Conveyor belts with textile ropes and cords

Abstract

The present invention concerns conveyor belts having a rubber matrix body (1) and one or more cords (2) embedded therein, wherein the cords are predominantly constituted from UHMWPE yarns and the rubber matrix body comprises a thermoplastic elastomer. In addition, the present invention is directed at processes for the manufacture of respective conveyor belts as well as the use of one or more cords, which are predominantly constituted from UHMWPE yarns, in a conveyor belt having a rubber matrix body as a replacement for steel cords in order to reduce the weight of the conveyor belt.

Description

[0001] Description

[0002] Title

[0003] CONVEYOR BELTS WITH TEXTILE ROPES AND CORDS

[0004] The present invention concerns conveyor belts having a rubber matrix body and one or more cords embedded therein, wherein the cords are predominantly constituted from ultra-high molecular weight polyethylene (UHMWPE) yams and the rubber matrix body comprises a thermoplastic elastomer. In addition, the present invention is directed at processes for the manufacture of respective conveyor belts as well as the use of one or more cords, which are predominantly constituted from UHMWPE yarns, in a conveyor belt having a rubber matrix body as a replacement for steel cords in order to reduce the weight of the conveyor belt.

[0005] State of the art

[0006] To transport bulk goods of all kinds such as stones, ores or coal in mining applications or grains, groceries or waste, conveyor belts are often used, which are subject to a wide variety of requirements depending on the application.

[0007] In general, due to the usually relatively long conveying distances, especially in the longitudinal direction, the conveyor belt must have a certain elasticity in connection with a low bending stiffness in order to minimize an elongation of the conveyor belt during operation and at the same time, for example, to prevent the conveyor belt from deflecting around snub, deflecting and / or to drive pulleys.

[0008] Steel cables and cords currently still represent the predominant means of reinforcement in conveyor belts in order to limit their elongation and to provide general reinforcement to the belts. In steel reinforced belts, multiple cords or cables are usually positioned parallel to one another and are embedded in a rubber matrix which fully surrounds the cords / cables. In this manner, the steel is protected from deleterious influences from the outer environment such as moisture.

[0009] While steel provides many favorable properties for reinforcement such as high strength, low elongation, and a good connectivity to rubber materials, steel has the downside that it may be affected by corrosion in case the protecting belt cover and zinc coating are damaged by transported material and it is comparatively heavy, which, when incorporated into conveyor belts, strongly affects the total weight of the belts. This applies in particular when the belts cross larger gaps between supporting members or rolls, as the belts own weight adds to the weight of material conveyed thereon, which may in turn lead to irreversible deformation and / or damage to the belt body or a cover layer thereon.

[0010] As in addition, higher weight belts have higher energy demands for operation, there is a demand for belts with a similar reinforcement thereof in terms of strength, but which have a lower weight than conveyor belts which are reinforced with conventional steel cords.

[0011] In addition, a further problem associated with steel cords is when conveyor belts comprising respective cords surpass their intended lifetime. In this case, it is desirable to recycle the steel as a valuable raw material for which in a first step the steel cords must be separated from their surrounding rubber environment. Such separation increases the costs for the recovery of the steel, and in addition, the steel is eventually recycled by melting the same, which involves the use of large amounts of energy. Thus, given that the energy prices have recently strongly increased, there is a need for a conveyor belt system, which can be recycled or “reused” with lower energy demands.

[0012] The present application addresses these needs.

[0013] Detailed description of the invention In the investigations which are underlying the present invention, it has unexpectedly been discovered that steel cords or cables in conveyor belts can be replaced by cords which are prepared from UHMWPE yarns to provide belts with a strength and elongation, which is comparable to steel cord reinforced conveyor belts. In addition, as the UHMWPE as well as the thermoplastic elastomer can be converted to a melt at elevated temperature, the entire belt body can be disintegrated in a single step, which can be processed into a homogeneous mixture. This mixture can then be reused for the preparation of other objects, wherein partial dilution of the thermoplastic elastomer by the additional UHMWPE is not critical, or, if the UHMWPE content is controlled (e.g. via adjustment by addition further thermoplastic elastomer), can be reused as rubber matrix material in combination with new UHMWPE cords in new conveyor belts. In addition, since UHMWPE is not vulnerable to corrosion, the respective conveyor belts provide for an advantage over steel cable-based conveyor belts also in this respect.

