Industrial Casters
Casters are an essential component in the industrial world, although technically, the wheel is only one part of the caster assembly. The full caster assembly consists of a wheel housed within a framework or housing, allowing for the mobility of otherwise stationary objects.
Casters come in various sizes to support different load capacities. They can be made from a wide range of materials, and may include features like swiveling, locking, running on tracks, or working in tandem with other casters. Some casters are designed to function as traditional wheels, while others include bearings that enable smooth and multidirectional movement. Additionally, certain casters are designed with shock-absorbing capabilities to provide further stability.
Casting Through History
The history of the caster is closely tied to the history of the wheel. Evidence suggests the use of a wheeled device around 5,500 B.C. The early configuration of the wheelbarrow meets the criteria for a caster and wheel, predating the cart wheel by about 1,000 years, although not all historians agree on this.
Some revisionist theories propose that casters or similar devices were used in the construction of the pyramids (around 2,600 B.C.) and the erection of Stonehenge (around 2,000 B.C.).
In the 1700s, leather bowls or glides were placed under furniture legs to facilitate the easy movement of desks and tables, allowing them to be adjusted to capture light from windows.
Modern historians generally credit David A. Fisher with inventing the caster as we know it today. Fisher was granted a patent in 1876 for a heavy-duty industrial caster, which featured a metal wheel mounted on an axle and attached to a frame, enabling mobility for furniture and equipment.
By 1900, casters with glass wheels wrapped in leather were commonly used to move furniture without damaging floors. Wheeled chairs, bicycles, tricycles, and carts began incorporating rubber wheels, which provided better traction and some shock absorption.
In 1907, John Weigel began developing and selling small shoe rack casters from his garage in Hamilton, Ohio.
In 1925, the kingpinless caster was introduced, further advancing caster technology.
Designing Casters
A well-designed caster takes into account the specific needs of its intended application, creating a custom solution that optimizes performance. Many workplace injuries result from improper lifting, carrying, pushing, or pulling. By providing the right casters for each situation, the ergonomics of movement can be improved, contributing to employee well-being and reducing the likelihood of accidents and injuries.
Larger diameter wheels are necessary for handling heavier loads. For loads exceeding 250 pounds, bearing casters should be used. Shock and impact loading must also be factored into overall load ratings. Using the largest feasible diameter wheel improves rollability, making it easier to move the caster. Additionally, the larger the swivel radius, which is the distance from the center of the kingpin to the outer edge of the tread, the smoother the turning capability of the caster.
In medical and food service applications, casters must meet strict standards for safety, materials, and functionality. Both ANSI and OSHA have established guidelines to ensure the reliability and cleanliness of casters used in these environments. A trustworthy caster manufacturer will provide products that meet or exceed these standards.
Parts of a Caster
A basic caster consists of several key components. The frame, often referred to as the yoke, rig, fork, or housing, provides the primary support for the caster. It is typically a "U" shaped metal bracket, with the legs of the bracket fitted over a wheel. The axle is secured through the wheel to hold it in place, while the frame also serves as the mounting surface for the caster plate or swivel head.
The axle can be a tubular rivet or a hardened bolt, which may be zinc plated or stainless steel, and it could also be forged or construction molded for added strength.
Caster wheels come in various diameters and widths, made from materials such as urethanes, polymers, plastics, rubber, composites, glass, wood, metal, or leather. Pneumatic tires are often used for heavy-duty applications. The wheels are designed to endure the weight of the equipment they support, the distance they need to travel, the surface over which they move, and the frequency of use.
Bearings are another essential rolling mechanism for casters. Packaged in a round housing known as a race, bearings can be used vertically to ensure smooth rolling of the wheels, horizontally as a "skate," or incorporated into the swivel head to enable horizontal rotation or swiveling motion of the caster.
The rotation of the caster head is a secondary action in a swivel caster
. The bearing race attached to the mounting plate or stem allows furniture or machinery to be moved in any direction. Some casters include a swivel lock, which prevents the turning motion but still allows the caster to roll.
Bearing casters are designed to support very heavy loads or allow equipment to move in multiple directions. These bearings, which can be ball or roller types, generally require lubrication at regular intervals to function properly. Many bearing assemblies are equipped with a receptacle called a zerk fitting, into which grease is periodically pumped.
