Abstract:
An elongatable conveyor belt capable of traversing horizontal curves during its conveying run while still allowing for retention of the material to be conveyed thereon, the conveying belt being made of a stretchable or elongatable elastomeric material and including an upper layer of transverse reinforcing cords and a substantially heavier lower layer of transverse reinforcing cords disposed at opposing angles relative to the transverse axis of the conveyor belt. The belt also includes an internal stretch limiter such as an angularly woven fabric in the central region of the belt.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to conveyor belts and, in particular, to a conveyor belt capable of traversing horizontal curves during its conveying run while still allowing for retention of the material to be conveyed thereon, the conveyor belt being made of a stretchable or elongatable elastomeric material and including upper and lower layers of reinforcing material. 
     2. Description of the Prior Art 
     As is known, conveyor belts have been developed for traveling through an orbit with a generally horizontally extending conveying run overlying a generally horizontally extending return run with the conveying and return runs being stretched or elongated to provide tension in the sides of the conveying run so that such sides remain in tension as the conveying run traverses a horizontal curve. A description of such a tensioned conveyor belt is set forth in U.S. Pat. No. 4,387,801 wherein one embodiment of a conveyor belt is disclosed and described having a selected limited elongation for establishing the overall length of an orbital conveyor belt. A conveyor belt including an internal stretch limiter and an upper and lower layer of reinforcing material is disclosed in Marshall U.S. Pat. No. 5,004,098. 
     A problem with the prior art conveyor belts is that the belt ants to roll out from under edge roller flanges which are intended to hold the belt in turns. Further, the belt wants to lift out from under the edge roller flanges and go straight up in severe dips. The force that the flanges exert on the belt prevent this, but in order for this to be effective, the belt must be relatively stiff. However, in order to take a troughed shape so as to effectively carry material, the belt has to be relatively flexible. The problem thus has been to make the belt flexible enough to trough, but relatively stiff to help resist buckling in the opposite direction. This has resulted in a compromise design. Present conveyor belts have two layers of reinforcing cords near the bottom surface, and two layers near the top surface, and all four of the cords that constitute these layers are the same size. The purpose of this reinforcement is to provide the required stiffness. 
     SUMMARY OF THE INVENTION 
     This invention provides an elongatable conveyor belt capable of traversing horizontal curves during its conveying run while still allowing for retention of the material to be conveyed thereon, the conveying belt being made of a stretchable or elongatable elastomeric material and including upper layers of transverse reinforcing cords and substantially heavier lower layers of transverse reinforcing cords. The belt also includes an internal stretch limiter such as an angularly woven fabric in the central region of the belt. 
     One of the principal features of the invention is to provide a belt with differential stiffness in cross sectional bending. Thus, the belt&#39;s top strand will flex more easily to become concave upwards and so will trough as readily as a standard belt, but the bottom strand will resist flexing to become convex upwards and so will resist the bending that allows it to come out from under the edge roller flanges that overhang the belt edges. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of the conveyor belt according to the present invention; 
     FIG. 2 is an cross sectional view of a conveying apparatus including the conveyor belt of the invention; 
     FIG. 3 is a partially broken away enlarged view of one end of the conveyor belt shown in FIG. 1; 
     FIG. 4 is a further enlargement of the upper corner of the end of the conveyor belt shown in FIG. 3; and 
     FIG. 5 is a further enlargement of the lower corner of the end of the conveyor belt shown in FIG.  3 . 
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Use of “including” and “comprising” and variations thereof as used herein is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items. Use of “consisting of” and variations thereof as used herein is meant to encompass only the items listed thereafter and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, the figures show a conveyor belt generally designated as  10 . As is known, conveyor belts may be formed from materials such as natural rubber or various rubber compounds such as neoprene, which materials will be referred to herein as “rubber”, as well as reinforcing materials. Conveyor belts, such as those previously used in conveying coal commonly comprise a plurality of elongated belt sections (not shown) joined at each end to an end of an adjacent elongated section by means of a connector to form an elongated orbital conveying belt  10 . A typical conveyor apparatus  14  which uses such a belt  10  is illustrated in FIG.  2 . The conveyor belt  10  provides an upper conveying run  18  which overlies a return run  22  with the end portions of the orbital belt  10  traveling over belt reversing end rollers (not shown). Such belts  10  are typically frictionally driven by the end rollers by suitable means connectable to shafts on the end rollers. Additionally, rollers  26  are typically provided along the length of the belt  10  and may cause the belt  10  to traverse a varied horizontal and vertical path which may particularly include horizontal curves. Further, side rollers  28  may be provided to deflect the lateral edges of the belt  10  in order to retain material in the central portion thereof. Flanged edge rollers  30  are also provided to guide the belt  10  around horizontal curves and to keep the belt from rolling out on those turns or lifting up in vertical dips. The conveyor belt  10  includes an upper surface  34  on which the material to be conveyed may be placed and a lower surface  38  which is engaged by the driving and/or support rolls. 
