Note: Descriptions are shown in the official language in which they were submitted.
~88412
The present lnvention relates to gas-fired radian~
heaters and to equipment with which they are used. Such heaters
are described in U.S. Patents 3,785,763; 3,248,099 and 3,824,064. ~
Such heaters are very efficient a~d very desirable for generating ~ ;
extremely large quantitles of concentrated infra-red energy. ~ -
Such a heater utilizes a panel of interfelled ceramic fibers,
a gaseous combustion mixture being continually passed through ~
the panel and ~urnt at the panel face from which it emerges. `
The combustion takes the form of a flame that extends over the
entire area of the face from which the combustion mixture emerges,
the flame length being very small so that the surface fibers at
the flame are heated to red heat or hotter and form an essentially
continuous wall of heat that makes a very effective heat radlator.
By increasing or decreasing the rate of flow and/or composition
of the combustion mixture, the temperature of the heated ~ibers
can be controlled.
Among the ob~ects of the present invention is the ~;
provision of novel heater structures that are simpler to construct
or provide improved operation or both.
The foregoing as well as additional ob;ects of the
present invention will be more fully understood from the follow-
ing de cription of several of its exemplifications, reference
belng made to the accompanying drawings in which:
Fig. 1 is a face view of an infra-red heater according
to the present invention;
Fig. 2 1~ a sectional detail view of the heater of
Fig. 1, taken along the line 2-2;
Fig. 3 is a plan view of a component that can be used
in the making of the heater of Figs. 1 and 2;
Fig. 4 is a detail view similar to that of Fig. 1,
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showing some structure features suitable for the infra--red heaters
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of the present invention;
Fig. 5 is a view similar to that of Fig. 2 showlng an
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optional method of constructing the heaters of the present invention;
Fig. 6 is a sectional view of a gas-fired radiant heater according
to another aspect of the present invention;
Fig. 7 is a plan view of an assembly of heaters of the type
illustrated in Fig. 6;
Fig. ~ is a sectional view similar to Fig. 6 of a modified heater
construction pursuant to another aspect of the present invention;
Fig. 9 is a plan view of the heater of Fig. 8;
Fig. 9A, appearing on the same sheet as Fig. 10, is a plan view
o a component of the structure of Figs. 8 and 9;
Fig. 10 is a broken-away plan view of a portion of a heater showing
a detail feature suitable for use according to thc present invention;
Pig. 11 is a sectional view Oe the construction Oe Fig. 10, taken
along line 6-6;
Fig. 12 is a sectional view of a different heater construction
pursuant to a further aspect of the present invention;
~igs. 13 and 13A are sectional views of a heater construction
typifying yet another aspect of the present invention;
Figs. 14, 15 and 17, all appearing on tho same sheet are views of
still further embodiments of the present invention; and ;
~ig. 16 is a vertical sectional viow partly diagrammatic of a ;
heating arrangement pursuant to the present invention.
According to one aspect of the present invention in a gas-fired
radiant heater having a combustion mixture plenum covered by a face of a
porous refractory panel through the thickness of which combustion mixture
passes from that plenum to burn on the opposite face of the panel, there is
provided the improvement according to which the panel extends beyond the
margins of that plenum, a second plenum encircles the combustion mixture
plenum and has gas-discharge openings covered by extending portions of the
first panel face, for discharging a non-combusting gas through the thickness
of the panel from its first face to its exposed face all around the combustion
mixture in the panel, to keep that combustion mixture from reaching the panel ;
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edges.
According to another aspect of the pTesent invention in the : .:.
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operation of a gas-fired radiant heater havi.ng a ~orous réfractory panel .
through the thickness of which a stream of combustion mixture is passed
from one face of the panel to the opposite face where it burns to generate
heat, there is provided the improvement according to which a thin stream
of non-combusting gas encircling the combustion mixture stream is also
passed through the panel thickness from said one face of the panel to said .
opposite ace to confine the combustion mixture stream and keep combustion
10 mixture .~rom reaching the edges of the panel. The ;~ .
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porous refractory panel can be fla~, convex, concaveJ cup-shaped,
hat-shaped,or have any other desired configuration.
This non-combustlble gas stream acts as a barrier
which directs ~he combustible mixture ~hrough the refractory panel
and minimizes leakage of combustible gases past the frame members
that hold the panel. By acting as a combustible gas barrier,
the non-combustible gas stream significantl~ reduces the importance
of the seal shown in Patents 3,785,763 and 3,824,064, greatly
reducing burner assembly time and parts tolerance. The non-
combustible gas stream also greatly reduces contact of the hot -
gaseous products, resulting from the combustion at the panel
surface, on the frame members keeping them much cooler and reducing
heat warpage.
The narrow stream of relatively cold gas is conveniently ;
provided by holding the porous panel on the ledge carried by the
combustion mixture plenum for the porous panel, and a slot extends
along the ledge and is connected to a supply of the non-combustible
gas.
