High-frequency Sealing Device

Abstract

For the prevention of wave leakage from within a chamber of a high-frequency sealing device such as a heating device (especially one for food-processing applications), there is provided a hollow metal door having a resilient inner surface for leakageproof contact with the inner edges of the open end of the chamber. A leaking wave, if any, from between the inner surface of the door and the inner edges of the heating chamber is guided into the hollow interior of the door through an elongated window provided on the inner surface thereof. The door may contain a dielectric for absorption of the leaking wave, and its window may be permanently closed with a dielectric thereby to prevent the entrance of any extraneous matter (e.g., water and dust) into the door interior without rendering the window itself impervious to the leaking wave.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to high-frequency sealing devices, and in particular to some improvements made between a door and a high-freqeuency enclosure for the prevention of wave leakage therefrom.

A high-frequency sealing device, for example, a high-frequency heater for the processing of food, among many other applications thereof, is generally known as a "microwave oven" in the consumer market. Although the microwave oven can rapidly and hygienically heat food by using an ultrahigh frequency wave of 2,450 MHz. or thereabouts, the microwave oven has an intrinsic drawback in that said wave may leak from between the enclosure and the door thereof.

Varieties of contrivances have been introduced in prior microwave ovens for the prevention of wave leakage. One is the provision of a resilient gasket at the contacting surface of an oven itself and its door in order to insure close contact therebetween. However, since no perfect contact is possible due to inevitable errors in the manufacturing stage, complete prevention of wave leakage cannot be expected by this means.

Second another expedient is metal-to-metal contact between the enclosure and the door of an oven, in which sparking is caused between the contacting metals, thus greatly deteriorating contacting state of contact metals in the course of time. Moreover, considerable wave leakage is almost unavoidable.

Thirdly, there is the so-called "choke-door" system, in which a cavity is formed in the door toward the enclosure of an oven. According to this system, the cavity must have a depth equal to .lambda./4 (.lambda. : fundamental wavelength of the ultrahigh frequency wave in use), so that the door itself has to be of greater thickness than that constructed for the above-described metal-to-metal contact with the enclosure. This, of course, leads to higher manufacturing costs and other undesirable results.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a high-frequency sealing device in which the inner surface of a door itself is made of resilient material for leakage-free contact with an enclosure.

Another object of the invention is to provide a high-frequency sealing device whose door has a hollow interior into which the wave is guided, if any, leaking from between the door and the enclosure.

Still another object of the invention is to provide a high-frequency sealing device whose door contains a dielectric for the dissipation or the absorption of leaking wave.

Yet another object of the invention is to provide a high-frequency sealing device in which no sparking occurs between the contacting portions of its main enclosure and door, whereby it is made possible to prevent the device from wave leakage for an extremely long period of time.

A further object of the invention is to provide an extremely hygienic high-frequency heating apparatus in which its door is so constructed as to prevent the entrance of any extraneous matter (e.g., food crumbs, water and dust) into the interior thereof but not to suffer in its capabilities of leakage prevention.

All these and the other objects of the invention as well as the characteristic features thereof will become more apparent from the following description of several preferred examples as embodied in microwave oven, taken in connection with the accompanying drawings in which like reference characters designate like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 schematically illustrates a microwave oven for the explanation of the present invention; and

FIGS. 2 through 7 are enlarged, fragmentary, vertical sectional views of part of the microwave oven, each representing a different embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the reference numeral 11 indicates a main body of an example of microwave oven in which may be incorporated the improvements of the present invention. A metal-made heating chamber 12 having its front side opened is provided within the main body 11. A magnetron 13 and a stirrer fan 14 are disposed on the top surface of the heating chamber 12. Hence, a ultrahigh frequency wave of approximately 2,450 MHz., for example, generated by the magnetron 13 is turbulently diffused by means of the stirrer fan 14, with the result that a constant electric field is produced in the heating chamber 12 for the uniform heating of food 15 placed therein.

The aforesaid open side of the heating chamber 12 is ordinarily kept closed by means of an openable metal-made door 16 the lower edge of which is pivoted to the main body 11. Above this door 16 there is provided a decorative front plate 17 that is secured to the main body 11.

