JP2020075849A - Method for producing ceramic beads - Google Patents

Abstract

To produce ceramic beads having a uniform shape, which is used as a grinding medium such as a bead mill, while preventing strain beads from being mixed into a pulverized product.SOLUTION: The method for producing ceramic beads has one or a plurality of classification processes of classifying the ceramic particles after molding. In at least one of the classification processes, a mass-classification utilizing a difference in mass of the ceramic particles is performed.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a method for producing ceramic beads suitable for use as a grinding medium or the like.

  A bead mill method is known as a method of mixing and pulverizing inorganic powder and the like (see, for example, Patent Document 1). Ceramic beads used in a bead mill (hereinafter sometimes simply referred to as beads) can be obtained by forming a starting ceramic powder into a spherical shape.

  As a method for molding the ceramic beads, a spray drying method, a submerged granulation method, a tumbling granulation method, or the like is used. Since the beads obtained by such a molding method generally have a distribution in particle size, the object to be crushed cannot be stably mixed and crushed as it is. Therefore, it is necessary to make the particle diameters of the beads after molding uniform.

  As a means for making the particle diameters of the ceramic beads uniform, sieve-type classification in which a mesh-shaped sieve is used to perform classification according to the particle diameter has been mainly used (Patent Document 2).

JP, 2009-155142, A JP 2002-29824A

  When ceramic beads are used as a grinding medium, if agglomerates in which multiple beads are bound together or distorted beads such as shards generated by breaking spherical beads are mixed, the force on the beads will be partially increased. Concentrate and join. As a result, the beads are liable to be broken and fine fragments tend to be generated, which may be mixed in the crushed object. Further, since the beads are quickly worn, it may be difficult to industrially stably produce the target object to be ground. However, with conventional sieve classification alone, even such agglomerates may pass through the sieve depending on the shape, and even fragments may not pass through the sieve depending on the shape, so that both eventually In order to obtain a product, it may be mixed in the bead fraction used in the next step, and it was difficult to prevent the distorted beads from being mixed in the final product.

  The present inventors have found that by incorporating classification by mass, that is, classification using the mass difference of particles into the manufacturing process of ceramic beads, distorted beads can be effectively removed and beads having a uniform shape can be manufactured. It was

  That is, the present invention for solving the above-mentioned problems is a method for producing ceramic beads having one or more classification steps for classifying ceramic particles, wherein the mass difference of the ceramic particles is at least once in the classification step. A method for producing ceramic beads, characterized in that mass classification is performed using

  In addition, in the present specification, a molded body obtained by molding a raw material powder, a sintered body in a manufacturing stage obtained by firing the molded body, a ceramic sintered body as a final product, etc. The ceramic molded body of 1 is generically referred to as "ceramic particles" or simply "particles", and among them, the ceramic sintered body as a final product is referred to as "ceramic beads".

  INDUSTRIAL APPLICABILITY According to the present invention, distorted beads can be removed and uniform-shaped ceramic beads can be produced, and even when used as a grinding medium such as a bead mill, it is possible to prevent the distorted beads from being mixed into an object to be ground. You can

Flowchart for explaining the manufacturing method of the ceramic beads of Example 1 Flowchart for explaining the manufacturing method of the ceramic beads of Example 2 Flowchart for explaining the manufacturing method of the ceramic beads of Example 3 Flowchart for explaining the manufacturing method of the ceramic beads of Example 4 Flowchart for explaining the manufacturing method of the ceramic beads of Comparative Example 1

  The ceramic particles produced by the present invention are preferably powders obtained by granulating ceramic powder. Although the granulation method is not limited, a spray drying method, a submerged granulation method, a tumbling granulation method, or the like is preferable. The spray drying method is not particularly limited, but it is preferable to use a spray dryer, and the particles can be formed by drying with a normal spray dryer such as a disc system or a nozzle system. The granulation conditions are not particularly limited, but it is desirable to adjust the slurry and spray it in consideration of the shape of the particles to be formed and the strength of the molded body. In the tumbling granulation method, a drum having an inclined columnar shape is rotated, and a ceramic powder, a liquid binder containing a binder and water are alternately added into the drum to form a liquid binder between the powder and the powder. To form spherical particles. After that, the ceramic particles are grown by rotating the drum and supplying the ceramic powder to the particles, whereby a spherical molded body can be obtained.

