This article will take an in-depth look at caster wheels.
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This chapter will cover the following topics: an overview of caster wheels, their manufacturing process, and their operational functionality.
A caster is a non-powered wheel mounted on the bottom of larger objects to facilitate movement. Caster wheels are commonly found in shopping carts, office chairs, medical beds, and material handling equipment.
Caster wheels come in a variety of types to suit different applications, providing essential mobility features like strength, corrosion resistance, water resistance, and weather resistance. Selecting the appropriate caster wheel depends on the terrain and the weight it needs to support. For heavy items, sturdier wheels are required, and larger objects may need multiple casters to distribute the weight evenly.
This section will explore the manufacturing processes involved in producing caster wheels.
The first step in the manufacturing process is cutting the top plate, which is used to mount the caster underneath an object, such as an industrial cart. This begins with a thick sheet of steel that is cut using a CNC machine, which combines oxygen and electricity to produce plasma. Plasma cutting is a thermal process that utilizes ionized gas to melt the metal, rather than mechanically cutting it. This method is widely used for both thick metal plates and sheet metal due to its accuracy and speed.
The next part to be cut is the fork. Forks are the arms that hold each side of the wheel axle. The forks are made out of steel coil, a more flexible and thinner type of steel. The steel coil is rolled out and fed into a punch press machine which breaks it with the yoke shaped dye. The broken yoke shaped pieces are placed onto a forming press. The press bends the piece into the required shape and it also makes a circular groove around the hole in the middle. The hole is filled with steel ball bearings that allow the yoke to swivel. A steel retainer is fitted to hold the ball bearings in place. The grooves of the steel cap are filled with ball bearings as well then they place it onto a punch press and position the yoke on top. The press joins the cap to the yoke’s retainer, sandwiching the ball bearings in between. After riveting the top plate to the yoke, put a steel seal over the retainer and lock it in place with a pneumatic press.
The next machining process on the production of caster wheels is the extrusion of the wheel material. To make the wheels, nylon inserts are required. The inserts are placed in an injection molding press, which melt neoprene rubber and injects it into the mold. Once it cools to a solid state, the machine ejects rubber edged wheels. The rubber edge absorbs shock, reduces noise, and prevents damage to the floor or surface.
For larger wheels, a different molding press is employed to accommodate the required size, though the molding process remains the same. These larger presses typically produce one wheel at a time. After molding, the wheel is placed on a cooling rack for approximately two and a half hours. The mold consists of two parts that form a single piece when assembled. Once removed from the mold, the rubber is ground down to ensure a smooth surface.
A two-part bearing is installed inside the wheel and secured with a pneumatic press. Steel guides are then placed on either side of the wheel to prevent foreign objects from entering and to stabilize the wheel. These guides position the wheel between the yokes and facilitate the insertion of the steel axle. One end of the axle is secured with a bolt head, while a nut is fastened to the other end. Finally, grease is injected to lubricate the ball bearings.
The wheel undergoes a series of quality control tests to determine how many revolutions it can withstand before failing.
When choosing caster wheels, several key factors should be considered:
Fixed casters are often sufficient for equipment that only needs to move in a straight line, such as large machinery that is repositioned for cleaning and then returned to its original spot. However, if increased maneuverability is required, swivel casters may be a better option. Additionally, consider whether swivel locks are necessary for equipment that will predominantly travel in a straight path. While casters enable movement, it is also important to assess the degree of freedom required for that movement.
Although it might seem like a minor detail, the type of mounting can significantly affect the choice of caster. Many applications require stem-mounted casters, but this type may limit the caster's weight capacity. Heavy-duty applications often use plate-mounted casters to distribute the load more effectively across a larger area. Understanding the mounting requirements can help narrow down the options when selecting casters from a broad range of choices.
What type of machinery will the casters be mounted on? While this may seem like a straightforward question, it's crucial for determining the appropriate caster type. This assessment helps decide whether light-duty, medium-duty, or heavy-duty casters are needed based on the weight they will support. Additionally, consider the operating environment: will noise reduction be a significant factor?
Caster wheels vary widely based on their applications, including medical, industrial, and furniture uses, among others.
Soft treaded caster wheels are ideal for offering a comfortable ride while also safeguarding delicate floor surfaces. They are chemical, oil, and acid resistant because they are composed of thermoplastic and mold-on rubber. While a soft tread allows wheels to roll over small debris and is usually quieter than other materials, it also makes it more difficult to roll and reduces the caster's overall load capacity. Thermoplastic rubber, rubber tread on iron core, and polyurethane tread on plastic core are all common soft tread caster wheels.
Soft tread wheels are commonly used in medical and pharmaceutical equipment, as well as in food service equipment and processing plants, where they handle light to medium loads.
