KR20120064647A - A device for a continuous dispersion by a strong shearing - Google Patents

Abstract

An object of the present invention is to provide a dispersing apparatus capable of dispersing raw materials efficiently and continuously by reliably applying shear force to all raw materials.
The shear dispersing device according to the invention comprises a first rotor 1 and a second rotor 2 facing each other. The raw material is dispersed between the first and second rotors in the circumferential direction of the rotor. The apparatus comprises a first rotating means (8) for rotating the first rotor (1) in a first direction (R1) and a second rotor (2) in a second direction (R2) opposite to the first direction. A second rotating means 9 for rotating is provided. The raw material outlet 20 through which the said raw material is supplied is provided in the rotation center of a 1st rotor or a 2nd rotor.

Description

High shear continuous disperser {A DEVICE FOR A CONTINUOUS DISPERSION BY A STRONG SHEARING}

The present invention relates to an apparatus for continuously and effectively dispersing powdery substances in a plurality of liquids or slurries (a mixture of powdery substances and liquids).

Devices are known for uniformly and continuously dispersing powdery material in a plurality of liquids or slurries. In the apparatus, a plurality of liquids or slurries pass through a narrow space between a circular rotor that rotates at high speed and a stator that does not rotate. Therefore, by the high centrifugal force and the shear force generated by the high speed rotation, the powdery substance in the plurality of liquids or slurries is uniformly and continuously dispersed (for example, see FIG. 1 of Japanese Patent Laid-Open No. 2000-153167). . Here, "dispersion" means disperse | distributing the powdery substance in a slurry uniformly, or mixing a some liquid uniformly.

However, since the flow velocity of the raw material on the surface of the stator that does not rotate is zero, shear energy is hardly applied to the raw material near the stator surface. Therefore, the conventional apparatus has the drawback that a dispersion efficiency falls.

In addition, although a raw material is disperse | distributed in a narrow area | region by shear force, the part from which a dispersion state differs as a whole becomes ubiquitous. Therefore, in order to obtain a uniform mixture, it was necessary to remix the raw materials in a wide area. For this reason, it was necessary to provide a batch type dispersion apparatus in a subsequent process.

In one process, when it does not reach the target dispersion state, it is also necessary to circulate a raw material, or to connect plural dispersion apparatuses continuously, and to perform repeated dispersion. Therefore, there is a problem in that the cost, area, or processing time of installing an additional circulation system or a plurality of dispersing devices increases.

This invention is made | formed in view of said problem. Therefore, one object of the present invention is to distribute raw materials efficiently and continuously by reliably applying shear force to all raw materials and by combining both the dispersing force in a narrow region and the dispersing force in a large region by the shear force in the apparatus. It is to provide a distributed device that can.

In order to achieve the above object, the shear dispersing device of the first aspect of the present invention is, for example, as shown in Figs. 1 and 2, the first rotor 1 and the second rotor 2 facing each other. It includes. The raw material is dispersed through the rotors 1 and 2 in the outer circumferential direction of the rotor. The apparatus comprises a first rotating means (8) for rotating the first rotor (1) in a first direction (R1) and a second direction (opposite to the first direction (R1)). And second rotating means 9 for rotating with R2). The raw material outlet 20 which supplies a raw material is provided in the rotation center of the 1st rotor 1 or the 2nd rotor 2.

With this configuration, the first rotor 1 and the second rotor 2 rotate in opposite directions. Therefore, shear energy is reliably given to all raw materials. Therefore, it is possible to obtain a dispersing device which effectively and continuously disperses the material.

In the shear dispersing device of the first aspect, for example, as shown in FIG. 1, the flat surface 21 and the second rotor 21 of the first rotor 1 are located outside the raw material outlet 20. The space 3 is formed by the plane 31 of (2). Outside the space 3, a buffer portion 6 is formed in which the distance between the first rotor 1 and the second rotor 2 is wider than the space 3. An outer circumferential side surface 32 is formed in the second rotor 2 outside the buffer portion 6. The outer circumferential side 32 makes the distance between the first rotor 1 and the second rotor 2 narrower than the buffer portion 6. This is the second aspect of the present invention.

In this configuration, the space has a dispersing force in a narrow region due to shear force, and the buffer portion has a dispersing force in a large region. Therefore, it is possible to obtain a shear type dispersing device which effectively and continuously disperses the material.

