Note: Descriptions are shown in the official language in which they were submitted.
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PAChGROU~D 0~' THE lNVENI~ION
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r ULTI-I~ASI~ SPRAY BOOrl'~-
This invention relates to a spray booth, and,
more particu]arly, to a water was!l spray booth that
employs a plurality of water was1les to more completely
remove particulates from the air and also has an
improvecl air flow pattern therethrollgh.
In spray booths, it is necessary to ~intain a
steady, even flow of air therethrough Eor two clistinc-t,
but equally important reasons. Constan~ air flow keeps
the airborne particu]ates sprayed in the booth, which
are often toxic, away from workers who might inhale
them. Presently, occupational safety an~ healtll
standards man~late that if spraying is to be performed by
a worker, rather than automatically by a machine, there
is to be a minimum uniform air flow past the worker of
100 cfm. The constant air flow also keeps away from the
spray equipment and workpiece oversprayed particulates,
which might otherwise cover the spray equipment or come
to rest upon the workpiece and cause an uneven finish
or, perhaps, to form drips on the workpiece.
Additionally, environmental clean air standards require
that the emissions from spray booths conform to certain
maximums with regard to the parts per million of
particulates.
Prior art spray booths have hacl limited success
in attaining these objects because of uneven air flow
patterns throughout the booths or because they employed
high-priced replaceable fibrous filter elements, throu~h
which air is circulated. Indeed, when such filters
become clogged with sprayed particulates, the air flow
therethrough is substantially reduced, thus decreasinc~
the air flow past the operator. Further, the air
cleaning ability of the spray booth is greatly reduced
and productivity is reduced due to the need to shut down
the system to replace the filters.
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Today, more and more paint spraying is done with automatic
spray equipnlent and often the equipment is used to spray different
articles. In some instances, the article may be sprayed from underneath
while -for other articles in the same spray booth the articles may be
sprayed from above. For still other particles, the spray nozzle may be
reciprocated vertically and up close to the ceiling of the booth, which is
usually a relatively dead air location. Thus, there is a need for a spray
booth which is versati1e enough to handle such different types of spraying
and, yet meet environmental standards as to emissions.
Emission standards are set very high today such that spray
booths which were previously used have been taken off the market because
of their failure to meet emission standards. While the prior art may
suggest various techniques for spraying water in a spray booth which
have a superficial resemblance to booths which meet current industry and
government standards as to air flow and as to emissions, such booths and
techniques can not and do not meet today's rigorous requirements as does
the present invention.
Generally speaking, the present invention may be considered as
providing a method of capturing air borne sprayed particles by within a
spray booth by wetting the same with a liquid with a plurality of liquid
washes, the method comprising the steps of: flowing a first stream of
air carrying sprayed particles from a spray chamber and through a
vertically extending wash means having staggered panels coated with a d~wn-
wardly flowing film of water to wet the spray particles contacting the
water film, flowing a second stream of air through a floor in the booth
and flowing the second stream of air across a lower second liquid wash
means beneath the floor, joining the first and second air stream together
and increasing the velocity of air flow sufficiently to lift water
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particles and de-flecting the combined air streams into a swirling
turbulent flow to wet sprayed particles being subjected to the turbulent
flow, and removing water particles from the combined air streams and
discharging the same.
The present invention also provides apparatus especially adapted
for carrying out the above method.
These and other features and advantages of -the invention will
become apparent from the following detailed description taken in
conjunction with the accompanying drawinys in which
FIG. 1 is a cross-sectional view of a multi-water-wash spray
booth embodying the present invention;
FIG. 2 is an enlarged fragmentary, cross-sectional view of one
of the water washes utilized in the spray booth illustrated in FIG. 1.
FIG. 3 is an enlarged, fragmentary, cross-sectional view of
another of the water washes
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utili~ed in -the spray booth illustrated in FIG~ l; and
FIG. 4 is an enlarged, fragmentary,
cross-sectional view o-f a further water wash includinq a
tur~ulence amplifier utilized in the spray booth
illus~rated in FIG. 1.
