EP3026349A1 - Cooking device component and method for producing same - Google Patents

Abstract

Cooking appliance component (1) and method for producing a cooking appliance component (1), in particular with a cooking chamber (2) suitable for carrying out pyrolysis and a component wall (3) delimiting the cooking appliance component (1), the component wall (3) being a metal substrate (4) comprising an enamel coating (5) at least partially applied thereto. The component wall (3) has a surface section (6) kept free from the enamel coating (5) and therefore electrically conductive for electrical contacting of the metal substrate (4), and the metal substrate (4) consists of a heat-resistant as well as austenitic or ferritic steel.

Description

The present invention relates to a cooking appliance component and to a process for producing such a cooking appliance component, wherein the cooking appliance component in particular has a cooking chamber suitable for carrying out pyrolysis and has a component wall which at least partially delimits the cooking appliance component. In this case, the component wall comprises a metal substrate with an enamel coating provided thereon.

In the prior art, various cooking appliances have become known, which have a pyrolysetauglichen cooking chamber. In most cases, the cooking chamber wall consists of black sheet metal on which an enamel coating is applied for the purpose of corrosion protection. Enamel-coated metallic cooking chamber walls do not change their visible surface properties even at repeated pyrolysis at temperatures above 400 ° C. The enamel coating reliably protects the surface against color change due to tarnishing or corrosion.

The DE102012109147 describes a domestic appliance in which a component has an enamel layer and a conductive coating arranged thereon.

It is more difficult if metallic shiny surface areas are desired for decorative reasons or for technical reasons. When using black plate this would quickly corrode by the existing within the cooking chamber and outside of the cooking water vapor and thus change its technical and surface properties. When using stainless steel, no pyrolysis should be carried out, since with multiple heating to the pyrolysis temperature, a tarnish of the stainless steel surface occurs, which is visually unattractive. A protective measure against tarnishing is the application of a thin glass layer to visible metallic surfaces, but this makes electrical contacting impossible, since the additional glass layer has an electrically insulating effect.

It is therefore the object of the present invention to provide a cooking appliance component and a method for producing a cooking appliance component which comprises a cooking chamber suitable for carrying out pyrolysis and which no longer has at least some disadvantages of the prior art.

This object is achieved by a cooking appliance component having the features of claim 1 and by a method for producing a cooking appliance component having the features of Claim 11. Preferred developments of the invention are the subject of the dependent claims. Further advantages and features of the present invention will become apparent from the general description and the description of the embodiment.

A cooking appliance component according to the invention has in particular a cooking chamber suitable for carrying out pyrolysis, wherein the cooking appliance component comprises at least one component wall which at least partially delimits the cooking appliance component. The component wall comprises a metal substrate having an enamel coating at least partially applied thereto. The cooking chamber wall has at least one surface portion kept free of the enamel coating and therefore electrically conductive for electrically contacting the metal substrate, and the metal substrate consists at least partially of a heat-resistant as well as austenitic or ferritic steel.

The cooking appliance component according to the invention has many advantages. A significant advantage of the cooking appliance component according to the invention is that the cooking appliance component is formed pyrolysetauglich and simultaneously has an electrically conductive surface portion for electrical contacting of the metal substrate. Thereby more technical and also decorative possibilities of the design are available.

A cooking appliance component according to the invention can be designed as a baking muffle in simple cases. It is also possible and preferred to design the cooking appliance component as a cooking appliance on which at least one pyrolysis-capable baking muffle is provided. In particularly preferred embodiments, the cooking appliance component is basically capable of microwave or high frequency operation. In such applications, high-frequency radiation such as microwaves or the like are introduced into the interior of the cooking chamber in order to heat the cooking product present in the interior of the cooking chamber at least partially via radiation energy. In such applications, electrical contacting of the cooking chamber wall is usually necessary in order to achieve a reliable shielding. The escape of high-frequency radiation from the interior of the cooking chamber should be reliably avoided. For this purpose, it is advisable to protect the cooking chamber completely from the escape of high-frequency radiation. The cooking appliance component can also be designed as a container or other functional part of a cooking appliance, for example as a steam generator.

