WO2000029665A1

WO2000029665A1 - Device for defibrating fibrous sheets

Info

Publication number: WO2000029665A1
Application number: PCT/US1999/024731
Authority: WO
Inventors: Viktor Mikhailovich Drobosyuk
Original assignee: Pragmatic Vision, Inc.
Priority date: 1998-11-16
Filing date: 1999-10-25
Publication date: 2000-05-25
Also published as: AU1319700A; RU2153546C2

Abstract

The device comprises a preliminary grinding machine (100) represented by a cylindrical rotor (5) with beaters (6) placed in staggered order on its surface, converging-diffusing connecting channel (9), centrifugal breaker (10), and output channel (20) that house a centrifugal fan (16) connected to said breaker via a central opening (15) that is overlapped in the axial direction by the breaker's disk (12). The hopper (1) of preliminary grinding machine is equipped with an inlet pipe (7) for air supply, and the plane of the axial section of said inlet pipe is tangential to the rotor surface, while the part of the hopper adjacent to the inlet pipe is made as a curvi-axial channel bending around the rotor on one side and having the section that is the same as the shape of the input section of said inlet pipe. The material is ground through breakage, and there is practically no shortening of fibers in the process. To facilitate fiber breaking, the material can be moistened in advance.

Description

DEVICE FOR DEFIBRATING FIBROUS SHEETS

FIELD OF THE INVENTION

The present invention relates to devices for producing an aerosuspension of fibers when making paper by an aerodynamic method, and, more particularly to devices intended for grinding fibrous sheets and other pulp materials.

BACKGROUND OF THE INVENTION

Devices for breaking (or grinding) pulp are known in the art. One such device comprises a rotor having a plurality of teeth, a main cutter, and extra cutter mounted in a housing. The extra cutter is fitted to the main cutter at an angle in such a manner that the option of varying an operating gap is provided. See, for example, USSR Author's Certificate 297735, D 21 D 1/38, published 03/11/71 , Official Bulletin 10. A guiding throat (or inlet channel) is mounted on the housing. A reflector that provides for the adjustment of the guiding throat's width is installed inside the guiding throat.

Pulp breaking proceeds in two stages. At the first stage, pulp breaking is performed when the rotor teeth interact with the main cutter. At the second stage, pulp breaking is performed when the rotor teeth interact with the extra cutter. Two-stage grinding enables one to obtain a high degree of dispersion of the source material.

One of the main requirements imposed on pulp grinding when making paper by an aerodynamic method, and particularly when making tissue paper, is the ability to provide a minimal degree of shortening of the fibers. The main disadvantage of the above-described pulp breaker lies in the fact that it significantly shortens the fibers because of the cutting operation, hence resulting in a loss of quality in the paper being produced. This disadvantage is inherent in all known devices for grinding fibrous materials that employ the grinding principle based on cutting.

Also known is a method for producing fluffed pulp-containing materials through moistening source material up to the moisture content of 3-6 % and subsequent separation into individual fibers in a disk refiner (i. e., disk mill) in the conditions of continuous supply of air into the gap between the disks. See, for example, US Patent No. 3475791 , Cl. 119- 156.3, 1969. Moistening of the source pulp-containing material enhances its degree of plasticity and facilitates subsequent grinding. However, significant shortening of pulp fibers also takes place when the pulp web is milled in the disk refiner.

According to another known method, fluffed pulp is produced through the pre-moistening of source material up to a moisture content of 15-75%, grinding, and subsequent separation of ground material into individual fibers in interacting jets of compressed air, where the speed of air jet flow is 150-1100 m/s. See, for example, USSR Author's Certificate 690104, D 21 D 1/01 , published 10/05/79, Official Bulletin 37. Using this method, one can grind a pulp web without shortening the fibers. However, practical implementation of this method often presents a problem because considerable energy consumption is required.

A device that practically implements a method for grinding dry pulp believed to be closest to the claimed invention in the engineering essence is described in US Patent No. 3,596.840. The method for grinding the pulp implies that source material (i.e., pulp) is ground in advance into pieces of 1-5 cm in size and then it is separated into individual fibers in disk refiners. The device implementing this method comprises an input channel, a preliminary grinding machine, a connecting channel, and a final grinding machine, all of which are located in series one above the other. The preliminary grinding machine comprises a hammer mill having a rotor with beaters and a breaking plate. The final grinding machine comprises a disk mill with a gap intended for withdrawal of the ground material. A wire is placed between the preliminary grinding machine and the final grinding machine. The grinding process takes place in the presence of a flow of air supplied into the device through the input channel.

