WO1998021408A1

WO1998021408A1 - Dual feed flow system apparatus for a paper web coater

Info

Publication number: WO1998021408A1
Application number: PCT/US1997/020459
Authority: WO
Inventors: Alfred C. Li; Andrew W. Osburn; Rex A. Becker; Xuekui Lan
Original assignee: Beloit Technologies, Inc.
Priority date: 1996-11-15
Filing date: 1997-11-12
Publication date: 1998-05-22
Also published as: AU5251198A

Abstract

A flow system apparatus has a dual chamber for directing countercurrent flows of coating within the chambers from inlet to exit ends in each chamber. Each chamber has a plurality of longitudinally extending flow openings for permitting the coating flowing within a chamber to exit from the chamber in a direction substantially perpendicular to the longitudinal flow within the chamber. The flow openings in both of the chambers are connected to a mixing chamber where their flows are combined to be directed into a coater head for application to a traveling paper web substantially uniformly along an opening extending across the web substantially perpendicular to the direction of web travel. In a preferred embodiment, control of the flow of the aqueous slurry near the edges of the traveling paper web is effected by a plurality of control openings extending between the dual chambers near their inlet and exit ends. The overflow from the exit ends of each of the dual chambers can either be recycled into the system producing the aqueous flow, or it can be redirected into the inlet ends of either of the dual chambers.

Description

PATENT APPLICATION DUAL FEED FLOW SYSTEM APPARATUS FOR A PAPER WEB COATER

BACKGROUND OF THE INVENTION

Field of the Invention This invention relates to a coater apparatus for applying an aqueous slurry of coating material to a traveling paper web. More particularly, this invention relates to a flow system apparatus for introducing an aqueous slurry of coating material to a coater head in a paper web coating apparatus. Still more specifically, this invention relates to a dual feed, counterfiow system for combining two, counterflowing streams of aqueous slurries of coating material, which are fed to, and combined in, a mixing chamber to be uniformly conducted to the coater head in a paper coating apparatus.

Description of the Prior Art In prior coaters for applying coating material to a traveling paper web, particularly apparatus utilizing multiple inlets for the coating material, the coating material was sometimes introduced at opposite ends of a header for the purpose of trying to equalize the hydraulic pressure within the coating apparatus, particularly at each end, along the length of the coating apparatus, which extended substantially perpendicularly across the width of the traveling paper web relative to its direction of travel. Such an arrangement does provide substantially equal pressure and rate of flow from the header into the coating apparatus, but there is a requirement for a high pressure drop in the relatively narrow feed channel so as to suppress flow variations developing in the feed chamber. This creates two operational problems: 1 ) a high energy requirement is necessary to overcome the pressure drop, and 2) a noticeable gap variation in the feed slot of the coater often occurs due to substantial thermal expansion caused by the relatively hot flows of the aqueous slurry of coating material entering the apparatus from opposite ends.

Other inlet flow system arrangements have utilized a plurality of inlets aligned along the longitudinal length of the flow system apparatus such, that, when the apparatus is installed with its longitudinal length extending substantially perpendicular to the direction of web travel, the inlets are disposed along the width of the traveling paper web to be coated. This apparatus operates quite well, but it has disadvantages. So-called dead-zones are formed near the outer ends of the header of the flow system apparatus, since none of the inlets is located at either end of the header, and midway between inlets, where flows from adjacent inlet ports meet and are required to mix. In order to alleviate such problems, a higher flow rate of the aqueous slurry of coating material is often maintained then is necessary. This either requires larger pumps, more energy, or both, and may also introduce more turbulence into the coating material than is necessary to maintain the desired flow of coating material through the coater apparatus. Further, more coating material is run through the coater (i.e., a greater flow rate) than is necessary for the particular coating operation.

Another known type of flow system apparatus relates to the use of a tapered inlet header having a single inlet and a single outlet which is arranged such that the flow of the aqueous slurry of coating material enters the larger inlet and exits the relatively small outlet with the coating material being removed through openings in the header extending longitudinally from the inlet to the exit ends. Since the header is tapered from the larger inlet end to the smaller exit end, this is theoretically designed to result in uniform streams of the aqueous slurry of coating material exiting through the plurality of openings. Theoretically, the tapered design of this type of header results in uniform pressure and velocity distributions along its length, but this does not always result due to small deviations in the manufacture of the header and or paper edge effect conditions. Further, each header must be engineered for a specific longitudinal length corresponding to a specific width of a traveling paper web to be coated.

