Note: Descriptions are shown in the official language in which they were submitted.
2~2
SPRAY BOOTH
BACKGROUND OF THE INVENTION
1'he invention relates to a spray booth of the
type wherein air flows through the booth and water
washes remove particulate matter from the air.
Booths of the type to which the present
invention relates are frequently used in spray
painting operations wherein an article to be painted
is transported through the booth on a conveyor and is
spray painted either by hand-held spray nozzles aimed
and operated by workers within the booth or by
automatic spraying equipment. It is desirable that
such booths be suitable for spraying of articles of
different shapes and sizes, and suitable ~or spraying
from various directions and locations within the booth.
To provide an even coating on an article
being sprayed, it is desirable that only paint
particles striking the article directly from a no~zle
adhexe thereto. It is undesirable that particles
deflected from the article be permitted to settle on
the article. To these ends, and to supply clean air
for workers to breathe, air ~lows downwardly through
the booth at a predetermined rate. The air flow
removes particulate material from the booth to prevent
undesirable adherence thereof to the workers, to the
articles being sprayed, or to other objects within the
booth. Cartain minimum air flow rates may be needed
to Rupply clean air for workers to breathe for
compliance with occupational safety and health
standardSo
One problem associated with operation o~
~pray booths is that air which is received beneath the
floor of the booth after having passed downward
through the booth interior typically is laden with a
relatively high concentration of particulate matter
which must be separated from the air. Dis~harge of
particle-laden air is generally undesirable for
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environmental reasons, and amission standards
presently applicable to many industrial operations
speciy maximum concentrations of particulate ~atter
for spray booth emissions. In the past, various
air-cleaning systems have been proposed to reduce the
particle content of spray booth emissions, but such
systems have generally been incapable of meeting the
above-referenced standards. There is a continuing
need for improved means for reducing the
concentrations of particulate matter in spray booth
emissions~
Another problem associated with operation of
some paint spray booths is adherence of particulate
matter to the interiors of the side walls of the
booths. It is desirable to maintain the interiors of
the walls reasonably clean Also, in booths where
windows are provided in the side walls to enable
illumination of the interior of the booth from outside
the booth, it is desirable to prevent particles from
adhering to the interiors of the windows. Thus there
is a need for means to prevent build-up of particulate
matter on the intexior surfaces of booth side walls.
Other considerations which influence the
design of spray booths include eeonomy of operation
and noise level, which are omewhat interrelated. In
industrial spray painting of automobile bodies and th~
like, it is generally desirable that the power
required for pulling air downwardly through a spray
booth and through air cleaning apparatus beneath the
booth not exceed a predetermined value. Also; it is
generally desirable that the noise level inside the
booth and around the booth be relatively low. The
noise level is partially dependent on the power of the
equipment used for moving air through the booth, and
dependent on other considerations as well, including
air velocity and the configuration of the air cleaning
equipment beneath tha booth.
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Accordingly, it is a genaral object of the
invention to provide a spray booth which is suikable
for use in industrial operation and which includes
improved apparatus for removing particulate matter from
air beneath the booth. It i5 an additional obiect of
the invention to provide a spray booth having improved
means for preventing or reducing adherence of particles
to interior wall surfaces of the booth. Adaitional
objects and advantages of the invention are set forth
below.
SUMMARY OF THE INVENTION
In accordance with the invention, a spray
booth includes improved air cleaning apparatus which is
capable of removing particulate matter from air flowing
therethrough. The air cleaning apparatus preferably
comprises a pair of air cleaning units, one extending
along each side o~ the booth, prcviding dual air
intakes beneath the booth floor.
The booth further includes means for providing
air curtains along the interiors of the side walls of
the booth to reduce adherence of particles thereto.
Each of the air curtains is preferably produced by
passing air through a relatively narrow slot extending
the length of the booth adjacent the upper extremity of
each side wallO
BRIEF DESCRIPTION OF THE DRAWI~GS
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FIG. 1 iS a perspective view of a spray booth
in accordance with a first embodiment of the invention,
with portions broken away for clarity.
FIG. 2 is an enlarged sectional view taken
substantially along line 2-2 in FIG. 1 and looking in
the ~lirection of the arrows.
FIG. 3 is an enlarged sectional view o~ air
cleaning apparatus in accordance with a first
embodiment of the invention, taken substantially along
line 3-3 in FIG. 1 and looking in the direction of tha
arrows.
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FIG. 4 is a sectional view illustra~ing air
cleaning apparatus in accordance with a second
embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention is preferably embodied in a
spray booth which provides an enclosure for containing
paint or other material during a spraying operation.
While the apparatus is described herein in connection
with a spray painting operation, the usefuln~ss of the
apparatus of the invention is not limited to painting
operations, but may extend to various other types of
operations as well.
