US3814322A

US3814322A - Mist coating of strip material

Info

Publication number: US3814322A
Application number: US00378766A
Authority: US
Inventors: J Waldrum
Original assignee: Amchem Products Inc
Current assignee: Suez WTS USA Inc
Priority date: 1973-07-12
Filing date: 1973-07-12
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: SE7402726L; AU468462B2; GB1457187A; FR2236562A1; CA1016574A; DE2409618A1; AU6543974A; IT1009232B; JPS5028541A

Abstract

Apparatus for spraying an aerosol mist of a liquid onto a moving strip to coat the strip and prepare it for subsequent painting. The apparatus comprises a spray chamber in which a pair of rotating spray heads are disposed and through which the strip passes between the spray heads. The spray heads each include plural nozzles which rotate under the jet action of the exhausting aerosol to provide a fine aerosol mist which uniformly coats the moving strip. No liquid tight seals are used in the spray heads and the liquid for the aerosol is directed without leakage to the spray nozzles by centrifugal force. Exhaust means are provided to maintain a slight vacuum within the chamber and to preclude the egress of the coating liquid or vapor therefrom. A liquid bath filter is provided to filter the exhausted atmosphere from the chamber and a surface filter is provided to filter the atmosphere from the liquid bath and to release it to the ambient atmosphere.

Description

United States Patent Waldrum June 4, 1974- l l MIST COATING OF STRIP MATERIAL R nary Examiner-Robert S. Ward, Jr. [75] Inventor, John E waldrum Ambler Pa Attorney, Agent, or Firm-Caesar, Rivise, Bernstein &

Cohen [73] Assignee: Anchem Products, Inc., Ambler, Pa. 221 Filed: July 12, 1973 {57] ABSTRACT [21 L N 378,7 Apparatus for spraying an aerosol mist of a liquid onto a moving strip to coat the strip and prepare it for sub- I t 52 us. 01 239/251, 239/124, 239/226, Seque" Pam 239/433 8/50, 18/316 118/326 The apparatus compnses a spray chamber in wh1ch a 1 Int. u pan of rotating spray heads are disposed and through of Search I the strip passes between the spray heads. The 239/261 1 6 spray heads each include plural nozzles which rotate under the jet action of the exhausting aerosol to [56] References Cited provide a fine aerosol mist which uniformly coats the moving strip. No liquid tight seals are used in the UNITED STATES PATENTS spray heads and the liquid for the aerosol is directed 2,294,168 8/1942 Francis et al. 239/399 X i h k to the Spray nozzles by Centrifugal 2,763,575 9/1956 Bede ll8/3l6 X force. 2,888,903 6/1959 Faber ll8/3l6 X 3,642,207 2/1972 Krogman 239/251 Exhaust means are provlded I0 mfllmam a Sllght 3,736,902 6/1973 Glanzer 118/50 acuum within the chamber and to preclude the egress of the coating liquid or vapor therefrom. A liquid bath FOREIGN PATENTS Q APPLICATIONS filter is provided to filter the exhausted atmosphere 14,221 7/1955 Austral|a 239/26] from the Chamber and a Surface filter is provided to 540,872 ll/l94l Great Britain 239/399 filter the atmosphere from the liquid bath and to release it to the ambient atmosphere.

17 Claims, 8 Drawing Figures MIST COATING OF STRIP MATERIAL This invention relates generally to spraying apparatus and more particularly to apparatus for spraying aerosol liquids on moving metal strips.

In order to achieve good adhesion of paint to metal, it is a common practice to provide a preparatory or prepainting coating on the bare metal to thereby prepare its surface for the subsequent painting operation.

Commercial prepainting coating of metal strips involves relatively complex procedures or techniques owing to the fact that the strip must be coated at relatively high speeds, e.g. 400 feet per minute and up, while the thickness of the coating applied is maintained uniformly within close tolerances.

Of the various techniques proposed and used for the coating of moving metal strips, all suffer from one or more drawbacks.

One technique now used commercially for coating metal strip involves the use of rollers to apply the coating liquid on the surface of the strip as it moves past the rollers. However, this technique is expensive to maintain since the surfaces of the rollers become scored or damaged relatively quickly by contact with the burrs or sharp edges existing on the moving strip. Once the surfaces of the rollers become scored or otherwise damaged, the rollers are incapable of applying the prepainting coating evenly on the strip, thereby resulting in a non-uniform coating.

One technique which obviates the use of coatingapplying rollers involves the use of a bath of the coating liquid. In such a technique, the moving strip is immersed and moved through the bath and thereafter allowed to dry. This technique, while enabling the coating process to be effectuated quickly, is somewhat messy and frequently results in an uneven coating due to the fact that the liquid has a tendency to pool up on the surface of the strip after it exits the bath.

