GB2082644A

GB2082644A - Positive pulse dewatering blade

Info

Publication number: GB2082644A
Application number: GB8123066A
Authority: GB
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1980-08-22
Filing date: 1981-07-27
Publication date: 1982-03-10
Also published as: GB2082644B; FI812042L; AU7441281A; JPS5771492A; BR8104838A; SE8104009L; NO812243L; DE3129290A1; FR2488924A1

Abstract

A blade (22) for the removal of water from a sheet of material in paper- making has a leading edge (48) shaped to direct water on the underside of the wet web toward the web. This action loosens the web and facilitates further removal of water therefrom. The blade has a trailing edge portion (56) spaced from the next successive blade to provide a drainage opening for a liquid removed from the wet web as it completes passage over the wear surface of the blade. <IMAGE>

Description

SPECIFICATION Positive pulse dewatering blade This invention relates to a postive pulse "dewatering" blade for facilitating the removal of liquid from a wet web of material.

The word "dewatering" as used in this specification refers to the removal of any liquid, not necessarily water.

In dewatering machinery, particularly in the papermaking industry where dewatering processes are common on the wet end of a papermaking machine, development work is constantly being pursued to provide for a more efficient dewatering process.

An example of typical applicable machinery is a Fourdrinier paper machine utilizing a dewatering box with vacuum applied to draw water from a combination wire and sheet of material in the form of a wet web. A difficulty that occurs in a process of this type is that the material being dewatered accumulates in the form of a slurry on a wire and, as the combination progresses along the machinery, it has a tendency to compress or mat. This matting action makes it more difficult to remove water. This concern is enhanced when one considers that vacuum is applied at various points along the papermaking machinery particularly on the wet end portion. The constant application of vacuum results in a constant negative pulse to the wet web which further tends to mat the slurry and wire combination. The result is a reduction in efficiency as the process continues.

Various attempts have been made to increase dewatering efficiency. For example, increase in vacuum have been used, either as a constant greater suction force or as a progressively increasing suction force as matting increases during the dewatering process. A variety of different types of blades, foils and deflectors have been developed with a variety of different configurations to enhance the dewatering process by vacuum and negative pulse. This includes reversing traditional blade shapes and forming stepped blades in various shapes.

A positive pulse concept has been explored to a certan degree particularly in respect to table rolls. This involves bringing the wet web into engagement with table rolls which force the web upward and provide a possible positive pulse. However this action is uncontrollable and is limited to a direct speed/roll diameter relationship. It is not capable of being controlled to provide the more efficient dewatering procedure particularly when combined with blades and with vacuum. There is clearly room for an improved dewatering system which makes use of the advantages of blade configurations for negative pulsing and drawing water from the wet web and also for applying a positive pulse to the web to loosen the matted sheet and wire and enhance the dewatering negative pulse procedures conducted after the positive pulsing.Naturally the designed system should be adaptable for application of appropriate negative and positive pulses along the length of the dewatering machinery particularly if it is the wet end of a papermaking machine. Naturally a simple and inexpensive structure is desirable, for example an improved single blade configuration which can be removably mounted in stationary position on existing machinery such as a Fourdrinier machine.

With the above background in mind it is among the primary objectives of the present invention to provide a blade adapted to be mounted on a dewatering machine such as a papermaking machine. The blade is designed so that it can provide at least a positive pulse to a wet web passing over a wear surface thereon.

Also, if desired the blade can also have a further portion with a configuration facilitating the application of a negative pulse to the wet web for dewatering purposes.

It is an objective to provide a blade of the above type which is unitary in construction and is adapted to be mounted on a conventional well known type of machinery such as a Fourdrinier machine. The blade is adapted to be mounted in sequence as one of a row of blades having aligned wear surfaces for passage of a wire and sheet thereover in the form of a wet web. The blade is adapted to be mounted so that a suitable vacuum source will apply vacuum for dewatering purposes.

