Title of Invention

COOKING VESSEL METHOD FOR PRODUCING A COOKING VESSEL AND APPARATUS FOR CARRYING OUT THE METHOD

Abstract

The invention relates to a cooking vessel of' special steel with a bottom (12), with outer side surfaces (13), with an inner bottom surface (15), with rounded bottom surfaces (16) and with inner side surfaces (17), the inner bottom surface (15), the rounded bottom surfaces (16) and the inner side surfaces (17) forming the surfaces facing items to be cooked has a burnished/hard-rolled surface, characterized in that at least part of the surfaces facing items to be cooked had been burnished and/or hard-rolled after deep drawing. The invention also relates to a method for producing the aforementioned cooking vessel and an apparatus for carrying out the method. Representative Figure - Fig. 2

Full Text

FORM 2 THE PATENTS ACT, 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "COOKING VESSEL, METHOD FOR PRODUCING A COOKING VESSEL AND APPARATUS FOR CARRYING OUT THE METHOD" AMC INTERNATIONAL ALFA METALCRAFT CORPORATION AG, of Buonaserstrasse 30, CH-6343 Rotkreuz, Switzerland,a swiss company The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- 10 MAY 2004 The present invention relates to a cooking vessel, method for producing a cooking vessel and apparatus for carrying out the method. Background of the invention The invention relates to a cooking vessel of special steel with a bottom, with outer side surfaces, with an inner bottom surface, with rounded bottom surfaces and with inner side surfaces, the inner bottom surface, the rounded bottom surfaces and the inner side surfaces forming the surfaces facing items to be cooked. Furthermore, the invention relates to 'a method for producing a cooking vessel and an apparatus for carrying out the method. A wide variety of cooking vessels and methods for producing them are known from the prior art. In particular, it is known after shaping the vessel to treat its surface facing the items to be cooked. For this purpose, known methods such as grinding, polishing or pickling are used for special steels. The prior-art coating which is most well-known, used for aluminium cooking vessels, is coating with non-stick materials, such as with the material known by the Teflon brand. Such coatings have the disadvantage that they are very sensitive to damage of the coating and require particularly careful handling of the cooking vessel during the cooking procedure and also during cleaning. In the context of this document, cooking vessel is understood to mean any container which can be employed in a kitchen and is used for preparing meals, irrespective of the basic geometrical shape, which may in particular be round, oval, elliptical, square or polygonal. Apart from cooking pots, these also include frying pans, casseroles, saute pans, steam cooking systems, pressure steamers etc.. The term cooking is to be understood as meaning not only boiling but also other procedures such as roasting or baking, stewing, braising, deep frying etc.. The inner surface of a cooking vessel refers to the entire functional surface of a cooking unit that comes into contact with the items to be cooked during the normal cooking procedure. It is known that the structure of the surface of the cooking vessel facing the items to be cooked, that is in particular its inner bottom surface, has a decisive influence on the functional characteristics, here in particular during the initial browning of food and cleaning. In addition to the coating mentioned above, in the prior art these surfaces are also pickled, ground and/or polished after shaping. Summary of the invention Setting out from this prior art, the invention is based on the object of providing a cooking vessel of the type mentioned at the beginning which has certain non-stick properties, such as for example a Teflon surface known in the case of aluminium cooking vessels, combined with the robustness of a high-grade special-steel cooking vessel. Furthermore, it is an object of the present invention to specify a method for producing such a cooking vessel and a corresponding apparatus. This object is achieved for a cooking vessel of the type mentioned at the beginning according to the invention by at least part of the surfaces facing items to be cooked having a rolled surface. The facr that the surface is burnished and/or hard-rolled means that an increasing hardness and greater corrosion resistance are obtained at the same time. The greatly reduced roughness produces outstanding properties with respect to detachment, in particular for food which has baked on without grease, and permits simple cleaning. Burnishing and/or hard-rolling is a method of exerting a locally restricted pressure for hardening the surface of, in particular, components subjected to vibration, such as shafts and ball bearing races. This respectively involves rotationally symmetrical three-dimensional bodies and the method is used by those skilled in the art in the mechanical engineering industry, and the automotive sector in particular, for the purpose of avoiding crack formation under alternating loads. An advantageous method for producing a cooking vessel according to the invention comprises the method steps of circling from a piece of stainless, acid-resistant steel, deep drawing, trimming and edge stamping of the body of the pot, a first step of surface working, which comprises preworking and finishing of the outer surfaces and the inner surfaces, wherein the method further comprises at any desired place: a second step of surface working, in which a pressure is applied in a locally restricced area to the surface of at least part of the inner surface of the cooking vessel, at a direction essentially normal to it, by burnishing/hard-rolling. An apparatus for carrying out the method is characterized in that a holder for the cooking vessel is provided, with which holder the said cooking vessel is fixed or movable in one or more directions parallel or perpendicular to its axis of symmetry, in that a working tool for the burnishing and/or hard-rolling of three-dimensional bodies is provided, with which tool a pressure can be applied to the inner surface of the cooking vessel in a direction normal to it, and in that the working tool is fixed or movable in one or more directions by means of a displaceable holder, so that the working tip of the working tool can be moved in relation to the cooking vessel. Further advantageous embodiments are respectively characterized in the assigned subclaims. