This article will take an in-depth look at urethane wheels.
The article will bring more detail on topics such as:
This chapter will cover the nature of urethane wheels, their construction, and their operational principles.
Urethane wheels are constructed from molded urethane, commonly known as polyurethane. Urethane is an elastomer characterized by urethane carbamate linkages and is derived from the term "elastic polymer."
Urethane wheels combine the benefits of metal, plastic, and rubber wheels. They offer greater cost-effectiveness, enhanced flexibility, superior noise reduction, higher resilience, and improved resistance to impact, abrasion, and corrosion compared to metal wheels.
In terms of low temperatures, impact resistance, cold flow, abrasion resistance, and radiation resistance, urethane outperforms plastic. Urethane wheels also excel in noise reduction, resilience, elastic memory, and cost-effectiveness compared to plastic. Additionally, urethane surpasses rubber due to its wider range of hardness options, ease of customization, and superior impact resistance. Furthermore, polyurethane wheels can be retooled and recoated, which helps minimize the need for expensive fine-tuning.
Urethane wheels come from polyurethane molding is the process of placing a urethane polymer system into a tool or mold and allowing it to cure in order to fabricate or manufacture plastic items. Polyurethane's exceptional processability makes it a particularly effective material in the manufacture of typical consumer goods and industrial parts, just like any other type of plastic. Polyurethane molding can readily attain tight tolerances and complex shapes, which include urethane wheels.
Polyurethanes are highly versatile materials that can be formulated in numerous ways to achieve a broad range of plastic characteristics. They can exhibit various mechanical properties, from soft and pliable to hard and rigid. Additionally, certain formulations of polyurethanes can be engineered to produce high-performance, engineering-grade products.
This section will explore the construction of urethane wheels.
In the fabrication process, urethane wheels are made by combining standardized components through two distinct procedures.
Urethane is melted into a liquid and poured into a wheel-shaped mold, where it cools and hardens. This process can also involve synthetic resins. The liquid casting method is typically employed for prototyping and small-scale manufacturing.
It entails melting the urethane to a liquid state and injecting the liquid material into a wheel-shaped mold through fill holes with a low-pressure pneumatic injection gun. Injection molding machines are made up of a complex network of motors, heaters, and other moving parts that consume a lot of energy to run. However, research has been done to improve the energy efficiency of this process. Regardless, injection molding takes for around 32 percent of all plastic processing applications and is one of the most prominent plastic processing techniques today.
Secondary methods can also be used to make urethane wheels from molded urethane. Urethane wheels can be produced from solid urethane or a mixture of urethane and metals including cast iron, aluminum, and steel. For heavier-duty applications, these wheels are ideal. The core of a bonded-to-metal wheel is constructed of metal, while the tread is made of urethane. Urethane wheels are extremely cost-effective to manufacture, and the FDA has allowed their usage in clean rooms and other sterile situations.
Although polyurethane is a polymer variant of urethane, the two materials are essentially the same. Polyurethanes consist of several key components: polyols and diisocyanates are the primary constituents. Additionally, curatives and additives are included to impart unique properties to the polyurethane composition. For polyurethane foams specifically, blowing agents, surfactants, and catalysts are used to generate the gases needed to create the foam's structure.
Polyurethanes are composed of several materials, with polyols and diisocyanates being the primary components. Additional curatives and additives contribute specific properties to the polyurethane composition. For polyurethane foams, there are also blowing agents, surfactants, and catalysts that facilitate the generation of gases essential for forming the foam's structure.
A polyol is an organic molecule that contains one or more hydroxyl (OH) groups. In urethane casting, polyols are categorized into two types: polyether polyols and polyester polyols.
These polyols are produced through the reaction of organic oxides with glycol. Polyether polyols are known for their excellent impact resistance, low heat buildup in dynamic applications, hydrolysis resistance, and performance at low temperatures. In the polyurethane industry, PTMEG (polytetramethylene glycol) and PPG (polypropylene glycol) are commonly used types of polyether polyols. PTMEG is generally considered superior due to its better performance characteristics, though it is also more expensive.
These polyols are produced through the polycondensation reaction of di-acids and glycol. Polyester polyols offer superior abrasion resistance, oil resistance, heat aging resistance, shock absorption qualities, solvent resistance, and tear resistance compared to polyether polyols.
