Process For Manufacturing A Conveyor Belt

Abstract

Methods of manufacturing a conveyor belt (126) include applying a rubber composition (114) to a first side of fabric reinforcement (112) and scattering productive thermoplastic elastomer pellets (106) onto a second side of the fabric reinforcement to produce an uncured belt structure (120). The uncured belt structure (120) is continuous fed into a double belt press (116) to press the productive thermoplastic elastomer pellets (106) together with the fabric reinforcement (112) to produce an uncured belt (128). Uncured belt (128) is then heated in the double belt press (116) to a temperature of at least 300° F. and maintained in the double belt press (116) under a pressure of at least 12 psi and a temperature of at least 300° C. for a residence time of at least 20 minutes to produce a cured conveyor belt (130), which is continuously withdrawn from the double belt press (116).

Claims

1. A method of manufacturing a conveyor belt, the method comprising: providing a top layer, a bottom layer, and a fabric reinforcement layer; applying a rubber composition to the bottom side of a fabric reinforcement and scattering a productive thermoplastic elastomer composition onto the top side of the fabric reinforcement to produce an uncured belt structure; continuously feeding the uncured belt structure into a double belt press to press the productive thermoplastic elastomer composition together with the fabric reinforcement at a pressure of at least 12 psi to produce an uncured belt; heating the uncured belt in the double belt press to a suitable selected temperature; maintaining the uncured belt in the double belt press at a suitable selected pressure and at a suitable residence time to produce a cured conveyor belt; and, continuously withdrawing the cured conveyor belt from the double belt press and producing the uncured belt structure, the uncured belt and the cured conveyor belt in a single continuous operation.

2. The method of claim 1, further comprising blending a peroxide crosslinking agent supported on a powdered carrier to form the productive thermoplastic elastomer and forming non-productive thermoplastic elastomer pellets by extrusion with a co-rotating, intermeshing twin screw extruder; and a thermoplastic elastomer, at least one filler, and at least one processing oil are blended in the co-rotating, intermeshing twin screw extruder in making the nonproductive thermoplastic elastomer pellets.

3. The method as specified in claim 2, wherein the productive thermoplastic elastomer composition is made by dry blending the nonproductive thermoplastic elastomer pellets with the peroxide crosslinking agent which is supported on the powdered carrier.

4. A method of manufacturing a conveyor belt comprising: premixing raw materials by a powder mixer, the raw materials comprising and a curative co-agent; feeding the premixed raw materials into a co-rotating, intermeshing twin screw extruder to make nonproductive thermoplastic elastomer pellets; dry blending the nonproductive thermoplastic elastomer pellets from the extruder with a peroxide curing agent by a drum mixer to form productive thermoplastic elastomer pellets; scattering the thermoplastic elastomer pellets over a top surface of a fabric reinforcement by a pellet distributer to make an uncured belt structure; feeding the uncured belt structure into a double belt press and heating the structure to at least 300° F. in a heating zone of the double belt press and applying a pressure of at least about 12 psi to push a bottom layer of uncured rubber composition and the top layer of productive thermoplastic elastomer pellets into the fabric reinforcement; maintaining the uncured belt structure in the heating zone for at least 20 minutes to form a cured belt structure; and cooling the cured belt structure in a cooling zone of the double belt press to form the conveyor belt having the fabric reinforcement as a reinforcement layer between a pulley cover layer and a load carrying layer.

5. The method of claim 4, the peroxide curing agent comprising one or more organic peroxides.

6. The method of claim 5, the organic peroxides comprising one or more of a group comprising dicumyl peroxide, bis-(t-butyl peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, alpha-alpha-bis(t-butylperoxy) diisopropylbenzene, methylethyl ketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide.

7. The method of claim 5, the organic peroxides comprising dicumyl peroxide and di-t-butyl peroxide.

8. The method of claim 4, at least one antioxidant is further blended in the co-rotating, intermeshing twin screw extruder to make the nonproductive thermoplastic elastomer pellets.

9. The method of claim 4, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.1 mm to 2 mm.

10. The method of claim 4, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.2 mm to 1 mm.

11. The method of claim 4, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.3 mm to 0.7 mm.

12. A system for manufacturing a conveyor belt, the system comprising: a powder mixer configured to premix raw materials, the raw materials comprising and a curative co-agent; a co-rotating, intermeshing twin screw extruder to make nonproductive thermoplastic elastomer pellets from the premixed raw materials; a drum mixer to form productive thermoplastic elastomer pellets by dry blending the nonproductive thermoplastic elastomer pellets from the extruder with a peroxide curing agent; a pellet distributer to make an uncured belt structure by scattering the thermoplastic elastomer pellets over a top surface of a fabric reinforcement; a double belt press configured to feed the uncured belt into a structure and heat the structure to at least 300° F. in a heating zone of the double belt press and apply a pressure of at least about 12 psi to push a bottom layer of uncured rubber composition and the top layer of productive thermoplastic elastomer pellets into the fabric reinforcement; the double belt press configured to maintain the uncured belt structure in the heating zone for at least 20 minutes to form a cured belt structure; and a cooling zone of the double belt press to form the conveyor belt having the fabric reinforcement as a reinforcement layer between a pulley cover layer and a load carrying layer by cooling the cured belt structure.