  According to the present invention, at least one of one or a plurality of classification steps is performed, that is, classification using the mass difference of the ceramic particles after molding, that is, mass classification. The method of mass classification is not particularly limited, but classification is preferably performed by an airflow classifier.

  The airflow classifier is not particularly limited as long as it can separate the ceramic particles by the difference in mass. The airflow classifier includes a gravity classifier, an inertial force classifier, and a centrifugal force classifier, and a centrifugal classifier having high classification accuracy is preferably used. A centrifugal classifier is a forced vortex centrifugal classifier that applies centrifugal force to the object to be classified by the rotating force of the rotor inside the device, while exerting a drag force on the object to be classified due to the inward air flow passing through the inside of the device. A guide vane is provided without a rotor inside the machine or the device to create a swirling flow of air, and the swirling motion exerts a centrifugal force on the object to be classified, while the swirling flow itself exerts a drag force on the object to be classified. A working semi-free vortex centrifugal classifier can be used.

  Above all, it is preferable to use a forced vortex centrifugal classifier for mass classification in the present invention. In a forced vortex centrifugal classifier, particles are put into a rotor, and the particles with a large mass are separated by the centrifugal force generated from the rotation of the rotor, while the particles with a small mass are separated by air blown inward into the vortex flow. , Classification according to the mass of particles is possible. Particularly, for the production of ceramic beads having an average particle diameter of 10 to 154 μm, mass classification by a forced vortex centrifugal classifier can be preferably used. The average particle size of the particles used for mass classification is preferably 10 to 154 μm. By setting the average particle size to 10 μm or more, it is possible to suppress clogging of particles in the particle supply device that charges particles into the rotor of the forced vortex centrifugal classifier, and to stably supply particles. From the viewpoint of more stable introduction of particles, the average particle diameter is more preferably 20 μm or more. In addition, when the average particle size is 10 μm or more and less than 20 μm, when particles form a bridge in the hopper of the particle supply device or solidify into a rathole shape, a clogging suppression means such as a knocker, a vibrator, or an air pulse is used. It is preferable to suppress clogging. On the other hand, by setting the average particle size to 154 μm or less, the mass of the particles can be appropriately reduced, and the flow velocity of the air blown into the vortex can be adjusted to easily classify the particles having the desired mass. The particle size can be measured according to the measurement example 1 described later.

  There is no limitation on the method of supplying particles to the airflow classifier, but it is preferable to use a vibration feeder, a belt feeder, a circle feeder, or a screw feeder.

  In the present invention, the mass classification may be performed only once, or may be performed twice or more. For example, particles having a relatively large mass (hereinafter, the particles of a fraction having a relatively large mass or size after classification are referred to as “coarse particles”) are removed by the first mass classification to obtain The particles having a relatively small mass (hereinafter, the particles of a fraction having a relatively small mass or size are also referred to as “fine powder”) are subjected to mass classification again, and are sorted by the primary classification. It is possible to obtain ceramic particles having a uniform particle size and morphology by removing fine powder having a relatively small mass from the fine powder and selecting a coarse powder. The order of removing the coarse powder and the fine powder is not limited to the above and may be appropriately designed.

  In the production method of the present invention, the ceramic particles to be subjected to mass classification are particles after molding the metal oxide and further sintering, even after molding the metal oxide, particles before sintering. However, it is more preferable that the particles are particles after sintering.

  The method for producing ceramic beads of the present invention preferably has a step for firing the ceramic particles. By firing the ceramic particles, dense ceramic particles can be obtained. The firing temperature for sintering the ceramic particles varies depending on the type of raw material powder, but may be any temperature at which sufficient densification can be achieved. For example, alumina can be fired at 1550 ° C to 1650 ° C, and partially stabilized zirconia can be fired at 1350 ° C to 1500 ° C.

