Cookware formed of a single metal sheet and method for making same

Abstract

The profile shape of the vessel body and of handle portion is formed from a single sheet of metal to create a flat by cutting, stamping or blanking. An opening is created in the handle portion to reduce heat propagation. The shape of the pan body is formed by spinning with the flat handle portion. The handle is formed by creating three-dimensional contours in the handle portion of the blank. The neck portion has a flat section adjacent the pan body followed by sections of different curvature. One section of the neck portion has a deeply curved cross-section. That neck portion transitions to the hand grip portion which has a reduced curvature, particularly toward the unattached end of the handle. The neck portion may have a “W” cross sectional shape. The handle grip portion may have a “U” shaped cross-section for comfort.

Claims

1. A cookware vessel comprising a pan body with integral single piece handle fabricated from a single sheet of metal comprising first and second edges, a neck portion and a hand grip portion, said neck portion comprising a flat section extending from said first edge to said second edge adjacent the pan body, a concave “U” shaped section adjacent said flat section, said concave section having a cross-sectional curvature which transitions from a greater curvature to a lesser curvature from said flat section to said hand grip portion, said concave section comprising a portion which extends below the plane of the handle comprising first and second cut-outs spaced from each other.

2. The vessel of claim 1 wherein said cutouts comprise at least 30% of the handle width.

3. The vessel of claim 1 wherein the metal sheet comprises carbon steel.

4. The vessel of claim 1 wherein the metal sheet comprises stainless steel.

5. The vessel of claim 1 wherein the metal sheet comprises copper or titanium.

6. The vessel of claim 1 wherein said neck portion is 60 mm wide with a cross-section curvature of R200 mm or less.

7. The vessel of claim 1 wherein the portion of said concave section adjacent said flat section has a curvature of R100 mm or less.

8. The vessel of claim 1 wherein said concave section curvature transitions from a greater curvature to a lesser curvature within the range of approximately 100 mm to 270 mm from the pan body.

9. The vessel of claim 1 wherein said hand grip portion has a curvature within the range of R1000 mm to R10 mm.

10. The vessel of claim 1 wherein said hand grip portion has a curvature within the range of R500 mm to R30 mm.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS

(1) To these and to such other objects that may hereinafter appears, the present invention relates to single-piece formed sheet metal cookware and method of making same as described in detail in the following specification and recited in the annexed claims, taken together with the accompanying drawings, in which like numerals refer to like parts and in which:

(2) FIG. 1 is a schematic representation of the manufacturing steps used in fabricating a cooking vessel in accordance with the present invention;

(3) FIG. 2 is a perspective view of a the top and side of a cooking vessel fabricated by the method of the present invention;

(4) FIG. 3 is a perspective view of a the bottom and side of a cooking vessel fabricated by the method of the present invention;

(5) FIG. 4 is a plan view of the top of a cooking vessel fabricated by the method of the present invention;

(6) FIG. 5 is an elevation view of the side of a cooking vessel fabricated by the method of the present invention;

(7) FIG. 6 is a cross sectional view of the handle of a cooking vessel of the present invention taken along line 6-6 of FIG. 5:

(8) FIG. 7 is a cross sectional view of the handle of a cooking vessel of the present invention taken along line 7-7 of FIG. 5:

(9) FIG. 8 is a cross sectional view of the handle of a cooking vessel of the present invention taken along line 8-8 of FIG. 5:

(10) FIG. 9 is a cross sectional view of the handle of a cooking vessel of the present invention taken along line 9-9 of FIG. 5:

(11) FIG. 10 is a cross sectional view of the handle of a cooking vessel of the present invention taken along line 10-10.

DETAILED DESCRIPTION OF THE INVENTION

(12) As illustrated in FIG. 1, the fabrication method begins with a sheet of metal 10 of appropriate thickness. The metal sheet can be made of any suitable metal, preferably steel, iron, stainless steel, copper, or titanium although any other heat conductive metal suitable for cookware can be used.

(13) Sheet 10 is formed into the final shape using a combination of three key manufacturing methods: profile blanking, spinning to form the vessel and handle forming. Each of the methods is described in detail.

(14) 1) Profile blanking: The profile shape of the entire vessel (handle and pan body) is either cut or stamped/blanked from metal sheet 10 in a single flat piece 12. CNC laser cutting is preferred for this procedure because it has economical and practical advantages over other profiling or blanking methods, although other methods are possible. Waterjet cutting could also be used, but at a higher cost per unit.

(15) Blanking of the relatively large and unbalanced shape of the handle and pan body such as that of the present invention would require a very large and complex die set. Creation of such a die set would take a significant financial investment and therefore decrease price viability of the final product when that investment is amortized over each production unit.

(16) One desired goal of the invention—to reduce heat conduction up the handle—is achieved at this stage of processing by using creating multiple large perforations 14a, 14b and 14c in the handle neck portion to optimize the ratio of surface area to metal volume. This technique transfers more of the internal conducted heat to the air through radiation and convection, similar to the principle of fins on a heat sink or air-cooled engine.

