U.S. patent number 3,731,037 [Application Number 05/193,940] was granted by the patent office on 1973-05-01 for microwave kiln to cook food.
Invention is credited to Melvin L. Levinson.
United States Patent |
3,731,037 |
Levinson |
May 1, 1973 |
MICROWAVE KILN TO COOK FOOD
Abstract
A microwave oven is provided with a heat insulating structure
containing a work chamber lined with a microwave lossy material
where said lining: 1) can be porous to water, 2) can represent an
acceptable load to said microwave oven, 3) can define a closed
cavity, 4) can be a mixture of a lossy electrical material and a
lossy magnetic material, and 5) can be used in conjunction with a
non-magnetic-metal, heat-conducting workload container.
CROSS-REFERENCE TO RELATED APPLICATIONS This application is a
continuation-in-part of my copending application, U.S. Ser. No.
704,389, filed Feb. 9, 1968.
Inventors: |
Levinson; Melvin L. (Avenel,
NJ) |
Family
ID: |
22715659 |
Appl.
No.: |
05/193,940 |
Filed: |
October 29, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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704389 |
Feb 9, 1968 |
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Current U.S.
Class: |
219/756; 219/730;
219/759; 426/243 |
Current CPC
Class: |
H05B
6/6494 (20130101) |
Current International
Class: |
H05B
6/64 (20060101); H05b 009/06 () |
Field of
Search: |
;219/10.55,10.49
;99/192 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Jaeger; Hugh D.
Claims
I claim:
1. In a microwave oven comprising a chamber for receiving an
article to be heated, means for emitting microwave energy to said
chamber, and a heating member within said chamber, the improvement
in said heating member comprising:
a body of non-lossy, microwave-permeable, heat-insulating material
forming a chamber therein,
a lossy material lining the interior walls of said chamber, and
access means to said chamber for receiving an article to be
heated.
2. In a microwave oven according to claim 1, where said heating
member provides an acceptable load to said means for emitting
microwave energy.
3. In a microwave oven according to claim 1, wherein at least one
wall of said lining is provided with pockets of microwave-lossy,
arcing material.
4. In a microwave oven according to claim 1, wherein the roof of
the lining is more lossy than the base.
5. In a microwave oven according to claim 1, an aluminum container
for receiving said article to be heated.
6. In a microwave oven comprising a chamber for receiving an
article to be heated, means for emitting microwave energy to said
chamber, and a heating member within said chamber, the improvement
in said heating member comprising:
a body of non-lossy, microwave-permeable, heat-insulating material
forming a chamber therein,
a lossy material lining the base of said chamber, said base being
provided with a mixture of lossy electrical material and lossy
magnetic material, and
access means to said chamber for receiving an article to be
heated.
7. In a microwave oven according to claim 6, wherein the base is
porous to liquids.
Description
BACKGROUND OF THE INVENTION
This invention provides a microwave oven, per se, with means to
fry, bake, broil, brown and barbecue. Various systems are in use to
accomplish this purpose, for example, a conventional gas or
electric oven to which a microwave heating feature has been
appended, but none, completely microwave powered, that are
satisfactory.
Structures which enable a microwave oven to fry, bake, broil, brown
and barbecue are described in my copending application, U.S. Ser.
No. 704,389. Said application concerns heat insulating structures
which contain and direct heat released from microwave lossy
material onto a workload and include the use of heat conducting
material to better accomplish even, efficient heating. My U.S. Pat.
No. 3,469,053, Microwave Kiln, describes a dry-heat, oven structure
which can be an integral or removable part of a microwave oven. My
U.S. Pat. No. 3,585,258, Method of Firing Ceramic Articles
Utilizing Microwave Energy, describes methods of heating in a
microwave oven. My U.S. Pat. No. 3,539,751, Insulating Implement
for Use in a Microwave Oven, describes improved ways of containing
and directing the heat evolved from microwave irradiation of lossy
material. This invention describes novel combinations of my said
U.S. Pat. Application Ser. No. 704,389 and U.S. Pat. Nos.
3,469,053, 3,585,258 and 3,539,751 and new improvements.
