WO2000060165A1

WO2000060165A1 - Paper web release apparatus for pickup roll

Info

Publication number: WO2000060165A1
Application number: PCT/CA2000/000271
Authority: WO
Inventors: Dean Warren Mcdonald
Original assignee: Bowater Pulp And Paper Canada Inc.
Priority date: 1999-04-01
Filing date: 2000-03-14
Publication date: 2000-10-12
Also published as: AU3266400A

Abstract

The invention relates to an improvement in the pickup roll (26) of a press section contained in a closed draw paper production line, with the improvement facilitating removal of the paper web from the pickup felt (24). The pickup roll in the press section comprises a perforated roll, a suction box (36) disposed longitudinally in the perforated roll and a vacuum pump (38) connected to the suction box. The improvement involves the integration of a blowing apparatus (39) in the form of a fan into the suction box and manual or automated means which can be used to selectively engage the vacuum pump or fan as required. Utilizing the blowing apparatus, release of the paper web from the pickup felt can be quickly initiated and damage to the pickup felt or press section clothing thereby avoided.

Description

PAPER WEB RELEASE APPARATUS FOR PICKUP ROLL

BACKGROUND OF THE INVENTION

Field of Invention

The invention relates to the field of paper production and in particular to an apparatus and method for selectively releasing a paper web from the pickup felt located in the press section of the paper production line.

Description of the Related Prior Art

The basic sections of a paper production line are the forming section, the press section and the drying section. Between the forming and press sections and between the press and drying sections, a transfer of the paper web produced by the production process is required. There are two basic types of paper transfer systems typically in use: the "closed draw'^' system and the "open draw" system. In a closed draw system a nip is defined between two contacting members such as a forming wire and a felt, while in an open draw system the paper web passes across an open space from one paper processing section to another.

The transfer of the paper web has generally been facilitated by the use of suction boxes contained in perforated rolls which serve to attract the paper web by the application of negative pressure to the web. Additionally the use of positive pressure has assisted in the movement of the paper web from one paper processing section to another. Several examples of blowing apparatus which serve this function are contained in the prior art.

U.S. Patent 3,981,084 issued September 26 1976 is directed to an apparatus used in a closed draw system wherein air pressure is applied to the moving paper web to facilitate transfer of the paper web from the forming wire to a pickup felt in the press section or from the pickup felt to the surface of a dryer roll in the drying section. This is accomplished by the use of blow rolls positioned at the end of the forming and press sections respectively. The construction of these blow rolls is substantially the same as a suction roll, except that a pressure chamber is located therein. The disclosure suggests that the gas pressure in the pressure chambers is preferably air at a pressure of up to 50.0 psi. In the case of the forming section, the blow roll includes a single positive pressure chamber which works in combination with the suction from the pickup roll, to urge the paper web away from the mesh of the forming wire to the pickup felt extending around the pickup roll. At the other end of the press section, there is a roll with independent suctioning and blowing apparatus, which are used in combination to facilitate transfer of the paper web to the hot, smooth surface of a dryer in the drying section.

In a preferred embodiment, the blow roll contains two chambers, a pressure chamber and a vacuum chamber. The pressure chamber communicates with an air header which in turn communicates with a suitable source of air pressure. A vacuum source is connected to the vacuum chamber to provide the desired suction. Both the vacuum and pressure chambers are secured to a fixed support frame.

The pressure chamber and the suction chamber are not common, but are located adjacent one another with separate lines to their respective pressure and vacuum sources.