When using this device, high dispersity of the material being processed is attained because of the two-stage grinding. At the same time, however, this process results in substantial shortening of pulp fibers, because pulp is first broken into pieces between the rotor beaters and the breaking plate and then milled in the disk mill.

SUMMARY OF THE INVENTION

The present invention provides a device that enables grinding of webs of fibrous materials, preferably pulp webs, and avoiding substantial shortening of fibers, hence ensuring a high quality for the paper produced.

According to one embodiment of the present invention, a device for grinding sheet fibrous materials comprises a housing, a preliminary grinding machine, a final grinding machine, and a connecting channel. The housing includes an input portion that contains an input channel for receiving the sheets of fibrous material, and an output portion. The preliminary grinding machine is disposed within the input portion of the housing and functions to grind the sheets of fibrous material into particles of a first specified size. The final grinding machine is disposed in the output portion of the housing and functions to grind the particles of a first specified size into particles of a second specified size. The connecting channel connects the preliminary grinding machine to the final grinding machine, and directs the particles of a first specified size from the preliminary grinding machine to the final grinding machine. In addition, the input channel, the preliminary grinding machine, the connecting channel, and the final grinding machine are serially disposed in registry with one another.

The preliminary grinding machine can be constructed in the form of a rotor having a plurality of blades attached thereto. Additionally, the axis of the rotor can be oriented substantially perpendicular to the direction in which the sheet of fibrous material is being fed, and parallel to the plane of the sheet of fibrous material. The device of the present invention can be provided with an output channel connected to the final grinding machine for directing the particles out of the device. Further, an inlet can be provided at the input portion of the housing for supplying air to the device. If (and when) an inlet is provided, a plane of the axial section of the inlet pipe is tangential to the cylindrical surface of the rotor of the preliminary grinding machine. According to one embodiment of the invention, the final grinding machine is in the form of centrifugal breaker comprising a housing with stator elements, such as vanes, mounted on its inner surface. A disk with breaking elements, such as cutters, attached thereto is installed in the housing such that it is rotatable, and a gap is provided between the disk stator elements. A centrifugal fan is installed in the output channel, and connected to the final grinding machine via a central opening in a bottom a housing of the final grinding machine. The centrifugal fan is configured and positioned beneath the final grinding machine's disk in such a way that a flow section of the opening at the bottom of the housing is overiapped by the disk in the axial direction. Alternatively, the final grinding machine can comprise either a centrifugal breaker, a centrifugal fan, or both.

Such design of the device makes it possible to substitute cutting or milling of a material being ground by breaking operation that practically avoids shortening the fibers. For this purpose, the blades of the rotor of the preliminary grinding machine can be constructed as blades that don't cut the pulp web to be ground, but tear individual pieces away from it. These blades can be arranged in a staggered order which prevents tearing of long strips away from the pulp being ground. The breakdown of pieces into fibrous particles in the final grinding machine occurs due to the collision of pieces with the disk, cutters of the disk, and stator elements, thus avoiding cutting and milling of the material processed. In order to further facilitate the process of tearing portions of the fibrous material by the preliminary grinding machine, the sheets of fibrous material can be moistened prior to feeding into the device. The inlet for air supply in the input portion of the device provides additional pressing of the web being ground to the spinning rotor shaft, thus preventing the web from deviating in the direction of the spinning rotor. Hence, better conditions for tearing individual particles away from the fibrous material are created. In addition, the plane of the axial section of the inlet pipe air supply is tangential to the cylindrical surface of the preliminary grinding machine's rotor.

A feeding unit can be installed between the input channel and rotor to provide an optimal trajectory for feeding the web to be ground to the blades of the preliminary grinding machine's rotor. The feeding unit can comprise, for example, pressure rollers located along rotor's generatrix at a minimal distance from the rotor.

In order to provide a uniform air flow for carrying the particles of the ground web from the preliminary grinding machine to the finai grinding machine through the connecting channel, the part of the preliminary grinding machine that is adjacent to the inlet pipe for the air supply can be made so that it has the shape of a curvi-axial channel bending around the rotor on one side such that a cross-section of this channel repeats the shape of the input cross-section of the inlet pipe, while the gap between the opposite part of the hopper and rotor blades on the other side of the rotor is as minimal as possible.