Referring to FIG. 1, the illustrated booth 10
includes a pair of upstanding side walls 12 supporting
a roo~ assembly 14. ~n the illustrated booth 10, the
roof assembly 14 includes means defining a plenu~ 20
for air, and includes an air permeable ceiling assembly
22. A permeable 100r 16 extends between the side
walls 120
A blower 23 draws air downwardly from the
plenum 20 through the ceiling as embly 22 and through
the booth interior, carrying paint particles or the
like downwardly through the floor 16 of the booth 10 to
air cleaning appaxatus 18. A conveyor means having a
trac~ 24 extends longitudinally of the booth for
transporting thxough the booth objects to be painted.
~o permit the interior of the booth 10 to be
illuminated by exterior light sources, transparent
window panels 19 are provided in the side walls 12 and
roof assembly 140
In a typical spray painting operation, a
number of nozzles spray particles of paint at an o~ject
such as an automobile body at xelatively high
velocity. Although most of the paint adheres to the
~uxface of the object being painted, a relatively large
percentage, which may approach 50%, of the paint
particles generally either are deflected from the
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surfa~e or never reach the surface. Such particles are
generally very light, and may become suspended in the
air witnin the booth. As the air is drawn downwardly,
the particles travel downwardly with the air. Because
of the very large volume of paint being sprayed in
these booths, reductions in removal efficiency,
although small in number, for example from 99.96% to
99.98~, are commercially very significant in the amount
of paint particles discharged in a 24-hour period. It
is desirable that substantially all of the particles be
removed fro~ the air so that the air can be discharged
to the atmosphere or recycled through the booth.
In the past, various types of structures have
been employed to wet particles in air as it is drawn
through air cleaning apparatus by directing the air
through water curtains or washes. Wetting of the
particles increases their weight, thereby increasing
the tendency of the particles to drop out of the air as
it proceeds through the cleaning apparatus. Air flow
patterns in some prior art spray booths includa streams
of high velocity air which carry particles entirely
through the air cleaning apparatus without the
particles being wetted.
One object of the present inventivn is to
provide a new and improved spray booth to increase the
percentage of particles that are wetted and removed
from the air.
In accordance with one feature of the present
invention, the cleaning apparatus 18 includes water
that is directed in reverse directions to form water
curtains through which the air must pass and air flow
slots and de~lecting walls to cause the air and water
to mix turbulently and wet particulates. Also, the air
flows through several expansion chambers in which the
air velocity is substantially reduced to precipitate
the wetted paint particles from the air stream. In
accordance with a second feature of the invention,
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means are provided tc generate air curtains along the
interiors of the side walls 12 of the booth to prevent
adherence of paint particles to the walls 12 and
windows lg therein.
Turning to a more detailed description of the
air cleaning apparatus of FIGS~ 1 and 3, the air
cleaning units 26 are preferably shown disposed
symmetrically on each side of the center of the booth
10. The units 26 are mirror images of each other, and
only one will be described in detail herein.
Referring particularly to FIG. 3, there is
provided an illustration of one of the cleaning units
26 and the flow of air and water therethrough are
diagrammatically indicated. Vpper and lower subfloor
members 28 and 30 ~lope generally downwardly toward one
another, and each includes means 32, 34 to provide for
retention of water near its lower edge 42, 44. The
means 32 ~or retention of a water pool 45 near the
lower edge 42 of the upper member 28 includes an
upturned portion 46 and a weir 48 extending along the
lower edge 42.
The lower member 30 extends partially beneath
the upper member 28 so as to define a generally
horizontal air intake 52 therebetween. During
operation, particle-laden air flows downward toward the
subfloor members, then turns to flow along the subfloor
members and through the intake 52. A portion of the
particles in the air, particularly larger, heavier
particles, drop from the air before the intake 52.
Because the intake is oriented generally hori~ontally,
particles cannot fall down through the intake by
gravity alone as in some booths. ~his provides an
advantage over air cleaning apparatus having vertical
intaXes.
Air is wetted as it enters the intake 52 by a
curtain of water 68 flowing downwardly from the upper
subfloor member 28. Flow of water over the upper
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su~ loor member 28 is effected by provision of an
elongated reservoir 36 extending along the upper edge
38 ':hereof and a water supply pipe 40 which provides
steady inflow of water into the reservoir 36. Water
continuously overflows the reservoir 36 to flow over
the upper edge 38 of the upper subfloor member 28, down
the upper surface 50 thereof, and over the lower edge
42 and weir 48. The upper surface 50 is thus
substantially covered by a moving sheet of water which
continuously removes particulate matter therefrom.
To prevent variations in pressure along the
length of the supply pipe fro~ leading to
discontinuities in flow over the upper subfloor member
28, and to ensure smooth and evenly distributed outflow
from the reservoir 36, horizontal baffles 54, 56 are
provided above the supply pipe 40~ The uppermost
baf~le 54 extends away from the upper subfloor member
28 to define a slot 58 at its distal edge. The lower
baffle 56 spans the width of the reservoir 36 and has a
plurality of perforations formed therethrough for
upward flow of water. The lower baf~le 56 essentially
defines a plenum 60 therebeneath to distribute flow
evenly along the length of the reservoir 36. m e
reservoir 36 has a substantially rec~angular
cross-section, and is defined by a substantially
horizontal bottom wall 84 extending between a pair of
substantially vertical walls 86 and 88.
