Page 114 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

8.5.4.4 Determination of the flow-characteristic of enamel slips by means of 8.5.4.5 Determination of the flow-characteristic of enamel slips by means of
rotary viscosity meters viscosity testers

Purpose and scope Purpose and scope
The principle of rotary viscosity meters in combination with coaxial cylinder-measuring Viscosity testers are rotary viscosity meters, with which one is able to measure the
systems allows the absolute measurement of single flow-characteristics. In the ring slot, torsional shearing stress with the help of given velocity gradients. According to
be- tween the plates formed to cylinders, there is the to be measured liquid. By a construction and measuring-system, the measurements are directly comparable to
defined motion of the cylinders against each other and a measurement of the appearing continuous working de- vices. Due to the fact, that viscosity testers are only able to do
forces, the measuring problem can be solved in a mathematical way. point determinations, no flow diagram is available. As a measuring system, the Searle-
system is used predominantly. The adjustable velocity gradient steps should be in-between

-1
One distinguishes from two forms in the execution of the measuring system: 75 to 600 s .

1. The Searle-system: The inner cylinder (body of revolution) rotates with a constant or Viscosity testers provide very good measurements for the internal control of enamel
slips.
variable rate of revolutions, while the outer cylinder (measuring beaker) is in a fixed state.
The liquid in the ring slot flows and generates a torque, that is directly depending on the
liquid’s viscosity.

2. The Couette-system: The outer cylinder rotates and makes the liquid in the ring slot flow.
The resistance of the liquid against the shearing action transfers a directly on the viscosity
of the liquid depending torque onto the inner cylinder.

Details of standard measuring-systems are described in DIN 53018.

The relation between the torsional shearing stress and the velocity gradient are nowadays
automatically seized in a flow diagram. Out of this, the flow-characteristics of a liquid or a
mud can be seen. Because of the fact, that most of the laboratories are equipped with desk
calculators, single measurements can be printed and can be compared to one another.

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