CN219691822U - Volute for centrifugal fan and centrifugal fan - Google Patents

Abstract

The utility model relates to a volute for a centrifugal fan and the centrifugal fan, wherein the volute comprises a volute body with an air outlet, the volute body comprises a front cover plate, a rear cover plate and a ring wall, two ends of the length direction of the ring wall and corresponding parts of the front cover plate and the rear cover plate jointly define an air outlet section, the ring wall is provided with a volute tongue which is integrally arranged at the position adjacent to the air outlet and extends along the front and rear direction, the volute tongue is provided with a volute tongue surface protruding towards the inside of the air outlet section, the volute tongue surface is provided with at least two noise reduction units which are sequentially arranged along the front and rear directions, each noise reduction unit comprises a front inclined section and a rear inclined section which are sequentially arranged along the front and rear directions, the front inclined section gradually extends from front to rear to one side away from the plane of the air outlet of the volute, and the rear inclined section gradually extends from rear to one side away from the plane of the air outlet of the volute. The advantages are that: the air flow noise at the outlet of the volute can be reduced, and the static pressure loss at the volute tongue can be reduced so as to improve the efficiency of the fan.

Description

Volute for centrifugal fan and centrifugal fan

Technical Field

The utility model relates to the technical field of centrifugal fans, in particular to a volute for a centrifugal fan and the centrifugal fan.

Background

The centrifugal fan is an important air supply device and is commonly used in products such as range hoods, air conditioners and the like. Centrifugal fans typically include a volute, impeller, motor, etc. A volute tongue is arranged at the air outlet of the volute and is used for dividing the airflow at the outlet of the volute so as to prevent part of the airflow from circularly flowing in the volute. The traditional centrifugal fan volute tongue is generally of a straight circular arc structure, so that air flows through the volute tongue at the same moment, and then the air flows impact the volute tongue wall surface, larger noise is generated, and the user experience effect of the range hood is affected.

In order to solve the technical problems, for example, chinese patent application with the application number of CN201911258748.0 (with the application publication number of CN 110864010A) discloses a novel volute tongue structure, a fan volute and a fan, wherein the volute tongue structure comprises a wave unit, and a line on the wave unit along the trend of a parallel volute return air shaft is a non-straight line; the number of the wave units is one; or the number of the wave units is at least two and is distributed along the direction parallel to the return air shaft of the volute. The normal cross section of the wave unit in the air flow discharging direction is in an arc-shaped structure or a V-shaped structure or an inverted V-shaped structure. The line of going along parallel spiral case return air axle on the wave unit is the non-straight line for produce more efficient phase difference than current volute tongue, when centrifugal fan is at high-speed operation, can effectively reduce centrifugal fan operation noise.

From the design angle of the volute tongue, the smaller radial tongue clearance can enable the centrifugal fan to obtain better efficiency, and the clearance is increased to a certain extent, so that the noise of the centrifugal fan can be reduced. In the prior art, the large-gap volute tongue, the inclined volute tongue and the like reduce pressure pulsation on the surface of the volute tongue by increasing radial tongue gaps, so that noise of a fan is reduced, and the volute tongue structure with the wave unit in the patent application can be regarded as being formed by two inclined volute tongue structures with central symmetry. However, the degree of reduction of the volute tongue with the structure is related to the inclination angle, the radius, the clearance and the like of the inclined volute tongue, and the parameters directly influence the external characteristic properties of the fan, including full pressure, efficiency, noise and the like. The volute tongue in the above patent application is only a wave-shaped unit with repeated cross section along the air flow discharging direction, and the structure is relatively single, and the matching with the actual air flow is required to be improved. In particular, since the flow velocity of the volute tongue region of the volute is faster, the phase difference generated by the single volute tongue curved surface has a certain limit on the noise reduction effect of the fan, and if the radial tongue clearance is continuously increased, the efficiency of the fan is adversely affected, so that the efficiency of the centrifugal fan and the noise reduction effect of the centrifugal fan are difficult to be simultaneously considered in the existing volute tongue structural design, and further improvement is needed.

