JPS5939871B2 - Door seal device for high frequency heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a door seal device for a high frequency heating device.

BACKGROUND OF THE INVENTION In high-frequency heating devices such as microwave ovens, various devices have been proposed and put into practical use as radio wave leakage prevention devices, but these devices have complicated structures and are expensive.

That is, FIG. 1 shows an overall sectional view of a conventional microwave oven, and FIG. 2 shows an enlarged view of its door structure. In these drawings, the door rear plate 5 and the heating chamber flange portion 2 are designed to have metal plane contact, and radio wave leakage is prevented from occurring at this portion. However, there are times when it is impossible to create a perfect plane due to processing.
Uniform planar contact could not be achieved, and therefore radio waves were leaking from this area. Conventionally, a choke groove 6 (with a depth of approximately 1/4 wavelength from the opening 7) was further formed between the door rear plate 5 and the door front plate 4 to prevent leakage of radio waves. However, since this was still incomplete, it was necessary to form a sash portion 8 on the outside of the choke groove 6 when viewed from the heating chamber 1, and attach a ferrite rubber 9 or the like having radio wave absorbing properties to this sash portion 8. However,
Ferrite rubber is generally expensive, and due to its radio wave absorption properties, it can generate abnormal heat when excessive radio waves leak, and may even catch fire.
Safety was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art as described above and to provide a door seal device that is inexpensive and has excellent safety.

In the present invention, we focused on the fact that when leakage radio waves pass through a metal waveguide with a transmission width of approximately less than 1/2 wavelength of the radio waves used, a phase delay occurs compared to when passing through free space. A groove is provided in at least one of the flange parts of the heating chamber, and a continuously bent conductor plate similar to the above-mentioned waveguide is installed in the groove to separate leakage radio waves that do not pass through the bent conductor plate and leakage radio waves that pass through the bent conductor plate. By combining the leaked radio waves, the two leaked radio waves cancel each other out, resulting in an attenuating effect.

In addition, when installing the bent conductor plate in the groove around the door, the distance a between the corrugated plate and the door rear plate and the distance I between the corrugated plate and the front door frame are set so that a>a', so as to have a damping effect. The above objective has been achieved. The present invention will be explained in detail below with reference to Examples.

FIG. 3 shows an enlarged cross-sectional view of the door periphery according to an embodiment of the present invention. A groove 6 is provided in the door 3, and a continuously bent conductive plate (hereinafter referred to as a corrugated plate 10) is installed in the groove 6. The bending length 12 of this corrugated plate 10 is approximately less than 1/2 of the wavelength of the radio waves used. Radio waves that are about to leak from the heating chamber 1 to the outside through the gap between the door 3 and the heating chamber flange 2 facing it are transmitted through the depth and width of the groove 6 provided in the door 3 and the corrugated plate 10 provided within the groove. By appropriately selecting the impedance determined by the shape of , leakage can be made less likely. Furthermore, the leaked radio waves are
The radio waves are divided into radio waves transmitted within the corrugated plate 10 and radio waves transmitted elsewhere. Among these, the radio waves transmitted inside the corrugated plate 10 are surrounded by metal walls, and the transmission width is approximately 1.
Since it is less than /2 wavelength, it is subject to appropriate attenuation, and as is well known in waveguides, the phase is delayed compared to radio waves in free space. However, since the radio waves that pass through the gap between the heating chamber flange portion 2 and the corrugated plate 10 without passing through the corrugated plate 10 travel at almost free space wavelengths, when combined with the radio waves that have passed through the corrugated plate 10, There is a phase shift between the two radio waves, and the radio waves that are about to leak are significantly attenuated. Since this phase difference depends on the bending length 12, height 13, and width 14 of the corrugated plate 10, by appropriately selecting these, it has become possible to achieve a significant damping effect. Furthermore, regarding the position where the corrugated plate 10 is installed in the groove, at the upper and lower sides of the door, the relationship between the distance Al5 between the corrugated plate 10 and the end of the door rear plate and the distance a'16 between the corrugated plate and the door front plate frame is a >l, and similarly for the left and right sides of the door,
The relationship between the distance Bl7 between the corrugated plate and the door rear plate and the distance b'18 between the corrugated plate and the door front plate frame is b>d>O. The background to the creation of the above conditions is described below. FIG. 7 shows the experimental results regarding the position of the corrugated plate installed in the groove around the door and the amount of leakage radio waves.

