U.S. patent number 3,684,859 [Application Number 05/112,743] was granted by the patent office on 1972-08-15 for radiant heater.
This patent grant is currently assigned to Watlow Electric Manufacturing Company. Invention is credited to George B. Desloge.
United States Patent |
3,684,859 |
Desloge |
August 15, 1972 |
RADIANT HEATER
Abstract
A radiant heater is described which includes channel-shaped
radiating elements mounted side-by-side in a housing. The
channel-shaped elements are metal and give high strength with light
weight. The channel-shaped elements have a high emittance surface
backed by an air space for uniform distribution across the surface
through convection and radiation and are also backed by insulation
to reduce back side losses. In construction, each channel-shaped
element is formed from nested U-shaped members having a resistance
heater positioned therebetween and electrically insulated from the
U-shaped members by layers of dielectric material. Electrical
connections to the resistance extend from the ends of the elements
and may be connected across a suitable source of electrical energy
for operation.
Inventors: |
Desloge; George B. (Frontenac,
MO) |
Assignee: |
Watlow Electric Manufacturing
Company (St. Louis, MO)
|
Family
ID: |
22345630 |
Appl.
No.: |
05/112,743 |
Filed: |
February 4, 1971 |
Current U.S.
Class: |
392/432; 338/249;
392/437 |
Current CPC
Class: |
F24C
7/043 (20130101) |
Current International
Class: |
F24C
7/04 (20060101); H05b 001/00 () |
Field of
Search: |
;219/339,354,552,445,553
;338/226,306,247 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Bell; F. E.
Claims
What is claimed is:
1. A radiant heater comprising a housing having an open side,
sidewalls, and a base wall connected to and extending between the
sidewalls, the open side of the housing being located opposite to
the base wall; a plurality of radiating bars mounted side-by-side
in the housing between the sidewalls and exposed outwardly through
the open side thereof, each bar being generally channel-shaped and
having a high emittance outer surface portion and a resistance-type
heating element extending along the inner side of the high
emittance portion, and electrical insulation means between the
element and the inner side of the bar, the high emittance surfaces
of the bars being exposed outwardly from the open side of the
housing, a heat insulating material positioned in the housing
between the radiating bars and the base wall, an air space between
the inner side of the radiating bars and the insulating material,
and cross members between the sidewalls of the housing supporting
the radiating bars, one of the cross members being positioned near
the center of the housing and having an outwardly bowed portion
extending across the housing transverse to the bars, the outwardly
bowed portion having slots into which inturned flanges on the
radiating bars fit, the flanges being apertured behind the
outwardly bowed portion; and including a restraining pin extending
behind the outwardly bowed portion and through the apertures in the
bar flange whereby the bars cannot be withdrawn from the housing
when the restraining pin is in place, and the ends of the bars are
free to expand.
2. A radiant heater comprising a housing having an open side,
sidewalls, and a base wall connected to and extending between the
sidewalls, the open side of the housing being located opposite to
the base wall; a plurality of radiating bars mounted side-by-side
in the housing between the sidewalls and exposed outwardly through
the open side thereof, each bar being generally channel-shaped and
having a high emittance outer surface portion and a resistance-type
heating element extending along the inner side of the high
emittance portion, and electrical insulation means between the
element and the inner side of the bar, the high emittance surfaces
of the bars being exposed outwardly from the open side of the
housing, the sidewalls of the housing and the flanges on the
channel-shaped radiating bars being provided with aligned apertures
near the centers thereof, a removable pin means positioned through
the apertures to restrain the bars in the housing, a heat
insulating material positioned in the housing between the radiating
bars and the base wall, and an air space between the inner side of
the radiating bars and the insulating material.
3. A radiant heater comprising a housing having an open side,
sidewalls, and a base wall connected to and extending between the
sidewalls, the open side of the housing being located opposite to
the base wall; a plurality of radiating bars mounted side-by-side
in the housing between the sidewalls and exposed outwardly through
the open side thereof, each bar being generally channel-shaped and
having a high emittance outer surface portion and a resistance-type
heating element extending along the inner side of the high
emittance portion, and electrical insulation means between the
element and the inner side of the bar, the high emittance surfaces
of the bars being exposed outwardly from the open side of the
housing, cross members between the sidewalls of the housing
supporting the radiating bars, a heat insulating material
positioned in the housing between the radiating bars and the base
wall, an air space between the inner side of the radiating bars and
the insulating material, the housing having end caps at the ends of
the base and sidewalls, said end caps extending over the ends of
the radiating bars to cover the terminals and retain the bars in
the housing, said end caps being movable away from the ends of the
bars so that the bars can be withdrawn from the containing
member.
