US3717937A

US3717937A - Flighting for dehydrator drum

Info

Publication number: US3717937A
Application number: US00135078A
Authority: US
Inventors: S Thompson
Original assignee: S Thompson
Current assignee: Beloit Technologies Inc
Priority date: 1971-04-19
Filing date: 1971-04-19
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27

Abstract

A dehydrator includes a drum having an inlet and an outlet mounted for rotation about its longitudinal axis. Internal flighting for facilitating uniform drying of material passed through the drum includes a plurality of circumferentially spaced vanes which are rigid with the inner surface of the drum. At least a portion of the vanes are provided with laterally extending cleats which break up clumps of material falling off the vanes. Centrally disposed in the drum is another arrangement of flighting which acts as a retainer for catching material which gravitates from the aforementioned vanes. The central flighting comprises a shaft with a plurality of longitudinally extending axially projecting plates having one or more interference structures traversing the plane of a plate at oblique angles. When a pair of structures are utilized they are disposed in either parallel or perpendicular relationship to each other.

Description

United States Patent 91 Thompson a 1 Feb. 27, 1973 [76] lnventor: Stanley P. Thompson, 2718 Osborn Rd, Topeka, Kans. 66614 [22] Filed: April 19, 1971 [21] Appl. No.: 135,078

Related US. Application Data [63] Continuation-impart of Ser. No. 773,188, Nov. 4,

1968, Pat. NO. 3,593,430.

- FOREIGN PATENTS OR APPLICATIONS 362,969 Germany ......34/135 Primary Examiner-Milton Kaufman Assistant Examiner-Theophil W. Strculc Attorney-Bradley and Wharton [57] ABSTRACT A dehydrator includes a drum having an inlet and an outlet mounted for rotation about its longitudinal axis. Internal flighting for facilitating uniform drying of material passed through the drum includes a plurality of circumferentially spaced vanes which are rigid with the inner surface of the drum. At least a portion of the vanes are provided with laterally extending cleats which break up clumps of material falling off the vanes. Centrally disposed in the drum is another arrangement of flighting which acts as a retainer for catching material which gravitates: from the aforementioned vanes. The central flighting comprises a shaft with a plurality of longitudinally extending axially projecting plates having one or more interference structures traversing the plane of a plate at oblique angles. When a pair of structures are utilized they are disposed in either parallel or perpendicular relationship to each other.

9 Claims, 11 Drawing Figures PATENTEI] FEB 2 7 I975 sum 2 0P3 INVENTORL 57an ley P Thompson M 40/42:

4 f farneys FLIGH'IING FOR DEHYDRATOR DRUM This application is a continuation in part of my previously filed application Ser. No. 773,1 88 entitled Crop Dehydrator and filed Nov. 4, 1968 now U.S. Pat. No. 3,593,430. I

An important consideration in the drying of any material isproper distribution of the material to be dried within the drying acne. Distribution is a particular problem in the drying of crops such as alfalfa because of the tendency for the crop to bunch together. This results in inadequate drying of some of the alfalfa and overdrying and even charring of some of the alfalfa.

It is the normal process to dry crops such as alfalfa within elongated rotatable drying drums which continuously rotate to help distribute the crop being dried. It has also been the practice to incorporate flighting around the periphery of the drying drum to further facilitate even distribution. In spite of improvements inthe field of dehydrating apparatus, it is recognized that even distribution of a material to be dried, and particularly crops such as alfalfa which tend to bunch, is a problem which has not been completely solved.

It is therefore an object of the present invention to provide a dehydrator having flights of vanes strategically positioned and shaped to distribute the material as uniformly as possible across the entire cross section of the drum to cause maximum transfer of heat from the hot gases of combustion to the material as the latter travels through the rotating drum.

In carrying out the preceding object it is also another object of the invention to provide vanes configured to permit automatic separation of relatively light or leafy material from heavier or stemmy material so that the lighter particles may be carried out of the drum by the air stream in advance of the heavier particles, which require further time in the drum to achieve a uniformly dried product.

Still another object of the invention is a flighting arrangement for a rotating drying drum which incorporates cleat structure on the vanes of the flighting to facilitate breakup of any bunches of the material being dehydrated.

An important aim of this invention is also to provide a drying drum having flighting arranged both around the periphery of the drum and centrally within the drum to assure breakup of I the material being dehydrated as it falls from the outer peripheral flighting as the drum'rotates.

