JPH0443589A - sheet heating element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-temperature planar heating element used in cooking appliances, heaters, etc. used in general households.

Conventional technology Conventional high-temperature planar heating elements have a structure in which a heating wire is wound around an insulating substrate such as mica and sandwiched between upper and lower mica plates, or a heating wire of a predetermined shape is placed in a block made of alumina/silica fiber. It was a buried structure.

Problems to be Solved by the Invention However, the conventional technology has had the following problems.

That is, in the case of a mica heating element, the heating wire is embedded in mica, so in order to obtain high-temperature radiation, it is necessary to raise the temperature of the mica plate surface. For this reason, it is necessary to increase the temperature of the heating wire. As such high-temperature heating elements, nickel-chromium heating wires and iron-chromium heating wires are used in general household appliances. Of these, iron-chromium heating wires have a lifespan of about 1000 hours at 1200°C, but in the case of mica heating elements, if the contact between the mica and the heating wire becomes poor, heat conduction decreases, and that part becomes high temperature and generates heat. The wire is more likely to be fused. Therefore, in practical terms, the line temperature is designed to be 1000 to 1100°C. At this time, the surface temperature of the mica plate is only 500 to 600°C. Therefore, the equipment costs 500 to 600.
It is difficult to utilize radiation from a heat source of 700 to 800°C, which is advantageous for cooking or heating. In addition, radiation is not obtained directly from the heating wire, but from a mica plate or a steel plate provided for mechanical reinforcement, so it takes time for these radiant surfaces to heat up, resulting in rapid heating. I couldn't get it. The same thing happened with the nickel-chromium heating wire.

In addition, in the case of a heating element in which a part of the heating wire is embedded in a block made of alumina/silica fiber, etc., the mechanical strength of the block is low, and a sudden temperature difference occurs between the heating element and the block when energized. In some cases, cracks formed in the block, making it difficult to hold the heating wire. In addition, increasing the thickness to increase mechanical strength increases heat capacity, and
Since a considerable part of the heating wire is buried in the block, the heat is taken away by the block and the temperature of the heating wire is raised to a high temperature, e.g.
It took a considerable amount of time to bring it down to ℃.

In order to solve the above problem, as a sheet heating element l, a fourth
As shown in the figure, a configuration has been considered in which a heating element 2, for example, an iron-chromium steel plate is punched out in a serpentine shape, this is fixed to a holding member 3, and the object to be heated is heated by direct radiation from this heating element. However, this configuration also has the problems described below.

That is, the heating element is deflected as shown in FIG. 5 due to thermal stimulation of heat generation and cooling caused by turning on and off the power.

When this deflection occurs - times, the amount of deflection concentrated at that point gradually becomes larger, sometimes reaching 10 W or more. Then, the heating element comes into contact with other components, causing a short circuit accident. Fig. 5 (a) shows that the heating element is normal, Fig. 5 (b) shows that the heating element is deflected, and Fig. 5 (C) shows that the heating element is normal.
) shows a case where the deflection becomes large.

The present invention solves the above problems and provides a planar heating element that does not undergo large deflection and can reach a high temperature in a short period of time.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention adopts a configuration in which a plurality of cylindrical convex portions are provided on the same plane as the band-shaped metal heating element, or a configuration in which the convex portions are folded. This uses a band-shaped metal heating element.

action The present invention can solve the problems with the above configuration.

In other words, in the present invention, a portion of the metal heating element is provided with a convex portion, or this convex portion is further bent, so that even if thermal stimulation due to thermal expansion or contraction is applied, this white portion will hardly deform. do not. Therefore, the number of parts that deform due to thermal stimulation is reduced, and by distributing the convex portions at several locations according to the design, the parts to be deformed can be divided, so that large deflections can be prevented.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. In FIG. 1, a planar heating element 1 is obtained by arranging heating elements 2 in a meandering manner. By attaching and fixing this sheet heating element 1 to a holding material 3, it can be incorporated into a cooker or a heater as a heat source. can get. That is, the sheet heating element 1 is formed by punching out an iron/chromium/aluminum heating element, stainless steel heating element, or nickel/chromium heating element in a serpentine shape with a press, or by bending a strip of the heating element. I can do it. The heating element 2 may be used as it is, or may be coated with an inorganic coating to improve corrosion resistance or radiation efficiency.

A feature of the present invention is that the heating element 2 constituting the planar heating element 1 is provided with convex portions 4 at a plurality of locations as shown in FIG. FIG. 2 is a partially enlarged view of FIG. 1, showing how the convex portion 4 is arranged. Figure 2a shows the rectangular convex portion 4 (
In b), the convex portions 4 in the shape of mountains are arranged on both sides of the band-shaped heating element 2, and (C1 is the one in which the convex portions 4 are provided on one side).

