CA1123622A

CA1123622A - Composite metal sheet cooking utensil and manufacturing method

Info

Publication number: CA1123622A
Application number: CA336,766A
Authority: CA
Inventors: Svein Eide
Original assignee: Ardal og Sunndal Verk AS
Current assignee: Ardal og Sunndal Verk AS
Priority date: 1978-09-29
Filing date: 1979-10-01
Publication date: 1982-05-18
Also published as: DK406679A; JPS5547816A; GB2034173A; NL7907253A; NO783317L; NO147292B; FI793014A; NO147292C; SE7908057L; BE879053A; DE2938976A1; LU81731A1; IT7925983A0; GB2034173B; FR2437184A1

Abstract

Abstract of the Disclosure A composite metal sheet cooking utensil (laminated cooking utensil, cooking pot, frying pan) built up of a core of a metal having relatively good heat conductivity such as alumi-num, copper, common quality steel etc., coated on one or both sides with a relatively thin layer of a more corrosion resist-ive metallic material such as stainless steel, titanium etc.
The lamination layers (sheets) are bonded to one another across the bottom surface of the cooking utensil and some distance upwardly the lower portion of the cooking utensil wall.
A laminated circular blank for the cooking utensil comprises two or more flat round metal sheets provided with soldering agent and possibly flux agent on their central con-tact surfaces facing one another and corresponding to the area of the cooking utensil bottom and a part of the lower portion of the wall.
The cooking utensil is manufactured (shaped) by deep drawing and the sheets can be soldered (brazed) together before or after deep drawing to provide a lamination.

Description

-3~2~2 BACKGROUND OF THE INVENTION
1. Field of -the Invention The present invention relates to composite metal sheet cooking utensils and a method for manufacturing such utensils and more particular laminated cooking pots, frying pans or the like built up of a core material sUch as aluminum, copper, common quality steel, coated on one or both sides wi-th a relatively thin layer of a more corrosion resistive material such as stainless ~qteel, titanium and others.
l~ 2. Description of the Prior Art Cooking utensils made of enamel coated steel sheet, aluminum or stainless steel all have their advantages and draw-backs. It is known to experts in the art that a cooking utens-il made of a laminated blank is more advantageous in use than a cooking utensil made of a homogene,ous material. By way of example reference is made to a statement in the periodical 'iAluminio" 1973 pages 367-381: "Il pentolame di allumino pro-blemi e futuro" and an article in Metal Progress May :l975 "The Countertop Range" by William More~and.

2~ When a laminated cookin~ utensil (composite metal sheet cooking utensil) is heated through the bottom,the temp-erature in the side wall will alsoincrease and the outer dia-meter of the:pot will increase so that the bottom will not be strained contrary to what is the case w.ith a cooking utensil made of stainless steel and having an extra thick bottom. A
cooking utensil having a hea-t conducting metal layer on the side wall can, therefore, have a relatively thinner aluminium .~

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layer or copper layer in the bottom than what is necessary in a non-laminated cooking utensil of stainless steel. Therefore, cooking utensils can be produced having a better tempera-ture sensitivity and cooking efficiency than tradi-tional cooking utensils of stainless steel.
It is known that cooking utensils can be manufact-ured of a composite blank prepared by rolling together at high temperature a common quality steel sheet and -two stainless steel sheets. This product, however, is not particularly nopu-lar in Europe because it is liable to burn the contents of the utensil as most of the heat transfer is concentrated to the ring-shaped area along the peripheral portion of the bottom.
Laminated materi.als for cooking utensils can be prod-uced e.g. by "cladding". However, a sufficiently strong bond-ing between e.g. aluminum and stainless steel is difficult to obtain because both metals have relatively thick oxide layers.
A cladding method which has got some technical importance is rolling at high temperature and vacuum. A lamination (clad) o aluminum and stainless steel can also be made by explosion 2~ cladding but this method is still more expensive than vacuum . rolling.
Cooking utensils with very useful quality can be produced by laminating sheets of copper and stainless steel or aluminum and stainless steel but the price for the product is ; very high. A lamination (a composite sheet) consisting of a `~ core sheet of aluminum coated on both sides with 0,38 mm (0,15") , .

