An overspray extractor collects the overspray of a volatile organic compound coating material sprayed onto three-piece steel cans. The overspray extractor comprises a hood having five orthogonal walls, with the bottom wall having a slot of predetermined width that is placed above the cans and downstream of the coating material nozzles. The ratio of the height of the hood between the top and bottom walls to the width of the bottom wall slot is greater than one. The hood is connected by means of a throat located opposite an outside wall to an exhaust passage. When a vacuum is applied to the hood, coating material overspray and atmospheric air are drawn into the hood through the slot and through the hood into the exhaust passage. A slit in the outside wall permits atmospheric air to be drawn into the hood to flow along and scrub the top wall of solids from the coating material that coagulate on the top wall. The overspray extractor further comprises a face plate that removably covers an opening in the outside wall. Removing the cover enables the interior of the hood to be cleaned in place. The overspray extractor operates for much longer times without requiring cleaning and requires less power than prior equipment.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to environmental protection, and more particularly 
to apparatus for collecting and disposing of industrial coatings. 
2. Description of the Prior Art 
Millions of three-piece steel cans are manufactured daily. The process of 
manufacturing the bodies of the steel cans involves many carefully 
controlled steps. Generally, a flat sheet of steel is coated on both sides 
with a thin layer of an organic compound that protects the can from the 
product the can is to hold. Narrow margins on both faces along two opposed 
edges of the sheet are left uncoated. The sheet is rolled such that the 
uncoated edges abut to form a thin walled tube with a longitudinal axis. 
The tubes are propelled sequentially along their longitudinal axes in a 
downstream direction past a welding station. At the welding station, 
in-line continuous welding systems operate to weld together the abutting 
edges to form a stable thin walled tube that serves as the can body. 
From the welding station, the can bodies continue downstream to a liquid 
stripe application or coating station. At the coating station, stationary 
nozzles spray the continuously moving can bodies along their welded seams 
with the proper organic compound such that the entire inner and/or outer 
surfaces of the can bodies are properly coated. The coating materials 
typically are volatile organic compounds such as lacquers, enamels, and 
vinyls, and they are composed of known solids and solvents. From the 
coating station, the cans move downstream for further processing. 
Coating the welded seams of the can bodies presents several difficult 
problems. The coating material must be accurately directed so as to strike 
and coat the welded seams while at the same time coating as little of the 
adjacent can areas as possible. To avoid spraying excessive material, the 
coating equipment must operate in a carefully controlled manner so that 
the coating material is sprayed only when a can is present at the coating 
station during its continuous downstream motion. Two paramount 
requirements are to minimize overspray of the coating material and to 
prevent any overspray from continuing downstream or from entering the 
atmosphere. 
To collect coating material overspray and prevent it from entering the 
atmosphere, it is known to provide the liquid stripe application or 
coating stations of seamed can bodymakers with vacuum operated exhaust 
systems. The exhaust systems collect the overspray and direct it to a 
filter that traps the coating material solids for subsequent disposal. The 
solvents of the coating material overspray pass through the filter to be 
burned or otherwise properly disposed of. 
FIGS. 1 and 2 show simplified side and front views, respectfully, of a 
prior exhaust system 1 for a seamed can bodymaker. The can bodies 3 travel 
continuously at high speeds in the downstream direction of arrow 5. 
Stationary nozzles schematically represented by reference numeral 7 spray 
coating material on the external and internal surfaces of the can bodies 3 
along the welded seams 8 thereof as the can bodies travel past the 
nozzles. 
The prior exhaust system 1 includes a hood 9 with an open slot 11 that is a 
short distance above the spray nozzles 7. The hood 9 has an arcuate bend 
of approximately 90 degrees. Depending upon the specific application, the 
length of the slot 11 may range between approximately nine and 18 inches 
and have approximately a two inch width. The hood connects via a throat 13 
with an exhaust passage 15. The areas of the hood inlet slot 11 and outlet 
throat 13 are generally equal. The exhaust passage 15 opens into a filter 
box 17. 
To draw overspray from the nozzles 7 into the exhaust system 1, a vacuum is 
created in the filter box 17, exhaust passage 15, and hood 9 by a blower, 
not shown, that is connected to a filter box stack 19. The overspray thus 
flows through the hood to the filter box, where the solids in the coating 
material overspray are separated. The remaining solvents are drawn out 
through the stack 19 for appropriate processing. 
