JPS6351003B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electric liquid heating device having a bumping prevention layer. 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. Fig. 1 is a configuration diagram showing the electric liquid heating function of a typical conventional jar pot.As shown in Fig. 1, the outer surface of the container 1 of the electric liquid heating device made of special stainless steel (SUS444) To,
A 700W main heating element 2 and a 50W auxiliary heating element 3 are each insulated with a synthetic mica plate 4, reinforced with a metal belt-shaped reinforcing material, and mechanically fixed to the container 1 with a clamp. The drawbacks of this conventional method are as follows: (1) The band heater, which is composed of two synthetic mica plates, a ribbon heater, and a metal belt-shaped reinforcing material, is difficult to mass-produce;
The cost is high. (2) At first glance, the band heater looks like container 1.
Although it appears that the synthetic mica plate and metal belt-shaped reinforcing material are not very flexible, it is actually a point contact, and as a result, the band heater becomes hot, so it is difficult to insulate. This increases the cost and shortens the life of the heater.
(3) Since the contact between the band heater and the container 1 is poor, the thermal efficiency of the heating element is poor. (4) Since the temperature of the band heater becomes high, the watt density per unit area cannot be increased beyond the current level. (5) Since the heater becomes high temperature and the watt density cannot be increased, a heating element cannot be installed at the bottom of the container 1. (6) Since the heater is provided on the side surface of the container 1, the heating of the bottom surface is delayed, the bumping noise becomes louder, and as a result, temperature unevenness tends to occur in the heating of the liquid. (7) It has various drawbacks, such as poor thermal efficiency and the need for a large amount of heat insulating material for the heating element, making it difficult to make the jar pot lightweight and compact. Purpose of the Invention The present invention solves the problems of the conventional examples as described above, is mass-producible, is cost-effective, has high thermal efficiency, does not produce bumping or boiling noise, and is lightweight and compact. Furthermore, it is an object of the present invention to provide an electric liquid heating device having practical durability. Structure of the Invention In order to achieve the above object, the present invention forms a bumping prevention layer by surface enlarging treatment on the inner surface of a heat exchange section of a container of an electric liquid heating device. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. First of all, the present invention can be implemented in an embodiment in which a bumping prevention layer is formed on the inner wall of the conventional jar pot container shown in FIG. A heating device, that is, an electric liquid heating device in which a heating element is covered with a hollow glass layer and a bonded heating element is installed will be described as an example. In particular, the above-mentioned electric liquid heating equipment has an integrated container and heating element, so it is an excellent method in terms of heat transfer and transport, but due to the bumping phenomenon, the amount of heat transfer and transport becomes pulsating. The effectiveness of this method is also reduced by half. In contrast, the bumping prevention layer of the present invention is effective. FIGS. 2 to 4 show an example of the basic configuration of an electric liquid heating device according to an embodiment of the present invention. In the figure, 11 is a cylindrical container body that constitutes a jar pot, and this container body 11 is based on JIS standards.
It is made of 0.8mm thick special stainless steel, SUS444. 12 is a bottom substrate of the jar pot, and like the container body 11, this bottom substrate 12 is also made of SUS444. A bumping prevention layer 13 is formed on the inner surface of the bottom substrate 12, and a heat generating part 14 is formed on the outer surface of the bottom substrate 12. , which constitutes the container of the jar pot. FIG. 3 shows an enlarged sectional view of the bottom A of the jar pot in FIG. 2. As shown in FIG. 3, an insulating hollow layer 16 is provided on one side of the outer surface of the bottom substrate 12, and this insulating hollow layer 1
A planar heating element 17 obtained by pressing or etching a stainless steel ribbon of SUS430 with a thickness of 60 μm as shown in FIG. Bond and fix at step 18. Thereafter, the inner surface of the bottom substrate 12 is blasted and aluminum powder is plasma sprayed to form the bumping prevention layer 13. Next, the constituent elements of the present invention will be described. (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 the following table.
SUS304, 430, 444 etc. are good. especially among
SUS444 is most preferred.

