T h e r m o s e a l G r o u p L t d , G a v i n W a y , N e x u
s B u s i n e s s P o i n t , O f f H o l f o r d D r i v e , B i r
m i n g h a m , B 6 7 A FT e l 0 8 4 5 3 3 1 3 9 5 0 F a x 0 1 2 1
3 3 1 3 9 9 9 w w w . t h e r m o s e a l g r o u p . c o m
A large proportion of IG unit manufacturers in the UK are under
the illusion that if a desiccant is tested by a notified body (for
Moisture capacity) and the factory where the desiccant is
manufactured has a recognised quality system (i.e. ISO 9000) that
the desiccant is of a high quality.
7 Steps to selecting a quality desiccant
The primary role of a desiccant in the manufacture of a sealed
unit is to selectively adsorb moisture that isunavoidably trapped
within the unit during manufacture. The amount of moisture is
dependent upon the relative humidity at the time that the double
glazed unit is sealed and so it varies from unit to unit.
Throughout the lifetime of the unit moisture also passes through
the edge sealant where the two panes are fixed together. This is
referred to as the moisture vapour transition rate, or MVTR. The
desiccant also serves to adsorb this moisture throughout the
lifetime of the unit.
A GOOD QUALITY DESICCANT MUST HAVE THE FOLLOWING PROPERTIES TO
ENSURE THAT YOUR SEALED UNIT LASTS BEYOND ITS WARRANTY PERIOD:
1) PURE 3 ANGSTROM (3A)
3A desiccants are ideal for IG unit manufacture because the pore
size only allows for the selective adsorption of moisture water
vapour and not other gases trapped within the sealed unit.
Desiccant is available in different Angstrom sizes e.g. 3A, 4A and
10A beads sizes. Poor quality desiccant can be made up of a mixture
of Angstrom sizes which can all appear the same size to the naked
eye! Resultantly, poor quality desiccant will also adsorb gases
(e.g. Argon) from within the sealed unit airspace as apposed to
just moisture vapour. The desiccant will then cause premature
failure of the double glazed unit.
2) GOOD DELTA-T PERFORMANCE
An active desiccant generates heat upon contact with moisture.
The general rule of thumb is that the more active the sieve is, the
more heat it will generate.
A Delta-T test measures this temperature rise. To perform a
correct test, equal amounts of both desiccant and water should be
used in the test. Comparative tests between desiccants should be
carried out at the same temperature under the same conditions and
with the same quantities of water and desiccant.
A temperature rise of 25C or more indicates an active molecular
sieve.
Note: Molecular sieves can be manufactured to give extremely
good Delta-T test results when moisture capacity is actually very
low so that should be treated as an indicative test rather than a
conclusive test.
3) VERY LOW INITIAL MOISTURE CONTENT (LESS THAN 2%) A desiccant
needs to have a low initial moisture content of less than 2%. Some
poorer desiccants have been shown to have between 5% - 10% initial
moisture content (moisture content found on opening the sealed
storage container prior to production).
A desiccant is said to adsorb 1% of its capacity per year
depending upon the Moisture Vapour Transition Rate (MVTR) of the
sealant system. Therefore, a desiccant preloaded with 5 10%
moisture will have a reduced life span of approximately 5-10 years
within a unit.
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T h e r m o s e a l G r o u p L t d , G a v i n W a y , N e x u
s B u s i n e s s P o i n t , O f f H o l f o r d D r i v e , B i r
m i n g h a m , B 6 7 A FT e l 0 8 4 5 3 3 1 3 9 5 0 F a x 0 1 2 1
3 3 1 3 9 9 9 w w w . t h e r m o s e a l g r o u p . c o m
For further information contact Thermoseal Group Limited.Sales
Enquiries: 0845 331 3950 or [email protected]
THERMOSEAL GROUP LIMITED
4) MOISTURE ADSORPTION CAPACITY (MAC) - 16 TO 20%
A quality desiccant has the capacity to adsorb 18 24% moisture
at the point when it is sealed within a double glazed unit to
ensure that it is active enough to fulfil its role. Some of the
poorer desiccants have a lower total moisture capacity of around
12% @ 10% Relative Humidity.
A desiccant adsorbs moisture during frame manufacture and for
EN1279 purposes it is presumed that approximately 1% of its
capacity per year is used depending upon the MTVR of the sealant
system when it is sealed within a unit.
Example: A sample of a desiccant recently taken from an IG unit
manufacturer was tested for moisture capacity and gave the
following results: Initial Moisture Content - 5%; Moisture
Adsorption Capacity - 19% and Total Moisture Capacity of 14%. The
moisture content prior to sealing would be in this case 8-10%
leaving only 9% for the next ten or so years!
5) LOW DUST CONTENT
Poor quality desiccants have a very inconsistent bead size due
to excessive dusting or powdering (often ground down or crushed
during transport). This dust can block up desiccant filling
machines. It can also pass through spacer bar breather holes into
inside the sealed unit causing premature failure.
Many manufacturers do not separate the small broken beads
(called fines) using a filter system - they leave them in instead
of discarding them. This can account for as much as 20% of the bulk
contents of the desiccant.
6) VERY LOW GAS DESORPTION
Some cheaper low quality desiccants have very high gas
desorption qualities. This means that the desiccant beads will
adsorb inert gases if no water vapour is present. If the desiccant
adsorbs gas, then as moisture penetrates the unit the gas is given
up increasing the air volume which can cause deflection and
pressure on the edge seal. This is particularly important in
gas-filled units and may result in an in-balance of pressure within
the sealed unit and ultimately, deflection.
Gas Desorption Test: The test method for gas desorbtion is a
water displacement test carried out over 4 hours. Desiccant is
heated in a flask and any gas that is emitted displaces water into
another calibrated flask. The greater the quantity of water
displaced, the more gas that is desorbed by the desiccant.
Example: Various competitor samples tested displaced 110ml of
water in less than 1 hour. Eurosiv displaced 18ml in 4 hours! The
proposed industry standard is 50ml over 4 hours.
7) BULK DENSITY
Some of the cheaper, lower quality desiccants differ by up to
17% in terms of bulk density. This means that a product with higher
bulk density will not fill as many spacer bars because there is
less desiccant in the box (even though there is still 25kg). They
simply make the beads larger and heavier which results in fewer
beads per box!
Thermoseal Group Limited has its own testing facility for
insulated glass components, including Desiccant.Unlike all the
other distributors, Thermoseal Group tests all batches of desiccant
for: Delta-T temperature rise, Dusting, Moisture Capacity (Initial
and Total) and gas desorbtion.
Eurosiv is Thermoseal Groups own high quality desiccant and
complies with properties 1-7 as detailed in this document..
