Synchronous belts for linear motion applications — such as general transport conveyors or high-speed gantry positioning — are available in a wide range of materials suitable for virtually any application. The most common synchronous belt materials are neoprene and polyurethane, but specialty materials and backing surfaces are also available to address requirements such as temperature extremes, chemical resistance, food contact, and high speed operation.
Neoprene (polychloroprene, chloroprene rubber)
Synchronous (toothed) belts made of neoprene typically have a nylon covering on the toothed side to improve the shear strength of the neoprene teeth and provide better abrasion-resistance between the belt and pulley. However, even with a nylon coating, neoprene belts still exhibit higher abrasion than polyurethane versions.
Neoprene synchronous belts are primarily used for their high fatigue-resistance, but the lower noise generation of neoprene (relative to polyurethane) is also a benefit in some applications. Neoprene materials also tolerate exposure to water better than polyurethane, with less tendency to swell. But neoprene belts do have a higher tendency to degrade over time than polyurethane versions.
Polyurethane (PUR, PU)
Polyurethane synchronous belts are commonly used in precise registration or positioning applications due to their high stiffness and good dimensional stability. The teeth of a polyurethane belt exhibit good resistance to deflection, giving PU belts a lower tendency to ratchet. Polyurethane materials also exhibit better resistance to chemicals — including some acids and alkalis — and provide better abrasion resistance than neoprene, making polyurethane belts a better choice for applications where particulate contamination needs to be avoided, such as clean rooms.
Polyurethane is a compound that includes multiple urethane units. However, in the belting industry (and other industries), the two terms are often used synonymously, and belts made of polyurethane are sometimes referred to as “urethane” belts.
When a low coefficient of friction is required between the belt and pulley, polyurethane belts can be supplied with a nylon coating on the toothed side. A nylon coating also helps reduce noise between the belt and pulley in high-speed applications. Similarly, a nylon coating on the back (or carrying) side of the belt reduces friction between the belt and the product being transported, which is often required for applications such as accumulating conveyors.
One of the main drawbacks of polyurethane synchronous belts is their tendency to produce more noise than belts made of neoprene materials. (Although it should be noted that belt noise is influenced by a variety of factors, including pulley material, belt tension, mounting inaccuracies, and belt speed). Polyurethane belts are also less suitable for applications that expose the belt to water, since polyurethane materials have a greater tendency to swell, which can detrimentally increase belt tension.
Materials and backings for special requirements
In addition to polyurethane and neoprene, other materials suitable for synchronous belt applications include Hytrel (a thermoplastic elastomer manufactured by DuPont) and EPDM (a type of synthetic rubber). Hytrel has excellent low-temperature compatibility, withstanding temperatures as low as -40° C, and resistance to a wide range of chemicals. EPDM is well-suited for high-temperature applications, operating in temperatures up to 150° C.
There are also a variety of materials that can be applied to the back side of the belt, such as PTFE (known as Teflon from DuPont), FKM (a fluoroelastomer known as Viton from Chemours), synthetic and natural rubbers, PVC, and silicone. These are used when specific operating properties are required, such as additional hardness, better abrasion-resistance, FDA or USDA compliance, or a change in friction coefficient between the belt carrying surface and the product being transported.