CONVEYOR AND ELEVATOR BELT HANDBOOK

Transcription

1 ARPM: IP-1 Revised: 2011 Replaces: RMA 1989 Edition CONVEYOR AND ELEVATOR BELT HANDBOOK 2011 by the Association for Rubber Products Manufacturers, Inc. Published in the United States of America RMA First Edition 1973 RMA Second Edition 1980 RMA Third Edition 1989 ARPM Fourth Edition Shadeland Station Way, Suite 285, Indianapolis, IN Phone: Web:

2 INTRODUCTION PREFACE Conveyor and elevator belts are made to precise specifications and standards to service many useful functions. A better understanding of the complexities involved in manufacturing belting and the standards that are applied to it will be helpful in selecting the proper belt for the intended use and in obtaining good service after installation. Belting covered in this Handbook includes conveyor belting, used to transport bulk or packaged, boxed and bagged materials, and bucket elevator belting. The belting may be made of natural and synthetic rubbers as well as plastics, such as vinyl, with carcasses of textile fabrics, which are woven, nonwoven, solid woven, or stitched; fabric cords; or of steel cables. This handbook is intended for the general guidance and reference of persons interested in the selection and use of conveyor and elevator belting, but readers are urged to consult individual manufacturers for specific information and recommendations. ACKNOWLEDGMENT The Association for Rubber Products Manufacturers is the national trade association of the non-tire rubber manufacturing industry in the United States. ARPM represents manufacturers of finished rubber products (excluding tires), and their related suppliers. This publication is provided as a public service, and reference for users of conveyor belt products by U.S. manufacturers of conveyor belt products, including: Airboss Compounding Rubber (NC) Fenner Dunlop Americas (Pittsburgh, PA) Garlock Rubber Technologies (Paragould, AR) Price Rubber Corp. (Montgomery, AL) Veyance Technologies Inc. (Fairlawn, OH) 2011 by Association for Rubber Products Manufacturers, Inc Shadeland Station Way, Suite 285 Indianapolis, IN Published in the United States of America RMA First Edition 1973 RMA Second Edition 1980 RMA Third Edition 1989 ARPM Fourth Edition 2011 IP: Conveyor and Elevator Belt Handbook 2

3 TABLE OF CONTENTS Page PREFACE...2 ACKNOWLEDGMENT...2 CHAPTER 1 - MATERIALS...4 CHAPTER 2 - ELASTOMER CHARACTERISTICS...11 CHAPTER 3 - TEXTILE BELT TYPES AND MANUFACTURING METHODS...18 CHAPTER 4 - TEXTILE BELT CHARACTERISTICS AND BELT RATINGS...23 CHAPTER 5 - TEXTILE BELT TOLERANCES...35 CHAPTER 6 - TEXTILE BELT TEST METHODS...36 CHAPTER 7 - SPLICING CONVEYOR AND ELEVATOR BELTS...40 CHAPTER 8 - STEEL CORD BELT TYPES AND MANUFACTURING METHODS...51 CHAPTER 9 - STEEL CORD BELT CHARACTERISTICS & BELT RATINGS...53 CHAPTER 10 - STEEL CORD BELT TOLERANCES...56 CHAPTER 11 - STEEL CORD BELT TEST METHODS...58 CHAPTER 12 PART A - SPLICING FABRIC CORD CONVEYOR BELTS...61 CHAPTER 12 PART B - SPLICING STEEL CORD CONVEYOR BELTS...75 CHAPTER 13 - BELT MONITORING...91 CHAPTER 14 - OPERATION AND MAINTENANCE...96 CHAPTER 15 - STORAGE OF BELTING CHAPTER 16 - GLOSSARY OF CONVEYOR BELTING TERMS CHAPTER 17 - USEFUL TABLES APPENDIX IP: Conveyor and Elevator Belt Handbook 3

4 CHAPTER 1 MATERIALS INTRODUCTION The purpose of this chapter is to present general descriptions of the construction elements of conveyor belts and the materials which are presently available to produce belts for the various materials conveyed with suitable strength for the tensions and other conditions encountered in service. Conveyor belts are sometimes classified as Light and Heavy Weight belts. Light Weight = RMBT* < 160 PIW Heavy Weight = RMBT > 160 PIW *RMBT = Rated Maximum Belt Tension, in pounds per inch width (PIW) Light weight belting generally is used in very diverse applications such as food and tobacco products, agricultural products, wood products, baggage and packaging handling, metal stampings, and materials handling in the textile, printing, paper processing, postal, and electronics industries. Heavy weight belting generally conveys heavy and/or coarse abrasive materials like mineral ore, rock, sand, gravel, coal, and cement. In general, most conveyor belts consist of three elements: a top cover or conveying surface; a carcass; and a bottom cover, or pulley surface. In light weight belting there is a great diversity among the top cover or conveying surfaces used such as smooth or rough covers and raised patterns; whereas heavy weight belting often has smooth top covers. Custom fabrications with light weight belting are also more common, including attaching of cleats or V guides or hole punching, for example. The elements may also be grouped under several general classifications such as: elastomers; fabrics (woven or non-woven); spun; filament, or monofilament yarn or cord; and steel cords. A rubber or plastic elastomer is a compounded material that returns rapidly to approximately its initial dimensions and shape after substantial deformation by a weak stress less than the yield point. A fiber is a unit of matter having a length at least 100 times its diameter and which can be spun into a yarn. A steel cord, when used as the tension member, is usually multiple strands of steel wire twisted together. Yarn is a generic term for continuous strands of textile fibers or filaments. A fabric is a planar textile structure produced by interlacing yarns, fibers, or filaments. A fabric may be composed of yarns of cotton, glass, nylon, polyester, steel or other materials. A fabric may be made from one material or a combination of materials. RUBBER/PLASTIC ELASTOMERS Polymers are mixed with various chemicals to obtain reinforcement and develop the physical properties of the resulting elastomer necessary for meeting service conditions. Since it is not the purpose for this Handbook to discuss compounding ingredients or methods of compounding, discussion of polymers will be restricted to the general properties of the basic polymers. A wide choice of polymers is available. They can also be blended together to obtain many combinations with intermediate properties. Elastomeric compounds are used for the top and bottom covers or surfaces of conveyor belting and for bonding together components of the belt carcass. The elastomeric covering on belts is there to provide protection for the carcass and/or provide a specific property. The coverings are applied by several processes, depending on the material (rubber vs. thermoplastic) or thickness of the covering. It is possible to classify elastomers to some extent by the basic polymer used. They are listed in Table 1-1 with a brief description of their general properties. IP: Conveyor and Elevator Belt Handbook 4

