U.S. patent number 3,688,084 [Application Number 05/132,279] was granted by the patent office on 1972-08-29 for electric broiler heating unit.
This patent grant is currently assigned to The Detroit Edison Company. Invention is credited to Mitchell D. Charneski.
United States Patent |
3,688,084 |
Charneski |
August 29, 1972 |
ELECTRIC BROILER HEATING UNIT
Abstract
A composite radiating plate and rod heating unit for an
electric-heated broiler compartment has a generally flat but
arcuate-sided ceiling panel in the form of a rectangular metal
sheet whose bottom bears a series of parallel passes of "Calrod"
electric heating rod components. These, whether represented by
individual lengths electrically jumper-connected at their opposite
ends, or as arranged in sets of two or more in a serpentine
outline, are non-uniformly spaced from one another in at least some
of the successive components of the units, generally increasing in
spacing starting at a front or rear pass. They and the thermally
conductive sheet panels to which they are fixedly secured are
curved downwardly adjacent opposite side margins of the latter to
afford a warm dead air ceiling or dome space as installed at the
top of a broiler chamber.
Inventors: |
Charneski; Mitchell D.
(Southfield, MI) |
Assignee: |
The Detroit Edison Company
(Detroit, MI)
|
Family
ID: |
22453269 |
Appl.
No.: |
05/132,279 |
Filed: |
April 8, 1971 |
Current U.S.
Class: |
219/537; 219/405;
219/552; 219/397; 219/546; 338/217 |
Current CPC
Class: |
A47J
37/06 (20130101) |
Current International
Class: |
A47J
37/06 (20060101); H05b 003/06 () |
Field of
Search: |
;219/405,408,461,347,524-525,552-553,390,397,530,540,538,464
;338/217-218,287-288,319 ;13/22,25,31 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mayewski; Volodymyr Y.
Claims
1. An electrical heating unit comprising the combination, in
relatively fixed relation to one another, of a thermally conductive
sheet which is electrically non-conducting in the operation of the
unit, and sets of elongated, relatively localized, but
non-uniformly distributed, electrically and thermally energized
heating elements arranged in a generally parallel relation to one
another and disposed in direct and thermally conductive contact
with said sheet, said sheet having angularly offset and downwardly
angled side margins, said heating elements being conformed to and
fixedly secured in nesting contact with said offset sheet side
margins, the transverse spacing of certain of the respective
heating elements differing in a generally progressive way from an
element of one set to an element of another in a direction
transverse of the length of said elements, elements of the
respective sets being electrically connected in series with one
another and the sets being electrically
2. The unit of claim 1, in which said sheet and heating elements
are contoured in the direction of the length of the latter to
provide a hot air trapping dome space directly beneath the unit
which extends in a front-rear direction transversely of the element
length.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The heating units of the invention are particularly intended for
installation in company cafeterias or like food preparational or
dispensing facilities at which large scale broiling, baking,
heat-maintaining or like cooking operations are the normal order of
the day. However, the application of the invention is by no means
limited to such fields, since it may well have wide-spread use in
domestic broiler type ovens.
2. Description of the Prior Art
The most pertinent prior art patent of which I am aware is that to
Anderson, U.S. Pat. No. 3,342,977 of Sept. 19, 1967, relating to an
electric broiler heating element essentially comprised of a
corrugated, resistance heating sheet structure.
SUMMARY OF THE INVENTION
An objective of the invention is to provide an improved electric
broiler heating unit whose direct and primary heating source, as
energized electrically from an appropriate voltage supply, is in
the form of a so-called "Calrod" type heater, i.e., constituted of
a tubular metal sheath encasing an elongated resistance heating
conductor and its magnesium oxide electrical insulation. It is a
fact that in conventional electric broilers in which such heating
rod components are arranged in a symmetric or uniform distribution
of parallel lengths, a useful cooking area of about only half of
the total exposed lower heater rack area is in effect available,
the expression "useful cooking area" being empirically determined
as a function of combined temperature rise, time and area factors.
