Abstract:
An article of cookware is fabricated by a combination of a deep drawing a metal sheet or laminate to form a fluid retaining preform and then using an impact bonding process to attach a medallion to the outside bottom surface of preform. In another aspect, the impact bonding process alternatively provides a means to achieve a slightly concave exterior bottom surface, while maintaining a substantially flat and/or slightly concave interior bottom surface to minimize the use of cooking oil.

Description:
BACKGROUND OF INVENTION  
       [0001]     The present invention relates to an improved article of cookware, in particular a pot or pan having a flat interior surface.  
         [0002]     Cookware article such as pots and pans are routinely formed in a process that provides for the exterior bottom surface to have a concave shape, so that the pan rests on the periphery of the exterior bottom surface when disposed on a flat planar surface. This precludes the pots from turning or spinning, as would occur if the bottom where slightly convex so that the pan was supported by a small point or area at the center of the bottom surface.  
         [0003]     However, fabricating methods that create a concave outer exterior surface, also create a convex interior surface. Although consumer are largely used to a slightly convex interior surface, it is undesirable if one is trying to minimize the use of cooking oil. Oil poured into the center will run toward the interior edges of the pan, thus a larger quantity of oil is required to evenly cover the bottom interior of the pan as compared with a truly flat interior surface.  
         [0004]     It is a first objective of the invention to provide an article of cookware that will not spin when placed on a planar surface, but that can be used to successfully used to cook foods with a minimum quantity of cooking oil  
         [0005]     It is therefore a first object of the present invention to provide a cooking vessel having a concave exterior bottom surface, while maintaining a substantially flat interior bottom surface.  
         [0006]     It is a further objective of the invention to provide a cooking vessel having a concave exterior bottom surface, while providing a concave interior surface.  
         [0007]     It is another object of the invention to provide an efficient and economical process for manufacturing a cooking vessel having a concave exterior bottom surface, while maintaining a substantially flat interior bottom surface or a concave interior surface.  
       SUMMARY OF INVENTION  
       [0008]     In the present invention, the first object is achieved by a process of a forming a cooking vessel in multiple steps that comprises forming a pan shape out of a flat metal sheet or laminate and to then impart the final shape to the pan by impact bonding.  
         [0009]     Other objectives of the invention are met by utilizing during the process of impact bonding an interior mating die having a substantially planar surface or a slightly convex surface to impart a slightly concave surface to the interior of the article of cookware.  
         [0010]     A second aspect of the invention is characterized in that the above process permits the addition of decorative and protective features to the exterior bottom of the pan.  
         [0011]     Accordingly, in such articles of cookware the cooking oil does not initially run to the bottom edges of the pan, but more uniformly cover the central area of the bottom cooking surface.  
         [0012]     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  
       [0013]      FIG. 1  is a cross-sectional elevation view of prior art cookware exaggerating the shape of the pan bottom.  
         [0014]      FIG. 2A  is a cross-sectional elevation view of one embodiment of the invention.  FIG. 2B  is a magnified view of a portion of  FIG. 2A .  FIG. 2C  is a magnified view of a different portion of  FIG. 2A .  
         [0015]      FIG. 3  is a cross-sectional elevation view of the tooling and work piece deployed to form a second embodiment of the invention.  
         [0016]      FIG. 4  is a cross-sectional elevation view of the tooling and work piece deployed to form another embodiment of invention, comparable to that shown in  FIG. 2 .  
         [0017]      FIG. 5  is a cross-sectional elevation view of the tooling and work piece deployed in an alternative method to form the article shown in  FIG. 2 .  
         [0018]      FIG. 6  is a cross-sectional elevation view of another embodiment of the invention.  
         [0019]      FIG. 7  is a cross-sectional elevation view of the tooling and work piece deployed to form the embodiment of  FIG. 6 .  
     
    
     DETAILED DESCRIPTION  
       [0020]     Referring to  FIGS. 2 through 7 , wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved article of cookware, generally denominated  200  herein.  
