Note: Descriptions are shown in the official language in which they were submitted.
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B~CKGROUND O~ TIIE INYENTION
The present invention relates to an oven for drying or curing articles and
particularly relates to a reversible, convection air, cross flow drying or curing oven. More
particularly, the present invention relates to a drying or curing oven providing for manual
or automatic reversal of cross flow convection air currents within the oven at periodic
intervals to obtain uniform drying or curing characteristics substantially throughout the
entirety of the oven.
In batch type ovens, workpieces are frequently placed on carts and disposed in the
work zone or heat chamber of the oven for drying or curing. Heated air is then supplied
to the oven chamber through various ductwork and the workpieces are dried or cured over
time. The flow pattern of the convection air current thus obtains a uniformity with time
within the oven chamber. A uniform air flow pattern over a substantial period of time,
however, creates temperature gradients within the oven chamber. For example, in
certain ovens, the ductwork is arranged to flow heated air from one side of the oven to
the opposite side or vertically between the top and bottom of the oven. The incoming air
on the supply side is thus hotter than the outgoing air on the return side. This causes the
workpieces adjacent the incoming supply of hot air to dry or cure at a rate faster than the
workpieces located adjacent the relatively cooler, though heated, air near the return side
of the oven. Thus, the dryin~ or curing characteristics of the workpieces vary dependent
upon their location within the oven because a different temperature is applied thereto at
each location.
This variance in temperature within the oven chamber is particularly critical in
drying or curing flat sheets, for example, capacitor components which may vary in size
from 8~ inches by 11 inches to 4 feet by 8 feet. Flat sheets will often warp, crack or
otherwise distort when hot air at different temperatures is applied over the entirety of
the surface of the sheets. Moreover, it will be appreciated from the foregoing that the
optimum oven residence time for proper drying or curing of workpieces in batch type
ovens is not dependent on the workpiece which first dries or cures. Rather, if all the
workpieces are to be dried or cured, the residency time for all workpieces within the oven
is dependent on the workpiece which last dries or cures. Thus, economy of oven operation
is sacrificed in those batch type ovens ~yhere temperature gradients exist if all workpieces
are to be entirely dried or cured over the proper period of time. Also, economy of oven
operation is affected by the temperature necessary to dry or cure the workpieces. For
example, in batch type ovens, the temperature of the incoming air is usually higher than
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necessary in order that the workpieces closest to the return will
be dried or cured at the designed temperature. Thus because of
the existence of temperature gradients in batch ovens, heated air
must be supplied at non-optimum; e.g., higher, temperatures. The
operation of the oven therefore requires substantially greater
energy input than would be necessary if uniform temperatures
could be maintained throughout the oven chamber. Accordingly,
there has arisen a need for a new and improved drying or curing
oven of the convection air current type which minlmizes or
eliminates the foregoing and other problems associated with prlor
convection air current drying or curing ovens and provides a
heated air flow pattern affording substantially uniform heating
of the workpieces over the duration of their time within the
oven.
Accordingly the present invention provides an improved reversible
cross flow oven for uniformly and evenly drying or curing
workpieces within the oven.
The present invention again provides an improved reversible cross
flow oven for drying or curing workpieces within the oven chamber
wherein the workpieces are substantially uniformly heated over
the duration of their residency within the oven chamber.
The present invention further provides an improved reversible
cross flow oven for drying or curing workpieces which minimizes
or eliminates the tendency of workpieces to crack, warp other
otherwise distort upon application of heat to the workpieces
within the oven chamber.
The present invention again provides an improved reversible cross
flow oven of the batch type for drying or curing workpieces in
which the oven is controlled to match the heated air currents to
the particular drying or curing process; e.g., to achieve a
substantially precise and like drying or curing temperature for
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each workpiece within the oven regardless of its orientation and
location within the oven chamber.
According to the present invention there is provided a reversible
cross flow drying or curing oven comprising: an oven housing
having opposed side walls defining a drying or curing chamber
therebetween for receiving articles to be dried or cured, first
and second ducts disposed along the respective opposite side
walls of said housing and having openings for supplying air into
and receiving air from said oven chamber, a crossover air supply
duct within said oven overlying the curing chamber and connected
by supply passageways at opposite ends to said first and second
ducts for supplying air thereto, damper means located between the
supply passageways and the first and second ducts, a crossover
air return duct within said oven ad~acent the air supply duct
overlying the curing chamber and connected by return passageways
at opposite ends to said first and second ducts for receiving air
therefrom, a damper means located between the return passageways
and the first and second ducts a cupola housing overlying the air
supply and air return air from the return duct, having means for
conditioning the return air, and means for recirculating the air
to the air supply duct for return to the curing chamber, and
means for periodically opening and closing an air supply damper
and an air return damper to periodically reverse the flow of air
across said oven chamber.
