A caster is an assembly that includes a wheel and a base. Casters support and make it easy to maneuver carts, shelves, dollies and other equipment. Casters are available in different materials, wheel diameters, tread widths, load ratings and overall heights, making your equipment maneuverable in a variety of work environments.
To help determine which type of caster is best for your needs, consider the following questions:
- Is the work environment wet or greasy?
- How much load do these casters need to support?
- Will the casters be used for powered traction?
- Is exposure to chemicals or caustics a cause for concern?
- What type of floor or surface do you need to manipulate?
- What temperature range will the casters be exposed to?
- Need a brake?
- Are aesthetics or noise reduction an issue?
- Do you need certification to CA Prop 65, NSF Food Service Use, or other standards?
Mobility: rigid casters, swivel casters, swivel casters without kingpin
When considering mobility, there are two basic types of casters: rigid casters and swivel casters.
- Swivel casters have raceways that allow the wheels to turn. A raceway is the cylindrical portion of a swivel caster that contains one or more ball bearing tracks.
- Rigid casters, also known as fixed casters, can only roll back and forth.
Traditional swivel caster designs rely on a kingpin, which is a bolt or rivet that holds the races together. In this design, the kingpin is subject to a lot of stress, especially when the device encounters an obstacle or a heavy object falls on it. Because of this, kingpins are a common point of failure for traditional swivel casters.
A kingpinless caster is a special type of swivel caster whose races are not held together by bolts or rivets. Stress distribution is more even, which means kingpinless casters generally last longer than traditional swivel casters. They are recommended for power traction applications as they can better withstand the stress caused by high-speed rotation. They are also better at handling impacts such as rough terrain, obstacles and falls. However, kingpinless casters generally have a higher initial cost than traditional swivel casters.
Rigid and swivel casters are available for different applications in different configurations:
- The most common caster configuration uses two parallel swivel casters and two parallel fixed casters. This gives the cart good cornering and straight-ahead travel.
- Four rigid casters in a diamond pattern can be a cost-effective arrangement. In this configuration, the central pair of casters on the left and right are usually slightly higher than the pair on the front and rear. This makes it relatively easy to turn and pivot the cart when the load is arranged on central fixed casters.
- Carts with only swivel casters are easy to move in any direction, which is useful for maneuvering lighter loads in tight spots, but they are difficult to control. In this configuration, swivel locks on both casters make straight-line driving easier.
Caster Material and Dimensions: General Characteristics
Wheel material and size are important considerations when choosing casters. What the wheel is made of, how big or small it is, affects how easy it is to move (which in turn affects the ergonomics of the cart), how durable it is, the noise it makes, and more.
Carts with wheels made of harder materials are generally easier to move than carts with wheels made of softer materials. This is because Medical Caster Wheels made of harder materials have lower starting resistance, especially when the load weight increases. Starting resistance is the force that the wheel must overcome to move the wheel when it is stationary. Wheels made of harder materials also have lower rolling resistance, which means less force is required to keep them moving at a constant speed.
Wheels made from softer materials are generally quieter and more comfortable to use because they transmit less vibration. They can also help protect soft floor materials, such as hardwood or tile, that can be damaged by harder wheels.
Comparing wheel hardness: Shore A, Shore D, Brinell
Generally speaking, rubber casters are softer than plastic casters, which are softer than metal casters. The hardness of a particular caster is rated using three scales:
- Shore D scales are typically used for harder rubbers and plastics.
- The Shore A scale is used for softer rubbers.
- Brinell hardness testers are used for metals and have a Brinell hardness number (BHN).
Within each scale, higher numbers indicate stiffer materials.
Diameter and width are two measurements that provide wheel size. The diameter is the height of the wheel. (Total height of casters includes wheels and base.)
In general, wheels with larger diameters and widths have lower starting and rolling resistance – it’s easier to get them moving and keep them moving. They can handle heavier loads and are generally quieter.
However, larger diameter wheels also give the cart a higher center of gravity, which can reduce its stability, especially with higher loads stacked on the cart.
Caster rated load
The load rating of each caster increases the total capacity that can be supported. Each caster represents an incremental increase in rated load capacity. To find the load rating per caster required for your application, divide the weight of the load (including the weight of the cart itself) by the number of casters.
For safety reasons, remove one caster and divide by the weight of the load to get the load rating for each caster. Consider using a higher safety factor for power towing and in areas outdoors or where the wheel may roll over tall obstacles.