During normal operation, some overspray from the coating material 
coagulates into a gel like substance 20 on the hood concave inner surface 
18. The coagulant 20 tends to drip back through the hood slot 11 and onto 
the can bodies 3. Further, as the solids coagulate on the hood surface 18, 
the area in the hood 9 through which the overspray material must flow 
decreases. Consequently, the pressure drop required to maintain adequate 
overspray flow through the hood and the rest of the exhaust system 1 
increases, thereby resulting in increased power consumption by the blower. 
To maintain proper operation, the substance 20 must be removed from the 
surface 18 at regular intervals. For example, with some spray materials, 
the coagulant must be cleaned from the hood surface 18 after approximately 
eight hours of system operation. 
The prior exhaust system 1 functions adequately, and numerous installations 
have been in successful operation for many years. Despite the fact that 
the hood 9 must be removed from the rest of the exhaust system for 
cleaning the overspray solids 20, the frequency of cleaning is tolerable. 
However, increasingly stringent environmental considerations have made the 
problems associated with coating material overspray collection much more 
difficult to solve. Particularly, whereas formerly high solvent coating 
materials were acceptable, recent regulations dictate that high solid 
content coating materials now be used. Unfortunately, the prior exhaust 
system 1 does not work as well with high solid coating materials as with 
high solvent materials. High solid coating materials tend to coagulate at 
much faster rates on the hood surface 18 than high solvent materials. As a 
result, more frequent cleaning of the hood surface 18 is necessary. In 
some installations, the surface 18 must be cleaned approximately two times 
oftener with the new high solid coating materials than with previous 
coating materials. That increase in the frequency of cleaning is 
unacceptable. 
Thus, a need exists for an overspray exhaust system that is capable of 
handling high solid content coating materials. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an overspray extractor is 
provided that more efficiently controls overspray of volatile organic 
compounds than was previously possible. This is accomplished by apparatus 
that includes a spray collecting hood having a bottom wall with an inlet 
slot and a top wall located parallel to and above the bottom wall at a 
distance therefrom that is greater than the width of the bottom wall slot. 
In addition to the bottom and top walls, the hood is comprised of two end 
walls and an outside wall so as to form a five sided orthogonal enclosure. 
The bottom wall is generally horizontal, and it defines a generally 
rectangular slot that extends between the two end walls. The outside wall 
extends between the two end walls and between the top wall and the bottom 
wall. The side of the hood opposite the outside wall is open. 
The open side of the hood forms a throat that opens into a vertically 
oriented exhaust passage. The exhaust passage extends upwardly and 
downwardly from the hood throat. The lower end of the exhaust passage is 
closed. The upper end of the exhaust passage opens into the inlet end of a 
filter box. A blower is installed at the outlet end of the filter box. 
Typical dimensions of the hood components include top and bottom walls that 
range between approximately nine and 18 inches long between the end walls 
and approximately 10.5 inches between the hood throat and the outside 
wall. The outside and end walls are approximately seven inches high. The 
slot in the bottom wall is approximately two inches wide and is preferably 
located closer to the outside wall than to the throat. The ratio of the 
height of the end and outside walls to the width of the bottom wall slot 
is called the hood aspect ratio; in the example given, the aspect ratio is 
3.5. 
By operating the blower, overspray and atmospheric air are drawn at a 
relatively high inlet velocity through the bottom wall slot into the hood. 
From the hood, the mixed overspray and air are drawn through the throat 
into the vertical exhaust passage, and then through the filter box. 
Inside the hood, the velocity of the overspray and atmospheric air 
decreases considerably from their inlet velocity. The mixed overspray and 
air also leave the hood through the throat at a velocity lower than the 
inlet velocity. The ratio of inlet and outlet velocities is inversely 
proportional to the hood aspect ratio. 
The unexpected advantage of the overspray extractor employing the hood of 
the present invention is that the solids of sprayed high solid content 
volatile organic compounds do not readily coagulate inside the hood. While 
some coagulation does occur on the hood top wall, the buildup is much less 
than in prior overspray collection equipment and is well within 
commercially acceptable limits. 
