JP7629773B2 - Classifying rotor and centrifugal air classifier - Google Patents

Description

This disclosure relates to a classifying rotor and a centrifugal air classifier.

A centrifugal air classifier has a mechanism that rotates the built-in classifying rotor at high speed, and sends an air current containing powder from the side of the rapidly rotating classifying rotor to the opening in the center of the upper plate. The coarse powder contained in the air current is thrown out of the classifying rotor by the centrifugal force generated by the rotation of the blades, and the fine powder is removed from the opening in the center of the upper plate of the classifying rotor by the air current that overcomes the centrifugal force, and the powder contained in the air current is classified into coarse and fine powder.

For example, Patent Document 1 proposes a classification rotor for use in such a mechanism, which has multiple flat blades, both ends of which are sandwiched between two replaceable slit plates with radial slits, and the upper and lower plates of the classification rotor are supported by supports installed inside. It also states that the blades are made of a ceramic material.

Utility Model Registration No. 3103835

When classifying hard powders such as ceramic powder, the classification rotor proposed in Patent Document 1 has the problem that the metal components other than the blade (e.g., upper and lower plates) are easily worn out, and the weight increases as the proportion of metal components increases, resulting in a large load on the motor that rotates it.

The objective of this disclosure is to provide a classification rotor and centrifugal air classifier that are highly wear-resistant and lightweight.

The classification rotor according to the present disclosure comprises a lid body made of ceramics having a through hole in the thickness direction, and a bottomed cylindrical body made of ceramics having a bottom portion having an axial hole on the same axis as the through hole, and a peripheral wall portion connected to the bottom portion and having multiple slits. The lower surface of the lid body and the end surface of the peripheral wall portion are joined via a layer made of ceramics.

The centrifugal air classifier disclosed herein uses the above-mentioned classifying rotor.

The classification rotor and centrifugal air classifier disclosed herein are highly wear-resistant and lightweight.

FIG. 2 is a perspective view of a classifying rotor according to a non-limiting embodiment of the present disclosure. 2 is a cross-sectional view of the classifying rotor shown in FIG. 1 taken along an axis. 3 is an enlarged view of the periphery of a layer made of ceramics in the classifying rotor shown in FIG. 2 . FIG. 1 is a schematic diagram illustrating a centrifugal air classifier according to a non-limiting embodiment of the present disclosure.

<Classification rotor>
Hereinafter, a classifying rotor according to a non-limiting embodiment of the present disclosure will be described in detail with reference to the drawings. However, in each of the drawings referred to below, for the sake of convenience, only the main components necessary for explaining the embodiment are shown in a simplified form. Therefore, the classifying rotor may include any component not shown in each of the drawings referred to. Furthermore, the dimensions of the components in each drawing do not faithfully represent the dimensions of the actual components and the dimensional ratios of each component. These points are also true of the centrifugal air classifier described below.

The classification rotor 1 comprises a lid body 2 and a bottomed cylindrical body 3, as shown in the example in Figures 1 to 3.

The lid 2 has a through hole 21 in the thickness direction. The through hole 21 can function as an extraction hole for removing fine powder classified from the powder to the outside of the classifying rotor 1. The powder can be, for example, a hard powder such as a ceramic powder. The lid 2 may be disk-shaped.

The bottomed cylindrical body 3 has a bottom 31 and a peripheral wall 32. The bottom 31 has an axial hole 311 on the same axis S as the through hole 21. The axial hole 311 can function as an attachment hole for a motor that rotates the classifying rotor 1. The axial hole 311 may be a hole in the cylinder 312 that protrudes toward the lid 2.

The axis S may also be referred to as the axis of rotation. The classifying rotor 1 can rotate around the axis S. The classifying rotor 1 may also be shaped to extend along the axis S.

The peripheral wall portion 32 is connected to the bottom portion 31. The peripheral wall portion 32 may be formed integrally with the bottom portion 31. The peripheral wall portion 32 also has a number of slits 321. The slits 321 can function as a portion for passing an airflow containing powder inside the classifying rotor 1. The slits 321 can also function as a portion for flicking coarse powder contained in the airflow to the outside of the classifying rotor 1.

The number of slits 321 may be 24 or more and 120 or less. The multiple slits 321 may be positioned at equal intervals along the outer periphery of the peripheral wall portion 32. The multiple slits 321 may extend along the axis S.