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stainless steel costs three times as much as a corresponding blank of stainless steel.
In deep drawing operation of cylindrical utensils from laminated blanks consisting of material sheets having different modules of elasticity such as stainless steel and aluminum which are bonded together across their entire contact surface, it frequently'happens that the bonding between the lam-ination layers fails or that the weakest layer cracks. This phenomenon cannot be controlled during deep drawing so that the amount of wreckage can be rather great.
Laminations cannot be produced by brazing in rolling mills. Soldering of single circula-r blanks (rondels) across the whole surface is more expensive than rolling together at high pressure and temperature because the outfit is expensive and so is the solderin~ agent. Laminated circular blanks prod-uced by soldering are difficult to deep draw and the amount of rejects is still higher than for rolled lamination.
A drawback in usin~ laminated material is that lamin- ;' ated discard, cutting and trimming metals (composite sheets) are difficult to sell to steel mills or steel foundries.
Summary of the Invention '~
An object of this invention is to provide a cooking utensil of the art s-tated above which has a good heat transfer through the entire bottom and less heat loss through the wall than what is the case in conventional cooking u-tensils.

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Another object o~ the inventlon is ~o provide a cook-ing utensil which can be manufactured at a more reasonable price than the formerly known cooking utensils of laminated mat-erial.
A third object of the invention is to provide a cook-ing utensil which can be shaped by deep drawing without risk of cracking of the lamination layers in the cooking utensil wall.
A further object of the invention is to provide a laminated cooking utensil blank which reduces the amount of laminated discard to a minimum.
It is also an object Oe -the invention to provide a cooking utensiLbuilt up of laminated material at a reasonable price and in such a manner that the lamination process can be carried out by the producer of the cooking utensil.
A cooking utensil accordiny to the invention is char-acterised substantially~by the fact that the lamination layers - are fixedly bonded to one another over the bottom surface andsomewhat upwardly the side wall. Lamination layers can also be fixedly connected to one another along the top portion of the wall The outer layer can be "inflated" across a portion of the wall height so that an insulating space is provided between the outer layer and core layer of the wall. The bonding between the inner layer and the core layer can be less in radial and possibly in axial extension than between the core layer and the outer layer. The bonding between the lamination layers is pref-erably attained by soldering (brazing) The -~236:~2 bonding at the top edge of the cooking utensi:L can be provided by folding the outermost portlon of the inner layer or the outer layer possibly also using an adhesive. Al-ternatively, the conn-ection at the top edge can be provided by laminating an annulus shaped peripheral portion of the blank in a similar way as for the bottom surface.
A method according to the invention comprises the features that individual circular component blanks (rondels) are provided with soldering agent or the like and possibly sold-ering flux across the central portion thereof corresponding to the bottom and the lower portion of the wall of the cooking utensil, whereupon the circular blanks are deep drawn simultane-ously in one and same drawing press, whereupon soldering is Carried out by heating. Soldering or brazing can also be carried out before deep drawing.
I]l a lamina-ted circular blank for making a cooking utensil according to the inven-tion the lamination layers are Molecularly connected with one another across a central, circ-ular zone and optionally along a ring-shaped peripheral zone.
In a laminated round blank comprising three or more lamination layers one of the outer layers can be loosily mo~mted lnot sold-ered together with the remaining layers).
When a cooking utensil in accordance with the inven-tion is produced a circular blank sheet, e.g. of aluminum and a corresponding sheet of stainless steel are covered with flux agent and soldering agent in such a manner that only in the bottom portion and a portion of the wall of the I