U.S. Patent 1,581,656 issued April 20, 1926 discloses an apparatus used in an open draw system for freeing the paper web from the wire mesh of the forming section, to allow the pickup felt contained in the press section to draw the paper web onto the pickup roll. The apparatus advantageously uses the perforated couch roll of the forming section. Independent suction and blowing means are used with respective suction and blowing chambers positioned in the couch roll adjacent one another. The suction means removes excess moisture from the web as it nears the transfer point, while the blowing means produces a current of air under suitable pressure through the perforated couch roll to facilitate web transfer. The suction chamber communicates through a pipe to a suitable suction apparatus. The member containing the suction chamber has a partition at one end to form a pressure chamber to which air under pressure may be admitted. From the pressure chamber lead a plurality of passages which are formed in the casting. Air is moved through these passages along the length of the couch roll at a suitable pressure to free the paper web from the wire and forms a layer or cushion of air under the web to assist it in moving over to the press section. As in US Patent 3,981.084 described above, this device uses separate chambers for the suctioning and the pressurized blowing function. — -> —

U.S. Patent 1,163.252 issued December 7, 1915 provides yet another means of providing pressurized air across the length of a suction roll. A suction roll of the forming section is positioned adjacent a suction roll of the press section. As the paper web moves along the forming section, it encounters a suction box contained in the suction roll of the forming section. As the paper web passes the suction box and moves toward the transfer point to the press section, it encounters a slotted or perforated pipe which extends longitudinally along the inside of the suction roll. This perforated pipe is used for jetting air or steam from the suction roll to lift the paper web from the roll. A similar set up is encountered at the end of the press section where a suction roll contains both a suction box and a perforated pipe. The perforated pipe provides pressurized air to assist the paper web transfer from the press section to the drying section. In both the suction roll of the forming section and the suction roll of the press section, the perforated pipe is physically separate from the suction box and does not take advantage of any common valving.

Occasionally, repair of the press section is required and it is necessary to drive the paper web from the pickup felt of the press section down into the couch pit located at the end of and below the forming section. It is preferable that production in the forming section continue, due to the time and expense involved in restarting the machines of the forming section. By driving the paper web produced in the forming section into the couch pit. continued production in the forming section can be maintained, with the paper web produced being simply repulped and pumped to the broke system. In a typical press section, the pickup roll is a suction roll. The suction assists in moving the web from the forming wire to the pickup felt. If the operator wishes to drive the paper web into the couch pit, the suction is turned off and the weight of the wet paper web is relied on to break the seal formed between the pickup felt and the web. Removal of the web is complicated by the fact that the pickup roll takes several seconds to lift vertically off the forming wire when dumping of the web occurs. For a variety of reasons the web may adhere in an undesirable manner to the pickup felt (e.g. the pickup felt is smooth or dirty). If the web is not released in a timely manner, it will tend to adhere to the pickup felt as the pickup roll moves vertically upward, resulting in paper web jams, macro-folding of the paper web, and ultimately damage to parts of the press section. Particularly where the pickup felt is smooth from wear, simply relying on the weight of the paper web to break the seal between the web and the felt is often inadequate. Although all of the systems described above work satisfactorily for web transfer, none of the prior art describes an apparatus which can be used to drive the paper web from the pickup felt and into the couch pit.

SUMMARY OF THE INVENTION It is therefore the primary object of the present invention to provide an apparatus for attracting and releasing a paper web from a pickup felt at the pickup roll integral to the press section of a paper production line. It is a secondary object of this invention to provide a method of attracting and releasing a paper web from a pickup felt at the pickup roll integral to the press section of a paper production line. It is a third object of this invention to provide an apparatus for selectively applying pressure or suction to a common plenum disposed longitudinally in a perforated roll located in a paper production line.

In accordance with the primary object, the present invention provides, in a pickup roll contained in the press section of a paper production line, the pickup roll comprising a perforated roll and a suction box disposed longitudinally in the perforated roll, vacuum means connected to the suction box, wherein a gas permeable pickup felt carrying a paper web is in contact with at least a sector of the pickup roll and in close cooperation with the suction box, and wherein the suction box directs air through the contacting portion of the pickup felt, the improvement comprising

(a) air pressure means connected to the suction box; and

(b) switch means providing selective application of the vacuum or air pressure means to the suction box.

Preferably the paper production line is a closed draw system. More preferably the suction means includes a vacuum pump. Conveniently, the air pressure means includes a fan. More conveniently,

Switch means comprises a manually actuable switch or a programmable control feedback system.