[0014] Accordingly, in a first aspect, the present invention pertains to a conveyor belt having a rubber matrix body and one or more cords embedded therein, wherein the cords are predominantly constituted from UHMWPE yarns and wherein the rubber matrix body comprises a thermoplastic elastomer.

[0015] The term “predominantly constituted from” indicates that the cords to the predominant weight amount contain UHMWPE as yarn material, i.e. the content of UHMWPE to provide the yams in the cord is at least 55 wt.-%, preferably at least 70 wt.-% and more preferably at least 80 wt.-%. In one embodiment, the cords comprise UHMWPE as the only polymeric material. In another embodiment, the material cords comprise additional yams of a material, which is other than UHMWPE in an amount of 15 wt.-% or less and preferably 10 wt.-% of less (where a content of 0 wt.-% is excluded).

[0016] The term “fiber” in the context of this invention is meant to indicate a single strand of the smallest linear material to constitute a yam or cord herein. The term “yam” is meant to indicate an assembly of multiple fibers without twisting. The terms “cable”, “cord”, “wire” and “rope” are used interchangeably herein, and are intended to denote an assembly of multiple yarns, which are joined by twisting, braiding, cabling, spiral ising or other methods known in textile and steel industry.

[0017] The material, which may be present as additional yarns, is not subject to any relevant restrictions, as long as it does not dilute the strengthening effect of the UHMWPE yams to a relevant extent. Particularly suitable materials for the formation of yams to be used in combination with the UHMWPE yams include polyamide, polyethylene terephthalate, polyaramide, polyoxadiazole, polyolefin, in particular in the form of polyethylene (PE) or polypropylene (PP), glass fiber and cotton. The additional material may be present as yams, which together with UHMWPE yams are spiraled, braided, or otherwise twisted to form a secondary yam, which together with other secondary yams, which are constituted in the same manner, forms the cord. Alternatively, it is possible that one or more secondary yam are only formed from yams of the additional material, which is then combined with UHMWPE secondary yams to form a cord.

[0018] Constituents, which can be used in the yams and cord in addition to the polymeric material, include e.g. colorants, process aids, antioxidants, heat stabilizers, flame retardants, friction-modifiers and surfactants.

[0019] For the UHMWPE yams it is preferred that they are fabricated from fibers having a tenacity of at least 25 cN / dtex. More preferably, the UHMWPE fibers have a tenacity in the range of from 30 to 45 cN / dtex, even more preferably in the range of from 32 to 45 cN / dtex and yet even more preferably in the range of 35 to 45 cN / dtex.

[0020] In addition, it is preferred that the UHMWPE yams have an elongation at break of from 2 to 5 % and particularly preferably of from 3 to 4%. The tenacity and elongation at break for the purposes of this invention are determined according to ISO 2062:2009.

[0021] The UHMWPE yams regularly have a density of less than 1 .0 g / cm3and preferably of about 0.97 g / cm3. In addition, the UHMWPE in the UHMWPE yams usually have a melting point of between 144°C and 152°C. While this melting point (which limits the use temperature of the respective belts) is lower than for many other polymer fibres (e.g. aramid fiber often have a Tm of > 500°C), the fibers have no brittle point when tested at a extremely low temperatures (-150°C). Thus, respective cords and yarns are particularly suitable for use at working temperatures in the range of -40°C and + 70°C.

[0022] As noted above, the rubber matrix body comprises a thermoplastic elastomer. Here, it is preferred if the thermoplastic elastomer accounts for the major part of the weight of the rubber in the rubber matrix body, i.e. at least 60 wt.-%, preferably at least 80 wt.-% and more preferably at least 90 wt.-% thereof. In one particularly preferred embodiment, the rubber matrix body consists of thermoplastic elastomer as the rubber material.

