JPS6361760B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Object of the invention [Technical field of the invention] The present invention relates to a rod-shaped or wire-shaped plastic;
This invention relates to a method for uniformly and continuously heating elongated dielectric materials such as glass and ceramics at high speed using microwaves. [Prior art and its problems] During the manufacturing process of resin products and various textile products, there is a process of heating various materials for heat treatment drying or chemical treatment. Conventionally, hot air heating devices that use heated air as a heat medium, salt bath heating devices that heat molten salts, and infrared heating devices that heat with hot wire have been used. In all of these methods, heat reaches the core by conduction from the surface of the material, so
The speed of the heat processing process cannot be faster than the rate of heat conduction of the material. Furthermore, it goes without saying that the surface of the material is at a higher temperature than the inside, and the surface of the material is exposed to high temperatures for a longer time than necessary. Compared to these methods, the microwave heating method heats the material itself uniformly from the surface to the inside because the material itself generates heat due to microwave irradiation. Also, since no time is required for heat transfer,
Another great feature is that the temperature can be raised rapidly. The amount of heat generated when a dielectric material such as plastic or ceramic absorbs microwave energy is determined by the following formula. P=0.556・εr・tanδ・f・E ² ×10 ^-12 [W/cm ³ ]
…(1) Here, P: Calorific value per unit volume [W/cm ³ sec] εr: Relative permittivity of dielectric tan δ: Power factor of dielectric f: Microwave frequency [Hz] E: Microwave Wave electric field strength [V/cm] εr and tanδ in equation (1) are the electrical properties of the material to be heated, and have different values depending on the material. The frequency of electromagnetic waves used for microwave heating in Japan is 2450MHz, so in the above formula, 2450×
Substituting 10 ⁶ , depending on the value of εr・tanδ,
Even if the value of the electric field strength E is small, a sufficient heating rate can be obtained. For example, in a microwave oven used at home, the electric field strength is less than 50 V/cm, but since most of the material being heated is water, it easily generates heat. εr≒ of water at 25℃
76, tanδ≒0.16, so if εr・tanδ is the dielectric loss, the dielectric loss of water at 25℃ is
It becomes 12.16. However, in common plastics such as nylon, the value of εr·tanδ is 0.025, which is about 1/450 smaller than that of water. Therefore, a microwave heating device that can be put to practical use must have a strong microwave field strength of about 500 V/cm to 1000 V/cm. This is extremely difficult, and by the way, WRJ-2 specified in JIS
This can be inferred from the fact that when 1 kW of microwave power is supplied into a waveguide, the electric field strength at the maximum electric field strength point is only 124 V/cm. Figure 1A shows a JIS WRJ-2 rectangular waveguide, and Figure 1B shows the electric field strength distribution within the waveguide. The cross-sectional dimensions of the rectangular waveguide shown in the figure are approximately 109 on the long side a.
mm, the short side b dimension is approximately 45 mm, but the long side a
If the dimensions of 2a are reduced, the wavelength within the tube becomes longer
If the size is less than λ, microwaves cannot be transmitted, so it cannot be made unnecessarily small. The dimension of the short side b can be made small since it does not affect the wavelength within the tube. Using this, short side b
When the diameter is 10 mm, the electric field strength when transmitting 1 kW is approximately
The electric field strength is 290V/cm, but the required electric field strength of 500V/cm or more cannot be obtained. For this reason, as shown in Figure 2 A, a common method is to place the heating material at the center of the TMO1 mode circular waveguide, where the density of electric lines of force is highest, and to heat it by moving the heating material in the tube axis direction. It is taken as a target.
However, in this TMO1 mode, the electric lines of force are radial as shown in the figure (b), so when heating a thick heating material, the center will inevitably become high in temperature and the surface will inevitably become low in temperature. Furthermore, it is essential to always maintain the heating material accurately at the central axis position of the waveguide. When continuously heating a plastic wire with a diameter of 2 mm or less, the plastic wire may vibrate and deviate from the maximum electric field strength position, causing uneven heating in the wire direction.
This drawback cannot be solved as long as modes are used. [Technical Problem of the Present Invention] The technical problem of the present invention is to eliminate the above-mentioned drawbacks and efficiently create a linear, elongated dielectric material with low microwave loss even in a rectangular waveguide suitable for uniform heating. The purpose is to enable heating and to enable online temperature management and temperature control. (b) Structure of the Invention [Technical Means of the Invention] The technical means of the present invention taken to solve this technical problem include a matching box, a rectangular microwave heating waveguide, a phase shifter, and a reflector. the microwave heating waveguide and the reflection-free terminator in this order, adjust the matching device and the reflector to bring the inside of the microwave heating waveguide into a microwave resonant state, and adjust the electric field position within the microwave heating waveguide. A method of adjustment using a phase shifter is adopted. [Operation of technical means] According to the technical means of the present invention, a matching box is connected to the radio wave inlet side of the microwave heating waveguide, and a reflector is connected to the radio wave outlet side via a phase shifter. has been done. The heating material is continuously heated by supplying microwaves from the microwave generator to the microwave heating waveguide while passing the heating material through the microwave heating waveguide. At this time, the reflector is adjusted to reflect the microwaves that have passed through without being absorbed by the heating material.
