Forced air/gas burner and baking oven incorporating same

A ribbon gas burner for use in a baking oven has a row of gas apertures disposed between two rows of air apertures through which air is forced under pressure. The streams of air issuing from the two rows of air apertures are inclined inwardly towards the gas stream, thereby lengthening the ribbon flame produced by the burner and improving the uniformity of heating within the band oven.

FIELD OF THE INVENTION 
This invention relates to a forced air/gas burner and a baking oven 
incorporating such a burner. The invention also provides a process for 
baking dough goods using such an oven. 
BACKGROUND OF THE INVENTION 
In high-volume production 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 
baking chamber of considerable length; chambers in commercial ovens are 
typically around 300 feet (approximately 90 meters) long. A belt conveyor 
formed of a heat-resistant material, typically steel mesh, extends 
longitudinally through the baking chamber and extends beyond both ends of 
the baking 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 being baked remain within the baking chamber 
for the proper baking time, and the baked goods are continuously 
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 
apertures through which gas issues to form either a large number of 
individual flames lying close to one another, or a single continuous 
ribbon-like flame extending the full length of the row of apertures. 
Either form of flame wil hereinafter be referred to as a "ribbon flame". 
To render supervision and maintenance of the band oven as simple as 
possible, one side of the housing is provided with a series of removable 
plates, one adjacent the end of each gas burner, these removable plates 
each bearing a gas supply aperture through which gas is supplied to the 
burner and a transparent window 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 inlet for power connections to an igniter placed 
adjacent the gas burner to ignite the gas issuing from the burner. 
A major consideration in the operation of such band ovens is to ensure 
uniformity of heating along the band, since if non-uniform distribution of 
heat occurs, with the development of hot zones on the band adjacent each 
burner and cooler spots midway between adjacent burners, 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-uniformity of heating over the relatively short distances between 
adjacent gas burners and are not intended to refer to deliberate creation 
of zones of differing temperature along the length of the band oven which 
are often deliberately introduced, for example to ensure that the goods 
entering the oven are rapidly raised to a proper baking temperature.) 
Non-uniformity 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 457 mm.) along the length of the band, the burners being disposed in 
two rows above and below the band. 
Unfortunately, when such a large number of burners are employed the rate at 
which gas needs to be burned at each burner to maintain the requisite 
baking temperature within the insulated baking chamber is low, so that 
only a short flame is 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 within band ovens is desirable. 
U.S. Pat. No. 596,578 describes an acetylene burner 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 side to which the gas enters so that the column of gas 
is flattened. This flattened column of gas, following upwardly along the 
vertical face of the wall of the slot, passes out of the slot, where it is 
ignited and a flat, uniform and smokeless blaze is produced. 
U.S. Pat. No. 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 of apertures, which 
emerge from the burner adjacent the slot-like oil aperture, so that the 
steam is projected from the burner in a substantially fan-shaped form 
contacting and mixing with oil projected through the oil conduit to 
atomize the oil. 
U.S. Pat. No. 1,400,024 to Caracristi describes a gas burner in which 
control of the gas/air ratio is effected by providing an air supply 
conduit, which is separate from the gas supply conduit, 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-like air apertures disposed 
between adjacent pairs of the gas apertures, so that parallel alternating 
flat streams of gas and air emerge from the burner. It is stated that the 
alternate layers of gas and air emerging from 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 air to be provided depending upon 
the quality of the gas, thus providing maximum combustion effeciency. 
U.S. Pat. No. 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 trapezoidal chamber open at both top and bottom, flanked by two 
almost triangular prismatic gas chambers closed at their lower ends but 
having narrow, slot-like apertures at their upper ends. The jets of 
combustible gas emerging from the upper ends of these two gas 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 jets meet and, 
so the patent states, producing an intensely hot flame tip along this 
line. 
U.S. Pat. No. 2,418,533 to Walker describes a gas torch designed so that it 
is capable of being operated very hot with no possibility of flashbacks 
and so that high velocity and highly oxidizing flame jets 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 communicates with the 
base of the slot via a row of apertures, the two rows of apertures being 
on opposed sides of the slot. Oxygen is supplied through a third conduit 
from which extend a row of branch conduits, 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 terminate flush with the outer surface of the 
slot. 