5 Table 1-1. Rubber/Plastic Polymers Used in Belting Common Name ASTM Designation D Composition General Properties Acrylic ABR Acrylate-butadiene Brominated Butyl BIIR Butyl IIR Isobutene- isoprene Chlorinated Butyl EPDM CIIR EPDM Bromo-isobuteneisoprene Chloro-isobuteneisoprene Ethylene-propylenediene terpolymer Excellent for high temperature oil and air. Poor water resistance. Poor cold flow resistance. Similar properties as Butyl except that it can be more readily adhered to or used in combination with other polymers. Excellent resistance to heat. Very good resistance toozone and aging. Good resistance to abrasion. Similar properties BIIR. Excellent resistance to heat, ozone, and aging. Very good resistance to abrasion. Ethylene Propylene EPR Ethylene-propylene Same properties as EPDM. Hydrin* Hydrin* CO ECO Polychloromethyloxirane Ethylene oxide andchloromethyl-oxriane Excellent oil and ozone resistance. Good flame resistance and low permeability to gases. Fair low-temperature properties. Excellent oil and ozone resistance. Fair flame resistance and low permeability to gases. Good lowtemperature properties. Hypalon* CSM Chloro-sulfonyl-polyethylene Excellent ozone, weathering, and acid resistance. Good abrasion and heat resistance. Good oilresistance. Hytrel* PET Polyethylene Terephthalate Thermoplastic with excellent abrasion and cutresistance. Good chemical resistance. Limited temperature range. Natural Rubber NR Rubber, Natural Neoprene* CR Chloroprene Nitrile NBR Nitrile-butadiene Excellent resistance to cutting, gouging, and abrasion. Good elasticity and resiliency. Good low temperature flexibility. Good ozone and sun-checking resistance. Goodresistance to petroleum-based oils and to abrasion. Also good flame resistance. Excellent resistance to vegetable, animal and petroleum oils. Polybutadiene BR Butadiene A general purpose synthetic rubber. Generally used inblends with natural or styrene-butadiene rubber. Provides excellent abrasion resistance and high resiliency. Excellent low temperature flexibility. Polyisoprene IR Isoprene, synthetic Same properties as natural rubber. SBR SBR Styrene-butadiene Silicone VMQ Modifiedpolysiloxanes Excellent abrasion resistance and good resistance to cutting, gouging, and tearing. Excellent high and low temperature resistance. Can be made to give fair oil resistance. Poor physical properties at room temperatures. IP: Conveyor and Elevator Belt Handbook 5

6 Table 1-1. (continued) Rubber/Plastic Polymers Used in Belting Common Name Urethane ASTM ASTM Designation D AU Composition Polyester Urethane General Comments Excellent abrasion, cut and tear resistance. Good oil resistance. Urethane EU Polyether Urethane Excellent abrasion, cut, and tear resistance. Good oil resistance. Vinyl PVC Polyvinyl Chloride A thermoplastic material which has good resistance to abrasion. Excellent flame resistance. Good resistance to animal and vegetable oils. Limited temperature range. Viton* FKM Fluorocarbon Excellent high temperature and chemical resistance properties. Teflon* see manufacturer Polymers *Trade Names TEXTILES Many types of textiles are used in conveyor and elevator belting. Their use is based on their physical properties, such as strength, elongation, dynamic fatigue resistance, aging resistance, mildew resistance, heat resistance, and other special properties depending on service requirements. For special applications, consult the manufacturer. Yarns used for belt textile reinforcement are classified as either spun or filament depending on whether the base fiber is in staple (3/4-2 1/2 in long single fiber) or endless filament form. A spun yarn is made by twisting relatively short lengths of staple fiber together to form a continuous yarn, called a single s yarn. When two or more of these single s yarns are twisted together, the result is a plied yarn. When two a more plied yarns are twisted together, the result is cable cord. The tensile strength, elongation, and thickness of a yarn of any fiber type can be changed by varying twist, size and number of single s yarns included. Spun yarns may be made from natural or synthetic fibers. Spun yarn sizes are designated by the number of hanks of yarn it takes to weigh one pound. In the cotton system, one hank is 840 yards (770 m) long. One pound of a 12 s cotton yarn is: 12 x 840 yd (770 m) = 10,080 yd (9217 m) long A filament yarn is produced by extruding synthetic materials through an orifice in a continuous process. A single filament is called a monofilament. A number of small filaments are combined to form a multifilament yarn, which is normally called a filament yarn. Filament yarns are stronger than the same-size spun yarns of the same synthetic material. Filament yarns are designated by a denier number which is the weight in grams of 9000 meters of yarn, or a decitex number, which is the weight in grams of 100 meters of yarn.. Thus a 1650 denier yarn will weigh 1650 grams per 9000 meters. Table 1-2 provides information on some of the fiber yarns used in belting fabrics or cords. IP: Conveyor and Elevator Belt Handbook 6

