JP4047990B2

JP4047990B2 - Airflow classifier

Info

Publication number: JP4047990B2
Application number: JP36879498A
Authority: JP
Inventors: 浩之杉山
Original assignee: Nippon Pneumatic Manufacturing Co Ltd
Current assignee: Nippon Pneumatic Manufacturing Co Ltd
Priority date: 1998-12-25
Filing date: 1998-12-25
Publication date: 2008-02-13
Anticipated expiration: 2018-12-25
Also published as: JP2000189897A

Description

【０００１】
【発明の属する技術分野】
この発明は、複写機の現像用トナー等の粉体を粗粉と微粉とに遠心分離する気流分級機に関するものである。
【０００２】
【従来の技術】
この種の気流分級機として、図４および図５に示したものが従来から知られている。この気流分級機は、ケーシング２０内にセンタコア２１とセパレートコア２２を上下に対向して設け、そのセンタコア２１とセパレートコア２２の対向面間に形成された分級室２３の周壁に、外部から分級室２３内に二次空気を旋回流入させる案内羽根２４を設けている。
【０００３】
また、ケーシング２０の上部に設けられた粉体案内筒２５の上部外周に供給筒２６を接続し、この供給筒２６から粉体案内筒２５内に粉体と圧縮エアの固気混合流体を供給し、上記粉体案内筒２５内において旋回し乍ら下降する粉体を分級室２３内に流入させて旋回させ、案内羽根２４間から分級室２３内に流入する二次エアにより、粉体の旋回速度を増速して、粉体を粗粉と細粉とに遠心分離し、分級室２３の外周部で旋回する粗粉をセパレートコア２２の外周に形成された粗粉排出口２７から排出している。また、分級室２３の中央に移動する細粉を、セパレートコア２２の上面中央で開口する細粉排出筒２８内に吸引流入させるようにしている。
【０００４】
上記のような粉体の分級に際し、粉体が分級室２３において旋回するとき、その旋回気流の中央部に図５に示すように、細粉排出筒２８の入口の口径に略等しい空洞部２９が形成される。
【０００５】
ここで、上記空洞部２９が分級室２３の中心から半径方向にずれ動く不安定な状態であると、細粉が粗粉中に混入したり、あるいは逆に、粗粉が細粉に混入してシャープな分級を行うことができなくなる。
【０００６】
そのような不都合の発生を防止するため、センタコア２１の下面を中央が高くなる円錐面３０とし、その円錐面３０の中心に逆円錐形の突出部３１を設けて空洞部２９の安定化を図ることがなされている。
【０００７】
【発明が解決しようとする課題】
ところで、上記のように、センタコア２１の円錐面３０の中央に逆円錐形の突出部３１を設けた気流分級機においては、遠心分離された細粉は上記円錐面３０に沿って旋回しながら、分級室２３の中央に位置する突出部３１の表面と円錐面３０の交差部まで移動する。この交差部は、分級室２３内で形成される旋回気流の中央空洞部２９の内周からセンタコア２１の中心側に片寄った位置であるため、上記空洞部２９の内周に形成される下降気流の吸引力を受けることが少なく、細粉は突出部３１の表面と円錐面３０の交差部において旋回しつつ長時間滞溜する。この滞溜のため、現像用トナーのような低融点の粉体の場合、円錐面３０との接触、あるいは粒子同士の接触によって溶融し、付着堆積するという現象がしばしば見られる。
【０００８】
この場合、気流分級機の稼働を停止して清掃する必要が生じ、生産性を著しく低下させるという問題が生じる。
【０００９】
また、滞溜することにより、既に分級された細粉が二次凝集して造粒を生じ、これが粗粉として細粉に混入したり、交差部付近に付着した溶融物が剥離して細粉に混入するなど、細粉側の分級性能を低下させる要因となっている。
【００１０】
この発明の課題は、センタコアの下面への細粉の付着堆積や二次凝集による造粒を防ぐことにより、細粉への粗粉の混入を防止して分級精度の向上させるとともにメンテナンスの容易な気流分級機を提供することである。
【００１１】
【課題を解決するための手段】
