Thermal & Environmental Testing Equipment for Plastics

What Thermal and Environmental Testing Covers

Plastics soften, deform and age with heat, and thermal testing finds the temperature at which that starts. Heat deflection temperature shows where a plastic bar under a set flexural stress bends by the amount the standard defines. Vicat softening shows where a flat-tipped needle under a set load sinks into a thermoplastic. Both are run in a heated liquid bath that warms at a constant rate.

Environmental testing exposes specimens to heat, cold and humidity. Aging ovens hold specimens at high temperature to follow changes in properties such as hardness, elasticity and tensile strength, and temperature and humidity chambers condition specimens before they are tested.

Standards for Thermal and Environmental Testing

ASTM D648 and ISO 75 cover heat deflection. ASTM D1525 and ISO 306 cover Vicat softening, and ISO 2507 applies to samples from pipes and fittings. For heat aging, ISO 188 and ASTM D573 cover rubber, IEC 60216-4-1 covers thermal endurance of electrical insulation, and ASTM E145 specifies laboratory ovens.

Conditioning before testing is set by ASTM D618 and ISO 291, which cover conditioning plastics and the standard atmosphere for testing them. IEC 60068-2 covers temperature and humidity methods for environmental testing.

What Affects Thermal Test Results

The heating rate, the load and the evenness of the bath decide an HDT or Vicat result, so the temperature has to be measured at the specimen and the movement read by the instrument rather than by eye. In an oven or chamber the question is uniformity. The NG-EC chambers state temperature fluctuation of ±0.5°C, uniformity within 4°C and deviation of ±2°C for an empty chamber, and the NG-AGOV-ADV oven states uniformity of ±2°C at 100°C with 3 to 10 air exchanges per hour.

Thermal and Environmental Equipment from NextGen

The NG-HDT HDT/Vicat testing machine runs both methods on one frame in an oil bath rated to 300°C, with three or six test stations. The NG-AGOV-ADV aging oven offers programmable thermal cycles and PID control, and the NG-EC environmental chambers come in five sizes from 100 to 1000 liters. The HDT and Vicat subcategories below describe each method in detail.

The aging oven has a stainless steel chamber of 600 x 500 x 750 mm with adjustable trays, a touchscreen for heating steps, duration and air exchange, and over-temperature protection with real-time monitoring. The chambers are controlled from a 7 inch color touch screen with a large program capacity and various protection features, and each holds two stainless steel sample racks. The NG-HDT tests bars up to 130 x 15 x 13 mm for HDT and up to 50 x 16 x 6.5 mm for Vicat, and the result is saved on the machine and exported over Ethernet.