JP6188016B2 - Centrifugal blower - Google Patents

Description

  The present invention relates to a centrifugal blower that blows air sucked into an impeller side from a suction cone side disposed on a suction side by rotating an impeller fixed to a rotating shaft extending in a casing.

  Traditionally, blowers have been used extensively in all industries. And a large-sized thing has become a great power consumption machine whose motor output reaches several thousand kW. As an example of the amount of power used, it is said that the blower accounts for about 60% of the amount of power used in steelworks, and the blower accounts for about 40% of the amount of power used in the cement factory. .

  Not only such a large blower but generally improving the efficiency of the blower can provide a large energy saving effect and reduce the total power consumption.

  In addition, the noise generated by the blower is extremely large and can adversely affect the mind and body. For this reason, it is desired to reduce the noise generated by the blower.

  As shown in FIG. 7, a centrifugal blower has conventionally been composed of a casing, a suction cone, an impeller, a rotating shaft of an impeller, and the like. In such a centrifugal blower, air flows into the suction cone from the suction cone inlet, is pressurized by the centrifugal force action of the rotating impeller, passes through the spirally formed casing, and is blown to the outside.

  The impeller rotates at a high speed together with the rotating shaft, but the casing and the suction cone are stationary. For this reason, a gap (clearance) is provided between the impeller side plate and the suction cone so as to ensure safety.

  In the centrifugal blower, due to its structure, air flows in the radial direction in the direction away from the rotating shaft after flowing into the impeller from the rotating shaft direction of the impeller. In other words, the air flowing into the inlet of the impeller has its air path bent at a substantially right angle. When bent at a substantially right angle, the air flow drifts toward the main plate side of the impeller due to the inertial force of the flow. For this reason, the flow of air is less on the side plate side than on the main plate side.

  Due to the non-uniform flow velocity of air between the main plate side and the side plate side, a mismatch between the air flow and the inlet angle of the blade occurs in the two-dimensional blade. Where the air flow and the blade inlet angle are mismatched, air detachment occurs on the blade suction surface, and a vortex is generated. The separation of air at the blade negative pressure surface is particularly large near the side plate. In the side plate, the air flow is separated from the side plate, and the air flow in the vicinity of the side plate becomes worse. The deterioration of the air flow causes a decrease in the efficiency of the blower and an increase in the noise level.

  As a solution to this, there is a centrifugal blower equipped with a three-dimensional impeller having a blade shape that follows the flow of air, but the three-dimensional impeller has a problem that the manufacturing cost is significantly increased compared to the two-dimensional impeller. There are points. For this reason, the centrifugal blower in the case where the number of manufactured units is small and is designed and manufactured each time is generally manufactured using a two-dimensional impeller that is easy to manufacture. Therefore, a blower that can improve the drift of the blade inlet in a two-dimensional impeller and prevent air separation is desired.

  In general, in order to improve the separation of the air on the impeller side plate side, as shown in FIG. 7, the impeller side plate and a curved surface that expands the shape near the impeller side plate toward the tip near the impeller side. It is known that it is effective to generate a jet by overlapping a suction cone formed in a shape with a gap and reducing the gap (usually the gap). That is, when the impeller rotates, the outside of the suction cone becomes high pressure, and the inlet side of the impeller becomes low pressure, so that a high-speed jet due to air entering from the gap between the impeller side plate and the suction cone is generated on the impeller side. . Since this high-speed jet flows along the impeller side plate, the generation of vortices due to boundary layer separation in the vicinity of the impeller side plate can be suppressed.

  For example, there is a blower described in Japanese Patent Application Laid-Open No. 2000-130397 of Patent Literature 1 as a proposal for effectively suppressing the generation of vortices due to boundary layer separation. In Patent Document 1, the angle difference between the inclination angle of the impeller side plate and the tangent at the tip of the bell mouth (suction cone) is set to 15 degrees or less.

  That is, by taking the inclination angle between the impeller side plate and the tangent at the tip of the bell mouth as small as possible, the gas flow sucked from the bell mouth is transferred from the tip of the bell mouth to the impeller side plate of the impeller. As a result, the generation of vortices due to boundary layer separation inside the impeller side plate is reduced, thereby reducing noise. Thus, in order to improve the fan efficiency, it is effective to generate a jet by reducing the angle difference between the inclination angle of the impeller side plate and the tangent at the bell mouth tip (suction cone tip).

