GB2126859A

GB2126859A - High-frequency heating apparatus

Info

Publication number: GB2126859A
Application number: GB08322012A
Authority: GB
Inventors: Nobuo Ikeda
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-17
Filing date: 1983-08-16
Publication date: 1984-03-28
Also published as: FR2532144B1; JPS5933792A; GB2126859B; FR2532144A1; DE3328734A1; CH661401A5; DE3328734C2; GB8322012D0; JPS6313317B2

Abstract

High-frequency heating apparatus comprises a heating chamber for receiving a heating load, a high- frequency oscillator for feeding high- frequency waves to the heating chamber, and a door adapted to open and close a front opening of the heating chamber. The circumferential movement of a glass plate (15) which covers a see-through window of the door is controlled solely by the corners of a groove in the door for holding the glass plate. Preferably, the radius of curvature (R1) of the corners of the groove is greater than the sum of the radius of curvature (R2) of the corners of the glass plate and the clearance of the groove. <IMAGE>

Description

SPECIFICATION High-frequency heating apparatus The present invention relates to high-frequency heating apparatus and has particular reference to the door arrangement of such apparatus.

Conventionally, the door of high-frequency heating apparatus, such as a microwave oven, is provided with a see-through window for visual inspection of the progress of cooking of food in the heating chamber during cooking. To prevent high-frequency waves from leaking through the see-through window, a punched plate in the form of a metal plate having a number of small holes formed therein is used for the window. Further, to prevent particles of food from clogging the small holes of the punched plate, there is provided a cover in the form of a glass plate.Usually, this glass cover plate is held in a groove defined by the punched plate and the inner wall of the door, but since the dielectric constant of glass is higher than that of air, as is know in the art, the effective depth D' of the groove with the glass fitted therein is D. Thus, the depth becomes substantially greater than when there is no glass.

Accordingly, the effective dimension from the terminal end of the groove to the inlet approaches 1/4 of a wavelength to be used, with the result that the strength of the electric field at the inlet increases, tending to produce sparks and abnormal temperature rises at the inlet of the groove.

To solve this problem, it is necessary that the groove be as shallow as possible, but the shallowness is limited because of problems of fabrication and design.

There is therefore a need for high-frequency heating apparatus which eliminates the aforesaid drawback of the prior art and which has the quality and consistent reliability to prevent occurrence of abnormal heating and sparking in the glass holding groove.

According to the present invention there is provided high-frequency heating apparatus comprising a heating chamber, a high-frequency oscillator for feeding high-frequency waves to the heating chamber, and a door adapted to open and close a front opening of the heating chamber, wherein the transverse movement of a glass plate which covers a see-through window of the door is controlled solely by the corners of a groove in the door which is provided for holding the glass plate.

In the sides of the groove, the glass plate can be fixed in position without having to insert the glass plate deep into the groove, so that the effective depth of the groove with respect to highfrequency waves approaches the mechanical depth and becomes reduced and hence the strength of the electric field at the inlet of the groove becomes lower, thus preventing sparking and abnormal heating.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of high-frequency heating apparatus according to an embodiment of the present invention; Fig. 2 is a sectional view of a door region of the said apparatus; and Fig. 3 is a plan view of the door region.

Referring now to the drawings, there is shown in Fig. 1 a main body 1 internally provided with a heating chamber 2 having a front opening which is openable and closable by a door 3. The numeral 4 denotes an operating panel provided with fluorescent display lamps 5 used to give a display of timer settings and output settings, program selection keys 6, a start button 7, and a cancel button 8. The numeral 9 denotes the inner wall of the door forming a portion of a choke wall formed on the door 3 and 10 denotes a window for seethrough inspection.

