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Influence of incorrect desiccant on IG unit–Molecular Sieve 4A

    Source:未知 Author:admin Release time:2016-01-09

What will happen if we use molecular sieve 4A as insulating glass desiccant?
1.    Influence IG’s lifespan:
Glass will be expanded, shrinked and even broken.
2.    Threaten IG’s safety:
If molecular sieve 4A desiccant is employed too much or glass is too thin or not tempered, glass may shatter suddenly, or the entire piece of glass falls down.
                              
     expanded glass         shrinked glass                                     broken glass

How could that happen?
As molecular sieve is a crystalized aluminosilicate with network, it has very uniform pore and its pore size is perfect for small molecules to go through. Due to different models and specifications, their pore sizes are also different. According to insulating glass desiccant's requirement, only water molecules can go through pores rather than other molecules in the air. Water molecule is 2.8 Å (1 micron = 10,000 angstrom), while nitrogen, oxygen, argon's molecules are about 4Å. Molecular sieve 4A desiccant’s pore size is about 4.3 Å, so molecular sieve 4A can absorb nitrogen and oxygen in the air. For the components in the air, besides water, molecular sieve 4A is more based to adsorb nitrogen with strong polar adsorption, it mainly detects the adsorbed nitrogen as molecular sieve’s air adsorption.
For molecular sieve 4A , its air adsorption volume is about 7ml per gram while 3A’s will be less than 0.5ml. The nitrogen adsorbed by molecular sieve 4A is very sensitive to tiny temperature changes in common conditions.
In IG processing, we usually fill molecular sieve desiccant at indoor temperature. If the molecular sieve is 4A type, when the temperature decreases, the molecular sieve will adsorb a lot of air in the IG spacer and result in lower air pressure in the glass; on the contrary, when the temperature rises, the molecular sieve desiccant will release a lot of adsorbed air, so the pressure in the glass will increase.
After IG unit with molecular sieve 4A desiccant sealed, with the changes in day and night, as well as in seasons, molecular sieve 4A will adsorb and release air like breath, so IG glass will bear inward and outward pressures continuously. These inward and outward pressures significantly reduce the lifespan of insulating glass, especially for hidden frame glass whose two pieces of glass only depend on sealant’s adhesive force, it has very limited sealing ability to inner pressure, the glass sealant can lose efficacy at any time. What’s more dangerous: If molecular sieve 4A desiccant is employed too much or glass is too thin or not tempered, glass may shatter suddenly, or the entire piece of glass falls down. 

How to know whether it contains molecular sieve 4A?
According to the theory that the air molecular sieve 4A adsorbed will release when heated. Below is a simple test.
Tight seal 100g desiccant into plastic bag or balloon, heating it in boiling water for ten minutes, if inflated obviously, it means the desiccant would be molecular sieve 4A.