Blade for applying a flowable substance to a moving article
United States Patent 3899999
The coating machine employs a blade which has a chamber between the blade proper and the moving article to receive a pressurized supply of a flowable substance. The blade is pressed perpendicularly towards the path of the moving article under a force which is opposed by the pressure of the flowable substance to cause the blade to float on a cusion of the flowable substance. This force can be generated by directing the flowable substance into a thrust chamber on the far side of the blade while the chamber on the near side of the blade receives the substance at a lower pressure via restricted passageways. The difference in pressures provides the resultant thrust force.
US Patent References:
Impregnating apparatus
Rees - May 1932 - 1858111
Machine for continuously coating and/or permeating sheets
Evans - May 1944 - 2349256
Coating applicator
Recor - November 1966 - 3285225
Paper coating apparatus
Phelps et al. - December 1968 - 3418970
TONER APPLICATION APPARATUS
Noon - August 1969 - 3461843
Impregnating apparatus
Rees - May 1932 - 1858111
Machine for continuously coating and/or permeating sheets
Evans - May 1944 - 2349256
Coating applicator
Recor - November 1966 - 3285225
Paper coating apparatus
Phelps et al. - December 1968 - 3418970
TONER APPLICATION APPARATUS
Noon - August 1969 - 3461843
Inventors:
Christ, Alfred (Zurich, CH)
Tognola, Sergio (Zurich, CH)
Lehmann, Rolf (Mutschellen, CH)
Tognola, Sergio (Zurich, CH)
Lehmann, Rolf (Mutschellen, CH)
Application Number:
05/369194
Publication Date:
08/19/1975
Filing Date:
06/12/1973
View Patent Images:
Export Citation:
Assignee:
Escher Wyss GmbH (Zurich, CH)
Primary Class:
Other Classes:
118/411, 101/366
International Classes:
B05C3/18; B05C5/02; B05C9/06; B05C3/00; B05C9/00; B05C5/02
Field of Search:
118/410,411,261,259,405,126,122,404 101/366
US Patent References:
| 3698355 | APPARATUS FOR COATING AND/OR IMPREGNATING A SHEET MATERIAL | October 1972 | Heijnis et al. |
Primary Examiner:
Mcintosh, John P.
Attorney, Agent or Firm:
Kenyon & Kenyon Reilly Carr & Chapin
Claims:
What is claimed is
1. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, and means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including a fixedly mounted support member slidably receiving said blade therein for movement perpendicularly of the moving article, said member and blade defining at least one thrust chamber therebetween for receiving a pressurized medium.
2. The combination as set forth in claim 1 wherein said chamber of said blade is of reduced height relative to the width thereof.
3. The combination as set forth in claim 2 wherein said chamber of said blade is in the form of a plurality of interconnected grooves.
4. The combination as set forth in claim 1 wherein said thrust chamber is of smaller surface area than said first chamber.
5. The combination as set forth in claim 1 which further includes a means having hydraulic cylinders secured to said support member for moving said member relative to the path of the moving article.
6. The combination as set forth in claim 1 which further includes a ridge in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article.
7. The combination as set forth in claim 6 which further includes a plurality of lateral webs in each longitudinal chamber to further sub-divide each longitudinal chamber into a number of sub-chambers.
8. The combination as set forth in claim 7 wherein said webs are angularly inclined to the longitudinal axis of said blade, each web having a point of termination in a transverse plane relative to said blade coincident with a point of beginning of an adjacent web.
9. The combination as set forth in claim 6 wherein said ridge is removably mounted in said blade.
10. The combination as set forth in claim 6 wherein a doctor device defines a side wall of one of said longitudinal chambers on a downstream side of said blade.
11. The combination as set forth in claim 1 wherein said blade is rotatably mounted on a longitudinal axis thereof.
12. The combination as set forth in claim 1 wherein said means includes a resilient spring biasing said blade toward the path of the moving article.
13. The combination as set forth in claim 1 wherein said means includes means for mounting said blade above the path of the moving article whereby said force is the weight of said blade.
14. The combination as set forth in claim 1 wherein said blade is flexible.
15. The combination as set forth in claim 1 which further includes a roller for guiding the moving article across said chamber of said blade.
16. The combination as set forth in claim 1 which further includes a second said blade opposite said first blade for guiding the moving article therebetween across said chamber.
17. The combination as set forth in claim 16 wherein said second blade is fixedly mounted relative to said first blade.
18. The combination as set forth in claim 16 wherein said chamber of each blade has a rounded entry side adjacent the path of the moving article.
19. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, and means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including at least one thrust chamber on a side of said blade distal from said chamber for receiving a pressurized medium and at least one line connecting said first chamber and said thrust chamber whereby the pressurized medium in said thrust chamber is the flowable substance.
20. The combination as set forth in claim 19 wherein said line is a passage in said blade.
21. The combination as set forth in claim 19 wherein a restrictor is disposed in each said line to reduce the pressure of the flowable substance passing from said thrust chamber to said first chamber.
22. The combination as set forth in claim 21 wherein said restrictor is adjustable.
23. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including at least one thrust chamber on a side of said blade distal from said one chamber for receiving a pressurized medium and a passage in said blade communicating said first chamber with a side of said blade for passing a flow of the flowable substance to said first chamber.
24. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for contaiing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, a ridge slidably mounted in said blade and in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article, and a passage means for communicating a side of said ridge distal from the moving article with a pressurized medium.
25. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, a ridge in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article, a thrust chamber on a side of said blade distal from said first chamber, a longitudinal ridge in said thrust chamber for sub-dividing said thrust chamber into two longitudinal chambers and a line between each respective longitudinal chamber of said first chamber and said thrust chamber.
26. The combination as set forth in claim 25 wherein one of said longitudinal chambers in said first chamber receives a pressurized flow of flowable substance from one of said longitudinal chambers of said thrust chamber and the other of said longitudinal chambers in said first chamber delivers a surplus of the flowable substance to the other of said longitudinal chambers of said thrust chamber.
1. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, and means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including a fixedly mounted support member slidably receiving said blade therein for movement perpendicularly of the moving article, said member and blade defining at least one thrust chamber therebetween for receiving a pressurized medium.
2. The combination as set forth in claim 1 wherein said chamber of said blade is of reduced height relative to the width thereof.
3. The combination as set forth in claim 2 wherein said chamber of said blade is in the form of a plurality of interconnected grooves.
4. The combination as set forth in claim 1 wherein said thrust chamber is of smaller surface area than said first chamber.
5. The combination as set forth in claim 1 which further includes a means having hydraulic cylinders secured to said support member for moving said member relative to the path of the moving article.
6. The combination as set forth in claim 1 which further includes a ridge in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article.
7. The combination as set forth in claim 6 which further includes a plurality of lateral webs in each longitudinal chamber to further sub-divide each longitudinal chamber into a number of sub-chambers.
8. The combination as set forth in claim 7 wherein said webs are angularly inclined to the longitudinal axis of said blade, each web having a point of termination in a transverse plane relative to said blade coincident with a point of beginning of an adjacent web.
9. The combination as set forth in claim 6 wherein said ridge is removably mounted in said blade.
10. The combination as set forth in claim 6 wherein a doctor device defines a side wall of one of said longitudinal chambers on a downstream side of said blade.
11. The combination as set forth in claim 1 wherein said blade is rotatably mounted on a longitudinal axis thereof.
12. The combination as set forth in claim 1 wherein said means includes a resilient spring biasing said blade toward the path of the moving article.
13. The combination as set forth in claim 1 wherein said means includes means for mounting said blade above the path of the moving article whereby said force is the weight of said blade.
14. The combination as set forth in claim 1 wherein said blade is flexible.
15. The combination as set forth in claim 1 which further includes a roller for guiding the moving article across said chamber of said blade.
16. The combination as set forth in claim 1 which further includes a second said blade opposite said first blade for guiding the moving article therebetween across said chamber.
17. The combination as set forth in claim 16 wherein said second blade is fixedly mounted relative to said first blade.
18. The combination as set forth in claim 16 wherein said chamber of each blade has a rounded entry side adjacent the path of the moving article.
19. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, and means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including at least one thrust chamber on a side of said blade distal from said chamber for receiving a pressurized medium and at least one line connecting said first chamber and said thrust chamber whereby the pressurized medium in said thrust chamber is the flowable substance.
20. The combination as set forth in claim 19 wherein said line is a passage in said blade.
21. The combination as set forth in claim 19 wherein a restrictor is disposed in each said line to reduce the pressure of the flowable substance passing from said thrust chamber to said first chamber.
22. The combination as set forth in claim 21 wherein said restrictor is adjustable.
23. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, said means including at least one thrust chamber on a side of said blade distal from said one chamber for receiving a pressurized medium and a passage in said blade communicating said first chamber with a side of said blade for passing a flow of the flowable substance to said first chamber.
24. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for contaiing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, a ridge slidably mounted in said blade and in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article, and a passage means for communicating a side of said ridge distal from the moving article with a pressurized medium.
25. In combination, a blade for applying a flowable substance onto a moving article having at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article, means for pressing said blade towards the moving article under a force opposed to the pressure of the flowable substance in said chamber to cause said blade to float on a cushion of the flowable substance on the moving article, a ridge in said chamber to sub-divide said chamber into two longitudinal chambers, said ridge projecting towards the path of the moving article, a thrust chamber on a side of said blade distal from said first chamber, a longitudinal ridge in said thrust chamber for sub-dividing said thrust chamber into two longitudinal chambers and a line between each respective longitudinal chamber of said first chamber and said thrust chamber.
26. The combination as set forth in claim 25 wherein one of said longitudinal chambers in said first chamber receives a pressurized flow of flowable substance from one of said longitudinal chambers of said thrust chamber and the other of said longitudinal chambers in said first chamber delivers a surplus of the flowable substance to the other of said longitudinal chambers of said thrust chamber.
Description:
This invention relates to a blade for applying a flowable substance to a moving article, particularly a travelling web on a roller surface.
As is known, various machines have been used to coat a traveling web in order to produce a coated product. For example, as described in U.S. Pat. No. 3,486,482, a double-nip coater has been used which includes a coating impeller bar at a first nip cooperating with a pressurized pond of coating to impel coating into and onto the traveling web and a trailing blade at the second nip for finally metering and smoothing the coating.
However, the blade in these known machines has not usually been able to cooperate with a web of material guided on a roller to define an absolutely constant gap for the coating composition passing therethrough. This is because the blade sags very readily and, so, does not engage with the web at every point at the same pressure. As a result, it has been difficult and time-consuming to control the quantity of material applied. Furthermore, the parts of the blade which contact the web can easily damage the web and can experience heavy wear.
