perforation

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Perforation refers to the puncturing of a material with a harder (usually sharp) object to create a hole or aperture. Perforation also refers to the hole made by such an action. A series of small holes or perforations may be intentionally created in a line to allow easier separation of two sections, such as allowing paper to be torn easily along the line.

Methods of perforation

Perforation or microperforation can be created by pins, needles, die and punch or laser.

Pins and needles

"Volcanic" perforations made with a needle punch

A needle punch used in orienteering

Rotary pinned perforation rollers are precision tools that can be used to perforate a wide variety of materials. The pins / needles can be used cold or heated.

Cold needle perforation can cause a "volcanic cone" shaped structure in the material, which can be beneficial for a number of applications.^{[citation needed]} Cold perforation tools include needle punches.

Hot needle perforation melts the material being perforated, and creates a reinforcing ring around the hole. This can also be beneficial in many applications, as the ring assists in keeping the integrity of the material. There are a handful of manufacturers that specialize in hot and cold needle perforation tooling and equipment.

For microperforation, pinned rollers can be made from a variety of materials to include plastic, steel, aluminum, or other materials. Pinned sleeves can be slid onto a central shaft, so that pin patterns may be interchanged at will.

Die and punch

Die and punch sets can be used for thicker materials, or materials that require large gauge holes. The material is sheared by the sharp edges of the punch and die, and the chad is removed. One will see punched perforations in fruit produce bags. Other examples include hole punching and ticket punching. Punches can be designed for a desired hole shape.

Laser perforation

Laser perforation can place many precise holes in a web. Laser perforations look similar in many respects to hot needle perforations. However, laser systems can be expensive to purchase and maintain. Many use an array of mirrors to direct the beam of light.

Applications

Perforation holes on a pair of coil stamps

Perforation frequently refers to the practice of creating a long series of holes so that paper can be torn more easily along a given line, a "perforation line". Since the creation of perforation devices in the 1840s and 1850s, it has seen use in several areas. Postage stamps are one common application of this, where small round holes are cut in lines to create individual pieces (see postage stamp separation). Perforations on stamps are rather large, on the order of a millimeter, in comparison other perforated materials often have smaller holes. It is common for notebooks and legal pads to have perforations making it easier to tear out individual pages. In today's cases, 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. Screwcaps on glass or plastic bottles are sealed with a ring at the bottom of the cap attached by perforation. Twisting the cap has the effect of rupturing the perforation and indicating that the original seal has been broken.

Perforated punch card

Film stock is perforated to allow it to be moved precise distances at a time continuously. Similarly, punched cards for use in looms and later in computers input and output devices in some cases were perforated to ensure correct positioning of the card in the device, and to encode information.

Surform pocket planes feature a perforated steel cutting surface

Perforation of steel strips is used in the manufacture of some zesters, graters, rasps, and planes (see Microplane and Surform).

Orienteering card marked with a different perforation pattern at each control point

Historically, perforation patterns other than linear were used to mark stamps (see Perfin). Today, similarly elaborate perforation patterns continue to be used in orienteering.

Process characteristics

• A variety of shapes and number of holes desired can be produced using this mechanical reducing process.
• Punch and die clearance controls the quality of the hole.
• The material to be punched out is sheared from the workpiece when the punch pierces it and enters the die.
• Burrs are produced on the side of the workpiece that is against the die.
• Holes are punched in desired patterns.

Process schematic

Usually there are a number of punches and dies in a given set. The clearance (the measured distance between the outside circumference of the punch and the inner circumference of the die) must be maintained to ensure a clean cut from the workpiece. The punch is pressed through the material (either by machine or hand tool) and into the die removing a blank, or chad, resulting in a perforated workpiece.

Process purposes

There are a many different purposes for perforating a workpiece including:

• Filtration of fluids
• Enhancing sound deadening
• Allowing light, liquid, air, or gas through a material
• Creating holes to embed something into the workpiece
• To create an aesthetic design in a panel of material
• Braille

Setup and equipment

Perforating can be done either manually or by machine, such as a hydraulic-press. In both types, the punches and dies are arranged in a precisely measured design for the desired result.

See also

• Film perforations
• Hole punch
• Postage stamp separation
• Microperforation
• Hot needle perforation
• Gastrointestinal perforation

Further reading

Todd, Robert H.; Allen, Dell K.;(1994). Manufacturing Processes Reference Guide. New York: Industrial Press Inc. Pg.103-104

External links

Wikimedia Commons has media related to: Perforations