Abstract:
An improved blade for a scraper assembly used with the head pulley of a conveyor system. The improved conveyor blade has a metal base adapted to telescopically engage a rectangular plate projecting radially from a support shaft mounted for rotation about a rotary axis parallel to the head pulley axis, the metal base having sheet-like outer walls disposed in spaced parallel relation from a receptacle for the elastomeric body of the blade. The blade has an under surface confronting the head pulley which projects past the plane of the innermost wall of the metallic base and terminates in a tip engaging the belt on the head pulley.

Description:
This Appln is a cont-in-part of PCT/US97/15082 filed Aug. 20, 1997 and also claims the benefit of U.S. Provisional No. 60/024,928 filed Aug. 30, 1996. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to conveyor systems and is particularly applicable to a novel scraper adapted to bear against a head pulley to scrape the material from the belt as it travels around the head pulley. The invention has particular application to conveyors for conveying wet materials which tend to adhere to the conveyor belt. 
     BACKGROUND OF THE INVENTION 
     Conventional belt conveyors typically have a plurality of scraper assemblies disposed to remove deposits adhering to the surface of the conveyor belt. For example, it is common to provide a scraper assembly at or near the head pulley to clean the belt as the belt begins its return travel. Additionally, trailing arm scrapers are commonly located along the length of the belt in between the head and tail pulleys to provide additional cleaning. 
     A common type of scraper blade assembly comprises a plurality of mounted scraper blades extending across the transverse axis of the conveyor belt. The blades are mounted on support arms which are fixed to and extend from a transverse rotatable support shaft. Rotation of the transverse support shaft moves the scraper blades into and out of contact with the conveyor belt. Applying a torque to the support shaft increases the contacting force of the scraper blades against the belt. 
     During installation and use of the scraper blade assemblies, the belt scraper blades wear down. 
     A high durometer polyurethane scraping blade will not wear as quickly as a lower durometer blade, but the higher durometer blade will impart greater stress to the conveyor belt and it is more likely to damage poorly-made splices in the conveyor belt, and is less able to adapt itself to conform to the contour of the belt as it wears. 
     Where it is desirable to provide more flex in the scraper blade, it is desirable to use a 82-85 durometer blade which has a thickness of 1¼″ or less. When conventional blades of the prior art are used, the thickness of the blade gradually increases from the tip all the way back to the mounting base, and the greatest flexibility is at the tip where the blade sharply tapers to a relatively sharp edge along its length. After the blade wears through the sharply-tapered tip, the conventional blade loses its high flexibility. 
     With wet and sticky materials or materials which accumulate due to freezing or evaporation, the scraper blade tends to accumulate materials scraped from the belt on the under surface of the blade which confronts the belt. If the material accumulated on the blade builds up to a substantial degree, it cakes on the under surface and may engage the belt downstream from the scraping edge of the blade and cause the scraping edge to disengage the surface of the belt, or may serve as a dam or block against the bias of the blade holder forcing the scraping edge of the blade against the belt to take advantage of the flexible nature of the blade. 
     SUMMARY OF THE INVENTION 
     With the foregoing in the mind, the present invention provides a novel blade design which overcomes the deficiencies of the prior art blades. 
     More specifically, the present invention provides a blade configuration which enables the under surface of the blade to confront the belt at an angle which is sufficiently steep to allow some accumulation of material on the under surface of the blade without building up a cake which is large enough to displace the blade away from the belt. 
     In a preferred embodiment, the blade has a base adapted to be replaceably mounted on a support shaft which is operable to rotate the blade against the conveyor belt with a pressure bias, and the under surface of the blade extending from the base to the scraping edge is recessed. 
     Specifically, the preferred blade has a metallic base portion adapted to be releasably engaged on the support shaft with a resilient blade molded integrally with the metallic support base. The blade is formed of an elastomeric material such as plastic, capable of resiliently flexing to conform to the contour of the conveyor belt as it traverses past the blade on the head pulley. The resilience of the elastomeric material assists the dislodgment of material accumulated on the blade during operation. The elastomeric blade is offset adjacent the metal base so as to provide a straight under surface confronting the head pulley throughout the wear portion of the blade. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described more fully hereinafter with reference to the accompanying drawings, wherein: 
     FIG. 1 illustrates a prior art conveyor system having a support shaft mounting a blade for separating the conveyed material from the conveyor belt as it is entrained around a head pulley; 
     FIGS. 2,  3 ,  4  and  5  are end views illustrating novel blade configurations for use as replacements of the blade shown in FIG. 1; and 
     FIGS. 6,  7  and  8  are diagrammatic views illustrating the angular movement of the support shaft as the blade wears during use, the figures showing the blade of FIG. 2 as it wears down by engagement with the conveyor belts on head pulleys of differing diameters. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the prior art conveyor assembly, a conveyor belt  10  is trained around a head pulley  8 . A scraper blade  14  is pivotally mounted for rotation with a support shaft  20 . As shown, the blade  14  comprises a plastic body  23  mounted in a metallic base  21  which engages over and is supported by a support arm  22  which comprises a metallic plate extending radially outward from the support shaft  20  on a side which confronts the head pulley  8 . A suitable tensioning device (not shown) operates to provide an angular bias tending to rotate the support shaft  20  towards the head pulley so as to apply a pressure biasing the blade  14  into engagement with the pulley. 
