Heat-shrink tubing
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. |
Heat shrink tubing (or commonly "heat shrink") is a tube which shrinks in diameter when heated. Its diameter and thickness can vary, and there are three main categories, thin wall, medium wall and thick wall tube. Heat shrink is used to insulate wires, connections, joints and terminals in Electrical Engineering. It can also be used to repair wires, bundle wires together, and to protect wires or small parts from minor abrasion.
Composition
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.
Use
It 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), 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.
Manufacture
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.
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, 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.
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. Leading global producers today include Tyco (which owns Raychem), Sumitomo Electric Industries (through Sumitomo Fine Polymer), DSG Canusa (Shawcor), 3M, Shrinktek Polymers International, Grayline Inc., Ikebana and Frontec (Frontier Technologies Pvt Ltd).