How Windscreens Are Made

We all have seen videos of auto production lines before. Men and women welding on parts, machines doing a lot of the heavy lifting, tyres being fitted and balanced, and cars rolling off the assembly line and onto the double decker transports. Still, some things remain a mystery. Like how a car windscreen is made. Here’s a step by step guide.

Materials: You can’t have a windscreen without a certain type of glass. Things like silica, sodium oxide, and calcium oxide are in glass. However, for your windscreen lime is added to the liquid batch to make the windscreen harder and more chemically durable. Other chemicals generally found in windscreens include potassium oxide, magnesium oxide, and aluminium oxide.

Manufacturing: Once you have all of your elements in place, the whole batch is melted down with water and a component of broken waste glass. Once the whole thing is molten then it’s introduced to something called the “float chamber.” This is a pretty big (4 to 8 meters wide and 60 meters long) really hot (1000 C) place. The glass floats through here on a conveyer belt. The high temps clean the glass of impurity and the surfaces of the chamber cause the glass to be flattened. As the windscreen exits the chamber the temp is reduced and this allows the glass to harden before it’s moved into a furnace. Inside the furnace any coatings are added and the glass is cooled to around 200 C. Once the glass sheet exits it is cooled to room temperature and is the ready to be cut.

Cutting: The windscreen glass is cut using something called a diamond scribe. This tool has sharp metal points which contain diamond dust. Diamond is harder than glass. A line is drawn in the glass by the diamond scribe and the sheet is then broken off. Then the piece which will become the windscreen is cut and correctly shaped. The glass is typically put into a mould and then the mould is heated to the point where the glass conforms to the shape of the mould.

Tempering: Once the glass for the rear windscreen has been moulded it then hardens in what is known as “tempering.” The glass is heated rapidly to upwards of 850 C and then it’s blasted with cold air jets. Doing this is called “quenching.” What this does is allow the glass of the final rear windscreen, if and when it breaks, to do so into many smaller pieces which don’t have any sharp edges.

Laminating: The front windscreen glass is laminated. This is done through a machine called an autoclave. Glass is laminated because when it’s broken the pieces of glass remain bound to the internal layer. This means that even though the windscreen glass is “broken” it remains transparent. You’ve surely seen cars driving around with dinged or broken glass. It’s through this process of laminating that your windscreen glass doesn’t go flying all over the place, even if it is broken.

Once your car windscreen is melted down in big sheets, cooled, cut, laminated and assembled then it’s ready to be put into your car. Windscreen glass is extremely durable and has generally got plenty of room for driver error before anything bad will happen to it. You don’t want to tempt the fates but knowing all that you now know about the windscreen assembly process you can rest easy knowing that your windscreen is one of the last things to ever really go in your auto.
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Nick writes for Petrie Mechanical Repairs, the local and trusted mechanic in Petrie, near Brisbane. They specialise in regular car servicing, brake & clutch, diesel servicing and more.

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