CH615718A5 - Disc mill for comminuting starting material containing lignocellulose - Google Patents

Description

The invention relates to a disk mill for comminuting fibrous, lignocellulose-containing starting material into fibers, which is equipped with grinding disks rotating relative to one another, on which the mutually facing grinding surfaces are formed with radially arranged webs and with transverse ribs connecting them, with two grinding disks between them radial webs are rows of pockets separated by the transverse ribs with a radially curved bottom and the pockets on one grinding disc are radially offset from those on the other grinding disc.

The pulp produced according to the invention is primarily intended for use in the production of newsprint, cardboard, tissue paper and similar products, and fibrous, lignocellulosic parts of wood or other plants, such as e.g. B. Begasse, can be used. The process used is basically a mechanical defibration process and can be carried out under normal atmospheric conditions or in a steam atmosphere under elevated pressure at temperatures above 100 ° C, generally at a temperato in the range between 110 ° C and 140 ° C or under special conditions in the temperature range between 150 and 170 ° C. If the mechanical process is carried out at a temperature exceeding 100 ° C, it is usually given the special designation “thermomechanical” process.

A main purpose of the present invention is to improve the pulp production in such a way that the fibers of the starting material are separated from one another without excessive shortening and further refined in order to improve their paper-forming properties, i. H. are milled, which is basically achieved by generating frictional forces in the moist fibrous lignocellulose material. In the following description, the material that is already roughly ground between the grinding elements shaped according to the invention and is treated for treatment will be referred to as “grist”. Since the individual fibers in the fiber mill have a considerable spring force, a large number of capillary cavities are formed in the fiber mill, which considerably increase the ability of the mill to bind moisture.

Another purpose of the invention is to reduce the amount of energy required to produce pulp.

During the refining process, the fiber pulp is therefore a moist mixture of already roughly divided starting material, which, if it is made of softwood, e.g. Spruce wood, originating, consists of fibers which are for the most part 2.0 to 3.0 mm long tracheids with a length: width ratio of approximately 100: 1. In turn, these tracheids are anatomically constructed from three mutually surrounding layers of skin that are approximately one thousandth of a millimeter thick, and from a layer of fibrils that are arranged helically around a fourth skin, which in turn forms an innermost tubular cavity, the so-called lumens surrounds. Each fibril has a thickness of a few tenths of a thousandth of a millimeter and a length: width ratio of approximately 1000: 1; together the fibrils make up 70-80% of the substance of the single tracheid. Another purpose of the present invention is to separate the fibers from one another with a high degree of efficiency and, moreover, to cause the fibrils to be partially exposed by a kind of scraping of the skins located outside the fibril layer, which significantly improves the paper-forming capabilities of the pulp.

When realizing the inventive idea, the fiber pulp is introduced between the grinding disks of a refiner. Each grinding disk has rows of pockets which are separated from one another by radially arranged webs and are offset from one another in the longitudinal direction of each radial row in the annular parts of the opposing grinding disks. In radial cross section, the pockets have the outline of a curve, which is at least a segment of a circle in the non-rotating grinding disk. The pulp enters through inlet openings and is subjected to centrifugal forces. In the innermost circumferential pocket, the fiber pulp is deflected laterally from the curved inner surface to the non-revolving disc in order to force it to pass between friction surfaces which are formed by interaction between the webs of the revolving and the non-revolving grinding disc, after which it enters the adjacent pockets of the non-rotating grinding disc with its circular segment-shaped bottoms is pressed. The pulp is usually there with the fibers parallel to each other in a direction perpendicular to the s

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Pockets bordering pockets packed together. The fiber material deposited in the non-rotating pockets forms a relatively densely packed body or plug, which is acted upon by the grinding material still arriving from the rotating grinding disc, with the result that a part of the segmented body or plug of circular segment in the pocket gradually moves into the opposite pocket tilts over the rotating grinding disc. This part of the ground material from the non-rotating pocket is then gradually peeled off by the webs of the rotating grinding disc. In the friction surfaces, which are formed in the packed fiber pulp by the fast moving web, forces of very high intensity act on the individual fibers of the pulp, whereby the fiber pulp is mechanically refined. In the same way, the pulp is gradually moved outwards in the radial direction between the circumferential and non-circumferential pockets. Each time a part of the accelerated fiber pulp is transferred from one rotating pocket to an opposite non-rotating pocket, the speed of this fiber pulp is reduced to zero. The kinetic energy of the moving regrind is converted into mechanical force, which strongly packs the regrind in the non-rotating pocket. When the fiber material is completely decelerated, this kinetic energy has increased the temperature of the material by 3-5 ° C, depending on the angular speed of the refining disc. The compressive force contributes significantly to the formation of friction surfaces or fields between the webs and the fiber material and within the material to be ground.

