Abstract:
A scraper blade assembly which is configured to provide a rigid material scraping edge supported on a resiliently compliant material such that the scraping edge is adapted to move in response to irregularities in an associated conveyor belt. Further, supporting structure for the resiliently compliant material is configured so as to promote an upward deformation of the resiliently compliant material when a compressive force is applied to the rigid material scraping edge to thereby form the resiliently compliant material as a supporting surface above the scraping edge when such a force is applied.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The benefit of prior U.S. Provisional Application No. 60/344,838 filed Dec. 21, 2001 is hereby claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to conveyor belt scraper blades, and more particularly, to blades for scraping and cleaning of high speed conveyor belts. 
     Cleaning the return side of a high speed conveyor belt that carries loose bulk materials has always been a particularly difficult challenge for industrial and mining companies. While various designs have achieved successes in many areas, the companies operating high speed conveyors are constantly demanding continued improvements in performance from belt cleaning equipment. There are two areas that are of primary concern for scraper blade design: the first is cleaning performance; the second is scraper blade life. 
     Prior designs for scraper blades have incorporated various materials for the scraper blade media, including rubber urethane, steel and tungsten carbide. 
     The product offerings in metal blade media by other companies have, for the most part, been of a segmented design where a cleaner blade with a metal tip is designed with a plurality of individual elements, typically 2″ to 6″ in width thus requiring eight to twenty-four elements to clean a conveyor belt of 48″ width. These elements are typically of cast urethane design with a small piece of tungsten carbide typically {fraction (3/16)}″ thick×½″ high, molded to the wear edge of the cleaning element. The segmented design offers advantages and disadvantages. The elements are typically light weight and easy to handle. The fact that multiple units are used to cover the width of a conveyor belt however means that there is a joint between each element that can allow carryback material to pass between elements if the elements are not perfectly aligned and positioned. 
     Typical prior art metal edge cleaner blades of segmented design are installed with the tungsten edge at an aggressive attack angle to the conveyor belt. The accepted angle is typically 10 to 30 degrees beyond perpendicular to the conveyor belt. This design places the tungsten tip of the blade in sole contact with the conveyor belt. The hard urethane substrate portion of the element is used only as a tensioning device and as a device for possible pressure relief if the element is over stressed. There is no other support or protection for the conveyor belt. The conveyor belt is arched across the exposed tungsten cleaner blade edge. The design of the typical tension system is such that when irregular portions of the conveyor belt pass, the pressure applied by the conveyor belt toward the scraper blade is increased and the resistance of the scraper blade to the belt is increased as the flexing motion is limited by the elasticity of the urethane polymer being used to hold the tungsten carbide blade tip. 
     This aggressive attack angle for prior art blades and the fact that the tungsten tip is the sole portion of the element in contact with the conveyor belt means that any irregularities in the conveyor belt including vulcanized splices, metal splices and hanging threads are subject to serious damage from the tungsten cleaner edge. 
     The design of the cast urethane segments or elements with tungsten carbide tip is typically of a shape and configuration that allows each element to flex in the direction of belt travel. The hard urethane base that holds the tungsten tip is typically a hard material in the range of 85 to 90 durometer shore A hardness. This hard material does not move behind the tungsten tip and any flexing of the urethane element is accomplished by the structural design of the element. For example, the element is molded with a hollow cavity in it to make the support thinner and thereby allow it to bend. This is supposed to help prevent damage being caused to the conveyor belt by the element if a metal splice or some irregularity in the conveyor belt should pass the cleaner blade. 
     Accordingly, there is a continuing need for a scraper blade structure which effectively cleans high speed conveyors and which has an extended useful life and, in particular, there is a need for a continuous non-segmented blade using tungsten carbide or similar rigid media such as steel. 
     SUMMARY OF THE INVENTION 
     The present invention provides a scraper blade assembly which is configured to provide a rigid material scraping edge supported on a resiliently compliant material such that the scraping edge is adapted to move in response to irregularities in an associated conveyor belt. Further, supporting structure for the resiliently compliant material is configured so as to promote an upward deformation of the resiliently compliant material when a compressive force is applied to the rigid material scraping edge to thereby form the resiliently compliant material as a supporting surface above the scraping edge when such a force is applied. 