This is due in considerable measure to a loss of space heating
efficiency characteristic of passes or lengths of the heater rods
adjacent the front, rear and sides of the broiler chamber, coupled
with the air insulation of the rods from one another. On the other
hand, if such lengths are spaced more closely together in
perimetral zones where heating losses are greatest, then their life
is inevitably shortened. increased
Accordingly, the invention proposes to fixedly connect such rod
lengths in good heat transfer relation to the bottom of a generally
flat thermally conductive metal sheet or panel, with ends of the
rods and sides of the sheets curved for an intended dome outline,
all of which contributes to a useful cooking area increased to the
order of 80 percent, as compared with the prior figure of a bit
more than 50 percent. The individual heating rods themselves are
kept cooler for a long life, since a large measure of radiative
capacity is contributed by the supporting sheet or panel, acting in
effect as an extension of the rod capacity. Considering each set or
pair of rod components as operating at 240 volts a.c., 6 kw., the
combined rod and sheet broiler unit presents an increase in watt
density up to 14 watts per square inch of the broiler rack, as
compared with a prior available density of about 9 w./in.sup.2.
Assuming, for example, that as many as 100 steaks are to be broiled
simultaneously, the improvements mentioned above make possible a
shorter cooking time and an increased usable space, representing
about 25 percent at marginal areas. Substantially doubled cooking
capacity and greatly lessened operating cost are the result.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view, partially broken, in transverse vertical section
on line 1--1 of FIG. 2, showing the improved unit as typically
installed in a broiler compartment;
FIG. 2 is a fragmentary plan view, also partially broken, from the
line 2--2 of FIG. 1, being in larger scale; and
FIG. 3 is a fragmentary top perspective view of a schematic nature,
further illustrating the general arrangement of the heating plate
and rod parts.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows a typical installation of one or more (as dictated by
the size of the installation) of the improved combined metal sheet
and rod type heating units of the invention. Typically there are
two of these, front and rear, as generally designated by the
respective reference numerals 10, 11, mounted within the broiler
chamber or compartment 12 of a commercial oven. This compartment
has an outer casing 13 including miterunited outer side wall
members 14 and a connecting top wall member 15, and stamped sheet
metal panels 16 are fixedly secured in depending relation to top
wall member 15 to in part define a space 17 bottomed by a ceiling
or dome portion (later described) of the improved heating unit.
Space 17 is occupied by a high temperature insulation, such as
blanket aluminum silicate, to preserve efficiency. The units 10 and
11 are identical but oppositely oriented, with the rear of the
former adjacent the front of the latter to reverse the progression
of spacing of certain heating rods, as will appear; and they are
fixedly supported appropriately upon the top of insulated inner
side walls 18 of the broiler space 19 proper within the general
space 12 of outer broiler casing 13.
Referring to FIG. 2 in conjunction with FIG. 1, each of the heating
units 10, 11 comprises a sheet metal rod-supporting and heat
radiating plate 20 of rectangular cross section, relatively
elongated in the side-to-side direction of the broiler space 19. An
area of 15 inches by 28 inches would be typical. While the material
of the plate or sheet 20 is, of course, subject to selection, I
find a 20 gauge stainless steel sheet of, say, No. 304 having 8
percent nickel-18 percent chrome composition, to be very
satisfactory. It has sufficient rigidity for the purpose, coupled
with an acceptable heat-up time factor.
This sheet or plate 20 has a plurality of "Calrod" type heating rod
components 22 appropriately secured rigidly to its lower surface in
good heat-conducting relation to the plate. This may be effected by
spot weld connections; however, I find that for the purpose of the
invention, and as shown in FIG. 2, that an appropriate number of
aligned stainless steel tabs 23 (of which only a relatively few are
shown) spot welded to the sheet 20, with the rod lengths 22
received in bights of the tabs, afford a very satisfactory
connection, particularly in view of the cost consideration. This is
so, moreover, in view of the fact that heat build-up time in the
units 10, 11 at the commencement of a daily operation in a
commercial kitchen is a negligible operating factor; the rods and
sheets are brought to heat in a very reasonable time, and are
normally kept heated during a daily run.
