JP7657538B2 - Heat generating unit, heat treatment device, and heater design method for heat treatment device - Google Patents

Description

This invention relates to a heat generating unit and a heat treatment device for heating a heated part, and in particular to a heat treatment device that performs hybrid heating of a heated object stored in a chamber using two heating means, microwaves and a heater, and a heater design method for the heat treatment device.

A typical heat generating part that heats the heated part is, for example, a heater installed inside the chamber. Such a heater directly heats the heated part inside the chamber from the outside.

In addition, in a device that uses microwaves to heat an object placed in a chamber instead of a heater, the microwaves penetrate deep into the object, making it possible to shorten the heating process time and save energy.

However, if an object is heated using only microwaves, a large amount of heat is dissipated from the object, creating a temperature difference between the inside and outside of the object, which may result in a deterioration in the quality of the object.

Therefore, a heat treatment device has been proposed that performs hybrid heating using microwaves and other heating sources (Patent Document 1).

For example, in the hybrid heating heat treatment device shown in Patent Document 1, a susceptor heated by microwaves as another heating source is provided in the chamber, and the object to be heated is heated from the inside by microwaves, while the susceptor heated by microwaves heats the object from the outside, thereby achieving uniform heating of the object to be heated.

In addition, in the hybrid heating heat treatment device shown in Patent Document 2, a microwave absorber that is heated by microwaves as another heating source is provided on the side wall inside the chamber, and the object to be heated is heated from the inside by microwaves, while the microwave absorber heated by microwaves heats the object from the outside, thereby achieving uniform heating of the object to be heated.

Special table 2015-536434 publication JP 2004-352595 A

However, in the devices shown in Patent Documents 1 and 2, microwave heating and indirect heating (heating the object indirectly by heating a microwave absorber placed in the chamber with microwaves) are performed, so the capacity of the microwave irradiation device becomes large, and high costs are unavoidable.

The purpose of this invention is to improve the heating efficiency by improving the configuration of the heating section. It also aims to provide a heat treatment device that suppresses the variation in temperature rise of the heated object and improves the heating efficiency.

The heat generating portion of this invention is characterized by a meandering pattern in which the arrangement turns periodically, and absorbs energy when exposed to microwaves.

The arrangement pattern of the heat generating parts is a serpentine pattern that turns periodically, and when microwaves are irradiated, the serpentine pattern allows the heat generating parts to absorb microwave energy. Because the heat generating parts are able to absorb microwave energy and generate heat due to their serpentine pattern shape, there is no need to provide a separate structure such as a susceptor for absorbing energy. In addition, the heat generating parts can easily be configured with electric heaters, etc., and in such a configuration, the heat generating parts can be heated by both the heater and microwaves. Furthermore, the serpentine pattern shape makes it possible to suppress absorption of microwave energy, which allows microwaves to be used efficiently to heat the heated object.

In this way, the heating efficiency can be improved by adjusting the amount of microwave absorption.

By performing hybrid heating on the object to be heated, it is possible to suppress variations in temperature rise in the heated area.

For the following reasons, by devising the shape of the meandering pattern, it is possible to solve the problem of heater heating by microwaves, that is, to suppress the loss due to dielectric heating of microwaves in the heater. This further improves the heating efficiency.

In other words, as described later, various simulations were performed and it was found that there is a correlation between the wavelength (frequency) of the radiated microwaves and the heat generated by the heater. It was also found that there is a correlation between the shape of the heater and the heat generated by the heater for microwaves of the same wavelength. In other words, it is presumed that the heater behaves as an antenna for microwaves. If the performance as an antenna for the radiated microwaves is high, the microwave energy will be consumed as heat generated by the heater, and if the performance as an antenna is low, this consumption will be small.

In this invention, the heater is arranged in a meandering pattern, and is therefore thought to behave as a meandering antenna. By devising the shape of the meandering pattern, it is possible to reduce the antenna performance, prevent microwave energy from being consumed as heat generated by the heater, and increase the irradiation efficiency of microwave energy to the heated object, i.e., increase the heating efficiency of microwave energy to the heated object.

