Abstract:
A method of assembling a conveyor belt scraper which includes at least one scraping edge fixed to a support at least by means of a biasing member which includes the steps of prestressing the biasing member in a first sense, maintaining the biasing member prestressed, and mounting the conveyor belt scraper adjacent a surface of the belt whereby, in use, when the scraping edge exerts a scraping action on the belt and is deflected away from the belt, the biasing member is further stressed in the first sense.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to a conveyor belt scraper.  
         [0002]     It is known to make use of a conveyor scraper wherein the scraping element, or each scraping element when there are a plurality of such elements, is flexible or is mounted to a spring of suitable form which allows to-and-fro movement of the scraping element, during use.  
         [0003]     With the aforementioned type of scraper cleaning of a conveyor belt is achieved by adjusting each scraping element towards the belt surface and applying pressure so that the flexible scraping element, or the spring, as the case may be, is tensioned to remove slack and creep and to provide the necessary resistance to the moving belt so that material adhering to the belt is removed.  
         [0004]     The pressure which is applied to flex the scraping element or tension the spring is obtained by forcing an edge of the scraping element into contact with the belt surface, with a suitable degree of force. The pressurised contact surface between the belt and the scraping edge accelerates the wear rate of the tip of the scraping edge and can increase wear on the belt surface. It is also known that the pressure exerted by the scraping element on the belt surface must be increased, as belt speed increases, in order to provide the necessary cleaning resistance.  
         [0005]     Protrusions on the belt surface cause the scraping element to deflect away from the belt whereafter the element rebounds naturally to its original position. This action can cause additional damage to the belt surface. In certain instances the rebound results in ongoing oscillations and vibrations of the scraping element and if this movement occurs in harmony with the natural vibration frequency of the conveyor belt severe belt damage can result, an effect which is compounded as the conveyor speed increases.  
         [0006]     Also, unrestricted movement of the scraping element can cause additional damage when the belt reverses, and when used in the primary cleaning position if a belt joint/splice opens up, or other protrusions impact on the scraper.  
       SUMMARY OF INVENTION  
       [0007]     The invention provides a method of assembling a conveyor belt scraper which includes at least one scraping edge fixed to a support at least by means of a biasing member which includes the steps of: 
    (a) prestressing the biasing member in a first sense,     (b) maintaining the biasing member prestressed, and     (c) mounting the conveyor belt scraper adjacent a surface of the belt whereby, in use, when the scraping edge exerts a scraping action on the belt and is deflected away from the belt, the biasing member is further stressed in the first sense.    
 
         [0011]     “Stress” as used herein denotes a state which is brought about by tensile, compressive or torsional force, or a combination of any of these factors, and “pre-stress” means a state of the aforementioned kind which is brought about beforehand.  
         [0012]     The method may include the step of limiting the degree of movement of the scraper towards, and away from, the belt.  
         [0013]     The biasing member may be prestressed in a first direction which, once the conveyor belt scraper is installed, is generally in a direction which is away from a belt surface which is to be cleaned. The biasing member is restrained from moving towards the belt surface so that the biasing member is retained in its prestressed state. Movement of the scraping edge away from the belt surface, which occurs during use, leads to the biasing member being further stressed in the first direction.  
         [0014]     The invention may include the step of controlling the degree of prestressing in the first sense. Thus the biasing member may be prevented from being stressed beyond a predetermined level. This may be achieved in any appropriate way and for example a mechanical stop may be used which prevents the scraping edge from being moved beyond a predetermined point towards or away from the belt surface.  
         [0015]     In step (c) the conveyor belt scraper may be mounted so that the scraping edge is in light contact with, or slightly spaced from, the belt surface which is to be cleaned.  
         [0016]     The scraping edge may be provided on a scraper element which is fixed to the biasing member.  
         [0017]     The invention also extends to a conveyor scraper element which includes a biasing member and a component with a scraping edge supported by the biasing member and wherein the biasing member is engageable with a support, with the scraping edge not in contact with a belt surface and with the biasing member in a prestressed state.  
         [0018]     The biasing member may include any suitable device and may for example be a leaf spring which may be made from metal or a plastics material.  
