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Патент USA US3089949

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May 14, 1963
Filed May 11, 1960
27 2628
\s W/A
United States Patent Office
Patented May 14, 1963
obtaining uniform heating over a substantial area with a
William H. Norton, Mundelein, lll., assigner to Thermal
lneorporated, Franklin Park, lll., a corporation of Del
Eiietl May 11, 1960, Ser. No. 28,455
1 Claim.. (Cl. E9n-3d)
The present invention relates to improved heating de
vices and more particularly to a radiant heating unit.
The present invention contemplates the provision of a
heating unit employing an infra-red heat radiating surface
having improved emissivity to increase the capacity of the
heating unit with which the surface is used, and having
an improved dispersion pattern of heat transfer to im
prove its heating effect and broaden its adaptability. The
features of the invention are particularly useful in a heat
plurality of units was difficult to achieve.
Uniform heat
ing is important in a number of environments particularly
in such equipment as vacuum forming machines where
4broad surface areas are to be heated.
This feature of the
invention per-mits the entire heater to be moved closer to
the material to be processed thereby increasing without
detriment the total intensity of the radiant pattern.
Other features and objects will become more apparent
with the teaching of the principles of the present invention
in connection with the disclosure of the preferred embodi
ments thereof in the specification, claim, and drawings, in
FIGURE l is a side elevational view of a heating unit
of the type in which the principles of the present invention
may vbe embodied;
FIGURE 2 is an enlarged vertical sectional view taken
ing unit having an elongated electrical resistor contained
substantially along line Il--lI of FIGURE l;
within a tubular sleeve or sheath of thermally conductive
material such as metal with an electrically insulative re
FIGURE 3 is a detailed fragmentary view, shown par
tially in section, of a length of heater tube constructed
in accordance with the principles of the invention;
Fi-GURE 4 is a greatly enlarged plan View of a frag
mentary section of the surface of the heater tube; and
fractory particulate material filling the sheath and main
taining the resistor therein in closely spaced relation to the
sheath. The sheath is in the form of a cylindrical tube
with its outer surface having a pattern of projections
FIGURE 5 is a schematic end view of a bank of heater
thereon with each projection having sloping side surface 25 tulbes arranged to heat a work surface.
areas facing outwardly, such as are provided in a preferred
form -by knurling the outer surface of the tube. The sur
face areas each provide an infra-red emission surface area
As shown on the drawings:
As illustrated in FIGURES l and 2, a heating unit
10 includes a tubular type heating element 11, which is
shown in greater detail in `FIGURE 3.
and the entire surface emits the infra-red rays outwardly in
a dispersed pattern and each surface area is positioned 30
The tubular element `11 is suitably mounted at its ends
relative to other emitting areas so that the infra-red rays
in electrical boxes 12 and 13 with an electrical cable 14
will not strike the surfaces of adjacent areas or adjacent
leading into the «box l2. A conduit 15 extends across
between the boxes for containing a wire leading to the
It is accordingly an object of the invention to provide an
‘box 13.
improved heating unit with a surface capable of emitting
Attached to the conduit 15 and the boxes 12 and 13
increased infra-red rays to increase its heat radiation ca
are end plates 16 and 17. The end plates, as illustrated
by the plate 16 in FÍGURE 2, have openings 18 to slide
Another object of the invention is to provide an im
the plates over the conduit 15 and have set screws 19 for
proved heating unit having a cylindrical outer surface
locking to the conduit.
wherein the dispersion pattern of heat transfer is improved
The end plates have downwardly extending legs 2@ and
and heat is radiated to a work piece over a greater surface
area and the area is more uniformly heated.
A feature of the invention is the provision of a tubular
type of heating element having a plurality of infra-red
emitting surface such as are formed Áby knurling to im
prove the emissivity of the element and thereby increase
its capacity 'while maintaining the surface at a temperature
for obtaining optimum or maximum infra-red radiation.
