Updated: May 16
Hardness (appr. Rockwell R-value)
Up to 428F (220C)
Up to 300F* (148C)
*doesn't melt, burns
High load tolerance
Tensile strength, resists compression
Impact & wear resistance
What Is the Difference Between Nylon and Polyurethane?
Polymers are a subset of plastics most often formed from petroleum products. The toughest of these are lightweight, resilient materials suitable for use in industrial manufacturing. These plastics are resistant to warping, wear, and corrosion and are quiet and lightweight compared to steel components.
Polyurethane is a thermoset polymer that is incredibly tough. It holds up well to impact without cracking, and offers best in class resistance to wear. Thermoset polymers are made using two or more elements that combine to create an entirely new material, in a process similar to mixing epoxy. Once combined, the end product is heated and added into a mold to create the final shape. Polyurethane cannot be reheated and formed into a new shape, making it difficult to recycle. Instead of melting, polyurethane burns when exposed to heat above 300 F (148 C).
Nylon is a rigid thermoplastic characterized by high tensile strength and its resistance to compression. Unlike thermoset polymers, thermoplastics can be melted and reformed again without compromising the strength of the end product, making nylon components recyclable.
How Do Polymers Compare to Steel?
One of the main benefits of polymers is their reduced operating volume compared to steel. Both nylon and polyurethane are significantly quieter than steel, making polymer components a great substitute for steel in noise sensitive applications. They’re also significantly lighter than steel – useful in weight-sensitive applications with mild workloads.
Polymer components are low maintenance due to their self-lubricating characteristics and high wear tolerance. They’re a good fit for situations where access to the component is limited, such as a submerged drive shaft.
Of the two products, Nylon is slightly harder. This gives nylon the ability to run for longer periods of time without distorting due to friction, but also results in a higher noise floor than polyurethane.
Polymers are also highly resistant to corrosion. Of particular note is their inability to oxidize. When steel reacts with moisture, it forms iron oxide (rust). This is a type of corrosion, and compromises the structural integrity of the metal. Because polymers cannot rust, they are ideal materials for use in industries such as food and beverage manufacturing and packaging, where moisture would compromise steel components, and rust particulate would compromise the quality of the end product. Polymer sprockets are ideal in sanitary environments such as food and beverage, medical product, and cosmetics manufacturing where health and safety guidelines regarding contaminants are of particular note. They are also well suited for use in immersion environments (e.g. wastewater treatment plants), where oxidization is a primary cause of component failure and maintenance access is prohibitively difficult. Oxidization isn’t typically a concern with polymers, but they can still be damaged by acidic, caustic, or basic environments.
For their weight, both nylon and polyurethane possess impressive load bearing capabilities, but when compared to steel, they are still inferior in this regard. By density, steel exceeds the tensile strength of both polymers at least tenfold. Steel also has a significant advantage in shear strength, making it a better fit for applications where sudden force may be applied. Under heavy impact loads, a steel sprocket will survive impact loads that would damage both nylon and urethane sprockets. For this reason, polymers are offered both as a standalone sprocket and as a bushing material. As a bushing, polymers are thinner than comparable bronze equivalents, while still maintaining their self-lubricating, low-friction characteristics.
Polymers are an ideal material for work involving steady, low-pressure loads - generally when steel components are either too loud for the environment, the environment is too corrosive for steel, or to mitigate impact to aesthetic grade products such as plywood or hardwood/softwood lumber. Within these constraints, polymer components can be robust and resilient materials, often available at a much lower cost than their steel equivalents.
Are Nylon or Urethane Sprockets Better?
Both polymers have their own inherent strengths and weaknesses, and each will have an operating niche.
Generally speaking, nylon has a longer operating life compared to polyurethane due to its relative hardness. This means nylon sprockets don’t break down as fast under repetitive contact with chains, and hold up better against compression from heavy workloads. When molded into sprocket teeth, nylon’s strength and stiffness will offer better performance than ultra-high molecular weight polyurethane. Nylon has a coefficient of friction almost as low as urethane, making it an effective material either as a standalone sprocket or when used as a bushing for a steel sprocket.
Nylon also has a higher heat tolerance than urethane, melting at a temperature of 428F (220C), while polyurethane burns at a maximum temperature 300F (148C). Because nylon melts instead of burning, and does so at a higher temperature, it is the preferred polymer for applications involving heat, or where maximum fire safety is imperative. Steel will remain the most safe and effective option where heat is involved, but if it's not an option, nylon is generally the better choice in this regard.
In applications involving both tight tolerances and contact with liquids, urethane may outperform nylon. This is because nylon absorbs more liquid than polyurethane. Nylon-bushed stainless-steel sprockets, for example, while an effective corrosion resistant sprocket, may perform poorly when submerged, where the nylon may absorb liquid and expand, increasing friction on the shaft. This negatively affects maximum workload and increased the rate of wear on your bushing and shaft. It may also cause alignment issues accelerating sprocket and chain wear. In this scenario, polyurethane will offer better performance and increased component life.
Urethane can be formulated with a wide range of tolerances, some extremely hard, and some more ductile. Urethane on the high end of the spectrum has a hardness approaching nylon, and has an incredible flex life, meaning products made with ductile urethane bounce back to their original shape if malformed by pressure. Most commonly, polyurethane is used for roller chain idler sprockets in order to reduce noise on the factory floor, and in this application urethane products are top of their class.
At DROP Sprockets, urethane is one of the most common bushing materials. We use a proprietary urethane-based polymer blend with extended wear capabilities based on our years of R&D, and experience working with polymer compositions to optimize component lifespan under maximum workloads.
Substituting nylon or urethane for steel in industrial applications requires a deep understanding of all three materials. Contact us to speak with our team before changing materials to discuss the different polymer compositions and select the option best suited to your application.