EP1702104B1 - Method for grinding water-suspended paper fibers or cellulose fibers - Google Patents

Abstract

The method is used for refining a paper fiber suspension (S). This is refined chiefly by compressive forces between two refining surfaces ( 1, 2 ) that lie on refiner tools pressed against one another, since the refiner tools in the refining zone do not move or move very little relative to one another. The refining surfaces ( 1, 2 ) are embodied to be porous so that they can temporarily absorb or discharge part of the water (W) of the paper fiber suspension (S). An arrangement with central refiner cylinder ( 3 ) and refiner rolls ( 4 ) arranged on the periphery is particularly suitable as a device for carrying out the method. The refining surfaces can be embodied cylindrically or they can be provided with a toothing.

Description

The invention relates to a process for pulp treatment according to the preamble of claim 1.

It has been known for a long time that pulp fibers must be ground so that the paper produced therefrom has the desired properties, in particular strength, formation and surface. By far the most widely used grinding methods use grinding surfaces provided with strips called knives, which are moved past each other at high speed. The corresponding machines are usually called knife refiner. For special cases, grinding processes are also used in which at least one of the grinding surfaces is not kneaded, so that the grinding work is transmitted by friction or shearing forces.

The effect of the method can be controlled by changing the grinding parameters in a wide range, wherein in addition to the amount of grinding in particular also distinguishes whether a more cutting or more fibrillating grinding is desired. When pulp fibers are milled, their drainage resistance generally increases with increasing milling. A common measure of the drainage resistance is the degree of grinding according to Schopper-Riegler.

The increase in the freeness has an unfavorable effect on sheet formation on the paper machine, but is tolerated, since the already mentioned quality characteristics of the pulp play a paramount role for its applicability. In many cases, the grinding parameters are selected so that the degree of freeness which has occurred in order to achieve the required fiber quality is as low as possible. This influence is very limited. In addition, the grinding can be economically unfavorable.

From the US 4,685,623 is a grinding process is known, which is to get by with less energy. The paper fiber suspension to be ground is guided into narrow wedge gaps ("narrow nips") which form between a rotating central roller and a plurality of rollers rolling on the outside thereof. The Wedge gaps are very narrow because the central roll is provided with a plurality of circumferential grooves or grooves. The outer rollers are pressed with a defined force against the central roller, so that occurs in the wedge gap dewatering and squeezing of the fibers. In this case, a portion of the suspension and the wracked in the wedge gaps water is transverse to the direction of movement and passed in these grooves on the actual wedge gap, to be later mixed again with the already ground thickened pulp. In this way, problems in the operation of such a machine are to be avoided even with a larger throughput. In operation, the housing of this apparatus is filled with suspension, which is pumped through with an adjustable volume flow.

In order to hold the fibers in the wedge gaps during grinding, it is required in the US specification that the width of the wedge gaps is smaller than the fiber length. However, this means a high expenditure on equipment in an industrial grinding machine.

The invention is based on the object to provide a method for pulp treatment, with which it is possible to change pulp or paper fibers so that the strength of the paper produced therefrom are increased. The occurring increase in the drainage resistance should be as low as possible in known grinding processes. The method should be suitable for industrial grinding machines.

This object is achieved by the features mentioned in claim 1.

The grinding process works predominantly by compressive forces and avoids large relative movements of the grinding tools. As will be explained later, substantial fiber technological advantages can be achieved with the aid of such a milling process.

Unlike the conventional knife refiner with high relative speed between the grinding tools, which lead to the cutting and / or shear stress of the fibers, the grinding tools are not or only very little relative to each other moves in the grinding process considered here. The actual milling stress is therefore due to compressive forces. However, it has proved in many cases to be problematic to apply milling processes of this kind on an industrial scale. Namely, in the production of paper or paper-like products constantly very large amounts of pulp are made available for the paper machine. If at least part of the pulp used for papermaking (it may also be the entire pulp) are ground according to the new method, the machines must be designed for a considerable amount of production. The method according to the invention can help to limit the size of the machine, since the effectiveness of the fiber treatment in the grinding zone can be substantially increased for the reasons mentioned.

