EPISODE 6: All the ways to process the glass edge

Sarah: Hi and welcome back to Listen LiSEC, the podcast about all aspects of glass processing. My name is Sarah Hummelsberger, I am part of the LiSEC Marketing team, and my co-host and discussion partner is Harald.

Harald: Hello, I’m Harald Miksch and I’m a product manager here at LiSEC.

Sarah: Our podcast studio is located at our production site in Lower Austria and situated right inside the Training Center. So you might hear moving machines that process glass in the background. So far, we’ve covered a number of ways to process glass: cutting jumbos into panes, laminating them, and building IG units with them. But when our colleagues talk about glass processing, they don’t mean any of these processes.

Harald: You’re right! They mostly talk about edge processing, sometimes about drilling and in rare cases about waterjet cutting.

Sarah: Then let’s start with the most frequent one. What’s so special about glass edges that there are machines that do nothing else but process them?

Harald: What’s interesting about glass edges is that they are the weakest point of the glass, they can be sharp and dangerous, they can be slightly off measure, and the right kind of processing can add value to the whole product.

Sarah: Can you give me an example of added value through a processed edge?

Harald: Just imagine a glass door. The edge of the door is smooth and even – it’s usually either ground or polished, which is the highest form of edge processing quality. But that’s not necessary for every type of flat glass product. In many cases, the edges aren’t even visible – they are hidden by window frames, for example.

Sarah: So in those cases, edge processing is not necessary?

Harald: Quite the opposite! The primary reason why we process the edge of the glass pane is actually safety and stability. You need to consider that the edge is the weakest point of the flat glass pane because of the way glass is scored and broken. This process leaves micro-cracks and imperfections like chips. When there’s vibrations during transport, or if the sun shines on it, the stress makes cracks spread across the entire surface.

Sarah: That sounds quite dangerous! How can edge processing prevent this?

Harald: Well, edge seaming removes these imperfections by slightly bevelling the edges, thereby reducing the concentration of stress at these points. This not only makes the glass safer to handle but also significantly increases its resistance to cracking and breaking. This kind of edge processing is a crucial step in ensuring the durability and longevity of glass items in their various applications.

Sarah: That’s cool. So seaming is necessary for safety. What about the other two processes you mentioned: Grinding and polishing. Are those done purely for aesthetic purposes?

Harald: Mainly yes. The difference between the two is the level of quality, and the time needed. For a high-quality polished edge, you need multiple cycles with progressively finer tools.

Sarah: So now that we’ve established the outcome, let’s look into the process. What kind of tools are used for this?

Harald: Mostly rotating tools with abrasive diamond surfaces, which gently remove material from the edge of the glass. Depending on the coarseness of the tool, more or less material is being removed, hence the surface becomes shiny or dull.

Sarah: And how does this process look on the machine? I suppose it’s not done with a handheld sander?

Harald: It would work this way! But nowadays the lion’s share of edge processing is done on a fully automated machine, mostly even included in a line configuration. The glass leaves the cutting table with sharp edges, gets tilted into an upright position and moves into the processing machine on rollers or belts. In the machine, the glass is gripped by suction cups – can you guess why?

Sarah: I suppose the suction cups keep the glass still, because otherwise the drilling tool would cause too much vibration?

Harald: Quite right! The suction cups also ensure that glass is moving at a precisely measured speed, no matter how pressure is being applied by the tool. And as you said, the suction cups keep the glass pane still while the tool is moving up and down to process the leading and trailing edge. Conversely, to process the top and bottom edge, the tool stays stationary while the glass moves forwards and backwards.

Sarah: So now I understand how the glass door gets its shiny edge. But a door also needs hinges and a lock, which require holes and cut-outs. Can the machine handle this as well?

Harald: There are machines that can do both edge and inside process! But with that configuration, you sacrifice speed for space. Edge polishing can take up to several minutes, but so can drilling and milling process. If you split the process between two dedicated machines, you can double the throughput. With one machine doing both processes, the entire process takes twice as long, but you only need half the space on your shopfloor. And you need a seriously sophisticated machine.

Sarah: In what way?

Harald: For a fully automated machine without manual tool changes, you would easily need 40 tools and more to cover the whole range of edge and inside processings. Inside processes require very different tools from edge processes. We’re talking drilling, milling, countersinking.

Sarah: Which one of those do I need for the mickey mouse cut out for the door hinge?

Harald: Mickey mouse cut outs start from the edge, which might make you think they could be edge processing, but they go into the glass – the one thing that all inside processings have in common. Although it’s a complicated shape, you only need one, the milling tool. But for your door lock, you need a hole, which means first drilling into the glass and then enlarging the hole with a milling tool. If you want to put a screw into the door for some reason, you’d countersink the hole to make sure that the glass and the top of the screw are level. If these cutouts were supposed to be visible, you would also grind or even polish the edges. Or you can use a waterjet to cut them in the first place – then you don’t need to polish them.

Sarah: Waterjet sounds quite different from the other tools you mentioned. That’s probably not a standard feature in processing machines?

Harald: You’re right, vertical waterjet cutting is actually quite challenging. The waterjet does not as the name implies cut with a jet of water, but with sand particles mixed into the water. And right after cutting the glass, you have the next challenge: the waterjet needs to be decelerated, because it still carries a lot of pressure, and collected. The wastewater needs to be purified, because the sand can only be used once, but the water can be recycled.

Sarah: Water is my cue – I suppose water is needed at many points during edge processing, and probably ends up contaminated with a lot of glass dust. Can that be reused as well?

Harald: The water consumption is relevant for all types of processing because it plays a major role in cooling the tools and the glass. You can imagine that these machines use vast amounts of water, which can be an issue especially in arid areas and is a topic whenever sustainability is considered. Therefore, modern processing centres include water treatment solutions. They work by adding a flocculant which surrounds the dirt particles, making them easy to sieve from the water and collect. This way, the water can be reused while the dust and dirt can be disposed of appropriately.

Sarah: That’s good to know! Are there any other sustainability measures in development?

Harald: Of course! One of them is choosing abrasives with lower environmental impacts for grinding and polishing processes. Some abrasives are more easily recycled or have a lower manufacturing impact.

Sarah: Well, thank you for that journey into edge and inside processing! I feel after cutting, IG production, lamination, logistics and processing, we’ve now touched upon most of the important areas and processes in a glass factory.

Harald: Then next time, let’s consider the thing that pulls it all together: Software solutions.

Sarah: I’m really looking forward to it. Thank you for today!

Harald: Thanks for having me.

Sarah: And thank you to our listeners for staying curious.