HK1136015B - Fiber mat forming apparatus and method of preserving the hydrodynamic processes needed to form a paper sheet - Google Patents

Description

Fiber mat forming apparatus and method for maintaining hydrodynamic processes required for sheet formation

Technical Field

The present invention relates to an apparatus for sheet forming. More particularly, the present invention relates to a device for maintaining the hydrodynamic processes associated with the formation of fiber mats. The performance of the apparatus is not affected by the speed of the paper machine, basis weight or thickness of the mat being formed.

Background

In general, it is well known in the paper industry that proper drainage of liquid from the pulp on the forming fabric is an important step in ensuring product quality. This is done by using a drainage blade or foil (foil) which is typically located at the wet end of the machine (e.g., fourdrinier machine). (note that the term drainage doctor as used herein is intended to include doctor blades or chopping boards that cause dewatering or pulp activation or both.) there are today a very large number of different designs for these doctor blades. Typically, these blades provide a support surface for the wire or forming fabric and have a dewatering shoe at an angle to the wire. This creates a gap between the blade surface and the fabric and creates a vacuum between the blade and the fabric. This not only drains the water from the fabric, but also causes the fabric to be pulled down. When the vacuum subsides, the fabric returns to its original position, causing a pulse across the pulp, which may be desirable for pulp distribution. The degree of activation (caused by wire deflection) and the amount of water drained from the sheet are directly related to the vacuum created by the blade, and therefore they are related to each other. Drainage and activation caused by such blades can be enhanced by placing one or more blades on the vacuum chamber. This direct correlation between drainage and activation is undesirable because, while activation is generally desirable, excessive early drainage during sheet formation can have a detrimental effect on fiber and filler retention. Rapid drainage may also cause paper closure, making subsequent drainage very difficult. The prior art forces paper mills to compromise the desired activation in order to slow down early drainage.

Drainage may be accomplished by liquid-to-liquid transfer, as taught by Ward in U.S. patent No. 3,823,062, which is incorporated herein by reference. This document teaches the removal of liquid by impact of the pulp by means of a flash pressure. This document shows that the controlled liquid-liquid drainage of water in suspension is less vigorous than conventional drainage.

Corbellini teaches a similar type of drainage in U.S. patent No. 5,242,547. This patent teaches preventing the creation of a meniscus (air/water interface) on the surface of the forming fabric opposite the sheet to be drained. This is achieved by means of a vacuum box structure containing one or more scrapers for overflow and by means of a control mechanism for regulating the discharge of liquid. This is called "Submerged Drain". Drainage is said to be improved by using sub-atmospheric pressure in the suction box.

In addition to drainage, the doctor blade is also configured to purposefully produce activation in the suspension to provide the desired short fiber distribution. Fuchs teaches such a doctor blade in us patent No. 4,789,433. This document teaches the use of a wave blade (preferably with a rough dewatering surface) to create micro-turbulence in the fibre suspension.

Other types of blades are intended to avoid turbulence, but still drain effectively, as described by Kallmes in U.S. patent No. 4,687,549. This document teaches filling the gap between the blade and the web and indicates that the absence of air prevents the expansion of water and cavitation in the gap and substantially eliminates any pressure pulses. A number of such scrapers and other devices are disclosed in the following U.S. patent documents: 5,951,823, respectively; 5,393,382, respectively; 5,089,090, respectively; 4,838,996, respectively; 5,011,577, respectively; 4,123,322, respectively; 3,874,998, respectively; 4,909,906, respectively; 3,598,694, respectively; 4,459,176, respectively; 4,544,449, respectively; 4,425,189, respectively; 5,437,769, respectively; 3,922,190, respectively; 5,389,207, respectively; 3,870,597, respectively; 5,387,320, respectively; 3,738,911, respectively; 5,169,500 and 5,830,322, which are incorporated herein by reference.

Generally, high and low speed paper machines produce different grades of paper having a wide range of basis weights. Sheet formation is a hydraulic process, the movement of the fibers following the movement of the liquid, because the inertial force of the individual fibers is smaller than the viscous drag force in the liquid. The forming and drainage components affect three main hydrodynamic processes, namely drainage, pulp activation and directional shear. A liquid is a substance that reacts according to shear forces acting in or on it. Drainage is a liquid flow through a wire or fabric and is characterized by a flow rate that is generally time dependent.

Pulp activation, in the ideal sense, refers to random fluctuations in the undischarged fiber suspension flow rate, typically manifested by deflection of the forming fabric in response to drainage forces or changes in the momentum of the flow caused by the blade configuration. The main function of pulp activation is to break the network in suspension and to move the fibres. Directional shearing and pulp activation are shear-producing processes that differ only in the degree of orientation on a considerable scale, i.e. a scale larger than the size of the individual fibers.