The blade of the present invention is designed with a leading edge portion having a tapered configuration so that it angles upward in the direction of travel toward the web thereby facilitating the directing of water toward the web for positive pulsing purposes. For example, the taper can be at approximately a 10 degree angle with the upper wear surface which is generally in a substantially horizontal position when mounted on the machine. The value of 10 degrees isto be understood as exemplary. Ataper of as little as 3 degrees is within the scope of the invention. Tapers of about 3 degrees and up to 5 degrees have been shown to create the desired positive pulse.The greater the angle, the larger will be the positive pulse but the larger the pulse the more iikely it is to have a deleterious side effect on the wear surface or web. The blade of the present invention can also be formed with a configuration adjacent the trailing edge designed to facilitate the application of a negative pulse to aid in drawing water from the wet web. In one embodiment this would be in the form of a step to provide a recess adjacent the trailing edge for water to be drawn through and drained to an appropriate drainage slot after the blade in the direction of travel of the wet web.

Thus, it is an objective of the present invention to provide a blade with blade angles tending to impart both a positive and a negative pulse to the fabric and sheet in the form of a wet web of a papermaking machine during the forming process. The positive pulse tends to first loosen the matted sheet and fabric which thereafter is more efficiently dewatered when subjected to the negative pulse. In general, the positive pulse applied to the wet web permits more efficient dewatering by subsequent dewatering elements. The blade is adapted to be mounted on a dewatering box of a conventional Fourdrinier paper machine to remove water from the sheet. It is particularly adaptable for paper machine wet end dewatering devices, particularly on assemblies where vacuum is applied.

A beveled configuration adjacent the leading edge of the blade of the present invention facilitates the forming of water on the underside of the wet web into the nip between the web and the tapered surface so that it moves upward into and through the web while the web is held down by subsequent vacuum units.

It is an objective of the present invention to provide a combination blade with a positive angle tapered adjacent the leading edge to produce a positive pulse and then a step adjacent the trailing edge to facilitate the provision of a subsequent negative pulse when the blade is mounted in a vacuum augmented device thereby providing a more efficient dewatering structure.

It is an objective to provide a blade structure which induces positive pulses in locations including the first blade of a dewatering element on a Fourdrinier, in connection with wet boxes, in connection with vacu-foils, and in connection with flat boxes. Also, the blade concept of the present invention can be extended to include the leading edge of any stationary device located beneath the forming media such as foils and/or deflectors.

In summary, a positive pulse dewatering blade is provided for facilitating the removal of liquid from a wet web of material. The blade includes means for removably mounting the blade on the dewatering machinery.

An upper wear surface is on the blade in position for engagement with the wet web passing thereover. The blade has a leading edge with a configuration tending to direct liquid on the underside of the web toward the web to apply a positive pulse to the wet web upward and away from the upper wear surface of the blade to loosen the web and facilitate removal of liquid therefrom thereafter. The blade includes a trailing edge portion spaced from the next successive blade to provide a drainage opening for liquid removed from the wet web as it completes passage over the wear surface of the blade.

The blade can also be designed with a portion adjacent the trailing edge having a configuration tending to draw liquid from the web and apply a negative pulse thereto to facilitate removal of liquid from the web having been previously subjected to a positive pulse.

By way of example, an embodiment of the invention will be described with reference to the accompanying drawings, in which: Figure 1 is a fragmentary top plan view of the wet end of a papermaking machine with a succession of blades mounted thereon; Figure 2 is a fragmentary sectional elevational view thereof taken along the plane of line 2-2 of Figure 1; and Figure 3 is a side elevation view of a blade embodying the invention removed from the papermaking machine of Figures 1 and 2.

The top surface of a portion of the wet end of a Fourdrinier papermaking machine 20 is depicted in Figure 1. Figure 2 shows a side elevation view of a portion of machine 20 with a series of spaced aligned dewatering blades removably mounted thereon in a conventional manner. Of the depicted blades, blade 22 is designed in accordance with the present invention and is positioned between two conventional dewatering blades 24.

A slot 26 is provided between each pair of blades for application of vacuum to the upper surface of the machine 20. Suitable end deckels 28 are provided to seal the ends so that the slots 26 are located in the central portion of the machine 20. The wet web of material passes over the central portion of the machine.