In order for such protection to be permanently and reliably maintained even during the performance of pyrolysis processes, the use of an austenitic or ferritic heat-resistant steel is very advantageous, in which an electrically conductive Surface portion for electrical contacting of the metal substrate remains permanently free of oxide layers and the like.

Austenitic or ferritic heat-resistant steels are particularly preferably used which do not corrode even at the temperatures of up to 860 ° C. or optionally 880 ° C. or more occurring in the enamel coating, so that no or only slight reworking of the surface of the substrate is required. In this way, an enamel-free surface section on the cooking chamber wall can be produced directly during the application of the enamel layer by appropriately covering or masking the desired surface section, for example, before applying the enamel layer, in order to provide a metallically bright surface section there. By such measures using the listed austenitic or ferritic heat-resistant steels, it is possible to provide the substrate for the cooking space wall in total - with the release of at least one electrically conductive surface portion - with an enamel layer. There is no or only a slight impairment of the electrical conductivity of the electrically conductive surface portion. For the purposes of the present invention, a small effect on the electrical conductivity is here preferably understood to be a maximum of a fourfold increase in the electrical resistance and, in particular, an increase of at least twice or 1.5 times the electrical contact resistance at the electrically conductive surface section.

In particularly preferred developments and refinements, the metal substrate consists at least partially of a steel which is heat-resistant according to the standard DIN EN 10095. Particularly preferably, the metal substrate consists entirely of such a steel. Under the metal substrate is understood in particular the muffle wall or the steel wall of the cooking chamber.

The steel is in particular a special steel and preferably a stainless steel. It is possible to use ferritic heat-resistant steels with the designation of material number and material short name 1.4742, 1.4762 and optionally 1.4724 and 1.4713. Austenitic heat-resistant steels with the abbreviations 1.4878 and 1.4828 and 1.4821 as well as 1.4876 and 1.4872 and 1.4835 are possible and particularly preferred. The use of an austenitic heat-resistant steel from the group 1.4841 has proved to be advantageous. Steels from the group 1.4841 are heat-resistant up to 1120 ° C in air and contain components of carbon, chromium, nickel, silicon and possibly aluminum.

Particularly preferably, the metal substrate has an at least partially and in particular completely roughened surface. Such a configuration is particularly advantageous since stainless steels, as mentioned above, and also other stainless steels have a reduced adhesion between the steel and an enamel layer. It is possible to apply an additional primer layer to the substrate prior to the application of an enamel layer, but this regularly prevents or at least substantially worsens the electrical contacting of the metal substrate. This means that after the application of the enamel layer then a complex post-processing step must be carried out in order to allow electrical contacting of the metal substrate and to provide for the desired applications in sufficient quality.

It has now surprisingly been found that a roughened surface of the metal substrate allows a considerably improved and sufficient adhesion of the enamel layer to the high-alloyed special steel of the metal substrate. If such roughening takes place, for example, with an 80-grit grain, then a reasonable and sufficient adhesion can be achieved.

Particularly preferably, the surface of the metal substrate is at least partially roughened by brushing. It is also possible to at least partially roughen the surface of the metal substrate by grinding or, for example, sandblasting. It is also possible to use 2 or 3 different methods for producing the roughened surface. The brushing has proven to be particularly advantageous, since it can reliably and reproducibly provide a low-stress and roughened surface of the metal substrate. The use of a sandblasting process can lead to a local compaction of the surface, which can then lead to unwanted bent or bent surfaces on the cooking chamber wall if the parameters of the sandblasting process are chosen unfavorably.

Particularly preferably, the surface of the metal substrate is roughened on both sides. This is preferred for a variety of reasons, also because tensions in the metal substrate can occur due to possible stresses occurring due to the "bimetallic effect".

Certain parameters of the surface of the metal substrate have been found to be particularly suitable. In particular, a center roughness Ra between about 1 μm and 4 μm is preferred. Mean roughness values between 2 μm and 3 μm are particularly advantageous. The average roughness value is understood here as the arithmetic mean roughness value.

