What is a Heat Shrink Tubing?
Heat-shrink tubing (or, commonly, heat shrink or heat shrink sleeve) is a shrinkable plastic tube used to insulate wires, providing abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints and terminals in electrical work. 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. Heat shrink tubing is ordinarily made of nylon or polyolefin, which shrinks radially (but not longitudinally) when heated, to between one-half and one-sixth of its diameter.
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 microscopically-thin-wall tubing to rigid, heavy-wall tubing, each type has precise design and chemical additives that make it suitable for meeting any of a wide variety of environmental demands. Heat shrink tubing is rated by its expansion ratio, a comparison of the differences in expansion and recovery rate.
Heat Shrink Tubing use:
The unshrunk tubing is fitted on the wire before making the connection, and then slid down to cover the joint after it is made. If the fit is tight, silicone lubricant can be applied without compromising the heat-shrink material. The tubing is then shrunk to wrap tightly around the joint by heating in an oven or with a hot air gun or other source of hot gas flow. Convenient but less consistent methods for shrinking the tube include a soldering iron held close to but not touching the tube, or the heat from a lighter.
Uncontrolled heat can cause uneven shrinkage, physical damage and insulation failure, and these methods are not recommended by heat shrink suppliers. If overheated, heat shrink tubing can melt, scorch or catch fire like any other plastic. Heating causes the tubing to contract to between half and one sixth of its original diameter, depending on the material used, providing a snug fit over irregularly shaped joints. There is also longitudinal shrinking, usually unwanted and to a lesser extent than narrowing, of typically around 6%.
The tubing provides good electrical insulation, protection from dust, solvents and other foreign materials, and mechanical strain relief, and is mechanically held in place (unless incorrectly oversized or not properly shrunk) by its tight fit.
Some types of heat shrink tubing contain a layer of thermoplastic adhesive on the inside to help provide a good seal and better adhesion, while others rely on friction between the closely conforming materials. Heating non-adhesive shrink tube to very near the melting point may allow it to fuse to the underlying material as well .
Heat shrink tubing is sometimes sold in pre-cut lengths, with a solder blob at the centre of the length, as this configuration is specified by Daimler-Benz for automotive electrical repairs.
One application that has used heat shrink tubing 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 this way.
How to select the right size of Heat Shrink Tubing:
Size is very important when it comes to heat shrink tubing. Obviously, if the diameter is too small, the wires do not fit inside the tube; however, a too-large diameter presents problems, as well. Heat shrink tubing only shrinks as far as it is designed to. Therefore, a ratio of 2:1 means the heat shrink tubing reverts to a size that is half its current diameter. Similarly, other sizes, such as 4:1, 5:1, and 6:1, shrink only to the intended extent. Heat shrink tubing circumferences range from 1/16 of an inch to several inches; its standard length is 36 inches, although longer tubing is available if necessary.
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