Cookware

1. Field of the Invention

The invention pertains to a cooking utensil, for example a pot or a frypan with a container liner of stainless steel with a comparatively low wall thickness and a comparatively thick bottom plate of aluminum or a material of similarly good heat-conducting properties on the outside bottom of the container liner which plate is attached to a bottom disc on the outside of the bottom plate that is at least partially composed of magnetizable material.

2. Description of Related Art

As opposed to for example enamel-on-steel cooking pots, stainless steel utensils for gas or electric ranges are appreciated for durability, good cleaning properties and attractive appearance. However, since stainless steel has a comparatively low heat-conductivity the container of the cooking utensil with its comparatively thin wall thickness is commonly provided with a comparatively thick bottom plate of aluminum or a material of similarly good heat-conducting properties. As a result of its good heat-conductivity, even if only locally heated, the bottom plate ensures an even simmering process across the entire inner bottom surface. A cooking utensil according to DE-OS 22 58 795 has a bottom plate of aluminum or a material of similarly good heat-conducting properties which employs a protective layer of stainless steel on the outside of the bottom plate with features identical to those of the container liner.

Cooking utensils of the kind commonly described consist of austenitic steel, and therefore they are not suited for the use on so-called induction stoves, because steels of austenitic structure are not or are only minimally magnetizable for the heating of the cooking utensil including its food items with the help of magnetic alternating fields.

In order not to be limited to gas or electric range use, and to include applications for induction stoves as well, a cooking utensil of stainless steel has been disclosed in an earlier not pre-published patent application U.S. Pat. No. 36 34 841.4 which consists of a bottom plate comprised of an intermediate layer of ferritic steel which is encapsulated by outer layers of austenitic steel. This solution is relatively complicated and costly due to a bottom disc of three layers.

In an earlier not pre-published patent application U.S. Pat. No. 36 39 013.5 another type of cooking utensil of the kind described heretofore is disclosed that is suited for use on gas and electric ranges as well as for induction stoves. Therein a bottom disc of aluminum or a material of similarly good heat-conducting properties is connected on its outside surface to a bottom disc of austenitic steel with magnetizable material of low thickness applied to the outside surface of the latter.

It is an object of the present invention to introduce a cooking utensil of the kind heretofore described, which is of simpler construction and provides a more effective application to an induction stove while reliably retaining a good and even transmission of heat and an even contact surface when heated on an electric range.

According to the invention this object is accomplished with a bottom disc which essentially consists of nickel or a nickel alloy or at least an intermediate layer of a nickel alloy. Surprisingly it has turned out that at such construction of a bottom layer due to the bimetal effect and/or the mix-expansion when heated results in a compensation such that the contact surface of the bottom remains reliably flat. Nickel or nickel alloys furthermore are of a very high magnetic permeability so that a relatively low layer thickness is possible to provide a more effective use on induction type stoves. Nickel furthermore can easily be formed and is particularly well plated, which results in an inexpensive production.

Furthermore, bottom discs according to the invention exhibit good resistance to corrosion.

The invention pertains to a cooking utensil, for instance a pot or a frypan, with a container liner of stainless steel, with comparatively low wall thickness and a comparatively thick bottom plate of aluminum or a material of similarly good heat-conducting properties on the outside bottom surface of the container liner as well as with a bottom disc on the outside surface of the bottom plate that is at least partially composed of magnetizable material and characterized such that the bottom disc essentially consists of nickel or a nickel alloy or at least contains an intermediate layer of nickel or nickel alloy.

The concept of the invention in the preferred embodiment is such that the bottom plate can be composed of an intermediate layer of nickel and an outer layer of stainless steel, which serves as a protective layer.

Particularly favorable results are achieved in the expansion reaction under consideration with regard to the remaining material on the bottom of the container in combination with the reaction under magnetization under magnetic fields provided by common induction stoves and resistance against corrosion have been surprisingly achieved when the nickel alloy shows the following composition: Ni: 50-100%; Cr: up to 6%; Mo: up to 6%; Cu: up to 14%; Mn: up to 6%; Si: up to 1.5%; C: up to 0.7% and rest Fe.