Particularly preferably, the surface of the metal substrate has a surface roughness Rz of between about 10 μm and 40 μm. Advantageously, a roughness Rz between about 15 microns and 25 microns. Under The surface roughness is understood here as the average roughness depth and not directly the depth of individual grooves or points or furrows on the surface of the metal substrate.

Particularly preferably, the metal substrate has at least one sandblasted weld seam. Preferably, the metal substrate is bent to a Garraummuffel or the like and the two ends are welded together at the abutting edge to provide a completely closed baking muffle or the like. It is also possible and preferred to brush the weld to achieve the desired surface accuracy there. In the area of the weld, however, it may be cheaper and / or easier to carry out a (local) sandblasting.

Particularly preferably, the metal substrate has at least one enamel-free surface section.

In particularly preferred embodiments, the metal substrate is coated with 2 enamel layers applied to one another, which in particular are fired separately. But it is also possible to apply 2 layers of enamel one after the other and to burn together in one firing process.

The application of a first enamel layer to the metal substrate and the subsequent firing of the first enamel layer makes it possible, for example, to choose the ingredients and the mixing ratios in the first enamel slurry layer differently than in the second enamel slurry layer, which is applied to the already baked first enamel layer. As a result, it is possible to react accordingly to the different substrates for the first enamel layer and the second enamel layer. For the first enamel layer, the bare and roughened metal substrate is present as a surface, while the second enamel layer is applied to an existing enamel layer, so that the adhesion conditions for the respective enamel layers are fundamentally different.

The method according to the invention is used to produce a cooking appliance component, in particular with a cooking chamber suitable for carrying out pyrolysis, wherein a component wall which at least partially forms the cooking appliance component is produced from a metal substrate onto which at least partially an enamel coating is applied. In this case, at least partially an austenitic or ferritic heat-resistant steel is used for the metal substrate and the enamel coating is applied so that at least one electrically conductive surface portion for electrical contacting of the metal substrate remains on the component wall.

The method according to the invention also has many advantages, since it allows a cost-effective and simple production of a cooking appliance component according to the invention. In this case, an electrically conductive surface portion for the electrical contacting of the metal substrate of the component is made directly with the production. A complex post-processing is not necessary to electrically contact the component wall.

Preferably, the metal substrate is roughened at least in sections and in particular substantially completely and particularly preferably completely before the application of the enamel coating. As a result, an improved adhesion of the enamel coating to the metal substrate is allowed, so that a lasting and reliable adhesion of the enamel coating to the metal substrate is ensured. Insufficient adhesion could lead to undesired loosening of the enamel layer and thus to destruction of the cooking appliance component in the case of multiple pyrolysis operations and the resulting thermal stresses due to the heating and expansion of the metal substrate. Therefore, a reliable adhesion in the high thermal loads occurring during operation is very important.

More preferably, at least 2 enamel layers are applied, namely first a base enamel layer and then a top enamel layer. It is possible that first a base enamel layer is applied, which is fired after the application of the layer.

After firing and corresponding cooling of the metal substrate, the top enamel layer is applied and fired in a separate firing operation.

In other embodiments, it is also possible to apply the base enamel layer and the top enamel layer in succession, but to burn in a common firing process.

With particular preference, a considerably lower particle size is used for the base enamel layer than for the top enamel layer. Preferably, a particle size distribution is used for the base enamel slurry, which shows a milling fineness of 4-6 when tested with the Bayer sieve at 16,900 M per centimeter square. The fine grain content of the base enamel slurry up to a size of 5 μm should be 15-30% and in particular between 20 and 2.5%. The fine grain content up to a size of the enamel particles of up to 50 μm or 60 μm in diameter should be at least 90%. For the cover enamel layer an enamel slurry layer with coarser enamel particles can be used. There may be a particle size distribution which, when tested with the Bayer sieve, indicates 16,900 M per square centimeter, a fineness of 20-25 or the like. It is possible for the Deckemailschicht also a different grain fineness.

