JPH09266061A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater which can prevent leakage and is high in heat conductivity. SOLUTION: This ceramic heater 10 comprises a ceramic heater element 20 enclosed in a stainless case 40. Therefore even if a ceramic layer 12 on the surface of the ceramic heater element 20 is cracked, no water touches heater wiring 16 and so leakage does not occur. Further, an inorganic adhesive containing metal powder is packed between the ceramic heater element 20 and the case 40 to enhance heat conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater, and more particularly to a ceramic heater for liquid such as a ceramic heater for bath which keeps the hot water at a temperature at which it can be bathed constantly, or a ceramic heater for electric water heater. is there.

[0002]

2. Description of the Related Art Instead of a sheathed heater in which a nichrome wire is arranged in a glass tube, a ceramic heater having a metallized heater wiring built in between ceramic layers is used for heating a liquid. Ceramic heaters are characterized by their smaller size and longer life than sheathed heaters, but they are vulnerable to thermal shock and, for example, when air bubbles or foreign matter in the liquid adheres to the surface, only the temperature of that part However, there is a problem that the ceramic layer is likely to be cracked due to the increase of the temperature. In particular, when the ceramic heater is used in a highly conductive liquid, the heater wiring may be exposed at the cracked portion, which may cause electric leakage.

[0003]

Therefore, the inventor of the present invention stores the ceramic heater in a stainless steel case and prevents the surface of the ceramic heater from directly contacting water by the stainless steel case, whereby cracking occurs. We devised a structure that prevents leakage even if it occurs.

However, when the ceramic heater is housed in the stainless steel case, the problem that the temperature gradient between the ceramic heater and the liquid becomes steep is assumed. That is, when the bath water is heated by the ceramic heater, if the ceramic heater is brought into direct contact with the water, the surface of the ceramic heater does not exceed the hot water temperature of 50 ° C. On the other hand, when it is housed in the stainless steel case, the surface of the ceramic heater is expected to rise to nearly 100 ° C. due to the interposition of the stainless steel case.

Here, when heating the water of 10 ° C. to 50 ° C., if the ceramic heater is brought into direct contact with the water,
Since the temperature of the ceramic heater rises only from 10 ° C to 50 ° C, the increase in the resistance value of the heater wiring is not large. On the other hand, in the case where the heater is housed in the stainless steel case as described above, the temperature of the ceramic heater rises from 10 ° C. to nearly 100 ° C., so that the resistance value of the heater wiring becomes double or more. For this reason, in the case of housing in a stainless steel case, the heating start (10 ° C) at which a current several times as much as the steady current when the maximum temperature (100 ° C) is reached flows
The current capacity of the power supply circuit of the ceramic heater must be set in accordance with C), which causes an increase in the cost of the power supply circuit.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a ceramic heater capable of preventing leakage current and having high thermal conductivity.

[0007]

To achieve the above object, in a ceramic heater according to a first aspect of the present invention, a ceramic heater body formed by arranging heater wiring between ceramic layers, the ceramic heater body is housed, and It is a technical feature that it comprises a metal case for separating the ceramic heater body from the liquid to be heated, and an inorganic adhesive is filled between the ceramic heater body and the metal case.

According to another aspect of the ceramic heater of the present invention, there is provided a ceramic heater body having heater wiring arranged between ceramic layers, and a metal case for accommodating the ceramic heater body and separating the ceramic heater body from a liquid to be heated. The technical feature is that an inorganic adhesive containing metal powder is filled between the ceramic heater body and the metal case.

According to another aspect of the ceramic heater of the present invention, there is provided a ceramic heater body having heater wiring arranged between the ceramic layers, and a metal case for accommodating the ceramic heater body and separating the ceramic heater body from a liquid to be heated. The present invention is characterized in that a metal powder is filled between the ceramic heater body and the metal case, and the metal powder is sealed with an inorganic adhesive.

