US2678990A - Oven construction - Google Patents

Description

May 18, 1954 D. w. QUIRK OVEN CONSTRUCTION Filed Aug. 31, 1951 Patented May 18, 1954 OFFICE OVEN CONSTRUCTION Douglas W. Quirk, Chicago, 111., assignor to General Electric Company, a corporation of New York Application August 31, 1951, Serial No. 244,528

6 Claims. 1

This invention relates to cooking appliances, and in particular to an electric range incorporating an improved oven or similar enclosure in which foods are to be cooked.

It is an object of the invention to provide in an electric range, an oven liner having walls carrying an element for heating them directly and substantially uniformly and consisting essentially of an electrically conductive coating applied to the outer surfaces thereof.

It is another object of the invention to provide a cook stove oven or the like in which a vitreous enamel coating on the outer surface of the oven lining has an electrically conductive layer providing a desired resistance value per unit of area over a predetermined portion of the top, bottom, and side walls of the lining.

It is a further object of the invention to provide an improved arrangement for heating the oven of a cooking range without the usual extraneous resistance elements.

In the accompanying drawings, Fig. l. is a side elevation of an electric cooking range hav- 'ing an oven embodying my invention, certain portion of the range structure having been broken away; Fig. 2 is a perspective view of the oven liner incorporated in the range shown in Fig. l; and Fig. 3, Fig. 4, and Fig. are schematic representations of steps in a suggested method of manufacture of the oven liner shown in Fig. 2; Fig. 3 showing a final preparation step of this method, Fig. 4 representing a step of coating the liner ground coat with the electrically conductive material of this method, and Fig. 5 illustrating a final step of applying terminal conductor strips of this method.

An electric range is shown in Fig. 1 and embodying the features of the present invention. Such a range has a suitably structurally reinforced body 5 which carries a cooking top 2 hav ing the usual plurality of surface cooking units or hotplates 3 under the control of individual switches (not shown) which may be mounted on the upstanding rear panel or backsplasher 4, as is well understood. The range has an oven 5 suitably secured within the body and a bottom-hinged oven door 6. Either within the oven, or below the same as shown, broiler means may be provided. In the representation of Fig. l, the broiler heating unit 7 is secured to a body wall 8 which provides the roof of a broiler chamher 5 having its own door 10. Any suitable insulation l I may be placed about the live walls of the oven and as is now commonplace, the oven temperature may be thermostatically controlled by a conventional thermostat l2, usu lly .9 1 v ed on the backsplasher. Said thermostat has a suitably supported temperature sensing element i within the oven cavity and a capillary tube or equivalent 15 leading to circuit control mechanism within the thermostat 12. It is probable that the surface units 3 will be arranged for connection into a standard 3 wire Edison circuit in the usual fashion. providing for a selection of values of thermal output at each unit, and that the circuit will be arranged to impress the full voltage across the oven terminals.

The oven liner it (Fig. 2) is of conventional pattern. As such it may comprise a sheet of steel rolled or otherwise formed into a substantially rectangular shape and having a single line of weld H at some appropriate location. A rear closure wall i8 is suitably applied. Suitable support brackets 20 fixed to the range body are appropriately attached to the oven lining or to suitable brackets (not shown) extending therefrom, as is well understood. During the fabrication of the oven liner the side walls are formed with the usual embosses 21, 22 providing ribs and projections which extend into the oven for supporting the oven racks, trays, etc. (not shown) at various levels within the oven. In accordance with conventional practice, the oven lining is given the customary coating of vitreous enamel.

