Fasteners have come a long way since the early bone or horn pins and bone splinters. Many devices were designed later that were more efficient; such fasteners included buckles, laces, safety pins, and buttons. Buttons with buttonholes, while still an important practical method of closure even today, had their difficulties. Zippers were first conceived to replace the irritating nineteenth century practice of having to button up to forty tiny buttons on each shoe of the time.
In 1851, Elias Howe, the inventor of the sewing machine, developed what he called an automatic continuous clothing closure. It consisted of a series of clasps united by a connecting cord running or sliding upon ribs. Despite the potential of this ingenious breakthrough, the invention was never marketed.
Another inventor, Whitcomb L. Judson, came up with the idea of a slide fastener, which he patented in 1893. Judson's mechanism was an arrangement of hooks and eyes with a slide clasp that would connect them. After Judson displayed the new clasp lockers at the 1893 World's Columbian Exposition in Chicago, he obtained financial backing from Lewis Walker, and together they founded the Universal Fastener Company in 1894.
The first zippers were not much of an improvement over simpler buttons, and innovations came slowly over the next decade. Judson invented a zipper that would part completely (like the zippers found on today's jackets), and he discovered it was better to clamp the teeth directly onto a cloth tape that could be sewn into a garment, rather than have the teeth themselves sewn into the garment.
Zippers were still subject to popping open and sticking as late as 1906, when Otto Frederick Gideon Sundback joined Judson's company, then called the Automatic Hook and Eye Company. His patent for Plako in 1913 is considered to be the beginning of the modern zipper. His "Hookless Number One," a device in which jaws clamped down on beads, was quickly replaced by "Hookless Number Two", which was very similar to modern zippers. Nested, cup-shaped teeth formed the best zipper to date, and a machine that could stamp out the metal in one process made marketing the new fastener feasible.
The first zippers were introduced for use in World War I as fasteners for soldiers' money belts, flying suits, and life-vests. Because of war shortages, Sundback developed a new machine that used only about 40 percent of the metal required by older machines.
Zippers for the general public were not produced until the 1920s, when B. F. Goodrich requested some for use in its company galoshes. It was Goodrich's president, Bertram G. Work, who came up with the word zipper, but he wanted it to refer to the boots themselves, and not the device that fastened them, which he felt was more properly called a slide fastener.
The next change zippers underwent was also precipitated by a war—World War II. Zipper factories in Germany had been destroyed, and metal was scarce. A West German company, Opti-Werk GmbH, began research into new plastics, and this research resulted in numerous patents. J. R. Ruhrman and his associates were granted a German patent for developing a plastic ladder chain. Alden W. Hanson, in 1940, devised a method
After a slow start, it was not long before zipper sales soared. In 1917, 24,000 zippers were sold; in 1934, the number had risen to 60 million. Today zippers are easily produced and sold in the billions, for everything from blue jeans to sleeping bags.
The basic elements of a zipper are: the stringer (the tape and teeth assembly that makes up one side of a zipper); the slider (opens and closes the zipper); a tab (pulled to move the slider); and stops (prevent the slider from leaving the chain). A separating zipper, instead of a bottom stop that connects the stringers, has two devices—a box and a pin—that function as stops when put together.
Metal zipper hardware can be made of stainless steel, aluminum, brass, zinc, or a nickel-silver alloy. Sometimes a steel zipper will be coated with brass or zinc, or it might be painted to match the color of the cloth tape or garment. Zippers with plastic hardware are made from polyester or nylon, while the slider and pull tab are usually made from steel or zinc. The cloth tapes are either made from cotton, polyester, or a blend of both. For zippers that open on both ends, the ends are not usually sewn into a garment, so that they are hidden as they are when a zipper is made to open at only one end. These zippers are strengthened using a strong cotton tape (that has been reinforced with nylon) applied to the ends to prevent fraying.
Today's zippers comprise key components of either metal or plastic. Beyond this one very important difference, the steps involved in producing the finished product are essentially the same.
Another similar method originated in the 1940s. This entails a flattened strip of wire passing between a heading punch and a pocket punch to form scoops. A blanking punch cuts around the scoops to form a Y shape. The legs of the Y are then clamped around the cloth tape. This method proved to be faster and more effective than Sundback' s original.
The second method for spiral plastic zippers makes both the left and right spiral simultaneously on one machine. A piece of wire is looped twice between notches on a rotating forming wheel. A pusher and head maker simultaneously press the plastic wires firmly into the notches and form the heads. This process makes two chains that are already linked together to be sewn onto two cloth tapes.
Zippers, despite their numbers and practically worry-free use, are complicated devices that rely on a smooth, almost perfect linkage of tiny cupped teeth. Because they are usually designed to be fasteners for garments, they must also undergo a series of tests similar to those for clothing that undergo frequent laundering and wear.
A smoothly functioning zipper every time is the goal of zipper manufacturers, and such reliability is necessarily dependent on tolerances. Every dimension of a zipper—its width, length, tape end lengths, teeth dimensions, length of chain, slide dimensions, and stop lengths, to name a few—is subject to scrutiny that ascertains that values fall within an acceptable range. Samplers use statistical analysis to check the range of a batch of zippers. Generally, the dimensions of the zipper must be within 90 percent of the desired length, though in most cases it is closer to 99 percent.
A zipper is tested for flatness and straightness. Flatness is measured by passing a gauge set at a certain height over it; if the gauge touches the zipper several times, the zipper is defective. To measure straightness, the zipper is laid across a straight edge and scrutinized for any curving.
Zipper strength is important. This means that the teeth should not come off easily, nor should the zipper be easy to break. To test for strength, a tensile testing machine is attached by a hook to a tooth. The machine is then pulled, and a gauge measures at what force the tooth separates from the cloth. These same tensile testing machines are used to test the strength of the entire zipper. A machine is attached to each cloth tape, then pulled. The force required to pull the zipper completely apart into two separate pieces is measured. Acceptable strength values are determined according to what type of zipper is being made: a heavy-duty zipper will require higher values than a lightweight one. Zippers are also compressed to see when they break.
To measure a zipper for ease of zipping, a tensile testing machine measures the force needed to zip it up and down. For garments, this value should be quite low, so that the average person can zip with ease and so that the garment material does not tear. For other purposes, such as mattress covers, the force can be higher.
A finished sample zipper must meet textile quality controls. It is tested for laundering durability by being washed in a small amount of hot water, a significant amount of bleach, and abrasives to simulate many washings. Zippers are also agitated with small steel balls to test the zipper coating for abrasion.
The cloth of the zipper tapes must be colorfast for the care instructions of the garment. For example, if the garment is to be dry cleaned only, its zipper must be colorfast during dry cleaning.
Shrinkage is also tested. Two marks are made on the cloth tape. After the zipper is heated or washed, the change in length between the two marks is measured. Heavyweight zippers should have no shrinkage. A lightweight zipper should have a one to four percent shrinkage rate.
Petroski, Henry. The Evolution of Useful Things. Knopf, 1992.
Zipper! An Exploration in Novelty. W. W. Norton & Co., Inc., 1994.
Berendt, John. "The Zipper," Esquire. May, 1989, p. 42.
Getchell, Dave. "Zip It Up: How to Care For and Repair Zippers," Backpacker. May, 1993, p. 94.
Kraar, Louis. "Japanese Pick Up U.S. Ideas," Fortune, Spring-Summer, 1991, p. 66.
"Zip," The New Yorker. December 17, 1979, pp. 33-34.
Weiner, Lewis. "The Slide Fastener," Scientific American. June, 1983, pp. 132-144.
— Rose Secrest