US2531779A - Spreader stoker - Google Patents

Description

Nov. 28, 1950 Filed June 16, 1945 6 Sheets-Sheet 1 INVENTOR. Ernst lhMidget'ize w Robez'i W: Reid Attorney Nov. 28, 1950 E. L. MIDGETTE ETAL 2,531,779

SPREADER STOKER Filed June 16, 1945 6 Sheets-Sheet 2 INVENTOR. Lima- LMidgefie 3 BY Robez'fi WZReicl A Eterna Nov. 28, 1950 E. MIDGETTE EI'AL 2,531,779

SPREADER STOKER Filed June 16, 1945 6 Sheets-Sheet 5 BY RoelZW and Attorney Nov. 28, 1950 a E. 1.. MIDGETTE ETAL 2,531,779

SPREADER STOK'ER Filed June 16, 1945 I 6 Sheets-Sheet 6 IN VEN TOR. Ernst L.Midgel:fie d RaberZ' mReid fltborney Patented Nov. 28, 1950 SPREADER STOKER Ernst L. Midgette and Robert W. Reid, Philadelphia, Pa., assignors to American Engineering Company, Philadelphia, Pa a corporation of Pennsylvania Application June 16, 1945, SerialNo. 599,812

15 Claims. 1

This invention relates to stokers of the spreader type and more particularly to the fuel feeding and distributing mechanism for such devices.

One object of the present invention is to provide a generally improved and simplified stoker of the spreader type.

Another object is to provide novel andhighly improved fuel feeding and distributing devices for stokers of the stated character which evenly distribute the fuel over the entire grate area thereof.

A further object is to provide a fuel" feeding and distributing rotor for stoke'r furnaces of the stated character having blades extending lengthwise thereof and which are so formed as: to effectively propel the fuel through an opening. or openings in the front wall of the furnace and to evenly distribute it over the entire area of the grates thereof.

A stillfurther object is to provide. rotors having curved sectional blades thereon for feeding and distributing fuel over the grates of stoker furnaces;

Other and further objects will become apparent as the descriptionof the invention progresses.

f the. drawings:

Fig. 1 is a side elevational view partly in section taken through the. front end of a spreader stoker showing the fuel. feeding and distributing mechanism associated therewith.

Fig. 2 is a sideview ofa fuel feeding and distributing rotor for a, spreader stoker.

Fig. 3 is an end view of the rotor shown in Fig. 2.

Fig. 4 is a diagrammaticview showing projections of the lines of contact of the blades of the fuel feeding and distributing rotor on the developed surface of the supporting cylinder.

Fig. 5 is a plan view of a spreader stoker showing the area of the grate which is supplied with fuel by one of the blades of the fuel feeding and distributing rotor.

Fig 6 is awplan view similar to. Fig. 5, showing the area of the grate supplied with fuel from the other of the blades of thefuel feeding and distributing rotor.

Fig. 7 is a side view of a modified type of feeding and distributing rotor.

Fig. 8 is an end view of the rotor shown in Fig. .7. V

2 cation of the fuel feeding and distributing rotor.

Fig. 11 is an end view of the rotor shown in Fig. 10.

Fig. 12 is a side View showing a still further modification of the fuel feeding and distributing rotor.

Fig. 13 is an end view of the rotor shown in Fig. 12.

Fig. 14 is a side view of a still further modification of the fuel feeding and distributing rotor.

Fig. 15 is an end view of the rotor shown in Fig. 14, and

Fig. 16 is a diagrammatic view showing the projections of the lines of contact of the blades of the fuel feeding and distributing. rotor shown in Figs. 14 and 15 on the developed surface of the supporting cylinder.

Referring to the drawings the numeral l indicates a furnace having a front wall 2, side walls 3 and 4, and a rear wall 5. The furnace-l is fired by a stoker of the spreader type comprising a combustion grate 6, a fuel'feeding and distributing rotor l, and a fuel conveyor indicated generally at 8. The fuel delivered to the rotor I is propelled through an opening 9 provided in the front wall 2 of the furnace.

The specific construction of the grate B, the conveyor 8, and the operating means for the conveyor and rotor 1 forms no part of the present invention and, accordingly, a detailed description thereof isunnecessary. For a complete disclosure of such devices, reference may be had to the patents to George W. Olney, No. 2,001,152 and No. 2,099,618.

As shown more particularly in Figs. 1, 5. and 6, the conveyor 8 comprises a pair of spaced chains l0, l0 trained over sprocket" wheels H and I2.