In one embodiment of the present invention said recirculating
means includes a fan in the cupola housing for forcing heated air
through said ducts the fan being disposed to force air
unidirectionally through the cupola housing, the first and second
supply ducts and said first and second return ducts. Suitably
wherein the cupola housing includes an opening to atmosphere for
drawing make-up air into the cupola housing. Desirably wherein
the first and second duct openings are ad~ustable for controlling
the rate and direction of the air flow therethrough.
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In a further embodiment of the present invention in which:
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BREP Dr5CRlPTlON OP TIIE DRAWINGS
FIGURE 1 is a side elevational view of 8 reversible cross flow drying or curing oven
constructed in accordnnce with the present invention Qnd illustrating a portion of the
heated air circulating system therefor;
FIGURE 2 is an end elevational view thereof also illustrating a portion of the heated
air circulating system;
FIGURE 3 is a plan view thereof likewise illustrating a portion of the heated air
circulating system;
FIGURE 4 is a schematic perspective view of a portion of the heated air circulating
of the oven hereof with the top of the oven cupola broken out and particularly illustrating
the locations of flow control devices for establishing the flow patterns of heated through
the oven chamber; and
FIGURE S is a schematic illustration of a pneumatic circuit for operating the flow
control devices used in the air circulating system of the drying or curing oven hereof.
DESCRlPTION O~ A PRE~ERRED EMBODINIENT
.
Referring now to the drawings, particularly to Figures 1 and 2, there is illustrated a
reversible cross flow drying or curing oven constructed in accordance with the present
invention and generally designated 10. Oven 10 includes a generally box-like housing 12
having side walls 14, and end walls 16, and a top wall 18. Doors 20 are hingedly mounted
on each of the opposite end walls 16 and open outwardly to provide access to the interior
of oven 10 from opposite ends thereof. Articles for drying or curing, such as workpieces,
may be carried on racks, schematically illustrated at 15, mounted on rollers whereby the
articles may be rolled through open doors 20 at one end of oven 10 into the ovens heat
chamber, generally designated 22, defined between side and end walls 14 and 16,
respectively, and below top wall 18. Accordingly, dried or cured articles may be rolled
from heat chamber 22 through doors 20 at the opposite ends of the oven. Thus, oven 10 is
useful for drying or curing articles in a continuous batch type process. On top of oven
housing 12 is a cupola 24 housing mechanicals and ductwork described hereinafter.
The interior of oven 10 is provided with an air circulating system comprised of
ductwork including first and second elongated, generally horizontally extending, ducts 26
and 28, respectively, disposed along the respective opposite side walls 14 of housing 12.
Ducts 26 and 28 are spaced laterally one from the other and further define therebetween
the heat chamber 22. Each duct 26 and 28 includes a plurality of openings or apertures
30 longitudinally spaced one from the other along its inwardly facing wall for flowing air
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in~^ or out of heat chamber 22 in a manner described hereinafter. Each opening 30 is
provided with adjustable louvers 32 wl~ich control the rate of flow of heated air into and
out of oven chamber 22 as well as its direction when flowing into chamber 22. Louvers 32
may be manually adjusted for each drying or curing operation in accordance with the
characteristics of the articles to be dried or cured.
Cross over supply and return ducts 34 and 36, respectively, are provided.
Particularly, supply duct 34 includes a main supply passage 38 and a pair of downwflrdly
directed, supply passageways 40 and 42 in communication at their upper ends with the
respective opposite ends of main supply passage 38. Supply passageways 40 and 42
communicate at their lower ends, with first and second side ducts 26 and 28, respectively.
