A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a perforation. The process of creating perforations is called perforating, which involves removing bits of the workpiece with a tool. Old-fashioned lick-and-stick postage stamps are perforated. When a tool makes small cuts in the material (without removing anything) it is called 'rouletting', because that tool often resembles a roulette wheel, with blades around the edge. Raffle tickets are a good example of rouletting.
Perforations are usually used to allow easy separation of two sections of the material, such as allowing paper to be torn easily along the line. Packaging with perforations in paperboard or plastic film is easy for consumers to open. Other purposes include filtrating fluids, sound deadening, allowing light or fluids to pass through, and to create an aesthetic design.
Various applications include to allow the packages to breathe, medical films, micro perforated plate and sound and vapor barriers.
Processes
Pins and needles
There are a handful of manufacturers that specialize in hot and cold needle perforation tooling and equipment. In materials that have elasticity this can result in a "volcano" hole that is preferred in many applications.
Pinned rollers can be made from a variety of materials, including plastic, steel, and aluminum.
In more brittle films, cold perforation can cause slitting rather than creating a round hole, which can jeopardize the material's integrity under pressure. The solution to this is often heating the pin; i.e. hot pin perforation. Hot perforation melts a hole in the material, causing a reinforced ring around the hole. Hot needle perforation also assists when high density pin patterns are utilized, as the heat aids the perforation of the material.
Die and punch
Common applications are fruit and vegetable bags, and .
Laser perforation
Applications
are one common application of this, where small round holes are cut in lines to create individual pieces. Perforations on stamps are rather large, in the order of a millimeter, in comparison other perforated materials often have smaller holes.
It is common for , and to have perforations making it easier to tear out individual pages or leaves. Perforation is used in ways to separate loose leaf (or even a form of graph paper from a ringed binder). A fine perforation next to the rings allows the page to be separated from the book with no confetti.
on glass or are sealed with a ring at the bottom of the cap attached by perforation. Twisting the cap has the effect of rupturing the material between the perforations and indicating that the original seal has been broken.
The edges of film stock are perforated to allow it to be moved precise distances at a time continuously. Similarly, for use in and later in input and output devices in some cases were perforated to ensure correct positioning of the card in the device, and to encode information.
Perforation of steel strips is used in the manufacture of some and .
Historically, perforation patterns other than linear were used to perfin. A series of patents had been issued in the late 19th century for perforation machines to be used on rail lines for ticketing. Libraries and private collections used similar perforating stamps to mark ownership of books. End sheets, title pages, and image plates were punched with the namesake of the collection. Today, similarly elaborate perforation patterns continue to be used in orienteering.
Bread bags for some bread often have micro-perforations in the plastic, which is supposed to keep the bread fresh by releasing excess moisture. Similarly, bags of concrete use small perforations to allow air to escape while they are being filled.
See also
- Film perforations
- Punched tape
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