The heat treatment device of the present invention includes a microwave irradiation unit that irradiates microwaves to an object to be heated in a chamber, and a heater that includes the heat generating unit, and performs hybrid heating of the object to be heated using microwaves and the heater. The heat generating unit of the heater is disposed in the chamber.

In addition, since the heater's heat generating part is located inside the chamber, the heating efficiency of the heater's heat generating part on the heated object is improved.

In addition, by making the arrangement pattern of the heating parts of the heater a meandering pattern, the heater wiring becomes the pattern with the highest density. Since the heater output is determined by the length of the heater, the desired output density can be easily obtained. The meandering pattern can be adjusted and arranged according to the dimensions and shape of the wall surface inside the chamber. This makes it possible to avoid complicating the structure inside the chamber. And, by making the heater wiring dense, a heater with the desired heater output can be installed in a small space. Furthermore, when performing hybrid heating using microwaves and a heater, it is an issue to prevent the heater from being heated by the microwaves. In this invention, since the arrangement pattern of the heating parts of the heater is a meandering pattern, for the following reason, it is possible to solve the issue of not being able to adjust the amount of microwave energy absorption by the microwaves by devising the shape of the meandering pattern, that is, it is possible to suppress the loss due to dielectric heating of the microwaves in the heater. This further improves the heating efficiency.

As described above, in this invention, hybrid heating can suppress variations in temperature rise in the heated area. In addition, by arranging the heat generating part of the heater inside the chamber, the heating efficiency of the heat generating part of the heater for the heated object is improved. In addition, by making the heater arrangement pattern a serpentine pattern, it is possible to prevent microwave energy from being consumed as heat generated by the heater by devising the shape, and it is possible to further increase the heating efficiency. In addition, there is an advantage that a mechanism for isolating the heater from microwaves is not required, the desired output density can be easily obtained, and the structure of the heat treatment device can be simplified.

In this invention, the length L of one turn of the heater, calculated by adding the length of one straight section to the length of one turn, is set to a length that keeps the amount of microwave energy absorbed by the heater within a certain range.

When the heater arrangement pattern is a meandering pattern, the challenge is to determine which part of the shape should be devised to reduce the amount of microwave energy absorbed by the heater without reducing the total length (area) of the heater wire. According to the results of a simulation analysis, it was found that the amount of energy absorbed can be varied by adjusting the length of one turn L, which is the sum of the length of one straight section and the length of one turn of the heater. Therefore, the length of one turn L is set to a length that keeps the amount of microwave energy absorbed by the heater below a certain range.

In this invention, it is preferable that the length L of one turn is set to a length such that L/λ is within a certain range centered around 0.5, where λ is the wavelength of the microwave.

More specifically, it is desirable to set the length L of one turn to a length such that L/λ is in the range of 0.35 to 0.7. It is more preferable to set the length to a length such that L/λ is in the range of 0.4 to 0.6, and even more preferable to set the length to a length such that L/λ is in the range of 0.4 to 0.55.

According to this invention, the arrangement pattern of the heat generating portion is a meandering pattern that turns periodically, so that when microwaves are irradiated, the energy can be absorbed. Because the heat generating portion is capable of absorbing microwave energy and generating heat due to its meandering pattern shape, there is no need to provide a separate structure such as a susceptor for absorbing energy, which allows for miniaturization and improves heat generation efficiency. In addition, the heat generating portion can easily be configured with an electric heater, etc., so in such a configuration, the heat generating portion can be heated by both a heater and microwaves.

Hybrid heating can suppress variations in temperature rise in the heated area. In addition, by placing the heater's heat generating part inside, the heating efficiency of the heater's heat generating part on the heated object is improved.

In addition, the arrangement is a serpentine pattern, and by devising the shape, it is possible to prevent microwave energy from being consumed as heat by the heater, further improving heating efficiency.

