Patent Application
20230256453
The present invention relates to a bead mill that performs pulverization and dispersion processing on particles in a suspension of solid particles (referred to hereinafter as slurry) by stirring hard particles (referred to hereinafter as beads) serving as a stirring medium in a container.
A high-pressure jet mill, an ultrasonic homogenizer, a bead mill, and so on are available as devices for pulverizing and dispersing microparticles in slurry. Of these devices, a bead mill is capable of continuous processing and, due to being capable of pulverization and dispersion from micrometer size to nanometer size and so on, exhibits superior pulverization and dispersion functions. A bead mill is a device (a bead mill) in which a rotary member (a stirring rotor) rotates at high speed in a tightly sealed cylindrical container so that shearing force is generated between the cylindrical container and the stirring rotor, with the result that the particles in the slurry are pulverized and dispersed by the impact force of the beads suspended in the slurry.
For example, in a device (a bead mill 1) of an invention disclosed in the Patent Literature 1, a stirring rotor is provided in a lower portion of a cylindrical container, and by rotating the stirring rotor, pulverization processing is performed on particles and dispersion processing is performed on secondary particles formed from agglomerations of primary particles. To implement the pulverization and dispersion efficiently, the processing is performed by intermixing beads with a diameter of approximately 0.05 to 5 mm into the slurry. In the bead mill 1, the beads are separated from the slurry on which the pulverization and dispersion processing has been completed by a bead separation device provided in an upper portion. Further, in a bead mill (a bead mill 2) described in Patent Literature 2, a mixture of slurry and beads is stirred inside a cylindrical container by a large bead separation device instead of a stirring rotor.
In a bead mill having this type of bead separation mechanism, pressure loss occurs in the device, e.g., when the slurry flows through a bead filling layer and when the slurry flows against centrifugal force generated as the bead separation device rotates, and therefore, in order to cause the slurry to flow through the bead mill having this type of bead separation device, it is necessary to apply comparatively high pressure of 0.1 to 0.4 MPa inside the mill.
Here, the pulverization processing refers to dividing single particles into a plurality of particles, while the dispersion processing refers to establishing a state in which primary particles are individually dispersed by separating secondary particles constituted by a plurality of particles. Note that the primary particles are individual crystalline or non-crystalline particles of a substance, and the secondary particles are formed when the surfaces of typically several to several thousand primary particles contact each other so as to form pseudo-particles. The beads used in the pulverization processing and dispersion processing are particles formed from a ceramic such as alumina or zirconia, a metal such as stainless steel, or plastic, and range in size from several tens of micrometers to several millimeters. The beads are generally preferably spherical.
As noted above, a bead mill is capable of continuous processing and, due to being capable of pulverization and dispersion from micrometer size to nanometer size and so on, exhibits superior pulverization and dispersion functions. However, a bead mill has the following problems.
In a bead mill, the particles in the slurry are subjected to pulverization processing or dispersion processing by stirring the beads in a cylindrical container, and the beads are separated inside the cylindrical container. As described above, however, the push-in pressure applied thereto is high, while on the other hand, since a rotary driving portion of a rotary shaft for rotating the stirring rotor inside the cylindrical container comes into contact with the slurry, a rotating portion seal is required to prevent liquid leakage. To realize this rotating portion seal in the part where the pressure is comparatively high, a sealing structure realized by a mechanical sealing device is typically used.
A sealing device such as a mechanical seal is required to prevent slurry in a high-pressure container having a contact portion between a fixed component and a rotating component from leaking to the outside through a seal portion. To prevent leakage, it is necessary to apply pressure to the outside of the sealing device, and a mechanical seal is structured so as to house a sealing liquid. The seal contact portion component gradually becomes worn, which causes a problem in that the sealing performance deteriorates over time. As a result, a problem occurs in that the sealing liquid leaks into the slurry so as to contaminate the slurry. Another problem is that wear debris from the seal contact portion component (metal, ceramic, or the like) intermixes with the slurry. Furthermore, when the wear on the sealing device becomes severe, the sealing device has to be replaced, which costs money. Sealing portion wear occurs to a particularly large degree in slurry containing metal powder such as nickel, and this is a serious problem.