According to an embodiment of the invention, the connecting channel can be made as a diffusing-converging channel. Such an approach will provide for transformation of a flat airflow into an axially-symmetrical flow that will be fed later into the final grinding machine comprising the centrifugal breaker. Transformation of the airflow occurs without swirling if generatrices of the connecting channel in the plane of symmetry that is parallel to the longer side of the rectangle of the hopper's output section are straight lines.

Making a centrifugal fan as a disk having blades on its surface is the most preferable embodiment, from the standpoint of providing withdrawal of produced aerosuspension of fibers. This design can be simplified by installing the disk of the final grinding machine and the disk of the centrifugal fan on the same shaft that goes through the central opening connecting the final grinding machine with the fan.

The output channel having a centrifugal fan therein can be made as a scroll with a tangential outlet. In this instance, free withdrawal of the produced aerosuspension of fibers can be provided due to the action of centrifugal forces, and the probability of fibers sticking together at their collision is minimal.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a side-elevational view of an embodiment of a grinder for grinding sheet fibrous materials according to the present invention.

Fig. 2 is a front-elevational view of the grinder shown in Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figs. 1 and 2, the device of the present invention includes a housing 100, a preliminary grinding machine 110, a final grinding machine 120, and a connecting channel 9. The housing 100 includes an input portion such as a hopper 1 , and an output portion 130. The preliminary grinding machine110 is installed in the hopper 1 , and functions to grind sheets of fibrous material into particles of a first specified size. Additionally, the hopper 1 can be sized such that it has a width that is not less than the width of a pulp web 2 to be ground. The final grinding machine 120 is disposed in the output portion 130 of the housing 100 and functions to grind the particles of a first specified size into particles of a second specified size.

The hopper 1 also includes an input channel such as inlet opening 3 through which pulp web 2 is fed into the device. A feeding unit in the form of one or more pressure rollers 4 can be provided in registry with the inlet opening 3 to assist in feeding the pulp web 2 into the device. A cylindrical rotor 5 is installed in the hopper 1 beneath the pressure rollers 4 such that rotational axes of the rollers 4 and the rotor 5 are oriented parallel to the plane of the pulp web 2 and perpendicular to a direction of its movement. Double rows of rectangular vanes 6 are installed on the rotor 5 along its generatrix. The vanes 6 are arranged in staggered order along each row. The size of each individual vane 6 and a minimal distance between the rows on the circumference of the rotor 5 are determined by a specified size of particles into which pulp web 2 should be ground at the first stage of grinding. The rollers 4 and the rotor 5 are equipped with drives (not shown in Figs.1 and 2) that provide for their rotation. A distance between the rotor 5 and the rollers 4 is minimal and is determined by a specific design, providing for their independent rotation. The hopper 1 also comprises inlet pipe 7 having a rectangular cross- section for feeding air into the hopper 1. A piane along the axial section of the inlet pipe 7 is oriented tangentially to the cylindrical surface of the rotor 5 having the vanes 6. A portion of the hopper 1 adjacent to the inlet pipe 7 has a shape of a curvi-axial channel 8 bending around the rotor 5 at one side (at the left of Fig.1). A cross-section of the curvi-axial channel 8 in this portion of the hopper 1 has the same shape as the input cross-section of the inlet pipe 7. A gap between the outer edge of the vanes 6 of the rotor 5 and an inner wall of the opposite portion of the hopper 1 is minimal and is determined by specific design possibilities.

The device also comprises a connecting channel, such as diffusing- converging channel 9, connecting the hopper 1 with a centrifugal breaker 10 that represents a second stage of pulp web grinding (i. e., the final stage). The diffusing-converging channel 9 provides transformation of flat airflow that exits the hopper 1 into an axially-symmetrical flow of a substantially round (or circular) cross-section that is fed into the centrifugal breaker 10. Methods for calculating the shape of the channel 9, that provides coordination of the input airflow with the output airflow are known. See, for example, Idelchik I.E. Reference-book on Hydraulic Resistance (in Russian). Moscow: Izdatel'stvo "Machinostroyeniye", 1975 (p. 171). Further, as illustrated in the Figures, the input channel, the preliminary grinding machine 110, the diffusing-converging channel 9, and the final grinding machine 120 are serially disposed in registry with one another.

