CN1553979A - Method, apparatus and screen for fibrous pulp for screening machines - Google Patents

Abstract

The invention relates to a method, an apparatus and a screen for screening mechanical fibre pulp. According to the invention a short fibre material is separated using a gap screen, whereby said material can be very efficiently separated to form a specific fraction.

Description

Method, device and screen for fibrous pulp for screening machines

The invention relates to a method for sieving a mechanically produced fiber pulp mixture comprising fibers of different lengths, in which method the fiber pulp mixture obtained by mechanically separating wood fibers in the presence of water, Sieved into at least two fractions comprising fibers of mainly different lengths.

The invention also relates to a plant for screening a mechanically produced fiber pulp mixture comprising fibers of different lengths, the plant comprising screening means for screening obtained by mechanically separating wood fibers in the presence of water A fiber pulp mixture sieved into at least two fractions comprising fibers of predominantly different lengths.

The invention also relates to a screen for screening a mechanically produced fiber pulp mixture comprising fibers of different lengths into two parts comprising fibers of substantially different lengths, the screen comprising at least one screening surface through which , water is removed from the fiber pulp mixture, and some of the shorter fibers are removed together with the water, and the remaining fiber pulp mixture is removed from the screen from the same side of the screening surface to which it is conveyed.

Mechanical fiber pulp is produced into fibers by grinding or thermomechanically refining wood in the presence of water to obtain a fiber pulp mixture. Fibers with different freeness values are typically produced by prior art production methods. The separation of fibers is based on a process of separating fibers, and the materials used, and the ratio between fibers with different freeness values cannot be greatly adjusted in the actual fiber separation process. The result, therefore, is a fiber pulp mixture in which fiber fractions with different freeness values and handling properties are by no means the most satisfactory in terms of use. Thereafter, the fibrous material is sieved in a prior art manner, using a screen comprising various sieving surfaces, so that fibers smaller than a certain size and having passed a sieving surface are directed for use, and coarse fibers removed from the process , through rejects refining and back into the process. However, the end result is a fibrous pulp mixture in which the length of the fibers and thus their freeness value varies greatly, the structure of the fibrous pulp mixture and its properties not being as desired. When making a particular paper, it is preferred to use a mechanical fiber pulp comprising high quality long fibers, and short fibers with binding capabilities, but not substantially medium sized fibers. Such fiber pulp cannot be obtained by traditional machine fiber pulp screening methods.

The object of the present invention is to provide a method, a device and a screen which enable the use of fiber fractions comprising mainly fibers of different lengths for different purposes.

The method of the present invention is characterized in that, in at least one screening stage, a gap screen (gap screen) fiber pulp mixture or a part thereof is sieved to separate short fibers from the fiber pulp mixture or a part thereof, the gap screen The screen comprises a gradually decreasing gap, and at least one wire mesh (wire) delimiting said gap, whereby the screened fibrous pulp mixture or a portion thereof is supplied to said decreasing gap such that it Flows in the same direction as the wire mesh toward the output port at the tapering end of the gap, and the short fibers and some water fed into the gap exit through openings in the wire mesh, while the water and some remaining The fiber pulp mixture exits through the output port of the gap.

The device of the invention is characterized in that it comprises a gap screen for separating short fibers, comprising a gradually decreasing gap, and at least one wire mesh delimiting said gradually reducing gap, whereby the fibers to be screened The slurry mixture, or a portion thereof, is fed into said tapering gap so that it flows through the gap screen in the same direction as the wire mesh towards the tapering end of said gap so that the short fibers and some water Openings in the wire screen pass through and the remaining portion of the fiber pulp mixture exits the gap screen through output ports at the tapering ends of the gap.

The screen of the invention is characterized in that the screen is an interstitial screen comprising a gap delimited by a wire mesh, into which the fiber pulp mixture is fed, in the same direction as the wire mesh. The movement causes the water and short fibers to drain through the openings in the wire mesh and the remaining portion of the fiber slurry mixture to drain from the output port at the tapering end of the gap.

