JPH09289073A - Ceramic heater with current interrupting function and liquid heater unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater which can surely interrupt current by detecting temperature rises due to overheating or heating of an empty container of a heating unit, etc., with good sensitivity using relatively simple circuit arrangement, and to provide the liquid heating unit using the same. SOLUTION: This ceramic heater 1 has a current-interrupting mechanism 6, which is provided in the current path of a resistance heating element in the space inside a heater main body 10 having the resistance heating element embedded in a ceramic substrate, and which interrupts current to the resistance heating element when detecting that the heater main body 10 has been heated to a predetermined temperature or higher. This liquid heater unit 50 comprises a heater case 52, having an inlet 53 and an outlet 54 for a liquid W, and the ceramic heater 1, and causes the liquid W flowing in through the inlet 53 to be heated by the ceramic heater 1 and flow out of the outlet 54.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater having a current-carrying interruption function and a liquid heating unit using the same.

[0002]

2. Description of the Related Art Conventionally, a liquid heating unit using a ceramic heater has been used for heating while circulating liquid such as bath water and washing water for parts. In particular,
The ceramic heater is arranged in the case, and the liquid is heated by energizing the heater while circulating the liquid in the case. By the way, in such a liquid heating unit, when the heater is overheated and the liquid exceeds the set temperature, or when the liquid in the case is washed away for some reason and becomes a so-called empty heating state. ,
It is necessary to cut off the power supply immediately. In the conventional liquid heating unit, a circuit for shutting off such energization is provided outside the case, and an increase in temperature due to overheating of the heater or heating of the heater is also detected outside the case. .

[0003]

In the liquid heating unit as described above, the temperature rise of the liquid is detected outside the case, so that the sensitivity is not so good.
Further, since the cutoff circuit is provided separately from the energization circuit for the ceramic heater, there is a problem that the wiring becomes complicated. Therefore, it has been attempted to embed a temperature detection sensor (such as a resistance sensor) together with a resistance heating element in the ceramic heater to increase the detection sensitivity. This has to be performed by the control circuit provided, and there is a drawback that the device cost increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic heater which has a relatively simple circuit structure and which can detect a temperature rise due to overheating or air heating with high sensitivity to reliably cut off energization. And a liquid heating unit used.

[0005]

In order to solve the above-mentioned problems, the ceramic heater of the present invention has a structure in which a resistance heating element is embedded in a ceramic base, and a resistance heating element is provided in an inner space of the heater body. It is provided in the middle of the body's energization path, and has an energization interruption mechanism that senses when the temperature of the heater body reaches a predetermined value and interrupts energization to the resistance heating element. And

That is, since the ceramic heater is provided with an energization / interruption mechanism that senses a temperature rise and interrupts energization in the inner space of the cylindrical heater body, it has high temperature detection sensitivity. Since the energization cutoff mechanism is provided in the middle of the energization path to the resistance heating element, the circuit configuration is simple, and thus the ceramic heater having the energization interruption function can be made compact and inexpensive.

The cylindrical heater body can be formed in a cylindrical shape, for example. Further, it can be formed in a cylindrical shape with its tip side sealed.

The energization cutoff mechanism may include a fuse that is blown at a predetermined temperature or higher to open the energization path. Thereby, the energization cutoff mechanism can be configured more simply. Also, as the metal that constitutes the fuse,
By selecting a material having an appropriate melting point, it is possible to easily adjust the operating temperature for interrupting energization.

On the other hand, the energization interruption mechanism opens and closes the contact point for opening and closing the energizing path and the heater body when the temperature of the heater body reaches a predetermined upper limit value, and lowers the temperature to a predetermined lower limit value. In this case, the heat-sensitive contact drive unit for returning the open / close contact unit to the closed state may be included.
In this way, even if the heater temperature rises above a certain level and the energization interruption mechanism operates, the circuit closes when the temperature drops due to the interruption of energization, so that it is possible to energize the heater again. In this case, the thermal contact drive section opens the open / close contact section when the temperature of the heater body reaches a predetermined upper limit value,
If the temperature drops below the specified lower limit, the energization to the resistance heating element is turned off by returning the switching contact to the closed state.
It is also possible to turn on and thereby maintain the temperature of the heater body within a predetermined range. That is, the energization interruption mechanism can also be used as a temperature control mechanism that maintains the temperature of the heater constant. The upper limit value and the lower limit value of the temperature may be the same temperature.