The most common polyester polyols are polycarbonate and polycaprolactone. Polycarbonates are used as engineering materials due to their strength and hardness, while polycaprolactone enhances the water, oil, solvent, and chlorine resistance of cast urethane.
Diisocyanate compounds, like polyols, are essential components of the resin side of the polyurethane system. There are two primary types of diisocyanates: aliphatic and aromatic.
The most notable feature of aliphatic diisocyanates is their non-yellowing appearance. They also have lower reactivity, making them ideal for chemical-resistant coatings. Aliphatic diisocyanates are commonly used in polyurethane coatings, castings, and films where color stability is essential. The most frequently used aliphatic diisocyanates include hexamethylene diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).
Aromatic diisocyanates account for over 90% of total diisocyanate consumption. They are primarily categorized into three types: toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), and methylene diphenyl diisocyanate (MDI).
These are features that are specific to polyurethane foams. Aside from the prepolymer system of polyols and diisocyanates, blowing agents, surfactants, and, in some blends, catalysts are required to manufacture the product. These additional raw components produce foaming gasses and manage them in order to get the desired foam structure.
Blowing agents are used to introduce gas into the polymer system, creating the foam's cellular structure. Gas can be introduced chemically or physically. The first blowing agent used was CFC-11, or trichlorofluoromethane, which was considered ideal due to its non-combustibility, suitable boiling point, good compatibility with polyurethane, and low toxicity. However, due to its ozone-depleting properties, CFC-11 and other hydrochlorofluorocarbons were banned by the Montreal Protocol in 1987. Today, alternatives such as water, pentane, methylene chloride, hydrocarbons, halogen-free azeotropes, and other zero ozone depletion-potential blends have replaced CFCs.
Surfactants are additives that facilitate the formation, stabilization, and setting of polyurethane foams. Silicone-based surfactants are the most commonly used, as they play essential roles such as reducing surface tension, preventing foam collapse until cross-linking is complete, controlling cell size, minimizing cell shrinkage after curing, and compensating for deformities caused by the introduction of particles into the solution.
Catalysts are used to regulate both the reaction rate between isocyanate and hydroxyl groups and the rate of gas generation. These processes need to occur simultaneously for optimal foam formation. If polymerization occurs faster than gas generation, the cells can remain close together, leading to foam shrinkage during curing and cooling. Conversely, if gas generation happens too quickly, the cells may expand before the polymer can set and stabilize them. To achieve uniform, open cells, it is crucial to balance the rates of these two reactions.
Curatives and chain extenders are used to crosslink the long, chain-like molecules formed during the polyol-diisocyanate reaction. They are mixed with the prepolymer system of polyol and diisocyanate to produce a solid or semi-solid elastomer. These components are present in most thermosetting polyurethane formulations. The two most common types of curatives and chain extenders are hydroxyls and amines.
These curatives contain hydroxyl groups at the molecule terminals, which facilitate the linking of prepolymers. A commonly used hydroxyl curative at room temperature is 1,4-butanediol (BDO), which is frequently employed in MDI prepolymer systems.
In addition to hydroxyl groups, amine groups can also link to the prepolymer terminals. For TDI prepolymer systems, 4,4-methylenebis(2-chloroaniline) or MOCA is a commonly used amine curative. However, MOCA is classified as a carcinogen by OSHA. Consequently, other amine chain extenders, such as 4,4-methylenebis(3-chloro-2,6-diethylaniline), are now employed as alternatives.
Additives are used to impart additional properties to polyurethane products. The type and quantity of additive selected depend on the polymer system's formulation and the intended application. Common polyurethane additives include fillers, plasticizers, stabilizers, antistatic agents, degassing aids, flame retardants, pigments, and colorants.
Urethane wheels are often preferred over harder materials like steel or cast iron in industrial applications due to their quieter operation. Urethane acts as a shock absorber and cushioning agent, effectively absorbing bumps from uneven terrain. By reducing noise levels significantly, urethane wheels help comply with OSHA regulations and protect employees' hearing.
Compared to rubber, urethane tires are often chosen for their superior load-bearing capabilities. Urethane provides higher load-bearing strength while still delivering the benefits of rubber, including shock absorption, noise reduction, and floor protection.
Urethane wheels, with their larger surface area compared to tougher materials like nylon, effectively distribute shear forces, which helps preserve floor surfaces and prolong their lifespan. Additionally, urethane wheels enhance traction and grip, reducing the load on the wheel and delivering the necessary driving force more efficiently.