The main idea of the invention is to separate the fibrous pulp material of very fine short fibers from the fibrous pulp mixture by using an interstitial screen, preferably two wire meshes, resulting in a very short fibrous material with a high freeness value, It cannot be clearly called a specific pulp by other screening methods. According to a preferred embodiment of the invention, a portion of the fiber pulp mixture comprising medium-length and shorter fibrous materials which has been screened, preferably by separating long fibers, is re-screened by said interstitial screen formed with a double wire mesh . According to a second preferred embodiment of the present invention, the medium-sized fibrous material containing some fine fibers separated from the interstitial screen is further guided for refining. As a result, a portion comprising medium-sized and short fibers having the desired properties is obtained.

The present invention provides the advantage that a fiber fraction, shorter than a fraction of a specific length, can be precisely separated from a pulp mixture comprising fibers of different lengths. An advantage provided by a preferred embodiment of the invention is that the long-fibered fibrous material is first screened and then the very short fibrous material with high freeness values is separated from the remainder comprising medium-sized and short-fibered material using gap screens. The fibrous material, then the end result is three fibrous pulp fractions with different properties which can be mixed with each other or with other fibrous materials to achieve the desired quality of the web. Thus, long fibers can be combined with very short fibers to obtain a specific paper quality, which is not possible when medium sized fibers are contained in the fiber pulp.

Thus, fiber pulp fractions of different properties and lengths can be obtained as required from the mechanically produced fiber pulp, and thus the required fraction can be easily combined with the production of the fiber web and only the required fiber pulp fraction can be used to produce a specific Types of fiber webs. Thus, a web comprising only long and short fibers can be produced, and the resulting intermediate sized fibers can be used to produce another web.

The present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 schematically represents the method and apparatus of the present invention,

Figure 2 schematically represents the gap screen used in the method of the present invention,

Fig. 3 schematically shows the screening results using the gap screen of the present invention.

Figure 1 schematically represents the method and apparatus of the invention, wherein the freeness value of the particulate fiber pulp is set by way of example, on the basis of which value a division into different fiber pulp fractions can be performed.

Figure 1 shows schematically how the material 1 to be defibrated is led to a defibrator 2, which may be a grinder known per se or a refiner, typically a heat engine Refiner. The fiber pulp mixture obtained by defibration is conducted to a screening device, or first to a first screen 3, on which the mixture can be separated, for example according to a freeness value "16", so that it contains long fibers and has The fraction that passes the first screen 3 starts to be further processed and the fraction that contains long fibers and debris and that does not pass said screen is directed to a first recirculation refiner 4 for refining, where , the portion is returned to the first screen 3 for sieving. Fibers longer than required are then continuously circulated until they pass through the first screen and continue onwards in the process. The first refiner can be a separating refiner, or the portion to be returned can also be returned to an actual defibrator 2 shown by dashed lines.

The part of the fiber pulp that contains long fibers and that has passed through the first screen is directed forward to a second screen 5 where, on the basis of a set fiber length, for example a freeness value "28", This fraction is re-sieved according to fiber length. The fibrous pulp fraction that has passed through the second screen 5 is continuously forwarded for further processing, and the longer fibrous pulp fraction that cannot pass said screen is led to a second refiner 6, which is preferably a Refiners are known per se. The fibrous pulp obtained from the second refiner 6 is directed to a third screen 7, from which fibers shorter than a particular length (particular length) have passed through said screen, for example set to a freeness value "40" ” are directed forward for use, and thus fibers that cannot pass through the screen 7 are returned to the second refiner 6 for refining. Thus, the long fibers are circulated in the same way, passing through the third screen 7 and then waiting for use, until they are shortened to the desired size. The fibrous pulp fraction which has passed through the second screen 5 is guided according to the invention to a fine screen 8 on which the fine fibrous pulp fraction is separated from the fibrous pulp by means of a separate gap screen, e.g. The degree value is at least "200", and therefore the correspondingly longer fibers are led to a third refiner 9, which is preferably a refiner known per se. The resulting fibrous pulp fraction output from the third refiner 9 contains high quality fine and medium sized fractions.

