Method and Apparatus for Applying Paint

This invention relates to liquid activated apparatus for removing particulate matter from an air stream, commonly called "wet scrubbers," and more particularly to a wet scrubber apparatus having a highly efficient means for separating the liquid and particulates from the air stream prior to exhaust. The invention is especially useful in spray painting facilities.

It is customary to spray paint automobiles and other mass produced articles in a spray booth having the physical characteristics of an elongated corridor or chamber through which the automobiles are longitudinally conveyed and within which human and/or mechanical operators actuate paint spraying equipment. It is essential in the operation of a paint spray booth to maintain a proper supply of fresh air and to remove paint overspray by means of an air exhaust system.

Paint overspray is conventionally removed from the booth by drawing the air from the booth downwardly through hollow outlet structures which are disposed centrally of a subfloor within the booth at longitudinally spaced intervals. Depending on its angularity, the subfloor is either flooded or wetted with water. The water flows into and through the outlet structures to mix with the overspray-laden air passing downwardly therethrough and assists in the transfer of the overspray from the air to the water so that the air leaving the lower ends of the outlet structures can be substantially free of entrained overspray. See as examples U.S. Pat. Nos. 3,421,293 to Halls and 4,222,319 to Donohue, both of which show wet scrubbers in downdraft type spray booths.

Whereas this prior art system is generally satisfactory in removing overspray from the air, the air leaving the lower ends of the outlet structures continues to carry considerable water into and along the length of the exhaust system.

This invention is directed to the provision of a wet scrubber having improved dewatering means.

More specifically, this invention is directed to a wet scrubber for use in a downdraft type paint spray booth in which the air leaving the lower ends of the outlet structures in the wetted or flooded subfloor is caused to undergo a directional change of up to 270.degree., thereby effectively throwing off water in the immediate vicinity of the scrubber discharge; i.e., in the underfloor chamber where the paint-laden water is collected and directed by sluiceways to a treatment facility.

As a further refinement and in combination with the large-directional-change feature of the air flow pattern just described, the scrubber of the present invention may utilize the scrubber bodies themselves as dewatering devices by directing the exhaust air laterally through the depending bodies under the water-wetted or flooded subfloor.

A paint spray booth constructed according to the invention is of the type including an elongate housing defining a working area suitable for containing the article; a perforate working floor; a pan or floodsheet positioned in spaced relation beneath the perforate working floor; a plurality of longitudinally spaced vertically oriented outlet structures defining longitudinally spaced outlet passages opening at their upper ends in the pan or floodsheet beneath the perforate working floor and opening their lower ends beneath the pan; means for producing a flow of air to the working area from overhead and for causing the air to flow downwardly around the article and thence downwardly toward the outlet passages so as to entrain overspray from the spraying operation and carry it downwardly toward the outlet passages; and means for supplying water to the pan and for causing the water to cascade downwardly through the outlet passages to mix with the overspray-laden air passing downwardly therethrough and assist in the transfer of the overspray from the air to the water. According to the invention, the air leaving the lower ends of the outlet passages is directed in one lateral direction toward one side of the booth, thence upwardly toward the pan, and thence in the opposite lateral direction toward the other side of the booth for discharge through an exhaust positioned at the other side of the booth. The large directional change of the discharge air and the impact of the air/water operation on the structure of the underfloor chamber provides a simple and effective means of separating the entrained water from the discharge air in the underfloor chamber itself where the water is not easily collected and where maintenance is most readily performed.

According to a further feature of the invention, the outlet structures are arranged to present a combined longitudinal surface area that substantially precludes movement of the air therethrough in a direction normal to the longitudinal center line of the booth so that the air is made to move serpentinely between the outlet structures to increase the baffling action.

According to a further feature of the invention, each outlet structure is oblong and is arranged with its major axis disposed obliquely with respect to the longitudinal center line of the booth so that the air is caused to impact in a baffling manner against the outlet structures and then move obliquely between the outlet structures for discharge by the exhaust structure.

According to a further feature of the invention, the spray booth further includes a base floor positioned beneath the lower ends of the outlet structures, a generally horizontal, longitudinally extending partition positioned between the base floor and the pan in surrounding relation to the lower end portions of the outlet structures; and a generally vertical, longitudinally extending partition extending between the horizontal partition and the base floor at the side of the outlet structure facing the discharge side of the booth so as to prevent the air leaving the lower ends of the outlet passages from moving directly laterally toward the discharge and force it to move in the opposite lateral direction and thence upwardly and thence laterally between the outlet structures for ultimate discharge.

According to a further feature of the invention, a nozzle is provided at the lower end of each outlet structure to control the air and water exiting from the associated outlet structure and allow the airflow characteristics of the outlet structure to be varied by simply adjusting or changing the nozzle.

FIG. 1 is a perspective cross-sectional view of a paint spray booth according to the invention;

FIG. 2 is a transverse cross-sectional view of the paint spray booth of FIG. 1;

FIG. 3 is a cross-sectional view taken on lines 3--3 of FIG. 2; and

FIG. 4 is a transverse cross-sectional view showing an alternate embodiment of the invention paint spray booth.