  Further, the size of the gap between the impeller and the suction cone has a great influence on the fan performance. In the experiment, when the gap increases, the jet flow rate increases, so that leakage increases, fan efficiency decreases, and noise increases. On the other hand, the smaller the gap, the better the fan performance (blower efficiency) and noise. However, in the case of being completely sealed so that there is no gap, no jet flow is generated, so that the efficiency of the blower also deteriorates and noise increases.

  In other words, the gap between the impeller and the suction cone is better than it is not, and the smaller the better, the better. However, if the gap is too small, the impeller and the suction cone may come into contact with each other. If the impeller that rotates at high speed and the stationary suction cone come into contact with each other, there is a risk that it may lead to a major accident.

  As a device for simply reducing the gap between the impeller side plate and the suction cone, there is a blower proposed in Japanese Utility Model Publication No. 57-120798. However, in the blower disclosed in Japanese Utility Model Laid-Open No. 57-120798, the adjustment ring of the suction cone is attached below the straight end of the impeller side wheel, so that the impeller can be reduced even if the gap can be reduced. There is a problem in that the angle difference between the inclination angle of the side wheel and the tangent at the tip of the suction cone cannot be in a preferable angle range.

  Further, in Japanese Utility Model Publication No. 57-120798, since an adjustment ring is attached to the inner peripheral side of the suction cone, a step is generated between the adjustment ring and the suction cone, and this is a resistance to air flow along the suction cone. Therefore, there is a problem that a new vortex is generated. For this reason, there was a big problem in the point of effective vortex suppression by a jet.

  In addition, in the centrifugal blower disclosed in Japanese Patent Application Laid-Open No. 2010-138700 of Patent Document 3, another proposal for narrowing the gap has been made. In this case, the sealing material is attached so as to be flush with the tip of the bell mouth and the outer peripheral portion is horizontal.

  In addition, the present applicant has proposed a proposal for reducing the gap between the impeller and the suction cone while ensuring an appropriate jet from a viewpoint completely different from the above proposals, as disclosed in Japanese Patent Application No. 2009-185615. This was done with a blower or the like. This is composed of a stationary cone portion in which the suction cone is fixed to the casing side, and a rotating cone portion having a rotation shaft positioned between the stationary cone portion and the impeller. According to this, there is no relative displacement between the rotating cone portion and the impeller, and the gap between the rotating cone portion and the impeller can be extremely narrow while maintaining safety. It was.

Japanese Patent Application No. 2000-130397 Japanese Utility Model Publication No. 57-120798 JP 2010-138700 A Japanese Patent Application No. 2009-185615 (Japanese Patent Laid-Open No. 2011-38455)

  However, in the invention of Patent Document 1, there is a problem that if the gap between the impeller and the suction cone is reduced, they may come into contact with each other, so that the gap cannot be reduced to an effective value. . Further, in the invention of Patent Document 2, since the adjustment ring is attached to the inner peripheral side of the suction cone as described above, a step is generated between the adjustment ring and the suction cone, and this is the resistance of the air flow along the suction cone. As a result, there was a problem that a new vortex was generated. Further, the invention of Patent Document 3 has a problem that the effect of preventing the generation of vortices due to boundary layer separation by reducing the angle difference between the inclination angle of the impeller side plate and the tangent at the tip of the bell mouth is present. It was. Furthermore, the invention of Patent Document 4 has a problem that the cost becomes high.

  The present invention has been made paying attention to such problems of the prior art, and while ensuring safety, the gap between the impeller side plate and the suction cone is extremely reduced to improve the blower efficiency and noise. The objective is to provide a centrifugal blower that can be manufactured at low cost.

The gist of the present invention for achieving the object lies in the inventions of the following items.
[1] A suction cone (10) disposed on the suction side of air into the casing (C) by rotating the impeller (30) fixed to the rotary shaft (20) extending into the casing (C). In the centrifugal blower (1) for blowing air sucked from the side to the impeller (30) side,
The impeller (30) includes a main plate (31) fixed orthogonally to the rotation shaft (20), a plurality of blades (32) fixed to the main plate (31), and the blade (32). An impeller side plate (34) that is fixed to the tip end side of the blade and forms an air inlet,
The suction cone (10) has a curved surface portion (12) whose diameter increases toward the tip near the impeller side plate (34), and the rotating shaft (20) extends on the outer peripheral surface side of the curved surface portion (12). Having parallel portions (13) extending in the direction;
The tip near the impeller side plate (34) has a diameter smaller than the inner diameter of the tip of the impeller side plate (34) and is located inside the tip of the impeller side plate (34),
The parallel portion (13) includes a thin plate-like non-metallic gap maintaining member (14) extending so as to extend the shape of the tip from the tip of the suction cone (10) ,
The gap maintaining member (14) is a gap formed between the outer peripheral surface of the tip of the curved surface portion (12) of the suction cone (10) and the inner surface of the tip of the impeller side plate (34). Centrifugal blower (1) characterized in that (t) is made smaller inside the tip of the impeller side plate (34 ).

