CA2008577A1 - Novel suction box cover - Google Patents

Abstract

ABSTRACT OF THE INVENTION

A novel suction box for papermaking machine includes a cover for contacting a press fabric with an elongated slot. The slot has a generally zig-zag pattern to eliminate noise and to reduce wear and tear on the fabric.

Description

20~85i'~
2067-146 (FD90) NOVEL SUCTION BOX COVER

BACXGRO~ND OF T~I~ INVEN'rION
a. Field of Invention This invention pertains to an improved cover for a suction box used in paper and board making machines, wherein water is i ~ removed from a moving fabric or web by suction.

b. Description of the Prior Art Various types of paper may be made at high speed and economically on so-called paper making machines. In this machine, a slurry of wood pulp and other materials is dispensed onto an endless forming fabric. The forming fabric with the slurry moves across several suction boxes used to remove water from the slurry to form a continuous paper sheet. Since this sheet still has a high water content, it is then transferred to a press section where it is contacted with at least one continuous press fabric and fed through press nips for the further removal of water by mechanical means. The p ess fabric is then passed over another suction box ~ e water is removed from the press fabric. Usually, the press fabric is made of materials which may be woven and manufactured to form a continuous fabric, or which may have two opposite ends joined by a seam.

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` Z0085'~7 Other types of papermaking machines exist, especially those producing multi-ply boards for industrial uses such as gypsum wall board, and paper wrapping tubes. Here the sheet is formed in layers of plies directly onto a fabric. The stock is introduced via cylinders in vats filled with stock or using multiple small forming wires. As the press fabric passes over each rotating cylinder, it picks up a layer of stock~ The fabric S~
then carries this layered sheet through ~ e presses in the conventional sense. Therefore, in this case, the fabric has both forming and pressing functions. Suction boxes are utilized to dewater the fabric here also. While these types of paper machines are slower, and the fabrics used as the "making fabric"
are relatively light in weight, the principles of dewatering and pressing and the requirements of the fabric are still basically the same.
The suction boxes are normally provided with a cover having a straight slot extending transversely across the width of the press fabric. The slot size ranges from 3/8" to 3" in linear length. (The suction box is described herein as part of the press section of the paper machin ~ however it should be understood that it may also be used in the paper forming section). This type of suction box has been found to be unsatisfactory for a number of reasons. For e~ample, if a press fabric with a seam is used, as the seam goes over the slot, the fabric makes a loud, unpleasant popping sound which is not only irritating, but also increases the overall noise level produced -: .-" ~ ~
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by the machine. The seam also rubs against the slot edges causing the seam flap, formed of batt material, to wear out before the rest of the fabric. Thus the useful life of the press fabric is reduced drastically. The fabric may also fail due to the flexing of the fabric caused by the edges of the slot.
Another type of suction box cover is also used in which slots are made in a so-called herringbone pattern. These slots are usually defined by at least four contact edges. This type of cover has also been unsatisfactory because studies have shown that if the number of edges traversed by a fabric is increased, the wear and tear of the fabric also increases. This wear and tear is even more pronounced with fabrics having seams because the seam flap wears away faster as explained above. Another reason is that the open area (length X width) of the herringbone box cover usually is greater than a single straight slot. This reduces both the specific air flow (volume/area) and vacuum level, thus reducing the system's capability to properly dewater the press fabric. To overcome this problem a larger vacuum source may be necessary, requiring both capital expenditure and - 20 increased operating costs.
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; OBJECTIVB8 AND S~MNARY OF TH~ INVENTION
In view of the above-mentioned disadvantages of the existing suction box covers, it is an objective of the present invention to provide an improved suction box cover which has slot edges presented at an angle with respect to the direction of movement .~ .

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ZO~BS'77 (i.e. the machine direction) of the press fabric, thereby extending the useful life of the press fabric seam flap and the entire structure.
A further objective is to provide an improved box cover in which the flexing of the fabric at the slot is eliminated.
Yet another objective is to provide an improved box cover which reduces or eliminates the sound produced by prior art box covers.
A further objective is to provide a suction box cover in which the number of edges traversed by the press fabric is reducedO
Other advantages of the invention shall become apparent from the following description of the invention. Briefly, the suction box only constructed in accordance with this invention comprises a main body connected to a vacuum source to provide suction. A
cover is secured to the body and is constructed and arranged to support a press fab~icl ~ving continuously across it. The box cover is provide~ with a slot extending substantially across the width of the fabric (i.e. in a cross-machine direction) and in communication with the main body of the box to apply suction to the fabric to remove water therefrom. Advantageously, while the effective area of the slot is substantially equal to the area of a transversal slot, it comprises a plurality of straight slot segments, each segment being disposed at an angle of about 45 degrees with respect to the machine direction. The slot segments are joined end to end to form a continuous zig-zag pattern across the width of the fabric.