The bottom of the pockets has been given an arc shape such that it emphatically changes the direction of flow of the pulp in the lateral direction. Depending on the size of the refiner, the regrind can move at a tangential speed of 50-120 m / sec. The friction surfaces formed within the material to be ground split the fibers of the material to be ground and grind them into fibrils.

Accordingly, the device according to the invention for comminuting fibrous, lignocellulosic starting material into fibers is characterized in that radially directed grooves are arranged on both grinding disks, in which the radial webs, which are made separately from hard material, are inserted, whereby through these webs together with the transverse ribs the Width of the grinding gap present between the two grinding disks is determined, and that the radial webs attached in one grinding disk are of the same width as the pockets arranged on the other grinding disk, as a result of which, during the rotating movement of the grinding disks against one another, the pockets integrally formed on them are currently covered and by adjacent pockets the same row are separated. Thus, guide means are provided in order to forward the flow of the fiber pulp, which has already been roughly divided in a first grinding zone, between the grinding disks in such a way that it enters a large number of small pockets of limited size, which are arranged in the same center and with grinding webs as side walls on a rotating grinding disk, the pockets being shaped in such a way that the pulp is accelerated by centrifugal forces and then deflected sideways on the end wall of the pockets against a non-rotating or counter-rotating grinding disc with corresponding pockets and pockets opposite the rotating disc with a bottom of cylindrical shape such that these bags are filled with a compressed body or graft of fiber pulp, which is conveyed by pressure of the living force of the subsequent stream of fiber pulp, when it is stopped, gradually being conveyed into the line of attack of the leading edges of the webs of the rotating grinding disc t and is subjected to a shear stress with such force that the regrind particles are defibrated and fibrillated.

According to a particularly advantageous embodiment, the pockets on the non-rotating grinding disk are profiled in the shape of a cylinder segment in the radial direction and, on the other hand, on the rotating grinding disk, the pockets have a greater inclination angle on their inner flank - in the radial direction - than on their outer flank. If one of the grinding disks is not rotating, the pockets in this non-rotating grinding disk in radial section advantageously have the shape of a segment of a circle and the pockets in the rotating grinding disk in radial section have an outline with a larger angle of inclination on their radially inner wall surface than on their outer wall surface. Here, the contour of the pockets in the circumferential grinding disk, which is curved in axial section, can consist of a straight or almost straight, in the radial direction inner part, which is initially located at the center of the grinding disk, and forms an angle of approximately 90 ° with the plane of the grinding surface. and a straight or almost straight, in the radial direction outer part, which is inclined at a relatively acute angle to the plane of the grinding surface, and these two parts at the bottom of the pocket can merge tangentially into a part shaped into an arc.

The invention is explained in more detail below with reference to the drawings, for example.

Show it:

1 is a partially vertical side view of a refiner designed according to the invention;

FIG. 2 shows part of FIG. 1 on a larger scale;

3 shows a part of a grinding wheel belonging to the device and designed according to the invention in diagram form and in sections parallel to the central axis of the refiner;

4 shows an axial section through the grinding disk of the refiner;

Fig. 5A-5C is a section along the line V-V in Fig. 3;

6 finally shows a vertical section through cooperating refiner grinding disks, one of which represents a modified embodiment of the invention.

In the drawings, a housing of the refiner designated 10 contains a non-rotating grinding disk 12. This grinding disk works together with a grinding disk 16 seated on a rotating shaft 14. The shaft 14 is supported on both sides of the grinding disk 16 in bearings, which are shown in the drawings as little as a drive motor for the shaft 14. Three rings or groups of grinding elements 18, 20 and 50 are provided in the center of the non-rotating grinding disk 12. In the same way, the revolving grinding disc 16 has three rings or groups of grinding elements 22, 24 and 30 arranged in the same center. As a result, three grinding zones are formed, namely one between the elements 18 and 22, in which there is a first comminution of the starting material supplied, for example wood chips . In a second zone formed by the grinding elements 20 and 24, a further rough defibering takes place before the grinding material obtained thereby enters the third grinding zone formed by the grinding elements 30 and 50 shaped according to the invention. The two most internal grinding zones between the elements 18 and 22 or 20 and 24 can be formed with combs or ribs and channels in a manner known per se.