  Further, in the production method of the present invention, in addition to mass classification, it is more preferable to perform particle size classification similar to the conventional one in which classification is performed by utilizing the difference in particle size. By performing the particle size classification, both the distorted shape that is easily removed by the mass classification and the distorted shape that is easily removed by the particle size classification can be removed, and ceramic beads having a uniform shape can be obtained. The particle size classification is preferably performed on the ceramic powder after the firing step because ceramic particles having a distorted shape are likely to be generated in the firing step.

  The method of particle size classification is not particularly limited, but it is preferable to use a sieve classifier. The sieve classifier may be configured such that two sieves are stacked and the coarse powder having a relatively large particle diameter and the fine powder having a relatively small particle diameter are removed by one operation.

  The present invention can be applied to ceramic beads made of any metal oxide. Examples of the metal oxide include alumina, zirconia, silica, yttria, aluminum oxide, zirconium oxide, yttrium oxide, silicon nitride, silicon carbide, titanium nitride, zeolite, zircon, and the like, which may be used alone or may be appropriately mixed and used. Good. Above all, it is particularly preferable to apply it to ceramic beads made of zirconia.

  The ceramic beads produced by the method for producing ceramic beads of the present invention can prevent the distorted beads from being mixed into the object to be pulverized, and thus are suitably used as a pulverizing medium.

[Measurement Example 1: Average particle size and acicular ratio]
About 100 ceramic particles were photographed using a digital microscope VHX-2000 (manufactured by Keyence Corporation). In order to eliminate the variation in measurement and evaluate with high accuracy, a plurality of images taken for each visual field were combined to obtain a measurement image. Binarized image was obtained by separating the ceramic particle portion and the base material portion by binarizing the brightness of the measurement image using the image analysis / measurement software WinROOF (registered trademark: manufactured by Mitani Corporation) as a reference. . The binarized image was separated into circular figures, the diameter of each separated circle was measured, and the average particle diameter of the ceramic particles was determined.

Also,
-Absolute maximum length: A value that is the largest in the diameter of ceramic particles.
-Diagonal width: A value that is the largest diameter perpendicular to the absolute maximum length.
Seeking
The acicular ratio was calculated from acicular ratio = absolute maximum length / diagonal width. The smaller the acicular ratio, the more uniform the shape of the ceramic particles.

[Example 1]
Ceramic beads were produced by the procedure shown in FIG.

  First, ceramic particles (1) were prepared by molding zirconia powder by a spray drying method. The ceramic particles (1) were passed through a circular vibrating sieve machine (vibrating sieve 401 manufactured by Dalton Co.) having a sieve mesh of 90 μm to remove coarse powder that did not pass through the sieve mesh, and fine powder that passed through the sieve mesh. Were selected (particle size classification). Then, the fine powder was sintered at 1400 ° C. to obtain ceramic particles (2) having an average particle diameter of 60 μm and an acicular ratio of 1.30.

Subsequently, using a forced vortex centrifugal classifier (TC-15 manufactured by Nisshin Engineering Co., Ltd.) as an airflow classifier, airflow classification (1) was performed at a rotation speed of 500 rpm and an air volume of 8.5 m ³ / min. The coarse powder with a large mass was removed. Further, the remaining fine powder is selected, and the air-flow classification (2) is performed under the conditions of a rotation speed of 650 rpm and an air volume of 8.5 m ³ / min to remove the fine powder having a relatively small mass to obtain an average particle diameter of 50 μm. A ceramic particle (3) having an acicular ratio of 1.14 was obtained.