Disclosure of Invention

The utility model aims to solve the first technical problem of the prior art, and provides a volute for a centrifugal fan, which can reduce the airflow noise at the outlet of the volute, reduce the static pressure loss at the volute tongue and further improve the efficiency of the fan.

The second technical problem to be solved by the utility model is to provide a centrifugal fan applying the volute, aiming at the current state of the art.

The utility model solves the first technical problem by adopting the technical scheme that: the utility model provides a spiral case for centrifugal fan, includes the spiral case body that has the air outlet, the spiral case body includes preceding apron, back shroud and connects the rampart between preceding apron and back shroud, rampart length direction's both ends with the corresponding part of preceding apron and back shroud jointly limit the air outlet section, the rampart is adjacent air outlet department has the whole volute tongue that extends along fore-and-aft direction and sets up, this volute tongue has towards the inside convex volute tongue face of air outlet section, the volute tongue face has two at least noise reduction units that set gradually along fore-and-aft direction, each noise reduction unit of volute tongue face includes preceding sloping section and the back sloping section that sets gradually along fore-and-aft direction, preceding sloping section is from the back gradually to keeping away from the one side slope of the air outlet place plane of spiral case extends from the back to the one side slope of the air outlet place plane of spiral case gradually.

As an improvement, a molded line at the intersection position of the front inclined section and the rear inclined section of each noise reduction unit is marked as a first molded line, a molded line at the front end of the front inclined section is marked as a second molded line, a molded line at the rear end of the rear inclined section is marked as a third molded line, the front inclined section and the rear inclined section of each noise reduction unit are arranged symmetrically with the plane of the first molded line as a symmetrical center, and the first molded line and the third molded line are overlapped in the front-rear direction;

the first molded line comprises a first straight line section, a first circular arc section and a second straight line section which are sequentially connected from top to bottom, a point on the first circular arc section, which is tangent to a straight line passing through the center of the volute, is marked as a first vertex, the second molded line comprises a third straight line section, a second circular arc section and a fourth straight line section which are sequentially connected from top to bottom, a point on the second circular arc section, which is tangent to a straight line passing through the center of the volute, is marked as a second vertex, and the first vertex is closer to the axis of the volute relative to the second vertex.

The volute tongue deflection angle is increased within a certain range, so that the highest static pressure and efficiency point of the centrifugal fan can move towards the low-flow working point, in consideration of the pipe network resistance interval of the range hood operation, in order to reduce working noise as much as possible, preferably, a straight line passing through the center of the volute and the first vertex of the first circular arc section is marked as a first tangent line, an included angle formed by the intersection of the first tangent line and the vertical plane passing through the axis of the volute is marked as a first included angle, a straight line passing through the center of the volute and the second vertex of the second circular arc section is marked as a second tangent line, an included angle formed by the intersection of the second tangent line and the vertical plane passing through the axis of the volute is marked as a second included angle, and the first included angle is the same as the second included angle, and the value range is as follows: 22 deg. to 32 deg., preferably 26 deg..

From the aspect of variation of aerodynamic performance, the radius of the first arc segment and the radius of the second arc segment can be reduced to a certain extent, but at the same time, the magnitude of the pressure pulsation of the fan can be increased to different extents, so that in order to achieve better noise reduction effect, the radius of the double arcs (the first arc segment and the second arc segment) should be controlled within a reasonable range, specifically, the radius of the first arc segment is r1, the radius of the second arc segment is r2, wherein r1 is less than or equal to r2, r1 is less than or equal to 14mm, r2 is less than or equal to 12mm, and r1 is less than or equal to 18mm.

In order to ensure the noise reduction effect, the distances between the first vertex and the second vertex and the outer periphery of the impeller should be reasonably taken, the distance between the first vertex and the outer periphery of the impeller arranged in the volute body is denoted as s, and the distance between the second vertex and the outer periphery of the impeller arranged in the volute body is denoted as t, wherein s is more than or equal to 20mm and less than t is more than or equal to 50mm.