上記の課題を解決するために、この発明においては、ケーシング内に、下面が中央に向けて高くなる円錐面とされたセンタコアと、上面が中央に向けて高くなる円錐面とされたセパレートコアとを上下に対向して設け、上記センタコアとセパレートコアの対向面間に形成された分級室内で粉体を旋回させて粗粉と細粉とに遠心分離し、分級室の外周部で旋回する粗粉をセパレートコアの外周に形成された粗粉排出口から排出し、分級室の中央部に移動する細粉をセパレートコアの上面中央で開口する細粉排出筒内に吸引流入させるようにした気流分級機において、前記センタコアの円錐面中央部に、その円錐面と滑らかに連続し、少なくとも細粉排出筒の内周と上下で対向する位置が最上位に位置する滑らかな空洞安定面を形成した構成を採用している。
【００１２】
上記のように、センタコアの円錐面中央に滑らかな空洞安定面を形成することによって、分級室内の中央に移行する細粉はその空洞安定面に沿って流れてセンタコアの下面中央にスムーズに移行し、センタコアの下面で細粉が滞溜するのを防止することができる。
【００１３】
ここで、空洞安定面は、細粉排出筒における入口の中心軸上に中心を有して入口の内径と同径の水平面上での仮想円上に曲率中心をもつ円弧面であってもよい。あるいは、センタコアの軸心に中心をもつ円形の平坦面と、その平坦面の外周を円錐面に滑らかに連続させる円弧面とで形成し、上記平坦面の外周部を細粉排出筒の入口の内周と上下で対向する位置に配置したものであってもよい。
【００１４】
【発明の実施の形態】
以下、この発明の実施の形態を図１乃至図３に基づいて説明する。図１に示すように、ケーシング１は粉体案内筒２を上部に有し、その粉体案内筒２の外周上部に粉体供給筒３が接続されている。
【００１５】
粉体供給筒３は粉体案内筒２の外周接線方向に延び、その粉体供給筒３内に送られる粉体と圧縮空気の固気混合流体を粉体案内筒２内の外周に向けて噴射するようになっている。
【００１６】
粉体案内筒２内の下部には複数のリブ４により支持されたコアホルダ５が設けられ、このコアホルダ５の下面にセンタコア６がボルト７の締付けによって着脱自在に取付けられている。
【００１７】
センタコア６の下方にはセパレートコア８が設けられ、両コア６、８間に分級室９が形成されている。分級室９の周壁には、外部から分級室９内に二次エアを旋回流入させる案内羽根１０が円周方向に間隔をおいて設けられている。
【００１８】
セパレートコア８の外周とケーシング１の内周間には環状の粗粉排出口１１が設けられている。また、セパレートコア８には細粉排出筒１２が接続されている。この細粉排出筒１２は細粉をケーシング１の外部に導く案内筒部１２ａと、テーパ状外面を有する入口リング１５とから成り、上記案内筒部１２ａの一端はセパレートコア８の上側に形成された円錐面１３の中央において開口し、その開口部はテーパ孔部１４とされ、このテーパ孔部１４に前記入口リング１５が着脱自在に取付けられている。
【００１９】
入口リング１５は口径の異なる数種のものが用意され、その入口リング１５の取り替えによって分級点の調整が行われる。
【００２０】
図２に示すように、センタコア６の下面は中央が高くなる円錐面１６とされ、その円錐面１６の中央部に、分級室９内で形成される旋回気流の中央空洞部の安定化を図る空洞安定面１７が形成されている。
【００２１】
空洞安定面１７は、円錐面１６と滑らかに連続する円弧面１７ａで形成され、その円弧面１７ａの曲率中心Ｏ₁は、前記細粉排出筒１２の入口１５ａの中心軸Ｘ−Ｘ上の一点Ｏ₀ を中心とする半径ｒの仮想円上に位置し、その仮想円は、入口１５ａの口径と略同径とされている。なお、Ｏ₀ を中心とする半径ｒの仮想円は、図２のＯ₁、Ｏ₁を結ぶ直線を中心として９０°回転させた状態で図示している。
【００２２】
いま、図１に示す細粉排出筒１２内に吸引力を付与する状態で粉体供給筒３から粉体案内筒２内に固気混合流体を供給すると、その固気混合流体は粉体案内筒２内を旋回し乍ら下降して分級室９内に流入し、その分級室９内で旋回する。このとき、案内羽根１０間から分級室９内に二次エアが流入し、その二次エアによって分級室９内で旋回する旋回気流は増速され、旋回気流中の粉体は遠心力によって粗粉と細粉とに遠心分離される。
【００２３】
粗粉は分級室９内の外周部で旋回して粗粉排出口１１からケーシング１の下方に取り出され、一方、細粉は分級室９内の中央に移動する。
【００２４】
ここで、分級室９内で粉体が遠心分離されるとき、細粉排出筒１２には吸引力が付与されているため、分級室９内に形成される旋回気流の中心部には空洞部が形成されると共に、その空洞部内の外周部に下降気流が形成される。
【００２５】
このため、分級室９の中央部に移動した細粉は、この下降気流の流れにのって細粉排出筒１２内に流入する。
【００２６】