The caster can be mounted in various ways—screwed, bolted, welded, or pinned—to the foot of an object. The mounting plate, usually made from durable metal, may come pre-drilled to accept a fastener or include a hollow kingpin, which holds a locking pin attached to the object. It may also have a caster stem that fits into a hole at the bottom of the object. These stems can be square, tapered for wooden furniture, or feature locking grip rings, expanding adapters, or threads.
Some casters are equipped with shock-absorbing mechanisms, such as coiled steel, elastomeric, or hydraulic springs, to reduce vibration and noise during movement, and to lessen the impact of traveling across uneven or rough surfaces.
Caster Types
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swivel caster
These tools enhance the mobility of objects when attached, featuring a spherical rolling bearing enclosed in a housing, in contrast to wheeled casters.
Caster Wheels
Positioned between the legs of the caster, caster wheels facilitate movement.
Chair Casters
Wheel assemblies attached to the bottoms of chair legs to improve mobility and provide shock absorption.
Dual Wheel Casters
Equipped with resilient tread wheels to reduce overall height while maximizing load capacity. Their differential action minimizes the "scrubbing" effect of soft treads against the floor, enhancing stability and swivel action.
Furniture Casters
Mounted on various types of furniture for industrial, business, and consumer use, such as beds, TV stands, chairs, and portable tables.
Furniture Glides
Protect floors from damage caused by the movement of furniture.
Furniture Wheels
Attached to the bottom of furniture pieces to enable movement.
Heavy-Duty Casters
Designed for heavy weight applications, handling large or heavy loads and significant shock. These casters can support loads over 300 pounds.
Hollow Kingpin Casters
Held together by a tubular rivet, allowing a stem or bolt to attach the housing or yoke to furniture or equipment.
Institutional Casters
Used in the transportation of furniture and equipment within the pharmaceutical, scientific, and medical industries.
Kingpinless Casters
Built as a single piece unit without a separate axle, these casters are designed to withstand extremely heavy loads and harsh conditions.
Leveling Casters
Equipped with a height adjustment feature, typically operated by a screw mechanism, thumbscrew, ratchet, or wrench, allowing for adjustments to floor level differences.
Light-Duty Casters
Designed for light loads and low levels of shock, commonly used for small racks and stands. Their load capacity typically ranges from 75 to 190 pounds per caster.
Locking Casters
Feature a braking device to stop wheel rotation or the swivel from turning. The locking device may be a friction sleeve or a positive locking pin.
Medium-Duty Casters
Designed to handle moderate loads and shock, often used in storage racks, trash cans, and office furniture, with load capacities generally ranging from 200 to 290 pounds per caster.
Pneumatic Casters
Contain air to absorb vibration and shock, providing a smooth roll on bumpy or uneven surfaces. They are ideal for transporting sensitive items like medical equipment, electronics, and computers.
Rigid Casters
Do not swivel, allowing only forward and backward movement. Rigid casters, commonly paired with swivel casters, are useful for applications requiring straight-path transportation and vertical (up/down) movement.
Shock Absorbing Casters
Protect delicate cargo from shock, reducing noise and wear on floors.
Specialty Casters
Custom-made casters designed to meet specific needs, such as shock absorption and inversion.
Stainless Casters
Made of stainless steel, offering excellent corrosion, rust, and chemical resistance, as well as ease of cleaning.
Steel Casters
Mobility tools made with steel components.
Stem Casters
Feature a pin or "stem" attached to the top of the yoke, which fits into a hole on the bottom of the object to be moved. Plate casters operate similarly, but use a flat plate with pre-drilled holes for mounting via screws or bolts.
Swivel Casters
Include an additional bearing that allows the caster to rotate 360º, providing convenient vertical, horizontal, and diagonal movement, commonly used on office chairs.
Uses of Casters
Casters are most commonly seen on rolling chair and grocery carts, but their applications extend far beyond these everyday items. Heavier appliances like refrigerators and freezers often feature casters, as do lighter pieces of furniture such as tea carts and portable filing cabinets. Many luggage items are also equipped with casters, as well as shipping boxes and crates designed to transport fragile items like musical instruments or electronics. In the aviation industry, smaller aircraft can be moved by caster dollies, enabling a single person to maneuver an entire plane. Hospital gurneys and medical equipment are placed on casters that are designed to be antimicrobial, quiet, and capable of either total or directional locking.
In industrial environments, nearly every piece of machinery or equipment that is not permanently fixed is mounted on casters for ease of movement and maintenance. Maintenance carts that are used to service this equipment also rely on casters for mobility.
