KR20060108758A - Gap type forming section for a two fabric paper making machine - Google Patents

Abstract

A twin fabric gap former forming section (1) for paper making machine is described in which: the pitch of the fabric support elements (26, 27, 28) decreases progressively in the machine direction; the level of vacuum applied to the forming fabrics (2, 4) through the dewatering boxes (11, 12, 13, 14), increases in the machine direction; the two forming fabrics (2, 4) together with the stock (7) sandwiched between them traverse at least four separate and distinct vacuum zones (24, 19, 20, 21, 22, 23) within the forming section as they proceed in the machine direction; the level of vacuum applied to the last of the at least four separate and distinct vacuum zones is higher than the level of vacuum applied to the first of the separate and distinct vacuum zones; the level of vacuum applied to the at least four separate and distinct vacuum zones follows a pre-selected profile; and the dewatering boxes (11, 12, 13) and (14) carrying the fabric support elements (26, 27, 28) are arranged so that the fabric support elements (26, 27, 28) are located in an alternating sequence on the machine sides of both of the forming fabrics (2, 4).

Description

GAP TYPE FORMING SECTION FOR A TWO FABRIC PAPER MAKING MACHINE}

The present invention relates to a two fabric gap type forming part used in a papermaking machine for directly injecting stock into a gap between two ongoing forming fabrics from a headbox slice. Thus, the molded part of the present invention does not have an early open surface section using a single molded fabric. The present invention relates to a molding portion between a position where two molding fabrics converge to interpose stock between them, and a position where the two molding fabrics are separated while the stock is attached to one of the molding fabrics. The present invention is suitable for use in both the fabric molding part rebuild and the novel gap type molding part.

In the gap form of the paper machine, the two forming fabrics do not travel along a straight path. The two fabrics form a curved path by passing through a series of rolls and dewatering boxes alternately arranged on either side of the fabric. Each dewatering box has a curved surface, which is mounted with a series of fabric support elements, such as a blade, which contacts the machine side of the forming fabric. Each dehydration box can also be connected to a controlled vacuum source. By the plurality of curved surfaces, the moving molding fabric is traveling along a predetermined curved path. Applying a controlled level of vacuum to the dehydration box has two effects: promoting dewatering from the stock interposed between the two moving molding fabrics and moving two moving in the gaps between the fabric support elements. Refract the path of the fabric. When the two moving molded fabrics are refracted, a positive pressure pulse is generated that causes the movement of the fluid in the machine direction in the stock in the stock layer sandwiched between these fabrics.

The actual amplitude of each pressure pulse generated by the refraction angle of the moving forming fabric at the edge of each fabric support element has a significant impact on the quality of the final produced sheet. The intensity of the pressure pulse generated by each fabric support element should be chosen to match the condition and characteristics of the stock at the location of the fabric support element. Thus, the ability to change the intensity and / or amplitude of pressure pulses is required as more water is dewatered from the stock to form initial paper webs.

It has been found that poor control of the fabric's refraction in the molded part adversely affects the molding process and consequently negatively affects the quality of the paper produced.

It has been found that the actual fabric deflection angle at the edge of each fabric support element in the twin fabric forming in operation is controlled by a number of factors as follows.

1. The geometrical arrangement of the physical components used in the construction of the forming region including the pitch of the element-element of the fabric support element, the width of the machine direction of the fabric support element, and the radius of curvature of the surface to which the fabric support element adheres;

2. the level of vacuum applied to the dewatering box controlling the angle of the moving forming fabric refracting into the gap between the fabric support elements; And

3. The amount of tension in the machine direction applied to each of the two moving fabrics.

The term used herein has the following meaning.

(i) Machine direction (MD) means a direction generally parallel to the direction of movement of the two forming fabrics away from the headbox slice.

(ii) "Pitch" means the central portion for centering the spacing of continuous fabric support elements in the machine direction.

(iii) "fabric support elements" and "plural fabric support elements" means moving surfaces such as rolls in which the forming fabric is placed in rotational contact, blades, foils, etc., in which the forming fabric is placed in sliding contact. Means a stationary surface.

In the early stages of the papermaking process, when the level of vacuum applied on the machine side of the forming fabric and on the initial paper web is low, the geometry of the forming portion and the tension applied to both forming fabrics is a major factor in controlling the bending of the forming fabric. It becomes an argument. In addition, two different tensions may be used even if the tension applied to the two molding fabrics is the same. Within the overall control pattern, a predetermined level of pressure pulses are formed in the stock sandwiched between the two moving molding fabrics by setting the two tensions.

