[0001] This invention relates to a coater and more particularly to a so-called continuous
coater. Continuous coaters generally comprise a cabinet through which a product is
conveyed, and within which a coating of paint or other material is sprayed from nozzles
positioned interiorly of the cabinet. That sprayed material which is not deposited
on the product is generally recovered and recycled.
[0002] One of the most common problems encountered with all continuous coaters is that of
containing the material over-spray and solvents within the spray cabinet so that they
do not escape to the atmosphere through the product entrance and exit ports. Those
ports are never closed during the spray cycle so that it is difficult to prevent airborne
sprayed material and/or solvents from escaping through these ports. The problem is
compounded by the fact that the moving products create air currents which tend to
convey any airborne over-spray or solvents out of the cabinet.
[0003] In the past, continuous spray booths have existed which attempted to solve this problem
by withdrawing air from the interior of the booth through an exhaust system wherein
filtersor other devices extracted the over-sprayed material from the air before it
was exhausted to atmosphere. This type of booth air extraction system inherently creates
other problems while solving the problem of over-sprayed materials or solvents escaping
to the atmosphere. Specifically, it commonly reduces the efficiency of the system
in that it detracts from the percentage of sprayed material applied to the product.
Additionally, in the case of solvent base paints or sprays, it causes substantial
quantities of vaporized solvent to be withdrawn from the booth and thereby renders
it difficult to maintain a solvent saturated atmosphere within the booth. Such an
atmosphere is desirable to prevent build-up of oversprayed material on the interior
of the booth.
[0004] Another approach to the problem of preventing the escape of oversprayed material
from the entrance and exit ports of a continuous coater has been to place a vestibule
around the entrance and exit ports of the coater and to connect those vestibules to
an exhaust system within which a water spray is operative to remove air entrained
sprayed material from the air. This particular prior art system relied upon the water
flow within the exhaust system to create a relatively weak exhausting air flow from
the vestibules. But, this system suffered from several deficiencies, primary among
which was the fact that the ventilation flow from the vestibule was easily upset by
ordinary external air draughts and turbulence which caused air entrained spray to
billow forth from the coater cabinet into the atmosphere. Another deficiency of this
system was that it maintained a relatively continuous and substantial air flow from
the booth into the exhaust system with the result that it was difficult to maintain
a paint or solvent saturated atmosphere within the coater cabinet.
[0005] It has therefore been a primary objective of this invention to provide a continuous
coater which substantially overcomes such problems.
[0006] A continuous coater in accordance with this invention comprises a cabinet or booth
having vestibules which extend outwardly from either or both the product entrance
and exit ports. These vestibules are connected to an exhaust system including an exhaust
fan which is operative to pull outside air into the vestibule in sufficient quantities
and at a sufficient velocity to effectively form a barrier to the egress of oversprayed
material through the vestibules. The construction of the vestibule is such that very
nearly all of the air pulled into the vestibule to form the air flow barrier is air
from outside the booth. Consequently, there is minimal air flow disturbance within
the booth and therefore maximum sprayed material utilization.
[0007] Such a continuous coater not only minimizes the escape of oversprayed material to
the atmosphere but additionally, minimizes the quantity of air extracted from the
booth. By minimizing air extracted from the booth, it is possible to better control
the atmosphere inside the booth and to maintain it saturated or nearly saturated with
solvent preventing drying of oversprayed material and facilitating recovery and recycling.
[0008] In a preferred embodiment, there are air flow nozzles located within each vestibule
which provide an air curtain flow of air directed toward the coater cabinet. This
air flow minimizes the amount of airborne paint or sprayed material which escapes
from the coater cabinet into the vestibules and enables the interior of the cabinet
to be maintained saturated or very nearly saturated.
[0009] In addition to the advantages set forth hereinabove, a coater in accordance with
the invention has the advantage of being operable with lower total horsepower than
prior systems which relied upon water flow to generate the negative air pressure to
prevent the egress of over- sprayed material from the exit and entrance ports of the
booth. Heretofore, whenever water flow was relied upon to induce exhaust air flow
from adjacent the product exit and entrance ports, the system required very high horsepower
to pump large quantities of water and still was unable to effect the appropriate air
flow. The system of this invention which may include liquid scrubbing of the exhaust
gases is much more efficient and has been proven to require less horsepower than required
in water induced air flow systems of the prior art.
