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| Industry Terms
Thermal Brittleness Temperature That temperature, estimated statistically, at which 50% of the specimens would fail in the specified test. The test provides for the evaluation of long-time effects such as crystallization, or those that may be introduced by low-temperature incompatibility of plasticizers in the material under test. Plastics and elastomers are used in many applications requiring low-temperature flexing with or without impact. (ASTM D-746) Vicat Softening Temperature The temperature at which a flat-ended needle of 1mm² circular cross section will penetrate a thermoplastic specimen to a depth of 1mm under a specified load using a selected uniform rate of temperature rise. (ASTM D-1525) Glass Transition Temperature (Tg) The temperature at which a polymeric material loses its glass-like properties and makes the transition to a more rubbery material is the glass transition temperature. This is also the temperature at which small-scale local segment mobility occurs. "Tg" indicates the low temperature limit before molded or extruded parts become brittle. The majority of the popular TPU elastomers are flexible at room temperature, because of the fact that the Tg is well below room temperature. Excellent flexibility at low temperatures allows TPU elastomers to bend and flex at low temperatures without becoming brittle. In general, the polyether-based elastomers are best suited for low temperature performance. Among the polyether-based elastomers, the softer resins are even more flexible at low temperatures. Heat Deflection Temperature The heat deflection temperature for a particular plastic material is the temperature at which the test specimen deflects an arbitrary deflection of 0.010 inches in an oil bath under a constant flexural load of either 66 psi or 264 psi. This value should never be used as a prediction of the warp temperature of a plastic product. This can only be determined by testing the actual part. (ASTM D-648) Creep The dimensional change with time of a material under load, following the initial instantaneous elastic deformation. Creep at room temperature is called cold flow. Coefficient of Linear Thermal Expansion This measurement is very important in plastic sheet. It is simple to calculate and gives the amount of expansion or contraction of the plastic sheet over a given temperature range. (ASTM D-696) For example: Data shows 6 x 10.5 inches/inch/ºF You merely multiply .00006 x length of part in inches x no. of degrees in Fahrenheit change = total expansion or contraction of plastic in inches. |
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