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Exemplary embodiments of the invention are explained below by way of example in the drawings, in which: Figure 1 shows a flow diagram' of the production of a cooking vessel according to one exemplary embodiment of the invention, Figure 2 shows a schematized cross-sectional view of a cooking vessel according to one exemplary embodiment of the invention, and Figure 3 shows a diagram of the variation in hardness in relation to depth in the case of a cooking vessel according to the invention for the rolled region, and Figure 4 shows a schematized view of a cooking vessel according to a further exemplary embodiment of the invention, together with a schematized view of a working tool. Detailed description of the preferred embodiments Figure 1 represents in a schematized way a flow diagram of the production of a cooking vessel according -to one exemplary embodiment of the invention. The starting point of the method is a piece of stainless, acid-resistant steel 1. This is fed to the circling operation 2, after which the body of the .pot is produced in step 3 -by deep drawing, trimming and edge stamping. . This likewise includes production variants which produce the body of the pot from two or more individual, parts, for example by additional welding, in particular iaser welding. There follows an optional step 4 of inserting a bottom capsule or rhe application of a bottom to the pot. This may be carried out in particular by pressure welding, soldering or similar prior-art methods. Step 4 or 3 is followed by a first step of surface working 5. This comprises on the one hand the preworking and finishing of the outer surfaces or of the inner surfaces, not to be treated by the method according to the invention, as revealed by the description with respect to Figure 2. On the other hand, this step comprises the preworking of the inner surfaces. This working may be carried out, in particular, by pickling, grinding and polishing. The second step of the surface working 6 concerns the rolling according to the invention, which is specified in further detail in the description which follows. Step 7 concerns assembly and quality control, which is preceded by a washing step. Box 8 denotes the packing and preparation for delivery of the cooking vessel produced in this way. A cooking vessel 11 according to the invention, as schematically represented in Figure 2, consists of special steel. In the following, the production of a cooking vessel is described in a non-limiting way on the basis of a rotationally symmetrical unit. It has a bottom 12, outer side surfaces 13, an optional pouring edge 14, an inner bottom surface 15, rounded bottom surfaces 16 and inner side surfaces 17. Instead of the pot 11, of course any other cooking vessel may also be formed in a way corresponding to the invention. The reference numeral 18 denotes the axis of symmetry of the cooking vessel 11, i.e. the axis about which the cooking vessel 11 rotates during the working according to step 6. This involves lowering a working tool 20 with a working head 21 onto the inner bottom surface 15 and pressing it onto the said surface under high pressure. Consequently, a circular ring with the radius of the distance between the axis of symmetry 18 and the working head 21 is worked according to the invention. By a displacement of the working tool 20 along the double-headed arrow 22, the worked circular ring is changed and thus the entire inner bottom surface 15 is progressively worked by selection of suitable advancements. When using a working tool 20 with a working head 21 which rolls transversely to the rolling direction when there is a movement in each direction 22, re-shaping without the occurrence of additional shear stresses can be achieved. For the working of the inner side surfaces 17, the cooking vessel 11 likewise rotates about the axis 18, the tool 20 merely being directed essentially at right angles to the position represented in the figure. During the working of the rounded bottom surfaces 16, a largely orthogonal angle is likewise maintained between the tool and the surface to be worked, the tool having to be correspondingly guided. In addition to the position at right angles, the tool may also deviate from an orthogonal angle by, for example, plus/minus 15 degrees. The tool 20 is a tool for burnishing or hard-rolling. This tool, envisaged for example in the prior art for use in the automotive industry, serves for hardening the surface of ball bearings and shafts to increase the resistance to alternating loads. Full surface working, for working of the centre region as well, was produced in the exemplary embodiment by eccentric rotation of the unit. Particularly advantageous is a tool 20 which has a head similar to a ballpoint pen, this being a hydrostatic burnishing tool with which complex