Page 112 - 20250602 EEA QM Edition 6.0

Quality Requirements Edition 6.0 European Enamel Association

8.5.3 Conditions of grinding When the fine grains are washed out, the coarse particles, being bigger than the mesh
aperture of the test sieve, remain on the test sieve. The sieving procedure is over as
8.5.3.1 Test of the fineness of grinding
soon as clear water runs out of the sieving funnel. Then, close the measuring tube
with the stop- per, fill it with water and put the sieving funnel on it. Allow a strong jet of
Purpose and scope
water to pass from the outside through the sieve. Remove any existing air bubbles by
Wet milling of enamels requires to focus on the fineness of grinding and to strive for gentle knocking and dislodge the sieve residue by agitation after which it drops into
an always stable grain structure. For testing the fineness of grinding, simple devices, the measuring tube, where the amount can be read on the graduation of the scale.
which are easy to attend, are available. For usual enamellings, adequate results are
obtainable. But one must be aware of too high expectations from these hand tests. The percentage of the coarse particles in the slip is calculated by a multiplication of the
Simple test equipment cannot be precise and has not been geared for that purpose.
read off units by factor 1.7. It would be absurd to calculate the percentage down to the
decimal point, because the sensitivity of this test is not that precise. It is just a typical
The PEMCO enamel test sieve proved itself in practice. It comprises the following handy check, suitable in the best manner for the shop.
items: Sieving funnel of transparent plastic with test sieves made of phosphor bronze
in a plastic screw base (different colours depending on the screen aperture):
- Measuring tube with scale and stopper PEMCO and Vibrantz developed test methods for the determination of the fineness of
- Funnel tube grinding, but with distinguished graduation figures. The existing relations between
- Measuring beaker of plastic (formerly brass) these two methods can be tabulated:

The screen aperture of test sieves is depending on the purpose of the slip. For Graduation on the devices of PEMCO and Vibrantz
dipping or spraying, black sieves of 100μm mesh aperture = 3600 mesh per cm , for 0.5 3.5
2
electrostatic applications, blue sieves of 75μm mesh aperture = 6400 mesh per cm
2
are in use. Aluminium enamels are even finer ground. Test white sieves of 40μm 1 5.5
2
mesh aperture = 16900 mesh per cm are essential. The sieves are standardized in 2 7.3
accordance with EN ISO 3310-1
3 8.7
Operating instructions 4 10.0

To check the fineness of grinding, fill the measuring beaker (12.5 ml) to the brim with The test method PEMCO requires a sample of 12.5 ml, whereas the test with the conical
the slip under test. Rinse the sample through the funnel tube onto the test sieve and Vibrantz test sieve needs 250 ml.
wash the slip through the test sieve. Best is to swing the sieving funnel in a container
1)
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
1) The widespread method to press the slip through the test sieve by means of a strong jet of water is test sieve which permits a test sieve residue of at least 3 scale graduations. Preferably
wrong. By this, the test sieve netting expands, so that the coarser particles are forced through. An use test sieves of 6400 to 10000 mesh instead of 3600 mesh test sieve. One can also
experienced checker will be able to measure almost any desired fineness of grinding.
use a laser particle size analyser to get a full grain size distribution.

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