Abstract:
The present invention provides a heating apparatus including: a power source for heating; a heating element; and a bimetal-type thermostat placed between the power source and the heating element, the bimetal-type thermostat cutting off energization upon temperature reaching to a first temperature and restoring the energization upon temperature dropping and reaching to a second temperature, the bimetal-type thermostat having a resetting temperature of 0° C. or lower.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a heating apparatus, and particularly to a heating apparatus having a function to automatically prevent an excessive temperature rise.  
       BACKGROUND OF THE INVENTION  
       [0002]     For example, in a manufacturing apparatus of a semiconductor element, an FPD (Flat Panel Display) or the like, a mantle heater is conventionally frequently used in order to heat a pipe, a joint, a valve and the like up to a specified temperature and to keep it (see, for example, reference 1).  FIG. 3  is a perspective view showing an example of a mantle heater, and a mantle heater  100  shown in the drawing is constructed such that a heating element  103  is sandwiched between an inner layer material  101  made of a flexible synthetic resin sheet and an-outer layer material  102 . Electric power is applied to the heating element  103  in a state where it covers a pipe  104  as an object to be heated, so that the pipe  104  is heated.  
         [0003]     In order to prevent an excessive temperature rise, the mantle heater  100  as stated above is constructed such that for example, as shown in  FIG. 4 , a temperature fuse  112  is placed between a power source  110  and a heater element  111 , and when the temperature fuse  112  is heated to a melting temperature or higher, the energization to the heater element  111  is cut off.  
         [0004]     Besides, there is also known a structure in which as shown in  FIG. 5 . a thermostat  121  is disposed in the vicinity of a heater element  111 , the temperature of the heater element  111  is always monitored, and when the temperature reaches a specified temperature, the energization to the heater element  111  is cut off based on a signal from the thermostat  111 . Further, there is also known a structure in which as shown in  FIG. 6 , a thermocouple  131  is used instead of the thermostat  121 .  
         [0005]     Besides, there is also known a structure in which in the excessive temperature rise prevention mechanism shown in  FIG. 4 , a bimetal-type thermostat is placed instead of the temperature fuse  112 . In the bimetal-type thermostat, when the temperature reaches to a specified temperature (operating temperature), operating metals, which are in contact with each other at first, are separated from each other by thermal expansion, so that the energization to the heater element  111  is cut off.  
         [0006]     [Reference 1] JP-A-2002-295783  
         [0007]     In the foregoing excessive temperature rise prevention mechanism, and in the structure using the temperature fuse  112 , the temperature fuse  112  is thermally degraded during long time operation and can fuse at a temperature lower than the specified melting temperature, and there is a problem in long-term reliability. Besides, when the temperatures fuse  112  is once melted, it must be replaced, and there is also a problem of not being economical.  
         [0008]     In the structure using the thermostat  121  or the thermocouple  131 , although there is an advantage that it can be used repeatedly, a separate circuit to control the thermostat  121  or the sensor  131  is required, and the cost is increased in total.  
         [0009]     In the excessive temperature rise prevention mechanism using a bimetal-type thermostat, since energization/cutoff is performed by using the thermal expansion of the operating metals, in the process where the energization is cut off and the temperature drops, the operating metals, which were separated from each other at the time of the excessive temperature rise, are thermally contracted at a certain temperature (resetting temperature) to come in contact with each other again, and the energization is resumed. In recent years, particularly in the manufacturing apparatus of a semiconductor element, an FPD or the like, in view of safety, there is adopted a system in which an operator or a manager can recognize that the excessive temperature rise occurs in the mantle heater  100 . However, the resetting temperature of the conventional bimetal-type thermostat is a temperature lower than the operating temperature, at which the operating metals start to be separated, by at most 10 to 30° C. Thus, there is a possibility that early restoring occurs automatically, the mantle heater  100  is restarted, and it can not be recognized that the excessive temperature rise occurs.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention has been made in view of such circumstances, and has an object to provide a heating apparatus in which an excessive temperature rise is appropriately detected and it can be certainly recognized that the excessive temperature occurs.  