1 is a schematic structural diagram of a heat treatment apparatus according to an embodiment of the present invention; 1 shows a part of the arrangement pattern of meander-shaped heaters. Simulation results over a wide frequency range are shown. Simulation results for four different heater shapes are shown. Simulation results for three different heater geometries are shown. Simulation results for four additional heater geometries are presented. The simulation results for the degree of microwave absorption and the amount of heat generated are shown below.

Figure 1 is a schematic diagram of a heat treatment device according to an embodiment of the present invention. Figure 1 (A) is a front cross-sectional view of the heat treatment device, and (B) is a diagram of the heater arrangement pattern.

The heat treatment device 1 is equipped with a chamber 4 composed of a heat insulating material 2 made of a material such as ceramic, and a metal cover 3 surrounding the heat insulating material 2, which is formed so that the cross section is a hollow box shape. An object to be heated 5 is placed inside the chamber 4. The object to be heated 5 is a processing item that is heated by absorbing microwaves, and the material of the object to be heated 5 is not limited. In addition, a microwave irradiation device 6 that irradiates microwaves to the object to be heated 5 inside the chamber 4 is placed outside the chamber 4, and the microwave irradiation device 6 and the chamber 4 are connected by a waveguide 7.

In the illustrated example, the chamber 4 is provided with transport rollers 8 on which the object 5 to be heated is placed and transported in the forward and backward directions toward the paper surface. The transport rollers 8 are used as a means for transporting the object 5 to another chamber provided in front or behind the paper surface when the object 5 to be heated is continuously processed. It is also possible to process the object 5 to be heated alone in the chamber 4 without providing the transport rollers 8.

An electric heater (hereinafter, heater) 9 is provided on the inner wall of the chamber 4 of the heat treatment apparatus 1. The heater wire, which is the heat generating part of the heater 9, is made of a metal such as Kanthal or Nichrome. In this example, the heater 9 is configured by arranging the heater wire on the upper inner wall and the left and right inner walls of the chamber 4 in FIG. 1, and generates heat by being supplied with power from an external power source (not shown). Hereinafter, this heater wire will be simply referred to as the heater 9. Also, as shown in FIG. 1(B), the heater 9 is a single heater wire arranged in multiple rows as a whole, and each row is made to meander. By making the arrangement pattern of the heater 9 into a multiple-row meandering pattern in this way, the density is increased.

The heater 9 can be made of ceramics such as SiC and MoSi2, in addition to Kanthal and Nichrome.

In place of heater 9, it is also possible to use other heaters that generate heat by being connected to an external heat source (electricity, gas, etc.) and whose exposed parts inside the chamber are made of metal or ceramic, such as sheath heaters or regenerative radiant tube burners. In this case too, the heating parts are placed on the upper inner wall and the left and right inner walls of chamber 4.

In the above configuration, the heater 9 heats the object 5 from the outside by setting the atmospheric temperature in the chamber to a predetermined temperature, and the microwave irradiated from the microwave irradiator 6 heats the object 5 from the inside. This eliminates the temperature difference between the inside and outside of the object 5, uniformly heats the object, and suppresses the temperature rise variation of the heated part. In addition, by configuring the heater 9 as a metal-based electric heater made of nichrome or the like, the output is determined by the resistance value of the heater 9, i.e., the length of the heater 9, so the desired output density can be easily obtained. In addition, by making the heater 9 arrangement pattern into a meandering pattern of multiple rows, the heater wiring becomes high density and the heating efficiency for the object to be heated is improved. And by arranging the heater 9, which is the heat generating part, on the upper inner wall and the left and right inner walls of the chamber 4, it is not necessary to isolate the heat generating part of the heater from the microwave, and the heater 9 is arranged in the space irradiated with the microwave. Therefore, from the viewpoint of this structure, the heating efficiency for the object to be heated is improved.

In this embodiment, the shape of the heater 9 is optimized so that microwaves are not absorbed. As described above, the heater 9, which has a meandering arrangement pattern, is presumed to behave as a meandering antenna for the irradiated microwaves. If the heater 9 has high performance as an antenna for the irradiated microwaves, microwave energy is consumed as heat generation by the heater 9, and if the heater 9 has low performance as an antenna, the consumption is reduced.