An even greater simplification of the oregoing heater
construction and operation is effected by squeezing the panel
margins to that they are compressed at least about 10% from their
uncompressed thickness, inasmuch as this simple expedient also
h~lps reduce the e~cape of combustion mixture through the panel
ed~es. When combining a marginal gas stream seal with the edge
compression, very effective edge sealing is accomplished with
only a fraction of the ~low of non-combustible gas otherwise re-
quired. With either arrangement however, no other assistance
is needed to sesl against edge leakage of combustion mixture, and
edge impregnation as well as edge wrapping of the panel is com-
pletely dispensed with.
Turning now to the drawings, the basic radiant heaterof Flgs. 1 and 2 has the usual porous refractory panel 10 held
at its margin~ ~y uppe~ frame mem~ers 21, 22, 23, 24, against a
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lower frame 30. Frame 30 has four lengths of tubular supports,
two of which are shown in Fig. 2 at 31, 32, secured to the margins
of a rçctangular back plate 40 by welding, brazing, cementing as
wi~h epoxy or other cement, or otherwise joining in a gas-tight
manner, indicated at 42. Back plate 40 and the four tubular
supports thus define a plenum for the comhustion mixture fed to
the panel lO. A pipe connection can be welded through an aperture
in the back plate in the standard manner for receiving a com-
bustion mixture supply conduit, and a baffle,a portion of which
0 i9 shown at 44, can be fitted to help equalize the combustion
mixture flow toward all portions of panel 10.
One or more lengths of the tubular support frame can
also have a connector 53 welded through an aperture Eor the
supply of air from a pump or a storage tank or the like. A slot
55 i~ also provided along the top wall 57 of the support frame
for discharge of the air from the interior of the tubular support
lengths through the margin of the porous refractory panel. The ~ -
individual tubular supports are mitered together at the corners
of the frame with the mitered ~oint sealed as by welding, brazing, ;
cementing or otherwise securely ~oining, to keep combustion mix- ;
ture from leaking out of the plenum as well as from being non-
uniformly diluted with the air moving through the tubular supports.
The upper frame members 21, 22, 23, 24 are shown as
angles each having an upper flange 61 that overlies a margin of
the outer face of panel 10, and a depending flange 62 that is
secured to a low~er frame member, as ~y means of the screws 64.
The screws can ~e threadedly received in the outer walls of the
tubular support members, and can pass through openings in the
flsnge 62. Such openings can be elongated in the direction
perpendicular to the wall 57 if adJustability is to be provided
for the spacing between wall 57 and flange 61.
The porou3 panel 10 permlts the gaseous combustion
mixture to freely pass through it so that pressures 1ll the plenum
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need only be about 2 to 7 lnches of water above the ambient
atmosphere to provide very effective uniform combustion over the
entire outer face of panel 10. A slmilar air pressure in the
interior of the tubular support will cause streams of a~r to pass
through the margin of porous panel 10 and emerge from ~ts outer
face. The porous interfelted fibrous structure of the panel
surprisingly does not permit much change in the width of the air
stream moving through the panel, particularly when the pressure
that propels the air stream from the tubular support is within an
inch or two of water height with respect to the pressure that
propels the gaseous combustion mixture from the plenum. This is
readily noted when the burner is in operation inasmuch as the
outer surface of the panel glows red hot over its entire area
except for a narrow and ~harply defined band around its periphery
and ad~acent the outer rame mem~ers.
The frame members are thus kept much cooler than they
would be wlthout the marginal air stream, particularly where the -
burners are operated with the outer surface of their panels 10
positioned in a generally vertical plane, or positioned facing
downwardly. In those positions the very hot gaseous products
resulting from the combustion at the panel's surface, rise and ~;
flow over the frame members of the burners of Patents 3,785,763
and 3,824,064 to heat them up to high temperatures that can reach
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jO0F in some cases. The marginal air stream of thc present in-
vention, on the other hand, acts as a barrier layer against the
hot combustion products, keeping those hot gases from directly
, reaching the rame members in substantial volume. Marginal stream' ;
taXen from the air at ambient temperatures and passing throuyh a
panel as much as 1 1/2 inch thick will generally keep the outer
faces of 1/16 inch thick steel frame members several hundred
~egrees F below the temperatures corresponding ~rame members reach ~, ''',
in the constructions of the above patents. The temperature o~ the '"' ~ '
rames of the present invention will be even lower where the heater ; '
is used to heat objects that do not cause ~uch re1ection of the ,;,
burner'a radiating heat back to those ~rame members. '
A further benefit of the present invention is that by,,
minimizing contact of the hot combustion gases with the ~rame
members and thus keeping them much cooler, emission of radiation , '~
from the ~rame members themselves is greatly reduced, The heaters ; '.;
of the pxesent invention can be positioned much closer to their ,
,targets, than prior art heaters and still permit minimizing damage
to the target in the event o~ emergency shutdown~ The porous
reractory panel itself cools down very sharply when the fuel gas
~low into the plenum is s~opped and the air flow is mai~tained
but the ram_ me~bers of the ~rior art heaters take much longer to
cool down. Thus when using such~heaters to ,heat a moving web of
heat-sensitive'material, the heaters are preferably arranged to , ~,
generate much more heat than the web can tolerate should the web
Is~op moving. With the prior art heaters the rate o cool-down
¦Ifor the ~rame members can become a cr~tical factor that determines
~how ciose the prior art heater can be brought to ~he we'b without
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maging ~he web in the event the web suddenly stops'ana the h~ater '
cannot be mechanicall~ pulled away from it. The heat~rs of the '-
pre.~ent invention don't have to be pulled away and can therefore
be installed in a less expensive manner. Their closer proximity
to the target makes the heat transfer to the target more efficien ,~;;
and enables the use of less fuel to achieve the desired xesu~ts. '~
~oreover in some treatments such as the volatilizing of ~, "
. water from a 'target web, the most effective wave-leng~hs are ,.,.