         [0021]      FIG. 1  illustrates a prior art article of cookware  100 . The article  100  is optionally a pan or pot, depending on the relative diameter of the bottom  120  to the height of the surrounding and substantially upright sidewall  110 , which together form a fluid containing vessel. The article  100  has an inner bottom cooking surface  120   a  which receives foodstuffs, cooking oil and the like, whereas the outer bottom cooking surface  120   b  rests on a table, heating element, burner grid and the like. Accordingly, the article of cookware  100  is shown in  FIG. 1  as resting on surface  10 . It is desirable that the article of cookware  100  rest firmly on a planar surface and not spin or otherwise move when foodstuff inside the article  100  are manipulated, primary by stirring. Accordingly, the common industrial practice is to avoid surface  120   b  from being convex outward, that is having its lowest point at or near the center, and more preferably to form surface  120   b  such that is slightly concave, as shown in  FIG. 1 , with respect to the resting surface  10 . In this preferred form, shown with an exaggerated vertical dimension in  FIG. 1 , the article of cookware contacts the resting surface  10  only at the perimeter of the bottom surface,  121 . Forming the article of cookware with such a concave bottom surface results in the article being more stable on the resting surface  10 , as the greater contact provides proportionately more frictional resistance to rotation or other movement. Further, the concave surface in a manner strengthens the bottom of the article of cookware, making it less likely to be deformed from wear and use into a convex shape, which would be especially undesirable.  
         [0022]     However, the article of cookware  100  in  FIG. 1  has a disadvantage. The manufacturing process used to form article  100  to deliberately render surface  120   b  slightly concave also results in the inner bottom surface  120   a  having a matching shape and being slightly convex with respect to the interior thereof. Thus, when oils or other cooking fluids are initially added to the article of cookware  100  they tend to flow toward the perimeter of the interior cooking surface  121   a . Therefore, the cook will generally tend deploy at least enough butter, cooking oil or the like to entirely coat the inner cooking surface  120   a . This is especially problematic for persons trying to restrict their use and intake of butter, oils and fats in cooking, as they would prefer to use the least amount of oil possible to cover the cooking surface, and thus avoid the absorption of larger quantities of butter or oil into the food during cooking.  
         [0023]     In accordance with the present invention,  FIG. 2  illustrates a first embodiment of an improved article of cookware  200  that satisfies the need to have a stable article of cookware, yet minimize the use of fats and oils in cooking, and hence thier consumption. The article of cookware  200  has a substantially upright surrounding wall  210  connected to the substantially circular bottom  220  to form a fluid retaining vessel. The article  200  is optionally a pan or pot depending on the diameter of the bottom cooking surface  220  relative to the height of sidewall  210 . The article  200  has a substantially planar interior bottom surface  220   a  which receives foodstuffs, cooking oil and the like, whereas the outer bottom surface  220   b  rests on a table, heating element, burner grid and the like. As in the article of  FIG. 1 , outer bottom surface  220   b  is slightly concave with respect to the exterior. However, the inner cooking surface  220   b  is substantially flat or planar. Such an article of cookware is achieved through the processes described below in more detail with reference to  FIG. 3, 4  and  5 .  
         [0024]     The article of cookware  200  has the advantage that the minimum quantity of oil to coat the inner cooking surface will depend on the flow characteristic of the oil, as determined by its viscosity and wet ability on the inner coking surface, rather than the degree of convexity, permitting the use of less cooking oil than would be required with the prior art article of  100  shown in  FIG. 1 . Further, the article of cookware  200  is more conducive to using expensive and exotic cooking oil more as a flavoring ingredient, as less will be required to provide a heat transfer medium or to prevent foodstuff from sticking to the inner cooking surface  
         [0025]     In another aspect of the invention, shown enlarged in a magnified view in  FIG. 2 , article of cookware  200  has a medallion  240  embedded in the center of the outer cooking surface  220   b . The medallion  240  is used to provide brand or other information of use to the consumer, as it may be embossed with alphanumeric text. Alternatively, in the more preferred embodiments the medallion is made of a different material or metal than the materials that surrounds it in outer cooking surface  220   b , provides a decorative variation to the cookware. However, the use of medallion need not be purely decorative, as the color, texture or pattern of the medallion can communicate to the user useful information about the pot, such as the composition. For example, a laminated article of cookware having a cooper core might deploy a copper colored medallion.  
         [0026]     Note also, that in this preferred embodiment, the perimeter  221   a  of the substantially planar interior bottom surface  220   a , shown enlarged in the magnified view in  FIG. 2C , has a rounded surface in the transition to surrounding upright wall surface  210 . Further, the exterior bottom surface is formed with bevel or footing  221  to provide a secure resting surface, obviating any tending for the article of cookware to laterally wobble, as might occur if the exterior perimeter had the safe rounded profile as the inner cooking surface perimeter.  
         [0027]     The bottom  220  of the article of cookware  200  preferably has a thickness of about 4 mm, whereas the surrounding sidewall  210  preferably have the same or a slightly lower thickness, such as about 3.4 mm. Further, the height of the bevel  221  in  FIG. 2C , labeled h, is about 3 mm.  