Here, the lid 2 is made of ceramics. The bottomed cylindrical body 3 is also made of ceramics. The bottom surface 22 of the lid 2 and the end surface 322 of the peripheral wall portion 32 are joined via a layer 4 made of ceramics. As a result, since the lid 2, bottomed cylindrical body 3 and layer 4 are made of ceramics, the wear resistance of the classifying rotor 1 is increased and the mixing of wear powder generated from the members constituting the classifying rotor 1 into the powder is suppressed. In addition, since the entire classifying rotor 1 is lighter, the load on the motor for rotating the classifying rotor 1 is reduced, and it can be used for a long period of time.

The ceramic may have aluminum oxide as its main component. The main component may mean the component that is the most abundant out of a total of 100% by mass of all components that make up the ceramic. The main component may be, for example, 80% by mass or more. When the main component of the ceramic is aluminum oxide, it may contain at least one of silicon, magnesium, and calcium as an oxide.

The components that make up the ceramics can be identified using an X-ray diffraction device (XRD) using CuKα radiation, and then the elemental content can be determined using an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) emission spectrometer (ICP) and converted into the content of the identified components.

The ceramics in the lid 2, bottomed cylindrical body 3, and layer 4 may be the same or different. For example, layer 4 may be made of ceramics with the same main component as the ceramics in the lid 2 and bottomed cylindrical body 3. In this case, the lower surface 22 of the lid 2 and the end surface 322 of the peripheral wall portion 32 can be firmly joined. The thickness of layer 4 may be set to, for example, about 40 μm or more and 60 μm or less.

The layer 4 may have a first protrusion 41 connected to the layer 4 on the inner circumferential side of the bottomed cylindrical body 3. The presence of the first protrusion 41 makes it difficult for powder to be pinched between the layer 4 and the lower surface 22 of the lid 2 and between the layer 4 and the end surface 322 of the peripheral wall portion 32, reducing the risk of the pinched powder being mixed in as a foreign object even when different powders are classified in front and behind. The main component of the first protrusion 41 may be the same as the main component of the layer 4.

The average diameter of the closed pores in the first convex portion 41 may be 1.5 times or less the average diameter of the closed pores in the vicinity of the first convex portion 41 of the lid body 2. In this case, since the closed pores in the first convex portion 41 are small, the occurrence of microcracks originating from the closed pores in the first convex portion 41 and the progression of the microcracks to the lid body 2, the bottomed cylindrical body 3, and the layer 4 can be suppressed.

The average diameter of the closed pores present in the first convex portion 41 may be 0.8 times or more the average diameter of the closed pores present in the vicinity of the first convex portion 41 of the lid body 2. In addition, the average diameter of the closed pores present in the first convex portion 41 may be smaller than the average diameter of the closed pores present in the vicinity of the first convex portion 41 of the lid body 2.

The average diameter of the closed pores is not limited to a specific value. For example, the average diameter of the closed pores present in the first convex portion 41 may be set to approximately 0.8 μm or more and 1.7 μm or less. In addition, the average diameter of the closed pores present in the vicinity of the first convex portion 41 of the lid body 2 may be set to approximately 1 μm or more and 2.1 μm or less.

The average diameter of the closed pores present in the vicinity of the first convex portion 41 and the first convex portion 41 of the lid body 2 may be measured, for example, by cross-sectional observation using a scanning electron microscope. A sample including a part of the lid body 2 to be measured and the first convex portion 41 in contact with the lid body 2 is cut out and embedded in a polyester-based resin to form a cylindrical sample. Here, the cross section of the sample may be mirror-finished using diamond abrasive grains. The magnification may be set to, for example, 500 times. The observation range for observing the cross section of the sample may be set to, for example, a horizontal length of 256 μm and a vertical length of 192 μm, dividing the lid body 2 and the first convex portion 41.

The vicinity of the first convex portion 41 of the lid body 2 refers to the remainder of the lid body 2 when the cross-sectional area of the first convex portion 41 in the observation range, including a part of the lid body 2 and a part of the first convex portion 41 in contact with the lid body 2, is set to 100%, and the cross-sectional area of the first convex portion 41 in this observation range is set to be 25% to 50%. The cross-sectional area of the remainder of the lid body 2 is also set to be 25% to 50% in this observation range.

Each divided observation area may be analyzed, and the average diameter of the closed pores may be determined by applying a particle analysis technique using the image analysis software "Azokun (Ver. 2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.). The average diameter of the closed pores may be the average value of the equivalent circle diameters.

In the analysis, the particle analysis setting conditions are: particle brightness is dark, binarization method is manual, threshold is 70 to 100, small figure removal area is 0.3 μm ^{2 ,} and a noise removal filter is used.