If these specifications are taken into account, it is likely that urethane wheels will provide a positive experience in industrial applications.
When used correctly, polyurethane is an exceptionally durable material. However, its durability significantly decreases in high-temperature environments or applications that generate heat. Most standard urethane cannot withstand temperatures above 110 degrees Celsius for more than 60 to 90 minutes without damage. Additionally, internally generated heat from cyclic urethane deflection at around 121 degrees Celsius can cause the material to liquefy within 15 minutes.
Polyurethane used in industrial applications must possess properties that surpass those of urethanes used in non-dynamic applications. To select the best urethane for specific needs, it is essential to consider factors such as tensile strength, tear strength, modulus, and abrasion resistance.
The only method suitable for producing industrial wheels is hot casting. Hot-cast urethanes, which are poured at temperatures between 60 and 76 degrees Celsius and cured at 87 to 114 degrees Celsius, yield stronger wheels that can withstand demanding dynamic applications. Urethanes produced and cured at room temperature typically lack the physical properties needed for industrial wheel applications.
Factors to consider when selecting urethane wheels include:
Each wheel has a small contact point with the surface it rolls on, making weight distribution essential. An overloaded wheel can deform over time, leading to increased friction, resistance, and eventual failure. To select the right wheel, it is important to understand and account for the maximum load it will need to support.
Urethane wheels, while durable and adaptable to rough surfaces, are still affected by the type of surface they traverse. Depending on whether the wheel is used on smooth concrete or rough terrain, a different material or diameter might be more suitable. Additionally, wheels may encounter chemicals, and although urethane performs exceptionally well in such environments, it remains an important consideration.
Braking and acceleration requirements can affect wheel specifications, particularly if they are extreme or precise. It is crucial to ensure that traction remains consistent and predictable while maintaining stable contact with the rolling surface. Urethane wheels generally offer excellent traction, but this can be compromised in conditions where dust, grease, or oils accumulate. Addressing these environmental factors during the planning stage is important. Implementing a regular cleaning strategy for surfaces and tracks helps to extend the lifespan and efficiency of the wheels.
Urethane wheels, similar to rubber, will expand and contract in response to environmental conditions. Understanding these temperature ranges is important for applications involving short-term exposure to extreme temperatures, such as transitioning in and out of a deep freezer or operating in mining environments. For extreme conditions, specialized formulas are available to enhance wheel durability and extend their lifespan.
Extreme temperatures beyond the normal range often cause irreversible damage. High heat can permanently degrade a urethane wheel, while exposure to temperatures outside the low-temperature spectrum may lead to brittleness and result in irreversible damage.
When transitioning wheels from indoor to outdoor environments, several environmental variables come into play, including temperature, humidity, and the physical characteristics of different surfaces. Transition points, such as saddles or seams, can wear down or damage the wheels. While urethane wheels are robust and resilient, minimizing drastic environmental changes is crucial to maintaining their integrity and preventing delamination. A smoother work area with fewer surface transitions can help extend the lifespan of the wheels.
Unexpected environmental conditions often lead to traction loss or wheel deformation, which can result in buildup on the wheel, caster, or track. Such accumulation can cause premature wheel failure. To prevent these issues, it is essential to regularly inspect and maintain the ventilation system, ensuring that airflow is directed away from the tracks, and to perform routine cleaning of the tracks.
In demanding environments, wheels may experience bumps, sudden loads, or drops. While urethane is formulated to be rigid enough to handle impact, these conditions can still cause wear on the axle, wheel, or load bearings. Impact is assessed differently from load, and even if a wheel is well-designed for its load capacity, it may not be sufficient for handling impact, drops, or shocks. In such cases, a new material design that offers greater resistance to damage might be necessary.
What are the key machines used for producing urethane wheels in the United States and Canada? These machines play a crucial role in modern manufacturing, enabling the production of high-quality, durable, and customizable wheels for various industries, thereby contributing to innovation and technological advancement. We will explore several of these leading machines below.
Features: Wabash MPI Compression Molding Presses are renowned for their precision and consistency in molding urethane wheels. They employ compression molding techniques to produce durable and high-quality products.
Features:These injection molding machines are noted for their efficiency and automation in producing urethane wheels. They enable high production rates and precise control over wheel dimensions.
Features: These machines are favored for manufacturing urethane wheels with diverse profiles due to their ability to handle various sizes and provide flexibility in the production process.
