Abstract:
A cooking vessel is formed with one or more annular rings rising above a laminate structure that exposes at least one more thermally conductive material of a contrasting color. The raised rings reveal the nature of the thermally conductive material, yet protect it from scratches and abrasion during use, such as when the cooking vessel is resting on a stove top.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   None 
   BACKGROUND OF INVENTION 
   The present invention relates to improve cooking vessels, in particular those having more durable wear resistant bottom surfaces. 
   Cooking vessels, such as pots and pans, are constructed out of a wide variety and combinations of metals as well as non-metallic coatings. Certain materials are selected for their heat transfer properties, while others are deployed as external surfaces, and frequently selected to improve durability in that they offer a consistent external appearance, despite the propensity for scratching or marring that occurs from contact with heating elements during use, stirring utensils or cleaning agents. 
   Copper in particular is a favorite material for constructing cooking vessels, because of its unique appearance, but also for its superior heat transfer properties compared to other metals. A popular design for cooking vessels is to utilize a laminate construction in which a layer of copper is sandwiched between other materials that form the interior of the cooking vessel as well as the bottom surface of the cooking vessel. However, these constructions, while protecting the copper layer from abrasion that will degrade the appearance, also hide the copper. This can be disadvantageous to manufactures as well, as the presence of copper in the construction will not be readily apparent to consumers, who might confuse such products with inferior merchandise. Thus, consumers looking for copper based cookware, may readily forego purchasing such products although they might have nearly equivalent heat transfer properties compared to pure copper cookware products. 
   It is therefore a first object of the present invention to provide cooking vessels that predominantly display the copper construction in their bottom surface. 
   It is a further object of the invention to provide cooking vessels constructed predominantly of copper, in which the copper in the bottom surface is protected from scratches or mars that might arise from contact with heaters and other burner elements. 
   SUMMARY OF INVENTION 
   In the present invention, the first object is achieved by forming a cooking vessel having a copper sheet or plate partially laminated between one or more exterior layers, such as stainless steel or another hard or durable material, with regions of the copper exposed where the hard or durable material is absent. Thus, the stainless steel extends from the bottom of the pan as a profile to protect the visible, but indented, copper layer from scratches and abrasion by the heaters or burner elements. 
   A second aspect of the invention is characterized in that the hard durable material in the exterior laminate layer is partially removed to expose one or more rings of copper that are concentric with the center of the pans, being recessed below the hard durable exterior layer and thus protected from abrasion during cooking. 
   The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a prospective view of the bottom surface of a cooking vessel according to a first embodiment of the invention. 
       FIG. 2  is a cross-sectional elevation showing the laminate construction of the cooking vessel in  FIG. 1 . 
       FIG. 3  is a cross-sectional elevation showing the method of forming the laminate construction of the cooking vessel in  FIG. 1 . 
       FIG. 4A  is a prospective view of the bottom surface of a cooking vessel according to a second embodiment of the invention. 
       FIG. 4B  is a cross-sectional elevation of the cooking vessel in  FIG. 4A . 
       FIG. 5A  is a partial cut-away of an elevational cross-section showing the laminate construction of the cooking vessel in  FIG. 3 . 
       FIG. 5  B is plan view corresponding to  FIG. 5A . 
       FIGS. 6A ,  6 B,  6 C and  6 D are a sequence of cross-sectional elevations to illustrate the steps in constructing the cooking vessels of  FIG. 5A  and  FIG. 5B . 
       FIG. 7  is a prospective view of the bottom surface of a cooking vessel according to another alternative embodiment of the invention. 
       FIG. 8  is a cross-sectional elevation to illustrate the multiple steps in one method of forming the cooking vessel of  FIG. 7 . 
   

   DETAILED DESCRIPTION 
   In accordance with the present invention,  FIG. 1  depicts an inverted cooking vessel  100  of a first embodiment, in which external bottom surface  120  is upright and surrounded by upright wall  130  that extends therefrom, having outer surface  131 . Upright wall  130  extends to outer rim to define the fluid retaining cavity  140 . Accordingly, for the purposes of this illustration cooking vessel  100  may be considered to be resting on rim  150 . 