As the height of the gap or nip is affected very considerably by the viscosity of the applied material and since the blade cannot be positioned just anywhere on the roller as the apparatus must be operated with an excess of coating composition, a doctor blade has usually been required to deal with the surplus. Still further, because of the need for a surplus of composition, the coating composition has been allowed to circulate. This is bad of itself. Also, relatively large conveying pumps are needed for the coating composition.
It is an object of the invention to provide a simple and easily controlled blade for providing an application of very constant thickness.
It is another object of the invention to provide a blade which is able to readily adapt to changes in thickness of a coated article.
It is another object of the invention to provide for a remote control of a coating blade in a coating machine.
It is another object of the invention to operate a coating machine without a surplus.
Briefly, the invention provides a blade for applying a flowable substance onto a moving article, such as a traveling web or a rotating roller, which has at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article. In addition, means are provided for pressing the blade towards the moving article under a force opposed to the pressure of the flowable substance in the chamber to cause the blade to float on a cushion of the flowable substance on the moving article.
Because of the continuous cushion or constant film of flowable material, a blade of this kind cooperates with the article to define an absolutely constant gap over the width of the article. As a result, the thickness of the applied coating also becomes absolutely constant. The blade is in intimate "engagement" with the article by way of a constant gap; the "engagement" of the blade with the article being understood herein to denote a floating of the blade on the article. The ability to engage intimately with the article is increased by the fact that the blade is very flexible. Thus, the blade can adapt very readily to changes in the overall thickness and changes in the height of the article and to local thickenings.
The pressure of the applied coating composition is a parameter which can be used to provide direct control of pin size and thickness of application. Thus, the quantity applied can be controlled very readily on a stepless variable basis. It is therefore a simple matter to arrange for remote control.
The blade can be positioned to engage by way of a large area with the flowable substance on the top of the article, so that the article is treated gently and the pressure of the coating composition acts on the article by way of a large contact zone. Also, the blade can be disposed anywhere on an article-guiding roller independently of gravity. Further, high-speed operation is possible, for in contrast to what happens with applicator rollers, there is no film splitting, i.e., there is no detachment from the article of some of the applied composition after application. Also, operation without a surplus or excess is possible. Thus, no doctor device is required and there is no need to circulate the coating composition. The feed pumps for the coating composition can therefore be very small.
According to one embodiment of the invention, the chamber is of very reduced height in relation to the width. In this case, all or some of the chamber can be in the form of discrete interconnected grooves. Also, those parts of the chamber which engage with the article can engage therewith by way of large areas.
According to another embodiment of the invention, in order to produce the force for pressing the blade towards the moving article, the flowable material is also directed to apply pressure to that side of the blade which is distal from the article. Consequently, the pressure of the flowable substance acts on the blade side near the article and on the blade side remote therefrom. The blade is thus retained solely by pressures and, therefore, enters very readily into intimate engagement with the article and is therefore easy to control. Also, the blade is pressed evenly against the article over the whole width, thus obviating unwanted sag of the blade.
Preferably, each chamber is connected by at least one line to the blade side distal from the article. In this case, the line can be a passage in the blade, so that the flowable substance can be supplied through the blade to each chamber. In order to enable the pressures acting on the blade, and therefore, the nip size, to be varied, an adjustable restrictor can be disposed in each line. Also, the pressured blade surface distal from the article can be smaller than the oppositely pressured side of the chamber.
In another embodiment of the invention, the blade is disposed on a support member to be slidable substantially perpendicularly to the article so as to cooperate with the support member to define at least one sealed thrust or bearing chamber which is supplied with the flowable substance or some other pressure medium. Also, the flowable substance can be supplied to each chamber via the blade side near the article or to the bearing chamber via a suitable line. Also, the chamber can be sub-divided into two longitudinal chambers by a ridge or web or the like which extends along the blade and which preferably engages with the article. The use of different pressures in these longitudinal chambers helps to improve tilting stability and reduce edge wear. Also, longitudinal edges of the blade which engage with the article can cooperate therewith by way of a gap whose size can be varied, and two coating compositions can be applied to the article simultaneously. Also, one coating agent can be applied via one longitudinal chamber and surplus agent can return through the other longitudinal chamber.
In this case, the ridge can be slidingly mounted in the blade, and the flowable substance or a controllable pressure agent can act on the ridge side distal from the article, so that the gap between the ridge and the article is controllable. Also, ridges or webs or the like which preferably engage with the article can sub-divide each chamber or longitudinal chamber. The stability with which the blade floats on the article can be improved by supplying the flowable material to the chambers through separate lines. Also, this feature enables the gap height to be varied over the article width, i.e., the thickness of the application on the left-hand side of the article can be different from the thickness of the application on the right-hand side of the article. Also, the ridges can extend at an inclined angle relative to the blade longitudinal axis and can be so disposed that at the place where one ridge terminates, another ridge begins on the opposite side. This feature leads to a uniform stripe-free coating.
Conveniently, the support member is retained by hydraulic cylinders. Also, those parts or ridges of the chambers which engage with the article can be replaceable. If there are two longitudinal chambers, the bearing chamber can be sub-divided into two longitudinal thrust chambers by a longitudinal ridge or web or the like and each longitudinal thrust chamber can be connected via at least one line to the corresponding longitudinal chamber. In this case, one longitudinal chamber can serve for the supply of flowable substance and the other longitudinal chamber can serve for the return of surplus substance. If there are two longitudinal chambers, the wall disposed on the runout side of the article can be a doctor device.
