At the time, its design was governed mainly by the requirements of the mining industry. The mining industry proved to be a trendsetter once again. Particularly, in the field of underground mining where stringent requirements gave rise to a high standard of belting. Also, the new ignite surface mines were responsible for bringing about major improvements in the design of heavy-duty conveyor belts. These changes were subsequently adopted by other industries. Over the years, the belt materials and their properties have undergone considerable changes. The need for increased tensile properties, abrasion resistance, and higher economy has encouraged belt users to join with belting manufacturers as well as plane engineers to develop tougher and more economical conveyor belting.
The belt reinforcement was originally in the form of cotton plies. These were later replaced by plies such as rayon, polyester, polyamide, and especially steel cords, which were to carry the tension loads of the belt. Steel cords not only proved to have outstanding flexibility but were also able to carry the highest belt tensions. The belt plies were originally embedded in natural rubber. In the course of time, the rubber compounds were considerably improved to meet the stringent safety requirements for underground use, and inflammable natural rubber was superseded by non-inflammable or self-extinguishing rubber, or even plastics such as PVC. Extremely wear-resistant belts were developed for use in surface mining. In 1913, Henry Ford introduced conveyor-belt assembly lines at Ford Motor Company’s Rouge factory, in Dearborn Michigan. In 1972, the French society REI created in New Caledonia the then longest straight-belt conveyor in the world, at a length of 13.8 km.
Basic Properties Required Includes
Conveyor belts have to meet rather different requirements, depending on the particular application.
- High strength and flexibility
- Low extension in service
- Resistance to abrasion
- Impact and tearing resistance
- Resistance to moisture, oils and chemicals
- Temperature resistant
- Fire resistant
In addition to the above properties, conveyor belt material should also exhibit-
- Harmless as regards hygiene
- Good adhesion of the constituent plies and good adhesion to the driving drums
- Minimal tendency to electrostatic charging and last but not least,
- Should be reasonably priced.
The importance of these individual factors may considerably vary in different products.
The two main components in conveyors belts are the rubber and the reinforcing member that carries the load.
The rubber has two primary functions;
- first to act as a binding element and
- second to protect the tension member.
The performance level of the conveyor belt, of course, posed on reinforcement materials as regards both fibre properties and fabric construction. The traditional reinforcement materials are woven textile fabric and steel cord. The selection is determined by the working tension in the system.
Conveyor Belt Construction
Conveyor belts generally are composed of three main components:
1. Carcass
2. Skims
3. Covers (carry cover and pulley cover)
Carcass
The reinforcement usually found on the inside of a conveyor belt is normally referred to as the “carcass.” In a sense, the carcass is the conveyor belt since it must:
a) Provide the tensile strength necessary to move the loaded belt.
b) Absorb the impact of the impinging material being loaded onto the conveyor belt.
c) Provide the bulk and lateral stiffness required for the load support.
d) Provide adequate strength for proper bolt holding and/or fastener holding.
The carcass is normally rated by the manufacturer in terms of “maximum recommended operating tension” permissible (pounds per inch i.e., ppi).
Primary Belt Material
Aramid: Aramid fibers exhibit good impact resistance, toughness, low elongation, and resistance to damage by penetration of powders or siIt.
Cotton / Canvas: Any weave of cotton, cotton blends, or heavy-duty canvas.
EPDM: Good resistance to sunlight, weathering, and ozone. It has poor resistance to petroleum oils and fuel. Good heat and compression set resistance. The suggested operating temperature was -70° to 275° F. Trade names include Nordel® (Dupont Dow Elastomers), Vistalon® (Exxon Mobil Chemical), Epsyn® (DSM Elastomers), Royalene® (Uniroyal Chemical), and Epcar® (B.F. Goodrich).
Hydrin®: Good gas impermeability and maintains physical properties over a wide temperature while maintaining resistance to petroleum oils. Ozone, oxidation, weathering, and sunlight resistances are other qualities. Suggested operating temperatures (_600 to 3000 F). Hydrin® is a registered trademark of Zeon Chemicals L.P.
Kevlar®: Kevlar® is a man-made organic fiber developed by DuPont. The general features of Kevlar are high tensile strength at low weight, structural rigidity and durability, high chemical, flame, and cutting resistance, and low electrical conductivity. It is used in many safety and heavy-duty industrial applications.
Leather: The characteristics of leather include flexibility, toughness, and resistance to abrasion. It is composed of high-strength interlocking fibers. There are two main advantages to using leather as a sealing material, its ability to absorb and retain lubricants and its effectiveness sealing against rough surfaces.
