Vicat softening temperature of plastics: why is it important?

The ASTM D1525 Vicat Softening Temperature (VST) test gauges the ability of a plastic product to retain its surface mechanical properties at high temperatures.

The high temperature mechanical properties of plastics can limit their widespread application. Some polymers are capable of withstanding temperatures of 200°C or higher, while others fail before reaching 100°C. 

Vicat Apparatus Test Procedure

The Vicat Softening Temperature test, also known as Vicat Needle test, is performed by applying a point load onto the specimen, and raising the temperature of that specimen at a steady rate. As soon as the point load has penetrated 1mm into the specimen, the test is ended and the temperature recorded.

The results can then be used for development or quality control purposes, but should not be used in design calculations. The test itself is quite flexible as there is no prescribed specimen size or shape (beyond a particular minimum footprint) and specimens can have a range of thicknesses.

ASTM D1525/ISO 306

The ASTM D1525 Vicat test is shadowed by the ISO equivalent, ISO 306. This test is technically equivalent in many ways, but does not account for initial creep as does this standard. Moreover, the ASTM D1525 standard is allowing the use of the fluidized powder as a heat transferring medium.

This new system has been found satisfactory and safe for short-term heat cycles up to 500°C. It has open the door to thermo-mechanical tests for all those materials (e.g. PEEK, PEI, LCP, etc) where standard softening temperature is greater than 300°C.

HDT Vicat Tester Solutions

With regard to testing, the Instron HV series of thermo-mechanical testers is perfectly positioned to comply with all of these standards.

Featuring intuitive on-board control (optional automation) and easily changed testing heads, these machines are versatile and adaptable to your changing thermo-mechanical testing needs.

We can even supply the Instron HV500 with oil-free heat transfer medium for laboratories where oil-based systems are inappropriate.

Additionally, we can supply a number of specimen preparation solutions for punching and milling your specimens ready for test.

In order to run an ASTM D1525 test, please consult the standard.

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