なお、細粉排出筒１２はバッグフィルタ等の捕集装置に接続され、細粉排出筒１２内に流入した細粉は上記捕集装置に送られて捕集される。
【００２７】
上記のような粉体の分級において、分級室９を形成するセンタコア６の下面中央部には円弧面１７ａにより形成された空洞安定面１７が設けられ、この空洞安定面１７は細粉排出筒１２の入口１５ａの口径と対向する位置で最上位とされ、それより外又は内に至るに従って次第に浅くなるため、旋回気流の中央の空洞部は半径方向にずれ動くことが少なく、分級室９内できわめて安定した旋回気流が形成される。
【００２８】
このため、細粉中に細粉が混じり、あるいは細粉中に粗粉が混入することがきわめて少なく、シャープな分級を可能とすることができる。
【００２９】
また、空洞安定面１７は円弧面１７ａで形成されているため、センタコア６の円錐面１６に沿って旋回しつつ中央部に移動する細粉は、上記円弧面１７ａに沿って中央部へとスムーズに移動することになり、センタコア６の下面において細粉が滞溜し、溶着により付着して堆積するという不都合の発生は殆どなく、粉体の分級作業を連続して能率よく行うことができる。
【００３０】
図３は、センタコア６の他の例を示す。この例ではセンタコア６の下面中央部に形成された空洞安定面１７をセンタコア６の軸心に中心をもつ円形の平坦面１７ｂと、その平坦面１７ａの外周をセンタコア６の下面外周部に形成された円錐面１６に滑らかに連続させる円弧面１７ｃとで形成し、上記平坦面１７ｂの外径を細粉排出筒１２の入口１５ａの口径と略同径としている。
【００３１】
このように、センタコア６の下面中央に、入口１５ａの口径と略同径の円形の平坦面１７ｂを形成することにより、分級室９内で旋回する旋回気流の中央の空洞部が半径方向へのずれ動くのを防止することができる。このため、分級室９内において、きわめて安定した旋回気流を得ることができると共に、センタコア６の円錐面１６に沿って旋回する細粉を滞溜させることなく中央へとスムーズに移動させることができる。
【００３２】
【発明の効果】
以上のように、この発明においては、センタコアの下面に形成された円錐面の中央に、この円錐面と滑らかに連なり、細粉吸引筒の入口の内周と上下で対向する位置が最上位とされる滑らかな空洞安定面を設けたことにより、分級室で形成される旋回気流の中央の空洞部の安定化を図ることができ、シャープな分級を可能とすることができる。
【００３３】
また、センタコアの下面に沿って旋回する細粉の滞溜を防止し、上記下面に細粉が溶融して付着するのを防止することができる。
【図面の簡単な説明】
【図１】この発明に係る気流分級機の実施の形態を示す概略図
【図２】同上気流分級機のセンタコアを示す断面図
【図３】同上センタコアの他の例を示す断面図
【図４】従来の気流分級機を示す概略図
【図５】同上気流分級機のセンタコアとセパレートコアとを示す断面図
【符号の説明】
１ケーシング
６センタコア
８セパレートコア
９分級室
１１粗粉排出口
１２細粉排出筒
１３円錐面
１５ａ入口
１６円錐面
１７空洞安定面
１７ａ円弧面
１７ｂ平坦面
１７ｃ円弧面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an airflow classifier for centrifuging powder such as developing toner for a copying machine into coarse powder and fine powder.
[0002]
[Prior art]
As this type of air classifier, those shown in FIGS. 4 and 5 are conventionally known. In this airflow classifier, a center core 21 and a separate core 22 are provided in a casing 20 so as to face each other vertically, and a classification chamber is provided from the outside on a peripheral wall of a classification chamber 23 formed between opposing surfaces of the center core 21 and the separate core 22. A guide vane 24 for swirling inflow of secondary air is provided in 23.