With particular preference, a separate enamel slurry layer is first applied for each enamel layer, which is then fired separately, in particular. For the base enamel layer firing temperatures of 780 ° C to 835 ° C are preferred. Particular preference is given to using temperatures of between 800 ° C. and 830 ° C. Firing temperatures of 840 ° C to 850 ° C can be used in the firing process for the enamel covering layer.

In particularly preferred embodiments, the enamel slurry layer of the base enamel layer is thinner than the enamel slurry layer of the top enamel layer. It is also preferable that the base enamel layer has a smaller thickness than the top enamel layer. The application preferably takes place in such a way that a ratio of a layer thickness of the top enamel layer to the layer thickness of the base enamel layer is between 0.75 and 2 and in particular between 1 and 1.5.

Further advantages and features of the present invention will become apparent from the embodiment, which is explained below with reference to the accompanying figures.

Figur 1

eine schematische Vorderansicht eines erfindungsgemäßen Gargeräts; und

Figur 2

einen stark schematischen und vergrößerten Querschnitt durch einen Abschnitt der Garraumwandung;

In the figures show:

FIG. 1

a schematic front view of a cooking appliance according to the invention; and

FIG. 2

a highly schematic and enlarged cross-section through a portion of the cooking chamber wall;

FIG. 1 shows a highly schematic front view of a cooking appliance component 1, which is designed here as a total cooking appliance 100 and a baking muffle 10 includes. It is also possible that the cooking appliance component 1 comprises only the baking muffle 10 or only one component wall 3 or a container or another functional part of a cooking appliance or is designed as such. In the embodiment shown, the component wall 3 is formed by a cooking chamber wall, which is therefore provided below with the same reference numeral 3.

The cooking appliance 100 has a cooking chamber 2 provided by the baking muffle 10, which is delimited laterally and rearwardly by a cooking chamber wall 3. A door is provided in front.

The cooking chamber 3 consists of a metal substrate 4, on which an enamel coating 5 is applied to the surfaces 7 and 8 on the outside and the inside of the cooking chamber 2.

The cooking chamber wall 3 is made of an originally flat metal substrate 4, which is deformed to form the cooking chamber. At the abutting edges at the ends of a weld 9 is provided to provide a completely dense cooking chamber 2. The weld 9 is shown here in a corner of the cooking chamber 2, but may in principle be provided at any point of the cooking chamber 2.

FIG. 2 shows a greatly enlarged cross-section of a portion of the cooking chamber 3. In the cross section, the metal substrate 4 is schematically drawn. Both the outer surface 7 and the inner surface 8 of the metal substrate 4 are here covered with an enamel layer having a thickness 12. It is also possible that the surface 7 forms the inner surface of the cooking appliance component 1 and that the surface 8 is arranged on the outside of the cooking chamber 2.

In the in FIG. 2 shown enlarged schematic cross-section of the enamel-free surface portion 13 is shown on the surface portion 6, where on the metal substrate 4 no enamel layer 5 is provided. In the surface portion 6, the metallic surface of the metal substrate 4 is directly accessible. As a result, an electrically conductive connection of the metal substrate 4 and thus of the cooking chamber wall 3 is possible in order to provide an electrical shielding.

The cooking substrate 4 has a rough surface which has been created by brushing the originally substantially smooth surface of the metal substrate. It is also possible to roughen the surfaces 7 and / or 8 of the metal substrate 4 by grinding or needling or optionally sand blasting so as to provide a reasonable and sufficient surface roughness of at least one surface 7, 8 of the metal substrate.

Preferably, both surfaces 7 and 8 are roughened in basically the same way and - apart from at least one surface section 6 - essentially completely covered with the enamel layer 5. As a result, an electrically conductive connection of the cooking chamber wall 3 is made possible to reliably prevent the escape of high-frequency radiation such as microwave radiation or the like from the cooking chamber 2.

The metal substrate 4 is made of an austenitic or ferritic heat-resistant steel. It is possible that the cooking chamber wall is formed from a plurality of substrate parts, but then at least one metal substrate consists of such a heat-resistant austenitic or ferritic steel. Here, on the metal substrate on which an electrically conductive surface portion is provided and formed, this metal substrate is made of an austenitic or ferritic heat-resistant steel. Particular preference is given to using a steel of material class 1.4841 which is suitable for introduction both at the high temperatures the enamel layer is reliably protected against corrosion at the later operating temperatures on the pyrolysis level. As a result, a permanently reliable electrically conductive connection to the cooking chamber wall 3 can be made possible.