[0010] Another advantage of the system of this invention over water induced air flow systems
is that it may be applied to much larger coaters than is practical in a water flow
induced system.
[0011] The invention will now be further described by way of example with reference to the
accompany drawings in which:
Figure 1 is a perspective view of one embodiment of a continuous coater in accordance
with the invention.
Figure 2 is an end elevation of the coater illustrated in Figure 1.
Figure 3 is a diagrammatic top plan view of the coater illustrated in Figure 1.
Figure 4 is a side elevation of the coater illustrated in Figure 1.
Figure 5 is a perspective view, partially broken away, of the vestibule portion of
the coater illustrated in Figure 1.
Figure 6 is a diagrammatic top plan view of a second embodiment of continuous coater
incorporating the invention of this application.
Figure 7 is a side elevation of a third embodiment of the continuous coater incorporating
the invention of this application.
Figure 8 is a top plan view of the continuous coater illustrated in Figure 7.
[0012] Referring to Figures 1-5, the coater 10 comprises a coating booth or cabinet 11 having
vestibules 12 and 13 extending from opposite ends through which product to be coated
interiorly of the booth enters and exits from the booth. The vestibules 12, 13 are
connected through duct systems 15, 16 to the atmosphere via suction fans 17, 18 respectively.
[0013] The coater booth 11 comprises a pair of side walls 20, 21, a downwardly sloping bottom
wall 22, a ceiling 23 slotted at the top as indicated at 24 to permit the passage
of conveyor suspension hooks 25 through the ceiling, and end walls 26, 27. The end
walls are also slotted as indicated at 28 for the passage of the conveyor hooks through
those walls. Additionally, the end walls 26, 27 have entrance 30 and exit 31 ports
formed therein through which product suspended from the conveyor hooks 25 may pass
into and out of the booth.
[0014] The slots 24 in the ceiling and the slots 28 in the end walls are closed by overlapping
pliable strips 29 which close across the top and end wall slots of the coater cabinet
so as to permit entry of the conveyor hooks 25 but limit overspray or air escape to
or from the cabinet through the slots. In the embodiment illustrated in Figures 1-5,
paint or other coating material is pumped from a reservoir (not shown) via a hydraulic
pump (not shown) to rotating nozzles 35 mounted on the ends of rotating spray arms
36. Paint is pumped from the reservoir to these arms under high pressure and is forced
through the nozzles as an atomized spray. Coating material which is not applied to
the work falls to the bottom 22 of the coater booth where it is drained away through
a siphon port 38 by a scavenger pump and returned to the main pump reservoir.
[0015] The two vestibules 12, 13 are identical. One vestibule 12 which is located adjacent
the entrance port 30 of the booth will be described in detail. It will be understood
that an identical vestibule 13 surrounds the exit port 31 and is attached to the opposite
end 27 of the booth. The vestibule 12 functions as an enclosed passageway through
which product may enter the spray cabinet 11. It has a pair of side walls 40, 41,
a ceiling 42, and a floor or bottom wall 43. These walls 40, 41, 42 and 43 all are
sealingly attached to the end wall 26 of the cabinet 11.
[0016] The ceiling 42 is longitudinally slotted as shown at 42a to facilitate the passage
of the conveyor suspension hooks 25 through the vestibule. As in the case of the passage
24 in the spray cabinet, the slot 42a is closed by overlapping pliable strips 44 which
extend across the slot. The pliable strips permit the entry of conveyor hooks but
limit overspray or air from escaping through the slot to the atmosphere and additionally
function to prevent the ingress of air into the vestibule through the slot 42a.
[0017] A central section of each of the side walls 40, 41 of the vestibule taper outwardly
from adjacent the outer end 47 of the vestibule so as to provide a rectangular air
collector passage 48 on each side of the vestibule. These air collector passages 48
are defined by the outwardly flared sections of the side walls 45, 46, the unflared
side wall sections 49, 50 as well as the ceiling 42 and bottom walls 43 of the vestibules.
Each of these rectangular collector slots 48 is connected by a funnel-shaped section
of conduit 52, 53 to a circular duct 54, 55 respectively. The funnel-shaped sections
of ducts 52, 53 are rectangular at the input end which is connected to the air collector
slot 48 and are circular at their output end at which point they are connected to
the circular ducts 54, 55.
