26 , and a tubular partition  28 . 
     The configuration of the furnace body  10  according to the present embodiment will be described with reference to  FIG. 3 . The furnace body  10  forms a furnace chamber  40 . The furnace chamber  40  is divided into a lower heat treatment chamber  46 , an upper heat treatment chamber  48 , a lower heating chamber  50 , an upper heating chamber  52 , a lower furnace chamber communication portion  54 , and an upper furnace chamber communication portion  56 . In the present embodiment, the lower heat treatment chamber  46  is a space in which a solution treatment which is a type of heat treatment is performed. The upper heat treatment chamber  48  is a space in which an aging treatment which is a type of heat treatment is performed. The lower heating chamber  50  is a space in which gas is heated. The lower hot air supply device  20  and the lower heating device  22  are arranged in the lower heating chamber  50 . Also, the upper heating chamber  52  is a space in which gas is heated. The upper hot air supply device  24  and the upper heating device  26  are arranged in the upper heating chamber  52 . The lower furnace chamber communication portion  54  allows the lower heating chamber  50  and the lower heat treatment chamber  46  to communicate with each other. Hot air passes through the lower furnace chamber communication portion  54 . The upper furnace chamber communication portion  56  allows the upper heating chamber  52  and the upper heat treatment chamber  48  to communicate with each other. Hot air passes through the upper furnace chamber communication portion  56 . 
     The furnace body  10  includes an annular partition  60 , a furnace body supporting leg  62 , an exhaust tube  64 , a sand seal portion  66 , and an exhaust tube  68 . The annular partition  60  divides the lower heat treatment chamber  46  and the upper heat treatment chamber  48 . The furnace body supporting leg  62  supports the entire furnace body  10 . The exhaust tube  64  discharges a part of the gas inside the upper heat treatment chamber  48  therethrough. The sand seal portion  66  is disposed on the inner peripheral surface of the annular partition  60 . Known sand is stored inside the sand seal portion  66 . The exhaust tube  68  discharges a part of the gas inside the lower heat treatment chamber  46  therethrough. 
     Workpiece passing openings according to the present embodiment will be described with reference to  FIGS. 1 and 4 . As illustrated in  FIG. 4 , the furnace body  10  has lower inlet openings  70  and lower outlet openings  72 . As illustrated in  FIG. 1 , the furnace body  10  further has upper inlet openings  74  and upper outlet openings  76 . In the present embodiment, the lower inlet openings  70 , the lower outlet openings  72 , the upper inlet openings  74 , and the upper outlet openings  76  are collectively referred to as “workpiece passing openings”. The lower inlet openings  70  and the lower outlet openings  72  allow the lower heat treatment chamber  46  and the outside of the furnace body  10  to communicate with each other. The upper inlet openings  74  and the upper outlet openings  76  allow the upper heat treatment chamber  48  and the outside of the furnace body  10  to communicate with each other. Doors are attached to the respective workpiece passing openings. The number of workpiece passing openings is set to any number by a designer of the heating furnace according to the present embodiment. 
     The configuration of the workpiece loading unit  12  according to the present embodiment will be described with reference to  FIG. 5 . The workpiece loading unit  12  is arranged inside the furnace chamber  40 . The workpiece loading unit  12  includes a lower shelf  80 , a partition plate  82 , an upper shelf  84 , a lower direction guide body  86 , and an upper direction guide body  88 . The lower shelf  80  is placed on the hearth  14 . The lower shelf  80  and the hearth  14  are fixed to each other. The lower shelf  80  is arranged inside the lower heat treatment chamber  46  of the furnace chamber  40 . A workpiece  200  is placed on the lower shelf  80 . The partition plate  82  is placed on the lower shelf  80 . The partition plate  82  and the lower shelf  80  are fixed to each other. A partition ring  90  is disposed on the outer periphery of the partition plate  82 . The partition ring  90  is fitted into the sand seal portion  66  of the annular partition  60 . As described above, sand is stored in the sand seal portion  66 . This prevents heat transfer from the lower heat treatment chamber  46  to the upper heat treatment chamber  48 . The upper shelf  84  is placed on the partition plate  82 . The upper shelf  84  and the partition plate  82  are fixed to each other. The upper shelf  84  is arranged inside the upper heat treatment chamber  48  of the furnace chamber  40 . A workpiece  200  is also placed on the upper shelf  84 . The lower direction guide body  86  is fixed to the hearth  14  together with the lower shelf  80 . The lower direction guide body  86  is arranged at the position nearer the rotation center of the heath  14  than the lower shelf  80 . The upper direction guide body  88  is placed on the partition plate  82  together with the upper shelf  84 . The upper direction guide body  88  is also fixed to the partition plate  82 . The upper direction guide body  88  is arranged at the position nearer the rotation center of the hearth  14  than the upper shelf  84 . In the present embodiment, the lower shelf  80  and the upper shelf  84  are collectively referred to as “shelves”. Further, the lower direction guide body  86  and the upper direction guide body  88  are collectively referred to as “direction guide bodies”. 
