|
Clearly different
|
01/04/2007
|
| |
Improvements to polycarbonate glazing allow complex shapes to be more easily moulded while adding to robustness, but glass still has advantages. Ian Adcock looks at developments
At the Geneva Salon, local Swiss tuner Rinspeed usually manages to spring an eccentric concept on the visitors. This year was no exception with the eXasis, a cigar shaped two-seater with the driver and passenger sitting in tandem and powered by a 750cc two-cylinder engine running on bioethanol.
For the third year running the concept was designed and built in collaboration with Bayer’s AutoCreative team. It followed the bubble topped zaZen last year and the Senso in 2005.
Apart from their avant garde designs, the common factor linking all three is the extensive application of Bayer’s Makrolon polycarbonate.
The first application of Makrolon by Rinspeed was in the Senso, a fairly straightforward, almost horizontal windshield supported on four legs to deflect air over the driver’s head.
The following year’s zaZen was a far more complex and ambitious project. Based on the running gear and floorpan of a Porsche 911 it featured a large, single-piece teardrop Makrolon roof, the tail end of which incorporated a luminous holographic area that forms a third brake light.
“During normal driving the area is transparent and invisible, but when braking the light shines as if from nowhere,” says Johannes Seesing of the AutoCreative team.
During the injection moulding process the entire transparent roof dome down to the belt line was produced as a single section from polycarbonate Makrolon AG2677, specially developed for automotive glazing. A scratchproof coating ensures the necessary robustness.
As well as saving a considerable amount of weight over a glass dome, this roof concept offers an alternative manufacturing/assembly process, since it doesn’t have to be mounted onto the bodywork until the end of assembly. The interior of the car remains accessible from above during the entire production process.
This year’s offering is technically one of the boldest this co-operation between Bayer and Rinspeed has created. The outer Makrolon shell was moulded by Swiss specialist Mecaplex and coated with a yellow tint by German hard coatings specialist KRD. The transparent body parts of Makrolon were produced by thermoforming with tools made of polyurethane modelling foam based on Desmodur and Desmophen raw materials.
Bayer hopes this extreme application of Makrolon will encourage OEMs to be bolder in their use of lightweight plastic glazing.
The chief advantage plastic glazing has over traditional glass is weight reduction, especially in vehicles with a high centre of gravity.
GE Plastics says its Lexan GLX PC resins not only offer enhanced design flexibility for the stylists but also a 50% weight reduction compared with glass. Used in conjunction with Exatec coating for rear window applications it will meet 10-year weatherability standards.
But windows nowadays are much more than a means of separating vehicle occupants from the elements. They also carry heating elements for defrosting, aerials and protection from excessive sun and heat. Features such as defrost grids, blackout areas, masking and antenna printing are all possible with Lexan PC glazing. And Exatec glazing’s advanced priming process improves adhesion to the final protective layers; blackout surrounds can be implemented in two-component moulding processes, and seals and attachment points can be consolidated into a single injection moulded part, thus reducing assembly time and costs. Panoramic roofs made from Lexan GLX resin can be up to 50% lighter with fewer assembled parts than glass.
Polycarbonate glazing tends to be used for side windows and increasingly in panoramic sunroofs, such as the Exatec 500 in the Porsche Cayenne and Nissan Quest. While these installations are fairly conservative in their design and structure, the flexibility of polycarbonate mouldings is well illustrated by the new Honda Civic which features a three-dimensional polycarbonate rear window developed by Freeglass, a joint venture between Saint-Gobain and Schefenacker.
But the glass industry isn’t taking this aggressive approach quietly. For legal reasons glass is still the preferred material for windscreens while durability and a lifetime resistance to scratches means it is also still used for door windows that are repeatedly moved up and down.
One of the most dramatic applications of glass in a concept car in recent months has been the Giugiaro designed Mustang seen at last year’s Los Angeles motor show featuring an all-in-one windscreen, panoramic roof and rear window in one continuous piece of glass.
Produced by Saflex, a division of Solutia, the Giugiaro concept incorporates a Saflex polyvinyl butyral (PVB) glass interlayer that has solar-absorbing properties. This interlayer absorbs infrared energy and radiates it back outside. It also provides a sun protection factor (SPF) of 50.
Because Saflex is a single interlayer it is well suited to curved applications as in the Mustang by Giugiaro concept roof.
The increasing area of glazing in cars means suppliers are having to develop windscreens that block more of the sun’s harmful rays.
Solutia’s laminated glass made with Vanceva and Saflex interlayers provide 50+ ultraviolet protection factor by blocking the UVB and UVA rays across a range of 280 to 400nm, as well as providing 10 times the SPF of ordinary tempered glass. As well as protecting the occupants, these interlayers also help to reduce ageing effects the sun has on the interior surfaces and materials.
PPG says its Sungate Windshield cuts passenger time to comfort (when first getting into a hot car) by half and can improve fuel efficiency by 3 to 4% as the air-conditioning system does not have to work so hard.
Glass is more than a barrier to the elements and the sun, it also helps to reduce NVH. Wind and road noise are major contributors to interior NVH and simply installing a laminated windshield can reduce that by up to 2dB.
Using laminated side glass made with Solutia Saflex protective interlayer can reduce wind and road noise by up to 6dB compared with tempered glass, while providing a 10% weight savings versus the same thickness of glass. A 4mm overall thickness laminate is quieter than a 5mm tempered piece of glass. This reduction is achieved between 1kHz and 7kHz, which is where the human ear is the most sensitive to wind and road noise and equates to an articulation index (AI) improvement of up to 10%.
Japanese glass maker Sekisui claims its S-LEC SSF is the worlds’ first five-layer PVB film providing a 40% improvement in both acoustic and solar (IR) energy.
S-LEC SSF is made by sandwiching a sound insulation resin layer and a coloured layer between PVB, and evenly distributing solar control particles on that multi-layer structure. Now technology from Sekisui allows particles to be distributed evenly in a multi-layered ultra-thin interlayer film.
The sales pitch for these interlayer glasses varies according to the market: in Europe it’s seen very much as an enhancement to vehicle security, whereas in the USA safety issues are more dominant.
But whatever the reason the future is likely to be a blend of both glass and polycarbonates. The big breakthrough will come when plastics equal the optical and durability quality of glass.
That could then present a challenge for body engineering as plastics will not contribute to the vehicle’s stiffness like glass does.
|
| |
Author
Ian Adcock
|
| |
| |
|
| Email this article |
| |
|
|
|
|