         [0019]     The biasing member may extend from the support and the scraping edge may be positioned remote from the support.  
         [0020]     The biasing member may be located between two deflector surfaces. The deflector surfaces may be formed by individual components or by respective surfaces on a composite or integral component.  
         [0021]     The biasing member may be secured to the component by means of any suitable fasteners, eg. rivets or bolts, or it may be engaged with the component by means of interengageable complementary formations on the component and the biasing member.  
         [0022]     The biasing member may be secured to the support in any appropriate way and use may for example be made of rivets of other fasteners to secure the biasing member to the support. Again it is possible to secure the biasing member to the support by means of interengeable complementary formations on the biasing member and the support.  
         [0023]     In one form of the invention the scraper element includes first and second deflector plates and the scraping edge component is secured to respective first ends of the plates. The biasing member is positioned between the plates and preferably is secured to one of the plates. One of the plates may abut the support, or any other structure, thereby to retain the biasing member in a prestressed condition. The extent to which the biasing member may be prestressed may be limited when the other plate is brought into contact with the support or other structure or adjustable stops for, in this way, movement of the biasing member may be controlled.  
         [0024]     In a different form of the invention the scraper element includes a body formed from a suitable material, eg. a plastics material using an injection moulding or casting process, and respective surfaces of the body form deflectors or deflector surfaces. The biasing member is engaged with a suitable formation or formations in the body.  
         [0025]     An additional formation on the body may be engageable with the support or any other structure to retain the biasing member in a prestressed state. Similarly a formation on the body can be brought into engagement with the support or other structure or an adjustable stop or stops thereby to control the degree of stress, whether in tensile, compressive or torsional form, which is imparted to the biasing member.  
         [0026]     A plurality of the scraper elements may be assembled to provide a scraper assembly. This may be done using any appropriate technique and for example the scraper elements may be slidably engaged with an appropriate support structure. The scraper elements may be assembled in any appropriate configuration in an elongate array, eg. in-line, or in a staggered array.  
         [0027]     The complete scraper assembly may be supported on adjustable or resilient mountings to accommodate normal scraper wear and to allow the passage of protrusions and joints in the conveyor belt. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The invention is further described by way of examples with reference to the accompanying drawings each of which has two figures respectively illustrating a conveyor scraper element according to the invention from the side and from an end respectively.  
         [0029]     In the accompanying drawings:  
         [0030]      FIG. 1  illustrates a conveyor scraper element according to a first form of the invention mounted adjacent a belt surface which is to be cleaned and used as a primary scraper,  
         [0031]      FIG. 2  shows a conveyor scraper element which is similar to that shown in  FIG. 1  but wherein the conveyor scraper element is used as a secondary scraper,  
         [0032]      FIG. 3  shows a conveyor scraper element according to a second form of the invention suitable for use as a primary scraper, and  
         [0033]      FIG. 4  illustrates a variation of the configuration shown in  FIG. 3  suitable for use as a secondary scraper. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0034]      FIG. 1  of the accompanying drawings illustrates a conveyor scraper element  10  according to a first form of the invention from a side and from one end respectively. In this example the conveyor scraper element includes a body  12  which is moulded from a suitable plastics material, eg. reinforced nylon, and which has a roughly triangular shape in cross section. An upper end or apex of the body has an elongate groove  14  which is narrower at its mouth than at its base. Sides  16  and  18  of the body taper outwardly and downwardly from the apex and are referred to herein as deflector surfaces.  
         [0035]     At its lower end the body has two wings or ribs  20  and  22  respectively projecting downwardly from the deflecting sides  16  and  18 .  
         [0036]     A central portion of the body is formed with a fairly substantial slot  24  which has a base  26  which is in the nature of a circular cylinder.  
         [0037]     A scraping component  28  is mounted to the slot  14 . The component  28  has a rib  30  which is of complementary shape to, and which is slideably engageable with, the slot  14 . The rib is held firmly in the slot by means of rivets or other fasteners  32  which pass through holes in the upper end of the body  12  and registering holes in the rib.  