The sprocket wheels i l and 12 are secured to shafts i3 and 14-, respectively, mounted in suitable bearings provided in a supporting framework 15. As shownin Figs. 5 and 6, the chains [0, 10 are transversely spaced and have secured "thereto at spaced intervals therealong feeding bars. 16 which slide across a fuel supporting plate 11, Accordingly, upon operation of the said chains and sprocket wheels the bars. 16 feed the fuel across plate H and over the inner end of the conveyor 8, the. fuel then gravitating. upon the rotor l, which in turn propels it through the opening 9 in the front wall 2 and onto the grates 6 of the stoker. Fuel is supplied to the conveyor 8 from a hopper 20: mounted at the upper end of the casing 21 for said conveyor and associated parts. Theyhopp'er 2!) isdisposed immediately above. the-conveyor sand has a partition 22 pro- 3 vided intermediate the side walls 23 and 24 thereof forming a pair of discharge openings 25 and 26 at the bottom thereof. The discharge openings 25 and 25 may be opened or closed by a pair of closures 27 and 28, respectively, slidably mounted in any suitable guideways 29 mounted in and extending longitudinally of partition 22 and the lower ends of the side walls 23 and 25 of the hopper 25. The closures 2'5 and 28 may be operated manually by means of handles and 3|, respectively, provided at the outer ends thereof. The partition 22 extends downwardly, the lower edge 32 of which being spaced slightly from the top of conveyor 8. Fuel gravitating onto conveyor 8 from the hopper 25 is prevented from overflowing the ends of said conveyor by means of a pair of plates 35 and 55 pivoted immediately below the front and rear walls 35 and 371', respectively, of hopper 25. The framework l5, on which the conveyor 8 is supported, is movable along the bottom wall 38 of the casing 2| towards and from rotor l by means of a screw shaft 35. As shown in Fig. 1, screw shaft 39 engages a nut provided in a member il secured to and depending from the framework l5. The screw shaft 35 is mounted for rotary movement in a bearing 52 provided in the front wall 53 of casing 2|,

The rotor is provided with a central bore 48 for receiving a drive shaft 44, to which the said rotor is keyed or otherwise secured. Shaft is mounted in suitable bearings, not shown, provided exteriorly of front wall 2 of the furnace. A sub-casing 45 is provided around a substantial portion of rotor l, as shown in Fig. 1, thereby confining the feeding action to the upper inner portion thereof. The rotor is driven in a clockwise direction (Fig. 1) by an electric motor 55 through a chain and sprocket mechanism indicated generally at 41.

Referring to Figs. 2, 3 and l, the rotor 1 comprises a cylindrical base portion 5| and a pair of curved blades 52 and 53 extending over the entire length thereof. Blade 52 is provided with a relatively sharply curved portion 54 at one end thereof which becomes progressively more gradual toward the other end, the portion 55 extending from a point substantially midway between the ends of the blade and the end of the rotor being relatively straight. Blade 53 is of similar construction having a relatively sharply curved portion 55 and a gradually curving or relatively straight portion 5?. The curved portions 55 and 55 of the blades 52 and 53, respectively, are oppositely disposed and propel the fuel in opposite directions, as will appear more fully hereinafter. Fig. 4 is an extended projection of the rotor l, the numeral 5| disclosing the circumferential area of the rotor, the lines 52 and 53 indicating the lines of contact of the blades 52 and 53 with the cylinder 5|, and the numerals 54, 56 and 55, 57 indicating the curved and relatively straight portions, respectively, of the blades 52 and 53.

Referring to Figs. 5 and 6, the broken lines extending from the blade 52, shown in Fig. 5, indicate the portion of the grate 6 supplied with fuel by said blade 52; while the broken lines extending from blade 53, shown in Fig. 6, indicate the portion of the grate supplied with fuel by that blade. It is seen that the end of the curved portion 54 of blade 52 propels the fuel to the area of the grate 6 at the corner 60 thereof and that the remainder of the blade propels the fuel fanwise over substantially one-half the entire area of said grate. It is also seen that the end of the curved portion 56 of blade 53 propels the fuel to the area at the corner 6| of the grate 6 and that the remainder of the blade propels the fuel fanwise over the other half of said grate.

