EP1209282A1 - Process for milling a fibrous material - Google Patents

Abstract

To even out the characteristics of a suspended paper fiber material (1), using a controlled wet grinding (6), the suspended paper fibers are initially separated into fractions by a wet sieve (5) according to size and/or shape and/or flexibility. The amount of solid matter in the overflow (3) is determined, and the overflow is linked to the wet grinder on an increase in the solid content and, on a reduced solid content the overflow is lowered. To smooth out the characteristics of suspended paper fibers, the solid mater in the overflow is measured by density at a constant volume flow. The specific grinding action is proportional to the measured solid content at the overflow. The wet grinder is a perfecting mill, with its capacity set by positioning the grinding units to the grinding effort. It can also be set by a shift in the rotary speed at the same drive torque, so that the specific edge loading is constant. The material density is measured at the overflow, and then controlled by the addition of water on a time constant value. The wet sieve action is in a closed pressure sorter, so that the sieve separates the paper fiber suspension into fractions, so that the stiff and longer fibers and chips pass through the overflow and the more flexible and shorter fibers pass through.

Description

The invention relates to a method for grinding a paper pulp according to the preamble of claim 1.

Methods of this type are used in the processing of paper pulp Paper production used. You will find a preferred application if the Paper pulp for graphic papers, e.g. SC papers or LWC papers used shall be. Such types are often very thin, around 50 to 60 µm, and are high Optical quality requirements. Therefore, it is important to be particularly homogeneous To maintain leaf structure and surface, which also presupposes the fibers are particularly homogeneous in terms of their geometry.

Either native fibers or come as raw materials for such types Secondary fibers, e.g. made from deinked waste paper. Relative in that too Homogeneously producible native pulp is occasionally coarser Fiber components or splinters, e.g. separated by a fractionating machine can be. Such fractionation machines work on the principle of Wet screening. In the case of secondary fibrous materials it is always larger Quality fluctuations to be expected, which can only be explained by an elaborate Have stock preparation sufficiently eliminated. Therefore, often at the end of the Preparation process once again used grinding apparatus, which for a Uniformity of the paper pulp, especially with regard to the geometric Fiber properties should provide. Apparatus for wet grinding of paper pulp are known and are referred to as refiners.

A method for controlling a refiner is known from US Pat. No. 3,604,646 the amount of substance supplied to it is determined from the consistency and volume flow. The specific work is regulated to a fixed constant value.

The previously known methods cannot address the problems mentioned at the outset solve satisfactorily. In many cases, an undesirably high resale must be paid for be taken to achieve an acceptable leveling. That weakens not only the strength potential of the paper fibers, but also costs unnecessarily much Grinding energy. It also leads to a further increase in Dewatering resistance with negative effects when pressing and drying the paper web made from it.

The invention is therefore based on the object of creating a method with which the equalization can be carried out better, more gently and cheaper.

This object is achieved by the features mentioned in the characterizing part of claim 1 solved.

With the aid of the method according to the invention, it is first determined whether there is any Overflow of a wet sieve upstream of the grinding the proportion of grinding resistant Ingredients, e.g. Splinters or long fibers, changes. An important indicator of this is the amount of solids in the overflow of this wet sieving, measurable e.g. With which Consistency. The effectiveness of the grinding plant is based on the so determined Variations matched by the specific grinding work according to the invention is increased or decreased if larger or smaller amounts of meal-resistant Substance is present in the pulp suspension to be ground. So it will takes into account the fact that not only the amount of the substance to be ground, i.e. the Overflow, changes, but also the composition of the contained therein Solid. With this simple measure, the substance that is based on its geometry and rigidity to impair the sheet made from it would lead to timely and economical regrinding. The specific Grinding work is the transferred grinding work after deduction based on the amount of solids the idle work consumed by the grinder.

Fig. 1

ein einfaches Verfahrensschema zur Durchführung des endungsgemäßen Verfahren;

Fig. 2

ein einfaches Diagramm zur Steuerung;

Fig. 3 und 4

jeweils eine Variante.

The invention and its advantages are explained and described with reference to drawings. Show:

Fig. 1

a simple process scheme for performing the method according to the invention;

Fig. 2

a simple diagram for control;

3 and 4

one variant each.

