JPH0372938A - Granulator for preparing microspherical body - Google Patents

Abstract

PURPOSE:To enhance spheroidicity by forming uneven grooves to the inner wall surface of a cylindrical stirring tank. CONSTITUTION:A fine powder of fine ceramics such as zirconia, alumina or mullite, an org. solvent and water being a binder are received in a cylindrical stirring tank in predetermined amounts and said stirring tank is rotated at about 1000-2500rpm. After the completion of granulation, the obtained granules are baked at about 1200-1450 deg.C in the oxidative atmosphere within an electric furnace to obtain baked balls. Uneven grooves are formed in parallel to the rotary shaft of rotary stirring blades so that the cross-section of each groove when the stirring tank is cut at the surface vertical to the rotary shaft becomes a U-shape, a V-shape or a circular arc shape. By this method, the dispersion of a ceramics raw material can be performed within a short time.

Description

Detailed Description of the Invention (1) Purpose of the Invention [Field of Industrial Application] The present invention relates to a submerged granulator for producing dense, heavy, and highly spherical microspheres from fine ceramic powder. It is something.

[Conventional technology]

In recent years, hard microballs have been attracting attention as they have found many uses in various industries. In particular, high-strength, highly wear-resistant microspheres with a diameter of 500 μm or less made from fine ceramics such as zirconia are said to be suitable for pulverizing, dispersing, or mixing hard raw materials and high-purity raw materials, and demand will increase in the future. It is predicted that this will happen. However, it is difficult to produce microspheres with a diameter of 500 μm or less using conventional granulation methods, and the development of a new granulation method is desired.

These hard microballs are manufactured by molding raw material powder into a ball shape and sintering it at high temperature. Conventional methods for forming balls include transfer granulation, fluidized bed granulation, and axial pressing. The transfer granulation method is a method in which a binder is added to the raw material powder, kneaded, and then extruded to form granules into a columnar shape, for example, and then rotated in a pan-shaped or drum-shaped container to gradually form them into a spherical shape. be.

In the axial press method, instead of molding by extrusion, a mixed material is placed in a two-split spherical mold and molded, but there is a protruding part at the joint of the upper and lower molds, and a transfer process is required to remove it and make it spherical. Is required.

These methods require highly skilled techniques to produce microscopic balls of 500 μm or less and have poor yields, making them unsuitable for commercial production.

On the other hand, in the fluidized bed granulation method, a stirring blade is installed inside the granulator, and the supplied ceramic raw material powder is formed into a fluidized bed inside the machine by the rotating stirring blade. grow into a ball shape. It is difficult to make dense balls using this method.

In addition, as another method, a method using an Ebara PBS type device as an example of a submerged granulation method is a method for treating wastewater containing suspended solids, and a flocculant is added to a suspension of solids and water. In this method, a polymer is added and stirred to form granules, but the spherical bodies produced have a diameter of llIn or more and a low degree of sphericity.
It also lacks density, making it unsuitable for manufacturing fine ceramic microspheres.

(Problems to be Solved by the Invention) In order to manufacture fine ceramic fired balls with a diameter of 500 μm or less, fine ceramic spherical bodies with a diameter of 600 μm or less must be granulated as an element body.
However, the transfer method and axial press method require a high level of skill, have low yields, and are economically disadvantageous, and fluidized bed granulation You can't play a precise ball with the law. Further, even with conventional granulation methods in liquid, it is not possible to obtain spherical bodies with a diameter of 600 μm or less.

An object of the present invention is to provide a granulator capable of producing fine spherical bodies having a diameter of 50 to 600 μm, high sphericity, and denseness by granulating fine ceramic powder in a liquid as a raw material.

(Means for Solving the Problems) As a result of research, the present inventors have developed a granulator that granulates dense ceramic spherical bodies with a spherical shape of 600 μm or less and a high degree of sphericity in a liquid. It was confirmed that the microspheres obtained by firing the granules obtained by this granulator at a high temperature in a conventional manner can be put to practical use.

That is, the present invention provides a submerged granulator in which a fine powder, a solvent, and a binder are placed in a cylindrical stirring tank equipped with a rotating stirring blade, and the stirring blade is rotated to produce a granulated product. This is a submerged granulator characterized by having uneven grooves formed on the wall surface.