As shown in FIG. 2, the door 16 is formed by an outer sheet metal frame 18 and an inner thin metal plate 19 attached to that inner side of the door 16 which is opposed to the main body 11. This metal plate 19 is formed slightly larger than the opening 21 of the heating chamber 12, and is secured to the outer frame 18 by means of a support member 20 disposed at a position spaced over a certain desired distance toward the center from the edges. A contact portion 19a of the metal plate 19 is equipped with a resiliency, and is slightly inclined at its edges toward the outer frame 18 so that it abuts on the lower edge of front-end wall 12a of the heating chamber 12 at its portion near the edge. And a dielectric material 21a having the desired resiliency is contained in the inside cavity 21 of the door 16.

The edge of the outer frame 18 is bent inwardly, i.e., toward the metal plate 19, in the shape of an upside-down "U" over a door end with t, and a spacing x adapted to form an elongated window is provided between the bent end 18a of the outer frame 18 and the edge of the metal plate 19. The bent end 18a is at such a position that when the door 16 is closed, a spacing y exists between itself and the front-end wall 12a of the heating chamber 12.

The width s of the door 16 at its middle portion, of course, is greater than the width t. Further, in order to insure the relation x> y between the aforesaid spacings x and y, x is set at a value in the range of from one-tenth to one-fortieth of a fundamental wavelength .lambda. of a ultrahigh frequency wave in use, while y is set at a value in the range of 0< y< .lambda. /40.

In this first embodiment of the present invention, constructed as in the foregoing and illustrated in FIGS. 1 and 2, a force Fa exerted toward the heating chamber 12 by the door 16 when this door is closed is counterbalanced by a force Fb working in the opposite direction of the force Fa as the contact portion 19a of the metal plate 19 is pressed against the lower edge of the front-end wall 12a of the heating chamber 12. Hence, the door 16 is closed stably, with the forces Fa and Fb at equilibrium as in FIG. 2.

The contact portion 19a of the metal plate 19 thus pressed stably against the lower edge of the front-end wall 12a insures the tight closure of the heating chamber 12 and, accordingly, prevents the leakage of a ultrahigh frequency wave therefrom. Moreover, even though there was some wave leakage from between the contact portion 19a and the front-end wall 12a of the heating chamber 12, this leaking wave is unfailingly absorbed by the dielectric material 21a charged inside the door 16 through the spacing x between the bent end 18a and the upper end of the contact portion 19a, because the spacing y between the bent end 18a and the front-end wall 12a is smaller than the mentioned spacing x. Practically no wave is thus permitted to leak outside of the heating chamber 12.

Another embodiment of the invention is shown in FIG. 3. As illustrated, a door 16 is constructed essentially in the same way as that of FIG. 2 except for a few differences. The part of the dielectric material 21a of FIG. 2 is replaced by a cavity 21. Further, a window 22 is so disposed that a distance l between its center and a bottom A of the cavity 21 is less than .lambda./4 and a distance l between its center and a position B at which a contact portion 19a contacts the front-end wall 12a of the heating chamber 12 is equal to .lambda./4 of a ultrahigh frequency wave in use, while a door end width t is set at a value less than .lambda./4. A distance between the position inside of the contact portion 19a corresponding to the aforesaid position B and a sheet metal outer frame 18 is also set at .lambda./4, and an electric conductor 23 having the desired resiliency is provided therebetween.

In this second embodiment of the above construction, the bottom A of the cavity 21 is in a condition electrically short-circuited, as it were, and the electric field is most weakened there. Accordingly, the electric field is also weakest at a position spaced over a distance of .lambda./2 from the bottom A of the cavity 21, i.e., the point B at which the contact portion 19a contacts the front-end wall 12a of the heating chamber 12, so that any sparking at this point B is prevented. The contact portion 19a thus protected from damage due to sparking is capable of maintaining a leakage-free contact over an extremely long period of time. Moreover, wave leakage, if any, from between the contact portion 19a and the front-end wall 12a of the heating chamber 12 does not cause any trouble because this leaking wave is absorbed in the cavity 21. With provision of the conductor 23 having .lambda./4 width inside the door 16 at a position spaced .lambda./4 from the window 22, the total of the width of this conductor 23 and the length between the window 22 and one of the ends of the conductor 23 is .lambda./2, so that a "choking" effect is obtainable for the surer prevention of wave leakage.

