JPH0262037B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) This invention is an ink-melt type microwave in which a material to be processed is supplied to a metal crucible and irradiated with microwaves to melt and solidify the material in the crucible. It relates to melting furnaces.

(Prior art) In an ink-melt type melting furnace, the material to be processed is melted and solidified in a metal crucible, so when the crucible is stored in a storage room, the cross-sectional shape of the metal crucible greatly affects the storage efficiency during storage. . In other words, in order to increase the storage efficiency in the storage, it is necessary to create a shape that minimizes the space between the crucibles. As for the cross-sectional shape of the crucible that meets this purpose, it is preferable to use a rectangular crucible, that is, a square or hexagonal crucible, rather than a round shape.

Microwave is an electromagnetic wave with a frequency of 100KHz or higher, and the frequency generally used in the heating field is
They are 2450MHz and 915MHz. A magnetron tube is mainly used as a microwave oscillator for these microwaves, and from the viewpoint of transmission efficiency, the oscillated microwaves are usually transmitted to a target location using a rectangular waveguide. As a result, as a melting furnace using a rectangular crucible, a rectangular crucible with the same cross-sectional shape as the waveguide or a rectangular waveguide expanded into a rectangular shape at the tip of the rectangular waveguide were used. A melting furnace equipped with a rectangular crucible is also used. In such a melting furnace approximately 1000
Although it is possible to melt materials with a melting point below 1000°C, it is possible to melt materials with a melting point of 1000°C or higher, such as incineration ash of paper, cloth, etc. (melting point is approximately 1250°C or higher)
There is a problem with melting at temperatures of 1,300°C (1,300°C) that some of the incinerated ash remains unmelted in the crucible.
This was a major drawback when using a rectangular crucible.

The reason why the above-mentioned unfused portion occurs can be clarified by the transmission characteristics of microwaves in the waveguide, as explained below. That is, the sixth
The figure shows an example of a melting furnace in which a crucible is attached to the tip of a waveguide. If the short side of the rectangle has a length a, the long side has a length of 2a, which is certified by the standard for waveguides. Reference numeral B designates a melting furnace in which the tips of the rectangular waveguides 1 are expanded to long surfaces 2a and a square crucible 22 is attached. The objects to be processed are placed in a hopper 4, fed into a crucible through a feeder 5, and irradiated with microwaves transmitted through a waveguide to heat and melt the objects to generate a melt 6. ing. Off-gas generated by heating is discharged out of the furnace through an exhaust pipe 7.

Figure 7A shows the electromagnetic field distribution of microwaves in the cross section of a rectangular waveguide. In the cross section of the waveguide, current flows in the directions shown by the lines of magnetic force shown by the broken line and the solid line, and the electric field distribution that affects heating. is strong at the part where the magnetic field lines and the current flow closely intersect, that is, at the center of the rectangular cross section, becomes weaker as it spreads left and right, and becomes zero at the tube wall surfaces at both ends. In addition, in a rectangular waveguide, the tube surface facing parallel to the current line is E.
The plane parallel to the lines of magnetic force is called the H-plane to indicate the position, and the manner in which electromagnetic waves propagate is called the mode. The propagation mode having the above electromagnetic field distribution is called TE ₁₀ mode. In all of the melting furnaces shown in Figure 6, a crucible of the same square shape as the waveguide is attached to the tip of the waveguide, and in such a melting furnace, it can be understood from the electric field distribution shown in Figure 7A As the electric field distribution near the E plane is zero, there is no microwave necessary for heating, so the object to be processed near the E plane is not heated sufficiently, and in the case of crucible 21, the 7th As shown in Figure B, and in the case of the crucible 22 as shown in Figure C, an unmelted portion is generated near the E plane. In the case of a workpiece with a relatively low melting point, the workpiece near the E-plane melts due to heat conduction from the high-temperature part at the center of the crucible, and the influence of this E-plane can be reduced. In the case of a processed material having a high melting point, an unmelted portion will be generated near the E-plane.

