Scraper, axial fan, and method of operating an axial fan

Abstract

To elongate a life by improving friction resistance.SOLUTION: A scraper 30 comprises: a holder 40 having a holder recess which is recessed to a turbine wheel 5 side from a face opposing a downstream-side inner cylinder 3B, and fixed to the turbine wheel 5; and a scraper piece 50 comprising an engagement part 52 accommodated in the holder recess and engaged with the holder recess, held to the holder 40, protruding to the downstream-side inner cylinder 3B with respect to than the holder 40, and formed of ceramic. A pair of recess side faces for regulating both ends of the holder recess in a peripheral direction are inclined so that the recess side faces approach each other as progressing toward the downstream-side inner cylinder 3B side. Also, a pair of protrusion side faces being peripheral faces of the scraper piece 50 abut on the recess side faces.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a scraper and an axial fan, and a method for operating an axial fan. [Background technology]

[0002] The axial flow fan includes an outer cylinder, an inner cylinder disposed inside the outer cylinder, and a main shaft disposed inside the inner cylinder. The main shaft is supported by bearings and rotates about a central axis by driving force from a drive source. An impeller is attached to the main shaft. A plurality of rotor blades are provided at the radially outer end of the impeller, protruding radially outward. The rotor blades are attached at equal intervals in the circumferential direction. The rotor blades are provided so as to protrude into an annular flow path formed between the inner cylinder and the outer cylinder. Gas flows through the flow path as the impeller and rotor blades rotate. Stator blades are disposed in this flow path on the upstream and downstream sides of the rotor blades. The downstream and upstream end faces of the outer end of the impeller face the end face of the inner cylinder, forming a gap of a predetermined length (approximately 3 mm to 5 mm). The downstream end face and upstream end face of the outer end of the impeller face the end face of the inner cylinder, forming a sealing portion that seals between the inner space of the inner cylinder and the outer space of the inner cylinder (i.e., the flow path through which gas flows).

[0003] For example, when an axial flow fan is used in an exhaust gas system discharged from a boiler, the rotation of the rotor blades causes exhaust gas containing foreign matter such as combustion ash to flow through the flow path. As the exhaust gas flows through the flow path, foreign matter flows into the seal section, solidifying and adhering to the end surface of the inner cylinder, where it grows. If the foreign matter (deposit) adhering to the inner cylinder grows, the deposit comes into contact with the impeller as the impeller rotates, causing wear on the impeller. When the impeller wears, problems such as impeller vibration occur. To solve this problem, repair work is required, in which the axial flow fan is disassembled, the worn parts are overlaid with welds, and the axial flow fan is reassembled. This has resulted in increased labor and costs associated with maintenance by workers.

[0004] As a countermeasure to this problem, it has been known to provide scrapers at the outer ends of the inlet and outlet end faces of the impeller to scrape off deposits that have adhered to the inner cylinder, and to attach an annular liner to the end face of the inner cylinder so that it faces the scraper (for example, Patent Document 1).

[0005] Patent Document 1 describes an axial flow fan in which a plurality of U-shaped recesses are bored at equal intervals in the circumferential direction on the outer periphery of the outlet and inlet end faces of the impeller, and scrapers are formed by applying Stellite hardfacing to these recesses. In this axial flow fan, an annular liner made of a highly corrosion-resistant and water-repellent material such as Teflon (registered trademark) is fastened to the end face of the casing inside the casing with countersunk screws, and this liner faces the scraper with a small gap (3 to 5 mm) between them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3735174 Summary of the Invention [Problem to be solved by the invention]

[0007] Scrapers wear out as they scrape off deposits such as combustion ash. Therefore, scrapers need to be repaired during periodic inspections of axial flow fans. In the structure described in Patent Document 1, the scrapers are formed by applying a stellite hardfacing, so they need to be repaired by overlay welding during periodic inspections. Furthermore, if wear extends to the impeller to which the scraper is attached, overlay welding repair is required over the entire circumferential area of ​​the impeller, which can complicate the repair work. Furthermore, overlay welding repair on the impeller can cause welding distortion in the impeller. Furthermore, machining is required after overlay welding to obtain the required small gap, which can further complicate the repair work on the impeller and scraper and extend the periodic inspection time.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a scraper and an axial fan, as well as a method for operating an axial fan, that can improve wear resistance and simplify maintenance. [Means for solving the problem]

[0009] In order to solve the above problems, the scraper, axial fan, and method of operating the axial fan of the present disclosure employ the following measures. A scraper according to one aspect of the present disclosure is a scraper provided at the opposing portion of an axial flow fan including: a cylindrical portion defining a flow path through which gas flows between an inner cylinder and an outer cylinder; and an impeller having an opposing portion opposing the inner cylinder of the cylindrical portion, the impeller rotating about a central axis by a driving force from a driving source to cause the gas to flow through the flow path, The inner cylinder The rotor has a recess recessed toward the impeller from a surface facing the rotor, and includes a holding portion fixed to the facing portion and an engaging portion accommodated in the recess and engaging with the recess. The rotor is held by the holding portion and is positioned closer to the cylindrical portion than the holding portion. The inner cylinder a pair of recess side surfaces defining both ends of the recess in the circumferential direction, the pair of recess side surfaces being formed of ceramic and projecting toward the cylindrical portion; The inner cylinder The recess side surfaces are inclined so as to approach each other as they approach the cylindrical portion. The inner cylinder The side surfaces of the protrusions are inclined so as to approach each other toward the side.

