NZ205964A - Three layer metal laminate for cooking vessels - Google Patents

Description

#» 2059 Priority Date(s): Complete Spouiication Filed: Class: Publication Data: P.O. Journal, No: - 8 AUG 1986 ; "/i'i'c NEW ZEALAND PATENTS ACT, 1953 ,<V If' °- I! f^os No.

Date: COMPLETE SPECIFICATION "THREE-LAYER METAL LAMINATE WITH BIMETALLIC EFFECT, AND THE APPLICATION OF THIS LAMINATE IN COOKING VESSELS" )(/We, ARDAL OG SUNNDAL VERK A.S., of Sorkedalsveien 6, Maj., Oslo 3, Norway, a Norwegian company, hereby declare the invention for which xk/ we pray that a patent may be granted to tffM/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - I - (followed by page la) 205 9 64 1 c\ This invention relates to the construction of a three-layer metal laminate consisting two different metals, the two outer, thinner, layers being of the same metal, whilst the middle layer, which is of a different metal, is thicker, with the result that the laminate acquires a bimetal effect. The invention also concerns the application of this laminate in vessels for preparing and keeping food.

It is known that in vessels for preparing food by means of heat, there arises a temperature gradient in the base which can result in its bulging. This deformation impairs the efficiency of heat transfer from flat hotplates, and furthermore results in local overheating of the vessel with scorching of the contents and other unpleasant consequences .

To avoid these difficulties, several possibilities have been tried. In the case of thin-based saucepans it is necessary, for example, to curve the base inwards to prevent the saucepan from "dancing" on the hotplate.

In the case of saucepans of stainless steel of type 18/8 steel, or of a laminate of stainless steel, it is necessary, in order to make the utensil satisfactory in use, to apply a comparatively thick extra base, usually of copper or aluminium, in order to improve heat distribution. It is further necessary to have comparatively thick material in the sides and in the base to achieve satisfactory stability. As a result of this, saucepans in stainless steel, or in a stainless steel laminate, are comparatively heavy, and production costs are high.

One of the objects of this invention is to rectify this shortcoming by producing thin-walled saucepans of laminated sheet with surfaces of stainless steel, thus achieving better use properties than found in 2059^4 2 earlier, known solutions, whilst at the same time these saucepans are cheaper to produce.

The prior art toaches of a three-layer metal laminate which consists of a core material of a metal with good thermal conductivity and which is clad with thinner steel on both sides. The thickness of these layers is stated to be about 11$ of the thickness of the middle layer. The layers are of equal thickness. No bimetal deflection is referred to, and neither can this be expected when the laminate is used for producing cooking vessels, frying pans and the like.

The three-layer metal laminate according to the prior art would therefore, if used for making the base of cooking vessels, deflect outwards (dance on the hotplate) when the base is heated; this lis oecause the temperature on the inside of the vessel will of necessity always be lower than on the outside, with the result that the outside of the base expands more than the inside.

Cooking vessels according to the present invention counteract this bulging in that there is incorporated bimetal deflection in the opposite direction.

When a three-layer metal laminate is used for making cooking vessels and the like, the thermal deflection referred to is achieved, according to the present invention, when the middle of the laminate consists of a thick plate of a metal with moderate or good thermal conductivity and which is clad on each side with thinner sheets of some other metal with considerably lower thermal conductivity, coupled with the fact that the metals have different coefficients of thermal expansion, and that the cladding on the one side preferably has a thickness of from 5 - 10? of the thickness of the middle layer, and further that one of the outer layers is preferably at least twice as thick as the other. This results in bimetal deflection.

The laminate according to the invention, on being heated, deflects in the desired direction and to the desired degree. When this laminate is used for making thin-walled saucepans, the stresses which arise on account of the difference in temperature on the outside and the inside and which normally"result in bulging of the base, are counteracted, or entirely overcome, by the in-built bimetal effect which operates in the opposite direction, i.e. inwards, so that the base remains stable compared with the normal heating pattern.

Thermal deflection of this nature is achieved, according to the invention, by a three-layer metal laminate which in the middle consists of a comparatively thick plate of a metal with moderate or good the conductivity and which on both sides is clad with thin sheets of different metal with considerably inferior thermal conductivity, 2 0 5 9 £>4 further that t.lu: ratals have different coefficients of thermal expansion, and in uiiich the layer on the one side preferably has a thickness of b—10% of the thickness of the middle layer, whilst the other side preferably has a thickness of 10-30% of the middle layer, and further th^it one of the outer layers is preferably at least twice as thick as the other, so that on being heated there arises bimetal deflection.

Experience has shown that when the middle metal has a lower coefficient of thermal expansion than that of the metal in the two outer layers, then one of the outer layers can have a thickness of 15-20% of the middle layer, whilst the other layer has a thickness of 5-10% of the middle layer. 205964 A When the middle in.-tal has a higher coefficient of thermal expansion 1.1 Kin l.l ic metal in Llic two outer layers, then the tliicker outer layer must be even thicker compared with the other outer layer. The thicker layer can then be 30$ of the middle layer, whilst the thinner outer layer is 10% of the middle layer.

