Patent Publication Number: US-2007095620-A1

Title: Conveyer belt brake

Description:
BACKGROUND OF THE INVENTION  
      THIS invention relates to conveyer belt braking apparatus.  
      Conveyer belts supported by idler rollers are widely used for transporting material in mining, quarrying and many other industries. The idler rollers are mounted on frames and support the conveyer belt which is typically driven by a head pulley.  
      Particularly where conveyer belts are inclined and carry relatively heavy loads, the consequences of a belt breakage can be severe. In the case of an inclined conveyor belt, breakage normally takes place in the vicinity of the head pulley, with the result that the upper and lower runs of the belt tend to slip back under gravity over the idler rollers. The normal slippage of the belt is assisted by the stored tension in the unbroken belt which is released when the belt is broken. The result, if the broken belt is not arrested in some way, is that the broken belt slips back all the way to the lowest point. A breakage resulting in a runaway of the belt and its load can cause substantial damage to the lower idlers and nearby equipment, and possible injury to nearby personnel.  
      Various conveyer belt braking systems have been proposed to deal with the problem of belt breakages. Known systems of this kind range from relatively large and complex braking mechanisms to relatively simple brakes acting on the idler rollers themselves.  
      It is an object of the invention to provide an alternative conveyer belt braking apparatus.  
     SUMMARY OF THE INVENTION  
      According to the first aspect of the invention there is provided conveyer belt braking apparatus comprising: 
          an idler roller rotatable about an axle;     a brake member mounted adjacent the idler roller and movable relative to the roller between a first, inoperative position adjacent a belt supported by the roller and a second, braking position against the belt; and     an operating mechanism arranged to sense the direction of rotation of the roller and to move the brake member from the first, inoperative position to the second, braking position when the direction of rotation of the roller reverses in use.        

      Preferably, the brake member is arranged to be located between the belt and the roller when the brake member is in the second, braking position.  
      The brake member may be a plate mounted parallel to the roller and pivotable between the first and second positions.  
      Preferably, the plate is pivotable about an axis that coincides substantially with the axle of the roller.  
      The plate is preferably connected to a shaft that extends through a bore in the axle of the idler roller, the shaft being rotatable relative to the axle, with a one-way clutch mechanism within the body of the idler roller fixed to the shaft and to the body of the roller, so that the roller can rotate freely relative to the shaft in a forward direction but, when the roller rotates in a reverse direction, the clutch engages, causing the shaft to rotate and to move the brake member from the first, inoperative position to the second, braking position thereof.  
      Alternatively, the plate may be connected to a sleeve fitted about the axle, the sleeve being rotatable relative to the axle, with a one-way clutch mechanism within the body of the idler roller fixed to the sleeve and to the body of the roller, so that the roller can rotate freely relative to the sleeve in a forward direction but, when the roller rotates in a reverse direction, the clutch engages, causing the sleeve to rotate and to move the brake member from the first, inoperative position to the second, braking position thereof.  
      The apparatus may include at least one locking member associated with the idler roller and arranged to engage the brake member and to hold the brake member in the second, braking position thereof when the brake member moves from the first, inoperative position thereof to the second, braking position thereof.  
      Preferably, said at least one locking member comprises a bracket fixable to the axle of the roller and having a projection that engages a portion of the brake member when the brake member moves to the second, braking position thereof.  
      According to a second aspect of the invention there is provided conveyer belt braking apparatus comprising: 
          a brake member mountable adjacent the return path of a conveyer belt and movable relative to the conveyer belt between a first, inoperative position adjacent the return path of the belt and a second, braking position in which the brake member engages the belt frictionally; and     an operating mechanism responsive to a belt breakage to move the brake member from the first position to the second, braking position thereof.        

      The brake member may be a plate mounted adjacent and transverse to the return path of the conveyer belt, the brake member being pivotable between the first and second positions.  
