Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
12~j9~ ~
METHOD OF LENGTHENING THE FLAME FROM A GAS BURNER
Field of the Invention
This invention relates to a method of lengthening the
flame from a gas burner, particularly in a baking oven,
and is a divisional of Canadian application Serial No.
506,928, filed April 17, 1986.
Background o~ the Invention
In high-volume productlon of baked goods, for
example cookies, crackers, bread, rolls etc., baking of
the goods is conventionally effected using a band oven.
Such a band oven comprises an insulated housing
enclosing a baklng chamber of considerable length;
chambers ln commercial ovens are typically around 300
feet (approximately 90 meters~ long. A belt conveyor
formed Or a heat-reslstant material, ty`pically steel
mesh, extends longltudinally through the baking chamber
and extends beyond both ends oP the baklng chamber.
Goods to be baked are placed on the inlet end of the
belt conveyor, which moves continuously and thus carries
a continuous stream of goods through the baking chamber.
The speed of the conveyor is regulated so that the goods
be'ng baked remain wlthln the baking chamber for the
proper baklng tlme, and the baked goods are continuously
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1269~
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discharged from the outlet end of the conveyor.
Heating of the baking chamber is conventionally
effected by means of elongate gas burners which extend
transversely across the conveyor at spaced intervals,
each of these gas burners being provided with a row of
apertureq through which gas isques to form either a
large number of ind~vidual ~lame~ lylng cloqe to one
another, or a single continuous ribbon-llke flame
extending the full length of the row of apertures.
Either form oP flame will hereinafter be referred to as
a "ribbon flame". To render supervlsion and maintenance
of tne band oven as simple as possible, one side of the
housing ls provided with a serles of removable plates,
one ad~acent the end of each ga~ burner, these removable
plates each bearlng a gas supply aperture through whlch
gas ls supplled to the burner and a transparent wlndow
through which an operator can observe the gas burner to
ensure that proper combustion is taking place. The
plate may also be provided with an lnlet for power
connections to an ignlter placed ad~acent the gas burner
to ignite the gas issuing from the burner.
A ma~or consideration in the operation of such band
ovens ls to ensure uniformity of heating along the band,
since if non-uniform distribution of heat occurs, wlth
the development of hot zones on the band ad~acent each
burner and cooler spots midway between ad~acent burners~
l~i9~
the baking of the goods may be deleteriously affected,
and excessive gas consumption may occur. (References to
non-uniformity of heating herein refer to such
non-un ~ormity of heating over the relatively short
distances between ad~acent gas burner~ and are not
intended to refer to deliberate creation of zone~ of
differing temperature along the length of the band oven
which are often dellberately introduced, for example to
ensure that the goods entering the oven are rapidly
ralsed to a proper baking temperature.) Non-uniformlty
of heating can be reduced by using a large number of
burners spaced apart by relatively small distances. For
example, in prior art band ovens burners may be spaced
at intervals of 12 to 18 inches (305 to ~57 mm.) along
the len~th of the band, the burners being dlsposed ln
two row9 above and below the band.
Unfortunately, when such a lar~e number of burners
are employed the rate at which gas needs to be burned at
each burner to maintain the requisite baklng temperature
within the insulated baking chamber is low, so that only
a short flame ls produced at each burner, and the burner
thus provides a concentrated heat source, thereby
tending to produce non-uniformity of heating within the
baking chamber. Thus, improvement in the uniformity of
heating wlthin band oven~ is de~irable.
U.S. Patent 596,578 describes an acetylene burner
12~i9~3~9
in which gas is forced under pressure through a duct
into a slot where it comes into contact with air
contained within the slot and contacts a flat vertical
wall of the slot opposite the qide to which the gas
enters so that the column of gas is flattened. This
flattened column Or gas, follow ng upwardly along the
vertical face Or the wall of the slot, pas~es out of the
slot, where it is ignited and a flat, uniform and
smokeless blaze is produced.
