US3692015A - Windowed doors for self-cleaning ovens - Google Patents

Abstract

Windowed doors for self-cleaning household ovens where the window assembly has a series of spaced parallel glass window panels secured in alignment with two of such panels near the oven cavity enclosing a dead-air insulating space, and a third of such glass window panels being separated from the oven cavity by two dead-air space enclosing glass panels, with the space between the third panel and the two dead-air enclosing panels being ventilated for replacement of heated air therein by natural circulation of cooler air, and a thin grid-like foraminous reflective coating on at least one of the glass panels disposed in the ventilated air space to reflect a relatively large proportion of radiant oven heat and to be cooled by the air wash during such ventilation.

Description

[151 3,692,015 1 Sept. 19, 1972 United States Patent Chase et a1.

7/1965 Rosenau et al. [26/200 X 2/l968 Belliveau.................. 6/1969 .219/406 ....l26/2OO 126/200 X Huff..............

drisak, both of Northvme; Harold E. 3,457,138 Miller Mcxelvey Plymouth an of Mich Primary Examiner-Carroll B. Dority, Jr. [73] Assignee: Shatterproof Glass Corporation, y- C y, Greene & H ell Detroit, Mich.

June 1, 1971 ABSTRACT Windowed doors for selfcleaning household ovens bly has a series of spaced ls secured in alignment with the oven cavity enclosing a [22] Filed:

Appl. No.: 148,616

where the window assem parallel glass window pane Related U.S. Application Data [62] Division of Ser. No. 848,547

two of such panels near dead-air insulating space, and a third of such glass window panels being separated from the oven cavit Aug. 8, 1969, Pat. No. 3,612,825.

by two dead-air space enclosing glass panels, with th space between the third panel and the two dead-air enclosing panels being ventilated for replacement of heated air therein by natural circulation of cooler air, g on at 606 5mm ,3 82 .4 B 2 mo 5 "2 0 m 0 o n "0 6 mm H "6 2 mwm mnr. mu 1 l W d S M UhF 1]] 2 8 555 iii and a thin grid-like foraminous reflective coatin [56] References Cited least one of the glass panels disposed in the ventilated air space to reflect a relatively large proportion of UNITED STATES PATENTS radiant oven heat and to be cooled by the air wash during such ventilation.

5/1963 Grahn et al. ...........126/200 X 2/1965 3,168,089 Larkin ...................126/200 X 5 Claims, 7 Drawing [Figures iiiiiiii Ll iliitiill.

P'A'IENTEDSEP 19 m2 SHEET 1 [IF 4 FIG.

WV WILLIAM B. CHAS QT JOSEPH E. JENDRISAK a HAROLD E. McKELVEY BY M0304 Queue 8 Jewel! ATTORNEYS PATENTEDSEP 19 m2 SHEET 2 BF 4 INVENTORS. WILLIAM B.CHASE, JOSEPH E JENDRISAKE HAROLD E. McKElLVEY BY Ma ay, Q zeeae a /owed ATTORNEYS PATENTED l 9 I972 3 6 92 015 sum 3 or 4 ATTORNEYS WILLIAM B. CHASE. JOSEPH E. JENDRISAK a FIG- 6 HAROLD E. McKELVEY BY M0 604;, Gwene A? Jewell P'A'IENTEDSEP 19 I922 SHEET U 0F 4 FIG? INVENTORS. CH ASE WILLIAM B.

JOSEPH E. JENDRISAK a HAROLD E. McKELVEY BY M0 (304;, gm 8 Jewell ATTORNEYS WINDOWED DOORS FOR SELF-CLEANING OVENS This application is a division of application Ser. No. 848,547, filed Aug. 8, 1969, now US. Pat. No. 3,612,825.

THE INVENTION The present invention relates to windowed selfcleaning ovens and more particularly to doors for such ovens having multiple-pane insulating windows with air-cooled grid-like semi-transparent foraminous reflectors.

Self-cleaning ovens have been in use for many years (see, for example, Hurko U.S. Pat. No. 3,121,158). A typical household self-cleaning oven has a cooking range between 150 and 550F., and cleaning is accomplished by raising the oven temperature to between about 150 and 950F. Housewives have insisted that their ovens be provided with windows to permit viewing of the food being cooked without opening the oven door, and oven manufacturers have provided such windows in the doors of their self-cleaning ovens.

However, windows in self-cleaning ovens present very serious problems because, during cleaning, relatively large amounts of heat escape through the window, greatly reducing the efficiency of the cleaning operation and causing uneven heat distribution in the oven itself, and also because the oven window becomes exceedingly hot, much hotter than the remainder of the oven exterior, thereby creating a safety hazard.