As shown in FIG. 2(a), when comparing the cross section of the portion with the convex portion 4 along the line XX' and the cross section of the portion without the convex portion 4 along the Y-Y' line, the former has a larger cross-sectional area. becomes larger. Therefore, since the resistance of this portion is small, for the same current value, the temperature rise value of the portion with the convex portion is lower than that of the portion without the convex portion. The conductive path becomes longer and the resistance increases as you get closer to the tip of the convex portion, so it becomes difficult for current to flow to that portion and the temperature does not rise much. When the surface temperature of the heating element 2 is designed to be 800°C, due to the above-mentioned reason,
The surface temperature of the heating element 20 in the area without the protrusions 4 reaches 800°C, but the area with the protrusions 4 does not reach 800°C, and the difference in temperature causes shading of red heat. In order to reduce the degree of shading of this red heat, the inside of the heating element 2 is made into a punched-out cavity as shown in FIG. It is best to make it close to the cross-sectional area. The size of the convex portion may be determined such that the cross-sectional area of the portion with the convex portion 4 is 10% or more larger than the cross-sectional area of the portion without the convex portion 4. If it is less than 10%, the temperature difference between the two will not change much and the mechanical strength due to the temperature difference will not change much, and the resistance to deflection due to the increase in width will not increase much, and the effect of preventing deflection of the heating element will be negligible. do not have. When it exceeds 10%, the resistance to deflection of the heating element increases. This resistance increases as the cross-sectional area ratio increases, but in practice it is 20
0% (ie, twice) is sufficient. The cross-sectional area is 2
When the temperature increases by about 00%, the temperature at the tip of the convex portion becomes equal to the cross-sectional area Y-Y.
'The temperature is considerably lower than that of the other parts. However, there is also an effect of increasing the deflection, and there is almost no deflection at the 4 convex portions. Therefore, most of the deflection occurs between the convex parts, but if the length between the convex parts is not too long, even if deflection occurs in that part, the deflection will not be concentrated there, resulting in a large deflection and a short circuit. Accidents will not occur.

As mentioned above, the spacing between the protrusions 4 may be designed so that large deflection does not occur, and it may be determined based on the usage conditions.

Further, in order to reduce the deflection, it is preferable to fold the convex portion 4, that is, fold the dotted line portion in FIG. 2. FIG. 3(a) shows the case where the dotted line portion of the pattern in FIG. 2(a) is folded. The folded part has a large resistance to bending (deflection) and hardly deforms. Third
Figure (b) shows the deflection pattern after repeated heating/cooling cycles. For the same reason as when the convex portion 4 is not bent, deformation due to bending is small.

Specific examples of the present invention will be described below.

Example 1 A 0.05 mm steel plate made of iron, chromium, and aluminum was punched out in a serpentine shape with convex portions as shown in FIG. 1, and attached to a ceramic substrate as a planar heating element.

This planar heating element is 2 m long and 6 square meters wide. As shown in FIG. 2a, the convex portions were rectangular and were alternately provided on both sides of the strip in the same plane. The convex portion had a width of 5 mm and had a cross-sectional area of 200% of the cross-sectional area of the portion without the convex portion.

The center distance between the convex parts is 20 degrees. When we conducted a thermal cycle test with this configuration between the actual operating design temperature of 800''C and room temperature, we observed a sag of approximately 1 lI11 after 100 cycles.
You can see that it has been greatly improved compared to the sagging that can be seen. Also, with this design, it took about 1 minute and 30 seconds to reach 700°C, and the temperature completely reached 800°C after 3 minutes.

Example 2 The convex portion of the planar heating element in Example 1 was used by folding it approximately at right angles to the strip as shown in FIG. 3(a). When the same test as in Example 1 was conducted, the deflection after 100 cycles was less than 1 inch.

Further, the temperature increase rate was also the same as in Example 1.

Effects of the Invention As described above, the planar heating element of the present invention provides the following effects.

That is, the planar heating element of the present invention has a convex portion at a plurality of locations on the band-like heating element, or the convex portions are bent. The heating element hardly flexes even when subjected to the cycling load of heating and cooling between high temperature and room temperature due to cutting. Therefore, it is possible to prevent short-circuit accidents due to contact between the heating element and other components, and short-circuiting of the lifespan due to deformation of the heating element.

Further, in the present invention, since the heating element is a direct radiant, the temperature rises quickly, the temperature can be reached in a short time, and the object to be heated can be heated by high-temperature radiation.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a planar heating element according to an embodiment of the present invention, and FIG.
Figures (a) (C) and (d) are plan views of the main parts showing the shape of the convex portion of the coplanar heating element, respectively, and Figures (a) and (g))
are side views showing the bending of the convex portion of the planar heating element and the deflection after cooling and heating cycles, respectively; FIG. 4 is a plan view of the conventional planar heating element; FIGS. 5(a), (b) and C) is a perspective view showing the occurrence of deflection due to turning on and off of the conventional power supply. 1... Planar heating element, 2... Heating element, 4
...Convex part. Name of agent Patent attorney Shigetaka Awano Haka1 person 1 Figure 2 Figure 1-1 Rollo 1pu (From TaPshi 1\Z-“-From horizontal integral 4-Convex part? Do

Claims (3)

[Claims] (1) A planar heating element consisting of a band-shaped metal heating element in which a plurality of convex portions are provided in the same plane. (2) A planar heating element consisting of a band-shaped metal heating element in which a plurality of convex portions are provided on the same plane and the convex portions are folded. (3) The planar heating element according to claim 1 or 2, wherein the cross-sectional area of the portion having the convex portion is 10% or more larger than the cross-sectional area of the portion without the convex portion.