[Table] (2) Electric heating element The heating element 17 applicable to the present invention is basically a ribbon-shaped element. The surface of the heating element 17 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 heating element. The thickness of the heating element ribbon is suitably 10 to 200 μm, preferably 30 to 100 μm.
A ribbon with a diameter of 10 μm or less is difficult to process into a ribbon, and when manufacturing a sheet heating element, the ribbon may be torn, bent, or bent, 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 6060 μΩ・cm at 20°C and a coefficient of thermal expansion of 104×10 ^-7 deg ^-1 at 100°C is suitable; We take into account the type, shape, and wall thickness, and choose from austenitic stainless steel, Fe-Cr-Al alloy,
-Cr alloy, Ni-Cr alloy, Ni-Cr-Al alloy,
It is possible to obtain a thin ribbon from Fe-Cr-Ni-Al alloy or the like and use it for a heating element. (3) Insulating Hollow Layer The electrical insulation of the glass layer that fixes the heating element 17 of the heating section of the present invention is 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 1 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] Since the glass coating layer is required to have high insulation properties in the application examples of the present invention, the slip compositions shown in Table 2 were used. In Table 2, as the organic solvent, in addition to benzyl alcohol, isophorone, microhexanol, carbitol, etc. can also be used. Further, as a colloid stabilizer, it is possible to use a small amount of a thickener that is soluble in an organic solvent and undergoes oxidative combustion at 150 to 350°C.

[Table] (4) Formation of bumping prevention layer (a) Surface enlarging treatment of base material In Fig. 3, the bottom substrate 12 on which the heat generating part is formed
As a pretreatment of the bottom substrate 12 before forming the bumping prevention layer 13 on the other inner surface of the bottom substrate 12,
surface enlargement processing is required. Sandblasting is most suitable for this pretreatment.
The surface roughness at this time was measured using a Talysurf surface roughness meter.
Ra is preferably 2 to 20 μm, and most preferably about 5 to 10 μm. Below this range, adhesion will not be obtained, and if it exceeds this range, adhesion will deteriorate and the corrosion test will not yield favorable results, so the range shown in Table 3 is suitable for the purpose of the present invention. .