contours can be rolled, since a lateral displacement does not lead to the occurrence of additional shear stresses in the surface. During the burnishing with this tool, described in this exemplary embodiment, the ball diameter, the rolling rate, the rolling advancement and the rolling pressure are decisive, the result also depending on the preworking state of the cookinq vessel before the burnishing/hard-rolling. By contrast with the known use of this tool for producing elements which are resistant to alternating loads, in the case of cooking vessels the geometrical stability and surface structure after working are decisive. Full surface working, including of the centre region, is necessary and the possibility of working cooking vessels which are not rotationally symmetrical is desired. The rolling rate used in the case of test specimens was, for example, around 150 metres/minute for a ball diameter of 6 millimetres. The advancement has advantageously been set to 0.05 of a millimetre. The rolling pressure was increased in 50-bar steps at a time, a satisfactory surface, and accompanying case hardening, being obtained from about 100 bar. The variation in hardness in relation to depth is schematically represented in Figure 3. The hardness has been provided with the reference numeral 30 and the depth (distance from the surface) has been provided with the reference numeral 31. The resultant curve 32 is typical of rolling operations and can be used for clearly identifying the use of the method according to the invention. Blasting, grinding or polishing do not have the maximum 33 for hardness at a distance of approximately 0.05 to 0.1 of a millimetre from the surface of the cooking vessel worked, corresponding to the interval 34. Furthermore, a hardness depth of preferably at least 0.3 of a millimetre is obtained. The hardness depth or total depth of penetration of the hardening is the range in the depth of the material in which the hardness is greater than the initial hardness before the rolling step according to the method. The maximum 33 may also have a smaller value, of for example 0.02 of a millimetre, for the distance from the surface of the cooking vessel worked. The a'-martensite fraction increases with increasing roll pressure. If at a roll pressure of 100 bar it is still about 1/3 per cent, in the exemplary embodiments it exceeds 1 per cent and 2 per cent at 150 and 200 bar, respectively. The rolling rate led to no change in the roughness achieved at rates of between 50 and 500 metres/minute. The rolling advancement should advantageously be kept as small as possible to avoid rolling traces. To avoid such traces, values of less than 0.2 of a millimetre are necessary; a value of 0.05 of a millimetre is very advantageous. From about 100 bar, the rolling pressure led to roughnesses of less than 2 micrometres, no further appreciable reduction in the roughness below 1 micrometre being observable from approximately 150 bar. A test for the quality of the cooking vessel produced can be assessed in a comparative test with cooking vessels not treated in a way corresponding to the invention based on methods known from the prior art (i.e. grinding or polishing of the inner surfaces) , in particular with respect to three points. - The baking-on characteristics. In the prior art, baking on leads to considerable sticking of baked-on food, which leads to breaking up of the food when it is detached and turned. - Cleaning when there is burnt-in stock. When prior-art cooking vessels have burnt-in stock baked on them, it can only be removed by means of commercially available steel cleaners and vigorous mechanical cleaning, for which great time and effort have to be expended. The abrasive particles contained in the steel cleaner activate the surface. - Quality of cleaning, in particular in the case of cleaning by machine. The known cooking vessel is often'not cleaned without remains being left behind, which is hygienical Iy unsatisfactory and also the starting point for damage in the surface region of the cooking vessel. With the invention it is possible to produce a cooking vessel which ensures improved, quick and non-destructive detachment of baked-on food, which has clearly improved cleaning characteristics with functional surfaces free of any remains. The method according to the invention produces an inner surface of a cooking vessel which has a metallically bright, slightly lustrous to lustrous appearance, and has non-stick properties and greater corrosion resistance. Comparative tests with cooking vessels produced from the same raw material, simply omitting step 6, have given: - an increase in the corrosion resistance of 30 per cent (potentiodynamic analysis) - an increase in hardness of 20 per cent - a reduction in roughness to below 2 micrometres, starting from 5 micrometres in the case of the untreated cooking vessel ~ production of a non-stick and, for water, non-wetting inner surface of the Cooking vessel. With the two first-mentioned points, improvements are obtained in the physical properties, which lead to greater tolerance with respect to misuse of the cooking vessels at or by the customer. Figure 4 shows a schematized view of a cooking vessel according to a further exemplary embodiment of the invention, together with a schematized view of a working tool. The same features are provided with the same reference numerals in all the drawings. Also represented in Figure 4 is a cooking vessel 11 which is rotationally symmetrical about the axis 18. The bottom surface 15 may, however, also be oval or essentially rectangular, for example, or have any other predetermined shape. Only one rolling tool 20 with one working head 21 is