Insulated glass unit (IGU), also known as Double glazed unit (DGU) consists of two glass panes separated by dry air with an aluminum spacer. IGU has been in use in many countries since 1960s, except in the middle-east and Asia, where they are recently becoming popular. Since they are known for their excellent sound and heat insulation properties, they have become an essential component in most green rated buildings.
An IGU, as mentioned above, is made of two glass panes, of which one could be a solar control glass and the other could be a normal clear glass or a thermal insulating glass (numerous combinations could be developed based on the requirement for each building). The two glass panes are held together by a spacer, made of aluminum, which also acts as a bed for the desiccant. The spacing could be of 6 mm, 12 mm or 16 mm. A desiccant is a drying agent and performs the role of absorbing the humidity inside the IGU. A Butyl sealant is applied between the aluminum spacer and glass panes, apart from this a secondary seal of Silicon or Poly-sulphide is also applied, which provides structural integrity to the unit. It has to be noted that the air gap inside the IGU can never be vacuum, but at times inert gases like Argon or Krypton is filled so as to increase the thermal insulating properties of the IGU.
Latest technology adapted by many leading processors involve the usage of CNC bending machines to bent the Aluminum spacers. This is followed by the filling of the desiccant in a filling station inside the IG processing unit. The drying agent is filled in such a way that it never makes contact with the outside air. This is followed by the joining process, when the channel is sealed at the joint using a straight joining key. There is also a practice of filling desiccant into a straight channel and then join the corners with a corner bending key, this would be a less recommended procedure as it could impact the humidity absorbing property inside the IGU and also it makes the IGU structurally weaker (This process is banned i many countries).
Finally, the bent and joined spacers are stuck to the first glass pane on one side using the primary Butyl sealant. This is followed by the attachment of the second glass pane, where proper care is taken to ensure that there is no low pressure or vacuum inside the IGU, which may lead to the weakening of it’s structural integrity. Once the hermetic seal is made, the secondary sealant is applied from the outside, which is usually made of silicon or poly-sulphide, this is what contributes mostly to the structural strength of the IGU. IGU made for structural glazing, since it is completely exposed to UV rays, it is a must to use silicon as a secondary sealant, as poly-sulphide sealants are susceptible to UV rays.
Major precautions to be taken while IGU assembly includes maintaining a de-humidified environment inside the processing unit, and preserving the secondary sealants in prescribed temperatures (secondary sealants start curing at 15 to 20 degree Celsius).
The applications and properties of IGU to be discussed in next posts.