4. A radiant heater comprising a housing having an open side,
sidewalls, and a base wall connected to and extending between the
sidewalls, the open side of the housing being located opposite to
the base wall; a plurality of radiating bars mounted side-by-side
in the housing between the sidewalls and exposed outwardly through
the open side thereof, each bar generally channel-shaped and having
a high emittance outer surface portion and a resistance-type
heating element extending along the inner side of the high
emittance portion, and electrical insulation means between the
element and the inner side of the bar, the high emittance surfaces
of the bars being exposed outwardly from the open side of the
housing, a cross member between the sidewalls of the housing
supporting the radiating bars, a heat insulating material
positioned in the housing between the radiating bars and the base
wall, an air space between the inner side of the radiating bars and
the insulating material, housing end caps at the ends of the base
and sidewalls of the housing, said end caps extending over the ends
of the radiating bars to cover the terminals and retain the bars in
the housing, each end cap comprising side flanges which extend
along the sidewalls, and means for detachably securing the side
flanges of the end cap to the sidewalls of the containing
member.
5. A radiant heater comprising a housing having an open side,
sidewalls, and a base wall connected to and extending between the
sidewalls, the open side of the housing being located opposite to
the base wall; a radiating bar mounted lengthwise in the housing
between the sidewalls and exposed outwardly through the open side
thereof, the bar having a high emittance outer surface portion and
a resistance-type heating element extending along the inner side of
the high emittance portion, and electrical insulation means between
the element and the inner side of the bar, the high emittance
surface of the bar being exposed outwardly from the open side of
the housing, means for retaining the bar in the housing, a heat
insulating material positioned in the housing between the radiating
bar and the base wall, a movable end cap at one end of the housing,
said end cap extending over the end of the radiating bar and being
movable away from the end of the bar so that the bar can be
withdrawn from the housing, and means for locking the end cap to
the housing.
6. A radiant heater according to claim 5 wherein an air space is
provided between the inner side of the radiating bars and the
insulating material.
7. A radiant heater according to claim 5 wherein legs extend beyond
the base wall of the housing for mounting the heater.
8. A radiant heater according to claim 3 wherein the end cap is
hinged to the base wall.
9. A radiant heater according to claim 3 wherein the end cap has
projections beyond the base wall of the containing member to form
mounting legs for mounting the heater on a supporting structure.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to electric heaters and more
particularly to electric radiant heaters.
Present radiant heaters generally operate from high temperature
sources of heat and distribute the heat by reflectors or by
diffusion through a quartz, ceramic, or glass panel.
The glass or ceramic diffusers are not durable even though heavy
and bulky.
It has been proposed to use flattened tubes backed with insulation
over a surface as a heat distributor. These structures were weak
structurally even though heavier than the nested channels of this
invention. As there was no air space behind the strips, there was
no even distribution of heat of temperature on the surface.
The radiant heaters of current manufacture which utilize reflectors
behind their radiating elements do it to try to achieve effective
distribution of the heat from the heating elements. These radiating
elements should be positioned at the focal point of the reflector
since any displacement from that point will scatter the infra-red
rays. Reflectors, furthermore, may increase the size and weight of
such heaters significantly. Moreover, reflector-type radiant
heaters of current manufacture operate with the heaters at
relatively high temperatures and these temperatures are detrimental
to the materials from which the heaters are made, resulting in
short life in many instances. The high temperatures further
necessitate the use of ceramic parts in many locations, but ceramic
parts crack easily and therefore must be replaced.
Also, the radiating elements of most conventional radiant heaters
are difficult to replace, and since those radiating elements have a
limited life, many heaters are inoperative for extended periods for
want of a repairman skilled enough to replace burned out radiating
elements.