[0010] A method for operating an axial flow fan according to one aspect of the present disclosure includes: Between the inner and outer cylinders a cylindrical portion defining a flow path through which gas flows; The inner cylinder a scraper provided at the opposing portion, the scraper being configured to rotate by the gas flowing through the flow path; The inner cylinder The rotor has a recess recessed toward the impeller from a surface facing the rotor, and includes a holding portion fixed to the facing portion and an engaging portion accommodated in the recess and engaging with the recess. The rotor is held by the holding portion and is positioned closer to the cylindrical portion than the holding portion. The inner cylinder a pair of recess side surfaces defining both ends of the recess in the circumferential direction, the pair of recess side surfaces being formed of ceramic and projecting toward the cylindrical portion; The inner cylinder The recess side surfaces are inclined so as to approach each other as they approach the cylindrical portion. The inner cylinder The side surfaces of the protrusions are inclined so as to approach each other as they approach the cylindrical portion. The inner cylinder The method further includes a removal step of removing any deposits that have adhered to the surface. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to improve wear resistance and simplify maintenance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a longitudinal cross-sectional view of an axial flow fan according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged view of a main part of FIG. 1, showing a portion II of FIG. [Figure 3] FIG. 1 is an exploded perspective view showing a main portion of a blade wheel and a scraper according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a perspective view of a holder according to an embodiment of the present disclosure. [Figure 5] FIG. 1 is a front view of a holder according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a plan view of a holder according to an embodiment of the present disclosure. [Figure 7] FIG. 1 is a side view of a holder according to an embodiment of the present disclosure. [Figure 8] FIG. 1 is a perspective view of a scraper piece according to an embodiment of the present disclosure. [Figure 9] FIG. 1 is a side view of a scraper piece according to an embodiment of the present disclosure. [Figure 10] FIG. 1 is a plan view of a scraper piece according to an embodiment of the present disclosure. [Figure 11]10A and 10B are diagrams illustrating a holder and a scraper according to a modified example of an embodiment of the present disclosure. [Figure 12] 10A and 10B are diagrams illustrating a holder and a scraper according to a modified example of an embodiment of the present disclosure. [Figure 13] 10A and 10B are diagrams illustrating a holder and a scraper according to a modified example of an embodiment of the present disclosure. [Figure 14] 10A and 10B are diagrams illustrating a holder and a scraper according to a reference example of an embodiment of the present disclosure. [Figure 15] 10A and 10B are diagrams illustrating a holder and a scraper according to a reference example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a scraper, an axial fan, and an operating method for an axial fan according to the present disclosure will be described below with reference to the drawings. Hereinafter, the term "axial direction" refers to the direction in which the central axis C of the axial fan rotates, and the terms "radial direction" and "circumferential direction" refer to the radial direction and the circumferential direction, respectively, based on the central axis C. In each drawing, the axial direction is designated as the X-direction, the radial direction as the Z-axis, and the circumferential direction as the Y-axis.

[0014] The axial flow fan 1 according to this embodiment is installed in an exhaust gas system through which flue gas discharged from a boiler (not shown) that generates steam by burning fuel flows. For example, the axial flow fan 1 may be installed in a desulfurization device that removes sulfur oxides from the flue gas in the exhaust gas system. When the axial flow fan 1 is installed in a desulfurization device, the inside of the axial flow fan 1 may be a highly corrosive environment.

[0015] As shown in FIG. 1, the axial fan 1 includes an outer cylinder 2 extending axially about a central axis C, an inner cylinder 3 disposed concentrically within the outer cylinder 2, a main shaft 4 disposed inside the inner cylinder (cylindrical portion) 3, and an impeller 5 attached to the axial end of the main shaft 4. The inner cylinder 3 includes an upstream inner cylinder 3A disposed upstream of the impeller 5 and a downstream inner cylinder 3B disposed downstream of the impeller 5. Air for sealing is filled inside the inner cylinder 3. The main shaft 4 is rotatably supported by bearings about the central axis C. A plurality of rotor blades 6 protruding radially outward are provided at the radially outer end of the impeller 5. The rotor blades 6 are attached at equal intervals in the circumferential direction. The rotor blades 6 are disposed so as to protrude into an annular gas flow path 7 formed between the inner cylinder 3 and the outer cylinder 2. An upstream stator vane 8 is disposed in the gas flow path 7 upstream of the rotor blades 6. Further, downstream stator vanes 9 are provided in the gas flow passage 7 downstream of the rotor blades 6. The upstream stator vanes 8 and downstream stator vanes 9 are installed between the inner casing 3 and the outer casing 2.

