Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a new and im-proved indus-
trial oven having means for recirculating air to produce a hot
air curtain for effectively minimizing the loss of hot air
through one or both of the access openings through which the
articles to be heat treated are conveyed into and out of the
oven.
Typically, a mechanical conveyor is employed to carry
a continuous series of the artlcles to be heat treated into the
oven through one access opening, through the tunnel space in
the oven, and out of the oven through another access opening.
Some of the hot air in the oven tends to escape through the
access openings, which must be kept continuously open. The
escape of the hot air causes wastage of energy. Moreover, the
interior of the oven is cooler near the access openings than in
the central portion of the oven. Furthermore, the escaping hot
air raises the room temperature outside the oven, in the vicin-
ity of the access openings, so that uncomfortably hot working
conditions may be produced in the room.
One object of the present invention is to provide an
industrial oven having new a.nd improved means for minimizing
the escape of hot air from the oven through the conveyor access
openings, so as to minimize the wastage of energy, while also
reducing the ambient temperature in the room outside the oven
and improving the uniformity of the high temperature within the
oven.
A further object is to provide a new and improved heat
retention system which is readily applicable to both new and
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existing industrial ovens, at low cost.
These and other objects of the present invention can
be achieved by providing an industrial oven for heat treating
a series of articles, such oven comprising a tunnel enclosure
having a tunnel space therein through which the articles to be
heat treated may pass, the tunnel enclosure having side walls
and upper and lower walls, the side walls including terminal
walls having access openings through which the articles to be
heat treated may pass into and out of the tunnel space, con-
veyor means for carrying the articles through the access open-
ings and the tunnel space, heating means for supplying heat to
the tunnel space to heat treat the articles, a nozzle communi-
cating with the tunnel space near the upper wall and near one
terminal wall for directing a stream of hot air downwardly
across the corresponding access opening in such terminal wall,
the nozzle being angled downwardly into the tunnel space and
away from the corresponding access opening to resist the escape
of hot air from the tunnel space through the access opening, an
exhaust structure having an exhaust opening communicating with
the tunnel space in the vicinity of the nozzle to provide for
thelowering of the air pressure in the tunnel space near the
upper portion of the corresponding access opening, and air
handling means for withdrawing hot air from the tunnel space
through the exhaust opening while blowing hot air into the tun-
nel space through the nozzle for minimizing the escape of hot
air from the tunnel space through the corresponding access opsn-
ing. The nozzle is preferably aimed downwardly into the tunnel
space and away from the access opening at an inclined angle
which is less than 90 to the horizontal. Such inclined angle
is preferably in the range -from ~5 to 85 with reference to
the horizontal, and preferably is approximately 65.
The air handling means may comprise a circulating
blower connected between the exhaust opening and the nozzle for
withdrawing hot air from the tunnel space through the exhaust
opening and for blowing the hot air into the tunnel space
through the nozzle.
The heating means may include an air heating and cir-
culating system for drawing air from the tunnel space, heating
such air and discharging the heated air into the tunnel space.
As an alternative to a separate blower, the air handling means
may comprise an exhaust duct connected between the exhaust open-
ing and the intake side of the air heating and circulating
system, and a supply duct connected between the nozzle and the
discharge side of such system, for withdrawing air through the
exhaust opening while supplying heated air to the nozzle.
Further objects, advantages and features of the
present invention will appear from the following description,
taken with the accompanying drawings, in which:
Fig. 1 is a diagrammatic end view of an industrial
oven to be described as an illustrative embodiment of the
present invention.
Fig. 2 is a diagramma-tic plan view of the industrial
oven.
Fig. 3 is a fragmentary diagrammatic longitudina]
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section, taken through the industrial oven of Figs. 1 and 2.
Fig. 4 is an exploded perspective view of a nozzle
construction for the oven of Figs. 1-3.
Fig. 5 is a fragmentary diagrammatic longitudinal
section, similar to Fig. 3, but showing a modified construction.
Fig. 6 is a temperature chart showing the variation
of the oven temperature along the length of the oven, with and
without the present invention.
As just indicated, Figs. 1-4 illustrate an illustra-
tive embodiment of the present invention, in the form of anindustrial oven 10 comprising a tunnel enclosure 12 having a
pair of longitudinal side walls 14, a pair of end or terminal
side walls 16, an upper wall 18, and a lower wall or floor 20.
A heated tunnel space 22 is provided within the tunnel enclo-
sure 12, as shown in Fig. 3.
