EP1470371B1 - Domestic electric oven - Google Patents

Abstract

The present invention relates to a domestic electric cooking oven (1) comprising an enclosure (2) defined by two side faces (4a, 4b), a top face (4c), a bottom face (4e), and a rear face (4d), main heater means of the radiant type that emit essentially in the infrared arranged inside the enclosure (2), said oven (1) including a cabinet (16) surrounding the major portion of the enclosure (2) over the side faces (4a, 4b) and the top face (4c), the front face of the oven being fitted with a door and with a control panel, the oven (1) being characterized in that it includes means for limiting heating of the oven cabinet (16), selected from the following: confinement by partitioning the space between the top (4c) of the enclosure (2) and the top portion (18c) of the cabinet (16); a reflector (20); no ventilation openings in the cabinet (16); and a metal face plate (28) disposed substantially over the door, and connected to the cabinet (16) by an insulating rod (30).

Description

The present invention relates to electric oven-type cooking appliances enclosing a cooking chamber inside which are arranged radiant type heating means, essentially in the infrared. The present invention relates in particular to ovens that can be placed on a table, as opposed to so-called "built-in" ovens.

An oven of this type is known from US-A-3828163 which forms the preamble of claim 1.

The ovens are kilns of very variable capacity, ranging from about 10 liters to nearly 40 liters, but all generally have cooking temperatures of up to 250 ° C inside the cooking chamber . The present invention relates to furnaces comprising means for heating the air of the enclosure and food therein by heating elements radiating in the infrared, which can be completed by means of stirring the air . Such furnaces thus see the temperature of their walls rise, as opposed to microwave ovens in particular.

This temperature constraint frequently causes the cooking chamber to be clad with a metal structure consisting of steel sheets that can be lacquered or enamelled externally and that constitute the outer casing of the oven. These plates becoming heated in turn represent a burn hazard for the user.

Efforts have already been made to protect the user from burns when handling the oven door. The document FR 2 732 097 describes in particular a baking oven door comprising a frame on which are mounted a glass inner wall and a plastic outer wall, said door comprising ventilation means between the two walls in order to reduce the temperature. of the outer wall.

However, in the case of furnaces placed on a worktop, the door is not the only source of potential burns. The same is true for the outer walls of the oven, easily accessible by the user or other people, especially children.

The present invention aims to reduce the risk of burn by contact of the outer parts of a household appliance operating by radiation and convection, using simple and inexpensive means.

The present invention is achieved with the aid of an electric cooking appliance having the characteristics of the characterizing part of claim 1.

By considerably reducing the temperature of the outer walls of the oven, users and their entourage are warned of the risk of burns by contact with the walls of the oven.

In addition, the lowering of the temperature of the furnace cladding makes it possible to use a material that is not very resistant to heat, a material that is generally of low cost.

Advantageously, the covering also covers most of the rear face of the cooking chamber. Indeed, although the rear face of the oven is less accessible than the side faces and the upper face, it is interesting that the covering also covers a significant portion of the rear face of the enclosure to minimize the risk of burns.

According to the invention, the means limiting the heating of the cladding of the furnace comprise a confinement by partitioning the space separating the vault of the enclosure from the upper part of the cladding.

The term containment must therefore be understood and interpreted as imprisonment or isolation of the volume of air between the vault of the enclosure and the roof of the covering.

This confinement can be obtained in different ways, including performing no ventilation opening in the cladding, especially at the roof and parts of the side walls located at and above the vault of the enclosure, thus minimizing air circulation.

Indeed, a flow of air in the volume between the vault of the enclosure and the roof of the casing causes an increase in the temperature of said roof, by mixing the air produced. In addition, hot spots are then generated at the openings of the cladding, locally increasing the temperature, and may lead to a degradation of the material used to achieve the cladding.

This closure of the space is however not waterproof but qualitatively means a maximum limitation of air exchanges with the outside. Thus, the residual openings of construction do not participate significantly in the heat exchange with the outside.

In addition, such an arrangement avoids the introduction of foreign bodies that could cause hygiene problems and / or thermal bridges between the enclosure and the cladding.