[0016] In the axial flow fan 1, the main shaft 4 rotates about a central axis C due to the driving force from an electric motor (not shown) connected to the main shaft 4. When the main shaft 4 rotates, the impeller 5 and the rotor blades 6 are also driven to rotate about the central axis C. At this time, the rotor blades 6 rotate within the gas flow path 7, so that exhaust gas containing ash and the like is sucked into the gas flow path 7 and flows through the gas flow path 7, as shown by the arrows in FIG. 1. The exhaust gas flowing through the gas flow path 7 passes through the upstream stator vanes 8, the rotor blades 6, and the downstream stator vanes 9 in that order, before being discharged from the gas flow path 7.

[0017] A downstream end face 5a of the impeller 5 at the radially outer end thereof faces the inner cylinder 3. Specifically, as shown in FIG. 2, the downstream end face 5a of the impeller 5 faces the upstream end face 3Ba of the downstream inner cylinder 3B. A first gap G1 is formed over the entire circumferential area between the downstream end face 5a of the impeller 5 and the upstream end face 3Ba of the downstream inner cylinder 3B. The axial length of the first gap G1 is approximately 3 mm to 5 mm. A seal structure 10 is provided between the impeller 5 and the downstream inner cylinder 3B to seal between the inner space of the inner cylinder 3 and the outer space of the inner cylinder 3 (i.e., the gas flow path 7).

[0018] The seal structure 10 includes a protruding seal portion 11 that protrudes axially downstream from the downstream end face 5a, and multiple seal fins 12 that protrude radially inward from the inner circumferential surface 3Bb of the downstream inner cylinder 3B. The protruding seal portion 11 is a cylindrical member, and its outer circumferential surface faces the inner circumferential surface 3Bb of the downstream inner cylinder 3B. A second gap G2 is formed between the outer circumferential surface 11a of the protruding seal portion 11 and the inner circumferential surface 3Bb of the downstream inner cylinder 3B. The multiple seal fins 12 are arranged side by side at predetermined intervals along the axial direction. The seal fins 12 are substantially annular members, and their radially outer ends are fixed so as to be embedded in the inner circumferential surface 3Bb of the downstream inner cylinder 3B. The radially inner ends of the seal fins 12 are close to the outer circumferential surface 11a of the protruding seal portion 11.

[0019] Next, the scraper 30 and the impeller recess 31 in which the scraper 30 is provided will be described in detail with reference to FIGS. The scraper 30 according to this embodiment is provided on the impeller 5, as shown in Figures 2 and 3. More specifically, the scraper 30 is provided on the downstream end face (opposing portion) 5a of the impeller 5, which faces the upstream end of the downstream inner cylinder 3B in the axial direction. It is more preferable that a plurality of scrapers 30 are arranged side by side at predetermined intervals in the circumferential direction on the downstream end face 5a. Note that, for convenience of illustration, Figure 3 shows only a portion of the impeller 5 in the circumferential direction.

[0020] The downstream end face 5a is formed with a wheel recess 31 that is recessed axially upstream. The scraper 30 is fitted into this wheel recess 31. In detail, a wall (not shown) that defines the radial outside of the space formed inside the wheel recess 31 is formed lower than the other walls surrounding the wheel recess 31. In the following description, the radially outer wall is referred to as the outer wall 32. The outer wall 32 separates the space formed inside the wheel recess 31 from the space radially outside the wheel 5 (i.e., the gas flow path 7).

[0021] A plurality of bolt holes 34 (four in this embodiment, for example) into which bolts 33 are inserted are formed in the bottom surface 31a of the impeller recess 31. A female thread is formed on the inner peripheral surface of each bolt hole 34. The tip of the bolt 33 is screwed into each bolt hole 34.

[0022] 3, the scraper 30 has a holder (holding portion) 40 fixed to the impeller recess 31, and a scraper piece (protruding portion) 50 protruding toward the downstream inner cylinder 3B side (axially downstream side) from the holder 40. The scraper 30 has the holder 40 fitted into the impeller recess 31.

[0023] The radial position of the radially outer end of the scraper 30 is the same as the radial position of the radially outer end of the liner 20. In other words, the scraper 30 does not protrude further into the gas flow path 7 than the liner 20. The scraper 30 is provided so that the radially outer end does not protrude further in the radial direction than the radial outer peripheral surface 5b of the impeller 5 as much as possible. By configuring it in this way, it is possible to prevent the scraper 30 from obstructing the flow of exhaust gas flowing through the gas flow path 7.

[0024] The holder 40 is made of a metal material (for example, a stainless steel material). The holder 40 is fitted into the impeller recess 31. The holder 40 is detachably fixed to the impeller recess 31 by a plurality of bolts 33 (four bolts in this embodiment, for example).

[0025] As shown in Figures 4 to 7, the holder 40 has an engaging portion 41 that engages with the impeller recess 31, two fixing portions 42 that are arranged on the downstream inner tube 3B side (axially downstream side) of the engaging portion 41, a holder recess 43 that is provided between the two fixing portions 42, and an outer plate portion 44 that is provided radially outward.