Furthermore, in the above granulator, the uneven grooves formed on the inner wall surface of the cylindrical stirring tank are parallel to the rotation axis of the rotary stirring blade, and the stirring tank is cut in a plane perpendicular to the rotation axis. It is preferable that the cross section of the groove is concave, square, or arcuate. Moreover, in the said granulator, it is preferable that it is a submerged granulator in which the distance between the tip of the rotating stirring blade and the convex part on the inner wall surface of the cylindrical stirring tank is 2 to 15 mm.

The present inventor focused on the fact that fine ceramic powder has no affinity with organic solvents and has a high affinity with hydrochloric acid, and suspended fine ceramic powder in an organic solvent, using water as a binder. A granulated product was obtained by stirring in the presence of the solution. Furthermore, in this system, the size, sphericity, and density of the granules are controlled by several factors, including the shape of the inner wall surface of the cylindrical stirring tank of the granulator, and the tip of the rotating stirring blade. It has been found that the distance from the inner wall surface (convex portion) of the cylindrical stirring tank is deeply related to the formation of granules.

The main body of the submerged granulator of the present invention is a cylindrical stirring tank, which has rotating stirring blades, and the inner wall of the cylindrical stirring tank has the entire length of the cylindrical stirring tank preferably parallel to the axis of the rotor. A groove is formed throughout. (See FIG. 1) The shape of the groove when the stirring tank is cut along a plane perpendicular to the rotation axis is preferably a beam shape, a square shape, or an arc shape. (See Figure 2) There is no particular limit to the depth of the groove, but when producing a spherical body with a diameter of 50 to 1500 μm, it is preferably 1 to 3 depths. It is possible to manufacture spherical bodies having a relatively large particle size (for example, 800 μm or more) even without grooves on the inner wall surface. There is no particular restriction on the distance (peach) between the center line of a groove and the center line of an adjacent groove, but it is 55
When manufacturing a spherical body with a diameter of 0-1500a, 1mm+~
250mm is desirable.

The grooves may be formed on the inner wall surface of the cylindrical stirring tank by cutting the inner wall surface, or by attaching a plate of a predetermined shape to the inner wall surface to form the grooves as a result.

There is no particular limit to the distance (clearance) between the tip of the rotor blade and the inner wall surface (convex part) of the stirring tank, but it is 50 to 1500 with high density.
In the case of manufacturing a spherical body of μm, the thickness is preferably 2 to 15 mm.

The distance between the tip of the rotor blade and the inner wall surface (convex part) of the stirring tank is 1.5 m.
If it exceeds m, the granules will become large, and if it is less than 2 m, the machining accuracy will be high and it is not economical.

There are also no restrictions on the shape and number of rotor blades. The shape of the rotor blade may be either horizontal or S-shaped, or a combination of the horizontal S-shape and the horizontal S-shape. In the case of a combination, there is no particular restriction on the number of each.

Fine ceramics that can be made into microspheres by the submerged granulator of the present invention include zirconia, alumina, mullite, silicon nitride, barium titanate, magnesium oxide, and ferrite.

As the organic solvent, an organic solvent having low affinity with water can be used, and paraffinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, or mixtures thereof are preferred.

The granulator of the present application is used as follows.

In a circular or cylindrical stirring tank, fine powder of Fine Ceramics,
Predetermined amounts of an organic solvent and water as a binder are added, and a rotating stirring blade is rotated at 1,000 to 2,500 rpm to perform granulation. The temperature inside the stirring tank gradually rises, but usually no temperature adjustment is performed, from 30 to 120
The granulation is completed in minutes, and the granulated product is then fired at 1200 to 1450°C in an oxidizing atmosphere in an ordinary electric furnace to obtain fired balls.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

Powder used: A commercially available zirconia powder (containing a partial stabilizer) whose main properties were as follows.