The paint spray booth shown in FIG. 1 is epecially designed for automobiles or other mass produced articles and includes an elongate housing structure 10 defining a large open interior area through which automobiles or other articles are towed by means of a conveyor 12 and around which a human or robotic operator or machine may move to spray paint on the automobile bodies as they pass longitudinally through the structure 10. Above the main working area is an air supply plenum 14 having adjustable baffles 16 and a diffusion ceiling 18 made of porous urethane foam or the like. Lights 20 are disposed continuously along the spray booth structure to illuminate the working area and windows 22 are disposed in the side walls of structure 10 to permit the interior operations to be viewed and to create an open airy atmosphere with the spray booth.

The working floor is defined by a semi width gratings 24 between which the conveyor 12 is centrally traversed. Disposed approximately 18 inches beneath the grating 24 is a subfloor 26 in the form of a deep pan which is substantially flat. A plurality of longitudinally spaced, vertically oriented outlet structures 28 are positioned in pan 26 in longitudinally spaced relation along the longitudinal center line of the spray booth. The structures 28 are preferably fabricated from thin gage metal, galvanized or plated for corrosion resistance, and welded or otherwise secured to pan 26.

Each outlet structure 28 has a rectangular shape in cross section and is positioned with its major axis disposed obliquely with respect to the longitudinal center line of the booth. The upper portions 28a of the outlet structures extend above the pan 26 by approximately three inches to thereby create a pool of approximately three inches when pan 26 is supplied with water as, for example, through conduits 30 extending longitudinally along either side of the booth beneath the pan 26. Outlet structures 28 further include lower portions 28b which extend below pan 26 for several feet, and a nozzle 32 is secured to the lower end of the lower portion 28b of each outlet structure 28 and defines a lower opening 32a whicch is restricted both laterally and longitudinally with respect to the cross-sectional dimensions of the outlet structure. The nozzles may comprise fized structures or may, as seen in FIGS. 2 and 3 include fixed end plates 32b and side plates 32c hinged at 32d so as to be pivotally adjustable to vary the size of outlet 32a.

A base floor 34 is positioned beneath the lower ends of nozzles 32. A generally horizontal, longitudinally extending partition 36 is positioned at the lower end of lower outlet structure portions 28b and sealingly surrounds the lower ends of the outlet structures. A further generally vertical, longitudinally extending partition 38 extends between one lateral edge of partition 36 and base floor 34 at the right-hand side of outlet structures 28 as viewed in FIG. 2. The lower end of vertical partition 38 coacts with portions 34a and 34b of base floor 34 to form a trough or water pond 40 immediately underlying outlet structures 28. Water pond 40 extends the full length of spray booth 10 and is positioned generally along the longitudinal center line of the booth. A sloping surface 34c of base floor 34 defines a spillway extending between the pond 40 and a sluice 42 extending longitudinally along the left side of booth 10 as viewed in FIG. 2.

As best seen in FIG. 3, a baffle 44 is secured so and extends perpendicularly with respect to each outlet structure 28 and one or more troughs 45 are formed in partition 36 and extend obliquely from a baffle 44 to the free or left edge 36a of partition 36. Further baffles 46 and 48 extend between pan 26 and base floor 34 on the right-hand side of the outlet structures 28 as viewed in FIG. 2. An exhaust stack or conduit 50 communicates with the lower right-hand side of the spray booth. Conduit 50 in turn communicates with an exhaust stack 52 positioned exteriorally of the spray booth.

In operation, car bodies 54 or other articles to be sprayed are moved through spray booth 10 on conveyor 12 and paint is applied in a spraying operation to the car bodies by human operators or suitable robotic equipment. Suitable exhaust means (not shown) cause fresh air to flow into supply plenum 14 and thence downwardly through the diffusion ceiling 18 around automobile bodies 54 and thence downwardly through grate 24. The air as it moves downwardly around the car bodies entrains the overspray generated in the spraying operation. Water is delivered on a continuing basis through conduits 30 to pan 26 to fill the pan to the height of upper outlet structures 28a. The air flowing downwardly through edge 24 is pulled downwardly through outlet structures 25 and as the air flows downwardly through structures 28, it mixes with the water flowing in cascade style downwardly through structures 28 and the vast majority of the paint spray entrained in the air is transferred in the mixing action occurring within structures 28 from the air to the water. As the paint-laden water exits through nozzles 32, it is deposited in pond 40 and thereafter overflows the pond 40 and flows down spillway 34c and into sluice 42 where it is carried away for recirculation through conduits 30.