7 Table 1-2. Some Materials Used in Belting Reinforcement Common Name Composition General Comments Cotton Glass Kevlar* Nomex* Nylon Polyester Steel Cord *Trade Name Natural Cellulose Glass Aramid Aramid Polyamide Polyester Steel Only natural fiber used to any great extent for belting. High absorption of moisture. Susceptible to mildew attack and loss of strength. High strength. Very low elongation. Used in high temperature applications. Very low elongation and very high strength. Does not melt but does decompose at high temperature. Very high strength, low elongation. Excellent high temperature properties. High strength and high elongation, with good resistance to abrasion, fatigue, and impact. Moderate moisture absorption. High resistance to mildew. High strength, low elongation. Good abrasion and fatigue resistance. Low moisture absorption. Excellentresistance to mildew. Very high strength, very low elongation. Superiortroughing characteristics. Excellent heat resistance. Good fatigue and abrasion resistance. TEXTILE REINFORCEMENTS Textile fabrics are the most commonly used materials for reinforcing plies in conveyor and elevator belting. Textile fabrics are also used for conveyor belt breakers plies. Fabric properties are governed by the yarn material and size and by the fabric construction and weave. Fabric is made of warp yarns, which run lengthwise, and filling (weft) yarns, which run crosswise, as the fabric is woven, usually at right angles to each other. Non-woven fabric is a mat of fibers bonded together chemically and/or needle-punched, usually to a single-ply of woven scrim. The most common, and least complicated, fabric pattern used for flat belts is the plain weave, Figure 1-1. In this construction the warp and filling yarns cross each other alternately. A belt with two or more of these plies of fabric is known as a multi-ply belt. Other common constructions used to a lesser degree include broken twill, Figure 1-2 and Leno weave, Figure 1-3, which has an open mesh and is usually used for a breaker fabric. Solid woven, Figure 1-4, consists of interwoven multiple layers of warp and filling yarns. Straight warp weave, Figure 1-5, contains basic tension-bearing warp yarns which are essentially straight, that is, without crimp. Also, binder warp yarns are interwoven with the filling yarns to provide mechanical fastener holding strength. Some of the most commonly used belting fabrics known by their major fiber content are: Cotton - A fabric with cotton in both the warp and filling yarns. Cotton-Synthetic - A fabric with cotton warp yarns and synthetic filling yarns or a fabric with cotton/synthetic blended warp and/or filling yarns. The synthetics most commonly used are nylon, and polyester. Polyester - A fabric with polyester fiber warp yarns and filling yarns. Nylon - A fabric with nylon fiber warp and filling yarns. IP: Conveyor and Elevator Belt Handbook 7

8 Polyester-Polyester A fabric with polyester warp and filling yarns. Polyester-Nylon - A fabric with polyester warp and nylon filling yarns. Solid woven fabrics are composed of spun and/or filament yarns. The spun yarns commonly used may be either cotton or synthetic or combinations thereof. The filament yarns are usually nylon or polyester. Figure 1-1. Plain Weave Figure 1-2. (Broken) Twill Figure 1-3. Leno Weave IP: Conveyor and Elevator Belt Handbook 8

9 Figure 1-4. Solid Woven Figure 1-5. Straight Warp Weave IP: Conveyor and Elevator Belt Handbook 9

10 Steel Cord STEEL REINFORCEMENTS Steel cord is used in belting where the properties of steel cord reinforcement are better able to satisfy the requirements of the service conditions. Steel cord is used to obtain high strength, excellent length stability, low bending stresses and, in some cases, to provide superior troughing characteristics. The wires, or filaments, used in conveyor belt steel cords are usually made of high carbon steel and have a surface finish to facilitate adhesion to the surrounding rubber, and provide protection against corrosion. Common constructions are 7 x 7, Figure 1-6, and 7 x 19, Figure 1-7, although many other constructions are possible. Steel cords used in conveyor belts are specially manufactured from high carbon steel to meet the high strength requirements demanded of these belts. The cord is fabricated from strands of wires, or filaments, twisted together. This gives the cord good flexibility and fatigue resistance when subjected to cyclic loading and bending around pulleys. Two common constructions are illustrated in Figures 1-6 and 1-7. In order to protect the steel from corrosion, zinc or brass coatings are applied to the wire before drawing it to the final filament size. Zinc is the most commonly used coating. Typically, the minimum zinc coating expressed in grams per square millimeter is 60 times the filament size in millimeters. Figure x 7 Construction Figure x 19 Construction During belt manufacture, the steel cord is encapsulated in a special core rubber that normally has properties different to the belt covers. It is important during manufacture that the core rubber penetrates right to the center of the steel cord as this stops adjacent filaments from contacting one another and fretting during bending and stretching of the cord in service. Once embedded in the core rubber, the cord strength increases by up to 5% and it becomes less likely to suffer from corrosion caused by water penetrating the cord. The effectiveness of the rubber penetration can be determined by a special test (AS 1333) which measures if there is any loss in air pressure along the cord when air is applied to one end of the cord at 14.5 psi (1 bar), and maintained for 1 minute on a 16 in long belt sample. 5% is the maximum acceptable pressure loss. Core rubber to cord adhesion should be adequate to maintain the belt and its splices integrity during its normal service life. Due to the very specialized nature of this cord and the difficulties in manufacturing cord to achieve these properties, there are only a few manufacturers in the world producing steel cord for conveyor belts. Other Wire Components Several other forms of wire are used in belting for special purposes, such as rip resistance and transverse stiffness. A variety of wire structures are used, some of which include: (1) steel filling leno weave breakers, (2) straight warp steel fabrics. IP: Conveyor and Elevator Belt Handbook 10

