Today, recycling of used glass has become something totally natural for us and used glass is a raw material normally used in industry. This is the case for round glass, i.e. bottles and glasses but also for other types of glass that are collected by recycling centers to be then shipped to valorization facilities.
All types of glass are not identical. While the only difference with round glass is color, flat glass is subdivided into various categories. In order to allow for a good quality recycling it is necessary to proceed to a separate collection of for instance car windows and other window glass.
How is flat glass produced ?
95% of all types of flat glass are nowadays produced by the « floating glass » procedure, a procedure which is already used at industry level since the sixties. Glass melted at 1100°C is transported to a liquid tin bath ; the lighter glass (for about 2/3) swims at the surface and regularly spreads to form an oil layer. The glass then solidifies in the coldest part of the bath with however a temperature of still about 600°C and is then progressively extracted.
What types of flat glass exists ?
Many categories of flat glass can be found in daily life.
- Window glass, glass for showcases, wardrobes and frames : « white » flat glass without any special treatment except for maybe a coating.
- Safety glass : it is tempered and will break into little pieces if damaged, which reduces the risk of getting injured.
- Compound glass : it is composed of at least 2 plates and an intermediary layer in plastic (plastic or resin foil). If tempered, the glass obtained is a compound security glass used for instance in front doors, showcases in museums and car windows.
- Mirrors : thanks to a special coating, glass can be made more or less reflective.
- Opaque glass (for instance for bathrooms) and armour-plate are generally produced in a continuous casting.
In opposition to screens with cathode tubes, flat screens are not made out of glass but out of plastic.
Valorization of flat glass
At the difference of bottle glass – new bottles are made out of old ones – it is not possible to directly recycle flat glass because of its heterogeneity. However, recycling of flat glass also allows saving raw materials and energy and should therefore be obvious in an economy characterized by long-term development.
Secondary material in flat glass is for instance used to produce isolation material. Glass wool may contain up to 70% of used glass. Such products carry the German environmental label « Blauer Engel ». Another isolation material produced out of used glass is cellular glass (« foam glass »). As a mineral substance, glass is also used as additive in construction. Contribute to recycling and make sure flat glass is shipped to a valorization facility. Flat glass is accepted by all recycling centers. Attention : Flat glass should not be dumped into glass and bottle collection containers.