         [0028]      FIG. 3  illustrates a first embodiment for forming an article of cookware comparable to that shown in  FIG. 2 , using tooling system  300 . The work piece is a fluid retaining preform  330  that is formed in the first step of the process Thus, like the completed article of cookware shown in  FIG. 2 , the preform  330  has a bottom surface  331  and surrounding sides  332  extending upward therefrom to form a fluid containing vessel with an interior surface and an exterior surface. Preform  330  may be fabricated by deforming a substantially planar sheet of metal. The planar metal sheet, when used to fabricate preform  330 , may be homogenous, consisting of a single layer of one material, or be a laminate of different layers of different materials. The first step in the fabrication process can deploy any method to make perform  330 , either a conventional drawing process or casting of molten metal to form preform  330 .  
         [0029]     The next step of the process uses an impact bonding press to impart the final shape to the pan. Thus, as shown in  FIG. 3 , preform work piece  330  is inserted between dies of an impact bonding press that comprises an upper tooling member  320  and a lower tooling member  310 . The upper portion exterior surface  310   b  of the lower tooling member  310  has a convex shape, and the lower interior surface  320   a  of the upper tooling member  320  has a substantially planar shape.  
         [0030]     Thus, in the next step in the process, impacting the preform  330  between the dies upper and lower tooling members  320  and  310  imparts the shape of the respective tooling member to the exterior and interior surfaces of the preform  330 , as well as reshaping the contour of the upward extend walls, if desired. The exterior surface  320   a  of the upper tooling member  320  imparts the interior shape, including the substantially planar interior bottom surface  220   a  of the completed cookware article  200  in  FIG. 2 . The exterior surface  310   b  of the lower tooling member  310  imparts the exterior shape to preform  330 , resulting in the concave exterior bottom surface  220   b  of the completed cookware article  200  of  FIG. 2 . In additional conventional steps of cookware fabrication one or more side handles are added to the article of cookware  200 .  
         [0031]     In a further embodiment of the invention, the process described above is used to bond a medallion in the exterior bottom surface as illustrated in  FIG. 4  and  FIG. 5 . The medallion thickness is between about 0.4 to 2 mm, but is preferably about 1 mm.  
         [0032]     Thus, the embodiment illustrated in  FIG. 4  provides one method of forming the article of cookware shown in  FIG. 2  using tooling system  400 . As in  FIG. 3 , the work piece is the fluid retaining preform  330  that is formed in the first step of the process by deforming a substantially planar sheet of metal or casting.  
         [0033]     The next step of the process uses an impact bonding press to impart the final shape to the cookware article. Thus, as shown in  FIG. 3 , work piece preform  330  is inserted in the die of an impact bonding press that comprises an upper tooling member  320  and a lower tooling member  310 .The upper portion exterior surface  310   b  of the lower tooling member  310  has a convex shape, and the lower interior surface  320   a  of the upper tooling member  320  has a substantially planar shape. A coin or medallion  240  is inserted between surface  310   b  of the lower tooling member  310  and the bottom surface  331   b  of the perform  330 .  
         [0034]     Thus, in the next step in the process, impacting the preform  330  between the dies upper and lower tooling members  320  and  310  impart the shape of the respective tooling member to the exterior and interior surface of the perform, as well as reshaping the contour of the upward extend walls, if desired. The exterior surface  320   a  of the upper tooling member  320  imparts the interior shape resulting in the substantially planar interior bottom surface  220   a  of  FIG. 2  in the completed cookware article  200 . The upper exterior surface  310   b  of the lower tooling member  310  imparts the exterior shape to preform  330 , resulting in the concave exterior bottom surface  220   b , while simultaneously embedding the coin or medallion  240  in the exterior bottom surface  220   b  of the article of cookware  200 , shown in  FIG. 2 .  
         [0035]      FIG. 5  illustrates another embodiment of the process for embedding a medallion  240  in the exterior bottom surface  531   b  of perform  530 , using tooling system  500 . Work piece  530  is a fluid retaining perform that is formed in the first step of the process by deforming a substantially planar sheet of metal. However, preform  530  has a circular cut out  533  in the exterior bottom surface  531   b . The coin or medallion  240  is inserted between surface  510   b  of the lower forming die or tool  510  and the pocket  533  in the exterior bottom surface  531   b  of the perform  530 . At least a portion of the coin or medallion  240  is intended to fit into the cut out  533 .  