  Next, a circular vibrating screener (vibrating screen 401 manufactured by Dalton Co., Ltd.) was fitted with two sieve meshes with openings of 66 μm and openings of 35 μm, and classification (particle size classification) was carried out by a sieve classifier to open the openings. The coarse powder that did not pass through the 66 μm sieve and the fine powder that passed through both sieves were removed, and ceramic particles (4) were obtained from above the sieve with an opening of 35 μm. The average particle size of the obtained ceramic particles was 50 μm, and the acicular ratio was 1.04.

[Example 2]
Ceramic beads were produced by the procedure shown in FIG.

  Ceramic particles (1) were produced by granulating zirconia powder by a tumbling granulation method. The ceramic particles (1) were passed through a circular vibrating screen machine (vibrating screen 401 manufactured by Dalton Co.) having a screen with an opening of 154 μm to remove coarse powder that did not pass through the screen and select fine powder that passed through the screen. (Particle size classification). The fine powder was sintered at 1400 ° C. to obtain ceramic particles (2) having an average particle diameter of 110 μm and an acicular ratio of 1.28.

Subsequently, using a forced vortex centrifugal classifier (TC-15 manufactured by Nisshin Engineering Co., Ltd.) as an airflow classifier, airflow classification (1) was performed at a rotation speed of 400 rpm and an air volume of 9.0 m ³ / min. The coarse powder having a large mass was removed. Further, the remaining fine powder is subjected to airflow classification (2) under the conditions of a rotation speed of 500 rpm and an air flow rate of 8.7 m ³ / min to remove the fine powder having a relatively small mass to obtain an average particle diameter of 100 μm and a needle shape. Ceramic particles (3) with a ratio of 1.13 were obtained.

  Next, as a particle size classification by a vibrating screen classifier, a circular vibrating screen machine (vibrating screen 401 manufactured by Dalton Co., Ltd.) was equipped with a sieve net of 132 μm openings and 77 μm openings in two stages, and classification by the screen classifier (particles By carrying out size classification), ceramic particles (4) were obtained from above the sieve having an opening of 77 μm. The obtained ceramic particles had an average particle size of 100 μm and an acicular ratio of 1.03.

[Example 3]
Ceramic beads were produced by the procedure shown in FIG.

  First, ceramic particles (1) were produced by granulating a zirconia powder by a spray drying method. The ceramic particles (1) were passed through a circular vibrating sieve machine (vibrating sieve 401 manufactured by Dalton Co.) having a sieve mesh of 90 μm to remove particles that did not pass through the sieve and select fine powder that passed through the sieve. (Particle size classification). Then, the fine powder was sintered at 1400 ° C. to obtain ceramic particles (2) having an average particle diameter of 60 μm and an acicular ratio of 1.30.

  Subsequently, as a means for classifying by the particle diameter by the vibrating screen classifier, a circular vibrating screen machine (Dalton vibrating screen 401) was equipped with a sieve net of 66 μm openings and 34 μm openings in two stages, and classification by the screen classifier ( By performing particle size classification), ceramic particles (3) were obtained on a sieve mesh having an opening of 34 μm. The obtained ceramic particles (3) had an average particle diameter of 50 μm and an acicular ratio of 1.18.

Next, a forced vortex centrifugal classifier (TC-15 manufactured by Nisshin Engineering Co., Ltd.) was used as an airflow classifier, and airflow classification (1) was performed at a rotation speed of 500 rpm and an air volume of 8.5 m ³ / min, and relatively. The coarse powder having a large mass was removed. Further, the remaining fine powder is subjected to airflow classification (2) under the conditions of a rotation speed of 650 rpm and an air volume of 8.5 m ³ / min to remove the fine powder having a relatively small mass to obtain an average particle diameter of 50 μm and a needle. Ceramic particles (4) having a state ratio of 1.05 were obtained.

[Example 4]
Ceramic beads were produced by the procedure shown in FIG.

  Ceramic particles (1) were produced by granulating zirconia powder by a tumbling granulation method. The ceramic particles (1) are passed through a circular vibrating screener (vibrating screen 401 manufactured by Dalton Co.) having a screen of 90 μm openings to remove particles that have not passed through the screen and select fine powder that has passed through the screen. (Particle size classification). Then, the fine powder was sintered at 1400 ° C. to obtain ceramic particles (2) having an average particle diameter of 60 μm and an acicular ratio of 1.30.