(17) A flat handle has the significant disadvantages of being uncomfortable and too weak to support heavy vessels, particularly with food loads. Those disadvantages are overcome in the present invention by imparting a gradually changing curvature to the handle, as explained in detail below.

(18) 2) Spinning to form vessel body: The flat profiled sheet 12 with integral pan and handle portion shape is loaded on the platform 16 of a CNC spinning machine (not shown). The spinning machine forms the pan body shape 18 over a suitably shaped mandrel with a CNC-controlled roller, in the normal metal spinning method. The long protruding handle portion remains flat as an extension from the formed pan body 18, untouched by the pan body forming process.

(19) At this point the pan could be used, but would have some serious limitations for commercial cookery; being too weak in the handle (bending too readily when loaded, for viable handle widths and sheet thicknesses), and too uncomfortable (or at least no advantage over other common traditional long strip handles).

(20) Though a manual spinning machine may be employed, the long projecting and rotating handle creates a safety hazard for operators, and the forces involved for forming sufficiently thick sheets of metal are greater than those easily manually produced.

(21) Sheet thicknesses for ideal conduction and strength will vary according to material properties and the purpose of each cooking vessel, but a guide would be in the range of 1 mm to 8 mm, with the 2 mm-5 mm range being preferred for steel sheets (low carbon mild steels, carbon steels, stainless steels).

(22) An advantage of spinning to form the pan body, as compared to traditional pressing, is that the thickness of the base of the pan body is not reduces from the original sheet thickness, while the wall if the pan body is thinned through deformation and ‘wiping’ the sheet metal along the rotating forming mandrel (which is a hardened die with dimensions of the desired form of the inside of the vessel). Heat conduction can therefore be very good in the relatively thick metal base, while the weight can be minimized by the thinner pan body wall which is mostly only required for containing the food, particularly liquids.

(23) 3) Handle forming: To form the handle 20 into a comfortable and dynamically performing handle shape with suitable three-dimensional contours, and to impart additional strength in the crucial vertical plane with curved cross-sections, the most viable forming method was found to be a traditional stamping-forming die set 22, 24 operated by any suitable press of sufficient tonnage.

(24) The flat unformed handle profile is inserted between the upper and lower die set 22, 24 and pressed with sufficient force to permanently deform the flat handle profile into the desired three-dimensional form, while sheet thickness remains constant.

(25) A cross-sectional shape like a classic ‘U’ section is most comfortable for the hand grip portion 26 of the handle 20, while a ‘W’ section would be stronger for a section of the neck portion 28 but less comfortable for the hand grip portion 26. While a simple ‘V’ section would impart strength, it would not be ideal for handle comfort in the hand grip portion.

(26) For most practical metals and thicknesses, a flattened ‘U’ shape is sufficient for strength in the handle grip portion, and desirable for comfort (though comfort will be reduced at some point with decreasing cross-sectional radius).

(27) Additional strength is imparted to the handle shape with increasing the depth of a section of the neck portion. Accordingly, the neck portion 28 can be formed with deeper curved cross-section 29 for strength, and the hand grip portion 26 can have a reduced curvature as load decreases toward the unattached end 32, for more hand comfort. The end 32 of the hand grip portion 26 can have an additional opening 33 to permit the vessel to be suspended from a hook.

(28) As best seen in FIG. 5, the handle section 15 situated between cut-out portions 14a and 14b of the neck portion 28 is arcuate and formed in this operation to extend below the plane of the remainder of the handle. This structure imparts additional strength to the neck portion 28 without increasing thermal conduction from the pan body 18 to the hand grip portion 26.

(29) The curve in the neck portion 28 would need to be deeper for thinner and lower tensile strength metals. Preferably, a wide neck of 60 mm, with venting cut-outs 14 of 30% of the width, in 2 mm low carbon mild steel would benefit from a neck curvature in cross-section of R200 mm or less as seen in FIG. 6. However, section 30 of the neck portion immediately adjacent the pan body 18 can be substantially flat to aid the transition between handle and pan body wall with minimal distortion. The radius of the wall of the pan body itself adds strength to flat portion 30.

(30) Section 29 of the neck portion benefits from deeper curvature for strength, ideally R100 mm or less as seen in FIG. 7, though a slight curvature of R500 mm would support most regular pan vessel types, with materials of reasonable strength and width (for example, low carbon mild steel of 2 mm thickness and 40 mm width, at a distance around 50 mm from the vessel walls).

(31) The handle 20 transitions to the portion 26 normally gripped by the hand. Typically, the hand grip portion 26 is located approximately between 100 mm and 270 mm from the pan body wall. It is necessary for the handle profile in the hand grip portion to become less wide for the comfort of fingers wrapped around the handle, and less deep in cross-section. As seen in FIG. 8. this portion can be curved from R1000 mm to R10 mm, though an optimal range would be from R500 mm to R30 mm for combination of handle strength and finger comfort.