It is most desirable that there be a
continuous flow of water along the longitudinal length
Of the reservoir 36 and across the entire surface of
the upper sub~loox member 28; and to this end, there is
provided an adjustable weir 62 at the upper edge 38 of
the subfloor member 28. The adjustable weir 62 is
preferably made of angle irons comprising substantially
vertical webs 64 extending upward from the wall 86 on
which the weir 62 is mounted and to which the weir is
fa~tened by fasteners ~not shown) and substantially
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horizontal webs 66 extencling partially over the
subfloor member 28. Th~ weir 62 is preferably made up
of a plurality of independently adjustable lengths of
angle iron so that the height of a particular portion
can be adjusted by loosenin~ its fasteners to
compensate for nonuniformity in flow rate.
The weir 48 is adjustable vertically by
fasteners (not shown) fastening the weir to lip edge 42
of the subfloor member 28. The weir 48 is broken into
separate sections each of which can be adjusted
vertically in height to develop a large pool 47 of
water behind the weir. The large pool of water assures
that even with variations of water flow down the sheet
that there will be ample water flowing across the
weir's ~op edge to provide a continuous, uninterrupted
water curtain 68 flow across the slot formed beneath
the weir. Approximately 20 gallons of water per lineal
foot flow over the weir from the pool 47 into the
underlying pool 71. Thus, there are no unwetted
surfaces on the subfloor member 2B or the weir 48 and
hence, there are no dry areas or discontinuities in the
wetted surface along the longitudinal length of the
weir 48.
To provide for flow of water from the upper
edge of the lower subfloor member 30 to its lower edge,
a reservoir 72 similar to that described above in
connection with the upper subfloor member 28 is
provided at the upper edge of the lower subfloor ~ember
30. This reservoir 72 is essentially a mirror image of
the first described reservoir 36, including a lower
baffle 74 and an upper baffle 76 extending generally
horizontally between a pair of vertical side walls 78
which ex~end upward from a generally hori~ontal bottom
wall 80. An adjustable weir 82 is provided along the
upper edge of the lower subfloor member to function in
substantially the same manner as the above described
adjustable weir 62~ The flow of water over the lower
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edge of the lower subfloor member 3Q provides a second
water curtain 83. The subfloor 30 has an upturned edge
30a to form the large longitudinall~ extending pool 71
of water to assure that there are no discontinuities in
the wetted surface along the edge 44 across which watsr
continuously flows at a rate, e.g. of 15 gallons per
lineal foot.
As noted above, water flowing over the weir 48
at the lower edge 42 of the upper subfloor member forms
a first water curtain 68 in the path of paxticle-laden
air entering the intake 52. The water curtain 68 wets
a substantial portion of the particulate matter in the
air entering the intake 52. The lowPr edge of the weir
48 defines a slot 70 at the entrance to the intake 52.
The velocity of the air flowing into the intake 52
across the b~ttom edge of the weir 48 is relatively
high, and accordingly, a portion of the water in the
curtain 68 is drawn into the intake 52, is carried
entirely therethrough by the air, and emerges as a
spray or mist. Another portion flows down into the
pool 71 at the lower edge of the lower member 30.
Water flowing over the upper ed~e of the weir
48 flows downwardly along the side of over the weir and
enters the intake slot 70 from above with a
predetermined vertical velocity component. As the
water flows across and into the slot 70, it begins to
mix with air flowing into the slot 70 and to wet
particulate matter in the air. The flow immediately
downstream of the slot 70 is highly turbulent and
effects mixing of air and water to wet a further
percentage of the particles in the air. Provision of a
water curtain having a small vertical dimen~ion at the
slot 70 enables a high percentage of particulate matter
to be wetted at this point. Some such wetted
particulate matter drops into the pool 71, and other
wetted particulates are carried through the in~ake 52
and drop out downwstream therefrom.
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E'or a given flow rate, decreasing the width of
the slot 70 increases the average flow velocity of the
slot and decr~ases the vertical dimension of the first
water curtain 68. Generally, a high flow velocity
through the slot provides good mixing and accordingly
good wetting downstream of the slot 70~ However, high
velocity through the intake slot results in high noise
levels in the booth, and narrowing the slot also
increases the pressure gradient across the slot,
increasing power requirements for the air cleaning
apparatus. Thus, it may be desirable to maintain a
slot width which provides less than optimal wetting
performance in order to comply with other constraints.
The achievement of highly effective air cleaning in the
apparatus of FIGS. 1 and 3 at acceptable noise levels
and with acceptable power consumption is due in part to
the provision of dual air intakes 52 as shown in FIG~
1, whereby each air intake 5~ handles only one-half the
flow volume handled by single intakes in prior art
booths. Also, the air flow through the first water
wash has changed its direction of flow from vertical to
substantially horizontal which aids in creating
turbulence at the intake 52.