In this way, when a rectangular waveguide is used for melting in a rectangular crucible, the TE ₁₀ mode, which is the transmission mode unique to the rectangular waveguide described above, will be affected, resulting in the problems described above. . As a countermeasure to this, TM ₀₁ as another transmission mode of rectangular waveguide
It is possible to use the TM ₀₁
This mode cannot be used because stable transmission is difficult with current technology.

Various transmission modes necessary for heating can be easily created by combining rectangular waveguides and circular waveguides. This includes
TE ₁₁ mode, TM ₀₁ mode, TE ₂₁ mode, TE ₀₁
mode, TM ₁₁ mode, etc. The transmission mode in this case is determined by the pipe diameter of the circular waveguide, and TE ₁₁
The mode is formed from the smallest pipe diameter, and as the pipe diameter becomes larger, the TM ₀₁ mode and the TE ₂₁ mode are formed sequentially. The most commonly used circular transmission modes are TE ₁₁ mode and TM ₀₁ mode.
In the TE ₁₁ mode, as shown in FIG. 8A, there is a dense area in the center where magnetic lines of force and current flow, and as a result, the heating section has a band-like heating shape as shown in B. this
The TE ₁₁ mode is a circular projection of the basic shape of the circular transmission format, that is, the rectangular transmission format TE ₁₀ mode, and as the pipe diameter increases, the shape of the TE ₁₁ mode becomes weaker, and as shown in D, the shape of the TE 11 mode becomes The mode changes to TM ₀₁ mode C in which the heating section has a shape that expands. Since a variety of circular transmission modes can be produced, melting furnaces using circular crucibles have already been developed.

(Objective of the Invention) This invention was made against the above technical background, and aims to enable complete melting using a rectangular crucible, thereby making it possible to store the crucible efficiently. This is what I did.

(Structure of the Invention) The present invention provides an incan melt type heating melting furnace that supplies a workpiece into a crucible having a rectangular shape with even numbered corners and melts and solidifies the workpiece by irradiating it with microwaves. A rectangular waveguide, a circular waveguide, and a square crucible are sequentially connected to a microwave oscillator, and at the connection part between the circular waveguide and the square crucible, the square crucible is circumscribed by the circular waveguide in a plane projection shape. The rectangular crucible is arranged in a circular shape so that the direction connecting the pair of opposing corners is perpendicular to the E plane of the rectangular waveguide, and the supply port of the processed material is arranged parallel to the E plane. It is formed in a waveguide.

(Example) In FIG. 1, a rectangular waveguide 1 connected to a microwave oscillator (not shown) has a circular waveguide 8 connected to its tip, and a rectangular crucible at the lower end of the circular waveguide 8. 2 are connected. In the drawing, the planar shape of the rectangular crucible is square, but it may be rectangular. A cylindrical head tuner 10 for matching microwaves in the furnace is disposed at the upper end of the circular waveguide 8 so as to be movable up and down. Further, a chute 5 connected to the hopper 4 is coupled to the circular waveguide 8, and an exhaust pipe 7 for discharging off-gas is attached. The circular waveguide 8 and the rectangular crucible 2 are connected to each other by a flange 9, and the connection portion thereof is configured in a planar projection shape such that the rectangular crucible 2 circumscribes the circular waveguide 8, as shown in FIG. has been done. The direction connecting the corners a and c of the rectangular crucible 2 is arranged perpendicular to the E plane of the rectangular waveguide 1, and the feeder 5 for supplying the processed material is parallel to the E plane (corner parts b-d direction).

In the above structure, when microwaves are irradiated in the TM ₀₁ mode, which allows heating of the entire surface, the entire surface is melted without any unmelted portions, as shown in FIG. 2B.

As shown in FIG. 5A, the sides a-d and b-c of the rectangular crucible 2 are arranged parallel to the E plane of the rectangular waveguide 1, and the microwave is applied in the TM ₀₁ mode in the same manner as above. When irradiated with , the side a as shown in B
-d and b-c, or as shown in C, unmelted parts e are formed at corners a, b, c, and d, respectively. On the other hand, if a circular crucible is attached instead of the rectangular crucible 2 and heating is performed in the same manner, no unmelted portion will be generated. The reason for this is thought to be as follows. In other words, the basic transmission mode in a rectangular waveguide is TE ₁₀ mode, which is changed to TM ₀₁ mode in a circular waveguide, but this change involves the process of TE ₁₀ mode → TE ₁₁ mode → TM ₀₁ mode. In the case of a circular crucible, (1) one side is not straight, so the E of the rectangular waveguide is
(2) Because the part corresponding to the E plane is a circular arc, it is easily affected by the heat of the high-temperature heating area near the center, so it is melted by heat conduction. It is thought that the entire surface was melted due to the following.

