DESCRIPTION

Technical Field

This invention relates generally to ovens for cooking and heating foods, and also for maintaining food cooked by such ovens at constant temperatures. More particularly, the invention relates to an oven for providing a combination of convection and conduction cooking and heating through an individually thermalized shelf. The combined convection/conduction heating is provided by passing thermal energy through a heating channel having a serpentine configuration.

Background of the Invention

Ovens for cooking and heating foods are well known in the art. Some of these ovens facilitate convective

cooking in which heat is indirectly transferred to the food through the air between the heat source and that food. Others facilitate conductive cooking where the food is heated by direct contact with a surface at an elevated temperature.

A few ovens provide combinations of convective and conductive cooking. U.S. Patent No. 4,224,862 discloses a shelf and serpentine, widely spaced-apart hollow tubing within that shelf for the transport of heating fluids. Trays or shelves for a hot food cabinet are disclosed in FIGS. 4 and 5 of U.S. Patent No. 3,030,486. This patent further discloses electric heating elements, and steam as a heating medium.

A prior art device also featured a vertical cabinet having a plurality of individually thermalized vertically spaced apart rectangular support shelves. These shelves were made from a heat conductive material. Specifically, the shelves were made from two aluminum sheets of differing thickness. The thicker sheet, having a thickness of about 40/1000th inch defined a top surface of the shelf. The thinner sheet, having a thickness of about 30/1000th inch defined a bottom surface. The two shelves were roll-bonded together in a manner forming a serpentine fluid channel in the bottom surface. A heated fluid may be passed through the channel by a fluid inlet and outlet positioned along one width side of the shelf. As a result of such inlet positioning, the serpentine channel undulates in a manner parallel to the shelf

width.

While the foregoing prior art device was an improvement over prior art heating and holding cabinets, it was determined that•the top surfaced sheet was insufficiently thick. This caused the top surface to become uneven and indented during the roll-bonding process. As a result, the top surface had high and low spots which prevented even and uniform conductive thermalization of a food product placed thereon. In addition, the undulation of the serpentine channel in a manner generally parallel to the width of the shelf did not efficiently and uniformly thermalize the complete surface area of the top surface of the shelf. Unthermalized zones on the top surface thereby resulted. These and other problems of prior art heating and holding cabinets were addressed by the development of the present invention.

Summary of the Invention

Generally, the present invention comprises a vertical cabinet for transferring heat to food articles within that cabinet. The cabinet includes a plurality of vertically spaced-apart, individually thermalized, support shelves, made from a heat conductive material, for supporting food articles. Integrally constructed within each shelf is a heating channel having a serpentine configuration. An energy circulation element is carried at an upper portion of the cabinet for passing

thermal energy through the serpentine channel. Inlet and outlet connectors on each shelf facilitate passage of thermal energy into and out of the serpentine channel. Supply conduits are provided within the cabinet for transferring the thermal energy from the energy circulation element to the thermalizing channel. Return conduits within the cabinet facilitate return of the thermal energy to the energy circulation element.

Brief Description of the Drawings FIG. 1 is a perspective view of one embodiment of the present invention having fluid heated shelves;

FIG. 2 is a partial section side elevational view of the oven of FIG. 1;

FIG. 3 is a ^' perspective view of a bottom surface of a preferred embodiment of a liquid heated shelf;

FIG. 4 is a perspective view of a top surface of the shelf disclosed in FIG. 3;

FIG. 5 is a rear elevational view taken along lines 5-5 of FIG. 2; FIG. 6 is a partial section from elevational view of an oven having electrically heated shelves;

FIG. 7 is a top plan view of a shelf having a serpentine electrical heating element; and,

FIG. 8 is a perspective view of the shelf of FIG. 7 with its insulating material peeled away.

