GB2076530A

GB2076530A - A High Frequency Heating Appliance

Info

Publication number: GB2076530A
Application number: GB8114796A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-28
Filing date: 1981-05-14
Publication date: 1981-12-02
Also published as: FR2485676A1; DE3116664A1; NL189894B; SE8102647L; FR2485676B1; NL8102279A; JPS6116637Y2; DE3116664C2; NL189894C; CH658562A5; GB2076530B; JPS56173907U; SE449131B

Abstract

A high frequency heating appliance comprises in its main body a heating chamber (10), a high frequency oscillator (14), a hot air circulating fan (12), a door (6) for opening and closing an access opening in the front wall of the heating chamber (10) and a gasket (19), interposed between surface portions of the front wall which surround the access opening, and the door (6) to reduce leakage of heat and high frequency radiation. The gasket (6) comprises an interwoven mixture of heatproof dielectric fibre (20), such as glass fibre, and fibrous corrosion- resistant metal (21) such as fibrous stainless steel. <IMAGE>

Description

SPECIFICATION A High Frequency Heating Appliance The present invention relates to a high frequency heating appliance of the type which in its main body comprises a heating chamber, a high frequency oscillator and a door for opening and closing an access opening in a front wall of the heating chamber.

In a high frequency heating appliance of that kind, and more particularly when provided with a combustion self-cleaning feature, it is necessary to keep the interior of the heating chamber at about 5000C during the cleaning operation. A gasket made of woven glass fibre is often used to prevent heat from leaking out between the door and the front wall of the heating chamber.

However, in the case where a dielectric member, such as a glass fiber gasket, is inserted between the front wall of the heating chamber and the door, the thickness of the dielectric member amounts to 3 to 4 millimetres or more so that an increased amount of high frequency radiation may leak therethrough. A gasket made of glass fibre surrounded by metallic wires or ribbons and a gasket of woven glass fiber covered with a mesh or metal wires are both known.

The first of these two kinds of gasket however had the disadvantage that when the metallic wires were wound around the glass fiber and woven into the gasket, the metallic wires themselves tended to sink into the glass fibre due to the tension of knitting because the metallic wires were thin and relatively rigid compared with the soft glass fiber. No or only very few metallic wires appeared on the surface of the completed mixture. By increasing the number of the metallic wires or using metallic ribbons, a small number of the metallic members appeared on the surface, but failed to give satisfactory results in reducing the leakage of high frequency radiation. The gasket became rather stiff as a whole and less flexible so that it was hard to bend to conform to a surface of the door.

When the gasket was more than 10 millimetres thick and highly flexible, a gasket of the second kind was able to reduce the leakage of heat and gases expelled during self-cleaning to some extent. Since a choke, which was provided as a measure to seal high frequency radiation, usually did not permit the gasket to be thick enough, the gasket in itself was less flexible consequently with greater likelihood that heat and gases would leak readily even though the gasket was covered by the metallic net. In view of the foregoing, it is desirable for such a gasket to be highly flexible, for the stitch of the gasket to be fine enough to seal off gases and heat, for its surface to be electrically conductive and for it to be soft and flexible so as to conform to the door.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a high frequency heating appliance embodying the present invention, Figure 2 is a cross-sectional view of the appliance in side elevation, and Figures 3 and 4 are enlarged cross-sectional views of an essential feature of the appliance.

Referring now to the drawings, figure 1 shows a heating appliance in the form of an electric cooker of the built-in type for four electric heating elements 1 on its top for cooking purposes. The electric heating elements 1 are controlled by knobs 2 on a front panel of the heating appliance, which panel also carries control knobs 3 for operation of an oven of the heating appliance.

Ventilating apertures 4 for cooling air are provided below the control panel and above a door 6 provided with a handle 5. A drawer 7 is provided below the main body of the heating appliance for receving attachments or other small articles.

Referring now to figure 2, the door 6 is mounted to be slidable on a rail 8. The door 6 is provided at its inner face with a shelf 9 on which food or the like may be carried.

It is thus very convenient to introduce and remove food, since the shelf 9 pulls out with the door 6. The oven is formed by a heating chamber 10, which is provided with an upper heater 11 substantially parallel with the top wall of the oven and a lower heater 11' at the outer bottom wall of the oven for heating or cooking food.

A hot air circulating fan 12 is installed behind the heating chamber 10 to render the temperature distribution more uniform within the heating chamber. A heat insulator 1 3 is provided on the periphery of the heating chamber 10 to reduce loss of heat through the outer walls of the heating chamber and promote a higher degree of efficiency. A high frequency oscillator 14, such as a magnetron, is adapted to supply high frequency energy through a Z-shaped waveguide 15, one end of which is in communication with a feeding aperture 1 6 formed substantially in the center of the top wall of the heating chamber 10. A rotary antenna 1 7 extends through the feed aperture 1 6 and directs high frequency energy from the waveguide 1 5 towards the interior of the heating chamber.

A cooling fan 32 for the magnetron 14 is adapted to draw and discharge air through an air guide 33 and the ventilating apertures 4.

A choke 18, which has a groove equal in depth to a quarter of the wavelength of the high frequency radiation, is secured on the door 6 for reducing leakage of high frequency radiation.

A gasket 1 9 is disposed outside the choke 1 8 for reducing leakage of heat and high frequency radiation from inside the heating chamber. The gasket 1 9 comprises an interwoven mixture of glass fibre 20 and fibrous stainless steel 21 in a suitable proportion as best shown in Fig. 4.

Because of both the components being fibrous, the mixture neither becomes too stiff nor loses flexibility even when the proportion of the stainless steel is increased. The mixture is therefore easy to handle in fixing the gasket to the door and efficient in reducing leakage of heat.

Furthermore, since the metal material does not creep into the glass fibre, only a small amount of stainless steel is required to insure good surface conductivity as well as provide excellent shielding of high frequency energy. In the event that wires, ribbons or the like are used to provide comparable shielding, a substantial amount of metal would be required at consequently increased cost. The aforedescribed device on the other hand provides inexpensive, yet excellent high frequency shielding. Moreover, wires or the like may become deformed or broken after a relatively short working life through repeated opening and closing of the door. However, in the case of the fibrous stainless steel, the gasket is better able to provide a stable performance over the whole operating life of the appliance.

Claims

1. A high frequency heating appliance comprising a heating chamber, a high frequency oscillator, a door for opening and closing an aperture providing access to the heating chamber and a gasket, which is interposed between the door and external surface portions around the aperture to reduce leakage of heat and high frequency radiation and which comprises an interwoven mixture of heat-resistant dielectric fibre of low thermal conductivity and fibrous corrosion-resistant metal.

2. A high frequency heating appliance as claimed in claim 1, wherein the dielectric fibre comprises glass fibre.

3. A high frequency heating appliance as claimed in claim 1, wherein the metal comprises stainless steel.

4. A high frequency heating appliance substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.