In plastic product design, service temperature is a critical consideration. Unfortunately, this aspect is often overlooked, leading to product malfunctions and failures once the product reaches the market.
This is unfortunate, as most of these issues can be avoided by addressing them during the design phase.
We hope you find the tips below helpful in improving your product.
Short-Term Use
Carefully determine the temperatures at which your product will be used, as these may differ significantly from the temperature in your workshop.
Study the types of stresses your product must withstand and consider potential misuse scenarios.
Consider the operating temperature as an essential factor in material selection. Remember that the properties of heat-resistant and so-called high-temperature thermoplastics also vary with temperature.
Do not rely solely on the operating temperature range provided by the material manufacturer's datasheet. For example, you may find a PMMA grade with an operating temperature of 90°C, but at this temperature, PMMA becomes waxy and barely supports its weight.
Most data-sheets indicate the Heat Deflection Temperature (HDT) of the material. This value allows for some degree of material comparison. However, please do not use it as the sole selection criterion; practical testing is essential.
Request a Thermal Stress-Strain diagram from the material supplier, which shows how the plastic's strength and stiffness vary with temperature.
All semi-crystalline polymers have a Glass Transition Temperature (Tg), beyond which the material's nature might change more rapidly. Find out the Tg of the material and check whether it is within the operating temperature range of your product. If so, verify that the product meets the requirements on both sides of the Tg.
Find a reference product of the same material, heat it, and observe how its properties change at different temperatures.
Determine the temperatures your product might be exposed to during transport or storage. It is good to remember that the temperature in a parked car may rise to 70°C.
Despite the pressure to launch, be sure to allocate enough time to validate the function and durability of the final product using the actual materials.
Long-Term Use
Long-term stress (constant or cyclic) combined with high temperatures poses a significant challenge for plastic products. Overengineering (making the construction significantly stronger than short-term calculations would suggest) is the way to prevent creep-rupture or failure due to fatigue.
Dimensioning must be based on the material's properties at the expected operating temperature.
In extreme conditions, consider thermal aging, which refers to the gradual degradation of the polymer due to prolonged exposure to high temperatures. This process causes the material to lose its toughness and become brittle.
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