In a typical indu~trial spray painting
operation, an air flow rate o~ about 2,000 cubic feet
per minute per foot of booth length is maintained~ In
the apparatus of FIGS. 1 and 3, provision of dual air
intakes 52 enables a flow rate o~ about 1,000 cubic
feet per minute per foot of booth length to be
maintained for each air intake 52. When a four inch
slot 70 is provided at the entrance to each intake 52,
the average velocity in the slot is about 4,000 feet
per minute~
After flowing through the intake 52, air
enters a relatively large precipitation chamber 90
defined between the upper subfloor member 28 and an
inclirled ~ottom wall 92 dispo~ed therebeneath and
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substantially parallel thereto. The subfloor member 28
and bottom wall 92 are connected by the vertical
wall 86~ Provision of the large chamber 90 at this
point decelerates the air emerging from the intake 52,
causing a substantial portion of the wetted particles
to drop out. For example, the deceleration may be from
about 4000 fpm at entry to about 800 fpm for the exit
velocity from the precipitation chamber 90. This
sudden drop in velocity causes wetted particles to drop
out of the air stream. As air enters this chamber 90,
it has a relatively high horizontal velocity component
directed toward the left of FIG. 3 and a relatively
small, downwardly directed vertical velocity
component. Its horizontal velocity component reverses
direction in the chamber 90, and the air flows
downwardly and to the right. This change in flow
direction augments the gravitational force in removal
of relatively heavy wetted particles, and a substantial
percentage of such particles impact the bottom wall 92
of the chamber where they become entrained in the water
92a flowing downardly therealong. Because the bottom
wall 92 is covered with water, paint doesn't stick to
it but is carried away by the water flowing along and
covering the top surface of the bottom wall 92.
To prevent buildup of particles on the
vertical waLl 86, a sloping deflector 94 extends
downwardly from the upper subfloor member 28,
deflecting flow downward. The deflector 94 is
preferably curved so that its slope increases,
proceeding away from the intake 52. A portion of the
water emerging from the intake 52 strikes the deflector
94 and flows downward therefrom to the bottom wall 92,
then downwardly therealong.
~o exit the precipitation chamber 90, the
partly cleaned air flows through the second water
curtain 83 into an outlet throat 96. The water from
the water curtain 83 joins the water 92a flowing down
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the bottom wall 92 to flow into a pool 95 formed at a
deflector 97. The air proceeds at relatively low
velocity through this curtain 83, enabling a large
percentage of remaining particulate material to be
wetted and removed from the air. The air is deflected
upwardly toward an upper wall 98 by the deflector 97.
It will be appreciated that b~cause there is a thirty
five gallon per lineal foot flow of water across the
deflector 97 the water will have sufficient momentum to
flow upwardly and to the right ~o hit the wall 98 and
form a third water wash at the throat 96. ~he
deflector 97 includes an adjustable baffle 102
projecting toward the upper wall 98. The outlet throat
96 is defined between a downwardly sloping upper wall
98 and a yenerally parallel lower wall 100. To effect
turbulent mixing of air and water in the lower region
106 of the downwardly sloping outlet throat 96, the
baffle 102 extends upwardly from the lower wall 100 and
defines a slot 104 adjacent the upper wall. The
deflector 97 also causes a change in direction of air
flow directing the air upwards and to the right as seen
in FIG.3 against the wall 98 which again deflects the
air and causes air turbulence at the ~lot 104. This
baffle 10~ is preferably adjustable to enable control
of the slot width over a range of about 8 to 4 in. The
water flowing across the upper edge of the baffle 102
has sufficient iner.tia to hit the wall 98 as does the
air stream and the deflected air and water mix in a
highly turbulent fashion to wet paint particles.
Because the slot 104 is narrow, the air increases its
velocity in a lower region 106 below the outlet throat
96. Thus, there is a turbulent flow of air and water
particles and a mixing thereof and wetting of a further
percentage o~ remaining paint particles at the slot 104.
Another final mixing operation is effected
after the air ~nd water exit the outlet throat 96 by
provision of a relatively narrow outle~ slot 108
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defined between a pair of transverse walls 110, 112
which extend toward one another at the lower ends of
the walls 98, 100. The outlet slot 108 preferably
defines the minimum width of the flow path through the
air cleaning uni~ 26, thus accelerating air and water
to their highest velocities at this location. Because
the slot 108 is relatively remote from the booth
interior, the noise resulting from the high velocity
~low therethrough does not result in unacceptably high
noise le~els in the booth. The water from the slot
drops downwardly to hit a corner formed at the junctur~
of the wall 100 and the plate 112 and forms a pool in
the corner with water being deflected by the plate 112
upwardly and to the right and across the entrance of
this slot 108. Air flowing into this water at the
outlet slot 108 lifts watex and creates a spray and a
turbulent mix of spray and air above the slot 108.
