MECHANICALLY RAKED BAR SCREEN WITH CONVEYOR SYSTEM HAVING ELASTOMERIC RAKES

Abstract: A bar screen (10) conveyor system (20) for collecting debris or the like in a stream of liquid (8), including collector rakes (40) for attachment to the conveyor which are made of a tough, abrasion-resistant and corrosion-resistant elastomer. The preferred elastomers for use in rake fabrication are polyurethane elastomers. The conveyor systems which include the elastomeric rakes have greater durability and use life without problems than the heretofore conveyor systems utilizing metal rakes.

Description: MECHANICALLY RAKED BAR SCREEN WITH CONVEYOR SYSTEM HAVING ELASTOMERIC RAKES This application is a continuation-in-part of United States Application Serial No. 06/560,395 filed December 12, 1983 entitled "Mechanically Raked Bar Screen With Conveyor System Having Elastomeric Rakes," now United States Patent No. 4,521,306 issued June 4, 1985. FIELD OF INVENTION AND BACKGROUND The present invention relates to a conveyor system for removing debris, trash, and similar material from a moving body of water such as in a sewage treatment plant. More par¬ ticularly, the invention is directed to a new and improved rake member for installation on a conveyor, which rake is con¬ structed of a tough, highly abrasion-resistant and corrosion- resistant elastomer. Mechanically raked bar screens are used in a variety of circumstances, for example in the treatment of sewage to remove suspended solids from a flow of liquid. Such screens comprise a series of parallel grating bars which extend across the channel, duct, or other opening carrying the liquid, the bars being preferably upwardly inclined in a vertical plane. The teeth of rake members carried by an endless conveyor pro¬ ject through the grating bars, and as the endless belt is con¬ tinuously rotated debris or the like is cleared from the face of the bar screen by the rake teeth. In the case of a back- cleaning rake, the rake teeth are long and pass through the bar screen. The rake teeth which extend through the bar screen carry the debris. The backing portion of the rake which carries the teeth rides against the grating bars as the rake is carried upward to deposit the collected debris or the like at the top of the conveyor. In the case of a front- cleaning rake, the rake teeth are short, usually less than the depth of the bar, and extend into the bars of the screen from the front. The debris is carried by the backing portion of the rake in front of the bar screen. The configuration of the bar screen and the conveyor system varies. For example, the bars may be aligned either vertically or obliquely to the ver¬ tical or they may be curved, in which case they will generally be arranged with their concave sides facing upstream of the flow of liquid to be screened. Regardless of the nature of the construction, however, the teeth of the rake must pass between and through the bars in close-fitting relation in order to remove all of the debris, including finely divided debris. In the past construction of the mechanically raked bar screens, the bars have been constructed of steel rods, spaced apart and welded; and the rake has been similarly con¬ structed of a metal such as steel. Heretofore it was believed essential that the rakes, including the teeth of the rakes, be constructed of steel or other heavy metal in order to ensure the necessary durability and carrying strength. The construc- tion of the rakes from metal was with the recognition of the problems which occur when the teeth of the rakes do not align exactly so as to pass between the spaced parallel bars, which leads to a jamming of the teeth into and against the bars. Since the jamming or damage usually occurs at the point of alignment of the teeth and bars which is below the surface of the stream of liquid being treated, resolution of the jamming problem necessitates closing down the operation and, more often than not, the emptying of the liquid being treated from the channel to permit replacement or repair of the rakes. Further, the metal rakes, because of the corrosive nature of the effluent carried, particularly in sewage treatment plants and the riding of the backing member of the rake against the bars, have only a limited life. PRIMARY OBJECT AND GENERAL DESCRIPTION OF INVENTION Accordingly, it is a primary object of the present invention to provide a conveyor system for removing debris, trash, and similar materials from a moving body of water, for example in a sewage treatment plant, wherein the rake members of the system are constructed of a tough, highly abrasion- resistant and and corrosion-resistant elastomer. The elasto¬ mer must have the necessary strength so that the teeth will carry the collected debris or the like, but yet must be suf- ficiently flexible so that the teeth will deflect in the event the teeth do not align exactly with the spaced parallel bars. Of primary consideration and concern, therefore, is to provide an elastomer which is strong enough to lift out