KR101114959B1 - Forming Sieve for the Wet End Section of a Paper Machine - Google Patents

Abstract

A wet end sieve of a paper machine is described, which is compressed by at least one of increased temperature, pressure and / or humidity. Such treatment allows the yarn plots and knuckles to have a sieve having at least one side to be reshaped and the sieve to exhibit at least one generally flatter surface for the production of paper. This process is a current technique of abrasively scrubbing the surface without causing any physical damage to the surface of the sieve, thus allowing the fabric to have improved properties and lifetimes.

Paper machine, sieve, compression, calendaring.

Description

Forming Sieve for the Wet End Section of a Paper Machine}

The present invention relates to a single or multiple layer forming sieve for the wet end of a paper machine according to the pre-feature of claim 1.

In conventional Fordrinier paper-making methods, aqueous pulp or suspension of cellulose fibers (known as paper stock) is known as endless web made of wire and / or synthetic material. Lies on the upper surface of the. This wire fabric acts as a filter, which causes the cellulose fibers to separate from the aqueous medium and form a so-called wet-paper sheet. During the formation of this wetland, the shaped body acts as a filter that separates the aqueous medium from the cellulose fibers as the aqueous medium passes through the opening of the sieve.

To facilitate the removal of moisture, the filtration process is very often carried out with additional vacuum action applied to the bottom of the sieve, ie on the machine side. Once the paper leaves the forming end, it is transported to the press section of the paper machine, where it is a pair or several pairs of pressure rollers, so-called "press felts, from which another fabric is stretched thereon. (press felt) is guided through the gap. The pressure of the roller acting on the paper removes additional moisture and is often strengthened due to the presence of a "mat" layer in the press felt. After passing through the crimp, the paper is sent to a dry section of the machine to further remove moisture. After drying, the paper is ready to be sent to a second process to be launched and finally packaged.

The sieves used in papermaking are made infinitely useful and are manufactured in one of two ways. According to the first method, the free ends of the individual flat woven papers are connected together by a process known as "splicing" and thus infinite papers are formed. In a flat woven paper machine body formed in this way, warp threads advance in the machine derection and filling or weft threads advance in the transverse direction. According to the second production technique, papermaking bodies are made directly in the form of continuous strips, also known as the infinite paper-based method. In this way, the warp yarn runs in the transverse direction of the machine and the weft yarn runs in the longitudinal direction. In related literature, abbreviations of these terms are commonly used, where MD stands for "portrait orientation" and CMD stands for "landscape orientation".

In the wet end section of the paper machine, it is very important to keep the cellulose fibers in suspension on the paper side of the sieve and to avoid marking in the forming sheet. These patterns occur when individual cellulose fibers are oriented in a paper sheet in such a way that their ends coincide with the gaps between the threads of the individual sieves. In general, attempts are made to solve this problem by providing a permeable body structure having a coplanar surface and also allowing paper fibers to form bridges over adjacent yarns in the fibers and not penetrate into the gaps between them. . As used herein, "coplanar" defines the paper-forming surface of a sieve and the top of the yarn, respectively called float or knuckle, is generally "planar" at approximately the same height. It means to represent the surface of phosphorus. Good quality papers, such as those used for good quality prints, carbonization, tobacco, electric capacitors, and other similar quality papers, are those that exhibit the flattest surface and were previously produced in well-woven sieves.

To make the fabric surface as close to the plane as possible, especially in the case of sieve shaping, the surface is very often ground with particulate emery paper. Such grinding improves the topography of the paper and results in a better final surface. Unfortunately, by grinding the surface in this way, the thread float and knucles of the sieve are damaged: this can be seen in FIGS. 3 and 4 when compared to FIGS. Figure 1 shows the part of the molded body that has not been processed, ie the plots or knuckles have not been ground to emery paper. FIG. 2 shows a part of the sieve of greater magnification according to FIG. 1.

3 and 4 correspond to the photographs shown in FIGS. 1 and 2 except for the sieve according to FIGS. 3 and 4 where the topography of the paper was flattened by pulling plots or knuckles. This particular leveling procedure does not reduce the internal volume of the sieve, while the thickness is slightly reduced. This has very disadvantageous side effects, ie the stability of the sieve is consequently adversely affected: mainly, the loss of material involves the rigidity of the sieve being lowered. In addition, it has been found that as a result of these mechanical interventions, the sieve undergoes increased wear and therefore has a shorter operating life. For small diameter yarns, for example 0.11 mm to 0.13 mm, the grinding process reduces the cross section of the yarn by 30-40%. Such severe mechanical changes in yarn and sieve can be seen as the underlying reason for the reduction in the rigidity of the sieve. This can be a further problem, because the current trend in the paper industry is to gradually move to much thinner sieves with thinner thread diameters. Along with this trend, limitations are placed on the possible mechanical changes to produce coplanar surfaces.