As conventional heaters have a high temperature source and wide
radiating segments, it is hard to get a variety of width increments
so that practically all radiant heaters of current manufacture are
offered in a few limited sizes, and as a result in most instances
it is impossible to match a heater to the demand on it. Usually, a
heater oversized in wattage or dimensions is employed and by reason
of the oversize it cycles at relatively frequent intervals. This
cycling in turn decreases the life of the heater.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a uniform
source of heat without glass, ceramic, or reflectors which has a
high energy output with a low temperature source. Another principal
object of the present invention is to provide a radiant heater
which is compact in size and light in weight. Another object is to
produce a radiant heater which effectively distributes heat without
a reflector. A further object is to provide a radiant heater which
is rugged in construction because it has no glass or ceramic parts.
Another object is to provide a radiant heater which operates at a
relatively low temperature so as to extend the life of the
materials from which it is constructed, and to give greater
efficiency because more materials are receptive to the radiant
energy from a low temperature source. An additional object is to
provide a radiant heater which has radiating elements which are
easily replaced. Still another object is to provide a radiant
heater which may be made in a variety of sizes from standard parts
without a significant increase in production costs, thereby
enabling heaters to be matched with the demand so as to avoid
cycling of the heaters. Yet another object is to provide a heater
which radiates from substantially one entire surface. An additional
object is to provide a heater which is easily installed on
supporting structures. These and other objects and advantages will
become apparent hereinafter.
The present invention is embodied in a radiant heater including a
housing having a plurality of channel-shaped radiating elements
contained therein in side-by-side relation. The elements have a
very high emittance surface, the backside of which is spaced from
an insulation wall to reduce heat losses and provide even
distribution of heat across the radiating surface. The invention
also resides in the individual radiating elements and in the parts
and in the arrangements and combinations of parts hereinafter
described and claimed.
DESCRIPTION OF THE DRAWINGS
In the accompanying drawings which form part of the specification
and wherein like numerals refer to like parts wherever they
occur:
FIG. 1 is a perspective view of a radiant heater constructed in
accordance with and embodying the present invention;
FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1;
FIGS. 3 and 4 are sectional views taken along lines 3--3 and 4--4,
respectively, of FIG. 2;
FIG. 5 is a transverse sectional view of a radiating bar which
forms part of the present invention;
FIG. 6 is a fragmentary longitudinal sectional view of the
radiating bar;
FIG. 7 is an exploded perspective view of the radiating bar;
and
FIG. 8 is a fragmentary elevational view, partially broken away and
in section, of the end of a radiant heater provided with electrical
terminals in its end cap.
DETAILED DESCRIPTION
Referring now to the drawings, 2 designates a radiant heater which
basically includes a housing 4 (FIG. 1) a plurality of radiating
bars 6 located side-by-side in the housing 4, and an insulating
material 8 (FIGS. 2-4) contained within the housing 4 behind the
radiating bars 6.
The housing 4 includes a channel-shaped containing member 10 (FIGS.
2-4) preferably formed from stainless steel and consisting of a
base wall 12 and a pair of side walls 14 formed integral with and
presented perpendicularly with respect to the base wall 12.
Outwardly from the base wall 12, the sidewalls 14 are doubled back
upon themselves and into the interior of the containing member 10
to form a longitudinally extending interior lip 16 (FIGS. 3 and 4)
and a curved outer edge 18. The sidewalls 14 are reinforced by end
cross members 20 (FIGS. 2 and 3) which extend between those walls
14 slightly inwardly from their ends. The cross members 20 are
located against the inner edges of the lips 16, that is to say they
extend across the housing 4 at the inwardly presented edges of the
lips 16. In one form of the invention illustrated in detail in
FIGS. 2 and 4, the mid-portions of the walls 14 are connected by
another or center cross member 22 including an outwardly bowed
portion 24 having slots 26 extending transversely through it, but
not through the continuous lateral portions on each side of that
bowed portion 24. The bowed portion 24 projects outwardly almost to
the curved edge 18 and its ends are spaced slightly inwardly from
the lips 16, which are in turn spaced inwardly from the sidewalls
14. The center cross member is attached to the walls by upturned
ends 28.