Typically, a conveyor 24 is employed to carry a con-
tinuous series of articles 26 through the tunnel space 22 in
the oven 10. In this way, the articles 26 are baked or other-
wise heat treated by the heat in the oven 10. For example, the
oven 10 may be employed to bake paint which has been applied to
the articles 26.
The illustrated conveyor 20 comprises a longitudinal
rail 28 extending through the tunnel space 22 of the tunnel 10.
The rail 28 is adapted to support a continuous series of car-
riages 30 having rollers 32 adapted to travel along the rail 28.
~ach carriage 30 includes a hanger 33 for supporting one of
the articles 26 to be heat treated. A continuous conveyor chain
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34 may be e~mployed to advance the carriages 30 along the rail
28. It will be understood that the conveyor 24 includes
suitable driving means, not shown, for advancing the conveyor
chain 34.
Each of the end walls of the oven ~O is formed with
a conveyor access opening 36, through which the articles 26 to
be heat treated are carried by the conveyor 24. The upper
portion of each access opening 36 is in the form of a slot 38
through which the conveyor rail 28 extends. Each access opening
36, including the slot portion 38, is kept open at all times to
accommodate the movement of the articles 26 and the conveyor
carriages 30 through the openings 36. The present invention
deals with the problem of minimizing the escape of hot air from
the oven 10 through the conveyor access openings 36.
As shown in Fig. 3, the tunnel space 22 within the
oven 10 may be heated by the heating system 40 which recircu-
lates and heats the air in the tunnel space 22. As shown, the
heating system 40 comprises a main oven fan ox blower 42 which
draws air from the tunnel space 22 through a return duct 44.
The fan 42 then blows the air through a furnace or heat ex-
changer 46, which heats the air. The hot air from the furnace
46 is discharged into an oven duct 48 which distributes the hot
air throughout the oven 10 and discharges the hot air throug'n a
plurality of nozzles or openings 50, into the tunnel space 22
within the oven 10.
Typically, an oven exhaust fan 52 is provided for
exhausting waste gases, vapors and smoke from the tunnel space
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22 in the ovenlO, preferably through the upper wall 18. Some
of the hot air in the tunnel space 22 is also exhausted by the
oven exhaust fan 52. The intake side of the oven exhaust fan
52 is connected to the upper portion of the tunnel space 22 by
an exhaust duct 54. The discharge side of the fan 52 may be
connec ted to a discharge duct 56, leading to the atmosphere
through a suitable pollution control system, not shown.
The oven exhaust fan 52 reduces the pressure within
the tunnel space 22 in the oven 10, with the result that the
10 fan 52 effective]y draws outside air into the tunnel space 22
through the conveyor access openings 36. Such outside air re-
places the air and the waste products discharged by the oven
exhaust fan 52.
It has been found that, in the absence of the present
invention, there is a significant loss of hot air from the
oven 10 through the conveyor access openings 36, particularly
through the upper portions of such openings. This loss of hot
air results in a cooling of the tunnel space 22 within the oven
10 in the vicinity of the conveyor access openings 36. More-
20 over, the hot air, spilling out of the oven 10 through the open-
ings 36, produces a significant heating of the room, so that
uncomfortably hot working conditions can result in the vicinity
of the openings 36. Of course, the loss of hot air from the
oven 10 represents a waste of energy.
The present invention provides heat retention means 58
for reducing and minimizing the loss of hot air through the
conveyor access openings 36. As indicated in Fig. 2, such heat
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retention means 58 may be provided at both ends of the oven lO,
in connection with both of the conveyor access openings 36.
The details of the heat retention means 58 are shown in Fig. 3
in connectlon with one of the access openings 36. The heat re-
tention means 58 may be the same at the opposite end of the
oven 10~
As shown in Fig. 3, the heat retention means 58 may
comprise a nozzle 60 communicating with the tunnel space 22 in
the oven lO near the upper wall 18 and near the terminal wall
16, in which the conveyor access openi.ng 36 is provided. The
nozzle 60 is adapted to direct a stream o~ hot air downwardly
within the oven, across the opening 36. The nozzle 60 is
angled downwardly into the tunnel space 22 and away from the
access opening 36 to resist the escape of hot air from the
-tunnel space 22 through the opening 36.
The heat retention means 58 may also include an ex-
haust structure 62 which provides an exhaust opening 64 corNmun-
icating with the tunnel space 22 in the vicinity of the nozzle
60 to provide for the lowering of the air pressure in the tunnel
space 22 near the upper portion of the access opening 36. In
Fig. 3, the region of relatively low pressure is indicated in
broken lines at 66.