DETAILED DESCRIPTION
Referrinc~ to the figures of the drawings, there
is illustrated a syray booth, generally indicated by 10,
embodying tlle present invention. The spray hooth 10
inclucles an open-faced spraying section 11, and an ai~
cleaning section wherein paint-laden air that is drawn
through the booth 10 is cleanecl. The air cleaning
section 12 inc]udes three water wasl-les 14-16 that
provide water to entrain oversprayed paint particles. A
water reservoir 18 is located in the air cleaning
section 12 downstream of the water washes 14-16.
Disposed in the water reservoir 18 is a level
sensing device, not shown, and replacement water is
automatically supplied to the reservoir to prevent the
water level from falling below a desired minimum. A
pump, not shown, circulates water from the reservoir 18
to the various water washes 14-16. As air borne
particles of paint are wetted by water or water
particles, they become heavier and drop into the water
reservoir 18 resulting in relatively clean air being
exhausted from a water eliminator section 20. Paint
particles are transported by the water l9 into and are
held in the reservoir 18 as the air flows outwardly into
a rear water eliminator section 20. The paint
particles, being heavier than water, will sink to the
bottom of the reservoir 18, from which they are
periodically removed. Alternatively, paint particles
may be held up on the surface of the water by a
flocculant and periodically skimmed from the tank.
The water eliminator section 20 includes
baffles 21 that remove water particles from the air
prior to its being exhausted. A centrifu~al blower ~2
~lisposed within the passageway 20 is sufficiently
powerful so as to pull air through the bc)oth 10 at a
rate of 1()0 cfm past the spray booth operator, if any,
who woul.l be stancling in the front of the booth. r.y
maintaining the air moving at at least this rate, it is
assllred that air~orne paint particles ~ill not collect
and coat surfaces in the spray bocth or agglomerate in
stagnant air areas ancl ultimate]y clrop onto equipment in
the ~ooth or, worse yet, on an article 28, but ins-tead
are carried tl~roug1l tlle water washes.
Referring in yreater detai] to FIG. 1, the
spray booth 10 includes a housing 2~, typically made
from metal panels, that clefines a user porta] 25. In
i)ractice, the user portal 25 may typically be
approximately nine feet high, ten feet wide, and seven
and one-half feet deep. Within the portal 25, a user or
automated equipment directs a paint spray nozzle 26 or
the like at an article 28 suspended on a eonveyor hoolc
29 of a conveyor system 30 -that earries suceessive
objects laterally across the booth 10 in front of the
user. (While the present invention will be clescribed in
connection with a paint spray device, the spray booth
may be used for other spraying operations.) Some of the
solid airborne spray particles will not adhere to the
article 28 and constitute "overspray", initially coming
within an area symbolically defined by the lines 31.
The spray nozzle may be pointed downwardly to paint some
articles with the spray being directed towards the floor
of the booth. For other articles, the spray nozzle may
be pointed upwardly to spray the undersides of the
artieles. In still other applications, the nozzle 2~ is
reeiproeated vertieally while spraying.
Although the eentrifugal blowex 22 is powerful,
and, in practice, is able to cireulate air therethrough
at a high flow rate, e.g. at a rate of 18,000 efm, the
air veloeity throughout the spray booth is not
eonstant. Generally, veloeity is a function of the
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cross-sectionl~l area of the air fLow passageway at any
particular point. ~lile an air flow of 100 cfm must be
maintained past tlle user, it is founcl that in the front
of tile booth, where the cross-sectional area is the
largest, pockets of relatively "dead" air (i.e., pockets
of a1r moving at a slow velocity) may form around or
near the conveying system 30. As a result, overspra~ed
particulates tencl to remain in the dead air space and,
consequently, are more likely -to settle upon the
conveying equipment 30 or the wo~lcpiece 2S, causin~
undesirable coating of these i-tems. In order to prevent
such a dead air space from forming in the spray booth
and to keep paint from accumulating at or around the
ceiling of the spray booth particularly where the nozzle
2G is directed upward]y, the invention provides
auxiliary air circulation means, generally indicated by
32, supported on the roof and having nozzles 34
extending through the ceiling and spaced across the
width of the booth from the front to the rear thereof.
