JPS62126580A - Panel heater - 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 Industrial Application This invention relates to a thin planar heating element that generates heat when energized, and is used as a heat source for cooking utensils, heaters, dryers, and the like.

BACKGROUND OF THE INVENTION Currently, a nichrome wire or nichrome foil is inserted between two sheets of silicone rubber, asbestos, etc. and bonded together.

Problems to be Solved by the Invention The surface heating elements currently in use have the following drawbacks.

l) Since the nichrome wires or foils are arranged, the interval between the heat generation is large, and therefore the temperature difference between the heat generation surfaces is large and the heat distribution is poor.

2) It is easy to break the wire, and once the wire breaks, it is impossible to reuse it.

3) Products using silicone rubber as the heat generating surface cannot be used at high temperatures of 260°C or higher.

Also, those using asbestos tend to have unevenness on the heating surface.

4) The surface heating elements currently on the market are expensive.

The present invention has been made in order to eliminate these drawbacks.

Means to solve the problem Two hard mica plates are bonded together using a conductive adhesive made of graphite. Therefore, since the entire adhesive surface constitutes an electrical resistor, heat generation is uniform, and when good conductors of carbon fiber bundles are arranged at equal intervals between the terminals, the current distribution is even more uniform, and the heat distribution is dramatically improved. Become.

In addition, even if a part of the heating surface is damaged, there is no problem with use and there is no fear of wire breakage.

Operation FIG. 1 shows an example of the surface heating element of the present invention. A portion is shown cut away.

FIG. 2 shows an enlarged view of section A in FIG.

In the figure, (1) is a hard mica plate with a diameter of 0.2 to 0.
3. He is very strong. (2) shows a conductive film formed from fine graphite powder. This adhesive is prepared by uniformly dispersing and suspending fine graphite powder having a particle size of 2 to 3 .mu.m in an aqueous sodium silicate solution as a fixing agent using an organic dispersant, and then heating and pressurizing the adhesive.

By adjusting the thickness of this conductive film, any electrical resistance can be achieved. (3) is an electrical terminal made of copper foil of 0.05 to 0.1 mm, which is also temporarily fixed to mica with an adhesive. (3) has a copper washer (5
) and is fixed with a rivet (6) and connected to the lead wire (7). Thus, the current (8) flows uniformly through the conductive film (2).

Next, FIG. 3 shows a case in which carbon fiber bundles are arranged parallel to each other at constant intervals between both terminals of the surface heating element shown in FIGS. 1 and 2.

In the figure, the current entering from the terminal (9) flows in the direction of the arrow through the conductive film (10) as shown.

In this case, if there is a slight difference in the thickness of the conductive film, there will be a slight difference in the amount of current flowing.

However, when the current reaches the carbon fiber bundle (11), (11
) the current is uniformly redistributed along the B-C direction.

The volume resistivity of the conductive film (10) is 0. This is because (11) has a low specific resistance of o and ootΩ, and disperses electricity well, whereas o5Ω. In this way, the uniformly redistributed current is redistributed again by the following (12), and by repeating this process, a uniform current flows throughout the conductive film at the poles. Therefore, the temperature distribution on the heat generating surface becomes uniform, and the time it takes to reach a constant temperature when electricity is applied (rise time) becomes short.

Embodiment FIG. 5 is an embodiment of the present invention and shows a heating element of a toaster.

In the figure, the surface heating element is composed of outer parts (18) and (15) and central part (14). You can bake two slices of bread at the same time by adding bread from E and F.

(16) is a reflecting plate. In this case, the current enters from G, flows through I3→I4→15, and is taken out from H.

The electric circuit is in series and is designed so that the resistance (14) is slightly larger so that the central part generates more heat.

The resistance of the surface heating element can be freely designed by changing the thickness of the conductive film.

FIG. 6 shows the voltages of the circuit of the embodiment shown in FIG.

FIG. 7 shows the case where it is used in a dryer.

In the figure, (17) is a net conveyor, and three wood-invented surface heating elements are arranged in series on the upper and lower sides of the net conveyor (17).

(18), (19), (20)... Upper heating element (21
), (22), (23)...lower heating element is shown.

Materials are inputted from I, dried on a net conveyor (17), and taken out from J. (24), (25)
is the driving sprocket.

Effects of the Invention The invention will be described in detail by comparing a commercially available surface heating element and the surface heating element of the wooden invention.

(2) Compared to commercially available products, the surface heating element of the present invention has a very small temperature difference on the heating surface and a good temperature distribution.

FIG. 8 shows a commercially available surface heating element.

In the figure, a nichrome wire or nichrome foil (27) is sandwiched between two silicone rubber plates (26).

In this case, the heat generation interval is long, and therefore the temperature difference on the heat generation surface is large, and the temperature distribution is not good.

