Page 113 - 20250602 EEA QM Edition 6.0

Quality Requirements Edition 6.0 European Enamel Association

8.5.3.2 Examination of test sieve residue
8.5.4 The flow characteristics of enamel slip (slurry)

Purpose and scope
Elucidation
In order to reduce the share of defects in enamelling, it is recommendable to
Enamel slips do belong to the muds and are in the widest meaning not a Newtonian
investigate the collected sieve residue, that is left over from the test of fineness of
liquid. For the most part, muds are colloidal systems i.e. one phase is very fine
grinding, thoroughly. Such residue delivers references to mill damage and other
distributed but embedded in another phase. The media can be in a solid, liquid or
dragged-in contamination.
gaseous state. Colloids are not in a thermodynamic equilibrium. One of their most

important properties is, that their internal surface is much larger than their external one.
After the test of fineness of grinding, the sieve residue is in the measuring tube. Pour Systems with solid state particles embedded in liquids are called suspensions.
a part of the supernatant water, shake and mix the sieve residue with the rest of the Independence of the size of the solid-state particles, one has to differentiate between
water and pour it onto a filter paper or white cloth. Should the sieve residue consist coarse dispersive, colloid dispersive and molecular dispersive systems. The transitions
not only of enamel particles but also of other materials, then further measures are are floating and are numerically not defined. If in a colloidal system, the gaps between
recommended to find out which foreign matter it is and from where it originates. the solid-state particles are repleted with liquid and are then getting smaller than their
White, very hard particles are mostly porcelain or steatite caused by broken milling average diameter, the system solidifies; the liquid suspension becomes a gel. The
balls or mill lining. Smudgy or sticky, greyish looking pellets which can be crushed, viscosity of muds mainly depends on the velocity gradient, the flow duration and
are clay minerals. In this case, after the mill was loaded, clay formed a big clot in the pressure. In aqueous solutions temperature only plays a subordinated role and is
mill, not being wetted by the mill water. Also, particles of rust are no rarity. Their origin sufficiently described as room temperature, quite different to oil emulsions. In this case,
can be of various kinds. In any case, one should search for the sources of the functional relationship of the oil temperature strongly influences the rheological
contamination, because black, grey or white specks in the enamelling often arise properties.
from contaminated slips. In most of these cases these contaminations can be
recognized in the sieve residue. Enamel slips are intrinsic viscous liquids with a flow limit and superimposed thixotropy.
They consist of a mixture of ground frits, water and additions like clay, quartz, colouring
To make sure, that the sieve residue is not causing defects in the enamelling, take a oxides, setting agents and substances which subsequently influence the dry enamel
bigger quantity of slip, screen it and stir about 5 - 10 g of this residue into 100 ml of layer.
slip in use. Test plates enamelled with this mixture will indicate the defects which can
derive from the sieve residue. Various demands are imposed upon the flow behaviour of the enamel slip. It is
supposed to be relatively viscous; it is not allowed to settle and must have an easy
workability for application. It must be uniformly distributed on the article. The applied
wet layer should not move when transported. The dried biscuit must be free of cracks
and has to have enough biscuit strength to withstand the transfer onto the firing chain
without any damage.

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