Oven manufacturers have, for many years, sought practical solutions to these problems without success. Prior to the present invention, it was thought that the safest and most practical approach to the problem was 0 retains a relatively large amount of heat in the oven to provide a movable opaque metal shield which is placed across the window during cleaning and to provide a safety mechanism which prevents activation of the cleaning cycle'until the movable shield is in place. The windowed self-cleaning ovens were made in this manner for many years prior to this invention, but the equipment was relatively costly and inconvenient to use and has not been wholly effective in minimizing heat loss or in keeping the outer window temperature within safe limits.

The present invention provides the long-sought solution to the above problems and makes it possible, for the first time, to manufacture inexpensive self-cleaning ovens having safe, effective insulating windows without the expense, inconvenience and other disadvantages characteristic of previous constructions. Briefly, the present invention solves the problem by providing the oven door with a window which includes two spaced parallel glass panels disposed innermost with their peripheral edges surrounded by a wrap-around member forming an enclosed chamber or dead-air space between the panels; at least one additional window panel spaced outwardly from the two inner. panels; means for ventilating the space between this additional panel and the inner panels; and, a reflective, semitransparent, highly conductive metal grid disposed in said ventilated space, preferably on the outer surface of the outer panel of the aforesaid inner pair of panels.

The dead-air space between the inner panels serves as a partial insulator. The decorative semi-transparent reflective metal grid permits a view of the oven interior but reflects back into the oven cavity a relatively large cavity.

An object of the present invention is to provide an effective, low-cost windowed oven door for high temperature self-cleaning ovens.

A further object of the present invention is to provide a window for high temperature ovens which will minimize heat loss through the window.

A still further object of the present invention is to provide a window for self-cleaning ovens in which the temperature of the outer window panel will not exceed the manufacturers recommended safety level.

Another object of the present inventionis to provide a high temperature self-cleaning oven with a windowed door in which no part of the outer window panel will exceed 230F. when the oven is in the heat cleaning cycle of about 750 to 950F. for 2 hours in F. ambient air. I

A further object of the present invention is to pro-. vide a window assembly or windowed oven door for high temperature self-cleaning ovens which does not require inconvenient or expensive safety mechanisms such as movable shields.

Further objects and advantages of the present invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various things in which the principle of the invention may be employed.

In the annexed drawings:

FIG. 1 is a side elevational view, partly broken away and partly in section, of a household range embodying the present invention;

FIG. 2 is an enlarged fragmentary section elevational view of the door of FIG. 1;

FIG. 3 is an enlarged fragmentary perspective sectional view of the door of FIG. 1;

FIG. 4 is an enlarged fragmentary view of one corner of the door taken along the lines 4-4 of FIG. 5 showing the reflective metal grid;

FIG. 5 is an enlarged elevational view, partly broken away and partly in section, taken along the line 55 of FIG. 6;

FIG. 6 is a perspective view of a second embodiment of the invention; and

FIG. 7 is a perspective view of a third embodiment of the present invention.

Referring more particularly to the drawings, in which like parts are identified by the same numerals throughout the several views, there is shown in FIGS. 1 to 3 a household free-standing electric self-cleaning range 1 having a top cooking surface 2 with a plurality of surface heating elements 3, an oven cavity 4 directly beneath the top cooking surface 2 and formed by a box-like oven liner cooperating with a front-opening drop door 6. The oven cavity 4 is suppliedwith two standard heating elements, namely, a lower baking element 7 and an upper broiling element 8. Suitable thermal insulation 9, such as fiberglass or the like, surrounds the oven liner 5 to retain the heat developed by the heating units 7 and 8 in the oven cavity 4 for a more efficient utilization of the heating energy as well as to retain the outer surface of the range body 10 at a relatively cool temperature which would not be injurious to the human touch.

An oven lamp 11 is arranged in the rear wall 12 of the oven liner 5 to illuminate the oven cavity 4 in a conventional manner. Further, the opposite side walls of the oven liner carry the usual shelf-supporting means (not shown) which support one or more removable shelves in the oven cavity in the usual manner.

The range 1 is provided along the back edge of the top cooking surface with a raised backsplash 14 which contains the various circuit control elements, switches, thermostats, clock timers, etc., which enable he housewife to control the various heating elements of both the top cooking surface 2 and oven 4. Preferably, the heating elements and their switches are arranged to provide the normal cooking operations and the high temperature self-cleaning operations.

As best seen in FIG. 2, the windowed oven door 6 has a frame 15 which is generally of sheet metal construction and includes a front or outer door panel 16, a middle door panel 17, and a rear or inner door panel 18. The front door panel 16 has a narrow rearwardlyturned peripheral flange 19. The middle door panel 17 is of mating construction with the outer door panel 16 having a front-turned peripheral flange 20 which fits within the flange 19 of the front door panel 16.

