PRESSURIZED FORMING BOARD

Description

[0001] This invention is concerned with the initial formation of paper on machines of the type wherein an aqueous slurry known as the stock is deposited onto a continuous moving forming fabric.

[0002] In this type of machine, the stock which contains both fibers and other substances in an amount of from about 0.1% to about 1.5% by weight, is fed from a head box slice onto a moving forming fabric. Water is progressively drained from the stock through the forming fabric as it passes over various drainage elements until at the end of the forming section the stock contains some 2% to 4% by weight of solid material. At that point, the distribution and orientation of the fibers and other solids in the still very wet stock is largely determined, and will not change very much in the later paper making steps. Thus at the end of the forming section the formation of the paper is largely completed.

[0003] In outline, a conventional paper making machine forming section includes a forming fabric which is supported at the head box slice end by a breast roll, which is followed in sequence by a forming board, and thereafter by a sequence of drainage devices which complete the forming section. The nature and placement of these drainage devices varies considerably, and is determined at least in part by whether either a conventional open fabric forming section or a twin wire or gap former is being used.

[0004] It is well known that the jet of stock delivered onto the forming fabric from the head box slice is often far from uniform. In a uniform stock, all of the various components therein would be evenly and uniformly distributed throughout. Similarly, the jet of stock that exits the head box slice would also be of constant depth, constant linear velocity, and free from ripples and other disturbances across the full width of the head box slice. These ideals are rarely, if ever, achieved in practice. Within the stock itself, there is also significant point-to-point variation in the distribution of the various materials in the stock, in both a vertical and a horizontal direction. It is desirable that these imperfections in the stock should either be removed or at least controlled so that they get no worse, before they are set into the paper web as a consequence of water drainage from the stock in the forming section. A high and uncontrolled rate of drainage in the initial part of a forming section tends to set these stock imperfections into the formation of the paper. This effectively precludes any remedial action.

[0005] Calehuff, in United States Patent No. 3 066 068 proposes to improve the drainage of the stock through the forming fabric. It is proposed that in the Fourdrinier-type machine, suction and positive pressure are alternately applied to the incipient paper web on the forming fabric, by means of a series of sealed drainage chambers, alternately containing a "relatively high vacuum", of the order of 3'' to 12'' mercury (that is, from about 104 cm to about 415 cm water gauge), and a "substantially higher pressure", which is "slightly below atmospheric, atmospheric, or slightly above atmospheric, depending on operating conditions". According to Calehuff, rapid application of this level of suction and relaxation to about ambient pressure, will agitate the fibres and tend to break up lumps. However, it appears that the vacuum levels advocated by Calehuff are far too high, and cause the incipient web to form a sealed mat on the forming fabric. Rather than improving drainage, such a sealed mat restricts and hinders further drainage.

[0006] It has now been realized that if this very high rate of drainage in the initial part of the forming process could be curtailed, then an improvement in the overall paper making process will result. The remaining drainage elements in the forming section must of course be able to handle the increased drainage load that such a step will cause.

[0007] The concepts of this invention are equally applicable to both a twin wire machine, and to a conventional open-surface forming section, that is to improve stock formation in the region of the forming section immediately adjacent the head box slice.

[0008] Curtailing the drainage rate through a conventional design forming board would appear to be simple: all that is needed is to decrease the available drainage area, by widening the support surfaces, and/or moving them closer together. Experiment shows that this is not so and the drainage rate is not significantly reduced. Further, the paper web is marked severely with streaks, of uneven fibre weight across the width of the paper. In other words, such changes can cause significant deterioration in paper quality.

[0009] It has now been discovered that these difficulties can be overcome, and a much reduced rate of drainage obtained, by modifying the forming board in such a way that a low value of air pressure (above ambient atmospheric) can be applied to the machine side of the forming fabric. Additionally, means can be provided to induce some beneficial agitation within the stock on the new design of forming board.

[0010] Thus in a first embodiment this invention provides a paper making machine having a forming section including at least a continuous travelling forming fabric which passes over a breast roll adjacent a head box slice through which aqueous stock is deposited onto the forming fabric, and a foraminous forming board surface supported by a drainage box, which surface both supports the forming fabric and provides a pressure tight seal between the forming fabric and the drainage box; characterized in that

(a) the drainage box has attached thereto air supply means including a source of positive air pressure and air pressure control means, such that a positive air pressure above ambient atmospheric pressure sufficient to hinder water drainage from the stock through the foraminous forming board surface, but insufficient to interfere with stock formation on the forming fabric on the forming board surface, is maintained in the drainage box;

(b) the drainage box also includes a drainage means which contains the applied positive air pressure above ambient atmospheric pressure within the drainage box and permits the flow of the drained white water out of the drainage box;

(c) the foraminous board surface provides a path through which the forming fabric moves which induces a controlled level of uniformly spaced periodic harmonic agitation in the stock;
and

(d) the drainage box includes at least one compartment extending across the width of the forming fabric, which has separate air pressure control means and drainage means.