In an alternate form of the invention (not specifically
illustrated) the center member has the same configuration as the
end members 20. In this form, the radiating bars 6 rest on and are
supported by the three cross members 20.
The ends of the containing member 10 are closed by end caps 30
which also form part of the housing 4 and are likewise preferably
formed from stainless steel. Each end cap 30 includes an end wall
32 (FIG. 2) which is backed on its interior face by a layer of high
temperature dielectric material 33 such as mica and is connected to
the base wall 12 by a hinge 34 so that the end cap 30 can be folded
outwardly away form its closure forming position at the end of the
containing member 10 (FIG. 8). This affords access to the interior
of the containing member 10. If desired, the ends can be removably
fastened by screws, detents, or other suitable means. Each end cap
30 also includes a pair of side flanges 36 (FIGS. 1 and 3) which
are formed integral with the end wall 32 and overlie the sidewalls
14 when the end wall 32 is folded against the ends of the sidewalls
14. In addition, each end cap 30 includes a cross flange 38 (FIGS.
1 and 2) which is also formed integral with the end wall 32 and
extends between the ends of the side flanges 36 so as to overlie
the curved edges 18 on the sidewalls 14 of the containing member
10. The end caps 30 are maintained in their closure forming
positions at the ends of the containing member 10 by the screws 40
which extend through the side flanges 36 and thread into the
sidewalls 14. The end walls 32 and side flanges 36 on each end cap
30 furthermore extend beyond the hinge 34 so as to form mounting
legs 42 for supporting the heater 2 from a suitable supporting
structure (not shown).
The base wall 12 is fitted with a pair of threaded electrical
terminals 44 (FIG. 2) which are electrically isolated therefrom and
connect with longitudinally extending bus bars 46 on the inwardly
presented side of the wall 12. One bus bar 46 extends
longitudinally to one end of the containing member 10 while the
other bus bar 46 extends in opposite direction to the other end of
the containing member 10. The bus bars 46 are also formed from
stainless steel and turn away from the base wall 12 at the ends of
that wall 10 in the provision of connecting tabs 48 which are
spaced inwardly from the end walls 32 of the end caps 30. Each bus
bar 46 is separated from the base wall 12 by a thin sheet of high
temperature dielectric material 50.
The insulating block 8 can withstand high temperature and further
does not conduct electricity. For all practical purposes, it fills
that portion of the housing 4 located between the base wall 12 on
one hand and the cross members 20 and 22 on the other. "PV"
Supertemp Block which is marketed by Eagle-Picher is suitable for
the insulating block 8.
The radiating bars 6 fit into the portion of the housing 4 not
occupied by the insulating pad 8, that is the portion located
outwardly beyond the cross members 20 and 22, and they are disposed
between the interior lips 16 on the side walls 14. The bars 6 are
positioned against the cross members 20 and 22 (FIGS. 2-4) and are
further positioned side-by-side between the lips 16 which prevent
the bars 6 from shifting laterally in the housing 4. The end walls
32 on the end caps 30, on the other hand, obscure the ends of the
bars 6, while the cross flanges 38 on the end caps 30 overlie the
outwardly presented surfaces on the bars 6.
Each radiating bar 6 has U- or channel-shaped configuration (FIG.
5), possessing a pair of spaced side flanges 56 and a connecting
bight or base portion 50 extending between the flanges 56. The
outwardly presented surface of the bight portion 58 is treated to
produce a surface of high emissivity. This can be done in a number
of ways, such as coating with a high temperature paint, flame
sprayed coatings, sand blasting, etc. The spacing between the
inwardly presented surfaces of the opposed flanges 56 is slightly
greater than the spacing between the closest margins of adjacent
slots 26 in the bowed portion 24 of the center cross member 22
(FIG. 4). In other words, the length of each bowed segment of the
bowed portion 24 is slightly less than the spacing between the
flanges 26. Moreover, the width of each slot 26 is slightly greater
than twice the thickness of a flange 56. If the flat center cross
member is used, this is not relevant, of course.
