Abstract:
A cookware article in which the multiple continuous layers of metal form both the bottom cooking surface and surrounding sides that define the fluid containing region has a protected rim formed on the inner laminated layers, which curls over and is then bonded to the outermost layer of the laminate slightly below the rim.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a Continuation-In-Part application claiming priority to the U.S. Utility patent application for “Laminated Cookware”, filed on Jun. 21, 2005 and now having application Ser. No. 11/157,352, which is incorporated herein by reference. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     The present invention relates to improved cookware vessels, and in particular generally circular shaped pots and pans.  
         [0003]     Multi-ply and laminated cookware vessels, such as pots and pans, are well known in the art. They typically deploy copper and/or aluminum as one or more core layers, with surrounding layers to form the exposed interior and/or exterior surface of the cookware.  
         [0004]     Among other benefits, the copper and/or aluminum core layers enhance the thermal performance of the cookware; enabling both a faster heating of the foodstuffs and a more uniform temperature distribution. Outer layers of the laminate, that surrounds the copper and/or aluminum core, can provide an exterior surface that is easier to clean or maintain a particularly desired appearance in the kitchen.  
         [0005]     Such laminated articles of cookware are fabricated starting with pre-laminated sheet stock. Methods of making sheet stock suitable for eventually forming cookware are disclosed in U.S. Pat. No. 6,427,904 to Groll, titled “Bonding of Dissimilar Metals”, as well as U.S. Pat. No. 6,109,504, also to Groll, and titled “Copper Core Cooking Griddle and Method of Making Same”. The &#39;504 patent teaches the desirability of forming a sheet stock laminate of stainless steel/copper/stainless steel useful for fabricating cookware via the sequential reduction of thickness by repeated hot roll bonding steps. The preferred compositions in the construction is a diffusion bonded composite of 304L grade stainless steel outer layers with an inner core of high purity C-102 grade copper. However, explosion bonding is initially used to laminate the three layers.  
         [0006]     The cookware is then fabricated from the laminated sheet stock by first cutting or trimming the sheet stock into round shape. The round trimmed pieces are then deformed or drawn in a die to form a fluid containing cookware vessel. The trimming process, whether done at the beginning or end of the drawing process, exposes all the layers in the cookware article. Thus, the softer copper or aluminum used in the core of the laminate, along with the stainless steel outer cladding layer, are exposed at the rim. The core materials at the rim being softer and exposed at the rim are susceptible to denting or damage. The strength of the rim is a factor in the selection of the laminating material used to form the cookware article. That is, but for the softer materials exposed at the rim and the need to make the rim strong to resist deformation, the article of cookware could be made of thinner laminates, thus reducing weight as well as saving on material cost.  
         [0007]     It is therefore a first object of the present invention to provide multi-ply or laminated cookware that overcomes the above deficiencies in prior art laminated cookware.  
         [0008]     Specifically, it is an object of the invention to provide alternative methods of forming laminated cookware that provide a means to protect the exposed core material at the rim.  
         [0009]     It is a further object of the invention to provide potentially lighter weight laminated cookware, yet without the deficiency that the softer materials in the laminate can easily be damaged or dented at the rim.  
       SUMMARY OF INVENTION  
       [0010]     In the present invention, the various objects and advantages of the invention are achieved by providing a clad article of cookware that comprises a substantially circular bottom having an interior cooking surface formed of a first metallic layer, substantially vertical walls surrounding said bottom to form a vessel capable of retaining fluid, said vertical walls terminating at a rim, wherein the interior surface of said vertical walls are contiguous with said interior cooking surface being formed of the first metallic layer, and at least a portion of the exterior surface of said vertical walls are formed of a second metal, and further wherein a portion of the first metal extends beyond the rim and extends down at least a portion of the exterior surface of said vertical walls whereby the second metal is not exposed at the rim.  
         [0011]     Another aspect of the invention is characterized by a process for forming an article of cookware that includes forming a proto-vessel having an interior metal layer and an exterior metal layer, the exterior metal layer terminating at a first rim below the height of the interior metal layer that defines a second rim, and then folding the portion of the interior metal layer that exceeds the height of the first rim whereby such portion of the interior layer forms the interior and exterior layer of the cooking vessel at the rim thereof.  
         [0012]     The above aspects of the invention provide the advantages that one of the two or more clad or laminated layers are protected at the rim from denting and related physical or chemical degradation.  
         [0013]     A further advantage is achieved by using a stronger material, such as stainless steel or titanium, for the inner layer to reinforce a thinner or softer middle or outer layer, allowing a reduction in the weight of the pan, as well as a thicker bottom layer for superior heat transfer to the foodstuffs and thermal uniformity.  
         [0014]     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  
       [0015]      FIGS. 1A and 1B  are cross-sectional elevations of the initial steps in forming the article of cookware.  
         [0016]      FIGS. 2A and 2B  are cross-sectional elevations illustrating the steps of forming the rim of the article of cookware.  
