This article will take an in-depth look at urethane wheels.
The article will bring more detail on topics such as:
This chapter delves into urethane wheels, exploring their composition, structure, and the core principles of their operation.
Constructed from molded urethane, also referred to as polyurethane, urethane wheels belong to a class of elastomers known for urethane carbamate linkages, derived from the concept of "elastic polymers."
Urethane wheels skilfully amalgamate the advantages of metal, plastic, and rubber wheels. They present superior cost-efficiency, heightened flexibility, enhanced noise dampening, resilience, and stronger defenses against impacts, abrasion, and corrosion when compared to metal wheels.
When dealing with low temperatures, impact resistance, low cold flow, abrasion, and radiation resistance, urethane surpasses plastic. In comparison with plastic wheels, urethane wheels excel in noise reduction, resilience, elastic memory, and cost-related benefits. Furthermore, urethane's extensive hardness range, ease of customization, and outstanding impact resistance give it an edge over rubber. Additionally, urethane wheels can be retooled and recoated, which helps avert costly fine-tuning tasks.
Urethane wheels are produced through polyurethane molding, which involves the encapsulation of a urethane polymer system within a tool or mold, allowing it to cure, thereby fabricating or manufacturing plastic entities. Thanks to polyurethane's superior processability, it stands out as an effective material used in producing various consumer goods and industrial components just as other plastics. Polyurethane molding can achieve precise tolerances and complex shapes, including those used in urethane wheels.
Polyurethanes, being versatile materials, can be formulated to accomplish a wide spectrum of plastic attributes, showcasing different mechanical properties ranging from soft and flexible to hard and strong. Some formulations can produce high-performance engineering-grade outputs.
This part delves into the way urethane wheels are constructed.
Fabricating urethane wheels involves the integration of standardized components through two primary methodologies.
Urethane is heated into a liquid and poured into a mold resembling a wheel, where it gradually cools and solidifies. Synthetic resins may also be incorporated in this procedure, primarily used for prototyping and small-batch manufacturing.
This method involves melting urethane into a liquid state then injecting it into a wheel-shaped mold via fill holes with a low-pressure pneumatic injection gun. Injection molding systems incorporate numerous motors, heaters, and other moving parts, consuming significant energy. Research aims at enhancing this process's energy efficiency. Injection molding accounts for approximately 32% of all plastic processing applications, remaining a prevalent plastic processing approach today.
Alternative methods can be employed to craft urethane wheels from molded urethane. These can be made from solid urethane or composite materials including cast iron, aluminum, and steel. Such wheels are ideal for heavy-duty applications. In bonded-to-metal wheels, the core is metal, and the tread is made of urethane. Manufacturing urethane wheels is notably cost-effective, and their usage is FDA-approved for clean rooms and sterile environments.
Though polyurethane is a form of urethane polymer, there's no substantial difference between the two materials. Polyurethanes primarily comprise polyols and diisocyanates, complemented by curatives and additives for specialized property enhancement. For polyurethane foams, blowing agents, surfactants, and catalysts are vital for developing foam structures.
Polyurethanes include several materials with primary polyols and diisocyanates, and additional curatives and additives for specific polyurethane enhancement. Blowing agents, surfactants, and catalysts assist in generating the gases required for the foam structure formation.
Polyol is an organic molecule possessing one or more hydroxyl (OH) groups. In urethane casting, polyols fall into two categories: polyether polyols and polyester polyols.
Generated through the interaction of organic oxides with glycol, polyether polyols are noted for outstanding impact resistance, low heat buildup in dynamic scenarios, hydrolysis resistance, and low-temperature performance. In the polyurethane domain, PTMEG (polytetramethylene glycol) and PPG (polypropylene glycol) prevail, with PTMEG being a superior choice due to better performance albeit higher costs.
Formed through the polycondensation of di-acids and glycol, polyester polyols exhibit superior abrasion and oil resistance, heat aging resistance, shock absorption, solvent resistance, and tear resistance compared to polyether polyols.
Common polyester polyols include polycarbonate and polycaprolactone. Polycarbonates are valued for their strength and rigidity, while polycaprolactone boosts resistance against water, oil, solvent, and chlorine in cast urethanes.
Diisocyanate compounds, similar to polyols, are fundamental components of the polyurethane system's resin. The two major categories of diisocyanates are aliphatic and aromatic.
A defining trait of aliphatic diisocyanates is their non-yellowing nature. Their reduced reactivity makes them apt for chemical-resistant coatings. These compounds are prevalent in polyurethane coatings, castings, and films where color stability is paramount. Leading aliphatic diisocyanates include hexamethylene diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).
Aromatic diisocyanates constitute more than 90% of total diisocyanate usage. They segregate into toluene diisocyanate (TDI), naphthalene diisocyanate (NDI), and methylene diphenyl diisocyanate (MDI).
Specific features of polyurethane foams also arise. In addition to the prepolymer system's polyols and diisocyanates, blowing agents, surfactants, and optional catalysts are employed to manufacture the foam. These elements play a role in generating foaming gases and regulating them for ideal foam structure realization.
These agents introduce gas into the polymer system, forming the foam's cellular framework. Gas introduction can be chemical or physical. Originally, CFC-11 (trichlorofluoromethane) was favored for its non-combustibility, suitable boiling point, compatibility with polyurethane, and low toxicity. However, it was banned due to ozone depletion concerns under the Montreal Protocol of 1987, leading to replacements like water, pentane, methylene chloride, hydrocarbons, and other zero ozone depletion potential blends.