and carry the debris or the like from the liquid stream and which is flexi- ble enough to allow deflection when in jamming engagement with the metal bar screens. Elastomers which have been found suit¬ able are those having a durometer reading of from about 80 Shore A to about 85 Shore D, and which will have at least about 75% elongation before failure. Preferably the elastomer will have a durometer reading of 95 Shore A to 60 Shore D. The preferred elastomers are the castable polyurethane elastomers. However, certain castable nylon block copolymers and certain high molecular weight polyolefins also have the essential characteristics. Heretofore it was not considered possible to make the rakes from a material other than metal, and the abil¬ ity to fabricate a rake for use with a conveyor system of the type described herein is surprising. THE DRAWING AND PREFERRED EMBODIMENTS The invention will be described with reference to the drawing which illustrates the presently preferred embodiment of the invention. In the drawing, FIGURE 1 is an elevational view, partly in section and with certain elements omitted, showing a conveyor system installed in a sewage treatment channel; FIGURE 2 is a perspective view of the rake attached to the chain drives; FIGURE 3 is an enlarged perspective view of one end of a section of the conveyor system partly broken away; FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 1; FIGURE 5 is a view showing how the rake is attached to and removed from the rake carrier bar; FIGURE 6 is a side elevational view of a conveyor system utilizing a modified back-cleaning rake of the type shown in FIGURES 1-5; FIGURE 7 is a perspective view of the rake shown in the embodiment of FIGURE 6; FIGURE 8 is a sectional view taken along line 8-8 of FIGURE 6; FIGURE 9 is a perspective view of another modified back-cleaning rake of the type disclosed in FIGURES 1-5; FIGURE 10 is still another modification of the back- cleaning rake of the type used in FIGURES 1-5; FIGURE 10A is still another modification of the back- cleaning rake of the type used in FIGURES 6-8; FIGURE 11 is a side elevational view of a further back-cleaning rake embodiment utilizing a combination of rake sections, one such section having a cam; FIGURE 12 is a view taken along line 12-12 of FIGURE 11; FIGURE 13 is a perspective view of a first of the rake sections utilized in FIGURES 11 and 12; FIGURE 14 is a perspective view of a second of the rake sections used in the rake embodiment of FIGURES 11 and 12; FIGURE 15 is a side elevational view of a further embodiment utilizing a front-cleaning rake; FIGURE 16 is a sectional view taken along line 16-16 of FIGURE 15; FIGURE 17 is a sectional view taken along line 17-17 of FIGURE 16; FIGURE 18 is a side elevational view of a further embodiment utilizing a bucket-type front-cleaning rake; FIGURE 19 is a sectional view taken along line 19-19 of FIGURE 18, and FIGURE 20 is a sectional view taken along line 20-20 of FIGURE 19. Referring first primarily to FIGURES 1, 2 and 4 of the drawing, there is shown a vertically extending bar screen 10 comprising an array of parallel bars 12 anchored at a first lower end 14 in the base or floor 16 of a channel 8 carrying a liquid such as in a sewage treatment plant. The bar screen will be stabilized at its second or upper end, not shown. A conveyor system 20 comprising a pair of endless sprocket chain 22 carried by suitably mounted upper and lower sprocket wheels 26 and 28 are vertically positioned in the liquid-carrying channel adjacent to and downstream from the bar screen. The sprocket wheels are driven by a motor attached to a drive shaft of the conveyor system, not shown. The sprocket chains carry a plurality of transversely extending rake members 40 as shown in FIGURE 1. As best shown in FIGURES 2 and 3, the rakes 40 are attached to an angle bar 50 and bolted with bolts 52. Angle bar 50, in turn, is attached to the sprocket chain through angle bar members 54. The angle bar member 50, as shown in FIGURE 2, extends transversely the full distance be¬ tween sprocket chains 22. As best shown in FIGURES 2, 3, and 5, the elastomeric rake 40 comprises teeth 42 integrally molded with a backing member 44 for attachment of the rake to angle bar rake carrier 50. The backing member includes a vertically extending leg 46 and a horizontally extending member 48. Member 48 terminates in an ear 49 for receiving the edge of the angle bar 50. Ear 49 also, as will be described later, provides a wear surface. in the preferred embodiment the rake is made in section, as shown in FIGURE 2, each section preferably being from 15 to 18 inches. Making the rake in sections simplifies repair in the event a single tooth of the rake is broken or damaged. The rakes, as previously stated, are attached to carrier bar 50 with bolts 52. As best shown in FIGURE 3, the teeth of the rake are spaced to provide close fitting engagement with the parallel bars of the bar screen. It is essential to have close fitting engagement in order to ensure