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Basic Knowledge
8.10 Viscometer
  • Detailed description

1. The principle of viscometer
The viscometer is used to test the viscosity of fluid. A spring drive a rotor rotating in the fluid and the distortion is the torsion. The torsion is proportional to the resistance. So the torsion is proportional to the fluid viscosity.
The viscosity is relative to the rotor size and shape and rotation speed. To a specific rotor, if the torsion is determined, the actual viscosity of fluid is in inverse proportion with the rotation speed. To the fluid with determined viscosity, the torsion will increase with increase of the rotor size and rotation speed. So when the fluid viscosity is low, use big rotor and high rotation speed; when the fluid viscosity is high, use small rotor and low rotation speed.

2. The formation and classification of viscometer
The viscometer has four types rotor, and they can be recognized by the no. on the nut. The rotation speed has 8 gears. They are 0.3/0.6/1.5/3/6/12/30/60 r/min respectively. Choose the suitable rotor according to the fluid viscosity.
There are rotation type and digital display type two kinds viscometer. The rotational viscometer can not read the fluid viscosity directly. The reading multiply the spindle factor is the viscosity. Digital display type viscometer can read the viscosity directly.

3. The operation procedure of viscometer
a. Pour the fluid into the beaker. The diameter of this beaker should not smaller than 70mm, and the height of liquid level should not below 90mm. if there are bubbles in the fluid, place it for   a certain time to eliminate the bubbles first and then test it.
b. Estimate the fluid viscosity, choose a suitable spindle. Screw the spindle to the viscometer connect end. Pay attention to the connect end. When connecting, one hand pinches the connect end gently, and another hand screws the spindle.
c. Put down the spindle slowly and sink it into the liquid. The liquid level reach to the groove on the spindle rob and not bubbles is the best.
d. Turn on the viscometer’s switch, choose a suitable rotation speed. The pointer locates between the 20 and 90 is the best, this is more precious. If the number the pointer pointed is too big or small, change the rotation speed and spindle.
e. When the pointer is stable, read and write down the readings. If the speed is fast, and can’t read the reading, press down the pointer control rob and the viscometer switch at the same time. This can make the pointer stop at the dial, and then read and write down the data.
f. After the test, turn off the viscometer switch and power. Unscrew on the spindle and wash it. Put is into the spindle box after cleaning.

4. The maintenance of viscometer
a. Install the spindle carefully, the force should not be too big and don’t forces the spindle transversely in order to protect the spindle from bending.
b. To ensure the viscometer is stable and vertical, and the speed only can be changed when the motor is running.
c. Washing the spindle after every experiment, forbid washing it on the viscometer, and put the spindle into the box after washing.
d. The viscometer should be used in the room temperature condition.

When the viscometer go up and down, support it with your hands, this can protect it from falling. And protect the spindle and beaker.
Avoid the spindle is adhered by the bubbles. And the spindle should be placed in the central of beaker when testing.