represented. The use of multi-element tools, tools with more than one rolling element, is also possible. Producing the relative movement of the tool with respect to the workpiece (working direction and direction of advancement) can be brought about by choosing the number and type of moving axes for the workpiece 18, 41, 42 and 43 and for the tool 51, 52, 53, 54, 55 and 56 that are favourable for the respective geometry of the cooking vessel. Consequently, full-surface working of any desired vessels is possible. In addition to the inclusion described of burnishing/hard-rollinq in the production of the cooking vessel, this step may also be performed at any other place desired. Consequently, however, the properties described above may only be partially obtained. The particularly fine structure of the surface can be produced only by burnishing/hard-rolling as a surface-finishing operation. It is also possible in particular for cooking vessels which are already in' use, i.e. cooking vessels surface-worked by prior-art methods, to be subsequently treated, and consequently for the improved properties to be produced at a later time. By choosing the point in time for carrying out the additional burnishing/hard-rolling in the course of the process, some or all of the following properties of the surface can be achieved: hardening, increased corrosion resistance, patterning by a predetermined choice of the rolling paths, reduced surface stress and non-stick effects. By choosing the curves of the paths along which a pressure is respectively applied in a locally restricted area to the surface at a direction normal to it, and the advancing movement, a planar-rolled surface is achieved and the surface properties mentioned are set. WE CLAIM: 1. Cooking vessel of special steel with a bottom (12), with outer side surfaces (13), with an inner bottom surface (15), with rounded bottom surfaces (16) and with inner side surfaces (17), the inner bottom surface (15), the rounded bottom surfaces (16) and the inner side surfaces (17) forming the surfaces facing items to be cooked has a burnished/hard-rolled surface, characterized in that at least part of the surfaces facing items to be cooked had been burnished and/or hard-rolled after deep drawing. 2. Cooking vessel as claimed in claim 1, wherein the rolled surface has a roughness of less than 2 micrometers and the variation in hardness in relation to depth has a maximum of at least 1.2 times the initial hardness of the base material at a distance of 0.05 to 0.1 of a millimeter from the rolled surface, with a total depth of penetration of the hardening of at least 0.3 of a millimeter. 3. Method for producing a cooking vessel (11) as claimed in claim 1, with the method steps of circling (2) from a piece of stainless, acid-resistant steel (1), deep drawing, trimming and edge stamping (3) of the body of the pot, a first step (5) of surface working, which comprises preworking and finishing of the outer surfaces (12, 13) and the inner surfaces (16, 17), characterized by after deep drawing of the body of the pot: a second step (6) of surface working, in which a pressure is applied in a locally restricted area to the surface of at least part of the inner surface (15) of the cooking vessel (11), at a direction normal to it, by burnishing and/or hard-rolling. Method as claimed in claim 3, wherein the first step (5) of surface working only comprises preworking of the inner surfaces (15) to be treated by the second step subsequently carried out and/or the first step (5) of surface working comprises pickling, grinding and/or polishing. Method as claimed in claim 3 or claim 4, wherein in the said second step (6), a working tool (20) with a working head (21) is placed under pressure onto the inner surface (15) to be worked, respectively in a direction normal to it, and rolling paths are produced on the said inner surface by a relative movement between the cooking vessel and the tool, by which paths inner surfaces (15) worked partially or completely over a planar area can be produced. 6. Method as claimed in claim 3 or claim 4, wherein in the second step (6), the cooking vessel (11) is turned about its axis of symmetry (18), a working tool (20) with a working head (21) is placed under pressure onto the inner surface (15) to be worked, respectively in a direction normal to it, so that a rolled circular ring with the radius of the distance between the axis of symmetry (18) and the working head (21) is produced, and subsequently the working tool (20) is displaced radially (22) in order to act progressively on the predetermined portion of the inner surface (15). 7. Apparatus for carrying out the method as claimed in any one of claims 3 to 6, wherein a holder for the cooking vessel is provided, with which holder the said cooking vessel is fixed or movable in one or more directions (18, 41, 42) parallel or perpendicular to its axis of symmetry (18), a working tool (20, 21) for the burnishing and/or hard-rolling of three-dimensional bodies is provided, with which tool a pressure can be applied to the inner surface (15) of the cooking vessel (11) in a direction normal to it, and said working tool (20, 21) is fixed or movable in one or more directions (51, 52, 53) by means of a displaceable holder, so that the working tip of the working tool (20, 21) can be moved in relation to the cooking vessel (11). 8. Apparatus as claimed in claim 7, wherein the working tool (20) has a working head (21) which rolls transversely to the rolling direction when there is a movement in each direction (22), so that re¬shaping without the occurrence of additional shear stresses can be achieved. Dated this 13th day of December, 2000.