[2] The gap maintaining member (14) has a plurality of cuts (15) from the tip (14a) side toward the base end (14b) side fixed to the parallel part (13) over substantially the entire length. Centrifugal blower (1) according to item [1], which is contained.

[3] Item [1] or [2], wherein the gap maintaining member (14) is made of a heat-resistant material having a friction coefficient as small as that of Teflon (registered trademark) or non-asbestos gasket. Centrifugal blower (1).

[4] Item [1], [2] or [4], wherein the outer diameter of the tip (14a) of the gap maintaining member (14) is larger than the inner diameter of the tip of the impeller side plate (34). 3] Centrifugal blower (1).

The present invention operates as follows.
In the centrifugal blower (1) of the item [1], when the rotating shaft (20) starts rotating by the motor, the impeller (30) fixed to the rotating shaft (20) rotates. Each blade (32) of the impeller (30) is formed into a shape that sucks air from the suction cone (10) side to the impeller (30) side by rotation.

  Air is sucked from the inlet serving as the air suction portion of the suction cone (10) and flows toward the impeller (30). In the casing (C) in which the impeller (30) is rotating, the pressure on the inlet side of the impeller (30) is lower than the outside of the suction cone (10). Through the gap (t) with the cone (10), the air outside the suction cone (10) is sucked into the impeller (30) as a jet.

  The air flows along the gap maintaining member (14) fixed to the parallel portion (13) provided on the outer peripheral surface side of the curved surface portion (12) of the suction cone (10), and the air of the gap maintaining member (14). It flows to the impeller (30) through a gap (t) between the tip (14a) and the impeller side plate (34). The gap maintaining member (14) extends toward the impeller side plate (34) so as to extend the shape of the tip portion of the suction cone (10), and the gap maintaining member (14) and the impeller A very small gap (t) suitable for the side plate (34) can be formed. Further, the angle difference between the inclination angle of the impeller side plate (34) and the tangent at the tip (14a) of the gap maintaining member (14) of the suction cone (10) can be set to a suitable angle, for example, 15 degrees or less. .

  A jet flow is generated on the impeller (30) side by the air passing through the gap (t) formed by the gap maintaining member (14). By this jet flow, generation of vortices due to air boundary layer separation in the vicinity of the impeller side plate (34) is suppressed. Further, since the gap maintaining member (14) is provided on the outer peripheral surface side of the curved surface portion (12) of the suction cone (10), a new vortex or other disturbance in the air flow sucked from the suction cone (10) is obtained. There is no cause for flow.

Therefore, the efficiency of the centrifugal blower (1) can be improved and noise can be reduced. Further, since the gap maintaining member (14) is a thin plate and made of non-metal, it is important that the gap maintaining member (14) contacts the rotating impeller side plate (34). It is possible to drive safely. In addition, as described in the item [3], the material of the gap maintaining member (14) has a heat resistance and a friction coefficient as small as that of Teflon (registered trademark) or non-asbestos gasket .

  According to the centrifugal blower (1) of the item [2], the base end fixed to the parallel portion (13) from the tip (14a) near the impeller side plate (34) over the substantially entire length of the gap maintaining member (14). Since there are a plurality of cuts (15) toward the part (14b), it is possible to easily extend the shape of the tip of the suction cone (10). That is, of the cut (15) at the joint point (X) near the tip of the curved surface portion (12) of the portion where the outer peripheral surface of the curved surface portion (12) and the parallel portion (13) of the suction cone (10) are joined. By positioning the terminal end (15z), the tip end side of the suction cone (10) can be extended by easily and appropriately bending the tip end side from the terminal end (15z).

  According to the centrifugal blower according to the present invention, the gap maintaining member that extends toward the impeller side plate so as to extend the shape of the tip portion of the suction cone allows a very small gap between the tip of the gap maintaining member and the impeller side plate. And the angle difference between the inclination angle of the impeller side plate and the tangent at the tip of the suction cone gap maintaining member can be set to a small suitable angle, so that a new vortex that disturbs the flow of air sucked from the suction cone Without generating vortices, it is possible to prevent the generation of vortices due to boundary layer separation by the jet flow, and thus it is possible to easily improve the blowing efficiency and reduce the noise.