To describe the technique shown in FIGS. 1 to 4 in more detail, reference is made to FIGS. 5 and 6 as well as FIGS. 7 and 8. 5 shows the contact surface of the sieve, untreated sieve according to FIGS. 1 and 2, wherein about 30% of the total surface comprises the contact surface of the sieve. FIG. 6 shows the “standard” appearance of plots and knuckles in the untreated sieve according to FIGS. 1 and 2. 7 and 8 detail the structure of the ground sieve, whereby the contact surface of the sieve is increased by about 34% by removing 0.02 mm of overhanging plots and knuckles. The shape of the plots or knuckles after grinding is shown in FIG. 8.

One object of the present invention is to prepare a sieve which exhibits a highly coplanar surface at least on the paper side but preferably on both the paper and the machine side. This can be achieved with a significantly thinner sieve than those disclosed in the prior art, and with a relatively reduced yarn diameter. In view of the various problems described above, this object is particularly achieved with a so-called shaped body, ie a sieve used in the wet end of a paper machine.

This object is achieved by characterizing the features given in claim 1 together with the advantageous developments and embodiments described in the dependent claims.

Disclosed are single- or multi-molded bodies for wet end portions of an initial sheet having upper longitudinal-MD and transverse-vertical CMD yarns facing the paper side, and lower MD and CMD yarns facing the machine. The shaped body has at least one paper-side thread inflection region reshaped by one or a combination of temperature, pressure and / or humidity.

1 shows a portion of a shaped body that has not been processed, ie, the plots or knuckles have not been ground to emery paper;

2 is an enlarged view of a part of the sieve according to FIG. 1;

3 and 4 correspond to FIGS. 1 and 2 in addition to the flatness of the paper;

5 and 6 show the contact surfaces of the untreated sieve according to FIGS. 1 and 2;

7 and 8 show a ground sieve;

9a to 9c show equipment for compressing a fabric;

10 and 11 show protruding knuckles or plots flattened as a result of compression; And

12 and 13 show the compressed sieve.

The production of papermaking sieves of the present invention is based on squeezing or " hot calendering " systems to fabricate the sieves in press equipment. This action begins with at least one or a combination of increased pressure, increased temperature and / or increased humidity level for a particular time; This particular time is the result of the selected yarn and the desired features of the workpiece.

When fabrics with infinite structures are provided, ie there are no ends joining seams, they are usually made of two warp systems. Calendering or compacting of the fabric takes place between at least two rollers, which can be seen in the embodiment shown in FIG. 9. Three possible structures are shown in this figure which details the equipment for compressing the fabric, which is not considered to limit the invention in any particular way, and is shown only as an example.

9B shows the most simplified structure, where only two rollers are provided between where the fabric is compressed. To increase the usable area of the heated roller, which means that the fabric can be in contact with the heating for a long time, a third roller (c) can be provided as shown in FIGS. 9a and 9c. In addition, if additional heating action to the fabric is needed during the process, these additional rollers can be heated. The specific number and relative positions of the fabrics can be selected depending on the exact requirements of the fabric and the structure ultimately desired in its structure.

For compressing or calendering the fabric of the sieve, two rollers need to be provided which are brought together and the desired pressure is applied between them. These are represented by reference numbers A and B in FIG. 9. Here, the sieve fabric passes between the gaps provided between the two rollers and the required pressure is applied; This pressure is generally between 10 and 40 kPa. The roller A, called a press roller, is formed of a plurality of parts running along the width of the sieve fabric and can be rotated to provide different pressures across the sieve. These multiple rollers allow the final sieve to be formed into specific and selectable cross-sectional shapes.

As shown in the embodiment of FIG. 9, at least one rollers may be heated to a temperature between 100-190 ° C., and an optimal process is taken in the range of 140-170 ° C. The particular temperature chosen depends on the final desired structure for the surface of the yarns and sieves in the fabric. As the fabric is compressed, it is possible to heat one or both sides of the fabric, and during such a process it is also possible to adjust the temperature profile along the width and depth of the fabric. This will produce a fabric in which the specific temperature and pressure at each point along the length and width of the fabric are tailored to meet the desired final requirements of the sieve in a targeted manner.

For fabrics with two ends joined through a seam to form an endless structure, the compression process is slightly different. Initially, it is necessary to specifically control the pressure exerted at the start and end points of the fabric. This is accomplished by ramp control of the applied pressure, where the machine knows the start and end points of the fabric and does not undergo a change. All other processes of the fabric follow the method described above for the preformed endless fabric.

The specific tension applied to the fabric during the calendering process depends on the individual fabric design, which is connected to the preformed seams. During the compression process the fabric will change its length to ± 1.5%, which is a fact that needs to be considered at the fabric forming stage and before the calendering process. In addition, the width change of the fabric in the 0-3% range is generally observed and compensated for by simultaneous heat treatment of the fabric.