The shape of the heater 9 is optimized on the premise that the heater 9 behaves as a meander-shaped antenna for microwaves, as described above. That is, as a result of the following considerations, it was found that the amount of microwave energy absorbed by the heater varies by adjusting the length L of one turn (hereinafter sometimes simply referred to as the turn length L). Therefore, the turn length L is set to a length that keeps the amount of microwave energy absorbed by the heater within a certain range.

Figure 2 shows a portion of the arrangement pattern of meander-shaped heaters. In the figure, the turn length L is equal to the length L1 of one turn portion plus the lengths L2, L3 of two straight portions above and below that connect to length L1. L2 and L3 are each half the length of one straight portion L4 that connects to length L1 of the turn portion. For convenience, hereafter, the turn length L will be defined as the length L1 of the turn portion plus the length of one straight portion L4.

The following is a detailed simulation of the turn length L, which is the sum of the length of the turn section L1 and the length of one straight section L4. The simulation was performed with no current flowing through the heater in the configuration shown in Figure 1.

First, we performed a wide frequency simulation as shown in Figure 3.

In Fig. 3(A), microwaves were irradiated onto a test heater wire (turn length L = 174 mm) with a meandering pattern, and the microwave frequency was swept to investigate the position where the VSWR peak appeared. This investigation revealed that the first peak was the maximum. Note that the higher the VSWR value, the worse the heater's microwave absorption, i.e., the worse the antenna performance. From Fig. 3(A), the position of the first peak is approximately 0.8 GHz (λ = 375 mm). At this time, L/λ = 174/375 = 0.5. Fig. 3(B) shows the position where the VSWR peak appears when the frequency is swept with L/λ on the horizontal axis. From the same figure, the position where the first peak is the maximum is L/λ = 0.5.

In Figure 3(A), L = 174 mm, but even when L was changed, the peak was greatest when L/λ = 0.5.

From the above, the VSWR value can be maximized by determining the turn length L such that L/λ = 0.5.

Next, to determine the shape of the turn length L, a simulation was performed as shown in Figures 4 and 5 with L1 and L4 (= L2 + L3) as parameters. For convenience, the turn portion L1 is referred to as the interval L5, and the straight portion L4 is referred to as the row width L4.

Figures 4 and 5 show the VSWR values when the microwave frequency is swept for four types of shapes (1), (26), (79), and (13) (numbers indicate the shape number and have no particular meaning). Also, Figure 4 (B) shows the VSWR values when the frequency is swept with the horizontal axis set to L/λ for four types of shapes (1), (26), (79), and (13).

In Figure 4 (A), from the VSWR values of shapes (1), (26), (79), and (13), it can be seen that as the turn length L increases, the VSWR peak position moves toward lower frequencies.

In Figures 4(A) and (B), the VSWR values for shapes (26) and (79) show that for the same turn length L, the smaller spacing L5 has a higher VSWR value.

In Figures 4(A) and (B), the VSWR values for shapes (1), (79), and (13) show that for the same spacing L5, the VSWR peak value is larger when the row width L4 is larger. Also, the VSWR peak value for the larger row width L4 shifts toward lower frequencies.

In addition, simulations were performed for three other shapes (5), (9), and (12) with the same turn length, as shown in Figures 5(A) and (B). In this example, too, the VSWR value is higher for the smaller spacing L5 with the same turn length.

Furthermore, simulations were performed for four other types of shapes (23), (17), (24), and (25) at the same interval L4, as shown in Figures 6(A) and (B). In this example, as in Figures 4(A) and (B), at the same interval, the VSWR peak value is larger for the larger row width L4, and the VSWR peak value for the larger row width L4 shifts toward lower frequencies.

The above simulation results show that when the microwave frequency is 2.45 GHz, shape (79) is preferable among the four types in FIG. 4 for preventing microwave absorption. Furthermore, shape (5) is preferable among the three types in FIG. 5, and shapes (24) or (25) are preferable among the four types in FIG. 6.