between about 3.2 to about 3.6 microns, a range ~hat is most ,.,.. ~ ~
eficien~1y produced at relatively low radiation temperatures~ ' ... .. .
By moving,the heaters of the present invention closer to their ta~ ~
gets, their radiation temperatuxes can be diminished to thus make ' ,
more.e~icient use o~ the fuel ,energy and with less uel, without , , ,
decreasing the treatment e~ectiveness. ,, "
~ eaters placed very close to targ.ets may be desirably ~'
made to extend beyond the edges of the target to attain greater
treatment uniformity. Each such e~tension can be approxima.ely
equal to the distance from ~he heater to the target, for good ` ,,
results. , ,
2Q' ~ocating slot 55 immediately opposite the panel margins
alongside the inner edges of the upper rame members 21,'22, 23,
, 24 helps guide the protective streams to the desired location~ ~. -
i This guiding action is further improved by sealing ~he edges of ~ .,:. .
the panel so that not much non-combustible gas can escape ,.".
laterally. Fig. 2 illustrates a prior art edge sealing te~hnique
according'to which a ~hin foil of aluminum 70, about 2 mils thick .. ',~
~¦ is wrapped around each panel edge, and,the lower face of ~he foil ..
¦ is sealed against wall 57 by a ~arrow line o~ seala~t 7:2 such as
¦ a sll~cone rubber vulcanized in place.
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` Accordiny to the present invention, whcn edge se~ling of
the panel is desircd, the sealant 72 can be of a ma~erial such as
~ordinary rubber or neoprene, that need not be resistant to high
temperatures. However during normal operation of the burner con-
struction o the present invention, only air from the interior of
the tubular support will tend to leak out from the margins of the
panel~ Such leakage is not dangerous nor is it extensive when
sealant 72 is entirely omitted. Omitting the ~oil 70 can cause
extensive air leakage unless the outer frame is a ver~-close fit
against the support frame. The marginal air stream with or withou-
leakage keeps the combustion mixture from leaking out the edges o~
the panel.
The slot 55 does a very e~ective job when it is about
1/4 inch wide, although it can be as little as 1/16 inch or as muc
as 1/2 inch wide and still gi~e good results. The width of pro-
tectiva gas stream emerging from the ~ace of the porous panel is
generally a little larger than the width of the slot, and changes
in gas pressure vary this broadening ef~ect. A desirable gas
pressure in the tubular frame is one that approximatel~ e~uàls the
~20 pressure in the combustio~ mixture plenum. ;~
The cooling a~d combustion-mixture-leak-blocking e~fects
of the marginal stream of ~he present invention are also obtained
when the discharge slot 55 is located ~urther toward the outer ac
of the frames so that the gas discharged thxough the slot is dir-
;; ected partly o~ completely a~ frame flange 61. Most of the di-~-
charged gas will then move along t~e interior of panel 10 and
-escape just past the inner margin o f that ~rame flange.
' ~ ¦ It ~5 not essential to make the tubu~ar support me~bers~
gas-tight where they are threadedly en~aged by screws 64. Even
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~ere relatively expensivc inert gas is used rathcr than air, the
leakage through such threaded connections is minisculc as com- :
¦ parea with the discharge through slot 55~ The threaded engagement
~an be sealed however, as by applying pipe-~hread dope or the lik :~
to the mating threads before they are engaged. Alternatively the :
connection between the outer and inner ~rames can be made as shown
in U. S. Patents 3,785,763 and 3,824,064. - :~
. Instead of making tubular frame 30 of our separate
lengths, it can be made from a single piece of formed sheet metal,
as illustrated in Fig. 3. An elongated strip of sheet metal
. twent~ to fifty thousandths of an inch thick can be bent into the .
~orm illustrated by the sectional view in Fig. 2, or a standard
. metal kube oE rectangular section can be milled to cuit the slot
55 through one wall, and the resulting ~hape then subjected to ~ ;
mitering cuts 81, 82, 83, 8~ and 85 as shown in Fig. 3. These cut - : .
leave wall 88 intact and the mitered length then bent to form a ¦ ~ -
one-piece tubular ~rame a corner of which is shown in Fig. 4. The
. inner edge of each corner is therl welded, brazed, cemented or
o~herwise joined as at 89 to seal the en~ire height of that corne ~.
and the tubular frame is ready for similar joinir.g to the back
. plate 40~
It is not necessary to seal ~he outer face 90 of the
mitered joints, particularly if the joints are a close fito A ..
little extr~ leakage at those locations from the in~erior of the ......... .
tubular frame does no particular harm~ However, that outer face
can be sealed, especially if lateral leakaige from the :Eram~ ~argin
taXes place~
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The tubular frame need not extend inwardly of the slot
`~55, although it helps to have that frame provide an additional
flat support 73 for the porous panel 10. Such support can be
reduced to the thickness of the metal from which the tubular frame
is made, as by suitably shaping the tube from which it is sliced,
or by milling the slot 55 alongside the inner wall of the tubular
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frame.