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finished cookinq utensil a molecular bonding will be provided. Deep drawing can be carried out before Gr after brazing.
A substantial advantage of this invention is that cracking during deep drawing of the laminated blank is reduced to a minimum because the bonding only extends over a less por-tion of the wall. Since the blanks are laminated over the por-tions only comprising the bonding, cuttings and trimmings of the blanlc material are practically free for soldering metal and the single layers of the discarded material are not bonded to one another so that they can be sorted easily and sold. Cook-ing utensil blanks can be made by the cooking utensil producer himself as it is not articularly difficult to coat the ready cut circular blanks with foils of soldering metal and flux agent across the areas where the bonding is to be brought about.
Heating takes olace preferably after deep drawing and more pre-ferably at pressure. Heating can be provided by means of medium frequent or high frequent induction. If desirable, deep drawing can be performed after soldering. Sealing of the outer edge can be carried out before or after deep drawing. The seal-ing can be made by ultra sonic welding, folding or glueing. ;~
As already mentioned,in accordance wi-th an advantage-ous embodiment of the invention,the wall of the cooking utensil can be "inflated" after deep drawing and sealing of the edges, so that an insulating space is provided between the outer layer of stainless steel and the inner layer of aluminum or copper.
In this manner a laminated cooking utensil is provided having ' , . ~ . ~ .

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a good head conductivity in the bottom and the wall wherein the wall is effectively insulated at. the outside.
Other materials than aluminum and copper can be used as heat conducting layers, such ascommon quality steel. In addi-tion to brazing other bonding processes can be used, such as ultra sonic welding, friction welding, adhesive bonding etc.
Brief Description of the Drawings The invention will be disclosed more fully in the following with reference to the drawings, wherein . 10 Figure 1 is a cross section of a half part of a round blank for a cooking utensil in shape of a lamination of two layers, Fi~lre ~isa corresponding eross section through a round blank consisting of three layers, Figure 3 is a cross seetion through a round blank eonsisting of three layers . with the inner layer and outer layer bonded in different extension to the eore layer,and ~` Figure 4 resembles Figure 3 apart from the edge por-~ tion.
Figure 5 is a eross seetion through a half part of a eooking utensil produeed from the round blank of Figure 1, and Figure 6 a corresponding eross seetion through a cooking utensil made from the blank according to Figure 4.
Figure 7 shows a folded seam along the top portion of a cooking utensil, and Figures 8 and 9 are eross sectional views of eooking ~Z3~2 utensils made of blanks according -to Figure 3 and 4,-respect-ively, but with an "inflated" side wall.
Description of the Preferred Embodime,nt.s ___ Figures 1 and 2 are cross sectional views of circular blanks, so-called rondels. Figure 1 shows a blank in shape of a lamination 1 consisting of a main sheet 2 of material having relatively good heat conductivity, such as copper or aluminum, and a relatively thin sheet 3 of stainless steel. The lamina-tion sheets 2 and 3 are fixedly bonded to one another across a central circular area A and an annulus shaped peripheral area B, at which locations a soldering agent or welding agent 4, 5 is placed between the sheets. The round blank according to Figure 2 departs from the blank according to Figure 1 by the fact that the lamination 6 in addition to the above mentioned sheets 2 and 3 has a thin outer sheet 7 of stainless steel loos-ily connected (not soldered) to the core sheet 2. Further, the inner sheet 3 has a free peripheral portion 8 for providing a folded seam (Figure 7).
Figure 3 shows a lamination b]ank 9 having a core sheet 10 of aluminum or copper and an outer sheet 11 and an inner sheet 12 of stainless steel. The inner sheet 12 is bond-ed to the core sheet across a central circularly shaped area C
provided with a soldering~agent 19 extending radially somewhat beyond the bottom of the coo];ing ute,nsil to be produced. The outer sheet 11 is bonded to the core sheet 10 across a corresponding central circularly shaped area D having remarkably greater radial extension than the area C. The inner sheet 12 has a 9 ~

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free peripheral edge portion 13 withou-t the lamination 14 for provision of the folded seam as shown in Figure 7.
Figure 4 shows substantially the same blank 15 as Figure 3 except that both outer sheets 16 and 17 are bonded to the core sheet 18 along a peripheral annulus shaped portion E
across which portion soldering agent 19' is located between the sheets.
Figure 5 shows a cross section through a cooking utensil made of the round blank according to Figure 1. The bottom area where -the sheets are bonded to one ano-ther is denot-ed by A and a corresponding peripheral area is denoted by B, as in Figure 1.