[0023] In addition to the thermoplastic elastomer the rubber matrix body may contain conventional additives and additives for formulation purposes, such as fibers for reinforcement, or formulation auxiliaries. In most instances, the rubber matrix body contains such components in a proportion of at most up to 40% by weight, for example in a proportion of 10 to 30% by weight. In one embodiment, the rubber matrix body does not contain fibers or filaments.

[0024] While the specific type of the thermoplastic elastomer in the rubber belt body is not of particular importance, it has been found that thermoplastic polyurethanes and thermoplastic vulcanisates (i.e. elastic material, which have crosslinks between individual polymer molecules, but which still can be formed at elevated temperatures), due to their mechanical properties, are particularly suited for incorporation into the rubber belt body. Accordingly, it is preferred if the thermoplastic elastomer in the rubber matrix body of the inventive conveyor belt comprises and preferably is selected from a thermoplastic polyurethane and a thermoplastic vulcanisate.

[0025] Particularly suitable thermoplastic polyurethanes are those which are based on a polyether polyol, preferably polytetramethylene glycol, or a polyester polyol as the polyol component. Particularly advantageous polyester polyols are for example adipate-based polyester polyols, in particular in the form of polybutylene adipate, or polycaprolactone-based polyester polyol. To provide the respective thermoplastic polyurethanes, the polyols are reacted with a polyisocyanate or a mixture of polyisocyanates, wherein the polyisocyanate preferably comprises and in one embodiment consists of aromatic polyisocyanates. Particularly preferred aromatic polyisocyanates for the production of thermoplastic polyurethanes for use in the invention include toluene diisocyanate, methylene diisocyanate or mixtures thereof. In addition to polymeric polyols, the thermoplastic polyurethane may also comprise segments resulting from the incorporation of monomeric polyols, in particular a,o-diols such as 1 ,4-butane diol.

[0026] If the thermoplastic elastomer, which is used in the inventive conveyor belt, is a thermoplastic vulcanisate, it is preferred that the vulcanisate is formed form ethylene-propylene-diene rubber (EPDM) and polypropylene by dynamic vulcanisation of the respective mixture thereof. In such mixtures the ratio of EPDM and polypropylene is preferably in the range of 80:20 to 20:80, more preferably 60:40 to 40:60 and even more preferably about 50:50.

[0027] The conveyor belt of the present invention belts are preferably configured to have a breaking strength in the range of 500 N / mm to 10,000 N / mm and more preferably of from 500 to 5400N / mm.

[0028] A schematic figure to show the principal construction of the conveyor belt of the invention is shown in figure 1 , where 1 indicates the rubber belt body and 2 indicates the embedded cords.

[0029] In addition to the belt body and the cords, the conveyor belt of the invention may further comprise additional layers, such as transverse reinforcements (called breaker) to provide enhanced toughness of the belt surface, bottom cover to reduce the running resistance or layers for further reinforcement, e.g. in the direction perpendicular to the running direction of the belt. In one preferred embodiment the inventive conveyor belt comprises a rubber cover layer on the carrying side (i.e. the side intended to have the material to be transported applied thereon) and / or on the pulley side, wherein the cover layer is formed form a thermoplastic elastomer. In a particularly preferred embodiment, the inventive conveyor belt comprises respective rubber cover layers on both of the pulley side and the carrying side, wherein the respective layers are preferably formed form a thermoplastic elastomer. An example of an inventive conveyor belt comprising respective upper and lower cover layers 3 is shown in Figure 2, where the cover layers are applied to the load- and the pulley side of the TPE matrix body of the belt.