[0010]

In the structure of the first aspect, since the ceramic heater body is housed in the metal case for separating from the liquid to be heated, even if the ceramic heater body is cracked, the liquid to be heated is not directly contacted, so that electric leakage occurs. Absent.

According to the second aspect of the present invention, since the ceramic heater body is housed in the metal case that separates it from the liquid to be heated, even if the ceramic heater body is cracked, it does not come into direct contact with the liquid to be heated, so that electric leakage occurs. Absent. In addition, since the inorganic adhesive containing metal powder is filled between the ceramic heater body and the metal case, the thermal conductivity is high.

According to the third aspect of the present invention, since the ceramic heater body is housed in the metal case for separating it from the liquid to be heated, even if the ceramic heater body is cracked, it does not come into direct contact with the liquid to be heated, so that electric leakage occurs. Absent. Moreover, since the metal powder is filled between the ceramic heater body and the metal case, the thermal conductivity is high.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described below with reference to the drawings. FIG. 1 shows a ceramic heater 10 according to the first embodiment of the present invention.
The ceramic heater 10 is a rod-shaped ceramic heater body 20 in which a first ceramic layer 12 on the outer side and a second ceramic layer 14 on the inner side are arranged on the outer periphery of a hollow ceramic porcelain tube 30.
And a stainless steel case 40 accommodating the ceramic heater body 20.
Between the ceramic layer 12 and the second ceramic layer 14,
The heater wiring 16 is provided. A flange 42 is formed integrally with the stainless case 40. A terminal 16 a for connecting to the heater wiring 16 is attached to an upper position of the ceramic heater body 20.

The ceramic heater of the first embodiment is used for keeping the hot water of the bath at a temperature at which it can be bathed at all times, and is arranged in a purification tank (not shown) for pumping the hot water of the bath and purifying it with ozone. . This ceramic heater 1
In the case of 0, the case 40 is immersed in the hot water of the purification tank by inserting the lower portion from the flange 42 through the through hole formed in the upper surface of the purification tank, and the current is passed through the heater wiring 16 by the current. It is configured to heat hot water.

Next, a method of manufacturing the ceramic heater according to the first embodiment will be described with reference to FIGS. First, a method of manufacturing the first and second ceramic layers 12 and 14 will be described. 2% of MgO (weight ratio, the same below), 2% of CaO, and 4% of SiO ₂ were mixed with alumina powder, wet-milled in a ball mill for 50 to 80 hours, and then dehydrated and dried. 3% methacrylic acid isobutyl ester in this powder,
Butyl ester (3%), nitrocellulose (1%) and dioctyl phthalate (0.5%) are added, and trichloroethylene and n-butanol are added as a solvent and mixed by a ball mill to obtain a fluid slurry. After degassing under reduced pressure, it was poured into a flat plate and gradually cooled to release the solvent.
As shown in (A), a first alumina green sheet 12γ having a thickness of 0.05 mm to be the first ceramic layer 12 and a second alumina green sheet 14γ having a thickness of 0.5 mm to be the second ceramic layer 14 are formed. To do.

Next, in order to form the heater wiring 16, a high resistance metallized ink is formed by mixing a large amount of impurities such as alumina into tungsten powder to form a slurry.
The tungsten metallized ink is screen-printed on the second alumina green sheet 14γ to form a metal paste layer 16γ. FIG. 2B shows a plan view of the second alumina green sheet 14γ shown in FIG. 2A as seen along the arrow B. Here, FIG. 2A corresponds to the C-C cross section of FIG.

Then, the first and second green sheets 12γ and 14γ are thermocompression bonded as shown in FIG. 2 (C).
Then, this thermocompression bonded alumina green sheet 12
A through hole (not shown) for forming a terminal 16a for connection from the heater wiring is bored at one end of γ, 14γ, and a metallized ink for the terminal is filled in the through hole. Then, the alumina green sheets 12γ and 14γ thus laminated are wound around the ceramic porcelain tube 30 shown in FIG. 1 and simultaneously fired in a non-oxygen atmosphere at 1400 ° C. to 1600 ° C. After the terminals 16a are nickel-plated on the ceramic heater formed by firing, a lead wire for external power supply is silver-brazed to the terminals 16a to complete the ceramic heater body 20.

