JPH0435169B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electric liquid heating device with excellent thermal efficiency, and in particular, to a metal substrate having a hollow layer, a planar heating element is covered with a hollow layer and bonded to an integrated heat generating device. This invention relates to an electric liquid heating device using the body. Configuration of conventional examples and their problems As a representative example of electric liquid heating equipment, a jar pot, which has grown significantly in recent years and has deep-rooted latent demand among users, will be explained. Jar pots have the functions of a thermos bottle and an electric kettle, and are energy-efficient, so they have become explosively popular in recent years. Therefore, as the penetration rate gradually increases, the effectiveness of mass production increases, and we are now in a situation where we must pursue even greater economic benefits in terms of cost and thermal efficiency. Figure 1 is a configuration diagram showing the electric liquid heating function of a typical _conventional jar pot.
On the outer surface of the container 1 of the electric liquid heating device consisting of,
A band heater 5 in which a 700W main heating element 2 and a 50W auxiliary heating element 3 are insulated with a synthetic mica plate 4 and reinforced with a metal belt-shaped reinforcing material is mechanically fixed to the container 1 with a clamp. There is. Switching between the main heating element 2 and the auxiliary heating element 3 is set by the thermostat 6 so that the main heating element 2 is turned off when the liquid temperature is 95°C, and the main heating element 2 is turned on when the liquid temperature is 70°C. Further, the container 1 and both heating elements 2 and 3 are kept warm by a heat insulating material 7, and the entire body is housed in an outer case. The reason why the conventional jar pot is equipped with the main heating element 2 and the reinforcing heating element 3 is as follows. If on-off control is performed only with the main heating element 2, the band heater 5 and the container 1 have different expansion rates, so if the on-off cycle is repeated, the band heater 5 will expand and expand significantly, and eventually the container 1 and the band heater 5 are no longer in contact with each other, the life of the heater is shortened, and the band heater 5 may fall. In order to prevent this, a method is adopted in which the liquid is constantly heated by an auxiliary heater 3 having a relatively small wattage during heat retention. Listing the drawbacks of such conventional jar pots, they are as follows: (1) A band consisting of two ribbon heaters, a main heating element and an auxiliary heating element, stacked on top of each other with a synthetic mica plate interposed between them, and reinforced with a metal reinforcing material. The heater 5 is expensive. (2) At first glance, the band heater 5 appears to be in close contact with the container 1, but since the expansion rate of the synthetic mica plate and the belt-shaped reinforcing material is different from that of the container 1, if the cycle life is repeated, The container 1 and the band heater 5 come into point contact or no contact, and as a result, not only the thermal efficiency decreases, but also the heater becomes abnormally high temperature, and the life of the heater is shortened. (3) The heat from the band heater 5 is transferred to the synthetic mica plate 4,
Since the heat is conducted to the liquid in the order of the belt-shaped reinforcing material and the container 1, heat is radiated during these heat transfers, resulting in poor thermal efficiency. (4) Main heating element 2 and auxiliary heating element 3 are connected to thermostat 6
Since it is a control method, energy efficiency and
Uniformity of liquid temperature, cost advantage
TRS control (thermistor control) is not possible. (5) Since a large amount of heat insulating material is required from the viewpoint of thermal efficiency, it is difficult to make the jar pot lightweight and compact. (6) In the conventional configuration, the reinforcing heating element 3 is energized during heat retention, and even if the liquid evaporates and the boiling state is dry, the reinforcing heating element 3 does not break.
There is a problem in terms of safety. As a way to solve this problem, a method has been proposed in which a temperature fuse (set to break at approximately 150°C) is installed so that the temperature fuse blows during dry boiling and the electricity is stopped. If dry boiling is performed, replacing the temperature fuse is complicated and is not a preferable method. Purpose of the Invention The present invention solves the problems of the conventional examples as described above, and can be mass-produced, is cost-effective, has excellent thermal efficiency, is lightweight and compact, is easy to control temperature, and has a liquid temperature control system. The object of the present invention is to provide an electric liquid heating device that is uniform, highly safe in a dry boiling state, and has excellent practical durability. Structure of the Invention In order to achieve the above-mentioned object, the present invention makes the bottom of the container protrude toward the inside of the container, and provides an insulating hollow layer in the recess formed by the protrusion that does not come into contact with the liquid. A planar heating element made of a metal ribbon is coated and bonded with a hollow layer and a covering hollow layer to form an integrated structure. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. Fig. 2 shows an example of the basic configuration of a jar pot in an embodiment of the present invention. In Fig. 2, reference numeral 11 indicates a _cylindrical container constituting the jar pot. The bottom part is configured to protrude convexly upward, that is, toward the inside of the container 11, and a thin planar heating element 13 is inserted into the recessed part 12 on the non-liquid contact side with an insulating hole. Covered and bonded by layers. To give an example of control of the planar heating element 13, the temperature of the liquid in the container 11 is detected by the thermistors 15 and 16, the electronic temperature relay _TR1 sets a specified temperature, and another temperature relay TR is set. ₂ sets a temperature rise limit, and when the temperature of the liquid exceeds the set temperature of the temperature relay _TR1 , the circuit of the planar heating element 13 is opened. The control circuit is shown in FIG. FIG. 4 shows an enlarged sectional view of the bottom of the jar pot in FIG. 2. As shown in FIG.
First, an insulating hollow layer 17 is provided in the concave portion 12 on the liquid non-contact side, with the concave portion 12 protruding upward, that is, toward the inside of the container 11, and then on this insulating hollow layer 17, a SUS layer having a thickness of 60 μm is provided. A planar heating element 13 obtained by pressing or etching _{a 430} stainless steel ribbon into the shape shown in FIG. 5 is provided, and this heating element 13 is bonded and fixed with a covering hollow layer 18. ing. In the configuration of the present invention, since the planar heating element 13 is directly bonded to the bottom substrate 11a of the container 11, the energy efficiency is high, the heater life is also long, and the system is excellent in uniformity of liquid temperature. It is. The results are shown in Table 1.