11 CHAPTER 2 ELASTOMER CHARACTERISTICS HEAVY WEIGHT CONVEYOR BELT RUBBER COVER CHARACTERISTICS AND CLASSIFICATIONS Elastomeric covers for general purpose conveyor belts with textile/cord reinforced carcasses will be defined as either Grade 1 or Grade 2. The properties, test values and minimum requirements described below can serve as a guideline for acceptable performance in most general purpose applications. It is recognized however that there is no direct correlation between test results and the performance of the belt in service. The test values as outlined are recognized as obtained from new or factory condition belting. Reference Documents ASTM D 378 Standard Test Methods for Rubber (Elastomeric) Belting, Flat Type ASTM D 412 Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers -- Tension CONVEYOR BELT RUBBER COVER GRADES General Purpose Rubber Covers ARPM Grade 1- Will consist of natural or synthetic rubber or blends which will be characterized by high cut, gouge, and tear resistance and very good to excellent abrasion resistance. These covers are recommended for service involving sharp and abrasive materials, and for severe impact loading conditions. ARPM Grade 2- The elastomeric composition will be similar to that of Grade 1 with good to excellent abrasion resistance in applications involving the conveying of abrasive materials, but may not provide the degree of cut and gouge resistance of Grade 1 covers. When covers are tested in accordance with ASTM D 412, the tensile strength, elongation at break shall comply with the requirements of Table 2-1, for the grade of cover, as appropriate. The tensile strength and elongation at break values are not always sufficient in themselves to determine the suitability of the belt cover for a particular service. The values in Table 2-1 should only be specified for conveyors or materials with a known history of performance, and where it is known that compliance with the value will not adversely affect other in-service properties. Covers for Special Applications Belt covers may be required to perform in various environments e.g. high heat, exposure to fluids, abrasive conditions, high ozone concentrations, low temperature exposure and noise generation limits. Cover and Ply Adhesion When belting is tested in accordance to ASTM D 378, the adhesion for covers and between adjacent plies should not be less than the values given in Table 2-2. Table 2-2 applies to continuous filament carcass. ABRASION RESISTANCE As per RMA s description and classification for both Grade 1 and 2 belt covers; both of these cover types will provide good to excellent abrasion resistance. There are several specific tests used by manufacturers to determine the relative abrasion resistance of different cover formulations. The most common is ISO 4649 (DIN 53516). While there are no specific U.S. industry limits, maximum or minimum, for test results from abrasion test for General Purpose (ARPM Grades 1 & 2) Belt Covers; there is enough data to suggest acceptable abrasion values. IP: Conveyor and Elevator Belt Handbook 11

12 A customer preparing to purchase a conveyor belt for abrasion service should, therefore, proceed as follows: 1. Describe as accurately as possible the conditions under which the belt will operate, the nature and composition of the material being carried, the range of particle size, loading conditions, and tons per hour being handled. In those instances where a replacement belt is being ordered, indicate in as complete detail as possible the construction of the belt being replaced and describe the nature of its failure. 2. Point out any condition which might accelerate cover wear, such as excessive heat, moisture, or the presence of oil or other solvents in the installation. Table 2-1. Properties of Covers Grade Minimum Tensile Strength (p.s.i.) Minimum Tensile Strength (MPa) Minimum Elongation at Break (%) Maximum Volume Loss (mm3) ISO 4649 Part B p.s.i. 17 MPa 400% 125 mm p.s.i. 14 MPa 400% 175 mm 3 Table 2-2. General Purpose Rubber Cover and Ply Adhesion Adhesion between adjacent plies Adhesion between cover & ply 30 lbs/in 5 kn/m Top Cover Thickness 1/32 in (0.8 mm) Cover Thickness Covers greater than 1/16 (1.6 mm) 1/16 (1.6 mm) 16 lbs/in 3 kn/m 30 lbs/in 5 kn/m COVER THICKNESS The major function of a heavy weight belt cover is to protect the strength-bearing carcass from wear or damage during the life of the belt. In a light weight belt, the cover functions also to provide the required degree of sanitation in food contact applications or the desired friction characteristics, or the required surface characteristics for incline/decline conveying. The cover thickness required for a specific belt is a function of the material conveyed and the handling methods used. Increased cover thickness is required as the conditions become more severe: e.g. material abrasiveness, maximum lump size of material, material weight, height of material dropped onto the belt, loading angle, belt speed, frequency of loading, etc. The following table shows the suggested minimum belt cover thicknesses for favorable conditions. Wear rates with identical material under adverse loading conditions have been observed to be as much as 6 times the wear rate under favorable conditions. Grade 1 - Top Cover Thickness Grade 1 covers should be considered for heavy crushed material over 3 in (75 mm) and when large lumps occur if cut or gouge resistance is the main design criteria. Consult the manufacturer for cover thicknesses. Grade 2 - Top Cover Thickness (Table 2-3) Table 2-3. Guide for Minimum Top Cover Thicknesses Under Favorable Conditions for Grade 1 and Grade 2 Belting Note: Cover thicknesses are nominal values subject to manufacturers tolerances. Table 2-3 Class of Material Examples Minimum Thickness in mm Package handling Cartons, food products Friction Surface Friction Surface Light or fine, non-abrasive Wood chips, pulp, grain, bituminous coal, potash ore 1/ Fine and abrasive Sharp sand, clinker 1/8 3 Heavy, crushed to 3 in (75 mm) Sand, gravel, crushed stone 1/8 3 Heavy, crushed to 8 in (200 mm) ROM coal, rock, ores 3/16 5 IP: Conveyor and Elevator Belt Handbook 12

13 Steel Cord Belt Covers Cover Carcass Dimensions: To protect the steel cords from impact, abrasion, and water or any other environmental factors, which could cause a loss of strength, during the entire service life of the belt, a minimum thickness of rubber must encapsulate the cords. This cover thickness is usually dictated by the service conditions, but should never be less than 5/32 in (4.0 mm). Failure to respect these limits may lead to uneven, accelerated cover wear or cord damage which would result in reduced belt life. Table 2-4 indicates the minimum thickness F above and below the cords that is required for this protection. Figure 2-1. A = Protective covering for cords during the entire belt life. (A = 2F + D) B = Amount of top cover used for the service life of the belt. C = Amount of bottom cover used for the service life of the belt. D = Diameter of the cord. E = Rubber encapsulating the steel cords and especially compounded for compatibility with the cover rubber and bonding to the steel cords. F = Thickness of rubber to protect the cords during service. This protective rubber is not part of the top or bottom wear covers used to estimate belt tonnage. Table 2-4. Guide for Minimum Protective Rubber F Cord Diameter Minimum Thickness F (above & below cords) mm mm in * * This value has been lowered from the calculated 6.6 mm as a result of favorable field experience. For thickness of covers B and C consult belt manufacturer. Note: Minimum thickness of protective rubber F should not be less than 3.5 mm or 0.7 times the cord diameter, whichever is greater.for larger diameter cords contact manufacturer. IP: Conveyor and Elevator Belt Handbook 13

