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Automotive Glass History
Prior
to 1919, "horseless carriages" were very few in number and operated at
relatively low speeds. When they first appeared on the scene, they
weren’t equipped with windshields. For protection against bad weather,
insects, and other road debris, drivers and passengers alike used
goggles. Just imagine driving in your car today without a windshield.
The wind in your face, blowing through your hair, while you drive down
the road at high speeds. Sounds pretty neat huh.
As
motorized vehicles grew more common and their speed increased, the wind
and debris thrown into the faces of drivers became a more serious
matter. To alleviate this concern, manufacturers included glass as,
literally, a wind shield. While the new windshields made the drive more
comfortable, they did not adequately protect from flying debris. These
first windshields were hand cut from plate glass. The problem with
these plate glass windshields was they easily shattered into large,
dangerously sharp pieces upon impact.
In
1919 Henry Ford addressed the problem by using a new technology,
developed in France, called glass laminating. Windshields made using
this process were actually two layers of glass with a cellulose inner
layer that held the glass together. Between 1919 and 1929 Ford ordered
the use of laminated glass on all of his vehicles.
Today,
windshields are no longer held together with cellulose, but with a
high-strength vinyl called polyvinyl butyral (PVB). This type of glass
is ideal for automobile windshields because of it's strength and
reliability.
Today
most windshield damage is caused by small rocks that get caught between
the treads of vehicle tires. As the car builds up speed these rocks are
flung into the air... and onto your windshield. When this happens the
glass, depending on the angle of the hit and how fast you are going,
can become 'dinged'. Upon impact, even if the glass shatters, it sticks
to the inner plastic laminate instead of showering the occupants with
pieces of flying glass. The laminated glass also provides a cushioning
effect during collisions. Because of its strength, this plastic layer
absorbs much of the shock upon impact and keeps the occupants from
being ejected through the windshield.
The
glass in the rest of the car is different. Around the 1950's the door
glass and the back glass changed to a tempered glass. It is just one
piece of glass that is sent into an atmospheric oven that heats and
quenches the glass to harden it. This tempered or "toughened" glass is
also considered safety glass. It is strengthened through the
application of heat and pressure. Upon impact it crumbles into rounded
glass pebbles instead of shattering into large dangerous pieces.
Glass
is very susceptible to quick changes in temperature. Rapid expansion or
contraction will cause it to crack. This can happen in the winter when
your defroster rapidly heats a frozen windshield, or in summer when a
hot windshield comes in contact with the cold water of a car wash.
No
matter how it gets there, if you have either a 'ding' or cracked
windshield, your safety is being compromised. Even though the
windshield won't cave in on you, it isn't exactly safe. All cars must
pass roll over tests, and as the car manufacturer lightened the weight
of the vehicle, they made the windshield an important factor in roll
over safety. If you have a cracked, or 'dinged' windshield you are
compromising the structural integrity of your vehicle.
Let
me give you an example of this that your science teacher might have
used back in school. Take an egg. Place two fingers on the top with
your thumb on the bottom of the egg. Now squeeze with all your might...
what happened... nothing right? Mother nature created the perfect
non-breakable structure so when the mother hen sat on her nest the eggs
wouldn't break. Okay... now take a needle and poke a hole in the egg...
you have just compromised it's structural integrity. Next, hold the egg
in your hand like before and squeeze hard... :-) You probably have egg
all over your hand... right? If your windshield has a crack or rock
chip in it, the structural integrity has been compromised much like the
egg with a needle hole in it.
The
reason for different types of glass in vehicles today is safety. We can
not have tempered glass for windshields on the roads in the United
States. Although harder to break than a windshield, tempered glass can
be very unstable. If the skin is broken, it might explode in your face
while you are driving. The real reason for this product is in case of
rollover. It is very difficult to cut through laminated glass. So if
you are ever trapped in your car, its easier to get through tempered
glass than laminate.
Today’s
windshields have evolved into complex, engineered glass systems with
heating elements to melt ice, or, coatings to repel ultra-violet
radiation. Shade bands, radio & telephone antennas, satellite
uplinks, heads-up holographic instrument displays, or even sensors to
activate windshield wipers or close convertible tops are now common.
The
modern windshield is also thinner and lighter to reduce overall vehicle
weight and thereby contribute to increased fuel economy. In short,
consumer demands have influenced engineers to design enhancements into
the glass and, in so doing, have made windshields more costly to
produce.
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