     In normal operation, the plastic body  23  of the blade  14  flexes to conform to the contour of the conveyor belt  10  as it is traversed past the blade by the head pulley  18 . Any material adhering to the belt is dislodged by the scraper blade  14 . The body of the blade  14  is sufficiently long to permit substantial wearing down of the body during operation of the conveyor, and normally the blade is allowed to wear down until the blade allows disengagement of the blade from the belt on the pulley, or until the metallic base  21  of the blade is exposed sufficiently to contact the conveyor belt or the material. 
     The base  21  provides a rigid support for the blade on the plate  22  which extends radially from the shaft  20  on a side of the shaft which confronts the head pulley. The base  21  has four parallel side walls, the first and fourth walls (the outer side walls)  15  and  16  are open at the top to receive the elastomeric material of the blade member  23  and are connected at the bottom to the second and third walls (the internal side walls)  17  and  18 . Internal side walls  17  and  18  are connected at their top at a location intermediate the tops and bottoms of the side walls  15  so as to form a generally W-shaped cross-section forming a hollow slot  19  at the bottom to telescopically engage the plate  22 . The first and fourth side walls  15  and  16  are spaced apart to provide a receptacle for the body member  23  of the blade. At the bottom, the body member engages in the receptacle formed between the outer walls  15  and  16  and has an under surface  25  confronting the head pulley and an outer surface facing away from the head pulley. The outer surface  28   a  and  28   b  extends upwardly from the first wall  15  and the undersurface  25  extends upwardly from the fourth wall  16 . The thickness of the body member  23  corresponds to the spacing between the side walls  15  and  16  at the bottom of the body member and the thickness diminishes from the base  21  toward the top where the body member  23  terminates in a blade tip  27 . 
     When handling wet materials which tend to adhere to the conveyor belt, there is a tendency for the wet material, as it is scraped from the belt surface, to adhere to the tip of the blade, both on the outer face and along the under surface. Depending on the character of the wet material, the material adhering to the blade may tend to build up on the under surface of the blade adjacent the scraping tip. When this occurs, the accumulation of the material on the under surface of the blade may tend to cause the scraping edge to disengage the surface of the belt, or may serve as a dam or block against the bias of the blade holder  22  forcing the scraping edge of the blade against the belt. 
     With the foregoing mind, the present invention provides an improved scraper blade which overcomes the problems described above. Specifically, the improved scraper blade of the present invention is designed to replace the conventional blade  14  shown in FIG.  1 . FIGS. 2-5 illustrate different configurations of the scraper blade which overcome the problem of build-up on the under surface of the blade. To this end, the blades shown in FIGS. 2-5 each comprise a metallic base member and a body member formed of an elastomeric material such as plastic. The body member of each scraper is capable of resiliently flexing to conform to the contour of the conveyor belt as the conveyor belt traverses past the scraper blade on the head pulley. This resilient flexing aids in breaking up the build-up of material that may accumulate on the back of the blade. 
     In FIG. 2, the base member of the blade  14   a  is designated with the reference character  21 , and the body member is designated with the reference character  23 . In FIG. 3, the base and body members of the blade  14   b  are designated as  31  and  33 , respectively. In FIG. 4, the base and body members of the blade  14   c  are designated  41  and  43 , respectively, and in FIG. 5, the base and body members of the blade  14   d  are designated  51  and  53 , respectively. 
     FIG. 2 illustrates the preferred embodiment in which the body member  23  has a flat under surface  25  which confronts the conveyor belt  10  on the pulley  8 . At its upper end, the under surface  25  merges with an angular tip surface  26  to provide a shearing edge  27  extending along the length of the body portion of the blade. The outer surface of the blade has an intermediate surface  28   a  which extends angularly rearwardly as indicated at a more shallow angle than the surface tip  26  and then the outer surface  28  extends at a less steep angle to the base  21 . The base  21  has a hollow slot  19  which telescopically engages the holder  22  so as to be removable when the blade wears and needs replacement. 