      The operating mechanism may be a linkage connecting the brake member to a brake member of a conveyer belt braking apparatus such as that defined above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a pictorial view of a conveyer idler arrangement including a conveyer idler roller provided with braking apparatus according to a first embodiment of the invention;  
       FIG. 2  is a pictorial view of the centre conveyer idler shown in  FIG. 1 , with the braking apparatus thereof in a first, inoperative position;  
       FIG. 3  is a similar view to that of  FIG. 2 , showing the brake member in a second, braking position thereof;  
       FIG. 4  is a partially cutaway pictorial view corresponding to  FIG. 2 , showing the construction of the braking apparatus;  
       FIGS. 5   a  to  5   c  are end views of the roller shown in FIGS.  2  to  4 , showing the operation thereof in use;  
       FIGS. 6 and 7  are similar views to those of  FIGS. 2 and 3 , respectively, of a second embodiment of a conveyer roller incorporating braking apparatus according to the invention;  
       FIG. 8  is a sectional side view of the roller of  FIGS. 6 and 7 ; and  
       FIGS. 9 and 10  show auxiliary braking apparatus of the invention in a first, inoperative position and a second, braking position thereof, respectively. 
    
    
     DESCRIPTION OF EMBODIMENTS  
       FIG. 1  shows a frame which supports a set of idler rollers intended for use in a conveyer installation. A central, horizontal roller is flanked by inclined wing rollers, for supporting a conveyer belt in a troughed configuration, which is conventional as such. However, the central roller is fitted with a belt braking mechanism according to the present invention, which will be described below in more detail.  
      Referring now to  FIGS. 2, 3  and  4 , a conveyer idler roller  10  comprises a cylindrical tube or shell, typically formed of high density polyethylene (HDPE) or steel tubing, on which a conveyer belt runs in use. The illustrated shell  10  is formed from HDPE and is fitted with solid cylindrical end plugs  12  of HDPE or another suitable plastics material. Each plug  12  has a length of approximately 80 mm in the prototype system.  
      Each plug  12  supports inner and outer roller bearings  14  and  16  which are received in respective bores in the plug, at opposite ends thereof. The bearings  14  and  16  are fitted to a stub axle  18 , so that the shell  10  of the idler roller is freely rotatable about the stub axles  18 . Each stub axle  18  has an end portion  20  which extends beyond the end of the shell  10  and the plug  12 , and has a pair of opposed flats  22  formed in it to enable the ends of the stub axles  20  to be dropped into suitably shaped slots in a support bracket.  
      As described so far, the construction of the idler roller is generally conventional, except that such rollers generally have a unitary axle extending the length of the idler roller, with a single roller bearing located near each of the opposed ends of the roller.  
      At the center of the shell  10 , the material of the shell extends inwardly to define a diametric wall  24  in which is seated a one-way roller clutch bearing  26 . Such bearings are commercially available, for example, from SKF and other manufacturers of bearings. The outer ring of the bearing  26  is a tight fit in a circular opening defined in the wall  24 . A cylindrical shaft  28  is a tight fit in the central opening  30  of the roller clutch bearing, and extends beyond the outer ends of the roller through a bore  32  formed in the stub axle  18 , in which the shaft  28  is freely rotatable.  
      The outer ends outer ends  34  of the shaft  28  pass through holes  36  formed in triangular brackets  38  which extend transversely from opposed ends of a flat braking plate  40  which extends adjacent the roller. Where the shaft  28  passes through the apertures  36 , it is welded to the metal of the brackets  38 . Thus, the braking plate  40  pivots with the shaft  28  about the same axis as the stub axles  18  of the idler roller assembly.  
      Fitted to the extreme ends of the stub axles  18  are locking members, each comprising a generally U-shaped bracket  42  with an outwardly extending flange  44  at one end thereof. The U-shaped bracket  42  defines an opening that is sized to fit snugly over the opposed flats  22  at the end of the stub axle  18 , and the bracket is then tack welded into position on the end of the stub axle. The flats  22  are sufficiently wide to accommodate both the brackets  42  and a mounting bracket for the idler roller assembly, enabling the idler roller assembly to be mounted in the same way as a conventional idler roller.  
      A notch  46  is formed in one edge of each of the triangular brackets  38  which engages the L-shaped flange  44  of the locking member in use, as described below.  
      Referring now to  FIGS. 5   a  to  5   c , which are end views of the roller assembly of FIGS.  2  to  4 , the operation of the braking mechanism of the invention will be described in greater detail. Referring first to  FIG. 5   a , the idler roller of the invention is disposed beneath a conveyer belt  48 , traveling in the direction of the arrow. The belt and any load on it are supported by the roller, and the roller rotates counterclockwise as the belt moves. The brake member  40  is in a first, inoperative position adjacent the underside of the belt  48 , and the roller clutch bearing  26  turns freely in its forward direction.  