Figure 5 shows another tubular frame co~struction of
the present invention which is simple to manufacture. ~ere a flat
support 173 takes the place of support 73 and extends toward the
center of the plenum. ;
It is also helpful to seal the outer margin of panel
10 as by dipping it in or brushing on a hardenable liquid resin
that hardens to a temperature-resistant solid. Solutions of
silicone rubber, colloidal s-llica, and sodium silicate are ex- ;;
amples of suitable hardenable materials. When this type o edge ~`
sealing is used, the aluminum foil is not needed.
In some installations the panel temperature is so hot
and there i6 80 much reflection of heat from the surfaces being
heated by the heater, that aluminum can be damaged. Other metals
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such as stainless steel can then be used for the sealing foil. -`
Fig. 6 illu~trates a heater 100 w1th improved edge
sealing. Heater 100 ha~ a cup shaped panel 102 of lnterfelted
refractory fibers, clamped by its edges around a sllpport assemble
104 made of stainless steel or other metal members shaped from
relati~ely thin stock, about 1/16 inch thick. A central dish 106 -,
has a~floor 105 and inclined walls 107 with raised edges 108
a8ainst whlch the panel 102 is preased to deflne a combustion
i mixture plenum L10. Outer face 103 of panel 102 is of rectangular-
shape, and 90 i8 plenum 110.
Secured to the outer margin of the floor 105 of dlsh
106 is a series of angles two of which are shown at 112, 114, de-
fining a rectangular frame against whlch the edges }20 of panel
102 are fitted. These angles are illustrated as having horizontal
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¦~ ~s 122 welded or brazed to the floor of dish 106, and vertical webs -
~¦124 that approach but do not quite reach the dish edges 108. The
¦frame angles define with dish walls 107 an outer plenum 130 that
¦encircles combustion mixture plenum 110 and 'has a discharge slot
¦132 that is engaged by the margin of panel 102. The rame members
¦are mitered or otherwise interfitted at the corners of the frame
¦to minimize,or completely seal the outer plenum against,leakage
in those locations. Supply nipples 146, 148 are fitted'in opening
¦in the floor 105 and one or more of the frame angles 112, to - ';~
~0 ¦deliver, respectively, combustion mixture and non-combustible yas.
¦Baffles such as the U-shaped deflector 116 can also be provided
¦to help more uniformly distribute the incoming gases. Inasmuch
¦as air is generally the non-combustible gas that ~lows through
¦plenum 130, a little leakage doesn't do any particular harm other
than consume a little excess air. '- '
I Anchoring of panel 102 in place is shown as effected wit ;
¦the help of a series of four or more clamping angles 136, 138, ~ '
¦clamping the panel edges 120 against the frame angles, with the
help of screws 140 that penetrate through aligned openings in the ;~
20 ¦ angles and are threaded ir.to self-locking nuts 142 mounted in webs
l 124 as by securing clips or welding. The screws which need be no
¦ thicker than about 3/16 inch, are readily pushed through the edges
of the panel without seriously damaging the panel, and any damage
l that might promote gas leakage is more than compensated by drawing
'' 'I up the clamps sufficiently to compress the panel edges. Standard -
l panels have a wall thickness of about 1 1/8 inches and an inter-
¦ ~iber spacing such that more than half that thickness is fiber
I and binder, so that compressing the edges to reduce t'he overall
¦ thickness only about 10% sharply reduces the air space between
30 ¦ fibers and greatly limits leakage.
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However very effective panels of interfelted fibers
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can be made by needling a mat of such fibers without the help of
binder. Such needled panels can be extremely pliable, as com-
pared to molded binder-containing mats that are stiff like boards
and can have their edges compressed down to as little as about
30% of their uncompressed thickness. Even compressing such ~ ;
edges that are originally about one inch thick down to a~out 3/8
inch provides an extremely effective back-up for the air seal.
For such pliable panels it is preferred that the edge
0 compression be down to about half the original thickness, or
less. If desired however a pliable panel can be stiffened over
its edges alone, or over its entirely, as by impregnating it
with a water solution of starch or the like. In such stiffened
condition, the degree of edge compression can be reduced.
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To reduce any effect that the compression may have in
breaking panel fibers that are binder-impregnated, the panel ;~;
edges to be compressed are first dipped in water or other solvent ~;
for the binder carried by the fibers. Such wetting makes the
edges more readily deformable so that the compressing is easily
effected without seriously stressing the clamping structures.
