US 2507245 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
May 9? E950 A. o. DADY STOKER APPARATUS ,INCLUDING A UNIFORMLY INCREASING PTCH FEED SCREW 2 Sheets-Sheet l Filed July l2, 1944 Mayv 9, 1950J A. o. DADY STOKER APPARATUS INCLUDING A UNIFORMLY INCREASING FITCH FEED SCREW 2 Sheets-Sheet 2 Filed July l2, 1944 Patented May 9, 1950 S'KER APPARATUS, INCLUDING A UNI- FORMLY INCREASING FITCH FEED SCREW Arthur O. Dady, Flossinoor, Ill., assignor to Sears, Roebuck and Co., Chicago, Ill., a corporation of New York Application July 12, 1944, Serial No. 544,497
Claims. (Cl. Mil- 45) This invention relates to stokers and is concerned more particularly with the feeding of coal or other granular material which is beset with characteristic impedimenta such as packing or coking effects.
It is an object of my invention to provide a feed screw which will deplete the hopper substantially uniformly throughout the length of the hopper.
Another object is to provide a coal feeding mechanism by means of which the coal is accurately metered to the burner.
An additional object is to provide a coal feeding mechanism requiring substantially less Work to feed a given quantity of coal per hour than is true of conventional coal feeding devices particularly when low fire conditions in a stolzer retort produce back draft burning and coking in the feed screw terminal iiights.
Another object is to provide a coal feed screw having terminal flights of increased wall thickness whereby to better resist wear under severe abrasive conditions while yet maintaining equal or slightly increased volumetric characteristics as regards space intervening the screw flights.
1t is also an object of my invention to provide a novel method of forming a coal feed screw.
Further objects and advantages of the invention will appear as the description proceeds.
The invention will be better understood upon reference to the following description and the accompanying drawings, in which:
Fig. l is a longitudinal view of a tube and screw in assembly with a coal hopper, feed tube and burner or retort in accordance with one form of my invention.
Fig. 2 is'an enlarged sectional View taken as indicated by the line 2 2 in Fig. l.
Figs. 3 and 4 are views similar to Fig. l showing additional modifications of feed screws.
Fig. 5 shows a part of an apparatus for forming a ribbon or other elongated strip, rod or bar into a conveyor worm flight.
Figs. 6 to 9 show various flight cross-sectional shapes. y n
Referring now more particularly to the drawings, there is shown at 2li a gear case from which projectsr the usual square or other polygonal end of the coal feed screw drive shaft 22 received in a correspondingly formed socket Zd formed on the core 25 of a feed screw 26. The portion 28 of the flight 3B disposed within the entering sleeve 32 of the coal hopper 34 -is preferably of substantially uniform diameter with relatively small clearance from thesleeve' to 'prevent escape of coal from the hopper in the direction of the gear case 2t. I
The diameter of the flight 35 at the Wall 36 of the hopper Sli is relatively small, as shown at 33, and gradually'in'creases in diameter, Without change in pitch,'substantially to a point not less than approximately one pitch or turn before reaching the opposite wall lo of the hopper, i. e., substantially throughout that portion of the screw which serves as the coal collecting section.
This construction is considerably advantageous over the conventional collecting section, which is of substantially uniform diameter. With the conventional collecting section,the Yonly portion thereof which collects coal from the hopper is they portion nearest the drive end which is in contact with the coal, and thus it .willbe seen that the hopper gradually empties from the drive end toward the burner end, and accordingly increasingV portions of the feeding section of the flight become progressively idle. It has been found in practice' 'that under these circumstances the smaller size coal in the hopper segregates or settles lto the bottom, and thus the burner does' not receive the'desred mixture of coal. Since the flow rate'of combustion air is determined by the proportions of the mixture of large and small coal fed to thebu'rner, and inasmuch as`this mixture affects the fuel bed resistance to the flow of air, it will be apparent that under such circumsta ncesl the air flow rate will not be beoptimum at all times.
