JPH08190981A - Heating element and electric heater, and their manufacture - Google Patents

Abstract

PURPOSE: To obtain a heating element and an electric heater using the heating element which have a good thermal efficiency, and do not generate a burnout or a removal from a substrate, by forming an electric resisting heating element made by compounding a heat resisting ceramics, and a metal or an alloy for electric heating, on the surface of a heat resisting ceramic substrate in the film form by a flame coating. CONSTITUTION: A mixture powder of a heat resisting ceramics powder consisting of a ceramics such as an alumina or an aluminum nitride, and an electric insulating material such as a heat resisting glass; and a metal powder or an alloy powder for electric heating; is flame coated on the surface of the substrate of a heating element. As a result, a heating element can be formed on the surface of a heat resisting ceramics substrate easily, in a film form which is hardly removed. An electric heater made by providing an electrode at the end of a heating element has a good heating efficiency, generates no burnout and removal of the heating element, and generates the heating stably. In this case, it is favorable to include the heat resisting ceramics of 60 to 90vol.% in the heating element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element used in a plate heater or the like, an electric heater using the heating element, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional planar heater is disclosed in Japanese Laid-Open Patent Publication No. 59-59.
-130080, JP-A 61-277186 and JP-A 63-64280. These are ones in which a ceramic heating element or a metal resistor is sprayed on an electrically insulating substrate (hereinafter referred to as a substrate) to provide an electrically insulating coating layer (hereinafter referred to as a coating layer).

However, Japanese Patent Laid-Open No. 59-130080.
When an oxide semiconductor is used as a resistor, such as TiO ₂ in Japanese Patent Laid-Open Publication No. 2003-242242, the sprayed film can be formed easily, but the temperature resistance coefficient of the resistor becomes negative, making temperature control difficult. JP 61
When a metal wire is used as in Japanese Patent Publication No. 277186, a coating layer such as enamel is required, and the heat capacity of the heat generating substrate is increased, so that the responsiveness and heat efficiency of the heater are deteriorated. Further, when a thermal sprayed coating of a general metal such as aluminum or copper is used as the resistor as in Japanese Patent Laid-Open No. 63-634280, there is a problem of peeling due to the difference in the thermal expansion coefficient between the substrate and the metal resistor, and the metal resistance. Due to the low electrical resistivity of the body, it requires a dedicated power supply to carry large currents at low voltages.

That is, in the conventional sheet heater, the resistance temperature of the resistor is negative, the heat capacity of the heater is large, the resistor is easily peeled off, and a resistor having a large resistance cannot be produced. There was a problem.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a heating element which has good thermal efficiency and is free from disconnection and separation from the substrate, an electric heater using the heating element, and a method for manufacturing the same. The purpose is.

[0006]

Means for Solving the Problems The present inventors have obtained an electric resistance heating element in which a heat resistant ceramic and a metal or an alloy for electric heating are combined and formed into a film on the surface of the heat resistant ceramic substrate by thermal spraying. The above-mentioned problem was solved by doing.

The metal or alloy for electric heating, which is a component of the heating element, has a small temperature coefficient of resistance, excellent resistance to oxidation in air, and a large volume electric resistivity as a metal. As its name implies, it is excellent for electric heating. There is. It is preferable that the material of the heater substrate and the heat-resistant ceramic that is a component of the heating element are the same material or similar in composition, or an electrically insulating material that is a heat-resistant ceramic that thermally reacts with the substrate. It is possible to reduce the difference in the coefficient of thermal expansion between the heating element and the heating element and further improve the adhesion strength.

When the content of the heat-resistant ceramics, which is a component of the heating element, is less than 60% by volume, sufficient adhesion strength with the substrate cannot be obtained, which is caused by the difference in thermal expansion coefficient between the substrate and the heating element. It becomes easy to peel off. On the other hand, when the content is more than 90% by volume, it becomes difficult to conduct electricity, the surface load density of the conductive portion becomes large, and even if electricity is applied, heat is locally generated and the wire is broken. Therefore, the content of the heat-resistant ceramics, which is a component of the heating element, is preferably 60 to 90% by volume.

