Abstrict An air curtain conveyor protection system that prevents airborne
particles from entering a slot through which the product support
members extend from the conveyor mechanism housing into the product
treatment booth. A continuous stream or curtain of high velocity
air flows across the slot in the conveyor housing, exiting from
an outlet or supply nozzle formed by a plenum on one side of the
slot and entering into a suction nozzle formed on the opposite side
of the slot by a second plenum. A fan or blower is associated with
each plenum to force ambient air through the supply nozzle and to
draw air through the suction nozzle. Ambient air flowing between
the nozzles forms an air curtain across the slot to prevent ingress
of the deleterious atmosphere in the product treatment booth into
the conveyor housing.
Claims What is claimed is:
1. A method of conveying articles with a conveyor having a conveyor
housing substantially surrounding the conveyor through a booth having
a slot connecting an internal chamber within the booth with abn
interior of the conveyor housing and having process equipment and
a treating atomosphere in the booth's internal chamber deleterious
to the conveyor,
traveling a conveyor through the interior of the enclosed conveyor
housing having clean air therein,
treating articles within the enclosed internal chamber in the booth
and within the deleterious atmosphere,
moving a portion of the conveyor projecting through the slot for
travel within the slot and extending from the clean air in the conveyor
housing interior into the deleterious atmosphere in the enclosed
chamber in the booth,
blowing air across the slot between the conveyor housing and the
enclosed chamber to separate the clean air in the conveyor housing
from the deleterious atmosphere,
pulling the air flowing across the slot and conveying the pulled
air from the booth,
preventing clean air from flowing downwardly through the slot from
the enclosed conveyor housing into the deleterious atmosphere within
the enclosed internal chamber and adversely affecting the treating
atmosphere within the enclosed internal chamber, and
preventing the upward flow of the deleterious atmosphere from the
booth's internal chamber into the enclosed conveyor housing and
adversely affecting the conveyor within the conveyor housing.
2. A method in accordance with claim 1 in which the step of treating
of articles includes the steps of washing the articles in a washer
booth and in which the clear air is prevented from flowing and intermixing
washing atmospheres in the washer booth.
3. A method in accordance with claim 1 in which the step of treating
of articles includes heating the articles in a curing oven booth
with a high temperature atmosphere and in which the clean air is
at a lower temperature and is prevented from intermixing with the
higher temperature deleterious atmosphere in the curing oven booth.
4. A method in accordance with claim 1 in which the step of treating
articles includes a paint spray booth and in which the clear air
is prevented from interfering with a paint spraying operation within
the internal chamber of the paint spray booth.
5. A booth for treating articles with a treating atmosphere deleterious
to a conveyor carrying the articles through the booth, said apparatus
comprising:
an enclosed booth having an article treating means within an internal
chamber and having the treating atmosphere deleterious to a conveyor,
a conveyor having an upper portion and a lower portion for traveling
along a predetermined path through a booth and for carrying articles
through the internal chamber of the booth,
a conveyor housing substantially surrounding the upper portion
of the conveyor and having an interior with clean air therein,
means defining a slot interconnecting the internal chamber of the
booth with the interior of the conveyor housing and through which
slot projects the lower portion of the conveyor,
a conveyor housing being closed to the ambient atmosphere to prevent
escapes of the deleterious atmosphere to the ambient atmosphere,
means for blowing clean air across the slot and means for pulling
clean air across the slot and preventing clean air from flowing
downwardly through the slot from the enclosed conveyor housing into
the deleterious treating atmosphere and adversely affecting the
treating atmosphere and preventing the upward flow of deleterious
atmosphere from the booth internal chamber into the conveyor portion
in the enclosed conveyor housing. Description This invention relates to a device for protecting the mechanism
of a conveyor system that carries particles through deleterious
atmospheres existing within paint spraying booths, washer or filter
air cleaning systems, finish-baking ovens, and other product treatment
booths.
