EP0053189A1

EP0053189A1 - Heat cooking oven

Info

Publication number: EP0053189A1
Application number: EP81901507A
Authority: EP
Inventors: Mitsuo Akiyoshi
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1980-06-04
Filing date: 1981-06-03
Publication date: 1982-06-09
Also published as: WO1981003536A1; AU7226681A; EP0053189A4

Abstract

A heat cooking oven for heating the atmosphere in a heating chamber (5) by an electric heater to a high temperature for cooking food. The electric heater has a heating element (1) in a container (3) and the lead part (11) of a lead wire (2) as sealed at the container in such a manner that the lead part (11) is disposed within the chamber (5) and is projected out of the chamber (5). Since the element (1) is sealed in the container (3), it can be prevented from oxidizing and can heat at high temperature, thereby accelerating the cooking speed. Since the sealed lead part (11) is cooled by the outer atmosphere and retained at a low temperature, this invention can prevent damage to the lead wire due to the difference of thermal expansion coefficients between the container (3) and the lead wire (2) and can prolong its lifetime.

Description

TECHNICAL FIELD

This invention relates to a cooking appliance having a heating chamber adapted to have its atmosphere heated to high temperature for cooking food therein and more particularly it relates to a cooking appliance characterized by high cooking speed, energy saving and long heater life.

BACKGROUND ART

A conventional cooking appliance having a heating chamber adapted to have its atmosphere heated by an electric heater to high temperatures for cooking food therein uses as said electric heater a sheathed heater or a heater having a heater coil enclosed in a heat-resistant insulating material, such as quartz tubes, or the so-called quartz tube heater. Both of said heaters, however, have their heat- generating sections exposed to the air, so that if heated to very high temperatures, they would be damaged by oxida- .tion; it has heretofore been impossible to heat the heat- generating sections to temperatures above 1,000°C. Therefore, it takes much time for the atmosphere in the heating chamber to reach a high temperature, lowering the cooking speed, and the energy loss involved has been very large.

DISCLOSURE OF THE INVENTION

Accordingly, this invention.provides a cooking appliance characterized by high cooking speed, energy saving and long heater life.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a frount view of a cooking appliance, showing an embodiment of the present invention;
Fig. 2 is a front view, in section, of said cooking appliance;
Fig. 3 is a sectional view of the principal portion of said cooking appliance;
Fig. 4 is a sectional view of the principal portion.of a cooking appliance according to another embodiment.of the invention; and
Fig. 5 is a perspective view of the principal portion of Fig. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

In Figs. 1 through 5, a filament 1 made of a high melting-point material, such as tungsten, used as a heater has lead-out wires 2, such as molybdenum wires, fixed to the opposite ends thereof, said filament 1 and lead-out wires 2 being housed in an elongated container 3 made of a heat-resistant. insulating material, such as quartz and crystallized glass. One end of each of said lead-out wires 2 is led out of each end of said container 3, and the container 3 is constricted as shown at a lead-out portion 11 to provide a seal construction.
In addition, the lead-out wires 2 led out of the container 3 each have a lead wire 4 connected thereto. The container 3 has an inert gas, such as argon, enclosed therein after evacuation, so as to prevent oxidation of said filament 1. A heating chamber 5' is divided by a partition net 5' into a main heating chamber 7 for receiving a food 6 and an auxiliary heating chamber 8 for receiving said container 3, and the partition net 5' has a number of openings of such a size that the net allows passage of infrared rays but blocks high frequency electromagnetic waves. The partition net 5' is disposed close to the container 3 and heavily irradiated with the radiant heat from the filament 1, so that it thermally expands to a large extent. Particularly, repetitive energization and deenergization of the filament 1 subjects the net to local deformation, particularly in prolonged operation, causing the net to rent or tear. If the partition net 5' tears, the high frequency electromagnetic waves fed from a magnetron 9, used as an example of a high frequency oscillator, to the main heating chamber 7 enter the auxiliary heating chamber 8, causing not only spark breakage to the filament 1 but also leakage of high frequency electromagnetic waves into the outside of the heating chamber 5, which is a .serious problem.
Accordingly, in this embodiment of the invention, the opening-defining edges 5A of the partition net 5' extending along the container 3 are bent into wave form, as shown in Fig. 5. Thus, since the partition net 5' is subjected to thermal expansion due to the heat from the filament 1 and since it is fixed at both ends thereof to the walls of the main heating chamber 5, bending stress is produced in the partition net 5', but this stress is distributed among the many bends or curves, so that the deformation. of each bend can be minimized. As a result, the danger of the partition net 5' being torn or otherwise damaged, is eliminated, and so is the danger of leakage of high frequency electromagnetic waves. Further, the opposite walls of the auxiliary heating chamber 8 are each provided with a hole 8A for the opposite ends of said container 3 to extend therethrough. The lead-out portions 11 of the lead-out wires 2 at both ends of the container 3. project outside the heating chamber 5 through said holes 8A. The diameter of the holes 8A is larger than the outer diameter of said container 3 to give a generous allowance. In addition, said magnetron 9 and main heating chamber 7 are connected together by a wave guide 10.
With the cooking appliance arranged in the manner described above, a food 6 put in the main heating chamber 7 is first dielectrically heated in the interior by the high frequency electromagnetic waves from the magnetron and then it can be done to a beautiful brown in a short time by the radiant heat from the filament 1, which can be heated to a high temperature as soon as it is energized through the lead wires 4 and lead-out wires 2. Since the filament 1 is heated to as high a temperature as 1,500°C or above, the temperature of the container 3 rises to about. 900°C or above and the upper surface of the auxiliary heating chamber 8 and the partition net 5' rise in temperature to 500°C or above.
This brings about a big problem that the difference in thermal expansion coefficient between the container 3-and the lead-out wires 2 causes damage to the lead-out portions 11 at which said container 3 and lead-out wires 2 contact each other, resulting in the outside air-entering the container 3 to cause oxidation of the filament 1. However, according to the present embodiment, since the lead-out portions 11 project outside the auxiliary heating chamber 8, they are cooled by the outside-air and thereby maintained at low temperature, thus prolonging the service life of the filament 1. Also, since the lead-out wires 2 do not generate heat, the temperature therearound is-low and, although it is rather difficult to provide a sufficient insulating distance between the same and the wall of the auxiliary heating chamber 8, the temperature is such that the insulating requirement for the container- 3 is met.
Qualtz or crystallized glass, which is a material of which the container 3 is made, rarely develops thermal expansion even at a temperature of as high as about 1,000°C, but the stainless steel or other metal plates generally used for the walls of the auxiliary heating chamber 8 develop largo thermal expansion even at a temperature of as low as about 500°C. Therefore, in the present embodiment, with consideration given to such properties, opposite walls of the auxiliary heating chamber 8 are formed with holes 8A for receiving the container 3 therein, as previously described, so that even if the width of said auxiliary heating chamber 8 changes owing to heat, there is no danger of excessive force acting on the container 3 to damage the latter.
Opposite end portions of the container 3, as shown in Fig. 3, extend through a double wall structure comprising a first heat insulating plate 12 of metal'and a second heat insulating plate 13 of metal, with a heat insulating elastic body 14 being provided therebetween for holding the container 3. Further, the distance.between said first and second heat insulating plates 12 and 13 is about 1/4 of the wave length λg of the high frequency electromagnetic waves in the heating chamber 5, thus forming a portion of high impedance to high frequency electromagnetic waves. More particularly, even if said partition net 5' fails to block electromagnetic waves and the latter enter.the auxiliary heating chamber 8, the heat insulating plates 12 and 13 spaced a distance of λg/4 apart selectively block them, preventing them from escaping outside the-auxiliary heating chamber 8, thus providing increased safety. The two heat insulating plates 12 and 13, together with the elastic body 14, also serves to prevent the hot air.in the auxiliary heating chamber 7 and main heating- chamber 7 from escaping outside the heating chamber 5, thereby increasing the efficiency of heating the food 6, making speedy cooking possible. They also prevent oil smoke and other gases from the food 6 from entering the machine chamber.in which the magnetron 9 and the like are installed. As a result, possibilities of insulation failure are precluded.
In addition, if metal pipes 12A are provided between the insulating plates 12 and 13 to extend along the container 3, as shown in Fig. 4, a perfect λg/4 choke construction is formed, heightening the high frequency electromagnetic wave leakage preventing effect.
In addition, the front opening in the heating chamber 5 is adapted to be opened and closed by the door 15 and the heating chamber 15 is contained in a body case 16.