By preference, the rod-type heating elements or components 22 are
of, say, 1/4" or 3/8" outer diameter having an Incoloy or stainless
steel sheath part within which an electrical resistance heating
component, as embedded in magnesium oxide electrical insulation, is
disposed. The rod components are of themselves conventional and
readily available on the market, being readily shaped for the
purpose of the invention.
Options are available in regard to the specific configuration of
the several rod components, as non-uniformly or non-symmetrically
related to one another in regard to their front-to-rear spacing, as
will later be described. This, FIG. 1 shows, for each sheet 20, a
total of 12 such individual rods, although the number may be less
or more, which are each 120 volt-rated straight elements. They are
electrically coupled as pairs at the left-hand end thereof by
conventional jumpers 21, thus rating each coupled pair for a 240
volt alternating current supply, and the right-hand ends thereof
(FIG. 2) are connected in parallel in a conventional way to such
voltage source. At their left and right hand ends the rods 22 are
terminated in relatively cool zones, at which they extend through
openings 24 (FIG. 3) of the plates or sheets 20, and beneath the
insulation-enclosing panels 16. These terminal rod portions are
appropriately configured as required by space limitations within
the outer broiler casing walls 14 and the inner walls 18.
As an alternative contouring of the pairs of rod lengths or passes
22, and as indicated in dotted line in FIG. 2, they may be of a
loop-like or U-shaped configuration, joined at an end thereof by an
arcuate connecting bight or loop formation 25, integral component
pairs as thus joined being specially designated 22' in FIG. 2. As a
still further available alternative, more than two heating rod
lengths or passes may be arranged in a serpentine or zig-zag
configuration, with successive lengths integrally joined as
opposite sides or ends, as by bights or loops similar to the loops
25. In such case, the un-looped ends of the individual serpentine
configuration will be appropriately connected electrically to a 240
volt source, just as the U-shaped pairs 22' will be connected to a
similar source at the un-looped right-hand ends thereof (FIG.
2).
Pursuant to the invention, and for obtaining a maximum usable
cooking area (as arbitrarily defined above) which contributes along
with the combined heating rod and sheet construction feature to a
faster cooking time and generally improved thermal efficiency, the
spacing of the parallel rod components 22 or 22' from one another
in the front-to-rear direction will vary at several zones
transverse of that direction, thus normalizing or rendering uniform
the radiant heating effect upon the rack or grid area throughout
the entire dimension of the rod-sheet construction, i.e.,
offsetting or compensating for the radiative loss normally
characteristic of heating components at the extreme front, rear and
side margins of the broiler space.
Thus, reference being had to FIG. 2, and always bearing in mind
that dimensional variations are contemplated, the front and
rear-most component lengths or passes of the combined panels 10, 11
may be positioned 1/4 inch from the front and rear margins of the
combination, hence correspondingly related dimensionwise to the
food-supporting rack (not shown) in the broiler chamber 19.
Succeeding pairs of similar components may then be spaced
successively from one another distances increasing progressively,
as shown in FIG. 2, from 1/2 inch to 1 inch, with a spacing of the
front-most pass of, say, 1/2 inch in a zone in which adjacent edges
of the units 10 and 11 adjoin one another. It will be understood
that the progression of variable spacings of the front unit 11 will
be the reverse of that of rear unit 10, so that the spacings
diminish outwardly from the mid-point of the two.
The plate or sheet units 10, 11 are fixedly mounted atop the inner
broiling chamber walls 18 at angled side flange extensions 20' of
the respective sheets or plates 20, which downwardly straddle those
walls.
The domed space 27 directly beneath the units 10, 11 serves as an
accumulator pocket and continuous reservoir extending from the
front zone of the broiler and trapping hot air surrounding the rods
22 and beneath the sheet 20. This materially reduces convection
losses.
It is seen that the invention affords an electrical broiler heating
unit of great simplicity and low production cost in which there are
combined in fixed relation to one another, a sheet-like thermally
conductive and electrically non-conducting means, and a relatively
localized, but non-uniformly distributed, electrically and
thermally energized means disposed in direct and thermally
conductive relation to said sheet-like means, this combination
affording the various advantages in point of thermal and electrical
efficiency discussed above at some length.
* * * * *