Ferrous wheels offer superior load capacity, impact resistance, temperature tolerance, and rollability compared to other caster wheels, thanks to their solid construction. Made from forged steel or cast iron, ferrous wheels are ideal for demanding environments like warehouses and manufacturing plants, where floor protection is not a primary concern.
The wheel is a key component of a caster, making it essential to choose the right wheel for the specific location and application. Factors to consider include impact resistance, chemical resistance, rollability, and load capacity, all of which play a critical role in ensuring optimal performance.
Soft tread wheels, while harder to roll compared to polyurethane tread wheels, offer excellent floor protection. Made from solid urethane, these wheels can be chemically or mechanically bonded to plastic, cast iron, or aluminum cores. They have a capacity of up to 3,000 pounds and provide strong impact resistance.
One downside of poly wheels is that if the wheel is overloaded or the tread sustains other damage that undermines its construction, the tread can separate from the core. However, solid urethane wheels are one approach to prevent these issues. The concern of tread separation and core corrosion is minimized because the entire wheel is made of molded urethane with no core.
Synthetic wheels with a harder tread feature lower rolling resistance and higher impact strength and reliability. These include wheels made from solid elastomer, polypropylene or polyolefin, fiberglass-reinforced polypropylene, phenolic, and solid nylon. While synthetic wheels are ideal for high-impact and harsh conditions, they tend to be noisier and less forgiving when encountering debris compared to softer materials.
Phenolic wheels, constructed from phenolic resin and macerated canvas, are a popular choice for push-pull applications. They are strong and resistant to grease and chemicals, facilitating smoother mobility. However, some synthetic tread materials are not suitable for wet environments, so it is crucial to consider the intended use location when selecting a synthetic tread material.
Gray iron is used to manufacture cast iron wheels, which are known for their abrasion resistance and ease of rolling. These wheels are exceptionally durable, designed for high-capacity applications, and can withstand significant heat. They are suitable for use on concrete and smooth steel surfaces. Typical specifications for these caster wheels include a hardness of 90-95A and a Brinell hardness of 145. They are equipped with various types of bearings, such as roller bearings, precision ball bearings, and Delrin bearings. Cast iron wheels are capable of operating under conditions involving mild chemicals, oily and greasy environments, metal chips on the surface, high temperatures (up to +250°F), and extreme cold (down to -45°F).
Flanged wheels are designed to run on steel tracks, which reduces guiding and rolling effort. This design helps to minimize the load on floors, allowing for higher capacities, smoother rolling, and better floor protection. Typically, these wheels are made from cast iron or steel for enhanced strength and durability.
Flanged wheels have a hardness of 130–150 Brinell. They may use bearings such as plain bore, straight roller, or precision tapered roller. With proper bearings and lubrication, these wheels can operate at temperatures up to 800°F. They are suitable for conditions involving mild chemicals, oily and greasy areas, and metal chips on the surface.
Solid wheels are used when loads are too heavy for floor-protecting wheels or when floor protection is not a concern. These wheels are virtually unbreakable under normal use, can withstand high temperatures, and absorb shock and impact without failure. Forged steel wheels, in particular, offer superior load capacity, impact strength, and rollability compared to ductile steel wheels.
Forged steel caster wheels are suitable for use on concrete and smooth steel surfaces. They have a Rockwell hardness of 80B. Bearings that can be used with these wheels include plain, tapered, Teflon, and roller bearings. They perform well in conditions involving mild chemicals, oily and greasy areas, and metal chips on the surface.
Glass-filled nylon wheels are engineered to endure extreme temperatures and harsh conditions. Made from a combination of nylon and glass, these wheels are tough, non-marking, and resistant to hard impacts, oils, greases, and cleaning agents. They have a hardness rating of 65D and use either plain, roller, or spanner bearings.
These wheels can operate within a temperature range of up to 490°F continuously or 550°F intermittently. They are suitable for various floor types including carpet, brick, concrete, linoleum, asphalt, terrazzo, wood, smooth steel, and tiled floors. Glass-filled nylon wheels can handle environments with conditions such as water, steam, mild chemicals, oily and greasy surfaces, metal chips, high heat (+250°F), extreme cold (+45°F), and even animal fats on the ground.
Molded in a single piece, hard rubber wheels are commonly black or gray. They offer a higher load capacity compared to soft rubber wheels and do not flatten under heavy loads. Hard rubber wheels provide good rolling ability, are easy to start, and are durable. They are resistant to most chemicals, oils, greases, solvents, and cleaning agents, though they are not non-marking. These wheels typically have a hardness rating of 70-80 D.