Another problem of a sealing device is that a mechanical seal has a complicated structure including a plurality of components, which is due to the existence of seams and uneven portions. In a bead mill having a sealing device, a problem occurs in that the slurry adheres to the seams and uneven portions. Especially when processing raw materials for foodstuffs and pharmaceuticals, problems occur in that due to putrefaction of solid matter, the product slurry cannot be used as a commercial product, and due to poor cleaning, the slurry is contaminated after changing the product type. Hence, problems occur due to wear of the sealing device and adhered substances, and therefore new technology for solving these problems is required.
(1) A bead mill device having a rotary shaft disposed in a vertical direction includes a slurry storage vessel disposed above a container that processes slurry using beads. A slurry passage hole is disposed in a lower portion of the container, and a slurry flow passage through which the slurry can pass is disposed between an upper lid of the container and the slurry storage vessel. Further, the rotary shaft extends from above the slurry storage vessel through a space in the slurry flow passage into the container. Furthermore, a mechanism that causes the slurry in the slurry flow passage to flow downward is provided on the rotary shaft, and a swirl promoting component that swirls the slurry as the rotary shaft rotates is disposed in a higher position than a stirring rotor or a centrifugal bead separation device disposed in an uppermost portion of the cylindrical container.
(2) The bead mill having the structure described above in (1) is structured such that the slurry is supplied through the slurry passage port disposed in the lower lid of the cylindrical container, whereby the slurry flows upward. A centrifugal bead separation device is disposed on the rotary shaft in a position in an upper portion of the container. Further, a hollow passage through which the slurry that has passed through the centrifugal bead separation device flows out into the slurry storage vessel is disposed in the interior of the rotary shaft.
(3) In the bead mill described above in (2), a flow passage fixed to a slurry outlet of the hollow passage formed in the rotary shaft causes the slurry to flow in a direction away from the rotational center of the rotary shaft and discharges the slurry into the slurry in the slurry storage vessel so that the slurry flow is suctioned from the slurry outlet by centrifugal force.
(4) In the bead mill described above in (2) or (3), a screen that filters the rising slurry so as to separate the beads is disposed in the slurry in the slurry storage vessel.
(5) In the bead mill described above in (4), a component that causes the slurry in a space between the screen and the rotary shaft to flow downward and/or a component for swirling the slurry below the screen is disposed on the rotary shaft.
(6) In the bead mill of (2) or (3) above, a partition plate that divides the slurry stored in the slurry storage vessel into upper and lower parts is disposed, the partition plate has an opening portion through which the rotary shaft passes vertically, and a component for swirling the slurry is disposed on the rotary shaft below the opening portion.
(7) The bead mill described above in (1) is structured such that after the slurry is supplied from the slurry storage vessel into the cylindrical container through the slurry flow passage and then stirred together with the beads in the cylindrical container, the beads are separated by a contact-type bead separation device, whereupon the slurry is discharged through the slurry passage port.
(8) In the bead mill described above in any of (1) to (7), a component for preventing swirling of the slurry is disposed in the slurry in the slurry storage vessel.
(9) In the bead mill described above in (8), the component for preventing slurry rotation, disposed in the slurry storage vessel, is constituted by a plurality of vertical direction plates arranged so as to divide the interior of the slurry storage vessel in a circumferential direction.
(10) In the bead mill described above in (8), the component for preventing slurry rotation, disposed in the slurry storage vessel, is constituted by a combination of a structure that surrounds the rotary shaft and has a cylindrical shape, a polygonal shape, or another shape, and a vertical direction plate disposed so as to divide the interior of the slurry storage vessel in a circumferential direction.
(11) In the bead mill described above in any of (2) to (6), the diameter of an outermost peripheral portion of the swirl promoting component that swirls the slurry in the uppermost portion of the cylindrical container is at least 0.82 times that of an outermost peripheral portion of a component of the centrifugal bead separation device that swirls the slurry.
The bead mill of the present invention does not include a rotating portion sealing device that contacts the slurry, and therefore the problem caused by wear of the contact members of the rotating portion sealing device, namely contamination of the product slurry with debris from the worn sealing components and the sealing liquid, is eliminated. The problem of particles in the slurry adhering to the rotating portion sealing device, making cleaning difficult, can also be solved.