The ceramic heater body 20 is housed in a stainless case 40 as shown in FIG. It is difficult to keep the outer dimensions of the ceramic heater body 20 constant because the first and second alumina green sheets 12γ and 14γ shrink about 20% during firing. Therefore, the outer peripheral surface 20a of the ceramic heater body 20 and the inner peripheral surface 4 of the case 40 are
A clearance of about 0.25 mm is provided between 0a and 0a. In addition, the lower surface 20b of the ceramic heater body 20
The ceramic heater body 20 is fixed by a jig (not shown) so that a clearance of about 0.25 mm is left between the bottom portion 40b of the case 40 and the bottom portion 40b. In addition, an inclined portion 42a is formed on the inner peripheral side of the flange 42 of the case 40 in order to facilitate filling of an inorganic adhesive described later.

Next, between the ceramic heater body 20 and the case 40, an Aron Ceramic (registered trademark) having a heat resistance of about 1300 ° C. provided by Toagosei Co., Ltd. as an inorganic adhesive is shown. Do not pour using a funnel-shaped member. Then, the ceramic heater body 20 and the case 40 are carried into a vacuum chamber and placed in a vacuum state to remove bubbles in the inorganic adhesive 50 between the ceramic heater body 20 and the case 40. Then, after drying at 90 ° C., the inorganic adhesive 50 is cured at 150 ° C. to complete the ceramic heater 10. In addition to the inorganic adhesive, it is possible to use an organic adhesive as the adhesive, but since the heat resistance is low and stable adhesive force cannot be exhibited over a long period of time, in the present embodiment, An inorganic adhesive is used.

In the ceramic heater 10 according to the structure of the first embodiment, since the ceramic heater body 20 is housed in the case 40, the first ceramic layer 12 on the surface of the ceramic heater body 20 is cracked. Even
Heater wiring 1 embedded in the first ceramic layer 12
6 does not come into direct contact with water and does not generate electric leakage.

Incidentally, in the conventional ceramic heater of the type which is directly immersed in water, after the flange is manufactured separately,
Since it was connected to the ceramic heater body, a gap was easily generated between the flange and the ceramic heater body. As described above, in the ceramic heater 10, the flange 42 is brought into contact with and fixed to the peripheral edge of the through hole formed in the upper surface of the purification tank, and the lower portion of the through hole is inserted, whereby the case 4
0 is immersed in the hot water of the purification tank. For this reason, if there is a gap, water leaks, and the above-mentioned terminal 16a gets wet, so that electric leakage easily occurs. On the other hand, in the configuration of the first embodiment, since the flange 42 is integrally formed on the upper portion of the case 40, there is no gap between the flange 42 and the case 40 that causes electric leakage.

Next, a second embodiment of the present invention will be described with reference to FIG. Also in this second embodiment, the same ceramic heater body 20 and case 40 as those in the above-described first embodiment are used. However, the first
In the embodiment, the 0.25 mm gap between the ceramic heater body 20 and the case 40 was filled with the inorganic adhesive. However, in the second embodiment, the 0.25 mm gap is filled with the inorganic adhesive as shown in FIG. Inorganic adhesive containing metal powder 5
Fill 2

Here, Aron ceramic is used as the inorganic adhesive, and copper powder of 325 mesh (particle diameter of about 50 μm) is used as the metal powder. As the metal powder, in addition to copper, oxygen-free copper, aluminum, or the like, which has a high thermal conductivity, is resistant to rust, and is an inexpensive material, can be used. This metal powder is mixed in an inorganic adhesive and poured between the ceramic heater body 20 and the case 40. Then, the ceramic heater 110 is completed by depressurizing and degassing, drying at 90 ° C., and then curing the inorganic adhesive 52 at 150 ° C. In the second embodiment,
A mixture of metal powder in a weight ratio of 9% with an inorganic adhesive, a mixture of 10%, a mixture of 30%, and a mixture of 50% were prepared, and a heat conduction test was conducted as described later. It was Here, the inorganic adhesive in which the metal powder is mixed by 50% in weight ratio has a lower flow rate, so that it is difficult to flow into the gap of 0.25 mm, which is the upper limit value that can be used in the method of the second embodiment. Was judged.