In accordance with the secondary object, the present invention provides, in the press section of a paper production line, a method of attracting and releasing a paper web from a pickup felt, the pickup felt in contact with at least a sector of a perforated pickup roll and in close cooperation with a suction box disposed longitudinally inside the perforated pickup roll, vacuum and air pressure means connected to the suction box. and switch means to selectively apply the vacuum or air pressure means, the method comprising the steps of

(a) engaging the vacuum means to attract the paper web onto the pickup felt; and

(b) engaging the air pressure means to release the paper web from the pickup felt, wherein the released paper web is directed into a couch pit integral to a forming section of the paper production line.

Preferably, the vacuum means includes a vacuum pump. More preferably, the air pressure means includes a fan. Conveniently, the switch means comprises a manually actuable switch or a programmable control feedback system.

In accordance with the third object, the invention provides, in a paper production line, a paper web control apparatus comprising:

(a) a perforated roll;

(b) a common plenum disposed longitudinally in the perforated roll; (c) vacuum means connected to the common plenum;

(d) air pressure means connected to the common plenum: and

(e) means for selectively applying the vacuum means and the air pressure means to the common plenum, wherein a gas permeable felt carrying the paper web is in contact with at least a sector of the perforated roll and in close cooperation with the common plenum, the common plenum directing air through the contacting portion of the gas permeable felt.

Preferably, the paper production line is a closed draw system. More preferably, the air pressure means includes a fan. Conveniently, the vacuum means includes a vacuum pump. More conveniently, the means for selectively applying the vacuum source and the air pressure source to the common plenum comprises a manually actuable switch or a programmable control feedback system. The advantages of the present invention are readily apparent. Through the use of a paper web releasing and attracting apparatus in the pickup roll, the paper web can be quickly and decisively dumped into the couch pit, thereby avoiding damage to the press section clothing, particularly tearing of the expensive pickup felt. Further, through the use of a simplified and integrated vacuum and air pressure apparatus contained in a perforated roll, an operator can readily choose to apply positive or negative pressure to the paper web at any desired point in the production line.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be obtained by reading the description of the invention below, with reference to the following drawings in which:

Figure 1 is a cross-sectional view of the forming section of a conventional paper production line

Figure 2 is a cross-sectional view of the press section of a conventional paper production line;

Figure 3 is a cross-sectional view of a conventional pickup roll integral to the press section;

Figure 4 is a schematic drawing of the suction and blowing apparatus in accordance with the present invention; and

Figure 5 is a cross-sectional view of the pickup roll in accordance with the present invention, highlighting the movement of the paper web.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figure 1 , the forming section of a conventional paper production line is depicted. The stock which is to be made into paper which is in the form of pulp mixed with a quantity of water, is fed to headbox 2 and then delivered onto wire mesh 4 through slice 6. Wire mesh 4 is supported first by breast roll 8, from which point the wire and stock are carried by forming boards 10, and then by vacuum foils 12. the prime removers of water from the stock, so that the fibres may be left interwoven on wire mesh 4 in the form of a wet paper web (shown as 5 in Figure 3). Wire mesh 4 passes over suction boxes 14 and couch roll 16. The last major roll in the forming section is wire drive roll 18 which serves to drive wire mesh 4. and thus the rest of the rolls. Couch pit 20 is designed to collect excess water from the wet paper web 5, as well as paper web 5 itself if the press section (shown generally at 22) is stopped. The portion of the paper web 5 falling into couch pit 20 is broken down and recycled back to the broke system (not shown). From couch roll 16 the paper web 5 is led into press section 22, where water is removed mechanically. Pickup felt 24 extends around pickup roll 26 and, as is typical in a closed draw system, is seated next to, and impinges on. wire mesh 4.

