Abstract:
A conveying belt suitable for powerturn conveying applications. The conveying belt has a mult-layer structure with layers of parallel laid yarns disposed in various angles relative to the machine direction. The parallel yarns are stitchbonded to a multiply interwoven scrim to form a subassembly. A batt of staple fibers is needled to the scrim and the batt and subassembly are encapsulated by a polymer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/859,376 filed on Nov. 16, 2006, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to conveyor belt applications and specifically, powerturn conveyor belt applications. 
       BACKGROUND OF THE INVENTION 
       [0003]    Powerturn conveyor belt applications have the following characteristics: the movement of the endless belt around the conveying path includes a curvilinear path with conveying angles ranging from approximately 30 degrees to 180 degrees. As the belt rounds the curve, the principal load axes change continuously and there is no well-defined machine direction (“MD”) axis. Also, the surface velocity of the belt varies across radial direction as the belt travels around the curvilinear path. To achieve dimensional stability in powerturn conveyors, certain belt characteristics are desirable such as low to moderate stretch, isotropy in tensile moduli and flexural rigidity within the 2-D belt plane. Accordingly, there is a need for a stronger, lighter belt for powerturn conveyor belt applications. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention meets the above described need by providing a belt design that enables control of desired directional belting properties, imparts exceptionally high tear strength, enables lower belt weight, and enables thinner designs for conveyor belts. 
         [0005]    The conveyor belt includes a scrim having a first side and a second side. A first plurality of parallel laid yarns are arranged at a first angle relative to a machine direction. The first set of yarns overlay on at least one of the first or second sides of the scrim. A second plurality of parallel laid yarns are arranged at a second angle relative to the machine direction. The second angle is different than the first angle, and the second yarns are disposed in a layer on top of the first yarns. A third plurality of parallel laid yarns are arranged at a third angle relative to the machine direction. The third angle is different from the first and second angles. The third yarns are disposed in a layer on top of the second yarns. The first, second, and third yarns are attached to at least one of the first and second sides of the scrim to form a subassembly having a first and second side. A fibrous material, in the form of discrete staple fibers consolidated together through entanglement of the individual fibers, is attached to at least one of the first and second sides of the subassembly. A polymeric material encapsulates the subassembly and the fibrous material to form a conveying belt. 
         [0006]    The modulus and tear strength in multiple directions for the conveying belt of the present invention is superior to conventional belts. 
         [0007]    The present invention may be used in many conveying belt applications including but not limited to powerturn conveying belting applications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which: 
           [0009]      FIG. 1  is a schematic illustration of the composite showing the layered composition of the present invention; 
           [0010]      FIG. 2  is a table showing example test results for a powerturn belting made using a reinforcement constructed of a woven scrim stitchbonded to triaxial yarns; 
           [0011]      FIG. 3  is a table comparing test results of conventional belting used in powerturn applications against a powerturn belting made using a reinforcement constructed of a woven scrim stitchbonded to triaxial yarns; 
           [0012]      FIG. 4  is a radial graph showing tensile moduli at 45° intervals of belt made using conventional woven biaxial reinforcement; 
           [0013]      FIG. 5  is a radial graph showing the tensile moduli at 45° intervals of a belt made using a balanced conventional woven biaxial reinforcement; 
           [0014]      FIG. 6  is a radial graph showing the tensile moduli at 45° intervals of a belt according to the present invention; 
           [0015]      FIG. 7  is an elevational view illustrating the needling of a non-woven web of staple fibers to a scrim; 
           [0016]      FIG. 8  is an elevational view illustrating the subassembly moving through a bath of elastomeric material; 
           [0017]      FIG. 9  is a schematic diagram illustrating a top coat step; 
           [0018]      FIG. 10  is a schematic diagram showing the subassembly passing through a heated platen press; 
           [0019]      FIG. 11  is a partial plan view of a scrim; 
           [0020]      FIG. 12  is a cross-sectional view of an interwoven two-ply fabric; 
           [0021]      FIG. 13  is a diagrammatic view of a multi-axial yarn feed device; 
           [0022]      FIG. 14  is a perspective view showing the orientation of the yarns in the woven scrim and parallel laid yarns; and, 
           [0023]      FIG. 15  is a side elevational view of one embodiment of the composite belt of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIG. 1 , the base fabric for the present invention may be a conventional woven scrim  10  (strength member made of woven machine direction yarns and cross-machine direction yarns) or an interwoven design as discussed below. The machine direction yarns and the cross-machine direction yarns are provided in an open weave cloth as the scrim. Any weave may be used including a plain weave as shown in  FIG. 11 . The weave in  FIG. 11  includes machine direction warp yarns  110  and cross machine direction weft yarns  113 . The yarn selection, the weave selection and the yarn density of warp and weft yarns is selected so as to achieve a balanced fabric structure of the stitchbonded composite. Low thermal shrinkage behavior in yarns is desirable in selection of yarns. Choice between spun, filament or other yarn types is made based on the belt design constraints. Also, the yarns may be selected from a wide variety of synthetic yarns, such as polyester, polyamide, viscose rayon and like yarns or natural yarns like cotton or silk. 