The gap screen is a screen composed of a single wire mesh or a double wire mesh. Such a screen is capable of effectively removing the required amount of fibrous pulp of a particular length or shorter than that from the fibrous pulp mixture, thus separating the fractions strongly and providing the desired ratio. Other screens are known, each screen representing a separate screen or two or more screens forming a multi-stage screen. An interstitial screen is then used to separate short fibers.

FIG. 2 schematically shows a gap screen 10 of double wire mesh construction. The gap screen preferably allows the fibrous pulp to be screened into two fractions according to the invention. The interstitial screen consists of two movable wire meshes 11 and 12 forming opposing screen surfaces which move through the interstitial screen and back, in a closed loop, so that within the interstitial screen in the direction of its movement A converging gap 13 is formed. Support structures 14 and 15 are placed behind the lines 11 and 12 , ie on opposite sides of the gap 13 . The wire meshes 11 and 12 are supported against support structures 14 and 15 which naturally include openings for receiving water and fine fibrous material removed from the openings of the wire meshes 11 and 12, and from as schematically indicated by arrows A This fine fibrous material is removed on the gap screen shown. Wire meshes 11 and 12 circulate around rolls 16 and 17, shown by way of example, as is well known in the art. The sides of the gap 13 at the edges of the wire screens 11 and 12 are naturally closed so that the fibrous slurry mixture can be properly fed under pressure from the feed channel 18 to the gap screen, thereby removing water and fine fibrous material as required. Also schematically shown are motors 19 and 20 which rotate one of the rollers 16 and 17, respectively, although normally the motors would be able to rotate each roller individually, or all of them in a manner known in the art. Roll the desired number of turns. The motors 19 and 20 are in turn connected to a control unit 21 included in the control unit, allowing to adjust, for example, the rotational speed of the motors so that the wire meshes 11 and 12 move at a desired speed, which can be compared with the fiber pulp passing through the screens. The flow rate varies and preferably exceeds the flow rate of the fiber pulp mixture.

During screening, the fibrous pulp mixture is conveyed from the feed channel 18 to the gap screen and thus the mixture passes through the gap 13 of the screen and exits from the narrower output port 22 of the gap 13, i.e. the output port has a smaller cross-section than the feed opening outlet from the same side of the screen surface or the same side of the wire mesh to which the fibrous slurry mixture was originally conveyed. At the same time, due to the structure of the wire meshes 11 and 12, water and short fibers are removed from the openings of the wire meshes. Depending on the amount of fibrous material to be removed, the moving speed of the wire screen can be adjusted relative to the delivery rate of the fibrous slurry mixture onto the screen until the desired screening result is obtained. At the same time, more water can be removed from the fiber pulp mixture with the short fiber pulp fraction than remains in the fiber pulp fraction that does not pass through the wire mesh, ie flows out through the outlet port of the gap 13 . Thus, the longer fiber pulp fraction can be thickened at the same time as well, and the consistency can go up to 10%. In this application and claims, the output port 22 refers to the part of the screen from which water and fibers are no longer removed by passing through one or more wire screens and the remaining fiber pulp mixture is conveyed directly from the screening stage to a subsequent possible or conveyed to a possible subsequent processing stage controlled by various conveying means and control means such as wire mesh or the like.

What can necessarily also affect the quality of this part is an appropriate choice of the size and penetration of the wire meshes 11 and 12, so that wire meshes with different penetration characteristics are used for different purposes. Also affecting the sieving is the fact that one or both screens are arranged to move towards the gap along the raised support structure, so that water and fine fibers are more efficiently removed from the fibrous pulp fraction at the delivery end of the screens , and correspondingly move more slowly toward the output port of the gap screen. If a single wire mesh structure is used, one of the wire meshes 11 and 12 can for example be replaced by a fixed wall surface, and a combination can preferably be used, wherein the wire mesh 11 faces an arch support structure 14 moves and a specific wall surface replaces the wire mesh 12 moving directly in the gap area.

