We often get questions from companies that are trying to move really heavy loads – think 30K to 100K total load – that are concerned about the terrain they have to traverse and what options they have with industrial heavy duty casters. Some applications are lucky in that they only move over smooth concrete or asphalt with limited to no obstructions. Yet there are many applications that are moving over uneven floors, expansion joints, railroad tracks, potholes, curbs, etc.
When moving really heavy loads, engineers typically run some sort of stress analysis to determine worst-case conditions that the structure (and casters) may see. They try to reduce these stresses by adding features to their casters that help deal with uneven terrain. The most common options utilized in heavy duty casters are large, soft wheels, oscillating axles, and springs/shock absorbers.
The first option usually turned to is to try and utilize a wheel that is larger in diameter and has a softer tire material. This could be larger urethane tires with thicknesses of 2’’ or more or could be a large solid rubber wheel. The urethane holds more weight per size than rubber, so typically rubber is avoided unless traveling at high speeds. The difference in sizes between two wheels that carry 17,000 pounds is rubber will be approximately 33’’ in diameter, while the urethane can be closer to 24’’. We tend to look at softer materials as it has more deflection and can absorb some of the impacts from rolling over objects. Harder materials are going to impart more shock loading to the structure.
Oscillating axles are also popular options for uneven flooring conditions. These “floating” axles have a center pivot point that allows the wheels to oscillate a set amount of degrees from parallel. So if traveling on asphalt that isn’t totally smooth, this is a good option. If traveling over potholes, expansion joints, and other obstacles, the oscillating axle will not help absorb those impacts.
Springs and other shock-absorbing systems are the best way to tackle uneven surfaces, bumps, potholes, etc., with heavy duty casters. Spring systems have been developed to provide shock absorption for loads up to 100,000 pounds and can typically be customized to fit a specific application, including load capacity and wheel travel. The spring systems are designed to be at half deflection at the stated load and then provide travel both up to handle obstructions and down to navigate holes while minimizing stress on the cart structure.
For severe applications, we have designed and manufactured casters that have all three features – large soft wheels, oscillating axles, and a shock absorption system. This caster had to carry 30,000 pounds and was used in the aerospace industry to move a tool from outside the factory to inside.
So, if you need to move something heavy and move it over some extreme terrain, there are ways to design a heavy duty caster to meet your application needs.