Understanding Flat (Float) Glass Production – Bishop Ltd

There are two types of glass manufacturing, blown glass (by hand or machine) or flat (float) glass; we will be talking about the latter below.

Glass is a rigid material which may be either transparent or translucent and, unless a process is applied, brittle in nature. The machine required to produce flat glass was first designed by Sir Alistair Pilkington in 1952 and is now the standard method of making flat glass. The production line, from the furnace to flat glass, can be half a kilometer long and the machine can churn out 6,000 tons a week, amounting to a staggering 6,000 thousand kilometers of glass a year!

The Process

Flat glass is manufactured by the fusion of limestone, Silica Sand, Soda Ash, Dolomite, and Feldspar, using the steps below.

Step 1 – Smelting and Refining

By far one of the most important steps. It highly influences the overall quality of the glass produced. The furnace melts the glass at around 1400-1600°C to ensure it is refined and homogenized and the glass coming out onto the float bed is removed of any gas bubbles or insertions.

Step 2 – Float Batch

The spout pushes out the heated glass onto a layer of liquid molten tin. The molten glass sticks together and does not mix with the liquid molten tin, literally ‘floating’ on top. This, with a little help from gravity, creates a perfectly leveled contact surface (and a sheet of glass!). The thickness of the glass is controlled by the speed at which the molten glass is spread over the molten tin.

Step 3 – Coating

Coatings are applied to the glass according to the customer specifications. This is done at an area in the production line that uses advanced high temperature wielding robots to apply the coatings. Another way to add coatings to the floating glass is through a chemical vapor depositor (CVD), which can cover the liquid glass with a variety of coatings less than a micron in thickness as it passes beneath the applicator.

Step 4 – Annealing

This is to further ensure that the glass has no unwanted insertions or bubbles, which can occur if the glass was cooled unevenly. Along furnace cools the glass at varying temperatures best suited to keep the glass perfect. More recent technology includes a sensor to detect the stress level of the glass and in turn controls the temperatures of the furnace.

Step 5 - Inspection

Occasionally a grain of sand, tremor or a single bubble will create a lower quality sheet of glass. To prevent this, improved automated and highly sensitive technology is used to pick up these glitches. This automated inspection method can also control the cutters and take 100 million measurements a second across the ribbon of glass.

Step 6 – Cutting to Order

The final step is also controlled by a computer program. This is where the glass is cut to the client’s requirements. Any waste material produced is fed right back into the furnace as cullet.

Major Properties of Glasses:

•                 Transparency
•                 Strength
•                 Workability
•                 Transmittance
•                  U value
•                  Recycle property

Transparency

Transparency is the main property of glass, allowing us to see through it. Glass can be transparent from both sides or from one side only. In one side transparency, glass behaves like a mirror on the obscured side.

Strength

In general, glass is a brittle material but by adding admixtures and heat processes we can strengthen it.

Workability

Generally, you can find any type, size or shape of glass you need. Glass is very adaptable. However, some glass panes and units can be extremely heavy and there is always the greater risk of breaking the glass. Great care and attention need to be taken when handling a glass of any form.

Transmittance

Transmittance refers to the percentage of radiation that can go by throughout glazing, that being, visible transmittance, UV transmittance, or entire solar energy transmittance. With the advances in glazing technology, manufacturers can control how glazing materials behave in such instances. The basic underlying properties of the material (glass or plastic) can be altered, and coatings can be added to the surfaces. For example, a window optimized for daylighting and for reducing heat gain can be tinted on one side to reflect the sun’s rays, without losing visibility through the glass from the other side.

U value of Glass

The nationally recognized rating method is for the whole window, including glazing, frame, and spacers. U-factor of the center-of-glass is also sometimes referenced, and describes the performance of the glazing alone; note that the whole window U-factor reading is always more than the center-of-glass U-factor. High-performance double-pane windows can have U-factors of 0.30 or lower, while some triple-pane windows can attain U-factors as low as 0.15. The lower the U factor, the greater a window's resistance to heat flow and enhanced its insulating properties.

Recycle Property of Glass

All glass is 100% recyclable, therefore, causing less impact on the environment.