U.S. Patent 1,213,675 to Maynard describes an oil
burner having a slot like aperture through which the oil
is discharged, and a steam conduit through which steam
passes into a large number Or apertures, which emerge
from the burner ad~acent the slot-like oil aperture, so
that the steam is pro~ected from the burner in a
substantially fan-shaped form contacting and mixing with
oil pro~ected through the oil conduit to atomize the
o~l.
U.S. Patent 1,400,024 to Caracristi describes a gas
burner in which control of the gas/air ratio is effected
by provldlng an air supply conduit, which is separate
from the gas supply condult, and through which air is
forced under pressure. The combustible gas emerges from
the burner through a set of slot-like gas apertures
arranged parallel to one another, while the air emerges
through a set of slot-llke air apertures disposed
~Xf~9~19
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between adJacent pairs of the gas apertures, so that
parallel alternating flat streams of ga~ and air emerge
from the burner. It is stated that the alternate layers
of gas and air emerging Prom the slotted outlets form a
stratified stream at the exit, the gas and air then
becoming thoroughly intermixed so that the regulation of
the air both as to velocity, pressure and volume enables
a proper quantity of ai~ to be provided dependin~ upon
the quality of the gas, thus providing maximum
ro combustlon effeciency.
U.S. Patent 1,702,625 to Anderson et al. describes
a gas burner having the form of an elongate trapezoidal
prism. This prism is hollow, having an internal
trapezoldal chamber open at both top and bottom, flanked
by two almost t-iangular prlsmatlc gas chambers closed
at their lower ends but having narrow, slot-llke
apertures at their upper ends. The Jets of combustible
gas emerging from the upper ends of these two ga3
chambers are angled inwardly towards one another so that
they meet along a line lying above the central chamber
of the gas burner. This arrangement allows air to be
drawn up through the central chamber of the gas burner,
thereby augmenting the air supply along the line at
which the gas ~ets meet and, so the patent tates,
producing an inten~ely hot flame tlp along this line.
U.S. Patent 2,418,533 to Walker describes a gas
lZtj9~19
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torch designed so that lt is capable of being operated
very hot with no possibility of flashbacks and so that
high velocity and highly oxidizing flame ~ets can be
employed without danger of the flames blowing away from
the tip or blowing out. This gas torch has a tip of
elongate rectangular form having a slot of rectangular
cross-section extending longitudinally therein.
Combustible gas is supplied to two gas conduits each of
which communlcates with the base of the slot via a row
of apertures, the two rows of apertures be!ng on opposed
sldes of the slot. Oxygen ls ~upplled through a third
conduit from which extend a row of branch condults, this
row of branch conduits running parallel to the length of
the slot. However, the oxygen branch conduits do not
open into the slot, as do the gas conduits, but instead
terminate in nozzles which extend upwardly along the
central plane of symmetry of the slot and termlnate
flush with the outer surface of the slot.
U.S. Patent 2,638,159 to Wlnkleman et al. describes
a gas burner intended for producing very hlgh
temperatures for use ln stripping coatings such as rust,
scale, paint and other organic coatings from the
surfaces of wood, metal and other bodies. In this
burner, combustible gas emerges from a single row of
apertures. Oxidizing gas is supplied via two rows of
apertures, parallel to each other and to the row of
i9~
-7
apertures for the combustible gas, both rows of
oxldizing gas apertures lying on the same side as the
combustlble ga~ apertures. The two sets Or condult3
whlch terminate in the two rows of oxidlzing gas
apertures are angled both with respect to each other and
with respect to the set of conduits which terminate in
the combustible gas aperture~, so that the stream Or
combustible gas and the two streams of ox$dizing ga~
intersect along a single line. Thi 9 retards the
velocity at whlch the oxidizing gas ls supplied to the
surface coatlng to be treated, and thus causes the
oxidation actlon Or the burner to be uniform over the
width covered by the burner, rather than concentrated ln
narrow paths correspondlng to separate Jets of oxidlzlng
gas.
