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Up until 1935 many cars had hinged windshields that could be folded
on the hood of the car or opened up. Today, most windshields are
stationary. They are fixed in place with a weather-strip made of
rubber. The strip has a groove on the inside and a groove on the
outside. The inside groove holds the glass; the outside groove holds
the metal rim of the windshield opening in place. The glass "floats"
in a plastic sealant that is spread out between the edge of the glass
and the frame of the windshield.
Windshields are made of laminated safety plate glass, which is a
sandwich of glass and clear plastic. The plastic acts as a soft,
protective barrier, keeping the glass in place, if it is struck
during a collision. The glass sticks to the plastic to eliminate
glass from flying around the interior and injuring someone.
Safety glass for windscreens was one of the first passive safety
devices introduced into cars in the 1930s, but its use remains a
controversial question. North America and Scandinavia favor a
laminated glass, which consists of two sheets of annealed glass,
separated by a layer of transparent plastic. The rest of Europe and
Japan favor toughened glass because it is cheaper. This type is a
single sheet of glass which is heat strengthened, and which on impact
fractures into small cubic fragments without very sharp edges. In
recent years, laminated glass has been improved by changes in the
properties of the plastic interlayer. Research has demonstrated that
this new laminated glass is about 4 times safer than toughened glass,
but because it is more expensive, controversy continues as to whether
or not toughened glass windscreens should be banned by legislative
action and replaced by laminated glass.
Recent developments have combined the benefits of both laminated and
toughened material in that a laminated construction is used, but the
sheet next to the inside of the car is made of toughened glass.
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