Window & Door Glass Production
Standard Glass forms a foundation product that can later be processed to a higher-quality product, such as float- and ornament-glass, or bulletproof glass. Standard Glass can also be used in its unprocessed form, which finds common usage in building exteriors.
Manufacturing Float glass consisting of Limestone-Natrionsilicat is manufactured transparent or colored with a coplanar, fire polished surface, according to EN 572-2. The raw materials, consisting of 60% quartz-sand, 20% sodium carbonate and sulphate, as well as 20% limestone and dolomite are mixed and melted at a temperature of approx. 1600°C. After the outgassing of the liquid mixture, which is known as the purification, the glass mass cools down to approximately 1200°C in a cool-down-tank, before it flows down the lip-stone into a liquid-tin-bath. Because glass is lighter than tin, the still liquid mass then spreads out over the tin. The name “Float glass”, originates from the coplanar state the glass that is facing the tin exhibits towards the opposite site, which is continuously fuelled.
The float-process takes place in an inert-gas-atmosphere consisting of N2H2. This ensures that the thin won’t oxidase. Tin is ideal for this application, as there is no interfering vapor pressure up to the temperature at which the glass solidifies, whilst it is still heavier than glass at high temperatures.
A controlled and defined cool-down phase in the role-cool oven follows, in which the glass is cooled down from 600°C to 60°C. This defined cool-down process is vital for later process-ability, as it avoids stress inside the material. Only after this the 3,4m wide and infinite Glass strip, which has been created through this process, becomes visible. This is followed by quality-controls, the cutting of initially 6m long strips, sideboard removal, as well as the de-stacking of the then 3,21 x 6,00 m tableaus. From the input mixture to the de-stacking the floating-plats are approx. 500m in length.
The special feature of glass is that the molecules do not rearrange into crystals when cooling down, which still gives them the properties of a liquid despite its solidity. This is why glass is commonly described as an undercooled liquid.
The most widespread Float glass is clear glass. Special decolored glass (“white glass”) also exists however, as well as well as colored float glasses that are colored green, grey, blue, pink, or bronze in the glass mass. When creating the white glass, the quartz-sand is freed from the iron that naturally occurs inside of it. The iron is responsible for the slight green coloration of normal float. Because the iron is removed from the material, the green shimmer on the sides that float glass usually exhibits disappears, making the glass especially clear and color neutral.
Float- and ornament glasses are only used in small quantities as standard glass in direct applications. The majority is refined in further processing processes to make it suitable for the demands of modern, transparent construction.
Toughened Safety Glass
Toughened safety glass is known as thermally prestressed glass. This kind of glass has three defining characteristics: It features a flexural tensile strength that is five times higher than unstressed glass. This increases the strength of the glass facing pull or blunt forces. Additionally, the durability inside the panes facing frequent temperature changes, and high differences in temperature is substantially increased. If a toughened safety glass is overstressed and breaks, it disintegrates into a net of blunt-edged, loosely connected crumbs, which pose a far smaller risk of injury than the sharp-edged panes of glass that isn’t prestressed.
Basic material for the production of toughened safety glass is float- or ornament glass. Through the controlled and even heating of the tailored and processed basic glass to over 600°C and subsequent rapid cooling through cold air compressive stress is created on the glass surface, whilst further cooling increases tensile stress in the glass cross-section towards the centre line.
Insulating glass is the umbrella term for nearly all transparent exterior applications, in windows and doors, as well as facades of all kinds. The official definition of the term of “insulating glass”, which is determined according to EN 1279-1, goes as follows: “An insulating glass unit is an assembly consisting of at least two panes of glass separated by one or more spacers, hermetically sealed along the periphery, mechanically stable and durable.”
Situated in the room between the panes, called the glazing cavity, one can find a special heat-insulating noble gas or air – not a vacuum, as it is often erroneously assumed. A two-stage gluing-process is used today to produce the insulating glass. This involves laying a butyl chord on the two edges of a perforated Aluminum-spacer which corresponds in size to the pane-dimensions and is filled with drying agent. This inner seal prevents water vapor from entering and leakage of the noble gas.
The second close- and gluing stage takes place through filling up the emerging cavity between the indented spacer and outer edges of the pane with polysulfide or polyurethane. For specialised applications with an unprotected insulating glass edge a special UV-resistant silicone is applied instead. Insulating glass with an UV-resistant composite edge is usually filled with air, which constitutes a higher U-value.
An alternative to the standard Aluminum-spacer are stainless steel or plastic composite profiles. Plastics and stainless steel exhibit a decreased thermal conductivity than Aluminum. Additional options are thermoplastic spacers or spacers created from silicone foam with foil application. Functional insulating glass is defined by physical characteristics, such as thermal- and sound insulation, as well as sun-protection, which have to be met.