To assure uniformity of co~pression of board like panels, the
screws 140 are no more than about 8 inches apart when the angles
have the above-noted wall thickness. Where the heaters are
operated in confined spaces so that the clamping angles are
subjected to considerable reflected heat, it is helpful to cut
slots about six lnches apart through the vertical webs of those
angles, to allow for thermal expansion and contraction without
distortion of the support. Such slots need only be about 20 mils
wide, but can be omitted where the clamping angles do not engage
each other at the corners of the frame so that expansion is possi -
ble at those corners.
A feature of the heater construction of Fig. 6 is that
a plurality of such heaters can be juxtaposed to make an effectiv ,_
ly continuous radiant heating assembly that covers an extended
area. Thus individual heaters are conveniently made with rec-
tangular heater faces about one foot by two feet in siæe, larger
sizes of stiff board-like panels being somew~at awkward to manu-
facture because the molding and handling is more difficult. How-
ever by making the smaller sized panels so that their edges 120
are bent down at least about 90 degrees from the plane of the
panel body, considering such edye as a flange ben~ clown from a
f~at sheet, and loca~ing the edge mountings 30 they~are at least
partially inboard of the outer face of that flange and not pro-
~ecting beyond that ~ace more than about 5 m~liimeter3, theyjuxtapose in a very desirable manner as illustrated iIl Fig. 7.
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In Fig. 7 an assembly 200 of individual heaters 100 is
made with the adjacent faces o their panel l_dges 120 about 3
millimeters apart as indicated at 202~ The margins of the panel
faces 102 can be made so that they have an essentially zero radius
of curvature where they bend into the edges 120, but it is some-
times simpler to make them with a radius of about 1/8 inch, and
the foregoing 3 millimeter spacing of such rounded corners does
not significantly detract from an effectively continuous heater
surace junction, particularly where the combustion mixture is
.0 arranged to burn over the entire rounded corner. Increasing the
spacing from about 3 millimeters to about 5 millimetexs does make
a significant discontinuity in the radiation uniformity but this
can generally be tolerated.
While the clamping screws 140 are shown as having round
heads and thus project out the furthest from the outer faces of
the refractory panel edges, such projection is not a problem so
long as it i9 not over the 5 millimeter limit noted above, or the
preferred 3 millimeter limit. These screws can be in unsymmetrica L
~ locations along each edge, so that the screws on one heater are
!0 offset from the screws of an adjacently positioned heater, as also
illustrated in Fig. 7. Indeed the round-head screws can be re-
placed by socket-head screws which project a trifle more but are
easier to install during manufacture. Flat-head screws can
alternatively be used with the screw openings in the clamping
angles countersunk 90 that the screw heads do not project beyond
those angles, if minimum or zero spacing 202 is desired. ~-
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The burner construction of Fig. 6 can also have panels . :.
of the pliable needled type described above. Such a pliable ~
panel behaves very much like a blanket, and can have its edges ... :. .
fold,d and tucked in place between the side anch`orage members.
Because of their high pliability, the corners of such panels .~.. ..-.
will squeeze into shape, although it may be helpful to cut away
all excess corner material, and to even notch out some of the -
panel corners to make it easier to clamp these panels into
place. It is preferred to confine any notching to portions ~ `
of the corners covered by the anchorage members so as to reduce : ` :
e leaKage of gas at ~he notch-s.
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¦ It is not necessary to have the entire margin of each
¦refractory panel lQ2 flanged over as at 120. Thus each of the
¦panels in Fig, 7 has at least one margin that is not juxtaposed
Ito another panel, and some have two such non-juxtaposed margins.
¦Whexe only two panels are to be juxtaposed, each can have only one
¦margin provided with a flanged-over edge 120, in which event the
¦remaining three margins can have simpie constructions as shown in
¦the flat panel exemplifications of Fi~s. 1 to 5 as well
¦a5 in Figs, 8 and 9.
¦ Very close juxtaposition can also be provided by molding
lor 9haping juxtaposed edges 120 so that they are bent down more
¦than 90 degrees from the horizontal as measured by the angle 150
¦in Fig. 6. A panel can thus b~e molded around a suitably shaped
¦molding screen with as many as three of its four sides having
¦~lanyed edges bent as much as lOO or 110 degrees measured at angle
¦150, and the thus molded panel can then be slipped sidewat~s o~f
¦the mold in the direction away from its fourth side. Where only
¦one flanged edge margin i5 de~ired, it can be made when rnolding
¦the panel, or by ben~ing down the edge of a flat-molded panel,
¦after that edge is softened by wetting.
¦ The construction of Figs. 8 and 9 is one that is easily `
¦manufactured from readily available sheet metal, for flat heater
¦panels. It has a pane~ support which is a welded-together assembl~ '
1f a rectangular plenum box 30~ and a hollow-centered rectangular ¦
¦encirclin~ plenum tube 304. Plenum box 302 is conveniently pre-
¦pared by suitably notching out the corners o~ a rectangular sheet,
¦then bending up the ~our wings tnus formed, and welding the
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resulting corners gas tight. A hole can then be punched in the
floor of the box to receive a PTM half close nipple 306 also
welded on gas tight A baffle 308 can also be spot welded over
the hole to distribute the combustion mixture fed through it. If
desired an extra tap 310 can also be provided at a second hole in
the box floor, for a pressure gage or the like.