The pressure forces in the grinding zone can be used for dewatering the paper fiber. In the method according to the invention, this primarily results in the water being either taken up by the porous grinding surface for a short time and later released again, or that water can flow off into other regions of the grinding device through the porous grinding surface. The new method has several advantages:

First, the compressive force is transmitted to the fiber less damped and therefore used more to their technological change. In addition, the fiber is fixed on the grinding surface, i. it is prevented from leaving the milling zone untreated. This effect occurs essentially independently of the fiber length. In addition, with the same volume more fibers can get into the milling zone, since the seeped water is missing. As a result, the size of the grinding machine used can be reduced accordingly. In addition, the fiber applies under considerable pressure to a provided with many small bumps surface, which can affect the grinding low.

In typical applications, the grinding surfaces are on grinding tools that perform a rotational movement, in such a way that the liquid picked up in the grinding zone of the pores is thrown off again after leaving the grinding zone. In particular, in the case of open-pore material layers whose pores are not only connected to the grinding surface but also to other surfaces, the picking up of liquid and the centrifuging of the liquid can be carried out particularly effectively.

Particularly suitable materials for producing a porous grinding surface for carrying out the method are hard metals, chrome steel, plastics (eg polyethylene, GRP), ceramics or copper alloys. These materials can be sintered. As you know, but also from Composite materials targeted open-porous workpieces are produced, which are suitable for the application considered here. The pore size can be individually adjusted according to requirements between 5 μm and 0.5 mm.

• 1. Die Faserlänge bleibt wesentlich besser erhalten.
• 2. Die Faseroberfläche wird nicht oder bedeutend weniger fibrilliert
• 3. Die spezifische Mahlarbeit zur Erreichung der gewünschten Festigkeiten ist im Allgemeinen geringer.

The grinding technology advantages of the method are as follows:

• 1. The fiber length is much better preserved.
• 2. The fiber surface is not or significantly less fibrillated
• 3. The specific grinding work to achieve the desired strengths is generally lower.

Comparative tests with long-fiber pulp have shown that in order to achieve a breaking length of 8 km, 45 ° SR grinding was produced by knife grinding and only 18 ° SR with the new method. The required specific grinding work was up to 50% lower.

It is believed that the new refining process alters the surface of the fibers to provide improved flexibility and bondability without the need to remove fibrils from the outer surface of the fibers. The production of fines, so fiber fragments, is avoided.

If the process is applied to recycled fibers, the advantages mentioned can play a special role. Recycled fibers already have at least one, often even several grinding operations behind them, so that any further comminution is gladly avoided.

Fig. 1

Detailansicht einer Mahlzone mit leistenförmigen Mahlflächen zur Erläuterung des Verfahrens;

Fig. 2

eine Variante mit zylindrischen Mahlflächen;

Fig. 3

Teil einer speziellen Mahlvorrichtung;

Fig. 4

eine Mahlvorrichtung mit zentralem Mahlzylinder und peripher angeordneten Mahlwalzen;

Fig. 5

eine Mahlvorrichtung, bei der die poröse Schicht des Mahlzylinders mit rückseitigen Kammern versehen ist.

The invention and its advantages will be explained with reference to drawings. Showing:

Fig. 1

Detail view of a grinding zone with strip-shaped grinding surfaces to explain the process;

Fig. 2

a variant with cylindrical grinding surfaces;

Fig. 3

Part of a special grinding device;

Fig. 4

a grinding device with central grinding cylinder and peripherally arranged grinding rollers;

Fig. 5

a grinding apparatus in which the porous layer of the grinding cylinder is provided with back chambers.