complete removal of debris in the liquid medium, including finely divided debris, or the like. Heretofore, with metal rakes, as a result of the close fitting engagement of the bars with the rake teeth, there was a high degree of wear at the point where the bars engage the teeth and ride against the backing member of the rake. Addi- tionally, because of the close fit of the teeth between the bar elements, any misalignment could cause a binding or jam¬ ming of the rake against the bar, leading to down time. With the present elastomer rakes, the rake teeth, while having the necessary carrying strength, have a sufficient degree of flex- ibility to compensate for minor misalignments. To further compensate for misalignment, as best shown in FIGURE 5, the leading ends of the teeth are tapered from the bottom to a flat top in the vertical direction and are also tapered, ex¬ tending in the horizontal direction. As shown in FIGURE 5, in attaching and removing the teeth the ear 49 of the backing portion of the rake is fitted around the metal angle bar 50. The elasto eric material per¬ mits sufficient flexing to allow the rake to be snapped into a tight-fitting relation with the angle bar. Accordingly, the rake is primarily supported on the angle bar by its seating on the angle bar with the ear taking the primary stress. The bolts merely serve to hold the rake in place. Since little or no support is provided by the bolts, there is no problem with respect to tearing or failure of the backing member at the • bolt holes. As shown in the embodiment of FIGURE 1, the bar screen and the conveyor positioned adjacent to the bar screen are in vertical relation. In operation, the rake members en- gage the bar screen at the lower end of the bar screen, with the rake teeth passing between the spaced bars. With the up¬ ward movement of the rake, the rakes will collect any debris which is in contact with the bar screen. The debris is car¬ ried upward, passes over the top of the sprocket wheels of the conveyor and removed. To prevent having debris fall back into the channel, a sheet metal shield member 25 is positioned at the top of the conveyor. The wear surface of ear 49 on backing member 44, as shown in FIGURE 1, rides on the shield as the rake passes around the sprocket wheel, cleaning and keeping the shield free of debris. The elastomer being flex¬ ible will not bind on the shield, but will provide a continu¬ ous cleaning of the shield. Being of tough polymer, the backing member has excellent wear characteristics. The debris is removed from the rakes at the top as the rakes start their downward movement. As shown in FIGURE 1, the bar screen and the conveyor are in a vertical position. As will be apparent, however, the bar screen and conveyor can be placed at an obli¬ que angle. The placing of the bar screen and conveyor at an angle can facilitate removal of the debris particularly in instances where the channel or duct being cleaned has only limited vertical height. In one preferred embodiment of a bar screen/conveyor system in a sewage treatment plant, the bar screen and con- veyor system will have a height of approximately 35 to 60 feet. The sprocket wheels are approximately three feet in diameter and the rakes are positioned on the conveyor drive chains at approximately every ten feet. The conveyor moves at a speed of approximately one to two feet per minute. The rakes which are approximately ten feet long are constructed in approximately seven separate sections as shown in FIGURE 2. The teeth of the rack are approximately four to ten inches extending in the horizontal direction and have a height of approximately one and one-half to three inches. The spacing between the teeth and the thickness of the teeth is determined by the thickness of the grate bars in the bar screen and the distance between the bars. The bars are normally rectangular from three-eighths to three-quarters inch in width, with the spacing between the bars being from one-half to one and three- quarters inches wide, depending partially upon the degree of fineness of the debris to be collected. The depth of the bars is commonly from one and one-half inches to two and one-half inches. The bars need not be rectangular, but can be round. The vertical leg of the backing member is approximately four to eight inches, with the horizontally extending member being approximately three to six inches. The ear is indented ap¬ proximately one-half to three-quarters inch. A rake is cast molded from an elastomer which, when cured, will have a hardness measured on the durometer scale of from about 80 Shore A to 85 Shore D, and preferably from about 95 Shore A to 60 Shore D. The elastomer should have an elon¬ gation before failure of at least about 20%, and preferably from about 75% to 300%, which will provide the essential de- gree of flexibility. In a preferred embodiment, 100 parts ADIPRENE L-167 which is a diisocyanate based polyether ure- thane prepolymer is mixed or blended with nineteen parts of 4,4'-methylene-bis(2-chloroaniline) curing