It is sectional drawing which looked at the centrifugal blower which concerns on one embodiment of this invention from the side surface side. It is a front view of the centrifugal blower which concerns on one embodiment of this invention. It is sectional drawing which shows the principal part in FIG. FIG. 4 is a development view showing a part of a development of the gap maintaining member in FIG. 3. FIG. 4 is a cross-sectional view of the gap maintaining member in FIG. 3 with different attachment states. It is a performance comparison figure which compared the performance of the centrifugal blower which concerns on this invention, and the conventional centrifugal blower. It is sectional drawing which looked at the conventional centrifugal blower from the side surface side.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.
1 to 6 show an embodiment of the present invention.
FIG. 1 is a cross-sectional view of a centrifugal blower according to an embodiment of the present invention as viewed from the side, but hatching is omitted. FIG. 2 is a front view of the centrifugal blower according to the embodiment of the present invention. 3 and 5 are cross-sectional views showing the main part in FIG. 1. FIG. 3 and FIG. 5 are different in the attachment state of the gap maintaining member. FIG. 4 is a developed view showing a part of the developed gap maintaining member. FIG. 6 is a graph showing a comparison of performance between the centrifugal blower according to the present invention and a conventional centrifugal blower.

  As shown in FIGS. 1 and 2, the centrifugal blower 1 includes an impeller 30 fixed to a rotary shaft 20 that extends into the casing C thereof. The centrifugal blower 1 rotates the impeller 30 so that the air sucked from the suction cone 10 provided in the casing C is sucked into the impeller 30 and blown.

  A disk-shaped main plate 31 (hub) orthogonal to the direction in which the rotation shaft 20 extends is fixed to the rotation shaft 20. The main plate 31 is provided with a plurality of blades 32 at equal intervals in the radial direction of the rotary shaft 20.

  Each blade 32 is formed in a shape that sucks air from the suction cone 10 side to the impeller 30 side by rotation of the rotating shaft 20 in a predetermined direction. An impeller side plate 34 is provided at the tip of each blade 32.

  The impeller side plate 34 is attached so as to intersect the tip of the blade 32, and is inclined from the top to the bottom toward the suction cone 10 on the paper surface of FIG. The impeller side plate 34 may be attached so as to extend in parallel with the main plate 31. As shown in FIG. 1, the impeller side plate 34 is formed in a cross-sectional shape in which a lower end portion is bent in a curved shape and extends toward the suction cone 10 side. Moreover, as shown in FIG. 2, the lower end edge of the impeller side plate 34 is connected so as to form a circular peripheral edge. The circle drawn by the lower edge of the impeller side plate 34 serves as an inlet through which air from the suction cone 10 flows into the impeller 30. In FIG. 2, about 1/3 of the impeller side plate 34 is shown, and the remaining about 2/3 is cut away.

  The rotating shaft 20 has an outer end portion of the casing C connected to a drive unit (not shown) including a motor. The impeller 30 is disposed near one side surface of the casing C in the casing C. An opening A for sucking outside air from the casing C is formed in a side surface opposite to the side surface. In the opening A, an inlet side end portion of the suction cone 10 serving as an air suction portion is attached.

  As shown in FIG. 1, the suction cone 10 is formed into a shape that narrows the opening diameter by a straight portion 11 whose cross section linearly appears from the inlet end of the opening A of the casing C into the casing C. A curved surface portion 12 whose cross section appears in an arc shape is formed following the straight portion 11. The curved surface portion 12 is formed in a shape that expands from the middle toward the tip near the impeller side plate 34.

  As shown in FIGS. 3 and 5, a parallel portion 13 that extends substantially parallel to the direction in which the rotation shaft 20 extends is provided on the outer peripheral surface side of the curved surface portion 12 of the suction cone 10. The parallel portion 13 is joined to the distal end side of the curved surface portion 12 at a joint point X. Since the curved surface portion 12 has a shape that increases in diameter, the distal end portion of the curved surface portion 12 extends outward from the direction in which the parallel portion 13 extends.