[0011] Preferably, the positive pressure will generally decrease from a high value adjacent the head box slice to a value approaching ambient atmospheric at the end of the forming board.

[0012] Preferably, the air supply means provides a positive pressure above ambient atmospheric of from about 0.1 kPa (1 cm water gauge) to about 2.5 kPa (25 cms water gauge).

[0013] The forming board surface preferably comprises a plurality of thin elongate blades extending across the full width of the forming fabric, so placed as to contribute toward controlled agitation of the stock on the forming fabric. More preferably, at least some of the thin elongate blades are provided with a top surface contour which will induce controlled agitation in the stock on the forming fabric.

[0014] In a second embodiment, the invention provides a method for improving stock formation in a paper making machine having a forming section including at least a continuous travelling forming fabric which passes over a breast roll adjacent a head box slice through which aqueous stock is deposited onto the forming fabric, a forming board surface adjacent the head box slice supported by a drainage box, which surface both supports the forming fabric and provides a pressure tight seal between the forming fabric and the drainage box; in which method an aqueous stock is discharged from the head box slice onto the moving forming fabric, characterized in that

(i) the forming fabric moves over a foraminous forming board surface having a pressurized drainage box including at least one chamber to which a controlled level of pressure is applied which is sufficient to hinder drainage from the stock on the forming fabric, but insufficient to interfere with the stock formation on the forming fabric; and

(ii) a desired level of uniformly spaced periodic harmonic agitation is induced in the stock on the forming fabric on the foraminous forming board.

[0015] Preferably, the air pressure is controlled to be from about 0.1 kPa (1 cm water gauge) above ambient atmospheric pressure to about 2.5 KPa (25 cms water gauge).

[0016] Preferably the desired level of agitation is caused and controlled within the stock by controlling the spacing of the support-surfaces comprising the forming board. More preferably, the desired level of agitation is caused within the stock by a support surface with a top surface contour which induces controlled agitation within the stock on the forming fabric.

[0017] Preferably, in each of these embodiments, the drainage box is either a single box divided into separate compartments by pressure tight transverse walls, or a plurality of contiguous separate boxes, to each of which a different level of pressure can be applied.

[0018] The invention will now be described in more detail by way of reference to a conventional open-surface forming section. It is to be understood that the invention is not so limited, and may be used with other paper making machines of the 2 wire, twin-wire, or gap former type. In the attached drawings:

Figure 1 shows diagrammatically the initial part of a paper making machine;

Figure 2 shows schematically one forming board of this invention;

Figure 3 shows several possible support surfaces of the forming board of Figure 2.

Figure 4 shows schematically an alternative forming board of this invention.

[0019] In these Figures, relevant like parts have been given the same numbers.

[0020] In Figure 1, the initial part of a paper making machine is shown, incorporating a forming fabric 1, which moves in the direction of the arrows shown at 1A and 1B. The forming fabric moves over a breast roll 2, and various tensioning and idling rollers 3. The stock is deposited onto the forming fabric 1 from the head box shown diagrammatically at 4, through a slice opening 5, which extends transversely across the forming fabric 1.

[0021] Adjacent the breast roll 2 and the head box slice 5 is a forming board followed by the first of the many drainage units which comprise the forming section, which in this case is shown as a foil unit 7, based on that originally described by Wrist in US 2,928,465.

[0022] The forming board unit 6 is provided with a plurality of support surfaces shown generally at 12, 13 and 14, of which that nearest the head box slice, 5, is generally wider, than the others. Each of these surfaces is mounted on a T-bar, as at 10. As shown, the drainage box 6 is merely left open at its bottom to provide gravity drainage.

[0023] In Figure 2 is shown one embodiment of the forming board of this invention. Two differences to the detail of the conventional forming board of Figure 1 are immediately apparent: the unit is now a closed box 20 with a pressurized air supply pipe 28, and the drain pipe 32 has an integral pressure leg, to contain the applied pressure. The forming board support surfaces again comprise a T-bar 10 onto which is mounted the elongate blade 17, which extends across the width of the forming fabric. At each side of the forming fabric sealing pieces (not shown)- are inserted between the blade units to seal the forming fabric effectively to the top surface of the drainage box. The shape of the top surface, and also their lateral spacing, will be discussed in more detail below.