Bearings used in hard rubber caster wheels include plain, ball, and Delrin bearings. These wheels can operate intermittently within temperatures ranging from -40°F to 180°F. They are suitable for use on various floor types, including carpet, brick, concrete, linoleum, asphalt, terrazzo, wood, smooth steel, ribbed steel, and tiled surfaces. Hard rubber caster wheels are effective in conditions such as water on the surface, steamy environments, mild chemicals, metal chips on the floor, and extreme cold (down to +45°F). They also contribute to noise reduction and floor protection.
Pneumatic wheels, which are rubber wheels filled with air, offer excellent floor protection and the ability to roll over various obstacles. These wheels provide cushioning and stress absorption, making them ideal for transporting sensitive loads across different floor surfaces. Pneumatic caster wheels are particularly well-suited for aerospace applications and other settings where impact resistance and smooth movement are crucial.
These wheels are lightweight and cost-effective, featuring a strong tread that can withstand harsh impacts. They offer floor protection, are non-marking and non-conductive, and have superior abrasion resistance compared to hard rubber wheels. Resistant to water, oils, grease, solvents, and many chemicals, these wheels are ideal for use in bakeries, dairies, food processing facilities, meat processing, laundries, supermarkets, warehouses, and manufacturing environments.
Featuring an extra-thick, precisely molded gray rubber tread bonded to a robust aluminum core, these wheels offer exceptional durability and smooth movement. They provide a quiet, cushioned ride even on rough surfaces and deliver outstanding floor protection. Additionally, they are non-marking and non-conductive, ensuring superior safety and performance.
Gray iron castings are used to make these wheels. The load is directed to each face of the inverted angle iron track by the 90° grooves drilled into the face of the wheels. V-Groove wheels can also be used to manage the flow of a load over vast distances in a variety of procedures. For big loads, these wheels are perfect. The "V" groove's design ensures optimal weight distribution per wheel.
Brakes are a common feature for heavy-duty industrial casters, providing a way to stop and secure carts in place. This functionality is particularly useful for preventing runaway carts and enhancing safety. There are several types of caster brakes, each offering unique characteristics. This article will explore some of the most commonly used heavy-duty caster brake designs.
Polyurethane cam brakes use a cam mechanism to lock the wheel in place by pressing a plate against the wheel’s running surface. The cam, made of polyurethane, provides excellent holding force and can be adjusted based on how much the cam is turned into the wheel. This type of brake can be operated via handles or levers integrated into the cam, and can also be actuated with the foot, reducing strain on the operator. Polyurethane cam brakes can be installed on either the leading or trailing edge of a caster.
Face contact brakes operate by pressing a plate against the wheel’s running surface using a threaded rod that is adjusted manually with a handle. This design provides a strong holding force, making it suitable for heavy-duty applications. Face contact brakes can be installed on either the leading or trailing edge of a caster. However, they require the operator to bend over and manually tighten or loosen the brake, which can be physically demanding and time-consuming compared to foot-actuated brakes.
Side brakes work by pressing a washer into the wheel’s hub when a foot pedal on the side of the caster is pressed. Locking and unlocking these brakes is simple and can be done with the operator's foot. They also take up very little space because they are attached to the caster’s side and fit within the caster wheel's swivel radius. The disadvantage of these brakes is that they don't have a lot of holding power and so are better suited for light-duty situations. These are only a few of the most common brake designs for industrial casters with brakes. The caster application's operation and safety can be improved by selecting the right brake design.
This chapter will explore the various applications and benefits of caster wheels, along with guidelines for their maintenance.
In residential settings, lightweight casters are often employed to facilitate the movement and support of furniture and household appliances. Items like bookshelves and computer desks can be enhanced with stylish casters. Conversely, heavy-duty casters are predominantly used in industrial environments, such as factories and warehouses, to manage large and heavy objects that need to be moved.
In aerospace and aviation, heavy-duty caster wheels are essential for handling substantial workpieces, machinery, and equipment. These casters play a crucial role in aircraft engine stands, allowing for easy repositioning and secure locking. Similarly, high-speed bearings are incorporated into heavy-duty casters used on aircraft tow bars.
Heavy-duty casters are also utilized in aviation hangar doors, where they must support the substantial weight of these large doors. While rigid casters are an option, the ability to move these doors with ease, whether manually or via an automatic mechanism, is crucial. Additionally, heavy-duty casters are applied to helicopter landing pads and trolleys to facilitate the movement of helicopters post-landing.
Landing trolleys equipped with heavy-duty wheels provide enhanced stability and ease of movement on the landing platform. These casters are also used to transport shipping containers, being attached via specialized corner brackets.
In supermarkets, casters are integral to the smooth operation of shopping carts, aiding in the effortless transport of groceries. Unlike assembly lines, hospitals prioritize patient care and comfort over efficiency. Ensuring smooth movement within the hospital is essential for patient recovery. This is why high-quality, reliable casters are crucial for the transportation of patients and equipment.
