This article gives detailed insights into polyurethane rollers. Read further to learn more about:
Polyurethane rollers are cylindrical rollers coated with an elastomer material known as polyurethane. The inner roller core, depending on the application, can be susceptible to scratches, dents, corrosion, and other forms of damage. The polyurethane layer provides intrinsic properties that protect the inner roller core, including abrasion resistance and impact strength. These rollers are widely used in various manufacturing processes to perform operations such as:
Polyurethane is the most widely used elastomer material for rollers. By blending different types and proportions of compounding ingredients, various mechanical properties can be achieved to suit specific applications. The most desirable properties of polyurethane include its toughness, high impingement resistance, shock absorption, and fatigue resistance.
Polyurethane formulations can produce rollers that range from hard and firm to soft and pliable. These rollers are processed in various durometers, depending on the application's requirements. Polyurethane's durability and shock resistance make it one of the most popular roller compositions. Additionally, polyurethane is an elastomer that can be thermoformed into virtually any shape.
Polyurethane and rubbers, such as nitrile and neoprene, belong to a family of materials called elastomers. Their elastic properties make them an ideal choice as roller-covering material. Polyurethane rollers have several advantages over ordinary rubber rollers. Their impressive mechanical properties make them more viable than other types. The many benefits of polyurethane rollers include:
Carbon Blacking – Rubber roller linings have carbon black added as a filler and reinforcing material. When rolled against a hard surface with sufficient force, they leave black streaks and marks damaging in applications such as finished goods handling and printing. Polyurethane rollers do not require carbon roller linings as extra support, which avoids the potential of carbon blacking.
Processing polyurethane is straightforward and cost-effective, requiring only a basic batch mixer for blending—no heating equipment is needed. This contrasts with other types of rubber, which necessitate more complex and expensive equipment for mastication and heating.
Rubber roller linings often include carbon black as a filler and reinforcing agent, which can leave marks on surfaces under pressure—an issue for applications like finished goods handling and printing. In contrast, polyurethane rollers avoid this problem because they do not contain carbon black.
Polyurethane's resistance to water, oils, and other petroleum-based solvents varies based on the polymer system used. Water resistance is essential for rollers exposed to wet conditions or frequent washdowns, while oil resistance is crucial for handling hydrocarbon-based solvents or chemicals, such as inks.
The engineering involved in polyurethane rollers primarily occurs during the creation of the elastomer lining. This material consists of four key components: the polyol compound, the diisocyanate compound, the chain extender or curatives, and various additives.
The combination of polyol and diisocyanate compounds results in the formation of prepolymer resin. This process creates a simple polymer chain through the reaction of a polyol component (a carbon-chained molecule with alcohol groups on both ends) with a diisocyanate component (a molecule with isocyanate groups on both ends). The reaction produces a molecule with a reactive alcohol on one end and a reactive isocyanate on the other. The alcohol end connects with another isocyanate group or terminal, while the isocyanate end of the chain reacts further with chain extenders or curatives such as hydroxyls and amines. This ongoing process results in the creation of a long, chained polyurethane molecule.
The mechanical properties of the polyurethane depend on the formulation of the prepolymer resin and the curatives used. Additives can enhance specific properties of the polyurethane, such as curing time, machinability, color, and UV protection. However, careful proportioning of additives relative to the amount of resin in the mixture is crucial, as improper ratios can weaken the final product's properties.
In the previous chapter, we briefly covered the process of making polyurethane and explored the roles of the four different components. This chapter will delve into the various chemicals used in polyurethane production and their impact on the final properties of the product.
Similar to polyols, diisocyanate compounds contribute to the resin component of the polyurethane system. Diisocyanates are categorized into two primary types: aliphatic and aromatic.
Polyurethane is considered an engineering material due to its exceptional properties, primarily stemming from its high elasticity. The following are some key properties of polyurethane that are particularly relevant for roller applications.
Materials are graded according to their hardness relative to one another. For elastomers, hardness is characterized by the Shore Hardness Number. This is measured by a durometer. There are 12 different Shore Hardness Scales; each scale has its indenter configuration, profile, and force applied. The Shore scales used for polyurethanes are Shore A and D. Shore A scale measures the hardness of soft, semi-rigid polyurethanes, while Shore D measures hard rubbers and rigid polyurethanes. However, keep in mind that high hardness does not correspond with high rigidity or strength.
With impingement abrasion, the paths of the particles impacting the surface of a material can be perpendicular or at an angle. The attacks of the particles strike specific areas, causing high strain and breaking off small bits of the surface.
Regardless of the type of abrasion, polyurethane is highly capable of resisting both sliding and impingement. Since it has a low friction coefficient and high strength, it is unaffected by sliding abrasion. With impingement abrasion, it absorbs the energy from the particulate attacks, distributes the stress, and immediately recovers without any signs of damage.
Polyurethane is blended to produce a low coefficient of friction, high tear strength, and elasticity, properties that help it withstand abrasion. The composition of its resin produces its exceptional abrasion resistance. Among the polyol compounds for making polyurethane, polyesters have the best tear and abrasion resistance.
Polyurethane tear strength is measured in pounds per inch of thickness. The testing for tear strength is dependent on the application for which the polyurethane will be used. Tear strength tests have been established by the American Society for Testing Materials (ASTM). There are three ASTM tests used to determine the tear strength of polyurethane, which are:
Polyurethane exhibits good thermal aging resistance when formulated with certain compounds such as PPDI and CHDI. Typical polyurethanes have a maximum operating temperature of about 90 to 100°F (32 to 37.7°C). Special but more expensive formulations can reach 302° F (150°C).