13. The system of claim 12, the peroxide curing agent comprising one or more organic peroxides.

14. The system of claim 12, the organic peroxides comprising one or more of a group comprising dicumyl peroxide, bis-(t-butyl peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, alpha-alpha-bis(t-butylperoxy) diisopropylbenzene, methylethyl ketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide.

15. The system of claim 12, the organic peroxides comprising dicumyl peroxide and di-t-butyl peroxide.

16. The system of claim 12, at least one antioxidant is further blended in the co-rotating, intermeshing twin screw extruder to make the nonproductive thermoplastic elastomer pellets.

17. The system of claim 12, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.1 mm to 2 mm.

18. The system of claim 12, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.2 mm to 1 mm.

19. The system of claim 12, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.3 mm to 0.7 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawing, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figure illustrates the various implementations described herein and is not meant to limit the scope of various technologies described herein, and wherein FIG. 1 is a schematic drawing of one method aspect according to the disclosure, for manufacturing a conveyor belt which utilizes a double belt press.

DETAILED DESCRIPTION

[0016] The following description of the variations is merely illustrative in nature and is in no way intended to limit the scope of the disclosure, its application, or uses. The description and examples are presented herein solely for the purpose of illustrating the various embodiments of the disclosure and should not be construed as a limitation to the scope and applicability of the disclosure. In the summary of the disclosure and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the disclosure and this detailed description, it should be understood that a value range listed or described as being useful, suitable, or the like, is intended that any and every value within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors had possession of the entire range and all points within the range.

[0017] Unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0018] In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of concepts according to the disclosure. This description should be read to include one or at least one and the singular also includes the plural unless otherwise stated.

[0019] The terminology and phraseology used herein is for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited.

[0020] Also, as used herein any references to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily referring to the same embodiment.

[0021] Some aspects of the disclosure provide methods for continuous production of a cured rubber conveyor belt having high temperature resistance by a simple process which is less labor intensive than prior art methods. These methods reduce or eliminate the requirements for Banbury mixing and calendaring, and accordingly reduce overall production cost. Additionally, these methods result in improved rubber formulation consistency and in some cases reduced energy requirements.

[0022] In some embodiments, methods of manufacturing a conveyor belt having a top layer, a bottom layer, and a fabric reinforcement layer which is sandwiched between the top layer and the bottom layer, include (1) applying a rubber composition to the bottom side of a fabric reinforcement and scattering a productive thermoplastic elastomer composition onto the top side of the fabric reinforcement to produce an uncured belt structure, (2) continuously feeding the uncured belt structure into a double belt press to press the productive thermoplastic elastomer composition together with the fabric reinforcement at a pressure of at least 12 psi to produce an uncured belt, (3) heating the uncured belt in the double belt press to a temperature of at least 300° F., (4) maintaining the uncured belt in the double belt press under a pressure of at least 12 psi and a temperature of at least 300° C. for a residence time of at least 20 minutes to produce a cured conveyor belt, and (5) continuously withdrawing the cured conveyor belt from the double belt press.

[0023] In the practice of some aspects of the disclosure, an uncured rubber composition is applied to the bottom side of a fabric reinforcement and a productive thermoplastic elastomer composition is scattered onto the top side of the fabric reinforcement to produce an uncured belt structure. The rubber utilized in the uncured rubber composition can be chosen from a wide variety of natural and synthetic rubbers. For instance, the rubber can be natural rubber, styrene-butadiene rubber, polybutadiene rubber, synthetic polyisoprene rubber, nitrile rubber, ethylenepropylene-diene monomer rubber (EPDM), polychloroprene, and the like or blends thereof. The uncured rubber composition will also typically include a curative as well as one or more of accelerators, antioxidants, fillers, processing oils, extending oils, and other desired rubber compounding chemicals. The curative will typically be sulfur, a sulfur containing compound, or a peroxide curative. The filler will typically be one or more of carbon black, silica, clay, and lignin.