[0026] The fitting portion 41 fits into the impeller recess 31. This restricts radial and circumferential movement of the holder 40 relative to the impeller 5. In particular, the radial outer surface of the fitting portion 41 abuts against the outer wall portion 32 of the impeller 5, restricting radial outward movement of the holder 40 relative to the impeller 5.

[0027] The two fixing portions 42 are provided at both circumferential ends. Two bolt insertion holes 45 are formed in each fixing portion. The two bolt insertion holes 45 are arranged side by side in the radial direction. Each bolt insertion hole 45 penetrates the holder 40 in the axial direction. A bolt 33 is inserted into each bolt insertion hole 45. Each bolt insertion hole 45 has a large diameter portion capable of accommodating the head 33a of the bolt 33 and a small diameter portion capable of accommodating the shank 33b of the bolt 33. The head 33a of the bolt 33 is entirely housed within the bolt insertion hole 45 and does not protrude from the fixing portion 42 toward the downstream inner cylinder 3B.

[0028] The holder recess 43 is provided in the circumferential center. The holder recess 43 is formed over substantially the entire radial area. The radial inner end of the holder recess 43 is open, allowing the scraper piece 50 to be inserted from the inner end. The radial outer end of the holder recess 43 is closed by a restricting portion 47 of the outer plate portion 44. In other words, the scraper piece 50 engaged with the holder recess 43 is restricted from moving radially outward by the restricting portion 47.

[0029] Both circumferential ends of the holder recess 43 are defined by a pair of recess side surfaces 46. The pair of recess side surfaces 46 are inclined so that the opposing recess side surfaces 46 approach each other as they approach the downstream inner cylinder 3B side (axial downstream side). That is, the recess side surfaces 46 are tapered. As shown in FIG. 6 , the inclination angle θ1 of the recess side surfaces 46 is smaller than 45 degrees. Here, the inclination angle θ1 is the angle between the recess side surface 46 and the axial direction when the holder 40 is viewed from above. When the scraper piece 50 is housed in the holder recess 43, the recess side surface 46 and the scraper piece side surface 51 abut or are in close proximity. Note that the value of the inclination angle θ1 is not limited to the above value and may be an angle other than 45 degrees. 11, the scraper pieces may be formed in a T-shape at both circumferential ends of the holder recess 43, as will be described later. In this case, the recess side surfaces 46 may be formed to surround the periphery of the scraper piece 50 except for the tip portion 53 that protrudes from the holder 40.

[0030] The outer plate portion 44 is provided at the radially outer end portion. As shown in Fig. 2, the radially outer end portion of the outer plate portion 44 is located at the same radial position as the radially outer end portion of the liner 20 provided on the downstream-side inner cylinder 3B. 4, the circumferential center portion of the outer plate portion 44 protrudes in the axial direction beyond the bottom surface 43a of the holder recess 43. This protruding portion serves as a restricting portion 47 that restricts the radially outward movement of the scraper piece 50.

[0031] The scraper piece 50 is made of ceramic. As shown in FIG. 2, the radially outer end of the scraper piece 50 is located at the same radial position as, for example, the radially outer end of the liner 20 provided on the downstream inner cylinder 3B. As shown in FIGS. 8 and 10, the scraper piece 50 is trapezoidal in plan view. A pair of scraper piece side surfaces (protruding portion side surfaces) 51, which are circumferential surfaces of the scraper piece 50, abut against the recessed portion side surfaces 46 and are inclined so that the scraper side surfaces approach each other as they approach the downstream inner cylinder 3B (axially downstream side). In other words, the scraper piece side surfaces 51 are tapered surfaces. The inclination angle θ2 of the scraper piece side surfaces 51 is set to be smaller than 45 degrees. Here, the inclination angle θ2 is the angle between the scraper piece side surfaces 51 and the axial direction when the scraper piece 50 is viewed in plan. The inclination angle θ2 of the scraper piece side surface 51 is set to be substantially the same as the inclination angle θ1 of the recess side surface 46. Additionally, the scraper piece 50 may be formed in a T-shape as described above.

[0032] 6 and 8 to 10, the scraper piece 50 is housed in the holder recess 43 and integrally includes an engaging portion 52 that engages with the holder recess 43 and a tip portion 53 that protrudes from the holder 40. The engaging portion 52 and the tip portion 53 are not separate members fixed together, but are formed as an integral unit. The tip portion 53 is connected to the downstream inner cylinder 3B side (axial downstream side) of the engaging portion 52.

[0033] 8 and 9, a step 54 is formed on the radially outer side of the engaging portion 52. As shown in Fig. 2, the radially outer surface of the step 54 abuts against the radially inner surface of the restricting portion 47. The abutment between the step 54 and the restricting portion 47 restricts the scraper piece 50 from moving radially outward.

[0034] The scraper piece 50 is fixed in a state where it is pressed toward the downstream inner cylinder 3B, as shown by arrow P in Figure 6. That is, the scraper piece 50 is fixed so that the scraper piece side surface 51 is pressed against the recess side surface 46 of the holder 40. Note that any means may be used to press the scraper piece 50 toward the downstream inner cylinder 3B. For example, the scraper piece 50 may be pressed by a bolt or the like. The scraper piece 50 may also be pressed by press-fitting an adhesive or the like.

