ASTM D792:20 pdf free download – Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics bv Displacement.
11. Test Specimen
11.1 The test specimen shall be a single piece of material with a size and shape suitable for the testing apparatus, provided that its volume shall be not less than 1 cm3 and its surface and edges shall be made smooth. The thickness of the specimen shall be at least 1 mm for each 1 g of weight. A specimen weighing I to 5 g was found to be convenient, but specimens up to approximately 50 g are also acceptable (see Note 7). Care shall be taken in cutting specimens to avoid changes in density resulting from compressive stresses or frictional heating.
NOTE 7—Specifications Ir certain plastics require a particular method of specimen preparation and should be consulted if applicable.
11.2 The specimen shall he free from oil. grease. and other foreign matter.
12. Procedure
12.1 For density calculation, measure and record the water temperature. This is not needed for specific gravity calculation.
12.2 Weigh the specimen in air. Weigh to the nearest 0.1 mg for specimens of mass I to 10 g and density less than 1.00 g/cm3. Weigh to the nearest I mg for other specimens.
12.3 If necessary, attach to the balance a piece of fine wire sufficiently long to reach from the hook above the pan to the support for the immersion vessel. In this case attach the specimen to the wire such that it is suspended about 25 mm above the vessel support.
12.3.1 If a wire is used, weigh the specimen in air after hanging from the wire. In this case, record the mass of the specimen. a = (mass of specimen + wire, in air) — (mass of wire in air).
12.4 Mount the immersion vessel Ofl the support, and completely immerse the suspended specimen (and sinkers, if used) in water (see 10. 1) at a temperature of 23 ± 2°C. The vessel must not touch sample holder or specimen. Remove any bubbles adhering to the specimen, sample holder, or sinker, by rubbing them with a wire. Pay particular attention to holes in the specimen and sinker. If the bubbles are not removed by this method or if bubbles are continuously formed (as from dissolved gases). the use of vacuum is recommended (see Note
8). Determine the mass of the suspended specimen to the required precision (see 12.2) (see Note 9). Record this apparent mass as b (the mass of the specimen, sinker, if used, and the partially immersed wire in liquid). Unless otherwise specified, weigh rapidly in order to minimize absorption of water by the specimen.
Note 8—Some specimens may contain absorbed or dissolved gases. or irregularities which tend to trap air bubbles: any of these may affect the density values obtained. In such cases, the immersed specimen may be subjected to vacuum in a separate vessel until evolution of bubbles has substantially ceased before weighing (see Test Method B). It must also be demonstrated that the use of this technique leads to results of the required degree of precision.
Nom 9—It may be necessary to change the sensitivity adjustment of the balance to overcome the damping effect of the immersed specimen.
12.5 Weigh the sample holder (and sinker, if used) in water with immersion to the same depth as used in the previous step (Notes 10 and 11). Record this weight as w (mass of the sample holder in liquid).
NOTE 10—If a wire is used. it is convenient to mark the level of immersion by means of a shallow notch filed in the wire. The liner the wire, the greater the tolerance is permilLed in adjusting the level of immersion between weighings.