Fabric conveyor belt with layered PVC and polyester coating and method of forming the same

A fabric carcass defines the base of a conveyor belt. A first polymer is coated or otherwise disposed over an exterior side of the fabric carcass to cure with a first layer thickness. The first polymer may be a polyvinyl chloride resin with a plasticizer additive to provide an added robustness to belt at a relatively low cost. Due to deterioration that may occur when certain polyvinyl chloride resins are used as the exterior surface of the conveyor belt, a second polymer is disposed over the cured layer of polyvinyl chloride to define an exterior surface that is configured for resiliently interfacing with a die press of a cutting or stamping station. The second polymer may be a polyester to provide improved resiliency and an exterior surface with better durability than the first polymer.

FIELD OF THE INVENTION

The present invention generally relates to a conveyor belt construction and an associated forming method of the belting, and more particularly to a fabric conveyor belt that is coated with polymer or other compositions that may be adapted for carrying heavy rigid objects or interfacing with a die press of a cutting or stamping station.

BACKGROUND OF THE INVENTION

It is generally known to use woven textiles that are treated with polymer or other thermoplastic material for conveyor belting to increase the ability of the belt to withstand longitudinal tensile stresses and generally maintain transverse stability. Such a polymer coating can be applied to the fiber strands of belt before weaving the fabric or applied directly to the woven fabric to increase the stability of the belting. Common methods to treat woven fabric include laminating methods, polymer extrusion methods, and cured liquid treatment methods. However, treating fabric used in conveyor systems presents challenges, in that the polymer of a treated belt may experience cracking and other failure when placed under tension and when the belt is bent around rollers of a conveyor system. In addition to these general operating conditions of a conveyor system, conveyor belting that is adapted for carrying heavy rigid objects or interfacing with a die press of a cutting or stamping station undergoes significant compressive forces usually perpendicular to the planar extent of the belting. Accordingly, there are significant challenges in forming a conveyor belt that uses economical materials and forming processes that can also durably perform in such an operating environment.

SUMMARY OF THE INVENTION

The present invention provides a conveyor belt that may be configured to be used conveying objects, such as sharp and rigid material being recycled, or in a continuous cutting or stamping station that applies compressive forces perpendicular to the planar extent of the belt. The conveyor belt includes a fabric carcass that continuously supports and defines the base of the conveyor belt. The fabric carcass may be made of up of a woven structure of filaments, with at least some of the filaments arranged longitudinally in a conveyance direction to withstand tensile stresses put on the conveyor belt. A first polymer is coated or otherwise disposed over an exterior side of the fabric carcass to cure with a first layer thickness. The first polymer may be a polyvinyl chloride resin with a plasticizer additive to provide an added robustness to belt at a relatively low cost. Due to discovered deterioration that may occur when certain polyvinyl chloride resins are used as the exterior surface of the belt, a second polymer is disposed over the cured layer of polyvinyl chloride to define an exterior surface that is configured for resiliently interfacing with the die press of a cutting or stamping station. The second polymer may be a polyester to provide improved resiliency and an exterior surface with better durability for conveyor systems than the first polymer.

According to one aspect of the present invention, a conveyor belt is provided with a fabric carcass having woven filaments in longitudinal and lateral directions, such that the fabric carcass is configured to convey objects in the longitudinal direction. A reinforcing polymer that includes polyvinyl chloride is disposed in a first defined layer over an exterior side of the fabric carcass to form a first thickness. An exterior polymer that includes polyester is disposed in a second defined layer over the first defined layer to fused therewith and form a second thickness. The exterior polymer provides greater compressive resiliency than the reinforcing polymer.

According to another aspect of the present invention, a conveyor belt for interfacing with a die press includes a fabric carcass having filaments disposed longitudinally in a conveyance direction. A polyvinyl chloride resin is impregnated in the fabric carcass and is disposed over an exterior side of the fabric carcass to cure with a first layer thickness. A polyester resin is disposed over the cured layer of polyvinyl chloride resin to form a second layer thickness and define an exterior surface that is configured for resiliently interfacing with the die press that compresses and bites down into the polyester substrate.