The raw material to be milled, e.g. Chopped wood or pieces of other fibrous, lignocellulosic material is fed through an opening 32 in the housing 10 and from there by means of a thread-shaped

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Carriers 36 equipped feed screw 34 entered through openings in the middle part of the non-rotating and rotating grinding disks. A center ring 38 with drivers 39 is fastened on the rotating grinding disk 16 in order to convey the raw material pieces to the first grinding zone.

In the third grinding zone, the two grinding elements 30 and 50 are preferably designed as coherent circular rings, in the mutually facing grinding surfaces of which a number of circular grooves are formed with the same center as that of the grinding disks 12, 16 or the shaft 14. These channels have a curved shape in cross section. Furthermore, 30.50 grooves with a radial or at least almost radial extension are provided in the two circular rings, and webs are inserted into these, which divide the circular grooves into separate pockets. In the rotating grinding element 30, the pockets are designated 41-46 and their number in each radial row is therefore six, but can of course be larger or smaller. The webs separating these pockets from one another are designated by 47. In the non-rotating grinding element 50, the pockets arranged radially in a row are designated 61-66 and the webs separating them are designated 67. The pockets therefore have a hollow, round inner surface and are delimited on the sides by the flat webs, as can best be seen from FIG. 3. The cross section of the pockets 61-66 in the non-rotating grinding element 50 follows an arc. For the fiber ground material body that is to move in the pockets of the grinding element 50, it is necessary that the center point of the segment of the circle lies in the upper edge of the web. The pockets 41-46 of the rotating grinding element 30 can have the same cross section. However, in the embodiment shown in FIGS. 1-5, its part facing the center has been expanded in such a way that the cross section of the pockets becomes somewhat larger than that of the circle segment, as can best be seen from FIG. 4. The rows of pockets in the two grinding disks are radially offset from one another, e.g. by half a division. The pre-shredded fiber pulp is fed through an inlet 40, which merges into the most inner pocket 41. The most outward-lying pocket 66 of the non-rotating grinding element 50 is cut off such that it forms an outlet for the finished ground material.

The webs 47, 67 are made of a material which is considerably harder than that of the circular rings 30, 50 and, apart from the radial grooves in them, they are formed by the sections 51 and 52 of the ring material which separate the pockets in each radial row supported. These sections protrude to the same level as the narrow edges of the associated webs. The distance between the grinding surfaces of the annular grinding elements 30 and 50 in the axial direction forms the grinding gap, the width of which can be regulated by axial adjustment of the shaft 14 of the refiner. A hydraulic servo motor is often used for this purpose, which in some cases can be adjusted to exert an axial pressure of 30 tons in order to keep the size of the distance between the grinding elements 30 and 50 and thus the width of the grinding gap as constant as possible. This distance can be adjustable from 0.5 mm down to 0.05 mm or even less to ensure that the desired refining effect is obtained. A distance of 0.8 mm has been used for special types of pulp. Preferably, the servo motor should be able to extend the width of the grinding gap, i.e. H. to keep the distance between the grinding elements 30 and 50 constant with a play of at most 0.01 mm.

As an example of the structural design of grinding devices designed according to the invention, it should be mentioned that the grinding element ring 30 on the rotating grinding disk 16 in the case of the drawing. 1-4 underlying embodiment has an outer diameter of 1270 mm and an inner diameter of 1016 mm. It is provided for the rotating grinding disk 16 to be driven at a speed of 1500-1800 rpm. The individual pockets 41-46 then have a width of 0.38 cm and a cross section of 1.5 cm2, which results in a volume of 0.57 cm3. The webs then have a thickness of 3 mm and a width of 15 mm and a length of 127 mm. In this case, the grinding wheel has 504 ridges around the circumference, which are arranged in 72 groups of 7 ridges parallel to each other, which creates scissor-like cuts instead of the long, parallel cuts that occur when the ridges are all arranged radially. In the grinding element ring 50 of the non-rotating grinding disk 12, the pockets and webs can have essentially the same dimensions and be arranged in the same way as in the ring 30 of the rotating grinding disk 16. The grouping of parallel webs contributes to a more even distribution of the torque during the Operation at. Such a combination of the webs in parallel groups also simplifies the mechanical production of the grinding zone elements 30 and 50 by allowing a larger number of grooves or slots to be milled in one operation.

