GB2140277A

GB2140277A - Cooking vessel

Info

Publication number: GB2140277A
Application number: GB08405028A
Authority: GB
Inventors: Yanta H T Lam; Massy Umehara
Original assignee: Meyer Manufacturing Co Ltd
Current assignee: Meyer Manufacturing Co Ltd
Priority date: 1983-05-26
Filing date: 1984-02-27
Publication date: 1984-11-28
Also published as: GB8405028D0; GB2140277B

Abstract

A cooking vessel, such as a stainless steel pan 1, is provided in which the base 2 and part 4 of the side wall 3 extending from the base is provided with a hard anodised aluminium surface 5. <IMAGE>

Description

SPECIFICATION Cooking vessel The present invention relates to an improved cooking vessel and process for its manufacture.

It is known to provide cooking vessels of the type which are used directly on heat energy producing surfaces such as gas rings or electric rings with exteriors which are entirely coated with hard anodised aluminium which not only increases the absorption of heat energy into such vessels and so speeds cooking but also provides a surface which has increased durability and scratch-resistance.

Unfortunately, the presence of such an exte rior also increases the amount of heat energy which is radiated from the cooking vessel when it is removed from the heat energy producing surface and so on removal from the heat energy producing surface, the food in such a cooking vessel cools more rapidly than in known cooking vessels in which the exterior is light in colour or brightly polished.

Hard anodising a cooking vessel which is made of aluminium or which has its entire exterior clad with aluminium provides a surface which has a hardness which is two times greater than stainless steel, viz: between 350 and 400 on the micro Vicker's scale. Because the hard anodised surface increases the durability and scratch-resistance, the aesthetic appeal of the cooking vessel is maintained even after prolonged use.

We have sought to provide a cooking vessel which has improved heat absorption when on a heat energy producing surface but which has a heat loss when removed from the heat energy producing surface which is not significantly different from that of known cooking vessels.

Accordingly, the present invention provides a cooking vessel in which the base and part of the side wall extending from the base is provided with a hard anodised aluminium surface.

That part of the side wall of the cooking vessel which is not to be anodised is masked before the anodising process is carried out.

The present invention also provides a method of manufacturing a cooking vessel which comprises forming the cooking vessel from stainless steel, applying an aluminium surface to the desired part of the exterior surface of the cooking vessel, masking the remaining exposed stainless steel surface of the cooking vessel, hard anodising the exposed aluminium surface of the cooking vessel and removing the masking.

To achieve better adhesion of the aluminium to the stainless steel, the cooking vessel is degreased in a hot water/detergent bath or in an alkaline bath prior to the brazing whereby the aluminium surface is applied to the cooking vessel.

Brazing is preferably achieved by high frequency induction heating. Firstly, an aluminium disc is formed to fit the shape of the base of the cooking vessel and to wrap round the lower side wall to the desired extent.

Between the base of the stainless steel cooking vessel and the aluminium disc is a layer of flux and brazing powder and overlying the aluminium disc is a susceptor which is sub stantialiy saucer shaped to ensure the aluminium surface is wrapped securely around the base and lower side walls of the cooking vessel.

If the base of the cooking vessel has become deformed under the high heat involved in the brazing step, it should be flattened and the rough edges of the aluminium should be trimmed before proceeding to the next stage of masking the exposed stainless steel surface. The aluminium base of the cooking vessel may be spiral cut to provide an attractive finish.

It is desirable to further degrease the cooking vessel and dry it thoroughly before the stainless steel is masked so that the masking adheres better.

Since stainless steel is a better conductor of electricity than aluminium, without the masking of the stainless steel parts, hard anodising of the aluminium will not be properly achieved. Several means of masking the stainless steel surface can be used such as masking with tape, spraying the surface with an organic material or silk screening the surface-the aim being to achieve a non-porous film on the stainless steel.

After masking, the boundary between the aluminium and the stainless steel can be retrimmed to ensure a sharp boundary between the two after hard anodising.

Before the hard anodising step, the cooking vessel is racked.