14 Pulley Cover Thickness The major function of a pulley cover is the same as that of a top cover: to protect the carcass material. In addition, field studies of conveyor power have shown that energy is lost by the pulley cover as it passes over each idler roll. This is called rubber indentation loss and can account for over 60% of the total belt drive power. Special pulley cover rubbers have been developed called Low Rolling Resistance (LRR) covers to reduce the amount of power lost. Further details can be obtained from individual belt manufacturers.. Since a pulley cover is not subjected to the severe conditions imposed upon a conveyor cover, its thickness does not need to be equal to top cover. See below section Cover Thickness Ratio. Table 2-5. Suggested Minimum Pulley Cover Thickness for Grades 1 & 2 Belting Operating Conditions Minimum Thickness in mm Slider bed package conveyors bareback or friction surface bareback or friction surface Abrasive materials 1/32 1 *Impact loading 3/ * Increased cover thickness helps protect the carcass; however, if impact is severe, the complete system design, including carcass construction, top cover thickness, and impact rolls in the conveyor, must be considered. Note: Cover thicknesses are nominal values subject to manufacturers tolerances. Cover Thickness Ratio The thickness of the cover on conveyor belting must be selected on the basis of the service conditions to which the belting is to be subjected. The ratio of the thicknesses of the top and bottom covers must also be considered. This factor becomes increasingly important with conveyor belting where the carcass is thinner than those of comparably rated multi-ply conveyor belts. A large cover thickness ratio, such as greater than 4:1, where one cover, the top, is much thicker than the other, the bottom - may cause a conveyor belt to assume a permanent transverse curl or cup, wherein the edges of the belt curl up on the carrying run and down on the return run. In its more severe state, this curl can adversely affect the training of the belt, especially on the return run. When the curl has progressed to the point that only the edges of the belt contact the return idlers, training of the belt is virtually impossible. The transverse belt curl that results from a large cover thickness ratio is a result of the shrinkage that occurs in rubber compounds after vulcanizing. With a large cover thickness ratio, the shrinkage force of the thicker cover dominates, causing the belt to curl toward the thicker cover. Multi-ply type belts, with their relatively thick and transversely stiff carcass, tend to resist the curl forces, but thin belt carcasses offer less resistance. Although transverse curl may occur in any size of conveyor belt, it is most likely to cause operational problems in narrower belts, up to 36 in (900 mm) wide. To a lesser degree, it can cause problems with 48 in (1200 mm) widths. With the wider belts, the belt weight usually forces the center of the belt down into contact with the return idlers, thus allowing normal training action to occur. Generally, a maximum ratio of 4:1 for multi-ply and 2:1 for single-ply belting is recommended. Cover thickness ratio specifications vary among manufacturers of conveyor belting. Individual belting manufacturers should be consulted for their specific recommendations on cover thickness ratios for belting. POLYVINYL CHLORIDE (PVC) CHARACTERISTICS PVC is a resin produced from polymerizing vinyl chloride. The term PVC in the belting trade is generally applied to the elastomeric material that results from the resin having been mixed with various liquids and powders and heat treated to change the mixture into a usable elastomeric condition. The mixture of PVC, liquids, and powders may be used in the form of a liquid plastisol for saturating and top coating fabric or as a film to laminate and top coat fabric. The PVC elastomer is thermoplastic. It hardens and stiffens with reduced temperature and softens and becomes more flexible with elevated temperatures. PVC belting operates well in the range of 20 to 180 F over conventional size pulleys. With special handling, operation down to - 30 F is possible. General purpose PVC belting becomes hard and cracks when subjected to certain hydro-carbons and oils, which cause a softening and swelling action on general purpose rubber. PVC can be compounded to prevent the deleterious effect of those hydrocarbons and oils. PVC can be compounded to promote good flexibility at -40ºF and to improve flame propagation resistance. PVC elastomers are resistant to acids, alkalies, strong oxidizing agents and strong chlorinated cleaning agents. IP: Conveyor and Elevator Belt Handbook 14