     FIG. 2  is a cross-sectional illustration showing the laminate construction of cooking vessel  100  in  FIG. 1  The bottom  120  of cooking vessel  100  comprises at least three layers of materials, with the upper or outer layer  123 , (that is at the bottom of the pan when the FIG. is inverted for normal use) being discontinuous, as it extends above the middle layer  122 . Accordingly, when cooking vessel  100  is resting on a burner or stove top in the normal non-inverted position, only the outer layer  123  makes contact with the supporting surface. While the inner layer is preferably copper, other substitutes include copper alloys as well as a copper clad layer of another thermally conductive material in particular aluminum. A portion  122   c  of layer  122  is exposed in this perspective view. Also at the bottom edge of the pan  126  inner layer  122  is exposed. In a preferred embodiment, the inner surface  121   a  of the fluid retaining cavity  140  at the bottom of cooking vessel  100 , the first layer  121  is the same material that forms upright wall  130 , being contiguous from inner wall surface  132  across the bottom inner surface  121   a , to line the inside of fluid retaining cavity  140 . Next, a copper layer  122  is disposed above layer  121 , forming an interface  122   a  therewith. The inner copper layer,  122  is thus surrounded by bottom  133 , having a continuous interface  122   a  therewith, and partially covered by an outer layer  123 , which forms a discontinuous interface  122   b  therewith, but projects outwards from the bottom surface of the cooking vessel  100 . The copper layer  122  provides high thermal conductance between the last or outer layer  123 , such that surface  121   a  reaches a substantially uniform temperature over its width or lateral dimension. As outer layer  123  only partially covers copper layer  122 , at interface  122   b , a central region  122   c  of the copper layer is exposed at the center of bottom  120 . Further, as layer  122  extends to the outer edge of the pan, being warped or deformed to conform to the contour of inner surface  121 , it is exposed as portion  126  of side wall exterior surface  131 . Thus, the upper or outer layer  121  projects outward from the middle layer  122  in normal use such that the cooking vessel will rest on outer layer  123 . Accordingly, the visible portion  122   c  of the middle layer  122  will not be subject to damage from the supporting surface, that is a gas burner ring, electric heating element and the like. As the middle layer  122  is preferably copper and the outer layer is preferably stainless steel, the configurations available in the various embodiments reveal that the cooking vessel processes the superior thermal characteristics of copper cookware, while at the same time offering the greater durability and more consistent shiny appearance afforded by constructing the outer layer  123  of stainless steel. In the preferred embodiments the outer layer has a thickness of between about 0.5 mm to 2 mm, whereas the copper layer has a preferred thickness of about 1 to 2 mm. 
     FIG. 3  is a cross-sectional elevation to illustrate a method of forming the laminate construction of the cooking vessel in  FIG. 1 . In this embodiment, cooking vessel  100  is formed from three components,  323 ,  322  and  345 . The first component is an upper disk  323  having a concentrically disposed circular hole that defines opening  122   c  in  FIG. 1 . The second component is a circular plate of copper  322 , which ultimately is bonded, at surface  322   a , to the outer bottom surface  121   b  of a fluid containing vessel  345  to form middle layer  122  in  FIG. 2 . The other side  322   b  of copper plate  322  is bonded to the bottom surface  323   a  of upper disk  323 , laminating the copper layer between the bottom portion  121  of the liquid containing vessel  345  and the upper disk  323 . The upper disk  323  is optionally bonded to the copper plate at the same instance that copper plate  322  is bonded to surface  121   b  of vessel  345  by impact or friction bonding. Further, as the upper disk  323  is smaller in diameter than the projected diameter between walls  130  of fluid containing vessel  345 , portions  322   e  of copper plate  322  extends outside the perimeter of disk  323 . Thus, in the impact bonding process these portions  322   e  are deformed to form the side edge  126 , as shown on the finished cooking vessel  100  in  FIG. 2 . 
   In this embodiment, the impact bonding die in contact with surface  323   b  of upper disk  323  is preferably contoured to match the exterior profile of the finished outer surface of bottom portion  122  such that sufficient pressure is applied to the area that forms interface  122   a  directly below region  122   c . Further, product or brand identifying information may be embossed in the copper plate  122  during the impact bonding process in region  122   c . As alternative methods of fabrication will be described with respect to other embodiment, it should be understood that the method of fabrication are substantially interchangeable to achieve the same result regardless of the profile in bottom portion  120  of the cooking vessels disclosed in the various figures. 