In the shear dispersing device of the second aspect, for example, as shown in FIG. 1, the outer circumferential side surface 32 is parallel to the rotation axis 8 of the first rotor 1 or with respect to the rotation center. It is arranged to be inclined. This is the third aspect of the present invention.

In this configuration, since the outer circumferential side 32 is arranged to be parallel to the rotational axis of the first rotor or to be inclined with respect to the rotational center, the raw material is removed from the buffer unit as long as the raw material in excess of the capacity of the buffer unit is not introduced. Do not spill. Therefore, the raw material is accumulated in the buffer portion. Therefore, the additional raw materials flow in from the space at high speed toward the raw material accumulated in the buffer part and are mixed violently with each other, so that the raw material is uniformly dispersed in the buffer part.

In the shear dispersing device of the second or third aspect, for example, as shown in FIG. 4, the front end of the outer circumferential side 32 is provided as an overhang 62 extending toward the rotation center. Formed. This is the fourth aspect of the present invention.

In this configuration, since the tip of the outer circumferential side 32 is formed as a protrusion extending toward the rotation center, the raw material does not flow out of the buffer unit unless the amount of raw material in excess of the capacity of the buffer unit flows in. . Therefore, the raw material is accumulated in the buffer portion. Toward the raw materials accumulated in the buffer portion, additional raw materials flow in from the space at high speed and are mixed violently with each other, so that the raw materials are uniformly dispersed in the buffer portion.

In the shear type dispersing apparatus of a 2nd or 3rd aspect, as shown, for example in FIG. 1, the space 3 is arrange | positioned adjacent to the raw material discharge port 20 which supplies a raw material. This is the fifth aspect of the present invention.

If comprised in this way, the centrifugal force by rotation of a 1st and 2nd rotor will be applied to the raw material in space. Therefore, as the raw material flows outward, the flow rate increases. In addition, negative pressure is generated inside. Thus, additional raw material is drawn into the space through the raw material outlet.

In the shear dispersing device of the second or third aspect, for example, as shown in FIG. 1, the plane 23 of the first rotor 1 and the second rotor (outside the buffer portion 6). The 2nd space 4 is formed by the plane 33 of 2). The spacing between the first and second rotors in the second space 4 is equal to or less than the spacing of the space 3. The second buffer part 7 is formed outside the second space 4. The distance between the first and second rotors 1, 2 in the second buffer part 7 is larger than the distance of the second space 4. A second outer circumferential side surface 24 is formed in the first rotor 1 outside the second buffer portion 7. The second outer circumferential side 24 makes the gap between the first and second rotors 1, 2 narrower than the gap of the second buffer portion 7. This is the sixth aspect of the present invention.

When comprised in this way, in addition to a space and a buffer part, a 2nd space has the dispersion force of the raw material in a narrow area | region by shear force. The second buffer portion has a dispersing force of the raw material in a wide area. Therefore, it is possible to obtain a dispersing device that effectively, continuously and repeatedly disperses raw materials.

In the shear dispersing device of the sixth aspect, for example, as shown in FIG. 1, the buffer portion 6 is formed by recessing the first rotor 1. The outer circumferential side 32 is formed in the second rotor 2. The second buffer portion 7 is formed by recessing the second rotor 2. The second outer circumferential side surface 24 is formed in the first rotor 1. This is the seventh aspect of the present invention.

In this configuration, the space, the buffer portion, the outer circumferential side, the second space, the second buffer portion, and the second outer circumferential side are all formed and interlocked by recessing the first and second rotors. Therefore, it becomes easy to manufacture a dispersing apparatus in which dispersion in a narrow region by a shear force and mixing in a wide region are effectively performed alternately to make the material uniform.

The present invention provides a shear type dispersing apparatus which effectively and continuously disperses raw materials by effectively applying shear energy to all raw materials. The apparatus includes a first rotor and a second rotor facing each other. The raw material is dispersed between two rotors in the circumferential direction of the rotor. The apparatus includes first rotating means for rotating the first rotor in a first direction, and second rotating means for rotating the second rotor in a second direction opposite to the first direction. At the rotation center of the first rotor, a raw material outlet through which the raw material is supplied is provided.