The second stage of the pulp web grinding is conducted in the centrifugal breaker 10 which comprises a disk 12 having a plurality of cutters 13 attached thereto. The disk 12 is installed on a shaft 11 that is mounted within the housing. Stator elements, represented by a plurality of vanes 14, are installed on the inner surface of the centrifugal breaker's housing. The centrifugal breaker 10 is connected to a centrifugal fan 16 via an opening 15 provided at the bottom of the centrifugal breaker 10 and beneath the disk 12. A diameter of the disk 12 selected such that it is significantly greater than size (or diameter) of the opening 15. Thus, the disk 12 overlaps the opening 15 in the axial direction. The indicated relationship among the diameters and placement of the disk 12 prevents pieces of the fibrous material from being directly transferred from the breaker 10 into the centrifugal fan 16.

The centrifugal fan 16 includes a disk 17 installed on the shaft 11. The disk 17 also includes a plurality of rectangular vanes 18 attached thereto. When the disk 17 rotates, the rectangular vanes 18 direct an influx of airflow and carry-over of the ground fibrous material from the breaker 10 through the opening 15, an annular cavity 19, and a tangential outlet pipe 20.

The claimed device operates in the following manner. The material to be ground (i. e., the pulp web 2 that has been pre-moistened to attain better grinding) is fed through the inlet opening 3 by the rollers 4 onto the spinning rotor 5 having the vanes 6. When the web 2 intersects a trajectory of the rotating vanes 6, pieces of the material break away from the pulp web 2. The size of these pieces is determined by the width of the vanes 6, linear velocity of the web 2, a number of rows of vanes 6 contained on the rotor 5, and an angular velocity of the rotor 5. The arrangement of the vanes 6 can be such that they are staggered in order to reduce the possibility that long strips of the material equal in width to the web 2 will break away. Individual pieces of the material being ground away are directed into the airflow fed into the hopper 1 through the inlet pipe 7 by the vanes 6. This airflow also provides additional pressing of the web 2 down to the rotating shaft 5, thus preventing the former from shifting in the direction of the shaft's rotation.

Pieces of the pulp web produced after the first stage of grinding are then transported by the airflow, which is fed through the inlet pipe 7, from the hopper 1 into the diffusing-confusing channel 9 and further into the centrifugal breaker 10.

When entering the breaker 10, pieces of the pulp web arrive at the rotating disk 12. The rotating disk 12 throws these pieces away to the stator vanes 14. Grinding of the pulp web pieces into fibrous particles occurs due to collision of the pieces with the disk 12, cutters 13, and the stator vanes 14. Further, the collision takes place in a vortex flow produced by the disk 12.

Rotation of disk 17 produces an axial airflow along the shaft 11. The axial airflow is directed from the breaker 10 to the fan 16 through the opening 15. Fibrous pulp particles in a suspended state beneath disk 12 are subjected to a concurrent action of: centrifugal forces directed radially at side walls of the breaker 10, and the force of aerodynamic pressure of airflow directed along the shaft 11 through the opening 15. The mode of operation of the device is selected so that for the pulp particles have an average diameter within a range 1.5 - 3 mm, and the force of the aerodynamic pressure of the airflow exceeds the centrifugal force. As a result, pulp particles having the described average diameter are sucked by fan 16 through opening 15, while the particles of greater size remain in the mill and experience further reductions in size. The fibrous pulp particles are fed from the fan 16 through the tangential output pipe 20 to the next technological operation by the centrifugal airflow produced by the spinning disk 17 in the form of aerosuspension.

The present invention makes it possible to grind fibrous materials while avoiding shortening of the fibers. Such an ability beneficially effects the quality of the final product (i. e., paper).

While this invention has been described in connection with what is

presently considered to be the most practical and preferred embodiments,

it is to be understood that the invention is not limited to the disclosed

embodiments, but, on the contrary, is intended to cover various

modifications and equivalent arrangements included within the spirit and

scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A device for grinding sheets fibrous material comprising:

a housing comprising an input portion and an output portion, said input portion including an input channel for receiving the sheets of fibrous material;

a preliminary grinding machine disposed within the input portion of said housing for grinding the sheets of fibrous material into particles of a first specified size;

a final grinding machine disposed in the output portion of said housing for grinding the particles of the first specified size into particles of a second specified size; and

a connecting channel for connecting said preliminary grinding machine to said final grinding machine, and directing the particles of the first specified size from said preliminary grinding machine to said final grinding machine;

wherein said input channel, said preliminary grinding machine, said connecting channel, and said final grinding machine are serially disposed in registry with one another.