Between the first intervening stock between the two moving fabrics and the second separating fabric, the density of the stock continuously increases as water is dewatered from the initial paper web. At the same time as the density of the stock increases, the mobility of the individual fibers in the stock decreases. These changes require more powerful pressure pulses that can provide advantageous fiber mobility to improve the properties of the sheet of the initial paper web. However, the density of the initial paper web eventually reaches a density where the fibers can no longer move. From this point to the point where the two moving fabrics separate, by carefully selecting the level of vacuum at which dehydration can continue, the radius, so that the intensity of the pressure pulse is controlled to a level that does not damage the initial paper web, Careful selection of the pitch of the fabric support element and the width of the fabric support element should control the intensity of the pressure pulse.

During the initial sheet forming period, during which beneficial fiber migration is taking place, there is an increasing demand for larger pressure pulses at a faster rate than achieved by control of the vacuum level applied only to the forming fabric. This is because the excess vacuum should limit the vacuum level to a level that prevents the mobility of the fibers and prevents the fixing of the sheet properties before achieving the desired molding advantages. Thus, by increasing the pitch between the fabrics and / or by increasing the radius of curvature of the structure to which the fabric contact fabric support element is attached, and / or to increase the degree of refraction of the fabric into the gap between the fabric support elements. By using fabric support elements, such as a plurality of oppositely disposed blades, it is necessary to obtain larger pressure pulses by increasing the degree of refraction of the molded fabric at both edges of the fabric support element.

Thus, there is a matrix of variables to consider in order to optimize the quality of sheet products. The present invention is based on the recognition that the following factors should be taken into consideration in providing an improved twin fabric gap forming apparatus for forming the forming part of a paper machine.

(a) the pitch of the fabric support element should gradually decrease along the machine direction;

(b) the level of vacuum applied to the forming fabric through the dehydration box should increase along the machine direction;

(c) the two forming fabrics interposing the stock must pass through at least four independent and distinct vacuum zones during the machine direction within the forming section;

(d) the level of vacuum applied to the vacuum region of the last position of the at least four independent and distinct vacuum regions is higher than the level of vacuum applied to the vacuum region of the initial position of the independent and distinct vacuum regions;

(e) the level of vacuum applied to the at least four independent and distinct vacuum zones should be in accordance with preset data;

(f) The dehydration box mounting the fabric support elements should be arranged so that the fabric support elements can be installed in an alternating sequence on the machine side of both forming fabrics.

Accordingly, a first broad embodiment of the present invention is to provide a two-sheet fabric forming part of a gap type for a paper machine having a conveying forming fabric and a backing forming fabric,

(i) each forming fabric has a paper side and a machine side;

(ii) both molding fabrics move along the machine direction with a stock layer interposed therebetween;

(iii) both molding fabrics are supported by a series of fabric support elements, on top of them the machine side of each molding fabric passes in sliding contact, and both fabric support elements are supported on a series of dewatering boxes, The dewatering box having a surface supporting a curved fabric support element;

(iv) the dehydration box provides a separate dewatering zone to which at least part is connected to a vacuum source providing a separate vacuum zone,

here,

(a) the forming region includes a forming portion between a position where both forming fabrics converge to intervene the stock and a position where both forming fabrics are separated with the stock supported on one of the fabrics;

(b) the dehydration box in the forming section provides at least four independent and distinct vacuum zones;

(c) the radius of curvature of the curved surface supporting the fabric support element is gradually reduced along the machine direction, or the radius of curvature of the curved surface supporting the fabric support element is decreased on the continuous support surface along the machine direction,

(d) the pitch of the fabric support elements in each vacuum region is constant and the pitch of the fabric support elements on successive vacuum regions decreases along the machine direction, or the pitch of the continuous fabric support elements in each vacuum region is machine direction Decrease along;

(e) the dewatering box for supporting the fabric support element is configured and arranged to position the fabric support element in contact on the machine side of the transfer molded fabric and the backing molded fabric in an alternating order along the machine direction;

(f) All fabric support elements on all of the dewatering boxes have the same width along the machine direction, or all fabric support elements have unequal widths along the machine direction.

Preferably, the pitch of the fabric support elements in each vacuum region is constant, and the pitch of the fabric support elements in the continuous vacuum region decreases along the machine direction. Alternatively, the pitch of the fabric support element in each vacuum region is not constant, and the pitch of the fabric support element in the continuous vacuum region decreases along the machine direction.