Detailed Description

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to embodiment illustrated. Referring now to the drawings, FIGS. 1-5 disclose one embodiment of the present invention comprising a vertical cabinet 10 for transferring heat to food, such as poultry or meat products. Typically, these cabinets are made of stainless steel or another lasting, noncorroding and ^' attractive metal. To reduce energy consumption and lower the danger of burns to those who may inadvertently contact its exterior, heat loss through the walls of each cabinet 10 is reduced by insulating those walls. A plurality of vertically spaced-apart rectangularly shaped support shelves having substantially flat top and bottom surfaces are located in the vertical cabinet 10. Cabinet 10 may typically include ten of these support shelves. In FIGS, l and 2 the topmost three support shelves within the cabinet 10 are exemplified by reference numerals 12, 14 and 16. Each of the support shelves shown in FIG. 1 is removably secured to the walls of the cabinet 10 and is sufficiently sturdy to support

as much as fifty pounds of food articles, such as poultry, fish, or meat, within the cabinet 10. The support shelves 12, 14 and 16 are each made of a heat conductive material, preferably aluminum. A pair of doors 18 and 20 provide access to the shelves 12, 14 and 16. These doors are hinged and are retained in place with magnetic catches 22 and 24, respectively. A control panel 26 at the top of the cabinet 10 enables the operator to control the temperatures of each of the individual shelves in that cabinet 10.

A centrifugal pump 28 is provided at the upper end of the cabinet 10 for circulating a heated fluid through the shelves. The pump used in this embodiment is manufactured by March Manufacturing of Glenview, Illinois, Model BC-4K-MD. Adjacent pump 28 is a reservoir 30 which also includes a heating element for initially heating the fluid and for reheating the fluid after its return from the shelves. This reservoir/heating element 30 is available from Watlow. Preferably, reservoir 30 is coupled to a pressure relief cap (Hydro Craft, Detroit, Michigan) not shown in the drawings. A ventilation fan 31 maintains pump 28 and reservoir 30 at acceptable operating temperatures. FIGS. 3 and 4 disclose the structure of the shelves 12 utilized in the heated fluid embodiment of the present invention. Shelf 12 is manufactured from aluminum and is formed by bonding two sheets together by use of a roll-

bonding technique. One sheet defines a top surface 32 of shelf 12 and the bottom sheet defines a bottom surface 34- of shelf 12. The sheet used to form top surface 32 is thicker than the sheet used for forming bottom surface 34. Preferably, the ratio of top surface sheet thickness to bottom surface sheet thickness should be at least 1.75:1 and preferably about 2.25:1. A top/bottom sheet thickness ratio of 2.25:1 dictates a top surface sheet thickness of 90/1000ths and a bottom surface sheet thickness of 40/1000ths. Such highly disparate thicknesses between top surface sheet thickness relative to bottom surface sheet thickness has been found necessary in order to assure that top surface 32 have a even surface from edge to edge with no high or low spots caused by the roll-bonding process.

As disclosed in FIGS. 3 and 4, shelf 12 becomes thermalized by passage of a heating fluid through a serpentine heating means 36 comprising a serpentine channel which undulates along bottom surface 34. Unlike the aforementioned prior art device, such undulations are generally parallel to the length of rectangular shelf 12. Serpentine channel 36 generally has inner dimensions approximating 1 inch. Heating fluid is passed through serpentine channel 36 through an inlet connector 38 and an outlet connector 40 along a rear side of shelf 12.

Unlike prior art devices in which inlet and outlet connectors are positioned along a width edge of a rectangular shelf, inlet and outlet connectors 38 and 40

are positioned along the rear length side of shelf 12. This permits the undulations of serpentine channel 36 to run parallel to the length of shelf 12 thereby increasing heating efficiency by causing a higher percentage of top surface 32 to be heated. This minimizes unheated zones along top surface 32 and assures uniform heating of all food product placed on top surface 32.

Shelf 12 and serpentine channel 36 are formed by a roll-bonding process. This process is generally known in the aluminum forming art, and includes photographically etching a serpentine pattern on one surface of the bottom sheet. This pattern will define serpentine channel 36. Next, the top sheet and bottom sheet are rolled together under exceedingly high pressure which bonds the top sheet and bottom sheet'together, but does not bond portions of the surface of the bottom sheet on which the serpentine pattern is photographically etched. As a result, a serpentine channel is partially formed which can be completed by introduction of high air pressure into channel 36 which causes serpentine channel 36 to assume a full three-dimensional shape.

As also disclosed in FIGS. 3 and 4, shelf 12 includes downwardly turned flanged edges along both width sides of shelf 12 and along the length side of shelve 12 opposite from inlet and outlet connectors 38 and 40. As disclosed in FIG. 1, flange edges 42 engage support rails 44 to support the shelves within vertical cabinet 10. Also disclosed in FIGS. 3 and 4 are a pair of

upwardly directed retainers 46 formed along a rear edge of shelf 12. Retainers 46 permit trays of food product to be properly positioned on top surface 32.