2. The device of claim 1 , further comprising a feeding unit mounted between said input channel and said preliminary grinding machine for directing the sheets of fibrous material into said preliminary grinding machine.

3. The device of claim 2, wherein said feeding unit includes at least one pressure roller disposed in registry with said input channel.

4. The device of claim 3, wherein the at least one pressure roller is positioned at a prescribed distance from said preliminary grinding machine.

5. The device of claim 1 , wherein said preliminary grinding machine comprises:

a grinder mounted within the input portion of said housing for grinding the sheets of fibrous material into said particles of a first specified size, said grinder being positioned in registry with said input channel; and

an inlet for supplying air into said the input portion of said housing.

6. The device of claim 5, wherein said grinder comprises a rotor having a plurality of blades attached thereto.

7. The device of claim 6, wherein the blades of said rotor are arranged in a staggered order.

8. The device of claim 1 , wherein said connecting channel comprises a diffusing-converging channel for transforming a flat airflow into an axially-symmetrical flow having a substantially circular cross-section, and directing said particles of a first specified size into said final grinding machine.

9. The device of claim 1 , wherein said final grinding machine comprises:

a centrifugal breaker containing a first grinder therein for grinding the particles of a first specified size into particles of an intermediate specified size; and

a centrifugal fan containing a second grinder therein for grinding the particles of an intermediate specified size into particles of said second specified size.

10. The device of claim 9 wherein said centrifugal breaker comprises:

a breaker housing containing apertures in upper and lower surfaces thereof;

a shaft rotatably mounted in the output portion of said housing and extending through the apertures of said breaker housing;

a disk secured to said shaft, said disk including a plurality of cutters attached thereto; and

a plurality of vanes installed on inner surfaces of said breaker housing.

11. The device of claim 9, wherein said centrifugal fan comprises:

a fan housing containing apertures on upper and lower surfaces thereof, wherein the apertures of said fan housing are sufficiently sized to accommodate said shaft therethrough; and

a second disk mounted on said shaft, said second disk including a plurality of rectangular vanes attached thereto.

12. The device of claim 9, wherein said centrifugal fan comprises an outlet pipe for directing said particles out of said device.

13. A method of grinding sheets of fibrous material comprising the steps:

feeding the sheets of fibrous material into an input channel of a grinder;

supplying a flow of air into the grinder;

grinding the sheets of fibrous materials into particles of a first specified size using a preliminary grinding machine;

transporting the particles of a first specified size to a final grinding machine;

grinding the particles of a first specified size into particles of a second specified size; and

directing the particles of a second specified size out of the grinder.

14. The method of claim 13, wherein the step of grinding the particles of a first specified size comprises the steps:

grinding the particles of a first specified size into particles of an intermediate specified size; and

grinding the particles of an intermediate specified size into particles of a second specified size.

15. The method of claim 14, wherein the step of grinding the particles of a first specified size comprises a step of grinding the particles of a first specified size into particles of an intermediate specified size using a centrifugal breaker.

16. The method of claim 14, wherein the step of grinding the particles of an intermediate specified size comprises a step of grinding the particles of an intermediate specified size into particles of a second specified size using a centrifugal fan.

17. A device for grinding sheet fibrous materials that comprises an input channel intended for feeding material to be ground, a preliminary grinding machine, a connecting channel and a final grinding machine, all located in series one above the other, and said preliminary grinding machine being made as a cylindrical rotor with beaters installed in a hopper, and an axis of said rotor being oriented substantially perpendicular to the direction of sheet material fed for grinding and parallel to the plane of said sheet material, said preliminary grinding machine including an output channel intended for withdrawing ground material connected to the final grinding machine, wherein said hopper includes an extra inlet pipe for air supply, said inlet pipe being placed in the upper part of said hopper, and the plane of the axial section of said inlet pipe is tangential to the cylindrical surface of said preliminary grinding machine's rotor, and said rotor beaters are in the form of blades located along the rotor generatrix, and the plane of said blades is oriented substantially radially to the rotor, and the final grinding machine is represented by a centrifugal breaker comprising a housing with stator elements on its inner surface and a disk with breaking elements fitted to its periphery, and said disk is installed in said housing such that the option of rotation and a gap relative to stator elements are provided, and a centrifugal fan installed in the output channel and connected to the final grinding machine via a central opening made in the bottom of said final grinding machine's housing underneath said final grinding machine's disk in such a way that flow section of said opening is overlapped by said disk in the axial direction.