In one embodiment of the invention, the blade can be rotatable around a longitudinal axis, thus giving very good engagement and accurate controllability. Also, the flowable material can be introduced into and removed from the chambers through lateral passages of the blade.
As an alternative, the blade is pressed against the article by a controlled pressure medium or a resilient medium or by its own weight. Also, the blade can be so flexible as to engage intimately with the article. Finally, where the moving article is in the nature of a traveling web or surplus surface, the article can be guided on a roller at the place where the blade engages with the web or the web can be guided on a similar second blade disposed opposite the first blade. In this case, the second blade can be nondisplaceable, i.e., mounted in a fixed manner.
The chamber parts which engage with the moving article are rounded or nozzle-shaped on the side where the article first impinges. The article is therefore treated gently and a speed-dependent hydrodynamic pressure increase is produced at the runout side and at central webs.
These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:
FIG. 1 illustrates a cross-sectional view through a blade with a longitudinal chamber and a bearing or thrust chamber according to the invention;
FIG. 2 illustrates a cross-sectional view through a blade having two longitudinal chambers and a bearing or thrust chamber according to the invention;
FIG. 3 illustrates a side view of a blade disposed on a roller according to the invention;
FIG. 4 illustrates a cross-sectional view through a blade having two longitudinal chambers and two bearings or thrust chambers according to the invention;
FIG. 5 illustrates a cross-sectional view through a blade adapted for rotation around a longitudinal axis and having two longitudinal chambers, one bearing or thrust chamber and a doctor device according to the invention;
FIG. 6 illustrates a cross-sectional view through two contiguous blades according to the invention with a web of material passing through between them; and
FIG. 7 illustrates a plan view of the longitudinal chambers of the blade of FIG. 2 with the roller removed.
Referring to FIG. 1, the coating machine includes a plastics or metal blade 1 which engages, by way of a wear resistant layer, e.g. of plastics or ceramic, and/or by way of replaceable edges 2a, 2b on a web of material 12 guided by a roller 5. The blade 1 has a flat chamber 4 on one side which extends over the whole width of the web 12 to receive a flowable substance, such as a coating composition of known type. This chamber 4 can be of similar flatness to the flatness of the liquid bearing (i.e., flat) sources known in bearings and can therefore take the form simply of discrete interconnected grooves. The web 12 cooperates with the blade 1 to define the boundaries of the chamber 4.
The blade 1 is mounted in a support member 9 for sliding perpendicularly to the web 12. The support member 9 cooperates with the blade 1 to define a bearing or thrust space or chamber 11 which extends over the whole of the blade side distal from the web 12. A sealing ridge or ledge 7 and a resilient cylindrical member 8, are mounted, as shown, between the blade 1 and support member to seal the thrust chamber 11. The blade 1 can be ledge-like or ridge-like on the underside or can take the form of discrete short pistonlike elements which engage in discrete cyclinders formed by the support member 9, so that the chamber 11, as considered transversely of the web 12, comprises a number of component chambers.
The blade 1 is pressed against the web 12 either by a resilient element (not shown) or by its own weight or, as shown, by a pressure medium supplied to the thrust chamber 11 via an inlet 10. The pressure medium can be in the flowable substance which is to be applied to the web 12 and which passes from the chamber 11 to the chamber 4 via a passage or line 6 formed in the blade 1. The pressure of the flowable substance therefore acts on two opposite sides of the blade 1. As a result, by action on the pressured surfaces of the blade 1, the blade 1 can be urged toward the roller 5 or web 12 at a predetermined pressure.
In operation, as a pressure builds up in the chamber 4, the pressure also acts against pressure in the thrust chamber 11 and causes the blade 1 to float on a cushion or film of the coating composition. Depending upon the amount of the coating composition pressure, a corresponding amount of coating composition flows through between the blade edges 2a, 2b and the web 12 and issues on the runout or delivery side as a correspondingly thick coating. The coating thickness can, therefore, be controlled just by controlling the pressure of the coating composition. In addition or as an alternative, however, an adjustable restrictor 3 in the line 6 can be used for control purposes. This restrictor 3 can be disposed inside or outside the blade 1 and can be adjustable either manually or automatically.
The gap 13a defined by the blade edge 2a and web 12 on the web entry side can be so adjusted that the drag force of the paper web 12 on the coating composition is exactly the same as the issue of composition through the gap 13a. The two edges 2a, 2b can also vary in width to suit requirements, and very good adaptation of the blade 1 to the web 12 can be achieved if blades which are of very reduced height or made of a flexible material are used.
The blade 1 need not be disposed perpendicularly to the web as shown in FIG. 1. Further, the side walls of the thrust chamber 11 can be inclined at an angle to the web 12. Also, the blade 1 can be heated.
Referring to FIG. 3, the blade 1 remains completely straight even though the support member 9 sags, since the constant liquid pressure in the chamber 11 ensures that the blade 1 is borne uniformly. As shown, the support member 9 is mounted at the ends in two hydraulic cylinders 51, so that the support member 9 and blade 1 can be moved into and out of operative position very rapidly. As also shown, the roller 5 is supported at bearing points 52 by suitable bearings mounted in machine frame supports 50 while the hydraulic cylinders 51 are pivotally mounted at the ends in the support 50.
