The
zipper is one of the simplest machines of modern times and
arguably one of the least essential, but it is an immeasurably
useful device in our everyday lives. Think how much easier it
is to close a pants fly, a suitcase, the back of a dress, a
sleeping bag or a tent flap with a zipper than with buttons or
cords. The zipper is so effective and reliable that in less
than a hundred years, it has become the de facto fastener for
thousands of different products.
In this edition of HowStuffWorks,
we'll examine the various parts that make up a zipper and see
how these components lock together so easily and securely. The
system is ingenious in its simplicity.
Hook and Wedge Zippers can only be
manufactured using modern machines, but they are built around
two of the oldest and simplest tools in the history of
civilization: the wedge and the hook.
A wedge is just an object with a slanted (inclined)
surface. If you push a wedge forward against an object, it
will push the object to the left or right. In other words, the
force
exerted by a wedge is always perpendicular to the direction in
which the wedge is moving. A door stop is a good
example of this principle: When you shove it under a door, it
applies an upward force on the bottom of the door. A
plow is another common wedge -- when you drive it
forward, it pushes dirt or snow to the sides.
A hook, of course, is a curved piece of material that can
be used to grab onto another piece of material. Hooks have
been used as fastening devices for thousands of years because
they are simple and generally sturdy. When used as a fastening
device, a hook is generally coupled with a loop, eye or hollow
area, which receives the hook.
The Track A zipper track is made up of
dozens of teeth, each of which combines a hook and a
hollow. The idea is to latch every hook on each of the
two tracks into a hollow on the opposite track. The latching
mechanism, called the slide, is just a collection of
wedges. You can see how this system works in the diagram
below.
As the slide moves up the zipper, the two teeth strips must
enter at a specific angle. As the strips move through the
slide, the slide's inclined edges push the teeth toward each
other. The strips are offset from each other, so each
hollow settles onto a hook in sequence. For this to work
properly, each tooth must be exactly the same size and shape,
and they all must be perfectly positioned on the track. This
would be all but impossible without modern manufacturing
technology.
In a well-made zipper, the interlocking teeth form an
incredibly secure bond -- it is very difficult to separate the
teeth by pulling the two strips apart. But the slide can
easily separate the teeth, using a simple plow-shaped wedge.
When the slide is pulled down, the wedge pushes against the
slanted edges of the hooks, pivoting each tooth off of the
tooth below it. Just like that, the zipper tracks are
detached.
For more information on zippers, including the story of
their invention, check out the links in the next section.