Tubular plenum 304 is easily made from sheet metal bent
into the shape of a channel having a web 312, and unequal flanges
314, 316. The channel is cut into four lengths each of which is
mitered and then welded together gas tight, if desired. The
tubular plenum can then be affixed to the plenum box as by spot
wclding the ~langes 316 to the floor of the box. A gas inlet 320
in the form of half a close nipple can be affixed to the tubular
plenum, along with an extra tap 322 in the same manner as for the
box plenum, and a baffle 324 can be fixed over inlet 320 by spot
welding to either the outside of the box plenum or the inside of
the tubular plenum. ;
A slot 330, preferabLy l/4 inch wide, encircles the top
o~ the box plenum. ~he refractory matrix is clamped in place by a
clamping frame 342 of angular section as illustrated in Fig. 8
and having slits 344 cut in the web overlying the face of the
panel as shown in Fig. 9. The slits can be about 8 inches apart
and preferably 1/16 inch wide to take care of the most severe ~ -
thermal conditions. The clamping frame is secured by screws 346
as in the construction of Fig. 6, although sheet metal screws can
be used instead in either construction,in which event the nuts can
be omitted and if desired locking washers fitted under the screw
heads.
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In severe thermal conditions, such as firing face down
or when firing directly at opposing burners, it is desirable to
insulate the clamping frame 342 from the radiated and convected :~
heat by over-wrapping with a high tempera~ure insulating material
such as mineral fibers felted or needled in blanket form. Fig. 8
shows a fiber blanket 350, approximately 1/2-inch thick, clamped
and compressed between clamping frame 342 and re~ractory matrix .
340 is wrapped around the clamping frame 342 and web 312 and .:.
secured to flange 316 by means of clamp 360 and sheet metal or .
other screws 362. The fiber blanket 350 insulates the clamping
rame from convected heat and its pure white color reflects some ; :
radiated energy from opposing burners making the system more
efficient. In very high ambient operating conditions it may be
desirable to completely wrap the non-radiant surfaces of burner . ~:
300 with the fiber blanket. : .
Fig. gA shows the fiber blanket 350 as prepared for
instat`lation, having a tuck-in margin 370 which is inserted under
the face of clamping frame 342. . . . .
In less severe appl~cations it may be desirable justto :. :.
l20 cover the face o 342 and hold the blanket in place with the screws .; ..
3~6 and washers under their heads. . ;:.-
The radiant heaters of the present invention can be -:
eguipped with automatic igniters such as electric spark igniters
or pilot lights. Figs.lo andll show a particularly desirable . ;.:
automatic igniter construction fitted.into a heater of the type ;.
illustrated in Fig9. 8 and 9. A standard combination 500 o~ spark ~:.
rod 501, ground rod 502 and flame-checking rod 503 is mounted so ~:
that the rods are generally parallel to and about 1/16-inch above
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the outer face 505 of t~e porous refractory panel 340. Below
¦the opposite face of the panel underneath the rod assembly, the
box plenum is provided with a partition 507 that isolates a
chamber 509 from the remaining space in the box plenum, an~ the .
chamber is fitted with its own supply connector 511 to receive a - .
separate combustion mixture. .;. .:
The spark rod 501 and *lame-checking rod 503 are each . .... .
housed in two identical insulators 550 which go through aligned ~. :
openings punched in the top flange 520 of the clamping frame 342 : :
~in~e 1anges 316 and 314 o plenum 304 as shown in Fig.ll. .
~round rod 502 i9 welded or brazed to 1ange S20. The ends of
rods 501 and 503 by flange 316 are threaded to accept connector ;
542 ~hich holds them in place and provides a ready connection for ~ :
. necessary wiring. -
. The construction of Figs 10 andll is operated to start .~
the burners using a safety check. A separate pilot combustion : . :
mixture is first started into cha~ber 509 and at the same time the .:`
spark rod is electrically energized to begin sparking. I~ the . .
. ~lame rod does not sense a flame withln a short period o~ time,
such as lO to 30 seconds, the flow o combustion mixture can be
automatically cut of~ and the starting sequence must then be :~
manually rec~cled, preferably after the combustion mixture flow .
. is checked as by purging chamber 509. When the starting sequence
cause ignition o the separate combustion mixture, the 1ame-
ecking rod 503 senses the ignition and opens the valve that *eed .:
the main combustion mixture into plenum 302 which i9 then ignited ~ -.
by the 1ame at chamber 509. .
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~y using a small chamber 509 with a low BTU~hour input
for the automatic ignition test, the danger of explosion at ~'
ignition is minimized. A chamber volume of about 100 cubic
centimeters or less is very effective for this purpose. ,~,' ,
The pilot combus~ion on the radiating surface of the ~ ,'
panel contribut,es to the overall radiation.