In addition, for performance comparison with the door seal provided with the corrugated plate of the present invention, the characteristics of the conventional door seal having a chiyoke structure shown in FIG. 2 are also listed. In FIG. 7, the horizontal axis represents the gap between the door rear plate and the oven flange, and the vertical axis represents the amount of leakage radio waves. A characteristic curve 19 is a leakage radio wave amount characteristic of a conventional chiyoke structure door seal.

Further, characteristic curves 20, 21, and 22 are leakage radio wave amount characteristics of the corrugated plate door seal shown in FIG. Comparing the characteristics of the chiyoke structure and the corrugated plate door seal in this figure, it can be seen that the corrugated plate door seal is more effective in preventing leakage radio waves. The legal regulation value for the amount of leakage radio waves of high-frequency heating equipment is as follows: When the door is closed, the amount of leakage radio waves must be less than ▼? It is as follows.

In the case of a chiyoke structure, the gap between the door and the door rear plate must be 2 mm or less in accordance with the legal regulations, but a corrugated plate door seal has a margin of 3 to 4 mm. Therefore, mass productivity can be improved. Next, we will discuss the installation position of the corrugated plate in the groove and the amount of leakage radio waves. The dimensions of the corrugated plate used here are, as shown in FIG. 4, the height 13 is 27 mm, the bending length 12 is 15 mm, and the width 14 is 10 mm.

In FIG. 6, the characteristic curve 20 in FIG.
212.5m1L. ．． This is the case when a=b: -7.5 mm, and the characteristic curve 21 is when a'=b'=Ab=10 mm, that is, when the corrugated plate is installed on the center line of the groove. And the characteristic curve 22 is a'=b'=7.5mm1a
=b=12.5mm1. Looking at these three leakage curves, it is clear that the amount of leaked radio waves is reduced when the corrugated plate is installed and fixed outside the groove. This means that the position of the corrugated plate within the groove is dependent on the leakage prevention effect, and this can be said to be due to the condition that the phases of the radio waves passing through the corrugated plate cancel each other out.

The cavity in which the corrugated plate is installed is covered with a plastic cover 11. By creating such a door seal device, it is possible to remove the ferrite rubber that has been used in the past, making it possible to obtain a door seal device that is inexpensive and has excellent safety.

As detailed above, according to the present invention, it is possible to obtain a door seal device that has good radio wave leakage prevention performance, can be manufactured at low cost, and has excellent safety, and can be used in microwave ovens and other high-frequency heating devices. You can get great results by doing this.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional high-frequency heating device, FIG. 2 is an enlarged sectional view of the area around the door of the device, and FIG. 3 is an enlarged sectional view of the area around the door showing an embodiment of the present invention. FIG. 4 is a perspective view of the corrugated plate used in the example. FIG. 5 is a view of the installation of the corrugated plate in the door groove, and FIG. 6 is a partially enlarged view of FIG. FIG. 7 is a characteristic diagram showing the relationship between the position where the corrugated plate is installed and the amount of leakage radio waves. 2...Heating chamber flange portion, 3...Door, 4...Door front plate, 5...Door rear plate, 6...... Groove section, 10...corrugated plate.

Claims (1)

[Claims] 1. In order to prevent radio wave leakage from the area around the door of the high-frequency heating device, a groove is provided in at least one of the door and the heating chamber wall facing the door, and a bending length of approximately less than 1/2 wavelength of the radio wave used in the longitudinal direction of the groove is provided. A door seal device for a high-frequency heating device, characterized in that a metal plate bent into a wave shape is installed, and the installation position is fixed toward the outside of the door from the center of the width of the opening of the groove.