In Fig. 2, the numeral 11 denotes a choke groove having a depth equal to about 1/4 of a wavelength to be used. The choke groove 11 is defined by the inner wall 9 of the door, the outer wall 12 of the door, and a separate metal member 1 3 connected to the inner wall as by spot welding. The numeral 14 denotes a punched plate formed with a number of small holes to form the peep window, and 1 5 denotes a glass plate for preventing particles of food from clogging the small holes. The numeral 1 6 denotes another glass plate provided at the outside of the door 3, and 1 7 denotes a handle to be grasped in opening and closing the door 3.

The assembly of inner door wall 9 and separate metal member 13 is screwed to the outer wall 12 of the door, and the punched plate 14 and glass plate 1 5 are clamped and fixed therebetween.

The numeral 1 8 denotes a gasket which prevents cracking of the glass and leakage of heat and vapour emanating from the food being cooked.

in addition, since the surface of the glass plate 1 6 is formed with a coating 19, said screwed portion is hidden and cannot be seen from the surface.

A clearance d is formed between the glass plate 1 5 and the separate metal member 13 which controls the circumferential movement of the glass plate, while the circumferential movement of the glass plate 1 5 is controlled by making the radius of curvature R1 of separate metal member greater than the curvature R2 of the glass plate 1 5, as shown in Fig. 3.The reason why the positional control of the glass plate 15 must be effected solely by the corners and why the clearance d must be provided between the end surface of the glass plate 15 and the separate metal member 13 in each side is as follows: Spot welding the separate metal member 1 3 to the inner door wall 9 makes it necessary to make some allowance (about 7mm) for the spot welding, and if to this are added an allowance for accommodating dimensional variation and the thickness of the plate, the depth of the groove for receiving the glass plate 1 5 is about 9 mm, but if the glass plate 1 5 is inserted fully into this groove, the effective depth D' with respect to high-frequency waves is D'=9 .20 mm, approaching A/4, so that abnormal heating takes place at the inlet of the groove.This problem could be solved by decreasing the depth of the groove, but the groove cannot be made shallower in consideration of the need for spot welding. If, instead, the dimension of the glass plate 1 5 is made 3 mm, the effective depth D' with respect to highfrequency waves is D'=3W+6=12.7 mm, which is sufficiently small for A/4, so that abnormal heating at the inlet of the groove can be prevented.

Simply providing the clearance d between the separate metal member 1 3 and the glass plate 1 5 would not be effective to control the position of the glass plate, but this positional control of the glass plate 15 can be attained by making the radius R, of the corners of the member 1 3 greater than the sum of the radius R2 of the plate 1 5 plus the clerance d between the plate 1 5 and the member 13. Although the glass plate 1 5 enters the groove fully only at the corners, in these areas there is no possibility of abnormal heating.

In the case of heating apparatus according to the said embodiment of the invention, the following effects can be obtained: (1) Even if the depth of the groove for holding the glass plate is given the structurally necessary value, occurrence of sparking and abnormal heating at the inlet can be prevented.

(2) The glass plate only partially enters the groove, and the depth can be set to an effective value sufficiently greater than the value at which abnormal heating, etc. would occur, so that even if there is some variation in the size of the glass plate and of the separate metal member, consistent quality can be ensured.

(3) Although the glass plate enters the groove only partially in the sides, the circumferential positional control on the glass plate is effected at the corners, so that there is no danger that the glass plate is displaced to one side to cause sparking, abnormal heating, etc.

(4) Since there is no need to insert the glass plate fully into the groove, the size of the glass plate can be decreased and hence the cost of the glass plate can be decreased by the corresponding amount.

Claims

1. High-frequency heating apparatus comprising a heating chamber for receiving a heating load, a high-frequency oscillator for feeding high-frequency waves to the heating chamber, and a door adapted to open and close a front opening of the heating chamber, wherein the circumferential movement of the glass plate which covers a see-through window of the door is controlled solely by the corners of a groove in the door for holding the glass plate.

2. Apparatus as claimed in claim 1, wherein the radius of curvature of the corners of the groove is greater than the sum of the radius of curvature of the corners of the glass plate and the clearance of the groove.

3. High-frequency heating apparatus substantially as hereinbefore described with reference to the accompanying drawings.