US2287853A - Centrifugal fan - Google Patents

Description

June 30, 1942. T. B. ALLARDICE CENTRIFUGAL FAN Filed Sept. 26, 1941 3 3 m a i@ 7 oo n 2 oo .a rw/m a 40.1-..- 4. 2 0d m .b Q A 7 Z Patented June 30, 1942 cENrmFUGAL FAN l Thomas B. Allardlce, New York, N. Y., assignor to B. F. Sturtevant Company, Boston, Mass., a. corporation of Massachusetts Application September 26, 1941, Serial No. 412,441

(Cl. Z30-128) 3 Claims.

' The present linvention relates to centrifugal fans and more particularly to a centrifugal fan designed and adapted for the handling of air and other gases carrying abrasive material such as ily ash in the exhaust gases from furnaces burning powdered coal.

-In the attempt to increase the capacity of steam generating plants there has been, among other things, a constant increase in the. speeds of centrifugal fans in order to increase their output both in volume and in pressure. To enable such fans to withstand the greatly increased centrifugal forces resulting from such high rotational speeds, a design has been developed which comprises a centre integral annular steel plate disk, clamped between two hub members, with the fan blades riveted to one or both faces of the disk adjacent its periphery, according to whether it is a single or double intake fan. The free inlet ends ofthe blades are supported by a ring or shroud to which the, blades are riveted. This construction not only affordsample strength for y abrasive material, such as fly ash in the exhaust gases from powdered coal burning furnaces, there is a scoring or erosion from such material on portions of the fan rotor which, on account of the high velocity of the gas through the fan, causes rapid deterioration, necessitating frequent inspection and repair.

Experience shows that erosion is most severe in the angle formed by the centre disk, and more particularly adjacent the outer edges of the blades and peripher:y of the disk. This is believed to be due to the concentration of the abrasive material. at these points, the inertia of such material and resistance to turning ninety degrees from axial to radial direction, carrying the material into the back portion of the fan where a very substantial portion contacts either with the centre disk or the inner ends .of the blade, passing along these parts into the angle between the disk-and the blades until finally discharged from the outer periphery of the fan. Such concentration and movement at high velocity cuts the metal'of bpth disk and blade where they join, and it vis not at all uncommon to find in such an induced draft lfan after only a few weeks of operation, that erosion has progressed in the joint between the blade and disk until one or more of the blade securing rivets have been severed and the fan rendered unsafe for continued operation.

It is the objectf` of the present invention to prevent such erosive action by abrasive materials carried in the air and gases handled by a double intake fan, and this is accomplished by eliminating or removing from the centre disk a sufficient portion thereof adjacent the advancing face of Aeach fan blade so that the streams of abrasive material in the air or gas entering from the opposite intakes of a double intake fan', instead vof being concentrated in the angle between the centre disk and the ends of the blades and caused to pass over the surface of the metal at high velocity and under substantial pressure, will impinge upon one another in the free space thus provided, seeking their own paths of ow outwardly over the faces of the blades without being directed or concentrated at any particular point. Thus severe erosion in a limited area is avoided and the life of the fan before repairs or replacements are required is greatly prolonged.

A further feature of the present invention consists in providing a protective surface on the advancing face of the blades at their middle portions Where the two converging streams of air or gas deliver the greater proportion of abrasive material, thus eliminating all possibility of destruct'ive erosion of any portion of the fan struc. ture so long as such protective surface remainsv intact. Preferably, such surface will be in a form adapted for easy and quick renewal, thereby enabling the fan to operate as safely and efliciently. and for as long a period of time while handling abrasive material as with dust-free air or gas.

In the accompanying drawing which illustrates one embodiment of the present invention', Fig. 1 is a side elevation of a fan wheel or rotor, with a portion broken away to show more clearly the construction of blade and protective facing; Fig. 2 is a longitudinal section on line 2-2 of Fig. 1; Fig. 3 is a side elevation of the centre disk of the fan wheel before assembly; and Figs. 4 and'5 are detail views, on an enlarged scale, showing the construction and method of connectionof the centre disk, blade and protective facing, taken on lines 4 4 and 5 5, respectively, of Fig. 2.

Mounted upon the shaft Il and secured there'- on by the usual keys I3 and clamping screws I5,`

are the hub members l1 spaced slightly apart at their adjacent outer margins to receive theregether by means of a series of rivets 23 passing through the outer margins of the hub members and thev inner margin of the disk.

Mounted upon the disk is a series of forwardly curving, rearwardly inclined blades 25. A convenient and satisfactory construction is that shown in the drawing where each blade comprises two portions or halves extending from opposite sides of the centre disk. Right angled flanges 21 extending from the rear of the blades are secured to the centre disk 'by means of rivets 29 passing through the anges of adjacent blade sections and the centre disk. The outer or distant ends of the blades are-supported upon the inclined rings or shrouds 3l, being attached thereto by means of rivets passing through the rearwardly turned flanges of such rings. A short cylindrical inlet ring 33 is riveted to the inner periphery of the shrouds.

Heretofore it has been the practice to provide a centre disk having an integral or continuous surface extending from the inner to the outer periphery thereof.. Such a construction, however, as already pointed out, is subject to severe erosion, particularly at the joint between the disk and the fan blades when abrasive material is carried through the fan with the air or gas.