In the above measurements, the threshold value was set to 70 to 100, but the threshold value can be adjusted according to the brightness of the image, which is the observation range. The particle brightness is set to dark, the binarization method is set to manual, the small figure removal area is set to 0.3 ^μm2 , and a noise removal filter is used. The threshold value can then be adjusted so that the markers appearing in the image match the shapes of closed pores.

The layer 4 may have a second protrusion 42 connected to the layer 4 on the outer periphery of the bottomed cylindrical body 3. In this case, even when used in a highly corrosive environment, the layer 4 is less susceptible to corrosion, reducing the risk of separation between the lid 2 and the bottomed cylindrical body 3, allowing for long-term use. The main component of the second protrusion 42 may be the same as the main component of the layer 4.

The average diameter of the closed pores in the second convex portion 42 may be 1.5 times or less the average diameter of the closed pores in the vicinity of the second convex portion 42 of the lid body 2. In this case, since the closed pores in the second convex portion 42 are small, the occurrence of microcracks originating from the closed pores in the second convex portion 42 and the progression of the microcracks to the lid body 2, the bottomed cylindrical body 3, and the layer 4 can be suppressed.

The average diameter of the closed pores present in the second convex portion 42 may be 0.8 times or more the average diameter of the closed pores present in the vicinity of the second convex portion 42 of the lid body 2. In addition, the average diameter of the closed pores present in the second convex portion 42 may be smaller than the average diameter of the closed pores present in the vicinity of the second convex portion 42 of the lid body 2.

For example, the average diameter of the closed pores present in the second convex portion 42 may be set to approximately 0.8 μm or more and 1.7 μm or less. Also, the average diameter of the closed pores present in the vicinity of the second convex portion 42 of the lid body 2 may be set to approximately 1 μm or more and 2.1 μm or less.

The average diameter of the closed pores present in the vicinity of the second convex portion 42 and the second convex portion 42 of the lid body 2 may be measured, for example, by cross-sectional observation using a scanning electron microscope. A sample including a part of the lid body 2 to be measured and the second convex portion 42 in contact with the lid body 2 is cut out and embedded in a polyester-based resin to form a cylindrical sample. Here, the cross section of the sample may be mirror-finished using diamond abrasive grains. The magnification may be set to, for example, 500 times. The observation range for observing the cross section of the sample may be set to, for example, a horizontal length of 256 μm and a vertical length of 192 μm, dividing the lid body 2 and the second convex portion 42.

The vicinity of the second convex portion 42 of the lid body 2 refers to the remaining part of the lid body 2 when the observation range including a part of the lid body 2 and a part of the second convex portion 42 in contact with the lid body 2 is taken as 100%, and the cross-sectional area of the second convex portion 42 is set to 25% or more and 50% or less.

When the second convex portion 42 is not in contact with the lower surface 22 of the lid body 2 (i.e., the outer peripheral surface 35 of the bottomed cylindrical body 3 and the outer peripheral surface of the lid body 2 are flush), the vicinity of the second convex portion 42 of the lid body 2 refers to the remainder of the lid body 2 when the cross-sectional area of the second convex portion 42 in the observation range is set to be 25% to 50%, assuming that the observation range including the corner formed by the outer peripheral surface of the lid body 2 and the lower surface of the lid body 2 and a part of the second convex portion 42 is 100%. In either case, the cross-sectional area of the remainder of the lid body 2 is set to be 25% to 50%.
After this, the average diameter of the closed pores can be obtained using the same method as described above.

The average diameter of the closed pores present in the lower layer 23 including the lower surface 22 of the lid 2 may be smaller than the average diameter of the closed pores present in the upper layer 25 including the upper surface 24 of the lid 2. In this case, the hardness of the lower surface 22 is higher than that of the upper surface 24, improving the wear resistance of the lower surface 22. On the other hand, the upper surface 24 is more likely to vibrate due to the rotation of the motor than the lower surface 22, but this vibration can be reduced.

The lower layer 23 may be located closer to the lower surface 22 than the center 2a in the thickness direction of the lid 2. The upper layer 25 may be located closer to the upper surface 24 than the center 2a in the thickness direction of the lid 2. For example, the thickness of the lid 2 may be set to about 15 mm or more and 30 mm or less. The average diameter of the closed pores present in the lower layer 23 may be set to about 2 μm or more and 7 μm or less. The average diameter of the closed pores present in the upper layer 25 may be set to about 3 μm or more and 8 μm or less.