U.S. Patent 2,911,035 to Nleman et al. describes a
gas burner ~or producing a soft, silent flame Or
extremely hlgh temperature. In thl~ burner, a ~ingle
casing is provided wlth a large number Or apertures,
some belng connected to the combustlble gas supply and
the remainder to the oxygen supply, the oxygen and
combustible gas apertures belng intimately mlxed
together 90 that mixlng of oxygen and combustible gas
take~ place only after the gases have left the burner,
thereby preventing flashback. However, the oxygen and
combustible gas apertures are so close together that
126~319
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'nt~mate mlxlng takes place almost at once and complete
burnlng takes place with a very short dl3tance from the
plate.
U.S. Patent 3,418,062 to Hovis et al. describes a
substantially cyllndrlcal burner lntended for use ln a
soaklng p1t. In thls burner, a central fluld fuel
outlet ls surrounded by two consentric rings of
combustion air outlets. The fuel outlet and the inner
rlng Of 8a~ outlets direct fuel and air reRpectlvely
parallel to the axis of the burner, while the outer ring
of gas outlets proJects ~ets of air diverglng away from
the axi3 of the burner.
U.S. Patent 3,706,520 to Grimm et al. describes a
compllcated fuel gas burner for a vertical shaft
furnaceO This burner includes a slngle shaft containing
four concentric conduits, the conduits containing fuel,
alr, fuel and air re~pectively reading from the
lnnermo~t conduit. The three inner conduits terminate
ln separate plena each prov'ded with a plurality of
outlets arranged to d~rect the fuel or air ~ubstantlally
perpendlcular to the axis of the shaft. The outermost
conduit opens lnto a ~acket which directs the air
backwards in the oppo~ite dlrectlon to the main fuel and
alr flow, so that the outermost air is directed
backwards parallel to the axis of the shaft.
U.S. Patent 3,850,571 to Zlnk et al. de~crlbes a
6~
g
hlgh energy flame burner intended to produce a long,
slender, rod-Jet of flame of small diameter. The flame
burner has a substantially cylindrical tube the tip Or
which is provided with a principal gas outlet orifice
through which a combustible gas Jet flows axially of the
burner. In the side wall~ of the burner are cut a
plurallty Or 3econd~ry gas outlets, whlch i~sue lnto fl
collar surrounding the burner. The forward end of this
collar is provided with a forwardly-diverging
frusto-conical flange, whlle the rear wall of the collar
ls provided with a plurality of apertures. The flow of
combustible gas through the secondary gas apertures
draws air through the apertures in the rear wall of the
collar and the resultant mlxture of gas and air is
caused by the frusto-conical flange to ~ssue from the
forward end of the collar as an outwardly diverging ring
of flame encaslng the principal gas ~et so as to assist
in the lgnltlon of the gas ln the princlpal Jet, and
prevent it from being blown out due to the hlgh velocity
of the ~et.
None of the above patents indicate any way in whlch
the rlbbon gas ~et from a gas burner used in a band oven
could be modlfled so a3 to lmprove the unlformity of
heatlng within the band oven, and there ls thus 3till a
need for a solution to the problem of non-uniformlty of
heat distrlbution in band ovens. The present inventlon
12699~9
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provides a way of improving the uniformity of heat
distribution in a band oven.
Summary of the Invention
This invention provides a method of lengthening the
flame from a gas burner which produces an elongate flame,
the method comprising directing two streams of air from
opposed sides of the flame inwardly towards the flame,
each stream of air being directed at an acute angle to the
direction of the gas issuing from the gas burner, thereby
causing the streams of air to impinge upon and lengthen
the flame.