agent. ADIPRENE L-167 is marketed by the duPont Company. The blend of pre¬ polymer and curing agent is cast into an aluminum mold and heated for twenty minutes at a temperature of about 212°F. The rake is then removed from the mold for a final curing of approximately three hours at 212°F. The resultant molded rake has the essential hardness and flexibility as well as excep¬ tional resistance to abrasion and the corrosive influences of the environment. Other elastomers which can be used are the ultra-high molecular weight polyolefins; the nylon block copolymers such as the copolymer supplied under the tradename NYRIM by the Monsanto Chemical Company; thermoplastic urethanes; copoly- ether-esters such as polytetramethylene ether glycol-phthalic acid esters such as duPont's HYTREL; polycarbonates such as General Electric Company's LEXAN; polyacetals such as duPont's DELRIN, or certain hard rubbers. It is preferable that the elastomer be castable. However, the elastomer can be machined, or fabricated, or injection or compression molded. It is es¬ sential that the elastomer contain the characteristics as above defined. "Elastomer," as the term is used herein, includes the elastoplastics such as the above referred to nylon and poly¬ olefins. Additionally, the elastomer can be reinforced with glass fibers or other reinforcing fibers or fillers. In the embodiment shown in FIGURES 1 - 5, the rake can be replaced, depending upon the design of the machine, with other back-cleaning rakes of alternate design as shown in FIGURES 6-14. Alternatively, the conveyor system can be modi- fied and the rakes replaced with front-cleaning rakes as shown in FIGURES 15-20. In FIGURE 6 there is shown an elevational view of a conveyor utilizing a modified back-cleaning rake. As shown, the teeth 42 of elastomeric rake 40 extend through bars 12 of the bar screen 10 made up of an array of parallel bars 12 anchored as shown in FIGURE 1. As the rake teeth pass upward in the direction of movement of the rake, the teeth of the rake collect the debris. As shown in FIGURE 7 which is a perspective view of the rake shown in FIGURES 6 and 8, the rake 40 is attached to angle bar 50 with bolts 52. Angle bar 50 is, in turn, attached to the sprocket chain 22 through angle bar members 54. Rake 40 differs from the rake shown in FIGURE 1 primarily in the configuration of the teeth 42 and in back member 44. In this modified embodiment the backing mem¬ ber includes a vertical extension 60. Additionally, the teeth 42 have a different shape. The embodiment shown in FIGURE 9 is an alternative modification of the design of the rake member shown in FIGURES 1-5. In this modification the teeth 42 have a different shape and the rake includes gussets 61 for added strength. FIGURE 10 differs from the design of the rake shown in FIGURES 1-5 again in the design of the backing member 42. In the design shown in the rake of FIGURE 10, horizontally extending member 48 extends beyond the U-member 49. This embodiment also includes gussets 61. FIGURE 10A differs from the rake member shown in FIGURE 10 in that the leg of the U-member is omitted. FIGURE 11 is a side elevational view of a conveyor system illustrating a further back-cleaning rake embodiment utilizing a combination of the rake sections shown in FIGURES lS and 14. Thus, as best shown in FIGURES 11, 12 and 13, a first of the rake sections includes cam member 62 which, in view of the arrangement of the sections, are spaced periodi¬ cally along the length of the rake. These cam members assist in the stripping of trash from the teeth of the rake. The second section of the rake, as best shown in FIGURES 12 and 14, is a substantially flat section having a backing member 44 wherein horizontally extending member 48 includes a vertically extending member 64 forming a notch 66 which will fit over the end of angle member 50. FIGURE 15 is a side elevational view of a modified conveyor system utilizing a front-cleaning rake. As shown, the sprocket 28 and chain mechanism 22 carrying the rake member 40 is positioned in front of the bar screen 10. As such, the teeth 42 of the rake 40 are short, extending only substantially through the bars 12 of bar screen .10. Trash is collected'by the rake on the front side of the screen and carried out of the stream as before. As also shown, in this embodiment the carrying surface 64 of the rake is flat. FIGURES 16 and 17 further show the front-cleaning rake of FIGURE 15. As shown, the rake is attached to angle member 50 of the conveyor system by bolts 52. The relative length of the teeth of the front-cleaning rake is also illustrated. FIGURE 18 is a side elevational view of a conveyor system carrying still a further embodiment of a front-cleaning rake. As shown in FIGURES 19 and 20, the rake member includes teeth 42 which pass between bar screen members 12 to effec¬ tively clean the bar screen of debris. The buckets 66, up- stream of the rake, scoop up sludge and silt which collect on the floor of the channel. Excess water