     The configuration of the hearth  14  according to the present embodiment will be described with reference to  FIG. 2 . The hearth  14  is arranged under the furnace body  10 . The furnace body  10  has an opening formed on the lower end thereof. The hearth  14  is arranged to close the opening. The hearth  14  faces the furnace chamber  40 . The workpiece loading unit  12  is placed on the hearth  14 . The hearth  14  has a sand hopper  100 . The sand hopper  100  is arranged right under the workpiece loading unit  12 . Sand falling from the workpiece  200  is accumulated on the sand hopper  100 . The accumulated sand is discharged to the lower side of the hearth  14 . 
     The hearth supporting unit  16  and the hearth rotating unit  18  according to the present embodiment will be described with reference to  FIG. 2 . The hearth supporting unit  16  supports the hearth  14 . A roller is disposed on the tip of the hearth supporting unit  16 . The heart  14  is placed on the roller. The hearth rotating unit  18  penetrates the center of the hearth  14 . The hearth rotating unit  18  drives the hearth  14  to allow the hearth  14  to rotate around the hearth rotating unit  18 . Accordingly, the hearth  14  rotates around the hearth rotating unit  18 . Since the workpiece loading unit  12  is placed on the hearth  14 , the workpiece loading unit  12  rotates inside the furnace chamber  40  along with the rotation of the hearth  14 . 
     The lower hot air supply device  20 , the lower heating device  22 , the upper hot air supply device  24 , and the upper heating device  26  according to the present embodiment will be described with reference to  FIGS. 1 and 2 . The lower hot air supply device  20  is arranged inside the lower heating chamber  50  of the furnace body  10 . The lower hot air supply device  20  sends out hot air into the lower heat treatment chamber  46 . The hot air that has circulated inside the lower heat treatment chamber  46  again flows into the lower heating chamber  50 . In the present embodiment, the lower hot air supply device  20  is composed of a sirocco fan. The sirocco fan sucks gas and sends out hot air to the lower heat treatment chamber  46 . The lower heating device  22  is also arranged inside the lower heating chamber  50 . The lower heating device  22  is arranged to face a gas suction port of the lower hot air supply device  20 . The lower heating device  22  heats the hot air that has again flown into the lower heating chamber  50  from the lower heat treatment chamber  46 . In the present embodiment, the lower heating device  22  is composed of a combustion burner. The upper hot air supply device  24  is arranged inside the upper heating chamber  52  of the furnace body  10 . The upper hot air supply device  24  sends out hot air into the upper heat treatment chamber  48 . The hot air that has circulated inside the upper heat treatment chamber  48  again flows into the upper heating chamber  52 . In the present embodiment, the upper hot air supply device  24  is composed of a sirocco fan having the same structure as the lower hot air supply device  20 . The upper heating device  26  is also arranged inside the upper heating chamber  52 . The upper heating device  26  is arranged to face a gas suction port of the upper hot air supply device  24 . The upper heating device  26  heats the hot air that has again flown into the upper heating chamber  52  from the upper heat treatment chamber  48 . In the present embodiment, the upper heating device  26  is composed of a combustion burner having the same structure as the lower heating device  22 . 
     The arrangement and function of the tubular partition  28  according to the present embodiment will be described with reference to  FIG. 4 . The tubular partition  28  is arranged in the lower heat treatment chamber  46 . The tubular partition  28  arranged in the lower heat treatment chamber  46  divides a part of the furnace chamber  40  from the lower heating chamber  50  through the lower heat treatment chamber  46  into an inner space  110  and an outer space  112 . The inner space  110  is located inside the tubular partition  28 . The lower shelf  80  of the workpiece loading unit  12  is arranged in the inner space  110 . Accordingly, the tubular partition  28  arranged in the lower heat treatment chamber  46  surrounds the lower shelf  80 . The outer space  112  is located outside the tubular partition  28  in the furnace chamber  40 . Thus, the lower heating chamber  50  is a part of the outer space  112 . 
