Page 111 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

These requirements exclude any subjective opinion of the slip. Its physical characteristics 8.5.4.1 Terms of rheology

like density, flow behaviour etc. must be secured by defined data and permissible limits.
Viscosity

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

flows uniformly and fast, paste is viscous and emulsions like body lotions are viscous but
can be liquidfied by shaking. In order to describe the flow of a substance, some more From a scientific point of view, viscosity is the proportion of shearing strength to the slope
rheological terms are in use (see also DIN 13342). of velocity. This interdependence graphically represented in the corresponding 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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