     The structure of the conveyor belt  10  includes a lower or first rubber body component  40  upon which two layers of angularly disposed reinforcing cords  70 ,  72  are provided (shown together as  44  in FIG.  1 ). These cords are preferably of polyester material. The individual cords in the first layer  72  are laid at an angle of +7½° to the transverse axis of the belt and the individual cords of the second layer  70  are laid at an angle of −7½° to the transverse axis so that the cords of layer  70  are at an included angle of 15° with respect to the cords of layer  72 . The conveyor belt  10  further includes an intermediate rubber body component  48 . In addition, two upper layers  60 ,  62  of polyester reinforcing cords are provided substantially above the intermediate component  48  within the conveyor belt  10 . (These layers are shown together as  52  in FIG. 1) The upper two layers  60 ,  62  are also at plus and minus 7½° to the transverse axis of the belt and so the cords of these layers also lie at 15° included angle with respect to each other. A rubber body component  56  is provided in the upper portion of belt  10 . 
     The cords of layers  70 ,  60  and  62  are substantially the same length and extend not quite the full width of the belt. However, the cords of layer  72  are substantially longer so that they may wrap around the ends of cords  70 ,  60  and  62  as is shown in FIG.  3 . 
     In the prior art the cords of all four layers are the same diameter. In this invention, however, a substantially heavier or larger diameter cord is used in the lower layers  70  and  72 . The heavier cords in the lower layers increase the stiffness of the belt in cross-sectional bending when in compression, while the same cords in tension have a negligible effect. Thus, by putting heavier cords near the bottom surface  38  of the belt  10 , the belt  10  will trough as readily as a standard belt but will resist coming out of its path with twice the strength of a standard belt. It can be seen in FIG. 2 that edge rollers  30  have flanges that overhang the edges of the belt. In horizontal turns the edge of the belt wants to rise into this flange and if unrestrained would rise and roll out of the set of rollers that guides it. It is the strength to resist this rolling out that is provided by the heavier cords since they resist the bending of the belt in its cross section that must accompany the distortion required to disengage from the overhanging flange. This is critical for wider belts such as 42 inch wide belts. Further, with this construction, the belt top strand resists loads pushing down on the edges, but conforms more readily to loads pushing up. 
     In other embodiments, less or more layers of cords can be used in either the upper or lower composite layers. It is only necessary that at least one layer of cord in the lower composite layer be heavier, thereby increasing the resistance to compression of the belt  10  in the lower layer of the belt. More particularly, in the preferred embodiment, the two upper layer cords are 1000 two ply polyester cords, and the two lower layer cords are 1000 four ply polyester cords. Further, in the preferred embodiment, the belt is about 42 inches (106 cm) wide and about ⅞ths inch (2.2 cm) deep. As illustrated in FIGS. 3 through 5, the lowermost cord  72  is turned upwardly at the edges of the belt  10 , and then placed over the uppermost cord  60  in the upper layer of the belt  10  a distance of about 3 inches (7.5 cm) from the edge of the belt  10 , in order to help reinforce the belt edges. 
     The conveyor belt  10  further includes an internal stretch limiting means  76  in the lateral center of the intermediate body section  48 . The internal stretch limiter  76  preferably comprises an angularly woven high strength band which is embedded into the belt  10 . The internal stretch limiter  76  is preferably formed of an aramid fiber such as that sold under the trademark KEVLAR® by E. I. DuPont de Nemours &amp; Company. The weave of the stretch limiter  76  has the property of elongating a predetermined distance when subject to tension during the initial stretching of the belt  10 , and then its resistance to further elongation increases rapidly to resist any appreciable over-stretching of the belt  10  in operation. Preferably, the various components of the belt  10  are laid out and then passed through a vulcanizing press and the belt is vulcanized at a temperature of approximately 300° F. and at a pressure of 300 p.s.i. for approximately one hour. During such a process, the rubber-like material passes into the interstices between the cords in the lower and upper reinforcing layers  44  and  52 , respectively, and in the stretch limiting means  76 . 
     The conveyor belts produced in accordance with the present invention serve to provide an internal stretch limiting means which allows the conveyor belts  10  to be elongated by a predetermined distance; however, once the predetermined amount is reached, resistance to further elongation increased rapidly. The belt  10  is elongatable only up to 10% and preferably 8%, during installation and start-up of the belt  10 . 
     It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.