INDUSTRIAL APPLICABILITY

As described hereinbefore, according to the present invention, since the heater is sealed in the container, there is no possibility of said heater being oxidized and hence the heater can be heated to a very high temperature so as to quickly elevate the temperature of the atmosphere in the heating chamber and cooking can be accelerated with the intense radiant heat, achieving the corresponding amount of energy saving.
Further, since the portions of the lead-out wires which are led out of the container extend outside the heating chamber, there is no danger of said lead-cut portions being damaged to allow entry of air into the container and hence there is no possibility of the heater being oxidized. As a result, the service life of the heater is very long.

Claims

1. A cooking appliance comprising a heating chamber for receiving food,. a container of sealed construction disposed inside said heating chamber, a heater disposed inside said container, and lead-out wires connected to said heater and having the other ends thereof led out of said container, wherein said lead-out portions of said lead-out wires led out of said container extend outside said- heating chamber.

2. A cooking appliance as set forth in Claim 1, wherein said container-is in the form of an elongated straight tube, through the opposite ends of which said lead-out wires are led. out.

3. A cooking appliance as set forth in Claim 2, wherein the portions of said straight tube which extend outside said heating chamber are supported by elastic bodies.

4. A cooking appliance as set forth in Claim 1, including a high frequency oscillator for supplying high frequency electromagnetic waves to the. heating chamber.

5. A cooking appliance as set forth in Claim 4, wherein said heating chamber is partitioned by a partition net to provide a main heating chamber which is supplied with the high frequency electromagnetic waves and an auxiliary heating chamber in which said container is installed, said partition net having a plurality of openings having such a size as to allow passage of infrared rays but prevent passage of the high frequency electromagnetic waves.

6. A cooking appliance as set forth in Claim 5, wherein- the opening-defining edges of said partition net are bent.

7. A cooking appliance as set forth in Claim 4, wherein said container is in the form of an elongated straight tube, which extends through two heat insulating plates into the heating chamber, the distance between said heat insulating plates being 1/4 of the wave length of the high frequency electromagnetic waves in the heating chamber.

8. A cooking appliance as set forth in Claim 7, including.elastic bodies for supporting the ends of the straight tube.

9. A cooking appliance as set forth in Claim 4, wherein the container is in the form of an elongated straight tube and the portions of said straight-tube extending outside the heating chamber are provided with a choke construction.

LIST OF REFERENCE CHARACTERS IN THE DRAWINGS

1 ... Filament

2 ... Lead-out wires

3 ... Container

4 ... Lead wires

5 ... Heating chamber

5' ... Partition net

5A ... Net opening-defining edges

6 ... Food

7 ... Main heating chamber

8 ... Auxiliary heating chamber

8A ... Holes

9 ... Magnetron

10 ... Wave guide

11 ... Lead-out portions

12 ... First heat insulating plates

12A ... Metal pipes

13 ... Second heat insulating plates

14 ... Elastic bodies

15 ... Door

16 ... Body case