In
In the device of the present invention, due to the effects of the rotary motion of the slurry in the cylindrical container and the rotation of the rotary shaft 4, a vortex may be formed in the slurry storage vessel 6 such that the liquid surface enters the slurry flow passage 7. In this case, air enters the mill, causing problems such as a reduction in the stirring efficiency of the beads and foaming of the slurry. These problems are particularly likely to occur when the stirring rotor 5 rotates at high speed or when highly viscous slurry is processed. In response to these problems, a component for preventing the slurry in the slurry storage vessel 6 from swirling may be disposed.
The component for suppressing swirling of the slurry may take any shape as long as swirling can be suppressed, but for example, a component (swirl prevention plates 18) shown in
The bead mill of the present invention uses two methods. In method 1, as shown in
First, the bead mill of method 1 will be described in detail. A feature of this type is a structure including a component that causes the slurry to flow downward through the slurry flow passage 7 and a component that forms a slurry flow from the center toward the periphery in the slurry between the upper surface of the centrifugal bead separation device 11 and the upper lid 1 and prevents bead leakage by applying centrifugal force. By employing this structure, a bead mill not having a sealing structure in the rotating portion is formed. Note that in
In the example of
In a case where microbeads of 0.3 mm or less are used or the like, the amount of beads flowing back through the slurry flow passage 7 may increase, and therefore, as shown in
An outer peripheral diameter of the swirling blades 13 is preferably not less than 0.82 times an outermost peripheral diameter of the component of the centrifugal bead separation device 11 that swirls the slurry. More preferably, the outer peripheral diameter is from 0.82 times to 1.48 times the outermost peripheral diameter. These are optimum values for a ratio of the centrifugal force formed by the swirling blades 13 to the centrifugal force formed by the centrifugal bead separation device 11. When the centrifugal force formed by the swirling blades 13 is too strong, the amount of slurry that circulates from the slurry storage vessel 6 to the cylindrical container through the slurry flow passage 7 may become too large, and as a result, the amount of slurry passing through the centrifugal bead separation device 11 may become excessive. Further, when the centrifugal force formed by the swirling blades 13 is too weak, a slurry flow flowing from the upper portion of the cylindrical container into the slurry flow passage 7 is formed. In this case, the component of the centrifugal bead separation device 11 that swirls the slurry may take any shape as long as the slurry is swirled thereby. Note, however, that components that are fixed to a disc or the like and have clear surfaces for pushing and separating the slurry in the rotation direction, such as the bead separation plates 33 shown in
In the device of the present invention shown in
The swirling slurry discharge component 29 may take any form as long as it is structured so as to swirl the slurry flow. However, a structure in which tubes having a circular shape, a square shape, or another shape are disposed at the slurry outlet of the rotary shaft inner flow passage 12, which is divided into 2 to 4 locations, a structure in which a plurality of plates are disposed on an upper/lower pair of discs that apply centrifugal force to the slurry discharged from the rotary shaft inner flow passage 12, or the like is preferable. For example,
Further, as a structure for applying centrifugal force to the slurry after the slurry is discharged from the rotary shaft inner flow passage 12, an upper/lower pair of circular fixing discs may be disposed on the rotary shaft 4, and a plurality of plates may be disposed thereon so that the slurry is pushed out in the outer peripheral direction by the motion of the plates. This structure is similar to the view of the centrifugal bead separation device shown in
In the device of the present invention shown in
The screen 19 is preferably fixed to the inner surface of the slurry storage vessel 6 so that there is no gap in a contact portion between the screen 19 and the slurry storage vessel 6. However, there is a gap between the screen 19 and the rotary shaft 4, and therefore, depending on the conditions, the beads suspended in the slurry may pass through the gap. When this phenomenon occurs, a component such as an under-screen swirling component 20 or a pumping component 21 is preferably disposed on the rotary shaft 4 to prevent the slurry from rising through the gap. Note that the under-screen swirling component 20 also has the effects of causing the slurry between the rotary shaft 4 and the screen 19 to flow downward and swirling the slurry so that the beads are prevented from approaching the gap between the rotary shaft 4 and the screen 19 by centrifugal force. As long as the under-screen swirling component 20 exhibits a function for causing the slurry to flow outward from the center by rotating, the shape thereof is not limited. A structure in which a plurality of radially arranged linear projections are mounted on a disc, i.e., a similar structure to the disc 24 and the swirling blades 13 disposed in the cylindrical container, as shown in
When the bead leakage suppression function of the under-screen swirling component 20 is sufficient, the slurry does not pass through the screen 19, and bead leakage can be prevented by causing the slurry to pass only through the gap between the screen 19 and the rotary shaft 4. In other words, below the screen 10, the beads are pushed out in an outward direction from an outer peripheral portion of the under-screen swirling component 20 by the centrifugal force of the swirling slurry, and therefore there are no longer any beads in the slurry that rises through the gap between the screen 19 and the rotary shaft 4. As a result of this effect, no beads leak above the screen 19 through the gap. Hence, by providing the under-screen swirling component 20, the screen 19 may be a partition plate structured so that the slurry does not pass therethrough.