It is also one of the aims of the present invention to permit uniform pneumatic conveying of a material to be dried through a drying drum by incorporating flighting within the drum to assure that all of the material being dried falls a uniform distance as it gravitates from one side of the drum to the other as the drum rotates.

.As a corollary to the aim of the invention set forth above, one of the objects of the invention is also to maximize the minimum distance which any material falls in gravitating from one side of the drum to the other, yet assuring that this distance is uniform for all of the material.

In the drawings:

' FIG. 1 is a fragmentary, side elevational view on a reduced scale and partially schematic of a dehydrator system incorporating the principles of this invention,

to reveal details of construction;

FIG. 2 is a vertical, cross-sectional view through the dehydrator drum transversely thereof;

FIG. 3 is a fragmentary, vertical cross-sectional view through the drum longitudinally thereof, the flighting appearing in elevation;

FIG. 4 is a schematic vertical cross-sectional view taken longitudinally of the drum with the internal flighting removed to illustrate an alternative form of hanger arrangement for supporting the central shaft upon which a portion of the flighting is mounted;

FIG. 5 is an enlarged, vertical cross-sectional view taken transversely of the drying drum with the central flighting removed and illustrating in further detail the alternative hanger arrangement for securing the central shaft axially of the drum;

FIG. 6 is an enlarged, fragmentary view looking at the end of the central shaft and further illustrating the hanger arrangement;

FIG. 7 is an enlarged, fragmentary side elevational taken transversely of the drying drum and illustrating an alternative form for the central flighting which is disposed about the axially aligned shaft;

FIG. 9 is an enlarged, fragmentary, side elevational view of the sloping T-bar which forms a part of the central flighting, with an alternative position for the trans verse member illustrated in broken lines;

FIG. 10 is an enlarged, fragmentary, side elevational view similar to FIG. 9 and illustrating an optional intermediate cleat shown disposed on the T-bar; and

FIG. 11 is an enlarged,'fragmentary, side elevational view similar to FIGS. 9 and 10 and illustrating an optional second transverse member disposed on the T-bar with an alternative position for this optional member being shown in broken lines.

Referring initially to FIG. 1 of the drawings, the dehydrator of this invention includes an elongated, cylindrical drum 10 having a sidewall 12 and an outlet end wall 14. A furnace 16 communicates with the inlet end of drum 10 and a fan broadly designated 18 is interposed in a material discharge conduit 20 which communicates with the outlet end of drum 10 through a discharge opening 22 best seen in FIG. 7. A material inlet conveyor 24 is provided adjacent furnace 16 at the inlet end of drum 10 for the purpose of introducing the material to be dehydrated into the drum. The latter is mounted for rotation about its longitudinal axis on roller means 26 and is powered by drive means (not shown) to effect rotation of the drum in the direction of the'arrow in FIG. 2.

Furnace 16 includes a blower 28 for providing air to be mixed with the fuel which is introduced into furnace 16 through a fuel line 30. The hot gases of combustion are directed into the interior of drum [0 for drying the material as the latter progresses'through the drum. To

this end, blower or fan 18 serves to draw the gases parts being broken away and revealed in cross section through the drum so that the dried material is drawn toward outlet opening 22 and into conduit 20. It will be understood that conduit 20 may communicate with a cyclone separator or the like (not shown) so that the dehydrated material may be separated from the airstrearn for further processing as: may be desirable or required.

In the drying of hay or other materials it is particularly important that as much surface area of the material particles as possible be exposed to the drying influence of the hot gases passing through the drum. To this end, the interior of drum is provided throughout its length with a flighting adapted to engage the material upon rotation of the drum and to distribute the material as uniformly as possible across the entire hollow cross section of the drum. Manifestly, upon lifting of the material to a given position as the drum rotates, the material is dropped for gravitation toward the bottom of the drum. The material is thereupon again lifted by the flighting for subsequent distribution to permit gravitation of the particles of material through the hot stream of gases and toward the bottom of the drum whereupon the process continues successively until the material is sufficiently dehydrated to be carried to the discharge end of the drum by the hot gases.

The flighting to accomplish the foregoing operation on the material in the drum includes a plurality of vanes secured in annular rows to the inner surface of the cylindrical drum wall 12. Each row of vanes includes a series of differently shaped vanes. Thus, a vane 32 comprises a substantially flat generally planar panel 34 having one end thereof secured as by welding or the like to the inner surface of wall 12. The panel 34 extends radially inwardly of the drum and terminates in a lip 36 at the end of panel 34 remote from wall 12. Thus, the ou- -termost end of each vane travels in a first circular path during rotation of the drum.