Another technique which obviates the use of coatingapplying rollers involves the spraying of an aerosol coating onto a moving strip. Presently existing spray techniques for applying prepainting coatings on moving metal strip are frequently ecologically damaging due to the fact that, in the absence of extensive protective measures, large amounts of the mist of the coating material escape to the surrounding atmosphere, thereby contaminating it. In addition, commercially available spraying apparatus are not capable of providing a fine mist or an aerosol of the coating liquid onto the fast moving strip without some liquid pooling up in places on the surface of the strip and thereby resulting in an uneven coating.

Accordingly, it is a general object of this invention to provide a spraying apparatus which overcomes the various disadvantages of the prior art.

It is a further object of this invention to provide a spraying apparatus including rotating sprayheads not requiring liquid-tight seals.

It is yet a further object of this invention to provide a spraying apparatus including a chamber in which an aerosol mist is created to coat a metal strip moving therethrough and means for precluding the egress of the mist to the atmosphere.

It is still a further object of this invention to provide a spraying apparatus including means for filtering the contaminated atmosphere, produced during the spraying operation, to the ambient atmosphere.

These and other objects of this invention are achieved by providing apparatus for spraying an aerosol mist of a liquid onto a moving strip to coat the strip. The apparatus comprises a spray chamber through which the strip passes. A rotating sprayhead is disposed within the chamber and comprises plural nozzles for producing an aerosol from a liquid and a gas provided from separate supply means and for directly the aerosol to the strip. Vacuum means are provided for drawing the atmosphere out of the chamber to create a slight vacuum within the chamber with respect to the ambi ent atmosphere to thereby preclude the direct egress of the aerosol to the ambient atmosphere. Filter means are also provided for removing residual liquid and vapor from the atmosphere which is withdrawn from the chamber.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. I is a side elevational view of a spraying apparatus in accordance with this invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 3 and showing a portion of the spraying apparatus of FIG. 1;

FIG. 3 is a sectional view taken. along line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is an enlarged sectional view taken along line 5-5 of FIG. 3;

FIG. 6 is an enlarged sectional view taken along line 6-6 of FIG. 3;

FIG. 7 is a sectional view taken along line 7-7 of FIG. 1; and

FIG. 8 is an enlarged exploded perspective view of a portion of the filter shown in FIG. 7.

Referring now in greater detail to the various figures of the drawing wherein like reference characters refer to like parts, there is shown at 20 in FIG. 1 a spray apparatus embodying the present invention.

The apparatus is supported on a stand 21 and basically comprises a spray chamber 22 through which a strip 24 of metal to be treated passes. The strip may be of any width up to 5 feet and greater. The strip 24 is drawn at a high speed, e.g., 400 feet per minute and higher from a coil (not shown) through the apparatus where it is coated with a preparatory or prepainting coating. Once coated and dried, the strip is reeled up upon another coil (not shown).

Spraying means 26 (FIG. 2) are provided within the chamber 22 to create an aerosol or a mist of fine liquid droplets which effectuates the uniform coating of the strip as it passes therethrough. As will be considered in detail later, the spraying means creates the aerosol from a pre-paint coating liquid and high pressure air. The coating liquid is provided to the spraying means via means 28 (FIG. 1) and the high pressure air is provided to the spraying means via means 30 (FIG. 1).

Exhaust means 32 is provided at the top of the spraying chamber 22 to create a slight vacuum within the chamber relative to the ambient atmosphere. This action prevents the direct egress to the atmosphere of the mist and vapors, hereinafter referred to as contaminated air, created within the chamber during the spraying operation, while effecting the venting of the contaminated air into a filter system 34. The filter system 34 removes substantially all of the contaminants, e.g. prepaint coating liquid, mist and vapors thereof, from the air before releasing the filtered air to the ambient atmosphere. Accordingly, the apparatus is ecologically clean.

As can be seen in FIGS. 2, 3 and 4, the spraying chamber 22 basically comprises a boxlike housing having a pair of

end walls

36 and 38, a front wall 39, a top wall 40, a back all 41 and a bottom wall 42. The front wall is pivotably connected by means (not shown) to the end wall 36 of the housing to provide access to the interior of the spraying chamber. The

end walls

36 and 38 include elongated

horizontal slots

44 and 46, respectively. Each slot includes a lip or flange 48 projecting normally to the plane of the end wall and about the periphery of the slot. The slot 44 serves as the opening through which the strip 24 enters chamber 22 for treatment therein and the slot 46 serves as the opening through which the treated strip exits the chamber.

At the top of the spraying chamber 22 is a box-like exhaust chamber 50 having side walls 52 which are joined to the top wall 40 of the housing 22. The top of the exhaust chamber includes a pivotable cover 54 which serves to support the exhaust means 32. The exhaust means preferably comprises a two stage turbine, like that used in a conventional vacuum cleaner, which when operating, draws the contaminated air from the interior of chamber 22 in the direction of the arrows shown in FIG. 2 into the exhaust chamber.

