HISTORY OF THE ZIPPER

Inventors: American Whitcomb L. Judson (clasp locker), 1893; Swedish engineer Gideon Sundback (Plako model zip fastener in the United States), 1908; Catharina Kuhn-Moos and Henri Forster (Swiss patent with most of the features of modern zippers), 1911; Gideon Sundback (improved on the Kuhn-Moos/Forster design with the Hookless No. 2, with spring clips in place of hooks and eyes), 1913; Bertram G. Work of the B. F. Goodrich Company (the name “zipper”), 1923 Largest manufacturers: Japanese YKK Group and Chinese SBS Zippers together produce more than half the world’s zippers. Zippers earned their name from the metallic hiss heard when a slider is pulled quickly up or down.

Keeping clothes closed is an engineering feat of modern times. Ancient peoples fastened their hides with bone or horn pins secured by bone splinters. We’ve come a long way from these early efforts to keep warm.

Many devices were designed later that were more efficient. Early 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 invented to replace the irritating nineteenth-century practice of buttoning up 20 to 40 tiny buttons on each shoe.

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 on 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 connected 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.

Closure for Clothes 

The first zippers were not much of an improvement over buttons, and innovations came slowly over the next decade. Judson invented a zipper that parted completely (like the zippers found on today’s jackets), and discovered that it was better to clamp the teeth directly onto a cloth tape that could be sewn into a garment, rather than having the teeth themselves sewn onto the garment.

The first hookless zippers were manufactured for use on corsets, gloves, money belts, sleeping bags, and tobacco pouches.

Zippers were still prone to popping open and sticking as late as 1906, when Gideon Sundback joined Judson’s company, then called the Automatic Hook and Eye Company. Sundback’s first Plako model fastener was not very successful, but is considered to be the beginning of the modern zipper.

Sundback’s “Hookless No. 1,” a device in which jaws clamped down on beads, was quickly replaced by “Hookless No. 2,” 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 step made marketing the new fastener possible.

The first zippers were introduced for use in World War I as fasteners for soldiers’ money belts, flying suits, and life vests. Because of the war, many materials were in short supply for civilian use. Therefore, Sundback developed a new zipper 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 them for use in its company galoshes. It was Goodrich president, Bertram G. Work, who came up with the word “zipper,” but he meant it to refer to the boots themselves, and not the device that fastened them, which he felt was more properly called a “slide fastener.”

Zippers changed again after World War II, due to scarcity of metal. Zipper factories in Germany had been destroyed. 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. In 1940 Alden W. Hanson devised a method that allowed a plastic coil to be sewn into the zipper’s cloth, which was followed by a notched plastic wire, developed independently by A. Gerbach and the firm William Prym-Wencie, that could actually be woven into the cloth.

After a slow start, zipper sales began to soar. In 1917, a total of 24,000 zippers were sold; in 1934, the number had risen to 60 million. Today zippers are easily produced and sold by the billions, for everything from blue jeans to sleeping bags.

Zipper Materials 

The basic elements of a zipper are:
 1. The stringer (the tape and teeth assembly that makes up one side of a zipper)
 2. The slider (which opens and closes the zipper)
 3. A tab (which is pulled to move the slider)
 4. Stops (which prevent the slider from leaving the chain)

Instead of a bottom stop to connect the stringers, a separating zipper has two devices—a box and a pin—that work 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 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 (as in a jacket), 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 keep the cloth from fraying.

The Manufacturing Process 

Today’s zippers have key components made of either metal or plastic. Beyond this one very important difference, the steps involved in producing the finished product are basically the same.

Making Stringers—Metal Zippers

1. A stringer consists of the tape (or cloth) and teeth that make up one side of the zipper. Early production methods were slow and tedious. Faster manufacturing methods, originating in the 1940s, involved 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.

2. Yet another method, developed in the 1930s, uses molten metal to form teeth. A mold, shaped like a chain of teeth, is clamped around the cloth tape. Molten zinc under pressure is then injected into the mold. Water cools the mold, which then releases the shaped teeth. Any leftover metal is trimmed off.

Making Stringers—Plastic Zippers

1. Plastic zippers can be spiral, toothed, ladder, or woven directly into the fabric. Two methods are used to make the stringers for a spiral plastic zipper. The first involves notching a round plastic wire before feeding it between two heated screws. These screws—one rotating clockwise, the other counter-clockwise—pull the plastic wire out to form loops. A head maker at the front of each loop then forms it into a round knob. Next, the plastic spiral is cooled with air. This method requires that a left spiral and a right spiral be made simultaneously on two separate machines so that the chains will match up on a finished zipper.

2. The second method for spiral plastic zippers makes both the left and the right spiral simultaneously on one machine (see figure 3). 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.