Prior to recirculation through conduits 30, the water is passed through a separator to remove the entrained paint and through a treatment station where chemicals are added to minimize the tendency of the entrained paint to stick to the metalwork of the scrubber and to facilitate separation of the entrained paint from the water in the separation station. The air leaving the lower ends of nozzles 32 is substantially free of entrained paint spray but does continue to contain a substantial amount of entrained chemically treated water. The air leaving the lower ends of nozzles 32 flows to the left as viewed in FIG. 2 between subfloor 34 and partition 36 until it reaches the left-hand edge portion 36a of partition 36, whereafter it flows abruptly upwardly toward the undersurface of pan 26. As the air turns and flows abruptly upwardly, most of the entrained water is thrown against the lower left wall 55 of the booth from where it drains downwardly into sluice 42. After turning abruptly upwardly to throw off most of the entrained water, the air reverses lateral direction and flows toward outlet conduit 50. As the air flows toward outlet conduit 50, or to the right as viewed in FIG. 2, it passes through the spaces between the lower portions 28b of outlet structures 28.

As best seen in FIG. 3, the outlet structures are positioned and dimensioned such that their combined longitudinal surface area, when projected onto the imaginary longitudinal center plane of the booth, substantially covers that plane and in fact may provide a small degree of overlap as between the successive outlet structures. The air moving through the outlet structures is therefore precluded from moving directly between the structures in a direction normal to the longitudinal center line of the booth so that the air is baffled by the outlet structures and gives up the remaining entrained water to the baffle structures. Specifically, as best seen in FIG. 3, the air moves between the outlet structures 28b through oblique passages 34 and in so moving is forced to impact against the longitudinal surface of at least one outlet structure lower portion 28b. The air moving between the outlet structures also impacts partitions 44 to further ensure that all remaining spray is removed and further impacts against one or more of baffles 46 and 48 which, as seen in FIG. 3, are staggered with respect to each other so as to preclude direct movement of the air therethrough and so as to ensure impacting of the air against at least certain of these baffles. Water removal by structures 28 and baffles 44 is removed by troughs 45 for drainage onto spillway 34c for discharge into sluice 42.

The air leaving the spray booth through discharge 50 is thus substantially totally free of entrained water spray and may be discharged through exhaust stack 52 to the atmosphere without further treatment. Specifically, the air exiting stack 52 has been substantially dewatered so that it may be discharged into the atmosphere without fear of staining of adjacent surface areas or derogation of adjacent finishes by the chemicals added to the water to facilitate paint separation.

In the alternate embodiment shown in FIG. 4, the water pan 26 includes sloping portions 26a on either lateral side of the longitudinal center line of the booth which may also feed into a central longitudinal trough 26b into which the upper ends 28a of the outlet structures 28 project. Water is supplied to the pan 26 through troughs 26c extending along the longitudinal edges of the pan. In this embodiment, the sloping base floor spillway surface 34c is eliminated and the sluice 42 is eliminated. The pond 40 also constitutes a sluice in this embodiment and provision is accordingly made to move the water continuously in a longitudinal direction through the pond. This arrangement has the advantage of more effectively removing large items of debris such as paint sludge or the like that may fall downwardly through the outlet structures 28 and into the pond. The structure and operation of the embodiment of FIG. 4 is otherwise similar to that described with respect to the FIG. 1-3 embodiment.

The invention spray booth structure will be seen to provide many important advantages. Specifically, the arrangement whereby the air exiting the lower ends of the outlet structures is caused to travel between the outlet structures before exiting the spray booth provides a simple and effective means for dewatering the air without adding any significant further structure to that already provided and necessary to accomplish the cascading and mixing function occurring between the air and water moving downwardly through the outlet structures. The invention arrangement thus provides an effective dewatering function without any substantial additional structures. In addition to the dewatering action provided by the outlet structures as the air is moved between the outlet structures, the air is also forced to give up entrained water by the sharp turn imparted to it as it leaves the lower ends of the nozzles and moves toward the left side of the booth as viewed in FIG. 2. The sharp turn thus imparted to the air, in combination with the baffling action achieved by the passage of the air between the outlet structures and through the further baffles 44, 46 and 48, ensures that the air leaving the spray booth is substantially dewatered and totally fit for discharge into the atmosphere. Further, the nozzles provided on the lower ends of the tubes provide a convenient way of altering the flow characteristics of the tubes without actually changing the tubes. Specifically, various sized nozzles may be selectively interchanged to provide different sized openings at the lower ends of the nozzles and therefore provide different flow characteristics specifically tailored to specific spray booth applications or nozzles may be adjustable, as seen in FIG. 5, to provide the desired specific flow characteristics by selected adjustment of the nozzle opening size. The alternate embodiment shown in FIG. 4 has the advantage of combining the water pond with the sluice so that large articles falling into the pond are effectively carried away by the continuous flow of water in the pond.

Although preferred embodiments of the invention have been illustrated and described in detail, it will be apparent that various changes may be made in the disclosed embodiments without departing from the scope or spirit of the invention. For example, the scrubber tubes or outlet structures 28 need not be rectangular in shape but could be square, round or oval on the booth centerline. Offset, staggered and paired arrangements are feasible. Further, the structures 28 may function with a flat, deep-flooded floor or with a sloping, wetted floor or with a combination. Of course, the invention is not limited to paint spray booths as the scrubber can remove particulates other than paint.