As can best be seen in FIG. 2, the exhaust chamber 50 includes a filter and condenser stack 56 which is mounted over an opening 58 in the top wall 40 of the spraying chamber 22 and under the turbine 32. The filter and condenser stack 56 comprises a pair of fine mesh screens 60 mounted horizontally on upstanding vertical calls 60 by flanges 64. The screens56 serve to condense and filter out some of the prepainting coating liquid from the contaminated air that is drawn into the exhaust chamber 50 by the action of the turbine. The cover 54 is pivotably such that is may be tilted out of the horizontal plane to provide access to the filter and condenser stack 56 disposed therebeneath.

In order'to preclude any liquid which condenses on top wall 40 of the spraying chamber 22 from dripping down onto the strip 24 and thereby affecting the uniformity of the coating applied thereto, condensation collecting means 66 (FIG. 3) are provided within the chamber 22. The condensation collecting means comprises a pair of inclined condensation panels 68 extending the full width of the chamber 22. Each panel is mounted, e.g. welded, at its bottom edge and extends at an upwardly slanting angle to its associated end wall. The free ends 70 of the panels extend through opening 58 and into the exhaust chamber 50.

A separate open ended, condensation-receiving trough 72 is mounted on each end wall immediately below the joint of the condensation panel and the end wall. The troughs extend for substantially the full width of the chamber with'mid portion of the trough being disposed at a higher elevation than the ends thereof such that liquid received at any intermediate point in the trough tends to flow, down the trough to the closest end thereof. The ends are open to enable the liquid to flow out of the trough.

- and the filter and condenser stack 56 is as follows: The

spraying means 26 produces a fine aerosol or mist of coating liquid droplets within the chamber to uniformly coat the strip moving therethrough. At the same time. the turbine 32 draws the contaminated atmosphere produced within the chamber through the opening 58 and into the exhaust chamber 50, whereupon some liquid from the contaminated atmosphere condenses on the filter screens. A substantial amount of the mist and- /or vapor within the chamber condenses on the condensation panels 68, whereupon the condensate flows under the influence of gravity down the inclined face of the panel to the associated trough therebeneath. Since the troughs open ends are at a lower elevation than its midportion, the liquid received by the trough flows out its open end to the bottom of the spray chamber 22.

As can be seen in FIGS. 2 and 3, the bottom wall 42 of the spray chamber is of generally funnel-like shape and serves to channel any liquid which condenses on the spray chambers walls or condensation panels into a liquid collecting cavity 74 disposed at the low point of the bottom wall. A drain pipe 76 is provided at the bottom of liquid collecting cavity 74 to drain the collected liquid out of the cavity and back to the liquid supply means 28.

In accordance with one aspect of this invention, the spraying means 26 comprise a pair of rotating spray heads 78 and 80. Each spray head includes a plurality of nozzles 82 mounted in a horizontal plane and equally spaced about a central axis. As will be described in detail later, each spray head rotates about its axis as a result of the reaction caused by the egress of aerosol mist from its plural nozzles.

The upper spray head 78 is mounted within the spray chamber 22 and above the plane of the strip 24 by support arms or struts 84. The struts 84 project from the inside surface of the front wall 39 to a point directly over the center of the strip (see FIG. 3).

In order to preclude the liquid which condenses upon the struts 84 from dropping onto the strip therebelow and thus changing the uniformity of the coating, the struts 84 for the upper spray head 78 extend at an upward angle from the front wall 39 of the housing. In so doing, any liquid condensing on the struts flow down the struts and to the inside face of the front wall from whence it flows to the liquid collecting cavity 74.

The lower spray head is of identical construction to the upper spray head 78 and is mounted directly below the strip and aligned with the upper spray head.

Each nozzle is of. the conventional atomizer-type which, as can be seen in FIG. 6, includes a longitudinally extending liquid input port 86, a narrow diameter air input port 88 oriented at a slight angle to the liquid input port and an enlarged mixing chamber 90. Both the liquid and air input ports lead to the mixing chamber. The mixing chamber is slightly domed and terminates at the top of the domed portion at an outlet or exit port 92.

As will'beappreciated by those skilled in the art, when liquid is supplied via inlet port 86 and compressed air is supplied via inlet port 88, the two fluids mix within the domed mixing chamber and are expelled from the outlet port 92 under the force of the compressed air to form an aerosol mist or spray.

Each of the nozzles 82 is mounted at the end of a pair of

pipes

93 and 94 which radiate from the axis of rotation of the spray head. The pipes serve to support the associated nozzle in position while serving as the conduits through which the liquid and the compressed air flow to their associated nozzle input ports. For example, pipe 93 serves as the liquid conduit and, as can be seen in FIG. 6, communicates with liquid input port 86, whereas pipe 94 serves as the air conduit and communicates with the air input port 88.

