Plastics HDT Heat Deflection Vicat Softening Point Tester VST definition: The sample is placed in a liquid medium or a heating box, and the temperature of the standard press needle is determined when it is pressed into 1mm of the sample cut from the pipe or pipe fitting under the action of (50+1) N force under the condition of constant temperature rise HDT definition: The standard sample is subjected to a constant three-point bending load in a flat (preferably) or side-standing manner, so that it generates one of the bending stresses specified in the relevant part of GB/T1634, and the temperature is measured when the standard deflection corresponding to the specified bending strain increment is reached under the condition of constant temperature rise.
