This time, we focus on one specific temperature-related property of plastics: the Heat Deflection Temperature, also known as the “Load Deflection Temperature.”
You may also hear it referred to as the “Heat Distortion Temperature.” While not a commonly used term in daily life, it plays a key role in evaluating the heat resistance of plastic materials—similar to what we discussed in the previous article about melting points.
The heat deflection temperature is determined through specific test methods. In simple terms, a constant load (or stress) is applied to a plastic sample, and the temperature at which it reaches a predefined amount of deflection is recorded.
In other words, if the applied stress changes, the resulting deflection temperature also changes.
Typical stress values used in catalog testing are:
- 1.8 MPa
- 0.45 MPa
This means that the measured HDT is not a fixed property—it varies depending on test conditions. That’s why the value alone has limited meaning in isolation. Instead, it becomes useful when comparing two or more materials under identical conditions.
For example, if you’re trying to determine whether plastic A or plastic B is more suitable for a high-temperature environment, comparing their HDT values under the same stress conditions can guide your material selection.
Quite simply: the higher the deflection temperature, the more heat-resistant the material is under load.
So when selecting plastics for heat-exposed applications, HDT serves as one helpful benchmark.
At Kashima Bearings, we always consider load, temperature, and other usage conditions when selecting the right material for ball bearings, plain bearings, or other plastic components. The heat deflection temperature is one of the reference values we use in the process.
That said, we don’t rely solely on HDT values for material selection. As mentioned earlier, the result varies depending on the applied load and test method. However, if the expected load and temperature in an application match a test condition, the HDT becomes a practical reference for narrowing down suitable materials.
If you’re ever uncertain about which material to choose for your specific conditions, please don’t hesitate to contact us. We’re happy to help you select the most suitable option for your application.
