IMPELLER FOR AN AXIAL FLOW FAN

Abstract: In an impeller for an axial flow fan comprising vanes adjustable under operation the vanes are suspended in a rigid supporting ring (1), which is centered and fastened by means of radial supporting plates (2, 3). The supporting plates (2, 3) comprise at their periphery circumferential collar parts (5, 6) in engagement with recesses (7, 8) on opposite sides of the supporting ring (1). The supporting plates (2, 3) are moreover connected with the supporting ring (1) by means of connecting bolts (9, 10) and are connected to each other by means of a distance member (11) which at the same time forms a slide guide for an axially movably adjusting disc (27). The vanes are suspended in the supporting ring (1) in such a way that they can be adjusted individually in their direction for adaption of the casing play.

Description: Impeller for an axial flow fan. This invention relates to an impeller for an axial flow fan having vanes adjustable under operation and connected with a vane pitch control device arranged internally in the impeller. In conventional axial flow fans the impeller comprises usually an impeller ring in which the vanes are suspended in rigid connection with a hub section, and the impeller ring and the hub section have mostly been constructed as a casted unit which complicates and increases the cost of the manufacture, especially in the case of large and relatively high speed impellers which under operation must be able to take up a consi¬ derable amount of dynamic load due to the centrifugal force, the adjustment forces etc. With a. view of simplifing and reducing the cost of manufacture, especially of very large impellers, a construction is known from Danish patent no. 149694 in which the vanes are suspended in a supporting ring connected with front and back plates through welded joints with the particular ability of having a certain resiliency in the radial direction so that the forces are mainly taken up by the supporting ring itself. Although this construction entails various advantages, it is subjected to limitations with respect to loading just as a result of the resilient welded joints, and it is especially less suitable for use in fans with variable speed where a change of the number of revolu¬ tions produces big momentary loads on the impeller. It is an object of the invention to provide an impeller of the type mentionned which remedy these problems and moreover has the advantage of being com¬ posed of relatively uncomplicated individual parts connected in such a way that they can take up a very considerable amount of load and changes of load which make the impeller suitable for use in high speed fans with variable number of revolutions, and in addition it is made possible with regard to the tolerances in the impeller to individually adjust the vanes in order to obtain an optimal adaption of the play between the vane edges and the surronding casing. This is acheived according to the invention in that the vanes are suspended in a rigid supporting ring which is centered and kept in position by means of mainly radial supporting plates one of which forms a connection to a hub section journalled on a drive shaft, said supporting plates having circumferential collar parts engaging recesses on opposite sides of the supporting ring and being furthermore connected with the supporting ring by means of parallel connecting bolts and being connected with each other by distance members parallel to the axes and forming slide guides for said vane pitch control device designed as an axially movable control disc, the vanes being suspended in said supporting ring so as to be individually adjus¬ table in their axial direction. In the impeller according to the invention the supporting ring and the supporting plates are preferably designed as forged pieces. The engagement between the supporting ring and the supporting plates provides an accurate centering of the supporting ring and at the same time the connecting bolts offer the possibility of obtaining an easy acces to the interior of the impeller for inspection of the vane suspension bearings and the control means. In a preferred imbodiment each vane is fixed in a predetermined angular position on one end of a short vane shaft extending through a bore provided in the supporting ring and forming at the inner side of the supporting ring a bearing casing for a vane suspension bearing which is kept in position in the bearing casing by means of a nut screwed onto said vane shaft and forming a bottom of the bearing casing, a vane balancing device and a control arm connected with said control disc being formed as an integral unit which is removably retained in the axial direction and in a predetermined angular position on the other end of said vane shaft, said nut being turnable between a number of discrete angular positions relative to said integral unit. By this construction a simple possibility is achieved for adjusting the vanes in their axial direc- tion by turning said nut between said discrete angular positions relative to the balancing and control unit. Moreover it is preferred that the diameters of said supporting plates is greater than the outer diameter of the supporting ring, said supporting plates accommodating at their circumference an impeller rim which is