JPS6019117B2 - heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for holding a heating element in which an electrical resistor is formed into a coil shape and an electrically insulating layer is formed on the surface thereof.

Generally, nickel-chromium heating elements and iron-chromium-aluminum heating elements are used as heating elements. Among these, iron-chromium-aluminum systems are common as heating elements that require high-temperature characteristics. Conventionally, coil-shaped heating elements have generally been used in which the relationship between the line width d and the coil pitch p is p>phantom, as shown in FIG.

If p<phantom, the heating element may come into local contact and cause a discharge phenomenon, which may lead to melting and disconnection. In addition, even if there is no contact, the proximity of the part will cause a local temperature rise in that part, causing the structure of the heating element to become coarser,
Alternatively, oxidation progresses rapidly, resulting in the wire diameter becoming thinner and causing wire breakage. Because of these problems, it has become impossible to reduce the pitch noise of the heating element to a level close to 0, and there have been various difficulties in obtaining a high-temperature heating element. As conventional example 2, a heating element having a configuration as shown in FIG. 2 has also been proposed.

In this invention, a metal rod or metal tube 2 is coated with a heat-resistant material 1 having good electrical insulation on the surface, a resistance heating element 3 is wound around the surface of the metal rod or metal tube, and the metal-like or metal tube is coated with a heat-resistant material 1 having good electrical insulation properties. The structure is such that the entire surface of the electrical resistor 3 is coated with electrically insulating ceramic 4, but since this type of heating element integrates a metal tube, electrically insulating layer, electrical resistor, and electrically insulating ceramic, Due to the large difference in thermal expansion coefficients between electrical resistors and metal pipes and electrical insulators, cracks occur in the electrical insulators due to thermal cycles, and as the process progresses further, the electrical insulators peel off, the electrical insulation is destroyed, and the coil A short circuit occurs between metals and coils, leading to disconnection.

It has the disadvantage of being particularly susceptible to thermal cycles at high temperatures (100 and above 0). In addition, tight winding is not possible due to the electrical insulation properties of the metal tube. In Conventional Example 3, various proposals have been made regarding methods of forming an electric resistor into a coil shape and providing an electric insulating layer on the surface. In order to eliminate the drawbacks of Conventional Examples 1 and 2, the present inventors previously investigated a heating element in which an electric resistor is wound into a coil and coated with a metal oxide, and the coil pitch is 2. We confirmed that it can be used even under similar conditions. That is, as shown in FIG. 3, by providing an electrically insulating layer 4 of metal oxide on the surface of the electrical resistor 1, short circuits between the coils can be prevented even if the electrical resistor 1 is tightly wound. This succeeded in reducing the oxidation of

Another method for providing an electrical insulating layer on the surface of an electrical resistor is to immerse a Fe-Cr-A type electrical resistor in a molten alkali bath and coat the surface of the electrical resistor with mainly iron hydroxide. This method involves forming a film and then heating it in a strongly oxidizing atmosphere to change the film mainly composed of iron hydroxide to a film mainly composed of aluminum oxide.

Although the electrical insulation layer obtained by this method is too thin to provide sufficient insulation between the coils, there is no problem in practical use. Furthermore, a well-known method is to heat an electrical resistor to a high temperature in an oxidizing atmosphere to selectively oxidize aluminum on the surface to form an insulating film mainly composed of aluminum oxide. However, this type of heating element has a problem in how it is held.

In other words, since the coils are in close contact with each other, when the heating element is energized as shown in FIG. 4, it bends excessively due to its own weight and does not return to its original state. In particular, when the temperature rises, this tendency is further exacerbated, and the material no longer functions as a heat generating element. In order to solve the above-mentioned problems, the present invention conducted various studies on the method of holding the heating element, and solved this problem by inserting a rod-shaped insulator into the central axis of the coil.

Next, specific features of the present invention will be described.

Iron-chrome-aluminum heating wire (JI
S. FCH-1) is used to form a tightly wound coil,
After cleaning the surface, the coils are stretched within the elastic limit, gaps are provided between each coil, and while the coils are being rotated, the surface is roughened by blasting at a pressure of 5k9/m using SICIOO. The blasting method is to rotate the blast nozzle in the direction perpendicular to the coil, 45 degrees to the left and right.
Blast while moving the blast nozzle parallel to the coil while facing each other in the direction o.

By blasting using the above method, both the inner and outer surfaces of the coil can be uniformly roughened. After the blasting was completed, zirconia powder stabilized with yttria was coated by plasma spraying.