With'a collecting section having a gradually increasing night diameter, [the draining of coal bysaid' sectionI from 'the hopper is made substantially uniform' because the subsequent screw nightsl havegreater intervening space capacity and hence takeon additional coal' as the diam'- ete'r increases.r With this construction, it has been"forid of additional advantage that the smaller size coaldo'es not'seg'regate in the hopper, but rather thatthe coalY is deliveredin the desired mixture to the burner, and thus the combustion air' flow is 'substantially optimum at all times.
welded as at t2 te the' van of the hopper ai is amtering and crushing bloei; housing dit `witl'i which is yassociated a block it held in assembly therewithv by av cam 5 pivoted on a hail whose ends '(not shown) engage under fianges (not shown) extending laterally from'Y the housing Welded as at 52 to the housing is or formed integrally therevvith'l is' a recessed flange 5s for the reception of one'end 58 of a coal'feed vtube `6l). vlvelded as at 2 to the adjacent portion of the alwfeed tubeils ra ilallge 6d. Bolts 66 applied to the flanges 54 and 64 hold the housing 44 and coal feed tube 60 in tight abutment. The other end 68 of the coal feed tube G is suitably coupled to the neck 'I0 of a burner or retort l2.
The screw 26, from a point approximately at 14, preferably within the hopper and adjacent the inner wall 40 thereof, to a point approximately at 16, preferably slightly beyond the metering and crushing block assembly, is of uniform pitch and uniform diameter, said diameter being only slightly smaller than the interior diameter of said assembly, the lit being such as substantially to preclude leakage of any coal between the flight and said assembly, and to prevent the passage of gas or fumes back into the hopper. This portion of the screw serves as the metering section, insuring the delivery of a precise quantity of coal to the burner or retort.
From approximately the point 16 to the free end 18 of the screw, the screw is of uniformly increasing pitch. The delivering section extends from the metering section to approximately the point 80, at the burner end of the delivery tube 60, and, throughout the metering and delivery sections, the flight is of uniform diameter. The interior diameter of the coal feed tube 60 preferably exceeds that of the metering and crushing assembly, providing a slight clearance 82 between the tube and the flight. The purpose of the increased pitch of the delivering section over. that of the metering section is to allow the level of the coal issuing from the Crusher block assembly to drop as indicated by the dash-dot line 84 and thus materially cut down the resistance between the coal and the tube as the coal is moved toward the burner by the screw. In this connection it is to be observed that the delivering section of the screw, due to its greater pitch, has a capacity for delivering a greater quantity of coal than is supplied to it from the metering region. Since obviously the delivering section cannot deliver more coal than is supplied to it. the corresponding portion of the feed tube 60 will run partly full, with resulting slippage of a portion of the coal between the tube and the edges of the flight, thereby reducing crushing and preventing packing. This is essential or at least desirable particularly in a, long screw such as is used in a bin feed stoker where frictional resistance is proportionately greater.
Adjacent the burner end 68 of the tube 60 the level of the coal rises substantially to the top of the tube, due to the resistance offered by the green coal within the burner. From approximately the point 80 to the free end 18 of the screw, the flight is of abruptly reduced diameter generally conforming to the curvature of the adjacent bottom portion of the burner 12. From the drive end to approximately the point 88 the flight may be of substantially uniform thickness. From approximately the point 88 to the free end 18, the flight 30 is of increased thickness to provide increased surface for wear. Failure generally results from the Wear of this portion of the screw before the remainder of the screw is seriously aifected. Since the pitch of the screw flight is a, gradually increasing one and since the wall thickness is correspondingly of increasing degree the portage volume between the flights may remain constant or at but slightly increasing capacity.
In accordance with the form of my invention shown in Fig. 3, the diameters of the various sections of the flight 92 of the screw 03 correspond with those of the flight 30 of Fig. 1. However, in
Fig. 3 the flight is of uniformly increasing pitch from the point 94, at the drive end of the hopper, to the burner end 96. With this construction the coal in the coal feed tube (not shown) levels 01T as indicated in dash-dot lines at 84 with resulting reduction in crushing and packing. The discharge end portion |00 of the flight of the screw 93 is gradually thickened like the corresponding end of the screw 26 of Fig. 1.
The flight |06 of the screw |01 in Fig. 4 is of uniform diameter throughout, except, of course, at its discharge or burner end |08, and is of uniformly increasing pitch from its drive end |09 to its burner end. The discharge position, i. e., approximately the last two turns of the flight |06, is thickened as in the screws shown in the other gures.