     In accordance with one aspect of the invention, a scraper blade assembly for a conveyor belt scraper is provided comprising: an elongated blade body including a resilient backing member formed of a resilient material and defining a central longitudinal scraper blade axis, the resilient backing member including opposing sides, first and second faces extending longitudinally between the sides, and an upper surface located between the first and second faces and extending longitudinally between the sides; a longitudinally extending support frame attached to the elongated body and defining opposing first and second ends; end plates attached to the first and second ends for attaching the blade assembly to support structure such that the elongated body extends transversely of an associated conveyor belt; and the elongated body further including an elongated metal face plate attached to the first face of the resilient backing member and comprising a continuous strip of material having an upper edge adjacent the upper surface extending from the first end to the second end of the support frame. 
     In accordance with another aspect of the invention, a scraper blade assembly for a conveyor belt scraper is provided comprising: an elongated blade body including a resilient backing member formed of a resilient material and defining a central longitudinal scraper blade axis, the resilient backing member including opposing sides, first and second faces extending longitudinally between the sides, and an upper surface located between the first and second faces and extending longitudinally between the sides; a longitudinally extending support frame attached to the elongated body for supporting the elongated body extending transversely of an associated conveyor belt; the resilient backing member including an upper portion extending upwardly from an upper edge of the support frame; the elongated body further including an elongated metal face plate attached to the first face of the resilient backing member at the upper portion and having an upper edge adjacent the upper surface of the resilient backing member; a rigid backing member extending upwardly from the upper edge of the support frame along a substantial portion of the second face of the resilient backing member for supporting the upper portion of the resilient backing member against movement when a force is applied against the metal face plate. 
     In accordance with yet another aspect of the invention, a scraper blade assembly for a conveyor belt scraper is provided comprising: an elongated blade body including a resilient backing member formed of a resilient material and defining a central longitudinal scraper blade axis, the resilient backing member including opposing sides, first and second faces extending longitudinally between the sides, and an upper surface located between the first and second faces and extending longitudinally between the sides; a longitudinally extending support frame attached to the elongated body for supporting the elongated body extending transversely of an associated conveyor belt; the resilient backing member including an upper portion extending upwardly from an upper edge of the support frame; the elongated body further including an elongated rigid face plate attached to the first face of the resilient backing member at the upper portion and having an upper edge for scraping material from an associate conveyor belt, the upper surface of the resilient backing member being coextensive with the upper edge of the face plate for providing support to the conveyor belt; the rigid face plate comprising a continuous rigid structure supported out of contact with the support structure, and extending the entire length of the elongated blade body for extending substantially the entire width of an associated conveyor belt; a rigid backing member extending upwardly from the upper edge of the support frame along a substantial portion of the second face of the resilient backing member for supporting the upper portion of the resilient backing member against movement when a force is applied against the rigid face plate. 
     Other aspects of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the scraper blade assembly of the present invention; 
     FIG. 2 is an exploded view illustrating the components forming the scraper blade assembly; and 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-3, the present invention comprises a scraper blade assembly for use in applications such as described in U.S. Pat. No. 5,628,392, which patent is owned by the assignee of the present application and is incorporated herein by reference. The present design is of a scraper blade assembly  10  with a continuous metal face plate  12 , which is preferably 36,000 psi mild steel, and including a wear edge  18  of tungsten carbide  14 , or similar abrasion resistant material, fused thereto in a continuous length, such that the abrasion resistant element extends the full width of a conveyor belt without the need for a plurality of elements. The metal face plate  12  of the blade assembly  10  is molded to a solid yet soft resilient backing member  16  having a durometer hardness of 40 to 60 shore A. The resilient backing member  16  is preferably formed of a rubber material, which is preferably a natural and synthetic rubber blend, and extends the full width of the blade assembly  10  behind the metal face plate  12 . In addition, the resilient backing member  16  extends downwardly to a main steel support frame  20  whereby an upper portion  22  of the resilient backing member  16  is supported for flexing movement above the support frame  20 . 
     The support frame  20  is formed with a structure similar to that described for the support frame in the above referenced U.S. Pat. No. 5,628,392 and includes first and second elongated frame plates  24 ,  26  extending the length of the blade assembly  10  and formed with a plurality of apertures  28 . Rectangular metal slugs  30  extend between the frame plates  24 ,  26 , passing through the apertures  28 , and through apertures  32  formed in a lower portion  34  of the resilient backing member  16 . The ends of the metal slugs  30  are welded to the frame plates  24 ,  26  to form a rigid structure for the support frame  20 . In addition, end members  36 ,  38  are provided welded to the ends of the frame plates  24 ,  26  to thereby define opposing ends for supporting the blade assembly  10  in a support structure, such as an air pressure actuated tension system as is disclosed in U.S. Pat. No. 4,969,553, which patent is owned by the assignee of the present application and is incorporated herein by reference. 