The next successive vane 38 in the row proceeding in a counterclockwise direction is spaced circumferentially from vane 32 and comprises a panel 40 having one marginal edge thereof secured as by welding or the like to the inner surface of sidewall 12 similar to the attachment of panel 34 to the drum. It should be noted, however, that the panel 40 is provided with aline of bend 42 in spaced relationship from wall 12 and from the innermost end of the panel. Thus, the panel comprises a portion extending radially inwardly of the drum and a second portion deviates at an angle from the direction of the first portion as illustrated. clearly in FIG. 2. The outermost end of panel 40 is provided with a lip 44 similar to lip 36 of panel 34.

The next successive vane 46 of the series of vanes is similar to vane 38 in that it is provided with a line of bend 48 intermediate its ends. However, the angle of bend of the portions of the vane 46 is such that the vane is straighter than vane 38. Again, vane 46 is provided with a lip 50 at its innermost end. Although the specific arrangement of the different vanes in the series depicted has been found desirable, other arrangements for the vanes will also produce advantageous results.

Referring to FIGS. 2 and 3, it may be seen that each row 52 of vanes may be identical to the adjacent rows but it has been found to be desirable that each successive row longitudinally of the drum be rotated with respect to the preceding row. Thus, a vane 32 is not directly adjacent an identical vane 32 of the adjacent row. Rather, it is adjacent a vane 38 or a vane 46. Similarly, the

vanes

42 and 46 are disposed beside dissimilar vanes of the adjacent row.

Certain of the vanes are provided intermediate their lengths with cleats 54 which may be formed .of key stock material welded to the leading surface of the vane. The cleats 54 serve to retard the slippage of the material along the surface of the vane for a purpose to be more fully explained hereinafter.

A longitudinally extending shaft 56 is disposed axially of drum l0 and is secured to the latter by a plurality of hangers 58. Each hanger 58 includes an arcuate portion 60 having one end thereof secured to the outer surface of shaft 56 by welding or the like and an integral straight portion 62 having its outermost end welded to the inner surface of drum 10. It will be understood that as many hangers 58 are provided as are necessary for securing the shaft in its proper position. Further, the provision of the arcuate portion 60 disposed in a wrapped-around manner adjacent the outer surface of shaft 56 insures that the latter is maintained in its proper axial position even when the hangers 58 and shaft 56 are exposed to the extreme temperatures caused in drum 10 by the hot dehydrating gases provided by furnace 16. It should be noted that the straight portions 62 of hangers 58 extend tangentially of shaft 56 so that heating of the hangers 58 merely causes a rotation of shaft 56 without moving the latter from its axial position.

Shaft 56 mounts a plurality of vanes 64 extending radially outwardly from the shaft. The vanes 64 are connected with brace members 66 as illustrated best in FIG. 2. Further. each vane 64 is provided with a cleat 68 on its leading and its trailing surface to reduce the slippage of material on the vane. Shaft 56 rotates with the drum 10 thereby rotating the vanes 64.

Referring now to FIGS. 4-7 where the alternative hanger arrangement for the shaft 56 is illustrated, it is seen that the shaft is again held by a plurality of hangers 158. Each hanger 158 includes an arcuate portion 160 which at least partially surrounds the shaft 56, and a pair of longitudinally extending straight portions 162 and 162' which are integral with and extend from the opposite ends of the arcuate portion 160. The outermost ends of the straight portions 162 and 162' are rigidly secured to the inner surface of the sidewall 12 by welding or other appropriate means. It may also be desirable'to spotweld the arcuate portion 160 to the shaft 56. It is desirable to provide three of the hangers 158 at each supporting location of the shaft 56 with the hangers being disposed in a complemental arrangement as best illustrated in FIG. 6. In this manner, the arcuate portions 160 essentially completely surround the shaft 56, and as is clear from viewing FIG. 7, the shaft is precluded from moving in any direction away from the center of the drum 10.

It will also be noted from viewing FIG. 5, that each of the

vanes

32, 38 and 46 is provided with a cleat 54 as previously described for the embodiment of FIGS. l-3. In this alternative form, however, instead of utilizing the cleats 54 only on selected vanes, each of the vanes is provided with the intermediate cleat 54. It has also been found desirable in certain instances to provide a gusset plate 70 between each of the

vanes

32, 38 and 46 and the drum wall 12 to strengthen the vanes and reduce the possibility of breakage.