The originally smooth metal substrate is preferably roughened on both sides to reliably avoid stresses due to different surface treatments on both sides.

The surfaces 7 and 18 are particularly preferably roughened such that an arithmetic mean roughness Ra of between 2 μm and 3 μm is present. Particularly preferably, at least one surface 7, 8 of the metal substrate 4 has a surface roughness Rz between about 15 μm and 25 μm, and particularly preferably about 20 μm.

The average roughness preferably corresponds to the arithmetic mean of the deviation of the distance of the surface points from the center line. In a one-dimensional extension, the average roughness would be the height of the rectangle that has the same length as the track to be examined and the same area as the area between the reference altitude and the profile. In a corresponding manner, the average roughness depth is determined by known methods.

Therefore, the depth 11 of individual grooves or spots does not regularly coincide with the mean roughness or the average roughness, but rather a statistical evaluation is carried out.

The original smooth metal substrate 4 made of the austenitic or ferritic heat-resistant steel is first preferably roughened on both sides on the surfaces 7, 8 by brushing or the like for producing the cooking appliance component 1. Following this, after a cleaning step that may be carried out, a first enamel slurry layer 16 is applied, which is only schematically shown in FIG FIG. 2 indicated by dashed lines.

In the enamel slurry layer 16, a density of the enamel slurry layer 16 is set between preferably 1.62 and 1.68 g per cubic centimeter. A fine particle size distribution is used in the enamel slurry layer which, when tested with a Bayer sieve, shows 16,900 M per square centimeter with a fineness of 4-6. Here, the fine grain content is up to 5 microns between 20 and 25% and the total proportion of the enamel particles up to a diameter of 50 microns at least 90%. After addition of demineralized water (demineralized water) customary grinding, settling and Schlickerhilfsmittel be adjusted and the enamel layer 16 is applied to here the surface 7 of the metal substrate 4. Previously, preferably the surface portion 6 is covered or masked so that this surface portion 6 is not provided with an enamel coating.

Thereafter, the enamel slurry layer 16 is dried at temperatures between 20 and 80 ° C until the residual moisture content of the enamel bismuth after drying is less than 4% and in particular less than 2%. Following this, the covering for the surface section 6 can be removed and the first or inner enamel layer 15 is burned in, which in the finished state preferably has a layer thickness between 60 and 120 μm and preferably between 80 and 100 μm. The baking of the enamel layer is preferably carried out at temperatures which are a maximum of 830 °. The baking is preferably carried out at reduced speed and adapted heating and cooling to achieve the desired conditions of adhesion.

Following this, the second in FIG. 2 also schematically indicated by dashed lines second or outer Emailschlickerschicht 26 are applied to the now finished enamel layer 15, in turn, the surface portion 6 is recessed. The enamel slip layer 26 may be applied at conventional densities between about 1.7 and 1.82 g per cubic centimeter, with the grain distribution of the base enamel having a fineness of, for example, 20-25 measured with a Bayer sieve 16,900 M per square centimeter.

The stoving and drying of the second enamel layer 25 can be done essentially conventionally, since the adhesion to the first enamel layer 15 meets the usual requirements.

Overall, the invention provides an advantageous cooking appliance component 1, in which an austenitic or ferritic heat-resistant steel is used for the metal substrate 4 and wherein the metal substrate is substantially coated with at least one enamel coating. In this case, at least one surface portion remains free and can be contacted electrically conductive and without special rework. In order to achieve the necessary adhesion, the surface of the metal substrate 4 is roughened in a defined manner, with an 80-grit grain having proved to be advantageous. The roughening with too coarse or too fine grain, however, has not led to the desired results.

The application of a separate bonding agent on, for example, nickel-based is not necessary in the present invention. The surface of the austenitic or ferritic heat-resistant steel is roughened directly and then directly a first enamel layer and then a second enamel layer is applied.