Preferably, the hard anodising step employs an aqueous solution of sulphuric acid 10-20% by weight and the temperature is kept between 0 and 5 C. An initial voltage input if 1 8 v DC rising to 50 v DC is used to give an amp density of 3-4 amp/dm2. Under these circumstances, anodising takes about 40 to 50 minutes. Since a temperature of 0, to 5"C must be maintained and the anodising process itself generates heat, the cooking vessel must be cooled. To ensure a high amp density flow, good contact between the cooking vessel and the conductor is needed. This can be achieved by having copper electrodes held close to the cooking vessel by a rubber ring which in no way interferes with the anodising process.

After hard anodising, the anodising solution is washed away and in order to provide greater corrosion resistance, the porosity which develops made during the anodising step is sealed preferably by steam.

The cooking vessel is now ready for assembly with handles, etc.

It has been found that if the base of a saucepan and the exterior side thereof to a depth of 2 cm from the base is anodised, heat absorption into the pan is about 25 to 30% faster than with a similar saucepan having a mirrored exterior and the cooking rate is about 20% slower than with a similar saucepan having a totally anodised exterior. Furthermore, the anodised base which "wraps" around the lower side wall of the saucepan results in a saucepan with no "hot" spots particularly where the side wall joins the base-the heat is distributed evenly.

The present invention is further illustrated in the accompanying drawings wherein: Figure 1 is a composite representation of a saucepan in accordance with the present invention in which that half of the representation left of the centre line is a vertical crosssection and that half of the representation right of the centre line is an exterior view of the pan; Figure 2 is a vertical cross-section through a pan and assembly for brazing aluminium to the base and lower side wall of the pan; Figure 3 is a vertical cross-section through a pan and assembly for hard anodising the aluminium surface of the pan; and Figure 4 is a flow diagram showing the steps involved in manufacturing a cooking vessel in accordance with the present invention.

The drawing shows a pan 1 fabricated from stainless steel with a base 2 and side wall 3.

The base 2 and part 4 of the side wall 3 is clad in an aluminium alloy which is hard anodised to form a darkened exterior surface 5.

Fig. 2 shows the assembly for brazing an aluminiun disc 6 to the base and lower side walls of the pan 1. The aluminium disc 6 is so shaped as to wrap around the base and lower side wails of the pan 1 and located between the aluminium disc 6 and the pan 1 is a layer of flux and brazing powder 7. A specially shaped susceptor 8 made of mild steel is provided and brazing is achieved by means of an induction coil 9.

Fig. 3 shows the assembly for hard anodising the aluminium disc 6 which has been brazed to the base and lower side of the pan 1. The exposed stainless steel parts of the pan and masked with a masking layer 10 and copper electrodes 11 attached to the pan 1.

These are held in place by a rubber ring 1 2 and the assembly is floated in an anodising bath of 10-20% by weight aqueous sulphuric acid.

Fig. 4 shows the manufacture of a pan with a hard anodised base and lower side wall in a step by step manner.

Claims

1. A cooking vessel in which the base and part of the side wall extending from the base is provided with a hard anodised surface.

2. A cooking vessel as claimed in Claim 1 in which the base and part of the side wall extending to a depth of 2 cm from the base is provided with a hard anodised aluminium surface.

3. A method of manufacturing a cooking vessel which comprises forming the cooking vessel from stainless steel, applying an aluminium surface to the desired part of the exterior surface of the cooking vessel, masking the remaining exposed stainless steel surface of the cooking vessel, hard anodising the exposed aluminium surface of the cooking vessel and removing the masking.

4. A method as claimed in Claim 1 in which the aluminium surface is applied to the cooking vessel by means of high frequency induction heating.

5. A method as claimed in Claim 3 or 4 in which the masking of the stainless steel surface is achieved by applying tape thereto, or by spraying the surface with an organic material or by silk screening the surface.

6. A method as claimed in any of claims 3 to 5 in which the hard anodising step employs a 10-20% by weight aqueous solution of sulphuric acid at a temperature of between 0 and 5"C and the initial voltage input is of 18 v DC rising to 50 v DC to give an amp density of 3-4 amp/dm2.

7. A cooking vessel as claimed in Claim 1 substantially as herein described and with reference to the accompanying drawings.

8. A method as claimed in Claim 3 substantially as herein described and with reference to the accompanying drawings.