Herein, the slot width may be varied by two adjustably
mounted plates 111 and 113 each fastened to a
transverse wall 110 and 112 and movable toward or from
each other to increase or decrease the size of the
outlet slot therebetween. Because all of the air and
water flowing through one-half of the booth at the slot
108, there will be water and air mixing and flowing in
a turbulent manner about the narrow slot 108 with a
build-up of static pressure above the slot 108. Thus,
the air and water will be mixing in a very turbulent
manner in a small space above the slot 108 causing a
very high removal of particulates to obtain the extra
efficiency not hereto~ore achieved with these kinds of
booths. The water flow across the slot 108 creates a
fourth water curtain or wash. While it is difficult to
designate w~ich portion of the overall apparatus
provides the inal increase in removal efficiency, it
is thought, based on experimental designs and tests,
that the air expansion chambers 90 and 114 on the
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opposi~e sides of the turbulence form slot 108 removes
paint particles which heretofore would have escaped
removal.
As the spray enters the separation chamber
114, its velocity is directed generally downwardly and
toward the center of the booth 10. Upon entering the
separation chamber 114 it decelerates and changes
direction, turning further downward, then left (as seen
in Fig. 3~ ~oward the outer wall 116 of the booth, then
upwardly into an exhaust du~t 118. The separation
chamber is very large in volume so that the large water
and paint particles will decelerate to 600 feet per
minute or less and will drop to the floor 120 which
will be covered by water. In the separation chamber
114, gravity, augmented by the momentum o the water
and wetted paint particles, causes all but a very small
percentage of the water and wetted paint particles to
drop to the inclined floor 120 of the separation
chamber 114, which is sloped toward a longitudinally
extending drainage channel 122 that carries the mixture
to water treatment apparatus ~not shown~.
While the larger water particles precipitate
xeadily, some of the smaller particles tend to remain
suspended in the air flowing through the separation
chamber 114 in the form of a fine mist. To control the
flow of the~e mist water particles, a first deflector
124 extends downwardly from the lower wall 100 to
direct air flow downwardly rather than letting the mist
flow through a short direct path to the exhaust duct
118. The forty five gallons per lin~al foot of water
flowing from the slot 108 creates another or fifth
water wash for the air which must change direction to
flow to the left and through the fifth water wash
before exiting the booth. To further change the
direction of air flow and to lengthen the travel path
of mist water particles, a second deflector 126 extends
upward immediately downstream of the drainage channel
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122 to deElect the air and mist upwardly into a very
large expansion chamber 115 defined by overhead plates
92 and 10~ and a floor plate 1217 Thu8, the air and
mist particles will experience a further reduction in
velocity eigi to 400 fpm or less in the chamber 115. A
final reduction in the water content of air entering
the exhaust duct 118 may be provided by an eliminator
128 at the lower end of the exhaust duct 118. The
eliminator 128 comprises a series of horizontal angle
irons or pla~es 129 and 131 spaced closely to one
another and arranged in the usual chevron arrangement.
Turning to a description of air flow in the
interior of the booth 10, and referring particularly to
FIGS. 1 and 2, air is introduced into the booth rom
the large ceiling plenum 20, which is located above the
permeable ceiling assembly 22 and coextensive
therewith, and a pair of elongated side plenums 132
extending along the upper ends of the respective side
walls 12 A substantially horizontal filter layer 130
coextensive with th~ permeable ceiling assembly 22 and
parallel thereto is disposed within the ceiling plenum
20. Air enters the ceiling plenum 20 through ducts or
openings above the filtex layer 130 and passes downward
through the filter layer 130 prior to passing through
the ceiling assembly 22. The air in the ceiling plenum
20 is maintained at generally uniform pressure so that
generally uniform downward air velocity results.
Curtains of relatively high velocity,
downwardly flowing air are provided by the by the side
plenums 132 to aid in keeping the side walls 12 of the
booth clean. Each of the side plenums 132 has an outer
wall 134 (FIG. 2) defined by the uppermost portion of
the booth side wall, and has an inner wall 135 which
extends downwardly from the roof assembly 14 and
includes a vertical upper portion 138 and a lower
portion 140 which ~lopes downward toward the side wall
12 of the booth~ At the bottom of th~ sloping portion
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140 is provided a substantially vertical lip 142 which
is parallel to the side wall 12 of the b~oth and spaced
therefrom to define a relatively narrow passage ~r
throat 144. As air emPrges from this passage 144, it
has a relatively high downward velocity component which
enables it to prevent particles from adhering to the
interiors of the side walls 12. The average velocity
of air in the air curtains is preferably greater than
the average velocity of air flowing downward through
the ceiling assembly 22 into the interior of the booth
1~ .