(32) According to beam theory, the handle material is subject to less tensile force toward the unattached end 32 of the handle, away from the pivot point of the hand grip portion, so less curvature and less width of handle is required to resist the forces involved, allowing more freedom for choosing a comfortable handle section. Accordingly, the end 32 of the handle portion has only a slight curvature as seen in FIG. 10.

(33) An important consideration during professional cookware handle design is that chefs largely grip pans with an ‘underhand’ grip (fingers on top and palm under handle), while consumers typically grasp pans with an ‘overhand’ (fingers underneath) grip. A handle intended for both markets needs to accommodate both styles of grip, handle sectional radii shouldn't be extreme in either direction, and sharp edges should be removed to avoid pinching fingers in either direction.

(34) While it would be possible to form the handle into an open rounded or oval tubular section with more die forming operations, the thick metal (since the cookware base is made of the same sheet, and therefore has the same thickness as the handle) required for quality cookware is not easily formed into tight handle radii without splitting, and complex forms in the longitudinal plane are difficult to achieve. Most tubular pan handles are essentially straight for this reason. A folded hollow handle with longitudinal split and open ends would also create a hygiene hazard. Furthermore, the rounder a handle becomes, the more squeezing of the hand (subconsciously) is required to generate the friction to control the previously mentioned rotational forces when the pan is in motion.

(35) The same principles discussed above may be employed to make any style of cookware that has a round body shape. Further, the same manufacturing techniques can be used to produce single piece lids for cookware that have extended handles.

(36) Because the handle thickness is necessarily the same thickness as the base of the pan body, being profiled from the same sheet of metal, most viable thicknesses for commercial cooking (ideally 2 mm-4 mm for most pans) need additional strengthening in the vertical plane by pressing the handle to sufficient cross-sectional depth in that plane to increase beam strength.

(37) As seen in FIGS. 2, 3 and 4, the handles used in the present invention have deeper concave pressed sections in the neck portion 28 where strength is most required (particularly with large venting holes), transitioning through to shallow concave sections in the hand grip portion toward the end 32 of the handle for hand comfort. The whole of the handle could be pressed in a convex section (opposite to the current invention shown and described above) though comfort would be sacrificed. Only the end of the handle could be pressed in the convex direction, though some rotational stability would be lost.

(38) The handle shape in the present invention achieves sufficient strength, while at the same time improving dynamic hand strain.

(39) The broad concave end 32 of the handle resists the rotational forces present whenever cooks are handling the pan with the classic sauté toss (often for restaurant chefs). The fingers rest on the comfortable convex surface under the handle, while the ball of the hand is cupped by the concave end 32 on top. The handle design also works with an alternative grip used by cooks, with fingers on top and ball underneath handle. With that handle design, the fingertips rest in the concave hollow of the handle on top, while the ball of the hand controls the broad slightly convex end portion of the handle from underneath.

(40) Therefore, to achieve the above handle goals, the present invention utilizes a deep concave U-shape through the neck portion of the handle that must carry the most load to provide a greatly increased strength to counter the handle bending force. This deep section transitions to a shallow and less concave U-shape in the hand grip portion 26 to provide more comfort, avoiding uncomfortable edges or ridges from more vertical section edges.

(41) The end 32 of the handle where the ball of the hand typically rests is designed to take half of the load (the digits taking the other half in the opposing vertical direction), the handle in this incarnation of the invention utilizes a significantly broader shallow concave end 32 to assist the hand's ability to counter rotational forces (with reduced squeezing force required from the hand).

(42) Reduced heat transfer to hand is achieved by creating openings 14a, 14b and 14c in the handle. While these openings may appear decorative, the system of offset openings in the neck portion of the handle is arranged to maximize heat dissipation within constraints of required handle strength. This follows the principle of increasing the surface area relative to total cross-sectional area (or volume), to encourage dissipation of internally-conducted heat through thermal radiation and convection. It was found that as this ratio is increased, the portion 26 of the handle gripped by the hand could receive a low enough level of conducted heat to allow the pan to be lifted with a bare hand from the stove top, for most normal cooking operations. This venting was a vast improvement over traditional solid steel or iron handles of nominally round cross-section, or flat rectangular metal handles with no venting features.

(43) The same principles described above can be employed for fabricating cookware lids, whereby the lid has a long extended handle similar to the cookware, thus solving the common lid issues of hot and fragile handles. The lid handle may be formed to a similar shape as the cookware handle, so as to nest neatly on top of the cookware handle. Such a lid with long handle may be configured to also double as a low-walled griddle or crêpe pan.

(44) Presently, there exists no cookware which combines the manufacturing processes and handle design features of the present invention to achieve commercially viable cookware, with all the significant performance advantages detailed above, for professional chefs or home cooks.

(45) While only a single preferred embodiment of the present invention has been disclosed for purposes of illustration, it is obvious that many modifications and variations could be made thereto. It is intended to cover all of those modifications and variations which fall within the scope of the present invention, as defined by the following claims.