With the invention it is possible to provide pyrolysis available that have metallic bare surfaces to electrically contact the cooking chamber or to achieve corresponding optical properties.

LIST OF REFERENCE NUMBERS

1

Gargerätkomponente

2

oven

3

Komponantenwandung

4

metal substrate

5

enamel coating

6

surface section

7

surface

8th

surface

9

Weld

10

baking muffle

11

depth

12

thickness

13

Enamel-free surface section

15

(inner) enamel layer

16

Emailschlickerschicht

25

(outer) enamel layer

26

Emailschlickerschicht

100

Cooking appliance

Ra

roughness

March

average roughness

Claims (17)

Cooking appliance component (1), in particular with a cooking chamber (2) suitable for carrying out pyrolysis, and with a component wall (3) at least partially delimiting the cooking appliance component (1), wherein the component wall (3) has a metal substrate (4) at least partially thereon comprises applied enamel coating (5),
characterized,
in that the component wall (3) has at least one surface section (6) kept free of the enamel coating (5) and therefore electrically conductive for electrically contacting the metal substrate (4), and that the metal substrate (4) consists at least partially of a heat-resistant as well as austenitic or ferritic one Steel exists. Cooking appliance component (1) according to claim 1, characterized in that the metal substrate (4) consists of a steel which is heat-resistant according to the standard DIN EN 10095. Cooking appliance component (1) according to one of the preceding claims, characterized in that the metal substrate (4) has a roughened surface (7, 8). Cooking appliance component (1) according to the preceding claim, characterized in that the surface (7, 8) of the metal substrate (4) is roughened by sandblasting, grinding or brushing. Cooking appliance component (1) according to the preceding claim, characterized in that the surface (7, 8) of the metal substrate (4) is roughened on both sides. Cooking appliance component (1) according to one of the preceding claims, characterized in that the surface (7, 8) of the metal substrate (4) has an average roughness (Ra) of between about 1 μm and 4 μm. Cooking appliance component (1) according to one of the preceding claims, characterized in that the surface (7, 8) of the metal substrate (4) has a surface roughness (Rz) between about 10 microns and 40 microns. Cooking appliance component (1) according to one of the preceding claims, characterized in that the metal substrate (4) has at least one sandblasted weld seam (9). Cooking appliance component (1) according to one of the preceding claims, characterized in that the metal substrate (4) has at least one enamel-free surface section (13). Cooking appliance component (1) according to one of the preceding claims, characterized in that the metal substrate (4) is coated with two mutually applied enamel layers (15, 25) which are fired separately. Method for producing a cooking appliance component (1), in particular with a cooking chamber (2) suitable for carrying out pyrolysis, wherein a component wall (3) at least partially forming the cooking appliance component (1) is made of a metal substrate (4) onto which at least partially Enamel coating (5) is applied,
characterized,
in that at least partially a heat-resistant as well as austenitic or ferritic steel is used as the metal substrate (4) and that the enamel coating (5) is applied such that at least one of the enamel coating (5) is kept free on the component wall (3) and therefore more electrically conductive Surface portion (6) for electrically contacting the metal substrate (4) remains. Method according to the preceding claim, characterized in that the metal substrate (4) is roughened before applying the enamel coating (5). Method according to one of the two preceding claims, characterized in that at least two enamel layers (15, 25) are applied, namely first a base enamel layer (15) and then a cover enamel layer (25). Method according to the preceding claim, characterized in that the base enamel layer (15) is formed with a significantly lower particle size than the top enamel layer (25). Method according to one of the four preceding claims, characterized in that for each enamel layer (15, 25) first a separate enamel slurry layer (16, 26) is applied, which is fired separately. Method according to one of the five preceding claims, characterized in that the enamel slurry layer (16) of the base enamel layer (15) has a lower density than the enamel enamel layer (26) of the top enamel layer (25). Method according to one of the six preceding claims, characterized in that a ratio of a layer thickness of the top enamel layer to the layer thickness of the base enamel layer (15) is between 0.75 and 2 and in particular between 1 and 1.5.

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