Page 114 - 20250602 EEA QM Edition 6.0

Quality Requirements Edition 6.0 European Enamel Association

These requirements exclude any subjective opinion of the slip. Its physical 8.5.4.1 Terms of rheology
characteristics like density, flow behaviour etc. must be secured by defined data and
permissible limits. Viscosity

Viscosity is a measure of the internal friction of a substance, i.e. the force to conquer the
The science of flowing is called rheology. The term “flowing” is not to be explained in
interior of a body to affect its appearance.
just one sentence. One knows about fast, viscous, uniformly and jerky flowing. Water

e.g., flows uniformly and fast, paste is viscous and emulsions like body lotions are
From a scientific point of view, viscosity is the proportion of shearing strength to the
viscous but can be liquefied by shaking. In order to describe the flow of a substance,
slope of velocity. This interdependence graphically represented in the corresponding
some more rheological terms are in use (see also DIN 13342).
coordinate system for perfect liquids shows a straight line intersecting the origin of the
coordinates. Liquids without this behaviour, e.g. enamel slips, are non-Newtonian.

Yield point
The start of flow is called yield point. Flow only starts after some defined force has been
applied or stops after force removal.

Thixotropy

Thixotropy is the transition of a substance from a gel to a liquid and vice versa.

Shearing strength

Shearing strength is the requisite force to shift two plates against each other having a
liquid in between them.

Slope of velocity

The shearing strength allows a liquid to flow in the gap between two plates.
Consequently, different decreases of velocity will arise in dependence of each kind of a
liquid.

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