The web is in the form of a sheet of material to be dewatered on a moving foil. The sheet is initially in the form of a slurry which is compacted during travel when subjected to normal gravitational forces and additional vacuum forces applied during processing. A conventional vacuum source (not shown) is applied to the machine so that suction is present at each slot 26. In this manner, water is drawn through the slots in a conventional suction box, pipe, or similar structure as air is drawn through the wet web collecting water and the mixture of water and air is later separated by well known separation procedures.

As the wet web passes across the upper surface of the blades in the direction of the arrow of Figure 2 it engages with upper wear surface portions of the blades and is subjected to the vacuum, the combination of which draws air and water from the web through slots 26 for collection and removal.

Blades 24 are conventional step type blades with a leading horizontal wear surface portion 30 which terminates in a shoulder 32 communicating with recessed surface 34. The vertical space between surfaces 30 and 34 forms enlarged area for vacuum to be applied to the wet web through communication with slots 26 thus adding to the efficiency of removal of water from the web moving across the blade. The vacuum action in this respect is commonly known as applying a negative pulse to the web. This action also tends to compact and mat the slurry and wire combination of the wet web thus making further withdrawal of water more difficult. To loosen the matted wet web, blade 22 is utilized.

As shown in Figure 3, blade 22 includes a downwardly extending projection 36 from its undersurface 38 for interlocking engagement with receiving surfaces on the machine. An appropriate locking rod 40 in engagement with blade 22 to resist in the mounting action is shown in Figure 2. This type of structure is common to blades 24 which also include a similar downward projection 42 for mounting on the machine in engagement with a locking rod 44. Thus, blades 22 and 24 are interchangeable and can be positioned on the machine in a desired arrangement and location for maximizing the efficiency of the dewatering process.

Blade 22 includes a leading edge for initial communication with the moving web. The lower portion 46 of the leading edge is beveled down and toward the direction of travel facilitating drainage of water being drawn through the adjacent slot 26 under the influence of the vacuum force. The upper portion 48 of the leading edge is tapered upward in the direction of travel to form a nip with the horizontally moving wet web.

Tapered portion 48 terminates in an upper horizontal wear surface 50 which engages with the undersurface of the web. The combination of the undersurface of the web, the tapered leading edge portion 48, and the wear surface 50 forms a nip which captures water from the web and pulses the water upward through the web to loosen the matted slurry on the wire so that water can be withdrawn from the wet web more easily and efficiently thereafter. This action is identified as applying a positive pulse to the web. Thereafter the web reaches step 52 communicating with recessed surface 54 adjacent to the trailing edge 56. This recessed surface provides a space for application of vacuum in a manner similar to that described with the recess portions of blades 24.Thus the web is then subjected to a negative pulse and the loosened web having been subjected to a previous positive pulse is more efficiently dewatered. The water is then drained through the following slot 26 with the help of beveled downward and outward rear surface 58. A suitable notch 60 is in rear surface 58 for facilitating mounting of end deckles 62 which seal the ends of the papermaking machinery so that the vacuum is concentrated in the open central portion of slot 26 where wet web passes over.

The positioning of blade 22 in relation to blades 24 is a matter of choice. It can be the first, last or intermediate blade as shown. Also, the number of blades 22 in respect to the number of blades 24 is also a matter of choice depending upon the desired pulsing action desired in the system.

In operation, as the wet web passes in the direction of the arrow in Figure 2 over the foils 24 and 22 it engages with the wear surface portion 30 of foils 24 and wear surface 50 of foil 22. Vacuum is applied through slot 26 to draw air through the wet web and direct the mixture of air and water through the slots for collection in a conventional manner. As the wet web approaches wear surface 50 on blade 22 its undersurface forms a nip with beveled leading edge portion 44. Water being drawn through the wet web and in the lower portion of the web engages this nip and is directed upward through the wet web to loosen the matted sheet. The loosened sheet then passes over wear surface 50 into alignment with recess 54. Vacuum applied in recess 54 draws water from the wet web and the water is drained through slot 26 at the trailing end of blade 22 assisted by the beveled surface 58.Efficiency in draining the web is enhanced by the positive pulse prior to the introduction of suction to the web to provide a negative pulse to dewater the web. The web, which is still relatively loose, can then be subjected to conventional types of blades such as blade 24 which imparts only a negative pulse. A positive pulse can be introduced by means of a foil 22 at any desired time in the process for purposes of loosening the matted slurry forming the sheet on the foil.