The burner used in a baking oven comprising a housing
having walls defining a chamber, transport means for
moving articles to be baked through the chamber, and a
plurality of gas burners mounted within the chamber and
spaced from one another. At least one of these gas
burners comprises a gas supply conduit, and an elongate
gas plenum communicating with the gas supply conduit, the
gas plenum having walls defining a row of apertures spaced
from one another along the length of the gas plenum and
extending from the interior of the gas plenum to the
external surface thereof, such that gas issuing from these
apertures will burn to produce a flame extending along the
length of the gas plenum. The burner or burners further
comprises an air supply conduit and at least one air
plenum communicating with the air supply conduit, this air
~:6991~
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plenum or plena having walls defining two rows of apertures
extending from the interior of the air plenum or plena to
the external surface thereof, the two rows of apertures
being disposed on opposed sides of the rows of apertures
in the gas plenum and being directed towards the row of
apertures in the gas plenum such that air issuing from the
two rows in the air plenum will impinge upon the flame
produced by the gas issuing from the row of apertures in
the air plenum and lengthen the flame.
The lengthened flame may be used in a baking process
comprising transporting the dough goods through a baking
oven provided with a plurality of gas burners each having
walls defining a row of gas apertures, supplying gas to
the burners, whereby a stream of gas passes through the
gas apertures and burns adjacent the gas burner, and, in
at least one of the gas burners, directing two streams of
air from opposed sides of the flame produced by the burning
gas inwardly towards the flame, each stream of air being
directed at an acute angle to the direction of the gas
issuing from the gas apertures, thereby causing the streams
of air to impinge upon and lengthen the flame.
The gas burner which is used comprises an
~Z~951~L~
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elongate gas plenum having a row of gas apertures
through whlch gas can issue and burn to produce a ribbon
flame, and at least one alr plenum having walls definlng
two rows of air apertures dlsposed on opposed sldes Or
the row of gas apertures, the two rows of air apertures
belng arranged to produce two streams of air incllned
lnwardly toward the gas lssulng from the row Or gas
apertures with the streams ot air being directed at
acute angles to the stream of gas.
Brief Description Or the Drawin~s
Flgure l ls a side elevation of part of a band oven
of the lnvention wlth part of the houslng broken away to
show the arrangement of the band, the gas burners, and
associated parts o~ the oven;
Figure 2 is a vertlcal section through one of the
gas burners shown in Figure 1, this sectlon being taken
in a plane parallel to that of Figure 1 and
perpendicular to the long axis Or the burner;
F_gure 3 is a plan vlew of the burner shown in
Fi~ure 2 looking in the directlon of arrow A ln Figure
l; .
Figure 4 is a section along the line 4-4 in Figure
3; and
Figure 5 is a side elevation of the removable plate
ln the wall Or the band oven associated with the burner
2 6 9
-13-
~hown in Flgures 2, 3 and 4.
Detailed Description o~ the Drawing~
The baking oven (generally de~lgnated lO) shown ln
Figure l comprises a housing having, at lts top and
sides, an inner wall 12, an outer wall 14 and a layer of
insulation 16 formed of, for example, fiberglass
dlsposed between the inner and outer walls. The housing
will typically be about 300 feet (90 meters) long, and
only a small portion of the housing 1~ shown in Figure
1.
The houslng encloses an elongate cuboldal baking
chamber 18 along the length of which runs a belt
conveyor formed of a heat-resistant material, for
example steel wire mesh. The upper land 20 of the belt
conveyor is supported at intervals by idler rollers 22
and lies ln a horizontal plane approximately half-way up
the baklng chamber 18. The upper land 20 of the belt
conveyor transportq dough goods 24 being baked (from
lert to right in Figure 1) longltudinally through ~he
baking chamber 18, the speed of movement Or the conveyor
and the temperatures within the chamber 18 being
ad~usted so that the goods 24 are properly baked as they
pass through the oven. The lower land of the belt
conveyor runs longitudinally through the baking oven
adJacent the bottom Or the chsmber 18 and is supported
~2~i9~19
-14-
by ldler rollers 26. Although for purpo~es of lllustra-
tion the spacing between the rollers 26 has been made
the same as that between the rollers 22 in Flgure 1, ln
practice the spacing between the idler rollers 26, which
support the non-load bearing lower land of the conveyor,
can u~ually be greater than the space in between the
rollers 22, which must support the upper land 20 Or the
conveyor and the goods 24 resting thereon.