Also, from Fig. 4(B), Fig. 5(B) and Fig. 6(B), it is seen that the length L per turn is set to a length such that L/λ is in the range of 0.35 to 0.7 with 0.5 as the center, preferably 0.4 to 0.6, and more preferably 0.4 to 0.55, to prevent absorption of microwaves. That is, when the microwave frequency is 2.45 GHz, λ=122 mm, so it is desirable that the length L per turn is 42.7 mm to 85.4 mm, preferably 48.8 mm to 73.2 mm, and more preferably 48.8 mm to 67.1 mm. Also, from Fig. 4 and Fig. 5, it is better that the interval L5 is small. In practice, from the viewpoint of bending workability of the heater wire, it is better to set the radius of the turn portion to about 10 mm.

The reason why it is better for the distance L5 or the radius of the turn portion to be small is that the directions of the magnetic fields generated in the upper and lower straight portions L2 and L3 connected to the turn portion are opposite to each other, so the smaller the distance L5 or the radius of the turn portion, the smaller the distance between the straight portions L2 and L3, making it easier to cancel out these magnetic fields, i.e., the antenna efficiency is thought to decrease. In practice, from the perspective of the bending workability of the heater wire, the radius of the turn portion should be around 10 mm, and preferably around 9 mm to 12 mm.

The length L of one turn is selected within the range of 42.7 mm to 85.4 mm as described above, so once the radius of the turn portion, i.e., the length L1 of the turn portion, is determined, the spacing L4 is determined from L = L4 + L1.

Figure 7 shows the results of a simulation showing the degree of microwave absorption (Figure 7(A)) and the amount of heat generated (Figure 7(B)) for the shapes (1) and (79) shown in Figure 4. The microwave frequency is 2.45 GHz.

As can be seen from the figure, when the frequency is 2.45 GHz, the VSWR value of shape (1) is 5, while the VSWR value of shape (79) is 80, resulting in the amount of heat generated by shape (79) being the smallest value compared to the amount of heat generated by shape (1).

In this way, in this invention, by optimizing the shape of the heater 9 so as to reduce microwave absorption, it is possible to prevent the heater 9 from consuming energy output from the microwave irradiation device 6, making it possible to configure a heat treatment device with good heating efficiency. In addition, there is no need to design a structure that isolates the heater 9 from microwaves.

1-Heat treatment device 2-Insulating material 3-Metal cover 4-Chamber 5-Heated object 6-Microwave irradiation device 9-Heater

Claims (6)

A meandering pattern that is connected to a power source or heat source to generate heat and has a periodically turning arrangement pattern,
The meandering pattern is
A heat generating portion characterized in that a length L of one turn, which is the sum of the length of one turn portion of the meandering pattern and the length of one straight portion connected to this turn portion, is set in a shape such that L/λ is within a range of 0.35 to 0.7, when the wavelength of the microwave during microwave irradiation is λ. 2. The heat generating portion according to claim 1 , wherein the length L of one turn is set to a length such that L/.lambda. falls within a range of 0.4 to 0.6. 2. The heat generating portion according to claim 1 , wherein the length L of one turn is set to a length such that L/λ falls within a range of 0.4 to 0.55. The heat generating portion according to any one of claims 1 to 3 , wherein the heat generating portion is an electric heater. A chamber that accommodates an object to be heated;
A microwave irradiation unit that irradiates microwaves onto the object to be heated in the chamber;
a heater including the heat generating portion according to any one of claims 1 to 4 ,
A heat treatment apparatus, characterized in that a heat generating portion of the heater is disposed within the chamber. A chamber that accommodates an object to be heated;
A microwave irradiation unit that irradiates microwaves onto the object to be heated in the chamber;
A heater.
In a heat treatment apparatus, the heating parts of the heaters are arranged in the chamber in a meandering pattern that periodically turns,
a length of one turn of the heat generating part plus a length of one straight section connected to the turn part, the length of the turn part being used as a parameter to determine an amount of energy absorption by the heater for the frequency of the microwave through a simulation, and to determine a length of the turn part at which the amount of energy absorption is reduced to within a predetermined range.

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