[0024] The first blade 18 has to counter the impact of the jet of stock as it exits the slice 5 onto the forming fabric 1. Conventionally as shown in Figure 2, this first blade is usually much wider than the others, often being twice the width of the later ones. It has now been found that this need not be so, and a blade substantially the same width as the others can often be used. This first blade will also generally have a flat top surface. As is the case with all of the blades, it is mounted onto a conventional T-bar arrangement.

[0025] The placement and shape of the remaining blades 19 is important. It is now known that almost any surface used to support a forming fabric has an effect on the behaviour of the stock on the fabric. The characteristics of the surface can be chosen to produce agitation in the stock which can range from sufficient effectively to lift the stock bodily off the fabric ranging downwardly through visible macroscopic agitation to microscopic agitation which can only be observed by using careful photography and strobe light illumination (i.e., with a simple flat surfaced blade such as the first blade 18). Further, it is also now known that the placement of these blades along the forming fabric is important, particularly for static drainage devices. Although the hydraulic phenomena causing the agitation are not fully understood, it is nevertheless known that they exhibit harmonic characteristics. This concept can be usefully utilized in the forming board of this invention. As a first step, the blades 19 can be placed so that the microscopic agitation which they induce is harmonically spaced apart along the length of the forming board. It then follows that by controlling the amount of agitation imparted by any one blade, the overall level of stock agitation can be controlled.

[0026] The amount of agitation imparted by the blades is largely determined by the shape of the support surface. A simple flat blade generates some agitation in the microagitation range, which can be enough for some purposes. Generally speaking the blade used to provide microagitation in the stock will cause low or zero drainage. Suitable blade types are described by Johnson in US 3,874,998 and by Saad in US 4,420,370. These blades can be constructed using the now standard T-bar support concepts. This invention does not preclude the use of devices which cause some drainage as well as providing the desired amount of agitation.

[0027] Figures 3A and 3B show blades which agitate without draining, as described by Johnson, in U.S. 3,874,998. In each case, the blade 37 or 38 mounts on a T-bar 10. Referring first to Figure 3A, the blade 37 has a central depression 39, in its top surface, so that a cross-machine gap of a flat triangular shape, having a depth x, is created below the plane of the forming fabric. Alternatively, as shown in Figure 3B, this depression rather than being triangular, can be a shallow concave shape. In both cases, as is shown in Figure 3A, water enters this depression from the stock on the forming fabric 1, and re-enters the stock, as indicated by the arrows 40 in Figure 3A. Careful choice of the distances x, y₁, y₂ and z then controls the amount of agitation imparted to the stock. The amount of agitation that is needed at this early stage of paper formation is small, in the microagitation range mentioned earlier, and therefore it is possible that not all of the blades will have a depression at all, since, as is noted above, a flat-blade surface also causes some agitation.

[0028] Typical dimensions for a blade such as those shown in Figure 3A or Figure 3B when used to cause microagitation are:

(i) total width (i.e. y₁ + y₂ + z): 25 mm to 75 mm

(ii) flat surface width: generally y₁ and y₂ are equal, but are not necessarily so; the minimum for each is about 5 mm, with a minimum of 10 mm being preferred

(iii) the width, z, of the depression: 15 mm to 65 mm

(iv) the depth, x, of the depression: 0.25 mm to 2.5 mm, for both a triangular and a curved depression.

[0029] The preferred value for the depression width z is that it is about half the total width of the blade. This then leaves adequate leading and trailing flat portions (y₁ and y₂) to get a water seal with the fabric onto the blade in these areas. As the depth also affects the amount of agitation, a wider blade will not necessarily require a deeper depression. In many cases it is found that if the blade is widened then the depth, x, should not be changed, although the width z will increase, to maintain it at about half the total blade width. In selecting a blade for a given circumstance, some care is needed. The narrowest blade that gives adequate support should be used, which will mean that a forming board according to this invention usually will use more support blades than a conventional board. Further, all of the blades used can be of the same width. Similarly, the shallowest depression should be used that is needed to cause the desired amount of agitation. If the blade is made too wide, and the depression is made too deep, then the level of agitation can go far beyond the microagitation needed in this area of the forming fabric to a level where the forming fabric with the stock on it lifts clear of the blades. This is not conducive to the making of good paper. Although it is simpler to use a blade with a single depression, it is realized that in certain circumstances a wider blade with more than one depression might be desirable. If such a blade is used, then the central flat portion between the depressions should be about as wide as the leading and trailing flat surfaces.