[Table] Although the configuration of the present invention described above shows very excellent effects, since the planar heating element 13 of the present invention is bonded and fixed by the covering hollow layer 18, it does not reach abnormally high temperatures (600°C or more). In this case, the covering hollow layer 18 peels off. Here, in actual use, the temperature is
Although the temperature is below 100℃, it can reach abnormally high temperatures in dry boiling conditions. Therefore, although the planar heating element system of the present invention shows excellent effects, it cannot be commercialized unless measures are taken to prevent dry boiling. Therefore, the present invention is particularly aimed at preventing dry boiling. The constituent elements of the present invention will be described below. (1) Metal base material The metal base material constituting the electric liquid heating device of the present invention must have corrosion resistance, thermal conductivity, and hollow coating properties as a heating device. Therefore, the base material used in the present invention is preferably a stainless steel base material, as shown in Table 2.
SUS304, 430, 444 etc. are good. especially among
SUS ₄₄₄ is most preferred.

[Table] (2) Electric heating element The heating element 13 applicable to the present invention is basically a ribbon-shaped element. The surface of the heating element 13 must be completely covered with the hollow layer 18. For example, if a coil-shaped or thick band-shaped heating element is used, the thickness of the hollow layer 18 will increase accordingly. As a result, the adhesion of the hollow layer 18 is extremely reduced, and the hollow layer 18 is easily peeled off by an external shock, exposing the electric heating element. The thickness of the heating element ribbon is suitably 10 to 200 μm, preferably 30 to 100 μm.
It is difficult to process thin strips of 10 μm or less into thin strips, and when manufacturing planar heating elements, the strips may tear, fold, or bend, resulting in significantly poor workability. . Further, if the thickness is 200 μm or more, in addition to the above-mentioned reason, if a heat cycle is applied to the planar heating element, cracks may appear in the hollow layer, which is not preferable. In addition to the usual methods of cold rolling and hot rolling, metal can be made into a thin ribbon using an ultra-quenching method. Etching and press working are suitable methods for forming a thin metal strip into a desired pattern. The etching method can be applied when the production quantity is small, and the press processing method can be applied for mass production. The film thickness and pattern shape of the electric heating element can be arbitrarily determined in consideration of the rated power, heat generating area, temperature distribution, etc. Various electric heating materials can be used as the material for the heating element, but it is important that the specific resistance and coefficient of thermal expansion, which are factors that determine the shape of the heating element (pattern width, length, thickness), etc., are set to appropriate values. A material with excellent adhesion to the hollow layer, workability, etc. is selected. From these points of view, ferritic stainless steel with a resistivity of 60 μΩ・cm at 20°C and a coefficient of thermal expansion of 104×10 ^-7 deg ^-1 at 100°C is suitable; Considering the type, shape, and wall thickness, we will select austenitic stainless steel, Fe-Cr-Al alloy, Fe-Cr
Alloy, Ni-Cr alloy, Ni-Cr-Al alloy, Fe-
It is possible to obtain a thin ribbon from a Cr-Ni-Al alloy or the like and use it for a heating element. (3) Insulating Hollow Layer The electrical insulation properties of the glass layer to which the heating element 13 of the heating section of the present invention is fixed are particularly important. In the present invention, in particular, since the heating element is constructed in a laminated manner, a low-alkali glass having excellent electrical insulation properties is required. Table 3 shows the preferred range of glass necessary to achieve the purpose of the present invention and typical glass compositions used in the following examples.