         [0011]     The present inventors have made eager investigation to examine the problem. As a result, it has been found that the foregoing objects can be achieved by the following heating apparatus. With this finding, the present invention is accomplished.  
         [0012]     The present invention is mainly directed to the following items:  
         [0013]     1. A heating apparatus comprising: a power source for heating; a heating element; and a bimetal-type thermostat placed between the power source and the heating element, the bimetal-type thermostat cutting off energization upon temperature reaching to a first temperature and restoring the energization upon temperature dropping and reaching to a second temperature, the bimetal-type thermostat having a resetting temperature of 0° C. or lower.  
         [0014]     2. The heating apparatus according to item 1, wherein the resetting temperature of the bimetal-type thermostat is −35° C. or lower.  
         [0015]     In the bimetal-type thermostat incorporated in the heating apparatus of the invention, the resetting temperature is 0° C. or lower and is remarkably low as compared with the conventional bimetal-type thermostat. Thus, when the heating apparatus causes an excessive temperature rise, the cutoff state continues in a general use environment (temperature is generally room temperature: approximately 20 to 25° C.), and the occurrence of the excessive temperature rise can be certainly recognized. In order to make such a function more certain, it is preferable that the resetting temperature of the bimetal-type thermostat is made −35° C. or lower. Furthermore, it is preferable that the resetting temperature of the bimetal-type thermostat is −196° C. or more. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a main part sectional view showing an embodiment of a heating apparatus of the invention.  
         [0017]      FIG. 2  is a circuit diagram showing an excessive temperature rise prevention mechanism of the heating apparatus of  FIG. 1 .  
         [0018]      FIG. 3  is a perspective view showing an example of a mantle heater.  
         [0019]      FIG. 4  is a circuit diagram showing an example (temperature fuse is used) of a conventional excessive temperature rise prevention mechanism.  
         [0020]      FIG. 5  is a circuit diagram showing another example (thermostat is used) of a conventional excessive temperature rise prevention mechanism.  
         [0021]      FIG. 6  is a circuit diagram showing still another example (thermocouple is used) of a conventional excessive temperature rise prevention mechanism. 
     
    
       [0022]     The reference numerals used in the drawings denote the followings, respectively.  
         [0023]      10  heating apparatus  
         [0024]      11  outer layer material  
         [0025]      20  heater element  
         [0026]      21  heater wire  
         [0027]      22  inorganic fiber sheet  
         [0028]      23  non-combustible fire-resistant fiber sheet  
         [0029]      30  excessive temperature rise prevention mechanism  
         [0030]      31  power source  
         [0031]      32  bimetal-type thermostat  
       DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0032]     In the present invention, a heating apparatus comprises a power source for heating, a heating element, and a bimetal-type thermostat. The bimetal-type thermostat is placed between the power source and the heating element. The bimetal-type thermostat cuts off energization when temperature reaches to a first temperature and restores the energization when temperature drops and reaches to a second temperature. The bimetal-type thermostat of the invention has a resetting temperature of 0° C. Furthermore, as described above, the resetting temperature of the bimetal-type thermostat is preferably −35° C. or lower.  
         [0033]     Hereinafter, the invention will be described in detail with reference to the drawings.  
         [0034]      FIG. 1  is a main part sectional view showing an embodiment of a heating apparatus of the invention, and  FIG. 2  is a circuit diagram showing an excessive temperature rise prevention mechanism. Incidentally, in the invention, the kind of the heating apparatus is not limited, and the invention can be applied to, for example, the mantle heater shown in  FIG. 3 .  
         [0035]     As shown in the drawings, in a heating apparatus  10  of this embodiment, a heater element  20  and a bimetal-type thermostat  32  constituting an excessive temperature rise prevention mechanism  30  are connected in series to each other and are housed inside a thermal insulating layer  11 .  