The refiner works as follows: in the first grinding zone formed by elements 18 and 22, the starting material, e.g. the wood chips, subjected to a rough breakdown with moderate energy consumption. In the second grinding zone, the material between the elements 20 and 24 is ground more finely to a relatively uniform consistency. It can then have a grinding degree of, for example, 800 ml, determined according to the “Canadian Standard Freeness” (CSF). This ground material therefore enters the inlets 40 of the third grinding zone with this consistency and continues into the innermost circle of pockets in the circumferential grinding element ring 30. The curved inner wall part 48 of the pocket 41, where the angle of the tangent to the direction of the radius increases, now deflects the fiber pulp by 90 ° to the innermost pocket 61 of the non-rotating grinding disk, as indicated by arrow 40 'in FIG. 4.

4, the pockets in the two grinding elements are shown open to one another, which corresponds to the position according to FIG. 5A. When the ring 30 rotates in the direction indicated by the arrow 31, the webs 47 move from this position, where they are exactly opposite the webs 67, into the position according to FIG. 5B and then into that according to FIG. 5C where they cover the pockets in the opposite grinding disc. This covering is complete, with the exception of the very small distance h between the grinding disks, as determined by the hydraulic servo motor, by determining the axial position of the shaft carrying the rotating grinding disk. Given the dimensions and operating speeds of the refiner and the pockets designed according to the invention, 10 800 pockets of the rotating grinding disc pass each individual pocket in the non-rotating grinding disk every second, which means that the web 47 is displaced between the layers 5A-5C during one There is a time interval of approximately 0.001 seconds. The flow of fiber pulp from the pockets in the rotating grinding disc to the pockets in the non-rotating grinding disc is not stopped despite these brief interruptions. This can be observed when the power from the wood chips fed into the refiner is switched off and the rotating grinding disc of the refiner is stopped. Then when the refiner is open for inspection s

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it turns out that the pockets of the rotating disc are completely empty. When the driving actuation by the grinding material coming from the rotating grinding disc has stopped, the grinding material remains in the non-rotating pockets.

The fiber pulp peeled out of the pocket 41 moves at a very high speed of about 82 m / sec. to the pocket 61, into which it is pressed and is currently stopped. In the non-circulating pocket 61, the fiber material that has acquired a considerable amount of kinetic kinetic energy collects and is compressed, the kinetic energy being converted into heat, which increases the temperature in the selected exemplary embodiment by approximately 1 degree C. When thrown into the non-circulating pocket, the fiber pulp exerts considerable mechanical pressure on the pulp already located there, as a result of which it is packed together to a density of approximately 0.79 g / cm 3. The internal friction that is created when the edge of the next striking cut cuts into the body of fiber pulp causes the desired refining. The degree of refining can be changed by adjusting the distance between the grinding disks. For example, if pulp is made for newsprint, a distance between 0.1 and 0.2 mm can be used. When making boiling paper, a distance of 0.3-0.5 mm can be used. Pulp for egg containers can be produced with a set distance of up to 0.7 mm.

When the pulp is pressed out of the circumferential pocket 41 against the pulp body located in the non-circulating pocket 61, as indicated by the arrow 40 'in FIG. 4, a wedge-shaped part of the body is tipped over into the pocket 42. This part is then peeled off by a web 67 and then accelerated by the centrifugal force and finally deflected into the pocket 62.

Each time the fiber grist comes to a standstill, the kinetic energy of the rotary motion is converted into heat, which increases the temperature in the grist. Since the temperature of the ground material influences the quality of the pulp, it is of some importance to counteract these temperature fluctuations. Since the whole refining process is carried out at a temperature that is very close to the boiling point of water, regardless of whether the refining is carried out under atmospheric conditions or under steam pressure in a refiner under pressure, this heat also causes such an extensive evaporation that the moisture content of the pulp can be reduced. Since the strength of the thrust forces developed in the friction surfaces in the fiber pulp body depends to a large extent on the amount of moisture present, the evaporated water must be replaced. This is done by injecting an amount of water adapted to the evaporation e.g. through line 55.

