When automobile manufactures broadcast advertisements on television boasting their vehicle’s new safety features, the windshield and surrounding windows are rarely mentioned. Nevertheless, the glass in these vehicles has been designed and constructed with your safety in mind. Although automotive glass resembles other types of glass in appearance, it performs significantly differently.
In the majority of homes, each room’s windows are manufactured from a standard type of glass that breaks into big pieces. With the exception of sliding glass doors and front doors, these windows do not experience the same level of pressure as a car window. In contrast, a car will face several potholes, rocks, and fender benders over its lifetime. Automotive glass is therefore made into two distinct types of safety glass to protect both the vehicle’s structure and its occupants. The windshield is made of laminated glass, which is the first form of glass. The second form of glass is tempered glass, which is utilized for the side and rear windows of a car.
Later, we’ll learn how laminated glass is created by inserting a thin layer of film between two layers of glass and fusing them together using heat and pressure. In addition, we will examine how tempered glass gets its strength through a process of fast heating and cooling. Without these various production and strengthening techniques, vehicle glass would be little more than a mere shield against the weather.
Laminated and tempered glass have separate purposes, but when combined, they keep you inside the car after an accident, protect you from flying sharp glass, maintain the roof’s stiffness during a rollover, and allow the side air bag to protect you when deployed.
The History of Automotive Glass
Early in the 20th century, horseless carriages began employing glass to shield their drivers from strong winds. Nevertheless, the common kind of glass employed at the time did not provide significant protection against flying debris. In the event that an object struck the glass or the car was engaged in an accident, it also posed a threat to the occupants.
The French chemist Edouard Benedictus accidentally discovered the key to shatter-resistant glass in 1903 when he dropped a glass flask containing dried collodion film. He discovered that the film-coated glass fractured but retained its original shape. But, until the 1920s, this laminated glass was not used in autos [source: Time].
Automobile manufacturers incorporated laminated glass onto their windshields to maximize occupant safety during collisions and screen passengers from projectiles under normal driving situations. Despite all of its advantages, the initial varieties of laminated glass had low resistance to puncture. Currently available laminated glass comprises of a thin film of polyvinyl butyral (PVB) sandwiched between two layers of solid glass.
In the late 1930s, automakers began using tempered glass in addition to laminated glass. This type of glass is utilized for the side and rear windows of a car and obtains its strength through a heating and rapid cooling process that reinforces both the outer surface and the core.
In the 1960s, the American public became increasingly conscious that automobiles required design considerations beyond aesthetics. Ralph Nader’s efforts exposing the hazards posed by particular vehicles and the necessity for government safety regulations contributed to this conclusion. In response, the U.S. government established the National Highway Traffic Safety Administration (NHTSA) in 1970, which had been signed into law by President Lyndon Johnson in 1966 [source: Zanona].
Since then, the NHTSA has enacted standards pertaining to all aspects of vehicle safety, including automobile glass. Federal Motor Vehicle Safety Standards (FMVSS) for automobile glass include the following:
- FMVSS 205 establishes explicit criteria for automobile window transparency and the requisite strength of automotive glass to protect occupants within the vehicle during collisions.
- FMVSS 212: This windshield mounting standard was established to assure a specific amount of windshield retention strength in the event of an accident.
- This law established a requirement for roof stiffness in the event of a rollover.
- FMVSS 219 specifies that no portion of a passenger vehicle may penetrate the windshield by more than 6 millimeters (0.24 inches) in the event of a collision.
Now that we understand the origin of automobile glass, let’s examine its production.
Laminated Glass and PVB
Two pieces of glass are sandwiched with a layer of polyvinyl butyral (PVB) to create laminated glass. The glass and PVB are then heated after being sealed by a succession of pressure rollers. This combination of pressure and heat attaches the PVB to the glass chemically and mechanically. The mechanical bond is established by the adhesiveness of the PVB, whilst the chemical bond is formed by hydrogen bonding between the PVB and the glass.
Its PVB layer is what allows the glass to absorb energy upon impact and provides the glass with resistance to projectile penetration. It also deflects up to 95% of the sun’s ultraviolet (UV) rays. It is possible to break and puncture laminated glass, but it will remain intact due to its chemical link with the PVB. The material’s density also allows it to deflect road noise and assist calm a vehicle’s interior [source: AIS Glass].