Outside the said raw material discharge port, the space is formed by the plane of a 1st rotor and the plane of a 2nd rotor. On the outside of the space, a buffer portion in which a distance between the first and second rotors is wider than the space is formed. On the outside of the buffer portion, an outer circumferential side surface is formed on the first rotor or the second rotor or both the first rotor and the second rotor. The outer peripheral side makes the gap between the first and second rotors narrower than the buffer portion. Therefore, after the function of dispersing the raw material in the narrow region by the shear force occurs, the function of mixing the raw materials in the wide region to make the material uniform occurs. These functions are combined to effectively disperse the raw materials.

This application is based on patent application 2009-222997 for which it applied in Japan on September 28, 2009, The content is integrated in this application as a reference.

In addition, the present invention will be more fully understood by the following detailed description. However, detailed description and specific embodiment are only preferable embodiment of this invention, and are described only for the purpose of description. Based on this detailed description, various changes and modifications are apparent to those skilled in the art.

Applicant has no intention of offering any of the described embodiments to the public. Any of the disclosed modifications and alternatives, which may not be included in the claims within the claims, are part of the invention under the equivalent theory.

In the description of the present specification and claims, the use of nouns and the same directives should be interpreted as including both the singular and the plural unless specifically indicated otherwise or unless clearly indicated by the context. The use of all illustrative or exemplary terms (eg, "etc.") provided herein is only intended to facilitate describing the present invention, and the scope of the present invention unless specifically stated in the claims. It does not impose any restrictions on.

1 is a schematic cross-sectional view of two rotors arranged.
2 is a schematic cross-sectional view of a main part of a dispersion apparatus.
3 is a schematic diagram of a cross-sectional flow velocity distribution of the apparatus of the present invention and a conventional apparatus.
4 is a structural diagram of an embodiment in which the capacity of the buffer unit is increased.

EMBODIMENT OF THE INVENTION Hereinafter, the best form for implementing this invention is demonstrated. In the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted. The present invention relates to an apparatus for uniformly dispersing a plurality of raw materials. In the above apparatus, two rotors which rotate at high speed in opposite directions to each other are arranged. By centrifugal force, the raw material passes through the narrow space formed by the rotors. As shown in Fig. 1, two concave rotors 1 and 2 are arranged on the same axis of rotation so as to face each other in the vertical direction. By matching the respective recesses and convex portions, narrow spaces 3, 4 and 5 and wide spaces 6 and 7 are alternately formed. Here, the narrow spaces 3, 4, and 5 that generate high shear force are called shear force generation units. The wide spaces 6 and 7 for mixing the raw materials in the wide area are called buffer sections. As shown in Fig. 2, the rotors 1 and 2 are connected to the hollow rotating shafts 8 and 9, respectively. The rotary shafts 8, 9 are supported by a bearing case 16 via a bearing 15. The case 16 is firmly fixed (the method of fixing the case is not shown). The rotary shafts 8, 9 are driven by motors (not shown), respectively, via belts, chains or gears, rotating in opposite directions. Clockwise rotation is assumed as viewed from the raw material feed ports 12, 14. The rotational speed of the shaft is arbitrarily selected according to the kind of raw material, the degree of dispersion desired, and the like. The raw material supplied to the raw material supply ports 12 and 14 is supplied between the two rotors through the raw material outlet 20 disposed at the rotation center of the rotors 1 and 2 through the hollow portion of the hollow rotating shaft. In the present embodiment, the raw material outlet of the hollow rotating shaft 9 is closed by the plug 10 to prevent the raw material from reflowing and reflowing.

In the dispersion apparatus of FIG. 1, the outer diameters D of the rotors 1 and 2 are 200 mm, respectively, and the heights h1 and h2 are 55 mm and 15 mm, respectively. Although the clearance gap of the shear force generating parts 3, 4, and 5 is adjustable to 0.05 mm-2 mm, it does not need to be the same. It is arbitrarily changed depending on the shape and dimensions of the rotors 1 and 2 and the design intention. For example, starting from the shear force generating portion 3, the gap gradually decreases in the order of the shear force generating portion 4 and the shear force generating portion 5. In this way, the aggregated particles in the raw material are sequentially decomposed into fine particles, and uniformly dispersed. The angles α and β of the outer circumferential sides 32 and 24 of the buffer portions 6 and 7 are 50 degrees and 70 degrees, respectively. However, it is not limited to this value. Depending on the shape and dimensions of the rotors 1, 2, they may be inclined at an acute angle or at a right angle, ie in the direction toward the center of rotation (the direction toward the hollow shafts 8, 9), or the hollow shaft 8, Parallel to 9), arbitrarily selected. In this dispersion apparatus, the rotation speed is adjusted to 0-1720 rpm by inverter control. This is arbitrarily changed by selecting an electric motor, a pulley, a gear and the like.