The rear door panel 18 has a narrow front-turned peripheral flange 21 and is mountedon the rear surface of the middle door panel 17. The inner door panel 18 has a diameter roughly corresponding to the inner diameter of the oven opening and, when the door 6 is in the closed position, the inner doorpanel 18 projects slightly into the oven cavity in the manner of a plug, whereas the middle door panel 17 overlays the oven opening. A vapor and heat resistant gasket 22 is fastened to the middle door panel 17 around the periphery of the inner door panel 18 to prevent escape of heat and vapor around the door edges.

A handle 23 is mounted on the outer surface of the front door panel 16 at the top portion of the oven door 6 and the door 6 is hinged at its bottom edge to the range body.

A window assembly or unit 24 is located in the oven door 6 and is constructed according to the present invention to maintain its outermost glass panel at a relatively low temperature when the oven is operating in the high temperature cleaning range of about 750 to 950F. While this is the preferred temperature range for cleaning operations, the upper limit of this cleaning temperature range can be as high as about 1,050F. Above this temperature, however, the oven is likely to suffer enamel failure and/or softening of the window glass.

The window assembly 25 includes three spaced substantially parallel transparent glass panels 28, 29 and 30. Window apertures 25, 26 and 27 are formed in the front, middle and rear door panels 16, 17 and 18, respectively, and are visually registering in the assembled door 6. The three transparent glass panels 28, 29 and 30 are secured in spaced parallel relation between the front and rear door panels 16 and 18 at those window openings 25, 26 and 27. The glass panels 28, 29 and 30 consist of a first or inner glass panel 28, a second or intermediate glass panel 29 adjacent to the first panel 28 and separated from the oven cavity 4 by the first panel 28, and a third or outer glass panel 30 separated from the first panel 28 by the second panel 29, so that the glass panels 28, 29 and 30 are arranged in the order of first 28 to second 29 to third 30 proceeding from the oven cavity 4 out to the front of the oven.

A first spacer member 31 is disposed between the first and second panels 28 and 29 at their peripheral edges, and a second spacer member 32 is likewise disposed between the second and third panels 29 and 30 at their peripheral edges. A wrap-around or clamping member 33 encloses the peripheral edges of all three glass panels 28 to 30 and cooperates with the spacer members 31 and 32 to secure the panels 28 to 30 in spaced parallel relation. Vent apertures 34 are provided in the second spacer member 32. Additional vents 45 are also provided in the adjacent region of the wrap-around member 33 so that the space between the second and third panels 29 and 30 communicates with the space between the front and middle door panels 16 and 17. Additional vent apertures 35 are provided in the upper and lower edges of the door 6 so that heated air may escape from between the second and third glass panels 29 and 30, through the oven door 6, and into the ambient atmosphere outside the oven 1.

There are no vent apertures to ventilate the space between the first and second glass panels 28 and 29, so that such space is a dead-air space tending to insulate the oven cavity 4 and retard heat loss at the window 24. Additional dead-air spaces may be formed by employing additional spaced parallel transparent panels, but a single dead-air space is usually satisfactory.

A thin semi-transparent metallic reflector 36 (the thickness of which is greatly exaggerated in the drawings for purposes of illustration) in the form of a grid-like or foraminous reflective coating 36 is deposited on the front or outer surface of the second glass panel 29, so that the reflector 36 is located in the ventilated or air-wash space between the second and third glass panels 29 and 30. This reflector is preferably of gold or platinum or an alloy containing one or both of these since gold and platinum are highly conductive (having a thermal conductivity in excess of 40 BTU/(ftFhLF/in.) at 212F. and can form thin opaque surfaces having low surface emissivity (less than about 0.50) between 750F. and 950F., so that it reflects a vlarge amount of radiant heat and retains very little.

Platinum and gold are also relatively chemically inactive and resist oxidation and corrosion at oven cleaning temperatures. Thin layers of those materials retain satisfactory opacity at high temperatures. These characteristics make them highly suitable and preferred for use in the present invention. A platinumgold alloy may be used when a silver color reflector is desired.

At high temperatures, the reflector 36 reflects a substantial proportion of the radiant heat emanating from the oven cavity 4, thereby reducing heat loss at the win dow 24. At the same time, heat that is picked up by the foraminous reflector 36 is readily conducted away in the air wash so that the space between the second and third members 29 and 30 is kept relatively cool, thereby permitting the exposed portion of the outer surface of the outer or third glass panel 30 to be maintained at a relatively cool temperature, i.e., less than about 230F. when the oven 1 is at a heat cleaning temperature of about 950F. for 2 hours in 70F. ambient air. Oven manufacturers specify that the room-side glass panel temperature should not exceed 265F.