To prevent this destructive abrasion, portions of the outer periphery of the centre disk of general V-shape are removed immediately in advance of the front face of each blade leaving -the openings or spaces 35 such that the currents of air or gas carrying the cinders or abrasive dust from the opposite inlet, instead of being carried into contact with and over the centre disk, are projected against one another, and their destructive energy very largely dissipated. Further, by reason of the yielding character of the air streams, the abrasive material tends to spread over a substantial length of the blades instead of being concentrated in theangle between disk and blade, thereby distributing the wear and increasing greatly the period of use before repairs are 'required To increase still further the period of safe, continuous operation of the fan, there may be provided a protective facing on the advancing faces of the blades over the middle portions where the abrasive material tends to concentrate. Such a protective coating is shown at 4| and comprises a metal plate of generally trapezoidal shape covering the middle portions only of the blade and curved to the contour thereof. 'I'he inner edge of such plate is formed with a hook 43 to embrace the inner edge of the blade and to take part in carrying the strains developed by the centrifugal action of this plate at high rotational speeds. Rivets I5 at the face of the blades and the blade sections hold it securely in position.

A configuration or surface which has been found particularly efllcacous in resisting abrasive wear is that shown in the drawing and commonly known as stair tread, with its series of longitudinal ridges and grooves extending lengthwise of the blades.

It will be noted that in the fan illustrated in the drawing, the inner portion of the disk extending from the hub to the inner edges of the blades is continuous and integral, and that only in front of each blade is any of the disk removed, suiilcient portions of the disk being left behind each blade to provide ample material for securing-the blade thereto and ,toV aordf-the ref quired strength to resist all operative strains and pressures. Since the inner portions of the disk, that is, those of the shorter radius, carry more of the driving strain, a greater peripheral width of support behind each blade is provided at the inner than at the outer portions of the blade.

By eliminating the erosion at the Joint between the vblade and the centre disk, and preferably over the face of the blades, without apprel ciably reducing the inherent strength of thecentre disk construction. there has been pro-` duced a fan capable of handling air and gases containing highly abrasive material over long periods of time, without the need of repair or replacement, as in the present type of fan now. in use.

Having thus described the invention, what -is claimed is: l

1. A double intake centrifugal fan for handling abrasive-carrying gas, comprising a rotor having a shaft, a pair of hub members flxed upon the shaft, an integral annular centre plate with its inner margin clamped rigidly between the outer margins of the hub members, blades secured to the centre plate and extending axially across the rotor with their outer edges Ysubstantially ilush with the outer periphery of the plate, means for supporting the intake ends of the blades, the periphery of the plate being removed immediately in advance of each blade for a depth not exceeding the radial depth of the blade and to a limited extent peripherally, leaving the disk intact immediately to the rear of each blade with an integral annular portion between the inner edges of the blades and the hub members, thus providing a limited free space in front of each blade in which space the opposite, inwardlyilowing streams of abrasive-carrying gas will impinge directly upon one another, a suiicient peripheral portion of the integral plate being retained behind each blade to afford ,y

ample strength for the support thereof.

2. A double intake fan for handling abrasive-. "I carrying gas, comprising a rotor having a shaft,

a pair of hub members fixed upon the shaft, a

integral annular centre plate with its inner mar- L' flush with the outer periphery of the plate, an-

nular rings to which the intake ends of the blade sections are attached, a section of the centre plate of generally V-shape being removed immediately in advance of each blade to a depth not exceeding the radial depth of the blade, leaving `the disk intact immediately to the rear of each blade with an integral annular portion between the inner edges of the blades and the hub members-thus providing a limited free space in front of each blade in which space the opposite inwardly flowing streams of abrasive-carrying gas will impinge upon one another, a suiiicient peripheral portion of the integral plate being retained behind each blade to afford ample strength for the support thereof, and a facing of wear resisting material of lesser length than the blade secured to and protecting the middle portion of the advancing face'oi' each blade.

3. A double intake centrifugal fan for han-l hub, blades extending-axially across the rotor i with their outerredges substantially flush with the outer periphery o! the disk, each ladenbeing formed of blade sections extending axially in opposite directions from opposite faces oi the plate adjacent its periphery, the blade sections having end flanges turned rearwardly of the din rection of rotation for securing the sections to the plate with the outer edges of the blade sectionssubstantially flush with the outer periphery of the plate, means for supporting the intake ends oi' the blade sections, the periphery of the plate being cut away immediately in advance of each blade to a depth not exceeding the radial depth of the blade but lett intact immediately to the rear of each blade, with an integral annular portion between the inner edges ot the blades and the hub, thus providing a limited free space in front of each blade in which space the opposite, inwardly flowing streams of abrasive-carrying gas will impinge upon Aone another, a sufllcient peripheral portion of the integral plate being retained behind each blade to ailord ample strength for the support thereof. and an integral facing oi' wear resisting material secured to the advancing face of each blade, each facing covering the adjacent end portions only of the pair of blade sections oi' each blade and being of greater axial length along the inner edges of the blades than along the outer edges.

THOMAS B. ALLARDICE.

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