Referring to FIG. 2, wherein like reference characters indicate like parts as above, a rib or ridge 16 is disposed within the blade 1 to sub-divide the chamber 4 into two longitudinal chambers 4a, 4b. Each of these chambers 4a, 4b is connected to the thrust chamber 11 by one passage 6a, 6b each and a respective adjustable restrictor 3a, 3b. The two chambers 4a, 4b can be operated at different coatingcomposition pressures, a feature which helps to stabilize the blade 1, i.e., which reduces the tendency of the blade 1 to tilt. As shown, the rib 16 bears against the web 12.
Referring to FIG. 4, wherein like reference characters indicate like parts as above, the thrust chamber 11 can also be subdivided into two longitudinal chambers 11a, 11b which have one inlet or outlet passage 10a, 10b each and which are connected to the respective longitudinal chambers 4a, 4b above by way of passages 6a, 6b and adjustable restrictors 3a, 3b. The blade 1 can therefore operate with two different coating compositions so that a single blade can apply two different coating compositions to the web 12, or alternatively, the composition is applied by the longitudinal chamber 4a on the web entry side and surplus composition is returned via the longitudinal chamber 4a on the web entry side and surplus composition is returned via the longitudinal chamber 4b on the web exit side. In this embodiment, the ridge 16 is mounted in the blade 1 for sliding perpendicularly to the web 12. The bottom or back of the ridge 16 cooperates to bound a chamber 37 and is acted upon by a pressure medium, e.g. the coating composition, supplied through passages or lines 6c, 10c. The support member 9 has a ridge 27 which separates the two longitudinal chambers 11a, 11b from one another and extends into a corresponding recess 11c in the blade 1. The recess 11c connects passage 10c in the support member 9 to the passage 6c in the blade 1 and is of the same width as chamber 37, to ensure that the pressure medium which acts on the ridge 16 has no effect on the blade 1. As shown, the blade 1 is sealingly mounted in the thrust chambers 11a, 11b by similar sealing elements as above.
Referring to FIG. 5, the coating composition can also be supplied via a passage 14 to the longitudinal chamber 4a on the web entry side, while surplus coating composition passages from the longitudinal chamber 4a on the web exit side through passage 6b into the thrust chamber 11, then through a discharge passage 10 which has a restrictor 3c back to a feed pump (not shown). The passage 6b has a restrictor 3b, and a passage 6a which is parallel to passage 6b and which has a restrictor 3a extends from chamber 4a to chamber 11. In addition, a doctor device 101 in the form of a blade is mounted in a holder 103 to define one side wall of the chamber 4b on the web exit side. The blade 1 has a lateral inlet passage through which a pressure medium can be supplied to the chamber 37 to act on the ridge 16.
The blade 1 is mounted for rotation around its longitudinal axis, the underside of the blade 1 being convex and being received in a matching recess in the support member 9. The recess in the support member serves as the thrust chamber 11. As in the other embodiments, the chamber 11 can receive a compression spring 92 to act on the blade 1 to apply further pressure, in addition to the pressure medium, on the blade 1 in a direction perpendicularly to and towards the web 12.
Referring to FIG. 6, the blade 1a has two longitudinal chambers 4a, 4b and two longitudinal chambers 11a, 11b, the web being guided not by a roller but by a second blade 1b disposed opposite the first blade 1a. The blade 1a differs from the blade shown in FIG. 4 in that in FIG. 6 the coating composition is supplied to the chambers 4a, 4b not via the chambers 11a, 11b but via side passages 31a, 31b having external restrictors 3a, 3b. Also, the blade 1b is non-movably disposed instead of being mounted for sliding in a support member. The coating composition is supplied to the chambers 4c, 4d of the blade 1b through distributing chambers 76, 82 an through passages which have restrictors 3c, 3d. With this arrangement, both sides of the web 12 can be coated simultaneously. In order to reduce stressing of the web 12, those parts of the chambers 4a to 4d which contact the web 12 have rounded corners 69 at the entry edges. A speed-dependent hydrodynamic pressure increase is also produced at the central ridge 16 and at the exit side during operation.
Referring to FIG. 7, the chambers 4a, 4b, for example, of the blade 1 of FIG. 2, are subdivided into a number of sub-chambers by ridges or webs 18 extending in spinefashion. This feature enables the thickness of the web coating to be varied transversely of the direction of web movement -- an important consideration, if the absorptivity of the web 12 varies over the web width, as may occur because of differences in production.
The ridges 18 are so disposed that wherever a ridge 18 starts at the edge 2a or 2b, another ridge 18 terminates at the ridge 16 on the opposite side of the chamber. The proportion of ridges 18 is therefore constant over the whole width of the web 12. Two passages 6a, 6b extend to each of the sub-chambers.
In the foregoing description, the blade has been described as applying a flowable substance to a web; however, the blade according to the invention can be used to coat a surface or roller with a flowable composition directly, such as e.g. a paint applicator roller or a drying roller, inter alia for the production of powdered milk.
It is virtually impossible for the blade shown in FIG. 1 to rotate around its longitudinal axis. However, the bottom part of the blades shown in FIG. 4 and in the top part of FIG. 6 can be convex, so that the blade can rotate around its longitudinal axis the resulting rotatability improving the adaptation between the blade and the web or roller.
As is known, various machines have been used to coat a traveling web in order to produce a coated product. For example, as described in U.S. Pat. No. 3,486,482, a double-nip coater has been used which includes a coating impeller bar at a first nip cooperating with a pressurized pond of coating to impel coating into and onto the traveling web and a trailing blade at the second nip for finally metering and smoothing the coating.