Spending extended periods in a hospital bed while awaiting procedures can be challenging. Patients often need to move their personal health monitors, making reliable and smooth-rolling casters vital. Efficient movement is necessary as patients are transferred between beds, surgical rooms, and recovery areas throughout the hospital.
Pneumatic wheels excel in shock absorption, making them ideal for both rugged terrains and scenarios where the cart's cargo needs protection from sudden impacts. These wheels are suitable for a range of applications, including both off-road and paved surfaces, thanks to their ability to handle uneven ground effectively.
Noise Reduction: Pneumatic wheels are designed to minimize noise, contributing to a more pleasant working environment. The soft rubber tread and inherent shock-absorbing properties of these tires help in reducing noise, which can otherwise be harmful to hearing. They also protect flooring from damage, as the softer wheel material prevents scratches and other types of surface wear.
By facilitating movement, wheels and casters alleviate physical strain and effort for employees who handle heavy loads. This makes tasks easier and less physically demanding.
In manufacturing and storage settings, wheels and casters enhance the efficiency of moving parts and inventory, streamlining various operations and processes within the plant.
Casters are designed for ease of use, offering maximum support with minimal resistance. For example, in supermarkets, caster wheels on shopping carts are engineered to allow smooth movement with minimal effort. Similarly, industrial casters facilitate the movement of large machinery and equipment with ease, offering low resistance against the floor.
One of the key benefits of casters is their ability to bear significant weight without failure. Since caster wheels rotate around an axle and bearing system, they experience less direct pressure compared to traditional wheels. This design allows them to support heavier loads more effectively.
Casters are available in various shapes, sizes, and materials, providing versatility for different applications. Larger casters can reduce the effort needed to move heavy items and are more durable when handling substantial loads, making them suitable for equipment that exceeds typical manual handling capacity.
When evaluating whether a pneumatic wheel is suitable for your needs, there are several factors to consider. One key aspect is the amount of force required to initiate movement. Due to their larger contact area and the flexibility of the air-filled tire, pneumatic wheels require a greater initial push force. Additionally, the larger footprint can make maneuvering and swiveling the wheels more challenging, often necessitating a longer swivel lead. It's also crucial to monitor the air pressure regularly. Pneumatic wheels require more upkeep as they are prone to flats and punctures. To mitigate this issue, some opt for semi-pneumatic wheels filled with polyurethane foam. These wheels eliminate the risk of flats since they don't rely on air, though they do sacrifice some of the cushioning benefits provided by air-filled tires.
Maintaining caster wheels involves several important considerations:
To maximize the lifespan of caster wheels, regular lubrication is essential. Typically, this means applying lubricant to both the wheels and their fittings approximately every six months. This practice should be part of a routine maintenance schedule where all casters and related components are inspected, lubricated, and tested to ensure optimal performance.
However, the six-month interval is not a one-size-fits-all recommendation. Certain types of casters are used in more challenging environments where they may be exposed to moisture or corrosive substances. In such cases, more frequent maintenance is required. For casters subjected to regular exposure to water or harsh chemicals, it is advisable to grease them at least once a month to maintain their functionality and prevent damage.
The hardware components that secure the wheels in place are just as important as the caster's lubrication. These critical parts often experience significant wear and tear, as they counteract gravity and other stresses regularly. To ensure everything remains in good condition, it is recommended to inspect these fittings monthly. This involves lifting or tilting the equipment to examine the connections between the casters and the machine, including nuts, bolts, screws, and other fasteners.
Any signs of misalignment, wear, or damage should be addressed promptly. Neglecting minor issues can lead to more serious problems and potentially require a full caster replacement. Timely repairs or replacements are essential to maintaining the caster's performance and longevity.
While lubrication and secure fastenings are important, maintaining the integrity of the caster wheel itself is equally vital. Many casters feature a tread or rubber covering designed to ensure smooth and quiet movement. However, the surfaces these treads roll on can lead to flattening or damage over time. Such wear can accelerate the deterioration of the caster wheel and compromise the effectiveness of previously applied lubricants and fastenings.
Regularly inspect the treads and overall condition of the caster wheels for signs of wear and tear. Replace any damaged wheels or treads promptly to prevent more significant issues that could necessitate replacing the entire caster assembly. Implementing a monthly inspection routine can help ensure the long-term reliability and performance of your casters.
To ensure that casters remain in excellent condition and achieve their full expected lifespan, regular inspections are essential. With consistent lubrication, timely maintenance, and thorough checks, casters can perform reliably for many years, minimizing the need for costly replacements and installations.
A caster is a non-powered wheel that is designed to be fitted to the bottom of a bigger object and used to move it. Caster wheels are attached on the base of device moving equipment and bring about mobility of those objects. They enable movement of heavy objects with less force being applied. Caster wheels require regular maintenance to live longer in operation.
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