         [0017]      FIG. 3  is a cross-sectional elevation of the finished cookware vessel, prior to the addition of a side handle.  
         [0018]      FIGS. 4A and 4B  are cross-sectional elevations of the initial steps in forming the article of cookware according to an alternative embodiment of the invention.  
         [0019]      FIGS. 5A and 5B  are cross-sectional elevations illustrating the steps of forming the rim of the article of cookware in the embodiment illustrated in  FIG. 4   
         [0020]      FIG. 6  is a cross-sectional elevation of the alternative embodiment of the cookware article, prior to the addition of a side handle, as resulting from the processes shown in  FIGS. 4 and 5 .  
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIGS. 1 through 6 , wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved cookware article having a reinforced rim, generally denominated  100  herein.  
         [0022]     In accordance with the present invention,  FIG. 1-2  illustrate a sequence of steps in forming the article of cookware  100 , whereas  FIG. 3  is a cross-sectional elevation of the completed article of cookware, ready for the attachment of one or more side handles.  
         [0023]     The completed article of cookware  100 , as shown in  FIG. 3  has a bottom  32  surrounded by substantially upright sidewalls  31  to form a fluid containing vessel  100 , which terminates at rim  33 . The upright side  31  has an inner layer  10 ′ formed from an inner vessel  10  that is nested inside an outer vessel  20  (as shown in  FIG. 1B ). Thus, sidewall  31  has an outer layer  20 ′ formed from the side wall of outer vessel  20 . Referring back to  FIG. 1A , rim  33  is formed by the upper end  14  of the sidewall  11  of inner vessel  10  that extends above the rim  23  of the outer vessel  20 . As shown in  FIGS. 2B and 3 , this upper end  14  is bent or drawn over rim  23  such that a portion  15  extends downward from the rim  33  covering a portion of outer sidewall  20 ′.  
         [0024]     In  FIG. 1A , a fluid containing inner vessel  10  having a bottom  12  is surrounded by substantially upright sidewalls  11  which terminates at rim  13  is nested inside a slightly larger outer vessel  20 . The generally fluid containing outer vessel  20  has a bottom  22  and is surrounded by a substantially upright sidewall  21  that terminates in rim  23 .  
         [0025]     In the first step in the process of forming the cookware article  100 , the inner  10  and outer vessel  20  are bonded to form proto-vessel  30 , shown in  FIG. 2B . It should be noted that a portion  14  of the upright wall  11  of inner vessel now extends above the rim  23  of outer vessel  20 . In proto-vessel  30 , bottom portion  32  is formed from bottom  12  and  22  of the inner vessel  10  and the outer vessel  20  respectively. Further, sidewall  31  is formed from sidewalls  11  and  21  of the inner vessel  10  and the outer vessel  20  respectively.  
         [0026]     The inner vessel  10  is preferably formed from stainless steel or titanium. The outer vessel  20  is preferable formed of aluminum. It should be further appreciated that the outer vessel  20  is alternatively copper.  
         [0027]     Preferably, the bonding of the inner vessel  10  and outer vessel  20  employs at least one of the steps of impact bonding and/or brazing. If brazing is used to bond the inner vessel  10  and outer vessel  20 , then a brazing compound is applied to at least one of the exterior of the inner vessel  10  or the interior of the outer vessel  20  prior to the nesting.  
         [0028]     To complete the brazing process, the temperature of the proto-vessel  31  is raised to melt the brazing compound, which upon cooling forms a metallurgical bond at interface  112 , uniting the inner vessel  10  and outer vessel  20 . Pressure is applied to compress the inner vessel  10  and outer vessel  20  against each other at the common interface  112 , facilitating the consolidation and flow of the liquid brazing compound. It should be appreciated that each of the inner vessel  10  and outer vessel  20  are drawn in with sufficient dimension tolerances to facilitate the nested insertion to form unbounded proto-vessel  30 . It is also preferable that a slight gap be present after nesting to accommodate the solid brazing compound (as well as for the eventual wicking of the molten brazing compound or liquid flux) at the common interface  112 , of proto-vessel  30 .  
         [0029]     It is further preferred that an “ironing process” be used after brazing or impact bonding. “Ironing” is done by the repetitive steps of deep drawing of proto-vessel  30  in a set of dies with the clearance between male and female die members that are progressively smaller than the actual combined thicknesses of the sidewall  31 .  
         [0030]     As the outer layer  21 , of sidewall  31  to be protected is generally softer than inner layer  11 , the thickness of layer  21  is generally reduced. As it can be difficult in the brazing process to fully reflow the liquid flux over the entire areas to be bonded in interface  112 , air and moisture can be trapped within this gap. The “ironing process” is also advantageous as it gradually expels air and moisture trapped at the common interface  112 . For example, when the outer layer  11  is stainless steel layer, it will remain substantially the same height as in inner vessel  10 . However, as the wall thickness of a softer outer layer  21 , such as aluminum or copper, will be reduced, the height of this wall will increase as this material is pushed upward during the ironing process. Thus, the final position of the rim of the outer vessel in proto-vessel  30  is shown in  FIG. 2A  as  23 ′.  