In fact, the adjustment of the sieving is mainly based on the fact that the gap screen adjusts the basis weight of the fibrous slurry mixture of fibrous material comprising long fibers flowing through said gap screen. This is achieved by adjusting the consistency of the fiber pulp mixture fed to the screen, or the speed of the wire mesh relative to the delivery rate of the fiber pulp mixture. When a dilute fiber pulp mixture is fed into the interstitial screen, more short fibers can be removed from the fiber pulp mixture than when a thicker fiber pulp mixture is fed under the same conditions. Thus, if the speed of the wire screen is increased relative to the delivery rate of the fiber slurry mixture, more short fibers can be removed from the fiber slurry mixture. Thus, by adjusting the feeding consistency and/or the speed of the wire mesh, the separation value of the short fibers can be set at a desired level, so that the result obtained is a distinct fraction of fiber pulp in which the A portion contains only very short fibers and correspondingly a portion flowing through the interstices of the interstitial screen contains longer fibers but very few short fibers. The speed of the wire screen can be adjusted in various ways so that it remains below, above, or equal to the fiber pulp delivery rate. The choice of speed is based on the properties of the fiber pulp mixture to be screened and the desired screening result.

Fig. 3 schematically shows the screening results obtained by the gap screen shown in Fig. 1 according to the method of the present invention. Figure 3 shows the screening results, or fiber fractions with different freeness values in the fed fiber pulp mixture, and correspondingly in the fraction passing through the gap and exiting from the output port of the gap screen. Figure 3 shows the fiber fractions with different freeness values, represented by the different fiber fractions in the supplied fiber pulp mixture of the entire fiber pulp mixture represented by black bars, and the fiber fraction contained in the fiber pulp fraction discharged from the output port The corresponding fiber fractions with corresponding freeness values are indicated by white bars. Figure 3 shows that the fiber fraction with a freeness value of 30 or greater is close to 30%, the fiber fraction with a freeness value ranging from 50 to 30 is close to 16%, and the fiber fraction with a freeness value ranging from 100 to 50 is approximately 13%, the fraction of fibers with a freeness value ranging from 200 to 100 is close to 7%, and the amount of very fine fibers with a freeness value of 200 is 34%. In this case, the average freeness value of the fed fiber pulp mixture was 100.

The fibrous pulp that had been sieved showed a proportional increase in the coarse fiber fraction of close to 50%, the next-best fibers by close to 25%, and the shorter fibers only slightly. The very short fibers together with the water have been removed to a great extent by means of the wire mesh, and thus the short fiber fraction has been proportionally reduced by 60%. In practice, this means that only very short fibrous material, which in this case has a freeness value close to 200 or higher, is substantially removed in the interstitial screen from the fed fibrous pulp mixture. Thus, extremely short fibers can be efficiently removed from the fiber pulp mixture to be screened, and thus by partially mixing the desired amount of fiber pulp into e.g. long fibers, a specific fiber pulp is obtained which can be used for various purposes Parts, in order to manufacture specific forms of fiber webs with specific characteristics. The average freeness value of the fiber pulp mixture passing through the gap screen is thus increased.

Figure 3 shows that the amount of long fibers in the portion passing through the wire mesh is essentially zero, and correspondingly the amount of short fibers in the long fiber portion passing through the gap screen is very low. This means that the gap screen operates very efficiently and divides the fibrous pulp mixture strongly into two parts of distinctly different lengths. The structure of the wire mesh in the interstitial screen is appropriately chosen according to the application, allowing to determine suitable screening conditions for fibers of different lengths and to adjust the screening efficiency by controlling the speed and/or consistency of the fiber pulp mixture.

