Testing flexural heat distortion temperature

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

We use a variant of flexural testing to measure a sample s heat distortion temperature. In this test, we place the sample in a three point bending fixture, as shown in Fig. 8.6 b), and apply a load sufficient to generate a standard stress within it. We then ramp the temperature of the sample at a fixed rate and note the temperature at which the beam deflects by a specified amount. This test is very useful when selecting polymers for engineering applications that are used under severe conditions, such as under the hoods of automobiles or as gears in many small appliances or inside power tools where heat tends to accumulate. 

Heat Distortion Temperature. Heat distortion temperatures were obtained in flexure, using a load of 264 psig on molded bars 5 X % X % inches. The heat distortion temperatures were taken as the temperatures at which test specimens had deformed 0.010 inch, where a heating rate of 2°C per minute was applied. 

The heat distortion temperature (HDT) is standardized in ISO 75 1-3. Here the test specimens are loaded in a flatwise three point bending device. The heating rate is 120 K h . Plastics and ebonite are loaded with a maximum flexural stress of 1.8 MPa (procedure A), 0.45 MPa (procedure B) or 8 MPa (procedure C). The specimens dimension is 80 x 10 x4 mm, the support span is 64 mm (Fig. 3.5). 

It is always good design practice to minimize the amount of molded-in stress. However, most designs retain some level of this kind of stress. If this must be limited to ensure proper part functioning, a quality control test with limits should be specified, such as a part s heat-distortion temperature or impact, flexural, or tensile ratings. 

The common heat distortion test is made in flexure with a test specimen (5 in. x Vz in. x Vz in.) supported at two points with a 4-in. span. The load is either 66 psi or 264 psi and is applied at the midpoint of the test specimen. The specimen is placed in a liquid silicone bath which is heated at a rate of 2 deg C per min. The heat distortion temperature is that temperature at which the test specimen has deformed 0.010 in. 

FIGURE 2.80 Test for deflection temperature of plastics under flexural load. Heat distortion temperature is the temperature at which a sample deflects by 0.1 in. (2.5 mm). Two measurements are madp and quoted (a) with a stress of 66 Ibflin. (4.6 kgf/cm ) and (b) with a stress of 264 Min. (18.5 kgf/cm ). Standard test methods ASTM D648, BS 2782 method 102, ISO R75. 

HOT Heat Distortion Temperature, or heat deflection under load (HDUL). A three-point flexural test is performed on a bar by applying a load to create a stress of either 1.80 MPa or 0.45 MPa at the midpoint. The temperature is raised by a predetermined rate and when the specimen deflects by a set amount, the temperature is quoted, in °C. 

HDT heat deflection temperature under flexural load (1820 kPa) Heat distortion test (HDT) ASTM D-648-72 CEAST 6005... 

A good applications-oriented measure of the use temperature for a ma-teral is the heat distortion or heat deflection test (HDT). The HDT is described by ASTM-D648 as the temperature at which a sample of defined dimensions (5 X Vi X Vs (or Va) in.) deflects under a flexural load of 66 or 264 psi placed at its center. In case of a largely amorphous polymer, the HDT temperature is typically slightly (10 to 20 °C) lower than the Tg as determined by DSC or DTA, whereas with more-crystalline polymers, it more closely correlates with the Tm. The HDT temperature is a useful indicator of the temperature limits for structural (load-supporting) applications. A loaded cantilever beam is used in another heat deflection test called the Martens method. 

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