In many industrial product-treatment processes, the atmosphere
within a product treatment booth through which a conveyor system
transports the product is quite corrosive or contaminated and, consequently,
is capable of binding up or corroding the support and drive components
of the conveyor system within a very short period of time. This
can dramatically increase the power required to operate the conveyor
and, ultimately, cause a breakdown of the conveyor system, often
entailing great expense due to the cost of repairs as well as the
loss of production during the time which the conveyor is nonfunctional.
Additionally, it is desirable to prevent contamination and marring
of the product being treated in the booth due to the dripping of
contaminants that may have collected on the conveyor system or by
the introduction of other particles or environmental effects from
the conveyor system.
Efforts to overcome these problems by maintaining a cleaner atmosphere
for the conveyor have resulted in the conveyor system shown in U.S.
Pat. No. 4,207,833, having the same assignee as the present invention.
In this system, a shrouded conveyor is shielded from the deleterious
atmosphere, while the product being treated is protected from conveyor-introduced
contaminants, by means of an air curtain directed laterally across
a slot in the conveyor housing through which the conveyor hangers
extend, along with a flow of clean air flowing downward through
the slot from the conveyor housing itself. The air curtain forms
a barrier that prevents the ingress of a deleterious atmosphere
through the slot toward the conveyor mechanism, while carrying away
from the product contaminants that may drip from the conveyor system
and otherwise fall through the slot onto the product. The air curtain
is then exhausted through the air exhaust for the product treatment
booth.
Such a system has proven successful in preventing the migration
of deleterious atmospheric fluid into the conveyor housing, thus
maintaining the conveyor mechanism generally clean, and in protecting
the workpiece from being marred due to drippings from the conveyor,
etc. However, such a system introduces large quantities of air into
the treatment booth, which pressurizes the booth and introduces
additional air which, in many cases, must be washed or filtered
prior to being exhausted to the outside atmosphere. This burdens
the booth's existing air cleaning systems. Further, because the
air curtain introduces ambient temperature air into the booth, e.g.,
air at 68.degree. F., the use of this air curtain in ovens has required
that additional heated air be introduced into the oven to maintain
the desired temperature, resulting in higher energy costs. Also,
conventional conveyor protection devices for high temperature ovens
often are insulated to protect against heat transfer to the conveyor.
But even so, the conveyor elements are raised to high temperatures,
e.g., 200.degree. F. in their travel through the oven. It is desirable
to reduce this temperature substantially to overcome lubrication
problems and the dropping of lubricant from the conveyor.
Accordingly, it is an object of the present invention to provide
an improved conveyor shrouding structure that keeps deleterious
environmental fluids from collecting on and corroding the conveyor
mechanism.
It is more particularly an object to provide an air curtain conveyor
shrouding structure that is substantially self-contained and does
not affect the internal atmosphere of the booth.
These objects as well as others that will become apparent upon
reference to the accompanying drawings and following detailed description
are provided by means of an air curtain conveyor protection system
that prevents airborne particles from entering a slot through which
the product support members extend from the conveyor mechanism housing
into the product treatment booth. A continuous stream or curtain
of high velocity air flows across the slot in the conveyor housing,
exiting from an outlet or supply nozzle formed by a plenum on one
side of the slot and entering into an suction means or suction nozzle
formed on the opposite side of the slot by a second plenum. Fan
or blower means are associated with each plenum to force ambient
air through the supply nozzle and to draw air through the exhaust
nozzle. Thus, the ambient air forming an air screen across the slot
will not be discharged into the booth to mix with air in the booth
and to cool the same (when the booth is an oven). Further, the booth
will not be pressurized.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a finish baking oven of a type that may
advantageously utilize the inventive conveyor protection system;
FIG. 2 is an enlarged cross-sectional view of the baking oven taken
substantially along lines 2--2 of FIG. 1;
FIG. 3 is a fragmentary portion of FIG. 2 further enlarged to show
details of the conveyor protection system;
FIG. 4 is a further enlargement of a portion of the conveyor protection
system of FIG. 3; and
FIG. 5 is an enlarged sectional view of the conveyor protection
system taken substantially along line 5--5 of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings, the invention is generally used in connection
with a protective chamber or booth, indicated by 10, through which
articles 11 are transported by a conveyor system 12 in order to
treat the articles 11 by, for example, spraying a finish thereon,
baking on a finish, etc. Referring to FIGS. 1 and 2, the illustrated
booth 10 is a baking oven having insulated vertical side walls 14,
top wall 15, and a heating plant 16 and exhaust stacks 17. Typically,
the booth 10 provides an enclosed environment that contains an atmosphere
which may contain excessive amounts of sprayed liquid, liquid vapor,
airborne particles, heat, acidic air, phosphates, etc., which are
deleterious to the conveyor system. Usually, an air cleaning system
(not shown) is included with the booth 10 to remove the bulk of
such deleterious impurities in the air before the air is discharged
into the atmosphere ambient the outside of the booth 10.