In reference to the cited criteria, in particular with nickel alloys, the following composition has proven particularly favorable: Ni: 70-80%, preferably approx. 75%; Cr: 1 to 3%, preferably approx. 2%; Cu: 3 to 7%, preferably approx. 5%; Mn: 0.3 to 0.7, preferably approx. 0.5%, Si: 0.1 to 0.3%, preferably approx. 0.2%; C: 0.001 to 0.01%, preferably approx. 0.02% and rest Fe, or the following composition: Ni: 75 to 85%, preferably approx. 80%; Mo: 4 to 6%, preferably approx. 5%; Mn: 0.3 to 0.7%, preferably approx. 0.5%; Si: 0.2 to 0.4%, preferably approx. 0.3%; C: 0.001 to 0.01%, preferably approx. 0.02% and rest Fe.

The bottom disc mainly comprised of nickel or a nickel alloy or the intermediate layer of nickel or a nickel alloy preferably has a thickness of approx. 0.2 to 2 mm.

It has further been found to be advantageous if the bottom disc has a thickness which approximately corresponds to the wall thickness of the container.

The bottom plate for example on the outside bottom of the container and possibly the bottom disc on the outside of the bottom plate can be attached with the help of a commonly known hammer-press technique at an increased temperature preferably with an intermediate foil of aluminum or a material of similarly good heat-conducting properties.

The comparatively thick bottom plate of aluminum or a material of similarly good heat conducting properties promotes evenness of the heat flow into the inside of the cooking utensil when heating as is commonly provided by gas or electric ranges. When heating by induction the bottom plate additionally assumes the function of a damping element. As is known the heat flow disappears immediately from the bottom of the cooking utensil causing it to cool down instantly with the switching off of the magnetic alternating field if a bottom plate of comparatively thick aluminum or a material of equally good heat-conducting properties is not utilized, which would then necessitate a frequent on-off switching process of the induction range to maintain a constant temperature for the food items inside the cooking utensil. The comparatively thick bottom plate of aluminum or a material of similarly good heat-conducting properties, however, functions as a heat retainer so that a switching on and off of the induction stove to maintain a relatively constant cooking temperature is merely required for longer time intervals. This in particular is important in regard to the registration regulations for induction stoves which determine that within a given time frame a certain number of switching processes must not be exceeded. On the other hand with the invention the advantages of instant heating associated with inductive cooking are essentially sustained despite the comparatively thick bottom plate of aluminum or a material of similarly good heat-conducting properties.

The invention in its preferred embodiment is further explained hereinafter with reference to the drawing.

The sole Figure illustrates schematically the essential constituents of a cooking utensil suitable for induction stoves presenting the innovative aspects of the invention in the form of a pot prior to its assembly.

The cooking utensil has a container liner 1 of the customary austenitic stainless steel (for example No. 1,4301 according to DIN 17007) with a wall thickness of for example between approx. 0.8 and 1.0 mm. The bottom side of the container liner 1 is attached to a bottom plate 22 with a thickness of several millimeters that is composed of aluminum, an aluminum alloy or another material with good heat-conducting properties. On the outside of the bottom plate 2 a bottom disc 3 is attached, which according to the invention either essentially consists of nickel or a nickel alloy or as presented is comprised of an intermediate layer 4 of nickel or a nickel alloy and an outer layer 5 of stainless steel. The bottom disc 3, essentially comprised of nickel or a nickel alloy or the intermediate layer 4 of nickel or a nickel alloy, has a thickness of approximately between 0.2 mm and 2 mm. The thickness of the bottom plate 2 preferably is equivalent to the wall thickness of the container liner 1. The application of the bottom plate 2 on the outside of the bottom of the container liner 1 can take place at an increased temperature through applying an intermediate aluminum foil of for instance a thickness between 0.02 and 0.1 mm by utilizing an impact pressure welding technique as known from DE-OS 22 07 448 wherein preferably pressure impacts are utilized between approx. 1,000 and 1,500 k/cm2 and temperatures between 300.degree. and 500.degree. C. The bottom disc 3 essentially comprised of nickel or a nickel alloy or the intermediate layer 4 of nickel or a nickel alloy can alternatively be plated onto the lower side of the bottom plate 2 or the inside of the outer layer 5 of stainless steel.

1. Container liner

2. Bottom plate

3. Bottom disc

4. Intermediate layer

5. Outer layer