ASTM D4212 Standard Test Method for Viscosity by Dip-Type Viscosity Cups
10. Procedure
10.1 Choose the proper cup so that the time of efflux will be between 20 and 80 s. See Table 1 for viscosity ranges for the various cups.
NOTE 3 - The formulas used in this test method to describe the conversion from Zahn seconds to stokes are linear, the actual cup response is not. The range of 20 to 80 s covers the most linear portion of each cup. In addition, below 20 s, turbulent flow may cause additional inconsistencies. Above 80 s, factors that may impact on the precision include; loss of solvent (and therefore varying viscosity), "skinning" of the liquid in the cup, intermittent flow.
10.2 Immerse the cup in the container, which may be a can or beaker, but is more likely to be a thinning or mixing tank or even a resin reactor. Stir or agitate the fluid well to give uniform temperature and density. Allow the cup to remain in the fluid for 1 to 5 min to attain thermal equilibrium. (Because of their greater mass, Shell cups should remain in the fluid for the full 5 min.)
NOTE 4 - Dip cups are not recommended for use with thixotropic (time dependent) materials but if used for them (such as gravure or flexographic inks), more vigorous agitation will be necessary to break up the structure before the measurement is made.
10.3 Lift the cup vertically out of the material in a quick, steady motion. As the top edge of the cup breaks the surface, start the timer. During the time of flow, hold the cup vertically no more than 15.2 cm (6 in.) above the level of the liquid. Stop the timer at the first definite break in the stream at the base of the cup. The efflux time in seconds constitutes the viscosity. It is common to make only a single measurement, but for greater precision and accuracy the mean of two or more measurements should be taken.
NOTE 5 - The cup should not be held by the loop handle during the measurement process. Most manufacturers equip the cup with a ring through the loop handle. Holding the cup by this ring will help to ensure that the cup hangs vertically.
11. Care of Cups
11.1 Following each determination, clean the cup with a suitable solvent and a soft brush. Use no metal tools in contact with the instrument as nicks or wear of the drilled orifice affect the accuracy of the cup.