One object of this invention is to provide structure for a
microwave oven which will fry, bake, broil, brown and/or barbecue
food.
Another object of this invention is to provide a new oven, a
combination of an infra red oven and a microwave oven.
Another object of this invention is to provide structure for a
microwave oven which will safely accept, defrost and cook TV
dinners prepackaged in aluminum trays.
Another object of this invention is to describe means and methods
of cooking meat in metal containers in a microwave oven to provide
rare and medium rare cooked portions.
SUMMARY OF THE INVENTION
This invention concerns an improved microwave heating member which
can be an integral or removable member of a microwave oven. Said
member being a heat-insulating structure containing a work chamber
therein. Said heat-insulating structure designed to confine and
allow for a build up of heat energy. Said work chamber contains a
microwave lossy material capable of, on exposure to microwave
energy, producing a hot dry heat. A foodstuff in a container placed
within said chamber heats from the direct action of microwave
radiation and from heat transfer into the container from said
microwave lossy material.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cut-away, side view of the invention for use in a work
chamber of a microwave oven.
FIG. 2 is a cross section view of invention taken along line 2--2
of FIG. 1.
FIG. 3 is a cross-section, composite view depicting additional
embodiments of the invention.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIGS. 1 and 2 in the drawing, there is depicted a
cut-away, side view and a cross section view of a heat insulating
box 1, containing a work chamber 2, resting on a floor or shelf 13
in an oven chamber (not shown) of a microwave oven (not shown). The
heat insulating walls 3 of work chamber 2 are lined with a
microwave lossy lining 4. Section 5, consisting of the entire front
plus a small part of top and top sides of box 1, can be removed to
expose work chamber 2 and permit the insertion and removal of a
foodstuff 6. Foodstuff 6 is shown contained in a removable
container 7 provided with a handle.
Heat insulating walls are best made of a low-loss, low-mass,
heat-insulating material capable of withstanding the high
refractory temperatures, circa 2,000.degree.F, generated by
microwave lossy lining 4. Heat insulating walls 3's insulating
capabilities can be further enhanced by means described more fully
in my U.S. Pat. No. 3,539,751. Illustrated are a planned pattern of
holes 8--8 drilled in heat insulating walls 3 and sealed by seals
9--9 to lower mass of walls 3. Fired insulating refractory material
as manufactured by General Refractories Company for their
insulating fire brick, for example GR-25, is satisfactory.
The microwave lossy lining 4 can be made of many suitable materials
constituted to withstand the temperature shock and repeated heat
recycling associated with normal oven usage. I find General
Refractories Company's Briklok A made lossy by the addition of
ferrite and carbon materials suitable. This material is a brick
mortar which adheres to the insulating firebrick material. It is
advisable to fire the assembled kiln before its initial use. Other
suitable materials for lining 4 include quartz or glass ceramic
made lossy by the inclusion of pockets of electrically arcing
particles, as described in my copending application No. 704,389, or
a lining of lossy glass ceramic or ferrite. Preferred is a lossy
material that also permits the passage of microwave energy there
thru while heating to a high temperature. Lining 4 need not be
smooth for a rough lining presents a larger surface area. Many
materials classified as "low loss" when heated to a high
temperature become lossy along with lossy lining 4, and when all is
hot and lossy, microwave power expends itself principally in the
densor lining 4 and work chamber 2 contents. The outer surface of
heat insulating walls 3 should be kept in their characteristic low
loss state by radiating heat to the cool oven chamber walls 13 and
kept cool from air normally circulated in a conventional microwave
oven's chamber.
In FIG. 3, it is preferred to make the roof lining 10 lossier than
floor lining 11. One way to accomplish this is to build into roof
lining 10 a pocket 30 of microwave lossy arcing material, as
ferrite particles 31, more fully described in my copending
application, U.S. Ser. No. 704,389. In operation, roof lining 10
heats to a higher temperature than the floor lining 11 and browns
the top of the foodstuff 6 principally by radiant heat
transfer.