Referring to Figure 2. the press section 22 of a paper production line is shown. Press section 22 is divided into the pickup felt section (shown generally at 28) and two press felt sections (shown generally at 30 and 32). Press section 22 serves two primary functions: transferring paper web 5 from the forming section; and pressing paper web 5 to remove as much water as possible to minimize the costs of drying the web by steam in the drying section. Paper web 5 is picked off wire mesh 4 and is carried by pickup felt 24 to first press felt section 30. Transfer of the paper web is accomplished by a vacuum transfer arrangement which works in conjunction with pickup felt 24. Vacuum is provided by suction box 36 which is connected to a vacuum pump (shown as 38 in Figure 4), and which moves air through pickup felt 24 which is air permeable.

As described in the description of the related prior art. regularly it becomes necessary to force paper web 5 off pickup felt 24, to facilitate repairs on press section 22 or to clean pickup felt 24. Conventionally, removal of paper web 5 is accomplished by simply closing the suction line and relying on atmospheric pressure in suction box 36 and the weight of paper web 5 to cause paper web 5 to drop into couch pit 20. This is frequently inadequate because paper web 5 has a tendency to stick to pickup felt 24 when pickup felt 24 becomes dirty or smooth due after extended use. In order to facilitate removal of paper web 5 from pickup felt 24. the present invention introduces positive pressure into suction box 36, to break the seal between paper web 5 and pickup felt 24.

Referring to Figure 3, a cross-sectional view of pickup roll 26 is depicted. When press section 22 is in operation (the so-called "steady state") pickup roll 26 is in the "down" position labelled as "B". In this position, pickup roll 26 and pickup felt 24 actually impinge on paper web 5 which serves to assist in transfer of the paper web from forming wire 4 of the forming section to pickup felt 24 of press section 22.. However, when press section 22 is stopped, pickup roll 24 retracts into the "up" position, labelled as "A". If paper web 5 is not released before pickup roll 26 is retracted, paper web 5 will tend to follow pickup roll 26. resulting in paper web jams, macro-folding of the paper web, and ultimately damage to parts of press section 22. downstream from the pickup roll 26.

As shown in Figure 4. avoidance of these problems is accomplished by the integration of a positive pressure apparatus with the already existing suction apparatus. The combined apparatus comprises suction box 36. vacuum pump 38, air pressure means

39. main line 40, main line pressure controller 41. bleed line 42. main line valve 43. bleed line valve 45 and bleed line valve 47 . Valves 42 and 43 are controlled by switch 44 located on the press operator^'s console (not shown). In operation, when pick up of paper web 5 is desired, pickup roll 26 is lowered until it impinges into paper web 5 carried on wire mesh 4. At this point, the operator picks up paper web 5 by turning switch 44 to the

"open^" position, which in turn causes main line valve 43 to open and bleed line valve 45 to close immediately. Boosters (not shown) facilitate rapid closure of valves 43. 45. When main line valve 43 opens, there is an immediate drop in the pressure in main line

40, so pressure controller 41 starts to close bleed line valve 47. The negative pressure produced by vacuum pump 38 is applied to suction box 36 and paper web 5 is attracted to pickup felt 24. It will be understood by those in the art that the air pressure means can comprise a fan or the like.

When the operator wants to remove the paper web from pickup roll 26. the operator turns switch 44 to the "close" position which in turn causes main line valve 43 to close, bleed line valve 45 to open and power to be applied to air pressure means 39.

Positive pressure from air pressure means 39 is applied to suction box 36 through bleed line 42 and is of sufficient magnitude to break the seal between pickup felt 24 and paper web 5. It should be noted that pickup roll 26 typically takes in the order of 17 seconds to go from the down position "B^" to the position where it no longer impinges on paper web 5. This is the critical period during which most of the paper web jamming, felt damage. etc. occurs. Accordingly, it is desirable that paper web 5 be blown off pickup felt 24 before retraction of pickup roll 26 is commenced.