     The under surface  25  is disposed at an angle to the center line of the base  21  and the holder  22  so as to provide an angle which is sufficiently steep to allow some accumulation of material on the under surface of the blade without building up a cake which is large enough to displace the blade away from the belt. The angular disposition of the under surface  25  relative to the belt  10  on the head pulley  18  provides a clearance space which may accommodate a substantial build-up of material. In addition, the tip  27  projects outwardly from the plane edge of the fourth wall  16  to provide a tip offset, which is designated “A”. In the present instance, the tip offset “A” is approximately ½-¾ inches (1.25-1.90 cm). A corresponding tip offset is also labeled A in each of FIGS. 3-5. The tip offset A provides additional clearance space which may accommodate a build-up of material. 
     In the preferred embodiment of FIG. 2, the flat under surface  25  has an angle which is sufficiently steep so that its projected continuation intersects with the base  21  between the walls  15  and  16 , to provide a base offset. To reduce the build-up of wet material in the base offset, the base  21  is embedded in the body  23  so that the plastic material of the body portion forms a fillet  29  between the inward edge of the base  21  and the flat surface  25 . In the present instance, the fillet  29  merges with the inner surface  25  at a point that is approximately coplanar with the plane of the fourth wall  16  of the base as designated by point B in FIG.  2 . In this way, after the scraper tip  27  has worn down to point B so that there is no longer a tip offset A, the fillet  29  functions as an offset to provide clearance for some build-up of wet material. 
     In the embodiment shown in FIG. 3, the flat surface  35  extends from the scraping tip  37  to the top of the inside edge of the base  31  without having a base offset. In other respects, the body  33  is comparable to the body  23 . 
     FIG. 4 is a similar blade in which the body portion  43  has an arcuate under surface  45  from the scraping tip  47  to the base  41 . At the tip, the tip surface  46  which meets the arcuate surface  45  to form the scraping tip is similar to the surface  26  of the embodiment of FIG. 2, but the rear wall  48  extends in a straight plane from the rear of the tip surface  46  to the rear edge of the base  41  without an intermediate surface. 
     FIG. 5 is a blade similar to FIG. 4 having a tip surface  56  merging with a flat under surface  55  to provide a scraping edge  57 . The rear surface of the blade is arcuate from the angular surface  56  to the rear surface of the base  51 . 
     The blade of FIG. 2 is deemed preferable for most materials, but for certain materials, it may be found desirable to utilize blades such as shown in FIGS. 3-5. 
     FIGS. 6,  7  and  8  illustrate the angular displacement of the blade shown in FIG. 2 as it wears down in use. As shown in these figures, the support shaft  20  with the blade holder  22  rotates under the bias provided for the shaft  20 , and the position of the blade at 15° and 30° rotation are shown in FIGS. 7 and 8. With a small diameter head pulley as indicated at  8 — 8 , the blade may wear down the full 30°, but with the small diameter pulley, there is a tendency for the blade to flip past the pulley at the 30° angle. For larger diameter pulleys, this problem does not arise, but as the pulley gets larger, the likelihood of the metallic base  21  being displaced against the belt on the pulley arises, and it will require replacement of the blade more quickly than in the case of the pulleys of intermediate size. 
     The flexibility of the blade varies based on several factors including the material used to form the blade, and the thickness of the blade between the under surface  25  and the outer surface  28 . It should be noted that the under surface  25  is substantially parallel to the outer surface  28   b , so that the resilient flexibility of the blade is not substantially reduced as the blade wears down, as shown in FIGS. 6-8. Preferably, the durometer of the blade is in the range of 82-85 durometer and the thickness of the blade between the under surface and the back surface is less than approximately 1¼ inch (3.2 cm). In many conventional blades, the blade thickness increases as the blade wears, so that the blade thickness increases to above approximately 1¼ inch (3.2 cm) for a substantial portion of the wear-life of the scraper blade. However, in the embodiment of FIG. 2, by providing the base offset, the blade thickness remains below the limit until the blade is worn down to within approximately ¾ inch (1.90 cm) from the metallic support in the base of the blade. Therefore, the flexibility of the scraper blade is maintained within a preferred range during a greater portion of the wear-life of the scraper blade. 
     Preferably, the body member of the blade is molded in the desired shape. The base is mounted in the mold during the molding operation so that the metallic base of the blade forms a reinforcing shield at the bottom of the molded blade and provides a rigid interconnection for the blade on the blade holder  22  of the shaft  20 . 
     While particular embodiments of the invention have been herein illustrated and described, it is not intended to limit the invention to such disclosures, but changes and modifications may be made therein and thereto within the scope of the following claims.