[0035] According to this embodiment, the following advantageous effects are achieved. In this embodiment, the scraper piece 50 protrudes toward the downstream inner cylinder 3B beyond the holder 40. As a result, if substances (such as ash) contained in the exhaust gas flowing through the gas flow path 7 adhere to the surface of the liner 20 provided in the downstream inner cylinder 3B and the deposits grow, the deposits come into contact with the scraper piece 50 (particularly the tip 53). The scraper piece 50 is fixed to the rotating impeller 5 via the holder 40, and therefore rotates together with the impeller 5. Therefore, the rotating scraper piece 50 can scrape off deposits that adhere to the downstream inner cylinder 3B. Furthermore, the scraper piece 50 wears when scraping off deposits, but in this embodiment, the scraper piece 50 is made of ceramic. Because ceramic has high wear resistance, the scraper piece 50 is less susceptible to wear. This extends the life of the scraper 30. Furthermore, even if the gas flowing through the gas flow path 7 is corrosive, the high corrosion resistance of ceramics makes it possible to make the scraper piece 50 less susceptible to corrosion, thereby extending the life of the scraper 30.

[0036] Furthermore, since ceramics are generally difficult to weld, it is difficult to directly fix a scraper piece 50 made of ceramic to the impeller 5 by welding, etc. However, in this embodiment, a holder 40 is provided that holds the scraper piece 50 made of ceramic, and the holder 40 is fixed to the downstream end face 5a of the impeller 5. This allows the scraper piece 50 made of ceramic to be provided on the downstream end face 5a of the impeller 5.

[0037] In this embodiment, a pair of recess side surfaces 46 defining both circumferential ends of the holder recess 43 are inclined so that the recess side surfaces 46 approach each other toward the downstream inner tube 3B. A pair of scraper piece side surfaces 51, which are circumferential surfaces of the scraper piece 50, abut against the recess side surfaces 46 and are inclined so that the side surfaces approach each other toward the downstream inner tube 3B. In this manner, the abutment between the recess side surfaces 46 and the scraper piece side surfaces 51 allows the holder 40 to restrict movement of the scraper piece 50 toward the downstream inner tube 3B. In other words, the relative position of the scraper piece 50 toward the downstream inner tube 3B with respect to the holder 40 can be determined. Thus, by adjusting the inclination angle of the recess side surfaces 46 during manufacturing of the holder 40, the length (protrusion length) of the tip portion 53 of the scraper piece 50 protruding from the holder 40 can be set to a predetermined length. For example, the recess side surface 46 of the holder 40 may be machined to match the actual dimensions of the scraper piece side surface 51 .

[0038] In addition, ceramics are difficult to process in a complex manner. In this embodiment, the length of the tip 53 of the scraper piece 50 can be set to a predetermined length by simply performing a relatively simple process of forming the scraper piece side surface 51 into an inclined surface.

[0039] Furthermore, in this embodiment, the holder 40 is detachably fixed to the downstream end face 5a of the impeller 5. This allows the holder 40, which holds the scraper piece 50, to be removed from the downstream end face 5a of the impeller 5 during periodic inspection of the axial fan 1, etc. This makes it easier to repair the scraper 30 compared to when the holder 40 and the scraper piece 50 are separately fixed to the downstream end face 5a of the impeller 5.

[0040] Furthermore, in this embodiment, the holder 40 has a restricting portion 47 that restricts the outward movement of the scraper piece 50 in the radial direction. As a result, even when centrifugal force acts on the scraper piece 50 due to the rotation of the impeller 5, the restricting portion 47 can restrict the outward movement of the scraper piece 50 in the radial direction. Therefore, the scraper piece 50 is less likely to fall off the holder 40.

[0041] In addition, in this embodiment, the radially outer end of the scraper piece 50 is located at the same position as the radially outer end of the liner 20 or at a position radially inward of the outer end of the liner 20. This makes it possible to configure the scraper piece 50 so that it is less likely to protrude into the gas flow path 7. Therefore, obstruction of the flow of gas circulating in the gas flow path 7 can be suppressed.

[0042] Furthermore, in this embodiment, the surfaces of the scraper piece 50 and the holder 40 on the downstream side of the inner cylinder 3B are covered with resin. This improves the corrosion resistance of the scraper piece 50 and the holder 40. Therefore, even if the gas flowing through the gas flow path 7 is a corrosive gas, the scraper piece 50 and the holder 40 are less likely to corrode. This increases the life of the scraper 30.

[0043] Furthermore, in this embodiment, the holder 40 is fitted into a holder recess 43 formed in the downstream end face 5a of the impeller 5. This makes it possible to restrict relative radial and circumferential movement of the holder 40 with respect to the impeller 5, even if, for example, the bolt 33 fixing the holder 40 to the downstream end face 5a of the impeller 5 is broken and the fixation between the holder 40 and the downstream end face 5a of the impeller 5 is released. Therefore, even if the fixation between the holder 40 and the downstream end face 5a of the impeller 5 is released and centrifugal force acts on the holder 40 as the impeller 5 rotates, it is possible to make it difficult for the holder 40 to fall off from the downstream end face 5a of the impeller 5.