In the bead mill having this structure, a partition plate that divides the slurry stored in the slurry storage vessel 6 into upper and lower parts is disposed in the position of the screen 19. Further, the rotary shaft 4 passes through an opening portion provided in the partition plate. Also, a component for swirling the slurry is disposed on the rotary shaft 4 below the opening portion. In the example of
Moreover, when the slurry in the slurry storage vessel 6 is swirled, a vortex may be generated, and as a result, the liquid surface of a central portion of the slurry may fall greatly below the screen 19. As a countermeasure, the swirl prevention plates 18 may be mounted in the interior of the slurry storage vessel 6, as described above. The swirl prevention plates 18 are vertical plates disposed so as to be oriented in the diametrical direction of the slurry storage vessel 6, and are provided in a plurality. An appropriate number of swirl prevention plates is from 3 to 12. By providing the swirl prevention plates 18, the swirling motion of the slurry inside the slurry storage vessel 6 is suppressed so that the beads settle more easily. As a result, the beads can return to the cylindrical container more easily by riding the downward flow through the slurry flow passage 7. The swirl prevention plates 18 are most typically structured so as to be fixed to the side surface of the slurry storage vessel 6, but may be fixed to the bottom surface of the slurry storage vessel 6 instead. Furthermore, although not shown in
Note that as an even more preferable embodiment of method 1 of the present invention, the component for suctioning the slurry in the rotary shaft inner flow passage 12, shown in
Next, using
The slurry supplied from the slurry storage vessel 6 to the cylindrical container through the slurry flow passage 7 forms a mixture with the beads and undergoes stirring processing, whereupon the beads are separated before the slurry is discharged from the cylindrical container. In the bead mill of method 2, a bead separation device of a type that separates the beads by passing the slurry through a narrower gap than the diameter of the used beads, such as the slit-type bead separation device 23, is disposed. In the example of
In the bead mill having the structure described above, when the rotation speed of the stirring rotor 5 while stirring the beads is high or when the slurry is highly viscous, centrifugal force is exerted on the slurry by the rotary motion of the stirring rotor 5, and as a result, the beads may rise through the cylindrical container up to the vicinity of the upper lid 1 and press against the slurry flow passage 7. In the present invention, this problem is dealt with by disposing a component for applying centrifugal force to the slurry above the position in which the stirring rotor 5 is disposed in the cylindrical container. This component is realized by attaching the swirling blades 13 to the upper portion disc 24, as shown in
Furthermore, due to the effects of rotation of the rotary shaft 4 and the pumping component 9 and swirling of the slurry in the cylindrical container, the slurry swirls inside the slurry storage vessel 6, but when the swirling becomes violent, a large vortex may be formed such that air is drawn into the cylindrical container from the space in the slurry storage vessel 6. As a result, it may become impossible to continue the processing due to foaming of the slurry, the stirring performed by the stirring rotor 5 may be insufficient, and so on. These problems are dealt with by disposing a rotation prevention component in the slurry storage vessel 6. As shown in the example of
In a conventional bead mill, a mechanical sealing structure (typically, a mechanical sealing device) is disposed between the upper portion of the cylindrical container and the rotary shaft. The reason for this is that in order to respond to liquid resistance during the processing in the cylindrical container and pressure loss in the bead separation device, a state in which the interior of the cylindrical container is pressurized by pushing the slurry into the mill using a pump or the like is established, and therefore a sealing mechanism is required on the periphery of the rotary shaft. In the device of the present invention, on the other hand, pressure is applied to the interior of the cylindrical container by the pumping component 9 and so on disposed between the rotary shaft 4, which is a rotating component, and the slurry flow passage 7, which is a fixed component, and therefore differential pressure can be created between the interior and the exterior (in the case of the present invention, the slurry storage vessel 6 is on the exterior) of the cylindrical container without the need for a sealing mechanism. As a result, a mechanical sealing device can be omitted.
