JPH02265149A - Microwave induction heating apparatus - Google Patents

Abstract

PURPOSE:To improve heating efficiency and make heat treatment of an object to be treated uniform by composing a short circuiting device which closes one end of a wave guide tube with a conductor and shaping the short circuit plane to be caved plane symmetric in both sides of a center project. CONSTITUTION:The opposite side 11b to a microwave oscillator side 11a of a wave guide tube 11 is electrically closed by a short circuiting device 14. The short circuiting device 14 is prepared from a conductor and its short circuiting plane is so shaped as to be a caved plane 16b symmetric in both sides of a center projected part 16a. Microwave transmitted in the rectangular wave guide tube 11 can be decomposed into a pair of plane waves proceeding while being reflected by the inner walls of the wave guide tube. By using the short circuiting plane 15 forming two parabolic planes, most of microwave can be concentrated on an object to be treated in the center. By this method, an electric field in the location of the object to be treated can be strengthend further and heating efficiency is improved.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention is a waveguide-type microprocessor for heat-treating a workpiece whose size is sufficiently smaller than the long side of a rectangular waveguide cross section. The present invention relates to wave heating devices, and particularly to improvements in short circuits thereof.

(Prior art) Waveguide type microwave heating devices that have been used in the past generate a standing wave in a waveguide, place the object to be processed in the area of maximum electric field strength, and efficiently heat the microwave. Heat treatment is performed by irradiating the workpiece with wave power.

(Problem to be Solved by the Invention) However, in the conventional microwave heating device, since the shorting surface of the short circuit is a flat surface, the electric field strength of the standing wave in the rectangular waveguide is The distribution is such that the electric field intensity is 0 on both side walls of the waveguide, that is, on the wall surface of the electric interface wall 13 parallel to the electric field E, in a direction parallel to the long side wall of the cross section of the waveguide 11, that is, the magnetic interface wall 12, which is perpendicular to the electric field E. , waveguide center C
The distribution changes sinusoidally, with the maximum electric field strength at .

Therefore, if the object to be processed is smaller than the width of the magnetic interface wall 12 of the waveguide 11, only a portion of the microwave power transmitted through the waveguide is used for processing, resulting in low efficiency. In particular, when the object to be treated is very small or very thin, heat treatment is difficult and very inefficient.

Furthermore, when heat-treating a workpiece with a large dielectric loss coefficient, conventional short circuits do not form sufficient standing waves, and the microwave oscillator side tends to be heated, which hinders uniform heat treatment. It becomes.

This invention was made in view of the above circumstances, and an object of the present invention is to provide a microwave heating device that can improve heating efficiency and uniformize the heat treatment of objects that cannot be heated. do.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, the short circuit for closing one end of the waveguide is made of a conductor, and the short circuit surface thereof has a concave curved surface symmetrically on both sides of the central protrusion. This is a microwave heating device.

(Function) According to the present invention, the reflected waves from the short circuit can be concentrated at the position of the object to be processed, and as a result, the electric field strength at the position of the object to be processed can be further increased. Therefore, heating efficiency is improved.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The microwave heating device according to the present invention is shown in FIGS. 1 and 2.
It is configured as shown in the figure, and one end of the waveguide 11 on the opposite side 11b from the unillustrated microwave oscillator side 11a is electrically closed by a short circuit 14. This short circuit 14 is made of a conductor, and as is clear from the figure, its short circuit surface 15 is formed with a concave curved surface 16b symmetrically extending from the central protrusion 16a toward the electric surface walls 13 on both sides. This concave curved surface 16b is preferably a paraboloid, and is perpendicular to the magnetic interface wall 12.

Further, a support rod 17 is attached to the short circuit 14, and the support rod 17 is driven to move the short circuit 14 within the waveguide 11 in the direction of arrow F. That is, the short circuit 14 is movable in the longitudinal direction of the waveguide 11.

Incidentally, the first object 18 is the object to be treated, and is placed at the center where the electric field intensity of the standing wave generated in the waveguide 11 is maximum, and is heated. Therefore, a through hole 19 is provided in each of the opposing wide surfaces of the waveguide 11, that is, in the center of the electric interface wall 13, so that an elongated object 18 to be processed can be inserted or transported into the center of the wide surface. .

Next, we will discuss heat treatment, and as an extreme example where the effect of heat treatment is difficult to increase or where treatment is impossible, we will discuss heat treatment of filamentous objects.

Note that when microwave heating or plasma generation is performed using microwaves, the T E mode is usually used, so the explanation here will also be based on the T E1o mode.

The microwave propagating in the rectangular waveguide 11 can be decomposed into a set of plane waves that propagate while reflecting off the inner wall of the waveguide, as shown by the dashed-dotted line arrows in FIG.

The angle θ between the plane wave traveling direction and the inner wall of the waveguide at this time can be easily calculated. In other words, the inner diameter of the waveguide or the long side (magnetic interface wall)
: 96 mm, short side (electrode surface wall): 27 mm, the angle θ is approximately 39.6°.

Therefore, by using the two plane waves and the short-circuiting surface 3 formed with two paraboloids as in the present invention, most of the waves can be concentrated at the position of the object to be processed at the center. Therefore, although there is a slight loss, the efficiency is much higher than that of the conventional example. Since the object to be processed is placed in this area, almost all of the microwaves will be incident on the object to be processed at least once, and an improvement in efficiency can be expected.

Note that the direction of the high-frequency electric field is perpendicular to the wide surface of the waveguide, and therefore parallel to the object to be processed, and has a uniform heating effect.

Also, using the same concept as in the above embodiment, it is possible to concentrate the electric field in other modes and specific locations, or to create a desired electric field distribution (for example, using the TE2o mode, making the curved surface a spherical surface, etc.) ).

Furthermore, when a workpiece having a large dielectric loss coefficient is heat-treated, the side closer to the microwave oscillator tends to be more easily heat-treated, but this can also be avoided.

The present invention is also suitable as an excitation device for activating gas into plasma, and is used by attaching a gas pipe to the position of the object to be treated.

[Effects of the Invention] According to the present invention, since the short circuit is made of a conductor that forms a symmetrical concave curved surface on both sides from the short circuit surface or the central protrusion, the wave reflected by the short circuit is not transmitted to the position of the object to be processed. I can concentrate,
The electric field strength can be further increased. Therefore, it is possible to improve heating efficiency.

[Brief explanation of drawings]

FIG. 1 is an axial sectional view showing a microwave heating device according to an embodiment of the present invention, FIG. 2 is a partially cutaway perspective view, and FIG. 3 is a standing wave in a waveguide. FIG. 2 is a perspective view showing the electric field strength distribution of FIG. 1... Waveguide, 2... Short circuit, 3... Short circuit surface, 5
...Object to be processed. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Scope of Claims] A microprocessor in which one end of a rectangular waveguide is closed with a short circuit, and the object to be processed is placed in the central part of the maximum electric field strength of the standing wave generated in the waveguide, and the object is heated. In the microwave heating device, the short circuit is comprised of a conductor whose short circuit surface forms a concave curved surface symmetrically on both sides from the central protrusion.