Since the plasma spraying method was the same as blasting, a uniform spray coating layer was formed on both the inner and outer surfaces. The conditions for plasma spraying are Plasma Dyne's 80KW SG-
Uses 100 type, current: 900A, voltage: 41V
, argon was used as the arc gas, and helium was used as the auxiliary gas. After the plasma spraying is completed, the rotation of the coils is stopped and the state in which the coils are held with gaps between them is released, returning to the original state of tightly wound coils. The reason for this is that the coil must be kept within its elastic limit, and the characteristic of plasma spraying is that the powder with a high melting point is turned into a semi-molten state. This is because a covering layer can be formed. It was also confirmed that the adhesion strength of the sprayed coating layer could be further strengthened by cleaning the coil surface after blasting, but it is necessary to use it properly depending on the application.

As described above, an electric resistor was created by providing an insulating coating layer 4 on a heating wire 3 formed in a coil shape, and a rod-shaped insulator having an electric insulating layer 2 formed on the surface of a metal tube 1 at the central axis of the coil. A heating element as shown in FIG. 5 was obtained by inserting the heating element. As an example of the rod-shaped insulator, a shape as shown in FIG. 6 was studied.

Figure 6 is a cross-sectional view of the shape, a is cylindrical, b is tubular,
c is a cylinder with two holes, d is triangular, E is plate-shaped, and F is square.

Other polygonal shapes are also possible, and as a special shape, a shape like G can be sufficiently used. The material is a heat-resistant alloy, Fe-C, 1A type, Ni-Cr type, etc. have a long lifespan.
Good results were obtained in terms of mechanical strength at high temperatures, etc.

The electrically insulating coating layer was formed using Prusma lacquering, similar to the method used to coat electrical resistors, but sufficient electrical insulation was also obtained with electrically insulating paint and heat-resistant hollow.

When used at high temperatures of 1,000 pm or higher, the plasma sprayed coatings withstood well against thermal shock.

Heat-resistant paints can withstand use at temperatures below 1000°C. Heat-resistant hollow hollow is suitable for use below 600 qo. As mentioned above, the formation of the electrically insulating coating layer needs to be divided depending on the conditions of use. The thickness of the electrically insulating coating layer should be 5 or more. Electrical insulation can be maintained, but if the coating layer is too thick, cracks will easily occur in the coating layer due to thermal shock, so it is preferably between 5 and 500 strands. should be.

In addition to forming an electrically insulating layer on a heat-resistant alloy, we also investigated the use of ceramics as the rod-shaped insulator. Suitable materials include ceramics such as alumina, mullite, talc, spinel, zirconia, beryllia, and thoria.
Other metal oxide scales, glass materials, nitrides, oxides, silicides, etc., and refractory materials can also be used as long as they have electrical insulation, mechanical strength, and heat resistance. . Next, we will discuss the relationship between electrical resistors and rod-shaped insulators. The heat generating device of the present invention is constructed by removably inserting a rod-shaped insulator into the central axis of an electric resistance heating element in which a Z electric resistance element is formed into a coil shape and an electric insulation layer is formed between each coil so that each coil can be disassembled. We have repeatedly considered various aspects of the body.
FIG. 7 shows the results of an investigation into the temperature rise speed of an electric resistance heating element due to the formation of two rod-shaped insulators. In addition,
The electric resistance heating element uses a Fe-Cr-A heating wire with a wire diameter of ◇0.5 ribs and a coil depression of 5 willow.
The material was adjusted so that it was W, and an insulating coating layer was provided on the surface by plasma spraying. The rod-shaped insulator has an outer diameter of 4.
Willow was used, and a heat-resistant alloy with an electrically insulating layer provided on the surface was used. As is clear from FIG. 7, the temperature rise speed was faster than in Conventional Example 2 no matter which shape of the rod-shaped insulator was used.

Among them, the smaller the heat capacity of the rod-shaped insulator, the greater the effect. Next, we will discuss the results of examining the clearance between the electric resistance heating element and the rod-shaped insulator.

D of the coil of an electric resistance electric heating body, and external law D of a rod-shaped insulator
A thermal cycle test was conducted by variously changing the relationship between No. 2 and the wire diameter d of the coil.

Experiment 1 The electric resistance heating element has a wire diameter of 00.5 mm and an inner diameter of the coil of 4.
Using a Fe-Cr-A heating wire on the 5 side, 100V,
The power was adjusted to 300 W, and the outer diameter of the rod-shaped insulator was varied.

Experiment 2 Wire diameter of electrical resistance heating element? 0.5 ribs, coil inner fold 6.5
The heating wire is based on the Fe-Cr-A type of skin, and the electric capacity is 100.
The voltage was adjusted to 300 W, and the outer diameter of the rod-shaped insulator was varied.

From the above experimental results, D. When -D2 was replaced with a multiple of the coil flea d and the function with the thermal cycle was graphed, the results shown in FIG. 8 were obtained.