Although not shown ln Flgure 1, the belt conveyor
proJects from both end~ of the baklng chamber 18 (the
ends of the houslng are of course provided wlth
appropriate apertures to allow entry and exit of the
conveyor) and the belt conveyor 18 powered by driven
rollers at either end. The baking oven i~ also provided
wlth conventional exhaust ducts, fans and fan motors,
these part3 being omitted from Figure 1 for ease of
illustration.
The baking chamber 18 1~ heated by a large number
of gas burners (generally deslgnated 28 and 30). The
gas burners 28 and 30 are of elongate, substantially
prlsmatic form and are arranged wlth thelr long axes
horizontal and extending transversely across the baking
chamber 18, these axe3 lying parallel to the horizontal
surface of the upper land 20 of the conveyor but
perpendicular to the direction of movement thereof. The
gas burners are arranged ln two rows above and below the
~269919
upper land 20 Or the conveyor, the burner~ 28 in the
upper row may be 3paced at interval~ of about 3 to 4
feet (0.91 to 1.22 m.) whlle the burners 30 ln the lower
row may be ~paced at interval~ of about 18 to 24 inche~
(457 to 609 mm.). The burners 28 in the upper row are
supported by U-ahaped hangerq 32 fixed to the top of the
inner wall 12, whlle the burners 30 ~n the lower row are
supported by sub~tantially H-shaped supports 34 re3tin~
on the base of the oven. Although not spparent from
Flgure 1, the hangers 32 and support~ 34 do not extend
the full wldth of the oven; in3tead, each hanger of
~upport has a width of only about 1 inch (25 mm.), two
separate hangers or support~ being provided rOr each
burner 28 or 30, one ad~acent each end of the burner.
Each of the burners 28 or 30 produces a flat ribbon
flame 36 or 38 respectively, these flames extending the
full width of the upper land 20 of the conveyor. The
flames 36 from the upper burners 28 are dlrected
downwardly toward the upper land 20 and down the
direction of the movement of thi~ land. Simllarly, the
flames 38 from the lower burners 30 are d~rected
upwardly toward~ the upper land 20 and down the
direction of movement of thi~ land.
For ease of operation, supervi~lon and main~enance,
the baklng oven 10 is arranged so that all the ga~
supply conduit and other connectlon~ are arranged in
12~9~19
-16-
one slde wall of the housing, thls side wall being
designated the "operating slde" of the oven. The oven
ls viewed ln Flgure l from its non-operating slde. To
provide the necessary gas and other connectlons to each
burner, a removable plate 40 is provided in the side
wall Or the housing on the operating side of the oven.
In addltion to the gas supply, the removable plate
carrles power connectlons to an electric igniter 42
dispo~ed ad~acent each burner.
The con~truction of the burner is shown in more
detail in Figures 2 and 3. Although as noted above, the
burners 28 and 30 are arranged so that their flames 36
and 38 are dlrected tran~versely downwardly or
transversely upwardly respec~ivelg within the baking
chamber 18, for ease of reference ln Flgures 2 and 3 the
burner ha~ been shown and will be described as though i~
produced a flame di~ected vertically upwardly.
As best seen in Figure 2, the burner 28 or 30
comprises a gas plenum (generally de~lgnated 50) having
the form of an elongate hollow tube 52 bearlng on its
uppermost part a substantially cuboidal extension 54.
The upper surface Or the extenslon 54 ls formed by a
strip of teel mesh 56 running along the length of the
tube 52. The apertures ln the mesh strip 56 constltute
the row of gas apertures Or the burner. It wlll be
apparent to those ~killed ln the art Or burner
~2~9~1~
-17
technology that gas i3suing from the apertures in the
mesh str~p 56 and burnlng adJacent these apertures will
provide a contlnuous rlbbon flame extending the full
length of the mesh strlp 56.
