Abstract:
Disclosed is a ceramic-resistor heating plate for preventing corona discharge which is characterized in that an extruded insulating part is provided around the peripheral of the plate-shaped heating body. Therefore, the distance between the electrodes of the fin plates sandwiching the heating body can be increased and the problem of corona discharge can be prevented with reduced cost and enhanced safety.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ceramic-resistor heating plate, more particularly, to a ceramic-resistor heating plate, which can prevent the problem of corona discharge. 
     2. Description of the Prior Art 
     The ceramic-resistor heating plate uses the infrared radiation to heat the object to be heated. Therefore, the ceramic-resistor heating plate is safer than the convention heater with real fire. However, since the ceramic-resistor heating plate is generally energized by electric power, the spark-induced problem, such as the burning of flock attached to the ceramic-resistor heating plate, is liable to occur. To prevent the above-mentioned problem, the distance between the electrodes of the ceramic-resistor heating plate is required to exceed 2.5 mm-3.0 mm to prevent the corona discharge and spark problem. 
     FIGS. 1,  2  and  3  show the structure of the conventional heating plate in an electric heater. The heating plate comprises a wave-shaped conductive fin plate  11 , a ceramic-resistor heating body  12  sandwiched therebetween, lateral frame  13 , and cover  14 . The connector  15  protruded from the cover  14  conducts electric power to the heating body  1  through the fin plate  11 . The front side and back side of the heating body  12  are coated with conductive film  121  and  122 , respectively, for conducting the electric power from the connector  15 . As shown in FIG. 3, the distance between the two electrodes (terminals)  110  of the heating body is required to be at least 3 mm to maintain the allowable voltage of the heating body. Therefore, the thickness of the heat body is increased. However, the material is wasted and the power consumption is increased. From the formula, R=ρ·L/A, for a fixed value of resistivity ρ, the resistance R is proportional to the length L and inversely proportional to area A. The increase of heating body thickness will increase the resistance thereof. Therefore, to make a thinner heating body and maintain normal operation thereof within allowable voltage range is an important design issue. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a heating plate which has a protruded insulating region for affording an extended surface for the electrodes of the fin plate on both sides of the heating body, thus increasing the electrode distance and preventing the corona discharge. 
     It is another object of the present invention to provide a heating plate wherein the applied region of the conductive is of groove shape, thus increasing the electrode distance and facilitating the assembling operation. 
     It is still another object of the present invention to provide a heating plate having an insulating and heat-resistant frame enclosing the heating body thereof, thus increasing the electrode distance. 
     It is still another object of the present invention to provide a heating plate having an insulating and heat-resistant frame of I-shape cross-section, thus increasing the electrode distance. 
     It is still another object of the present invention to provide a heating plate wherein an insulating ribbon is wrapped around the heating body thereof, thus increasing the electrode distance. 
     The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is the exploded view of a conventional heating plate; 
     FIG. 2 is the perspective view of a conventional heating plate; 
     FIG. 3 is the cross-section view of the heating body in a conventional heating plate; 
     FIG. 4 is the schematic view of the heating body in a heating plate according to one embodiment of the present invention; 
     FIG. 5 is the exploded view of the heating plate according to one embodiment of the present invention; 
     FIG. 6 is the partial cross-section view of the heating plate according to one embodiment of the present invention; 
     FIG. 7 shows another embodiment of the present invention; 
     FIG. 8 shows another embodiment of the present invention; 
     FIG. 9 shows still another embodiment of the present invention; 
     FIG. 10 shows still another embodiment of the present invention; and 
     FIG. 11 shows still another embodiment of the present invention. 
     Numeral 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 4 and 5, the ceramic-resistor heating body  3  of the inventive heating plate  2  is applied with conductive film  33  on the front side  31  and the back side  32  thereof. The heating body  3  receives electric power from the conductive fin plate  21  arranged on both sides thereof. As shown in FIG. 4, the conductive films  33  are such pasted that insulating part  34  is formed on the margin of the heating body  3 , wherein the height of the conductive film  33  is preferably the same as the height of the fin plate  21 . As shown in FIG. 5, the conductive plane  211  of the fin plate  21  is in contact with the conductive film  33  of each heating body to carry electric power. Each edge of the conductive plane  211  forms a conductive electrode (terminal)  210 . As shown in FIG. 6, after arranging the above-mentioned component, the extruded insulating part  34  of the heating body  3  provides a larger distance for the electrodes  210 . The distance between the electrodes  210  is preferably larger than 2.5 mm-3.0 mm to prevent the corona discharge. 
     With reference again to FIG. 5, the gap  30  is filled with insulating paste and the first/last heating body  3  in the same row is provided with insulating part  35  to further prevent the corona discharge. 
     As shown in FIG. 7, in another embodiment of the present invention, the heating body  3  has a groove  36  on the front/back side thereof and the height of the groove  36  is sufficient to accommodate the fin plate  21 . Moreover, a conductive film  33  is applied on the bottom of each groove for providing the conduction path. Therefore, the electrode distance is increased and the fin plate  21  can be easily assembled. 
     As shown in FIG. 8, a plurality of heating bodies  3  along the same row are applied with conductive film throughout except the rightmost and leftmost heating bodies. In other words, the inner heating bodies  300  are applied with conductive film throughout in a transverse direction, the rightmost and leftmost heating bodies are provided with insulating part  35  and the gap  30  between two heating bodies  30  is applied with insulating paste for preventing the corona discharge. 
     With reference again to FIG. 6, to protect the extruded insulating part  34 , a protective cap  37  is used to cover the insulating part  34  or a protective cap  37  is suspended to protect the insulating part  34 . 
     With reference now to FIG. 9, a hollow frame  4  with an upper frame  43 , a lower frame  44  and an opening  40  is used to enclose the heating body  3 . The heating body  3  is embedded into the opening  40  and the gap  30  is filled with insulating paste. The thickness of the insulating frame is preferably the same as that of the heating body. The opening  40  should be larger enough to accommodate the fin plate (not shown) if the thickness of the insulating frame is larger than that of the heating body  3 . By the arrangement of the frame  4 , the electrode distance is increased. 
     As shown in FIG. 10, the cross-section of the frame is of I-shape with bumps  41  and  42  on top end and bottom end, respectively. The frame  4  has an opening for the embedding of the heating body  3 . By using the bumps  41  and  42 , the electrode distance is increased. 
     As shown in FIGS. 9 and 10, the frame  4  can be formed by assembling the upper frame  43  and the lower frame  44 , and has an opening formed therein. 
     As shown in FIG. 11, a strip-shaped, insulating and heat-resistant ribbon  5  is wrapped around the heating body  3  and between two fin plates  11  and  21 , thus increasing the electrode distance. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.