How Windshields Are Made

The windshield has a lone and very rich history, which stems from 1905 when it was discovered that glass can be heat tempered. Heat tempering is a treatment widely used back then to make glass resistant to shattering. Heat tempered glass became the windshield material of choice up until the middle of the 20th century, when lamination proved to be a better alternative to heat tempering.

Laminated glass consists of one plastic layer bounded by two sheets of glass. Laminated glass can bend upon impact, instead of shattering and breaking. This feature made laminated glass the dominant trend in most countries. In fact, many states in the United States requires auto manufacturers to install windshields made of laminated glass because they pose less risks to passengers compared to heat tempered windshields.

Windshields have very complex material structure. Raw materials needed to make windshield glass include silica, sodium oxide, and calcium oxide. These chemicals are often derived from sand, soda ash and lime. Other materials needed for auto glass and windshield manufacturing are magnesium oxide, feldspar, and potassium oxide. In some instances, cullet (broken waste glass) is included in the mix.

 

How are Windshields Made?: The Manufacturing Process

1. The raw materials mentioned above are weighed carefully and are prepared in appropriate amounts. Once this is done, the materials are mixed together with a small amount of water to prevent segregation.
2. After the batch is made, it is then placed in a large tank where it is melted. This is called the float process. In this phase, the glass material is melted at 1,835 degrees Fahrenheit (1,000 degrees Celsius). After which, it is placed onto a bath of melted tin. Once the glass floats, it then rolls out from the flat chamber to the oven. Otherwise known as the annealing lehr.
3. In the lehr or furnace, the glass is significantly cooled to about 395 degrees Fahrenheit (200 degrees Celsius). Once the glass comes out of the furnace, it is significantly stronger and clean of impurities. At this point, the glass is ready to be polished into an auto windshield.
4. Once the design and dimensions are finalized using a diamond scribe, the glass is then cut. Modern glass cutting technologies have made this process faster and easier. Once the glass is cut, it is then bent and fitted into a mold. The mold is heated, which makes the glass to sag according to the shape of the mold.
5. After the shaping phase, the glass material will be tempered in a furnace to about 1,565 degrees Fahrenheit (850 degrees Celsius). After which, the glass is cooled with blasts of cool air. This cooling process, also known as quenching, toughens the glass and makes it durable even during collisions and impacts.
6. Once the glass is tempered and cleaned, it is then laminated. The lamination process involves bonding two sheet of glass with a layer of plastic and takes place in a furnace where the materials are heated and pressed to form a single unit that is highly resistant to shattering.
7. Plastic moldings are then attached to the glass, which makes it ready for car installation. Any other modifications, such as glazing, are usually done by the automobile manufacturer.

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Atlanta, GA 30318
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The History of the Automobile Windshield

At D&I Body Shop and Glass, we're passionate about the history of the automotive industry. In this, the first post on our brand new blog, we dive into the history of the automobile windshield - an important safety component that people often don't think about until it's time to get the windshield replaced or repaired.

A Brief History Overview

Back in the early 19th century, early forms of windshields were made of ordinary glass and were mostly fitted in horseless carriages to protect the driver from the elements. However, it offered little protection from debris and instead posed a threat to the occupants.

Shards of broken glass could easily cause serious injuries to both driver and passenger. Getting bumped from behind could send the motorists flying headfirst through the glass and may result to grave complications and even death.

In the early 20th century, two scientists revolutionized the structure of the automobile windshield. French scientist Edouard Benedictus discovered a way to make glass shatter-resistant. According to automobile historians, Benedictus dropped a flask containing dried collodion film. He then saw that although the film cracked, it retained its original shape.

British scientist John C. Wood was also working on similar project and developed a way to laminate the windshield. After successful tests, he began producing the product under the brand Triplex. By 1927, Henry Ford, founder of Ford Motors, began incorporating Triplex windshields in their automobiles. One obvious downside of laminated windshields back then was that the celluloid layer in the middle discolors due to exposure to the elements.

By 1950s, windshield technology took another step forward. Most automobiles manufactured by this time were fitted with tempered glass for windshields and windows. Its main quality was its toughness and durability. Windshields made of tempered glass can withstand tremendous force and will shatter into smooth beads rather than large shards when broken.

The strength of tempered glass lies in the process of its production. During its manufacturing process, materials undergo a thermal “toughening” phase which further increases the strength of the glass.

During the course of time, technological innovations were introduced to maximize windshield protection and performance.  In the 1980s, Ford cars adapted a windshield technology used on airplanes to prevent ice from building up on the window and impede the pilot’s vision. This innovation was branded “Quickclear”, which enabled electric current to run throughout the glass via a conducting layer of tin (IV) oxide to generate heat to prevent ice and frost build up.

Other car manufacturers followed suit, installing a grid of micro-thin wires to conduct the heat throughout the windshield. Notable manufacturers that employed this technology were Jaguar and Porsche.

While the windshield is ultimately designed for driver and passenger safety, it wasn’t until the 1960s that standards were created to define the safety parameters in windshield construction and installation.

In 1970, the US government formed the National Highway Traffic Safety Administration (NHTSA), the enforcing agency of traffic safety laws and policies in the country. NHTSA has made several provisions on windshield standards, including retention strength, transparency, and shatter-resistance among others.

If you're in metro Atlanta and you need your windshield replaced or repaired, give the experts at D&I a call for a quotation.