If you've ever thrown a ball through a home window as a child, you're probably aware of the danger that shards of glass present. Typical windows often break into dozens of these sharp, dangerous pieces that make cleaning up after an accident difficult. If you've experienced this, you might expect that auto accidents would result in a literal explosion of sharp projectiles lacerating everything in the area.
Fortunately, this isn't the case. That's because auto glass is made out of laminated safety glass. To understand why this is such an important safety feature in modern automobiles, you need to have a basic understanding how this glass is made.
Manufacturing Traditional Glass
Glass, as you may or may not know, is made from liquid sand. Even on a hot summer's day, you've probably never encountered liquid sand in your life's adventures. That's because the melting point for every type of substance is different--and sand's melting point is approximately 3900 degrees Fahrenheit.
Fortunately, this melting point is reduced when sand is mixed with sodium carbonate. However, this also causes the resulting glass to dissolve in water--a useless material to be sure. To combat this, limestone is added to the mixture as well. When this mixture is cooled, the result is the typical glass that you use every day.
Drawbacks to Traditional Glass
This basic type of glass is well suited to protect homes from the elements while allowing for a beautiful view. It's also great for the dinner table. Where it lacks is in it's durability. Traditional glass is very brittle, and will often break when it encounters even a slow-moving projectile.
This is made worse when exposed to the typical speeds encountered when operating a motor vehicle. Often, when dealing with traffic and motorways, cars moving in excess of 50 miles per hour or more encounter objects moving in the opposite direction at a similarly high speed. That's why even a small pebble can cause major damage to your car.
As glass became more and more widespread in it's use, scientists began playing with additives to change the properties of the finished product. For example, when lead is added to glass, it often tends to sparkle. Through experimentation, glass became a product that was suitable for a wider variety of uses than just home windows.
Eventually, scientists began experimenting with the heating and cooling process as well. This led to the discovery of tempered glass, which is rapidly heated and cooled--making it 4 to 5 times tougher than typical glass. It also breaks into smooth round pebbles, making it ideal for constructing the side windows in your automobile.
Laminated Safety Glass
However, even small, round pebbles can cause severe damage if they strike your face at high velocities. That means even tempered glass isn't ideal for the front windshield of your car. For windshields, glass that doesn't shatter at all is required.
Laminated safety glass is made by bonding two sheets of glass together with a heated plastic adhesive. When this process is repeated with multiple layers of glass, the result is an extremely durable product. More importantly, the addition of the plastic sheets prevents the glass from shattering into the jagged shards that you might expect from a typical glass window. Instead, the windshield will hold shape--even when there are obvious cracks present.
That's why your car's windshield is perfectly safe, even in the event of a high-speed collision. Hopefully, you'll never be put in a position to fully appreciate the properties of laminated safety glass. That said, the next time a pebble that would've destroyed your home's picture window glances harmlessly off of your windshield, you'll know why.
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