[0030] In addition thereto, the inventive conveyor belt may further comprise a transverse reinforcement on the load- and / or pulley side of the TPE matrix body, such as a thin steel cords, textile or fabric which may be applied to or partially or fully embedded into the TPE matrix body. If the inventive conveyor belt comprises such reinforcement, it is preferred that the reinforcement is provided on both the load- and the pulley side of the belt. An example of a belt having respective traverse reinforcements 4 applied to the load- and the pulley side of the TPE matrix body of the belt is shown in figures 3a and 3b.

[0031] In terms of simplicity for a recycling of the inventive conveyor belt after its lifetime, it is preferred that the fabric, which is incorporated for transverse reinforcement is based on a thermoplastic material, which can be melt blended with the thermoplastic elastomer and the UHMWPE of the belt body and UHMWPE comprising cords.

[0032] In a further aspect, the present invention is directed to a method for the manufacture of a conveyor belt as described above, wherein the method comprises the following steps: i) providing one or more cords, which are predominantly constituted from UHMWPE yarns, wherein, when there is more than one cord, the cords are arranged parallel to one another; ii) providing a rubber material thereon such that the rubber material fully surrounds the one or more cords and forms a flat surface above and below the one or more cords; iii) optionally applying a transverse reinforcement on at least one of the flat surfaces prepared in ii); iv) optionally applying a rubber cover layer on at least one of the flat surfaces prepared in ii) or on the transverse reinforcement applied in iii).

[0033] The step ii) can be performed thus, that molten rubber material is applied on a substrate, on which the one or more cords are subsequently arranged, followed by the application of further molten rubber material and solidification. Alternatively, it is possible that the rubber material in step ii) is provided in solid form, where a strip of rubber material is provided with one or more semi-circle shaped recesses with dimension to accommodate the one or more cords. The cords can then be inserted into the recesses for optimal parallel orientation, covered with a further corresponding strip of rubber material and heated to embed the cords into the rubber belt body, which is formed from the rubber material strips.

[0034] The transverse reinforcement can be attached to the belt body via e.g. use of a respective adhesive, by softening the upper surface of the rubber matrix body by application of heat and subsequent impressing the reinforcement into the surface of the rubber belt, or by applying the reinforcement onto the rubber belt body at a stage, where the cords are not yet embedded into the belt body and where the embedding of the cord or cords into the belt body and the attaching of the transverse reinforcement in then performed in a single step.

[0035] Similarly, the optional application of a rubber cover layer on at least one of the flat surfaces prepared in ii) or on the transverse reinforcement applied in iii) can be performed after prefabrication of the rubber belt body, which may have the transverse reinforcement attached thereto by use of an adhesive or by softening the belt body surface and impressing the rubber cover layer thereon, or can be combined with other steps such as the attachment of the transverse reinforcement or the embedding of the cord or cord into the rubber belt body. In a yet further aspect, the present invention pertains to the use of one or more cords, which are predominantly constituted from UHMWPE yams, in a conveyor belt having a rubber matrix body for reducing the weight of the conveyor belt relative to a respective conveyor belt having steel cords. In a preferred embodiment of this use, the rubber matrix body is based on a thermoplastic elastomer wherein more preferably the thermoplastic elastomer accounts for the entire amount of rubber in the rubber matrix body. For the use, the one or more cords, which are predominantly constituted from UHMWPE yams, are incorporated and preferably embedded into the rubber matrix to provide the respective conveyor belt.

[0036] The concept of combining cords constituted from UHMWPE yams with a rubber matrix based on a thermoplastic elastomer is not limited to and provides advantages for conveyor belts, but is equally favorable for an implementation into belts such as power transmission or timing belts. Thus, in a yet further aspect the present invention pertains to a power transmission belt or timing belt, which has a rubber matrix body (1 ) and one or more cords (2) embedded therein, wherein the cords are predominantly constituted from UHMWPE yams and wherein the rubber matrix body comprises a thermoplastic elastomer.

[0037] For specific embodiments of the latter aspect, the embodiments, which have been described above as preferred and favorable for the respective conveyor belts above, are likewise preferable for the power transmission belt or timing belts unless there is an obvious contradiction.