[Table] (b) Surface roughness of bumping prevention layer The role of the bumping prevention layer is to prevent bumping and bumping noise. When a liquid boils, the larger the temperature difference between the heat source and the liquid, the more nucleate boiling and film boiling occur, and the bumping phenomenon occurs at the heat transfer interface of the heat source, resulting in the following drawbacks. (1) Bumping sound,
Produces a boiling sound. (2) The amount of heat transfer becomes pulsating,
The heat source becomes hot. (3) Thermal efficiency decreases.
(4) Insulation becomes uneconomical. (5) It is difficult to make it lightweight and compact. Various obstacles will occur. The solution is to use a material such as aluminum, which is a good thermal conductor and has excellent corrosion resistance, to increase the surface area of the heat exchange surface with the liquid and to enlarge the surface so that the generated gas can easily dissipate from the heat exchange surface. It is an object of the present invention to perform a chemical treatment to form a bumping prevention layer. The surface roughness of this surface enlarging treatment is
As shown in the table, the ten-point average roughness Rz is 25 to 250μm
The range of 50 to 150 μm was particularly optimal. If Rz is less than 25 μm, it is not so effective, and conversely, if Rz is more than 250 μm, the surface area tends to become smaller, so the effect of preventing bumping is small, and therefore Rz is less than 50 μm.
The range of ~150 μm was optimal. This surface roughness is correlated with the Watts density per unit area and the viscosity, specific heat, and boiling point of the heated object.
Rz of about 50 to 150 μm was optimal in the practical range. (c) Material of bumping prevention layer As described above, the base material of the container used in the present invention is preferably a stainless steel base material. Stainless steel has Fe, Cr, and Ni as its basic elements, and trace amounts of Co, Ti, Mn, etc. are added depending on the purpose. The thermal spraying material for the bumping prevention layer to achieve the bumping prevention effect which is the object of the present invention is aluminum,
Metals or alloys such as copper, iron, nickel, stainless steel, iron-chromium alloy, nickel-chromium alloy, or Al ₂ O ₃ , TiO ₂ , SiO ₂ , ZrO ₂ ,
Metal oxides or composite oxides such as Cr ₂ O ₃ , MgO, CaO, and BaO were effective. Select a material from among these sprayed materials for the bumping prevention layer, taking into account the electrochemical potential difference with the container base material, corrosion resistance, thermal expansion coefficient, thermal conductivity, cost, productivity, bumping prevention effect, etc. There is a need to. According to the study results of the present inventors, aluminum, aluminum alloy, stainless steel,
Al ₂ O ₃・TiO ₂ etc. were suitable for compatibility with already commercially available melt base materials. (d) Method for forming the bumping prevention layer and its thickness In the present invention, suitable methods for forming the bumping prevention layer include the metallicon method, the arc method, and the plasma spraying method. In particular, the arc spraying method and the plasma spraying method were particularly effective from the viewpoint of being able to adjust the surface roughness of the bumping prevention layer arbitrarily depending on the intended use and from the viewpoint of adhesion strength, and had a large bumping prevention effect. As shown in Table 3 above, the thickness of the bumping prevention layer is preferably such that the ten-point average roughness Rz is in the range of 25 to 1000 .mu.m, most preferably in the range of 50 to 400 .mu.m. It has also been found that if the porous layer of the bumping prevention layer is too thin, it will not be very effective, and if it is too thick, the porous layer will act as a heat insulating layer, resulting in the opposite effect. Specific Example (Jear Pot) The slip was adjusted by milling in a ball mill for 2 hours using the low-alkali glass shown in Table 1 and using a highly insulating glass frit with the slip composition shown in Table 2. . The steps for implementing the jar pot will be explained with reference to FIGS. 2 to 4. First, as mentioned above, the wall thickness is 0.8mm.
A cylindrical container body 11 and a bottom substrate 12 are manufactured using the SUS444 base material. The part of the bottom substrate 12 where the heat generating layer is to be provided is first blasted using a 60-mesh alumina grid, and then the surface is blasted at 830°C in a nitrogen atmosphere using the slip shown in Table 2. Baking and fixing the insulating hollow layer 16 to one side of the bottom substrate 12 for ~8 minutes. then 60μ
100V, 550W heating element 1 obtained by punching out a m-thick SUS430 stainless steel plate as shown in Figure 4.
7 to the insulating hollow layer 16 using the slip described above.
The heating element 17 is bonded and fixed by the outer coating hollow layer 18 at 840° C. for 7 minutes in a nitrogen atmosphere. In this way, the heat generating section 14 is completed, but if necessary, the auxiliary heater can be constructed in a laminated structure on the heat generating element 17, and it is also possible to install it on the side surface of the main body. Next, a method for creating the bumping prevention layer 13 will be described. The other inner surface of the heat generating part 14 is subjected to surface enlarging treatment using alumina blasting material so that the surface roughness Ra becomes 5 to 10 μm, and then pure aluminum having a particle size of 62 to 84 μm is plasma sprayed. do. The plasma conditions were 42V and 550A, and spraying was performed using an argon-helium mixed gas flame so that the surface roughness Rz was 125 μm. The thickness of the sprayed layer is approximately 145 μm. Next, for comparison, Al ₂ O ₃ and 8 were used as bumping prevention layers.
An anti-bumping layer made of a composite oxide of Al ₂ O ₃ and TiO ₂ containing % of TiO ₂ is formed. Al ₂ O ₃ and
The particle size of Al ₂ O ₃ ·TiO ₂ was 62 to 84 μm, and the plasma conditions were 45 V and 630 A, and the spraying was performed using an argon-helium mixed gas flame so that the surface roughness Rz was 125 μm. In this way, the bottom substrate 12 constituting the base material
A heat generating part 14 and a bumping prevention layer 13 are provided on the surface of the container, and finally, the end surface 15 of the cylindrical container body 11 and the bottom substrate 12 are electrically welded to complete the jar pot container. In order to compare the three types of products of the present invention (550W) completed in this way and the conventional product (700W),
A temperature increase test was performed in which water 2 at 25°C was injected and the temperature reached 100°C. The conventional product required 700W for 15 minutes, but the present invention required 550W for 16 minutes. Next, we measured energy efficiency and bumping noise. The results are shown in Table 4.