Each of the above-described prior flow systems therefore has one or more undesirable characteristics, which include requiring higher pumping rates for pumping the coating material into the flow system apparatus, or larger pumps. Sometimes, the result is less uniform application of coating material across the width of the traveling paper web, or the systems are not flexible in changing the rate of application of the aqueous slurry of coating material, or the pressure or velocity of the coating material applied to the paper web substrate is inadequate, or the apparatus runs dirty (i.e., the operation creates build-up of dry coating in dead zones).

SUMMARY OF THE INVENTION The problems associated with the known flow system arrangements for introducing an aqueous slurry of coating material into a coater head for applying the coating material to a traveling paper web have been obviated by this invention. By utilizing a pair of parallel header chambers, disposed in opposed array with their inlets at opposite ends of their unified structure, and with substantially identically sized, shaped and arranged openings extending longitudinally along their effective length, the combined flow of the aqueous slurry along the effective length of the flow system apparatus is virtually uniform from one end of the flow system apparatus to the other. This is due to the uniformity of the parameters, such as hydraulic pressure and flow velocity, of the aqueous slurry introduced into the inlet ends on opposite sides of the apparatus. Such inlet flow can be made as close to uniform as practically possible by utilizing a single pump to supply the hydraulic force in the aqueous slurry as well as supplying piping identical in length, diameter, configuration, surface smoothness and material between the pump and the inlet for each of the dual header chambers.

In a preferred embodiment, the dual header chambers are constructed with a common interior wall which can be constructed to be either substantially rigid, or substantially flexible to further mitigate or equalize any variations in hydraulic pressure within the two, adjacent header chambers.

The openings in both header chambers are fluidly connected to a mixing chamber where the flow of the aqueous slurry of coating material from each of the header chambers is combined and mixed for the entire effective length of the flow system apparatus preparatory to introducing this combined flow into the coater head to be applied to the traveling paper web.

In a further preferred embodiment, a plurality of pressure equalization openings are located in a common wall extending between the dual header chambers near each end of the common wall so as to further promote the equalization of the relatively high pressure in the aqueous slurry near each inlet end with the relatively lower hydraulic pressure of the aqueous, slurry of coating material near each exit end of the dual header chambers. Thus, while each of the header chambers, particularly in the header chambers having a tapered configuration, is designed and intended to provide equal hydraulic pressure along their entire length, the pressure equalization openings provide for the possibility that their might be slight variations in tolerances or dimensions created during the manufacturing process, or different hydraulic pressures in the aqueous slurry entering each of the dual header chambers. These pressure equalization openings between the header chambers near each end are therefore intended to promote equalization of the hydraulic pressure at the ends of the header chambers such that the hydraulic pressure is substantially equal for the entire effective length of the header chambers regardless of small variations in operating conditions or construction of the header chambers.

Some header chambers are tapered in one dimension; some header chambers are tapered in two dimensions; some header chambers have constant cross-sectional dimensions for their entire effective length. In all of the embodiments, the aqueous slurry flowing out of the openings extending along the length of each header chamber is substantially perpendicular to the flow longitudinally along the header. The combined flow from the two header chamber is introduced into a mixing chamber to form a combined flow into the coater head.

Accordingly, an object, feature and advantage of this invention is to provide an improved paper web coating apparatus.

Another object of the invention is to provide coating apparatus appropriate for various coating applications having extreme rheological properties from a low viscosity level to a high viscosity level.

An advantage and feature of the invention is that the apparatus requires no excessive pressure drop within the feed system to operate efficiently.

Another advantage and feature of the invention is that it has an open design which facilitates routine clean-up and maintenance. These, and other objects, features and advantages of the invention will be obvious to those skilled in the art, particularly after reading the attached description of the preferred embodiments in conjunction with the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS . Fig. 1 is a somewhat schematic side elevational view of a prior art coater header having opposed inlets at either end of the header.

Fig. 2 is a somewhat schematic side elevational view of a prior art header having four lateral inlets fed by two pumps with the inlets spaced longitudinally along the length of the header.