Figure 6 is a cross sectional view of a cooking uten-sil made from the blank according to Figure 4. It appears clearly that the bonding between the coré sheet 18 and the inner sheet 17 (area C) covers the bot-tom portion and the roun-ded transitions towards the wall, whereas the bonding D between the core sheet 18 and the outer sheet 16 extends somewhat hi~her along the wall of the cooking utensil. Of course,-the inner ~0 bonding zone can be of the same extension as the outer bonding zone D or higher.
Figure 8 shows a cooking utensil made from the blank of Figure 3 with the connection between the top edge portions of the sheets 10,11,12 madebya folded seam as shown in Figure 7.
The folded seam can be applied with an adhesive agent. The space between the core sheet 10 of the wall and the outer sheet 11 of the wall is inflated so that an interspace 20 filled with gas or air is provided. The cooking utensil according to Figure 9 is prac~ically identical wi-th the cooking utensil of Figure 8 excep-t that the cooking utensil according to Figure 6 is made from the blank according to Figure 4.
The cooking utensil is shaped by simultaneously deep dra~ing of two, three or :Eour round blanks. Brazing can be per-for~ed in such a way -that a foil of brazing metal precoated wi-th flu~ agent is placed between each lamination sheet. The heating is preferably carried out at a pressure and can be provided by medium frequent or high frequent induction. The deep drawing operation can be performed before or after brazing.
In -the description two of the layers have been denoted as inner sheet and outer sheet, respectively, but it should be understood that the invention also covers embodiments where the round blank is turned upside down so that the top sheet will be- ,~
com~ ~ bottom sheet and vice versa. In an embodiment wherein one of the lamination sheets is not fixedly bonded across the bottom to the basis sheet, the effect can be obta~led that ~e bottom will "be lifted" to some extent from the cooking plate when a cer-tain temperature is attained so -that the heat transfer to the contents of the cooking utensil than will be reduced.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A cooking vessel of composite metal sheet comprising a bottom and a side wall formed out of a core material sheet having a good heat conductivity, a bottom and side wall laminat-ing metal sheet of good corrosion resistance covering one side of the bottom and the side wall of the core and bonded to the bottom substantially over the whole bottom surface and bonded only to the lowermost and to the uppermost portion of the side wall and providing an intermediate non-bonded portion at about the middle of the side wall.

2. The cooking vessel according to claim 1 comprising a second laminating sheet of good corrosion resistance bonded to the bottom surface and the side wall surface of the core material sheet on the side opposite to the first laminating sheet.

3. The cooking vessel according to claim 2 wherein the side laminating metal sheets are bonded to one another along the top edge of the wall.

4. The cooking vessel according to claim 2 wherein the bonding between the inner side laminating sheet and the core material sheet is of less radial and axial extension than between the core material sheet and the outer laminating sheet.

5. The cooking vessel according to claim 2 wherein the edge portion of the inner laminating sheet is folded over the top edge portion of the core material sheet and the outer laminating sheet to provide a folded seam.

6. The cooking vessel according to claim 2 wherein the edge portion of the outer laminating sheet is folded over the top edge portion of the core material sheet and the inner lamina-ting sheet to provide a folded seam.

7. The cooking vessel according to claim 1 wherein the non-bonded portion of the side wall comprises gas-inflated space between the core material sheet and the outer side laminating sheet.

8. The cooking vessel according to claim 1 wherein the bonding between the sheets comprises a soldering agent.

9. A round lamination blank for making a cooking vessel of composite metal sheet comprising a bottom and a side wall formed out of a core material sheet having a good heat conduct-ivity, a bottom and side wall laminating metal sheet of good corrosion resistance covering one side of the bottom and the side wall of the core and bonded to the bottom substantially over the whole bottom surface and bonded only to the lowermost and to the uppermost portion of the side wall and providing an intermediate non-bonded portion at about the middle of the side wall, said blank comprising at least two laminating sheets molecularly bonded to one another over a central circular zone only.

10. The lamination blank according to claim 9 wherein the lamination sheets are also bonded together along ring-shaped peripheral portions thereof.

11. The lamination blank according to claim 9 wherein the metal forming a first lamination sheet is selected from the group consisting of aluminum, copper and common quality steel and the metal forming a second lamination sheet is selected from the group consisting of stainless steel and titanium.