The durability of laminated automotive glass enables it to serve two crucial tasks in automobiles. First, it ensures that the passenger-side airbag deploys properly. When deployed, driver-side airbags tend to travel directly toward the driver from the steering wheel, whereas passenger-side airbags bounce off the windshield and toward the passenger. In less than 30 milliseconds, an airbag deploys with around 5 pounds (2.3 kilograms) per square inch of force. To protect the passenger during a collision, the windshield must absorb both the speed and force of the air bag. Due to its robustness, laminated glass helps keep car occupants within the vehicle after a collision. In the past, it was possible for occupants to be ejected through the windshield since the glass wasn’t strong enough; however, windshields today offer increased safety.
In addition to absorbing the impact of deployed air bags and keeping passengers within the vehicle, laminated windshields give the top of a car additional strength. During a rollover, windshields prevent the roof from sagging and collapsing completely onto the occupants. Without the stiffness and strength of laminated glass windshields, numerous roofs would pose greater dangers to passengers in certain types of collisions.
Don’t worry if you detect a minor crack in your windshield. It is not necessary to replace the complete windshield to maintain its strength. With a windshield chip repair kit, you may quickly and easily fix small chips in your windshield. These kits, which can be found in most auto parts stores for between $10 and $20, allow you to inject resin into the issue location and remove air from the area. Once you have fixed the glass, the patch will be nearly undetectable. Immediate detection and repair of a chip is essential. If neglected, a little scratch can quickly grow into a wider crack, necessitating a more costly windshield replacement.
Tempered glass is just as crucial to a vehicle’s safety as laminated glass, yet its appearance and functionality are vastly different. This type of glass is utilized for car side windows (also known as sidelites) and rear windows (or backlite). The creation of tempered glass involves heating and then fast cooling the glass to room temperature using a system of blowers.
The surface of the glass cools considerably more quickly than the core and compresses, resulting in compressive strains, whilst the center of the glass expands due to its temperature, resulting in tensile tensions. What does this entail? Consider a piece of glass that can be simultaneously pulled or stretched to a specific length (tensile stress) and pushed down and crushed (compressive stress). Tensile and compressive strength are imparted to tempered glass by the pulling and pushing stresses induced by the heating and cooling procedure. The disparities between these two provide five to ten times the original strength of the glass.
A typical piece of tempered glass has extremely fragile edges. This is due in part to the quick release of heat during the tempering process’s cooling phase. To compensate for this weaker area, the edges of the glass are ground down. When tempered glass fractures, it shatters into little, unremarkable fragments. The disparities between compressive and tensile stresses allow the glass to break in this manner. During the tempering process, the tugging and pushing of the glass produce a tremendous quantity of energy. This energy is released as the glass breaks, causing the glass to shatter into small pieces. [source: AIS Glass Solutions].
Because to its durability, tempered glass may resist the regular driving demands of an automobile. Without it, our vehicles would be inundated with broken glass whenever we hit a pothole, got into a collision, or closed a door.
Future Developments in Automotive Glass
The modern automobile incorporates more glass than ever before, including larger windshields, sunroofs, and even roof-replacing glass panels. Thus, strength and safety standards must evolve alongside the industry. One such invention in this arena is Gorilla Glass, a laminate material developed by Corning, a worldwide glass producer. The new material promises to be stronger, lighter, and more resistant to rock chips and hail damage than existing laminated windshields. Chrysler and McLaren have incorporated Gorilla Glass into their new factory models [source: Corning].
Large panoramic glass is being installed in the tops of several modern automobiles, either permanently or with electric sliding systems. These glass roofs can provide passengers with an excellent view outside the car, but also increase the vehicle’s weight, complexity, and manufacturing expense. [source: AIS].
AGC, a European glass maker, has also begun implementing silver-coated windshields, which protect against high heat and cold. The clear glass allows visible light to flow through while reflecting infrared light away from the cabin under high temperatures. This procedure, according to AGC, can reduce interior temperatures by approximately 60 degrees Fahrenheit on hot days. Silver also functions as an electrically conductive heating element throughout the winter. This enables the vehicle’s climate control system to defrost the entire windshield without the need for obtrusive wires. Volkswagen began selling the silver treatment as an option on several of its vehicles for the European market in 2017.
The design of automotive glass is not limited to safety and comfort. Glass manufacturers and automobile manufacturers are also looking for ways to recycle glass. Chemical treatments and polymers have historically made it difficult to recycle composite materials such as tempered and laminated glass. Nonetheless, automakers and glass producers have begun implementing recycling programs for windshields using machinery that can separate the pure glass from its synthetic components [source: Thompson].
Glass makers continue to investigate innovative ways to make glass more durable, safer, and adaptable to new vehicle designs. Without current tempered and laminated glass, the safety of our vehicles would be significantly compromised.