FIG. 4 shows still another embodiment of the invention, the construction of which is identical with the foregoing embodiment illustrated in FIG. 2. The only pronounced difference is that the conductor 23 of FIG. 3 is not provided in this particular embodiment.

According to this construction, too, the bottom A of the cavity 21 is in an electrically short-circuited condition, and the electric field is weakest there, and further the point B of contact between the contact portion 19a and the front-end wall 12a of the heating chamber 12, is at a position spaced .lambda./2 from the bottom A of the cavity 21, so that the electric field at said point B is also weakest and no sparking occurs at said point B. The contact portion 19a thus prevented from damage due to sparking is capable maintaining a favorable, leakage-free state of door closure over an extremely long period of time. Moreover, there is virtually no possibility of wave leakage outside of the door 16 because all the leaking wave, if any, from between the contact portion 19a and the front-end wall 12a of the heating chamber 12 is absorbed in the cavity 21. As an added convenience, the door 16 may be made to be adequately thin because the cavity 21 is provided lengthwise therein.

FIG. 5 illustrates a further embodiment of the invention, in which the edge of the contact portion 19a is slightly bent toward the outer frame 18 of the door 16, contacting the lower edge of the front-end wall 12a of the heating chamber 12 approximately at the bending point. And a resilient dielectric member 22 is provided at the window 21 formed by the bent end 18a of the frame 18 and the bent end of the contact portion 19a. One of the ends of this dielectric member 22 may be bifurcated to hold the bent end 18a of the outer frame 18 between its two branches, while the other end thereof is bent toward the interior of the door 16 so as to abut on the edge of the contact portion 19a from within the door 16.

By this construction, in which the window 21 formed between the edge of the contact portion 19a and the bent end 18a of the frame 18 is kept completely closed by means of the dielectric member 22, food crumbs, water, dust and the like are prevented from intruding into the interior of the door 16 via the window 21. Because of its very nature, the dielectric member 22 does not render the window 21 impervious to the wave, if any, leaking from between the contact portion 19a and the front-end wall 12a of the heating chamber 12. Moreover, since the contact portion 19a is not deprived of its resiliency by the dielectric member 22, it is capable of making close contact with the front-end wall 12a for prevention of wave leakage.

While one of the ends of the dielectric member 22 is bifurcated in the last described embodiment of the invention, it may be either simply bonded, as in FIG. 6, or screwed to the bent end 18a of the frame 18. As a further modification, as illustrated in FIG. 7, the bent end 18a and the contact portion 19a may be buried in a solid piece 22 made of a dielectric material.

Although the invention has been shown and described in the foregoing with reference to several currently preferred embodiments thereof, it will be obvious that many modifications thereof can be made without departing from the spirit of the invention.

Claims

We claim:

1. A high-frequency sealing device comprising a main body in which is provided a heating chamber having a front opening and a door for closing said opening, said door comprising an inner metal plate resiliently contacting the periphery of said opening and another metal plate spaced apart from said inner plate, the peripheral edge of said other plate being bent inwardly into the shape of a letter U, thus forming an annular cavity in said U-shaped peripheral edge, characterized in that said contact between the periphery of said front opening and said inner metal plate is direct metal-to-metal contact, that at least one opening is formed between said contact and the peripheral sidewall of said other plate at a distance of .lambda./4 from said contact, and that the distance between the center of said opening and said other plate is up to .lambda./4.

2. A high-frequency sealing device according to claim 1 wherein a dielectric material is contained in the space between said inner and other plate, said space including at least said cavity.

3. A high-frequency sealing device according to claim 2 wherein said dielectric material is resilient.

4. A high-frequency sealing device according to claim 1 wherein a conductive plate is inserted between said inner and outer plate at a point .lambda./2 apart from the bottom wall of the outer plate.