U.S. Pat. No. 2,638,159 to Winkleman et al. describes a gas burner intended 
for producing very high temperatures for use in 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 apertures for the 
combustible gas, both rows of oxidizing gas apertures lying on the same 
side as the combustible gas apertures. The two sets of conduits which 
terminate in the two rows of oxidizing gas apertures are angled both with 
respect to each other and with respect to the set of conduits which 
terminate in the combustible gas apertures, so that the stream of 
combustible gas and the two streams of oxidizing gas intersect along a 
single line. This retards the velocity at which the oxidizing gas is 
supplied to the surface coating to be treated, and thus causes the 
oxidation action of the burner to be uniform over the width covered by the 
burner, rather than concentrated in narrow paths corresponding to separate 
jets of oxidizing gas. 
U.S. Pat. No. 2,911,035 to Nieman et al. describes a gas burner for 
producing a soft, silent flame of extremely high temperature. In this 
burner, a single casing is provided with a large number of apertures, some 
being connected to the combustible gas supply and the remainder to the 
oxygen supply, the oxygen and combustible gas apertures being intimately 
mixed together so that mixing of oxygen and combustible gas takes place 
only after the gases have left the burner, thereby preventing flashback. 
However, the oxygen and combustible gas apertures are so close together 
that intimate mixing takes place almost at once and complete burning takes 
place with a very short distance from the plate. 
U.S. Pat. No. 3,418,062 to Hovis et al. describes a substantially 
cylindrical burner intended for use in a soaking pit. In this burner, a 
central fluid fuel outlet is surrounded by two concentric rings of 
combustion air outlets. The fuel outlet and the inner ring of gas outlets 
direct fuel and air respectively parallel to the axis of the burner, while 
the outer ring of gas outlets projects jets of air diverging away from the 
axis of the burner. 
U.S. Pat. No. 3,706,520 to Grimm et al. describes a complicated fuel gas 
burner for a vertical shaft furnace. This burner includes a single shaft 
containing four concentric conduits, the conduits containing fuel, air, 
fuel and air respectively reading from the innermost conduit. The three 
inner conduits terminate in separate plena each provided with a plurality 
of outlets arranged to direct the fuel or air substantially perpendicular 
to the axis of the shaft. The outermost conduit opens into a jacket which 
directs the air backwards in the opposite direction to the main fuel and 
air flow, so that the outermost air is directed backwards parallel to the 
axis of the shaft. 
U.S. Pat. No. 3,850,571 to Zink et al. describes a high 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 of which is 
provided with a principal gas outlet orifice through which a combustible 
gas jet flows axially of the burner. In the side walls of the burner are 
cut a plurality of secondary gas outlets, which issue into a collar 
surrounding the burner. The forward end of this collar is provided with a 
forwardly-diverging frusto-conical flange, while the rear wall of the 
collar is 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 mixture of gas and air is 
caused by the frusto-conical flange to issue from the forward end of the 
collar as an outwardly diverging ring of flame encasing the principal gas 
jet so as to assist in the ignition of the gas in the principal jet, and 
prevent it from being blown out due to the high velocity of the jet. 
None of the above patents indicate any way in which the ribbon gas jet from 
a gas burner used in a band oven could be modified so as to improve the 
uniformity of heating within the band oven, and there is thus still a need 
for a solution to the problem of non-uniformity of heat distribution in 
band ovens. The present invention provides a way of improving the 
uniformity of heat distribution in a band oven. 
SUMMARY OF THE INVENTION 
This invention provides 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 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. 
This invention also provides a process for baking dough goods, this 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. 
This invention also 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. 
Finally, this invention provides a gas burner for producing a ribbon flame, 
the gas burner comprising an elongate gas plenum having a row of gas 
apertures through which gas can issue and burn to produce a ribbon flame, 
and at least one air plenum having walls defining two rows of air 
apertures disposed on opposed sides of the row of gas apertures, the two 
rows of air apertures being arranged to produce two streams of air 
inclined inwardly toward the gas issuing from the row of gas apertures 
with the streams of air being directed at acute angles to the stream of 
gas.

DETAILED DESCRIPTION OF THE DRAWINGS 
The baking oven (generally designated 10) shown in FIG. 1 comprises a 
housing having, at its top and sides, an inner wall 12, an outer wall 14 
and a layer of insulation 16 formed of, for example, fiberglass disposed 
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 is shown in 
FIG. 1. 