Each of the nozzles 82 is positioned within a common plane, which is normal to the axis of rotation of the spray head. Furthermore, each of the nozzles is oriented in the direction such that its outlet port 92 is at an acute angle to the plane of the strip passing adjacent thereto, while having a directional component which is tangential to the axis of rotation of the spray head. Accordingly, upon the egress of aerosol from the nozzle, a jet force component is produced which is tangential to the axis of rotation of the spray head. This action results in the rotation of the spray head under the impetus of the force of the exiting aerosol and without other motive means.

The uniformity of the coating applied to the strip by the aerosol from the rotating spray heads is a function of several variables, such as the linear speed of the strip through the chamber, the number of nozzles in the spray head and the peripheral speed of the rotating nozzles in the spray head. As should be appreciated by those skilled in the art, the peripheral speed of the spray head is in turn a function of the speed of rotation of the spray head and the radial distance between the nozzles and the axis of rotation of the spray head.

lfthe spray head does not include a sufficient number of nozzles or if the linear speed of the strip is substantially greater than the peripheral speed of the nozzles, a stripe-like or non-uniform coating results.

Since from an economic standpoint, it is desirable to move the strip through the chamber at a relatively high rate of speed, the spray heads should include a substantial number of nozzles such that the speed of rotation of the spray head can be kept within a reasonable functional limit and still result in the provision of a uniform coating on the strip. In a preferred embodiment of this invention, the radial distance between the nozzles and the axis of rotation of the spray heads is 13 inches and the spray heads include 12 equally spaced nozzles. At a strip linear speed of 400 feet per minute and a spray head rotational speed of 1,000 rpm, a fine aerosol mist is created by the above described spray heads which effectively provides a uniform coating on both sides of the strip without any striping effect or any liquid puddles on the surface of the strip. Furthermore, the mist created applies the coating to the strip without run-off, thereby eliminating wastage and obviating the need for reclamation techniques.

As previously noted, the liquid is provided to the spray heads via liquid supply means 28. As best can be seen in FIG. 1, the supply means 28 basically comprises a liquid reservoir 95 for storing the coating liquid therein, a pump 96 for moving the liquid from the reservoir and from the filter system 34 through interconnecting conduit means 98 to a pair of constant pressure or

head devices

100 and 102. The constant head devices insure that the pressure or head of liquid applied to each spray head is kept at a predetermined constant value such that the volume of aerosol created by the spray head is constant for a given air pressure.

Each constant head device includes a cup assembly 104, whose elevation can be adjusted by suitable adjusting means (not shown), a liquid inlet line 106, a liquid outlet line 108 and a stand pipe (not shown) connected to a liquid return line 110. The inlet line 106 serves to carry liquid into the cup assembly from the pump 96. Each liquid outlet line 108 is connected between the interior of the associated cup assembly and an associated spray head and serves to carry liquid from the cup assembly to the spray head.

The height of the liquid within the cup is maintained at a constant level by the stand pipe. In that regard, the stand pipe is arranged to drain any excess liquid from the cup into the return line. The return line terminates at the reservoir such that any liquid drained from the constant head devices is returned to the reservoir.* (The drain pipe 76 from the liquid collecting cavity 74 also empties into the reservoir.)

As should be appreciated, the head or pressure of the liquid provided by the outlet line to the spray head is a function of the height of the liquid within the cup and the height of the liquid within the cup is in turn a function of the elevation of the cup and the relative height of the stand pipe within the cup. Accordingly, the pressure of the liquid at the input to either spray head can be established at any value by either adjusting the elevation of the cup or the stand pupe. In the preferred embodiment of this invention, the height of the stand pipe with respect to the cup is fixed, while the elevation of the cup is adjustable.

In order to prevent foreign matter which may be suspended in a liquid from gaining access to the spray heads, a porous filter 112 is connected in a liquid input line between the pump 96 and the constant head devices and 102.

As previously noted, compressed air is provided to the spray heads via air supply means 30. As best seen in FIG. 1, the air supply means 30 basically comprises a compressor unit 114 which, in a preferred embodiment of the invention, takes the air from an intermediate point in the filter system 34, compresses it and provides the compressed air through conduit means 116, a pair of

air filters

118 and 120 to a pair of

air input lines

122 and 124. The air input line 122 is connected to the upper spray head 78 and the air input line 124 is connected to the lower spray head 80. The filter 118 serves to remove moisture from the air, whereas the filter I20 removes other contaminants therefrom. An adjustable pressure valve and gauge 126 is connected in each air input line to enable the air pressure in the line to be regulated as desired.

In the preferred embodiment of the invention, the air pressure in the input line is set at approximately 40 pounds per square inch.