         [0025]    The nature of the cross-machine direction yarns is as critical as the machine direction yarns, and the yarns may comprise any conventional synthetic yarns. The denier of the machine direction and cross-machine direction yarns can be between 400 denier and 4000 denier without limitation. The density of the weave is selected to provide a scrim weight of from between about 8 ounces per square yard to about 24 ounces per square yard for optimum strength. The results with a woven scrim and triaxial stitchbonded yarns are discussed below in connection with  FIG. 2 . 
         [0026]    The woven scrim for the present invention comprises an interwoven multi-ply synthetic fabric shown in  FIG. 12 . The weave design change from a plain woven scrim to a multiply interwoven design allows for increased density in fabric cover resulting from increase in the yarn density in warp and weft yarns. The weave change also facilitates ease of penetration of stitch needles when forming the weft knit stitchbonded composite as described below. As shown in  FIG. 12 , there are multiple plies of machine direction warp yarns  150  interwoven with cross machine direction weft yarns  153 . 
         [0027]    A plurality of parallel laid yarns  13  having a denier of 400-4000 typical are overlaid on the base fabric or scrim  10  by means of a multiaxial yarn feed device  14  ( FIG. 13 ). The yarns may be arranged in multiple layers separately at orientation angles from 0 degree to 180 degrees with respect to the machine direction (0 degree). An example of an arrangement with triaxial parallel laid yarns is provided in  FIG. 14 . Other arrangements of the yarns such as quad-axial may also be suitable. 
         [0028]    The parallel laid yarn in multiple layers  13  at different orientation angles may be stitched and/or bonded to the base fabric  10  by means of weft knitting stitch-bonding machines or fused/bonded by other means (i.e., thermal bonding, epoxy adhesives). The bonding between the base fabric and the parallel laid yarn layers in weft knitting technology is achieved by forming stitches using synthetic textured yarns. The resulting composite textile yarn assembly thus may have yarns oriented in many independent directions (formed i.e., 0, 90, +45, and −45 degrees) and the assembly thus formed acts as the reinforcement member within the textile composite. 
         [0029]    Batts  16 ,  19  of staple synthetic fibers may be needled to either or both faces of the subassembly  20  created by stitchbonding the parallel laid yarns  13  to the scrim  10 . As shown in  FIG. 7 , the subassembly  20  may be conveyed from a roll  39  onto a conventional conveyor  40  rotating in a clockwise direction, as shown with respect to the orientation of  FIG. 1  moving the subassembly  20  from left to right. Discrete staple fibers  42 , such as are provided in a non-woven web of fibrous batt may be spread in a generally uniform distribution over the upper surface of the subassembly  20  from a web laying mechanism  44 . Multiple layers of fibrous web (batt) are laid onto subassembly  20  in a reciprocating manner to obtain desirable batt fiber weight. A needling apparatus  46  serves to consolidate the staple fibers  42  through entanglement and to thereby integrate the staple fibers  42  to the subassembly  20 . The batt  16 ,  19  may be of randomly oriented synthetic carded fibers. As an alternative, the fibers may be directionally oriented within the batt by methods known to those of ordinary skill in the art. The batt of staple synthetic fibers may have an overall weight from between about 2 oz. per square yard to 100 oz. per square yard. The staple fibers may have different fineness (denier/dtex) and a range of denier, which is preferred for the yarns in the scrim, may be selected. The batt may be pre-needled using conventional techniques to obtain some integrity of the staple fibers prior to needling the batt to the subassembly. The technique of needling is well-known and the details need not be recited here: see for example U.S. Pat. No. 2,059,132 describing conventional needling operations and which is incorporated herein by reference. The coarseness of the felting needles used, the barb configurations, number, size, and other variables are dependent somewhat on the degree of openness between the textile yarns, so as to avoid rupture of the textile yarns. In general, but not limited to, a No. 32 gauge needle is preferred, with the barbs oriented so as not to tear the machine direction yarns. Needling is carried out to produce a needled subassembly. The resulting nonwoven composite is comprised of a reinforcement member made of yarns, sandwiched on both sides by fiber batting  16 ,  19  where the fiber to fiber entanglement and the fiber to yarn entanglements resulting from the needle-punching process maintains the integrity of the nonwoven composite structure. 
