WO1984002456A1

WO1984002456A1 - Cooking vessels, made of aluminium or alloys thereof, as well as a process for the manufacture thereof

Info

Publication number: WO1984002456A1
Application number: PCT/SE1983/000482
Authority: WO
Inventors: Marcus Mueller
Original assignee: Marcus Mueller
Priority date: 1982-12-28
Filing date: 1983-12-28
Publication date: 1984-07-05
Also published as: FR2538236B3; FR2538236A1; SE8207450D0

Abstract

Cooking vessel of aluminium or aluminium alloy provided on the interior with an aluminium oxide layer, the micropores of which are coated or filled with carbon; and a process for the manufacture of the cooking vessel, the micropores of the aluminium oxide layer being supplied with an organic material which by heating is decomposed under carbonization to the deposition of carbon in the pores.

Description

TITLE OF INVENTION

COOKING VESSELS, MADE OF ALUMINIUM OR ALLOYS THEREOF, AS WELL AS A PROCESS FOR THE MANUFACTURE THEREOF.

TECHNICAL FIELD This invention relates to culinary vessels, pots and pans, in particular to frying pans made of aluminium or alloys thereof, whereby the surface exposed to the foodstuff to be prepared is covered with a layer of aluminium oxide constituting a certain part in depth of the total thickness of the pans construction material.

BACKGROUND ART

Culinary pots etc intended for cooking are traditionally made of aluminium or stainless steel. Vessels for cooking are also, though on a somewhat limited scale, produced of copper.

Vessels for frying, frying pans, are mostly made of cast iron, which after pre-frying have been given a black surface having good frying properties, meaning that the fried foodstuff receives a satisfactory roast brown appearanee and having non-sticking properties towards various foodstuff.

The only drawback of cast iron pans, and often disturbing, is its high weight.

It should be lying close to hand to make frying pans of aluminium in order to produce frying pans of lower weight. It has, however, been found that frying pans of aluminium do not give roast brown surfaces comparable to those achievable with cast iron pans, and that foodstuff like eggs, meat, fish etc have a pronounced tendency of sticking to the pan surface to a hardly acceptable degree. Therefore, today most frying pans of aluminium have the frying surface covered with Teflon or similar coatings with non-sticking properties.

Protective coatings of teflon (or similar coating) have, however, a disturbing mechanical sensitivity to scratching kitchen tools.

It is known within the industry of culinary equipment manufacture that a certain quality improvement, for example of frying pans made of aluminium, or alloys containing mainly aluminium, can be achieved by so called anodizing of the frying pan. The motive for this is to take benefit of the natural hardness of aluminium oxide.

By anodizing is here understood the electrolytic process whereby the surface of aluminium is converted from metallic aluminium to aluminium oxide.

As is well known within the electro plating industry, this converting from aluminium to aluminium oxide is carried out in an electrolytical process, in which the work piece (for example a culinary pot or pan) is connected as an anode and in which the electrolyte is a suitable acid such as sulphuric acid, oxalic acid, phosphoric acid or mixtures thereof.

The process is terminated with a final sealing of the micropores in the oxide layer by treating the workpiece in hot water during a certain time. Frying pans manufactured according to the principles indicated above do not, however, possess satisfactory properties regarding roast brown colou appearance of the fried foodstuff and also the non-sticking property is insufficient, and have therefore never been industrially fabricated.

It is also well known within the industry of culinary pots and pans to further improve the roast brown appearance of the fried foodstuff, as well as to improve the non-sticking properties by covering the pan surface with for instance teflon after the anodizing. This, however, does not take advantage of the natural hardness of the aluminium oxide layer hence the surface has only the hardness of the teflon itself and also the sensitivity to scratches equal to that of the teflon.

SUMMARY OF THE INVENTION

The present invention has for its purpose to provide culinary pots and pans, especially frying pans, of aluminiu or alloys thereof, having the frying characteristics equal to those of cast iron pans, but with a surface hardness far superior to that of teflon or similar coatings. It has now been shown that, according to this invention, it is possible to produce a frying pan of aluminium without a teflon or similar coating, having frying properties equally good to those of a traditionally well burnt-in cast iron pan, however without the high weight of the cast iron frying pan.

Characteristic for culinary pots and pans made in accordance with this invention is, that the micro pores in the aluminium oxide layer mentioned above are filled and covered with carbon, which preferably is created by heat treatment of organic material which has been brought into those pores before the heat treatment.

The aluminium oxide layer has preferably a thickness of 10-100 μm, suitably 25-75 μm, for instance 40-60 μm. According to a preferred way of producing culinary pots and pans in accordance with this invention a suitable metal is deposited in the bottom of the earlier mentioned pores, but before the carbon is created, thus giving the surface a specific stable colour, for instance black. Such metals are for instance nickel, copper, chromium. The invention also refers to a process for the production of such culinary pots and pans whereby the micro pores in the aluminium oxide layer are not hot water sealed, but are filled with an organic material, which upon heat heat treatment is decomposed into, inter alia carbon which then stays within the pores.

The organic material used is preferably one containing carboxylic groups, for instance fatty acids or esters hereof. Even if the invention is not limited by any definit theory, it is assumed that the organic material via the carboxylic groups is chemically bound to the aluminium, or other metal, in the bottom of the pores.