Figs. 7, 8 and 9 illustrate a modified rotor construction consisting of a cylindrical base portion 5| having a pair of blades 52 and 53 mounted thereon. Blades 52 and-53 comprise relatively sharply curved portions 54 and 56 and gradually curving or relatively straight portions 55 and 51 respectively, generally similar to the relatively sharply curved and gradually curving or relatively straight portions of the blades 52 and 53. The relatively straight portions 55 and 51, however, terminate inwardly of the ends 63 and 64, respectively, of the base portion 5| A relatively short blade 66, whose projected length is substantially equal to the distance between the end of blade 52 and the end 63 Of rotor I, is also provided on the base portion 5| Blade 66 lies between blades 52 and 53 and is curved slightly in the opposite direction from the curved portion 54 of blade 52 and in operation propels the fuel to the area adjacent one of the remote corners 57 of grate 6, shown in Figs. 5 and 6 of the drawings. A second relatively short blade 68 is provided near the opposite end 64 of rotor 1. Blade 68 is curved slightly in the opposite direction from the curved portion 56 of blade 53 and in operation propels the fuel to the area adjacent the other remote corner 69 of the grate '6.

Figs. 10 and 11 illustrate a further modification of the rotor l, which consists of a cylindrical base portion 5| and blades 52 and 53 generally similar in shape to the cylinder 5| and blades 52 and 53 shown in Figs. 2 and 3. In this construction, however, the blades 52 and 53 are constructed of a series of relatively short sections 70 and 1|, respectively, which are spaced slightly apart. By constructing the blades in sections greater allowance is provided for expansion and contraction and, accordingly, this structure is especially desirable in installations wherein the rotor is exposed to high temperatures. By constructing the blades in sections there is also less tendency for warping or cracking to occur when the rotor is manufactured by casting.

Figs. 12 and 13 illustrate a still further modification of the rotor 1. In this construction the cylindrical base portion 5|, as well as the blades 52 and 53, is also generally similar in shape to the base portion 5| and the blades 52 and 53, respectively, of the structure shown in Figs. 2 to 4. The blades 52 and 53 in this construction are also made up of a series of relatively short sections 12 and 13, respectively. The sections 12 and 13 overlap slightly with adjacent sections and thus in operation the blades present, in effect, continuous fuel propelling surfaces. In this construction, like that shown in Figs. 10 and 11, due to the sectional structure of the blades expansion and contraction thereof may take place without causing cracking or warping. This is true both in actual operation when the rotor is subjected to alternative periods Of heating and cooling, as well as in the manufacture thereof by casting.

Figs. 1a to 16 illustrate a still further embodiment of the present invention. This construction consists of a cylindrical base member 5| and four curved blades 14, I5, 16 and H. These blades are evenly spaced around the base member 5i the blades 14 and 16 having the same contour and feed and distribute the fuel to onehalf the grate. The blades l5 and Ti also have the same contour and feed the fuel to theother assure:

side of the grate," the curvature thereof being; o positeto that of blades"14' and i6: Theblades- H and 16 have sharply curved portions 18; 18 and gradually curvingor substantially straight portions 19, 19 extending from one-end of the rotor 1; while the'blades l5 and 11 have sharply curved portions 39, ligand gradually curving or relatively straight portions 81, 8| extending from the other endof saidrotor.

From theforegoing description it isseen'that various forms of simplified and efficient feeding anddistributing rotors havebeen provided. Theblades of the rotors are so shaped that one (if the'blades of the"constructions' shown in Figs: 1 to 13'of thedrawings feeds'anddistributes the fuel to substantially the area of the grate 6'; while the other blade of the said construction feeds thefuel to'theother half of the grate. Inthe constructionshown in Figs. 14 to lfitwo blades; for exalnple; the blades 14 and 15, feed the fuel to one-half the grate; while the other. two blades, '15 and i1; feedthefuel tothe other half of" the grate."

been'shown herein. Itis to be understood, how ever, that'rotorshavinga greater or lesser number of blades may be provided if it is so desired without departing from the invention.

It sometimes is desired to clean the grates whilefuel isbeing fed thereto'and without er:- tinguishing thefire. This is accomplished by moving one or theothe'r of the closures 21 or 28 to closed position. For example, when the closure 28 isin closedposition fuel willbe deposited only on theportion ofthe conveyor 8 disposedbeneath the'opening 25 of hopper 28. Accordingly; fuel willonly' be conveyed to onehalf of the rotor Fandthe curved portion 54'0f is delivered thereby to the half of rotor 1" on which the curved portion 55hr blade 53and the relatively straight portionlili of blade 52 are sittiated. Fuel is now fed and distributed over'the other half of thegrate l5. The ashes now may be drawn from the other half of said grate'through the opening 85 provided in the front wall 2. A second furnace door-86 normally. closes opening 85.