The radius of curvature of the curved surface supporting the fabric support element on the continuous vacuum region is preferably reduced along the machine direction. Or the radius of curvature of the curved surface supporting the fabric support element on the continuous vacuum region decreases gradually along the machine direction.

Each dehydration box preferably provides at least one vacuum region, more preferably the at least one dehydration box provides at least two vacuum regions. Most preferably all dehydration boxes provide one or more vacuum zones.

The ratio of the width of the gap between them to the width of the fabric support element is preferably from about 1:10 to about 1: 0.5.

Preferably, the molding part includes a turning roll having vacuum assisted dehydration means. Or the forming part has a turning roll without a vacuum assisted dehydration means.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 is a schematic view of a forming part of a gap type according to a first embodiment of the present invention;

2 is a detailed schematic view of the impact zone of FIG. 1;

3 is a detailed schematic view of the second, third and fourth dehydration boxes of FIG. 1;

4 is a schematic diagram of the modification structure of FIG. 3;

5, 6 and 7 are schematic diagrams of a modified structure of the collision shoe of FIG. 1;

8 is a structural diagram using a collision roll; And

9 is a schematic diagram of the modified structure of FIG.

FIG. 1 shows a molded part 1 in the form of two fabric gaps used in a paper machine. The molded part 1 is arranged in the vertical direction, and the arrow A indicates the vertical direction.

The forming section 1 has a position where the conveying forming fabric 2 enters the forming section 1 around the first forming roll 3 and the backing forming fabric 4 has a second position. It extends from the position entering the forming section 1 around the forming roll 5 to the position where the conveying forming fabric 2 and the backing forming fabric 4 are separated after passing through a turning roll 6. . Between the two forming fabrics 2, 4 in the forming part 1 there is a layer of stock 7 which is conveyed from the headbox slice 8 to the collision point 9. It is. The two forming fabrics 2, 4 simultaneously move through the forming part 1 in the machine direction indicated by the arrow 10. Thus, the stock 7 moves upward through the forming part 10. This can also be done in another arrangement as described later.

Four independent dehydration boxes 11, 12, 13 and 14 are disposed between the first forming roll 3 and the second forming roll 5 at one end of the forming section and the turning roll 6 at the other end of the forming section. have. Each dewatering box is provided with curved surfaces 15, 16, 17, and 18. These curved surfaces support a plurality of fabric support elements (not shown) to form support surfaces for supporting the molding fabrics 2, 4 on each of the dehydration boxes 11, 12, 13, 14.

As shown, the four dehydration boxes 11, 12, 13, 14 are alternately arranged on both sides of the molding fabric 2, 4. Thus, the forming fabrics 2, 4 sequentially wrap each supporting curved surface 15, 16, 17, 18 when moving in the machine direction 10 through the forming part 1.

The four dehydration boxes 11, 12, 13, 14 are not identical.

The first dehydration box 11 is an impingement shoe, in which vacuum is applied through a single space 24 from a controlled vacuum supply (not shown). A preferred form of collision shoe is disclosed in US patent application US 2003/0173048 filed by Buchanan et al., Other known configurations may be used.

The second dewatering box 12 is divided into two regions 19 and 10. Each of these areas 19 and 20 may have a separately controlled vacuum source (not shown).

The third dewatering box 13 is also divided into two regions 21 and 22, and each of these regions 21 and 22 is provided with two vacuum sources (not shown) which are independently controlled.

The fourth dehydration box 14 is not divided, and has a single space 23 provided with a controlled vacuum source (not shown). If necessary, the dehydration box 14 may also be configured to have two vacuum regions as in the dehydration box 13.

Thus, it can be seen that the four dehydration boxes provide at least six independently controlled vacuum zones. The two forming fabrics pass above this vacuum region. The vacuum regions 24, 19, 20, 21, 22, 23 are arranged sequentially along the machine direction. These six vacuum zones are constructed and arranged to sequentially expose the two forming fabrics 2, 4 and the stock 7 interposed therebetween under the following conditions:

1. a vacuum range having a range between the minimum value (about 0) of the vacuum region 24 and the maximum value of the vacuum region 23;

2. the range of curvature radius of the curved surface that supports the fabric support element having a range between the maximum radius of curvature of the curved surface 16 of the vacuum region 19 to the minimum radius of curvature of the curved surface 18 of the vacuum region 23;

3. The pitch of the fabric support element in the machine direction having a range between the maximum value on the surface 16 to the minimum value on the surface 18.

