How does a zip fastener work

A single individual fashioned the first zip fastener, but it was a later inventorwho made it into a practical product. Whitcomb L. Judson, a mechanical engineerby profession, filed the first patent applications on this device in and The invention, originally designed for shoes, consisted of a series of separatefasteners, each having two interlocking parts which could be fastened either byhand or by a movable guide.

No one has discovered how Judsonhappened to invent tliis fastener, although the patent records reveal that this wasby no means his first invention. It is interesting to note that from the time that Judson received his first patent on a slide fastener until the time he receivedhis fifth , no one else applied for patents on a similar contrivance. When the pull-tab is lowered, it locks.

When the pull-tab is raised, it unlocks. The pull moves along a rotating rail. The zipper opens and closes from either the front or back. Automatic Locks are made of metal. Opens and closes from either front or back. Non-Lock, Automatic. 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 s. This entails a flattened strip of wire passing between a heading punch and a pocket punch to form scoops. 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.