Further in accordance with the present invention, the hood is cleanable in 
place on the exhaust passage. For that purpose, the entire outside wall is 
not permanently joined to the end, bottom, and top walls. Rather, a 
portion of the outside wall is composed of a generally U-shaped face plate 
having opposed legs that overlie respective end walls. A wing nut and slot 
arrangement is employed to removably attach the face plate legs to the end 
walls. As a result, the face plate can be easily removed for providing 
access to the interior of the hood to clean most accumulated overspray 
solids. 
To further reduce coagulation of the overspray materials on the interior of 
the hood, the overspray extractor of the present invention also includes 
an auxiliary wiper. In the preferred embodiment, the auxiliary wiper is 
formed as a slit in the outside wall a short distance from its junction 
with the top wall. The slit extends between the two end walls. The slit is 
formed by the cooperation of the top wall and the free edge of an angled 
plate connected to the outside wall. The free end of the angled plate is 
spaced inwardly from the plane of the outside wall. Consequently, air can 
enter the hood through the slit between the plate free edge and the top 
wall. That construction directs air drawn by the blower to flow along the 
top wall to the hood throat. The flowing air creates a scrubbing action on 
the top wall that reduces the tendency of the solids in the volatile 
organic compounds to coagulate on the top wall, thereby contributing to 
the effectiveness of the overspray extractor. 
Other advantages, benefits, and features of the present invention will be 
apparent to those skilled in the art upon reading the detailed description 
of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Although the disclosure hereof is detailed and exact to enable those 
skilled in the art to practice the invention, the physical embodiments 
herein disclosed merely exemplify the invention, which may be embodied in 
other specific structure. The scope of the invention is defined in the 
claims appended hereto. 
Referring to FIGS. 3 and 4, an overspray extractor 21 is illustrated that 
includes the present invention. The overspray extractor 21 is particularly 
useful for collecting and controlling liquid coating materials sprayed on 
the bodies 3 of three-piece steel cans, but it will be understood that the 
invention is not limited to can bodymaking applications. 
GENERAL 
For purposes of background, the manufacture of three-piece steel cans 
involves the propulsion of the can bodies 3 on a continuous basis, with 
their longitudinal axes 22 horizontal, in the downstream direction of 
arrow 5 by known can transporting equipment, not shown. The can bodies are 
welded along respective longitudinal seams 8 at a welding station, not 
illustrated in FIGS. 3 and 4. Subsequent to being welded, the cans enter a 
coating station 23. At the coating station 23, the interiors and/or 
exteriors of the welded seams 8 are sprayed with a coating material from 
inner and/or outer nozzles 25 and 27, respectively. The coating material 
is normally a volatile organic compound, such as a lacquer, vinyl, or 
enamel. Volatile organic compounds used in modern seamed can bodymakers 
have a relatively high proportion of solid materials dissolved in a 
relatively low proportion of solvents. 
An inherent characteristic of the can seam coating process is that more 
coating material is sprayed from the nozzles 25 and 27 then is actually 
deposited on the cans 3. Consequently, the overspray must be collected and 
properly disposed of. For that purpose, a hood 29 of the overspray 
extractor 21 of the present invention is located immediately downstream of 
the coating station 23, and the hood overlies the can bodies 3 as they 
continuously move downstream from the coating station. The nozzles 25 and 
27 are positioned such that the coating materials sprayed from them are 
directed toward the underside 31 of the hood 29. 
The hood 29 defines a velocity reduction chamber 60 that has an entrance 
slot 43 and an exit throat 45. The velocity reduction chamber 60 opens 
through the throat 45 into a vertically oriented exhaust passage 47. A 
lower portion 49 of the exhaust passage 47 below the velocity reduction 
chamber throat 45 connects with a removable pan 50. The upper end 51 of 
the exhaust passage 47 is connected to the inlet end 53 of a filter box 
55. The filter box 55 has an outlet end 56 to which is mounted a blower 
57. By operating the blower 57, overspray from the nozzles 25 and 27 is 
drawn in the direction of arrows 58 through the slot 43 into the velocity 
reduction chamber 60 and from the velocity reduction chamber through the 
exhaust passage 47 and filter box 55. 