[0044] Furthermore, in this embodiment, the scraper piece 50 is made of ceramic, which is difficult to machine, making it difficult to machine the scraper piece 50 precisely. In particular, in this embodiment, the inclination angle θ1 of the recess side surface 46 and the inclination angle θ2 of the scraper piece side surface 51 are smaller than 45 degrees. Therefore, when engaging the holder recess 43 with the engagement portion 52 of the scraper piece 50, the circumferential tolerance significantly affects the axial tolerance. If the axial tolerance becomes too large, it may be difficult to accurately set the protruding length of the tip portion 53 of the scraper piece side surface 51. In this embodiment, the holder 40 is made of a metal material, which is easier to machine than ceramic. This allows the holder 40 to be machined precisely. Therefore, the circumferential tolerance between the holder recess 43 and the engagement portion 52 can be reduced, allowing the protruding length of the tip portion 53 to be accurately set.

[0045] The present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure. For example, in the above embodiment, an example has been described in which the holder 40 is fixed to the impeller 5 with four bolts 33, but the present disclosure is not limited to this. The holder 40 and the impeller 5 may be fixed with other fixing members. However, it is desirable that the holder 40 and the impeller 5 are fixed in a detachable manner.

[0046] 12 and 13, the holder 40 and the scraper piece 50 may be fixed together with a bolt 60. The scraper piece 50 of this modified example is T-shaped. The recess side surface 46 of the holder recess 43 formed in the holder 40 is not shaped or inclined according to the scraper piece 50, but is simply flat. The bolt 60 passes through the scraper piece 50, and its tip is threaded into the bolt hole of the holder 40. The bolt 60 may be installed so that its head presses against the surface of the scraper piece 50, as shown in FIG. 12, or may be installed so that its head is embedded in the scraper piece 50, as shown in FIG. 13.

[0047] With this configuration, the holder 40 and the scraper piece 50 can be integrated. As a result, the scraper 30 can be transported to the site where it will be attached to the downstream end surface 5a of the impeller 5 with the holder 40 and the scraper piece 50 fixed together. This eliminates the need to fix the holder 40 and the scraper piece 50 together at the site, thereby simplifying the work at the site.

[0048] [Reference example] Next, a reference example of the present disclosure will be described with reference to FIGS. In this embodiment, the holder and the scraper piece may be integrally formed from ceramic to form an integrated scraper 70. The integrated scraper 70 is installed inside a recess (impeller recess 80) formed in the downstream end face 5a of the impeller 5. The integrated scraper 70 is T-shaped. A tip 71 (the end on the liner 20 side) of the integrated scraper 70 protrudes beyond the downstream end face 5a of the impeller 5. The integrated scraper 70 is fixed to the impeller 5 with a bolt 60. The bolt 60 passes through the integrated scraper 70, and its tip is threaded into a bolt hole formed in the bottom surface of the impeller recess 80. The bolt 60 may be installed so that its head presses against the surface of the integrated scraper 70, as shown in FIG. 14, or may be installed so that its head is embedded in the integrated scraper 70, as shown in FIG. 15.

[0049] The scraper, the axial fan, and the method of operating the axial fan described in the above-described embodiment can be understood, for example, as follows. A scraper according to one embodiment of the present disclosure is a scraper (30) provided on the opposing portion (5a) of an axial fan, the scraper (30) having a cylindrical portion (3) that defines a flow path (7) through which gas flows, and an impeller (5) having an opposing portion (5a) that faces the cylindrical portion (3) and that rotates around a central axis (C) by a driving force from a driving source to cause the gas to flow through the flow path (7), the scraper (30) being provided on the opposing portion (5a), the scraper having a holding portion (40) that has a recess (43) recessed from the surface facing the cylindrical portion (3) toward the impeller (5) and fixed to the opposing portion (5a), and an engaging portion (52) that is accommodated in the recess (43) and engages with the recess (43), and a protruding portion (50) that is held by the holding portion (40), protrudes toward the cylindrical portion (3) more than the holding portion (40), and is made of ceramic.

[0050] In the above configuration, the protrusion protrudes toward the cylindrical portion beyond the retaining portion. As a result, if a substance contained in the gas flowing through the flow path adheres to the cylindrical portion and the adhesion grows, the adhesion and the protrusion come into contact. The protrusion is fixed to the rotating impeller via the retaining portion, and therefore rotates along with the impeller. Therefore, the rotating protrusion can scrape off adhesions that adhere to the cylindrical portion. Furthermore, the protrusion wears when scraping off adhesions, but in the above configuration, the protrusion is made of ceramic. Because ceramic has high abrasion resistance, the protrusion can be made less susceptible to wear. Therefore, the life of the scraper can be extended. Furthermore, even if the gas flowing through the flow path is corrosive, because ceramic has high corrosion resistance, the protrusion can be made less susceptible to corrosion. Therefore, the life of the scraper can be extended. Furthermore, since ceramics are generally difficult to weld, it is difficult to directly fix a protrusion made of ceramic to the impeller. On the other hand, the above configuration includes a retaining portion that holds the protrusion made of ceramic, and the retaining portion is fixed to the opposing portion. This makes it possible to provide a protrusion made of ceramic on the opposing portion. Furthermore, ceramic is difficult to process in a complex manner. With the above configuration, the length of the projection allowance (the portion where the projection protrudes from the holding portion) can be set to a predetermined length simply by processing the projection inclined surface.