Work chamber 2 (with section 5 in place) is a closed cavity. By its
nature heat energy in a closed, heat-insulated cavity must equalize
and become homogeneous. Heat is transferred amongst all parts of
work chamber 2, lining 4, foodstuff 6 and container 7 not only by
conducted, convected and radiant heat transfer, but by heat
transfer of water vapor condensing on colder sections and
evaporating from hotter sections. When floor lining 11 is
constructed of a porous material, as ceramic refractory mortar,
water condensing on the outer sides of container 7 drips off and is
absorbed and, by capillary action, dispersed in floor lining 11
where it presents a larger volume to the microwave energy, and,
because of direct microwave heating and heating by the lossy
material of floor lining 11, it speedily evaporates and condenses
ultimately on the cooler sections of the workload. This results in
more juices and gravies, no need for basting and easier cleaning
containers. Very little water is observed lost from heat insulating
box 1 6 until the foodstuff 6 approaches temperatures hotter than
are required for eating. In fact, the escape of observable steam
(note that section 5 does not form a vapor tight joint) generally
signals either too rapid heating or that the food is properly
heated and can be removed.
I prefer to equip my microwave kiln with a 50.degree.-500.degree.F
metal thermometer 12, as Weston Model 2261 or Model 2292, arranged
as to be viewed through a window in a microwave oven door (not
shown) so that the cooking process can be temperature
monitored.
The methods of using a microwave kiln for cooking are as varied as
the type of meals one can cook. One representative method is to
expose foodstuff in kiln to microwave energy for a fixed period of
time and then allow a resting time before kiln is opened. Food can
be cooked for a short time to start the cooking process and then
removed from the oven in the still unopened kiln for transporting
to a remote eating area while the food continues to cook from the
heat stored in lining 4, and, when the temperature of the work
chamber 2 and its contents finally equalize, insulating walls 3
continue to hold food hot, as in a Thermos bottle, for extended
periods of time. New skills must be learned and practiced to
capitalize fully on the usefulness of this microwave kiln. It must
be kept in mind that air temperature in work chamber 2 and radiant
heat temperature striking the food are both independent and
effective. For example, thermometer 12 may be reading 120.degree.F
air temperature while the food is burning from radiant heat
energy.
In another representative method of operation, a removable
microwave kiln 1 is inserted into a microwave oven's cavity (not
shown) with a frozen TV dinner, foodstuff 6 in its aluminum
container 7, in kiln's work chamber 2. The oven is energized. Since
the food is frozen, it is less lossy than when defrosted. Hence,
initially more microwave energy is available to heat up lining 4
and crust the surface of foodstuff 6. Thermometer 12 indicates the
air temperature of work chamber 2 and signals when to stop cooking
and remove cooked foodstuff 6 in its heated container 7. A second
TV dinner cooked imediately in the instant preheated work chamber 2
takes only slightly less time to cook because foodstuff 6
represents the real load to the microwave oven, and its mass and
the microwave power level determines the length of time for
cooking. The utility of the kiln is to cook a foodstuff to a
desirable internal and external temperature, and not, whether lossy
lining 4 reaches 500.degree. or 1,500.degree.F. The kiln's job is
to increase efficiency while affecting the flavor, color and crust
while microwave energy defrosts and cooks. Thermometer 12 helps
determine when cooking is completed when exact measurements, size
and composition of foodstuff 6 is not known. If conditions are
fixed as in industrial cooking or repeat cooking of the same
manufacturer's identical TV dinners, a simple conventional timer
(not shown) can be employed. I prefer a combination of timer and
thermometer.
In a second representative example of operation, either with or
without empty container 7 as desired, microwave kiln 1 is heated to
a predetermined temperature without foodstuff 6 in work chamber 2.
At the predetermined temperature, say 500.degree.F, (generally
hotter than would be proper for gas or electric ovens because
microwaves speed, in deep cooking and defrosting, leaves less time
for surface browning) foodstuff 6 is introduced into hot work
chamber 2. If empty container 7 was included in the preheating and
it is of sufficient mass, foodstuff 6 is seared when it first
contacts hot container 7, and thenceforth, microwave energy and
heat energy stored in lining 4 finishes the cooking and
browning.