However, the blade in these known machines has not usually been able to cooperate with a web of material guided on a roller to define an absolutely constant gap for the coating composition passing therethrough. This is because the blade sags very readily and, so, does not engage with the web at every point at the same pressure. As a result, it has been difficult and time-consuming to control the quantity of material applied. Furthermore, the parts of the blade which contact the web can easily damage the web and can experience heavy wear.
As the height of the gap or nip is affected very considerably by the viscosity of the applied material and since the blade cannot be positioned just anywhere on the roller as the apparatus must be operated with an excess of coating composition, a doctor blade has usually been required to deal with the surplus. Still further, because of the need for a surplus of composition, the coating composition has been allowed to circulate. This is bad of itself. Also, relatively large conveying pumps are needed for the coating composition.
It is an object of the invention to provide a simple and easily controlled blade for providing an application of very constant thickness.
It is another object of the invention to provide a blade which is able to readily adapt to changes in thickness of a coated article.
It is another object of the invention to provide for a remote control of a coating blade in a coating machine.
It is another object of the invention to operate a coating machine without a surplus.
Briefly, the invention provides a blade for applying a flowable substance onto a moving article, such as a traveling web or a rotating roller, which has at least one chamber for containing the flowable substance disposed transversely of the direction of the moving article and facing the moving article. In addition, means are provided for pressing the blade towards the moving article under a force opposed to the pressure of the flowable substance in the chamber to cause the blade to float on a cushion of the flowable substance on the moving article.
Because of the continuous cushion or constant film of flowable material, a blade of this kind cooperates with the article to define an absolutely constant gap over the width of the article. As a result, the thickness of the applied coating also becomes absolutely constant. The blade is in intimate "engagement" with the article by way of a constant gap; the "engagement" of the blade with the article being understood herein to denote a floating of the blade on the article. The ability to engage intimately with the article is increased by the fact that the blade is very flexible. Thus, the blade can adapt very readily to changes in the overall thickness and changes in the height of the article and to local thickenings.
The pressure of the applied coating composition is a parameter which can be used to provide direct control of pin size and thickness of application. Thus, the quantity applied can be controlled very readily on a stepless variable basis. It is therefore a simple matter to arrange for remote control.
The blade can be positioned to engage by way of a large area with the flowable substance on the top of the article, so that the article is treated gently and the pressure of the coating composition acts on the article by way of a large contact zone. Also, the blade can be disposed anywhere on an article-guiding roller independently of gravity. Further, high-speed operation is possible, for in contrast to what happens with applicator rollers, there is no film splitting, i.e., there is no detachment from the article of some of the applied composition after application. Also, operation without a surplus or excess is possible. Thus, no doctor device is required and there is no need to circulate the coating composition. The feed pumps for the coating composition can therefore be very small.
According to one embodiment of the invention, the chamber is of very reduced height in relation to the width. In this case, all or some of the chamber can be in the form of discrete interconnected grooves. Also, those parts of the chamber which engage with the article can engage therewith by way of large areas.
According to another embodiment of the invention, in order to produce the force for pressing the blade towards the moving article, the flowable material is also directed to apply pressure to that side of the blade which is distal from the article. Consequently, the pressure of the flowable substance acts on the blade side near the article and on the blade side remote therefrom. The blade is thus retained solely by pressures and, therefore, enters very readily into intimate engagement with the article and is therefore easy to control. Also, the blade is pressed evenly against the article over the whole width, thus obviating unwanted sag of the blade.
Preferably, each chamber is connected by at least one line to the blade side distal from the article. In this case, the line can be a passage in the blade, so that the flowable substance can be supplied through the blade to each chamber. In order to enable the pressures acting on the blade, and therefore, the nip size, to be varied, an adjustable restrictor can be disposed in each line. Also, the pressured blade surface distal from the article can be smaller than the oppositely pressured side of the chamber.
In another embodiment of the invention, the blade is disposed on a support member to be slidable substantially perpendicularly to the article so as to cooperate with the support member to define at least one sealed thrust or bearing chamber which is supplied with the flowable substance or some other pressure medium. Also, the flowable substance can be supplied to each chamber via the blade side near the article or to the bearing chamber via a suitable line. Also, the chamber can be sub-divided into two longitudinal chambers by a ridge or web or the like which extends along the blade and which preferably engages with the article. The use of different pressures in these longitudinal chambers helps to improve tilting stability and reduce edge wear. Also, longitudinal edges of the blade which engage with the article can cooperate therewith by way of a gap whose size can be varied, and two coating compositions can be applied to the article simultaneously. Also, one coating agent can be applied via one longitudinal chamber and surplus agent can return through the other longitudinal chamber.
In this case, the ridge can be slidingly mounted in the blade, and the flowable substance or a controllable pressure agent can act on the ridge side distal from the article, so that the gap between the ridge and the article is controllable. Also, ridges or webs or the like which preferably engage with the article can sub-divide each chamber or longitudinal chamber. The stability with which the blade floats on the article can be improved by supplying the flowable material to the chambers through separate lines. Also, this feature enables the gap height to be varied over the article width, i.e., the thickness of the application on the left-hand side of the article can be different from the thickness of the application on the right-hand side of the article. Also, the ridges can extend at an inclined angle relative to the blade longitudinal axis and can be so disposed that at the place where one ridge terminates, another ridge begins on the opposite side. This feature leads to a uniform stripe-free coating.
