Heat-shrink tubing
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Heat shrink tubing (or, commonly, heat shrink) is a mechanically expanded extruded plastic tube ordinarily made of nylon or polyolefin, which shrinks when heated in an effort to return to the original relaxed diameter as when it was extruded. Heat shrink tubing is manufactured in a multitude of varieties and chemical makeups with the exact composition of each type being dependent on the intended application. From near microscopic thin wall tubing to rigid heavy wall tubing, each type has precise design and chemical additives that are suited for a wide variety of environmental demands. Heatshrink tubing is rated by its expansion ratio, a comparative of the differences in expansion and recovery rate. Heat shrink is used to insulate wires offering abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints and terminals in electrical engineering. It can also be used to repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, and to create cable entry seals, offering environmental sealing protection between bulkheads and adding sealability to electrical junction boxes.
Contents
Utility
The tubing is placed over the connection to be protected and then heated with an oven, hot air gun or similar tool. Convenient, but less effective, methods for shrinking the tube include a soldering iron (held in close proximity, but not touching the tube) or the heat from a lighter. These processes cause the tubing to contract as far as one sixth of its original diameter (dependent on the heat shrink, 2:1 is the most common), providing a snug fit over irregularly shaped joints. This provides good electrical insulation, protection from dust, solvents and other foreign materials, as well as strain relief. If overheated, heat shrink tubing can melt, scorch or catch fire like any other plastic.
Some types of heat shrink contain a layer of thermoplastic adhesive on the inside to help provide a good seal and better adhesion, while others rely on friction from the closely conforming materials. Heating plain, non-adhesive shrink tube to very near the melting point may allow it to fuse to the underlying material as well.
One application that has used this product in large quantities since the early 1970s is the covering of fibreglass helical antennas used extensively for 27 MHz CB Radio. Many millions of these antennas have been coated with this versatile plastic shrink tube product.
Manufacture
Heat-shrink tubing is manufactured from a thermoplastic material such as polyolefin, fluoropolymer (such as FEP, PTFE or Kynar), PVC, neoprene, silicone elastomer or Viton.
According to the exact material used, there are two ways that heat shrink may work. If the material contains many monomers, then when the tubing is heated the monomers polymerise. This increases the density of the material as the monomers become bonded together, therefore taking up less space. Accordingly, the volume of the material shrinks[citation needed].
Heat shrink can also be expansion-based. This process involves producing the tubing as normal, heating it to just above the polymer's crystalline melting point and mechanically stretching the tubing (often by inflating it with a gas); finally, it is rapidly cooled. Later, when heated, the tubing will relax back to the un-expanded size.
The material is often cross-linked through the use of electron beams,[1] peroxides, or moisture. This cross-linking helps to make the tubing maintain its shape, both before and after shrinking.
For external use, heat shrink tubing often has a UV stabiliser added.
Materials
Different applications require different materials:
- PTFE (fluoropolymer) tubes have a wide operating temperature range (-55 to 175 °C), a low coefficient of friction, and high resistance to chemicals and punctures.[2]
- Viton, another fluoropolymer with high chemical resistance, is widely used in hydraulic equipment. It is highly flexible, with a very high operating temperature of -55 to 220 °C, making it suitable for protecting sensitive devices against heat.[2]
- Polyvinylidene fluoride (PVDF) tubes are intended for high temperature applications.[citation needed]
- Fluorinated ethylene propylene (FEP) is a lower-cost alternative to PTFE.[citation needed]
- Elastomeric tubes maintain high flexibility even at low temperatures, and meet stringent internation specifications. Their operating temperature range is -75 to 150°C. The material is resistant to many chemicals (including diesel and petrol) and has good resistance to abrasion, even in severe environmental conditions. Common shrink ratio is 2:1.[2]
- Silicone rubber offers excellent resistance to scrape abrasion and high flexibility.[citation needed]
- Polyolefin tubes, the most common kind, have maximum continuous use temperature from -55 to 135 °C, and are used by the military, aerospace and railway industries. They are flexible and fast-shrinking, and manufactured in a wide range of colors (including clear), which can be used for color-coding of wires. With exception of black, they tend to have lower resistance to ultraviolet light; only black is suggested for outdoor applications. Common shrink ratio is 2:1, while high-grade polyolefin heat shrink is available in 3:1.[2]
- PVC tubes are available in several colors, and can be used outdoors.[citation needed]
Other special materials exist, offering qualities such as resistance to diesel and aviation fuels, or woven fabric for increased abrasion resistance in harsh environments.
Heat shrink types
Heat shrink tubing is available in a variety of colours to allow easier colour coding of wires and connections. Recently heat shrink tubing has been used more in PC modding to tidy up the interior of computers and provide a more aesthetic finish. As a reaction to this new market opening up, manufacturers have started producing heat shrink tubing in luminous and UV reactive varieties.
Although most heat shrink is used to provide insulation, heat shrink tubing is also available with a conductive lining to avoid the requirement to solder a joint before covering it. This may be considered poor engineering practice.
Similar to heat shrink tubing is heat shrink end caps. Shaped like small mugs, these may be used to insulate cut ends of wires or cables.
Heat Shrink Tubing was invented by Raychem Corporation.
See also
References
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sv:Krympslang- ↑ Accelerator apps: heat-shrink tubing, Symmetry, Dimensions of Particle Physics. V. 7, Issue 2, Apr. 10
- ↑ 2.0 2.1 2.2 2.3 "3M Heat Shrink catalogue". 3M. Retrieved 28 May 2010.
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