In order to ensure the flow guiding effect of the volute tongue at the first molded line, the second molded line and the third molded line of the volute tongue, the first molded line of each noise reduction unit of the volute tongue is provided with an arc-shaped first chamfer, the second molded line of each noise reduction unit of the volute tongue or the third molded line of the volute tongue is provided with an arc-shaped second chamfer, and the range of values of the arc radiuses of the first chamfer and the second chamfer is as follows: 1 mm-2 mm.

In order to better split and guide the air flow at the outlet of the fan, a first flow passage which takes the second straight line section of the first molded line as the center and is approximately V-shaped and a second flow passage which takes the third straight line section of the second molded line as the center and is approximately V-shaped are further formed on the volute tongue surface, an included angle formed by the curved surfaces of the first flow passage is beta 1, and an included angle formed by the curved surfaces of the second flow passage is beta 2, wherein 110 degrees is more than or equal to beta 1 is less than or equal to 135 degrees, and 55 degrees is more than or equal to beta 2 is less than or equal to 75 degrees.

The radius of the first circular arc section is smaller than that of the second circular arc section, so that the circulating flow in the volute runner can be well prevented, and the static pressure conversion rate of the first runner of the volute tongue is improved. Furthermore, the interaction between the impeller wake jet and the second flow channel is reduced due to the relatively large distance of the second circular arc segment as a whole from the impeller outlet.

In general, the volute tongue may be directly formed on the annular wall of the volute body, but in order to facilitate processing and assembly and reduce production cost, the volute tongue is a split component mounted on the annular wall, the front end surface and the rear end surface of the volute tongue are respectively connected with the front cover plate and the rear cover plate correspondingly, and the volute tongue surface of the volute tongue is in smooth transitional connection with the inner wall surface of the annular wall.

In order to connect the volute tongue to the annular wall of the volute body, the volute tongue is mounted on the annular wall of the volute body in a sticking, threaded connection or snap connection mode.

The size of each noise reduction unit of the volute tongue is matched with the overall size of the volute body, as improvement, the size of each noise reduction unit of the volute tongue in the front-rear direction is marked as d, and the value range of d is as follows: 20-40 mm.

The utility model solves the second technical problem by adopting the technical proposal that: the centrifugal fan comprises a volute and an impeller rotationally arranged in the volute, wherein the volute adopts the volute for the centrifugal fan.

Compared with the prior art, the utility model has the advantages that: each noise reduction unit on the volute tongue surface of the volute tongue comprises a front inclined section and a rear inclined section which are sequentially arranged along the front-rear direction, wherein the front inclined section gradually extends from front to rear to one side of a plane where an air outlet of the volute is located, and the rear inclined section gradually extends from rear to front to one side of the plane where the air outlet of the volute is located.

Drawings

Fig. 1 is a schematic perspective view of a volute for a centrifugal fan according to an embodiment of the present utility model;

FIG. 2 is a top view of FIG. 1;

FIG. 3 is a cross-sectional view (section line through the first line) at A-A of FIG. 2;

FIG. 4 is a cross-sectional view (section line through the second line) at B-B of FIG. 2;

FIG. 5 is a cross-sectional view taken at A-A of FIG. 4;

fig. 6 is a perspective view of a volute tongue according to an embodiment of the utility model.

Detailed Description

The utility model is described in further detail below with reference to the embodiments of the drawings.

In the description and claims of the present utility model, terms indicating directions, such as "front", "rear", "upper", "lower", "left", "right", "side", "top", "bottom", etc., are used to describe various example structural parts and elements of the present utility model, but these terms are used herein for convenience of description only and are determined based on the example orientations shown in the drawings. Because the disclosed embodiments of the utility model may be arranged in a variety of orientations, the directional terminology is used for purposes of illustration and is in no way limiting, such as "upper" and "lower" are not necessarily limited to being in a direction opposite or coincident with the direction of gravity.