In addition, by adjusting the reflected radio wave so that it does not return to the micro-generator side using a matching device, the inside of the waveguide becomes in a resonant state, and a sufficient temperature can be obtained at the center of the waveguide. Therefore, even with a rectangular waveguide,
Even substances with poor microwave absorption can be heated sufficiently.
In the case of substances with high water content and good microwave absorption,
By adjusting the reflector or matching device to reduce the amount of reflection or making the reflector or matching device inoperable, you can easily obtain temperature conditions suitable for the heating material, making it possible to use various heating materials. Can be heated efficiently. Furthermore, by adjusting the phase shifter, the heating position can be set to the highest electric field strength, thereby obtaining optimal heating conditions. In particular, a temperature detector is installed near the location where the electric field strength is high, and the temperature of the heated material is instantly detected.
By feeding back to the microwave generator side, it is possible to immediately control the heating temperature of the heating material and to obtain a constant heating temperature at all times. [Embodiments of the Invention] Next, how the method for continuously heating a linear dielectric material according to the present invention is actually implemented will be explained using Examples. FIG. 3 is a perspective view showing an example of an apparatus for carrying out the method of continuously heating a linear dielectric according to the present invention. 1 is a microwave power generator. 2 is a microwave power meter that can simultaneously measure the incident power and reflected power within the waveguide. Reference numeral 3 denotes a matching device, which is used to reduce reflected power, and includes a 3-stub matching device, a slug matching device, an EH matching device, etc., but any device with low loss may be used. 4 is a waveguide for microwave heating, the details of which are shown in FIG. 5 is a phase shifter that can shift the phase by 1/4 to 1/2 of the tube wavelength. Reference numeral 6 denotes a reflector, which reflects a part of the incident power propagating from the microwave generator, and is preferably one that can be continuously varied from a non-reflecting state to a voltage standing wave ratio of 5 or more. 7 is a non-reflection terminator that absorbs excess microwaves. Reference numeral 8 denotes a long and thin linear microwave heating material, which is stretched and runs at a constant speed in the direction of the arrow within the microwave heating waveguide 4. In this way, the microwave power generator 1, the microwave power meter 2, the matching box 3, the microwave heating waveguide 4, the phase shifter 5, the reflector 6, and the non-reflection terminator 7 are connected in this order. Then, by passing the heating material 8 through the microwave heating waveguide 4 while supplying microwaves from the microwave power generator 1 into the microwave heating waveguide 4, the heating material 8
continuous heating is performed. FIG. 4 shows details of the microwave heating waveguide 4, with A being a plan view and B being a front view. This embodiment basically uses a rectangular waveguide, and as the incident wave progresses, the short side b
or make the fifth dimension smaller.
As shown in Figures A and B, the tube is made into a rigid tube with two opposing protrusions 9 in the center of the tube, and the space dimension C between the ribs 9 is gradually reduced. Then, the microwave heating waveguide 4 is formed to be narrowest at the center part 4c, and thereafter the b dimension or the C dimension between the ridges becomes wider again, and eventually becomes the basic dimension of a:b=2:1. . The microwave heating waveguide 4 is a radio wave introduction port 4.
a and the outlet 4b are bent at 90 degrees and connected to the matching device 3 and the phase shifter 5, respectively. As shown in FIG. 3, both ends of the microwave heating waveguide 4 are provided with holes 10 through which the heating material 8 passes, and if necessary, a trap is provided to prevent radio wave leakage. Now, when microwave power is transmitted from the microwave generator 1 of the device configured as described above, when the reflector 6 is in a non-reflecting state, the b dimension (or C dimension) of the microwave heating waveguide 4 will change. As explained earlier, the narrowest part 4c is 200 ~
It will be about 250V/cm. A portion of the advancing microwave power is absorbed by the heating material 8, while the rest is completely absorbed by the non-reflection terminator 7. In this state, as mentioned above, objects with large εr and tan δ can be heated sufficiently, but for objects with small εr and tan δ, the energy efficiency is poor and it is not practical. In such a case, if the reflector 6 reflects an appropriate amount of microwaves that pass through without being absorbed by the heating material 8, the conduction between the microwave generator 1 and the reflector 6 will be improved. Inside the wave tube, standing waves created by incident waves and reflected waves create a fixed wavy distribution of electric field. The position of the standing wave in the waveguide is determined by the phase shifter 5.
The phase shifter 5 can be changed arbitrarily by the waveguide for microwave heating, so if the phase shifter 5 is adjusted so that the deflection of the microwave detector 11 provided at the narrowest part 4c of the waveguide for microwave heating is maximized, the waveguide for microwave heating Narrowest part 4c of waveguide
The electric field strength can be made higher than that in the case of no reflection, and the electric field strength can be changed by varying the amount of reflection of the reflector 6. However, if this continues, the reflected microwave power will return to the microwave generator 1.