HOOD 
Looking also at FIGS. 5 and 6, the hood 29 is comprised of a top wall 33, 
an upstream end wall 35, a downstream end wall 37, a bottom wall 39, and 
an outside wall 41. The hood may be attached to the exhaust passage 47 by 
conventional angles 62. The walls 33, 35, 37, 39, and 41 define the 
velocity reduction chamber 60 of the hood. The bottom wall 39 is 
fabricated with two spaced apart coplanar panels 59 and 61. The panels 59 
and 61 extend for the full length of the hood between the end walls 35 and 
37. Connected to the facing edges of the panels 59 and 61 are respective 
angled strips 63 and 65. The angled strips 63 and 65 converge upwardly 
toward the top wall 33, making obtuse angles of approximately 150 degress 
with the panels 59 and 63, respectively. The free edges 67 and 69 of the 
angled strips 63 and 65, respectively, define the width of the hood slot 
43 and are spaced apart a distance W. The spacing between the end walls, 
and thus the length of the slot, preferably ranges from between 
approximately nine and 18 inches, depending on the application at hand. 
It is a feature of the present invention that the height H between the hood 
bottom wall 39 and top wall 33, and thus the height of the end walls 35 
and 37, is considerably greater than the width W of the slot 43. It is 
useful to define the ratio of the height H of the hood to the width W of 
the slot as the aspect ratio of the hood 29. Consequently, the aspect 
ratio of the hood is greater than 1, and the aspect ratio is preferably in 
the neighborhood of 3.5. Specifically, it has been found that a width W of 
approximately two inches and a height H of approximately seven inches 
works very well for many applications. With those two dimensions, the 
ideal length of the hood between the throat 45 and the outside wall 41 is 
approximately 10.5 inches, but that dimension may vary depending on the 
clearance available from nearby machinery. 
As mentioned, the hood velocity reduction chamber 60 opens into the exhaust 
passage 47 through the hood throat 45. To enhance collection of volatile 
organic compound solids precipitated from the solvents within the velocity 
reduction chamber and within the exhaust passage, the flowing overspray 
and atmospheric air are deflected slightly downwardly as they leave the 
velocity reduction chamber through the hood throat 45, as is indicated by 
arrows 58' in FIGS. 3 and 5. The deflection is created by a short tab 70 
bent in the hood top wall 33 at the throat and extending between the two 
end walls 35 and 37. A tab approximately one inch long and at 45 degrees 
to the plane of the top wall works very well. 
EXHAUST PASSAGE AND FILTER BOX 
The exhaust passage 47 has a trap portion 49 that extends several inches 
below the hood throat 45. The exhaust passage is open at its bottom end 
71, and the open bottom is covered with a removable pan 50. The lower end 
71 of the exhaust passage and the pan 50 serve as a liquid trap for any 
precipitated coating material solids leaving the hood 29. 
The upper end 51 of the exhaust passage 47 connects with the inlet end 53 
of the filter box 55. A number of mechanical filters 77, as are known in 
the art, are installed in the filter box. There is also a conventional 
liquid manometer 79 on the filter box, and a damper 81 between the outlet 
end 56 of the filter box and the blower 57. 
CLEAN IN PLACE 
Further in accordance with the present invention, the velocity reduction 
chamber 60 is easily and quickly accessible. That result is achieved by 
providing an opening 83 in the outside wall 41 and by covering the opening 
83 with a tight fitting but removable face plate 85. Preferably, the face 
plate 85 has a bottom angle 87 that wraps around the bottom wall 39 of the 
hood 29 and end angles 89 that wrap around the associated hood end walls 
35 and 37. For convenient removal and replacement, the face plate end 
angles 89 are cut out with slots 91. Studs or thumb screws 93 project 
through the hood and the face plate slots 91 and cooperate with wing nuts 
95 and washers 96 to removably hold the face plate to the hood 29. 
AUXILIARY WIPER 
In the preferred embodiment, the overspray extractor 21 is designed with an 
auxiliary wiper 97. Looking especially at FIG. 5, it will be noticed that 
the outside wall 41 of the hood 29 is formed with an inwardly extending 
angular plate 99 near the top wall 33. The outside wall angular plate 99 
does not join with the top wall. Instead, a narrow slit 101 is formed 
between the free edge of the angular plate and the hood top wall. The slit 
101 runs for the full length of the hood between the end walls 35 and 37. 