Referring to fig. 1-6, there is shown a preferred embodiment of a volute for a centrifugal fan of the present utility model, the volute comprising a volute body 10 having an air outlet 14, the volute body 10 comprising a front cover plate 11, a rear cover plate 12, and an annular wall 13 connected between the front cover plate 11 and the rear cover plate 12. An air inlet is formed in the front side plate of the volute body 10, and two ends of the annular wall 13 in the length direction and corresponding parts of the front cover plate 11 and the rear cover plate 12 together define an air outlet section, wherein the annular wall 13 is provided with a volute tongue 20 which is integrally arranged in a extending manner along the front-rear direction at the position adjacent to the air outlet 14 of the volute body 10. The volute tongue 20 of the present embodiment has a volute tongue surface 200 protruding toward the inside of the air outlet section, and the volute tongue surface 200 has at least two noise reduction units 21 disposed in sequence in the front-rear direction. As shown in fig. 2, the present embodiment shows 5 noise reduction units 21, and the size of each noise reduction unit 21 of the volute tongue 20 should be matched with the overall size of the volute body 10, preferably, the size of each noise reduction unit 21 of the volute tongue 20 in the front-rear direction is denoted as d, and the range of d is: 20-40 mm. Referring to fig. 6 again, each noise reduction unit 21 includes a front inclined section 211 and a rear inclined section 212 sequentially disposed along the front-rear direction, wherein the front inclined section 211 extends gradually from front to rear to one side away from the plane of the air outlet 14 of the volute, and the rear inclined section 212 extends gradually from rear to front to one side away from the plane of the air outlet 14 of the volute.

In a preferred embodiment, the line at the intersection of the front inclined section 211 and the rear inclined section 212 of each noise reduction unit 21 is denoted as a first line 22, the line at the front end of the front inclined section 211 is denoted as a second line 23, and the line at the rear end of the rear inclined section 212 is denoted as a third line 24, specifically, the lines between the front inclined section 211 and the rear inclined section 212 of each noise reduction unit 21 are arranged symmetrically about the plane in which the first line 22 is located as a center of symmetry, that is, the first line 22 overlaps the third line 24 in the front-rear direction. As shown in fig. 5, the second molded line 23 of the previous noise reduction unit 21 of the two adjacent noise reduction units 21 is the third molded line 24 of the next noise reduction unit 21.

In the embodiment, the air outlet 14 of the volute body 10 is disposed upwards, the first molded line 22 is formed by a first straight line segment 221, a first arc segment 222 and a second straight line segment 223 that are sequentially connected from top to bottom, wherein a point on the first arc segment 222 tangent to a straight line passing through the center of the volute is denoted as a first vertex 2220, correspondingly, a straight line passing through the center of the volute and the first vertex 2220 of the first arc segment 222 is denoted as a first tangential line 31, and an included angle formed by intersecting the first tangential line 31 with a vertical plane passing through the axis of the volute is denoted as a first included angle θ1. The second molded line 23 is composed of a third straight line segment 231, a second arc segment 232 and a fourth straight line segment 233 which are sequentially connected from top to bottom, a point on the second arc segment 232 tangent to a straight line passing through the center of the volute is denoted as a second vertex 2320, correspondingly, a straight line passing through the center of the volute and the second vertex 2320 of the second arc segment 232 is denoted as a second tangent line 32, and an included angle formed by the intersection of the second tangent line 32 and a vertical plane passing through the axis of the volute is denoted as a second included angle θ2. The deflection angle of the volute tongue 20 is increased within a certain range, which is favorable for improving the vortex structure of the volute tongue 20 area, so that the highest static pressure and efficiency point of the centrifugal fan moves to a low-flow working point, and in order to reduce working noise as much as possible in consideration of the pipe network resistance interval of the operation of the range hood, the first included angle theta 1 and the second included angle theta 2 of the embodiment are the same, and the value range is as follows: 22 deg. to 32 deg., preferably 26 deg..