         [0030]    The needled subassembly  50  may be heat set in an oven (not shown) to thermally stabilize the stitchbonded composite fabric comprising the woven scrim before the nonwoven is subject to the saturation step. During heat setting, the fabric may be tensioned in the machine direction under from between 0.5 to 22 lbs per inch. The tensioning obviates wrinkles across the width and along the length of the belting. Heat setting is carried out under hot air temperatures or other methods dependent on the nature of the fibers and yarns employed in the subassembly. Those skilled in the art will know which temperatures to select depending on the materials. 
         [0031]    A wide range of liquid polymeric saturants may be employed for saturation of the belting including acrylonitrile butadiene rubber, styrene-butadiene polymer, poly-butadiene, EPDM, polyurethane, silicone rubber etc. The saturation of the heat set needled subassembly will provide high loading of elastomer, substantially penetrating the stitchbonded base fabric so as to impregnate the fibrous layer. The majority of voids in the stitchbonded base fabric and in the fibrous layer are filled with the elastomeric material so that the elastomer is distributed throughout the body of the final product. The heat set needled subassembly  56  may be calendered by rollers  58  and  60  prior to being guided by rollers  62 ,  64  and  66  in and out of a vessel or tank  68  containing a solution of the polymeric elastomer material  70 . The depth of roller  64  below the level of liquid elastomer  70  may control the exposure time of subassembly  56  to the elastomeric material  70 . The subassembly  56  leaving container  68  is now saturated with the liquid elastomeric material  70  and if needed, a fourth roller  72  can be provided in conjunction with roller  66  to squeegee or wipe excess liquid elastomer from the belting. It will be appreciated that a single trip through tank  68  may suffice for saturating some beltings, while multiple saturation steps with intermediate squeeging or partial drying steps may be required to fully saturate dense fibrous layers in other needled beltings. Curing may be affected by any means appropriate for the polymeric saturant. For example, the belting may be cured by heat for heat curable elastomers. In  FIG. 9 , a thin topcoat  90  of thermoset acrylic, silicone, polyolefin, polypropylene, polyethylene, PVC, polyurethane, etc., cover may be applied to the top side of the composite assembly to enhance cut and scratch resistance, modify coefficient of friction or reduce noise, for example. As shown in  FIG. 10 , the saturated belting  75  can be passed through a heated platen press  80  at a temperature sufficient to cure the elastomer. Pressures from between about 50 lbs. per square inch to about 200 lbs per square inch are practical and illustrative of pressures that may be employed. The saturated belting  75  may be pressed between a top platen  83  and a bottom platen  86  and cured under pressures of from between about 90 lbs per square inch to 130 lbs per square inch. The addition of the elastomers will further consolidate the non-woven batt and add abrasion resistance. By using a patterned surface impression medium, the belting is molded during curing to mold the impregnated material so as to form at least one plane surface and one surface patterned or with raised portions, 
         [0032]    i.e., an impression surface. The impression surface is molded to provide a similar appearance and function as the surface of a traditional woven synthetic belt. The raised impression may be of any geometric configuration such as semi-hemispheres, bars, grooves etc. and is raised above off the lower portions of the top surface of the belting. 
         [0033]    Turning to  FIG. 15 , one embodiment of the present invention is shown. The woven substrate  200  is disposed between parallel laid multiaxial yarns  210  and a fibrous batt  220  is needled to both faces. The assembly is encapsulated in an elastomeric material  230 . 
         [0034]    Returning to  FIG. 2 , the physical properties of a composite belt according to the present invention made using an interwoven scrim stitchbonded to triaxial yarns as reinforcement are shown. 
         [0035]    In  FIG. 3 , a table comparing belting with a 2-ply interwoven polyester fabric stitchbonded to triaxial yarns according to the present invention to two prior art belts A and B is shown. Belt “A” is a conventional plied belting product made of plain woven reinforcement on one face and two-ply interwoven fabric impregnated with elastomer on the other face. Belt “B” is a nonwoven belting product that uses a conventional biaxial woven reinforcement. As shown, the modulus and tear strength in multiple directions is superior for the belt of the present invention considering the reduction in weight and thickness. 
         [0036]    In  FIG. 4 , a graph shows the tensile moduli (N/mm) at three different extensions for a belt made with conventional woven biaxial reinforcement. The tensile moduli are highest in the machine direction and are far lower in the other directions. 
         [0037]    In  FIG. 5 , a graph shows the tensile moduli (N/mm) at varying extensions for a belt made with balanced weave woven reinforcement. The tensile moduli are balanced in the machine and the cross machine directions, whereas the tensile moduli are much smaller in the bias (±45°) directions. 
         [0038]      FIG. 6  illustrates the tensile moduli (N/mm) at varying extensions for a belt according to the present invention. As shown the belt according to the present invention demonstrates significant improvement in isotropy in tensile moduli in 0°, 90°, +45° and −45° directions.