1, the Suspended paper pulp 1 is first fed to a wet sieve 5. This forms two fractions, namely run 2 and overflow 3. As a rule, for such a wet sieve 5 uses a pressure sorter or fractionator with one Siebelement, which is part of the supplied paper pulp 1 due to its Size, shape and / or flexibility. The amount of solids in the overflow 3 reached material is determined at a measuring point 9 and the measured value to a controller 8 forwarded. In the simplest case, the overflow 3 becomes wet grinding immediately 6 fed. The controllable grinding apparatus used for this contains a drive 7 and is preferably a refiner. After passing the grinding tools, the Material as ground paper pulp 4 in the subsequent processing stages. In In favorable cases, it can be mixed again with the run 2 of the wet screening 5 become. It is crucial when carrying out the method according to the invention that the specific grinding work transferred in the wet grinding 6 is matched to the determined amount of solids or the amount of solids in the overflow 3. In this case Example shown, the signal from the controller 8 is used to the To change the drive power of the grinding equipment. As you know, there is the possibility adjust the grinding pressure by positioning the grinding sets accordingly. Another option is the speed variation, which is usually is more complex, but it is possible to keep the secondary edge length constant makes. The latter measure is particularly good for maintaining one even grinding suitable. As is well known, the secondary edge length is one important parameter of the grinding. It is calculated as the total knife length of one Grinding set that moves past the counter knives every second.

According to the diagram in Fig. 2, the specific grinding work 13 is linear Function (curve 13 ') adjusted based on the overflow quantity 14. This approach is based on the assumption that the increase in the sieve residue to a correspondingly larger amount of hard fibers and splinters is to be attributed and that a larger specific grinding work must be carried out to the same extent. Of course, other functions are also possible and through simple experiments determine.

In the embodiment of the method shown in Fig. 3, the consistency of the Feed into the wet grinding 6 by controlled supply of water W constant held. In this case, the measuring point 9 is used to determine the consistency of the Overflow 3. This easy-to-get signal serves as an indication of a change the amount of solids accumulating in the overflow 3 and solves the control process described out. This leads to a changed throughput at the wet grinding 6 serving grinding apparatus, such a fluctuation is easier in the grinding process to compensate as a fluctuation in the consistency which occurs in the method according to FIG. 1 sets. In addition to the material density control itself, the W So determined consistency value also to control the grinding performance in the sense of Invention can be used.

Fig. 4 shows an application of the method according to the invention, in which the Wet grinding 6 is carried out as a high consistency grinding. As you know, with a high consistency grinding especially the strength potential of the paper pulp can be used well and without significant fiber shortening. The overflow 3 brought to the desired solids content by a thickening 12. That included accumulating water is divided here into the dilution water W for the Material density control circuit (if available) and the dilution water W 'for addition in the ground paper pulp 4. The wet grinding 6 is controlled by Measurement of the amount of substance with a measuring point 11, the value of which in a controller 10 is processed.

Claims (7)

Method for equalizing the properties of a suspended paper pulp (1) with the help of wet grinding (6) carried out in a controllable grinding apparatus,
characterized in that the suspended paper pulp (1) is first fractionated in a wet screening (5) due to its size and / or shape and / or flexibility,
that the amount of solids of the substance that has entered the overflow (3) is determined and
that the overflow (3) is then fed to the wet grinding (6),
the specific grinding work of the wet grinding (6) being increased as the amount of solids in the overflow (3) increases and decreasing as the amount of solids in the overflow (3) decreases. Method according to claim 1,
characterized in that the solids flow rate of the overflow (3) is determined by measuring its bulk density with the volume flow kept constant. The method of claim 1 or 2,
characterized in that the specific grinding work is set according to a linear function as a function of the solids flow rate determined in the overflow (3). The method of claim 1, 2 or 3,
characterized in that a grinding refiner is used as the grinding apparatus and that its output is adjusted by positioning the grinding tools in order to adapt the specific grinding work. Method according to one of claims 1 to 3,
characterized in that a grinding refiner is used as the grinding apparatus and that its grinding capacity is regulated by changing the speed at the same drive torque, so that the specific edge load remains constant. Method according to one of the preceding claims,
characterized in that the consistency of the overflow (3) is measured and then regulated by a controlled addition of water (W) to a constant value over time. Method according to one of the preceding claims,
characterized in that the wet sieving (5) is carried out in a closed pressure sorter, in such a way that the sieve element therein fractionates the suspended paper pulp (1) in such a way that stiff fibers, longer fibers and splinters are enriched in the overflow and in Pass through more flexible and shorter fibers.

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