Here, with reference to FIG. 1, the structure of the shear force generating part 3, 4, 5 and the buffer part 6, 7 is demonstrated. The surface of the upper rotor 1 facing the lower rotor 2 is formed as a plane 21 perpendicular to the axis of rotation outside the raw material outlet 20. A recess is formed on the outer side of the plane 21 by the inner circumferential side 22, the plane 23, and the outer circumferential side 24. Plane 23 is parallel to plane 21. The outer circumferential side surface 24 extends beyond the plane 21 toward the lower rotor 2 side. Moreover, the flat surface 25 parallel to the flat surface 21 is formed in the front-end | tip. On the surface of the lower rotor 2 which opposes the upper rotor 1, the plane 31 which faces in parallel with the plane 21 is formed. The plane 31 extends beyond the inner circumferential side 22 toward the outer circumferential side. The outer circumferential side 32 is formed from the plane 31 toward the upper rotor 1. From the tip of the outer circumferential side surface 32, a plane 33 parallel to the plane 23 is formed. The plane 33 forms a recessed part by the inner peripheral side 34 and the plane 35 which opposes parallel to the plane 25. The inner circumferential side 34 is located inside the outer circumferential side 24.

As described above, by arranging the upper rotor 1 and the lower rotor 2 having a surface, the shear force generating portion 3 is formed by the plane 21 and the plane 31. The shear force generating portion 4 is formed by the plane 23 and the plane 33. The shear force generating portion 5 is formed by the plane 25 and the plane 35. The buffer part 6 is formed as an area surrounded by an inner circumferential side 22, a plane 23, an outer circumferential side 32, and a plane 31. The buffer portion 7 is formed as an area surrounded by an inner circumferential side 34, a plane 23, an outer circumferential side 24, and a plane 35. The outer circumferential side surface 24 extends beyond the plane 21 toward the lower rotor 2 to form the buffer portion 7. Therefore, the capacity of the buffer part 7 becomes large and a raw material becomes uniform by dispersion in a wide area | region.

In the above embodiment, the outer circumferential side 24 has been described as extending beyond the plane 21 toward the lower rotor 2, but the outer circumferential side 24 may extend to the same position as the plane 21. That is, the plane 21 and the plane 25 may be disposed on the same plane. In such a structure, one concave portion is formed on the upper rotor 1, and one protrusion (outer peripheral side surface 32, plane 33, and inner peripheral side surface 34) is provided on the lower rotor 2. By forming an enclosed portion, three shear force generating portions 3, 4, 5 and two buffer portions 6, 7 can be formed. Therefore, it becomes easy to manufacture the dispersion apparatus which makes uniform material by disperse | distributing continuously in a narrow area | region by a shearing force and mixing in a wide area | region alternately. In addition, the outer circumferential side surface 24 does not have to extend beyond the plane 21.

The planes 21, 23, 25, 31, 33, 35 are described as being perpendicular to the axis of rotation and parallel to each other, but do not have to be arranged in this manner. Further, the planes forming the shear force generating sections 3, 4, 5 may not be parallel to each other. By making the clearance gap of the shear force generating parts 3, 4, 5 narrow toward the outer peripheral side, the aggregated particles in the raw material are sequentially decomposed into fine particles.

The buffer parts 6 and 7 are areas for accumulating liquids. These regions have a large capacity for mixing raw materials dispersed in a narrow region in the shear force generating sections 3 and 4. For this purpose, for example, the radius L1 of the plane 31 forming the buffer portion 6 is opposite to the plane 21 and the radius L2 of the plane forming the shear force generating portion 3. ) Is at least half, and is usually 1 or more times. The height of the buffer portion 6 (sum of the gap between the shear force generating portion 3 and the height of the inner circumferential side surface 22) is at least three times the height of the gap of the shear force generating portion 3, and is usually five times or more. .

