Technical
Description of EN 1279 part 2
The
Standard
Scope
Definitions
Moisture
penetration index
Requirements
Climate
conditions in cabinet
Measurement of dew
point
Measurement of moisture
content
This section is designed to explain why some of the tests and procedures
have come about. It will also help in designing your insulating glass
units to meet the new requirements, which, while requiring management
time should not increase prdduction costs. If you currently make units
that do not meet the BS 5713 standard, or only just meet the requirements,
then a change of design will be inevitable. For the purposes of EN1279
the design includes sealant type, sealant depth, desiccant type (and amount)
and other parameters, which will be identified in the following text.
Details given in the following section appear in the same order as they
do in the standard.
Scope
This defines the products covered by the standard, i.e. standard insulating
glass units (IGUs). It
excludes structural glazing, exposed curtain walling, and products having
artistic value only. There is also a note stating that compliance with
Part 2 also requires knowledge and compliance with other parts of the
standard.
The clear meaning is that, unlike BS 5713, where meeting the type test
was the only
requirement, with EN1279 meeting the type test also requires having the
sealant tested to
Part 4, and having a factory production control system based on Part 6.
You will also have to submit a system description indicating the materials
used and the cutting tolerances of the glass, spacer inserts etc.
See
Part I of EN 1279
See Part 4 of EN 1279
See Part 6 of EN 1279
Definitions
The definitions in the standard are an attempt to make comparisons more
meaningful; the definitions also rnake understanding the standard less
liable to misinterpretation. The standard laboratory condition is defined
precisely, and requires a properly equipped laboratory to maintain such
conditions.
Similarly the standard moisture absorption capacity of a desiccant is
a defined measure that will allow comparison without using manufacturer's
data. This is not an attack on the desiccant manufacturers, but an attempt
to allow users to compare information, and thus make decisions based on
fact rather than suggestion.
Moisture penetration
index
This index is a measure of the integrity of the insulating glass unit
edge seal. It defines how
much moisture enters the IGU during the test, and is therefore a measure
of the moisture penetration properties and adhesion of the edge seal.
The older Dew Point test has a limited valwe and does not indicate the
rate at which water is entering the IGU. Failure by dew point measurement
usually indicates a catastrophic failure or a poorly manufactured unit.
Requirements
The Moisture Penetration lndex (MPl) is quoted as O.20 average, with the
worst lGU having an MPl of O.25. Thus the requirement is that on average
only 20% of the available capacity is consumed during the test. It also
means that all IGUs within a batch must be made to the same standard.
Thus if the desiccant is incorrectly stored or used, or the time the filled
frames are left before unit assembly is too long, then the units can fail
part 2 even when o good quality sealant is used, It is also worth noting
that as the test has a degree of inter-laboratory variation, producing
units to just meet the standard could lead to failure at the official
test house.
Specialist opinion is that the assembled spacer bar should be used within
2 to 3 hours, and the desiccant should have a minimum temperature rise
of 30°C. Whatever limits are set in the factory, it is the management's
responsibility to ensure that the IGUs can meet the standard under the
worst-case scenario.
The MPI also differentiates between IGUs, which is better than having
a weak pass/fail system. As a consequence of the increased use of molecular
sieve desiccants to produce higher performing IGU's, the results meant
that most met the requirements of BS 5713 even when the units were poorly
made. Thus there was the perception, borne out in reality, that units
claiming to meet BS 5713 were of variable quality from very good to poor.
The new standard will still allow variations, but the worst acceptable
units should still give a reasonable service life. It is noted in the
standard that comparison of results is not feasible unless you are qualified
to interpret the data.
Climate conditions
in cabinet
These are accurately defined and, unlike the old BS 5713 where the units
are only cycled between moderate ambient temperatures, EN 1279 measures
the real temperature of the cabinets and the IGUs being tested, and hence
the stress imposed on those IGUs. Thus a poorly bonded sealant will rapidly
fail.
The thermal cycle always starts with the cooling phase. This tests the
IGU production where faults could be concealed, which could happen if
the heating phase occurs first. The theory here is that if the sealant
is relying on physical contact for the bond, and the IGU has been incorrectly
made, having the heating phase first could soften the sealant and repair
the bond. In reality most IGUs are fitted during the day and are subjected
to a cooling phase overnight.
It is also noticeable that the rate of heating and cooling is defined
very precisely, as is the tolerance of the IGU temperatures. This close
control is designed to prevent artificial cold cracking for higher modulus
sealants, and also ensures all IGUs are tested under identical conditions.
Following the thermal cycling phase of the test, the units are subject
to a constant high temperature/high humidity phase (heat soaking).
The reason for the above is that although a number of standards existed
with high humidity/thermal cycling as part of the test regime, they all
gave different results due to lack of accurate controls.