Directional shear is a shear flow with a uniquely identifiable pattern in an undrained fiber suspension. Cross direction ("CD") directional shear improves both sheet formation and testing. The primary mechanism of CD shearing (on a non-vibrating paper machine) is the formation, destruction, and subsequent reformation of good-profile machine direction ("MD") ridges in the pulp of the fabric. The source of these bumps may be a headbox straightening roll, a headbox slice lip (see, e.g., international application PCT WO95/30048 published on 11/9 of 1995) or a forming shower. The protuberances collapse and reform at constant intervals depending on the vehicle speed and the amount of material on the forming fabric. This is called CD shear conversion. The number of transitions and thus the CD shear effect is maximized if the fiber/water slurry retains its maximum value of initial kinetic energy and is subjected to a water discharge pulse just below (in the MD direction) the natural transition point.

In any shaping system, all of these hydrodynamic processes can occur simultaneously. They are generally not uniformly distributed in time or space and they are not completely independent of each other, they affect each other. In fact, each of these processes affects the overall system in more than one way. Thus, while the above-described prior art may contribute to certain aspects of the aforementioned hydrodynamic processes, they do not coordinate all of the processes in a relatively simple and efficient manner.

The activation of the pulp in the beginning of the table is the key to good paper production. Generally, pulp activation can be defined as the turbulence of the fiber-water slurry on the forming fabric. This turbulence occurs in all three directions. Activation of the pulp plays an important role in a good formation process by preventing delamination of the as-formed paper, dispersing short fibers, and causing random orientation of the fibers.

Generally, pulp activation quality is inversely proportional to sheet drainage, i.e., if the drainage rate is slowed or controlled, the degree of activation generally increases. Activation becomes more difficult as water is removed, because the paper begins to set and the lack of water, the primary medium for activation, becomes more scarce. A good operation of the paper machine is thus a balance between activation, drainage and shearing action.

The capacity of each former is determined by the forming elements that make up the wire pattern. After the forming board, the subsequent elements must be drained of residual water without damaging the formed mat. The purpose of these elements is to improve the work done by the former elements.

The thickness of the mat increases with increasing basis weight. With current forming/drainage elements, it is not possible to maintain a sufficiently strong controlled hydraulic pulse to create the hydrodynamic processes required to produce a well-formed sheet.

An example of a conventional apparatus for reintroducing the drainage water into the fiber slurry to facilitate activation and drainage can be seen in fig. 1-7.

The table roll 100 in fig. 1 causes a large positive pressure pulse to be applied to the sheet 96 as a result of the water 94 under the forming fabric 98 being forced into the nip formed by the guide plate in roll 92 and forming fabric 98. The amount of water reintroduced is limited to the water adhering to the surface of the roller 92. Positive pulse has good effect on paper pulp activation; which causes a flow perpendicular to the surface of the paper. Also, on the exit side of the roll 90, a large negative pressure is generated, which greatly promotes drainage and removal of fines. However, no reduction in the felt consistency was observed and therefore there was little improvement by increasing the degree of activation. Table rolls are generally limited to relatively lower speed paper machines because the desired positive pulses delivered to the heavy weight sheets at a particular speed are undesirably positive pulses that disrupt the lighter weight sheets at a faster speed.

Fig. 2 shows the gravity board 88. The vacuum created by the chopping board blade 86 increases as the chopping board angle and/or blade length increases. In this case, the vacuum degree increases in proportion to the square of the vehicle speed. As the drainage resistance of the fiber mat 96 increases, the vacuum force generated by the chopping board blade increases. The initial portion of the table typically uses a low table blade angle in the range of about 0.5-1 degrees. The angle increases to the dry end of the net pattern by 3-4 degrees. As the machine direction becomes less water, the angle chosen should be such that the diverging gap can be filled with water.

Fig. 3-7 show a low vacuum box 84 with different doctor arrangements. Gravity tables are also used in low vacuum boxes. By controlling the vacuum and pulse characteristics applied, these rough vacuum addition units 84 provide the paper machine with a means to significantly affect its process. Examples of doctor box configurations include:

a gravity board or board blade case 88 as shown in fig. 2;

a flat scraper or water bath (not shown);

a stepped blade 82 as shown in FIGS. 3-5 and 7;

an offset plane blade (offset plane blade)80 as shown in fig. 6; and

such as a positive pulse stepped doctor blade 78 shown in fig. 7.

Generally, the chopping board blade box, the offset plane blade box and the step blade box are mainly used in the forming process.

In use, the vacuum augmented foil blade box will create a vacuum like a gravity foil, water is continuously drained without control, the primary drainage process being filtration. Typically, the mat that has been formed will not be fluidized again.