centered by means of radial guides on-the supporting plates and fixed with the supporting plates by means of bolts. Hereby it is obtained that the impeller rim is formed by an independant element whereby impellers with different diameters can be manufactured only by changing the length of the blade shaft, but without changing the supporting ring and the remaining parts inside the hub. The invention will now be explained in more detail with reference to the drawings in which Fig. 1 is an axial cross-sectional view of an embodiment of an impeller for an axial flow fan according to the invention, Fig. 2 and 3 illustrate matching engagement means of a nut which forms the bottom of the bearing casing for a vane suspension bearing, and of a balancing and control unit, and Fig. 4 is an axial partial sectional view of another embodiment of an impeller for an axial flow fan according to the invention. The impeller illustrated in Fig. 1 comprises a vane supporting ring 1 in rigid connection with a rear supporting plate 2 and a front supporting plate 3. The supporting plates 2 and 3 keep the supporting ring centered in relation to the drive shaft (not shown) , on which a hub section 4 arranged in the lower part of the back plate 2 is fastened, in that each supporting plate comprises at its periphery a collar part 5 and 6, respectively, projecting towards the supporting ring and engaging with opposite sides of the supporting ring 1 on the external side of the • opposite recesses 7 and 8. In the axial direction the supporting ring 1 is connected with the supporting plates 2 and 3 by means of connecting bolts 9 and 10, and the suppor¬ ting plates 2 and 3 are moreover connected with each other by distance members 11 parallel to the axis. The supporting ring 1 serves for suspension and journalling of the vanes (not shown per se) so that their pitch can be adjusted during rotation of the impeller. In the embodiment shown each vane foot 12 is screwed on the outer end of a relatively short vane tap 13 which is guided through a bore 14 in the suppor¬ ting ring 1. The vane foot 12 is thereby fixed in a certain vane pitch relative to the vane shaft 13 by engagement between a wedge-ahaped locking pin 15 screwed in through the vane shaft 12 and a matching groove 16 in the end of the vane shaft 13. On the inner side of the supporting ring 1 the bore 14 forms a bearing casing 17 to receive a contrarotative axial thrust bearing 18 of the type disclosed in applicants Danish patent application no. 6233/86. The bottom of the bearing casing 17 is formed by a nut 19 screwed on the vane shaft 13 and which with a view of sealing against an oil lubricant intro¬ duced in the bearing casing 17 is sealed in relation to the bearing casing by means of a seal ring 20. To take up thermal expansion of oil lubricants a duct 32 may be provided in the top side of the nut 19. Under the nut 19 a balancing and control unit 21 is arranged on the vane shaft 13, said unit compri¬ sing two balancing arms 22 and 23 and a control arm 24. The unit 21 is removably fastened on the end of the vane shaft 13 by means of a set screw 25 and is secured against angular turning in relation to the vane shaft by means of a feather and groove engage¬ ment 26. The control arm 24 is in engagement with a control disc 27 which in a known manner is axially movably in the impeller by means of a hydraulic control device whereby the distance members 11 parallel to the axis form slide guides for the axial movement and the control disc 27 by means of which adjustment of the vane pitch of all the vanes can be effected simultanously during rotation of the impeller. In order to enable the individual adjustment of the vanes in their longitudinal direction the nut 19 and the unit 21, shown in Fig. 2 and 3, are formed on the sides facing each other with matching engagement means permitting the nut 19 to adopt one out of a number of discrete angular positions in relation to the unit 21 which in it self is kept in a fixed angular position in relation to the vane shaft 13 and conse¬ quently in relation to the vane shaft 12 and the vane not shown. Said engagement means may, as shown, be formed as two diametrically and in relation to each other downwardly projecting ribs 28 and 29 on the underside of the nut 19 and two grooves 30 and 31 matching thereto and intersecting each other perpendicularly on the top side of the unit 21. The individual adjustment can be performed in that the set screw 25 is loosened whereby the en¬ gagement between the unit 21 and the nut 19 is libe¬ rated, and the nut 19 can now be turned in steps of 90° before engagement with the unit 21 is reestablished by fastening the set screw 25. Fig. 4 shows another embodiment in which the periphery of the impeller is formed by an independant impeller rim 33. Said rim is fastened between the supporting plates 2 and 3 by means of the connecting bolts 34 and 35 and is centered by means of circumfe- rential recesses 36 and 37 in the supporting plates. In this embodiment the diameter of the impeller can be changed by changing the diameter of the supporting plates and the impeller rim or of the impeller rim alone depending of its actual form, and by adapting the length of the vane shaft 13, but without changing the supporting ring and the remaining ir.-ernal parts inside the hub.