[0024] The fabric reinforcement may be a material based upon cotton, a polyester, a nylon, polyaramid, fiberglass, or various blends thereof. For instance, the polyester may be polyethylene terephthalate or polyethylene naphthalate. In some cases the polyester may be a copolyester which contains repeat units that are derived from both terephthalic acid and isophthalic acid or dimethyl esters thereof. In such cases the copolyester will typically contain at least about 95 weight percent terephthalic acid and up to about 5 weight percent isophthalic acid. The copolyester may, in some cases, contain at least about 97 weight percent terephthalic acid and up to about 3 weight percent isophthalic acid. The polyester fabric may, in some aspects, be made from polyester staple yarn to improve adhesion characteristics. The nylon fabrics that may be used in conjunction with the disclosure, may be based upon virtually any type of nylon, such as nylon-6.6, nylon-6.12, nylon-6.10, nylon-6.9, nylon-6, nylon-11, or nylon-12. For commercial reasons, the nylon will typically be nylon-6.6 or nylon-6. In any case, the fabric material will normally be a woven fabric. The fabric reinforcement will normally be treated with a resorcinol-formaldehyde latex dip to improve the adhesion between the fabric and the rubber components of the conveyor belt (the top carry cover layer and the bottom pulley cover layer).

[0025] The productive thermoplastic elastomer composition may be a blend of non-productive thermoplastic elastomer pellets and a peroxide crosslinking agent which is supported on a powdered carrier. The nonproductive thermoplastic elastomer pellets may be made by extrusion with a co-rotating, intermeshing twin screw extruder. In an example extrusion process, a thermoplastic elastomer, at least one filler, and at least one processing oil are blended in co-rotating, intermeshing twin screw extruder to make the nonproductive thermoplastic elastomer pellets. A curative co-agent may be included in the nonproductive thermoplastic elastomer pellets. In some cases, such a curative co-agent may be an acrylate, a methacrylate, or a maleimide to attain a very fast cure rate or in the alternative may be a polybutadiene, a triallyl cyanurate (TAC), triallyl isocyanurate (TAIC) or triallyl phthalate (DAP) to attain a more moderate rate of cure. With reference to FIG. 1, these materials 100 may be premixed in a powder mixer 102 as before being fed into the co-rotating, intermeshing twin screw extruder 104. In some aspects, the non-productive thermoplastic elastomer pellets have an average particle size which is within the range of 0.1 mm to 2 mm and more typically have an average particle size which is within the range of 0.2 mm to 1 mm. The non-productive thermoplastic elastomer pellets may even have an average particle size which is within the range of 0.3 mm to 0.7 mm.

[0026] Productive thermoplastic elastomer pellets 106 are then made by dry blending the nonproductive thermoplastic elastomer pellets with peroxide curing agent 108, which is supported on the powdered carrier. For instance, this dry blending can be done in any suitable powder mixer such as a drum mixer 110 as illustrated in FIG. 1. The peroxide curing agents 108 which may be used in the practice of some aspects of the disclosure are those which are generally suitable for curing EPDM. Some representative examples of organic peroxides which can be used include, but not limited to, dicumyl peroxide, bis-(t-butyl peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, alpha-alpha-bis(t-butylperoxy) diisopropylbenzene, methylethyl ketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, pinane hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, and the like. Dicumyl peroxide and di-t-butyl peroxide are highly preferred peroxide compounds. In any case, the peroxide crosslinking agent will be supported on an inert powdered carrier, such as silica, clay or calcium carbonate. The peroxide may be present on the powdered carrier at a level which is within the range of about 40 weight percent to about 70 weight percent, or even within the range of about 50 weight percent to 60 weight percent, based upon the total weight of the peroxide and the carrier. In an embodiment, the curative co-agent can be included with the peroxide curing agent 108.

[0027] Referring again to FIG. 1, a fabric reinforcement (carcass) 112, having the uncured rubber composition 114 upon or applied to the bottom side thereof, may continuously advanced toward a double belt press 116 with productive thermoplastic elastomer pellets 106 being scattered from pellet distributor 118 over the top surface of the fabric reinforcement 112 to make an uncured belt structure 120. The productive thermoplastic elastomer pellets 106 may be distributed in a relatively uniform manner over the top surface of the fabric reinforcement 112 with pellet distributor 118.

[0028] The uncured belt structure 120 is then continuously fed into the double belt press 116 which heats the uncured belt structure 120 to a temperature at least about 300° F. in a heating zone 122. In some aspects, the double belt press 116 heats the structured fabric reinforcement by conduction heating. The uncured belt structure 120, in some cases, will be heated to a temperature which is within the range of about 320° F. to about 400° F., or even heated to a temperature which is within the range of about 325° F. to about 450° F. The uncured belt structure 120 may be held under a pressure of at least about 12 psi in the double belt press 116 to push the bottom layer formed of uncured rubber composition 114 and the top layer formed of productive thermoplastic elastomer pellets 106 into the fabric reinforcement 112. The pressure applied in the double belt press 116, in some aspects, may be within the range of about 14 psi to about 30 psi, or even within the range of about 15 psi to about 25 psi. Belts used as one or both belt component(s) of double belt press 116 may have surfaces which contain polytetrafluoroethylene (PTFE) impregnated fiber glass or even a thin layer of stainless steel.