The-distance that the fuel is propelled over the grate Bof the stoker by the various rotors shown and described herein, for anygiven speed of operation, is controlled toa certain extent by the manner in which the fuel is delivered to'th'e rotors by the conveyor8; When the fuel gravitates on the bladescnear the forward end thereof, it is thrown a greaterdistance into the furnace than when it strikes the blades at points inwardly from the forward or outer extremity thereof; Accordingly, by adjusting the conveyor 8*toward' and from the rotor, the proper feeding also controls to a certain extent the distance that Rotor constructions having two" and fourblades; respectively, have the fuel is propelled thereby intothe furn ce? The deeper the blades the greaterthe distance" the fuel is "propelled; and, conversely; the shorter the blades the lesser willbethe distance thatthe fuel will be propelled into the furnace thereby? The length and width of the grate therefor are determining factors in connection with the *positioning of the conveyor B-Withrespect to the rotor l, as well as in the selection of a rotor of It, therefore, is apparent that rotors of-varioussizes and dimensions may be employed without departing fromthe invenproper dimensions;

While the embodiments herein shown andde-* scribed areadmirably adapted to fulfill the objects primarily stated,- it 'is to be understood that the inventionis nottobe limited thereto since it may be embodied in other forms; all coming within the scope oftheclaimswhichfollow.

What is claimed is:

ing and distributing rotor mountedexteriorly of said wall adjacentsaid opening, a pair ofcircumferentially spaced feeding and distributing bladesextending-lengthwise of said rotor, curved and relatively straight fuel engaging portionsprovided' onone of said blades for feeding and distributing the fuelevenly over substantially one-half the area of saidgrate, curved andrela- .tively straight fuel erl'gaging portidns providedon the other of said blades fr'fe'edingand evenly distributing the fuel-over' substantially the other half of said grate, andth'e said relativelystraight portions of said 1 bladesextending substantially in parallel relation with the axis of saidrotor.

2. Ina device of the class described, the oombination of a stoker furnace havingfrom; sideand rear walls, a grate forming the bottom. walk of said furnace, one of saidwalls'having an-eia .larged opening therein throug-hwhi'ch fuel is fed to and distributed over said" grate; a fuelfeeding anddistributing rotor mounted ex'ter iorly of said wall adjacentsaid opening, a'pair of circnm'f eren'tially spaced feeding and distributing blades extending lengthwise of said rotor,

curvedand relativelystraight fuel engaging porevenly distributing the fuel over substantiallythe other half of said grate means for conveying fuel to said rotor; a hopperfor supplying fuel to said} fuel conveying means, and means for controlling the flow of fuel from said hopper to said fuelconveying means;

3. In a device of the class described, the coinbination of a stoker furnace having front, side andrear walls, a grate forming the bottom wall of'said furnace; one of said walls having an enlarged opening therein through which fuel is fed to and distributed over said grate, a fuel feeding and dietiibuting rotor"niounted exteriorly of said wall adjacent said opening, a pair ofcircurnferentially spaced feeding'and distributing blades extending lengthwise ofsaid rotor, curved. and

relatively straight fuel engaging portions provided on one of saidblades for "feeding anddistributing thefuel evenly over substantially one;

half the area of said grate, curved and relatively straight fuel engaging portions provided on the other of said blades for feeding and evenly distributing the fuel over substantially the other half of said grate, a conveyor for conveying fuel to said rotor, a hopper for supplying fuel to said conveyor, a pair of independently operable closures for closing the discharge opening of said hopper whereby upon opening one of said closures fuel is delivered by said conveyor to one end of said rotor which feeds and distributes the said fuel to one side of said grate, and when the other closure only is opened fuel is delivered to the other end of said rotor which feeds and distributes it to the other side of said grate.

4. In a device of the class described, the combination of a stoker furnace having front, side and rear walls, a grate forming the bottom wall of said furnace, one of said walls having an enlarged opening therein through which fuel is u fed to and distributed over said grate, a fuel feeding and distributing rotor mounted exteriorly of said wall adjacent said opening, a pair of circumferentially spaced blades extending lengthwise of said rotor, means on one of said blades for feeding and distributing fuel evenly over substantially one-half the area of said grate, means on the other of said blades for feeding and distributing fuel evenly over substantially the other half of said grate, an endless conveyor for conveying fuel to said rotor, a hopper having a pair of discharge openings overlying said conveyor, and a movable closure for each of said discharge openings whereby fuel from said hopper may be caused to discharge to either or both sides of said conveyor.