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~ Z0~1~5'77 BRIEF DESC~IPTION OF T}IB DRAWING8 Figure 1 shows an isometric view of a suction box with an novel cover constructed in accordance with the invention;
Figure 2 shows a plan view of the cover of Figure 1;
Figure 3 shows a side sectional view of the cover of Figures 1 and 2 and a press felt traversing the same; and Figure 4 shows a plane view of a prior art suction box with a standard herringbone cover.

DETAILED DESCRIPTION OF T~ INVENTION
Referring now to the Figures, a suction box 10 constructed in accordance with this invention includes a main body 12 which is connected to a vacuum source(not shown) by a connecting pipe 14.
The box is provided with a cover 16 which is secured to the main body in a known manner. For example in Figure 1, the cover 16 is secured to the main body in a dovetail joint, however other types of connections are equally suitable.
The cover is provided with a single slot 18. The slot 1~ is composed of a plurality of substantially straight slot segments, such as 18' and 18", each segment being disposed at an angle of about 45 degrees with respect to the machine direction indicated by arrow 20. The segments are ~oined end to end, with each two adjacent segments being perpendicular to each other to form a continuous zig-zag pattern as shown in Figure 2. Each segment may be for example about S inches long.

-- 20085'77 The operation of the suction box with the improved cover shall now be described. The suction box is disposed in a paper machine, such as for example its press section, along the continuous path of a press fabric 22. The press fabric 22 traverses the cover in a continuous movement indicated by the arrow 20. The vacuum in suction box 10 extracts water from the fabric through slot 18.
As shown in Figure 2, a fabric 22 traversing the box cover, overlaps only a small number of relatively narrow slot sections of the slot. For example, the section of fabric traversing an imaginary line 24 overlaps sections of five slot segments.
Between these segments the fabric is fully supported by the box cover so that the fabric does not travel over any edges transversal to its movement. Thus, the wear on the fabric and its seam flap (if any) resulting from both friction between the fabric and the box cover and the deflection of the fabric with a single transverse slot, is reduced when compared to prior art box covers. The box illustrated in the Figures 1-3 may also be disposed in the forming section, for removing water directly from a paper web through a forming fabric. Comparing Figure 4 to Figure 2 along a line A-B, any fabric area along line A-B must pass over four edges or slot edges as it moves over the conventional herringbone box cover. In Figure 2 of the invention, any fabric area moving along line A-B only passes over two slot edges, substantially reducing wear.
To demonstrate the validity of this concept, the following series of experiments were performed. A pilot press section .
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-- : ' ~ -` 20~577 using various seamed press fabric designs, was used to study the effect of cover design on the seam flap and over-all wear of the press fabric surface. All the covers were made of the same ; material. The box open area was kept constant at 1 square inch of area per inch of width. This was done to keep air flow and vacuum conditions for all box covers equal, with the exception of the standard herringbone cover which has 1.73 square inches of open slot area per inch of machine width. All other operating conditions were kept constant. Visual observations were made of 10 the flap area after various running times. The results are summarized in Table I.
ABLB I

FLAP CONDITION
BOX COVE~ TYPB AFTER 24 HOUR8 POPPING NOISE
Standard Herringbone ~ C~d Not detectable Straight Slot Very Poor Extremely loud Zig-Zag (Figs.1-3) Excellent Not detectable : :
Preferably, the cover is molded from a high impact plastic material with a low coeffi~ie~t/of friction such as polyethylene, although other materialSs ~ as silicone nitride and ceramics can be used.
Obviously, numerous modifications such as slot opening and slot angle may be made to this invention without departing from its scope as defined in the appsnded olaims.

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Claims (10)

1. A suction box for extracting water from a press fabric continuously moving in a papermaking machine, comprising:
a body connected to a vacuum source; and a cover secured to said body and having an elongated slot in communication with said body, and extending in a direction substantially transversal to said preselected direction, said slot comprising a plurality of slot segments forming a zig-zag pattern.

2. The suction box of claim 1 wherein each said segment is substantially straight and is disposed at a preselected angle with respect to said preselected direction.

3. The suction box of claim 1 wherein said preselected angle is about 45 degrees.

4. In a papermaking machine having a press fabric moving continuously in a preselected path in a machine direction for removing water from a paper sheet, a suction box comprising:
a box body connected to a source of vacuum; and a cover secured to said box body, said cover being disposed in said path for contacting said press fabric, said cover having a slot in communication with said box body for removing water from said press fabric by suction, said slot extending substantially in the cross-machine direction in a zig-zag pattern.

5. The suction box of claim 4 wherein said slot comprises a plurality of slot segments disposed end-to-end.

6. The suction box of claim 5 wherein each said slot segment is disposed at a preselected angle with respect to said machine direction.

7. The suction box of claim 6 wherein said preselected angle is about 45 degrees.

8. The suction box of claim 4 wherein said cover is made of a plastic material.

9. The suction box of claim 4 wherein said cover is made of silicone nitride.

10. The suction box of claim 4 wherein said cover is from the family of ceramic materials.