The bead mill according to the present invention can be applied to pulverization processing and dispersion processing of slurry containing a fine powder of ceramics, carbon nanotube, cellulose nanofiber, pigments, inks, paints, dielectric bodies, magnetic bodies, inorganic substances, organic substances, pharmaceuticals, foodstuffs, metals, and so on.
Two of the devices of the present invention (a mill 1 using the centrifugal bead separation method and a mill 2 using the slit-type bead separation device) were manufactured, and processing experiments were performed thereon by introducing beads while varying the component configuration. In a first device (method 1: mill 1), the experiment was performed with six component configurations, namely a mill 1a, a mill 1b, a mill 1c, a mill 1d, a mill 1e, and a mill 1f. The basic structure of the mills 1a to 1e was basically that shown in
In the mill 1a, the swirling blades 13 were disposed but nothing was disposed in the interior of the slurry storage vessel 6, while in the mill 1b, only the swirling blades 13 and the screen 19 were disposed, and in the mill 1c, the screen 19 and the swirl prevention plates 18 were disposed in addition to the swirling blades 13. Further, in the mill 1d, the under-screen swirling component 20 was disposed in addition to the configuration of the mill 1c. The under-screen swirling component 20 was structured as shown in
Further, a second device (method 2: mill 2) was a bead mill having the contact-type, slit-type bead separation device 23 in the bottom portion of the mill, and basically having the structure shown in
Moreover, as comparative examples, the experiment was also performed using a mill I and a mill II in which none of the swirling blades 13, the swirl prevention plates 18, the swirl prevention tube 22, the screen 19, and so on were disposed in a mill having the same cylindrical container as the mill 1 and the mill 2. The specifications of these mills are also shown on Table 1. In the processing experiment undertaken on the mill 1a to the mill I of method 1, the fluid supplied to the cylindrical container was water, while the fluid supplied to the mills 2a to II of method 2 was water and a highly viscous liquid with a viscosity of 550 mPa · s. The flow rate was set at 8 L/hour.
First, with the device configuration of the mill 1a, the effect on bead leakage of the ratio of the outer peripheral diameter of the swirling blades 13 to the outer peripheral diameter of the component of the centrifugal bead separation device 11 that swirls the slurry was investigated. Six swirling blades 13 with a length of 12 mm and a height of 5 mm were disposed. Note that in a prior experiment conducted by the inventors, the receding angle of the swirling blades 13 was most preferably 10 to 45 degrees, and therefore, in this experiment, the receding angle was set at 30 degrees. An experiment was also performed to determine an appropriate outer peripheral diameter for the swirling blades 13 in the device configuration of the mill 1a. In the device configuration of the mill 1a, the outer peripheral diameter of the component that swirls the slurry is defined as the diameter of the outermost peripheral portion of the component, other than a near-parallel surface (an angle of no more than approximately 30 degrees) to the rotation direction, such as the plate that holds the swirling blades 13.