In a vacuum augmented flat blade box, a slight positive pulse is generated on the blade/wire contact surface and the pressure exerted on the fiber mat is due solely to the vacuum maintained in the box.

In a vacuum build-up stepped doctor blade box as shown in figure 3, the various pressure profiles produced depend on factors such as step length, span between the blades, vehicle speed, step depth and vacuum level applied. The peak vacuum level generated by the stepped blade is related to the square of the vehicle speed at the beginning of the blade, the peak negative pressure causes water to be drained while the wire bends towards the step, part of the drained water is forced to flow back into the felt, re-fluidizes the fibers and disperses the short fibers due to the shear forces generated. If the vacuum applied is higher than desired, the wire is forced to contact the step of the blade, as shown in figure 4. After operating under such conditions for a period of time, as shown in FIG. 5, the chopping board accumulates dirt 76 in the step, loses the hydraulic pulse (drops to a minimum) and prevents the reintroduction of water into the mat.

The vacuum augmented compensated flat blade box shown in figure 6 has leading/trailing and intermediate flat blades 80 at two different heights below the wire line. An intermediate blade 80 is positioned below the wire to limit deflection of the wire under vacuum and create a fluid nip with the water below the forming wire.

The vacuum augmented positive pulse stepped blade low vacuum box shown in fig. 7 fluidizes the paper by causing each blade to draw a portion of the water removed by the previous blade back into the mat again. However, there is no control over the amount of water reintroduced into the paper.

While some of the foregoing documents have certain operational advantages, further improvements and/or alternatives are still needed.

Disclosure of Invention

It is an object of the present invention to provide a machine for maintaining the hydrodynamic processes of the paper sheet formed on the machine.

It is another object of the present invention to provide a machine that can be used with a forming board, and/or a speed-induced drainage machine.

It is yet another object of the present invention that machine efficiency is not affected by vehicle speed, basis weight and/or mat (mat) thickness.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

Drawings

The following detailed description, given by way of example and not intended to limit the scope of the invention solely thereto, is best understood in conjunction with the accompanying drawings, wherein like reference numerals denote like elements and parts, in which:

FIG. 1 illustrates a known table roll;

FIG. 2 illustrates a known gravity foil blade;

FIG. 3 illustrates a known low vacuum box with a stepped doctor blade;

figure 4 illustrates a known low vacuum box with a stepped blade, a wire in contact with the stepped blade;

FIG. 5 illustrates a known low vacuum box, dirt-accumulating stepped doctor blade;

figure 6 illustrates a known compensated flat blade low vacuum box;

FIG. 7 illustrates a known positive pulse (positive pulse) doctor low vacuum box;

FIG. 8 illustrates a doctor blade in accordance with an aspect of the present invention;

figure 9 illustrates the doctor blade of figure 8 with the support of the doctor blade 4 removed for clarity;

FIG. 9a illustrates the doctor blade of FIG. 9 with an offset section for controlling drainage in accordance with another aspect of the invention;

FIG. 10 illustrates a doctor blade according to another aspect of the present invention;

FIG. 10a illustrates the doctor blade of FIG. 10 with multi-angled micro-active areas;

FIG. 10b illustrates the blade of FIG. 10 with a pivot point;

FIG. 10c illustrates a cross-sectional view of the doctor blade and holder of FIG. 10;

FIG. 10d illustrates a cross-sectional view of the doctor blade of FIG. 10 with an alternative support;

FIG. 10e illustrates a top view of a support blade that may be used with the blade shown in FIG. 10;

FIG. 10f illustrates a cross-sectional view of the support blade of FIG. 10e when the support is opened to allow water flow through the support;

fig. 10g illustrates a cross-sectional view of the support blade of fig. 10e when the support blade is closed by the abutment 4 d;

figure 10h illustrates a side view of the support blade of figure 10 e;

FIG. 11 illustrates a doctor blade according to another aspect of the present invention;

FIG. 12 illustrates a doctor blade according to another aspect of the present invention;

FIG. 13 illustrates a doctor blade according to another aspect of the present invention;

FIG. 14 illustrates a doctor blade according to another aspect of the present invention;

FIG. 15 illustrates a doctor blade according to another aspect of the present invention;

fig. 15a illustrates the scraper blade of fig. 14 having a plurality of body parts between the chopping boards;

FIG. 15b illustrates the scraper blade of FIG. 15a with a pivot point on the body;

FIG. 15c illustrates the doctor blade of FIG. 14 with multiple activation regions extended;

FIG. 15d illustrates the blade of FIG. 15c with a pivot point;

FIG. 16 illustrates the hydraulic performance of a doctor blade in accordance with an aspect of the present invention;

FIG. 17 illustrates hydraulic performance of a doctor blade according to an aspect of the present invention;

