How to Assess Safe Working Loads

Determine load requirements for wheels in a vehicle assembly

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Steel industrial wheel features high safe working load

Wheels, like other load-bearing components, have their limits. It's important to know a few working parameters before determining suitability.

At its worst, wheel failure can result in serious harm to working staff or any at-risk bystanders. At the least, a poorly planned wheel assembly can shut down operations, causing unnecessary delays and need for repair.

Safe working load

A safe working load is the maximum mass that a product can carry without breaking. Safe working load ratings are typically determined by manufacturers to identify the limitations of their products. When evaluating industrial wheels, expect a product to fail when loaded beyond its safe working load.

Basic load evaluation

All Reliance Foundry wheels are designed, manufactured and evaluated to a specific load rating.

The following method for evaluation takes into account wheel applications for a cart or other vehicle bearing an equally distributed load while at rest. There are a number of additional factors to take into consideration when evaluating the suitability of a particular wheel for specific applications, which we look at below.

Double flanged wheel offers high load capacity

Double flanged wheel

First, know that vehicle loads must be considered per wheel. It's also important to include a safety variable for any unforeseen circumstances. We recommend a minimum variable of 25 percent, which does not take into account additional factors discussed below. For applications where human safety is an issue, this safety variable may need to be much higher.

To determine the required load capacity for a wheel used in a vehicle assembly:

  1. Identify the total weight of the vehicle and its maximum load.
  2. Add an additional 25 percent of the total weight to allow a margin of error.
  3. Divide the total weight including the additional 25 percent by the number of wheels supporting the cart. The resulting number must be lower than the safe working load of the wheel you intend to use.

For example, a 4,000-lb cart with 4 wheels required to carry a 6,000-lb load would use the following calculation:

[(4,000 lbs + 6,000 lbs) × 1.25] ÷ 4 = 3,125 lbs

According to this calculation, the vehicle mentioned above will require each wheel to have a safe working load greater than 3,125 lbs.

Other factors that can affect wheel performance

Single flanged wheel offers high load capacity

Single flanged wheel

When evaluating wheel products for a specific application, it's important to take into consideration all possible factors that will affect performance. We discuss a few potential factors here, but it's impossible for us to anticipate all, if any, of the issues that may affect your specific requirements. Be sure to consult a professional engineer for any specific wheel applications.

Load size and distribution: Loads can vary not just in mass, but also in volume and placement. Uneven placement may increase the force applied to certain wheels, and loads may shift during transportation. How materials are loaded into a vehicle can also increase the amount of force applied to a wheel, both vertically and laterally. For example, safe working loads assess downward forces (i.e., those resulting from gravity) and do not take into account horizontal impacts. Loads placed at higher velocities—i.e. dropped from above, or from an angled spout—will exert more force than a load at rest.

Vehicle operating speed: Safe working loads are assessed for wheels at rest. Vehicles travelling at speeds exceeding 3 mph should take this into account when assessing the suitability of a specific wheel product.

Uneven loads may increase the force applied to certain wheels

Frequency and duration of use: All materials wear with regular use. Wheels may also deteriorate quicker in adverse conditions. Safe working loads don't take into consideration use over any period of time. Be sure to consult a specialist to determine how long a wheel will last before it needs to be replaced.

Alterations: Any alterations performed on a wheel will affect its performance. Reliance Foundry's safe working load ratings apply only to wheels without alterations.

Environment: Environmental factors may include hot or cold temperatures and/or exposure to corrosive substances. Temperature variations can affect the hardness of wheel materials, and corrosive substances can compromise a wheel's integrity. Safe working loads are determined for wheels used under normal operating conditions—i.e. free of corrosive substances at room temperature.

Track conditions: Track conditions can affect the wear and operation of wheels. Tracks that are skewed or that are subject to significant vibrations can affect load capacities and may result in excess wear. Worn track surfaces, debris and even a track's material composition can also increase the rate of deterioration.

Standard and custom wheel products

Reliance Foundry offers both standard and custom wheel products. Detailed specifications, including safe working loads, are available for all in-stock products. All wheels are manufactured with a standard rough machine finish but can be customized with additional features and machining:

  • Boring
  • Bushings (purchase and installation)
  • Hardening
  • Machine finishing
  • Tread profiling

Don't see what you're looking for in our standard, in-stock products? Reliance Foundry will design and manufacture custom wheels for specific applications. Full customization services include consultation, design, prototyping, manufacture and shipment. Our experienced design staff is available to help identify the most suitable materials, pattern designs and manufacturing processes to ensure the best value and performance based on intended applications and volume requirements. For more information, contact Reliance Foundry's Sales Department.

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Reliance Foundry Co. Ltd. delivers the highest-quality stock and custom-designed products for architectural site furnishings, traffic management and industrial applications. Since 1925, Reliance Foundry has built upon a long tradition of metal casting expertise to become an award-winning supplier for high-profile and everyday needs across North America.