Tne nozzles 34 direct air from the front of the hooth
toward the rear, and, in practice in this illustrated
embodiment of the invention, the auxiliary blower 32 is
able to move air at a velocity of up to 800 fpm, with a
flow rate of up to 1050 cfm. Thus, upwardly directed
spray from a nozzle is taken away from the ceiling
before it can accumulate and drip down onto an article.
The floor of the spraying section 11 has air
passage therethrough and herein comprises a grate 35
t'nat extends the width of the spraying section from the
front to the rear so as to allow air and airborne
particulates to flow therethrough. In order to clean
the air flowing through the grated flooring 35, water
wash 14 underlies the flooring 35. With particular
reference to FIGS. 1 and 3, the water wash 14 includes a
spillway 36 that slopes downward from the front to the
rear of the spraying section a-t approximately a 10
angle. This ang'e allows water to flow more slowly and
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evenly across the spillway 36. Further, a more uniform air flow across the
bottom of the spray mg section is attained by the increasingly larger cross-
sectional area underneath the grated flooring 35 that accommodates the
increasing amcunt of air travelling towards the rear of the spraying
section. A continuous, thin sheet of water is introduced across the
spillway Æ face 36 by means of a reservoir, generally indicated by 38, that
includes an inlet manifold 39 that extends across the booth at substantially
the opening of the user portal 25. The manifold 39 includes a plurality of
downward pointing nozzles 40 that supply water to a trough 41. When the
trough 41 is filled, water will flow over the upper, laterally-e~tending
weir edge 42 of the trcugh 41, the edge 42 being coextensive with the upper
edge of the spillway 36, to widely distribute water aver the entire width of
the spillway 36. As the water continuously covers and flows down the
spillway 36, a downdraft of air and particulates will contact the water
only, thus entrainilg some of the airborne particles therein. A constant
and even thin film of water covering the spillway surface at all times
assures that it will not become coated with paint particles.
Referring to FIGS. 1 and 2, the second water wash 15 provides
cascading water flowing downwardly along tlhe surfaces of staggered baffles
44, the cascading water impinging airborne paint particles which are trapped
thereby. Such a water wash, (which is more particularly shown and described
in U.S. Patent, 4,4a4,513, issued November 27, 1984), includes a plurality
of ve,tically extendm g baffle panels which have their edges overlap in a
vertical and lateral direction to define slots. The slots extend the entire
height of the work area of the bcoth and the irregular path defined by the
slots creates air turbulence that pramotes contact between airborne paint
particles ~nd the water cascading down
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the surfaces of the baff]e panels. The baffles are
slightly tilted toward the front of the spray hooth at
approximately a 5~ angle from vertical in order to slow
the cascade and to more even]y clistribute the cascading
water across the baffle. A thin continuous film of
water wets the front surfaces of the baffle panels.
Upon contactin-3 the sheets of waters on -the pane]s, the
paint droplets will be carried by the water -to the
bottom edge of the spillway 36. Water is supplie~ to
the baffle surfaces by means of a reservoir, generally
indicated by 45, that includes an inlet manifold 46 that
extends across tlle width of the booth. The manifolcl 45
includes a plurality of downwardly pointing no~7.3es 4~3
extending therefrom. The manifold supplies water to a
distribution trough 49, and water overflows the upper,
laterally-extending weir edge 50 of the trough 49 to
widely distribute a continuous water film over the
entire width of the baffle surfaces to prevent their
becoming coated with paint.