The foraminous reflector 36 has a plurality of apertures or foramens 37 in regular disposition throughout, and the ratio of the reflectors total reflective surface area, (i.e., the area of one side of the reflector 36 less the sum of the areas of the foramens 37) to the total area of the viewing apertures 37 is preferably about 3 to 2 so that ones view through the center of the glass panel 39 is about 60 percent obstructed. This ratio could be raised or lowered, without departing from the spirit of the present invention, although either visibility or heat retention would be reduced respectively. Accordingly, in order for the reflector to both. transmit and reflect substantial portions of heat and light emanating from the oven cavity, the ratio should not exceed about 3:1 or be less than about 1:2. The

foramens 37 should be fairly small (preferably on the order of 3/64 inch square or about .02 square inch). As the foramen size in increased (with the same ratio of reflective surface area to viewing area maintained at about 3 to 2), so is the width of the opaque portions between the foramens 37, so visibility through the grid 36 becomes discontinuous and impaired. In addition, distinguishable alternating hot and cool areas form on the outer (third) panel, and the hot areas tend to exceed safe and/or acceptable temperature levels. Accordingly, foramen 37 size should not exceed about one-sixteenth sq. inch.

The reflector is preferably fired onto the glass in a thin coating according to standard techniques well known in the art. One method involves oil soluble compounds of gold and/or platinum and palladium, together with rhodium, silver and certain base metals in a resin/solvent system. This compound is applied to the glass by silk-screen process and then fired at a high temperature approaching the distortion point of the glass e.g., at 1,050F. or even higher where a very hard glass substrate is employed. For a grid-like or foraminous semi-transparent reflector the compound (commonly called liquid gold) is applied in sufficient quantities so that the residue of gold left after firing is sufficiently thick to be opaque and to retain opacity at oven cleaning temperatures but thin enough to cool readily in the air wash (e.g., on the order of 1,500 Angstroms). t

The thin reflective metal coatings may be fired into the glass during tempering of the glass, for example, when using such liquid gold. Very attractive decorative grids may be formed on the glass in fine detail when using such coatings. The grid-like. foraminous coatings used in the present invention are not only pleasing to the eye but are also durable so as to be ideal for household ovens. Such foraminous coatings are superior to any other type of semi-transparent coating for use in self-cleaning ovens.

The term semi-transparent reflector" as used herein is understood to include, but not be limited to, a reflector of the type shown in the drawings where visibly distinct foramens are formed in an otherwise substantially opaque reflective metal surface having a substantial thickness, such as 1,000 to 2,000 Angstroms. Such term also includes reflectors of the type where the metal coating is extremely thin (e.g., less than 200 Angstroms) so that the metal itself appears to be semitransparent. This is without regard to whether the transparency is due to minute discontinuities in the coating or whether the metal itself is actually transparent due to its thinness, so long as the reflector both transmits and reflects substantial portions of heat and light emanating from the oven cavity.

Accordingly, in alternative embodiments of the present invention, the reflector is a thin coating of gold or the, like, perhaps having a thickness on the order of between about 50 and 200 Angstroms. This thin coating is applied to the glass in an even, substantially continuous film without visibly distinct foramens. It is nevertheless so thin as to be semi-transparent and both transmits and reflects substantial portions of heat and light emanating from the oven cavity.

Thin semi-transparent reflective coatings may be applied to the glass in various ways, including by vacuum deposition, by electroplating, and. by the sputtering process. Glass so treated is commercially available, sold under the trademark Mirro-Pane". Suitable methods of applying the reflector metal to the glass are described in our copending allowed application Ser. No. 848,547. The entire disclosure of that application is incorporated herein by reference and made a part of this specification.

While gold, platinum or alloys of those metals are preferred for construction of the semi-transparent foraminous reflectors according to the present invention, other metals or alloys such as nickel, chromium, copper, aluminum, silver and/or their alloys may be satisfactory in certain embodiments, although they are typically either less reflective and/or less resistant to corrosion.

Inasmuch as the two innermost glass panels reach relatively highv temperature levels, those panels are preferably of heat resistant borosilicate glass (e.g., such as is sold under the registered United States Trademark Pyrex.) Such glass may be heated up to as high as l,200F. or higher without deformation or appreciable glowing, and it withstands rapid temperature variations satisfactorily.

Returning to a description of FIGS. 1 to 3 inclusive, the window unit 24 formed by the three glass panels 28 to 30, spacers 31 and 32, reflector 36, and wraparound member 33, is mounted at the oven doors window apertures 25 to 27 with L-shaped brackets 38 which are fastened to the middle door panel 17. In order to guard against the escape of gases and vapors, the outer or third glass panel 30 of the window unit 24 is resiliently held against the inwardly turned flange 39 defining the window aperture 25 of the front panel 16, and the inner or first glass panel 28 of the window unit is resiliently held against the outwardly turned flange 40 defining the window aperture 27 of the rear door panel 18. A heat resistant gasket (not shown) may be employed to seat the window unit 24 between the door panels 16 and 18 to seal against escaping gases and vapors.