The manufacturing of a polyurethane roller is a straightforward process that includes fabricating the roller core, balancing, blending polyurethane, bonding, building, curing, machining, and quality testing. This process is similar to that used for other types of rubber rollers. The key difference lies in the cover-building stage, where the polyurethane resin is in liquid form.
Polyurethane rollers have a solid core or a keyway and space for bearings, which are designed for one or both ends of the roller. Bearings reduce friction against the static and rotating parts. The configuration, mounting, and type of bearing can vary depending on the design of the roller.
All dimensions of a polyurethane roller must be accurate to attain the required diameter, roundness, and balance of the roller. After fabrication, the roller core is subjected to secondary processes such as blasting, lapping, and cleaning to remove any traces of corrosion and contaminants.
The formulation can be done through different processes. These are known as the single shot, prepolymer, and quasi-prepolymer processes.
The single-shot process involves having all components in separate chambers. These will then be blended by a mixing head and poured or injected into the mold.
The second option is the prepolymer process. This process is carried out by mixing the polyols and diisocyanates before pouring them into the mold. This process helps dissipate the heat produced from the exothermic reaction of the compounds.
Last is the quasi-prepolymer process. Quasi-prepolymers consist of polyols partially reacted with the diisocyanate compounds. This simplifies the formulation process since the quasi-prepolymers are less viscous and require low processing temperature.
Other rubber compounds used for roller linings are in the form of calendered sheets and strips. They are joined to the roller core by plying and extrusion. Polyurethane formulations are available as liquid mixtures. Thus, the processes of building polyurethane are casting and injection molding. Both of these methods use liquid resins.
Casting involves placing the roller core into a mold where the polyurethane polymer is poured. The process of casting is an economical method for manufacturing polyurethane rollers and is much less expensive than injection molding.
Injection molding requires expensive dies that must be machined and configured to the shape of the desired polyurethane roller. It involves a great deal of time and the use of expensive machinery and equipment.
Other polyurethane systems employ an additional curing process known as post-curing. Post-curing further improves the mechanical properties of the cast, as well as its temperature aging resistance.
In the United States and Canada, there is a wide range of machines available for producing polyurethane rollers. These machines are crucial for the mass production of polyurethane rollers, which play a significant role in industries such as manufacturing, transportation, and material handling. They contribute to enhanced efficiency and productivity in these sectors. Below, we provide information on many of the leading machines for producing polyurethane rollers.
Characteristics: The SC3000 is a high-precision spin-casting machine designed for efficient and accurate production of polyurethane rollers. It guarantees uniform material distribution and a superior surface finish.
Characteristics: The E-DM series is engineered for polyurethane injection molding, allowing for the production of rollers with complex designs and consistent quality.
Characteristics: The XJL-120 is an extrusion machine tailored for polyurethane rollers, providing continuous production capabilities with adjustable dimensions and hardness levels.
Characteristics: The Linden Polyurethane Casting Machine Series provides precise control over material mixing ratios, temperature, and curing time, ensuring consistent quality in polyurethane roller production. These machines are versatile, allowing for the creation of various roller sizes and hardness levels to meet specific industry needs.
Characteristics: The Delta Engineering PU Extruder DX Series is designed for continuous polyurethane extrusion, making it perfect for high-volume production of polyurethane rollers. These machines feature advanced controls for temperature and pressure, ensuring precise roller dimensions, uniform density, and an excellent surface finish. Additionally, they come with user-friendly interfaces for efficient operation and maintenance.
Please note that the availability and popularity of these specific models and their manufacturers may change over time. For the most current information on polyurethane roller production machinery, it is recommended to contact the manufacturers directly or consult with industry suppliers specializing in polyurethane roller equipment.
The selection of polyurethane rollers for industrial applications is primarily based on their durability and the availability of a wide range of durometers. Unlike the expensive and time-consuming tooling required for manufacturing rubber rollers, polyurethane casting utilizes aluminum molds that can be easily formed and shaped to the precise dimensions of the designed roller.
Despite their straightforward production process, polyurethane rollers offer exceptional durability, resistance to abrasion, and come in various sizes to accommodate all types of roller applications.
The choice of polyurethane rollers as conveyor rollers is due to their noise abatement and abrasion and solvent resistance. In packaging and shipping, conveying systems are the foundation of efficient and smooth operations. Materials have to move quickly without being damaged or mishandled. Polyurethane rollers are an important part of the effortless conveyance of parts, tools, customer orders, and equipment. Their noise suppression properties assist in keeping the work environment stress free for workers.
Idler rollers are a crucial component of a conveyor roller system, playing various roles to aid in the movement of materials along a conveyor belt. There are two main types of idler rollers: carrying rollers, which transport materials, and return rollers, which support the conveyor belt during its return phase.
On the return side, flat return idlers are used to support the return of the conveyor belt. They have a steel support rod and lifting brackets to keep the belt from stretching, deforming, and slacking.
Industrial polyurethane-coated casters are robust and durable, capable of supporting loads of up to five tons. They offer greater capacity than rubber wheels and are constructed from high-density, thick polyurethane. These casters are preferred for their ability to handle exceptionally heavy loads without damaging floors or other surfaces.
Similar to polyurethane rollers used in conveying systems, industrial polyurethane casters operate quietly and feature a larger footprint, which helps reduce stress on flooring. Their longevity is attributed to their elasticity, providing ergonomic benefits and enhancing their durability.
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