     A tubular partition having the same structure as the tubular partition arranged in the lower heat treatment chamber  46  is arranged in the upper heat treatment chamber  48 . However, in the tubular partition arranged in the upper heat treatment chamber  48 , the positions of furnace outside communication portions (described below) differs from that in the tubular partition arranged in the lower heat treatment chamber  46  in order to allow the furnace outside communication portions to face the upper inlet opening  74  and the upper outlet opening  76 . The tubular partition  28  arranged in the upper heat treatment chamber  48  also divides a part of the furnace chamber  40  from the upper heating chamber  52  through the upper heat treatment chamber  48  into an inner space and an outer space. The upper shelf  84  of the workpiece loading unit  12  is arranged inside the inner space. Accordingly, the tubular partition  28  arranged in the upper heat treatment chamber  48  surrounds the lower shelf  80 . 
     The configuration of the tubular partition  28  arranged in the lower heat treatment chamber  46  according to the present embodiment will be described with reference to  FIG. 6 . As described above, the tubular partition  28  arranged in the upper heat treatment chamber  48  has the same configuration as the tubular partition  28  arranged in the lower heat treatment chamber  46  excepting the positions of the furnace outside communication portions. In the present embodiment, the tubular partition  28  has a hollow cylindrical shape. 
     The tubular partition  28  includes a furnace chamber inside communication portion  130 , furnace outside communication inlet portions  132 , furnace outside communication outlet portions  134 , a hot air outflow portion  136 , and a hot air guide portion  138 . 
     The furnace chamber inside communication portion  130  allows the inner space and the outer space to communicate with each other. In the following description, “inner space” refers to a space surrounded by the tubular partition  28  in the lower heat treatment chamber  46  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to a space surrounded by the tubular partition  28  in the upper heat treatment chamber  48  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . In the following description, “outer space” refers to a space located from the lower heating chamber  50  through the lower heat treatment chamber  46  as well as outside the tubular partition  28  in the furnace chamber  40  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to a space located from the upper heating chamber  52  through the upper heat treatment chamber  48  as well as outside the tubular partition  28  in the furnace chamber  40  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . 
     The furnace chamber inside communication portion  130  includes a hot air inflow portion  140  and the hot air replenishment portion  142 . The hot air inflow portion  140  faces the furnace chamber communication portion. In this paragraph, “furnace chamber communication portion” refers to the lower furnace chamber communication portion  54  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to the upper furnace chamber communication portion  56  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . The hot air inflow portion  140  allows the inner space and the outer space to communicate with each other. The hot air replenishment portion  142  is arranged on the downstream side of the flow of hot air with respect to the hot air inflow portion  140 . The hot air replenishment portion  142  allows the inner space and the outer space to communicate with each other. 
     The hot air replenishment portion  142  has an upstream opening portion  150  and a downstream opening portion  152 . Holes  158  are formed on the upstream opening portion  150 . The holes  158  allow the inner space and the outer space to communicate with each other. The downstream opening portion  152  is arranged on the downstream side of the flow of hot air with respect to the upstream opening portion  150 . Holes  158  are also formed on the downstream opening portion  152 . The opening area per unit area of the lower opening portion  152  by the holes  158  is larger than the opening area per unit area of the upstream opening portion  150  by the holes  158 . 
     The furnace outside communication inlet portions  132  and the furnace outside communication outlet portions  134  allow the inner space and the workpiece passing openings to communicate with each other. That is, each of the lower inlet openings  70  communicates with the inner space through either one of the furnace outside communication inlet portions  132 . Further, each of the lower outlet openings  72  communicates with the inner space through either one of the furnace outside communication outlet portions  134 . The same applies to the upper inlet openings  74  and the upper outlet openings  76 . In the present embodiment, the furnace outside communication inlet portions  132  and the furnace outside communication outlet portions  134  are collectively referred to as “furnace outside communication portions”. 
     The hot air outflow portion  136  is arranged on the downstream side of the flow of hot air with respect to the hot air replenishment portion  142 . The hot air outflow portion  136  faces the furnace chamber communication portion together with the hot air inflow portion  140 . Hot air inside the inner space flows out through the hot air outflow portion  136 . 