Heated fluid is moved from the pump 28 and heating reservoir 30 through a series of conduits along the frame of the cabinet. As best disclosed in FIGS. 2 and 5, a supply conduit 48 within the cabinet 10 feeds the heated fluid, to the inlet connector 38 on each shelf. Parallel to supply conduit 48 is a fluid return conduit 50. A bottom portion of conduit 48 is connected to a bottom portion of return conduit 50 by means of linking conduit 52. Linking conduit 52 returns to fluid pump 28 and heating reservoir 30 whatever portion of the heated fluid did not pass through channel 36 of the shelves. Inlet tubing 54 removably couples the inlet connector 38 to supply conduit 48. Outlet tubing 56 removably couples the outlet connector 40 to return conduit 50. As a result of such coupling, each shelf is independently thermalized. The preferred heating fluid includes a solution of 50% water and 50% propylene glycol (DOWFROST ^® HD, Dow Chemical, USA). It is understood that if heater 30 is replaced with a conventional refrigerating compressor, the glycol water solution may then function as a chilling fluid thereby converting cabinet 10 into a refrigerating unit.

FIGS. 6-8 disclose another embodiment of the present invention which utilizes electrical heating rather than

fluid heating shelf thermalizing means. As shown in FIG. 6, this embodiment also includes a vertical cabinet 58 and a plurality of vertically spaced-apart, individually heated support shelves, such as shelves 60, 62 and 64 carried within the vertical cabinet for supporting foods. Like the embodiment of FIGS. 1-5, the support shelves of this embodiment are made of a heat conductive material. The heat conductive material in this embodiment is stainless steel. Thermal energy for shelves 60, 62 and 64 is provided by an electrical power source 66 at the upper end of the cabinet 58. Power source 66 is a conventional alternating current device which can circulate electrical current through conducting elements in the shelves. As may be seen in FIGS. 7 and 8, a serpentine electrical power conduit 68 is enclosed entirely within shelf 60 and comparable serpentine channels are enclosed in each of the other shelves. As may be seen in FIG. 1 , the area of this serpentine power conduit 68 is in excess of one-half of the area of the shelf 60. In addition, because it is entirely enclosed by the shelf construction, serpentine conduit 68 provides for both uniform conductive heating for the top of the shelf and some convective heating for food products carried on below-positioned shelves. The enclosed serpentine conduit 68 also assures uniform heating of at least the upper surface of each shelf, and thereby eliminates unintended temperature gradients along the surface of the

shelf .

Preferably, serpentine conduit 68 is a metallic heating conductor. The conductor material may be a resistance heating alloy, such as copper, brass or aluminum. Typically, the material is very thin, on the order of 10 to 100 micrometers.

As disclosed in FIG. 8, an insulating material 70, such as polycarbonate, overlays the serpentine heating conduit 68 to form a heating foil 72. Insulating material 70 peeled away, that insulating material 70 should be quite thin on the order of 3/32 to 1/8 inch. The insulating material 90 may also be selected from any suitable group of insulators, including polyvinyl chloride, polyester, silicone rubber and micanite. Heating foil 72 includes at least one current inlet connector 74 and one current outlet connector 76 through which alternating current enters and leaves the conduit 68 of shelf 60. The location of inlet 74 and outlet connectors 76 can vary and is a matter of design choice largely dependent on the particular configuration of the serpentine heating element. Electrical supply wiring 78 within the cabinet transfers the electrical current from the electrical power source 66, while electrical ground wiring (not shown) within the cabinet returns the electrical current from the serpentine heating conduit 68.

Finally, cabinet 58 includes first electrical junction means for securing the inlet connector to the

electrical supply wiring and second electrical junction means for securing the outlet connector to the electrical ground wiring. In this way, conduit 68 can be removably plugged into the electrical supply wiring 78 and the ground wiring.

While the specific embodiments have been illustrated and described, numerous modifications come to mind without markedly departing from the spirit of the invention. The scope of protection is thus only intended to be limited by the scope of the accompanying Claims, rather than by the description of this preferred embodiment.