EPISODE 3: Past, present and future of insulating glass

Sarah: Hello and welcome back to the Listen LiSEC podcast, where we discuss everything to do with glass processing! My name is Sarah Hummelsberger, I am a part of the LiSEC Marketing team, and my expert and discussion partner is Harald.

Harald: Hi everyone, glad to be here. My name is Harald Miksch, and I work as a product manager here at LiSEC.

Sarah: We are recording at our production site in Lower Austria, and around our recording studio, customers are trained to use our machines – so there might be some background noise. Today, we will be talking about some of the very machines you hear, because we will discuss how insulating glass is made.

Harald: IG glass is all around us – most moderns windows use a type of IG unit. There’s a wide range of combinations, but the simplest is glass pane – spacer – glass pane. This goes back hundreds of years. Most know the box windows on old farmhouses, where the space in between the glass is wide enough for a geranium and a cat.

Sarah: So why do we do this? What’s the main advantage?

Harald: Historically, the main reason was thermal insulation. The glass lets the light in but does not insulate. Air insulates better than glass and helps to keep the heat in and the cold out. Based on this principle, in the 1930ies French and American companies built units of glass with a dedicated spacer material. The energy crisis in the 1970ies pulled this technology into the spotlight. New regulations required new buildings to meet standards for energy efficiency when it comes to heating and cooling. Since then, major technological advancements have been made to improve the production and the insulation capabilities.

Sarah: Fascinating. Is the thermal insulation the only advantage of this technology?

Harald: It’s surely the most important, but not the only one. Another major function IG units are known for are their capabilities in sound insulation.

Sarah: How does that work – do glass and air insulate well against sound?

Harald: To a certain degree, yes! Sound waves pass through glass with different thicknesses in different waves. That means, using different thicknesses of glass in an IG unit filters sound waves. However, very often laminated glass is used in IG units which contains a foil that absorbs sound waves. Another way to add function to an IG glass is to use coated glass, which can filter ultra-violet or infrared light. This helps to protect interiors from deterioration due to sunlight.

Sarah: So, there are a lot of options depending on the glass panes used in the IG element – what about the spacer in between? Or the air pocket?

Harald: Glad you asked! If we consider a box window, there is no actual spacer material – the walls of the house create the space, which was filled with air. The technological advancements throughout the last decades led to dedicated spacer materials, such aluminium frames, or thermoplastic spacers. These spacer materials have different capabilities when it comes to insulation, and different production requirements. But the actual insulation happens through the chamber that’s created between the panes, which is nowadays filled with Argon or Krypton gas.

Sarah: Those are all amazing capabilities! How can I make sure my window keeps these properties over its whole lifetime?

Harald: That’s the question of questions. It is fairly easy to create insulating glass, but it’s very hard to keep them insulating for a long time. There are mainly two components that ensure long-term gas-tightness: the Butyl cord along the frame which glues the frame to the glass, and the sealing material that fills up the outer space between the spacer material and the edge of the glass. The sealing material not only adds air or gas tightness but also increases the stability of the entire IG unit.

Sarah: How can I check if my windows are still airtight, so still working?

Harald: It’s not easy to see until the deterioration has gone very far. Once you see condensation on the inside of your IG units, in between the glass panes, that means air has penetrated the sealing. The insulating gas has probably leaked at that point, and the insulation is a lot weaker. Another indicator of deterioration is state of the spacer material itself: when the butyl glue weakens, the material protrudes into the visible part of the window due to the pressure conditions inside the unit.

Sarah: So how does the production process ensure that most IG windows stay intact? What are the main steps to produce perfect IG units?

Harald: In our previous episode, we already discussed how glass is cut. So, let’s start the process from the cut and pre-processed glass pane. Once they are loaded on the IG line in the right sequence, the first step is to wash them, because if there is any contamination on the glass, it will stay inside the IG unit forever. After getting completely dried using a technology an air knife, the spacer can be applied.

Sarah: Spacer is an umbrella term, right? Can you tell us a bit more about the different types and their advantages?

Harald: Sure! On the one hand, there are rigid spacers. They have been on the scene for a long time, and they will still be relevant for years to come. Material-wise, they are comparably cost efficient, but they require a separate production sequence. They need to be bent, filled with desiccant and the butyl cord needs to be applied. Only then, the frame is ready to be put onto the glass.

Harald: A more recently developed alternative to rigid spacers is flexible spacers. In the 1980ies, Superspacers were introduced. They are made from a non-metallic foam with an integrated desiccant and applied directly to the glass pane from large rolls of material. In the 1990ies, another alternative became widely available: Thermoplastic spacers, a highly viscous polymer that’s applied to the glass via nozzle.

Sarah: So, all those spacers have at least one point where two ends are joint. Is this not a weak point of the spacer?

Harald: Yes, it is! A lot of research went into finding a solution for this problem. The material which offers the best solution is the thermoplastic spacer, which can simply be pressed into one infinite loop. Superspacers are cut in a 45° angle, so the beginning and the end fit perfectly together. The joint is reinforced by insulating tape on the outside. Rigid frames use plug connectors, which are still manually applied.

Sarah: So, now the frame is on the glass, what’s the next step?

Harald: The next step is to press the glasses and the frame together and fill them with gas, which happens – surprise – in the gas filling press.

Sarah: But if the frame is already closed, how do you make sure the complete unit is filled with gas?

Harald: It’s a matter of sequence! The press itself provides an airtight chamber, which is filled completely with gas before the unit is closed. That means up to the height of the glass there is no air anymore within the press.

Sarah: Is this not wasteful?

Harald: Not really, though it depends on the machine. Modern machines decrease the width of the chamber to the dimensions of the IG unit so that only the amount of gas needed to fill the unit is used. Since the gas is heavier than air, the chamber fills from the bottom, like an aquarium. As a side note, this has been the process for a two-pane unit. These steps can be repeated to create a unit with three or even more panes.

Sarah: But this is not the final step to ensure gas tightness – there is still something missing, right?

Harald: Indeed. Right after the press the space between frame and glass edge is filled with a sealing material. This material not only supports the gas tightness, but it also provides stability to the whole unit. There are numerous different sealing materials used in that step. Some of them require two components, while others, like Hotmelt, consist of only one component.

Sarah: And since we checked the quality of the glass panes at the start of the process, I suppose there’s another check at the end?

Harald: There is supposed to be! Quality regulations require periodic tests by a quality engineer who verifies the sealing, the butyl, even the gas filling. Some of these tests can be automated using scanner technology at the end of the line.

Sarah: So, this is the final step?

Harald: No, wait! You need to unload the panes.

Sarah: And this is a noteworthy process step?

Harald: It sure is! This is the moment where you see if production sequence has been planned correctly. The IG elements are placed on a rack, and each unit must be smaller than the preceding unit. Otherwise, you will not be able to stack them in front of each other! Sometimes, the IG units are unloaded onto more than one rack, which increases the complexity.

Sarah: So now, I’ve got my IG units, ready to be installed in my house, or even say, in my shop front.

Harald: Wait a moment! If you want to install an IG unit in a shop window, you should consider safety only provided by laminated glass.

Sarah: Fair point – but let’s discuss the details in our next episode.