FIG. 18 illustrates the hydraulic performance of a doctor blade in accordance with an aspect of the present invention;

FIG. 19 illustrates hydraulic performance of a doctor blade according to an aspect of the present invention;

FIG. 20 illustrates the hydraulic performance of a doctor blade in accordance with an aspect of the present invention;

FIG. 20a illustrates hydraulic performance of a doctor blade according to another aspect of the present invention;

FIG. 21 illustrates water flow in a doctor blade in accordance with an aspect of the present invention;

FIG. 22 illustrates water flow in a doctor blade in accordance with an aspect of the present invention;

FIG. 23 illustrates water flow in a doctor blade in accordance with an aspect of the present invention;

FIG. 24 illustrates water flow in a doctor blade in accordance with an aspect of the present invention;

FIG. 25 illustrates a detailed view of a blade geometry in accordance with at least one aspect of the present invention;

FIG. 26 illustrates a blade geometry basis for calculating pressure in accordance with an aspect of the present invention;

FIG. 27 illustrates a blade geometry basis for calculating pressure in accordance with another aspect of the present invention;

FIG. 28 illustrates water flow in a doctor blade in accordance with an aspect of the present invention.

Detailed Description

One aspect of the invention can be seen in fig. 8, 9a, 10a and 10 b. In fig. 8, the body 3 includes a leading end 3a that contacts the forming fabric 2. As shown in fig. 8, the leading end 3a, which is in contact with the forming fabric, is planar and parallel to the forming fabric 2. In this embodiment, it is desirable that the leading end 3a be in full contact with the forming fabric. The leading end 3a is followed by a diverging surface 3b inclined away from the leading end 3 a. The angle of the diverging surfaces relative to the leading end is preferably in the range of about 0.1 to 10 degrees. However, angles less than 10 degrees are preferred.

Followed by a channel 5 leading to a controlled turbulence zone 8 and then to a micro-activation zone 12. The micro-activation region 12 may be planar, as shown in fig. 8 and 9, or may include a step 15 as shown in fig. 10 to create controlled turbulence. Alternatively, the micro-activation region 12 may have a divergent section 12c and a convergent section 12d, as shown in FIGS. 10a and 10 b. The diverging portions 12c are angled from the horizontal at an angle α and the converging portions 12d are angled from the horizontal at an angle β. The angle α and angle β may be the same, or preferably may be different to optimize the activation process in the micro-activation region. The micro-activation region 12 may also include an offset plane 12a to retain water for improved and controlled activation, as shown in fig. 9 a. In practice, the use of a planar, angled, or stepped micro-activation zone will depend on the vehicle speed, the consistency of the mat, and its basis weight.

Between the channel 5 and the micro-activation zone 12 there is a support blade 4. The support blade 4 helps to maintain the forming fabric 2 separate from the body 3 (or 3 and 16 as shown in figure 15, described below). The supporting doctor 4 also forms a channel 5. The channels 5 allow water 7 to drain from the fiber slurry 1, through the fabric 2 and to the controlled turbulence zone 8, and then to the micro-activation zone 12. The support blade 4 is positioned by a spacer (spacer)14 and fixed by a bolt 6 and the spacer 14. The bolts 6 are evenly distributed along the width of the paper machine so that the supporting doctor is not deflected and a turbulent flow is not created. After the micro-activation zone 12, i.e., where the forming fabric 2 is closest to the doctor blade, the water is drained into the drainage zone 10.

Another aspect of the invention is shown in fig. 10c and 10d, in which the supporting blade 4a is shown in more detail. Figures 10c and 10d are cross-sectional views of the blade taken at different locations of the blade in the cross-machine direction. Fig. 10c is a section taken along a part of the supporting blade 4a at the location of the spacer 4 b. The cross section of fig. 10c shows a substantially solid supporting blade 4 a. In contrast, fig. 10d is a section taken along a different part of the supporting blade 4a at a location without the spacer 4b but with the channel 5, wherein said channel 5 passes through the supporting blade 4a so that water can flow under the supporting blade 4 a. Further details of this aspect of the invention can be found in fig. 10e-h, which show top, cross-sectional, and front views, respectively. The spacer 4b is preferably substantially circular to promote steady water flow through the channel 5, as shown in figure 10 e. The seats 4d are preferably uniformly distributed along the entire width 4 e. This configuration facilitates the mounting or replacement of the support blade 4a, preferably made in one piece, as shown in fig. 10 a-h.

In practice, another blade 11 may be installed immediately after the drain 10. The leading end of the second blade 11 can be seen in fig. 8. The number of blades required on the table is determined on the basis of the thickness T of the fibre stock 1, the pulp consistency, the basis weight, the dwell and the vehicle speed.