The present invention has been described in the specification and drawings by way of example, but is not limited thereto. Its essence is to screen the mechanically produced fibrous pulp with an interstitial screen in such a way that the short fiber fraction is separated therefrom and a desired number of fibrous pulp fractions of a predetermined fiber length is obtained, and preferably such that the short fiber fraction is removed from such The long fibers have been separated from the fiber pulp from which they were separated, and thus the short fibers can be separated as efficiently as possible from the rest of the fiber material.

Claims (19)

1. the method for the fiber slurry mixture made of a sieving machine, this mixture comprises the fiber of different length, in the method, fiber slurry mixture is by mechanically separating xylon and obtain having under the situation of water, this fiber slurry mixture is screened into the two parts that comprise the fiber that mainly is different length at least, it is characterized in that, in at least one screening stage, adopt a gap screen cloth (10), fiber slurry mixture or its part are sieved, the staple fibre that comes from the separation of fiber slurry mixture or its part, this screen cloth comprises a gap that reduces gradually (13), with at least one woven wire (11 that limits described gap, 12), thereby will be delivered into the described gap that reduces gradually (13) by the fiber slurry mixture that will sieve or its part, make it flow with the output port of the direction identical towards the place, the end that reduces gradually in described gap with woven wire, and staple fibre and some water that are transported in the gap withdraw from by the opening in the woven wire, and water withdraws from the output port of some remaining fiber slurry mixtures by the gap.

2. method as claimed in claim 1, it is characterized in that, adopt this gap screen cloth (10) fiber slurry mixture or its part to be sieved the staple fibre of the separation that becomes to come from fiber slurry mixture or its part, this screen cloth comprises two screening surfaces, move with identical direction, and one facing to a ground placement, and at two woven wires (11,12) form the described gap that reduces gradually (13) between, described fiber slurry mixture or its part are fed between two woven wires, make mixture flow with the output port that the direction identical with woven wire is in towards the end that reduces gradually in described gap between the woven wire, and staple fibre and some water of being transported in the gap withdraw from by the opening in two woven wires, and water withdraws from the output port of some remaining fiber slurry mixtures by the gap.

3. as the method for claim 1 or 2, it is characterized in that long fiber at first separates and forms long stapled part, adopts described gap screen cloth to separate staple fibre then from remaining fiber slurry mixture from fiber slurry mixture.

4. method as claimed in claim 3 is characterized in that, after staple fibre separated, remaining fiber slurry mixture was further guided to carry out defibrination.

5. as the method for claim 3 or 4, it is characterized in that, the long stapled part that comprises of separating from fiber slurry mixture is carried out defibrination by further guiding, and sieved by further guiding at the fiber slurry mixture that defibrination obtains later on, with the part of the fiber that obtains comprising length-specific, and the waste material that obtains from screening is returned again with defibrination.

6. as each method in the claim of front, it is characterized in that, from the defibre of wood material and the fiber slurry mixture that obtains at first be directed sieving, and comprise the fiber of different length and the part by described screening be directed into subsequently screening stage, comprise that the part of remaining long fiber and chip material is directed carrying out defibrination from this screening, should partly be directed turning back to described screening by the fiber pulp of defibrination then.

7. the equipment of the fiber slurry mixture made of a sieving machine, this mixture comprises the fiber of different length, this equipment comprises screening plant, be used to sieve having and mechanically separate xylon under the situation of water and obtain fiber slurry mixture, this fiber slurry mixture is screened into the two parts that comprise the fiber that mainly is different length at least, it is characterized in that, this equipment comprises a gap screen cloth (10) that separates staple fibre, comprise a gap that reduces gradually (13), with at least one woven wire (11,12) limit the described gap that reduces gradually, thereby the fiber slurry mixture or its part that are sized are fed into the described gap that reduces gradually, make it flow through the gap screen cloth towards the end that reduces gradually in described gap with the direction identical with woven wire, make staple fibre and some water withdraw from, and the output port that the fiber slurry mixture of remainder is located by the end that reduces gradually of (13) in the gap withdraw from from the gap screen cloth by the opening in the woven wire.