     The blade assembly  10  further includes a rigid sacrificial fiber backing plate  40  located on a back side  42  of the resilient backing member  16  wherein the fiber material forming the backing plate  40  is preferably formed of a phenolic resin impregnated fiber. The fiber backing plate  40  is set or positioned in an off-set recess  44  formed in the back side  42  of the resilient backing member  16 , and includes a plurality of apertures  45  for passage of the metal slugs  30  therethrough. The fiber backing plate  40  additionally includes an upper beveled edge  46  located below the level of an upper edge surface  48  of the resilient backing member  16 . The fiber backing member  40  extends from a location below the upper edge of the support frame  20  upwardly along a substantial vertical portion of the upper portion  22  of the resilient backing member  16  and operates to support the resilient backing member  16  and prevent it from folding backward in the direction of belt travel. The beveled edge  46  prevents debris from collecting between the upper edge of the fiber backing plate  40  and a conveyor belt. 
     A further fiber backing plate  50 , formed of the same material as the fiber backing plate  40 , is provided located on a front side  52  of the resilient backing member  16 . The fiber backing plate  50 , is set or positioned in an off-set recess  54  formed in the front side  52  of the resilient backing member  16 , and includes a plurality of apertures  57  for passage of the metal slugs  30  therethrough. The fiber backing plates  40 ,  50  are preferably vulcanized with the rubber material during the molding operation forming the resilient backing member  16 . 
     It should be noted that the recesses  44 ,  54  are generally L-shaped in section and extend longitudinally the length of the resilient backing member  16 . In addition, a rib  58  extends longitudinally of the resilient backing member  16  separating the face plate  12  from the fiber backing plate  50 , and the face plate  12  is positioned in an L-shaped recess  59  located above the rib  58  in the upper portion  22  of the resilient backing member  16 . 
     The present invention provides a sandwich construction for the blade assembly  10  wherein the resilient backing member  16  is approximately 1 to 1-½ inch thick, the metal face plate  12  is {fraction (3/16)} to ¼ inch thick, the tungsten carbide  14  wear edge is ⅛ inch thick or less, and the fiber back plates  40 ,  50  are ½ inch thick, such that the overall thickness of the components within the frame structure is approximately 1-¾ to 2 inches. It should be understood that the metal face plate  12 , and fiber backing plates  40 ,  50  are positioned within the mold forming the resilient backing member  16 , such that they are bonded together with the resilient backing member  16  in the molding process. 
     For the present invention, the resilient backing member  16  is of critical importance when used in conjunction with the rigid debris scraping structure comprising the metal face plate  12  and tungsten carbide edge  18 . The metal face plate  12  with the tungsten carbide wear edge  18  is molded to the resilient backing member  16 , such that there is no substantial contact between the face plate  12  and the rigid structure forming the support frame  20 , which rigidly holds the lower portion  34  of the resilient backing member  16  with the rigid fiber backing plates  40  and  50 . This allows the face plate  12  to “float” in the resilient backing member  16 . This float characteristic essentially allows the face plate  16  to react to forces imposed on it in the same manner as the resilient backing member  16  reacts. 
     When the blade assembly  10  is placed into service, the tungsten wear edge  18  is positioned perpendicular to the conveyor belt  62  in such a manner that the upper edge surface  48  of the resilient backing member  16  is also in contact with the conveyor belt  62 . This sandwich construction is important for safety, as well as for efficient cleaning of the conveyor belt  62 . When the conveyor belt  62  is in operation, the motion of the conveyor belt  62  exerts a force on the tungsten wear edge  18 . The resilient backing member  16  backing up the tungsten wear edge  18  is contained in front by the steel element of the face plate  12  and it is contained in the rear by the fiber board backing plate  40 . An important functional feature of this sandwich design is held in the fact that the resilient backing member  16 , such as rubber, does not compress, it simply moves or forms a different shape when acted upon by an outside force. The material of the resilient backing member  16  will not occupy less space regardless of the compression force exerted upon it. That is why the proper material is a compound consisting primarily of soft rubber. The momentum of the conveyor belt  62  moving across the edge  18  of the scraper blade assembly  10  creates a force on the steel face plate  12  and tungsten carbide wear edge  18  that attempts to compress the rubber that is directly behind it. Since the rubber is contained in front and back by rigid materials the only place left for the rubber to move to is upward toward the conveyor belt  62 , as is illustrated diagrammatically in dotted lines by 16′. The rubber media exerts a force on the conveyor belt  62 , via the upper edge surface  48 , that prevents the tungsten wear edge  18  from gouging or scalping the conveyor belt  62 . The resistance of the rubber effectively limits the amount of force that is able to be exerted on the conveyor belt  62  by the tungsten carbide wear edge  18 . 