Also in the second embodiment, since the ceramic heater body 20 is housed in the case 40, even if the ceramic heater body 20 is cracked, no leakage current is generated.

Next, a third embodiment of the present invention will be described with reference to FIG. Also in this third embodiment, the same ceramic heater body 20 and case 40 as those in the above-described first and second embodiments are used. In the third embodiment, first, the metal powder 54 is introduced into the 0.25 mm gap between the ceramic heater body 20 and the case 40 as shown in FIG. As this metal powder, 325 mesh (particle diameter about 50 μm) copper powder is used. Here, as the metal powder, in addition to copper, various materials such as oxygen-free copper and aluminum which have high thermal conductivity, are resistant to rust, and are inexpensive can be used. After that, an inorganic adhesive (aron ceramic) is placed on the metal powder 54 filled in the gap.
50 is poured, degassed in a vacuum chamber, dried at 90 ° C., and then the inorganic adhesive 50 is cured at 150 ° C. to seal the metal powder 54 and prevent rust. The case 40 is fixed to the ceramic heater body 20 while preventing the generation thereof. Note that reference numeral 50a in the figure denotes the inorganic adhesive 50 that has penetrated into the metal powder 54.

In the third embodiment, since the particle diameter is small, the metal powder 54 can be easily poured into the gap of 0.25 mm. Here, in the second embodiment described above, it is considered that the thermal conductivity can be improved by increasing the amount of the metal powder, but the metal powder is added in a weight ratio of 5%.
The inorganic adhesive mixed with 0% or more was difficult to flow into the gap of 0.25 mm and was difficult to manufacture. For this reason, it has been impossible to use an inorganic adhesive in which the weight ratio of metal powder exceeds 50%. On the other hand, in the third embodiment, more than 50% of the metal powder with respect to the inorganic adhesive can be poured into the gap of 0.25 mm.

Next, the experimental results for comparing the thermal conductivity of the ceramic heaters of the first, second and third embodiments will be described. In this experiment, 10 liters of water was heated by each ceramic heater. In the figure, the horizontal axis represents elapsed time (minutes) and the vertical axis represents temperature (° C).

The curve (e) in the drawing shows the case where the ceramic heater body 20 of the first embodiment is directly immersed in water for heating. It heats water in the shortest time and has the highest thermal conductivity. Curve (d) shows the case where the metal powder of the third embodiment is heated by the ceramic heater 210 with the gap filled. It can be seen that in the ceramic heater 210 of the third embodiment, the thermal conductivity is comparable to that when the ceramic heater body 20 is directly immersed in water for heating.

The curve (c) in the figure shows the result by the ceramic heater 110 using the inorganic adhesive in which the content of the metal powder is 50% in the second embodiment, and the curve (b) shows the content. The result by the ceramic heater 110 using the inorganic adhesive whose rate is 10% is shown. Furthermore, the curve (a) shows the result of the ceramic heater 10 of the first embodiment using an inorganic adhesive containing no metal powder. Here, although not shown, in the ceramic heater 110 using the inorganic adhesive containing 9% of the metal powder, an experiment similar to that of the ceramic heater 10 of the first embodiment using the inorganic adhesive containing no metal powder was performed. Results were obtained. Therefore, it is considered that the thermal conductivity can be improved by setting the content of the metal powder to 10%.
Further, by setting the metal powder content of the inorganic adhesive to 50%, the thermal conductivity can be greatly improved, but as described above, the manufacturing becomes difficult and the adhesive strength between the case 40 and the ceramic heater body 20 is increased. Is reduced. Therefore, the metal powder content rate of 30% of the inorganic adhesive is considered to be the optimum value in the second embodiment because the production is easy and the adhesive strength between the case 40 and the ceramic heater body 20 is high. To be