In order to preclude the egress of contaminated air from the

slots

44 and 46 provided in the side walls of the spraying chamber during operation thereof, the turbine 32 is arranged to create a slight vacuum within the chamber. To that end, the turbine is run at a rate to exhaust slightly more air than is supplied by the spray heads during operation, whereupon the pressure within the chamber is maintained slightly lower than the ambient pressure. Accordingly, air flow through the

slots

44 and 46 is maintained into the chamber. This action effectively precludes the egress of contaminants out of the chamber via the slots during the spraying operation.

In accordance with a preferred embodiment of this invention, the spray heads 70 and 78 each rotate on loose bearing assemblies which do not require fluidtight seals to prevent liquid or air from leaking out before entrance into liquid and

air pipes

93 and 94 respectively, associated with each nozzle. This feature is of significant importance from a manufacturing as well as a maintenance standpoint since it enables the manufacture of a relatively simple spray head which does not require constant attention to keep it fluid-tight.

The structural details of the seal-less bearing assemblies of the spray heads 78 and 80 and can best be seen in the sectional view of FIG. 5. As can be seen therein, the central portion of each spray head includes a bearing assembly 128. The bearing assembly basically comprises a fixed portion 130, which is connected to the stationary fluid supplies 28 and 30, and a rotating portion 132, which is connected to the

fluid pipes

93 and 94 and their associated nozzles 82.

The fixed portion of the bearing assembly includes a stationary housing 134 which, as can be seen in FIG. 3, is mounted at the free end of the central strut 84 by a clamp 136. The housing 134 of the spray head 78 includes a threaded inlet port 138 into which a threaded end of the compressed air line 122 is screwed. Similarly, the housing 134 of the spray head 80 includes a threaded inlet port (not shown) .into which a threaded end of the compressed air line 124 is screwed.

Each fixed portion of the bearing assembly also includes a threaded outlet port 140 disposed normally to and in communication with the inlet port 138. An elongated shaft 142, having a threaded end 144, is screwed into the outlet port of the spray head 78 and is fixed in position by a set screw 146. The shaft 142 serves as the means about which the spray head 78 rotates. A similar shaft is screwed into the outlet port of the fixed housing of spray head 80 and serves as the means about which that spray head rotates.

Each shaft 142 includes a hollow passageway 148 throughout its length which communicates with outlet port 140. The shaft 142 also includes a sleeve 150 connected at its free end. The sleet/e150 terminates in a free end flange 152. An outer sleeve 154 is disposed about shaft 142. A pair of plastic rings 156 are interposed between the inner surface of the outer sleeve 154 and the outer surface of the shaft 142 adjacent the ends of the outer sleeve to close the space therebetween.

An input port 158 is provided in the side wall of the outer sleeve 152 adjacent the end closest to the housing 134. The liquid outlet lines 108 from the

constant head devices

100 and 102 are connected to the input ports 158 of the spray heads 78 and 80, respectively. A plurality of output ports 160 are provided in the sidewalls of the outer sleeve 152 adjacent the other end thereof.

The rotating portion 132 of the bearing assembly 128 comprises a housing defining a liquid-receiving chamber 162 and a compressed air-receiving chamber 164. The housing includes a cylinder 166 having a recess 168 and a recess 170 on opposed sides of a barrier wall 172. The recess 168 forms a portion of the liquidreceiving chamber and the recess 170 forms a portion of the compressed air-receiving chamber. A central opening 174 is provided through the barrier wall along the axis of the cylinder 166.

A hollow, conical cap 176 is provided to complete the liquid-receiving chamber 162. The cap includes a bore 178 having an inner surface which tapers from a large diameter opening 180 to a small diameter opening 182. The cap 176 is connected to the cylinder 166 by the frictional engagement of the portion of its wall contiguous with its large diameter opening and the inside surface of the sidewall of the cylinder 166.

A plurality of threaded orifices 184 are provided equally spaced about and through the sidewall of the cylinder 166 in the liquid-receiving chamber 162 immediately adjacent the barrier wall 172. One end of each of the pipes 93 is fitted with a screw-in connector 186 which is screwed into a respective threaded orifice 184. The orifices serve as the means through which the liquid that is introduced into the liquid-receiving chamber flows into pipe 93 and to the nozzle 82 connected thereto.

As can be seen in FIG. 5, the outer sleeve 154 extends through the small diameter opening 182 in a conical cap, with the sleeve 150 extending through the central opening 174 in the barrier wall. No gasket, grease or any other sealing means is utilized to seal the space between the wall of the conical cap contiguous with its small diameter opening and the outer sleeve 154 of the fixed portion of the bearing assembly. All of the liquid which is introduced into the liquid-receiving chamber by pipe 108 is moved along the tapered wall of the cap in the direction toward the orifices 184 (towards the large diameter opening) under the influence of the centrifugal force created as the spray head rotates, irrespective of the orientation of the spray head. Accordingly, a column of liquid is directed under pressure to its ultimate destination without leakage and without sealing means by the very rotation of the spray head.