Over the range of wavelengths for infra-red emission there
are optimum wavelength spans wherein energy transmis
sion is at a maximum. The wavelength at which infra
red radiation occurs from the surface of the heater is de
pendent on the heater surface temperature. Therefore
for a radiant heater with a given size of heater emission
21 which are notched to provide a support for a heat re
flector 22 which is concavely shaped and extends across
above the heater element 1l.
As illustrated in FlGURE 3, the heater element 11 in
cludes an electrical resistance wire 23 contained within
an outer metal sleeve or sheath 25. Within the sheath
is an electrically insulative compacted refractory particu
late material 24 maintaining the resistance wire Z3 in
closely spaced relation to the sleeve. The tubular sleeve
25 is formed of a heat conducting material, preferably
such as those known as Inconel or Incolloy, or other suit
able metals or materials capable of withstanding tern
peratures of 900-1100° F.
On the outer surface of the sleeve 25 are a plurality
area, the electrical input is limited by the capacity of the
of raised surface projections 26 preferably formed by
area to emit infra-red heat energy.
knurling the outer surface of the tube 25. Each of the
surface projections has infra-red radiating side areas
To further increase
temperature merely results in moving out of the range for
optimum infra-red emission.
A feature of the present invention is to provide an in
crease in emissivity of a radiant heat surface to thereby
increase the electrical input for a given heater, thereby
increasing its capacity without requiring an increase in
size and the accompanying increase in space consumed
and increase in expense. The invention particularly con
templates increasing the emissivity of a heating element
of the tubular sheath type.
Another feature of the invention obtained from the
provision of a pattern of heat emitting projections with
facing generally outwardly from the tube, shown at 27,
2S, 29 and 3ft for the projection 25. Each of the areas
radiates infra-red with the surfaces shown as being at an
angle to the outer cylindrical plane of the tube and to
each other to provide a diffused pattern. The side sur
faces of the raised projections are at an angle so that the
infra-red rays emitted therefrom do not strike adjacent
projections but project outwardly to a work surface.
The projections increase the infra-red radiating surface
to increase the total ernissivity of the tube.
The projections 26 are shown as formed by a diamond
infra-red radiating surfaces on the outer surface of the
lrnurling tool and are fully raised to a peak. Knurling
heating unit is the improved heat dispersion pattern. 70 of a less depth will work although the side surface areas
With tubular heating units heretofore provided the heat
will not be as large and emissivity will not Ibe increased
was directed downwardly along a narrow line so that
as much.
'The diffused pattern of infra-red rays formed by the
projections avoids a concentration of heat pattern as
occurs with a tube having a smooth outer surface. Be
cause of the increase in surface area and the diffused
pattern the entire heater can be moved closer to material
being processed, thereby increasing, without detriment
the total intensity of the radiant pattern. For example,
as illustrated in FÍGURE 5, tubular heating elements 3f,
32, and 33 are shown arranged in a bank above a work
surface 34. With the use of ordinary tubular heating
elements a concentration of the heat pattern will occur
in a straight line below each tube inasmuch as the infra
red rays will be emitted radially and the intensity varies
inversely as the square of the distance, so that uniform
intensity could be achieved only along an arcuate surface
at constant radius from the tube. With present arrange
ment the heater banks can be moved more closely to the
work surface while obtaining a more uniformly heated
Another factor obtained from the present improved
arrangement permits the heaters to operate cooler and a
greater power input can be used within the same con
ñnes than as heretofore been possible with a smooth tube.
The more power which can be concentrated and directed
on a uniform basis, the faster and more effective and
more eiiîcient the entire system becomes.
have also shown that a tubular element having a smooth
outer surface will create a straight line intense pattern of
heating which will burn a surface at a given distance
Whereas the same tubular element when knurled will op
erate a much broader pattern of heat of uniform tem
perature without burning the surface thereby illustrating
the feasibility of positioning the element closer to the
work surface.