The fiber pulp deflected out of the pocket 41 has a speed of approximately 80 m / sec, which gives it a centrifugal force acceleration of 1330 g, and is pressed against the ground material in the pocket 61, where it is stopped immediately. The non-circulating pocket 61 is already filled with packed fiber material, the fibers of which are oriented essentially perpendicular to the webs. The kinetic energy of the stopped ground material is converted into heat, which causes moisture in the ground material to evaporate. This transformation is repeated every time the pockets in both grinding disks open to each other. When the webs 47 pass through the packed fiber pulp, friction surfaces are formed between which the fibers are separated and fibrillated. The motive force emanating from the motor driving the rotating grinding disc is transmitted to the grinding stock through the webs 47, whereby the grinding stock is accelerated to a centrifugal force acceleration of the order of magnitude 1,000-1,500 g. The routing of the regrind flow through the pockets in the rings 30 and 50 enables the development of such large internal frictional forces on the thrust surfaces that the intended fiber separation and fibrillation is ensured.

As already mentioned, each time a connection is established between the pockets 41 and 61 of the circumferential and non-circumferential rings 30 and 50, as illustrated in FIG. 5A, a new amount of fiber pulp is introduced into the circumference by a circumferential web 47 non-circulating pocket 61 pressed. Because of their geometric shape as a segment of a circle, as already mentioned, the fiber material body or plug compressed in the non-circulating pockets executes a rotary movement around the geometric center 49 of the segment when each web 47 forming a thrust surface passes, as shown by line 69 in FIG 4 is indicated.

This means that the refined material flow is maintained by the refiner as long as new material, comminuted in the two inner grinding zones, is fed through the inlet 40 to the pocket 41. This in turn means that when regrind is continuously fed to the inlet side of the stationary pocket 61 and compressed there, a corresponding quantity of fiber regrind is pressed out of the outlet part of the pocket 61 and peeled off into the opposite pocket 42 of the grinding element ring 30 of the rotating grinding disk 16. During the transition into this pocket, new friction surfaces are formed in the regrind by the fast-moving web 47 passing through the packed fiber stock body, while the web 67 prevents it from rotating. In this way, the fiber pulp is made to move alternately between the circumferential and non-circumferential pockets until it leaves the non-circumferential grinding element ring 50 on its outer circumference through one of the pockets 66 provided with an outlet.

Depending on the set width of the grinding gap between the grinding disks and also the degree of filling of the non-rotating pockets, part of the ground material can emerge radially through the grinding gap from the pocket 41 past the transverse rib 51 through the friction surface formed there (see Fig. 4).

5A-5C it can be seen that when the webs 47 pass by the webs 67, the passages between the pockets of the rotating and the non-rotating grinding element ring are alternately opened and closed. In the structural design specified above, for example in terms of dimensions, this process is repeated for each web at a frequency of approximately 10,000 times per second. As a result, the regrind that emerges from the non-rotating pockets is subjected to a hammering action by forces whose size fluctuates between a few kg / cm 2 and zero, which facilitates the rotation of the grinding media or plugs and thus the uniform flow of the regrind through the pockets. This vibration-generating hammer action also contributes to the compression of the material to be ground, in such a way that very strong friction work is brought about at the transition point between a non-rotating pocket and an opposite rotating pocket.

The distance h between the narrow edges of the webs of the grinding elements 30 and 50, designated 47 and 67 in FIG. 5A, in the outermost grinding zone of the refiner corresponds to the grinding wheel spacing or grinding gap set for the refiner. Its width can be 0.2 mm and more

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amount to. This width is an important operational factor for the refiner. It is determined by the working conditions, the type of raw material used and the type and quality of the fiber pulp to be produced. In some cases, where a very finely refined pulp is desired, the distance h between the webs 47 and 67 can even be reduced to 0.05 mm, but in these cases the performance of the refiner is reduced at the same time. With this setting of the grinding gap, pulps with a CSF freeness down to 2 ml can be produced.

In most cases, the distance in the grinding zone, which is determined by the grinding elements of the grinding disks that are closest to one another, is a multiple of the diameter of a fiber of most vegetable raw materials, e.g. for spruce tracheids is generally between about 0.02 and 0.03 mm. A direct cutting off of the fibers between the leading edges of one grinding wheel while the other is rotating is practically impossible. The refining of the fiber material to be ground in the grinding zone between the grinding elements 30 and 50 is brought about by the interaction between the front edge of the individual webs and the material to be packed together. The mechanical impact on the fiber therefore depends on the nature of the frictional forces developed within the fiber pulp. This in turn depends on the mechanical strength of the refiner, which is intended to give it sufficient rigidity so that direct metallic contact between the surfaces of the grinding disks is avoided.

In order to separate the fibers from one another and further split them into e.g. To bring about the anatomical components of the softwood tracheid and thus the desired refining effect on the regrind, it must be pressed together so strongly that force fields (of microscopic size) that develop locally and point by point can develop and thrust forces of high intensity can develop.

