Thermoseal Group has prepared a full document detailing the seven properties that a good quality desiccant must have to ensure that a sealed unit lasts beyond its warranty period.
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 recognized quality system (i.e. – ISO 9000) that the desiccant is of a high quality. Thermoseal Group advises that this is not necessarily so.
Throughout the life of a sealed unit moisture passes through the edge sealant where the two panes of glass are fixed together. This is referred to as the moisture vapour transmission rate, or MVTR. The desiccant serves to adsorb this moisture throughout the lifetime of the unit so its quality is vital.
Problems in the quality of desiccant can be due to various factors including: its original manufacturing process; deterioration during transport, and ineffective storage methods. Often you cannot detect a quality issue by simply looking at the product, so quality-assurance testing is essential.
A good quality desiccant must have the following seven properties to ensure that a sealed unit lasts beyond its warranty period:
1) pure 3A Angstrom construction;
2) a Good Delta-T test performance;
3) very low initial moisture content (Less than 2%);
4) moisture adsorption capacity 16-20% @ 10% relative humidity;
5) low dust content;
6) very low gas desorption below 50ml water displacement;
7) an acceptable bulk density.
Thermoseal Group has prepared a full document detailing the above requirements in seven steps and detailing the tests required, which can be downloaded on the company website or requested by e-mail.
The Group also offers a desiccant testing service, or can supply a test kit so that sealed unit manufacturers can perform tests themselves.