As best seen in FIG. 2, the baking oven 10 has tandem conveyor
systems 12a,b that transport the articles 11 on a U-shaped path
through the booth 10 so as to enter and exit the booth 10 at the
same end. The conveyor 12 includes hangers 18 extending downwardly
therefrom on which the articles 11 are placed in order to be transported
through the booth 10. The conveyor system 12 may be of various configurations
and, as illustrated, includes an elongated channel or beam support
20 (best seen in FIG. 3) secured to the top wall 15 of the booth
10 with rollers 21 being maintained within the channel 20 for axial
movement therealong by means of a flexible chain 22 and drive system
(not shown). Typically, the channel 20 and chain 22 are endless,
i.e., in the form of a continuous loop, which allows bidirectional
movement of the conveyor system 12. As illustrated, the rollers
21 carry hook supports 24 which are secured to certain of the rollers
21 at spaced intervals along the length of the chain 22 for carriage
of the hangers 18. Each article 11 to be conveyed through the booth
10 is hung from the lower end of the hanger 18, typically at a distance
considerably spaced from the conveyor support channel 20. The space
heretofore was preferably on the order of two to two and one-half
feet in paint spray booths. This distance heretofore insured that
any air flow from the air curtain downward toward the article 11
was dissipated before it could contact the article and mar the finish
with particles carried thereby or ripple the paint due to the air
velocity.
Within the booth 10, the conveyor components, except for the lower
portions of the hangers 18, are located within a housing or shrouding,
generally indicated by 25, constructed of a fluid-impervious L-shaped
sheet material 26 and generally surrounding the conveyor system
except for an elongated continuous slot 28 defined by adjacent longitudinally-extending
edges 29, 30 on the lower or bottom walls 31, 32, respectively,
of the housing 25. The conveyor hangers 18 extend through the slot
28 to provide the lower, exposed portion on which the articles 11
can be carried. In the illustrated baking oven 10, the outer surfaces
of housing 25 support an insulating material 34 in order to protect
the components of the conveyor system 12 from the high temperatures
in the oven which might otherwise vaporize the lubricants on the
conveyor or cause other problems. Despite the insulating material
34, which could be one inch thick sheets, the temperature of the
conveyor leaving a high-temperature oven of 900.degree. F. would
be about 200.degree. F. Temperatures of this magnitude have an adverse
effect on the conveyor lubrication and bearings. At such high temperatures,
lubricants degrade or become liquid and drip from the conveyor onto
the articles being conveyed. Also, it is preferred to limit this
heat transfer so that the insulating material may be eliminated
for the lower and medium temperature ovens operating at temperatures
below 800.degree. F.
The amount of ambient air exhausted into a large booth such as
a washer or paint bake oven from a conventional conveyor protection
device is quite large. For example, the air flowing through the
slot of the air protection device at ambient temperatures may be
ten percent of the air being heated in and recycled in the booth.
For a booth having a 12,000 cfm flow therethrough, it is necessary
to supply heat in sufficient quantities to raise the 1200 cfm flow
at 68.degree. F. to the oven temperature, e.g., 850.degree. F. Also,
it will be seen that fans supplying air at 1200 cfm through the
slots of conventional conveyor protection devices will soon pressurize
the acidic air in the washer. To reduce the air pressure, acidic
air must be withdrawn and normalized before discharge. The discharge
of acidic air from a washer also results in the loss of steam, heat,
phosphates, etc. that are in a typical washer atmosphere.