flows from bucket 66 through holes 68 in the bottom of the buckets of the rake. As will be apparent, while there is shown a number of different embodiments of the elastomeric rake of the type according to the present invention, other modifications are also possible. Advantages of the elastomeric rakes over steel rakes for use on a conveyor system of the type defined include the following: (1) Being flexible, the rakes have some give and, accordingly, even if the rake teeth do not pro- perly mesh with the bars of the bar screen they will not jam or damage the bar screens. (2) The polyurethane and other elastomers are highly resistant to abrasion and, accordingly, have excellent wear characteristics including when the rake is used as a scraper as it passes around the sprocket wheel and in contact with a debris-collecting shield. The elastomer rakes, having a degree of lubricating characteristics, are less noisy when in contact with the metal shield, and require less power consumption. (3) Being flexible, the rakes can be convenient¬ ly replaced on a metal carrier bar by snapping the rake into position on the bar. This is not possible with a metal rake. (4) The lighter weight of the elastomer seg- ments, together with the lower strength requirements of the angle bar, creates a significantly lighter weight rake assembly. This will reduce the stress in operation which, in turn, will allow (a) lower power drive requirements; (b) lighter weight chains; (c) re- duced strength requirements throughout the machine, and (d) lesser power requirements. Overall structural and operating costs are significantly reduced. Furthermore, although the improved elastomeric rakes have been described primarily with respect to a sewage treatment system, the bar screen conveyor system utilizing the improved rakes can be used in all applications requiring a high volume of water taken from a source which contains debris. Such appli- cations include in (1) power plant cooling water systems; (2) pumping station inlets; (3) chemical plant cooling water; (4) pottable water treatment plants; (6) papermaking mills, including wood pulping processes, and (6) steel mills. As will be apparent to one skilled in the art, var- ious other modifications can be made within the scope of the aforesaid description. Such modifications being within the ability of one skilled in the art form a part of the present invention and are embraced by the appended claims.

Claims: C L A I M S 1. In a bar screen/conveyor system comprising a screen bar, a continuous conveyor carrying rakes for meshing with said screen bar and carrying debris collected at the upstream side of said screen bar when positioned in a stream of liquid, the improvement wherein said rakes are fabricated from an elastomeric material, said elastomeric material having a hardness measured on the durometer scale of 80 Shore A through 85 Shore D, and an elongation of at least 75% before failure. 2. The bar screen/conveyor system of claim 1 wherein said elastomeric material has a hardness measured on the duro¬ meter scale of 95 Shore A through 60 Shore D. 3. The bar screen/conveyor system of claim 2 wherein the elastomer has an elongation before failure of from about 150 - 300%. 4. The screen bar/conveyor system of claim 1 wherein said elastomeric material is a castable polyurethane. 5. The screen bar/conveyor system of claim 1 wherein said elastomeric material is a castable nylon block copolymer. 6. The screen bar/conveyor system of claim 1 wherein said elastomeric material is an ultra-high molecular weight polyolefin. 7. An elastomeric rake for attachment to a conveyor system for utilization in cleaning a bar screen comprising horizontally extending teeth and a backing member for attach¬ ment of said rake to a conveyor in a conveyor system, said elastomeric material having a hardness measured on the duro¬ meter scale of 80 Shore A through 85 Shore D, and an elonga¬ tion of at least 75% before failure. 8. The elastomeric rake of claim 7 wherein said elastomeric material has a hardness measured on the durometer scale of 95 Shore A through 60 Shore D. 9. The elastomeric rake of claim 8 wherein the elastomer has an elongation before failure of from about 150 - 300%. 10. The elastomeric rake of claim 7 wherein the elastomeric material is a castable polyurethane. 11. The elastomeric rake of claim 7 wherein the elastomeric material is a castable nylon block copolymer. 12. The elastomeric rake of claim 7 wherein the elastomeric material is an ultra-high molecular weight polyolefin. 13. The elastomeric rake of claim 7 wherein said backing member includes a vertically extending leg and a hori¬ zontally extending leg, said horizontally extending leg ter¬ minating in a substantially U-shaped configuration, the legs of said U being constructed and arranged for mating with a member on a conveyor system.

Inventors: DAY JOHN T, DAY, JOHN, T.
Applicants: RUBBER MILLERS INC, RUBBER MILLERS, INC.
Application year: 1985
Main classification: B01D35
IPC codes: B01D29, E02B8