JPS61284090A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a structure for preventing radio wave leakage from a high frequency heating device such as a microwave oven equipped with an electric heater.

Conventional technology In the case of a conventional microwave oven with an electric heater, there is no problem if the oven wall is made of stainless steel, etc., but if the iron plate has a surface treatment such as enamel or heat-resistant paint, this may cause insulation. Because of this, electrical contact cannot be made at the part where the heater is fixed to the oven wall, so radio waves are carried on the heater and leak out of the oven from the part where the heater penetrates the oven wall. A problem occurs. To counter this, conventionally, as shown in FIG. 5, a spring material 8 is used on the outside where the heater 3 penetrates the oven wall 5 to electrically connect the heater 3 and the part of the oven wall 5 where the enamel 9 is not applied. The method used was to connect. Also, heater 3
When the heater 3 is not brought into electrical contact with the oven wall 5, a choke 9 is provided on the oven wall 5 through which the heater 3 passes, as shown in FIG. 6, to prevent radio wave leakage.

Problems to be Solved by the Invention There are two problems with the prior art methods of obtaining electrical contact between the heater 3 and the oven wall 5 using spring properties. One of the points is that the surface temperature of the electric heater 3 reaches approximately 700°C or more in the part where the heater element is located, and even in the part where the heater element is not located and extends outside the oven wall, due to conduction heat, the temperature rises to 150°C. Since the temperature is higher than C, the spring material 8 in contact with it receives conduction heat and becomes annealed after being used for a long time, deteriorating its spring properties and making it impossible to maintain good electrical contact. . The second reason is that when contact is made with spring characteristics, it becomes a point contact or a line contact as shown in Figure 5, and since the contact area is small, the contact resistance becomes large. It is difficult to pass an earth test, which is performed by passing an electric current.

The present invention aims to improve these conventional problems, and provides a high-frequency heating device having a simple structure and reliable structure for preventing leakage of radio waves from the heater.

Means for Solving the Problems The high-frequency heating device of the present invention includes a heating chamber, a high-frequency oscillator, an electric heater, and a flat metal fitting for mounting and fixing the electric heater in the heating chamber. An insulating layer such as enamel or heat-resistant paint is provided on the surface of the metal fitting, and the metal fitting is fixed approximately perpendicularly to the axial direction of the electric heater, and the dimension from the outer periphery of the electric heater to the end face of the metal fitting is an abbreviation of the wavelength used. The structure is such that the length is reduced to 1/4.

Function The present invention is configured such that when the electric heater is fixed to the oven wall,
The plate-shaped metal fitting is in close contact parallel to the oven wall, but at this time, the distance between the end face of the metal fitting and the oven wall is almost an open end from a high frequency perspective, that is, close to the maximum electric field point, and therefore, from this point The heater portions separated by /4 wavelengths are in a substantially short-circuit state, that is, the electric field is at a very low point, which has the effect of making it difficult for radio waves to leak outside through the heater.

EXAMPLE Hereinafter, a high frequency cooking device according to an example of the present invention will be explained with reference to the drawings.

In FIG. 1, 1 is an oven and 2 is a high frequency oscillator. The electric heater 3 is provided in the upper part of the oven 1 and is fixed onto the oven wall 5 using a flat metal fitting 4. FIGS. 2a and 2b show a plan view and a front view of the electric heater 3 alone. Further, FIG. 3 is a detailed longitudinal sectional view of a portion where the electric heater 3 penetrates the oven wall 5. A flat metal fitting 4 is fixed to the electric heater 3 at a substantially right angle by caulking.

Therefore, perfect electrical contact is obtained during this time.