The housing encloses an elongate cuboidal 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 in a horizontal plane 
approximately half-way up the baking chamber 18. The upper land 20 of the 
belt conveyor transports dough goods 24 being baked (from left to right in 
FIG. 1) longitudinally through the baking chamber 18, the speed of 
movement of the conveyor and the temperatures within the chamber 18 being 
adjusted 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 of the chamber 18 and is supported by 
idler rollers 26. Although for purposes of illustration the spacing 
between the rollers 26 has been made the same as that between the rollers 
22 in FIG. 1, in practice the spacing between the idler rollers 26, which 
support the non-load bearing lower land of the conveyor, can usually be 
greater than the space in between the rollers 22, which must support the 
upper land 20 of the conveyor and the goods 24 resting thereon. 
Although not shown in FIG. 1, the belt conveyor projects from both ends of 
the baking chamber 18 (the ends of the housing are of course provided with 
appropriate apertures to allow entry and exit of the conveyor) and the 
belt conveyor is powered by driven rollers at either end. The baking oven 
is also provided with conventional exhaust ducts, fans and fan motors, 
these parts being omitted from FIG. 1 for ease of illustration. 
The baking chamber 18 is heated by a large number of gas burners (generally 
designated 28 and 30). The gas burners 28 and 30 are of elongate, 
substantially prismatic form and are arranged with their long axes 
horizontal and extending transversely across the baking chamber 18, these 
axes 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 in two rows above and below the upper land 20 of the 
conveyor; the burners 28 in the upper row may be spaced at intervals of 
about 3 to 4 feet (0.91 to 1.22 m.) while the burners 30 in the lower row 
may be spaced at intervals of about 18 to 24 inches (457 to 609 mm.). The 
burners 28 in the upper row are supported by U-shaped hangers 32 fixed to 
the top of the inner wall 12, while the burners 30 in the lower row are 
supported by substantially H-shaped supports 34 resting on the base of the 
oven. Although not apparent from FIG. 1, the hangers 32 and supports 34 do 
not extend the full width of the oven; instead, each hanger of support has 
a width of only about 1 inch (25 mm.), two separate hangers or supports 
being provided for each burner 28 or 30, one adjacent 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 directed 
downwardly toward the upper land 20 and down the direction of the movement 
of this land. Similarly, the flames 38 from the lower burners 30 are 
directed upwardly towards the upper land 20 and down the direction of 
movement of this land. 
For ease of operation, supervision and maintenance, the baking oven 10 is 
arranged so that all the gas supply conduits and other connections are 
arranged in one side wall of the housing, this side wall being designated 
the "operating side" of the oven. The oven is viewed in FIG. 1 from its 
non-operating side. To provide the necessary gas and other connections to 
each burner, a removable plate 40 is provided in the side wall of the 
housing on the operating side of the oven. In addition to the gas supply, 
the removable plate carries power connections to an electric igniter 42 
disposed adjacent each burner. 
The construction of the burner is shown in more detail in FIGS. 2 and 3. 
Although as noted above, the burners 28 and 30 are arranged so that their 
flames 36 and 38 are directed transversely downwardly or transversely 
upwardly respectively within the baking chamber 18, for ease of reference 
in FIGS. 2 and 3 the burner has been shown and will be described as though 
it produced a flame directed vertically upwardly. 
As best seen in FIG. 2, the burner 28 or 30 comprises a gas plenum 
(generally designated 50) having the form of an elongate hollow tube 52 
bearing on its uppermost part a substantially cuboidal extension 54. The 
upper surface of the extension 54 is formed by a strip of steel mesh 56 
running along the length of the tube 52. The apertures in the mesh strip 
56 constitute the row of gas apertures of the burner. It will be apparent 
to those skilled in the art of burner technology that gas issuing from the 
apertures in the mesh strip 56 and burning adjacent these apertures will 
provide a continuous ribbon flame extending the full length of the mesh 
strip 56. 
The burner 28 or 30 further comprises an air plenum 58. The air plenum 58 
has six flat faces 60, which form four complete sidewalls, and part of two 
further sidewalls of a regular nonagonal prism, two further flat faces 62 
and 64 which lie in planes including the superimposed axes of the tube 52 
and the nonagonal prism and at an angle of 140.degree. to one another, and 
a part-cylindrical section 66 which extends in contact with and 
surrounding the tube 52 over the 220.degree. sector of the tube between 
the faces 62 and 64. 