[0038] In the following, the present invention will be further illustrated by means of Examples, which, however, should not be construed as being limiting to the scope of the invention.

[0039] Example In the following, it was assessed whether conveyor belts according to DIN EN ISO 15236-2, Belt type A can be provided with UHMWPE cords instead of steel cables.

[0040] Table 1

[0041] (1) Based on Dyneema SK78; (2) based on Dyneema DM20

[0042] As can been seen from table 1 above, UHMWPE cords can be used to replace steel cords to provide conveyor belts, which still comply with DIN EN ISO 15236-2 and other international standards in terms of belt diameter and break strength. The respective mass of the UHMWPE cables is about 1 / 5 of the mass of the respective steel cable, which provides of a significant weight reduction of the resulting conveyor belt.

Claims

Claims1. A conveyor belt having a rubber matrix body (1 ) and one or more cords (2) embedded therein, wherein the cords are predominantly constituted from UHMWPE yams and wherein the rubber matrix body comprises a thermoplastic elastomer.

2. Conveyor belt according to claim 1 , wherein the UHMWPE yarns have a tenacity of at least 25 cN / dtex, preferably of 30 to 40 cN / dtex and more preferably of 32 to 40 cN / dtex.

3. Conveyor belt according to claim 1 or 2, wherein the cords further comprise one or more yams of an additional material selected from the group consisting of polyamide, polyethylene terephthalate, polyaramide, polyoxadiazole, polyolefine, in particular in the form of polyethylene (PE) or polypropylene (PP), glass fiber and cotton.

4. Conveyor belt according to any one of claims 1 to 3, wherein the rubber matrix body consist of thermoplastic elastomer as the rubber material.

5. Conveyor belt according to any one of the preceding claims, wherein the thermoplastic elastomer is selected from a thermoplastic polyurethane and / or a thermoplastic vulcanisate.

6. Conveyor belt according to any one of the preceding claims, wherein the thermoplastic polyurethane is based on a polyether, preferably polytetramethylene glycol, or polyester polyol, preferably an adipate-based polyester polyol or a polycaprolactone-based polyester polyol, as the polyol component.

7. Conveyor belt according to claim 5 or 6, wherein the thermoplastic polyurethane is based on an aromatic polyisocyanate, preferably selected from toluene diisocyanate or methylene diisocyanate.Conveyor belt according to claim 5, wherein the thermoplastic vulcanisate is based on a dynamically vulcanized mixture comprising ethylene-propylene- diene rubber and polypropylene. Conveyor belt according to any one of the preceding claims, wherein the cords have a breaking strength in the range of rom 2 to 300 kN and preferably of from 5 to 250 kN. Conveyor belt according to any one of the preceding claims, wherein the belt further comprises a rubber cover layer on the load- and / or pulley side and preferably on the load- and pulley side. Conveyor belt according to claim 1 , wherein the belt further comprises a transverse reinforcement on the load- and / or pulley side and preferably on the load- and pulley side. Process for the manufacture of a conveyor belt according to any one of claims 1 to 12, comprising the steps of: i) providing one or more cords, which are predominantly constituted from UHMWPE yams, wherein, when there is more than one cord, the cords are arranged parallel to one another; ii) providing a rubber material thereon such that the rubber material fully surrounds to one or more cords and forms a flat surface above and below the one or more cords; iii) optionally applying a transverse reinforcement in at least one of the flat surfaces prepared in ii); iv) optionally applying a rubber cover layer on at least one of the flat surfaces prepared in ii) or on the transverse reinforcement applied in iii). Use of one or more cords, which are predominantly constituted from UHMWPE yams, in a conveyor belt having a rubber matrix body forreducing the weight of the conveyor belt relative to a respective conveyor belt having steel cords. Power transmission belt or timing belt having a rubber matrix body (1 ) and one or more cords (2) embedded therein, wherein the cords are predominantly constituted from UHMWPE yarns and wherein the rubber matrix body comprises a thermoplastic elastomer.

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