The fundamental elements of a zipper include the stringer or the teeth and tape assembly that consists one part of the zipper); the slider that closes and opens the zipper; a tab that is pulled for the slider to move; and the stops that ensure that the slider doesn’t leave the chain. Instead of the bottom stop connecting the stringers, separating zippers have two devices, a pin and a box, that act as the stops once put together.
The hardware of metal zipper could be made of aluminum, stainless steel, brass, nickel-silver alloy, o zinc. There are instances when steel zippers are coated with zinc or brass, or it can also be painted to match the garment or cloth tape’s color.
Zippers that have plastic hardware, on the other hand, are made from nylon or polyester, while the pull tab and slider are often made from zinc or steel. The cloth tapes could be made from polyester, cotton, or a combination of both.
For zippers opening on the two ends, the ends are often not sewn to the garment that keeps them hidden as they are once the zipper is opened at just one end. This kind of zippers is made more durable with a strong cotton tape reinforced with nylon that is applied to the ends to avoid fraying.
The Manufacturing Process of Metal Zippers
The zippers today comprise primary components of plastic or metal. Beyond this single very important difference, all the steps involved to produce finished product are basically the same.
A stringer consists of the cloth or tape and teeth that composed one part of the zipper. The most aged process for producing the stringers for metal zippers is the process that Otto Sundback invented in 1923.
A round wire gets sent through the rolling mill then shapes it to a Y-shape. The wire is sliced to create a tooth with the appropriate width for the desired type of zipper. The tooth will then be put into the slot on the rotating turntable where it will get punched to a scoop’s shape by the die.
This turntable will rotate 90 degrees, and one more tooth will be fed to the slot. After one more turn of 90 degrees, the first tooth gets clamped to the cloth tape. This tape should be raised a bit more than twice the scoop’s thickness—the cupped tooth—after clamping to give room for the completed zipper’s opposite tooth on. A tedious and slow process, its popularity started to wane.
One more similar method was developed during the 1940s. It involves a flattened wire strip passing between a pocket punch and a heading punch to create scoops. A blanking punch will cut around the scoops for forming a Y shape. The Y’s legs get clamped around the cloth tape. The method has been proven to be faster and even more effective compared to the original method of Sundback.
One more method created during the 1930s made use of molten metal for forming teeth. A mold that is shaped like a teeth chain gets clamped around the cloth tape. The molten zinc under pressure will be injected to the mold. The mold will be cooled by water which will then release the shaped teeth. Residues are then trimmed.
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