[Table] That is, the energy efficiency of the product of the present invention was improved by about 6% compared to the conventional product, and the value was closer to the theoretical energy efficiency. The reason why the energy efficiencies of Al ₂ O ₃ and Al ₂ O ₃ ·TiO ₂ are slightly lower is thought to be due to the difference in thermal conductivity. A sound level meter was used to measure the bumping noise. Conventional products produce a bumping sound from 45 to 50℃, large nucleate boiling bubbles, and a temperature of 70℃ at the boiling point.
A bumping sound of ~82 phon was produced. However, the product of the present invention generates so many microscopic bubbles that you can't see the bottom until it approaches 60℃, and there is no sound, and from 60℃ to the boiling point, it does not make a slight noise of 30 to 49 phon, which is almost unnoticeable. be. Other advantages of the product of the present invention are (1)
The energy saving rate can be approximately 6%. (2) Approximately 1/2 of the insulation material
can be halved. (3) Bumping and boiling noises can be almost eliminated. (4) As a measure against bumping, a space of 3 to 4 cm is provided at the top as a boiling countermeasure, but this space should be reduced by 1/2 to
It is possible to reduce it by 1/3. (5) Since the bumping space and insulation space can be reduced, the container space can be reduced by 20
~25% reduction is possible. It also becomes possible to extend the practical durability life. Effects of the Invention As described above, according to the present invention, nucleate boiling and film boiling due to bumping are eliminated when a liquid is rapidly heated, so there are no complaints due to bumping or boiling noises as in conventional products. Therefore, convective diffusion by microscopic bubbles is also effective during heating, improving energy efficiency, increasing the wattage density per unit area, and reducing the space required to prevent bumping. As a result, the electric liquid heating device can be designed to be more lightweight and compact than before, which is also advantageous in terms of cost.

[Brief explanation of the drawing]

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 one embodiment of the present invention, FIG. 3 is an enlarged sectional view of section A in FIG. 2, and FIG.
The figure is a plan view of a planar heating element used in an embodiment of the present invention. 11... Container body, 12... Bottom substrate, 13...
... Bumping prevention layer, 14 ... Heat generating part, 16 ... Insulating hollow layer, 17 ... Heat generating element, 18 ... Exterior coating hollow layer.

Claims (1)

[Scope of Claims] 1. An electric liquid heating device characterized in that a bumping prevention layer is formed on the inner surface of a heat exchange portion of a container of the electric liquid heating device by surface enlarging treatment. 2. The electric liquid heating device according to claim 1, wherein the surface enlarging treatment as the bumping prevention layer has a ten-point average roughness Rz in the range of 50 to 150μ. 3. The electric liquid heating device according to claim 1 or 2, wherein the bumping prevention layer has a thickness in the range of 50 to 400 μm. 4. The bumping prevention layer is made of metal or alloy such as aluminum, copper, iron, nickel, stainless steel, iron-chromium alloy, nickel-chromium alloy, or Al ₂ O ₃ ,
_TiO2 , _SiO2 , _ZrO2 , _Cr2O3 , _MgO , CaO, BaO
The electric liquid heating device according to any one of claims 1 to 3, which is formed of at least one member selected from the group consisting of metal oxides and composite oxides such as metal oxides and composite oxides. 5. The electric liquid heating device according to any one of claims 1 to 4, wherein the bumping prevention layer is thermally sprayed by any one of metallicon, electric arc, and plasma spraying. 6. A heating part consisting of a heating element covered and bonded with hollow glass on one side of the base material of the container of an electric liquid heating device, and a bumping prevention layer formed on the other inner surface of this heating part. An electric liquid heating device according to any one of claims 1 to 5.