Next, in the above-mentioned ceramic heater, the outside of the heater body is covered with a metal case, and the space between the inner surface of the metal case and the outer surface of the heater body is made of a metal having a melting point lower than that of the material of the metal case. It can be filled with layers. By covering the outside of the heater body with a metal case, there is no need to polish the surface of the heater body,
Further, since the space between the heater body and the metal case is filled with the metal layer, it is possible to obtain a heater having high heat conduction efficiency. In this case, the material of the metal layer is preferably selected so that its melting point is higher than the normal operating temperature of the heater. The metal layer can be a cast layer.

A liquid heating unit can be constructed using the ceramic heater. The unit specifically includes a heater case having a liquid inlet and a liquid outlet,
The ceramic heater is provided with the above-mentioned ceramic heater, and the liquid flowing from the inflow port is heated by the ceramic heater to flow out from the outflow port. That is, by using the ceramic heater of the present invention, a liquid heating unit having a function of shutting off energization to the heater when the liquid temperature excessively rises or becomes empty is configured in a compact and inexpensive manner. You can

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows a ceramic heater (hereinafter, simply referred to as a ceramic heater) 1 having an energization / interruption function, which is an embodiment of the present invention, together with its internal structure. That is, the ceramic heater 1 includes a cylindrical heater main body 10 and an energization interruption mechanism 6 arranged in the inner space 10a thereof. Also, the heater body 1
0 has one end open, and the other end (tip) is sealed by joining the ceramic plate 2 or filling glass.

As shown in FIG. 2A, the heater body 10 has a structure in which a resistance heating element 12 is embedded in a ceramic base 11 having a cylindrical shape. The ceramic substrate 11 is made of alumina (Al ₂ O ₃ ), silica (Si
O ₂ ), zirconia (ZrO ₂ ), titania (Ti
O ₂ ), magnesia (MgO), mullite (3Al ₂ O ₃
・ 2SiO ₂ ), zircon (ZrO ₂ · SiO ₂ ), cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), etc. To be done. In addition, the resistance heating element 12
Can be made of refractory metals such as tungsten, molybdenum and platinum, or alloys thereof, and various resistance heating metal materials such as stainless steel and nichrome. Tungsten carbide (WC), molybdenum silicide (MO ₂ Si ₃ ) ,
It may be made of a conductive ceramic such as a composite of tungsten carbide and silicon nitride (Si ₃ N ₄ ).

The heater body 10 as described above is manufactured, for example, as follows. That is, as shown in FIG. 2B, resistance heating is performed by using a paste containing resistance heating material powder on the plate surface of a powder molded body 100 (for example, a green sheet) in which ceramic powder is molded into a plate shape with a binder. The body pattern 101 is printed. Print pattern 1
In 01, as shown in FIG. 2B, a plurality of main body portions 104 extending along the long sides of the rectangular powder molded body 100 are
The molded body 100 is arranged at a predetermined interval in the short side direction, and those adjacent to each other are formed in one continuous form in which both ends are sequentially connected by the connecting portions 105.

Next, as shown in FIG. 2D, the powder compact 100 is placed on the outer peripheral surface of a separately formed cylindrical powder compact 102, and the surface on which the pattern 101 is formed is on the inside. The cylindrical molded body 103 is wound and wound. Then, by firing the compact 103, the powder compacts 100 and 102 are sintered and integrated into the ceramic base 11, and the printed pattern 101 is formed by sintering the resistance heat-generating powder. Becomes In the resistance heating element 12, a plurality of straight line portions corresponding to the main body portion 104 of the print pattern 101 extend in the axial direction of the ceramic base 11, and these are arranged at predetermined intervals in the circumferential direction of the cross section.

Returning to FIG. 1A, terminals 4 which are electrically connected to both ends of the resistance heating element 12 are provided on the outer surface of the heater body 10 near the open end so as to project outward. The terminals 4 are connected to the respective ends of the lead portions 5 and 7 that form the current-carrying path to the resistance heating element 12. The above-described energization interruption mechanism 6 is provided in the middle of the one lead portion 5. As shown in FIG. 3A, the energization / interruption mechanism 6 is made of a fuse 22 connected in series with the lead portion 5 and a transparent material such as glass, and covers the fuse 22 from the outside along the longitudinal direction thereof. And a tubular casing 21.