3. To make the stringers for a toothed plastic zipper, a molding process is used that is similar to the metal process described in step 2. A rotating wheel has several small molds on its edge that are shaped like flattened teeth. Two cords run through the molds and connect the finished teeth.
Semimolten plastic is fed into the mold, where it is held until it solidifies. A folding machine bends the teeth into a U-shape that can be sewn onto a cloth tape.

4. The stringers for a ladder plastic zipper are made by winding a plastic wire onto alternating spools that protrude from the edge of a rotating forming wheel. Strippers on each side lift the loops off the spools while a heading and notching wheel simultaneously press the loops into a U-shape and form heads on the teeth, which are then sewn onto the cloth tape.

5. Superior garment zippers can be made by weaving the plastic wire directly into the cloth, using the same method as is used in cloth weaving. This method is not common in the United States, but such zippers are frequently imported from other countries.

Completing the Manufacturing Process

1. Once the individual stringers have been made, they are joined together with a temporary device similar to a slider. They are then pressed, and, in the case of metal zippers, wire brushes scrub down any sharp edges. The tapes are then starched, wrung out, and dried. Metal zippers are waxed for smooth operation, and both types are rolled onto huge spools to be formed later into complete zippers.

2. After being stamped or die-cast from metal, the slider and pull tab are assembled separately. The continuous zipper tape is then unrolled from the spool and its teeth are removed at intervals, leaving spaces that surround smaller chains. For zippers that only open on one end, the bottom stop is clamped on, and the slider is threaded onto the chain. Next, the top stops are clamped on, and the gaps between lengths of teeth are cut at midpoint. For zippers that separate, the midpoint of each gap is coated with reinforcing tape, and the top stops are clamped on. The tape is then sliced to separate the strips of chain again. The slider and the box are then slipped onto one chain, and the pin is slipped onto the other.

3. Finished zippers are stacked, placed in boxes, and trucked to clothing manufacturers, luggage manufacturers, or any of the other manufacturers that rely on zippers. Some are also shipped to fabric shops for direct purchase by the consumer.

Why YKK?

Most zippers have the letters YKK on them because that is the name of the Japanese company that makes them. The company was founded in 1934 as San-es Shokai, but later changed its name to Yoshida Kogyosho, and still later to Yoshida Kogyo Kabushikikaisha. In 1946, the company registered the trademark “YKK.” YKK Group is now is made up of 71 companies with facilities in 111 countries. The YKK Fastening Products division handles all elements of zipper production, from the dyed fabric around the zipper to the brass used in the zipper itself.

Quality Control 

Zippers, despite their nearly worry-free use, are complicated devices. They rely on the smooth, almost perfect linkage of tiny cupped teeth, and, because they are usually designed as fasteners for clothing, they must pass a series of tests to ensure that they can withstand frequent washing and the stress of everyday wear.

Every dimension of a zipper—its width, length, tape-end lengths, teeth dimensions, length of chain, slide dimensions, and stop lengths—is subject to checking values that must fall within an acceptable range. Samplers use statistical analysis to check the range for a batch of zippers. Generally, the dimensions of the zipper must be within 90 percent of the desired measurements, 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 over the zippper set at a certain height; if the gauge touches the zipper several times, that zipper is defective. To measure straightness, the zipper is laid across a straightedge and checked for any curving.

Zipper strength is very important. 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 then pulls, and a gauge measures the force at which the tooth separates from the cloth. These same tensile testing machines are used to determine 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 be stronger than a lightweight one. Zippers are also compressed to establish their breaking point.

To measure a zipper for ease of closure, a tensile testing machine measures the force needed to zip it up and down. For clothing, this value should be quite low, so that the average person can zip with ease and so that the cloth 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, with a significant amount of bleach and abrasives, to imitate many washings. Zippers are also agitated with small steel balls to test the coating for abrasion.

The cloth of the tapes must be colorfast. For example, if the garment is to be dry-cleaned only, its zipper must be colorfast during the dry-cleaning process.

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. Heavy-weight zippers should have no shrinkage. A lightweight zipper should have a 1–4 percent shrinkage rate.

All this testing and checking have paid off. Despite the continued use of buttons, bows, rivets, and snaps, the zipper is still the frontrunner when it comes to clothing closures. Even the introduction and invasion of Velcro closures haven’t chased them off the market. Zippers are still popular for their flexible strength and reliability. They’re hidden in seams for simple function or stitched in obvious spots to make a colorful fashion statement. Today zippers are used in clothing, shoes, luggage, tents—almost anything made of cloth that needs to be opened and closed.

Written by Andrew Terranova and Sharon Rose in "How Things are Made- From automobiles and Zippers", Black Dog & Leventhal, New York, USA, 2018. Digitized, adapted and illustrated to be posted by Leopoldo Costa.