Temperature measuring points (28) on the heat generating surface were set and the temperature at each point was measured, and the temperature difference distribution at each measuring point with respect to the average temperature of 250°C is shown in FIG.

In the figure, the maximum temperature difference is ±7.8% with respect to the average temperature of 250°C.

On the other hand, actual measured values of the surface temperature of the surface heating element of the present invention are shown in FIG. The temperature difference distribution for an average temperature of 250°C is shown, and (29) is the measurement point. In this case, the maximum temperature difference is ±2.6% for an average of 250°C.

The commercially available heating element has a heating element of ±7.8%, while the present invention has a heating element of ±2.6%.
% indicates that the temperature distribution was significantly improved.

Next, Fig. 11 shows the actual temperature distribution (3θp measurement value) when four carbon fiber bundles are inserted at equal intervals between both terminals of the surface heating element shown in Fig. 1O. is the measurement point. In this case, the maximum temperature difference is ±10.4 or less with respect to the average temperature of 250°C.

The temperature distribution is thus significantly improved compared to commercially available products.

2) Since commercially available surface heating elements use nichrome wire or foil, wire breakage is likely to occur, and if the wire breaks, it is impossible to reuse it. On the other hand, the surface heating element of the present invention generates heat over the entire surface, so there is no disconnection, and even if a hole is formed in a part, there is no problem in use.

3) Commercially available products mainly use silicone rubber plates and cannot be used at temperatures above 260°C, but the products of the present invention use hard mica plates. Can be used at temperatures up to 550°C. or,
Unlike asbestos boards, there is no distortion or deformation due to surface temperature differences during use.

4) 0 In the surface heating element of the present invention, after adhesion
Since it is baked for about 10 minutes at a temperature of °C to 450 °C, the electrical resistance value is stable and does not change even after long-term use. Next, the baking process will be explained. The conductive adhesive used in the present invention is prepared by dissolving fine particles of graphite in an aqueous solution of sodium silicate as a fixing agent and uniformly dispersing the mixture using an organic dispersant. After adhesion, the electrical resistance is low at first because the dispersant is mixed between the graphite particles, but when heated above 400°C, the dispersant completely decomposes and dissipates, resulting in a significant drop in electrical resistance and the ability to conduct electricity. The condition improves and becomes stable from then on. When bonded, it has a value of about 0.50.alpha. After baking, it becomes stable at about 0.05Ω.(7).

Sodium silicate is 700°C or higher, graphite is 1000°C
It is stable in the above range.

5) The surface heating element of the present invention has a thickness of 0.4 to 0.5
Since they are extremely thin and have an extremely small heat capacity, they take less time to reach the set temperature when energized, and those with carbon fiber bundles have even faster response times.

FIG. 12 is a graph showing the time it takes for various surface heating elements to reach a set temperature after being energized. In the figure, (31)...A commercially available surface heating element (32) shown in Figure 8.
...Surface heating element (33) of the present invention shown in Fig. 1...Third
The surface heating element shown in the figure further includes a carbon fiber bundle6)0The surface heating element of the present invention has a simple structure, and the materials used and manufacturing costs are low, so its selling price is low. They are very cheap, with the one shown in Figure 1 costing 4 yen/i, and the one shown in Figure 3 containing carbon fiber bundles costing around 5 yen/i.

On the other hand, commercially available silicone rubber plates with nitenichrome wires (wiring type wires cost 15 to 30 yen/
It is at crA position.

[Brief explanation of drawings]

FIG. 1 shows an example of a surface heating element of the present invention. FIG. 2 shows details of section A in FIG. 1. FIG. 3 shows an arrangement of carbon fiber bundles in addition to that shown in FIG. FIG. 4 shows details of section D in FIG. 3. FIG. 5 shows a heat generating part of a toaster as an embodiment of the present invention. FIG. 6 shows the voltage distribution of the heating element in FIG. 5. FIG. 7 shows a dryer as an embodiment of the invention. FIG. 8 shows commercially available surface heating elements and their measurement points. FIG. 9 shows the temperature difference with respect to the average surface temperature at the measurement points shown in FIG. Figure @10 shows the temperature difference between the measurement points and the average surface temperature for the surface heating element of the present invention shown in Figure 1. Fig. it shows the temperature difference between the measurement points and the average surface temperature for the surface heating element of the present invention shown in Fig. 3. FIG. 12 is a graph showing the rise time of various surface heating elements. ”1-MuE-Figure Z

Claims (2)

[Claims] (1) A surface heating element characterized in that two hard mica plates are provided with electrical terminals on both end faces and bonded together with a conductive adhesive made of graphite. (2) Two hard mica plates are provided with electrical terminals on both end faces, and a good conductor of carbon fiber bundles is placed parallel to the terminals at regular intervals between the two terminals, and a conductive adhesive made of graphite is used. A surface heating element characterized by being glued together.