The heat retention means 58 may also include air
handling means 68 for withdrawing hot air from the tunnel space
22 through the exhaust opening 64 while blowing hot air into
the tunnel space through the nozzle 60. The stre~m of hot air
from the nozzle 60 travels downwardly across the inner side of
the opening 36 and angles away from the opening 36 and into the
tunnel space 22. Such stream of air tends to be reflected up-
wardly by the oven duct 48 and the floor 20, as indicated by
the arrows in Fig. 3, so that a considerable portian of the air
stream tends to return to the exhaust opening 64.
In the embodiment o-E Fig. 3, the air handling means
68 may comprise a separate recirculating blower or fan 70,
driven by a motor 72. The intake side of the blower 70 is con-
nected by a duct 74 to the exhaust opening 64, while the dis-
charge side o~ the blower 70 is connected by a duct 76 to thenozzle 60. The downwardly inclined air stream from the nozzle
60 and the withdrawal of air through the exhaust opening 64 have
the combined e~fect of substantially reducing and minimizing the
loss of hot air through the adjacent access opening 36. As
shown in Fig. 3, the nozzle 60 is quite close to the upper
portion of the access opening 36 and is located between the
opening 36 and the exhaust opening 64. The nozzle 60 is aimed
downwardly into the tunnel space 22 and away from the access
opening 36 at an inclined angle which is less than 90 to the
horizontal. For satisfactory results, it is believed that the
inclined angle of the nozzle 60 should be in the range from 45
to 85 with reference to the horizontal. An inclined angle of
approximately 65 to the horizontal has been found to be partic-
ularly advantageous and effective in reducing the loss of hot
air from the oven 10 through the conveyor access opening 36.
The nozzle 60 preferably has a discharge opening 80
which is generally in the form of a narrow rectangle to produce
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a flat stream of air having a width corresponding generally to
the width of the access opening 36. ~ shown in Fig. 3, the
nozzle 60 extends downwardly below the level of ~he conveyor
rail 28. It will be seen from Fig. 4 that the nozzle 60 is
formed with a notch ~2 to afford clearance for the conveyor rail
28. Fig. 4 also shows the manner in which the duct 76 is
flared to join with the nozzle 60.
The stream of air from the nozzle 60 should have a
relatively low velocity so that the air stream will not unduly
disturb the articles 26 which are carried on the hangers 32 of
the conveyor 24. If the velocity of the air stream is exces-
sive, the air stream may tend to blow some of the articles 26
off the hangers 33. It has been found that a low velocity air
stream is effective to minimi.ze the loss of hot air through the
conveyor access openings 36.
The desirable velocity oE the air stream depends upon
the height of the conveyor access opening 36, across which the
air stream is to travel. It has been found that good results
are achieved by an air stream velocity which is 900 feet per
minute for each foot of height of the opening 36. Thus, for an
access opening 36 having a height of 5 feet, the air velocity
should be 4500 ft/min., pursuant to this formula.
It has been found that good results are achieved with
a nozzle 60 having an aperture width of 1 inch, when the height
of the conveyor opening 36 is 5 feet or less. When the height
of the conveyor opening 36 is greater than 5 fee~ it is prefer-
able to employ a nozzle 60 having an aperture width of 2 inches,
~5~g
to provide an air stream having an initial thickness of 2 inches.
Fig. 5 illustrates the fact that it is not always
necessary to provide a separate blower to circulate hot air out
of the nozzle 60 and into the exhaust opening 64. The modified
embodiment of Fig. 5 has modified heat retention means 88,
whereby the main heating system 40 of the oven 10 produces a
circulation of the hot air out of the nozzle 60 and into the
exhaust opening. As shown, hot air is supplied to the nozzle
by a duct 90 connected between the nozzle 60 and the main oven
duct 48 which receives hot air from the discharge side of the
10 heat exchanger or furnace 46. The circulation of the hot air
is produced by the main oven fan 42.
In Fig. 5, a return duct 92 is connected between the
e~aust opening 64 and the main return duct 44 of the oven heat-
ing system 40. Thus, the main oven fan 42 is effective to draw
hot air into the exhaust opening 64. In the modified embodiment
of Fig. 5, the main oven heating system 40 must be capable of
circulating the additional hot air which must be discharged from
the nozzle 60 and drawn into the exhaust opening 64. In the
embodiment of Fig. 5, the velocity of the air stream from the
20 nozzle 60 should be approximately the same as in the case of
the embodiment of Fig. 3, as previously discussed.