In accordance with the present invention, the conveyor protection
device protects the conveyor by an air curtain discharged across
the slot 28 with only a minimal discharge of the air curtain fluid
or air flowing into the interior of the booth 10 which would lower
the temperature in the booth or pressurize the booth. This is achieved
by discharging air from a first nozzle means 45 on one side of the
slot and by receiving the discharged air in a suction means or second
nozzle means 46 on the other side of the slot which draws the discharged
air and pulls the same into an air discharge duct. Thus, there is
a push-pull effect across the slot with air being pushed from the
air supply nozzle and pulled across the slots and taken off by the
pull or suction means 46. Because the ambient air flowing across
the slot is removed at the same rate as it is discharged into the
slot, there is little spillage of ambient air into the conveyor
or into the booth. As will be explained, this air curtain also acts
as a barrier to heat transfer from the oven to the conveyor so that
the conveyor operates at a lower temperature.
More specifically, and in accordance with the present invention,
rising airborne particles from the booth 10 are prevented from entering
slot 28 into the protective conveyor housing 25, while any particles
dripping from the conveyor system 12 are kept from entering the
interior of the booth 10, by means of a continuous stream or curtain
of high-velocity air across the slot 28 defined by the edges 29,
30 of the housing 25. The air curtain exits from an outlet nozzle
means formed by a plenum on one side of the slot and is received
into an inlet nozzle formed by a plenum on the opposite side of
the slot. Fan or blower means are associated with the two plenums
to force the air into the plenum defining the outlet nozzle and
to pull the air through the plenum defining the inlet nozzle. Thus,
the flow of air across the slot 28 prevents the deleterious atmosphere
within the booth 10 from entering the conveyor housing 25 and damaging
the conveyor system 12.
Referring more particularly to FIGS. 3 and 4, plenums 35, 36 are
formed interior of the conveyor housing 25 on opposite sides of
the slot 28 by means of substantially impermeable L-shaped sheet
members 38, 39 respectively. As illustrated, the bottom walls 40,
41 of the sheets 38, 39 are substantially parallel to the bottom
walls 31, 32 of the housing 25, with the edges 42, 44 of the bottom
walls 40, 41 being substantially perpendicularly aligned with the
edges 29, 30 that define the slot 28 in the housing 25. Accordingly,
the bottom walls 30, 41 together define an outlet or supply nozzle
45 for the plenum 35, while the bottom walls 31, 42 together define
an inlet or exhaust nozzle 46 for the plenum 36.
Connected to each plenum 35, 36 through the top wall 15 of the
booth 10 are blower or fan means, generally designated 48, 49. With
reference to FIG. 1, blower system 48 supplies air to the outlet
plenum 35 by means of a fan 50 powered by motor 51, with the downstream
side of the fan 50 operably connected to the plenum 35 at spaced
intervals along the length of the conveyor system by means of supply
ducts 52 which are secured to duct fittings 54 extending through
the top wall 15 into the plenum 35. Extending between the blower
means 48 and the individual supply ducts 52 is a common air delivery
duct 53 which has sections 53a, 53b and 53c of reduced cross-sectional
area in the downstream direction to aid in having each supply duct
52 receive a substantially uniform flow of air. Similarly, blower
system 49 exhausts air from the inlet plenum 36 through duct fitting
55 and exhaust ducts 56 by means of fan 58 powered by a motor 59.
Downstream of the fan 58 is an exhaust stack 61 through which the
air from the conveyor or protection system is exhausted into the
ambient atmosphere. Like the supply plenum 35, the exhaust ducts
56 are spaced at intervals along the plenum 36 for the length of
the conveyor system.
Accordingly, a substantially-uniform, high-velocity flow between
the supply nozzle 45 and the exhaust nozzle 46 forms an air curtain
across the slot 48, generally indicated by the arrow 60 in FIGS.