     The force placed on the blade assembly  10  by the tension system supporting the blade assembly  10  is adjustable, such as by adjusting an air pressure that energizes the tension system, as discussed in the above . The resistance provided by the rubber portion of the sandwich insures against aggressive introduction of the tungsten carbide wear edge. The tungsten wear edge  18  is in contact with the conveyor belt and the tungsten edge  18  effectively peels off carry-back material. The tungsten provides a rigid and sharp departure point for any carry-back material. The rubber supports the conveyor belt and prevents the conveyor belt from being raked over the exposed edge of the tungsten carbide. 
     In accordance with an additional aspect of the invention, a fabric layer  60  is molded into the resilient backing member  16 , adjacent to and behind the face plate  12 , and is preferably located approximately ¼ inch from the face plate  12  such that the fabric  60  is fully embedded within the material of the resilient backing member  16 . The fabric layer  60  is preferably formed of a material having a tensile strength of at least about 200 pounds per square inch. An acceptable fabric is a square woven cord such as a calendered composite of high tensile strength nylon fabric (840/1) and high quality skim compound. The fabric layer  60  limits over-stretching of the resilient backing member  16  supporting the metal face plate  12 , and in particular operates to prevent the material of the resilient backing member  16  from being pulled or stretched in an upward direction by the force of the conveyor belt  62  if the metal face plate  12  should crack or break. 
     Support of the conveyor belt by the resilient backing member  16  in this manner is also a critical factor in protecting splices in the conveyor belt. Splices that are vulcanized are subject to damage from over aggressive belt cleaner devices. The present design prevents the extreme stresses that occur with tungsten/urethane cleaner blades. Conveyor belts are also frequently spliced with metal fasteners. The present design, because of the tungsten/rubber combination, permits the sandwich blade assembly  10  to be used on belts where metal splices are present. The rubber forming the resilient backing member  12  in the present blade assembly  10  helps support the belt and the splice while maintaining an angle between the conveyor belt and the cleaner blade of 90 degrees. When the attack angle of the cleaner blade exceeds 90 degrees, the potential for accelerated wear and damage to metal splices exists. 
     The blade assembly  10  is positioned and oriented with its length being perpendicular to the conveyor belt and is provided in various lengths so that the length of the blade assembly  10  is the same as the width of the conveyor belt on which it is employed. 
     The continuous metal (or tungsten carbide) edge  18  of the blade assembly  10  prevents carryback material from passing by the blade assembly  10 . There are no segments and therefore no joints between segments that would allow carryback material to pass through. The tungsten wear edge  18  of the present blade assembly  10  utilizes a flexible unfired tungsten material that is first formed to the shape of the cleaner blade and then fired at high temperatures so the steel face plate  12  and the tungsten  14  are fused together as one piece. 
     The blade assembly  10  can be made in various shapes including but not limited to a straight rectangular shape, a convex shape and modified straight or modified convex shapes to accommodate the conveyor belt conditions being encountered. 
     It should be noted, however, that the present design particularly facilitates a construction in which a continuously curved metal blade may be installed for conveyor belt cleaning. In particular, the conveyor belt typically may take on an upwardly curved shape across the width of the belt in the area where it passes the blade assembly, and it is desirable to have the upper scraping edge of the assembly shaped to a curved contour. While prior blade assemblies having curved scraping edges defined by a resilient material are known, a metal blade having a continuous curvature spanning the width of the conveyor belt has not been available and is made possible by the present resilient mounting configuration for the tungsten carbide coated metal blade. 
     Accordingly the blade assembly of the present invention provides several key features and advantages including a continuous one piece rigid metal element across (perpendicular to) the width of the belt, preventing carry-back material migration between segments; a rubber matrix which holds, supports and cushions the metal edge; a rubber matrix design which supports the conveyor belt as it passes over the metal edge of the blade assembly helping prevent belt wear, wear on splices and damage to splices and prevents damage to the conveyor belt; and including the rigid fiber board backing material that is the last part of the sandwich behind the rubber preventing the rubber from flexing too far, allowing the rubber to provide the necessary support for the conveyor belt as it passes the blade edge. It has been found the present blade design additionally provides for extended blade life, and is capable of providing a blade life at least five times that of an equivalent rubber cleaning blade. 
     While the form of apparatus herein described constitutes a preferred embodiment of this invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.