[0051] In the scraper according to one aspect of the present disclosure, the holding portion (40) is detachably fixed to the opposing portion (5a).

[0052] In the above configuration, the holding portion is detachably fixed to the opposing portion. This allows the holding portion, while holding the protruding portion, to be removed from the opposing portion during periodic inspection of the axial fan, etc. This makes it easier to repair the scraper than when the holding portion and the protruding portion are separately fixed to the opposing portion.

[0053] In addition, in a scraper according to one embodiment of the present disclosure, a pair of recess side surfaces (46) defining both circumferential ends of the recess (43) are inclined so that the recess side surfaces (46) approach each other as they move toward the tubular portion (3), and a pair of protrusion side surfaces (51) which are the circumferential surfaces of the protrusion (50) abut against the recess side surfaces (46) and are inclined so that the protrusion side surfaces (51) approach each other as they move toward the tubular portion (3).

[0054] In the above configuration, a pair of recess side surfaces that define both circumferential ends of the recess are inclined so that the recess side surfaces approach each other as they move toward the tubular portion. Furthermore, a pair of protrusion side surfaces, which are the circumferential surfaces of the protrusion, abut against the recess side surfaces and are inclined so that the side surfaces approach each other as they move toward the tubular portion. In this way, the abutment between the recess side surfaces and the protrusion side surfaces allows the retainer to restrict movement of the protrusion toward the tubular portion. In other words, the relative position of the protrusion toward the tubular portion with respect to the retainer can be determined. This allows the length (protrusion length) of the portion of the protrusion that protrudes from the retainer (hereinafter referred to as the "protrusion allowance") to be a predetermined length by adjusting the inclination angle of the recess side surfaces during manufacturing of the retainer.

[0055] In addition, in the scraper according to one aspect of the present disclosure, the holding portion (40) has a restricting portion (47) that restricts the outward movement of the protruding portion (50) in the radial direction.

[0056] In the above configuration, the holding portion has a restricting portion that restricts the radially outward movement of the protrusion. This allows the restricting portion to restrict the radially outward movement of the protrusion even when centrifugal force acts on the protrusion due to rotation of the impeller. Therefore, it is possible to make it difficult for the protrusion to fall off the holding portion.

[0057] In addition, in a scraper according to one embodiment of the present disclosure, the radially outer end of the protrusion (50) is located at the same position as the radially outer end of the liner (20) provided in the tubular portion (3) or at a position radially inward of the outer end of the liner (20).

[0058] In the above configuration, the radially outer end of the protrusion is located at the same position as the radially outer end of the liner or at a position radially inward of the outer end of the liner. This makes it possible to prevent the protrusion from protruding into the flow path, for example, when a flow path through which gas flows is formed on the radially outer side of the inner cylinder. Therefore, it is possible to suppress obstruction of the gas flow through the flow path.

[0059] In addition, in the scraper according to one aspect of the present disclosure, the holding portion (40) is fitted into the impeller recess (31) formed in the opposing portion (5a).

[0060] In the above configuration, the holding portion fits into a recess formed in the opposing portion. This restricts relative radial and circumferential movement of the holding portion with respect to the opposing portion (impeller) even if, for example, a fixing member that fixes the holding portion to the opposing portion is damaged and the fixation between the holding portion and the opposing portion is released. Therefore, even if the fixation between the holding portion and the opposing portion is released and centrifugal force acts on the holding portion due to rotation of the impeller, the holding portion is less likely to fall off the opposing portion.

[0061] In addition, in the scraper according to one aspect of the present disclosure, the holding portion (40) and the protruding portion (50) are fixed.

[0062] In the above configuration, the holding portion and the protruding portion are fixed. That is, the holding portion and the protruding portion are integrated. This allows the scraper to be transported to the site where it is to be attached to the opposing portion while the holding portion and the protruding portion are fixed. Therefore, the work of fixing the holding portion and the protruding portion at the site can be omitted. This simplifies the work at the site.

[0063] An axial flow fan according to one embodiment of the present disclosure includes a tubular portion (3) that defines a flow path (7) through which gas flows, an opposing portion (5a) that faces the tubular portion (3), an impeller (5) that rotates about a central axis (C) by a driving force from a driving source to cause the gas to flow through the flow path (7), and a scraper (30) described above that is provided on the opposing portion (5a).