Documents:

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in-pct-2000-00729-mum-abstract(28-05-2004).doc

in-pct-2000-00729-mum-abstract(28-05-2004).pdf

IN-PCT-2000-00729-MUM-ABSTRACT(28-4-2004).pdf

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IN-PCT-2000-00729-MUM-CANCELLED PAGES(7-8-2007).pdf

IN-PCT-2000-00729-MUM-CLAIMS(7-8-2007).pdf

in-pct-2000-00729-mum-claims(granted)-(28-05-2004).doc

in-pct-2000-00729-mum-claims(granted)-(28-05-2004).pdf

in-pct-2000-00729-mum-correspondence(07-08-2007).pdf

IN-PCT-2000-00729-MUM-CORRESPONDENCE(7-8-2007).pdf

in-pct-2000-00729-mum-correspondence(ipo)-(27-01-2009).pdf

IN-PCT-2000-00729-MUM-CORRESPONDENCE(IPO)-(31-12-2008).pdf

IN-PCT-2000-00729-MUM-DESCRIPTION(COMPLETE)-(7-8-2007).pdf

IN-PCT-2000-00729-MUM-DRAWING(10-5-2004).pdf

in-pct-2000-00729-mum-drawing(28-05-2004).pdf

in-pct-2000-00729-mum-form 1(29-09-2000).pdf

in-pct-2000-00729-mum-form 13(09-08-2007).pdf

in-pct-2000-00729-mum-form 13(28-05-2004).pdf

in-pct-2000-00729-mum-form 1a(09-08-2007).pdf

in-pct-2000-00729-mum-form 1a(28-05-2004).pdf

in-pct-2000-00729-mum-form 2(7-8-2007).pdf

in-pct-2000-00729-mum-form 2(granted)-(28-05-2004).doc

in-pct-2000-00729-mum-form 2(granted)-(28-05-2004).pdf

IN-PCT-2000-00729-MUM-FORM 2(TITLE PAGE)-(7-8-2007).pdf

in-pct-2000-00729-mum-form 3(10-05-2004).pdf

in-pct-2000-00729-mum-form 3(13-12-2000).pdf

in-pct-2000-00729-mum-form 4(26-02-2004).pdf

in-pct-2000-00729-mum-form 5(13-12-2004).pdf

in-pct-2000-00729-mum-form-pct-ipea-409(29-09-2000).pdf

IN-PCT-2000-00729-MUM-OTHER DOCUMENT(7-8-2007).pdf

IN-PCT-2000-00729-MUM-PCT-IB-306(7-8-2007).pdf

IN-PCT-2000-00729-MUM-PCT-ISA-210(7-8-2007).pdf

in-pct-2000-00729-mum-petition under rule 137(10-05-2004).pdf

in-pct-2000-00729-mum-power of authority(08-12-2000).pdf

in-pct-2000-00729-mum-power of authority(10-05-2004).pdf