[0029] The uncured belt structure 120 is maintained in the double belt press 116 at the desired temperature and under the desired pressure for a period of at least 20 minutes, in some cases. In some aspects, the uncured belt structure may have a residence time in double belt press 116 which is within the range of about 25 minutes to about 45 minutes and, may even have a residence time in double belt press 116 which is within the range of about 30 minutes to about 35 minutes. After being cured, the cured conveyor belt 130 will be cooled in a cooling zone 124 and continuously withdrawn from the double belt press 116, as finished belt 126. In some embodiments, excess material is continuously trimmed off of the edges of the cured conveyor belt 130 after it is continuously withdrawing from the double belt press 116.

[0030] Conveyor belts 126 manufactured in accordance with the disclosure include an elastomeric body having a load carrying surface (top surface) 140 and a parallel pulley engaging surface (bottom surface) 142, where a fabric reinforcement 112 is disposed within the elastomeric body of the belt 126. In other words the fabric reinforcement 112 is situated between the pulley cover layer 142 and the load carrying layer 140 of the belt.

[0031] Some embodiments of the disclosure are illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the disclosure or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Example 1

[0032] In this experiment a series of productive thermoplastic elastomer compositions for use in manufacturing conveyor belts in accordance with the disclosure were prepared. Previous testing on a twin screw extruder using only Tafmer D610 thermoplastic elastomer as the feed showed that a constant linear temperature profile of 390° F. at a screw speed of 75 rpm and a feed rate of 5 pounds per hour gave the most consistent, smooth pellets. The lab pelletizer could not pull at a constant rate at this low speed so a puller was employed to improve strand diameter, and was utilized in the following examples.

[0033] Experimental blends were made by first feeding the ingredients identified in Table 1 below into a Plastic Lab 25 mm Twin Screw Extruder using one loss-in-weight feeder located prior to Zone 1 of the extruder. In Table 1, all ingredient levels are shown in parts by weight. The strands were later fed at the end of the run to a pelletizer to achieve pellets in the 2 mm to 3 mm diameter range. The pressure at the die increased from 300 psi with the pure Tafmer D610 thermoplastic elastomer to 700 psi with polymer blend of Example 1. Pressures in the 400-430 psi range were observed with the polymer blends of Example 2 and Example 3. The screw motor ran at the 18 amp current level in the case of all of the materials tested. The temperature of the extrudate was measured by with an IR thermometer to be within the range of 360° F. to 370° F. and the extruder die thermometer measured the melt temperature to be 380° F.

[0034] All three of the non-productive thermoplastic polymer compositions made were dry mill mixed with a peroxide curative to make productive thermoplastic elastomer compositions which were suitable for use in making conveyor belts in accordance with the disclosure.

TABLE-US-00001 Example 1 Example 2 Example 3 Non-Productive Thermoplastic elastomer 100 100 100 N-330 carbon black 35 40 40 Silica 10 - - Antioxidants 8 9 9 Processing Aid 1 1 1 Zinc Oxide 10 5 5 Paraffinic Processing Oil 5 5 5 Curative Co-Agent 0 0 2.75 Productive Bis(t-butylperoxy) isopropylbenzene 4.5 4.5 4.5 Curative Co-Agent 2.75 2.75 -

[0035] This series of experiments illustrates that mixing of the non-productive materials can be done in a co-rotating, intermeshing twin screw extruder with a peroxide curative being added later by dry blending to make productive formulations. These productive formulations can then be used in manufacturing conveyor belts in accordance with the disclosure.

[0036] List of Reference signs (part of the description):

TABLE-US-00002 100 Raw Materials 102 Powder Mixer 104 Intermeshing Twin Screw Extruder 106 Productive Thermoplastic Elastomer Pellets 108 Peroxide Curing Agent 110 Drum Mixer 112 Fabric Reinforcement 114 Uncured Rubber Composition 116 Double Belt Press 118 Pellet Distributor 120 Uncured Belt Structure 122 Heating Zone 124 Cooling Zone 126 Finished Belt 128 Uncured Conveyor Belt 130 Cured Conveyor Belt 140 Top Layer 142 Bottom Layer

[0037] The foregoing description of the embodiments has been provided for purposes of illustration and description. Example embodiments are provided so that this disclosure will be sufficiently thorough, and will convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the disclosure, but are not intended to be exhaustive or to limit the disclosure. It will be appreciated that it is within the scope of the disclosure that individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0038] Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.