As can be seen in fig. 3 and 4, the first molded line 22 of the present embodiment is generally closer to the outer periphery (outer diameter) of the impeller than the second molded line 23, and specifically, the first vertex 2220 of the first molded line 22 of the present embodiment is closer to the axis of the volute than the second vertex 2320 of the second molded line 23. In order to ensure the noise reduction effect, the distances between the first vertex 2220 and the second vertex 2320 and the outer periphery of the impeller should be reasonably taken, the distance between the first vertex 2220 and the outer periphery of the impeller disposed in the volute body 10 in this embodiment is denoted as s, and the distance between the second vertex 2320 and the outer periphery of the impeller disposed in the volute body 10 is denoted as t, wherein s is more than or equal to 20mm and less than t is more than or equal to 50mm. From the aspect of variation of aerodynamic performance, the radius of the first arc segment 222 and the second arc segment 232 may be reduced to a certain extent to increase the static pressure of the blower, but at the same time, the amplitude of the pressure pulsation may be increased to a different extent, so, in order to achieve better noise reduction effect, the radius of the double arcs (the first arc segment 222 and the second arc segment 232) should be controlled within a reasonable range, specifically, the radius of the first arc segment 222 is r1, the radius of the second arc segment 232 is r2, where r1 is equal to or less than r2, and r1 is equal to or less than 8mm is equal to or less than 14mm, and r2 is equal to or less than 12mm is equal to or less than 18mm. Because the radius of the first arc segment 222 is smaller than that of the second arc segment 232, the circulation flow in the volute flow channel can be well prevented, and the static pressure conversion rate of the first flow channel 261 of the volute tongue 20 is improved.

Referring to fig. 6, in order to ensure the flow guiding effect of the volute tongue 20 at the first molded line 22, the second molded line 23 and the third molded line 24, the first molded line 22 (specifically, the first arc segment 222) of each noise reduction unit 21 of the volute tongue 20 is provided with an arc-shaped first chamfer 251, and the second molded line 23 or the third molded line 24 (specifically, the second arc segment 232) of each noise reduction unit 21 of the volute tongue 20 is provided with an arc-shaped second chamfer 252, wherein the range of the arc radii of the first chamfer 251 and the second chamfer 252 is: 1 mm-2 mm.

With continued reference to fig. 3 and 4, after defining the shape of the first line 22 and the second line 23 (the third line 24) of the scroll casing, the radius of the corresponding arc segment, and the inclination angle of the corresponding apex, a first substantially V-shaped flow channel 261 centered on the second line segment 223 of the first line 22 and a second substantially V-shaped flow channel 262 centered on the third line segment 231 of the second line 23 are formed in the volute tongue surface 200, wherein the curved surface of the first flow channel 261 forms an included angle β1 and the curved surface of the second flow channel 262 forms a clip angle β2, and wherein 110 ° - β1 is not more than 135 °,55 ° - β2 is not more than 75 °. The first and second flow passages 261, 262 of the volute tongue 20, when combined, provide a "W" shaped arrangement in the axial direction of the volute (i.e., in the fore-aft direction), as seen in the A-A direction shown in FIG. 4. The interaction between the impeller wake jet and the second flow passage 262 is reduced due to the relatively large distance of the second circular segment 232 as a whole from the impeller outlet. Specifically, the first flow channel 261 acts on the air backflow at the outlet of the fan, and the second flow channel 262 acts on the air outflow at the outlet of the fan, so that not only is the unsteady phase difference of the inclined volute tongue 20 realized in the prior art, but also the noise superposition effect is smaller than that generated by the traditional volute tongue 20. The V-shaped first flow channel 261 and second flow channel 262 on the volute tongue 200 improves the inherent diversion and diversion effect of the volute tongue 20, so that the outlet airflow is smoother, and the static pressure loss and flow separation at the volute tongue 20 are reduced, therefore, the centrifugal fan and the range hood with the volute tongue 20 structure can improve the full-pressure efficiency of the whole range hood and reduce noise.