According to another aspect of the present invention, a method for forming a conveyor belt includes providing a fabric belt carcass and impregnating the fabric belt carcass with a polyvinyl chloride resin. A reinforcing polymer comprising polyvinyl chloride is applied over an exterior side of the fabric belt carcass. An exterior polymer comprising polyester is applied over the reinforcing polymer to define an exterior surface of the conveyor belt.

According to another aspect of the present invention, a method for forming a conveyor belt includes providing a fabric carcass having filaments woven in a longitudinal direction. The fabric carcass is placed under generally constant tension in the longitudinal direction. The fabric carcass is impregnated with a liquid polyvinyl chloride resin to form a substantially impervious belt. A first polymer resin comprising polyvinyl chloride is applied over an exterior side of the fabric carcass to define a first layer. The first polymer resin is leveled with a doctor blade to regulate a first gauge thickness of the first layer and to define an outer surface thereof. A second polymer resin comprising polyester is applied over the outer surface of the first layer to define a second layer. The second layer is leveled with a doctor blade to regulate a second gauge thickness of the second layer and to define an exterior surface of the conveyor belt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and the illustrative embodiments depicted therein, a conveyor belt10in accordance with the present invention is shown with a belt carcass12that continuously supports and defines the base of the conveyor belt10. The belt carcass12may be made of up of a fabric structure of filaments14, with at least some of the filaments arranged longitudinally in a conveyance direction CD to withstand tensile stresses put on the conveyor belt10. A first polymer16is impregnated in the belt carcass12and is disposed as a layer over an exterior side of the belt carcass12to cure with a define thickness away from the belt carcass12. The first polymer16may be a polyvinyl chloride resin with a plasticizer additive to provide robustness to the belt at a relatively low cost. Due to discovered deterioration that may occur if the first polymer16is used as the exterior surface of the belt, the present invention provides a second finishing polymer18over the cured layer of the first polymer16to define an exterior surface20of the conveyor belt10. The second polymer18may be a polyester resin, such as a polyester elastomer, that is configured to provide improved resiliency and an exterior surface20with enhanced durability for conveyor systems, such as for resiliently interfacing with a die press of a cutting or stamping station.

With reference to the embodiment of the conveyor belt10shown in the schematic process diagram depicted inFIGS. 1 and 2, the fabric carcass12is provided on a wound spindle22that may freely rotate to release the sheet of fabric belting12. Prior to any resins or treatments being applied to the fabric, the fabric carcass12may be placed under tension in the longitudinal direction with a pretension winder24. The tension applied is carried through the production line, which allows the polymer resins to cure to the fabric belting in tension, thereby reducing initial failure, such as cracking, to the polymer on the conveyor belt when placed under tension in operation of conveyor system. Accordingly, the tension applied with the pretension winder24may be similar to the tension applied during the operating conditions of the conveyor system under which the belt is intended to perform.

As also generally shown inFIG. 2, multiple stations may be provided in the production line that are treating the conveyor belt10in a continuous operation, thereby having the potential to start the production line with an untreated fabric belt12and have a finished conveyor belt10at the final roller26. However, it should be understood that the multiple stations are merely provided for illustration, as a single station could conceivable be adjusted and repeatedly used to provide the same effective treatments to the conveyor belt10, albeit at a less efficient process. Accordingly, the stations start treating the fabric by first impregnating the belt carcass12with a resin comprising the first polymer16and applying the first polymer16in layer over an exterior side of the fabric belt carcass. A resin comprising the second polymer18is then applied in a layer over the resin having the first polymer16to define an exterior surface20of the conveyor belt. Due to the advantages of applying these resins in multiple layers to achieve a desired thickness, the number of stations used can vary and therefore the final station is depicted as station N to indicate a modifiable number of total stations in accordance with the desired thicknesses, properties of the resin materials be applied, and intended use of the conveyor belt being processed.

