Casters

Casters are composed either of wheels or ball bearings as well as housings, axles and bolts (if necessary). Chair casters are one of the most common types of furniture casters; such furniture wheels allow for the easier movement of furniture throughout an area. Furniture glides, unlike casters, are wheel-less furniture leg attachments that allow furniture to sit or be moved across the floor with minimal friction and scratching. Swivel casters allow caster wheels to pivot, which allows for additional freedom of movement for the objects to which they are attached. While casters are important tools in homes, they are equally important in places of business. Industrial casters are used in warehouses, hospitals, institutions and a variety of other contexts for the movement of tables, chairs, equipment platforms, workstations, IV racks and many other kinds of equipment. Heavy duty casters, which are often equipped with pneumatic wheels with locking capabilities, are generally restricted to use in industrial contexts. Industrial casters are also often made of steel and are designed to resist the many hazards that can be present in industrial contexts. 

Caster wheels, axles, wheel centers and housings are fabricated from different types of polymers, stamped metals and rubber materials. Wheels are most often made from a grey, non-marking thermoplastic, although rubber, polyamide and tread polyurethane are used for heavy-duty casters. Rubber-wheeled casters with pneumatic wheels in both medical and industrial applications provide quiet, shock-absorbing movement when moving heavy tables, workstations or beds. Caster brackets are the hardware that attach to the furniture, while caster housings are the hardware that connect the caster wheel axle to the bracket. Brackets and housings for casters are made from stamped steel, while lighter-duty office and household casters are usually thermoformed polypropylene. Hospital bed casters, equipment table casters and similar equipment use locking casters to safely secure furniture in place; locking casters have an additional piece of locking hardware attached to the wheel housing. Locking casters are valued because of the control that they give their users. Locking casters prevent the unwanted movement of objects to which casters are mounted. 

Industrial caster applications require heavy duty casters, often made of steel, which can withstand heavy loads, uneven floor surfaces and jarring against ledges. For this reason, industrial casters are fabricated from stamped steel housings and brackets, aluminum or cast iron wheel centers and axle nuts and thermoplastic rubber or tread polyurethane caster wheels. Some caster assemblies are two-wheeled, providing a broader, more stable support for heavy equipment. Medical and hospital casters are medium-duty with soft rubber or polyamide wheels and polypro injection molded housings for smooth, quiet operation. Office and household chairs are made from lower-duty thermoplastic materials, although bed casters typically have strong metal housings. In cases when wheel casters are inappropriate, ball bearing casters, which feature a simple, spherical bearing in a housing, can be used instead. They are quiet, reliable and are ideal in situations where a short caster is necessary. Their pricing is also often similar to the pricing for wheel casters, which makes them an overall viable alternative to wheel casters when necessary. 

In the past, all swivel casters used kingpins both to attach the caster housing to the caster bracket and to provide pivot motion. Kingpins absorb a significant amount of stress, particularly in high-impact industrial applications, and they are consequently the number one cause of swivel caster failure. Caster failure can be very damaging, especially in healthcare and industrial contexts. For example, if a caster on a hospital gurney failed, it could result in patient injury. In an industrial context, if a heavy duty equipment caster failed, it could result in worker injury or product loss. "Kingpinless" casters have become quite common among medical casters, office casters and even industrial casters. In kingpinless casters, a raceway of ball bearings connects the upper bracket to the caster housing in place of a kingpin. These are not only far more wear-resistant, but they provide smoother swivel motion as well. Office tables and household furniture that remain stationary and do not need casters usually use furniture glides as alternatives to casters. Furniture glides are smooth-bottomed leg attachments that allow furniture to be moved only when needed, without causing floor scratching or damage to the furniture.

Caster Types

• Ball bearing casters are tools that, when affixed to an object, improve the mobility of that object. In contrast to wheeled casters, ball bearing casters feature a rolling, spherical bearing enclosed in a housing.
• Caster wheels are positioned between the legs of the caster to enable mobility.
• Chair casters are wheel assemblies that are attached to the bottoms of chair legs to improve mobility and shock absorption.
• Dual wheel casters have resilient tread wheels that help to minimize overall height and maximize load capacity. The differential action of dual wheel casters reduces the "scrubbing" effect of soft treads against the floor, thus improving stability and swivel action.
  
• Furniture casters are attached to a variety of furniture for industrial, business and consumer use. Furniture caster applications include beds, T.V. stands, chairs and portable tables.
  
