Abstract:
Multi-ply composite cookware consisting of different metal combinations to include the beauty of copper on the exterior coupled with its excellent heat distribution/conductivity properties within the interior to provide thermally efficient, durable and cosmetically pleasing cookware. In several embodiments of the present invention, a layer of silver is also preferably employed in the interior thereof between adjacent aluminum layers to further improve thermal conductivity.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/921,100 filed Mar. 30, 2007, and is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to cookware and, more particularly, to composite roll bonded multi-ply cooking vessels containing layers of copper, aluminum and stainless steel in various combinations including, in some embodiments, a layer of silver bonded within the interior core of the composite. 
         [0004]    2. Description of Related Art 
         [0005]    Several prior art known constructions employing discrete roll bonded layers of copper, aluminum and stainless steel are shown in  FIGS. 1 and 2  and, in themselves, are well known in the art and commercially available products marketed by All-Clad Metalcrafters LLC., the owner of the present patent application.  FIG. 1  depicts a commercial line of cookware of All-Clad Metalcrafters LLC marketed under the registered trademark COP.R.CHEF. The composite cookware  1  is a three-ply bonded construction comprising an exterior layer  2  of copper bonded to a layer  3  of aluminum which, in turn, is bonded to a layer  4  of stainless steel such as austenitic 18/10 grade of stainless steel which forms the interior of the cookware  1 . Copper layer  2  and aluminum layer  3  are prebonded separately and then hot roll bonded to the layer  4  of stainless steel. 
         [0006]    The cookware  5  depicted in  FIG. 2  is directed to a five-ply bonded composite comprising outer and interior layers  6  and  6 ′, respectively, of stainless steel roll bonded to an innermost layer  8  of copper and interfaced between the stainless steel and copper layers with layers  7  and  9  of pure aluminum. This commercial cookware  5  is sold by All-Clad Metalcrafters LLC under the registered trademark COPPER-CORE and more fully disclosed in U.S. Pat. No. 6,267,830 to Groll which is incorporated by reference herein. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is intended to provide different metal combinations in multi-ply composite cookware to include the beauty of copper on the exterior coupled with its excellent heat distribution/conductivity properties within the interior to provide thermally efficient, durable and cosmetically pleasing cookware. In several embodiments of the present invention, a layer of silver is also preferably employed in the interior thereof between adjacent aluminum layers to further improve thermal conductivity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross section of a prior art three-ply composite construction for cookware; 
           [0009]      FIG. 2  is a cross section of another commercial five-ply cookware construction; 
           [0010]      FIG. 3  is a cross-sectional view of one presently preferred embodiment of the present invention; 
           [0011]      FIG. 4  is a further presently preferred embodiment of the present invention; 
           [0012]      FIG. 5  is yet another presently preferred embodiment of the present invention; 
           [0013]      FIG. 6  is still yet another presently preferred embodiment of the present invention; and 
           [0014]      FIG. 7  is another presently preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 3  depicts a cross-sectional view of a first embodiment  10  of cookware made according to the present invention. The composite cookware  10  comprises an outer layer of copper  12  cold roll bonded to a layer of aluminum  13  which may be pure aluminum,  3003  aluminum alloy or an Alclad aluminum. Copper layer  12  and aluminum layer  13  form a first prebond composite  11 . A second prebond composite  11 ′ is made up of a copper layer  12 ′ sandwiched between aluminum layers  14  and  14 ′. First and second prebond composites  11  and  11 ′ are then hot roll bonded to a layer  15  of stainless steel which forms the interior cook surface of the cookware  10 . 
         [0016]      FIG. 4  depicts a second presently preferred embodiment of the present invention in the form of cookware generally designated  20 . The multi-layer composite making up cookware  20  is the same as that described above with respect to  FIG. 3  except for the addition of a layer of silver  25  positioned between and roll bonded to aluminum layer  13  of first composite  11  and the layer of aluminum  14  of second composite  11 ′. The silver material in layer  25  is preferably in the form of a thin foil having a thickness of about 0.003 to 0.005 inches. The silver layer  25  could also be applied by plating or other known means. 
         [0017]      FIG. 5  depicts a third presently preferred embodiment of the present invention in the form of a composite cookware construction  30 . Composite cookware  30  comprises an outer layer  32  and an inner layer  32 ′ of stainless steel (cook surface side) roll bonded to first and second prebonded composites  35  and  35 ′ made up respectively of a copper layer  36  cold roll bonded to and between layers  34  and  34 ′ of aluminum. In prebonded composite  35 ′ a layer of copper  36 ′ is cold roll bonded between layers  38  and  38 ′ of aluminum. A layer of stainless steel  25 ′ faces the aluminum layers  34 ′ of the first composite  35  and the aluminum layer  38  of the second prebond composite  35 ′. In embodiment  30 , a stacked array comprising stainless steel layer  32 , first prebond composite  35 , stainless steel layer  25 ′, second prebond composite  35 ′, and stainless steel layer  32 ′ are placed together as shown in  FIG. 5  and hot roll bonded together at an appropriate temperature in a rolling mill. 
         [0018]      FIG. 6  shows a fourth presently preferred embodiment  40  of the invention which comprises a first prebond composite  46  made up of a layer of copper  44  cold roll bonded to a layer of stainless steel  42  and a second prebond composite  46 ′ comprising a layer of copper  44 ′ cold roll bonded to a layer of stainless steel  42 ′. The prebonded composites  46  and  46 ′ are then hot roll bonded together with a layer of silver  45  interposed therebetween. 
         [0019]    In all of the above examples, the roll bonded composite materials  10 ,  20 ,  30  and  40  may be subjected to a post rolling heat treatment at about 650° F. to further strengthen the bond achieved during rolling. This in itself is well known in the art. The composite shapes can then be deep drawn into appropriate cookware shapes, such as pots, pans and the like. The exterior copper layer is given a final polish/buffing treatment to provide a beautiful cosmetic appearance to the finished cookware. The interior surface can also have a non-stick coating applied thereto if desired. In the embodiments of  FIGS. 5-7 , the outer layer of stainless steel, such as layer  32  and layer  34  of aluminum in  FIG. 5 , can be machined away to form one or more skived rings (not shown) around the perimeter of the cookware to show the underlying copper layer  36  as a decorative effect. 
         [0020]      FIG. 7  depicts a fifth presently preferred embodiment  50  of my invention which includes outer layers  52 ,  52 ′ of stainless steel, aluminum layers  54 ,  54 ′,  57 ,  57 ′, and copper layers  55 ,  58 . The embodiment  50  is essentially the same as embodiment  30  of  FIG. 5  except that the layer  56  is silver in embodiment  50  rather than stainless steel layer  25 ′ in embodiment  30  of  FIG. 5 . 
         [0021]    As used herein, the term “aluminum” can include pure aluminum of EC grade of the 1000 series of alloys, 3003 aluminum alloy, or Alclad aluminum. The stainless steel layer is preferably austenitic stainless steel, although a ferromagnetic grade may be substituted for outer layer  32 ′,  52 ′ if the cookware is to be induction heated. The copper layer in the prebond composites  11 ,  11 ′,  35 ,  35 ′,  59  and  59 ′ preferably occupies at least about 80% of the thickness thereof, wherein the thickness of the prebond is about 0.035 inches. The surfaces of the metal sheets/prebond composites to be roll bonded are first mechanically abraded and cleaned to remove surfaced oxides and contaminants. Heating prior to hot rolling takes place in a slightly reducing furnace atmosphere at about 650° F. Hot rolling is done preferably in two passes at 1-10% reduction and 5-30% reduction, more preferably 5% and 15%.