Features: Haas VF Series Vertical Machining Centers are used for precision machining of urethane wheel molds, allowing for the creation of intricate designs and achieving smooth surfaces.
Features: Baulé machines are utilized for small to medium-scale production of urethane wheels, thanks to their excellent repeatability and efficiency.
It's important to recognize that the popularity and technological advancements in the manufacturing industry can change rapidly. For the most current and accurate information on leading machines used for urethane wheel production in the United States and Canada, it is advisable to consult industry-specific sources, manufacturers, or equipment suppliers directly.
What types of urethane wheels are available?
Crowned poly wheels offer significantly reduced rolling resistance compared to standard flat-treaded wheels. They typically range from 100 to 200 mm in diameter and feature a silent-running urethane tire encasing a lightweight aluminum center.
They are also resistant to solvents and abrasive wear, featuring precision ball bearings for extended bearing life. With a load capacity of up to 600 kg, they are commonly used in conveyor systems.
These wheels feature engraved patterns, such as brand names, identification marks, or serial numbers. They have higher rolling resistance compared to crowned wheels, as they are standard flat-treaded wheels. Available in various sizes, they typically have a lower load capacity.
These wheels are commonly found in document processing equipment, where they help orient documents for improved optical reading. Desk wheels are often used in light roller applications and can be designed as soft-touch wheels with varying spring rates, achieved through different urethane harnesses.
Urethane drive wheels are particularly common due to their adaptability to any required hardness for specific applications. These wheels typically use a key slot or bolt to attach to a hub. They are widely employed in various industries for efficiently moving large items and are especially effective when directional changes are needed.
Compliant wheels enhance the abrasion resistance of industrial machinery and are used in applications that handle documents or materials of varying thicknesses. Their spring-like motion allows the equipment to process papers of different thicknesses without the need for expensive spring mechanisms.
Compliant wheels are also referred to as no-crush wheels, zero-crush wheels, and compliance wheels.
The benefits of urethane compliant wheels include:
This chapter will explore the applications and benefits of urethane wheels.
Urethane wheels are used in a variety of applications, including:
Overhead conveyors, like many other objects, frequently employ wheels to move items. These wheels are used to transfer products down the rails of overhead conveyors and in conjunction with various carrying devices. These rails frequently contain joints in their construction, which, like expansion joints in a floor, can cause chunking and tearing. Urethane wheels can withstand a wide range of load requirements while also resisting wear, chunking, and tearing. They are designed to be exactly round and smooth, eliminating wear and wobbling.
Carts come in various sizes and strengths to accommodate different needs. Urethane wheels are commonly used on equipment carts that handle parts and components on automotive assembly lines. These carts and wheels are designed with high load capacities to support the heavy products they transport.
Urethane wheels are also well-suited for railroad applications. For instance, Stellana's urethane wheels are employed in tugger systems to move boxcars along train tracks. This material allows the wheels to operate directly on the rails while delivering reliable grip on a minimal surface area.
Several components work in tandem to dry clothing inside large industrial dryers. Urethane wheels are used in the drum's idler wheels, allowing them to rotate smoothly. As the load dries, these wheels help tumble the clothing for even drying.
In the metal construction sector, this equipment shapes metal sheets into rain gutters, siding, metal roofing, and other products. Urethane wheels serve two key functions on the equipment: the drive wheel pulls the aluminum sheets through, while the idler wheels assist in creating the required angles and bends.
Elevator contractors often choose urethane for their elevator guide wheels. These guide wheels are crucial components, working in conjunction with guide rails installed along the elevator shaft to ensure smooth movement of the elevator car. In regular operation, the guide wheels help the car travel smoothly up and down the rails. Additionally, the system includes backup safety mechanisms to quickly stop the car if the cable snaps, ensuring the car is securely halted on the rail.
Hyperloop, the high-speed transport system being developed by Tesla and SpaceX, relies on a vacuum to operate efficiently. In the event of a pressure loss that disrupts the vacuum, urethane wheels play a critical safety role by stabilizing the vehicle and gradually slowing it down from high speeds. Although the vehicle is designed to float above the ground, these urethane wheels are essential for ensuring a safe and controlled stop, highlighting the remarkable capabilities of polyurethane in demanding applications.
Urethane wheels find diverse applications across various industries. They are used in carrying cases, conveyor bearings, grocery carts, skateboard wheels, forklift drives, roller coaster wheels, and load wheels. Industries such as medical, athletic equipment, retail, transportation, industrial manufacturing, and material handling all benefit from the durability and performance of urethane wheels.