     FIG. 4A  is a prospective view of the bottom surface of a cooking vessel  400  according to a second embodiment of the invention. Cooking vessel  400  has a circular bottom portion  420  surrounded by substantially upright wall  430  connected at the periphery thereof  FIG. 4A  shows the outside portion  435  of wall  430  whereas  FIG. 4B  shows the inner portion  436  of wall  430  which define an inner fluid retaining cavity  440 . Cavity  440  extends from the inside bottom  421  of the vessel to rim  450 , which flairs outward at the unconnected end of wall  430 . Wall  430  and bottom  405  that define cavity  440  are integral to a vessel portion  445 , whereas the remainder of the bottom  420  of vessel  400  is formed by adjacent layers  410 ,  415  and  416  with layer  410  being disposed in contact with the outer surface  405   a  of bottom  406  of vessel portion  445 .  FIG. 4B  also displays the laminar construction of bottom portion  420 , starting from inner or cooking surface  405   b , layer  410 , which is preferably aluminum, or a suitable alloy thereof, and an outer layer  416  of stainless steel to surround a middle layer  415 , which preferably comprises copper, or an alloy thereof  FIG. 5A  is a plan view of the bottom portion  420  of cooking vessel, and is aligned with the partial cut-away portion of the corresponding elevation in  FIG. 5B  to further illustrate the location and definition of the recesses  433  and  431  that display middle layer  415 , being disposed between extending rings  422  and  421 . In use the upright cooking vessel  400  rests on the outward extending portions of layer  416 , which is arranged as concentric rings  421  and  422 . It should be appreciated that in  FIG. 4B  the vertical axis is greatly expanded to illustrate the detailed construction of the laminated layers that form bottom portion  420 . 
   The extending portions of layer  416  form concentric rings to define recessed portions that expose layer  415 . Thus, the outer surface of bottom portion  420  includes a concentric circular cavity  433 . The nature and/or composition of middle layer  415  is also exposed in region  426 , at the edge of the cooking vessel adjacent upright wall portion  430 , as well as between upward extending concentric rings  421  and  422 , defining an annular exposed region  431  of layer  415 . The central circular exposed region  433  of layer  415  is thus defined by the perimeter of inner periphery of ring  422 . Further, as illustrated in  FIG. 4B  an additional layer  410  of conductive material is disposed between layer  415  and the bottom  421  of vessel  445 . Further, while layer  415  is preferably copper with a thickness of about 1 to 2 mm, layer  410  is preferably aluminum and has a thickness of about 2 to 5 mm. The outer or supporting rings  421  and  422  are preferably formed of stainless steel, with layers  415  and  410  providing a high thermal conductance for the later and uniform distribution of heat across the inside bottom  421  used as the cooking surface. The middle copper layer, being more thermally conductive than the adjacent surrounding aluminum layer  410  transfers heat absorbed from the burner element or flame laterally before reaching layer  410 . Thus, despite the poor heat transfer characteristics of stainless steel used to construct layer  416 , the inside bottom surface  421  will have a uniform lateral temperature profile for cooking foodstuff, thus accommodating a range of heating methods and burner or flame configurations that contact the bottom of surface  420  of cooking vessel  400 . 
     FIGS. 6A , B, C and D are cross-sectional elevations to illustrate multiple stages optionally deployed in constructing the cooking vessel  100 , shown in  FIGS. 1 and 2 , but more preferably to form cooking vessel  400  shown in  FIGS. 4 and 5 . The initial stage of fabrication is depicted in  FIG. 6A , in which a laminate  620  of a copper layer  622  and a stainless steel layer  624  is made or obtained. The laminate is further fabricated to form a circular disc  630  with portion of the stainless steel layer  624  being milled or machined away leaving a sequence of extending annular rings  623  that expose a portion of the underlying copper layer  622 , especially those now denoted as a central circular region  622   a , and concentrically disposed annular regions  622   b  surrounding  622   a , with the outer annular region  622   c , which in turn surrounds region  622   b.    