It has been found effective to provide an angle for tapered leading edge portion 48 with respect to the substantially horizontal wear surface portion 50 of approximately 10 degrees. This provides the desired angle in the nip and facilitates direction of the water up through the web as a positive pulsing action. The lower part of the leading edge 46 is beveled down and away with respect to the direction of travel of the web, at appoximately a 30 degree angle with respect to the vertical, so that water and air previously drawn from the web during the dewatering process is directed downward for collection in an efficient manner.

The blades 22 and 24 are interchangeable and removable so that they can be replaced or interchanged in any desired time. Additionally, they can be formed of a conventional plastic or nylon material in a conventional well known manner.

Thus the several aforenoted objects and advantages are most effectively attained. Although several somewhat preferred embodiments have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

Claims

1. A positive pulse "dewatering" blade for facilitating the removal of liquid from a wet web of material comprising; means on the blade for removably mounting the blade on "dewatering" machinery with a space adajcent thereto for drainage of the removed liquid therethrough, an upper wear surface on the blade in position for engagement with the wet web passing thereover, a leading edge on the blade having a configuration tending to direct liquid toward the web to apply a positive pulse to the wet web upward and away from the upper wear surface of the blade to facilitate removal of liquid thereafter, and a trailing edge leading to the drainage space for disposal of liquid removed from the wet web as it completes passage over the wear surface of the blade.

2. The invention in accordance with claim 1 wherein the portion adjacent the trailing edge has a configuration tending to draw liquid from the web and apply a negative pulse thereto to facilitate removal of liquid from the web having been previously subjected to a positive pulse.

3. The invention in accordance with claim 1 or 2 wherein the blade is mounted on the wet end of papermaking machinery for dewatering the wet web.

4. The invention in accordance with claim 3 wherein the blade is mounted on a dewatering box of a Fourdrinier machine to remove water from the wet web in the form of a sheet and wire.

5. The invention in accordance with any preceding claim wherein the blade is adapted to be mounted as one of a sequence of blades in the direction of travel of the wet web with the blade providing at least a positive pulse and at least one of the other blades providing at least a negative pulse with the alternating pulse applied to the wet web providing an efficient "dewatering" of the web.

6. The invention in accordance with any preceding claim wherein the "dewatering" machinery includes a source of vacuum applied to the blade and the space adjacent thereto to draw liquid from the wet web and "dewater" the wet web.

7. The invention in accordance with any preceding claim wherein a portion adjacent the leading edge is beveled to extend angularly upward toward the wet web in the direction of travel of the web so as to form a nip for liquid on the underside of the web to be forced into and moved upward into the web.

8. The invention in accordance with claim 7 wherein the "dewatering" machinery includes a vacuum source applied to the blade so that as liquid is being moved upward adjacent the trailing edge of the blade into the web the web will be held down by the vacuum applied thereto.

9. The invention according to claim 7 or 8 wherein the beveled portion adjacent the leading edge is formed at an angle in the range of from about 3 to about 10 degrees with respect to the upper wear surface of the blade.

10. The invention according to claim 7 or 8 wherein the beveled portion adjacent the leading edge is formed at a 10 degree angle with respect to the upper wear surface of the blade.

11. The invention according to claim 7 or 8 wherein the beveled portion adjacent the leading edge is formed at a 3 degree angle with respect to the upper wear surface of the blade.

12. The invention according to claim 7 or 8 wherein the beveled portion adjacent the leading edge is formed at an angle of up to 5 degrees with respect to the upper wear surface of the blade.

13. The invention in accordance with any of claims 7 to 12 wherein a second portion adjacent the leading edge is beveled downward and in the direction of travel of the web to facilitate drainage of liquid not directed into the nip, the first portion of the nip located between the second portion and the wet web.

14. A positive pulse "dewatering" blade for facilitating the removal of liquid from a wet web of material, the blade being substantially as herein described with reference to and as illustrated by the accompanying drawings.

15. An apparatus for removing liquid from a wet web of material the apparatus including a positive pulse "dewatering" blade as claimed in any preceding claim.