15 SPECIAL SERVICE BELT COVERS AND SPECIFIC CHARACTERISTICS Belting can be designed to operate in various conditions and environments. No one belt type will handle all conditions well. Specific environments that require special service belts include: static conductive, flame/fire resistance (MSHA), high (and low) temperature, oil service, high temperature and oil service, high temperature abrasion, etc. Specific test protocols are used to determine the elastomer s response to these conditions and environments. An abbreviated listing of these tests are offered in Table 2-6 for reference in regards to belt recommendations. Table 2-6. Test Protocols for Special Service Belt Covers Condition Friction (Coefficient) Flame Resistance Heat Resistance Heat Resistance Low Temperature Low Temperature Oil Service / Chemical Ozone Tear Resistance Test Method ASTM D Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Filmand Sheeting ASTM D (MSHA CFR: part 14) ASTM D Heat Resistance ASTM D Standard Test Method for Rubber-Deterioration by Heating in Air (Test Tube Enclosure) ISO Conveyor belts -- Heat resistance -- Part 1: Test method; ISO Conveyor belts -- Heat resistance -- Part 2: Specifications ASTM D Standard Test Method for Coated Fabrics -- Low Temperature Bend Test ASTM D Standard Test Methods for Rubber Property -- Brittleness Point of Flexible Polymersand Coated Fabrics ASTM D Standard Test Method for Rubber Property -- Effect of Liquids ASTM D Standard Test Method for Rubber Deterioration -- Surface Ozone Cracking in a Chamber ASTM D Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers RECOMMENDATIONS FOR OIL SERVICE BELTING Various levels of oil service may be required from belt products. These service levels may or may not involve elevated temperatures. The ARPM classifies belting (or cover formulations) to meet either MOR/VOR (Moderate / Vegetable Oil Resistant). Service requirements or EOR (Extreme Oil Resistance) service requirements based on the following test criteria. Table 2-7. %Volume Swell (ASTM D 471) C Oil Resistance ASTM #1 Oil ASTM #3 or #903 Oil MOR / VOR Moderate / Vegetable Oil Resistant 15% Max. 140% Max. EOR / SOR Extreme Oil Resistance 5% Max. 30% Max. MOR / VOR - Belting is designed to resist swelling and deterioration from vegetable based oils as well as light (napthenic / paraffin / low aromatic) petroleum oils. EOR / SOR - Belting is designed for use in extremely oily environments, especially where polar aromatic materials are expected to be encoutered. Depending on temperature requirements and manufacturers recommendations, this class of belt may be suitable in Hot Asphalt applications. Additionally, in coal fired power generation facilities where the fuel is being enriched with petroleum waste oils or fuel / diesel oils, this may be the belt type required. Consult the manufacturer for recommendations when abnormal conditions are anticipated. Most of the cover formulations for belting meeting these classifications will be comprised of, or contain a certain percentage of, one or more of the following polymers: CR (Polychloroprene / Neoprene), NBR (Nitrile), PVC, Urethane (AU / EU), CPE (Chlorinated Polyethylene) or other oil resistant types listed in Table 1-1. IP: Conveyor and Elevator Belt Handbook 15

16 HIGH TEMPERATURE SERVICE CLASSIFICATIONS Belting designed and manufactured to handle elevated temperatures in service will be classified by type depending on the belt cover characteristics when tested to ASTM D 865 at the specified times and temperatures. Table 2-8. High Temperature Testing (ASTM D 865) Time 70 hr - Test Temperature Retained Tensilefrom original Retained Elongation from original ISO 4195 is referenced as another testing and classification tool. While the classifications and value limits are similar between these tests, they differ in both time of exposure (70 hr vs. 168 hr) and method of sample preparation. ISO 4195 calls for the entire belt sample to be exposed, with test specimens to be cut / prepared from the exposed belt samples. ASTM D 865 allows for test specimens to be prepared before exposure. The correlation between these methods has not been determined and differences are expected, since the mass of ASTM sample is small relative to the dimensionally large ISO sample size. Hence the shorter time of exposure per the ASTM / ARPM protocol. While these tests and classifications do not validate product usefulness or acceptability in specific environments, they are used as tools by the industry to more narrowly define criteria for applications involving elevated temperatures. It must be noted that temperature alone may not be the overriding / determining factor in product suitability. Certain conveyed materials may degrade various elastomers at test temperatures that the elastomers may be expected to perform based on test conditions. Consult the belt manufacturer for specific recommendations. FLAME RESISTANCE SERVICE CLASSIFICATIONS WARNING: All belting will burn when adequately ignited Hardness pt. change ARPM-HR Class F (100 C) -25% (max.) -50% (max.) +20 (max.) ARPM-HR Class F (125 C) -30% (max.) -50% (max.) +20 (max.) ARPM-HR Class F (150 C) -40% (max.) -60% (max.) +20 (max.) Table 2-9. Flame Resistance Testing (ASTM D865) Belt Designation Sample Size (Qty.) Method (Time) Pass Criteria ARPM-HR Class 1 60 x 9 (3) 1524 mm x 229mm ASTM D378 13:1 Burner (5 min) Some undamage belt in each sample ARPM-HR Class 2 6 x 0.5 (4) 152mm x 13mm ASTM D378 13:2 Bunsen Burner (1 min) Flame out average < 1 min No afterglow after 3 min A wide variety of flame tests for conveyor belts exists throughout the world. The standard used in a particular country is usually dictated by a national or local governing body. For general flame resistant conveyor belting, the selection of the most suitable quality may be made by the ARPM-FR class designations. ARPM-FR Class I Based on the December 31, 2008 U.S. Mine Safety & Health Administration s (MSHA), CFR Title 30 Section 14, Requirements for the Approval of Flame-Resistant Conveyor Belts, also known as the Belt Evaluation Laboratory Test or BELT test, this new ARPM-FR standard provides a flame resistance quality that is currently mandated by MSHA in the USA for underground coal mines. This belt quality is appropriate for belts that require flame resistance and which are included in the December 31, 2008 CFR, Title 30, Mineral Resources, Section 14, which primarily applies to conveyor belts used in underground coal mines. The test procedure is described in ASTM D 378 Section 13.1 and employs 60 in x 9 in sized belt test samples. Following the original MSHA guidelines, the acceptance criteria for three belt samples tested to this ARPM-FR Class I standard is each tested sample must exhibit an undamaged portion across its entire width. IP: Conveyor and Elevator Belt Handbook 16

