Determination of Viscosity of Semisolid by Using Brookfield Viscometer

The LV Brookfield viscometer is dial reading (analog) type. It is supplied with spindles suitable for most applications within the viscosity range of the instrument.

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APPARATUS

a). LV Brookfield Viscometer.

b). 500 ml Beaker.

c). Thermometer

The Brookfield viscometer is of the rotational variety. It measures the torque required to rotate an immersed spindle in a fluid. The spindle is driven by a synchronous motor through a calibrated spring; the deflection of the spring is indicated by the pointer and dial.

For a given spindle geometry and speed, an increase in viscosity will be indicated by an increase in the deflection of the spring.

When performing a test according to an existing specification or procedure using the spindle and speed specified. 

When conducting an original test, the best method for spindle and speed selection is trial & error. The goal is to obtain a viscometer dial reading between 10 and 100 remembering that accuracy improves as the reading approaches 100.

When the reading is over 100, select a slower speed and /or a smaller spindle. Conversely, if the reading is under 10, select a higher speed and/or a larger spindle. If the approximate viscosity of the sample fluid is known, a faster method for homing in on the right spindle/speed combination is available by referring to the factor finder supplied with the viscometer.

Procedure for Viscosity Testing 

a). Take the sample fluid in a beaker and remove any entrapped air by gently tapping the container on the tabletop. The sample should be at a constant and uniform temperature. Be sure to bring the sample and spindle to the same temperature before taking a viscosity reading.

b). Connect the required spindle in the viscometer. Immerse the spindle in the fluid taken in the beaker up to the middle of the indentation in the shaft. Switch on the viscometer to start rotation and allow it to run until a constant reading is obtained.

c). Once a valid reading is obtained; multiply it by the spindle factor for the spindle/speed combination used to get the viscosity in centipoises.

Calculation 

Viscosity, cps = x f at -------------ºC

Where 

x = Dial reading.

f = Spindle factor.