Ceramics such as alumina and aluminum nitride, and electrically insulating materials such as heat-resistant glass are suitable as the heat-resistant ceramics as a component of the heating element. Furthermore, although there are various methods for forming the heating element of the invention on the substrate, the surface of the heat-resistant ceramic substrate can be easily coated on the surface of the heat-resistant ceramic substrate by spraying a mixed powder of the heat-resistant ceramic powder and the metal or alloy powder for electric heating. It is possible to form the heating element in a film shape that is difficult to peel off. The electric heater having electrodes formed at the end portions of the heating element thus formed does not require the layer to be covered as described above, so that the heating efficiency is high and there is no disconnection of the heating element or peeling from the substrate. Also produces stable heat.

In the case of thermal spraying, when the substrate is heated by the flame of thermal spraying, the thermal sprayed film is likely to be peeled off, and the thermal spraying is generally performed while cooling the substrate so that the substrate does not overheat. However, when spraying a mixed powder of a heat-resistant oxide powder and a powder of a metal or an alloy for electric heating onto a heat-resistant ceramic substrate, by heating the substrate, a stronger sprayed film can be formed. That is, it is considered that by heating the substrate, the cooling rate of the sprayed coating becomes slower, and a bond due to mutual diffusion occurs between the sprayed high temperature heat-resistant ceramics or the oxide film of the metal for electric heating and the substrate. The effect of heating the substrate appears from 300 ° C., on the other hand, the temperature is preferably 800 ° C. or lower because deformation of the substrate and excessive oxidation of the metal or alloy for electric heating proceed. However, if the substrate is heated, the thermal spray film is likely to be peeled off at the time of cooling after completion of thermal spraying, so it is necessary to match the thermal expansion coefficients of the thermal spray film and the substrate as much as possible.

It should be noted that, as the composition of the heating element of the present invention becomes closer to the substrate, the component of the heat resistant ceramics increases,
If the components are tilted, the stress caused by the difference in the coefficient of thermal expansion between the substrate and the sprayed film can be reduced, and a combination of a heating element and a substrate can be obtained that serves as an electric heater that generates more stable heat over time.

[0012]

The present invention will be described in detail with reference to the following examples.
What is taken up here is representative of the present invention and is not limited thereto. For example, the thermal spraying method may be low pressure plasma spraying, explosive spraying, flame spraying, or the like.

[0013]

Example 1 A thermal spraying powder composed of heat-resistant ceramics and a nickel chromium alloy and having the components shown in Table 1 was prepared.

[0014]

[Table 1]

This powder was added to a crystallized glass substrate 1 (100
mm × 25 mm × 3 mm), as shown by the hatched portion in FIG. 1, plasma coating was performed in the atmosphere to form the coating 2. During plasma spraying, residual heat of the substrate was applied at 500 ° C. Table 2 shows the peeled state and thickness of this coating, and the measurement results of the electrical resistance.
The unit of numerical values in FIG. 1 is mm.

[0016]

[Table 2]

An exothermic test was conducted by passing an electric current through the test pieces that did not peel off. The current was set to 60w according to each resistance value.

Table 2 shows the results of the peeled state and the temperature reached by the coating film after the current-carrying test. As shown in the results in Table 2, by using a mixture of nickel-chromium alloy and heat-resistant ceramics, particularly a mixture containing 60-90% by volume of heat-resistant ceramics, a film can be formed on the surface of crystallized glass, and As shown in Table 3, the coating was able to generate heat by energization.

[0019]

[Table 3]

[0020]

Example 2 A thermal spraying powder having the components shown in Table 4 consisting of heat resistant ceramics and a nickel chromium alloy was prepared.

[0021]

[Table 4]

This powder was applied to a crystallized glass substrate (100 mm
(× 25 mm × 3 mm) was plasma sprayed in the atmosphere in the same manner as in Example 1. Preheat the substrate to 500 ° C during plasma spraying
I went in. Table 5 shows the peeled state and thickness of this coating, and the measurement results of the electrical resistance.