The fuse 22 has a melting temperature of, for example, 1
Those in the range of 00 to 230 ° C can be used. Then, by changing the material of the constituent metal of the fuse 22 to one having a different melting point, the operating temperature of the energization interruption mechanism 6 can be changed. Here, the fusing temperature of the fuse 22 is the ambient temperature of the fuse 22 plus a temperature rise due to resistance heating of the fuse itself. In this case, increase the energization cross section or shorten the energization length to fuse 22
If the resistance is set to a predetermined value or less, melting does not occur even when a relatively large current flows when the ambient temperature is low, and when the ambient temperature rises above a certain level, the melting does not occur even when the energizing current value is small. Can occur. In this case, the fuse 22 can be regarded as playing a so-called thermal fuse. In this embodiment, for example, the fuse 22
This is convenient when it is not desired to limit the value of the current supplied to the heater body 10 by the allowable current value of. On the other hand, the fuse 22
If the energizing current value becomes larger than a certain value, for example, the allowable current value (or the rated current value) of the heater body 10 even when the ambient temperature is low, by adjusting the resistance by the energizing cross section or the energizing length, Alternatively, it may be configured to be fused by the resistance heating. In this case, it can be seen that the fuse 22 also serves as a so-called current fuse. However, it is needless to say that even if the energization current value is not so high, it will blow if the ambient temperature rises due to heating for example, so that it also functions as a thermal fuse.

As shown in FIG. 1 (a), the lead portion 5 is folded back at its intermediate portion, and is inserted inside the heater main body 10 from the open end side together with the energization interruption mechanism 6.
In addition, the energization cutoff mechanism 6 has a longitudinal direction in which the heater main body 1
Along the 0 axial direction (that is, the extending direction of the resistance heating element 12 (FIG. 2)), a predetermined position in the axially intermediate portion of the heater body 10, specifically, the heater temperature becomes the highest.
It is positioned near the center of the axially extending portion of the resistance heating element 12. By doing so, it is possible to increase the detection sensitivity of the heater overheating. It is more desirable to position the energization / interruption mechanism 6 so as to contact the inner wall surface of the heater body 10. In this case, as shown in FIG. 1B, the lead portion 5 is U-shaped so that the outer width D1 of the portion where the energization interruption mechanism 6 and the lead portion 5 face each other is slightly larger than the inner diameter D2 of the heater body 10. If it is folded back in a letter shape and is pushed into the heater body 10 from the folded back end side, the energization interruption mechanism 6 is pressed against the heater body 10 by the elastic force of the lead portion 5, and the friction energizes the electricity interruption mechanism 6. Since the heater can be held at any position in the axial direction of the heater body 10, the above positioning and the like can be easily performed. In addition, portions of the folded back lead portions 5 facing each other are covered with an insulating tube 13 to prevent a short circuit. This insulating tube 13 has a part of the lead portion 5 arranged in the inner space 10 a of the heater body 10,
It is desirable to use a heat-resistant resin such as a fluororesin (for example, polytetrafluoroethylene (trade name: Teflon)) or a silicone resin.

Next, FIG. 4 is a schematic view showing a structural example of the liquid heating unit of the present invention. Liquid heating unit 50
Is a box-shaped case 5 made of plastic or metal.
Two. The case 52 has a liquid inlet 53 and a liquid outlet 54 formed at both ends of the upper surface, and the heater body 10 of the ceramic heater 1 described above is laterally inserted into the case 52 from one side surface thereof. ing. The heater body 10 is integrally provided with a flange-shaped mounting plate 3 that projects from the outer peripheral surface in the vicinity of the open end, and a screw 3a penetrating the mounting plate 3 is screwed into the side surface of the case 52. That is fixed to this. In addition, a seal member 3b that holds the both in a liquid-tight manner is interposed between the mounting plate 3 and the case 52.

The method of using the ceramic heater 1 and the liquid heating unit 50 will be described below. FIG. 5 schematically shows an example of circulating and heating water in a tank such as a bath using the liquid heating unit 50.
One end of each of the pipelines 60, 61 is arranged, and the other ends thereof are respectively an inlet 53 and an outlet 5 of the liquid heating unit 50.
4 is connected. Then, by operating the pump 62 provided on the conduit 60, the water W in the tank B is
Is pumped out through the conduit 62 and introduced into the case 52 through the inflow port 53. Then, by connecting the lead portions 5 and 7 to a power source (not shown) and energizing them, the heater body 1
0 generates heat, and the introduced water W is heated by this and flows out from the outflow port 54. The heated liquid W is returned to the tank B through the pipe 61, is pumped out again by the pump 62, and is returned to the case 52 for circulation.

Here, if the pump 62 stops for some reason, the circulation of the water W stops, and the water W accumulated in the case 52 is stopped.
Is heated by the heater body 10 and its temperature rises. Further, when the pump 62 is operated and the heater body 10 is energized in a state where the water W does not exist in the tank B, the case 52
The inside becomes a so-called empty state and the temperature similarly rises. However, when the temperature of the heater main body 10 becomes higher than the operating temperature of the power interruption mechanism 6 (FIG. 1), the temperature of FIG.
As shown in (4), the fuse 22 of the energization cutoff mechanism 6 is blown and the energization to the heater body 10 is cut off, and the subsequent temperature rise is avoided.