A particularly suitable apparatus for carrying out the method may comprise a rotating grinding cylinder 3, to which a number of grinding rollers 4 is pressed from the outside. The grinding surfaces 1 and 2 are located on them. The pressing force influences the grinding action and can therefore preferably be adjusted. Fig. 1 shows a part of such a grinding device, in particular the point at which arises by the interaction of grinding cylinder 3 and grinding roller 4, a grinding zone. In the example shown, both grinding cylinder and grinding roller are provided with grinding bars 5 and 6, of which only a part is shown. They extend substantially perpendicular to the direction of movement of the grinding tools and are distributed uniformly over the circumference. The Mahlleisten are dimensioned and arranged so that in the grinding zone, the grinding bar 5 of a grinding tool extends into the spaces between the Mahlleisten 6 of the other grinding tool, whereby there reduces the volume between them and in the suspension therein S (indicated by an arrow ) a considerable pressure is built up. Both the grinding strips and the associated cylindrical outer layer of the corresponding grinding tool are made here of porous material. Under certain circumstances, it is sufficient to produce only the Mahlleisten of porous material and to attach to the grinding cylinder or on the grinding roller.

As already described, the water in the grinding zone under increased pressure of the pulp suspension can penetrate into the pores of the grinding surface, whereby the pulp itself is thickened. After passing through the grinding zone, the volume lying between the grinding tools increases again, and the water W (indicated by an arrow) can escape from the pores again. This effect is strongly supported by the fact that both grinding surfaces rotate, so that a centrifugal force acting perpendicular to the grinding surface is generated. Since the Mahlleisten form a toothing, within the grinding zone, the relative speed of the two grinding tools to each other low, which shearing movements and acting on the fibers shear forces are largely avoided. The toothing also has a grinding technology effect, which is that the pressure forces acting on the fibers occur pulsating, which is in many cases required by grinding technology. Another application is shown in Fig. 2 with cylindrical grinding surfaces, ie those that are not provided with strips and roll to perform the process without slip or with little slip together. It can be seen in this illustration that the grinding cylinder 1 'is provided with a porous layer 8' and the grinding rollers 4 'with a porous material layer 7'. In another embodiment, not shown, it may also be sufficient that only one of the two grinding tools, which together form a grinding zone, has a porous grinding surface. This applies both to cylindrical grinding surfaces (see Fig. 2) and to strip-shaped (see Fig. 1).

The advantages offered by the method according to the invention are particularly effective when the grinding device is not completely filled with suspension during operation. This principle is explained by way of example in FIG. In turn, one recognizes a grinding cylinder 3, to which a plurality of toothed grinding rollers 4 are pressed, two of which are shown here. The grinding surfaces are porous. Since the housing of the grinding device is filled only to a small extent with suspension, the suspension S is thrown off centrifugal forces from the interdental spaces 20 into free space after leaving the grinding zone and reaches the next grinding roller. In free space, the liquid has a much higher density than the surrounding air. The water, which was pressed into the pores when passing through the grinding zone due to the porosity of the grinding surfaces, can now also be thrown out and reach the next grinding zone. Fig. 3 also shows that the mill bars may be in the form of involute gearing, which optimizes the rolling conditions in the milling zone, but is somewhat more expensive to produce than e.g. the Mahlleisten shown in Fig. 1. The grinding rollers 4 rotate here in a fixed slide 11. The grinding cylinder 3 has at the axial end faces annular circumferential shoulders 12 which axially seal the volume formed between the grinding bars 5, 6 in the grinding zone.

The grinding device shown in Fig. 4 for carrying out the method is shown only schematically. One recognizes a horizontal grinding cylinder 3, on which a plurality of predominantly uniformly distributed over the circumference arranged grinding rollers 4 are located, wherein in the region of the material outflow 13 a gap 9 is left without grinding roller. The suspension S is added through an inlet 14. This can be done over a wide nip or over a headbox, similar to that one knows from paper machines. The addition point is located next to the material drain 13 and is separated by a guide plate 15 of this. Thus, forced delivery is ensured over almost 360 ° over the entire circumferential course of the housing 16. The suspension flow through this grinding device is defined and can be adjusted easily and safely. The housing is preferably not completely included for the reasons already mentioned Filled suspension. However, a suspension level can form on the material outlet 13. The housing 10 can - as drawn here - inside cylindrical or be provided in accordance with FIG. 3 with a link 11 in which the grinding rollers rotate with a small gap distance.