      In the event of a belt breakage, causing the belt to reverse direction as indicated by the arrow in  FIG. 5   b , the direction of rotation of the roller is reversed, causing the roller clutch bearing  26  to lock. As the roller rotates counterclockwise together with the reversing belt, the shaft  28  rotates with it, pivoting the brake member  40  upwards into engagement with the underside of the belt  48 . Once the upper edge of the brake member engages the underside of the belt, it is pulled by the belt clockwise into its second, braking position shown in  FIG. 5   c , in which the flat surface of the brake member engages the underside of the belt fully. The notches  46  in the triangular end plates of the brake member engage the respective flanges  44  on the locking members at each end of the roller, holding the brake member in the correct position under the belt.  
      In a prototype roller of the invention, the above described braking mechanism was applied to a center idler roller of 400 mm length and 127 mm outside diameter, and the braking member was formed from 5 mm mild steel plate, supported on a mild steel shaft of 8 mm diameter. The one-way clutch roller bearing was conservatively rated to withstand a torque of 30 Nm.  
      The surface finish of the brake member can be selected according to requirements. In the prototype, the steel plate used to form the brake member had a checkered or waffled pattern, making it suitable for use with a conveyer belt having a rubber undersurface. In some cases, a smooth metal finish may be preferred. It is also possible to coat or paint the brake member, for example with a layer of epoxy based primer with a relatively coarse texture, in order to increase the friction between the brake member and the belt in use. If required, a friction lining with desired frictional characteristics could be applied to the brake member.  
      In a typical installation, the conveyer belt  48  could be a multi-ply belt with a top layer of rubber, a fibre reinforcing layer and a bottom layer of rubber which is somewhat thinner than the top layer. Alternatively, a steel reinforced rubber belt, comprising a rubber belt body with a core of steel cables, might be used. In the latter case, a belt of 1050 mm width has a mass of approximately 45 kg/m, and might be rated to carry a load of approximately 40 to 50 kg/m. Depending on the angle of inclination of the conveyer, this creates a substantial longitudinal force in the event of breakage of the belt near the head roller of the conveyer. Experiments showed that a conveyor installation having a belt inclined at 12° to the horizontal, and utilising the above described prototype rollers in a troughed configuration and with a brake member 100 mm wide, required approximately 15 to 20% of the conventional centre idlers to be replaced in order to provide sufficient braking capacity, with a suitable safety margin, for efficient braking of the conveyer belt.  
      The above described conveyer belt braking mechanism is relatively simple in design and construction, and has the advantage that it does not require a separate, external installation to be added to a conveyer system, but merely the replacement of conventional idler rollers with the special rollers of the invention.  
      Compared with prior art braking rollers, where friction between the roller itself and the underside of the belt is used to provide a braking force, the braking mechanism of the invention has a much greater braking surface area. In the above described example, the area of contact between the belt and the surface of the roller is approximately 10 mm wide, compared with the width of the braking member of 100 mm. It will be appreciated that the brake member can be made even wider if required, and it may be provided with a friction surface which is superior to the conventional HDPE or steel roller surface. If required, the surface of the brake member can be curved convexly to match the curvature of the belt due to the sagging of the belt between rollers, to enhance contact between the belt and the brake member.  
      Because the one-way roller clutch bearing  26  is used only to pivot the brake member into position under the belt, and not to apply the braking force to the belt, a relatively small and inexpensive roller clutch bearing can be utilised for this purpose.  
      It will be appreciated that the brake member of the above described apparatus engages the underside of the belt fully after a quarter turn of the associated idler roller, so that the belt does not move far before it is braked and stopped.  
       FIGS. 6, 7  and  8  show a second embodiment of the roller and associated braking apparatus. In this embodiment, the roller has a full-length shaft or axle  112  instead of a pair of stub-axles, which support the roller shell  110  on roller bearings  114  and  116 . The bearings  114  and  116  are received in respective bores in plugs or end caps  118  and  120  and are held in position by clips  122  and  124 . The shaft  112  has end portions  126  and  128  which extend beyond the end of the shell  110 , and has a pair of opposed flats  130  and  132  formed in it at each end of the shaft to enable the ends of the shaft to be dropped into suitably shaped slots in a support bracket.  
