Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~ 78
This invention relates to cookware of the non-stic~ type.
Cookware is well known in which the cooking surface i~
treated with various fluorocarbon polymer compositions, such
as those sold under the trade marks DURON and TEPI~N, in order
to inhibit the sticking to the ~urface of food being cooked;
more recently other organic polymeric coatings having similar
properties have become available. In spite of continuing improve-
ments, such surfaces are subject to wear or damage which limits
their durability unless special care is taken in their use, and
~0 they have various other potential or actual disadvantages. Such
a coating cannot provide the attractive appearance of polished
metal finish and particularly if damaged can contain pits or
roughness which can harbour contamination, and can allow corrosion
of the substrate metal. Moreover the thicker and tougher
coatings in particular have a significant resistance to
heat transfer, and in certain cases there appears to be an
increased tendency for liquid foods to burn in contact with the
surface, possibly because of the lack of a polished surface.
Other materials for the cooking surfaces of cookware which -
have found favour are stainless steel, because of its ability to
retain a polished finish and resist corrosion, and cast iron - -
or heavy gauge steel because of its high thermal capacity resulting
; in even heat transfer to the food. In order to co~bine these --
properties, heavy gauge carbon steel clad with stainless ~teel has
been u~ed in cookware.
It is known that titanium, like stDinless steelO has a
hlgh corro~ion re~i~tance and will retain a polished finish, but
~ince it 1~ much more c08tl~ and mN¢h more difficult to work than
~tainlo~ ~teel, there ha~ b en no rea~on to employ this metal in
cookware, ~
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78
We have found, most unexpectedly, that a titanium cooking
surface provides non-stick properties similar to tho~e a~sociated
with polyfluorocarbon fini~hes, but without the disaavantage~
of the latter and whilst at the same time providing the advantages
associated with stainless steel sy utilizing a steel substrate
Cos7
explosively clad with a surface layer of titanium, the ~t i~
reduced, and by using a substrate of suitable thickness, some
of the advantageous properties of cast iron cookware can also
be achieved.
However, we have found that it is not possible to use the
normal fabrication methods used for cookware upon titanium and
titanium-clad ~ubstrates, and our initial attempts to produce
acceptable cookware were unsuccessful. We have found that it is
essential to maintain a continuous and uninterrupted layer of ~--
titanium over the cooking surface, and thus unless the cooking
surface is ~L~ u~b~planar, as in a griddleO there are difficult- ~ -
ies in fabrication. For manufacturing hollow cookware, we have
found the satisfactory techniques to be either to build up the
cookware from separate parts~J welding the seams in the cooking
surface with pure titanium so as to maintain continuity of the -~
titanium surface, or explosively forming of a titanium clad
.
~substrate ~L sheet to the desired configuration. The former
technique i8 preferred where deep cooking vessels are to be ~-
produced, or where the base of the cooking vessel is to be -~
~ub~tantially thicker than the sidewalls, a~ is desirable when
the cookware i8 to incorporate integral electric heating elements~ -
Further feature~ o the invention will be apparent from
the following de~cript~on of exemplary embodim~nts of the invention
~ith reference to the accompanying arawings, in which:
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~.0~49t78
Eigure 1 is an isometric view of the pan portion of an
electric frying pan of the tilting type,
Figure 2 is a fragmentary vertical section on the line 2-2
in Figure 1, and
Figure 3 is a fragmentary vertical section l:hrough a
side wall and pa~t of the base of a skillet.
Referring to Figures 1 and 2, the pan shown is of the
known type in which a pan 2 with electrical elements 4 encased
beneath the pan is mounted by trunnions 6 upon a base (not shown)
so that the pan may be tilted to pour off excess fat or liquid
or solid food being cooked from lips 8 with a spout 10. The
construction of the pan is also largely conventional, except for the
materials and fabrication techniques employed.
Whereas in a convention81 pan of this type the base of
the pan would commonly be of carbon steel clad on its upper surface
with itainless steel, in the present case the upper surface of
the carbon steel layer 12 is explosively clade with a titanium layer
14. A suitable material is sold by E.I. du Pont de Nemours & Co.
lnc. under the trade mark DETACLAD. Typically, the titanium
layer is 1/16 inch thick and the carbon steel substrate is of 3/8 -
inch thickness. The su~strate may be tapped in conventional manner
to recelve studs 16 for nuts 18 which tight~n clamps 20 by means
of which the elements 4 are secured to the base. Stainless steel
skirts 22 are welded at 24 to the substrate layer 12 so as to
; shroud the elements and support the trunnions ~, enclosure of the - - elements being completed by a base plate 26.
The side walls 34 and lips 8 of the pan are formed from a
strip of 1/16 inch thick titanium sheet. The upper edge of the
sheet i~ folded outwardly to form a bead 20~ except in the area of
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the lips 8 which are formed by outward bending of the strip
material. The lower edge of the sheet is notched at the positions
of the corners 30 of the pans and bent inwardly to form curved
transitions 32 whose inner ends abut the edges of the layer 14.
The spout 10 is separately formed and the seams in the strip and
between the strip and the spout and the strip and the layer 14
are ~oined by titanium welds 36 so as to maintain continuity of
the titanium cooking surface. Although titanium welding is
difficult and requires great skill, alternative methods of bonding
such as silver soldering have not been found to work.
Where hollow cookware with a relative thin base is
satisfactory, as in much stove-top cookware, a unitary sheet of
steel explosively clade with titanium may be explosively formed
to provide the body of an article of cookware. In accordance with
conventional explosive forming techniques, the sheet to be formed
is positioned so as to close the opening of a hollow mould, which
is evacuated, and an appropriate explosive charge is applied
to the titanium clad surface of the plate and detonated so as --
plastically to deform the plate into a comp}ement of the mould
cavity whilst maintaining the integrity and continuity of the
titanium cladding. A section of part of a skillet formed in this
manner is shown in Figure 3~ both the titanium layer 40 and the --
steel layer 42 being continuous as between the base 44 and the side
- wall 46 of the skillet.
Although both the welding of titanium and explosive forming
are known techniques, it it not believed that they have previously -
been used to form cookware. The added expense as compared with
more conventional fabrication techniques is only ~ustified in the
present instance by the advantageous properties thereby secured
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in the product. 1~ 78
In some cases, neither welding nor explosive forming
will be required. Thus a g~iddle may be formed from a plate
of carbon steel explosively clad on its upper surface with
titanium, the necessary fixtures and fittings required to
complete or install the griddle being formed into ar attached
to the steel plate without penetrating the cooking surface.
Stove-top ware could be explosively formed or titanium
weld~d from titanium sheet throughbots, although clad material
will usually be preferred 80 as to reduce the co~t of material
and increase the thermal capacity of the cookwareO The substrate
layer of the clad material could comprise metals other than
steelt for example, the lower surface of the base of an article
of cookware can sometimes advantageously be clad with copper to
improve thermal conductivity~
~he term ~non-stick" is used as applied to cookware
in this specification and the appended claims in its normal
commercial sense to imply a ~ubstantially reduced tendancy
for food to ~tick to the cooking surface as compared with
the ~uraces of conventional metal cookware, and is noteto
< be understood as a representation that no sticking will occur
under aDy circum~tance~. :
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