The radiating bars 6 fit into the housing 4 with the flanges 56
projecting inwardly toward the insulating block 8 and the emissive
surfaces of the bight portions 58 presented outwardly (FIGS. 3 and
4). As previously noted the bars 6 are positioned side-by-side, and
when so disposed the side flanges 56 on adjacent bars facewise abut
each other. These abutting side flanges furthermore fit into the
slots 26 of the bowed portion 24 on the center cross member 22. The
outermost side flanges 56 on the two outer bars 6, of course, do
not abut against any other flanges 56, but instead abut against the
interior lips 16 formed on the side walls 14 of the containing
member 10. These outermost flanges 56 furthermore fit into the
spaces between the ends of the bowed portion 24 and the interior
lips 16 of the side walls 14.
The side flanges on the radiating bars 6 are provided with aligned
apertures 60 (FIGS. 4) which open into the trough or interior of
the bowed portion 24 on the center cross member 22, and likewise
the side walls 14 and interior lips 16 are also provided with
apertures 62 which align with the bowed portion 24 as well as with
the apertures 60. Fitted through the apertures 62 and 60 as well as
through the interior of the bowed portion 24 aligned with those
apertures is a restraining pin 64 which prevents the radiating bars
6 from bowing outwardly or sliding longitudinally as their
temperature rises.
The pin 64 holds the assembly together while still allowing for
longitudinal expansion of the channel-shaped radiating bars 6.
If the flat center cross member is used with the restraining pin
64, the pin 64 fits through the openings 62 in the side walls 14,
16 and the openings 60 in the radiating bars 6. There is no
connection to the cross member in this form of the invention.
In certain types of construction it is possible to eliminate the
center pin and utilize the end caps as a retaining means for the
radiating bars.
Each radiating bar 6 comprises (FIGS. 5-7) an outer channel-shaped
member 70 and an inner channel-shaped member 72, both of which are
formed from stainless steel and have the same general configuration
as the bar 6 itself, that is to say they both have a pair of side
flanges connected by a bight or base portion. The inner
channel-shaped member 72 is slightly smaller than the outer member
70, and fits or nests within the outer member 70. Furthermore, the
inner member 72 is somewhat shorter than the outer member 70 so
that the outer member 70 projects beyond both ends of the inner
member 72. The side flanges of the two members 70 and 72 may be
spot welded or otherwise joined together to create a unitary
channel-shaped structure.
Fitted between the bight or connecting portions of the two
channel-shaped members 70 and 72 are two thin strips 74 nd 76 of
sheet-like dielectric material which is capable of withstanding
high temperatures. Mica insulating strips are ideally suited for
this purpose. In lieu of the separable dielectric strips 74 and 76
a spray deposit such as aluminum oxide or an insulating cement such
as those made by Savereisen may be used. The dielectric strip 74
extends the full length of the outer channel-shaped member 70,
against which it lies, whereas the strip 76 is slightly longer than
the inner channel member 72 against which it lies but is still
shorter than the outer channel-like member 70 and its dielectric
strip 72.
The dielectric strips 74 and 76 have a resistance-type electrical
heating element 78 fitted between them, and that element 78
preferably is a sinuated wire. Other types of elements such as
sprayed coatings, notched ribbons, etc. may be used. The strips 74
and 76, of course, electrically isolate the element 78 from the
channel-shaped members 70 and 72 so that the exposed surfaces of
the bar 6 remain at ground potential. Each end of the sinuated wire
element 18 is connected to a flexible connector tab 80 which
projects beyond the ends of the dielectric strips 74 and 76 and is
bent in the direction of the side flanges 56. Thus, the connector
tabs 80 are disposed between the side flanges 56 and project away
from the bight portion 58 of the bar 6.
The connector tabs 80 are connected to the connecting tabs 48 on
the bus bars 46 or to the connecting tabs 80 in adjacent radiating
bars 6, depending on the type of connection which is desired.
Likewise, the heater 2 may be wired for three phase electrical
power by incorporating another threaded terminal 44 and bus bar 46
into the housing 4.
When the threaded terminals 44 are placed across a suitable source
of electrical energy, current is conducted through the bus bars 46,
connecting tabs 80, and sinuated wire elements 78. This causes the
temperature of the wire elements 78 to rise and this in turn
elevates the temperature of the radiating bars 6. The electrical
energy supplied to the heater 2 at the threaded terminals 44 should
be sufficient to raise the temperature of the bars 6 to a range of
approximately 600.degree. F. to about 1,400.degree. F.