The thermal cycle conditions at this time were a voltage of 120V and a
The test was carried out in a laboratory by energizing for a few minutes and letting it cool for one minute, and the number of thermal cycles when each sample broke was measured.

As is clear from FIG. 8, it was found that when D.-D2 exceeds 3d, the life due to thermal cycling decreases rapidly.

This means that if the gap between the inner diameter of the electrical resistance heating element and the outer diameter of the rod-shaped insulator becomes more than three times the wire diameter, the mechanical deformation of the electrical resistance heating element due to thermal cycles will become too large. This is because the electrical insulating layer formed on the surface of the coil is destroyed, causing contact between the coils and hastening disconnection. As described above, in the present invention, it has been confirmed that a long-life heating element can be obtained by setting D, -D2<Red.

As mentioned in the section <Rod-shaped insulators>, methods for providing electrical insulation layers on electrical resistors and rod-shaped insulators include gas spray coating, plasma spray coating, heat-resistant coating, heat-resistant hollow, etc. In the embodiments of the invention, adhesion to the base material,
The plasma spray coating method was used to evaluate thermal shock properties and other factors.

The most significant feature of the coating layer is its porous layer.

In other words, the base material and the oxide layer are in close contact with each other, and the oxide layer is made porous in order to withstand high temperatures and severe thermal cycles, thereby buffering the extreme differences in coefficient of thermal expansion. It's there. Therefore, it exhibits its effectiveness as an electrical insulating layer without peeling during severe thermal cycle tests. Formation of an alloy layer as a base treatment for the oxide layer is also effective.

In other words, as mentioned above, when there is a problem in adhesion strength due to the extreme difference in thermal expansion coefficient between the base material and the oxide layer (this is determined by the operating temperature, usage conditions, etc.), the thermal expansion between the base material and This is a method of thermally spraying an alloy powder having relatively similar coefficients onto the base of an oxide layer, and then thermally spraying the oxide layer thereon.

In this way, the adhesion strength becomes stronger because the thermal expansion coefficients of the base material and the alloy layer for surface treatment are similar, and the adhesion strength between the metal layer and the oxide layer increases because the surface area of the metal layer is expanded. The thermal cycle strength increases.

However, as the surface area of the metal layer increases, the weight gain due to oxidation tends to increase slightly, so it is necessary to use them appropriately depending on the application. However, even in this case, the effects of the present invention will not be exhibited unless the metal outer layer is necessarily provided with an electrically insulating layer made of an oxide layer.

The powder used in this case is preferably the same powder as the base material, and alloys such as Fe-Cr-A, Ni-Cr, etc. can give good results.

It was also confirmed that the oxide layer having electrical insulation properties applied in this example is effective as an electrical insulation layer if it is a powder that is stable at high temperatures and used for thermal spraying.

Although there are some oxides that have conductivity at high temperatures, the conductivity of the metal heating element is small and negligible compared to the conductivity of metal heating elements, and the effect was actually achieved without any problems. The yttria-stabilized zirconia used in the examples is also an oxide that becomes conductive at high temperatures, but there were no problems. Applicable oxides include Aso203, Y203, Si02, F
e203, Ti02, Ca○, Na20, B203Li
20, Cr203, Z^] 2, N bee○, Be○, Nj○
, Tho2, Hf02La2Q, Ce02, etc., materials made of metal oxides or double oxides having a spinel structure, MgA204, CoA204, ZnA204
, MgCr204, etc., or a material containing some or more selected materials was good. As detailed above, the advantages of the heating element of the present invention can be summarized as follows: 1. The heat generation temperature can be increased with the same electric capacity.

2. It should be possible to improve defects such as wire breakage, withstand voltage defects, and insulation resistance defects.

3. Highly effective in suppressing high-temperature oxidation.

4 4-type, high capacity.

5. Coil diameter is not limited.

6. It has many features such as a longer lifespan, and can significantly improve the value of applied products by making them smaller.

[Brief explanation of drawings]

Figures 1 to 4 are sectional views of a heating element showing a conventional example, Figure 5 is a sectional view of a heating element showing an embodiment of the present invention, and Figure 6 is a sectional view of an embodiment of a rod-shaped insulator. , FIG. 7, and FIG. 8 are explanatory diagrams for explaining the effects of the heating element of the present invention. 1...Heat-resistant material, 2...Metal tube, 3...Resistance heating element, 4...Ceramic. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A rod-shaped insulator is removably inserted into the central axis of an electric resistance electric heating element in which an electric resistance body is formed into a coil shape, and an electric insulation layer is formed so that each coil can be separated from the other. Inner diameter D_1 and outer diameter D_2 of the rod-shaped insulator
and the wire diameter d of the coil is set to D_1-D_2<3d, and the rod-shaped insulator is made of a heat-resistant alloy with electrical insulation formed on the surface or ceramics.