The invention relates to a cooking device door according to the preamble of claim 1.
Cooking devices generally have a cooking area located in a housing which can be closed using a cooking device door. DE 196 38 241 A1 discloses a cooking device and specifically a baking oven with a genre-forming cooking device door having a viewing window, made of glass ceramic for example, on the side oriented in the direction of the cooking area. The viewing window completely covers an opening of the cooking area and forms a contact surface with a contact flange or extends beyond a seal. Such viewing windows are also called full-surface viewing windows. A metal frame encompassing the viewing window can be dispensed with and dirty edges caused thereby on the inside of the viewing window facing the cooking area can be avoided. In addition, a large field of view can be achieved.
A disadvantage however, is that as a result of transverse heat conduction inside the viewing window, heat and therefore thermal energy can be transferred from the cooking area outwards via the contact surface. This firstly results in a loss of heat and secondly, in cooking devices with a pyrolytic self-cleaning unit, this can lead to residual contamination in the area of the contact surface between the viewing window and the contact flange and specifically because as a result of the transverse heat conduction, the temperature of the viewing window decreases to such an extent in the direction of transverse heat conduction to the contact surface that the temperature falls below that required for the pyrolysis process in this area. In order to reduce the transverse heat conduction in the area of the contact surface, cooking devices are known wherein the housing of the cooking device is heated by additional heating elements in the area of the contact surface of the cooking device door. Another disadvantage is that full surface viewing windows according to the prior art are made of high-quality special glasses, e.g. glass ceramic in order to avoid fracture of the glass as a result of high thermal stresses during pyrolytic operation.
The object of the invention is to further develop a generic cooking device door and specifically an advantageous thermal insulation should be achieved with a design that is both simple and space saving.
The object is achieved according to the invention by the features of claim 1 while advantageous developments and refinements of the invention can be deduced from the dependent claims.
The invention relates to a cooking device door which has a viewing window on the side facing towards a cooking area which is located in a housing of a cooking device, said viewing window completely covering an opening of the cooking area and forming a contact surface with a contact flange.
It is proposed that the viewing window has a recess oriented in the direction of the cooking area, at least in one area. Advantageous thermal insulation in the inner hot area can be achieved by means of an enlarged insulating space or window distance in an overall especially space-saving design. Loss of heat via the cooking device door can be reduced and energy can be saved.
The cooking device door according to the invention can also be used especially advantageously in cooking devices with a thermal self-cleaning unit. The recess oriented in the direction of the cooking area can be heated more strongly and an advantageous cleaning result can be achieved. By means of improved insulation, a temperature gradient and associated thermal stresses can be reduced in the area of the recess. In a flank area of the recess in which a relatively high temperature gradient occurs, a spring effect can be achieved by sloping flanks by which means stresses in the glass can be equalised. As a result of the reduced stresses in the area of the recess and the stress equalisation made possible by the spring effect, it is possible to use economical materials such as especially borosilicate glass, soda lime glass etc. However, glass ceramic could also be used with the loss of the cost advantage.
The viewing window especially advantageously has only one recess extending over a major part of the opening of the cooking area. With a large-area recess, the largest possible area having an especially advantageous insulation, an especially advantageous cleaning result in a pyrolysis process and low stresses can be achieved in a simple design and at low cost. The recess advantageously has a distance of less than 4 mm at the side and at the bottom, especially in the case of a cooking device door pivoted about a lower axis, a distance of less than 6 mm from the contact flange. An extremely small external area excluded from a pyrolysis process can be achieved.
Moreover, especially by means of a smallest possible distance from the contact flange a labyrinth effect can be achieved and specifically with regard to dirt constituents and with regard to heat or hot gases. The outer cooler area can be shielded from dirt constituents and hot gases whereby contamination of the outer area can be reduced and burning of dirt constituents in the outer area can be avoided by a high temperature but not sufficient for a pyrolysis process. Moreover, low temperatures can be achieved in the area of the contact flange or in the area of a seal whereby economical sealing materials can be used, such as especially silicone etc. Instead of one large recess, it is however fundamentally also feasible to have a plurality of individual and/or one ring-shaped recess extending along the contact flange. Especially by means of recesses extending along the contact flange and by means of a ring-shaped recess extending along the contact flange, it is possible to achieve an advantageous labyrinth effect and a stress-equalising spring effect. In addition to pivoted cooking device doors, the solution according to the invention can also be used for sliding oven doors with trays attached, wherein the recess should be located in the transverse direction within contact surfaces of hook rails.
The recess advantageously has a depth between 10 and 35 mm wherein good insulation can be achieved in this area with an acceptable space requirement. In particular, especially advantageous insulation can be achieved with a depth of 35 mm and the insulation shows merely an insignificant improvement from a depth of 35 mm. Moreover, the recess advantageously possesses flanks with an angle between 90° and 55°. An especially effective labyrinth effect and spring effect can be achieved with a steep angle.