Conveniently, the support member is retained by hydraulic cylinders. Also, those parts or ridges of the chambers which engage with the article can be replaceable. If there are two longitudinal chambers, the bearing chamber can be sub-divided into two longitudinal thrust chambers by a longitudinal ridge or web or the like and each longitudinal thrust chamber can be connected via at least one line to the corresponding longitudinal chamber. In this case, one longitudinal chamber can serve for the supply of flowable substance and the other longitudinal chamber can serve for the return of surplus substance. If there are two longitudinal chambers, the wall disposed on the runout side of the article can be a doctor device.
In one embodiment of the invention, the blade can be rotatable around a longitudinal axis, thus giving very good engagement and accurate controllability. Also, the flowable material can be introduced into and removed from the chambers through lateral passages of the blade.
As an alternative, the blade is pressed against the article by a controlled pressure medium or a resilient medium or by its own weight. Also, the blade can be so flexible as to engage intimately with the article. Finally, where the moving article is in the nature of a traveling web or surplus surface, the article can be guided on a roller at the place where the blade engages with the web or the web can be guided on a similar second blade disposed opposite the first blade. In this case, the second blade can be nondisplaceable, i.e., mounted in a fixed manner.
The chamber parts which engage with the moving article are rounded or nozzle-shaped on the side where the article first impinges. The article is therefore treated gently and a speed-dependent hydrodynamic pressure increase is produced at the runout side and at central webs.
These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:
FIG. 1 illustrates a cross-sectional view through a blade with a longitudinal chamber and a bearing or thrust chamber according to the invention;
FIG. 2 illustrates a cross-sectional view through a blade having two longitudinal chambers and a bearing or thrust chamber according to the invention;
FIG. 3 illustrates a side view of a blade disposed on a roller according to the invention;
FIG. 4 illustrates a cross-sectional view through a blade having two longitudinal chambers and two bearings or thrust chambers according to the invention;
FIG. 5 illustrates a cross-sectional view through a blade adapted for rotation around a longitudinal axis and having two longitudinal chambers, one bearing or thrust chamber and a doctor device according to the invention;
FIG. 6 illustrates a cross-sectional view through two contiguous blades according to the invention with a web of material passing through between them; and
FIG. 7 illustrates a plan view of the longitudinal chambers of the blade of FIG. 2 with the roller removed.
Referring to FIG. 1, the coating machine includes a plastics or metal blade 1 which engages, by way of a wear resistant layer, e.g. of plastics or ceramic, and/or by way of replaceable edges 2a, 2b on a web of material 12 guided by a roller 5. The blade 1 has a flat chamber 4 on one side which extends over the whole width of the web 12 to receive a flowable substance, such as a coating composition of known type. This chamber 4 can be of similar flatness to the flatness of the liquid bearing (i.e., flat) sources known in bearings and can therefore take the form simply of discrete interconnected grooves. The web 12 cooperates with the blade 1 to define the boundaries of the chamber 4.
The blade 1 is mounted in a support member 9 for sliding perpendicularly to the web 12. The support member 9 cooperates with the blade 1 to define a bearing or thrust space or chamber 11 which extends over the whole of the blade side distal from the web 12. A sealing ridge or ledge 7 and a resilient cylindrical member 8, are mounted, as shown, between the blade 1 and support member to seal the thrust chamber 11. The blade 1 can be ledge-like or ridge-like on the underside or can take the form of discrete short pistonlike elements which engage in discrete cyclinders formed by the support member 9, so that the chamber 11, as considered transversely of the web 12, comprises a number of component chambers.
The blade 1 is pressed against the web 12 either by a resilient element (not shown) or by its own weight or, as shown, by a pressure medium supplied to the thrust chamber 11 via an inlet 10. The pressure medium can be in the flowable substance which is to be applied to the web 12 and which passes from the chamber 11 to the chamber 4 via a passage or line 6 formed in the blade 1. The pressure of the flowable substance therefore acts on two opposite sides of the blade 1. As a result, by action on the pressured surfaces of the blade 1, the blade 1 can be urged toward the roller 5 or web 12 at a predetermined pressure.
In operation, as a pressure builds up in the chamber 4, the pressure also acts against pressure in the thrust chamber 11 and causes the blade 1 to float on a cushion or film of the coating composition. Depending upon the amount of the coating composition pressure, a corresponding amount of coating composition flows through between the blade edges 2a, 2b and the web 12 and issues on the runout or delivery side as a correspondingly thick coating. The coating thickness can, therefore, be controlled just by controlling the pressure of the coating composition. In addition or as an alternative, however, an adjustable restrictor 3 in the line 6 can be used for control purposes. This restrictor 3 can be disposed inside or outside the blade 1 and can be adjustable either manually or automatically.
The gap 13a defined by the blade edge 2a and web 12 on the web entry side can be so adjusted that the drag force of the paper web 12 on the coating composition is exactly the same as the issue of composition through the gap 13a. The two edges 2a, 2b can also vary in width to suit requirements, and very good adaptation of the blade 1 to the web 12 can be achieved if blades which are of very reduced height or made of a flexible material are used.
The blade 1 need not be disposed perpendicularly to the web as shown in FIG. 1. Further, the side walls of the thrust chamber 11 can be inclined at an angle to the web 12. Also, the blade 1 can be heated.
Referring to FIG. 3, the blade 1 remains completely straight even though the support member 9 sags, since the constant liquid pressure in the chamber 11 ensures that the blade 1 is borne uniformly. As shown, the support member 9 is mounted at the ends in two hydraulic cylinders 51, so that the support member 9 and blade 1 can be moved into and out of operative position very rapidly. As also shown, the roller 5 is supported at bearing points 52 by suitable bearings mounted in machine frame supports 50 while the hydraulic cylinders 51 are pivotally mounted at the ends in the support 50.