An improvement of this confinement of the space above the vault consists in providing a peripheral rim to the vault face of the enclosure.

Advantageously, a heat shield is disposed in the confinement space, between the upper part of the casing and the vault of the enclosure, making it possible to further reduce the temperature of the roof of the casing. In order to reinforce its action, the heat shield covers at least the entire surface of the vault of the enclosure.

Advantageously, the heat shield has vertical walls inclined downwards and extending, at the side faces and the rear face, to the cladding of the oven, thus creating a double partitioning of the air , on the one hand between the vault of the enclosure and the heat shield, and on the other hand between the heat shield and the cladding of the oven.

The extension of the heat shield along the vertical rear and side faces of the casing thus makes it possible to further protect said walls against excessive heating, thus reducing their temperature. The risk of burns are thus reduced.

According to one embodiment of the invention, a spacer made of a material of low thermal conductivity (for example less than 1 W m ^-1 K ^-1 ) is arranged substantially in the middle of the heat shield extending from both sides. other of said screen, perpendicular to it, on the one hand to near the vault of the enclosure, and other by up to the dressing.

This spacer thus makes it possible to keep a minimum distance between, on the one hand, the vault of the enclosure and the heat shield, but also between the roof of the covering and the said heat shield.

It also allows, especially when the furnace chamber is large, to constitute a mechanical reinforcement and avoids creating an arrow, for example by the provision of a mass object on top of the furnace cladding.

Advantageously, a metal strip is disposed substantially vertically above the door, on at least the length of the cooking chamber, said strip being connected to the casing by an insulating ring.

The provision of a metal strip above the oven door makes it possible to locally absorb the rising heat of the oven at the door, thus generally constituting a thermal brake to the temperature increase of the cladding.

Although it is possible to achieve a dressing, above the door, having the characteristics mentioned above, for example by multiplying the heat shields, a simple solution may be to replace locally and on a shallow depth, the dressing by a metal wall which will allow to dissipate calories by acting as a safety valve since the calories will preferentially be exchanged with the outside by this headband, and without mixing air. This aspect is particularly important when the cooking is carried out with the door open, generating a significant heat flow upwards, directly above the door.

Advantageously, the metal strip has thin openings to promote the exchange of calories between the inside of the enclosure and the outside and thus increase the thermal brake effect. These thin openings in the upper part and the front of the oven are however sufficiently thin and eccentric not to cause a consequent air mixing or air circulation.

The insulating rod has a local thermal brake function between the metal zone and the cladding. Advantageously, this ring is made of heat-resistant plastic, such as poly (butanediol-1,4 terephthalate), more commonly known as PBT.

"Heat-resistant" means a material with good mechanical properties, when its temperature increases, over a wide temperature range. The term technical plastic is commonly used to characterize such materials. One of the advantages of using PBT, from this point of view, is to keep a high Young's modulus up to temperatures close to its melting point. Moreover, PBT has a high rigidity.

Different properties make it possible to qualify the heat-resistant appearance of plastic materials. One can quote the temperature of deflection according to the standard NF T 51-005, the temperature of resistance to the ball according to the standard NF C 62-411, even the temperature of softening Vicat B according to standard NF T 51-021. Therefore, materials having high properties according to the cited standards will be preferred.

According to a preferred embodiment of the invention, the cladding of the oven is thermoplastic plastic type.

By using a thermoplastic material, such as for example polypropylene (PP), the costs of such a covering are considerably reduced, while offering more flexibility in the production of shapes and colors.

Furthermore, the use of a plastic material also brings the advantage of having a contact temperature between the skin and this material lower than it would be with a conventional enamelled or coated sheet cladding, for the same temperature. dressing. This is due to the difference between the effusivities PP and metal materials such as steel.

Thus, for the same temperature of the covering, the contact of the skin with this coating will be established at a lower temperature if the covering is made of PP rather than enamelled sheet or coated for example.

In addition, plastic allows easily automated molding operations that allow greater freedom in the design of the product.

• la figure 1 est une vue éclatée en perspective des différents éléments constitutifs du four selon l'invention,
• les figures 2 et 3 sont des vues partielles de la face avant du four,
• la figure 4 est une vue selon la coupe A-A de la figure 2,
• la figure 5 est une vue agrandie de la figure 4 selon le cercle indiqué.

