ISO 2555:1989 pdf download – Plastics – Resins in the liquid state or as emulsions or dispersions – Determination of apparent viscosity by the Brookfield Test method

03-05-2022 comment

ISO 2555:1989 pdf download – Plastics – Resins in the liquid state or as emulsions or dispersions – Determination of apparent viscosity by the Brookfield Test method
2 Principle
A spindle, of cylindrical or related form (disc), is driven at a constant rotational frequency in the product being studied. The resistance exerted by the fluid on the spindle, which depends on the viscosity of the product, causes a torque which is indicated by a suitable meter. This measurement may be based on tightening of a spiral spring depending on the torque, indicated by the movement of a needle on a dial. The apparent viscosity by the Brookfield Test method is obtained by multiplying this dial reading by a coefficient which depends on the rotational frequency and characteristics of the spindle. The products to which this International Standard is applicable are generally non-Newtonian and the measured viscosity depends on the velocity gradient to which the products are subjected during the measurement. With these types of viscometer, the velocity gradient is not the same for every point of the spindle. Thus, for a non-Newtonian fluid, the result is not strictly the true “viscosity at a known velocity gradient” and therefore is conventionally called the apparent viscosity.
4 Choice of rotational frequency and spindle
Choose the rotational frequency-spindle combination taking into account the value of the viscosity to be measured, the desired precision and the velocity gradient. It is necessary to make this choice in such a way that no measurement cor- responds to less than 20 % or more than 95 % of full-scale deflection. However, for the best accuracy it is advisable to keep to the range 45 % to 95 % of full scale. If a comparison of viscosities between non-Newtonian pro- ducts is desired, it is necessary to use the same rotational frequency-spindle combination for all the measurements, even if the accuracy of one of the measurements is markedly decreased. The choice of rotational frequency automatically involves the choice of one or more types of viscometer. In this connection, it is recommended that, if possible, a rotational frequency of 1 0 min-1 be used. The rotational frequency-spindle combination to be used shall be specified in the document that prescribes the measurement (see annex A, clause A.1 1. The choice may be made in terms of the stated or expected viscosity, using table 2 and noting that the most suitable range is between 45 % and 95 % of full scale.
5 Procedure
Mount the viscometer, with its guard stirrup, when applicable (see sub-clause 8.3.3 in annex B) on its support. Fill the beaker (3.3.2) with the product to be tested, taking care not to introduce air bubbles, then place it in the bath (3.2) for a suffi- cient time to reach the desired temperature. If the product con- tains volatile matter or is hygroscopic, take care to close the beaker tightly during this operation. With the beaker still in the bath, hold the spindle at an angle of approximately 45’ to the surface of the product and immerse it in the product. Orientate the spindle vertically, and connect it to the shaft of the apparatus. Check that the spindle is vertical, using the bubble level, that the lower end of the spindle is more than 1 0 mm from the bottom of the beaker and that the spindle is immersed to the underside of the mark on its shaft. Immerse the thermometer (3.3.3) in the product. Wait until the temperature of the product is between the prescribed limits. Start the motor and run at the desired rota- tional frequency, taking into account the manufacturer’s recommendations. Allow the instrument to run and read the torque meter to the nearest 0,25 % of maximum value indication, in accordance with the manufacturer’s recommendations, when a stable value has been reached on the meter. Lock the needle and stop the motor to take the reading.

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