Consequently, the bars 6 radiate heat from their exposed surfaces.
Since the exposed surfaces are highly emissive, the emissivity of
the unit approaches that of a theoretical black body, making the
heater 2 extremely efficient.
The insulating block 8 keeps the base wall 12 of the housing 4
relatively cool.
The space 22 between the insulating block 8 and the backside of the
bars 6 serves to evenly distribute the heat and prevent one part of
the emissive surface from building up to a high temperature. Thus,
the entire emissive surface is usable and evenly radiates heat.
The rearward extension of the mounting legs 42 positions the
hottest part of the heater 2 away from the supporting structure. In
some installations the legs 42 are not necessary.
Should the sinuated wire heating element 78 in one of the heater
bars 6 break, the adjacent bars 6 will conduct heat to the
defective bar 6 so that its exposed surface will continue to
radiate, provided of course that the bars 6 are wired in parallel
or some other way which does not disrupt the circuit through the
remaining bars 6.
In this connection, a defective radiating bar 6 is quickly and
easily replaced merely by removing the screws 40 and swinging the
end caps 30 away from the containing member 10 (FIG. 8) so as to
expose the ends of the bars 6. The connecting tabs 80 on the
defective bar are then disconnected from the connecting tabs 80 on
adjacent bars 6 or the connecting tabs 48 on the bus bars 46,
whatever the case may be. Finally, the restraining pin 64 is
withdrawn from the apertures 60 in the side flanges 56 of the
defective bar 6, and the defective bar 6 is removed. Anew radiating
bar 6 is thereafter installed by utilizing the reverse of the
foregoing procedure.
The exposed surfaces of the radiating bars 6 occupy almost one
entire side or face of the radiant heater 6 (FIG. 1). Indeed, only
the cross flanges 38 on the end caps 30 and the curved edges 18 on
the side walls 14 do not serve as effective radiating surfaces, but
these surfaces are extremely small in comparison to the exposed
surfaces of the bars 6. By reason of this fact, the radiant heater
2 is extremely compact. In this connection, it should be noted that
the heater 2 does not possess any reflector as do conventional
radiant heaters, and accordingly considerable space is saved.
Aside from being highly compact, the radiant heater 2 is also light
in weight and extremely rugged in construction. As to the latter
feature, most of the components are formed from stainless steel so
that oxidation of the metal does not occur even at high
temperatures. Moreover, no ceramic parts are used and therefore the
cracking problem associated with ceramic materials does not
exist.
Finally, it is not necessary to elevate the temperature of the bars
to extremely high values in order to achieve effective radiation as
is true of the heating elements in conventional reflector-type
heaters. It is preferred to operate the radiating bars 6 in the
range of about 600.degree. F. to about 1,500.degree. F. which
creates wave lengths capable of being absorbed by most substances,
irrespective of color or opacity. The lower operating temperatures
coupled with the extremely durable materials enable the heater 2 to
operate for extremely long periods of time, even when cycled.
From a production and marketing standpoint the radiating bars 6 may
be provided in standard lengths, and housings 4 may be provided to
accommodate the standard lengths in various numbers. For example,
one housing may hold three 15-inch bars, while another housing may
hold six 15-inch bars. Thus, it is possible to provide a great
variety of heaters or to even design custom heaters for different
applications, all without incurring a significant increase in
production costs.
It is possible to install the threaded terminals 44 in the end caps
30 (FIG. 8), in which case flexible metal connecting strips 82
should connect the terminals 44 with the bus bars 46 or connecting
tabs 80 in the radiating bars 6, depending on the type of
connection which is desired. The connecting strips 82 should
furthermore contain several accordion-like creases 84 so that the
strip 82 will extend when the end cup 30 is swung outwardly on the
hinge 32 and will contract when the end cap 30 is closed.
The terminals also can be mounted through the sides 28 if desired.
In fact the mounting of the terminals is relatively unrestricted
except for the radiating surface.
This invention is intended to cover all changes and modifications
of the example of the invention herein chosen for purposes of the
disclosure which do not constitute departures from the spirit and
scope of the invention.
* * * * *