The average diameter of the closed pores present in the lower layer 23 and the upper layer 25 may be measured by, for example, cross-sectional observation using a scanning electron microscope. Samples including the lower layer 23 and the upper layer 25 to be measured may be cut out, and the cross-sections of the samples may be mirror-finished using diamond abrasive grains. The magnification may be set to, for example, 500 times. The observation range for observing the cross-section of the sample may be set to, for example, a horizontal length of 256 μm and a vertical length of 192 μm.
After this, the average diameter of the closed pores can be obtained using the same method as described above.

The inner bottom surface 33 and inner peripheral surface 34 of the bottomed cylindrical body 3 and the underside 22 of the lid body 2 may be burned surfaces. If the surfaces are burned surfaces, there is no fractured layer on the burned surfaces, so that falling off of the particles from the burned surfaces is suppressed.

The outer peripheral surface 35 of the bottomed cylindrical body 3 may be a ground surface. In this case, the dimensional accuracy of the outer peripheral surface 35 is high. Therefore, the outer peripheral surface 35 can suppress circumferential runout relative to the inner peripheral surface 34 that forms the axial hole 311, so that runout can be reduced when the classifying rotor 1 is rotated.

The classifying rotor 1 is not limited to a specific size. For example, the maximum length of the classifying rotor 1 in the direction along the axis S may be set to approximately 150 mm or more and 220 mm or less. The outermost diameter of the classifying rotor 1 in the direction perpendicular to the axis S may be set to approximately 280 mm or more and 350 mm or less. The maximum length of the slit 321 in the direction along the axis S may be set to approximately 120 mm or more and 160 mm or less. The maximum width of the slit 321 in the direction perpendicular to the axis S may be set to approximately 5 mm or more and 10 mm or less.

The cross-sectional shape of the slit 321 shown in FIG. 1 is rectangular, but it may be racetrack-shaped or elliptical.

Next, the manufacturing method of the classification rotor disclosed herein will be explained using the manufacturing of the above-mentioned classification rotor 1 as an example.

First, a powder mixture is weighed out so that the magnesium hydroxide is 0.3% to 0.42% by mass when converted to oxide (MgO), silicon oxide is 0.03% to 0.05% by mass, calcium carbonate is 0.01% to 0.02% by mass when converted to oxide (CaO), and the remainder is aluminum oxide. The powder mixture is then placed in a rotary mill together with a solvent such as water and mixed with ceramic balls made of aluminum oxide with a purity of 99.5% to 99.99%.

Next, a molding binder such as polyvinyl alcohol, polyethylene glycol, or acrylic resin is added and mixed to obtain a slurry. Here, the amount of molding binder added is 2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the mixed powder.

Next, the slurry is spray-dried using a spray drying device to obtain granules. The granules are molded by a CIP (Cold Isostatic Pressing) method, for example, at a pressure of 80 MPa to 100 MPa, to obtain disk-shaped and cylindrical bodies. These bodies are then subjected to cutting or other processing to obtain precursor A of the lid body 2 and precursor B of the bottomed cylindrical body 3, respectively.

Here, a paste containing aluminum oxide powder, cellulose polysaccharides, and a solvent is prepared.

Specifically, a solvent such as water or ethanol is added to the mixed powder so that the volume ratio of mixed powder to solvent is 55-60:40-45, and the total of this solvent and mixed powder is 100 parts by mass. To this 100 parts by mass, 8 parts by mass to 20 parts by mass of cellulose polysaccharide is added, and these are placed in a storage container in a stirring device and mixed and stirred to obtain a paste.

Here, the cellulose polysaccharide is, for example, at least one of methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, carboxymethyl ethyl cellulose, and carboxyethyl cellulose.

The average diameter of the closed pores may be adjusted, for example, by the conditions when stirring the paste. For example, if the average diameter of the closed pores in the first convex portion 41 is to be 1.5 times or less than the average diameter of the closed pores in the vicinity of the first convex portion 41 of the lid body 2, the rotation speed of the stirring device may be set to 1200 rpm or more and 1600 rpm or less, and the rotation time may be set to 5 minutes or more and 15 minutes or less. Also, if the average diameter of the closed pores in the first convex portion 41 is to be smaller than the average diameter of the closed pores in the vicinity of the first convex portion 41 of the lid body 2, the rotation speed may be increased to 1400 rpm or more and 1600 rpm or less, and the rotation time may be set to 5 minutes or more and 15 minutes or less.

By stirring the paste within this range of stirring conditions, it is possible to adjust the average diameter of the closed pores to the above-mentioned relationship. The above points can also be applied to adjusting the average diameter of the closed pores present in the second convex portion 42.

