Float Glass - An Overview

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Glass is being used more and more in modern architecture and can be found in many commercial and domestic products as well. Float glass has many practical applications, and as such float glass can be manufactured from the ranges of 0.4mm to 25mm, whereas when the process was first being used, the only thickness possible for float glass was 6mm.

Thirty countries are now licensed to use the float process, and plants can operate for between 10 to 15 years, producing an estimated 6000km of glass per year.

How is Float Glass Made?

Float glass is manufactured using a melt process whereby 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.
The process by which float glass is made is also called the Pilkington process, named after the glass manufacturer that pioneered the float glass production technique in 1952.

Tinted Float Glass

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

The following elements are added to produce the different colors:

  • Iron – green tints
  • Cobalt and iron – blue tints
  • Iron, cobalt, and selenium – bronze or grey tints

Reflective Glass

Reflective glasses are also available for applications where light transmittance is an important design factor. These glasses have a metallic coating applied during manufacture, and there are two different methods of producing it.

Pyrolytic Process

The semi-conducted metal oxide coating is applied during the float glass manufacture.

Magnetron Process

One or more metal oxide coatings are used in this process. They are applied in a vacuum on the inner sides of the panes of glass and are successful when used in double glazing.

It has a high visual appeal, and, as it reflects a higher amount of heat than conventional float glass, it is less susceptible to thermal breakages. Additionally, visibility is prevented when looking from the outside in, which enhances privacy for those inside the building.

Key Properties

The main properties that float glass possess include:

  • A high degree of light transmission
  • An ability to be produced in a range of colors
  • An ability to be produced in a variety of opacities
  • Good chemical inertness
  • Attacked by hydrofluoric (HF) acid.

Applications

There is a wide range of applications for float glass, that is still expanding today.

Building Industry

Float glass is used for smaller windows in residential 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, while at the same time letting in light.

Commercial Glazing

Float glass is becoming more and more popular in commercial applications. It allows structures to be constructed that give the impression of being outside with the benefits of being inside protected from the elements (except for 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 put on environmentally friendly practices in both the workplace and in domestic settings, it is critical to consider the materials used in construction for large commercial buildings. In this application, several design factors are involved apart from aesthetics. Factors such as light and heat transmittance can play a significant 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. This can have substantial effects on the environmental impact of a structure as well as its running costs.

Commercial 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 many 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.

Sources and Further Reading

This article was updated on 7th February, 2019.

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