Description of lnsulating Glass Unit for test purposes
The IGUs are defined as being 502+/-2mm x 35+/-2mm in size, and being
constructed of 2 panes of 4mm clear float glass with a 12mm cavity. If
you do not manufacture a 12mm cavity unit, the nearest size to that is
taken. Therefore those manufacturers who only manufacture 18/20mm cavity
IGUs would have them tested 'as made', rather than purchase 12mm spacer
especially for test purposes. For Part 2 it is normal to only use ordinary
air filled units, but if you only manufacture gas filled units these can
be submitted. The intention is to use as closely as possible products
representing actual manufacture, and not an artificial construction.
The size and shape also yields a test unit having high stresses at the
corners, and thus the type test is indicative of the IGUs ability to withstand
seasonal and diurnal thermal changes. Remember that the standard is for
IGUs to be used anywhere in Europe, and they must demonstrate performance
capabilities for cold as well as hot climates.
You will have noted in Part 1 that a system description is required. This
will define the type of spacer you use and the quantity of desiccant,
among other details. The test units must conform to this description,
The system description will also contain details of spacer return, sealant
depth and PIB width. Your defined tolerances form part of your specification.
If you produce a description with wide tolerances, you will be required
to show that IGUs at both extremes are capable of passing Part 2.
Your system description will also detail acceptable/unacceptable criteria
for butyl application, glass condition, bubbles in sealants and quality
of mix with two part systems, plus any other quality consideration. You
are advised in the standard to stipulate the basic glass product standards
for visual quality, and not claim 'defect free' as this will require all
units to meet your description.
See Part I EN 1279
Fifteen units are made for the test; and all of them must have a dew point
of within 10°K of your anticipated maximum. If the desiccant used
is molecular sieve and sufficient is used, then the anticipated dew point
should be below -60°C. Note here that anything below -60degC is counted
as being the same. The manufacturer is strongly advised that a minimum
of two long sides is filled for 12mm cavity units, and all 4 sides filled
for smaller cavities. You will also note in Part 6 there is a requlrement
for the desiccant to have no more than 3% water. It will not be acceptable
to use the desiccant manufacturer's assurance that a temperature rise
of 25 or 30°C meets the requirements unless they can show that it
relates to 3% or less water content. Consequently there is also an emphasis
on the way the desiccant is stored and used prior to unit assembly.
See Part 6 of EN 1279
Measurement of
dew point
The method described is very specific and requires the correct piece of
apparatus. However, for those who have measured dew points for BS 5713
qualification purposes, then providing that your method of test can be
verified against the standard, you will be able to confinue using your
current method. Those manufacturers wanting to carry out dew point tests
for the first time should obtain or make a test piece as defined.
It is permissible to reduce the temperature to -60°C rapidly and hold
for 3 minutes where sufficient desiccant is used to ensure the dew point
is below that level. If however a dew point is observed, then the lGU
will have to be stored for 24 hours and the dew point measured as defined.
This is a slow process, and the time spent carrying it out could far outweigh
the cost of using a good quality and quantity of desiccant.
In Part 2 the dew point is only used to grade the IGU's for further tests,
and is not in itself part of the standard, unless the partial pressure
method for determining water contents is used. The dew point ranking could
have an effect on the results if there is a wide variation; however the
variation is limited (see above).
Measurement of
moisture content
The first point that needs to be mentioned is that values for moisture
content cannot be mixed, and, with the exception of the final result,
they cannot be compared.
There are three methods used for measuring moisture content. The first,
which will be most commonly used, is the drying at 950°C method, whereby
the desiccant taken from the IGUs is totally desiccated.
This will give results for water content which is different from pubiished
data, as the technique also removes water not normally considered part
of the drying matrix. At temperatures of 950°C the desiccant is also
rendered inactive. When the method is used correctly the values of moisture
content are reproducible for that product. Where desiccants have been
bulked up for commercial reasons using inert filler, the method for determining
water content is more complex, and extreme care is required in the interpretation
of results. In this test the entire desiccant is used from the IGU, and
therefore any variation around the edge due to variable airflow, or a
corner break down, is eliminated.
The second deals with the moisture content of desiccant incorporated in
an organic spacer, which is more complex than high temperature drying,
and can only be carried out by laboratory personnel. It is called the
Karl Fischer method. In this method the temperature at which the water
Is removed is lower, to prevent the organic matrix thermally decomposing.
However the test takes longer than for desiccant in a spacer, and this
may be reflected in the test price.
In the Karl Fischer method the water is removed by passing a dry nitrogen
stream over thee sealant sample that has been heated to 200°C. The
water is chemically absorbed by the Karl Fischer reagent and then back-titrated,
using a well established technique for determining water presence in a
sample. By calculating the weight of water present and knowing the weight
of the sample of sealant, the water content of the desiccant can be computed.
The final method is the measurement of partial vapour pressures in units
without desiccant. Such units usually have a non-polymeric seal normally
of soldered metal. Although the calculations are given in the standard,
uniess you are used to calculating partial pressures it is better to let
the test laboratory carry it out.
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