  From the parallel part 13 to the tip of the suction cone 10, a thin plate-like non-metallic gap maintaining member 14 is fixed on the outer peripheral side thereof. As shown in FIGS. 3, 4 and 5, the gap maintaining member 14 is a non-metallic elongated thin plate. FIG. 4 shows one end side of the gap maintaining member 14 before being attached to the suction cone 10. The gap maintaining member 14 is annularly attached to the outer periphery from the parallel portion 13 to the tip of the suction cone 10. The material of the gap maintaining member 14 is preferably a material having a low coefficient of friction and heat resistance. Examples of such a material include Teflon (registered trademark) and non-asbestos gaskets. The thickness of the gap maintaining member 14 is preferably about 0.5 to 5.0 mm.

  The gap maintaining member 14 has a plurality of cuts 15 extending from the distal end 14a toward the proximal end portion 14b over substantially the entire length. In addition, a plurality of bolt mounting holes 16 are formed in the base end portion 14 b away from the terminal end 15 z of the cut 15. The bolt mounting hole 16 may be a long hole extending in the direction in which the cut 15 extends.

  Although not shown, a plurality of bolt mounting holes are also formed in the parallel portion 13 of the suction cone 10. The gap maintaining member 14 is fixed to the parallel portion 13 by inserting the bolt B together with the bolt mounting hole 16 and the bolt mounting hole of the parallel portion 13 and tightening with the nut N. The notch 15 is formed such that when the gap maintaining member 14 is fixed to the parallel portion 13, the terminal end 15 z substantially overlaps the junction X between the parallel portion 13 and the distal end side of the curved surface portion 12.

  Thereby, the tip 14a of the gap maintaining member 14 is bent along the R shape of the tip of the suction cone 10 and spreads in a trumpet shape. Thus, the outer diameter (dc) of the tip 14a of the gap maintaining member 14 is larger than the diameter of the tip of the suction cone 10. As a result, the gap t with the impeller side plate 34 can be made extremely small. Further, the angle difference between the inclination angle of the impeller side plate 34 and the tangent at the tip end portion of the suction cone 10 is formed by appropriately forming the shape of the lower end portion of the impeller side plate 34 and the tip end of the curved surface portion 12 of the suction cone 10. The desired small angle difference can be easily obtained.

Next, the operation of the centrifugal blower 1 according to the present embodiment will be described.
In the centrifugal blower 1, when the rotating shaft 20 starts rotating due to rotation of a motor (not shown), the impeller 30 fixed to the rotating shaft 20 rotates and starts to suck in air.

  Air is sucked from an inlet serving as an air suction portion of the suction cone 10 and flows to the impeller 30 side. When the impeller 30 is rotating, the pressure on the inlet side of the impeller 30 is lower in the casing C than on the outside of the suction cone 10. For this reason, the air outside the suction cone 10 passes through the gap t between the adjacent impeller 30 and the suction cone 10 and is sucked into the impeller 30 as a jet.

  The air flowing from the outside of the suction cone 10 toward the impeller 30 side flows along the gap maintaining member 14 fixed to the parallel portion 13 provided on the outer peripheral surface side of the curved surface portion 12 of the suction cone 10. This air flow is squeezed at a gap t between the tip 14 a of the gap maintaining member 14 and the impeller side plate 34 and flows into the impeller 30 as a jet. Since the gap t is extremely narrow, the jet is a high-speed jet. For this reason, the air sucked through the inside of the suction cone 10 collides with the jet when it reaches the vicinity of the lower end of the impeller side plate 34. By this jet flow, generation of vortices due to boundary layer separation in the vicinity of the impeller side plate 34 can be prevented. The occurrence of boundary layer separation can be effectively prevented by setting the angle difference between the inclination angle of the impeller side plate 34 and the tangent at the tip 14a of the gap maintaining member 14 of the suction cone 10 to 15 degrees or less.

  The gap maintaining member 14 is provided on the outer peripheral surface side of the curved surface portion 12 of the suction cone 10. For this reason, the provision of the gap maintaining member 14 does not hinder the air flow sucked from the suction cone 10 and never causes a new vortex or other turbulent flow. In this way, the efficiency of the centrifugal blower 1 can be improved. At the same time, noise can be reduced.

  Further, the gap maintaining member 14 is formed of a non-metallic material in a thin plate shape, and has a small friction coefficient and heat resistance, so that the gap maintaining member 14 and the rotating impeller side plate 34 are separated from each other. Even if contact is made, the gap maintaining member 14 has a large number of cuts 15, so even if it is partially contacted, only the contact portion on the gap maintaining member 14 side is easily bent. As a result, both are not in strong contact and do not become important.