In the event of overheating a saucepan, with contents, the bimetal deflection will increase, and an air space will be formed between the base of the saucepan and the hotplate.

This increases safety because the burning or scorching of the contents is less, and the danger of spontaneous ignition of the contents is less. In principle, this bimetal defletion can also be considered utilized for controlling the wattage transferred. As the base is thin, yet remains flat, an entirely new principle arises in the use of hotplates. The inertia of heat absorption becomes less, and reaction speed thus greater. In short, the cooking vessel will react faster to adjustments to the energy provided.

Another example of the practical application of the laminate according to the invention is in canteen containers for use in water baths. Standardized canteen containers are to-day in wide use. They are made of stainless steel sheet. Known embodiments of such containers cannot be used for preparing food involving boiling or frying. The bulging of the base and local overheating prevents this. The food has to be prepared in some other way and poured into the container. This has an unwanted mashing and breaking-up effect. The water bath does not provide sufficient heat, and if the contents are to be kept hot for some time, it may be necessary to empty them back into the sucepan for heating on a hotplate. It would be a considerable advantage if canteen containers of sheet metal which fit into standardized water baths could also be used as saucepans. 205964 s / It in thus nl:;o an object of this invention to use a three-layer metal laminate for saking cooking vessels or cooking vessels for keeping food hot. In connection with the latter application, reference is made in particular to thin-walled canteen containers with surfaces of austenitic stainless steel, which can be used as saucepans on all heat sources of interest. By way of example, it may be mentioned that mild steel has 330? better thermal conductivity than stainless steel, whereby a steel inlay in the laminate will result in more uniform distribution of heat throughout the base of the vessel.

A description will now be given, with reference to the drawings, of the application of the three-layer laminate, in which the laminate is used for cooking vessels or for vessels for keeping food hot.

Fig. 1 is a cross-section of a laminate consisting of mild steel clad with austenitic steel, in the cold state.

Fig. 2 shows the laminate as in fig. 1 in the hot state.

Fig. 3 shows the laminate with a core of aluminium clad with austenitic stainless steel, in the cold state.

Fig. 4 shows the laminate according to fig. 3 in the hot state.

Fig. 5 illustrates a vessel made of the laminate according to fig. 3, in both cold and hot states.

Fig. 6 represents a canteen container made of the laminate according to fig. 1 in the hot and cold states.

In the drawings, the various layers are shown enlarged. The middle layer can be a metal with a coefficient of expansion which is less t- p 205964 than the coefficient of expansion of the cladding metal, and has thus been given designation 1. When the middle layer has a coefficient of expansion larger than that of the cladding metal, it is given designation 2. The cladding is always of different thicknesses on the two sides. The thicker side is designated 3> and the thinner, 4. Preferably, the thicker cladding is 10 - 30? the thickness of the middle layer.

In a preferred embodiment, the three-layer laminate consists of a middle layer of aluminium whilst the outer layers consist of stainless steel, usually 18/8 austenitic steel.

In certain embodiments, it can be avantageous to have mild steel in the middle layer, whilst the two outer layers consist of stainless steel.

There is nothing against coating or cladding the outer layers with a thin layer of some other material, for example, copper on the outside and/or Teflon on the inside. Also other coatings can be applied.

Claims (6)

205964 i 7 WHAT $ WE CLAIM IS: CLAIM3

1. Three-layer metal laminate for use in cooking vessels and the like which in the middle consists of a comparatively thick plate of a metal with moderate or good thermal conductivity and which on both sides is clad with thinner sheets of some other meta], with considerably lower thermal conductivity, the two metals having different coefficients of thermal expansion, characterized in that the cladding on the one side preferably has a thickness of from 5 - 10? of the thickness of the middle layer, and further in that one of the -outer layers is preferably at least twice as thick as the other, so that, on being heated up, there arises bimetallic deflection.

2. Three-layer metal laminate according to claim 1, characterized in that the middle layer is of aluminium and the two outer layers of stainless steel.

3. Three-layer metal laminate according to claim 1, characterized in that the middle layer is of mild steel and the two outer layers are of stainless steel. *1.

Application of three-layer metal laminate according to claim 1, characterized in that the laminate is used for making cooking ^ " vessels or vessels for keeping food hot. u ■» 3 JUN1986

5. A laminate as claimed in any one of claims 1 to 3 substantially as hereinbefore described with reference to the accompanying drawings^

6. The application as claimed in claim 4 substantially as hereinbefore described with reference to the accompanying drawings. DATED THISCyd DAY OF A. J. PARK & SON PER AGENTS FOR THE APPLICANTS