The oven 1 has an air circulation chamber 41 formed between the oven frame 42 and the oven liner 5. An air intake vent 43 is provided in the rear of the oven frame 42 at the lower rear of such chamber 41. A mechanical fan 44 is positioned in the chamber 41 at the vent 43 to draw cool air into the chamber 41. Vents (not shown) are provided in any suitable portion of the oven frame 42 so that warm air in the chamber 41 may escape and keep the side, front and rear walls of the oven frame 42 relatively cool for safety.

A second embodiment of the present invention is shown in FIGS. 4 to 6, wherein FIG. 6 shows a gas selfcleaning range 50 of the type having a plurality of burners 51 below and an oven 52 above. The oven cavity 53 has a side-hinged windowed door 54 covering its front opening. The range 50 is of standard self-cleaning construction in many respects, having a sheet metal outer frame 55 and an insulated inner oven liner 56 defining the oven cavity 53. The heating control panel 57 is located to the right of the windowed door 54.

The windowed oven door 54 has a frame 58 which is generally of sheet metal fabrication and comprises a front or outer door panel 59, a middle door panel 60,

and rear or inner door panel 61. The front door panel 59 has a rearwardly extending flange portion 49 at its outer peripheral edge which overlays and mates with the inner and middle door panels 61 and 60, which are integrally formed with one another, joined at their peripheral edges by a common connecting portion 62. The front, middle and rear panels 59, 60 and 61 have rearwardly or frontwardly directed flange portions 63, 64 and 65, respectively, generally bordering the window opening. A glass window unit or assembly 69 is located in the oven door 54 and mounted on such flanges.

j The window assembly 69 includes three rectangular transparent glass panels 70, 71 and 72 secured in spaced parallel relation between the front and rear door panels 59 and 61 at the window opening. The first glass panel 70 is adjacent to the oven cavity 53. The second or intermediate glass panel 71 is spaced forward of the first panel 70 and separated from the oven cavity 53 by the first panel 70. A third glass panel 72 is spaced forward of the second panel 71, being thus separated from the first panel 70 by the second panel 71.

A first spacer member 73 of generally U-shaped cross section is disposed between the adjacent peripheral edges of the first and second glass panels 70 and 71, and a second similarly shaped spacer member 74 is likewise disposed between the adjacent peripheral edges of the second and third glass panels 71 and 72.

A wrap-around or clamping member 75 encloses the peripheral edges of allthree glass panels 70 to 72 and cooperates with the spacer members 73 and 74 to secure the glass panels 70 to 72 in spaced parallel relation. A plurality of ventilating apertures 77 are also provided in that portion of the clamping member 75 adjacent the second spacer member 74 so that the space between the second and third glass panels 71 and 72 is ventilated to form an air-wash space in communication with the space between the front and middle door panels 72 and 71. Additional vent apertures 78 and 79 are provided in the upper and lower edges of the door 54, i.e., in the rearwardly directed peripheral flange portion 49 of the outer door panel 59, so that hot air between the second and third glass panels 71 and 72 may escape therefrom through the oven door 54, into the ambient atmosphere outside the oven 50.

There are no corresponding vent apertures to ventilate the space between the first and second glass panels and 71, so that such space is a dead-air space tending to insulate the oven cavity 53 and retard heat loss at the window 69.

A thin semi-reflective metallic reflector 80 in the form of a grid-like reflective metallic foraminous coating 80 with small foramens 89 is disposed on the front or outer surface of the second glass panel 71 so that it is located in the ventilated air-wash space between the second and third panels 71 and 72. This grid 80 has the same general physical and chemical characteristics as does the grid 36 described with reference to FIGS. 1 to 3, hereinabove. The thickness of the coating 80 is greatly exaggerated for purposes of illustration and is on the order of about 1,500 Angstroms in actuality. Such thickness is usually no greater than 1,500 Angstroms and is preferably at least about 1,000 Angstroms and no more than about 2,000 Angstroms.

Standard fibrous insulating material 81 fills the space between the rear and middle panels 71 and 72 outside the window area, i.e., between the clamping member 75 and the common portion 62 connecting the outer edges of the rear and middle door panels 61 and 60.

A heat resistant gasket 82 encircles the window aperture of the rear door panel 61, secured by a suitable bracket 83, to form an airtight seal at the interface of the oven door 54 and the oven body 55 to prevent the escape of heat and moisture vapor'from the oven cavity 53 during operation.

A conventional door handle 84 is mounted on the front door panel 59.