         [0031]      FIGS. 2A-2B  illustrate the next step in the inventive process in which the portion  14  of sidewall  11  is rolled over rim  23 ′ to form the final rim  33  of the completed vessel  100 . The direction of bending and rolling rim portion  14  is shown by arrow  61 , with phantom portions  62  and  63 , in broken lines, to show the progressive movement of portion  14  until the rolling process is completed ( FIG. 2B ). Thus, it should be appreciated that the aforementioned process provides method of forming an article of cookware that does not use expensive pre-laminated sheet stock and also results in protecting the softer outer layer of the laminate that would otherwise be exposed and susceptible to damage at the rim.  
         [0032]     Another preferred aspect of the fabrication process, illustrated in  FIG. 2 , is to fabricate a groove  24  along the circumference of the outer vessel  20  below the rim  23 ′. The edge  25  of the rim forming portion  14  is pressed into groove  24  after the rim is rolled or folded over. Pressing the edge  25  results in a flush exterior profile on the cooking vessel that is less likely to trap dirt and debris, as well as being easier to clean. The groove can fabricated by milling before or after forming outer vessel  20 . Alternatively, the groove can be produced by stamping the sheet used to form outer vessel  20 .  
         [0033]     In alternative embodiment of the invention, the article of cookware  100  may include one or more middle layers laminated between either or both of the sidewall pairs  11  and  21  or the bottom pairs  12  and  22 . Such middle layer(s) are preferably copper or aluminum, being of a higher thermal conductivity than a stainless steel or titanium inner or outer layer.  
         [0034]     When the outer layer  21  is aluminum, it is also preferable to anodize the outer aluminum vessel  20  after folding. If the inner vessel  10  is fabricated from stainless steel it needs to be masked or otherwise protected form the corrosive anodizing bath during this process. In alternative embodiments the outer vessel is titanium, or an alloy thereof. As titanium is generally resistant to the acidic anodizing bath, it need not be masked during the anodizing process.  
         [0035]     Generally the sidewall  11  of inner vessel  10  has a thickness that is between about ½ to 1/10 the thickness of the sidewall  21  of the outer vessel  20 . It should be appreciated that as the primary strength requirement of a fluid containing vessel is the rim. Thus, folding the rim as shown in  FIG. 2  and  FIG. 3  to double the thickness may allow a 2× reduction in thickness of the sidewall  11  of inner vessel  10 , without a significant reduction in durability of the cookware article. Thus, in the case of using titanium metal to produce an extremely light weight cooking vessel, this 2× reduce in titanium thickness has a significant commercial advantage, as titanium metal is considerably more expensive, that is generally between about 3 to 10× the material cost of stainless steel.  
         [0036]     In accordance with another embodiment of the present invention,  FIG. 4-5  illustrate a sequence of steps in forming an alternative article of cookware  100 . Cookware article  100  is shown in a cross-sectional elevation in  FIG. 6  in a state that is ready for the attachment of one or more side handles.  
         [0037]     In  FIG. 4A , a fluid containing inner vessel  10  having a bottom  12  is surrounded by substantially upright sidewalls  11  which terminates at rim  13 . The inner vessel  10  is nested inside a slightly larger outer vessel  40 . The generally fluid containing outer vessel  40  has a bottom  42  and is surrounded by a substantially upright sidewall  41  that terminates in rim  43 . Outer vessel  40  however is optionally formed by deep drawing a laminate of an inner metal layer  45  and an outer metal layer  46 . Thus, when the inner vessel  10  and outer vessel  40  are nested and bonded to form proto-vessel  50 , shown in  FIG. 4B , the inner metal layer  46  becomes the inside or core layer in the laminated cookware article,  100 , shown in  FIG. 6 . However, it should also be appreciated that in other embodiments of the invention the inner vessel  10  and the outer vessel  40  can be impact bonded either with or without ironing.  
         [0038]      FIG. 5A-5B  illustrate the next step in the inventive process in which the portion  14  of sidewall  11  is rolled over rim  43  to form the final rim  55  of the completed vessel  100  in  FIG. 6 . The direction of bending and rolling rim portion  14  is shown by arrow  61 , with phantom portions  62  and  63 , in broken lines, to show the progressive movement of portion  14  until the rolling process is completed as shown in  FIG. 5B . Thus, the process of bonding nesting the inner and outer vessel, as shown in  FIG. 4B , and rolling in  FIG. 5  the extended edge portion  14  results in the enter outer metal layer  46  of the outer vessel  40  being totally encapsulated as well as reinforcing the rim  33 . It should be understood that a circular peripheral groove can be provided below rim  33  to receive by insertion the periphery of the interior metal layer that defines the edge of the final rim  55 .  
         [0039]     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.