Next, a forced vortex centrifugal classifier (TC-15 manufactured by Nisshin Engineering Co., Ltd.) was used as an airflow classifier, and airflow classification (1) was performed at a rotation speed of 500 rpm and an air volume of 8.5 m ³ / min, and relatively. The coarse powder having a large mass was removed. Further, the remaining fine powder is subjected to airflow classification (2) under the conditions of a rotation speed of 650 rpm and an air volume of 8.5 m ³ / min to remove the fine powder having a relatively small mass to obtain an average particle diameter of 50 μm and a needle. Ceramic particles (4) having a state ratio of 1.15 were obtained.

Further, using the forced vortex centrifugal classifier, airflow type classification (3) was performed at a rotation speed of 500 rpm and an air flow rate of 8.5 m ³ / min to remove coarse powder having a relatively large mass. Further, the remaining fine powder is subjected to airflow classification (4) under the conditions of a rotation speed of 650 rpm and an air volume of 8.5 m ³ / min to remove the fine powder having a relatively small mass to obtain an average particle diameter of 50 μm and a needle. Ceramic particles (4) having a state ratio of 1.10 were obtained.

[Comparative Example 1]
Ceramic beads were produced by the procedure shown in FIG.

  Ceramic particles (1) were produced by granulating zirconia powder by a tumbling granulation method. The ceramic particles (1) are passed through a circular vibrating screener (vibrating screen 401 manufactured by Dalton Co.) having a screen of 90 μm openings to remove particles that have not passed through the screen and select fine powder that has passed through the screen. (Particle size classification). Then, the fine powder was sintered at 1400 ° C. to obtain ceramic particles (2) having an average particle diameter of 60 μm and an acicular ratio of 1.30.

  Next, as a particle size classification by a vibrating screen classifier, a circular vibrating screener (Dalton vibrating screen 401) was equipped with a sieve mesh with openings of 66 μm and openings of 34 μm in two stages, and classification with a screen classifier (particle size By performing classification), ceramic particles (3) were obtained on a sieve mesh having an opening of 34 μm. The obtained particles had an average particle size of 50 μm and an acicular ratio of 1.20.

  Further, classification was repeated once again under the same conditions using a circular vibrating screener (vibrating screen 401 manufactured by Dalton) to obtain ceramic particles (4) from a screen of 34 μm. The obtained particles had an average particle size of 50 μm and an acicular ratio of 1.19.

Claims (10)

A method for producing ceramic beads having one or more classification steps for classifying ceramic particles, wherein mass classification using a mass difference of the ceramic particles is performed in at least one of the classification steps. Method for producing ceramic beads. The method for producing ceramic beads according to claim 1, wherein the mass classification is performed by an airflow classifier. The method for producing ceramic beads according to claim 2, wherein a forced vortex centrifugal classifier is used as the airflow classifier. The method for producing ceramic beads according to claim 1, wherein the ceramic particles used for the mass classification have an average particle diameter of 10 to 154 μm. The method for producing ceramic beads according to claim 1, wherein the ceramic particles to be subjected to the mass classification are ceramic particles obtained by molding a metal oxide and further sintering the metal oxide. The method for producing ceramic beads according to any one of claims 1 to 4, wherein the ceramic particles used for the mass classification are ceramic particles after molding a metal oxide and before sintering. The method for producing ceramic beads according to claim 1, wherein the classification step is performed a plurality of times, and in addition to the mass classification, particle size classification utilizing a difference in particle diameter is performed. The method for producing ceramic beads according to claim 7, wherein the particle size classification is performed by a sieve classifier. The method for producing ceramic beads according to any one of claims 1 to 8, wherein ceramic beads used as a grinding medium are produced. The method for producing ceramic beads according to any one of claims 1 to 9, for producing ceramic beads made of zirconia.

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