The burner 28 or 30 Purther compri~e~ an air plenum
58. The air plenum 58 has siX flat races 60, which form
fou- complete sldewalls, and part of two further
sidewalls of a regular nonagonal prlsm, two further flat
faces 62 and 64 which lie in plane~ lncluding the
superimposed axe~ of the tube 52 and the nonagonal prism
and at an angle of 140 to one another, and a
part-cylindrlcal section 66 which extends in contact
with and surrounding the tube 52 over the 220 sector of
the tube between the Pace~ 62 and 64.
As best seen in Figure 3, the two surfaces 62 and
64 each have provided therein a row of air apertures 68
and 70 respectively. These air apertures 68 and 70 are
the outlets Or alr conduits whlch are drilled normally
through the surfaces 62 and 64 into the hollow lnterlor
Or the alr plenum 58. ~ecause of the 140 angle between
the surface~ 62 and 64, and the ~ymmetrlcal dispo~tion
o~ these surfaces about the extenslon 54 of the ga~
plenum 50, ~hen Jets of air (produced a~ explained
below) emerge Prom the aperture~ in the surfaces 62 and
64 re~pectively, these Jet~ oP air converge inwardly
towards a Jet of gas (al~o produced as described below)
~Z6~919
--18--
emerging from the apertures ln the mesh str~p 56, so
that the gas and air Jets meet along a ~lngle llne 72
(Fig. 2). The convergence of the air ~ets from either
side on to the flame produced by the burning gas
increases the length of the flame, thereby lmproving the
uniformity of heating of the baked goods on the upper
land 2Q of the belt conveyor (Fig. 1). ~y proper
adJustment Or the pressures Or the gas and air red to
the gas and alr plena 50 and 58 respectlvely (such
adJustment being easlly effected empirically by routine
methods)the air streams allow very marked elongation of
the flame. For example, it has been found that using a
gas pressure of 6 psig gauge (41.5 kPaO), and alr
apertures 0.125 inch (3.2 mm.) in diameter and spaced at
1 lnch (25 mm.) lnte-vals along the ~urfaces 60 and 62,
wlth an alr pressure of 16 inches water gauge (4 kPa.)
-esults ln a flame approxlmately 6 lnches (152 mm.)
long, as compared to a flame approxlmately 1 1/2 lnches
(38 mm.) long when no alr supply is used.
As shown in Figure 3, at the end Or the burner
whlch lies ad~acent the non-operatlng slde wall of the
oven (the rlght-hand end in Figure 3) the alr plenum is
closed by a flat endplate 74. As best seen in Flgure 4,
thls endplate 74 has a form correspondin6 to the
cross-sectlon of the air plenum 58 except that it ls
provlded with an axial cut-out surrounded by a collar
1~i9~19
76, whlch i3 integral wlth the endplate 74. the
endplate 74 iq secured to the body of the alr plenum 58
by set screws 78. A blind nipple 80 extends axially
from the adJacent end of the tube 52 and passes through
the collar 76. The collar 76, and thus the gas plenum
58, is fixed in position relative to the tube 52 by set
screws 82.
At the left-hand end (in FiB. 3) of the burner,
whlch lies ad~acent the operating slde wall o~ the oven,
the al. plenum extends axially beyond the end of the
tube 52 to an endplate 84, which is integral with the
side walls 60, 62 and 64 of the air plenum 58. The
endplate 84 carrles an integral collar 86. Unllke the
collar 76 already described, the collar 86 extends
ax ally both inwardly and outwardly from the endplate
84; the part-cylindrical recess ln the air plenum
provided by the section 66 terminates short of the
endQlate 84 so that the hollow interior of the collar 86
ln effect forms a reduced-diameter contlnuation of this
reces~. -
A gas supply tube 88 extend~ axially from the tube
52 and pa~ses through the collar 86, which ls clamped to
the gas supply tube 88 by set screw~ 90. The gas supply
tube 88 communicates wlth the lnterlor of the tube 52 of
the gas plenum and supplies combustible gas thereto.