For example, when the pump 62 stops and the water W stays in the case 52, the temperature of the water W rises and starts to boil. When the pressure in the case 52 rises due to the steam accompanying the boiling, the water W is pushed out from the inflow port 53 and the outflow port 54, and the liquid level in the case 52 lowers. When the heater body 10 is partially exposed from the liquid surface due to the liquid level lowering, the exposed portion may overheat to generate thermal stress, and the heater body 10 may be cracked. Therefore, if the inflow port 53 and the outflow port 54 are provided above the heater body 10 as in the present embodiment, the water W is less likely to flow out from the inflow port 53 or the outflow port 54, and as a result, the heater body is obtained. The state where 10 is immersed in water W is maintained for a relatively long time. In this case, the heater body 10
From the liquid surface of the water W remaining in the case 52 to the upper edge of the heater body 10 by setting the vertical distance d between the upper edge and the lower edge of the inlet 53 (or the outlet 54) to 10 mm or more. Is increased, the exposure of the heater body 10 from the liquid surface due to evaporation of the water W or the like is less likely to occur, and the above effect can be further enhanced.

Next, the energization / interruption mechanism 6 can be constructed as shown in FIG. That is, in this structure, the energization interruption mechanism 6 is provided with two terminal portions 28 and 29 which are connected to the lead portion 5 of FIG. A fixed contact 25 is provided at the tip of the. On the other hand, the other terminal portion 29 has a bimetal piece 23 as a heat-sensitive contact drive portion.
Are joined, and a movable contact 24 facing the fixed contact 25 is fixed to the tip thereof. Reference numeral 30 is a casing formed of glass or the like. The fixed contact 25 and the movable contact 24 form an open / close contact portion 26, and the bimetal piece 23 is slid outward to open / close the open / close contact portion 26 when the temperature of the heater body 10 reaches a predetermined upper limit value. Is opened (FIG. 6 (d)), and when the temperature drops to a predetermined lower limit value, it is returned to the closed state (FIG. 6 (c)). In this way, when the temperature of the heater 1 rises above a certain level, the switching contact portion 26 is opened to interrupt the energization, and when the temperature decreases, the switching contact portion 26 is closed and the heater 1 can be energized again. Become. in this case,
It is also possible to use the opening / closing operation of the opening / closing contact portion 26 as the temperature rises / falls to turn off / on the power supply to the heater body 10, thereby maintaining the temperature of the heater body 10 within a predetermined range. .

Further, as shown in FIG. 7, the heater body 10
It is also possible to cover the outer surface of the metal case 31. The metal case 31 has a cylindrical shape whose one end is closed by copper or a copper alloy, stainless steel, or the like, and the end on the opening side is expanded in diameter to form a step 32, and the step 3 is formed.
A flange 33 corresponding to the above-mentioned mounting portion 3 is integrally provided on the outer peripheral surface of 2 (note that this step portion 32 may not be particularly formed). The heater body 10 having an unpolished outer surface is inserted inside the metal case 31, and the tip portion 35 is included between the inner surface 31a of the metal case 31 and the surface 10a of the heater body 10. A metal having a melting point lower than that of the material of the metal case 31, specifically, a Zn-5 wt% Al alloy (melting point 385 ° C.) is filled by casting, and the heater body 10 is cast into a predetermined thickness. Of the metal layer 37 are formed. Note that instead of the above alloy, an alloy having a lower melting point, for example, Sn-38.
1 wt% Pb alloy (so-called eutectic solder, melting point 183
℃) etc. can also be used.

As a method for forming the metal layer 37 by casting, the heater case 10 in which the metal case 31 is heated and melted by putting a predetermined amount of metal into the metal case 31 with its opening side facing upward and heating it to a predetermined temperature, A method is exemplified in which the molten metal is pushed in while overflowing, and the molten metal is positioned coaxially with respect to the case 31 and then the metal is cooled and solidified to be integrated. On the other hand, the heater body 10 is provided at the center of the metal case 31.
May be inserted in advance, and then molten metal may be poured into the gap to solidify.