A flat cap 188 is provided to complete the airreceiving chamber 164 in the rotating portion of the bearing assembly. Preferably, the cap is in the form of a flat disc which is connected to the top edge of the portion of the side wall of the cylinder 166 forming recess 170, by screws 189.

A plurality of threaded orifices 190 are provided equally spaced about the sidewall of the cylinder in the compressed air-receiving chamber immediately adjacent the barrier wall 172. One end of each of the pipes 94 is fitted with a screw-in connector 192 which is screwed into a respective threaded orifice 190. The orifices 190 serve as the means through which the compressed air that is introduced, via passageway 148, into the air-receiving chamber flows into pipe 94 and to the nozzle 82 connected thereto.

No lubrication is provided between the sleeve 150 and the central opening 174 and the rotating portion of the bearing assembly rotates with respect to the sleeve 154 on a cushion of air resulting from the introduction of compressed air into the air-receiving chamber 164.

As can be seen in FIG. 5, the upper rotating spray head 78 is provided with a large diameter planar disc 194 connected to the cap 186 by screws 189. The disc 194 is provided to preclude liquid which condenses on the upper spraying head or structure disposed thereabove from dropping onto the moving strip therebelow and resulting in an uneven or non-uniform coating on the strip. Any liquid which does condense on the disc 194 is thrown radially outward and away from the strip by the action of a centrifugal force generated as the spray head rotates. Since no condensation on the lower spray head could possibly drop on the strip disposed above it, the lower spray head does not include the large diameter disc 194.

As previously noted, the contaminated air which is drawn out of the spraying chamber by the turbine 26 is provided to a filter system 34 to remove all the contaminants therefrom before releasing the air to the surrounding atmosphere.

The filter system 34 basically comprises two stages, an initial filter in the form of a liquid bath 196 which is connected, via hose 199, to the output of the turbine 26 and a subsequent filter in the form of a surface condensation filter 198 for removing residual contaminants remaining after the filter bath.

The details of the filter system 34 are best seen in the sectional view of FIG. 7 and the exploded perspective view of FIG. 8.

As can be seen, the liquid bath 196 comprises a vertically oriented tank 200 having a cover 202 thereon. The tank contains a substantial volume of the same liquid as is used in coating the strip 24, with the level of the liquid within the tank being maintained by a stand pipe (not shown). The stand pipe serves to draw any excess liquid which enters the tank' during the filtering operation (to be discussed later) and provides the excess liquid, via a return pipe 204 (FIG. 1), back to the liquid reservoir 94.

At the bottom of the tank 200 is an aerator 206 in the form of a hollow plate having a large number of small orifices 208 in its top surface 210. A pipe 212 is connected between the hose 199 and the interior of the aerator. A plurality of mounting rods 214 are provided interposed between the aerator and the cover 202 to hold the aerator in position at the bottom of the tank.

In operation, the contaminated air from the spraying chamber is carried into the exhaust chamber 50, through turbine 26 to hose 199 and into the aerator 206. The contaminated air exits the plural orifices in the aerator and rapidly bubbles up through the liquid bath, whereupon a substantial amount of liquid vapor and/or droplets in the rising air bubbles is extracted therefrom by the liquid in thebath, leaving the air which gets to the surface of the bath relatively clean. The air which gets to the surface of the bath is hereinafter referred to as once filtered air" and still contains some residual contamination whichshould be removed before it is released to the ambient atmosphere.

The cover 202 of the first stage filter tank includes a central opening 216 through which the once filtered air flows into the bottom of the second stage surface filter 198.

The details of the bottom of filter 198 can best be appreciated with reference to FIGS. 7 and 8.

As can be seen therein, the bottom of filter 198 is in the form of a cylinder 218 which includes a mounting flange 220 connected to the cover of the first stage fil' ter contiguous with its central opening. A plurality of fine mesh screens 222 and apertured plates 224 are alternately disposed over one another within the cylinder 218 to form a stack therein. As can be seen, the plates each include an arcuate opening 226. The arcuate openings of the plates in the stack are not axially aligned but are rather staggered. In so doing, the air entering the bottom of the stack is forced into a zig-zag path upward through the stack. The screens and plates are paired in groups of one screen and one plate, with the screen below the plate. Plural spacers 228 are provided between adjacent groups to furnish an air space therebetween. The screens and plates are held together via plural tie rods 230 which extend through aligned holes 231 therein. Plural chips 232 of a closed foam are disposed in the air space between adjacent groups of the stack. The screens preclude the chips from dropping through the arcuate openings 226.

Operation of the bottom portion of filter 198 is as follows: The once filtered air enters the stack and passes through the fine mesh screen 222 and then through the arcuate opening in the immediately adjacent plate. From there the air flows through the adjacent plural foam chips 232, whereupon additional contaminants condense out. The air then flows to the next group of screens, plates and foam and so on until it reaches the top of the stacked screens and plates. Due to the fact that the arcuate openings in the plates are staggered, the air is forced to flow in a somewhat zig-zag course through the stack and its component chips. This action increases the distance that the air flows through the stack thus exposing the air to more condensation surface area per unit height, which in turn results in more contaminants condensing out of the contaminated air.

The upper portion of filter 198 comprises a large tank 234 having an opening 236 at the bottom which communicates with the top of the stacked screens and plates. The tank also includes an opening 238 at the top which communicates with the ambient atmosphere. The tank is filled with large volume of the same closed foam chips 232 and therefore presents an extremely large condensation surface area to the entering air. Accordingly, the upper portion of filter 198 effectively removes residual contaminants from the air. In addition, the large number of chips within the tank 234 slows the velocity of the rising air prior to its release to the ambient atmosphere.

It is to be pointed out at this juncture that of all the air introduced into the spraying chamber 22 of the apparatus 20, the major portion thereof is provided by the spray heads from the air supply means 30, Le. the compressor 1 14 and associated components. The remaining portion of the air introduced into the apparatus is a small volume of air drawn into the chamber via

slots

44 and 46 by the action of turbine 32 in maintaining a partial vacuum therein.

If all of the air provided into the spraying chamber is to be released to the ambient atmosphere, an extremely large surface filter 198 would be required to insure that the released air is sufficiently clean. However, if the spraying apparatus constantly recirculates some of its air, without releasing the recirculated air to the atmosphere, a substantial reduction in the size of the surface filter can be affected without sacrificing clean" operation. To that end, in the embodiment shown in FIG. 1, the major portion of the air used in the apparatus, i.e. the air provided by the air supply means, is constantly recirculated and not allowed to vent to the ambient atmosphere and only the small portion of the air which is drawn into the spraying chamber to maintain the vacuum therein is ever released. Accordingly, only that portion of the systems air has to be filtered completely. This action is accomplished by providing an air return hose 240 between the lower portion of the tank of surface filter 198 and the input of the compressor 214. Ac cordingly, the major portion of the air from the spraying chamber is constantly recircled with only a partial filtering, i.e. the filtering which occurs in the liquid bath filter 196 and in the lower portion of the surface filter 198.

While the foregoing apparatus and its component sealless spraying heads has been described for use in providing a prepainting coating on metal strip, it should be appreciated that the apparatus can be used to coat metal strips with any liquid material and that the spray head has utility in any two-fluid spray applications wherein one fluid is a gas and the other fluid is a liquid. Furthermore, the equipment and technique of this invention can also be employed in other coating applications such as painting or coating of fabrics or other materials.

Without further elaboration, the foregoing will so fully illustrate our invention that others may, by applying current or future knowledge, readily adapt the same for use under various conditions of service.

What is claimed as the invention is:

1. Apparatus for spraying an aerosol mist of a liquid onto a moving strip to coat the strip, comprising a spray chamber through which said strip passes, a rotating spray head disposed within said chamber and comprising plural nozzles for producing an aerosol from a liquid and a gas provided from separate means and for directing said aerosol to said strip, vacuum means for drawing the atmosphere out of said chamber to thereby create a slight vacuum within the chamber with respect to the ambient atmosphere to preclude the direct egress of the aerosol to the ambient atmosphere and filter means for removing residual liquid and vapor from the atmosphere which is withdrawn from the chamber.

2. The apparatus of claim 1 wherein said spray head rotates about an axis and wherein said nozzles are directed at an acute angle to the plane of said strip with a directional component thereof tangential to said axis in order to cause said spray head to rotate thereabout by the reaction of the aerosol exiting from the nozzles.

3. The apparatus of claim 2 wherein the liquid and gas supplies are stationary and wherein the spray head produces a centrifugal force on the liquid provided to it during its rotation and including means operative in conjunction with said centrifugal force to direct the liquid to the nozzles without leakage and without any liquid sealing means therebetween.

4. The apparatus of claim 3 wherein said last mentioned means comprises a liquid-receiving chamber having a wall including a tapered bore through which said axis extends longitudinally and a liquid inlet port, said chamber wall having at least one outlet port extending radially outward therethrough adjacent to the large end of the bore, said outlet port being connected to a nozzle.

5. The apparatus of claim 4 wherein said spray head includes a gas-receiving chamber having a wall forming a cylindrical bore and separated from the liquidreceiving chamber by a barrier wall, said bas-receiving chamber including at least one outlet port extending radially outward through the wall thereof, said outlet port being connected to a respective nozzle.

6. The apparatus of claim 5 wherein a tubular shaft extends through the axis of the spray head and through the barrier wall to communicate with the interior of said gas-receiving chamber, said shaft serving as the means about which the spray head rotates and the means for providing the gas from the gas supply to the gas-receiving chamber.

7. The apparatus of claim 6 wherein a shell having at least one orifice therein, is disposed about the shaft and within the liquid-receiving chamber, with said orifice communicating with the interior of said liquidreceiving chamber, said shell serving as the means for providing liquid from said liquid supply into said liquidreceiving chamber.

8. The apparatus of claim 3 wherein said liquid supply means comprises a constant head device for providing a constant volume of liquid to said spray head during rotation thereof.

9. The apparatus of claim 8 wherein said constant head device is adjustable to vary the volume of liquid provided to the spray head.

10. The apparatus of claim 3 wherein said filter means comprises a liquid bath through which the atmosphere from the spray chamber is bubbled to extract liquid droplets and vapor therefrom.

11. The apparatus of claim 10 wherein said filter means also comprises a surface filter coupled to the outlet of said liquid bath and having a large condensing surface area over which the atmosphere exiting from the liquid bath passes to remove residual liquid droplets and vapor therefrom, said surface filter venting to the ambient atmosphere.

12. The apparatus of claim 10 wherein a substantial portion of the atmosphere exiting from the liquid bath is fed directly back to the gas supply means.

13. A spray head for producing an aerosol spray from a liquid and a gas provided from associated stationary supplies, said spray head being rotatable about an axis normal to the plane of said spray head and including a plurality of nozzles spaced radially from the axis of said spray head and directed at an acute angle to the plane of said spray head with a directional component thereof tangential to said axis in order to cause said spray head to rotate about said axis by the reaction of the aerosol exiting said nozzles, the rotation of said spray head producing a centrifugal force on the liquid provided to it by said liquid supply and including means operative in conjunction with said centrifugal force to direct the liquid to said nozzles without leakage and without any liquid sealing means.

14. The spray head of claim 13 wherein said last mentioned means comprises a liquid-receiving chamber having a wall forming a tapered bore through which said axis extends longitudinally and a liquid inlet, said chamber wall having at least one outlet port extending radially outward therethrough adjacent to the large end of the bore, said outlet port being connected to a nozz e.

15; The spray head of claim 14 additionally comprising a gas-receiving chamber having a wall forming a cylindrical bore and separated from the liquid-receiving chamber by a barrier wall, said gas-receiving chamber including at least one outlet port extending radially outward through the wall of the bore, said outlet port being connected to a nozzle.

16. The spray head of claim 15 wherein a tubular shaft extends along the axis of the spray head and through the barrier wall to communicate with the interior of the gas-receiving chamber, said shaft serving as the means about which the spray head rotates and the gieans for providing the gas to the gas-receiving cham- 17. The apparatus of claim 16 wherein a shell having an orifice therein is disposed about the shaft and within the liquid-receiving chamber, with said orifice communicating with the interior of said liquid-receiving chamber, said tubular member serving as the means for providing the liquid into the liquid-receiving chamber.

Claims

5. The apparatus of claim 4 wherein said spray head includes a gas-receiving chamber having a wall forming a cylindrical bore and separated from the liquid-receiving chamber by a barrier wall, said bas-receiving chamber including at least one outlet port extending radially outward through the wall thereof, said outlet port being connected to a respective nozzle.

7. The apparatus of claim 6 wherein a shell having at least one orifice therein, is disposed about the shaft and within the liquid-receiving chamber, with said orifice communicating with the interior of said liquid-receiving chamber, said shell serving as the means for providing liquid from said liquid supply into said liquid-receiving chamber.

14. The spray head of claim 13 wherein said last mentioned means comprises a liquid-receiving chamber having a wall forming a tapered bore through which said axis extends longitudinally and a liquid inlet, said chamber wall having at least one outlet port extending radially outward therethrough adjacent to the large end of the bore, said outlet port being connected to a nozzle.

15. The spray head of claim 14 additionally comprising a gas-receiving chamber having a wall forming a cylindrical bore and separated from the liquid-receiving chamber by a barrier wall, said gas-receiving chamber including at least one outlet port extending radially outward through the wall of the bore, said outlet port being connected to a nozzle.

16. The spray head of claim 15 wherein a tubular shaft extends along the axis of the spray head and through the barrier wall to communicate with the interior of the gas-receiving chamber, said shaft serving as the means about which the spray head rotates and the means for providing the gas to the gas-receiving chamber.

17. The apparatus of claim 16 wherein a shell having an orifice therein is disposed about the shaft and within the liquid-receiving chamber, with said orifice communicating with the interior of said liquid-receiving chamber, said tubular member serving as the means for providing the liquid into the liquid-receiving chamber.