The endplate 84 of the air plenum 58 also has an
9~L9
-20-
aperture provided thereln, but in thls case the aperture
~s spaced from the axls of the gas plenum and lle~
adJacent one of the side walls of the alr plenum. The
aperture in the endplate 84 ls surrounded by a
cyllndrical stub tu~e 92, whlch ls connected to a
flexlble metal tube 94, through whlch alr is supplied
under pressure to the air plenum. The electrlc lgnlter
42 ia provided at thi~ end Or the burner, but ln order
to show the construction Or the burner at ~hls end of
the burner more clearly, the lgniter 42, whlch serves to
ign'te gas lsquing from the burner and whlch i8 of a
conventional type, and lts assoclated power connectlon~
95 a-e lndlcated only schematlcally ln broken llnes ln
Flgure 3.
Figure 5 show~ the removable plate 40 di~posed ln
the operating side wall Or the oven adJacent each burner
28 or 30. The plate 40 ls circular and covers a
somewhat smaller clrcular aperture ln the operat!ng slde
wall Or the oven, be~ng releasably ~ecured to the slde
wall by screws. The plate 40 has a central ga~ lnlet
aperture 96, through which passes a tube whlch ls
secured to the ga~ supply tube 88 shown in Figure 3.
The plate 40 is also provided wlth an orr-center alr
inlet aperture 98 through which passe a tube whlch is
secured to the flexlble metal tube 94 connected to the
alr plenum 58. The use Or the flexlble metal tube 94
~2~i99~9
enables the same plate 40 to be used ~or both the upper
and lower rows of burners 28 and 30 respectively (Figure
1) despite the difference in the posltlons of the stub
tube 92 because of the different orientations of the two
rows of burners. A transparent window 100 is formed in
the upper part of the plate 40; thls window is of course
formed of a material reqlstant to the temperatures to
which it will be exposed by vlrtue of its proximity to
the flame issulng from the burner. The window 100 ls
provided to enable an operator to check that a proper
flame is being produced by the burner. Finally, the
plate 40 is provided with an lgniter power inlet 102
through which pass wires connected to the power
connections 95 of the igniter 42.
A~ will be apparent to those skilled ln the art,
the tubeq passing through the apertures 96 and 98 in the
plate 40 are connected to conventional gas an~
compre~sed air lines via appropriate pressure-reduction
or metering valves in order to ensure that air and gaq
are qupplled to the burner at the proper pressures,
while the power connections to ~he lgniter 42 are
connected to an appropriate power supply via a
conventional switch.
To aqqemble the burnerq 28 and 30 the blind nipple
80 and the ga~ supply tube 88 are first lnser~ed into
their respectlve apertures in the ga~ plenum 50;
1~69~1
~22--
although not shown in the drawings the appropriate ends
of the nipple 80 and the tube 88, and the apertures into
which they fitS are provided with cooperat'ng sc-ew
threads. Apart from the separate nlpple 80 and tube 88,
the gas plenum 50 is a single, integral casting.
The air plenum 58, with itq endplate 74 and
aqqociated collar 76 removed, has its part-cyllndrlcal
section 66 engaged with the left-hand end (in Figure 3)
of the tube 52, and is slid along the tube 52, from left
to ri8ht in Figure 3 until the end of the tube 52
carrying the gas supply tube 88 abuts the shoulder where
the part-cylindrlcal sectlon 66 meets the collar 86.
The endplate 74 and it~ as~oclated collar 76 are slid
over the nipple 80 to their correct positions relative
to the air plenum 58, fastened to the air plenum by
means of the set screws 78 and finally clamped to the
nipple 80 by means of the set screws 82. Flnally~ the
set screws 90 are inserted to clamp the collar 86 to the
tube 88. The nipple 80 and the tube 88 can then be
placed on the hangers 32 or supports 34 and the gas and
air supplies connected.
It will be seen that, if either the gas plenum or
the air plenum of the burner has to be replaced because
of, for example, wear or mechanical fallure, either
plenum can be replaced without the other, simply by
disassembling the burner in precisely the reverse of the
-23-
assembly operatlon descrlbed above.