Comrnunication between supply passageways 40 and 42 and ducts 26 and 28 is controlled
by suitable flow control devices, such as dampers 44 and 46, respectively. Thus, flow of
air through main supply passage 38 may be directed to one or the other of side ducts 26
and 28 through its corresponding passageways 40 or 42 by operating supply dampers 44 and
46 to close or open the passages therebetween. That is, by closing damper 46 and opening
damper 44, flow of air may be directed from main supply passage 38 through passageway
40 into side duct 26 and into oven chamber 22 through openings 30 in side duct 26.
conversely, by closing dampet 44 and opening damper 46, flow of air may be directed from
main supply passage 38 through passageway 42 into side duct 28 and into oven chamber 22
through openings 30 in side duct 28.
Return duct 36 includes a main return passage 48 and a pair of downwardly directed
passageways 50 and 52 in communication at their upper ends with the respective opposite
ends of main return passage 48. Return passageways 50 and 52 communicate, at their
lower ends, with first and second ducts 26 and 28, respectively. Communication between
return passageways 50 and 52 and ducts 26 and 28 is similarly controlled by suitable flow
control devices, such as damper 54 and 56, respectively. Thus, flow of return air from one
or the other of ducts 26 and 28 may be directed to main return passage 36 through the
associated return passageway 50 or 52 by opening the corresponding dampers 54 or 56.
Similarly, return flow of air from one or the other of side ducts 26 and 28 may be blocked
from returning to main return passgge 36 by closing the associated damper 54 or 56. That
is, by closing damper 54 and opening d~amper 56, return air may flow from duct 28 through
return passageway 52 into main return passage 36. Conversely, by closing damper 56 and
opening damper 54, return air may flow from duct 26 through return passageway 50 into
main return passage 36.
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Referring now to FIGURE 5, there is illustr~ted a pneumatic control circuit for
operating dampers 44, 46, 54, and 56. Partlcularly, each damper is controlled by an
associated air cylinder 44a, 46a, 54a, and 56a. A supply line Sl provides air under
pressure from a supply source 53 through a four way, two position, solenoid actuated,
spring returned valve 55, the solenoid and spring being designated 57 and 59, respectively.
Thus, in the illustrated position of valve 55, air is supplied cylinders 44a and 56a to
retract the associated pistons and consequently rotate, through an appropriate linkage,
not shown, dampers 44 and 56 to their illustrated open positions. Similarly, air supplied
cylinders 46a and 54a extends the associated pistons and consequently rotates, through an
appropriate linkage, not shown, dampers 46 and 54 to their illustrated closed positions. By
energizing solenoid 57, valve 55 is shifted. Thus, in the shifted position of valve 55, air is
supplied cylinders 46a and 4a to retract the associated pistons and close dampers 46 and
54. Simultaneously, air is supplied cylinders 44a and 56a to extend their associated
pistons and open dampers 44 and 56. Thus, the dampers operate in pairs; i.e., a supply and
a return damper, each on opposite sides of the oven chamber from the other, are always
open or closed, while the other pair of the supply and return dampers on opposite sides of
the oven chamber are always closed or open, respectively.
Referring back to FIGURE 4, cupola 24 comprises a generally box-like housing 60
secured above both cross over main supply and return passages 34 and 36, respectively.
Openings 62 and 64 are provided through the tops of ducts 34 and 36, respectively. Thus,
communication is provided between the interior of cupola 24 at one end thereof with
supply duct 34 through opening 62 and at its opposite end with return duct 36 through
opening 64. Disposed between openings 62 and 64 and within cupola housing 60 is a heater
66. Heater 66 may comprise any conventional heating element, such as a steam heating
coil with suitable external connections to a source of steam, or an electric heating coil
suitably connected to a source of electric current. Preferably, heater 66 is removably
mounted within cupola housing 66 by means of an access door, not shown, in the side of
housing 60. Porward of heater 66 is a recirculating fan 70 driven by a motor 72 mounted
externally of cupola housing 60. At the rear end of cupola housing 60 are a series of
adjustable openings 74 in the housing end wall. Openings 74 permit the fan to drawing
atmospherlc air into the air circulati~g system, as needed to make up for hot air loss
during the operation of the oven, which will now be described.
In use, the articles to be dried or cured are loaded on racks and disposed within the
oven chamber 22 through the open doors 20 at one end of oven housing 12. With doors 20
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cl~ d and tlle adjustable louvers 32 set as desired for the particular drying or curing
operation, heater 66 and fan 70 are energized. In keeping with the principles of the
present invention, heated air is provided in oven chamber 22 in an alternating cross air
flow pattern. That is, heated air is directed to nOw from one side duct; e.g., duct 26,
toward the other side duct; e.g., duct 28, for a predetermined time period. At the
expiratiOn of this predetermined time period, the heated air is directed to flow from the
other side duct; e.g., duct 28, toward the one side duct; e.g., duct 26. The direction of the
cross over air flow pattern is thus reversed within oven chamber 22 at periodic intervals.