         [0038]     A scraping edge  34  of any appropriate scraping material known in the art is mounted to a slot  36  in a projecting outer surface of the component  28 .  
         [0039]     A leaf spring  40  is engaged with the formation  24 . The spring has a rounded upper end  42  which is complementary in shape to the cylindrical base  26  of the formation. At its lower end the spring has a rounded base  44  which is positioned in a gap formed at a central location in a mounting and supporting track  50 .  
         [0040]     The spring is made from a suitable material, eg. spring steel or an appropriate plastics material, with adequate corrosion resistant properties, which has an acceptable cycle life time.  
         [0041]     The support and mounting track or rail  50  is generally in the nature of an inverted “U” to fit over square tubing and has an upper elongate slotted formation  52  which is used for mounting the scraping component. The formation  52  corresponds in shape to the lower end of the spring  40  and the base  44 . It is apparent that the spring can be engaged with a sliding action with the support by sliding the base  44  into the formation  52 .  
         [0042]     The geometry of the body and the design of the support  50  are such that, in order for the body to be engaged with the support, the spring must be prestressed. In the illustrated example this is achieved by bending the body in the direction of an arrow  56  which is away from the surface  58  of a belt  60  which is to be cleaned. The spring is thereby flexed and the body can be pushed over the support with the ribs  20  and  22  extending downwardly on opposing sides of the support. Once the force which is used to bend the spring in the direction  56  is released, the spring attempts to revert to a neutral position and in so doing moves the body in a direction opposite to that indicated by the arrow  56 , to a limited extent. A lower inner surface of the rib  20  is thereby brought into contact with an upper left hand corner of the support  50  and this limits the degree to which the spring can relax. The spring is thereby held in a tensioned or prestressed state.  
         [0043]      FIG. 1  shows the scraper element  10  mounted adjacent the belt surface  58  and acting as a primary scraper. The support  50  is positioned so that the scraping edge  34  is lightly in contact with the belt surface  58 . The spring is, as noted, constantly held in a biased or prestressed condition.  
         [0044]     The degree of flexing or pivoting of the body, which is permitted, is restricted and the body can move to a limiting position, away from the belt surface, indicated by means of a dotted line  62 . At this stage the rib  22  abuts an upper right hand corner of the support  50  and this limits the permitted extent of movement of the body and hence of the scraping edge  34  away from the belt surface  58 . The body is allowed sufficient movement to allow the scraper blade or edge  34  to follow variations in the belt thickness or undulations in its outer surface and to deflect sufficiently to allow protrusions, which are generally encountered, to pass the scraper edge. These features have the following benefits: 
    (1) less applied pressure is required for the scraper element to resist the forces of the carry-back material on the belt, in order to perform its cleaning function. This reduces scraper blade and belt wear;     (2) deflection of the scraper element is limited thereby reducing rebound impact;     (3) oscillation of the scraper element is restricted thereby interrupting any vibration cycle and preventing sympathetic vibrations and resulting chatter, damage etc.;     (4) in situations where the conveyor belt is reversed over the scraper element, forward movement of the scraper element is restricted, preventing it from digging into the belt, an action which could damage the belt or the scraper element;     (5) when the scraper element is used as a primary cleaning device the restriction on forward movement reduces the possibility of the scraper element being snagged by a protrusion from the conveyor belt, a factor which could cause damage to the belt or the scraper element.    
 
         [0050]      FIG. 2  illustrates a variation  10 A of the arrangement shown in  FIG. 1  wherein the scraper element is used as a secondary scraper. The configuration shown in  FIG. 2  is not described in detail and, where applicable, components which are the same as those shown in  FIG. 1  are designated with similar reference numerals.  
         [0051]     The upper edge of the body  12  has a scraping component  28 A attached to it with the element being oriented so that the scraping edge  34 A extends upwardly and not to the side, as in  FIG. 1 . This allows the scraper element to be mounted in a vertical configuration, similar to what is shown in  FIG. 1 , but with the scraping edge being available for a secondary scraping action as opposed to the primary scraping action of  FIG. 1 .  