From the foregolng de~crlption o~ the preferred
burner shown ln the accompanylng drawings, lt wlll be
apparent that the constructlon of thls burner allows for
easy retrofltting of exlsting band ovens provided wlth
conventional burners. Most conventional burners closely
resemble the gas plenum 50 oP the preferred burner of
the present invention, and hangers and supporters
suitable for supportlng such a conventlonal burner can
also be used wlth the preferred burner of the present
invention, s~nce the rod 74 and the gaq supply tube 80
of the burner of the present inventlon can have
dimensions identical to the cor-esponding parts of a
conventlonal burner. Moreover, existlng burners can be
mod~fled simply by sliding a gas plenum over the burner,
as already described. It will of course be necessary to
modlfy conventional plates correspondlng to the plate 40
shown in Figure 5 to provide for a pressurized alr
inlet, but in many cases it may be possible to re-use
plates already provided with a gas inlet aperture,
window and igniter power inlet s~mply by bor~ng or
otherwlse cutting an appropriate aperture 98 in the
plate. The use of the flexible metal tube 94 allows
considerable latitude ln the placing of the aperture 98
in the plate 40. The provision of the necessary
compresYed air llne and appropriate branch lines
l~t;9~
-24- .
involved to supply compressed air to the burners is well
withln the capacity of those skilled in the art, and
does not involve any difficult design considerations,
especially in view of the very low (and consequently
safe) air pressures involved.
It will be apparent to those skilled ln the art
that numerous changes and ~odifications can be made in
the preferred embodiment of the invention described
above without departing from the scope of the lnvention.
For example, the 20 angle between the gas and air
streams in the preferred burner can be varted. In fact,
almost an acute angle can be used over the range of both
(say) 5 to 80. However, a relatively small acute
angle within the range of about 10 to about 30 is
preferred, since it has been found that the use of an
angle within thi range gives maxiumum lengthening of
the flame ls~uing from the burner. Since it is
desirable to avold deflecting the gas flame from the
plane ln which it would lie if no forced air streams
were pre~ent, it is desirable that the acute angles
between the two air streamq and the gas stream be equal
to one another.
The dimen~ions of the oven of the present invention
and the burners therein can vary very widely~ and the
following suggestions are given solely by way of general
guidance. If the housing of the oven ls to be a typical
l~9t319
-25-
commercial houslng having a length of approximately 300
feet (90 meters), a helght of approximately 5 feet (1.5
meters) and a belt conveyor having a width of 38 nches
(965 mm.), it has been found appropriate to use a burner
measuring 42 1/2 inches (1079 mm.) between the endplates
74 and 84, wlth a g;lp of 1 1/2 lnche.~ (3~ ~m.) h~tw~en
the endplateq ô4 and the adJacent end o~ the tu ~e 52 .
In this burner, the surfaces 62 and 64 are each provlded
with 39 holes 0.125 lnch (3.2 mm.) ln d ameter spaced at
intervals of 1 inch (25 mm.) beginning 1 inch (25 mm.)
from the endplate 74 and termlnating 2 inches (51 mm.)
short of the opposed end of the tube 52. The tube 52 is
1 3/4 inches (44 mm.) ~n internal diameter, with the
mesh 56 spaced 1 15/16 inch (49 mm.) from the axis of
the tube 52. With the air stream~ angled at 20 to the
gas stream, as shown in the drawings, a burner of these
dimensions has the line 72 oP intersection of the air
and gas streams ~paced 5 1/8 inches (130 mm.) from the
axis of the tube 52. The air pressure used is desirably
in the range of about 8 to about 32 inches water gauge
(about 2 to about 8 kPa. gauge).
In view of the numerous possible changes and
modificatlons ln the oven, baking process and method of
the present inventlon (the~e changes and modifications
not being limited to those already discussed), the whole
of the foregoing descrlption is to be construed in an
~2~9~319
--26--
illustrative and not in a limitative sense, the scope of
the invention being defined solely by the appended
claims.