  As shown in FIG. 3, when the centrifugal fan 1 is assembled, the outer diameter (dc) of the tip 14a of the gap maintaining member 14 of the suction cone 10 is larger than the inner diameter (De) of the tip of the impeller side plate 34. When it arrange | positions so that it may become large, the gap maintenance member 14 uses the thing with the bolt attachment hole 16 being a long hole. Thus, when the leading end side of the gap maintaining member 14 is inserted into the impeller 30, the leading end 14 a of the gap maintaining member 14 is shifted from the predetermined position to a position where De> dc. In this state, the front end side of the gap maintaining member 14 is inserted into the impeller 30.

  Next, the gap maintaining member 14 is advanced along the elongated bolt mounting hole 16 so that the tip 14a thereof approaches the impeller 30 side. Thereby, De <dc can be satisfied, and the gap t between the impeller side plate 34 and the tip 14a of the gap maintaining member 14 of the suction cone 10 can be sufficiently reduced.

  Further, as shown in FIG. 5, when the centrifugal fan 1 is assembled, the outer diameter (dc) of the tip 14a of the gap maintaining member 14 of the suction cone 10 is larger than the inner diameter (De) of the tip of the impeller side plate 34. In the case where the gap maintaining member 14 is arranged so as to be small, it is not necessary that the bolt mounting hole 16 has a long hole, and after the gap maintaining member 14 is fixed to the parallel portion 13 of the suction cone 10 with a bolt, it remains as it is. What is necessary is just to insert and assemble in the impeller 30.

  Thus, the centrifugal blower 1 according to the present embodiment can easily make the gap t between the tip of the impeller side plate 34 and the tip 14a of the gap maintaining member 14 extremely small.

  The embodiments of the present invention have been described above with reference to the drawings. However, the specific configuration is not limited to the above-described embodiments, and the present invention can be changed or added without departing from the scope of the present invention. Included in the invention.

  For example, although the parallel portion 13 has been described as extending substantially parallel to the direction in which the rotation shaft 20 extends, the parallel portion 13 may extend at an angle with the direction in which the rotation shaft 20 extends. Further, as a means for attaching the gap maintaining member 14 to the parallel portion 13, it is fixed to the parallel portion 13 by winding a band around the outer periphery of the gap maintaining member 14 without making a mounting hole 16 in the gap maintaining member 14. It is good.

  The present invention can be widely applied to those having a configuration in which the impeller is rotated to deliver the fluid sucked from the fluid suction / intake means corresponding to the suction cone.

A ... Opening C ... Casing De ... Inner diameter of impeller side plate dc ... Outer diameter of tip of gap maintaining member t ... Gap X ... Junction point 1 ... Centrifugal blower 10 ... Suction cone 11 ... Linear portion 12 ... Curved portion 13 ... Parallel part 14 ... Gap maintenance member 14a ... Tip 14b ... Base end 15 ... Incision 15z ... Terminal 20 ... Rotating shaft 30 ... Impeller 31 ... Main plate 32 ... Vane 34 ... Impeller side plate

Claims (4)

In the centrifugal blower that blows the air sucked into the impeller side from the suction cone side disposed on the air suction side into the casing by rotating the impeller fixed to the rotating shaft extending in the casing,
The impeller includes a main plate fixed orthogonally to the rotation axis, a plurality of blades fixed to the main plate, and an impeller side plate fixed to the tip side of the blade and forming an air inlet. Consisting of
The suction cone has a curved portion that expands toward the tip near the impeller side plate, and a parallel portion that extends in the direction in which the rotating shaft extends on the outer peripheral surface side of the curved portion,
The tip near the impeller side plate has a diameter smaller than the inner diameter of the tip portion of the impeller side plate, and is located inside the tip portion of the impeller side plate,
The parallel portion includes a non-metallic gap maintaining member made of a thin plate extending so as to extend the shape of the tip from the tip of the suction cone ,
The gap maintaining member has a gap formed between the outer peripheral surface of the tip of the curved portion of the suction cone and the inner surface of the tip of the impeller side plate inside the tip of the impeller side plate. A centrifugal blower characterized by being made smaller .   2. The centrifugal blower according to claim 1, wherein the gap maintaining member has a plurality of cuts from a distal end side toward a proximal end portion side fixed to the parallel portion over a substantially entire length. The centrifugal blower according to claim 1 or 2, wherein the gap maintaining member is made of a heat-resistant material having a friction coefficient as small as that of Teflon (registered trademark) or a non-asbestos gasket .   The centrifugal blower according to claim 1, 2, or 3, wherein an outer diameter of a tip of the gap maintaining member is larger than an inner diameter of a tip of the impeller side plate.

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