Does Your Cart Design Put Your People at Risk?
The ergonomic and economic importance of a good caster.
By: Doug Backinger, Contributor
In the landscape of modern workplaces where efficiency and productivity often take center stage, it’s easy to overlook the significant impact that carts and casters have on workplace ergonomics and injury prevention.
According to the National Safety Council, overexertion and bodily reaction are the second leading nonfatal injury or illness events involving days away from work, representing 22% of all such injuries. These stress injuries consistently rank among the leading causes of lost time accidents and have a significant impact on productivity and employee morale.
To offset the business impact of overexertion injuries, well-designed carts can improve safety related to push forces and environmental noise, mitigating lost time injuries while enhancing productivity and fostering a better working environment.
The weight of the problem
When an employee must move a heavy load, there are three times when they are most likely to experience an injury – when starting the movement, when maneuvering around an obstacle and when stopping the movement.
Ergonomic casters minimize these stress injuries by reducing friction between the wheel and the floor. For employees, loaded carts become easier to start, stop, and turn. Lower exertion forces mean less injury risk.
Ergonomic product design
It’s important for material handling specialists to know the ergonomic challenges customers face in a variety of applications, and develop innovative product designs to address these challenges. For example, tapered treads, independently rotating wheels and dual-swivel caster designs can reduce the risk of stress injuries. In fact, a major tire manufacturer reported a 71% reduction in push force after trialing four ergonomic cart designs.
Ergonomic designs can also feature a multiple wheel-in-one design that allows each wheel to spin independently and at different rates of speed to reduce friction and lower initial and continuous push force. The advantages of this type of design for manual material handling carts means load capacity can be increased without increasing push force; or loads with higher push force ratings can be reduced to help prevent operator injury.
A good example is swivel-on-swivel casters, which can reduce the initial push force needed to rotate the caster. A push force rate below 45 pounds is within a safe range for close to 90% of the population, significantly reducing the number of workers at risk for a potentially costly injury.
Our swivel-on-swivel caster design features a swivel caster on top of another swivel caster. This setup aids in rotation and also reduces the amount of shifting that can occur by enabling the second swivel section to transfer energy to the first swivel section. By reducing shifting and the force needed to rotate the caster when changing direction, operator fatigue and the risk of an overexertion injury are greatly reduced.

A cart with swivel-on-swivel casters featuring Twergo Wheels on back wheels with ErgoXcel Wheels on front. Image courtesy of Caster Concepts.
The proper load capacity
Choosing the proper wheel goes a long way in alleviating or preventing ergonomic-related problems. First and foremost, when you think wheel size, think load. Start by determining the maximum load weight that you will be loading on your cart or dolly. Once that is established, you’ll want to add in a margin of safety. You should factor the weight capacity for your casters to be 30% over your maximum load weight.
This safety margin is designed to compensate for unbalanced or shifting loads. Remember, three points make a plane, so there will be times when only three of your four casters will be supporting the total cart load, so they must be rated to carry the total weight.
Safety factors to consider
Casters are usually an afterthought when designing a new cart or dolly for a production system. Yet, many factors affect the push force of a battery cart or dolly that typically weighs between 2,500 pounds and 3,500 pounds — and most of these factors revolve around the casters.
Wheel width: The wider the wheel, the easier it is to get the wheel to start rolling. The tire has less of a contact patch length because it’s spread over the tire’s width. When paired with a swivel section, extra scrubbing can occur because of the different speeds the inner and outer part of the wheel are rotating when swiveling. This scrubbing can be negated by going to a split wheel design that features multiple independently rotating discs.
Caster placement: The typical setup we see in the industry is two swivel casters in the front of the cart and two rigid casters in the rear. This setup works well for most applications. The drawback is when the swivel casters are on same side of the cart, they can oppose each other while swiveling and spike the starting push force.
It’s possible to rectify this by situating more of the load over to the rigid casters. For example, a diamond pattern caster layout puts the rigid casters in the center directly underneath the load. This reduces the force added by the swivel casters while swiveling.
Swivel sections with high hardness and tight tolerances: The higher the hardness of a swivel section bearing design, the more resistant it is to galling or brinelling. This means the shape of the raceway stays intact and the bearing elements roll easier. Tighter tolerances help by spreading the load more evenly among the bearing elements.
The ergonomic and economic importance of a good caster
With heavier loads and more demanding applications, there are many situations that can lead to caster failure. Avoiding or minimizing these situations can help ensure your casters last longer and perform to spec, all while safely reducing worker compensations costs, increasing plant productivity, and enhancing employee satisfaction. WMHS
Doug Backinger is vice president of sales at Caster Concepts, a leader in industrial caster and wheel solutions for virtually every industry. With its state-of-the-art manufacturing facility and highly trained employees, Caster Concepts offers ergonomically designed solutions, and a diverse range of products and services. Learn more at www.casterconcepts.com.
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