In FIGS. 8 and 9 an alternative central flighting arrangement has been illustrated and designated generally by the numeral 72. The central flighting 72 comprises a plurality of longitudinally extending, radially projecting vanes or plates 74 which are secured to theshaft 56 at one end by fluting, welding or the like and are further supported by a plurality of brace bars 76 which extend between successive plates 74 and are welded to the latter. The other end of each plate 74 extends outwardly into the drum for travel in a second circular path spaced circumferentially inwardly from the path of travel of the ends of the vanes secured to the inner surface of the drum. It is to be understood that each of the plates 74 which is visible in FIG. 8 is the first in a longitudinally extending row of the plates. Thus there are a plurality of the plates 74 disposed in end-to-end, closely spaced relationship in rows which extend longitudinally of the shaft 56. Each of the plates 74 is provided with a plurality of interference structures such as cross members 78 disposed at the outermost ends of the plates 74 and secured thereto by welding or the like, with gusset plates 80 providing structural support. It is to be understood that while only one of the cross members 78 is illustrated at the end of each of the plates 74 in FIG. 8, a number, of the members 78 would normally be disposed in closely spaced relationship at intervals along the entire length of each of the plates. Similarly, a number of cross braces 76 are normally provided at spaced intervals along the length of the shaft 56. The cross members 78 .are generally planar, longitudinally extending structures of any desired cross section. Thus, each of the members 78 cooperates with the plate 74 to form a T-bar which is highly instrumental in facilitating aneven distribution of a crop such as alfalfa while preventing bunching of the alfalfa as it is distributed in the drum 10. Each of the members 78 is provided with laterally extending

cleat projections

82 and 84 at its respective ends. As illustrated in FIG. 10, it is sometimes desirable to provide a third cleat projection 86 which extends laterally of the member 78 intermediate the previously two mentioned

cleat projections

82 and 84.

As clearly shown in FIG. 9, the member 78 is disposed to transverse the plane of the plate 74 to which it is attached at an oblique angle. While reasonable variations in the angle can be tolerated, it has been found that an angle of approximately 45 is particularly advantageous for optimum results in facilitating even distribution of a material to be dehydrated. As indicated by the phantom illustration in FIG. 9, this 45 angle between the member 78 and the plate 74 can be formed by sloping the member 78 in either one of two directions. While various positions intermediate the two positions shown in FIG. 9 for the member 78 are acceptable, in general an angle of from 25 to 45 between the member and a corresponding plate 74 is desirable.

Referring now to FIG. 11 wherein an alternative arrangement for the central flighting 72 is illustrated, it is seen that in addition to the interference structure formed by the member 78, a second interference structure which is formedby a pair ofaligned cross members 88 and 90 is disposed in spaced relationship to the member 78 inwardly therefrom along the plate 74. Although the members 88 and 90 are shown in aligned relationship in FIG. 11, it is to be understood that while this is the preferred arrangement, the members can be disposed at other locations along the plate 74. Each of the members 88 and 90 is of generally the same configuration as the cross members 78, although slightly shorter in length, and is rigidly secured to the plate 74 in a manner similar to the member 78. Each of the members 88 and 90 is provided with a laterally extending cleat projection 92 at its end which projections generally complement the

projections

82 and 84 on the members 78. The common plane of the members 88 and 90 transverses the plane of the plate 74 at an oblique angle as previously described for the member 78. The angle between each of the members 88 and 90 and the corresponding plate 74 is againpreferably 45, and in no case should it be less than 45, although this angle may be formed with the members 88 and 90 disposed either parallel or perpendicular to the member 78 as shown by the phantom illustration in FIG. 11.

In operation, fuel is burned in the furnace l6 and the hot combustion gases are directed into the drum by blower 28. The material to be dried is conveyed to the interior of the drum by conveyor 24, and the drum 10 is rotated on its longitudinal axis to distribute the material throughout the interior of the drum. The fan or blower 18 is also operated to insure a sufficient flow of combustion gases and air longitudinally of the drum to pneumatically convey the material being, dried.

