Preventing Polyurethane Wheels Failure
Wheels and rollers in dynamic applications experience cyclic loading and unloading. When this occurs, the mechanical energy is converted into heat energy which causes the parts to heat up. If they have a polyurethane tread and the heat build-up is too great, the urethane could melt and cause the wheel or roller to experience blowout. This article will cover some ways to decrease the chance of polyurethane wheels failure in your industrial wheel application.
1. Harder Durometer Material
Generally when determining the polyurethane needed for a wheel or roller application, the load-bearing capability is the first consideration. Under loading, the tread will deflect. The amount of deflection can be calculated using the urethane compressive modulus and the dimensions of the part. Less than five percent deflection is recommended to prevent the wheel or roller from experiencing blow out. As a rule, harder urethanes will deflect less than softer ones. Therefore, polyurethane with a greater durometer can be specified for applications with heavier loads.
2. Increase Diameter or Width of Wheel
Perhaps a hard urethane cannot be used due to performance attributes such as traction or ride comfort. In situations like this, one option is to re-design the roller or wheel. Giving the part a larger diameter will effectively lower the speed and reduce the mechanical energy generated. Also, the part could be made wider to spread the load out over a larger area. Finally, additional wheels or rollers could be added to the overall design to spread the load.
3. Change the Type of Polyurethane
If the polyurethane needs to be softer and the wheel or roller cannot be re-designed, a high performance urethane may be used in these applications. Typically NDI, PPDI and TODI polyurethanes are used in applications requiring high speeds and/or high loads. These elastomers generally have higher compressive moduli than other elastomers of similar hardness. However, it is their ability to generate less heat under cyclic loading conditions that cause them to be thought of as high performance materials. Thus with less heat generated, the tread of the wheel or roller is less likely to blow out in demanding dynamic applications. The main disadvantages with the high performance urethanes are that they are considerably more expensive than the standard urethanes and are more difficult to process.
Polyurethane-treaded wheels and rollers in dynamic applications can experience blow out if they generate too much heat from the cyclic loading and unloading. To prevent this, a greater durometer elastomer can be used, the wheel or roller can be re-designed, or a high performance urethane can be used. The solution will depend on the application and the budget of the project.
The engineering staff at Caster Concepts, Inc. can assist you in determining the proper wheel or roller for your demanding dynamic applications. Proper planning, up front, can lead to extended life in the application and lower maintenance costs.