The oven 50 has an air circulation chamber 85 formed between the oven frame 55 and the oven cavity 53. The air circulation chamber 85 has an air outlet (not shown) in the upper region of the oven frame 55 to permit hot air to escape so that the side walls of the oven frame 55 are kept relatively cool during cleaning. A first fan (not shown) may be provided at an air intake vent in the base of the oven frame (also not shown) to direct cool air into the air circulation chamber 85, but use of such a fan is optional. It is preferable to allow air to enter the intake vent naturally by convection.

A portion of the oven frame 55 at the lower front edge of the oven cavity 53 projects forward to extend beneath the lower peripheral edge of the oven door 54 and thereby extend the air circulation chamber 85 into that region. A plurality of apertures 86 are formed in the horizontal surface 87 of that projecting portion of the oven frame 55 to communicate with the apertures 79 in the lower peripheral edge of the oven door 54 so that air may pass from the air circulation chamber 85 into the air-wash space between the second and third glass panels 71 and 72 housing the reflective metal foraminous coating 80. A fan 88 may be mounted in the air circulation chamber 85 on the inner surface of the front wall of the oven frame 55 adjacent to and directed at the apertures 86 communicating with the apertures 79 in the lower peripheral edge of the oven door 54 so that relatively cool air from the air circulation chamber 85 is forced into the air wash space to facilitate cooling of the oven door 54. While this fan 88 provides generally better cooling, it is optional and can be eliminated to reduce cost and the oven door 54 will be cooled sufficiently by convection and the natural displacement of hot air by cooler air.

A third embodiment of the present invention is shown in FIG. 7 wherein a window assembly or unit 90 has four transparent glass panels 91 to 94, inclusive, secured inspaced parallel relation and adapted to be mounted in the door of a self-cleaning oven. The first glass panel 91 is intended to be mounted adjacent the oven cavity. A second or intermediate glass panel 92 is spaced forward of the first panel 91 so that it would be separated from the oven cavity by the first glass panel 91. A third or outermost glass panel 93 is separated from the first panel 91 by the second panel 92. And, in addition to those three panels 91 to 93, a fourth panel 94 is disposed between the second and third panels 92 and 93, so that the third panel 93 is spaced from the first panel 91 by the fourth panel 94 as well as by the second panel92.

First, second and third spacer members 95 to 97, inclusive, of U-shaped cross section are disposed between the adjacent peripheral edges of the first and second glass panels 91 and 92, the second and fourth panels 92 and 94, and the fourth and third panels 94 and 93, respectively.

A wrap-around or clamping member 98 encloses the peripheral edges of all four glass panels 91 to 94 and cooperates with the spacer members 95 to 97 to secure the glass panels 91 to 94 in spaced parallel relation. A plurality of ventilating apertures 99 are provided in both the horizontal and vertical sides of the second and third spacer members 96 and 97, and also in that portion of the clamping member 98 adjacent the second and third spacer members 96 and 97 so that the spaces between both the second and fourth panels 92 and 94 and between the fourth and third panels 94 and 93 are ventilated, to form airwash spaces, whereas the space between the first and second panels 91 and 92 is completely enclosed to form a dead-air space.

An oven door or wall for reception of the window unit 90 would be provided with air circulation passages communicating between the aforesaid air-wash spaces and the ambient atmosphere.

A thin semi-transparent metallic reflector 100 in the form of a grid-like foraminous coating is disposed on the inner surface of the fourth glass panel 94 so that it is washed by air passing through the space between the second and fourth panels 92 and 94. Alternatively, the reflector 100 may be disposed on the outside surface of the second panel 92 or the outside surface of the fourth panel 94 or on the inside surface of the third or outermost panel 93.

Reflective coatings of the type described may also be disposed simultaneously on two separate glass panel surfaces in the window assembly located in the air wash, such as on both sides of the fourth panel 94. At least one of the two gridlike reflective coatings should have a position which is fixed. The other coating may be movable with its associated glass panel but preferably has a fixed position with its foramens aligned foraminous reflective coating, best :results are obtained using either one or two foraminous reflective coatings. It is also possible to employ a gridlilte foraminous coating having foramens thatare not fully transparent but are semi-transparent. For example, the foramens may be partially or fully coated with a thin reflective metal coating (for example, a gold coating with a thickness of 50 to Angstroms).

A window unit formed in the manner shown in FIG. 7 as described herein provides an admirable outer window surface temperature, e.g., less than about F. in a self-cleaning oven in the heat cleaning range of about 950F. for 2 hours in 70F. ambient air. Accordingly, a window unit of the four panel variety illustrated in FIG. 7 may be employed as a substitute for the window units 24 and 69 shown in the self-cleaning ranges I and 50 of FIGS. 1 to 3 and FIGS. 4 to 6.