FIG. 2 shows the collision point 9 of FIG. 1 in more detail. At the impingement point 9 the two forming fabrics 2, 4 are combined and a stock jet 7 is injected between both fabrics at this point. The two moving fabrics then run along a curved path formed in part by the machine-side shape and curved surface 15 of the fabric support element. In the case of using the collision shoe disclosed in the above-described US patent application US 2003/0173048 filed by Buchanan et al., The curved surface 15 is provided with a series of slots (not shown) which can be oriented at a predetermined angle with respect to the machine direction. .

FIG. 3 shows the dehydration boxes 12, 13, 14 of FIG. 1 in more detail. Several aspects of these dehydration boxes can be clearly understood from FIG. 3.

First, it can be seen that the radius of curvature of the three curved surfaces 16a, 16b, 17a, 17b, 18 decreases according to the machine direction indicated by arrow 10.

Second, the pitch of the three sets of fabric support elements shown below is more apparent.

A first set 26 on the dehydration box 12;

A second set 27 on the dehydration box 13; And

Third set 28 on the dehydration box 14.

In these sets, the width of the face of the fabric support element supporting the molded fabric is constant. The pitch of the fabric support element is more complicated:

The pitch in each set 26, 27, 28 attached to the curved surfaces 16, 17, 18 is the same.

The pitch used in each set decreases along the machine direction. Thus, the pitch of the set 26 is wider than the pitch of the set 27, and the pitch of the set 27 is wider than the pitch of the set 28.

Thus, the pitch and curvature radius of the set decrease in order along the machine direction.

4 shows a modified configuration of FIGS. 1 and 3. 1 and 3, all the dehydration boxes have convex curved surfaces. Thus, the two moving molding fabrics 2, 4 wrap around the fabric support element by the tension formed on the fabric. On the opposite side of the dehydration box 12 in FIG. 4, an additional dehydration box 30 is provided. Since this dehydration box is located on the outside of the convex side of the two forming fabrics, the fabric support element 31 must be installed using flexible mounting. Suitable mounting is disclosed in US Pat. No. 6,361,657, filed by McPherson.

5, 6 and 7 show the alteration structure of the collision shoe 11. 1 uses a shoe with a slot as disclosed in US Patent Application US2003 / 0173048 by Buchanan et al.

The structure of the collision shoe 11 shown in FIG. 5 includes a slot portion 33 according to the concept of Buchanan et al., And downstream of this slot portion is provided with a set of opposedly disposed fabric support elements 32. . The fabric support element mounted on the impact shoe 11 is a combination of the curved surfaces 15 shown in FIG. 2 and provided by the dehydration box 30 of FIG. 4.

6 shows a known crash shoe 34 equipped with a set of short fabric support elements 35. Note that the two molding fabrics 2, 4 are shown moving in the opposite direction to the direction shown in FIG. 1.

The crash shoe 11 shown in FIG. 7 also follows the concept of FIG. 1 of US patent application US 2003/0173048 by Buchanan et al., But this crash shoe is the first dewatering box 12 of the other side of the two forming fabrics. It is located nearby. Thus, the impact shoe is in contact with the machine side of the forming fabric 4 without contacting the machine side of the forming fabric 2 in motion.

8 shows a different structure using impingement rolls 40. The impingement roll 40 is provided with a controlled vacuum source (not shown) and is provided with a vacuum region 41. Vacuum rolls of this type are well known. In this structure, the impact point 9 of the stock jet is located at the part 42 where the two forming fabrics 2, 4 in motion are in contact with the vacuum roll.

FIG. 9 illustrates a modified structure of FIG. 1. In comparison with FIG. 1 a dewatering box 30 with a fabric support element 31 is installed. The dewatering box 13 of FIG. 1 has two chambers 21 and 22, but the dewatering box 40 of FIG. 9 is replaced with one having three chambers 41, 42 and 43. In addition, the single dehydration box 14 of FIG. 1 is replaced with the dehydration box 44 provided with two chambers 45 and 46. As shown in FIG.

In the figure, the fabric support elements are all schematically shown as having the same width in the machine direction. In practice, the width of the fabric support element is not the same for all dehydration boxes. Some dewatering boxes require fabric support elements of different widths to accommodate the amount of white water drained from the forming fabric. It is also necessary to vary the width of the fabric support element to obtain a pressure pulse of the desired level of stock at a given location. Experience shows that the ratio of the width of the gap between them to the width of the fabric support element shows between about 1:10 and about 1: 0.5.

