Materials in Motion

Pneumatic Vs. Polyurethane—Let’s Talk Casters

If you’ve been searching for the right gantry crane, lift truck, or rolling lift system for your specific application, there are several options to consider. It’s important to ask yourself questions like: do I need a light-weight system that can be moved from one location to another quickly and easily, or does my application require system flexibility for height, span, and tread adjustability? There are dozens of customizable options and accessories for these type of crane systems to meet their specific application duties. But, two questions we often receive are: what is the difference between pneumatic and polyurethane casters, and which type would best benefit my application?

Most gantry cranes come standard with a polyurethane caster, which is comparable to the tires on a wagon wheel. Although there are a wide variety of polyurethane casters available for multiple industries, applications, and overall uses, most gantry cranes stick with a standard polyurethane caster, which is perfect for most indoor applications that don’t require travel over rough terrain or soft roof tops.

A BRIEF HISTORY

Pneumatic casters are (generally) made from synthetic rubber, natural rubber, fabric and wire, and several chemical compounds. They are built with tread to provide traction, while the body of the tire contains compressed air. These tires are ones that you see on cars, most tractors, and anything else that needs to travel over multiple types of terrain outdoors. For cars, trucks, tractors, and the like, pneumatic casters are almost always preferred. Rubber tires, specifically pneumatic, have been around for more than a hundred years, whereas polyurethane casters have been used extensively for less than fifty years.

A German scientist discovered a material called polyurethane during World War II, and since then, polyurethane casters have become the go-to for the material handling industry.

SO WHAT ARE THE DIFFERENCES BETWEEN THE TWO, AND WHICH ONE WILL BENEFIT YOUR APPLICATION?

Pneumatic (or rubber tires with air and tread) and polyurethane casters each have specific strengths and weaknesses, dependent on their own unique properties. In the manufacturing industry, material handling industry, construction industry, and other types of industrial applications, pneumatic casters are used most extensively on systems that are used both indoors and outdoors. For outdoor-only applications, pneumatic casters are preferred for an easier ride and better traction.

On the other hand, polyurethane casters are limited to electric lift trucks and material handling systems that are used primarily indoors, where the floor is made of smooth concrete. The benefit of a polyurethane caster is that its load capacity greatly exceeds that of rubber pneumatic casters. In other words, a pneumatic caster must be larger than a standard polyurethane caster to handle greater capacities.

ROLLING RESISTANCE, TRACTION, AND CUSHIONING

The chemical makeup of polyurethane gives it a lower rolling resistance than pneumatic casters. High rolling resistance can reduce the efficiency of an electric lift system. Overall, it is usually best to use a polyurethane caster for an electric lift system to keep rolling resistance to a minimum.

Traction also differs between the two types of tires as noted above. Rubber tires will have a softer tread surface than polyurethane casters, which tend to be hard and provide less traction. This fact is why pneumatic casters are best suited for outdoor or rooftop applications.
Cushioning is related to a tire’s hardness (also known as its durometer).

The higher the durometer number, the harder the tire. Pneumatic casters will typically be in the range of 67-75 durometer, while polyurethane casters will fall between 83 and 95 durometers. In other words, the softer the tire, the more impact it can absorb. Because polyurethane is typically harder, it is known for providing a rougher ride than rubber. On average, rubber is about 15 durometer points softer than the softest polyurethane compound. If a soft ride is important to an overhead crane operator, a pneumatic caster is the way to go. However, if the system is electric, a polyurethane caster will be the softest compound recommended to maximize load capacity while minimizing rolling resistance.

WEAR AND TEAR, LOAD CAPACITY, AND FLOOR MARKING

Although pneumatic casters offer a much softer ride and better traction over gravel, grass, and other outdoor environments, it will not wear as well as polyurethane. As pneumatic casters are used over time, they lose pieces of tread. However, polyurethane does not experience similar wear due to its overall toughness.

In the world of material handling and manufacturing, load capacity is a very important consideration. Polyurethane casters can carry two times the load of pneumatic casters. For this reason, many manufacturers prefer polyurethane casters for their indoor applications.

As for floor marking, polyurethane casters are the way to go for indoor applications. Although polyurethane casters come in a variety of colors, the basic chemistry used in their production does not allow any colorant to mark factory floors. Pneumatic casters, however, can mark factory floors. Carbon black and other chemical compounds used in rubber are the primary reasons for floor-marking. There are non-marking rubber tires available on the market that will not mark the floor. But, these tires tend to be grey because they lack the carbon black
additive.

PRICE

As a general rule, pneumatic casters are more expensive than polyurethane casters. Although this rule is not always true, it’s often the case due to raw material costs associated with pneumatic substance. Because rubber tires can be used in multiple applications, pneumatic casters are often a great substitute for polyurethane casters. However, many material handling applications occur indoors and require a higher-load capacity, making the polyurethane caster a popular choice. It’s also important to remember that while polyurethane casters can cost less than their pneumatic counterpart, polyurethane can also last up to four times longer.

Attributes Pneumatic Polyurethane
Rolling Resistance Lower Higher
Traction Excellent Good Indoors
Cushioning Excellent Fair
Wear and Tear Fair Excellent
Load Capacity Good  Excellent
Floor Marking Fair Excellent
Price Slightly Higher Lower Cost

 

Kristina Harman

Technical Writer | Spanco.com

Kristina Harman is the senior technical writer and content manager for Spanco, Inc. Kristina has twelve years of experience in content development, technical communications, and copyediting. She holds a Bachelor of Science Degree in English from Towson University and a Master of Education Certification in English from Johns Hopkins University. She is a member of the Society for Technical Communication and the American Medical Writers Association.

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