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The Role of Auto Glass in Your Vehicle

What is the purpose of the windshield in a modern vehicle? Is it a weather barrier, a projectile shield, a bug screen? In reality, a windshield is all those things and more, including a safety device. It is as important to your security while on the road as a seat belt, child seat, or even the air bag.

The windshield is designed to keep occupants from being thrown from the vehicle in case of a frontal impact, to support the roof in a rollover accident and to position the passenger-side airbag for the most effective protection. Properly bonding that windshield to the vehicle's body is paramount to the safety of the occupants.

Glass Basics

Glass is a material made naturally, when extreme heat and sand are combined. This material, first found at the foot of volcanoes, is called obsidian. The first use of obsidian was for jewelry and other decorative products. Later, it was used for arrowheads, cutting utensils, and weapons. As the centuries passed, artisans learned to alter glass, after heating it, to form many usable items such as drinking vessels, bowls, and window glass.

Raw Materials

Modern glass is made up of four major ingredients; sand, soda ash, dolomite and limestone. Each of these materials contributes to the success of the manufacturing process. Silica sand contributes as much as 70% of the glass recipe. Soda ash, the most expensive ingredient in glass, provides easier melting of the raw materials. Dolomite provides better working and weathering properties. Limestone adds to the durability of the finished product. Most glass manufacturers also utilize recycled glass, called cullet, in the manufacturing process. In addition to reducing material costs, cullet also melts at a lower temperature, thus reducing energy costs.

Once the glass is manufactured and cut to shipping sizes, it is sent to be fabricated. Fabrication is the act of refining a manufactured item into a finished product for sale. When auto glass is fabricated, it becomes a windshield or a tempered auto glass part. A windshield today is made up of the two pieces of annealed glass with polyvinyl butyral (PVB) sandwiched in between. A tempered piece is a single piece quickly cooled to provide extra impact resistance, as we will explain later in this module.

Methods of Manufacture

There are two types of manufacturing processes used in making glass: the sheet method, and the float method.

To make glass using the sheet method, the glass is vertically stretched, in the molten state, to the desired thickness. Because the quality capabilities are very limited with this process, today this flat glass method of production is usually found only in less developed countries.

The float method is by far the most widely used process, today. The float method starts with the raw materials, mixed and melted in a refractory tank. Once the molten glass is melted and refined, it is forced through a narrow opening onto a bed of molten tin. Glass is lighter than molten tin, so it floats, much like oil on water. The glass is then slowly cooled to a temperature of 1130°F, where it becomes rigid and is lifted off the molten tin by a series of lift out rollers. The glass is then slowly cooled or annealed. This allows the glass to be cut and shaped later.

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