In order to achieve a frying surface of the pan appearing as black as possible and thus resembling the appearance of a conventional cast iron pan, the filling of the pores with organic material can be preceded by first depositing a thin layer of some suitable metal at the bottom of the pores. The thickness of such a metal deposit is for instance 1-5 μm. The aluminium oxide is created by an electrolytic process referred to as anodic oxidation. Also the optional deposition of a metal is made electrolytically. In the following the process in general, for procuding culinary pots and pans according to this invention, is described, although it should be noted that the invention by no means is limited by the specific conditions given here below.

The starting material is a round of aluminium of the quality normally used by the industry for these purposes.

The round has, for example, the form of a frying pan produced by embossing, lathing, casting or the like.

The material is first treated in a hot solution of sodium hydroxide, 5-10% NaOH, at a temperature of appr. 50ºC. Thereafter following rinsing in water and a dip cleaning in 301 nitric acid.

The workpiece is then anodized in the traditional way for instance in sulphuric acid of 201 concentration at 20ºC and until the aluminium oxide layer has a thickness of for instance 40-60 μm.

Contrary to previously mentioned or indicated processes the anodizing, according to this invention, is not followed by a water sealing, but the workpiece is rinsed in cold water and thereafter quickly air dried at room temperature. The pores of aluminium oxide have a natural tendency of self sealing by absorbing moisture from the air. Depending upon the humidity of the surrounding atmosphere, this process takes shorter or longer time, (hours, days, weeks). Thus, the still open pores in the aluminium oxide layer are then filled with organic material, preferably containing carboxylic groups such as fats or fatty acids of various sorts. When the workpiece is then heated to a temperature of appr. 200-300ºC, the organic material is decomposed to form a carbon deposit (carbonization), which fills the pores and stays there. From then on frying in the pan is made on a surface mainly consisting of carbon in the same way as in a traditionally well burnt-in cast iron pan.

The invention permits within its scope that the pores of the aluminium oxide, before the carbonization, are dyed by depositing metal (for instance nickel) by well known electrolytical standard processes, whereby, however, only a minute part of pore depth is required.

EXAMPLES

The invention is further illustrated by the following examples, which, however, are in no way limiting the invention. Example 1

A round aluminium to become a frying pan was pickled in a 51 water solution of sodium hydroxide for 3 minutes and at a temperature of +50ºC.

The pickled workpiece was thereafter rinsed in water and then further chemically cleaned by a dip into 30% nitric acid for one minute, whereupon followed a thorough water rins. The workpiece was then connected as an anode in a conventional anodizing bath, made up of 20% sulphuric acid, in which the oxidation took place at a voltage of 13-16 Volts and with a current density of 1 A/dm² at a temperature of +20ºC and for a time long enough to reach a thickness of the oxide layer of 40 μm, which in this example took 90 minutes.

The workpiece was then rinsed in water and air dried at room temperature.

Immediately hereafter the workpiece was covered with corn oil (maize oil), of the Swedish brand FELIX^®, which was then absorbed by the still open micro pores in the oxide layer. The workpiece was then heated to 250°C, whereby the corn oil was thermally decomposed and the decomposition products, amongst others carbon,remained inside the micropores. Frying tests with the frying pan produced as described above, carried out into practice, gave quite satisfactory results in respect of roast surface appearance and non-sticking properties. Example 2 A frying pan round of aluminium produced as in Example 1, but using butter instead of corn oil, gave equally good results. Example 3

Example 1 was repeated with the modification that, before the application of the oil, the bottom of the micropores were electrolytically covered with a nickel deposit of a thickness of a few microns, thereby giving a pan a black appearance resembling that of a conventional cast iron pan.

Claims

PATENT CLAIMS:

1. Cooking vessel, particularly frying pans, of aluminium or aluminium alloy, the surface exposed to the foodstuff to be prepared essentially consisting of an aluminium oxide layer extending to a limited depth, characterized thereby that the micropores of this oxide layer are coated or filled with carbon, preferably applied by heating of organic material.

2. Cooking vessel according to claim 1, characterized thereby that the aluminium oxide layer has a thickness of about 10-100 μm, suitably about 25-75 μm.

3. Cooking vessel according to claim 1 or 2, characterized thereby that the micropores also contain a deposited metal for blackening of the said exposed surface, said metal being for example nickel.

4. A process for the manufacture of cooking vessels of aluminium or aluminium alloy, the inner surface of the vessel exposed to the foodstuff to be prepared being provided with an aluminum oxide layer by oxidation, characterized thereby that the micropores in said oxide layer without so-called post-sealing of the pores with water are supplied with an organic material, and that said material by heating is decomposed by carbonization to the deposition of carbon in the pores.

5. A process according to claim 4, characterized thereby that the micropores are filled with an organic material containing carboxylic groups, for example a fatty acid or a fatty acid ester.

6. A process according to claim 4 or 5, characterized thereby that the heating takes place at a temperature of about 200 to 300°C.

7. A process according to any of claims 4-6, characterized thereby that the filling of the micropores with organic material is preceded by deposition of a thin layer of a metal for the purpose of blackening the aluminium surface.

8. A process according to any of claims 4-7, characterized thereby that the aluminium layer is formed electrolytically by anodic oxidation.

9. A process according to claim 7 or 8, characterized thereby that the metal is deposited electrochemically.

10. A process according to any of claims 7-9, characterized thereby that the layer of a metal is deposited to a thickness of about 1-5 μm.