In a further development of the invention it is proposed that the viewing window is pre-stressed and especially by means of a thermal or chemical process advantageously with a compressive stress at its surface whereby the strength of the viewing window can be increased. In the outer cooler region the pre-stress and an associated high strength can always be maintained especially with regard to the heat by means of the attainable labyrinth effect.
The recess can be completely arched or it can advantageously have at least one flat area whereby this can be produced especially simply and economically without the view through the viewing window being affected thereby.
In order to further enlarge the insulating area or the distance between the inner viewing window and a second viewing window adjacent to the viewing window, facing away from the cooking area, without reducing the size of the cooking area, the second viewing window can advantageously be designed with a recess oriented in the direction away from the cooking area.
The solution according to the invention can be used in numerous cooking devices which appear logical to the person skilled in the art, but especially in cooking devices with a thermal self-cleaning unit, such as especially domestic baking ovens.
Further advantages are deduced from the following description of the drawings. An embodiment of the invention is shown in the drawings. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will more appropriately also consider the features individually and combine them into logical further combinations.
In the drawings:
FIG. 1 is a schematic front view of a domestic baking oven,
FIG. 2 is a view of a baking oven door of a domestic baking oven from inside,
FIG. 3 is a schematic view of a section along the line III-III in FIG. 1 and
Figure is a schematic view of a section along the line TV-TV in FIG. 1.
FIG. 1 shows a domestic baking oven which has a cooking area 11 in a housing 10. The cooking area 11 is bounded by a muffle 28 and has an opening 13 which is closed with a baking oven door (FIGS. 3 and 4). On its side facing towards the cooking area 11 the baking oven door has a viewing window 12 which completely covers the opening 13 of the cooking area 11 and forms a contact surface 27 with a contact flange 16 of the muffle 28 and specifically with a silicone seal 29 affixed to the contact flange 16. The contact surface 27 is shown by a dashed line in FIGS. 1 and 2. The viewing window 12 can be cleaned by means of an inherently known thermal self-cleaning unit or pyrolytic unit located in the housing 10 of the domestic baking oven.
According to the invention, the viewing window 12 is constructed as bowl-shaped and has a recess 14 oriented in the direction of the cooking area 11, which extends over a major part of the opening 13 of the cooking area 11 and has a distance 15 of 2 mm at the side, a distance 17 of 2 mm at the bottom and a distance 18 of 4 mm at the top from the contact flange 16. As a result of the small distances 15, 17, 18 from the contact flange 16, there is an advantageous labyrinth effect towards the outside with respect to dirt constituents and heat or hot gases. The recess 14 has a depth 19 of 30 mm and lateral flanks 21 having an angle 23 of 70° and flanks 20 at its top and bottom having an angle 22 of 80°. After its flanks 20, 21 the recess 14 has a flat area 24 which forms a major part of the recess 14. The viewing window 12 can additionally have a heat-reflecting coating and/or suitable printing which specifically impedes the transparency of the window.
The recess 14 is moulded onto the viewing window 12. In a first step the viewing window 12 is placed on a plate having an indentation corresponding to the recess and is heated in its flank area by means of heat sources until a flowable state is established. In a second step the area forming the recess 14 is then sucked into the indentation of the plate by means of vacuum. The viewing window 12 is made of borosilicate glass and is thermally pre-stressed at its surface by means of compressive stresses.
- REFERENCE SYMBOLS
In addition to the inner viewing window 12, the baking oven door has two further viewing windows 25, 30 and specifically a central viewing window 25 and an outer viewing window 30 facing away from the cooking area 11. The viewing windows 12, 25, 30 are held together by means of a support not shown in detail and are interconnected in an almost airtight fashion by means of plastic seals 31, 32. The central viewing window 25 has a recess 26 oriented in the direction away from the cooking area 11, having approximately the same height and width as the recess 14. By means of the recess 14 and the recess 26 an advantageous insulating space 33 is formed between the viewing disks 12, 25. The central viewing disk can alternatively also be constructed as completely flat or it can be omitted if the temperature requirements are reduced.
- 10 Housing
- 11 Cooking area
- 12 Viewing window
- 13 Opening
- 14 Recess
- 15 Distance
- 16 Contact flange
- 17 Distance
- 18 Distance
- 19 Depth
- 20 Flank
- 21 Flank
- 22 Angle
- 23 Angle
- 24 Area
- 25 Viewing window
- 26 Recess
- 27 Contact surface
- 28 Muffle
- 29 Silicone seal
- 30 Viewing window
- 31 Seal
- 32 Seal
- 33 Insulating space