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How Windshields are Made

Windshield Factory

The process of making a windshield is a complex one that requires highly specialized equipment. What may seem like a single sheet of glass to the average person is actually a highly specialized component that serves to protect you in the event of an accident.

From Regular Glass to Tempered Glass to Today's Laminated Glass

In the early days, a windshield was made from pure glass. This was unsafe as it shattered upon impact. Toward the middle of the century, windshields started using tempered glass. This helped to make the glass harder and stronger through the application of a special heat treatment

While tempered glass was stronger than normal glass, it still wasn't as safe as our modern laminated windshields. Windshields today are made of safer materials that are designed to maintain a protective layer even in the event of an impact.

Materials in a Modern Windshield

Large pile of sand

A modern windshield is made of a multi-layered laminated glass that is strong like the tempered glass from the middle of the century. However, the multiple layers also make it more flexible and it can actually bend in the event of an accident. This provides protection against shattering that tempered glass simply can't afford. Many countries, including the United States, have made laminated glass compulsory.

Primary Materials

While different manufacturers may have different materials used in the making of a windshield, there are a few components that are standardized in most all windshields made today:

  • Silica (sand) (SiO2)
  • Soda Ash (Na2 CO3)
  • Dolomite ((CaMg)(CO3)2)
  • Limestone (CaCO3)
  • Cullet

Role of Each Ingredient

  • Silica (sand) makes up about 60 to 70 percent of the total structure of laminated glass. Silica is really what gives glass its structure.
  • Some small amounts of potassium oxide and aluminum oxide may also be used.
  • The Soda Ash used in the mixture reduces the melting point of the substances and dolomite is used to improve malleability.
  • Limestone is used to improve the overall durability of the final product.

Mix all the ingredients together, add some water and heat at a high temperature, and you've got the basic recipe for creating a windshield.

The Required Properties of a Modern Windshield Lead to the Invention of Laminated Safety Glass

Heavily shattered laminate windshield still in one piece

Clarity and Strength

Glass must retain a high level of clarity to be useful to a driver. It also needs to be strong enough to prevent objects from intruding into the cabin and to keep passengers inside the vehicle while still providing some amount of give. The windshield is really your last resort when your seatbelt and airbags have failed you.

Strong and Shatter-Resistant

In addition, a windshield needs to be tough enough that it won't shatter in a minor accident. If you had to get a new windshield every time a rock hit it or you had a minor fender bender, the glass would quickly become one of the most expensive parts of your vehicle. Most importantly, the glass must be shatterproof. In the past, shards of glass flying from an accident were often a cause of serious injuries.

Laminated Safety Glass Allows a Windshield to Fulfill All its Required Duties and Properties

Enter the invention of laminated safety glass. This unique three-layer glass is able to provide all of the basic requirements of a safe windshield.

3 Layers for Strength and Shatter-Resistance

The inner layer contains a polyvinyl butyral, and it is surrounded on either side by tempered glass that offers a clear view. This is why a rock can crack the outside of your windshield, but you won't be able to feel the crack from the inside of the vehicle. The inner layer provides a level of protection that prevents the windshield from shattering.

The Making of a Windshield

Molten glass moving through a commercial float chamber

The Float Method is Used to Make Windshield Glass

Step 1: Melting the ingredients and sending them to the float chamber.

A method known as the float method is most commonly used to create windshield glass. In this process, the glass floats inside of a chamber during the first step of the process. The glass is initially mixed together with the ingredients chosen by the manufacturer.

They are then subjected to a very high temperature that melts the glass. Once the glass melts, it is passed through a short and broad opening that leads into another tank. This tank is the float chamber.

Step 2: Annealing - cooking and cooling the glass.

The float chamber consists of molten tin that is aligned in a very thin layer. The molten glass is then moved along the line onto a set of rollers. It gets sent to a new chamber known as the lehr.

In this chamber, a special furnace is used to gradually cook the glass in a process known as annealing. At this point, the raw glass is formed, and it will be used to make the windshield.

Step 3: Forming the glass into its final shape.

A diamond cutting tool called a scribe is then used to cut the glass to the required dimensions. It is then shaped and tempered by placing the glass into a mold.

The mold will be made to the exact specifications of the car that it is designed to protect. The glass is heated again up to the point where it begins to sag but just short of melting. It's then quickly cooled with jets of cold air. This strengthens and hardens the glass.

Step 4: Laminating the glass.

Finally, the two sheets of tempered glass are placed on a very thick layer of PVB. It's then sent through an autoclave and pressed between sets of rollers. This fuses the PVB to the glass and creates a single piece of laminated safety glass.

A SAFETY PRECAUTION

Yellow safety first sign

The windshield on your vehicle acts as a safety mechanism to protect you in the event of an accident. When a windshield is installed improperly, it can pop out and the vehicle's roof may cave in. This is why it's so important to choose a reliable company to install your windshield.

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