The Float Glass Laws of Demand and Supply
Christoph Dichmann and Elissa Brunato
How can the industry of float glass maintain continuous production?
Float glass is created in the process of melting down sand together with a few other ingredients in a sort of gigantic furnace, equivalent to two swimming pools full of liquid glass. From this furnace the glass is poured onto a bath of hot liquid tin. This all happens within a controlled atmosphere. The molten glass slowly cools down on top of the layer of tin until it’s ready to be lifted off as sheet material by robots. Working with such high temperatures, the material is sensitive to changing temperatures, so the production line relies on consistency in temperature and a steady input of raw material to feed the furnace and maintain a continuous pouring velocity. This whole operation is a constant flow, a constant process of input and output over around a 400 metre line—and it’s like a mesmerising, untamed wild dragon.
In the 1960s, this was a revolutionary process as it enabled glass to be produced flat and smooth without having to be polished at the end. At the same time, stopping this process would be extremely wasteful. Turning it off and back on would waste a production length of material. That’s why these machines run for 15 to 20 years, continuously. Therefore, companies need to ensure supplies of silica sand and other raw materials.
There is a rule of thumb in the glass industry that estimates that 15 million people create enough demand to consume one float glass line. In the UK, there are currently three float glass lines. In the float glass industry, the globe is mapped roughly according to this rule and the Pilkington process, which we described earlier, was adopted all over the world because of its effectiveness compared with other technologies.
How does the float glass industry react to changing geographies and economies?
Urban geographies change continuously but the float glass production can only react within 15 to 20 years. Once a machine is built, the demand needs to cover for 15 years worth of material going out. The decision where to place production lines depends on projections of growth of populations and building booms.
Building booms in developing economies are benefitting from the fact that the patent for the popular Pilkington technique has run out and the technology can be applied more or less freely. Today, about half the float glass lines are found in China because of a building boom and because modern architecture, which commonly relies on glass as a building material, is understood as a way of developing economies out of poverty.
It’s expensive to globally trade glass. Productions are generally intended to take place within a certain radius of a source of silica sand and an economically booming area. The float glass plant will be somewhere in the middle. It’s a heavy material to transport.
How does the float glass industry need to be regulated in the future?
Sand glass for glass production needs to have specific characteristics. It’s not the sand you find on a beach like the sand used for concrete. Sand used for glass production is typically from ancient shorelines that have existed for millions of years. Geographically, these are places with formerly subtropical or tropical climates from 50 to 100 million years ago. The particles of sand are of a precise size range, which is naturally organised by the movement of water along these ancient shorelines, and the sand has a high silica content, which makes it snow-like in appearance. For the production of float glass, these two characteristics are extremely important.
Humans tend to take what’s readily available. That’s the cheapest way to attain these materials. But what our research has been uncovering is that there are also a lot of ecological mechanisms that sand plays a role in. This is why we need more regulation around the extraction of silica sand. Maybe then, sand has to come from secondary sources which would make it more expensive but it would not destroy those ancient ecosystems.
Sand provides a habitat for countless species. It acts as a filter to the groundwater and is intimately linked with the groundwater table. Sand and water really go hand-in-hand. It protects from erosion and acts as a natural barrier. So in contrast to, for example, petroleum, we should not see sand as a dead material.
In the course of our research, we spoke to ecologist Dr. Aurora Torres and Louise Gallagher from the UN environmental programme trying to define regulations which could work in this context. Existing regulations around mining, like the mining code, refer to other processes of extraction. Sand is often overlooked and it’s not part of such regulations, yet. But while regulations are important, it’s also relevant to understand the extraction of sand on a case to case basis.
Regulations are not only needed in relation to mining but also considering the recycling of glass.It’s not just about whether we should recycle but we need to understand why it is important. When we’re talking about recycling glass, in this case, we’re not talking about container glass where that cycle is quite quick. We’re talking about glass that goes onto a building for 50 to 100 years. The quality of glass made when a building was constructed may be different to the quality standards when that building is demolished. Recycling glass without knowing what actually went into it and putting it into a new production line 100 years later is difficult, risky even. It might mess up a whole batch of material in an endless production line. So manufacturers are very cautious of the material going back into the furnace.
There needs to be more regulation on what is built, too. Architects need to start considering applications of glass in a sustainable, maybe by incorporating modular building building units of glass that can be interchangeable between buildings. Glass can be infinitely recyclable but if it’s mixed with metal or rubble from demolished buildings the cycle is short. Generally speaking, we need a more holistic understanding of the effects of producing and using float glass.