Specific surface area: -7,4 bo/g (Measurement method: BET method, measuring machine: MICROMERITICS model 220) True specific gravity: -5,699 (Measurement method: Liquid phase displacement method is used and the measuring device is AUTOTRUE DEUCERMAT-5000 manufactured by Seishin Enterprise Co., Ltd. Average particle diameter (50% weight) - ~ 0.47 μm (Measuring method is sedimentation method and the measuring device is SED I manufactured by M ICROMERIT IC3)
C, RAPH5000D) Component analysis'-'-'-'z
ro2 94.81 (wt%) Y, 0.
4.61 Ca0 0.03 Na20 0.02 Roasting loss 0.24 Granulation conditions: Amount of zirconia powder...-57.6g Organic solvent and its amount...-11---Paraffin hydrocarbon, 290 (1. Binder and its amount - Tap water, 6.5 d Stirring blade rotation speed - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - −−−−−・−1−−
- The time from the start of rotation of the stirring blade until the entire amount of zirconia powder is granulated and the stirring interpolation stops. Granulator: The stirring tank and rotating stirring blade are important. The stirring tank is horizontal and has an effective internal volume. 3001! It is. The rotating shaft is driven by an electric motor to rotate it, and the rotation speed can be changed.

- Measurement of granule size: ■ An image analysis method using LUZEX500 manufactured by Nireco was used. Using this, the Feret diameter of the microsphere was measured, and was defined as the diameter of the spherical body. Sphericity is L/W (L is the maximum diameter, W is L
(the largest diameter perpendicular to the diameter).

The Feret diameter is the distance between two parallel lines when the image of a spherical object projected onto a plane is sandwiched between two parallel lines, and the average value of the above distances for multiple spherical objects is considered to be a statistical average value. .

Fired balls: Fired balls made by firing the spherical bodies obtained by the above granulator in an oxidizing atmosphere at high temperatures (maximum 1450''C) in an ordinary electric furnace were also measured using an image analyzer LUZEX500 manufactured by Nireco. The density was determined using the Archimedes method.

Example 1 Groove shape on the inner wall of the stirring tank Mold: Groove depth: 0.5 ws: Inside the groove
0.5 〃 Groove pitch 1.0 mm 〃 Yamanaka 0.5 Distance between the tip of the stirring blade and the inner wall surface (convex part) IIIl 3 sets of stirring blade shape and number [type, 1 set of 4 blades]. One set is in the center of the rotation axis,
The other two sets are mounted at symmetrical positions with respect to the center set 01 of the rotation axis.

Granulation time: 40 minutes Particle diameter of obtained microspheres: 305 μm Sphericity
1.04 Particle diameter of fired pole after sintering of the above microspherical bodies 2
47μm Sphericity 1.04 Density 6.001g/cI11 Example 2 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall (convex) U-shaped l 3 sets of 15-mark stirring blade shape and number [specimen type, 1 set of 4 blades]. One set is in the center of the rotation axis,
The other two sets are mounted at symmetrical positions with respect to the central one.

Granulation time: 90 minutes Particle diameter of the obtained microspheres: 615 μm Sphericity: 1.07 Fired balls after sintering the above microspheres.

Particle diameter 492 μm Sphericity 1.07 Density 5,881 g/all Example 3 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex portion) U Mold 1, w llll1 6ff [distance W from ln rIm, stirring blade shape and number, etc. [separate mold, 4 pieces 1&Il], 3 sets. im is mounted at the center of the rotating shaft, and the other two sets are mounted at symmetrical positions with respect to the central set.

Granulation time: 40 minutes Particle diameter of obtained microspheres: 328 μm Sphericity
1.03 Particle diameter of fired balls after sintering the above microspherical bodies 2
62μm〃Sphericity 1.03〃Density 6.004g/cIIlExample 4 Groove shape on the inner wall of the stirring tank〃Groove depth〃Groove width〃Groove pitch〃Yamanaka stirring blade tip and inner wall surface (convex part) Mountain shape IIIll Distance from 3 cabinets mm 3flll11 5IllINl Stirring blade shape and number, etc. [S type, 1 set of 4 blades] are 3 sets. One set is mounted at the center of the rotation axis, and the other two sets are mounted at symmetrical positions with respect to the central set.