The present invention will be better understood from the description which follows, with reference to the appended figures, among which:

• FIG. 1 is an exploded perspective view of the various constituent elements of the furnace according to the invention,
• Figures 2 and 3 are partial views of the front face of the oven,
• FIG. 4 is a view according to section AA of FIG. 2,
• Figure 5 is an enlarged view of Figure 4 along the indicated circle.

With reference in particular to FIG. 1, the oven 1 according to the present invention comprises, as is known, a cooking chamber 2 composed of five sheets defining faces 4a to 4e, said sheets being assembled forming an open parallelepipedal volume. in part before. A door, not shown, is disposed at this opening and closes the volume of the enclosure.

The lateral faces 4a, 4b comprise grooves 6 for the positioning of a cooking grate. The control portion of the oven, not shown, is adjacent to the face 4b, outside the enclosure.

The horizontal faces of the arch 4c and sole 4e respectively comprise embossed bosses 8 and 10 which make it possible to maintain heating resistors 32, visible in FIGS. 2, 4 and 5, at a distance from the surface of said faces. The sole bosses 10 further comprise hooks 12 for fixing the resistance. The arch face 4c is bordered by a peripheral rim 14, derived from either of said faces by folding or lateral faces.

This enclosure is arranged on a base, not shown, which may be metal or high temperature resistant PBT type plastic as previously explained. In a more economical variant, the base can be in PP with PBT supports.

According to one of the features of the invention, the oven comprises a casing 16 of the enclosure consisting of four walls 18a to 18d. One of the peculiarities of this dressing is to cover the faces of the cooking chamber, except the horizontal side of hearth 4e. Furthermore, this dressing has no openings or ears, as it is frequently encountered in the ovens trade. In particular, the face 18c forming the roof of the casing creates, with the rim 14 and the beginning of the vertical faces, a partition which creates a confinement of the space above the vault 4c of the enclosure. By thus avoiding cold air inlets from outside, it limits the circulation of hot air in contact with the vault of the enclosure, which would cause an increase in the temperature of the cladding.

The walls 18a and 18b have a return 19 to the front face of the oven, to hide the inner edges of the metal carcass while giving the oven a homogeneous shape.

This furnace covering is disposed on the base supporting the enclosure, by means of locking clips 40 which are positioned in suitable housings made in said base. In order to limit thermal transfers between the enclosure and the casing, the areas of contact between the enclosure and the base are spaced as far as possible from the fixing zones of the clips. In addition, the plate of the enclosure is cut at the contacts with the base to minimize thermal bridges between the enclosure and the base.

In an alternative embodiment, the base has significant vertical walls, further limiting the heat transfer from the base to the cladding.

To further limit the temperature rise of the casing, a heat shield 20 is disposed between the roof 4c of the enclosure and the roof 18c of the casing. This heat shield covers the entire surface of the vault of the cooking chamber and extends even beyond the wall 4b above the oven control part. This heat shield 20 also has parts folded at the ends of its four edges, and folded down. The lateral portions 22a and 22b, as well as the rear portion 22d, visible in FIGS. 2 and 3, are rather long and extend as far as the cladding, coming to be positioned on locking lugs 34. This enables them to protect effectively the respective walls 18a, 18b and 18d of the cladding by closing the hottest space at the upper part of the enclosure, while ensuring the correct positioning of the screen relative to the dressing.

The front portion 22c is shorter and is positioned against the rim 14 before, which allows a predetermined distance between the vault 4c of the enclosure and the heat shield 20 and reinforces the partitioning of the space between the reflector and speaker.

In addition a cylindrical spacer 24 is positioned in an opening 26 of the heat shield, substantially in the middle thereof. This spacer 24 has a recess in its diameter so as to have a bearing surface for its positioning on said heat shield.