As shown in the experiment results on table 2, at an outer peripheral diameter ratio of 0.75 and an outer peripheral speed of 8 m/sec or less in the bead separation plates 33, a very small amount of bead leakage occurred, whereas at an outer peripheral speed of 6 m/sec or less, a considerable amount of bead leakage (1 g/min or more) occurred. Meanwhile, when the outer peripheral diameter was set at 36 mm (outer peripheral diameter ratio: 0.82), only a very small amount of bead leakage occurred at 4 m/sec, and therefore an improvement was observed. Further, when the outer peripheral diameter was set at 40 to 60 mm (outer peripheral diameter ratio: 0.91 to 1.36), no bead leakage was observed. At 65 mm (outer peripheral diameter ratio: 1.36), meanwhile, a very small amount of bead leakage (0.1 g or less over a one-hour operation) occurred at the maximum speed of 12 m/sec. Favorable results were obtained at an outer peripheral diameter ratio of 0.82 or more, and therefore the range is preferably 0.82 to 1.48. A range of 0.91 to 1.36 is even more preferable. On the basis of these results, the outer peripheral diameter of the swirling blades 13 of the mills 1a to 1 g was set at 46 or 50 mm.
In the mills 1a to 1f and the mill I, the bead leakage situation was checked using beads with diameters of 0.1 mm and 0.3 mm. As regards the processing conditions, the beads were introduced using room temperature water until a filling ratio of 75% was realized in the mill. The experiment was performed while varying the outer peripheral speed of the slurry swirling component (the bead separation plates 33) of the centrifugal bead separation device 11 from 4 to 12 m/sec at intervals of 2 m/sec. The experiment results are shown on Table 3. In the experiment using beads with a diameter of 0.3 mm, bead leakage was observed in the mill I of the comparative example when the outer peripheral speed of the bead separation plates 33 was 4 m/sec.
On the other hand, bead leakage was not observed in any of the mills 1a to 1f, regardless of the conditions. Note that when the outer peripheral speed was 4 m/sec, a very small amount of beads became intermixed in the slurry storage vessel 6 during the processing of the mills 1a and 1b. However, these beads did not flow out to the exterior of the mill. In the mills 1c to 1f, no beads became intermixed in the slurry storage vessel 6.
In the experiment using beads with a diameter of 0.1 mm, intermixing of the beads in the slurry storage vessel 6 was observed in all mills during processing with the outer peripheral speed of the bead separation plates 33 set at 6 m/sec or less, and in the experiment performed on the mill I of the comparative example, beads leaked to the outside of the device from the slurry storage vessel 6 15 minutes after the start of the processing at 6 m/sec. In the experiment performed on the mill 1a, on the other hand, bead leakage did not occur until the outer peripheral speed of the bead separation plates 33 reached 6 m/sec, and at 4 m/sec, a small amount of beads leaked to the outside of the device from the slurry storage vessel 6 30 minutes after the start of the processing. At this point in time, as shown on Table 2, a considerable amount of beads had accumulated in the interior of the slurry storage vessel 6.
Hence, the beads showed a tendency to accumulate in the interior of the slurry storage vessel 6, and in the mill 1a in which only the swirling blades 13 were disposed, although an effect for preventing bead leakage was achieved, the effect was somewhat limited. In the processing of the mill 1b, no bead leakage from the slurry storage vessel 6 was observed during processing performed with the outer peripheral speed of the bead separation plates 33 set at 6 m/sec or more, and even during the processing performed at 4 m/sec, only a very small amount of leakage was observed 50 minutes after the start of the processing. Hence, by disposing the screen 19, it was possible to prevent bead leakage. Note, however, that a small amount of beads had accumulated in the slurry storage vessel 6 at the end of the processing.
In the experiment performed on the mill 1c, no bead leakage from the slurry storage vessel 6 was observed during the processing performed with the outer peripheral speed of the bead separation plates 33 set at 6 m/sec or more, and even during the processing performed at 4 m/sec, only a very small amount of leakage was observed 90 minutes after the start of the processing. Hence, by disposing the swirl prevention plates 18 in addition to the screen 19, it was possible to prevent suspended bead leakage of the beads in the slurry storage vessel 6. The amount of beads remaining the slurry storage vessel 6 following all of the processing was a very small amount. The reason for this is believed to be that since swirling of the slurry in the slurry storage vessel 6 is reduced such that suspension of the beads is suppressed, it becomes easier to feed the beads to the cylindrical container together with the slurry using the pumping component 9. Note that the reason why a small amount of bead leakage occurred is believed to be that since the under-screen swirling component 20 and so on were not provided, the beads leaked upward through the space between the screen 19 and the rotary shaft 4.