[0018] Referring to Figures 2, 3 and 5 it will be seen that there is combined within each
vestibule, means for creating an air curtain 108. This air curtain 108 is created
by pressurized air discharged from conduits 109 through holes or slots 112 aligned
so as to form a flow of air in the vestibule at a location between the air collector
slots 48 and the vestibule/coater cabinet 11 interface. These conduits 109 conform
to the cross-sectional silhouette of the vestibule opening. The slots 112 in the conduits
109 are operative to create an air flow curtain 108 directed at a selected angle inwardly
toward the paint spray cabinet. Flow of air within the air curtains 108 may be adjusted
and varied by air pressure regulators 110 located in the air line 111 which supplies
the conduits 109. By properly adjusting the regulators 110, and balancing the air
pressure at each vestibule/coater cabinet 11, it is possible to slightly pressurize
the coater cabinet 11 thereby minimizing the amount of airborne paint and solvent
coming out of the coater cabinet 11 and being exhausted into the collector slots 48
and maintaining a more nearly saturated atmosphere inside the coater cabinet 11.
[0019] At the outer ends, the vestibule's side walls 40, 41 preferably have an outwardly
extending flange 56 which forms an extension of the side wall. These flanges extend
at an angle of approximately 45° to the vertical plane of the side walls and serve
as wind or draft deflectors at the outer opening of the vestibules.
[0020] As may be seen most clearly in Figures 1, 2 and 4, the ducts 54, 55 extend in a generally
horizontal direction but slope slightly downwardly. At the inner ends each duct 54,
55 is connected to a vertical section of expansion chambers 74, 75 respectively which
extends up the sides of spray cabinet 11 to baffle boxes 78 and through ducts 58,
59 respectively. At the upper end each vertical section of duct 58, 59 is joined as
illustrated at 60 and connected to the exhaust fan 17. When the fan 17 is operating
it is operative to pull air through the outer end 47 of the vestibule as indicated
by arrow 65 through the air collector slots 48 into the duct systems via the conduit
54, expansion chamber 74, baffle box 78, conduit 58, conduit 55, expansion chamber
75, baffle box 78, and conduit 59. As is explained more fully hereinafter, this air
movement forms a flow barrier at the outer end of the vestibule to the escape of oversprayed
paint or solvents from the spray cabinet 11.
[0021] The coater illustrated in Figures 1-5 may be used for spraying either dry powder
materials or wet liquid paints or materials onto products passing through the cabinet
11. The coater illustrated in Figures 1-5 is primarily intended to be used for the
application of wet paints or liquid sprayed material and for that reason is equipped
with a liquid scrubbing system for extracting any airborne paints or sprayed material
from the exhaust air before it is exhausted to atmosphere. To that end there is included
in each of the ducts 54, 55 a liquid spray nozzle 70 through which liquid is sprayed
to create a liquid scrubber 71 within each of the ducts 54, 55. These liquid scrubbers
71 are effective to catch any air entrained particles and cause those particles to
run out of the duct system through a liquid outlet 73 to a separation tank (not shown).
[0022] The expansion chambers 74, 75 are sized so as to be of approximately twice the cross-sectional
area as the ducts 54, 55.
[0023] Located within the expansion chamber 74, 75 there is a downwardly curved deflector
76. This deflector is slightly wider than the diameter of the entering duct 54, 55
but narrow enough to allow a cross-sectional area past the deflector at least equal
to the area of the entering duct. The downwardly curved deflector in combination with
the expansion chamber functions to cause some of the heavier particles entrained in
the air stream entering from the ducts 54, 55 to drop out of the entrained air and
to flow via the drain pipes 73 to the separation tank.
[0024] Located above the arcuate deflector 76 in each of the expansion chambers 74, 75 are
baffles 78. These baffles function as final stage filters to prevent any liquid/air
entrained solid particles from escaping through the duct systems 15 and 16 to the
atmosphere.
[0025] At its upper end each vertical duct 58, 59 contains a manually adjustable butterfly
valve 80 for controlling the relative quantity of air pulled through each of the ducts
58, 59. Thus, it is possible by manually rotating the valves 80 to adjust the air
flow through each of the ducts 58, 59 so as to bring the air flow through each of
the ducts 58, 59 into balance, thereby insuring that there is a uniform flow of air
through each of the collector slots 48 located on the opposite side of the vestibule
12.