When the reflector 6 is set to total reflection, the electric field strength is only 1.4 times the electric field strength when there is no reflection, but if the matching box 3 is adjusted so that the reflected power of the microwave power meter 2 is minimized, the situation changes. It changes completely. That is, at this time, the matching device 3, microwave heating waveguide 4, phase shifter 5, and reflector 6 are in a resonant state. Q at this time can be varied depending on the amount of reflection from the reflector 6. The electric field strength of the narrowest part 4c of the waveguide for microwave heating during resonance can be more than four times the electric field strength when there is no reflection, so even materials with low microwave absorption can be sufficiently heated. . As a result of conducting a heating experiment using the apparatus constructed as shown in FIG. 3, the values shown in the table below were obtained. Note that the heating material is nylon.

[Table] The above values are within the practical range, as they reach the specified temperature with several times less power than a conventional rectangular TEO1 mode device that uses only a heating waveguide. I feel that I am still unsatisfied.
This is because the microwave losses of the phase shifter, matching device, and reflector are large, and as these devices become more sophisticated in the future, it is expected that the same performance can be obtained with less than half the microwave power mentioned above. thinking. (c) Effects of the invention The advantages of the continuous heating method for a linear dielectric according to the present invention explained above are summarized as follows: 1. Since the TE10 mode of the rectangular waveguide is used,
Heating can be more uniform than when using the circular waveguide TMO1 mode. 2 By changing the amount of reflection with a reflector and matching with a matching box, the electric field strength during microwave heating can be adjusted arbitrarily, allowing heating from large to small εr/tanδ with one device. can. 3. Since a high electric field can be obtained, the length of the waveguide for microwave heating can be shortened, and the maximum electric field position can be changed using a phase shifter. Among the above three points, the third one is particularly useful. The reason for this is that the heating temperature reached by a dielectric passing through a microwave electric field is determined by the amount of heat absorbed by any one point of a linear dielectric while passing through a microwave electric field, according to equation (1). Since it is proportional to the total amount of wave energy, in devices with low electric field strengths, the heated material must be kept in the electric field for a long time until the required temperature is reached. This means either providing long microwave heating waveguides or delivering the heating material very slowly. This is a particular problem when it is desired to measure the temperature of a heated material. This is because when we consider the case when the microwave output or material feeding speed is intentionally changed, information on temperature changes is obtained when the heated material passes through the microwave heating waveguide and the temperature is measured. This is because it is obtained by the time delay until reaching the point. In such a device, it is very difficult to provide an automatic control configuration that controls the microwave output based on the electrical quantity of the temperature measuring device to obtain a constant heating temperature. However, in the method of the present invention, sufficient electric field strength can be obtained, so that the length of the part where microwave heating is performed is sufficient to be 1/2 to 1 wavelength, and the maximum electric field position is at the phase shifter. Therefore, a small hole is made in a part of the waveguide for microwave heating that is slightly closer to the phase shifter than the center part, and the infrared radiation emitted from the surface of the heating material is captured by an infrared radiation thermometer, and the temperature of this part is measured. When adjusted with a phase shifter to indicate the maximum temperature, the microwave heated position and the temperature measurement point can be brought very close together, so there is almost no delay time for information on temperature changes, and the electrical output of the infrared radiation thermometer can be directly The temperature of the heating material can be controlled to be constant by providing negative feedback to the control of the wave output.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a rectangular waveguide and the electric field distribution inside it, Fig. 2 is a diagram showing a circular waveguide and the electric field distribution inside it, and Fig. 3 is a diagram showing the continuous heating of a linear dielectric material according to the present invention. a perspective view illustrating an embodiment of the method;
FIG. 4 is a plan view and a front view showing an example of a rectangular waveguide used in the same embodiment, and FIG. 5 is a cross-sectional view showing another embodiment of the rectangular waveguide and the electric field distribution inside it. FIG. In the figure, 1 is a microwave power generator, 2 is a micropower meter, 3 is a matching box, 4 is a rectangular waveguide,
4c is the narrowest part of the rectangular waveguide, a is the long side, b is the short side, 5 is a phase shifter, 6 is a reflector, 7 is a non-reflection terminator, 8 is a heating material, 9 is a ridge, 10 indicate the introduction and outlet holes for the heating material, respectively.

Claims (1)

[Claims] 1 Connect a matching box, a rectangular waveguide for microwave heating, a phase shifter, a reflector, and a non-reflection terminator in this order, and adjust the matching box and reflector to make the inside of the microwave heating waveguide 1. A method for continuously heating a long and narrow dielectric material using microwaves, characterized by bringing the waves into a resonant state and adjusting the electric field position within a waveguide for microwave heating using a phase shifter.