A variety of configurations may be used for different aspects of the invention, including:

1. as shown in fig. 11, a blade having a planar surface;

2. as shown in fig. 12, a blade having a step 15;

3. as shown in fig. 13, an alternate type blade having a step 15 and a planar surface;

4. as shown in fig. 14, a blade having an edge guide 16, said edge guide 16 being actually removed from the rest of the blade, its leading end being at an angle to the forming fabric and having a planar surface 12;

5. as shown in fig. 15, a blade with an edge guide 16, said edge guide 16 being actually removed from the rest of the blade, its leading end being at an angle to the forming fabric and having a step 15;

6. as shown in fig. 15a and 15b, a blade having an edge guide 16, said edge guide 16 being removed from the rest of the blade, having its leading end at an angle to the forming fabric and having an activated zone formed by the converging and diverging portions 12d, 12c, with or without a pivot point 22; or

7. As shown in fig. 15c and 15d, blades 24, 25 having elongated micro-active regions comprising a plurality of diverging and converging portions 12c, 12d, with or without pivot points 22.

Other scraper arrangements according to certain aspects of the invention may also be used within the scope of the invention.

The blades, as shown in figures 8, 9a, 10a and 10b, run a forming cycle in which the hydrodynamic processes required for sheet formation are carried out. At the leading end 3a, a positive pulse P1 is formed to produce a shearing effect. At the diverging surface 3b, water 7 is discharged from the paper or fibre stock 1 due to an increase in kinetic energy and a decrease in potential energy. This is the second hydrodynamic process on the blade. The support blade 4 then forms a second positive pulse P2 similar to P1. The drainage water 7 then passes continuously through the channel 5. A portion of the drained water is then reintroduced into the paper sheet 2 in the micro-activation zone 12 and the controlled turbulence zone 8. The drainage continues as the water leaves the blade through the drainage 10. Thus, within one forming cycle, three hydrodynamic processes take place in these regions of the blade.

Figure 10b shows a pivot point 22 which allows the trailing portion of the blade 23 to be adjusted as necessary according to the operating parameters of the device. Fig. 15c shows another aspect of the invention, with multiple cycles of diverging and diverging portions angled on a single long blade 25. These multiple cycles help to maintain the degree of activation of the initial portion of the screen. Figure 15d shows the same multi-cycle doctor blade 24 with a pivot point 22.

The thickness T of the pulp 1 has no influence on the operation performance of the support blade 4 or the vehicle speed. In fact, the size of the steps a and B of the first stage shown in fig. 25 is determined according to the slurry thickness and the vehicle speed. In this way, the performance of the apparatus can be optimized for a specific pulp thickness and vehicle speed, since the step a can be adjusted by adjusting the support blade 4.

As a result of the hydrodynamic processes carried out by the blade and the reintroduction of water in the initial part of the blade, the invention makes it possible to obtain the following improvements:

I. there is no filtration process in the initial part of the blade;

the power required to drive the wire is reduced because there is no drag of the wire on the blade since it is supported by water along its length;

no dirt build up on the blade as the water flow is continuous;

redispersion and activation of the fibres on the wire with the same water;

v. the retention of the fine fibers is increased and the fine fibers are uniformly distributed in the whole thickness of the paper;

vi, the forming process is improved;

and VII, if necessary, controlling the squareness of the paper.

VIII, the drainage is controlled, and the filtering process can be removed; and

IX. the physical properties of the paper sheet are improved or controlled as desired.

Figures 14 and 15 show another aspect of the invention in which the leading end 3 is separated from the body of the scraper. When drainage has been performed in the preceding elements without the need for water removal, or in the case of a limited space on the table, such a structure can be used in a paper machine, so that a large but controlled amount of water can be removed from the fibre pulp 1.

Fig. 16, 17, 18, 19, 20 and 20a show the hydraulic performance of a doctor blade according to certain aspects of the present invention. In fig. 16, in section 3a, a positive pulse P1 is formed to produce a shearing effect. The diverging portion 3b discharges the water 7 due to the increase of kinetic energy and the decrease of potential energy. This is the second hydrodynamic process of the scraper. The support blade 4 forms a second positive pulse P2 similar to P1. The drainage water 7 then passes continuously through the channel 5.

In fig. 17, the drainage 7 is performed by a chopping board 17 having a leading end 3a and a diverging portion 3b and located at the blade separating portion. The leading end 3a of the chopping board 17 again forms the positive pulse P1 and produces a shearing effect. The diverging surfaces 3b drain water 7 from the fiber slurry to promote activation, the water flow continuing through the channels 5. The backing blade 4 again forms a pulse P2 similar to P1 (alternating positive pulses, creating a shearing effect in the cross-machine direction).

