Limitations Of PU Products
The useful temperature range for polyurethanes is from around 30 degrees C to an upper limit of 70 to 80 degrees C. Above this upper limit ageubg processes set in and the operating life is curtailed.
In Most Dynamic applications we recommend staying at temperatures below 160°F (70°C ). The normal, high property working range is -40°F to 160 °F(-40°C to 70°C). At 160°F (70°C) the properties of the elastomer begin to show a decline. The bond between urethane and metal weakens considerably above 160°F (70°C).
Polyurethane rubber should not be used un dynamic applications above 200°F (93°C). When testedat 200°F (93°C) their properties are only half of those measured at 75°F (25°C) . They heat age well however, and the effect of high temperatures up to 250°F (120°C) for weeks on physical properties is almost completely reversible when tested again at 75°F(25°C) .
Intermittent exposures to higher temperatures upto 100 degrees C or 110 degrees C is acceptable but not recommended.
Polyurethanes have limited resistance to water. Continuous immersion in water above 50 degrees C can result in hydraulic breakdown and for this reason a maximum upper limit of around 70 degrees C under these conditions should apply. Again all aspects of the application must be considered and where instances of high wear and tear are involved, polyurethanes give a longer life at 60 degrees C in water than do other elastomers of better hydrolic stability.
Urethane exhibit high hysteresis and low thermal conductivity. They do not dissipate heat built up by a dynamic action quickly. Avoiding heat build-up in an elastmeric part is a paramount consideration in design. In practice, this is usually done by controlling the amplitude of the deflection.
Long term exposure to hot, humid environments should be avoided. Some urethanes are much more resistant than others to this environment.
Certain chemicals such as concentrated acids and polar solvents attack urethanes, and urethanes should not be put into continuous service in these environments.