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Float Glass - Properties and Applications

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Float glass is manufactured using a melt process, where recycled glass, silica sand, lime, potash and soda are melted in a furnace and floated onto a bed of molten tin.

The molten mass solidifies slowly while flowing over the bed of molten tin, after which it is annealed to remove stresses induced during the cooling process. Annealing also allows the glass to reach a more stable state resulting in a higher density and higher refractive index.

Tinted float glasses are made by adding coloring agents during the melting process. Common colors include grey and bronze tints made from iron, cobalt and selenium, green tints made with iron, and blue tints made from cobalt and iron. While tinting may provide aesthetic alternatives to clear glass, tinted glasses also provide materials with different properties, including heat and light transmission (and/or reflectance), ultraviolet transmission and insulation properties.

Reflective glasses are also available for applications where light transmittance is an important design factor. These glasses have a metallic coating applied during manufacture through two different methods. Pyrolytic processes include using a semi-conducted metal oxide coating during manufacture, and magnetron processes use one or more metal oxide coatings. These coatings are applied in a vacuum in the inner sides of the glass panes.

Typical thicknesses range from 0.4 mm to 25 mm.

Key Properties of Float Glass:

  • High degree of light transmission
  • Ability to be produced in a range of colors
  • Ability to be produced in a range of opacities
  • Good chemical inertness
  • Attacked by hydrofluoric (HF) acid.

Applications

Building industry

Float glass is used for smaller windows in domestic housing, whereas larger windows are made from toughened glasses. Glass is used for windows for both aesthetic and functional purposes, allowing the occupants to see out and at the same time allowing light in.

Commercial Glazing

Float glass is becoming more and more popular in commercial applications. It allows structures to be constructed and gives the impression of being outside with the benefits of being inside protected from the elements (except the sun).

Glass is also playing an increasing role in buildings where it provides an attractive and easy to maintain exterior surface. It should be noted that most glass used for this application is subject to a post heat treatment toughening process before use.

In an era when a lot of attention is being shone on environmentally friendly practices in the workplace and in domestic settings, considering the materials used in construction for large commercial buildings is key.

In this application, several design factors are involved apart from aesthetics. Factors such as light and heat transmittance can play a big role in glass selection as they will influence the amount of heating and cooling that will be required inside a building according to the differences in seasons and climates. Having better control over heating and cooling in a building can have significant effects on the environmental and financial impact running a building can have.

Displays

Based on its transparency, hardness and ease of cleaning, glass is often used for display cases in retail outlets and countertops. However, many of these applications are being superseded by toughened glass due to its superior strength.

Summary

Float glass has several applications in modern architecture, both in commercial and domestic builds. But, with more advancements in float glass manufacturing such as ultra-thin float glass, new applications are being discovered in electronics and technology, for instance in TV, computer, and phone screens. There are also implications that further advancements in float glass production could lead to more sustainable or environmentally friendly builds.

This article was updated on the 26th June, 2019.

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