3 and 4. Such an air curtain 60 serves to prevent both the ingress
of particles into the conveyor housing 25 and the egress of drippings
from the conveyor system 12 through the slot 28 into the booth 10.
It has been found that an air curtain having a velocity between
about approximately 1,200 to 1,500 feet per minute produces an effective
barrier at the slot 2S. In the booth 10 illustrated and described
herein, which has approximately 60 feet of conveyor system mechanism
in each of the tandem systems 12a, b, it has been estimated that
for each system supply and exhaust fans 50, 58, having a capacity
of 3,000 cubic feet per minute, provide such a velocity. Airborne
particulates and other contaminants that are not repelled by the
air curtain 60 become entrained therein and are exhausted through
the plenum 36 to the conveyor air curtain exhaust stack 61. If the
level of the contaminants in the air curtain exhaust dictates, additional
filtration or washer units (not shown) can be positioned on the
exhaust side of the air curtain system intermediate the plenum 39
and the conveyor exhaust stack 61.
To prevent a major portion of the air flow 60 from spilling from
the supply nozzle 45 into the oven 10, the exhaust nozzle 46 is
sized to have a larger cross-sectional area than the supply nozzle
45. This ensures that as the wake of the flow 60 expands as it crosses
the slot 2B, substantially all the flow 60 is captured by the inlet
nozzle 46 of the exhaust plenum 36. In practice, it has been found
that satisfactory flow containment is achieved if the distance between
the supply plenum walls 31, 40 is on the order of approximately
1/2 in., the distance between the exhaust plenum walls 32, 41 is
between approximately 2 to 4 in., and the width of the slot 28 is
between approximately 3 to 8 in. To maintain the proper width for
the nozzles 45, 46 spacers 62 are secured to the nozzle walls at
predetermined intervals along the length of the conveyor system
12. Spillover of the air curtain 60 is further minimized by substantially
aligning the center lines 64, 65 of the supply and exhaust nozzles
45, 46 respectively, as best seen in FIG. 4.
In the illustrated embodiment of the invention, in which the oven
booth 10 was operated at about 850.degree. F. but with the use of
the conventional conveyor protection device having its walls insulated
with one inch of insulation, there was sufficient heat transfer
to the conveyor to heat its parts to 200.degree. F. as these parts
exited the oven. Such temperatures degrade lubricants and cause
lubricants to flow and are detrimental to bearings. With the present
invention, there is a marked reduction in heat transfer from the
booth to the conveyor with the conveyor parts having a temperature
of 140.degree. F. when leaving the 850.degree. F. oven. Another
advantage of this low heat transfer is that for lower temperature
ovens, e.g., a 350.degree. F. oven, it is possible to dispense with
the cost of adding the insulating material 34 to the conveyor housing.
As previously noted, such an air curtain conveyor protection system
is particularly advantageous when used in conjunction with finish-baking
ovens. It is estimated that for an air curtain of approximately
1,000 cubic feet per minute having an ambient air temperature of
approximately 70.degree. F. in an oven having a temperature of approximately
650.degree. F., approximately 47,520 BTUs per hour are saved over
a system in which the air curtain spills over completely into the
oven and which, consequently, must be heated.
It will be appreciated that the protection device may be used with
a variety of conveyor mechanisms different from the illustrated
chain and hanger conveyor. For instance, the conveyor may be floor
mounted with a conveying pedestal projecting upwardly through a
slot to hold the conveyed article above the slot and conveyor, with
air being pushed and pulled across the slot. Further, the conveyor
protection device can be used in a wide variety of environments
and is not limited to the environments of paint spray booths, washers,
and ovens herein described.
Accordingly, it can been seen an air curtain conveyor system has
been provided that fully meets the objects of the invention. While
a preferred embodiment has been shown and described, it will be
understood that there is no intent to limit the invention by such
disclosure, but, rather, it is intended to cover all modifications
and alternate constructions falling within the spirit and scope
of the invention as defined in the appended claims. |