     The hot air guide portion  138  guides hot air fed into the furnace chamber  40  from the heating chamber to the hot air inflow portion  140 . The hot air guide portion  138  guides hot air flowing out through the hot air outflow portion  136  to the heating chamber. In this paragraph, “heating chamber” refers to the lower heating chamber  50  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to the upper heating chamber  52  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . 
     The heating furnace according to the present embodiment further includes inlet passage forming tubes  30  and outlet passage forming tubes  32 . In the present embodiment, the inlet passage forming tubes  30  and the outlet passage forming tubes  32  are collectively referred to as “passage forming tubes”. The configuration of the inlet passage forming tubes  30  and the configuration of the outlet passage forming tubes  32  according to the present embodiment will be described with reference to  FIGS. 6, 7, and 8 . Each of the inlet passage forming tubes  30  is arranged between a furnace outside communication inlet portion  132  of the tubular partition  28  and an inlet opening of the furnace body  10  facing the furnace outside communication inlet portion  132 . In this paragraph, “inlet opening” refers to the lower inlet opening  70  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to the upper inlet openings  74  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . Each of the inlet passage forming tubes  30  forms a passage. The workpiece  200  is placed on the workpiece loading unit  12  through the passage. The inlet passage forming tubes  30  are members which also reduce leakage of hot air from the furnace body  10 . In the present embodiment, the inlet passage forming tubes  30  have a rectangular tubular shape. Each of the inlet passage forming tubes  30  has hot air guide holes  160 . The hot air guide holes  160  are formed on three side surfaces of the inlet passage forming tube  30 . Each of the outlet passage forming tubes  32  is arranged between a furnace outside communication outlet portion  134  of the tubular partition  28  and an outlet opening of the furnace body  10  facing the furnace outside communication outlet portion  134 . In this paragraph, “outlet opening” refers to the lower outlet opening  72  when the tubular partition  28  is arranged in the lower heat treatment chamber  46  and refers to the upper outlet openings  76  when the tubular partition  28  is arranged in the upper heat treatment chamber  48 . Each of the outlet passage forming tubes  32  forms a passage. The workpiece  200  is taken out of the workpiece loading unit  12  through the passage. The outlet passage forming tubes  32  are members which also reduce leakage of hot air from the furnace body  10 . In the present embodiment, the outlet passage forming tubes  32  have a rectangular tubular shape. Each of the outlet passage forming tubes  32  also has hot air guide holes  160 . The hot air guide holes  160  are formed on four side surfaces of the outlet passage forming tube  32 . 
     The heating furnace according to the present embodiment further includes a flow end wall  34 . The configuration of the flow end wall  34  according to the present embodiment will be described with reference to  FIGS. 4 and 8 . The flow end wall  34  is arranged between the inner peripheral surface of the furnace chamber  40  and the tubular partition  28 . The flow end wall  34  blocks hot air. In the present embodiment, the flow end wall  34  is arranged on the downstream side of the flow of hot air with respect to the furnace outside communication portions. In the lower heat treatment chamber  46 , the flow end wall  34  is in contact with side surfaces of the inlet passage forming tubes  30 , the side surfaces having no hot air guide hole  160 . 
     [Method of Using Heating Furnace] 
     A method of using the heating furnace according to the present embodiment based on the above configuration will be described. 
     An operator previously activates the lower hot air supply device  20 , the lower heating device  22 , the upper hot air supply device  24 , and the upper heating device  26 . Accordingly, the temperature inside the lower heat treatment chamber  46  becomes a temperature suitable for a solution treatment. Further, the temperature inside the upper heat treatment chamber  48  becomes a temperature suitable for an aging treatment. Then, an operator activates the hearth rotating unit  18 . Accordingly, the hearth  14  starts rotating. The hearth  14  rotates in a counterclockwise direction when viewed from the upper side of the heating furnace according to the present embodiment. The workpiece loading unit  12  also rotates along with the rotation of the hearth  14 . 
     Then, an operator opens the door of the lower inlet opening  70  and inserts the workpiece  200  into the lower heat treatment chamber  46  from the outside of the heating furnace using an appropriate jig. After the workpiece  200  is inserted, the door of the lower inlet opening  70  is closed. Since the workpiece loading unit  12  rotates, the workpiece  200  placed thereon also rotates. 
