JPH0129039B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the heat resistance and heating efficiency of an inductor of an induction heating device.

As is well known, the induction heating method generates alternating magnetic flux in an inductor using electric power supplied from a power supply.
This is a method in which the alternating magnetic flux generates eddy currents in metal within or near the inductor, and the metal is heated by resistance heat generated by the eddy currents.

Therefore, after the material to be heated is determined, an important point in the design is how to effectively penetrate the alternating magnetic flux into the material to be heated.

In general, the narrower the opposing gap between the inductor and the heated material, the less leakage of the alternating magnetic flux occurs, and the magnetic resistance due to the air layer also decreases, increasing the alternating magnetic flux penetrating the heated material and increasing the heating efficiency. The gap between the inductor and the heated material is kept as narrow as possible.

However, on the other hand, if this gap is narrowed,
The inductor receives radiant heat from the heated material and increases its temperature.
There is a problem in that the electrical insulation applied to the inductor's magnetic core, conductor, and induction coil deteriorates, causing an electrical short circuit to occur within a short period of time, which is likely to cause equipment failure.

Current heat resistance measures in electrical insulation technology, for example, even with the highest class H insulation, have a relatively low upper temperature limit of 180°C, so in order to protect the inductor, it is necessary to It is necessary to minimize the amount of heat.

For this reason, traditionally, the inductor is wrapped in heat insulating material or refractory material, or the surface of the inductor facing the heated material is fitted with heat insulating material or fire retardant material with low thermal conductivity. itself deteriorates due to radiant heat,
Also, as mentioned above, from the point of view of heating efficiency, the gap between the inductor and the heated material is originally narrow;
The heat insulating materials and refractory materials installed during this time were thin, and the heat shielding effect was not sufficient.

The present invention provides an inductor protection device that solves the problems in the conventional method, and its gist is that in a metal induction heating device, an inductor that is placed close to a material to be heated can be heated. On the surface facing the material,
An induction device characterized in that a metal surface with a high radiation reflection characteristic is provided through a heat-resistant insulating material, and the metal surface is constructed by arranging a plurality of thin plates or thin films electrically insulated from each other. Located in the inductor protection device of the heating device.

The present invention will be explained in detail below based on the illustrated embodiments.

Figure 1 is a front view (partial sectional view) showing an example of heating a plate-shaped material to be heated with a transverse flux type inductor, and Figure 2 is a tubular (or rod-shaped)
FIG. 2 is a partial front view (partially sectional view) showing an embodiment in which a material to be heated is heated by a longitudinal flux type inductor.

The materials to be heated 1a and 1b are heated by the alternating magnetic flux generated by the coils 2a and 2b. The magnetic core 6a is for concentrating magnetic flux on a predetermined portion of the heated material 1a. Coils 2a, 2b and magnetic core 6a
In order to prevent electrical insulation breakdown due to heat from the heated material, it is thermally protected by heat insulating materials 3a and 3b, fireproof material 7a, fireproof mold 5a, and protective outer cylinder 5b, and a group of metal flakes with high radiation reflection properties. 4a and 4b reflect radiant heat from the heated material.

Aluminum, gold, copper, silver, etc. can be used as metals that reflect radiation well. Depending on the direction of the magnetic field, the metal flakes can be arranged in parallel with long strips with gaps between them (the direction of the magnetic field is perpendicular to the plane of the paper), as shown in the bottom view of Figure 3a, 3
As shown in FIG. b, short strip-shaped flakes can be aligned with gaps in the vertical and horizontal directions (the direction of the magnetic field is in the horizontal direction of the paper).

The reason for arranging the individual thin pieces with gaps is that metals with high radiant heat reflectivity are generally good conductors of electricity, so under the strong alternating magnetic field used for induction heating, the metal is heated just like the material to be heated. The purpose is to cut the metal into small pieces, electrically insulate them from each other, and reduce the induced current.

The width of each thin piece 11a, 11b is preferably about 10 to 20 mm. Also, the width of the gaps 12a and 12b for electrically insulating the individual thin pieces from each other is 0.5 to 1
Approximately mm is desirable. The thickness of the thin pieces 11a and 11b is desirably thinner, and is suitably about 1 to 20 microns.

According to the experimental results, small pieces of aluminum foil 17 μ thick x 9 mm wide x 70 mm long were arranged as shown in Figure 3b with a gap of 1 mm wide, and each piece of aluminum foil was glued to the insulation material. Then, a transverse flux type inductor as shown in Fig. 1 was constructed, two of these inductors were placed facing each other, and the coil power was 50KW and the magnetic flux density in the air gap was 2.3KG. 180
The amount of temperature rise in the group of aluminum foil pieces due to the magnetic field after seconds had elapsed was approximately 30°C at most.

As shown in Figure 3a and b, the effective reflectance of radiant heat when a strip-shaped thin metal piece is used as a reflector r _e
is r _e = r _p (1-a/ _le ) (1-b/l _s ) where, r _p ; reflectance of the metal flake l _e ; length of the long side of the metal flake l _s ; short length of the metal flake Side length a; Width in the long side direction of the gap b; Can be determined as the width in the short side direction of the gap.

For example, when the aforementioned aluminum foil with a width of about 10 to 20 mm is arranged as shown in Figure 3b, the effective reflectance is:
It is approximately 75-85%. In addition, the effective reflectance in the case of gold plating is approximately 85 to 90%.

In addition, in the above-mentioned example, aluminum foil was used as the radiant heat reflecting material, but gold, gold,
Thin plates of copper, silver, etc. can also be used, and instead of gluing thin plates of these metals, these metals can be plated (for example, by vapor deposition plating) on a heat-resistant insulating substrate.
You may also use the In addition, the means for creating gaps for electrically insulating each small piece from each other may be provided by machining the gaps (grooves) after bonding the thin metal plate to a heat insulating material or after plating, or by creating gaps (grooves) before plating. Appropriate means such as applying plating non-adherence treatment to the surface may be adopted.

As described above, according to the present invention, the heat load on the inductor from the heated material can be drastically reduced, the inductor can be completely protected, and the thickness of the heat insulating material can be reduced. This has the excellent effect of narrowing the gap between the inductor and the heated material and greatly improving heating efficiency.

Note that even if the radiant heat reflecting material used in the apparatus of the present invention described above is installed in the middle of the gap between the inductor and the heated material to block the radiant heat from the heated material, the induction Of course, it has a heat-insulating effect on children.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional front view of an example of the inductor protection structure of the present invention applied to a plate-shaped heated material, and FIG. 2 is a cross-sectional front view of an example of the inductor protection structure of the present invention applied to a tubular heated material. The applied partial cross-sectional front view, Figures 3a and b are the first
FIG. 3 is a bottom view showing an example of a method for arranging thin metal pieces that are radiant heat reflecting materials shown in FIGS. 1a, 1b; material to be heated; 2a, 2b; coil;
3a, 3b; heat insulating material, 4a, 4b; metal flake group,
5a; fireproof mold, 5b; protective outer cylinder, 6a; magnetic core, 7a; fireproof material, 11a, 11b; metal flake,
12a, 12b; electrical insulation grooves.

Claims (1)

[Claims] 1. In a metal induction heating device, a metal surface with high radiation reflection characteristics is provided via a heat-resistant insulating material on the surface of an inductor placed close to the material to be heated that faces the material to be heated, and the metal surface 1. An inductor protection device for an induction heating device, comprising a plurality of thin plates or thin films arranged in an electrically insulated manner from each other.