As best seen in FIG. 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 of air conduits which are drilled normally 
through the surfaces 62 and 64 into the hollow interior of the air plenum 
58. Because of the 140.degree. angle between the surfaces 62 and 64, and 
the symmetrical disposition of these surfaces about the extension 54 of 
the gas plenum 50, when jets of air (produced as explained below) emerges 
from the apertures in the surfaces 62 and 64 respectively, these jets of 
air converge inwardly towards a jet of gas (also produced as described 
below) emerging from the apertures in the mesh strip 56, so that the gas 
and air jets meet along a single line 72 (FIG. 2). The convergence of the 
air jets from either side on to the flame produced by the burning gas 
increases the length of the flame, thereby improving the uniformity of 
heating of the baked goods on the upper land 20 of the belt conveyor (FIG. 
1). By proper adjustment of the pressures of the gas and air fed to the 
gas and air plena 50 and 58 respectively (such adjustment being easily 
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 kPa.), and air apertures 0.125 inch (3.2 
mm.) in diameter and spaced at 1 inch (25 mm.) intervals along the 
surfaces 60 and 62, with an air pressure of 16 inches water gauge (4 kpa.) 
results in a flame approximately 6 inches (152 mm.) long, as compared to a 
flame approximately 11/2 inches (38 mm.) long when no air supply is used. 
As shown in FIG. 3, at the end of the burner which lies adjacent the 
non-operating side wall of the oven (the right-hand end in FIG. 3) the air 
plenum is closed by a flat endplate 74. As best seen in FIG. 4, this 
endplate 74 has a form corresponding to the cross-section of the air 
plenum 58 except that it is provided with an axial cut-out surrounded by a 
collar 76, which is integral with the endplate 74. The endplate 74 is 
secured to the body of the air 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 FIG. 3) of the burner, which lies adjacent the 
operating side wall of the oven, the air 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 or the air plenum 58. The endplate 84 carries an 
integral collar 86. Unlike the collar 76 already described, the collar 86 
extends axially both inwardly and outwardly from the endplate 84; the 
part-cylindrical recess in the air plenum provided by the section 66 
terminates short of the endplate 84 so that the hollow interior of the 
collar 86 in effect forms a reduced-diameter continuation of this recess. 
A gas supply tube 88 extends axially from the tube 52 and passes through 
the collar 86, which is clamped to the gas supply tube 88 by set screws 
90. The gas supply tube 88 communicates with the interior of the tube 52 
of the gas plenum and supplies combustible gas thereto. 
The endplate 84 of the air plenum 58 also has an aperture provided therein, 
but in this case the aperture is spaced from the axis of the gas plenum 
and lies adjacent one of the side walls of the air plenum. The aperture in 
the endplate 84 is surrounded by a cylindrical stub tube 92, which is 
connected to a flexible metal tube 94, through which air is supplied under 
pressure to the air plenum. The electric igniter 42 is provided at this 
end of the burner, but in order to show the construction of the burner at 
this end of the burner more clearly, the igniter 42, which serves to 
ignite gas issuing from the burner and which is of a conventional type, 
and its associated power connections 95 are indicated only schematically 
in broken lines in FIG. 3. 
FIG. 5 shows the removable plate 40 disposed in the operting side wall of 
the oven adjacent each burner 28 or 30. The plate 40 is circular and 
covers a somewhat smaller circular aperture in the operating side wall of 
the oven, being releasably secured to the side wall by screws. The plate 
40 has a central gas inlet aperture 96, through which passes a tube which 
is secured to the gas supply tube 88 shown in FIG. 3. The plate 40 is also 
provided with an off-center air inlet aperture 98 through which passes a 
tube which is secured to the flexible metal tube 94 connected to the air 
plenum 58. The use of the flexible metal tube 94 enables the same plate 40 
to be used for both the upper and lower rows of burners 28 and 30 
respectively (FIG. 1) despite the difference in the positions 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; this 
window is of course formed of a material resistant to the temperatures to 
which it will be exposed by virtue of its proximity to the flame issuing 
from the burner. The window 100 is 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 igniter power inlet 102 through which pass wires 
connected to the power connections 95 of the igniter 42. 
