Page 109 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

8.5.3 Conditions of grinding When the fine grains are washed out, the coarse particles, being bigger than the mesh

8.5.3.1 Test of the fineness of grinding aperture of the test sieve, remain on the test sieve. The sieving procedure is over as soon

as clear water runs out of the sieving funnel. Then, close the measuring tube with the stop-
Purpose and scope per, fill it with water and put the sieving funnel on it. Allow a strong jet of water to pass from
Wet milling of enamels requires to focus on the fineness of grinding and to strive for an al- the outside through the sieve. Remove any existing air bubbles by gentle knocking and
ways stable grain structure. For testing the fineness of grinding, simple devices, which are
dislodge the sieve residue by agitation after which it drops into the measuring tube, where
easy to attend, are available. For usual enamellings, adequate results are obtainable. But
the amount can be read on the graduation of the scale.
one must be aware of too high expectations from these hand tests. Simple test equipment
cannot be precise and has not been geared for that purpose. The percentage of the coarse particles in the slip is calculated by a multiplication of the

read off units by factor 1.7. It would be absurd to calculate the percentage down to the
The PRINCE enamel test sieve proved itself in practice. It comprises the following
decimal point, because the sensitivity of this test is not that precise. It is just a typical handy
items: Sieving funnel of transparent plastic with test sieves made of phosphor bronze in a
check, suitable in the best manner for the shop.
plastic screw base (different colours depending on the screen aperture) :

- Measuring tube with scale and stopper
PRINCE and FERRO developed test methods for the determination of the fineness of
- Funnel tube grinding, but with distinguished graduation figures. The existing relations between these
- Measuring beaker of plastic ( formerly brass) two methods can be tabulated:

The screen aperture of test sieves is depending on the purpose of the slip. For dipping or Graduation on the devices of PRINCE and FERRO
spraying, black sieves of 100 μm mesh aperture = 3600 mesh per cm , for electrostatic
2
0.5 3.5
applications, blue sieves of 75 μm mesh aperture = 6400 mesh per cm are in use. Aluminum
2
1 5.5
enamels are even finer ground. Test white sieves of 40 μm mesh aperture = 16900 mesh
2 7.3
per cm are essential. The sieves are standardized in accordance with ISO3310/1
2
3 8.7

4 10.0
Operating instructions
The test method PRINCE requires a sample of 12.5 ml, whereas the test with the conical
To check the fineness of grinding, fill the measuring beaker (12.5 ml) to the brim with the
FERRO test sieve needs 250 ml.
slip under test. Rinse the sample through the funnel tube onto the test sieve and wash the

1)
slip through the test sieve. Best is to swing the sieving funnel in a container of water. By using this test method, one catches the coarse grains only; consequently only a few
percent of the total grain structure. In order to diminish this lack, it is advisable to use a test
1) The widespread method to press the slip through the test sieve by means of a strongjet sieve which permits a test sieve residue of at least 3 scale graduations. Preferably use test
of water is wrong. By this, the test sieve netting expands, so that the coarser particles are sieves of 6400 to 10000 mesh instead of 3600 mesh test sieve. One can also use a laser
forced through. An experienced checker will be able to measure almost any desired fine- particle size analyser to get a full grain size distribution.
ness of grinding.
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