[0026] In operation, paint is supplied at a relatively high pressure to the nozzles 35 of
the rotating arms 36 via a pumping system (not shown). The paint is ejected through
the spray nozzles 35 onto product as the product is conveyed through the cabinet.
Excess paint is collected from the bottom of the booth via the siphon 38 and is returned
to the paint reservoir (not shown). Simultaneously, the suction fans 17 and 18 are
operated so as to cause air to be pulled from outside the openings 47 of the vestibules
into the vestibule collector slots 48. The butterfly valves 80 in each of the vertical
legs 58, 59 of the duct system are adjusted so that a relatively even and balanced
air flow is maintained through each of the slots 48. The applicants have found that
a minimum air flow velocity of approximately 800 feet per minute should be maintained
through each of the slots and that the optimal velocity is on the order of a thousand
feet per minute. By maintaining a balanced flow of air through the opposed slots 48
of each vestibule, an even flow of air is maintained over the full cross section area
of the vestibule openings 47. This even flow of air across the full cross section
of the vestibule functions as an effective air flow barrier to the escape of any airborne
spray through the entrance and exit ports of the vestibule. Since that air flow barrier
extends over the full area in the vertical plane of the vestibule openings the egress
of any airborne particles to the outside atmosphere is effectively prevented.
[0027] The cabinet 11 is substantially sealed against the inflow of air. The construction
of the vestibule and collector slots 48 is such that very nearly all of the air pulled
into the vestibule to form the air flow barrier is from outside the booth. Consequently,
there is a minimum air flow from the interior of the cabinet into the vestibule. Any
airborne paint particles or solvent though contained within the air and entering the
vestibule through the air curtain 108 is caused to flow by the air stream into the
air collector slots 48. Those airborne particles then are removed from the air stream
by the liquid scrubber 71 located within the ducts 54, 55. That liquid then flows
from the duct system via the drain pipe 73 to a liquid separation tank. The exhaust
air flows upwardly through the duct system and out through the exhaust fans 17, 18.
[0028] The very minimal flow of air from the paint cabinet 11 out through the exhaust system
enables the atmosphere within the cabinet 11 to be very closely controlled. The atmosphere
within the cabinet can be maintained very nearly solvent saturated and thereby the
build-up of paint on the interior walls of the cabinet can be avoided. w
[0029] The coater described hereinabove and illustrated in Figures 1-5 is primarily intended
for use in the application of a wet paint or spray material to products passing through
the coater. The system though is equally applicable to the application of a dry paint
or sprayed material in the form of a powder. Such a system as illustrated in Figure
6 is equally applicable to dry powder or wet spray operation. In general, this coater
is identical to the system illustrated in Figures 1-5 except that it has no liquid
cleansing system for extracting the airborne particles from the exhaust system. In
other words, the liquid spray nozzles are omitted from the system as is the liquid
drain pipe 73. Instead, dry collection filters 90 are placed in the exhaust slots
so as to collect any sprayed material which would otherwise be drawn into the exhaust
system. In all other respects this system is identical to that described in Figures
1-5 and operates in exactly the same way to prevent the exhausting of airborne sprayed
materials to the atmosphere.
[0030] Referring now to Figures 7 and 8, there is illustrated still a third embodiment of
the invention. This embodiment again is primarily intended for use in the coating
of liquid paints or spray material onto products passing through the coater. Those
components of this embodiment which are identical to components of the embodiment
of Figures 1-5 have been given identical numeral designations.
[0031] In the embodiment illustrated in Figures 7 and 8, the spray cabinet 11, the vestibules
12 and 13, and the system for supplying paint to the booth and for draining paint
away from the booth are identical to the corresponding components of the embodiment
illustrated in Figures 1-5. Similarly, the system for preventing the escape of air
entrained sprayed particles and/or solvent to the atmosphere is identical through
the vestibule exhaust ducts 54, 55 and expansion chambers 74, 75. Above the baffles
78 though the systems differ in that the two vertical ducts 58 on one side of the
paint cabinet 11 are interconnected to a single exhaust fan 100 and the two vertical
exhaust ducts 59 on the opposite side of the cabinet 11 are similarly interconnected
to a common exhaust fan 101. As in the embodiments of Figures 1-5 though it is important
that the air exhausted from the air collector slots 48 on opposite sides of a single
vestibule be balanced from side- to-side so as to effectively maintain an air curtain
barrier across the outer openings 47 of the vestibules 12, 13. To that end each vertical
leg 58 of the duct system contains its own air balancing butterfly valve or damper
103, 104 and similarly each vertical duct 59 on the opposite side of the cabinet contains
its own air flow control butterfly valves (not shown). These air flow control butterfly
valves 103, 104 are manually operated and adjusted so as to maintain the flows from
the opposite sides of each vestibule balanced, even though those flows are controlled
by different fans 100, 101.