Prerequisites for this are created in particular in those pressure force fields which form at the transition points from the circumferential pockets 41-46, where the fiber pulp is compressed under the action of a centrifugal force of approximately 500 g and even more than 1000 g up to 1500 g when it is suddenly stopped in the non-circulating pockets 61-66.

The friction surfaces or fields formed at the transition points from the pockets 61-65 of the grinding element ring 50 on the non-rotating grinding disc 12 to the pockets 42-46 of the grinding element ring 30 of the rotating grinding disc 16 have a different character in some cases from the friction surfaces or fields which occur during the Transition from the pockets of the rotating grinding disc into the pockets of the non-rotating grinding disc. If the fiber pulp is accelerated into the pocket 42 by the web 47, the mode of action is different and more the effect of a blunt knife that passes through a piece of cheese is comparable. When the fiber material is compressed, it emerges from the pockets of the non-rotating grinding element ring and creates the peripheral webs of the friction surfaces. In the circumferential pocket 42, the already packed fiber pulp is caught by the circumferential web 47 and a thin layer of it is peeled off and accelerated to considerable speed, as a result of which it moves outward in the pocket 42 in a radial direction and is deposited and compacted before it is deflected over the edge 49 and transferred into the non-circulating pocket 62, etc. There it is brought to a standstill again, which means a loss of kinetic energy and a renewed increase in temperature due to the loss of angular velocity.

Because of its chemical structure, the lignocellulosic wood substance is hydrophilic and thermoplastic when moist, within the temperature range from just below 100 ° C, where it begins to soften, to 140-150 ° C, where the bond between the tracheids is more or less completely loses its power depending on the nature of the various lignocellulosic starting materials.

The refining work according to the invention is therefore preferably carried out in closed plants, where the refining process can be carried out under steam pressure, which means that an appropriate temperature can be maintained during the refining process. The heat allowance required for heating the millbase can in this way be easily obtained from the heat generated by the friction work taking place in the millbase during the refining process. Since considerably more heat is released during this process than is required to keep the ground material at a suitable temperature, a large part of the moisture contained in the ground material is evaporated. If, for example, 800 kWh per ton of pulp produced, calculated as dry matter, is used in the refining work carried out according to the present invention, the regrind receives a heat allowance of 688,000 kcal per ton of dry matter. If the refining is now carried out at a temperature of 120 ° C. (and with the appropriate vapor pressure) in order to take advantage of the thermoplastic softening of the wood substance then obtained, 1309 kg of water per ton of wood treated are evaporated from the moisture present in the ground material.

Assume that the wood chippings fed into the refiner had a moisture ratio of 2: 1, i.e. H. contained 33% dry wood substance, the evaporation would reduce the moisture quotient to 0.7: 1. Since maintaining a uniform viscosity of the material to be ground has now proven to be an indispensable prerequisite for achieving a good grinding result, a corresponding amount of water must be added to the grinding zone through the lines 55 provided in the non-rotating grinding element ring 50. This addition is expediently carried out automatically in a refiner designed according to the invention. So much water must be added that the moisture quotient does not become lower than 1.5: 1. The added water spreads quickly over the surfaces of the fibers of the regrind and thus influences the state of the friction between the fibers and thus the entire refining process. With increasing moisture quotient of the regrind, the strength of the liquid film surrounding the fibers increases. A film that is too thick acts as a lubricant between the fibers and thus impairs the usefulness of the refining process. Conversely, if the moisture ratio drops to 1: 1 or less, there is a considerable risk of microscopic knots or bundles of fibers being formed, which are difficult to unravel even with subsequent refining. A sufficient amount of water added to avoid this danger also increases the consumption of energy to accelerate the ground material in the pockets of the rotating grinding disc.