The volute tongue 20 of the present embodiment is a separate component mounted on the annular wall 13, and the volute tongue 20 may be mounted on the annular wall 13 of the volute body 10 by means of adhesion, threaded connection or snap connection. After the volute tongue 20 is installed in place, the front end face and the rear end face of the volute tongue 20 are correspondingly connected with the inner walls of the front cover plate 11 and the rear cover plate 12 respectively, and smooth transition connection is adopted between the volute tongue face 200 of the volute tongue 20 and the inner wall face of the annular wall 13.

The embodiment also relates to a centrifugal fan, which comprises a volute and an impeller rotationally arranged in the volute, wherein the volute adopts the volute structure for the centrifugal fan.

The spiral case and the centrifugal fan of this embodiment's advantage lies in:

1. the distances from the points on the volute tongue surface 200 of the volute tongue 20 to the outer edge of the impeller are different, so that the air flow at the outlet of the impeller does not flow through the volute tongue 20 at the same time, and the noise source formed in this way counteracts partial energy due to a certain phase difference, so that the purpose of reducing noise is achieved.

2. The double-arc volute tongue 20 of the embodiment is arranged in a W-shaped structure on the axial height of the volute, and is divided into a first flow passage 261 and a second flow passage 262 according to the air flow direction, so that the flow dividing and guiding functions of the volute tongue 20 are improved, the air flow is smoother, the static pressure loss at the volute tongue 20 is reduced, and the noise of the outlet air flow is reduced.

3. Compared with the traditional single-arc flat volute tongue 20, the surface area of the double-arc volute tongue 20 is increased, the curved surface of the volute tongue 20 is relatively dispersed due to the impact of the gas inflow, and noise generated by unsteady pulse power on the wall surface of the volute tongue 20 is reduced.

4. Through experimental tests, the centrifugal fan and the whole-machine full-pressure efficiency of the range hood with the double-arc volute tongue 20 are improved, and noise is reduced.

Claims (11)

1. The utility model provides a spiral case for centrifugal fan, includes spiral case body (10) that has air outlet (14), spiral case body (10) include front shroud (11), back shroud (12) and connect ring wall (13) between front shroud (11) and back shroud (12), both ends of ring wall (13) length direction with the corresponding part of front shroud (11) and back shroud (12) jointly limit the air outlet section, ring wall (13) are adjacent air outlet (14) department has on the whole along the scroll tongue (20) of fore-and-aft direction extension setting, this scroll tongue (20) have towards the inside convex scroll tongue face (200) of air outlet section, its characterized in that: the volute tongue surface (200) is provided with at least two noise reduction units (21) which are sequentially arranged along the front-back direction, each noise reduction unit (21) of the volute tongue surface (200) comprises a front inclined section (211) and a rear inclined section (212) which are sequentially arranged along the front-back direction, the front inclined section (211) gradually extends from front to back to one side of a plane where an air outlet (14) of the volute is located, and the rear inclined section (212) gradually extends from back to front to one side of a plane where the air outlet (14) of the volute is located.

2. The volute for centrifugal fans according to claim 1, wherein: a molded line at the intersection position of a front inclined section (211) and a rear inclined section (212) of each noise reduction unit (21) is marked as a first molded line (22), a molded line at the front end of the front inclined section (211) is marked as a second molded line (23), a molded line at the rear end of the rear inclined section (212) is marked as a third molded line (24), and the first molded line (22) and the third molded line (24) are arranged symmetrically in the front-rear direction by taking the plane of the first molded line (22) as the symmetrical center between the front inclined section (211) and the rear inclined section (212) of each noise reduction unit (21);

the first molded line (22) is formed by a first straight line segment (221), a first circular arc segment (222) and a second straight line segment (223) which are sequentially connected from top to bottom, a point on the first circular arc segment (222) tangent to a straight line passing through the center of the volute is marked as a first vertex (2220), the second molded line (23) is formed by a third straight line segment (231), a second circular arc segment (232) and a fourth straight line segment (233) which are sequentially connected from top to bottom, a point on the second circular arc segment (232) tangent to a straight line passing through the center of the volute is marked as a second vertex (2320), and the first vertex (2220) is closer to the axis of the volute relative to the second vertex (2320).