In the aerospace sector, casters capable of supporting several tons are employed to move large parts and equipment. Industrial manufacturing facilities depend on casters to transport various items of all sizes and weights across different surfaces, even in extreme conditions such as high heat or humidity.
Choosing a Caster
Casters are selected based on their intended application, with several factors influencing the decision when purchasing or designing custom casters for a project. One of the most important considerations is the material used for both the caster wheel and the body, which is largely determined by the load capacity—the total weight the caster needs to support.
For lighter-duty applications, such as replacement casters for furniture, wheels are commonly made from plastic. In some cases, historical reproduction casters may feature glass or wooden wheels for aesthetic purposes.
Heavy-duty casters, designed to support larger weights, are typically made from hardened metals like stainless steel or zinc-plated steel. However, newer composite materials are also gaining popularity in this category. These casters often feature wheels with rubber or polymer coatings, solid rubber, polymers, or urethane. Some heavy-duty wheels are mounted on solid or pneumatic tires attached to metal or composite rims. The type, composition, and density of the tires directly impact the caster's weight capacity.
Additionally, the type of wheel should be chosen based on the floor surface it will be operating on. It's important to consider whether the floor is carpeted, steel, concrete, or wood, as well as factors such as its smoothness, whether it's bumpy, cracked, uneven, or littered with debris. The environment—such as humidity, extreme temperatures, or exposure to toxic or caustic substances—also plays a significant role in determining the best wheel composition for the caster.
Preventing Problems in Casters
Caster flutter, also known as shimmy or "speed wobble," occurs when the caster wheel begins to oscillate as the speed increases. This issue is commonly observed in shopping carts and wheelchairs and can be minimized by increasing friction on the swivel joint. In some cases, caster flutter can be controlled by extending the trailing distance, or increasing the distance between the front and rear wheels, or by adding more weight to the front end of the vehicle.
Improper maintenance or exposure to environmental elements can cause caster wheels to malfunction. Failing to lubricate the bearings or allowing debris to accumulate around the wheels or swivels can slow down the movement or even stop it entirely. Regular cleaning and lubrication will help ensure smooth operation. If the caster becomes irreparable, replacement casters are available for many applications.
Caster Terms
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Axle
The part of the caster mechanism that connects the caster wheel to the leg, in conjunction with the nut or bolt.
Bore Size
The amount of space required for inserting the caster wheel.
Caster Wheel
The rolling component of the caster that enables movement of the equipment. It is positioned between the legs of the caster and attached by the axle.
Dust Cap
The protective enclosure for the hard cap that shields the raceway from foreign debris.
Frame
Also known as a "fork," "yoke," or "rig," this part houses the caster wheel. It consists of two legs that are connected to the caster wheel via an axle, nut, or bolt, and a top plate. Swivel casters additionally contain a swivel bearing between the top plate and the legs.
Hardcap
The upper raceway that supports the thrust.
Hub
The core of the caster wheel.
Leg
The component of the caster attached to the top plate. The legs are connected to the caster wheel through the axle.
Kingpin
A rivet inserted into a hole in the center of the top plate to link the top plate to the rest of the swivel assembly in swivel casters.
Load Capacity
The maximum load a caster can handle under standard operating conditions.
Mounting Height
The distance from the bottom of the unit to the rolling surface.
Offset
The distance from the center of the axle to the center of the attachment point.
Shock Load
The largest load a caster can withstand under shock conditions such as bumps, uneven surfaces, or dropped items.
Spanner Bushing
A cylindrical, stationary sleeve placed between the bracket legs, within the bearing and over the axle, through which the axle runs.
Static Load
The maximum load a caster can bear when stationary and not subject to shock.
Swivel Lock
A mechanism on a swivel caster that prevents the swivel from rotating, but allows forward and backward movement like a rigid caster.
Swivel Raceway
Also called the “swivel bearing,” this is the plate located between the top plate and the legs of a swivel caster that allows for the swivel movement.
Thread Guard
An accessory that encases the wheel bearing and protects the caster wheel hub and frame from substances like threads that might otherwise accumulate between the two caster parts.
Top Plate
Also known as the “base plate” or “mounting plate,” this part of the caster attaches the caster to the equipment. It is located on top of the legs or, in swivel casters, the swivel bearing. A rigid top plate has four holes, one in each corner, while a swivel top plate has an additional central hole for the kingpin.
Yoke
A component that supports the upper and lower raceways of the caster.