Fig. 3 is a somewhat schematic perspective view of a prior art header having a tapered construction with a single inlet on one end and a single outlet at the other end.

Fig. 4 is a perspective view, shown somewhat schematically of a preferred embodiment of this invention in which dual header chambers are arranged co-extensively, each header having an inlet at its larger end and an outlet at its smaller end.

Fig. 5 is a perspective view of another preferred embodiment of the invention where dual, opposed array headers are arranged about a wedge- shaped plug to form dual channels directing the separate streams of stock into a mixing chamber.

Fig. 5A is an end view of the apparatus shown in Fig. 5, and additionally showing the structure for forming the channels and mixing chamber.

Fig. 6 is another preferred embodiment of the invention showing dual chambers, each chamber being rectangular in shape and not tapering end- to-end.

Fig. 7 is a somewhat schematic perspective view of another embodiment of the invention showing the dual chambers in circular cross- section, and also showing the channels leading from the respective chambers into a mixing chamber.

Fig. 8 is a somewhat schematic end view of a preferred embodiment of a mixing chamber for this invention.

Fig. 9 is a schematic, end view, in cross-section of the flow system apparatus of this invention as it is positioned relative to the backing roll in a coater apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this application, the term "coating" will be used generically to denote longer, more awkward terminology, such as, for example, "aqueous slurry of coating material" and "aqueous slurry" and "coating material" in order to simplify the description of the invention and the recitation in the claims.

Also, to the extent necessary to clarify the description of the invention, corresponding elements in the various figures of the various embodiments of the invention will be identified with the same numbers, but with different alphabetical subscripts to facilitate reference to specific figures. Therefore, the same number will refer to the same, or similar, item in the invention. In a similar manner, prime marks will be used to distinguish similar elements in the same embodiment.

With reference to the prior art embodiment shown in Figs. 1 -3, in Fig. 1 , the flow of coating has attempted to be equalized by introducing the coating through inlets 8a, 8a' at both, opposed ends of the header in the belief that the flow of the coating exiting the header 1 1 a designated by the arrows 1 0a will be equal along the length of the header 1 1 a, which is mounted to extend at right angles to the direction of paper web travel, as designated by the arrow 1 2a. In Fig. 2, four inlets 8b, 8b', 8b", 8b'", two of which are fed by separate pumps 1 6b, 1 6b' are shown for directing the flow of coating into the back of the header 1 1 b substantially in the direction of paper travel 1 2b.

In the prior art embodiment shown in Fig. 3, a single inlet 8c is shown for directing coating into a tapered header 1 1 c which extends transversely of the direction of paper travel 1 2c. A outlet 1 4c is utilized to operate in conjunction with the taper of the header so as to provide uniformity along the length of the header for the coating flow 1 0c to emerge uniformly along the length of the header.

As described in the Summary section, each of these prior art configurations has one or more deficiencies in providing uniformity to the coating flow along the length of the header.

With reference to the embodiment of the invention shown in Fig. 4, in this invention, two parallel, opposed flow, dual chambers 1 8d, 1 8d' having rectangular cross-sections are juxtaposed such that the inlet 20d, 20d' of each chamber 1 8d is adjacent to the outlet 22d, 22d' of the other chamber 1 8d'. Since the width 24d, 24d' of each chamber is constant for its entire length 26d, 26d', and since the height 28d, 28d' of each chamber tapers from a larger inlet end 20d, 20d' to a smaller outlet end 22d,. 22d', each chamber is said to be tapered in one dimension.

The two chambers are preferably formed with a common wall 30d. Each chamber has a plurality of flow openings 31 d, 31 d' extending longitudinally for its effective length. Although not shown in Fig. 4, but as is shown in Fig. 7, these flow openings direct the flow of coating, as designated by the arrows 10d, 10d' into a mixing chamber 32g, 32h (shown in Figs. 7 and 8), from which it is applied to a traveling paper web W by the flow system apparatus, generally designated by the numeral 34 in Fig. 9, as the traveling paper web is supported on the surface of a rotating backing roll 36 in a papermaking machine, or an off-machine coating apparatus. The two dual chambers, flow openings, mixing chamber, and related fluid connecting equipment, generally comprise the header 1 1 d for the flow system.