[0026]

EXAMPLE A liquid heating unit 50 shown in FIG. 4 comprises a ceramic heater 1 (output 800 W) having a heater body 10 in which a ceramic base 11 is made of alumina and a resistance heating element 12 is made of tungsten, and a polyamide resin. It was manufactured by using the prepared case 52 and incorporated into the water heating system shown in FIG. 5 (system A).
The inner dimensions of the case 52 are 50 mm in the front and rear, 60 mm in width,
The height is 80 mm, the outer diameter of the heater body 10 is 13.5 mm,
The height from the bottom surface of the tank B to the center of the heater was 30 mm. Further, as the energization interruption mechanism 6, one having a fuse 22 (FIG. 3) that operates (melts) at 150 ° C. is used. On the other hand, as a comparative example, as shown in FIG. 8, a system in which the ceramic heater 1 was replaced by a heater having a thermostat 201 directly connected to the heater body 10 was also manufactured (system B). The thermostat 201 is fixed to the upper surface of the case 52, and its operating temperature is 9
It is adjusted to 5 ℃.

In each system as described above, the flow rate of water W is set to 8 by the pump 62 while the heater body 10 is energized.
When the solution was circulated at a rate of 1 liter / minute, the water temperature was equilibrated at 40 ° C. In this state, the water circulation was stopped and the subsequent changes in water temperature and heater temperature were measured. Next, water is drained from the case 52 and the tank B, and in that state, the heater body 10
Then, the heater temperature was changed by measuring the heater temperature. Table 1 shows the above results.

[0028]

[Table 1]

In the case of stopping the water flow, the fuse 22 or the thermostat 2 is opened after 2 minutes in any system.
The power supply to the heater was cut off by the operation of 01. on the other hand,
In the case of empty heating, in the system A, the fuse was blown after 20 seconds (heater temperature of 300 ° C.) and the current was cut off, and no deterioration of the heater or deformation of the case was observed. 2), it took 2 minutes for the thermostat 201 to operate, and the heater temperature rose to 800 ° C. Further, deterioration of the heater and thermal deformation of the case 52 were slightly observed.

[Brief description of drawings]

FIG. 1 is a front partial cross-sectional view showing an example of a ceramic heater of the present invention.

FIG. 2 is a plan sectional view of a heater body and an explanatory view of a method for manufacturing the heater body.

FIG. 3 is a schematic view showing an example of a power supply interruption mechanism using a fuse.

4A and 4B are a schematic view of a liquid heating unit using the ceramic heater of FIG. 1 and a BB sectional view thereof.

FIG. 5 is an explanatory view showing a method of using the same.

FIG. 6 is a schematic view showing an example of an energization interruption mechanism having an opening / closing contact portion and an operation explanatory view thereof.

7A and 7B are front and plan sectional views showing an example of a ceramic heater in which the outside of the heater body is covered with a metal case and a metal layer.

FIG. 8 is a schematic diagram showing a conventional liquid heating unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 5 Lead part (energization path) 6 Energization interruption mechanism 11 Ceramic base 12 Resistance heating element 22 Fuse 23 Bimetal piece (heat-sensitive contact drive part) 26 Opening / closing contact part 50 Liquid heating unit 52 Heater case 53 Inlet 54 Outlet

Claims (5)

[Claims] 1. A heater body having a structure in which a resistance heating element is embedded in a cylindrical ceramic base, is provided in the middle of a current path of the resistance heating element, and the temperature of the heater body has a predetermined value. A ceramic heater with an energization interruption function, which is provided with an energization interruption mechanism that senses this when the electric resistance reaches the above, and interrupts the energization to the resistance heating element. 2. The ceramic heater according to claim 1, wherein the energization interruption mechanism includes a fuse that is blown at a predetermined temperature or higher to open the energization path. 3. The energization cutoff mechanism opens and closes the opening and closing contact portion when the temperature of the heater body reaches a predetermined upper limit value, and opens and closes the opening and closing contact portion when the temperature of the heater main body reaches a predetermined upper limit value. The ceramic heater according to claim 1, further comprising a heat-sensitive contact drive unit that returns the open / close contact unit to a closed state when the lower limit value is reached. 4. The thermal contact drive unit opens the open / close contact unit when the temperature of the heater body reaches a predetermined upper limit value, and opens / closes the switch when the temperature drops to a predetermined lower limit value. 4. The contact point part is returned to a closed state to turn off / on the electric power supply to the resistance heating element, thereby maintaining the temperature of the heater main body within a predetermined range. Ceramic heater. 5. A heater case having a liquid inlet and a liquid outlet, and an inner space of a heater main body having a structure in which a resistance heating element is embedded in a cylindrical ceramic substrate, in the middle of a conduction path of the resistance heating element. And a ceramic heater provided with an energization interruption mechanism that senses when the temperature of the heater body reaches a predetermined value and interrupts energization to the resistance heating element. A liquid heating unit, wherein a liquid flowing in from an inflow port is heated by the ceramic heater to flow out from the outflow port.