5. A feeding and distributing rotor comprising a cylindrical base portion, a pair of circumferentially spaced blades secured to and projecting outwardly from said base portion and extending over the entire length thereof, each of said blades having a curved portion extending from one end thereof over a portion of its length and a relatively straight portion extending over the remainder of its length, and said curved portions lying at opposite ends respectively of the rotor and extending angularly with respect to the axis of the rotor with the working faces thereof presented respectively toward the opposite sides of a plane normal to the rotor axis, and each of said blades presenting a smooth working face free from obstruction extending over the full length of the blade.

6. A feeding and distributing rotor comprising a base portion, and a pair of circumferentially spaced blades extending lengthwise of said base portion, the portion of one of said blades extending from one end of said rotor being sharply curved and terminating in a more gradually curving portion, the curvature of said last mentioned portion becoming progressively more gradual as it approaches the said other end of said rotor and terminating in a portion extending substantially in parallel relation with the axis of said rotor, and the portion of the other of said blades extending from the said other end of said rotor being sharply curved and terminating in a more gradually curving portion, the curvature of said last mentioned portion becoming progressively more gradual as it approaches the said first mentioned end of said, rotor, and terminating in a portion extending substantially in parallel relation with the axis of said rotor, and the working faces of the curved portions of both blades being presented angularly to a plane normal to the axis of and intermediate the ends of the rotor, each of the blades presenting a smooth working face free from obstruction extending over the full length of the blade and over a major part of the rotor length.

7. A rotor comprising an extended cylindrical base portion, a curved relatively long material feeding and distributing blade extending lengthwise of said base portion from one end thereof, a second curved relatively long material feeding and distributing blade extending lengthwise of said base portion from the other end thereof, a relatively short curved blade provided near said one end of said base portion, and a second relatively short blade provided at said other end of said base portion, the said working faces of the said long blades being presented substantially throughout and respectively toward the areas at opposite sides of a plane normal to the axis and intersecting the rotor, and the working faces of the short blades being presented toward the areas at the opposite sides of said plane, and each of said blades exhibiting a smooth working face free from obstruction extending over the full length of the blade and being circumferentially spaced with respect to the adjoining blades.

8. A rotor comprising an extended cylindrical base portion, a curved relatively long material feeding and distributing blade extending lengthwise of said base portion from one end thereof, said blade terminating inwardly from the other end of said base portion, a second curved relatively long material feeding and distributing blade extending lengthwise of said base portion from the other end thereof, said last mentioned blade terminating inwardly from the said first mentioned end of said base portion, and a pair of spaced relatively short blades provided at the opposite ends of said base portionpsaid short blades extending inwardly a distance corresponding to the spaces between the ends of said relatively long blades and the corresponding ends of said base portion, the working faces of the said long blades being presented throughout and respectively toward the areas at opposite sides of a plane normal to the axis of and intersecting the rotor, and the working face of each of the short blades being presented toward the areas at the opposite sides of said plane respectively, and all of the blades being circumferentially spaced with respect to each other.

9. A rotor comprising an extended base portion and a relatively long continuously curved material feeding and distributing blade extending lengthwise of said base portion and over a major part of the length of the rotor, the curvature of said blade being relatively sharp at one end thereof and becoming progressively more gradual toward its other end, and toward the said other end extending progressively closer to a relation of parallelism with the rotor axis and said blade comprising a series of spaced sections disposed in end to end relation over the length thereof and exhibiting a smooth working face free from. obstruction extending over the full length of the blade.

10. In a device of the class described, the combination of a stoker having front, side and rear walls, a grate forming the bottom wall of said furnace, one of said walls having an enlarged opening therein through which fuel is fed to and distributed over said grate, a fuel feeding and distributing rotor mounted exteriorly of said wall adjacent said opening, a curved relatively long material feeding and distributing blade extending lengthwise of said rotor from one end thereof for feeding and distributing fuel over substantially one-half the area of said grate, a second curved relatively long material feeding and distributing blade extending lengthwise of said rotor from the other end thereof for feeding and distributing fuel over the other half of said grate area, said blades lying in spaced relation and the curvature of one of said blades being oppositely Y disposed to that of the other, a relatively short blade extending inwardly from one end of said base portion for feeding fuel to one of the remote corners of said grate and a second relatively short curved blade extending inwardly from the other end of said base portion for feeding fuel to the other of said remote corners of said grate, and said short blades lying in spaced relation with said relatively long blades.