As described above, in the second and third embodiments, since the thermal conductivity is high, the power supply circuit for supplying electric power to the ceramic heater can be constructed at low cost. That is,
When water of 10 ° C is heated to 50 ° C, the thermal conductivity is high, so the temperature of the ceramic heater changes from 10 ° C to 50
Since the temperature rises only to about ° C, the change in the resistance value of the heater wiring from the start of heating with the lowest resistance value to the steady state with the highest resistance value is small. Therefore, the amount of change in current between the start of heating and the steady state is small, and it is no longer necessary to provide a large capacity for the steady state and design to withstand the current capacity at the start of heating. Can be suppressed.

In the first, second, and third embodiments described above, Aron ceramic was used as the inorganic adhesive, but other than this, various inorganic adhesives such as water glass and cement are used. be able to. Further, although stainless is used as the material of the case 40, various metals having corrosion resistance such as copper, aluminum, or a steel plate plated with nickel can be used.

Further, in the above-mentioned embodiment, the ceramic material mainly containing alumina was used as the ceramic constituting the ceramic layer, but various ceramic materials such as AlN, glass ceramic, SiC, mullite, glass ceramic, etc. may be used. Can be adopted. The material of the metal paste layer forming the heater wiring may be appropriately selected according to the ceramic material. For example, molybdenum, platinum or the like may be used in addition to tungsten. Further, in the above-described embodiment, the ceramic heater used for heating the hot water of the bath is described as an example, but the present invention can be suitably applied to ceramic heaters for various purposes.

[0033]

According to the present invention, since the ceramic heater body is housed in the metal case, even if the ceramic heater body is cracked, the ceramic heater body does not come into direct contact with water, so that electric leakage does not occur.

[Brief description of drawings]

FIG. 1 is a perspective view showing a ceramic heater according to a first embodiment of the present invention.

FIG. 2 shows a manufacturing process of the ceramic heater shown in FIG. 1, and FIG. 2 (A) shows a first green sheet and a second green sheet before lamination.
Fig. 2 (B) is a cross-sectional view of the green sheet.
2B is a sectional view of the first green sheet and the second green sheet after lamination.

FIG. 3 is an explanatory view showing a filling state of the inorganic adhesive between the ceramic heater body and the case according to the first embodiment.

FIG. 4 is an explanatory view showing a filling state of an inorganic adhesive between a ceramic heater body and a case according to a second embodiment.

FIG. 5 is an explanatory view showing a filling state of metal powder and an inorganic adhesive between the ceramic heater body and the case according to the third embodiment.

FIG. 6 is a graph showing test results of thermal conductivity of the ceramic heaters of the first, second and third embodiments.

[Explanation of symbols]

 10 Ceramic Heater 12 First Ceramic Layer 14 Second Ceramic Layer 16 Heater Wiring 20 Ceramic Heater Body 40 Case 42 Flange 50 Inorganic Adhesive 52 Inorganic Adhesive 54 Metal Powder

Claims (3)

[Claims] 1. A ceramic heater body formed by arranging heater wiring between ceramic layers, and a metal case for accommodating the ceramic heater body and separating the ceramic heater body from a liquid to be heated. A ceramic heater characterized in that an inorganic adhesive is filled between the heater body and the metal case. 2. A ceramic heater body formed by arranging heater wiring between ceramic layers, and a metal case for accommodating the ceramic heater body and separating the ceramic heater body from a liquid to be heated. A ceramic heater characterized in that an inorganic adhesive containing metal powder is filled between a heater body and the metal case. 3. A ceramic heater body formed by arranging heater wiring between ceramic layers, and a metal case for accommodating the ceramic heater body and separating the ceramic heater body from a liquid to be heated. A ceramic heater characterized in that a metal powder is filled between a heater body and the metal case and the metal powder is sealed with an inorganic adhesive.