• Furniture glides protect floors from damage caused by movement of furniture.
• Furniture wheels are added to the bottom of various pieces of furniture to enable mobility.
• Heavy-duty casters are used in heavy weight applications involving large or heavy loads and significant shock. Heavy-duty casters can withstand loads of more than 300 pounds. 
• Industrial casters are mobility-enhancing tools that are employed in industrial contexts.
• Institutional casters are used for the transportation of furniture and equipment in the pharmaceutical, scientific and medical industries.
  
• Light-duty casters are designed to handle light loads and low levels of shock and are used for small racks and stands. Load capacities for light duty casters usually range from approximately 75 to 190 pounds per caster. 
• Locking casters are mobility-enhancing tools that can be locked in place to prevent unwanted movement.
• Medium duty casters are designed to handle moderate loads and shock. Used for storage racks, trash cans and office furniture, medium duty casters have load capacities that usually range from approximately 200 to 290 pounds per caster.
  
• Pneumatic casters contain air that aids in the absorption of vibration and shock and provides the caster with a smooth roll on bumpy and uneven surfaces. Pneumatic casters are useful in the transportation of sensitive items like medical, electronic and computer equipment.
  
• Rigid casters do not swivel but provide only forward and backward motion. Rigid casters, often used in conjunction with swivel caster pairs, are useful in applications involving the transportation of items through an aisle or in a straight path, as they facilitate vertical (up/down) movement.
  
• Shock absorbing casters aid in protecting delicate cargo from shock and reduce noise levels and wear on floors.
  
• Specialty casters are custom-made casters that fulfill a particular need, such as shock absorption and inversion.
  
• Stainless casters are made of stainless steel. Stainless casters have great corrosion, rust and chemical resistance and are easy to clean. 
• Steel casters are mobility enhancing tools that are constructed with steel components.
• Swivel casters contain an extra bearing that allows the caster to rotate 360º. Swivel casters, commonly found on office chairs, provide convenient vertical, horizontal and diagonal movement.

Caster Terms

Axle - Caster mechanism that, in conjunction with the nut or bolt, connects the caster wheel to the leg.
 
Bore Size - The amount of space required for caster wheel insertion.
 
Caster Wheel - The rolling caster part that provides movement to the equipment to which the caster is attached. Caster wheels are positioned between the legs of the caster and connected by the axle.
 
Dustcap - The enclosure in which the hardcap sits. The dustcap protects the raceway from foreign materials.
 
Frame - Caster part, also referred to as a "fork," "yoke" or "rig," inside of which the caster wheel rests. The frame consists of two legs to which the caster wheel is attached by means of an axle, nut or bolt and a top plate; swivel casters also contain a swivel bearing between the top plate and the caster legs.
 
Hardcap - The upper raceway that bears the thrust.
 
Hub - The caster wheel core.
 
Leg - Caster part that is connected to the top plate. Legs are also attached to the caster wheel by the axle.
 
Kingpin - In a swivel caster, the rivet inserted into a hole in the center of the top plate to connect the top plate to the rest of the swivel assembly.
 
Load Capacity - The recommended load that an individual caster can accept during standard operation conditions.
 
Mounting Height - Distance measured from the bottom of the unit to the rolling surface.
 
Offset - Distance measured from the center of the axle to the center of the attachment method.
 
Shock Load - The largest load a caster can handle under conditions of shock, such as bumps, uneven surfaces and the dropping of items onto the caster.
 
Spanner Bushing - The round, cylindrical stationary sleeve between the bracket legs, within the bearing and over the axle, through which the axle runs.
 
Static Load - The largest load that a caster can accept while stationary and under no exposure to shock.
 
Swivel Lock - Mechanism on a swivel caster that prevents the swivel from rotating but not from moving forward and backward like a rigid caster.
 
Swivel Raceway - Also known as a "swivel bearing," it is the plate of a swivel caster located between the top plate and the legs that facilitates the swivel movement.
 
Thread Guard - Caster accessory that encases the wheel bearing and shields the caster wheel hub and frame from substances and materials, like threads, that might otherwise gather between the two caster mechanisms.
 
Top Plate - Also referred to as the "base plate" or "mounting plate," it is a part of the caster that connects the caster to the equipment and is located on top of the legs or, in the case of swivel casters, the swivel bearing. A rigid top plate contains four holes, one in each corner of the plate, while a swivel top plate contains an additional central hole through which the kingpin is inserted.
 
Yoke - A component that supports the upper and lower raceways.