Fig. 18, 19, 20 and 20a show the following hydrodynamic effects: the planar micro-activation region in fig. 18; the micro-active area with compensation planes in fig. 19; and fig. 20a micro-activation region with steps. In each of these figures, a portion of the drainage water 7 is reintroduced into the paper 1 in the micro-activation zone 12 and/or the controlled turbulence zone 8. Continuous drainage is also performed. As described above, shearing is generated at the leading end 3a, and the supporting blade 4 generates pulses P1 and P2. When water 7 is reintroduced into zone 8, redistribution of the fibers occurs, thereby creating activation in zone 8. If necessary, a slight shear is formed by the step 15 as shown in fig. 20. To enhance micro-activation of the micro-activation region 12, a compensation plane 12a may be employed as needed to retain additional water. The micro-activation region 12 includes offset portions 12a and 12 b. These compensating portions may be planar or angled. The final configuration of the compensating portions 12a and 12b is determined based on the slurry thickness and the vehicle speed. Typically, drainage is controlled at the rear of zones 12, 12a and 12 b.

Figure 20a shows a device that can be operated without additional vacuum. This can be done by using the diverging and converging portions 12c and 12d already discussed above. In use, the diverging portion 12d creates a vacuum through the angle of divergence, resulting in a loss of potential energy. The vacuum thus created then draws water out of the pulp. After which part of the water is reintroduced into the pulp by the radiolucent portion 12d and forms an activation of the pulp. However, most of the water is discharged from the drain region 10.

Another aspect of the invention is shown in fig. 21. The water 7 flowing through the channel 5 forms a flow line 19 in the area 21. As soon as the hydraulic cross-section of the flow channel of the water 7 is decreasing, the water 7 is pressed in and is guided through the forming wire 13 again and into the fibre pulp 1. The force of reintroducing the water 7 may cause the forming fabric 13 to flex. However, this is offset at least to some extent by the vacuum created by the increase in kinetic energy. In region 18, fiber activation and shearing occurs, resulting in improved formation of the fiber mat. Unlike some known paper production processes described above, the forming fabric 12 does not contact the surface of the micro-activation region 12 due to the continuous flow of water through the passage 5. As a result, the shearing and fiber activation in the paper sheet 1 are not interrupted.

In fig. 22, in order to retain a certain amount of water 7 for the micro-active area 12, there is a compensation plane containing portions 12a and 12 b. The portion 12b may be designed to have an angle of 0.1-10 degrees to control drainage. The preferred angle for portion 12b is 1-3 degrees.

A doctor blade that uses a step 15 to generate a high degree of turbulence is shown in fig. 23. The actual size of the step 15 is determined by the slurry thickness, slurry concentration and vehicle speed.

Figure 24 shows the streamlines 19 of water flow as the forming fabric passes over the step 15. It can be seen that the vortex is formed in the machine longitudinal direction and is induced along the entire width of the machine. When viewing a device having a machine direction as shown in fig. 24, the vortex is generally rotating in a clockwise direction. The water flow 7 becomes stable at the point of recombination. The size of the reverse flow zone depends on the vehicle speed, the step size and the amount of water on the step. The vortex generates a high turbulence, which creates a velocity difference between the fibre pulp and the vortex. This action disperses the short fibers of the fibers, thereby redistributing the fibers and improving sheet formation.

Another aspect of the invention relates to doctor blade geometry. In fig. 25, the area between the exit side of the supporting blade 4 and the edge guide of the subsequent blade 11 is where the shearing, activation and drainage (three hydrodynamic processes required to form the sheet) occur. Hydrodynamic shearing and activation occurs on side a of the blade and drainage occurs on side B of the blade. The first stage is from the outlet side of the supporting blade 4 to the edge of the step 15. The step a is dimensioned according to the amount of water coming from the preceding element and the amount of water discharged at this stage. In the first stage, water is reintroduced into the fibre pulp 1 and subjected to high-efficiency shearing. High activation is caused by turbulence at the step and the instantaneous speed difference between the water 7 and the forming fabric 13 from the start of the second stage up to the point of maximum wire deflection. Side a is the higher pressure side of the blade, so water always flows to side B of the blade, eventually resulting in drainage.

FIG. 26 provides a model for determining the dynamic pressure developed on a forming fabric, which can be calculated from the following equation:

wherein "m" is the degree of deflection in inches of the wire; "c" is the span of the wire in inches; "Vm" is the vehicle speed in feet per minute; and "K" is a constant with a value of 0.82864451984491991898 e-3.

The dynamic pressure developed on the forming fabric is proportional to the gravitational or centrifugal force to which the forming fabric is subjected, generally referred to as the 'g-force', and is generally in the range of 1-10, but preferably 3-5.