Specific to the conveyor belt discussed herein, the first polymer resin16includes a thermoplastic resin, such as polyvinyl chloride (PVC), combined with a liquid plasticizer to increase the elasticity of the resin. However, it is contemplated that the first polymer16may be one or more other thermoplastic polymers or a thermosetting polymer, such as polyurethane, although for thermosetting polymers a different forming process without heat application may be required. The second polymer resin18includes a thermoplastic resin, such as polyester, which may be a thermoplastic elastomer, such as DuPont™ Hytrel®. Further, the fabric carcass may be formed with polyester, polyamide, rayon, cotton, nylon, or any combination thereof. Also, the fabric carcass of the present invention can be any convention weave, but a weave with relatively wide opening is preferred to allow for impregnation with resin. It is also contemplated that the belt carcass of the present invention may be a composite with strands of monofilaments, such as carbon fibers, metals, or any of the fabric materials listed above, extending in the longitudinal direction and interconnected with other conceivable materials. Optionally, the belt carcass may also be a non-woven carcass, such as a polyester or aramid needle felt.

At the first station26, as generally shown inFIGS. 1-4A, the resin comprising the first polymer16is in liquid form, having PVC and plasticizer, and is applied substantially uniformly over the upper surface of the belting, which during operation is the interior side28or roller side of the fabric belting (FIG. 3A). This application of the first polymer resin16at least partially impregnates the fabric carcass12with the liquefied resin, as illustrated inFIGS. 3-3A. The impregnation of the fabric carcass12includes any resin that is absorbed by the filaments of the fabric or otherwise disposed in the open pores between the filaments14of the fabric. As the fabric carcass continues to move through the first station26, a doctor blade30that spans laterally across the entire belt10is positioned with a distal edge32of the blade in abutting contact with the upper surface or interior side28of the fabric belting, thereby shaving a portion of the resin comprising the first polymer16off the fabric carcass12to expose portions of the woven filaments14(FIGS. 4-4A). The shaving of the interior side surface of the fabric carcass12may also spread uneven levels of resin and remove discontinuities that might cause the belt to experience lateral movement or generally inconsistent behavior when moving over rollers of a conveyor system. Also, the shaving of the interior surface of the fabric carcass12to exposed portions of the woven fabric may provide added friction during use of the final conveyor belt, such as when the interior side28of the belt abuts against a powered roller of a conveyor system. More specifically, the distal edge32of the doctor blade30scraps the excess polymer resin from the uppermost portion the woven threads of the fabric carcass12, leaving the polymer resin intact that is otherwise impregnated in the fabric carcass. This remaining portion of polymer resin may be substantially adhered and cured to the fabric carcass12, as discussed in more detail below, and may thereby form a substantially impervious belt. It is also contemplated that the first polymer may be delivered or applied to the fabric carcass or in a layer over an existing polymer on the fabric carcass in other conceivable manners, such as by lamination or extrusion of the PCV in solid form (e.g. pellets).

After the optional initial impregnation with the resin comprising the first polymer16, the belt may receive a coating of the resin comprising the first polymer16on the exterior side34of the fabric carcass, as shown at the second station36inFIG. 1and inFIGS. 5-5A. It is contemplated that a coating of the first polymer resin16may be applied to a belt that has not been impregnated or otherwise treated, as the coating of the first polymer resin may be sufficient to provide the intended reinforcement and/or thickness to the belt. To apply the first polymer resin16to the exterior side34, the belt may be flipped in a series of rollers38that gradually twist the belt 180° to present the exterior side34of the belt substantially horizontally as the uppermost side of the belt. The additional layering of the first polymer resin16may provide a reinforcing layer of the PVC and plasticizer additive to increase the robustness, hardness, and overall gauge of the conveyor belt. This reinforcing polymer may be formed in a first defined layer40over the exterior side of the fabric carcass to form a thickness elevated away from the uppermost surface of the filaments of the fabric carcass. Specially, for use in conveying recyclable materials that may be sharp, the reinforcing layer of PVC may be beneficial to prevent unwanted damage to the fabric carcass. In some instances, the reinforcing layer may be sufficient or complete with a single impregnation layer of the first polymer resin16that is applied to either the interior or exterior side28,34of the fabric carcass, such that the final belt10is sufficiently reinforced for its intended use.

Once a reinforcing layer of the first polymer resin16is applied to the exterior side34of the fabric carcass, as shown inFIGS. 6-6A, it may again be leveled or spread by a doctor blade30that has the distal edge32elevated from the fabric carcass12. Accordingly, the doctor blade30is used to regulate the gauge thickness40of the layer of the first polymer resin16and to define a level outer surface42thereof. The doctor blade30may accumulate a pool44of resin on the intake side of the blade as the layer of resin is smoothed and leveled, which may be reduced by occasionally adjusting the flow of resin that is pumped to the distribution head46(FIGS. 1-2). After passing through the doctor blade30, this layer of the first polymer16may be again be substantially adhered and cured to the fabric carcass and any other thermoplastic resin it may contact, as explained in greater detail below.