Molded urethane offers several advantages, including exceptional durability due to its resistance to cuts and rips. It also provides heat resistance, chemical resistance, noise reduction, and elastic memory. Urethane wheels can vary in hardness, ranging from sponge-soft to iron-hard, and can be customized to various hardness levels in between. Additionally, they can be manufactured in a range of colors, sizes, and shapes to meet specific needs.
Urethane wheels are resistant to ultraviolet radiation, ozone, oxygen, and various environmental conditions. They also withstand abrasive substances better than other materials. Under similar conditions, urethane experiences slower wear, extending its lifespan. Additionally, due to its higher tensile strength, urethane can support heavier loads effectively.
Urethane's chemical manufacturing process allows for a wide range of variants, enabling adjustments to its density and physical properties based on specific applications. Urethane wheels can support 6 to 7 times the load capacity of rubber caster wheels of the same size. Additionally, urethane's high elastic memory and flexibility make it suitable for various applications where traditional plastics might not perform as well.
Urethane manufacturing supports automatic and continuous production with minimal waste. Notably, some of the waste residues can be recycled into new urethane products, reducing environmental impact. Liquid casting, a straightforward process used in the production of no-cord casting wheels—often referred to as the "green wheels" of the 21st century—demonstrates urethane's efficiency. With its growing range of applications in the automotive sector, urethane wheels are poised to be a key trend in the future of automotive tires.
Failures of urethane wheels on drive wheels, industrial rollers, and industrial caster wheels can lead to significant costs for companies, including the expense of replacing the wheels and downtime for equipment. Many of these failures are preventable and can be attributed to:
In wheel or roller applications, polyurethane is often chemically bonded to a plastic or metal substrate. Delamination occurs when the tread separates from the wheel or hub, which can be caused by several factors. Poor application of adhesive before attaching the polyurethane to the hub, overheating the wheel, or exposing it to water and/or solvents at the bonding line can contribute to this issue. Additionally, some hub materials are challenging to bond. If adhesive was correctly applied, external conditions did not interfere, and delamination still occurs, considering a mechanical bond might be a better solution.
When a wheel is stationary under load, a flat spot can develop on the polyurethane tread. When the wheel starts spinning again, this flat area may or may not "roll out," making it more difficult to move the wheel from a standstill. The compression set value of the polyurethane material influences its tendency to develop flat spots. To address this issue, you can use polyurethane with a lower compression set value. Alternatively, opting for a larger diameter or wider wheel can reduce the stress on the urethane and help mitigate flat-spotting.
When urethane treads experience cyclic loading and unloading, friction within the material generates heat due to mechanical hysteresis. If the heat buildup exceeds the material's ability to dissipate it, the urethane can melt internally, leading to pressure buildup and potentially a blow-out. This problem is often caused by operating the wheel or roller at excessive speeds, overloading, or uneven loads. To address this issue, consider using urethanes with lower heat generation properties, increasing the diameter or width of the wheel, or adjusting other operational parameters to better manage heat and load conditions.
If a wheel is subjected to excessive loading in a dynamic position, the polyurethane tread may develop cracks. To mitigate this issue, you can replace the tire material with one better suited for the application. Alternatively, redistributing the weight by increasing the wheel's width or expanding its diameter can help reduce stress on the tread and minimize cracking.
Despite some drawbacks, the benefits of urethane wheels far outweigh their limitations.
Urethane wheels are made of molded urethane. They come from polyurethane molding which is the process of placing a urethane polymer system into a mold and allowing it to cure in order to fabricate or manufacture plastic items. Polyurethane's exceptional processability makes it a particularly effective material in the manufacture of wheels. Polyurethane molding can readily attain tight tolerances and complex shapes, which include urethane wheels.
Types of urethane wheels include crowned, drive, engraved, compliant, and desk. All benefits of metal, plastic, and rubber wheels are found in urethane wheels. They are more affordable, more flexible, have better noise reduction, are more resilient, and are more impact resistant, abrasion, and corrosion than metal. In terms of low temperatures, impact, cold flow, abrasion, and radiation resistance, urethane outperforms plastic. They can also reduce noise, are more resilient, have superior elastic memory, and are less expensive than plastic. However like any other material they have their disadvantages as discussed above.
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