[0030] In Figure 4 a preferred embodiment is shown. The drainage box shown generally at 6 is divided into a series of pressure tight smaller compartments 20, 21, 22, and 23, by transverse walls 24, 25 and 26. Four are shown, but this number is not crucial. Similarly, a series of separate boxes could also be used, with their side walls contiguous. Each of the compartments 20 through 23 extends across the full width of the forming fabric. In each case, a blade, as at 27, is placed over each of the transverse walls. Each of the compartments is provided with a pressurized air supply pipe 28, 29, 30 and 31, which incorporates a pressure control means (not shown), and also with a drainage leg 32, 33, 34 and 35, which includes suitable means to contain pressure in the compartment while also allowing free drainage. This arrangement permits a different marginal pressure above ambient to be applied to each of boxes 20, 21, 22 and 23.

[0031] In most cases, the applied pressure will decrease in a stepwise fashion from box 20, adjacent the head box slice, to box 23 to which a low pressure, or even none at all, is applied. It is also contemplated that situations might arise wherein such a progression is not desirable, and for example the highest pressure might be found desirable in box 21.

Claims

1. A paper making machine having a forming section including at least a continuous travelling forming fabric (1) which passes over a breast roll (2) adjacent a head box slice (5) through which aqueous stock is deposited onto the forming fabric, and a foraminous forming board surface (17,18,19) supported by a drainage box (6), which surface both supports the forming fabric and provides a pressure tight seal between the forming fabric and the drainage box;
characterized in that

(a) the drainage box has attached thereto air supply means (28,29) including a source of positive air pressure and air pressure control means, such that a positive air pressure above ambient atmospheric pressure sufficient to hinder water drainage from the stock through the foraminous forming board surface, but insufficient to interfere with stock formation on the forming fabric on the forming board surface, is maintained in the drainage box;

(b) the drainage box also includes a drainage means (32,33) which both contains the applied positive air pressure above ambient atmospheric pressure within the drainage box and permits the flow of the drained white water out of the drainage box;

(c) the foraminous forming board surface provides a path through which the forming fabric moves which induces a controlled level of uniformly spaced periodic harmonic agitation in the stock; and

(d) the drainage box (6) includes at least one compartment (20,21) extending across the width of the forming fabric, which has separate air pressure control means and drainage means (32,33).

2. An apparatus according to claim 1 characterized in that the forming board surface comprises a plurality of uniformly spaced thin elongate blades (17,18,19) extending across the full width of the forming fabric (1), together with sealing strips interposed between the ends thereof.

3. An apparatus according to claim 2 characterized in that the first elongate blade (18) adjacent the head box slice (5) is wider than the remainder.

4. An apparatus according to claim 2 characterized in that at least one of the elongate blades has a top surface contour (39,62) adapted to contribute toward agitation of the stock on the forming fabric.

5. An apparatus according to claim 4 characterized in that the top surface contour comprises a flat surface having a leading and a trailing portion in the direction of forming fabric movement separated by at least one shallow depression (39,62) extending along the blade for the width of the forming fabric, and wherein each of the leading and trailing portions, and any flat portions intermediate shallow depressions, are of sufficient width to provide a hydraulic seal to the machine side of the forming fabric, and the level of agitation is controlled by controlling the depth, or the shape, or both the depth and shape of the shallow depression.

6. An apparatus according to claim 1 characterized in that the drainage box (6) comprises either a single box extending from adjacent the head box slice (5) to the end of the forming board which is provided with a plurality of pressure tight transverse divisions (24,25,26) between each of which a separate controlled positive pressure can be applied and each of which has a separate drainage means (32,33,34,35), or a plurality of contiguously adjacent boxes (20,21,22,23) extending from adjacent the head box slice, to each of which a separate controlled positive pressure can be applied, and each of which has a separate drainage means (32,33,34,35).

7. An apparatus according to claim 2 characterized in that the drainage box (6) comprises either a single box extending from adjacent the head box slice (5) to the end of the forming board which is provided with a plurality of pressure tight transverse divisions (24,25,26) between each of which a separate controlled positive pressure can be applied, and each of which has a separate drainage means (32,33,34,35), or a plurality of contiguously adjacent boxes (20,21,22,23) extending from adjacent the head box slice (5) to each of which a separate controlled positive pressure can be applied and each of which has a separate drainage means (32,33,34,35), and in that an elongate blade (18,17,27) is placed above the first, the last, and any intermediate (24,25,26) transverse pressure tight divisions in the drainage box (6).