In the manufacture of coal feed screws, it is considerably less expensive to apply the flight as a ribbon and Weld it to the core, than it is to form the screw by casting. Indeed it is impossible to cast screws such as those shown in Figs. 3 and 4 with patterns which screw out of the mold. I have devised an effective, efficient and inexpensive method of forming the flight from a ribbon, strip or other attenuated material. In accordance with the embodiment of the invention shown in Fig. l, for example, I form a short flight section 28 from a strip on a suitable mandrel of the same diameter as the core 25 of the screw, the outside diameter of this flight section being uniform and slightly less than the inside diameter of the hopper sleeve 32, then slip the section 28 onto the core until the section bears substantially the relation to the core shown in the drawing, and then Weld the section to the core. I then secure an end of the core, or a mandrel ||2, to a chuck H4 carried by a shaft ||5 driven as by a motor or belt drive I6 through suitable reduction gearing (not shown) so as to rotate the mandrel at a relatively low speed. Through suitable means such as gearing in a gear case H8, the shaft H5 may drive a lead screw |20 and, by using an appropriate gear ratio or other suitable means, the screw may be driven at the desired speed. The lead screw |20 is parallel to the mandrel ||2 and substantially coextensive therewith. A tool post carriage |22 has a nut |24 about the lead screw |20 and is constrained to linear movement by suitable guides (not shown). The carriage may be provided with spaced vertical hardened steel guide rolls |26 arranged to engage the faces of a ribbon or other strip |28 and a spool-like rearwardly disposed guide member Whose core or shaft portion |30 engages the upper edge |32 of the strip and whose flanges |34 engage the faces of the strip. If desired, an additional hardened steel roll may be provided for engagement with the inner (lower) edge of the strip |28, although such roll may be dispensed with since the strip will tend to be thrust upward as it is applied to the mandrel ||2.
The chuck ||4 has a drive pin, hook or other suitable strip-gripping or retaining means |40. When the carriage |22 is disposed adjacent said retaining means |40, the starting end |42 of the strip is extended to said means after passing beyond the spool and rolls. When the machine is in operation with the structure thus far described, the lead screw |20, rotating in the direction indicated by the arrow |44, will move the carriage |22 to the right at a uniform speed, the speed depending on the selection of the interchangeable gears in the gear case I8. This is the construction which could be employed if it were desired to form a flight of uniform pitch throughout the length of the core.
However, where it is desired to form a flight of uniformly increasing pitch, either throughout the length of the .core as shown in Figs. 3 and 4, or throughout a portion of the coreV as shown in Fig. i, this could be done by mechanism operating to advance the lead screw axially in the direction of feed of the carriage |22 simultaneously with the rotation of the lead screw, in such manner that the carriage would be caused to translate at a progressively increased speed. This result may be obtained in various ways. Forexample, I may provide a cam |50 mountedon a shaft |52 driven from the shaft I5 through suitable gear reduction mechanism |54, the camacting on'the lead screw |20 through a follower |56 journaled in the screw and abutting the screw at |51 to advance it at uniformly increasing speed. The cam may of course be varied in design to correspondingly move the lead screw. The follower is held against rotation by guide means |58. If it is desired to form a flight of which a portion is of uniform pitch and another portion of progressively varying pitch, as shown in Fig. 1, the cam would be designed with a portion of zero grade and a ramp of progressively or uniformly increasing grade. A spring 6u may be employed to constantly urge the lead screw and follower toward the cam.
The strip |28, being first formed with the desired variations in width and thickness corresponding to the desired design of night, has imparted to it by the above mechanism an edgewise curvature substantially equal to the curvature of the core or mandrel H2. The free end |42 is pointed either before or after the formation of the coil, and the coil is then arranged in the desired position on the core and tack-welded or continuously welded thereto as shown at |62 in the various figures.