[0032] Except for this different exhausting technique, i.e., the use of a single exhaust
fan connected to the vertical ducts on the same side of the paint booth rather than
a single fan connected to the exhaust ducts 58, 59 on the opposite sides of the paint
cabinet as in the embodiment of Figures 1-5, the two systems are identical. Since
each duct has its own balancing valve 103, 104, the operation of the system is identical
after that air flow balancing is achieved.
[0033] In practice, the primary advantage of the continuous coater described in each of
the three embodiments of this application resides in the fact that it maintains a
very effective barrier to the egress of sprayed material from the booths through either
the product entrance or exit ports. Specifically, the incoming air passing through
the vestibule entrance and/or exit
port 47 insures that neither the sprayed material nor solvents evolved from those
sprayed materials escaped from the coater to the atmosphere. Instead, those materials
which might otherwise escape to the atmosphere are entrapped within the duct exhaust
system and there removed from the air before the air is exhausted to the atmosphere.
[0034] We have described this invention as being applicable to both solvent and solvent-free
spray materials but we do not intend by such description to limit the invention to
any particular type of spray materials. Solvent type spray materials include water
base paints and sprays in which the water acts as the solvent.
1. A coater comprising, an enclosed coating chamber adapted to have an object conveyed
through it, from an entrance to an exit means being provided for spraying an object
in the course of passage through the chamber, characterised in that the chamber has
an air flow control vestibule extending extending outwardly from one or both of its
ends surrounding the entrance and/or exit openings, each of the vestibules having
an outer opening longitudinally aligned with but remote from the associated entrance
and exit openings of said chamber, means being provided for preventing air entrained
sprayed material from escaping from the coating chamber into and through the air flow
control vestibules, said air escape means comprising means for creating an air flow
from outside the vestibules through the vestibule openings over the complete cross
sectional area of the outer openings of the vestibules and exhausting the air from
the vestibules.
2. A coater as claimed in Claim 1 including an exhaust fan or the like for drawing
air from the vestibules.
3. A coater as claimed in Claim 1 or 2 including air collector slots located on opposite
sides of each of the vestibules, each air collector slots being connected to the exhaust
fan whereby air is caused to flow into each of the vestibules from the said outer
openings and to be exhausted from the vestibules through the collector slots.
4. A coater as claimed in either Claim 1,2 or 3 including removal means for removing
sprayed material from the air before the air is exhausted to atmosphere.
5. A coater as claimed in any of the preceding claims including means for adjusting
or balancing the flow of air through the collector slots on the opposite sides of
one or both of the vestibules.
6. A coater as claimed in any of the preceding claims wherein the ducting connects
the fans and collector slots and contains a liquid scrubber through which exhausted
air is caused to pass.
7. A coater as claimed in Claim 6 wherein the ducting includes a baffle section located
between each liquid scrubber and the exhaust fan.
8. A coater as claimed in any of the preceding claims including means located within
each of the vestibules for creating an air curtain within the vestibules directed
inwardly toward the coating chamber.
9. A coater as claimed in Claim 8 wherein the air curtain creating means is operable
to create an air curtain between the air collector slots and the coating chamber openings.
10. A method of preventing airborne sprayed material from escaping from a spray booth
in which conveyed products are continuously coated with the sprayed material, which
method comprises, sealing the booth against the ingress and egress of air except through
entrance and exit ports of the booth through which product enter and exit from the
booth, creating a vestibule sealed relative to the booth around the entrance and exit
ports of the booth, connecting an exhaust system to each vestibule for withdrawing
air from the vestibule, drawing air from outside said booth into the vestibule exhaust
system without simultaneously drawing any substantial quantity of air from inside
the booth so as to create a relatively high velocity air flow barrier to the escape
from said booth of airborne sprayed material.
11. A method as claimed in Claim 10 including the step of creating an air curtain
within each of the vestibules directed inwardly toward said booth.