The spacer 24 thus extends on both sides of the heat shield 20, in particular to come into contact with the roof 18c of the covering. A game is left with the vault 4c of the enclosure, essentially to avoid creating a thermal bridge with this surface which is raised to high temperature during operation of the oven. In addition, this game makes it possible to overcome the differences in tolerances on the parts, in order to ensure assembly of the cladding without deformation of said cladding and / or the heat shield.

In addition, this spacer serves to mechanically reinforce the roof 18c of the cladding and prevents a heavy object placed on the roof does not come to create a significant deformation of the dressing.

Usefully, this spacer is made of a material having a low thermal conductivity. A material such as plastic fulfills these conditions, having a thermal conductivity of the order of 0.2 - 0.3 W m ^-1 K ^-1 . However, this plastic will have to withstand high temperatures, since the contact with the vault of the enclosure is possible.

The reduction of heat exchange and the arrangement of the screen can significantly reduce the temperature of the coating, so that plastics, such as polypropylene (PP) can be used. The realization of such a dressing, by molding, is then possible, its monobloc form facilitating the mounting of the oven.

However, such materials having low melting points, it is then necessary to protect the hottest points when in contact with the metal parts of the cooking chamber or the heat shield. Thereafter, preference will be given to heat-resistant pads of thermoplastic or thermosetting material compatible with these temperatures and having a low thermal conductivity, for example less than 1 W m ^-1 K ^-1 . In the case presented, the heat shield descends sufficiently low along the enclosure so that it is not necessary to use a heat-resistant plastic, in particular for the realization of the support tabs 34 of the screen, made also in PP.

Advantageously, the cladding of the oven comprises a strip 28 at the base of the oven door. This strip is metallic and is connected to the plastic covering by two rods 30, 31 insulating.

Indeed, directly above the oven door, the temperature can increase suddenly and reach high values when the door is between open or when the seal is defective, or in the absence of seal. The limitation of the rise in temperature of the covering can then be achieved by multiplying the heat shields and increasing their quality.

However, it can be more economically interesting, without significantly altering the safety, especially with respect to the risk of burns, to have a metal strip at this location, which will thus raise the temperature and dissipate the calories to the outside. It is then necessary to isolate this strip of plastic parts of the furnace cladding. The rods 30 and 31, made for example of PBT, play this role of thermal brake. They also provide a mechanical link between the upper part of the plastic covering and the strip that can be linked to the cooking chamber.

The links between the ring and the strip and between the ring and the plastic covering are such that the number of contact points is limited to the number necessary to ensure the mechanical positioning without local creep of the materials at the points of contact, and thus limit the transfer by thermal conduction. Particular care should be taken to keep the points of contact between the strip and the ring of the points of contact between the ring and the covering as far as possible in order to minimize the heat transfer from the strip to the cover via the ring.

Moreover, as clearly visible in FIG. 5, the strip bears on and under the rim 14 on the front face of the oven, producing a recess 36 on which the door is pressed in the closed position. In this way, the calories escaping through the front face of the cooking chamber, not shown, are inevitably collected by said strip.

Figure 4 clearly shows that the spacer is used to maintain the heat shield 20 substantially midway between the vault 4c of the cooking chamber and the roof 18c of the cabinet.

Moreover, as is clearly visible in the figures, the roof 18c of the cladding is curved, which ensures a better mechanical stability of said cladding when it is brought to a certain temperature.

Advantageously, the wall of the reflector and the walls of the enclosure facing the cladding may be treated to minimize radiation emission, either by a mechanical treatment and / or a specific coating, as known in the art. field. It will be ensured that the thermal emissivity coefficient is less than 0.3 for the faces considered and for temperatures between 150 ° C and 300 ° C.

In operation, the heat generated by the heating resistors 32 is essentially reflected by the heat shield 20, or even partially absorbed by the metal strip 28 when it is present. The confinement of air at above the vault of the enclosure, significantly limiting air movement, including the reduction of air intake assembly leaks, can significantly reduce the temperature of the cabinet 16 of the oven.

Moreover, the latter being made of plastic, whose effusivity is much lower than that of steel, the contact temperature with the skin is considerably reduced, which further limits the risk of burns.