[Table] In the application examples of the present invention, the glass coating layer is required to have high insulation properties, so the slip composition shown in Table 4 was used. In Table 4, in addition to benzyl alcohol, isophorone, microhexanol, carbitol, etc. can also be used as the organic solvent.
It is also soluble in organic solvents as a colloidal stabilizer.
It is possible to use small amounts of thickeners that oxidize and burn at 150-350°C.

[Table] As shown in Table 1 above, integrating the jar pot container 11 and heating element 13 through the hollow layer 18 as in the present invention means that energy efficiency, heater life, liquid temperature, etc. This is an excellent method from the viewpoint of uniformity. By processing the bottom of the jar pot as in the present invention, a jar pot with even greater safety can be realized. Next, this will be explained using a specific example. Using the low alkali glass shown in Table 3 above,
Slips were prepared using the slip compositions shown in Table 4 by milling using a ball mill for 2 hours. A cylindrical container 11 and a bottom substrate 11a are made from a SUS ₄₄₄ base material with a wall thickness of 0.5 mm. The bottom substrate 11a is machined using a press by selecting from various shapes shown in FIGS. 6a and 6b, 7a and 7b, and 8a and 8b.
Then, the part of the bottom substrate 11a where the heat generating layer is to be provided is first polished using 60 mesh alumina abrasive material.
After that, the insulating hollow layer 17 is placed in the recess 1 of the bottom substrate 11a in a nitrogen atmosphere at 830° C. for 7 minutes using the slip shown in Table 4 on that surface.
2. Burn and fix. After that, a wall thickness of 60 μm was formed.
Heating element 13 obtained by etching a SUS ₄₃₀ stainless steel thin plate into the heater pattern shown in Figure 5.
(550W at 100V) is placed on the insulating hollow layer 17 using the above-mentioned slip, and the heating element 13 is fixed by baking at 840°C for 7 minutes in a nitrogen atmosphere using the covering hollow layer 18. . This was joined to a cylindrical container 11 by welding to form a sample of the present invention. Furthermore, for comparison, a sample with a heat generating element formed on a conventionally used bottom substrate was also fabricated using the same method. As shown in FIGS. 7a and 7b, water in these samples was placed in a container, and the water was heated by energizing the heat generating part. During heating, water was not replenished and the behavior was observed under dry conditions. In this case, the temperature at the bottom of the container was checked with a CA thermocouple. The temperature-time curve at this time is shown in FIG. In the configuration of the present invention shown in Figure 9a, when the boil is about to dry, a small amount of water remains at the bottom of the container, so the temperature of the heat generating part does not rise abnormally, and The safety device is activated and the heat generating part is turned off, but in the sample configured in the conventional shape shown in Figure 9b, the water evaporates and at the same time the safety device activates, during which time the heat generating part turns off. As shown in Figure 10, the temperature of the heat generating part rose abnormally, and as a result, cracks occurred in the hollow layer constituting the heat generating part, making it unusable. Effects of the Invention As described above, according to the present invention, the bottom of the container is made to protrude convexly toward the inside of the container, and the planar heating element is covered and bonded to the concave portion on the non-liquid contact side with the hollow layer. As a result, it is superior not only in terms of energy efficiency, lifespan of heat generating parts, and uniformity of liquid temperature, but also in terms of safety during dry boiling.Furthermore, it is lighter and more compact than before, and has excellent design freedom. This is also advantageous in terms of cost.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a conventional jar pot, Figure 2
The figure is a longitudinal sectional view of a jar pot showing an embodiment of the present invention, FIG. 3 is a temperature control circuit diagram of the jar pot, FIG. 4 is an enlarged sectional view of the heat generating part of the jar pot, and FIG. 5 is an embodiment of the present invention. A plan view of a planar heating element used in an embodiment, FIGS. 6a, b to 8 a, b are a plan view and a sectional view of a main part of a bottom substrate used in an embodiment of the present invention, and FIGS. FIG. 10b is a diagram illustrating the state of the jar pots of the present invention and the conventional shape when they are on the verge of dry boiling, and FIG. 10 is a diagram showing the temperature-time curve of the jar pots of the present invention and the conventional shape. 11... Container, 11a... Bottom substrate, 12...
Recessed portion, 13... Planar heating element, 17... Insulating hollow layer, 18... Covering hollow layer.

Claims (1)

[Claims] 1. The bottom of the container is made to protrude convexly toward the inside of the container, and an insulating hollow layer is provided in the concave portion formed by the convexity that the liquid does not come into contact with, and the insulating hollow layer and the coating hollow layer form a surface shape of the metal ribbon. An electric liquid heating device characterized by an integrated heating element that is coated and bonded.