EPISODE 4: Adding function to glass with lamination

Sarah: Hello! Welcome to the Listen LiSEC podcast, where we explore everything related to glass processing. My name is Sarah Hummelsberger, and I am a member of the LiSEC Marketing team. And the expert across from me is Harald.

Harald: Hello everyone, it’s great to be here. My name is Harald Miksch and I’m a product manager here at LiSEC.

Sarah: We are currently recording at our production site in Lower Austria, so maybe there may be some background noise from customers being trained to use our machines. Harald, today I must start with an anecdote. On my last holiday, I had an interesting experience with glass – I had to trust a pane of glass with my life.

Harald: Really, what happened?

Sarah: I was at the Dachstein glacier, and there they offer an attraction called Stairway to Nothingness, which is basically a platform with a glass floor suspended the foot of the wall, 400 meters or 1.300 feet in the air. And I wondered… what do you need to do with glass to make it so reliable?

Harald: Well, I don’t know for sure, but to me this sounds like laminated glass.

Sarah: So, what would have happened if the glass beneath had my feet cracked?

Harald: Not much! There would have been a nice spider web pattern, and you might have gotten a real fright – but the platform would have held. Whatever shock caused the first glass pane to break would have been absorbed by the foil, and the glass underneath it would remain intact.

Sarah: Phew. I’m not sure I would care to test that, though. Can you talk more about how this type of glass is made?

Harald: Sure! Let’s start at the basics: What is laminated glass? Basically, two or more glass sheets bonded together by a foil. This composition appears as one pane of glass, that’s why it seemed like only one thin glass sheet when you walked across it.

Sarah: That’s actually brilliant. Who had that idea first?

Harald: Like so many inventions, this solution was discovered by accident. A French man by the name of Edouard Benedictus dropped a glass flask filled with cellulose nitrate, which shattered by did not break into pieces. He realized that the plastic coating on the inside held the broken glass together, and boy did he patent it.

Sarah: So, when did that happen?

Harald: What do you think?

Sarah: I’d say around the time the float glass process was invented – so in the 50ies? 60ies?

Harald: Close miss, actually it was fifty years earlier, around 1900. It was not immediately commercially viable because you need flat, clean glass surfaces for a strong bond with the foil. The first widespread application was during World War I, where they used it as the eyepieces in gas masks and glasses for pilots.

Sarah: So, I suppose the applications diversified once float glass became available?

Harald: Definitely! Among the first adopters where car manufacturers, who use laminated glass for windshields. Today, laminated glass can be found almost everywhere: of course, in death-defying staircases, but also ordinary circumstances, like store fronts in urban areas, or glass facades on skyscrapers. Wherever you need safety and security.

Sarah: I would assume not only the applications changed, but the production process also evolved over time?

Harald: Of course, the industrial production of laminated glass nowadays requires a way more sophisticated approach. The assembly happens in a clean room – not to be confused with a cleaned room, but a temperature and climate controlled, hermetically sealed, pressurized room. There, glass, foil, and glass are put together into a sandwich—

Sarah: Is sandwich the technical term?

Harald: Funny enough, it actually is. Two glass panes are the minimum, but you can stack your sandwich up to around 10 centimetres or 4 inches high. This used to be a quite manual process, in the last decades those steps became more and more automated. Especially moving and positioning the glass panes required precision, because any misalignment of the panes is easily noticeable, for example if you run your hand along the edge of a staircase railing.

Sarah: You mentioned the positioning of the glass, what about the foil?

Harald: In many productions, this remains a manual step, but there are automation options available. Consider that these foils need to be handled with care – stretching or folding them would lead to bad lamination quality. Using a modern foil magazine can help to avoid that by storing a certain number of foil rolls above the assembly area. The foil is unwound over a chute and measured. Below, the unwound foil is clamped by the foil laying machine, cut at the correct length by a Cross Cut knife and positioned on the bottom glass pane. Then the carry over lifter picks up the next glass and positions it precisely on top. The last step of the assembly is trimming the foil around the edges of the glass, leaving a small overhang. This can be either done manually or by the foil trim cut, if the double-layer glass is rectangular.

Sarah: You said the edges need to be perfectly aligned for a good result – why the overhang of the foil?

Harald: Well, that’s because next the sandwich goes into the oven, where the applied heat slightly shrinks the foil. Without the overhang, there would be not lamination on the edges. There are quite a few things that need to be considered when the package goes through the oven – it’s a little more complicated than making a breakfast sandwich. Depending on the glass thickness and the type of foil used, the transport speed, application of heat and the temperature vary.

Sarah: How many ways to apply heat are there?

Harald: There are two technologies at play to heat up the package. The foil is heated using radiation that travels through the glass, while convection is used to heat up the glass itself. Only when the right temperature is reached, the glass and foil join evenly and reliably. Additionally, rollers apply force to squeeze out any air trapped in the sandwich and improve the lamination result.

Sarah: And that’s that, lamination achieved?

Harald: Not yet – everything we discussed so far can be summarized as pre-lamination. There’s a final step necessary to create a lasting laminate and to restore the transparency of the glass package. This happens in an autoclave, another big oven which applies not only heat but also pressure – 12 bars, to be exact. The autoclave is loaded with several packages of prelaminated glass and heated up to 140 °C for 2 to 6 hours. This causes the molecules of the foil and the glass to link together. Voila: laminated glass ready to be delivered and installed.

Sarah: So, what are typical installation sites? What can laminated glass be used for?

Harald: As mentioned earlier, the main applications are wherever safety and security are of paramount importance. This is especially true for skyscraper facades, where any falling splinter might harm or even kill people passing by. Laminated glass also provides protection against crime and vandalism in shop windows, especially jewellers. If the package is thick enough, it could even be bulletproof.

Sarah: Those are all exterior applications, does laminated glass also play a role in interior glazing?

Harald: Certainly! Obviously, it can be used in stairs and balustrades, but that’s also where the additional functions of the foil come into play. Laminated glass is used to soundproof studios and meeting rooms. Different colour foils can add a splash of design to doors, walls, and windows. One of the coolest applications is probably switchable glass, where the click of a button and the use of electricity render the glass either transparent or opaque. And of course, walkable glass is used for thrilling attractions.

Sarah: It seems we’ve come full circle. I wouldn’t have guessed how much went into my little Dachstein adventure. It’s been a fascinating discourse, and I look forward to our next episode, where we’ll talk about logistic.

Harald: That can be a real game changer in glass processing. Thanks again for having me.

Sarah: Thanks for your insights, and until next time.