The efficacy of a window assembly according to the present invention in providing a relatively cool outer window surface is illustrated by the following:

A standard gas-fueled self-cleaning oven range sold under the trademark Modern Maid by Tappan Corp. was specially fitted with a windowed oven door according to the present invention, replacing a solid door. The particular window assembly employed was similar to the third embodiment described herein except that the outermost window panel (herein the so-called third" panel) was oversized (on the order of 15 inches X 22 inches) to give the appearance of an all-glass oven door for decorative purposes. The first and second glass panels (the inner lite and the lite adjacent thereto) were 0.140 inch X 5 31/32 inches X 5 31/32 inches borosilicate and spaced 0.884 inch from one another. The so-called fourth glass panel was 3/ 16 inch X 5 31/32 inches X 15 31/32 inches crystal, spaced 0.523 inch outwardly from the second glass panel. These three inner panels were held at their edges in fixed relation by a metal wrap-around or clamping member and a pair of metal spacer members of suitable dimensions and of the type described and illustrated herein. The entire assembly was mounted in the oven door approximately one-half inch behind the large third or outer glass panel. A thin gold film was deposited on the inner surface of the fourth glass panel and the inter-panel space in which the gold film was located was ventilated by a plurality of 7/8 inch diameter circular vent apertures spaced about one-sixteenth inch along the outermost spacer member and also in the clamping member adjacent that spacer. The upper edge of the oven door was similarly vented. The oven door included a metal inner panel positioned generally above the innermost or first glass panel. A second metal panel was mounted frontward of and parallel to the inner door panel and was positioned generally above the second glass window panel, the space between the aforesaid metal door panels being filled with a standard heat insulating material, such as asbestos. A third metal panel was mounted frontward of and parallel to the second metal panel and was positioned generally above the fourth glass panel. The space between the aforesaid second and third metal door panels was open to permit circulation of air from the window space housing the gold film to the vents in the upper edge of the oven door. A similar passage was afforded in the lower region of the oven door for the intake of cool air. ln addition, the space between the front (third) oversize glass panel and the fourth glass panel was ventilated at the upper and lower oven door edge so that there was an air wash on both sides of the fourth glass panel bearing the gold film. The gold film was opaque, but provided with horizontally and vertically aligned 3/64 inch square apertures regularly spaced three sixty-fourths inch apart so that the gold coating formed a semi-transparent grid. The gold grid was bounded by a solid 1% inch gold peripheral border.

The oven was operated over its standard cleaning cycle, comprising a 15-hour warm-up period and a subsequent 2-hour cleaning period. A standard Leeds & Northrup potentiometer was used to obtain contemporaneous measurements at regular intervals of the temperatures of (a) the air in the room containing the oven, (b) the outer or room-side surface of the third or outer glass panel taken at a point opposite the upper edge of the fourth glass panel, and (c) the oven interior taken adjacent the upper edge of the oven door. These temperature values are set forth in Table 1.

TABLE 1 Room Temp. Outside Glass Oven Time (F.) Temp. (F.) Temp.

Temperature variance in columns (1:) and (c) after 0:50 are due to thermostatic control; values represent range of temperatures occurring during 3-5 minute time intervals following time indicated.

From the above table, it can be seen that the present invention provides an oven window for a self-cleaning oven which is safe, minimizes heat loss, and is well within the specifications of the oven manufacturers.

In various embodiments of the present invention, spacing of the glass panels in three-panel units of the type illustrated in FIGS. l-6 herein may vary, but spacing on the order of 1 inch between adjacent glass panels is generally preferred, providing satisfactory insulatingcooling characteristics in a relatively compact unit. A four-panel unit of the type illustrated in FIG. 7 preferably embodies approximately l-inch spacing between the first and second panels, but the spacing between the second and fourth panels and between the fourth panel and third outermost panel is preferably on the order of one-half inch. Thus the total width of the spaces between panels in the four-panel unit is preferably no more than 2 inches and the distance between the inner face of panel 91 and the outer face of panel 93 may be less than 3 inches.

Except for the thickness of the gridlike foraminous reflective coatings, the drawings are drawn substantially to scale to facilitate an understanding of the invention, but it will be apparent that the size and shape of a household self-cleaning oven may vary somewhat from what is illustrated herein.

It will be understood that, in accordance with the provisions of the patent laws, variations and modifications of the specific apparatus shown herein may be made without departing from the spirit of the invention.