In prior art booths, the provision of a
single, central air intake located centrally at the
conveyor track caused air to flow inwardly to a single
slot located directly beneath the conveyor and hence
influenced the flow of air about the articles on the
conveyor. This may interfer with uniform application
of paint. The provision of dual intakes 52 beneath the
floor of the booth of the present invention, in
combination with the provision of air curtains along
interiors of the side walls 12, results in relatively
uniform downward flow of air without undesirable
adherence of paint particles to the interiors of the
side walls 12.
While the bulk of the air in booth flows
directly down from the ceiling plenum 20 through the
pervious floor 16, some of the air in the ceiling
plenum is diverted to the ~ides of the booth to
provide a supply of clean air f or the air curtains.
Herei~, blowers 216 effect flow of air from the
ceiling plenum 20 beneath the filter layer 130 through
duc~s 214 into the side plenums 132. The ducts 214
are located outside of the booth 10 so as not to
interfele with airflow therein. To aid in uniform
distribution of air emerging from the ducts 214,
filters 218 are provided at the outlets of the ducts,
Thus, the windows 141 and the lights 143 for
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illuminating the articles being painted are protected
from being ~overed by paint thereby reudcing the booth
maintenance cost for cleaning the windows and lights.
FIG. 4 illu~trates an air cleaning unit 146
in accordance with a second embodiment of the
invention. The air cleaninq unit 146 can be
substituted for the air cleaning unit 26 in the booth
illustrated in FIG. 1.
Like the air cleaning unit 26 described
above, the unit 146 of FIG. 4 includes upper and lower
subfloor members 148 and 150 which slope downwardly
toward one another and include means 152 and 154 to
provide for retention of water to ~orm large po~ls of
water to flow over their lower edges 156 and lS8. A
generally hori~ontal intake 160 i~ defined between
lower portions of the subfloor members 148 and 150.
The intake 160 of the unit 146 of FIG. 4 functions in
substantially the same manner as that in FIG. 3. As
in the embodiment of FIG. 3, an adjustable weir 162
retains a water pool near the lower edge of the upper
subfloor member 148 while defining a slot 174 to
restrict flow into the intake. Flow of water over the
weir 162 provides a first water curtain 163 across the
slot 174.
As in the embodiment of FIG. 3, reservoirs
164 are provided at the upper edges 166 of the
subfloor members 148 and 150 and supply pipes 170
provide water to the reservoirs. Each reservoir is
defined by a pair of vertical walls 186 and 188 and a
bottom waIl 190 extending therebetween. In the
embodi~ent of FIGo 4, the supply pipes 170 are
disposed beneath the respective reservoirs 164 and
connected thereto by a plurality of relativ~ly short
diætributor pipes 172, rather than being submerged in
the reservoirs. Thus, the entire surfaces of the
subfloors 14B and 152 will be wetted and have a
continuous flow of water thereacross to prevent paint
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from accumulating thereon, and large water pools 145
and 171 as~ure that entire longitudinal length of each
of the edges subfloor is wetted and covered with a
flow of water thereacross at all times that the booth
is operating. About twenty gallons per lineal foot of
water flows over the weir 162 to form a first water
wash ~or the air which is deflected from a downward
flow to flow to the left and horizontally in FIG. 4.
A precipitation chamber 176 of larye volume
receives the high velocity flow of air and water
particles from the intake slot and dramatically
reduces the air velocity, e.g., from about 4000 fpm at
the slot to about 600 fpm in the chamber 176. In the
precipitation chamber, some paint particles ~etted in
the intake 160 precipitate from the air due to the low
flow velocity. Air and water entering the
precipitation chamber 176 flows downward and to the
left as viewed in FIG. 4. Approximately 45 gallons
per lineal foot flow down from the intake slot to
define the second water wash 181. The horizontal
component of the average air flow velocity then
reverses direction, which aids in separation of heavy
wetted particles from the flow stream, and proceeds at
relatively low velocity through the second water
curtain 181 before entering the outlet throat 180.
The precipitation chamber 176 and outlet
throat 180 of the embodiment of FIGo 4 are configured
differently from those illustrated in FIGS. 1 and 3.
The precipitation chamber 176 in the embodiment of
FIG~ 4 is larger, being defined by a pair of
downwardly sloping, converging walls 18~ and 184
located b~neath and generally coextensive with the
subfloor members 148 and 150. The sloping walls 182
and 184 are connected to the subfloor members by
vertical re~ervoir walls 186. A curved deflector 192
extends downwardly into ~he precipitation chamber 176
from the bottom o~ the upper ~ubfloor member 148
adjacent the intake 160.
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One of the sloping wallæ 182 is pivotally
connected to its associated vertica]. wall 186 by a
hinge 187. This enables the wall 182 to swing
downward to provide convenient access to the interior
of the precipitation chamber 176 for inspection and
cleaning purposes.
