ASTM D3104 Standard Test Method for Softening Point of Pitches (Mettler Softening Point Method)
3. Summary of Test Method
3.1 In this test method, the softening point is defined as the temperature at which pitch, suspended in a cylindrical cup with a 6.35 mm hole in the bottom, flows downward a distance of 19 mm to interrupt a light beam, as the sample is heated at a linear rate in air.
4. Significance and Use
4.1 Pitch does not go through a solid-liquid phase change when heated, and therefore does not have a true melting point. As the temperature is raised pitch gradually softens or becomes less viscous. For this reason, the determination of the softening point must be made by an arbitrary, but closely defined, method if the test values are to be reproducible.
4.2 This test method is useful in determining the consistency of pitches as one element in establishing the uniformity of shipments or sources of supply.