The selection of material for container 11 can be used to vary the
results. For instance, it is easier to cook a hamburger well done,
in a glass ceramic container 7 than in an aluminum container 7. Non
lossy glass ceramic tends to become lossy as it heats and it
retains its heat longer to keep food hotter longer on subsequent
service. An aluminum pan is generally manufactured with less mass
than a comparable glass ceramic pan so has less thermal capacity.
Aluminum is a good heat conductor, and heat, which its outer
surfaces (acting as heat absorbent fins) collect from the hot work
chamber 2, is readily transferred to cooler foodstuff 6. It is
easier to cook a hamburger rare or medium in an aluminum container
7. Aluminum collects more gravy as it shields the gravy from direct
microwave action. I prefer to cook my hamburgers in small 4 inch
aluminum foil pie dishes, but it must be understood that while
aluminum may slightly favor glass ceramic for rare hamburgers, it
is relatively easy to also cook hamburgers rare in glass ceramic
(e.g. glass ceramic's larger mass takes longer to heat and oven
would have to be preheated).
In FIG. 3, aluminum representative of other non-magnetic metals,
can be additionally used as follows: I have discovered that a
mixture of two microwave lossy materials 31, 32, one which is lossy
because of its electrical properties 32, as carbon, mixed with a
second material which is principally lossy because of its magnetic
properties 31, as ferrite, with or without a refractory mortar
binder, and spread out as a thin floor lining 11, draws power more
evenly from both the electric and magnetic fields and results in
better loading with less spot heating. Said better loading and
evener heating is advantageous when kiln is preheated empty. And,
when aluminum container 7 subsequently rests on said preheated
mixture, the electrical material 38 is not lossy in juxtaposition
as the electric field is at a minimum close to metal aluminum
container 7. The magnetic field and the heating of the magnetic
material 31 is at maximum close to the aluminum surface. This rule
I find true if microwave energy can also approach the upper side of
container 7. The heat conducting properties of aluminum and the
relatively cool container 7 and foodstuff 6 operate together to
keep the magnetic material 31 in thermal contact with aluminum
container 7 below its Curie point. The other sections of floor
lining 11, not covered by aluminum container 7, remain lossy in
response to both the electric and magnetic field and readily
evaporate and recycle condensed water dripping off the outside of
aluminum container 7. Note that, in this case, proximetry with
aluminum container 7 "turns off" some of the lossiness of floor
lining 11 and so effectively makes more microwave energy available
for roof lining 10 and foodstuff 6. To make the roof lining 10
hotter use shiny aluminum rather than glass ceramic.
Food shielded from microwave energy by being placed in a
closed-to-microwave-energy metal container can be baked in a heated
kiln. More than one container 7 can be used simultaneously, and
each can be of different material. One metal container can hold a
second. Container 7 may be made of lossy material and foodstuff 6
may be non lossy. Crusted frozen baked products can be defrosted
directly without container 7.
Meat can be barbecued in work chamber 2 by heating lining 4 hot
enough to ignite fat. Barbecuing can take place with either section
5 off, in which case flames will issue, or, can be operated with
section 5 in place where lacking oxygen slow combustion takes
place. When barbecuing with section 5 in place, care must be
exercised opening work chamber 2, if flames shoot out, replace
section 5 until work chamber 2 cools below ignition point. In
either case means for venting (not shown) products of combustion
must be employed.
Work chamber 2 is self cleaning in the manor of typical self
cleaning ovens that are heated empty to such temperature as will
burn off accumulated mess and splatter.
The top temperature work chamber 2 can reach is fixed by the
thickness and material of heat insulating walls 3 multiplied times
the highest power level of the microwave oven's generator.
Although this invention has been described with a certain degree of
particularity, it is understood that the present disclosure has
been made only by way of example and that numerous changes in the
details of construction and the combination and arrangement of
parts may be resorted to without departing from the spirit and
scope of the invention, as a disposable, one time kiln to heat a
foodstuff 6 in an aluminum container 7 where walls 3 are
polyurethane foam and lossy floor lining 11 is water 33 as
illustrated in FIG. 3.
* * * * *