GB676406A - Improvements in fan impellers - Google Patents

Abstract

676,406. Screw fans. SPENCER, T. D., and PATENT LIGHTING CO., Ltd. Nov. 3, 1950. No. 26934/50. Class 110(i) A fan impeller comprises a boss and four blades integral therewith, wherein the leading edge 10 of each blade is substantially straight as viewed in the direction of the impeller axis, and the blade width is greater near the inner end of the blade than near the outer end and is not less than one-fifth (and may be one-quarter) of the impeller diameter at a distance from the impeller axis not greater than one-sixth of the impeller diameter. The trailing edge 12 is displaced axially of the impeller with respect to the leading edge 10, with which a substantial portion of its radially outer part makes an angle of 5 degrees and 25 degrees, but preferably 17 degrees. The inner trailing portion 13 is curved in such a manner that the generator of its concave surface is a substantially straight line 14-14, which always remains parallel to itself. The line 14-14 makes a trailing angle of 15 degrees to 35 degrees, but preferably 25 degrees, with a perpendicular X-X from the middle of the blade tip to the impeller axis. Preferably, the leading edge 10 is in a plane of rotation, but may lie between a backward angle of 10 degrees, and a forward angle of 15 degrees, with respect to the plane. Its pitch angle with respect to the plane may be slightly positive or negative. As shown, it preferably makes a leading angle with respect to the line X-X. The impeller boss extends from the plane of rotation of the leading edge 10 towards the plane of rotation of the most rearward part of the trailing edge 12 by a distance equal to at least half, and preferably three-quarters, of the distance between the two planes. The impeller is moulded from synthetic resin, or is diecast. Specification 502,740, [Group XXXIII]., is referred to.