When examining microphotographs of cuts of spruce wood fibers (tracheids) in 50x magnification, individual fibers can also be easily observed in cross-section and also how their size changes within the annual rings. Statistical evaluation shows that the size of the fibers in cross-section is approximately 0.03x0.03 mm, which is approximately 100,000 fibers per cm2

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corresponds. The fiber length is about 2.5 mm, making the number of fiber tracheids about 400,000 per cm3. The dry weight of spruce wood is approximately 0.42 g / cm3, and accordingly one g (= 2.4 cm3) of spruce wood contains approximately 1,000,000 fibers and the total surface area of separated whole fibers is approximately 3 m2 per g of wood. It also follows that the total fiber length per cm3 is approximately 100,000 cm or 240,000 cm per g. With a cross-section of the tracheids of 0.03x0.03 mm, the circumference becomes 0.12 mm and the total surface area is 28 800 cm2 per gram of wood. Refined fiber pulp can have a surface ten times larger, depending on its CSF freeness. The liquid film spread over the particles is a thin skin, the thickness of which has been calculated, according to calculations, to be less than a thousandth of a millimeter. However, in view of the large surface area available and the hydrophilic properties of the wood substance, a limited excess of water can be permitted without fear of an intolerably large loss of refining effect when using grinding elements according to the invention. A refiner equipped with grinding disks according to the invention creates a larger number of effective friction surfaces within the material to be ground than has previously been possible with any known design of refiners. The invention also enables the use of webs and ribs which are more resistant to wear than in previously known refiner designs, in particular also thanks to the novel embedding of the webs in the grinding wheel body.

The friction surfaces or fields formed in the fiber material to be ground are offset within the material to be ground in relation to the distance between the surfaces of the circumferential webs and the fixed webs in such a way that grinding to a certain degree of refinement is obtainable with a greater distance between the grinding disks than with previously known devices is. This means less wear on the opposite surfaces of the webs. Such an increased distance also counteracts an excessive shortening of the fibers by cutting.

In order to achieve the intended separation of the fibers from one another and their fibrillation by mechanical refining, in practice nowadays one always works with the formation of friction surfaces or fields which are generated mechanically between grinding disks of many different patterns in the gradually more finely distributed regrind by the friction surfaces are created by changes in direction between different regrind surfaces.

According to the invention, a high degree of efficiency is achieved in utilizing the kinetic energy which repeatedly accelerates the regrind from a drive motor of the rotating shaft. Due to the special design of the channels that determine the flow of the regrind, where the regrind is compressed locally to form bodies or plugs of such strength that friction surfaces can be formed in which internal mechanical processing takes place, extensive separation or fibrillation of the in the The mill base already has more or less largely separated fiber components before the mill base finally loses all of its kinetic energy locally and is returned to the rotating grinding disc in order to be subjected to the same treatment again.

With an axially adjustable ring 56 outside the circumference of the non-rotating grinding element ring 50, it is possible to regulate the outlet cross section of the outermost non-rotating pockets 66 and thus the size of the material flow between the grinding element rings 30 and 50.

The webs 47 and 67 can be made of a very hard material, such as carborundum, silicon carbide or other ceramic materials. The rings 30 and 50 carrying the grinding elements can be made of softer material that can be easily machined and can therefore be made in one piece. The webs are inserted into the milled radial grooves or slots, which advantageously have vertical side walls, and preferably there by means of binders, expediently organic synthetic resins with high binding power, such as polyimides or fluoropolymers of the "Teflon" (R), "Ryton" (R) or type Polyparaphenyl sulfide such as «Eko-nol» (R). The webs can also be kept cast in the slots. Thanks to the curved outline of the channels in which the pockets 41-46 and 61-66 are formed, the webs are held particularly well in the grooves.

According to a modified embodiment, the grinding elements of the second grinding zone between the rings 20 and 24 can be shaped similarly to the grinding element rings 30 and 50. The working surfaces of the grinding elements of the grinding disks often require post-processing to the highest possible accuracy after assembly of the refiner in order to ensure the best possible performance in the operation of the refiner.

The first pocket 41 of the circumferential grinding element ring 30 has an innermost radius of 528 mm. If the regrind is accelerated with a moisture ratio of 3: 1 to a speed of 83 m / sec, the required input effect amounts to 14.5 kWh per ton of absolutely dry pulp. When the pulp enters the pocket 61 of the non-rotating grinding element ring 50, it is braked to zero speed; but when it leaves this pocket again, it is accelerated again in the opposite circumferential pocket 42. The regrind passing through the refiner's third grinding zone is thus accelerated and stopped six times alternately, once in each row of pockets. This corresponds to a power consumption of approximately 95 kWh per ton of pulp produced. As described above, when the pulp material emerges in a packed form from the non-circulating pockets, friction surfaces or fields are formed by the edges of the webs. The strength of this friction can, as already indicated above, be changed by changing the distance between the grinding disks. The power used for the refining process can therefore be changed from a few hundred to a thousand kWh per ton of pulp of ordinary types. If pulp with particularly low grind values is to be produced, up to 2000 kWh per ton of pulp can be used. By increasing the distance between the grinding disks, a short cut can be created, which allows a part of the fiber material to be transferred directly from one pocket into the next radial pocket via the transverse ribs 51. This means a significant loss in refining power, but at the same time a possibly more desirable reduction in power consumption.