     Hot air is blown to the workpiece  200  placed on the workpiece loading unit  12  at a high speed. The workpiece  200  is rapidly heated by the hot air blown thereto. Hot air is blocked by the flow end wall  34 , which increases the amount of hot air flowing into the inner space  110  from the outer space  112 . Therefore, hot air is blown at a high speed. The increase in the amount of hot air results in an increase in the velocity of flow of hot air. Further, the increase in the velocity of flow of hot air results in an increase in the heat transfer coefficient. Further, the increase in the heat transfer coefficient results in an increase in the amount of heat transferred to the workpiece  200 . Due to the increase in the amount of heat, the workpiece  200  is rapidly heated. 
     Since the lower hot air supply device  20  has been already operating, when the heated workpiece  200  reaches a position that faces the hot air inflow portion  140  of the tubular partition  28 , the workpiece  200  is further heated by hot air flowing from the hot air inflow portion  140 . Then, hot air flowing through the holes  158  of the hot air replenishment portion  142  is sequentially blown to the workpiece  200  which rotates inside the lower heat treatment chamber  46  along with the rotation of the workpiece loading unit  12 . Sequentially blowing hot air maintains the temperature of the workpiece  200  constant while the workpiece  200  rotates inside the lower heat treatment chamber  46 . 
     When the workpiece  200  placed on the workpiece loading unit  12  reaches a position that faces the corresponding lower outlet opening  72 , an operator opens the door of the lower outlet opening  72  and takes the workpiece  200  out of the lower heat treatment chamber  46  to the outside of the heating furnace using an appropriate jig. 
     An operator performs a quenching treatment by a known method on the workpiece  200  taken out of the lower heat treatment chamber  46 . An operator opens the door of the upper inlet opening  74  and inserts the workpiece  200  on which the quenching treatment has been performed into the upper heat treatment chamber  48  using an appropriate jig. After the workpiece  200  is inserted, the door of the upper inlet opening  74  is closed. Since the workpiece loading unit  12  rotates, the workpiece  200  placed thereon also rotates. 
     The workpiece  200  rotating in the upper heat treatment chamber  48  is heated in the same manner as when the solution treatment is performed on the workpiece  200  in the lower heat treatment chamber  46 . However, the temperature inside the upper heat treatment chamber  48  is lower than the temperature inside the lower heat treatment chamber  46 . Thus, a heat treatment applied to the workpiece  200  inside the upper heat treatment chamber  48  is an aging treatment. 
     When the workpiece  200  placed on the workpiece loading unit  12  reaches a position that faces the corresponding upper outlet opening  76 , an operator opens the door of the upper outlet opening  76  and takes the workpiece  200  out of the upper heat treatment chamber  48  to the outside of the heating furnace using an appropriate jig. 
     [Effect of Heating Furnace According to Present Embodiment] 
     With the heating furnace according to the present embodiment, it is possible to perform heat treatment within a single furnace in the above manner. In the heat treatment, even when hot air that has previously flown into the inner space  110  loses its thermal energy by heating the workpiece  200 , hot air flowing into the inner space  110  thereafter compensates the lost thermal energy. Since the lost thermal energy is compensated, it is possible to reduce variation in temperature between various points inside the furnace chamber. 
     The hot air inflow portion  140  faces the furnace chamber communication portion. Thus, a part of the hot air that has flown into the furnace chamber  40  directly flows into the inner space  110 . Accordingly, it is possible to reduce the loss of thermal energy caused by transfer of the thermal energy of hot air to the furnace body  10 . 
     Further, hot air is prevented from flowing into the inner space  110  on the upstream side of the flow of hot air. Therefore, it is possible to prevent the temperature of the workpiece  200  from unnecessarily increasing. 
     Further, it is possible to reuse hot air that has flown out through the hot air outflow portion  136 . Accordingly, it is possible to more efficiently use thermal energy for heating the workpiece  200  than when thermal energy is not reused. 
     Further, it is possible to prevent hot air fed into the furnace chamber  40  and hot air guided to the heating chamber from slowing their flow velocities each other. As a result, hot air smoothly flows. 
     Since the flow end wall  34  blocks hot air, the hot air flows into the inner space  110  before reaching the flow end wall  34 . The hot air flowing into the inner space  110  makes the velocity of flow of hot air inside the inner space  110  higher than that when no hot air flows thereinto. The increase in the velocity of flow results in an increase in the heat transfer coefficient of hot air in a place where the velocity of flow increases. Further, the increase in the heat transfer coefficient accelerates a rise in the temperature of the workpiece  200 . 