11. In a device of the class described, the combination of a stoker having front, side and rear walls, a grate forming the bottom wall of said furnace, one of said walls having an enlarged opening therein through which fuel is fed to and distributed over said grate, a fuel feeding and distributing rotor mounted exteriorly of said wall adjacent said opening, a curved relatively long sectional material feeding and distributing blade extending lengthwise of said rotor for feeding and distributing fuel over one-half of said 12. In a device of the class described, the combination of a stoker furnace having front, side and rear walls, a grate forming the bottom of said furnace, one of said walls having an enlarged opening therein through which fuel is fed to and distributed over said grate, a fuel feeding and distributing rotor mounted exteriorly of the wall adjacent said opening, circumferentially spaced fuel impelling blades extending inwardly from one end of said rotor, and at least in part being inclined longitudinally to the axis of the rotor for feeding and distributing fuel over substantially one-half the area of the grate, and circumferentially spaced blades extending inwardly from the other end of said rotor and at least in part being inclined to the axis of the rotor for feeding and distributing fuel over substantially the other half of the grate, each of said blades exhibiting a smooth working face free from obstruction and extending over the full length of the blade.

13. In a device of the class described, the combination of a stoker furnace having front, side and rear walls, one of a grate forming the bottom of said furnace, said walls having an enlarged opening therein through which fuel is fed to and distributed over said grate, a fuel feeding and distributing rotor mounted exteriorly of said front wall adjacent said opening, a pair of circumferentially spaced blades extending inwardly from one end of said rotor, one of said blades being longer than the other and having curved and relatively straightportions provided thereon for feeding and distributing fuel over substantially one-half the area of said grate, a pair of circumferentially spaced blades 10 extending inwardly from the other end of said rotor, one of said blades being longer than the other and having curved and substantially straight portions provided thereon adapted to feed and distribute fuel over substantially the other half of said grate.

14. A feeding and distributing rotor comprising an extended base portion, a pair of circumferentially spaced blades extending inwardly from one end of said base portion, one of said blades being longer than the other and having curved and relatively straight portions provided thereon with the relatively straight portion extending approximately in parallelism with the rotor axis and with the working surface of the curved portion facing angularly toward the area in front of the rotor confronted by the relatively straight portion, a second pair of circumferentially spaced blades extending inwardly from the other end of said base portion, and one of said last mentioned blades being longer than the other and having curved and substantially straight portions provided thereon in reverse position longitudinally of the rotor from the corresponding portions of the longer blade of the first named pair, and the relatively straight portion of the longer blade of the second pair ex tending approximately in parallelism with the rotor axis and the working surface of the curved portion of said blade facing angularly toward the area in front of the rotor confronted by the relatively straight portion of the said blade.

15. A rotor comprising an extended base portion, a relatively long curved material feeding and distributing blade extending lengthwise of said base portion, a second relatively long curved material feeding and distributing blade extending lengthwise of said base portion in circumferentially spaced relation with said first mentioned blade, each of said blades being con structed in two or more longitudinal sections disposed in end to end relation, each of said blades having a portion thereof extending substantially in parallel relation with the axis of said rotor and having the remaining curved portion disposed so that the working face thereof is presented angularly toward a plane normal to the rotor axis, which plane intersects the portion of the blade which substantially parallels said axis, and each of said blades exhibiting a. smooth working face free from obstruction extending over the full length of the blade and over a major part of the rotor length.

ERNST L. LIHDGE'I'IE. ROBT. W. REID.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 578,630 Erickson -1 Mar. 9, 1897 767,084 Reagan Aug. 9, 1904 944,959 Eitle Dec. 28, 1909 1,975,224 Cox Oct. 2, 1934 2,045,357 Hoffman June 23, 1936 2,075,736 Lower Mar. 30, 1937 2,099,618 Olney Nov. 16, 1937 2,146,469 Foster Feb. 7, 1939 2,255,841 Bower Sept. 16, 1941 2.258.757 Hanna Oct. 14, 1941 Certificate of Correction Patent No. 2,531,779 November 28, 195Q ERNST L. MIDGETTE ET AL It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 9, line 60, strike out the words one of and insert the same in line 61 before said;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 6th day of March, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant C'ommz'ssz'oner of Patents.

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