Those skilled in the art will recognize that other "K" values may be used to make this calculation without departing from the scope of the present invention, however, the values provided above have been determined to be preferred values.

Fig. 27 shows an enlarged view of the blade with the converging and diverging portions 12c and 12 d. Although shown here as having the same lengths C1 and C2, these lengths may be optimized for the production process as desired. Furthermore, the angles α and β to form the vacuum and to reintroduce water into the pulp, respectively, can be optimized.

Finally, fig. 28 generally shows a flow diagram of the water carried by the pulp as the wire 2 passes over the support blade 4 and through the diverging and converging portions 12c and 12 d. It can be seen that water is removed at several locations along the blade and reintroduced into the pulp.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (55)

1. A drainage device to drain liquid from pulp passing over the device on a fabric and reduce cross-machine direction sheet or mat mass variations, said device comprising:

a main blade having a leading end support surface adjacent the web to support the web, and a trailing end surface diverging downwardly from a trailing end of the leading end support surface, a channel being formed between the web and the trailing end surface;

wherein the channel directs liquid drained from the pulp to a controlled turbulence zone or a micro-activation zone formed between the main blade and the fabric,

wherein the drained liquid is partly or wholly reintroduced into the pulp.

2. The apparatus of claim 1, wherein the primary blade is flat.

3. The apparatus according to claim 1, wherein the primary scraper comprises one or more steps.

4. The apparatus of claim 1, wherein the primary blade comprises one or more diverging portions and one or more converging portions.

5. The apparatus of claim 1, wherein the primary blade comprises a combination of steps, diverging portions, and converging portions.

6. The apparatus according to claim 3, wherein the step is formed at a trailing end of the primary blade.

7. The apparatus according to claim 4, wherein the diverging and converging portions are formed at a trailing end of the main blade.

8. The device of claim 4, wherein the diverging portions are at an angle α to the horizontal and the converging portions are at an angle β to the horizontal.

9. The device according to claim 1, further comprising a support blade positioned between the web and the micro-activation region, wherein the support blade separates the web from the primary blade and forms the channel.

10. The device of claim 1, further comprising a drainage zone located after said micro-activation zone.

11. The apparatus of claim 1, wherein the primary blade is disposed about a pivot point.

12. The apparatus according to claim 1, wherein the primary blade comprises alternating stepped and planar surfaces.

13. The apparatus of claim 3, wherein the step is sized based on pulp thickness and vehicle speed of the apparatus.

14. The device according to claim 8, wherein the angle α and the angle β are 0.1 to 10 degrees.

15. The apparatus of claim 1, wherein the primary scraper further comprises a compensating portion to control the drainage of liquid.

16. The apparatus of claim 1, wherein the fluid pressure developed on the fabric is determined by:

wherein m is the degree of deflection of the fabric in inches;

c is the span of the fabric in inches;

vm-the speed of the device in feet per minute;

K＝0.82864451984491991898e-3。

17. the device according to claim 1, wherein the primary blade is elongated and forms a plurality of micro-activation regions.

18. The apparatus of claim 17, wherein the primary blade is disposed about a pivot point.

19. The apparatus of claim 1, wherein the pulp is a fiber slurry.

20. The device of claim 1, wherein the liquid is water.

21. A method of draining liquid from a pulp contained on a fabric of a paper making machine, the method comprising the steps of:

providing a drainage device comprising a main blade having a leading end support surface adjacent the web to support the web, and a trailing end surface diverging downwardly from a trailing end of the leading end support surface, a channel being formed between the web and the trailing end surface; and

liquid drained from the pulp is directed into a controlled turbulence zone or a micro-activation zone formed between the main blade and the fabric, so that at least part of the drained liquid can be forced through the fabric back into the pulp.

22. The method according to claim 21, further comprising the step of providing a support blade between the web and the micro-activation region, wherein the support blade separates the web from the primary blade and forms the channel.

23. The method of claim 22, wherein the support blade is secured with a washer and a bolt.

24. The method of claim 22, wherein the support blade is secured without shims and bolts to enable liquid flow through the channel.

25. The method according to claim 21, further comprising the step of creating a fluid pressure on said fabric determined by the formula:

wherein m is the degree of deflection of the fabric in inches;

c is the span of the fabric in inches;

vm-the speed of the device in feet per minute;

K＝0.82864451984491991898e-3。

26. an apparatus that can be used with a forming plate or a drainage system, the apparatus comprising:

a forming fabric upon which the fiber slurry is conveyed; the forming fabric having an outer surface and an inner surface; and

a primary blade having a planar leading end support surface parallel to and in sliding contact with the inner surface of the forming fabric and a trailing end surface inclined away from the leading end at an angle after the leading end, thereby conveying water discharged from the fiber slurry into a controlled turbulence or micro-activation zone formed below the forming fabric;

wherein the angle of the trailing end relative to the leading end is 0.1-10 degrees.