   In the subsequent fabrication step, illustrated in  FIG. 6B , the circular disc  630  is concentrically aligned with a circular aluminum disc  640  and with a vessel preform  645  with respect to a common axis a line passing through the center of both an upper welding electrode  661  and a lower welding  662 . The electrodes  661  and  662  are then energized to weld the assembly together, forming assembly  646 , with upper electrode  661  making contact at center of the upper surface of disk  630  and lower welding electrode  662  making contact with the inner bottom surface of vessel preform  645 . It should be appreciated that alternatives to this step include bonding two of the three components together by a first separate welding step prior to joining the third component by a second welding step. Although the vertical dimensions in  FIG. 6  are exaggerated to be a large multiple of the vertical scale to illustrate the laminate construction, it should be understood that the aluminum disc will generally be thicker than the copper and stainless steel disk, as well as narrower, as the aluminum undergoes significant flow and deformation during the subsequent impact bonding step illustrated in  FIG. 6C . 
   In  FIG. 6C , the spot-welded assembly  646  of  FIG. 6C  is impact bonding using a mating upper die  671 . The upper die  671  matches the contour of the exterior profile formed in disk  630  such that sufficient pressure is uniformly applied across entire interface  622   a , which is defined as the interface between disk  630  and aluminum disk  640 , during impact bonding. In addition, product or brand identifying information is preferably embossed in the copper plate  622  during the impact bonding process in region  622   c . Further, prior to impact bonding the lower portion of the assembly  646  is supported by mandrel  672 , which is inserted into the fluid containing cavity  440  of vessel  645 , matching the interior profile thereof. 
   During the step of impact bonding that occurs in transforming the assembly of  FIG. 6C  into the cooking vessel  400  of  FIG. 6D , the profile of the concentric extending rings and recessed regions in disk  630  is preserved. However, the softer aluminum layer  640  is spread by deformation to the lateral edges of vessel portion  645 , where it is confined or encapsulated within the continuous copper layer  622 . Copper layer  622  is deformed to match the inner edge profile of forming die  671 , ultimately forming a sloped bottom edge  426 . 
     FIG. 7  is a perspective view of cooking vessel  700  according to another alternative embodiment of the invention showing the bottom  720  and the outer surface  730   a  of upright wall  730  that extends therefrom, surrounding bottom  720  to form a fluid retaining cavity  740  Accordingly, cooking vessel  700  may be considered to be resting on rim  750  for the purposes of this illustration. Referring to the cross-sectional elevation of vessel  700  in  FIG. 8 , the bottom surface  720  has a pair of concentrically disposed grooves  731  and  732  formed in the outer bottom layer  735  that, along with a central circular recess  733  in the outer bottom layer  735  define three concentric annular rings  721 ,  722  and  723  that extend from the outer surface  735   a  of bottom layer  735  and protect the middle layer of copper  725 . Note that the middle layer of copper  725  is also visible from the edge of the cooking vessel as surface  726  that form a band surrounding the circumference of wall  730  at the lower section of the cooking vessel  700 . 
   Cooking vessel  700  is optionally fabricated in a manner substantially corresponding to the steps illustrated in  FIG. 6 . Alternatively, vessel  700  in  FIGS. 7 and 8  can be fabricated by first forming the vessel shown in  FIG. 1 , and thereafter machining or milling annular rings into the bottom outer layer  323  to form annular groves  731  and  732 . Alternatively, both the annular grooves  731  and  732  and the central circular region  733  can be formed by milling away portions of a continuous outer layer formed of stainless steel, or any other material or combinations of layers to reveal one or more inner or laminated layers. 
   It will be apparent to one of ordinary skill in the art that the construction and fabrication methods are readily modified by providing additional layers to any of the laminated portions described above, or subdividing any of the laminated components into laminates that contain additional layers, as may be preferred to enhance the bonding or adhesion of various materials during the impact bonding process. 
   Further, it should be understood that the middle layer to be exposed need not be continuous across the entire bottom surface of the cooking vessel, but is preferably continuous in those portions in which subsequent exposure is intended. Accordingly it should be appreciated that the copper layers described above can be bonded between one or more rings or disks of other materials, with the annular or circular regions between the disks being a continuous copper layer, and the other regions of the copper having perforations so that a stronger bond is formed between the surrounding layers where they meet at the holes or perforation in the copper, such that they bond and thus embed the copper disk or preform there between. 
   While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.