3. The volute for centrifugal fans according to claim 2, wherein: the straight line passing through the center of the volute and the first vertex (2220) of the first arc section (222) is marked as a first tangent line (31), an included angle formed by the intersection of the first tangent line (31) and a vertical plane passing through the axis of the volute is marked as a first included angle (theta 1), a straight line passing through the center of the volute and the second vertex (2320) of the second arc section (232) is marked as a second tangent line (32), an included angle formed by the intersection of the second tangent line (32) and the vertical plane passing through the axis of the volute is marked as a second included angle (theta 2), and the first included angle (theta 1) is the same as the second included angle (theta 2), and the value range is as follows: 22-32 deg.

4. The volute for centrifugal fans according to claim 2, wherein: the radius of the first circular arc section (222) is r1, the radius of the second circular arc section (232) is r2, wherein r1 is less than or equal to r2, r1 is less than or equal to 8mm and less than or equal to 14mm, and r2 is less than or equal to 12mm and less than or equal to 18mm.

5. The volute for centrifugal fans according to claim 2, wherein: the distance between the first vertex (2220) and the outer periphery of the impeller provided in the volute body (10) is denoted as s, and the distance between the second vertex (2320) and the outer periphery of the impeller provided in the volute body (10) is denoted as t, wherein s < t < 20mm < t < 50mm.

6. The volute for centrifugal fans according to claim 2, wherein: the first molded line (22) of each noise reduction unit (21) of the volute tongue (20) is provided with an arc-shaped first chamfer (251), the second molded line (23) or the third molded line (24) of each noise reduction unit (21) of the volute tongue (20) is provided with an arc-shaped second chamfer (252), and the range of values of the arc radiuses of the first chamfer (251) and the second chamfer (252) is: 1 mm-2 mm.

7. The volute for centrifugal fans according to claim 2, wherein: the volute tongue surface (200) is also provided with a first flow passage (261) which takes a second straight line section (223) of the first molded line (22) as a center and is approximately V-shaped, and a second flow passage (262) which takes a third straight line section (231) of the second molded line (23) as a center and is approximately V-shaped, wherein an included angle formed by curved surfaces of the first flow passage (261) is beta 1, and an included angle formed by curved surfaces of the second flow passage (262) is beta 2, wherein 110 degrees is more than or equal to beta 1 and less than or equal to 135 degrees, and 55 degrees is more than or equal to beta 2 and less than or equal to 75 degrees.

8. The scroll casing for a centrifugal fan according to claim 7, wherein: the volute tongue (20) is a split part arranged on the annular wall (13), the front end face and the rear end face of the volute tongue (20) are respectively correspondingly connected with the front cover plate (11) and the rear cover plate (12), and a volute tongue face (200) of the volute tongue (20) is in smooth transition connection with the inner wall face of the annular wall (13).

9. The volute for centrifugal fans according to claim 8, wherein: the volute tongue (20) is mounted on the annular wall (13) of the volute body (10) in a sticking, threaded connection or buckling connection mode.

10. The volute for a centrifugal fan according to any one of claims 1 to 9, wherein: the size of each noise reduction unit (21) of the volute tongue (20) in the front-rear direction is marked as d, and the value range of d is as follows: 20-40 mm.

11. The utility model provides a centrifugal fan, includes spiral case and rotates locates impeller in the spiral case, its characterized in that: the scroll casing according to any one of claims 1 to 10 is used as a scroll casing for a centrifugal fan.