The rotating drum constantly moves the vanes in a counterclockwise direction as viewed in FIG. 2 so that the material in the drum is picked up by the vanes as they rotate along their lowermost positions within the drum. The material is retained on the vanes as the same is lifted thereby until the vane reaches a position along its path of travel where the vane drops the material for gravitation across the drum toward the bottom of the drum. The different shapes of the vanes insure that the material release point for the various vanes is reached at different positions of rotation of the drum. Thus, a substantially uniform curtain of material in relatively small clumps is alternatively picked up and then released by the successive vanes for gravitation across the drum. It has been found that clumps of material being dried have a tendency to slide toward the edges 7 of the

vanes

32, 38 and 46, and in some instances a clump of material will actually pivot over the upwardly projecting

lips

36, 44 and 50 respectively to continue as a clump as it gravitates across the drum. For this reason, the cleats 54 are extremely important in assuring a breakup of any bunches of material before the lip of the respective vane is reached. The result is that the material tends to dribble downwardly from the terminal edge of the vane and clumping is largely eliminated.

Since the conveying media comprised of combustion gases and air from the atmosphere is regulated so as to be incapable of supporting the material being dried against gravitation until a portion of the water has been removed from it, a portion of the material gravitates from the

vanes

32, 38 and 46 toward the center of the drying drum.

The

central vanes

64 or 74, however, prevent the material from gravitating to the bottom of the drum by the corresponding

vanes

32, 38 and 46. The shortened paths of gravitation of the material insures that the gas flow through the drum does not have sufficient time to act on the material while falling to move the material through the drum at too fast a rate for proper drying.

The utilization of the central vanes 74 with members 78 disposed transversely thereof has been found to be particularly useful in facilitating even distribution of material throughout the drum 10. It will be appreciated that the cross members 78 at the ends of the vanes 74 provide an extension of the vanes in the direction of the

peripheral vanes

32, 38 and 46, thereby reducing the possibility of any of the material falling past the vanes 74 without being caught. At the same time, the members 78 interfere substantially with the dumping of material from the vanes 74 as the latter rotate through their circuitous paths of travel, thus further breaking up any clumps of material and achieving the same dribbling action in the lower half of the drum 10 as is achieved in the upper half by the

vanes

32, 38 and 46.

The incorporation of the optional intermediate cleats 86 and the optional interference structure comprised of cross members 88 and 90 depends largely on the nature of the material being dried and the need for further breakup and distribution of the material.

The

cleats

54, 68, 82-86, and 90-92 on the respective vanes further tend to dribble the material from the vanes rather than releasing the same in a clump when the vane reaches a position for discharging material. This also serves to enhance the distribution of the material uniformly across the drum for maximum exposure of the material to the hot gases of combustion for dehydrating the material.

Not to be overlooked is the effect of the rows of vanes which are disposed in series and in offset relationship longitudinally of the drum. This arrangement for the vanes which are secured to the inner surface of the cylindrical sidewall 12 retards against the material from bunching as the material moves longitudinally through the drum.

From the foregoing description, it is apparent that a method of dehydrating a crop is presented which includes providing a drying zone at a sufficiently elevated temperature to effect removal of water from the crop. The drying zone is confined to a longitudinally extending cylindrical area and drying gases are directed longitudinally through the zone. Next, the crop to be dried is pneumatically conveyed through the drying zone with the conveying media being regulated so as to be incapable of supporting the crop against gravitation until a portion of the water has been removed therefrom This results in a portion of the crop gravitating to the outer periphery of the drying zone. This portion of the material is then moved toward the center of the zone by elevating the same and then allowing it to gravitate through the conveying media toward the center of the zone. Before reaching the center, however, the portion is caught and held for a period of time during which it is rotated within the drying zone to further effect removal of water therefrom. The previously caught material is then dumped at a point circumferentially spaced from the point where it was caught to redirect it through the conveying media to the outer periphery of the zone.

The steps of moving a portion of the material through the conveying media toward the center of the zone, catching the portion as it travels toward the center, holding the previously caught material and then redirecting it toward the outer periphery of the zone. are continuously repeated until a sufficient amount of water has been removed from the material to allow the conveying media to support the same and remove the material from the drying zone.