Granulation time: 45 minutes Particle diameter of obtained microspheres: 315 μm Sphericity: 1.03 Particle diameter of fired balls after sintering the above microspheres: 2
65 μm Sphericity 1.03 Density 6.001 g/d Example 5 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex portion) Shape mm 3 Distance from 6IllII1 mm l1lal Stirring blade shape and number, etc. Two sets of [seed type, 1 set of 4 blades] and 1 set of [S type, 1 set of 4 blades], a total of 3 sets, both sides are The S type is placed in the center of the seed mold, and the seed mold is attached at a symmetrical position to the S type.

Granulation time: 45 minutes Particle diameter of obtained microspheres: 322 μm Sphericity
1.04 Particle diameter of fired balls after sintering the above microspherical bodies 2
58μm 〃 Sphericity 1. o4 〃 Density 6.002g Yagomi Example 6 Groove shape on the inner wall of the stirring tank〃 Groove depth〃 Groove width〃 Groove pitch〃 Yamanaka stirring blade tip and inner wall surface (convex part) Mortar type 1 mm mm mm mm Distance: 5 m Two sets of stirring blades (type, 4 blades in 1 set) are installed at the three equal points of the length of the rotating shaft.

Granulation time: 50 minutes (rotation speed: 220 Orpm) Particle diameter of obtained microspheres: 330 μm
Sphericity 1.04 Particle diameter of fired pole after sintering the above microspherical body 2
68 μm Sphericity 1.04 Density 5.980 g/cd Example 7 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex part) Mortar type 2 [1III1 llll1 6 mm Distance 4 3 sets of stirring blade shape and number [specimen type, 1 set of 4 blades]. One set is in the center of the rotation axis,
The other two sets are mounted at symmetrical positions with respect to the central one.

Granulation time: 50 minutes Particle diameter of obtained microspheres: 314 μm Sphericity
1.03 Particle diameter of fired balls after sintering the above microspherical bodies 2
511Jm 〃 Sphericity 1.03 〃 Density 6.024g/cnY Example 8 Groove shape on the inner wall of the stirring tank〃 Groove depth〃 Groove width〃 Groove pitch〃 Yamanaka stirring blade tip and inner wall surface (convex part) Eye shape rIn 311111 6 +nm Distance from 3IW+ lff1 There are 3 sets of stirring blade shapes and numbers [specimen type, 1 set of 4 blades], 1 set is in the center of the rotation axis,
The remaining two sets are installed in symmetrical positions with respect to the central one.

Granulation time: 55 minutes Particle diameter of obtained microspheres: 252 μm Sphericity
1.035 Particle diameter of fired balls after sintering the above micro-spherical bodies 〃 Sphericity 1.03 〃 Density 6.040 g/d Example 9 Groove shape on inner wall of stirring tank〃 Groove depth〃 Groove width〃 Groove pitch: Distance between tip of Yamanaka stirring blade and inner wall surface (convex part) Concave 1 mm 1.2 m + nm 111 5 Cabinet Shape and number of stirring blades [horizontal type, 1 set of 4 blades] 3 sets. One set is in the center of the rotation axis,
The remaining two sets are installed in symmetrical positions with respect to the central one.

Granulation time: 55 minutes Particle diameter of obtained microspheres: 580 μm Sphericity
1,04 Particle diameter of fired balls after sintering the above microspherical bodies 4
64 μm Sphericity 1.04 Density 5.993 g/cd Example 10 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex) Mountain shape mm mm 4 mm Distance from the 21-meter 5-inch stirrer blade shape and number of blades [horizontal type, 1 set of 4 blades] are 3 sets. lu is at the center of the rotation axis,
The remaining two sets are installed in symmetrical positions with respect to the central one.

Granulation time: 50 minutes Particle diameter of obtained microspheres: 792 μm Sphericity
1.04 Particle diameter of fired balls after sintering the above microspherical bodies 6
34 μm Sphericity density 1.04 5.957 g/C Example 11 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex) Mold 1 [ 11111 3 cabinets 48 mm 5 mm Distance to nm Three sets of stirring blade shape and number [horizontal type, 1 set of 4 blades]. One set is located in the center of the rotation axis,
The remaining two sets are mounted at symmetrical positions with respect to the central one.

