Car & Truck
Windshields
In the early
days 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 windshields
glass sticks to the plastic to eliminate glass from flying around the
interior and injuring someone.
Safety glass for
windshields 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 windshields 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 windshields 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 windshield glass.
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