17 ARPM-FR Class II Based on the pre - December 31, 2008 U.S. Mine Safety & Health Administration s (MSHA), CFR Title 30 Section 18.65, Requirements for the Approval of Flame-Resistant Conveyor Belts, also known as the 2G test, this new ARPM-FR standard provides a basic flame resistance quality that was formerly mandated by MSHA and was used successfully in the USA for many years. This belt quality is appropriate for belts, such as above ground belts, that require flame resistance and which are not included in the December 31, 2008 Code of Federal Regulations, Title 30, Mineral resources, Section 14, which primarily applies to conveyor belts used in underground coal mines. The test procedure is described in ASTM D 378 Section 13.2 and employs 6 in x 0.5 in sized belt test samples.following the original MSHA guidelines, the acceptance criteria for belt samples tested to this ARPM-FR Grade II standard is defined as the tests of four specimens cut from any belt sample shall not result in, either duration of flame exceeding an average of 1 minute after removal of the applied flame, or the continuation of visible glowing of a specimen after flaming has ceased (afterglow) exceeding an average of 3 minutes duration. ARPM-FR Class Test Responsibility Each belt manufacturer is responsible to ensure tests are conducted to the appropriate ARPM-FR class specification on each belt order claiming the ARPM-FR class quality. Tests may be witnessed at any time by the customer or his representative to ensure compliance to the test standard. Marking A ARPM-FR class conveyor belt must be permanently and legibly marked with the appropriate ARPM-FR class designation (and/or MSHA approval number for ARPM-FR Class I) for the service life of the product. The marking must be at least 0.5 in (1.27 cm) high and placed at intervals not to exceed 60 ft (18.3 m) repeated once every foot (.3 m) across the width of the belt. Records of the initial sale of each belt order having the ARPM-FR class marking and actual test conditions and test results must be retained for at least 5 years. POLYURETHANE (PU) CHARACTERISTICS Polyurethane is generally characterized as a cut and abrasion resistant polymer with excellent mechanical properties in the range of about -65 to 212 F (-54 to 100 C). There are both thermosetting and thermoplastic grades used in belting, and polymer back bones that enhance oil resistance or water resistance. The thermoplastic grades are easily spliced in belt constructions, and food contact polyurethane compounds are available. General When it is the user s opinion there is a potential fire hazard, he should consult the belt manufacturer and consider whether belting manufactured to the above specifications is suitable for the application. In each installation, consideration should also be given to the following: a. Fire detection systems b. Automatic fire suppression systems c. Slip and sequence interlock systems d. Sprinklers at transfer points to reduce flammable dust e. Belt lateral alignment controls f. Elimination of combustible materials near the conveyor belt g. Conductive paths to ground for static electricity including conductive grease in bearings h. Chute probe or level indicators at transfer points i. Fire retardant, static electricity conducting drum lagging, skirts, scrapers, and chute lining j. Heat sensors for conveying pulley bearings. Effective December 31, 2008, the United States changed the minimum standard for flame performance of underground coal mine conveyor testing. Until December 31, 2009 conveyor belts placed in service in underground coal mines shall be either approved under Part 14; or accepted under Part 18. Part 18, is an old MSHA standard, Code of Federal Regulations, Title 30, Mineral Resources, Section 18.65, Flame Testing of Conveyor Belting and Hose. Part 18 is commonly known as 2G. Effective December 31, 2009 conveyor belts placed in service in underground coal mines shall be approved under Part 14. If MSHA determines that Part 14 approved belt is not available, the Agency will consider an extension of the effective date. Effective December 31, 2018 all conveyor belts used in underground coal mines shall be approved under Part 14. Effective December 2, 2005, in Canada, the CAN/CSA M422 M87 Fire Performance and Antistatic Requirements for Conveyor Belting standard was withdrawn. Formerly this standard was the minimum standard for flame performance and electrostatic conductance for underground belting which was tested in accordance with the CAN/CSA M422 M87 Fire Performance and Antistatic Requirements for Conveyor Belting by Energy, Mines and Resources, Canada, Canadian Explosives Atmospheres Laboratory. They formerly assigned an approval number for each different belt which number, together with other information in M422, which was branded on the belt at least once every 15m (approx. 50 ). Conformance to the M422 specification about branding was enforced by Provincial Regulatory Agencies. IP: Conveyor and Elevator Belt Handbook 17

18 CHAPTER 3 TEXTILE BELT TYPES AND MANUFACTURING METHODS INTRODUCTION This chapter describes types of textile belting in terms of carcass types and of edge protection. This will be followed by a description of belt cover designs and textile belt manufacturing methods. BELT CARCASS TYPES The belt carcass primarily provides resistance to tension forces that build up in the conveyor system. Also it provides strength to resist belt tear and loading impact and for load support, troughing, mechanical fastener holding ability, and resistance to wrinkling or edge cupping. Textile Fabric Carcass - (See Figure 3-1) The textile fabric carcass may have one or more plies of fabric bonded by elastomeric compounds to both themselves and to the belt cover. Belt strength and load support characteristics depend on the fabric construction and the number of plies used. Flexibility/ stiffness are functions of the fabric construction and number of plies of fabric, and skim and cover thicknesses and their elastomeric properties. The elastomeric compounds in heavy weight belting are often thermosetting. Light weight belting is reinforced in some constructions by one or more plies of fabric like the heavy weight belting or in other constructions by solid woven or interwoven fabric or by non-woven fabric which generally has a woven scrim component. The individual plies in light weight belting often have monofilaments in the weft to impart transverse stiffness, and the elastomeric materials in the plied constructions are predominantly thermoplastic. Figure 3-1. Textile Fabric -- Multi-Ply Belt Shown with Three Fabric Plies and Cut Edges* * Refer to Glossary for definition of cut and slit edges.. Solid Woven Carcass Solid woven belting consists of a single ply carcass made up of multiple layers of warp and filling yarns interwoven. The carcass is usually impregnated and/or coated with thermoplastic compounds. Molded (Capped) Edge Belting BELT EDGE PROTECTION - MOLDED EDGES Historically all conveyor belting was made with molded (capped) edges (Figure 3-2). Molded edges were necessary to protect the cotton fiber in the carcass against mildew or chemical action. Thus the carcass, in addition to being covered, was encapsulated around the edge with the elastomeric compound of the covers, and molded into a square capped edge. It must be recognized this was only a temporary expedient; since, when the covers were cut, gouged or worn to the fabric and the molded edges were torn or worn off, the absorption of water and chemicals would occur. With the availability of nylon and polyester fabrics, cut edge belting is now commonly used. In light weight belt applications capped edges are used in applications where improved edge protection is required. For example: food processing to eliminate edge fraying and subsequent absorption of fluids. IP: Conveyor and Elevator Belt Handbook 18

