ASTM D3236 Standard Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials
7. Calibration
7.1 The viscometer is precalibrated using Newtonian fluids by the manufacturer. No zero adjustment is provided, since experience has shown that the zero point will not vary due to changes in the torque sensor. The viscometer and spindles are precision equipment and should be kept from undue shock and mishandling. Physical damage to the instrument will often reveal itself as erratic torque indication or no oscillation of the shaft when the instrument, with or without the spindle in place, is operated in air. When operating normally, the torque indication will be stable and have free oscillation about the zero point in air.
7.2 The instrument may be further calibrated using standard reference fluids. Suitable fluids are available in nominal viscosities up to 15 000 mPa·s at 149 °C (300 °F). The procedure for instrument calibration using standard reference fluids is that encompassed by this test method. Results obtained using standard reference fluids should not deviate from the nominal viscosity by more than 2 %.
7.3 To further check the controller and further establish controller settings, use the following procedure: Place a sufficient quantity of low viscosity (500 mPa·s or less) hot melt in the sample container to permit immersion of the appropriate ASTM thermometer to the proper depth.
NOTE 6 - Do not permit the temperature sensor to rest on the bottom of the sample container.
7.3.1 Insert the temperature sensor through the insulating cover of the sample container and hold it in place at the point required for proper immersion depth. Adjust the thermal controller to provide the desired test temperature. Rotate the temperature sensor during temperature reading to minimize the effect of thermal gradients in the sample. Continue temperature readings and controller adjustment until minimum deviation from test temperature is obtained. Minimum deviation may vary between laboratories, depending upon the controller, but should in no case exceed +/- 0.5 °C (0.9 °F). Repeat this procedure for any test temperature desired within the scope of this test method.