         [0036]     The depth of cut out  533  will very with the thickness of medallion  240 , but is generally less than half the thickness of the bottom of the cooking vessel, and up to about the thickness of the medallion. More specifically, such a cut out might have a depth of between about 0.2 mm to about 2 mm. As shown in  FIG. 5 , the lower tooling member  510  has a perimeter profile  521   b  on surface  510   b  to create the beveled perimeter  221  shown in  FIG. 2C . The upper tooling member  520  has a substantially planar bottom surface  520   a.    
         [0037]     Thus, in the next step in the process, impacting the preform  530  between upper and lower tooling members  520  and  510  imparts the interior and exterior shape of the die to the preform while simultaneously embedding the coin or medallion  240  in the exterior bottom surface  220   b  of the article of cookware  200 , as shown in  FIG. 2 .  
         [0038]     In accordance with the present invention,  FIG. 6  illustrates another embodiment of an improved article of cookware  200  that satisfies the need to have a stable article of cookware, yet minimize oil use and hence its consumption. The article has a substantially upright surrounding wall  210  connected to the bottom cooking surface  220  to form a fluid retaining vessel. The article  200  is optionally a pan or pot depending on the diameter of the bottom  220  relative to the height of sidewall  210 . The article  200  has an inner bottom cooking surface  620   a  which receives foodstuffs, cooking oil and the like, whereas the outer bottom surface  620   b  rests on a table, heating element, burner grid and the like. As in the article of  FIG. 2 , outer bottom surface  620   b  is slightly concave with respect to the exterior. However, the inner cooking surface  620   a  is slightly concave with respect toe the interior region. Such an article of cookware is achieved through the processes described below in more detail with reference to  FIG. 7 . The slight inner concavity assure causes cooking oil to initially runs towards and pool in the center of the pan. This allows the cook to vary the quantity of oil used in proportional to the amount of food being cooked, rather than having to coat the entire inner cooking surface  620   b . Thus, when the foodstuffs to be cooked when spread in a single layer will occupy less than the entire inner cooking surface  620   b , the can be cooked primary in the center region which contains a smaller quantity of cooking oil or fat. The inner concave shape provides the cook with the option to push foodstuff articles toward the periphery of the inner cooking surface, as they cook such that any surface retained oil will drain toward the center of the pan away from the food, further limiting additional absorption of oil and fats by the cooked food stuffs.  
         [0039]      FIG. 7  illustrates an embodiment of the method of forming an article of cookware  200 , as shown in  FIG. 6 , using tooling system  700 . As in the other embodiments of the method, the work piece  330  is a fluid retaining preform formed in the first step of the process.  
         [0040]     The next step of the process uses an impact bonding press to impart the final shape to the pan. Thus, as shown in  FIG. 7 , preform work piece  330  is inserted between the upper tooling member  720  and a lower tooling member  310  of the impact press die. The upper portion exterior surface  310   b  of the lower tooling member  310  has a convex shape, and the lower interior surface  720   a  of the upper tooling member  720  also has a convex shape.  
         [0041]     Thus, in the next step in the process, impacting the preform  330  between the dies upper and lower tooling members  320  and  310  impart the shape of the respective tooling member to the exterior and interior surface of the preform, as well as reshaping the contour of the upward extend walls, if desired. The exterior surface  720   a  of the upper tooling member  720  imparts the slightly concave interior shape to cookware article  200  in  FIG. 6 .  
         [0042]     In other and alternative embodiments of the invention the sidewall and bottom surfaces of the preform, and hence completed article of cookware, may be formed of stainless steel, copper, aluminum, titanium and combinations thereof, including laminations of sheets of different and similar metals. Such laminations may be applied to the entire article of cookware, to form a clad cooking vessel, or to just the bottom surface of the cookware.  
         [0043]     Further, the coin or medallion  240  need not be circular, however to the extent the process in  FIG. 5  is deployed, the shape and dimension of the cutout  533  should substantially match that of medallion  240 . Further, depending on the material selected for medallion  240 , the printed information may be embossed from a complimentary pattern formed directly in the lower tooling member  310 .In additional and preferred embodiments the medallion is titanium metal and the sidewall and bottoms of the cookware are aluminum. In more preferred embodiments of the invention, the medallion is titanium metal and sidewall and bottom of the cookware are anodized aluminum. As titanium is fairly resistant to corrosion in the highly acidic baths used to anodize aluminum, the anodizing process may be carried out after the forming processes described with respect to  FIG. 3, 4 ,  5  and  7 .  
         [0044]     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.