An air-deflecting panel 51 is provided behind
the baffle panels 44 to direct the air which has passed
through the baffles toward the bottom of the booth. The
panel 51 is a substantially flat sheet which slants
towards the back of the booth from the front toward the
bottom at an angle of approximately 15 from vertical,
thus providing an increasingly larger cross-sectional
area behind the baffle surfaces 44 in a downward
direction to accommodate the increasing amount of air
being deflected downward. Thus, a more uniform air flow
across the lower ends of the baffle surfaces 44 is
maintained. The water flowing down the spillway 36
flows under the bottom edges of the baffle surfaces and
the spillway 36 define a slot or space 52 therebetween
through which air and the water can flow. All of the
air flowing through floor grate must flow through the
slot 52 and through a water fall wash of the water
falling from the bottom ends of the panels and this also
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aids in removin(~ air borne partic]es. That ls, water
~ropping from the panels creates a water curtain through
wllich t]le air stream passing through the qrate mllst flow
with particles in the air being wetted in this water
curtain.
In order to maximize the air cleaning
capability of the spray booth, a thircl, hiqh-velocity,
high-tllrbulence water wash lG is employed to scrub the
air after it has passe-l through bo-th the downclraft an(1
baffle water washes 14, 15. This water wash 16 forms a
narrowecl or restricted throat or passageway 63 throucJh
whicll all o-f the air ancl all of the water must pass in
this embodiment of the invention. The restricted throat
~3 greatly accelerates the air passing therethrough to a
predetermined velocity, e.g. in excess of 5,000 fpm,
with a predetermined static pressure drop across the
passageway of approximately four to five inches of
water. ~isposed within the passageway is a water lift
and turbulence amplifier 62 that promotes formation of
water vapor and the mixing between the airborne
particulates and the water vapor or water droplets in
the air.
Referring now more particularly to FIG. 4, the
turbulent water wash 16 inclucles a curvecl ramp 54
integral with the lower end of the spi]lway 36 and
sloping downward from the space 52 defined by the lower
end of the baffle panels 44 and the surface of the
spillway 36. Accordingly, the water flowing down off
the lower end of the baffle panels 44 is added to the
water flowing down the spillway 36 to further flow down
the ramp 54 into the restricted throat 63. Depending
from the bottom edge of the air-deflecting panel 51 is a
water distribution trough 55 that is supplied wit~ water
by an inlet manifold 56. The manifold 56 extends across
the booth and is provided with a plurality of clownward
pointing nozzles 58. Adjacent to the upper laterally
extending weir edge 59 of the trough is a deflector
plate G0 whose distal end 61 terminates in a
semi-circul.ar section that is spacecl from the surface of
the ramp 54. Tlle water overElows -the weir edge 59 of
the trough 55, and is widely distributed to wet ~nd
cover -the entire width of the deElector pla-te 60 and the
water drops into the restrictecl throat or slot 63
between the distal end Gl oE the deflector plate 60 ancl
the ramp surEace 54 and into the high-velocity air.
I-ierein, tlle dis~al end is curved upwardly and rear~ard7y
so that the water theron may fall under gravity into t'ne
throat 63 to become air borne because the high velocity
of air flow throu~h the slot.
It has been found that there is a tenclency clue
to surface tension for the water flowing down the ramp
54 to remain thereon and it is desired to break this
surface tension and to lift a substantial quantity of
this water from the ramp and mix it turbulently with the
air in orcder to wet any paint particles havi.ng passed
through the previous water washes. To the end of
increasing the amount of water lifted by the high
velocity air flow through the throat 63, usually the air
velocity is in the range of 4000 to 5000 fpm. To these
ends the ramp 54 may be provided with a water lift means
62 in the form of an upwarclly inclined ramp or ski jump
that raises the water into the high velocity air stream
and defines at its edge 68 the smallest cross sectional
area and hence the higllest air velocity within the
throat 63. Thus, the water flowing down the ramp 54
flows up an inclined face 67 of the wedge ancl is picked
off the edge G8 of the wedge by tlle high velocity ai.r
flow through the slot. After passing through this
restricted throat 63, the air is expanded and swirlecl in
a turbulent area 70 on the downstream side of the
deflector plate G0. l~le area 70 is an area of high
turbulence ancd swirling and mixing of water borne air
and paint particles to wet the same. The high velocity
air leaving the throat 63 e~pands immediately into a
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larye open space or area 70 and is directed to hit a
cleElector panel 64 to cause the air to bounce and swirl
upward]y as indicated by the arrows in FIG. 4. This
increases the air turbulence ancl the amount of time tllat
the water alld air borne water particles stay in t~e
turbu]ent area ~0 and also a;ds in having the paint an-l
water particles contact the surface of the water 19 in
-the reservoir 18 hefore traveling up the eliminator ~0.