In FIG. 1, the flow of a raw material is shown by the arrow. For convenience, only one arrow is shown, but similar flow occurs throughout the area formed by the rotors 1, 2. Here, reference is again made to FIG. 2. In the state in which the rotors 1 and 2 are rotating, the raw material supply port 12 is connected to the rotary joint 11 provided with a stopper (not shown) connected to the hollow rotary shaft 8 to stop the rotation. Raw materials are supplied. The raw material is supplied to the space between the rotors 1 and 2 through the raw material outlet 20. All of the raw materials are the shear force generating portion 3, the buffer portion 6, the shear force generating portion 4, the buffer portion 7, the shear force generating portion formed by the first rotor 1 and the second rotor 2 ( 5), flows in the direction of centrifugal force. The raw material is discharged from the raw material discharge part 13 which discharges the raw material. The raw material discharge part 13 is arrange | positioned at the outer peripheral side of a rotor. Since the raw material flows in the direction toward the outer circumference by centrifugal force, the flow velocity increases. The pressure of the raw material outlet 20 becomes negative pressure. Therefore, the flow of the raw material from the raw material outlet 20 increases.

The plug 10 may be removed from the outlet of the hollow rotating shaft 9 to supply other raw materials from the raw material supply port 14. Therefore, the raw material from the raw material supply port 12 and the raw material from the raw material supply port 14 can be mixed. However, in this case, since the negative pressure at the raw material outlet 20 is usually not large enough to suck the raw material by the height along the entire length of the hollow rotating shaft 9, the center axes of the rotor and the hollow shaft are horizontal. Or a pump for the raw material must be installed.

In the present dispersing device, the two rotating shafts are described as being driven by separate electric motors. However, when distributing power by a gear or the like, it can also be driven by one electric motor. Such electric motors, belts, chains, gears, etc. constitute the rotating means of the hollow rotating shafts 8, 9.

The dispersion | distribution process of a raw material is demonstrated using FIG. First, when a raw material passes through the shear force generation part 3, it receives a high shear force. Thus, emulsification or decomposition of the aggregated particles is performed. When the two rotors 1 and 2 rotate at the same speed, the speed distribution of the raw material of the A-A line and the B portion becomes as shown in Fig. 3A. There is no velocity zero part. On the other hand, in the conventional system in which one of the rotors 1 and 2 is fixed, assuming that the fixed rotor is the lower rotor 2, the velocity distribution is as shown in Fig. 3B. The speed at the surface of the lower rotor 2 becomes zero in the rotational direction and in the same radial direction as the direction by the centrifugal force. Therefore, the raw material near the lower rotor 2 surface is difficult to disperse. In the apparatus of the present invention, even in the center position between two rotors 1 and 2 where the speed in the rotational direction is zero, the radial speed is not zero due to the movement generated by the centrifugal force. That is, the movement by centrifugal force in both sides adjacent to the center position is the same direction as the outward direction. Therefore, the raw material at the center position is pulled outward by the shear force (viscosity) caused by this movement. Since there is no portion which becomes the velocity zero, the shear force is reliably applied to all the raw materials. Thus, a dispersing effect is obtained. Specifically, as shown along the line A-A in Fig. 3A, the shearing force is weak at the center position between the two rotors. However, unlike a fixed rotor with zero speed, the speed fluctuates violently because of the high speed rotation. Therefore, the shear force does not affect the dispersion effect. The raw material receives a high shear force in the shear force generating section 3, and emulsification, decomposition of aggregated particles, or dispersion of particles is performed in a narrow region. After discharged from the shear force generating section 3, the raw material flows into the first buffer section 6. In the buffer part 6, the outer peripheral side 32 is formed so that the space | interval between the rotors 1 and 2 may become narrow. Therefore, the raw material which flowed into the buffer part 6 accumulates without flowing out from the buffer part, unless the raw material of the quantity exceeding the capacity | capacitance of a buffer part flows in. The raw material in the buffer part 6 is pressed against the outer peripheral side 32 by centrifugal force. As shown in FIG. 1, the outer circumferential side surface 32 of the buffer unit 6 is inclined to resist the flow of the raw material. Therefore, in order for the raw material to flow out from the buffer part 6, an amount of raw material exceeding the capacity of the buffer part 6 must flow into the buffer part 6. The raw material which flows in and accumulates in the buffer part 6 mixes violently with the raw material which flows in later from the shear force generation part 3 into the buffer part 6. Therefore, the raw material which has been emulsified or dispersed in a narrow region becomes uniform by mixing in a wide region. Next, the raw material passes through the second shear force generating portion 4 and the second buffer portion 7 and is dispersed similarly to the first shear force generating portion 3 and the first buffer portion 6. The raw material is further dispersed through the final, ie, third shear force generating unit 5.

