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To understand the precautions for the use of rotational viscometers, we must first understand rotational viscometers, including the concept and principle of rotational viscometers. So what is a rotational viscometer? Technically speaking, a rotational viscometer is an instrument widely used to measure the dynamic viscosity of various fluids such as oils, paints, coatings, plastics, foods, medicines, and adhesives. The instrument is popular because of its simple structure, low price, convenience and practicality. However, many users report that the data is highly skewed when testing samples. Below, Guangzhou Shenhua will conduct a simple analysis on how to correctly use this type of instrument to obtain accurate and reliable measurement results.

First, let's understand how a rotational viscometer works

After the rotational viscometer is turned on, it must first detect the zero position. The rotational viscometer is driven by a miniature synchronous motor. The rotational viscometer is rotated at a stable speed by the synchronous motor, connected to the scale disc, and then drives the rotor through the hairspring and the rotating shaft. Rotation, if the rotor is not resisted by the liquid, the hairspring, the pointer and the dial rotate at the same speed, and the pointer indicates zero on the dial. On the contrary, if the rotor of the rotary viscometer is subjected to the viscous resistance of the liquid, the hairspring will generate torque, and the balance will be reached after competing with the viscous resistance. At this time, the pointer connected with the hairspring will indicate a certain reading on the dial. It is equipped with a pointer fixing control mechanism, which is used for accurate reading. When the rotation speed is fast, it cannot be read while rotating. At this time, you can gently press the pointer control lever to fix the pointer for easy reading; it is also equipped with a fixed bracket and The lifting mechanism should be fixed in the laboratory for small amount and constant temperature measurement, and the instrument should be fixed on the bracket to ensure the measurement accuracy; the helical gear and the damping lifting mechanism ensure the stable lifting of the instrument; the extension cable is convenient for the liquid to be measured. Use when the container is large and the liquid level is low, and when the temperature of the liquid to be measured is too high.

According to its measurement principle, in order to obtain accurate and reliable measurement data, the following points must be paid attention to.

First, the performance indicators of the instrument must meet the requirements of the national metrological verification regulations. The instruments in use should be periodically verified, and if necessary, intermediate self-checks should be carried out to confirm that their measurement performance is qualified, and the coefficient error is within the allowable range, otherwise accurate data cannot be obtained.

Second, pay special attention to the temperature of the liquid being measured. Special attention should be paid to keeping the temperature of the liquid under test constant around the specified temperature point, and it is best not to exceed 0.1°C for accurate measurement.

Third, the choice of measurement container. For the dual-cylinder rotational viscometer, read the instrument manual carefully, and different rotors match the corresponding outer cylinder, otherwise the measurement results will deviate greatly. For a single-cylinder rotational viscometer, in principle, the radius of the outer cylinder is required to be infinite. In actual measurement, the inner diameter of the outer cylinder, that is, the measuring container, is required to be no less than a certain size.

Fourth, select the rotor correctly or adjust the speed so that the displayed value is between 20 and 90 grids. If the indication value is above 90 grids, the torque generated by the hairspring will be too large, which will easily cause creep and damage the hairspring. Therefore, the rotor and speed must be selected correctly.

Fifth, frequency correction. The correction formula is that the actual viscosity is equal to the indicated viscosity times the nominal frequency divided by the actual frequency.

Sixth, the depth of the rotor immersed in the liquid and the influence of air bubbles. The rotational viscometer has strict requirements on the depth of the rotor immersed in the liquid, and must be operated according to the instructions. When the rotor is immersed in the liquid, there are often bubbles. Most of them will float and disappear after the rotor rotates for a period of time. Sometimes the bubbles attached to the lower part of the rotor cannot be eliminated. Slowly immersing the rotor is an effective method.

Seventh, the cleaning of the rotor. The rotor used for measurement should be clean and free of dirt. Generally, it should be cleaned in time after measurement, especially after measuring paint and adhesive. Pay attention to the cleaning method. It can be soaked in a suitable organic solvent. Never use hard scraping such as metal products, because serious scratches on the surface of the rotor will cause deviations in the measurement results.