Modern windshields are generally made of laminated safety glass, a type of treated glass, typically consisting of two curved sheets of glass with a layer of plastic laminated between them for added safety and adhered to the window frame. Laminated glass is formed by a thin layer of vinyl between two layers of glass. This creates a thicker, stronger window. They are considered one of the safest types of glass because they are not easy to break or break.
Most vehicle windshields are made of laminated glass. They are considered effective in preventing break-ins because of the effort required to break them. Safety glass is used in all automotive glass. It is made to reduce the likelihood of injury, should it break.
Windshields are manufactured from a lamination process. Your car's windshield glass is made of laminated glass, which is designed to offer the highest levels of safety in the event of an accident. Laminated glass is made up of two pieces of glass, with a thin layer of vinyl between them. The three pieces are laminated together by applying heat and pressure in a special oven called an autoclave.
When a small object hits a piece of safety glass, usually only the outer layer of the windshield that is hit breaks. Laminated glass is made by sandwiching a layer of polyvinyl butyral (PVB) between two pieces of glass. Glass and PVB are sealed by a series of pressure rollers and then heated. This combination of pressure and heat chemically and mechanically bonds PVB to glass.
Mechanical bonding occurs through the adhesiveness of PVB, whereas chemical bonding is created through hydrogen bonding of PVB to glass. Automatic glass is not made of the same material as glass jars or bottles. In fact, it is made of layers of glass and plastic that fuse together. Never recycle car glass with glass bottles because they are handled differently.
Float glass is used to create laminated glass. Nearly all windshields in North America are made of laminated glass. Laminated windshields are composed of two pieces of float glass with an interlayer of plastic between them. Think of a sandwich where glass is bread and plastic is a slice of mortadella.
The resulting glass is much stronger than simple float glass. When laminated glass breaks, it breaks into small pieces instead of large fragments, which also makes safety that way. This glass meets original safety and quality specifications, such as glass that came from the factory. The glass then enters a special furnace called a furnace, where the glass is gradually cooled to approximately 200°C before cooling to room temperature when it is ready to be cut.
This type of glass is used in the side and rear windows of the vehicle and gains strength through a rapid heating and cooling process that strengthens the outer surface of the glass and its core. If broken, tempered glass is designed to disintegrate into small pieces of glass the size of rock salt. In 1903, French chemist Edouard Benedictus stumbled upon the secret of shatter-resistant glass when he dropped a glass jar filled with a dry collodion film. This “tempering process” makes glass many times stronger than untempered glass of the same thickness.
That inserted layer of PVB is what allows the glass to absorb energy during an impact and gives it resistance to the penetration of flying projectiles. However, in severe impact situations, the glass “breaks”, but usually does not separate because broken glass pieces generally adhere to the vinyl inner liner. For windshield replacement, you have the option of selecting a replacement made by a company that makes OEM windshields, or glass made by non-OEM manufacturers, known as aftermarket glass. Glass manufacturers continue to explore new ideas to make glass stronger, safer and more adaptable to new vehicles.
Ellen Rogers has been involved with the glass industry for nearly 20 years and is the editor of USGlass Magazine and Architects' Guide to Glass magazine. Current laminated glass consists of a thin layer of polyvinyl butyral (PVB) sandwiched between two layers of solid glass. Because of this, automotive glass is manufactured in two different types of safety glass to protect both the vehicle structure and the occupants inside. Laminated glass may bend slightly under impact and is less likely to break than normal safety glass.