The structure thus finds advantage in use in environ
ment such as in vacuum forming machines, heat banks
for paint dryers, physiotherapy infra-red, comfort heaters,
cooking, and uses where conductive or convective trans
fer of heat is impractical or inefficient.
Thus it will be seen that l have provided an improved
radiant heater for infra-red radiation which meets the
objectives and advantages hereinbefore set forth. The
provision of the surface with the projections and the
infra-red radiating surface areas, such as provided by
knurling, increases the available surface area and pro
vides a greater emissivity directly in proportion to area
increase; provides a greatly dispersed heat transfer pat
tern avoiding concentration of heat transfer; permits
moving the heater closer to the work surface to be
processed permitting an increase in the total intensity of
radiant pattern; obtains increased capacity and energy
input for a heating unit of a given size operating at op
Another advantage in the present structure which has
been discovered is that long tubes do not sag or warp
out of shape under radiant temperature. This is of im
portance particularly when the present arrangement per
timum infra-red temperature radiation; and permits the
use of longer heating elements without support.
The drawings and specification present a detailed dis
mits bringing the tubes closer to the work so that any
and it is to be understood that the invention is not limited
sag would be highly objectionable and intensities occa
sioned by a sag could be critical. With the present
to the specific forms disclosed, but covers all modifica
tions, changes and alternative constructions and methods
closure of the preferred embodiments of the invention,
knurled eiement long spans up to 4 or 5 feet have shown
faliing within the scope of the principles taught by the
no tendency to sag and there is absolute uniformity of
the heater. Furthermore the need for an interim sup
port is eliminated and an interim support is objectionable
l claim as my invention:
in electrical heater comprising an electrical resistance
wire, a heat resistant electrically insulating material sur
rounding said wire, an elongated tube of high temperature
resistant heat conducting material enclosing said Wire and
said insulating material with the material compacted
therein and having a cylindrical outer heat emitting sur
face with a plurality of pyramidally shaped radial pro
inasmuch as it will normally create a cold spot on the
surface of the element.
While a pattern of projections on the heater element
surface formed by a standard diamond knurling tool is
preferred for convenience in obtaining a good diffusion
pattern, other projection shapes may be employed. A
jections having planar' side surfaces facing away from
plurality of conical surfaces would be advantageous al
though in mass production these projections would be 45 the tube forming a uniform pattern on said surface ex
tending for the full length of the surface and for the full
expensive to achieve. Another operation which would
circumference thereof so that the infra-red emission is
obtain the projections and the infra-red radiation sur
increased and the size of the tube is reduced for a given
faces would be to roll cross threads on the surface. A
right hand thread rolled in the surface and then repassed
heat emission capacity, said projections having planar
with a left hand thread would give a double crossing.
side surfaces at an angle relative to the planar side sur
faces of the adjacent pyramidal projections so that infra
However, it has been found that a single standard thread
is unsatisfactory inasmuch as the radiant rays emitted
red rays emitted normal to the surfaces Will not strike
from the surfaces of the threads strike adjacent threads.
surfaces of adjacent projections, and a heat reliector
In some instances it will be satisfactory to form the pro~
positioned behind said tube and extending parallel there
jections by a very coarse sand blasting or shot blasting 55 to to reiiect heat from >one side of the circumference in
of the surface thereby forming a pattern of projections
the same direction as the heat is emitted from the other
with infra-red emitting areas. This will not be as uni
side of the circumference.
form or as effective in forming surfaces although it may
References Cited in the file of this patent
be less expensive to accomplish.
Tests have indicated that increased emissivity due to 60
providing projections by knurling on a tube surface de
creases the temperature of the surface on the order of
100° to 150° F. when normally running in the range of
900° F. to 1150” F.
This indicates an efficiency be
tween 15% `and 20% greater emissivity.
Kercher et al. _________ __ Oct. 4, 1927
Trent _______________ _„ Apr. 4, 1939
Kolb _______________ __ Ian. 27, 1953
Steen _______________ __ Nov. 1l, 1958
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