On the other hand, for a square crucible, (1) change the transmission mode from TE ₁₀ mode → TE ₁₁ mode →
Even when changing to TM ₀₁ mode, since the square crucible is connected to the circular waveguide again, the TM ₀₁ mode easily returns to the basic transmission mode of TE ₁₀ mode. (3) The corner is located at the farthest distance from the center of the crucible, and is therefore less susceptible to the effects of the high temperature area in the center. (3) The corner is composed of two surfaces and has a large amount of heat dissipated to the outside. It is thought that unmelted parts occur due to , etc.

For these reasons, as shown in FIG. 2, the corner portions a and c were arranged in the direction of the E plane, and the feeder 5 for supplying the processed material was arranged parallel to the E plane.

In addition, when the feeder 5 is installed in the direction perpendicular to the E plane as shown in FIG.
occurs. The reason for this is thought to be as follows, but there is no such effect in the case of FIG.

(1) In the case of Fig. 2, the material to be processed is supplied to the center of the rectangular waveguide 1, which is the high-temperature heating section, where it is melted and flows to corners a and c in the crucible. Therefore, no unmelted portions are formed at the corner portions a and c.

(2) Corner parts b and d are the center of the rectangular waveguide 1,
Therefore, since it becomes a high-temperature heating part, it is melted well in either case.

FIG. 3 shows another embodiment of the present invention, in which a rectangular crucible 25 has a hexagonal planar shape, and its corners a and c are arranged in a direction perpendicular to the E plane. The rest of the configuration is the same as that in FIG. 1. Even with such a hexagonal crucible, complete melting can be achieved in the same manner as described above.

FIG. 4 shows yet another embodiment, in which the tip of the rectangular waveguide 1 is widened in a tapered shape and connected to a circular waveguide 8 in the axial direction. Even with such a configuration, the effects are the same as those described below.

(Effects of the Invention) As explained above, the present invention sequentially connects a rectangular waveguide, a circular waveguide, and a rectangular or hexagonal crucible to a microwave oscillator, and emits microwaves in a mode that can melt the entire surface. The crucibles are irradiated and melted, and since the crucibles are rectangular and can be stored without gaps between each other, storage efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is an overall perspective view showing an embodiment of the invention;
2A and 2B are plan view and explanatory diagram of the melted state, FIG. 3 is a plan view showing another embodiment, FIG. 4 is a perspective view showing still another embodiment, and FIG. 5A, B and C are explanatory diagrams showing the relationship between the arrangement of the waveguide and crucible and the molten state, Figures 6A and B are perspective views of conventional structures, respectively, and Figure 7A, B, and C are microwave modes. Fig. 8A, B, C, and D are explanatory diagrams of the relationship between other modes and the molten state, and Fig. 9 is an explanatory diagram of the relationship between the chute mounting position and the molten state. A is a plan view and B is an explanatory view of the melted state. 1... Rectangular waveguide, 2, 25... Square crucible, 5... Feeder, 8... Circular waveguide, a,
b, c, d... corner.

Claims (1)

[Claims] 1. In an ink-melt type heating melting furnace that supplies a workpiece into a crucible with an even-numbered rectangular shape and melts and solidifies it by irradiating it with microwaves, a rectangular waveguide is connected to a microwave oscillator. A pipe, a circular waveguide, and a square crucible are connected in sequence, and at the connection part between the circular waveguide and the square crucible, a pair of square crucibles is connected so that the square crucible circumscribes the circular waveguide in a plane projection shape, and The waveguide is formed into a circular waveguide so that the direction connecting the opposing corners is perpendicular to the E-plane of the rectangular waveguide, and the supply port of the processed material is arranged parallel to the E-plane. A microwave melting furnace characterized by: