US3067060A

US3067060A - Method and apparatus for curtain coating

Info

Publication number: US3067060A
Application number: US789891A
Authority: US
Inventors: Glaus Bernhard
Original assignee: Ulrich Steinemann AG
Current assignee: Ulrich Steinemann AG
Priority date: 1959-01-29
Filing date: 1959-01-29
Publication date: 1962-12-04
Anticipated expiration: 1979-12-04

Description

Dec. 4, 1962 B. GLAus 3,067,060'

METHOD AND APPARATUS FOR CURTAIN COATING Filed Jan. 29, 1959 3 Sheets-Sheet l INVENTOR.

Dec. 4, 1962 B. GLAus METHOD AND APPARATUS FOR CURTAIN COATING 3 Sheets-Sheet 2 Filed Jan. 29, 1959 INVENTOR. Bevnhahcl G lav ATaR/VEYS Dec. 4, 1962 B. GLAUS METHOD AND APPARATUS FCR CURTAIN coATTNG 3 SheetS-Shee'?I 3 Filed Jan. 29, 1959 |96 CU \ON CoA-HN@ SIA MA'VF-WAL- .COATINQ MATERIAL INVENTOR. @unhaul Glaub atea iidatent Fatented Dec. 4, M262 3,967,060 METHOD AND ASPAIRATUS EUR CURTAEN CATING Bernhard Glane, St. Gallen, Switzerland, assigner to Ulrich Steinemann AG. Ltd., St. @Saiten-Winkeln, witaeriand, a corporation of' Switzerland Fiied dan. 29, 1959, Ser. No. 789,891 il? tlairns. pt. ith-102) This invention relates to improvements in curtain coating apparatus and methods particularly for coating with varnish, resin, lacquer and paint compositions, which are flowed from a pouring head in liquid phase, in an unbroken or uninterrupted curtain `of substantially uniform thickness, through which the objects to be coated are passed, by a conveyor or otherwise, and upon which objects, a coating of uniform thickness is deposited.

This application is a continuation-in-part of my prior copending applications Serial Nos. 723,777 and 723,778, iiled March 25, 1958, now US. Patents 2,963,002 and 2,935,424, respectively.

In the spray coating of objects with liquid paint, lacquer and varnish compositions the coating is usually propelled against the object to be coated with compressed air 0r gas so that the liquid coating composition is interspersed with gas bubbles, some of which remain in the coating film. Also in spray coating operations a great amount of the expensive coating material is wasted and unpleasant fumes are released.

One of the objects of this invention is to overcome all these objections to the prior art spray coating methods.

Another object of the invention is to provide a method of curtain coating which provides coatings free of bubbles, blisters and other imperfections which are commonly found when objects are spray coated.

Another object of the invention is to provide a method and apparatus for curtain coating which is more economical and provides superior coating to the methods of spray coating commonly used heretofore.

Another object of the invention is to provide an improved pouring head for curtain coating machines by which the thickness of the curtain and therefore the thickness of the deposited coating may be more accurately controlled.

Another object of the invention is to provide improved A,

conveyance of the objects to be coated through the coating curtain, whereby vibration, bouncing or skipping of the objects on the conveyor belts will be avoided and a uniform coating free of ripples, ridges or visible imperfections produced on the objects to be coated.

Various other objects and advantages of my invention will become apparent as this description proceeds.

Referring now to the drawings which illustrate a preferred form of embodiment of the invention- FIG. l is a diagrammatic longitudinal sectional view through one form of coating machine showing a preferred arrangement of the conveyor, curtain pouring head, etc.

FG. 2 is a diagrammatic plan view of the embodiment of coating machine illustrated in FIG. 1.

FIG. 3 is an end view of this embodiment as viewed from the left end of FIG. l.

FIG. 4 is a detailed illustration of the pumping system for the coating material.

FIG. 5 is a diagrammatic illustration of the pouring head and of the pumping connections thereto.

FIG. 6 is a detailed cross sectional View through a preferred form of pouring head taken approximately on the line 6 6 of FIG. 5.

FIG. 7 is a sectional View of the pouring lip retractor shaft approximately on the line 7 7 of FIG. 5.

FIG. 8 is a detail of the end of the pouring lip retractor shaft, and

CII

FIG. 9 is a detailed view along the line 9-9 of FIG. 5.

As illustrated in FIGS. l to 3 the preferred embodiment of coating machine comprises a transverse frame l and two side walls 2; and 3 of a conveyor table within which the conveyor belts 5 pass from the end A over roller 6 under roller 7 over roller 8 toward the end B then over roller 9 around idler roller lo, around the main drive shaft roller Il and back to the end A over roller I2. The conveyor belt or belts 5 are continuous and are constructed, as described below, to be substantially free of seam irregularities.

In travelling over roller 6, under roller 7 and over roller 8, the belt or belts S form a triangular pocket in which the collection and return trough I3 :for the coating material is positioned so that the parts 4 being coated will be conveyed by the conveyor belts through the curtain of coating material lea flowing from the pouring head I4 and over the return trough 13 and on toward end B where they are removed either manually or mechanically.

The conveyor drive motor I7 is mounted on movable mount IS. The motor mount is moved by lever Scz. On the motor shaft is a self-adjusting variable speed pulley 1S. Pulley 18 is connected to reduction pulley i6 by V-belt t9. As the motor i7 and mount l5 are moved by lever 15a the variable speed pulley il@ contracts or expands as the case may be, and thereby changes the speed of pulley I6. Pulley Ztl is connected to pulley t6 by a V-belt and pulley 2@ is mounted on drive shaft roller 11. By this construction the speed of the belt or belts 5 may be infinitely varied as is well understood in the art.

In beginning operation, the coating material is poured into reservoir 21. Pump 22 pumps material to pouring head 14 from which it ows as an unbroken curtain Ida into trough I3 and returns to reservoir 2l for recirculation. The objects l are passed through the curtain 14a at the desired speed to deposit the required thickness of coating material thereon. Idler pulley l@ is used to adjust the tension in belts 5. Under the influence of certain solvents the belts tend to contract or expand and this adjustment is necessary under these conditions.

The belts 5 are preferably assembled on the machine as they are glued at the joint in lieu of other methods of splicing such as alligator clips. The splice is made in such a way that the thickness of the splice is no greater than the thickness of the belt as a whole. This eliminates the possibility of a part skipping or bouncing as it is coated while the belt joint crosses rollers 6 and 8. If such bouncing or skipping occurred at this point as the part passes through the curtain Mn, then a visible line would result on the finished surface of the coating on parts Il.

The pouring head ld may be raised or lowered by means of a control wheel Mb operating, elevating and lowering screws or other means les through cross shaft Md to adjust the pouring head i4 to the height necessary for proper coating of different types of surfaces and different velocities of the belts 5 and of the curtain 14a itself.

A sight glass ide is provided in the pouring head ltd to indicate when the level of the coating material is at the proper height as will be described in connection with the detailed description of the pouring head. The location of a second pouring head and trough is indicated at Eidg.

By using continuous belts 5 passing over roller 6, under roller 7 and return trough i3 and over roller 3 in lieu of separate belts for the infeed and outfeed side of the conveyor all possibility of any difference in the speed of the conveyor belts on opposite sides of the trough 13 is eliminated. If two separate 4belts are used, one passing around roller 6 and returning to end A of .the coating machine and one passing over roller 8 and returning to end B of the machine there is always the possibility of different speeds for the separate conveyors even when a common drive is used. rhis would cause the parts 4 to have a change of speed while passing through the coating curtain and lead to ununiforrn coating.

As illustrated in greater detail in PEG. 4 the pumping system for the coating material comprises the pump 22 which receives the coating material from reservoir 2l. Normally pump 22 is a positive displacement `gear pump, but for coating with certain varieties of abrasive materials and other special types of coating material a eentrifugal pump is used. `lf pump 22 is a centrifugal pump, by-pass Z3 illustrated in FiG. 4 need not be used. When pump 22 is a positive displacement pump by-pass 23 and control valve 23a is used as a pressure relief and as a control over the quantity of material going to lthe pouring head i4.

Valve 2d directly controls the quantity of material going to head i4. The material then goes through lilter 25 to remove any foreign matter. The connection between filter 25 and head M- is a flexible 'hose 26, which permits pouring head lld to be adjusted upwardly or downwardly without disturbing the connection 2d. The inlet in head id for hose f2.6 is at the level where the coating material should be maintained in the head for proper operation. If the level of material is materially higher or lower than the inlet from hose Z6 bubbles tend to form as the material goes into the pouring head. As the coating material passes through pouring head ld it pours in =a continuous unbroken curtain ida into trough i3 which extends transversely for the full Width of the conveyor 'belt or belts S las illustrated more clearly in application Serial No. 723,777 and slopes toward an outlet 13a which discharges into the reservoir 2l. Bai'lie 29, when placed in the trough 13 tends to minimize the formation of bubbles as the curtain drops into trough i3. Baflies 3d in reservoir 2l minimize the formation of bubbles as the coating material drops from the trough 13 into the reservoir 2li.

Pump 22 may be driven through fa variable speed pulley from the motor 22a in order to increase or decrease the quantity of coating material which is circulated. lf the coating material tends to heat up quickly because of friction caused by the pump speed and the circulation speed, a variable speed pulley and indirect drive is preferably used.

The coating material circulating system may be cleaned by circulating a solvent for the particular type of coating material used therethrough. The pumping system may be drained through petcock 3l in the line 32 leading from the `reservoir 2l to the pump 22.

The pouring head ld is illustrated in greater detail in FIGS. to 9. As illustrated in FlG. 5 the coating material is pumped through the flexible hose 26 into a cast aluminum pouring head lil. and 34 are in a closed position until the level of material is approximately two inches from the top of the pouring head as indicated by the sight glass lie. Valve 35 in flexible overiiow line 345 is open until the proper level is reached in order for the air in the head to escape as it is displaced by the material to [be poured. When the proper level is reached, valve 3S is closed to maintain an air cushion above the top of the coating material in head 14 and lip 33 is moved by means of lever 37 to obtain a uniform slot between lips 33 and 3d. The coating material is continuously pumped into the coating head lli and flows out of the slot 4d to produce a continuous curtain 14a which drops into the trough i3 and returns to the reservoir 2li to be recirculated again or is applied to whatever objects d are passed through the curtain.

By pumping the coating material continuously against the air cushion 58 in the top of the pouring `head M a steady pressure is maintained, no air introduced into the applied coating, there is no fog or blow back The pouring lips 33 il and all material reaching the surraces to be coated remains there in a smooth film. The air cushion equaliZes the pressure over the entire length of the pouring 4head Lid and causes the coating material to flow uniformly over the entire length of the slot thereby avoiding spotty fiow of the curtain or ununiform curtain thickness.

Pouring lip 3d is stationary and is fastened to the side wail of head ld by bolts 3i; spaced approximately 6 inches apart along the length of the lip. yPouring lip 33 is movable and is fastened to three |bearing slides 39 as shown in PEG. 5. Between the lip 33 and the side wall of head le there is a thin gasket made preferably of Teflon, not shown. rl`he properties of Teflon lend themselves very well to a gasket of this type as the Teflon is relatively slick, and there is no interference in the movement of lip 33. Pouring lip 33 is also attached to head le by bolts 33a spaced approximately 6 inches apart and extending .through elongated slots in lip 33; however, these bolts are not tightened completely so that movement of lip 33 will not be restricted.

A shaft 41 extends the entire length vof pouring head la and iits into slots 39a in the bearing slides 39. A brass set screw da holds the bearing slides 39 and shaft fil to a snug fit. The shaft 4l is machined with an eccentric center ilb at Iboth ends as shown in FIGS. 7 and S. Thus the shaft 4l becomes a cam arrangement .to open and close lip 33. Each end of shaft il is yfitted into bearings 42 which are permanently secured to head M. Lever 37 is fastened to one end of shaft 4l, therefore, when lever 37 is moved, shaft il also turns. As shaft 4l turns and presses against bearings 39, because of the cam movement, the pouring lip 33 is moved thereby increasing or decreasing the width of the slot 4@ between

lips

33 and 34. Since the direction of movement for lip 33 is always the same, the

lips

33 and 34 at the slot opening 4G always remain in a vertical position regardless of the width of the slot.

In order to insure that .the slot opening dit is the same at the cen-ter as on the ends of the pouring head, a special cam adjustment is provided at the center as shown in FIG. 9. Around shaft el a machined part 43 is iitted, with the same cam pattern as is machined on the ends of shaft 4l described above and spot welded to the shaft 41. Around the outside of part 43 there is another circular ring 45 which is secured to the side wall of head 14 adjacent the center bearing slide 39 by a bracket 45a. This ring contains three adjustment bolts d4 spaced at 120 degree intervals. lf the opening at the center of lip 33 varies from the opening at the ends, it is necessary to change adjustment bolts ad until the cam d3 is set in the proper position to exert the correct pressure on the shaft il to properly adjust the center bearing slide 39. Bolts i4 are locked in place by nuts d3. This adjustment is used to counteract bows which might develop in lip 33 `because of the length of the lip itself.

The arrangement whereby a top 47 is fastened onto pouring head 14 is illustrated in FIG. 6. Top 47 is also cast aluminum and is bolted to the head 14 by bolts not illustrated, so that pressures may be maintained. Gasket i6 is preferably made of either rubber or polyethylene. ln the embodiment illustrated the slot between

lips

33 and 34 is adjustable between 0 and .196 inch. By adjustment of the slot opening it is possible to obtain both negative and positive pressures. The system is a closed hydraulic system and whatever quantity of coating material is pumped into the head 14 must come out regardless of the width of the slot opening. The cast head allows for relatively high pressures and for certain coating operations such as on grooved work, this pressure is necessary in order to adequately coat all surfaces uniformly. A high pressure is also necessary when attempting to apply a very thin coating at high conveyor speeds so that the curtain will not break due to the Velocity of the part being coated.

Another method for changing the pressure at the pouring lips is by throttling or closing the by-pass valve 23a in the pumping system. This of course allows more material to circulate in the head and createsY a higher pressure for a given slot adjustment. However, if one does not wish to obtain more material but desires a higher pressure, then the slot opening must be decreased and the by-pass valve 23a remains unchanged. The

lips

33 and 34 are mounted at an angle of approximately 30 to the side walls of head 1li and since there are no 90 corners in the cast head, the problem of cleaning out pockets of color pigments is eliminated. This is very important when frequent changes of material of different colors are required.

As previously stated the edges of

lips

33 and 34 are always in a vertical position with the edges of lip 33 parallel to the edges of lip 34. This is very important when working with material with certain viscosities, as well as when attempting to maintain a very thin curtain.

While I have illustrated a preferred embodiment of my invention it will be readily understood that various modifications and changes may be made therein without departing from the spirit of my invention or the scope of the following claims. Thus the conveyor belts 5 may be tilted longitudinally to give an upward or downward inclination to the work pieces 4 thereon or may be given a sidewise tilt as described in my application Serial No. 723,778, now Patent Number 2,935,424. The pumping system may be modified as illustrated in my application Serial No. 723,777, now Patent Number 2,963,002; the pouring head 14 may be tilted from a vertical position and other changes made within the skill of persons skilled in the art.

I claim:

l. The method of curtain coating objects with a liquid iilm of coating material, from the group consisting of lacquer `and paint compositions, which comprises continuously pumping the liquid coating material into an elongated pouring head against a confined air cushion, discharging the coating material in a continuous unbroken substantially rectangular vertical curtain of substantially uniform thickness and many times wider than its thickness over substantially the entire length of the head, under the pressure of said air cushion and passing the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and leaving the objects to be coated unsupported at the point of application of the coating material to uniformly coat the upper surface of said objects in a single passage through said curtain.

2. The method of curtain coating objects with a liquid hlm of coating material, from the group consisting of lacquer and paint compositions, which comprises continuously pumping the liquid coating material into an elongated pouring head against a confined air cushion, discharging the coating material in a continuous unbroken substantially rectangular vertical curtain of substantially uniform thickness and many times wider than its thickness over substantially the entire length of the head under the pressure of said air cushion, regulating the thickness of said curtain, and passing the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and leaving the objects to be coated unsupported at the point of application of the coating material to uniformly coat the upper surface of said objects in a single passage through said curtain.

3. The method of curtain coating objects with a liquid hlm of coating material, from the group consisting of lacquer and paint compositions, which comprises continuously pumping the liquid coating material into an elongated pouring head, maintaining a confined air cushion above the coating material in said pouring head, discharging the coating material through an adjustable slot in the bottom of said pouring head, in a continuous unbroken substantially rectangular vertical curtain of substantially uniform thickness and many times Wider than its thickness over substantially the entire length of the head, under the pressure of said air cushion, adjusting the opening of said slot to regulate the thickness of said curtain, maintaining the walls of said slot parallel and equally spaced apart at all points and passing the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and leaving; the objects to be coated unsupported at the point of application of the coating material to uniformly coat the upper surface of said objects in a single passage through said curtain.

4. The method of curtain coating objects with a liquid iilrn of coating material, from the group consisting of lacquer and paint compositions, which comprises continuously pumping the liquid coating material into a pouring head, maintaining a confined air cushion above the coatting material in said pouring head, discharging the coating material through an adjustable slot in said pouring head in a continuous unbroken substantially rectangular vertical curtain of substantially uniform thickness and many times wider than its thickness under the pressure of said air cushion, pumping coating material into said pouring head at a rate to maintain said air cushion at superatrnospheric pressure, adjusting the opening of said slot to maintain said pressure and regulate the thickness of said curtain, maintaining the walls of said slot parallel and equally spaced apart at all points and passing the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and leaving the objects to be coated unsupported at the point of application of the coating material to uniformly coat the upper surface of said objects in a single passage through said curtain.

5. The method of curtain coating objects with a liquid film of coating material, from the group consisting of lacquer and paint compositions, which comprises continuously pumping the liquid material into a pouring head,

maintaining an air cushion above the coating material in' said pouring head, discharging the material through a slot in said pouring head in a continuous unbroken elongated substantially rectangular vertical curtain under the pressure of said air cushion, controlling the pressure of said air cushion by changing the pumping rate and the width of said slot, passing the objects to be coated through said curtain and leaving the objects to be coated unsupported at the point of application of the coating material.

6. The method of curtain coating moving objects with a liquid film of coating material which comprises continuously discharging a coating material in an unbroken substantially rectangular vertical curtain of substantially uniform dimensions and many times wider than its thickness from an elongated pouring head over substantially the entire length of said head, conveying the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and to uniformly coat the upper surfaces of said objects in a single passage through said coating curtain while leaving the under surface of the objects to be coated unsupported by conveying means at the point where said objects pass through said curtain, recovering the coating material which is not deposited on the objects to be coated in an open trough below the objects being coated, flowing the so recovered coating material from said trough into a coating .material reservoir, continuously pumping the coating material from said reservoir back into said elongated pouring head and regulating the pumping to maintain a substantially uniform supply of coating material in said pouring head whereby substantial uniformity of said curtain is maintained throughout the coating operation.

7. The method of curtain coating moving objects with a liquid film of coating material which comprises continuously discharging a coating material in an unbroken substantially rectangular vertical curtain of substantially uniform dimensions and many times wider than its thickness from an elongated pouring head over substantially the entire length of said head, conveying the objects to be coated through said curtain at a speed to deposit the desired coating thickness thereon and to uniformly coat the upper surfaces of said objects in a single passage through said coating curtain while leaving the under surface of the objects to be coated unsupported by conveying means at the point where said objects pass through said curtain, recovering the coating material which is not deposited on the objects to be coated in an open trough below the objects being coated, owing the so recovered coating material from said trough into a coating material reser- Voir, continuously pumping the coating material from said reservoir back into said elongated pouring head at substantially the level of the coating material in said pouring head and regulating the pumping to maintain a substantially uniform supply of coating material in said pouring head whereby substantial uniformity of said curtain' is maintained throughout the coating operation.

8. The method of curtain coating moving objects with a liquid lm of coating material which comprises continuously discharging a coating material in an unbroken substantially rectangular vertical curtain of substantially uniform dimensions and many times wider than its thickness from an elongated pouring head closed to the atmosphere at the top thereof over substantially the entire length of said head, conveying the objects to be closed through said curtain `at a speed to deposit the desired coating thickness thereon and to uniformly coat the upper surfaces of said objects in a single passage through said coating curtain while leaving the under surface of the objects to be coated unsupported by conveying means at the point where said objects pass through said curtain, recovering the coating material which is not deposited on the objects to be coated in an open trough below the objects being coated, flowing the so recovered coating material from said trough into a coating material reservoir, continuously pumping the coating material from said reservoir back into said elongated pouring head and regulating the pumping to maintain a substantially uniform supply of coating material in said pouring head whereby substantial uniformity of said curtain is mantained throughout the coating operation.

v9. The method of curtain coating moving objects with a liquid film of coating material which comprises continuously discharging a coating material in an unbroken substantially rectangular vertical curtain of substantially uniform dimensions and many times wider than its thickness from an elongated pouring head over substantially the entire length of said head, conveying the objects to be coate-d through said curtain at a speed to deposit the desired coating thickness thereon and to uniformly coat the upper surfaces of said objects in a single passage through said coating curtain While leaving the under surface of the objects to be coated unsupported by conveying means at the point where said objects pass through said curtain, recovering the coating material which is not deposited on the objects to be coated in an open trough below the objects being coated, Howing the so recovered coating material from said trough into a coating material reservoir, continuously pumping the coating material from said reservoir back into said elongated pouring head and regulating the pumping to maintain a substantially uniform supply of coating material in said pouring head with an air cushion above the supply of coating material in said coating head whereby substantial uniformity of said curtain is maintained throughout the coating operation.

10. In a liquid coating machine, an elongated pouring head for discharging liquid coating material in a continuous vertical liquid curtain, a trough into which said coating material is directly discharged when no objects to be coated are passing through said curtain, a continuous conveyor belt to convey objects to be coated under said pouring head and through said curtain, at a level above the top level of said trough and rollers adjacent the top and bottom of said trough to cause said conveyor belt to pass downward under said trough and up again to the normal level of said conveyor belt, the space between the rollers adjacent the top of said trough being less than the length of the objects to be coated, whereby the objects to be coated bridge the gap between the rollers adjacent the top of said trough and pass continuously and without interruption of movement through said curtain, means to maintain a supply of liquid coating material liowing into said pouring head and means to drive said conveyor belt to convey objects thereon through said liquid curtain of coating material without interruption of movement.

il. ln a liquid coating machine, an elongated rectangular pouring head, means to maintain an air cushion adjacent the top of said pouring head, said pouring head having an adjustable slot therein for discharging liquid coating material in a continuous substantially rectangular vertical liquid curtain, means to adjust the width of said slot while keeping the walls thereof parallel, a tf-shaped trough into which said coating material is discharged, a continuous belt conveyor under said pouring head at a level above the top level of said trough, a roller adjacent each side of said trough and above the level thereof, a single roller below said trough, said conveyor belt travel ing over said rollers adjacent each side of said trough and under the roller below said trough to form a V-shaped loop under said trough with the top walls of the V closely adjacent the walls of said trough, a supply reservoir for liquid coating material, means to pump liquid coating material from said supply reservoir continuously into said pouring head, means to conduct the liquid coating material falling into said trough back to said supply reservoir, and means to drive said conveyor belt to convey objects thereon over the top of said trough and through said liquid coating curtain.

l2. ln the machine of claim ll, means to move one Wall of said slot relative to the other in a constantly parallel relationship to` adjust the Width of the slot in said pouring head and means to adjust the speed of said conveyor belt.

13. In a liquid coating machine an elongated substantially rectangular pouring head, means to pump liquid coating material into said pouring head, means to maintain an air cushion under pressure in said pouring head above the liquid coating material therein, said pouring head having an elongated substantially rectangular discharge slot therein through which a liquid curtain of coating material is discharged vertically at the pressure of said air cushion, a trough for receiving said curtain of liquid coating material and means to convey objects to be coated under said pouring head and through said coating curtain above said trough while leaving the objects to be coated unsupported at the point of application of the coating material.

14. In a liquid coating machine, an elongated substantially rectangular pouring head, a supply reservoir for liquid coating material, means to pump liquid coating material from said supply reservoir into said pouring head, means to maintain a substantially rectangular air cushion of uniform thickness under pressure in said pouring head above the liquid coating material therein, said pouring head having a discharge slot therein through which a vertical substantially rectangular liquid curtain of coating material is discharged at the pressure of said air cushion, an elongated trough for receiving said curtain of liquid coating material, at atmospheric pressure, means to conduct the liquid coating material from said trough to said supply reservoir and means to convey objects to be coated under said pouring head and through said coating curtain above said trough while leaving the objects to be coated unsupported at the point of application of the coating material.

15. In a liquid coating machine, an elongated substantially rectangular pouring head, having substantially vertical side walls, means to pump liquid coating material into said pouring head, means to maintain an air cushion under pressure in said pouring head above the liquid coating material therein, said pouring head having a discharge slot therein through which a liquid curtain of coating material of substantially the length of said pouring head is discharged vertically, and means to adjust the width of said slot comprising a stationary lip at an angle of ap proximately 30 to a vertical side Wall of said pouring head, a movable lip at an angle of approximately 30 to the other vertical side Wall of said pouring head, means to move the movable lip toward and away from the stationary lip in an inclined plane at an angle of approximately 30 to a vertical side Wall of said pouring spout, the facing edges of said lips forming said discharge slot being bevelled to form a discharge slot with vertical sides, said vertical sides of said discharge slot remaining parallel and equally spaced apart at all points `as ysaid slot is narrowed or widened by the movement of said movable lip, and means to convey objects to be coated under said pouring head and through said coating curtain while leaving the objects to be coated unsupported at the point of application of the coating material.

16. In a liquid coating machine, an elongated pouring head for discharging liquid coating material in a continuous vertical liquid curtain, a trough into which said coating material is directly discharged when no objects to be coated are passing through said curtain, conveyor means to convey objects to be coated under said pouring head and through said curtain at a level above the top level of said trough, and rollers adjacent said trough to cause said conveyor means to pass downward adjacent one side of said trough and up adjacent the vother side of said trough to maintain the normal level of said conveyor belt at the level said objects are to be conveyed through said curtain, the space between the rollers adjacent the top of said trough being less than the length of the objects to be coated, whereby said objects to be coated bridge the gap between the rollers adjacent the top of said trough and pass continuously and without interruption of movement through said curtain and do not contact the conveyor means at the point where said objects pass through said curtain, means to receive the unused coating material from said trough, means to pump coating material from said receiving means into said pouring head, means to maintain a supply of liquid coating material flowing in said pouring head, at a substantially constant level, and

means to drive said conveyor means to convey the objects thereon through said liquid coating material without interruption of movement.

17. in a liquid coating machine, a pouring head having a slot therein for discharging liquid coating material in a continuous vertical liquid curtain, a trough into which said coating material is directly discharged when no objects to be coated are passing through said curtain, a continuous conveyor belt to convey objects to be coated under said pouring head and through said curtain, at a level above the top lef/el of said trough and rollers adjacent the top and bottom of said trough to cause said conveyor belt to pass downward under said trough and up again to the normal level of said conveyor belt, the space between the rollers adjacent the top of said trough being less than the length of the objects to be coated, whereby the objects to be coated bridge the gap between the rollers adjacent the top of said trough and pass continuously and without interruption of movement through said curtain, means to maintain a supply of liquid coating material ilowing into said pouring head, means to drive said conveyor belt to convey objects thereon through said liquid curtain of coating material without interruption of movement and means to provide an infinite number of speed variations for said conveyor belt.

References Cited in the tile of this patent UNITED STATES PATENTS 909,574 Ford lan. 12, 1909 924,501 Sala June 8, 1909 1,688,149 Massarella Oct. 16, 1928 1,775,475 Savy Sept. 19, 1930 1,953,288 Caton Apr. 3, 1934 1,981,956 Jorgensen Nov. 27, 1934 2,935,424 Glaus May 3, 1960 2,963,002 Glaus Dec. 6, 1960 FORElGN PATENTS 59,392 Germany Oct. 17, 1891 156,267 Germany Dec. 3, 1903 250,400 Great Britain Apr. 12, 1926 445,170 Great Britain Apr. 3, 1936 437,968 Great Britain Nov. 8, 1955 525,839 Canada June 5, 1956

Claims

6. THE METHOD OF CURTAIN COATING MOVING OBJECTS WITH A LIQUID FILM OF COATING MATERIAL WHICH COMPRISES CONTINOUSLY DISCHARGING A COATING MATERIAL IN AN UNBROKEN SUBSTANTIALLY RECTANGULAR VERTICAL CURTAIN OF SUBSTANTIALLY UNIFORM DIMENSIONS AND MANY TIMES WIDER THAN ITS THICKNESS FROM AN ALONGATED POURING HEAD OVER SUBSTANTIALLY THE ENTIRE LENGHT OF SAID HEADED, CONVEYING THE OBJECTS TO BE COATED THROUGH SAID CURTAIN AT A SPEED TO DEPOSIT THE DESIRED COATING THICKNESS THEREON AND TO UNIFORMLY COAT THE UPPER SURFACES OF SAID OBJECTS IN A SINGLE PASSAGE THROUGH SAID COATING CURTAIN WHILE LEAVING THE UNDER SURFACE OF THE OBJECTS TO BE COATED UNSUPPORTED BY CONVEYING MEANS AT THE POINT WHERE SAID OBJECTS PASS THROUGH SAID CURTAIN, RECOVERING THE COATING MATERIAL WHICH IS NOT DEPOSITED ON THE OBJECTS TO BE COATED IN AN OPEN TROUGH BELOW THE OBJECTS BEING COATED, FLOWING THE SO RECOVERED COATING MATERIAL FROM SAID TROUGH INTO A COATING MATERIAL RESERVOIR, CONTINOUSLY PUMPING THE COATING MATERIAL FROM SAID RESERVOIR BACK INTO SAID ELONGATED POURING HEAD AND REGULATING THE PUMPING TO MAINTAIN A SUBSTANTIALLY UNIFORM SUPPLY OF COATING MATERIAL IN SAID POURING HEAD WHEREBY SUBSTANTIAL UNIFORMITY OF SAID CURTAIN IS MAINTAINED THROUGHOUT THE COATING OPERATION.