Your windshield is durable for a reason. It acts as a shelter that protects passengers and the car’s interiors from debris and weather conditions. It prevents your vehicle’s roof from caving in during rollover accidents and high-impact collisions. When it breaks, it doesn’t shatter into sharp jagged pieces the way normal glass would, thus minimizing the risk for injury.
But have you ever stopped and asked yourself why this is? After all, windshields are still made of glass. In this guide, we’ll walk you through the process of how windshields are made, so you would understand why they’re not your average glass.
What is auto glass made of?
Car glass is comprised of a combination of oxides. When heated, it creates a reaction which causes them to fuse and form glass.
Below are the three main components found in auto glass:
- Silicone dioxide is a type of sand consisting of tiny quartz particles. It makes up 60 to 70 percent of a windshield and has a high melting point of over 2000° C.
- Sodium carbonate lowers the melting point of silica to 1000° C so the glass is easier to mold.
- Calcium oxide or lime counters the water-solubility of sodium carbonate and produces glass that is harder and more durable.
Potassium oxide, magnesium oxide, aluminum oxide, and cullet (or waste glass) are also added to facilitate the glass-making process.
Step 1: Manufacturing Auto Glass
The ingredients used to make glass are measured and then melted. The molten materials form into glass as they float inside a specially designed chamber, above a bed of molten metal.
Once the “float glass” is formed, it moves through a conveyor belt. Initially, the glass will be exposed to temperatures of 1000° C to rid it of impurities. Then it is exposed to cooler temperatures of 600° C so the glass would harden enough for the next phase.
By the time it leaves the float chamber, a solar coating is applied. Afterward, the glass passes through a furnace where it is slowly cooled to 200° C. During the final phase, the auto glass is cooled at room temperature.
Note: Solar coating prevents too much heat from getting into the vehicle during summers. By winter, it keeps the car’s interiors warm and toasty.
Step 2: Tempering Auto Glass
Now that the glass is cool, it can be cut and fit to size. A diamond scribe is used to create cut lines so that any excess glass can be broken off. The auto glass is then placed inside a mold and heated to achieve the desired shape. Finally, the glass is tempered by quickly heating it and then rapidly cooling it off with cold air.
Note: Tempering is the process which strengthens the windshield and prevents it from breaking into pieces with sharp edges. This way, it is less likely to cause cuts and wounds.
Step 3: Laminating Auto Glass
During lamination, two pieces of auto glass are bonded with a layer of tear-resistant plastic between them. The process occurs in an autoclave, where the materials are heated and placed under pressure to create the windshield that you know today.
Note: The laminate is a safety feature that prevents injury in two ways. First, it keeps broken glass from scattering since they will likely stick to the laminate. Second, when an object hits the windshield and breaks it, the damage will be limited to the outside layer of glass.