GB816921A - Improvements in or relating to axial flow fans - Google Patents

Abstract

816,921. Axial-flow fans. AIR CONTROL INSTALLATIONS Ltd., and REEVES, H. C. Oct. 11, 1956 [July 11, 1955], No. 20047/55. Class 110(1). To reduce blade flutter in an axial-flow fan, each blade is formed either in one part or in two parts arranged end-to-end, and a pivotal connection is provided either between the inner extremity of each one-part blade and the hub or between an outer part of each two-part blade and an inner part secured to the hub so that the axis of pivotal movement extends across the width of the blade substantially parallel to the general plane thereof or to a chord of the blade section; and the pivotal connection between the hub and each one-part blade or between the two parts of a two-part blade or the connection between the hub and the inner part of each twopart blade is rotatably adjustable about an axis radially disposed with respect to the axis of rotation of the fan, clamping means being provided for maintaining the adjustment. In the three-bladed fan shown, each blade 10 is of curved or aerofoil cross-section and formed from sheet metal riveted at 28 to a cast steel shoe 25 having two bosses 26 by which it is pivoted about a pin 23 carried by a block 17, the pivotal axis being substantially parallel to the general plane of the blade or to a chord of the blade section at the locality of the pivotal connection. The block 17 can be turned to adjust the blade angle after loosening the nut 18 which fixes it to the impeller hub 11. Each boss 26 is attached to the pivot-pin 23 by means of a rubber bush 31 bonded to outer and inner sleeves 29, 30 fixed to the boss and pin respectively, so that pivotal movement is torsionally resisted. Alternatively, conventional lubricated bushes may be used, providing free pivotal movement. The shoe 25 carries a part-circular sleeve 32 which limits the pivotal movement relative to the block 17. In an alternative construction, the pivot is provided between a radially inner part and a radially outer part of the blade. For this purpose, the inner end of the outer blade part is riveted to a shoe 25, and a block corresponding to the block 17 is carried by a further shoe riveted to the outer end of the inner blade part. The block may be adjustably secured to the further shoe or integral with it. In the former case, the adjustable connection between the inner blade part and the impeller hub may be replaced by a fixed connection. The inner blade part may depart from true aerofoil form for strength purposes.