     When the passage forming tubes are arranged, it is possible to reduce the amount of hot air that flows through the outer space and then flows out of the furnace body  10  through the workpiece passing openings. The reduction in the amount of hot air makes it possible to reduce the loss of thermal energy caused by hot air flowing out of the furnace. 
     Further, the flow of hot air is guided to a rotation direction of the hearth  14 . Thus, the hot air heats the workpiece  200  while flowing in the inner space. Accordingly, it is possible to efficiently transfer thermal energy to the workpiece  200  from hot air. 
     [Description of Modifications] 
     The embodiment disclosed herein is an example in all points. The scope of the present invention is not limited to the above embodiment. It is needless to say that various modifications may be made without departing from the gist of the invention. 
     For example, a heat source, for example, an electric heater may be arranged as the lower heating device  22  or the upper heating device  26  instead of the combustion burner. 
     The tubular partition  28  may have slits instead of the holes  158 . Not only the size of the holes  158  or slits, but also the number of holes  158  or slits per unit area may differ in the tubular partition  28 . A specific structure of the furnace chamber inside communication portion  130  for allowing the inner space  110  and the outer space  112  to communicate with each other is not limited to the one descried above. 
     A specific form of the workpiece loading unit  12  is not particularly limited. The number of stages of the lower shelf  80  and the number of stages of the upper shelf  84  are not particularly limited. The number of doors attached to the lower inlet openings  70  and the lower outlet openings  72  is not particularly limited. For example, a large door may be attached in order to allow the workpieces  200  to be taken out and put in two stages of the workpiece loading unit  12 . In this case, the number of doors is reduced. 
     The heat treatment chamber may be divided into three or more chambers. The heat treatment chamber may be a single chamber. The number of heat treatment chambers is preferably equal to the number of heating chambers, but may differ from the number of heating chambers. The furnace chamber  40  may not be divided into a heating chamber, a heat treatment chamber, and a portion allowing the heating chamber and the heat treatment chamber to communicate with each other. The role of each of the heat treatment chambers is not limited to the one described above. A part of each of the heat treatment chambers close to the hearth  14  may be used for an aging treatment. A part of each of the heat treatment chambers far from the hearth  14  may be used for a solution treatment. The hearting furnace according to the present invention may be used for heat treatment other than a solution treatment and an aging treatment. Examples of “heat treatment other than a solution treatment and an aging treatment” include an annealing treatment. The hearting furnace according to the present invention may be used for heating other than heat treatment. Examples of “heating other than heat treatment” include drying. 
     The hearth  14  may be rotated by a device other than the hearth rotating unit. The workpiece loading unit  12  may not include the lower direction guide body  86  and the upper direction guide body  88 . The heating furnace may include no passage forming tube. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
         
           
               10 : Furnace body 
               12 : Workpiece loading unit 
               14 : Hearth 
               16 : Hearth supporting unit 
               18 : Hearth rotating unit 
               20 : Lower hot air supply device 
               22 : Lower heating device 
               24 : Upper hot air supply device 
               26 : Upper heating device 
               30 : Inlet passage forming tube 
               32 : Outlet passage forming tube 
               34 : Flow end wall 
               40 : Furnace chamber 
               46 : Lower heat treatment chamber 
               48 : Upper heat treatment chamber 
               50 : Lower heating chamber 
               52 : Upper heating chamber 
               54 : Lower furnace chamber communication portion 
               56 : Upper furnace chamber communication portion 
               62 : Furnace body supporting leg 
               64 ,  68 : Exhaust tube 
               66 : Sand seal portion 
               70 : Inlet opening 
               72 : Outlet opening 
               80 : Lower shelf 
               82 : Partition plate 
               84 : Upper shelf 
               86 : Lower direction guide body 
               88 : Upper direction guide body 
               90 : Partition ring 
               100 : Sand hopper 
               110 : Inner space 
               112 : Outer space 
               130 : Furnace chamber inside communication portion 
               132 : Furnace outside communication inlet portion 
               134 : Furnace outside communication outlet portion 
               136 : Hot air outflow portion 
               138 : Hot air guide portion 
               140 : Hot air inflow portion 
               142 : Hot air replenishment portion 
               150 : Upstream opening portion 
               152 : Downstream opening portion 
               158 : Hole 
               160 : Hot air guide hole 
               200 : Workpiece