It is usual for electric range ovens to be heated from the inside or outside, or both, by means of electrical resistance elements suitably supported relative to top and bottom oven liner walls. See for example the United States Patent No. 2,498,583 granted February 21, 1950, to H. W. Schulze for Electric Oven, and No. 2,392,796 granted January 8, 1946, to L. F. Berg for Electrio Oven, both of which are assigned to my present assignee. Such oven heating elements are arranged in various sinuous patterns designed to provide an appropriate distribution of heat with a minimum of hot spots or other uneven heat pattern. Of the conventional heating element practices, units arranged within the oven appear to give best heat distribution; but among other disadvantages they and. their support structures interfere with cleaning the oven. The external unit, of course, leaves the oven unobstructed for cleaning but in practice may produce a less satisfactory heat distribution. And in each case the transmission of heat to the oven liner itself is rather inefficient. This, plus the fact that only two of the four major sides are heated, makes the conventional oven slow to preheat unless high wattages are used. In the convention- .inches.

al oven the necessary disposition of heating elements relative to the oven liner slows the response oi: the oven to the application of heat, with a result that thermostatic control is characterized by relatively high amplitude swings with respect to the desired control level.

In accordance with the present invention, an electrically conductive resistance coating is applied to the vitreous ground coat of the exterior of the four sides of the oven liner so as to apply heat directly to the liner. Specifically, I apply a coating of material which is well known for use on glass or fired vitreous products, namely hydrated stannic chlorideor hydrated stannous chloride. A satisfactory solution may comprise one part of anhydrous stannic chloride in one part absolute alcohol by volume, added to one part (by volume) water. This mixture is applied by roller coatin or other method to the previously treated ground coat and heated, as presently explained. The final coating is homogenous, has a thickness of about 16 millionths of an inch, a wattage density of 2.5 per sq. inch over an area of approximately 1,000 Terminal strips are applied to provide for connection into the oven circuit.

A satisfactory method of treating the oven liner and applying the electrically conductive material is briefly as follows:

The oven liner is vitreous enameled in the customary manner. For example, the sheet metal liner as received from the forming machine first thoroughly cleaned with an alkaline cleaner to remove oil, grease, and other contaminants. The liner is then pickled by subjection to a sulfuric acid spray, and thoroughly rinsed in water. It is usually advantageous to apply a nickel sulfate treatment before enamelling, and the liner may be immersed in a nickel sulfate bath, rinsed, and subjected to an alkaline neutralizer. It is then suitably dried.

The liner is then dipped into the ground coat enamel solution dried at about 350 degrees F. By manual spraying, the ground coat is reinforced at any points where it may have run thin, and the coated liner is fired at approximately 1550 degrees F. to fuse the enamel. The final thickness of the vitreous enamel coating is of the order of .004 inch.

In preparing the liner for completion in accordance with the present invention, the enamelled liner is pickled in a bath of dilute sulfuric acid to remove any traces of thebase metal which may be present on the surface of the vitreous enamel. The liner is then thoroughly washed in minerahfree water.

The washed may then be mounted on an appropriate frame 23 having a shaft M mounted "for slow speed rotation. Using a squeegee 25 of suitable pattern the liner is wiped thoroughly dry. With the liner on the same frame the tin chloride solution. is applied. The solution may be sprayed on to the liner but Iprefer to apply it by roller coating with an ordinary printing roller;

and I have therefore schematically shown a roller coater hav ng a support structure 25, a suitably porous roller El through which the tin chloride solution may exude, and a supply conduit 28 communicating with a reservoir of solution (not shown) from which the solution may be pumped or otherwise fed through conduit 28 to the roller at a controlled rate. :As is conventional, the roller 2'! may be journalled in a suitable guard frame 29, the conduit 28 entering the roller through any conventional journal fitting 28cc solution compounded with Rochelle salt.

The sides, top, and bottom of the liner are coated with the tin chloride solution except for the narrow strip 30 which may extend on either side of the line of welding ll. It will be understood that although it is generally adequate to apply the tin chloride coating at a uniform thickness, localized areas of increased thickness may be applied by subsequent coating steps if desirable to have a non-uniforrn wattage density.

I then apply metallic terminal strips 3| to the opposite edges of the coating to provide means for connection into the oven circuit. I may apply strips of silver .ioil along the margins of the coating, .or .znayapplv a silver solution by means of a fixture 32 having the appropriately spaced applicators 33 for applying a silver-ammonia Following this treatment the liner is fired at about 1100 degrees F. to reduce the coating to its ultimate condition in which it comprises a hard, electrically conductive, film M which has high scratch resistance and sufiicient hexibility to expand and contract with the oven liner without rupture or separation from the vitreous enamel coating. An oven liner of normal mass will attain the desired temperature in about twenty minutes, and cooling is at normal rate inair. At 1100 degrees F. the vitreous ground coat becomes plastic but nevertheless accepts the tin chloride coating in a firm bond without penetration of the conductive coating into the ground coat. During the final firing the silver solution deposits metallic silver on the tin chloride layer. Suitable conductors 35 may then be electrically attached by silver soldering to the silver terminal strips 3 l.