8. A method for improving stock formation in a paper making machine having a forming section including at least a continuous travelling forming fabric (1) which passes over a breast roll (2) adjacent a head box slice (5) through which aqueous stock is deposited onto the forming fabric, a forming board surface adjacent the head box slice supported by a drainage box (6), which surface both supports the forming fabric and provides a pressure tight seal between the forming fabric and the drainage box; in which method an aqueous stock is discharged from the head box slice onto the moving forming fabric, characterized in that

(i) the forming fabric moves over a foraminous forming board surface (17,18,19) having a pressurized drainage box (6) including at least one chamber (20) to which a controlled level of pressure is applied which is sufficient to hinder drainage from the stock on the forming fabric, but insufficient to interfere with stock formation on the forming fabric; and

(ii) a desired level of uniformly spaced periodic harmonic agitation is induced in the stock on the forming fabric on the foraminous forming board.

9. A method according to claim 8 characterized in that the foraminous surface provides a path through which the forming fabric moves which causes a controlled level of agitation in the stock.

10. A method according to claim 9 characterized in that the foraminous surface comprises a plurality of uniformly spaced thin elongate blades (17,18,19) extending across the full width of the forming fabric, together with sealing strips interposed between the ends thereof.

11. A method according to claim 10 characterized in that the drainage box (6) comprises either a single box extending from adjacent the head box slice to the end of the forming board which is provided with a plurality of pressure tight transverse divisions (24,25,26) between each of which a separate controlled positive air pressure can be applied and each of which has a separate drainage means (32,33,34,35) or a plurality of contiguously adjacent boxes (20,21,22,23) to each of which a separate controlled positive pressure can be applied and each of which has a separate drainage means (32,33,34,35), and wherein an elongate blade (17,18,27) is placed over the first, the last and any intermediate pressure tight transverse divisions in the drainage box.

Ansprüche

1. Papierherstellmaschine mit einem Formungsabschnitt, der mindestens ein kontinuierliches laufendes Siebtuch (1) enthält, das über eine Umlenk- oder Brustwalze (2) benachbart zu einem Auflaufkastenschlitz (5) läuft, durch welchen wäßrige Papiermasse auf das Siebtuch abgeschieden wird, und eine mit Öffnungen versehene Siebtischauflagefläche (17, 18, 19), die durch einen Entwässerungskasten (6) abgestützt ist, welche Flache sowohl das Siebtuch trägt als auch eine Druckabdichtung zwischen dem Siebtuch und dem Entwässerungskasten schafft;
dadurch gekennzeichnet, daß

(a) der Entwässerungskasten mit daran angebrachtem Luftzuführmittel (28, 29) versehen ist, das eine Quelle für Luft mit positivem Druck und ein Luftdruck-Steuermittel enthält, so daß ein über dem Umgebungs-Atmosphärendruck liegender positiver Luftdruck in dem Entwässerungskasten aufrecht erhalten wird, der ausreicht, den Wasserablauf von der Papiermasse durch die mit Öffnungen versehene Siebtischauflagefläche zu behindern, jedoch nicht dazu, die Papiermassenausbildung auf dem Siebtuch an der Siebtischauflagefläche zu behindern;

(b) der Entwässerungskasten auch ein Entwässerungsmittel (32, 33) enthält, das sowohl den über Umgebungs-Atmosphärendruck liegenden angelegten positiven Luftdruck in dem Entwässerungskasten aufrecht erhält als auch das Abfließen des ablaufenden Siebwassers aus dem Entwässerungskasten zuläßt;

(c) die mit Öffnungen versehene Siebtischauflagefläche einen Weg für die Bewegung des Siebtuchs schafft, der ein gesteuertes Ausmaß von mit gleichem Abstand auftretender periodischer harmonischer Bewegungsbildung in der Papiermasse induziert; und

(d) der Entwässerungskasten mindestens ein sich über die Breite des Siebtuchs erstreckendes Fach (20, 21) enthält, das separate Drucksteuermittel und Entwässerungsmittel (32, 33) besitzt.

2. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß die Auflagefläche umfaßt eine Vielzahl von mit gleichmäßigen Abständen versehenen dünnen länglichen Leisten (17, 18, 19), die sich, zusammen mit zwischen ihre Enden gesetzten Dichtstreifen, über die Gesamtbreite des Siebtuchs (1) erstrecken.