When the strip is bent around the core, the portion outside the neutral axis is stretched and thereby thinned, and the portion at the inside of the neutral axis is compressed and hence thickened. Thus if a strip of rectangular crosssection is used, the flight will become trapezoidal in cross-section, with the thicker portion encircling the core. A rectangular flight section may be obtained by using a trapezoidal strip of the proper dimensions with the thicker part at the edge which will be disposed outside during the coiling process. The brunt of the Wear must be borne by the outside of the flight, it is therefore preferred that the outside be thicker to vprolong the life of the night. With a strip trapezoid of suitable dimensions, a flight could be formed with a resulting trapezoid which is thicker at the outside than at the inside, as shown at |10 in Fig. 6, or special shapes of Hight with the outside portions thickened on the coal-conveying face, i. e., the face directed toward the burner, as shown by way of example only in Figs. 7, 8 and 9 at |12, |14 and |16, respectively, may be employed.
While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the scope of the invention, and that the same is not limited to the particular forms herein disclosed.
l. A stoker mechanism for feeding coal to a heating unit comprising, a coal supply hopper,
a heating unit retort, a cylindrical conduit ex-.'
tending from the hopper to theV retort and through which coal is delivered from said hopper to said retort, and a rotary screw conveyor extending within said conduit comprising an axial core around w-hich are secured spiral screw l heating systems comprising in combination, a.
coal supply bin' provided with a discharge'hopper, a retort having an under-feed opening' on a horizontal level with said bin hopper, a cylindrical conduit connecting said retort With said ybin and including an intermediate section functioning as a volume metering chamber, and a feed screw rotatable within said conduit comprising an axial shaft having at one end a rotary power coupling and having wound spirally about it a screw flight having a progressively increasing pitch from said metering chamber to said retort whereby to counteract against packing effects of coal such as is induced by coking during low-fire burning conditions within said retort.
3. A screw feed mechanism for coal burning heating systems comprising, a coal supply bin equipped with a discharge hopper, a retort having an under-feed opening, a cylindrical conduit connecting said hopper with said retort including an intermediate section provided with a metering passageway, a feed screw extending to a point of marginal entry Within said retort, and having close fitting engagement within said metering section, said feed screw comprising an axial shaft around which is wound a spiral flight having a progressively increasing pitch at least from the metering section to said retort whereby, as coal is advanced towards said retort, a continuously increasing portage space is provided lbetween the flights of said screw to prevent packing of coal as during low-fire burning conditions within said retort.
4. Stoker' feed apparatus for coal burning systems comprising, in combination with a supply hopper and a combustion retort, a conveyor including a cylindrical conduit extending between said .supply hopper and said combustion retort and having a conduit metering section, and a screw confined in said conduit with a portion underlying said supply hopper and a foremost end marginally extending into said retort, said conveyor screw comprising a screw metering section intermediate said supply hopper and said combustion retort having close tting chambered reception in said conduit metering section, and said screw for a major portion of its length and extending to the retort having a flight having a progressively increasing pitch and a diameter substantially constant within said metering section and continuing constant into said combustion retort whereby coal advanced to said retort is afforded continuously increasing space between the flights of said screw in order to offset packing effects such as result from coking during back-draft conditions in said retort.
5. Stoker feed mechanism comprising, in combination with a supply hopper and a combustion retort, means for preventing coke packing during low-fire burning conditions within said re- 7. tort including a' conveyor comprised of a tubular conduit extending lbetween said hopper and said retort, and a conveyor screw extending from within said hopper through said tubular conduit and having marginal entry into said retort, said screw having a plurality of helical ight portions, the conduit adjacent the hopper having relatively snug t with the ight portions thereat to constitute a metering section, and the conduit between the metering section and said retort having signicant clearance with the flight portion of said screw thereat and constituting a delivery section, said screw being of uniformly increasing pitch in the direction of feeding and continuing to said retort whereby to aiord continuously increasing space accommodations to coal as it is advanced to said retort.
ARTHUR O. DADY.
REFERENCES CITED The following references are of record in the le of this patent:
UNITED STATES PATENTS Number Name Date 390,357 Gathmann Oct. 2, 1888 1,371,497 Lower Mar. 15, 1921 1,379,307 Lower May 24, 1921 1,767,248 Leach June 24, 1930 1,867,573 Leach July 19, 1932 1,939,080 Pickard Dec. 12, 1933 2,094,204 Carter et al Sept. 28, 1937 2,127,018 Young Aug. 16, 1938 2,170,277 Richardson Aug. 22, 1939 2,208,757 Fitch July 23, 1940