[0003]
Further, a supply cylinder 26 is connected to the upper outer periphery of a powder guide cylinder 25 provided at the upper part of the casing 20, and a solid-gas mixed fluid of powder and compressed air is supplied from the supply cylinder 26 into the powder guide cylinder 25. Then, the powder that swirls in the powder guide cylinder 25 and then descends is caused to flow into the classification chamber 23 and swirled, and the secondary air flowing into the classification chamber 23 from between the guide vanes 24 causes the powder to flow. The swirling speed is increased, the powder is centrifuged into coarse powder and fine powder, and the coarse powder swirling on the outer periphery of the classification chamber 23 is discharged from the coarse powder outlet 27 formed on the outer periphery of the separate core 22. is doing. The fine powder moving to the center of the classification chamber 23 is sucked into the fine powder discharge cylinder 28 opened at the center of the upper surface of the separate core 22.
[0004]
During powder classification as described above, when the powder swirls in the classification chamber 23, as shown in FIG. 5, at the center of the swirling air flow, a cavity 29 substantially equal to the diameter of the inlet of the fine powder discharge tube 28 is provided. Is formed.
[0005]
Here, when the hollow portion 29 is in an unstable state in which the cavity 29 is displaced in the radial direction from the center of the classification chamber 23, fine powder is mixed into the coarse powder, or conversely, the coarse powder is mixed into the fine powder. And sharp classification cannot be performed.
[0006]
In order to prevent such an inconvenience, the lower surface of the center core 21 is formed as a conical surface 30 whose center is raised, and an inverted conical protrusion 31 is provided at the center of the conical surface 30 to stabilize the cavity 29. Things have been done.
[0007]
[Problems to be solved by the invention]
By the way, in the airflow classifier provided with the inverted conical protrusion 31 at the center of the conical surface 30 of the center core 21 as described above, while the centrifugally separated fine powder swirls along the conical surface 30, It moves to the intersection of the surface of the protrusion 31 located at the center of the classification chamber 23 and the conical surface 30. Since this intersecting portion is a position offset from the inner periphery of the central cavity portion 29 of the swirling airflow formed in the classification chamber 23 toward the center side of the center core 21, the descending airflow formed on the inner periphery of the cavity portion 29. The fine powder stays for a long time while turning at the intersection of the surface of the protrusion 31 and the conical surface 30. Due to this retention, in the case of a powder having a low melting point such as a developing toner, a phenomenon is often observed in which it melts and adheres to deposit by contact with the conical surface 30 or particles.
[0008]
In this case, the operation of the air classifier needs to be stopped and cleaned, which causes a problem that the productivity is remarkably lowered.
[0009]
In addition, the fine powder that has already been classified is secondarily agglomerated and granulated as a result of stagnation, and this is mixed into the fine powder as a coarse powder, or the melt adhering to the vicinity of the intersection is peeled off and the fine powder is separated. This is a factor that degrades the classification performance on the fine powder side.
[0010]
An object of the present invention is to prevent fine powder from adhering to the lower surface of the center core and prevent granulation due to secondary aggregation, thereby preventing coarse powder from being mixed into the fine powder, improving classification accuracy and facilitating maintenance. It is to provide an air classifier.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, in the casing, a center core having a conical surface whose lower surface becomes higher toward the center, and a separate core having a conical surface whose upper surface becomes higher toward the center, Are arranged opposite to each other, and the powder is swirled in a classification chamber formed between the opposed surfaces of the center core and the separate core, centrifuged into coarse powder and fine powder, and swirled around the outer periphery of the classification chamber. An air flow that discharges the powder from the coarse powder discharge port formed on the outer periphery of the separate core, and sucks and flows the fine powder that moves to the center of the classification chamber into the fine powder discharge cylinder that opens at the center of the top surface of the separate core. In the classifier, a smooth cavity stabilizing surface is formed in the center portion of the conical surface of the center core that is smoothly continuous with the conical surface and at least the position facing the inner periphery of the fine powder discharge tube at the top and bottom is at the top. Take composition It is.
[0012]
As described above, by forming a smooth cavity stabilizing surface in the center of the conical surface of the center core, fine powder that moves to the center of the classification chamber flows along the cavity stabilizing surface and smoothly moves to the center of the lower surface of the center core. It is possible to prevent fine powder from accumulating on the lower surface of the center core.