Near the lower edges of the sloping walls 182
and 184 are baffles 194 and 196 deEining a relatively
narrow slot 198 at the entrance to the outlet throat
180. ~ach of the baffles 194, 196 comprises an angle
iron having its webs joined at an angle greater than
90, so that one web of each baffle lies flat against
one of the sloping walls so as to be supported thereby
and the other web of each baffle extends substantially
horizontally inward.
To enable the baffles 194 and 196 to be
adjusted between positions in overlapping relation
wherein they de~ine a narrow passage and position~
defining a wider passage, they are slidable upwardly
and downwardly on their respectiva sloping walls 182
and 184. When in overlapping relation, fluid flow into
the outlet throat undergoes two sharp changes in
dire~tion of greater than 90. The passage defined
between the baffles 194 and 196 when they are in
overlapping relation may have a minimum width as small
as 2 to 4 in. in this position. ~pproximately, forty
five gallon~ per lineal foot of water flows across the
top of the bafle plate 194 and continues generally
horizontally acxoss a gap, be~ore hitting the baffle
plate 196: and creates a third water wash thru which
~he air must flow before it can flow between the
parallel bafle~ 194 and 196. The air coming from the
expansion chamber is flowing down and to the right to
hit the wall 184, the air is deflected at the wall 184
to change direction to flow to the left and
horizontally between the baf~les 194 and 196.
Accordingly, the large volume of water particles and
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air all changing direc:ions and trying to flow
simultaneously between the baffles 194 and 196 are
deflected in so many d fferent and intersecting
directions that there is a highly turbulent mixing
which effects wetting of parti~les that remain
suspended in the air after passing through the
precipitation chamber 176.
Downstream of the baffles, the outlet throat
180 compri~es a pair of substantially vertical walls
200 and 202 disposed about 4 in. apart which assures a
relatively high velocity for the air flowing through
the throat. To increase turbulence and mixing in the
outlet throat 180, horizontal baffles 201 and 203
project inwardly fxo~ walls 200 and 202~
The baffles 201 and 203 are preferably angle
irons which are disposed at vertically offset
elevations. To effect repeated reversal of the
horizontal velocity component of the flow into and
through the throat, the baffles 194, 196, 201 and 203
project alternately fro~ left and right into the outlet
throat. That is, the uppermost baffle 194 projects
from the left; the second baffle 196 projects from the
right; the third baffle 201 projects from the le~t; and
the lowermost baffle 203 projects from the right.
Accordingly, as water flows across the top of the
baffle 194, it will strike the vertical wall 200 and
changeQ its direction and 1OW downwardly onto the top
surface of the baffle 201 which deflects the water
generally horizontally across a small gap to hit the
right hand vertical wall 202. This water flowing
across this gap constitutes a fourth water wash. The
air flowing to left between the baffles 194 and 196 is
also deflected by the left wall 200 to reverse its
direction of flow and the air then is caused by the
right hand vertical wall to flow downward through the
ourth water wash Pormed by the baffle 201~ Similarly,
the water flowing from the fourth water wash flows down
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along the right vertical wall 202 to hit the top
surface of the baffle 203 projecting outwardly and
~oxizontally from the right vertical wall 202. The
baffle 203 deflects the water to change its direction
of flow to the left to form a fith water wash across
the gap between the left edge of the baffle 203 and the
left vertical wall 200. The latter deflects the water
which then flows down through the gap. ~he air is
likewise reversed from a hoxizontal rightward flow to a
l~ leftward horizontal flow and the air is deflected
downward to flow through the fifth water wash at the
gap between the baffle 203 and the left vertical wall
200. Because of the high velocity of air flow through
third, fourth and fifth water washes at these baffles,
and the rapid changes in flow direction for the water
and air, much of the water becomes spray particles and
is so mixed with the air so as to wet substantially all
of the paint particles being carri~d by the air.
After mixing takes place in the outlet throat
180, air and water flow generally downwardly into the
separation chamber 178 which has a very large volume
and causes the air leaving the throat to drop very
substantially in velocity, e>g. to 400 fpm or less at
which the paint and most of the water particles drop
out of the air. Thus, all but a small percentage of
the wetted paint particles and water particles ~all to
the floor 204 of the separatiGn chamber 178 and into a
drainage channel 206 which is shown in FIG. 3. To
prevent development of flow patterns which might carry
mist, i.e. very fine water parti~les to the exhaust
duct 208, a de1ector 210 extends substantially
vertically downward from one side of the outlet throat
l~0. The deflector 210 is preferably contiguous with,
and may be integral with, the vertical wall 200. Ihe
210 deflector forces water particles to flow downwardly
around i~s lower edge so tha~ their momentum auyments
gravitational forces in directing them into the
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drainage channel 206, rather than per~itting them to
pass to the exhaust duct 208.