Another preferred embodiment is shown in Figs. 5 and 5A. In this embodiment, the two juxtaposed chambers 1 8e, 1 8e' are each tapered two dimensionally, that is they are tapered to be more narrow in both the height 28e, 28e' and width 24e, 24e' dimensions as they extend from their inlet 20e, 20e' (designated by arrows for clarity) to their outlet 22e, 22e' (designated by arrows for clarity). As in all of the preferred embodiments, the inlet of one chamber is adjacent to the outlet of the juxtaposed chamber.

In this embodiment, an inverted, wedge-shaped flow guide 38e is disposed on an outlet side of each of the chambers and is aligned between the chambers to co-extend therewith. Structure 40e, 40e' in the header forms a wall 41 e, 41 e' which is disposed adjacent the corresponding converging walls 42e, 42e' forming the inverted wedge-shaped flow guide so as to form a pair of co-extending channels 44e, 44e' which are in fluid communication at one end with each of the dual chambers and with the mixing chamber 32e at their other end. The mixing chamber is, in turn, in fluid communication with the outlet of the header (not shown) which leads to the application of the coating to the paper web as shown by the arrow 1 2 in Fig. 9. Thus, in the apparatus shown in Figs. 5 and 5A, the coating is separately fed into the inlets 20e, 20e' where they flow along the two- dimensional converging lengths thereof as the coating material is directed into the channels 44e, 44e' on either side of the inverted wedge-shaped flow guide to eventually flow into the mixing chamber 32e which is in fluid communication with the other, upstream, end of the channels 44e, 44e'.

Fig. 6 illustrates a preferred embodiment wherein each of the chambers 1 8f , 1 8f ' is rectangular in cross-section and does not taper at all from their inlet ends 20f, 20f to their outlet ends 22f, 22f . The flows 1 0f, 1 0f of coating are in fluid communication with a mixing chamber (not shown), such as shown, for example, in either Figs. 5A or 7, where they are mixed to provide even greater uniformity before being directed onto the paper web in the coating process.

As shown in Fig. 6, it is contemplated to recirculate coating, designated by arrows 50f, 50f, flowing out of the outlets 22f, 22f into either the adjacent inlets 20f, 20f of the other chamber, or even for recirculation back into the supply of coating to be redirected into the apparatus by the pumps (not shown).

In the preferred embodiment shown in Fig. 7, the juxtaposed chambers have circular cross-sectional shapes, where, like all of the other embodiments, the inlet 20g of one chamber is adjacent to the outlet 22g' of the other chamber. Also, Fig. 7 shows more clearly the channels 44g, 44g' leading from each chamber into a mixing chamber 32g for mixing the flow of coating before it is brought into coating engagement with the paper web. Also, while the cross-sectional shape remains constant from one end to the other in the embodiment shown, it is contemplated that these chambers could taper to be smaller from the inlet end to the outlet end. In such a case, the taper would be three-dimensional.

Fig. 8 shows a cross-section of a coating chamber having a plug 45 in a circular (in cross-section) shape so as to promote mixing of the coating streams from each of the chambers by increasing their speed as they pass through the narrow channels 46h, 46h' between the plug and the walls of the mixing chamber.

In Fig. 9, the coating flow system apparatus denoted generally by the arrow 34, receives the flow of coating, denoting by the arrow 1 2, from the mixing chamber where the coating is applied by the apparatus to the paper web W which is supported by the backing roll 36 rotating in the direction of arrow 39 in a coating apparatus.

With reference again to the preferred embodiments shown in Figs. 4, 5 and 6, with particular reference to the embodiment shown in Fig. 4, a plurality of pressure equalization openings 48d are located in the common wall 30d between the juxtaposed chambers near the ends of the chambers. These pressure equalization, or control, openings are for the purpose of equalizing any pressure differential between the coating entering the inlet of one chamber and the coating leaving the adjacent outlet of the other chamber. They can comprise circular holes, slots, or other shapes. While it is not anticipated that such openings are necessarily required, they are contemplated to optionally be included for this purpose.