[0013]
Here, the cavity stabilizing surface may be an arc surface having a center on the central axis of the inlet in the fine powder discharge cylinder and having a center of curvature on a virtual circle on a horizontal plane having the same diameter as the inner diameter of the inlet. . Alternatively, it is formed by a circular flat surface having a center at the center of the center core and an arc surface that smoothly connects the outer periphery of the flat surface to the conical surface, and the outer periphery of the flat surface is the inlet of the fine powder discharge tube. You may arrange | position in the position which opposes an inner periphery up and down.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the casing 1 has a powder guide tube 2 at the top, and a powder supply tube 3 is connected to the upper periphery of the powder guide tube 2.
[0015]
The powder supply cylinder 3 extends in the outer peripheral tangential direction of the powder guide cylinder 2, and the solid-gas mixed fluid of powder and compressed air sent into the powder supply cylinder 3 is directed toward the outer periphery of the powder guide cylinder 2. It comes to inject.
[0016]
A core holder 5 supported by a plurality of ribs 4 is provided at the lower part in the powder guide tube 2, and a center core 6 is detachably attached to the lower surface of the core holder 5 by tightening bolts 7.
[0017]
A separate core 8 is provided below the center core 6, and a classification chamber 9 is formed between the cores 6 and 8. On the peripheral wall of the classification chamber 9, guide vanes 10 that swirl and flow secondary air into the classification chamber 9 from the outside are provided at intervals in the circumferential direction.
[0018]
An annular coarse powder outlet 11 is provided between the outer periphery of the separate core 8 and the inner periphery of the casing 1. In addition, a fine powder discharge cylinder 12 is connected to the separate core 8. The fine powder discharge tube 12 includes a guide tube portion 12a for guiding the fine powder to the outside of the casing 1 and an inlet ring 15 having a tapered outer surface. One end of the guide tube portion 12a is formed on the upper side of the separate core 8. An opening is formed at the center of the conical surface 13, and the opening is a tapered hole 14. The inlet ring 15 is detachably attached to the tapered hole 14.
[0019]
Several types of inlet rings 15 with different diameters are prepared, and the classification point is adjusted by replacing the inlet ring 15.
[0020]
As shown in FIG. 2, the lower surface of the center core 6 is a conical surface 16 whose center is raised, and the central cavity portion of the swirling airflow formed in the classification chamber 9 is stabilized at the central portion of the conical surface 16. A cavity stabilizing surface 17 is formed.
[0021]
The cavity stabilizing surface 17 is formed by a circular arc surface 17a smoothly connected to the conical surface 16, and the center of curvature O ₁ of the circular arc surface 17a is a point on the central axis XX of the inlet 15a of the fine powder discharge tube 12. It is located on a virtual circle having a radius r centered on O ₀ , and the virtual circle has substantially the same diameter as the diameter of the inlet 15a. The virtual circle having a radius r centered on O ₀ is shown in a state where it is rotated by 90 ° about the straight line connecting O ₁ and O ₁ in FIG.
[0022]
Now, when a solid-gas mixed fluid is supplied from the powder supply cylinder 3 into the powder guide cylinder 2 in a state where a suction force is applied to the fine powder discharge cylinder 12 shown in FIG. It turns in the cylinder 2 and descends and flows into the classification chamber 9, and turns in the classification chamber 9. At this time, the secondary air flows into the classification chamber 9 from between the guide vanes 10, the swirling airflow swirling in the classification chamber 9 is accelerated by the secondary air, and the powder in the swirling airflow is coarsened by centrifugal force. Centrifugation into powder and fine powder.
[0023]
The coarse powder turns around the outer periphery of the classification chamber 9 and is taken out of the casing 1 from the coarse powder discharge port 11, while the fine powder moves to the center in the classification chamber 9.
[0024]
Here, when the powder is centrifuged in the classification chamber 9, since a suction force is applied to the fine powder discharge cylinder 12, a hollow portion is formed in the center of the swirling airflow formed in the classification chamber 9. Is formed, and a descending airflow is formed on the outer periphery of the cavity.
[0025]
For this reason, the fine powder moved to the central portion of the classification chamber 9 flows into the fine powder discharge cylinder 12 along the flow of the descending airflow.
[0026]
The fine powder discharge cylinder 12 is connected to a collection device such as a bag filter, and the fine powder flowing into the fine powder discharge cylinder 12 is sent to the collection device and collected.
