One of mankind's earliest innovations, glass has been crafted for thousands of years dating back to ancient Mesopotamia and Egypt in 3000 BC. Initially glass was produced by happening upon naturally formed glass, called obsidian. Later discoveries allowed glass to be intentionally produced through controlled cooling of molten materials such as silica sand, soda ash, limestone and other minerals. The Phoenicians are credited with producing the first glass objects around 1500 BC and glass making slowly advanced throughout the Roman and medieval eras. Major developments in glass production emerged in the late 19th century with the advent of automated production processes and gas-fired furnaces.
Key Ingredients and Materials for Glass Manufacturing
At its most basic level, glass is composed of domestic sand or recycled flat glass. The key ingredients that allow the sand to fuse together when heated are sodium carbonate (soda ash), limestone, recycled glass cullet and other mineral additives. Soda ash lowers the melting point of silica sand allowing it to flow and form before cooling. Limestone adds durability and strength to the glass. Recycled glass, known as cullet, is a valuable resource that requires less heat to melt than raw materials and results in energy savings of up to 40%. Additional refining agents may be added to alter characteristics like thermal resistance, density or solar control. Metals are sometimes mixed in to create tinted, reflective or speciality glass.
Melting and Refining
The raw materials are carefully weighed and fed into large gas-fired furnaces capable of reaching temperatures over 2500°F. Here the materials are completely melted and blended homogeneously. Refining continues as gases bubble up through the molten glass to remove any impurities. The Glass Manufacturing is periodically sampled to check consistency and composition. Once fully melted and refined, the liquid glass reaches a workable viscosity around 2000°F and is ready for forming. Precise control of the melting process is crucial to producing high quality, defect-free glass sheets and containers.
Forming Flat or Container Glass
For flat glass, the molten glass flows from the furnace onto a floating bath of molten tin. Here it is annealed and flattened by its own weight into wide ribbons called 'fawns'. The fawns pass under rollers that control thickness and are cooled steadily on the tin bath. Once cooled and annealed they become strong, float glass sheets ready for cutting, toughening, coating or insulating processes.
Container glass forming uses alternative techniques. The molten glass may be blown or pressed into molds to shape bottles and jars. For blown glass, gatherers of molten glass are lifted from the furnace on blowpipes by skilled glassworkers who inflate and shape the glass before dropping it to an annealing lehr. For pressed glass, the molten glass is placed in block molds where it is pressed and blown into shape using air. Either way the formed pieces cool and anneal together in large furnaces.
Cutting, Edging, Drilling and Insulating
Flat glass sheets undergo further processing depending on the product. Cutting uses computer controlled high pressure waterjets or diamond tipped saws. Edging machines apply a pyrolytic or chemical edge to the glass for safety and beauty. Advanced machines can drill, engrave, polish and apply coatings or films in an continuous process line. Specialised flat glass may include acoustic tiles, fire rated glass, solar control low-E glass, bullet proof and laminated or insulated glass using polymeric interlayers.
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