The spacing of the rod assembly from the refractory ~ '
panel is preferably kept very small so that the rods do not
interfere with placing the radiating surface close to the materiai
being radiated, such as a moving textile web that is being dried. '' "
Because the effectiveness of the heater increases when brought ,
c}ose t,o the material treated, the spacing o the panel from that
matexial ls sometimes arranged to be as little as two inches or
even less. ' , '
Pig.12 illustrates a radiant heater 700 of,the present
invention particularly adapted for the sealing of metal tubes in ,
a metal sheet,
Heater 700 has a dome-shaped holder 70~ welded gas-
tight to a ~upport ring 704 that is shaped to fit'and receive the ~,
brim 710 of a hat-shaped refracto;ry ceramic panel 720.,,The crown ,,,
portion 712 of the panel is thus held in spaced relatlon to the
dome-shaped holder 702~to define a plenum 730 for the combustion "
, mixture to be burned on the concave surface of the crown 712. An
inlet 732 and pressure gauge tap 734 are shown as fitted to the '~
~' holder 702. ' ' ',~ '
The brlm of panel 720 is shown as clamped against , ''
, support ring 704 by a clamping ring 706 which is bolted to an ~,
extensi,on 708 of support ring 704 and is offset from it to form a
cylindrical wall 740 that deines an an~ular plenum 750 for the ~," ,
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non-combustible gas. If deslred the offset can be made integral
^~- wlth the clamping ring so that support ring extension 708 can be
in the general plane of the main portion of the support ring.
Alternatively wall 740 can be divided into upper and lower short
cylinders separately integral with the separate rings. An inlet
760 and a pressure gauge tap 770 are also provided for the annular
plenum.
Non-combustible gas pumped into plenum 750 of heater ~ -
700 flows through the brim 710 of the porous refractory panel 720 -
.
and keeps the combustion mixture fed through plenum 730 from
reaching the lowest portion of the internal surface of the panel
where it is aligned with plenum 750. No external cooling coil or ;~
~acket is needed for the heater 700, inasmuch as the non-combustible -
gas emerging from the lower portion of the interior of the panel ~;
flows outwardly along the bottom of clamping ring 706 and keeps
it a~ well as the a~ociated metal parts sufficiently cool. Holder
702 as well as the remaining members that hold panel 720 can all
be made of aluminum about 60 mils thick.
Flg. 12A shows a modified sealing arrangement of the
~ust-described embodiment. Here a burner 1500 having a generally
flat burner face 1520 is used. This extends the heat-up time
somewhat as compared to the construction of Fig. 12, and as a
result wide assemblies may take as much as 50~ more time to seal.
However the sealing time i9 still far less than obtainable from
the prior art.
The burner 1500 of Fig. 12A can be constructed in~ the
manner described above preferably along the lines of its Fig. 5
where the ceramic fiber mat has its margin merely fitted to a frame
havlng an inert gas blow-through arrangement in which the inert -;~
gas thus blown through the margins of the mat acts as to seal --
those marglnA against combustible mixture leakage. No other margin
sealing i3 then needed.
Another feature of the present invention is that the
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heaters with the air seal construction are particularly sulted for
use in house hot air and/or hot water heating furnaces. The air
seal effectively prevents diffusion of the combustion mixture to
edge locations where it can burn at a low feed rate and thus
gsadually burn back deeply into the binder holding the refractory ~.
fibers, eventually creating a line of weakness at which an un- ~:
needled panel tends to readily break. Indeed the burn-back can ~:
sometimes burn back far enough to cause ignition within the mixture `.
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plenum itself, rendering the heater unsuited for continued opera-
tion. The edge seal construction of the present invention accord-
ingly provides a very long life ~or tha refractory panel, and is
also so simple that it is inexpensively constructed and thus more
attractive for relatively small home-type equipment.
Figs. 13and13A show a hot air heat exchanger constructior
for house heating pursuant to the present invention. Here a
cylindrical heat exchanger 800 has a hollow interior 802 in which
is received a ibrous panel 804 also of generally cylindrical
shape. The panel has an open end 806 clamped to a mounting plate
808 as by means of a rib 810 formed or welded on the plate and
around which the panel end is squeeæed by a split sheet metal
strap 812 w~.ose ends can be pulled together by a tightening screw
814. -
Before the panel is fitted in place a partition disc
820, held on a tubular support 822 having an externally threaded
extension, i9 mounted on mounting plats 808 which has a threaded
aperture 826 that threadedly receives the threaded extension 824.
Partition disc 820 has its periphery located just above ;~
the edge of rib 810, to define a marginal slot 830 for discharge
of a sealing gas stream through the marginal portion of the panel
804. An inlet nipple 832 provides for the delivery of the sealing
as stream to the sealing plenum 840 below partition disc 820. ;-~
xtension 824 provides for the supply of combustion mixture to the -
lenum 850 above the partition disc.
Strap 812 is also shown as carrying a ring of outwardly-
extending ears 842 that heIp retain a mass of insulation packing
844 ~itted axound the open end of panel 804 when mounting plate
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808 is brought into engagement with the mouth 846 of heat
exchangex 800. Some of those ears are also perforated to receive
an ignition and test assembly 860 shown in the form of a series
of ceramic tubes 862 each having an enlarged head 865 and threaded
into aligned openings in the mounting plate. Through the pas- -
sageway in each ceramic tube there penetrates a rod 867 having a `
disc-shaped inner end 870 and staXed as at 872 so that it is
appropriately located with respect to the ceramic tube. A washer
874 can be slipped over each rod before it is inserted in the
ceramic tube, to ~urnish better positional coaction with the
tube and the staking. The outer edge of each rod can be threadedl
engaged to a mounting tip 876.