      At one end of the roller shell  110 , the plug  120  supports a one-way roller clutch bearing  134  similar to that described above. The outer ring of the bearing  134  is a tight fit in the wall  136  of the plug  120 . A clutch sleeve  138  formed from stainless steel is a tight fit in the inner ring  140  of the roller clutch bearing  134  and extends beyond the outer end of the roller around the shaft  112 . The clutch sleeve  138  is freely rotatable around the shaft  112  and is supported by a roller bearing  142 .  
      The outer end  144  of the clutch sleeve  138  supports one of two triangular brackets  146  which extend transversely from opposed ends of a curved braking plate  148  which extends adjacent and parallel to the axis of the roller. The other bracket  146  is supported by a brass bush  150 . The bracket can rotate about the bush, which can itself rotate about the shaft  112  on a pair of O-rings  152  and  154 . Where the clutch sleeve  138  supports the triangular bracket  146  it is welded to the metal of the bracket. Thus, the braking plate  148  pivots with the clutch sleeve  138  about the shaft  112  of the idler roller assembly.  
      Fitted to the ends of the shaft  112  are locking members, each comprising a generally U-shaped bracket  156  which is generally L-shaped in section, with an inwardly extending flange  158  at one end thereof. Each U-shaped bracket  156  is sized to fit snugly over the opposed flats  130 ,  132  at the ends of the shaft  112 , and the bracket is then tack welded into position on the end of the shaft. The flats  130 ,  132  are sufficiently wide to accommodate both the brackets  156  and a mounting bracket for the idler roller assembly, enabling the idler roller assembly to be mounted in the same way as a conventional idler roller. The idler roller is secured in the support bracket by means of lock nuts  160  on both ends of the shaft  112 .  
      A notch  162  is formed in one edge of each of the triangular brackets  146  which engages the flange  158  of the locking member in use, in the same way as described above. The triangular brackets  146  have a finger  164  that rests against the lowermost end of the flange  158  and keeps the braking plate  148  in a vertical position when inoperative, as shown in  FIG. 6 .  
      The inner part of the roller shell  110  is protected from dust and moisture by means of seals  166 . The clutch sleeve  138  has an inner seal  168  to keep lubricants on the roller clutch bearing  134 .  
      The second embodiment of the roller/brake apparatus operates similarly to the first embodiment. If the roller reverses direction, the roller clutch bearing locks and the clutch sleeve  138  rotates the brake member  148  into engagement with the underside of the belt in the same way as described above with reference to the first embodiment.  
       FIGS. 9 and 10  show an auxiliary braking mechanism designed for use adjacent the return run of a conveyer belt fitted with the above described braking apparatus. Referring first to  FIG. 9 , a bracket  50  supports an auxiliary brake member  52  which extends approximately the full width of the belt. The brake member  52  is, again, formed from steel plate with transversely extending triangular brackets  54  at each end, with additional reinforcing brackets  56  being provided to secure the brake member to a shaft  58 . The shaft is fixed to the brackets  54 , which are formed with notches  60  similar to the notches  46  described above, and upstanding brackets  62  which carry the shaft  58  pivotably are formed with integral locking or stop members  64  which engage the notches  60  in the same manner as the flanges  44  described above.  
      A linkage (not shown) connects the brake member  52  to a brake member  40  (or  148 ) of a corresponding idler roller, so that when the brake member of the idler roller is moved into its second, braking position, the brake member  52  is pivoted from the inoperative position shown in  FIG. 9  to the braking position shown in  FIG. 10 , engaging the belt and helping to brake it. In some instances, the auxiliary braking mechanism of  FIGS. 9 and 10  could be used independently of the braking rollers described above, with a different operating mechanism.  
      It will be appreciated that the braking apparatus of the invention could be implemented in a number of different ways. For example, although the use of a one-way roller clutch bearing housed within an idler roller is an elegant way of operating the brake member of the apparatus, another separate operating mechanism could be used to move the brake member into its operative position. Thus, the brake member of the invention could be installed adjacent a conventional idler roller and an external mechanism used to operate it.