After the paste is applied to the opposing surfaces of at least one of precursor A and precursor B, the opposing surfaces are placed facing each other and precursor A and precursor B are pressurized, for example, at a pressure of 20 kPa to 40 kPa. At this time, the paste may be allowed to overflow from the opposing surfaces on the inner and outer circumferential sides of precursor B. Then, a precursor in which precursor A and precursor B are connected is obtained by the above pressurization.

Next, the paste is dried by holding it at room temperature for 12 to 48 hours while adjusting the humidity. The precursor is then fired in an air atmosphere at a temperature of 1500°C to 1700°C for 5 to 8 hours to obtain the classification rotor 1.

To obtain a classification rotor in which the average diameter of closed pores in the lower layer, including the lower surface of the lid body 2, is smaller than the average diameter of closed pores in the upper layer, including the upper surface of the lid body 2, precursor B is made thick in advance (for example, at least twice the thickness of the lid body 2), and after firing, the upper and lower layer sides are ground so that the amount of grinding is greater on the upper layer side than on the lower layer side.

The above manufacturing method is one example of a method for manufacturing the classification rotor 1. Therefore, it goes without saying that the classification rotor 1 is not limited to being manufactured by the above manufacturing method.

<Centrifugal air classifier>
Next, a centrifugal air classifier according to a non-limiting embodiment of the present disclosure will be described with reference to the drawings, taking as an example a case in which the above-described classifying rotor 1 is used.

As shown in the example in FIG. 4, a centrifugal air classifier 100 (hereinafter sometimes referred to as "classifier 100") is configured using a classification rotor 1. Since the classifier 100 is configured using a classification rotor 1 that is highly resistant to wear and lightweight, stable classification is possible over a long period of time.

The classifier 100 may include a casing 101 that houses the classifying rotor 1, a motor 102 that rotates the classifying rotor 1, a supply pipe 103 that supplies raw material to the inside of the casing 101, a number of nozzles 104 that are located below the supply pipe 103 and supply compressed air to the inside of the casing 101, and an outlet pipe 105 that transports the fine powder classified by the classifying rotor 1 to the outside of the casing 101.

Although the above provides examples of embodiments of the present disclosure, it goes without saying that the present disclosure is not limited to the above embodiments and may be any embodiment without departing from the gist of the present disclosure.

Reference Signs List 1: Classification rotor 2: Lid 21: Through hole 22: Lower surface 23: Lower layer 24: Upper surface 25: Upper layer 2a: Center 3: Bottomed cylindrical body 31: Bottom 311: Shaft hole 312: Cylinder 32: Peripheral wall 321: Slit 322: End face 33: Inner bottom surface 34: Inner peripheral surface 35: Outer peripheral surface 4: Layer 41: First convex portion 42: Second convex portion 100: Centrifugal air classifier 101: Casing 102: Motor 103: Supply pipe 104: Nozzle 105: Discharge pipe S: Shaft

Claims (8)

A lid body made of ceramic having a through hole in a thickness direction;
a bottomed cylindrical body made of ceramic having a bottom portion having an axial hole coaxial with the through hole and a peripheral wall portion connected to the bottom portion and having a plurality of slits;
the lower surface of the lid body and the end surface of the peripheral wall portion are joined via a layer made of ceramics,
A classification rotor, wherein an average diameter of closed pores present in a lower layer portion including a lower surface of the lid body is smaller than an average diameter of closed pores present in an upper layer portion including an upper surface of the lid body. The classifying rotor according to claim 1 , wherein the layer has a first protrusion connected to the layer on an inner circumferential side of the bottomed cylindrical body. 3. The classification rotor according to claim 2 , wherein an average diameter of closed pores present in the first convex portion is 1.5 times or less an average diameter of closed pores present in the vicinity of the first convex portion of the lid body. The classifying rotor according to any one of claims 1 to 3 , wherein the layer has a second protrusion connected to the layer on the outer circumferential side of the bottomed cylindrical body. 5. The classification rotor according to claim 4 , wherein an average diameter of closed pores present in the second convex portion is 1.5 times or less an average diameter of closed pores present in the vicinity of the second convex portion of the lid body. The classification rotor according to any one of claims 1 to 5 , wherein the inner bottom surface and inner peripheral surface of the bottomed cylindrical body and the lower surface of the lid are as-fired surfaces. The classification rotor according to any one of claims 1 to 6 , wherein the outer circumferential surface of the bottomed cylindrical body is a ground surface. A centrifugal air classifier using the classification rotor according to any one of claims 1 to 7 .

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