In the embodiment according to the drawing figure 6, the pockets 61-66 and 71 in the non-rotating grinding element ring 50 have the outline of a segment of a circle, the radius of which is the same as the greatest depth, in the axial section in the same way as in the embodiment illustrated in FIGS. 1-5 the pocket or something greater than this depth. In the circumferential grinding element ring 30, the individual pockets also have a curved outline in axial section through the grinding element. 4, the individual pocket has a slightly inclined wall part 72 on its radially outer side, which is flat or nearly flat and tangentially merges into a circular-shaped part 73 at the bottom of the pocket, which in turn is on the radial inner side the bag in an s

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Wall part 74 merges, which is perpendicular or at least almost perpendicular to the grinding surface formed by the edges of the webs 47 and the ribs 51. The circular arc part 73 can have a radius of curvature whose length is approximately half the greatest depth of the pocket. As a result, the circumferential pockets are given an outline with a relatively long but flat deflecting surface 72 for the regrind. This is introduced on the radial inside of the circumferential grinding element ring 30 through inlets 41 and flung at high speed in the direction of arrow 40 into the innermost non-circulating pocket 61, where the ground material is stopped immediately and fills the pocket, forming a tightly packed plug or body is pressed together. This is then transferred into the innermost circumferential pocket 42, the plug passing between the webs 47 and 67 and thrust or friction surfaces forming in which the individual fibers and fibrils of the material to be ground are separated from one another. Due to the circular segment section of the non-circulating pockets, the ground material plug packed into these will rotate about a center point 40 through the subsequent ground material thrown through the inlet 41, as indicated by the line 69 s. The plug then comes into contact with the circumferential webs 47, which cut the ground material under peeling. In the revolving pocket 42, the regrind is now accelerated to the high speed of the revolving grinding element, whereby it is packed together and, thanks to the weakly inclined, elongated plane 72, with favorable distribution of the radially and axially directed force components, it is introduced into the next pocket 62, where again a segmented ground plug is formed. This course is repeated in the outward direction of the millbase alternately between the non-circulating and the circulating pockets until the end product contained in this way emerges through the last non-circulating channel 71.

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3 sheets of drawings

Claims (3)

615718 1. Disc mill for comminuting fibrous, lignocellulosic starting material into fibers, which is equipped with grinding discs that rotate relative to one another, on which the mutually facing grinding surfaces are formed with radially arranged webs and with transverse ribs connecting them, with both grinding discs between these radial webs Rows of pockets separated from one another by the transverse ribs are formed with radially curved bottoms and the pockets on one grinding disc are radially offset from those on the other grinding disc, characterized in that radially directed grooves are arranged on both grinding discs (16; 12) in which the radial webs (47; 67) made separately from hard material are inserted, with these webs (47; 67) together with the transverse ribs (51; 52) the width of the between the two grinding disks (16; 12) existing grinding gap (h) is determined, and that the d he radial discs (47) attached to a grinding disc (16) have the same width as the pockets (61 to 66) arranged on the other grinding disc (12), so that during the rotating movement of the grinding discs (16; 12) against each other the pockets (41 to 46; 61 to 66) formed on the same are currently covered and separated from adjacent pockets in the same row. 2. Disk mill according to claim 1, with a stationary grinding disk, characterized in that on the one hand on the non-rotating grinding disk (12) the pockets (61 to 66) are profiled in the radial direction in the form of a cylinder segment and on the other hand on the rotating grinding disk (16 ) the pockets (41 to 46) on their - in the radial direction - inner flank have a larger angle of inclination than on their outer flank. 2nd PATENT CLAIMS 3. Disc mill according to claim 2, characterized in that on the rotating grinding disc (16), the axial, curved cross section of the pockets (41 to 46) from an - with respect to the center of the grinding disc (16) - inner, at least approximately straight section (74), which forms an angle of almost 90 ° with the grinding surface, and consists of an outer, likewise at least approximately straight section (72), the latter being inclined at an acute angle to the grinding surface, the pocket on the bottom of the pocket merge the two straight profile sections (74 and 72) tangentially into an arcuate section (73), the radius of which preferably corresponds approximately to half the depth of the pockets (41 to 46).