Granulation time: 50 minutes Particle diameter of obtained microspheres: 876 μm Sphericity
1.04 Particle diameter of fired balls after sintering the above microspherical bodies 7
01 μm Sphericity 1.04 Density Example 12 Groove shape on the inner wall of the stirring tank Groove depth Groove width Groove pitch Yamanaka stirring blade tip and inner wall surface (convex) 5.950 g/c concave Nr1 mm 243+11 [11 Distance from 240mm 5+nm Three sets of stirring blade shape and number [horizontal type, 1 set of 4 blades]. One set is located in the center of the rotation axis,
The remaining 2&ll are mounted at symmetrical positions with respect to the central pair.

Granulation time: 105 minutes Particle diameter of obtained microspheres: 1323 μm Sphericity: 1.04 Particle diameter of fired balls after sintering the above microspheres: 1
058μm 〃 Sphericity 1. o4 〃 Density 5.913 g/cd Example 13 Groove shape on the inner wall surface of the stirring tank Groove depth Groove width Groove pitch Distance between Yamanaka stirring blade tip and inner wall surface (convex part) Arc type M 3flII1 M mm 1ml1 There are 3 sets of stirring blade shape and number (1 set of 4 blades). One set is mounted at the center of the rotation axis, and the other two sets are mounted at symmetrical positions with respect to the central one.

Granulation time: 65 minutes Particle diameter of obtained microspheres: 330 μm Sphericity
1.04 Particle diameter of fired balls after sintering the above microspherical bodies 2
64μm 〃 Sphericity 1.04 〃 Density 5.990g/d Example 1
4 Groove shape on the inner wall of the stirring tank ■Type Groove depth ll1lffl Groove width
3IIl! Il〃 Groove bift 6 ribs〃 Yamanaka 3mm Distance between the tip of the stirring blade and the inner wall surface (convex part) mm Shape and number of stirring blades [type, 4 blades in 1 set] are 3 & li, 1 set is in the center of the rotating shaft, The other two sets are mounted at symmetrical positions with respect to the central one.

Granulation time: 70 minutes Particle diameter of obtained microspheres: 345 μm Sphericity
1.05 Particle diameter of fired balls after sintering the above microspherical bodies 2
76μm 〃 Sphericity 1.04 〃 Density 5.987g/c111 Example 15 Groove shape U-shaped on the inner wall of the stirring tank〃 Groove depth 1 groove width 3㎓〃 Groove pitch 6ma +〃 Yamanaka 3mm stirring blade tip and inner wall surface (Protrusion)
Distance from 5 cabinets 3 sets of stirring blades shape and number [specimen type, 1 set of 4 blades]. One set is mounted at the center of the rotation axis, and the other two sets are mounted at symmetrical positions with respect to the central set.

Rotary blade rotation speed 1450 rpm Granulation time
Particle diameter of microspheres obtained in 125 minutes: 71 μm Sphericity: 1.0
3 Particle diameter of fired pole after sintering of the above microspheres
57μm 〃 Sphericity 1.03 〃 Density 6.002 g/c1! Note: The specific surface area of the zirconia powder used in Example 15 is 2
The other properties were approximately the same as those of Examples 1 to 14.

Example 16 The powder used had the same main properties as commercially available aluminum powder.

Specific surface area: ---4, Oryf/g (measured using BET method) True specific gravity: ---3,94 (measured using JIS H1902 method) Average particle diameter (50% weight)
-Track-0.5μm (SEDIGRAPH5000D) Component analysis---=1203 99.8 (wt%)
Nato 0.01 or less MgOO, O4 Granulation conditions Amount of alumina powder --- One song --- Song 80g Organic solvent and its amount -------・-------・-- −・
- Paraffinic hydrocarbon, 280o binder and its amount - One song - Open - Tap water,
Groove shape on the inner wall of the 15mf granulator stirring tank Mortar type Groove depth 1 [l1II]
Groove width 1m1Il
Mizo Bifuchi
2 dishes〃 Mountain width
1. Distance between the tip of the stirring blade and the inner wall surface (convex part) 3 sets of 10-rib stirring blade shape and number [type, 1 set of 4 blades], one set at the center of the rotation axis, and the other two sets at the center It is installed in a symmetrical position with respect to one set of.