As will be apparent to those skilled in the art, the tubes passing through 
the apertures 96 and 98 in the plate 40 are connected to conventional gas 
and compressed air lines via appropriate pressure-reduction or metering 
valves in order to ensure that air and gas are supplied to the burner at 
the proper pressures, while the power connections to the igniter 42 are 
connected to an appropriate power supply via a conventional switch. 
To assemble the burners 28 and 30 the blind nipple 80 and the gas supply 
tube 88 are first inserted into their respective apertures in the gas 
plenum 50; although not shown in the drawings, the appropriate ends of the 
nipple 80 and the tube 88, and the apertures into which they fit, are 
provided with cooperating screw threads. Apart from the separate nipple 80 
and tube 88, the gas plenum 50 is a single, integral casting. 
The air plenum 58, with its endplate 74 and associated collar 76 removed, 
has its part-cylindrical section 66 engaged with the left-hand end (in 
FIG. 3) of the tube 52, and is slid along the tube 52, from left to right 
in FIG. 3 until the end of the tube 52 carrying the gas supply tube 88 
abuts the shoulder where the part-cylindrical section 66 meets the collar 
86. The endplate 74 and its associated 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. Finally, 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 
failure, either plenum can be replaced without the other, simply by 
disassembling the burner in precisely the reverse of the assembly 
operation described above. 
From the foregoing description of the preferred burner shown in the 
accompanying drawings, it will be apparent that the construction of this 
burner allows for easy retrofitting of existing band ovens provided with 
conventional burners. Most conventional burners closely resemble the gas 
plenum 50 of the preferred burner of the present invention, and hangers 
and supporters suitable for supporting such a conventional burner can also 
be used with the preferred burner of the present invention, since the rod 
74 and the gas supply tube 80 of the burner of the present invention can 
have dimensions identical to the corresponding parts of a conventional 
burner. Moreover, existing burners can be modified simply by sliding a gas 
plenum over the burner, as already described. It will of course be 
necessary to modify conventional plates corresponding to the plate 40 
shown in FIG. 5 to provide for a pressurized air 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 simply by boring or otherwise 
cutting an appropriate aperture 98 in the plate. The use of the flexible 
metal tube 94 allows considerable latitude in the placing of the aperture 
98 in the plate 40. The provision of the necessary compressed air line and 
appropriate branch lines involved to supply compressed air to the burners 
is well within 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 in the art that numerous changes and 
modifications can be made in the preferred embodiment of the invention 
described above without departing from the scope of the invention. For 
example, the 20.degree. angle between the gas and air streams in the 
preferred burner can be varied. In fact, almost an acute angle can be used 
over the range of both (say) 5.degree. to 80.degree.. However, a 
relatively small acute angle within the range of about 10.degree. to about 
30.degree. is preferred, since it has been found that the use of an angle 
within this range gives maximum lengthening of the flame issuing from the 
burner. Since it is desirable to avoid deflecting the gas flame from the 
plane in which it would lie if no forced air streams were present, it is 
desirable that the acute angles between the two air streams and the gas 
stream be equal to one another. 
The dimensions 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 is to be a typical 
commercial housing having a length of approximately 300 feet (90 meters), 
a height of approximately 5 feet (1.5 meters) and a belt conveyor having a 
width of 38 inches (965 mm.), it has been found appropriate to use a 
burner measuring 421/2 inches (1079 mm.) between the endplates 74 and 84, 
with a gap of 11/2 inches (38 mm.) between the endplates 84 and the 
adjacent end of the tube 52. In this burner, the surfaces 62 and 64 are 
each provided with 39 holes 0.125 inch (3.2 mm.) in diameter spaced at 
intervals of 1 inch (25 mm.) beginning 1 inch (25 mm.) from the endplate 
74 and terminating 2 inches (51 mm.) short of the opposed end of the tube 
52. The tube 52 is 13/4 inches (44 mm.) in internal diameter, with the 
mesh 56 spaced 1 15/16 inch (49 mm.) from the axis of the tube 52. With 
the air streams angled at 20.degree. to the gas stream, as shown in the 
drawings, a burner of these dimensions has the line 72 of intersection of 
the air and gas streams spaced 51/8 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 modifications in the oven, 
baking process and method of the present invention (these changes and 
modifications not being limited to those already discussed), the whole of 
the foregoing description is to be construed in an illustrative and not in 
a limitative sense, the scope of the invention being defined solely by the 
appended claims.