A heat generation test was conducted by passing an electric current through these test pieces. The current was set to 60w according to each resistance value. Table 3 also shows the results of the peeled state and the temperature reached by the coating film after the current-carrying test. As shown in the results of Table 5, by spraying the mixture of the nickel-chromium alloy and the heat-resistant ceramics while changing the mixing ratio, it was possible to form the coating film on the surface of the crystallized glass. As shown in Table 3, the coating film was able to generate heat by energization, and the coating film was much less likely to be broken due to temperature change due to breaking of energization.

[0024]

[Table 4]

[0025]

[Table 5]

[0026]

Example 3 A thermal spraying powder having the components shown in Table 6 made of heat resistant ceramics and iron-chromium-aluminum alloy was prepared.

[0027]

[Table 6]

This powder was applied to a cordierite substrate (100
(mm × 25 mm × 3 mm) was plasma sprayed in the atmosphere in the same manner as in Example 1 to form a coating. During plasma spraying, the substrate was preheated at 500 ° C. Table 7 shows the peeled state and thickness of this coating, and the measurement results of the electrical resistance.

[0029]

[Table 7]

An exothermic test was conducted by passing an electric current through the test pieces that did not peel off. The current was set to 30w according to each resistance value. Table 8 shows the results of the peeled state and the temperature reached by the coating film after the current application test. As can be seen from the results in Table 7, a coating can be formed on the surface of cordierite by using a mixture containing an iron-chromium-aluminum alloy and a heat-resistant ceramics, especially a mixture containing 30 to 75% of that, and the coating is formed in Table 8. It was possible to generate heat by energizing as shown in FIG.

[0031]

[Table 8]

[0032]

As described above, the heating element according to claims 1 and 2 has good thermal efficiency because it does not have a coating layer that covers the heating element, and the heating element according to claim 3 using this substrate is a substrate. Since the difference in the coefficient of thermal expansion between the heating element and the heating element is not large, stable heat generation is achieved without disconnection or peeling from the substrate, oxidation resistance is improved, and the life is greatly extended compared to conventional ones.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

[Explanation of symbols]

 1. Substrate 2. Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Yoshida 2- 1-47 Shiobara, Minami-ku, Fukuoka City Kyushu Electric Power Co., Inc. Electric Power Co., Ltd.

Claims (6)

[Claims] 1. A heating element comprising a composite of heat resistant ceramics and a metal or alloy for electric heating. 2. The heating element according to claim 1, which contains 60 to 90% by volume of heat resistant ceramics. 3. A heating element made of a composite of a heat-resistant ceramic and a metal or alloy for electric heating is formed in a film shape on the surface of a heat-resistant ceramic substrate, and electrodes are arranged at the end of the heating element. Characteristic electric heater. 4. A heat-generating ceramic film is formed on the surface of a heat-resistant ceramic substrate by spraying a mixed powder of the heat-resistant ceramic powder and a powder of a metal or alloy for electric heating, and then the heat-generating ceramic is formed on the end of the heat-generating body. A method for manufacturing an electric heater, characterized in that electrodes are provided. 5. When a heat-generating ceramics powder and a powder mixture of an electric heating metal or an alloy powder are sprayed to form a heating element in the form of a film on the surface of the heat-resistant ceramics substrate,
The method for manufacturing an electric heater according to claim 4, wherein the heat-resistant ceramic substrate is heated to 300 ° C. or higher and 800 ° C. or lower. 6. A mixed powder comprising the heat-resistant ceramic powder and the metal or alloy powder for electric heating is repeatedly sprayed by changing the mixing ratio of the heat-resistant ceramic powder and the metal or alloy powder for electric heating every spraying. 5. The method for manufacturing an electric heater according to claim 4, wherein the heating element is such that the mixing ratio of the metal or alloy for electric heating increases stepwise as it goes away from the substrate.