In the experiments performed on the mill 1d and the mill 1e, no bead leakage was observed during all of the processing performed with the outer peripheral speed of the bead separation plates 33 set at 4 to 12 m/sec. This was due to the centrifugal effect of the under-screen swirling component 20 and the effect of the downward slurry flow formed by the pumping component 21. Moreover, in the processing performed on the mill 1d and the mill 1e, the amounts of beads remaining in the slurry storage vessel 6 following the processing performed on the mill 1d and the mill 1e were much smaller than in the processing performed on the mills 1a, 1b, and I, while the amount of accumulated beads was slightly smaller than in the processing performed on the mill 1c.
In the experiment performed on the mill 1f, an effect of sucking out the slurry in the rotary shaft inner flow passage 12 was obtained by the slurry rotating tube 30, thereby stabilizing the flow of slurry into the centrifugal bead separation device 11 so that bead leakage into the slurry storage vessel 6 was smaller than in the processing performed on the mill I of the comparative example and also the processing performed on the mills 1a to 1e.
The experiment performed on the mill 1g is an example in which the partition plate through which the slurry does not pass was disposed instead of the screen 19. A component having the structure shown in
In the mills 2a and 2b and the mill II, the processing experiment was performed using 0.5 mm beads together with water and highly viscous slurry with a viscosity of 550 mPa · s. The diameter of the swirling blades 13 of the mill 2b was 50 mm, which is larger than the diameter of the stirring rotor 5, and it was therefore possible to form a sufficient downward flow in the interior of the slurry flow passage 7 by means of the slurry suctioning effect generated by the centrifugal force of the swirling blades 13. Accordingly, the pumping component 9 was omitted. Note, however, that in order to increase the passage resistance in the slurry flow passage 7, a cylinder (with no grooves or projections) having the same diameter as the pumping component 9 was disposed.
These experiment results are shown on Table 4. In the mill II of the comparative example, when the outer peripheral speed of the stirring rotor 5 was set at a high speed of 8 m/sec or more, the phenomenon whereby the beads are pushed against the upper lid 1 by the centrifugal force created by the stirring rotor 5 occurred. As a result, the beads entered the slurry flow passage 7 and then entered the slurry storage vessel 6. The flow of slurry traveled from the slurry storage vessel 6 toward the cylindrical container, and therefore no beads were intermixed in the slurry after the processing. However, a problem occurred in that the pumping component 9 became worn. Moreover, when the outer peripheral speed of the stirring rotor 5 was 10 m/sec or more during the processing using water and 8 m/sec or more during the processing using highly viscous slurry, a large vortex was formed in the slurry storage vessel 6, causing air to enter the mill, and as a result, slurry foaming occurred.
In the mill 2a, the disc 24 and the swirling blades 13 were disposed as components for swirling the slurry in the upper portion of the mill, and by rotating the slurry near the upper lid 1, the beads were prevented from approaching the slurry flow passage 7. Hence, the pumping component 9 did not become worn, and the beads did not flow back to the slurry storage vessel 6. However, the effects of swirling of the slurry were not resolved, and therefore, when the outer peripheral speed of the stirring rotor 5 was 10 m/sec or more during the processing using water, air entered the cylindrical container from the slurry storage vessel 6, causing the slurry in the cylindrical container to foam, and as a result, the slurry flow deteriorated, making the processing impossible. In the mill 2b, on the other hand, both the combination of the swirling blades 13 and the disc 24 serving as the slurry swirling device and the swirl prevention plates 18 and swirl prevention tube 22 for preventing rotation were disposed, and therefore breakage of the cylinder and the foaming phenomenon did not occur in any of the processing.
As described above, with the bead mill of the present invention, slurry processing can be performed with no bead leakage even without a mechanical seal disposed in a conventional bead mill.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-173771 | Oct 2020 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/032041 | Sep 2021 | WO |
| Child | 18134265 | US |