Fig. 6 is a reproduction of two temperature charts 96
and 98, produced by a recording thermometer, showing the vari-
ation of the temperature along the length of the -tunnel space
22 in the oven 10. Each of these charts was made by mounting a
temperature sensor on one of the conveyor hangers 22, so that
the temperature sensor was carried through the oven lO along
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the length thereof. The recording thermometer than produced
a chart showing the temperature as a function of time.
The temperature chart 96 was produced without the
present invention, while the -temperature chart 98 was produced
with the present invention. It will be seen that the chart 96
shows a considerable variation in the temperature along the
length of the oven 10. Following entry of the temperature
sensor into the oven 10 through one of the access openings 36,
the chart 96 shows a gradual upward slope 96a, representing a
temperature rise in the oven near the first access opening 36,
a temperature peak 96b in the central portion of the oven 10,
and a gradual downward slope 96c, representing a decreasing tem-
perature near the exit opening 36.
The second temperature chart 98, representing the tem-
perature variation with the use of the present invention, shows
a much steeper temperature rise 98a, a broad temperature plateau
98b, and a steep downward slope 98c, representing the rapid drop
in the temperature at the access opening 36. The broad temper-
ature plateau 98b indicates that the temperature in the oven 10
is uniformly high for much of the length of the oven. The
plateau 98b rises to a somew'nat higher temperature from the peak
96b, thus indicating a greater retention of heat in the oven.
It thus clearly appears that the present invention
results in a somewhat higher temperature within the oven and
significantly improved temperature uniformity along the length
of the oven.
The heat retention means of Figs. 2 and 3, or the
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alternate means 88 of Fig. 5, may be provided at either or both
end walls 16, to minimize the loss of heat through either or
both access openings 36. There is a particular advantage in
providing the heat retention means at both ends of the oven, in
that the downwardly inclined streams of air from the nozzles 60
at both ends o~ the oven travel in opposite directions along
the length of the oven toward the central portion of the oven,
where the oppositely directed streams impinge upon each other
and neutralize each other, so that neither stream travels to
the far end of -the oven. Thus, there is no tendency for either
stream of air to produce an outwardly current of air at the far
end of the oven.
As previously indicated, the stream of hot air from
each nozzle 60 is deflected upwardly and also in a retrograde
direction by the oven duct 48, which thus acts as baffle means
to prevent the air stream from travelling any great distance
along the length of the oven 10. If some other heating arrange-
ment is used, not involving the oven duct 48, separate baffle
means may be provided to deflect the air stream from the nozzle
60, so as to break up the longitudinal flow of the air toward
the far end of the oven.
It will be evident that the present invention mini-
mizes the escape of hot air from the oven through the conveyor
access openings, so as to reduce the wastage of energy, while
also improving the uniformity of the high temperature within the
oven along its length. The present invention also minimizes the
heating of the room by the oven, particularly in the regions
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near the conveyor access openings in the oven walls.
The present invention effectively minimizes the
escape o smo'~e and other waste products from the oven through
the convey~ access openings, as well as minimizing the escape
of hot air. Because of the reduced loss of hot air from the
oven, it is possible to install the oven in a smaller room,
without causing excessively hot conditions in the room around
the oven.
The stream of air from the nozzle 60 spreads laterally
and scrubs alony the sidewalls 14 of the oven, -thus effectively
blocking the entire width of the oven, against the escape of
hot air. The present invention may be used with ovens of all
si~es, and with conveyor access openings of all sizes in the
walls of industrial ovens.
The nozzle 60 preferably projects downwardly, substan-
tially below the level of the exhaust opening 64. With this
construction, the low pressure zone produced by the exhaust
opening 64 does not cause any significant deflection of the
air stream from the nozzle 60.
The exhaust opening 64 and the nozzle 60 should be
quite close to the access opening 36 in the end wall 16~ If the
exhaust opening 64 is moved farther away from the nozzle 60, the
exhaust opening tends to produce a greater bending of the air
stream from the nozzle 60.
In the illustrated oven, the conveyor 24 carries the
articles 26 along a straight path through the oven. However,
the present invention may also be employed very effectively in
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connection with an oven in which the conveyor carries the
articles along a winding or serpentine path. The present in-
vention is still very effective to minimize the escape of hot
air through the conveyor access opening or openings.
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