NZ210144A - Making cast iron cooking vessel with electric heating element and aluminium heat sink in base - Google Patents

Description

210144 Priority Date(s): ...(.'.(.4.'.$!?.

Complete Specification Filed: F.ft Ciass: £&!&?,. A&?fZ7f.CP. .

Publication Date: ....HP. ?£? J?!®.?....

P.O. Journal, No: ../*?. £2 ;K-Z. ;a*r£N Z2^f!C£ a»ovi98< Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "IMPROVEMENTS IN COOKING VESSELS" -t, WE BREVILLE HOLDINGS PTY. LIMITED a company incorporated under the laws of the State of New South Wales, of 45 Murray Street, Pyrmont, New South Wales, Australia, hereby declare the invention, for which 5-/we pray that a patent may be granted to ne/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 2i0144 The present invention relates to improvements in cooking vessels and particularly to a method of incorporating a heater element and an aluminium heat sink in the base of a cast iron cooking vessel.

Cast iron cooking vessels such as frying pans have certain culinary advantages and it has been proposed to provide such a cooking vessel with an electric heating element associated with an aluminium heat sink attached to the underside of the base of the vessel. In order to ensure good contact between the aluminium heat sink and the underside of the cast iron vessel it is necessary that the underside of the vessel be machined flat, which is a relatively expensive procedure.

The object of the present invention is to provide a method of manufacture for incorporating an electric heater and an aluminium heat sink in a cast iron vessel which effects significant economies in manufacture while providing a very satisfactory article.

The present invention takes advantage of the fact that in the finishing of cast iron vessels it is usual to porcelain enamel them, which involves heating the vessel to a temperature of about 800°C.

The present invention consists in a method of incorporating an electric heating element and an aluminium heat sink in the base of a cast iron cooking vessel which consists of the steps of:- 1. Forming a cooking vessel by casting from iron to provide a cavity on the underside of the bottom of the vessel; 2. Securing an electric heating element in the cavity in contact with the underside of the bottom of the vessel by mechanical means; 3. Spraying the vessel with porcelain frit; 4. Placing the vessel in an oven at a temperature sufficient to liquefy the frit and thereafter allowing the temperature to fall to between 650 and 750°C; . Placing a nitrided steel die with a bell-mouthed funnel preheated to between 650 and 750°C on top of the said cavity to leave a gap between the die and the underside of the vessel; 6. Pouring molten aluminium through said funnel to-'v|^Lll the 210144 space between the die and the vessel; and 7. Removing the die when the vessel has cooled sufficiently.

It is preferred that the cavity in the underside of the vessel be provided with undercut portions into which the molten aluminium can flow. It is further preferred that the mechanical means for securing the electric heating element to the vessel are saddle clamps screwed to bosses cast in the underside of the vessel.

In order that the nature of the invention may be better understood a preferred form thereof is hereinafter described by way of example with reference to the accompanying drawings in which:- Figures 1 to 5 which show portions of a cast iron vessel in cross section, the vessel being in the inverted position and the figures showing different stages in the method of manufacture A vessel such as a frying pan is formed by casting from cast iron in a conventional manner. As shown in the drawings the vessel is provided on its underside with a cavity 10 defined by a side wall 11. On the underside of the bottom 12 of the vessel in the centre of the cavity is formed a central boss 13 and a number of smaller bosses 14, the latter being for initial attachment of the electric heating element 15. The central boss 13 is used ultimately for the attachment of the cover to the underside of the vessel.

The electric heating element is attached to the underside of the base 12 by means of saddle clamps 16 secured by screws to the bosses 14 as shown in Figure 2. As will be seen from Figure 2 there is a free space beneath the saddle clamps 16 into which molten aluminium can run and this 4 - 2 1 44 feature together- with an undercut 17 formed around the inside of the periphery of the wall 11 and a similar undercut 18 formed around the central boss 13 provide a key for the aluminium heat sink.

, ■ The next step is to spray the whole of the vessel including the heater element with porcelain frit and place it in a oven at about 800°C to liquify the frit which then forms a substantially even coating over the whole surface of the vessel. The temperature is then allowed to fall to 10 700°C and a nitrided steel die 20 with a bell-mouthed funnel is placed in position as shown in Figure 3. The underside of the die is shaped to define a space for the reception of molten aluminium, which is poured in through the bell-mouthed funnel 21 and fills the space available as shown 15 in Figure 4 by the stippling. When the vessel is sufficiently cool the die 20 is removed. Being of nitrided steel it does not adhere to the aluminium and may be readily removed, leaving the aluminium heat sink 22 in position and, as is seen in Figure 5 this is engaged in the undercuts 17 20 and 18 and beneath the saddle clamps 16 and is thus held firmly in position on the underside of the vessel.

Major advantages of the method described above are that the underside of the vessel does not require machining as molten aluminium will take up the surface irregularities in 25 the casting. In addition to this the method of manufacture is such that relatively low grade aluminium may be used quite satisfactorily and it has been found that a saving of the order of 12% in the manufacturing cost of the article can be achieved against methods previously used and described 30 above. The finished article functions very satisfactorily and the aluminium heat sink serves to spread the heat produced by the electric heating element substantially evenly over the face of the vessel thus leading to even cooking of foodstuffs over the whole area on the bottom of the vessel. 35 The embodiment of the invention as described above is 210144 given by way of .example only as constituting a preferred embodiment of the invention defined broadly in the succeeding claims. # 210144

Claims (4)

WHAT WE CLAIM IS; 1. A method of incorporating an electric heating element and an aluminium heat sink in the base of a cast iron cooking vessel which consists of the steps of:-

1. Forming a cooking vessel by casting from iron to provide a cavity on the underside of the bottom of the vessel;

2. Securing an electric heating element in the cavity in contact with the underside of the bottom of the vessel by mechanical means; 3. Spraying the vessel with porcelain frit; 4. Placing the vessel in an oven at a temperature sufficient to liquefy the frit and thereafter allowing the temperature to fall to between 650 and 750°C; 5. Placing a nitrided steel die with a bell-mouthed funnel preheated to between 650 and 750°C on top of the said cavity to leave a gap between the die and the underside of the vessel; 6. Pouring molten aluminium through said funnel to fill the space between the die and the vessel; and 7. Removing the die when the vessel has cooled sufficiently. h 2. A method as claimed in claim 1 wherein the forming of c4~' i ~jjv* the cooking vessel the cavity is provided with undercut portions into which molten aluminium can flow.

3. A method as claimed in claim 1 or claim 2 wherein the mechanical means for securing the electric heating element to the vessel are saddle clamps secured by screws to bosses cast into the underside of the vessel.

4. A method of incorporating an electric heating element and an aluminium heat sink in the base of a cast iron cooking vessel as hereinbefore described with reference to the accompanying drawings. NGS PTY. LIMITED