8. equipment as claimed in claim 7, it is characterized in that, this gap screen cloth (10) comprises two screening surfaces, move with identical direction, and one facing to a ground placement, and at two woven wires (11,12) form the described gap that reduces gradually (13) between, fiber slurry mixture or its part are fed between two woven wires, make mixture flow with the output port of the direction identical towards the place, the end that reduces gradually in this gap with woven wire, make staple fibre and some water withdraw from, and the fiber slurry mixture of remainder withdraw from the gap screen cloth by the output port between the woven wire of locating in the end that reduces gradually in this gap by the opening in two woven wires.

9. as the equipment of claim 7 or 8, it is characterized in that this equipment comprises one first screen cloth (3), be used to separate oversize fiber and fragment from the fiber slurry mixture that forms after the defibre.

10. equipment as claimed in claim 9, it is characterized in that, this equipment comprises, is used for carrying out the device of defibrination to comprising by the isolated oversize fiber of the fiber slurry mixture of first screen cloth (3) and the part of fragment, and is used for described part is turned back to this first screen cloth.

11. the equipment as claim 10 is characterized in that, this device that is used for the fiber slurry mixture that comprises oversize fiber and chip material is carried out defibrination comprises one first fiberizer (4), and this fiber pulp partly is directed into carries out defibrination in this fiberizer.

12. as each equipment among the claim 9-11, it is characterized in that this equipment comprises one second screen cloth (5), be used for the fiber slurry mixture by first screen cloth (3) is separated into two parts.

13. the equipment as claim 12 is characterized in that, this second screen cloth (5) is connected to described gap screen cloth (10), is used for the fiber slurry mixture by second screen cloth is directed to the gap screen cloth in order to separate staple fibre there.

14. equipment as claim 12 or 13, it is characterized in that, this equipment comprises one second circulation fiberizer (6), be used for partly carrying out defibrination from the isolated long stapled fiber pulp of second screen cloth (5), one the 3rd screen cloth (7) sieves and is used for turning back to by this part of the 3rd screen cloth the device of the second circulation fiberizer to the fiber slurry mixture that obtains from the second circulation fiberizer.

15. as each equipment among the claim 7-14, it is characterized in that this equipment comprises a fiberizer (9), be used for the long fiber from gap screen cloth (10) is partly carried out defibrination.

16. the fiber slurry mixture with the fiber that comprises different length of machine-building sieves and becomes to comprise the two-part screen cloth of the fiber of different length substantially, this screen cloth comprises at least one screening surface, by this screening surface, water is removed from fiber slurry mixture, and some short fibers are removed with water, and remaining fiber slurry mixture is removed from the screening surface same side that is supplied to fiber slurry mixture from screen cloth, it is characterized in that, this screen cloth is a gap screen cloth (10), comprise by a woven wire (11,12) gap (13) that reduces gradually of Xian Dinging, fiber slurry mixture is fed into this gap, with with woven wire (11,12) identical direction moves, water and staple fibre withdraw from by the opening of woven wire (11,12) thus, and the output port that the fiber slurry mixture of remainder is located by the end that reduces gradually of gap (13) withdraws from.

17. screen cloth as claim 16, it is characterized in that, this gap screen cloth (10) comprises two woven wires (11,12), move with identical direction, and form relative screen surface, form the described gap that reduces gradually (13) between this woven wire, fiber slurry mixture or its part are delivered into this gap to move with identical direction between two woven wires, water and staple fibre are by two woven wires (11 thus, 12) opening withdraws from, and the fiber slurry mixture of remainder withdraws from by the output port between two woven wires (11,12) at the place, the end that reduces gradually in this gap.

18. the screen cloth as claim 16 or 17 is characterized in that, this screen cloth comprises that control device is used to adjust each woven wire (11,12) is transported to the transfer rate of this screen cloth with respect to fiber slurry mixture movement velocity.

19., it is characterized in that this screen cloth comprises the device of the denseness that is used to adjust the fiber slurry mixture that will be transported to this screen cloth as each screen cloth in claim 16 or 18.

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