As shown inFIGS. 1-2 and 7-7A, the curing process for a thermoplastic resin may be done by heating the belt, such as with an oven or other mechanism that creates a heated and/or dehydrated environment for the resin to cure on the fabric carcass12. In the illustrated embodiment, an oven tunnel48with infrared heaters50is provided after the doctor blade30to heat the conveyor belt to a preferred curing temperature, such as at least about 100° C. The temperature provided by the infrared heaters50is configured to be less than the melting point of the fabric carcass12, such as about 150° C., or any other temperature that would otherwise compromise the structural integrity of the fabric carcass12. It is also contemplated that other convention heating ovens may be used or, in the case of a thermosetting resin, ovens may not be necessary. The heat applied in the illustrated embodiment is generated by infrared waves that correspond with the infrared absorption characteristics of the polymer resin. Upon application of the heat, the resin viscosity initially drops and then begins to increase as the chemical reactions increase the average length and the degree of cross-linking between the constituent oligomers, ultimately resulting in gelation, adhesion, and curing of the resin to the fabric carcass12.

After the conveyor belt passes through the oven tunnel48, the partially cured resin on the fabric carcass12may have a dimpled or otherwise uneven surface. The belt then may passes through a series of compression rollers52(FIGS. 8-8A) that compresses the resin into the fabric carcass12, remove trapped air, and further provide a smooth and flat finished surface54. The conveyor belt10may receive multiple layers of the first polymer resin16by repeating the steps shown inFIGS. 5-8A, until the desired gauge thickness of the first polymer resin16is achieved. Each additional layer of the first polymer resin16will adhere and cure into the previous layer and the fabric carcass upon passing the belt thought the tunnel oven48and the compression rollers52. In instances of thin layers that have few irregularities from the tunnel oven48, the compression rollers may not be necessary, since the reinforcing layer of the first polymer resin does not form the outer exterior surface20of the finished conveyor belt10(FIG. 9) that interfaces with objects that are conveyed in operation of a conveyor system.

As depicted inFIGS. 9-9A, the illustrated embodiment of the conveyor belt10includes multiple layers, including a finishing layer56of a second polymer resin18that includes polyester over the outer surface54of the first layer. The polyester resin18may be formed with granulated pellets mixed with a plasticizer and applied to the layer of the first polymer resin in a substantially identical manner as described above with reference to application of the first polymer layer having PVC and plasticizer additive. It is also contemplated that the polyester layer may be extruded, laminated, or applied in another conceivable manner to the outer surface54of the first polymer resin16. Furthermore, it is conceivable that the PVC and/or polyester layers may in any combination be extruded, laminated, or applied in another conceivable manner to the outer surface54of the first polymer resin16. In the case of applying the second polymer resin18in a liquid form, the layer may be leveled and spread the with a doctor blade30to regulate a second gauge thickness56of the second layer and to define the exterior surface20of the conveyor belt10. Again, heat may be applied with a tunnel oven48to cure and adhere the second polymer resin18to the cured first layer40of the first polymer resin16, and the second polymer resin may be compressed to further adhere to the first polymer resin by compression rollers, similarly providing a smooth and consistent exterior surface. Should it be desired, it is also conceivable that the final exterior surface20may be modified to have ridges, grooves, or other embossment, by the final compression roller which may include such embossing indicia on the outer circumferential surface thererof. Similar to the first polymer resin16, the second polymer resin18may be applied in multiple layers to add to the overall thickness of the polyester layer. The exterior polymer18provides greater compressive resiliency than the reinforcing polymer16, such that the exterior polymer is configured for interfacing with a die press of a stamping station that compresses and bites down into the exterior polymer (i.e. the polyester substrate). Also, the first polymer resin layer or layers may have an overall thickness that is greater than the second thickness of the second defined layer of the exterior polymer, such that conveyor belt is configured to transport sharp rigid objects, such as recyclable material.