In order to uniformly mix the raw materials by the present dispersion device, the particles in the raw material supplied to the present device are preferably decomposed into an emulsion or agglomerated particles smaller than the minimum gap of the shear force generating portion. Further, it is uniformly mixed in units having a capacity at least equal to the capacity of the minimum shear force generating portion (volume = shear force generating portion area x clearance). This process is performed by premixing as a whole process. If the raw material is not decomposed into the emulsion or aggregated particles passing through the gap of the shear force generating section 3, droplets or agglomerated particles larger than the gap at the time of entry into the shear force generating section 3 will cause the shear force generating section 3 to fail. It is difficult to flow into). Accordingly, this may cause non-uniform dispersion of the raw material or clogging of the flow path. In addition, excessive shear forces may damage the device. Mixing uniformly in a unit having a volume equal to the volume of the minimum shear force generating portion means that when a part of the premixed raw material having the same volume as the volume of the minimum shear force generating portion is taken from the raw material, the capacity of each of the plurality of raw material portions is constant. it means. This is irrelevant to the state of emulsification or decomposition of the aggregated particles. For example, in FIG. 1, the minimum shear force generating portion is a space in the shear force generating portion 3. If the gap is 0.1 mm, the volume is about 0.3 ml. However, when the apparatus of the present invention is used for preliminary mixing, all of the above conditions need not be satisfied.

The shape of the buffer parts 6 and 7 is not limited to the inclined shape, as shown by the outer peripheral side surfaces 32 and 24 in FIG. In order to increase the capacity of the buffer portions 6 and 7, as shown in Fig. 4, the ends of the outer circumferential side surfaces 6 and 7 extend toward the center of rotation (to the hollow shafts 8 and 9). Overhangs 62 and 54 may be formed. Further, since the plane 63 of the projection 62 facing the plane 23 of the upper rotor 41 is part of the shear force generating portion 4, the shear force generating portion 4 expands in the radial direction. Thus, dispersion in a narrow area is performed. Similarly, the shear force generating portion 5 is enlarged by the plane 55 facing the plane 35 of the lower rotor 42. Thus, dispersion in a narrow area is performed.

The number of shear force generating sections and buffer sections were described as three and two, respectively. However, it is not limited to this value and may be adjusted according to the raw material to be processed or the degree of dispersion to be targeted.

Claims (7)

A shear continuous dispersing device comprising a first rotor and a second rotor facing each other, and dispersing a raw material by passing between the rotors in an outer circumferential direction of the rotor:
First rotating means for rotating the first rotor in a first direction;
A second rotating means for rotating the second rotor in a second direction opposite to the first direction,
Shear type continuous dispersing device, the raw material outlet for supplying the raw material is installed in the rotation center of the first rotor or the second rotor. The method of claim 1,
Outside the raw material outlet, a first space is formed by a flat surface of the first rotor and a plane of the second rotor;
An outer side of the first space, a first buffer portion having a larger distance between the first rotor and the second rotor than an interval between the first space is formed;
And a first outer circumferential side surface of the second rotor outside the first buffer part, the first outer circumferential side of which narrows the distance between the first rotor and the second rotor than the first buffer part. The method of claim 2,
And the first outer peripheral side is arranged to be parallel to the axis of rotation of the first rotor or to be inclined toward the center of rotation. The method according to claim 2 or 3,
Shear type continuous dispersion apparatus in which the front-end | tip of the said 1st outer peripheral side surface was formed as the overhang extended toward a rotation center. The method according to claim 2 or 3,
The first continuous dispersing device, wherein the first space is disposed adjacent to a raw material outlet for supplying the raw material. The method according to claim 2 or 3,
Outside the first buffer portion, a second space is formed by the plane of the first rotor and the plane of the second rotor, the interval between the first rotor and the second rotor in the second space is the Is equal to or less than the interval of the first space,
The second buffer portion is formed outside the second space, the interval between the first rotor and the second rotor in the second buffer portion is wider than the interval of the second space,
And a second outer circumferential side surface of the first rotor outside the second buffer part such that a distance between the first rotor and the second rotor is narrower than an interval of the second buffer part. The method according to claim 6,
The first buffer portion is formed by recessing the first rotor,
The first outer circumferential side surface is formed in the second rotor,
The second buffer portion is formed by recessing the second rotor,
And said second outer circumferential side surface is formed in said first rotor.

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