It is readily possible to produce porous layers in which the capillary cavities are interconnected. The dewatering effect can be decisively improved if the water pressed into the pores is removed again after leaving the grinding zone. For this, e.g. Centrifugal forces are used. The water is then not such. For filter elements constantly pressed in one direction through the pores. Rather, the pores serve as storage volume with a flow reversal, which immediately rinses away the adhering or possibly penetrated fines.

It is easy to see that the drainage effect of the porous grinding surface can be particularly effective if it is possible to keep the pores free of blockages. In order to avoid any difficulties in this regard, it may be expedient to provide a chamber on the back of the porous layer (ie, the side of the layer opposite the grinding surface). This can be fed in case of need with pressurized water. Eventually, the water is mixed with suitable cleaning chemicals. An easy way of realizing such a chamber 17 is shown in Fig. 5 by the example of a grinding cylinder 3 "peripherally surrounded by grinding rollers 4 '. and the cylinder body of the grinding cylinder 3 "spacer strips 18 are mounted, between which the volumes of the chambers 17 remain free. The rinse water is added through lines 19.

In a further embodiment of the method, the chamber 17 shown in FIG. 5 and the lines 19 connected thereto can be used to remove water penetrated through the pores of the material layer 8 '. It is also a temporal sequence of drainage and - in case of need - flushing conceivable.

Of course, this embodiment shown here on cylindrical grinding surfaces with chambers 17 can also be used on other grinding surface shapes.

Claims (34)