The panel 64 depen~s from the bottom edge of the wa-ter
distribution trough 55, in this instance. The panel 64
extends to a predetermined distance above the surface of
the wa-ter 19 so as to define a slot 77 through ~ich the
air and air borne particles must flow before flowing
into the eliminator section 20.
The velocity of the air passing throuqh the
space de-fined by the ramp surface 54 and the deflector
plate 60 may be altered by adjusting the cross-sectiona]
area of tlle slot 63. Thus, in keeping wi-th the
invention, the air deflector plate 60 is pivotahle about
its upper end. To this end, the deflector plate 60
includes ears 65 that capture an axle 66, about which
the deflector plate 60 may rotate. The deflector plate
60 may be maintained in its desired location by any well
known means such as clamps, etc. In use the operator
will adjust the width of the slot 63 by pivoting the
deflector plate 60 to increase or decrease the space
between the wedge edge 68 nd facing curved distal end 61
of the deflection plate to increase or decrease or the
maximum air flow velocity through the slot 63. It is
preferred to swing the defelctor plates until and the
static air pressure at the slot is between 4 and 5
inches of wa-ter and at this pressure the air velocity
will be in the range of 4000 to 5000 fpm for the booth
illustra-ted and described herein. ~t this air velocity,
the water will be lifted and air borne as the water
discharges from both the rampe 54 and from the deflector
plate and is carried rearwardly into the turbulent area
7~ for the final wash of paint particles. If the air
velocity is ~oo high, the water particles may he carried
by -the air through the eliminator section 20; and, if
too low, sufficient water wll] not be liftecl.
Generally speaking, the action is akin to a
no-pump spray lift action which usually re~uires about
40~0 to 5000 fpm velocity -to lift the water to form a
water wash.
In order to cause water particles to he remove~l
from the air prior to the air being exhausted throucJ~
the eliminator seetion 20, a plurality of haffles 21 are
provided therein to interdiet upwarc1 flowing air and to
defleet the same. The baffles 21 are génerally flat,
narrow sheets extending across the booth that slant
downwardly within the exhaust duct. Flanges 78 are
formed along and extend perpendicularly from each edge
of the baffles 21 to add rigidity thereto. The baffles
interdict the air and cause it to change direction and
this eauses the veloeity of air borne water partieles to
slow down and to drop. In order to further reduce the
ability of the air exhausting through the passageway to
carry water and/or paint partieles, the eross-seetional
area of the duet inereases in the upward direetion so as
to reduee the velocity of the air flowing therethrough.
The water partieles eolleet on the baffles and also drop
into the underlying reservoir tank for recircu]ation
Thus, substantially clean air is exhausted through -the
duet.
In actual tests, the spray booth described
herein has had emissions of only .75 grains per hour and
has been tested to provide a 99.98% effieieney on smoke
tests. Sueh effieieneies clemonstrate the effeetiveness
of the present invention.
Thus, it ean be seen that a multi-water-wash
spray booth has been provided that provides an improved,
more uniform eirculation of air past the operator and
more effectively cleans the air of oversprayed
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part:iculates. WhiLe the invention has been describe~ in
terms of a preferred embodiment, it is not intende(l to
so lim.it tl~e invention. On the contrary, it is intended
to cover all alternatives, modifications and equival.ents
~itl~in the scope of the invention as clefined hY the
appended claims.