Referring to FIG. 2, wherein like reference characters indicate like parts as above, a rib or ridge 16 is disposed within the blade 1 to sub-divide the chamber 4 into two longitudinal chambers 4a, 4b. Each of these chambers 4a, 4b is connected to the thrust chamber 11 by one passage 6a, 6b each and a respective adjustable restrictor 3a, 3b. The two chambers 4a, 4b can be operated at different coatingcomposition pressures, a feature which helps to stabilize the blade 1, i.e., which reduces the tendency of the blade 1 to tilt. As shown, the rib 16 bears against the web 12.
Referring to FIG. 4, wherein like reference characters indicate like parts as above, the thrust chamber 11 can also be subdivided into two longitudinal chambers 11a, 11b which have one inlet or outlet passage 10a, 10b each and which are connected to the respective longitudinal chambers 4a, 4b above by way of passages 6a, 6b and adjustable restrictors 3a, 3b. The blade 1 can therefore operate with two different coating compositions so that a single blade can apply two different coating compositions to the web 12, or alternatively, the composition is applied by the longitudinal chamber 4a on the web entry side and surplus composition is returned via the longitudinal chamber 4a on the web entry side and surplus composition is returned via the longitudinal chamber 4b on the web exit side. In this embodiment, the ridge 16 is mounted in the blade 1 for sliding perpendicularly to the web 12. The bottom or back of the ridge 16 cooperates to bound a chamber 37 and is acted upon by a pressure medium, e.g. the coating composition, supplied through passages or lines 6c, 10c. The support member 9 has a ridge 27 which separates the two longitudinal chambers 11a, 11b from one another and extends into a corresponding recess 11c in the blade 1. The recess 11c connects passage 10c in the support member 9 to the passage 6c in the blade 1 and is of the same width as chamber 37, to ensure that the pressure medium which acts on the ridge 16 has no effect on the blade 1. As shown, the blade 1 is sealingly mounted in the thrust chambers 11a, 11b by similar sealing elements as above.
Referring to FIG. 5, the coating composition can also be supplied via a passage 14 to the longitudinal chamber 4a on the web entry side, while surplus coating composition passages from the longitudinal chamber 4a on the web exit side through passage 6b into the thrust chamber 11, then through a discharge passage 10 which has a restrictor 3c back to a feed pump (not shown). The passage 6b has a restrictor 3b, and a passage 6a which is parallel to passage 6b and which has a restrictor 3a extends from chamber 4a to chamber 11. In addition, a doctor device 101 in the form of a blade is mounted in a holder 103 to define one side wall of the chamber 4b on the web exit side. The blade 1 has a lateral inlet passage through which a pressure medium can be supplied to the chamber 37 to act on the ridge 16.
The blade 1 is mounted for rotation around its longitudinal axis, the underside of the blade 1 being convex and being received in a matching recess in the support member 9. The recess in the support member serves as the thrust chamber 11. As in the other embodiments, the chamber 11 can receive a compression spring 92 to act on the blade 1 to apply further pressure, in addition to the pressure medium, on the blade 1 in a direction perpendicularly to and towards the web 12.
Referring to FIG. 6, the blade 1a has two longitudinal chambers 4a, 4b and two longitudinal chambers 11a, 11b, the web being guided not by a roller but by a second blade 1b disposed opposite the first blade 1a. The blade 1a differs from the blade shown in FIG. 4 in that in FIG. 6 the coating composition is supplied to the chambers 4a, 4b not via the chambers 11a, 11b but via side passages 31a, 31b having external restrictors 3a, 3b. Also, the blade 1b is non-movably disposed instead of being mounted for sliding in a support member. The coating composition is supplied to the chambers 4c, 4d of the blade 1b through distributing chambers 76, 82 an through passages which have restrictors 3c, 3d. With this arrangement, both sides of the web 12 can be coated simultaneously. In order to reduce stressing of the web 12, those parts of the chambers 4a to 4d which contact the web 12 have rounded corners 69 at the entry edges. A speed-dependent hydrodynamic pressure increase is also produced at the central ridge 16 and at the exit side during operation.
Referring to FIG. 7, the chambers 4a, 4b, for example, of the blade 1 of FIG. 2, are subdivided into a number of sub-chambers by ridges or webs 18 extending in spinefashion. This feature enables the thickness of the web coating to be varied transversely of the direction of web movement -- an important consideration, if the absorptivity of the web 12 varies over the web width, as may occur because of differences in production.
The ridges 18 are so disposed that wherever a ridge 18 starts at the edge 2a or 2b, another ridge 18 terminates at the ridge 16 on the opposite side of the chamber. The proportion of ridges 18 is therefore constant over the whole width of the web 12. Two passages 6a, 6b extend to each of the sub-chambers.
In the foregoing description, the blade has been described as applying a flowable substance to a web; however, the blade according to the invention can be used to coat a surface or roller with a flowable composition directly, such as e.g. a paint applicator roller or a drying roller, inter alia for the production of powdered milk.
It is virtually impossible for the blade shown in FIG. 1 to rotate around its longitudinal axis. However, the bottom part of the blades shown in FIG. 4 and in the top part of FIG. 6 can be convex, so that the blade can rotate around its longitudinal axis the resulting rotatability improving the adaptation between the blade and the web or roller.