3. Vorrichtung nach Anspruch 2, dadurch gekennzeichnet, daß die erste dem Auflaufkastenschlitz (5) benachbarte längliche Leiste (18) breiter als die restlichen Leisten ist.

4. Vorrichtung nach Anspruch 2, dadurch gekennzeichnet, daß mindestens eine längliche Leiste eine Kontur an der oberen Fläche (39, 62) besitzt, die dazu ausgelegt ist, zu der Bewegungsbildung der Papiermasse an dem Siebtuch beizutragen.

5. Vorrichtung nach Anspruch 4, dadurch gekennzeichnet, daß die Oberflächenkontur einen ebenen Flächenteil umfaßt mit einem in Richtung der Bewegung des Siebtuchs vorderen und einem hinteren Abschnitt, welche Abschnitte getrennt sind durch mindestens eine flache Vertiefung (39, 62), die sich in Längsrichtung der Leiste über die Breite des Siebtuches erstreckt und bei der jeder vordere und hintere Abschnitt und etwaige ebene Abschnitte zwischen den flachen Vertiefungen von ausreichender Breite sind, um eine hydraulische Abdichtung der Maschinenseite des Siebtuches zu schaffen, und der Pegel der Bewegungsbildung gesteuert wird durch Steuern der Tiefe oder der Gestalt oder sowohl der Tiefe wie der Gestalt der flachen Vertiefung.

6. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß der Entwässerungskasten (6) entweder einen einzigen Kasten umfaßt, der von einer dem Auflaufkastenschlitz (5) benachbarten Stelle bis zum Ende der Auflagefläche reicht und mit einer Vielzahl von druckdichten Querteilungen (24, 25, 26) versehen ist, zwischen denen jeweils ein separater gesteuerter positiver Druck angelegt werden kann, und jeweils ein separates Entwässerungsmittel (32, 33, 34, 35) besitzt, oder eine Vielzahl von aneinanderstoßend benachbarten Kästen (20, 21, 22, 23), die sich von der Nachbarschaft zum Auflaufkastenschlitz erstrecken, und an die jeweils ein separater gesteuerter positiver Druck angelegt werden kann und von denen jeder ein separates Wasserablaufmittel (32, 33, 34, 35) besitzt.

7. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß der Entwässerungskasten (6) entweder einen einzelnen Kasten umfaßt, der von einer Stelle benachbart zum Auflaufkastenschlitz (5) bis zum Ende der Auflagefläche reicht und mit einer Vielzahl von druckdichten Querteilungen (24, 25, 26) versehen ist, zwischen denen jeweils ein separater gesteuerter positiver Druck angelegt werden kann, und jeweils ein separates Entwässerungsmittel (32, 33, 34, 35) besitzt, oder eine Vielzahl von aneinander anstoßend benachbarten Kasten (20, 21, 22, 23), die sich von der Nachbarschaft zum Auflaufkastenschlitz erstrecken, an die jeweils ein separater gesteuerter positiver Druck angelegt werden kann und von denen jedes ein separates Wasserablaufmittel (32, 33, 34, 35) besitzt, und daß je eine längliche Leiste (18, 17, 27) über die erste, die letzte und irgendwelche zwischenliegende quer verlaufende druckdichte Unterteilungen (24, 25, 26) in dem Entwässerungskasten (6) gesetzt ist.

8. Verfahren zur verbesserten Papiermassen-Ausbildung bei einer Papierherstell-Maschine mit einem Formungsabschnitt, der enthält mindestens ein kontinuierlich laufendes Siebtuch (1), das über eine Umlenk- oder Brustwalze (2) benachbart einem Auflaufkastenschlitz (5) läuft, durch welchen wäßrige Papiermasse auf dem Siebtuch abgeschieden wird, eine dem Auflaufkastenschlitz benachbarte, durch einen Entwässerungskasten (6) abgestützte Siebtischauflagefläche, welche Fläche sowohl das Siebtuch abstützt, als auch eine Druckabdichtung zwischen dem Siebtuch und dem Entwässerungskasten schafft; bei welchem Verfahren eine wäßrige Papiermasse von dem Auflaufkastenschlitz auf das sich bewegende Siebtuch entlassen wird, dadurch gekennzeichnet, daß

(i) das Siebtuch über eine mit Öffnungen versehene Siebtischauflagefläche (17, 18, 19) bewegt wird mit einem unter Druck stehenden Entwässerungskasten (6), der mindestens eine Kammer (20) enthält, an die ein gesteuertes Druckniveau angelegt wird, das ausreicht, die Entwässerung von der Papiermasse an dem Siebtuch zu behindern, jedoch nicht dazu, die Papierstoffausbildung an dem Siebtuch zu stören; und

(ii) ein gewünschtes Niveau von mit gleichförmigem Abstand aufgebrachter periodischer harmonischer Bewegungsbildung in die Papiermasse an dem Siebtuch an der mit Öffnungen versehenen Siebtischauflagefläche induziert wird.