With further reference to the embodiments shown in Figs. 4, 5, 6 and 7, recirculation of coating from the outlet of each of the dual chambers is beneficial to the economical and functional operation of the flow system. By directing all or some of the coating exiting from the outlet of a chamber into the inlet of the adjacent chamber, less newly prepared coating needs to be used. Also, recirculating coating back into the inlet of the same chamber would have a similar effect. Finally, it is contemplated that the coating exiting from one or both of the dual chambers could be recirculated back into the coating preparation system so as to operate to maintain the greatest possible uniformity in the coating composition and rheology.

In this context, recirculation from the outlet 22d in Fig. 4 into inlet 22d is indicated generally by arrows 50d, 50d'.

Also, it is contemplated that in these embodiments shown in Figs 4, 5 and 6, the common wall 30d between the chambers can be constructed to be either relatively rigid or flexible. Thus, the relatively rigid wall might contain the pressure equalization openings 48d, while a flexible wall would deform responsive to any pressure fluctuations between the adjacent chambers so as to not necessarily require such pressure equalization openings.

Further, it is contemplated that, while the embodiment of fluid communication 44e, 44e' and 44g, 44g' are shown as channels, other forms of fluid communication between the dual chambers and the mixing chamber, such as a plurality of aligned pipes, could be used.

Thus, the invention has been described in the context of a plurality of preferred embodiments. These embodiments are intended to expository only and are not intended to limit either the concept of the invention or the specific embodiments described. Other embodiments or different structural elements of the embodiments will become apparent to those skilled in the art without departing from the spirit and scope of the invention which is intended to be limited only by the claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1 . A flow system for directing coating into coating apparatus, including a coater head, for applying the coating to a traveling paper web, the flow system comprising, in combination: dual chambers, each having a longitudinal extension, and each having inlet and exit ends, for receiving and discharging the coating, respectively, the dual chambers arranged adjacent to each other to extend longitudinally together, each dual chamber with its inlet and exit ends arrayed to be adjacent to the corresponding exit and inlet ends, respectively, of the other dual chamber; a plurality of flow openings in each of the dual chambers, the flow openings aligned to extend substantially between the inlet and exit ends thereof; a mixing chamber operatively associated with the coater head and dual chambers, and substantially coextensive therewith, for receiving and mixing together the flow of coating from the plurality of flow openings in each of the dual chambers, and for directing a stream of the mixed coating into the coater head along a path extending substantially parallel to the path of web travel; fluid communication means is disposed in the system for fluidly linking the flow openings from each of the dual chambers with the mixing chamber; whereby the dual chambers are so constructed and arranged as to permit the establishment of a counter-current flow of the coating into the mixing chamber such that the hydraulic pressure and rate of flow of the mixed coating flowing from the mixing chamber into the coater head is substantially equal and uniform along the length of the mixing chamber which is in fluid communication with the coater head and is substantially coextensive therewith.

2. A flow system as set forth in claim 1 , wherein: the cross-sectional shape of each of the dual chambers being selected from either rectangular, square or circular designs.

3. A flow system as set forth in claim 2, wherein: the shape of each of the dual chambers tapers in the direction proceeding from the inlet end of the exit end.

4. A flow system as set forth in claim 2, wherein: the dual chambers have a common wall therebetween extending for substantially the effective length of the flow system apparatus.

5. A flow system as set forth in claim 4, wherein: the wall between the dual chambers is either rigid or flexible.

6. A flow system as set forth in claim 5, further including: opening means in the wall near either end thereof, the opening means establishing fluid communication between the inlet end of each dual chamber and the exit end of the other dual chamber.

7. A flow system as set forth in claim 6, further including: means for establishing fluid communication between the exit end of each of the dual chambers and the inlet end of a selected one of the inlet ends of each of the dual chambers.

8. A flow system as set forth in claim 7, wherein: the means establishing fluid communication from the exit ends of each of the dual chambers establishes fluid communication with the inlet end of the same dual chamber.

9. A flow system as set forth in claim 8, wherein: the means establishing the exit end communication from each of the dual chambers is in fluid communication with the inlet end of the other of said dual chambers.

10. A flow system as set forth in claim 1 , further including: a plug disposed in the mixing chamber for enhancing the mixing of the coating from the dual chambers.

1 1 . A flow system as set forth in claim 1 , wherein: the fluid communication means comprises an inverted wedge-shaped structure which defines a separate channel extending from a dual chamber to the mixing chamber.