By the present method even distribution of the material being dried is permitted to a degree heretofore not possible, and the detrimental bunching of materials such as alfalfa is largely eliminated. It is inherent in the method that the heavier stemmy materials commonly found in crops such as alfalfa and which require significantly more drying time than the relatively light leafy materials also present, are held within the drier for the additional time required, while the lighter material is removed through the conveying airstream. This greatly reduces the danger of the lighter leafy materials being charred from overdrying and at the same time assures that the heavier materials will be adequately dried.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a dehydrator including an elongated drum having a material inlet and an outlet, means mounting the drum for rotation about its longitudinal axis, and furnace means for providing hot gases of combustion to the drum, means in the drum for distributing the material across the drum comprising:

a plurality of generally planar circumferentially spaced vanes extending around the inner surface of the drum,

one end of each vane being secured to said inner surface, the other end projecting inwardly therefrom, said other end traveling in a first circular path during rotation of the drum; lip carried by each vane respectively at the end thereof remote from the inner surface of the drum, each of said lips projecting at an angle from the plane of the corresponding vane to retard slippage of material from the vane until the latter reaches a material discharging position during rotation of the drum; first cleat means carried by at least a portion of said vanes, said cleat means being secured to the surface of a respective vane in generally perpendicular relationship to the latter and disposed intermediate the drum and the lip; plurality of axially and radially disposed longitudinally extending generally planar retainer plates positioned in spaced relationship to each other and to said vanes for catching material gravitating from said vanes, each of said plates having one end extending outwardly into said drums, said one end of said plate traveling in a second circular path spaced circumferentially inwardly from said first path; generally planar longitudinally extending interference structure secured to each of said plates and extending transversely on either side of the latter to provide a drying area for said material prior to the material reaching the area between adjacent plates; and second cleat means disposed on said structure and extending longitudinally of the latter in generally perpendicular relationship to the plane of the ship to the first-mentioned structure and traversing the plane of said one plate at an oblique angle.

6. The invention of claim 5, wherein said second structure is disposed in parallel relationship to the firstmentioned structure.

7. The invention of claim 5, wherein said second structure is disposed in perpendicular relationship to the first-mentioned structure.

8. The invention of claim 1, said retainer means comprising a shaft extending axially of the drum and including a plurality of elongated supports coupling said shaft with the drum, each support having one end secured to the shaft, an arcuate stretch adjacent said one end extending at least partially around the shaft, and a portion integral with said stretch spanning the distance across said drum, said portion being rigidly secured to said drum.

9. The invention of claim 8, wherein each of said supports includes a second portion integral with said stretch at the end of the latter opposite the first-mentioned portion and spanning the: distance across said drum, said second portion being rigidly secured to said drum.

Claims

1. In a dehydrator including an elongated drum having a material inlet and an outlet, means mounting the drum for rotation about its longitudinal axis, and furnace means for providing hot gases of combustion to the drum, means in the drum for distributing the material across the drum comprising: a plurality of generally planar circumferentially spaced vanes extending around the inner surface of the drum, one end of each vane being secured to said inner surface, the other end projecting inwardly therefrom, said other end traveling in a first circular path during rotation of the drum; a lip carried by each vane respectively at the end thereof remote from the inner surface of the drum, each of said lips projecting at an angle from the plane of the corresponding vane to retard slippage of material from the vane until the latter reaches a material discharging position during rotation of the drum; first cleat means carried by at least a portion of said vanes, said cleat means being secured to the surface of a respective vane in generally perpendicular relationship to the latter and disposed intermediate the drum and the lip; a plurality of axially and radially disposed longitudinally extending generally planar retainer plates positioned in spaced relationship to each other and to said vanes for Catching material gravitating from said vanes, each of said plates having one end extending outwardly into said drums, said one end of said plate traveling in a second circular path spaced circumferentially inwardly from said first path; generally planar longitudinally extending interference structure secured to each of said plates and extending transversely on either side of the latter to provide a drying area for said material prior to the material reaching the area between adjacent plates; and second cleat means disposed on said structure and extending longitudinally of the latter in generally perpendicular relationship to the plane of the structure to retard slippage of material from the structure during rotation of the drum.

2. The invention of claim 1, wherein said structure forms an angle from about 25* to 45* with said one plate.

3. The invention of claim 2, wherein said second cleat means comprises first and second cleat projections at opposite ends of said structure.

4. The invention of claim 3, and a third cleat projection intermediate said first and second projections.

5. The invention of claim 1, and second interference structure secured to said one plate in spaced relationship to the first-mentioned structure and traversing the plane of said one plate at an oblique angle.

6. The invention of claim 5, wherein said second structure is disposed in parallel relationship to the first-mentioned structure.

9. The invention of claim 8, wherein each of said supports includes a second portion integral with said stretch at the end of the latter opposite the first-mentioned portion and spanning the distance across said drum, said second portion being rigidly secured to said drum.