Because of the otherwise adequate continuous electrically conductive path around the oven liner, the interruptions in the coating .caused by the various embosses have no practical adverse effect. The completed oven liner safely withstands temperatures up to 700 degrees R, which very appreciably exceeds the maximum usable range oven temperature. Because of the direct application of heat to the oven liner there is very littleloss through insulation .orairgap, and the much. sought after balance betweenradiation and conduction is attained to aliighdegree. The direct heat application, plus the superior heat balance improves response to thermostatic control to the extent that temperature swings relative to the control point are reduced to the extent that for all practical purposes, straight line control is achieved.

It is an importantfeature of the invention that the unooated side of the oven liner radiates approximately twice as much heat as the coated side since the film itself acts as a metallic .refiector. For maximum efficiency, therefore, the coating should always be applied to the external surface of theoven so that the uncoated vitreous enamel surface or" the inside of the oven liner faces the substance or object to be heated. An oven lining having a 2500 watt coating in accordance with the present invention will achieve baking results equal to or better than conventionally heated ovens having .the usual 800 Watt upper unit and 3000 watt lower unit, and in ad dition, attain baking temperature more rapidly from a cold start.

While there has been described what is at present considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim:

1. In an electric range including a body housing a metal liner defining an oven compartment having a front opening, and a front door carried by said body and movable between open and closed positions with respect to said front opening, said liner being provided with top and bottom and end walls and a pair of side walls; the combination comprising a first vitreous enamel coating carried by the interior surfaces of said top and bottom and end and side walls, a second vitreous enamel coating carried by the exterior surfaces of said top and bottom and side walls, a thin mirror-like and metallic-like film of electrically conducting material carried by the exterior surface of said second vitreous enamel coating, said film having an area substantially commensurate with that of each of said top and bottom and side walls, and a pair of terminals electrically connected to two spaced-apart portions of said film, said film constituting a resistance electric heater for supplying heat to said second vitreous enamel coating and through said top and bottom and side walls into said oven cavity when said terminals are connected to a source of current supply, said film also constituting a thermal heat reflector effecting preferential radiation of heat from the interior surface thereof with respect to the exterior surface thereof so that the larger fraction of the heat generated therein is directed toward said oven cavity.

2. An oven liner comprising a hollow sheet metal shell provided with four connected boundary walls and a fifth connected end wall defining an open-ended oven compartment, a first vitreous enamel coating carried by the interior surfaces of said boundary and end walls, a second vitreous enamel coating carried by the exterior surfaces of said boundary walls, a thin mirror-like and metallic-like film of electrically conducting material carried by the exterior surface of said second vitreous enamel coating, said film having an area substantially commensurate with that of each of said boundary walls, and a pair 01 terminals electrically connected to two spacedapart portions of said film, said film constituting a resistance electric heater for supplying heat to said second vitreous enamel coating and through said boundary walls into said oven cavity when said terminals are connected to a source of current supply, said film also constituting a thermal heat reflector effecting preferential radiation of heat from the interior surface thereof with respect to the exterior surface thereof so that the larger fraction of the heat generated therein is directed toward said oven cavity.

3. The oven liner set forth in claim 2, wherein said film has a surface area of at least 1,000 square inches and a continuous rating of at least 2% watts per square inch of surface thereof.

4. The oven liner set forth in claim 2, wherein said film is capable of continuous operation at a temperature of at least 550 F.

5. The oven liner set forth in claim 2, wherein said film has a thickness of the order of 16 10- inch.

6. The oven liner set forth in claim 2, wherein said film consists essentially of a salt of tin.

References Cited in the file of this patent UNITED STATES PATENTS

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