OPERATION 
In operation, overspray of coating material from the inside nozzle 25 
escapes through gaps G between successive cans 3 as the cans pass 
longitudinally in the downstream direction 5 under the overspray extractor 
hood 29. The blower 57 is energized to draw atmospheric air and overspray 
from both nozzles 25 and 27 through the hood slot 43 into the velocity 
reduction chamber 60 along a flow path generally indicated by arrows 58. 
The damper 81 is positioned within the filter box outlet 56 in light of 
information provided by the manometer 79 to calibrate the overspray 
extractor 21 for optimum performance. 
As the overspray and air flow through the slot 43 into the velocity 
reduction chamber 60, their velocity is decreased considerably. In the 
velocity reduction chamber, a small amount of the solids of the coating 
material overspray precipitates from the solvents. Some of those solids 
collect on the inside surfaces 103 of the hood angled plates 63 and 65 and 
drain to the flat inside surfaces 105 of the bottom wall sections 59 and 
61. Accordingly, the hood region adjacent the angled surfaces 103 act as a 
liquid trap. 
As the overspray and air are drawn along in the direction of arrows 58 
through the hood throat 45 into the exhaust passage 47, they are deflected 
slightly downwardly as indicated by the arrows 58' of FIG. 5 by the angled 
tab 70. Additional amounts of overspray solids precipitate out of the 
coating material as the overspray and air flow through the throat 45. The 
downward deflection of the overspray and air caused by the tab 70 results 
in those solids falling by gravity to the bottom pan 50, where they are 
collected for easy and proper disposal. The great majority of the solids 
remain dissolved in the solvent of the coating material as it passes up 
the exhaust passage to the filter box 55. There, the filters 77 
mechanically remove the remainder of the volatile organic compound solids 
in dry form, enabling those solids to be easily and properly handled. The 
overspray solvent passes directly to the atmosphere or to an incinerator 
for burning, as is known in the art. 
The outstanding benefit of the overspray extractor 21 is that the solids in 
the can coating material have much less propensity to coagulate inside the 
hood 29. In addition, the overspray extractor 21 requires less power to 
operate compared to prior exhaust systems. Specifically, the collection of 
solids of high solid content coating material on the inside surface 107 of 
the top wall 33 is far less than on analogous surfaces of prior equipment. 
The slit 101 contributes to keeping the hood surface 107 clean over the 
slot 43. That is because during operation a stream of air is drawn into 
the velocity reduction chamber 60 through the slit by the blower 57, as is 
indicated by arrow 109. The air stream 109 passes along the top wall 
surface 107 on its way to the hood throat 45. The air stream acts to scrub 
any coagulated coating material solids from the surface 107. Some of those 
solids may be redissolved in the solvent of the main overspray flow of 
arrows 58. Other of those solids fall to the liquid trap in the pan 50 or 
onto the hood bottom wall inside surface 105. 
Other reasons for the greatly reduced tendency of the solids in the coating 
material to coagulate on the top wall inside surface 107 are not fully 
understood. A factor for reduced solid coagulation has to do with the 
reduction in velocity of the overspray and air as they pass into the 
velocity reduction chamber 60 through the slot 43. In any event, downtime 
for cleaning the inside of the hood 29 is greatly reduced. When cleaning 
coagulated overspray solids is eventually required, it is a simple matter 
to remove the face plate 85 by means of the wing nuts 95 and thus quickly 
and easily clean in place the velocity reduction chamber 60. 
The reduction in power requirements of the overspray extractor 21 is 
another benefit of the reduction of overspray solid coagulation on the 
hood top wall surface 107. The reduction in power is related to the 
reduction in velocity within the velocity reduction chamber 60 and to the 
increased amount of air drawn through the hood 29. The reduction in 
overspray coagulation and the reduction in power requirements combine to 
render the overspray extractor 21 a significant advance in the art of 
collecting coating material overspray in seamed can bodymakers. 
Thus, it is apparent that there has been provided, in accordance with the 
invention, an overspray extractor that fully satisfies the aims and 
advantages set forth above. While the invention has been described in 
conjunction with specific embodiments thereof, it is evident that many 
alternatives, modifications, and variations will be apparent to those 
skilled in the art in light of the foregoing description. Accordingly, it 
is intended to embrace all such alternatives, modifications, and 
variations as fall within the spirit and broad scope of the appended 
claims.