In the figure, each dehydration box has one or more chambers to which a controlled level of vacuum is applied. If the vacuum levels of a plurality of adjacent chambers or a plurality of dewatering boxes are not the same, the curvature of the curved surface and possibly the pitch of the corresponding fabric support element should not be the same. Experience has also shown that the vacuum levels of a plurality of series of dewatering boxes or chambers increase relatively slowly in the machine direction. The vacuum level in two adjacent dewatering boxes or chambers can be kept constant, but should not be reduced in the machine direction, and steep pressure spikes should be avoided. In other words, not all variables necessarily necessarily change gradually in stages, and a plurality of adjacent regions may have the same value for at least some variables.

Several kinds of newspaper papers were manufactured by using a papermaking machine having a twin fabric forming part schematically shown in FIG. 9. Using the vacuum levels shown in Table 1, it has been found that better paper can be produced than other paper machines with twin fabric moldings. In Table 1, the position numbers indicate the numbers of the dehydration box chamber and the collision shoe shown in FIG.

TABLE 1

location Vacuum, kPa 11 1.2 20 3.8 41 8.5 42 12.2 43 14.6 45 22.6 46 27.9 A 38.6 B 51.0 C 62.1

Claims (11)

A two-part fabric forming part of a gap type for a paper machine having a conveying forming fabric and a backing forming fabric, (i) each forming fabric has a paper side and a machine side; (ii) both molding fabrics move along the machine direction with a stock layer interposed therebetween; (iii) both forming fabrics are supported by a series of fabric support elements selected from the group consisting of a plurality of rolls, a stationary fabric contact fabric support element, and a roll and a stationary fabric contact fabric support element; The upper side of the machine side of each forming fabric passes in sliding contact, both fabric support elements supported on a series of dewatering boxes, the dewatering boxes having a surface supporting a curved fabric support element; (iv) the dehydration box provides a separate dehydration zone at least partially connected to a vacuum source providing a separate vacuum zone, here, (a) the forming region includes a forming portion between a position where both forming fabrics converge to intervene the stock and a position where both forming fabrics are separated with the stock supported on one of the fabrics; (b) the dehydration box in the forming section provides at least four independent and distinct vacuum zones; (c) the radius of curvature of the curved surface supporting the fabric support element is gradually reduced along the machine direction, or the radius of curvature of the curved surface supporting the fabric support element is decreased on the continuous support surface along the machine direction, (d) the pitch of the fabric support elements in each vacuum region is constant and the pitch of the fabric support elements on successive vacuum regions decreases along the machine direction, or the pitch of the continuous fabric support elements in each vacuum region is machine direction Decrease along; (e) the dewatering box for supporting the fabric support element is configured and arranged to position the fabric support element in contact on the machine side of the transfer molded fabric and the backing molded fabric in an alternating order along the machine direction; (f) all fabric support elements on all of the dewatering boxes have the same width along the machine direction, or all the fabric support elements have unequal widths along the machine direction. Two fabric molding parts. 2. The gap type paper machine of claim 1, wherein the pitch of the fabric support elements in each vacuum region is constant and the pitch of the fabric support elements in the continuous vacuum region decreases along the machine direction. Fabric forming part of the falcon. The method of claim 1 wherein the pitch of the fabric support elements in each vacuum region is not constant and the pitch of the fabric support elements in the continuous vacuum region decreases along the machine direction. Two fabric molding parts. The two-sheet fabric forming part of the papermaking machine of claim 1, wherein the radius of curvature of the curved surface that supports the fabric support elements on the continuous vacuum region decreases along the machine direction. 2. The two-sheet fabric forming part of the papermaking machine of claim 1, wherein the radius of curvature of the curved surface that supports the fabric support elements on the continuous vacuum region decreases gradually along the machine direction. The two-sheet fabric forming part of claim 1, wherein each dewatering box provides at least one vacuum area. The two-sheet fabric forming part of claim 6, wherein the at least one dehydration box provides at least two vacuum zones. 8. The two fabric forming sections of the papermaking machine of claim 7 wherein each dewatering box provides at least two vacuum zones. 2. The two piece fabric forming section of claim 1 wherein the ratio of the width of the gap between them to the width of the fabric support element is between about 1:10 and about 1: 0.5. 2. The two fabric forming portions of the paper making machine of the gap type according to claim 1, wherein the forming portion includes a turning roll having vacuum assisted dehydration means. 2. The fabric forming part of claim 1, wherein the forming part includes a turning roll without a vacuum assisted dewatering means.

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