In addition, the dimension from the outer periphery of the electric heater 3 to the end of the flat metal fitting 4 is λ/4, which is the abbreviation of the wavelength of the radio wave used, as shown in Figure 3.
In the case of a microwave oven, the operating frequency is 2450 MH2, so this dimension is about 3 Qmm, but the actual mechanical dimension is enamel 6 on the surface of the oven wall 5.
Because of this, if you take into account the dielectric constant of enamel, it will be about half of that, about 15. The oven wall surface of the portion 5a in contact with the flat metal fitting 4 has a flat metal fitting 4 so as to easily create a high-frequency open condition at the end of the flat metal fitting 4.
There is a step diaphragm 5b facing toward. When the end of the flat metal fitting 4 is open, the outer circumference of the heater 3, which is V4 away from it, is close to a short circuit in terms of high frequency and the electric field is zero or very small, so no radio waves are transmitted from here to the outside. is less likely to leak. FIG. 4 is an enlarged cross-sectional view of the portion where the electric heater 3 penetrates the oven wall 5, viewed from above.

The flat metal fitting 4 has screw holes 11 at a total of three locations on the outside of both poles of the electric heater 3 and between them, and by tightening the three screws 7.7a and 7b from the outside of the oven, It is fixed to the oven wall 5. screw 7.7a
A protrusion 10 is provided on the back side of the head of and 7b,
Furthermore, since the enamel on the oven wall 5 is designed so that it does not touch the tightening part of the screw, the protrusion 10 sinks into the oven wall by tightening the screw, and a good electrical contact is obtained during this time, so the screw A good electrical contact can also be obtained between the oven wall 5, the flat metal fitting 4, and the electric heater 3 through the opening.

Effects of the Invention As described above, the present invention reduces the dimension between the outer circumferential end of the flat metal fitting fixed to the electric heater and the outer circumference of the heater to approximately λ/4.
When the electric heater is attached to the oven wall using the metal fittings, the electric field in the part where the electric heater penetrates the oven wall is minimized, so the amount of radio waves transmitted to the heater and leaked is kept to a very low level. I can do things. In addition, unlike the conventional method of preventing radio wave leakage through electrical contact using spring properties, there is no concern that performance will deteriorate due to repeated use at high temperatures, and a highly reliable radio wave leakage prevention structure can be achieved. . Furthermore, by screwing the flat metal fitting from outside the oven using screws with protrusions on the back surface, good and stable electrical contact can be obtained between the oven wall and the exterior of the electric heater. Furthermore, since no spring material is used and the connection is made with only screws, the cost can be reduced, which is extremely advantageous in practical terms.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a high-frequency heating device that is an embodiment of the present invention, Fig. 2 a and b are a plan view and a front view of the electric heater alone, and Fig. 3 is a longitudinal cross-section showing details of the main parts. 4 are sectional views seen from above, and FIGS. 5 and 6 are sectional views of main parts showing a conventional example. 1... Oven (heating chamber), 2... High frequency oscillator, 3... Electric heater, 4...
・Flat metal fittings, 5...Oven wall, 5b...
...Step diaphragm, 7.7a, 7b...Screw. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Ward / -1-Own'5--Own wall (b) Fig. 5 Fig. 6

Claims (4)

[Claims] (1) It has a heating chamber with an insulating layer such as enamel or heat-resistant paint on its surface, a high-frequency oscillator, an electric heater, and a flat metal fitting for fixing the electric heater in the heating chamber, and the metal fitting is an electric heating chamber. A high-frequency heating device that is fixed substantially perpendicularly to the axial direction of the heater, and has a length from the outer periphery of the electric heater to the outer periphery end surface of the metal fitting that is approximately 1/4 of the wavelength of the radio waves used. (2) The high-frequency heating device according to claim 1, wherein the metal fitting has a substantially rectangular shape and is screwed to the oven wall at three or more locations between the two poles of the electric heater and on the outside thereof. (3) The high-frequency heating device according to claim 1, wherein the metal fitting is provided with a screw hole and the metal fitting is fixed to the heating chamber by screwing from outside the heating chamber. (4) The high-frequency heating device according to claim 1, wherein the oven wall surface in contact with the metal fittings is stepped toward the metal fittings.