1. Method for beating aqueously suspended paper fibres or pulp fibres, in which method the fibrous substance is guided through at least one beating zone which is situated between beating faces (1, 2),
   in which method the beating faces (1, 2) are situated on beating tools which are pressed against one another, as a result of which mechanical beating work is transmitted to the fibres in such a way that the strengths of the paper which is produced as a result are changed, with the beating faces (1, 2) being moved relative to one another in such a way that the relative speed between the fibrous substance and the beating faces, as viewed in the main direction of motion of the beating faces, at the point at which two beating faces (1, 2) in the beating zone are closest to one another, is at most 10% of the absolute speed of the beating face which is moved most quickly,
   characterized
   in that at least one of the beating faces (1, 2) which interact in the beating zone is porous.
2. Method according to Claim 1,
   characterized
   in that both of the beating faces (1, 2) which interact in the beating zone are porous.
3. Method according to Claim 1 or 2,
   characterized
   in that the porous beating face (1, 2) is formed by at least one material layer (7, 7', 8, 8') which is open-pored towards the beating face (1, 2).
4. Method according to Claim 3,
   characterized
   in that the material layer (7, 7', 8, 8') is composed of sintered material.
5. Method according to Claim 4,
   characterized
   in that the material layer (7, 7', 8, 8') is composed predominantly of chrome steel.
6. Method according to Claim 4,
   characterized
   in that the material layer (7, 7', 8, 8') is composed predominantly of hard metal.
7. Method according to Claim 4,
   characterized
   in that the material layer (7, 7', 8, 8') is composed predominantly of a copper alloy.
8. Method according to Claim 4,
   characterized
   in that the material layer (7, 7', 8, 8') is composed predominantly of ceramic.
9. Method according to Claim 4,
   characterized
   in that the material layer (7, 7', 8, 8') is composed predominantly of plastic.
10. Method according to one of Claims 3 to 9,
    characterized
    in that the layer thickness of the material layer (7, 7', 8, 8') is at least 1 mm and at most 30 mm, preferably 10 - 20 mm.
11. Method according to one of the preceding claims,
    characterized
    in that the mean pore width of the porous beating face (1, 2) is less than 0.5 mm.
12. Method according to one of the preceding claims,
    characterized
    in that the relative speed between the fibrous substance and the beating faces, as viewed in the main direction of motion of the beating faces (1, 2), at the point at which two beating faces (1, 2) in the beating zone are closest to one another, is less than 5% of the absolute speed of the beating face (1, 2) which is moved most quickly.
13. Method according to one of Claims 1 to 11,
    characterized
    in that the relative movement of the beating faces (1, 2) in the beating zone is a rolling movement.
14. Method according to one of the preceding claims,
    characterized
    in that the mechanical beating work is transmitted by compression of the fibrous substance.
15. Method according to one of the preceding claims,
    characterized
    in that at least one beating face (1, 2) is provided with beating strips (5, 5', 6, 6') which run transversely with respect to the main direction of motion of the moved beating face.
16. Method according to Claim 15,
    characterized
    in that the beating strips (5, 5', 6, 6') have a height of at least 2 mm and a width, in the direction of motion of the moved beating faces, of at least 2 mm.
17. Method according to Claim 15 or 16,
    characterized
    in that both beating faces (1, 2) are provided with transversely-running beating strips (5, 5', 6, 6').
18. Method according to one of the preceding claims,
    characterized
    in that the absolute speed of at least one beating face (1, 2) is held at a value of between 5 and 30 m/sec.
19. Method according to one of the preceding claims,
    characterized
    in that the beating faces (1, 2) are pressed against one another in such a way that a linear force of between 2 and 10 N/mm is generated in the beating zone.
20. Method according to one of the preceding claims,
    characterized
    in that at least one of the beating tools has, on the beating face (1, 2), spaces, in particular tooth spaces (20), which are moved in the beating zone in such a way that they transport the suspension (S) through the beating zone in the direction of motion of the beating tools.
21. Method according to Claim 20,
    characterized
    in that the spaces are emptied of the fibres outside the beating zone.
22. Method according to Claim 21,
    characterized
    in that the emptying of the spaces takes place by means of centrifugal forces.
23. Method according to Claim 20, 21 or 22,
    characterized
    in that one of the beating tools is a beating cylinder (3, 3', 3"), and in that the other beating tools are beating rollers (4, 4') which are arranged parallel to said beating cylinder (3, 3', 3") and which, at the peripheral face of the beating cylinder (3, 3'), are set in a rolling motion.
24. Method according to Claim 23,
    characterized
    in that the beating cylinder (3, 3', 3") is driven, and in that the beating rollers (4, 4') rotate about spatially fixed axes.
25. Method according to Claim 23 or 24,
    characterized
    in that the beating cylinder (3', 3") is provided with a cylindrical porous surface, and in that the spaces are situated on the periphery of the beating roller.
26. Method according to one of Claims 23 to 25,
    characterized
    in that the beating cylinder (3, 3', 3'') and beating rollers (4, 4') lie substantially horizontally, and in that the direction of the suspension transport through the beating device which is used is substantially that of the peripheral direction of the beating cylinder.
27. Method according to one of the preceding claims,
    characterized
    in that the pressure forces for beating the paper or pulp fibres are transmitted to faces at which the beating tools roll on one another.
28. Method according to one of Claims 23 to 27,
    characterized
    in that the diameter of the beating cylinder (3, 3', 3'') is at least 1.5 times, preferably double the diameter of the beating roller (4, 4').
29. Method according to Claim 28,
    characterized
    in that the beating rollers are arranged, at the periphery of the beating cylinder (3, 3', 3''), closely adjacent to one another such that as many beating zones as possible are formed on one beating cylinder.
30. Method according to one of the preceding claims,
    characterized
    in that the beating is carried out on a suspension which is guided continuously through the beating device which is used.
31. Method according to one of the preceding claims,
    characterized
    in that the aqueous suspension is supplied into the beating device which is used with a consistency of 1 - 6 %.
32. Method according to one of Claims 1 to 30,
    characterized
    in that the aqueous suspension is supplied into the beating device which is used with a consistency of 6 - 15 %.
33. Method according to one of Claims 1 to 30,
    characterized
    in that the aqueous suspension is supplied into the beating device which is used with a consistency of 15 - 25 %.
34. Method according to one of the preceding claims,
    characterized
    in that the force with which the beating tools which form in each case one beating zone are pressed together is adjustable, in particular diversely adjustable for different beating zones.

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