Surfactants, predominantly silicone-based, assist in foam formation and stabilization of polyurethane foams. They essentially reduce surface tension, prevent foam collapse pre-cross-linking, control cell size, minimize post-cure shrinkage, and counteract particle-induced solution deformations.
Catalysts control the reaction speed between isocyanate and hydroxyl groups and the gas production rate. Both these processes must synchronize for optimal foam formation. If polymerization outpaces gas creation, the cell formation collapses resulting in curing shrinkage and cooling. Conversely, rapid gas generation risks premature cell expansion before stabilization. Balanced reaction rates are crucial for forming uniformly open cells.
Used to crosslink long chain-like molecules formed in the polyol-diisocyanate reaction, curatives and chain extenders mixed with the prepolymer system produce solid or semi-solid elastomers, featured in most thermosetting polyurethane formulations. The predominant variants include hydroxyls and amines.
These curatives comprise hydroxyl group terminal molecules, facilitating prepolymer linkage. A regularly used hydroxyl curative at ambient temperatures is 1,4-butanediol (BDO), often utilized in MDI prepolymer systems.
Apart from hydroxyl groups, amine groups can attach to prepolymer terminals. For TDI prepolymer systems, 4,4-methylenebis(2-chloroaniline) or MOCA is used but is considered carcinogenic by OSHA. Thus, alternatives like 4,4-methylenebis(3-chloro-2,6-diethylaniline) are increasingly adopted.
Additives elevate polyurethane product characteristics. Type and amount depend on polymer formulation and the intended application. Common polyurethane additives include fillers, plasticizers, stabilizers, antistatic agents, degassing aids, flame retardants, pigments, and colorants.
Preferred over harder materials such as steel or cast iron in industrial use, urethane wheels offer quieter operations. They serve as shock absorbers and cushion against uneven landscapes, decreasing noise levels to help adhere to OSHA guidelines, safeguarding employee hearing.
In contrast to rubber, urethane tires, known for their load-bearing prowess, deliver enhanced strength while retaining rubber's shock absorption and quiet operation alongside floor protection.
The larger surface area of urethane wheels versus tougher materials like nylon aids in spreading shear forces, preserving floor surfaces for longer. Furthermore, urethane wheels increase traction, lowering wheel load and transferring driving force more effectively.
Considering these specs, urethane wheels are set to deliver a satisfactory experience in industrial settings.
Correctly used, polyurethane displays impressive durability. Yet, its endurance can wane in high-heat environments or applications creating heat. Conventional urethane fails to endure over 110 degrees Celsius longer than 60-90 minutes without harm. Internal heat from cyclic urethane deflection at about 121 degrees Celsius can render it liquid within 15 minutes.
Industrial-grade polyurethane needs to outperform urethanes used in non-dynamic contexts. Optimal selection requires considering properties like tensile strength, tear strength, modulus, and abrasion resistivity.
The hot casting method is exclusive for creating industrial wheels. Hot-cast urethanes, poured at 60 to 76 degrees Celsius and cured at 87 to 114 degrees Celsius, yield robust wheels for challenging dynamic conditions. Room temperature-produced urethanes lack the physical attributes needed for industrial wheel usage.
Here's what to remember when picking urethane wheels:
A wheel's small contact area with the rolling surface makes weight distribution critical. Overloading risks deformation and thus heightened friction, resistance, and eventual failure. Understanding maximum supportable loads ensures proper wheel selection.
Even with urethane's adaptability to rough surfaces, surface type influences wheel performance. Smooth concrete versus rough terrain might entail alternative materials or diameters. Encountering chemicals, while urethane performs well in such environments, is another crucial factor.
Extreme braking and acceleration can impact wheel specs. Ensuring consistent traction while maintaining contact with rolling surfaces is critical. Although urethane wheels generally offer great traction, dust, grease, or oil can threaten it. Tackling these during planning is beneficial. Maintaining clean surfaces and tracks extends wheel efficiency and longevity.
Like rubber, urethane wheels respond to environmental temperature changes by expanding and contracting. Comprehending temperature ranges is essential for short-term exposure operations, like entering/exiting a freezer or mining scenarios. Specialized formulas exist for extreme conditions to boost wheel durability and lifespan.
Extremes beyond normal may cause irreparable harm. High heat can degrade a urethane wheel permanently, while very low temperatures risk brittleness, causing irreversible damage.
Shifting wheels between settings introduces environmental variables like temperature, humidity, and surface variations. Transition points, like seams, might harm wheels. Despite urethane wheels' robustness, reducing environmental variability maintains their integrity, preventing delamination. A smoother area with minimal surface transitions boosts their lifespan.
Unexpected conditions often lead to traction loss or deformation, risking build-up on wheels, casters, or tracks. Such accumulation can lead to premature failures. Regular inspection and maintaining ventilation directing airflow from tracks is vital, along with consistent track cleaning.
In challenging environments, wheels encounter bumps, sudden loads, or drops. While urethane is designed to withstand impacts, wear still affects axles, wheels, or bearings. Understanding impact dynamics beyond load handling capacities is vital. A redesign utilizing materials capable of higher damage resistance may prove necessary in such cases.
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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