Claims: P A T E N T C L A I M S 1. An impeller for an axial flow fan having vanes adjustable under operation and connected with a vane pitch control device arranged internally in the impeller, characterized in that the vanes are suspended in a rigid supporting ring ( 1 ) which is centered and kept in position by means of mainly radial supporting plates (2,3) one of which forms a connection to a hub section (4) journalled on a drive shaft, said supporting plates (2,3) having circumferential collar parts (5,6) engaging recesses (7,8) on opposite sides of the supporting ring ( 1 ) and being furthermore connected with the supporting ring ( 1 ) by means of parallel connecting bolts (9,10) and being connected with each other by distance members (11) parallel to the axes and forming slide guides for said vane pitch control device designed as an axially movable control disc (27), the vanes being suspended in said supporting ring ( 1 ) so as to be individually adjustable in their axial direction. 2. An impeller as claimed in claim 1 , " charac¬ terized in that each vane is fixed in a predetermined angular position on one end of a short vane shaft (13) extending through a bore (14) provided in the supporting ring ( 1 ) and forming at the inner side of the supporting ring a bearing casing (17) for a vane suspension bearing (18) which is kept in position in the bearing casing (17) by means of a nut (19) screwed onto said vane shaft (13) and forming a bottom of the bearing casing (17), a vane balancing device (22,23) and a control arm (24) connected with said control disc (27) being formed as an integral unit (21) which is removebly retained in the axial direction and in a predetermined angular position on the other end of said vane shaft (13), said nut (19) being turn- able between a number of discrete angular positions relative to said integral unit (21). 3. An impeller as claimed in claim 1 or 2, characterized in that each vane is fixed in said angular position on the vane shaft (13) by engagement between a locking pin (15) retained in a bore in the vane foot (12) and a groove (16) formed parallel to the axis in said one end of the vane shaft. 4. An impeller as claimed in claim 2 or 3, characterized in that said unit (21) is fixed in said angular position on the other end of the vane shaft (13) by means of a feather and groove engagement (26) . 5. An impeller as claimed in claim 2, 3 or 4, characterized in that the underside of said nut (19) and the'upper side of said unit (21) are provided with matching engagement means in the form of grooves (30,31) in one part and projecting ribs adapted thereto on the other part. 6. An impeller as claimed in claim 5, charac¬ terized in that the upper side of said unit (21) is " provided with two grooves (30,31) intersecting each other substantially perpendicularly. 7. An impeller as claimed in claims 2 to 6, characterized in that the upper side of said nut (19) a duct (32) is provided for taking up thermal expansion of an oil lubricant introduced in said bearing casing (17). 8. An impeller as claimed in one of the pro¬ ceeding claims characterized in that the diameters of said supporting plates (2,3) is greater than the outer diameter of the supporting ring ( 1 ) , said sup- porting plates accommodating at their circumference an impeller rim (33) which is centered by means of radial guides (36,37) on the supporting plates (2,3) and fixed with the supporting plates by means of bolts (34,35).

Inventors: MORTENSEN BENT MOELLER, MORTENSEN, BENT, MOELLER
Applicants: NOVENCO AS, NOVENCO A/S
Application year: 1989
Main classification: F04D29
IPC codes: F01D7, F04D29