Casters - A Helpful Guide
|The following is VERY basic information about casters and
caster wheels. You may find it informative.
A wheel and a
caster are not the same thing, but often these words are used to refer to the
same object. When a customer uses the words, "wheel" and "caster"
interchangeably, it often creates confusion. Here is the difference: A wheel is
a round object that rolls. A wheel rotates on an axle or shaft that passes
through the center of the wheel. A wheel can be solid or spoked. Wheels made of
just one material include solid all polyurethane wheels, steel wheels, V-groove
wheels, hard rubber wheels, polyolefin wheels, phenolic wheels, nylon wheels
and high temperature wheels. Wheels that are made essentially of just one
material are almost always solid rather than spoked design.
are made in a spoked design usually have a tire molded to another material.
Most of the time tires are molded to a solid core which is the center or
circular disk supporting the tire. Wheels with a solid core tend to be stronger
than wheels that have spokes for a center.
The phrase "mold-on wheels"
refers to wheels that have a tire molded onto another material that comprises
the center of the wheel. Most of the time the center or core of a wheel is made
out of one of the following materials: aluminum, iron, steel, nylon or
The tire that gets molded onto the center of a wheel is
usually made from rubber or polyurethane. Rubber tires are made from many
different compounds and in many durometers (hardness). The same is true of
polyurethane tires. When selecting a wheel it is rare that any consideration is
given to the proper tire compound or hardness for a specific application.
Most people choose a wheel on
the basis of its rated capacity or its diameter. We have included on our web
site a Tips Section
called "Factors to Consider Before Selection", which describes most of the
major factors one should consider before making a selection. When you do not
select the proper wheel for your special application, it will not perform as
efficiently as it would had you chosen the right wheel.
most sales people who sell wheels know too little about them. Our staff is a
valuable resource ready to assist you in the selection of the right wheel for
your specific application. They have a vast amount of product knowledge and
experience in wheel applications.
Now that we have explained what a
"wheel" is, let us distinguish it from a "caster". All too often, customers
call and say they want to buy "wheels" when in reality, they wish to purchase
"casters". So, what is a "caster"?
To start with, one component of a
caster is a wheel. Once a wheel is installed in a frame it becomes part of a
caster. The frame is often called a caster bracket, rig or fork. All of these
words are used to refer to the frame which houses or holds the wheel. The major
components of a caster are the wheel and the frame in which it is held.
A caster frame can be either a swivel or a rigid frame. If the frame is a
swivel type, then with a wheel installed, it is called a "swivel caster". A
swivel caster is capable of rotating 360°. A chair caster or a caster on
the bottom of a furniture mover's dolly, are examples of a swivel caster that
most people are familiar with.
If the caster frame is rigid, then with
a wheel installed, it is called a "rigid caster". A rigid caster is primarily
utilized for straight line travel, meaning rolling forward or backward.
In most instances, both a swivel caster and a rigid caster have two "legs". One
leg is on each side of the wheel that is installed in the caster frame. The
wheel is held in place between the legs of the caster frame by a bolt or axle.
Above the legs on a swivel caster is the swivel bearing, which allows a swivel
caster to rotate or turn 360°. Above the legs on a rigid caster there is no
swivel bearing because a rigid caster is designed only to go forward or
A wheel held between the legs of a caster frame is the lowest
part of a caster because its function is to roll on a floor surface. The top of
a caster is used to attach the caster to the equipment. There are many ways to
attach a caster to a piece of equipment. The most common means is a mounting
plate, often called the top plate. The mounting plate on a swivel caster is
connected to the swivel bearing and to the legs below the swivel bearing. On a
rigid caster the mounting plate is connected directly to the legs, forming a
"U" shaped frame to hold the wheel. Most mounting plates on casters contain
four holes used to bolt the caster on. Sometimes casters are attached by
welding the mounting plate of the caster to the equipment.
Some of the
other popular ways to attach a caster to equipment include the following: an
expandable rubber stem to insert into tubing; a round or square solid metal
stem, also inserted into tubing; an octagonal shaped stem with cross drilled
holes to be bolted to angle iron legs; a threaded stem to either go into a
tapped hole or to pass through a hole and held in place with a lock nut. There
are many other means to attach or fasten a caster onto equipment. When you call
for assistance in selecting a caster, it obviously helps if you know which
means of attachment you want. We can be very helpful if you are at least
familiar with where the casters are to be attached and the kind of equipment
the casters are going to be attached to.
A typical piece of equipment
supported by casters has either four swivel casters or a combination of two
swivel casters and two rigid casters. The main purpose of having four swivel
casters is that the equipment can be moved in any direction-forward, backward
and sideways. This caster configuration is especially useful when you have to
move castered equipment when there is little space to maneuver. When your
application requires that the equipment travel in a straight line, such as down
an aisle, it is easier to control the direction if there are two swivel casters
used in combination with two rigid casters. Most of the time if there is a
handle to push or pull on the equipment, it is located on the end where the
swivel casters are located. The one exception to this rule would be if the
weight to be moved was so light that you could still easily steer from the end
where the rigid casters are located, such as on a shopping cart in a grocery
There are applications where more than four casters are needed
to support a piece of equipment. One example is a piece of equipment so large
that it needs to be supported in the center as well as on the four corners. In
addition to size, sometimes the application necessitates the use of more than
fours casters. An example of this would be the "U" shaped narrow tilt cart used
in grocery stores to bring boxes of food from the warehouse into the store
aisles to be put onto the shelves. The two rigid casters in the middle are
taller than the four swivel casters in the corners. This enables the long
narrow tilt cart to maneuver in confined spaces and still go in a straight line
down aisles without difficulty.
The large number of caster applications
and the many factors to be considered, are two reasons our knowledgeable and
experienced staff are a valuable resource. They can assist you in selecting the
right wheel and caster.
It is our view that you are not purchasing mere
casters or wheels. You are buying a product that must work for you. The
internal handling of materials is an expense. Properly designed wheels and
casters can reduce this expense.
Caster City is your source for "Quality
Casters and Caster Wheels".