Viscometer

A viscometer is an instrument for measuring the viscosity ( " toughness " ) of a liquid. There are different types of viscometers, which differ primarily in the fact, for which they are suitable viscosity ranges. In contrast to the rheometer viscometer can measure only Newtonian fluids correctly.

Capillary

The underlying measurement principle here is the flow of the liquid to be measured through a thin tube. A fixed volume of liquid V runs at constant pressure p through a capillary of length l and radius r, and the time required for this t is measured. The kinematic viscosity can be determined by multiplying the number of seconds with the constant of the capillary. Capillary are eg Ubbelohde or Cannon -Fenske capillary. The (dynamic ) viscosity is then given by the Hagen- Poiseuille. The capillary viscometer is not to be confused with the Hochdruckkapillarrheometer used for rheometric characterization of highly viscous, non-Newtonian substances.

Rotational

In a rotational body is rotated in a liquid by a motor. During the rotation, the torque needed is measured. Thereof, as well as the exact geometry of the rotary body used and the outer vessel, and the rotational speed, the dynamic viscosity of the fluid can be determined. The usual arrangements for such equipment are: plate against plate (there are two discs ), tapered to disk and cylinder tube. As the cylinder rotates in the stationary tube ( as with most rotary viscometers ), one speaks of the Searle type, in a vertical cylinder and a rotating pipe from the Couette Hatchek type.

Viscosity measuring cup ( Ford cup, viscosity cup )

In this method, the liquid is placed in a beaker, the conical bottom in a hole (nozzle) runs with exactly known diameter. Due to the beaker volume of the nozzle diameter and the measured duration of the flow of the fluid whose viscosity can be determined. This type of viscosity measurement is approximately described in the standards ASTM D 1200:1994 and DIN EN ISO 2431:2011 ( withdrawn standards: DIN 53211, DIN EN 535 - October 1996). It is commonly used with a viscosity similar in their testing of paints, inks, resins and liquids, especially in the Anglo- Saxon countries. Usually, the flow duration is specified ( with reference to the standard and nozzle size ) here as a measure of the viscosity easy. There are also diving flow cup, in which the liquid is removed by dipping the measuring cup so that a filling is not required. For the viscosity measurement with the flow cup speaks fast and easy to use, reasonable design of the measuring instrument ( a cup ) and the possibility to perform in-process measurements. However, the method is less suitable for highly accurate viscosity measurements. Furthermore, it is feasible only for a relatively limited range of viscosities.

Mooney viscosity

This procedure is often used to measure the viscosity of rubber and blends. A standardized method for determining the Mooney viscosity measured while the torque of the mixture by increasing the temperature ( outer temperature usually 100 ° C). After the appropriate pre-heating the rotor rotates with constant 2/min. The torque is thereby measured in MU converted (8.3 Nm = 100 MU). The rotors used are ( for large 38.1 mm (1.5 inch) S for small 30.5 mm ( 1.2 inches ) L ) is also normalized in two sizes. The measuring cell has a diameter of 50.9 mm ( 2 inches). As a result of measuring the Mooney viscosity is reported as follows:

8.3 Nm = 100 MU

Fallkörperviskosimeter

This measurement method is based on the Stokes' law. The liquid to be measured is located in a measuring cylinder with radius. In a falling ball falls a sphere with radius through the liquid. Since at a speed dependent upon the viscosity of the ball, a balance between the force acting on the ball of gravitational force, the buoyancy and the frictional force is adjusted, the ball is lowered at a constant rate to the ground. By Stokes' law is followed for the viscosity of the liquid:

Process viscometer

The process viscometer is used for " in -situ" measurement of viscosity in a process plant, such as in a reactor or in a pipe. The advantage is that no samples must be taken. Since it can not be measured at a defined temperature, the measured value at the standard temperature (typically 25 ° C) must be converted, but for modern automation systems is not a problem. If possible the viscosity of the torque and the rotational speed of the stirrer drive of a reactor is calculated. Suitable stirring drive ( measuring stirrer ), these values via an interface.