Zipper Manufacturing Process

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.

1). Making stringers — metal zippers

A stringer consists of the tape (or cloth) and teeth that make up one side of the zipper. The oldest process for making the stringers for a metal zipper is that process invented by Otto Sundback in 1923. A round wire is sent through a rolling mill, shaping it into a Y-shape. This wire is then sliced to form a tooth whose width is appropriate for the type of zipper desired. The tooth is then put into a slot on a rotating turntable to be punched into the shape of a scoop by a die. The turntable is rotated 90 degrees, and another tooth is fed into the slot. After another 90 degrees turn, the first tooth is to make the stringer for a spiral plastic zipper, a round plastic wire is notched and then fed between two heated screws. These screws, one rotating clockwise, the other counterclockwise, pull the plastic wire out to form loops. A head maker at the front of each loop then forms it into a round knob. This method requires that a left spiral and right spiral be made simultaneously on two separate machines so that the chains will match up on a finished zipper clamped onto the cloth tape. The tape must be raised slightly over twice the thickness of the scoop—the cupped tooth—after clamping to allow room for the opposite tooth on the completed zipper. A slow and tedious process, its popularity has waned.

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.

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 residue is trimmed.

2). Making stringers — plastic zippers

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 right spiral be made simultaneously on two separate machines so that the chains will match up on a finished zipper.

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.

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 above. A rotating wheel has on its edge several small molds that are shaped like flattened teeth. Two cords run through the molds to connect the finished teeth together. Semi-molten 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.

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 presses the loops into a U shape and forms heads on the teeth, which are then sewn onto the cloth tape.

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.

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Jessica Kung

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