9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, daß die mit Öffnungen versehene Fläche einen Weg für die Bewegung des Siebtuches schafft, der ein gesteuertes Bewegungsbildungs-Niveau in der Papiermasse verursacht.

10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, daß die mit Öffnungen versehen Fläche umfaßt eine Vielzahl von mit gleichmäßigem Abstand angebrachten dünnen länglichen Leisten (17, 18, 19), die sich zusammen mit zwischen deren Enden eingesetzten Dichtstreifen über die volle Breite des Siebtuchs erstrecken.

11. Verfahren nach Anspruch 10, dadurch gekennzeichnet, daß der Entwässerungskasten (6) umfaßt entweder einen einzigen Kasten, der sich von der Nachbarschaft zum Auflaufkastenschlitz bis zum Ende der Siebtischauflage erstreckt, mit einer Vielzahl von druckdichten Querunterteilungen (24, 25, 26) versehen ist, zwischen denen jeweils ein separater gesteuerter positiver Luftdruck angelegt werden kann und von denen jedes ein separates Entwässerungsmittel (32, 33, 34, 35) besitzt, oder eine Vielzahl von aneinander anstoßend benachbarten Kästen (20, 21, 22, 23), an die jeweils ein separater gesteuerter positiver Druck angelegt werden kann, und von denen jeder ein separates Entwässerungsmittel (32, 33, 34, 35) besitzt, und wobei eine längliche Leiste (17, 18, 27) über die erste, die letzte und irgendwelche dazwischen befindliche druckdichte Querteilungen in dem Entwässerungskasten gesetzt ist.

Revendications

1. Machine de fabrication de papier comportant une section de formage qui comprend au moins un tissu de formage (1) en déplacement continu qui passe au-dessus d'un rouleau de tête (2) adjacent à une règle (5) de bâche d'alimentation à travers laquelle de la pulpe aqueuse est déposée sur le tissu de formage, et comprenant une surface de plaque de formage poreuse (17, 18, 19) supportée par une boîte de drainage (6), laquelle surface supporte le tissu de formage et assure un joint étanche à la pression entre le tissu de formage et la boîte de drainage, caractérisée en ce que

(a) des moyens d'alimentation d'air (28, 29) sont attachés à la boîte de drainage, comprenant une source de pression d'air positive et des moyens de commande de la pression d'air, de manière à maintenir dans la boîte de drainage une pression d'air positive au-dessus de la pression atmosphérique ambiante et suffisante pour empêcher le drainage de l'eau depuis la pulpe à travers la surface de plaque de formage poreuse, mais insuffisante pour interférer avec la formation de la pulpe sur le tissu de formage sur la surface de la plaque de formage;

(b) la boîte de drainage comprend également des moyens de drainage (32, 33) qui confinent la pression d'air positive appliquée au-dessus de la pression atmosphérique ambiante à l'intérieur de la boîte de drainage et permettent l'écoulement des eaux blanches drainées hors de la boîte de drainage;

(c) la surface de plaque de formage poreuse procure un trajet à travers lequel se déplace le tissu de formage et qui induit un niveau contrôlé d'agitation harmonique périodique à intervalles uniformes dans la pulpe; et

(d) la boîte de drainage (6) comprend au moins un compartiment (20, 21) qui s'étend à travers la largeur du tissu de formage, et qui comprend des moyens séparés pour la commande de la pression d'air, et des moyens de drainage (32, 33).

2. Appareil selon la revendication 1, caractérisé en ce que la surface de plaque de formage comprend une pluralité de lames allongées minces (17, 18, 19) uniformément espacées et s'étendant à travers la totalité de la largeur du tissu de formage (1), ensemble avec des bandes d'étanchéité interposées entre les extrémités de celles-ci.

3. Appareil selon la revendication 2, caractérisé en ce que la première lame allongée (18) adjacente à la règle (5) de la bâche d'alimentation est plus large que les autres.

4. Appareil selon la revendication 2, caractérisé en ce que l'une au moins des lames allongées présente au niveau de sa surface supérieure un contour (39, 62) adapté à contribuer à l'agitation de la pulpe sur le tissu de formage.