As shown in FIG. 9C, an additional drying unit may be provided that heats the fabric after the compression process. This is shown in the drawing provided with a heat box with a tenter to dry the fabric from above. Obviously, other options exist in this drying step and are not limited to those disclosed in the figures.

The yarns forming the fabric of the sieve may comprise a polymer such as made of one or a combination of polyesters, polyamides and / or polyolefins. In addition, the calendering process can be performed on a sieve having a warp present on the paper side with a diameter between 0.09 and 0.20 mm and a machine-side warp with a diameter between 0.15 and 0.30 mm as disclosed. In particular the paper side thread is selected with a diameter of 0.13 mm and the machine-side thread is selected with a diameter of about 0.18 mm. In addition, the compression process can be used on fabrics with one or multiple layers.

As shown in Figures 10 and 11, fabrics processed in accordance with the present invention generally have a structure different from those processed by conventional grinding techniques. The interwoven knuckles or plots may appear to have a compressed or flattened shape on the side facing the paper and / or papermaking machine. However, the main difference here is that the plots or knuckles are not mechanically damaged when being ground when comparing Figs. In addition, the calendered fabric has the further advantage that there is no loss of material, as FIG. 12 shows, which eliminates the problems associated with a sieve with reduced rigidity.

Protruding knuckles or plots can be seen in FIGS. 10 and 11 which become somewhat flat as a result of compression. This produces a relatively wide "thread ellipse" that moves quickly in the paper machine as the fabric moves. As a result of this "thread ellipse," the width of the permanently flattened plots and knuckles is greater than the rest diameter of the yarn, which can be best observed in FIG. In fact, it is desirable that the width of the flattened plots and knuckles is about 5-15% larger than the diameter of the rest of the yarn. In addition, the heights of the flattened plots and knuckles are reduced by about 10-30%, preferably about 20% smaller than the diameter of the rest of the yarn. In other words, compression reduces the diameter by about 30-50%.

By compressing the yarn in the fabric of the sieve at the plot or knuckle point, the contact area of the paper and sieve increases by about 25-30% compared to the untreated sieve. This increase causes the sieve to have a contact area that is about 40-45% of the total area of the sieve. Such a measurement is shown in FIG. 4 where it can be seen that the treated fabric has a contact area of 41% of its entire surface area. Comparing FIG. 13 with FIGS. 5 and 7, it is clear that the present invention shows significantly improved surface features over the prior art. In addition to increasing the area of contact for calendered fabrics, these sieves have a much smoother surface compared to untreated or ungrounded fabric, which results in a much improved final paper topography. In addition, sieves with properly compressed plots on the paper-machine side as well as on the paper side do not show different weft knuckle heights, as caused by other materials when the fabric is loaded: As it decreases on the side of the paper, the final paper surface is improved and other problems associated with the new sieve moving on the machine are drastically reduced. The most important of these problems is the load required to be supported by the paper machine, and starting the machine with a new sieve that is not running properly. In particular, as a result of a wide and already formed "silent ellipse", the sieve applied to the machine is obtained more rapidly. Sieves made in accordance with the present invention in paper machines can be started more rapidly, which requires less subsequent adjustments and starts running very quickly when compared to currently provided sieves.

Plotted or knuckle shaped sieves according to the invention show no or significantly reduced differences at the point of change between the seam area and the solid fabric. This ensures that the sieve does not produce markings on top of paper that are highly sensitive. As a result of the slightly wider and flat plot shape, the sieves show higher stability and rigidity, because the interwoven threads are less disposed relative to one another.

Clearly, the process of calendering the fabric results in a permanent reduction in fabric thickness as a result of the applied pressure. According to the particular treatment applied, the thickness of the fabric can be reduced between 1 and 20% of the original one. To achieve this, the refractive height and shape of the individual threads going through the fabric are permanently changed. Since there is no loss of material in this technique, only by compression, the weight per unit area of the fabric remains constant.

Not only does the geometry of the yarn in the sieve change after calendering, but the internal volume of the fabric body decreases permanently. Clearly, when the fabric is compressed and the geometry of the yarn is adjusted, it is necessary for the yarns to move somewhere, in which case the size of the void spaces between them decreases as they get closer to each other. The reduction of the cavity size between the fabrics has a beneficial effect on the sieves because they move on the paper machine. When sieves are used to hold paper stock as the aqueous medium is removed, it is possible for the cavities in the fabric to cause turbulence as they move. Such vibrations often cause unwanted side effects of drawing water along the cavity as the sieve moves through the machine. Clearly, if water remains in the sieve, drying of the stock is adversely affected. However, with the reduction in cavity size associated with the fabric processed by the current process, problems associated with vibration and water logging are reduced. Also by treating with certain fabrics, the cavities can be reduced in size between 1 and 15%.