Mylar®: Mylar® is a polyester film and laminating substrate, designed by DuPont. Its primary characteristics include excellent flexibility, machinability, and puncture resistance while providing a barrier against gas and water vapor. It also retains its form and function within very high or low temperatures. Its uses are extremely varied, from foodservice; to seals, barriers, and personal protection; to heavy-duty industrial applications.
Neoprene: A synthetic rubber that resists degradation from sun, ozone, and weather. It performs well in contact with oils and many chemicals. Neoprene remains useful over a wide temperature range, displays outstanding physical toughness, and resists burning inherently better than exclusively hydrocarbon rubbers. Neoprene also offers resistance to damage caused by flexing and twisting. Suggested operating temperature (-45° to 230° F). Trade names include Neoprene (DuPont Dow), Baypren® (Mobay), and Butachlor® (Ditsugil).
Nitrile: Good resistance to petroleum hydrocarbons and fuels. Widely used with most oils, hydraulic fluids, and alcohol. Many compound variations are available for specific applications. Suggested operating temperature (-30° to 275° F). Trade names include Breon® (BP Chemicals), Chemigum® (Goodyear), Hycar® (B F Goodrich), Krynac® (Polysar Ltd.), Nipol® (Zeon Chemicals), Nysyn® NBR, (DSM Elastomers), Paracril® (Uniroyal Chemical), and Perbunan® (Mobay).
Nylon: Nylon, comprising several grades of polyamides, is a general-purpose material in wide use; it is tough and resistant and has good pressure ratings.
Polyester: Polyethylene Terephthalate, also called polyester fiber, refers to any one of a large family of synthetic polymers composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid. General characteristics of this family include high tensile strength; chemical, wrinkle, and abrasion resistance; and ease of drying and washability. Industrial uses include belting, hoses, cords, and threads; essentially any application where the fiber must be highly flexible, yet durable.
Polyurethane / Urethane: Polyurethane is a diverse class of materials exhibiting good elongation, recovery, and toughness properties. They are flexible and have good abrasion resistance. (NOTE: The urethanes of the plastics industry are so named because the repeating units of their structures resemble the chemical urethane.) Trade names include Texin® (Bayer), Adiprene® and Vibrathane® (Uniroyal Chemical), Estane® (B F Goodrich), Genthane® (General Tire and Rubber), Millathane®, and Peliethane® (Dow Chemical).
PVC: PolyVinyl Chloride is a widely used material that has good flexibility, smooth surface, and non-toxic qualities. Some grades are used in food and chemical processes due to the inert nature of PVC. Brand names include ACP® and Dural® (Alpha Gary), Geon® (Geon), Benvic® (Solvay), Flexalloy® (Teknor Apex).
Rubber: Natural compounds such as gum rubber (polyisoprene) and latex.
Silicone: Silicones are polymers in which organics groups, such as methyl and phenyl groups are bonded to the silicone atoms in chains of inorganic siloxanes (-Si-O-Si-). Their properties include heat, cold and weather resistance, electrical insulation, release, water repellency and defoaming.
Steel Belt: Includes all grades of carbon, mild, and other non-stainless steel.
Steel Belt – Stainless: Includes all grades of stainless steel belting.
Steel Cord: “Belt” consists primarily of steel cord for high tensile strength; usually contained within a binding matrix.
Tape – All Materials: Very thin section most frequently made of steel or other metal; usually for light-duty tracking and control operations.
Teflon®: Teflon® refers to a class of fluoropolymer resins used for a wide variety of commercial applications. They are highly resistant to temperature, chemical reactions, corrosion, and stress cracking. Teflon is a registered trademark of DuPont Dow Elastomers.
Wire Mesh or Weave: Meshed or woven wire can exhibit high-temperature stability and material toughness. Gaps or openings in the mesh can be desirable for certain types of food and material processing.
Skims
The rubber, PVC, or urethane between plies is called a “skim.” Skims are important contributors to internal belt adhesions, impact resistance, and play a significant role in determining belt “load support” and “trough ability.” Improper or marginal “skims” can adversely affect belt performance in general and can lead to ply separation and/or idler junction failure.
Covers
Covers are used in conveyor belt constructions in order to protect the base conveyor belt carcass and, if possible, to extend its service life. In addition, covers do provide the finished belt with a wide variety of desirable properties, including the following:
A. Textures
- To increase friction
- To increase inclination
- To control product
B. Cleanability
C. e. A specific coefficient of friction
D. A specific color
E. Cut resistance
F. Enhanced impact resistance, etc.
G. Hardness
H. Fire Resistance, Oil & Chemical Resistance
Cover type, quality, and thickness are matched to the service life of the belt involved. A specific cover formulation used in an individual belt construction is determined by the material to be carried and the environment in which the belt will operate.