Rotary blade rotation speed-----------
-11------2200 rpm granulation time--90 minutes Particle diameter of the obtained microspheres-340 μm 〃 Sphericity - 1,05 Particle diameter of the fired ball after sintering the above microspheres (at a maximum temperature of 1500'C for 2 hours) - 1111 - - - - - - 272μm〃
Sphericity - 11 - 4.05 Density - 3,96 g / d Example 17 The powder used was commercially available silicon nitride, and its main properties were as follows. It was uri.

Specific surface area---1111---・−・・−・−−−−
-1-------11.1 bo/g average particle diameter (50% weight)--0.2 μm fractional analysis-----
-・・・-・----------N > 38 (wt%) Si > 59 〃 0 1.29 〃 C1 < 100100 pp <lQQ 〃 Ca < 5Q // 1 < 50 ” Crystallinity ( Weight %) > 99.5 Granulation conditions Amount of silicon nitride powder - - - - - - - - - - - - - - - - - - -
--・80g organic solvent and its amount----
-------- Paraffinic hydrocarbon, 2800
Magnetic binder and its amount ------- Tap water, 15.5 ml Groove shape on the inner wall of the granulator stirring tank
U type〃 Groove depth 1 Japanese groove width 3 Ceramic〃 Groove pitch
6 T-kaku〃 Mountain width
Distance between the tip of the 3M stirring blade and the inner wall surface (convex part): 5mm There are 3 sets of stirring blade shape and number [specimen type, 1 set of 4], one set is located at the center of the rotation axis, and the other two sets are located at the center of the rotating shaft. It is installed in a symmetrical position with respect to the pair.

Rotating blade rotation speed----1・・・・・−・−・−−−1−
・−・−・−2150rpm granulation time−・・・−・・−
---Particle diameter of microspheres obtained in 115 minutes ---374 μm Sphericity ---
-4,02 A summary of Examples 1 to 17 is shown in Tables 1 to 2.

The fired balls produced by sintering the cylindrical bodies have a diameter of 50 to 500 μm, high sphericity, and high density, and have high hardness, high sphericity, and excellent wear resistance. Because of its excellent properties, a mill using this fired ball as a media can crush, disperse, and mix raw materials for fine ceramics production, or crush and disperse pigments in a short time and efficiently, without contaminating foreign substances such as abrasion particles. can be done.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the cylindrical stirring tank of the present application in the direction of the rotation axis. In FIG. 1, l...Cylindrical stirring tank 2...Rotating stirring blade 3...Rotating shaft 4...Groove 5...Bearing. 2-1 to 2-3 are cross-sectional views showing special cross sections of the cylindrical stirring tank of the present application taken along a plane perpendicular to the rotation axis,
Figure 2-1 is a sectional view when the groove has a U-shaped cross section, Figure 2-2
The figure is a cross-sectional view when the groove has a V-shaped cross section, and FIGS. 2-3 are cross-sectional views when the groove has an arc-shaped cross section. In addition, in Fig. 2, 11... Groove depth 12... Groove width 13...
Groove pitch 14...Yamanaka 15...Protrusion.

Claims (1)

[Claims] 1. In a submerged granulator that produces a granulated product by placing fine powder, a solvent, and a binder in a cylindrical stirring tank equipped with a rotating stirring blade and rotating the stirring blade, the cylindrical type A submerged granulator characterized in that uneven grooves are formed on the inner wall surface of a stirring tank. 2. The uneven groove formed on the inner wall surface of the cylindrical stirring tank is a cross section of the groove when the stirring tank is cut along a plane parallel to and perpendicular to the rotation axis of the rotating stirring blade. 2. The submerged granulator according to claim 1, wherein the submerged granulator has a ■ shape, a V shape, or an arc shape. 3. The distance between the tip of the rotary stirring blade and the convex portion on the inner wall surface of the cylindrical stirring tank is 2 to 15 mm.
Submerged granulation machine.