Consequently, temperature gradients resulting from heated air flow in one direction
across chamber 22 are evened out by the heated air flow across oven chamber 22 in the
opposite direction resulting in application of heat to articles undergoing the drying or
curing process at a substantially more constant temperature and more uniformly
throughout oven chamber 22. This enables substantially even drying or curing of the
articles regardless of their orientation and location within the oven chamber 22 and
minimizes or eliminates the danger of cracking, warping or otherwise distorting the
articles.
To accomplish this periodic reversal of heated air flow patterns within oven
chamber 22, air is supplied through valve 55 as illustrated in FIGURE 5 to cylinders 44a
and 56a to open the corresponding dampers 44 and 56 enabling communication between
main supply passage 34 and duct 26 on the supply side and communication between mflin
return 36 and duct 28 on the return side. Also, air is supplied through valve 55 to
cylinders 46a and 54a to close the corresponding damper 46 and 54 preventing
communication between main supply passage 34 and duct 28 on the supply side and
communication between main return 36 and duct 26 on the return side. Consequently,
heated air is suctioned by fan 70 in cupola 24 through heater 66 and directed through
opening 62 into main supply passage 34. From there, the heated air flows through supply
passageway 40 into duct 26 and outwardly thereof through openings 30 in duct 26 into
oven chamber 22. The air thus crosses in chamber 22 from duct 26 to duct 28 and enters
the latter through the openings 30 in its side walL From there, this return air flows past
open damper 56 into return passageway 52 and main return passage 36 and through
opening 64 into cupola 24. With thi~s air flow pattern, the closed dampers 46 and 54
prevent reverse flow of supply air through supply passageway 42 into duct 28 and reverse
flow of return air through return passageway 50. Thus, a cross flow of heated air from
duct 26 across the oven chamber 22 to duct 28 is established and continues for a
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pre tcrmined time intervnl. At the end of this time interval, the direction of the flow
across the chamber is reversed.
To reverse the flow, cylinders 46a and 54a are actuated by shifting valve 55 to its
other position thereby closing dampers 46 and 54. With the fan and heater running
continuously, heated air is thus supplied oven chamber 22 by flow through opening 62 into
main supply passage 34 and supply passageway 42, and past the open damper 46 into duct
28 for outflow through openings 30 into oven chamber 22. The air in oven chamber 22 is
returned by flowing through openings 30 into duct 26, into main return passage 36 via open
damper 54 and return passageway 50 and through opening 64 into cupola 24. Thus, a cross
flow of heated sir from duct 28 across oven chamber 22 to duct 26 is established. It will
be appreciated that this latter flow across oven chamber 22 is in the reverse direction
from the previously described cross flow and that these cross flOws are alternated at
periodic intervals; e.g., every five minutes or every few hours or days, depending upon the
drying or curing characteristics desired. With each cross flow, it will also be appreciated
that air is made up by atmospheric air entering cupola 24 through openings 74 and thus a
constant supply of heated air is provided.
As illustrated, the cylinders controlling the dampers are under the control of a
single two position, solenoid actuated, spring returned valve 55. Actuation of the solenoid
may be accomplished manually or automatically. For example, the solenoid may be
coupled to an electrical circuit having a current supply and a manually actuated switch
with a releasable mechanical hold. Thus, closing the switch, and mechanically holding the
switch closed, will cause a supply damper and a return damper on opposite sides of the
oven to open while maintaining the other of the supply damper and the return damper on
opposite sides of the oven to close. This establishes a heated air flow pattern across
chamber 22 in one direction. After a predetermined time inter-ral, the switch is manually
opened to permlt the valve to spring return it its other position. This reverses the motion
of the pistons of the cylinders causing the previously open dampers to close and the
previously closed dampers to open establishing a heated air flow pattern across oven
chamber 22 in the reverse direction. It will also be appreciated that reversing the heated
air flow pattern may be accomplished automatically by actuating the solenoid of valve
55 by means of a timer. Thus, autom~tic reversal of the heated air flow pattern across
oven chamber 22 at desired periodic intervals depending upon the drying or curing
characteristics of the articles may be obtained.
