ASTM D4212 Standard Test Method for Viscosity by Dip-Type Viscosity Cups
7. Test Materials
7.1 The material to be tested should be visibly homogeneous and free from any foreign material or air bubbles.
8. Temperature of Testing
8.1 Measurements should be made at 77°F (25°C) unless otherwise specified. Temperature drift during the test should be kept to a minimum. The viscosities of paints and related materials are highly dependent on temperature. Differences in temperature between measurements can give substantially different viscosities (up to 5 % per °F). For careful work, the temperature should be taken in the efflux stream, but for process control (such as monitoring a dip tank), this is not necessary.
8.2 A temperature correction curve may be constructed for each liquid by plotting viscosity (seconds) against temperature over the expected temperature range. With this curve, a viscosity determined at one measured temperature may be converted quickly to a viscosity at another temperature.
NOTE 2 - When dip cups are used for original purposes, that is thinning or monitoring of materials in tanks, coaters, etc., temperature is not important. This is because the key to good operation is to maintain the fluid within a certain range of dip cup-seconds regardless of the temperature of the fluid.
9. Checking and Calibration of Cups
9.1 Cups should be checked in accordance with the procedure described in Appendix X2. The frequency of this depends upon the amount of use and care that the individual cup receives, and the level of precision required.
9.2 Cups may be calibrated with standard fluids according to the procedure in Appendix X3. However, because the viscosity of standard fluids can vary significantly with temperature and due to difficulty in obtaining adequate temperature control with dip cups, calibration is a difficult procedure that must be done with great care and knowledge.
