Volume 11, Issue 2 -March/April 2009

Innovation Central
A Look at the Latest Developments in Automotive Glass Technology
by Rod Watson

Despite challenges in the auto industry, vehicle technology continues to advance as automakers focus on products that excite and engage their customers. Engineers and designers work together to push the limits of technology and bring new ideas to life. 

Glass is playing an increasingly important role in this process. Design, interior comfort, safety, fuel economy and emissions requirements can benefit from glass innovation. It’s surprising to discover how glass helps achieve all these important—and sometimes conflicting—objectives. Let’s take a closer look at how these trends are impacting the auto glass industry. 

Flush-Mounted Glass
One trend impacting windshields and backlites is the flush look, which allows glass to make a smooth transition into the surrounding sheet metal without visible mouldings. This provides a clean look while also helping reduce wind noise. The glass must have smooth edges all around (known in the industry as a “No.-1 edge”) for both appearance and safety. The 2010 Lincoln MKT windshield is one of the newest vehicles to benefit from this technology. 

The auto glass technician has a few special challenges when no mouldings are used. When cutting out the windshield, the pinchweld may get scratched, requiring the application of pinchweld primer to protect against rust. Also, the installer should be extra careful during cutout, even when protective tape is applied around the pinchweld. Fortunately, many auto manufacturers now use one-sided U-lip-type mouldings, which provide the flush look while hiding the gap between the edge of glass and the pinchweld and any stray pinchweld primer or urethane. 

Laminated Side Glass – Quiet and Cool
Windshields have been laminated since the 1920s, but side- and backlites typically has been made of tempered glass since the early 1960s. Acoustic and UV-blocking vinyls in laminated side glass (e.g., polyvinyl butyral) help filter exterior noise and screen out damaging ultraviolet light. Laminated glass is lighter than an equivalent tempered part in size and thickness, which offers weight reduction and better fuel economy. 

Laminated side glass has safety benefits, as well. It doesn’t shatter like tempered glass, which helps keep occupants inside the vehicle during a crash. This characteristic also helps deter auto theft since it takes time to smash through a laminated window—more time than many thieves are willing to risk. 

Laminated glass is more expensive to produce due to the costs associated with PVB, additional manufacturing processes and the incremental cost of producing glass to the desired thickness. In float manufacturing, when the molten glass flows onto the tin bath, it tends to reach an equilibrium thickness of about .25 inch. Therefore, it has to be stretched along its length and width to produce the thinner sheets (typically 0.090 inch or less) required for automotive laminated glass. To produce 3.8-mm-thick laminated door glass, the glass must be thinned down to approximately 0.067 inch or about 1.7 mm. 

If not done correctly, stretching can introduce optical distortion, which can result in higher scrap. Thinner glass also can break more easily during processing steps prior to lamination. Installation of laminated side glass, however, is no different from tempered glass; it mounts and functions the same way. 

Fuel Economy and Greenhouse Gases
Better fuel economy and reduced greenhouse gas emissions are a high priority for the auto industry. New glass technologies are being developed and existing technologies adapted to help the auto industry meet these challenges. 

One area of focus is reducing the energy needed for air conditioning. Auto glass can help control interior temperature both during driving and after returning to a vehicle that has been parked in the hot sun. There are several methods of achieving this. First, solar absorbing glass, such as solar tints and privacy glass, reduces the amount of solar energy transmitted into the vehicle by absorbing a portion of the energy and re-radiating some of it to the exterior. Another method is to reflect the sun’s energy through the use of engineered coatings applied either directly to the glass or to a plastic film that is included in a laminated glass system. A combination of absorption and reflection can be employed, as well. 

Glass also can be used as a substrate for photovoltaic cells that convert the sun’s energy to electricity. Solar panels on vehicles can be used to power ventilating fans to draw heat from the vehicle when it is parked in the hot sun, or to trickle-charge batteries. One new hybrid vehicle available today has an optional solar panel in its moon-roof for running ventilating fans. 

California is considering legislation that would require the use of solar reflecting glass (see story on page 26). Plans call for implementation in windshields first, followed by the rest of the automotive glass a few years later. This essentially would require a shift to 100 percent laminated glass, because today’s coatings capable of meeting the solar control requirements are not sufficiently durable to be used on monolithic tempered parts. 

Trade-offs for these benefits include significantly higher costs for the glass, both in initial vehicle price and replacement costs. Production processes, material usage and end-of-life (disposal) issues related to this special glass can reduce or even cancel out the projected carbon-reducing benefits intended by this legislation. 

Glass Roofs
One of the “biggest” developments in auto glass is the evolution from sunroofs and moonroofs to panoramic roof systems. The 2009 Ford Mustang features an optional all-glass roof. Other vehicles on the road or in development sport combinations of fixed and movable panoramic panels to provide various levels of open-air access and shaded vision areas. Replacing glass roof panels doesn’t require special tools or procedures, but may require two people or special handling equipment. On some vehicles, large fixed-glass panels are adhered with urethane and require cut-out and reinstallation similar to a windshield or fixed backlite. Because of their large size and position on the roof, they can offer challenges to the technician, especially on taller vehicles. Otherwise, the roof glass replacement should be fairly straightforward. 

Keep Your Sensors About You
To improve safety and add convenience, more sensors are showing up on windshields (see related story on page 51). These sensors can turn on wipers, dim high-beam headlights to low beam, detect condensation on the inside of the windshield to automatically control defogging and give the driver a warning if the vehicle departs from its lane. Many of these sensors are attached to brackets that are bonded to the windshield. Generally, replacement windshields come with just the brackets, but some include the sensors. Whatever their purpose, the sensors must be removed carefully, inspected for damage, kept clean and reinstalled precisely during windshield replacement in order for those systems to continue to function properly. 

Down the Road
The next technological frontier could be the use of glass for new and more exotic shapes. Designers would love to add a crease here and a deeper bend there, but it’s difficult to achieve dramatic shapes in glass without adding unacceptable levels of optical distortion. However, glass engineers and bending-furnace suppliers continue to make improvements in existing bending and tempering technologies, as well as create cutting-edge technologies to meet the ever more challenging designs from vehicle designers. 

What about plastic? It’s true that some plastics are showing up in certain vehicle window applications, primarily because they can be shaped more easily. But plastic’s limited abrasion resistance and higher relative cost will help glass keep its place in cars for a long time to come. You can bet the industry will continue to find new ways to make glass more functional, versatile, efficient and affordable. 

Rod Watson is the Carlite® technical services manager at Zeledyne LLC, in Allen Park, Mich. He can be reached at rod.watson@zeledyne.com. 


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