It will be understood by those skilled in the art that removal of the paper web can be facilitated in an automated manner, instead of being operator initiated. A programmable control feedback system integral to the press section is commonly used to monitor several parameters while paper production is in the steady state. These parameters include, but are not limited to: the presence of sufficient vacuum in the suction boxes, the speed match between the forming section and the press section, and unloading of the centre roll doctor blade (shown in figure 2 as 46, with the centre roll labelled as 48). In the event that one of these parameters falls outside the desired ranged, engagement of the blowing apparatus can be automatically engaged by the control feedback system in the manner described above.

Figure 5 depicts a cross-sectional view of pickup roll 24 and the end of the forming section, highlighting the removal of paper web 5 from pickup felt 24 in accordance with the present invention. Once air pressure means 39 are engaged, the seal between pickup felt 24 and paper web 5 is broken, and paper web is directed downwardly in direction "C" towards couch pit 20. As detailed above, paper web 5 is then broken down and recycled back to the broke system (not shown).

A person skilled in the art will appreciate that an apparatus for selectively applying pressure or suction to a suction box or common plenum could be incorporated into any perforated roll in the paper production line where this functionality is desired.

Such other embodiments, are meant to be included within the scope of this invention as described in the claims which follow.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a paper production line, a paper web control apparatus comprising:

(a) a perforated roll;

(b) a common plenum disposed longitudinally in said perforated roll;

(c) vacuum means connected to said common plenum;

(d) air pressure means connected to said common plenum; and

(e) means for selectively applying said vacuum means and said air pressure means to said common plenum,

wherein a gas permeable felt carrying said paper web is in contact with at least a sector of said perforated roll and in close cooperation with said common plenum, said common plenum directing air through the contacting portion of said gas permeable felt.

2. The apparatus of claim 1 wherein said paper production line is a closed draw system.

3. The apparatus of claim 2 wherein said air pressure means includes a fan.

4. The apparatus of claim 3 wherein said vacuum means includes a vacuum pump.

5. The apparatus of claim 4 wherein said means for selectively applying said vacuum source and said air pressure source to said common plenum comprises a manually actuable switch.

6. The apparatus of claim 4 wherein said means for selectively applying said vacuum source and said air pressure source to said common plenum comprises a programmable control feedback system

7. In a pickup roll contained in the press section of a paper production line, said pickup roll comprising a perforated roll and a suction box disposed longitudinally in said perforated roll, vacuum means connected to said suction box. wherein a gas permeable pickup felt carrying a paper web is in contact with at least a sector of said pickup roll and in close cooperation with said suction box. and wherein said suction box directs air through the contacting portion of said pickup felt, the improvement comprising

(a) air pressure means connected to said suction box; and

(b) switch means providing selective application of said vacuum or air pressure means to said suction box.

8. The apparatus of claim 1 wherein said paper production line is a closed draw system.

9. The apparatus of claim 6 wherein said suction means includes a vacuum pump.

10. The apparatus of claim 7 wherein said air pressure means includes a fan.

1 1. The apparatus of claim 8 wherein said switch means comprises a manually actuable switch.

12. The apparatus of claim 8 wherein said switch means comprises a programmable control feedback system.

13. In the press section of a paper production line, a method of attracting and releasing a paper web from a pickup felt, said pickup felt in contact with at least a sector of a perforated pickup roll and in close cooperation with a suction box disposed longitudinally inside said perforated pickup roll, vacuum and air pressure means connected to said suction box, and switch means to selectively apply said vacuum or air pressure means, said method comprising the steps of

(a) engaging said vacuum means to attract said paper web onto said pickup felt; and

(b) engaging said air pressure means to release said paper web from said pickup felt, wherein the released paper web is directed into a couch pit integral to a forming section of said paper production line.

14. The apparatus of claim 1 1 wherein said vacuum means includes a vacuum pump.

15. The apparatus of claim 12 wherein said air pressure means includes a fan.

16. The apparatus of claim 13 wherein said switch means comprises a manually actuable switch.

17. The apparatus of claim 13 wherein said switch means comprises a programmable control feedback system.