Workplace ergonomics play a vital role in today’s facilities, particularly in environments where there is a focus on transporting heavy loads. There are numerous areas in which workplace ergonomics best practices can be followed to reduce workplace injuries. An often overlooked and surprisingly important area is cart design.
Designing and equipping carts for transporting heavy loads is a crucial area of focus. Creating the best cart for the specific application can have a major impact on workplace ergonomics. Not only is the design of the structure of the cart important (e.g. handhold height/orientation/type, design, stability, size), but the casters used on the cart can have a significant effect as well.
There are two key wheel factors that should be examined. When applied correctly, these two factors can significantly reduce push/pull forces decreasing the risk of workplace injuries:
- Caster wheel material
- Caster wheel diameter
The Science of Caster Wheel Material
Material sciences have progressed the capabilities of providing some of the most ergonomically advanced caster wheels in market to date. Wheels can now be selected depending on a variety of factors including floor type and condition that will significantly reduce the forces an end user would need to apply to move a cart.
When it comes to rolling resistance, the combination of floor type, condition and wheel material play a large role in the values. Rolling resistance can be measured using the following formula: F= μ*W/r where;
F = rolling resistance (lbf)
μ = coefficient of rolling friction (between a wheel material and floor surface) (in)
W = normal force (lbf) = m*g = mass*gravity
r = radius of the wheel (in)
What this equation tells us is that as the coefficient of friction increases (keeping the load capacity and radius of the wheel constant), the rolling resistance also increases. As mentioned in the above point, the coefficient of friction is a product of the wheel material and floor surface, which means that each different wheel material on a similar floor will give different rolling resistance values. The chart shows the calculated rolling resistance forces for a polyurethane wheel (PU), cast iron wheel (CI) and a phenolic wheel (P) as they are rolled over a smooth, steel floor.
At relatively low load capacities, the wheels perform similarly. The difference becomes more evident when loads are heavier, demonstrating the increasing dependence on the wheel material. This is significant for a company that has an ergonomic or health and safety mandate to lower push/pull forces of a cart. As an example, if the goal was to achieve a 35 lb push/pull force, the table demonstrates that polyurethane wheels would not be suitable and phenolic wheels are borderline acceptable. It’s important to note that in this example, the floor is a smooth, clean level surface. In many cases, the cast iron wheel would be a poor choice if the floor is rough, uneven or dirty.
The Science of Caster Wheel Diameter
The wheel diameter (or radius) is also a significant contributing factor in the ergonomic performance of caster wheels. The chart shows how the radius of a caster influences rolling resistance for each wheel material for a load capacity of 4500 lbf. For example, if a rolling resistance of 50 lbs is required, a 4” diameter cast iron wheel should be used. However, if a polyurethane wheel is required, a 6” diameter wheel would be needed.
Apply the Science of Caster Wheel Radius and Material to Choose the Optimal Wheel
Combining the science of caster wheel radius and material can help you choose the optimum wheel design to meet your company’s ergonomic needs. Other factors that may play a role in choosing the right wheel material are shock absorption, noise reduction or debris resistance. If you missed them, check out some our previous blog posts:
- 5 Questions to Ask when Choosing a Caster
- Why Noise Reducing Casters Are Important for Workplace Ergonomics
- Caster Technology: Why a Soft Wheel Outperforms a Hard Wheel
For a thorough overview of workplace ergonomics and push/pull tasks, download the Guide to Workplace Ergonomics.
Darcor has a modern test facility where we can measure ergonomic performance of various wheel materials under various conditions. If you’re interested in testing a particular wheel on a specific floor surface, please feel free to contact our caster technology engineering team.