5. Appareil selon la revendication 4, caractérisé en ce que le contour de la surface au sommet comprend une surface plane ayant une partie d'attaque et une partie de queue dans la direction du mouvement du tissu de formage, séparées par au moins une dépression de faible profondeur (39, 62) qui s'étend le long de la lame sur la largeur du tissu de formage, et en ce que chacune des parties d'attaque et de queue et toutes les parties planes éventuelles situées entre les dépressions, ont une largeur suffisante pour réaliser un joint hydraulique du côté de la machine pour le tissu de formage, et le niveau d'agitation est commandé en commandant la profondeur ou la forme ou à la fois la profondeur et la forme de la dépression.

6. Appareil selon la revendication 1, caractérisé en ce que la boîte de drainage (6) comprend soit une boîte unique qui s'étend depuis le voisinage de la règle (5) de la bâche d'alimentation jusqu'à l'extrémité de la plaque de formage, et qui est pourvue d'une pluralité de divisions transversales étanches à la pression (24, 25, 26), entre chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35), soit une pluralité de boîtes adjacentes et contiguës (20, 21, 22, 23) s'étendant depuis le voisinage de la règle de la bâche d'alimentation, à chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35).

7. Appareil selon la revendication 2, caractérisé en ce que la boîte de drainage (6) comprend soit une boîte unique qui s'étend depuis le voisinage de la règle (5) de la bâche d'alimentation jusqu'à l'extrémité de la plaque de formage, et qui est pourvue d'une pluralité de divisions transversales étanches à la pression (24, 25, 26), entre chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35) soit une pluralité de boîtes adjacentes et contiguës (20, 21, 22, 23) s'étendant depuis le voisinage de la règle (5) de la bâche d'alimentation, à chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35), et en ce qu'une lame allongée (18, 17, 27) est placée au-dessus de la première, de la dernière et de toutes les divisions transversales intermédiaires (24, 25, 26) étanches à la pression dans la boîte de drainage (6).

8. Procédé pour améliorer la formation de la pulpe dans une machine de fabrication de papier qui comporte une section de formage comprenant au moins un tissu de formage (1) en déplacement continu qui passe au-dessus d'un rouleau de tête (2) adjacent à une règle (5) de bâche d'alimentation, à travers laquelle de la pulpe aqueuse est déposée sur le tissu de formage, une surface de plaque de formage adjacente à la règle de la bâche d'alimentation supportée par une boîte de drainage (6), laquelle surface supporte le tissu de formage et procure un joint étanche à la pression entre le tissu de formage et la boîte de drainage, procédé dans lequel on décharge une pulpe aqueuse depuis la règle de la bâche d'alimentation sur le tissu de formage en déplacement, caractérisé en ce que

(i) le tissu de formage se déplace au-dessus d'une surface de plaque de formage poreuse (17, 18, 19) qui comprend une boîte de drainage sous pression (6) qui inclut au moins une chambre (20) à laquelle est appliqué un niveau commandé de pression qui est suffisant pour empêcher le drainage depuis la pulpe sur le tissu de formage, mais qui est insuffisant pour interférer avec la formation de la pulpe sur le tissu de formage; et

(ii) un niveau désiré d'agitation harmonique périodique à intervalles uniformes est induit dans la pulpe sur le tissu de formage sur la plaque de formage poreuse.

9. Procédé selon la revendication 8, caractérisé en ce que la surface poreuse réalise un trajet le duquel se déplace le tissu de formage et qui provoque un niveau contrôlé d'agitation dans la pulpe.

10. Procédé selon la revendication 9, caractérisé en ce que la surface poreuse comprend une pluralité de lames allongées minces uniformément espacées (17, 18, 19) s'étendant à travers la totalité de la largeur du tissu de formage, ensemble avec des bandes d'étanchéité interposées entre les extrémités des lames.

11. Procédé selon la revendication 10, caractérisé en ce que la boîte de drainage (6) comprend soit une boîte unique qui s'étend depuis le voisinage de la règle de la bâche d'alimentation jusqu'à l'extrémité de la plaque de formage, et qui est pourvue d'une pluralité de divisions transversales étanches à la pression (24, 25, 26), entre chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35) soit une pluralité de boîtes adjacentes et contiguës (20, 21, 22, 23), à chacune desquelles peut être appliquée une pression positive commandée séparément, et ayant chacune des moyens de drainage séparés (32, 33, 34, 35), et en ce qu'une lame allongée (18, 17, 27) est placée au-dessus de la première, de la dernière et de toutes les divisions transversales intermédiaires étanches à la pression dans la boîte de drainage.

Drawing