         [0036]     As a material forming the thermal insulating layer  11 , a fluorocarbon resin is preferably used. Specifically, PTFE (polytetrafluoroethylene), PFT (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) or the like is preferable. Besides, PCTFE (polychlorotrifluoroethylene), ETFE (tetrafluoroethylene-ethylene copolymer), ECTFE (chlorotrifluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride) or the like can also be used.  
         [0037]     As the heater element  20 , one obtained by fixing a heater wire  21  of Ni—Cr or the like, which is insulation coated with a heat insulation cloth, to a glass cloth of an inorganic fiber sheet  22  can be used. This heater element  20  is attached to a non-combustible fire-resistant fiber sheet  23 . As the non-combustible fire-resistant fiber sheet  23 , an inorganic fiber sheet or an organic fiber sheet can be used. As the inorganic fiber sheet, it is preferable to use one obtained by applying needling to an inorganic fiber material such as glass fiber, ceramic fiber, or silica fiber. As the organic fiber sheet, sheets made of aramid, polyamid, polyimide and the like are enumerated.  
         [0038]     The structure of the heating part of the heating apparatus  10  is roughly as described above, and in the invention, an excessive temperature rise prevention mechanism  30  as shown in  FIG. 2  is provided. The excessive temperature rise prevention mechanism  30  is such that instead of the temperature fuse  112  shown in  FIG. 4 , a bimetal-type thermostat  32  is placed between a power source  31  and a heater element  20 . The heater element  20  heats the heater wire  21  by electric power from the power source  31 . When an excessive temperature rise occurs, operating metals of the bimetal-type thermostat  32  are separated from each other, and the energization is cut off.  
         [0039]     In the invention, as the bimetal-type thermostat  32 , one having a resetting temperature of 0° C. or lower is used. For example, since the use environment of a manufacturing apparatus of a semiconductor element or an FPD is approximately 20 to 25° C., when the resetting temperature is 0° C. or lower, the operating metals separated by the excessive temperature rise are not automatically returned to the contact state again. Thus, as compared with the case where the bimetal-type thermostat having the resetting temperature lower than the operating temperature by 10 to 30° C. as in the related art, the reliability is greatly improved. In order to make the function as stated above more certain, it is preferable to use the bimetal-type thermostat  32  having a resetting temperature of −35° C. or lower.  
         [0040]     The operating temperature of the bimetal-type thermostat  32  is suitably set according to the usage or heating place, and for example, in the manufacturing apparatus of a semiconductor element or an FPD, it is generally set to about 250° C.  
         [0041]     As the bimetal-type thermostat  32  having the resetting temperature of 0° C. or lower as stated above, one generally available in the market may be used.  
         [0042]     In order to restore the bimetal-type thermostat  32 , that is, in order to realize the resetting temperature, liquid nitrogen is dropped onto a portion where the bimetal-type thermostat  32  of the heating apparatus  20  is disposed, or dry ice is pressed thereto and cooling is performed.  
         [0043]     The operation of the heating apparatus  10  of the invention is the same as the conventional heating apparatus, electric power is applied to the heater element  20 , and when an excessive temperature rise occurs, the bimetal-type thermostat  32  operates to cut off the energization. By this, the heat generation of the heater element  20  is stopped, the temperature of the heating apparatus  10  continues to drop, and keeps, for example, room temperature. Since the bimetal-type thermostat  32  is not restored at the room temperature, in order to restart the heating apparatus  10 , the operator or the manager must use liquid nitrogen or dry ice to restore the bimetal-type thermostat  32 . Thus, the operator or the manager can certainly recognize the occurrence of the excessive temperature rise of the heating apparatus  10 .  
         [0044]     As described above, according to the heating apparatus of the invention, the excessive temperature rise is appropriately detected, and the occurrence of the excessive temperature rise can be certainly recognized.  
         [0045]     While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.  
         [0046]     The present application is based on Japanese Patent Application No. 2005-102741 filed on Mar. 31, 2005, and the contents thereof are incorporated herein by reference.