To further increase the distance, mist
particles must travel to exhaust and to cause the mist
particles to change direction and remain for a longer
time in the separation chamber, there is provided a
second deflector 212 extending upwardly from the floor
204 of the separation chamber immediately down~trea~ of
the drainage cha~nel 206. The deflector 212 has its
lower edge 213 spaced above the floor 204 to allow
water flowing across the inclined floor to carry paint
particles i.nto the drainage channel 206. 'Fhe
illustrated channel 206 is substantially deeper than
usual so hat the surf~ce 215 of the water in the tank
is substantially below the inclined floors 204 and
205. Thus, air flowing across the right hand floor 205
will not pick up water from the surface 215 of the
water in the channel 206. Because of the high volume
of water flow and because of the inward slope o~ both
the bottom floors 204 and 205 into the drainage
channel, the wetted paint particles will be washea from
the floors and be accumulated in the drainage channel
and the cleaning of the floor~ will be alleviated. As
in the embodiment of FIG. 31 eliminators (not shown in
FIG. 4) may be provided in the exhaust duct to remove
fine particles or mist from the air. FIGURE 4
illustrates only the left half of the air handling
equipment and a second right hand half thereof of
mirror image construction i9 provided, as shown in the
first embodiment of the invention, in FIG. 1.
To review briefly the flow through the air
cleaning unit of FIG. 4, the subfloors 148 and 150 are
continually wetted by water flowing over the adjustable
weirs to form large pools of water 145 and 171 at the
lower edges of the subfloors. These pools assure a
continuous uninterrupted water flow, preferably at 20
and 15 gallons per lineal foot across their lower edges
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to form waterfall types of water washes. Air is
deflected horizontally flow through the first waterfall
water wash 163 and then flows th~ough the intake 160
ge~erally horizontally, and then flows generally
S downwardly and to the left as viewed in FIG. 4 into the
precipitation chamber 176. In the precipitation
chamber 176, air velocity drops substantially e.g. from
4000 fpm through the slot to 6Q0 or 800 fpm and the
horizontal component of the average flow velocity
reverses direction, and the air flows downwardly to the
right, through the second water curtain 181. The water
flows to the right across the top of the baffle 194 and
creates ~he third water curtain as it drops down onto
the top of the baffle 196. The air having passed
through the second water curtain and flowing downwardly
and to the right hits the wall 184 and the tops of the
baffle plates 194 and 196 and flows through the third
water curtain at the slot 198. Thus, the ~ir and water
are deflected and mixed and the air increases in
velocity flowing through the slot 198 and there is a
large static pressure build-up is caused at the throat
due to small size thereof. The air velocity in the
throat increases very substantially. The air and water
flowing to the left through the slot hit the left
vertical wall 200 and are deflected to cause a
turbulent air and water mix. The air flows down and
reverses in dir~ction to flow to right over the top of
the baffle 200. The water flowing over ~he riyht edge
of the baffle 200 creates a fourth water curtain and
air must reverse its direction and ~low down through
the fourth water curtain before hitting the left
vertical wall 200. The water also hits the vertical
wall 200 and flows down therealong to create a sixth
water curtain as the water drops therefrom into the
underlying deep drainage channel 206. The air in ~he
right hand portion o the separation chamber drops
quickly in velocity from several thousand fpm to about
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400 fpm. The volume of the chamber 178 is huge so the
air drops in velocity to less than the carrying
velocity for wetted paint or large water particles,
e.g. to a velocity of less than 400 fpm. The air in
the right hand portion of the separation chamber flows
through the sixth water curtain before flowing acxoss
the top of drainage channel. Because the water level
or surface 215 may be about a foot or so below the
floors 204 and 205, the air flowing over the channel
does not pick up more water~ ~he deflector 212
de~lects the air upwardly to assure that water entrain
from the sixth water curtain is not carried out within
the air stream that flows into the ~xhust duct 208. In
the embodiment of F16.4, an eliminator is not provided
in the exhaust duct although one may be provided if it
is thought to be desirable.
The air cleaning unit of FIG. 4 has been found
to be capable of removing over 99% of particulate
matter rom air during simulated industrial pain~ing
use. The combination of change of air flow directions
and of the highly turbulent mixing of air and water in
the intake 160 and the outlet throat 180, with the
slower, less turbulent flow in the precipitation
chamber 176 and separation chambPr 178 is responsible
for the high performance of the unit of FIG. 4. Also
partially responsible is the configuration of the
outlet throat 180. To achieve optimal performance, the
slot widths should be adjusted to particular values
determined by parameters such as the particle
concentration, the air flow rate, and the water 10w
rate. The independent adjustability of the widths of
the slots 174 and 198 enables the unit 126 to be
"tuned" to compensate for variation in these parameters.
FIG. 4 illustrates the preferred embodi~ent of
the invention which has been tested by an independent
testing company at very high rates of paint flow such
as about 97 lbs of paint being sprayed per hour in a
~en foot spray booth. The outlet lbs/hr. of paint
particles averaged only .27 lbs/hour with an air flow
rate of about 10,400 cfm.
From the foregoing, it will be appreciated
that the invention provides a novel and improved paint
spray booth. The invention is not limited to the
embodiment described above or any particular
embodiments.
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