19 Figure 3-2. Multi-Ply Belt Shown with Four Plies of Reinforcing Fabric, A Breaker Ply, Covers and Rubber-Capped Edges Cut/Slit Edge Belting The general use of nylon and polyester yarn for conveyor belt carcasses has eliminated the concern for protecting the belt carcass with molded edges. The nylon and polyester fibers are resistant to mildew attack and the polyester to most chemicals. Thus most belting is now supplied with slit edges. CARCASS PROTECTION Breaker Before the use of nylon and polyester carcass fabric, breaker plies of open texture leno weave cotton or nylon yarn were frequently used between the carrying cover and the belt carcass. It was believed a breaker ply improved the adhesion of the cover. The breaker ply next to the carcass improved cover cut and gouge resistance and provided material loading impact resistance. Breaker plies are used where severe impact conditions exist. Sometimes a breaker fabric in a molded edge is wrapped around the fabric edge to provide edge protection. BELT COVER DESIGNS For most applications, conveyor belts have a smooth top and/or bottom cover made of elastomeric compound suitable for the material to be conveyed. There are, however, some special purpose belt surface finishes described in the following. Bareback Surface The outer surface of the top or bottom of the fabric of a bareback belt has neither an elastomeric compound cover nor is it impregnated with an elastomeric compound. A bare fabric surface provides a low coefficient of friction. A slider bed package conveyor with the bareback surface down against the slider bed or the bareback surface up in connection with a diverter bar are examples of bareback surface applications. Friction Surface The outer top and/or bottom surface of the fabric of a friction surface belt has a light impregnation of elastomeric compound. Brushback Surface Certain friction compounds may be buffed to further reduce the coefficient of friction while retaining the elastomeric compound in the interstices of the fabric. Bareback, brushback and friction surface belts can be provided with a cover on one side of the belt. Impression (Rough Top) Surface Impression belts have an embossed profile in a cover made by curing the elastomeric cover against a mold, fabric, or stamped metal or by embossing a thermoplastic cover. Impression belts are often used to convey material on inclines and declines where slippage may occur. Cleated, Flanged (Sidewall) or Ribbed Top Surface Cleats, flanges or ribs in transverse, longitudinal, continuous or intermittent, and of angular, straight or curved design may be molded onto or affixed to the cover. They improve the ability to carry coarse material on incline and decline applications. The height and spacing of the cleats, flanges or ribs depend on the size of the material to be conveyed. IP: Conveyor and Elevator Belt Handbook 19

20 BELT MANUFACTURING METHODS SINGLE AND MULTI-PLY BELTS Drying Cotton and spun synthetic yarn fabrics must be heated before they are frictioned so the friction rubber can be properly impregnated into the interstices of the fabric. Also the cotton, rayon, and nylon spun yarn fabrics must be thoroughly dried to remove moisture which in the belt curing operation could cause blisters between the plies of fabric or under the covers. Textile Fabric Treatment Generally, most multi-filament textiles (nylon, polyester, etc.) require an RFL treatment to ensure adequate adhesion in service. RFL is an industry term designating a treatment mixture of resorcinol formaldehyde latex (RFL), whereby the woven textile is dipped in the emulsion and dried under specific temperature and tension conditions. This process is used for most rubber based belting (Natural, SBR, NBR, CR, EPDM, etc.). For thermoplastic type belt, the treatment can involve acylics, polyurethane, PVC or other treatment for the respective textile reinforcements. Rubberizing (Skimming, Bank Coating, and Frictioning) The fabric is impregnated with a suitable elastomer by frictioning and/or skim coating on 3-roll or 4-roll calenders. Frictioning forces the pre-softened rubber compound into the interstices of the fabric by the wiping action of two calender rolls running at different surface speeds. In skim coating the calender roll speeds are essentially the same, and a thin layer of rubber compound is laid on the fabric. During the calendering operations, uniform tensions are maintained on the fabric to prevent undesirable distortion. Carcass Building Calendered plies of fabric are laminated and consolidated by squeezing between two rolls of a building unit. Depending on equipment design, from two to five plies can be laminated in a single pass through the unit. Uniform tension is maintained on each ply to ensure maximum efficiency during service. Longitudinal seams (ply splices) result when it is necessary to use more than one strip of fabric to make the full ply width. The seam is made by bringing the two edges together and, if necessary, placing a rubber cord over the joint so that a void does not occur when vulcanizing the finished belt. Longitudinal seams are generally made during the laminating pass through the building unit. Seams shall be at least 4 in from the edge, separated by 12 in within the ply and be removed from the idler junction area. Number of seams are limited by belt width. Tranverse seams (ply splices) result when the fabric length is less than the full length of the finished belt. The ends of the two or more pieces are prepared by cutting on a 20 to 45 bias angle. The ends are then butted against each other and if necessary, a strip of rubber compound is placed over the joint to prevent a void from forming during subsequent manufacturing operations. The preparation of the bias cut ends is done during the actual laminating operation at the carcass building machine, which results in a good matching of the two ends being joined. Transverse seams shall be at an angle between 26.5 and 70, shall be separated by at least 50 ft, and be at least 50 ft from the end of the belt. No transverse seams are allowed in the outer plies. Belt Covers The elastomeric covering on belts is there to provide protection for the carcass, and/or provide a specific property. These coverings are applied by several processes, depending on the material (rubber vs. thermoplastic) or thickness of the covering. For rubber belting covers are either extruded or calendered. Extruded rubber sheets of specific widths and thickness are then laminated or press plied onto the carcass. similarly, thermoplastic covers can also be extruded and laminated. For most thin belt covers (i.e. pulley side covers), less than 1/8 in (3.2 mm), application is performed at a calender unit where the elastomeric compound is skimmed onto the textile. This process can accommodate some thermoplastic materials as well as rubber. PVC covers are also applied with roll or knife coating processes. IP: Conveyor and Elevator Belt Handbook 20