         [0052]      FIG. 2  also illustrates that the support, designated  50 A, can be engaged with a sliding action with a base support  64 . The base support  64  is attached to fixed structure adjacent a belt  60 A, at an appropriate location, and the support  50 A, which is assembled with the scraping element or elements under factory conditions, is then readily engaged on-site by sliding the support  50 A onto the base support  64 .  
         [0053]      FIG. 3  shows a conveyor scraper element  10 B which includes a body of two metal deflector plates  70  and  72  respectively which are joined at an apex formed by upper ends  74  to which a scraping component  76  is attached. The component  76  has a scraping edge  78  of a suitable hard-wearing material fixed to it in a manner which is known in the art. The scraper element  10 B is secured to the deflector plates by means of rivets or bolts  80 .  
         [0054]     The deflector plates extend downwardly and away from each other giving a generally triangular or pyramid-type construction. A leaf spring  82  of any suitable material is fixed to an inner surface of the deflector plate  70 . A lower end of the spring is clamped between angle brackets  84  which are fixed to an upper surface of a support  50 . A lower end of the deflector plate  70  abuts an upper left hand corner of the support  50  and retains the spring  82  in a permanently prestressed condition with the spring attempting to move to a neutral position in a direction of an arrow  86 .  
         [0055]     A lower end of the deflector plate  72 , designated  88 , is spaced from a right hand upper corner of the support  10 . It is evident that the scraper element  10 B is similar to what is shown in  FIG. 1  and that if the scraping edge  78  is moved in a direction opposite to that indicated by the arrow  86  the lower end  88  of the deflector plate  72  limits the extent to which movement of the scraping edge can take place away from a belt surface which is being cleaned.  
         [0056]     Apart from limiting the degree of movement of the spring  82  the deflector plates protect the spring and shield it, at least to some extent, from mechanical damage, and from foreign material, water and the like.  
         [0057]      FIG. 4  illustrates a scraper element  10 C which is a variation of the configuration shown in  FIG. 3 . The scraper element includes deflector plates  70 A and  72 A respectively with the plate  70 A being shaped in a different form to the plate  70 . A scraping component  76 A, with a scraping edge  78 A, is positioned between upper edges of the plate  70 A and  72 A and is riveted in position.  
         [0058]     A lower end of a centrally positioned spring  82 A is damped between two brackets  84 A which, in turn, are attached to a base plate  90 . A channel  92  with inwardly sloping side walls is fixed to an upper surface of a support  50 . The base plate and the brackets can be engaged with a sliding fit with the channel  92 .  
         [0059]     Although the scraper element  10 C is a variation of the arrangement shown in  FIG. 3  it is evident that it is used as a secondary scraper in a manner similar to what has been described in connection with  FIG. 2 .  
         [0060]     It is also to be noted, in connection with all of the embodiments of the invention, that only one scraper element has been described. It is evident that a plurality of scraper elements may be positioned in line with each other to form a longitudinally extending array of scraper elements with each scraper element being positioned above the support  50 . Clearly it is possible to arrange the scraper elements in other configurations, eg. in a staggered array of two or more rows.  
         [0061]     Another factor is that the support  50 , in each embodiment of the invention, may itself be supported on a vertically and horizontally adjustable mounting  66 , see  FIG. 2 , or it may be supported on a torsion arm  68  which allows resilient movement, or it may be mounted to shock absorbing structures or self-support mechanisms such as airbags, pneumatic or hydraulic cylinders, counterweights or torsion-type mounting assemblies.  
         [0062]     It is also possible to modify the conveyor scraper element to adjust the degree of bias, or prestressing, which is applied to the element. For example  FIG. 1  illustrates two grub screws  100  which are mounted in the body  12 , bearing against the support  50 , which can be adjusted to deflect the spring  40  to a greater or lesser extent, but which still act as a stop to prevent the spring from moving to a de-stressed condition.  
         [0063]     Similarly, in  FIG. 3 , a screw  102  which is fixed to the spring  82  bears against an inner surface of the deflector plate  70  and can be adjusted to increase or reduce the degree to which the spring is prestressed.