Having described our invention, we claim:

1. A hinged oven door for closing a door opening in a household oven, said door comprising:

a hollow sheet metal frame having a central opening and a window closing said opening, the rear of said hollow frame which is adapted to close an oven cavity being covered with insulation surrounding and in abutting relationship with said window unit;

said window comprising four transparent panels mounted in predetermined spaced parallel relation in said central opening including an inner glass panel, a first intermediate glass panel near and spaced from said inner panel, a second intermediate glass panel outwardly of said first intermediate panel and spaced therefrom, and an outer transparent panel spaced from said second panel, said first intermediate panel being located between said inner panel and said second intermediate panel, said second panel being located between said first panel and said outer panel;

means essentially sealing the space between said inner panel and said first intermediate panel to provide an insulating dead-air space between said panels and near the inner side of the oven door;

a gridlike foraminous reflective coating located on said second intermediate panel, the foramens of said coating having an average area no greater than 0.02 square inch, said coating having a thickness no greater than about 1,500 Angstroms and being formed of a substantially non-chemically-reactive metal having a thermal conductivity in excess of about 40 BTU/ (ftFhr. F/in.) at 212F. and a surface emissivity less than about 0.50 throughout a temperature range between 750 and 950F. and selected from the group consisting of gold, platinum and alloys thereoff;

a cool air inlet means in the lower part of said door communicating with the spaces on both sides of the panel provided with said reflective coating, and a warm air outlet means in the upper part of said door communicating with said air inlet means, so that, when heat escapes through said dead-air space, substantial amounts of the escaping heat impinge upon said gridlike foraminous reflective coating, portions of which are reflected back toward the inner panel and other portions of which are absorbed by said coating, said coating being cooled by the flow of air across it from said air inlet means to said outlet means to maintain the outermost exposed surface of the outer transparent panel at a temperature below 230F. when the door is exposed to an oven temperature of 950F.,said air inlet and air outlet means providing a natural upward circulation of air over the inner and outer faces of said second panel, the ratio of the total reflective surface area of said gridlike foraminous coating to the total area of the foramens of said coating being between 311 and 2. An oven door as defined in claim 1 wherein said reflective coating has a thickness of at least 1,000 Angstroms.

3. An oven door as defined in claim 1 wherein a second gridlike foraminous reflector is provided between said first intermediate panel and said outer panel, said second reflector being mounted in a predetermined position during normal use to permit viewing through the door.

4. An oven door as defined in claim 3 wherein said second foraminous reflector is mounted in a fixed posi tion relative to the first reflector.

5. An oven door as defined in claim 4 wherein said second reflector comprises a reflective coating on one face of said second intermediate panel and said first reflective coating is located on the opposite face of said second panel.

Claims (5)

1. A hinged oven door for closing a door opening in a household oven, said door comprising: a hollow sheet metal frame having a central opening and a window closing said opening, the rear of said hollow frame which is adapted to close an oven cavity being covered with insulation surrounding and in abutting relationship with said window unit; said window comprising four transparent panels mounted in predetermined spaced parallel relation in said central opening including an inner glass panel, a first intermediate glass panel near and spaced from said inner panel, a second intermediate glass panel outwardly of said first intermediate panel and spaced therefrom, and an outer transparent panel spaced from said second panel, said first intermediate panel being located between said inner panel and said second intermediate panel, said second panel being located between said first panel and said outer panel; means essentially sealing the space between said inner panel and said first intermediate panel to provide an insulating dead-air space between said panels and near the inner side of the oven door; a gridlike foraminous reflective coating located on said second intermediate panel, the foramens of said coating having an average area no greater than 0.02 square inch, said coating having a thickness no greater than about 1,500 Angstroms and being formed of a substantially non-chemically-reactive metal having a thermal conductivity in excess of about 40 BTU/ (ft.2hr. *F/in.) at 212*F. and a surface emissivity less than about 0.50 throughout a temperature range between 750* and 950*F. and selected from the group consisting of gold, platinum and alloys thereoff; a cool air inlet means in the lower part of said door communicating with the spaces on both sides of the panel provided with said reflective coating, and a warm air outlet means in the upper part of said door communicating with said air inlet means, so that, when heat escapes through said deadair space, substantial amounts of the escaping heat impinge upon said gridlike foraminous reflective coating, portions of which are reflected back toward the inner panel and other portions of which are absorbed by said coating, said coating being cooled by the flow of air across it from said air inlet means to said outlet means to maintain the outermost exposed surface of the outer transparent panel at a temperature below 230*F. when the door is exposed to an oven temperature of 950*F., said air inlet and air outlet means providing a natural upward circulation of air over the inner and outer faces of said second panel, the ratio of the total reflective surface area of said gridlike foraminous coating to the total area of the foramens of said coating being between 3:1 and 3:2.

2. An oven door as defined in claim 1 wherein said reflective coating has a thickness of at least 1,000 Angstroms.

3. An oven door as defined in claim 1 wherein a second gridlike foraminous reflector is provided between said first intermediate panel and said outer panel, said second reflector being mounted in a predetermined position during normal use to permit viewing through the door.

4. An oven door as defined in claim 3 wherein said second foraminous reflector is mounted in a fixed position relative to the first reflector.

5. An oven door as defined in claim 4 wherein said second reflector comprises a reflective coating on one face of said second intermediate panel and said first refLective coating is located on the opposite face of said second panel.

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