RSSV 4 2013.indd - Stazione Sperimentale del Vetro

4-2013
studies
studi
Rivista della Stazione Sperimentale del Vetro
5. Can edge-coating removal cause any problem?
Since very high “I” and “Li” values were reported
in some cases, it was necessary to check if this was
only due to the warm-edge spacer. To investigate
this, we have tested samples with warm edge and
with aluminium spacer both with removed L.E.
glass produced in the same time in different factories.
“Butterfly tests” are carried out on a regular basis
by these manufacturers and the edge-coating removal
turned out to be always effective, because of
the good adhesion between the glass and the sealant.
The test outcomes showed that, for at least 10 producer
over 20, I and Li values were very high even
with aluminum spacers for manufacturers whose I
values had always been close to 5% for at least 10
years and Li values between 0.5 and 0.8 for I.T.T.
Some samples fitting both warm-edge spacers and
aluminum spacers with low-emission glass showed
a permanent glazing unit deformation along the
sealed edge of the low-emission sheet, after the ageing
cycle. Figures 7 and 8 show the double glazing
with a composition of 4/15/4 mm (with an expected
overall thickness of about 23 mm).
Figures 7. 8. Sealant deformation on an IGU:
with warm-edge spacer; with aluminum spacer
By way of example, table 2 shows the thickness after
ageing of a standard IGU measured on the corners
and at the center of the sides. A difference in thickness
between the minimum and the maximum value
is pointed out, in the order of 2 mm. Although the
external sealant does not lose adhesion to the glass
surface, it has undergone a permanent deformation
on the low-emission glazing side.
Comparing these values with those of another glazing
unit in table 3 and figure 9 , it can be noticed that
in this case deformation occurred to a greater degree
in corner No. 4, and not at the center as in the previous
example.
It is necessary to analyze more thoroughly the interaction
between the external sealant, the type of
grinder and the coating removal process.
It is necessary to point out that the phenomenon:
- occurred with different grinder types and edgecoating
removal methods;
- does not depend on the type of low-emission
glazing;
- does not develop evenly on all sealant materials.
Conclusions
Our findings have proved that the outcomes of gas
leakage tests with “rigid” warm-edge spacers improved
with time. This is due to a greater knowledge
of the critical issues and to the changes in the usage
of this material. The penetration index tests, instead,
have not highlighted significant improvements yet, to
reach the low level we had with traditional materials.
Although the results of our tests on “flexible” warmedge
spacers were not reported herein, at present
only one tested glazing unit over five passes the gas
leakage (Li %) test (that is 20% success).
The edge-coating removal process, which is now
carried out on nearly all double glazing units, has
proved to be a high risk factor to successfully pass
the tests.
Unfortunately, EN 1279/2 and 1279/3 allows system
validation for CE by testing glazing units with
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