[0064] A method for operating an axial flow fan according to one aspect of the present disclosure is a method for operating an axial flow fan including: a cylindrical portion (3) defining a flow path (7) through which gas flows; an impeller (5) having an opposing portion (5a) opposing the cylindrical portion (3) and rotated by the gas flowing through the flow path (7); and a scraper (30) provided on the opposing portion (5a), wherein the scraper (30) has a recess (43) recessed toward the impeller (5) from a surface opposing the cylindrical portion (3), and includes a holding portion (40) fixed to the opposing portion (5a) and an engaging portion (52) accommodated in the recess (43) and engaging with the recess (43), and is held by the holding portion (40). and a protruding portion (50) formed of ceramic and protruding toward the tubular portion (3) beyond the retaining portion (40), a pair of recess side surfaces (46) defining both circumferential ends of the recess (43) are inclined so that the recess side surfaces (46) approach each other as they approach the tubular portion (3), and the pair of protruding portion (50) side surfaces, which are the circumferential surfaces of the protruding portion (50), abut against the recess side surfaces (46) and are inclined so that the protruding portion side surfaces (50) approach each other as they approach the tubular portion (3), and a removal step is provided in which deposits adhering to the tubular portion (3) are removed by the scraper (30). [Explanation of symbols]

[0065] 1: Axial fan 2: Outer cylinder 3: Inner cylinder (cylindrical part) 3A: Upstream inner cylinder 3B: Downstream inner cylinder 4: Spindle 5: Winged wheel 5a: Downstream end face (opposing part) 5b: Outer surface 6: Moving blade 7: Gas flow path 8: Upstream stator vane 9: Downstream stator vane 10:Seal structure 11: Protruding seal part 12: Seal fin 20: Rina 30: Scraper 31: Impeller recess 31a: Bottom 32:Outer wall 33: Bolt 33a: Head 33b:Shaft part 34: Bolt hole 40: Holder (holding part) 41: Fitting part 42:Fixed part 43: Holder recess (recess) 43a: bottom 44: Outer panel part 45: Bolt insertion hole 46: Side of recess 47: Regulation Department 50: Scraper piece (protruding part) 51: Scraper piece side (side of protruding part) 52: Engagement part 53:Tip 54 :Double part

Claims

1. a scraper provided at the opposing portion of an axial flow fan including: a cylindrical portion that defines a flow path through which gas flows between an inner cylinder and an outer cylinder; and an impeller that has an opposing portion of the cylindrical portion that faces the inner cylinder and rotates about a central axis by a driving force from a driving source to cause the gas to flow through the flow path, a holding portion having a recess recessed toward the impeller from a surface of the cylindrical portion facing the inner cylinder, the holding portion being fixed to the facing portion; a protrusion formed of ceramic, the protrusion including an engaging portion that is accommodated in the recess and engages with the recess, the engaging portion being held by the holding portion, and protruding toward the inner tube side of the cylindrical portion beyond the holding portion; a pair of recess side surfaces defining both ends of the recess in the circumferential direction are inclined so that the recess side surfaces approach each other toward the inner cylinder side of the cylindrical portion, A scraper in which a pair of protrusion side surfaces, which are circumferential surfaces of the protrusion, abut against the recess side surfaces and are inclined so that the protrusion side surfaces approach each other as they approach the inner tube side of the cylindrical portion.

2. The scraper according to claim 1 , wherein the holding portion is detachably fixed to the opposing portion.

3. 3. The scraper according to claim 1, wherein the holding portion has a restricting portion that restricts radial outward movement of the protruding portion.

4. 4. The scraper according to claim 1, wherein the radially outer end of the protrusion is located at the same position as the radially outer end of a liner provided on the inner tube of the cylindrical portion or at a position radially inward of the outer end of the liner.

5. 5. The scraper according to claim 1, wherein the holding portion is fitted into a wheel recess formed in the opposing portion.

6. 6. The scraper according to claim 1, wherein the holding portion and the protruding portion are fixed to each other.

7. A cylindrical portion defining a flow path through which gas flows between an inner cylinder and an outer cylinder; an impeller having a facing portion facing the inner cylinder of the cylindrical portion, and rotating about a central axis by a driving force from a driving source to cause the gas to flow through the flow path; An axial flow fan comprising: the scraper according to any one of claims 1 to 6, which is provided at the opposing portion.

8. A method of operating an axial flow fan comprising: a tubular portion defining a flow path through which gas flows between an inner tube and an outer tube; an impeller having an opposing portion facing the inner tube of the tubular portion and rotated by the gas flowing through the flow path; and a scraper provided at the opposing portion, The scraper is a holding portion having a recess recessed toward the impeller from a surface of the cylindrical portion facing the inner cylinder, the holding portion being fixed to the facing portion; a protrusion formed of ceramic, the protrusion including an engaging portion that is accommodated in the recess and engages with the recess, the engaging portion being held by the holding portion, and protruding toward the inner tube side of the cylindrical portion beyond the holding portion; a pair of recess side surfaces defining both ends of the recess in the circumferential direction are inclined so that the recess side surfaces approach each other toward the inner cylinder side of the cylindrical portion, a pair of protrusion side surfaces, which are circumferential surfaces of the protrusion, abut against the recess side surfaces and are inclined so that the protrusion side surfaces approach each other as they approach the inner cylinder side of the cylindrical portion; A method for operating an axial flow fan, comprising a removing step of removing deposits adhering to the inner cylinder of the cylindrical portion by the scraper.

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