Further advantages arise from changes in the refraction points between the yarns in the fabric and form their changed geometry. With the increase in the area of contact for the fabric, there is an increase related to the level of friction between the sieve and the paper forming machine. This reduces the delay in the movement of the fabric when the machine first starts and further leads to a decrease in the transverse motion while the machine is running. Such improvements increase the efficiency of the paper drying process and require reduced belt control with further processing. In addition, in the existing seams, the seal-silk friction increases with this change in refraction between the warp and the weft, resulting in seam stabilization and increased strength.

Usually, non-calendered sieves that are not formed with seams tend to experience a thickness mismatch of the fabric between the seam and the area of the main body of the fabric. This difference in the surface can have a detrimental effect on paper production, pattern the page, and increase the wear level in these areas. However, the compression technique of the present invention alleviates these problems by providing a fabric that has a constant thickness along its entire length. In addition, the internal stresses and tensions on the fabric yarns resulting from these inconsistencies in the untreated sieves are generally equivalent to the calendered fabric according to the present invention.

The final property of the fabric changed by the compression treatment is permeability. It is not surprising that the compression of the fabric is a natural cause of the reduction in fabric thickness, with variations corresponding to the void size and density leading to the change. Depending on the initial fabric and the treatment applied thereto, the permeability can be reduced between 0 and 30%, which is usually considered when a particular process and fabric is selected.

Although various features and embodiments of the invention have been described above, they can be combined with others that result in other embodiments of the invention.

Included in this specification.

Claims (20)

Single-use for wet end of paper machine with upper longitudinal (MD) and transverse-vertical (CMD) threads facing the paper side and lower longitudinal-side (MD) and transverse-length-direction (CMD) threads facing the machine Or as a multilayered molded body, At least the paper side seal plots and knuckles are reshaped to one or a combination of temperature and pressure, The temperature is between 100 ° C and 190 ° C, The pressure is between 10 kPa and 40 kPa, The total contact area of the sieve is 40 to 45% of the total surface area of the sieve, As a result of the paper side yarn refractive regions being reshaped, the size of the void space between the paper side and machine side yarns is reduced by between 1% and 15% compared to the original void space size before the refractive zone was reshaped. The molded body for wet end parts of a paper machine. The method of claim 1, Wherein said paper-side and machine-side threads are made of or comprise at least one of a polymer such as polyester, polyamide or polyolefin. delete The method of claim 1, And said temperature is between 150 ° C and 170 ° C. delete The method of claim 1, And the yarns on the paper side have a diameter between 0.09 mm and 0.20 mm, and the machine-side threads have a diameter between 0.15 mm and 0.30 mm. The method of claim 1, And the yarns on the paper side have a diameter of 0.13 mm, and the machine-side threads have a diameter of 0.18 mm. The method of claim 1, Wherein the width of the yarn plots and knuckles is between 5% and 15% greater than the diameter of the remaining portions of the paper side and machine side yarns. The method of claim 1, Wherein the height of the yarn plots and knuckles is between 10% and 30% smaller than the diameters of the remaining portions of the paper side and machine side yarns. The method of claim 9, And the height of the yarn plots and knuckles is less than 20% less than the diameter of the remaining portions of the paper side and machine side yarns. The method of claim 1, And the yarn plots and knuckles comprise a flat "thread ellipse" extending parallel to the plane of the sieve. delete delete The method according to any one of claims 1, 2, 4 or 6 to 11, One or more of the shape of the yarn refraction, the width of the yarn plots and knuckles, the height of the yarn plots and knuckles, the degree of ellipse of the yarn, the total contact area of the sieve and the size of the void space between the yarns At least one combination varies across each point in the width of the sieve. Calendering the plurality of rollers and the sieve fabric at one or a combination of temperature and pressure to permanently reshape the yarn refractive region on at least the paper side of the sieve, The temperature is between 100 ° C and 190 ° C, The pressure is between 10 kPa and 40 kPa, The total contact area of the sieve is 40 to 45% of the total surface area of the sieve, As a result of the paper side yarn refractive regions being reshaped, the size of the void space between the paper side and machine side yarns is reduced by between 1% and 15% compared to the original void space size before the refractive zone was reshaped. A method for molding a wet end portion sieve of a paper machine. The method of claim 15, At least one of the plurality of rollers is formed from a plurality of parts that can be individually adjusted to a change in pressure on the fabric so that the resulting sieve is cross-sectional contoured across the width to form the wet end sieve of the paper machine. How to. 17. The method according to claim 15 or 16, At least one of the plurality of rollers may be adapted to apply a predetermined heat to the sieve during the process, and the temperature may vary along the length of the roller to give a particular contour to the sieve. How to mold. delete delete The method of claim 15, And said temperature is between 150 ° C and 170 ° C.

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