The discs 870 of each rod are arranged so that they are
in edge-to-edge opposition suitable for sparking and for flame
detection, as described in connection with Figs 10 and 11.
The outside of hea~ exchanger 800 can be located in the
circulating air plenum of a standard house heater, or if desired
in a water tank containing water to be heated. This heat ex-
changer can be made o metal or even of glass, borosilicate glass
being particularly suited when the heat exchanger i9 used to heat
water. Water to be heated in this way can be colored with dyes
for example, to better absorb radiant energy transmitted through
a transparent heat exchanger. Metal heat exchangers are desirably ~
ribbed to increase their effective surface area and thus increase ~-
their heat transfer to surr0unding air or the like.
Another feature o~ the present invention is the ability
to use an inert or reducing gas to seal the combustion mixture
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on its way through the porous refractory panel. Thus ~he sealing
gas can contribute to make the burnt combust:ion mixture provide
an atmosphere of exceedingly low oxygen content, or even of
strongly reducing ability as for example by reason o a signifi-
cant hydrogen content.
Fig.l4 show~ an annealing tunnel furnace 900 having
upper and lower radiant heaters 902, 904 facing each other and
held in fixed relation by sid~ blocks 906 o~ thermal insulation.
A wire mesh conveyor 908 is arranged to slide through-the furnace
interior to carry workpieces that are to be annealed or brazed.
A strip curtain 9lO closes off the entrance to the furnaceJ above
the converyor, the portion of the entrance below the conveyor "
being closed by a one-piece wall 91~.
~ he heaters 902, 904 are operated in the manner des-
cribed above, except that the sealing gas streams, indicated by
arrows 920, can be cracked ammonia, or a propane-nitrogen mixturet
or pure propane or the like. With such sealing gases, it is
preferable to adjust the combustion mixtures so that they have
little or no surplus oxygen. ~he urnace interior then becomes
a very efective reducing atmosphere that will prevent oxidation
of the workpieces and even reduce any oxidation present on those
pieces when they are introduced into the furnace. ~otwithstanding
the strongly reducing character of the furnace interior, the
burning of the combustion mixture takes place very effectively to
pr de radi-tion at temperatures at least as high as red heat.
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- Fig. 16 shows a partqcularly effective heating
arrangement for heat treatment of a moving web 1200, such as
textile drying and curing or paper processing, the directive of
movement is shown by arrow 1202. In thls arrangement a series
of burners 1210 face the moving web adjacent each other on opposite
sides of the web. Immediately facing each burner 1210 is a re-
radiator 1220 having a very thin layer of heat-absorbing material ~ ;
such as oxidized stainless steel 1222, backed by a high temperature
insulator 1224 such as refractory felt. The re-radiators are
preferably substantially wider than the burners and in use the
heat absorbing layer 1222 absorbs substantial quantities of heat
which penetrate web 1200 so that the layer becomes quite hot and
re-radiates heat back to the web 1200. To improve the drying or
gas-removing effect of the heat treatment process, intake and
exhaust ducts 1230 and 1232, respectively introduce streams oE
poorly saturated air ad~acent the location where the web approaches
the burner, and withdraw more saturated air ad~acent the locations
where the web leaves the burner. To further improve the efficiency
of this system, heat from the withdrawn air can be used to pre-
heat the incoming poorly saturated air.
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~ 1088~1Z
The needled ceramic fiber panels described above are
conveniently manufactured in very long lengths, as long as 25
feet or even longer. Such panels are particularly suited for
use with very long radiant heaters, and a construction of this
type is shown in Fig. 15.
Here a ceramic fiber panel lOlO about fifteen feet long
and about one foot wide, has its edges clamped against the face
of an air seal plenum 1020 surrounding a rectangular combustion
mixture plenum 1030. Angles 1040 compress and clamp the panel
edges, being drawn against the air seal plenum face by screws
1050 that can be fitted with shoulders 1052 against which they
can be tightened at relatively high torque with a min:imum oE
attention.
A panel lOlO that is not stiffened with binder or the
like, will belly out as shown at 1060, under the influence OL the
pressure in plenum 1030. This is not particularly harmful, and
is in some respects desirable because it reduces the heat ~ -
radiation from the face of the panel to the clamping angles.
The bellying action can be reduced by pretensioning
the panel when it is mounted.
Another technique for stiffening a pliable panel is
; to needle it around a stiffener as shown in Fig 16, for example.
In this construction a wide mesh metal screen 1102 is laid in
between two layers 1108, 1110 of ceramic fibers, and a needling
o ation then perform~d to Interfelt the two fiber layers.
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Obviously many modifications and variations of the
present invention are possible in the light of the above
teachings. It is, therefore,.to be understood that within the
scope of the appended claims the invention may be practiced
otherwise than as specifically described. ~;
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