Heat shrink tubing, also known as heat shrink, is a shrinkable tube that shrinks radially when exposed to heat. Produced using a two-step process, heat shrink is available in a wide range of materials to suit almost any application. Heat shrink tubing has many useful applications, including to provide electrical insulation to wires, connections, joints, terminals, and splices, as well as bundling loose items such as wires and as a protective covering.
The first step in the manufacturing of tubing uses a standard extrusion process. In this process the tubing material is chosen based on the properties of the material to match the environment the tube is ultimately going to be used in. The base material is mixed with other additives such as colorants and UV stabilizers.
In the second step, which usually is proprietary to each manufacturer of tubing, heat and force are used to expand the diameter of the tubing. After the second step, the tubing is allowed to cool to room temperature in its expanded state. When the cooled tubing is exposed to a sufficient amount of heat, it shrinks down to its original size provided it is not restrained from doing so.
Benefits of Heat Shrink Tubing
When used as a protective covering, heat shrink provides protection from abrasion, cutting, scuffing, and low impact situations. It’s able to be used with virtually any design of conductor. Heat shrink can also be used to create cable entry seals providing protection from the surrounding environment.
This protection allows components to be used in areas where they could be exposed to moisture and chemicals as well as dust and other fine particulates.
Examples of Heat Shrink Tubing
Other applications for heat shrink are as a strain relief for color-coding specific components, identifying various components through the use of various colored tubes, and to change the texture of the finish of an object. In addition, heat shrink can be used over small parts and wires to provide minor abrasion resistance.
Heat Shrink Tubing Material
Polyolefin based tubes are by far the most popular and most commonly used. Polyolefin based materials have many advantages over other materials. The main advantage is its ability to withstand high temperatures up to 125°C–135°C.
If pricing is a major concern when choosing a heat shrink material, heat shrink can be produced using PVC based material. PVC cannot withstand the higher temperatures as polyolefin materials do; typically 105°C is the maximum temperature.
PVC, however, is much more competitively priced at roughly 10%-50% less than polyolefin. PVC based heat shrink tubes offer brighter and more vibrant colors and better clarity if a clear tube is needed. PVC is also available in flame retardant versions and has better tensile strength and abrasion resistance than polyolefin materials.
Some versions of heat shrink tubing are available as an adhesive-lined product. This version, also known as dual wall tubing, includes an inner wall of adhesive that melts and flows when the tube is exposed to the heat needed to shrink it. Since the adhesive flows, it fills and voids and conforms easily to the shape of the object inside the tube. The adhesive then hardens and provides an environmental seal, protecting the items under the tube from moisture and other contaminants.
Heat shrink tubing is also available in other materials such as elastomeric, FEP, PVDF, silicon rubber, PTFE, Viton, and other specialty materials. The use of these materials would be dictated by the environment that the shrink tube is to be used in.
Heat shrink tubing shrinks by heating the material in an oven or by using a hand-held hot air gun. Other methods can be used such as holding a solder gun close to the tube or by using a hand-held lighter, but these methods are not recommended.
Heat shrink tubing is classified by the material it is made from the inside diameter of the un-shrunk tube and the shrink ratio. The shrink ratio is the size of the original tubing in relation to its shrunken final form. The more popular ratios are:
- 2:1 – Tube will become half of its original size when heat is applied. Another way to look at the ratio is that the original size will be twice as large as its shrunken form.
- 3:1 - Tube will become one third of its original size when heat is applied. Another way to look at the ratio is that the original size will be three times as large as its shrunken form.
- 4:1 - Tube will become one quarter of its original size when heat is applied. Another way to look at the ratio is that the original size will be four times larger than its shrunken form.
Choosing the correct heat shrink tubing size for the application rests solely on being able to make the right measurements. The smallest and largest components to be covered will determine the size of the shrink tube needed. The tubing ID should be roughly 25% larger than the diameter of the largest component to be covered. This difference allows for ease of sliding the tube over the component. The measurement of the smallest component dictates the shrink ratio of the tubing that will be needed. The tubing when shrunk should fit snug on all of the components.
Summary
Heat shrink tubing can be used in many applications. When used as a means to bind wires together it is a viable substitute for a cable jacket. Shrink tubing offers the same or better temperature ranges as does a cable jacket and has the same ability to offer material isolation of the components under it as a cable jacket.
