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Just what is a Safe Working Load?

Determining how much weight an industrial wheel can hold may not be as simple as you think…

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A model R-3547 steel wheel by Reliance Foundry is shown on a white surface with no background.

People often ask what load an industrial cart wheel can withstand, but unfortunately the answer is not always a simple one. Many different factors affect how much weight a wheel can carry and every application is different. The “capacity” of a wheel to carry weight, or a wheel’s ability to sustain a load will differ from application to application, and will depend greatly on;

  • the variety of stresses and strains placed on the wheel
  • in what direction loads are applied to the wheel
  • how often loads are applied to the wheel
  • how fast loads are applied to the wheel
  • the manner in which a load is set against the wheel
  • environmental rigours – temperatures, caustic mediums, etc.
  • the speed at which a wheel is made to travel
  • the number of wheels that will be used together to carry a load, and how they interact with one another

“Daily, we get asked how much weight our wheels can hold” says Reliance Foundry’s Sales Manager, Rick Pasternak; “unfortunately, the unique demands of every application make it difficult to provide a clear-cut answer.”

Providing a straightforward answer is difficult but rating systems have been developed to provide some insight. To give some idea of a wheel’s suitability for an application, manufacturers and suppliers often discuss a “load rating” or “load capacity.” Both terms are general and provide a basic description of the maximum amount of force that can safely be applied to a wheel in an ideal situation. A more definite term, and the term that Reliance Foundry provides for its wheels, is safe working load (SWL).

A screen shot of a wheel product is shown with an arrow pointing out where “safe working loads” are listed is shown.

Safe working loads are clearly listed on every wheel’s product page.

Safe working load, sometimes referred to as normal working load, is the maximum weight that a manufacturer suggests a wheel can safely hold or transfer under ideal circumstances. It is calculated by determining the wheel’s breaking point under a static load, and then dividing that number by an appropriate factor of safety. To help ensure jobsite safety and to mitigate its customers’ risk, Reliance Foundry uses conservative factors when determining suggested SWL limits. Determining the SWL requirement for an application requires an assessment by a competent person of the maximum load the wheel can sustain in the environment in which it will be used.

Not all applications are performed under ideal circumstances and wheels are often made to perform in hostile environments that may adversely affect a wheel’s ability to bear weight. In these situations, it may be necessary to consult a professional. Some additional adverse factors that may indicate that a professional assessment is necessary include:

  • a moist or damp environment
  • abnormally hot or cold conditions
  • any customizations to the dimensions of the wheel
  • potential exposure to any chemicals
  • speeds that will exceed 3 mph (4.82 kph)
  • load that cannot be distributed evenly against the tread of the wheel
  • multiple load or stress conditions; that is an operating environment where the wheel may be exposed to more than one type of load and/or more than one load direction
A freshly manufactured steel wheel sits on a bench at the old Reliance Foundry.

It is also necessary to consider the condition of the track on which the wheels will perform. An old, untrue (“skewed”) or vibrating track may damage the wheels and limit their ability to bear weight. For ideal performance, wheels should be used with tracks that are well aligned, level and composed of a material with a similar hardness to the wheels. An engineer or other qualified professional should always be consulted when a wheel is used for applications that fall outside of the manufacturer’s recommendations.

Safe working loads, provided by suppliers, are only suggestions and the manufacturer assumes no liability. Specifically, Reliance Foundry does not market its wheels for use in specific applications and determining a wheel’s suitability for any application may require consulting an engineer. Product drawings for all of Reliance Foundry’s wheels can be easily accessed online, and the sales department will gladly provide material and design data about their wheels to help professionals determine if a wheel is suitable for an application.

“When asking how much a wheel can hold, it’s really necessary to examine the application and the stresses that will be placed on the wheels,” says Reliance Foundry’s Product Manager, Len Cranmore; “over the years we’ve noted a lot of factors that can affect a wheel’s ability to bear weight and sometimes it’s things as simple as the way the load is placed in the cart.”

Assuming that the load placed in a cart will be distributed in an even manner and the wheel will be used in ideal conditions, determining what the wheel requirements are for an application is easy. Remember: using a greater number of wheels will decrease the strain placed on each wheel. A rule of thumb for calculating the safe working load requirement for each wheel is to add 25% to the total load the cart will carry and then divide that number by the number of wheels that will be used. For example, if an industrial cart has four wheels and must carry 10,000lbs, the equation would be:

(10,000 lbs. + 25%) ÷ 4 = 3,125 lbs.

Therefore the safe working load requirement for each wheel would be 3,125 lbs, when the wheels are used in ideal conditions.

With eight varieties of double flanged wheels and six varieties of single flanged wheels normally kept in stock, Reliance Foundry has the wheel solution to fill the requirements of most applications. To learn the safe working loads of Reliance Foundry’s steel wheels, visit their informative, industrial cart wheel website.

About Reliance Foundry Co. Ltd.
Reliance Foundry has been a trusted supplier of cast metal products since 1927. Specialists in wheel design, production and usage, Reliance Foundry’s innovative catalogue also features innovative bollards and cutting-edge bike parking systems. Reliance Foundry sources cast metal solutions from across the globe to provide competitive prices and conveniently ships to all locations within North America. For more information on Reliance Foundry’s many innovative cast metal solutions and services, please visit www.reliance-foundry.com.

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