[0027]
In the powder classification as described above, a cavity stabilizing surface 17 formed by an arcuate surface 17a is provided at the center of the lower surface of the center core 6 forming the classification chamber 9, and the cavity stabilizing surface 17 is provided with the fine powder discharge cylinder 12. In the classification chamber 9, the central cavity of the swirling airflow is less likely to shift in the radial direction because it becomes the highest position at a position opposite to the diameter of the inlet 15 a of the inlet, and gradually becomes shallower outside or inside. A very stable swirling airflow is formed.
[0028]
For this reason, the fine powder is very rarely mixed in the fine powder, or the coarse powder is hardly mixed in the fine powder, and sharp classification can be realized.
[0029]
Further, since the cavity stabilizing surface 17 is formed by the circular arc surface 17a, the fine powder that moves to the central portion while turning along the conical surface 16 of the center core 6 smoothly moves to the central portion along the circular arc surface 17a. Therefore, there is almost no inconvenience that fine powder stays on the lower surface of the center core 6 and adheres and accumulates by welding, so that the powder classification operation can be performed continuously and efficiently.
[0030]
FIG. 3 shows another example of the center core 6. In this example, the cavity stabilizing surface 17 formed at the center of the lower surface of the center core 6 is formed as a circular flat surface 17b centered on the axis of the center core 6, and the outer periphery of the flat surface 17a is formed at the outer periphery of the lower surface of the center core 6. The outer surface of the flat surface 17b is substantially the same as the diameter of the inlet 15a of the fine powder discharge tube 12.
[0031]
Thus, by forming the circular flat surface 17b having the same diameter as the inlet 15a at the center of the lower surface of the center core 6, the central cavity of the swirling airflow swirling in the classification chamber 9 can be moved in the radial direction. It can prevent shifting. Therefore, a very stable swirling airflow can be obtained in the classifying chamber 9, and the fine powder swirling along the conical surface 16 of the center core 6 can be smoothly moved to the center without stagnation. .
[0032]
【The invention's effect】
As described above, in the present invention, the center of the conical surface formed on the lower surface of the center core is smoothly connected to the conical surface, and the position facing the inner periphery of the inlet of the fine powder suction cylinder vertically is the highest position. By providing such a smooth cavity stabilizing surface, the central cavity of the swirling airflow formed in the classification chamber can be stabilized, and sharp classification can be achieved.
[0033]
Further, it is possible to prevent accumulation of fine powder swirling along the lower surface of the center core, and to prevent the fine powder from melting and adhering to the lower surface.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of an air flow classifier according to the present invention. FIG. 2 is a cross-sectional view showing a center core of the air flow classifier. FIG. 3 is a cross-sectional view showing another example of the center core. ] Schematic diagram showing a conventional airflow classifier [FIG. 5] Cross-sectional view showing the center core and separate core of the airflow classifier
DESCRIPTION OF SYMBOLS 1 Casing 6 Center core 8 Separate core 9 Classification chamber 11 Coarse powder discharge port 12 Fine powder discharge cylinder 13 Conical surface 15a Inlet 16 Conical surface 17 Cavity stable surface 17a Arc surface 17b Flat surface 17c Arc surface

Claims

In the casing, a center core whose bottom surface is a conical surface whose height is increased toward the center and a separate core whose top surface is a conical surface whose height is increasing toward the center are vertically opposed to each other, and the center core and the separate core A coarse powder discharge port formed on the outer periphery of the separate core by rotating the powder in the classification chamber formed between the opposed surfaces and centrifuging the coarse powder and fine powder into centrifugal particles and rotating the coarse powder on the outer periphery of the classification chamber In the airflow classifier that sucks and flows the fine powder that is discharged from the center and moves to the center of the classification chamber into the fine powder discharge cylinder that opens at the center of the upper surface of the separate core. An air classifier characterized in that a smooth cavity stabilizing surface is formed which is smoothly continuous with a conical surface and at least the position facing the inner periphery of the fine powder discharge cylinder at the top and bottom is at the top.

The cavity stabilizing surface is a circular arc surface having a center on the central axis of the inlet of the fine powder discharge cylinder and having a center of curvature on a virtual circle on a horizontal plane having the same diameter as the inner diameter of the inlet. The air classifier according to claim 1.

The cavity stabilizing surface is composed of a circular flat surface centered on the center axis of the center core, and an arc surface smoothly connecting the outer periphery of the flat surface to the conical surface of the center core, and the outer periphery of the flat surface is a fine powder. The airflow classifier according to claim 1, wherein the airflow classifier is located at a position facing the inner periphery of the inlet of the discharge tube in the vertical direction.