27. The apparatus according to claim 26, wherein the primary doctor blade includes a compensating flat to retain water for improved and controlled activation.

28. The apparatus according to claim 26, further comprising a support blade disposed between the fabric and the micro-activation zone, wherein the support blade separates the fabric from the main blade and forms a channel that directs water drained from the fiber slurry into the controlled turbulence zone or micro-activation zone.

29. The apparatus of claim 28, wherein the support blade enables water flow freely through the channel.

30. The apparatus according to claim 26, wherein the primary blade comprises one or more steps to create controlled turbulence.

31. The apparatus according to claim 26 wherein the leading end of the primary blade is at an angle to the forming fabric and has a planar surface.

32. The apparatus according to claim 26, wherein the leading end of the main blade is at an angle to the forming fabric and has an active zone formed by a converging portion and a diverging portion, with or without a pivot point.

33. The device according to claim 26, wherein the primary doctor blade is elongated and forms a plurality of micro-activation regions.

34. The apparatus of claim 26, wherein the primary blade comprises one or more diverging portions and one or more converging portions.

35. The apparatus of claim 28, wherein the support blade is positioned with shims and bolts that are evenly distributed across the apparatus so that the support blade does not shift from its original position.

36. The device according to claim 28, wherein the support blade is insertable into the body of the device in a single piece, thereby facilitating easy installation.

37. The apparatus according to claim 28, wherein the support blades have a substantially circular shape to promote steady water flow through the channel, the support blades being evenly distributed along the entire width of the apparatus.

38. The apparatus of claim 26, wherein the primary blade comprises a combination of steps, diverging portions, and converging portions.

39. The apparatus of claim 34, wherein the diverging portions are at an angle α to the horizontal and the converging portions are at an angle β to the horizontal.

40. The apparatus of claim 26, wherein the primary blade is disposed about a pivot point.

41. The apparatus according to claim 26, wherein the leading end is at an angle to the forming fabric and comprises a step.

42. The apparatus of claim 26, wherein said drained water is reused during at least a portion of the forming process to produce a desired hydrodynamic effect.

43. The apparatus according to claim 26, further comprising a table for generating fluid pressure for dewatering said fiber slurry, said fluid pressure being generated by vacuum.

44. The device of claim 34, wherein the diverging and converging portions are disposed about a pivot point.

45. The apparatus of claim 26, wherein the primary blade comprises alternating stepped and planar surfaces.

46. The apparatus of claim 30, wherein the step is sized based on the thickness of the fiber slurry and the vehicle speed of the system.

47. The apparatus according to claim 26, wherein the fluid pressure developed on said forming fabric is determined by the following equation:

wherein m is the degree of deflection in inches of the forming fabric;

c is the span of the forming fabric in inches;

vm is the machine speed in feet per minute;

K＝0.82864451984491991898e-3。

48. a method of maintaining one or more hydrodynamic processes associated with a papermaking process, the method comprising the steps of:

providing an apparatus comprising a main blade having a planar leading end support surface parallel to and in sliding contact with the inner surface of the forming fabric, and a trailing end surface inclined away from the leading end at an angle after the leading end, thereby directing water discharged from the fiber slurry into a controlled turbulence zone or a micro-activation zone formed below the forming fabric;

wherein the angle of the trailing end relative to the leading end is 0.1-10 degrees.

49. The process according to claim 48, further comprising the step of providing a support blade between said fabric and said micro-activation zone, wherein said support blade separates said fabric from said main blade and forms a channel that directs water drained from said fiber slurry into a controlled turbulence zone or micro-activation zone.

50. The method according to claim 48, wherein the leading end of the primary blade is at an angle to the forming fabric and has a planar surface.

51. The method according to claim 48, wherein the leading end of the main blade is at an angle to the forming fabric and has an active zone formed by a converging portion and a diverging portion, with or without a pivot point.

52. The method of claim 49, wherein the support blade is secured with shims and bolts that are evenly distributed across the device so that the support blade does not shift from its original position.

53. A method according to claim 49, wherein the support blade is insertable into the body of the device in a single piece, thereby facilitating easy installation.

54. The method according to claim 48, further comprising the step of providing a chopping board that generates a fluid pressure for dewatering said fiber slurry, the fluid pressure being generated by a vacuum.

55. A method as in claim 54, wherein the fluid pressure established on said forming fabric is determined by the formula:

wherein m is the degree of deflection in inches of the forming fabric;

c is the span of the forming fabric in inches;

vm is the machine speed in feet per minute;

K＝0.82864451984491991898e-3。