EP0032810B1

EP0032810B1 - Continuous coater

Info

Publication number: EP0032810B1
Application number: EP81300151A
Authority: EP
Inventors: James L. Kennon; Lawrence J. Macartney; Gerald W. Crum; John C. Dunn; Donald R. Hastings
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 1980-01-14
Filing date: 1981-01-14
Publication date: 1986-01-02
Also published as: CA1162732A; JPS6362265B2; JPS56108563A; EP0032810A1; DE3173335D1

Description

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.
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.
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 filters or 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Additionally, in the case of solvent base paints or sprays, it causes substantial quantities of vaporized solvent to be withdrawn from the booth and thereby renders it difficult to maintain a solvent saturated atmosphere within the booth.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.
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.
In US-A-3750622, another approach to the problem of preventing the escape of oversprayed material from the entrance and exit ports of a continuous coater is disclosed. Vestibules around the entrance and exit ports of the coater are provided in which an air flow is caused to move from one side of the vestibules to the other side thereof, thereby creating an air curtain at the entrance and exit openings of the vestibules. This airflow in the vestibules, however, also picks up any air coming out of the coating chamber together with the atomized coating material and solvent vapors carried thereby.
Such draw of air causes some air movement in the coating chamber, thus resulting in some air flow disturbance within the chamber and some loss of sprayed material utilization.
It has therefore been a primary objective of this invention to provide a continuous coater which substantially overcomes such problems.
A coater in accordance with the invention comprises a 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, and an air flow control vestibule extending outwardly from one or both of the chamber's ends and surrounding the entrance and/or exit openings, each vestibule having an outer opening remote from, but longitudinally aligned with, the associated entrance and exit openings of said chamber, wherein the coating chamber is substantially enclosed except for the entrance and exit openings, and air exhaust means are provided opening through one or both side walls of one or both vestibules between the outer opening of the respective vestibule and the entrance/exit opening of the chamber, the air exhaust means creating an air flow barrier in the vestibule without causing significant air flow disturbance in the coating chamber characterised in that the air exhaust means draw air from the surrounding atmosphere, through the complete cross-section area of the outer opening thereof and exhausts the drawn air through respective air collector slots in the side walls of one or both vestibules.
The 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 over- sprayed 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.
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. 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 materail which escapes from the coater cabinet into the vestibules and enables the interior of the cabinet to be maintained saturated or very nearly saturated.
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 oversprayed 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 whcih may include liquid scrubbing of the exhaust gases is much more efficient and has beeen proven to require less horsepower than required in water induced air flow systems of the prior art.
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.
The invention will now be further described by way of example with reference to the accompanying 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.

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.
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 celing, 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.
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.
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.
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 over- spray 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.
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.
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.
At the other 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.
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.
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).
The expansion chambers 74, 75 are sized so as to be of approximately twice the cross-sectional area of the ducts 54, 55.
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.
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.
At the 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 opposite sides of the vestibule 12.
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 4 m/s (800 feet per minute) should be maintained through each of the slots and that the optimal velocity is on the order of 5 m/s (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.
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.
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.
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.
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.
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.
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.
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.
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.

Claims

1. A coater comprising a 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, and an air flow control vestibule extending outwardly from one or both the chamber's ends and surrounding the entrance and/or exit openings. each vestibule having an outer opening remote from, but longitudinally aligned with, the associated entrance and exit openings of said chamber, wherein the coating chamber is substantially enclosed except for the entrance and exit openings, and air exhaust means are provided opening through one or both side walls of one or both vestibules between the outer opening of the respective vestibule and the entrance/exit opening of the chamber, the air exhaust means creating an air flow barrier in the vestibule without causing significant air flow disturbance in the coating chamber characterised in that the air exhaust means (15,17, 48) draw air from the surrounding atmosphere, through the complete cross-section area of the outer opening (47) thereof and exhausts the drawn air through the respective air collector slots (48) in the side walls of one or both vestibules (12, 13).

2. A coater as claimed in Claim 1 including an exhaust fan (17) or the like for drawing air from the vestibules.

3. A coater as claimed in Claim 2 wherein air collector slots (48) are located on opposite sides of each of the vestibules (12,13),each air collector slots being connected to the exhaust fan (17).

4. A coater as claimed in any preceding Claim including removal means (70, 78) for removing sprayed material from the air before the air is exhausted to atmosphere.

5. A coater as claimed in Claim 4 wherein the removal means forms a liquid scrubber (71) and/ or includes a baffle section (78), through which the exhausted air is caused to pass.

6. A coater as claimed in any preceding Claim wherein the vestibules (12, 13) have an inner (50) and outer section (45), the inner section (50) being of substantially constant cross sectional area while the outer section (45) is of gradually increasing cross sectional area between the outer opening (47) of the vestibule and said inner section (50).

7. A coater as claimed in any of the preceding Claims including means (80) for adjusting or balancing the flow of air through the air collector slots (48) on the opposite sides of one or both of the vestibules.

8. A coater as claimed in any of the preceding Claims including means (109) located within each of the vestibules for creating an air curtain (108) 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 (108) between the air collector slots (48) and the coating chamber openings (30, 31).