Indeed, the thermal effusivity of the steel is of the order of 14000 W m ² K ^-1 s ^1/2 . The PP has an effusivity of the order of 400 W m ² K ^-1 s ^1/2 , while that of the skin is close to 1800 W m ² K ^-1 s ^1/2 .

où T₁ et ε₁ (respectivement T₂ et ε₂) sont la température et l'effusivité thermique du solide 1 (respectivement du solide 2).It is shown that in steady state, the contact temperature is given by the expression: $$T=\frac{\left(T_1{\epsilon }_1+T_{\mathrm{two}}{\epsilon }_{\mathrm{two}}\right)}{\left({\epsilon }_1+{\epsilon }_{\mathrm{two}}\right)}$$

where T ₁ and ε ₁ (respectively T ₂ and ε ₂ ) are the temperature and the thermal effusivity of the solid 1 (respectively solid 2).

To illustrate this formula, consider two plates, one made of steel, the other of plastic, such as PP, these two plates being brought to 85 ° C. By estimating the temperature of the hand at about 37 ° C, the calculation according to the above formula results in a contact temperature between the hand and the steel plate of about 80 ° C, while this temperature of contact between the hand and the PP plate is just 46 ° C. So touching a steel plate raised to 85 ° C, so we have a burning sensation, feeling non-existent when the plate, raised to the same temperature, is plastic, such as PP.

This shows the interest of using a plastic material for the cladding of an oven and therefore the importance of reducing the temperature of the cladding to such an extent that it is possible to use a cheap plastic material for such dressing.

Claims (11)

1. A domestic electric cooking oven (1) comprising an enclosure (2) defined by two side faces (4a, 4b), a top face (4c), a bottom face (4e), and a rear face (4d), main heater means (32) of the radiant type that emit essentially in the infrared arranged in the enclosure (2), said oven (1) having a cabinet (16) surrounding the major part of the enclosure (2) over its side faces (4a, 4b) and its top face (4c), the front face of the oven being fitted with a door and a control panel, the oven (1) including means limiting the heating of the oven cabinet (16), and being characterized in that said means comprise confinement by partitioning the space between the top (4c) of the enclosure (2) and the top portion (18c) of the cabinet (16), and in that the cabinet (16) does not include any ventilation openings.
2. A domestic electric cooking oven (1) according to the preceding claim, characterized in that the cabinet (16) also covers the major part of the rear face (4d) of the cooking enclosure (2).
3. A domestic electric cooking oven (1) according to any preceding claim, characterized in that the top face (4c) of the enclosure includes a rim (14) contributing to confining the space between said top (4c) from the cabinet (16).
4. A domestic electric cooking oven (1) according to any preceding claim, characterized in that a heat screen (20) is disposed in the confinement space between the top portion of the cabinet (18c) and the top (4c) of the enclosure (2).
5. A domestic electric cooking oven (1) according to the preceding claim, characterized in that the heat screen (20) covers at least the entire surface of the top (4c) of the enclosure (2).
6. A domestic electric cooking oven (1) according to claim 4 or claim 5, characterized in that the heat screen (20) has vertical walls (22a, 22b, 22c, 22d) sloping downwards and extending over the side faces (22a, 22b) and the rear face (22d) as far as the cabinet (16) of the oven.
7. A domestic electric cooking oven (1) according to any one of claims 4 to 6, characterized in that a spacer (24) of material having low thermal conductivity is placed substantially in the middle of the heat screen (20) extending on either side of said screen, perpendicularly thereto, both to the vicinity of the top (4c) of the enclosure (2), and to the cabinet (16).
8. A domestic electric cooking oven (1) according to any preceding claim, characterized in that a metal face plate (28) is disposed substantially over the door, at least over the length of the cooking enclosure (2), said face plate (28) being connected to the cabinet (16) by an insulating rod (30).
9. A domestic electric cooking oven (1) according to the preceding claim, characterized in that the insulating rod (30) is made of a temperature-resistant plastics material such as PBT.
10. A domestic electric cooking oven (1) according to any preceding claim, characterized in that the cabinet (16) is made of a thermoplastic type plastics material, such as PP.
11. A domestic electric cooking oven (1) according to any preceding claim, characterized in that the metal face plate (28) includes fine openings.

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